Near Field Environment Process Model Report Rev 00, ICN 01

TDR-NBS-MD-000001

July 2000


EXECUTIVE SUMMARY 
Waste emplacement and activities associated with construction of a repository system potentially 
will change environmental conditions within the repository system. These environmental 
changes principally result from heat generated by the decay of the radioactive waste, which 
elevates temperatures within the repository system. Elevated temperatures affect distribution of 
water, increase kinetic rates of geochemical processes, and cause stresses to change in magnitude 
and orientation from the stresses resulting from the overlying rock and from underground 
construction activities. The recognition of this evolving environment has been reflected in 
activities, studies and discussions generally associated with what has been termed the Near-Field 
Environment (NFE). 
The NFE interacts directly with waste packages and engineered barriers as well as potentially 
changing the fluid composition and flow conditions within the mountain. As such, the NFE 
defines the environment for assessing the performance of a potential Monitored Geologic 
Repository at Yucca Mountain, Nevada. The NFE evolves over time, and therefore is not 
amenable to direct characterization or measurement in the ambient system. Analysis or 
assessment of the NFE must rely upon projections based on tests and models that encompass the 
longterm processes of the evolution of this environment. This NFE Process Model Report 
(PMR) describes the analyses and modeling based on current understanding of the evolution of 
the near-field within the rock mass extending outward from the drift wall. 
The NFE PMR is one of nine PMRs that address the technical basis supporting the Total System 
Performance Assessment. The PMRs are supported by Analysis Model Reports. The NFE PMR 
is supported by four Analysis Model Reports and one Calculation, which provide detailed 
descriptions of the various near-field models. The Analysis Model Reports summarize thermal 
test results, thermal-hydrological-chemical (THC) processes and their abstraction, and features, 
events and processes (FEPs) used in Total System Performance Assessment. The Calculation 
summarizes thermal-hydrological-mechanical (THM) processes. Direct inputs to Total System 
Performance Assessment from the NFE PMR include the near-field host rock water and gas 
composition and the percolation flux above the crown of the emplacement drift. These serve as 
inputs for the Total System Performance Assessment in-drift geochemical environment model 
and the Total System Performance Assessment seepage model. Inputs to Total System 
Performance Assessment also include the drift wall temperature and relative humidity. 
Repository heat driven variability of each performance driver listed above is inherently included 
since the supporting process models used to characterize the heat and fluid flow processes 
occurring in the near-field host rock include repository heating as a model input. 
In addition to description of the process models and abstraction models, this PMR also addresses 
the Evolution of the Near-Field Environment Key Technical Issue, and the related Issue 
Resolution Status Report that the Nuclear Regulatory Commission considers important to 
repository performance. The PMR also addresses issues related to the NFE that have been 
identified by the Nuclear Waste Technical Review Board and by peer-review panels. 
The NFE evolves as a result of the coupling of thermal, hydrological, chemical, and mechanical 
processes. This environment develops principally in response to heat generated by decay of the 
radioactive waste. The resulting elevated temperatures drive coupled processes that cause
changes in the environment to occur. The elevated temperatures affect distribution of water, 
increase kinetic reaction rates of geochemical processes (resulting in potential for changes in 
water and gas chemistry), and cause stresses to change in magnitude and orientation. Heat from 
the emplaced waste results in enhanced coupled thermal-hydrological-chemical processes in the 
near-field rock mass that may extend for time periods of up to 10,000 years (driftwall 
temperatures have decreased below ~ 50C by 10,000 years). 
The major issues discussed in this PMR are: evolution of water and gas chemistry, thermally 
induced changes in hydrological conditions (such as saturation) that can influence seepage or 
percolation flux, changes in hydrological properties (such as fracture permeability) due to 
chemical processes, and changes in fracture hydrological properties due to mechanical responses. 
The PMR discusses the coupling in terms of: 
 thermal-hydrological responses (temperature regime evolution, moisture redistribution, 
relative humidities) 
 THC responses (water chemistry, gas composition, mineralogy changes, and changes in 
hydrological properties, such as fracture-plugging potential), and 
 THM responses, mainly in terms of changes in water flow patterns or hydrologic 
properties. 
Thermal-hydrological models have been used to determine the hydrological responses of the 
system. The models consider three infiltration cases, and three climates provided by activities 
from the Unsaturated Zone Flow and Transport PMR. The current best estimate of average (over 
the potential repository footprint) net-infiltration is 4.6 mm/yr, which is projected to be the netinfiltration 
rate for the next 600 years. This is then projected to be followed for the next 
1,400 years (until 2,000 years from present) by a warmer and wetter climate with net-infiltration 
of 12.2 mm/yr. For the next 8,000 years (the remainder of the 10,000 year compliance period), 
net-infiltration is estimated to be 17.8 mm/yr. These averages are as reported in the Unsaturated 
Zone Flow and Transport PMR; however, the models used to evaluate the near-field incorporated 
the detailed Unsaturated Zone Flow and Transport infiltration estimates for individual chimneys 
or cells evaluated in the model. This, therefore, considered the variations of infiltration over the 
footprint. As a result, the average infiltration values used in these models were higher than the 
overall footprint averages. The average of the infiltration values used were 6, 16, and 25 mm/yr, 
respectively. 
The NFE models incorporate the repository layout of Enhanced Design Alternative II(EDA II), 
which has greater drift spacing and is expected to result in lower temperatures below those of 
previous designs upon which NFE calculations were based, including the DOEs 1998 Viability 
Assessment of the Yucca Mountain site. The results of the NFE model analyses indicate that 
temperature increases within the rock mass may extend 600 m laterally from the potential 
repository footprint, with estimated temperature increases of 30 to 35C at the water table, and 
up to 5C at the ground surface. The temperatures do not entirely return to ambient levels for 
50,000 to 100,000 years.

 xi 
With the assumed design options (Enhanced Design Alternative II and 50-year ventilation, 
currently under revision), boiling will occur around the drifts; and the region experiencing the 
boiling temperature (~96C) will extend to a maximum diameter of about 24 meters with a zone 
of dryout that extends to 34 meters diameter. The above boiling temperature and dryout regions 
are not symmetrical around the drifts. The dryout zone extends about 17 meters into the pillars 
from the drift centerline and 10 and 22 meters above and below the drift centerline, respectively. 
Temperatures in the middle of the regions (pillars) between the waste emplacement drifts 
(tunnels) will increase to 80 to 85C. 
It should be noted that the Enhanced Design Alternative II design used in these analyses included 
backfilled drifts. The current design does not include backfill. This document (ICN 01) includes 
thermal-hydrological analyses of the no-backfill design, and THC and THM analyses are 
ongoing. These results will be included in Total System Performance Assessment modeling that 
supports the Site Recommendation. 
Additionally, a three-dimensional mountain-scale thermal-hydrological model indicates that 
temperatures above boiling are primarily located near the repository horizon. Rock drying is 
also limited to regions around the repository horizon specifically in locations with low 
infiltration rates. The models indicate that condensate from mobilized waters should drain 
through the pillar regions, although they also indicate regions of increased saturation that extend 
from a region in the pillar at the repository elevation, to include the rock above the drifts in the 
higher infiltration case. Sufficient drainage of condensate is predicted by the Unsaturated Zone 
Flow and Transport PMR analyses such that matrix saturation above the drifts during the thermal 
period will not be greatly or persistently increased for most locations within the potential 
repository. The drainage capacity is due to the relatively high fracture permeabilities of the 
potential repository hydrogeological units. The multiscale thermohydrologic model used as the 
basis for Total System Performance Assessment abstraction of the emplacement drift 
thermodynamic environment and near-field host rock percolation flux also indicates significant 
condensate drainage during the early heating period. An analogous response for each of the 
analyses (Unsaturated Zone Flow and Transport PMR and NFE PMR) is expected since both 
process models apply the same hydrologic property sets, infiltration rate boundary conditions, 
and conceptual flow models used to determine the flow of water through the fractures and rock 
matrix. 
The thermal test results to date are generally consistent with temperatures and saturations 
calculated by NFE models. The local and temporary differences observed are likely due to 
heterogeneity of the natural system which is not fully included in current models. 
The THC models, which are consistent with observations in thermal tests, indicate that the 
chemistry of water in the NFE will have relatively neutral pH values, ranging from 7 to 9, and 
total chloride concentrations that increase to a maximum of about four times the concentrations 
in the ambient pore water. The pH of the water decreases during the period from closure until 
around 10,000 years, when the pH begins to slowly return to higher values. Most of the 
chemical constituents return to values that are similar to those prior to waste emplacement. This 
implies that there are no long-term perturbations in water chemistry, with the possible exception 
of bicarbonate (HCO3
-), and silica (SiO 2). There is a significant decrease in carbon dioxide

 xii 
(CO2) concentration in fractures during drying period. The models indicate an increase in CO2 
gas and carbonate concentrations around the drift during rewetting. 
Changes to hydrologic properties were evaluated using the THC model, based on interaction of 
the constituents in the water with the rock, in response to temperatures. Specifically, the models 
were used to calculate dissolution and precipitation of minerals that would change the porosity 
and permeability of the fracture system. These analyses were done using revised estimates of 
fracture porosity (approximately 100 times the porosities used in past analyses) to assess the 
potential for changes to hydrologic properties. Given the current understanding of fracture 
porosities, the precipitation or dissolution of various chemical species or minerals was found to 
have negligible effects on fracture and matrix hydrological properties, for the 1% fracture 
porosity used as an initial condition. 
Because of the complexity of THC coupling, there are differences in approaches or views 
regarding how to address this coupling. The Total System Performance Assessment Viability 
Assessment peer review expressed concern about the basis for accepting the results as indicative 
of repository behavior. Further, analyses of CO2 and water pH for the Drift Scale Test matched 
the data better when using a less complete suite of minerals. Possible reasons that the more 
complex model, which might be expected to more closely match the data, did not match the data 
as well include: uncertainties in rate parameters and thermodynamic properties, and the short 
duration of the test. Further, there is limited geochemical data for high ionic strength solutions at 
elevated temperatures. However, for the potential repository model, results have shown that 
higher ionic strengths are reached only when the liquid saturations are typically less than 1% and 
are therefore basically immobile and less important to fundamental changes in seepage chemistry 
and permeability modification. 
The Yucca Mountain Site Characterization Project has changed the repository design to lower 
the temperatures, in an attempt to reduce some of the uncertainty caused by elevated 
temperatures. The concern regarding uncertainty is based, in part, upon the fact that increased 
temperatures increases the rates of chemical reactions and introduces additional complexity of 
vapor phase reactions and transport. 
While some of the uncertainties may be reduced by lower temperatures, other uncertainties may 
not be reduced or may even be increased. The higher chemical reaction rates will lower kinetic 
barriers to reach equilibrium for all kinetically inhibited reactions. Although there may be 
increased uncertainty for kinetic rate parameters due to a lack of data, much of the data collected 
on kinetic rates was obtained in experiments that were necessarily at higher rather than lower 
temperatures (to shorten the time for reactions to be observed). Furthermore, because of the 
higher rates of reaction, the divergence of the system from equilibrium is smaller at higher 
temperatures and the length of time to reach equilibrium is smaller. There is much less 
uncertainty in assessing equilibrium chemical processes than kinetic processes. Even with the 
uncertainties noted, the THC models have matched the field data sufficiently that the models are 
considered appropriate for use in analyses of THC processes associated with the NFE. 
The final topic of concern for the NFE is that of the geomechanical responses and how they 
couple to other processes within the NFE. Based on the calculated deformations, permeability 
increases of about 40 percent might be experie nced above the drifts due to normal (widening or

 xiii 
narrowing) deformations of the fractures, and larger increases of 3 to 6.5 times preheat values 
due to shear (slip) displacements, during the peak of the thermal pulse. After 1,000 years, the 
permeability in the regions above the drifts is approximately twice the pre-emplacement value, 
due to normal deformations, and about an order of magnitude higher due to shear displacements. 
Assessment of model confidence indicates that the models are appropriate for the analyses. The 
models have produced thermal-hydrological projections that compare well with the results of 
three field tests that have considerably varied geometry. The THC models used calculated trends 
of chemistry that were consistent with field tests, although the actual concentrations of 
constituents did not match field results as closely as did the temperature and saturation results of 
the thermal-hydrological models. In considering uncertainties with respect to field-test 
comparison, the greatest uncertainty was with the less mature THM model results. However, the 
THM responses are not currently linked as directly to performance as are the thermalhydrological 
and THC models. 
Based on these analyses, it is concluded that the model results are suitable for input to the site 
recommendation decision process and, further, that the models are appropriate for Total System 
Performance Assessment. Ongoing work to refine and test the models is expected to reduce 
uncertainty and increase confidence in performance assessment results.

