Engineered Barrier System Degradation, Flow, and Transport Rev 00, ICN 01

TDR-EBS-MD-000006

July 2000
 
1. INTRODUCTION 
Performance of a potential Yucca Mountain high-level radioactive waste repository depends on 
both the natural barrier system (NBS) and the engineered barrier system (EBS) and on their 
interactions. Although the waste packages are generally considered as components of the EBS, 
the EBS as defined in the Engineered Barrier System Degradation, Flow, and Transport Process 
Model Report (PMR), herein referred to as the EBS PMR, includes all engineered components 
outside the waste packages. Waste packages and waste-form performance is described and 
modeled in other PMRs. Performance of the drip shield as a means of diverting water is included 
here, both as-built and following degradation because of various processes. The specific 
mechanisms and rates of drip shield failure from corrosion and seismic activity are described and 
modeled in the WP PMR. 
To evaluate the postclosure performance of a potential repository at Yucca Mountain, a total 
system performance assessment (TSPA) will be conducted. A set of nine PMRs, of which this 
document is one, is being developed to summarize the technical basis for each of the process 
models supporting the TSPA model. These reports cover the following areas: 
.. Integrated Site Model 
.. Unsaturated Zone Flow and Transport 
.. Near Field Environment 
.. Engineered Barrier System Degradation, Flow, and Transport 
.. Waste Package Degradation 
.. Waste Form Degradation 
.. Saturated Zone Flow and Transport 
.. Biosphere 
.. Disruptive Events. 
These PMRs are supported by analysis/model reports (AMRs) that contain the more detailed 
technical information to be input into each PMR and the TSPA. This technical information 
consists of data, analyses, models, software, and supporting documentation that will be used to 
defend the applicability of each process model for its intended purpose of evaluating the 
postclosure performance of the potential Yucca Mountain repository system. The PMR process 
will ensure the traceability of this information from its source through the AMRs, PMRs, and 
eventually to how that information is used in the TSPA. 
This chapter summarizes the purpose for the EBS PMR, its basic organization, technical content, 
relationship to other PMRs, and other key Yucca Mountain Site Characterization Project (YMP) 
documents such as topical reports, the site recommendation report (SRR), and the license 
application (LA). It also provides a brief summary of the PMR technical content. 
The purpose of the EBS PMR is to describe the EBS, to summarize its contribution to controlling 
the waste package and drip shield environment, and to document the thermal, mechanical, 
hydrologic, chemical, and radionuclide transport processes arising from the interaction of 
emplaced waste with the EBS and the surrounding host rock. EBS technical information, 
supporting data, analyses, models, abstractions, and software for evaluating postclosure 
performance of the EBS are documented in 23 AMRs. Finally, the EBS PMR supports the
Yucca Mountain SRR, by summarizing the AMR results used in the Total System Performance 
Assessment (TSPA) and the degree of confidence in the validity of conclusions based on those 
results. 
1.1 OBJECTIVE 
The objectives of the EBS PMR are to: 
 Summarize the technical and scientific bases providing confidence that results from the 
analyses and models are reasonable bounds on the actual future behavior of the EBS as 
it affects repository performance 
 Describe and quantify how the following in-drift processes and/or environments 
change with time after emplacement of nuclear waste in a potential repository: 
- Effects or controls of the EBS design on liquid water entry into the drift from the 
surrounding host rock, its distribution within the drift, and its removal by evaporation 
or by drainage back into the host rock 
- The physical and chemical environment within the different components of the EBS, 
and near the waste packages and drip shields. Specific items include the coupling 
among thermal hydrology, gas and water chemistry, effects of microbes, cementitious 
and other introduced materials, precipitates and salts, and the potential for colloid 
formation 
- The transport of radionuclides released from breached waste packages through the 
EBS, particularly through the invert below the drip shield 
- Variability of thermal-hydrologic responses within the emplacement drifts at various 
locations spanning the potential repository footprint 
- The degradation of the EBS as a result of features, events, and processes (FEPs) that 
are determined to be applicable to the various barriers 
 Provide a guide to the use of modeling and analysis results developed in the AMRs and 
submitted to the Technical Database Management System (TDMS) to support the 
TSPA and other documents, such as the Unsaturated Zone Flow and Transport Model 
Process Model Report (CRWMS M&O 2000o), the Near-Field Environment Process 
Model Report (CRWMS M&O 2000u), the Waste Package Degradation Process 
Model Report (CRWMS M&O 2000n), and the Waste Form Degradation Process 
Model Report (CRWMS M&O 2000z). 
 Evaluate the performance of the various EBS barriers in support of the Site 
Recommendation, and for consistency with the Repository Safety Strategy (CRWMS 
M&O 2000al). 
 Address resolution of Nuclear Regulatory Commission (NRC) key technical issues 
(KTIs) and related issue-resolution status reports (IRSRs) such as the Repository

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Design and Thermal-Mechanical Effects IRSR (NRC 1999c), the Evolution of the 
Near-Field Environment IRSR (NRC 1999b), the Thermal Effects on Flow IRSR 
(NRC 1999d), and the Container Life and Source Term IRSR (NRC 1999a). 
1.2 SCOPE 
Details of input data, analyses, and output are given in individual AMRs and will not be repeated 
here. The scope of this report is to summarize and integrate the analyses, models, and results of 
the supporting EBS AMRs and their abstractions and to provide guidance on the use of 
developed data and information to support TSPA, SR, and regulatory evaluations. This report 
also describes predicted long-term performance of the EBS and the reasonable representation of 
its contribution to the RSS and the use of testing and other information to enhance the credibility 
of the long-term performance predictions. 
Table 1-1 lists the titles, EBS PMR report sections, planning identification (ID) numbers, and 
document identifier (DI) numbers for the 23 AMRs contributing to the EBS PMR. The major 
process model AMRs (shown in bold type) provide bounding analyses of related processes that 
can be used to develop engineering design bases. The other AMRs provide more detailed 
analyses of specific processes.

 1-4 
Table 1-1. Analysis/Model Reports Supporting the Engineer 
Process AMR Title Report 
Section 
ID 
Number 
DI Number 
Water Distribution and Removal Model (CRWMS M&O 
2000q) 
3.1.1 E0090 ANL-EBS-MD-000032 
Ventilation Model (CRWMS M&O 2000an) 3.1.1 E0075 ANL-EBS-MD-000030 
Drift Degradation Analysis (CRWMS M&O 2000ad) 3.1.1 E0080 ANL-EBS-MD-000027 
Water Drainage Model (CRWMS M&O 2000af) 3.1.1 E0070 ANL-EBS-MD-000029 
Water Diversion Model (CRWMS M&O 2000ae) 3.1.1 E0085 ANL-EBS-MD-000028 
In-Drift Thermal-Hydrological-Chemical Model (CRWMS M&O 
2000y) 
3.1.1 E0065 ANL-EBS-MD-000026 
Engineered Barrier System: Physical & Chemical 
Environment Model (CRWMS M&O 2000t) 
3.1.2 E0100 ANL-EBS-MD-000033 
In-Drift Corrosion Products (CRWMS M&O 1999g) 3.1.2.3 E0020 ANL-EBS-MD-000041 
Seepage/Backfill Interactions (CRWMS M&O 2000v) 3.1.2.3 E0030 ANL-EBS-MD-000039 
In-Drift Gas Flux and Composition (CRWMS M&O 2000e) 3.2.1.1.1 E0035 ANL-EBS-MD-000040 
In-Drift Microbial Communities (CRWMS M&O 2000f) 3.1.2.4.2 E0040 ANL-EBS-MD-000038 
In Drift Colloids and Concentrations (CRWMS M&O 2000d) 3.2.1.1.5 E0045 ANL-EBS-MD-000042 
Seepage/Cement Interactions (CRWMS M&O 2000l) 3.2.1.1.2 E0055 ANL-EBS-MD-000043 
Seepage/Invert Interactions (CRWMS M&O 2000m) 3.2.1.1.2 
3.1.2.3 
E0060 ANL-EBS-MD-000044 
In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g) 3.1.2.5 E0105 ANL-EBS-MD-000045 
Engineered Barrier System Radionuclide Transport 
Model (CRWMS M&O 2000b) 
3.1.3 E0050 ANL-EBS-MD-000034 
Invert Diffusion Properties Model (CRWMS M&O 2000h) 3.1.3 E0000 ANL-EBS-MD-000031 
Multiscale Thermohydrologic Model (CRWMS M&O 2000i) 3.1.4 E0120 ANL-EBS-MD-000049 
Engineered Barrier SystemFeatures, Events, and 
Processes/Degradation Modes Analysis (CRWMS M&O 
2000c) 
2.4 E0015 ANL-EBS-MD-000035 
Physical and Chemical Environment Abstraction Model 
(CRWMS M&O 2000j) 
3.2.3.1 E0010 ANL-EBS-MD-000046 
Engineered Barrier System Degradation Modes & Features, 
Events, and Processes Abstraction (CRWMS M&O 2000r) 
2.4 E0110 ANL-WIS-PA-000002 
Abstraction of Near-Field Environment, Drift Thermodynamic 
Environment, and Percolation Flux (CRWMS M&O 2000w) 
3.2.3.3 E0130 ANL-EBS-HS-000003 
EBS Radionuclide Transport Abstraction (CRWMS M&O 
2000a) 
3.2.3.2 E0095 ANL-WIS-PA-000001 
1.3 QUALITY ASSURANCE 
The activities documented in this technical report were evaluated prior to 02/09/00 in accordance 
with CRWMS M&O procedure QAP-2-0, Conduct of Activities, and determined to be subject to 
the requirements of the Quality Assurance Requirements and Description (QARD) document 
(DOE 2000). That evaluation remains in effect, in accordance with CRWMS M&O procedure 
AP-2.16Q Activity Evaluation. This evaluation is documented in the activity evaluation for 
Engineered Barrier System Performance Modeling (CRWMS M&O 1999a). The drip shield and 
Table 1-1. Analysis and Model Reports Supporting the Engineered Barrier System Degradation, 
Flow, and Transport Process Model Report

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other components of the Ex-Container System are identified as QL-1 on the Q-list (YMP 2000). 
They are therefore important to radiological safety, and important to waste isolation (YMP 2000; 
p. II-11). The physical and chemical environment in the drifts is not specifically addressed by the 
Q-list but is a characteristic of the waste emplacement drift system that primarily affects waste 
isolation. 
This document was prepared in accordance with AP-3.11Q, Technical Reports, and the 
Development Plan for the Engineered Barrier System Degradation, Flow, and Transport 
Process Model Report (CRWMS M&O 1999c), which was prepared in accordance with 
AP-2.13Q, Technical Product Development Planning. A Technical Change Request 
(T2000-0039) was processed in accordance with AP-3.4Q, Level 3 Change Control. 
The qualification of data used in the AMRs supporting this report is addressed in the AMRs. 
The qualification and use of input data follows the requirements of AP-3.10Q, Analyses and 
Models, and AP-3.15Q, Managing Technical Product Inputs. The qualification status of 
software is also described in the AMRs supporting this report. Qualification of software 
(including routines and macros) is based on the requirements of AP-SI.1Q, Software 
Management. 
1.4 RELATIONSHIP TO OTHER PROCESS MODEL REPORTS AND KEY 
PROJECT DOCUMENTS 
The calculated in-drift environmental conditions provided by the EBS process model provide 
input to determine the degradation modes and rates for the drip shields, waste packages, and 
waste forms. These effects are abstracted by TSPA from the appropriate EBS AMRs and 
integrated with abstractions from AMRs supporting other PMRs, to develop the radionuclide 
source term. 
There are direct data feeds from the EBS PMR to TSPA, but there are no direct feeds from the 
current version of the EBS PMR to other PMRs. The EBS PMR receives input data from other 
PMRs, particularly hydrologic and thermal properties from the UZ PMR (CRWMS M&O 
2000o), which are based on the Groundwater Flow Model in the Integrated Site Model Process 
Model Report (CRWMS M&O 2000am). 
The EBS is not a principal factor in the repository safety strategy, as determined by the 
Repository Safety Strategy (CRWMS M&O 2000al). The EBS PMR is intended to provide 
input to the Site-Recommendation Consideration Report and the License Application. 
1.5 OVERVIEW 
This section briefly describes the characteristics of Yucca Mountain relevant to EBS 
performance, the conceptual design and functions of the EBS, and the processes affecting or 
affected by the EBS. 
One unique feature of the Yucca Mountain site is its 700-meter-thick vadose zone. Although this 
zone is partially water-saturated, it is generally called the unsaturated zone (UZ). The 
emplacement drifts for the potential repository will be located about halfway between the ground

 1-6 
surface and the water table (Figure 1-1), where the ambient water saturation in the host rock is 
more than 90 percent. Figure 1-2 shows a schematic plan view of the potential repository layout, 
an enlargement of a section containing several emplacement drifts connecting the service drifts, 
and a drift cutaway showing the three most numerous types of waste packages. 
The engineered barriers are intended to complement the geologic system, taking advantage of its 
unique characteristics, to prevent water from contacting waste. Figure 1-3 presents a schematic 
cross-section of an emplacement drift, showing the EDA II conceptual design for the EBS, 
comprising the waste package (WP), waste form (WF), waste package support, drip shield (DS), 
backfill, invert, and ground support. The flow paths of liquid water seeping into the drift are also 
indicated, along with an indication that rockfall may occur after degradation of the ground 
support system. 
The major functions of the EBScombined with suitable preclosure thermal management 
operationsare to control the amount of water contacting the containers, to control the time at 
which water contact occurs, and to provide predictable in-drift environmental conditions. The 
Near-Field Environment Process Model Report (CRWMS M&O 2000u) describes the 
contribution of the host rock to these functions. Successful implementation of these functions 
will provide defense in depth and reduce uncertainty in performance analyses. 
Figure 1-4 is a schematic cross-section of an emplacement drift for the EDA II conceptual 
design, showing major components and processes that are addressed in the EBS PMR. These 
processes include the evolution of heat by radioactive decay, seepage into and flow within the 
drift, evaporation and condensation, deposition of salts and precipitates, gas exchange with the 
surrounding rock, chemical reactions between water, rock, and introduced materials, corrosion, 
formation of colloids, growth of microbes, and transport of radionuclides through the invert by 
advection and diffusion. 
All model results summarized in this report are based on AMRs developed in calendar 1999 for 
the EDA II conceptual design, which was the Project Baseline design until late January, 2000. 
These AMRs are listed in Table 1-1. 
Change requests have been initiated to remove backfill from the reference design and to change 
the emplacement drift orientation to minimize the effects of rockfall. The effects of this design 
change are currently being assessed, and will be documented by change or revision of selected 
AMRs. They will be incorporated in the next revision of this PMR. The following AMRs will 
be the most significantly affected: 
 E0120 Multiscale Thermohydrologic Model (CRWMS M&O 2000i) 
 E0100 Physical & Chemical Environment Model(CRWMS M&O 2000t) 
 E0010 Physical and Chemical Environment Abstraction Model (CRWMS M&) 2000j) 
 E0015 EBS FEPS/Degradation Modes Analysis (CRWMS M&O 2000c) 
 E0110 EBS FEPS/Degradation Modes Abstraction (CRWMS M&O 2000r) 
 E0050 EBS Radionuclide Transport Model (CRWMS M&O 2000b) 
 E0095 EBS Radionuclide Transport Abstraction (CRWMS M&O 2000a) 
 E0080 Drift Degradation Analysis (CRWMS M&O 2000ad) 
 E0090 Water Distribution & Removal Model (CRWMS M&O 2000q)

 1-7 
The removal of backfill will have major effects on temperature and relative humidity within the 
drift during the first few thousand years, on the importance of rockfall, on the flow pathways of 
water entering the drifts, and on the chemistry of water contacting the drip shields and waste 
packages. Detailed evaluations are underway as of this writing. It is expected that detailed 
analyses of the impact of removing backfill, coupled with detailed design of the EBS, will 
produce a system with the performance equal to or better than the EDA II conceptual design 
The waste package is the principal engineered barrier, and it has been designed to last well 
beyond the 10,000-year design life for the potential Yucca Mountain repository (CRWMS M&O 
1999b, Performance Criterion 1.2.1.3). Degradation by corrosion is the expected WP failure 
mode, and materials have been selected to have very small corrosion rates under anticipated 
environmental conditions. However, other degradation modes, including material or 
manufacturing defects, undetected damage in handling, and other factors may lead to early 
failure of a small number of waste packages. 
Other components of the EBS, such as drip shields and backfill, are collectively referred to as the 
EBS in this PMR. The WP lifetime will depend to some degree on EBS system performance and 
other operational controls on the waste package environment. Key environmental variables 
controlling waste package corrosion rate include the presence and chemical composition of 
liquid water on the waste package surface. The flux of liquid water at the waste package surface 
has little effect on the corrosion rate, and is not a factor in the waste package degradation model. 
However, it is the most important determinant of the rate of waste-form degradation and, 
ultimately, the rate of radionuclide mobilization and release, after the WPs are breached. 
Both design and pre-closure operations affect these processes and their impact on repository 
performance. For example, the drip shield and backfill work together to divert water from 
contact with the waste package and direct it to the invert, from which it must drain into the 
host-rock fracture system. The backfill also performs the following functions: 
 Protects the drip shield from damage by rockfall 
 Provides a capillary barrier reducing water seepage through a degraded drip shield 
 Limits salt deposition directly on the drip shield 
 Helps moderate the water chemistry inside the drift, providing some buffering of pH 
and silica concentration 
Ventilation is an example of a preclosure operation affecting postclosure processes that 
determine the evolution of the in-drift environment. Ventilation removes heat from the drifts and 
moisture from the surrounding rock, resulting in a cooler and drier initial condition at closure 
than would be the case without ventilation. Evolution of the in-drift physical and chemical 
environment also depends upon the choice of materials for engineered components, such as 
ground support, invert, backfill, and others. 
After closure, evolution of the in-drift physical and chemical environment for the EDA II design 
must take into account the following processes and phenomena:

 1-8 
 Exchange of liquid water and its dissolved species between the drift and the 
surrounding rock 
 Exchange of water vapor, CO2, and O2 between the drift and its surroundings, 
including the host rock, access drifts, and other underground openings 
 Formation of corrosion products 
 Chemical reaction of water with introduced materials (e.g., rockbolts, grout, rails, 
copper bus bars, backfill, and invert ballast) 
 Growth of microbes 
 Changes in water chemistry resulting from reactions with rock, gases, and introduced 
materials 
 Deposition and dissolution of salts and precipitates 
 Formation of colloids that sorb radionuclides. 
Corrosion may be accelerated if conditions favor microbial growth, and radionuclide solubility 
may be affected by the concentration of major ions in water within the drift. Colloids produced 
by corrosion of carbon steel strongly sorb some radionuclides, potentially increasing their total 
concentration in contaminated water above the amount in solution. 
After release from the waste packages, radionuclides dissolved, or suspended as colloids, will be 
transported through the invert, either by advection or diffusion. If the advective flux is small 
enough, and the water content of the invert is low, diffusion will be the dominant radionuclidetransport 
mechanism through the invert, and the diffusion coefficient will be small. Under these 
conditions, the mass-release rate at steady state could be reduced by the presence of the invert. 
Otherwise, the invert will not contribute significantly to overall performance of a potential 
repository because it will provide, at most, a small transient delay between the time of release 
from the waste package and the time of entry into the host rock. 
Process-model results addressing topics introduced in the preceding paragraphs were developed 
for selected locations within the potential repository footprint. To assess the effects of laterally 
variable boundary conditions (e.g., infiltration and thermal edge effects), the Multiscale 
Thermohydrologic (TH) Model (CRWMS M&O 2000i) provides both the spatial variation and 
the temporal evolution of thermohydrologic environmental conditions, accounting for the 
interactions among emplacement drifts. Output data from that model include temperature, 
relative humidity, liquid saturation and flux, gas flux and air-mass fraction, capillary pressure, 
and evaporation rates as functions of time. These data are calculated for selected locations 
within and near the emplacement drifts. 
Features, events, and processes (FEPs) potentially affecting system performance are addressed in 
a formal screening process. They are also used to develop an analysis of possible failure modes 
for the EBS as a whole.

 1-9 
Finally, results of the major process models are abstracted for input to the Total System 
Performance Assessment for Site Recommendation (TSPA-SR). 
As stated previously, this PMR is closely related to other PMRs, specifically the Unsaturated 
Zone Flow and Transport Model Process Model Report (CRWMS M&O 2000o), the Near-Field 
Environment Process Model Report (CRWMS M&O 2000u), the Waste Package Degradation 
Process Model Report (CRWMS M&O 2000n), and the Waste Form Degradation Process 
Model Report (CRWMS M&O 2000z). These and other PMRs support the Repository Safety 
Strategy (CRWMS M&O 2000al), which is an integrated approach to demonstrating waste 
isolation performance of the repository system. The PMRs will support the Site 
Recommendation decision, and possibly the License Application subsequently. The approach to 
licensing will address resolution of Nuclear Regulatory Commission (NRC) key technical issues 
(KTIs) and related issue-resolution status reports (IRSRs) such as the Repository Design and 
Thermal-Mechanical Effects IRSR (NRC 1999c), the Evolution of the Near-Field Environment 
IRSR (NRC 1999b), the Thermal Effects on Flow IRSR (NRC 1999d), and the Container Life 
and Source Term IRSR (NRC 1999a). Further discussion of the IRSR acceptance criteria is 
provided in Appendix A. 
1.5.1 Features, Events, and Processes for the Engineered Barrier System 
The purpose of the EBS is to ensure that any release of radioactive materials from the waste 
material in the repository into the environment results in doses to potentially impacted 
populations that are below allowable levels as set by the EPA. While the primary barrier to such 
release is the waste package within which the high level nuclear waste is placed prior to 
emplacement in the repository, there are many aspects of the remainder of the engineered portion 
of the repository that have a significant influence on repository performance. Key features of the 
EBS (drip shield, invert, etc.), EBS-impacting events that may occur over the life of the 
repository (seismic activity, igneous activity, etc.), and processes that go on within the EBS 
(mechanical and/or corrosive damage to the drip shield, transport of released radionuclides 
through the EBS, etc.) must be considered when evaluating repository performance. 
The TSPA will represent the performance of the repository system by considering those FEPs 
that have potentially significant probability and consequences. A FEPs screening process is 
required to identify the potentially significant FEPs for inclusion. Many of the process models 
documented in this report are specifically intended for use in FEP screening. The goal of this 
approach is to cast the waste isolation performance of the site in terms of FEPs, which are 
evaluated using process models and data which comply with the model acceptance criteria 
described in the Issue Resolution Status Reports (see Section 4). This section summarizes the 
rationale for determining which FEPs should be included in, or excluded from the TSPA, 
and identifies the associated key issues for the EBS. A more complete discussion of how these 
FEPs were identified, and a description of the included FEPS can be found in Section 2.4. 
Based on the experience obtained from other geologic repository programs, prior TSPAs, and a 
general scientific understanding of the processes that may go on within the entire repository, it is 
possible to develop a comprehensive list of FEPs that may be important to repository 
performance. In determining importance relative to the EBS in a potential repository at Yucca 
Mountain, there are three important issues that must be considered; (a) how the EBS impacts the

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failure (corrosion or mechanical) of the waste package, (b) how the EBS impacts mobilization of 
contaminants subsequent to waste package failure, and (c) how the EBS impacts the transport of 
contaminants from the drift. The criteria are further discussed below: 
(a) Corrosion and/or mechanical failure of the waste packages is an EBS issue with 
respect to how the EBS impacts these processes. Specifically one must be concerned 
with such issues as the amount of water (liquid or vapor) transported to the waste 
package, the chemistry of such water, and the degree to which the EBS may limit 
mechanical damage due to rockfall. Key aspects of the EBS that are important for 
water transport include the drip shield and backfill (if used). For the water chemistry, 
corrosion of metallic components within the EBS (ground supports, pedestal, rails, 
etc.) and interaction with cementitious materials (grout around rock bolts) is important. 
For mechanical failure assessment, the drip shield, backfill (if used), and the pedestal 
are potentially important. 
(b) Mobilization of contaminants is an EBS issue with respect to how the EBS impacts 
such mobilization. Of specific importance are 1) the volumetric rate of liquid water 
directed to the container/container carcass (focusing of drip/flow by the drip shield or 
ground support), and 2) the chemistry of the liquid water redirected to the 
container/container carcass (as altered by engineered materials and mineral 
dissolution). 
(c) Transport, diffusion and advection, from the EBS is specifically an EBS problem with 
respect to EBS control of 1) physical alteration of drainage (fines, TM fracture closure, 
colloid filtration, etc), and 2) chemical alteration of drainage (THC mineral alteration 
in fractures and pores in the floor, colloid agglomeration, etc). 
A FEP must generally be considered in the TSPA, unless it can be demonstrated that one or both 
of the following two criteria are met: 
 Exclude on the basis of Low Probability, if a FEP has less than one chance in 10,000 
of occurring over 10,000 years. 
 Exclude on the basis of Low Consequence, if omission of the FEP does not 
significantly change the expected annual dose. 
The above exclusion criteria are based on 10CFR63.114(d) and 40CFR197.40, and are discussed 
in more detail in the EBS FEPS/Degradation Modes Abstraction (CRWMS M&O 2000r, Section 
4.2) 
Based on the three EBS-important issues discussed above and the two exclusion criteria, 
comprehensive screening and assessment of candidate EBS FEPs have been performed 
(CRWMS M&O 2000c; CRWMS M&O 2000r). A summary of the results of this assessment is 
provided in Table 1-2. FEPs identified as Exclude have been determined to be unimportant by 
virtue of having met one of the two criteria above. FEPs that did not meet one of these criteria 
are by default designated Include and are to be considered in the various TSPA scenarios, e.g. 
the nominal, disruptive, and human intrusion scenarios. FEPs that are relevant to the important

 1-11 
EBS issues (designated a, b, or c above) are identified. Some of the included FEPs are 
applicable to process model reports other than the EBS PMR. These FEPs are identified as 
N/A for the EBS PMR, and the applicable PMR is referenced parenthetically. Some FEPs are 
addressed in the repository design process, and are identified as Design FEPs. They are 
included, but are not part of TSPA. Several FEPs are excluded because they go beyond what 
the regulations require of TSPA. An example of such FEPs are operational accidents. These 
exclusions are explained as regulatory. In these cases the applicable design regulations and 
requirements are relied upon to minimize the FEP detrimental effects.

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Table 1-2. Summary of EBS FEP Screening 
FEP Name and Reference YMP FEP Number Screening 
Result 
Exclusion 
Rationale or 
Exclusion Basis 
Important 
EBS 
Issues A 
Excavation/Construction - YMP 1.1.02.00.00 Exclude Low Consequences 
Site Flooding (During Construction and Operation)  YMP 
1.1.02.01.00 
Exclude Regulatory 
Effects of Preclosure Ventilation  YMP 1.1.02.02.00 Include (a) 
Undesirable Materials Left  YMP 1.1.02.03.00 Exclude Low Consequences 
Error in Waste or Backfill Emplacement  YMP 1.1.03.01.00 Exclude Regulatory 
Repository Design  YMP 1.1.07.00.00 Include Design FEP (a), (b), 
(c) 
Quality Control  YMP 1.1.08.00.00 Include Design FEP (a), (b), 
(c) 
Accidents and Unplanned Events During Operation  YMP 
1.1.12.01.00 
Exclude Regulatory 
Retrievability  YMP 1.1.13.00.00 Include Design FEP (a), (b), 
(c) 
Igneous Intrusion into Repository  YMP 1.2.04.03.00 Include N/A (see DE PMR) (a), (b), 
(c) 
Corrosion of Waste Containers  YMP 2.1.03.01.00 Include N/A (see WP PMR) (a) 
Container Healing  YMP 2.1.03.10.00 Include N/A (see WP PMR) (b) 
Container Failure (Long-term)  YMP 2.1.03.12.00 Include N/A (see WP PMR) (a), (b), 
(c) 
Preferential Pathways in the Backfill  YMP 2.1.04.01.00 Include (a) 
Physical and Chemical Properties of Backfill  YMP 2.1.04.02.00 Include (a), (b), 
(c) 
Erosion or Dissolution of Backfill  YMP 2.1.04.03.00 Exclude Low Consequences 
Mechanical Effects of Backfill  YMP 2.1.04.04.00 Include (a) 
Backfill Evolution - YMP 2.1.04.05.00 Include 
Properties of Bentonite  YMP 2.1.04.06.00 Exclude Not in Baseline 
Buffer Characteristics  YMP 2.1.04.07.00 Exclude Not in Baseline 
Diffusion in Backfill  YMP 2.1.04.08.00 Exclude Low Consequences 
Radionuclide Transport Through Backfill  YMP 2.1.04.09.00 Exclude Low Consequences 
Degradation of Cementitious Materials in Drift  YMP 2.1.06.01.00 Include (a), (b), 
(c) 
Effects of Rock Reinforcement Materials  YMP 2.1.06.02.00 Include (a), (b), 
(c) 
Degradation of the Liner  YMP 2.1.06.03.00 Exclude Not in Baseline 
Flow Through the Liner  YMP 2.1.06.04.00 Exclude Not in Baseline 
Degradation of Invert and Pedestal  YMP 2.1.06.05.00 Include (a), (b), 
(c) 
Effects and Degradation of Drip Shield  YMP 2.1.06.06.00 Include (a), (b), 
(c)

 1-13 
FEP Name and Reference YMP FEP Number Screening 
Result 
Exclusion 
Rationale or 
Exclusion Basis 
Important 
EBS 
Issues A 
Effects at Material Interfaces  YMP 2.1.06.07.00 Exclude Low Consequences 
Rockfall (Large Block)  YMP 2.1.07.01.00 Exclude Low Consequences 
Mechanical Degradation or Collapse of Drift  YMP 2.1.07.02.00 Exclude Low Consequences 
Movement of Containers  YMP 2.1.07.03.00 Include N/A (see WP PMR) (a) 
Hydrostatic Pressure on Container  YMP 2.1.07.04.00 Exclude Low Probability 
Creeping of Metallic Materials in the EBS  YMP 2.1.07.05.00 Exclude Low Consequences 
Floor Buckling  YMP 2.1.07.06.00 Exclude Low Consequences 
Increased Unsaturated Water Flux at the Repository  YMP 
2.1.08.01.00 
Include (a) 
Enhanced Influx (Philip's Drip)  YMP 2.1.08.02.00 Exclude Low Consequences 
Condensation Forms on Backs of Drifts  YMP 2.1.08.04.00 Include (a), (b), 
(c) 
Flow Through Invert  YMP 2.1.08.05.00 Include (c) 
Wicking in Waste and EBS  YMP 2.1.08.06.00 Include (c) 
Pathways for Unsaturated Flow and Transport in the Waste and 
EBS  YMP 2.1.08.07.00 
Include (a), (b), 
(c) 
Induced Hydrological Changes in the Waste and EBS  YMP 
2.1.08.08.00 
Include (a), (b), 
(c) 
Saturated Groundwater Flow in Waste and EBS  YMP 
2.1.08.09.00 
Exclude Low Consequences 
Resaturation of Repository  YMP 2.1.08.11.00 Include (c) 
Properties of the Potential Carrier Plume in the Waste and EBS  
YMP 2.1.09.01.00 
Include (a), (b), 
(c) 
Interaction with Corrosion Products  YMP 2.1.09.02.00 Include (b), (c) 
In-drift Sorption  YMP 2.1.09.05.00 Exclude Low Consequences 
Reduction-oxidation Potential in Waste and EBS  YMP 
2.1.09.06.00 
Include (b), (c) 
Reaction Kinetics in Waste and EBS  YMP 2.1.09.07.00 Exclude Low Consequences 
Chemical Gradients/Enhanced Diffusion in Waste and EBS  YMP 
2.1.09.08.00 
Exclude Low Consequences 
Waste-Rock Contact  YMP 2.1.09.11.00 Exclude Low Consequences 
Rind (Altered Zone) Formation in Waste, EBS, and Adjacent Rock 
 YMP 2.1.09.12.00 
Include 
Complexation by Organics in Waste and EBS  YMP 2.1.09.13.00 Exclude Low Consequences 
Colloid Formation in Waste and EBS  YMP 2.1.09.14.00 Include (b), (c) 
Formation of True Colloids in Waste and EBS  YMP 2.1.09.15.00 Exclude Low Consequences 
Formation of Pseudo-colloids (Natural) in Waste and EBS  YMP 
2.1.09.16.00 
Include (b), (c) 
Formation of Pseudo-colloids (Corrosion Products) in Waste and 
EBS  YMP 2.1.09.17.00 
Include (b), (c) 
Table 1-2. Summary of EBS FEP Screening (Continued)

 1-14 
FEP Name and Reference YMP FEP Number Screening 
Result 
Exclusion 
Rationale or 
Exclusion Basis 
Important 
EBS 
Issues A 
Microbial Colloid Transport in the Waste and EBS  YMP 
2.1.09.18.00 
Exclude Low Consequences 
Colloid Transport and Sorption in the Waste and EBS  YMP 
2.1.09.19.00 
Exclude Low Consequences 
Colloid Filtration in the Waste and EBS  YMP 2.1.09.20.00 Exclude Low Consequences 
Suspensions of Particles Larger than Colloids  YMP 2.1.09.21.00 Exclude Low Consequences 
Biological Activity in Waste and EBS  YMP 2.1.10.01.00 Include (a), (b), 
(c) 
Heat Output / Temperature in Waste and EBS  YMP 2.1.11.01.00 Include (a), (b), 
(c) 
Exothermic Reactions in Waste and EBS  YMP 2.1.11.03.00 Exclude Low Consequences 
Temperature Effects / Coupled Processes in Waste and EBS  
YMP 2.1.11.04.00 
Include (a), (b), 
(c) 
Differing Thermal Expansion of Repository Components  YMP 
2.1.11.05.00 
Exclude Low Consequences 
Thermally-induced Stress Changes in Waste and EBS  YMP 
2.1.11.07.00 
Include (a) 
Thermal Effects: Chemical and Microbiological Changes in the 
Waste and EBS  YMP 2.1.11.08.00 
Include (b), (c) 
Thermal Effects on Liquid or Two-phase Fluid Flow in the Waste 
and EBS  YMP 2.1.11.09.00 
Include (c) 
Thermal Effects on Diffusion (Soret effect) in Waste and EBS  
YMP 2.1.11.10.00 
Exclude Low Consequences 
Gas Generation  YMP 2.1.12.01.00 Exclude Low Consequences 
Gas Generation (He) from Fuel Decay  YMP 2.1.12.02.00 Exclude Low Consequences 
Gas Generation (H2) from Metal Corrosion  YMP 2.1.12.03.00 Exclude Low Consequences 
Gas Generation (CO2, CH4, H2S) from Microbial Degradation  
YMP 2.1.12.04.00 
Exclude Low Consequences 
Gas Generation from Concrete  YMP 2.1.12.05.00 Exclude Low Consequences 
Gas Transport in Waste and EBS  YMP 2.1.12.06.00 Exclude Low Consequences 
Radioactive Gases in Waste and EBS  YMP 2.1.12.07.00 Include N/A (see WF PMR) (c) 
Gas Explosions  YMP 2.1.12.08.00 Exclude Low Consequences 
Radiolysis  YMP 2.1.13.01.00 Include N/A (see WF PMR) 
Radiation Damage in Waste and EBS  YMP 2.1.13.02.00 Exclude Low Consequences 
Mutation  YMP 2.1.13.03.00 Exclude Low Consequences 
Episodic / Pulse Release from Repository  YMP 2.2.07.06.00 Include N/A (see NFE 
PMR) 
(a), (b), 
(c) 
Redissolution of Precipitates Directs More Corrosive Fluids to 
Containers  YMP 2.2.08.04.00 
Include (a), (b), 
(c) 
Gas Pressure Effects  YMP 2.2.11.02.00 Exclude Low Consequences 
NOTE: A See Section 1.5.1 for definitions of criteria (a), (b), and (c). 
Table 1-2. Summary of EBS FEP Screening (Continued)

 1-15 
The degradation of some repository elements may be initiated simultaneously by events or 
processes that are referred to as common mode degradation events or processes. These 
include: increased seepage, thermal-hydrologic-mechanical (THMC) coupled processes, THMC 
rock alteration, thermal-hydrologic-chemical (THC) coupled processes, THC salt production, 
Faulting, and seismicity. Common mode degradation events and processes are discussed in more 
detail in Section 2.4. 
1.5.2 Water Distribution and Removal 
The Water Distribution and Removal Model (CRWMS M&O 2000q) bounds the fraction of 
liquid water entering the drift that will be prevented from contacting waste by the combined 
effects of engineered controls on water distribution and on water removal. The approach is 
flexible, yet detailed enough to analyze different design solutions for water diversion (e.g., drip 
shields alone, drip shields with backfill, capillary barriers with or without drip shields). Water 
can be removed during preclosure operation by evaporation from ventilation and after closure by 
drainage into the fractured host rock. Engineered drains could be used, if demonstrated to be 
necessary and effective, to ensure that adequate drainage capacity survives the thermal pulse. 
1.5.3 Description of Physical and Chemical Environment Process Model 
This section provides an overview of the Engineered Barrier System: Physical & Chemical 
Environment Model (CRWMS M&O 2000t), hereafter referred to as the P&CE AMR, its 
supporting models, and the eight in-drift geochemical environment process models listed below 
the P&CE AMR in Table 1-1. The P&CE model provides predictions for changes in aqueous 
chemistry and gas-phase composition within the emplacement drifts as a result of interaction of 
the host rock, and engineered materials, with heat and water. It accounts for some variability in 
seepage and drainage fluxes, the effects of temperature changes on chemical equilibria and 
reaction kinetics, the physical processes of evaporation and condensation, and the effects of 
rockfall debris. 
1.5.4 Engineered Barrier System Radionuclide-Transport Model 
The radionuclide transport model quantifies and evaluates radionuclide transport within the 
emplacement drift invert, as a result of releases from one or more breached waste packages. 
Advective-dispersive-diffusive contaminant transport and the sorption of radionuclides are 
described in the radionuclide transport model. Results generated by the Water Distribution and 
the Removal Model (CRWMS M&O 2000q) provide the input to the one-dimensional 
contaminant transport equation used in this analysis. 
1.5.5 Multiscale Thermohydrologic Model 
The heat decay emitted from nuclear waste emplaced in the potential geologic repository will 
change the original condition of the host rock. One of the most obvious disturbances is the 
change in thermal-hydrologic (TH) conditions in both the near field and far field. The Multiscale 
TH Model (CRWMS M&O 2000i) simulates the thermally-driven physical changes to the water 
(evaporation and condensation) and host rock (heating and cooling) surrounding the potential 
repository. The Multiscale TH Model draws heavily from the Unsaturated Zone Flow and 
Transport Model Process Model Report (CRWMS M&O 2000o) and the Integrated Site Model

 1-16 
Process Model Report (CRWMS M&O 2000am), for stratigraphic information, and both thermal 
and hydrologic properties. 
In this model, THM, THC, and THMC coupled effects are not included explicitly; flow 
properties such as fracture and matrix porosity and permeability are unaltered by thermal 
processes. This approach is consistent with previous sensitivity studies (CRWMS M&O, 1998g; 
Sections 3.6.8.1.3 and 3.6.8.2) which showed that TH effects from order-of-magnitude decreases 
in fracture permeability, are small because the initial permeability greatly exceeds that required 
to sustain TH flow processes. Also, recent modeling work (CRWMS M&O 2000x) indicates 
that absolute changes in fracture porosity from mineral dissolution and precipitation are on the 
order of 10-4, which is much smaller than the values for fracture porosity (approximately 10-2) 
used for the host rock in these models. 
The need for a multi-scale modeling approach stems from the fact that the performance measures 
depend on TH behavior within a few meters of the emplacement drifts and also on thermal and 
TH behavior on a potential repository (or mountain) scale. A single numerical model (e.g., 
embedding a 3-D drift-scale model with a relatively fine mesh into a 3-D mountain-scale model 
with a coarse mesh) would require an unfeasible number (millions) of grid blocks. The 
Multiscale TH Model has been developed for estimating the results that would be obtained if 
such a single model were feasible. In addition to coupling the drift scale and mountain scale, the 
Multiscale TH Model also allows for consideration of the effect of different waste packages 
types (e.g., different CSNF waste packages, co-disposal of defense HLW) on the various 
performance measures. 
The Multiscale TH Model includes multiple scales (mountain and drift), multiple dimensions 
(1-D, 2-D and 3-D) and varying assumptions regarding the coupling of heat transfer to fluid flow 
(conduction-only and fully coupled thermohydrologic). The Multiscale TH Model estimates the 
temporal evolution of the key TH response variables, including liquid-phase flux, temperature, 
relative humidity, gas-phase air-mass fraction, and evaporation rate, at selected locations within 
and near the drift. The model accounts for the following effects: 
 Site-scale variability of percolation flux 
 Temporal variability of percolation flux 
 Uncertainty in percolation flux 
 Site-scale variability in hydrologic properties 
 Edge-cooling effects 
 Dimensions and properties of the EBS components 
 WP heat variability 
 Site-scale variability in thermal conductivity and overburden thickness. 
Key output variables (as functions of time) include host-rock, WP-surface, and drift-wall 
temperatures; relative humidity values at the DS and WP surfaces; and fluxes of water vapor and 
liquid within and near the drifts.

 1-17 
1.5.6 EBS Model Abstractions 
For the Physical and Chemical Environment Abstraction Model (CRWMS M&O 2000j), 
aqueous flow and transport paths in the emplacement drifts define representative locations where 
important chemical and physical processes occur, such as changes in water composition, 
corrosion of drip shields and waste packages, and dissolution of waste forms. These locations, 
and associated processes, are given below: 
 Air Gap and Backfill - Seepage and capillary fluxes of water 
 Drip Shield Surface - Water diversion, and possible leakage to the WP 
 WP Surface - Water diversion, and possible leakage to the WF 
 Waste Form - Advective transport and molecular diffusion of radionuclides from the 
WF to the invert 
 Invert - Mixing of water from different flow paths, and radionuclide transport to the 
host rock by advection and molecular diffusion 
 Except for the waste form location, inputs for the P&CE abstraction are obtained from 
AMRs supporting the EBS PMR. These include the AMRs listed under the P&CE 
heading in Table 1-1. 
The P&CE abstraction model includes processes affecting gas composition in the drift, and the 
flux of gas-phase components to the drift from the host rock. The major processes that can affect 
composition include: 
 Ambient and thermally perturbed gas-phase mass flux through the drifts 
 Liquid-phase seepage flux 
 Boiling, evaporative concentration, and evaporative precipitation in the emplacement 
drifts 
 Possible sources and sinks involving water in the host rock 
 Chemical reactions in the emplacement drifts, including those which involve 
introduced materials.

 1-18 
The effects of introduced materials on the P&CE are abstracted from AMRs: Seepage/Cement 
Interactions (CRWMS M&O 2000l), Seepage/Backfill Interactions (CRWMS M&O 2000v), 
Seepage/Invert Interactions (CRWMS M&O 2000m), and In Drift Corrosion Products 
(CRWMS M&O 1999g). These address the following processes: 
 Evaporation of influent seepage water 
 Precipitation of dissolved solids 
 Dissolution of quartz and redissolution of precipitates 
 Porosity reduction from precipitates 
 Corrosion and consumption of oxygen 
 Formation of colloids that sorb radionuclides. 
The In Drift Microbial Communities model (CRWMS M&O 2000f) is used to bound the mass of 
microbes and biomass that could be present, per meter of drift, as a function of time. Outputs 
from this model are used to describe microbially induced corrosion (MIC) of the WP, and the 
potential generation of microbial colloids. 
The In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g) is abstracted to determine the 
effects of evaporative processes on water composition in the EBS. Important parameters include 
relative humidity, temperature, CO2 fugacity, influent seepage composition, and rates of liquid 
influx and evaporation. Calculated results include pH, chloride concentration, and ionic strength, 
which are used to estimate DS and WP corrosion rates, and for estimating dissolved and colloidal 
radionuclide concentrations. 
The In-Drift Colloids and Concentrations AMR (CRWMS M&O 2000d) is abstracted to 
estimate the role of colloids in radionuclide transport through the EBS to the host rock. 
The Multiscale TH Model abstraction provides a modified description of the Multiscale TH 
Model output, which directly supports TSPA-SR. The abstracted information includes 
appropriately averaged temperature, liquid saturation, relative humidity, evaporation rate, and 
percolation flux as functions of time and location in the potential repository. The abstracted 
quantities used by TSPA are based on assignment of waste packages to bins based on the local 
infiltration rate. Additionally, the hottest and coolest waste packages are identified. 
Abstraction includes characterization of the spatial and temporal variability, and uncertainty in 
model results represented by sets of calculations run with different input parameter sets. 
The EBS Radionuclide Transport Abstraction model accounts for water contact with the waste 
packages by condensing under the DS, by flow through a failed DS, or by leakage through an 
intact DS. Proper design and placement of the DS may eliminate the latter contact pathway. 
Pathways into the breached waste package include stress corrosion cracks and corroded patches 
through the sides of the WP. Pitting of the WP is not anticipated to occur because of the 
chemical environment around the WP.

 1-19 
The radionuclide-transport abstraction model is based on 1-D advective and diffusive transport. 
The transport pathway from the WF downward to the drift wall is defined using model cells in 
the following order: 
 A WF/WP cell that represents the release of radionuclides from the WF and the 
transport of radionuclides in the WP through breaches in the WP 
 A cell that represents transport through the granular invert. 
These cells require definitions of volume, material properties, and radionuclide solubility limits. 
Both advective- and diffusive-transport mechanisms are included in the transport connections 
between cells. 
The two primary inputs are: 1) the release rate of radionuclides from the WF, and 2) the flux and 
chemistry of water moving through the WP and invert. These two inputs are boundary 
conditions for the transport abstraction. Dissolved radionuclide concentrations mobilized from 
the WF are constrained by the solubility limit of each radionuclide. The solubility constraints are 
described as functions of the water composition along the transport pathway. Similarly, the flux 
and chemistry of water moving through the EBS is based on abstractions from NUFT 
calculations and other chemistry calculations. 
1.5.7 Validity of the Abstractions 
Abstraction analyses and reports are categorized according to those that support quantitative 
models that are used directly in TSPA-SR, and those that are conceptual in nature and provide 
more qualitative input. Discussion of validity is limited to the quantitative models: 
 In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g) 
 In Drift Microbial Communities (CRWMS M&O 2000f) 
 EBS Radionuclide Transport Abstraction (CRWMS M&O 2000a). 
Given accurate inputs, the In-Drift Precipitates/Salts Analysis is expected to provide results that 
are within an order of magnitude for chloride concentrations and ionic strength, and within a pH 
unit for pH predictions (Section 3.2.1.1.4). These accuracy criteria can provide useful reduction 
of uncertainty on the listed parameters. To test the High Relative Humidity (HRH) Salts Model, 
results were compared to measured data from three laboratory evaporation tests. Each test 
involved evaporation of representative waters under particular test conditions. Two used 
synthetic J-13 water and one used synthetic Topopah Spring tuff porewater. For each test, the 
HRH Salts Model calculated the pH within one unit, and the chloride concentration within 20 
percent. The ionic strength calculation was within a factor of two. 
Empirical data are not available to test the accuracy of the Low Relative Humidity (LRH) Salts 
Model. However, the model produces plausible results for chloride concentration and ionic 
strength in the relative humidity range 50 percent to 85 percent, while adequately negotiating the 
transition to the HRH Salts Model at relative humidity of 85 percent. Although simplifying 
assumptions are used in these models, they tend to contribute conservatism.

 1-20 
Three general validation tests were conducted for the In Drift Microbial Communities model 
(CRWMS M&O 2000f). The first test replicated a predictive model that was developed for the 
Swiss low-level waste repository program (Section 3.2.1.1.3). The second test demonstrated that 
the model can simulate certain observed features of the host rock in the Exploratory Studies 
Facility (ESF), and observations from an analog site in another tuff unit. The calculated results 
agree with observations, to within an order of magnitude. The results are also consistent with 
laboratory-based findings that availability of water and phosphorous are limiting factors to 
microbial growth. A third comparison showed that the numbers of organisms calculated by the 
model are within an order of magnitude of measured values. Together these tests provide 
confidence that the model satisfactorily represents the factors controlling microbial growth, and 
that microbial growth and activity in the host rock are in fact nutrient-limited. 
The EBS Radionuclide Transport Abstraction (CRWMS M&O 2000a) presents a conservative, 
bounding model, which helps to ensure that it is valid for use in TSPA-SR (Section 3.2.1.2). 
Bounding approximations used in the model include: 
 After stress corrosion cracks form in the lid of the WP, the WF is assumed to be 
covered with a thin liquid film that supports radionuclide diffusion. This is a 
conservative approach for two reasons (quantification of the conservatism is not 
estimated at this time). First, thin films may not be able to flow through the stress 
corrosion cracks in the lid of the WP. And second, the heat from the WP may 
evaporate all liquid from the inside of the waste package, leading to a dry environment 
that does not support diffusive or advective transport. 
 Release of radionuclides by advective transport is proportional to the total axial length 
of all patches divided by the total axial length of the barrier (DS or WP). This 
assumption is conservative because it assumes that all the flux on the barrier will flow 
into an open patch if its flux is located at the same axial location as the patch (a factor 
of 2 is estimated for this part). It is also conservative because it ignores the factor of 2 
inherent in flux splitting to the right-hand or left-hand side of the crown. 
 Diffusive transport through the invert uses a conservative calculation for the value of 
the diffusion coefficient. First, the free water diffusion coefficient is based on the 
self-diffusivity of water, a bounding value for all radionuclides of interest for the 
TSPA-SR. Second, the correction to the diffusion coefficient for porosity and 
saturation in the invert is based on a conservative version of Archies law. 
Conservatism is probably within one order of magnitude for the first part, and no 
estimate is made for the second part at this time. 
1.6 DESCRIPTION OF THE ENGINEERED BARRIER SYSTEM AND OTHER INDRIFT 
COMPONENTS 
The engineered barrier system includes those components within the emplacement drift that 
contribute to waste containment and isolation. The current design includes the following 
components as engineered barriers: 1) waste package, 2) emplacement drift invert, and 3) drip 
shield. Certain design features have been considered, and subsequently eliminated, including

 1-21 
chemical retardation and sorption materials in the invert (CRWMS M&O 1999d, Section 4); and 
a precast concrete emplacement drift lining (DOE 1998a, Sections 5.2 and 5.3). The following 
discussion describes the design and projected performance of the drift invert, backfill, drift 
ground support, and the drip shield. The waste package and its supporting structure are also 
briefly described; the reader is referred to other sources for details of these elements (CRWMS 
M&O 2000n). 
1.6.1 Drift Invert 
The term invert in this design includes the structures and materials that form a platform that 
supports the pallet and waste package, the drift rail system, and the drip shield. The invert will 
be composed of two parts: the steel invert structure; and the ballast composed of granular 
crushed rock material. 
Steel Invert Structure  The steel invert structure is designed for construction loads, waste 
package emplacement and retrieval loads, drip shield loads, backfill loads, and thermal and 
seismic loads. The invert configuration will accommodate and support the other structures inside 
the emplacement drifts, namely the waste package pallet, waste package emplacement gantry, 
inspection gantry, drip shield emplacement gantry, and backfill emplacement equipment. The 
invert structures will support repository preclosure operations for up to 300 years, with limited 
maintenance. Additionally, the invert design will be coordinated with the pallet design to 
maintain the waste packages in a horizontal emplacement position for 10,000 years after closure 
(CRWMS M&O 2000ag, Sections 1 and 4). 
Steel materials will be used for the invert structure to limit uncertainty associated with the use of 
cementitious materials (CRWMS M&O 2000ag, Section 6.2). Figure 1-5 illustrates the proposed 
invert steel structure in place in the drift. This figure shows the relationship of the invert steel 
structure with the invert ballast, drift wall, ground support structure, pallet and waste package, 
and drip shield. Figure 1-6 provides a perspective view of a section of emplacement drift, 
illustrating the location of the invert component with respect to a ground support steel rib. The 
steel drift invert will not be part of the ground control system. The transverse support beams for 
the invert will be installed between the structural steel ground control components, as shown in 
Figure 1-6. To maintain structural independence of the invert, the ground control components 
will not contact the steel invert components. 
The transverse support beams, which are part of the structural steel invert frame, will rest on the 
drift wall in such a way that they transfer the loads directly to the rock. Installation of the invert 
steel structure will include shimming, aligning, and anchoring the attached base plates to the drift 
rock wall. The pallet loaded with a waste package, and the drip shield, will rest directly on the 
structural steel invert frame. The steel invert frame will also support the drip shield and backfill 
material. The drip shield will transmit the weight of backfill placed directly above it to the invert 
structure. The invert structure will also support transportation loads from the waste package 
gantry and the remote inspection gantry (CRWMS M&O 2000ag, Section 6.4), on the steel 
gantry rails (Figure 1-5). 
The invert structure will have three longitudinal support beams that provide continuous support 
for the emplacement pallets (Figure 1-6). The spacing of the gantry rail centerlines 
accommodates the drip shield gantry used for shield emplacement operations. When the 
assembly details are specified, the invert design will be checked against dynamic seismic loads

 1-22 
to ensure structural integrity and to ensure that the loaded pallet and the drip shield are not 
moved significantly from their original locations because of seismic events (CRWMS M&O 
2000ag, Section 6.4). Movement of the loaded pallet and drip shield can be mitigated, if 
necessary, by the installation of guide beams made of structural steel, as shown in Figures 1-5 
and 1-6. The emplacement drift invert can be periodically monitored and repaired or replaced as 
necessary to ensure that the intended emplacement position of each waste package is maintained 
during the preclosure period of up to 300 years (CRWMS M&O 2000ag, Section 6.4). 
Selection of the invert structure materials was based on structural strength properties, 
compatibility with the emplacement drift environment, and expected longevity in the preclosure 
and postclosure environments. These requirements are contained in the Emplacement Drift 
System Description Document (CRWMS M&O 2000ac, Section 1.2.1). The structural members 
of the emplacement drift invert will be made of ASTM A 572/A 572M steel. A crane rail of 
ASTM A 759 carbon steel will be used for the gantry rail. Compatibility of the carbon steel 
invert materials with the materials forming the drip shield base is being evaluated to determine 
the potential effects of corrosion. Drip shields will be made of titanium alloy (Grade 7). A 
structural angle made of Alloy 22 will be used as a base (at the bottom of the vertical sides of the 
drip shield) to separate the titanium materials from the carbon steel invert materials (CRWMS 
M&O 2000ag, Section 6.5). 
Invert Ballast  The repository subsurface layout is configured so moisture entering the 
emplacement drifts during preclosure and postclosure periods will tend to drain back into the 
surrounding host rock without accumulating and flowing along the drift. A design criterion 
requires that the invert ballast material be crushed tuff (CRWMS M&O 2000ag, Section 4.3.3). 
Ballast material will be produced by crushing the rock that is removed by excavating the 
emplacement drifts. Crushed tuff and carbon steel will be stable with respect to the temperatures 
expected, even for maximum thermal loading conditions (CRWMS M&O 2000ag, Section 6.5). 
Representative hydrologic and thermal properties for the crushed tuff material are given in 
Tables 1-3 and 1-4. 
The waste isolation function of the invert ballast material is to slow the transport of radionuclides 
from the waste package to the drift wall, in circumstances where a waste package is breached but 
the overlying drip shield is intact (CRWMS M&O 2000ag, Section 6.4). This issue is currently 
being tested and investigated; the results will be incorporated into future design enhancements. 
Ballast material will be placed in and around the steel members of the invert structure to an 
elevation just below the top of the longitudinal and transverse support beams (Figures 1-5 and 
1-6). This level of fill will ensure that the pallets and drip shields initially do not rest on the 
ballast material, but are fully supported by the steel invert beams. This level of fill will also 
ensure that backfill materials will not flow under the drip shield during placement. The ballast 
material will be sufficiently compacted to consolidate it to the point where settlement of the 
ballast over time will be insignificant. 
1.6.2 Backfill 
The primary purpose of backfill is to limit damage to the drip shield or waste package from 
rockfall during the postclosure period. Additional potential benefits from backfill include 
improved predictability of postclosure hydrologic and chemical performance, and thermal

 1-23 
insulation of the drip shield and waste package to extend the duration of dry conditions. The 
backfill material selected for design and performance analysis activities described in this report 
Table 1-3. Hydrologic Properties for EBS Granular Materials 
Material 
Permeability 
(m2) 
Porosity 
van 
Genuchten 
(1/Pa) 
van 
Genuchten 
m 
Residual 
Saturation 
Satiated 
Saturation 
Backfill 1.43x10-11 0.410 2.7523x10-4 0.50 0.024 1 
Invert 6.15x10-10 0.545 1.2232x10-3 0.63 0.092 1 
Source: CRWMS M&O 2000q (Table 7) 
Table 1-4. Thermal Properties for EBS Granular Materials 
Material 
Rock Grain 
Density 
(Kg/m3) 
Rock Grain 
Specific Heat 
(J/Kg K) 
Dry 
Conductivity 
(W/m K) 
Wet 
Conductivitya 
(W/m K) 
Tortuosity 
Backfill 2700 795 0.33 0.33 0.7 
Invert 2530 948 0.66 0.66 0.7 
Source: CRWMS M&O 2000q (Table 8) 
Note: a Wet conductivity value assumed to be the same as the dry conductivity value. 
is fine quartz sand, which can be obtained from a local quarry (Overton Sand) as well as other 
sources. Represenative hydrologic and thermal properties for the quartz sand backfill material 
are given in Tables 1-3 and 1-4. 
Backfill will be emplaced at the time of permanent closure of the facility, using a system of 
remotely controlled, electrically powered shuttle cars and conveyors. Stacking equipment will 
be used to raise the backfill to a height of approximately 1.2 m above the top of the drip shield 
(Figure 1-3). The sides of the backfill pile will assume a natural repose angle. The total amount 
of emplaced backfill will be approximately 8.5 cubic meters per meter of emplacement drift. 
1.6.3 Ground Support 
The primary purpose of ground support systems is to maintain the stability and geometry of the 
emplacement drifts during the preclosure period. The previous design (DOE, 1998a) used a 
precast concrete liner, that could also serve as an engineered barrier by diverting some water 
flow into the drifts (at locations where seepage occurs). However, this barrier function would last 
only while the concrete liner remains intact. Also, concrete would contribute alkaline leachate 
and cementitious particles to the drift environment, which could accelerate the transport of 
radionuclides. Consequently, the current design consists of steel sets with steel wire fabric and 
rockbolts (CRWMS M&O 2000ao, Section 6). These measures will support waste isolation only 
by preventing rockfall during the preclosure period. The steel sets will continue to provide 
ground support after closure, but will eventually fail from corrosion during cool-down.

 1-24 
Fully grouted rockbolts will be used only in the middle nonlithophysal unit of the Topopah 
Spring host rock. Six rockbolts will be used every 1.5 meters of drift length, in a radial array that 
will be offset with the steel sets, on the same spacing. An expansive, high-strength, lowpermeability 
Portland-type cement grout will be used with steel bolts. 
1.6.4 Support Assembly for the Waste Package 
According to the design criteria, the waste package must remain in its emplacement position for 
300 years (CRWMS M&O 2000ag, Section 6). This requirement satisfies waste package 
retrieval needs, if that option is exercised during the preclosure period. Another design criterion 
is that the horizontal position of the waste package must be maintained for 10,000 years after 
closure (CRWMS M&O 2000ah, Section 4.2). This criterion supports waste isolation by 
keeping the waste package under the drip shield. The design of the emplacement pallet will 
fulfill these requirements using materials that will last 10,000 years, and using simple and stable 
design. Horizontal movement of the waste package will be caused primarily by support beam 
corrosion, ballast settlement, and seismic ground motion. Evaluation of support beam corrosion, 
ballast settlement, and response to ground motion will be performed during planned design 
activities (CRWMS M&O 2000ah, Section 6.2.2). 
The emplacement pallet design will permit close end-to-end placement of waste packages within 
10 cm of each other. The pallet will be shorter than the waste package (Figure 1-7), so it will not 
interfere with the close placement requirement. Pallets will be fabricated from Alloy 22 plates 
welded together to form the waste package supports. Two supports, one at each end, will be 
connected by four square stainless steel tubes to form the completed emplacement pallet 
assembly (Figure 1-8). These tubes will be fabricated from 316L stainless steel (CRWMS M&O 
2000ah, Section 4.1). The Alloy 22 supports will have a V-shaped top surface to accept all waste 
package diameters (CRWMS M&O 2000ah, Section 6.2.1). All surfaces of the emplacement 
pallet that contact the waste package outer barrier will be Alloy 22 (CRWMS M&O 2000ah, 
Section 6.2.2). Pallet design will ensure that the waste packages remain in the normal 
emplacement position during the preclosure period of up to 300 years (CRWMS M&O 2000ah, 
Section 6.5), and will help maintain the waste package horizontal position for 10,000 years after 
closure. Further analyses of loaded pallet response to the seismic design basis event will be 
performed as design details are specified. 
As described above, the steel invert structure will have transverse support beams that rest on the 
rock wall. Attached to these transverse support beams will be three longitudinal support beams 
that provide continuous support for the emplacement pallets (Figures 1-5 and 1-6). The 
transverse support beams and longitudinal support beams will transfer the waste package load to 
the rock. When humidity conditions return to the emplacement drifts, the steel members in the 
invert will corrode, and the waste package (on its support structure) will come to rest directly on 
the invert ballast material. 
1.6.5 Drip Shield 
The drip shields will be installed over the waste packages before closure. The function of the 
drip shields will be to divert the liquid water seepage from the host rock, around the waste 
packages, and onto the drift invert. They will be emplaced in segments that link together 
forming a single, continuous barrier for the entire length of each emplacement drift. Figure 1-2 
illustrates a typical section of an emplacement drift with a series of emplaced waste packages of

 1-25 
different sizes and with the drip shields emplaced. Some of the drip shields are eliminated in the 
illustration for clarity in showing the waste packages. 
Design requirements for drip shields include corrosion resistance and structural strength. 
Corrosion resistance is required so the drip shields can perform their moisture diversion function 
with high reliability for 10,000 years. Structural strength will ensure that the waste packages are 
protected from damage by rockfall, withstanding damage from rocks weighing several tons 
(CRWMS M&O 2000ah, Section 4.2). The drip shields will withstand static loads from backfill, 
in addition to rockfall. The drip shield will be fabricated from Grade 7 titanium plates for the 
water diversion surfaces, Grade 24 titanium for the structural members, and Alloy 22 for the feet 
(Figure 1-10). The drip shield feet will be mechanically attached to the titanium drip shield 
skirts, since the two materials cannot be welded together. The feet will prevent direct contact 
between the titanium and the carbon steel members in the invert (CRWMS M&O 2000ah, 
Section 6.1.1). 
All the drip shields will be uniformly sized, so one design will suffice for any waste package. 
The drip shield sections will interlock to prevent separation between sections (Figure 1-9). The 
interlocking joint design includes water diversion rings to divert any dripping water that may 
penetrate the joint. The interlocking will be accomplished by using pins and holes, and also by 
using an overlapping section with connector guides. The Grade 7 titanium thickness of 15 mm 
(0.6 in.) is selected for long-term corrosion resistance. Grade 24 titanium is selected for the 
structural components because of its superior strength in comparison with Grade 7 titanium. 
The drip shield feet will rest on the transverse support beams of the invert structure, and 
alongside the longitudinal guide beams (Figures 1-5 and 1-6). These longitudinal guide beams 
will center the emplacement pallet, and also create a separation barrier between the pallet and the 
drip shield.

 F1-1 
NOTE: This artists rendering was developed for this report. 
Figure 1-1. Schematic Cutaway View of the Yucca Mountain Unsaturated Zone, Showing 
Emplacement Drifts and Processes That Determine Water Entry In the Drifts

 F1-2 
NOTE: This artists rendering was developed for this report. The design-related information 
content is consistent with Wilkins and Heath (1999). 
Figure 1-2. Schematic View of the Potential Repository Layout, Drift Connections and 
Representative Waste Package Types Within an Emplacement Drift

 F1-3 
NOTE: This artists rendering was developed for this report. The design-related information 
content is consistent with Wilkins and Heath (1999). 
Figure 1-3. Schematic Cross-section of an Emplacement Drift Containing a 21-PWR Waste 
Package, Showing Major Elements of the EDA II Design for the EBS 
00018DC EBS PMR 16.ai

 F1-4 
NOTE: This artists rendering was adapted from Figure 4-15 of CRWMS M&O (1998d). 
Figure 1-4. EDA II Emplacement Drift Cross-section Showing the Processes Considered in the 
Evolution of the Physical and Chemical Environment Within the Emplacement Drifts

 F1-5 
NOTE: Taken from Figure 5 of CRWMS M&O 2000ag 
Figure 1-5 Emplacement Drift Cross-Section with Invert Structure in Place (shown without backfill)

 F1-6 
NOTE: Taken from Figure 6 of CRWMS M&O 2000ag 
Figure 1-6 Emplacement Drift Perspective View with Steel Invert Structures in Place

 F1-7 
NOTE: Taken from Figure 4 of CRWMS M&O 2000ah 
Figure 1-7 Emplacement Pallet Loaded with Waste Package

 F1-8 
NOTE: Taken from Figure 3 of CRWMS M&O 2000ah 
Figure 1-8 Emplacement Pallet Isometric View

 F1-9 
NOTE: Taken from Figure 2 of CRWMS M&O 2000ah 
Figure 1-9 Drip Shield Interlocking Connection

 F1-10 
NOTE: Taken from Figure 2 & 5 of CRWMS M&O 2000ai 
Figure 1-10. Drip Shield Isometric View

 2-1 
2. EVOLUTION OF THE ENGINEERED BARRIER SYSTEM PROCESS MODELS 
In early calendar year 1999, the Yucca Mountain Site Characterization Project (YMP) 
Management and Operating Contractor (M&O) personnel began developing process model 
reports (PMRs) to provide the primary documentation in support of the Site Recommendation 
and, ultimately, the License Application for a potential Yucca Mountain high-level radioactive 
waste repository. 
Initial analyses and models for EBS components were developed for the License Application 
Design Selection (LADS) process. A number of alternative conceptual designs were evaluated 
for possible improvements in the projected total system performance beyond that presented in 
the Total System Performance AssessmentViability Assessment (TSPA-VA; DOE 1998a). 
Although the site characteristics alone are expected to prevent the release of most radionuclides 
to the accessible environment, additional engineering measures were proposed to reduce 
uncertainty and to provide defense in depth. The LADS effort resulted in the adoption, in June 
1999, of Enhanced Design Alternative II (EDA II) (Wilkins and Heath 1999). The design 
concepts in EDA II include the following: 
 Improved Waste Packages incorporating a corrosion resistant outer barrier 
 The use of drip shields (DSs) and backfill to protect waste packages (WPs) from water 
contact and rockfall 
 The use of ventilation to remove heat before closure 
The EBS PMR summarizes and integrates 23 analysis/model reports (AMRs) developed to 
address the performance assessment of EDA II. A brief description of the component AMRs is 
given in Section 1. 
2.1 DEVELOPMENT PHILOSOPHY FOR THE ENGINEERED BARRIER SYSTEM 
PROCESS MODEL REPORT 
Where possible, EBS performance models are based on measured data for engineered material 
properties and on experiments designed to test the validity of approximations used in the models. 
Coping with the timing of design-selection decisions, and the continued evolution of design 
details requires a very flexible approach to both modeling and testing in support of the EBS 
PMR. Defensible bounds are presented where data are not available to support more rigorous 
process models.

 2-2 
2.2 PAST ENGINEERED BARRIER SYSTEM MODELING, ANALYSIS, AND 
ABSTRACTION 
2.2.1 Process Models and Abstractions Prior to Total System Performance Assessment of 
1995 (TSPA-95) 
In analyses completed prior to the Total System Performance Assessment of 1995 (TSPA-95) 
(Barnard et al. 1992; Wilson et al. 1994; CRWMS M&O 1994) the EBS was incorporated as a 
number of compositional variables within subsystem models or implicitly within some of the 
ranges used for performance parameters (e.g., solubility-limited radionuclide concentrations) 
where the interior conditions of failed (or perforated) WPs were immediately the same as the 
drift conditions. The radionuclide release from the EBS was then available to the unsaturated 
zone (UZ) for transport in the geosphere. 
At this time, much of the EBS process modeling was simplistic and generally only dealt with WF 
and WP modeling under ambient conditions. 
2.2.2 TSPA-95 Process Models and Abstractions 
Likewise, at the time TSPA-95 was developed, much of the EBS chemical modeling was 
simplistic and generally only dealt with WF and WP modeling under ambient conditions. All 
conceptual models that were available were used to constrain EBS processes. The following 
paragraphs describe some of the highlights of the TSPA-95 models for in-drift chemistry, flow, 
and transport. 
The EBS chemistry and transport models for TSPA-95 incorporated the ambient water 
composition from Well J-13 and atmospheric oxygen and carbon dioxide fugacities. The 
impacts of pH variation and temperature variation were explicitly entered into models of WP 
degradation, WF dissolution, and the solubility-limited concentrations of neptunium (Np), 
plutonium (Pu), and americium (Am) (CRWMS M&O 1995). A variable pH condition covering 
values of 6 to 9 (with 7 taken as the base case) was incorporated implicitly into the distributions 
of solubility-limited concentrations to define the mobile radionuclide concentration. This range 
of pH reflected the range of measurements for fluids from Well J-13. Gas-phase composition 
was assumed to be buffered to atmospheric values because of ready gas flow through the 
mountain. 
For TSPA-95, EBS transport modeling of the drift was handled within the Repository Integration 
Program (RIP) software code using the following conceptual models for radionuclide release 
(CRWMS M&O 1995). 
Drips-On-Waste FormThis conceptual model assumed that after one pit penetrated a WP, 
conditions inside of the WP became the same as those of the drift environment. Advective flux 
through the WP and onto the WF was also permitted as soon as a single pit penetrated the WP. 
Diffusive releases depended on the surface area of the WP, which was degraded or pitted 
through, and on the water-film thickness on the WF. 
Drips-On-Waste PackageThis conceptual model assumed only diffusive releases out of the 
WP. Advective flow remained on the surface of the WP and did not flow into the WP. The

 2-3 
corrosion products in the pits were assumed to prevent the advective or dripping water from 
entering the WP. 
No Advective Transport through the DriftThis conceptual model assumed no advective flow 
into the drift, leading to only diffusive release from the EBS. This model could be operational if 
the engineered system provided for diversion of all advective flow away from the drift by means 
of mechanisms such as a capillary barrier or a drip shield. 
2.2.3 Total System Performance AssessmentViability Assessment Process Models and 
Abstractions 
After finalization of TSPA-95 and prior to development of the Total System Performance 
AssessmentViability Assessment (TSPA-VA), the development of performance assessment 
models was integrated with the development of process models. Workshops were held to solicit 
inputs, discuss important processes, and provide input about those process models that could be 
used directly and those that should be developed (e.g., CRWMS M&O 1997). 
In some areas, such as the TH modeling, where the process models were sufficiently developed, 
the process models provided input that could be used directly. In other areas, the models were 
not at a sufficient state of development to be used. Therefore, simplified process models were 
developed using process conceptual models (Hardin 1998; Triay et al. 1996) that could be used 
directly or be abstracted for TSPA-VA. 
The following subsections summarize the improvements to the TSPA-95 model that were 
incorporated into TSPA-VA: 
2.2.3.1 In-Drift Geochemical Environment 
A more detailed representation of the chemical processes within the potential emplacement drifts 
was included for TSPA-VA. This in-drift geochemical environment (IDGE) component 
included changing the composition of gas, water, colloids, and solids within the emplacement 
drifts under the perturbed conditions of the potential repository environment (CRWMS M&O 
1998d). A set of five models was developed for TSPA-VA to represent the IDGE: 
 Incoming gas, water, and colloids model (compositions of those phases as they entered 
the drift): this model represented the boundary conditions that were imposed on the indrift 
environment 
 In-drift gas phase model (composition of the gas phase relative to major gas sinks in 
the drift) 
 In-drift watersolid chemistry model (evolution of water composition reacting with 
major materials and the in-drift gas phase) 
 In-drift colloids model (stability and quantity of clay and iron-oxide colloids in the 
drift) 
 In-Drift Microbial Communities

 2-4 
Some of the five models listed previously contained process-level calculations to represent the 
evolution of water, solid, and gas reactions in the system. Other models consisted of bounding 
arguments for applying observed values. In all five of these models, efforts were made to remain 
consistent to the results of the thermal-hydrologic process models and other boundary-condition 
process models that governed the temperature and hydrology of the EBS environment. These 
models were abstracted or used to develop parameters for the TSPA model. 
2.2.3.2 EBS Transport 
In the TSPA-VA model, the release of radionuclides into the natural environment was controlled 
by the transport of the radionuclides out of the WPs and through the concrete invert (included in 
the VA conceptual design, but replaced in EDA II by crushed tuff). Key factors affecting the 
transport of radionuclides through the EBS were the following (CRWMS M&O 1998e): 
 Performance of the WP 
 Protection provided by cladding 
 Matrix dissolution rate 
 Entry and movement of water through WPs 
 Colloidal transport of radionuclides 
 Sorption affinity of radionuclides to the concrete below the WPs. 
These key factors to EBS transport were abstracted and modeled by PA. 
2.3 PROCESS-MODEL DEVELOPMENT FOR THE ENGINEERED BARRIER 
SYSTEM 
A complete list of reports documenting the analyses and models developed for the EBS PMR is 
given in Table 1-1. Section 1.2 summarizes the scope of the different reports and their 
relationship to each other. Of necessity, many of these reports, including the performance 
assessment (PA) abstractions, have been developed in parallel, and the EBS PMR has been 
developed concurrently with other, closely related PMRs [those covering unsaturated-zone (UZ)] 
flow and transport, waste package, and waste form). The EBS process model was developed for 
a baseline EBS design implementation consistent with EDA II (Wilkins and Heath 1999), with 
details documented in Table 2 of the Water Distribution and Removal Model report (CRWMS 
M&O 2000q, p. 20). 
The potential repository design has continued to evolve, resulting in some changes in details, but 
the overall preclosure thermal-management goals, EBS system elements, and their intended 
functions remain consistent with EDA II. Forced ventilation will continue throughout the 
preclosure period to remove heat and moisture, WP spacing will be selected to optimize thermal 
performance, and the choice of drift orientation will minimize rockfall. Just prior to closure, a 
titanium DS will be placed over the packages. In EDA II, the DS will be covered with 
engineered backfill. The backfill protects the DS from rockfall; provides a more predictable 
in-drift thermal, hydrologic, and chemical environment than would be provided by rockfall; and 
works with the DS and the invert ballast to control the distribution of water within the drift.

 2-5 
To accommodate integration among concurrently developed AMRs contributing to the EBS 
PMR, and to maintain the flexibility needed to analyze changes in design details, many of the 
calculations documented in the AMRs were performed as sensitivity analyses. This strategy also 
assists in integration with other PMRs being developed in parallel. For example, ranges of 
parameters (e.g., seepage flux) were used instead of direct feeds from other process models. The 
intent is to provide the basis for assigning performance benefits to the EBS to compensate for 
uncertainty in the long-term predictions of natural system behavior. Model parameters for the 
UZ can only be loosely constrained by the application of accepted scientific principles in 
analyzing available data. They cannot be measured directly. As the EBS process models 
mature, the confidence limits for their parameter values may be narrowed for the EBS PMR. 
2.4 ENGINEERED BARRIER SYSTEM FEATURES, EVENTS, AND PROCESSES 
This section summarizes the process of identifying features, events, and processes (FEPs) that 
are applicable to the EBS (CRWMS M&O 2000c, 2000r). The screening of candidate FEPs 
identified in a preliminary draft of the Yucca Mountain Site Characterization Project (YMP) FEP 
Database is discussed. The results are presented as a list of FEPs that are addressed in EBS 
process models. The FEPs are provided as input to the YMP FEP Database for consideration in 
the Total System Performance Assessment (TSPA). Common-mode degradation events and 
processes that affect the repository are identified for system-wide impact analysis. 
2.4.1 Engineered Barrier System Feature, Event, or Process Identification Process 
This section summarizes the analysis documented in Engineered Barrier System Features, 
Events, and Processess and Degradation Modes Analysis (CRWMS M&O 2000c). The 
baselined enhanced design alternative EDA II (Wilkins and Heath 1999) for the potential 
repository was used as the reference design to determine basic EBS design features and events. 
A basis for EBS FEPs was then developed by identifying a number of process categories (based 
on issues, concerns, and advice from various principal investigators) relevant to degradation of 
the EBS. Table 2-1 lists these process categories, and significant potential processes in each 
category. Conceptual figures to assist in visualizing these performance factors were developed. 
A context of event and process occurrence and water availability conditions was defined to 
permit the organization of the EBS FEPs, and to provide a perspective of their importance. A 
logic diagram was then developed to systematically identify the EBS FEPs (CRWMS M&O 
2000c, Figure 7). 
The FEPs that were identified in the comprehensive and systematic process described above are 
listed and described in Table 2-2, using ebsxnumbers. Table 2-2 also lists EBS FEPs that have 
initially been identified as candidate database FEPs (w.x.y.z.00). These candidate FEPs have 
all been dispositioned as include in TSPA, based on a screening process described in Section 
2.4.2. While the listing of FEPs from different sources (signified by w.x.y.z.00 and ebsx 
FEP numbers) may be redundant, they are listed to ensure completeness. Table 2-2 is a 
comprehensive list of all EBS FEPs that are recommended for consideration in the various TSPA 
scenarios pertaining to the EBS.

 2-6 
Table 2-1. Basis for Engineered Barrier System Features, Events, and Processes Identification A 
Process 
Categories 
Significant Potential 
Processes 
Remarks 
1. Flow Types Weeps Locally-saturated flow, presumed to be 
fracture flow 
Drip Dropping of water from the drift crown or 
fracture openings 
Matrix flow Classic two-phase flow through the matrix 
2. Water Sources Infiltrate Fracture and matrix flow of water entering 
from the surface 
Condensate Condensate formed in rock and in drift, 
accumulated because of thermal-hydrologic 
processes 
Condensate under the drip 
shield (DS) 
Condensation of water vapor beneath the DS 
from water in the invert 
Rockwater interactions for 
condensate 
Alters solutes for corrosion processes 
Rockwater interactions for 
infiltrate 
Alters solutes for corrosion processes 
Rockwater interactions for WP 
effluent 
Interaction of dissolved and colloidal 
contaminants with invert and drift floor for 
transport 
Rockwater interactions of fines 
and minerals in fractures along 
flow pathways 
Interactions potentially plugging fractures 
3. Chemistry 
Colloids Stability in the invert; filtration and alteration in 
the exit transport 
Thermomechanical interaction, 
stress-evolution 
Rotation of least principal stress; fracture 
closure; thermal expansion of rock; residual 
drift size 
Thermochemical interaction, 
transport, and sorption 
Temperature rate and phase dependencies 
4. Heat 
Thermochemical interaction, 
corrosion of ground support, 
pedestals, rails, etc. 
Temperature rate dependencies 
Floor heave (buckling) Buckling due to mechanical stress relief and to 
thermomechanical coupling 
Ground-support failure Failure due to mechanical stress relief and 
thermomechanical coupling 
Rockfall 
Stopping up fracture zones Localized rockfall affecting water intrusion 
5. Drift Alteration 
Invert movement Associated with floor and wall movement 
6. Pathways Infiltrate entering the EBS Fracture and matrix flow of surface water 
Condensate entering the EBS Condensate in the rock and in the drift 
providing a local water source 
Movement around the DS DS functions as designed 
Movement through the DS DS failure in some locations 
Movement under the DS in the 
invert 
Condensate flows along DS inner wall and 
then drips 
Movement through the invert Water chemistry changes, affects 
consequences of ponding

 2-7 
Process 
Categories 
Significant Potential 
Processes 
Remarks 
Flowtransport exiting in open 
fractures 
Fracture exits in the drift floor 
Flowtransport exiting in 
plugged fractures 
Fines, clays, mineral alterations, etc plug 
fracture exits. 
Flowtransport exiting as matrix 
flow 
Idealized transport in porous media 
Chemical properties of infiltrate 
and condensate 
Rockwater interactions expected to provide 
different water constituents for these different 
sources 
Corrosion of DS Direct corrosion (water contact) and contact 
corrosion (with WPs or rails). 
Corrosion of pedestals Pedestal failure putting WP on or in invert 
7. Corrosion 
Corrosion of ground support Failure of rockbolts, wire mesh, and steel sets 
affecting drift stability 
FuelWF effects on mobilization Effects on solubility, speciation, colloid 
formation, stability 
Interaction with invert Alteration of solute phases; sorption 
Interaction with drift floor Alteration of solute phases; sorption 
8. Mobilization of 
Contaminants 
Interaction with fractures and 
fracture-plugging 
Mineral alterations (e.g., reaction with fines); 
possible ponding 
Through invert Alteration of solute phases; sorption 
Along drift floor Alteration of solute phases; sorption 
Through drift floor Fracture and matrix flowtransport, including 
plugging 
9. Transport 
Ponding and localization of flow Ponding, episodic release, solubility limited 
transport 
Mine: water removal or dryout Establishes initial conditions 
Mine: heat removal Establishes initial conditions 
Mountain: background Heat driven: postclosure affects temperature, 
moisture, exchange with atmosphere 
10. Ventilation 
Mountain: chimney effects Chimney behavior of fault zones 
Ramps Not in the waste-emplacement drifts 
Shafts Undefined in the EBS 
11. Seals 
Drifts Undefined purpose 
Location Floor, lower ribs 
Design Rock-filled; intercepts likely locations of 
stress-relief fractures 
Functional lifetime Probably not needed during the thermal period 
(no liquid water) 
12. Drains 
Plugging and other failure 
modes 
Thermomechanical compression; fines; 
mineralogical changes 
NOTE: A The reader is referred to CRWMS M&O (2000c) for details of the FEP development logic.

 2-8 
Table 2-2. Engineered Barrier System Features, Events, and Processes 
FEP Category B FEP Number FEP Name FEP Description 
Features 
ebs 2 Drip shield Liquid water contact with the waste package is 
believed to affect the rate of corrosion of the 
metals, thus exposing the waste. The drip 
shield is intended to reduce direct liquid 
contact with the containers. 
F1 Drip Shield 
ebs 3 Drip-shield supports Failure of the drip-shield supports allows the 
drip shield to make contact with the waste 
package or with the rails. Because the drip 
shields are made of Ti, the rails of steel, and 
the waste packages of a high-nickel alloy, 
contact results in contact corrosion, possibly 
affecting the integrity of the waste package. 
F2 Ground 
Support 
ebs 21 Ground support  wire 
mesh and rockbolts 
The expected life of ground support after the 
operational phase of the potential repository is 
unknown. Failure of ground support allows 
rockfall and development of a chimney or 
enlarged drift and filling of fracture or fault 
zones. 
ebs 22 Ground support  
rockbolts and grout 
Ground support introduces materials (Fe, 
grout, etc.) into the facility, which affects water 
chemistry. All ground support eventually fails, 
allowing rockfall, altering drift size and 
properties, and affecting flow pathways. 
2.1.06.01.00 Degradation of 
cementitious materials 
in drift 
Degradation may occur through physical, 
chemical, and microbial processes. 
Degradation of cementitious material used for 
any purposes in the disposal region may affect 
long-term performance. 
2.1.06.02.00 Effects of rockreinforcement 
materials 
Degradation of rock bolts, wire mesh, and 
other materials used in ground control may 
affect the long-term performance of the 
potential repository. 
F3 Backfill ebs4 Backfill Crushed rock is placed as protection for the 
waste package, or the drip shield and waste 
package, from rockfall and failure of ground 
support and possibly as a Richards barrier for 
flow. Location of backfill and the size and 
material type all affect water chemistry (as well 
as the corrosion rates for drip shield and waste 
packages and dissolution rates for waste) and 
thermal properties (as well as waste 
temperatures and cladding failure). 
Suggestions for material type currently include 
sand, crushed limestone, marble, and crushed 
tuff. The last is the subject of investigation. 
2.1.04.02.00 Physical and chemical 
properties of backfill 
The physical and chemical properties of the 
backfill may affect groundwater flow, waste 
package and drip shield durability, and 
radionuclide transport in the waste-disposal 
region.

 2-9 
FEP Category B FEP Number FEP Name FEP Description 
2.1.04.05.00 Backfill evolution Properties of the backfill change through time 
because of processes such as silica 
cementation, alteration of minerals, thermal 
effects, and physical compaction. These 
changes then affect the movement of water 
and radionuclides in the backfill. 
F4 Invert ebs5 Invert The invert materials, currently expected to be 
crushed rock, form the bed for the rails and will 
be the resting place for the waste package 
after the support pedestals fail. The invert is 
part of the flow pathway from the waste to the 
drift bottom and exit from the drift. The invert 
is also part of the flow pathway for water 
deflected by the drip shield from the waste 
packages. Water can accumulate in the invert, 
acting as a water-vapor source for corrosion or 
possibly ponding. Accordingly, invert materials 
can affect water chemistry for transport. 
F5 Drains (if 
used) 
ebs23 Drains (if used) Water accumulation in the drift would wet the 
invert materials, possibly pond, and provide a 
continuing source of water vapor beneath the 
drip shield and backfill for interaction with 
waste packages and their supports. 
F6 Operational 
Equipment 
ebs7 Rails Rails represent a material, steel, added to the 
potential repository, which is not necessary to 
long-term isolation, but which may have an 
impact on corrosion of the drip shield and on 
water chemistry for transport. If the Ti drip 
shield and the steel rails are in contact, contact 
corrosion is expected, which could affect the 
long-term ability of the drip shield to divert 
water from the waste package. Such contact 
would be expected locally as a result of a 
seismic disturbance, rockfall, or groundsupport 
failure. 
ebs8 Pedestal The pedestal may be distorted or racked 
because of floor heave (thermomechanical 
stress adjustment) and ground motion (seismic 
event) or may fail because of corrosion. 
Failure by any mode will drop the waste 
package onto or into the invert. 
Events 
ebs6 Rockfall-loading 
distortion of drip shield 
Contact corrosion, compromising the drip 
shield or the waste package, develops as a 
result of displacement or distortion of the drip 
shield. 
E1 Rockfall 
2.1.04.04.00 Mechanical effects of 
backfill 
Backfill may alter the mechanical evolution of 
the drift environment by providing resistance to 
rock creep and rockfall, by changing the 
thermal properties of the drift, or by other 
means. Impacts of the evolution of the 
properties of the backfill itself should be 
considered.

 2-10 
FEP Category B FEP Number FEP Name FEP Description 
E2 Seismic 
Event 
ebs9 Ground motion Ground motion, generated by seismic events, 
provides accelerations to components of the 
potential repository, including the waste 
packages, drip shield, backfill, surrounding 
rock, and ground support. These 
accelerations cause relative motion of the 
components and could generate groundsupport 
failure, rockfall, and damage to waste 
packages and drip shields. 
ebs11 Relative seismic 
motion 
Ground motion in the potential repository could 
generate waste package displacement; 
relative displacement between waste package, 
drip shield, and rails; ground-support failure; 
and rockfall. 
E3 Ground 
Support 
Failure 
ebs12 Ground-support failure Failure of ground support, for whatever 
reason, would allow rockfall, displacement of 
backfill and waste packages, and development 
of new flow pathways. Possible cases include 
ground motion, thermomechanical stress 
adjustment, and corrosion. 
2.1.11.07.00 Thermally induced 
stress changes in 
waste and EBS 
Thermally induced stress changes in the waste 
and EBS may affect performance of the 
potential repository. Relevant processes 
include rockfall. 
Processes 
P2 Dryout of 
Rock 
2.1.08.11.00 Resaturation of 
potential repository 
Water content in the potential repository 
increases following the peak thermal period. 
P4 Thermomechanical 
Evolution of 
Potential 
repository 
Rock 
ebs13 Thermomechanical 
evolution of a potential 
repository block 
Thermomechanical coupling, which alters the 
stress state of the rock surrounding the 
potential repository, affects floor buckling, 
fracture sealing and openings to the EBS, and 
loading and unloading of ground support. 
2.1.04.04.00 A Mechanical effects of 
backfill 
2.1.08.08.00 Induced hydrologic 
changes in the waste 
and EBS 
Thermal, chemical, and mechanical processes 
related to the construction of the potential 
repository and the emplacement of waste may 
induce changes in the hydrologic behavior of 
the system. 
2.1.11.01.00 Heat output and 
temperature in waste 
and EBS 
Temperature in the waste and EBS will vary 
through time. Heat from radioactive decay will 
be the primary cause of temperature change, 
but other factors to be considered in 
determining the temperature history include 
the in situ geothermal gradient; thermal 
properties of the rock, EBS, and waste 
materials; hydrologic effects; and the 
possibility of exothermal reactions. 
Considerations of the heat generated by 
radioactive decay should take into account 
different properties of different waste types, 
including U.S. Department of Energy spent 
nuclear fuel.

 2-11 
FEP Category B FEP Number FEP Name FEP Description 
2.1.11.07.00 A Thermally induced 
stress changes in 
waste and EBS 
2.1.11.09.00 Thermal effects on 
liquid or two-phase 
fluid flow in the waste 
and EBS 
Temperature differentials may result in 
convective flow in the waste and EBS. 
P5 Shear 
Fracture/Fault 
Movement 
and 
Relaxation 
ebs14 Shear fracture and 
fault movement and 
relaxation 
Fractures that might otherwise be closed 
during the thermal period, because of 
compression from thermal expansion, are 
maintained as open pathways because of 
shear movement. Movement also allows 
distortion of the drift and the relative location of 
drip shield, rails, and waste packages, with 
possible contact being established. 
P6 Condensation ebs15 Condensation beneath 
drip shield 
Condensation on the inner surface of the drip 
shield circumvents its performance and 
provides water to drip onto the waste package 
and its supporting pedestal. Enhanced 
corrosion of waste package and pedestal 
becomes possible. 
2.1.06.06.00 Effects and 
degradation of drip 
shield 
The drip shield will affect the amount of water 
reaching the waste package. Behavior of the 
drip shield in response to rockfall, ground 
motion, and physical and chemical 
degradation processes should be considered. 
Effects of the drip shield on the disposal region 
environment (for example, changes in relative 
humidity and temperature below the shield) 
should be considered for both intact and 
degraded conditions. Degradation processes 
specific to the chosen material should be 
identified and considered (for example, oxygen 
embrittlement should be considered for 
titanium drip shields). 
2.1.08.04.00 Condensation forming 
on backs of drifts 
Emplacement of waste in drifts creates a large 
thermal gradient across the drifts. Moisture 
condenses on the roof and flows downward 
through the backfill. 
P8 Reflux ebs16 Reflux drainage of 
condensate zone 
Condensate zones could contain a substantial 
amount of mobile water able to flow back into 
the drifts, perhaps as a single extended 
episode. 
P9 Flow Along 
Drip Shield 
Wall 
ebs17 Flow along drip shield 
(inside) wall 
Water vapor is available from water otherwise 
diverted from the waste packages, which flows 
down the drip shield and enters the invert, 
where it may accumulate.

 2-12 
FEP Category B FEP Number FEP Name FEP Description 
ebs24 Flow along drip shield 
(outside) wall 
Because the segmented drip shield will see 
liquid water, the concerns are the 
effectiveness of the diversion (i.e., will liquid 
flow pass through the overlaps) and the 
corrosion resistance of the drip shield material 
to the water chemistry in the impinging water. 
2.1.04.01.00 Preferential pathways 
in the backfill 
Preferential pathways for flow and diffusion 
may exist within the backfill and may affect 
long-term performance of the waste packages. 
Backfill may not preclude hydrologic, chemical, 
and thermal interactions between waste 
packages within a drift. 
2.1.08.01.00 Increased unsaturated 
water flux at the 
potential repository 
An increase in the unsaturated water flux at 
the potential repository affects thermal, 
hydrologic, chemical, and mechanical behavior 
of the system. Extremely rapid influx could 
reduce temperatures to below the boiling point 
during part or all of the thermal period. 
Increases in flux could result from climate 
change, but the cause of the increase is not an 
essential part of the FEP. 
ebs18 Flow through backfill Flow through the backfill reacts chemically with 
the backfill. This chemically altered water then 
interacts with the drip shield and rails to 
eventually reach the invert. 
2.1.04.01.00 A Preferential pathways 
in the backfill 
P10 Flow Through 
Backfill 
2.1.08.01.00 A Increased unsaturated 
water flux at the 
potential repository 
ebs19 Movement of backfill 
through gaps and 
separations in drip 
shield 
The continuity of the drip shield and its ability 
to deflect liquid water could be compromised 
as a result of movement produced by 
thermomechanical or seismic processes. 
P11 Movement of 
Backfill 
Through 
Gaps and 
Separations 
in Drip Shield 2.1.04.04.00 A Mechanical effects of 
backfill 
ebs20 Fluid flow into gaps 
and separations in drip 
shield 
The ability of the drip shield to deflect liquid 
water could be compromised as a result of the 
movement of liquid water through gaps or 
spaces that develop between drip-shield 
segments. 
P12 Fluid Flow 
Into Gaps and 
Separations 
in Drip Shield 
2.1.06.06.00 A Effects and 
degradation of drip 
shield 
P13 Microbial 
Activity 
ebs25 Microbial activity The concern is microbially accelerated 
corrosion and mobilization occurring in the 
warm, moist environment of the EBS.

 2-13 
FEP Category B FEP Number FEP Name FEP Description 
2.1.10.01.00 Biological activity in 
waste and EBS 
Biological activity in the waste and EBS may 
affect disposal-system performance by altering 
degradation processes such as corrosion of 
the waste packages and waste form (including 
cladding), by affecting radionuclide transport 
through the formation of colloids and biofilms, 
and by generating gases. 
2.1.11.08.00 Thermal effects: 
chemical and 
microbiological 
changes in the waste 
and EBS 
Temperature changes may affect chemical 
and microbial processes in the waste and 
EBS. 
2.1.04.02.00 A Physical and chemical 
properties of backfill 
P14 Alteration of 
Infiltrate 
Chemistry 
(abiotic) 2.1.09.01.00 Properties of the 
potential carrier plume 
in the waste and EBS 
When unsaturated flow in the drifts is 
reestablished following the peak thermal 
period, water will have chemical and physical 
characteristics influenced by the near-field 
host rock and EBS. Water chemistry may be 
strongly affected by interactions with 
cementitious materials. 
ebs26 Rockbolt and grout 
corrosion 
Corrosion and alteration changes the flow path 
for water entrance and alters the chemistry of 
the water following those flow paths. 
2.1.06.01.00 A Degradation of 
cementitious materials 
in drift 
P15 Rockbolt & 
Grout 
Corrosion 
2.1.06.02.00 A Effects of rock 
reinforcement 
materials 
2.1.09.02.00 Interaction with 
corrosion products 
Corrosion products produced during 
degradation of the metallic portions of the EBS 
and waste package may affect the mobility of 
radionuclides. Sorption/desorption and 
coprecipitation/dissolution processes may 
occur. 
P16 Wire Mesh 
Corrosion 
2.1.09.02.00 A Interaction with 
corrosion products

 2-14 
FEP Category B FEP Number FEP Name FEP Description 
P17 Drainage 
With 
Transport 
ebs27 Drainage with 
transport  sealing and 
plugging 
Normal functioning of drainage in the drifts is 
not established, so how drainage will change if 
fractures are plugged is unclear. Suggestions 
include ponding until fractures in the wall are 
reached by the water level or until there is 
sufficient head to clear the fractures. 
ebs28 Drainage with 
transport  through 
constructed drains 
Water accumulation would be possible in a 
drift, particularly in a region of floor buckling, if 
normal drainage is blocked. Such blockage 
could occur if fines and debris were deposited 
in fractures or as sediment along the drift floor. 
Excess water could allow more rapid corrosion 
and contaminant mobilization. The conundrum 
here is that rapid draining of water sooner 
might also mean rapid draining of 
contaminated water later. 
ebs29 Drainage with 
transport  ponding 
Water could accumulate in the invert in 
sufficient amounts to flood the waste package, 
enhancing corrosion and eventual 
mobilization. Criticality could be a possible 
consequence. 
2.1.08.05.00 Flow through invert Flow through invert results in transport of 
contaminants to the unsaturated zone 
2.1.08.06.00 Wicking in waste and 
EBS 
Capillary rise, or wicking, is a potential 
mechanism for water to move through the 
waste and engineered barrier system. 
2.1.08.07.00 Pathways for 
unsaturated flow and 
transport in the waste 
and EBS 
Unsaturated flow and radionuclide transport 
may occur along preferential pathways in the 
waste and EBS. Physical and chemical 
properties of the EBS and waste form, in both 
intact and degraded states, should be 
considered in evaluating pathways. 
P18 Drip Shield 
Corrosion 
ebs25 A Microbial activity 
ebs30 Drip-shield corrosion  
flow of backfill through 
corroded elements 
The continuity of the drip shield and its ability 
to deflect liquid water could be compromised 
because of holes produced by corrosion. 
ebs31 Drip shield corrosion  
fluid flow through 
corroded elements to 
waste packages 
Deflection of liquid water away from the waste 
packages depends on continuity of the drip 
shield and the absence of penetrations. 
ebs32 Corrosion of waste 
packages 
Corrosion may contribute to waste-package 
failure. Corrosion is most likely to occur at 
locations where water drips on the waste 
packages, but other mechanisms should be 
considered. 
2.1.06.06.00 A Effects and 
degradation of drip 
shield

 2-15 
FEP Category B FEP Number FEP Name FEP Description 
ebs1 Pedestal collapse As a result of pedestal collapse, the waste 
package lies on or in the invert and could be in 
contact with the drip shield and the rails and 
thus be exposed to contact corrosion. While 
bedded in the invert, the waste package is 
more likely to see local ponding and the 
enhanced corrosion and mobilization that 
might accompany it. 
ebs6 A Rockfall-loading 
distortion of drip shield 
ebs10 Drip-shield movement 
relative to waste 
packages and rails 
Contact of the Ti drip shield with the waste 
package or with the steel rails will cause 
contact corrosion. In the former case, 
corrosion of the waste package will be 
enhanced; in the latter case, corrosion of the 
drip shield will be accelerated. Presumably, 
the fate of the rails is inconsequential. 
ebs11 A Relative seismic 
motion 
P19 Drip Shield 
Movement 
Relative to 
Waste 
Package/ 
Rails 
2.1.06.05.00 Degradation of invert 
and pedestal 
Degradation of the materials used in the invert 
and the pedestal supporting the waste 
package may occur by physical, chemical, or 
microbial processes and may affect the longterm 
performance of the potential repository. 
2.1.04.02.00 A Physical and chemical 
properties of backfill 
P20 Alteration of 
Temperature- 
Dependent 
Chemical 
Activity 
2.1.09.06.00 Reduction-oxidation 
potential in waste and 
EBS 
The redox potential in the waste and EBS 
influences the oxidation of barrier and wasteform 
materials and the solubility of 
radionuclide species. Local variations in the 
redox potential can occur. 
2.1.09.12.00 Rind (altered zone) 
formation in waste, 
EBS, and adjacent 
rock 
Thermochemical processes involving 
precipitation, condensation, and redissolution 
alter the properties of the waste, EBS, and 
adjacent rock These alterations form a rind, or 
altered zone, with hydrologic, thermal, and 
mineralogical properties that are different from 
the current conditions. 
2.1.09.14.00 Colloid formation in 
waste and EBS 
Colloids in the waste and EBS may affect 
radionuclide transport. Different types of 
colloids may exist initially or may form during 
the evolution of the system by a variety of 
mechanisms. This FEP aggregates all types 
of colloids into a single category.

 2-16 
FEP Category B FEP Number FEP Name FEP Description 
2.1.09.16.00 Formation of pseudocolloids 
(natural) in 
waste and EBS 
Pseudo-colloids are colloidal-sized 
assemblages (between approximately 1 
nanometer and 1 micrometer in diameter) of 
nonradioactive material that have 
radionuclides bound to them. Pseudo-colloids 
include microbial colloids, mineral fragments, 
and humic and fulvic acids. This FEP 
addresses radionuclide-bearing colloids 
formed from host-rock materials and all 
interactions, except corrosion, of the waste 
and EBS with the host rock environment. 
Pseudo-colloids formed from corrosion of the 
waste form and EBS are discussed in FEP 
2.1.09.17.00. 
2.1.09.17.00 Formation of pseudocolloids 
(corrosion 
products) in waste and 
EBS 
Pseudo-colloids are colloidal-sized 
assemblages (between approximately 1 
nanometer and 1 micrometer in diameter) of 
nonradioactive material that have 
radionuclides bound to them. Pseudo-colloids 
include microbial colloids, mineral fragments, 
and humic and fulvic acids. This FEP 
addresses pseudo-colloids such as iron 
oxyhydroxides formed from corrosion and 
degradation of the metals in the waste form 
and EBS. Radionuclide-bearing colloids 
formed from host-rock materials and all 
interactions, except corrosion, of the waste 
and EBS with the host rock environment are 
discussed in FEP 2.1.09.16.00. 
2.1.11.04.00 Temperature effects / 
coupled processes in 
waste and EBS 
This FEP broadly encompasses all coupledprocess 
effects of temperature changes within 
the waste and EBS. 
2.1.11.09.00 A Thermal effects on 
liquid or two-phase 
fluid flow in the waste 
and EBS 
2.2.08.04.00 Redissolution of 
precipitates directs 
more corrosive fluids 
to waste packages 
Redissolution of precipitates, will have plugged 
pores as a result of evaporation of ground 
water in the hot zone, produces a pulse of fluid 
reaching the waste packages when gravitydriven 
flow resumes; this pulse of fluid is more 
corrosive than the original fluid in the rock. 
P21 Ventilation 1.1.02.02.00 Effects of preclosure 
ventilation 
The duration of preclosure ventilation acts 
together with waste-package spacing (as per 
design) to control the extent of the boiling 
front. 
NOTES: A A repeated FEP. 
B The reader is referred to CRWMS M&O (2000c) for details of the FEP development logic.

 2-17 
2.4.2 Screening of Candidate Database Features, Events, and Processes 
To initiate the development of a FEP database, a preliminary set of FEPs was defined and 
subjected to screening. The screening confirmed the applicability of the initial candidate FEPs to 
the Yucca Mountain EBS. The criteria for screening and resulting dispositions (include and 
exclude) are defined and summarized in Section 1.5.1 and Table 1-2. Included FEPs are 
listed in Table 2-2. 
2.4.3 Common Mode Degradation 
The potential repository is designed so that there is defense-in-depth, that is, individual barriers 
can degrade or fail to perform without compromising repository performance. It is conceivable 
that certain events or processes affect the degradation of multiple components simultaneously, 
and thus produce common-mode degradation. Typically, common mode describes the 
degradation of multiple, redundant components due to a single event that simultaneously affects 
all critical components. A more complete definition distinguishes between repository 
components, and processes that cause radionuclide release and transport. The definition used in 
conjunction with the repository includes degradation of multiple, critical repository components 
by: 1) a single event such as faulting through the repository; 2) a single process such as increased 
water flow; and 3) multiple processes initiated by a single event, such as increased water inflow 
and creation of new transport pathways, caused by faulting. 
To cause common-mode degradation, an event or process must have the potential to affect 
release of radionuclides from the repository. The degradation can be local (affecting only a few 
waste packages), or non-local (affecting a large part of the potential repository). The 
consequences of an initiating event or process may be delayed by varying degrees, but these 
situations are not distinguished in this description. 
A simplified fault tree for common-mode degradation is shown in Figure 2-1, to help identify 
initiating processes and events. If common degradation modes exist, the initiating event or 
process appears beneath multiple branches. The fault tree starts at the top with increased 
radionuclide release from the potential repository, and the branches identify changes that must 
occur to reach initiating processes or events. Three principal branches are identified: 
1) increased water contacting waste packages; 2) decreased waste package lifetime; and 
3) increased rate of radionuclide release from the waste form. Increased seepage into 
emplacement drifts, for example, is a common-mode initiating process for many branches of the 
fault tree. Table 2-3 summarizes the common modes for the repository based on Figure 2-1. 
Further details and references are provided in the detailed EBS FEPs analysis (CRWMS M&O 
2000c), and process model reports pertinent to the specific event or process. It is noted that the 
common-mode events and processes are covered in the screening summary of Table 1-2 and in 
Table 2-2. They are identified here as a subject for system-wide analysis.

 2-18 
Table 2-3. Summary of Common Modes Identified in Figure 2-1 
Common Mode Description Remarks 
Increased seepage Increased water flow into drifts from long-term 
or episodic increases in infiltration, or locally 
from modification of flow pathways. 
Infiltration changes associated with 
possible future climate changes, are 
incorporated in predictive models. 
Seismicity Disruptive ground motion produced by an 
earthquake occurring outside the potential 
repository 
Likelihood estimated in the Probabilistic 
Seismic Hazard 
Faulting Rupture of a new or existing fault within the 
potential repository causes disruptive ground 
motion, displacement of engineered 
components, and changes to flow pathways 
through the host rock. 
Likelihood estimated in the Probabilistic 
Seismic Hazard Assessment 
Thermal-hydrologicchemical-
mechanical 
(THCM) alteration of 
host rock characteristics 
Stress changes cause rockfall and ground 
support failure 
Uncertain importance; thought to be 
limited by gradual and local failure of 
ground support 
Thermal-hydrologicchemical 
(THC) salt 
production 
Thermally driven processes involving water 
and chemical constituents, concentrate salts 
and precipitates originating from the host 
rock, and deposit them in the EBS. Aqueous 
corrosion can begin at lower values of relative 
humidity, and the chemical environment can 
be more corrosive. 
Likely only during the thermal period, 
and related directly to seepage 
Microbially influenced 
corrosion (MIC) 
The corrosion rate of Alloy 22 is enhanced by 
microbial activity on the waste package 
surface 
Moderate rates of MIC are observed in 
lab experiments, and may occur in the 
potential repository if sufficient nutrients 
are present 
Igneous intrusion A basaltic intrusion intersects potential 
repository drifts, or transport pathways for 
radionuclides, and may reach the surface. 
Likelihood estimated in Probabilistic 
Volcanic Hazards Assessment 
(CRWMS M&O 1996) 
2.5 REFERENCE CASE FOR THE ENGINEERED BARRIER SYSTEM 
The reference case used in the development of the engineered barrier system (EBS) 
analysis/model reports (AMRs) and process model report (PMR) is based on the technical 
requirements baseline of the Civilian Radioactive Waste Management System program (Wilkins 
and Heath 1999). In this reference case, the capacity of the potential repository is designed for 
the emplacement of 70,000 metric tons of uranium (MTU) (63,000 MTU commercial spent 
nuclear fuel (CSNF) + 7,000 MTU U.S. Department of Energy (DOE) spent nuclear fuel (SNF) 
and high-level waste (HLW)). 
An areal mass loading of approximately 60 MTU/acre, combined with preclosure ventilation for 
50 years, will prevent the boiling zones from coalescing in the pillars between emplacement 
drifts. Waste packages are placed in the emplacement drifts in a line load configuration with a 
WP to WP spacing of approximately 10 cm. The diameter of a waste emplacement drift is 
5.5 m. Emplacement drifts are arranged with a uniform spacing of 81 m between their 
centerlines. The total emplacement drift length is calculated from adding the WP inventory

 2-19 
(including DOE WPs) and the WP-to-WP gaps. The emplacement area encompasses 1050 acres 
in the upper emplacement level of the characterized area. 
The WP design for this case consists of two layers. The inner layer is stainless steel 
(Alloy 316L), approximately 5 cm thick, and the outer layer is Alloy 22, approximately 2 cm 
thick. Waste packages heat output at emplacement is not to exceed 11.8 kW. This specification 
requires blending fuel assemblies to no more than 20 percent above the average pressurizedwater 
reactor (PWR) thermal heat output (9.8 kW per package). The average age of the CSNF is 
assumed to be 26 years, with no additional aging beyond that imposed by reactor and potential 
repository operation schedules. 
The potential repository is designed to allow closure at 50 years after the start of emplacement 
and to accommodate up to 125 years of operation if necessary. Each emplacement drift segment 
will be ventilated during the entire preclosure period (50 years for the reference case), at a 
ventilation rate selected to remove at least 70 percent of the WP heat output before closure. 
Quartz sand and crushed tuff were selected as reference materials for the EBS backfill and invert, 
respectively. The reference drip shield is made of titanium Grade 7 with a minimum thickness of 
2 cm.

 F2-1 
NOTE: This figure was developed using information derived from CRWMS M&O (2000c). 
Figure 2-1. Common-mode Degradation Events and Processes 
Initiating Common-mode Processes/ Events 
Increased Radionuclide Releases 
from Engineered Barriers 
Increased 
Water 
Contacting 
WPs 
Decreased 
WP 
Lifetime 
Increased 
Waste Form 
Release 
Ponding in 
Drifts 
Penetration 
of Drip Shield 
Condensation 
Drip Shield 
Displacement; 
Rockfall; 
Salt/Ppt 
Contact 
Seepage; 
THCM 
Fracture 
Plugging 
Invert 
Saturation 
 Increased 
seepage 
 Increased 
seepage 
 THCM rock 
alteration 
 Faulting 
 Seismicity 
 THC salt 
production 
 Increased 
seepage 
 THCM rock 
alteration 
Mechanical 
Penetration 
Corrosion 
Penetration 
Microbial 
Activity; Salt/ 
Ppt Contact 
Rockfall & 
Ground 
Support 
Failure 
 Increased 
seepage 
 THC salt 
production 
 THCM rock 
alteration 
 Faulting 
 Seismicity 
Increased 
Dissolution 
Colloidal 
Release 
Intrinsic 
Colloid & 
Pseudo- 
Colloid 
Formation 
 Increased 
seepage 
 Increased 
seepage 
THCM  Thermal-hydrologic-chemical-mechanical coupled processes 
THC  Thermal-hydrologic-chemical coupled processes 
Notes: 
Igneous intrusion into the potential repository, or along transport pathways, 
could initiate increased releases along many branches of the tree. However, 
igneous intrusion is not shown for simplicity. 
The initiating processes and events shown here are limited to common 
modes; those limited to a single branch of the tree are not shown.

 3-1 
3. MODELS AND ABSTRACTIONS 
The EBS PMR includes four major process models, and the associated abstractions whereby the 
processes are incorporated in TSPA. The process models are organized as follows: 
 Water Distribution and Removal (WD&R) Model 
 Physical & Chemical Environment (P&CE) Model 
 EBS Radionuclide Transport (EBS RNT) Model 
 Multiscale Thermohydrologic (TH) Model 
Section 3.1 describes these models and summarizes their results. Section 3.2 describes the 
abstraction process, including model integration and representing uncertainties. 
3.1 MODEL DESCRIPTIONS 
Sections 3.1.1 through 3.1.4 describe the four major EBS process models and their constituent 
submodels. For each submodel (model and submodel are used interchangeably in this 
context) there is discussion of model inputs, assumptions, uncertainties, and validation, in 
addition to model development and results relevant to the potential repository. The discussion is 
generally taken directly from the cited AMRs, but other sources are used where appropriate. The 
source documents can be consulted for additional details, particularly regarding software, data 
sources (e.g., Data Tracking Numbers), and additional discussion of the open literature. 
This section describes a range of models and submodels, which are organized within the four 
major EBS process models, as shown in Table 3-A. It is noted that several of the contributing 
EBS AMRs each contain several submodels. Likewise, some of the submodels are supported by 
multiple AMRs. These relationships are described in Table 3-A. 
The models and submodels described in this report have these general objectives: 
 Provide supporting models for disposition of FEPs 
 Support the design basis (e.g. specify EBS environmental conditions) 
 Provide direct feeds to TSPA in the form of computational results or modeling 
approaches 
The Physical and Chemical Environment Model (Section 3.1.2) contains several submodels, 
covering a range of topical areas that includes thermal-hydrology, estimation of gas composition 
in the repository drifts, effects of introduced materials, microbial process modeling, precipitates 
and salts, and colloids generated in the EBS. Some of these submodels provide direct feeds to 
TSPA, and some are limited to evaluation of FEPs as indicated in Table 3-A. 
The Physical and Chemical Environment Model section culminates in a description of the 
Chemical Reference Model (Section 3.1.2.7), which is not a direct feed to TSPA, but a tool for 
assessing some of the processes that control the in-drift environment. The Chemical Reference

 3-2 
Table 3-A. Summary of EBS Process Models and Abstraction Models 
Section Model Name (AMR Reference) Purpose Intended Use Brief Summary of Results A 
3.1.1 Water Distribution and Removal Model 
(CRWMS M&O 2000q) 
3.1.1 Water Drainage Model 
(CRWMS M&O 2000af) 
Simulate effects of extreme 
seepage flow, and fracture 
plugging below the invert; 
estimate water content in the 
invert, for EBS radionuclude 
transport modeling 
FEP Screening 
Support Repository 
Design Basis 
Complete saturation of the invert is 
unlikely, even with complete plugging of 
fracture drainage pathways, unless 
there are extreme seepage conditions. 
Fracture plugging does not necessarily 
mean ponding in the invert, depending 
on the seepage rate. 
3.1.1 Water Diversion Model 
(CRWMS M&O 2000ae) 
Bound the relative humidity 
conditions for flow through 
cracks and pores in the drip 
shield or waste package. 
FEP Screening 
Support Repository 
Design Basis 
Flow through cracks or pores is limited to 
very small flows along thin films, until 
relative humidity permits capillary 
plugging. Flow of capillary water, thick 
films, and droplets may occur depending 
on local seepage. Moisture can enter 
breaches as vapor, and form thin films. 
3.1.1 In-Drift THC Model 
(CRWMS M&O 2000y) 
Simulate TH processes that 
could cause condensation 
under the drip shield. 
FEP Screening 
Support Repository 
Design Basis 
High percolation flux could lead to 
moisture conditions in the invert, that 
could produce condensation under the 
drip shield. (These are preliminary 
results, and the predicted conditions for 
onset of condensation are approximate.) 
3.1.2 Physical and Chemical Environment Model 
(CRWMS M&O 2000t) 
3.1.2.1 Thermal-Hydrology Model 
(CRWMS M&O 2000t; Section 6.1) 
Conservative representation of 
total evaporation, and 
associated TH conditions. 
FEP Screening 
Support Repository 
Design Basis 
Characterize evolution of temperature and 
RH condiitons for center/edge locations, 
and low/high infiltration flux. 
3.1.2.1.7 Conservative Solute Analysis 
(CRWMS M&O 2000t; Section 6.1.6) 
Select a thermal-hydrology case 
for Chemical Reference Model 
FEP Screening 
Support Repository 
Design Basis 
Potential accumulation of salts in the drifts 
is maximized for center location with 
high seepage flux. 
3.1.2.2 Gas Flux and Fugacity Model 
(CRWMS M&O 2000t; Section 6.2) 
3.1.2.2.3.1 Mass Balance Model for Ambient, 
Steady-State 14CO2 Transport in UZ 
(CRWMS M&O 2000t; Section 6.2.3) 
Ambient steady-state total CO2 
recharge to the UZ 
FEP Screening 
Support Repository 
Design Basis 
Approx. 586 mg/yr/m2 of CO2 are required 
to recharge at the surface, to maintain 
1-D isotopic steady state in the UZ. 
3.1.2.2.3.2 Model for 1-D Transport of 14CO2 for 
Ambient Conditions 
(CRWMS M&O 2000t; Section 6.2.3) 
Derive diffusion-dispersion coeff. 
for 1-D ambient gas model 
FEP Screening 
Support Repository 
Design Basis 
The gas-phase diffusion-dispersion 
mechanism for ambient CO2 transport is 
about an order of magnitude greater 
than diffusion alone.

 3-3 
Section Model Name (AMR Reference) Purpose Intended Use Brief Summary of Results A 
Gas Flux and Fugacity Model, Cont. 
3.1.2.2.3.3 Model for Gas Transport During the 
Thermal Period 
(CRWMS M&O 2000t; Section 6.2.3.4) 
Apply 1-D gas model to thermal 
conditions, in an approximate 
model for estimating gas 
composition; support Chemical 
Reference Model 
FEP Screening 
Support Repository 
Design Basis 
The relationship between gas flux and 
fugacity is described as inverse linear. 
1-D mass transfer model results are 
comparable with the air mass-fraction 
approach, and THC calculations. 
Oxygen needed to corrode steel in the 
EBS is delivered in 2000 yr or less. 
3.1.2.3 Introduced Materials Models 
(Various AMR references; see below) 
3.1.2.3.1 Inventory of Materials Present in the 
Emplacement Drifts 
(CRWMS M&O 1999g) 
Inventory for consistent use in 
Introduced Materials Models 
TSPA Sensitivity 
FEP Screening 
Support Repository 
Design Basis 
Structural steel is an important part of the 
inventory of introduced materials. 
3.1.2.3.3.1 Kinetic Model for Water-Quartz 
Interaction 
(CRWMS M&O 2000t; Section 6.7.2.3) 
Determine if chemical equilibrium 
with quartz sand backfill, can 
be used for chemical modeling 
Support Chemical Reference 
Model 
FEP Screening 
Support Repository 
Design Basis 
Water-quartz interaction can be modeled 
as an equilibrium process, for elevated 
temperatures and residence times, 
when strongly alkaline waters can be 
produced by evaporative concentration. 
3.1.2.3.3.2 Model for Seepage-Backfill Interaction 
at High Ionic Strength 
(CRWMS M&O 2000v) 
Determine saturation indices for 
quartz backfill under a range of 
environment conditions 
FEP Screening 
Support Repository 
Design Basis 
Dissolution of quartz by evaporatively 
concentrated waters, is not favored 
except for unlikely conditions. 
Backfill porosity will not be plugged 
significantly, except for strongly 
localized conditions. 
3.1.2.3.4 Model for Corrosion of Carbon Steel 
(CRWMS M&O 2000t; Section 4.1.7.7) 
Select correlation model for steel 
penetration rate, based on data 
FEP Screening 
Support Repository 
Design Basis 
Corrosion rate correlation function based 
on experimental data. 
3.1.2.3.5 Cementitious Materials Effects Model 
(CRWMS M&O 2000t; Section 6.3) 
Bound leachate composition and 
flow rate for rockbolt grout 
Support Chemical Reference 
Model 
FEP Screening 
Support Repository 
Design Basis 
Leachate flow rate will be limited by grout 
permeability. Alkaline leachate will be 
buffered by contact with quartz backfill, 
and CO2 in the drift environment. 
3.1.2.4 Microbial Effects Models 
(Various AMR references; see below) 
3.1.2.4.1 Threshold Conditions Model for 
Microbially Influenced Corrosion 
(CRWMS M&O 2000t; Section 6.4) 
Evaluate environment conditions 
that support biotic activity 
TSPA Microbial growth and activity will be limited 
to T < 120C and RH > 90%, except for 
extremophiles which are ignored. Fungi 
can be active at lower RH.

 3-4 
Section Model Name (AMR Reference) Purpose Intended Use Brief Summary of Results A 
3.1.2.4.2 Microbial Communities Model 
(CRWMS M&O 2000f) 
Quantify biomass produced and 
sustained by biotic activity 
TSPA When microbial activity resumes, biomass 
on the order of 10 g/meter of drift can be 
sustained, and will be energy-limited. 
3.1.2.5 Precipitates and Salts 
(Various AMR references; see below) 
3.1.2.5.2 Normative Precipitates and Salts 
Model 
(CRWMS M&O 2000t; Section 6.5) 
Identify minerals and salts from 
complete evaporation of waters 
Support Chemical Reference 
Model 
FEP Screening 
Support Repository 
Design Basis 
Precipitates and salts will include mainly 
carbonates, sulfates, and silica. Salts 
from monovalent cations are important. 
Hydroxides are not observed in testing 
at atmospheric PCO2. 
3.1.2.5.3 Low RH Salts Model 
(CRWMS M&O 2000g; Section 6.4.1) 
Interpolate brine composition 
from initial deliquescence. 
TSPA Brine composition vs. time, during the 
transition from RH = 50% to 85%. 
3.1.2.5.3 High RH Salts Model 
(CRWMS M&O 2000g; Section 6.4.2) 
Calculate water composition for 
RH > 85% 
TSPA Water composition as a function of 
temperature, evaporative concentration, 
and PCO2, for RH > 85%. 
3.1.2.5.3 Condensed Water Model 
(CRWMS M&O 2000g; Section 6.4.3) 
Calculate composition of 
condensate reacted with CO2 
TSPA Water composition on the WP, before DS 
breach. Dilute waters result from interaction 
with CO2 only. 
3.1.2.6 EBS Colloids Model 
(CRWMS M&O 2000t; Section 6.6) 
Bound the potential enhancement 
of transport by ferric 
colloids in the EBS 
FEP Screening 
Support Repository 
Design Basis 
Pu-transport capacity of waters, due to 
ferric colloids, may increase up to 100- 
fold, but only if sufficient dissolved Pu is 
available outside the WP. 
3.1.2.7 Chemical Reference Model 
(CRWMS M&O 2000t; Section 6.7) 
Evaluate CO2 balance in the 
drifts and host rock, including 
precipitates and salts 
Compare reference water 
compositions with cement 
leachate. 
FEP Screening 
Support Repository 
Design Basis 
CO2 budget is net positive (produced) 
averaged spatially and temporally. 
Dissolution/precipitation of carbonate 
salts is a major source/sink for CO2. 
Evaporatively concentrated water 
composition in the drifts is similar to 
potential leachate from cement grout. 
3.1.2.8 Drift Degradation Model 
(CRWMS M&O 2000ad) 
Predict rockfall frequency and 
block size distribution; include 
thermal and seismic effects 
FEP Screening 
Support Repository 
Design Basis 
Probabilistic distributions for rockfall size 
and frequency, with modifications to 
represent thermal and seismic effects. 
3.1.3 Engineered Barrier System 
Radionuclide Transport Model 
(CRWMS M&O 2000b) 
Represent solute transport by 
advection and diffusion in the 
invert 
TSPA Sorption and liquid flux are the most 
sensitive parameters for radionuclide 
transport in the invert. The diffusion 
barrier depends on low moisture content 
in the invert.

 3-5 
Section Model Name (AMR Reference) Purpose Intended Use Brief Summary of Results A 
3.1.4 Multiscale Thermohydrologic Model 
(CRWMS M&O 2000i) 
Predict key thermal-hydrologic 
variables for the in-drift 
environment and the host rock 
TSPA Comprehensive suite of predictions for 
thermal-hydrologic conditions in the drift, 
and at the surfaces of the DS and WP. 
3.2.1 Model Abstraction for TSPA 
(Various AMR references; see below) 
3.2.1.1 Physical and Chemical Environment Abstraction Model 
(CRWMS M&O 2000j) 
3.2.1.1.1 In-Drift Gas Flux and Composition 
(CRWMS M&O 2000e) 
Evaluate gas chemistry boundary 
conditions for TSPA models 
TSPA Gas fugacity changes from in-drift 
processes will be minor. In-drift gas 
composition will be uniform. Diffusion 
could contribute additional fluxes of gasphase 
constituents. 
3.2.1.1.2 Introduced Materials 
(CRWMS M&O 2000v; 
CRWMS M&O 2000l; and 
CRWMS M&O 2000m) 
Represent seepage interaction 
with backfill, cement, and invert 
TSPA Quartz backfill dissolution is not predicted. 
Plugging of backfill porosity from evaporation 
of seepage water is negligible. 
Invert chemistry will affect radionuclide 
transport, colloid abundance, and colloid 
stability. Preferential flow paths in the 
invert may develop through time. 
3.2.1.1.3 Microbial Effects 
(CRWMS M&O 2000f) 
Quantify sensitivity of in-drift 
processes to microbia activity 
TSPA The bulk effect of microbial activity is 
predicted to an order of magnitude. 
3.2.1.1.4 Precipitates and Salts 
(CRWMS M&O 2000g) 
Abstract brine composition 
from initial deliquescence. 
TSPA Response surfaces define pH, chloride 
concentration, and ionic strength as 
dependent variables; with temperature, 
RH, PCO2, and evaporative concentration 
as independent variables. 
Physical and Chemical Environment Abstraction Model, Cont. 
3.2.1.1.5 Colloids 
(CRWMS M&O 2000d) 
Represent colloids available for 
interaction with radionuclides 
TSPA Colloids are available from the host rock, 
EBS, and waste form. The colloidal 
distribution of radionuclides, including 
reversibility, is strongly influenced by the 
manner of release from the waste form. 
3.2.1.2 EBS Radionuclide Transport Abstraction Model for TSPA-LA 
(CRWMS M&O 2000a) 
3.2.1.2.1 Flow and Transport Pathways 
(CRWMS M&O 2000a; and 
CRWMS M&O 2000m) 
Establish connectivity of flow 
pathways in the EBS 
TSPA Seepage through the DS always falls on, 
and uniformly wets, the WP. There is no 
liquid flow through stress-corrosion 
cracks. After WP breach, the WF will be 
covered by thin liquid films that support

 3-6 
Section Model Name (AMR Reference) Purpose Intended Use Brief Summary of Results A 
diffusion releases. Advective release 
rates are independent of the number of 
breaches. Cracks and pits are assumed 
to be filled with liquid-saturated 
corrosion products. 
EBS Radionuclide Transport Abstraction Model for TSPA-LA, Cont. 
3.2.1.2.2 Colloid-Facilitated Transport 
(CRWMS M&O 2000d) 
Quantify potential colloid 
partitioning and transport of 
radionuclides in the EBS 
TSPA Colloidal radionuclides will be produced 
from the waste form (assume smectite 
with reversible and irreversible sorption); 
iron oxide (assume reversible sorption 
for transport through the host rock); and 
groundwater colloids (assume smectite 
with reversible sorption). The amounts 
of radionuclides irreversibly associated 
with colloids are determined by within 
the WP. Reversible partitioning is 
determined from dissolved concentrations 
of radionuclides, colloid concentrations, 
and distribution coefficients. 
3.2.2.3 Abstraction of Near-Field Drift 
Thermodynamic Environment and 
Percolation Flux (CRWMS M&O 2000w) 
Describe key thermohydrologic 
variables for probabilistic TSPA 
TSPA Probabilistic description of the evolution of 
temperature and RH on the DS and WP, 
drift-wall temperature, in-drift evaporation 
rate, liquid flux in the host rock, and 
pillar temperature. Edge vs. center 
location, and local percolation flux, are 
the most important controlling variables. 
NOTE: A Abbreviations: DS = drip shield, PCO2 = CO2 fugacity, RH = relative humidity, TH = thermal-hydrology, THC = thermal-hydrologic-chemical, 
WF = waste form, WP = waste package, UZ = unsaturated zone.

 3-7 
Model is based on a thermal-hydrologic simulation that was selected to represent the maximum 
evaporation likely to occur in any emplacement drift during the thermal period. This is 
combined with an approximate model for estimating CO2 and O2 fugacities (Section 3.1.2.2), and 
an approach for assessing which precipitates will form in the drifts (Section 3.1.2.5.1), to support 
reference chemical calculations in Section 3.1.2.7. The approach couples thermal-hydrology, 
gas-phase processes, and aqueous chemistry, to calculate water compositions that can be 
compared to other compositions such as leachate that may be produced from cementitious grout. 
An important application of the Chemical Reference Model is evaluation of the CO2 budget for 
in-drift processes, which also includes a representation of chemical processes in the host rock 
(Section 3.1.2.7.5.7). The Chemical Reference Model, with its submodels, supports some of the 
assumptions and approximations used in TSPA, including constant fugacities for CO2 and O2, 
and negligible impact from cement leachate. 
The Chemical Reference Model does not simulate brines, which exceed the ionic strength limit 
for the model. Therefore, it cannot predict the full range of possible solution compositions in the 
drifts during the thermal period. However, brine compositions are described by the LRH Salts 
Model, and the HRH Salts Model (Section 3.1.2.5.3). 
In the sections that follow, the purpose and the intended use for each model and submodel are 
described in the introductory paragraphs. This information is also summarized in Table 3-A. 
Those models that provide direct feeds to TSPA are discussed further in Section 3.2. 
Summary and Comparison of Thermal-Hydrologic Models  Thermal-hydrologic modeling 
is used in several of the models described in this report, and is based on model input data from 
the Unsaturated Zone Flow and Transport Process Model Report (CRWMS M&O 2000o, 
Section 3). The thermal and hydrologic properties used, and the boundary conditions at the 
ground surface and water table (or below the water table, as applicable) are consistent with the 
inputs used for the UZ Model and its submodels. The UZ Process Model Report and its 
supporting documentation also describe thermal-hydrologic modeling. A comparison of certain 
results from all of these models is provided in this section. 
Table 3-B shows a comparison of thermal-hydrologic models, that includes models presented in 
this report, and those documented for the UZ Process Model Report. The following models are 
compared: 
 Mountain-Scale Coupled Processes (TH) Models (CRWMS M&O 2000aj)  The 2-D and 
3-D mountain-scale TH models are included in Table 3-B. 
 Multiscale Thermohydrologic Model (CRWMS M&O 2000i)  Representative 2-D 
chimney models are selected for comparison in Table 3-B, and in Figures 3-B and 3-C. 
(Chimney models are so-named because they are slender symmetry models that extend 
across half the drift spacing in the horizontal direction, and from the ground surface to the 
water table in the vertical direction.) In addition, selected results from the multiscale 
abstraction procedure, which incorporates 3-D drift-scale and mountain-scale heat 
transfer effects, are also selected for comparison.

 3-8 
 Physical and Chemical Environment Model (CRWMS M&O 2000t)  Selected results 
from the thermal-hydrology component (Section 6.1) of this report are included in Table 
3-B, and Figures 3-B and 3-C. 
 Water Distribution and Removal Model (CRWMS M&O 2000q)  Representative results 
from numerical simulations of water distribution and drainage are included in Table 3-B, 
and Figures 3-B and 3-C. 
 In-Drift Thermal-Hydrological-Chemical Model (CRWMS M&O 2000y)  This model 
assessed the conditions that could lead to condensation under the drip shield, considering 
thermal-hydrology only. Representative results are included in Table 3-B, and Figures 3- 
B and 3-C. 
 Drift-Scale Coupled Processes (DST and THC Seepage) Models (CRWMS M&O 2000x) 
 This report describes a set of fully-coupled THC simulations, with which the TH results 
are directly comparable. Representative results are included in Table 3-B, and Figures 3- 
B and 3-C. 
The Mountain-Scale Model and the Multiscale TH Model each include a 3-D site-scale model, 
and 2-D local submodels. The other models, including the 2-D chimney model type 
(designated LDTH) that is used with the Multiscale TH Model, are 2-D thermal-hydrologic 
models. 
The Multiscale TH Model (Section 3.1.4) simulates the thermal-hydrologic response at 31 
locations throughout the repository area, whereas the other models (except the Mountain-Scale 
Model) consider specific locations. Locations near the center of the repository layout (mainly 
the L4C4 location from Figure 3-70) are selected for comparison in Figures 3B and 3C. 
All models employ a drift spacing of 81 meters, except the Multiscale TH Model and the 
Physical and Chemical Environment TH models. For these models the drift spacing is increased 
near the repository edges, to represent the edge-cooling effect. For example, the Physical and 
Chemical Environment TH model at the L4C1 location is constructed with a grid spacing of 
67.5 m, which has been determined (as part of the Multiscale TH Model development) to 
approximate the effects of edge cooling, without modifying the thermal loading. 
The Water Distribution and Removal Model uses the 1-D, drift-scale hydrostratigraphic 
properties for the mean infiltration distribution, while the In-Drift THC Model uses the 1-D, 
drift-scale properties for the upper infiltration distribution. The other models use drift-scale or 
mountain-scale properties, as appropriate, with property sets that correspond to the lower, mean, 
or upper infiltration conditions used to represent infiltration at the upper boundary. The EBS 
component properties and geometry are consistent among all the models, except the Mountain- 
Scale Model which does not explicitly simulate the EBS. 
One difference between the models that is important for predicting conditions inside the drifts, is 
the treatment of air gaps between the waste package and the drip shield, and between the upper 
surface of the backfill and the drift wall. The Physical and Chemical Environment TH model, 
and the Water Distribution and Removal Model, combine the drip shield and waste package into

 3-9 
a monolithic body with representative thermal properties. These models also fill the drift 
completely with backfill so there is no air gap. The In-Drift THC Model explicitly incorporates 
the air gap exists under the drip shield, with radiative coupling, but fills the remainder of the drift 
with backfill so there is no air gap. The Multiscale TH Model (DDT submodel) explicitly 
models the air gap under the drip shield using radiative coupling, and the air gap above the 
backfill using effective thermal conductivity. The LDTH submodel uses a monolithic body to 
represent the waste package and drip shield, and effective thermal conductivity to represent the 
air gap above the backfill. 
Temperatures ranging from 16 to 19 degrees C and total gas pressures ranging from 84,000 to 
86,000 Pa are specified at the top boundaries of these models. As indicated in Table 3-B, some of 
the models set the lower boundary at the water table, while others set it below the water table. 
For the water table boundary condition, temperatures range from 28 to 32 degrees C, and gas 
pressures in the range 91,000 to 92,000 Pa are used. The Mountain-Scale Model and the 
Multiscale TH Model (SMT submodel) extend the lower boundary to 1,000 m below the water 
table with a fixed temperature of 65 degrees C, while the pressure is determined from the static 
head of water, assuming total gas pressure of 92,000 Pa at the water table. 
All models use essentially the same heat output for the waste package with a peak average lineal 
thermal loading of 1.54 kW/m at emplacement. The exception is the Mountain-Scale Model 
which uses an average thermal load of 72.7 kW/acre (1.455 kW/m at 81-m drift spacing). All the 
models assume that 70% of the heat is removed by ventilation during the 50-yr preclosure 
period, that all the waste is emplaced simultaneously, and that all the spent fuel waste has the 
same characteristics at emplacement (corresponding to fuel that is approximately 20 yr out-ofreactor). 
The Water Distribution and Removal Model and the In-Drift THC Model assume 
100% heat removal during the first 100 yr, which simplifies the models and maximizes the liquid 
flux during the thermal period, but produces temperatures that are too low for the first few 
hundred years after closure. 
Figures 3B and 3C compare the modeling approaches, and data inputs, for the 2-D drift-scale TH 
models (i.e. chimney models, or the LDTH models described in Section 3.1.4) presented in 
this report and other reports as noted. Results from the Mountain-scale TH models referred to in 
Table 3-B are not plotted because they have very different model gridding, and are not closely 
comparable. From the Multiscale TH Model, only 2-D drift-scale LDTH model results are 
plotted, because they are directly comparable. The figures show that the evolution of 
temperature and humidity (or air mass-fraction) is similar for all the models. As discussed in 
Sections 3.1.2.1 and 3.1.4, infiltration flux is an important determinant of TH response. Using 
the lower and upper infiltration distributions, the Multiscale TH Model (LDTH) and the Physical 
and Chemical Environment TH models, tend to bracket the other results. The same observation 
could be made using results calculated for another location. 
The In-Drift THC Model results differ slightly from the other models, with cooler, more humid 
results in early time, because this is an ECM (equivalent continuum model) calculation, whereas 
the others are for the DKM (dual permeability model) approach. The peak temperatures 
calculated for the Physical and Chemical Environment TH models are higher immediately 
following closure, because the drifts are filled completely with backfill, without an air gap to 
accommodate radiative transfer. (As indicated in Table 3-B, the other models in which the drift

 3-10 
is completely filled with backfill, start the calculation at 100 yr after emplacement, and do not 
explicitly model the transition from preclosure to postclosure conditions.) The Physical and 
Chemical Environment TH models also predict higher humidity than the corresponding 
Multiscale TH Model (LDTH) submodels, because the backfill capillary response induces water 
to flow into the drift from the host rock. 
Finally, it is noted that differences among these models (caused by infiltration flux, and to a 
lesser extent, modeling approach) translate principally to differences in the timing of thermal 
evolution. Each model predicts the same progression of humidity, and evolution of humidity is 
very similar among the models, but the timing can vary by several thousand years depending on 
the infiltration flux.

 3-11 
Table 3-B Comparison of Thermal-Hydrologic Model Types and Input Data 
Model Mountain-Scale TH 
Drift-Scale Coupled 
Processes (DST/THC) Multiscale TH 
EBS Physical & Chemical 
Environment 
Water Distribution & 
Removal In-Drift THC 
AMR Document 
Identifier/Revision 
MDL-NBS-HS-000007 
Rev.00 
CRWMS M&O 2000aj 
MDL-NBS-HS-000001 
Rev.00 
CRWMS M&O 2000x 
ANL-EBS-MD-000049 
Rev.00 
CRWMS M&O 2000i 
ANL-EBS-MD-000033 
Rev.00 
CRWMS M&O 2000t 
ANL-EBS-MD-000032 
Rev.00 
CRWMS M&O 2000q 
ANL-EBS-MD-000026 
Rev.00 
CRWMS M&O 2000y 
Modeling Code A TOUGH2 V1.4 TOUGHREACT 2.2 NUFT 3.0s/MSTHAC A NUFT 3.0s NUFT 3.0s NUFT 2.0s 
Dimensionality 2-D & 3-D 2-D  3-D Mountain-Scale 
Conduction-only 
 3-D Drift-Scale 
Conduction & 
Radiation 
 2-D Drift-Scale TH 
 1-D Column TH 
2-D 2-D 2-D 
Model Domain Mountain-Scale, from 
ground surface to 1000 m 
below the water table. 
Grid dimensions: 556 m x 
40.5 m; domain extends 
from ground surface to 
water table. 
Multiscale; 3-D conduction-
only model extends 
from the ground surface to 
1000 m below the water 
table. Other models extend 
to water table. Drift spacing 
is adjusted to represent 
reduced thermal loading 
near the repository edges. 
Grid dimensions: 620m x 
67.5m (L4C1) and 739m x 
40.5m (L4C4); extra width 
of L4C1 model (67.5 m) 
represents repository-edge 
cooling effect; model 
domain extends vertically 
from the ground surface to 
the water table. 
Grid dimensions: 739 m x 
40.5 m (L4C4); domain 
extends from ground 
surface to water table. 
Grid dimensions: 675 m x 
40.5 m; domain extends 
from ground surface to 
water table. 
Location for 
Accompanying Plots 
(Not Plotted) Location of borehole SD-9 Location L4C4 (as shown 
in Figure 3-70) 
Location L4C4 (as shown 
in Figure 3-70) 
Location L4C4 (as shown 
in Figure 3-70) 
Repository center 
(N233,760m, E170,750m) 
Fracture Flow Modeling 
Approach A ECM, DKM, & DKM/AFC DKM DKM/AFC DKM/AFC DKM/AFC ECM 
EBS Modeling Approach Drift openings are each 
represented by one model 
grid block, with no EBS 
features or air gaps. 
Air gaps between DS & WP 
and between backfill & 
drift crown. Effective 
thermal conductivity used 
for coupling. 
Air gap between DS & WP 
(radiative coupling); air gap 
between backfill & drift 
crown (effective thermal 
conductivity). 
Monolithic DS + WP; 
backfill fills the remainder 
of the drift. 
Monolithic DS + WP; 
backfill fills the remainder 
of the drift. 
Air gap between DS & WP 
(radiative coupling); 
backfill fills the remainder 
of the drift. 
Hydrologic and Associated 
Thermal Properties B 
Mountain-scale, mean 
infiltration base-case 
Drift-scale properties for 
lower, mean, and upper 
infiltration 
Drift-scale properties for 
lower, mean, and upper 
infiltration 
Drift-scale properties for 
lower, mean, and upper 
infiltration 
Drift-scale properties for 
the upper infiltration 
distribution 
Drift-scale, mean 
infiltration base-case 
EBS Component 
Properties B 
N/A Base-case properties Base-case properties Base-case properties Base-case properties Base-case properties 
Scope of Models 
Developed 
2-D and 3-D grids based on 
GFM 3.1 geologic model; 
repository in tsw34, tsw35, 
or tsw36 unit. 
2-D grid representing 
repository center, at 
borehole SD-9; repository 
in tsw34 unit 
31 locations (designated 
L*C*) shown in Figure 3- 
70; repository in tsw34, 
tsw35, or tsw36 unit. 
L4C1 edge location: 
repository in tsw34 unit. 
L4C4 center location: 
repository in tsw35 unit. 
L4C4 center location: 
repository in tsw35 unit. 
Repository center location 
(N233,760m, E170,750m); 
repository in tsw35 unit. 
Infiltration Rates 
(Present day/Monsoon/ 
Glacial transition; mm/yr) 
1.2 / 4.6 / 2.4 mm/yr 
4.6 / 12.4 / 18.0 mm/yr 
11.2 / 20.1 / 33.5 mm/yr 
6 / 16 / 25 mm/yr 
15 / 26 / 47 mm/yr 
0.6 / 6 / 3 mm/yr 
Range of flux, mm/yr: 
0 / 0.07 / 0.05 (min.) 
37.9 / 72.1 / 125.1(max.) 
0 to 82 mm/yr (L4C1) 
0.2 to 34 mm/yr (L4C4) 
10 to 42 mm/yr 
uniform or focused 
35 and 68 mm/yr

 3-12 
Model Mountain-Scale TH 
Drift-Scale Coupled 
Processes (DST/THC) Multiscale TH 
EBS Physical & Chemical 
Environment 
Water Distribution & 
Removal In-Drift THC 
Surface Boundary 
Conditions A 
Temp.=18.2 C 
Pressure from lower B.C. 
Temp. = 17.7 C 
Pres. = 86,339 Pa 
Temp. = 15.9 to 17.4 C 
Pres. = 84,500 to 86,000 Pa 
Temp. = 17 C (L4C1) 
Pres. = 85,587 Pa (L4C1) 
Temp. = 15.9 C (L4C4) 
Pres. = 84,511 Pa (L4C4) 
Temp. = 15.9 C 
Pres. = 84,500 Pa 
Temp. = 19.1 C 
Pres. = 86,000 Pa 
Lower Boundary 
Conditions A 
Temp. = 65 C 
Pres. 1000 m below WT 
(WT at 0.92 bar) 
Temp. = 31.7  C 
Pres. = 92,000 Pa 
For LDTH Models: 
Temp. = 28.6 to 32.5 C 
Pressure from surface B.C. 
Temp. = 32.4 C 
Pres. = 92,000 Pa 
Temp. = 32.5 C 
Pres. = 92,000 Pa 
Temp. = 32.0 C 
Pres. = 91,000 Pa 
WP Thermal Loading 72.7kW/acre; 0 or 70% 
preclosure removal 
1.54 kW/m lineal load; 70% 
preclosure removal 
1.54 kW/m lineal load; 70% 
preclosure removal 
1.54 kW/m lineal load; 70% 
preclosure removal 
1.54 kW/m lineal load; 
100% preclosure removal 
for 100 yr 
1.54 kW/m lineal load; 
100% preclosure removal 
for 100 yr 
Process Model Report 
Where Model Presented 
UZ PMR 
(CRWMS M&O 2000o) 
NFE PMR 
(CRWMS M&O 2000u) 
EBS PMR 
(this report) 
EBS PMR 
(this report) 
EBS PMR 
(this report) 
EBS PMR 
(this report) 
NOTES: AAbbreviations: MSTHAC = Multiscale TH Abstraction, DKM = Dual Permeability Model, AFC = Active Fracture Concept, ECM = Equivalent Continuum Model, LDTH = Multiscale TH 
Model designator for 2-D TH model, SMT = Multiscale TH Model designator for 3-D mountain-scale conduction model, B.C. = boundary condition, WT = water table. 
B The reader is referred to the source documents (AMRs) for details on the hydrologic and thermal property sets.

 3-13 
3.1.1 Water Distribution and Removal Model 
This section presents a set of models which together describe the movement of water within the 
emplacement drifts, for ambient and thermally driven conditions, and are collectively referred to 
as the Water Distribution and Removal Model (CRWMS M&O 2000q). This section combines 
results from: 
 Water Diversion Model (CRWMS M&O 2000ae) 
 Water Drainage Model (CRWMS M&O 2000af) 
In addition, results from the Ventilation Model (CRWMS M&O 2000an) and the In-Drift 
Thermal-Hydrological-Chemical Model (CRWMS M&O 2000y) are used to support conceptual 
development. 
The intended use for the Water Distribution and Removal Model is FEP screening, and support 
of the repository design (Table 3-A). Principal model features needed for these applications are 
continuity of mass flow, simulation of unsaturated flow, and representation of EBS geometry. 
The Water Drainage Model is used to evaluate the conditions of drift seepage, and permeability 
modification in the host rock, that could lead to complete saturation (ponding) of the invert. This 
information is appropriate for evaluating the selection of invert materials, the invert 
configuration, and the needed drainage capacity to ensure free drainage throughout the evolution 
of the hot rock. The Water Diversion Model bounds the flow of liquid water through a crack or 
hole in the drip shield or waste package wall, in the presence of backfill. It is appropriate for 
evaluating the drip shield design, to determine the needed level of performance for the joint 
between segments. 
Water movement in the drifts is also predicted for repository thermal conditions, and the selected 
model is fundamentally the same as models described in Sections 3.1.2.1 and 3.1.4 of this report. 
The Water Distribution and Removal Model provides direct support for: 
 EBS Radionuclide Transport Model (CRWMS M&O 2000b) 
 Engineered Barrier System Features, Events, and Processes and Degradation Modes 
Analysis (CRWMS M&O 2000c) 
Invert moisture conditions are used in developing the EBS Radionuclide Transport Model 
(Section 3.1.3). Water distribution is the focus of several FEPs, for which process descriptions 
are provided by this model. Direct feed of water distribution information to TSPA is provided 
by the Multiscale TH Model (Section 3.1.4). 
The sections that follow first discuss the conceptual basis for modeling water diversion by the 
engineered barriers, and water distribution and drainage from the drifts. The text then decribes, 
in some detail, a set of numerical simulations that were performed to assess water distribution 
and drainage performance under extreme seepage conditions. Related models that describe 
ventilation effects (CRWMS M&O 2000an), and drift degradation by rockfall (CRWMS M&O 
2000ad), are considered in the development of these calculations. Preliminary results from

 3-14 
calculations to predict condensation under the drip shield (CRWMS M&O 2000y) are also 
discussed. 
Finally, this section describes an analytical model that bounds the flow through breaches in the 
drip shield or waste package, based on the Water Diversion Model (CRWMS M&O 2000ae). 
Breaches are represented by cracks or pores, and liquid flow from the backfill into these features 
is possible only when the relative humidity is sufficiently high. 
Conceptual Basis for Types of Flow on the Drip Shield  Water that enters the emplacement 
drifts as seepage can flow along three types of pathways: (1) flow through the backfill directly 
to the invert; (2) flow through the backfill that contacts the drip shield, but is diverted to the 
invert; and (3) flow through breaches in the drip shield or waste package. The following 
discussion pertains to water that flows through breaches in the drip shield or waste package. 
Breaches in the drip shield or waste package can take different forms, ranging from fine cracks 
caused by stress-corrosion cracking, to patches where general corrosion has penetrated a larger 
area (CRWMS M&O 2000n; Section 3.2). Thin films of water can form on any solid surface 
that is at least partially wettable, and the thickness of such films can be predicted theoretically 
(Middleman, 1995; Chapter 9). Films can then flow because of gravity, and possibly because of 
other differences in water potential on the surface. Film flow capacity is limited by viscosity, the 
extent of flow area, surface roughness, and other factors. Film flow on the engineered barriers 
can deliver liquid water at significant flow rates, and could be significant to waste isolation 
performance. However, film flow through breaches in the drip shield is likely to continue as film 
flow on the underside of the drip shield, and thus will tend to be diverted from the waste 
package. Also, film flow through fine cracks into the waste package will be limited by heat 
generation within the package, which will cause water to be rejected as vapor. 
Depending on the aperture of a breach, capillary flow and droplet flow modes can occur. For 
fine cracks, flow will be dominated by capillarity. In capillary flow, water will be either imbibed 
in a crack, or excluded, depending on whether the internal surfaces are wetting or non-wetting, 
respectively. Wetting behavior is required for capillary effects to occur, and the assumption of 
wetting behavior is conservative because it increases liquid mobility. If the crack surface is 
nonwetting, water cannot enter and bridge the crack except if pushed by greater water pressure, 
which is unlikely in the emplacement drifts. 
If the local environment has sufficiently low relative humidity, which can only occur during the 
thermal period, any crack may dry out. Molecular films of water could then form on the crack 
surfaces, but the flow capacity would be negligible because the films would be very thin. As the 
relative humidity increases during cool-down, water films will thicken, and fine cracks will 
become increasingly water-saturated. 
As saturation increases and water bridges a fine crack or pore, it is held there at a negative 
potential by capillarity. It will not flow unless the adjacent downstream flow pathway is at a 
more negative potential, or unless sufficient water pressure is applied upstream to overcome the 
negative potential. For the case of water flowing through a breached drip shield or waste 
package, under the impetus of gravity, neither of these conditions is likely unless the water 
evaporates at the downstream end. Thus, the movement of water through fine cracks is limited

 3-15 
to thin water films that can form in the crack, and evaporation of water from the downstream end 
when humidity conditions permit. 
Conceptual Basis for Modeling Water Distribution in the Drifts  The Water Distribution 
and Removal Model (CRWMS M&O 2000q) uses numerical simulation to evaluate the 
distribution of liquid water within emplacement drifts, and drainage into the host rock below the 
drifts. Conceptually, this approach is suitable because it imposes continuity conditions on the 
flow system, and supports simulation of unsaturated flow conditions. The model comprises a set 
of (2-D) numerical simulations using the NUFT computer code, plus ancillary calculations. 
These calculations are reported as parts of the Water Drainage Model (CRWMS M&O 2000af) 
and the Water Distribution and Removal Model (CRWMS M&O 2000q). Most of the 
simulations describe water distribution and drainage for ambient temperature (post-thermal), 
steady-state conditions. Thermal-hydrology simulations are included also, and the results 
include a reconnaissance of changes in water distribution and drainage during the thermal period. 
The Water Drainage Model (CRWMS M&O 2000af) evaluates the conditions that could be 
produced by water ponding in the invert, and the potential effectiveness of engineered measures 
to prevent ponding. The Ventilation Model (CRWMS M&O 2000an) is only briefly discussed 
because the focus of these process models is on post-closure performance. Also, the Ventilation 
Model is used to estimate the proportion of waste-generated heat that will be removed by preclosure 
ventilation, whereas for the TH calculations described here, ventilation is assumed to 
remove 100 percent of waste-generated heat. Results from the Ventilation Model are the basis 
for pre-closure heating conditions used in Section 3.1.2 and 3.1.4. 
The In-Drift Thermal-Hydrological-Chemical Model (CRWMS M&O 2000y), in the version 
cited here, is briefly discussed and is used as the basis for reporting that conceptually, moisture 
conditions in the invert can control moisture condensation underneath the drip shield. 
3.1.1.1 Water Distribution and Removal Model Input Data 
For developing the model geometry of the NBS, the Water Distribution and Removal Model 
receives stratigraphic information and 1-D drift-scale hydrologic properties from the 
Unsaturated-Zone (UZ) Model (CRWMS M&O 2000o, Section 3.6.5; CRWMS M&O 2000ak, 
Section 6). Based on this input, a lithostratigraphic column is developed corresponding to a 
location near the geographic center of the potential repository (the L4C4 location). The 
methodology and results for extracting stratigraphic information from the UZ Model are the 
same as for the Multiscale TH Model (Section 3.1.4). The geohydrologic stratigraphy at this 
geographic location is typical for much of the potential repository layout area. 
The EBS model geometry is developed from the License Application Design Selection (LADS) 
Enhanced Design Alternative II (EDA-II) (CRWMS M&O 2000q, Table 2). A 2-D model is 
justified for simulating water flow and drainage in the potential repository drifts, because the 
strategy for controlling flow and drainage, in its simplest form, does not require axial flow in the 
drifts. Because of symmetry, a 2-D model of NUFT is constructed to include only half of the 
WP, half of the drift, and half of the adjacent pillar. The width of the NUFT model grid is 
40.5 m, which is half of the drift spacing in the conceptual design. The two vertical edges of the 
model grid are treated as no-flow boundaries. The model extends from the ground surface to the

 3-16 
water table about 340 m below the potential repository. A model grid for the entire domain is 
shown in Figure 3-1, with the grid spacing varying from 0.02 to 45.0 m. A schematic of the 
emplacement drift with the drip shield and WP, is shown in Figure 1-3. Figure 3-2 shows the 
model grid in more detail, where it represents the EBS. 
The following hydrologic and thermal properties for the host rock and other stratigraphic units at 
the site, are used in this model (CRWMS M&O 2000q, Tables 36): 
 Fracture porosity 
 Matrix porosity 
 Tortuosity factor 
 Fracture bulk permeability 
 Matrix bulk permeability 
 Maximum and residual saturation in fractures, 
 Maximum and residual saturation in matrix 
 van Genuchten parameters a and m (or .) for fractures 
 van Genuchten parameters a and m (or .) for matrix 
Hydrologic and thermal properties for the backfill, the invert, and a material representing both 
(where they are in contact) are also defined (CRWMS M&O 2000q, Tables 7 and 8). The source 
of data for temperature and pressure boundary conditions at the ground surface and water table, 
and infiltration at the ground surface for present-day and glacial conditions, is the Unsaturated 
Zone Flow and Transport Model Process Model Report (CRWMS M&O 2000o; see CRWMS 
M&O 2000q, pp. 20, 21 and 41, for details). 
Several NUFT models include the effects of potential repository heating, whereby the geometry 
and heat generation characteristics of the WPs are also input. These characteristics include the 
WP dimensions and thermal properties, and time-dependent heat-generation (CRWMS M&O 
2000q, p. 27). 
3.1.1.2 Water Distribution and Removal Model Assumptions 
Use of the NUFT code requires a number of assumptions (CRWMS M&O 2000q, p. 30) which 
are summarized below. Also, ancillary calculations are used to analyze flow through breaches in 
the drip shield, and several additional assumptions are used for this purpose. 
To facilitate NUFT simulations, the top of the drip shield is represented by a stepped contour 
(Figure 3-2). The drip shield is assumed to be impermeable and to have the same effective 
physical properties as the WP (CRWMS M&O 2000q, p. 30). The dimensions of the drift, invert 
material, and drip shield correspond to the EDA II design. For ancillary calculations of flow 
through breached drip shields, the modeled thickness is 2 cm. 
Crushed tuff (CRWMS M&O 2000q, p. 30) is used as the invert ballast material. The invert will 
contain steel structural members, but the flow characteristics will be controlled mainly by the 
ballast. Crushed tuff also provides radionuclide retardation performance for certain conditions 
(Section 3.1.3).

 3-17 
Overton Sand (CRWMS M&O 2000q, p. 30) is used for the backfill material. In these NUFT 
models, the backfill completely fills the outer annulus between the drip shield and the drift wall, 
rather than leaving an air gap above the backfill. This has the effect that the total water flux 
through the drift is approximately equal to the ambient percolation flux that impinges on the drift 
opening, in these models. In this way, seepage inflow, including extreme seepage conditions, 
can be readily simulated with little sensitivity to model gridding and other uncertainties that 
attend to seepage modeling. 
It is important to note that this approach is different from model used to describe diversion of 
seepage around drift openings. This approach allows unsaturated flow of percolation flux in the 
host rock, directly into drift openings. By contrast, seepage models address the fact that for 
dripping to occur into an air gap, the water must achieve locally saturated conditions at the drift 
wall. With the presence of saturation gradients in the surrounding host rock, there is the 
potential for diversion of unsaturated flow around the drift openings. The approach described 
here is conservative, and represents extreme seepage conditions that might occur in a small 
portion of the potential repository. 
The Drift Degradation Analysis (CRWMS M&O 2000ad) provides information on the potential 
changes in drift geometry during the postclosure period. The expected drift geometry is a nearly 
circular, 5.5-m diameter opening. Deviations from circular geometry, caused by rockfall, are 
assumed to be insignificant for evaluation of water distribution in response to extreme seepage 
conditions. The circular configuration is used for all NUFT models discussed for the Water 
Distribution and Removal Model. 
The Ventilation Model (CRWMS M&O 2000an) analyzes the effects of preclosure continuous 
ventilation in the emplacement drifts. The principal purpose is to provide heat-removal data for 
EBS design. The Ventilation Model is used to show that removal of 70 percent of the wastegenerated 
heat is feasible during the preclosure period. 
For the Water Distribution and Removal Model (CRWMS M&O 2000q), the thermal-hydrology 
models assume 100 percent heat removal for a preclosure period of 100 years. This 
approximation minimizes the time until return of water, and resultant water inflow to the EBS, 
and is therefore conservative. (It is non-conservative for predicting peak temperature, but is not 
used that way.) For the ambient models (Table 3-1) no heating is imposed. 
A tortuosity factor value of zero is assigned to the WPs and drip shields in the NUFT models, 
because these barriers are impermeable (except where breached, but such failures are not 
considered in the NUFT models). A factor of 0.7 is assigned to the invert ballast material 
because it is a granular, with behavior similar to the host rock. This coefficient was estimated 
for soils, over a range of liquid saturation, and found to be approximately 0.7 (CRWMS 
M&O 2000q, p. 30). 
The NUFT models are used to evaluate the distribution of flow, the effects of flow focusing in 
the host rock, and the effects of fracture plugging below the drifts (CRWMS M&O 2000q, 
p. 34). To evaluate flow-focusing effects, 90 percent of the total infiltration at the ground 
surface is distributed over the smaller region of the ground surface directly above the drift 
opening. The remaining 10 percent is distributed over the rest of the ground surface.

 3-18 
To evaluate fracture plugging in NUFT models, the potential thermal-hydrologic-chemical 
(THC) and thermal-hydrologic-mechanical (THM) effects are simulated by decreasing the 
permeability of the fractured rock directly below the invert to that of the rock matrix. The 
conservative basis for this assumption is that THC processes would likely impact the flow 
properties of existing fractures, and that permeability would not be increased by THM processes 
(CRWMS M&O 2000q, p. 38). For these runs the fracture permeability is zero to a distance of 
3 m from the invert, representing penetration of fracture plugging into the host rock. Such 
penetration could be associated with the extent of boiling conditions and a dryout zone around 
the drift. 
To assess the function of engineered drainage features, as a measure to mitigate the possible 
expected effects of fracture plugging, NUFT runs are presented which include a drainage feature 
extending 6 m below the invert and filled with the same Overton Sand material used as backfill 
(Case 9). These NUFT models are 2-D, so the modeled drain feature represents a slot or a linear 
array of closely spaced borings. 
As discussed above, several assumptions are used in ancillary analyses of flow through the drip 
shield. The overlapping joint between drip shield segments is described as a parallel plate 
aperture (CRWMS M&O 2000q, p. 33). Flow through the overlap aperture is assumed to be 
limited by the local moisture potential. As a bounding calculation, the flow-aperture is assumed 
to be the maximum aperture that could retain pendular water at a specified value of the moisture 
potential. 
3.1.1.3 Water Distribution and Removal Model Uncertainties 
Models for water flow in the EBS describe the response of engineered materials with known 
hydrologic properties, in the designed configuration, to specified rates of seepage inflow. An 
alternative view is that thermal effects on flow, and coupled-process effects on hydrologic 
properties, could change water distribution and movement in the EBS so as to degrade the 
performance of the potential repository. Modeling presented in this report (Section 3.1.2.3.3.2) 
shows that two of the most plausible mechanisms for changes in EBS or near-field properties, i.e. 
fracture plugging and backfill porosity reduction, are negligible or can be controlled using design 
measures. 
Another effect that is not emphasized in this model is reflux of liquid water in the backfill during 
the thermal period. This effect is limited to the thermal period, localized to the drift, and will not 
contribute to advective release of water-borne radionuclides. It is addressed in the TH 
calculations performed in Section 3.1.2.1, in which fluxes between the backfill and the drip 
shield surface (Zones 3 and 4) are calculated. 
3.1.1.4 Water Distribution and Removal Model Development 
The EBS domain for modeling water distribution and removal consists of backfill, the drip 
shield, the invert, and the surrounding fractured host rock. Backfill in these simulation models 
contacts the host rock, throughout the upper part of the drift opening. The resulting capillary 
communication minimizes diversion of percolation through the host rock around the openings, 
and maximizes flow into the drifts (referred to as seepage in this discussion). Water enters the

 3-19 
drift and flows through the backfill, where it is partitioned into: 1) water flow through potential 
breaches in the drip shield; 2) water flow through the backfill directly to the invert; and 3) water 
flow that contacts the drip shield but is diverted through the backfill to the invert. Water 
diversion by the backfill and drip shield, and accumulation in the invert, is addressed using 
NUFT modeling (CRWMS M&O 2000q, Section 6.2). The NUFT runs performed for this 
model are described in Table 3-1. 
The foregoing approach tends to maximize the liquid flow rate through the upper drift wall, 
because of direct contact between the backfill and the host rock. This is done specifically to 
control the rate of liquid flow into the drift, so that water distribution and drainage response can 
be evaluated for extreme seepage conditions. This is not a realistic representation of drift 
seepage; the reader is referred to the UZ Flow and Transport Model Process Model Report 
(CRWMS M&O 2000o, Section 3.9) for the Drift Seepage Model. It is noted that water can also 
flow from the host rock, directly into the backfill in the lower part of the drift, and that this mode 
of flow is also possible in the model. 
The host rock contains a freely draining system of fractures which has sufficient capacity to 
drain water that enters the drifts as seepage, unless fracture permeability is insufficient or 
occluded by thermally driven processes. The potential effects of fracture plugging are addressed 
by several NUFT runs that are described in Table 3-1 (cases indicated as Plugged). The Water 
Drainage Model (CRWMS M&O 2000af) is based on NUFT simulations using a 2-D, 
steady-state, ambient temperature model with the seepage flux equivalent to the percolation flux. 
Coupled processes during the thermal period may significantly alter hydrologic properties that 
influence reflux activity and seepage. Changes in host rock permeability are discussed below. 
Scoping calculations of potential changes in backfill permeability are discussed in 
Section 3.1.2.3.3. 
The In-Drift Thermal-Hydrological-Chemical Model (CRWMS M&O 2000y) simulates the 
open-air void space inside the drip shield to evaluate the potential for moisture condensation. 
The model evaluates the tendency for liquid water to evaporate from the invert and condense 
elsewhere in the annular space between the waste package and the drip shield. The model is 
implemented using NUFT, with properties and boundary conditions similar to those discussed 
above. Preliminary results from this set of calculations are described below. 
The Water Diversion Model (CRWMS M&O 2000ae, p. 36) provides an analysis of drip shield 
performance in conjunction with the Overton Sand backfill, based on analytical solutions for 
unsaturated flow around a cylindrical inclusion, and for flow through capillary bundles 
representing breaches in the drip shield. When seepage into the drift occurs, saturation increases 
above the drip shield, with increased potential for flow through a breached drip shield. The 
presence of sand backfill ensures that moisture tension (i.e. negative moisture potential) exists on 
the drip shield surface for a wide range of seepage conditions. For water to flow through a 
breach in the drip shield, requires that the hydrologic characteristics of the breach are sufficient 
to imbibe water from the unsaturated sand. Such conditions are associated with decreased 
transmissivity of the breach to water, which implies limited flow and a threshold-type response. 
Breaches through the drip shield are modeled as fully-wetted capillary bundles, and parallel plate

 3-20 
apertures, which have negligible transmissivity until fully saturated at a threshold moisture 
potential (i.e., relative humidity). 
The use of capillary bundles to represent breaches or gaps in the drip shields, depends critically 
on the presence of the sand backfill. If seepage occurs, it will be readily absorbed and conducted 
by the backfill material, as unsaturated flow. Droplets of water cannot form in the backfill unless 
conditions approach full saturation, which will not occur even for extreme seepage, according to 
the Water Distribution and Removal Model (CRWMS M&O 2000q) discussed below. The fine 
sand has high unsaturated hydraulic conductivity, and can readily handle any seepage flow 
without becoming saturated in the upper part of the drift. The results discussed below also show 
that high backfill saturation is most likely in the lower part of the drift, near the contact with the 
invert, where the flow area is restricted. Flow through potential breaches in the lower part of the 
drip shield would be limited geometrically, and of low consequence to performance. Thus the 
hydrologic characteristics of the backfill will produce a capillary barrier effect such that droplets 
will not form on the upper part of the drip shield.

TDR-EBS-MD-000006 REV 00 3-21 March 2000 
Table 3-1. Summary of Parametric Cases for the Water Distribution Model 
Infiltration Rate Focusing Heating Plugging Design Case Number 
Glacial 
Monsoon 
Current 
Uniform 
Focused 
Ambient 
Elevated 
None 
Plugged 
No Sand 
Drains 
Sand 
Drains 
1 X X X X X 
2 X X X X X 
3 X X X X X 
4 X X X X X 
5 X X X X X 
6 X X X X X 
7 X X X X X 
8 X X X X X 
9 X X X X X 
10 X X X X X 
11 X X X X X 
12 X X X X X 
13 X X X X X

 3-22 
3.1.1.5 Water Distribution and Removal Model Validation 
NUFT Calculations 
The thermal-hydrology calculations in this section are principally ambient temperature, steadystate 
simulations of water movement through the EBS. Calculations for the Water Distribution 
and Removal Model are performed using the same numerical simulator (NUFT), and the same 
modeling concepts described in Sections 3.1.2 and 3.1.4. The most important difference is that 
the range of infiltration flux conditions used, includes the upper infiltration distribution 
combined with other model features to produce extreme seepage. Model validity is ensured 
through the following features of the model: 
 Mass continuity is imposed by the simulation code 
 The properties for natural and engineered materials are based on measured and 
calibrated values 
 Seepage conditions include bounding values, which do not depend on numerical 
gridding 
In addition, pilot-scale tests for backfilled openings, and data comparisons with model 
predictions, are underway. 
The properties used for the host rock are taken directly from the 1-D drift-scale results of the 
Unsaturated Zone Flow and Transport Model Process Model Report (CRWMS M&O 2000o, 
Section 3.6.4). The properties are defined in a way that describes the unsaturated hydrology of 
the host rock according to current understanding (e.g., using the AFC). Property values are 
estimated using a procedure by which they are constrained using appropriate observations and 
measured data from Yucca Mountain. The temperature boundary conditions used for these 
models are based on average temperatures for the ground surface and water table, which are 
constrained by measured data. Similarly, the average total pressure boundary conditions are 
consistent with known variation of atmospheric pressure. 
Values for average surface infiltration flux are also taken directly from the UZ Model, for a 
central location that is typical of the average over the repositoy layout area. The infiltration flux 
boundary condition is selected from the upper infiltration distribution developed for the 
Unsaturated Zone Flow and Transport Model Process Model Report (CRWMS M&O 2000o, 
Section 3.5.2) using an extraction process developed originally for the Multiscale 
Thermohydrologic Model (Section 3.1.4). The models described in this section are configured to 
minimize the diversion of seepage around drift openings, thus the seepage flow approaches the 
incident percolation flux over the drift footprint, and extreme seepage is produced. 
From this discussion it is concluded that the TH models used for the Water Distribution and 
Removal Model are valid for their intended use in FEP screening, and supporting the design 
basis. The models are based on appropriate inputs, including properties and boundary 
conditions. The principal difference between these calculations and those presented in Sections 
3.1.2.1 and 3.1.4, is the use of model features and input data to maximize seepage flow.

 3-23 
A small subset of calculations presented in this section includes transient response to repository 
heating, as a check on results obtained for ambient temperature. Validation for thermalhydrology 
models of this type is addressed in Section 3.1.4. 
Analytical Models for Water Diversion and Leakage 
Bounding approaches are developed for: 1) identifying the moisture potential conditions for 
which capillary flow can occur through breaches in the drip shield; and 2) bounding the potential 
flow rate of water through breaches in the drip shield (i.e., fully wettable surfaces, unit flow 
potential gradient). These approaches are bounding only for the current design which includes 
fine sand backfill in contact with the drip shield. In addition, a bounding approach is taken that 
all leakage through the drip shield is available at the waste package surface. Film flow effects 
that could divert water from the waste package are not taken into account, but their effects are 
relatively small compared with the bounds developed using parallel-plate flow. Accordingly, the 
modeling approach is a valid bounding approximation for flow through cracks in the drip shield, 
or partings between adjacent segments. 
3.1.1.6 Water Distribution and Removal Model Results 
Table 3-1 summarizes the parametric studies performed using NUFT for the Water Distribution 
and Removal Model (CRWMS M&O 2000q). The glacial infiltration rate is used as a 
conservative, bounding representation of the rate of percolation in the host rock. Results are 
presented for the glacial climate, with uniform and focused infiltration at the ground surface, 
with ambient temperature and heated conditions, and without fracture plugging (Cases 1 through 
4). Results are also presented for the same hydrologic conditions, but with fracture-plugging, 
and also for the combination of plugging and an engineered drainage feature. In addition, 
another run (Case 10) is presented with a drainage feature, but without fracture plugging, to 
evaluate the effect of such a feature on nominal performance of the EBS. 
Base Case and Infiltration Focusing at the Ground Surface  NUFT Results 
The results of NUFT simulations for the Water Distribution and Removal Model, ambient 
temperature base case (Case 1) are presented in Figures 3-3 through 3-6. The following aspects 
of the calculated hydrologic results are discussed below: capillary water potential, liquid water 
flux in fractures, and liquid water saturation in the fractures and matrix. 
For the base case, the capillary pressure (i.e. moisture tension) ranges from approximately 
370 cm in the rock matrix above the drift, to 220 cm in the drift backfill above the drip shield 
(Figure 3-3). Saturation levels are somewhat elevated immediately above the drip shield. These 
changes are similar to the moisture potential values predicted at the drip shield surface, by the 
analytical solution used in the Water Diversion Model (CRWMS M&O 2000ae, p. 36). 
Below the drip shield, the capillary pressure in the host rock ranges from approximately 370 cm, 
to 510 cm in drier regions. A relatively dry, shadow region is predicted to occur in the host rock 
below the drift, consistent with the analytical solution used in the Water Diversion Model 
(CRWMS M&O 2000ae, p. 36).

 3-24 
Figure 3-6 illustrates that the liquid flux is increased adjacent to, and somewhat below the drip 
shield, to a value of approximately 145 mm per year (4.6  10-6 kg/m2-sec in the figure). This is 
caused by the flow-focusing geometry of the drip shield and backfill (with seepage flux into the 
drift that is comparable in magnitude to percolation flux in the host rock). These values are in 
qualitative agreement with predictions from the Water Diversion Model (CRWMS 
M&O 2000ae, Figure 16) and the Water Distribution and Removal Model (CRWMS 
M&O 2000q, p. 52). 
The NUFT model results for the infiltration conditions and hydrologic properties used, show that 
matrix saturation in the host rock is approximately 0.90, while fracture saturation is at or near the 
residual saturation (i.e., a few percent; Figure 3-4). Flow in the host rock is dominated by 
unsaturated flow in fractures. 
For comparison, other cases were examined whereby the same average infiltration flux was used 
at the ground surface, but 90 percent of the flow was focused onto the part of the surface located 
directly above the drift opening. This was done for both the ambient and thermal calculations 
(Cases 2 and 4). Comparison with the base case (Cases 1 and 3) shows that given the simulation 
approach, the flow regimes are nearly identical, and that focusing of infiltration at the surface has 
no significant effect on flow at the potential repository horizon. This is equivalent to a statement 
that hydrologic features responsible for focusing flow into potential repository drifts, where such 
features exist, must be situated within a few tens or hundreds meters from the drifts, in the 
vertical direction. Effects from more distant features tend to be smoothed by dispersive behavior 
in the UZ. 
Effects of Heating in the Base Case  NUFT Results 
Results from NUFT modeling of focused flow with potential repository heating, are presented in 
the Water Distribution and Removal Model (CRWMS M&O 2000q, p. 54) for conditions at up to 
1,000 years after waste emplacement. Peak temperatures in the backfill are predicted to occur 
during the period 100 to 1000 years. The predicted effects of potential repository heating on 
water distribution in the EBS generally include less seepage into the drift opening, lower 
saturation in the backfill, and increased capillary pressure (i.e., drier conditions; increased 
moisture tension). 
After approximately 1000 years liquid water returns to the EBS. (Note that the 2-D NUFT 
models of the L4C4 location represent potential repository center conditions, and that return of 
water will occur sooner at the potential repository edges.) The capillary pressure in the backfill 
decreases during cooldown, as saturation increases. Examination of the liquid flux within the 
drift during cooldown shows that as water returns to the EBS, thermally-driven reflux activity 
subsides, and the flux distribution in the backfill resembles ambient conditions (Figure 3-7) 
(CRWMS M&O 2000q, p. 55). 
Extreme Seepage and Fracture Plugging  NUFT Results 
Results from NUFT simulation with fracture plugging, and focused flow at ambient temperature, 
are presented in the Water Distribution and Removal Model (CRWMS M&O 2000q, p. 55). The 
results show that liquid flux into the drift, and liquid flux through the backfill, are decreased

 3-25 
slightly compared with the base case (not plugged). This probably results from flow diversion 
around the drift opening, because of decreased permeability in the plugged region. Compared to 
the base case, the capillary pressure in the backfill is decreased slightly (i.e., less moisture 
tension), and saturation is increased. 
The most important effect from fracture plugging below the drift is increased saturation in the 
invert and adjacent rock (CRWMS M&O 2000q, p. 62). Saturation in the invert increases to 
nearly full saturation, and the capillary pressure approaches zero (i.e., nearly free water 
conditions). Saturation in the invert increases to approximately 0.98 (i.e. nearly full saturation). 
These results show that even with extreme seepage conditions, plugging below the invert 
produces flow diversion in the host rock, while maintaining unsaturated conditions in the backfill 
and invert. 
Potential Engineered Drainage Features  NUFT Results 
The results of NUFT analysis for cases that include an idealized, 2-D engineered drainage 
feature at ambient temperature, are presented in Figure 3-8 through Figure 3-11. The current 
design does not include any engineered drainage features. However, the results show that a 
drainage feature filled with Overton Sand strongly influences the flow regime in the invert and in 
the host rock below the potential repository horizon. The distribution of capillary pressure in and 
around the drainage feature (Figure 3-8) shows that capillary pressures are greater (i.e., drier 
conditions) in the invert and the adjacent host rock. Saturation within the drainage feature 
increases with distance below the drift, and there is nearly full saturation at the base. The 
drainage feature strongly influences the liquid flux in the invert, as shown in Figure 3-11. 
Liquid flux in the drainage feature is much greater than in the invert of backfill, within the drift 
opening. The drainage feature causes increased capillary pressure (drier conditions) and 
decreased saturation in the invert above the region of plugged fractures. The capillary pressure is 
approximately 200 cm for this case; without the drainage feature the capillary pressure in the 
invert was nearly zero (i.e. nearly complete liquid saturation). 
Flow Through the Drip Shield to the Waste Packages  Analytical Model 
For the models for which results are described above, the drip shield is impermeable. In this 
section an analytical model is developed to describe the flow rate through small breaches in the 
drip shield (CRWMS M&O 2000ae, p. 37) in contact with a fine sand backfill. The boundary 
condition for the state of moisture at the drip shield surface, is obtained from the base-case 
NUFT model discussed previously. This base-case model shows that for ambient temperature 
conditions, capillary pressure in the backfill is uniformly negative, around the drip shield and in 
the invert. This result is consistent with steady-state percolation at a rate equal to the unsaturated 
hydraulic conductivity, flowing along the gravitational potential gradient. 
An aperture in the region of overlap between drip shields is characterized by a moisture potential 
(.). A water retention expression relates the largest aperture that can retain capillary water at 
potential . (CRWMS M&O 2000ae, p. 31):

 3-26 
. . 
s = 1 
g 
2 
B 
w 
(Eq. 3-1) 
where s is the surface tension of water, .w is water density, and g is the acceleration of gravity. 
For a uniform, parallel-plate gap, the aperture extent is the perimeter of the overlapping joint. 
Substituting Equation 3-1 into the cubic law (CRWMS M&O 2000ae, p. 31) and applying a unit 
head gradient (P), gives an expression for the maximum flow rate as a function of the potential: 
P 
g 
2 
12 
g 
Q 
3 
w 
w  . .
.
. 
. .
.
. 
.   . 
s  
 
. 
 . 
= (Eq. 3-2) 
where . is the dynamic viscosity. Figure 3-12 presents the relationships for flow rate through the 
backfill around a drip shield, and through the gap between adjacent drip shields, plotted against 
the backfill percolation rate determined from the moisture potential and the unsaturated hydraulic 
conductivity at that potential (CRWMS M&O 2000ae, p. 22). The backfill flow rate is 
determined from the unsaturated hydraulic conductivity for the backfill, and the drift diameter. 
The limiting value of the aperture (B) for which a breach can imbibe water from the sand at 
moisture potential (.), is given by Equation 3-1. (For more negative potential the breach will be 
effectively dry.) A bounding flow rate through breach, once it becomes saturated, is given by 
Equation 3-2. The analysis shows that over the range of moisture potential expected within the 
backfill for ambient conditions, the bounding flow rate through the drip shield is a fraction of the 
backfill flow rate. Importantly, this is a bounding expression that does not take into account 
features of the drip shield joint that could inhibit leakage, and also assumes a unit head gradient 
(i.e. the flow path through the joint is assumed vertical). 
The foregoing discussion has analyzed a breach in the drip shield, as a parallel-plate opening. 
This type of breach could arise from relative displacement of adjacent drip shield segments, due 
to rockfall, faulting, or seismic ground motion. For such a breach to form, the joint between 
segments would have to fail. The probability of such a breach depends for each cause, on the 
probability of the initiating event and the probability of failure. Further discussion of the EBS 
abstractions is provided in Section 3.2.1. 
Moisture Condensation Under the Drip Shield  Preliminary NUFT Results 
The In-Drift Thermal-Hydrological-Chemical Model (CRWMS M&O 2000y) results show that 
evaporation in the invert is regulated by the relative efficiency of conductive heat transfer in the 
invert, and of heat transfer directly from the waste package to the drip shield, compared to latent 
heat transfer by evaporation in the invert. If the volumetric moisture content in the invert ballast 
material is relatively high, the evaporation rate may be significant so that condensation 
underneath the drip shield is possible, whereas if the moisture content is low, the unsaturated 
permeability of the invert ballast material limits the moisture flux available for evaporation. 
Moisture-retention relations for the invert ballast material, based on unsaturated flow 
measurements by centrifugation, have been developed for moisture potential values of 100 cm 
and greater (i.e. more moisture tension) (CRWMS M&O 2000ad, p. 37). Interpretation of these

 3-27 
measured data with respect to the evaporation rate model discussed above, shows that for 
moisture potential of 100 cm or greater (i.e., drier), the volumetric moisture content in the 
crushed tuff invert will be low, such that the evaporative flux from the invert below the drip 
shield will be limited by unsaturated permeability. With less heat transferred from the waste 
package to the invert and converted to latent heat by evaporation, there is relatively more heat 
transferred to the drip shield. The temperature of the drip shield is thereby greater, which 
inhibits condensation. 
It is noted that the results reported here for conditions leading to condensation under the drip 
shield are preliminary. There are alternative approaches, such as application of computational 
fluid dynamics, which includes momentum effects on thermally driven bouyant convection. The 
numerical values for flux and potential conditions that could cause condensation are 
approximate. 
3.1.1.7 Summary of Results from the Water Distribution and Removal Model 
Models for water distribution in the EBS use properties and boundary conditions that are 
consistent with the UZ Site-Scale Model. Hydrologic conditions in the EBS are evaluated for the 
conditions of greatest infiltration, that are used with the UZ Model (glacial, upper infiltration 
distribution). The EBS models are configured to show how the engineered diversion barriers 
perform, even if the seepage flux into potential repository drifts approaches the ambient 
percolation flux in the host rock, which may occur with increasing percolation rates. 
The geometry of the drip shield and the drift opening causes flow focusing in the backfill, such 
that liquid flux magnitudes of up to four times the ambient percolation flux, may occur locally in 
the drifts. Potential repository heating causes lower saturation, lower liquid flux, and greater 
capillary pressure (i.e. greater moisture tension) during the thermal period. Thermally driven 
reflux cells in the backfill may increase the calculated liquid flux magnitude, locally in the drifts, 
during the thermal period. Liquid water flow from the host rock returns to the EBS at 
approximately 1,000 years, for potential repository center locations. 
Fracture plugging below the invert can cause high saturation (or full saturation) in the invert, for 
all infiltration conditions evaluated. Engineered drainage features such as vertical boreholes 
filled with sand, can control saturation conditions in the invert even with the conditions of 
greatest infiltration, and fracture plugging. 
Liquid flux through possible gaps between drip shields is bounded using a simple modeling 
approach, and further decreases in the bounding result may be possible if refinements to the 
design and to the model assumptions, are incorporated. 
Results reported for condensation under the drip shield are preliminary, and include approximate 
values for conditions that could lead to condensation. Condensation under the drip shield 
requires that the vapor pressure at the surface of the drip shield exceed the saturated vapor 
pressure at the drip shield temperature. The water vapor pressure in the air space under the drip 
shield will tend to be uniform (especially before the onset of condensation) because of gaseous 
diffusion and circulation.

 3-28 
Hydrologic conditions in the invert can control the water vapor pressure under the drip shield. 
During the gradual cooldown process, the humidity in the air space under the drip shield will be 
in thermodynamic equilibrium with the invert. If the invert saturation is great enough, 
condensation on the underside of the drip shield can occur, but if the invert is dry enough, 
condensation will not occur. The possibility of condensation is thus controlled by factors such as 
seepage into the drift, which could increase the invert saturation. This explanation has not 
considered mass exchange between the gas-phase under the drip shield, and the gas-phase 
outside the drip shield. However, the drift wall will generally be cooler than the drip shield or 
the invert, so mass exchange would tend to decrease the humidity under the drip shield, and the 
potential for condensation. 
To apply the Multiscale TH Model results (Section 3.1.4) for prediction of the onset of 
condensation under the drip shield, the vapor pressure at the invert (related to air mass-fraction) 
would be compared to the saturation vapor pressure at the drip shield temperature. A direct 
comparison of temperatures at the invert and the drip shield would be less accurate, because of 
the vapor pressure lowering effect from partial saturation in the invert material. This conceptual 
model, supported by calculations, demonstrates the benefits from keeping the invert relatively 
dry. Simulations have shown that engineered drainage features could help to decrease the invert 
saturation, and thereby contribute to prevention of condensation under the drip shield. 
3.1.2 Physical and Chemical Environment Model 
The overall purpose of the EBS Physical and Chemical Environment (P&CE) Model is to 
evaluate changes in the bulk environment that could affect drip-shield and waste-package 
degradation, and radionuclide migration. This includes changes in aqueous chemistry resulting 
from interaction of introduced materials with heat, and water seeping into the drift, taking into 
account thermal effects on chemical equilibria and rate processes, and physical processes such as 
evaporation and condensation. The Physical and Chemical Environment Model comprises 
several submodels as shown in Table 3-A. The intended uses for these submodels vary: some 
are intended mainly for FEP screening and to support the subsurface repository design basis, 
while others provide direct feeds to TSPA. 
The submodels of the Physical and Chemical Environment Model emphasize specification of 
environmental conditions for corrosion and mechanical performance of the drip shield, and 
corrosion performance of the waste package. This emphasis supports the design basis by 
describing environmental conditions that are extreme, and too unlikely for explicit consideration 
in TSPA, but should receive consideration in the design development. Accordingly, aspects of 
the submodels discussed in this section are bounding, for example, selection of a reference TH 
model for chemical modeling. 
Some submodels described in this section directly support TSPA, which includes assessment of 
EBS environmental conditions and their consequences. Importantly, the TSPA incorporates 
models and data which are outside the scope of this PMR (e.g., UZ flow and drift seepage) for a 
more complete overall assessment of potential repository performance, including performance of 
the EBS. Description (i.e., abstraction) of EBS processes in the TSPA is described in Section 
3.2.

 3-29 
Many of the submodels described below support the Chemical Reference Model (Section 
3.1.2.7), which does not support TSPA directly. Specifically, the TH submodel described in 
Section 3.1.2.7, the Gas Flux and Fugacity submodel in Section 3.1.2.2, and the Precipitates and 
Salts Normative Model in Section 3.1.2.5.2, are integrated in the Chemical Reference Model, 
from which conclusions are drawn concerning the bulk chemical environment. Other submodels 
such as the Cementitous Materials Model (Section 3.1.2.3.5), are also considered in the 
integrating discussion. 
General Remarks on Modeling the In-Drift Physical and Chemical Environment 
The engineered barrier system (EBS) is defined to include all the engineered components of the 
subsurface repository, outside the waste packages (Section 1). Thus the EBS is limited to inside 
the drift wall (except for rockbolts). Nevertheless, for modeling the in-drift environment, the 
model domain extends from the ground surface to the water table (or deeper in the saturated 
zone, as discussed in Section 3.1). This is appropriate because the effects of heating penetrate 
well into the host rock, affecting conditions in the rock at the drift-wall, and controlling the 
boundary conditions for the in-drift environment. Many EBS models extend beyond the drift 
openings because the host rock response controls the in-drift processes, and it is more difficult to 
completely specify the thermal, hydrologic, pneumatic, and chemical boundary conditions at the 
drift wall, than further away (e.g., the ground surface, or the water table). Conversely, it is 
relatively simple to compare simulation results from EBS models with other models, to verify 
that they produce consistent results at the drift wall (or anywhere else). 
For TSPA, the thermal-hydrologic conditions at the drift-wall, within the drift, and in the host 
rock, are simulated using the Multiscale TH Model (Section 3.1.4). The chemical conditions at 
the drift-wall (i.e. water composition and mineral precipitates present), are simulated using the 
Drift-Scale Coupled Processes (DST and THC Seepage) Models (CRWMS M&O 2000x). 
Chemical conditions within the emplacement drifts are simulated using a reaction-cell approach, 
with a Pitzer formulation (Section 3.1.2.5.3). All of these models depend on, and use extensive 
input from, the hydrologic model for the UZ at Yucca Mountain (CRWMS M&O 2000o). 
In this report, the approaches for modeling thermal-hydrology, gas-phase transport, and the 
chemical evolution of waters in the host rock, also include model domains that extend into the 
host rock. Thermal-hydrologic models described in Section 3.2.1.1 are based on the Multiscale 
TH Model (Section 3.1.4). For chemical modeling, the host rock and the emplacement drifts are 
represented by a set of reaction cells, or zones. Changes in temperature and hydrologic 
conditions in these zones are simulated using the TH model (Section 3.1.2.1), and the chemical 
conditions are simulated for the Chemical Reference Model (Section 3.1.2.7). 
Geochemical modeling concepts are used to describe the chemical evolution of each zone 
through time, incorporating the effects of temperature, evaporative concentration, and interaction 
with solid mineral phases present. For the Chemical Reference Model (Section 3.1.2.7), 
chemical reactions are described by equilibrium models using the B-dot activity expression, 
which is limited to approximately 1 molal ionic strength (CRWMS M&O 2000t). Another 
approach using an extended Pitzer formulation is described in Section 3.1.2.5.3, and is developed 
for use in TSPA. The B-dot approach was developed for more accurate representation, although 
for a more limited range of solution conditions.

 3-30 
The Chemical Reference Model includes chemical modeling of the host rock as well as the EBS, 
because the host-rock temperature is high enough during the thermal period to change the 
composition of naturally percolating waters. The modeling approach for the host rock is similar 
to that used for in-drift processes and is based on temperature and water flux information from 
the same TH models. Processes including cement leaching, colloid formation, and microbial 
activity are evaluated using related, but separate models to evaluate whether there are likely to be 
important effects on the bulk chemical environment. 
Relationships Among Submodels Described for the In-Drift Physical and Chemical Environment 
As stated above, the following sections present submodels that are used to support TSPA 
directly, or are used in the Chemical Reference Model, or are used to address the importance of 
microbial activity, coupled processes, and cement leaching. These submodels are summarized 
for the Physical and Chemical Environment, in Table 3-A. In addition, the information flow 
between all the submodels, including those that support TSPA, is depicted in Figure 3-13. 
Referring to Figure 3-13, the following are submodels used in the Chemical Reference Model: 
 Physical and Chemical Environment TH Model (Section 3.1.2.1) 
 Gas Flux and Fugacity Model (Section 3.1.2.2) 
 Precipitates and Salts Normative Model (Section 3.1.2.5.2) 
while the following generate additional information that is used to evaluate sensitivity of the bulk 
chemical environment to different processes: 
 Introduced Materials Models (including the Kinetic Model for Water-Quartz 
Interaction, Model for Seepage-Backfill Interaction at High Ionic Strength, Model for 
Corrosion of Carbon Steel in the EBS, and the Cementitious Materials Model; Section 
3.1.2.3) 
 Microbial Effects Models (including the Threshold Conditions Model for microbial 
activity, and the Microbial Communities Model; Section 3.1.2.4) 
 Other precipitates and salts models (including the LRH Salts Model, Condensed Water 
Model, and the HRH Salts Model; Section 3.1.2.5.3) 
 EBS Colloids Model (Section 3.1.2.6) 
Together, these elements represent current process-level understanding of the bulk EBS P&CE. 
The following models provide input directly to TSPA: 
 Microbial Communities Model 
 LRH Salts Model 
 HRH Salts Model 
The results from these submodels are transferred to the EBS P&CE Abstraction Model (Section 
3.2.3), where they are incorporated in the TSPA.

 3-31 
3.1.2.1 Thermal Hydrology 
This section describes application of the NUFT code to simulation of thermal-hydrologic (TH) 
conditions in discrete zones representing the host rock and the emplacement drifts. The 
calculated temperatures, fluxes between zones, and other results are used in the Gas Flux and 
Fugacity Model, the Cementitious Materials Model, and the Chemical Reference model. These 
results represent the effects of heating and hydrologic flow that can affect chemical processes in 
the EBS. 
This submodel supports the Chemical Reference Model (Section 3.1.2.7). The overall purpose 
of this submodel is to describe thermal-hydrologic conditions in the emplacement drifts, and the 
adjacent host rock. The intended use is FEP screening, and support of the design basis by 
exploring the range of thermal-hydrologic conditions likely to occur in the repository. A range 
of TH cases is considered, and one is selected for the Chemical Reference Model based on 
criteria that include environmental conditions that are potentially more adverse to corrosion of 
the drip shield and waste package. The range of conditions considered includes repository edge 
vs. center locations, and low vs. high infiltration. 
3.1.2.1.1 Conceptual Model Development and Alternative Models 
The TH simulations reported here implement energy balance and mass balance in multiphase gas 
and liquid flow systems that are described by Darcys Law for partially saturated media. These 
models describe heat and mass transfer the host rock and the EBS, during and after the thermal 
period. They predict development of a dryout zone around the drifts (Figure 3-14), which 
collapses over time in response to ambient percolation, as thermal output decays. Heat is 
transferred by thermal conduction, liquid- and gas-phase convection, and latent heat effects (i.e., 
evaporation and condensation). 
An important conceptual aspect of TH modeling is representation of fractured rock, which 
exhibits strongly bimodal and spatially heterogeneous flow characteristics. The fracture system 
is represented as a porous continuum, to save computational effort, while the rock matrix is 
represented by a separate continuum having different properties. This approach has been 
demonstrated in modeling of results from field testing (discussed later in this section). Fractures 
can also be represented effectively as discrete discontinuities, but the computational effort is 
prohibitive for meaningful applications. 
The TH models described in this report represent fractured rock using a dual-permeability 
continuum approach based on the active-fracture concept (AFC) of Liu et al. (1998). The AFC 
conceptual model is also used in the Unsaturated Zone Flow and Transport Model Process 
Model Report (CRWMS M&O 2000o; referred to as the UZ Model in this discussion) and the 
extraction of input data from the UZ Model is discussed in the Multiscale Thermohydrologic 
Model report (CRWMS M&O 2000i). The TH models described in this section are based on the 
Multiscale TH Model (Section 3.1.4), using the same model stratigraphy, properties, boundary 
conditions, and calculation procedure as the 2-D drift-scale TH models (CRWMS M&O 2000t). 
Thermal-hydrology models have been used extensively to design field thermal tests at Yucca 
Mountain and elsewhere, and to interpret the data obtained from such tests (Hardin 1998,

 3-32 
Chapter 3; Wilder 1996, Section 1; also see Sections 3.1.4.4.1 and 3.1.4.4.2). As discussed in 
Section 3.1.4 below, field testing has resulted in improved understanding of thermally-driven 
flow processes, and revised property sets. The TH calculations described here are based on this 
foregoing body of work, and support reaction-cell modeling of the bulk chemical environment. 
3.1.2.1.2 Thermal and Hydrologic Input Data, Assumptions, and Uncertainties 
Drift-scale, two-dimensional (2-D) TH simulations using the NUFT code are reported here for 
the L4C1 and L4C4 locations (Figure 3-70). Preclosure ventilation is represented by diminished 
heat output, closure is at 50 years after emplacement, and backfill is included at closure. 
The L4C1 and L4C4 locations are developed in the Multiscale Thermohydrologic Model 
(CRWMS M&O 2000i). That model represents, by an array of discrete locations, variation of 
TH conditions throughout the potential repository (Figure 3-70). These two locations are used 
because: 
 L4C4 is typical for locations internal to the potential repository layout. It is near the 
geographic center of the potential repository layout, where temperatures and 
evaporation rates will be relatively high. Thermal loading for the L4C4 model is 
equivalent to the average for the potential repository layout (60 MTU/acre), and the 
infiltration flux is close to the average. 
 L4C1 is located at the potential repository edge where the rate of cooling will be 
relatively high because of conductive heat loss to external regions. Drift spacing for 
the L4C1 model is increased so that the thermal loading is equivalent to 36 MTU/acre 
with the same thermal output, which is appropriate for edge locations (CRWMS M&O 
2000i). 
For each of these locations, the TH conditions are simulated with both the lower and upper 
infiltration distributions from the UZ Model (CRWMS M&O 2000t), for a total of four NUFT 
cases. Different 1-D drift-scale hydrologic property sets, also from the UZ Model, are associated 
with the different infiltration conditions. 
In-Drift Properties and Processes 
The NUFT cases developed in this report are 2-D symmetry models. The model domain is a 
vertical plane perpendicular to the axis of a single emplacement drift, and is reflected 
symmetrically about the drift centerline and the pillar centerline. The vertical boundaries of the 
model domain (passing through the center of the drift and through the center of the pillar) are 
adiabatic, no-flow boundaries. 
For the calculations described here, the backfill extends to the drift crown so there is no head 
space in the drift opening. This has the effect that percolation flux in the backfill is 
approximately equal to the percolation flux in the host rock, for ambient (post-thermal) 
conditions. By eliminating head space in the drift opening, the model can more readily simulate 
locations in the potential repository where seepage occurs. The result is conservative in that EBS 
performance is analyzed for conditions in which diversion of percolation flux in the rock around 
the drift openings, is minimized.

 3-33 
Greater evaporation rates are achieved with greater seepage flux because of the proximity of 
percolating waters to the hottest parts of the EBS. Production of water vapor causes 
displacement of air, thus decreasing CO2 fugacity (other factors can cause CO2 fugacity to 
increase). Decreased CO2 promotes high pH and is conservative with respect to corrosion of 
EBS components. Thus the choice of upper infiltration, a potential repository-center location, 
and conditions for which seepage occurs, support a conservative design basis for the EBS. 
Geometry of the Drift, Drip Shield, and Waste Package 
The drift diameter is 5.5 m. For these NUFT cases the waste package (WP), drip shield (DS), 
and the WP support are combined into a single composite body with outside dimensions 
representing those of the DS, and thermal properties scaled to represent the composite body. 
This is based on a simplifying assumption that heat and mass transport between the WP and DS 
are not critical to the bulk physical and chemical environment, and that if water penetrates the 
DS for any reason then the WP is exposed to the same chemical environment as the DS. The 
NUFT grid is designed so that the regions of grid blocks representing the drift, invert, backfill, 
and the DS have cross-sectional areas that are approximately the same as those specified in the 
design. 
Thermal Loading and Aging of Waste Inventory 
The NUFT simulations described here are 2-D calculations in which the WPs are represented as 
a line-heat source. The line-source strength decays with time, to represent the radioactive decay 
of a composite of (SNF) spent nuclear fuel and defense high-level waste (DHLW) (CRWMS 
M&O 2000t). The line-source strength is modified for heat-removal by ventilation in the 
preclosure period; the source strength is decreased by 70 percent, which was shown to be 
feasible by the Ventilation Model (CRWMS M&O 2000an). 
Hydrostratigraphic Unit Thicknesses, Contact Elevations, and Properties 
The UZ Model unit thicknesses, contact elevations, and lateral extents are honored in these 
calculations. The hydrologic properties used in the TH portion of this report are fully consistent 
with the one-dimensional (1-D), drift-scale property sets from the UZ Model (CRWMS 
M&O 2000t). Each property set contains descriptions for the rock matrix and for the fracture 
network for each hydrostratigraphic unit. The continuum properties assigned to the fracture 
network, are homogeneous within each hydrostratigraphic unit (CRWMS M&O 2000t). The UZ 
Model derives the unit properties that are used in this model, so the same assumptions apply 
here. 
The property sets also include parameters that describe nonequilibrium fracturematrix 
interaction using the AFC, which are used directly in NUFT. The effective tortuosity for gasphase 
diffusive mass-transfer in both the matrix and fracture continua is assumed to have a value 
of 0.7, which is the scale-invariant path tortuosity that would be encountered in a medium 
composed of impervious, cubical blocks (CRWMS M&O 2000t). The tortuosity value for 
liquid-phase mass-transfer is negligible by comparison and is assumed to be zero.

 3-34 
Net Infiltration Boundary Conditions 
Grid files describing the variation of infiltration over the site area were obtained from the U.S. 
Geological Survey (USGS) (CRWMS M&O 2000t). These data were reformatted and 
interpolated for use as boundary conditions in NUFT models (CRWMS M&O 2000t). For the 
climate model represented by these files, the climate state changes from present-day conditions 
to a monsoonal climate beginning at 600 years after waste emplacement, and to a glacial climate 
at 2,000 years. To represent uncertainty in present and future infiltration values, both the 
lower and upper infiltration distributions from the USGS grid files are used in this model. 
Temperature, Total Pressure, and Air Mass-Fraction Boundary Conditions 
For the TH models described here, the model domain extends from the ground surface to the 
water table, and temperature and total pressure conditions are specified at each boundary. 
Values for the L4C1 and L4C4 locations are interpolated from the UZ Model results (CRWMS 
M&O 2000t). The air mass-fraction at the ground surface is calculated from the temperature and 
total pressure such that the relative humidity is 100 percent. This prevents water from diffusing 
upward through the ground surface in the NUFT simulations, a mode of mass transfer that is 
already taken into account in the prescribed infiltration boundary condition. At the water table, 
the air mass-fraction is assigned a small value (comparable to the solubility of air-constituent 
gases in water). 
Thermal Properties for Natural Barrier Materials 
The thermal properties used by NUFT are: dry thermal conductivity (zero liquid saturation), wet 
thermal conductivity (at 100 percent water saturation), specific heat, and grain density for each 
hydrostratigraphic unit. The values used for these properties are idendified in CRWMS M&O 
(2000t). For partially saturated conditions, the NUFT code linearly interpolates between dry and 
wet values, based on liquid saturation. 
Thermal and Hydrologic Properties for EBS Materials 
The EBS backfill and invert materials are Overton Sand (quartz sand) and crushed tuff, 
respectively. These materials are unfractured but are represented in the DKM model by splitting 
the total property value between the fracture and matrix continua, with strong interaction 
between the continua (CRWMS M&O 2000t). The AFC is not used for EBS material properties 
because these are better represented as porous media. There are no open cavities; therefore, 
there is no radiative heat transfer in the NUFT models described in this report. 
Component Properties 
Vapor-pressure lowering is active for these calculations. This feature of the NUFT code 
simulates the interaction between capillary water potential and the vapor pressure governing 
water mass-transfer between the liquid and gas phases. The vapor pressure is lowered by an 
amount determined from the capillary pressure, which increases the boiling temperature for 
water in partially saturated capillary media (CRWMS M&O 2000t).

 3-35 
Zero values are assumed for dispersion coefficients, thus the hydrodynamic dispersion of water 
moving as liquid or vapor is assumed to be negligible. This is justified because thermal and 
hydrologic changes occur slowly (over many years) in these simulations. 
Environmental Conditions That Promote Corrosion of Drip Shield and Waste Package 
Environmental conditions that accelerate corrosion rates and the accumulation of damage from 
general, localized, and stress-cracking mechanisms, include: 
 Duration of exposure to adverse conditions 
 Temperature at which adverse chemical conditions occur 
 Precipitation of salts that provide ions needed for some corrosion processes and that 
promote aqueous conditions at higher temperatures by osmolality 
 Alkaline (high-pH) conditions in the bulk chemical environment, which are associated 
with low CO2 fugacity caused by evaporation that decreases the air mass-fraction. 
It is anticipated that ongoing testing and modeling will verify these aspects of corrosion 
performance. 
Thermal-Hydrologic Model Uncertainties 
The Thermal-Hydrology Model presented in this section has associated uncertainties which 
derive from consideration of alternative models and other views (discussed in Section 3.1.2.1.8), 
and from model validation issues (Section 3.1.2.1.4). In addition, the discussion of model 
uncertainties related to the TH modeling approach using NUFT, in Section 3.1.4.1, also apply. 
3.1.2.1.3 Modeling Approach and Numerical Simulation 
Separate but linked NUFT runs are used for initialization and to represent preclosure and 
postclosure conditions. The initialization model calculates ambient saturation and temperature 
conditions without a drift opening. The preclosure model uses the initialization results as initial 
data, adds the drift opening without backfill, and adds preclosure heating. The postclosure 
model uses the final preclosure saturation and temperature fields as initial data, adds backfill, and 
increases heating to account for the cessation of ventilation. A total of 12 NUFT runs are needed 
for the four TH cases (CRWMS M&O 2000t). 
Specific TH performance measures calculated for the continuum representing the rock matrix are 
temperature, saturation, relative humidity, and the rate of evaporation. For the continuum 
representing the fracture network, these same measures and the air mass-fraction are calculated. 
In addition, the gas-phase total mass flux (air plus water vapor) in the matrix and fractures 
combined is reported, as a vector field.

 3-36 
Postprocessing NUFT Output 
Postprocessing is used to prepare and simplify NUFT output for further analysis. Zone 
processing is used to describe the spatial subdomains and the temporal intervals for chemical 
reaction cell modeling. Vertical profiles of key variables are used for modeling gas fluxes. The 
conservative solute analysis is used to support selection of a reference TH model for chemical 
modeling. 
Zone Fluxes 
To represent TH changes taking place in key parts of the NUFT model domain, six zones are 
defined a priori for the NUFT models (Figure 3-15 and Figure 3-16). These zones are as 
follows:
 Zone 0: The far-field host rock. Within Zone 0, the temperature rises after closure 
and then falls as the WP heat output decays with time, but there is little evaporation or 
condensation, hence no significant change from ambient water chemistry. Zone 0 
above the emplacement drift is the source of water entering Zone 1, and provides the 
boundary condition for chemical composition. 
 Zone 1: Host rock above the drift  Extends outward from the drift wall 
approximately 10 m, or beyond the extent of dryout. Boiling and evaporative 
concentration can occur in Zone 1, and vapor generated in the drift is likely to 
condense. Zone 1 is above the drift midplane (the horizontal plane passing through the 
drift springlines). 
 Zone 2: Host rock at the drift wall  Includes the grid blocks that represent host rock 
at the drift wall, along the upper half of the drift opening above the spring line. 
 Zone 3: Backfill above the spring line 
 Zone 4: Backfill at the drip shield surface  Includes the grid blocks that represent 
backfill at the drip-shield surface, along the upper part of the drip shield above the 
midplane 
 Zone 5: Lower backfill  Includes the grid blocks that represent backfill outside the 
DS, below the mid-plane, and above the invert 
 Zone 6: Invert below the backfill, DS, and WP 
Using NUFT output files, a software routine collects the output for each zone and produces a 
summary table of gas and liquid fluxes between zones, combining fracture and matrix fluxes as a 
function of time. Figure 3-17 is an example plot showing the liquid fluxes between zones for the 
L4C4 location and upper infiltration distribution. The zone fluxes are transferred to a 
spreadsheet routine for further analysis prior to use in chemical modeling.

 3-37 
Zone-Averaged Temperature, Saturation, and Air Mass-Fraction 
Zone-averaged scalar variables describe the state of each zone as a function of time. To compute 
zone averages, the value for each grid block is weighted by its volume (CRWMS M&O 2000t). 
The zone-averaging procedure is implemented in a software routine that produces a table of 
zone-averaged values for each time step listed previously. For each NUFT model, the 
zone-averaged output for the matrix and the fractures are transferred to a spreadsheet routine for 
further analysis. 
Vertical Mass-Flux Profiles 
Another software routine is used to sort NUFT output and produce a table containing the vertical 
component of the gas-phase total mass flux (air and water components) in the fracture continuum 
along a vertical profile passing through the drift centerline. A plot of the vertical component of 
the gas-phase total mass flux for the L4C4 location, upper infiltration, and simulation time of 
1,000 years is shown in Figure 3-18. For each NUFT model the vertical mass-flux profile is 
transferred to a spreadsheet routine for further analysis. 
3.1.2.1.4 Thermal-Hydrology Model Validation 
Thermal-hydrology calculations for the EBS Physical and Chemical Environment Model are 
made using the same numerical simulator, and the same model concepts as the models described 
in Sections 3.1.1 and 3.1.4. The results include evolution of key performance measures (e.g., 
temperature, saturation, fluxes, air mass-fraction) through the 10,000-yr performance period. 
Comparison of TH models developed for this report, with other published models is discussed in 
Section 3.1 (Table 3-B and Figures 3-B and 3-C) and Section 5.3.4. In general the calculated TH 
results are found to be closely comparable, particularly comparing the Physical and Chemical 
Environment TH calculations, with 2-D, drift-scale TH simulations for the same locations, from 
the Multiscale TH Model. The 2-D, drift-scale modeling approach used here is the same as that 
used for the Multiscale TH Model (LDTH models), except for representation of the EBS. In the 
Multiscale LDTH models the waste package and drip shield are represented by discrete elements, 
instead of the monolithic body used here. The difference is appropriate because the Physical and 
Chemical Environment Model focuses on conditions outside the intact drip shields, while the 
Multiscale TH Model provides waste package and drip shield temperature and humidity histories 
directly to TSPA. 
In addition, for the Multiscale LDTH models there is an air-gap above the backfill, whereas in 
these models the backfill completely fills the drift opening outside the drip shield. This 
difference is appropriate because the additional backfill promotes liquid water flow into the 
drifts. The Chemical Reference Model represents a situation in which seepage is not diverted 
around the drift openings, so evaporation in the drifts is maximized. Inspection of Figures 3-B 
and 3-C shows that despite these differences, very similar histories for temperature and relative 
humidity are obtained. 
Validity of model results is established by comparison of similar models, using the same 
properties, boundary conditions, and other inputs, to field-scale test results (Large-Block Test,

 3-38 
Drift-Scale Test; see Sections 3.1.4.4.1 and 3.1.4.4.2). Such comparisons for thermal-hydrology 
models are discussed in Section 3.1.4. 
Validation also requires appropriate selection of model inputs: 
 Hydrologic properties for natural and engineered materials 
 Thermal properties for natural and engineered materials 
 Thermal output of emplaced waste 
 Temperature, total pressure, and infiltration flux boundary conditions 
 Numerical gridding, convergence criteria, and other model settings 
which are also discussed in Section 3.1.4. The 1-D drift-scale hydrologic properties used for 
these models are taken directly from the UZ Model (CRWMS M&O 2000o). Thermal properties 
are based on laboratory-measured data. It is noted that values for wet thermal conductivity are 
currently under review. Thermal output of the emplaced waste is based on best-available 
information for the characteristics of spent fuel and defense high-level waste. 
The temperature and pressure boundary conditions used for these models are based on averages 
for the ground surface and water table, constrained by measured data. Values for average 
infiltration flux are also taken directly from the UZ Model, for representative center and edge 
locations. Alternative infiltration flux boundary conditions are selected from both the lower 
and upper infiltration distributions developed for the UZ Model, to represent the range of 
uncertainty. These alternative values are used comparatively in several cases discussed in this 
section. 
From this discussion (and Section 3.1.4.4) it is concluded that the TH models developed for the 
Physical and Chemical Environment Model are valid for their intended use in FEP screening, 
and support of the design basis (Table 3-A). The TH models presented in this section are based 
on appropriate inputs, including properties, boundary conditions, and thermal output. They are 
also based on the 2-D TH models developed for the Multiscale TH Model, which have been 
shown to represent field thermal test results (Section 3.1.4.4). 
3.1.2.1.5 Model Results Representing a Range of Potential Repository Conditions 
Plots of temperature, saturation, and gas-phase air mass-fraction for Zone 4 at the DS surface are 
shown in Figure 3-19 through Figure 3-21. These figures were generated in the spreadsheet 
routines used to analysis zone-averaged data (CRWMS M&O 2000t). The plots compare results 
from the four NUFT cases, which are summarized in the following sections. 
Temperature 
 Cooldown occurs sooner at the potential repository edge. 
 Low-flux conditions produce greater peak temperatures and slower cooldown because 
less liquid water is available to evaporate and transfer heat. 
Saturation

 3-39 
 The spatial extent of dryout (zero or low liquid saturation) is greater for low-flux 
conditions. 
 Water returns to the EBS environment sooner for high-flux conditions, and near the 
potential repository edge. 
 After cooldown, the liquid water saturation in the upper part of the backfill is 
approximately 10 percent to 20 percent, depending on the infiltration magnitude. 
Air Mass-Fraction 
The air mass-fraction represents the displacement of air by water vapor from evaporation. At 
high relative humidity, when the temperature is near the boiling point, the air mass-fraction 
approaches zero. This is importance because the partial pressures of CO2 and O2 may also 
approach zero. Evaluation of the calculated air mass-fraction has shown: 
 Matrix air mass-fraction is smaller, and relative humidity is greater, than in the 
fractures. This is due to vapor pressure lowering, which retains water in the matrix. 
 The minimum air mass-fraction is approximately 103 when thermal output and 
infiltration (seepage) are maximized, i.e. for the L4C4 location and upper infiltration. 
Evaporation Rate 
Evaporation rate is calculated by NUFT using a mass balance on liquid and gas-phase water 
fluxes, for the entire model domain, and for both the matrix and the fractures. A plot of the 
evaporation rate in the fracture continuum at the L4C4 location with upper infiltration, at a 
simulation time of 1000 years, is shown in Figure 3-22. The total evaporation rate (all zones, 
fractures plus matrix) versus time is plotted in Figure 3-23 for all four NUFT cases, and 
compared with the potential repository thermal output vs. time (CRWMS M&O 2000t). 
Examination of evaporation rate plots shows the following: 
 The rate of evaporation in the fracture continuum is greater than that in the matrix at the 
same locations, during the thermal period, because of vapor pressure lowering. 
 Evaporation tends to be localized to a narrow zone above the drift, where condensate 
water and ambient percolation meet the dryout zone. The evaporation zone recedes 
toward the DS surface as the heat source strength decays with time. 
 For the upper infiltration distribution, there is more sustained evaporation that occurs 
sooner for the L4C1 location (repository edge) than for the L4C4 location (center). 
 For all cases, the rate of evaporation for all zones is much smaller than the total thermal 
output of the WPs for the first few hundred years. At later time (after 4,000 years) the 
proportion of thermal output that causes evaporation decreases for all cases.

 3-40 
Gas-Phase Mass Flux 
Calculations show that the vertical component of the gas-phase total mass flux (air + water 
vapor), along a vertical profile passing through the drift center, is generally upward during the 
thermal period (CRWMS M&O 2000t). This is caused by a combination of buoyant convection 
and the upward egress of water vapor produced in the host rock. Excess pressure from 
evaporation, causes gas to be expelled at the ground surface. The maximum value of upward 
vertical flux does not necessarily occur at the drift wall but may occur in the host rock. 
A horizontal profile of the vertical component of the gas-phase total mass flux for the L4C4 
location and upper infiltration is shown in Figure 3-24 for a simulation time of 1,000 years. 
This figure shows that there is buoyant convection in the host rock because of downward flux 
near the center of the pillar, but that gas-phase circulation is dominated by egress of water vapor 
from evaporation. The maximum upward mass flux occurs directly above the drift. 
3.1.2.1.6 Representing Thermal-Hydrologic Evolution by Uniform Time Intervals 
To support chemical-reaction cell modeling, the potential repository thermal evolution is 
simplified to a series of intervals during which zone temperatures and fluxes are held constant, as 
shown in Table 3-2. 
Table 3-2. Intervals During Which Zone Temperatures and Fluxes Are Held Constant 
Time Interval (yr) 
Nominal Time (yr) 
From To 
100 50 300 
500 300 700 
1000 700 1,500 
2000 1500 2,500 
5000 2500 10,000 
Source: CRWMS M&O 2000t 
The assigned time intervals correspond approximately to the assumed transitions in climate at 
600 and 2000 years, so the effects of those transitions are incorporated at 700 and 2500 years. 
The stepwise representation of temperatures, and fluxes between zones, plots reasonably close to 
the NUFT output (e.g. zone-to-zone fluxes represented in Figure 3-17). 
Preclosure (=50 years) TH conditions in the EBS are not evaluated because they will be 
dominated by ventilation. Whereas the heat-removal effects of ventilation are explicitly 
simulated, the drying effects on the host rock are not. (The effects of preclosure processes on the 
composition of mobile waters and the accumulation of precipitates in the host-rock fractures and 
matrix are assumed to be negligible.)

 3-41 
3.1.2.1.7 Selection of a Reference Model for Bounding Chemical Calculations 
Conservative Solute Analysis Using Zone-to-Zone Fluxes 
The zone-averaged saturations and fluxes between zones are analyzed to gain insight into 
requirements for chemical modeling. The four calculated TH cases are analyzed and compared, 
and one is chosen for additional chemical system modeling (CRWMS M&O 2000t). 
An ideal conservative solute tracer (a substance that can be present in any concentration) is 
assumed to be present at a constant concentration (C0 = 1) in water entering the host rock 
(Zone 1) from above (Zone 0). The solute is then transported between zones at rates that are 
determined by the solute concentration in each zone and by the liquid flow rates between zones. 
The approach is used with the zone-averaged, stepwise constant descriptions of liquid mass and 
fluxes between zones. The result describes the potential accumulation of a conservative solute 
with unlimited solubility (an approximation for soluble salts such as NaCl) in a system described 
by stepwise variation of liquid and vapor fluxes. 
Derivation of Conservative Solute Analysis 
In the conservative solute analysis for a given zone, when the influent concentration is greater 
than the outfluent concentrations, the concentration tends to increase; when the outfluent 
concentration is greater than the influent concentrations, the concentration tends to decrease. In 
each cell, the concentration tends to be increased by evaporation and decreased by condensation. 
For a single zone, the rate of change of the concentration is
. - . = 
. 
. 
j 
ik 
i
i 
j 
j ji 
i 
i q 
V
C 
C q 
V
1 
t 
C 
(Eq. 3-3) 
where
Ci = concentration in the ith zone (normalized mass/kg solvent) 
qji = steady inflow rate from the jth zone into the ith zone (kg/sec) 
Cj = concentration in the jth zone (normalized mass/kg solvent) 
Vi = volume of the ith zone (volume of solvent; can be expressed as mass assuming 
1 kg/liter) 
qik = steady outflow rate from the ith zone to the kth zone (kg/sec) 
This formulation represents the change in concentration during a time interval during which the 
hydrologic conditions are constant but the solute concentration can vary. The fluxes (qji, qik) and 
volumes (Vi) are provided from NUFT calculations. The volume, or alternatively the mass of 
solvent present in each cell, is invariant during each time interval. The mass of solute in each 
cell is determined from the product of the volume and the concentration. Expanding Equation 
3-3 to represent all possible connections between zones, a system of simultaneous differential 
equations is developed and solved for each time interval (CRWMS M&O 2000t).