July 2000

1. INTRODUCTION 
This Chapter presents the purpose of this report, its basic organization, and related issues. This 
section also provides a high-level summary of how the NFE Process Model Report (PMR) 
relates to technical topics presented in the other PMRs, and other key Yucca Mountain Site 
Characterization Project (YMP) documents. 
1.1 BACKGROUND 
The U.S. Department of Energy (DOE) is investigating the suitability of Yucca Mountain as a 
potential site for the nations first high-level nuclear waste repository. If the site is found 
suitable, the goal is to seek a license to construct, subsequently to operate, and eventually close a 
high-level waste disposal facility. The determination of suitability relies on evaluations of 
performance of the repository engineered barrier system (EBS) and natural barrier characteristics 
of the site. 
To evaluate or assess the postclosure performance of a potential repository at Yucca Mountain, a 
series of Total System Performance Assessments (TSPAs) are being conducted. A set of nine 
PMRs, of which this is one, is being developed to summarize the technical basis for each of the 
process models supporting the TSPA model for the Site Recommendation (SR). These reports 
cover the following topics: 
 Integrated Site Model (ISM) 
 Unsaturated-Zone Flow and Transport (UZ F&T) 
 Near Field Environment (NFE, this PMR) 
 EBS Degradation, Flow, and Transport 
 Waste Package (WP) Degradation 
 Waste Form (WF) Degradation 
 Saturated-Zone Flow and Transport 
 Biosphere 
 Disruptive Events (DE). 
These PMRs are supported by Analysis Model Reports (AMRs) that contain the more detailed 
technical information for input into each PMR and the TSPA. This technical information 
consists of data, analyses, models, software, and supporting documentation that will be used to 
describe 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 the uses of that information in the TSPA. 
Favorable aspects of YM as a potential repository site include its isolated location, arid nature, 
and the sorptive properties of the rock materials. The arid environment results in unsaturated 
conditions at the potential emplacement horizon, the Topopah Spring Tuff (Tpt) of the 
Paintbrush Group. The major advantage of unsaturated conditions is minimization of water 
contact that can contribute to container corrosion, waste-form leaching, and radionuclide 
transport.

 1-2 
The emplacement of waste and the activities associated with construction of a repository system 
have the potential to change the environmental conditions within the repository system, 
specifically those that affect the WP and WF, and engineered barriers within the drifts. These 
environmental changes are principally a result of heat generated by decay of the radioactive 
waste that elevates temperatures within the repository system. The elevated temperatures affect 
distribution and chemistry of NF water, increase kinetic rates of geochemical processes, and 
cause stresses to change, in magnitude and orientation, from stresses resulting from the overlying 
rock and from underground construction activities. As described in the EBS PMR (CRWMS 
M&O 2000g), within the drifts themselves, thermally driven reactions of the altered NF water 
and the materials introduced into the drifts by construction can have strong influence on WP 
corrosion and WF degradation. Furthermore, ventilation associated with construction can cause 
significant drying of the rock immediately surrounding the drifts. Recognition of this evolving 
environment has been reflected in activities, studies and discussions generally associated with 
what has been termed the NFE. 
The NFE evolves over time in response to construction and heat-producing waste, as well as 
changes in the natural environment (e.g. changed climates). Therefore, it is impossible to 
directly characterize the NFE by measurements, as that environment does not currently exist. 
Characterization of the NFE must rely on projections based on tests and models that encompass 
the long-term processes of the evolution of that environment. NFE characterization must rely on 
models that include detailed process evaluations as well as those that include simplifications and 
abstractions. The combination of detailed and abstracted-model assessments supports the site 
recommendation. 
There have been modifications in design (as discussed in the Introduction to Chapter 2), 
operational concepts, and in development of the Repository Safety Strategy (CRWMS 
M&O 2000s; Sections 1.2 and 1.3). Earlier reports on the NFE which are based on earlier 
designs are useful, but may be limited by all of these factors. They are referenced for historical 
purposes, because they were part of the basis for many issues that are addressed in this PMR, and 
to provide corroborative evidence for the model analyses reported here. 
1.2 DEFINITION OF NEAR-FIELD ENVIRONMENT 
This section reviews the definition of NFE and how this relates to this PMR. 
1.2.1 Definition of the Near-Field Environment 
The Site Characterization Plan (DOE 1988, Volume III, Part A, Sections 7.1 and 7.4.1) 
associates the NFE with the WP Environment and with environmental-condition changes in the 
rock surrounding boreholes (borehole emplacement was the design being considered at that 
time). A distinction in definitions between near- and far-field environments was made based on 
whether analyses needed to consider specifics of the design (NF) or merely the overall mass 
loading of the waste (far-field) (DOE 1988, Volume VIII, Part B, Glossary, pp. G-38 and G-68). 
Subsequent to the Site Characterization Plan, design changes as well as changes in the 
organization of effort have evolved the definition.

 1-3 
The NFE Report was identified in the Waste Package Plan (Harrison-Giesler et al. 1991) as the 
formal means for transmitting and documenting information regarding the NFE. As defined in 
the Preliminary Near-Field Environment Report (Wilder 1993), it included the in-drift 
environment that contacted the WPs and WFs, all of the materials within the drifts, and the 
environment that developed within the rock mass and extended into the rock mass a distance that 
depended on the physical process being considered. The extent of the NFE, for some processes, 
was as large as tens of meters (e.g., saturation changes in response to heat) or limited to a few 
centimeters into the rock (e.g., radiation effects). Furthermore, the extent of the NFE for any 
given process was a function of time and depended very strongly on repository design and 
operational parameters. Thus, the NFE was defined based upon impacts or changes in the 
environmental parameters that were significant to performance of the repository system. The 
issues related to the NFE were reported to be more of processes and how they related to various 
designs than of the more typical environmental descriptions associated with site characterization. 
Subsequent to the Preliminary Near-Field Environment Report, and within the Viability 
Assessment (VA), the NF has been described as being limited to the environment within the 
drifts and the region of rock in close proximity to the drifts where the temperatures exceed 
boiling. The evolving environment within the surrounding rock mass was described as the 
Altered Zone (AZ) (Wilder 1997, Figure 1-2), and the rock beyond the AZ with only small heatdriven 
changes was termed the Far-Field. Potential far-field thermal effects include chemical 
reaction zones in the heated part of the saturated zone, and in the capillary fringe area just above 
the water table, and a convection cell in the heated part of the saturated zone. These effects for 
the EDA-II design, are expected to be both temporary and small in magnitude. Rock-water 
interactions are quite efficient at temperatures just below boiling (and are far more efficient at 
any temperature above the ambient). This report does not address these issues. For high thermal 
load repository designs, the AZ may extend throughout the unsaturated zone (UZ) above and 
below the repository horizon (Hardin 1998, p. 1-1). Figure 1-1 depicts the timedependent 
locations of these regions, as defined at the time of the Viability Assessment (VA). 
1.2.2 The Host-Rock Portions of the Near-Field Environment (this PMR) 
The definition of the NFE continues to include the in-drift environment and immediately 
surrounding host rock. However, the increased emphasis on engineered barriers created a need 
to consolidate discussions related directly to the EBS into a separate PMR. Thus, this PMR 
describes models used to evaluate the rock part of the NFE, while the Engineered Barrier System 
Degradation, Flow, and Transport (EBS DFT) PMR (CRWMS M&O 2000g) describes models 
used to evaluate the in-drift part of the NFE. In this PMR, the term NFE refers to the 
environment that develops within the rock extending from the drift walls, outward to a distance 
where heat or excavation-driven changes in the properties or processes within the rock affect 
performance assessment parameters, such as water flow paths and water chemistry. Figure 1-2 
depicts the part of the NFE described in this PMR. As can be observed by comparing 
Figures 1-1 and 1-2, the overall region of perturbation is similar (design and operational 
modifications result in a somewhat smaller region of perturbation, ignoring heterogeneity). The 
differences relate to which PMR discusses the various portions of the NFE. As noted, a 
distinction is no longer made between NF and AZ in this PMR. The NFE as described in this 
PMR subsumes what had been separately identified as the AZ. This description of the NFE 
reflects the current organization of effort within the YMP.

 1-4 
The basic characteristic of the NFE is that it is an environment that evolves within the rock mass 
due to coupled processes involving heat transfer, fluid mobilization and phase changes, chemical 
interactions, and mechanical deformations and stresses. It is thus characterized by coupled 
processes, that is coupling between thermal, hydrological, geochemical and geomechanical 
processes. This coupling is sometimes binary, but can involve all four processes and can include 
feedback. For example, heat from the waste (thermal process) can mobilize water (hydrological 
process), which can dissolve and precipitate minerals (geochemical processes), which can affect 
flow paths (hydrological process). This is referred to as coupled thermal-hydrological-chemical 
(THC) processes. 
Source: Wilder 1997, Figure 1-2 
Figure 1-1. Schematic Representation of the Near-Field Environment, Altered Zone, 
and Far-Field Environment, used in the Viability Assessment

 1-5 
NOTE: The red portions represent regions of extensive dryout. The stippled portions represent regions of 
significantly increased temperatures and decreased saturation. The Host-Rock portions of the NFE (red and 
stippled) are those reported in this Process Model Report. 
Figure 1-2. Schematic Representation (Not to Scale) of the Near-Field Environment