 3-42 
Results from Conservative Solute Analysis 
The procedure described in the foregoing subsection is repeated for each of the four TH cases. 
The results are plotted as normalized solute mass vs. time for each zone (Figure 3-25 through 
3-28). Solute mass is normalized to that present in 1 kg of solvent at the reference concentration 
(C0 = 1). 
The maxima on these plots represent conditions for which there is liquid inflow to a zone, but no 
liquid outflow, so all the transported solute is accumulated. When liquid through-flow 
conditions return to such a zone, the solute rapidly disperses (infinite solubility of an ideal 
conservative tracer). Accordingly, these calculations underestimate the time for which the 
accumulated solute remains in each zone. For solutes with finite solubility and prograde 
solubility variation with temperature (e.g., silica), an accumulation of solute could actually 
remain for hundreds or thousands of years. The minima on these plots represent conditions for 
which there is either condensation, or no inflow. The conservative solute approach is intended 
only to serve as the basis for selecting a TH case for the Chemical Reference Model. The 
conservative solute analysis is a method for interpreting the TH models, and quantitative results 
are not carried forward. 
The results of the conservative solute calculations are summarized as follows: 
 When zones have significant transitory or continuous inflow, but no liquid outflow, a 
substantial mass of soluble salts could accumulate (the zones need not be dry for this to 
occur). 
 Solute mass on the order of 105 times that present in 1 kg of the reference water 
composition may accumulate near the DS surface (Zone 4; see Figure 3-27). As a 
scoping calculation, if chloride is present in the reference water at 7 mg/l (J-13 water), 
these results indicate that the accumulated chloride mass could exceed 1 kg per meter 
of drift. 
 Solute mass on the order of 108 times that present in 1 kg of the reference water 
composition is calculated for the invert (Zone 5; Figure 3-26). This is clearly 
impossible, and is an artifact of the spatial and temporal discretization of the model. 
Also, the use of a unit concentration may not be realistic (evaporating waters in this 
zone could be more dilute). The results from the Conservative Solute Analysis are 
therefore somewhat qualitative, and indicate where and when precipitation is most 
likely in the EBS. 
 For certain conditions, there is potential for solute accumulation in the backfill to 
migrate to the invert (Zones 5 and 6). This may occur because, for an interval of time, 
salts in the backfill are redissolving, while the invert is the hottest part of the drift that 
is accessible to liquid flow. 
 There is the potential for solute to accumulate in the backfill and at the DS surface 
(Zones 3 and 4) before these zones have cooled through boiling. Thus, there is the 
potential for brines to form at temperatures greater than 96C.

 3-43 
 For locations at the edge of the potential repository (L4C1) the potential accumulation 
of soluble salts is less than at center locations (L4C4) because there is less heat 
available for evaporation. 
 Comparing the upper and lower infiltration distributions (e.g., Figure 3-25 and 
Figure 3-26) less solute accumulates at the DS surface (Zone 4) for lower infiltration 
conditions because there is less evaporation there, even though temperatures may be 
greater. 
 For certain conditions, there is potential for solute accumulation in the backfill, to 
migrate to the invert (Zones 5 and 6). This may occur because, for an interval of time, 
salts in the backfill are redissolving, while the invert is the hottest part of the drift that 
is accessible to liquid flow. 
The principal factors that limit solute accumulation on the DS are rapid cooling (e.g., to less than 
96C) and less seepage. These factors are not correlated because greater flux causes faster 
cooling, but also increases drift seepage. 
It should be noted that NUFT, as used for this report, does not modify liquid boiling 
temperatures to account for solute concentration. Thus, there is the potential to underpredict 
solution migration toward heat sources, and solute accumulation. However, the effect is 
probably small because the fluids in question are evaporated by at least 100- to 1000-fold; thus, 
their volume is small. 
Selection of a Thermal-Hydrologic Model for Chemical Modeling 
The L4C4 location with the upper infiltration distribution is selected for the Chemical 
Reference Model, to represent the in-drift environment. This is a repository-center location 
(Figure 3-70), which tends to maximize the peak temperature and extent of dryout, while the 
upper infiltration tends to maximize the amount of evaporation that occurs in the drift. 
Selection of this model is based on assessment of the TH calculation results with respect to the 
environmental conditions that promote corrosion (identified previously): duration of adverse 
conditions, potential for accumulation of precipitated salts, and the potential for alkaline (highpH) 
conditions. (Alkaline conditions arise from evaporation, with bicarbonate-type waters as 
discussed in Section 3.1.2.5.2.1.) 
From discussion of the TH calculations described in this section, the following criteria are found 
to represent the environmental conditions that promote corrosion: 
 Potential for accumulation of salts in Zone 4 (Figure 3-25 through Figure 3-28) 
 Duration for which adverse conditions occur at elevated temperature in Zone 4 
(Figure 3-19 and Figure 3-21) 
 Proportion of thermal output that produces evaporation, especially during sustained 
periods when aqueous conditions occur in Zone 4 (Figure 3-23)

 3-44 
The L4C4 location with upper infiltration is selected based on these criteria. It is noted that 
the computed zone solute concentrations are subject to artifacts of discretization, and that 
whereas Zone 5 had highest potential concentration, Zone 4 conditions were used to select the 
TH case for the reference model. This is because failure of the drip shield at Zone 4 could cause 
water to contact the waste package, whereas failure of the drip shield at Zone 5 would not. 
For chemical modeling, the zones are further consolidated to expedite chemical calculations: 
 Zone 1-2 represents the host rock above the drift 
 Zone 3-4 represents backfill between the DS and the drift crown 
 Zone 5-6 represents backfill and invert materials in the lower part of the drift 
The calculation details are described in the source documentation (CRWMS M&O 2000t). 
These results are used as input to the Chemical Reference Model (Section 3.1.2.7). 
3.1.2.2 Gas Flux and Fugacity 
This submodel supports the Chemical Reference Model (Section 3.1.2.7). The overall purpose 
of this submodel is to describe the carbon dioxide (CO2) and oxygen (O2) composition of the gas 
phase that will be present in the emplacement drifts, and the adjacent host rock. The intended 
use is FEP screening, and support of the design basis (Table 3-A). 
In formulating the Gas Flux and Fugacity Model, assumptions and approximations are made 
which tend to produce lower estimates of the CO2 available for chemical reactions in the drifts, 
during the thermal period. This is consistent with a conservative approach, whereby predicted 
chemical conditions are more alkaline, and therefore potentially more adverse to corrosion of the 
drip shield and waste package. The corrosion rate for carbon steel increases with pH, as well as 
temperature, and chloride concentration (Section 3.1.2.3.4). Current corrosion models for drip 
shield and waste package materials (CRWMS M&O 2000n, Section 3.1.5) show that corrosion 
rates are very small, and are insensitive to pH, temperature, or any other variables used in 
laboratory corrosion testing. However, tests to evaluate whether these materials are senstive to 
strongly alkaline pH are under development or still ongoing. 
For TSPA, the CO2 and O2 fugacities (i.e., chemical activites, which can be described by the 
partial pressures in the gas phase), are calculated using the Drift-Scale Coupled Processes (DST 
and THC Seepage) Models (CRWMS M&O 2000x). These fugacities are developed in 
simulations of coupled THC conditions in the host rock, and are used as boundary conditions on 
the reaction-cell models used to represent in-drift conditions for TSPA (Section 3.2.1.1). 
The model developed in this section is approximate, and is used to represent gas-phase 
composition for the Chemical Reference Model. The model is used to investigate the 
precipitates formed when waters are completely evaporated, coupling of processes such as those 
that will consume CO2, and the composition of the gas phase. A more complete representation 
of chemical processes related to CO2 in the unsaturated zone is provided in the Unsaturated Zone 
Flow and Transport Process Model Report (CRWMS M&O 2000o, Sections 3.8 and 3.10). It is 
noted that modeling of reactions and transport processes involving CO2, and in particular, 
consistent modeling of ambient hydrologic and chemical observations involving CO2, is a

 3-45 
difficult problem because of carbonate chemistry (CRWMS M&O 2000x, Sections 6.2.7.2 and 
6.3.5.2). 
Alternative approaches are available, including the air mass-fraction method, and the fully 
coupled THC reactive transport simulations used for TSPA (CRWMS M&O 2000x). Some 
results from these approaches are compared with the Gas Flux and Fugacity Model, in Section 
3.1.2.2.6. All the approaches yield comparable results with respect to the evolution of CO2 
fugacity at the drift wall during the thermal period, probably because the air mass-fraction has 
the greatest impact on gas fugacity. Besides the very different approaches to modeling chemical 
interactions, a major difference in the underlying assumptions for these models is that the 
reference composition for mobile water in fractures of the UZ, is assumed to be J-13 water in this 
report, but a composition resembling tuff matrix porewater is used for the THC reactive transport 
simulations. The approach developed in this section permits estimation of the effect of sources 
or sinks on CO2 fugacity, but the THC reactive transport approach (CRWMS M&O 2000x) 
probably provides a more realistic description of gas-phase and aqueous-phase chemical 
processes in the host rock. 
Introduction to the Gas Flux and Fugacity Model  This section develops an analytical model 
for fugacities of CO2 and O2 in the potential repository during the thermal period. The model 
provides conservative estimates of gas fugacities, using input from TH calculations (Section 
3.1.2.1). First, an analytical solution is developed to describe the distribution of 14C in the 
unsaturated zone, and is calibrated using 14C abundance measurements from boreholes at Yucca 
Mountain. Next, a mass-transfer function is developed to describe gas movement during the 
thermal period. This results in a simple inverse relationship between fugacity and flux, which 
can be used to calculate the respective increase or decrease in fugacity that would be associated 
with a source or sink of CO2 or O2 in the EBS. 
In the Chemical Reference Model (Section 3.1.2.7) the analytical model is used to constrain CO2 
and O2 fugacities. The results are conservative in the sense that low CO2 concentration 
contributes to higher pH, which may promote degradation of engineered materials such as steel 
or titanium. The approach allows comparison of the calculated rate of CO2 consumption in the 
EBS, with the flux-fugacity relationship from the model, to evaluate whether in-drift processes 
are likely to strongly perturb the CO2 fugacity in the host rock and EBS. A similar comparison is 
made for consumption of O2 by corrosion of structural steel in the EBS. 
The model development and discussion in this section includes the following elements: 
 Identify the processes that control the flux and fugacity for CO2 and O2. 
 Estimate the magnitude of gas-phase mass transfer, applicable to both CO2 and O2 
gases, based on mass balance of 14CO2 for ambient conditions. Develop a masstransfer 
function that can represent gases other than CO2, and modify the function to 
represent thermal effects. 
 Develop reasonable lower-bound estimates for CO2 and O2 fugacities in the gas phase 
and the relationships between flux and fugacity for the thermal period extending to 
10,000 years.

 3-46 
Two alternatives to the analytical mass-transfer model are discussed: (1) the air mass-fraction 
approach and (2) reactive transport simulation. Each is shown to produce CO2 fugacity values 
for the thermal period, which are comparable to results from the analytical mass-transfer model. 
3.1.2.2.1 Gas Flux and Fugacity Conceptual Model Development 
Carbon dioxide can strongly affect pH for solutions present in the emplacement drifts during the 
thermal and post-thermal periods. The gas-phase CO2 concentration can range over several 
orders of magnitude, and the associated solution compositions can range from sub-alkaline to 
pH 11 or greater. Within this range, there are important differences in mineral solubility 
conditions and corrosion rates for engineered materials. 
Conceptual Discussion of Transport Processes for Gas Species 
Carbon dioxide is present in the host rock under ambient conditions in three forms: CO2 gas, 
dissolved inorganic carbon species in fracture and matrix waters, and mineral carbonate solids. 
Gaseous and dissolved inorganic carbon are readily available for chemical reactions. Carbonate 
solids may dissolve and contribute to the available labile carbon, and they are common 
secondary minerals at Yucca Mountain. 
Gas-phase CO2 at Yucca Mountain can be transported by three processes: 
 Molecular diffusion  Fickian diffusion along a concentration gradient. 
 Advective-dispersive transport  The gas column in the UZ undergoes volume 
reduction and expansion in response to changes in barometric pressure at the ground 
surface. Gas molecules move back and forth and disperse in a manner that is 
mathematically analogous to diffusion (CRWMS M&O 2000t). 
 Convective circulation  Gas-phase convection in the UZ could be driven by seasonal 
changes in gas density at the ground surface, and associated effects from variable 
topography. Convective circulation has been shown to readily displace air in the Tiva 
Canyon caprock, but the effect apparently does not extend deeper (CRWMS 
M&O 2000t). Ambient, large-scale convective circulation could contribute to mass 
transport of CO2 and other gases, but is neglected in this bounding model. 
Liquid-phase, dissolved inorganic carbon at Yucca Mountain can be transported by 
two processes: 
 Advective transport  Percolation occurs in the fractures and the rock matrix. Flow 
velocity is small in the matrix, such that tens of thousands of years could be needed for 
penetration of porewater to the potential repository depth. Borehole 14C activity data 
show that CO2 in the UZ has apparent age of at most a few thousand years, so a faster 
transport mechanism is apparently available. Accordingly, aqueous transport of 
dissolved inorganic carbon, if it occurs, must be primarily in fractures. 
 Molecular diffusion  Aqueous diffusion is approximately four orders of magnitude 
slower in liquids than in gases, and is restricted by path tortuosity. For the Gas Flux

 3-47 
and Fugacity Model, diffusive transport is limited to isotopic equilibration of matrix 
porewater with nearby fractures. This is justified because 14C activity for gas-phase 
and matrix porewater samples from the same or nearby locations are isotopically 
similar (CRWMS M&O 2000t). 
From the above discussion, the two most important processes for ambient transport of CO2 to the 
host rock are gas-phase diffusion-dispersion and liquid-phase advective transport. Episodic 
recharge occurs, so transport of CO2 through the host rock is evidently a nonequilibrium process 
in which rapid recharge in fractures penetrates the host rock, with limited isotopic interaction and 
therefore limited mass exchange. This is verified by inspection of measured 14C activity versus 
depth for borehole SD-12 (Figure 3-29). Radiocarbon exists as 14CO2, for which transport 
behavior is similar to CO2 (interpreted differences in relative abundance of 14C must be small 
compared to isotopic fractionation). The distribution of 14CO2 can be interpreted as that which 
would be observed for average CO2, with a sink analogous to radioactive decay. The increase of 
14C activity near the bottom of the Topopah Spring welded tuff occurs at a transition from mostly 
fracture flow in the host rock, to mostly matrix flow in the underlying vitrophyre and nonwelded 
Calico Hills unit. 
The Gas Flux and Fugacity Model distinguishes the 14CO2 flux transported in rapid aqueous 
recharge, from the 14CO2 flux required to replenish radioactive decay in the host rock. The 
14CO2 flux to the host rock may be due entirely to gas-phase processes. This approach is used to 
develop lower bounds on gas-phase transport. It is bounding because it maximizes the 
contribution of recharge waters for replacing 14C decay deep in the UZ, thus minimizing the need 
for gas-phase transport to penetrate there, and thus minimizing the efficacy of gas-phase 
transport through the host rock. 
Interpretation of 14C data from the site shows that barometrically driven advective processes 
increase the transport of CO2 to the UZ. This is represented in the Gas Flux and Fugacity Model 
as a process whereby barometric pressure fluctuation at the surface causes 1-D oscillatory gas 
movement in UZ, resulting in diffusive-dispersive gas-phase mass transport. 
Gas Transport Processes During the Thermal Period 
Processes that can affect gas-phase composition in the EBS during the thermal period are 
summarized in Figure 3-30. Nitrogen gas (N2) is included in the discussion because it is a 
component in the Microbial Communities Model (Section 3.1.2.4) and O2 is included because it 
is a reactant in the EBS (Section 3.1.2.7). The source of these gases is the atmosphere, or soil 
gas where a soil zone covers the surface. Soil zone processes cause the CO2 concentration to 
exceed that of the atmosphere. In response to heating, CO2 is produced by degassing of pore 
water, and by reaction of calcite with other minerals in the presence of water. During heating, 
large volumes of water vapor are also produced which tend to dilute the concentrations of CO2, 
O2, and N2 gases. Where this water condenses, the gases tend to redissolve in the condensate. 
Convective circulation in the gas phase can occur because of buoyancy caused by density 
changes from thermal expansion and increased humidity. Through the combined effects of 
flow-field geometry, flow resistance from lower-permeability units above and below the host 
rock, and displacement of air by water vapor, convective activity will be maximal at the potential

 3-48 
repository edges and may be nil near the potential repository center. Large-scale convective 
circulation is neglected as a CO2 transport process for this bounding model. The conceptual 
model for ambient processes, and the associated 1-D model, are applied to the thermal period 
with modification to account for thermally driven transport processes. 
Conceptual Discussion of O2 Transport 
Oxygen is more abundant than CO2 in air. Measured values for gas-phase O2 concentration in the 
UZ are in the range 20 percent to 22 percent and are generally indistinguishable from 
atmospheric values (CRWMS M&O 2000t, Section 6.2.2.1). Oxygen is much less soluble than 
CO2 in water, so the gas phase is the most important reservoir and transport pathway for O2. 
Both gases exhibit decreased (retrograde) solubility with increasing temperature, but this effect is 
insignificant for O2 transport. 
Tuff mineralogy is mostly oxidized, and minerals containing reduced species tend to be armored 
by oxides and are not accessible. Thus, oxidation of the tuff is slow, and the ambient O2 
concentration in the gas phase is closely similar to atmospheric composition. Oxygen can react 
with materials such as steel in the potential repository environment. 
Alternative Models: Air Mass-Fraction Approach 
Previous mountain-scale TH modeling showed that gas-phase convective circulation during the 
thermal period may be limited (CRWMS M&O 1998d, Chapter 4). Calculation of the air 
mass-fraction at the potential repository horizon, which decreases because of the displacement of 
air by water vapor, showed that the CO2 fugacity (as a proportion of the air mass-fraction) could 
decrease by many orders of magnitude from prerepository levels (Figure 3-31). However, 
temporal integration of the gas-phase convective circulation showed that the flow of gas moving 
through the host rock could deliver significant amounts of CO2 and O2 gases to the emplacement 
drifts over time. 
Two example figures from the Total System Performance AssessmentViability Assessment 
(TSPA-VA) Technical Basis Document are reproduced here as Figure 3-31 and Figure 3-32, 
(CRWMS M&O 1998d, Figure 4-16 and Figure 4-18). These plots summarize results from 
simulation using a 2-D, mountain-scale NUFT model, to represent gas-phase circulation for the 
VA potential repository design. The conceptual basis for these plots is discussed further in the 
In-Drift Gas Flux and Composition (CRWMS M&O 2000e). They are presented here for 
comparison purposes and are not used directly in the Gas Flux and Fugacity Model. It is noted 
that the Viability Assessment (VA) design was intended to produce higher peak temperatures 
and a longer-lasting thermal period than is the current conceptual design. 
Several interesting points emerge from the comparison. For the potential repository center 
location, the air mass-fraction decreased by as many as nine orders of magnitude during the time 
period from approximately 300 to 1,000 years. At the same time, the flux of air through the 
potential repository horizon decreased to effectively zero. In contrast, at the potential repository 
edge location, the air mass-fraction was much greater, and the air mass flux was always greater 
than zero.

 3-49 
With the current potential repository design concept, the thermal loading is less, and the drift 
spacing is greater than for the VA design. The 2-D drift-scale TH models described in the 
previous section predict more mixing of the gas phase and a small downward circulation in the 
pillar (Section 3.1.2). The calculated air mass-fraction at the drip shield, for the potential 
repository center (L4C4 location; Figure 3-21) is similar to, or greater than the air mass-fraction 
calculated for the VA design (Figure 3-31). The 2-D drift-scale model does not include 
mountain-scale circulation, so the air mass-fraction calculations in Section 3.1.2.1 are probably 
lower bounds. 
The mass-transfer approach used in this report is a departure from the air mass-fraction approach 
based on TH modeling, primarily for the following reasons: 
 Mountain-scale TH processes are not taken into account in the mass-transfer approach. 
The advantage of not including large-scale TH processes is that the results do not 
depend on large-scale hydrologic properties of the mountain, which vary and for which 
data are sparse. 
 Natural advective-dispersive mass-transfer processes that operate in the UZ were not 
included in the air mass-fraction approach. An advantage of including data on the 
ambient distribution of radiocarbon in the UZ is integration of models and their 
supporting data. 
For both the air mass-fraction and the mass-transfer approaches, there is a time period during 
which evaporation is active and the CO2 and O2 fugacities are small (e.g., 1 percent of ambient 
values). Therefore, with either approach there is the potential for the development of alkaline 
solution conditions in the drift, and the potential for changes in corrosion processes due to 
decreased O2 fugacity. 
Decreased O2 fugacity may have the effect of temporarily, for tens to hundreds of years, 
hindering the rate of oxidative corrosion of steel, and possibly other metals in the drifts. This is 
based on a mass balance argument: if O2 is being consumed, and limited transport of O2 to the 
drifts is depressing PO2, then it is limiting the rate of O2 consumption. Steel corrosion is the most 
important potential cause, because of its abundance and potential rate of oxidation. The available 
steel corrosion data are for fully oxic conditions. Actual reduction, e.g. of Fe(III) to Fe(II), would 
require very low PO2 that is unlikely to occur in the drifts. 
Alternative Models: Multicomponent Reactive Transport Simulation 
Coupled reactive transport simulations couple TH with transport of chemical components, mass 
balance of components, chemical speciation and heterogeneous reactions, and rate-dependent 
reactions. Modeling of this type for the potential repository host rock, including the 
emplacement drifts, is presented in the Drift-Scale Coupled Processes (DST and THC Seepage) 
Models (CRWMS M&O 2000x). Gas-phase composition is an appropriate basis for comparison 
of chemical models because the pH and mineral precipitation depend strongly on the CO2 
fugacity.

 3-50 
Host-rock water composition and CO2 fugacity values were calculated, for several different 
assumptions on the infiltration flux magnitude, in this series of drift-scale reactive transport 
simulations. Results for the upper infiltration distribution (CRWMS M&O 2000t) are shown in 
Figure 3-33. Two cases are discussed here: Case 1 includes representative clay and zeolite 
minerals in addition to silica and calcite, and Case 2 includes only silica and calcite. 
The CO2 fugacity at the drift wall as a function of time, calculated from reactive transport, the air 
mass-fraction approach, and the 1-D mass-transfer approach, is shown in Figure 3-33. The air 
mass-fraction and mass-transfer approaches are discussed in more detail in later sections of this 
report. The CO2 fugacity from reactive transport simulations is reported at the drift crown, 
which is the highest point on the drift wall directly above the DS. For all three modeling 
approaches considered, the values are generally within a factor of approximately 30 during the 
thermal period. At late time, the reactive transport simulations show increased CO2 fugacity as 
the air mass-fraction increases and as the gaseous CO2 liberated during heating returns to the 
drift environment. The other approaches effectively require that the CO2 released by heating, is 
dissipated before cooldown. 
The reactive transport simulations are subject to ionic strength limitations that also exist for other 
approaches to chemical modeling. The chemical activity models (e.g., B-dot model; (CRWMS 
M&O 2000t) can be used for ionic strength values up to approximately 1 molal. When 
evaporative concentration causes solution ionic strength to exceed this limit, approximations are 
used to represent chemical conditions. In the reactive transport simulations, chemical speciation 
and dissolution/precipitation reactions are suspended when the ionic strength limit is reached and 
until dilution by water returning during cooldown. The extreme values for CO2 fugacity occur 
during this period of approximation. 
An advantage of the reactive transport approach is the integration of chemical processes, with 
spatial and temporal resolution limited only by the model design. Disadvantages include 
computational effort, the representation of the host rock and simulation of engineered barriers 
using only a few chemical species and precipitates, and restricted flexibility in handling 
ionic-strength limitations. Simulations of this type will be incorporated in this model as 
applicable calculations become available. 
3.1.2.2.2 Input Data, Assumptions, and Uncertainties 
CO2 and 14C Data from SD-12 and Other Surface-Based Boreholes 
Total gas-phase CO2 concentration data from several surface-based boreholes are used to support 
the average value of 1000 ppm for the concentration of CO2 in the UZ gas phase, used in this 
report. This is an average value consistent with surface-based borehole data (CRWMS M&O 
2000t). Gas composition measurements obtained from the Exploratory Studies Facility (ESF), or 
from boreholes drilled from the ESF, are not used for this purpose because of the potential for 
contamination by ventilation air. 
Measured data for the dissolved inorganic carbon content of porewater samples extracted from 
samples of SD-12 drill core, are used to quantify the transport of dissolved CO2 in recharge 
water (Figure 3-34). As a suitable approximation, the total dissolved inorganic carbon in

 3-51 
recharge waters is represented by bicarbonate concentration, because the waters are at 
near-neutral pH (CRWMS M&O 2000t). 
Additional Input Data and Assumptions Used to Analyze CO2 Transport at Borehole SD-12 
In addition to the data discussed previously, additional input includes hydrostratigraphic unit 
definitions and properties, including fracture and matrix porosities and stratigraphic contact 
elevations in borehole SD-12 (CRWMS M&O 2000t). Ambient matrix saturation for 
hydrostratigraphic units intercepted by borehole SD-12 is estimated from published data 
(CRWMS M&O 2000t). 
Three values of the present-day average infiltration flux at Yucca Mountain are used to represent 
the range of conditions. The average flux over all multi-scale TH model locations (CRWMS 
M&O 2000i) for the lower, middle, and upper flux distributions are 0.56, 5.98, and 14.56 mm/yr, 
respectively. 
The mass transfer model described in this section is a tool for estimating gas fluxes and 
fugacities. Several assumptions are made in developing this model: 
 Steady-State, 1-D Conditions  A dynamic steady state is assumed for interpretation 
of present-day isotopic conditions and mass transfer. The assumption of vertical, 1-D 
transport is conservative, in the sense that multi-dimensional effects are associated with 
mixing that would tend to increase the flux and fugacity of gas-phase components, and 
low CO2 fugacity contributes to high pH, which could potentially increase corrosion 
rates for the drip shield and waste package. 
 Dissolved Inorganic Carbon  The composition of water from Well J-13 is used as an 
analogue for the dissolved inorganic carbon content of percolating waters in the UZ. 
The nominal reported bicarbonate alkalinity is 128.9 mg/L (CRWMS M&O 2000t). 
 Limited Interaction of CO2 with Solid-Phases  CO2 interaction with solid-phase 
carbonates is limited. For ambient conditions, this is consistent with a dynamic 
steady-state whereby near-equilibrium of waters with calcite is maintained throughout 
the UZ. During the thermal period, exsolution of CO2 by warming and evaporation, 
and dissolution of carbonate by condensate, are compensating processes. 
 Representative Formation Properties  For interpreting ambient 14C data, 
depth-averaged fracture porosity, volumetric water content, temperature, total pressure, 
and other properties are assumed. 
 Other Assumptions  Ambient temperature values for gas diffusion coefficients and 
gas solubility, are used in the bounding mass transfer model for thermal response. 
Isotopic fractionation associated with dissolution or exsolution of 14CO2 is assumed to 
be a small effect compared with variations in 14C activity caused by radioactive decay. 
The average ambient 14C signature for CO2 in recharge water or gas is assumed to be 
100 pmc (percent modern carbon).

 3-52 
Additional detail on input data and assumptions is provided in the source documentation 
(CRWMS M&O 2000t). Uncertainty is addressed in the Gas Flux and Fugacity Model primarily 
through the use of a bounding approach and also by comparison to other approaches. 
Gas Flux and Fugacity Model Uncertainties 
The foregoing discussion has shown that this model has associated uncertainties which derive 
from consideration of alternative models, and from assumptions related to input data and from 
selections made in model development. Uncertainty is addressed by making this a bounding 
model. The greatest uncertainty is probably associated with the assumption of limited CO2 
interaction with solid phases, in application of the model to gas transport during the thermal 
period. This uncertainty can be addressed through additional modeling using alternative 
methods, calibrated to ambient CO2 data and gas-phase composition observations from field 
thermal testing. 
3.1.2.2.3 Analytical Models for Gas Flux and Fugacity 
Oxygen fugacity is an important chemical boundary condition for corrosion of metals. Flux and 
fugacity for O2 gas are more strongly dominated by gas-phase processes than they are for CO2 
because the solubility of O2 in water is smaller and because the gas phase contains more O2. 
Oxygen has limited solubility in water, and when it is consumed by aqueous reactions, the local 
fugacity can be strongly depleted relative to the bulk environment. 
3.1.2.2.3.1 Mass Balance Model for Ambient, Steady-State 14CO2 Transport in the UZ 
Using a steady-state radiocarbon mass balance, the 14CO2 flux delivered to the host rock by 
ambient natural processes is estimated from the 14C activity of the carbon found there: 
( ) 
mat 
14 
14 in , gas 
14 
in 
14 
out 
14 
in 
14 
aq in , aq 
14 
mat 
14 
M m 
a 
a a q C 
0 
dt 
M d 
. - + 
- 
= = (Eq. 3-4) 
where
14Mmat = mass of 14CO2 per unit area, principally in the matrix porewater (kg/m2) 
14Caq,in = concentration of 14CO2 in recharge water (kg/m3) 
qaq = flux of recharge water (m/sec) 
14mgas,in = mass flux of 14CO2 transported in the gas phase (kg/m2-sec) 
.14 = 14C decay constant (3.84  1012 sec1) 
14ain = 14C activity for influent water, e.g. recharge (pmc) 
14aout = 14C activity for effluent water, e.g. to the saturated zone (pmc) 
A steady-state mass balance approach based on Equation 3-4 can be applied to the entire UZ or 
to intervals, such as above and below a hydrologic confining unit that acts as a barrier to gas flux 
but not to liquid flux. Below a confining unit, aqueous flux must be the predominant mechanism 
for transport and storage of 14CO2. Such confinement is inferred in borehole SD-12 immediately

 3-53 
below a depth of 397 m (Figure 3-29) where a hydrologic confining unit has been inferred from 
barometric efficiency observations (CRWMS M&O 2000t). 
The following discussion analyzes the 14CO2 data from borehole SD-12, using a mass-balance 
approach (CRWMS M&O 2000t). The stratigraphic column is divided into a set of discrete 
intervals, and the water content, dissolved inorganic carbon, and 14C activity are determined for 
each interval from site data. The steady-state influx of modern CO2 needed to replace the 14C 
lost to radioactive decay is calculated for each interval. The results for borehole SD-12 are 
plotted as both the incremental and cumulative CO2 flux (Figure 3-35). The mass balance results 
are summarized as follows: 
 CO2 demand in the UZ  The 14C mass balance for the entire UZ thickness at borehole 
SD-12 shows that approximately 586 mg/m2-yr of modern carbon (100 pmc) are 
required to replace 14C decay and maintain the inventory at steady state (CRWMS 
M&O 2000t). This is a minimum flux that is not adjusted for through-flux of 14CO2 to 
the saturated zone. 
 Below the confining zone  For the interval below 397 m depth in borehole SD-12, the 
flux of modern CO2 required to replace 14C decay is approximately 287 mg/m2-yr. 
This flux is aqueous because of confining conditions present in the rock. It is also a 
minimum flux that is not adjusted for through-flux of 14CO2 to the saturated zone. 
 Host rock and other units above the confining zone  For the interval above 397 m 
depth in borehole SD-12, the flux of modern CO2 required to replace 14C decay is 
approximately 299 mg CO2/m2-yr. Because the aqueous infiltration flux at this 
location is not enough to transfer this much aqueous CO2 (in addition to that 
transferred to the lower interval) except under extreme infiltration conditions, gasphase 
transfer is evident. 
3.1.2.2.3.2 Model for 1-D Transport of 14CO2 for Ambient Conditions 
Murphy (1995) derived an analytical expression for ambient CO2 fugacity and fluxes that is 
based on the idea that CO2 transport occurs mainly in the gas phase. The 1-D, steady-state 
model assumed that the UZ has uniform properties and that the surface boundary composition is 
constant. Transport behavior was assumed to include both molecular diffusion and advectivedispersive 
effects. The following discussion modifies this analytical model by addition of an 
advective term to represent aqueous transport; it then evaluates gas-phase CO2 transport in 
borehole SD-12. The resulting mass transfer relation is used to represent transport of gases into 
the potential repository. 
Another study by Codell and Murphy (1992) investigated transport of 14CO2 released from waste 
packages, through the gas phase in the unsaturated zone. The approach included chemical 
interactions between gaseous CO2, aqueous CO2 species, and solid-phase carbonates, along a 
1-D pathway from the repository horizon to the ground surface. It thus included more chemical 
interactions than the approach developed in this section. It showed that much of the CO2 in the 
UZ exists as aqueous species, and that repository heating will cause repartitioning of this CO2 to 
the gas phase. During cooldown, or as the gas migrates to cooler regions, the model indicated

 3-54 
that CO2 will tend to redissolve in porewater. The results suggest that the approach developed 
below, based on the model of Murphy (1995) for ambient conditions, will underestimate the 
availability of CO2 in the EBS environment during the thermal period. 
In the discussion that follows, diffusive and analogous dispersive processes are assigned to the 
gas phase, while advection occurs in the liquid phase as percolation. A mass-balance equation 
taking into account transport and decay of 14C is 
gas 
14 
d aq 
14 
aq 
14 
aq gas 
14 
gas bulk 
14 
14 
14 
aq 
14 
2 
gas 
14 2 
gas gas 
bulk 
14 
C K C 
C C C 
0 C 
z
C 
u 
z
C 
D 
t 
C 
= 
f + f = 
= . - 
. 
. 
- 
. 
. 
f = 
. 
. 
(Eq. 3-5) 
where
14Cbulk = bulk concentration of 14CO2 in the UZ (kg/m3) 
14Cgas = 14CO2 concentration in the gas phase (kg/m3) 
14Caq = 14CO2 concentration in the aqueous phase (kg/m3) 
Dgas = diffusion-dispersion coefficient for gas-phase 14CO2 transport (m2/sec) 
faq = volume fraction liquid, predominantly in matrix porewater 
fgas = volume fraction gas in which diffusive-dispersive transport occurs, 
predominantly fracture porosity 
u = liquid flux that is isotopic equilibrium with gas (m/sec) 
Kd = dimensionless distribution coefficient for CO2 partitioning between gaseous and 
aqueous phases 
Making the necessary substitutions, Equation 3-5 is linear with constant coefficients. Obtaining 
a solution and applying the boundary condition 14Cgas (z.0) = .14ainCgas,in yields (CRWMS 
M&O 2000t) 
( ) 
( )
.. 
.. 
. 
.. 
.. 
. 
. . 
.
. 
. . 
.
. 
f 
f + f f . + - 
= 
.. 
.. 
. 
.. 
.. 
. 
. . 
.
. 
. . .
. 
f 
f + f f . + - 
= 
gas gas 
d liquid gas gas gas 14 d 
2 
d 
in 
14 14 
gas gas 
d liquid gas gas gas 14 d 
2 
d 
in , gas in 14 gas 
14 
D 2 
K D 4 K u uK 
z exp a a 
D 2 
K D 4 K u uK 
z exp C a g C 
(Eq. 3-6)

 3-55 
where Cgas,in is the concentration of total carbon (all isotopes) representing the influent or 
recharge composition. Equation 3-6 is fit to measured data for 14C activity vs. depth in borehole 
SD-12 (Figure 3-36). The following additional details are needed to obtain solutions and are 
discussed more fully in the source documentation (CRWMS M&O 2000t): 
 Gas-liquid CO2 distribution coefficient  CO2 partitioning is estimated using the 
1000 ppmv CO2 concentration for the gas phase and 94 mg CO2/L for matrix 
porewater. Converting to common units (kg/m3) and taking the ratio of aqueous to 
gaseous concentrations yields a distribution coefficient Kd = 53.1 (dimensionless). 
 Gas volume fraction in the UZ (fgas)  The gas volume fraction in which transport 
occurs is dominated by the fracture porosity, which is estimated for the host rock and 
overlying units at the SD-12 location using hydrostratigraphic properties. 
 Liquid volume fraction (faq)  The aqueous liquid volume in which CO2 is stored and 
retarded is dominated by the matrix porewater, which is estimated for the host rock and 
overlying units at the SD-12 location using hydrostratigraphic properties and saturation 
data. 
 Diffusion-dispersion coefficient (Dgas)  The diffusion-dispersion coefficient in 
Equation 3-5 and Equation 3-6 is calculated as a multiple of the molecular diffusion 
coefficient for CO2 in air: 
t 2 CO gas D D = (Eq. 3-7) 
where 
DCO2 = diffusion coefficient for gas in air (1.60  105 m2/sec for CO2 and 
2.1  105 m2/sec for O2; at 298 K) 
t = tortuosity-dispersion coefficient (dimensionless) 
In Equation 3-7, the effect of gas-phase advective-dispersion is represented by a coefficient (t) 
rather than by an additive term. This is consistent with the conceptual model, in which 
molecular diffusion works in the same manner as path-dispersion to increase bulk dispersion. 
The tortuosity-dispersion coefficient (t) describes the mobility of CO2 in the ambient system. It 
is then applied to thermal conditions with the use of additional assumptions and approximations. 
Ambient 14CO2 Transport in Borehole SD-12 
Plots of 14C activity versus depth, calculated using Equation 3-6, are compared with measured 
data in Figure 3-36 (CRWMS M&O 2000t). The measured data are represented by separately 
calculated curves for lower, mean, and upper average infiltration values. A value of t = 5 
is used for fitting, indicating that gas-phase mobility of CO2 is five times greater than with 
molecular diffusion alone. As discussed previously, gas-phase transport is required because the 
ambient percolation flux is insufficient to account for recharge of all of the 14C present in the UZ.

 3-56 
Comparison with Data from Other Boreholes 
Equation 3-6 has also been plotted with 14C activity data from boreholes UZ-6/6S, UZ-1, 
NRG-5, and SD-7 (CRWMS M&O 2000t). The same input data are used, with a range of values 
for the tortuosity-dispersion coefficient (t). Transport behavior is apparently stronger for the 
other boreholes, and a value of t = 13 is selected to calculate gas fugacity estimates for the 
Chemical Reference Model. (The value t = 13 is a representative value for these borehole data, 
not a bounding one.) 
3.1.2.2.3.3 Model for Gas Transport During the Thermal Period 
Gas-phase flux of CO2 or O2 is estimated using diffusion and advection terms, corresponding to 
the first two terms on the right-hand side of Equation 3-5. The approach calculates gas-phase 
mass flux in response to a sink at the potential repository horizon, such as would be caused by 
chemical reactivity, analogous to the effect of radioactive decay. Mass flux is calculated for 
constant concentration conditions at the ground surface and at the potential repository level as 
gas gas 
gas 
gas gas gas C v 
z 
C 
D m f - 
. 
. 
f - = (Eq. 3-8) 
where
mgas = flux (i.e. consumption from decay or reaction) of gas-phase reactant (kg/m2sec) 
Dgas = gas diffusion coefficient (m2/sec, different for O2 and CO2) 
v = velocity of gas phase (positive upward, m/sec) 
and the other notation is the same as that of Equation 3-5. The gradient .Cgas/.z is calculated 
from the difference between the gas concentration at the surface and that in the potential 
repository. Use of a single value of Dgas in Equation 3-8 instead of multiple values 
corresponding to the layered stratigraphy, is analogous to the effective 1-D hydraulic 
conductivity for a stack of layers with different conductivity values (CRWMS M&O 2000t). 
The binary gas-diffusion coefficients for CO2 and O2 increase with temperature, and the effect is 
bounded in this model by using tabular values at 298K. Coefficients of binary diffusion for CO2 
and O2 gases in water vapor are assumed to be no less than the coefficients in air. 
Calculations show that gas-phase velocity (v) above the drifts tends to be negative (directed 
upward) during the thermal period because water vapor is convected upward. Although 2-D 
drift-scale TH simulations (Section 3.1.2.1) show that the gas-phase may actually circulate in the 
pillars, which would tend to increase availability of CO2 and O2 gases, the upward velocity 
above the drift openings is used in this bounding model. The gas-phase velocity varies with 
depth and location in the host rock; however, for this bounding model the maximum upward 
velocity in the host rock directly above the drift is used (CRWMS M&O 2000t). Note that 
absolute concentration (Cgas times the air mass-fraction) is used to compute the gradient in 
Equation 3-8. 
Equation 3-8 is rearranged to relate the gas flux and concentration (or fugacity), using 
(Cgas,in-Cgas)/z to represent .Cgas /.z. The maximum concentration at depth (Cgas) is found by

 3-57 
setting the mass flux (mgas) to zero, and the maximum mass flux is computed by setting the 
concentration at depth to zero. Both of these limits vary with time, as the air mass-fraction and 
the gas-phase velocity change with thermal evolution of the potential repository. This mass-flux 
relation is implemented for the L4C4 location and the upper infiltration flux (CRWMS M&O 
2000t). The L4C4 location is near the geographic center of the potential repository, where 
large-scale thermally-driven gas-phase convection is likely to be smallest. Selection of the L4C4 
location and upper infiltration distribution is discussed in Section 3.1.2. 
3.1.2.2.4 Gas Flux and Fugacity Model Validation 
An analytical solution is developed to describe the variation of ambient 14C activity gas phase 
with depth in the UZ. This model is extended to describe the transport of CO2 and O2 gases in 
the UZ during the thermal period in response to chemical sources or sinks at depth. 
Conservative values are used for most parameters of these models, in the sense that the values 
tend to lower the estimated fugacities of CO2 and O2 gases during the thermal period, or when 
these constituents are being consumed by chemical reactions in the drift environment. (Lower 
CO2 fugacity elevates the pH when bicarbonate-type waters are evaporatively concentrated, and 
lower O2 fugacity maximizes the predicted deviation of gas-phase composition from ambient 
pre-repository conditions.) The key parameter is the diffusion-dispersion parameter that controls 
gas-phase transport. This parameter is calibrated to field data from SD-12 and other boreholes at 
Yucca Mountain. The results show that trends in 14C observations can be represented by an 
envelope of curves corresponding to uncertainty in the infiltration flux (Figure 3-36). 
Conservative aspects of the model can be inferred by comparison to other methods of estimating 
CO2 fugacity (Section 3.1.2.2.6). Based on this discussion, it is concluded that the Gas Flux and 
Fugacity Model is valid for the intended use in FEP screening and supporting the design basis. 
3.1.2.2.5 Results for Gas Flux and Fugacity in the EBS Environment 
Calculated results for CO2 and O2 gas fugacity, as functions of time after emplacement, are 
shown in Figure 3-37 and Figure 3-38. In these plots, both the fugacity values and the mass flux 
values are normalized to their maximum values. The normalized results for CO2 and O2 differ 
only with respect to the values used for diffusion coefficients. 
The mass-transfer model shows that for a maximum CO2 fugacity of 1000 ppm, the minimum 
CO2 fugacity during the thermal period is approximately 1 ppmv. Similarly, for a maximum O2 
fugacity of 0.2 atm, the minimum values for O2 fugacity are approximately 200 ppmv. The 
model indicates that further decrease of either the CO2 or O2 fugacity by consumption in the EBS 
environment would not be substantial until the rate of consumption approached 90 percent of the 
maximum mass flux. 
Further calculation details are described in the source documentation (CRWMS M&O 2000t). 
These results are used for the Chemical Reference Model calculations in this report (Section 
3.1.2.7).

 3-58 
3.1.2.2.6 Comparison with Alternative Models and Approaches 
Comparison of the mass-transfer model represented by Equation 3-8 with the air mass-fraction in 
Figure 3-37 and Figure 3-38 shows that the mass-transfer model predicts greater minimum 
fugacities, but is slower to recover during cooldown. The air mass-fraction estimation approach 
is most similar to the mass-transfer model with low flux (i.e., low consumption in the potential 
repository environment). This is appropriate because the air mass-fraction approach does not 
relate fugacity with flux. 
Discussion of Conservatism in Calculated Results 
The estimated gas-phase CO2 and O2 fugacities, and their variation with mass flux, are 
conservative representations of the availability of these constituents for chemical reaction in the 
drifts for the following reasons: 
 Aqueous fluxes of CO2, and O2 to a lesser extent, are neglected in the model 
 One-dimensional transport is assumed, but there are indications from the TH models 
that multidimensional gas-phase circulation may occur because of the wide drift 
spacing 
 Release of CO2 by exsolution and evaporation of pore water, is neglected in the model. 
 Increase of molecular diffusion coefficients with temperature is neglected in the model. 
The use of conservative estimates for CO2 availability is appropriate because alkaline conditions 
are potentially more adverse to the performance of corrosion-resistant materials. High-pH could 
accelerate corrosion of the drip shield or waste package during the thermal period, relative to 
near-neutral pH conditions (e.g., pH 5 to 9). Even for such thermally altered, alkaline 
conditions, the corrosion rates for drip shield and waste packages materials will be low 
(CRWMS M&O 2000n, Section 3.1.5) such that liquid water entry into waste packages will be 
delayed until the drifts have cooled. 
During cool-down the relative humidity will increase, the CO2 fugacity will approach prerepository 
conditions (Figures 3-33 and 3-37) and evaporation in the drift will decrease (Figure 
3-23). Water composition in the drifts will return to pre-repository conditions, with near-neutral 
pH. Near-neutral, or slightly acidic conditions could accelerate waste form degradation, 
compared to alkaline conditions during the thermal period, depending on the waste form type 
(e.g., spent fuel or glass) and other factors. 
From the foregoing discussion, the use of conservatively low estimates for CO2 fugacity during 
the thermal period is conservative from the standpoint of potential effects on drip shield or waste 
package degradation during the thermal period, while more neutral water compositions can later 
enter breached waste packages and interact with the waste form.

 3-59 
3.1.2.3 Introduced Materials Models 
This section presents a set of models used primarily for analysis of the sensitivity of bulk 
chemical conditions in the EBS, to changes in the properties and composition of introduced 
materials. A typical inventory of EBS materials in addition to the quartz sand backfill and 
crushed tuff invert ballast, is presented as a starting point for discussion. For quartz sand 
backfill, the importance of kinetic dissolution/precipitation behavior is evaluated for inclusion in 
the Chemical Reference Model (Section 3.1.2.7). Potential dissolution of quartz backfill by 
evaporatively concentrated waters, and potential changes in backfill porosity from evaporative 
precipitation, are evaluated and found to be minor. Potential consumption of O2 by corrosion of 
steel used in the EBS is estimated from laboratory corrosion rates. Consumption of O2 by 
corrosion of the DS and WP is much less important. Leaching of the cement that will be used in 
grouted rockbolts is evaluated and found to be a minor contributor to the bulk chemical 
environment, in the repository design that includes backfill. 
The overall purpose of these submodels is to describe the effects of introduced material 
degradation on the bulk chemical environment. The intended use is FEP screening, and support 
of the design basis (Table 3-A). 
3.1.2.3.1 Materials Present in the Emplacement Drifts 
The EBS design calls for a backfill composition of quartz sand (>99% SiO2). The non-quartz 
fraction will have predominantly feldspar mineralogy, and limited concentrations of halides and 
organic material (CRWMS M&O 2000t). Additional information on backfill composition and 
quantity is provided in Section 1.6. The invert ballast material will be composed of Topopah 
Spring welded tuff that has been crushed to gravel-sized particles ranging in size from 9.5 mm to 
19 mm. The mineralogy of the ballast will be substantially the same as host rock from which the 
drifts are excavated. 
The materials to be used for the WPs and their supports are inventoried in Table 3-3. Other 
materials to be used in the potential repository emplacement drifts, and committed for the 
postclosure period, are inventoried in Table 3-4 (CRWMS M&O 1999g). Information on the 
EBS configuration is also provided in Section 1.6. 
Use of cementitious materials will be limited to fully grouted rockbolts, which will be used only 
in the nonlithophysal host rock (the lithophysal host rock will not have rockbolts; CRWMS 
M&O 2000t). An average of four rockbolts per meter of drift will be used. The rockbolt steel is 
included in Table 3-4. The grout will be a Type K expansive cement, with admixtures to 
promote workability and to decrease permeability. Additional information on grout composition, 
properties, and quantity is provided in Section 3.1.2.3.5.

 3-60 
Table 3-3. Quantities and Compositions of Materials Used per Each Meter of a 21 PWR Waste Package 
and Its Supports, Excluding the Waste Form Inside the Package 
Composition b ( percent) 
Material Material 
Quantity 
a (kg/m) Fe Mn Ni Mo Ti Al Cr B 
WP supports Alloy 22 267 6.0 0.5 50.015 14.5 n/a n/a 22.5 n/a 
WP supports Stainless Steel 128 62.05 2.0 14.0 3.0 n/a n/a 18.0 n/a 
WP Outer Barrier Alloy 22 1173 6.0 0.5 50.015 14.5 n/a n/a 22.5 n/a 
WP Inner Barrier Stainless Steel 2106 62.06 2.0 14.0 3.0 n/a n/a 18.0 n/a 
Thermal Shunt Aluminum 63 0.7 0.15 n/a n/a n/a 95.85 0.35 n/a 
Absorber plates Neutronit A 978 387 66.66 n/a 13.0 n/a n/a n/a 18.5 1.6 c 
Basket Guides Steel 1073 97.91 1.3 n/a n/a n/a n/a n/a n/a 
Drip Shield Titanium Grade 7d 563 0.3 n/a n/a n/a 98.665 n/a n/a n/a 
Drip Shield Alloy 22 16 6.0 0.5 50.015 14.5 n/a n/a 22.5 n/a 
NOTES: a Quantity refers to 1-m length of potential repository drift. 
b This table presents only selected constituent elements, not the total composition of every material. 
c See (CRWMS M&O 1999g) for source of this value 
d Titanium composition also contains 0.25 percent palladium (CRWMS M&O 1999g) 
Table 3-4. Quantity and Compositions of Materials to Be Used for Facilities and Ground Support in the 
Potential Repository Emplacement Drifts 
Composition b ( percent) 
Material Material 
Quantity a 
(kg/m) Fe Mn Ni Mo Co W Cr Cu 
Rockbolt Sets c Steel 48 99.022 n/a n/a N/a n/a n/a n/a n/a 
Welded Wire Fabric Steel 70 98.8 n/a n/a N/a n/a n/a n/a n/a 
Gantry Rail Steel 133.9 97.59 1.0 n/a N/a n/a n/a n/a n/a 
Rail Fittings Steel 13.4 74.44 n/a n/a N/a n/a n/a n/a 25.0 
Steel Sets Steel 369 97.48 1.65 n/a N/a n/a n/a n/a n/a 
Conductor Bar Fittings Steel 0.2 97.48 1.65 n/a N/a n/a n/a n/a n/a 
Communications Cable d Copper 0.79 N/a n/a n/a N/a n/a n/a n/a 50.0 
Conductor Bar e Copper 5.32 N/a n/a n/a N/a n/a n/a n/a 100 
Steel Invert Steel 587 97.48 1.65 n/a N/a n/a n/a n/a n/a 
NOTES: a Quantity refers to 1-m length of potential repository drift. 
b This table presents only selected constituent elements, not the total composition of every material. 
c Rockbolts will be used only for the nonlithophysal portion of the potential repository drift design 
(CRWMS M&O 1999g). 
d Wire conductor is not included because its relative abundance is small compared to other materials. 
e Loading-docks, isolation doors, and related components which will be used only at the ends of the 
emplacement drifts and not in the waste emplacement area, are not considered here. 
3.1.2.3.2 Conceptual Models for Degradation of Introduced Materials 
Environmental Conditions 
The abundances of O2 and N2 pore gases from the UZ are close to atmospheric values (CRWMS 
M&O 1999g). Measurements of gas composition from various UZ boreholes demonstrate that

 3-61 
gas-phase CO2 concentration averages approximately 1000 ppmv (Section 3.1.2.2). Water 
composition in the host rock is represented by J-13 well water. Use of this composition in 
models of the chemical environment is discussed in Section 3.1.2.5. J-13 water is 
compositionally similar to both perched water from Yucca Mountain (CRWMS M&O 1999g) 
and perched water collected flowing from fractures at Rainier Mesa (Harrar et al. 1990, pp. 6.5 
and 6.6, Table 6.1). The composition of J-13 water is consistent with model predictions for 
water interaction with the host rock. Porewaters extracted from Yucca Mountain tuff generally 
contain more Ca, Mg, chloride, and sulfate and proportionately less bicarbonate than J-13 water. 
However, composition similar to J-13 water is reasonable for water in fractures of the Topopah 
Spring welded tuff at ambient and elevated temperature (CRWMS M&O 2000t). 
Increased temperatures will evaporate much of the water in the potential repository drifts and 
produce a boiling zone in the host rock at or near the drift wall. As thermal output decays with 
time, all introduced materials will eventually have been subjected to boiling-zone conditions. In 
the boiling zone, mineral precipitates, including salts, will form and can contribute to 
degradation of introduced materials through formation of brines. Evaporatively concentrated 
water will be enriched in alkalis, chloride, and sulfate; with pH 9 or greater (CRWMS 
M&O 1999g). Mineral precipitation will occur, and chemical species that remain dissolved can 
become concentrated by 1,000-fold or more relative to J-13 water. The composition of 
evaporatively concentrated waters depends on the gas-phase composition and on the opensystem 
assumptions that can be made in modeling. 
Quartz-Sand Backfill 
Interaction of quartz in the environment will result primarily from aqueous dissolution and 
precipitation rate processes. The solubility of quartz in the potential repository environment will 
be affected by pH, temperature, solution composition, and ionic strength. At pH 9 and above, 
the solubility of silica increases by as much as several orders of magnitude, as the species 
H3SiO4
 and H2SiO4
2 become increasingly abundant. The presence of quartz or other silica 
minerals in the potential repository environment can therefore serve to buffer the pH in these 
ranges. 
The dissociation constants for silica species and the equilibrium solubility constant for quartz are 
affected by changes in temperature. A temperature increase from 25C to 100C increases the 
solubility of quartz and other forms of silica, including amorphous silica, by an order of 
magnitude. Solubility also increases when other ions modify the solution; thus, for brines, the 
solubility can increase 100-fold in the presence of alkali and alkaline earth cations. 
The postulated dissolution rate for quartz, at conditions expected in the potential repository, is 
relatively slow compared to other minerals such as cristobalite (CRWMS M&O 2000v). Quartz 
dissolution and precipitation rates in the potential repository environment will be controlled by 
intrinsic factors, including temperature, solution composition, and pH (CRWMS M&O 2000v) as 
well as the specific surface area available for reaction. The rates generally increase with 
temperature; for example, the quartz dissolution rate increases 1000-fold at temperatures from 
25C to 100C. The quartz dissolution rate also increases with greater concentrations of 
dissolved salts. For dilute aqueous solutions, equilibrium with quartz typically does not occur at 
temperatures less than 200C, but other factors such as salt concentration may decrease this

 3-62 
temperature to 190C or less. The dissolution and precipitation rates for lower-order SiO2 
precipitates such as chalcedony are not as strongly inhibited over the temperature range of 25C 
to 100C (CRWMS M&O 2000v). Therefore, any lower-order precipitates present in the 
potential repository environment would tend to dissolve faster than quartz, and silica 
precipitation is more likely to occur as the lower-order forms unless the reactive surface area of 
quartz is large. 
Three conceptual approaches are used for modeling of aqueous processes involving quartz-sand 
backfill:
 Kinetic model for waterquartz interaction  This involves modeling the effects of 
quartz dissolution and precipitation on pH, for conditions when water is flowing in the 
emplacement drifts. This approach is incorporated in the Chemical Reference Model 
(Section 3.1.2.7). The emphasis is on the effect of quartz on the composition of waters 
present in the emplacement drifts. 
 Effects of quartz backfill at high ionic strength  This involves evaluation of quartz 
solubility at high ionic strength (CRWMS M&O 2000v). This approach considers the 
composition of fluids that have been evaporatively concentrated well beyond 100-fold 
and which are present in very small amounts in the potential repository environment. 
Quartz behavior is inferred from calculated saturation indices, which indicate whether 
precipitation or dissolution is thermodynamically favored. The emphasis is on the 
potential for dissolution or precipitation of quartz, which could change the backfill 
properties. The possibility that dissolved solids from influent seepage water could 
precipitate and plug the backfill porosity, is also discussed qualitatively. 
Structural Steel and Waste Package Alloys 
The alteration of steels and alloys, as discussed in In-Drift Corrosion Products (CRWMS 
M&O 1999g) will produce metal oxide and metal hydroxide corrosion products in the drift and 
may also form metal-silicate minerals. As the iron and other metals corrode, they represent a 
sink for oxygen. Oxidation reactions represent a source of metabolic energy for microbial 
activity, which can enhance the rate of metal corrosion. The corrosion products have potentially 
important sorptive properties and may form colloidal particles that can transport radionuclides. 
Of the 12 elements addressed in Table 3-3 and Table 3-4, and discussed in the source 
documentation (CRWMS M&O 1999g), the following will each be present in amounts less than 
1 percent of the total of introduced materials: Pd, Co, W, B, and Cu. Because such small 
quantities are present, a simplifying assumption is made to exclude these elements from 
assessment of the bulk chemical environment. Accordingly, the following elements are 
discussed further: Fe, Mn, Ni, Mo, Cr, Ti, and Al. Natural waters from the site contain low 
concentrations of these metals, so introduced materials represent a potentially significant 
perturbation on the chemical environment. Literature information on the behavior of these 
elements (CRWMS M&O 1999g) is summarized below: 
 Iron (Fe)  Corrosion of the structural steel and corrosion-resistant alloys will cause 
precipitation of hematite or goethite, depending on pH, temperature, and

 3-63 
Ti-concentration. The hematite or goethite can act as sorbents for Ni, Mn, or Mo, and 
Fe may coprecipitate to form solid solutions. (CRWMS M&O 1999g, Sect. 6.5.1.1). 
 Manganese (Mn)  Corrosion of the steel and alloys can lead to precipitation of a form 
of MnO2 (e.g., pyrolusite). These oxides are active sorbents and act as oxidants for 
other metal species. In the presence of iron, Mn could be reduced to Mn(II) and may 
precipitate with hematite or goethite to form solid solutions. (CRWMS M&O 1999g, 
Sect. 6.5.1.2). 
 Nickel (Ni)  Corrosion of the corrosion-resistant alloys will cause precipitation of 
Ni(OH)2. In the presence of Fe and Mn, Ni could also precipitate with hematite, 
goethite, or MnO2 to form solid solutions. Aqueous nickel will compete with other 
metal species for sorption sites on metal oxides. (CRWMS M&O 1999g, Sect. 6.5.1.3). 
 Chromium (Cr)  Corrosion of the corrosion-resistant alloys will cause precipitation 
of Cr2O3. The oxide can dissolve very slowly, yielding aqueous Cr(III). In the 
presence of ferric iron or manganese oxides, Cr(III) will strongly sorb and can 
coprecipitate to form solid solutions. Chromium(III) will slowly oxidize, and the 
resulting chromate (CrO4
2) may be present as a trace species. (CRWMS M&O 1999g, 
Sect. 6.5.1.4). 
 Molybdenum (Mo)  Corrosion of the steel and corrosion-resistant alloys will cause 
precipitation of Mo3O8. Molybdenum may also be found in solution as the molybdate 
ion (MoO4
2) and can precipitate with hematite or goethite to form solid solutions or 
can compete with other aqueous metal species for available sorption sites on Fe and 
Mn oxides. (CRWMS M&O 1999g, Sect. 6.5.1.5). 
 Titanium (Ti)  Corrosion of Ti alloys will cause precipitation of TiO2. Relatively 
small amounts of Ti may also precipitate with hematite or goethite to form solid 
solutions or may compete with other aqueous metal species for available sorption sites 
on Fe and Mn oxides. (CRWMS M&O 1999g, Sect. 6.5.1.6). 
 Aluminum (Al)  Corrosion of aluminum components inside the WP may cause the 
precipitation of Al(OH)3 or AlOOH. Aluminum oxide solids can be sorbents for both 
anions and cations in solution. Aqueous aluminum will form clay minerals in the 
presence of silica. On exposure to alkaline fluids (e.g., pH 11) Al can react to form 
hydrogen gas, which is possible in association with evaporatively concentrated fluids 
inside the waste package. (CRWMS M&O 1999g, Sect. 6.5.1.7). 
The geochemical environment will eventually corrode the steels and alloys that contain these 
elements. The metals are thermodynamically unstable and will react with water and the 
available oxygen to produce corrosion products. Some introduced materials will be more 
resistant to corrosion (typically because of passivating metal-oxide films), while others may 
corrode more readily, especially in the presence of waters concentrated by evaporation and 
boiling.

 3-64 
Corrosion of introduced materials, particularly steel, can alter radionuclide transport in the EBS 
environment. The presence of metal oxides could retard radionuclide transport, and at the same 
time, contribute colloidal material that increases radionuclide mobility. The two elements with 
the greatest potential to contribute colloidal corrosion products are Fe and Al. Ferric colloids 
from introduced materials from corrosion processes will be more abundant in the EBS, than 
natural ferric colloids contributed by groundwater inflow. Aluminum-hydroxide colloids may be 
formed by corrosion of materials inside the WPs. 
Crushed Tuff Invert Ballast Material 
This discussion provides justification for treatment of the invert in process models and 
performance assessment. It is concluded that the invert is not likely to exert a significant and 
permanent influence on the chemistry of seepage exiting the drift. The discussion is taken from 
the analysis/model report on Seepage/Invert Interactions (CRWMS M&O 2000m). The 
emphasis of this discussion is mainly on the potential effect of the crushed tuff invert on the 
composition of waters flowing through. 
If waterrock interaction in the invert reproduces reactions that occur elsewhere in the host rock, 
the small size of the invert argues that invertseepage interactions are not important. Iron is 
present in the host rock (CRWMS 1999g; Section 6.2.2) in various minerals including hematite. 
It is also noted that iron oxides, including hematite, are insoluble at oxidizing conditions such as 
those which are likely to be encountered in the emplacement drifts (CRWMS 1999g; Section 
6.5.1.1). Thus the dissolution of iron oxides will produce only small changes in the dissolved 
concentrations of ferric iron species in waters that have probably been previously exposed to 
ferric iron oxides in the host rock. Chemical reactions in the host rock will replicate seepage 
invert interactions because the invert ballast will consist of locally derived tuff. The invert will 
also contain appreciable amounts of steel, which will eventually form Fe-oxides. The invert will 
contain copper, which may support reactions that do not occur in the host rock. No significant 
effect of copper on waste isolation performance has been recognized, but further analysis would 
be required to identify and evaluate reactions involving copper. 
The importance of the invert in conditioning the chemistry of water depends on the flow rates. 
Low-flow conditions in the invert will effectively decrease the waterrock mass ratio for 
chemical interaction and can diminish the mobility of chemical species, including radionuclides, 
from hydrologic and chemical considerations. The water quality of the water in contact with the 
invert may be dominated by the invert itself, possibly to the extent that invert composition differs 
from the host rock and resulting in higher metals concentrations than would exist under highflow 
conditions. If the flow of water circulating through the drifts is large, the importance of the 
invert is minimized, and water-rock interactions will be dominated by the host rock because 
more surface area will be available for reactions in the host rock within a short travel time from 
the drift wall. 
The invert component parts (ballast and metal materials) are not present in significant quantities 
with respect to the host rock and other introduced in-drift materials to exert a significant 
influence on the chemistry of the seepage exiting the drift.

 3-65 
Flow of water from breached WPs is not considered for the thermal period, but only for ambient 
conditions (CRWMS M&O 2000s). Changes in composition of water returning to the invert will 
be caused primarily by leaching, dissolution, and alteration of the waste forms. For an 
environment in which drift seepage flows through the backfill, and through breaches in the DS 
and the WP to reach the WF, much of the seepage will never encounter the WF. Thus, changes 
in water chemistry caused by flow through the WP, will be subject to dilution in the invert. 
Further discussion of radionuclide transport in the invert is presented in Section 3.1.3. 
Cementitious Materials 
The mineralogy of the cement grout proposed for use with rockbolts, will determine how it reacts 
with groundwater. Mineral phases present in young cement are represented by portlandite, 
ettringite, tobermorite, and brucite. Young cement also contains a major fraction of 
calcium-silicate-hydrate (C-S-H) gel, a noncrystalline phase with composition similar to 
tobermorite. The C-S-H gel converts to crystalline phases as the cement ages. With further 
aging, the initial mineral assemblage tends to alter as minerals convert to more 
thermodynamically stable crystalline phases. Finally, reaction with CO2 causes carbonation of 
alkaline minerals such as portlandite, producing less soluble, less alkaline carbonate minerals 
such as calcite. 
For bounding potentially deleterious effects from leaching of alkaline constituents from cement 
grout, the young cement assemblage is used because it is least thermodynamically stable, most 
soluble, and potentially most alkaline. The conceptual model for interaction of percolating water 
with these mineral phases consists of gradual dissolution. The constituent phases dissolve 
incongruently in relation to their solubilities. The resulting leachate can have high pH and 
elevated concentrations of anions such as sulfate, which will vary with temperature because of 
temperatures effects on solubility. 
As an alternative model, carbonation of the cement will cause the leachate pH to become more 
neutral with time, but the rate of carbonation depends on access of the gas-phase to unreacted 
grout minerals, which has not been established for the current models. While CO2 fugacity in the 
potential repository environment has been investigated, access of CO2 to rockbolts has not been 
established; thus, the carbonation process is not incorporated explicitly in present models of 
leachate composition. Carbonation will be at least partial, however, so calcite and similar 
carbonate mineral phases will be present. Calcite is included in chemical models of cement 
leaching, to represent the effects of partial carbonation. 
Factors that lessen the potential impacts of cement leachate on the bulk chemical environment 
include:
 Partitioning of seepage flow such that most seepage is not affected by cement 
 Carbonation of the cement minerals 
 Buffering of leachate pH by interaction with CO2 in the gas-phase 
 Buffering of leachate pH by interaction with quartz backfill (or other siliceous 
minerals) 
 Dilution of leachate by mixing with other waters

 3-66 
Only a portion of the potential seepage flow into potential repository drifts will be affected by 
cement, and the effects will be chemically moderated and diluted downstream from the 
rockbolts. 
3.1.2.3.3 Models for Interactions Involving Backfill 
3.1.2.3.3.1 Kinetic Model for Water-Quartz Interaction 
As a backfill material, quartz reaction rates are kinetically limited to some extent, and quartz 
sand is comparatively free of impurities that could promote corrosion or microbial activity. The 
kinetic model for water-quartz interaction is used to determine whether quartz should be 
included as a kinetically hindered reactant, or an equilibrium solid, in the Chemical Reference 
Model. In other words, the model addresses whether quartz equilibrium can be used in the 
calculation of silica buffering activity in Section 3.1.2.7; specifically, whether quartz should be 
an equilibrium solid in Zone 3/4, Time Period 3, and Zone 5/6, Time Period 4. 
Input Data, Assumptions and Uncertainties 
Grain-size distribution for the Overton Sand backfill material (unsieved) is obtained from 
measured data (CRWMS M&O 2000t). A corresponding lower-bound specific surface area, 
calculated assuming spherical particles, is used in kinetic calculations. Using volumes for the 
zones defined in Section 3.1.2.1, the total surface area of quartz sand in each zone is calculated. 
The surface area could be as much as three times greater if irregular particle geometry is taken 
into account. The presence of a very fine fraction (< 0.053 mm particle size) with relatively 
large surface area is also not accounted for. These estimates for surface area are therefore 
lower-bound values. 
Although the backfill will be unsaturated and the flow field will probably be nonuniform, the 
entire surface area of particles constituting the backfill is used in kinetic calculations. This is 
consistent with the capillary nature of sand, which tends to disperse water on the surfaces of all 
particles, and the reaction cell approach to chemical modeling (used in Section 3.1.2.7). The 
calculated surface area and residence time values are averages for the backfill present in each 
zone. 
The principal uncertainties associated with this model are the residence time of liquid water in 
the backfill, and the effective surface area for reaction. Channeling of flow in the backfill from 
heterogeneity of flow properties, or focusing of seepage sources, could limit the contact time for 
reaction. Reactive surface area could be much greater than the specific surface area used in this 
model, but this would support water-quartz equilibrium. 
Development of Kinetic Model for Water-Quartz Interaction 
The kinetics of quartz precipitation is potentially important with the use of quartz sand as 
backfill. In the host rock, quartzand its less stable polymorph, cristobalitecoexist in a 
steady, chemical disequilibrium over geologic time because the growth (precipitation) rate of 
quartz is small. The concentration of dissolved silica in J-13 water and similar waters 
corresponds to near-equilibrium with cristobalite and to supersaturation with respect to quartz. 
This condition is maintained because of the slow growth kinetics of quartz. The relationship can

 3-67 
be inferred directly from measured water compositions and the observation of quartz and 
cristobalite as constituent minerals. 
Because of the increased reactive surface area for quartz and the lack of other silica phases in the 
backfill, the quartz-cristobalite disequilibrium will be modified as water enters the backfill. The 
dissolved silica concentration will decrease, all other factors such as temperature and evaporative 
concentration held constant. The decrease in silica concentration will decrease the associated pH 
buffering capacity from pH buffers such as H3SiO4
/SiO2(aq), NaH3SiO4(aq)/cristobalite, and 
NaH3SiO4(aq)/quartz. These relationships are included in the Chemical Reference Model 
calculations (Section 3.1.2.7). 
A published rate law and data (Rimstidt and Barnes 1980) for quartz growth are used to examine 
the rate of quartz precipitation in the backfill via overgrowth (CRWMS M&O 2000t). The 
precipitation and dissolution of silicate minerals are generally considered to be surface area 
mediated processes (i.e., the rates are proportional to the area of the water-mineral interface). In 
the backfill, the surface area of quartz exceeds that accessible by fracture waters in the 
surrounding rock (per unit mass of water). Contact of influent water with the sand backfill can 
cause development of quartz overgrowths and a significant decrease in the dissolved silica 
concentration. As the water flows back into the rock, the dissolved silica will increase again 
from dissolution of cristobalite. 
Results from Kinetic Model for Water-Quartz Interaction 
The following briefly describes a set of calculations performed for the Chemical Reference 
Model (Section 3.1.2.7). An EQ6 calculation is performed for composite Zone 3/4, in Time 
Period 3 after redissolution of evaporative precipitates deposited in previous time periods. The 
calculation starts with the composition of seepage water from the host rock, modified by 
temperature, CO2 fugacity, and evaporative concentration. It uses the kinetic rate law and 
surface area data discussed previously. 
The computation yields a decline in dissolved silica, to a concentration corresponding to quartz 
equilibrium, in less than 1 year. The actual reactive surface area is probably greater because of 
surface roughness, so less time could be required to produce the same result. Also, the silica 
concentration declines exponentially with time, so that most of the decline takes place early, and 
most of the effect could be achieved in less time. On the other hand, the water is assumed to 
access the entire surface area of the unsaturated sand, which could lead to overestimation of the 
extent of interaction if the flow field is highly nonuniform. These are compensating 
uncertainties, and it is likely that for residence time on the order of 1 year, water-quartz 
interaction approaches equilibrium. Accordingly, final calculations for the Chemical Reference 
Model that involve backfill, are made assuming equilibrium with quartz. 
3.1.2.3.3.2 Model for Seepage-Backfill Interaction at High Ionic Strength 
This section describes an approximate model used to evaluate whether precipitation or 
dissolution of quartz in the backfill is likely during the thermal period when waters in the EBS 
are evaporatively concentrated (relative to fracture waters in the host rock). The approach uses 
saturation indices to evaluate backfill stability, i.e. whether quartz dissolution or precipitation is

 3-68 
likely to be important. The model is based on the Pitzer formulation for thermochemical 
modeling, with an extended data base developed to include silica at elevated temperature, as 
discussed in Section 3.1.2.5.3. The results indicate that quartz dissolution and precipitation will 
be limited for environmental conditions that are likely to occur in the emplacement drifts, and 
therefore are unlikely to change the properties of the backfill. 
Input Data, Assumptions, and Uncertainties 
The quartz solubility calculations require thermodynamic properties of backfill and key 
groundwater constituents, at high ionic strength and elevated temperature. The thermodynamic 
data set used in the model simulations is the Pitzer (PT4) database discussed in Section 3.1.2.5.3, 
and developed for the In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g). In addition 
to the Pitzer database, other input parameters for this model include: 
 Composition and flow rate for influent seepage 
 Temperature 
 Fugacity of CO2 
 Relative evaporation rate (expressed relative to seepage; inversely related to 
evaporative concentration factor) 
The composition of J-13 well water is adopted for the incoming seepage, which is conservative 
from the perspective of high pH produced by evaporative concentration, and the potential 
interaction of alkaline fluid with quartz. 
Important uncertainties for this model include applicability of the extended Pitzer (PT4) 
database, particularly to carbon species and silica. In addition, the significance of 
under-saturation or super-saturation of concentrated waters with respect to quartz, does not 
indicate whether the implied dissolution/precipitation reactions would be kinetically hindered. 
Development of Model for Seepage-Backfill Interaction at High Ionic Strength 
The model is implemented using the EQ3/6 geochemical modeling code. The model 
development and results are described in detail, in the In-Drift Precipitates/Salts Analysis report 
(CRWMS M&O 2000g). 
Results from Model for Seepage-Backfill Interaction at High Ionic Strength 
Quartz saturation indices were obtained for each combination of the following: 
 Temperatures of 95, 75, 45, and 25C 
 CO2 fugacity of 101, 103, and 106 atm 
 Relative evaporation rates of 0, 0.1, 0.5, 0.9, 0.99, and 0.999 
The CO2 fugacity could be less than 10-6 atm, as indicated in Figure 3-33, which compares 
predictions made by several methods. However, there is low likelihood that much, if any, water 
will be present in the backfill when such conditions occur.

 3-69 
The results show that the interaction of quartz sand with seepage derived from partially 
evaporated J-13 well water, will likely be negligible. Dissolution of quartz, which makes up 
more than 99 percent of the backfill, is generally not favored except in the most unlikely 
scenarios (even for the high-pH conditions produced by selecting J-13 water as the influent 
composition). Saturation indices calculated for the cases described above are summarized in 
Figure 3-39. 
The composition of evaporated seepage water predicted by the EQ3/6 Pitzer model is already at 
or near saturation with respect to quartz, when it contacts the backfill. The only cases for which 
quartz dissolution is predicted (saturation indices less than zero) are unlikely combinations 
involving high temperature (95C), low CO2 fugacity (106 atm), and low relative evaporation 
rates (seepage rate more than 10 times the evaporation rate). The high temperature makes low 
relative evaporation an unlikely condition, and the low evaporation rate makes the low CO2 
fugacity an unlikely condition. From these results, dissolution or precipitative overgrowth of the 
quartz backfill is not predicted. 
Another possible source for precipitates which could plug the backfill porosity is dissolved solids 
present in seepage water. Porosity reduction from this source will be insignificant, based on the 
following argument. For a limited period of time, up to a few thousand years, minerals could 
precipitate from seepage water because of elevated temperature, possibly associated with 
evaporative concentration. Only the least soluble minerals such as calcite, gypsum, anhydrite, 
and silica (e.g. amorphous silica) can cause porosity reduction. The more soluble species (i.e. 
chloride salts, and sulfate or carbonate salts with sodium or potassium) would dissolve in the 
presence of seepage water. Accordingly, the argument needs to consider only the calcium, 
magnesium, and silica present in seepage water. 
Seepage during the thermal period will have compositions between pure condensate and 
evaporatively concentrated waters. There is an inverse relationship between the extent of 
evaporative concentration and the available seepage volume. For this discussion, reference water 
compositions are considered, which represent mobile waters in fractures in the host rock. These 
compositions are probably typical for seepage, and will serve to support this argument. Two 
reference water compositions that have been considered are the sodium-bicarbonate type (e.g., J- 
13 water) and the chloride-sulfate type (representing tuff matrix porewater). Calcium, 
magnesium, and silica are present in millimolar concentrations (i.e., approximately 10-3 molar, or 
up to a few tens of milligrams per liter) in these waters, as discussed in Section 3.1.2.3.3.2 
(Tables 3-10 and 3-15). 
One millimole of a precipitate such as calcite, gypsum, anhydrite, or amorphous silica will weigh 
approximately 100 milligrams, and occupy a volume of approximately 50 microliters (assuming 
the precipitates have density of 2  106 milligrams per liter). Thus for every liter of backfill or 
invert ballast material (0.41 or 0.545 porosities, respectively, from Table 1-3), at least 8,000 
liters of seepage would be required to completely plug the porosity. For 8.5 cubic meters of 
backfill, more than 60 million cubic meters of seepage would be required to plug the porosity. 
This is far more seepage than is likely to enter any emplacement drift during the thermal period 
(CRWMS M&O 2000o, Section 3.9.6), which will last only a few thousand years at most. 
Accordingly, it is very unlikely that the backfill or invert porosity will be plugged, except if the 
precipitates are somehow concentrated in a small portion of the available volume.

 3-70 
The relationship between water volume, and plugged porosity that is described by the foregoing 
argument, has been explored previously by other authors. An example is shown in Figure 3-40. 
3.1.2.3.3.3 Summary of Models for Interactions Involving Backfill 
The foregoing models and discussion show that changes in backfill properties will be limited. 
Water interaction with the quartz backfill will approach equilibrium at elevated temperature 
during the thermal period, for residence times on the order of months or years. However, 
maintaining the equilibrium will not involve much precipitation or dissolution. Even when 
influent seepage waters are evaporatively concentrated with elevated pH, the extent of 
precipitation or dissolution will be limited. (This result is for evaporative concentration of J-13 
water.) The dissolved solids present in the influent seepage, are not likely to accumulate in the 
backfill such that the porosity will be significantly changed. 
3.1.2.3.4 Model for Corrosion of Carbon Steel in the EBS 
Steels and alloys introduced to the potential repository from ground-support materials, drip 
shields, and waste packages will corrode with time, and the aqueous metal concentrations will 
depend on precipitation, coprecipitation, and sorption processes. The important effects of metal 
corrosion on the bulk environment, and the approaches used to represent those effects in the EBS 
process models are summarized as follows: 
 Oxygen in the drift environment will be consumed, decreasing the O2 fugacity while 
corrosion is active. This effect is modeled by converting rates for metal corrosion to 
rates of O2 consumption, and comparing with mass-flux values developed for the Gas 
Flux and Fugacity Model (Section 3.1.2.2). 
 Corrosion products can increase in volume because they have greater molar volume 
than the original metals; this can change the geometry and flow characteristics adjacent 
to metal surfaces. Also, particles of corrosion products can move in the backfill and 
invert and can change flow characteristics in the EBS. These effects are neglected in 
this report because the liquid flux in the drifts will be orders of magnitude smaller than 
the flow capacity of the backfill or invert, so impact on the flow distribution will be 
minor. The potential impact of introduced materials and thermal effects on drainage 
capacity of the drifts is addressed elsewhere in this report (Section 3.1.1) 
 Metal-oxide colloids with affinity for radionuclides can be produced. This can lead to 
increased mobility for certain radionuclides, and is considered in Section 3.1.2.6. 
 Released radionuclides can be retarded by sorption or coprecipitation involving 
corrosion products. This effect has the potential to enhance waste-isolation 
performance, and is addressed in Section 3.1.2.3. 
The following sections present a corrosion-rate model for structural steel, converted to oxygenconsumption 
rate, for comparison to estimates of oxygen availability. The potential consumption 
of oxygen from structural steel vs. other alloys is also compared.

 3-71 
Input Data, Assumptions and Uncertainties 
Corrosion rates for A516 steel have been measured for vapor-phase (not immersion) conditions, 
elevated temperature, and proximity to synthetic groundwater with composition similar to 
evaporatively concentrated J-13 water. The tests were performed with alloy A516 because it had 
been selected as the corrosion-allowance material for the Viability Assessment (VA) WP design. 
Test data for conditions representing the potential repository environment when water returns 
during the thermal period are not available for A572 steel, so the A516 data are used to develop 
rough estimates for steel-corrosion effects. 
A constant corrosion rate for structural steel is assumed for each time period in this model. The 
rate can vary with temperature, pH, and water composition. Modification of the corrosion rate 
from accumulation of corrosion products is assumed to be insignificant because of the tendency 
for spallation of corrosion products from steel surfaces. 
Steel corrosion is assumed to be insignificant until the relative humidity exceeds 70 percent 
(predicted histories for RH are shown in Figure 3-61). This is consistent with the approach used 
to model the Viability Assessment waste-package corrosion allowance material (CRWMS M&O 
1998c, Section 5.5.3.1, pp. 5-31). The threshold humidity could be greater, except that the 
presence of precipitates and salts on the steel can form brines at lower humidity. 
Laboratory data (CRWMS M&O 2000t) suggest an approximate 6- to 7-fold increase in the 
corrosion rate for C1020 steel, once moisture returns to the emplacement drifts, due to microbial 
activity for environmental conditions representative of the potential repository. Carbon steel 
(A572) used for ground-support and invert material is assumed to have similar behavior. 
Additional discussion of microbially influenced corrosion of carbon steel is provided in Section 
3.1.2.4.1.1. Note that this microbially influenced corrosion behavior is for carbon steel, and not 
for the drip shield or waste package materials. This rate of steel corrosion is consistent with the 
Microbial Communities Model for bounding microbial effects on the bulk chemical environment 
(Section 3.1.2.4.2). 
The principal uncertainty associated with this model concerns the effect of steel corrosion on 
decreasing the in-drift oxygen fugacity, and any corresponding change in the steel corrosion rate. 
If measured corrosion rates at atmospheric O2 fugacity are applied to repository conditions, then 
comparison with results from the Gas Flux and Fugacity Model indicates that the O2 fugacity 
could greatly decrease. This could impact other chemical processes in the drift such as 
radionuclide speciation and waste package corrosion. 
Surface Area of Exposed Structural Steel 
The surface area of steel that will be used for ground support and the invert structural supports 
was obtained from design calculations, for which the results are shown in Table 3-5.

 3-72 
Table 3-5. Mass and Surface Area for Structural Steel Used in the Engineered Barrier System 
Zone 
Steel Mass 
(kg/m) 
Surface Area 
(m2/m) Remark 
3 260 6.95 Ground support above springline (full drift)maximum value 
developed for 30 percent of drifts in which rockbolts will be 
installed 
5 140 1.49 Ground support and other structures above invert and below 
springline (full drift) 
6 785 2.50 Ground support and other structures within the invert (full drift) 
Composite 1/2 0 0 
Composite 3/4 260 6.95 
Composite 5/6 925 3.99 
Source: CRWMS M&O 2000t 
Model Uncertainties 
Steel corrosion may proceed rapidly where humidity conditions permit, accelerated by the 
presence of evaporatively deposited precipitates and salts. Corrosion could proceed at a rate 
similar to that measured in laboratory tests under oxidizing conditions, possibly accelerated by 
microbial activity, decreasing the O2 fugacity to sub-oxic or anoxic conditions. Anoxic 
conditions could change mechanisms for degradation of engineered materials, and alter the 
microbial ecology. The importance of this uncertainty depends on the corrosion rate of steel for 
potential repository conditions. The measured data used as the basis for the current model were 
acquired for oxidizing conditions. In the potential repository the corrosion rate will tend to slow 
as the O2 fugacity decreases, and the manner in which this occurs will determine the fugacity. 
This can be evaluated, if necessary, through testing of abiotic and microbially influenced 
corrosion of structural steel under oxygen-deprived conditions. 
Development of Model for the Corrosion Rate of Carbon Steel 
Rate data for general corrosion of A516 steel are taken from laboratory test results (CRWMS 
M&O 2000t). The correlation function developed for these data is 
. .. 
. 
. .. 
. 
 +  + 
+ 
+ = NaCl 3 2 1 0 C b pH b 
273 T
1000 
b b exp r (Eq. 3-10) 
where
r = Penetration rate (m/yr) 
b0 = 10.035 
b1 = 0.4657

 3-73 
b2 = 1.5795 
b3 = 1.8258 
T = Temperature (C) 
CNaCl = Concentration of NaCl in the aqueous phase, expressed as weight percentage 
This model is a curve fit to scattered data, so the uncertainty of the corrosion rate is as much as 
one order of magnitude. This function applies to corrosion in a system that is based on J-13 
water composition; the parameter CNaCl is a surrogate for evaporative concentration of the system 
up to 1,000-fold (chloride is conserved during such evaporation). Oxygen fugacity was not 
measured in the test series, but the operant air mass-fraction may be inferred from the 
temperature, assuming saturated humidity at ambient pressure. A small flow of air was 
circulated in the apparatus, so consumption of O2 by corrosion did not significantly affect the O2 
fugacity in the bulk test environment. 
Results from the Model for the Corrosion Rate of Carbon Steel 
Equation 3-10 is applied to A572 steel in the potential repository environment. Values for 
temperature and RH are obtained from the TH model for the L4C4 location, with the upper 
infiltration distribution (Section 3.1.2.1). These values are specified for composite zones, which 
are defined in Section 3.1.2.1.3. Zone-averaged values are used for conditions in the backfill 
(composite Zone 3/4) and the invert (composite Zone 5/6). The TH conditions are specified for 
finite time periods, which are defined in Section 3.1.2.1.6. 
Zone-averaged pH and NaCl concentrations are obtained from the Chemical Reference Model 
(Section 3.1.2.7). Steel-corrosion rates are calculated separately for the zones and summed. The 
results (CRWMS M&O 2000t) are summarized as follows: 
 Steel present in the drifts will completely corrode in a few decades or at most a few 
hundred years, starting during the thermal period when humidity and water return to 
the potential repository drifts. Depending on the infiltration flux and the location 
within the repository, steel corrosion will begin when relative humidity exceeds 70 
percent, at times from approximately 300 to 2,000 years (Figure 3-61). 
 The calculated rate of steady-state oxygen consumption (forming Fe2O3) exceeds the 
maximum 1-D mass flux of O2 calculated to intercept the 5.5-m diameter drift footprint 
(Section 3.1.2.2). This means either that O2 will be scavenged from gas present in the 
pillars, or the rate of steel corrosion will be limited by O2 depletion, or both. 
 The steel corrosion rate is sensitive to pH, which is predicted to vary by approximately 
2 pH units during the thermal period. Equation 3-10 shows that the rate sensitivity to 
pH is an order of magnitude greater than the sensitivity to temperature, and is greater 
than the sensitivity to salt concentration except for the extremes of solution 
composition calculated in Section 3.1.2.7. 
Results indicate that O2 fugacity in the EBS could be substantially decreased through a 
combination of steel corrosion and the air mass-fraction effect discussed in Section 3.1.2.1. Steel 
will start to corrode when the relative humidity exceeds approximately 70 percent. Corrosion

 3-74 
will first occur when the EBS temperature is near boiling and the air mass-fraction is small, so 
steel corrosion could drive the O2 fugacity even lower. How much lower will depend on the 
corrosion rate response to oxygen fugacity, and the composition of water contacting the steel. 
Steel corrosion rates calculated using Equation 3-10 are upper bounds for the potential repository 
because the tests were ventilated, so O2 availability was not limiting. Additional measured data 
and modeling can further constrain and bound the effects of steel on O2 fugacity in the potential 
repository. 
The important issue for predicting the EBS environment is the relation between the corrosion 
rate for steel and the O2 fugacity in the bulk chemical environment. Improved prediction can be 
based on measurements of the corrosion rate versus O2 fugacity for structural steel. 
Advancement in modeling of gas transport in the host rock could be useful for elucidating the O2 
fugacity in the drift, for a given rate of steel corrosion. However, in modeling of gas transport, 
values of O2 fugacity less than approximately 10-3 atm may be indistinguishable from zero. 
Accordingly, sensitivity of the rate of steel corrosion to O2 fugacity is the principal uncertainty in 
predicting the O2 fugacity in the drifts. 
Microbial activity has been shown to accelerate the corrosion rate for carbon steel by a factor of 
approximately six. Thus, microbial activity could further affect the O2 fugacity in the bulk 
chemical environment. The steel corrosion rate, the O2 fugacity in the bulk chemical 
environment, and the overall rate of microbial activity in the EBS are interrelated. 
Comparison of Oxygen Consumption by Corrosion of Steel versus Other Alloys 
The DS, WP, and pedestal are made of titanium, Alloy 22, and stainless steel. Compared with 
corrosion of carbon steel, corrosion of these materials is slow to consume oxygen and produce 
corrosion products. Slow consumption of oxygen by corrosion of Ti-7 or Alloy 22 could 
contribute slightly to depletion of oxygen in the EBS. However, the potential rate of 
consumption is a small fraction of the oxygen availability calculated from the Gas Flux and 
Fugacity Model (Section 3.1.2.2). 
For example, a DS made of Ti having surface area of 10 m2 per meter of drift, corroding to TiO2 
at a rate of 1 m/yr, would require an oxygen flux of 
Ti 
O 
Ti 2 MW 
MW 
Ar Flux Mass O 2  . = (Eq. 3-11) 
where
A = area (e.g., 10 m2/m) 
r = general corrosion penetration rate (e.g., 106 m/yr = 3.17  1014 m/sec) 
.Ti = Ti density (4.5  103 kg/m3; (CRWMS M&O 2000t) 
MWO2 = molecular weight of O2 (0.032 kg/mol; (CRWMS M&O 2000t) 
MWTi = formula weight of Ti (0.0479 kg/mol; (CRWMS M&O 2000t)

 3-75 
Substituting these values gives a mass flux of 9.5  1010 kg O2/sec per meter of drift, for general 
corrosion of 1 m/yr. This is less than the maximum flux calculated using the model presented 
in Section 3.1.2.2, when it is applied to the drift diameter of 5.5 m. Corrosion of the WP and its 
supports would consume oxygen at a similar rate because the surface area, corrosion rate, and 
stoichiometry are similar. 
In summary, corrosion of the DS and the WP will consume oxygen at a rate that is substantially 
less than the maximum rate for corrosion of structural steel, and will be comparable to, or less 
than the maximum O2 availability from Section 3.1.2.2. Corrosion of the steel will be complete 
long before corrosion of the other alloys; thus, O2 consumption will continue at a lower level for 
the long-term (e.g., beyond 1,000 years). Uncertainty associated with rates of oxygen 
consumption by steel corrosion increases uncertainty of predictions of the in-drift chemical 
environment for a period with duration of tens to hundreds of years. The duration of oxygen 
depletion trades off against the intensity of the effect. 
3.1.2.3.4.1 Results from Scoping Calculations on the Effects of Steel Corrosion 
Order-of-magnitude estimates for steel corrosion rate and O2 consumption (CRWMS 
M&O 2000t) indicate the following: 
 Steel present in the drifts can completely corrode in a few decades or a few hundreds of 
years. The corrosion rate for steel is especially sensitive to increased pH. Equation 3- 
10 shows that the pH effect is greater than the temperature effect and the salt 
concentration effect, except when CNaCl exceeds 1 percent, which occurs only when 
evaporative precipitates are dissolved in Time Periods 3A and 4A (time periods are 
defined in Section 3.1.2.1.6). 
 The rate of steady-state oxygen consumption can exceed the maximum 1-D flux 
calculated to intercept the 5.5-m diameter drift, by applying the mass flux rate 
calculated in Section 3.1.2.2 (CRWMS M&O 2000t). 
3.1.2.3.5 Cementitious Materials Effects Model 
This section describes a bounding model for the effects of cement grout used in rockbolts. The 
model is based on dissolution of cement mineral phases and subsequent interaction of cement 
leachate with CO2 and silica in the drift environment. The potential contribution of chemical 
constituents to the bulk chemical environment is minor, compared with the overall chemistry of 
seepage modified by elevated temperature and gas-phase chemistry. 
Input Data, Assumptions, and Uncertainties 
The rockbolts evaluated for this model are nominally 2.15-m long, 1.125-in. diameter steel bolts 
grouted into 2.5-inch diameter holes (CRWMS M&O 2000t). They will be installed in the rock 
roof in radial arrays of six bolts installed every 1.5 m along drift. The rockbolts will be used in 
addition to steel sets in those areas of the potential repository constructed in the middle 
nonlithophysal unit of the Topopah Spring tuff.

 3-76 
A modified, Type-K (Portland-based) expansive cement will be used for rockbolt anchorage. 
The mix will contain silica fume (5 percent dry weight), an organic plasticizer to improve 
workability (1 percent of dry weight), and a watercement ratio between 0.4 and 0.6 to promote 
strength and durability. To allow for loss to voids in the rock, the total grout used for each 
rockbolt will be limited to three times that needed to fill the annulus around the steel bolt. The 
mass of cement used in the grout will be 22.65 kg per rockbolt (including the three-fold excess). 
With six rockbolts every 1.5 m along the drift opening, the cement usage will be 91 kg/m. 
Saturated permeability of the grout will initially be 0.1 darcy (1019m2) This value can be 
readily achieved for the initially cured grout (CRWMS M&O 2000t). As aging and carbonation 
of the grout progress, permeability is assumed to remain at this value for purposes of calculating 
leaching rates. This is justified because: 1) aging and carbonation cause regrowth of mineral 
phases with reduction of porosity; and 2) additional water flow could occur through flaws that 
form in the grout, but such flow will tend to bypass unreacted cement. 
For as long as the grout remains alkaline (e.g., pH > 10) at the surface of the steel, the rockbolt is 
assumed not to fail in a way that significantly changes the quantity or composition of leachate. 
Centering of the steel bolts in the holes would tend to increase the time until this type of failure 
occurs. Corrosion of the steel bolt accelerates when pH decreases because grout constituents are 
leached or carbonated. 
Potentially important uncertainties associated with this model include the transient effects of 
rockfall, which could cause rapid rockbolt failure and comminution of the grout. Conversely, the 
model does not consider cement carbonation from diffusion of gas-phase CO2, which could 
completely neutralize the alkaline constituents well within the 10,000-yr performance period. 
Input Data and Assumptions for Chemical Modeling of Cement Grout Leaching 
Chemical equilibrium calculations for young cement are performed using the PHREEQC code 
and thermodynamic database, with additional thermodynamic data for cement mineral phases 
taken from the com database associated with the EQ3/6 modeling code (CRWMS 
M&O 2000t). 
The temperature and CO2 fugacity conditions used for modeling cement grout correspond to the 
L4C4 model location with the upper infiltration distribution, from calculations described in 
Sections 3.1.2.1 and 3.1.2.2. 
The cement mineral assemblage shown in Table 3-6 is assumed, based on the assemblage for 
young cement grout (CRWMS M&O 2000t). Mineral assemblages representing modification 
of Portland cement by aging and carbonation are available from the same sources, but they tend 
to produce less alkaline leachate; therefore, young cement minerals are used in this model.

 3-77 
Table 3-6. Grout Mineral Assemblage Used for the Cementitious Materials Model 
Phase 
Weight 
percent 
Mass per Rockbolt a 
(kg) 
Tobermorite (also representing C-S-H [1.7] gel and gehlenite hydrate) 57.5 13.0 
Ettringite 18.0 4.08 
Portlandite 21.5 4.87 
Brucite 3.0 0.68 
From (CRWMS M&O 2000t) 
NOTE: a Mass of each mineral in the grout used for one rockbolt, including 3 excess grout use, totaling 22.65 
kg per rockbolt 
In developing this assemblage, the C-S-H gel and gehlenite hydrate phases in young cement are 
represented by tobermorite, which has better known characteristics and similar elemental 
composition. This assumption is justified because aging of the cement at elevated temperature 
during the preclosure period of 50 years or more will cause the C-S-H gel to crystallize, and 
tobermorite is a likely product. The gehlenite hydrate is a minor phase used to account for 
aluminum in the assemblage that is not incorporated in ettringite. Thermodynamic solubility 
data are not available for gehlenite hydrate, so it is represented by tobermorite (instead of 
ettringite, thereby preserving the ratio between ettringite and portlandite). In the chemical 
calculations, partial carbonation of the grout assemblage is represented by the presence of 
calcite. 
When first installed, the grout will be fluid-saturated from make-up water that will be similar to 
J-13 water in composition. The potential contribution of make-up water to grout chemistry is 
minor because key species such as cations, chloride, and sulfate are much more abundant in the 
cement. 
For significant leachate to form and flow into the drifts, the source of the water will mainly be 
fracture flow because the matrix permeability is low and the availability of water is limited. 
Accordingly, the initial composition of water that interacts with the cement is likely to be that of 
fracture water, and the composition of groundwater from well J-13 is used to represent fracture 
water. The potential contribution of influent water to the composition of cement leachate is 
minor, particularly for the range of plausible water compositions, because leachate composition 
(before equilibration with CO2 or backfill) will be dominated by changes in Ca and sulfate 
concentrations that are controlled by the cement. For the same reason, only the major chemical 
constituents of J-13 water are considered in models of leachate composition. 
Conceptual Development for WaterGrout Chemical Interaction 
The following information is documented in the Physical & Chemical Environment Model report 
(CRWMS M&O 2000t). Chemical equilibrium is assumed along the cement-water reaction path, 
so solubility equilibria control the leachate composition. This model is suitable for slowly

 3-78 
changing, low-flux conditions that will occur in the grout. Reaction of groundwater with the 
grout is assumed to be closed with respect to gas-phase constituents, particularly CO2. This is 
justified for the following reasons: 
 The grout will be very fine-grained, and the pore structure will retain capillary water at 
in situ moisture potentials, so gas saturation will be small. 
 The intrinsic permeability of the grout will be very low, which will provide resistance 
to diffusion. 
 The grout column around each rockbolt will be surrounded by intact rock matrix over 
much of its length. Exposure of the grout to gas-phase CO2 is thus limited by the 
surrounding host rock. 
Flowing water and gas-phase CO2 will most readily access the grout at fracture intersections. If 
the grout is near liquid saturation, access by gas-phase CO2 to unreacted grout will be limited. If 
cracks form in the grout, water and gas will penetrate them, and more surface area could become 
available for diffusion of CO2; however, the leachate composition would still be bounded by the 
closed-system calculations. 
Biotic processes such as those that could be related to the presence of the plasticizer and the steel 
rockbolt, are assumed to have negligible effect on leachate composition and rockbolt lifetime. 
The organic content of the plasticizer admixture is probably biologically recalcitrant (CRWMS 
M&O 2000t). 
Equilibrium with CO2 and Quartz Sand in the Drift Environment 
Once the leachate flows into the drift opening or the surrounding rock, it will be exposed to 
ambient CO2 conditions. Because of the small amount of leachate compared to the total 
percolation through the host rock, open-system conditions are assumed for evaluating leachate 
reaction with CO2 and quartz backfill. 
After it emerges from the grout, leachate will interact chemically with the quartz-sand backfill. 
The interaction will produce silica-buffering activity whereby silica dissolves to form aqueous 
SiO2, which then interacts with water and speciates to produce H3SiO4
 and H2SiO4
2 ions, with 
release of protons that increases acidity. In this model, the leachate is assumed to equilibrate 
with quartz, although the dissolution of quartz is rate-limited at temperatures at or less than 
boiling. This is a reasonable approximation for the following reasons: 
 The rate of quartz dissolution declines exponentially with time, so substantial 
silica-buffer activity will result even if dissolution does not proceed to equilibrium. 
 The alkaline leachate will be greatly undersaturated with respect to quartz. 
 The leachate will readily disperse in the unsaturated backfill because of unsaturated 
flow processes, thus maximizing the surface area available for reaction.

 3-79 
Model Uncertainties 
Cementitious materials such as rockbolt grout may degrade structurally, possibly with rockfall, 
and become available for rapid leaching. A transient pulse of alkaline leachate could result from 
such failure. Models for the effects of cementitious materials that are presented in this report, do 
not explicitly address the breakup of rockbolt grout. However, they show that the chemical 
composition of leachate would be similar to evaporatively concentrated waters that can form in 
the drift, so the engineered barriers would not be exposed to chemical conditions that are not 
already included in the models. In addition, estimates show that small quantities of leachate are 
likely to be produced, allowing margin for greater quantities should the flow area increase due to 
structural degradation. Finally, other models would be used to describe the interaction of water 
with cement grout in a disturbed, particulate state. Diffusion of CO2 into the unreacted cement, 
and equilibration of leachate with the drift environment, would be more important in such a 
model and would tend to moderate the leachate composition. 
3.1.2.3.5.1 Development of the Cementitious Materials Model 
The Cementitious Materials Model is used to evaluate the potential impact on the EBS bulk 
chemical environment from percolating water that contacts grouted rockbolts and subsequently 
interacts with quartz-sand backfill and gas-phase CO2. Grouted rockbolts are planned for use in 
the portion of the potential repository that is constructed in the middle nonlithophysal tuff. The 
Cementitious Materials Model does not address mixing of cement-affected waters with seepage 
in the drift, nor does it address thermal effects on flow in the host rock. These are considered in 
the other parts of the Physical & Chemical Environment Model (CRWMS M&O 2000t). 
The PHREEQC Code 
The U.S. Geological Survey (USGS) solution equilibrium modeling code PHREEQC 
(pH-REdox EQuilibrium equation program in C language) was used for the Cementitious 
Materials Model to assess three types of geochemical effects: 
 Changes in water and solid composition resulting from groundwater contacting grout 
 Effects from grout-modified groundwater interacting with the CO2 in the gas phase in 
the emplacement drift 
 Effects of the grout- and gas-modified groundwater contacting backfill material 
Two capabilities of PHREEQC were used for this model: 1) speciation and saturation-index (SI) 
calculations, and 2) reaction-path calculations involving specified irreversible reactions and 
mineral- or gas-phase equilibria. Different CO2 conditions were used to represent formation of 
leachate within the grout column and reaction of the leachate with the environment outside: 
 Grout system closed with respect to CO2 (i.e., the CO2 available within the grout 
column is that dissolved in the influent water) 
 Leachate and quartz-sand system open with respect to CO2 (i.e., fugacity is held 
constant so that no reaction extent is limited by the availability of CO2)

 3-80 
Analysis of Flux Through a Water-Saturated Grout Cylinder 
Flow through a saturated vertical grout cylinder is estimated using Darcys Law (CRWMS 
M&O 2000t). Substituting the listed values for grout geometry, saturated permeability of 
10-19 m2, and a unit hydraulic gradient yields a flow rate through one vertical grout cylinder of 
less than 0.1 mL/yr. Allowing for flow through several grout faces (for example, if the rock 
containing a rockbolt is broken up and falls into the drift) each rockbolt will contribute less than 
1 mL/yr leachate to the drift environment. 
The time to completely dissolve a mineral phase for the stepwise, steady-flow conditions 
developed in Section 3.1.2.1 is given by 
SQ 
m 
t = (Eq. 3-12) 
where m is the mass present, S is the solubility, and Q is the flow rate of water. Using the 
ettringite solubility of 10.1 kg/m3 at 90C, and a mass of 4.08 kg ettringite per rockbolt, the time 
to dissolve the ettringite with a flow rate of less than 1 mL/yr is on the order of half a million 
years. This may be unrealistic, but the practical implication is that ettringite will be present for 
thousands of years, especially if the grout cylinder remains intact. The flux-scaling approach 
presented subsequently offers an alternative that addresses the possibility that the grout will be 
fractured and subject to the same flux as the surrounding rock. 
Estimating the Leachate Flow Rate from Flux-Scaling 
An alternative bounding approach is to consider the seepage flux intercepted by the grout at the 
drift wall. Taking the interception area for one rockbolt as the cross-sectional area of grout, the 
flow of water that could interact with the grout is 
seep grout Aq Q = (Eq. 3-13) 
where
Qgrout = flow of water interacting with one rockbolt (m3/sec) 
A = exposed area of grout (2.53  103 m2) 
qseep = seepage flux calculated from seepage inflow and drift geometry (m2/m-sec) 
For the 300- to 700-yr time period (defined in Section 3.1.2.1.6), the seepage inflow is 2.51  
10-6 kg/sec per meter of drift (Table 3-7). Dividing by the density of water (965.254 kg/m3 at 
90C) and the drift diameter (5.5 m) and multiplying by 2 for full-drift inflow gives a seepage 
flux of qseep = 29.8 mm/yr. Substituting in Equation 3-13 gives a flow rate of approximately 75 
mL/yr per rockbolt. Implementation of this calculation for all time periods used in chemical 
modeling (except Time Period 1, for which there is no seepage flow) is shown in Table 3-7.

 3-81 
3.1.2.3.5.2 Results from the Cementitious Materials Model 
Calculations show that leachate composition will differ strongly from the influent fracture-water 
composition for at least several thousand years. For the mineral assemblage and environmental 
conditions considered, the solubilities of portlandite and ettringite cause them to be completely 
leached before tobermorite, brucite, and calcite are leached. As temperature increases, 
portlandite solubility decreases, whereas ettringite solubility increases. The PHREEQC 
modeling results show that for temperatures greater than approximately 50C, ettringite is the 
most soluble constituent phase and will strongly affect leachate composition until completely 
dissolved. 
Leachate composition will be controlled by the dissolving phases until they are completely 
dissolved. Any changes in leachate composition during this period will be caused primarily by 
direct temperature and CO2 effects on leachate composition rather than by mineralogical changes 
in the cement phases. 
Table 3-7. Summary of Leaching Conditions for Rockbolt Cement Grout (L4C4 Location; Upper 
Infiltration)
Time 
Period 2 
Time 
Period 3 
Time 
Period 4 
Time 
Period 5 
Time Period from (yr) 300 700 1500 2500 
To (yr) 700 1500 2500 10000 
Temperature (in Zone 1/2 representing the host rock; C) 90.05 88.42 79.96 51.69 
Water Density (kg/m3) 965.254 966.390 971.799 987.259 
Zones 3 and 4 Inflow Rate (kg/m-sec) 2.51E06 1.11E05 5.65E06 8.67E-06 
Seepage Flux (m/sec) 9.46E10 4.16E09 2.11E09 3.19E09 
Seepage Flux (m/yr) 2.98E02 1.31E01 6.67E02 1.01E01 
Scaled Flow per Rockbolt (m3/yr) 7.53E05 3.31E04 1.68E04 2.55E04 
Source: CRWMS M&O 2000t 
NOTE: Zones are defined in Section 3.1.2.1.3, and time periods are defined in Section 3.1.2.1.6. 
Sensitivity of Grout-Leachate Composition to Temperature, CO2, and Quartz Sand 
The calculations show that prior to contact with atmospheric CO2 and quartz backfill, the grout 
leachate is highly alkaline (Table 3-8). The alkalinity is caused primarily by dissolved calcium 
derived from portlandite. The leachate pH decreases with increasing temperature because of 
portlandite retrograde solubility.

 3-82 
Table 3-8. Grout Leachate pH for Equilibrium with Cement (Closed System) and for Equilibrium with 
Quartz and CO2 in the Drift Environment (Open System) 
Temperature 
Grout Leachate pH 30C 50C 70C 90C 
Before Reaction with CO2 or Quartz 12.3 11.6 11.1 10.5 
After Reaction with Quartz and Gas- 
Phase CO2 at 9.5 ppmv 
9.2 8.8 8.6 8.7 
After Reaction with Quartz and Gas- 
Phase CO2 at 952 ppmv 
8.0 7.8 7.6 7.7 
After Reaction with Quartz and 
Gas-Phase CO2 at 9520 ppmv 
7.4 7.4 7.1 7.2 
Source: CRWMS M&O 2000t 
At higher temperatures, the solution is calculated to contain more dissolved sulfate (as much as 
approximately 1200 mg/L) from dissolution of ettringite, with moderate increases in dissolved 
aluminum and calcium. 
Evolution of Leachate Composition for the Reference Model 
Modeling the evolution of leachate composition is based on the time steps used in the TH Model, 
with corresponding temperatures and fluxes (Section 3.1.2.1) and CO2 fugacity values 
(Section 3.1.2.2). As discussed previously, the cementwater equilibration is assumed to be 
closed to gas-phase CO2, while the leachate-quartz-CO2 equilibrium is assumed to be open. The 
water compositions predicted to result from grout-leachate and leachate-sand equilibria are 
presented in Table 3-9. Note that for Time Period 1 (defined in Section 3.1.2.1.6), the TH model 
predicts zero seepage. 
Upon equilibration of the leachate with CO2 and quartz-sand backfill, quartz dissolves, pH 
decreases, and calcite precipitates (Table 3-9). The magnitudes of calcite precipitation and 
quartz dissolution are sensitive to temperature, but are relatively insensitive to CO2 fugacity.

 3-83 
Table 3-9. Evolution of Leachate Composition with Time, for Reference Model Conditions (L4C4 
Location; Upper Infiltration) 
Time Period 2 
300700 yr 
T = 90.05C 
PCO2 = 10 ppmv 
Time Period 3 
7001500 yr 
T = 88.42C 
PCO2 = 9 ppmv 
Time Period 4 1500 
2500 yr 
T = 79.96C 
PCO2 = 20 ppmv 
Time Period 5 
2500-5000 yr 
T = 51.69C 
PCO2 = 53 ppmv 
Grout 
Equil. 
Quartz 
Equil. 
Grout 
Equil. 
Quartz 
Equil. 
Grout 
Equil. 
Quartz 
Equil. 
Grout 
Equil. 
Quartz 
Equil. 
Al (mg/L) 218.7 218.7 203.7 203.7 0.0 0.0 0.0 0.0 
CO2 (total) (mg/L) 0.4 0.9 0.4 0.9 0.4 2.5 0.3 21.4 
Ca (mg/L) 894.2 674.9 859.3 633.3 353.9 33.5 521.4 5.1 
Cl (mg/L) 7.1 7.1 7.1 7.1 7.1 7.1 7.1 7.1 
F (mg/L) 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 
K (mg/L) 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 
Mg (mg/L) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 
NO3 (mg/L) 8.78 2.0 8.78 2.0 8.78 2.0 8.78 2.0 
Na (mg/L) 45.7 45.7 45.7 45.7 45.7 45.7 45.7 45.7 
SO4 (mg/L) 1186.3 1186.3 1106.6 1106.6 18.4 18.4 18.4 18.4 
Si (mg/L) 0.0 209.8 0.0 210.4 0.0 203.3 0.0 110.7 
pH 10.5 8.7 10.5 8.7 10.8 8.9 11.6 8.9 
Portlandite dissolved (g/L) 0.05 0.1 0.85 1.2 
Ettringite dissolved (g/L) 10.1 9.4 Note A Note A 
Quartz dissolved (g/L) 0.45 0.45 0.43 0.24 
Calcite precipitated (g/L) 0.55 0.57 0.80 1.29 
Source: CRWMS M&O 2000t 
NOTES: Time periods are defined in Section 3.1.2.1.6. 
A Ettringite is completely dissolved after 1500 years. 
Cement Mineral Dissolution Times for the Reference Model 
The grout-dissolution model is used in conjunction with flow rates from the reference model to 
calculate the time until complete dissolution of ettringite and portlandite. The dissolution rate of 
an individual mineral phase is estimated by multiplying the flow of water through the grout 
(from the flux-scaling model discussed previously) by the calculated solubility at the prescribed 
temperature. 
The results show that the ettringite will be depleted in 1,500 years for the reference model 
(L4C4 location, upper infiltration distribution). Dissolution of the portlandite under the same 
conditions could require 10,000 years or more. These results do not consider the excess grout, 
which could increase the leaching times by as much as a factor of three. The time until complete 
dissolution is controlled by temperature, and to a lesser extent by CO2 
Summary of Cementitious Materials Model Results 
The grout permeability is small, which limits chemical interaction of the grout with the EBS 
environment while increasing the longevity of the grout to dissolution. Very small flow rates (a 
few mL/yr per rockbolt) are obtained using the saturated permeability of the grout. A more

 3-84 
conservative bounding approach is presented, based on the ratio of the rockbolt grout 
cross-sectional area to the drift diameter. This method produces flow rates on the order of 75 to 
330 mL/yr per rockbolt, or a few percent of the total seepage inflow to the drifts. For as long as 
the grout remains substantially intact inside the rockbolt holes, the flow of water that interacts 
directly with grout is projected to be a small fraction of the seepage inflow into the drifts. 
Conservative estimates are developed for the chemistry of grout leachate. Leachate pH values of 
10.5 to 11.6 are predicted; these are readily buffered on contact with CO2 and quartz-sand 
backfill in the drift environment. In the model, the leachate pH depends primarily on the 
solubility of portlandite, which increases at lower temperature, thus causing the leachate pH to be 
elevated at later stages of cooldown. Depending on the solubility of ettringite, sulfate 
concentrations as great as 1200 mg/L are predicted. 
It is noted that leachate contact with gas-phase CO2 can occur anywhere along the flow path 
through the backfill, and does not require that CO2 penetrates the grout, or the rock around the 
grout. In the backfill, uniform and constant CO2 fugacity is imposed as a condition on the 
chemical model. The use of constant CO2 fugacity is supported by the analysis of CO2 balance, 
discussed in Section 3.1.2.7.5.7, which shows that cement leachate equilibration is a minor 
addition to the cumulative CO2 budget (Table 3-32). 
After the leachate reacts with CO2 and quartz-sand backfill, pH of approximately 8.5 is 
predicted. Accordingly, elevated pH values for leachate will not apply at the DS or at the WP 
because of mixing with other water in the backfill and because of reaction with the quartz and 
gas-phase CO2. 
Neither ettringite nor portlandite completely dissolves until at least 1,500 years, depending on 
the water flow rate and the temperature. Other cement phases (e.g., tobermorite) are relatively 
stable to dissolution and tend to alter to even more thermodynamically stable minerals. These 
results are based on the reference TH Model (Section 3.1.2.1; L4C4 location, upper infiltration 
distribution) which produces conservatively high estimates for liquid flow into the drifts, and 
therefore tends to maximize the amount of leachate produced. 
3.1.2.3.6 Introduced Material Model Validation 
The introduced materials submodels consist of the kinetic model for water-quartz interaction, the 
model for seepage-backfill interaction at high ionic strength, an empirical model describing 
corrosion rates for carbon steel, and the Cementitious Materials Model. Each of these is a 
conservative, bounding model in the sense that chemical interaction and its potential deleterious 
effect on the bulk chemical environment are maximized. The models are valid for their intended 
uses in FEP screening, and support of the design basis. 
Kinetic Model for Water-Quartz Interaction 
This model implements a widely used rate law for quartz precipitation, from published scientific 
literature. The purpose of the model is to establish whether quartz kinetics is an important 
influence on water composition in the EBS, and should be implemented in the EBS Chemical 
Reference Model (Section 3.1.2.7). Surface area information is provided from measured data for

 3-85 
the Overton Sand, and underestimates the total surface area because the smallest size fraction is 
neglected, and the sand particles are assumed to be spherical. 
Kinetic rate laws tend to be uncertain, but the behavior of quartz is well understood compared to 
many other minerals. The model shows that water-quartz interaction approaches solubility 
equilibrium, for contact times of months to years in the backfill during the thermal period, as 
calculated by the Thermal-Hydrology Model (described in Section 3.1.2.1). Accordingly, 
water-quartz equilibrium is used in the EBS Chemical Reference Model. This approximation is 
conservative in the sense that precipitation of dissolved silica causes loss of silica buffering, with 
resulting increase of pH, which is conservative with respect to potential corrosion of the drip 
shield (which may increase at higher pH). The validity of this approximation is also supported 
by the exponential form of the rate law, which ensures that much of the water-quartz interaction 
occurs relatively soon after contact. Based on this discussion, it is concluded that the model is 
valid for its intended use in FEP screening, and support of the design basis (Table 3-A). 
Seepage-Backfill Interaction Model 
The seepage-backfill model is based directly on the High Relative Humidity (HRH) Salts Model 
developed in Section 3.1.2.5. Predictions from the HRH Salts Model are compared with 
experimental data in Section 3.1.2.5.3.8, and found to valid for approximating pH (to within one 
pH unit), ionic strength (to a factor of 2), solubilities for pure salts (to a factor of 2), and 
concentrations for major chemical species (to an order of magnitude). The tendency for quartz to 
precipitate in the sand backfill, during evaporative concentration of water in the drifts, is 
calculated along with the water composition. Chemical equilibrium is assumed, which is a 
conservative approximation because quartz precipitation can be relatively slow. 
For ranges of evaporative concentration and temperature, the model calculates whether quartz 
tends to dissolve or precipitate. From the foregoing discussion, it is concluded that the model is 
valid for its intended use in FEP screening and support of the design basis (Table 3-A). This 
model depends on the assumptions which are associated with extension of the Pitzer database for 
the HRH Salts Model (Section 3.1.2.5). Accordingly, the results are designated to-be-verified. 
Steel Corrosion Rate Model 
The correlation model for the corrosion rate of carbon steel as a function of pH, NaCl 
concentration, and temperature, is based on laboratory measured data for unsaturated conditions. 
The range of test conditions closely approximates the environment to which steel ground support 
will be exposed in the emplacement drifts. The test conditions were oxidizing, with atmospheric 
composition in the air fraction. This constitutes a conservative approximation that tends to 
maximize the corrosion rate, because some depletion of O2 fugacity can be expected to occur in 
the potential repository when oxygen is consumed by corrosion. Based on this discussion, the 
model is valid for its intended use in FEP screening and support of the design basis (Table 3-A). 
The test data were acquired for a steel alloy that is slightly different from the steel proposed for 
ground support, and the application of these data is to-be-verified. 
Also, laboratory tests have shown that microbial activity increases the corrosion rate for carbon 
steel, by a factor of 6 to 7 (see Sections 3.1.2.3.4 and 3.1.2.4.1.1 for discussion of these test

 3-86 
results). This result could be a lower bound on the microbial effect because these were closed 
reactors that may have become anoxic. The applicability of these results to repository conditions 
is also to-be-verified. 
Cementitious Materials Model 
This model calculates the composition and flow rate of leachate that has interacted with 
fully-grouted rockbolts. (Such bolts would be used only in the portion of the potential repository 
that is constructed in the Tptpmn unit, in the current design concept.) 
A mineral assemblage is selected based on young cement (Hardin 1998) with the exception 
that the gel phase is replaced by tobermorite, a compositionally similar crystalline phase. Use of 
a modified young is a conservative approximation because young cement alters to less 
alkaline, carbonate minerals over tens or hundreds of years, on exposure to atmospheric CO2. 
The result of the approximation is that alkaline leachate is produced for thousands of years from 
dissolution of portlandite. Other conservative approximations include equilibration of the 
leachate with cement minerals, and closed-system conditions whereby gas-phase CO2 does not 
interact directly with the grout. 
The flow rate of leachate associated with a rockbolt is calculated from seepage estimates, which 
are taken from the conservative TH models described in Section 3.1.2.1. Interaction of seepage 
with cement grout is calculated from the ratio of the grout annulus area of the rockbolt, to the 
plan area of the drift. This is a conservative approximation because the saturated hydraulic 
conductivity of the grout will be very small. If saturated permeability were used to limit the flow 
rate of leachate, the result would be orders of magnitude less than the area ratio result. 
Based on this discussion, the Cementitious Materials Model is valid for its intended use in FEP 
screening and support of the design basis. The model does not consider diffusive transport of 
alkaline species from the interior of the grout to the surface, nor transport of gas-phase CO2 to 
the interior. 
3.1.2.4 Microbial Effects Models 
This section presents models for evaluating potential changes in the EBS bulk chemical 
environment from microbial activity. The Threshold Conditions Model establishes the 
environmental conditions that permit microbial growth and activity, while potential changes in 
the bulk chemical environment are bounded by the Microbial Communities Model. The intended 
use for these models is direct support of TSPA. Other potential effects of microbial activity, 
such as microbially facilitated transport of radionuclides, are acknowledged but not addressed by 
this report. 
The greatest potential for microbial effects on potential repository performance is microbially 
influenced corrosion (MIC) of waste package materials. Timing of the onset of MIC is 
addressed by the Threshold Conditions Model. The rate of MIC for the WP, along with other 
aspects of WP performance, is reported in the Waste Package Degradation Process Model 
Report (CRWMS M&O 2000n).

 3-87 
3.1.2.4.1 Threshold Conditions Model for Microbially Influenced Corrosion 
The following discussion is taken from the Physical and Chemical Environment Model 
(CRWMS M&O 2000t). There are approximately 104 to 105 total bacteria per gram of Yucca 
Mountain tuff at the potential repository horizon, which is low compared to microbially rich 
environments (e.g., marine sediments, agricultural soils) that may contain as many as 109 
bacteria per gram, but high compared to barren environments such as arid-desert sands, or recent 
volcanics. Over time, the microbiological community in the potential repository may accelerate 
degradation of introduced materials, including the drip shields and waste packages. 
This section provides a survey of available literature, which justifies the selection of RH greater 
than 90%, and temperature less than 120C, as conditions necessary for microbial growth and 
activity. 
3.1.2.4.1.1 Conceptual Basis for Factors Limiting Microbial Activity 
Bacteria are ubiquitous in nature, but they require the following for growth and metabolic 
activity: favorable environmental conditions, nutrients, and energy sources. All of these have 
been observed to limit microbial growth and metabolic activity in Yucca Mountain tuff or in 
analogous settings. Additional discussion of these limitations is provided below. 
Water Availability 
Experiments have determined that the primary environmental factor limiting microbial growth in 
the Yucca Mountain welded tuff host rock is lack of water (CRWMS M&O 2000t). The 
experiments duplicated ambient environmental conditions at Yucca Mountain except for 
100 percent saturation with tuffaceous groundwater. (Saturated conditions are not expected in 
the potential repository, except for possible seepage caused by locally heavy flow in fractures.) 
Under these saturated conditions, microbial growth increased to 106 to 107 aerobic 
carbon-degrading cells per milliliter groundwater. Many types of microorganisms can survive 
long periods of desiccation because of specialized dormant structures such as spores, cysts, and 
resting stages. Free water, however, is required for resumption of active metabolism and growth. 
Microbiologists commonly use the term water activity (aw) to describe microbial water 
relationships in complex environments. Water activity has been defined as a ratio of vapor 
pressures, equivalent to relative humidity. Most bacteria require aw > 0.9 for active metabolism; 
a specialized group of salt-tolerant bacteria (halophiles) can remain active at aw values of 0.75 or 
less. Fungi are generally more tolerant of desiccation and remain active to aw as low as 0.55 but 
have specific metabolic requirements (CRWMS M&O 2000t). These values define bounding 
values for the relative humidity at which microbial activity in the potential repository can resume 
during cooldown. 
Elevated Temperature 
Elevated temperature can also limit microbial activity and growth. Mesophiles that inhabit 
temperate environments such as the potential repository host rock (before or after potential 
repository heating) typically have growth optima in the range of 25 to 40C (CRWMS 
M&O 2000t). Microorganisms found in extreme environments can exhibit higher optimal

 3-88 
growth temperatures. The consensus among workers in this field is that the upper limit to any 
bacterial growth is approximately 120C (CRWMS M&O 2000t). Where temperatures in the 
potential repository exceed 120C, no bacterial activity will be possible (although sporulated 
bacteria could survive such conditions). At temperatures less than 120C hyperthermophiles can 
become active if they are present and if water availability and other environmental conditions 
permit. Whether hyperthermophilic organisms are present at Yucca Mountain, or will be 
introduced into potential repository drifts by potential repository construction, is not determined. 
Gamma Irradiation 
Another factor that will limit bacterial growth in the potential repository is ionizing radiation 
generated by decaying radioactive waste. Because radiation must penetrate the waste package 
wall to affect the EBS environment, only gamma radiation is considered. Resistance of microbes 
to gamma irradiation varies depending on the species. Bacterial spores are relatively radiationresistant, 
and a dose of 0.3 to 0.4 Mrad is required to effect 90 percent kill. Most vegetative cells 
(active, nonsporulated) require only a tenth of this dose for the same rate of kill. Generally, a 
gamma dose of 2.5 to 3 Mrad is used to sterilize food and medical instruments. Gamma 
radiation doses will be on the order of 100 rad/hr immediately following emplacement of waste 
packages containing nuclear fuel assemblies. Thus, a dose of 1 Mrad could accumulate on the 
surface of waste packages within a period of just more than a year. 
When considering the effects of irradiation on activity and growth, it is important to consider the 
shielding provided by backfill, ground support materials, and rock. Organisms located a few 
meters from the waste packages will receive a much smaller gamma dose than will those at the 
waste-package surface. These organisms could readily re-enter the EBS during cooldown when 
liquid flux resumes; therefore, even if much of the EBS is sterilized by high radiation, later 
recolonization will occur. It can occur rapidly (relative to the 10,000-yr performance period) 
when liquid flux conditions are conducive to transport and environmental conditions (water, 
heat, radiation) are within ranges that permit growth. 
Nutrient Availability 
Phosphate  Testing has shown that when sufficient water is available, and temperatures and 
radiation are within ranges conducive to growth, phosphate availability is the primary factor that 
limits bacterial growth in cultures containing Yucca Mountain tuff. Phosphate is a principal 
component of nucleic acids (DNA and RNA) and phospholipids, which are major constituents of 
biological membranes. Phosphate is therefore an essential nutrient for activity and growth of all 
biological organisms. 
Phosphate is the predominant phosphorous species in groundwaters, and UZ waters contain low 
concentrations. J-13 water is an analogue to fracture waters in the host rock, and using standard 
methods of analysis, the phosphate concentration has been found to be approximately 120 g/L 
(CRWMS M&O 2000t). 
Experimental studies have shown that under saturated conditions, when Yucca Mountain tuff is 
used as a source of microbial inoculum and incubated in synthetic Yucca Mountain groundwater, 
microorganisms mobilize the phosphate contained in the tuff to support growth to densities of at

 3-89 
least 106 bacteria per milliliter of water (CRWMS M&O 2000t). When such cultures are 
amended with added phosphate, bacterial densities increase well beyond 106 to 107 bacteria per 
milliliter. Thus, it is likely that any EBS material that contains biologically labile phosphate will 
stimulate microbial growth beyond bacterial densities that are achieved with tuff only (other 
environmental conditions permitting). Other macronutrients (those used at higher 
concentrations), including carbon, sulfur, and nitrogen, have been found not to be limiting for 
growth to abundances up to 109 cells per milliliter. 
It is important to note that phosphate is cycled in microbial communities. This means that the 
same phosphate mass inventory can continue to sustain the activity of a microbial population 
even as the abundance of other nutrients fluctuates and despite the birth and death of individual 
organisms. For limiting microbial activity on the waste-package surface, this fact lowers the 
threshold for allowable phosphate transport to the waste package, relative to chemical species 
that are consumed such as energy sources. 
Investigation of phosphate limitation has focused exclusively on those types of organisms that 
degrade organic carbon (as a carbon source) and utilize oxygen (as a terminal electron acceptor). 
Investigations in progress are examining the growth of Yucca Mountain anaerobes, which use 
alternative electron acceptors such as sulfate, and are capable of using CO2 as a carbon source 
for growth. It is expected that these organisms will also be phosphate-limited. 
Carbon Sources  Investigations using Yucca Mountain tuff have examined only the growth of 
aerobic carbon-degrading organisms. These include organisms capable of obtaining carbon from 
the CO2 in air or equivalently from dissolved inorganic carbon. This selection is justified 
because there are no other significant natural sources of carbon in the host rock nor sources of 
organic carbon in the EBS, except the possibility of small concentrations of dissolved organic 
carbon in percolating groundwater. 
Like phosphate, the carbon contained in the biomass is cycled in microbial communities; thus, 
organic carbon may become available for supporting increasingly diverse types of organisms 
once a microbial community becomes established. Because of the availability of CO2 in the gas 
phase, it cannot be argued that a carbon source is limiting for any type of microbial activity for 
any location in the potential repository where conditions favor the growth of carbon-reducing 
bacteria. 
Energy Sources  Bacteria generally extract energy from the environment by mediating 
thermodynamically favored oxidation-reduction reactions. As part of a subsistence strategy, the 
organisms may alter their environment, and the alteration often has the effect of promoting 
solubilization of reactants. This is one important basis for microbially influenced corrosion 
(MIC) in which bacteria on metal surfaces change the local environment. 
Energy sources for bacteria exist in the host rock, as is evident from the existing population of 
viable organisms. The host rock contains reduced iron, manganese, and traces of other 
oxidation-reduction-sensitive metals (CRWMS M&O 2000t) that can act as electron donors. For 
potential electron acceptors, the environment has abundant oxygen in the gas phase, and UZ 
waters contain available sulfate and nitrate.

 3-90 
The potential repository environment will therefore be associated with some level of microbial 
activity after the return of moisture during cooldown. If the potential repository is constructed 
without adding electron donors or acceptors other than those already qualitatively present in the 
host rock, the types of energy sources will not change. The changes that will occur include the 
distribution of water, the effects of heat, the composition of the aqueous phase, and the relative 
amounts and spatial distribution of potential nutrients represented by introduced materials. 
The microbial population in the host rock may be capable of alternative exploitation strategies if 
environmental and nutrient conditions are substantially modified. This is the reason why other 
classes of organisms that are present in the host rock, particularly sulfate-reducing forms, are 
under investigation. Also, the in situ population will be augmented by exogenous organisms 
during construction and operation. The combined types are currently considered capable of 
metabolizing any energy sources present in the potential repository. 
Conceptual Basis for Microbially Influenced Corrosion of CRMs 
MIC can be important to waste isolation without significantly altering the bulk chemical 
environment. The hallmark of MIC is the establishment of a biofilm or accretion of a 
consortium of bacteria on a metal surface. Concentrations of various chemical species are 
greater within the micro-environment than in the bulk environment. As energy sources, the 
CRMs are electron donors similar to steel, but are less available for biological use because of 
their greater resistance to attack. Some alloy components (e.g., Ti) are spontaneously and 
abiotically oxidized in aerobic environments, thus forming products with low solubility and 
minimal availability to microorganisms, which is the basis for MIC resistance. 
Conceptual Basis for Interaction of Bacteria with EBS Materials 
The following discussion is included as background information and shows that under certain 
environmental conditions, microbial activity can degrade all of the materials present in the EBS. 
Carbon Steel  Historically, MIC of metals has been attributed to a single class of organisms: 
the sulfate-reducing bacteria. Currently, MIC is recognized as a group of interacting processes 
carried out by multiple classes of bacteria. Bacteria that secrete exopolysaccharides into the 
extracellular environment form slime capsules that obstruct the free diffusion of oxygen to the 
metal surface, thus creating a reducing environment. This condition is accentuated by aerobes 
within the slime layer that consume oxygen. The creation of anoxic regions within the slime 
layer facilitates the growth of anaerobic sulfate reducers. Differential oxygen gradients within 
the slime film contribute to creation of anodes, where metal dissolution occurs. In the aerobic 
regions of the film, iron and sulfur oxidizers may oxidize dissolved metal components and 
generate mineral acids. These conditions degrade the protective metal oxide film and produce 
pitting. These processes require the formation of biofilms and sufficient water availability to 
prevent desiccation. 
Electrochemical batch studies have shown that, for the experimental conditions employed, Yucca 
Mountain bacteria can increase corrosion rates of carbon steel alloy C1020 by a factor of 6 to 7 
(CRWMS M&O 2000t). This result may be a lower bound on the corrosion rate enhancement 
because the experimental batches were closed, and not replenished with reactants of any type.

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Continual-flow (i.e., replenished) experiments using synthetic J-13 groundwaters and nonsterile 
Yucca Mountain tuff are underway. Chemical analyses of the surfaces of corroded carbon steel 
alloy C1020 coupons showed accretion of calcite, greenalite (a reduced-iron silicate 
oxyhydroxide), rancieite (a calcium-manganese oxide), and an unidentified iron-silicate phase. 
A particulate phase detached from the coupons, and consisted of spalled corrosion products and 
tuff fines as well as precipitated minerals from the aqueous phase. In ongoing work, these results 
are being compared to identical systems containing sterilized tuff (i.e., not containing Yucca 
Mountain or other bacteria) to determine the contributions of microbial activity. 
It is noted that the degradation rate for carbon steel will be limited by the effective surface area 
occupied by biofilms, which may be less than the total exposed surface area of the steel 
components. 
Host Rock Degradation  As discussed previously, tuff can serve as a source of phosphate for 
the growth of Yucca Mountain organisms. The potential Topopah Spring host rock contains 
approximately 0.007 weight percent phosphate (CRWMS M&O 2000t). Microbial processes 
that produce acidity could enhance the extraction rate for phosphate. Manganese has been 
shown to solubilize from Yucca Mountain tuff in the presence of Yucca Mountain 
microorganisms, while iron contained in tuff is not mobilized to the same extent. 
Cementitious Materials  Certain types of microorganisms, such as sulfur-oxidizing bacteria, 
are capable of degrading cementitious materials by producing acids. Sulfur-oxidizing bacteria 
have been found in every sample of Yucca Mountain tuff tested for their presence (CRWMS 
M&O 2000t). In environments where reduced sulfur compounds are limited (e.g., at the ground 
surface), nitric acidproducing bacteria have been found to play a role in cement degradation. 
Concrete can also be corroded by organic acids produced by fermentative bacteria under 
reducing conditions. Fungi have also been implicated in concrete degradation and are present in 
Yucca Mountain tuff as well (CRWMS M&O 2000af). Notwithstanding such observations, 
microbial degradation of cement in the potential repository will be limited, because the use of 
cement is limited to rockbolt grout in only part of the waste emplacement area, and because other 
conditions associated with concrete degradation (e.g., organic carbon, and anoxic-oxic 
interfaces) will be scarce. 
3.1.2.4.1.2 Input Data, Assumptions, and Uncertainties for Threshold Model 
The following assumptions and the attendant uncertainties, are incorporated in the threshold 
model: 
Electrical Equipment and Removal of Organics  Haulage will be electrically driven (i.e., no 
hydrocarbon fuels will be used in the emplacement drifts). Hydrocarbon-based lubricants and 
other organic materials will be used in construction equipment, but will be recovered from the 
drift environment prior to waste emplacement. 
Purity of Backfill and Invert Materials  Backfill and invert materials will be washed and 
contain only trace amounts of organic matter. In addition, backfill material will contain only 
trace amounts of phosphate and electron acceptors such as sulfate.

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Organic Carbon Content of Host Rock  The organic carbon of the host welded-tuff rock units 
is zero, or insignificant as a carbon source to support microbial activity and growth. 
Microbial Growth and Activity on Waste-Package Surface  Microbially influenced 
corrosion of the waste-package surface (Alloy 22) may be negligible for humidity conditions 
(not liquid-saturated or dripping), even for relative humidity greater than 90 percent, as long as 
liquid groundwater (with its endogenous complement of phosphate and other nutrients) has not 
penetrated the drip shield. Investigations using Yucca Mountain tuff and unsaturated humidity 
conditions are currently under way to determine whether MIC can occur for these conditions. 
The results are expected to better define the capability of Yucca Mountain organisms to colonize 
surfaces as a function of relative humidity. 
Microbial Effect on Carbon Steel Corrosion Rate  Available test data show a six-fold 
increase in the corrosion rate for C1020 steel, relative to abiotic rates measured with sterile 
controls. Carbon steel used for ground support and invert material has a similar composition, 
and is assumed to exhibit similar corrosion behavior. 
3.1.2.4.1.3 Threshold Conditions Model Description 
Water-activity, temperature, and radiation-dose conditions can be combined to formulate limits 
for microbial activity. Published results based on extreme behaviors of known organisms are 
used as a guide where site-specific data are unavailable. More precise estimates based on 
characterization of organisms at Yucca Mountain are unwarranted because of uncertainty about 
which types of organisms will be present, and because of the potential for biological adaptation. 
Threshold Conditions for Microbially Induced Corrosion of the Waste Package 
 Growth and activity are nil until the waste-package surface temperature drops to less 
than 120C 
 Growth and activity on the waste-package surface are limited, and may be negligible, 
even after relative humidity increases above 90 percent, as long as water has not leaked 
through the drip shield onto the waste package, and the waste package has not directly 
contacted the backfill, invert, or corrosion products of the steel ground support. 
Threshold Conditions for Microbially Induced Corrosion of the Drip Shield 
 Growth and activity are nil until the drip-shield surface temperature decreases to less 
than 120C for all environmental conditions. 
 For water contacting the drip shield during the thermal period, microbial growth and 
activity are negligible as long as the relative humidity is less than 90 percent. 
Environmental Conditions for Aqueous Corrosion 
When threshold conditions for aqueous corrosion occur on the waste package or drip shield, it is 
assumed that MIC can occur at rates observed in laboratory tests. At present, test data are 
available to support an empirical model for MIC of Alloy 22, and testing is also under way to

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develop a model for Ti Grade 7 (results may show that MIC is not important for Ti). The results 
are expected to provide upper bounds on rates of MIC for potential repository conditions, 
because: 1) the test cells are augmented with glucose, which has no analogue in the potential 
repository environment; 2) test cells contain crushed tuff, whereas the upper part of the drip 
shield will contact quartz sand backfill, which is not a phosphate source; and 3) the waste 
package will be supported by a structure made from CRM, and will not contact crushed tuff until 
the support structure or the drip shield fails. 
3.1.2.4.1.4 Threshold Model Validation 
The threshold model is based on information from the literature, describing the environmental 
conditions for which microbial growth and activity are observed. The model is conservative in 
the sense that extreme microbial observations (e.g. halophiles and hyperthermophiles) are 
included, but these types of organisms will not necessarily be important in the potential 
repository. The basic threshold conditions for growth and activity are relative humidity 
(> 90 percent) and temperature (< 120C). No distinction is made between environmental 
conditions necessary for microbial activity, and for biofilm development, which is conservative. 
Use of these conditions constitutes a valid model that is based on accepted information. Based 
on this discussion, the model is valid for its intended use in TSPA to control the timing of the 
onset of MIC on the waste packages. 
3.1.2.4.2 Microbial Communities Model 
The following discussion is taken from the In Drift Microbial Communities AMR (CRWMS 
M&O 2000f). Microbes can promote corrosion of waste packages and other potential repository 
materials, modify the bulk chemical environment, and potentially alter the rate of radionuclide 
transport from breached waste packages. Under certain environment conditions, microbes may 
contribute to degradation of cementitious materials, and produce gas. These effects are depicted 
in Figure 3-41, as two major classifications of effects: impacts to EBS performance, and effects 
on radionuclide transport. The Microbial Communities Model provides a means to quantify the 
abundance and metabolic activity of microorganisms in the EBS environment. The Microbial 
Communities Model is intended for use in TSPA, to bound the effects of microbial growth and 
activity on the EBS bulk chemical environment. 
The Microbial Communities Model is based on models used in the Swiss and Canadian nuclear 
waste programs (CRWMS M&O 2000f). An idealized elemental composition for microbial 
biomass is used, consisting of carbon, nitrogen, sulfur, and phosphorous in fixed proportions, 
plus water. The rates of supply for these constituents are input as constant release rates for each 
introduced material in the EBS. The other major constraint is the energy available for microbes 
to grow, estimated from the free energy released by oxidation/reduction reactions. 
Application of the Microbial Communities Model to the TSPA-VA design, showed that 
approximately 10 to 12 grams of biomass would be produced per lineal meter of emplacement 
drift per year during the first 10,000 years (Figure 3-42). Based on this small generation rate, 
effects on the bulk chemical environment were considered negligible for the TSPA-VA. 
Localized effects of microbial activity, though not investigated in the In Drift Microbial

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Communities AMR (CRWMS M&O 2000f), could nevertheless alter the longevity of materials 
and the transport of radionuclides. 
The following description is taken from the In Drift Microbial Communities AMR (CRWMS 
M&O 2000f). 
3.1.2.4.2.1 Conceptual Development 
Ambient Environmental Conditions 
The presence of water, nutrients, and energy sources are required for microbial growth and 
activity. Environmental conditions (temperature, radiation, water activity) are also required. 
These conditions are summarized in the foregoing discussion of the threshold model. 
Introduced Materials 
There are three main categories of introduced materials that could potentially affect, or be 
affected by, microbial activity: steels/alloys, cementitious materials, and organic substances. 
 Steels and Alloys  The Fe, Mn, and other metals in the steel/alloys can oxidize, and 
serve as energy sources. Additionally, the steel/alloys contain trace elements needed 
for microbial growth. 
 Cementitious Materials  Cementitious materials are strongly alkaline and may 
contain organic compounds, sulfates, and nitrates. Alkaline pH does not preclude 
microbial activity, and some constituents of cement may be utilized by bacteria. 
 Organic Substances  Organic substances in the drifts will promote microbial activity. 
The effects of introduced materials on microbial growth and activity are incorporated by 
including these materials in the Microbial Communities Model. 
Code Development Concepts 
Three basic approaches to modeling microbial nutrient and energy balances are possible, and 
have been documented in previous reports (CRWMS M&O 2000f): 
 Nutrient Mass Balance  Biomass is limited by the inventory and/or supply rate of 
some essential element (e.g., C, N, P, and S). If the biomass is small, it may be 
justified to neglect microbial processes when compared with competing abiotic 
reactions. 
 Thermodynamic Approach  Microbial growth and activity are constrained by energy 
sources, in addition to nutrients. 
 Kinetic Approach  Microbial processes are explicitly modeled using measured or 
derived kinetic data, and representing metabolic activity by rate reactions.

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The MING modeling code (CRWMS M&O 2000f) combines the nutrient and thermodynamic 
approaches. Abiotic considerations are used to estimate the rates at which nutrients and energy 
sources become available to microorganisms. Introduced materials are decomposed into their 
basic elements, and their contributions to the microbial ecology are included with the 
constituents available from groundwater and gas fluxes through the potential repository. The 
model does not bound the potential phenomenology of individual microbial colonies or biofilms, 
but quantifies the overall effects on the bulk chemical environment. The kinetic approach is 
possible, but it is impractical to obtain the needed information describing all relevant microbial 
processes. 
3.1.2.4.2.2 Input Data, Assumptions, and Uncertainties 
The input data for the Microbial Communities Model includes quantities, compositions, and 
physical properties of introduced materials, and the degradation lifetimes for those materials in 
the potential repository environment. Similar information is required for each type of waste 
form, and for the materials that make up the waste package. Uncertainty with respect to 
degradation lifetime is addressed in the model interpretation and sensitivity analysis. Additional 
parameters required for modeling with MING consist of temperature cutoff values, humidity 
cutoff values, gas utilization parameters, and energy cutoff values that control the release of 
chemical constituents from potential repository materials. Descriptors for the potential 
repository environment include temperature, relative humidity, liquid seepage flux, and gas flux 
through the host rock as functions of time. In addition, the composition of seepage water is also 
used. 
Model Assumptions 
Major assumptions made in conjunction with MING modeling include those listed below 
(CRWMS M&O 2000f): 
 Relative Humidity  A representative value of relative humidity is used as a surrogate 
for water activity throughout the environment. 
 Degradation Lifetimes  Supporting information is sparse for estimating degradation 
lifetimes, particularly for cement grout and it components, so values are selected to 
represent reasonable ranges. 
 Iron Release Rates from Host Rock  Degradation lifetimes of 10 million years, and 
1 million years, and 100,000 years are assumed for release of iron from biotite. 
Model Uncertainties 
The principal uncertainty associated with the Microbial Communities Model results from the 
degradation rates assigned to EBS materials. This is the primary source of rate information 
incorporated in the model. 
Uncertainties associated with application of the Microbial Communities Model include 
competition between biotic and abiotic processes, and interpretation of the estimates for 
microbial biomass production. The model assumes that all available nutrients and redox energy

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sources are used for microbial processes, and is therefore bounding. The other point is that the 
Microbial Communities Model is not intended to quantify localized microbial activity or its 
consequences, but bounds overall microbial growth and activity in the EBS. 
3.1.2.4.2.3 Microbial Communities Model Development 
MING is used to evaluate potential impacts of the potential repository on microbial populations, 
and the associated effects on radionuclide release and transport. The MING code takes into 
account the availability of nutrients, the energy necessary to convert nutrients to microbes, the 
oxygen fugacity, and the temperature and humidity. 
The starting point for the MING model development was the model entitled: Estimation of 
Maximum Microbiological Activity also known as EMMA (CRWMS M&O 2000f) and is based 
on documented results from the Swiss Low/Intermediate Level Waste program. The MING 
model incorporates the same basic modeling approach and structure for calculating nutrient and 
energy limitations. Two main components were brought forward into MING from the original 
approach: 1) the numerical solution for the energy available for microbial growth; and 2) the 
general method for calculating nutrient availability. Other aspects brought forward include the 
average empirical microbial formula (C160H280O80N30P2S) with a dry weight of 3,998.1 g/mole. 
In addition, MING also uses an average microbial water content of 99 weight percent and an 
average microbial volume of 1.5  10-13 mL. MING uses the same basic approach to 
thermodynamic modeling, whereby microbes use oxidation-reduction couples to supply the 
energy required to carry out basic metabolic functions. MING uses the same limits of usable 
energy from oxidation-reduction reactions, whereby a minimum of 15 kJ are obtained per mole 
of electrons transferred, and 64 kJ are needed to maintain 1 g of biomass (CRWMS 
M&O 2000f). Some enhancements to the original code are as follows: 
 Addition of temperature dependence for free energy calculations 
 Incorporation of time-dependent gas flux among nutrient constraints 
 Time-dependent water composition entering the drift 
 pH dependence of the governing oxidation-reduction equations 
 Capability to sequence degradation of one potential repository material before another 
(e.g. for a layered waste package) 
 Incorporation of threshold conditions to temperature and relative humidity for 
microbial growth 
Within MING, only the standard-state free energies are used and these are not corrected for 
either Eh or the activity of dissolved species to derive the actual nonstandard-state free energies. 
By not calculating the nonstandard-state free energies, the calculation is not precise, but 
produces a rough estimate. The method for incorporating temperature dependence of free 
energies of reaction is also approximate, based on regression analyses of standard-state free

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energy values at various temperatures (0, 25, 50, 60, 75, 100, 125, and 150C) for selected 
half-reactions. 
3.1.2.4.2.4 Microbial Communities Model Validation 
The microbial communities model is based on an inventory of materials present in the drift 
(Section 3.1.2.3.1), and how degradation of those materials can support microbial nutrient and 
energy requirements. The model is implemented in the MING code. It is validated by 
comparison to laboratory and field data. In these applications, approximate agreement is 
obtained with observed microbial abundance data. The model can correctly identify nutrientlimited 
vs. energy-limited conditions, in agreement with other information from microbial 
investigations. Based on this discussion, the Microbial Communities Model is valid for its 
intended use in TSPA, for bounding the effects of microbial growth and activity on the bulk EBS 
environment. 
Comparison With Laboratory and Field Data 
Three sets of model validation tests for MING are documented (CRWMS M&O 2000f): 
 Replication of model results originally calculated for the Swiss potential repository 
program 
 Depiction of ambient conditions found in the ESF and at Rainier Mesa (a natural 
analog) 
 Modeling of independent lab tests conducted at LLNL 
Replication of the Swiss case demonstrates that MING functions correctly when compared to 
previous modeling activities, where natural barrier material components are combined with 
engineered material components to calculated microbial growth. 
Modeling of ambient data from the ESF and Rainier Mesa demonstrates that the selection of 
oxidation-reduction equations and the handling of material degradation produce reasonable 
results. The calculated results replicate the ambient system data (cell counts) to within an order 
of magnitude. This exercise confirms that water and phosphorous availability are limiting 
factors to microbial growth. Calculated results also show that the natural system is energy 
limited, because when material degradation lifetimes are lowered there is a notable increase in 
energy produced. 
Modeling of the LLNL lab tests provides perspective on the uncertainty associated with modeled 
results. Comparison with laboratory test data shows that the numbers of organisms calculated by 
MING can agree to within an order of magnitude with measured data from controlled tests. Both 
energy-limited and nutrient-limited tests are analyzed. The model confirms that the primary 
factor limiting microbial growth in the host rock is availability of water, and the primary limiting 
nutrient is phosphorous. An example showing how test data are modeled using MING, is 
described below.

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The test series conducted by LLNL used several different growth media to grow microbes. Each 
medium was selected to investigate limiting nutrients in the potential repository environment. 
The reader is referred to CRWMS M&O (2000f) for references to more detailed descriptions of 
the tests. Each medium was placed in a flask with a known quantity of Topopah Spring tuff, and 
cultured for approximately seven days. Microbial abundance in the liquid media was determined 
by live plating. Two types of tests were conducted: (1) a set of microcosm tests in which the 
growth medium was continuously supplied, and (2) a set of batch tests in which the tuff was 
exposed to a single aliquot of growth medium. The batch tests are best suited for modeling using 
MING because the conditions are easily specified. 
Comparison of the batch and microcosm results for the Dilute Complete medium, with the 
microbial abundance predicted by MING, shows reasonable agreement as shown in Figure 3-43. 
(The Dilute Complete medium was similar to J-13 water, and augmented with glucose.) The 
model also indicated that the system was energy-limited, i.e., the nutrients present could have 
produced more microbes. 
3.1.2.4.3 Summary of the Effects of Microbial Activity in the EBS 
Microorganisms are capable of degrading all EBS materials. The primary electron donors in the 
EBS will be metals (such as steel) or metal ions in reduced form. The primary electron acceptors 
will be sulfate, nitrate, and gas-phase oxygen. Microbial growth and activity in the host rock are 
limited by the availability of water and phosphate. Dryout of the EBS and high temperatures 
during the thermal period will arrest microbial growth and activity. Microbial activity will not 
occur at temperatures greater than 120C in aqueous environments. Reported dependence on 
humidity shows that growth and activity do not generally occur at less than approximately 
90 percent relative humidity. When salts are present, the threshold humidity may decrease 
depending on the deliquescent behavior of the salts and the presence of salt-tolerant organisms. 
When the titanium drip shield is exposed to sufficient humidity or liquid water, MIC may occur 
(if it can be shown to occur in laboratory tests). EBS water-diversion features (including the drip 
shield) will protect the waste package during the thermal period and beyond. Salts, and nutrients 
such as phosphate, will not be deposited on the waste package while the drip shield is intact. 
MIC will oxidize metallic barriers and likely consume oxygen as an energy source while 
obtaining carbon from an inorganic source such as CO2. Sulfur reduction may also occur. The 
effects of CRM degradation on the bulk chemical environment will be these processes will be 
small or negligible, because of inherent resistance of CRMs to microbial attack and consequent 
slow rates of corrosion. 
The corrosion rate for the carbon steel ground support and invert supports will increase because 
of MIC, and this is the major potential effect of microbial activity on the bulk chemical 
environment. Laboratory test data show that the corrosion rate can increase by a factor of at least 
6 to 7. Steel corrosion will consume oxygen and lower the O2 fugacity in the drift environment.

 3-99 
3.1.2.5 Precipitates and Salts 
Several modeling approaches are presented as submodels in this section: 
 Normative Precipitates and Salts Models  Based on laboratory data, and used to 
predict which minerals and salts will form when waters are completely evaporated, 
based on the starting composition of the water. Used in conjunction with the EBS 
Chemical Reference Model in Section 3.1.2.7. A simplified subset of precipitates and 
salts is used for TSPA in conjunction with the Low-Relative-Humidity Salts Model, as 
discussed below. 
 Condensed Water Model  Calculates the composition of condensate that can form on 
the waste package or the underside of the drip shield, affected only by gas-phase CO2. 
Used in TSPA to predict water compositions that can affect drip shield and waste 
package corrosion when there is no seepage, only condensation directly on the drip 
shield or waste package. 
 Low- and High-Relative-Humidity Salts Models  The Low-Relative-Humidity 
(LRH) Salts Model describes the behavior of salts at relative humidity less than 
85 percent, while the High-Relative-Humidity (HRH) Salts Model calculates water 
composition and dissolution/precipitation reactions for solutions that can occur when 
relative humidity is greater than 85 percent. These models are used in TSPA to 
determine the timing of environmental conditions that permit aqueous corrosion, and to 
estimate measures that describe the solution chemistry (pH, chloride concentration, and 
ionic strength). 
Each of these submodels is intended for use directly in TSPA, except the Normative Precipitates 
and Salts Model, which is supportive but not used directly. The Normative Precipitates and Salts 
Model provides input to the Chemical Reference Model, which is used for FEP screening and to 
support the design basis. 
3.1.2.5.1 Conceptual Models for Precipitates and Salts Formation 
Boiling and evaporation of water in the potential repository emplacement drifts will cause 
dissolved solids in the water to concentrate and precipitate. The precipitates that form will 
depend on water composition, temperature, gas fugacities, and rates of evaporation and seepage. 
Boiling temperatures (>96C) and low relative humidity are expected during the first few 
hundred years after closure. Seepage into the drifts during this period, if it occurs, may be 
transient, but the nonvolatile dissolved constituents can accumulate in the drifts as salts and 
minerals. These solids will include relatively insoluble minerals like silicates and carbonates, 
and also soluble salts with the potential to form brines when sustained humidity returns during 
cooldown. 
Dissolved salts in water decrease the saturation water vapor pressure because they reduce the 
chemical activity of water. The chemical activity of water is proportional to the mole fraction of 
water, and is equivalent to the equilibrium relative humidity of the solution (CRWMS M&O

 3-100 
2000g). As a result, brines reach liquidvapor equilibrium at relative humidity values below 100 
percent. There is a critical value of relative humidity, determined by the solubility of the salt, 
below which brine cannot exist at equilibrium with the gas phase, and will evaporate. Relative 
humidity above the critical value for a salt will cause moisture to condense and form a brine, 
even if there is no other liquid present. Impacts of brine formation on potential repository 
performance include earlier return of aqueous conditions, and potentially aggressive corrosion 
conditions. 
Studies of saline lakes in the western United States show that alkaline sodium carbonate brines 
are common. Many of these waters occur in volcanic terrain and have high silica content. They 
also are typically enriched in chloride and sulfate. Highly soluble components precipitate in the 
late stages of evaporation. In carbonate-rich brines, these components include sodium, chloride, 
sulfate, carbonate, and silica. The predominant components in carbonate-poor brines, such as 
those resulting from evaporation of sea water, are sodium, calcium, magnesium, chloride, and 
sulfate. Other dissolved components that have been observed to become enriched in some brines 
include fluoride, bromide, strontium, phosphate, and boron. Nitrate is highly soluble, but is not 
mentioned in these studies, perhaps because it has greater biological activity. 
During cooldown, dissolution of salts will occur rapidly when the relative humidity exceeds the 
critical value for each salt present. Rapid dissolution is consistent with the observation that 
puddles of dissolved salt (primarily NaCl) occur overnight on salt flats when the relative 
humidity exceeds the stability limit for NaCl but remains below the dew point (CRWMS M&O 
2000g). These puddles can then dry up during the day when the relative humidity decreases. 
The lowest critical relative humidity values important for the EBS environment, approximately 
50 percent, correspond to the nitrate salts niter (KNO3) and Na-niter (NaNO3). In the potential 
repository the corresponding temperature at 50 percent relative humidity will be less than 120C, 
which is the approximate boiling point for a concentrated solution of NaNO3. The next threshold 
will occur at approximately 80 percent relative humidity, when halite (NaCl), villaumite (NaF), 
thermonatrite (Na2CO3), sodium bicarbonate (NaHCO3), and sodium silicates (Na2Si2O5 and 
Na2SiO3) will dissolve, if these species are present. Except for halite, there are few data 
available on the critical relative humidity values for these salts. The final threshold will be at 
approximately 90 percent relative humidity, when thenardite (Na2SO4) dissolves. This will leave 
calcite (CaCO3) as the principal remaining salt. 
During cooldown, the rate at which liquid water enters the drift will eventually exceed the 
evaporation rate, so that liquid accumulates, brines are diluted, and the liquid-phase composition 
is no longer controlled by the behavior of salts. As the potential repository environment 
approaches ambient (pre-repository) conditions, water chemistry in the drifts will not depend on 
evaporative processes. 
3.1.2.5.2 Normative Precipitates and Salts Model 
This model predicts the set of precipitates and salts that will form when waters having a range of 
starting compositions are completely evaporated. Identification of the solids is also needed for 
mass balance involving gas-phase chemical components, for the Chemical Reference Model 
(Section 3.1.2.7), for FEP screening and support of the design basis.

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The Normative Model was developed to describe the laboratory data; however, a simplified set 
of precipitates and salts is used for TSPA to predict the composition of brines that form when 
humidity returns to the environment (LRH Salts Model; Section 3.1.2.5.3). This simplified 
assemblage consists of the nominal binary salts of the Na-K-NO3-Cl-SO4-CO3 system. For both 
the sodium-bicarbonate water (i.e., J-13 water) and the tuff matrix porewater (chloride-sulfate 
type) considered in the TSPA abstraction, these salts are: niter (KNO3), Na-niter (NaNO3), halite 
(NaCl), thenardite (Na2SO4), sodium bicarbonate (NaHCO3), and sodium carbonate (Na2CO3). 
Most of these same salts are predicted using the approach outlined below for J-13 water, namely, 
niter (KNO3), Na-niter (NaNO3), halite (NaCl), thenardite (Na2SO4), and thermonatrite 
(Na2CO3:H2O). 
3.1.2.5.2.1 Model Input Data 
Synthetic J-13 Water Evaporation Tests 
Well J-13 is a producing water well that is screened in the Topopah Spring welded tuff. J-13 
water is of the dilute sodium-bicarbonate type, and its composition is used as a chemical 
analogue for fracture waters in the potential repository host rock (CRWMS M&O 2000t). A 
synthetic J-13 well water was mixed for use in evaporation tests. Preparation was performed at 
room temperature, under ambient atmospheric gas conditions. The batch was decanted to 
remove undissolved reagents, and the resulting solution was analyzed for pH, metals (Ca, Mg, 
Na, K, and Si), and for anions (chloride, fluoride, nitrate, and sulfate). 
Laboratory batch tests were conducted at Lawrence Livermore National Laboratory in 1998 and 
1999. In the first two tests, 30 L of synthetic J-13 well water were evaporated down to 30 mL, 
resulting in an evaporative concentration factor of approximately 1000. In all tests, the actual 
concentration factors were estimated by total mass measurements and are accurate to 
approximately 10 percent. Synthetic J-13 water was pumped into a 1-L Pyrex beaker at a 
constant rate using a peristaltic pump, while the sample evaporated at 85C over a hot plate. The 
fluid-delivery rate and heat flux were balanced to maintain constant temperature in the fluid 
contained within the beaker. 
Aqueous samples for cation and anion analyses were collected in plastic syringes, and filtered 
through a rinsed 0.45-m filter. For analysis of total dissolved inorganic carbon, a small split of 
each unacidified sample was injected directly into an infrared CO2 analyzer. Speciation of DIC 
as bicarbonate or carbonate was determined from the measured pH. The anions of fluoride, 
chloride, nitrate, and sulfate were determined using ion chromatography (IC). The analytical 
protocol supports detection of several other anion analytes, but these four were the only ones 
detected (other than carbonate species). Cations were determined using inductively-coupled 
plasma emission spectroscopy (ICP). 
Solution pH was determined using a method recommended by the National Bureau of Standards; 
which is best suited for low ionic strength solutions, although useful measurements can be made 
up to ionic strength as great as that of seawater (0.7 molal). For J-13 water and similar 
compositions, accurate pH measurement is limited to less than 200 evaporative concentration. 
Accordingly, pH measurements for the rewet samples of the evap1 and evap2 runs are

 3-102 
approximate. No attempt was made to measure the pH of the batches concentrated to 1000 or 
greater. 
Solids samples (tests evap1 and evap2) were dried, weighed, and analyzed using x-ray 
diffraction (XRD). The purpose of the XRD analysis was to identify the phases produced, and 
quantification was not attempted. 
The tests were performed at sub-boiling conditions to represent evaporation of slowly migrating 
waters in the EBS, such as could occur in the backfill. The 85C temperature is similar to 
predicted conditions for inflow to the potential repository during the thermal period, should it 
occur, while maintaining sub-boiling conditions for the test. At these temperatures, the 
assemblage of mineral phases resulting from the evaporation is controlled predominantly by 
precipitation kinetics, and it is thought that the assemblages observed are representative of 
potential repository conditions. 
One potentially important aspect of the batch tests, is that the precipitates are still available for 
reaction after they form. Flowing water in the potential repository would tend to leave behind 
precipitates, and the precipitates would develop zones. While zonation is theoretically possible, 
it would require extensive evaporative concentration. The available flux of concentrated water is 
small and therefore slow in the unsaturated backfill, a porous medium. 
In the first test (evap1), detailed chemical analysis was performed on the initial starting water 
composition and on a sample collected after approximately 1000 concentration. A small split 
of the solids that had precipitated at the 1000 stage (not yet dry) was collected for mineralogic 
analysis. The solution was then evaporated to complete dryness, and another small split of the 
solids was collected. The remaining solids were then rewet with 200 mL of deionized water and 
evaporatively concentrated to 100 mL at 75C; the resulting solution was collected for detailed 
water-chemistry analysis. The rewetting step was incorporated to evaluate the reproducibility of 
precipitate formation at supersaturated conditions. Three water compositions (including the 
initial solution) and two solid samples were analyzed. 
The second test (evap2) was the same except that the beaker contained 10 g of crushed Topopah 
Spring welded tuff (CRWMS M&O 2000af). The tuff was prepared by sieving the original 
material (<2 mm grain size) to >0.5 mm to remove the fine fraction. The sized material was 
washed three times in isopropanol. The grains were allowed to settle before decanting to remove 
adhering fine particles and were then air-dried. The test was taken to complete dryness, and a 
rewetting step was incorporated as described previously. Three water compositions (including 
the initial solution) and two solid samples were analyzed. 
A short-term test (evap4) was conducted to further investigate the evolution of pH during 
evaporative concentration to approximately 100. The initial and final solutions were sampled

 3-103 
Table 3-10. Evolution of Water Composition in Test with Synthetic J-13 Water (evap1) 
Species 
(mg/kg) 
Synthetic J-13 
(mg/kg) 
Species Conc. (mg/kg) 
w/ Evap. Factor: 956 a 
Concentration 
Ratio 
Rewet b 
(mg/kg) 
Concentration 
Ratio 
Ca 6.40 29.9 4.70 3.48 0.54 
Cl 6.90 4.84x103 701 1.77x103 257 
F 2.20 1.55x103 705 530 241 
HCO3
 108 2.49x104 231 9.54x103 88.3 
K 5.30 4.79x103 904 1.36x103 257 
Mg 2.20 0.14 0.06 0.09 0.04 
Na 46 4.41x104 958 1.25x104 272 
NO3
 8.0 5.53x103 694 2.02x103 252 
SO4
2 18.1 1.29x104 714 4.63x103 256 
SiO2(aq) 11.3 1.80x104 1.59x103 c 3.61x103 319 
pH 7.84 d 10.6 
Source: CRWMS M&O 2000t 
NOTES: a 30 L of synthetic J-13 well water were evaporated to 30 mL, resulting in a concentration factor of 
approximately 1000. 
b After evaporation to complete dryness, the solids were rewet with 200 mL of deionized water and 
evaporatively concentrated to 100 mL. 
c The apparent concentration ratio for SiO2 is greater than that estimated from total mass measurements 
and the concentration ratios for other ions, possibly because of analytical errors associated with the high 
ionic strength. 
d Not analyzed 
for chemical analysis. The results of these tests (evap1, evap2, and evap4) are summarized in 
Table 3-10 through Table 3-14. 
Results from Synthetic J-13 Water Evaporation Tests 
The results summarized in Table 3-10 through Table 3-14 were obtained from an open system 
(free exchange with gas-phase CO2) under ambient atmospheric composition conditions. 
Following are some major findings from these tests: 
 Divalent cations (Ca2+, Mg2+) tend to precipitate early in evaporative evolution, both 
with and without tuff present (evap1 and evap2), from precipitation of carbonate, 
probably calcite (CaCO3) and low-Mg calcite ([Ca,Mg]CO3). 
 Halite (NaCl) and niter (KNO3) apparently contain the chloride and nitrate from the 
starting solution. Niter is among the last solids to precipitate.

 3-104 
Table 3-11. Evolution of Water Composition in Test with Synthetic J-13 Water and Tuff (evap2) 
Species 
(mg/kg) 
Synthetic J-13 
(mg/kg) 
Species Conc. (mg/kg) 
w/ Evap. Factor: 1114 a 
Concentration 
Ratio 
Rewet b 
(mg/kg) 
Concentration 
Ratio 
Ca 5.60 6.90 1.2 3.0 0.5 
Cl 7.20 6.12x103 850 2.35x103 326 
F 2.20 1.52x103 691 605 275 
HCO3
 104 3.14x104 303 1.34x104 129 
K 5.30 3.72x103 702 1.55x103 292 
Mg 2.10 < 0.28 c < 0.08 c 
Na 44.3 3.77x104 851 1.45x104 327 
NO3
 7.80 6.73x103 863 2.60x103 333 
SO4
2 18.3 1.57x104 858 6.14x103 336 
SiO2(aq) 9.40 7.12x103 758 2.69x103 287 
PH 8.03 9.99 
Source: CRWMS M&O 2000t 
NOTES: a 30 L of synthetic J-13 water were evaporated to 30 ml, for a concentration factor of approx. 1000. 
b After evaporation to complete dryness, the solids were rewet with 200 mL of deionized water and 
evaporatively concentrated to 100 mL. 
c Not analyzed 
Table 3-12. Evolution of pH in Short-Term Test with Synthetic J-13 Water (evap4) 
Concentration Factor PH 
1.00 8.46 
1.00 8.65 
1.05 9.04 
1.29 9.43 
1.60 9.58 
2.41 9.67 
6.08 9.67 
6.37 9.77 
7.59 9.79 
11.6 9.95 
12.6 10.00 
15.3 10.03 
20.9 10.08 
25.2 10.09 
34.4 10.12 
52.1 10.18 
104 10.18 
157 10.18 
Source: CRWMS M&O 2000t

 3-105 
Table 3-13. Mineralogical Results from Test with Synthetic J-13 Water (evap1) 
evap1956 evap1Complete Evaporation 
SiO2 (amorphous) SiO2 (amorphous) 
aragonite (CaCO3) aragonite (CaCO3) 
calcite (CaCO3) calcite(CaCO3) 
halite (NaCl) 
niter (KNO3) 
thermonatrite (Na2CO3:H2O) 
gypsum (CaSO4:2H2O) a 
anhydrite (CaSO4) a 
hectorite (Na0.33Mg3Si4O10(F,OH)2) a 
Source: CRWMS M&O 2000t 
NOTE: a Species is a minor constituent, and identification is uncertain. 
Table 3-14. Mineralogic Results from Test with Synthetic J-13 Water and Tuff (evap2) 
evap21114 a evap2Complete Evaporation a 
SiO2 (amorphous) SiO2 (amorphous) 
trona (Na3H(CO3)2:2H2O) trona (Na3H(CO3)2:2H2O) 
Thermonatrite (Na2CO3:H2O) thermonatrite (Na2CO3:H2O) 
halite (NaCl) halite (NaCl) 
calcite (CaCO3) calcite (CaCO3) 
Aragonite (CaCO3) aragonite (CaCO3) 
Anhydrite (CaSO4) anhydrite (CaSO4) 
smectite (Na.3(Al,Mg)2Si4O10(OH)2) smectite (Na.3(Al,Mg)2Si4O10(OH)2) 
niter (KNO3) niter (not detected by XRD) 
Source: CRWMS M&O 2000t 
NOTE: a Only the minerals produced by evaporation and not present in the starting tuff are reported. The 
major minerals constituting the tuff are probably crystobalite (a), K-feldspar, albite, anorthite, and 
quartz. 
 Polymorphic phases (e.g., aragonite and calcite, both as CaCO3) indicate that solubility 
constraints changed during the final stages of evaporation. 
 Test results provided no indication of hydroxides such as portlandite (Ca[OH]2) for 
evaporation under ambient atmospheric composition conditions. 
 The measured pH of the rewet solution with tuff present (evap2) was 9.99, compared to 
pH 10.59 without tuff (evap1), probably from buffering associated with the dissolution 
of SiO2 and silicates.

 3-106 
 pH was approximately 10 to 11 for concentrated J-13 water up to approximately 150, 
with and without tuff present, under ambient atmospheric conditions 
 The Si concentration was lower in the concentrated evap2 solutions than in the evap1 
solutions, which suggests that the presence of the silicate and aluminosilicate minerals 
in the tuff enhances precipitation. 
 The presence of tuff appears to have little effect on relative concentrations of the 
anions, except for fluorides; this indicates that fluorite (CaF2) precipitation may be 
enhanced by increased Ca concentration derived from tuff. 
Synthetic Porewater Evaporation Tests 
Another set of tests was performed to investigate precipitates that could be produced by 
evaporation of matrix porewater, a reference water composition based qualitatively on reported 
analyses for porewater extracted from the Topopah Spring welded tuff (CRWMS M&O 2000t). 
Such waters have substantially less Na and K and more Ca and Mg than J-13 water, and the 
anionic species are dominated by sulfate and chloride instead of bicarbonate. A synthetic 
porewater was created for use in evaporation tests. The preparation and analysis were performed 
in the same manner as for the synthetic J-13 water. 
The laboratory batch tests with synthetic porewater conducted at LLNL in 1998 and 1999 were 
completely analogous to those done with synthetic J-13 well water. An initial test investigated 
the evaporation of water to dryness (evap3) and a subsequent test added 10 g of Topopah Spring 
welded tuff (CRWMS M&O 2000af). Another test (evap5) investigated the evolution of pH 
during short-term evaporative concentration to approximately 100. The results of these 
experiments are summarized in Table 3-15 through Table 3-19.

 3-107 
Table 3-15. Evolution of Water Composition in Test with Synthetic Porewater (evap3) 
Species 
(mg/kg) 
SPW 
(mg/kg) 
Species Conc. (mg/kg) w/ 
Evap. Factor: 1243 
Concentration 
Ratio 
Rewet 
(mg/kg) Concentration Ratio 
Ca 57.2 15,629 273 6,010 105 
Cl 78.0 53,084 681 19,248 247 
F 2.30 < 577 b < 301 b 
HCO3
 16.2 < 35 b < 37 b 
K 4.20 2,779 661 973 232 
Mg 11.7 5,478 470 1,949 167 
Na 8.20 5,961 727 2,077 253 
NO3
 11.0 b b 2,647 241 
SO4
2 81.7 2,077 25 1,564 19 
SiO2(aq) 9.80 513 52 340 35 
PH 7.68 66.5 a 5.56 
Source: CRWMS M&O 2000t 
NOTES: a Semiquantitative measurement using pH paper 
b Not analyzed or determined

 3-108 
Table 3-16. Evolution of Water Composition in Test with Synthetic Porewater and Tuff (evap6) 
Species 
(mg/kg) 
SPW 
(mg/kg) 
Species Conc. with Evap. 
Factor: 564 
Concentration 
Ratio Rewet 
Concentration 
Ratio 
Ca 59.2 12,553 212 10,249 173 
Cl 76.1 37,198 489 30,359 399 
F 2.10 < 248 a < 284 a 
HCO3
 20.2 < 60 a < 36 a 
K 4.10 2,006 488 1,622 395 
Mg 12.0 3,615 300 2,889 240 
Na 8.70 4,420 508 3,574 411 
NO3
 10.5 5,267 501 4,344 413 
SO4
2 85.2 1,316 15.4 1,516 17.8 
SiO2(aq) 11.5 696 60.6 355 30.9 
pH 7.52 5.14 5.43 
Source: CRWMS M&O 2000t 
NOTE: a Not analyzed 
Table 3-17. pH and Carbonate Evolution from Short-Term Test with Synthetic Porewater (evap5) 
Concentration Factor pH HCO3
+ (mg/L) 
1.00 7.45 24.7 
1.06 8.69 a 
1.38 9.01 a 
1.76 8.99 a 
2.31 8.86 a 
4.19 8.57 a 
6.09 a 20.1 
6.36 8.55 a 
8.16 8.51 a 
8.19 a 19.5 
12.0 8.45 19.4 
29.9 8.29 14.0 
Source: CRWMS M&O 2000t 
NOTE: a Not analyzed

 3-109 
Table 3-18. Mineralogical Results from Test with Synthetic Porewater (evap3) 
evap31243 evap3Complete Evaporation 
gypsum (CaSO4:2H2O) gypsum (CaSO4:2H2O) 
tachyhydrite (CaMg2Cl6O10:12H2O) 
Source: CRWMS M&O 2000t 
Table 3-19. Mineralogical Results from Test with Synthetic Porewater and Tuff (evap5) 
evap6564 evap6Complete Evaporation a 
gypsum (CaSO4:2H2O) gypsum (CaSO4:2H2O) 
halite (NaCl) halite (NaCl) 
Mg-smectite (Na.3(Al,Mg)2Si4O10(OH)2) 
Kenyaite (NaSi11O20.5(OH) 4:3 H2O)b 
Source: CRWMS M&O 2000t 
NOTES: a Only the minerals produced by evaporation and not present in the starting tuff are reported here. 
The major minerals constituting the tuff are probably crystobalite (a), K-feldspar, albite, anorthite, 
and quartz. 
b Species is a minor constituent and identification is uncertain. 
Results for Synthetic Porewater Evaporation Tests 
The results summarized in Table 3-15 through Table 3-19 were obtained from an open system 
(free exchange with gas-phase CO2) under ambient atmospheric composition conditions. 
Following are some major findings from these tests: 
 Sulfate is the predominant anion; therefore, the effects of carbonate species are 
substantially less important in the synthetic porewater tests. 
 The pH decreases to approximately 5.5 to 6.0, with evaporative evolution of the 
Ca-sulfate porewater, instead of increasing to pH ~10 as was observed for the J-13 
water. 
Larger discrepancies between the concentration factors computed from measured species 
concentrations and the total mass concentration factor are noted for the porewater tests when 
compared to the J-13 water tests. For species such as chloride (e.g., Table 3-10 and Table 3-15) 
the apparent concentration factor for dissolved species is substantially less than the total mass 
concentration factor. This probably occurred because the greater dissolved-solids content of the 
porewater starting solution caused the system to exceed solubility conditions, so that 
precipitation occurred. 
Comparison of results from analogous tests using synthetic J-13 and porewater (Table 3-10 and 
Table 3-15) shows that bicarbonate waters such as J-13 are more likely to produce high-pH 
conditions than are chloride-sulfate type waters such as the synthetic porewater. Selection of 
J-13 water composition for investigating the EBS chemical environment is therefore bounding

 3-110 
with respect to alkaline pH. The J-13 composition is used for modeling the EBS chemical 
system in Section 3.1.2.7. 
3.1.2.5.2.2 Model Assumptions 
Bounding Water Composition 
With respect to the performance of corrosion-resistant materials, high-pH conditions and the 
presence of anions such as fluoride, chloride, and sulfate represent the most aggressive 
conditions for corrosion that are possible in the potential repository environment, and constitute a 
reasonable-bound composition for modeling the EBS chemical environment. 
3.1.2.5.2.3 Model Uncertainties 
The principal uncertainty associated with this model is caused by simplification of the reaction 
path that culminates in complete evaporation. Precipitates that form relatively early in the 
evolution of the mineral assemblage, are exposed to aqueous solution conditions, and are 
therefore available to redissolve and participate in further precipitation reactions. The 
implication is that salts can form other than those predicted. Agreement with test results is 
therefore important, and extension to other starting solution compositions should be verified by 
testing. 
Another uncertainty for low-CO2 conditions that may be encountered in the potential repository 
during the thermal period, it is that sufficient CO2 will be present to produce thermonatrite 
(Na2CO3:H2O) and calcite (CaCO3). If this assumption is incorrect, portlandite (Ca[OH]2) or 
sodium hydroxide (NaOH) could precipitate in the EBS (e.g., on the drip-shield surface). This 
could have different implications for corrosion of metallic barriers. Thermodynamic equilibrium 
calculations show that sufficient CO2 is likely to be available to prevent hydroxide formation 
(CRWMS M&O 2000t), but test data for low-CO2 conditions are not available. 
3.1.2.5.2.4 Normative Precipitates and Salts Model Development 
For waters having compositions similar to the synthetic J-13 and synthetic porewater, a set of 
precipitates is identified that is consistent with the observations reported in Table 3-13 and 
Table 3-18. This model describes an assemblage of precipitates formed by complete 
evaporation. The order of formation of different salts during evaporation, is not a feature of this 
model. 
Nitrate, Fluoride, and Chloride Salts 
Nitrate precipitates as niter (KNO3), which is the likely disposition for all nitrate (Table 3-20). 
The amount of KNO3 that forms is determined by the molality of K or NO3, whichever is 
smaller. If there is insufficient potassium to account for all the nitrate, sodium is used to form 
Na-niter (NaNO3). Any excess potassium is used to form sylvite (KCl). Halite (NaCl) is formed, 
limited by the available sodium or chloride, whichever is smaller. Fluorite (CaF2) is formed 
from Ca and fluoride, which is reasonable because of its relative insolubility. Any remaining 
fluoride is used to form as villiaumite (NaF), which is reasonable because sodium is abundant 
and NaF is generally less soluble than KF. For J-13 water, these steps eliminate nitrate, chloride,

 3-111 
fluoride, and potassium from the problem. For the synthetic porewater, some chloride may 
remain. 
Clays 
For waters similar to J-13, clays can form in relatively small amounts, limited by the available Al 
in solution. Mg-smectite, Ca-smectite and, ultimately, Na-smectite, compositions are used as 
needed to precipitate the Al (see Table 3-20 for the clay mineral formulae). The approach does 
not include precipitates that could accommodate Mg in excess of the Al or instead of Mgsmectite. 
However, calcite (CaCO3) is included in the model, and a low-Mg calcite 
([Ca,Mg]CO3) would be plausible in this case. With an open-system, constant-fugacity condition 
placed on CO2, the choice of clay or calcite as the endpoint for a minor amount of Mg is not 
critical to pH. 
Table 3-20. Normative Mineral Assemblage for Complete Evaporation of Waters Similar to J-13 under 
Near-Atmospheric CO2 Conditions 
Minerals in Assemblage Remarks a 
Niter (KNO3) Use all nitrate or all potassium 
Na-niter (NaNO3) Use all remaining nitrate 
Fluorite (CaF2) Use all fluoride 
Villiaumite (NaF) Use all remaining fluoride 
Sylvite (KCl) Use all remaining potassium 
Halite (NaCl) Use all sodium or chloride 
Mg-smectite (Mg0.165Al2.33Si3.67O10(OH)2) Use all magnesium or aluminum 
Ca-smectite (Ca0.165Al2.33Si3.67O10(OH)2) Use all calcium or aluminum 
Na-smectite (Na0.33Al2.33Si3.67O10(OH)2) Use all remaining aluminum 
Thenardite (Na2SO4) Use all sodium or all sulfate 
Anhydrite (CaSO4) Use all remaining sulfate 
Calcite (CaCO3) Use all remaining calcium (CO2 is from open-system) 
Thermonatrite (Na2CO3:H2O) Use all remaining sodium (CO2 is from open-system) 
Amorphous silica (SiO2) Use all remaining silica 
Source: CRWMS M&O 2000t 
NOTES: a Minerals are presented in order of calculation, not in order of precipitation. 
Sulfates and Carbonates 
Thernardite is used to precipitate sulfate, although gypsum and anhydrite were suspected or 
detected in the laboratory tests (Table 3-13 and Table 3-14). This selection is based on 
thermodynamic arguments (CRWMS M&O 2000t) which show that:

 3-112 
 Anhydrite (CaSO4) is thermodynamically favored over gypsum (CaSO4:2H2O) under 
the humidity conditions calculated for the EBS. 
 Calcite (CaCO3) is thermodynamically favored over portlandite (Ca[OH]2) under the 
CO2 fugacity conditions calculated for the EBS. 
 Thenardite (Na2SO4) and calcite (CaCO3) are a more stable assemblage than 
thermonatrite (Na2CO3:H2O) and anhydrite (CaSO4); therefore, thenardite is the more 
likely sulfate precipitate. 
Accordingly, thenardite is used to precipitate all the sulfate. If there is insufficient Na to 
precipitate all of the sulfate (e.g., synthetic porewater), anhydrite could form at the expense of 
calcite. This could happen sequentially so that anhydrite and thenardite are not in equilibrium. 
Any remaining chloride is precipitated as tachyhydrite (CaMg2Cl6O10:12H2O), which was 
observed in the laboratory tests with synthetic porewater. Calcite is then used to precipitate the 
remaining Ca, and thermonatrite is used to precipitate the remaining Na. Any remaining 
magnesium is precipitated, possibly as Mg-calcite, which is represented in the model by 
precipitation of magnesite (MgCO3). 
Silica 
The final species considered in the assemblage is amorphous silica (SiO2), which was detected in 
all of the laboratory samples derived from the synthetic J-13 water (Table 3-13 and Table 3-14). 
Amorphous silica is used to precipitate of all the remaining silica, leaving only trace and minor 
species, which have limited influence, on redissolution, on bulk chemical conditions such as pH. 
3.1.2.5.2.5 Discussion and Summary 
The trends in solution chemistry for the evap1 and evap2 tests using synthetic J-13 water 
(Table 3-10 through Table 3-11) are consistent with the XRD results for the solid precipitates 
produced (Table 3-13 and Table 3-14). The presence of the tuff allows for more geochemical 
processes to occur, particularly mineral dissolution and precipitation and silicate buffering. 
Test results for synthetic J-13 water are sensitive to the ambient atmospheric CO2 fugacity, 
which limits pH to the range 10 to 11 for evaporative concentration values up to 150 and 
probably higher. Smaller values for the CO2 fugacity will tend to cause higher pH. The 
empirical nature of these results is attributable to limitations on the state-of-the-art for measuring 
and modeling pH at high ionic strength. 
Bicarbonate-type waters such as J-13 water are more sensitive to CO2 fugacity, particularly 
during evaporative concentration, and are more likely to produce high-pH conditions than are 
sulfate-type waters such as the synthetic porewater investigated. The synthetic J-13 results are 
therefore bounding with respect to high-pH conditions at the surface of the drip shield or the 
waste package during the thermal period. Sulfate-type or chloride-type waters tend to produce 
lower pH values when concentrated evaporatively (a difference of 4 pH units was observed) and 
are therefore not bounding compositions. The J-13 water composition is used for modeling the 
EBS chemical system in Section 3.1.2.7.

 3-113 
Test results for synthetic J-13 water (with and without tuff) show that for pH >10, evaporative 
concentration factors greater than 150 are required. Thus, the potential volumes and flow rates 
of affected solutions will be small. Saturation of the backfill in affected locations will be small, 
and the relative permeability and consequent mobility of these solutions will be limited. 
If a water composition that is similar to, but more dilute than, J-13 water (e.g., condensate) is 
used, the results will be similar to the synthetic J-13 results presented here; however, greater 
evaporative concentration factors would be required to achieve the same high pH values. Thus, 
the mass of solute involved, and the potential volume of high-pH liquid, would be smaller. 
3.1.2.5.2.6 Normative Model Validation 
In this section, the normative approach described previously and summarized in Table 3-20, is 
applied quantitatively to the complete evaporation of synthetic J-13 water and synthetic 
porewater used in laboratory tests (Table 3-21 and Table 3-22). In these tables, compositionally 
equivalent predicted species (e.g. calcite and aragonite) are grouped. Also, observed and 
predicted species are grouped for comparison, even where they have different composition (e.g. 
thenardite and gypsum or anhydrite). 
The comparisons shown in Tables 3-21 and 3-22 show that the normative approach can produce 
qualitative agreement for the synthetic J-13 water and synthetic porewater. Silica (SiO2), 
thermonatrite (Na2CO3:H2O), halite (NaCl), niter (KNO3), and calcite (or aragonite, CaCO3) are 
identified as major products of J-13 evaporation in both the predictions and observed data. The 
normative model predicts thenardite (Na2SO4) to form where gypsum (CaSO4:2H2O) and 
anhydrite (CaSO4) are observed, so there evidently is some sensitivity to the relative availability 
of Ca and Na, which is not accounted for in the model. Minor species such as sylvite (KCl) or an 
alternative potassium-bearing phase identified by the normative model for synthetic J-13 water 
may not have been detected by XRD. Similarly, minor species such as the niters, fluorite (CaF2), 
halite, and calcite, and amorphous silica, which are predicted by the normative model for 
synthetic porewater, were not detected by XRD.

 3-114 
Table 3-21. Normative Model for Precipitates Formed from Evaporating 1 kg of Synthetic J-13 Water, 
Compared with Qualitative Laboratory Observations 
Predicted Normative Species Predicted Moles/kg Observed Species 
Species Constituting >90% of Total Molality 
silica (amorphous) 7.925E04 SiO2 (amorphous) 
thermonatrite (Na2CO3:H2O) 6.917E04 thermonatrite (Na2CO3:H2O) 
halite (NaCl) 1.975E04 halite (NaCl) 
thenardite (Na2SO4) 1.926E04 gypsum (CaSO4:2H2O) a 
anhydrite (CaSO4) a 
niter (KNO3) 1.274E04 niter (KNO3) 
calcite/Aragonite (CaCO3) 8.208E05 calcite (CaCO3) 
aragonite (CaCO3) 
Remaining Species 
magnesite (MgCO3) b 8.638E05 hectorite (Na0.33Mg3Si4O10(F,OH)2) a 
fluorite (CaF2) 6.263E05 
sylvite (KCl) 5.594E06 
Source: CRWMS M&O 2000t 
NOTES: a A minor constituent; identification is uncertain. 
b Magnesium may precipitate as Mg-calcite but is represented stoichiometrically as magnesite. 
Table 3-22. Normative Model for Precipitates Formed from Evaporating 1 kg of Synthetic Porewater, 
Compared with Laboratory Qualitative Observations 
Predicted Normative Species Predicted Moles/kg Observed Species 
Species Constituting >90% of Total Molality 
Gypsum/anhydrite (CaSO4) 8.734E04 gypsum (CaSO4:2H2O) 
Tachyhydrite (CaMg2Cl6O10:12H2O) 2.427E04 tachyhydrite (CaMg2Cl6O10:12H2O) 
Silica (amorphous) 7.925E04 
Calcite (CaCO3) 2.567E04 
Halite (NaCl) 3.021E04 
Remaining Species 
Niter (KNO3) 1.023E04 
Na-niter (NaNO3) 7.025E05 
Fluorite (CaF2) 5.684E05 
Source: CRWMS M&O 2000t 
From the above discussion, the normative model is valid for its intended use, to support TSPA 
and for FEP screening and support of the design basis. It provides a valid approximation to the 
major species formed on complete evaporation of waters with composition similar to J-13 water, 
and matrix porewater. It does not account for mineral replacement, such as gypsum 
(CaSO4:2H2O) for anhydrite (CaSO4), caused by commingling of precipitates with concentrated 
solutions. Accordingly, for species identification (e.g. salts that can form on the drip shield) this 
should be taken into account by inclusion of all possible minerals that can form.

 3-115 
3.1.2.5.3 LRH Salts Model, Condensed Water Model, and HRH Salts Model 
These models together are intended for use in describing the evolution of water composition in 
the emplacement drifts for TSPA. The following discussion is taken mainly from the In-Drift 
Precipitates/Salts Analysis (CRWMS M&O 2000g). 
3.1.2.5.3.1 Input Data 
Equilibrium Relative Humidity Values 
Handbook values are used for the equilibrium relative humidity associated with aqueous 
solutions that are saturated with respect to different sodium and potassium salts. These values 
represent the maximum relative humidity at which a salt is stable at the given temperature. 
Composition of Influent Seepage 
For the LRH and HRH Salt Models, the composition of water from well J-13 is used to represent 
influent seepage. Other compositions may also be used. 
Test Data Used for Model Validation  Three sources of test data from Lawrence Livermore 
National Laboratory are used in the model validation discussion: 
 Synthetic J-13 water evaporation tests 
 Synthetic Topopah Spring matrix porewater evaporation tests 
 Tuff leaching/Synthetic 100 J-13 evaporation tests 
The first two of these test series were described previously, for the normative model. The third 
test (called Batch 1) involved dripping of 100 synthetic J-13 water through a column of 
heated tuff into a TeflonTM beaker. The recipe used for synthetic 100 J-13 well water did not 
include Si, Al, or Fe. The beaker was open to the atmosphere and maintained at a constant 
temperature of 90C and relative humidity of 85 percent. The starting and final solution 
compositions are shown in Table 3-23.

 3-116 
Table 3-23. Water Composition Data from Tuff Leaching/Synthetic 100  J-13 
Evaporation Tests (CRWMS M&O 2000g) 
Constituent Units 
Synthetic 100 J-13 
Well Water 
Evaporated Synthetic 
100 J-13 Well Water 
Ca mg/L 5.48 26 
Mg mg/L 2.04 0 
Na mg/L 4210 79700 
K mg/L 517 10020 
NO3 mg/L 732 14600 
CO3 mg/L as HCO3 790 a 11370 
Cl mg/L 730 15200 
F mg/L 208 3500 
SO4 mg/L 1633 30400 
pH pH nr b nrb 
NOTES: a Calculated from concentration factor of 14.4 (CRWMS M&O 2000g) 
b not reported 
Ranges of Temperature, Relative Humidity, and CO2 Fugacity 
Model calculations are performed for the following conditions: 
 Temperature is evaluated at 95C, 75C, 45C, and 25C to develop a response surface 
that is intended to cover a range of conditions in the potential repository for use in 
TSPA. 
 Relative humidity as a function of temperature and time, was approximated using 
previous TSPA-VA calculations (CRWMS M&O 2000g) corresponding to a 
simulation for which no backfill was included in the drift. 
 CO2 fugacity values are 10-1, 10-3, and 10-6 atm 
Relative Evaporation Rate 
The relative evaporation rate, or flux (Rrel) refers to the steady-state evaporation flux (Qevap) 
divided by the influent seepage rate flux (Qseep): 
seep 
evap 
rel Q
Q 
R = (Eq. 3-14) 
The values for Rrel used in this analysis are: 0, 0.1, 0.5, 0.9, 0.99, and 0.999. These are used to 
generate a lookup table that is intended to cover the range of evaporative concentration 
anticipated in TSPA.

 3-117 
Equilibrium Conditions 
The LRH and HRH models assume chemical equilibrium. Chemical reactions are assumed to 
occur rapidly compared to anticipated seepage and evaporation rates. Several slow-forming 
minerals are not allowed to precipitate (see below). 
3.1.2.5.3.2 Assumptions 
Assumptions for the LRH Salts Model 
Several simplifying assumptions are used in development of the LRH Salts Model. The LRH 
Salts Model assigns a constant seepage rate (Qseep) and a constant seepage composition to 
discrete time periods representing thermal evolution of the potential repository. The dissolved 
solids in the seepage composition are restricted to Na, K, NO3, SO4, Cl, and CO3 because, in 
accordance with previous discussions, these components are the most soluble and will dominate 
the solution composition as evaporation proceeds. 
The model begins by precipitating all dissolved components in the seepage flux, according to a 
normative distribution. As relative humidity increases, the salts are redissolved according to the 
tabulated threshold behavior discussed previously, to produce brine. This brine can then be 
transported out of the EBS at the liquid flow rate determined using the thermal-hydrologic 
models (Section 3.1.4) to estimate seepage. The amount and composition of brine produced are 
controlled by the solubilities of the salts and the assumed fraction of each salt that is allowed to 
dissolve as a function of time. For the nitrate salts the entire amount is allowed to dissolve when 
the relative humidity reaches 50 percent. For the remaining salts, the fraction dissolved is 
assumed to increase exponentially from zero to unity as time increases from relative humidity 
50 percent to 85 percent. At 85 percent relative humidity, all of the accumulated salts are 
completely dissolved. 
In addition to the foregoing discussion, the following other assumptions and uncertainties are 
identified: 
Vapor Pressure Lowering  In porous media or on solid surfaces, there are other mechanisms 
that decrease the saturation water vapor pressure of the liquid, such as capillary binding of water 
by surface tension, osmotic binding of water in double layers, and direct adhesion of water 
molecules to solid surfaces by London van der Waals forces (CRWMS M&O 2000g). For the 
LRH Salts Model it is assumed that these effects are negligible. 
Limiting Solubilities  As a simplifying assumption in the LRH model, the limiting solubilities 
are assumed to be 24.4 molal for nitrate salts (based on the pure-phase solubility of KNO3) and 
approximately 3 to 4 molal for non-nitrate salts. The latter range for the non-nitrate salts is 
chosen to provide a fit between the LRH Salts Model and the HRH EQ3/6 Pitzer model at 
85 percent relative humidity. This range of solubility is within the ranges for pure chloride, 
carbonate, and sulfate salts. 
Behavior of Carbonate  The carbonate concentration used in the LRH Salts Model is assumed 
to be soluble carbonate, which is determined from the Pitzer model of J-13 water evaporated to 
an ionic strength of approximately 10 molal (corresponding to approximately 85 percent relative

 3-118 
humidity). According to the EQ3/6 results, a considerable amount of carbonate precipitates with 
Ca and Mg, but carbonate continues to concentrate. At 10 molal ionic strength, the carbonate 
that remains in solution is considered "soluble" because it can only combine with K or Na. 
The LRH Salts Model assumes that dissolved inorganic carbon does not exchange with the 
atmosphere. To facilitate a smooth transition from the LRH Salts Model to the HRH Salts 
Model (at 10 molal ionic strength and 85% relative humidity) the carbonate concentration in the 
LRH brine composition is adjusted to achieve, for all values of relative humidity from 50 percent 
to 85 percent, a Na:CO3 ratio equivalent to the value of this ratio in the EQ3/6 model results for 
J-13 water concentrated to 10 molal. Thus as the normative assemblage of evaporatively 
precipitated salts dissolves with increasing relative humidity, the carbonate concentration is 
determined from the Na concentration. 
Charge Balance  Because of the approximations used to derive the water composition for the 
LRH Salts Model, particularly the treatment of carbonate, the composition is not necessarily 
charge balanced. Adjustments are made where appropriate, by adjusting the speciation of carbon 
between bicarbonate and carbonate. This is equivalent to an artificial adjustment of pH, and is 
needed because the mineral assemblage (minus nitrates) is dissolved congruently between 
50 percent and 85 percent relative humidity, rather than according to a mechanistic model that 
includes pH. 
Assumptions on Pitzer Database Development for the HRH Salts Model 
Modeling the behavior of electrolytes in concentrated aqueous solutions (>>1 molal ionic 
strength) is performed using ion-interaction equations, implemented in the EQ3/6 code. These 
semi-empirical equations are used to estimate activity coefficients that correct for non-ideal 
electrolyte behavior in concentrated saline waters. The EQ3/6 code includes the option to use 
Pitzer equations, with either of two Pitzer-type chemical databases. The Pitzer option extends 
the working range of the model from 1 molal ionic strength (using the B-dot equation) to 6 
molal, and possibly 10 molal or higher (CRWMS M&O 2000g) 
The two Pitzer databases included with EQ3/6 are the HMW and PIT databases (CRWMS M&O 
2000g). The HMW database is internally consistent, with 9 elements and 17 aqueous species. 
Many components important to potential repository modeling are not included in the HMW 
database, including Al, Fe, Si, F, and N. Also, the database is only applicable at 25C. 
The PIT database contains a larger set of components and aqueous species than the HMW 
database, and is applicable to temperatures spanning the range needed for potential repository 
modeling. However, the PIT database is not completely internally consistent, and does not 
include any carbon or silica species. The PIT database is unqualified and therefore designated as 
to-be-verified. 
A new Pitzer database was developed to include data from the HMW or PIT databases, and to 
add species not present in these databases. Specifically, the new PT4 database includes Na, K, 
Ca, Mg, Cl, F, CO3, SO4, NO3, SiO2, Fe(III), Al, H, and H2O at low and high ionic strength and 
temperatures ranging from 20C to 95C. Following published work on the extension of the 
Pitzer database (CRWMS M&O 2000g), coefficients for H3SiO4
-, Fe(OH)4
-, and Al(OH)4
- are

 3-119 
assumed to be identical to those for HSO4
-, while the coefficients for H2SiO4
-2 are assumed to be 
identical to those for SO4
-2. The Pitzer coefficients for aqueous SiO2 (or H4SiO4) are assumed to 
be identical to those for aqueous CO2 (or H2CO3). Further details of the construction of the PT4 
database are provided in the In-Drift Precipitates/Salts Analysis AMR (CRWMS M&O 2000g). 
For the PT4 database to claim a temperature range up to 100C, temperature derivatives of the 
cation-anion parameters are estimated. For the parameters not available in the PIT database, it is 
assumed that median values for all of the known species apply. Thirty values from the PIT 
database are used to determine the median values for this purpose. The same EQ3/6 basis 
species can be used in the COM, PIT, HMW, and PT4 databases, for the aqueous species and 
solids considered. Thus, the solubility data for minerals defined in the COM, PIT, and HMW 
databases can be imported to the PT4 database without recalculation. 
The PT4 database contains all of the minerals and gases originally within the PIT database plus 
CO2 (g) and a number of carbonates, silicates, and other minerals from the COM database. The 
additional gas and mineral phases were added because of their potential importance in potential 
repository modeling. 
Although validation of the PT4 database is demonstrated for the intended use in CRWMS M&O 
(2000t), the database is currently designated as to-be-verified. The identifications of minerals to 
be suppressed in the calculations are also to-be-verified. These assumptions do not affect 
calculations in dilute solutions. 
In addition to the foregoing discussion, the following assumptions and uncertainties are 
identified in development of the HRH Salts Model (Pitzer model): 
Standard State of Water or Brine  For the HRH Salts Model, non-standard state water is not 
considered. Only dissolved salts are considered to affect liquid-vapor equilibrium, and not 
capillarity, adsorption, double-layer effects, etc. This is justified because the effects are small, or 
affect only a small volume of the water present. 
Oxidizing Conditions  Redox conditions within the drift are assumed to be oxidizing. 
Reduced chemical species or oxidation-reduction reactions are not included in the model. This is 
justified because oxidizing conditions prevail in the host rock, both in the gas-phase and in the 
form of solid-phase precipitates such as hematite and MnO2. 
3.1.2.5.3.3 Model Uncertainties 
The principal uncertainties associated with the LRH and HRH Salts Models are related to 
representing solution composition at high ionic strength. The LRH Salts Model includes an 
approximation for the carbonate content, so pH is approximated during the interval of thermal 
evolution when this model applies. The HRH Salts Model is based on extensions to the Pitzer 
database, particularly the inclusion of new species and extrapolation to elevated temperatures. 
These are approximations, and there are corresponding limitations on model validity as discussed 
below. 
Another uncertainty is related to application of the LRH and HRH Salts Models to in-drift 
conditions. This concerns the mobility of fluids with the calculated compositions. Treating the

 3-120 
EBS as a flow-through system, whereby salts are redissolved and the brines are transported out 
of the EBS shortly thereafter, may underestimate residence times for salts and brines. This is 
because during this time interval: 
 Small volumes of liquid will be present in the EBS, so liquid saturation will be limited 
 Hydraulic conductivity of backfill and other EBS materials will be small, so flow 
velocities will be limited 
 Different salts will tend to form in different locations in the EBS, and there may be 
spatial heterogeneity of hydrologic processes. 
Accordingly, the drip shield could be exposed to concentrated solution conditions for longer than 
predicted using a flow-through model. Again, this uncertainty relates to the applicability of 
results from the LRH and HRH Salts Models, and not to the predicted chemical compositions. 
3.1.2.5.3.4 Model Development 
The LRH Salts Model is developed for relative humidity less than 85 percent, conditions for 
which the deliquescent behaviors of soluble salts control the aqueous chemistry. For such 
conditions, the seepage influx either evaporates completely, or concentrates to a stable brine. 
The LRH Salts Model consists of a set of algebraic calculations performed within a Mathcad file. 
The HRH Salts Model is developed for relative humidity greater than 85 percent, conditions for 
which soluble salts are fully dissolved, and the relative rates of evaporation and seepage control 
the aqueous chemistry. A modified Pitzer modeling approach is used in conjunction with the 
EQ3/6 chemical modeling code. 
The Condensed Water Model is developed for the relatively simple problem of water condensed 
on an inert surface, in the presence of gas-phase CO2 at elevated temperature. The EQ3/6 code is 
used for this application, in conjunction with the COM database. 
Each of these models is discussed in the following sections. 
LRH Salts Model Development 
In the LRH Salts Model, seepage water enters the drift and is subject to evaporation. At early 
times, the relative humidity is sufficiently low to vaporize all influent water, so the dissolved 
solids in the seepage accumulate. As discussed above, accumulated nitrate salts dissolve when 
the relative humidity increases 50 percent. For precipitates produced from evaporated J-13 
water, the nitrate brine is mostly from KNO3 and a small amount of NaNO3. 
As the relative humidity rises from 50 to 85 percent, the LRH Salts Model simulates brine 
generation by gradually dissolving the chloride, carbonate, and sulfate salts that have 
accumulated (and may continue to accumulate from seepage inflow). This period is divided into 
equal-length time intervals during which all the brine generated flows out of the drift (or reaction 
cell). (However, as discussed later, the model allows for some mixing between time increments.) 
The model dissolves these salts according to the assumed interpolation function:

 3-121 
50 85 
85 
t t 
) t t ( 4 
10 f - 
- 
= (Eq. 3-15) 
where f is the dissolved fraction of the total moles of chloride, carbonate, and sulfate present, and 
t is the time. The constants t50 and t85 are the times when relative humidity reaches 50 percent 
and 85 percent. The value of f increases exponentially as t approaches t85. The different salts 
that may be present at each time step are treated congruently. The fraction dissolved for NO3 and 
K is unity at the time relative humidity reaches 50 percent. 
The total amount of each component present at any given time is the sum of the dissolved and 
undissolved fractions. For each time interval, the total amount of each component is calculated 
by taking the amount from the previous interval, subtracting the dissolved fraction from the 
previous interval, and adding the contribution from seepage in the current time interval. The 
model thereby allows transport of the dissolved species out of the EBS. Mixing and dispersion 
are incorporated by subdividing each time increment into half-increments, and using a moving 
backward-average scheme. 
The dissolved/undissolved fractions and total inventory of Na at each time step are calculated by 
charge balance after the values for the other components are determined. The procedure 
maintains any charge balance errors introduced with the composition of influent seepage, but 
ensures that the aqueous phase composition is physically realizable. Further details are 
documented in the In-Drift Precipitates/Salts Analysis AMR (CRWMS M&O 2000g). 
Condensed Water Model Development 
This model calculates the composition of pH and ionic strength for water that may condense on 
inert surfaces, such as the underside of the drip shield. Water vapor condenses on such surfaces 
wherever the temperature and relative humidity permit. The model does not predict the timing, 
amount, or location of the condensation. Rather, it predicts the pH and ionic strength on 
equilibration with gas-phase CO2 at temperature. The condensing surfaces are assumed to be 
free from traces of soluble solids. EQ3/6 is used with the COM database for CO2 fugacity values 
of 10-1, 10-3, 10-4, 10-5, 10-6, 10-7, and 10-9 atm, and temperatures of 25, 45, 75, and 95C. The 
results are provided as look-up data. 
HRH (Pitzer) Salts Model Development 
The HRH Salts Model incorporates a modified Pitzer database, to calculate liquid phase 
compositions for ionic strength to approximately 10 molal. This is done within the framework of 
the existing EQ3/6 chemical modeling code. However, EQ3/6 includes Pitzer constants for only 
some of the components and temperature conditions needed for the HRH Salts Model. A 
modified Pitzer database (PT4) is used, which includes the species CO3, Si, Al, and Fe(III), for 
temperatures to 100C. Derivation of the PT4 database was discussed previously, and details are 
provided in the In-Drift Precipitates/Salts Analysis AMR (CRWMS M&O 2000g).

 3-122 
The HRH Salts Model is used in two modes: a simple evaporation mode, and a solid-centered 
flow-through mode. The simple evaporation mode is used to predict the evolution of a given 
solution (e.g., J-13 water) as it evaporates up to 10 molal. The second mode is used to predict 
the evaporative evolution of influent seepage. 
HRH Salts Model  Simple Evaporation 
Evaporation may be accomplished by the titration feature in EQ3/6 in two ways in this analysis. 
The traditional way is to declare an evaporation reactant (e.g., H2O) and designate it as an 
aqueous reactant type with a rate constant (rk1) value of -1. Reaction progress is allowed to 
proceed from zero to approximately 55.5, which is the number of moles of water in a kilogram of 
water. The reaction progress endpoint must be iteratively adjusted to achieve the final target 
ionic strength. Another method is to designate the evaporating water as a special reactant with 
appropriate molalities of H and O (approximately 111.0 molal and 55.5 molal, respectively). 
The rate constant (rk1) value is set to -1 and the reaction progress is varied from 0 to almost 1 
(depending the desired ionic strength). Either method can be used with the PT4 modified-Pitzer 
database to produce equivalent results. 
HRH Salts Model  Solid-Centered Flow-Through Model with Evaporation 
The EQ3/6 HRH Salts Model simulates evaporation within the drift using the solid-centered 
flow-through mode, addendum for EQ3/6. This software works with EQ3/6 and has the 
limitation that the liquid-phase water flux out of the cell is equal to the influent flux. For the 
HRH Salts Model, it would be more realistic for the liquid-phase water flux out of the cell to be 
equal to the difference between the influent seepage and evaporation mass fluxes. 
The approach used for the HRH Salts Model is to approximate the evaporative evolution of 
influent seepage, for steady-state boundary conditions, during discrete time intervals. The time 
intervals should, therefore, be defined so that the reaction cells have large flow-through liquid 
volume compared with the resident liquid volume. 
The steady-state solution composition calculated in this manner is controlled by the influent 
seepage composition and the relative evaporation rate defined previously. The evaporative 
concentration factor is calculated from 
rel in 
out 
R 1 
1 
C 
C 
- 
= (Eq. 3-16) 
which applies only for Rrel < 1. It should be noted that some components of the influent seepage 
will precipitate as evaporation occurs, so the concentration factor applies only to conservative 
species. 
The solid-centered flow-through option of the EQ3/6 is implemented by defining two reactants 
and reactant types, a displacer and a special reactant. The influent seepage is the displacer 
and water evaporation is the special reactant. By setting the displacer reactant rate constant 
(rk1) equal to unity for all simulations, the reaction progress is equivalent to the number of

 3-123 
liters (or pore volumes) entering the reaction cell. The reactant rate constant (rk1) for the 
special evaporation reactant is set equal to -Rrel, thus establishing the evaporation rate. 
The solid-centered flow-through approach described above is used with the PT4 modified Pitzer 
database. 
3.1.2.5.3.6 Model Validation for LRH Salts Model 
The LRH Salts Model is a simple interpolative model. The LRH Salts Model is constrained by 
the results of the HRH Salts Model at 85 percent relative humidity and by dry conditions below 
50 percent relative humidity. At 50 percent relative humidity and above, the brine composition 
is constrained by handbook properties for a saturated aqueous solution of sodium and potassium 
nitrate, and the volume of brine is constrained by mass balance. From 50 to 85 percent relative 
humidity, the LRH Salts Model makes a smooth transition in aqueous concentrations, as would 
be expected because the activity of water increases from 0.5 to 0.85, proportional to the relative 
humidity, during this transition. During this transition, mass balance and charge balance are 
maintained. Any remaining sulfate, chloride, and carbonate salts are increasingly dissolved as 
the relative humidity rises, subject to common-ion effects on solubility (CRWMS M&O 2000g). 
The LRH Salts Model results predict that as relative humidity increases above 50 percent, the 
chloride concentration quickly and conservatively approaches the high ionic strength end point 
of the EQ3/6 Pitzer model. High chloride concentrations are conservative because they can 
potentially increase corrosion rates. 
The LRH Salts Model results that are important for TSPA are a decrease in ionic strength and an 
increase in chloride concentration as the relative humidity rises from 50 to 85 percent. These 
performance measures constitute the intended use of the LRH Salts Model. From the foregoing 
discussion, the LRH Salts Model is valid for its intended use as an interpolative model for TSPA. 
Although there are no specific evaporation test data available to evaluate the accuracy of the 
LRH Salts Model, the model is valid because it produces reasonable trends and results for an 
evolving brine composition while negotiating the transition from dry conditions to 85 percent 
relative humidity, where the HRH Salts Model takes over. Given accurate inputs (e.g. seepage 
composition) the LRH Salts Model provides results that are conservative and within an order of 
magnitude of independently developed data for chloride concentration and ionic strength. This 
degree of accuracy is acceptable because it greatly reduces the potential ranges of these 
variables, thereby reducing uncertainty. 
Although simplifying assumptions are used to reduce complexity, especially where constraint 
data are lacking, these simplifications tend to be conservative. In particular, they tend to result in 
a shorter dry period, by not allowing dry conditions for relative humidity greater than 50 percent, 
in the presence of nitrate salts. The model also produces elevated chloride concentrations at low 
relative humidity, which is conservative and consistent with properties of pure salts (CRWMS 
M&O 2000k). 
The LRH Salts Model is constrained by the results of the HRH Salts Model at 85 percent relative 
humidity and by dry conditions below 50 percent relative humidity. At 50 percent relative 
humidity and above, the brine composition is constrained by handbook properties for a saturated

 3-124 
aqueous solution of sodium and potassium nitrate, and the volume of brine is constrained by 
mass balance. From 50 to 85 percent relative humidity, the LRH Salts Model makes a smooth 
transition in aqueous concentrations, as would be expected because the activity of water 
increases from 0.5 to 0.85, proportional to the relative humidity, during this transition. During 
this transition, mass balance and charge balance are maintained. Any remaining sulfate, 
chloride, and carbonate salts are increasingly dissolved as the relative humidity rises, subject to 
common-ion effects on solubility (CRWMS M&O 2000g). 
The LRH Salts Model results predict that as relative humidity increases above 50 percent, the 
chloride concentration quickly and conservatively approaches the high ionic strength end point 
of the EQ3/6 Pitzer model. High chloride concentrations are conservative because they can 
potentially increase corrosion rates. 
The LRH Salts Model results that are important for TSPA are a decrease in ionic strength and an 
increase in chloride concentration as the relative humidity rises from 50 to 85 percent. These 
performance measures constitute the intended use of the LRH Salts Model. From the foregoing 
discussion, the LRH Salts Model is bounding, and valid for its intended use. 
3.1.2.5.3.7 Condensed Water Model Validation 
The Condensed Water Model relies on well known and widely used chemical data which 
describe the solubility of CO2 in pure water as a function of temperature, and its aqueous 
speciation. The Condensed Water Model is therefore valid, subject to the validity of inputs 
which include CO2 fugacity vs. time in the potential repository environment. From this 
discussion the model is valid for its intended use in TSPA, to describe the composition of 
condensate that may contact the waste package under an intact drip shield. 
The model does not include the possible effects of dust that may be present on the waste package 
and drip shield surfaces. The presence of dust could lead to hydrolysis of silicate minerals, and 
dissolution of aerosols (e.g., sodium chloride). If the condensate were then evaporated, brines 
could form locally in small amounts. This behavior is currently under investigation. 
3.1.2.5.3.8 HRH Salts Model Validation 
This section describes model validation activities for the HRH Salts Model. The first approach 
taken involves modeling of laboratory tests described previously, in which synthetic J-13 water 
and synthetic porewater were evaporated. In the second approach, model calculations are 
compared with handbook solubility values for simple salts. 
Two evaporation tests using synthetic J-13 water are simulated using the HRH Salts Model. The 
first test was conducted in an open beaker at 85C (evap4). Detailed description of this test was 
provided previously in conjunction with the Normative Precipitates and Salts Model. The 
second test was conducted at 90C and fixed 85 percent relative humidity, and the test results 
were summarized previously in the section on input data.

 3-125 
Open-Beaker Evaporation of Synthetic J-13 Water at 85 C 
Figure 3-44 shows reasonable agreement between the measured and modeled values for pH, 
which increased to approximately 10, for the evap4 test. Modeling was performed using the 
modified Pitzer formulation with the PT4 database. The modeled pH is controlled by the 
fugacity of carbon dioxide which is fixed at 10-3.4 atm to approximate the open-beaker condition. 
For the data set shown in the figure, the water was evaporatively concentrated to 157. 
According to the HRH Salts Model calculations, the maximum ionic strength was approximately 
0.34 molal compared with 0.25 molal calculated from the measured data. 
Reported and modeled concentrations compare closely (within an order of magnitude) for Na, K, 
fluoride, bicarbonate, chloride, nitrate, and sulfate (CRWMS M&O 2000g). However, the model 
underestimates the reported concentrations of total dissolved Si and Ca by more than an order of 
magnitude, and underestimates the reported concentration of dissolved Mg by two orders of 
magnitude. These discrepancies may have been caused by kinetic limitations on precipitation, or 
by incorporation of particulate matter in the analytical samples, in the laboratory tests. 
Precipitates including chalcedony, calcite, and sepiolite are predicted by the model, but 
separation and analysis of precipitates were not performed at this stage of the test. 
Evaporation of Synthetic 100  J-13 Water at 90 C and 85 percent Relative Humidity 
A synthetic solution representing 100 concentrated J-13 water was contacted with crushed tuff 
at 90C, then dripped into a TeflonTM beaker that was open to a controlled atmosphere at 90C 
and 85 percent relative humidity (Batch 1 test). The solution was evaporated to approximately 
5 percent of the original volume. 
The composition of the final solution is calculated using the HRH Salts Model with the PT4 
database. Figure 3-45 shows the predicted change in pH and ionic strength as a function of the 
concentration factor. There were no pH measurements reported from the test. The CO2 fugacity 
was fixed at 10-3.4 atm, and the temperature at 85C. The ionic strength approximation for the 
final solution (based on the reported chemical analysis) was approximately 3.7 molal, which is 
close to the value calculated by the model. 
Model results agree with the observed concentrations for Na, K, fluoride, and sulfate (CRWMS 
M&O 2000g). For comparison of model results with the data, it is assumed that the reported 
nitrate concentration (relative to the original nitrate concentration) represents the bulk 
concentration factor for the solution. 
The model overestimates the reported bicarbonate concentration, probably because of the way 
the model corrects for charge imbalance by adjusting dissolved in organic carbon. In addition, 
the model underestimates the reported concentration of dissolved Ca by a factor of 30, and 
underpredicts the reported concentration of dissolved Mg by 2 orders of magnitude. These 
discrepancies may have been caused by kinetic limitations on precipitation, or by incorporation 
of particulate matter in the analytical samples, in the laboratory tests. Precipitates including 
calcite, brucite, sellaite, fluorite, and villiaumite are predicted by the model, but separation and 
analysis of precipitates were not performed in the test.

 3-126 
Open-Beaker Evaporation of Synthetic Porewater at 75 C 
Figure 3-46 shows reasonable agreement between the measured and modeled values for pH, 
which decreased to approximately 6.3 for the evap3 test. Modeling was performed using the 
modified Pitzer formulation with the PT4 database. The modeled pH was controlled by the 
fugacity of carbon dioxide which is fixed at 10-3.4 atm to approximate the open-beaker condition. 
For the data set shown in the figure the water was evaporatively concentrated to 1243. 
According to the HRH Salts Model calculations, the maximum ionic strength was approximately 
5 molal compared with 2.8 molal calculated from the measured data. 
Additional modeling results closely approximate the reported dissolved concentrations of Na, K, 
Mg, Ca, and chloride concentrations (CRWMS M&O 2000g). However, model results 
underestimate the reported concentrations of total dissolved Si, and dissolved sulfate, by at least 
an order of magnitude at a concentration factor of 1243. Concentrations of nitrate, bicarbonate, 
and fluoride were not reported. In the model, precipitation of chalcedony and anhydrite limited 
the total dissolved Si and dissolved sulfate concentrations predicted at a concentration factor of 
1243. Gypsum, which is similar to anhydrite, was identified in solid-phase separates using XRD. 
Upon evaporation to dryness, tachyhydrite, which was predicted to precipitate, was identified by 
XRD. Other minerals predicted to precipitate include calcite, carnallite, fluorite, sellaite and 
halite. These minerals were not observed using XRD, which may be the result of kinetic factors 
inhibiting precipitation, or of minute quantities making identification difficult. 
Evaporation of Pure Salt Solutions 
The HRH Salts Model was also used to model the solubility of several Na and K salts that are 
potentially important products of evaporating J-13 water. The solubilities calculated are 
compared to handbook values in Table 3-24. Salts that are predicted by the model to have 
solubilities exceeding 10 molal are shown as > 10 molal.