 1-6 
1.2.3 The In-Drift Portions of the NFE as Covered in the EBS PMR 
As noted, the EBS PMR discusses the portion of the NFE that resides within the drifts. 
Therefore, issues related to evolution of water and gas chemistry within the drift that interacts 
with the waste packages and with the waste form are covered within that PMR. Further, issues 
of water distribution within the drift, of relative humidity and temperature distributions within 
the drift, and the interactions with introduced materials are all within the scope of the EBS PMR. 
As a result, much of the discussion of engineering design options on the NFE (such as backfill 
options) are within the scope of the EBS PMR. 
1.3 OBJECTIVE 
The overall objective of the NFE PMR is to synthesize the necessary and sufficient technical 
information that the YMP will rely upon to make its site suitability evaluation and licensing 
arguments pertaining to the NFE. 
The detailed objectives of the NFE PMR are to 
1) Describe and summarize processes important to performance in the NFE 
2) Describe the models that simulate these processes 
3) Summarize the technical bases for these NF process models 
4) Abstract the detailed NF process models for use by TSPA 
5) Evaluate uncertainties inherent in the NFE modeling results 
6) Address resolution of the U.S. Nuclear Regulatory Commissions (NRCs) ENFE Key 
Technical Issue (KTI) and related Issue Resolution Status Reports (IRSRs). 
7) Provide results of NFE analyses to other PMRs, particularly EBS and UZ PMRs. 
Information provided includes, but is not limited to, changes in porosity and 
permeability, evolved water chemistry and mineralogy, thermal mobilization of water, 
and geomechanical condition changes (see Figure 1-5). 
In addition, because discussion of the NFE is not contained within a single PMR, there is a need 
to provide continuity with past reports or documents such as the NRCs ENFE IRSR 
(NRC 1999a). Thus, one of the functions of this PMR is to provide a mapping function between 
the current documents that discuss NF processes and past documents (see Chapter 4). 
This PMR supports key YMP milestone documents, including the Site Recommendation 
Consideration Report (SRCR), Site Recommendation Report (SRR), and the LA. 
1.4 SCOPE 
The major issues regarding the NFE in this PMR are thermally-driven changes in the rock-mass 
hydrological properties that determine flow of fluids in the rock, and mineral changes or salt

 1-7 
depositions that potentially impact water chemistry. The hydrologic properties can be affected 
by both THC and THM processes. 
This PMR summarizes: 
 The coupled thermal-hydrological-chemical (THC) processes and the coupled 
thermal-hydrological-mechanical (THM) processes that occur within the NF 
 The technical bases for evaluations made to identify the features, events, and processes 
(FEPs) associated with the NF and that might affect performance of the geologic 
repository 
 The use of analysis and modeling results developed in the AMRs to support the TSPA 
 The thermal-hydrological (TH) model evaluation and validation (model confidence 
assessment) activities associated with thermal testing in the Exploratory Studies Facility 
(ESF) 
 Issues related to changes in properties and water chemistry within the rock mass due to 
excavation or heat. 
 Issues associated with the NFE that are not discussed in detail in the NFE PMR but are 
discussed in other PMRs. 
Because of the coupling of processes, the discussion of the processes models used to evaluate the 
NFE must be in the context of the coupled processes. The forward-and-back coupling of 
processes makes the NFE an environment typified by interrelated interactions. There are 
multiple and complex ways in which coupling between processes can occur. The approach often 
used is to analyze only partially or singly coupled processes, then determine these responses 
before adding the other coupling. The scope of this PMR includes discussion of the TH, THC 
and THM coupled processes separately, synthesizes the NF THCM behavior from consideration 
of the TH, THC, and THM separate results. 
The scope of this PMR is limited to considerations of coupling that impact seepage into drifts, 
water chemistry, mineralogy and rock-property changes, as well as geomechanical responses 
based on ambient-property inputs from the Unsaturated-Zone Flow and Transport Model 
(UZ F&T) PMR. Ongoing work will incorporate additional complexity in coupling as well as 
potential changes in water chemistry and flow returned to the NF from the drifts. THMC 
processes in the NFE may also influence the stability of the rock surrounding the emplacement 
drifts, especially in the region within 1 drift diameter of the drift walls. A thermal-mechanical 
analysis of drift stability is presented in the EBS PMR (CRWMS M&O 2000g). 
1.4.1 Organization of this Process Model Report 
This report is divided into five chapters. 
Chapter 1 defines the NFE and relationships between this PMR and other PMRs and regulatory 
documents.

 1-8 
Chapter 2 provides a perspective against which the NFE PMR was developed. The section 
provides a general description of the background, evolution of the conceptual approach, past 
modeling efforts, the objectives and outcome of a performance assessment NFE workshop, and a 
discussion of the NFE FEP. 
Chapter 3 describes the process-level models, model abstractions, and supporting analyses that 
address the NFE processes. Discussions include the relationships among the process-level 
models, model abstractions, data, and supporting analyses. Chapter 3 also describes activities 
that relate to model confidence building or validation, including discussion of applicable natural 
analogs. 
Chapter 4 describes the relationship with the NRC IRSRs and how acceptance criteria in the 
IRSRs relevant to the NFE PMR have been addressed. 
Chapter 5 summarizes the conclusions of this PMR. 
1.4.2 Analysis Model Reports and Calculation Directly Supporting this Process Model 
Report 
This PMR summarizes the detailed analyses of constituent sub models from the following four 
AMRs and one calculation: 
AMR N0080: Features, Events, and Processes in Thermal Hydrology and Coupled Processes 
(CRWMS M&O 2000e) identifies and examines the effects of features, processes, and events 
that are related to the NFE on repository performance and provides the technical basis for 
evaluation of those FEPs. This AMR is referred to as the NFE FEPs AMR throughout this PMR. 
AMR N0000: Thermal Tests Thermal-Hydrological Analysis/Model Report (CRWMS 
M&O 2000a) has a primary purpose that relates to building confidence in the models that 
describe thermal-hydrological (TH) processes in the potential repository system. The AMR tests 
the various property sets proposed for use in design and TSPA to characterize the potential 
repository geologic setting. The AMR compares measurements from field tests to calculated 
temperatures and saturations using these property sets. The evaluation of the TH property sets 
inherently involves the evaluation of the coupled TH processes that are both numericallysimulated 
and field-measured. This AMR is referred to as the Thermal Test AMR throughout this 
PMR. 
AMR N0120: Drift-Scale Coupled Processes (DST and THC Seepage) Models Report 
(CRWMS M&O 2000b) discusses coupled THC processes. This AMR supports both this PMR 
and the UZ F&T PMR (and thus carries a second designation, U0110). The AMR focuses on the 
impact of coupled processes on fracture and rock hydrological-property changes, and on mineralwater-
gas reactions that drive changes to water and gas compositions that may enter the potential 
drifts. This AMR is referred to as the THC Process AMR throughout this PMR. 
AMR N0125: Abstraction of Drift-Scale Coupled Processes (CRWMS M&O 2000c) provides 
the technical basis for the TSPA abstraction of THC processes. It abstracts water and gas 
compositions in the rock and fractures outside of the drifts from the THC Process AMR for use in

 1-9 
TSPA. It also compares the TH results for process-level and abstracted TH and THC models. 
This AMR is referred to as the THC Abstraction AMR throughout this PMR. 
Calculation N0C30: Calculation of Permeability Change due to Coupled Thermal- 
Hydrological-Mechanical Effects (CRWMS M&O 2000d) discusses mechanical responses to the 
thermal pulse and the effects of consequent fracture closure or opening on the hydrological 
properties of the rock mass. This calculation is referred to as the THM Calculation throughout 
this PMR. 
Table 1-1 lists the reports that directly support the NFE PMR. 
Table 1-1. Near-Field Environment Analysis Model Report Identification 
AMR Title ID 
Number 
Abbreviated 
Designator 
DI Number and 
Reference 
PMR 
Section 
Features, Events, and Processes 
in Thermal Hydrology and Coupled 
Processes 
N0080 NFE FEPs AMR ANL-NBS-MD-000004 
CRWMS M&O 2000e 2.5 
Thermal Tests Thermal- 
Hydrological Analysis/Model 
Report 
N0000 Thermal Test AMR ANL-NBS-TH-000001 
CRWMS M&O 2000a 3.2, 3.6 
Drift-Scale Coupled Processes 
(DST and THC Seepage) Models N0120 THC Process AMR MDL-NBS-HS-000001 
CRWMS M&O 2000b 3.3 
Abstraction of Drift-Scale Coupled 
Processes N0125 THC Abstraction AMR ANL-NBS-HS-000029 
CRWMS M&O 2000c 3.4 
Draft Calculation of Permeability 
Change due to Coupled Thermal- 
Hydrological-Mechanical Effects 
N0C30 THM Calculation CAL-NBS-MD-000002 
CRWMS M&O 2000d 3.5 
In addition to summarizing the above documents, Section 3.6 of this PMR summarizes other 
pertinent YMP work, including results from laboratory and field thermal tests that were not 
discussed in the limited scope of the Thermal Test AMR. Laboratory tests deal with relatively 
simple processes and one medium at a time. For example, a laboratory test may study fracture 
healing in a rock sample with one single fracture. Therefore data from laboratory tests can only 
be used to build confidence on certain processes of a complex model that is used to predict the 
behaviors of the rock mass in a potential repository. Laboratory tests are summarized in 
Section 3.6.3. 
The following submodels are described in the indicated sections of this PMR and associated 
AMRs: 
 TH Sections 2.2.1, 3.2, 3.6.1, and 3.6.4.1; 
The THC Abstraction AMR (CRWMS M&O 2000c) and the Multiscale 
Thermohydrologic Model (CRWMS M&O 2000k) which supports the 
EBS PMR 
 THC Sections 2.2.2, 3.3, 3.4 and 3.6.4.2; 
The THC Process AMR (CRWMS M&O 2000b) and the THC Abstraction 
AMR (CRWMS M&O 2000c)

 1-10 
 THM Sections 2.2.3, 3.5, and 3.6.4.3; 
The THM Calculation (CRWMS M&O 2000d) 
Figure 1-3 shows the flow of information through the NFE submodels. Models are shown in 
bold rectangles, circled boxes are inputs, hexagonal boxes are output, and information categories 
label the flow-arrows. The TH submodel is shared by the NFE and EBS models, with the rock 
temperatures (T) and saturations being used by the NFE model and the in-drift temperatures and 
relative humidities (RH) being used by the EBS model. 
Figure 1-3. Flow of Information through the Nominal Case Near-Field Environment Models 
1.4.3 Near-Field Environment Issues and Processes 
The issues dealt with specifically in the PMR are: 
 Evolution of the NFE and how that evolution relates to the amount of water that can 
enter the drifts or potentially leave the drifts. This specifically includes an evaluation of 
changes to the porosity and permeability of the zone of rock surrounding the drifts and 
extends outward until there are no significant changes in those parameters. The changes 
may result from geochemical interactions between the rock and fluids that are a result of 
the elevated temperatures. They may also result from geomechanical processes related 
to excavation or elevated temperatures. 
 The impacts on NF water chemistry that may result from changes in mineralogy, 
dissolution and precipitation of minerals, vaporization and condensation of water in the 
matrix and fractures, and changes in gas chemistry. 
 Strongly coupled effects in which one process has a major impact on another process. 
Much of the coupling is the consequence of the thermal output from the waste and 
resulting temperature distribution. Therefore, the NFE is affected directly by the 
repository system design and operation, particularly the repository layout (thermal 
loading) and the preclosure ventilation. In this PMR, the analyses consider the