 3-127 
Table 3-24. Comparison of Handbook Aqueous Solubilities of Sodium and Potassium Salts at 100C 
with Values Calculated Using the HRH Salts Model with the PT4 Database 
Salt 
Handbook Aqueous 
Solubility at 100C (molal) 
Pure Phase Solubility at 100C Calculated by 
EQ3/6 Relative Humidity Model (molal) 
NaCl 6.70 7.21 
KCl 7.60 6.12 
Na2CO3H2O 4.2 3.99 
K2CO3 11.3 > 10 a 
NaF 1.21 1.01 
KF 26 > 10 a 
Na2SO4 3.01 1.55 
K2SO4 1.38 0.83 
NaNO3 21.2 3.60 
KNO3 24.4 3.60 
a Exceeds range of model 
Source: In-Drift Precipitates/Salts Analysis AMR (CRWMS M&O 2000g) 
The HRH Salts Model calculates solubilities for many salts that are within a factor of 2 of the 
handbook values (except for salts with solubilities exceeding 10 molal, the limit of the model). 
Among these, the largest differences are for the nitrates, which are underestimated by a factor of 
approximately 6. The consequence is that the model may predict the precipitation of nitrate salts 
from concentrating waters, when it should not. This discrepancy may be related to the procedure 
used to approximate Pitzer data for nitrate, in the PT4 database. 
Summary 
The HRH Salts Model provides valid approximations for pH and ionic strength in evaporated 
J-13 water and synthetic porewater, and for the solubilities of salts. These are key performance 
measures used in TSPA to model degradation of corrosion-resistant materials. For the test 
problems evaluated, pH was calculated to within 1 unit of observed values, and ionic strength to 
within a factor of 2. 
Greater discrepancies are encountered when the predicted concentrations of individual species 
are compared with observed values, particularly species for which Pitzer data are estimated 
(PT4 database). If the initial solution composition is dominated by such species, less agreement 
could result between predictions and observations, for pH and ionic strength. 
From this discussion, the HRH Salts Model is valid for its intended use in describing in-drift 
water compositions for TSPA. Despite limitations on the Pitzer (PT4) database, the model 
provides useful reduction of uncertainty in water composition.

 3-128 
3.1.2.5.4 Model Results 
The following sections summarize results reported in the In-Drift Precipitates/Salts Analysis 
AMR (CRWMS M&O 2000g) and provide some example figures. These results represent 
modeling that directly supports TSPA, with the final products being look-up tables. 
3.1.2.5.4.1 LRH Salts Model Results 
Results discussed in this section are for influent seepage flux of 1 L/yr, with the composition of 
J-13 water, and using a fixed CO2 fugacity of 10-3 atm. Reported results for the LRH Salts 
Models include the cumulative mass of each chemical component entering the drift (a reaction 
cell) over time, and the fraction of this mass for each component that is dissolved. The dissolved 
concentrations for several components are shown in Figure 3-47, plotted as functions of time 
according to the methods and assumptions for the LRH Salts Model. A constant rate of seepage 
inflow (1 L/yr) is assumed. 
The results also include mass balance calculations, which show the partitioning of mass for each 
component between dissolved and precipitated phases. Figure 3-48 shows the sum of nitrate, 
chloride, sulfate, and carbonate salts (primarily Na-salts) dissolved as brine, and the mass of 
water in that brine, as functions of time according to the methods and assumptions for the LRH 
Salts Model. 
The results are relatively insensitive to the CO2 fugacity. The effects of varying the CO2 
fugacity have been calculated and are incorporated into the lookup tables discussed above. The 
temperature is fixed at 95C for the LRH Salts Model because lower temperatures produce 
relative humidity values that are too high (>85 percent) for the model. The lookup table values 
tend to be insensitive to the influent seepage flux, within a range that is substantially less than 
percolation or seepage conditions that could impact the thermal-hydrologic conditions in the 
drifts. In other words, large values of the influent seepage flux would be associated with 
temperature perturbations, and would affect the duration of elevated temperature in the potential 
repository, so there is an upper limit of seepage for the application of LRH Salt Model results 
calculated using 1 L/yr. 
3.1.2.5.4.2 HRH Salts Model Results 
The HRH Salts Model is used to predict the composition of water subjected to simple 
evaporation, and to evaporation combined with addition of incoming seepage. The following 
discussion presents results for simple evaporation of J-13 water, and evaporation when a constant 
incoming seepage is allowed. The figures and text are taken from the In-Drift Precipitates/Salts 
Analysis AMR (CRWMS M&O 2000g) which provides additional details. 
3.1.2.5.4.3 Evaporation of J-13 Water 
Evaporation of average J-13 water is simulated using the modified Pitzer model and the 
PT4 database. The temperature is 95C and the CO2 fugacity is fixed at 10-3 atm. Figure 3-49 
shows the evolution of pH and ionic strength; the modeled pH approaches 10, then decreases to 
about 9 at a concentration factor of 10,000. Although the HRH Salts Model development is

 3-129 
limited to 10 molal ionic strength, results beyond this range are presented in this section to show 
the model response. 
Calculations show that the elements C, Cl, K, Na, N, and S simply concentrate without 
precipitating except in small amounts. Fluoride concentrates until fluorite (CaF2) precipitates. 
The elements Si, Al, Ca, Mg, and Fe precipitate in significant quantities relative to their aqueous 
concentrations. 
Figure 3-50 shows the evolution of precipitates formed. Among the precipitates included in the 
model, calcite and chalcedony are produced in the greatest quantity. Sepiolite and fluorite (at 
later times) are the next most abundant. The model predicts precipitation of several smectite 
clays (Ca-montmorillonite, Na-nontronite, and Ca-nontronite) and a zeolite (Na-clinoptilolite), at 
abundances which are several orders of magnitude less than for chalcedony and calcite. 
3.1.2.5.4.4 Results for Evaporation Combined with Constant Incoming Seepage 
When evaporation flux exceeds influent seepage flux, water in the reaction cell will become 
increasingly concentrated so that the only possible steady-state conditions are complete 
vaporization (i.e., dry conditions with salt deposits) or a brine system that is controlled by the 
relative humidity. When the influent seepage flux is less than the evaporation flux, evaporative 
concentration and steady through-flow occur, and the steady-state aqueous-phase composition 
predicted by the HRH Salts Model applies after a sufficient number of through-flow pore 
volumes. 
The evolution of water in the potential repository drifts, as temperature falls and relative 
humidity rises over time, can be generalized as evolution from brine to increasingly dilute water. 
This evolution is modeled as a succession of time intervals, during each of which the incoming 
seepage flux and composition are constant, the temperature and evaporation flux are constant, 
and the system composition reaches a steady state. At each time interval, the model converges to 
constant solution composition after approximately 10 pore volumes. The relative evaporation 
rate and the incoming seepage composition are the important factors in achieving steady 
conditions. 
The calculated figures and tables (response surfaces) represent steady-state conditions after a 
sufficient number of pore volumes have flowed through the reaction cell. Evaporative 
concentration results are calculated for J-13 water, equilibrated with CO2 fugacities of 10-1, 10-3, 
and 10-6 atm. Figure 3-51 and Figure 3-52 show the pH, calculated as a function of 
concentration factor, for two values of the CO2 fugacity. These results show that pH is more 
sensitive to CO2 than to the relative evaporation rate. 
The results for ionic strength indicate slight sensitivity to CO2 fugacity and temperature. For 
J-13 water, the ionic strength can reasonably approximated by direct application of the 
concentration factor. Deviations from this response are caused by precipitation. 
3.1.2.5.4.5 Condensed Water Model Results 
Calculations show that the pH and ionic strength of condensed water are sensitive to temperature 
and the CO2 fugacity. Figure 3-53 shows that the pH decreases considerably as the CO2 fugacity

 3-130 
increases above 10-5 atm. Increased temperature results in a higher pH, as CO2 exhibits 
retrograde solubility. At low CO2 fugacities, the pH is insensitive to the CO2 fugacity and 
temperature. Ionic strength is small for all conditions modeled, indicating that temperature is 
more important to ionic strength predictions when the CO2 fugacity is low. When the CO2 
fugacity is high, it determines ionic strength for condensed water. 
3.1.2.6 EBS Colloids Model 
This model bounds the impact of ferric-oxide and ferric-oxyhydroxide colloids on RN transport 
in the invert, specifically considering the impacts resulting from use of steel in the EBS. The 
results show that the effect of steel in the EBS can be bounded, depending on the affinity of 
corrosion products for radionuclides of interest (e.g. Pu). The intended use for this model is FEP 
screening, and support of the design basis. 
Colloidal processes are also described by other documents, in regard to releases from the waste 
form (CRWMS M&O 2000z), radionuclide transport through the unsaturated zone (CRWMS 
M&O 2000o), and transport through the saturated zone (CRWMS M&O 2000ab). In addition, 
the abstraction of EBS colloidal processes for TSPA is described in Section 3.2.1.1.5. Criteria 
for determining the relative importance of reversible and irreversible sorption vary for these 
model applications, so the same colloidal transport process may be considered reversible in one 
context and irreversible in another. 
In this model the size distribution and maximum concentration of colloids are estimated from 
natural analogs, and assumed to be entirely hematite colloids. Other colloid types may be 
present including clays, silica, and waste form colloids (spent fuel or waste glass). Laboratory 
results discussed below indicate that ferric-oxide colloids have greater affinity for radionuclides 
of interest than silica or clays. However, waste form colloids have the potential to transport 
radionuclides and are not considered in this model, therefore the model may not bound the 
overall potential for colloidal transport. 
Aqueous colloids are suspensions of solid particles in water. The diameters of the particles 
typically range from a few nanometers to a few thousand nanometers, which produces a very 
large surface area per unit mass of material. The behavior of colloids is, accordingly, controlled 
by surface forces and processes, including electrostatic repulsion or attraction and surface 
chemical reactions with species in solution. The stability and capacity of colloids to adsorb 
radionuclides are complex functions of solution chemistry, temperature, and other variables. 
Radionuclide-bearing colloids can adversely affect potential repository performance because 
they can travel large distances in groundwater with little or no retardation. Radioactive colloids 
include intrinsic colloids (i.e., radionuclides provide the dominant metal species in the particles, 
as in hydrous actinide polymers or colloidal actinide silicate and phosphates) and pseudocolloids 
(formed by the sorption, entrainment, or other incorporation of radionuclides on or within 
colloidal particles of other materials). 
Although they have been extensively studied in the laboratory, actinide polymers do not appear 
to be important for the potential Yucca Mountain potential repository. No actinide polymers 
have been reported in studies on the degradation by water contact of commercial spent nuclear

 3-131 
fuel (CSNF) and defense high-level waste (DHLW) glass (CRWMS M&O 2000t). However, 
intrinsic colloids of actinide silicates and phosphates were generated along with pseudocolloids. 
In addition, recent laboratory studies (CRWMS M&O 2000t) demonstrate that Pu is as rapidly 
sorbed by pseudocolloids from hydrous Pu(IV) polymers as it is from solutions of Pu(V). 
Hence, the bounding analysis that follows will focus on the behavior of radioactive 
pseudocolloids, and the term colloid should be understood to mean pseudocolloids in the 
remainder of this discussion. 
The most important colloid-forming materials for radionuclide sorption include clay minerals 
(particularly smectites) and colloidal iron oxides (such as hematite and goethite). Radionuclides 
can also be sorbed on colloidal silica, but with a generally smaller sorption coefficient than with 
clays and iron oxides. Clays are present as components of colloids naturally found in Yucca 
Mountain groundwater and are also generated when either waste form is corroded by water, as is 
documented extensively in (CRWMS M&O 2000t). Colloidal iron compounds may be 
generated from the large masses of ferrous alloys used in large quantities within the waste 
package as well as in the ex-container EBS. As shown in Table 3-4, even without including the 
iron content of the waste package and its internals, there is more than 106 g of Fe per meter of 
emplacement drift. 
A conceptual model for colloid generation, mobility, and affinity for radionuclides within the 
EBS is combined with available data on colloidal transport and sorption capacity for 
radionuclides to produce a bounding analysis of the degree to which colloids may increase the 
aqueous concentrations of radionuclides above their respective solubility limits 
3.1.2.6.1 Conceptual Framework for Colloids Model 
Colloids are considered stable if they do not agglomerate and settle out of a static suspension 
over the time period of interest. The stability of colloids suspended or entrained in groundwater 
(i.e., their tendency to remain suspended) is a function of pH, oxygen potential (Eh), ionic 
strength, composition of the colloidal particles, temperature, flow velocity, and the composition 
and structure of the medium through which the groundwater is moving (CRWMS M&O 2000t). 
It is unlikely that the evolution of these variables after closure of the potential repository can be 
predicted accurately, however, the available information does permit a bounding analysis that 
comprises the following elements: 
 Colloid particle size distributions have been measured in groundwater samples pumped 
from 18 wells in the vicinity of Yucca Mountain. The composition of these particles is 
being investigated, but this information is not yet available. The data represent the 
concentration of colloidal material that can be transported in groundwater along flow 
pathways between the potential repository and the accessible environment. The 
representation is conservative because colloid concentrations near a pumping well are 
probably increased by enhanced colloid detachment, caused by flow velocity that is 
greater than for undisturbed flow of natural groundwater. 
 The abundance of iron in the EBS will provide a large source of oxides and 
oxyhydroxide corrosion products. There is no compelling argument to preclude 
formation of colloids from these corrosion products, so it is conservative to assume that

 3-132 
all of the products are of colloidal size. Entrainment of colloids in the groundwater and 
release to the host rock will occur only after sufficient water reenters the drift to 
support advective flow. 
 When transport of ferric-oxide begins, the size distribution will be similar, and is 
assumed to be identical, to the distribution of natural colloids discussed previously. 
The underlying concept is that colloids outside the observed size range will not be 
transported over long distances, either because they are unstable or because they 
become attached to the porous media through which the water flows. 
 For this model, the total concentration of each radionuclide is expressed as the sum of 
the concentration in solution and that adsorbed on colloidal particles. It can be 
expressed as an enhancement factor (a simple function of colloid mass concentration 
and sorption coefficient) multiplied by the solubility limit for the radioelement. 
 Laboratory data shows that sorption of actinides on ferric-oxide colloids is essentially 
irreversible. In the model, sorption coefficients are bounded by laboratory data. 
 Sorption on silica and clays is reversible and of smaller magnitude than sorption on 
ferric-oxide colloids. Accordingly, considering only the ferric-oxide colloids results in 
a conservative approach for potential long-distance colloidal transport of radionuclides. 
3.1.2.6.2 Colloid Size Distribution and Concentration 
Data for size distribution and colloid concentration are plotted in Figure 3-54 and Figure 3-55. 
Particle concentrations in counts per milliliter are given for sizes ranging from 50 to 200 nm at 
10-nm increments. Analysis of the data shows that the normalized distribution (fraction of 
particles within each size range) is closely approximated by a log-normal distribution for each of 
the samples; it also shows that the parameters of these distributions are so similar that a single 
distribution can represent the colloid size distribution for all 18 wells. The distribution of 
measured data from each well, and two composite log-normal curves (one for nine Nye County 
well samples and one for nine Yucca Mountain well samples) are shown in Figure 3-54. The 
composite log-normal curves are nearly identical. 
Mathematically, the normalized log-normal distributions are represented as follows: 
. .. 
. 
. .. 
. 
s 
 - 
F = 
c 
c c 
c 
) D ( ln 
) D ( F (Eq. 3-17) 
where
Dc = colloid particle diameter, nm 
c = mean of the natural log of the colloid particle diameter, nm 
sc = standard deviation of the natural log of the colloid particle diameter, nm 
F(x) = normal probability integral for any variable x

 3-133 
The final average parameters recommended for the normalized colloid size distribution are 
c = 4.4258 and sc = 0.3509. The total number of colloid particles per milliliter in the 
18 groundwater samples is also closely approximated by a log-normal distribution, of the form 
. .. 
. 
. .. 
. 
s 
 - F = 
N 
N ) N ( ln 
) N ( F (Eq. 3-18) 
where
N = total number of colloid particles, counts per milliliter 
N = mean of the natural log of the total number of colloid particles per milliliter 
sN = standard deviation of the natural log of the total number of colloid particles per 
milliliter 
F(x) = normal probability integral for any variable x 
The parameters of the distribution are estimated by direct calculation of the natural-log mean and 
natural-log standard deviation from the data, resulting in  = 19.4841 and s = 1.9911. 
3.1.2.6.3 Sorption Coefficients 
Iron compounds are of particular importance because the corrosion products can readily form 
colloids. Also, two corrosion products (hematite and goethite) summarized in Table 3-25 have 
high sorption coefficients, and sorption on these minerals may be irreversible. Corrosion 
products of other metals are expected to be less important sources of colloids than ferric-oxide, 
primarily because of the abundance of steel in the drift. 
Table 3-25. Sorption Coefficient (Kd) Values in mL/g for Sorption of Pu(IV), Pu(V), and Americium-243 
on Hematite, Goethite, Montmorillonite, and Silica Colloids 
Sorption Coefficient Values 
Radionuclide Water Hematite Goethite Montmorillonite Silica PST-1 
Natural 2105 a 7104 3103 5103 Pu(IV) 
Synthetic 7105 2105 2105 3104 
Natural 1105 6104 1104 ND Pu(V) 
Synthetic 1105 2105 1104 ND 
Natural 1105 ND 1104 1104 243Am 
Synthetic 1105 ND 1104 5103 
Source: CRWMS M&O 2000t 
NOTES: Colloid concentrations are at 1000 mg/L for Pu and at 200 mg/L for Am. 
ND = no data

 3-134 
These experiments used both natural J-13 well water (NAT-J-13) and synthetic J-13 water 
(SYN-J-13). Suspensions of colloids in each of these dilute electrolytes were prepared for 
hematite, goethite, montmorillonite, and two different silica materials. Average particle sizes 
were 139 nm for both types of silica colloids, between 100 and 200 nm for goethite, 334 nm for 
montmorillonite, and 416 nm for hematite. Radionuclide solutions comprised Pu(V) at 
2.74  107 M in both electrolytes, colloidal Pu(IV) at 2.40  107 M in NAT-J-13 and 2.35  
10-7 M in SYN-J-13, and 243Am at 1.26  108 M in both electrolytes. The particle size of the 
Pu(IV) colloid was less than 10 nm. All solutions had pH values between 8.0 and 8.4. 
Three series of experiments were run: 
 Sorption of Pu(IV) and Pu(V) on 1,000 mg/L suspensions of each colloid (hematite, 
goethite, montmorillonite, two types of silica) 
 Sorption of 243Am on 200 mg/L suspensions of each of the above colloids except 
goethite 
 Sorption of Pu(V) and 243Am on suspensions of each of the above colloids except 
goethite for concentrations of 10, 50, 100, 150, 200, 1,000, and 5,000 mg/L 
Not all of the combinations listed were reported. The 243Am experiments in Series 3 were not 
completed at the time this report was prepared (CRWMS M&O 2000t). Partition coeffiient (Kd) 
values obtained in Series 1 and 2 are shown in Table 3-25. 
In addition to the sorption measurements, data were reported on the desorption of Pu(IV) and 
Pu(V) from Pu-loaded samples of hematite, goethite, montmorillonite, and silica colloids after 
96 hr of sorption. After 150 days of agitation in natural or synthetic J-13 water, desorption was 
far from complete for any of the colloids, per the following: 
 Essentially no Pu was desorbed from hematite. 
 Less than 1 percent of Pu was desorbed from goethite. 
 About 8 percent of Pu(IV) and less than 1 percent of Pu(V) was desorbed from 
montmorillonite. 
 About 20 percent of Pu(IV) and 6 percent of Pu(V) was desorbed from silica colloids. 
Based on this laboratory work, a bounding sorption coefficient value of Kd = 7  105 mL/g is 
used in this model. These laboratory results show that sorption is irreversible for Pu. It is 
possible that sorption on montmorillonite (and possibly other clays) and silica could be 
reversible over a time of decades, but complete reversibility is not evident from the reported 
data. However, given the large amount of steel in the emplacement drifts, iron colloids are likely 
to be present in greater amounts. Also, they have greater affinity for Pu, so behavior of the 
siliceous colloids is less important to radionuclide transport.

 3-135 
3.1.2.6.4 Bounding Values of Radionuclide Solubility Enhancement Factor 
The enhancement factor for colloidal transport represents the factor by which the total amount of 
a radionuclide in groundwater is increased over the amount in solution at the time the 
radionuclide was adsorbed. For irreversible adsorption, the amount in solution may be equal to, 
less than, or greater than the solubility limit at any point along the flow path after the colloid is 
loaded with radionuclide. Mathematically, the enhancement factor E is defined by 
C d 
0 
Total M K 1 
C 
C 
E + = = (Eq. 3-19) 
where: 
CTotal = total radionuclide concentration in solution and suspension (units consistent with 
C0) 
C0 = radionuclide solubility limit (units consistent with CTotal) 
Kd = sorption coefficient, mL/g colloid 
MC = mass concentration of colloids, g/mL of suspension. 
Assuming spherical particles, the mass concentration of colloids is given by 
N 
6
D 
M 
3 
C 
C  
p. 
= (Eq. 3-20) 
where . is the density of the colloid particles, assumed constant. In this equation, both DC and N 
are log-normally distributed random variables, with parameters discussed previously. These 
random variables appear to be independent, exhibiting little or no correlation in the data. The 
distribution of particle diameter is rather narrow, which implies that most of the uncertainty or 
variability arises from the total particle count. For a bounding analysis, one can average the 
mass concentration over the particle diameter distribution, as follows: 
N 
6
D 
M 
3
C 
D C c 
 
p. 
= (Eq. 3-21) 
where the left-hand side is a random variable representing the mass concentration averaged over 
the particle diameter distribution. 
The notation 
X denotes the average of the random variable x over its distribution. For a 
log-normal distribution with parameters  and s, the average of x3 is given by 
. .. 
. 
. .. 
. s +  = 
2 
9 
3 exp x 
2 
3 (Eq. 3-22) 
Using the parameters for the size distribution results in

 3-136 
3 6 
2 
3
C nm 10 x 0161 . 1 
2
3509 . 0 9 
4258 . 4 3 exp D = . .. 
. 
. .. 
.  +  = (Eq. 3-23) 
The density of anhydrous hematite (5.240 g/mL) (CRWMS M&O 2000t) is an upper bound on 
the density of hydrous hematite. This value is used to obtain an order of magnitude estimate for 
the mass of a spherical colloid particle with a diameter cubed equal to 1.0161106 nm3, using 
Equation 3-21. The result is 2.7878  109 g per particle. 
All that remains is to calculate the total mass of colloids per mL of suspension, which requires a 
value for the total number of particles per milliliter. As noted previously, N is also log-normally 
distributed, with parameters  = 19.4841 and s = 1.9911. Specific values for the enhancement 
factor require selecting a fractile on the cumulative distribution function (CDF) of N. 
Calculations for several fractiles are documented in Attachment XVI and are summarized in 
Table 3-26. At the 99th percentile, this analysis predicts an enhancement factor of less than 100. 
Table 3-26. Summary of Calculations for the Colloid Mass at Different Fractiles of the Log-Normal 
Distribution for the Number of Particles per mL 
CDF for Number of 
Particles 
per mL 
Standardized Normal 
Variable 
Colloid Particles per 
mL 
Colloid Mass 
g/mL 
Enhancement 
Factor for Kd = 
7.E+05 mL/g 
0.99000 2.3263 3.0E+10 8.3E+01 59 
0.97500 1.9600 1.3E+10 4.0E+01 29 
0.95000 1.6449 7.7E+09 2.1E+01 16 
0.90000 1.2816 3.7E+09 1.0E+01 8.3 
0.84027 0.9956 2.1E+09 5.9E+00 5.1 
0.75000 0.6745 1.1E+09 3.1E+00 3.2 
0.50000 0.0000 2.9E+08 8.1E01 1.6 
Source: CRWMS M&O 2000t 
NOTE: The enhancement factor estimate is also shown, based on the largest value of Kd reported in Table 3-25. 
The value of the standardized normal variable reported here was carried to one additional significant figure 
in the calculation, and is reported here without modification. 
The 84th percentile corresponds to the arithmetic mean number of particles predicted by this 
bounding analysis, resulting in an enhancement factor of approximately 1 percent. 
At the 99th percentile, the estimated total mass of colloidal hematite is 82.9 mg/L. For 
comparison, the total dissolved solids (TDS) content of J-13 water averages about 250 mg/L. 
Evaporative concentration, and interaction of seepage water with cement grout, would further 
increase the TDS. Except for the extreme right tail (p > 0.95) of the colloid mass CDF, colloids 
will be less than 10 percent of the TDS content.

 3-137 
Calculation of the enhancement factor as a function of Kd, at the 99th percentile gives the 
following results: 
 For Kd = 106, E = 83.9 
 For Kd = 105, E = 9.3 
 For Kd = 104, E = 1.8 
Factors of 2 are not generally considered significant in radionuclide release and transport 
calculations for potential repository performance assessment, so this bounding analysis suggests 
that colloid-enhanced radionuclide transport will be important only if the colloid has a sorption 
coefficient equal to or greater than 105 mL/g. 
3.1.2.6.5 Bounding Values for Colloid Diffusion Coefficient 
One potential function of the invert ballast in the ex-container EBS is to provide, under the drip 
shield, a diffusion barrier between the waste package and the host rock. If water is successfully 
diverted by the backfill/drip shield system and effectively drained from the drift into the host 
rock, little or no water would flow beneath the waste package. Potentially, the water content in 
this region could be kept so low that diffusion rather than advection would dominate 
radionuclide transport. A model for diffusivity of dissolved radionuclides is documented in the 
Invert Diffusion Properties AMR (CRWMS M&O 2000h). For an invert material with 
50 percent porosity and 5 percent water saturation, the diffusion coefficient of a dissolved ion 
will be about three orders of magnitude below its value in bulk solution (i.e., with no porous 
medium present). 
It could be supposed that no colloidal transport would be possible without advective flow. 
However, diffusion along a surface film of water is possible, at least for the smaller size colloids. 
Figure 3-56 summarizes values for the diffusion coefficient in dilute suspensions as a function of 
particle diameter, over a range of colloids (CRWMS M&O 2000t). These values apply in bulk 
suspensions and are reduced from typical values for dissolved species by two to three orders of 
magnitude. Even with an enhancement factor of 10 or so, diffusion-controlled radionuclide mass 
release as particles would be from 10 to 100 times lower than the diffusion of dissolved species. 
Actual diffusivity in a water film may be even lower because the StokesEinstein equation 
assumes no interaction of the diffusing particle with any substance other than the solvent. 
Therefore, diffusion of colloids through the invert can be neglected entirely in performance 
assessment. 
3.1.2.6.6 EBS Colloids Model Validation 
This model is based on inferences relating the abundance and size of natural colloids in Yucca 
Mountain groundwaters, with the concentrations of ferric-oxide and ferric-oxyhydroxide colloids 
in the EBS. In addition, sorption coefficients and reversibility are inferred from laboratory tests 
on hematite colloids. 
As stated previously, the intended use of this model is to bound the effect of steel in the EBS, on 
the potential for colloidal transport of radionuclides. The model is bounding because the entire

 3-138 
mobile colloid load in EBS waters is assigned to hematite colloids, which have relatively high 
affinity for radionuclides such as Pu. Other colloids such as clays and silica will be present and 
tend to decrease the hematite colloid concentration. The model is also bounding because 
sampling of groundwater from wells is more dynamic than percolation in the EBS will be, so 
colloids tend to be mobilized at greater concentrations. Another important bounding aspect of 
this model is that sorption of Pu is considered irreversible, so that once sorbed, the enhanced 
mobility of pseudo-colloidal transport in the groundwater system persists for the lifetime of the 
radionuclide. 
Whereas hematite is the most stable Fe-oxide likely to form in the potential repository, other 
solids such as goethite and ferrihydrite could also be present. These lower oxides could have 
greater surface area and sorption capacity for radionuclides. It is possible that these phases will 
mature to hematite with time in the repository, however, the endpoints and timing of such 
evolution are not established. It is likely that the bounding approximations mentioned above, 
would encompass any differences in potential radionuclide transport that could be attributed to 
the lower oxides. 
From this discussion it is concluded that the EBS Colloids Model is bounding, and valid for its 
intended use in FEP screening and support of the design basis. 
3.1.2.7 Chemical Reference Model 
The Chemical Reference Model calculates the evolution of water composition in the EBS, and 
the precipitation and dissolution of minerals, for time periods to 10,000 years. Results from the 
TH case selected in Section 3.1.2.1 are combined with gas fugacity results from Section 3.1.2.2, 
and normative mineral assemblages produced using the method of Section 3.1.2.5.2. A 
schematic of the submodel relationships for the Chemical Reference Model is show in Figure 
3-40. 
The Chemical Reference Model is intended to couple thermal-hyrologic, gas-phase processes, 
aqueous chemistry, and evaporative precipitates. In addition, it is used to evaluate CO2 balance, 
and the effects of cementitious materials. As stated in Section 3.1, the intended use of the 
Chemical Reference Model is FEP screening, and support of the design basis by identifying 
environmental conditions, such as identifying the salts that may be present on the drip shield. 
Descriptions of the waste package and drip shield, and the environments on the surfaces of these 
barriers, are provided in the Waste Package Degradation Process Model Report (CRWMS M&O 
2000n, Section 3.1). 
The Chemical Reference Model uses the evolution of maximum CO2 and O2 fugacities from 
Section 3.1.2.2, and also uses those results to evaluate CO2 mass balance in the drifts and the 
surrounding host rock, as a function of time. The effects of carbon steel corrosion, and leaching 
from cementitious materials, are evaluated by comparing reference model results with scoping 
chemical calculations. 
The Chemical Reference Model does not predict the full range of actual solution compositions 
that may occur in the emplacement drifts, particularly during the thermal period when it is most 
likely that ionic strength could exceed 1 molal. The model does not predict the composition or

 3-139 
behavior of brines. Other approaches have been developed to represent brines for TSPA 
(Section 3.1.2.5.3). 
The Chemical Reference Model addresses the evolution of water composition in the host rock 
above the emplacement drifts. This is needed to establish the compositional boundary condition 
for influent water to the drifts. It is noted that for TSPA, water composition at the drift wall is 
calculated using a fully coupled, reactive transport model (CRWMS M&O 2000x). The 
resulting water compositions are not closely comparable to the Chemical Reference Model 
because the starting composition for water in the host rock is different for the two approaches. 
(The Drift-Scale THC Seepage Model uses a starting composition resembling tuff matrix 
porewater, which produces more neutral pH when evaporatively concentrated.) 
3.1.2.7.1 Conceptual Model Development and Alternative Models 
The modeling approach represents the in-drift environment and the host rock as a set of zones, or 
reaction cells, which are defined in Section 3.1.2.1.3. Temporal evolution is represented by a 
series of discrete time periods extending to 10,000 years, which are defined in Section 3.1.2.1.6. 
Within each time period the environmental conditions at each zone, and the fluxes between 
zones, are constant. 
The host-rock processes that control the chemistry of water entering the drifts as seepage, are 
summarized in Figure 3-57. The composition of J-13 well water is used as a far-field reference 
composition because it is an analog for fracture waters in the host rock, and because it produces 
alkaline pH conditions when evaporatively concentrated. Unsaturated porewater samples from 
nonwelded tuff units above the potential repository horizon, and a small number of samples from 
the welded host rock (Tptpmn), have compositions that are enriched in chloride, sulfate, and 
calcium (CRWMS M&O 2000t). However, J-13 water is the composition predicted by chemical 
models based on host-rock mineralogy. Also, perched water samples from below the potential 
repository horizon, and natural-analog fracture water samples from Rainier Mesa, have 
compositions similar to J-13 water. 
Reaction cells in the Chemical Reference Model have residence times of months to years, so 
kinetic hindrance of dissolution/ precipitation reactions is not critical. As concluded in 
Section 3.1.2.3.3.1, quartz exhibits kinetics that are relatively slow among the minerals modeled, 
but quartz equilibrium is a reasonable approximation for the reference model. Important 
equilibrium processes include interaction of formation waters with cristobalite and calcite in the 
host rock, and redissolution of evaporatively precipitated minerals in the drifts. 
As pointed out in Section 3.1.2.2, reactive transport simulation that incorporates TH and 
chemical processes is a possible alternative to some parts of this system model. The fine spatial 
and temporal discretization that is possible with some numerical simulators, corrects some of the 
artifacts of granularity in the zones and time periods used in this model. For example, the mass 
accumulation of precipitates and salts in the invert, that is predicted by this model, is exaggerated 
because temporal granularity extends the time interval during which there is seepage inflow and 
no outflow, due to complete evaporation in the drift. Conversely, the peak temperatures, fluxes, 
and other environmental conditions in the drift can be underestimated when their evolution is 
represented by constant conditions within discrete time intervals. Reactive transport simulations

 3-140 
also have limitations, particularly with respect to modeling the chemistry of concentrated 
solutions and evaporative precipitation, and the number of species and mineral phases that can be 
considered. 
Modeling of Precipitates and Salts 
A simplified treatment of precipitates and salts accumulation, and the consequent chemical 
environment on the surface of the drip shield, is used in this model. One result is that for 
bounding the environmental conditions at the drip shield, salts or brines are considered to be 
present from the onset of liquid flow into the drift, through the duration of the 10,000-yr 
performance period. Salts will accumulate from episodic seepage, or movement of condensate 
that can form within the drifts. Over the long-term, brines will form as relative humidity 
increases, according to the discussion of brine formation in the Precipitates and Salts Model 
(Section 3.1.2.5). 
The predicted quantity of precipitates and salts, and the timing of their remobilization, are 
calculated but considered uncertain. This is justified because results presented in Section 3.1.2.1 
show that there is wide variation in the timing and potential quantity of salt accumulation in the 
backfill and the invert, for a range of potential repository conditions. For some locations and 
flux conditions, the potential salt accumulation in the drift will be slight (at the edge of the 
layout, with low flux or minimal seepage). For other conditions (center of the potential 
repository, high seepage) the accumulation could be 106 times greater (Figure 3-25 through 
Figure 3-28). For low-flux conditions the duration of boiling conditions may be 3,000 years or 
more, whereas for high-flux conditions the duration may be 400 years or less (Figure 3-19). 
Seepage conditions in the drifts are controlled by fractures and likely to be strongly 
heterogeneous, so in the same section of emplacement drift there could be large local differences 
in the accumulation and duration of precipitates and salts. 
3.1.2.7.2 Input Data, Assumptions, and Uncertainties for Chemical Modeling 
Reference Chemical Composition of Fracture Water in the Host Rock 
Naturally occurring percolating fracture waters have not been observed in the host rock, possibly 
because fracture flow is episodic. As discussed previously, J-13 water is a reasonable analogue 
for fracture water that percolates through the host rock and may seep into drifts. The major 
chemical constituents of J-13 water, and measured data representing the effects of evaporative 
concentration, are discussed in Section 3.1.2.5. That model shows how J-13 water, compared 
with matrix porewaters that contain relatively more chloride and sulfate than bicarbonate anions, 
produces more alkaline pH conditions during evaporative concentration. 
Thermal-Hydrologic Conditions 
Zone-averaged temperature, liquid fluxes, vapor fluxes, and liquid masses are calculated by the 
TH Model (Section 3.1.2.1). The composite zones representing the emplacement drifts, and the 
host rock, are defined in Figure 3-15 and Figure 3-16 (Section 3.1.2.1.3). Selection of the L4C4 
potential repository location with the upper infiltration distribution, as a reference model for 
use in chemical modeling, is described in Section 3.1.2.1.7. The liquid water and water vapor 
fluxes between composite zones, and the liquid mass, average temperature, and evaporative

 3-141 
concentration factor for each composite zone, are also calculated using the models discussed in 
that section. 
CO2 and O2 Fugacities 
For chemical modeling, the CO2 and O2 maximum fugacities for each time period are calculated 
in Section 3.1.2.2. These fugacities are considered uniform throughout the zones modeled 
(zones are defined in Section 3.1.2.1.3). A mass-transfer relationship between flux and fugacity 
is also developed, and is used for comparison with consumption rate estimates in this section. 
Thermodynamic Data 
The thermodynamic data used for these calculations consists of the data0.com file supplied 
with EQ3/6. Only a subset of the data in this file are important to the chemical modeling 
presented in this section. The majority of the data used are also part of the data0.sup file. 
A number of potential minerals removed from the calculations by artificially suppressing their 
formation. This is accomplished in part by using an input file-suppression option in EQ3/6. 
However, because the number of minerals to be suppressed exceeds the hard-coded array limits, 
a number of these minerals are eliminated from a special copy of the data0.com data file. This 
reduced data file ("data0.elh") and a list of the suppressed phases, are included in source 
documentation (CRWMS M&O 2000t). 
The rationale for suppressing certain minerals is twofold. First, it is recognized that kinetics 
generally prevents the formation of certain phases under the conditions of temperature and 
pressure in the potential repository system, on the pertinent time scale. Second, it is recognized 
that the existing thermodynamic database overestimates the stability of a number of silicate 
minerals with respect to clay minerals. Both arguments are supported by observed mineral 
assemblages, including those at Yucca Mountain in both fractures and the tuff matrix. The 
mineral assemblages in the calculations are thus partly controlled by judgment, and not just by 
the available thermodynamic data (CRWMS M&O 2000t). 
Kinetics of Quartz Precipitation 
The kinetics of quartz precipitation is potentially important because of the use of quartz sand 
backfill. In the rock surrounding the drift, quartz and cristobalite (a less stable, naturally 
occurring polymorph) coexist in chemical disequilibrium over geologic time. The concentration 
of dissolved silica corresponds to near-equilibrium with cristobalite and supersaturation with 
respect to quartz. This condition is maintained in the rock at Yucca Mountain because of the 
slow growth kinetics of quartz. That condition could be replaced in the sand backfill by one of 
near-equilibrium with quartz, resulting in a significant decrease in dissolved silica. 
The precipitation and dissolution of silicate minerals is generally accepted to be a surface areamediated 
process (i.e., the rate is proportional to the area of the mineral-water interface). A 
published rate law (Section 3.1.2.3.3.1) describing the kinetics for dissolution and precipitation 
of quartz and other SiO2 minerals is used to examine the rate of quartz growth (via overgrowths) 
in the backfill (CRWMS M&O 2000t). The results show that water-quartz equilibrium is a 
reasonable and conservative approximation for this model.

 3-142 
Model Uncertainties 
The principal uncertainties associated with this model arise from heterogeneity of hydrologic 
processes, and from spatial and temporal discretization. This model represents the host rock, 
backfill, and invert as reaction cells, but flow focusing and nonuniform hydrologic properties 
could cause flow to bypass regions of the EBS. One possible consequence would be that brine 
conditions derived from precipitates and salts, could persist on the surface of the drip shield for 
longer than predicted. Spatial and temporal discretization increase the accumulation of 
precipitates and salts (Section 3.1.2.7.5). 
3.1.2.7.3 Modeling Approach and Implementation 
The Chemical Reference Model combines input from the Thermal Hydrology Model, Gas Flux 
and Fugacity Model, Precipitates and Salts Model (CRWMS M&O 2000t) to produce a 
description of chemical processes in the EBS. The model describes the EBS environment for a 
set of bounding conditions selected so that the results can be used as the basis for design. 
3.1.2.7.3.1 Modeling Water Composition in the Host Rock Above the Drift (Zone 1/2) 
The host rock above the drift is represented by a compositional boundary condition at Zone 0 and 
by a reaction cell at Zone 1/2. (Zones are defined in Section 3.1.2.1.3; time periods in Section 
3.1.2.1.6.) The calculated composition in Zone 1/2 represents the composition of seepage, 
modified by elevated temperature, CO2 fugacity, partial evaporation, and chemical interaction 
with the host rock. The flux of water from Zone 0 to Zone 1/2 is calculated by the TH Model, 
and the composition of this flux is similar to that of J-13 water (CRWMS M&O 2000af). 
Using EQ3/6 to represent the host rock (Zone 1/2), separate models for each time period are 
prepared. These are equilibrium models using EQ3NR, which is part of the EQ3/6 code package 
(CRWMS M&O 2000t). The equilibrium approach is justified because the starting far-field 
(Zone 0) composition is already close to solubility equilibrium with host rock minerals. 
Estimates of reactive surface area for the host rock are not required. 
The calculations for the far-field and near-field host rock waters (Zone 0 and Zone 1/2) are based 
on a conceptual model for J-13 water in which the bicarbonate, H+, and Ca2+ components are 
mutually controlled by the fugacity of CO2, equilibrium with calcite, and electrical charge 
balance. The model also assumes that the minor Al3+, Fe2+, and Mg2+ components are controlled 
by equilibrium with selected ideal clay minerals and that minor Mn2+ is controlled by 
equilibrium with pyrolusite (MnO2). Other components are taken to follow specified 
concentrations based on previous work referenced in the EBS Physical and Chemical 
Environment Analysis/Model Report (CRWMS M&O 2000t), corrected for evaporative 
concentration. 
When applied to the reference composition of J-13 well water, using a subsurface CO2 fugacity 
of 10-3 atm, this modeling approach yields almost exactly the observed Ca2+ concentration and a 
pH of approximately 8.1. The model is also supported by the fact that because fracture water in 
the UZ very likely coexists with calcite, so that equilibrium with that mineral is highly likely. 
The calculated pH is higher than the average value of 7.41 reported for J-13 water (CRWMS

 3-143 
M&O 2000t), and the likely reason is different CO2 conditions in the aquifer compared with the 
UZ. 
The expected thermodynamic controls on the solution composition can be extrapolated up to 
approximately the boiling point of the water. One additional constraint is required to represent 
the concentration of aqueous silica. This is set to be the greater of: 1) the concentration reported 
for J-13 water (CRWMS M&O 2000t), or 2) the concentration corresponding to solubility 
equilibrium with cristobalite. Values of the CO2 fugacity from the Gas Flux and Fugacity Model 
(Section 3.1.2.2), and evaporative concentration factors calculated from the TH Model 
(Section 3.1.2.1) for Zone 1/2 waters, are also applied here. 
3.1.2.7.3.2 Modeling Water Composition and Mineral Precipitation in the Backfill 
(Zone 3/4) 
According to the TH Model results, water from the host rock (Zone 1/2) does not enter the 
backfill (Zone 3/4) until Time Period 2 (300 to 700 years). (Zones are defined in Section 
3.1.2.1.3; time periods in Section 3.1.2.1.6.) During this time period the liquid influx is balanced 
by vapor outflux, and the calculated liquid water mass in the backfill (Zone 3/4) is small. The 
cumulative liquid influx during the time period is approximately 104 times the resident mass. 
Accordingly, the formation of precipitates is calculated ignoring the liquid residue. This is 
justified because small amounts of water will be dispersed in the backfill as tightly held pore 
water, chemically bound water, and as brine (when humidity conditions permit). 
3.1.2.7.3.3 Modeling the Normative Assemblage of Evaporative Minerals Formed in 
the Backfill (Zone 3/4) 
Using the host rock (Zone 1/2) water composition for Time Period 2, an assemblage of minerals 
is calculated using the normative approach described in Section 3.1.2.5. (Zones are defined in 
Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) All of the solutes in the influent water are 
precipitated to form the assemblage, which is a simple approximation. The approximation is 
conservative in the sense that all the salts which can form, are considered to be in contact with 
the drip shield, and may form brines from interaction with gas-phase humidity, but are not 
remobilized during Time Period 2 regardless of the humidity. 
The LRH Salts Model described in Section 3.1.2.5 (applicable to relative humidity < 85 percent) 
allows the most soluble salts (e.g. nitrates) to dissolve as the relative humidity increases. The 
brines that can form (e.g., nitrates, chlorides, carbonates) are potentially mobile in the relative 
humidity range from 50 percent to 85 percent or greater. For the reference model described here, 
the relative humidity is calculated to be in approximately this same range when evaporative 
precipitation occurs, so concentrated brine can exist, but it is regarded as immobile. 
Note that trace species, particularly lithium and boron, are neglected in the normative 
assemblages identified in this model.

 3-144 
3.1.2.7.3.4 Modeling Redissolution of Precipitates When Liquid Flux Returns to the 
Backfill (Zone 3/4) 
All calculations involving reactions between influent water and backfill or evaporative 
precipitates, are performed using the EQ6 code (this is also part of the EQ3/6 package). The 
evaporative mineral assemblage comprises minerals many of which have solubilities greater than 
1 molal (e.g., niter, halite, thermonatrite). It is possible for much of the accumulated mineral 
mass to be redissolved by a small amount of water. However, it is also possible that salt 
dissolution could be hindered by spatial heterogeneity of flow processes, relative to the 
accumulation of salts. 
For this model, redissolution is assumed to occur congruently, with a resulting solution ionic 
strength of 1 molal (CRWMS M&O 2000t). Congruent dissolution means that the dissolution 
rate for each solid is proportional to its abundance, and that complete dissolution of all 
precipitates and salts occurs at the same time. Congruent dissolution is a simple concept that 
prolongs the residence time for the more soluble salts. 
The 1 molal ionic strength limit corresponds to the upper limit for use of the B-dot activity 
coefficient model (CRWMS M&O 2000t). Using this limit (in conjunction with discrete time 
periods and stepwise constant flow conditions) may overestimate the residence time for the 
normative mineral assemblage. It nevertheless indicates relatively rapid removal (within a few 
years; see below). This shows that even if large quantities of precipitates and salts are deposited, 
they can be readily redissolved and removed by seepage fluxes which are comparable in 
magnitude to those which evaporated to produce the precipitates in the first place. 
The use of 1 molal as the ionic strength limit is not bounding with respect to the most 
concentrated solution conditions that could exist on the drip shield. Instead, the bounding case is 
represented by the normative assemblage of salts, having equilibrated to the ambient relative 
humidity. The 1-molal calculation provides insight as to solution chemistry that will occur in the 
presence of seepage, whereby the salt accumulation is gradually remobilized, with less than full 
efficiency, by the dripping water. The solution ionic strength could be greater than or less than 
1 molal when seepage occurs, and will vary locally. 
Redissolution in the backfill is modeled by introducing the water composition from the host rock 
(Zone 1/2) into the backfill (Zone 3/4) at the start of Time Period 3 (700 to 1,500 years). (Zones 
are defined in Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) In the EQ6 model, the 
normative evaporative mineral assemblage is titrated congruently into 1 kg of liquid water until 
the ionic strength is 1 molal (within 1 percent). Quartz is present as the major component of the 
sand backfill, and controls the concentration of dissolved silica in the resulting liquid phase, as 
discussed below. 
A sensitivity calculation using EQ6, and a published rate law and kinetic data for quartz growth, 
is performed to assess the need to consider rate-limited reactivity for quartz. The calculation 
starts with a water composition whereby the other processes (e.g., precipitate dissolution) are 
completed to equilibrium. The quartz sand surface area discussed previously is used in the rate 
calculation. The calculation shows a marked decline in dissolved silica over a time of less than 
one year. Because the quartz sand surface area is a lower bound, a shorter time period could

 3-145 
produce the same result. Also, the decline in dissolved silica follows an exponential decay 
function in which most of the decline takes place early in any time interval; thus, most of the 
effect could be achieved in even less time. Because of these factors, all other calculations 
involving the quartz sand backfill were made using instantaneous equilibration with quartz. 
3.1.2.7.3.5 Modeling Water Composition and Mineral Precipitation in the Invert 
(Zone 5/6) 
According to the TH results (produced using the model described in Section 3.1.2.1) water from 
the backfill (Zone 3/4) does not enter the invert (Zone 5/6; which includes the lower backfill plus 
the crushed-tuff invert) until Time Period 3 (700 to 1,500 years). (Zones are defined in Section 
3.1.2.1.3; time periods in Section 3.1.2.1.6.) During this time period the liquid influx is balanced 
by vapor outflux, and the calculated liquid water mass in the invert (Zone 5/6) is limited. The 
cumulative liquid influx during the time period is approximately 3600 times the resident mass of 
liquid water. 
3.1.2.7.3.6 Modeling the Normative Assemblage of Evaporative Minerals Formed in 
the Invert (Zone 5/6) 
Using the backfill (Zone 3/4) water composition for both Time Period 3A and Time Period 3B, 
an accumulation of evaporatively precipitated minerals is calculated using the approach 
described in Section 3.1.2.5. (Zones are defined in Section 3.1.2.1.3; time periods in Section 
3.1.2.1.6.) The general approach is the same as the normative model for precipitates in the 
backfill, discussed above. During Time Period 3A the precipitates in the backfill (Zone 3/4) are 
dissolved, producing a water with assumed ionic strength of 1 molal, that subsequently flows to 
the invert (Zone 5/6) and evaporates. During Time Period 3B the composition of water flowing 
from the backfill to the invert is more dilute, because the accumulated precipitates are completed 
redissolved. The duration of Time Period 3B is approximately 100 times longer than Time 
Period 3A, so potentially significant solute mass is transported to the invert during this period in 
the model. Note that trace species, particularly lithium and boron, are neglected in the normative 
assemblages identified in this model. 
3.1.2.7.3.7 Modeling Redissolution of Precipitates When Liquid Flux Returns to the 
Invert (Zone 5/6) 
Like the backfill, the evaporative mineral assemblage in the invert will comprise mineral which 
have solubilities greater than 1 molal (e.g., niter, halite, thermonatrite). As discussed for 
Zone 3/4, it is possible for much of the accumulated mineral mass to be redissolved by a small 
amount of water, but other factors may hinder salt dissolution. Redissolution is assumed to 
occur congruently, with resulting solution ionic strength limited to 1 molal. 
Redissolution is modeled by introducing the water composition from the backfill (Zone 3/4) into 
the invert (Zone 5/6) at the start of Time Period 4 (1,500 to 2,500 years). (Zones are defined in 
Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) In the EQ6 model, the evaporative mineral 
assemblage is titrated into 1 kg of liquid water until the ionic strength is 1 molal (within 1 
percent). Equilibrium with quartz is again assumed because of the large surface area presented 
by the portion of the backfill that is present in Zone 5/6. Crushed tuff is present in the invert, and

 3-146 
it is likely that the concentration of silica may increase once the water reaches this material. 
However, the surface area of the tuff is much less than for the sand, so such a potential increase 
in dissolved silica is neglected in the present calculations. 
3.1.2.7.4 Chemical Reference Model Validation 
The Chemical Reference Model is valid for its intended use, which is FEP screening, and support 
of the design basis. It is not a bounding model, although the contributing submodels are 
developed using conservative approximations. There are limitations and uncertainties associated 
with the reference model, particularly the spatial and temporal discretization discussed 
previously. The model represents the host rock and the EBS as a small number of well-mixed 
reaction cells. Accordingly, use of the model is limited to investigating average conditions, and 
cumulative consumption of reactants such as CO2. 
3.1.2.7.5 Results for the Chemical Reference Model 
3.1.2.7.5.1 Water Composition in the Host Rock Above the Drift (Zone 1/2) 
The water compositions calculated for the host rock (Zone 1/2), for each time period, are shown 
in Table 3-27. (Zones are defined in Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) Water 
compositions are affected principally by temperature-dependent solubility and PCO2. Prograde 
solubility of cristobalite increases the silica concentration with temperature. 
Note that lower CO2 fugacities result in higher pH values. This pH increase corresponds to loss 
of CO2. Also, the pH values represent somewhat more alkaline conditions than would be 
calculated for ambient temperature (e.g., 31C) owing to the contraction of the upper end of the 
practical pH range at elevated temperatures. The pH is effectively controlled by the H3SiO4
- 
/cristobalite buffer (noting that solubility of aqueous SiO2 in these waters is controlled by 
cristobalite) and not by the HCO3
-/CO3
2- buffer. There is a loss of dissolved Ca2+ that is 
effectively due to precipitation of calcite. The dissolved components Al3+, Fe2+, Mg2+, and Mn2+ 
vary but remain minor. Small changes in the concentrations of relatively conservative species 
such as Cl-, F-, SO4
2-, NO3
-, Na+, and K+ are caused by evaporative concentration (or 
condensative dilution, represented by concentration factors less than unity). 
Normative Assemblage of Precipitates and Salts Formed in the Backfill 
Using the host rock (Zone 1/2) water composition for Time Period 2, an assemblage of minerals 
is calculated using the approach described in Section 3.1.2.5. The results are shown in 
Table 3-28 for a half-drift model. Approximately 20 kg (full-drift basis) of various precipitates, 
mostly amorphous silica, are predicted to accumulate in the backfill above the springline rises to 
about 10.8 in Time Period 3A (the maximum value encountered in the calculations presented 
here). This is mainly because of the strong evaporative concentration (90.6 percent), which 
concentrates the OH- component in solution to about 0.62 molal. In later time periods, the extent 
of evaporation is not so great, and the pH does not rise so high. Approximately 14.6 years are 
needed to redissolve the accumulated precipitates into a solution with 1 molal ionic strength, 
using the input data and assumptions adopted.

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3.1.2.7.5.2 Redissolution of Precipitates Formed in the Backfill (Zone 3/4) 
The results from EQ6 modeling of precipitate redissolution and other processes in the backfill 
(Zone 3/4), during Time Period 3A, are shown in Table 3-29. (Zones are defined in Section 
3.1.2.1.3; time periods in Section 3.1.2.1.6.) In Time Period 3A, quartz and calcite are 
precipitated as the evaporative precipitates (apart from calcite) are redissolved. Both of these 
minerals are present at the start of this time period, and more of each is deposited. CO2 is 
initially evolved during redissolution (including titration of calcite into solution) but is consumed 
in Time Period 3B (an open-system or constant-fugacity CO2 boundary condition is used). 
The pH increases to approximately 10.8 in Time Period 3A (the maximum value encountered in 
the calculations presented here). This is mainly because of the strong evaporative concentration 
(90.6 percent), which concentrates the OH- component in solution to about 0.62 molal. In later 
time periods, the extent of evaporation is not so great, and the pH does not rise so high. 
Approximately 14.6 years are needed to redissolve the accumulated precipitates into a solution 
with 1 molal ionic strength, using the input data and assumptions adopted.

 3-148 
Table 3-27. Calculated Water Composition in the Host Rock (Zone 1/2) for Time Periods 1 through 5 
Nominal Time (years) 
100 500 1000 2000 5000 
Temperature (C) 80.81 90.05 88.42 79.96 51.69 
PCO2 (atm) 9.084E-07 1.805E-06 1.536E-06 5.405E-06 3.314E-05 
PO2 (atm) 2.384E-04 4.736E-04 4.030E-04 1.416E-03 8.608E-03 
Evaporation/ 
Condensation Factor 1.088 0.9778 0.8782 0.9895 0.9995 
pH 9.318 9.139 9.162 9.140 9.243 
I (molal) 4.273E-03 4.041E-03 3.961E-03 2.924E-03 2.486E-03 
Al3+ 1.940E-06 2.407E-06 2.265E-06 1.417E-06 2.904E-07 
B(OH)3(aq) 1.365E-05 1.227E-05 1.101E-05 1.242E-05 1.255E-05 
Ca2+ 6.365E-04 6.392E-04 6.866E-04 2.385E-04 4.316E-05 
Cl- 2.191E-04 1.969E-04 1.769E-04 1.993E-04 2.013E-04 
F- 1.249E-04 1.122E-04 1.007E-04 1.135E-04 1.147E-04 
Fe2+ 8.812E-16 4.994E-16 5.449E-16 9.124E-16 5.698E-15 
HCO3
 2.250E-05 2.305E-05 2.194E-05 6.406E-05 7.237E-04 
K+ 1.403E-04 1.260E-04 1.132E-04 1.276E-04 1.288E-04 
Li+ 7.492E-06 6.771E-06 6.051E-06 6.771E-06 6.915E-06 
Mg2+ 3.148E-10 3.464E-10 3.460E-10 8.011E-10 7.715E-09 
Mn2+ 1.363E-14 3.649E-14 2.911E-14 2.578E-14 3.708E-15 
NO3
- 1.541E-04 1.385E-04 1.244E-04 1.401E-04 1.415E-04 
Na+ 2.167E-03 1.948E-03 1.750E-03 1.971E-03 1.991E-03 
SO4
2 2.084E-04 1.873E-04 1.682E-04 1.895E-04 1.914E-04 
SiO2(aq) 3.584E-03 3.741E-03 3.665E-03 2.804E-03 1.275E-03 
Sr2+ 5.022E-07 4.451E-07 3.995E-07 4.565E-07 4.565E-07 
Source: CRWMS M&O 2000t 
NOTE: All concentrations in mol/kg H2O unless otherwise specified 
a Calculated data from EQ3NR output files for Zone 1/2 (filenames "Z1w_0100.3o", "Z1w_0500.3o", 
"Z1w_1000.3o", "Z1w_2000.3o", and "Z1w_5000.3o")

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Table 3-28. Normative Evaporative Mineral Assemblage Predicted to Accumulate in the Backfill 
(Zone 3/4; multiply by 2 to obtain full-drift basis) during Time Period 2 (300 to 700 years) 
Mineral Formula 
Moles of Precipitates 
(mol/m) a 
Molar Mass 
(kg/mol) a 
Mass of 
Precipitates (kg/m) a 
Niter KNO3 3.993E+00 1.011E-01 4.038E-01 
Na-niter NaNO3 3.934E-01 8.500E-02 3.344E-02 
Fluorite CaF2 1.778E+00 7.808E-02 1.388E-01 
Villiaumite NaF 0.000E+00 4.199E-02 0.000E+00 
Sylvite KCl 0.000E+00 7.455E-02 0.000E+00 
Halite NaCl 6.239E+00 5.844E-02 3.646E-01 
Mg-smectite b Mg0.165Al2.33Si3.67O10(OH)2 6.652E-05 3.667E-01 2.439E-05 
Ca-smectite b Ca0.165Al2.33Si3.67O10(OH)2 3.266E-02 3.676E-01 1.201E-02 
Na-smectite b Na0.333Al2.33Si3.67O10(OH)2 0.000E+00 1.420E-01 0.000E+00 
Thenardite Na2SO4 5.934E+00 1.420E-01 8.429E-01 
Anhydrite CaSO4 0.000E+00 1.361E-01 0.000E+00 
Tachyhydrite CaMg2Cl6O10:12H2O 0.000E+00 6.776E-01 0.000E+00 
Calcite CaCO3 1.847E+01 1.001E-01 1.848E+00 
Magnesite MgCO3 0.000E+00 8.431E-02 0.000E+00 
Thermonatrite Na2CO3:H2O 2.161E+01 1.240E-01 2.679E+00 
Amorphous Silica SiO2 1.184E+02 6.009E-02 7.116E+00 
Total 1.344E+01 
Source: CRWMS M&O 2000t 
NOTES: a Values correspond to accumulation in a half-drift model. Multiply by two to obtain accumulation in the 
full drift cross-section.

 3-150 
Table 3-29. Composition of Water in the Backfill (Zone 3/4) after Return of Liquid Water, Starting with 
Redissolution of Evaporative Precipitates in Time Period 3A 
Time Period 
3A 3B 4 5 
Temperature (C) 96.05 96.05 86.95 56.95 
PCO2 (atm) 1.536E-06 1.536E-06 5.405E06 3.314E05 
PO2 (atm) 4.030E-04 4.030E-04 1.416E03 8.608E03 
Evaporation/Condensation Factor 10.635 10.635 1.0950 1.004 
pH 11.081 9.920 9.276 9.319 
I (molal) 1.001E+00 2.025E02 2.812E03 2.502E03 
Al3+ 1.815E-03 2.410E-05 1.551E-06 2.915E-07 
B(OH)3(aq) 1.170E-04 1.172E-04 1.360E-05 1.260E-05 
Ca2
+ 7.280E-06 3.548E-05 1.194E-04 3.061E-05 
Cl 1.485E-01 1.882E-03 2.182E-04 2.021E-04 
F 6.836E-02 1.072E-03 1.243E-04 1.152E-04 
Fe2+ 5.788E-15 5.372E-15 9.990E-16 5.721E-15 
HCO3 7.208E-02 1.549E-04 7.878E-05 8.148E-04 
K+ 9.502E-02 1.205E-03 1.397E-04 1.293E-04 
Li+ 6.427E-05 6.439E-05 7.414E-06 6.943E-06 
Mg2+ 5.583E-13 4.525E-11 8.771E-10 7.746E-09 
Mn2+ 5.583E-13 3.098E-13 2.823E-14 3.722E-15 
NO3
 1.044E-01 1.323E-03 1.534E-04 1.421E-04 
Na+ 1.469E+00 1.862E-02 2.158E-03 1.999E-03 
SO4
2 1.412E-01 1.790E-03 2.075E-04 1.922E-04 
SiO2(aq) 7.139E-01 7.821E-03 1.481E-03 5.339E-04 
Sr2+ 9.846E-08 8.840E-07 4.998E-07 3.648E-07 
Moles Dissolved (<0 = Formed) per 1 kg Influent H2O 
Halite 1.380E-02 
Niter 8.833E-03 
NaNO3 8.706E-04 
Mg-smectite 1.472E-07 
Thenardite 1.313E-02 
Thermonatrite 4.781E-02 
SiO2 (amophous) 2.620E-01 
Fluorite a 3.170E-03 
Ca-smectite 7.227E-05 
Calcite -3.900E-03 -6.832E-04 -1.295E-04 -1.267E-05 
Quartz -1.988E-01 -2.930E-03 -1.451E-03 -7.432E-04 
Moles Evolved (<0 = Used) per 1 kg Influent H2O 
CO2 (g) 3.720E-02 -6.800E-04 -1.400E-04 -1.000E-04 
Source: CRWMS M&O 2000t 
NOTES: All concentrations in mol/kg H2O unless otherwise specified. 
Normative species with zero predicted abundance are not reported in this table. 
Fluorite is solubility-limited and slow to dissolve; the figure shown results in removal of ~80% of the 
accumulated fluorite.

 3-151 
3.1.2.7.5.3 Water Composition After Redissolution of Precipitates and Salts in the 
Backfill (Zone 3/4) 
After Time Period 3, the water composition in Zone 3/4 returns to conditions that are similar to 
those in the host rock (Zone 1/2) except for the effects of evaporative concentration, and 
interaction with quartz. (Zones are defined in Section 3.1.2.1.3; time periods in Section 
3.1.2.1.6.) Calcite continues to precipitate as seepage flows from the host rock into the backfill, 
and CO2 continues to be consumed (Table 3-29). 
3.1.2.7.5.4 Normative Assemblage of Evaporative Minerals Formed in the Invert 
(Zone 5/6) 
Two normative mineral assemblages are calculated for the invert (Zone 5/6): one for Time 
Period 3A (when precipitates from the backfill are remobilized to the invert) and one for Time 
Period 3B (solute derived mainly from the host rock, and transported through the backfill). 
(Zones are defined in Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) The results are shown 
in Table 3-30 for a half-drift model. As much as 200 kg of various precipitates, mostly 
amorphous silica, is predicted to precipitate in the lower backfill and invert (full-drift basis). 
3.1.2.7.5.5 Redissolution of Precipitates and Salts Formed in the Invert (Zone 5/6) 
The evaporite minerals are redissolved from the invert (Zone 5/6) during Time Period 4A 
(analogous to the backfill in Time Period 3A). (Zones are defined in Section 3.1.2.1.3; time 
periods in Section 3.1.2.1.6.) The results from EQ6 modeling of precipitate redissolution are 
shown in Table 3-31. Quartz and calcite precipitate as the normative assemblage (apart from 
calcite) is redissolved. Approximately 7.1 years are required to redissolve the accumulated 
precipitates into a solution with 1 molal ionic strength. 
3.1.2.7.5.6 Water Composition After Redissolution of Precipitates and Salts in the 
Invert (Zone 5/6) 
After Time Period 4, the water composition in the invert (Zone 5/6) returns to conditions that are 
similar to those in the host rock (Zone 1/2); this can be verified by comparing water 
\compositions for Time Period 4B and Time Period 5 in Table 3-31. (Zones are defined in 
Section 3.1.2.1.3; time periods in Section 3.1.2.1.6.) As the normative assemblage is dissolved 
during Time Period 4A, CO2 is evolved, but during Time Period 4B there is little inter-phase 
transfer of CO2 (note that an open-system, or constant-fugacity, CO2 boundary condition is 
used). This is probably because the influent waters to the invert (Zone 5/6) have already reacted 
to elevated temperature, and contact with quartz and calcite, in the host rock and backfill. 
3.1.2.7.5.7 CO2 Consumption by Abiotic Chemical Processes in the EBS 
In this model, CO2 is consumed or produced by several types of chemical processes: 
 Evaporation/condensation processes in which CO2 is exchanged with the gas-phase 
 Precipitation/dissolution reactions involving species such as calcite and thermonatrite

 3-152 
Table 3-30. Normative Evaporative Mineral Assemblage Predicted to Accumulate in the Invert 
(Zone 5/6; multiply by 2 to obtain full-drift basis) during Time Period 3 (700 to 1500 years) 
Mineral Formula 
Moles 
Precipitates 
Time Period 3A 
(mol/m) a 
Moles 
Precipitates 
Time Period 3B 
(mol/m) a 
Total 
Moles 
Precipitates 
(mol/m) a 
Molar Mass 
(kg/mol) a 
Mass of 
Precipitates 
(kg/m) a 
Niter KNO3 6.228E+01 3.081E+01 9.309E+01 1.011E-01 9.413E+00 
Na-niter NaNO3 6.140E+00 3.037E+00 9.177E+00 8.500E-02 7.800E-01 
Fluorite CaF2 4.772E-03 9.075E-01 9.123E-01 7.808E-02 7.123E-02 
Villiaumite NaF 4.480E+01 2.560E+01 7.040E+01 4.199E-02 2.956E+00 
Sylvite KCl 0.000E+00 0.000E+00 0.000E+00 7.455E-02 0.000E+00 
Halite NaCl 9.733E+01 4.813E+01 1.455E+02 5.844E-02 8.501E+00 
Mg-smectite b Mg0.165Al2.33 
Si3.67O10(OH)2 
2.218E-09 7.014E-06 7.016E-06 3.640E-01 2.554E-06 
Ca-smectite b Ca0.165Al2.33 
Si3.67O10(OH)2 
0.000E+00 0.000E+00 0.000E+00 3.667E-01 0.000E+00 
Na-smectite b Na0.333Al2.33 
Si3.67O10(OH)2 
5.106E-01 2.646E-01 7.752E-01 3.676E-01 2.850E-01 
Thenardite Na2SO4 9.259E+01 4.578E+01 1.384E+02 1.420E-01 1.965E+01 
Anhydrite CaSO4 0.000E+00 0.000E+00 0.000E+00 1.361E-01 0.000E+00 
Tachyhydrite CaMg2Cl6O10:12H2O 0.000E+00 0.000E+00 0.000E+00 0.67764 0.000E+00 
Calcite CaCO3 0.000E+00 0.000E+00 0.000E+00 1.001E-01 0.000E+00 
Magnesite MgCO3 0.000E+00 0.000E+00 0.000E+00 8.431E-02 0.000E+00 
Thermonatrite Na2CO3:H2O 3.146E+02 1.539E+02 4.685E+02 1.240E-01 5.810E+01 
Amorphous 
Silica 
SiO2 4.660E+02 1.990E+02 6.651E+02 6.009E-02 3.996E+01 
Total 1.397E+02 
Source: CRWMS M&O 2000t 
NOTE: a Values correspond to accumulation in a half-drift model. Multiply by two to obtain accumulation in the full drift 
cross-section. 
 Cement leaching in which alkaline fluids are discharged to the EBS environment and 
react with gas-phase CO2 
These processes are summarized in Table 3-32 which combines results from EQ3 models of 
Zone 1/2 water composition, the CO2 demand represented by precipitation of the normative 
mineral assemblage in Zone 3/4 and Zone 5/6, the EQ6 models for the redissolution of these 
precipitates and the subsequent flow of water through the EBS, and the CO2 demand from 
cement leachate. In Table 3-32 the calculated CO2 budget is shown for the host-rock/EBS 
system defined two ways:

 3-153 
Table 3-31. Composition of Water in the Invert (Zone 5/6) after Return of Liquid Water, Starting with 
Redissolution of Evaporative Precipitates in Time Period 4A 
Time Period 
4A 4B 5 
Temperature (C) 88.46 88.46 58.90 
PCO2 (atm) 5.405E06 5.405E06 3.314E05 
PO2 (atm) 1.416E03 1.416E03 8.608E03 
Evaporation/Condensation Factor 1.046 1.046 1.003 
pH 10.952 9.268 9.320 
I (molal) 9.999E-01 2.931E03 2.504E03 
Al3+ 1.477E-03 1.622E-06 2.924E-07 
B(OH)3(aq) 1.419E-05 1.423E-05 1.264E-05 
Ca2+ 7.209E-06 1.219E-04 2.987E-05 
Cl 1.188E-01 2.282E-04 2.027E-04 
F 5.949E-02 1.300E-04 1.155E-04 
Fe2+ 1.042E-15 1.045E-15 5.738E-15 
HCO3
 1.538E-01 7.555E-05 7.912E-04 
K+ 7.605E-02 1.461E-04 1.297E-04 
Li+ 7.734E-06 7.755E-06 6.964E-06 
Mg2+ 2.381E-13 8.473E-10 7.769E-09 
Mn2+ 2.945E-14 2.953E-14 3.733E-15 
NO3
 8.355E-02 1.605E-04 1.425E-04 
Na+ 1.176E+00 2.257E-03 2.005E-03 
SO4
2 1.130E-01 2.170E-04 1.928E-04 
SiO2(aq) 4.039E-01 1.543E-03 5.355E-04 
Sr2+ 8.039E-08 5.228E-07 3.659E-07 
Moles Dissolved (<0 = formed) per 1 kg Influent H2O 
SiO2 (amophous) 5.171E01 
Halite 1.137E01 
Niter 7.277E02 
NaNO3 7.173E03 
Fluorite 7.906E04 
Villiaumite 5.533E02 
Mg-smectite 6.084E09 
Na-smectite 6.069E04 
Thenardite 1.082E01 
Thermonatrite 3.661E01 
Calcite 9.031E04 -2.856E-06 -8.281E-07 
Quartz 1.336E01 -5.682E-06 0.000E+00 
Moles Evolved (<0 = Used) per 1 kg Influent H2O 
CO2 (g) 2.178E01 0.000E+00 0.000E+00 
Source: CRWMS M&O 2000t 
NOTE: All concentrations in mol/kg H2O unless otherwise specified 
Normative species with zero predicted abundance are not reported in this table.

 3-154 
Table 3-32. CO2 Produced in the EBS and Host Rock from Evaporation/Condensation, 
Dissolution/Precipitation, and Cement Leachate Equilibration Processes 
Rate of CO2 Production 
Maximum In-Drift (Full- Incl. Host Rock In-Drift with Percent 
1-D CO2 Flux Drift) Total (wrt Zone 0) Cement Change in 
Nominal to Potential CO2 Budget CO2 Budget CO2 Budget CO2 Budget 
Time Time Repository Produced Produced Produced w/ Cement 
Period (yr) (kg/m-sec) (kg/m-sec) (kg/m-sec) (kg/m-sec) (%) 
1 100 8.03E-10 0.000E+00 -1.839E-10 0.000E+00 0.00 
2 500 8.03E-10 -1.726E-10 -1.053E-10 -1.741E-10 0.83 
3A 1000 8.03E-10 -7.630E-09 -6.935E-09 -7.637E-09 0.09 
3B 1000 8.03E-10 -8.243E-10 -1.291E-10 -8.310E-10 0.81 
4A 2000 8.03E-10 4.451E-08 4.454E-08 4.451E-08 -0.01 
4B 2000 8.03E-10 -4.472E-11 -1.294E-11 -5.028E-11 12.44 
5 5000 8.03E-10 -2.293E-11 7.244E-13 -3.888E-11 69.60 
Cumulative CO2 Production 
Cumulative In-Drift Incl. Host Rock In-Drift with 
Time 1-D CO2 Flux (Full-Drift) Total (wrt Zone 0) Cement 
Period to Potential Cumulative Cumulative Cumulative 
Time Duration Repository CO2 Produced CO2 Produced CO2 Produced 
Period (yr) (kg CO2/m) (kg CO2/m) (kg CO2/m) (kg CO2/m) 
1 250 6.34E+00 0.00E+00 -1.45E+00 0.00E+00 
2 400 1.65E+01 -2.18E+00 -2.78E+00 -2.20E+00 
3A 14 1.68E+01 -5.55E+00 -5.84E+00 -5.57E+00 
3B 786 3.67E+01 -2.60E+01 -9.05E+00 -2.62E+01 
4A 7 3.69E+01 -1.62E+01 7.94E-01 -1.64E+01 
4B 993 6.21E+01 -1.76E+01 3.89E-01 -1.79E+01 
5 5000 1.89E+02 -2.12E+01 5.03E-01 -2.41E+01 
Source: CRWMS M&O 2000t 
NOTES: Positive values for CO2 production signify release of CO2 to the gas phase; negative 
production signifies net consumption. 
Half-drift (symmetry model) results are multiplied by two to obtain full-drift results. 
 In-drift processes only, including solid-solution equilibrium, evaporation/condensation, 
and precipitation/dissolution reactions in the backfill (Zone 3/4) and the invert 
(Zone 5/6). 
 In-drift processes, plus all reactions in the host rock referenced to the Zone 0 
temperature. 
In other words, the CO2 produced and consumed as percolation moves within the host rock, at 
elevated temperature, outside the range of significant evaporation. The CO2 consumption rates 
from Table 3-32 are also plotted in Figure 3-58. For the reference model, in-drift processes 
dominate the CO2 budget in the system that includes the host rock. The maximum consumption 
of CO2 occurs in Time Period 3 when precipitates and salts are accumulating in the drift.

 3-155 
A long-term, cumulative CO2 deficit is calculated to occur (and would be replaced by transport 
of gas-phase CO2 or dissolution of carbonate). In Time Period 4A when the precipitates are 
mobilized out of the drift, the cumulative CO2 deficit decreases by approximately half. At the 
end of Time Period 5 the cumulative CO2 deficit represents calcite that undergoes the following 
transitions: 
 Calcite is precipitated in the drifts or in the host rock above the drifts 
 Percolating waters dissolve calcite in similar amounts from pre-existing calcite in the 
host rock below the drifts 
 The dissolved calcite is removed from the system by percolation. 
This sequence represents a net loss of CO2 from the system, because the drifts and the host rock 
above the drifts retain more calcite than initially. 
The maximum 1-D CO2 flux computed using the model developed in Section 3.1.2.2, multiplied 
by the drift spacing (81 m), is shown in Figure 3-58 for comparison to the consumption rates. 
For all time periods the available CO2 flux is greater than the consumption. However, the 
consumption rate in the drifts exceeds that which can be supplied by direct, 1-D transport as 
discussed in Section 3.1.2.2. 
In summary, most of the CO2 consumption in the system is associated with carbonate 
precipitation in the drifts. Peak consumption is driven by evaporative precipitation of 
carbonates, and gas-phase CO2 transport will probably be most important in meeting this 
demand. Calcite continues to precipitate in the drifts during cooldown, and to be dissolved in 
similar amounts from the host rock below the drifts. If the mass balance is expanded to include 
the host rock in the vicinity (defined by the Zone 0 temperature) some additional CO2 
consumption is included.

 3-156 
Table 3-33. CO2 Consumption by Cement Degradation and Other Processes in the Engineered Barrier 
System 
Time 
Period 
Nominal 
Time (yr) 
Leachate 
Flow per 
Rockbolt 
(m3/yr) 
Number of 
Rockbolts 
(m-1) 
Leachate 
Total Flow 
Rate 
(kg/m-sec) 
Effluent 
Aqueous 
Total CO2 b 
(mg/L) 
Calcite Ppt 
from Leachate 
Equilibration 
b,c (g/L) 
Total CO2 
Produced d 
(kg/m-sec) 
1 100 0 4 0.000E+00 0 0 0.000E+00 
2 500 7.520E05 4 9.532E09 1.00 0.62 -1.708E12 
3A 1000 3.310E04 4 4.196E08 1.00 0.64 -7.888E12 
3B 1000 3.310E04 4 4.196E08 1.00 0.64 -7.888E12 
4A 2000 1.680E04 4 2.129E08 4.00 0.82 -5.753E12 
4B 2000 1.680E04 4 2.129E08 4.00 0.82 -5.753E12 
5 5000 2.540E04 4 3.220E08 21.4 1.29 -1.591E11 
Source: CRWMS M&O 2000t 
NOTES: a Time Period 3A is 14.6 years, and Period 3B is 785.4 years; Period 4A is 7.1 years, and Period 4B is 
992.9 years (nominal values). 
b Use J-13 water as influent water composition, with bicarbonate 128.9 mg/L. 
c After equilibration with CO2 and quartz in the drift. 
d Negative production signifies consumption 
3.1.2.7.5.8 Potential Effects from Cementitious Materials 
The in-drift CO2 balance is expanded to include leachate from rockbolt cement. The leachate 
flow rate from 4 rockbolts per meter of drift, and the consumption of gas-phase CO2 by leachate 
equilibration, are shown in Table 3-33. (The consumption rate calculated in that table is also 
incorporated in the CO2 balance presented in Table 3-32.) The leachate flow rate and chemistry 
are described by the Cementitious Materials Model (Section 3.1.2.3). 
These results show that the CO2 demand from equilibration of the leachate with CO2 and quartz 
sand in the EBS is small compared with consumption and production from other causes, during 
the thermal period. This result is primarily controlled by the small flow rate of leachate, which 
in turn is related to the permeability of the grout. During the thermal period, the leachate flow 
could increase by an order of magnitude without substantially affecting the CO2 balance. This 
provides some margin for degradation of the rockbolt geometry and greater exposure of the 
grout. 
Leachate composition is similar to the water in the backfill that results from evaporative 
concentration during the thermal period (compare Table 3-9 with Table 3-29). In the 
Cementitious Materials Model degradation is represented by ettringite and portlandite 
dissolution, so the only aqueous species that will be significantly affected by the cement are Ca, 
sulfate, and pH. The pH is readily buffered by CO2 and quartz sand in the drifts, while the 
sulfate behaves as a conservative species for as long as water is present in the drifts. The 
principal difference between the composition of leachate and other water in the drifts is the 
concentration of Ca. Because the leachate flow rate will tend to be a small fraction of the total 
seepage flow rate, the excess Ca will be diluted, and the effect on the bulk chemical environment 
will be minor.

 3-157 
3.1.2.7.6 Summary of the Chemical Reference Model 
Chemical reaction-cell modeling shows that mobile water in the backfill can approach pH 11 or 
greater when evaporative salts and precipitates are present. As discussed in Section 3.1.2.5, 
higher pH may occur locally in waters that are saturated with respect to salts such as 
thermonatrite. As relative humidity increases during cooldown, the salt-saturated brines will 
eventually become diluted, and pH will decrease. These results are based on the use of a 
sodium-bicarbonate water (i.e. J-13 water) as the far-field compositional boundary condition. 
Laboratory data (Section 3.1.2.5.2) have shown that near-neutral pH is more likely with a 
sulfate-chloride water resembling the observed composition of tuff matrix porewater from the 
host rock. 
The Chemical Reference Model is intended to couple thermal-hyrologic, gas-phase processes, 
aqueous chemistry, and evaporative precipitates. In addition, it is used to evaluate CO2 balance, 
and the effects of cementitious materials. As stated in Section 3.1, the intended use of the 
Chemical Reference Model is FEP screening, and support of the design basis by identifying 
bounding environmental conditions. It does not predict the full range of actual solution 
compositions that may occur in the emplacement drifts, particularly during the thermal period 
when it is most likely that ionic strength could exceed 1 molal. The model does not predict the 
composition or behavior of brines. Other approaches have been developed to represent brines 
for TSPA (Section 3.1.2.5.3). 
Calculations performed for the Chemical Reference Model show that precipitates can be readily 
redissolved and removed, by seepage fluxes which are comparable in magnitude to those which 
evaporated to produce the precipitates. There are no chemical constraints that would prevent 
rapid redissolution of precipitates and salts, however, there may be hydrologic factors such as 
flow heterogeneity that limit access of water to soluble salts. 
The evolution of pH and ionic strength in reaction cells representing the host rock, backfill, and 
invert, using the reference model, is shown in Figure 3-59 and Figure 3-60. The reference model 
is chosen to maximize seepage influx, evaporative solution concentration, and formation of 
precipitates and salts. Some important comments on the reference model results are as follows: 
 Temporal and spatial granularity causes overestimation of the total mass of precipitated 
salts, and the residence time of salts in the backfill and invert. Spatial granularity also 
produces averaging of the calculated chemical conditions in the host rock, backfill, and 
invert, thus the pH and other factors may be under-predicted. 
 Redissolution of precipitates and salts may occur faster (with higher pH and dissolved 
solids) or slower (lower pH and dissolved solids) than predicted by the reference 
model. 
 Saturated brines will form when precipitates and salts are present, and there is sufficient 
humidity. The reference model considers the chemical effects when precipitated salts 
are diluted to 1 molal ionic strength by seepage, however, because of hydrologic 
uncertainty the bounding chemical condition is the continued presence of salts which 
are in equilibrium with the humidity in the drift environment.

 3-158 
For application of the reference model to bounding conditions for corrosion of the drip shield, 
saturated brine would be present after the start of Time Period 2 (300 to 700 years), when 
relative humidity exceeds 50 percent (for nitrate salts) or 85 percent (for other salts). The 
different salts can occur separately, or in mixtures. Brine concentration will decrease as the 
relative humidity increases. 
Based on the foregoing discussion, relative humidity can be used as a master variable in 
bounding models for water composition in contact with the drip shield or waste package. 
Evolution of relative humidity at the drip shield surface, for the four TH models calculated in 
Section 3.1.2.1, is shown in Figure 3-61. The implications of temperature and relative humidity 
threshold conditions on potential microbial growth and activity, is shown in Figure 3-62. 
3.1.2.8 Analysis of the Effects of Drift Degradation on the Physical and Chemical 
Environment 
This section describes the process and results of the Drift Degradation Analysis (CRWMS M&O 
2000ad) and its effects on the physical and chemical environment. The deterioration of the rock 
mass surrounding the potential repository emplacement drifts is predicted based on the 
probabilistic key-block analysis. This model provides a boundary condition for analysis of the 
potential mechanical degradation of the drip shield from rockfall, which is ongoing and not 
presented in this report. 
Key blocks are formed at the surrounding rock mass of an excavation by the intersection of three 
or more planes of structural discontinuities as shown in Figure 3-63. This analysis provides an 
assessment of the possible formation of key blocks within the repository horizon based on the 
orientations of discontinuities present in the ESF Main Loop and in the ECRB Cross Drift. 
Block failure due to seismic and thermal effects is also analyzed. 
3.1.2.8.1 Conceptual Basis for the Probabilistic Key-Block Analysis 
Key blocks are formed at the surrounding rock mass of an excavation by the intersection of three 
or more planes of structural discontinuities. The Drift Degradation Analysis provides an 
assessment of the possible formation of key blocks within the potential repository horizon, based 
on the orientations of discontinuities present in the Exploratory Studies Facility (ESF) main loop 
and in the enhanced characterization of the potential repository block (ECRB) cross drift. Block 
failure due to seismic and thermal effects has also been analyzed. 
As part of initial planning, technical literature sources were reviewed to determine the most 
appropriate approach to be used in developing a key-block analysis for the Yucca Mountain Site 
Characterization Project. As a result, the Discrete Region Key Block Analysis (DRKBA) 
software was selected. The DRKBA probabilistic approach is unique and is distinguished from 
traditional key-block analyses in that it not only assesses the maximum size of key blocks, but it 
also predicts the number of potential key blocks that will be formed within a referenced length of 
tunnel. The DRKBA approach also allows for a variety of tunnel and jointing configurations. 
DRKBA simulates structural discontinuities as circular discs placed in the rock mass according 
to probabilistic distributions determined from tunnel-mapping data. Joint planes are simulated 
by a Monte Carlo technique from probability distributions representing the orientation, spacing,

 3-159 
and trace length of the corresponding joint set. DRKBA then analyzes these blocks to determine 
if they are geometrically feasible and mechanically stable. 
The DRKBA software employs a bipolar Watson distribution for joint-orientation data. The 
principal axis orientation and a concentration factor k are the required inputs for the bipolar 
Watson distribution. The concentration factor k is an index of the concentration: the larger the 
value of k, the more the distribution is concentrated towards the principal axis orientation. Joint 
radii (see assumption 5.1), spacings, and positionings are simulated with Beta distributions 
(CRWMS M&O 2000ad). The Beta distribution is a four-parameter distribution with the 
following parameters: 
 Parameter arepresents one end of the closed interval upon which the Beta distribution 
is defined 
 Parameter brepresents the other end of the closed interval upon which the Beta 
distribution is defined 
 Parameter pdetermines the shape of the distribution curve; value is calculated from 
the mean deviation of the transformed data 
 Parameter qdetermines the shape of the distribution curve; value is calculated from 
the standard deviation of the transformed 
The transformed data were obtained by normalizing the data with the maximum value. The 
cohesion and friction angle of the joints are simulated as a bivariate normal distribution. Inputs 
for the mean and standard deviation of the joint strength parameters are required. 
3.1.2.8.2 Input Data and Assumptions 
Input Data 
Two sets of geometrical data for joints collected by field mapping or by laboratory testing were 
used in the drift-degradation analysis (CRWMS M&O 2000ad, Section 4.0). The first set, 
collected from the ESF main loop (i.e., the north ramp, main drift, and south ramp), is referred to 
as the ESF data. The second set, collected from the ECRB cross drift, is called the ECRB data. 
Qualified joint-mapping data for the Topopah Spring tuff crystal-poor upper lithophysal zone 
(Tptpul) and Topopah Spring tuff crystal-poor middle nonlithophysal zone (Tptpmn) lithologic 
units are available from the ESF data. Qualified joint-mapping data for the Tptpul, Tptpmn, 
Topopah Spring tuff crystal-poor lower lithophysal zone (Tptpll), and Topopah Spring tuff 
crystal-poor lower nonlithophysal zone (Tptpln) lithologic units are available from the 
ECRB data. 
Mapping data from the ESF being used in the analysis includes U.S. Geological Survey/U.S. 
Bureau of Reclamation (USGS USBR) full-periphery geologic maps (FPGMs) and the detailed 
line survey (DLS). Developed fracture data include joint-set orientation, joint spacing, 
joint-trace length, and joint offset from the DLS (CRWMS M&O 2000ad, Section 4.0). Fracture 
strike and dip data contained in the electronic files of the FPGMs were used to determine

 3-160 
fracture-set orientation; fracture-set spacing and trace-length data were obtained from the DLS. 
All fracture-spacing information for the primary joint sets has been converted to true spacing. 
The USGS USBR fracture data set includes those fractures with trace lengths greater than one 
meter. This data set was considered suitable for evaluating tunnel stability, including for 
supporting key block analyses. Supplemental mapping has been conducted in the Cross Drift to 
include small-trace-length fractures. The need for these data is primarily in response to assessing 
hydrology issues, including evaluating the effects of small-trace-length fractures on permeability. 
It is anticipated that the inclusion of the small-trace-length fracture data in the key block analysis 
may reduce the maximum block size, or it may reduce the probability of occurrence of the 
maximum block size. Therefore, not considering the small-trace-length fracture data should 
result in a more conservative block size assessment. 
Joint-strength parameters, including cohesion and friction angle based on laboratory 
shear-strength test data from core specimens, were used in the analysis (CRWMS M&O 
2000ad). Rock-density data and intact-rock elastic properties were obtained from laboratory 
tests performed on the rock cores from the north ramp geotechnical and the systematic drilling 
boreholes. 
Design-basis seismic ground motion parameters are provided for both Category 1 and Category 2 
design-basis events (CRWMS M&O 2000ad, Section 4.0). The peak ground accelerations for 
the horizontal motion in the frequency range of 5 to 10 Hz were selected for this analysis. Three 
levels of seismic events are included: 
 Level 1corresponds to a 1000-year event (Category 1) 
 Level 2corresponds to a 5000-year event 
 Level 3corresponds to a 10,000-year event (Category 2) 
The Level 2 (5000-year event) value was estimated based on the Category 1 and Category 2 
values. 
Assumptions 
The main assumptions used in the drift degradation analysis are as follows (CRWMS M&O 
2000ad, Section 5.0): 
 The key-block analysis simulated in the DRKBA software does not include a groundsupport 
element. All key blocks predicted in this analysis are therefore the blocks that 
fail in an unsupported opening. This assumption is necessary because of the limitation 
of the DRKBA program. The assumption apparently will lead to a conservative 
prediction of key blocks for the preclosure period and is considered adequate for the 
postclosure period. 
 The probabilistic key block analysis code DRKBA considers only gravity load in its 
assessment of mechanical stability of key blocks. Due to this limitation, seismic loads 
can not be directly applied to the opening in the DRKBA analysis. An alternative

 3-161 
quasi-static method was used to account for the seismic effect. The quasi-static 
approach applies a reduction of joint strength parameters that are used as inputs to the 
DRKBA analysis. The alternative method was verified using numerical simulation of a 
dynamic analysis, which was compared to the quasi-static analysis. The numerical 
simulation was completed using the distinct element code UDEC. The comparison 
between the results from the dynamic and quasi-static analyses shows a consistent 
prediction of block failure at the opening roof (CRWMS M&O 2000ad, Attachment 
V). 
3.1.2.8.3 Approach for the Probabilistic Key-Block Analysis 
The approach toward the drift-degradation analysis involves the following: 
 Analyze blocks that have fallen in the field and their associated joints. 
 Collect and assess joint-geometrical data and joint-frictional properties data from the 
ESF main loop and ECRB cross drift to develop the joint-modeling inputs for DRKBA. 
 Analyze the joint data, including the maximum block size, to assess potential formation 
of key blocks using DRKBA. 
 Analyze the seismic and thermal effects on joint and block movement. 
 Analyze the DRKBA block-size distribution data for each lithologic unit within the 
potential repository host horizon. 
 Determine the number and average volume of rockfall per unit length of drift for 
various levels of seismic hazard. 
 Evaluate postclosure frequency of block failure for 10,000 years. 
 Analyze the drift profile showing the progressive movement of joints and blocks with 
time. 
Details on each step of the approach are provided in the Drift Degradation Analysis (CRWMS 
M&O 2000ad, Section 6.3). 
3.1.2.8.4 Summary of Analysis Results 
The following discussion is extracted from the Drift Degradation Analysis (CRWMS M&O 
2000ad). For brevity, tables of results are presented only for the Tptpmn (middle nonlithophysal) 
host rock unit. Similar tables for the Tptpul (upper lithophysal) and the Tptpll 
(lower lithophysal) are available. The Tptpmn unit is selected because it contains the greatest 
abundance of fractures, and thus greater probability of consequential rockfall.

 3-162 
Prediction of Key-Block Size and Distribution for Static Conditions 
A range of drift orientations with the drift azimuth varied in 15 increments is considered in the 
static analyses. Figure 3-64 presents the key-block analysis results in the format of cumulative 
frequency of occurrence for the Tptpmn unit. The cumulative frequencies of occurrence 
corresponding to 50, 75, 90, 95 and 98 percentile block volume for this unit are listed in 
Table 3-34. 
The maximum block sizes predicted from the analyses are also presented, and the predicted 
block size is generally small. For example, the 95-percentile block ranges from 1.35 to 3.70 m3 
for the Tptpmn unit. For a layout azimuth of 105, the 98-percentile block 4.57 m3 for the 
Tptpmn unit. 
The predicted numbers of key blocks per unit length of emplacement drift are listed in 
Table 3-35 for the three potential host rock units. The numbers of key blocks formed in the 
lithophysal rock (i.e., the Tptpul and Tptpll units) are predicted to be scarce. Key blocks are 
more predominant in the Tptpmn unit; the number of blocks ranges from 26 to 63 per 1 km of 
drift. The orientations that are predicted to have a higher number of blocks are, in general, 
parallel to the major high-angle joint sets. This trend is consistent with that observed for the 
prediction of the maximum block size. 
Quasi-Static (Seismic) Analysis Results 
Figure 3-65 presents the key-blocksize distribution for Tptpmn unit for the three levels of 
seismic events considered. The cumulative frequencies of occurrence corresponding to the 50th, 
75th, 90th, 95th, and 98th percentile block volume for the Tptpmn unit are listed in Table 3-36. 
The maximum block sizes predicted from the analyses are included. The analysis results 
indicate that for the Tptpmn unit, a level 2 or level 3 seismic event could increase the maximum 
block size by a factor of approximately two.

 3-163 
Table 3-34. Block Volume Corresponding to Various Levels of Predicted Cumulative Frequency of 
Occurrence, Emplacement Drift in Tptpmn Unit 
Drift Orientation (Azimuth in degree) Cumulative 
Frequency 
of 
Occurrence 
(percent) 
0 15 30 45 60 75 90 105 120 135 150 165 
50 0.04 0.04 0.10 0.04 0.04 0.04 0.04 0.04 0.04 0.10 0.07 0.04 
75 0.24 0.38 0.50 0.27 0.21 0.16 0.21 0.33 0.35 0.44 0.33 0.24 
90 1.18 1.20 1.68 1.15 0.92 0.47 0.92 1.18 1.03 1.63 1.23 1.20 
95 3.04 2.93 3.70 2.85 1.71 1.35 1.60 2.45 2.17 3.04 2.11 2.79 
98 7.12 5.68 5.76 5.90 3.30 1.80 2.25 4.57 4.86 5.65 5.71 4.86 
maximum 19.86 9.84 17.34 11.34 12.64 5.00 8.20 9.19 10.89 19.33 21.39 9.47 
NOTES: Values shown are cubic meters. 
From CRWMS M&O 2000ad, Table 12 
Table 3-35. Predicted Number of Key Blocks per Unit Length (km) along Emplacement Drift 
Drift Orientation (Azimuth in degree) Lithologic 
Unit 0 15 30 45 60 75 90 105 120 135 150 165 
Tptpul 12 18 12 14 13 14 16 15 18 20 16 13 
Tptpmn 47 42 53 33 35 26 40 37 53 63 57 48 
Tptpll 4 5 5 4 3 2 1 3 5 3 6 5 
Tptpln 12 6 7 8 5 5 2 3 5 8 8 7 
Source: CRWMS M&O 2000ad, Table 15 
Table 3-36. Block Volume Corresponding to Various Levels of Predicted Cumulative Frequency of 
Occurrence, Performance Confirmation Drift in Tptpmn Unit, with Seismic Consideration 
Static Plus Seismic Cumulative 
Frequency of 
Occurrence Static Level 1 Level 2 Level 3 
50 percent 0.04 0.04 0.04 0.04 
75 percent 0.33 0.41 0.47 0.47 
90 percent 1.18 1.37 1.74 1.74 
95 percent 2.45 2.90 3.44 3.44 
98 percent 4.57 5.68 8.25 8.25 
maximum 9.19 19.89 19.89 19.89 
NOTES: Values shown are cubic meters. 
From CRWMS M&O 2000ad, Table 17

 3-164 
Table 3-37. Predicted Number of Key Blocks per Unit Length (km) along Emplacement Drift, with Seismic 
Consideration 
Static Plus Seismic 
Lithologic Unit Static Level 1 Level 2 Level 3 
Tptpul 15 15 17 17 
Tptpmn 37 38 40 40 
Tptpll 3 3 3 3 
Tptpln 3 3 5 5 
NOTE: From CRWMS M&O 2000ad, Table 20 
Table 3-38. Predicted Average Volume of Key Blocks per Unit Length along Emplacement Drift, with 
Seismic Consideration 
Static Plus Seismic (m3/km) 
Lithologic Unit Static (m3/km) Level 1 Level 2 Level 3 
Tptpul 4.9 5.0 9.5 12.1 
Tptpmn 18.2 25.9 32.3 32.3 
Tptpll 0.8 0.8 0.8 0.8 
Tptpln 3.0 5.5 14.4 14.4 
NOTE: From CRWMS M&O 2000ad, Table 21 
The predicted numbers of key blocks per unit length of drift are listed for the different units in 
Table 3-37. Static results are also included for comparison. The comparison shows that there is 
an insignificant impact on the number of rockfalls for a 1,000-year event earthquake (Level 1) 
and only a minor impact on the number of rockfalls for a 5,000-year event earthquake (Level 2) 
or a 10,000-year event (Level 3). 
The predicted average volume of rockfall per unit length of drift is listed in Table 3-38. The 
trend for the average volume of rock fall per kilometer is similar to that for the predicted number 
of key blocks per kilometer. 
3.1.2.8.5 Rock Fall Related to Time-Dependent and Thermal Effects 
The analysis uses an approach that accounts for the time-dependent and thermal effects with 
degradation of joint cohesion. The development and justification for this approach are described 
in the Drift Degradation Analysis (CRWMS M&O 2000ad, Section 6.3.5 and Attachment VI). 
Four different times are selected for the analysis: 0 yr (static condition), 200 yr, 2,000 yr, and 
10,000 yr. The corresponding degraded joint cohesion for each time is listed in Table 3-39. The 
reduction of joint-cohesion is predicted to be very small in the period between 2,000 and 
10,000 yr.

 3-165 
Because backfill is part of the EBS during the postclosure period, backfill is included in the 
analysis for the consideration of time-dependent and thermal effects. It is apparent that the 
blocks that form around the springline area will no longer occur in the analysis with backfill. 
The predicted number of key blocks per kilometer of drift for the drip shield orientation is listed 
in Table 3-40. Only minor increases in the number of key blocks are predicted between 200 and 
2,000 yr; no change is predicted from 2,000 to 10,000 yr. The predicted average volume of 
rockfall per unit length of drift is listed in Table 3-41. Thee results indicate that time-dependent 
and thermal effects will have a minor impact on rockfall. 
3.1.2.8.6 Effect of Drift Degradation on the Physical and Chemical Environment 
The predicted number of rock blocks, average volume of blocks, and detailed size-distribution of 
blocks, as presented in general, suggest minor impact of rockfall on the in-drift physical and 
chemical environment. The degradation analysis, however, does not address the effect of 
rockfall to the displacement of the backfill material and the potential structural damage to drip 
shields due to rockfall. 
Table 3-39. Reduced Joint Cohesion to Account for Time-Dependent and Thermal Effects 
Period (year) Joint Cohesion (Pa) 
0 (Static) 99,873 
200 21,674 
2,000 10,998 
10,000 10,776 
NOTE: From CRWMS M&O 2000ad, Table 22 
Table 3-40. Predicted Number of Key Blocks per Unit Length (km) along Emplacement Drift, with Time- 
Dependent and Thermal Consideration 
Lithologic Unit Static Year 200 Year 2000 Year 10000 
Tptpul 15 14 15 15 
Tptpmn 37 37 39 39 
Tptpll 3 4 4 4 
Tptpln 3 4 5 5 
NOTE: From CRWMS M&O 2000ad, Table 23

 3-166 
Table 3-41. Predicted Average Volume of Key Blocks per Unit Length (km) along Emplacement Drift, with 
Time-Dependent and Thermal Consideration 
Lithologic Unit Static Year 200 Year 2000 Year 10,000 
Tptpul 4.9 5.1 8.8 8.8 
Tptpmn 18.0 15.8 19.0 19.0 
Tptpll 0.8 0.8 0.9 0.9 
Tptpln 3.0 3.4 8.4 8.4 
NOTE: From CRWMS M&O 2000ad, Table 24 
3.1.3 Engineered Barrier System Radionuclide Transport Model 
The EBS radionuclide-transport model provides an analysis of the transport of radionuclides 
through the EBS, once they are released from breached waste packages. The model includes 
advective-dispersive-diffusive transport, and radionuclide sorption. Results generated by the 
Water Distribution and Removal Model (CRWMS M&O 2000q, Section 6.3.6) provide input to 
the one-dimensional transport equation used in the analysis. The following sections describe the 
model input, assumptions, development, validation, and results. 
3.1.3.1 Input Data 
The following sections summarize model input data from the Water Distribution and Removal 
Model (CRWMS M&O 2000q, Section 6.3.6) and other description of the drift environment as 
described by the Engineered Barrier System Radionuclide Transport Model (CRWMS 
M&O 2000b, Section 6.1). 
Input Data from the Water Distribution and Removal Model 
Hydrologic input corresponds to the base case of steady-state, focused seepage inflow at 
constant, ambient temperature, from the Water Distribution and Removal Model (CRWMS 
M&O 2000q, Section 6.2.4). This input shows that in the invert, liquid flux is decreased below 
the drip shield, and increased to the sides outside the protection of the drip shield. 
The most important aspect of the drift environment, for radionuclide transport in the invert, is the 
volumetric water content, represented by liquid saturation in the invert. Liquid saturation is 
influenced by inflow rate, water evaporation rate, and temperature. Saturation is also controlled 
by the drainage capacity of fractures in the host rock directly below the invert. These effects are 
discussed in detail in the Engineered Barrier System Radionuclide Transport Model (CRWMS 
M&O 2000b, Section 6.1). In thermal-hydrology simulations using the lower infiltration 
distribution, the dryout zone is relatively extensive and persists longer, and liquid flux in the 
invert is smaller. Conversely, for the higher infiltration distribution, water returns to the EBS 
environment sooner, and liquid flux in the invert is greater. These effects are acknowledged in 
this model, and addressed through selection of input data and interpretation of model results.

 3-167 
Properties and Hydrologic Conditions in the Crushed Tuff Invert 
The physical properties of the crushed-tuff invert include the path length and distance, porosity, 
and grain density. These model inputs are discussed in more detail by the Engineered Barrier 
System Radionuclide Transport Model (CRWMS M&O 2000b, Section 4.1). 
The hydrologic description of the invert includes the liquid flux rate, saturation, and pore-water 
velocity. The Water Distribution and Removal Model (CRWMS M&O 2000q, Section 6.3.6) 
presents these parameters for the glacial and present-day infiltration rates. 
Volumetric moisture content is the fractional volume in the invert material occupied by water, 
and is always less than or equal to the porosity. In results reported by the Water Distribution and 
Removal Model (CRWMS M&O 2000q; Table 7 and Table 20) the volumetric moisture content 
in the invert is determined to be 0.071 for the glacial climate. For drier conditions which could 
result from less infiltration (i.e., 1 mm/year) the volumetric moisture content would approach the 
residual moisture content of 0.05 (CRWMS M&O 2000ae). 
Dispersivity is the degree of hydrodynamic dispersion in the porous medium, and produces 
effects on solute distribution that are analogous to molecular diffusion. A conservatively small 
estimate for dispersivity of crushed tuff, over a flowpath distance of 1 m, would be 
approximately 10 cm. This is similar to values cited in the literature for laboratory and field 
experiments (CRWMS M&O 2000b, Section 5.9). Dispersivity can be much greater for regional 
groundwater flow; however, because of the scale of the invert, smaller values apply. A 
reasonable range of values for dispersivity for the invert is from 0.4 to 10 cm (CRWMS M&O 
2000b, Section 5.9). 
The molecular diffusion coefficient (units of m2/year) is a measure of the diffusion of a solute 
(CRWMS M&O 2000h, Section 6.2). An empirical relation based upon a one sided confidence 
interval that is validated against Archies Law from the Invert Diffusion Model (CRWMS M&O 
2000h, Section 6.6), is used to determine the soil/liquid diffusion coefficient. As bounding input 
for estimating diffusion coefficients for radionuclides derived from spent fueled and high-level 
waste, coefficients for tritiated water (CRWMS M&O 2000b, Section 5.6) in normal and heavy 
water, measured over a temperature range of 1 to 45C, are reported. The measurements show a 
temperature dependence from 1.1  105 cm2/sec at 1C to 3.6  10-5 cm2/sec at 45C. For this 
model a representative value of 2.30  10-5 cm2/sec (0.073 m2/yr) is used (CRWMS M&O 
2000b, Section 5.6). 
The partition coefficient is the ratio of the mass of dissolved material adsorbed by the invert 
material, to the mass in solution. Calculations of invert performance are performed for five 
ranges of partition coefficients (CRWMS M&O 2000b, Section 5.12), assuming a uniform 
parametric distribution for each. The selected ranges are 0 to 1, 1 to 5, 5 to 10, 10 to 50, and 50 
to 100 cm3/g. 
A summary of the parameters used as input to the EBS Radionuclide Transport Model, including 
representative values and alternative values used for sensitivity testing, is presented in 
Table 3-42.

 3-168 
3.1.3.2 EBS Radionuclide Transport Model Assumptions 
In addition to the 1-D modeling framework, and the property distributions discussed above, this 
model assumes that the solute concentration in the gas phase is negligible and that solutes do not 
react together. The invert is assumed to be compositionally homogeneous (CRWMS M&O 
2000b, Section 5.10). Other assumptions, such as neglecting transverse dispersion, are also 
identified. These assumptions are consistent with the 1-D transport modeling approach. 
3.1.3.3 EBS Radionuclide Transport Model Uncertainties 
Ponding of water could occur in the emplacement drifts due to clogging of drainage capacity in 
the invert and the drift floor. The possible consequences include high fluxes of liquid water 
through breached waste packages. Being mobilized in a flow of water parallel to the drift axis, 
radionuclides would be transported to a major fault or fracture where drainage through the host 
rock could occur. Transport of radionuclides through the UZ would thus occur at higher 
velocity, and with less water-rock interaction, than if releases are better distributed. Clogging 
could occur because of fines migration, geochemical alteration of EBS materials, or precipitation 
of uranium compounds derived from the waste form. This alternative view requires clogging of 
the natural drainage capacity in the drift floor, which was addressed in Section 3.1.1. 
The EBS flow models and radionuclide transport model, regard flow in the drifts to be steadystate. 
This is justified from a hydrologic perspective because the storage capacity for water in 
the drifts is small compared with the potential through-flow over time periods of interest (i.e. 
many years). However, there may be more storage capacity available for radionuclides, if they 
are retarded on substrates such as steel corrosion products. Stored radionuclides could be 
released as large pulses when flow conditions change. This uncertainty is probably not 
important because increased flow rates will cause increased dilution. For example, if the 
concentration of a given radionuclide is inversely proportional to the EBS flow rate, then the 
release rate is constant. Alternatively, if the concentration remains constant, there could be 
changes in the release rate but no change in storage. If the concentration is directly proportional 
to flow rate, changes in the release rate would be dampened by changes in storage. In any event, 
changes in storage would not change the peak concentration of any radionuclide that exhibits 
linear (or nearly so) sorption behavior. This discussion pertains to reversible sorption, because 
there can be no change in irreversibly stored species. 
3.1.3.4 Development of the EBS Radionuclide Transport Model 
The EBS is designed to divert water flow around the waste package, to the invert. Water that 
flows through any breaches in the drip shield may contact the waste package, and eventually 
cause advective release of radionuclides. Liquid flow bearing dissolved radionuclides will mix, 
in the invert, with water diverted by the drip shield. The release of radionuclides from the waste 
package will result in a time-dependent concentration of radionuclides that is considered a unit 
concentration in this model (Figure 3-66). Note that in a steady-state flow field where pore 
velocities and volumetric moisture content are constant, the contaminant-transport equation is 
linear, and the principle of superposition can be used to obtain a solution to the problem where 
inlet concentration varies with time.

 3-169 
If the transport of radionuclides through the invert is dominated by molecular diffusion, the 
breakthrough of radionuclides would be much slower compared to the breakthrough for 
advection-dominated transport. The invert material (crushed tuff) is considered to be 
nonsorbing, so sorption is excluded from the base case. 
The dispersion-diffusion coefficient (D) is calculated by dividing the effective dispersion 
diffusion coefficient (De), which is the summation of the hydrodynamic dispersion coefficient 
(Dlh) and the molecular diffusion coefficient (Dsl), by the volumetric moisture content (CRWMS 
M&O 2000b, Section 6.2.3). 
To assess radionuclide breakthrough times, calculations are performed for various cases, varying 
the volumetric moisture content, flux, temperature, and drainage capacity of the host rock. 
Table 3-42. Summary of Parameter Values and Ranges Used in Base Case of the Radionuclide- 
Transport Model 
Parameter Name, Units Representative Value Alternative Values for Sensitivity 
Flowpath length (m) 0.61 0.50.7 
Volumetric water content 0.071 0.050.07 
Porewater velocity (m/yr) 0.031 0.0130.031 
Liquid water flux (m/yr) 0.0022 0.0010.0042 
Porosity 0.55 0.280.55 
Dispersivity (m2/yr) 0.1 0.004 
Molecular diffusion coefficient (m2/yr) 0.073 0.0340.11 
Grain density (g/cm3) 2.53 2.492.72 
Partition coefficient (cm3/g) 0 01, 15, 510, 1050, & 50100 
NOTE: From CRWMS M&O 2000b, Table 4

 3-170 
Table 3-43. Summary of Sensitivity and Uncertainty Analysis for the One-Dimensional Solute- 
Transport Equation 
Fifth Percentile Time (y) 
to C/C0 = 
Fiftieth Percentile Time 
(y) to C/C0 = 
Partition 
Coefficient (Kd) 
Range, ml/g 
(Mean) 0.01 0.5 0.01 0.5 
Sensitivity Ranking 
01 (0.5) 2 16 13 104 Jw, Kd, al, L, f, ., .s, Dwl 
15 (3) 17 166 74 590 Jw, al, Kd L, f, ., .s, Dwl 
510 (7.5) 52 534 189 1487 Jw, al, L, f, ., Kd, .s, Dwl 
1050 (30) 162 1618 730 5842 Jw, al, Kd, L, f, ., .s, Dwl 
50100 (75) 520 5316 1883 14784 Jw, al,, L, f, ., Kd, .s, Dwl 
NOTES: Parameters listed in the sensitivity ranking, including range and mean for the simulations: 
Flowpath distance (0.50.7 m, 0.6 m) 
Jw Darcy velocity (04.2 mm/y, 0.021 mm/y) 
Kd Distribution coefficient (see column 1) 
f Porosity (0.280.55, 0.41) 
.s Grain density (2.492.72 g/cc, 2.61 g/cc) 
. Volumetric water content (0.050.07, 0.06) 
al Dispersivity ( 0.004 - 0.1 m, 0.052) 
Dwl Molecular diffusion coefficient (0.035 - 0.11 m2/yr, 0.074 m2/yr) 
All distributions are assumed to be uniform, between the limits indicated. Boldface indicates the absolute 
value of the Monte Carlo correlation coefficient is > 0.2. Boldface italic indicates the absolute value of the 
correlation coefficient is > 0.5. 
From CRWMS M&O (2000ad, Table 5. 
The 1-D advectiondispersiondiffusion equation is given by (CRWMS M&O 2000b, Section 
6.2.2): 
1 1 
2 
2 
1 C 
dz 
d 
V C 
dz 
d 
D C 
dt 
d 
 -  = (Eq. 3-24) 
If flow conditions are steady, and solute is instantaneously introduced at the inlet (at t=0), the 
solution to Equation 3-24 for nonretarded transport with inlet concentration C0 is (CRWMS 
M&O 2000b, Section 6.2.2): 
. .
.
. 
. .
.
. 
. .
.
. 
. .
.
. 
  