 1-11 
Enhanced Design Alternative (EDA) II design (see the Introduction to Chapter 2). This 
design includes titanium drip shields, no concrete drift liners, and backfill between the 
drip shield and drift walls. EDA II uses line-loading (close spacing of WPs) in widely 
spaced drifts. These design characteristics contribute to the spatial and temporal thermal 
regime that develops within the NFE. 
During development of this PMR, decisions have been made by YMP management to eliminate 
backfill from the design and to alter the orientation of the drifts. These modifications to the 
design have not been completely incorporated into the AMRs and PMR at this point. 
From a thermal perspective, backfill insulates the heat source (waste packages) from the NF heat 
sink; the consequence of a backfilled design (after a short period during which the backfill 
temperature equilibrates) is higher waste package temperatures with little overall change in NF 
rock temperatures. Depending on the backfill geometry and hydrological properties, there can be 
differences in distribution of temperature and saturation around the periphery of the drift for 
backfilled versus non-backfilled designs. 
Drift orientation (with respect to the orientation of major fracture sets) can change shear stresses 
at rock contact points and the size of key blocks for rock fall. The models described in this PMR 
are applicable to the initial SR design (backfill drifts oriented as in the viability assessment) and 
to the evolving SR design (no backfill and drifts oriented to reduce rock fall loads on the drip 
shield ). TH analyses for the no-backfill option is described in this PMR. 
This PMR is focused on processes that occur during the period of time when the thermal 
processes are active, and on the effects that may extend beyond the thermal period. Changes that 
occur either outside the region or time frame thus described are included in other PMRs; for 
example, climate change is included in the UZ F&T PMR (CRWMS M&O 2000f). Those 
changes in the environment that occur within the thermal period, but are long lasting or 
permanent, are identified in the NFE PMR. However, impacts on performance beyond the 
approximately 10,000 years limit for thermal processes are also considered in the UZ F&T PMR 
(see Section 3.12 of that document ); these impacts are primarily related to seepage and transport. 
To provide continuity with past reports or documents such as the NRCs ENFE IRSR 
(NRC 1999a), issues that have been identified in the past as associated with the NFE are 
identified here, with references to the appropriate PMR. This PMR also discusses model 
validation or confidence building for models that support the NFE (see Section 3.6.4). This is 
critical because it is impossible, during the evaluation and licensing process, to directly measure 
the NFE environment that will develop over long periods of time. Therefore, evaluations of the 
NFE evolution, by necessity, will involve use of complex predictive models that are based on 
detailed mechanistic models of the processes involved in that evolution. Confidence that the 
predictive models are appropriate is established by comparison of the model results to a series of 
accelerated field and laboratory tests. This PMR reports results of the underground (in situ) 
Single Heater Test (SHT) and Drift Scale Test (DST) performed as part of the ESF studies, as 
well as results of the Large Block Test (LBT) located on the surface near Yucca Mountain (see 
Section 3.6.1). The results of laboratory tests are discussed in Section 3.6.3. This PMR focuses 
on the thermal-hydrological aspects of the DST. Analyses and calculations are ongoing to 
investigate the fully coupled thermal-hydrological-chemical-mechanical (THCM) processes in

 1-12 
the test, including processes that are expected to occur in the cool-down phase. The cool-down 
phase of the test has not yet begun and confidence building will, therefore, not be fully addressed 
for several years. In spite of the uncertainties and also the incomplete testing of the models, as 
discussed in Section 3.6, there has been good agreement between model predictions of the 
coupled process responses (particularly for the critical processes of TH and THC) for the field 
tests with the actual responses monitored. 
Additional testing of model appropriateness can also be achieved through evaluations of 
comparable natural analogs. This PMR contains information regarding use of natural analogs to 
gain insight into coupled NF processes (see Section 3.6.2). Expert judgment and technical 
reviews have also been used to further assist in determining appropriateness of the models (see 
Sections 2.3 and 2.4). This information was obtained formally through use of Expert Elicitation 
and Technical Peer Review. 
1.5 QUALITY ASSURANCE 
The activities documented in this technical report were evaluated in accordance with 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). This is documented 
in the activity evaluation for the NFE PMR Work Package Plan (CRWMS M&O 1999b). The 
NF environment is also identified on the Q-list (DOE 1988) as important to waste isolation. 
This document was prepared in accordance with AP-3.11Q, Technical Reports. The Technical 
Development Plan for the PMR (CRWMS M&O 2000x) was prepared in accordance with 
AP-2.13Q, Technical Product Development Planning. The AMRs that support this PMR were 
prepared in accordance with AP-3.10Q, Analyses and Models. The calculation that supports this 
PMR was prepared in accordance with AP-3.12Q, Calculations. 
The qualification status of input data and references are tracked in the electronic Document Input 
Reference System (DIRS) in accordance with AP-3.15Q, Managing Technical Product Inputs. 
Data qualification was performed in accordance with procedure AP-SIII.2Q, Qualification of 
Unqualified Data and the Documentation of Rationale for Accepted Data. 
This document summarizes the major results and conclusions from AMRs and abstractions. 
Word-processing and graphic-illustration applications were used in the development of this 
document. 
This PMR includes results from the following software codes used for thermal, hydrological, 
chemical, and mechanical analyses, as documented in the supporting AMRs (Section 1.4.2). 
However, no software codes were used in the development of this PMR. The following 
statements listing software codes are presented for information only. Their qualification status is 
documented in the Configuration Management Database and DIRS database for the AMRs 
where used. 
 NUFT, Version 3.0.1s (LLNL 1999), which is a heat and mass-transfer code used for 
thermal-hydrological (TH) modeling. Appendix A is an evaluation of the status of 
NUFT, with respect to known physical data and processes.

 1-13 
 TOUGH2, Version 1.4 (LBNL 2000) is a heat and mass-transfer code used for TH 
modeling. The UZ F&T PMR and supporting documents discuss the validation status of 
the TOUGH2 code. 
 TOUGHREACT, Version 2.2 (LBNL 1999), is a heat transfer, mass transfer, and 
reactive-transport code used for THC analyses. Section 3.3 of this report and the THC 
Process AMR discuss the validation status of the TOUGHREACT code. 
 3DEC, Version 2.00 (Itasca Consulting Group 1998), is a heat transfer and distinct 
element stress-analysis code used for TM analyses. This code is commercial software 
that has been qualified for use on YMP. The validation of the models it implements is 
ongoing. 
These software codes are managed in accordance with procedure AP-SI.1Q, Software 
Management. 
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. 
1.6 RELATIONSHIP TO OTHER PROCESS MODEL REPORTS AND KEY 
PROJECT DOCUMENTS 
Section 1.1 listed the nine process models that support Site Recommendation (SR) and 
TSPA-SR. Figure 1-4 shows the flow of information through the eight process models that 
analyze scenarios with no disruptive events. This flow takes place at both the process-model 
level (between PMRs) and in TSPA abstractions. The boundaries between process models 
sometimes overlap for calculational convenience. The two circled models (ISM and WF) are 
starting points for PA calculations, and the hexagonal model (biosphere) is the end point for PA. 
Arrows represent the flow of information, with specific information categories shown as labels. 
The blue labels identify output information from the NFE PMR. 
The effects of coupled processes that occur within the emplacement drifts are discussed within 
the EBS PMR. Therefore, the environmental conditions that interact directly with the waste 
packages are described in the EBS PMR. The issues of coupling between the WP and the 
environment that help to determine the evolution of the environment (e.g., impact of corrosion 
products on water chemistry within the drift) are covered jointly within the EBS and 
WPD PMRs. Interactions between the environment within the drifts and the waste are less 
direct, in that the waste package materials or corrosion products are also involved. Therefore, 
these interactions are discussed in the EBS, WP, and WFD PMRs. Each of these PMRs depends 
on the thermal-hydrological conditions in the NF rock, as defined in the NFE PMR.

 1-14 
Figure 1-4. Flow of Information through Site Recommendation Process and the Nominal Case Total 
System Performance Assessment Models 
Coupled processes that occur outside of the drifts are discussed in this PMR and the UZ F&T 
PMR. Saturated-zone flow and transport is also subject to coupled processes, but much less 
significantly than in the unsaturated zone. In general, changes in UZ hydrological properties, 
moisture or fluid redistribution in response to coupled processes, geochemical changes in fluids 
and minerals due to coupled processes, and changes to the permeability, porosity or fracture 
characteristics as result of mechanical coupling are all discussed within the NFE PMR. Seepage 
into emplacement drifts and changes in the seepage that result from coupled processes are 
discussed in the UZ F&T PMR. Chemistry of ambient fluids within the mountain is discussed in 
the UZ F&T PMR. The UZ F&T PMR also discusses changes of mineralogy as it relates to 
transport, including changes in sorption or retardation capacity of the minerals. 
Figure 1-5 shows the spatial relationship between the processes reported by the NFE PMR and 
the EBS and UZ F&T PMRs as well as the interactions between those models.

 1-15 
Figure 1-5. Spatial Relationships of Processes and Interactions Among Three Process Model Reports 
The ENFE KTI (NRC 1999a) assesses all aspects of the evolution of the NFGE that have the 
potential to affect the performance of the proposed repository. The ENFE KTI subissues are 
addressed in various PMRs. Section 4.2 presents a correlation between the ENFE KTI subissues 
and the PMRs that address them. Chapter 4 and Appendix D of this PMR provide detailed 
explanations describing how the acceptance criteria relevant to the NFE PMR have been 
addressed. 
1.6.1 Process Model Report Interfaces 
The following sections summarize the PMRs with interfaces to the NFE PMR. 
1.6.1.1 Integrated Site Model Process Model Report 
The ISM PMR (CRWMS M&O 2000y) describes the geologic framework models of the site 
(e.g., stratigraphy, structural characteristics, rock properties, and mineralogy). This PMR 
describes how geological, geophysical and hydrological property information has been used to

 1-16 
model the geological properties of the site. The geologic al framework is used in the calculation 
and AMRs supporting the NFE PMR. 
1.6.1.2 Unsaturated-Zone Flow and Transport Process Model Report 
The UZ F&T PMR (CRWMS M&O 2000f) describes the processes affecting the amount of 
water entering the unsaturated zone above the potential repository and the subsequent seepage 
into emplacement drifts. It also describes the movement of water with dissolved radionuclides or 
colloidal particles through the unsaturated zone below the potential repository. The flow fields 
calculated by the UZ F&T PMR and supporting AMRs are used in the NFE PMR supporting 
analyses. Further, the mountain scale (MS) TH model, developed as part of the UZ effort and 
reported within the UZ F&T PMR, is an integral part of the THC model, the results of which are 
reported within the NFE PMR. Changes to hydrologic properties calculated by use of the THC 
model are reported in the NFE AMRs and are fed directly back to the UZ F&T analyses. 
1.6.1.3 Engineered Barrier System Degradation, Flow and Transport Process Model 
Report 
The EBS PMR (CRWMS M&O 2000g) describes how the in-drift processes and environments 
change with time after emplacement of nuclear waste in a potential repository, as affected or 
controlled by the EBS design. The processes in the EBS PMR include: 
 Evolution of heat by radioactive decay, and its removal by preclosure ventilation 
 Drift degradation by rockfall 
 Flow of water within the drift 
 Evaporation and condensation within the drift 
 Deposition of salts and precipitates within the drift 
 Gas exchange between the drifts and the surrounding rock 
 Chemical reactions between water, rock, and introduced materials (in the drift) 
 Colloids formed by corrosion products with high sorptive capacity for radionuclides 
 Growth and activity of microbes in the EBS 
 Transport of radionuclides through the invert by advection and diffusion 
 Chemistry of effluent leaving the drift, including colloids 
 Production of fine particles that could affect drift change through the NF rock 
A primary interface between the NFE and EBS PMRs involves the chemistry of seepage water 
from the NFE that enters the drift. This seepage interacts with such components as steel or 
cements within the drift. It affects the degree to which salts and precipitates form on EBS 
components during repository heating, and dissolution of such salts and precipitates during 
repository cooling. 
Another primary interface is the thermal source distribution from waste heating. The Multi-scale 
Thermohydrologic Model (MSTHM) (CRWMS M&O 2000k) describes the thermal-hydrologic 
(TH) evolution throughout the potential repository and is used by the NFE and EBS PMRs, and 
directly by TSPA. The model evaluates the period of reduced relative humidity on the WP 
surface and the extent to which the repository pillars remain below boiling, for example.

 1-17 
1.6.1.4 Disruptive Events Process Model Report 
The DE PMR summarizes the consequences of volcanic and seismic events that potentially could 
affect a potential geologic repository at Yucca Mountain. The consequence analyses rely on 
inputs from the probabilistic volcanic and probabilistic seismic hazard analyses to describe the 
frequency of disruptive events. Effects of igneous activity on drifts, waste packages, and the 
waste forms are also discussed in this PMR, and modes of radionuclide release resulting from 
igneous events are characterized. Incremental effects of seismic ground motion on rockfall are 
described. The consequences of fault displacement for the EBS and waste packages are also 
summarized. Finally, the potential effects of seismic activity on the hydrologic system are 
discussed. 
The NFE and DE PMRs both consider thermal and mechanical perturbation of NF rock, but the 
DE PMR uses bounding analyses to describe the effects on WPs of the thermal pulse generated 
by an intrusive dike. 
1.6.2 Process Model Report Inputs/Outputs 
The relationships between the PMRs are illustrated in Table 1-2. The PMRs are interrelated not 
only in overlapping issues, but also in exchanging information. The UZ F&T PMR and 
associated AMRs report information on the amount of water flowing through the mountain 
(percolation flux), pore and fracture-water chemistries, mineralogy, and hydrologic and 
mineralogic property sets. This information (some of which was assimilated from other PMRs, 
such as geological information from the ISM PMR) is used as inputs to the NFE models and 
analyses. The EBS PMR provides information regarding the impact of EBS design on the 
thermal source and temperature distributions within the drifts. The EBS PMR also documents 
the amount and spatial distribution of water that is expected to leave the drifts, the chemistry of 
that water, and colloid generation. EBS PMR determinations of water chemistry and colloid 
generation are made considering corrosion products identified in the WPD PMR (CRWMS 
M&O 2000o) and waste form dissolution products identified in the WFD PMR (CRWMS 
M&O 2000ab). Finally, the EBS PMR considers the potential consequences of fracture 
plugging below the drift invert resulting from construction and emplacement activities. 
Table 1-2. Summary of Relationships Between the Near-Field Environment Process Model Report and 
Other Process Model Reports 
Other Process 
Model Reports Inputs Provided to the NFE PMR Input Provided by the NFE PMR 
ISM Stratigraphic data (through UZ F&T PMR) None 
Unsaturated Zone 
Percolation flux (amount of water) 
Hydrologic property sets 
Ambient water chemistry (pore and 
fracture) 
Porosity and permeability changes from THC 
Porosity and permeability changes from THM 
Mineralogy changes and precipitates 
Thermally altered water chemistry 
EBS 
In-drift gaseous- and aqueous-phase 
compositions 
Chemistry of water leaving drifts 
Spatial distribution of water leaving drifts 
EBS thermal source term 
Thermally altered seepage water chemistry

 1-18 
The NF AMRs and PMR use this information to determine changes to properties and conditions 
within the NFE. This information is then used by the UZ F&T PMR to determine any impacts 
on percolation and seepage, and on transport. Inputs of NFE information to other PMR activities 
are through the UZ F&T PMR. 
The thermal-hydrological models used to support TSPA are shared by the NFE and EBS PMRs. 
The EBS primarily uses the TH models to determine in-drift conditions, while the NFE PMR 
focuses on conditions in the NF rock, to include chemical and mechanical coupling effects. The 
multi-scale TH models are discussed in the Multiscale Thermohydrological Model (CRWMS 
M&O 2000k). 
The inputs to TSPA, from the TH process-level models and abstractions, include the in-drift 
thermodynamic environment. The abstractions used in the TSPA model include direct input 
from the process-level model and appropriately averaged inputs based on representative 
infiltration rate bins defined by TSPA. The directly-applied input to the TSPA model is based on 
the location-dependent results described in detail in the Multiscale TH Model and In-Drift 
Environment Abstraction AMRs (CRWMS M&O 2000k and CRWMS M&O 2000m). Direct 
EBS inputs from the TH models to TSPA include: 
 Waste package surface temperature 
 Drip shield temperature distribution 
 Waste package relative humidity 
 Drip shield relative humidity 
 Top of drip shield evaporation rate 
 Volume flow rate at top of drip shield 
 Maximum waste package surface temperature 
The appropriately averaged EBS inputs from the TH models to TSPA include: 
 Waste package surface temperature 
 Invert liquid saturation 
 Invert temperature 
 Invert relative humidity 
 Invert evaporation rate 
 Absolute invert volume flow rate 
The inputs to TSPA, from the TH and THC process-level models and abstractions, also include 
the NF host rock environment. The abstractions used in the TSPA model include direct input 
from the process-level models and appropriately averaged input based on representative 
infiltration rate bins and time periods defined by TSPA. The directly-applied input to the TSPA 
model is based on the location-dependent results described in detail in THC Process, THC 
Abstraction, Multiscale TH, and In-Drift Environment Abstraction AMRs (CRWMS 
M&O 2000b, CRWMS M&O 2000c, CRWMS M&O 2000k, and CRWMS M&O 2000m). 
Direct NFE inputs to the TSPA include: 
 Percolation flux at 5 m above the drift crown 
 Water and gas compositions in the fractures above the drift crown

 1-19 
The appropriately averaged NFE inputs to TSPA include: 
 Drift wall temperature 
 Drift wall relative humidity 
1.6.3 Relationship to the Repository Safety Strategy 
The Repository Safety Strategy (RSS) (CRWMS M&O 2000s) guides development of the 
postclosure safety case. One purpose of the RSS is to identify factors that contribute to the 
safety case, in order to identify additional information needs or simplifications that can be made. 
Performance Assessment (PA) models and detailed process models support the RSS 
development. 
The RSS does not discuss details of the models and analyses regarding factors in the safety case. 
As noted in the RSS, Information relevant to the principal factors of the postclosure safety case 
to support the site recommendation (SR) and LA considerations will be provided in process 
model reports (CRWMS M&O 2000s, Section 3.6). 
Through a process of reviews and performance model analyses, the RSS identified (CRWMS 
M&O 2000s, Section 3.1) the principal factors that are central to determining and demonstrating 
the long-term safety of the repository system. In addition to these principal factors, the RSS also 
reviewed other factors (CRWMS M&O 2000s, Sections 3.3 and 3.4) that could potentially 
improve the long-term safety of the repository system or that must be specified to complete the 
TSPA analyses. Among the other factors considered in the RSS are the coupled-process 
effects on unsaturated-zone flow (CRWMS M&O 2000s, Section 3.3.2) and coupled-process 
effects on seepage (CRWMS M&O 2000s, Section 3.3.3). Ambient Seepage into drifts is a 
principal factor (CRWMS M&O 2000s, Section 3.2.1). Although other issues related to 
coupling were discussed in the RSS, they are covered in other PMRs, as noted in Sections 1.6 
through 1.6.2. The seven principal factors and twenty other factors of second-order importance 
identified in the RSS (CRWMS M&O 2000s, Table 3-1) are listed in Table 1-3. 
The NFE affects seepage into drifts in two ways. First, the thermal pulse can mobilize large 
quantities of water that could, in some locations, temporarily cause seeps. Secondly, changes to 
hydrologic properties could permanently alter seepage locations and seepage flux. Analyses of 
the principal factor of Seepage into Drifts are performed and reported by the UZ F&T PMR and 
its associated AMRs. The effects of the NFE on thermal perturbations to flux and on changes to 
hydrologic properties are considered in the NFE PMR, as direct effects on seepage into the drifts. 
NFE processes influence other factors including: Coupled Processes-Effects on UZ Flow, 
Coupled Processes-Effects on Seepage, Environments on Drip Shield, Environments on Waste 
Package (WP), and Coupled Processes-Effects on UZ Transport.

 1-20 
Table 1-3. Factors Potentially Important to Postclosure Safety 
Factors for the Enhanced Repository System 
Factors Directly 
Affected by NFE 
Processes 
Seepage into Drifts (indirect) 
Performance of Drip Shield 
Performance of Waste Package (WP) Barriers 
Solubility Limits of Dissolved Radionuclides 
Retardation of Radionuclide Migration in the UZ 
Retardation of Radionuclide Migration in the Saturated Zone (SZ) 
Principal 
Factors 
Dilution of Radionuclide Concentrations During Migration 
Climate 
Infiltration 
Unsaturated-Zone (UZ) Flow above Repository 
Coupled Processes-Effects on UZ Flow X 
Coupled Processes-Effects on Seepage X 
Environments on Drip Shield X 
Environments on WP X 
Environments within WP 
Commercial Spent Nuclear Fuel (CSNF) Waste Form (WF) 
Performance 
DOE-Owned Spent Nuclear Fuel (DSNF), Navy Fuel, and 
Plutonium Disposition WF Performance 
Defense High-Level Waste (DHLW) WF Performance 
Colloid Associated Radionuclide Concentrations 
In-Package Radionuclide Transport 
Transport through Drift Invert 
Advective Pathways in the UZ 
Colloid-Facilitated Transport in the UZ 
Coupled Processes-Effects on UZ Transport 
Advective Pathways in the Saturated Zone (SZ) 
Colloid-Facilitated Transport in the SZ 
Other Factors 
Biosphere Transport and Uptake 
1.7 REGULATORY FRAMEWORK 
This Section summarizes discussion of the NFE in the NRC proposed rule 10 CFR Part 63 
(64 FR 8640) and the DOE proposed rule 10 CFR Part 963 (64 FR 67054). 
The NRCs proposed rule on Disposal of High-Level Radioactive Wastes in a Proposed 
Geologic Repository at Yucca Mountain, Nevada, 10 CFR Part 63 (64 FR 8640) lists licensing 
criteria that will address performance of the repository system. As part of the proposed rule, the 
NRC states that Demonstrating compliance, by necessity, will involve the use of complex

 1-21 
predictive models that are supported by limited data from field and laboratory tests, site-specific 
monitoring, and natural analog studies that may be supplemented with prevalent expert 
judgment. (64 FR 8640, p. 8650). The THC Process AMR, THC Abstraction AMR, and THM 
Calculation described in Section 1.4.2 of this PMR, are documentation of the use of those 
models (CRWMS M&O 2000b, 2000c, 2000d). The Thermal Test AMR (CRWMS M&O 2000a) 
meets the further requirement stated in the same section of the proposed rule The performance 
assessment will relyon computer modeling. In most applications, it [modeling] is 
accompanied by a rigorous testing program, involving model validation and verification,. 
The proposed rule, 10 CFR 63 (64 FR 8640, p. 8650), also defines the need for the evaluation 
reported in the NFE FEPs AMR (CRWMS M&O 2000e). It states A defensible performance 
should contain a technical rationale for those FEP that have been included in the performance 
calculation, as well as those that have been considered but were excluded.. Further, the 
proposed rule states (64 FR 8640, Part 63.2) that Performance Assessment means a probabilistic 
analysis that: 
1) Identifies the features, events and processes that might affect the performance of the 
geologic repository, and 
2) Examines the effects of such FEP on the performance of the geologic repository; 
and 
The proposed rule, 10 CFR Part 63 (64 FR 8640, Part 63.21[c]), discusses the need for 
assessment of the coupled processes associated with the NFE, although it does not identify the 
NF by name. It states The Safety Analysis Report shall include:... (6) An assessment of the 
anticipated response of the geomechanical, hydrogeologic, and geochemical systems to the range 
of design thermal loadings under consideration, given the pattern of fractures and other 
discontinuities and the heat transfer properties of the rock mass and groundwater. 
The proposed rule, 10 CFR Part 63 (64 FR 8640, Part 63.114), defines the scope of the PMR 
report on model testing. It states (e) Provide the technical basis for either inclusion or exclusion 
of specific FEP of the geologic setting in the performance assessment and (g) Provide the 
technical basis for models used in the performance assessment such as comparisons made with 
outputs of detailed process-level models and/or empirical observations (e.g., laboratory testing, 
field investigations, and natural analogs). 
The DOE, in rule 10 CFR Part 960 and proposed rule 10 CFR Part 963 (Parts 960 and 963 
combined in 64 FR 67054, page 67054), proposed criteria and methodology to be used for 
evaluating relevant geological and other related aspects of the Yucca Mountain site Within 
these rules (64 FR 67054, Part 963.17[a]), the function of the PMRs is identified: 
Postclosuresuitability criteria reflect both the processes and the models used to simulate those 
processes. 
As noted in Sections 1.1 and 1.4.3 of this report, the PMR provides the technical basis for 
models used in the TSPA. This is consistent with 10 CFR 963, which notes the postclosure 
suitability criteria largely represent the process model components of the TSPA that DOE will