 + 
 . .. 
. 
. .. 
.  
+ . .
.
. 
. .
.
. 
  
 - 
= 
t D 2 
t V L 
erfc 
D
L V 
exp 
t D 2 
t V L 
erfc 
2
1 
C
C 
0
1 (Eq. 3-25) 
where C1/C0 is the ratio of outlet to inlet solute concentration, L is the flowpath distance, V is the 
porewater velocity, D is the dispersion-diffusion coefficient, and t is time. Retardation is 
incorporated by dividing the porewater velocity (V) and the dispersion-diffusion coefficient (D)

 3-171 
by a retardation coefficient calculated from the partition coefficient in the usual manner 
(CRWMS M&O 2000b, Section 6.2.2). 
The dependence of the dispersion-diffusion coefficient for crushed tuff on tortuosity and 
molecular diffusion has been investigated (CRWMS M&O 2000h). Measured diffusion 
coefficients are compared with values derived using a Millington Quirk relation, and Archies 
law, in Figure 3-67. This figure shows that at low volumetric moisture contents, the relation 
based upon Archies Law (CRWMS M&O 2000h, Section 6.1) is comparable to the 
MillingtonQuirk relation (CRWMS M&O 2000b, Section 6.2.3) and both are in approximate 
agreement with measured data for crushed tuff. 
3.1.3.5 EBS Radionuclide Transport Model Validation 
This model provides perspective on the characteristics of invert materials, and EBS hydrologic 
performance, that most affect radionuclide transport through the invert. An important 
assumption is that of 1-D vertical flow. Model results show that there is significant dependence 
of breakthrough time on the flowpath, from spatial variations in liquid water flux in the invert. 
The 1-D advective-dispersive-diffusive transport model represented by Equations 3-24 and 3-25 
is an accepted and valid model for solute transport, subject to assumptions on dimensionality, 
flow conditions, sorption reversibility, and other characteristics of solute-solid interaction. 
Significant uncertainty is associated with quantifying the partition coefficient (shown to be the 
most sensitive parameter) and specifying the flow path for thousands of years. Accordingly, for 
TSPA the partition coefficient is assumed to be zero, which means no credit is taken for 
retardation in the EBS. Use of the model for TSPA is therefore limited to describing transport by 
diffusion alone. For diffusive transport, the low velocity for advective transport also means that 
hydrodynamic dispersion (and the attendant uncertainty) is not a factor in the application of the 
model. 
3.1.3.6 EBS Radionuclide Transport Model Results 
Base Case 
The liquid water flux in the invert directly below the waste package is approximately 4 mm/yr, 
reduced from 42 mm/yr in the host rock for glacial infiltration conditions. The volumetric 
moisture content is approximately 0.071 for this case (CRWMS M&O 2000b, Section 6.3.2). 
The radionuclide breakthrough curve calculated using Equation 3-25, is presented in Figure 3-68 
(CRWMS M&O 2000b, Figure 9). Similar results are obtained for the present-day climate (not 
shown). These results show that the breakthrough is substantial after 10 yr and complete after 
100 yr. The analysis also shows that breakthrough occurs more rapidly for grid blocks off the 
drift centerline where the liquid water flux is greater. Porewater velocity in the vertical direction 
increases with distance from the centerline. 
Effect of Engineered Drainage Features on EBS Transport 
Several analyses addressed the effects of engineered drainage features, which are not 
incorporated in the conceptual design, but could be installed to mitigate insufficient drainage 
capacity in the host rock at the drift floor, caused by fracture plugging or initial conditions.

 3-172 
Because the effective 1-D flowpath distance is much greater with the potential use of engineered 
drainage features, the calculated radionuclide transport response is improved. The radionuclide 
breakthrough curve is compared to the base case in Figure 3-69. Similar improvement is 
calculated for the present-day climate (not shown). 
Sensitivity Analysis 
The Engineered Barrier System Radionuclide Transport Model (CRWMS M&O 2000b, Section 
6.3.3) includes a sensitivity analysis of breakthrough time, for radionuclide transport in the 
invert. The analysis applies the Monte-Carlo method, using the 1-D transport equation solution 
(Equation 3-25). The analysis determines the sensitivity of breakthrough time, to variation of 
each input parameter within the ranges shown in Table 3-42. The parameters are treated as 
statistically independent, uniformly distributed random variables. 
The Monte Carlo simulation is reported for 1,000 iterations. The random seed for initialization 
is fixed (at unity) to allow reproducibility of the results. Latin hypercube sampling is used to 
increase sampling density near the limits of the input distributions. 
Table 3-43 is a summary of the sensitivity analysis for 1-D solute transport. The results show 
that breakthrough time increases with increasing sorption, and that sorption is the most sensitive 
parameter. An invert comprised of a sorptive material would most effectively delay the release 
of radionuclides from the EBS. Further, the results show that liquid water flux is a sensitive 
parameter, while the molecular diffusion coefficient is least sensitive. Dispersivity, flowpath 
length, and volumetric moisture content are of intermediate sensitivity. 
3.1.4 Multiscale Thermohydrologic Model 
The Multicale TH Model and corresponding analysis (CRWMS M&O 2000i) describes the 
thermal-hydrologic (TH) evolution throughout the potential repository. (The terms 
thermohydrology and thermal-hydrology are used interchangeably in this discussion and the 
supporting documentation.) The Multiscale TH Model describes the evolution of thermodynamic 
conditions in the near-field environment (NFE) and the EBS. The principal intended use of the 
Multiscale TH Model is direct support to TSPA, particularly the temperature and humidity at the 
surfaces of the drip shield and waste package, water content in the invert, and liquid water flux in 
the host rock above the drifts. In addition, the Multiscale TH Model is used to support the design 
basis, particularly the demonstration of compliance with thermal management requirements. 
Figure 3-70 illustrates the potential repository footprint used in the model; this footprint closely 
approximates the actual plan view of the potential repository perimeter within which waste is to 
be emplaced. Thirty-one locations (or chimneys) are shown, spanning the potential repository 
block. These locations sample the lateral variability in properties (such as the thickness of each 
stratum) and in surface boundary conditions. These are arranged in five columns spaced 
approximately 250 m apart from east to west and in seven lines spaced about 500 m apart from 
north to south. For example, L4C4 is located approximately 1500 m southerly and 750 m 
westerly from L1C1, which is near the NE corner of the footprint.

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3.1.4.1 Input Data, Assumptions, and Model Uncertainties 
Input Data 
The calculations presented in this PMR are based on the following inputs or data: 
 The potential repository footprint is modeled for a total of 70,000 MTU of waste, 
including 63,000 MTU of CSNF and 7000 MTU of DHLW. 
 The TSPA-SR 1-D drift-scale base-case hydrologic property sets for the case of no 
perching are used. Three infiltration-flux scenarios are included: the mean, lower, 
and upper flux distributions. Future climate change is incorporated using a timevarying 
infiltration flux. 
 Areal mass loading (AML) is nominally 60 MTU/acre. 
 Waste packages are placed in the emplacement drifts in a line with approximately 10 
cm between the ends of waste packages. 
 Emplacement drifts are arranged with a uniform spacing of 81 m between centerlines of 
emplacement drifts. 
 The distribution of hydrostratigraphic units used in the UZ Flow and Transport Model 
(UZ Model), is based on the Geologic Framework Model (GFM V3.1). 
 The drift-scale models used in the Multiscale TH Model incorporate numerical grid 
discretization that is comparable to or finer than that used in previous Multiscale TH 
Model calculations (CRWMS M&O 2000i). 
 Each drift segment in the potential repository is ventilated during the entire preclosure 
period; for base case analyses, this is assumed to be 50 years. During the preclosure 
period, at least 70 percent of the heat generated by waste packages, is removed by 
ventilation. Emplacement drifts are backfilled at the end of the preclosure period, and 
drip shields are emplaced at the same time as backfill. 
The calculations presented in this PMR do not address the coupling of geochemical or 
geomechanical processes to TH behavior. Uncertainties associated with input data and 
calculations are documented in the Multiscale Thermohydrologic Model (CRWMS M&O 2000i). 
Assumptions 
The following assumptions are used in the Multiscale TH Model and corresponding analysis: 
 It is assumed that the 50 northernmost emplacement drifts are used for the 
emplacement of 70,000 MTU of waste. 
 The assumed value for tortuosity of the backfill and invert materials is 0.7. This 
assumption is used in all NUFT input files.

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 The assumed value for satiated saturation of the invert and backfill materials is 1.0, 
which is used in all NUFT input files. This is an upper bound for this parameter. 
 The thermal conductivity data is provided for both dry and wet conditions. The 
conduction-only SDT, DDT, and SMT models cannot explicitly represent the influence 
of liquid saturation on thermal conductivity. Because the rock matrix is nearly fully 
saturated initially, and for much of the thermal period, the wet value of thermal 
conductivity is assumed for conduction-only models. 
Model Uncertainties 
The following discussion identifies two categories of model uncertainties for the Multiscale TH 
Model: (1) related to the TH modeling approach using NUFT, and (2) related to the multi-scale 
estimation methodology. Uncertainties related to TH modeling are: 
 Dependence of thermal conductivity for the host rock, on water content. 
 Effects of episodic variation of percolation flux in the host rock, on water penetration 
into the drifts during the thermal period. 
 Effects of spatially heterogeneous fracture properties in the host rock, on the evolution 
of thermodynamic conditions in the drift. 
 Discrepancy between values of the water potential in the fracture continuum and the 
matrix continuum, at the same locations, for ambient, steady-state conditions. 
 Dependence of drift seepage on numerical model gridding, and spatial heterogeneity of 
hydrologic properties. 
These uncertainties can be addressed through further model development, and sensitivity studies, 
and do not necessarily require data collection. The Multiscale TH Model presents a large 
number of TH models that describe temperature, humidity, and flux conditions throughout the 
potential repository. It should be noted that drift seepage is not calculated directly from these 
models, rather, the calculated liquid flux in the host rock is used as input to an abstracted seepage 
model (for TSPA-SR) that is not described in this report. 
The key uncertainties related to multi-scale estimation methodology are: 
 Mountain-scale gas-phase circulation effects. 
 Representativeness of interpolation based on correlation of performance measures 
across different types of conduction-dominated and TH models. 
 Movement of mass (e.g. water vapor) along the drift axis, from warmer to cooler 
regions. 
These uncertainties can be addressed through comparison of Multiscale TH Model results with 
other (more computationally intensive) numerical simulations in which the potential repository is

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represented at mountain-scale, but drift-scale processes are represented by embedded fine-scale 
grids. 
3.1.4.2 Multiscale Thermohydrologic Model Development 
The Multiscale TH Model efficiently estimates TH conditions in the NFE and EBS as functions 
of time, waste package type, and location in the potential repository. Such estimation could 
require a numerical model with millions of grid blocks if a brute-force, monolithic model were 
used. The Multiscale TH Model relates the results from different types of smaller models, to 
capture the key factors affecting NFE and EBS TH conditions: 
 Potential repository-scale variability of percolation flux 
 Temporal variability of percolation flux (as influenced by climate change) 
 Uncertainty in percolation flux (as addressed by the mean, high, and low flux 
scenarios) 
 Potential repository-scale variability in hydrologic properties (e.g., those governing 
matrix imbibition diffusivity and capillary wicking in fractures) 
 Edge-cooling effect (which increases with proximity to the edge of the potential 
repository) 
 Dimensions and properties of the EBS components such as the drip shield, engineered 
backfill, and the invert 
 Waste package-to-waste package variability in heat-generation rate 
 Potential Repository-scale variability in overburden thickness 
 Potential Repository-scale variability in thermal conductivity (with an emphasis on the 
host-rock units). 
The Multiscale TH Model calculates 38 TH variables in the NFE and EBS for 610 subdomains in 
the potential repository and for 8 different WPs as a function of time for approximately 
352 calculational timesteps. The total of 38 TH variables arises from a combination of 
ten thermodynamic variables (such as temperature and relative humidity) and 13 drift-scale 
locations (such as the WP, and the drip-shield surface). These TH variables are determined for 
three infiltration flux scenarios: the mean, upper, and lower infiltration flux distribution 
scenarios. For each calculational timestep, the Multiscale TH Model calculates 38  610  8 TH 
data values, resulting in 185,440 data values. Multiplying by 352 calculational timesteps results 
in approximately 65 million TH data points for a complete time evolution, for a given 
infiltration-flux scenario. 
Table 3-44 lists specific thermal-hydrologic variables or parameters that can be predicted by use 
of the Multiscale TH Model.

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Table 3-44. Thermal-Hydrologic Variables Predicted with the Multiscale Thermohydrologic Model at 610 
Potential Repository Locations 
Thermal-Hydrologic Variable Drift-Scale Location at Which Predicted 
NFE host rock (5 m above crown) 
NFE host rock (mid-pillar at potential repository horizon) 
Maximum lateral extent of boiling 
Upper drift wall (crown of the drift) 
Lower drift wall (below invert) 
Drift wall (perimeter average) 
Backfill (crown) 
drip shield (perimeter average) 
drip shield (upper surface) 
waste package (surface average) 
Temperature 
Invert (average) 
Drift-wall (perimeter average) 
Backfill (crown) 
drip shield (perimeter average) 
waste package 
Relative humidity 
Invert (average) 
Drift wall (perimeter average) 
drip shield (perimeter average) 
Liquid saturation (matrix) 
Invert 
NFE host rock (5 m above crown) 
NFE host rock (3 m above crown) 
Drift wall (crown) 
drip shield (crown) 
drip shield (upper surface average) 
drip shield (lower side at the base) 
Liquid-phase flux 
Invert (average) 
Gas-phase air-mass fracture drip shield (perimeter average) 
Gas-phase pressure drip shield (perimeter average) 
drip shield (perimeter average) 
Invert (average) 
Drift wall (crown; in matrix) 
Capillary pressure 
Drift wall (crown; in fractures) 
Gas-phase (water vapor) flux Drift wall (perimeter average) 
Gas-phase (air) flux Drift wall (perimeter average) 
Backfill (crown) 
drip shield (crown) 
drip shield (perimeter total) 
Evaporation rate 
Invert (total)

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The need for a multi-scale modeling approach stems from the fact that the performance measures 
depend on TH behavior within a few meters of the emplacement drifts and also on thermal and 
TH behavior on a potential repository (or mountain) scale. A single numerical model (e.g., 
embedding a 3-D drift-scale model with a relatively fine mesh into a 3-D mountain-scale model 
with a coarse mesh) would require an infeasible number (millions) of grid blocks. The 
Multiscale TH Model has been developed for estimating the results that would be obtained if 
such a single model were possible. In addition to coupling the drift scale and mountain scale, the 
Multiscale TH Model also allows for consideration of the effect of different waste package types 
(e.g., different CSNF waste packages, co-disposal of defense HLW) on the various performance 
measures. 
The Multiscale TH Model consists of four major models and includes multiple scales (mountain 
and drift), multiple dimensions (1-D, 2-D, and 3-D), and different assumptions regarding the 
coupling of heat transfer to fluid flow (conduction-only and fully coupled thermal-hydrologic). 
The four types of models are: 
 LDTH (line-averaged-heat-source, drift-scale, thermal-hydrologic) model 
 SMT (smeared-heat-source, mountain-scale, thermal-conduction) model 
 SDT (smeared-heat-source, drift-scale thermal-conduction) model 
 DDT (discrete-heat-source, drift-scale thermal-conduction) model 
It is useful to think of the LDTH model as the core model. These 2-D drift-scale TH models 
are run for 31 locations spaced throughout the potential repository area, for several areal mass 
loading (AML) values (nominal value and lower) to represent the influence of edge-cooling 
effects. The LDTH model includes the hydrologic processes and parameters (e.g., surface 
infiltration rates, hydrologic properties). The potential repository-scale variability of the 
hydrostratigraphy within the potential repository footprint is represented by the 31 locations. 
These are regularly distributed over the potential repository footprint, and each has an associated 
hydrostratigraphic column. These 31 columns represent the mountain-scale lateral variability of 
hydrostratigraphy within the potential repository footprint (CRWMS M&O 2000i). 
In the LDTH models, the relative humidity at the ground surface is fixed at 100 percent to 
control the egress of moisture as vapor. The drip shield and waste package are represented as 
impermeable for the entire duration of the Multiscale TH Model simulations. Development of 
heat-generation histories for each of the submodels and locations is described in supporting 
documentation (CRWMS M&O 2000i; Sections 6.2.4, 6.3.4, 6.4.4, and 6.5.4). The same WP 
sequence is repeated for all model locations throughout the repository footprint. All emplaced 
WPs fall in one of four major WP categories: 1) 21-PWR WPs, 2) 44-BWR WPs, 3) HLW, and 
4) DSNF. All WPs within a given category follow the same average thermal decay function (as 
a percentage of initial heat output). In the model, drift ventilation removes 70 percent of the heat 
generated by the waste inventory for the entire 50-yr preclosure period. The 70 percent heatremoval 
efficiency, and the 50-yr ventilation period, are applied uniformly throughout the 
potential repository footprint. 
The remaining three models, which are conduction only, are required to account for the influence 
of 3-D mountain-scale heat flow and 3-D drift-scale heat flow on drift-scale TH behavior. The 
coupling of 3-D mountain-scale heat flow to 2-D drift-scale TH behavior is accomplished with

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the SMT and the SDT models. The SMT is 3-D and includes the influence of thermal-property 
variation in the mountain, lateral heat loss to conduction at the potential repository edges, and 
overburden-thickness variation with location, assuming a uniform, planar (i.e., smeared) heat 
source throughout the potential repository area. The SDT model is a 1-D (vertical) model, run at 
the same 31 locations and for the same AMLs as the LDTH models. To obtain the lineaveraged 
drift-wall temperature (which is roughly equivalent to an average waste package 
location), the relationship between the drift-wall temperature in the LDTH model, and the 
smeared potential repository-plane temperature in the SDT model is used to modify the 
temperatures in the SMT model; this results in an Multiscale TH Model drift-wall temperature 
that approximates the effects of the most important TH processes at the drift-scale and the 
geometry effects of the mountain scale. At this stage of the Multiscale TH Model abstraction 
methodology, the influence of 3-D drift-scale heat flow has not yet been added. 
Because the SMT and SDT models share the same smeared-heat-source approximation and 
thermal-conduction representation of heat transfer, the relation between the SDT model 
temperature and the LDTH model drift-wall temperature allows for the SMT model temperature 
to be corrected for the influence of TH processes on temperature and for the influence of 2-D 
drift-scale dimensionality (orthogonal to the axis of the drift). The SMT, SDT, and LDTH 
models all share a blended heat-generation history, which blends the heat-generation histories of 
the entire waste package potential repository; hence, the heat-generation history is effectively 
that of an average waste package. The DDT model is a 3-D drift-scale model, which includes 
individual waste packages (with distinctive heat-generation histories) and accounts for thermal 
radiation in addition to thermal conduction between the waste packages and drift surfaces. The 
drift-wall temperatures for an average waste packagecalculated with the combined use of the 
LDTH, SMT, and SDT modelsare then further modified to account for waste package-specific 
deviations using the DDT model. This is accomplished using relations between local 
temperatures at various point locations along the drift (such as on the drift wall, drip shield 
surface, and waste package surface) and the corresponding line-averaged temperature in the 
DDT model. 
For the DDT models, the waste package sequence in one modeled drift segment is repeated 
throughout the potential repository footprint. All emplaced waste packages fall into one of four 
major categories: 1) 21-PWR (pressurized-water reactor) waste packages, 2) 44-BWR 
(boiling-water reactor) waste packages, 3) HLW, and 4) drip shield NF. With respect to waste 
package-to-waste package variability, 42.9 percent of the waste packages are 21-PWR waste 
packages, 28.6 percent are 44-BWR waste packages, 21.4 percent are HLW waste packages, and 
7.1 percent are drip shield NF waste packages. All waste packages are emplaced at the same 
time. 
The results of the Multiscale TH Model are integrated with the use of the Multiscale TH 
Abstraction Code (MSTHAC). Details of MSTHAC and the four type of models (LDTH, SMT, 
SDT, and DDT) are documented in the Multiscale Thermohydrologic Model (CRWMS M&O 
2000i).

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3.1.4.4 Multiscale Thermohydrologic Model Validation 
The Multiscale TH Model is performed using a method based on industry-standard finitedifference 
software that includes both mass and energy balances. The results depend on the 
inputs, and all inputs to the Multiscale TH Model are to-be-verified. Model documentation 
addresses input data, assumptions, initial and boundary conditions, software, uncertainties, and 
other information as required to replicate the model results. 
Several different validation approaches are used for the Multiscale TH Model, including the 
following: 
 Inspection of model inputs and outputs  A comprehensive analysis has been performed 
(CRWMS M&O 2000i) to evaluate the relationships between model inputs and outputs. This 
analysis involved more than 150 plots covering a wide range of input and output conditions. 
The analysis indicates that the Multiscale TH Model produces results that are consistent with 
current understanding of the physical processes that are accounted for in the model. 
 Black-box testing of MSTHAC  Certain computational modules of the Multiscale TH 
Model abstraction code (CRWMS M&O 2000i) were evaluated using test problems that 
allowed for verification by independent hand calculations. 
 Comparison of NUFT TH model results against the Large Block Test  The Multiscale 
TH Model (CRWMS M&O 2000i) discusses the comparison of NUFT TH model results 
with data from the Large Block Test and the Drift Scale Test, and references other 
documentation that describes these results in more detail. A brief summary of this 
comparison is provided below. 
 Comparison of Multiscale TH Model results against an alternative numerical model  A 
direct comparison is reported between an earlier version the Multiscale TH Model, and a 3-D 
mountain-scale TH model (CRWMS M&O 2000i). A brief summary of this corroborative 
comparison is provided below. 
The validation strategy is to compare data from field-scale thermal-hydrologic tests, with direct 
simulations using NUFT, then compare results from the Multiscale TH Model with a mountainscale 
simulation performed using TOUGH2 (a different simulation code). 
On the basis of these multiple validation approaches and the results, it is concluded that the 
Multiscale TH Model is valid for its intended use. Direct validation is limited to temperature 
comparisons; validity for other parameters (e.g. RH, saturation) is inferred using the approach 
summarized here. 
Importantly, the 2-D, drift-scale TH models described here (LDTH, or chimney models) are 
the basis for all TH models described in this report (Sections 3.1.1 and 3.1.2.1), and the 
validation applies to them also.

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3.1.4.4.1 Comparison of NUFT TH Models with the Large Block Test 
The NUFT model is used to simulate the entire history of the Large Block Test (see CRWMS 
M&O 2000i for details and references). The NUFT TH model of the LBT used the same 
hydrologic property set as used in the Multiscale TH Model presented in this report. As an 
example of model comparison, Figure 3-71 shows the simulated temperature profile along 
Borehole TT1 at six times from 30 to 400 days, compared to observed temperature. The results 
show some over-prediction of temperature at earlier times, but the difference between simulated 
and measured temperatures decreases at later time. At 300 days and 400 days (25 days after 
power shutdown), the model is in close agreement. Evaluation of goodness-of-fit to measured 
temperatures shows accuracy of a few degrees Celsius, for temperatures measured along 
Borehole TT1. The difference improves markedly after power shutdown. 
Figure 3-72 shows the simulated and measured liquid-phase saturation profiles along Borehole 
TN3, which is a vertical borehole used for neutron probe measurements of water content in the 
LBT. The field measurement times, 103, 361, and 501 days are compared to simulation times of 
100, 365, and 500 days (the saturation varies slowly, so small differences between measurement 
and simulation times are negligible). The simulated dryout zone develops more slowly than 
observed, but the difference decreases with time. At 365 and 500 days, the model is in close 
agreement. 
3.1.4.4.2 Comparison of NUFT TH Models with the Drift Scale Test 
The NUFT model is used to simulate the Drift Scale Test (DST) heating period from test startup 
to the present (see CRWMS M&O 2000i for details and references). As an example of model 
comparison, Figure 3-73 compares the simulated and measured temperatures along Borehole 
ESF-HD-137 at 365 and 547 days. The model results are in close agreement with measured 
temperatures, only slightly overpredicting temperatures in the superheated (T>100C) zone and 
slightly underpredicting temperatures in the sub-boiling zone. 
In general, agreement between the 3-D model and measured temperatures is poor for all 
locations close to the heated drift, at times less than 100 days. This results from representing the 
heated drift cross-section in the 3-D model as square, rather than cylindrical. On the other hand, 
the 2-D LDTH submodels more closely represent the cylindrical geometry. At times greater than 
1 yr, agreement between 3-D model simulations and measured temperatures improves. The 
regions for which there is close agreement between simulated and measured temperatures fall 
into two categories: (1) the sub-boiling zone and (2) the zone of boiling and super-boiling 
temperatures along the heated drift. Close agreement in the sub-boiling zone indicates that heat 
flow there is dominated by conduction and that the assumed value of thermal conductivity is 
reasonable. Because of the relatively high, matrix liquid saturation in the sub-boiling zone, the 
wet value of thermal conductivity applies. Close agreement in the region close to the heated drift 
indicates that: (1) thermal radiation is adequately represented inside the heated drift, (2) heat 
flow in the boiling and above-boiling zones is dominated by conduction, and (3) the value of dry 
thermal conductivity is reasonable. 
These results show that the submodels used in the Multiscale TH Model, together with the use of 
the drift-scale hydrologic property set, are valid for their intended use. The results also show that

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the DDT submodel (which represents how thermal radiation affects 3-D heat flow in the EBS 
and near field) is valid for its intended use. 
3.1.4.4.3 Comparison of the Multiscale TH Model with an Alternative Numerical 
Model 
Figure 3-74 compares the drift-wall temperature predicted by the Multiscale TH Model with 
those predicted by an east-west cross-sectional mountain-scale TH model (see CRWMS M&O 
2000i for details of the property sets and other model inputs, and references). The mountainscale 
TH model is based on the TOUGH2 TH simulation code. It is a relatively coarsely gridded 
model, so the RH in the drift, and liquid-phase saturation at the drift wall, were not calculated. 
Accordingly, the comparison is limited to drift-wall temperature from the Multiscale TH Model, 
vs. drift temperature from the mountain-scale TH model. 
The NUFT and TOUGH2 thermal-hydrology simulation codes are very similar, and implement 
the same conceptual and mathematical models, using similar or identical (depending on the 
model) hydrologic properties, boundary conditions, and other Yucca Mountain site-specific input 
data. The NUFT code is used primarily for TH modeling, and elevated temperature conductiononly 
modeling, whereas TOUGH2 is used for the UZ Model (CRWMS M&O 2000o) and the 
mountain-scale TH model (CRWMS M&O 2000aj). The two codes have differences in 
structure, features, and execution time. The NUFT code is an integral part of the multi-scale TH 
modeling approach. 
Before comparing the two approaches (Figure 3-74) it is important to discuss other differences in 
the models: 
 The temperature predicted by the Multiscale TH Model is the perimeter-averaged driftwall 
temperature adjacent to an average 21-PWR medium-output WP. The Multiscale 
TH Model includes in-drift 3-D calculations of WP temperatures, therefore some driftwall 
locations are hotter than shown in Figure 3-74, while some are cooler. The 
temperature prediction in the mountain-scale model is for a grid block that occupies the 
entire drift, so it produces a lumped representation of the drift temperature. 
 The mountain-scale TH model uses a line-averaged heat source that axially smoothes 
the differences between hotter and cooler WP locations. 
 The initial areal power density (at emplacement) in the Multiscale TH Model is 92.3 
kW/acre, compared to 99.4 kW/acre in the mountain-scale TH model. 
 The mountain-scale TH model representation of the heated footprint of the potential 
repository extends slightly further to the west than in the Multiscale TH Model. 
At the center of the potential repository (L4C3) the approaches predict nearly the same duration 
of boiling (Figure 3-74a). At the edge location (L4C1) which is 100 m from the western edge of 
the repository in the Multiscale TH Model, the mountain-scale TH model predicts a longer 
duration of boiling (Figure 3-74b). During the post-boiling period, the temperatures predicted by 
the approaches are in close agreement. During the early heating period, the coarse gridding of

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the mountain-scale TH model does not capture the rapid drift-wall temperature rise that the more 
finely detailed Multiscale TH Model predicts. Because of the coarse gridding, the mountainscale 
TH model tends to overpredict the temperature at the mid-pillar location and thereby 
prevents condensate from draining between drifts. This results in greater condensate 
accumulation in the host rock above the potential repository horizon, which leads to unrealistic 
heat-pipe behavior. This behavior is demonstrated by the fluctuation in drift temperature from 
approximately 300 yr to 600 yr (Figure 3-74a). Note that at approximately 400 yr when the heat 
pipe zone has dried out, the temperature agrees with that predicted by the Multiscale TH Model. 
Given the obvious differences between the Multiscale TH Model and the mountain-scale model 
approaches, they are in reasonable agreement throughout much of the thermal evolution of the 
potential repository. 
3.1.4.5 Multiscale Thermohydrologic Model Results 
This section presents a brief summary of representative Multiscale TH Model results pertaining 
to predicted thermal-hydrologic conditions within the emplacement drifts. Multiscale TH Model 
predictions for the host rock are discussed and presented in the Near-Field Environment Process 
Model Report (CRWMS M&O 2000u, Sections 2.2.1.3 and 3.4.1). 
Waste Package Temperature  Figure 3-75 shows the predicted temperature on the surface of a 
21-PWR WP, for the mean infiltration distribution at two selected locations: the geographical 
center of the repository, and also near the eastern edge. During the preclosure period, host-rock 
temperatures remain below the boiling point for the mean- and upper-infiltration flux cases, 
while boiling occurs in the host rock for the lower-flux case. During the preclosure period, peak 
waste package temperatures of 100C (for the mean flux case) and 110C (for the low flux case) 
occur at 10 to 15 years; peak drift-wall temperatures of 86C (for the mean flux case) and of 
96C (for the low flux case) occur at 20 to 25 years. Edge-cooling effects do not strongly affect 
preclosure temperatures. After the initial heat-up stage, relative humidity on waste packages 
varies from 45 percent to 75 percent during the preclosure period. 
In addition to history plots, contour plots are provided for key time intervals to capture major 
trends in the spatial and temporal distribution of temperature across the repository layout. The 
spatial distribution of temperature predicted for the surfaces of 21-PWR waste packages 
throughout the repository is shown in Figures 3-76 through 3-78 for several time intervals. (The 
contoured quantity is the average temperature on the surface of the nearest 21-PWR waste 
packages, without consideration of the cooler temperatures that will always occur in the host 
rock.) It is noted that the repository design analyzed to generate these figures employs several 
design measures (such as fuel blending and line-load WP spacing) which minimize the variation 
of temperature between waste packages. Even considering the model uncertainties discussed 
previously, the calculated results are probably close to the temperature distributions that would 
be likely to occur in the repository. The model does not incorporate staging of waste 
emplacement through the preclosure period, but this becomes unimportant after a similar period 
of time (e.g. 50 years) passes during the postclosure period. 
During the postclosure period, peak waste package temperatures of 305C (for the mean flux 
case) and 315C (for the low flux case) are predicted to occur at 60 years. The model 
incorporates different types of waste packages, with different heat output, in a typical array that

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is repeated throughout the repository emplacement areas. Considering this variation in heat 
output, along with infiltration flux and location, the maximum difference in peak WP 
temperature, between the hottest and coolest packages, is 42 C. 
During the postclosure period, peak temperatures on the lower drift wall of 195C (for the mean 
flux case) and 205C (for the low flux case) are predicted to occur at 65 years; peak temperatures 
on the upper drift wall of 125C (for the mean flux case) and 134C (for the low flux case) are 
predicted to occur at 65 years. The large (70 C) temperature difference between the upper and 
lower drift wall locations arises because the backfill acts as an insulator (Kth = 0.33 W/mC). 
There is more backfill above the waste package and drip shield than below, so heat from the 
waste packages tends to be focused to the floor of the drift. To reduce this difference it would be 
necessary to rearrange the EBS geometry, or eliminate backfill. 
During the very early postclosure period, the edge-cooling effect has a small effect on 
temperatures. By 100 years, the influence of edge-cooling is considerable, with waste package 
temperatures varying by 120C from the repository edge to the center of the potential repository; 
with the outer 100 to 200 m of the repository layout being most influenced by edge-cooling at 
100 years after emplacement. The difference in temperatures between center and edge locations 
suggests a thermal-management strategy to limit peak temperatures; the hottest waste packages 
would be emplaced near the edges. 
Liquid Flux  Liquid-phase flux in the backfill, and in the invert, will depend on seepage flow 
into the drift. Even if seepage is zero or very minimal, liquid water will enter directly into the 
backfill and invert materials where they contact the host rock. The predictions of liquid flux in 
the EBS that are discussed here are based on models in which there is capillary flow in the drifts, 
but not seepage of free water through the rock roof. 
Predicted histories for liquid-phase flux in the emplacement drifts for the mean infiltration 
distribution, at two selected locations: the center of the repository and near the eastern edge, are 
presented in Figure 3-79 and Figure 3-80. Three estimates of liquid flux are presented: the 
average vertical flux at the upper surface of the drip shield, the average flux in the backfill to the 
side of the drip shield, and the average flux in the invert. Corresponding flux conditions in the 
host rock, are discussed and presented in the Near-Field Environment Process Model Report 
(CRWMS M&O 2000u; Section 3.4.1). 
Thermal-hydrologic behavior in the emplacement drifts is strongly influenced by the hydrologic 
properties of the quartz sand backfill. During the early part of the preclosure period, the backfill 
is dry. As the temperature at the drift wall declines below the boiling point, the TH models 
predict capillary flow of water from fractures in the host rock, into the backfill, at unsaturated 
conditions. 
Another process influencing liquid-phase flux in the drift is thermal refluxing, or the heat-pipe 
effect. As moisture content in the backfill increases, and the drift-wall cools, there is a tendency 
for liquid water to evaporate near the drip shield, and vapor to condense near the drift wall. This 
increases the liquid flux in the backfill while increasing the cumulative extent of evaporation 
near the drip shield. The onset of evaporation on the drip shield will occur first at the repository 
edge and then proceed inward toward the center of the repository layout. Another factor that

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influences liquid-phase flux in the drift is focusing of flow in the backfill beside the drip shield. 
Depending on the geometry of flow in the backfill, the flux can be focused by a factor of four at 
this location, relative to the magnitude of the ambient percolation flux in the host rock. 
Predicted histories for relative humidity on the surface of 21-PWR waste packages, for the mean 
infiltration distribution, at two selected locations: the center of the repository and near the eastern 
edge, are presented in Figure 3-81. In addition to history plots, contour plots are provided for 
key time intervals, to capture major trends in the spatial and temporal distribution of relative 
humidity across the repository layout. The spatial distribution of relative humidity predicted for 
the surfaces of 21-PWR waste packages throughout the repository is shown in Figures 3-82 
through 3-84 for several time intervals. (The contoured quantity is the average relative humidity 
on the surface of the nearest 21-PWR waste packages, without consideration of conditions in the 
nearby host rock.) 
An important measure of EBS performance is the length of time that the RH on the waste 
packages remains low. Relative humidity reduction on waste packages results from the 
following: 
 Relative humidity reduction at the drift wall (and in the host rock) decreases 
strongly with proximity to the edge of the potential repository; significant reduction in 
drift-wall RH persists for 100 to 1000 years (depending on proximity to the edge) for 
the mean and upper infiltration-flux cases and for about 200 to 2000 years for the low 
flux case. 
 Relative humidity reduction on the drip shield is relatively insensitive to proximity 
to the edge of the potential repository, with backfill in the drift. Eventually, RH on the 
drip shield will approach 100 percent, similar to the host rock. For the mean and upper 
infiltration cases, this will occur after approximately 1000 to 2000 years; for the low 
infiltration case, it will occur after approximately 3000 to 6000 years. 
 Relative humidity reduction on the waste package will persist long after RH 
reduction on the drip shield has ceased. The persistence of decreased RH at the waste 
package, arises because of the temperature difference between the waste package and 
the drip shield. Because the space between the waste package and the drip shield is an 
open cavity, thermal radiation will control the temperature difference. 
The maximum lateral extent of boiling temperatures in the host rock (away from the drift wall) 
indicates the spatial extent of rock dryout around the emplacement drifts. The lateral extent of 
boiling is considerably greater for the low infiltration-flux case than for the mean or upper flux 
cases. The hottest (and driest) waste package location in the low infiltration case has a maximum 
lateral extent of boiling of 18 m, therefore, because the drifts are 81 m apart, less than 44.4 
percent of the total repository layout area would be heated to the boiling point. The hottest (and 
driest) waste package locations in both the mean and upper infiltration cases have a maximum 
lateral extent of boiling of 9.7 m, so less than 24 percent of the total repository layout area would 
be heated to the boiling point. For the range of infiltration flux considered, the maximum extent 
of dryout will be between these two values. Further discussion of the extent of dryout in the

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pillars between emplacement drifts is presented in the Near-Field Environment Process Model 
Report (CRWMS M&O 2000u; Section 2.2.1.3). 
There is a greater difference in dryout behavior (as evidenced by the maximum lateral extent of 
boiling and by RH reduction) between the mean and low infiltration cases, compared to the 
difference between the mean and upper infiltration cases. Therefore, if one considers a 
percolation threshold above which rock dryout becomes substantially limited by percolation, the 
threshold would be near that predicted for the mean infiltration case. Greater values of the 
infiltration flux would strongly limit the extent of boiling temperatures and rock dryout. 
3.2 INTEGRATED MODEL DEVELOPMENT 
No single model can describe all aspects of the EBS and its interaction with the surrounding host 
rock, especially because the approach must remain flexible to accommodate an evolving 
engineering design. Rather, the focus is on the modeling and analysis of the basic processes of 
fluid flow, heat transfer, radionuclide transport, and chemical interaction, as controlled or 
influenced by design, operating practices, and characteristics of the disturbed natural system. 
The Engineered Barrier System Process Model Report documents the development and 
application of a linked set of process models, and their abstractions, as input to TSPA for 
determining the contribution of the EBS total system performance. As described at the 
beginning of Chapter 3, this PMR contains four major process models, documented in 
Sections 3.1.1 through Section 3.1.4. These sections summarize the conceptual development, 
model implementation, input data, codes and routines, model results, and limitations on use, for 
each process model. The EBS PMR also contains a major analysis of FEPs relevant to the EBS, 
in Section 2.4. 
Because the EBS is not associated with any Principal Factors in the Repository Safety Strategy 
(Rev 3), model development relies heavily on the use of defensible bounding calculations. This 
has been especially appropriate where data are limited, or the future evolution of the system is 
highly uncertain. 
Process model uncertainties and validation are discussed in Sections 3.1.1 through 3.1.4. 
Section 3.2.1 summarizes the abstraction and preparation of process model results for input to 
the TSPA Model. 
3.2.1 Abstraction of the Models 
3.2.1.1 Abstraction of the Physical and Chemical Environment Model 
In general, knowledge of the physical and chemical environment in the emplacement drifts is 
required to quantify EBS processes and to predict the quantitative transport of released 
radionuclides. Description of the environment includes: (1) evolution of groundwater flow in the 
EBS and transport pathways into the host rock, and (2) composition of groundwater moving 
along those pathways. Information on physical environment characteristics is needed to quantify 
groundwater movement is in the drift that transports radionuclides by advection. Brine 
composition is needed to predict breaching of drip shields and waste packages by corrosion, and

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to quantify processes that release and transport radionuclides. The purpose of the Physical and 
Chemical Environment Abstraction Model (CRWMS M&O 2000j) is to summarize: 
 The role of in-drift physical and chemical environments in the Total System 
Performance Assessment (TSPA) 
 The configuration of engineered components (features) and critical locations in drifts 
 Processes and critical locations of processes that can affect the EBS Physical and 
Chemical Environment (P&CE) 
 Couplings and relationships among features and processes in the drifts 
 Methods for using conceptual and parameter inputs to the TSPA 
 Parameters calculated by process models transmitted to . 
Note that the physical and chemical environment parameters ultimately used in the TSPA largely 
depend on the input requirements of the drip shield and waste package corrosion models, and 
the EBS transport model, as they are implemented in the TSPA. Physical and chemical 
environment parameters are used by the TSPA to simulate the following aspects of performance: 
 Corrosion of drip shields and waste packages 
 Salt precipitation, salt redissolution, and resulting groundwater compositions at one or 
more locations in the drifts and in released groundwater 
 Mobilization and release of materials from the engineered barrier system both in 
dissolved and colloidal form 
Specific parameters that are available for use in the TSPA are summarized in Table 3-45.

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Table 3-45. Parameters available for TSPA 
Applicable Process Water Composition Input Parameters to TSPA-SR 
Drip Shield Corrosion 
pH 
Chloride concentration 
Waste Package Corrosion 
pH 
Chloride concentration 
Model to calculate mass of microbes per unit drift length 
EBS Transport by Colloids in 
Invert 
Ionic strength 
Concentration and composition of colloids 
Radionuclide Mobilization and 
Release from Engineered 
Barrier System and 
Corresponding Groundwater 
Chemical Environment 
PH 
Ionic strength 
Total dissolved carbonate 
Chloride concentration 
Oxygen fugacity 
Carbon dioxide fugacity 
Concentration and composition of colloids 
The parameters listed in Table 3-45 specify groundwater compositions and microbial masses for 
potential application at the following three locations: 
 At the outer surface of the drip shield 
 At the outer surface of the waste package 
 Within the invert 
The following sections summarize the AMRs that provide abstracted physical and chemical 
environment parameters for use in the TSPA. 
3.2.1.1.1 In-Drift Gas Flux and Composition 
As summarized in this section, the In-Drift Gas Flux and Composition (CRWMS M&O 2000e) 
provides a basis for abstracting the values of the gas flux and composition in the emplacement 
drifts for the following major geochemical constituents: 
 Carbon dioxide (CO2) 
 Oxygen (O2) 
 Nitrogen (N2) 
 Steam or water vapor (H2O) 
This model includes the following important processes affecting gas composition in the drift: 
 Ambient and thermally perturbed fluxes of gas into the drift from the geosphere

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 Fluxes of aqueous solutions into the drift 
 Possible source terms for gas constituents in water just outside the drift 
 Boiling of the water in the emplacement drift 
 Possible chemical reactions among the groundwater, gases, and engineered materials 
within the emplacement drift 
 Radiolysis 
The major introduced materials that may act as sources or sinks for oxygen and carbon dioxide in 
the gas phase are evaluated for their potential to alter the in-drift gas composition. That is, 
mass-balance calculations that consider the major potential sinks of both O2 and CO2 are 
assessed to track gas composition within the drift relative to the incoming gas composition. 
This model predicts that gas composition everywhere within the drift is homogeneous because 
gas-transport rates are sufficiently high, even if only diffusive movement of gas constituents is 
considered, to mix gases in this unsaturated environment at the scale of a drift diameter. For 
consideration of local gas heterogeneity, more detailed process models of the in-drift 
environment would be needed. 
For the effects of radiolysis, this model assumes that the production of gaseous radiolytic 
products in the drift is bounded by the in-package capacity to produce gaseous radiolytic 
products and the availability of materials suitable for radiolysis, such as water. 
All metals and alloys in the disposal drifts are considered equivalent to iron (Fe) for the purpose 
of the mass-balance calculation for gas-phase constituents. This assumption is used only to 
simplify the calculation of the amount of oxygen consumed in corrosion of the metals and alloys. 
Other metals than Fe are present in the disposal drifts, particularly in the spent fuel wastes and 
associated packages and containers; this assumption, however, is expected to introduce an error 
of less than one order of magnitude in the calculated oxygen demand. This degree of uncertainty 
will have no effect on the scoping mass-balance approach used in this abstraction. 
The carbon (C) contained in the mild steel in the disposal drifts is assumed to not act as a 
significant source of CO2 to the in-drift gas mixture. Because the abstraction model has 
determined that more than ample CO2 is available (from the gas flux through the drifts) to 
completely saturate available CO2 sinks, this assumption can have no significant impact on the 
results of this analysis. 
The conceptual model and mass-balance calculations presented here suggest that the in-drift gas 
flux and composition will not be strongly affected by interactions with in-drift and near-drift 
materials. However, in-drift gases will be displaced by steam during the thermal period, thus 
reducing the amounts of all gases (except water vapor) in the drifts during that period. The 
resulting decrease in oxygen O2 fugacity, is not expected to be sufficient to affect redox reactions 
occurring in the repository.

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The conclusion that more than ample fluxes of CO2 and O2 are available to meet the 
requirements for chemical reactions taking place in the drifts is based on results from 
thermal-hydrologic models such as those for the TSPA-Viability Assessment, discussed in 
Section 3.1.2.2. It is noted that the gas fluxes predicted by these models result from large-scale 
circulation in the UZ throughout the volume of host rock occupied by the repository, thus 
knowledge of large-scale properties and processes is implicit in the use of these results. 
There is another mechanism for gas transport into the emplacement drifts that is not addressed by 
this model. If the concentration of any gas-phase component in the drift decreases by more than 
approximately one order of magnitude, gaseous diffusion could be incorporated to improve the 
realism of the model. The source of the diffusing component would be the water, and gas-filled 
porosity, in the host rock adjacent to the drift opening. Gas transport by this mechanism would 
be added to that transported by gas-phase advective circulation, and liquid seepage flux (where 
seepage occurs). More detailed discussion of uncertainties and limitations related to the 
conceptual model for in-drift gases, is provided in the In-Drift Gas Flux and Composition 
(CRWMS M&O 2000e).The model is considered valid and appropriate for its intended use 
(bounding the gas fluxes and compositions within emplacement drifts), because this abstraction 
uses conservative approaches. 
3.2.1.1.2 Introduced Materials 
Introduced materials include cement grout, backfill, invert, and metallic materials or alloys. The 
following section addresses cement, backfill, and invert materials. These materials are also 
discussed in Section 3.1.2.3, along with metals, alloys, and other materials. 
Seepage-Cement Interaction 
The purpose of the seepagecement interactions analysis (CRWMS M&O 2000l) is to predict the 
time required for carbonation through reaction with gas phase carbon dioxide of the calcium 
hydroxide [Ca(OH)2] and other susceptible calcium-bearing phases present within the 
cementitious grout used to anchor the rockbolts in the drift ground-support system. The time 
required for complete carbonation is calculated for three different partial pressures of CO2: 
1 ppm, 100 ppm, and 1000 ppm, reference Table 3-C. 
Table 3-C. Relationship Between CO2 Concentration and Duration Required for Carbonation 
CO2 Concentration (in ppmv) Corresponding Air Mass 
Fraction 
Duration for Carbonation 
(years) 
1 0.001 39,700 
100 0.1 397 
1,000 1.0 40

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For this analysis, Ficks First Law of Diffusion is used to make two estimates: 
 Amount of CO2 that can be provided by steady-state diffusion under for the stated 
conditions 
 Relationship between the degree of depletion of the atmospheric CO2 in the gas phase, 
and the distance to a rockbolt undergoing carbonation with a third analysis estimated 
time required for carbonation through reaction with aqueous-phase CO2 
From current understanding of geochemical carbonation processes, stoichiometry determines the 
mass of CO2 required to quantitatively transform portlandite or other reactive calcium phase into 
an equivalent amount of calcite. Because the transformation of portlandite into calcite is 
kinetically very fast, the transfer of atmospheric CO2 (by diffusion through the rock matrix to the 
grouted rockbolt) controls the rate of portlandite carbonation. In summary, this analysis has 
derived the time required for diffusion-controlled carbonation of the grout surrounding a 
rockbolt. This analysis shows that the time required for carbonation is proportional to the 
product of CO2 partial pressure and the gaseous diffusion coefficient of CO2. This analysis also 
establishes the relationship between the depletion, under steady-state conditions, of the local 
gaseous CO2 concentration and the distance from the rockbolt grout to the CO2 source. 
Seepage-Backfill Interaction 
A summary of the analysis of seepagebackfill interactions is discussed next. This analysis 
(CRWMS M&O 2000v) addresses potential dissolution and precipitation interactions of seepage 
with quartz sand backfill, and is presented in Section 3.1.2.3. Incoming seepage is affected by 
evaporation, which is addressed in a separate analysis/model report (CRWMS M&O 2000g). 
Evaporation in the drift and surrounding host rock will affect the quantity and composition of 
seepage, especially during the first few thousand years. Seepage composition is potentially 
important in evaluating interaction with the backfill. The following processes are incorporated in 
the seepagebackfill interactions model: 
 Evaporative concentration of incoming seepage 
 Precipitation of dissolved solids resulting from evaporative concentration 
 Dissolution of precipitates and backfill 
This model is an application of the High Relative Humidity (HRH) Salts Model (Pitzer model) 
developed in the In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g) and described in 
Section 3.1.2.5. It evaluates the potential interaction of evaporated seepage with the backfill. 
The seepage-backfill interaction model is conceptually identical to the HRH Salts Model 
described in Section 3.1.2.5, which calculates the composition of evaporatively concentrated 
seepage water, except that the solubility equilibrium of quartz is also monitored in the 
calculations. Solubility equilibrium for quartz-sand backfill is investigated by examining the 
quartz saturation indices for each of the cases simulated by the HRH Salts Model 
(Section 3.1.2.5). These cases include a set of simulations for solution composition

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corresponding to relative humidity (RH) of 85 percent and greater. Cases for RH less than 
85 percent are ignored in this model because such concentrated conditions favor precipitation of 
silica and supersaturation of quartz (CRWMS M&O 2000g). 
The results indicate that the interaction of the backfill with seepage derived from evaporated J-13 
well water will likely be negligible. Dissolution of quartz sand is not predicted except for 
unlikely scenarios. Predictions of quartz saturation are reasonable because evaporating water 
tends to favor precipitation rather than dissolution of silica. The greatest potential sources of 
uncertainty in these analyses are the predicted inputs (e.g., the seepage rate and seepage 
composition) that feed the analyses. 
Seepage-Invert Interaction 
A conceptual model for seepageinvert interactions is developed and reported in Seepage/Invert 
Interactions (CRWMS M&O 2000m). The model identifies possible pathways for seepage into 
the invert, and material interactions with the seepage. It estimates the conditions that will prevail 
as the environment evolves. The purpose of the model is to qualitatively evaluate the physical 
and chemical conditions and processes in the invert. 
The invert is composed of the same Topopah Spring welded tuff that makes up the host rock. 
During the thermal period, however, the invert is expected to experience thermal conditions not 
reached in the host-rock. Porosity in the invert will provide locations where silica, silicates, and 
evaporite minerals, including soluble alkali salts, will precipitate. 
The invert will contain steel and copper metal components, which will provide surfaces where 
transition-metal carbonates, hydroxides, sulfates, and chlorides may form by reaction with 
seepage. These phases are not likely to be sufficiently abundant to buffer conditions in the 
physical and chemical environment, or to alter the chemical composition of water passing 
through the invert. 
For a finite period, during cooling where the seepage flux exceeds the evaporative flux, liquid 
seepage passing through emplacement drifts will have elevated ionic strength. Seepage 
composition will evolve as the precipitated salts are dissolved. Depending on the mass of 
precipitates produced and the flux of seepage into the invert, the elevated ionic strength may be 
sufficient to destabilize colloids or to counteract sorption. 
Interaction with seepage will produce mineralogical and physical changes in the crushed tuff 
invert material. Expansion of alteration products, and long-term physical confinement by the 
overlying backfill, could decrease porosity and thereby decrease permeability. In the current 
design, the portion of the invert under the DS is not physically confined, and may therefore 
undergo smaller decreases in porosity or permeability. Conceptually, invertseepage reactions 
are therefore expected to create preferred flowpaths immediately beneath the WPs. However, 
the permeability in this portion of the invert will not increase, and the transmissivity of the invert 
overall, will tend to decrease with time. 
The invert component parts (ballast and metal materials) are not present in significant quantities 
with respect to the host rock and other introduced in-drift materials to exert a significant 
influence on the chemistry of the seepage exiting the drift.

 3-192 
3.2.1.1.3 Microbial Effects 
The purpose of the In Drift Microbial Communities AMR (CRWMS M&O 2000f) is to bound 
the biomass that could be present within a given length of repository drift. The outputs from this 
model support the microbially influenced corrosion (MIC) aspects of WP corrosion modeling, 
and evaluation of colloidal transport of radionuclides. Refer to Section 3.1.2.4 for a discussion 
of potential microbial effects on the EBS and a description of the microbial communities model 
(MING). 
The MING code is used in the In Drift Microbial Communities AMR (CRWMS M&O 2000f) to 
develop biomass and microbial abundance estimates for the potential repository. The code and 
the associated conceptual model do not attempt to quantify the effects of microbial colonies or 
biofilms on potential repository materials; instead, they attempt to bound the overall, bulk effect 
of microbes on the in-drift geochemical environment (IDGE). 
 For TSPA, the MING code will provide scenario-dependent results for abundance of 
microbes per meter of drip shield or WP through time, for each WP type and potential 
repository configuration. The different scenarios will include WP types (e.g. 21-PWR 
vs. DHLW) and other conditions: 
 Drift ground-support options (e.g. use of steel, and grouted rockbolts) 
 Different material lifetimes, based on estimates of general corrosion rates 
 Different drift boundary conditions, such as TH results for the center of the potential 
repository vs. the edge 
 Aqueous transport concepts (e.g. dripping conditions on the WP, vs. no dripping on the 
WP until the DS is breached) 
Each such scenario can be used by the WP-degradation model to represent the variability and 
distribution of microbes over the surface of the DS and the WP. Biomass will be applied to the 
WP surface by estimating the surface area that can be covered by a one-cell thick biofilm, thus 
the proportion of the WP surface that is subject to MIC will be estimated. The results of the 
WP-degradation model will be used directly in TSPA calculations. 
Figure 3-42 (Section 3.1.2.4) shows a typical abstraction given as a plot of grams of biomass 
produced per lineal meter of emplacement drift per year versus time. 
Three validation tests were conducted for the In-Drift Microbial Communities Model 
(Section 3.1.2.4). The first test replicated a model that was constructed for the Swiss low-level 
repository program. The result indicates that MING handles the types of calculations that are 
required where natural barrier components are combined with the engineered barrier components 
to calculate microbial growth. The second test demonstrates that the model can simulate ambient 
conditions within the Exploratory Studies Facility (ESF), and other analog measurements. The 
second test also confirms that water availability limits microbial growth in the potential 
repository host rock. Calculated results also show that the microbial community is limited by the

 3-193 
availability of redox energy. The third test indicates that the numbers of organisms reported by 
MING are generally within an order of magnitude of values measured in controlled laboratory 
tests. The model results confirm the conclusions reported from lab experiments, namely, that the 
availability of water (growth media) is a primary factor limiting microbial growth, and that 
phosphorous is the primary limiting nutrient in the potential host rock. The results also show 
that in energy-limited systems, the impacts due to gas availability, variations in pH and water 
chemistry, and material lifetimes, are relatively small. However, in nutrient-limited systems, 
these influences produce greater impacts. Results from these tests indicate that model 
predictions are accurate to within an order of magnitude, and that the model is valid for its 
intended use in TSPA. 
3.2.1.1.4 Precipitates and Salts 
The In-Drift Precipitates/Salts Analysis (CRWMS M&O 2000g) evaluates the effects of 
evaporation on water composition at a given location in the EBS (e.g. the drip shield surface). 
Evaporation has a marked effect on water composition and, for the current design, will likely 
produce brines and salts in the EBS. See Section 3.1.2.5 for more detailed description of the 
precipitates and salts process models, defined here to include the Low Relative Humidity (LRH) 
Salts Model, and the High Relative Humidity (HRH) Salts Model. 
Results from the precipitates and salts models will be implemented directly in TSPA 
calculations. For TSPA the evolution of the potential repository is divided into time periods, in 
each of which several environmental parameters are estimated (abstracted) as representative, 
constant values. Environmental parameters that are inputs to the In-Drift Precipitates/Salts 
Analysis include temperature, relative humidity, seepage flux, seepage flux composition, and 
evaporation rate. For each combination of these inputs, a unique solution from the precipitates 
and salts models is developed. 
Calculated results for a plausible subset of possible environmental conditions are used to develop 
a response surface, for use in TSPA to interpolate results for any combination of input 
conditions. Input variables are limited to a small number of values, including estimated minima 
and maxima. The response surfaces define the pH, chloride concentration, and ionic strength as 
dependent variables, and are implemented as lookup tables. The look-up tables include the 
following independent variables: temperature, relative humidity, and seepage flux composition, 
and relative evaporation rate (i.e., evaporation rate relative to seepage rate). At a particular time 
step, the pH, chloride concentration, and ionic strength are obtained or interpolated from these 
tables, from within the TSPA. Table 3-46. is an example of the lookup tables in In-Drift 
Precipitates/Salts Analysis (CRWMS M&O 2000g):

 3-194 
Table 3-46. Lookup Table for Average J-13 Well Water Seepage at PCO2 = 10-1 atm 
Input Parameters Precipitates/Salts Model Output 
RH (%) T (C) Res pH 
Chloride 
(molal) 
Ionic Strength 
(molal) 
< 50.3 naa na dry dry dry 
50.3 na na 8.65 3.77E-03 3.65E+01 
51.0 na na 8.65 4.52E-02 3.49E+01 
53.1 na na 8.65 1.87E-01 2.95E+01 
55.2 na na 8.65 3.06E-01 2.49E+01 
60.5 na na 8.65 6.03E-01 1.35E+01 
65.7 na na 8.65 7.26E-01 8.77E+00 
71.0 na na 8.65 7.56E-01 7.62E+00 
76.2 na na 8.65 7.62E-01 7.39E+00 
81.5 na na 8.65 7.58E-01 7.56E+00 
85.0 na na 8.65 7.52E-01 7.79E+00 
> 85 95 0 6.58 2.01E-04 3.74E-03 
> 85 95 0.1 6.62 2.23E-04 4.15E-03 
> 85 95 0.5 6.83 4.02E-04 6.85E-03 
> 85 95 0.9 7.31 2.01E-03 2.21E-02 
> 85 95 0.99 8.14 1.98E-02 2.09E-01 
> 85 95 0.999 8.67 1.73E-01 1.82E+00 
> 85 95 > or = 1 8.65 7.52E-01 7.79E+00 
> 85 75 0 6.42 2.01E-04 3.74E-03 
> 85 75 0.1 6.47 2.23E-04 4.15E-03 
> 85 75 0.5 6.71 4.02E-04 7.51E-03 
> 85 75 0.9 7.21 2.01E-03 2.44E-02 
> 85 75 0.99 8.03 1.98E-02 2.09E-01 
> 85 75 0.999 8.59 1.73E-01 1.82E+00 
> 85 75 > or = 1 8.65 7.52E-01 7.79E+00 
> 85 45 0 6.21 2.01E-04 3.74E-03 
> 85 45 0.1 6.25 2.23E-04 4.15E-03 
> 85 45 0.5 6.50 4.02E-04 7.47E-03 
> 85 45 0.9 7.03 2.01E-03 2.66E-02 
> 85 45 0.99 7.85 1.98E-02 2.16E-01 
> 85 45 0.999 8.47 1.73E-01 1.82E+00 
> 85 45 > or = 1 8.65 7.52E-01 7.79E+00 
> 85 25 0 6.08 2.01E-04 3.74E-03 
> 85 25 0.1 6.12 2.23E-04 4.16E-03 
> 85 25 0.5 6.37 4.02E-04 7.47E-03 
> 85 25 0.9 6.95 2.01E-03 2.91E-02 
> 85 25 0.99 7.74 1.98E-02 2.21E-01 
> 85 25 0.999 8.40 1.73E-01 1.84E+00 
> 85 25 > or = 1 8.65 7.52E-01 7.79E+00 
a not applicable 
From CRWMS M&O 2000g

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This set of results was obtained by implementing the precipitates and salts model for several 
values of each input parameter, spanning the possible combinations of values for the parameters. 
The input variables are limited to a small number of input parameter values, including 
approximate minima and maxima. The only input parameter that is not varied in this table is 
seepage composition, which is taken to be average J-13 well water. An additional lookup table 
was generated using the seepage composition developed in the THC model abstraction (CRWMS 
M&O 2000y). 
Validation tests are reported for the precipitates and salts models in Section 3.1.2.5, which show 
that the models are valid for their intended uses. The abstraction of process model results into 
TSPA through the use of lookup tables is valid as long as chemical conditions do not depend on 
the local history of such conditions, which requires that input conditions vary slowly over time. 
The HRH Salts Model results (for RH greater than 85 percent) are steady-state values derived 
from constant input conditions. The LRH Salts Model results (for RH less than 85 percent) are 
also controlled by RH. These two models are discussed further below. 
For the HRH model, it is shown in Section 6.6.1.2 of the In-Drift Precipitates/Salts Analysis 
(CRWMS M&O 2000g) that after as few as 10 pore volumes, the chloride concentration of the 
water within the reaction cell is not affected by the initial concentration. Instead, it depends 
primarily on the chloride concentration in the incoming seepage ( s 
i C ) and the relative 
evaporation rate (Res). The derived equation relating these parameters is: 
es R 1 
1 
si 
C
rs 
i C 
- 
= 
where rs 
i c is the steady state molal concentration of soluble component i in the reaction cell. For 
example, a Res value of 0.9 (i.e., an effective evaporation rate equal to 90 percent of the incoming 
seepage rate) implies that the steady-state concentration of a highly soluble component (e.g., 
chloride) will be 10 times the concentration in incoming seepage. This equation can be used if 
components do not reach solubility limits, which may change with time in conjunction with 
changes in pH and CO2 fugacity. If the chemical evolution of evaporated seepage in a 
flow-through cell is evaluated for constant input conditions, and sufficient through-flow (e.g., 
more than 100 reaction cell volumes following a sharp change of input conditions, fewer for 
more gradual changes) then the results will not be affected by history. 
For the LRH model, RH controls the composition of the equilibrated solution because it fixes the 
activity of water. Thus, the importance of RH, combined with the presence of Na, Cl, NO3, K, 
CO3, and SO4 which form hygroscopic brines, abates the effect of history on the brine 
composition. Although the abundance of accumulated salts may affect the quantity and 
characteristics of brine produced, the potential history effects on estimated chloride 
concentration and ionic strength are negligible (for the intended use of the model). 
3.2.1.1.5 Colloids 
Several types of radionuclide-bearing colloids are expected to be generated through several 
mechanisms within the potential Yucca Mountain repository system. Colloids may be generated

 3-196 
through degradation of the waste forms and waste packages and they also occur naturally in 
groundwaters. In terms of composition, several types of colloids have been considered for the 
potential Yucca Mountian repositoy system. As is discussed below, organic colloids, primarily 
microbes and humic substances, have negligible impact on radionuclide transport. Another type, 
polymeric macromolecules consisting of the radionuclides themselves (real colloids or 
Eigenkolloide) are also not important. However, mineral colloids, with either sorbed 
radionuclides or containing engulfed radionuclides, do potentially impact performance, and are 
included in the model. In the potential Yucca Mountain repository system, mineral colloids 
include clay minerals (smectite clays, specifically montmorillonite), iron oxides and 
oxyhydroxides (ferrihydrite, goethite, and hematite), and silica. 
Colloids will be present at the WF, in the drift, and in the unsaturated and saturated zones. At 
the WF, colloids will be produced during the degradation of the WF and WP. In the potential 
repository drifts, additional colloids may be produced from the degradation of steel and 
cementitious components of the EBS. Other types of colloids (mineral and organic) will be 
present in the UZ and SZ and may migrate into the potential repository, or along transport 
pathways. Colloids present in the WF and WP environments are discussed below, based on the 
conceptual models described in In-Drift Colloids & Concentrations Analysis/Model Report 
(CRWMS M&O 2000d). 
Intrinsic, or true colloids are formed from polymerization of hydrolyzed radionuclide ions. 
For intrinsic colloids to form the fluid composition must be saturated with respect to a solid 
phase, so formation of intrinsic colloids is limited by solubility. Intrinsic colloids were not 
detected in experimental investigations of spent fuel at Argonne National Laboratory (ANL). 
Pseudocolloids may be formed by the incorporation, adsorption, or ion-exchange of dissolved 
radionuclides onto existing colloids, which may be formed either from WF degradation, EBS 
material degradation, or introduced with groundwater. Radionuclides that might otherwise sorb 
to immobile substrates can instead attach to mobile, colloidal particles and thereby increase the 
source term which describes the total inventory of (dissolved plus colloidal) radionuclides. 
Colloids may facilitate radionuclide migration both within the potential repository and in the far 
field. 
Waste form colloids, or primary colloids, may provide the most significant contribution to 
colloid-facilitated radionuclide transport. These colloids form from nucleation of colloids from 
waste-form dissolution and spallation of colloid-sized waste-form alteration products that contain 
radionuclides; they have the potential for increasing mobile concentrations higher than 
achievable with real colloids or pseudocolloids. 
Three types of groundwater colloids may be present at Yucca Mountain: 
 Mineral fragments tend to be hydrophilic (i.e., hard particles that are kinetically 
stabilized or destabilized by electrostatic forces) and may consist of crystalline or 
amorphous solids. Steric coatings may enhance the stability of mineral fragments as 
colloids, by preventing close contact. Mineral fragments may act as substrates for 
sorption of radionuclides (they may also consist of precipitated or coprecipitated 
actinide solids).

 3-197 
 Humic substances are hydrophobic particles that are stabilized by solvation forces. 
They can be powerful substrates for uptake of metal cations and are relatively small (less 
than 100,000 atomic mass units). 
 Microbes are relatively large colloidal particles that are stabilized by hydrophilic 
coatings on their surfaces. Microbes may act as substrates for extracellular actinide 
sorption, or they may actively bioaccumulate radionuclides intracellularly. 
Because of the relatively large sizes of microbes, they are very susceptible to filtration in 
geologic media. Consequently, microbe-facilitated contaminant transport is not considered in 
the abstraction. Further, considering the limited complexation capacity of humic substances in 
the system, humic substances are not considered as groundwater colloids. 
The remainder of this section focuses on abstraction of Yucca Mountain relevant experimental 
results and observations of the natural system to produce a modeling approach suitable for large 
temporal- and spatial-scale performance assessments by PA. Clays, silica, hematite, and goethite 
colloids occur as mineral colloids in groundwater in the vicinity of Yucca Mountain, with clays 
and silica the most abundant. It is assumed for simplicity and conservatism that groundwater 
colloids are clays and that (1) iron oxide or oxyhydroxide colloids are present in very small 
amounts, and (2) plutonium (Pu) and (AM) sorb more strongly to, and generally desorb more 
slowly from, clays than silica colloids. Accordingly, silica colloids are neglected in this 
conservative approach. 
It is assumed that small quantities of these colloids will enter a failed WP and be available to 
interact with released radionuclides. Further, it is assumed that groundwater entering the drift 
and invert from the surrounding unsaturated zone will mix, under certain circumstances, with 
releases from a failed WP and that the groundwater colloids will likewise be available to interact 
with released radionuclides. The groundwater is assumed to contain smectite colloids whose 
stability and concentration are determined by the ionic strength and pH of the groundwater. 
There are three types of colloids in the release: (1) WF colloids, assumed to be smectite, (2) WP 
corrosion colloids, assumed to be iron oxide or oxyhydroxide, and (3) groundwater colloids, 
assumed to be smectite. Some of these colloids are associated with radionuclides as they exit the 
WP. The WF colloids may have irreversibly attached (embedded) or reversibly attached 
(sorbed) radionuclides. Sorption of radionuclides on groundwater colloids, or colloids derived 
from corrosion products, is assumed to be reversible. 
The mass of radionuclides irreversibly attached to WF colloids is determined from reaction 
within the WP. The mass of radionuclides reversibly attached to all three types of colloids is 
determined from the product of three parameters: (1) the mass concentration of dissolved 
(aqueous) radionuclide in the fluid, (2) the mass concentration of colloid material in the fluid, 
and (3) the radionuclide distribution coefficient (Kd) for each specific radioelement on each 
colloid type. 
The mass concentration of radionuclides leaving the WP is calculated at each time step, in the 
TSPA. The mass concentration of colloids is affected by the ionic strength and pH of the fluid,

 3-198 
and is also determined at each time step. The Kds for the various radionuclides on the two 
mineralogical colloid types have been measured in the laboratory. 
Once the groundwater and WP releases mix within the invert, a fluid of combined chemistry is 
produced, and new mass concentrations of dissolved radionuclides and colloids, as well as 
masses of radionuclides sorbed onto colloids, are calculated in the TSPA. The total mass of 
radionuclides sorbed onto colloids, comprises mass concentrations for radionuclides irreversibly 
and reversibly attached to WF (smectite) colloids, reversibly attached to corrosion product (iron 
oxide or oxyhydroxide) colloids, and reversibly attached to groundwater (smectite) colloids. 
3.2.1.2 Abstraction of the Engineered Barrier System Radionuclide Transport Model 
Radionuclide transport out of the WF and WP, through the invert system, and into the 
unsaturated zone (UZ) is dependent on several events. The WP must degrade, providing a path 
out of the WP, and the WF must also degrade to allow radionuclide release. The primary 
transport medium is water: either a water film or moving water is necessary for radionuclide 
transport out of the WP and through the remainder of the EBS. Following are the key factors 
affecting transport of radionuclides through the EBS: 
 Performance of the DSs 
 Performance of the WPs 
 Protection provided by cladding 
 WF degradation rate 
 Entry and movement of water through WPs 
 Solubilities of radionuclides 
 Transport of radionuclides through and out of the WPs 
 Transport of radionuclides through the invert below the WPs 
 Colloidal transport of radionuclides 
After the WPs are emplaced, radioactive decay of the waste will heat the drifts and locally 
perturb the normal percolation of water. As the drifts cool, some of the water percolating 
through the mountain may drip into the drifts and subsequently contact some of the DSs. Over 
time, the DS, WP, and other components of the EBS are expected to degrade. 
Once a DS is breached, water may contact the WP. Once a WP is breached, water may enter the 
package as water vapor or as drips. If the cladding is also breached, radionuclides may start to 
dissolve in the water. The dissolved concentration of each radionuclide mobilized from the WF 
cannot exceed the radionuclide solubility limit, unless suspended colloids are included. Colloids 
may be important for two reasons: they may increase the rate of release of radionuclides from the 
WP, and they may increase the transport velocity of radionuclides. The rate of release may be 
increased because the total mobile concentration for a particular radionuclide is not limited to 
solubility equilibrium. Colloidal transport could increase the transport velocity for radionuclides 
which would otherwise be retarded by interaction with immobile solids, but interact with mobile 
colloidal solids instead, and thereby move at the speed of the particles. 
Radionuclides mobilized in water as dissolved or colloidal species may then be transported by 
advective and diffusive transport from the WF, through the WP, and out of breaches in the WPs.

 3-199 
Once outside the package, the radionuclides will be transported through the invert predominantly 
by diffusion, if water is not flowing through the invert, or by advection, if an appreciable amount 
of water is flowing through the invert. 
The emphasis in the Engineered Barrier System Radionuclide Transport Abstraction (CRWMS 
M&O 2000a) is on a conservative approach that bounds the response of the EBS. These 
conservatisms are appropriate because of the uncertainty in the response of a very complex 
engineered system over long periods of time. This model is valid and appropriate for its 
intended use because this abstraction is designed to be a bounding, conservative model. 
Following are noteworthy features and conservatisms in this abstraction: 
 Seepage through the DS always falls on a WP  DS placement in the current potential 
repository design is such that any separations between shields should be above the small 
axial gap between adjacent packages. This feature is ignored because the quartz-sand 
backfill that falls through the DS separation will probably fill the axial gap and provide a 
flow path onto the WP. 
 Seepage is assumed to uniformly wet the DS and WP  Because seepage will vary 
spatially and temporally over the approximately 10,000 WPs in the potential repository, 
it seems reasonable to represent the response of groups of WPs as averages for 
performance assessment. In this average, the DS or WP is assumed to be uniformly wet 
so that each patch or pit, independent of its exact position on the surface of the WP, will 
always experience a small advective flux. Note that WP degradation modeling for the 
TSPA-SR only predicts the location of patches and pits in terms of the upper or lower 
surfaces of the WP; thus, the independence of position is consistent with WP 
degradation calculations. 
 There is no advective flow or transport through a stress-corrosion crack (SCC) in 
the WP  Current analyses show that a thin film will bridge the crack with a fluid-filled 
meniscus that prevents advective flow into the crack. In addition, such cracks will only 
occur in the shadow of the skirt around the welded end cap, making it unlikely that large 
volumes of water will reach the crack through vertical drips and seepage 
 The WF is assumed to be covered with a thin liquid film that supports radionuclide 
diffusion at all times  Radionuclides will be released by diffusion through a stresscorrosion 
crack, even when the DS is intact and there is no advective flux into the WP. 
Note that this transport pathway also functions in the TSPA model when the package is 
hot and in-package evaporation may be sufficient to maintain the WF in dry conditions. 
 Release of radionuclides through advective transport is independent of the number 
of patches or pits through the WP  Advective transport out of the WP is based on a 
flow-through model that is independent of the number of penetrations through the WP. 
For example, a WP with one or more penetrations on its upper surface and none on its 
lower surface will still have advective transport into the invert. 
 Cracks and pits are assumed to be filled with corrosion products and to be fully 
saturated  These assumptions enhance diffusion.

 3-200 
The use of a bounding diffusion coefficient for all radionuclides may overestimate the diffusivity 
of actinide complexes by an order of magnitude. The assumption to ignore the effect of 
saturation on diffusivity has the effect of overestimating diffusivity by two to three orders of 
magnitude. These assumptions enhance diffusion. 
The following sections provide a summary of the EBS transport abstraction model (CRWMS 
M&O 2000a). 
3.2.1.2.1 Flow and Transport Pathways 
The conceptual model for flow through the EBS identifies eight key flow pathways.: 
 Seepage Flux  This is the input flux or boundary condition. 
 Through the Drip Shield to the Waste Package  Flux through the DS is based on the 
ratio of patch and pit areas to the total surface area of the DS. Patch and pit areas of the 
DS and WP are calculated by the Waste Package Degradation software (WAPDEG). 
 Drip Shield to Unsaturated Zone (Diversion around DS)  Any seepage flux that 
doesnt go through the DS is assumed to bypass the EBS and flow straight into the UZ. 
 Through the WP to WF  Flux into the WP is proportional to the product of the flux 
through the DS and the ratio of patch/pit areas to total surface area of the WP. 
 Waste Package to Invert (Diversion around WP)  Flow that doesnt go through the 
WP is diverted to the invert. 
 Invert to WP (Evaporation)  If the DS is cooler than the invert, all the evaporative 
flux from the invert is assumed to drip on the WP. If the DS is hotter than the invert, 
there is no dripping on the WP from the evaporative flux. 
 Waste Form to Invert  All the flux from the WP flows to the invert, independent of 
patch/pit location on the WP. 
 Invert to UZ  All the flux into the invert is released into the UZ. 
The waste form is the source of all radionuclides in the potential repository system. 
Radionuclides can be transported downward, through the invert and into the UZ. Transport can 
occur through advection when there is a fluid flux through the waste package, and by diffusion 
through thin films in the waste package when there are stress corrosion cracks in the lids of the 
package. Diffusion through SCCs will probably be the only transport mechanism during the first 
few thousand years because SCCs are the only viable failure mechanism in this time frame. 
There will be no transport through the quartz sand backfill under any conditions. Upward 
diffusion through the backfill is impossible before the drip shield fails because a continuous flow 
path does not exist between the waste package and the backfill. After the drip shield fails 
upward diffusion will be negligible in comparison to the downward advective flux through the 
drip shield.

 3-201 
The diffusion coefficient in the invert is based on the self-diffusivity of water at 25C as a 
bounding value for all radionuclides. The effects of temperature are incorporated, based on the 
Nernst-Einstein formulation (CRWMS M&O 2000h). The effects of porosity and saturation are 
conservatively ignored. 
Partition coefficients for all radionuclides are conservatively set to zero in the waste package and 
invert. 
The drip shield is a potentially important component of the EBS. The thermal and mechanical 
response of the drip shield has been evaluated for five mechanisms: (1) thermal expansion, 
(2) floor heave, (3) rock fall, (4) seismic response, and (5) waste package support failure. 
Thermal expansion, floor heave and rock fall will produce minor structural response in relation 
to the potential slippage or overlap between adjacent drip shields. These mechanisms have 
therefore been screened out from the TSPA-SR. 
Seismic response is the key mechanism that may lead to separation of adjacent drip shields. The 
seismic analysis in this AMR is based on the 1-in-10,000 year earthquake. It is a conservative 
(bounding) analysis in the sense that it assumes that all the inelastic strain from the earthquake 
can be concentrated at one or a few locations and that the sand backfill is not represented in the 
analysis. The sand backfill is important because of its large mass relative to that of the drip 
shield. Future analyses will consider less probable earthquakes, such as a 1-in-100,000 year 
event, and the response of the other components (i.e., the backfill) of the EBS. 
Pedestal failure has the potential to shift the drip shield if the waste package falls to the invert 
and rolls into contact with the shield. This scenario is more likely during an earthquake, when 
the ground motions may increase the load on the pedestal and impart additional momentum to 
the waste package. Given this association and the bounding nature of the analysis for seismic 
response, the response to pedestal failure is assumed to be included in the seismic response for 
TSPA-SR. 
3.2.1.2.2 Colloid-Facilitated Transport 
It is anticipated that colloids will occur in the EBS from three sources: (1) waste package (WP), 
(2) groundwater, and (3) degradation of introduced materials. 
It is assumed that small quantities of groundwater colloids, and possibly colloids from 
degradation of introduced materials, will enter a failed WP, interact with released radionuclides, 
and then leave the failed WP. Further, it is assumed that groundwater entering the drift and 
invert from the surrounding UZ will, under certain circumstances, mix with releases from a 
failed WP, and the groundwater colloids will likewise be available to interact with released 
radionuclides. 
 If the DS and WP have failed, incoming groundwater from above flows downward 
through the breach in the DS, into and through the WP, and downward into the invert. 
Releases from a breached WP migrate downward through the invert and may mix with 
the groundwater in the invert. The mixed fluid migrates downward through the invert 
into the UZ.

 3-202 
The groundwater is assumed to contain smectite colloids whose stability and concentration are 
determined by the ionic strength and pH of the groundwater. The WP release is assumed to be a 
fluid containing colloids and dissolved radionuclides resulting from the reaction of waste with 
groundwater that has entered the WP. 
There are three types of colloids in the release: 
 Waste-form colloids, assumed to be smectite 
 Waste-packagecorrosion colloids, assumed to be iron (hydr)oxide 
 Groundwater colloids, assumed to be smectite 
Some of these colloids have associated radionuclides as they leave the WP. The WF colloids 
may have irreversibly attached (embedded) or reversibly attached (sorbed) radionuclides. The 
corrosion and groundwater colloids may have reversibly attached radionuclides. 
The mass of radionuclides irreversibly attached to the WF colloids is determined from reaction 
within the WP. The mass of radionuclides reversibly attached to all three types of colloids is 
determined by the product of three parameters: 
 Mass concentration of dissolved (aqueous) radionuclide in the fluid 
 Mass concentration of colloid material in the fluid 
 Radionuclide distribution coefficient (kd) of a specific radionuclide on a specific colloid 
mineralogical type 
3.2.2.3 Abstraction of the Multiscale Thermohydrologic Model 
The purpose of the analysis and model report, Abstraction of NFE Drift Thermodynamic 
Environment and Percolation Flux (CRWMS M&O 2000w), is to abstract the multi-scale, 
process-level thermal hydrology (TH) model results (CRWMS M&O 2000i) so that they can be 
implemented in the TSPA model. 
The Multiscale TH Model describes how potential repository decay heat affects the EBS and the 
near-field environment (NFE) host rock. That is, it provides a description of how the 
temperature, relative humidity (RH), and both the liquid- and gas-phase flows change with time 
in the EBS and the host rock. 
The purpose of the abstraction described in this section is to provide a simplified view of the 
process-level TH description, and to provide a direct feed to TSPA consisting of the following: 
 Temperature 
 Liquid saturation 
 Relative humidity 
 Evaporation rate 
 Percolation flux as a function of time.

 3-203 
An averaging process (binning) is used to compute these quantities, based on a subdivision of 
the repository footprint that preserves a wide range of TH variability. This process also 
transforms certain physical quantities: for example, the liquid water velocity in the invert (in 
mm/yr) to a volumetric flow rate (m3/yr) in the invert (multiplying by the appropriate flow area). 
Further, the maximum and minimum peak WP temperatures are identified in the abstraction. 
Finally, the process-level model raw output is written in a format that is readily input to TSPA. 
Process model results which are used directly in TSPA include: WP temperature, RH at the WP 
surface, and the percolation flux in the host rock 5 meters above the crown of the emplacement 
drift. The temperature and RH are used for the corrosion model, and the percolation flux is input 
to the seepage model. The abstraction of TH data must represent the potential variability and 
uncertainty in TH conditions. Therefore, this abstraction provides a qualitative and quantitative 
description of TH variability (e.g. from variability in the host rock unit, edge proximity, waste 
type, infiltration rate, and climate state), and also provides a description of the uncertainty of TH 
results associated with different infiltration-rate characterizations (lower, mean, and upper) and 
the associated hydrologic property sets. 
All abstracted TH results provided to TSPA are based on a subdivision of the potential repository 
into five bins according to the local infiltration rates (1,246 total combinations for each 
infiltration flux case). The five infiltration bins are: 0 to 3 mm/yr, 3 to 10 mm/yr, 10 to 
20 mm/yr, 20 to 60 mm/yr, and >60 mm/yr. The infiltration-rate characterization specified for 
this subdivision is the glacial-transition climate state. This climate state begins 2,000 years after 
waste emplacement and persists for approximately 106 years. Pre-defined infiltration rate ranges 
are specified to cover the entire range of possible glacial climate state infiltration rates. Location 
dependent data from the process model are then used to populate the five pre-defined infiltration 
bins. As an example, 21 WP location dependent data files (as described by the results of the 
Multiscale TH Model) populate the infiltration rate bin of 0 to 3 mm/yr for the low infiltration 
rate case. Therefore, the TH abstractions for this bin will be based on those 21 WP location 
dependent results from the process model. To assemble all the relevant TH data belonging in 
each particular infiltration bin, a procedure is used to sort the process-level TH results according 
to infiltration rate. 
All of the abstraction quantities previously described are computed (or reformatted) by a simple 
software routine developed for this abstraction model. The routine has the ability to accept input 
commands, based on infiltration-rate binning requirements, and compute (or reformat) the 
abstracted data necessary for input into the TSPA model on a per-bin basis. This means that the 
averaged quantities (e.g., WP RH), maximum/minimum WP peak surface temperature, and 
reformatted raw data will be computed (or abstracted) by the routine for each of the infiltration 
bins, as defined by TSPA (CRWMS M&O 2000w, Sections 5.1.1, 6.1, and 6.2). 
Finally, the abstracted TH data used by the TSPA model are analyzed (CRWMS M&O 2000w; 
Section 6.3) for resulting trends and indicators of potential repository performance. In particular, 
time-histories of temperature, liquid saturation, percolation flux, evaporation rates, and 
maximum and minimum WP surface temperatures are analyzed for each infiltration bin for 
locations in both the EBS and the NFE host rock.

 3-204 
The use of infiltration bin-averaged TH values obtained from the multi-scale TH abstraction is 
considered valid for a number of reasons: 
 The infiltration bin-averaged values preserve and emphasize the overall variability and 
uncertainty in the TH results used for TSPA. 
 For instances where an average value would not represent uncertainty or variability 
associated with a TH variable (e.g. the average WP temperature vs. the maximum WP 
temperature) a range of process model results is also input directly to TSPA. For 
example, in addition to the average curve, the abstraction routine provides temperature 
curves for the maximum and minimum WP temperatures in each of the predefined 
infiltration bins. The waste package temperature variability, and uncertainty with 
respect to infiltration rate, are thereby reported for each of the infiltration bins. 
 The percolation flux at 5 m above the crown of the drift is input to TSPA as repository 
footprint location-dependent data. An average value is not used for the percolation flux, 
so that more complete representation of variability (i.e. with respect to location, host 
rock unit, and edge proximity) and uncertainty (i.e. infiltration-rate cases: lower, mean, 
and upper) is be input to the TSPA seepage model. 
The TSPA corrosion model uses Multiscale TH Model results directly as input, thus capturing in 
the abstraction the potential variability and uncertainty included in the process model. 
3.3 KEY ISSUES FOR THE EBS DEGRADATION, FLOW, AND TRANSPORT PMR 
The Nuclear Regulatory Commission (NRC) has identified 10 key technical issues (KTIs) as a 
means of evaluating the technical adequacy of YMP technical work in support of a license 
application. 
Issue resolution status reports (IRSRs) are issued periodically by the NRC, providing a summary 
of the issue and its subissues, what is and is not known about them, and indicating where 
additional information may be required. Chapter 4 and the Appendix provide a detailed 
discussion of these issues and the degree to which acceptance criteria for their resolution are met 
by the current revision of the EBS PMR. 
Other issues concerning the EBS have been identified by peer reviews of Project documents and 
by the NWTRB. These issues are summarized in Table 3-47, along with a discussion of the 
current Project understanding for each issue.

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Table 3-47. Issues Germane to the EBS Process Model Report 
ISSUE (as stated in source) SOURCE DISCUSSION 
Additional supporting research is needed in 
a number of areas, including water 
compositions in contact with the waste 
package, critical crevice corrosion 
temperatures, neptunium solubility and 
technetium sorption on degraded waste 
package materials. 
VA, Volume 3, Section 
6.5.2.7, page 6-34 (DOE 
1998a) 
Both detailed process models and 
bounding models for the evolution of 
water chemistry over this time period are 
developed in supporting AMRs and 
summarized in Section 3.1.2. Other 
issues are covered in other PMRs. 
Modeling assumptions should be consistent 
across different process models, unless 
there is a defensible technical rationale. 
VA, Volume 3, Section 
6.5.3.3, page 6-35 (DOE 
1998a) 
The Analysis/Model Reports (AMR) are 
thoroughly reviewed to help ensure 
consistency among assumptions made in 
more than one document about a given 
parameter. In addition, the Process 
Model Reports (PMR) that summarize 
and integrate the results of the AMRs 
have been subjected to a review by a 
single review team, one of whose main 
objectives is to identify inconsistencies 
among the PMRs. Finally, assumptions 
used in the AMRs that feed TSPA are 
documented in the TSPA document. 
These measures provide confidence that 
consistent assumptions are used as 
appropriate among the various models 
that support the TSPA. 
Detailed documentation of the assumptions 
used in performance assessments is of 
fundamental importance to the 
transparency (and credibility) of the TSPA. 
VA, Volume 3, Section 
6.5.3.4, page 6-35 (DOE 
1998a) 
The transparency and traceability of 
TSPA analyses is required to ensure the 
calculations supporting the TSPAs are 
clear and consistent. As described in AP 
3.10Q, the purpose of Section 5 of the 
AMRs is to document the assumptions 
made to perform the analysis or to 
develop the model, along with a rationale 
for those assumptions. In support of 
meeting this goal, detailed 
documentation of assumptions is 
presented in section 5 of the AMRs 
supporting the PMRs. 
Rockfall effects need to be considered in 
the design and performance of the Yucca 
Mountain repository system. 
VA, Volume 3, Section 
6.5.3.7, page 6-36 (DOE 
1998a) 
Rockfall calculations based on key-block 
analyses are documented in the Drift 
Degradation Analysis AMR (CRWMS 
M&O 2000ad), and summarized in 
Section 3.1.2. Only a small percentage 
of the total length of emplacement drifts 
is expected to experience rockfall within 
10,000 years of closure, even without 
ground support, taking into account both 
seismic and thermal effects. The use of 
backfill in EDA II prevents significant 
mechanical damage from rockfall. In 
January 2000, a design change, 
prompted by thermal considerations, was 
initiated to remove backfill and change 
the drift orientation to minimize the size 
of key blocks. Revision or ICN of the 
AMR and the EBS PMR will assess 
consequences of this change.

 3-206 
ISSUE (as stated in source) SOURCE DISCUSSION 
The effects of the drip shield and backfill on 
the thermal and moisture regime between 
the drip shield and the waste package and 
evaluating the corrosion behavior of 
titanium when it is in contact with backfill or 
rockfall. The vulnerability of the drip-shield 
connections to vibratory earthquake motion 
also needs to be addressed. 
NWTRB Letter to DOE (8- 
3-99) (Cohon 1999) 
The thermal and moisture conditions 
between the DS and WP are the subject 
of ongoing experimental investigations, 
and are addressed in the Water 
Distribution and Removal AMR (CRWMS 
M&O 2000q), and Section 3.1.1. The 
remaining parts of this issue are 
addressed in the WP PMR and its 
supporting AMRs. 
Experimental data are lacking throughout 
the treatment of the waste package and 
EBS. In particular, the effect of realistic 
and extreme environments to come in 
contact with Alloy 22 and critical 
temperature for crevice corrosion of Alloy 
22. 
Final Report Total System 
Performance Assessment 
Peer Review Panel 
February 11, 1999 
Section II.C (Budnitz et al. 
1999) 
The bulk chemical environment within 
emplacement drifts is bounded by 
analyses summarized in section 3.1.2.7 
of the EBS PMR. The effects of the bulk 
chemical environment and local 
environments on corrosion of WP alloys 
is within the scope of the WP PMR 
Proper account has not been taken of the 
TH interactions between adjacent drifts and 
the effects of natural convection. The 
possibility of heat pipe instability in some 
locations, with resulting condensate 
seepage (as observed in the Large Block 
Test) cannot be predicted. The method 
also overpredicts the performance of drifts 
at the repository edge. Coarse scale 
factors, such as a reduction of the actual 
heat load to an effective value, are 
introduced to handle such problems. 
Although the methodology is a creative 
approach, it needs to be tested against real 
data (perhaps in conjunction with the Drift 
Scale Test) to validate the results of the 
analyses. 
Final Report Total System 
Performance Assessment 
Peer Review Panel 
February 11, 1999 
Section IV.B, Page 55 
(Budnitz et al. 1999) 
Heat pipe instability has not been 
observed in the field for any test except 
the Large Block Test (LBT). The LBT 
was specifically designed to produce 
conditions favorable to such instability. 
The design analyzed in this report was 
selected to maintain sub-boiling 
conditions in the central region of the 
pillars. This will provide drainage 
pathways for condensate and tend to 
eliminate heat pipe instabilities. Similar 
thermal modeling approaches with the 
NUFT code have been used to compare 
with the Drift Scale Test as part of model 
validation 
The project staff should initiate a detailed, 
on-going review of the EBS models and 
should include the actual use and 
comparison of modeled results from the 
RIP code to modeled results from other 
geochemical codes and databases. 
The present EBS analysis uses only limited 
experimental data and, more importantly, 
there has been no effort to demonstrate 
that such an approach produces 
reasonable results. This situation can be 
significantly improved by designing 
experiments to confirm the modeled results 
of the EBS... 
Final Report Total System 
Performance Assessment 
Peer Review Panel 
February 11, 1999 
Section IV.B, Page 98 
(Budnitz et al. 1999) 
EBS models and other key process 
models are documented in a series of 
process model reports (PMRs), subject to 
extensive review within the M&O and by 
DOE before final acceptance. 
Experimental data for specific processes 
and functions of the EBS are being 
obtained in ongoing work at the Atlas 
Test Facility. These data provide input 
for both development and confirmation of 
EBS process models. 
As has been properly noted by the project, 
the effects of colloid-facilitated transport 
remain one of the major sources of 
uncertainty. 
At present there is no convincing way to 
estimate the type, amounts or stability of 
colloids. 
Final Report Total System 
Performance Assessment 
Peer Review Panel 
February 11, 1999 
(Budnitz et al. 1999) 
A bounding model for colloid 
concentrations and associated sorbed 
radionuclides is summarized in Section 
3.1.2.6. According to this bounding 
calculation, iron oxyhydroxides, with high 
sorption capacity for actinides, are the 
most important. The total aqueous 
concentration of these radionuclides is 
expected to be less than 100 times the 
amount in solution.

 F3-A 
Figure 3-A. Relationships Among the Thermal-Hydrologic Models Discussed in This Report, and Model 
Inputs from the Unsaturated Zone Flow and Transport Process Model Report and its Submodels. 
Multiscale Thermohydrology 
Model 
Hydrologic Properties 
Thermal Properties 
Boundary Conditions 
In-Drift THC Model 
(see CRWMS M&O, 2000y) 
Physical & Chemical 
Environment Model 
(TH component) 
Water Distribution & 
Removal Model 
(TH and Ambient 
Temp. components) 
Hydrologic Properties (based on UZ Model) 
Thermal Properties (based on UZ Model) 
Boundary Conditions (based on UZ Model) 
Thermal Output 
Model Grid Features 
Repository/EBS Design 
& Waste Heat Output 
(see CRWMS M&O, 2000i) 
Section 3.1.4 
Section 3.1.2 
Section 3.1.1 
Unsaturated Zone Flow and 
Transport Model 
(see CRWMS M&O, 2000o) 
Calibrated Properties 
Model 
(see CRWMS M&O, 2000p) 
Other UZ Submodels 
(see CRWMS M&O, 2000o) 
Drift-Scale THC Model 
(see CRWMS M&O, 2000x) 
Models External to the EBS 
Degradation, Flow and 
Transport 
Process Model Report 
Section 3.1.1

 F3-B 
Temperature at the Drift Crown (L4C4 or vicinity, backfill case) 
20 
40 
60 
80 
100 
120 
140 
1 10 100 1000 10000 100000 
Time (yr) 
Temperature (C) 
In-Drift THC 
P&CE (Zone 2) 24.3-47.6-82 (mm/yr) 
P&CE (Zone 2) 0-10.1-2 (mm/yr) 
Drift-Scale THC 15-26-47 (mm/yr) 
Drift-Scale THC 0.6-6-3 (mm/yr) 
Multiscale LDTH 24.3-47.6-82 (mm/yr) 
Multiscale LDTH 0-10.1-2 (mm/yr) 
WD&R 42 mm/yr (focused) 
Climate State 
Transitions 
NOTE: Compiled from AMR data sources as indicated in Table 3-B. 
Figure 3-B. Model Results for 2-D Thermal-Hydrologic Models, Comparing Histories of Temperature at or 
Near the Drift Crown, for Repository Center Locations

 F3-C 
Air Mass Fraction at Drift Crown (L4C4 or vicinity; backfill case) 
0 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
0.9
1
100 1000 10000 100000 
Time (yr) 
Air Mass Fraction 
In-Drift T-H-C 
P&CE 24.3-47.6-82 (mm/yr) 
P&CE 0-10.1-2 (mm/yr) 
Drift-Scale THC 15-26-47 (mm/yr) 
Drift-Scale THC 0.6-6-3 (mm/yr) 
Multiscale LDTH 24.3-47.6-82 (mm/yr) 
Multiscale LDTH 0-10.1-2 (mm/yr) 
NOTE: Compiled from AMR data sources as indicated in Table 3-B. 
Figure 3-C. Model Results for 2-D Thermal-Hydrologic Models, Comparing Histories of Air Mass-Fraction 
at or Near the Drift Crown, for Repository Center Locations

 F3-1 
NOTE: Taken from Figure 4 of CRWMS M&O (2000q). 
Figure 3-1. Model Domain and Boundary Conditions 
0 10 20 30 40 
X(m) 
0 
100 
200 
300 
400 
500 
600 
700 
Ground Surface 
Water Table 
Reflective 
Boundary 
Reflective 
Boundary 
Z(m) 
Repository 
Host 
Horizon

 F3-2 
NOTE: Colors are for presentation only. Taken from Figure 5 of CRWMS M&O (2000q). 
Figure 3-2. Engineered Barrier Segment Block Model 
0 2 4 
X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
Z(m) 
Drip Shield and 
Waste Package 
Backfill 
Host Rock 
Invert

 F3-3 
NOTE: Taken from Figure 8 of CRWMS M&O (2000q). 
Figure 3-3. Matrix Capillary Pressure for Focused Flow at Steady State, and Isothermal Temperature, 
Near the Repository Horizon (Case 1) 
0 
5,000 
11,000 
16,000. 
21,000 
26,000 
31,000 
37,000 
42,000 
47,000 
52,000 
0 2 4 X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
Capillary 
Pressure 
(Pa) 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste Package 
Invert 
Z(m)

 F3-4 
NOTE: Taken from Figure 9 of CRWMS M&O (2000q). 
Figure 3-4. Fracture Saturation Levels for Focused Flow at Steady State at Isothermal Temperature Near 
the Repository Horizon (Case 1) 
0.00 
0.10 
0.20 
0.29 
0.39 
0.49 
0.59 
0.69 
0.78 
0.88 
0.98 
0 2 4 X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
Fracture 
Saturation 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste Package 
Invert 
Z(m)

 F3-5 
NOTE: Taken from Figure 10 of CRWMS M&O (2000q). 
Figure 3-5. Matrix Saturation Levels for Focused Flow at Steady State at Isothermal Temperature Near 
the Repository Horizon (Case 1) 
0.00 
0.10 
0.20 
0.29 
0.39 
0.49 
0.59 
0.69 
0.78 
0.88 
0.98 
0 2 4 X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
Matrix 
Saturation 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste Package 
Invert 
Z(m)

 F3-6 
NOTE: Taken from Figure 11 of CRWMS M&O (2000q). 
Figure 3-6. Fracture Mass Flux Rates (kg/m2-s) and Direction of Flow for Focused Flow at Steady State 
at Isothermal Temperature Near the Repository Horizon (Case 1) 
4.7E-09 
4.6E-07 
9.2E-07 
1.4E-06 
1.8E-06 
2.3E-06 
2.8E-06 
3.2E-06 
3.7E-06 
4.1E-06 
4.6E-06 
0 2 4 X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
Fracture Mass 
Flux Rate 
(kg/m2-s) 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Invert 
Z(m)

 F3-7 
NOTE: Taken from Figure 15 of CRWMS M&O (2000q). 
Figure 3-7. Fracture Mass Flux Rates (kg/m2-s) and Direction of Flow for Focused Flow for Repository 
Heating Near the Repository Horizon After 1,000 Years (Case 3) 
3.4E-09 
3.3E-07 
6.5E-07 
9.8E-07 
1.3E-06 
1.6E-06 
1.9E-06 
2.3E-06 
2.6E-06 
2.9E-06 
3.2E-06 
0 2 4 
X(m) 
389 
390 
391 
392 
393 
394 
395 
396 
397 
Fracture Mass 
Flux Rate 
(kg/m2-s) 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Invert 
Z(m)

 F3-8 
NOTE: Taken from Figure 20 of CRWMS M&O (2000q). 
Figure 3-8. Matrix Capillary Pressure for Focused Flow at Steady State at Isothermal Temperature Near 
the Repository Horizon for Plugged Fractures with an Engineered Drain (Case 9) 
Invert 
0 
9,000 
18,000 
28,000 
37,000 
46,000 
55,000 
64,000 
74,000 
83,000 
92,000 
0 2 4 
X(m) 
390 
392 
394 
396 
398 
400 
402 
Capillary 
Pressure 
(Pa) 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Engineered 
Drain 
Z(m)

 F3-9 
NOTE: Taken from Figure 21 of CRWMS M&O (2000q). 
Figure 3-9 Fracture Saturation Levels for Focused Flow at Steady State at Isothermal Temperature Near 
the Repository Horizon for Plugged Fractures with an Engineered Drain (Case 9) 
0.000 
0.036 
0.072 
0.11 
0.14 
0.18 
0.22 
0.25 
0.29 
0.32 
0.36 
0 2 4 
X(m) 
390 
392 
394 
396 
398 
400 
402 
Fracture 
Saturation 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Invert 
Engineered 
Drain 
Z(m)

 F3-10 
NOTE: Taken from Figure 22 of CRWMS M&O (2000q). 
Figure 3-10. Matrix Saturation Levels for Focused Flow at Steady State at Isothermal Temperature Near 
the Repository Horizon for Plugged Fractures with an Engineered Drain (Case 9) 
0.00 
0.10 
0.20 
0.29 
0.39 
0.49 
0.59 
0.69 
0.78 
0.88 
0.98 
0 2 4 
X(m) 
390 
392 
394 
396 
398 
400 
402 
Matrix 
Saturation 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Invert 
Engineered 
Drain
Z(m)

 F3-11 
NOTE: Taken from Figure 23 of CRWMS M&O (2000q). 
Figure 3-11. Fracture Mass Flux Rates (kg/m2-s) and Direction of Flow for Focused Flow at Steady State 
at Isothermal Temperature Near the Repository Horizon for Plugged Fractures with an Engineered Drain 
(Case 9) 
5.0E-09 
4.9E-07 
9.7E-07 
1.5E-06 
1.9E-06 
2.4E-06 
2.9E-06 
3.4E-06 
3.9E-06 
4.4E-06 
4.8E-06 
0 2 4 
X(m) 
390 
392 
394 
396 
398 
400 
402 
Fracture Mass 
Flux Rate 
(kg/m2-s) 
Approximate 
Outline 
of Drift 
Drip Shield 
and 
Waste 
Package 
Invert 
Engineered 
Drain 
Z(m)

 F3-12 
NOTE: Taken from Figure 25 of CRWMS M&O (2000q). 
Figure 3-12. Drip Shield and Backfill Flow Rates as a Function of Backfill Percolation Rate 
1 10 100 
1.10 5 
1.10 4 
1.10 3 
0.01 
0.1
1 
10 
100 
Drip Shield 
Backfill 
Percolation Rate (mm/yr) 
Flow Rates (m^3/yr) 

 F3-13 
NOTE: Developed for this report, using information presented in Section 3.1. Section numbers denote descriptions in this report. 
Figure 3-13. Relations Between Submodels Described in Section 3.1.2 
TH 2-D 
Simulation: 
NUFT 3.0s 
(Evaporation, T, 
RH, qliq ) 
Chemical 
Summary Model 
Multiple-Reaction 
Cell Model of EBS 
(EQ3/6) 
Materials 
Inventory/ 
Corrosion 
Products 
Energy/Nutrient 
Balance Microbial 
Model: 
MING 
Site Water 
Composition 
Data 
Precipitates & 
Salts Test 
Data 
Cementitious 
Materials 
Submodel 
(PHREEQC) 
Validation Tests: 
Evaporation 
THC Columns 
Microbial Growth/MIC 
Precipitates & 
Salts Normative 
Submodel 
Gas Flux & Fugacity 
Submodel (CO2,O2) 
LRH/HRH Salts 
Model 
Seepage/Backfill 
Interaction 
MIC Activity & 
Threshold 
Submodel TSPA 
FEP 
Screening 
FEP 
Screening 
EBS Physical & Chemical Environment AMR (CRWMS M&O, 2000t) 
Seepage/Backfill Interactions AMR (CRWMS M&O, 2000k) 
Precipitates and Salts Analysis AMR (CRWMS M&O, 2000g) 
In-Drift Corrosion Products AMR (CRWMS M&O, 1999g) 
Microbial Communities AMR (CRWMS M&O, 2000f) 
FEP 
Screening 
Physical & Chemical 
Environment 
Abstraction 
for TSPA 
Section 3.1.2.2 
Section 3.1.2.1 
Section 3.1.2.7 
Section 3.1.2.5.2 
Section 3.1.2.3 
Section 3.1.2.4.1 
Section 3.1.2.4.2 
Section 3.1.2.3 
Section 3.1.2.5.3 
Section 3.2.1.1 
Section 3.1.2.3

 F3-14 
NOTE: This artists rendering was developed for this report. 
Figure 3-14. Schematic of Thermal-Hydrologic Processes Affecting the Flux of Water as Liquid and 
Vapor.