 1-22 
use to evaluate the performance of the repository during the postclosure period. (64 FR 67054, 
page 67081). 
Nine postclosure suitability criteria related to the Nuclear Waste Policy Act as Amended 
(NWPA, Section 112[a]) factors are identified in the proposed rule (64 FR 67054, Table 2). 
These factors are specific processes pertinent to total system performance. Four additional 
postclosure suitability criteria are related to disruptive processes and events. These thirteen 
criteria correspond to the nine PMR reports. Two of the criteria in the proposed rule are 
combined in the UZ F&T PMR, and the four disruptive-event criteria are combined in the 
DE PMR. The other seven criteria in the proposed rule are one-to-one matches with the 
remaining seven PMRs Near-field environment characteristics is criterion 3, which 
corresponds to the NFE PMR. 
The proposed rule, 10 CFR 963 (64 FR 67054, page 67082), notes that the near-field 
environment characteristics, also relates to processes important to limiting the amount of water 
that could contact wastes. This criterion includes: (a) Thermal hydrology(b) near-field 
geochemical environment. These issues are discussed within the context of this PMR. 
The definition of the NF, in proposed rule 10 CFR Part 963 (64 FR 67054, Part 963.2), states 
Near-Field means the region where the adjacent natural geohydrological system has been 
significantly impacted by the excavation of the repository and the emplacement of the waste. 
The proposed rule continues in Part 963.17  and the temperature and humidity at the 
engineered barriers  and  water contacting the waste and the engineered materials. This 
definition is consistent with the overall definition of NFE used by the Project, with the rock part 
being described in this PMR and the in-drift part being described in the EBS PMR (CRWMS 
M&O 2000g). 
Chapter 4 of this PMR describes the NRCs KTIs and the subissues relevant to the NFE PMR. 
Section 4.2 lists the KTIs that contain subissues relevant to the NFE PMR. The relevant 
subissues are shown in italics. Appendix D lists the acceptance criteria relevant to the NFE PMR 
and provides a description of the PMR approach. In many cases, a given PMR may only 
partially address acceptance criteria. For acceptance criteria that are addressed in more than one 
PMR, cross-references to other PMRs are provided. For all acceptance criteria in the NRCs 
ENFE IRSR, pointers to other PMRs that contain details relevant to ENFE IRSR acceptance 
criteria are provided.

 2-1 
2. EVOLUTION OF THE NEAR-FIELD ENVIRONMENT PROCESS MODEL 
This chapter includes a general description of the background, the conceptual approach and 
evolution of the NFE process model; past modeling efforts; the performance assessment NFE 
workshop; and the NFE FEP. 
The NFE evolves in response to excavation and ventilation of the repository, and to 
emplacement of heat-producing waste and other materials, as well as to changes in the ambient 
site, such as climate change. Consequently, it is impossible to measure or characterize the NFE, 
because that environment does not currently exist. Therefore, the NFE must be projected by the 
use of models. Evolution of the NFE Process Models reflects increased understanding of the 
coupled processes and material properties, improvements in computer-code capabilities, and 
evolution of the repository design. Revisions to design or parameter values may influence 
projections of the NFE. However, they also impact the models used to evaluate performance or 
make those projections. At present, the advances in computational capabilities are insufficient to 
rigorously and simultaneously evaluate all processes and how they couple. Therefore, judgment 
decisions are required as to assumptions, approximations and simplifications that can be made. 
Changes in design result in changes to the models used to evaluate the processes. An example is 
the shift in model emphasis that occurred with change in drift spacing from 28 m in the Viability 
Assessment (VA) design to the current value of 81 m (CRWMS M&O 1999a, Table 6-3). One 
of the issues evaluated in the past was the potential to build-up significant volumes of condensate 
that might be thermally perched by the coalescence of boiling fronts in the pillars between 
emplacement drifts (CRWMS M&O 1999a, Section 7.2). Because of the wider pillars and lower 
temperatures in the current design, impacts of condensate perching in the pillar areas, refluxing 
above the condensate zone, and accompanying two-phase flow conditions have been reduced 
(CRWMS M&O 1999a, Section 7.2). The consequent issues of mass transport of minerals 
(dissolution and precipitation) are of less import due to the shorter duration and limited extent of 
near-boiling conditions. For the current design, the issues of greatest importance are thermalhydrological-
chemical (THC) effects (rock-water interactions), particularly in the pillar region 
where dry-out is not expected to be extensive and temperatures are sub-boiling. This contrasts 
with the analyses for the VA design, where part of the NFE THC response was dominated by 
refluxing. For that reason, the emphasis in this report is placed on expected conditions and on 
the coupled processes that may cause permanent changes in the environmental conditions. 
Details of the current understanding of the processes and models are contained in the supporting 
Analysis Model Reports (AMRs) and the calculation listed in Section 1.4.2. This understanding 
has evolved significantly over the years. Examples of this evolution include model revisions to 
include incorporation of condensate drainage, approaches to account for channelized flow in 
fractures and impacts on FMXs (FMXs) (AFM), improved or updated property sets and 
understanding, conceptual models of mechanical interactions with hydrological processes, and 
laboratory identification of chemical and mechanical processes and property measurements. In 
addition, the current understanding as reported in the AMRs and calculation is focused on 
current designs, and therefore includes analyses of processes that were not identified in earlier 
studies. Models used in previous analyses that focused on the VA design were reported in the 
Near-field Altered Zone (NF/AZ) Models Report (Hardin 1998) and in the Total System

 2-2 
Performance Assessment-Viability Assessment (TSPA-VA) Technical Basis Document 
(CRWMS M&O 1998b, Chapters 3 and 4). 
The License Application Design Selection (LADS) process (CRWMS M&O 1999a, Sections 4, 
5, and 6) considered a number of alternative conceptual designs to improve the projected total 
system performance beyond that presented in the Total System Performance Assessment 
Viability Assessment (TSPA-VA) (DOE 1998, Volume 3, Figure 4-26). Although the site 
characteristics alone are expected to prevent release of most radionuclides to the accessible 
environment (CRWMS M&O 2000s, Figure 2-1), engineered barriers were added in LADS to 
reduce uncertainty and to provide defense in depth (CRWMS M&O 1999a, Section O.2.1.4). 
The LADS effort resulted in adoption, in June 1999, of (EDA-II) (Wilkins and Heath 1999). 
The EDA-II design (Figures 2-1 and 2-2) includes the following (CRWMS M&O 1999a, 
Sections 6.5 and 7): 
 Blending of high and low thermal output waste in waste packages (WPs), to limit peak 
WP temperatures 
 Use of preclosure ventilation to remove heat before closure, limiting peak rock and WP 
temperatures 
 Line-loading of WPs in widely spaced drifts to enable drainage of ambient and 
mobilized percolation flux through the pillars between the drifts 
 Use of drip shields and backfill to protect WPs from water contact and rockfall 
 Reduction of the amount of concrete in the drifts, to reduce in-drift chemical processes 
 Use of a long-lived invert and WP-support to enhance drainage and limit water contact 
with the drip shields and WPs. 
As the Site Recommendation (SR) design work has progressed, additional changes have been 
made in the design. During development of this Process Model Report (PMR), decisions have 
been made by YMP management to eliminate backfill from the design. This change places more 
emphasis on understanding NF rock stresses and their contribution to rockfall. Within the EBS, 
elimination of backfill changes the seepage situation (the air gap extends around much of the 
periphery), increases the potential mechanical loading of the drip shields, and reduces peak WP 
and Waste Form (WF) temperatures. These modifications to the design and process models have 
not been completely incorporated into the AMRs and PMRs at this point. TH analyses for the 
no-backfill option are included in this PMR and THC and THM analyses are ongoing. For the 
NFE PMR, elimination of backfill is not expected to significantly change the conclusions of the 
report. Section 1.4.3 discusses the overall influence of backfill on the NFE. On an AMR by 
AMR basis the effect of backfill removal from the design is discussed below: 
 The Thermal Test AMR is unaffected by changes in repository design since the purpose 
of this AMR is to provide hydrologic and thermal property set testing and conceptual 
flow model validation with respect to a controlled heat input to the NF host rock.

 2-3 
 The THC Process AMR characterizes the chemical evolution of the NF host rock using 
the emplacement drift environment as a heat transfer boundary condition only. Any 
potential changes in the introduced chemical environment (either by including or not 
including backfill) and how they may influence the evolution of the host rock chemical 
environment are not considered in the process model. Consequently, only changes in the 
thermal (temperature) history at the drift wall will have an impact on the water and gas 
compositions there. These changes should primarily be limited to early times (after 
closure) since the peak and time-to-peak-temperature are affected by the inclusion or 
exclusion of an engineered backfill material. In the case without backfill, it is expected 
that the peak temperature at the crown of the emplacement drift will be slightly higher 
since it occurs earlier, the resistance to heat transfer is reduced, and the heat flow will be 
more isotropic, because the backfilled design has a higher fraction of the heat flow in the 
downward direction (CRWMS M&O 2000k, Sections 6.11.1.1 and 6.11.1.4). At times 
shortly after closure (possibly within 100 or 200 years), it is expected that the two design 
cases will exhibit nearly identical thermal histories at the drift wall and hence identical 
chemical histories in the host rock. 
 The THC Abstraction AMR is affected similarly to the THC Process AMR. 
 The NFE FEPs AMR may require modifications to FEPs excluded based on the 
emplacement-of-backfill screening argument. However, since these FEPs primarily 
impact the in-drift thermodynamic environment (by changing the environment near the 
drip shield and waste packages), it is expected that they will have less influence on the 
processes occurring within the NF host rock. Consequently, the FEPs associated with 
the NFE PMR are less affected by the removal of backfill from the repository design. 
 The THM Calculation is largely restricted to the host rock and will be affected primarily 
by changes in the thermal history as described above for the THC Process AMR. 
The design of the potential repository is controlled by a series of hierarchical design requirement 
documents. The lowest level of these documents is termed Subsystem Design Descriptions 
(SDDs). Five of these SDDs have been identified that have interfaces with the NFE PMR, as 
follows: 
 Subsurface Facility SDD (CRWMS M&O 2000aa) 
 Emplacement Drift SDD (CRWMS M&O 2000ad) (includes the invert) 
 Backfill Emplacement SDD (CRWMS M&O 2000ae) 
 Subsurface Ventilation SDD (CRWMS M&O 2000af) 
 Ground Control SDD (CRWMS M&O 2000ag).

 2-4 
Source: CRWMS M&O 2000g, Figure 1-2 
Figure 2-1. Schematic View of the Potential Repository Layout, Drift Connections and 
Representative Waste Package Types within an Emplacement Drift

 2-5 
Source: CRWMS M&O 2000g, Figure 1-3 
Figure 2-2. Schematic Cross Section of an Emplacement Drift Containing a 21-PWR 
Waste Package, Showing Major Elements of the Engineered Design 
Alternative II Design for the Engineered Barrier System 
During development of the SR design, based on EDA-II, there was considerable discussion of 
the capacity for an even lower temperature design, but within the footprint of the characterized 
area. The Subsurface Facility SDD establishes the requirements for the location of emplaced 
waste. The SDD limits the minimum thickness of rock above the emplacement drifts, the 
minimum unsaturated-rock thickness below the drifts, and the standoff from the main trace of 
Type 1 faults (those with movement in the Quaternary period, the last two million years, such as 
the Solatario Canyon fault). These criteria are being applied to the repository design in parallel 
with development of the TSPA-SR and its supporting PMRs. The design organization has 
recently changed the design from a plane with the highest elevations at the south end to a plane 
with a grade downward in the north and south directions from a selected (nominally east-west) 
emplacement drift (CRWMS M&O 2000i). Both designs include a  % grade downward from 
each drift midpoint, for drainage. This design change allows the emplacement area to extend 
farther to the south without exceeding the rock-cover minimum, and increases the potential 
emplacement area. This change will affect the detailed coupled process calculations for the 
NFE, but likely would not change overall conclusions about site suitability or performance, as 
discussed in Section 1.4.3, because NFE processes are more sensitive to thermal loading than to 
footprint and because the rock properties in the new area are similar to the original region.

 2-6 
Examples of the Subsurface Facility SDD (CRWMS M&O 2000aa) criteria that are direct inputs 
into NFE models include: 
1.2.1.4: The system shall provide emplacement space to allow for an average waste 
package spacing of TBD-3791. 
1.2.1.5: The system shall space the emplacement drifts 81 m center to center. 
1.2.1.7: The system shall orient emplacement drifts at least 30 degrees from dominant 
rock-joint orientations 
1.2.2.1.4 to 1.2.2.1.6: Standoff distances (these are the crit eria discussed above) 
1.2.2.1.8 and 1.2.2.1.9: Location of the repository 
As the design organization selects design parameters in accordance with these criteria, some of 
the details in the TSPA abstracted and process models will change. The models have been 
developed with this process in mind, and are intended to be suitably robust to permit such 
changes without extensive model redevelopment. 
The Subsurface Facility SDD criterion for emplacement-drift orientation (1.2.1.7) is being used 
to select the orientation of the drifts with respect to rock joints. The design organization recently 
changed the drift orientation from the generally east-west orientation of the VA design (CRWMS 
M&O 2000i). This change will have an effect on the representation of rock displacements and 
slip in NFE models (NFE PMR) and rock-fall calculations (EBS PMR). Since the purpose of 
such a change would be to improve performance and the orientation is based on analysis of 
mapped fractures, it is expected that the overall effects would be favorable. 
The Emplacement Drift SDD includes criteria regarding drift-wall temperatures, line- loading, 
drip shield, and invert. These criteria have been factored into TSPA abstracted and process 
models. 
The NFE coupled processes that have been studied for the VA design also occur in the EDA-II 
design, but for a shorter duration and a smaller spatial domain. The major element of the VA 
design that does not occur in the EDA-II design is large-scale boiling and dry-out of the pillars 
between the emplacement drifts; in the EDA-II design the capacity to drain percolation flux 
between the drifts is expected to be available at all times. 
2.1 THE NEAR-FIELD ENVIRONMENT PROCESS MODEL DEVELOPMENT 
PHILOSPHY 
Activities associated with the NFE have historically focused on how the evolving environment 
would impact repository performance. As stated earlier, the NFE does not presently exist, and 
therefore cannot be directly measured. Of necessity, evaluation of NFE impacts on performance 
must be based on model projections to first define the NFE. As such, although these activities 
are associated with site characterization, they have been dominated by model development, 
defining parameters and input to models, and obtaining measurements to provide testing of and 
insight into the physical processes that are to be modeled.

 2-7 
Development of the NF process models (Section 1.4.2) was based on a series of laboratory and 
field tests, as well as fundamental principles of heat and mass transfer, and of chemical 
equilibrium and kinetics. Conceptual process models using these scientific principles were 
implemented in numerical models, as computer software (codes). In some cases, these 
implemented models were benchmarked to laboratory and field test data, to validate selection of 
the conceptual processes and to calibrate input parameters, such as rock properties. 
The processes of the NFE are primarily driven by or coupled to the generation of heat from the 
waste. The laboratory work and early field studies that were related to development of the NFE 
models were reported in the Synthesis Report on Thermally Driven Coupled Processes (Hardin 
and Chesnut 1997). 
The emplacement of high-level radioactive waste, especially CSNF, in Yucca Mountain will 
release a large amount of heat into the rock adjacent to the repository. The heating rate will 
decrease with time, creating a thermal pulse. There is an imbalance between the declining heat 
source and the outward loss of heat from the volume of rock heated to a given temperature. 
Because the initial heat dissipation area is small, this imbalance initially favors increasing 
temperatures and an expanding volume of heated rock, with the drift wall reaching its peak 
temperature within several decades after repository closure. Thereafter, the imbalance favors 
decreasing temperatures at the drift wall; however, because of the thermal inertia of the heated 
rock and the continuing (though declining) heat source, the return to near-ambient temperatures 
takes many thousands of years. Percolating water can hasten the cooling process, but 
temperatures at the drift wall are calculated to remain above 50C for at least several thousands 
of years (see Section 3.2.3.1.3). 
In addition to raising the rock temperature through the relatively slow process of heat 
conduction, heat can be transported more effectively by the sensible (single-phase) heat process 
accompanied by advective transport of water, and by latent heat associated with vaporization of 
water accompanied by vapor transport. The latter can result in either escape of vapor from the 
NFE and EBS, or in gravity-driven heat-pipes in the fractured rock of the NF. In such a heatpipe, 
water present within the porous rock matrix near the heat source will absorb heat and 
vaporize. The vapor will be expelled into nearby fractures, and will flow though the fractures to 
a cooler location (e.g., upward above the drift, but downward below the drift). Eventually, the 
water vapor will condense into liquid water, releasing its latent heat. The condensate can be 
imbibed into the nearby matrix, can flow downward in the fracture system, or can move back 
toward the hotter, dryer region due to capillary forces. Depending on the condensation location, 
the fracture-system geometry, and the competition between imbibition, capillary movement in 
fractures, and gravity-driven movement in fractures, the water may drain below the repository 
horizon, or it may return to the heated region. The latter water can repeat the cycle, which is 
known as refluxing, greatly enhancing the rate of heat transfer away from the emplacement 
drifts. These processes are schematically illustrated in Figure 2-3 (CRWMS M&O 2000a, 
Figure 26).

 2-8 
Source: CRWMS M&O 2000a, Figure 26 
Figure 2-3. Schematic Representation of Thermal Hydrological Processes 
in an Unsaturated, Fractured Geological Medium 
When the water vaporization and condensate return (reflux) cycle is active, the heat pipe 
transports heat, in the form of the latent heat of vaporization of water, rapidly from the heat 
source into the surrounding rock. The mobilization of water temporarily (for decades to 
centuries) increases the percolation flux in the NF by a large amount. This creates the possibility 
that water may quickly drain back onto the drifts or that it may shed through the pillars 
between emplacement drifts. The thermal-hydrological aspects of models discussed in 
Sections 2.2.1, 3.2, 3.3, 3.4, and 3.6 include consideration of refluxing for both temperature and 
saturation distribution in the NF rock. 
Other effects, such as coupled chemical and mechanical processes (described in Sections 2.2.2, 
2.2.3, 3.3, 3.4, 3.5 and 3.6), may also influence the movement of water above, within, and below

 2-9 
the emplacement drifts. For example, the rapid movement of water generated by heat pipes, and 
the temperature changes experienced by the water in heat pipes, have the potential to create 
stills in which water deposits its dissolved minerals in the boiling region and aggressively 
dissolves new minerals in the condensation region. This THC process can affect seepage water 
chemistry and the hydrological pathways and properties. These processes are most intense when 
above boiling temperatures are present, but they operate to a lesser degree at sub-boiling 
temperatures, because the vapor pressure of water increases with temperature. Coupled THC 
processes have the potential to significantly alter the permeabilities of the fractured rock mass 
and to disperse and/or immobilize mineral constituents and released radionuclides. It is not 
likely that significant quantities of radionuclides will be released during the thermal pulse, due to 
the projected long lifetime of the engineered barriers (CRWMS M&O 2000ac, Figures 3-102 and 
3-103). 
Because the rock mass is fractured and heterogeneous, the temperature gradients generated by 
the thermal pulse in the near field have the potential to induce significant relative displacements 
of opposing fracture surfaces in the rock mass. Such movements, particularly shear 
displacements of rough fractures, have the potential to permanently alter fracture permeabilities 
in the affected regions by several orders of magnitude. 
Based on the body of work on coupled processes on unsaturated-zone repositories (see, for 
example, Hardin and Chesnut 1997; Hardin 1998; Wilder 1993, 1996, and 1997), the 
relationships among the coupled processes and the relative strengths of the processes can be 
assessed. As summarized below, at Yucca Mountain several of the coupled processes dominate 
the others. The discussion is a road map of the processes to enable the reader to evaluate more 
detailed descriptions of individual processes in the larger context. 
The NFE evolves in response to coupled processes in four categories, thermal (T), 
hydrological (H), chemical (C), and mechanical (M). The coupling of the processes is indicated 
by acronyms listing the processes involved; the sequence of letters in the acronym is not 
significant, and back-coupling is not indicated by listing letters more than once. In principle, 
thermal, hydrological, chemical, and mechanical processes in the NF are coupled through their 
process state-variables (such as temperature, liquid saturation, relative humidity, species 
concentrations, displacements, and corresponding process fluxes (such as heat flux, water and air 
fluxes, chemical- reaction rates). The couplings between these different processes, indicated in 
Figure 2-4, usually take place in both directions at different levels of strength and significance, 
e.g., the thermal effects impact the hydrological processes (T  H) and the back coupling 
hydrological effects impact the thermal processes (H  T). If the coupling between 
two processes is strong in one direction, while it is weak in the opposite direction, it is usually 
possible to neglect the weak coupling in the initial calculations and to evaluate its impact from 
the result of a calculation that is coupled only in one direction. Such approximations often 
significantly reduce the effort required to compute coupled problems.