 F3-15 
NOTE: Taken from Figure 2 of CRWMS M&O (2000t). 
Figure 3-15. Schematic Drawing Showing the Zones Defined for Chemical Modeling and the Connectivity 
of the Zones

 F3-16 
meters 
meters 
NOTE: Taken from Figure 3 of CRWMS M&O (2000t). 
Figure 3-16. Representation of Zone Boundaries in the Model Grid, Showing Boundaries Between 
Zones 1 through 6

 F3-17 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
Liquid Flux Between Zones 
L4C4 location, upper infiltration 
0.0E+00 
5.0E-06 
1.0E-05 
1.5E-05
100 1000 10000 
Time (yr) 
Drift 
Calc. Flux (Zone 1 to 2) 
Calc. Flux (Zone 2 to 3) 
Calc. Flux (Zone 3 to 4) 
Calc. Flux (Zone 3 to 5) 
Calc. Flux (Zone 4 to 5) 
Calc. Flux (Zone 5 to 6) 
 
 
 

Abstr. Flux (Zone 1 to 2)  
 
 

Abstr. Flux (Zone 2 to 3) 
 
 
 

Abstr. Flux (Zone 3 to 4) 
 
 
 

Abstr. Flux (Zone 3 to 5) 
 
 
 

Abstr. Flux (Zone 4 to 5) 
 
 
 

Abstr. Flux (Zone 5 to 6) 
NOTE: The flux values assigned to uniform time intervals, used for stepwise representation of the thermal 
evolution in chemical reaction cell modeling, are also plotted. Taken from Figure 4 of CRWMS M&O 
(2000t). 
Figure 3-17. Liquid Fluxes Between Zones, for the L4C4 Location and the Upper Infiltration Distribution

 F3-18 
NOTE: Simulation time of 1000 yr. Taken from Figure 5 of CRWMS M&O (2000t). 
Figure 3-18. Vertical Component of the Gas-Phase Total Mass Flux (Air and Water Vapor)

 F3-19 
Zone 4 Average Temperature (Sand Backfill). 
0 
50 
100 
150 
200 
250
100 1000 10000 
Time (yr). 
Temperature (C) 
L4C1 lower 
L4C1 upper 
L4C4 lower 
L4C4 upper 
NOTE: Backfill at the drip-shield surface. Calculated for the L4C1 and L4C4 locations, 
using the upper and lower infiltration distributions. Schematic shown above 
the plot, depicts the zones definitions used in the model. Zone 4 is the region of 
backfill contacting the upper part of the drip shield. Taken from Figure 6 of 
CRWMS M&O (2000t). 
Figure 3-19. Average Temperature for Zone 4 
1
2
3
4 
5 
6
0

 F3-20 
Zone 4 Average Saturation (Sand Backfill). 
0.00 
0.05 
0.10 
0.15 
0.20 
0.25
100 1000 10000 
Time (yr). 
Saturation 
L4C1 lower 
L4C1 upper 
L4C4 lower 
L4C4 upper 
NOTE: Backfill at the drip-shield surface. Calculated for the L4C1 and L4C4 locations, 
using the upper and lower infiltration distributions. Schematic shown above 
the plot, depicts the zones definitions used in the model. Zone 4 is the region of 
backfill contacting the upper part of the drip shield. Taken from Figure 7 of 
CRWMS M&O (2000t). 
Figure 3-20. Average Saturation for Zone 4 
1
2
3
4 
5 
6
0

 F3-21 
Zone 4 Average Air Mass-Fraction (Sand Backfill). 
0.0 
0.2 
0.4 
0.6 
0.8 
1.0
100 1000 10000 
Time (yr)... 
Air Mass-Fraction
L4C1 lower 
L4C1 upper 
L4C4 lower 
L4C4 upper 
NOTE: Backfill at the drip-shield surface. Calculated for the L4C1 and L4C4 locations, 
using the upper and lower infiltration distributions. Schematic shown above 
the plot, depicts the zones definitions used in the model. Zone 4 is the region of 
backfill contacting the upper part of the drip shield. Taken from Figure 8 of 
CRWMS M&O (2000t). 
Figure 3-21. Average Air Mass-Fraction for Zone 4 as a Function of Time 
1
2
3
4 
5 
6
0

 F3-22 
NOTES: The plotted variable is the evaporation rate from the fracture continuum. The color bar gives 
values for the mass rate of evaporation per unit volume (kg/m3-sec). Positive values indicate 
evaporation; negative values indicate condensation. The model grid is plotted for reference. 
Taken from Figure 9 of CRWMS M&O (2000t). 
Figure 3-22. Fracture Evaporation Rate Field for the L4C4 Location with the Upper Infiltration 
Distribution at Simulation Time of 1000 yr

 F3-23 
Evaporation Power (all zones, matrix+fractures, whole-drift). 
Comparison to Total Waste Heat Output 
0.1
1 
10 
100 
1000
100 1000 10000 
Time (yr) 
Power (W/m) 
Thermal Output 
L4C4 upper 
L4C4 lower 
L4C1 upper 
L4C1 lower 
NOTES: Compares the L4C1 and L4C4 locations and the upper and lower infiltration 
distributions. The average thermal output (lineal power loading) is plotted for 
comparison. Taken from Figure 10 of CRWMS M&O (2000t). 
Figure 3-23. Plot of Total Evaporation vs. Time for All Zones, Including Fractures + Matrix

 F3-24 
Horizontal distance from drift centerline (m) 
-2.00E-06 
-1.80E-06 
-1.60E-06 
-1.40E-06 
-1.20E-06 
-1.00E-06 
-8.00E-07 
-6.00E-07 
-4.00E-07 
-2.00E-07 
1.99E-13 
2.00E-07 
Gas phase vertical mass flux (kg/m2-sec) 
Time = 1000 yr 
5 10 15 20 25 30 
NOTES: For the L4C4 location and upper infiltration distribution. Upward mass flux is negative in 
this figure. Simulation time of 1000 yr. The elevation of the profile represented in this plot, 
corresponds to approx. 392 m depth on Figure 3-18. Taken from Figure 11 of CRWMS 
M&O (2000t). 
Figure 3-24. Vertical Component of the Gas-Phase Total Mass Flux (Air + Water Vapor) Along a 
Horizontal Profile Passing through the Drift Centerline

 F3-25 
Conservative Solute Accumulation in Zones. 
L4C4 location, upper infiltration 
1.E-02 
1.E+00 
1.E+02 
1.E+04 
1.E+06
100 1000 10000 
Time (yr)... 
Normalized Mass 
Zone 1 
Zone 2 
Zone 3 
Zone 4 
Zone 5 
Zone 6 
NOTE: Taken from Figure 12 of CRWMS M&O (2000t). 
Figure 3-25. Normalized Mass of an Ideal Conservative Solute in Each Zone for Each of Five Time 
Intervals for the L4C4 Location (Repository Center) with the Upper Infiltration Distribution 
1
2
3
4 
5 
6
0

 F3-26 
Conservative Solute Accumulation in Zones. 
L4C4 location, lower infiltration 
1.E-02 
1.E+00 
1.E+02 
1.E+04 
1.E+06 
1.E+08 
1.E+10
100 1000 10000 
Time (yr). 
Normalized Mass 
Zone 1 
Zone 2 
Zone 3 
Zone 4 
Zone 5 
Zone 6 
NOTE: Schematic shown above the plot, depicts the zones definitions used in the model. Taken from 
Figure 13 of CRWMS M&O (2000t). 
Figure 3-26. Normalized Mass of an Ideal Conservative Solute in Each Zone for Each of Five Time 
Intervals for the L4C4 Location with the Lower Infiltration Distribution 
1
2
3
4 
5 
6
0

 F3-27 
Conservative Solute Accumulation in Zones. 
L4C1 location, upper infiltration 
1.E-02 
1.E+00 
1.E+02 
1.E+04
100 1000 10000 
Time (yr) 
Normalized Mass 
Zone 1 
Zone 2 
Zone 3 
Zone 4 
Zone 5 
Zone 6 
NOTE: Schematic shown above the plot, depicts the zones definitions used in the model. Taken from 
Figure 14 of CRWMS M&O (2000t). 
Figure 3-27. Normalized Mass of an Ideal Conservative Solute in Each Zone for Each of Five Time 
Intervals for the L4C1 Location with the Upper Infiltration Distribution 
1
2
3
4 
5 
6
0

 F3-28 
Conservative Solute Accumulation in Zones. 
L4C1 location, lower infiltration 
1.E-02 
1.E-01 
1.E+00 
1.E+01 
1.E+02
100 1000 10000 
Time (yr) 
Normalized Mass
Zone 1 
Zone 2 
Zone 3 
Zone 4 
Zone 5 
Zone 6 
NOTE: Schematic shown above the plot, depicts the zones definitions used in the model. Taken from 
Figure 15 of CRWMS M&O (2000t). 
Figure 3-28. Normalized Mass of an Ideal Conservative Solute in Each Zone for Each of Five Time 
Intervals for the L4C1 Location with the Lower Infiltration Distribution 
1
2
3
4 
5 
6
0

 F3-29 
14C Measurements from SD-12 
0 
100 
200 
300 
400 
500 
600 
0 20 40 60 80 100 120 
14C Activity (percent modern carbon). 
Depth (m) 
Gas Samples 
(GS961108312271.002) 
Pore Waters 
(GS961108312271.002) 
Abstracted Profile 
Welded 
Topopah 
Spring 
Tuff 
Inferred 
Perched 
Water 
Table 
NOTE: Taken from Figure 16 of CRWMS M&O (2000t). 
Figure 3-29. Observed Distribution of 14C Activity with Depth in Borehole SD-12

 F3-30 
NOTE: Taken from Figure 4-7 of CRWMS M&O (1998d). 
Figure 3-30. Schematic of processes affecting the availability of CO2 and other gases during the thermal 
period.

 F3-31 
NOTE: Taken from Figure 4-16 of CRWMS M&O (1998d). 
Figure 3-31. Evolution of Air Mass-Fraction Calculated for Repository Center and Edge Locations, for the 
Viability-Assessment Repository Design

 F3-32 
NOTE: Taken from Figure 4-18 of CRWMS M&O (1998d). 
Figure 3-32. Cumulative Air Flux Flowing Through the Repository Horizon, Calculated for Repository 
Center and Edge Locations for the Viability-Assessment Repository Design

 F3-33 
0.00001 
0.0001 
0.001 
0.01 
0.1
1 
10 
100 
10 100 1000 10000 100000 
Time After Emplacement (yr) 
Mole Fraction CO2 at Drift Crown 
Normalized to 1000 ppmv 
Case 1 (Full Chemical Problem 
Statement) with 'Upper' Infiltration 
Case 2 (SiO2 & Calcite Solid Phases 
Only) with 'Upper' Infiltration 
EBS Model (Flux = 0.01 of Max. Value) 
with 'Upper' Infiltration 
EBS Model (Flux = 0.1 of Max. Value) 
with 'Upper' Infiltration 
EBS Air Mass Fraction - 'Upper' 
Infiltration 
NOTE: Reactive transport calculations are taken from files: case1_15.xls and case2_15.xls (CRWMS 
M&O 2000x). Results from the Gas Flux and Fugacity Model are described in this report. Taken from 
Figure 29 of CRWMS M&O (2000t). 
Figure 3-33. Comparison of Reactive Transport Simulation of CO2 Fugacity, with Results from the Gas 
Flux and Fugacity Model

 F3-34 
0 
100 
200 
300 
400 
500 
600 
0 50 100 150 200 
Aqueous CO2 Concentration (mg/l) 
Depth (m) 
Porewaters 
(GS970908312271.003) 
Porewaters 
(GS961108312271.002) 
Porewaters 
(LL990702804244.100) 
Abstracted Profile 
Welded 
Topopah 
Spring 
Tuff 
Inferred 
Perched 
Water 
Table 
NOTE: Analyses of core samples from borehole SD-12; within the welded Topopal Spring Tuff, 
analyses of core samples from the Drift-Scale Test heated drift. Taken from Figure 17 of 
CRWMS M&O (2000t). 
Figure 3-34. Observed Distribution of Porewater CO2 Concentration in Core Samples

 F3-35 
NOTE: From borehole SD-12 and in core samples from the Drift-Scale Test heated drift 
Expressed as the flux of aqueous total CO2 containing modern carbon. Taken from Figure 18 of 
CRWMS M&O (2000t). 
Figure 3-35. Calculated Flux of 14CO2 Required to Maintain Steady-State Isotopic Conditions 
in the Unsaturated Zone 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
  
  
 
   
 
 
 
Flux of Modern CO2 at the Ground Surface, Required to Maintain 
Steady-State Isotopic Mass Balance in the UZ 
0 
100 
200 
300 
400 
500 
600 
0 200 400 600 800 
Modern Carbon Demand as Total CO2 (mg/yr) 
Depth (m) 
Incremental CO2 Flux 
Integrated CO2 Flux 
Welded 
Topopah 
Spring 
Tuff 
Inferred 
Perched 
Water 
Table

 F3-36 
14C Measurements from SD-12 
0 
100 
200 
300 
400 
500 
600 
0 20 40 60 80 100 120 
14C Activity (percent modern carbon) 
Depth (m) 
Gas Samples 
(GS961108312271.002) 
Pore Waters 
(GS961108312271.002) 
Welded 
Topopah 
Spring 
Tuff 
Inferred 
Perched 
Water 
Table 
Dgas = 8x10-5 m2/sec 
In f i l t rat io n : 
Up p er 
Mean 
L o w er 
NOTE: Taken from Figure 19 of CRWMS M&O (2000t). 
Figure 3-36. Exponential Model Fit to 14C Activity vs. Depth in Borehole SD-12

 F3-37 
0.00001 
0.0001 
0.001 
0.01 
0.1
1 
10 100 1000 10000 100000 
Time After Emplacement (yr) 
Ratio of Fugacity to Maximum 
Mass Flux Ratio = 0.01 
Mass Flux Ratio = 0.1 
Mass Flux Ratio = 0.2 
Mass Flux Ratio = 0.5 
Mass Flux Ratio = 0.9 
Mass Flux Ratio = 0.99 
Drift-Scale Air Mass-Fraction 
NOTE: Ratios to the maximum value at the ground surface, vs. time, for different values of the CO2 
mass flux representing consumption in the drift, normalized to the maximum rate of mass 
transfer. Taken from Figure 24 of CRWMS M&O (2000t). 
Figure 3-37. Estimates of the CO2 Concentration (Fugacity) at Repository Depth, Expressed as a 
Fraction of the Pre-Repository Value, for Different Values of the Normalized Rate of CO2 Consumption

 F3-38 
0.00001 
0.0001 
0.001 
0.01 
0.1
1 
10 100 1000 10000 100000 
Time After Emplacement (yr) 
Ratio of Fugacity to Maximum 
Mass Flux Ratio = 0.01 
Mass Flux Ratio = 0.1 
Mass Flux Ratio = 0.2 
Mass Flux Ratio = 0.5 
Mass Flux Ratio = 0.9 
Mass Flux Ratio = 0.99 
Drift-Scale Air Mass-Fraction 
NOTE: Ratios to the maximum value at the ground surface, vs. time, for different values of the O2 mass 
flux representing consumption in the drift, normalized to the maximum rate of mass transfer. 
Taken from Figure 25 of CRWMS M&O (2000t). 
Figure 3-38. Estimates of the O2 Concentration (Fugacity) at Repository Depth, Expressed as a Fraction 
of the Pre-Repository Value, for Different Values of the Normalized Rate of O2 Consumption

 F3-39 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
-0.2 0.0 0.2 0.4 
25 
25 
25 
45 
45 
75 
75 
95 
95 
95 
Temperature (Celsius) 
Quartz Saturation Index 
fco2=1E-1 
fco2=1E-3 
 fco2=1E-6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
"Saturated with respect to mineral" "Supersaturated" 
NOTE: Taken from Figure 1 of CRWMS M&O (2000v) 
Figure 3-39. Plot of Quartz Saturation Indices for All Cases Evaluated for Seepage/Backfill Interaction

 F3-40 
NOTE: This figure was developed for this report, and is based on Figure 3-13. 
Figure 3-40. Submodel Relationships for the Chemical Reference Model 
TH 2-D 
Simulation: 
NUFT 3.0s 
(Evaporation, T, 
RH, qliq ) 
Chemical 
Summary Model 
Multiple-Reaction 
Cell Model of EBS 
(EQ3/6) 
Cementitious 
Materials 
Submodel 
(PHREEQC) 
Precipitates & 
Salts Normative 
Submodel 
Gas Flux & Fugacity 
Submodel (CO2,O2) 
FEPs 
Screening 
EBS Physical & Chemical Environment AMR (CRWMS M&O, 2000t) 
CO2 Mass 
Balance 
Section 3.1.2.2 
Section 3.1.2.3 
Section 3.1.2.1 
Section 3.1.2.7 
Section 3.1.2.5.2 
Section 3.1.2.7

 F3-41 
NEAR FIELD 
engineered barriers 
waste form 
FAR FIELD 
host rock 
groundwater 
Microbial 
Activity 
Environmental 
constraints 
e.g. temperature, 
toxins, pH, etc. 
Nutrients 
Energy 
Potential Microbial Effects on 
Repository Performance 
Barrier and waste 
degradation 
Changes in chemistry 
e.g pH, Eh 
Production of 
Complexants 
Radionuclide uptake 
by mobile organisms 
Gas production 
Enhanced 
radionuclide 
release 
Radionuclide 
speciation 
Solubility/ 
sorption 
Radionuclide 
mobility 
} 
(Modified from Grogan and McKinley, 1990) 
NOTE: Taken from Figure 3 of CRWMS M&O (2000f) 
Figure 3-41. Simplified Flow Diagram of the Potential Effects of Microbial Activity on Repository 
Performance

 F3-42 
NOTE: Taken from Figure 1 of CRWMS M&O (2000f). 
Figure 3-42. Results of TSPA-VA Model for Microbial Communities in the Repository Emplacement Drifts 
Biomass Produced 
TSPA-VA Results 
(Reference case with J-13 water added at 100k yr) 
Time (years) 
0 50000 100000 150000 200000 250000 300000 
Biomass Produced 
[gdry/year]/Lineal meter of Repository 
0.1
1 
10 
100 
1000 
10000 Nutrient Limit 
Total Energy Available 
Energy Limit 
Bugs Produced

 F3-43 
NOTE: Taken from Figure 14 of CRWMS M&O (2000f) 
Figure 3-43. Comparison of Growth Rate Experiments in Dilute-Complete Growth 
Media with Calculated Values in MING 
Dilute Comparison 
Days 
2 3 4 5 
Cells/ml Broth 
1e+2 
1e+3 
1e+4 
1e+5 
1e+6 
1e+7 
1e+8 
1e+9 
Microcosm Experiment 
Batch Experiment 
MING Results

 F3-44 
6
7
8
9 
10 
11 
1 10 100 1000 10000 
Concentration Factor 
pH 
0.001 
0.01 
0.1 
1
10 
100 
Ionic Strength (molal) 
Calculated pH 
Measured pH Data 
Calculated True Ionic Strength 
Calculated Ionic Strength Approximation 
Ionic Strength Based on Data 
NOTE: Taken from Figure 2 of CRWMS M&O (2000g). 
Figure 3-44. pH and Ionic Strength vs. Evaporative Concentration for Synthetic J-13 Water, Comparing 
Data and Model Calculations (evap4 test)

 F3-45 
6
7
8
9 
10 
11 
1 10 100 1000 10000 
Concentration Factor 
pH 
0.001 
0.01 
0.1 
1
10 
100 
Ionic Strength (molal) 
Calculated pH 
Measured True Ionic Strength 
Calculated Ionic Strength Approximation 
Ionic Strength Based on Data 
NOTE: Taken from Figure 8 of CRWMS M&O (2000g). 
Figure 3-45. pH and Ionic Strength for Synthetic 100x J-13 Water, Comparing Data and Model 
Calculations (Batch 1 test).

 F3-46 
3
4
5
6
7
8 
1 10 100 1000 10000 
Concentration Factor 
pH 
0.001 
0.01 
0.1 
1
10 
100 
Ionic Strength (molal) 
Measured pH Data 
Measured True Ionic Strength 
Calculated Ionic Strength Approximation 
Ionic Strength Based on Data 
Calculated pH 
NOTE: Taken from Figure 14 of CRWMS M&O (2000g). 
Figure 3-46. pH and Ionic Strength vs. Evaporative Concentration for Synthetic J-13 Water, Comparing 
Data and Model Calculations (evap3 test).

 F3-47 
0.01 
0.1
1 
10 
100 
0 200 400 600 800 1000 1200 
Time (yrs) 
Dissolved Concentration (molal) 
NO3 Cl 
SO4 CO3 
K Na 
NOTE: Taken from Figure 35 of CRWMS M&O (2000g). 
Figure 3-47. Dissolved Concentration vs. Time (J-13 water, Qseep = 1 L/yr, PCO2 = 10-3 atm).

 F3-48 
0.00 
0.05 
0.10 
0.15 
0.20 
0.25 
0.30 
0.35 
0.40 
0 200 400 600 800 1000 1200 
Time (yrs) 
Mass (kg) 
Cumulative Mass of Water in Brine Generated 
Cumulative Mass of Dissolved Solids in Brine 
NOTE: Taken from Figure 38 of CRWMS M&O (2000g). 
Figure 3-48. Cumulative Mass of Water and Dissolved Ions in Generated Brine vs. Time (J-13 water, 
Qseep = 1 L/yr, PCO2 = 10-3 atm).

 F3-49 
6
7
8
9 
10 
11 
1 10 100 1000 10000 
Concentration Factor 
pH 
0.001 
0.01 
0.1 
1
10 
100 
Ionic Strength (molal) 
Calculated pH 
Measured True Ionic Strength 
Ionic Strength Approximation 
NOTE: Taken from Figure 19 of CRWMS M&O (2000g). 
Figure 3-49. pH and Ionic Strength Predictions from Simple Evaporation of Average J-13 Well Water at 
95C and fCO2 of 10-3.

 F3-50 
1.E-10 
1.E-09 
1.E-08 
1.E-07 
1.E-06 
1.E-05 
1.E-04 
1.E-03 
1 10 100 1000 10000 
Concentration Factor 
Solid Phases Precipitated (moles) 
Calcite Nontronite-Ca 
Sepiolite Chalcedony 
Montmor-Ca Clinoptilolite-hy-Na 
Nontronite-Na Fluorite 
NOTE: Taken from Figure 24 of CRWMS M&O (2000g). 
Figure 3-50. Mineral Precipitation Predictions from Simple Evaporation of Average J-13 Well Water at 
95C and fCO2 of 10-3.

 F3-51 
6
7
8
9 
10 
11 
12
0.001 0.01 0.1 1 
1 - Res 
pH 
95'C 
75'C 
45'C 
25'C 
NOTE: Taken from Figure 27 of CRWMS M&O (2000g). 
Figure 3-51. J-13 Steady State pH vs. (1-Res) and Temperature (fCO2 = 10-3).

 F3-52 
6
7
8
9 
10 
11 
12
0.001 0.01 0.1 1 
1 - Res 
pH 
95'C 
75'C 
45'C 
25'C 
NOTE: Taken from Figure 28 of CRWMS M&O (2000g). 
Figure 3-52. J-13 Steady State pH vs. (1-Res) and Temperature (fCO2 = 10-6).

 F3-53 
4
5
6
7
8 
1.E-10 1.E-08 1.E-06 1.E-04 1.E-02 1.E+00 
fco2 
pH 
95'C 
75'C 
45'C 
25'C 
NOTE: Taken from Figure 39 of CRWMS M&O (2000g). 
Figure 3-53. Predicted pH of Condensed Water for a Range of Temperatures and CO2 Fugacities (fCO2).

 F3-54 
Colloid Size Distribution, Yucca Mountain Wells ... 
0 
10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
0 50 100 150 200 250 
Colloid Size, nm .. 
(A) 
Colloid Size Distribution, Nye County Wells .. 
0 
10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
0 50 100 150 200 250 
Colloid Size, nm .. 
` 
(B) 
NOTES: A Data from Yucca Mountain wells. 
B Data from Nye County wells. 
The upper solid curve is for a log-normal distribution with  = 19.2688 and s = 2.0441, based on 
regression. The lower solid curve is for a log-normal distribution with  = 19.4841 and s = 1.9911, 
calculated directly from the data. Both curves agree well with the data points 
Taken from Figure 30 of CRWMS M&O (2000t). 
Figure 3-54. Particle Size Distribution for Colloids in Groundwater Samples near Yucca Mountain

 F3-55 
Colloid Particle Count 
0 
10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11 
Particles per mL 
NOTES: Data points are shown for all 18 wells sampled. Two log-normal distributions are shown: The solid 
curve is based on Nye County data, and the dashed curve is based Yucca Mountain data. The 
distributions are almost indistinguishable in the plots, and the parameters are not significantly different 
at the 95% confidence level. Taken from Figure 31 of CRWMS M&O (2000t). 
Figure 3-55. Distribution of Total Number of Colloid Particles per Milliliter in Groundwater Samples 
Near Yucca Mountain

 F3-56 
Diffusivity vs. Particle Diameter 
y = 0.4217x-1.1625 
0.0001 
0.001 
0.01 
0.1
1 
10
0.1 1 10 100 1000 
Diameter, nm 
105*Diffusion Coeff., cm2/sec 
NOTES: Estimate appears conservative. 
Values shown with points are handbook values (Source: Perry and Chilton, 1973, Table 17-10, p. 17-38) 
Values plotted as a line are from Stokes-Einstein equation (CRWMS M&O 2000t) 
Taken from Figure 32 in CRWMS M&O (2000t). 
Figure 3-56. Estimated Diffusion Coefficient as a Function of Particle Size Using the 
Stokes-Einstein Equation, Compared with Handbook Values

 F3-57 
NOTE: Taken from Figure 4-8 of CRWMS M&O (1998d). 
Figure 3-57. Schematic of Processes Affecting the Composition of Seepage.

 F3-58 
NOTE: Taken from Figure 33 of CRWMS M&O (2000t). 
Figure 3-58. CO2 Budget for Reference Model (L4C4 location; upper infiltration) 
CO2 Budget from Chemical Reference Model 
(L4C4 location; "upper" infiltration) 
-1.0E-08 
0.0E+00 
1.0E-08 
2.0E-08 
3.0E-08 
4.0E-08 
5.0E-08 
6.0E-08 
7.0E-08
100 1000 10000 
Time (yr) 
CO2 Produced (kg/m-sec) 
In-drift CO2 budget 
With host rock, referred to 
Zone 0 
In-drift CO2 budget with 
cement 
Max. CO2 flux in pillar, from 
1-D model

 F3-59 
NOTE: Taken from Figure 36 of CRWMS M&O (2000t). 
Figure 3-59. pH vs. Time for the Chemical Reference Model 
pH Evolution for Reference Model 
8
9 
10 
11 
10 100 1000 10000 
Time (yr) 
pH 
Host Rock (Zone 1/2) 
Backfill (Zone 3/4) 
Invert (Zone 5/6) 
The backfill and invert are dry until Time 
Period 3 (700 to 1500 yr) and Time 
Period 4 (1500 to 2500 yr), respectively.

 F3-60 
NOTE: Ionic strength is limited to 1 molal in this model. Taken from Figure 37 of CRWMS M&O (2000t). 
Figure 3-60. Ionic Strength vs. Time, for the Chemical Reference Model 
Ionic Strength Evolution for Reference Model 
0.001 
0.01 
0.1
1 
10 100 1000 10000 
Time (yr) 
Ionic Strength (molal) 
Host Rock (Zone 1/2) 
Backfill (Zone 3/4) 
Invert (Zone 5/6) 
The backfill and invert are dry until Time 
Period 3 (700 to 1500 yr) and Time 
Period 4 (1500 to 2500 yr), respectively.

 F3-61 
RH vs. Time at the Drip Shield Surface (Zone 4, TH Models, P&CE AMR) 
0.0 
0.2 
0.4 
0.6 
0.8 
1.0
100 1000 10000 100000 1000000 
Time (yr) 
RH 
L4C1 edge location; "upper" infiltration 
L4C4 center location; "upper" infiltration 
L4C4 center location; "lower" infiltration 
L4C1 edge location; "lower" infiltration 
Nitrate, chloride, & sulfate brines form; 
most deliquescent are nitratres & divalent chloride salts. 
Brine dilution by humidity 
Possible flushing of salts by seepage 
NOTE: Taken from Figure 34 of CRWMS M&O (2000t). 
Figure 3-61. Relative Humidity vs. Time at the Drip Shield Surface

 F3-62 
NOTE: Taken from Figure 35 of CRWMS M&O (2000t). 
Figure 3-62. Conditions for MIC at the Drip Shield Surface 
Conditions for MIC at the Drip Shield Surface (Zone 4) ( CRWMS M&O 2000t) 
0.0 
0.2 
0.4 
0.6 
0.8 
1.0 
0 50 100 150 200 250 
Temperature (C) 
RH 
L4C4 center location; 
"upper" infiltration 
L4C4 center location; 
"lower" infiltration 
L4C1 edge location; 
"upper" infiltration 
L4C1 edge location; 
"lower" infiltration 
Halophile activity at RH>75% 
Microbial activity at RH>90% 
Microbial 
activity 
at T<120 C 
Arrows 
signify direction 
of TH evolution

 F3-63 
 
NOTE: Taken from Figure 1 of CRWMS M&O (2000ad). 
Figure 3-63. Illustration of a Typical Key Block and Associated Fracture Planes 
Key Block Formed by the Intersection of an 
Excavation with 
Three Fracture Planes 
Tunnel 
Excavation 
23 5 /8 7 
33 8/12 
N 
E 
S 
W 
133/8 3 
Stereographic Projection of 
Key-Block-Forming Fracture Planes 

 F3-64 
NOTE: Taken from Figure 10 of CRWMS M&O (2000ad). 
Figure 3-64. Cumulative Block Size Distribution for Various Drift Orientations in the Tptpmn Unit, 
Static Condition 
0.00% 
10.00% 
20.00% 
30.00% 
40.00% 
50.00% 
60.00% 
70.00% 
80.00% 
90.00% 
100.00%
0.01 0.10 1.00 10.00 100.00 
Block Volume (m^3) 
Cumulative Frequency of Occurrence 
0 
15 
30 
45 
60 
75 
90 
105 
120 
135 
150 
165

 F3-65 
NOTE: Taken from Figure 19 of CRWMS M&O (2000ad). 
Figure 3-65. Cumulative Key Block Size Distribution for Seismic Consideration in the Tptpmn 
Unit 
0.00% 
10.00% 
20.00% 
30.00% 
40.00% 
50.00% 
60.00% 
70.00% 
80.00% 
90.00% 
100.00%
0.01 0.10 1.00 10.00 100.00 
Block Volume (m^3) 
Cumulative Frequency of Occurrence 
Static 
Seismic Level 1 
Seismic Level 2 
Seismic Level 3 
NOTE: The seismic level 2 and seismic level 3 distribution curves are identical.

 F3-66 
Drip Shield 
Diversion 
Backfill 
Diversion 
Indrift Seepage 
 
 
Water Distribution and 
Removal Model 
Radionuclide Transport 
Model 
Invert Flow 
Z 
Concentration Co 
Waste Package 
Release 
Drip Shield Flow 
NOTE: Taken from Figure 1 of CRWMS M&O (2000b) 
Figure 3-66. Conceptual Model for Radionuclide Transport Model

 F3-67 
NOTE: Taken from Figure 6 of CRWMS M&O (2000b). The measured data are for granulated materials 
(Conca and Wright, 1992, page 5). 
Figure 3-67. Comparison of Measured Data for Crushed Tuff with Archies Law, and the Modified 
Millington-Quirk Relation. 
0 10 20 30 40 50 60 
1 .10 4 
1 .10 3 
0.01 
0.1
1 
10 
Data 
Empirical Fit 
Modified Millington Quirk 
Archie's Law 
Volumetric Moisture Content (%) 
Normalized Diffusivity

 F3-68 
NOTE: Taken from Figure 9 of CRWMS M&O (2000b) 
Figure 3-68. Breakthrough for One Dimensional Advection/Dispersion/Diffusion for the Base Case 
0.1 1 10 100 1 103 
0 
0.2 
0.4 
0.6 
0.8
1 
Base Case Center 
Base Case Adjacent 
Time(yr) 
C(t)/C0

 F3-69 
NOTE: Taken from Figure 12 of CRWMS M&O (2000b) 
Figure 3-69. Effect of Sand Drains on Breakthrough for the Glacial Climate 
0.1 1 10 100 1.103 1.104 1.105 
0 
0.2 
0.4 
0.6 
0.8
1 
Base Case Center (Case 1) 
Sand Drains (Case 9) 
Time(yr) 
C(t)/C0

 F3-70 
NOTE: Posted infiltration flux values are in mm per year, and correspond to the upper infiltration flux 
distribution. Taken from Figure 5.2 of CRWMS M&O (2000i) 
Figure 3-70. Repository Perimeter, Model Repository Footprint, Chimney Locations and Infiltration Flux 
Values

 F3-71 
30 days 
0
1
2
3
4
5 
Distance from top of block (m) 
20 60 100 140 180 
Temperature (C) 
NUFT 
Measured 
100 days 
0
1
2
3
4
5 
Distance from top of block (m) 
20 60 100 140 180 
Temperature (C) 
NUFT 
Measured 
0
1
2
3
4
5 
Distance from top of block (m) 
Distance from top of block (m) 
Distance from top of block (m) 
20 60 100 140 180 
Temperature (C) 
200 days 
NUFT 
Measured 
0
1
2
3
4
5 
20 60 100 140 180 
Temperature (C) 
NUFT 
Measured 
300 days 
0
1
2
3
4
5 
20 60 100 140 180 
Temperature (C) 
400 days 
NUFT 
Measured 
NOTE: Taken from Figure 6-47 of CRWMS M&O (2000i) 
Figure 3-71. Comparison of NUFT-Simulated , and Measured Temperatures from the LBT, Along 
Borehole TT1, at Six Times from 30 days to 400 Days.

 F3-72 
100 days 
0 0.2 0.4 0.6 0.8 1.0 
Liquid-phase saturation 
0 0.2 0.4 0.6 0.8 1.0 
Liquid-phase saturation 
0
1
2
3
4
5 
Distance from top of block (m) 
NUFT 
Measured 
500 days 
0
1
2
3
4
5 
Distance from top of block (m) 
NUFT 
Measured 
365 days 
0 0.2 0.4 0.6 0.8 1.0 
Liquid-phase saturation 
0
1
2
3
4
5 
Distance from top of block (m) 
NUFT 
Measured 
NOTE: Taken from Figure 6-48 of CRWMS M&O (2000i) 
Figure 3-72. Comparison of NUFT-Simulated, and Measured Liquid Saturation from the LBT, Along 
Borehole TN3, at Three Times from 100 days to 500 Days.

 F3-73 
NOTE: Taken from Figure 6-49 of CRWMS M&O (2000i) 
Figure 3-73. Comparison of NUFT LDTH Submodel Calculations, and Measured Temperatures from 
the DST, Along Borehole ESF-HD-137 at: (a) 365 Days and (b) 547 Days.

 F3-74 
NOTE: Taken from Figure 6-50 of CRWMS M&O (2000i) 
Figure 3-74. Comparison of Temperatures Calculated by the Multiscale Thermohydrologic Model and 
the Mountain-Scale TH Model, at (a) the Center of the Repository (L4C3 Location) and (b) 100 m from the 
Edge of the Repository (L4C1 Location). 
Time (yr) 
(b) repository edge at l4c1 location 
LBNL eastwest model 
LLNL multiscale model 
180 
160 
140 
120 
100 
80
0 
60 
40 
180 
160 
140 
120 
100 
80
0 
60 
40 
Temperature (C) 
(a) repository center at l4c3 location 
101 100 102 103 104 105

 F3-75 
NOTE: Taken from Figure 6-13 of CRWMS M&O (2000i) 
Figure 3-75. Temperature History on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case at 
(a) the Center of the Repository and (b) a Location 27.5 m from the Eastern Edge

 F3-76 
NOTE: Taken from Figure 6-7 of CRWMS M&O (2000i). 
Figure 3-76. Temperature on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 60, 
100, and 150 Years After Emplacement (50-yr Preclosure Period).

 F3-77 
NOTE: Taken from Figure 6-7 of CRWMS M&O (2000i). 
Figure 3-77. Temperature on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 200, 
500, and 1,000 Years After Emplacement (50-yr Preclosure Period).

 F3-78 
NOTE: Taken from Figure 6-7 of CRWMS M&O (2000i). 
Figure 3-78. Temperature on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 5,000, 
10,000, and 20,000 Years After Emplacement (50-yr Preclosure Period).

 F3-79 
NOTE: Location in Nevada State Plane Coordinates: easting 170535.03 m, northing 233640.08 m. 
Adapted from Figure 6-41 of CRWMS M&O (2000i). 
Figure 3-79. Histories of Liquid Water Flux for Points in the Emplacement Drift Located at the Geographic 
Center of the Repository, for the Mean Infiltration-Flux Case

 F3-80 
NOTE: Location in Nevada State Plane Coordinates: easting 171195.16 m, northing 233605.06 m. 
Adapted from Figure 6-41 of CRWMS M&O (2000i). 
Figure 3-80 Histories of Liquid Water Flux for Points in the Emplacement Drift, Located 27.5 m From the 
Eastern Edge of the Repository, for the Mean Infiltration-Flux Case

 F3-81 
NOTE: Taken from Figure 6-20 of CRWMS M&O (2000i). 
Figure 3-81. Relative Humidity History on the Surface of a 21-PWR WP for the Mean Infiltration-Flux 
Case at (a) the Center of the Repository and (b) a Location 27.5 m from the Eastern Edge

 F3-82 
NOTE: Taken from Figure 6-16 of CRWMS M&O (2000i). 
Figure 3-82. Relative Humidity on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 
150, 200, and 300 Years After Emplacement (50-yr Preclosure Period).

 F3-83 
NOTE: Taken from Figure 6-16 of CRWMS M&O (2000i). 
Figure 3-83. Relative Humidity on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 
500, 700, and 1,000 Years After Emplacement (50-yr Preclosure Period).

 F3-84 
NOTE: Taken from Figure 6-16 of CRWMS M&O (2000i). 
Figure 3-84. Relative Humidity on the Surface of a 21-PWR WP for the Mean Infiltration-Flux Case, for 
1200, 1400, and 1600 Years After Emplacement (50-yr Preclosure Period).

 4-1 
4. RELATION WITH THE NUCLEAR REGULATORY COMMISSION 
ISSUE-RESOLUTION STATUS REPORTS 
4.1 SUMMARY OF THE KEY TECHNICAL ISSUES 
As part of the review of site characterization activities specified in the Nuclear Regulatory 
Commission's (NRC) geologic repository regulations, the NRC has undertaken an ongoing 
review of information on Yucca Mountain site characterization activities so as to allow early 
identification and resolution of potential licensing issues. The principal means for achieving this 
goal is through informal, pre-licensing consultation with the DOE. This approach attempts to 
reduce the number of, and to better define, issues that may be in dispute during the NRC 
licensing review, by obtaining input and striving for consensus from the technical community, 
interested parties, and other groups on such issues. 
The NRC has focused pre-licensing issue resolution on those topics most critical to the 
postclosure performance of the proposed geologic repository. These topics are called Key 
Technical Issues (KTIs). Each KTI is subdivided into a number of sub-issues. The KTIs are: 
 Activities Related to Development of the EPA Standard 
 Container Lifetime and Source Term 
 Evolution of the Near-Field Environment 
 Igneous Activity 
 Radionuclide Transport 
 Repository Design and Thermal Mechanical Effects 
 Structural Deformation and Seismicity 
 Thermal Effects on Flow (TEF) 
 Total System Performance Assessment (TSPA) and Integration 
 Unsaturated Zone (UZ) and Saturated Zone (SZ) Flow under Isothermal Conditions. 
Identifying KTIs, integrating their activities into a risk informed approach, and evaluating their 
significance for post-closure performance helps ensure that NRCs attention is focused where 
technical uncertainties will have the greatest affect on the assessment of repository safety. 
Early feedback among all parties is essential to define what is known, what is not known and 
where additional information is likely to make a significant difference in the understanding of 
future repository safety. Issue Resolution Status Reports (IRSRs) are the primary mechanism that 
the NRC staff uses to provide DOE with feedback on KTI sub-issues. IRSRs focus on NRCs 
acceptance criteria for issue resolution and the status of issue resolution, including areas of 
agreement or when the staff currently has comments or questions. Open meetings and technical 
exchanges between NRC and the DOE provide additional opportunities to discuss issue 
resolution, identify areas of agreement and disagreement and develop plans to resolve such 
disagreements.

 4-2 
4.2 RELATIONSHIP OF THE ENGINEERED BARRIER SYSTEM PROCESS 
MODEL REPORT TO THE KEY TECHNICAL ISSUES 
The EBS PMR provides technical analyses that relate to five of the key technical issues (KTIs) 
and their associated issue resolution status reports (IRSRs). Table 4-1 shows these KTIs and 
their subissues that relate directly to this PMR. These are discussed in the subsequent 
subsections. 
Table 4-1. Issue-Resolution Status Report and Key Technical Issues Related to the Engineered Barrier 
System Process Model Report 
Key Technical Issues Subissues Applicable to EBS PMR 
Container Life and Source Term Subissue 1 
The Effects of Corrosion Processes on the Lifetime of the Containers 
Subissue 3 
The Rate at Which Radionuclides in Spent Nuclear Fuel are Released from 
the Engineered Barrier Subsystem Through the Oxidation and Dissolution of 
Spent Fuel 
Subissue 4 
The Rate at which Radionuclides in High-Level Waste Glass are Released 
from the Engineered Barrier Subsystem 
Subissue 6 
The Effects of Alternative Engineered Barrier Subsystem Design Features on 
Container Lifetime and Radionuclide Release From the Engineered Barrier 
Subsystem 
Evolution of the Near-Field 
Environment 
Subissue 1 
Effects of Coupled Thermal-Hydrologic-Chemical (THC) Processes on 
Seepage and Flow 
Subissue 2 
Effects of Coupled THC Processes on the Waste Package Chemical 
Environment 
Subissue 3 
Effects of Coupled THC Processes on the Chemical Environment for 
Radionuclide Release 
Subissue 4 
Effects of Coupled THC Processes on Radionuclide Transport Through 
Engineered and Natural Barriers 
Repository Design and Thermal- 
Mechanical Effects 
(TEF) 
Subissue 1 
Implementation of an Effective Design-Control Process Within the Overall 
Quality Assurance Program 
Subissue 2 
Design of the Geologic Repository Operations Area for the Effects of Seismic 
Events and Direct Fault Disruption 
Subissue 3 
Thermomechanical Effects on Underground Facility Design and Performance 
Thermal Effects on Flow Subissue 1 
Is the U.S. Department of Energy Thermohydrologic Testing Program,

 4-3 
Key Technical Issues Subissues Applicable to EBS PMR 
Including Performance Confirmation Testing, Sufficient to Evaluate the 
Potential for Thermal Reflux to Occur in the Near Field? 
Subissue 2 
Is the U.S. Department of Energy Thermohydrologic Modeling Approach 
Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in the 
Near Field? 
Subissue 3 
Does the U.S. Department of Energy Total System Performance Assessment 
Adequately Account for Thermal Effects on Flow? 
Total System Performance 
Assessment and Integration 
(TSPA) 
Subissue 4 
Scenario Analysis 
4.2.1 Container Life and Source Term IRSR 
The primary issue of this KTI on container life and source term (CLST) is adequacy of the EBS 
design and provision of reasonable assurance that containers will be adequately long-lived and 
that radionuclide releases from the EBS will be sufficiently controlled so that container design 
and packaging of spent nuclear fuel (SNF) and high-level waste (HLW) glass will make a 
significant contribution to overall potential repository performance. This IRSR is focused on the 
containers and waste forms as the primary engineered barriers, but it also considers other 
engineered subsystem enhancements (i.e., ceramic coatings, drip shields, backfill) incorporated 
as options in the EBS design (NRC 1999a, Section 2.0). 
There are six subissues associated with this KTI, as discussed in the CLST IRSR (NRC 1999a). 
Four of the six subissues are directly related to the EBS PMR and are described below: 
Subissue 1: The Effects Of Corrosion Processes On The Lifetime Of The Containers 
This subissue relates to the adequacy of DOE's consideration of the effects of corrosion 
processes on the lifetime of the containers. The applicable criteria relates to environmental 
conditions within the WP emplacement drifts that may promote the corrosion processes, taking 
into account the possibility of irregular wet and dry cycles that may enhance the rate of container 
degradation. The models presented in Sections 3.1.1 through 3.1.4 consider the effects of waste 
package heat generation in increasing temperature and evaporation within the EBS. For 
example, the EBS Physical and Chemical Model (Section 3.1.2) initially develops a TH model 
calculation for estimating water fluxes during the thermal period. This information is used to 
evaluate gas flux during the thermal period, CO2 and O2 fugacity which in turn are used to 
estimate the evolution of leachate composition, and the formation of salts and precipitates in the 
backfill and on the drip shield. 
Subissue 3: The Rate at Which Radionuclides in Spent Nuclear Fuel are Released from the 
Engineered Barrier Subsystem Through the Oxidation and Dissolution of Spent 
Fuel 
This subissue relates to the adequacy of the effect of the rate of degradation of SNF on the 
subsequent release of radionuclides and the rate of release from the EBS. The first acceptance 
Table 4-1. Issue-Resolution Status Report and Key Technical Issues Related to the Engineered 
Barrier System Process Model Report (Continued)

 4-4 
criteria relates to whether the DOE has considered all categories of SNF planned for disposal at 
the proposed YM repository. It should be recognized that the issue relates primarily to the 
performance of the waste package and waste form for all categories of SNF. For a given waste 
form/waste package releases, the EBS radionuclide transport model is based upon a unit release 
of radionuclides due to a breached WP that can be applied to the SNF. The EBS radionuclide 
model is a general release model that can be applied to all categories of SNF for a given waste 
package release. 
The DOE has identified and considered the likely processes for SNF degradation and the release 
of radionuclides from the EBS, and requires adequacy for numerical models by incorporating 
uncertainties, and utilizing spent fuel test results. Note that most of the criteria apply to the 
waste package and waste form. The EBS PMR provides information (Sections 3.1.3, 
3.2.3.1.3,3.2.3.2.3, and 3.2.3.1.5) on the drip shield corrosion environment and flow through the 
drip shield that affects radionuclide transport from the waste package. 
Subissue 4: The Rate at which Radionuclides in High-Level Waste Glass are Released from 
the Engineered Barrier Subsystem 
This subissue relates to the adequacy of DOEs consideration of the effects of degradation of 
HLW glass, taking into account the rate of degradation and its effect on the rate of radionuclide 
releases from the EBS. The EBS Water Distribution and Removal Model provides a bounding 
analysis of the amount of water that would flow through backfill and drip shield and potentially 
contact waste packages that is the primary influence on degradation of HLW. Discussions are 
presented (Section 3.2.3.1.3., 3.2.3.1.5 and 3.2.3.2.3) on colloids and microbial effects based 
upon available data relevant to the degradation of HLW glass. 
Subissue 6: The Effects of Alternative Engineered Barrier Subsystem Design Features on 
Container Lifetime and Radionuclide Release From the Engineered Barrier 
Subsystem 
This subissue addresses the effects of alternate EBS design features, such as backfill, drip 
shields, and ceramic coatings, on container lifetime and radionuclide release from the EBS. The 
subissue requires that the DOE consider likely processes for the degradation of HLW glass and 
the release of radionuclides from the EBS due to dissolution of the primary phase; formation of 
secondary minerals and colloids; microbial action; and radionuclide releases and transport from 
the WP emplacement drifts. Section 3.1.3 presents a discussion of radionuclide release through 
the EBS for a unit release that can be applied. 
The subissue involves identification and consideration of the effects of backfill, and the timing of 
its emplacement, on the thermal loading of the repository, WP lifetime (including container 
corrosion and mechanical failure), and the release of radionuclides from the EBS. Further the 
subissues involves specialized issues such as the humid-air corrosion regime, and the potential 
for condensate to form below the drip shield. The Water Distribution and Removal Model 
(Section 3.1.1), the EBS Physical and Chemical Environment Model (Section 3.1.2), and the 
Multiscale TH Model (Section 3.1.4) provide analyses incorporating the placement of backfill at 
the time of repository closure. The Multiscale model provides an analysis of the relative 
humidity surrounding the waste package that when coupled with corrosion data from the Waste

 4-5 
Package model allows a determination of humid air corrosion. The interaction of flowing water 
with introduced materials including the grout, steel, and backfill is considered in the Physical and 
Chemical Environment Model (Section 3.1.2). 
The subissue involves the geochemistry of the groundwater. The EBS Physical and Chemical 
Environment (P&CE) Model (Section 3.1.2) provides a Chemical Reference Model that 
integrates several submodels and describes the evolution of water composition and solid 
precipitates in the backfill above the drip shield, the invert, and the lower part of the backfill. 
Further, it evaluates CO2 mass balance in the drifts and the surrounding host rock as it evolves 
with time. The assessment includes the effects of carbon steel corrosion, leaching from 
cementitious materials, microbial processes, and colloidal processes on the bulk chemical 
environment. 
4.2.2 Evolution of the Near-Field Environment IRSR 
The primary focus of the near-field environment (NFE) KTI is the coupling of thermal 
hydrologic, and chemical processes that could effect the drift environment. The near field is 
considered to be the part of the site for which changes in the physical and chemical properties 
that result from construction of the underground facility or from heat generated by the emplaced 
radioactive waste will affect performance of the potential repository. Evolution of the near field 
is expected to include coupling of thermal, hydrologic, and chemical processes that could affect 
parts of the mountain. These coupled processes could affect components of the NBS and the 
EBS and thereby affect potential repository system performance. The introduction of potential 
repository construction materials and WP materials may also perturb the NFE (NRC 1999b, 
Section 2.0). 
There are five subissues associated with this KTI, as discussed in the ENFE IRSR (NRC 1999b). 
Four subissues are directly related to the EBS PMR and are described below: 
Subissue 1: Effects of Coupled THC Processes on Seepage and Flow 
As stated in the IRSR this subissue focuses on explaining the importance of the THC coupled 
processes to seepage and flow (NRC 1999b). Note that the subissue applies to seepage which is 
covered in the UZ Flow and Transport Model, and flow through backfill, drip shields, and invert 
which is the subject of the EBS PMR. 
The subissue involves the criterion that mathematical models for coupled THC effects on 
seepage and flow be consistent with conceptual models, based on inferences about the near field 
environment, field data and natural alteration observed at the site, and the expected engineered 
materials. The Water Distribution and Removal Model, the P&CE Model, and the Multiscale 
Model provide predictions of seepage and flow that are based upon the selection of a consistent 
set thermal properties, and hydrologic properties for the active fracture model. The active 
fracture model, and the drift scale properties sets for these models are consistent with properties 
sets used in the UZ model which were determined by inverse modeling methods.

 4-6 
Subissue 2 Effects of Coupled THC Processes on the Waste Package Chemical Environment 
The P&CE Model is based upon a two dimensional thermal hydrologic analysis that accounts for 
temporal waste heat loading, and variations in percolation rates. The P&CE Model analyzes 
evolution of leachate composition from the grout and backfill for the EBS is provided when 
contacted with J13 groundwater. The P&CE Model considers initially the composition of J13 
groundwater that is used for developing a precipitates and salts normative submodel which is in 
turn used in the chemical system model. Where appropriate, bounding calculations have been 
performed to estimate physical effects such as flow through drip shields (Section 3.1.1), the 
potential for condensation below the drip shield (Section 3.1.1) and chemical effects such as the 
alteration of groundwater chemistry (Section 3.1.2). 
Subissue 3 Effects of Coupled THC Processes on the Chemical Environment for 
Radionuclide Release 
The EBS radionuclide transport model (EBS PMR Section 3.1.3) provides an analysis of release 
based upon the thermal hydrological calculations in the WD&R model. The EBS radionuclide 
transport model (EBS PMR Section 3.1.3) is an advection/dispersion/diffusion model based upon 
TH coupled modeled in the WD&R model. The EBS radionuclide transport model (EBS PMR 
Section 3.1.3) provides an analysis of release based upon the thermal hydrological calculations in 
the WD&R model. 
The WD&R model considers the temporal variations in conditions affecting the TH effects, and 
provides a bounding calculation for chemical effects due fracture plugging that would alter 
saturation levels and porewater velocities. The EBS radionuclide transport (Section 3.1.3) 
model provides a sensitivity analysis for the chemical retardation that bounds temporal and 
spatial variations in the chemical retardation factor that reflects the chemical environment. For 
the base case, the EBS radionuclide transport takes no credit for chemical retardation which is a 
bounding assumption for radionuclide transport. 
The EBS Colloids submodel is based upon relevant data for the size and concentration of 
colloids that account for variability through probability distributions. Based upon these data 
bounding values for radionuclide solubility, and colloid diffusion coefficient were calculated. 
Subissue 4: Effects of Coupled Thermal-Hydrologic-Chemical Processes on Radionuclide 
Transport Through Engineered and Natural Barriers 
This subissue primarily focuses on explaining the importance of the results of different coupled 
processes to radionuclide transport(NRC 1999b). The EBS Radionuclide Transport model is 
based upon a two dimensional thermal hydrologic analysis that considers initial temperature and 
pressure boundary conditions. The EBS Radionuclide Transport Model provides bounding 
analysis for a conservative range of parameters. The base case analysis neglects the effects of 
chemical retardation on radionuclide transport and therefore conservatively neglects chemical 
sorption.

 4-7 
4.2.3 Repository Design and Thermal-Mechanical Effects IRSR 
The primary focus of the repository design and thermal mechanical effects (RDTME) KTI is the 
review of design, construction, and operation of the geologic repository operations area (GROA) 
with respect to the preclosure and postclosure performance objectives, taking into consideration 
long-term thermomechanical (TM) processes. Consideration of the time-dependent TM coupled 
response of a jointed rock mass is central to potential repository design and necessary for 
performance assessment (PA) at the Yucca Mountain (YM) site. Consequently, that is the focus 
of the preclosure and postclosure elements of this KTI (NRC 1999c, Section 2.1). 
Three of the four subissues for the RDTME KTI are directly related to this PMR, as described 
below. 
Subissue 1: Implementation of an Effective Design-Control Process Within the Overall 
Quality Assurance Program 
This subissue focuses on the NRC staff's evaluation of DOE's implementation of design control 
process for design, construction, and operation of the ESF (NRC 1999c). Note that in general 
design considerations as they relate to such criteria as design bases, appropriate quality 
standards, design interfaces, and the preparation of design calculations are not considered 
directly in this PMR. The acceptance criterion will be applied appropriately in the design 
process. 
Subissue 2: Design of the Geologic Repository Operations Area for the Effects of Seismic 
Events and Direct Fault Disruption 
As stated in the IRSR this subissue focuses on the design of the GROA for the effects of seismic 
events and direct fault disruption as identified in the seismic topical reports (NRC 1999c). 
Design considerations related to seismic issues are not included in this PMR. The acceptance 
criterion will be applied appropriately in the seismic design process. 
Subissue 3: Thermomechanical Effects on Underground Facility Design and Performance 
This subissue consists of three major components; (i) TM effects on underground facility design; 
(ii) effect of seismically induced rockfall on WP performance; and (iii) postclosure TM effects 
on flow into the emplacement drifts (NRC 1999c). 8. Both drift- and repository-scale models of 
the underground facility are used in TM analyses to establish the intensity and distribution of 
ground movement (rock deformations, collapse, and other changes that may affect the integrity 
or geometrical configuration of openings within the underground facility). The number and 
variety of models permit the examination of conditions along drift-parallel and drift-normal 
directions. The drift degradation analysis is based upon a drift scale model that considers 
changes in rock mass properties throughout the repository. Other issues regarding drift 
degradation are presented in Appendix A. 
Rockfall analysis considers the possibility of multiple blocks failing onto a WP, and the extent of 
the potential rockfall area around in individual emplacement drifts as well as over the entire 
repository as functions of time and seismic activity.

 4-8 
4.2.4 Thermal Effects on Flow IRSR 
The IRSR states that the primary technical aspects of the thermal effects on flow (TEF) KTI is 
the estimation of temperature, moisture content, and humidity at the WP surface and estimation 
of temperature and thermally driven water flux with respect to the transport of radionuclides 
from failed WPs. 
As explained in the IRSR, it is necessary to understand the spatial and temporal effects of the 
thermal load on liquid-phase and gas-phase fluxes and the resulting effects on temperature and 
relative humidity of the WP environment at the potential repository. This will provide 
confidence in predictions of containment and long-term waste isolation. Because the focus of 
the staff review of DOEs program is on the adequacy of DOEs treatment of thermally 
perturbed liquid-phase and gas-phase fluxes (particularly thermal reflux) in testing, modeling, 
and PA program areas, this KTI is divided into the following three subissues (NRC 1999d, 
Section 2.0). 
All three of the subissues for the TEF KTI are directly related to this PMR and are described in 
the following subsections. 
Subissue 1: Is the U.S. Department of Energy Thermohydrologic Testing Program, Including 
Performance Confirmation Testing, Sufficient to Evaluate the Potential for 
Thermal Reflux to Occur in the Near Field? 
This subissue focuses on information needed to verify conceptual models used to predict 
thermally driven flow in the near field. The most important technical element relates to 
designing and conducting tests to evaluate potential repository conditions that could lead to 
refluxing of water into the underground facility. (NRC 1999d, Section 4.1.2). Thermohydrologic 
tests are designed and conducted with the explicit objective of testing conceptual and numerical 
models so that critical thermohydrologic processes can be observed and measured. 
Tests are currently being planned and conducted for testing of the process models. Tests are 
being conducted at quarter scale to simulate thermal and hydrological effects within the drift. 
The tests record temperature, relative humidity, and saturation levels within the EBS components 
that can be directly compared with results from the Water Distribution and Removal Model or 
other TH models. The quarter-scale tests are being conducted with J13 groundwater. The tests 
simulate the interaction of the J13 groundwater with EBS components that would result in the 
formation of precipitates on EBS components. 
Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling Approach 
Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in the 
Near Field? 
This subissue focuses on the sufficiency of DOEs thermohydrologic modeling approach 
(process-level models) to predict thermally driven flow in the near field. The NRC staff review 
of the DOEs thermohydrologic analyses will place particular emphasis on technical elements of 
the acceptance criteria that are related to incorporating the physics of refluxing of water into 
conceptual and numerical models (NRC 1999d, Section 4.2.2). Sufficient data on EBS processes 
are not available at the current time for the Water Distribution and Removal Model

 4-9 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, 
bounding calculations have been performed to estimate physical effects such as flow through 
drip shields (Section 3.1.1), and chemical effects such as the alteration of groundwater chemistry 
(Section 3.1.4). 
The degree of multidrift dry-out zone coalescence will be a function of the thermal load specified 
in the final design of the repository. Recent, proposed design modifications by DOE to reduce 
the repository thermal load to approximately 60 MTU/acre will minimize, if not eliminate, 
dry-out zone coalescence. Recent DOE models that include the active fracture model adequately 
predict the extent of dryout surrounding the emplacement drifts. 
The EBS process models for thermal hydrological effects are based upon initial conditions, 
boundary conditions, and computational domains consistent with site characteristics. The 
thermal hydrology models used in Sections 3.1.1 through 3.1.4 are based upon the selection of 
NBS hydrologic and thermal properties used in the UZ process model. The initial conditions, 
and boundary conditions for the models for specific locations use the same infiltration rates, and 
temperature and pressure boundary conditions are consistent with the UZ process Model 
(Section 3.1.4). 
The potential repository-scale heterogeneity is represented by the drift scale active fracture 
properties set which captures the properties for various strata. Lateral variability within the 
potential repository footprint is represented by the 31 drift-scale-model locations used in the 
Multiscale TH Model. These locations are regularly distributed over the potential repository 
footprint. This reduces the general three dimensional problem to a series of two dimensional 
problems. 
Subissue 3: Does the U.S. Department of Energy Total System Performance Assessment 
Adequately Account for Thermal Effects on Flow? 
This subissue focuses on DOE adequately accounting for TEF in the TSPA. The NRC staff 
review will particularly emphasize on the potential adverse effects on repository performance 
resulting from the influx of liquid water or water vapor into an emplacement drift (NRC 1999d, 
Section 4.3.2). At the present time, data needs have been identified, and quarter scale testing is 
being performed to evaluate the performance of the EBS components for influxes of liquid 
water. Where appropriate, bounding calculations have been performed to estimate physical 
effects such as flow through drip shields (Section 3.1.1). 
4.2.5 Total System Performance Assessment (TSPA) and Integration IRSR 
The objective of this KTI is to describe an acceptable methodology for conducting performance 
assessments of repository. As stated in this IRSR the focus is to describe an acceptable 
methodology for conducting assessments of repository performance and using these assessments 
to demonstrate compliance with the overall performance objectives and requirements for 
multiple barriers (NRC 1998).

 4-10 
The acceptance criteria for each subissue address five fundamental elements of the DOEs TSPA 
model for the Yucca Mountain Site (NRC 1998 p. 10): 
 Data and model justification 
 Data uncertainty and verification 
 Model Uncertainty 
 Model verification 
 Integration. 
The subissue for scenario analysis for this KTI relates to the EBS PMR. 
This scenario-analysis subissue focuses on the attributes of an acceptable methodology for 
identifying, screening, and selecting Features, Events, and Processes (FEPs) for inclusion in the 
TSPA (NRC 1998, p. 4). FEPs that could affect future system performance are used to formulate 
scenarios. This includes construction of scenario classes, assignment of probabilities to scenario 
classes, and their incorporation in the TSPA to assure completeness. 
A systematic method was applied to identify and screen FEPs for the EBS process models. The 
FEPs have been identified and grouped into two broad categories of primary and secondary 
FEPs. The primary FEPs capture the issues associated with the secondary FEPs. The FEPs are 
further divided into included and excluded FEPs. Included FEPs are those directly 
represented in TSPA models and process models that support the TSPA. Analyses have focused 
on the identification and screening of FEPs; this work partially addresses this subissue.

 5-1 
5. SUMMARY AND CONCLUSIONS 
5.1 INTEGRATED EFFECTS OF THE ENGINEERED BARRIER SYSTEM 
The postclosure evolution of environmental conditions within the emplacement drift is the result 
of complex interactions of the engineered system with the surrounding host rock, including its 
contained fluids. In this context, engineered system includes the potential repository layout, 
the thermal management strategy, the design of physical components (waste packages, drip 
shields, supports, etc.) and the choice of materials and fabrication methods. 
Waste package surface temperature is one example of post-closure environmental conditions. 
Within a few years of closure, WP surface temperatures reach peak values and then begin to 
decline. The magnitude of this peak and its timing depend upon the WP location within the 
repository, the thermal-hydrologic properties of the host rock and the engineered materials, the 
duration and intensity of ventilation, the spacing between WPs and between drifts, and the WP 
thermal power decay curve. The Multiscale TH Model accounts approximately for the effects of 
all these on WP temperature, and also incorporates the effect of changes in infiltration flux 
estimated to occur as the climate changes over the next 10,000 years. The parameters subject to 
engineering and operating control are the drift and WP spacing, thermal management strategy 
(such as blending or aging the waste and ventilating the drifts after emplacement), and the 
thermal-hydrologic properties of the materials within the drift (particularly the presence or 
absence of backfill). 
This emphasizes the fact that the integrated effects of the EBS depend strongly on design details, 
and the results documented in this PMR are strictly valid only for the EDA II conceptual design. 
However, the collection of analyses and models presented here is flexible enough to assess the 
effects of different designs and operating practices on the performance of a potential repository. 
As this report entered its final draft stage, the design was modified to eliminate backfill. Change 
requests were initiated in January 2000 to remove backfill from the reference design and to 
change the emplacement drift orientation to minimize the effects of rockfall. Many of the 
quantitative results developed in the supporting AMRs will change as a result. However, it is 
expected that detailed analyses of the impact of removing backfill, coupled with detailed design 
of the EBS, will produce a system with performance equal to or better than the EDA II 
conceptual design. 
The potential for galvanic coupling and, consequently, accelerated corrosion rates of some of the 
metallic components of the EBS are under consideration. As documented in Section 3.1.2.3, a 
wide variety of alloys will be used in the system, all thermodynamically unstable, and spanning a 
wide range of reactivity. Galvanic effects are to be evaluated before final material selections are 
made. 
5.2 NATURAL AND ENGINEERED ANALOGS 
Analogs have limited application for the EBS. Many of the engineered materials have been 
manufactured for only a few decades or less, and there are no directly relevant observations on 
the longevity of, say, titanium drip shields exposed to conditions anticipated to occur in the 
potential repository over the next 10,000 years.

 5-2 
Consequently, direct measurement of material properties and the integrated behavior of EBS 
components provide the principal means of developing and testing these process models. 
Specific examples of such tests and experiments are: 
 Field-scale thermal tests are instrumental in building confidence in the TH models, 
which are used in Sections 3.1.1, 3.1.2.1, and 3.1.4. Laboratory-measured properties 
(heat capacitance, rock density, thermal conductivity, porosity, permeability, 
van Genuchten parameters of imbibition behavior) are used in all of these models. 
Water samples from the SHT and DST have been analyzed and are found to be similar 
to J-13 water. 
 The cement mineral assemblage adopted in Section 3.1.2.3 is based on observations 
documented in the engineering literature. 
 Direct laboratory testing is relied on to establish limiting conditions for microbial 
growth and activity in the host rock, as discussed in Section 3.1.2.4. 
 Direct laboratory testing of precipitates formed on evaporation of simulated J-13 water 
and matrix porewater, is used to establish normative mineral assemblages, and as 
validation for the extended Pitzer model. 
However, analogs have been used when available. As noted in a number of places in 
Section 3.1.2, the use of J-13 water as an analog for water percolating through the fractures is 
commonplace in most of the chemical modeling. Another use of analogs is in the application of 
the microbial communities model to Rainier Mesa, which is in many ways an analog to Yucca 
Mountain under the wetter climatic conditions expected to commence in another few hundred 
years. Specific examples of the use of analogs in the EBS PMR are given below: 
 Section 3.1.2.2 uses the behavior of radiocarbon at ambient conditions, as an analog for 
the transport of CO2 and other gases during the thermal period and after cooldown. 
This model corroborates other approaches for predicting gas-phase composition, 
including the air mass-fraction approach and reactive transport simulations of the host 
rock. 
 Section 3.1.2.4 relies on analogs to specify the behavior of microbes--the potential for 
growth and activity--at extreme environmental conditions. Specifically, the 
requirements that T < 120C and RH > 0.9, or RH > 0.75 for halophiles, or RH > 0.55 
for fungi, are derived from the microbiology literature. Also, field samples from the 
ESF and Rainier Mesa have been evaluated to determine microbial abundance. 
 Section 3.1.2.3 cites the Corrosion Products AMR, which heavily relies on the 
inorganic chemistry literature to describe the behavior of metals under conditions 
representative of the repository. 
 Section 3.1.2.5 supports the use of J-13 water as an analog for fracture waters in the 
host rock. Notwithstanding occurrence of matrix porewater that differs in composition 
from J-13 water, the fact that EQ3/6 correctly predicts the composition of J-13 water

 5-3 
based on a straightforward conceptual model, supports the use of J-13 composition to 
represent mobile water in fractures of the UZ. Perched waters from the site resemble 
J-13 water, and are also analogs for mobile fracture waters. 
 Section 3.1.2.6 uses observations of colloid size and abundance in natural 
groundwaters near Yucca Mountain, as analogs for use in the EBS Colloids Model. 
Steel in the EBS is identified as a potentially prolific source of colloids, analogous to 
observations of colloidal iron in nature (the corresponding possibility of acidification is 
not addressed in any of the EBS models, but is addressed in crevice corrosion models). 
5.3 SUMMARY OF RESULTS AND CONCLUSIONS FROM THE MAJOR 
ANALYSIS/MODEL REPORTS 
All of the following conclusions are based on the EDA II design, which includes engineered 
backfill. As noted above, a design change initiated in January 2000 requires the removal of 
backfill, and the selection of an emplacement drift orientation that minimizes the size of the 
largest key blocks that could fall on the drip shields. The change in drift orientation, coupled 
with a sufficiently robust drip shield system, is expected to adequately protect the WPs from 
mechanical degradation. 
Analyses and calculations performed for six of the AMRs supporting the EBS PMR are currently 
being revised. Since the EBS is not a principal factor in the Repository Safety Strategy 
(CRWMS M&O 2000al), the ultimate impact on total system performance is not expected to be 
significant. 
5.3.1 Water Distribution and Removal 
The following points summarize the important results and conclusions from the Water 
Distribution and Removal Model (CRWMS M&O 2000q): 
 Flow modeling of the EBS and the surrounding host rock, using capillary properties of 
the backfill combined with fracture parameters from the Mountain-Scale Coupled 
Processes (TH) Models (CRWMS M&O 2000aj), predicts that the backfill tends 
toward capillary equilibrium with the fractures as the host rock temperature and water 
content return to pre-emplacement values. The water saturation in the backfill 
ultimately reaches 30 to 40 percent with the estimated glacial infiltration flux of 42 
mm/year at the location modeled. 
 Thermal effects on the flow distribution and capillary pressure levels are almost 
completely dissipated by 1000 years after closure. 
 Potential impact of plugging fractures beneath the emplacement drift was investigated 
by a bounding analysis. As might be expected, if fractures plug, the saturation in the 
invert would increase to nearly 100 percent for glacial infiltration flux values. 
 Although not part of the baseline design, the model results show that engineered 
drainage features could maintain low moisture content in the invert if the fractures

 5-4 
were to plug. Also, such features could reduce liquid water flux through the invert by 
as much as 4 orders of magnitude, relative to natural drainage, even if there were no 
fracture plugging. Both of these conclusions depend on engineering the features to 
assure their intersection with high-permeability connected fractures. 
 A bounding analysis of the diversion capacity of the drip shield covered by capillary 
backfill shows that leakage flux at the drip shield joints should not exceed 10 percent 
of the total flux through the backfill. 
 Calculations described in this report indicate that condensation beneath the drip shield 
is unlikely, except possibly for conditions of high invert saturation. This is a 
preliminary finding, but is consistent with limited experimental data from quarter-scale 
experiments in progress. Condensation under the drip shield requires that the vapor 
pressure at the surface of the drip shield exceed the saturated vapor pressure at the drip 
shield temperature. The water vapor pressure in the air space under the drip shield will 
tend to be uniform (especially before the onset of condensation) because of gaseous 
diffusion and circulation. Hydrologic conditions in the invert can control the water 
vapor pressure. During the gradual cooldown process, the humidity in the air space 
under the drip shield will be in thermodynamic equilibrium with the invert. If the 
invert saturation is great enough, condensation on the underside of the drip shield can 
occur, but if the invert is dry enough, condensation will not occur. The possibility of 
condensation is thus controlled by factors such as seepage into the drift, which could 
increase the invert saturation. The foregoing explanation has not considered mass 
exchange between the gas-phase under the drip shield, and the gas-phase outside the 
drip shield. However, the drift wall will generally be cooler than the drip shield or the 
invert, so mass exchange would tend to decrease the humidity under the drip shield, 
and the potential for condensation. 
 The drift-degradation analysis (CRWMS M&O 2000ad) indicates that the combination 
of time-dependent reduction in joint cohesion, thermal stresses, and seismic events will 
produce rockfall in less than 2.5 percent of the total length of emplacement drifts. This 
analysis assumes that the ground system is not effective after closure. 
 The calculated percentage (from the Ventilation Model, CRWMS M&O 2000an) of 
decay heat removed at 10 cms is 68 percent after 50 yr, 73 percent after 100 yr, and 77 
percent after 200 yr. At 15 cms, the corresponding percentages were 74, 78, and 82 
percent, respectively. Based on these results it is technically feasible to remove 70 
percent of the heat from the emplacement drifts, throughout the 50-yr preclosure 
period.

 5-5 
5.3.2 Physical and Chemical Environment 
The following points summarize the important results and conclusions from the EBS Physical 
and Chemical Environment Model (CRWMS M&O 2000t), arranged by its submodels: 
5.3.2.1 Thermal-Hydrology 
 Location (center vs. edge) and the local infiltration flux (and its variation with time 
from the climate model) are the primary factors that determine peak temperatures, 
temperature history, humidity, and the potential for seepage and evaporation in the 
drifts. 
 The minimum air mass-fraction is approximately 103 under conditions of maximum 
thermal output and maximum infiltration flux. This is based on 2-D modeling which is 
inherently conservative; the minimum air mass-fraction may be greater. Comparison 
with similar estimates developed by other models shows that there is approximately 
one order of magnitude uncertainty on this estimate. 
 Evaporation tends to be localized to a thin zone that encompasses the dryout zone, and 
that recedes toward the drip shield surface with time, as the thermal source-strength 
decays. Thus there is the potential for accumulation and refluxing of solutes from the 
host rock in to the drifts. 
 Substantial accumulation of soluble salts may occur from evaporation, and the zones 
need not be dry for this to occur. Because of the timing of salt accumulation, there is 
the potential for aqueous corrosion conditions to occur at temperatures up to 
approximately 120C, because saturated brines can begin to form when the relative 
humidity increases to 50 percent. 
 There is less potential for the accumulation of soluble salts at repository-edge locations 
than at central locations because there is less heat available for evaporation. 
 There is greater potential for solute accumulation in the invert than elsewhere in the 
EBS, because the invert temperature is always higher during cooldown. 
5.3.2.2 Gas Flux and Fugacity 
 The broader pillars in the EDA II design, relative to previous designs, permit a slight 
circulation, whereby the gas-phase mass flux near the centers of the pillars is directed 
downward. The magnitude of the downward flux is much smaller than the upward flux 
near the drifts, but it probably results in mixing of air, which increases the minimum air 
mass-fraction significantly. The result is that calculated minimum fugacities for CO2 
and O2 are increased, compared to calculated values for previous repository design 
concepts (e.g. VA design). 
 Evaluation of ambient radiocarbon distribution in the UZ has shown that there is a 
substantial flux of CO2 (e.g., 586 mg CO2/yr/m2 at borehole SD-12) into the UZ from

 5-6 
the near-surface soil zone. It is inferred that this flux is carried by recharge water 
percolation, and by gas-phase dispersive transport in response to barometric 
fluctuations at the surface. Using estimates for liquid recharge flux and dissolved 
inorganic carbon concentration, gas-phase mass transfer is inferred to provide 299 mg 
CO2/yr/m2 to the UZ above the Calico Hills unit. This transfer is much greater than 
could be provided by molecular diffusion, which implies that advective-dispersive 
processes are active. 
5.3.2.3 Introduced Materials 
 Chemical modeling shows that the composition of evaporated seepage water is 
completely or nearly saturated with respect to quartz when it contacts the backfill. 
Conditions for which quartz dissolution is predicted to be possible are unlikely, 
involving high temperature, low CO2 fugacity, and high seepage flow rates through the 
drifts. 
 The calculations also show that significant porosity reduction in quartz-sand backfill is 
unlikely unless a high rate of seepage is sustained, and evaporated in a small fraction of 
the backfill volume. 
 Steel present in the drifts will begin to corrode when humidity increases during 
cooldown. Corrosion test data show that the structural steel used for ground support, 
invert structural support, and rails will corrode much faster than the drip shield or 
waste package. No credit has been taken for the contribution of the ground support 
system to drift stability after closure. 
 Oxidation of carbon steel will be complete in a few tens to hundreds of years. The 
most important effects will be to consume oxygen in the environment, and produce 
iron corrosion products. Some of the corrosion product material will be in the form of 
colloidal particles with the potential to increase the transport of radionuclides. 
 The invert contains crushed tuff ballast material as well as carbon steel. The effects of 
this material on the chemistry of water will depend on the seepage flow rate. Low flow 
rates will increase the effects of chemical interaction with the tuff, and diminish the 
mobility of chemical species including radionuclides. Larger flow rates will cause 
chemical interactions with the water to be dominated by the host rock. Because the 
invert represents a small mass relative to the mass of other materials present, and 
because of compositional similarity between the invert and the host rock, it is 
concluded that the invert is not likely to exert a significant and permanent influence on 
the chemistry of seepage exiting the drift. 
5.3.2.4 Microbial Effects 
 Laboratory tests and modeling results show that microbial activity in the host rock is 
limited primarily by lack of moisture, and that phosphate is an important limiting 
nutrient. The waste package may not be subjected to MIC for as long as the drip shield 
prevents contact with seepage water, backfill, steel, and crushed tuff.

 5-7 
 Laboratory tests show that MIC can accelerate the corrosion rate for carbon steel 
similar to that intended for use in the EBS, by a factor of 6 or more. This will tend to 
enhance the effects of steel corrosion on the bulk chemical environment. 
 Modeling of microbial growth and activity using nutrient mass and free energy 
balance, and estimated degradation rates for introduced materials, shows that the total 
production of biomass is on the order of 10 g per meter of drift per year during the first 
10,000 years. Based on such a small generation rate, effects on the bulk chemical 
environment are probably negligible, but localized microbial activity could accelerate 
corrosion. 
5.3.2.5 Precipitates and Salts 
 Seepage into the drifts during the thermal period will tend to evaporate, and if the rate 
of evaporation is great enough, precipitates and salts will form. The nature of these 
solids is predicted using a normative model based on laboratory test data. At the final 
stages of evaporation, the gas-phase CO2 composition will determine whether 
carbonates or hydroxides are formed (e.g., thermonatrite or sodium hydroxide). 
However, the formation of either sodium or calcium hydroxide is considered unlikely 
because these precipitates would occur only at an improbably low value of CO2 
fugacity. 
 For J-13 water, highly alkaline conditions occur at late stages of evaporation. For 
waters containing more sulfate or chloride compared with bicarbonate, the pH remains 
near neutral during evaporation, but the salts produced (e.g., sodium chloride, calcite) 
are qualitatively similar. Alkaline conditions are assumed to be most corrosive for the 
drip shield and the waste package, so J-13 water is used as a reference composition. 
 Salts formed by evaporation of J-13 water tend to be deliquescent, i.e. they will absorb 
water from the air and dissolve, at relative humidity (RH) less than 100 percent. 
Therefore, the bounding condition for performance of the drip shield is the presence of 
saturated brines, which will contain nitrates for RH greater than 50 percent, and 
chlorides, sulfates, and carbonates as humidity increases. The duration of contact with 
brines will vary across the potential repository, depending on local thermal-hydrologic 
conditions. Approximate chemical models have been developed to describe the 
evolution of water composition in the EBS as the deliquescent salts dissolve, and liquid 
water reenters the drifts during the thermal period. 
5.3.2.6 Colloids 
 The presence of structural steel in the EBS environment ensures that ferric-oxide and 
-oxyhydroxide colloids will be present, in addition to colloids from the host rock 
contributed by seepage flow. The best available analogs for colloids that can be 
transported through the UZ at Yucca Mountain are provided by the distributions 
groundwater colloids sampled in saturated-zone boreholes.

 5-8 
 The affinity of ferric colloids for radionuclides has been tested in the laboratory, and is 
probably most important for radioelements such as Pu and Am. These elements have 
limited solubility, but high affinity, so sorption to colloids can produce a relatively 
large increase in mobility. Under certain conditions, sorption of Pu to hematite 
colloids is apparently irreversible, i.e., significant desorption is not observed in 
laboratory tests. 
 Based on analog data for colloid concentration, and laboratory data for radionuclide 
affinity, the total concentration for Pu in EBS waters could increase by an order of 
magnitude or more, depending on the sorptive distribution coefficient. 
5.3.2.7 Chemical Reference Model 
 The Chemical Reference Model does not simulate brines, so it cannot predict the full 
range of possible solution compositions in the drifts during the thermal period. 
However, brine compositions are described by the LRH Salts Model, and the HRH 
Salts Model (Section 3.1.2.5.3). 
 The calculations show that evaporatively concentrated waters, or waters redissolving 
salts, can have pH 11 or greater during the thermal period. After the precipitates and 
salts are completely redissolved, and even if evaporative concentration is limited, the 
pH may remain elevated, up to a value of approximately 10, because of decreased CO2 
availability. As cooldown progresses the pH may decrease to values in the range 8 to 
9. These results are based on the use of a sodium-bicarbonate water (i.e. J-13 water) as 
the far-field compositional boundary condition. 
 With elevated pH and ionic strength, there are commensurate increases in the 
concentrations of Na, K, Ca, Mg, chloride, sulfate, and carbonate. These results are 
sensitive to the CO2 fugacity. Evaluation of CO2 mass balance in the drifts plus the 
host rock and cement used in grouted rockbolts, shows that the CO2 demand can 
probably be met by the predicted available supply. The CO2 is stored in precipitates 
such as calcite and thermonatrite, and released on dissolution of those precipitates. 
Calcite will precipitate in the host rock above the potential repository, and pre-existing 
calcite in fractures will dissolve at cooler temperatures below the potential repository. 
This is equivalent to a shift in calcite abundance that favors the host rock above the 
drifts. 
 Quartz sand is relatively inert and thus tends to provide minimal chemical input to 
biotic and abiotic corrosion processes that could impact the drip shields, however, it 
does provide readily available sites for quartz precipitation from high-pH silica-bearing 
solutions. Quartz can act as a pH buffer, lowering pH when it dissolves, but the pH 
tends to further increase when quartz is precipitated. 
 The effects of cement grout that may be used for rockbolts in a portion of the potential 
repository are small, primarily because the grout has very low permeability. The 
amount of water that interacts with the grout will be limited, even if the grout degrades 
structurally. The composition of cement leachate will be similar to evaporatively

 5-9 
concentrated waters that are predicted to result from heating. Mixing of the cement 
leachate with other seepage, and interaction with backfill and CO2, will neutralize the 
impact of leachate on the bulk chemical environment. 
5.3.3 Radionuclide Transport 
 A model for aqueous diffusion coefficients in partially saturated invert ballast material 
indicates that diffusivity may be reduced by orders of magnitude below the 
corresponding value in free water, provided the water content can be maintained low 
enough. 
 Retardation by the invert will not significantly reduce long-term (e.g. 10,000 years and 
beyond) radionuclide release rates. The effect is to delay the breakthrough of 
radionuclide transport through the invert by up to a few thousand years. 
 The steady-state diffusive flux through the invert, in the absence of significant 
advective flow, could result in very low release rates. 
5.3.4 Thermohydrology 
 The Multiscale Thermohydrologic Model (CRWMS M&O 2000i) calculates the key 
TH variables (liquid flux, temperature, relative humidity, gas flux, air-mass fraction, 
and evaporation rate) as functions of time, in the host rock and the emplacement drifts. 
Predictions of in-drift response are discussed in this report, while host rock response is 
discussed in the Near-Field Environment Process Model Report (CRWMS M&O 
2000u). 
 Parameters that significantly affect TH behavior in the drifts include: spatial and 
temporal variability of percolation flux, uncertainty in percolation flux (represented by 
alternative infiltration distributions), uncertainty in hydrologic properties (also 
represented by alternative infiltration distributions), edge-cooling effects, dimensions 
and properties of the EBS components, variability of heat output among different types 
of waste packages, spatial variability in host rock thermal conductivity, and spatial 
variability in overburden thickness. 
 Heat loss at the edges of the potential repository is predicted to not significantly affect 
pre-closure temperatures. (The Multiscale Thermohydrologic Model (CRWMS M&O 
2000i) includes the effects of heat removal by ventilation, but not mass transport, 
which would tend to further dryout the host rock.) 
 Before closure, the maximum predicted waste package surface temperature is 110C. 
Peak post-closure WP temperature is predicted to be 305C (for the mean infiltration 
case) and 315C (for the low infiltration case). Peak temperatures are calculated to 
occur at 60 yr after emplacement. The difference in peak temperatures between the 
hottest and coolest waste packages is 42C.

 5-10 
 Peak post-closure temperatures on the lower drift wall are predicted to be 195C (for 
the mean flux case) and 205C (for the low flux case). Peak post-closure temperatures 
on the upper drift wall are predicted to be 125C (for the mean flux case) and 134C 
(for the low flux case). These peak temperatures are calculated to occur at 65 yr after 
emplacement. 
 After the initial heat-up stage during the preclosure period, the average RH on waste 
package surfaces is predicted to range from 45 to 75 percent. 
 The Multiscale Thermohydrologic Model (CRWMS M&O 2000i) predicts that the 
duration of RH reduction at the drift wall will be smaller close to the repository edge. 
Decreased RH will persist for 100 to 1000 years after emplacement for the mean and 
upper infiltration cases, and for approximately 200 to 2000 years, for the low 
infiltration case. 
 The predicted duration of RH reduction at the surface of the drip shield is relatively 
insensitive to edge effects (for the backfill case considered in this report). Eventually, 
RH on the drip shield will approach 100 percent as it equilibrates with the host rock. 
For the mean and upper infiltration cases, this is predicted to occur at approximately 
1000 to 2000 years after emplacement. For the low infiltration case, it is predicted to 
occur at approximately 3000 to 6000 years. 
 The predicted duration of RH reduction on the WP is much longer than the duration for 
the DS, because the WP will remain hotter than the DS long after the RH outside the 
drip shield approaches 100 percent. 
 Thermal-hydrologic behavior in the emplacement drifts will be strongly influenced by 
the hydrologic properties of the quartz sand backfill. During the early part of the 
preclosure period, the backfill will be dry. As the temperature at the drift wall declines 
below the boiling point, the TH models predict capillary flow of water from fractures 
in the host rock, into the backfill, at unsaturated conditions. This is predicted to occur 
even if liquid seepage at the rock roof is zero, or small. 
 Thermal refluxing, or the heat-pipe effect, will influence liquid flux in the 
emplacement drifts. This behavior is closely related to the capillary properties of the 
backfill, and will increase the liquid flux in the backfill and the cumulative extent of 
evaporation near the drip shield. The onset of evaporation at the surface of the drip 
shield will occur first at the repository edge and then proceed inward toward the center 
of the repository layout. 
 Another factor that will influence liquid-phase flux in the drift is focusing of flow in 
the backfill beside the drip shield. Depending on the geometry of the flow, the flux can 
be focused by a factor of four at this location, relative to the ambient percolation flux in 
the host rock.

 5-11 
 A comparison of the TH models presented in this report, and TH models presented in 
the Unsaturated Zone Flow and Transport Process Model Report (CRWMS M&O 
2000o), and the Near-Field Environment Process Model Report (CRWMS M&O 
2000u), is provided in Section 3.1.1. The modeling approaches and key inputs are 
compared in Table 3-B. Direct comparison of temperature and air-mass fraction 
calculated at the drift crown, for a repository-center location using 2-D TH models, is 
shown in Figures 3-B and 3-C, respectively. 
 The TH model results are closely comparable. The medium properties and boundary 
conditions used by the models are very similar, or identical. The most sensitive 
parameter is the infiltration flux, which controls the percolation flux in the host rock. 
For example, the models calculated for the Physical and Chemical 
Environment/Chemical Reference Model (Section 3.1.2.1), using the upper and lower 
infiltration distributions, tend to bound the temperature and RH results for the other 
models. These results are very similar to the upper and lower infiltration results 
calculated by the Multiscale TH Model, for the same location. Where different 
simulation codes were used (i.e. NUFT and TOUGH2; Table 3-A), similar results are 
obtained, as expected. 
5.4 GENERAL CONCLUSIONS OF THE EBS DEGRADATION, FLOW, AND 
TRANSPORT PROCESS MODEL REPORT 
This report demonstrates that EBS performance is sufficiently well understood to support 
reasonable predictions of the environmental conditions at the drip shields and waste packages, 
and of conditions that will affect radionuclide transport in the emplacement drifts. Confidence 
has been increased through the use of available field and laboratory test data, and bounding 
models, to address predictive uncertainty. 
Process model uncertainties are identified in this report, and alternative models are discussed. 
Validation is addressed throughout the discussion of process model, with emphasis on 
comparison of model results to test data, and to analogs where such information is available. 
Where appropriate, collection of data that could result in further model improvement, is 
discussed in the text. Process model uncertainties are appropriately represented in the 
approaches to abstraction of model results for TSPA. 
This document may be affected by technical product input information that requires 
confirmation. Any changes to the document that may occur as a result of completing the 
confirmation activities will be reflected in subsequent revisions. The status of the input 
information quality may be confirmed by review of the Document Input Reference System 
database.

 6-1 
6. REFERENCES 
6.1 DOCUMENTS CITED 
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Bingham, F.W.; and Robey, T.H. 1992. TSPA 1991: An Initial Total-System Performance 
Assessment for Yucca Mountain. SAND91-2795. Albuquerque, New Mexico: Sandia National 
Laboratories. ACC: NNA.19920630.0033. 
Budnitz, B.; Ewing, R.C.; Moeller, D.W.; Payer, J.; Whipple, C.; and Witherspoon, P.A. 1999. 
Peer Review of the Total System Performance Assessment-Viability Assessment Final Report. 
Las Vegas, Nevada: Total System Performance Assessment Peer Review Panel. ACC: 
MOL.19990317.0328. 
Codell, R.B. and Murphy, W.M. 1992. Geochemical Model for 14C Transport in Unsaturated 
Rock. High Level Radioactive Waste Management, Proceedings of the Third International 
Conference, Las Vegas, Nevada, April 12-16, 1992. La Grange Park, Illinois: American 
Nuclear Society. Pp. 1959-1965. TIC: 204231. 
Cohon, J.L. 1999. Comments on the Scientific Program, June 1999 Nuclear Waste Technical 
Review Board Meeting. "Letter from J.L. Cohon (NWTRB) to L.H. Barrett (OCRWM), 
August 3, 1999." ACC: MOL.20000317.0405. 
Conca, J.L. and Wright, J. 1992. "Diffusion and Flow in Gravel, Soil, and Whole Rock." 
Applied Hydrogeology, 1, 5-24. Hanover, Germany: Verlag Heinz Heise GmbH. TIC: 224081. 
CRWMS M&O 1994. Total System Performance Assessment - 1993: An Evaluation of the 
Potential Yucca Mountain Repository. B00000000-01717-2200-00099 REV 01. Las Vegas, 
Nevada: CRWMS M&O. ACC: NNA.19940406.0158. 
CRWMS M&O 1995. Total System Performance Assessment - 1995: An Evaluation of the 
Potential Yucca Mountain Repository. B00000000-01717-2200-00136 REV 01. Las Vegas, 
Nevada: CRWMS M&O. ACC: MOL.19960724.0188. 
CRWMS M&O 1996. Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada. 
BA0000000-01717-2200-00082 REV 0. Las Vegas, Nevada: CRWMS M&O. ACC: 
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Results. B00000000-01717-2200-00188. Las Vegas, Nevada: CRWMS M&O. ACC: 
MOL.19980612.0027. 
CRWMS M&O 1998a. Not Used. 
CRWMS M&O 1998b. Not used.

 6-2 
CRWMS M&O 1998c. "Waste Package Degradation Modeling and Abstraction." Chapter 5 of 
Total System Performance Assessment-Viability Assessment (TSPA-VA) Analyses Technical 
Basis Document. B00000000-01717-4301-00005 REV 01. Las Vegas, Nevada: CRWMS 
M&O. ACC: MOL.19981008.0005. 
CRWMS M&O 1998d. "Near-Field Geochemical Environment." Chapter 4 of Total System 
Performance Assessment-Viability Assessment (TSPA-VA) Analyses Technical Basis 
Document. B00000000-01717-4301-00004 REV 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19981008.0004. 
CRWMS M&O 1998e. "Waste Form Degradation, Radionuclide Mobilization, and Transport 
Through the Engineered Barrier System." Chapter 6 of Total System Performance Assessment- 
Viability Assessment (TSPA-VA) Analyses Technical Basis Document. B00000000-01717- 
4301-00006 REV 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19981008.0006. 
CRWMS M&O 1998f. Not used. 
CRWMS M&O 1998g. "Thermal Hydrology." Chapter 3 of Total System Performance 
Assessment-Viability Assessment (TSPA-VA) Analyses Technical Basis Document. 
B00000000-01717-4301-00003 REV 01. Las Vegas, Nevada: CRWMS M&O. ACC: 
MOL.19981008.0003. 
CRWMS M&O 1999a. Engineered Barrier System Performance Modeling 
(WP#12012383MX). Activity Evaluation, July 12, 1999. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19990719.0317. 
CRWMS M&O 1999b. Uncanistered Spent Nuclear Fuel Disposal Container System 
Description Document. SDD-UDC-SE-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19991217.0512. 
CRWMS M&O 1999c. Development Plan for the Engineered Barrier System Degradation, 
Flow, and Transport Process Model Report. TDP-EBS-MD-000029 REV 00. Las Vegas, 
Nevada: CRWMS M&O. ACC: MOL.19991025.0033. 
CRWMS M&O 1999d. License Application Design Selection Report. B00000000-01717- 
4600-00123 REV 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990528.0303. 
CRWMS M&O 1999e. Not used. 
CRWMS M&O 1999f. Not used. 
CRWMS M&O 1999g. In Drift Corrosion Products. ANL-EBS-MD-000041 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.20000106.0438. 
CRWMS M&O 2000a. EBS Radionuclide Transport Abstraction. ANL-WIS-PA-000001 REV 
00 ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0459.

 6-3 
CRWMS M&O 2000b. EBS Radionuclide Transport Model. ANL-EBS-MD-000034 REV 00 
ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0460. 
CRWMS M&O 2000c. Engineered Barrier System Features, Events, and Processes and 
Degradation Modes Analysis. ANL-EBS-MD-000035 REV 00 ICN 01. Las Vegas, Nevada: 
CRWMS M&O. Submit to RPC URN-0468. 
CRWMS M&O 2000d. In-Drift Colloids and Concentrations. ANL-EBS-MD-000042 REV 
00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000509.0242. 
CRWMS M&O 2000e. In-Drift Gas Flux and Composition. ANL-EBS-MD-000040 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000523.0154. 
CRWMS M&O 2000f. In Drift Microbial Communities. ANL-EBS-MD-000038 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.20000331.0661. 
CRWMS M&O 2000g. In-Drift Precipitates/Salts Analysis. ANL-EBS-MD-000045 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000512.0062. 
CRWMS M&O 2000h. Invert Diffusion Properties Model. ANL-EBS-MD-000031 REV 01. 
Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0461. 
CRWMS M&O 2000i. Multiscale Thermohydrologic Model. ANL-EBS-MD-000049 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000609.0267. 
CRWMS M&O 2000j. Physical and Chemical Environment Abstraction Model. ANL-EBSMD-
000046 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000523.0155. 
CRWMS M&O 2000k. Environment on the Surfaces of the Drip Shield and Waste Package 
Outer Barrier. ANL-EBS-MD-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: 
MOL.20000328.0590. 
CRWMS M&O 2000l. Seepage/Cement Interactions. ANL-EBS-MD-000043 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.20000317.0262. 
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Vegas, Nevada: CRWMS M&O. ACC: MOL.20000523.0156. 
CRWMS M&O 2000n. Waste Package Degradation Process Model Report. TDR-WIS-MD- 
000002 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000620.0346 
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MOL.20000629.0915. 
CRWMS M&O 2000p. Not used. 
CRWMS M&O 2000q. Water Distribution and Removal Model. ANL-EBS-MD-000032 REV 
00 ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0463.

 6-4 
CRWMS M&O 2000r. EBS FEPs/Degradation Modes Abstraction. ANL-WIS-PA-000002 
REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000525.0373. 
CRWMS M&O 2000s. Summary of In-Package Chemistry for Waste Forms. ANL-EBS-MD- 
000050 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000217.0217. 
CRWMS M&O 2000t. Physical and Chemical Environment Model. ANL-EBS-MD-000033 
REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0462. 
CRWMS M&O 2000u. Near-Field Environment Process Model Report. TDR-NBS-MD- 
000001 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0469. 
CRWMS M&O 2000v. Seepage/Backfill Interactions. ANL-EBS-MD-000039 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.20000509.0243. 
CRWMS M&O 2000w. Abstraction of NFE Drift Thermodynamic Environment and 
Percolation Flux. ANL-EBS-HS-000003 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: 
MOL.20000504.0296. 
CRWMS M&O 2000x. Drift-Scale Coupled Processes (DST and THC Seepage) Models. 
MDL-NBS-HS-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: 
MOL.19990721.0523. 
CRWMS M&O 2000y. In-Drift Thermal-Hydrological-Chemical Model. ANL-EBS-MD- 
000026 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000113.0488. 
CRWMS M&O 2000z. Waste Form Degradation Process Model Report. TDR-WIS-MD- 
000001 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0464. 
CRWMS M&O 2000aa. Not used. 
CRWMS M&O 2000ab. Saturated Zone Flow and Transport Process Model Report. TDRNBS-
HS-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000502.0238. 
CRWMS M&O 2000ac. Emplacement Drift System Description Document. SDD-EDS-SE- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000121.0119. 
CRWMS M&O 2000ad. Drift Degradation Analysis. ANL-EBS-MD-000027 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.20000107.0328. 
CRWMS M&O 2000ae. Water Diversion Model. ANL-EBS-MD-000028 REV00. Las Vegas, 
Nevada: CRWMS M&O. ACC: MOL.20000107.0329. 
CRWMS M&O 2000af. Water Drainage Model. ANL-EBS-MD-000029 REV 00. Las Vegas, 
Nevada: CRWMS M&O. ACC: MOL.20000117.0216. 
CRWMS M&O 2000ag. Invert Configuration and Drip Shield Interface. TDR-EDS-ST- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000505.0232.

 6-5 
CRWMS M&O 2000ah. Design Analysis for the Ex-Container Components. ANL-XCS-ME- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000525.0374. 
CRWMS M&O 2000ai. Drip Shield Emplacement Gantry Concept. ANL-XCS-ME-000002 
REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000418.0817. 
CRWMS M&O 2000aj. Mountain-Scale Coupled Processes (TH) Models. MDL-NBS-HS- 
000007 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0528. 
CRWMS M&O 2000ak. Calibrated Properties Model. MDL-NBS-HS-000003 REV 00. Las 
Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0520. 
CRWMS M&O 2000al. Repository Safety Strategy: Plan to Prepare the Postclosure Safety 
Case to Support Yucca Mountain Site Recommendation and Licensing Considerations. TDRWIS-
RL-000001 REV 03. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000119.0189. 
CRWMS M&O 2000am. Integrated Site Model Process Model Report. TDR-NBS-GS-000002 
REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000121.0116. 
CRWMS M&O 2000an. Ventilation Model. ANL-EBS-MD-000030 REV 00. Las Vegas, 
Nevada: CRWMS M&O. ACC: MOL.20000107.0330. 
CRWMS M&O 2000ao. Ground Control for Emplacement Drifts for SR. ANL-EBS-GE- 
000002 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000414.0875. 
DOE (U.S. Department of Energy) 1998a. Viability Assessment of a Repository at Yucca 
Mountain. DOE/RW-0508. Washington, D.C.: U.S. Department of Energy, Office of Civilian 
Radioactive Waste Management. ACC: MOL.19981007.0027; MOL.19981007.0028; 
MOL.19981007.0029; MOL.19981007.0030; MOL.19981007.0031; MOL.19981007.0032. 
DOE 1998b. Not used. 
DOE 1998c. Not used. 
DOE (U.S. Department of Energy) 2000. Quality Assurance Requirements and Description. 
DOE/RW-0333P, Rev. 10. Washington, D.C.: U.S. Department of Energy, Office of Civilian 
Radioactive Waste Management. ACC: MOL.20000427.0422. 
Hardin, E.L. 1998. Near-Field/Altered-Zone Models Report. UCRL-ID-129179. Livermore, 
California: Lawrence Livermore National Laboratory. ACC: MOL.19980630.0560. 
Harrar, J.E.; Carley, J.F.; Isherwood, W.F.; and Raber, E. 1990. Report of the Committee to 
Review the Use of J-13 Well Water in Nevada Nuclear Waste Storage Investigations. UCID- 
21867. Livermore, California: Lawrence Livermore National Laboratory. ACC: 
NNA.19910131.0274. 
Liu, H.H.; Doughty, C.; and Bodvarsson, G.S. 1998. "An Active Fracture Model for 
Unsaturated Flow and Transport in Fractured Rocks." Water Resources Research, 34, (10), 
2633-2646. Washington, D.C.: American Geophysical Union. TIC: 243012.

 6-6 
Middleman, S. 1995. Modeling Axisymmetric Flows, Dynamics of Films, Jets, and Drops. San 
Diego, California: Academic Press. TIC: 246835. 
Murphy, W.M. 1995. "Contributions of Thermodynamic and Mass Transport Modeling to 
Evaluation of Groundwater Flow and Groundwater Travel Time at Yucca Mountain, Nevada." 
Scientific Basis for Nuclear Waste Management XVIII, Symposium held October 23-27, 1994, 
Kyoto, Japan. Murakami, T. and Ewing, R.C., eds. 353, 419-426. Pittsburgh, Pennsylvania: 
Materials Research Society. TIC: 216341. 
NRC (U.S. Nuclear Regulatory Commission) 1998. Issue Resolution Status Report Key 
Technical Issue: Total System Performance Assessment and Integration. Rev. 1. Washington, 
D.C.: U.S. Nuclear Regulatory Commission. ACC: MOL.19990105.0083. 
NRC (U.S. Nuclear Regulatory Commission) 1999a. Issue Resolution Status Report Key 
Technical Issue: Container Life and Source Term. Rev. 2. Washington, D.C.: U.S. Nuclear 
Regulatory Commission. TIC: 245538. 
NRC (U.S. Nuclear Regulatory Commission) 1999b. Issue Resolution Status Report Key 
Technical Issue: Evolution of the Near-Field Environment. Rev. 2. Washington, D.C.: U.S. 
Nuclear Regulatory Commission. ACC: MOL.19990810.0640. 
NRC (U.S. Nuclear Regulatory Commission) 1999c. Issue Resolution Status Report Key 
Technical Issue: Repository Design and Thermal-Mechanical Effects. Rev. 02. Washington, 
D.C.: U.S. Nuclear Regulatory Commission. ACC: MOL.20000306.0670. 
NRC (U.S. Nuclear Regulatory Commission) 1999d. Issue Resolution Status Report Key 
Technical Issue: Thermal Effects on Flow. Rev. 2. Washington, D.C.: U.S. Nuclear Regulatory 
Commission. ACC: MOL.19991021.0156. 
Perry, R.H. and Chilton, C.H., eds. 1973. Chemical Engineers' Handbook. 5th Edition. New 
York, New York: McGraw-Hill. TIC: 242591. 
Rimstidt, J.D. and Barnes, H.L 1980. "The Kinetics of Silica-Water Reactions." Geochimica et 
Cosmochimica Acta, 44, 1683-1699. Oxford, England: Pergamon Press. TIC: 219975. 
Triay, I.; Degueldre, C.; Wistrom, A.; Cotter, C.; and Lemons, W. 1996. Progress Report on 
Colloid-Facilitated Transport at Yucca Mountain. Milestone 3383. Los Alamos, New Mexico: 
Los Alamos National Laboratory. ACC: MOL.19970616.0061. 
Wilder, D.G., ed. 1996. Near-Field and Altered-Zone Environment Report. UCRL-LR-124998. 
Volume II. Livermore, California: Lawrence Livermore National Laboratory. ACC: 
MOL.19961212.0121; MOL.19961212.0122. 
Wilkins, D.R. and Heath, C.A. 1999. "Direction to Transition to Enhanced Design Alternative 
II." Letter from Dr. D.R. Wilkins (CRWMS M&O) and Dr. C.A. Heath (CRWMS M&O) to 
Distribution, June 15, 1999, LV.NS.JLY.06/99-026, with enclosures, "Strategy for Baselining

 6-7 
EDA II Requirements" and "Guidelines for Implementation of EDA II." ACC: 
MOL.19990622.0126; MOL.19990622.0127; MOL.19990622.0128. 
Wilson, M.L.; Gauthier, J.H.; Barnard, R.W.; Barr, G.E.; Dockery, H.A.; Dunn, E.; Eaton, 
R.R.; Guerin, D.C.; Lu, N.; Martinez, M.J.; Nilson, R.; Rautman, C.A.; Robey, T.H.; Ross, B.; 
Ryder, E.E.; Schenker, A.R.; Shannon, S.A.; Skinner, L.H.; Halsey, W.G.; Gansemer, J.D.; 
Lewis, L.C.; Lamont, A.D.; Triay, I.R.; Meijer, A.; and Morris, D.E. 1994. Total-System 
Performance Assessment for Yucca Mountain  SNL Second Iteration (TSPA-1993). SAND93- 
2675. Executive Summary and two volumes. Albuquerque, New Mexico: Sandia National 
Laboratories. ACC: NNA.19940112.0123. 
YMP (Yucca Mountain Site Characterization Project) 2000. Q-List. YMP/90-55Q, Rev. 6. Las 
Vegas, Nevada: Yucca Mountain Site Characterization Office. ACC: MOL.20000510.0177. 
6.2 CODES, STANDARDS, REGULATIONS, AND PROCEDURES 
AP-2.13Q, Rev. 0, ICN 4. Technical Product Development Planning. Washington, D.C.: U.S. 
Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: MOL.20000620.0067. 
AP-2.16Q, Rev. 0. Activity Evaluation. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20000207.0716. 
AP-3.4Q, Rev. 1, ICN 3. Level 3 Change Control. Washington, D.C.: U.S. Department of 
Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000525.0376. 
AP-3.10Q, Rev. 2, ICN 2. Analyses and Models. Washington, D.C.: U.S. Department of 
Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000619.0576. 
AP-3.11Q, Rev. 1, ICN 1. Technical Reports. Washington, D.C.: U.S. Department of Energy, 
Office of Civilian Radioactive Waste Management. ACC: MOL.20000714.0549. 
AP-3.15Q, Rev. 1, ICN 2. Managing Technical Product Inputs. Washington, D.C.: U.S. 
Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: MOL.20000713.0363. 
AP-SI.1Q, Rev. 2, ICN 4. Software Management. Washington, D.C.: U.S. Department of 
Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000223.0508. 
QAP-2-0, Rev. 5. Conduct of Activities. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19980826.0209.

Appendix A 
EBS PMR/IRSR Acceptance Criteria Matrix (includes only those that apply) 
IRSR Container Life and Source Term (Revision 2) 
Subissue CLST All Subissues 
Acceptance Criteria Applicable to All Six Subissues 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 1 The collection and 
documentation of data, as well as development and 
documentation of analyses, methods, models, and 
codes, were accomplished under approved quality 
assurance and control procedures and standards. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
Acceptance Criteria 2 Expert elicitations, when used, 
were conducted and documented in accordance with 
the guidance provided in NUREG-1563 or other 
acceptable approaches. 
No expert elicitation was conducted for this PMR. 
Acceptance Criteria 3 Sufficient data (field, 
laboratory, and natural analog) are available to 
adequately define relevant parameters for the models 
used to evaluate performance aspects of the subissues. 
The EBS PMR uses a combination of field, laboratory, and natural analog data that can be broadly categorized 
into the geological, thermal, mechanical, hydrological, chemical and biological data of the NBS, and the 
geological, thermal, mechanical, hydrological, chemical and biological data of the EBS which consists of 
introduced materials such as grout, steel support, backfill and invert materials. For each of the supporting 
models presented, different data are used as input as documented in the respective AMRs (Table 1-1). In 
general the geological, thermal and hydrological data of the NBS and EBS support analysis of the flux of 
liquid water or water vapor to and from the drift such as in the Water Distribution and Removal Model or the 
Multiscale Model. Thermal and mechanical data of the NBS support the analysis of drift degradation. 
Biological data support analysis of microbial activity (Section 3.1.2). The chemical data of the groundwater, 
and its initial alteration due to evaporation leading to chemical precipitation and subsequent redissolution 
support the analysis of the formation of salts within the EBS, and the Chemical Summary Submodel (Section 
3.1.2). 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
A-1 

Subissue CLST All Subissues 
Acceptance Criteria Applicable to All Six Subissues 
Acceptance Criterion PMR Approach and Section Reference 
chemical effects on the alteration of groundwater. 
Acceptance Criteria 4 Sensitivity and uncertainty 
analyses (including consideration of alternative 
conceptual models) were used to determine whether 
additional data would be needed to better define 
ranges of input parameters. 
In general where assumptions have been used and documented in individual AMRs (Table 1-1) in the absence 
of data, sensitivity and uncertainty analyses have been performed to assess their impact and the need to collect 
additional data. Where parameters for stated assumptions are uncertain, and performance is sensitive to the 
parameter, laboratory scale and quarter scale testing has been identified to provide confirmation of stated 
assumptions. As an example, the analysis methods that have been developed by the YMP for evaluating 
thermal-hydrological effects for a porous media apply in a limited way to predicting heat and mass transfer 
through the EBS. Sensitivity analyses have been used (Section 3.1.1) to assess flow through the drip shield, 
and quarter scale and column tests are being performed to evaluate flow through the drip shield. As another 
example, the thermal-hydrological models were used to conduct sensitivity analyses for the potential for 
condensation under the drip shield for the repository environment which is also being tested at quarter scale. 
Acceptance Criteria 5 Parameter values, assumed 
ranges, test data, probability distributions, and 
bounding assumptions used in the models are 
technically defensible and can reasonably account for 
known uncertainties. 
In the preparation of the respective AMRs (Table 1-1) for the EBS PMR, assumptions for parameter values, 
assumed ranges, test data, probability distributions, and bounding assumptions are documented through 
applicable QA procedures. The basis for each assumption is stated, and the need for confirmation is identified. 
For example, in evaluating the performance of the drip shield, an assumption was made as to the occurrence 
based upon the parallel plate theory. 
Acceptance Criteria 6 Mathematical model limitations 
and uncertainties in modeling were defined and 
documented. 
Section 3.2.1 documents model uncertainties as they relate to the performance of the NBS and the EBS. While 
data have been developed for the NBS, model uncertainties of a conceptual nature as they relate to episodic 
flow through the PTn are documented. Model uncertainties associated with the EBS are also stated. In 
addition, model uncertainties are documented in each of the respective AMRs (Table 1-1). The Multiscale 
Thermohydrologic Model (Section 3.1.4) presents a large number of TH models that describe variable 
temperature, humidity, and flux conditions throughout the potential repository. It should be noted that EBS 
process models provide the basis for selecting robust designs for EBS performance and waste isolation in the 
face of model uncertainty. 
Acceptance Criteria 7 Primary and alternative 
modeling approaches consistent with available data 
and current scientific understanding were investigated 
and their results and limitations considered in 
evaluating the subissue. 
Section 3.1.2 addresses alternative models involving fully coupled THC. Such simulation methods can be 
applied as they become available, and as the required data, including numerical settings used to operate the 
simulation codes are qualified. The approach used in this PMR is applied to address conceptual issues and to 
evaluate bounding conditions for the performance of engineered barriers. 
Acceptance Criteria 8 Model outputs were validated 
through comparisons with outputs of detailed process 
models, empirical observations, or both. 
The validation of thermal-hydrological effects in the EBS is being evaluated through laboratory and quarter 
scale testing. Where information is currently available, experimental data and observations have been used for 
model validation. For example, the HRH salts model which is based upon an EQ3/E6 chemical equilibrium 
analysis was validated against evaporation tests with reasonable agreement between modeled and measured 
values. 
A-2 

Subissue CLST All Subissues 
Acceptance Criteria Applicable to All Six Subissues 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 9 The structure and organization 
of process and abstracted models were found to 
adequately incorporate important design features, 
physical phenomena, and coupled processes. 
The EBS process and abstracted models incorporate the important design features such as drip shield, backfill, 
grout and steel support. The EBS process models (Sections 3.1.1 through 3.1.4) account for the important 
physical phenomena and coupled processes. For example, the analysis of CO2 and O2 fugacity is based upon 
flux of recharge from TH modeling and analysis. 
Subissue CLST Subissue 1: The Effects of Corrosion Processes on the Lifetime of the 
Containers 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 2 
DOE has identified the broad range of environmental 
conditions within the WP emplacement drifts that may 
promote the corrosion processes listed previously, 
taking into account the possibility of irregular wet and 
dry cycles that may enhance the rate of container 
degradation. 
The models presented in Sections 3.1.1 through 3.1.4 consider the effects waste package heat generation in 
increasing temperature and evaporation within the EBS. For example, the Physical and Chemical Environment 
Model Section 3.1.4) initially develops a TH model calculation for estimating water fluxes during the thermal 
period. This information is used to evaluate gas flux during the thermal period, CO2 and O2 fugacity which in 
turn are used to estimate the evolution of leachate composition, and the formation of salts and precipitates in 
the backfill and on the drip shield. The models analyze for a wide variety of environmental conditions that can 
develop due to irregular wetting and drying. 
Subissue CLST Subissue 3: The Rate at Which Radionuclides in Spent Nuclear Fuel are 
Released from the Engineered Barrier Subsystem Through the Oxidation and 
Dissolution of Spent Fuel 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 1 DOE has considered all 
categories of SNF planned for disposal at the 
proposed YM repository. 
The EBS radionuclide transport model provides an analysis for a unit release of radionuclides due to a 
breached WP that can be applied to the radionuclide release from SNF. 
EBS PMR Section 3.1.3 
Acceptance Criteria 4 
DOE has identified and considered likely processes 
for SNF degradation and the release of radionuclides 
from the EBS, as follows: dissolution of the irradiated 
Note that most of the criteria apply to the waste package and waste form. The EBS Water Distribution and 
Removal, and Physical and Chemical Environment Models provide information on drip shield corrosion 
environment, and flow through the drip shield. 
A-3 

Subissue CLST Subissue 3: The Rate at Which Radionuclides in Spent Nuclear Fuel are 
Released from the Engineered Barrier Subsystem Through the Oxidation and 
Dissolution of Spent Fuel 
Acceptance Criterion PMR Approach and Section Reference 
UO2 matrix, with the consequent formation of 
secondary minerals and colloids; prompt release of 
radionuclides; degradation in the dry air environment; 
degradation and failure of fuel cladding; preferential 
dissolution of intermetallics in DOE SNF; and release 
of radionuclides from the WP emplacement drifts. 
EBS PMR Sections 3.1.3, 3.2.3.1.3,3.2.3.2.3, and 3.2.3.1.5 
Acceptance Criteria 5 
DOE has demonstrated that the numerical models 
used for SNF degradation and radionuclide release 
from the EBS are adequate representations, including 
consideration of uncertainties, of the expected SNF 
performance and are not likely to overestimate the 
actual performance in the repository environment. 
The WP PMR provide special studies that evaluate that evaluate for given WP environment the release of 
radionuclides from the waste form that allows an evaluation of SNF performance. 
Acceptance Criteria 7 DOE has justified the use of 
SNF test results not specifically collected for the YM 
site for the environmental conditions expected to 
prevail after breaching of the containers at the YM site. 
A bounding analysis for colloid transport is based upon colloid size distributions measured and reported in 
groundwater samples pumped from 18 wells in the vicinity of Yucca Mountain. 
Subissue CLST Subissue 4: The Rate at Which Radionuclides in High-Level Waste Glass are 
Released From the Engineered Barrier Subsystem 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 1 DOE has taken into account all 
types of HLW glass planned for YM disposal. 
The EBS Water Distribution and Removal Model provides a bounding analysis of the amount of water that 
would flow through backfill and drip shield and potentially contact waste packages. 
Acceptance Criteria 4 
DOE has identified and considered likely processes 
for the degradation of HLW glass and the release of 
radionuclides from the EBS, i.e., dissolution of the 
primary phase; formation of secondary minerals and 
Section 3.1.3 presents a general discussion of radionuclide release through the EBS. Microbial effects on are 
presented in EBS PMR Section 3.2.3.1.3. EBS PMR Sections 3.2.3.1.5 and 3.2.3.2.3 identify and consider the 
likely processes for the transport of colloids. 
A-4 

Subissue CLST Subissue 4: The Rate at Which Radionuclides in High-Level Waste Glass are 
Released From the Engineered Barrier Subsystem 
Acceptance Criterion PMR Approach and Section Reference 
colloids; microbial action; and radionuclide releases 
and transport from the WP emplacement drifts. 
Subissue CLST Subissue 6: The Effects of Alternate Engineered Barrier Subsystem Design 
Features on Container Lifetime and Radionuclide Release From the Engineered 
Barrier Subsystem. 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 1 
DOE has identified and considered the effects of 
backfill, and the timing of its emplacement, on the 
thermal loading of the repository, WP lifetime 
(including container corrosion and mechanical 
failure), and the release of radionuclides from the EBS. 
The EBS WD&R, the EBS P&CE, and the EBS Multiscale Models provide analyses incorporating the 
placement of backfill at the time of repository closure. Further, the models consider the efficiency of initial 
heat removal due to preclosure ventilation. 
EBS PMR Sections 3.1.1 and 3.1.3. 
Acceptance Criteria 4 
DOE has identified and considered the effects of drip 
shields (with backfill) on WP lifetime, including 
extension of the humid-air corrosion regime, 
environmental effects, breakdown of drip shields and 
resulting mechanical impacts on WP, the potential for 
crevice corrosion at the junction between the WP and 
the drip shield, and the potential for condensate 
formation and dripping on the underside of the shield. 
Studies are ongoing. The Water Distribution and Removal Model considers the flow performance of drip 
shield connectors. The WD&R (Section 3.1.1) considers the potential for condensation to form below the drip 
shield. The Multiscale model provides an analysis of the relative humidity surrounding the waste package that 
when coupled with corrosion data from the Waste Package model allows a determination of humid air 
corrosion. The interaction of flowing water with introduced materials including the grout, steel, and backfill is 
considered in the Physical and Chemical Environment Model. The Physical and Chemical Environment 
identifies the quantities of materials and their potential environmental effects on the EBS (Section 3.1.2). Note 
that crevice corrosion is addressed in the Waste Package PMR 
EBS PMR Sections 3.1.1, 3.1.2, and 3.1.4 
Acceptance Criteria 6 DOE has identified the 
chemical composition of the water in the environment 
surrounding the WPs and its evolution with time. 
Section 3.1.2 provides a Chemical Summary Submodel that integrates several submodels and describes the 
evolution of water composition and solid precipitates in the backfill above the drip shield, the invert, and the 
lower part of the backfill. Further, it evaluates CO2 mass balance in the drifts and the surrounding host rock as 
it evolves with time. The assessment includes the effects of carbon steel corrosion, leaching from cementitious 
materials, microbial processes, and colloidal processes on the bulk chemical environment. 
EBS PMR Section 3.1.2 
A-5 

Subissue CLST Subissue 6: The Effects of Alternate Engineered Barrier Subsystem Design 
Features on Container Lifetime and Radionuclide Release From the Engineered 
Barrier Subsystem. 
Acceptance Criterion PMR Approach and Section Reference 
Acceptance Criteria 7 DOE has justified the use of test 
results for drip shields, ceramic coatings, and backfill 
materials not specifically collected for the YM site for 
the environmental conditions expected to prevail at 
the proposed YM repository. 
The EBS process models that have been developed are based upon assumptions that require test results for 
model validation. The quarter and laboratory scale test results are justified for model validation for the 
performance of the drips shield and backfill system. 
Acceptance Criteria 8 DOE has conducted a 
consistent, sufficient, and suitable corrosion testing 
program at the time of LA submittal. In addition, 
DOE has identified specific plans for further testing to 
reduce any significant area(s) of uncertainty as part of 
the performance confirmation program. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
A-6 

IRSR Evolution of the Near Field Environment (Revision 2) 
Subissue ENFE Subissue 1: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Seepage and Flow 
Data and Model Justification for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 3 Sufficient data were collected on the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, to establish initial and boundary conditions 
for conceptual models and simulations of THC 
coupled processes that affect seepage and flow. 
The Physical and Chemical Environment identifies the quantities of materials and data needs for the 
degradation of cementitious materials such as grout, steel and backfill materials and their potential for 
alteration of the backfill and the near field environment (Section 3.1.2). The effects of the coupled THC 
processes on EBS flow is considered in the Water Distribution and Removal Model and Multiscale 
Thermodydrologic Model. The Water Distribution and Removal Model uses bounding assumptions in regards 
to the reduction in permeability of fractures in the floor and evaluates the effects of such alteration on seepage 
through the EBS.(Section 3.1.1) due to such degradation. 
EBS PMR Sections 3.1.1 and 3.1.2 
Integration for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 DOE considered all the relevant features, 
events, and processes. The abstracted models 
adequately incorporated important design features, 
physical phenomena, and couplings, and used 
consistent and appropriate assumptions throughout. 
The FEPs for the EBS are identified in Table 2-2. Specifically, the relevant FEPs that relate to flow through 
the EBS components relate to the FEP categories for the drip shield, the invert, sand drains, condensation 
below the drip shield, refluxing of flow, flow along the DS wall, movement of backfill through gaps and 
separations in the DS, and fluid flow into gaps and separations in the DS. The major features, events and 
processes involving flow through the backfill, DS, and invert are presented in each of the respective AMRs as 
summarized in Sections 3.1.1 through 3.1.4. In addition, for FEPs involving probabilistic events associated 
with the degradation of design features such as separation of drip shield, and backfill in contact with WP, 
additional analyses are provided in EBS PMR abstractions. 
Criterion 2 Models reasonably accounted for known 
temporal and spatial variations in conditions affecting 
coupled THC effects on seepage and flow. 
The EBS Multiscale Thermohydrologic Model accounts for temporal variations due to changes in waste 
package heat loading, and spatial variations in infiltration flux, and stratigraphy for various chimney locations 
in the repository. These variations are incorporated into the Multiscale Thermohydrologic Model and results in 
variations in predicted seepage into the EBS. 
EBS Section 3.1.4 
Criterion 3 Not all THC couplings may be determined 
to be important to performance, and DOE may adopt 
assumptions to simplify PA analyses. If potentially 
important couplings are neglected, DOE should 
provide a technical basis for doing so. The technical 
In each of the respective AMRs (Table 1-1), the assumptions supporting the AMR are documented. In those 
models where assumptions are made neglecting important couplings, the technical basis for each assumption is 
stated. For example, the effects of chemical precipitation of salts within the floor fractures was evaluated 
through sensitivity studies in the Water Distribution and Removal model by assuming the fractures are plugged 
as a bounding assumption instead of a detailed THC analysis involving chemical precipitation for fracture 
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Subissue ENFE Subissue 1: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Seepage and Flow 
Integration for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
basis can include activities such as independent 
modeling, laboratory or field data, or sensitivity 
studies. 
plugging. 
EBS Section 3.1.1 through 3.1.4 
Criterion 4 Where simplifications for modeling 
coupled THC effects on seepage and flow were used 
for PA analyses instead of detailed process models, 
the bases used for modeling assumptions and 
approximations were documented and justified. 
As discussed above, for each of the respective AMRs (Table 1-1) involving PA analyses and abstraction, the 
bases for modeling assumptions are stated. 
See EBS Section 3.1.1 through 3.1.4 
A-8 

Subissue ENFE Subissue 1: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Seepage and Flow 
Model Uncertainty for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Appropriate models, tests, and analyses 
were used that are sensitive to the THC couplings 
under consideration for both natural and engineering 
systems, as described in the following examples. The 
natural-setting data indicate processes that should be 
evaluated include: (i) zeolitization of volcanic glass, 
which could affect flow pathways; (ii) precipitation of 
calcite and opal on the footwall of fracture surfaces 
and the bottoms of lithophysal cavities, which 
indicates gravity-driven flow in open fractures that 
could affect permeability and porosity; and (iii) 
potential dehydration of zeolites and vitrophyre glass, 
which could release water affecting heat and fluid 
flow. The effects of THC coupled processes that may 
occur due to interactions with engineered materials or 
their alteration products include: (i) changes in water 
chemistry that may result from interactions between 
cementitious materials and groundwater, which, in 
turn, may affect seepage and flow; (ii) dissolution of 
the geologic barrier (e.g., tuff) by a hyperalkaline 
fluid that could lead to changes in the hydraulic 
properties of the geologic barrier; and (iii) 
precipitation of calcite or calcium-silica-hydrate 
phases along fracture surfaces as a result of migration 
of a hyperalkaline fluid that could affect hydraulic 
properties. 
The effects of THC coupled processes for EBS cementitious materials are analyzed by the cementitious 
materials submodel. This model (Section 3.1.2) develops reasonable bound estimates for the chemistry of the 
grout leachate. The altered groundwater chemistry is considered in the Chemical Summary Submodel (Section 
3.1.2.3.7) that considers the evolution of water composition and solid precipitates in the backfill above the drip 
shield, and the invert and lower part of the backfill for the reference EBS Physical and Chemical Environment 
Model. While a detailed evaluation has not been made for the precipitation of calcite or calcium-silicahydrate 
phases along fractures in the invert as a result of the hyperalkaline fluid, a bounding analysis 
appropriate for THC effects assuming the fractures were plugged was made in the Water Distribution and 
Removal Model (Section 3.1.1) with the resulting hydraulic conductivity of the fractures equal to the 
permeability of the matrix. 
Sections 3.1.1, 3.1.2 and Section 3.1.2.3.7 
Criterion 2 Given the current design of the repository, 
it will be acceptable to ignore the potential effects of 
microbial processes on seepage and flow. 
The growth of microbes is limited by water, and nutrients. Water is not available in the unsaturated zone to 
sustain growth that would alter porosity. 
EBS PMR 3.1.2.4 
Criterion 3 Alternative modeling approaches 
consistent with available data and current scientific 
understanding were investigated, and their results and 
limitations were appropriately considered. 
Sections 3.1.1 through 3.1.2 present alternative models for Water Distribution and Removal, Bulk Physical and 
Chemical Environment in the EBS, and Radionuclide Transport respectively. 
Criterion 4 DOE provided a reasonable description of In each of the respective AMRs in Table 1-1, the DOE provided descriptions of conceptual, and detailed 
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Subissue ENFE Subissue 1: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Seepage and Flow 
Model Uncertainty for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
the mathematical models included in its analyses of 
coupled THC effects on seepage and flow. The 
description included a discussion of alternative 
modeling approaches not considered in its final 
analysis and the limitations and uncertainties of the 
chosen model. 
models as required by AP-3.10Q that provide a reasonable description of modeling thermal-hydrologic 
phenomena for predicting seepage and flow in the EBS. With regards to the Water Distribution and Removal 
Model, the P&CE model, and the multiscale models that use NUFT. 
Model Verification for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 The mathematical models for coupled 
THC effects on seepage and flow were consistent with 
conceptual models based on inferences about the nearfield 
environment, field data and natural alteration 
observed at the site, and expected engineered 
materials. 
The Water Distribution and Removal Model, the P&CE Model, and the Multiscale Thermohydrologic Model 
provide predictions of seepage and flow that are based upon the selection of a consistent set thermal properties, 
and hydrologic properties for the active fracture model. The active fracture model, and the drift scale 
properties sets for these models are consistent with properties sets used in the UZ model which were 
determined by inverse modeling methods. All EBS models use a consistent set of thermal and hydrologic 
properties for the backfill, invert, and drip shield. 
Criterion 2 DOE appropriately adopted accepted and 
well-documented procedures to construct and test the 
numerical models used to simulate coupled THC 
effects on seepage and flow. 
The DOE used appropriate procedures to construct and test numerical models for predicting seepage and flow. 
For the case of the Water Distribution and Removal Model, the results of the NUFT calculations were 
compared to a closed form analytical solution for the prediction of fluxes in and near the EBS (CRWMS M&O 
2000q). The software codes and routines used for the models are subject to verification and testing under the 
procedure AP-SI.1Q. 
Criterion 3 Abstracted models for coupled THC 
effects on seepage and flow were based on the same 
assumptions and approximations shown to be 
appropriate for closely analogous natural or 
experimental systems. Abstracted model results were 
verified through comparison to outputs of detailed 
process models and empirical observations. 
Abstracted model results were compared with 
different mathematical models to judge robustness of 
results. 
The following discussion considers EBS flow. The current abstracted EBS flow model for the Physical and 
Chemical Model Abstraction relating to the WP environment is conceptual in nature. The model abstractions 
are based upon similar assumptions in that similar flow path components such as flow in and around the drip 
shield is identified in the process model abstraction (CRWMS M&O 2000j). In certain cases, the process 
model abstractions develop probabilistic analysis approaches that are more appropriately handled in TSPA 
studies. For example, a probabilistic analysis is developed for drip shield separation, and the potential contact 
of water with the waste package in the model abstraction. 
Since the abstracted flow model for the EBS Physical and Chemical Model Abstraction is conceptual 
(CRWMS M&O 2000j), no comparisons have been made between outputs, and the empirical observations such 
as are currently being made in the quarter scale tests. 
Since the abstracted flow model for the Physical and Chemical Model Abstraction is conceptual, abstracted 
model results have not been compared with different mathematical models to address the robustness of the 
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Subissue ENFE Subissue 1: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Seepage and Flow 
Model Verification for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
results. 
Programmatic for Subissue 1 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Data and models were collected, 
developed, and documented under acceptable quality 
assurance (QA) procedures. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models (Table 1-1), and use and validation of software is subject to the requirements of 
procedures developed to implement quality assurance program requirements. 
Criterion 2 Deficiency reports concerning data quality 
on issues related to coupled THC effects on seepage 
and flow were closed. 
The AMRs are prepared according to the procedure Analyses and Models, AP-3.10Q which was developed to 
address data deficiency and quality issues. At the current time, the data used for the analyses and models 
(Table 1-1) are obtained from controlled sources that are undergoing qualification, and will be closed after 
completion of data qualification activities. 
Criterion 3 If used, expert elicitations were conducted 
and documented in accordance with the guidance in 
NUREG-1563 (Kotra, et al., 1996) or other acceptable 
approaches. 
No expert elicitation was conducted for this PMR. 
Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Data and Model Justification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Available data relevant to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on WP chemical environment were 
considered. 
The P&CE Model is based upon a two dimensional thermal hydrologic analysis that accounts for temporal 
waste heat loading, and variations in percolation rates. The P&CE Model analyzes evolution of leachate 
composition from the grout and backfill for the EBS when contacted with J-13 groundwater. 
EBS PMR Section 3.1.2 and Section 3.2.3.1.3 
Criterion 2 DOE's evaluation of coupled THC 
processes properly considered site characteristics in 
The P&CE Model is based upon a two dimensional thermal hydrologic analysis that considers initial 
temperature and pressure boundary conditions. The P&CE Model considers initially the composition of J-13 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Data and Model Justification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
establishing initial and boundary conditions for 
conceptual models and simulations of coupled 
processes that may affect the WP chemical 
environment. 
groundwater that is used for developing a precipitates and salts normative submodel which is in turn used in 
the Chemical Summary submodel. 
EBS PMR Section 3.1.2 
Criterion 3 Sufficient data were collected on the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, to establish initial and boundary conditions 
for conceptual models and simulations of THC 
coupled processes that affect the WP chemical 
environment. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), the 
potential for condensation below the drip shield (Section 3.1.1) and chemical effects such as the alteration of 
groundwater chemistry (Section 3.1.2). 
EBS PMR Sections 3.1.1 and 3.1.2 
Criterion 4 A nutrient and energy inventory 
calculation (e.g., McKinley, West, and Grogan, 1985; 
Grogan and McKinley, 1990; Noy, et al., 1996) was 
used to determine the potential for microbial activity 
that could impact the WP chemical environment. 
The EBS Physical and Chemical Model Environments consider these effects on the growth of microbial 
communities. The Microbial communities model considers steel alloys, and organic substances on the 
microbial growth rate. Further, the model is implemented with the MING V1.0 modeling code that combines 
the nutrient and thermodynamic approaches. The model assumes that all usable energy for microorganisms is 
derived from oxidation reduction (redox) reactions. 
EBS PMR Sections 3.1.2 and 3.2.3.1.3 
Criterion 5 Should microbial activity be sufficient to 
allow microbial influenced corrosion (MIC) of the 
WP, then the time-history of temperature, humidity, 
and dripping should be used to constrain the 
probability for MIC. 
The EBS P&CE Environment Model provides an analysis of the effects of temperature, humidity, and dripping 
on the growth of microbial communities. The Microbial Communities Model considers the relative humidity 
which in turn depends on the temperature and dripping environment. The model considers how temperature, 
humidity, and dripping constrain microbial growth such as dryout of the EBS and high temperatures during the 
thermal period. 
Section 3.1.2 and 3.2.3.1.3 
Criterion 6 Sensitivity and uncertainty analyses 
(including consideration of alternative conceptual 
models) were used to determine whether additional 
new data are needed to better define ranges of input 
parameters. 
In general where assumptions have been used and documented in individual AMRs (Table 1-1) in the absence 
of data, sensitivity and uncertainty analyses have been performed to assess their impact and the need to collect 
additional data. Where parameters for stated assumptions are uncertain, and performance is sensitive to the 
parameter, laboratory scale testing has been identified to provide confirmation of stated assumptions. As an 
example, EBS PMR Section 3.1.2 
Criterion 7 If the testing program for coupled THC 
processes on WP chemical environment is not 
complete at the time of license application, or if 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Data and Model Justification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
sensitivity and uncertainty analyses indicate 
additional data are needed, DOE has identified 
specific plans to acquire the necessary information as 
part of the performance confirmation program. 
Data Uncertainty and Verification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Reasonable or conservative ranges of 
parameters or functional relations were used to 
determine effects of coupled THC processes on the 
WP chemical environment. Parameter values, 
assumed ranges, probability distributions, and 
bounding assumptions were technically defensible and 
reasonably accounted for uncertainties. 
In the preparation of the respective AMRs (Table 1-1) for the EBS PMR, assumptions for parameter values, 
assumed ranges, test data, probability distributions, and bounding assumptions are documented through the AP- 
3.10Q procedure. The basis for each assumption is stated, and the need for confirmation is identified. 
Criterion 2 Uncertainty in data due to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on WP chemical environment were 
considered. 
Section 3.2.1 documents model uncertainties as they relate to the performance of the NBS and the EBS. While 
data have been developed for the NBS, model uncertainties of a conceptual nature as they relate to episodic 
flow through the PTn nonwelded tuff are documented. Model uncertainties associated with the EBS are also 
stated. In addition, model uncertainties are documented in each of the respective AMRs (Table 1-1). For 
example as discussed in Section 3.1.4, the Multiscale Thermohydrologic Model presents a large number of TH 
models that describe variable temperature, humidity, and flux conditions throughout the potential repository. 
It should be noted that EBS process models provide the basis for selecting robust designs for EBS performance 
and waste isolation in the face of model uncertainty. 
Criterion 3 DOE's evaluation of coupled THC 
processes properly considered the uncertainties in the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, in establishing initial and boundary 
conditions for conceptual models and simulations of 
THC coupled processes that affect the WP chemical 
environment. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
chemical effects such as the alteration of groundwater chemistry (Section 3.1.4). 
EBS PMR Section 3.1.2 
Criterion 4 The initial conditions, boundary 
conditions, and computational domain used in 
sensitivity analyses involving coupled THC effects on 
The EBS TH submodel used in the P&CE model are based upon initial conditions boundary conditions, and 
computational domains consistent with site characteristics. The thermal hydrology models used in Sections 
3.1.1 through 3.1.4 are based upon the selection of NBS hydrologic and thermal properties used in the UZ 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Data Uncertainty and Verification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
WP chemical environment were consistent with 
available data. 
Process Model. The initial conditions, and boundary conditions for the models for specific locations use the 
same infiltration rates, and temperature and pressure boundary conditions consistent with the UZ Process 
Model (Section 3.1.4) 
Further, the submodels used for evaluating CO2 and O2 gas fugacity is consistent with available data from 
borehole SD 12 (Section 3.1.2). The submodels used for evaluating precipitates, and salts, and alteration of 
groundwater consistently use the J-13 groundwater chemistry as input. 
EBS PMR Sections 3.1.1 through 3.1.4 
Criterion 5 DOE's performance confirmation program 
will assess whether the natural system and engineered 
materials are functioning as intended and anticipated 
with regard to coupled THC effects on WP chemical 
environment. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
Integration for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 DOE has considered all the relevant 
features, events, and processes. The abstracted 
models adequately incorporated important design 
features, physical phenomena, and couplings, and 
used consistent and appropriate assumptions 
throughout. 
Important features, events, and processes are identified in EBS PMR Section 2.4.1. 
The FEPs for the EBS are identified in Table 2-2. Specifically, the relevant FEPs that relate to Thermal- 
Hydrologic-Chemical Processes on the Waste Package Chemical Environment Release are addressed in the 
microbial activity Energy /Nutrient Balance Microbial Model (Section 3.1.2) The Cementitious Materials 
Submodel addresses the alteration of infiltrate chemistry due to physical and chemical properties of the EBS. 
as summarized in Sections 3.1.1 through 3.1.4. 
See EBS PMR Section 2.4.1 
Criterion 2 Models reasonably accounted for known 
temporal and spatial variations in conditions affecting 
coupled THC effects on WP chemical environment. 
The EBS P&CE Model is based upon the thermal hydrology that accounts for thermal refluxing. 
EBS PMR Section 3.1.2 
Criterion 3 Not all THC couplings may be determined 
to be important to performance, and DOE may adopt 
assumptions to simplify performance assessment 
analyses. If potentially important couplings are 
In each of the respective AMRs (Table 1-1), the assumptions supporting the AMR are documented. In those 
models where assumptions are made neglecting important couplings, the technical basis for each assumption is 
stated. For example in the Chemical Reference Submodel that is part of the P&CE Model, it is assumed that a 
normative assemblage of salts, having equilibrated to the ambient relative humidity (Section 3.1.2.7). The 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Integration for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
neglected, DOE should provide a technical basis for 
doing so. The technical basis can include activities 
such as independent modeling, laboratory or field 
data, or sensitivity studies. 
technical basis for this assumption is provided. 
EBS Section 3.1.1 through 3.1.4 
Criterion 4 Where simplifications for modeling 
coupled THC effects on WP chemical environment 
were used for performance assessment analyses 
instead of detailed process models, the bases used for 
modeling assumptions and approximations were 
documented and justified. 
The EBS P&CE Model states bases for process model development. 
EBS PMR Section 3.1.2 
Model Uncertainty for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Appropriate models, tests, and analyses 
were used that are sensitive to the THC couplings 
under consideration for both natural and engineering 
systems as described in the following examples. The 
effects of THC coupled processes that may occur in 
the natural setting or due to interactions with 
engineered materials or their alteration products 
include: (i) TH effects on gas and water chemistry; 
(ii) hydrothermally driven geochemical reactions such 
as zeolitization of volcanic glass, which could affect 
water chemistry and WP environmental conditions; 
(iii) dehydration of hydrous phases liberating moisture 
that may affect the WP environment; (iv) effects of 
microbial process on the WP environment; and (v) 
changes in water chemistry that may result from the 
release of corrosion products from the WP and 
interactions between cementitious materials and 
groundwater, which, in turn, may affect the WP 
chemical environment. 
The EBS P&CE model analyzes these effects. The Gas Flux and Fugacity Submodel analyzes TH effects for 
CO2 and O2 gas fugacity (Section 3.1.2.5). These results are then used in the Chemical Summary Submodel 
(Section 3.1.2.7) to estimate changes in groundwater chemistry during various stages of the thermal cycle. The 
Chemical Summary Submodel inputs information from the TH 2D submodel, and evaluates water composition 
in the surround rock such as in the drift above the repository. The Chemical Summary Submodel uses the 
composition for Time Period 2, and calculates an assemblage of evaporative minerals using the normative 
approach. The microbial growth submodel evaluates the potential for microbial growth, and concludes that 
microbial growth will occur for temperatures greater than 120 degrees C. The cementitious materials submodel 
evaluates interactions between the cementitious grout, and groundwater. 
EBS PMR Section 3.1.2 
Criterion 2 Alternative modeling approaches 
consistent with available data and current scientific 
The EBS P&CE Model considers alternative modeling approaches. 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Model Uncertainty for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
understanding were investigated, and their results and 
limitations were appropriately considered. 
The P&CE model is consistent with the available data regarding introduced materials, CO2 fugacity, TH 
effects, and groundwater chemistry. Alternative models for cementitious materials, steel corrosion, and gas 
phase mass fluxes of O2 and CO2 were investigated as summarized in Section 3.1.2. The alternative approach 
for modeling the EBS physical and chemical environment involves fully coupled, reactive transport 
simulations. These were investigated, but found to be restricted to a chemical species and precipitates with 
limited flexibility to handle ionic strength limitations. 
EBS PMR Section 3.1.2 
Criterion 3 DOE provided a reasonable description of 
the mathematical models included in its analyses of 
coupled THC effects on WP chemical environment. 
The description included a discussion of alternative 
modeling approaches not considered in its final 
analysis and the limitations and uncertainties of the 
chosen model. 
For the WP environment, the DOE provides a reasonable description of the mathematical models. The thermal 
hydrological model based upon NUFT is described in Section 3.1.2.1. Certain specialized models were 
developed as part of the EBS PMR. For example, these include the conservative solute analysis in Section 
3.1.2.1. The system of differential equations is described. Further, in Section 3.1.2.2, steady state methods for 
14CO2 transport in the UZ and through the EBS were described. Modeling limitations and uncertainties as 
they relate to the PC&E environment are described throughout Section 3.1.2. 
Note that the EBS PMR is a summary document. As part of the AP-3.10Q process for documentation, each of 
the respective AMRs presented in Table 1-1 is documented in detail. For example, the description of the 
EQ3/6 analysis for the Chemical Summary Submodel is presented in CRWMS M&O 2000t. 
As described above, and discussed in EBS PMR Section 3.1.2, alternative models are presented for fully 
coupled THC modeling. 
Model Verification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 The mathematical models for WP chemical 
environment were consistent with conceptual models 
based on inferences about the near-field environment, 
field data and natural alteration observed at the site, 
and expected engineered materials. 
The P&CE Model thermal hydrology provides a prediction of seepage and flow that are based upon the same 
conceptual active fracture model. The active fracture model, for the NBS is consistent with the active fracture 
model for the UZ. 
Criterion 2 DOE appropriately adopted accepted and 
well-documented procedures to construct and test the 
numerical models used to simulate the WP chemical 
environment. 
Each respective AMR (Table 1-1) which were prepared according to AP-3.10Q with discussion of quality 
assurance , computer software, model inputs, and model assumptions. For analyses involving the use of 
software routines, the routines were verified by separate hand calculations. In other cases, the more complex 
models are compared with experimental test data. For example, as discussed in Section 3.1.2.5, two 
evaporation tests using synthetic J-13 water were simulated using the HRH Salts Model. The comparison of 
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Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Model Verification for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
the model predictions for measured pH and ionic strength compare with measured data. 
EBS PMR Section 3.1.2 
Criterion 3 Abstracted models for coupled THC 
effects on WP chemical environment were based on 
the same assumptions and approximations shown to 
be appropriate for closely analogous natural or 
experimental systems. Abstracted model results were 
verified through comparison to outputs of detailed 
process models and empirical observations. 
Abstracted model results were compared with 
different mathematical models to judge robustness of 
results. 
The EBS PMR provides a discussion for the validation of the EBS P&CE Model. 
The current abstracted model for the Physical and Chemical Model Abstraction relating to the WP environment 
is conceptual in nature. The model abstractions are based upon similar assumptions in that similar flow path 
components such as flow in and around the drip shield and major chemical interactions such as the formation 
of precipitates and salts during repository heating, and the dilution of brines during repository cooling are 
identified in the process model abstraction (CRWMS M&O 2000j) In certain cases, the process model 
abstractions develop probabilistic analysis approaches that are more appropriately handled in TSPA. For 
example, a probabilistic analysis is developed for drip shield separation, and the potential contact of water with 
the waste package in the model abstraction. 
Since the Physical and Chemical Model Abstraction is conceptual (CRWMS M&O 2000j), no comparisons 
have been made between outputs, and the empirical observations such as are currently being made in the 
quarter scale tests. Moreover, abstracted model results have not been compared with different mathematical 
models to address the robustness of the results. 
EBS PMR Section 3.2.2 
Programmatic for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Data and models were collected, 
developed, and documented under acceptable quality 
assurance (QA) procedures. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
Criterion 2 Deficiency reports concerning data quality 
on issues related to coupled THC effects on waste 
package chemical environment were closed. 
The EBS P&CE model has been prepared according to AP-3.10Q and AP-3.15Q to address quality assurance 
deficiency issues. 
The AP-3.10Q procedure addresses previous deficiencies in obtaining input data from controlled sources of 
information, and in the documentation of software. AP-3.15Q provides the process for managing inputs to each 
AMR. Existing deficiencies are in the process of being closed with the preparation of the P&CE AMR 
A-17 

Subissue ENFE Subissue 2: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Waste Package Chemical Environment 
Programmatic for Subissue 2 
Acceptance Criterion PMR Approach and Section Reference 
according to AP-3.10Q. 
EBS PMR Section 1.3 
Criterion 3 If used, expert elicitations were conducted 
and documented in accordance with the guidance in 
NUREG-1563 (Kotra, et al., 1996) or other acceptable 
approaches. 
No expert elicitation was conducted for this PMR. 
Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Data and Model Justification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Available data relevant to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on the chemical environment for 
radionuclide release were considered. 
The EBS radionuclide transport model (EBS PMR Section 3.1.3) provides an analysis of release based upon 
the thermal hydrological calculations in the WD&R model. The EBS radionuclide transport model (EBS PMR 
Section 3.1.3) is an advection/dispersion/diffusion model. The WD&R model considers the temporal 
variations in conditions affecting the TH effects, and provides a bounding calculation for chemical effects due 
fracture plugging that would alter saturation levels and porewater velocities. The EBS radionuclide transport 
(Section 3.1.3) model provides a sensitivity analysis for the chemical retardation that bounds temporal and 
spatial variations in the chemical retardation factor that reflects the chemical environment. For the base case, 
the EBS radionuclide transport takes no credit for chemical retardation which is a bounding assumption for 
radionuclide transport. 
The EBS Colloids submodel is based upon relevant data for the size and concentration of colloids that account 
for variability through probability distributions. Based upon these data bounding values for radionuclide 
solubility, and colloid diffusion coefficient were calculated. 
EBS Sections 3.1.2.6 and 3.1.3 
Criterion 2 DOE's evaluation of coupled THC 
processes properly considered site characteristics in 
establishing initial and boundary conditions for 
conceptual models and simulations of coupled 
processes that may affect the chemical environment 
The EBS radionuclide transport model (EBS PMR Section 3.1.3) provides an analysis of release based upon 
the thermal hydrological calculations in the WD&R model. The physical processes in the EBS radionuclide 
transport model include advection, dispersion and diffusion. The advection through the EBS, and in particular 
in the invert is based upon initial and boundary conditions for the NBS and EBS in the Water Distribution 
Model (Section 3.1.1). 
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Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Data and Model Justification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
for radionuclide release. 
The EBS Radionuclide Transport Model (Section 3.1.1) provides analysis that can be scaled to the release of 
radionuclides from the WP. 
EBS PMR Sections 3.1.1 through 3.1.3 
Criterion 3 Sufficient data were collected on the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, in establishing initial and boundary 
conditions for conceptual models and simulations of 
THC coupled processes that affect the chemical 
environment for radionuclide release. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
chemical effects such as the alteration of groundwater chemistry (Section 3.1.4). 
EBS PMR Sections 3.1.1 through 3.1.3 
Criterion 4 A nutrient and energy inventory 
calculation was used to determine the potential for 
microbial activity that could impact radionuclide 
release. 
The EBS P&CE Model provides a bounding analysis for a nutrient and energy inventory. 
EBS PMR Sections 3.1.2 EBS PMR Section 3.1.2 and Section 3.2.3.1.3. 
Criterion 5 Should microbial activity be sufficient to 
potentially affect the chemical environment for 
radionuclide release, then the time-history of 
temperature, humidity, and dripping should be used to 
constrain the probability for microbial effects, such as 
production of organic by-products that act as 
complexing ligands for actinides and microbialenhanced 
dissolution of the HLW glass form. 
See discussion presented above. 
See EBS PMR Section 3.1.2 and 3.2.3.1.3 
Criterion 6 Sensitivity and uncertainty analyses 
(including consideration of alternative conceptual 
models) were used to determine whether additional 
new data are needed to better define ranges of input 
parameters. 
The EBS PMR provides a discussion of alternative conceptual models for the EBS P&CE and Radionuclide 
Transport Models. 
The EBS radionuclide transport model (EBS PMR Section 3.1.3) provides an analysis of release based upon 
the thermal hydrological calculations in the WD&R model. The EBS radionuclide transport model (EBS PMR 
Section 3.1.3) is an advection/dispersion/diffusion model. The WD&R model considers the temporal 
variations in conditions affecting the TH effects, and provides a bounding calculation for chemical effects due 
fracture plugging that would alter saturation levels and porewater velocities. The EBS radionuclide transport 
(Section 3.1.3) model provides a sensitivity or uncertainty analysis for the chemical retardation that bounds 
temporal and spatial variations in the chemical retardation factor that reflects the chemical environment. For 
A-19 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Data and Model Justification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
the base case, the EBS radionuclide transport takes no credit for chemical retardation which is a bounding 
assumption for radionuclide transport. 
The EBS Colloids submodel is based upon relevant data for the size and concentration of colloids that account 
for variability through probability distributions. Based upon these data bounding values for radionuclide 
solubility, and colloid diffusion coefficient were calculated. 
EBS PMR Section 3.1.2 
Criterion 7 If the testing program for coupled THC 
processes on the chemical environment for 
radionuclide release from the engineered barrier 
system is not complete at the time of license 
application, or if sensitivity and uncertainty analyses 
indicate additional data are needed, DOE has 
identified specific plans to acquire the necessary 
information as part of the performance confirmation 
program. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
Data Uncertainty and Verification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Reasonable or conservative ranges of 
parameters or functional relations were used to 
determine effects of coupled THC processes on the 
chemical environment for radionuclide release. 
Parameter values, assumed ranges, probability 
distributions, and bounding assumptions were 
technically defensible and reasonably accounted for 
uncertainties. 
The EBS Radionuclide Transport Model provides a bounding analysis based upon the thermal hydrology from 
the WD&R Model. The physical processes in the EBS radionuclide transport model include advection, 
dispersion and diffusion. The advection through the EBS, and in particular in the invert is based upon 
reasonable parameters for the NBS and EBS in the Water Distribution Model (Section 3.1.1). 
The EBS Radionuclide Transport Model (Section 3.1.1) provides reasonable estimates for dispersion and 
diffusion. The EBS Radionuclide Transport Model neglects chemical retardation for the base case analysis 
which is a conservative assumption. Further, it considers a reasonable range of parameters in defining the 
probability distribution functions for all parameters including chemical retardation in the sensitivity analysis. 
EBS PMR Section 3.1.1 through 3.1.3 
Criterion 2 Uncertainty in data due to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on the chemical environment for 
The EBS Radionuclide Transport Model is based upon thermal hydrology that accounts for the temporal and 
spatial variations. 
A-20 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Data Uncertainty and Verification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
radionuclide release were considered. Section 3.2.1 documents model uncertainties as they relate to the performance of the NBS and the EBS. These 
uncertainties in data due to temporal and spatial variations are addressed in the thermal hydrology submodel in 
which changes in the waste package heating are considered. Spatial variations are addressed by considering 
the L4C4 column in the center of the repository, and the L4C1 column at the edge of the repository. It should 
be noted that EBS process models provide the basis for selecting robust designs for EBS performance and 
waste isolation in the face of model uncertainty. 
The EBS Radionuclide Transport Model (Section 3.1.1) provides reasonable estimates for dispersion and 
diffusion. It compares the relationships for diffusion coefficients using two differe3nt methods, and measured 
data. The EBS Radionuclide Transport Model neglects chemical retardation for the base case analysis which is 
a conservative assumption. Further, it considers a reasonable range of parameters in defining the probability 
distribution functions for all parameters including chemical retardation in the sensitivity analysis. 
EBS PMR Section 3.1.2 
Criterion 3 DOE's evaluation of coupled THC 
processes properly considered the uncertainties in the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, in establishing initial and boundary 
conditions for conceptual models and simulations of 
THC coupled processes that affect the chemical 
environment for radionuclide release. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
chemical effects such as the alteration of groundwater chemistry (Section 3.1.4).EBS PMR Sections 3.1.2 
through 3.1.3 
Criterion 4 The initial conditions, boundary 
conditions, and computational domain used in 
sensitivity analyses involving coupled THC effects on 
the chemical environment for radionuclide release 
were consistent with available data. 
The EBS Radionuclide Transport Model (Section 3.1.1) provides reasonable estimates for dispersion and 
diffusion. The EBS Radionuclide Transport Model neglects chemical retardation for the base case analysis 
which is a conservative assumption. Further, it considers a reasonable range of parameters that address initial 
conditions, boundary conditions and computational domain for all parameters including chemical retardation in 
the sensitivity analysis. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 5 DOE's performance confirmation program 
will assess whether the natural system and engineered 
materials are functioning as intended and anticipated 
with regard to coupled THC effects on the chemical 
environment for radionuclide release from the EBS. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
A-21 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Integration for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 DOE considered the relevant features, 
events, and processes. The abstracted models 
adequately incorporated important design features; 
physical phenomena and couplings; and used 
consistent and appropriate assumptions throughout. 
Important features, events, and processes are identified in EBS PMR Section 2.4.1. 
The FEPs for the EBS are identified in Table 2-2. Specifically, the relevant FEPs that relate to chemical 
processes on the chemical environment of radionuclide Release are addressed in the microbial activity Energy 
/Nutrient Balance Microbial Model (Section 3.1.2) The Cementitious Materials Submodel addresses the 
alteration of infiltrate chemistry due to physical and chemical properties of the EBS as summarized in Sections 
3.1.1 through 3.1.4. 
EBS PMR Sections 2.4.1 and 3.1.3 
Criterion 2 Models reasonably accounted for known 
temporal and spatial variations in conditions affecting 
coupled THC effects on the chemical environment for 
radionuclide release. 
The EBS Radionuclide Transport Model (EBS PMR Section 3.1.3) does not take credit for chemical 
retardation. 
The EBS Radionuclide Transport (Section 3.1.3) model provides a sensitivity analysis for the chemical 
retardation that bounds temporal and spatial variations in the chemical retardation factor that reflects the 
chemical environment. For the base case, the EBS radionuclide transport takes no credit for chemical 
retardation which is a bounding assumption for radionuclide transport. 
The EBS Colloids submodel is based upon relevant data for the size and concentration of colloids that account 
for variability through probability distributions. Based upon these data bounding values for radionuclide 
solubility, and colloid diffusion coefficient were calculated. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 3 Not all THC couplings may be determined 
to be important to performance, and DOE may adopt 
assumptions to simplify PA analyses. If potentially 
important couplings are neglected, DOE should 
provide a technical basis for doing so. The technical 
basis can include activities, such as independent 
modeling, laboratory or field data, or sensitivity 
studies. 
In each of the respective AMRs (Table 1-1), the assumptions supporting the AMR are documented. In those 
models where assumptions are made neglecting important couplings, the technical basis for each assumption is 
stated. In the EBS radionuclide transport model, the base case neglects chemical retardation as determined 
from the chemical environment. This is a conservative assumption since the effects of chemical retardation 
would increase the breakthrough time. 
EBS Section 3.1.3 
Criterion 4 Where simplifications for modeling 
coupled THC effects on the chemical environment for 
radionuclide release were used for PA analyses instead 
of detailed process models, the bases used for 
modeling assumptions and approximations were 
The EBS Radionuclide Transport Model provides a bounding calculation. As stated in the previous comment, 
it is conservative to neglect chemical retardation due to sorption in the invert. 
EBS PMR Sections 3.1.2 through 3.1.3 
A-22 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Integration for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
documented and justified. 
Model Uncertainty for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Appropriate models, tests, and analyses 
were used that are sensitive to the THC couplings 
under consideration for both natural and engineering 
systems as described in the following examples. The 
effects of THC coupled processes that may occur in 
the natural setting or due to interactions with 
engineered materials or their alteration products 
include: (i) TH effects on gas and water chemistry; 
(ii) hydrothermally driven geochemical reactions, 
such as zeolitization of volcanic glass; (iii) 
dehydration of hydrous phases liberating moisture; 
(iv) effects of microbial processes; and (v) changes in 
water chemistry that may result from interactions 
between cementitious, or WP, materials and 
groundwater, which, in turn, may affect the chemical 
environment for radionuclide release. 
The EBS Radionuclide Transport Model provides a bounding calculation. For the base case, the effects of 
chemical retardation are neglected (Section 3.1.3) which is a conservative assumption. The effects of Ca, Si, 
and Mg precipitation that would result in possible reduction in porosity are investigated in Section 3.1.2.5, and 
are found to be negligible. It is unlikely that pore water velocities would be altered by a reduction in porosity. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 2 Alternative modeling approaches 
consistent with available data and current scientific 
understanding were investigated, and their results and 
limitations were appropriately considered. 
The EBS Radionuclide Transport Model considers alternative modeling approaches. 
Section 3.1.3 considers two alternative modeling approaches for radionuclide transport through the EBS. 
These include the potential for ponding of water which would result in the release of radionuclides through 
flow parallel to the drift and down a fault or fracture system. The second alternative involves steady state flow 
through the invert. 
Criterion 3 DOE provided a reasonable description of 
the mathematical models included in its analyses of 
coupled THC effects on the chemical environment for 
radionuclide release. The description included a 
discussion of alternative modeling approaches not 
considered in its final analysis and the limitations and 
uncertainties of the chosen model. 
In the Water Distribution and Removal AMR, the Physical and Chemical Environment Model and the EBS 
Radionuclide Transport AMR, the DOE provided descriptions of conceptual, and detailed models as required 
by AP-3.10Q that provide a reasonable description of modeling thermal-hydrologic phenomena for predicting 
seepage and flow in the EBS. 
EBS PMR Sections 3.1.1 through 3.1.3 
A-23 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Model Verification for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 The mathematical models for coupled 
THC effects on the chemical environment for 
radionuclide release were consistent with conceptual 
models based on inferences about the near-field 
environment, field data and natural alteration 
observed at the site, and expected engineered 
materials. 
The Water Distribution and Removal Model, the P&CE Model, and the Multiscale Thermohydrologic Model 
provide predictions of seepage and flow that are based upon the active fracture model. The conceptual model 
for the prediction of advection or pore water velocities, and radionuclide transport due to 
advection/dispersion/diffusion through the EBS is consistent with conceptual models for the UZ. 
Criterion 2 DOE appropriately adopted accepted and 
well-documented procedures to construct and test the 
numerical models used to simulate coupled THC 
effects on the chemical environment for radionuclide 
release. 
The DOE used appropriate procedures to construct and test numerical models for predicting seepage and flow. 
The Radionuclide Transport Model was developed using a closed-form analytical solution for one-dimensional 
contaminant transport implemented in software routines. The Radionuclide Transport Model represents an 
industry standard approach for contaminant transport based upon the TH analysis in the Water Distribution 
and Removal Model (CRWMS M&O 2000q). The results of the model from the software routines based upon 
the closed form solution were compared to hand calculations for verification. The software codes used for the 
models are subject to verification and testing under the procedure AP-SI.1Q. 
Criterion 3 Abstracted models for coupled THC 
effects on the chemical environment for radionuclide 
release were based on the same assumptions and 
approximations shown to be appropriate for closely 
analogous natural or experimental systems. 
Abstracted model results were verified through 
comparison to outputs of detailed process models and 
empirical observations. Abstracted model results were 
compared with different mathematical models to 
judge robustness of results. 
The current abstracted model for the Radionuclide Transport Abstraction is conceptual in nature. The model 
abstractions are based upon similar assumptions in that similar flow path components such as flow in and 
around the drip shield to the invert and major chemical interactions such as neglecting chemical retardation in 
the invert are identified in the process model abstraction (CRWMS M&O 2000a) In certain cases, the process 
model abstractions develop a probabilistic analysis approaches that are more appropriately handled in TSPA 
studies. 
Since the Radionuclide Transport Abstraction is conceptual (CRWMS M&O 2000a), no comparisons have 
been made between outputs, and the empirical observations such as are currently being made in the quarter 
scale tests. 
Since the Radionuclide Transport Abstraction is conceptual, abstracted model results have not been compared 
with different mathematical models to address the robustness of the results. 
A-24 

Subissue ENFE Subissue 3: Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment of Radionuclide Release 
Programmatic for Subissue 3 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Data and models were collected, 
developed, and documented under acceptable quality 
assurance (QA) procedures. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
Criterion 2 Deficiency reports concerning data quality 
on issues related to coupled THC effects on 
radionuclide release were closed. 
The EBS Radionuclide Transport Model is being prepared according to AP-3.10Q to address quality assurance 
deficiency issues. The EBS Radionuclide Transport PMRs is prepared according the procedure Analyses and 
Models, AP-3.10Q which was developed to address data deficiency and quality issues. At the current time, the 
data used for this model are obtained from controlled sources that are undergoing qualification, and will be 
closed after completion of data qualification activities. 
EBS PMR Section 3.1.3 
Criterion 3 If used, expert elicitations were conducted 
and documented in accordance with the guidance in 
NUREG-1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Data and Model Justification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Available data relevant to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on transport of radionuclides in the near 
field were considered. 
The EBS Radionuclide Transport Model is based upon a two dimensional thermal hydrologic analysis that 
accounts for temporal waste heat loading, and variations in percolation rates. 
Further, it considers a reasonable range of parameters that address spatial variations in conditions for all 
parameters including chemical retardation in the sensitivity analysis. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 2 DOE's evaluation of coupled THC 
processes properly considered site characteristics in 
establishing initial and boundary conditions for 
conceptual models and simulations of coupled 
processes that may affect radionuclide transport in the 
The EBS Radionuclide Transport model is based upon a two dimensional thermal hydrologic analysis that 
considers initial temperature and pressure boundary conditions. The EBS Radionuclide Transport Model 
provides bounding analysis for a conservative range of parameters. The base case analysis neglects the effects 
of chemical retardation on radionuclide transport and therefore conservatively neglects chemical initial and 
boundary conditions. 
A-25 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Data and Model Justification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
near field. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 3 Sufficient data were collected on the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, in establishing initial and boundary 
conditions for conceptual models and simulations of 
THC coupled processes that affect transport of 
radionuclides in the near field. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to not take credit for chemical retardation in the invert (Section 3.1.3) . 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 4 A nutrient and energy inventory 
calculation was used to determine the potential for 
microbial activity that could adversely affect 
radionuclide transport through engineered and natural 
barriers. 
The EBS P&CE Model provides a bounding analysis for a nutrient and energy inventory. 
EBS PMR Section 3.1.2 
Criterion 5 Should microbial activity be sufficient to 
potentially cause adverse microbial effects on 
transport of radionuclides through engineered and 
natural barriers, then the time-history of temperature, 
humidity, and water saturation in engineered and 
natural materials should be used to constrain the 
probability for these effects. 
See the discussion presented above. 
See EBS PMR Section 3.1.2. 
Criterion 6 Sensitivity and uncertainty analyses 
(including consideration of alternative conceptual 
models) were used to determine if additional new data 
are needed to better define ranges of input parameters. 
The EBS PMR provides a discussion of alternative conceptual models for the EBS Radionuclide Transport 
Model. In the EBS Radionuclide Transport model, assumptions have been used and documented. In the 
absence of data, sensitivity and uncertainty analyses have been performed to assess their impact and the need to 
collect additional data. 
EBS PMR Section 3.1.3 
Criterion 7 If the testing program for the effects of 
coupled THC processes on radionuclide transport is 
not complete at the time of license application, or if 
sensitivity and uncertainty analyses indicate 
additional data are needed, DOE has identified 
specific plans to acquire the necessary information as 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
A-26 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Data and Model Justification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
part of the performance confirmation program. 
Data Uncertainty and Verification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 2 Uncertainty in data due to both temporal 
and spatial variations in conditions affecting coupled 
THC effects on radionuclide transport in the near field 
were considered. 
The EBS Radionuclide Transport Model (EBS PMR Section 3.1.3) provides an analysis of release based upon 
the thermal hydrological calculations in the WD&R model. The EBS Radionuclide Transport Model (EBS 
PMR Section 3.1.3) is an advection/dispersion/diffusion model. The WD&R model considers the temporal 
variations in conditions affecting the TH effects, and provides a bounding calculation for chemical effects due 
to fracture plugging that would alter saturation levels and porewater velocities. The EBS Radionuclide 
Transport Model (Section 3.1.3) provides a sensitivity analysis for the chemical retardation that bounds 
temporal and spatial variations in the chemical retardation factor that reflects the chemical environment. For 
the base case, the EBS Radionuclide Transport takes no credit for chemical retardation which is a bounding 
assumption for radionuclide transport. 
EBS PMR Sections 3.1.1 through 3.1.3 
Criterion 1 Reasonable or conservative ranges of 
parameters or functional relations were used to 
determine effects of coupled THC processes on 
transport of radionuclides in the near field. Parameter 
values, assumed ranges, probability distributions, and 
bounding assumptions were technically defensible and 
reasonably accounted for uncertainties. 
The EBS Radionuclide Transport Model (EBS PMR Section 3.1.3) provides a bounding analysis (EBS PMR 
Section 3.1.3) based upon the thermal hydrology from the WD&R Model (EBS PMR Sections 3.1.1 through 
3.1.2). For the base case analysis, the conservative assumption to neglect chemical retardation effects is made. 
A sensitivity analysis is presented in Section 3.1.3 for the assumed range of parameters that is technically 
defensible, and that reasonably accounts for uncertainties. 
Criterion 3 DOE's evaluation of coupled THC 
processes properly considered the uncertainties in the 
characteristics of the natural system and engineered 
materials, such as the type, quantity, and reactivity of 
material, in establishing initial and boundary 
conditions for conceptual models and simulations of 
THC coupled processes that affect transport of 
radionuclides in the near field. 
The EBS Radionuclide Transport Model provides a bounding calculation. For the base case, the effects of 
chemical retardation are neglected (Section 3.1.3) which is a conservative assumption. The effects of Ca, Si, 
and Mg precipitation that would result in possible reduction in porosity are investigated in Section 3.1.2.5, and 
are found to be negligible. It is unlikely that pore water velocities would be altered by a reduction in porosity. 
EBS PMR Sections 3.1.1 through 3.1.3 
Criterion 4 The initial conditions, boundary 
conditions, and computational domain used in 
The WD&R TH Model used to provide pore water velocities and saturation levels in the Radionuclide 
Transport model is based upon initial conditions boundary conditions, and computational domains consistent 
A-27 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Data Uncertainty and Verification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
sensitivity analyses involving coupled THC effects on 
radionuclide transport in the near field were consistent 
with available data. 
with site characteristics. In general, the thermal hydrology models used in Sections 3.1.1 through 3.1.4 are 
based upon the selection of NBS hydrologic and thermal properties used in the UZ process model. The initial 
conditions, and boundary conditions for the models for specific locations use the same infiltration rates, and 
temperature and pressure boundary conditions consistent with the UZ process Model (Section 3.1.4) 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 5 DOE's performance confirmation program 
will assess whether the natural system and engineered 
materials are functioning as intended and anticipated 
with regard to coupled THC effects on transport of 
radionuclides in the near field. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
Integration for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 DOE considered all the relevant features, 
events, and processes. The abstracted models 
adequately incorporated important design features, 
physical phenomena, and couplings, and used 
consistent and appropriate assumptions throughout. 
Important features events, and processes are identified in EBS PMR Section 2.4.1. 
The FEPs for the EBS are identified in Table 2-2. Specifically, the relevant FEPs include drainage inhibited by 
fracture plugging, drainage through drains, and the influence of drift environment. Note that the effect of drift 
environment on the transport of colloidal species was adequately incorporated in Section 3.1.2.6. 
EBS PMR Sections 2.4.1, 3.1.1 and 3.1.2 
Criterion 2 Models reasonably accounted for known 
temporal and spatial variations in conditions affecting 
coupled THC effects on transport of radionuclides in 
the near field. 
The EBS Radionuclide Transport Model (EBS PMR Section 3.1.3) is based upon the thermal hydrology from 
the WD&R Model. 
The EBS Radionuclide Transport Model (EBS PMR Section 3.1.3) provides an analysis of release based upon 
the thermal hydrological calculations in the WD&R model. The EBS Radionuclide Transport Model (EBS 
PMR Section 3.1.3) is an advection/dispersion/diffusion model. The WD&R model considers the temporal 
variations in conditions affecting the TH effects, and provides a bounding calculation for chemical effects due 
to fracture plugging that would alter saturation levels and porewater velocities. The EBS Radionuclide 
Transport Model (Section 3.1.3) provides a sensitivity analysis for the chemical retardation that bounds 
temporal and spatial variations in the chemical retardation factor that reflects the chemical environment. For 
the base case, the EBS Radionuclide Transport Model takes no credit for chemical retardation which is a 
bounding assumption for radionuclide transport. 
A-28 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Integration for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
The EBS Colloids submodel is based upon relevant data for the size and concentration of colloids that account 
for variability through probability distributions. Based upon these data bounding values for radionuclide 
solubility, and colloid diffusion coefficient were calculated. 
EBS PMR Sections 3.1.1 through 3.1.3 
Criterion 3 Not all THC couplings may be determined 
to be important to performance, and DOE may adopt 
assumptions to simplify performance assessment 
analyses. If potentially important couplings are 
neglected, DOE should provide a technical basis for 
doing so. The technical basis could include activities, 
such as independent modeling, laboratory or field 
data, or sensitivity studies. 
The EBS Radionuclide Transport Model provides a bounding analysis. In each of the respective AMRs (Table 
1-1), the assumptions supporting the AMR are documented. In those models where assumptions are made 
neglecting important couplings, the technical basis for each assumption is stated. In the EBS Radionuclide 
Transport Model, the base case neglects chemical retardation as determined from the chemical environment. 
This is a conservative assumption since the effects of chemical retardation would increase the breakthrough 
time. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 4 Where simplifications for modeling 
coupled THC effects on radionuclide transport in the 
near field were used for performance assessment 
analyses instead of detailed process models, the bases 
used for modeling assumptions and approximations 
were documented and justified. 
The EBS Radionuclide Transport Model provides a bounding calculation. As stated in the previous comment, 
it is conservative to neglect chemical retardation due to sorption in the invert. 
EBS PMR Sections 3.1.2 through 3.1.3 
A-29 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Model Uncertainty for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Appropriate models, tests, and analyses 
were used that are sensitive to the THC couplings 
under consideration for both natural and engineering 
systems as described in the following examples. The 
effects of THC coupled processes that may occur in 
the natural setting or due to interactions with 
engineered materials or their alteration products 
include: (i) TH effects on gas and water chemistry in 
the unsaturated zone and saturated zone; (ii) 
precipitation of calcite and opal on the footwall of 
fracture surfaces and the bottoms of lithophysal 
cavities, which indicates gravity-driven flow in open 
fractures, and isolation of transport pathways from 
sorption sites in the rock matrix; (iii) zeolitization of 
volcanic glass, that could affect transport pathways; 
(iv) precipitation and dissolution of oxides and 
hydroxides on fracture surfaces, illitization of 
smectite, and recrystallization of zeolites to analcime, 
which could affect sorption characteristics; (v) effects 
of microbial processes; (vi) effects of corrosion 
products of container materials and waste forms on 
transport of radionuclides in the near field; and (vii) 
changes in hydraulic and sorptive properties of the 
natural system resulting from interactions between 
cementitious materials and groundwater. 
The EBS Radionuclide Transport Model provides a bounding analysis. As stated above the effects of chemical 
retardation in the EBS are not taken credit for in increasing breakthrough time in the invert. 
The EBS Colloids Submodel is based upon relevant data for the size, and concentration of colloids that account 
for variability through probability distributions. Based upon these data, bounding values for radionuclide 
solubility and colloid diffusion coefficients were calculated. 
EBS PMR Sections 3.1.2 through 3.1.3 
Criterion 2 Alternative modeling approaches 
consistent with available data and current scientific 
understanding were investigated, and their results and 
limitations were appropriately considered. 
The EBS PMR provides a discussion of alternative conceptual models for the EBS Radionuclide Transport 
Model (Section 3.1.3). The EBS Radionuclide Transport Model is consistent with available data regarding the 
properties of the invert. An alternative view regarding the effects of storage capacity was presented. It was 
found that this alternative view is not likely to be important because increased EBS flow rates will cause 
increased dilution. 
EBS PMR Section 3.1.3 
Criterion 3 DOE provided a reasonable description of 
the mathematical models included in its analyses of 
coupled THC effects on radionculide transport in the 
For the Radionuclide Transport Model, the DOE provides a reasonable description of the mathematical 
models. The thermal hydrological model based upon NUFT is described in Section 3.1.1. The basic 
contaminant transport equation is presented in Section 3.1.3. Alternative models were discussed in Section 
A-30 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Model Uncertainty for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
near field. The description included a discussion of 
alternative modeling approaches not considered in its 
final analysis and the limitations and uncertainties of 
the chosen model. 
3.1.3 with regards to reduction in drainage capacity, and storage capacity in the invert. (EBS PMR Sections 
3.1.1 through 3.1.3). 
Model Verification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 The mathematical models for coupled 
THC effects on radionculide transport in the near field 
were consistent with conceptual models based on 
inferences about the near-field environment, field data 
and natural alteration observed at the site, and 
expected engineered materials. 
The Water Distribution Model which was used for the Radionuclide Transport Model provides predictions of 
seepage and flow that are based on the active fracture model. The conceptual model for the prediction of 
advection or pore water velocities and radionuclide transport due to advection/dispersion/diffusion through the 
EBS is consistent with conceptual models for the UZ. 
Criterion 2 DOE appropriately adopted accepted and 
well-documented procedures to construct and test the 
numerical models used to simulate coupled THC 
effects on transport of radionuclides in the near field. 
The EBS Radionuclide Transport Model is based upon a well documented and accepted procedure for 
evaluating contaminant transport as stated in the previous comment. 
The Radionuclide Transport model was prepared according to AP-3.10Q with discussion of quality assurance, 
computer software, model inputs, and model assumptions. For analyses involving the use of software routines, 
the routines were verified by separate hand calculations. 
EBS PMR Sections 3.1.3, and 3.2.2.3. 
Criterion 3 Abstracted models for coupled THC 
effects on radionuclide transport were based on the 
same assumptions and approximations shown to be 
appropriate for closely analogous natural or 
experimental systems. Abstracted model results were 
verified through comparison to outputs of detailed 
process models and empirical observations. 
Abstracted model results were compared with 
different mathematical models to judge robustness of 
results. 
The current abstracted model for the Radionuclide Nuclide Transport Abstraction is conceptual in nature. The 
model abstractions are based upon similar assumptions in that similar flow path components such as flow in 
and around the drip shield to the invert and major chemical interactions such as conservatively neglecting 
sorption in the process model abstraction (CRWMS M&O 2000a) In certain cases, the process model 
abstractions develop a probabilistic analysis approaches that are more appropriately handled in TSPA studies. 
Since the Radionuclide Transport Abstraction is conceptual (CRWMS M&O 2000a), no comparisons have 
been made between outputs, and the empirical observations such as are currently being made in the quarter 
scale tests. 
Since the Radionuclide Transport Abstraction is conceptual, abstracted model results have not been compared 
with different mathematical models to address the robustness of the results. 
A-31 

Subissue ENFE Subissue 4: The Effects of Coupled Thermal-Hydrologic-Chemical Processes 
on the Radionuclide Transport Through Engineered and Natural Barriers 
Model Verification for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
EBS PMR Section 3.1.2,3.1.3, 3.2.3 and 3.3. 
Programmatic for Subissue 4 
Acceptance Criterion PMR Approach and Section Reference 
Criterion 1 Data and models were collected, 
developed, and documented under acceptable quality 
assurance (QA) procedures. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
Criterion 2 Deficiency reports concerning data quality 
on issues related to coupled THC effects on waste 
package chemical environment were closed. 
The EBS P&CE Model, and the Radionuclide Transport Model are prepared according to AP-3.10Q to address 
quality assurance deficiency issues. 
The AP-3.10Q procedure addresses previous deficiencies in obtaining input data from controlled sources of 
information, and in the documentation of software. AP-3.15Q provides the process for managing inputs to each 
AMR. Existing deficiencies are in the process of being closed with the preparation of the P&CE AMR 
according to AP-3.10Q. 
EBS PMR Section 3.1.2 
Criterion 3 If used, expert elicitations were conducted 
and documented in accordance with the guidance in 
NUREG-1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
A-32 

IRSR Repository Design and Thermal-Mechanical Effects (Revision 2) 
Subissue RDTME Subissue 1: Implementation of an Effective Design Control Process within 
the Overall Quality Assurance Program 
Acceptance Criterion PMR Approach and Section Reference 
1. The applicable regulatory requirements are 
identified. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
2. The design bases associated with the regulatory 
requirements are defined. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
3. The regulatory requirements of Acceptance 
Criterion 1 and the design bases of Acceptance 
Criterion 2 are appropriately translated into 
specifications, drawings, procedures, and instructions. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
4. Appropriate quality standards are specified in the 
design documents. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
5. Any deviations from the standards specified under 
Acceptance Criterion 4 are properly controlled, 
documented, and justified. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
6. Measures are established for selection of materials, 
parts, equipment, and processes that are essential to 
functions of structures, systems, and components that 
are important to safety and waste containment and 
isolation. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
7. Design interfaces are identified, controlled, and 
appropriately coordinated among participating design 
organizations. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
8. Procedures are established for review, approval, 
release, distribution, and revision of documents 
involving design interfaces. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
9. Measures are established for verifying or checking 
the accuracy of design calculations (e.g., performing 
design reviews using alternate or simplified 
calculational methods). 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
A-33 

Subissue RDTME Subissue 1: Implementation of an Effective Design Control Process within 
the Overall Quality Assurance Program 
Acceptance Criterion PMR Approach and Section Reference 
10. If testing is employed for verification of design 
adequacy for its intended service life, the testing is 
conducted under the most adverse conditions. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
11. The design verification is conducted by 
independent and qualified professionals who did not 
participate in the original design efforts. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
12. In addition to being applied to the original design, 
the design control process is also applied to design 
changes and to field changes, and these changes are 
properly documented. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
Subissue RDTME Subissue 2: Design of the Geologic Repository Operations Area for the 
Effects of Seismic Events and Direct Fault Disruption 
Methodology proposed in the TR is adequate if the following criteria are satisfied: 
Acceptance Criterion PMR Approach and Section Reference 
4. Uncertainties associated with the proposed 
methodology that would significantly affect or impede 
the repository design process and development of 
inputs to performance assessments have been 
considered adequately. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
6. To the extent that the proposed design methodology 
depends on site-specific test data, such data are 
available now, are being gathered now, or there are 
plans for gathering such data during site 
characterization and before submittal of the license 
application. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
5. The various steps involved in the proposed 
methodology are transparent. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
2. If available, documented case histories of the Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
A-34 

Subissue RDTME Subissue 2: Design of the Geologic Repository Operations Area for the 
Effects of Seismic Events and Direct Fault Disruption 
Methodology proposed in the TR is adequate if the following criteria are satisfied: 
Acceptance Criterion PMR Approach and Section Reference 
performance of structures, systems, and components 
important to safety designed using the proposed 
methodology are presented in the topical report. In the 
absence of documented case histories, no serious 
problems have been identified that would impede 
applying the methodology. 
applied appropriately in the seismic design process. 
1. Sufficient technical reasoning is provided for the 
proposed methodology. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
3. The proposed methodology does not contradict 
established methodologies and principles tested and 
documented in the license applications for nuclear 
power plants and independent spent fuel storage 
installations. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
8. Any major assumptions or limitations to the 
proposed methodology are identified, and the 
implications regarding design and performance are 
discussed in the topical report. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
7. To the extent that the proposed methodology 
depends on analytical/computer models, such models 
have been verified, calibrated, and validated to the 
extent practical, or there are plans for such activities 
prior to license application submittal or during the 
performance confirmation period, as appropriate. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
9. The contents of TR-2 are consistent with the 
contents of TR-1 and, taken together, the two topicals 
reports support the development of inputs for design 
and performance assessments, as described in TR-3. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
A-35 

Subissue RDTME Subissue 2: Design of the Geologic Repository Operations Area for the 
Effects of Seismic Events and Direct Fault Disruption 
TR adequacy depends on initial acceptance review of TR-2 meeting these criteria: 
Acceptance Criterion PMR Approach and Section Reference 
2. The subject of the topical report is currently 
undergoing pre-licensing evaluation. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
1. The topical report addresses all important-to-safety 
(or important-to-waste-isolation) topics pertaining to 
the scope of the topical report. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
3. NRC's acceptance of the topical report would result 
in increased efficiencies in the staff review of DOE's 
license application. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
4. The topical report contains complete and detailed 
information on each element of the scope of the report. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
Subissue RDTME Subissue 3: Thermal-Mechanical Effects on Underground Facility Design 
and Performance 
Component 1 - Thermal-Mechanical Effects on Design of Underground Facility 
Acceptance Criterion PMR Approach and Section Reference 
1. Approved QA control procedures and standards 
were applied to collection and documentation of data, 
methods, models, and codes. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. If used, expert elicitations are conducted and 
documented in accordance with the guidance in 
NUREG-1563 or other acceptable guidelines. 
No expert elicitation was conducted for this PMR. 
3. TM analyses of the repository design are based on 
site-specific thermal and mechanical properties, the 
spatial variation of such properties, and temporal 
variations caused by post-emplacement TMHC 
processes, as appropriate, including the consideration 
of seismic effects relevant to the YM site within the 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
A-36 

Subissue RDTME Subissue 3: Thermal-Mechanical Effects on Underground Facility Design 
and Performance 
Component 1 - Thermal-Mechanical Effects on Design of Underground Facility 
Acceptance Criterion PMR Approach and Section Reference 
rock mass. 
4. The process to develop inputs to TM design 
includes consideration of associated uncertainties and 
documents the potential impacts on design. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
5. The seismic and fault-displacement data inputs for 
design are consistent with those established in seismic 
design TR-3. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
6. The methodologies used for the TM design and 
analyses are consistent with that established in DOE 
Seismic TR-2. 
Design considerations related to seismic issues are not included in this PMR. The acceptance criterion will be 
applied appropriately in the seismic design process. 
7. The TM design and analyses make use of 
appropriate constitutive models that represent jointed 
rock mass behavior under prolonged heated 
conditions. The models are tested as appropriate 
(verified, validated, and calibrated) before the 
submittal of the LA. (For those aspects of the models 
for which long-term experimental data are needed, 
continued verification and validation during 
performance confirmation are considered acceptable 
as long as detailed plans and procedures for such 
continued activities are found in the LA.) 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
8. Both drift- and repository-scale models of the 
underground facility are used in TM analyses to 
establish the intensity and distribution of ground 
movement (rock deformations, collapse, and other 
changes that may affect the integrity or geometrical 
configuration of openings within the underground 
facility). The number and variety of models permit the 
examination of conditions along drift-parallel and 
drift-normal directions. 
The Drift Degradation Analysis is based upon a drift scale model that considers changes in rock mass 
properties throughout the repository. The Drift Degradation Analysis presented in Section 3.1.2.8 analyzes 
data at the drift scale based upon data from the ESF main loop and the ECRB cross drift. Maximum block 
sizes within the several units of the repository horizon are analyzed. The distribution of block sizes due to 
variations in strength, deformational and geometrical properties of the rock matrix and the fractures in 
underground conditions is analyzed. The DRKBA is a three dimensional analysis that takes into account the 
orientation of the joints relative to the drift orientation. 
EBS PMR Section 3.1.2.8 
9. The principles formulating the TM analytical 
methodology, underlying assumptions, resulting 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
A-37 

Subissue RDTME Subissue 3: Thermal-Mechanical Effects on Underground Facility Design 
and Performance 
Component 1 - Thermal-Mechanical Effects on Design of Underground Facility 
Acceptance Criterion PMR Approach and Section Reference 
limitations, and various steps involved in the design 
procedures are clearly explained and justified. 
10. Time sequences of thermal loading used in TM 
design and analyses are clearly defined. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
11. The TM design and analyses consider the presence 
of roof supports (bolts, shotcrete, concrete, and steel 
liners, as applicable), consider the interaction between 
rock and supports, and address the degradation of 
supports with time under high temperature moisture 
conditions as they affect the maintainability of stable 
openings during the extended preclosure period. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
12. Results of the TM analyses, including the 
consideration of ground support (e.g., liners), are 
accounted in the determination of maintenance 
requirements for the underground facility. 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
13. The design discusses maintenance plans for 
keeping the underground openings stable, with 
particular attention to maintaining the option for 
retrieval. (if the details of retrieval operations/plans 
are found in other sections of the LA, a reference to 
such sections would be acceptable.) 
Design considerations are not included in this PMR. The acceptance criterion will be applied appropriately in 
the design process. 
Component 2 - Effects of Seismically Induced Rockfall on Waste Package Performance 
Acceptance Criterion PMR Approach and Section Reference 
1. Approved QA and control procedures and standards 
were applied to collection, development and 
documentation of data, methods, models, and codes. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. It used, expert elicliation is conducted and 
documented in accordance with the guidance in 
NUREG-1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
A-38 

Subissue RDTME Subissue 3: Thermal-Mechanical Effects on Underground Facility Design 
and Performance 
Component 2 - Effects of Seismically Induced Rockfall on Waste Package Performance 
Acceptance Criterion PMR Approach and Section Reference 
3. The seismic hazard inputs used to estimate rockfall 
potential are consistent with the inputs used in the 
design and PAs as established in DOE's TR-3 
reviewed and accepted by NRC. 
The Drift Degradation Analysis is based upon design basis seismic ground motion. The seismic hazard inputs 
used to estimate rockfall potential are consistent with the inputs used in the design and PAs as established in 
DOE's TR-3 reviewed and accepted by NRC. Both Frequency-Category-1 and Frequency-Category-2 design 
basis ground motion as defined in DOE's TR-3 have been considered in the Drift Degradation Analysis to 
estimate rockfall potential. The peak ground accelerations associated with each Frequency-Category were 
provided by NEPO and used as inputs in the Drift Degradation Analysis. 
EBS PMR 3.1.2.8 
4. Size distribution of rocks that may potentially fall 
on the WPs is estimated from site-specific data (e.g., 
distribution of joint patterns, spacing, and orientation 
in three dimensions) with adequate consideration of 
associated uncertainties. 
The Drift Degradation Analysis is based upon a probabilistic key block analysis. The key block analysis 
presented in Section 3.1.2.8 is based upon the collection of data for joint patterns, spacing, and orientation 
from underground detailed line surveys conducted in the ESF main loop and the ECRB cross drift. The joint 
data is analyzed statistically to account for uncertainties in joint properties. 
EBS PMR Section 3.1.2.8 
6. The TM analyses that provide the background 
conditions on which seismic loads are superimposed 
consider time-dependent jointed rock behavior. 
The Drift Degradation Analysis considers the change in rock mass properties due to thermal loading. As 
discussed in Section 3.1.2.8, the analysis accounts for time-dependent and thermal effects with joint cohesion 
degradation as discussed in CRWMS M&O 1999d. 
EBS PMR Section 3.1.2.8 
7. Rockfall analyses consider, in a rational and 
realistic way through dynamic analyses, the 
possibility of multiple blocks failing onto a WP 
simultaneously, and the extent of the potential rockfall 
area around an individual emplacement drift as well as 
over the entire repository as functions of ground 
motions. 
The Drift Degradation Analysis is a probabilistic model that considers the probability of multiple blocks falling. 
Rockfall analyses consider, in a rational and realistic way through dynamic analyses, the possibility of multiple 
blocks failing onto a WP simultaneously, and the extent of the potential rockfall area around an individual 
emplacement drift as well as over the entire repository as functions of. ground motions. 
EBS PMR Section 3.1.2.8 
A-39 

Subissue RDTME Subissue 3: Thermal-Mechanical Effects on Underground Facility Design 
and Performance 
Component 3 - Thermal-Mechanical Effects on Flow into Emplacement Drifts 
Acceptance Criterion PMR Approach and Section Reference 
1. Approved QA, control procedures, and standards 
were applied to collection, development and 
documentation of data, methods, models, and codes. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. If used, expert elicitation is conducted and 
documented in accordance with the guidance in 
NUREG-1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
3. Time-dependent changes in size and shape of the 
emplacement drifts due to thermally induced ground 
movements (rock deformations, collapse, and other 
changes that may affect the integrity and geometrical 
configuration of underground openings) are estimated 
taking into account the uncertainties in the context of 
their impacts an performance. 
The Drift Degradation Analysis estimate the changes in size and shape of emplacement drifts. 
Time-dependent changes in size and shape of the emplacement drifts due to thermally induced ground 
movements are estimated in the Drift Degradation Analysis. The full range of joint geometry variability based 
on tunnel mapping data has been used in the Drift Degradation Analysis to account for uncertainty in rock 
mass behavior. Furthermore, a conservative approach to estimate the time-dependent effects on opening size 
and shape has been used in the Drift Degradation Analysis to account for uncertainty. 
EBS PMR Section 3.1.2.8. 
A-40 

IRSR Thermal Effects on Flow (Revision 2) 
Subissue TEF Subissue 1: Is The U.S Department Of Energy Thermohydrologic Testing 
Program, Including Performance Confirmation Testing, Sufficient To Evaluate The 
Potential For Thermal Reflux To Occur In The Near Field? 
Programmatic Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
1. DOE's thermohydrologic testing program was 
developed under acceptable quality assurance 
procedures (QAP). Data were collected and 
documented under purview of these procedures. 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. Expert elicitation may be used for, but not 
necessarily limited to, assessing if conceptual models 
bound the range of thermally driven refluxing 
expected at YM, in addition to thermohydrologic 
testing to provide conservative bounds to estimates. 
All expert elicitation are conducted and documented 
in accordance with NUREG - 1563 or other acceptable 
approaches. 
No expert elicitation was conducted for this PMR. 
Technical Acceptance Criteria 
Acceptance Criterion PMR Approach and Section Reference 
1.1 Thermohydrologic tests are designed and 
conducted with the explicit objective of testing 
conceptual and numerical models so that critical 
thermohydrologic processes can be observed and 
measured. 
Tests are being conducted at quarter scale to simulate thermal and hydrological effects within the drift. The 
tests record temperature, relative humidity, and saturation levels within the EBS components that can be 
directly compared with results from the Water Distribution and Removal Model or other TH models. 
1.4 Thermohydrologic tests are designed and 
conducted for temperature ranges expected for 
repository operating conditions. 
The tests being conducted simulate waste package heating with a waste package heater, and repository heating 
through peripheral heaters. These heaters develop a temperature environment within the EBS that is identical 
to the EBS repository environment. 
1.3 Thermohydrologic tests are designed and 
conducted at different scales to discern scale effects 
on observed phenomena. 
The quarter scale test simulate repository conditions at an increased scale relative to bench scale experiments to 
discern scale effects on observed effects. 
1.2 Thermohydrologic tests are designed and The quarter-scale tests are being conducted with J-13 groundwater. The tests simulate the interaction of the JA-
41 

Subissue TEF Subissue 1: Is The U.S Department Of Energy Thermohydrologic Testing 
Program, Including Performance Confirmation Testing, Sufficient To Evaluate The 
Potential For Thermal Reflux To Occur In The Near Field? 
Technical Acceptance Criteria 
Acceptance Criterion PMR Approach and Section Reference 
conducted with explicit consideration of TH, thermalchemical, 
and hydrologic-chemical couplings. 
13 groundwater with EBS components that would result in the formation of precipitates and salts due to 
evaporation of water, and the resulting concentration of solutes. 
1.8 Thermohydrologic tests are designed and 
conducted such that the thermal test environment is 
sufficiently characterized so that uncertainty in 
property values does not result in unacceptable 
uncertainty in thermal test results interpretation 
The Quarter Scale Tests provide information on temperature, relative humidity and saturation levels at 
representative sampling locations to account for uncertainty in property values. 
1.7 Thermohydrologic tests are designed and 
conducted to account for all mass and energy 
losses/gains in the thermal test system. 
The Quarter Scale Tests measure the amount of water injected into the test cell, the amount of water stored in 
EBS components, and the amount of water ejected by weighing of the test cell. 
1.6 Thermohydrologic tests are designed and 
conducted to evaluate the possibility for occurrence of 
cyclic wetting/drying on WP surfaces. 
The quarter scale tests simulate repository conditions by setting central heater and peripheral heater power that 
results in the drying effects due to temperature increase, and wetting effects due to temperature decrease within 
EBS components. 
1.5 Thermohydrologic tests are designed and 
conducted to determine if water refluxes back to the 
heaters during the heating or cool-down phases of the 
tests. 
The quarter scale tests simulate the thermal-hydrologic environment during the cooldown phase, and at high 
percolation rates that bounds water seepage due to refluxing. 
3. If the thermohydrologic testing program is not 
complete at the time of LA submittal, DOE has 
explained why the testing program does not need to be 
completed for the LA and identified specific plans for 
completion of the testing program as part of the 
performance confirmation program. 
See M&O Status response presented above. The EBS PMR provides bounding calculations in the absence of 
complete data, and model uncertainties. For example, for the base case analysis for radionuclide transport, the 
calculations do not consider chemical retardation which is a conservative assumption. 
EBS PMR Section 3.1.3 
Performance confirmation is not addressed in this PMR. The acceptance criterion will be applied appropriately 
to the Performance Confirmation Program. 
1.9 Thermohydrologic tests are designed and 
conducted such that the accuracy in the measurement 
of the test environment saturation is sufficient to 
discern the relative ability of different conceptual 
models to represent TH processes in heated partially 
Heat Dissipation Probes are used to assess saturation levels in the EBS backfill and invert components. The 
probes have sufficient resolution to discern changes in saturation levels, and to provide a comparison to the 
predictions of TH models. 
A-42 

Subissue TEF Subissue 1: Is The U.S Department Of Energy Thermohydrologic Testing 
Program, Including Performance Confirmation Testing, Sufficient To Evaluate The 
Potential For Thermal Reflux To Occur In The Near Field? 
Technical Acceptance Criteria 
Acceptance Criterion PMR Approach and Section Reference 
saturated fractured porous media. 
Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Programmatic Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
1. DOE's thermohydrologic modeling analyses were 
developed and documented under acceptable quality 
assurance procedures (QAP). 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. Expert elicitation may be used for, but not 
necessarily limited to, selecting a conceptual model 
and its parameters.. All expert elicitation are 
conducted and documented in accordance with 
NUREG - 1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
A-43 

Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
1.1 Sufficient data are available to adequately define 
relevant parameters, parameter values, and conceptual 
models. Specifically, DOE should demonstrate that 
uncertainties and variabilities in parameter values are 
accounted for using defensible methods. The technical 
bases for parameter ranges, probability distributions or 
bounding values used are provided. Parameter values 
(single values, ranges, probability distributions, or 
bounding values) are derived from site-specific data or 
an analysis is included to show the assumed parameter 
values lead to a conservative effect on performance. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
chemical effects such as the alteration of groundwater chemistry (Section 3.1.4). 
The technical bases for the parameter ranges for the process models are presented in the PMR. 
EBS PMR Sections 3.1.1 through 3.1.4 
1.2 Sufficient data are available to adequately define 
relevant parameters, parameter values, and conceptual 
models. Specifically, DOE should demonstrate that 
analyses are consistent with site characteristics in 
establishing initial conditions, boundary conditions, 
and computational domains for conceptual models 
evaluated. 
Data on EBS processes are being collected at the current time for the Water Distribution and Removal Model 
(Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding calculations 
have been performed to estimate physical effects such as flow through drip shields (Section 3.1.1), and 
chemical effects such as the alteration of groundwater chemistry (Section 3.1.4). 
The EBS Process models are consistent with the site characteristics for the models developed. 
EBS PMR Sections 3.1.1 through 3.1.4. 
2.1 Models are based on well-accepted principles of 
heat and mass transfer applicable to unsaturated 
geologic media. 
The EBS Process Models are based upon well accepted principles for heat and mass transfer. The NUFT and 
TOUGH2 codes are used by DOE to simulate heat and mass transfer through partially saturated, fractured 
porous media. These codes are based on well-accepted principles of heat and mass transfer applicable to 
unsaturated geologic media. 
EBS PMR Sections 3.1.1 through 3.1.4. 
2.2 Models include, at a minimum, the processes of 
evaporation and condensation and the effects of 
discrete geologic features 
The EBS Process Models are based upon NUFT calculations incorporating phase changes for the fracture 
model. Currently, they do not simulate evaporation and condensation for an open void space. 
Data on open void space EBS processes being collected at the current time for the Water Distribution and 
Removal Model (Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, 
bounding calculations have been performed for seepage flow to the drift. 
EBS PMR Sections 3.1.1 and 3.1.2 
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Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
2.3 Models include, at a minimum, an evaluation of 
important thermohydrological phenomena, such as: (i) 
multidrift dry-out zone coalescence, (ii) lateral 
movement of condensate, (iii) cold-trap effect, (iv) 
repository edge effects, and (v) condensate drainage 
through fractures. 
The EBS Multiscale Thermohydrologic Model provides analysis of repository of thermohydrological 
phenomena at various locations within the repository. The degree of multi-drift dry-out zone coalescence will 
be a function of the thermal load specified in the final design of the repository. Recent, proposed design 
modifications by DOE to reduce the repository thermal load to 60 MTU/acre will minimize, if not eliminate, 
dry-out zone coalescence. Recent DOE models that include the active fracture model appear to adequately 
predict the extent of dryout surrounding the emplacement drifts. 
EBS PMR Sections 3.1.1, 3.1.2, and 3.1.4 
2.4 Models include all significant repository design 
features. 
The models are based upon the current significant EDA-II repository design features as stated in the PMR. 
All EBS-PMR sections apply. 
2.5 Models are capable of accommodating variation in 
infiltration. 
The models have analyzed thermal-hydrological phenomena for the present day, monsoon, and glacial climates. 
See EBS PMR Sections 3.1.1 through 3.1. 
2.6 Conceptual model uncertainties have been defined 
and documented and effects on conclusions regarding 
performance assessed. 
Each of the supporting EBS Process Models address specific issues of model uncertainty. For uncertain 
conditions, bounding assumptions are used throughout where appropriate. 
See EBS PMR Sections 3.1.1 through 3.1. 
2.7 Mathematical models are consistent with 
conceptual models, based on consideration of site 
characteristics. 
In each EBS process model, the mathematical models are consistent with conceptual models. Note the AP- 
3.10Q process requires that detailed process models are consistent with conceptual models. 
The EBS process models for thermal hydrological effects are based upon initial conditions boundary 
conditions, and computational domains consistent with site characteristics. The thermal hydrology models 
used in Sections 3.1.1 through 3.1.4 are based upon the selection of NBS hydrologic and thermal properties 
used in the UZ process model. The initial conditions, and boundary conditions for the models for specific 
locations use the same infiltration rates, and temperature and pressure boundary conditions consistent with the 
UZ process Model (Section 3.1.4) 
EBS PMR Sections 3.1.1 through 3.1.4 
2.8 Alternative models and modeling approaches, 
which are consistent with available data and current 
Section 3.1.2 addresses alternative models involving fully coupled THC. Such simulation methods can be 
applied as they become available, and as the required data, including numerical settings used to operate the 
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Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
scientific understanding, have been investigated, 
limitations defined, and results appropriately 
considered. 
simulation codes are qualified. The approach used in this PMR is applied to address conceptual issues and to 
evaluate bounding conditions for the performance of engineered barriers. 
2.9 Results from different mathematical models have 
been compared to judge robustness of models. 
Different mathematical models are used for comparison between closed form and numerical solutions. 
The DOE used appropriate procedures to construct and test numerical models for predicting seepage and flow. 
For the case of the Water Distribution and Removal Model, the results of the NUFT calculations were 
compared to a closed form analytical solution for the prediction of fluxes in and near the EBS (CRWMS M&O 
2000q). The software codes used for the models are subject to verification and testing under the procedure APSI.
1Q. 
EBS PMR Sections 3.1 
See also CRWMS 2000b, CRWMS 2000i CRWMS 2000q and CRWMS 2000t. 
2.10 Models used to predict shedding around 
emplacement drifts are shown to contain an adequate 
level of heterogeneity in media properties. 
The EBS Multiscale Thermohydrologic Model considers 31 chimney locations within the repository that 
captures an adequate level of heterogeneity in percolation rates at the repository horizon. 
EBS Section 3.1.4 
2.11 TH models have been demonstrated to be 
appropriate for the temperature regime expected at the 
repository. 
The thermal hydrological calculations are appropriate for the expected regime. 
The current EDA-II design is based upon an 80 m emplacment drift spacing with waste canisters placed 
together to develop a line thermal loading. The repository is a subboiling repository. The models are based 
upon the NUFT thermal hydrological code that is appropriate for this temperature regime. 
EBS PMR Sections 3.1.1 through 3.1.4 
2.12 Models include radiative heat transport unless it 
is shown that radiative heat loss by a WP is not 
significant. 
The EBS Multiscale Thermohydrologic Model includes radiative heat transfer. For thermal effects within the 
drift, the NUFT calculations consider radiative heat transport. The RADPRO software routine calculates view 
factors using a standard approach in heat transfer analysis. 
EBS PMR Section 3.1.4 
2.13 Models include the effect of ventilation 
particularly if ventilation could result in deposition or 
Ventilation effects are included in the EBS multiscale thermal hydrological model. Data on EBS processes for 
evaporation and condensation are being collected at the current time for the Water Distribution and Removal 
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Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
condensation of moisture on a WP surface. Model (Section 3.1.1), and the Physical and Chemical Environment Model. Where appropriate, bounding 
calculations have been performed to estimate physical effects such as the formation of condensation. 
EBS PMR Section 3.1.4 
3. Coupling of processes has been evaluated using a 
methodology in accordance with NUREG-1466 or 
other acceptable methodology. Coupled processes 
may be uncoupled, if it is shown that the uncoupled 
model results bound the predictions of the fullycoupled 
model results. 
The EBS Process models provide bounding calculations in the absence of data or uncertainty in data. 
Section 3.1.2 addresses alternative models. Such simulation methods can be applied as they become available, 
and as the required data, including numerical settings used to operate the simulation codes are qualified. The 
approach used in this PMR is applied to address conceptual issues and to evaluate bounding conditions for the 
performance of engineered barriers. 
See EBS PMR Sections 3.1.1 through 3.1.4 
4. The dimensionality of models, which include 
heterogeneity at appropriate scales and significant 
process couplings, may be reduced, if shown that the 
reduced dimension model bounds the predictions of 
the full dimension model. 
The EBS Multiscale Thermohydrologic Model considers the appropriate dimensions for specific problems. 
The potential repository-scale heterogeneity is represented by the drift scale active properties set which 
captures the properties for various strata. Lateral variability within the potential repository footprint is 
represented by the 31 drift-scale-model locations used in the MSTH model. These locations are regularly 
distributed over the potential repository footprint. This reduces the general three dimensional problem to a 
series of two dimensional problems. 
EBS PMR Section 3.1.4 
5. Equivalent continuum models are acceptable for the 
rock matrix and small discrete features, if it can be 
demonstrated that water in small discrete features is in 
continuous hydraulic equilibrium with matrix water. 
Significant discrete features, such as fault zones, 
should be represented separately unless it can be 
shown that inclusion in the equivalent continuum 
model (ECM) produces a conservative effect on 
calculated overall performance. 
Equivalent continuum models are used as appropriate where conservative bounding assumptions are made. In 
the Water Distribution and Removal Model, an active fracture concept for a dual continuum model is used for 
the NBS with properties selected from inverse modeling. This modeling approach simulates matrix-fracture 
interaction. 
For evaluating the condensation below the drip shield, the ECM approach was used, and is considered a 
bounding calculation since the treatment of the fractured rock as an equivalent continuum tends to retain water 
within the EBS. 
EBS PMR Section 3.1.1 
6. Accepted and well-documented procedures have 
been adopted to construct and calibrate numerical 
models used. 
Inverse modeling is used to calibrate properties for the natural barrier system in the EBS Process Models. 
See EBS PMR Section 3.1.3 
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Subissue TEF Subissue 2: Is the U.S. Department of Energy Thermohydrologic Modeling 
Approach Sufficient to Predict the Nature and Bounds of Thermal Effects on Flow in 
the Near Field? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
7. Results of process-level models have been verified 
by demonstrating consistency with 
results/observations from field-scale, 
thermohydrologic tests. In particular, sufficient 
physical evidence should exist to support the 
conceptual models used to predict thermally driven 
flow in the near field. 
Comparison of the EBS Process Models to field scale tests is in progress. 
Subissue TEF Subissue 3: Does The U.S. Department Of Energy Total System Performance 
Assessment Adequately Account For Thermal Effects On Flow? 
Programmatic Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
1. DOE's analyses were developed and documented 
under acceptable quality assurance procedures (QAP). 
Activities associated with development of this Process Model Report and its related Analysis/Model Reports 
were determined to be subject to the quality assurance program as described in the Quality Assurance 
Requirements and Description (DOE 2000) document. As such, collection of related data, development of 
analyses and models, and use and validation of software is subject to the requirements of procedures developed 
to implement quality assurance program requirements. 
2. Expert elicitation may be used for, but not 
necessarily limited to, justifying the use of abstracted 
models in DOE's TSPA. All expert elicitation are 
conducted and documented in accordance with 
NUREG - 1563 or other acceptable approaches. 
No expert elicitation was conducted for this PMR. 
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Subissue TEF Subissue 3: Does The U.S. Department Of Energy Total System Performance 
Assessment Adequately Account For Thermal Effects On Flow? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
2.1 Sufficient data are available to adequately define 
relevant parameters, parameter values and conceptual 
models. Specifically, DOE should demonstrate that 
uncertainties and variabilities in parameter values are 
accounted for using defensible methods. The technical 
bases for parameter ranges, probability distributions or 
bounding values used are provided. Parameter values 
(single values, -ranges, probability distributions, or 
bounding values) are derived from site-specific data or 
an analysis is included to show the assumed parameter 
values lead to a conservative effect on performance. 
The technical bases for the parameter ranges for process models are stated throughout. Data on EBS processes 
are being collected at the current time for the Water Distribution and Removal Model (Section 3.1.1), and the 
Physical and Chemical Environment Model. Where appropriate, bounding calculations have been performed 
to estimate physical effects such as flow through drip shields (Section 3.1.1), and chemical effects such as the 
alteration of groundwater chemistry (Section 3.1.4). 
EBS PMR Section 3.1 
2.2 Analyses are consistent with site characteristics in 
establishing initial conditions, boundary conditions, 
and computational domains for conceptual models 
evaluated. 
The EBS process models for thermal hydrological effects are based upon initial conditions boundary 
conditions, and computational domains consistent with site characteristics. The thermal hydrology models 
used in Sections 3.1.1 through 3.1.4 are based upon the selection of NBS hydrologic and thermal properties 
used in the UZ process model. The initial conditions, and boundary conditions for the models for specific 
locations use the same infiltration rates, and temperature and pressure boundary conditions consistent with the 
UZ process Model (Section 3.1.4) 
EBS PMR Sections 3.1.1 through 3.1.4 
3.1 Performance affecting heat and mass transfer 
mechanism, including processes observed in available 
thermohydrologic tests and experiments, have been 
identified and incorporated into the TSPA. 
Specifically, it is necessary to either demonstrate that 
liquid water will not reflux into the underground 
facility or incorporate refluxing water into the TSPA 
and bound the potential adverse effects of: (i) 
corrosion of the WP; (ii) accelerated transport of 
radionuclides; and (iii) alteration of hydraulic and 
transport pathways that result from refluxing water. 
The EBS process models incorporate thermal refluxing in the thermal hydrological calculations. The Water 
Distribution Model, and the Multiscale Thermohydrologic Model consider the waste package heat loading for 
the EDA-II design. The TH calculations consider the effects of this heat loading on the reduction of liquid 
moisture content, and the reduction in capillary pressure due to initial heating in EBS components, and the 
surrounding media. After waste package heat decays, the models simulate the increase in liquid moisture 
content, and increase in capillary pressure due to the refluxing of water. 
EBS PMR Sections 3.1.1 through 3.1.4 
3.2 Significant Geologic Repository Operations Area 
(GROA) underground facility design features, such as 
the addition of backfill or drip shields, that can result 
in changes in TSP have been identified and 
incorporated into the TSPA. 
The EBS Process Models incorporate significant design features of the underground facility. 
The process models incorporate underground design features with the inclusion of backfill and drip shields. 
The hydrologic performance of components as governed by their flow properties are incorporated into the 
models. 
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Subissue TEF Subissue 3: Does The U.S. Department Of Energy Total System Performance 
Assessment Adequately Account For Thermal Effects On Flow? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
EBS PMR Sections 3.1.1 through 3.1.4 
3.3 Conceptual model uncertainties have been defined 
and documented, and their effects on conclusions 
regarding TSP have been assessed. 
Each of the major EBS process models is documented in a referenced report that includes a discussion of the 
model uncertainties. 
EBS PMR Section 3.1.1 through 3.1.4 
3.4 Mathematical models are consistent with 
conceptual models, based on consideration of site 
characteristics. 
The EBS process models for thermal hydrological effects are based upon initial conditions boundary 
conditions, and computational domains consistent with site characteristics. The thermal hydrology models 
used in Sections 3.1.1 through 3.1.4 are based upon the selection of NBS hydrologic and thermal properties 
used in the UZ Process Model. The initial conditions, and boundary conditions for the models for specific 
locations use the same infiltration rates, and temperature and pressure boundary conditions consistent with the 
UZ Process Model (Section 3.1.4) 
EBS PMR Sections 3.1.1 through 3.1.4 
3.5 Alternative models and modeling approaches, 
consistent with available data and current scientific 
understanding, are investigated; limitations defined; 
and results appropriately considered. 
Alternative models are presented. 
Section 3.1.1 through 3.1.3 present alternative models for Water Distribution and Removal, Bulk Physical and 
Chemical Environment in the EBS, and Radionuclide Transport respectively. Section 3.1.2 addresses 
alternative models. Such simulation methods can be applied as they become available, and as the required 
data, including numerical settings used to operate the simulation codes are qualified. The approach used in this 
PMR is applied to address conceptual issues and to evaluate bounding conditions for the performance of 
engineered barriers. 
3.6 Results from different mathematical models have 
been compared to judge robustness of results. 
The results of the numerical calculations have been compared to hand calculations where appropriate. 
The DOE used appropriate procedures to construct and test numerical models for predicting seepage and flow. 
For the case of the Water Distribution and Removal Model, the results of the NUFT calculations were 
compared to a closed form analytical solution for the prediction of fluxes in and near the EBS (CRWMS M&O 
2000q). The software codes used for the models are subject to verification and testing under the procedure APSI.
1Q. 
EBS PMR Sections 3.1.1 through 3.1.4 
4. Coupling of thermal processes has been evaluated 
using a methodology in accordance with NUREGThe 
EBS Process Model use bounding calculations where appropriate. Section 3.1.2 addresses alternative 
models. Such simulation methods can be applied as they become available, and as the required data, including 
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Subissue TEF Subissue 3: Does The U.S. Department Of Energy Total System Performance 
Assessment Adequately Account For Thermal Effects On Flow? 
Technical Acceptance Criterion 
Acceptance Criterion PMR Approach and Section Reference 
1466 (Nataraja and Brandshaug, 1992) or other 
acceptable methodology. Coupled processes may be 
uncoupled, if it is shown that the uncoupled model 
results bound the predictions of the fully-coupled 
model results. 
numerical settings used to operate the simulation codes are qualified. The approach used in this PMR is 
applied to address conceptual issues and to evaluate bounding conditions for the performance of engineered 
barriers. 
EBS PMR Sections 3.1.1 through 3.1.4 
5. The dimensionality of models used to assess the 
importance of refluxing water on repository 
performance may be reduced if it is shown that the 
reduced dimension model bounds the prediction of the 
full dimension model in performance. 
The EBS Process Model use boundary calculations where appropriate. The potential repository-scale 
heterogeneity is represented by the drift scale active properties set which captures the properties for various 
strata. Lateral variability within the potential repository footprint is represented by the 31 drift-scale-model 
locations used in the MSTH model. These locations are regularly distributed over the potential repository 
footprint. This reduces the general three dimensional problem to a series of two dimensional problems. 
EBS PMR Sections 3.1.1 through 3.1.4 
6. Results of the TSPA related to TEF have been 
verified by demonstrating consistency with results of 
process-level models. 
The EBS Process Model use bounding calculations where appropriate. 
See EBS PMR Sections 3.1.1 through 3.1.4. 
7. Sensitivity and importance analyses were 
conducted to assess the need for additional data or 
information with respect to TEF. 
Sensitivity analyses are conducted where appropriate in the EBS Process Models. Data on EBS processes are 
being collected at the current time for the Water Distribution and Removal Model (Section 3.1.1), and the 
Physical and Chemical Environment Model. Where appropriate, sensitivity and importance analyses have 
been performed as described by the parametric studies in Sections. 3.1.1 through 3.1.4. 
EBS PMR Sections 3.1.1 through 3.1.4. 
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IRSR Total System Performance Assessment Integration (Revision 1) 
Subissue TSPAI Subissue 4: Scenario Analysis 
Element 1 
Acceptance Criterion PMR Approach and Section Reference 
T1 - DOE has identified a comprehensive list of 
processes and events that: (1) are present or might 
occur in the Yucca Mountain region and (2) includes 
those processes and events that have the potential to 
influence repository performance 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides a list of 
the processes and events applicable to this PMR. The AMR provides a description of the screening arguments 
and dispositions for the FEPs and has been thoroughly reviewed by subject mater experts. Also, in parallel 
with the release of Revision 0 of the FEPs database, documentation will be produced to describe the 
development of the FEPs database. It is planned to include a description of the FEPs process in sufficient 
detail to demonstrate the comprehensiveness of the database. It will describe how FEPs were identified by a 
variety of methods, including expert judgment, informal elicitation, event tree analysis, stakeholder review, 
and regulatory stipulation. 
Element 2 
Acceptance Criterion PMR Approach and Section Reference 
T1 - DOE has provided adequate documentation 
identifying how its initial list of processes and events 
has been grouped into categories. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. Documentation is maintained 
of all mapping of FEPs into primary and secondary categories. For comprehensiveness, traceability is 
maintained from the secondary to the related primary FEPs. 
In addition, in parallel with the release of Revision 0 of the FEPs database, documentation will be produced to 
describe the development of the FEPs database. It is planned to include a description of the categorization 
scheme with justification on why it is sufficient. 
T2 - Categorization of processes and events is 
compatible with the use of categories during the 
screening of processes and events. 
In parallel with the release of Revision 0 of the FEPs database, documentation will be produced to describe the 
development of the FEPs database. It is planned to include a description of the categorization scheme with 
justification on why it is sufficient. In addition, documentation is maintained of all mapping of FEPs into 
primary and secondary categories. For comprehensiveness, traceability is maintained from the secondary to the 
related primary FEPs. 
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Subissue TSPAI Subissue 4: Scenario Analysis 
Element 3 
Acceptance Criterion PMR Approach and Section Reference 
T1 - Categories of processes and events that are not 
credible for the Yucca Mountain repository because of 
waste characteristics, repository design, or site 
characteristics are sufficient justification is provided 
for DOE's conclusions 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. Documentation includes a 
statement of the screening decision for each FEP. Justification is provided for each excluded FEP including 
the criterion on which it was excluded and the technical basis for the screening argument. 
T2 - The probability assigned to each category of 
processes and events is consistent with site 
information, well documented, and appropriately 
considers uncertainty. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. Probability estimates for 
FEPs are based on technical analysis of the past frequency of similar events consistent with site information, 
well documented, and appropriately considers uncertainty. 
T3 - Processes and events may be screened from the 
performance assessment on the basis of their 
probability of occurrence, provided DOE has 
demonstrated that they have a probability of less than 
one chance in 10,000 of occurring over 10,000 years. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. Justification is provided for 
each excluded FEP including the criterion on which it was excluded and the technical basis for the screening 
argument. For excluded FEPs, documentation includes the criterion on which it was excluded and the 
technical basis for the screening argument. The probability assigned to FEPs may be one of the screening 
criteria. FEPs may be excluded from the TSPA only if they can be shown to have a probability of occurrence 
of less than .0000001/year. 
T4 - Categories of processes and events may be 
omitted from the performance assessment on the basis 
that their omission would not significantly change the 
calculated expected annual dose, provided DOE has 
demonstrated that excluded categories of processes 
and events would not significantly change the 
calculated expected annual dose. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. For omitted categories, 
documentation includes the criterion on which it was excluded and the technical basis for the screening 
argument. 
Element 4 
Acceptance Criterion PMR Approach and Section Reference 
T1 - DOE has provided adequate documentation 
identifying: (1) whether processes and events have 
been address through consequence model abstraction 
or scenario analysis and (2) how the remaining 
categories of processes and events have been 
combined into scenario classes. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. FEPs that have not been 
excluded are identified as either expected FEPs or disruptive FEPs. Expected FEPs will be included in the 
TSPA-SR nominal scenario, which is simulated by the base case model described in the TSPA-SR 
documentation. 
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Subissue TSPAI Subissue 4: Scenario Analysis 
Element 4 
Acceptance Criterion PMR Approach and Section Reference 
T2 - The set of scenario classes is mutually exclusive 
and complete. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
documentation and justification for screening arguments and TSPA dispositions. Also, in parallel with the 
release of Revision 0 of the FEPs database, documentation will be produced to describe the development of the 
FEPs database. It is planned to include in the documentation, a description of the FEPs process in sufficient 
detail to demonstrate the set of scenario classes is mutually exclusive and complete. 
Element 5 
Acceptance Criterion PMR Approach and Section Reference 
T1 - Scenario classes that are not credible for the 
Yucca Mountain repository because of waste 
characteristics, repository design, or site 
characteristics, individually or in combination, are 
identified and sufficient justification is provided for 
DOE's conclusions. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
justification for screening arguments and TSPA dispositions. Scenarios are screened using the same 
regulatory, probability, and consequence criteria used for screening individual FEPs. Documentation of this 
process includes identification of any scenarios that have been screened from the analysis and the technical 
basis for that screening decision. 
T2 - The probability assigned to each scenario class is 
consistent with site information, well documented, 
and appropriately considers uncertainty. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
justification for screening arguments and TSPA dispositions. Probability estimates for scenario classes are 
based on analyses similar to probabilities assigned for individual FEPs. 
T3 - Scenario classes may be omitted from the 
performance assessment on the basis of their 
probability of occurrence, provided: (1) the 
probability used for screening the scenario class is 
defined from combinations of initiating processes and 
events and (2) DOE has demonstrated that they have a 
probability of less than one chance in 10,000 of 
occurring over 10,000 years. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
justification for excluding scenario classes. The probability assigned to scenario classes is one of the screening 
criteria. Scenario classes may be excluded from the TSPA only if they can be shown to have a probability of 
occurrence of less than 10-8/year. Justification is provided for each excluded scenario class, including the 
criterion on which it was excluded and the technical basis for the screening argument. In addition, in parallel 
with the release of Revision 0 of the FEPs database, documentation will be produced to describe the 
development of the FEPs database including a description of screening and specifying scenarios for TSPA 
analysis. 
T4 - Scenario classes may be omitted from the 
performance assessment on the basis that their 
omission would not significantly change the 
calculated expected annual dose, provided DOE has 
demonstrated that excluded categories of processes 
and events would not significantly change the 
calculated expected annual dose. 
Sections 1.5.1 and 2.4 of this PMR describes the features, events, and processes in this PMR. The AMR 
supporting this section, EBS Features, Events, and Processes/Degradation Modes Analysis, provides 
justification for excluding scenario classes. For excluded scenario classes, documentation includes the 
criterion on which it was excluded and the technical basis for the screening argument. In addition, in parallel 
with the release of Revision 0 of the FEPs database, documentation will be produced to describe the 
development of the FEPs database including a description of screening and specifying scenarios for TSPA 
analysis. 
A-54