 2-10 
Figure 2-4. Coupling Between Thermal, Hydrological, Chemical, and Mechanical Processes 
During the heating phase, TH processes in the NF are always strongly coupled in both directions: 
 In the T  H direction, the temperatures affect fluid densities and fluid saturations as a 
result of thermal expansion, and evaporation and condensation. 
 In the H  T direction, the fluid saturation, relative humidity and vapor and water 
movement affect the transport of sensible and latent heat. As noted in Section 3.2.1.1, 
heat pipes can prevent temperature rises above the boiling point, as has been 
demonstrated in field tests (Section 3.6.1.1). 
For these reasons, fully coupled thermal-hydrological (TH) modeling of T and H processes is a 
mandatory requirement for NF modeling. The thermal effects on hydrology are the strongest, 
ranging from halting flux to enhancing it. The hydrological effects on thermal are significant, 
reducing NF temperatures and extending the near-boiling region for tens to ~100 meters, 
depending on the design. When H  T coupling is strong, latent-heat transfer dominates 
sensible-heat transfer. Most NFE work in the past has focused on TH, including that described 
in Sections 2.2.1, 3.2.3, and 3.6.1. 
In thermal-chemical (TC) coupled processes, the coupling is strong in one direction and weak in 
the other. Further, back-coupling is actually ternary, rather than binary: 
 In the T  C direction, chemical processes depend strongly on thermal processes 
through the temperature dependence of kinetic rates and phase changes. The solubility 
of CO2 in water is a function of temperature. At high temperature, CO2 degasses from

 2-11 
solution with pH shifting to higher values. This higher partial pressure gas migrates 
down temperature gradients to dissolve into cooler solutions, with pH shifting to lower 
values. These solutions cause more mineral dissolution to occur. 
 In the C  T direction, the coupling is weak with chemical reactions having little 
impact on the NF energy balance of the system that is dominated by TH processes. 
There are also potential thermal effects in the far-field due to the endothermic alteration 
of zeolitic minerals (e.g., dehydration, conversion of clinoptilolite to analcime). These 
reactions are energy sinks and would probably result in retardation of higher 
temperatures beyond the zone being altered. 
 There can be C  H  T coupling, which then can affect temperature through the 
H  T coupling described in the previous paragraph. However, chemically-driven 
changes in hydrological properties require significant reflux durations at near-boiling 
temperatures, and thus there would be a delay well beyond the peak of the temperature 
pulse before changes occur. This will limit the net C  T coupling from the ternary 
coupling. 
In HC coupled processes, the coupling can be strong in both directions or strong only in one 
direction, depending on repository design and site characteristics. 
 In the H  C direction, chemical processes depend strongly on hydrological processes 
through fluid flow rates that affect the availability of water, air and other chemical 
species that participate in the chemical reactions. 
 In the C  H direction, there is a potential for permeability of pore and fracture flow 
pathways in the rock to be significantly altered through the precipitation and dissolution 
of solid phases, particularly when extended refluxing occurs. The significance of the 
chemically-driven hydrological property changes depends on repository design (drift and 
WP spacing, which impacts the duration and spatial extent of near-boiling conditions in 
the rock); the ambient hydrological properties, primarily fracture porosity; and the 
spatial localization of the boiling region. In Sections 3.3 and 3.4, calculations conclude 
that mineral precipitation will not significantly change fracture permeability. These 
calculations use the current design (which induces a limited duration and extent of nearboiling 
conditions compared to the VA design), a higher (~1 percent) fracture porosity, 
and a local boiling region at least 10 cm thick (the smallest zone size). While there are 
uncertainties, (e.g., including for computational simplicity the use of calcite precipitation 
rates decreased from those measured in the laboratory), the models reproduced the 
results of field tests and therefore are considered applicable to these calculations. 
Furthermore, sensitivity to permeability values is included in TSPA-SR to accommodate 
the uncertainty in C  H coupling. 
Thus, in THC modeling, the T  H, H  T, T  C, and H  C couplings are strong. The 
C  H couplings can be strong or weak, depending on design and site characteristics. The 
C  T coupling is weak. In most calculations, the C  H has been treated as a weak coupling; 
and calculated separately.

 2-12 
Mechanical processes must be introduced in the context of ternary THM processes accounting 
for TH, TM, and HM coupled processes: 
 In the T  M direction, mechanical processes depend strongly on thermal processes 
through the impact of temperature on thermal expansion and thermally induced cracking 
of rock. 
 In the M  T direction, mechanical processes have little impact on the energy balance 
of the system that is dominated by TH processes, and this coupling may be neglected. 
 In the H  M direction, the impact of hydrological processes on mechanical processes 
in the unsaturated zone is small, because the pressure change in the gas phase, which 
determines the overall fluid-phase pressures, is quite small compared to thermal stress 
changes in the rock matrix. 
 In the M  H direction, coupling between the mechanical processes and the 
hydrological processes can be strong, because large thermal stresses developed in the 
near field can cause significant fracture displacements and changes in rock permeability 
in the near field. These permeability changes arise from both shear and normal 
displacements that are induced across pre-existing fractures, and from the creation of 
new micro-fracture systems that link into pre-existing fracture systems. While normal 
displacements can recover during the cooling phase, the impact of shear displacements 
and (less likely) micro-cracking on rock permeability is likely to be more permanent and 
to persist far into the future. Section 3.5 focuses on T  M coupling and the consequent 
change in fracture hydrological properties (thus becoming T  M  H). It should be 
noted that changes in the fracture hydrological properties are different during the early 
heating period and the later cool-down period. At early times (first few decades to a 
century after repository closure), feedback from hydrological property changes could 
affect peak temperatures. At later times, as the rock cools back to sub-boiling 
temperatures, there is little significance to the feedback to temperature, but there may be 
significant changes in seepage into the drifts. These potential changes in seepage are 
termed thermal seepage in this report because they are driven by the thermal pulse, 
even though they may not occur until later times when temperatures are well below 
boiling. 
Thus, in THM modeling of NF processes, T  H, H  T, T  M, and M  H processes are 
strongly coupled while H  M, and M  T couplings are weak. 
Finally, the impact of CM coupled processes must be considered to complete the full suite of 
coupled processes in the NF: 
 In the C  M direction, chemical processes can strongly affect mechanical processes 
through cementation or healing and dissolution processes in fractured rock that, given 
sufficient time, can significantly change rock deformability in the NF. Therefore, the 
C  M coupling must also be considered to be potentially strong.

 2-13 
 In the M  C direction, the direct energy transfer from mechanical processes to 
chemical processes is very small and this coupling can usually be neglected. The main 
coupling is if mechanical processes create more surface area for reactions. 
To summarize the binary couplings contributing to full THMC coupling, of the twelve possible 
couplings: 
 Seven are likely to be strong: T  H, H  T, T  C, H  C, T  M, M  H, 
C  M. 
 One can be weak or strong depending on repository design and site characteristics: 
C  H. 
 Four are likely to be weak: C  T, H  M, M  T, M  C. 
The strength of coupling and significance on performance depends on the time of coupling as 
well as the strength, as discussed above. 
2.2 PREVIOUS NEAR-FIELD MODELING 
A series of NFER have been published that summarize evolution of the NFE. These reports 
(Wilder 1993, 1996, and 1997) documented the results of model analyses of the NFE based on 
the repository design, parameter values, and understanding of the physical processes that existed 
at the time. 
The NFERs were identified in the Waste Package Plan (Harrison-Giesler et al. 1991) as the 
formal means for transmitting and documenting information regarding the NFE and its evolution. 
The Preliminary Near Field Environment Report (Wilder 1993) included the environment that 
developed within the drifts and contacted the WPs and waste forms (WFs), all of the materials 
within the drifts, and the environment that developed within the rock mass and extended into the 
rock mass a distance that depended on the physical process being considered. 
The Near-Field and Altered Zone Environment Report (Wilder 1997) describes the environment 
within the drifts NF, the evolving environment within the rock mass, and the AZ). Another, 
more recent, discussion and summary of the models and model development is contained in the 
Near-Field Altered-Zone Models Report (Hardin 1998). 
Finally, the Total System Performance Assessment-Viability Assessment (TSPA-VA) Analysis 
Technical Basis Document, Chapter 3, Thermal-Hydrology (CRWMS M&O 1998b), provided a 
historical presentation of previous TSPAs (with respect to thermal-hydrology analyses), the 
abstraction and testing workshop leading into the viability assessment, the process model and 
abstracted base case for the TSPA-VA, and important TH sensitivity studies including, among 
others, the influence of rockfall on the thermal hydrologic in-drift environment and THM 
alteration of fractures below the repository horizon. 
The previous modeling efforts will be discussed as TH, TC, and thermal-mechanical (TM) 
models in the following section.

 2-14 
2.2.1 Thermal-Hydrological Models of Near-Field Processes 
Liquid water is the agent common to most, if not all, of the coupled NFE processes. Therefore, 
development of TH models is a necessary prerequisite for predicting the long-term coupledsystem 
response to inputs representing repository-design parameters. 
TH conceptual models are implemented in thermal-hydrological software codes, such as NUFT, 
VTOUGH and TOUGH2. These programs solve systems of partial differential equations 
representing the various flow and transport processes (e.g., saturated darcy flow, boiling and 
unsaturated flow, capillary imbibition, thermal diffusion and advection of heat) that are 
anticipated to be pertinent to the subsurface regime of Yucca Mountain. However, before the 
systems of equations can be solved to yield desired information about the state of the potential 
repository, a representation of the model must be input in the form of a defining list of physical, 
hydrodynamic and thermal properties that may exhibit dependence on a variety of other 
parameters, including location, time, and temperature. Depending on the degree of complexity, 
the list may involve constants, analytic functions of one or more variables (e.g., x, y, z, t) or 
other discretely specified parameter distributions that contribute to completely defining the 
equations to be solved, along with the boundary and initial conditions that uniquely determine 
the solutions to the equations. Of course, the model is not complete without specifying the 
geometry, as embodied by the choice of coordinate system, computational-domain shape and 
symmetry. It should be noted that the software codes are capable of obtaining solutions to the 
differential equations (i.e., simulations) using a variety of numerical techniques. In the context 
of run-time, accuracy and numerical stability, the analyst implements a solution procedure for 
addressing a particular design or the input needs of performance assessment. 
Past modeling efforts considered the NF to include what is now referred to as the EBS (see 
Section 1.2.1). Therefore, a discussion of past TH models will also discuss the EBS. During the 
thermal period (i.e., the period during which decay- heat strongly influences fluid flow), the 
potential sources of water seeping into emplacement drifts are heat-driven condensate flow and 
ambient percolation. During the post-thermal period (which primarily corresponds to the postboiling 
period), ambient percolation is the dominant source of drift seepage. In both instances, 
the likelihood of water seeping into the drift increases with local ambient percolation flux. 
Besides seepage, another source of moisture flux in the drift is the condensation of water vapor 
at relatively cooler locations in the drift; this effect, which is called the cold-trap effect, is 
facilitated if there is a large disparity in local heat flux among the WPs and if the WPs are spaced 
far apart, so that heat is not effectively shared. The use of line-load WP spacing, in which the 
WPs are placed nearly end to end, and blending of spent nuclear fuel minimize local heat-flux 
variability as well as the corresponding tendency for the cold-trap mechanism to occur. 
Section 3.2.3.3 provides conclusions from a numerical study that contrasts designs with different 
degrees of thermal-hydrological coupling. 
Within the emplacement drifts, the most important time-dependent NFE conditions are the 
relative humidity and temperature at the drip shield and WP surfaces, and the amount of liquid 
water (and its chemical composition) contacting the drip shields, WPs, and waste forms 
(CRWMS M&O 1998b, Volume 3, Section 3.4). These conditions depend primarily on design 
choices (e.g., the thermal-loading density, the choice of drift-liner materials, and the presence or 
absence of backfill) and secondarily on far-field boundary conditions (e.g., surface topography

 2-15 
and infiltration flux and the pre-emplacement state of the mountain). Thus, typical output from a 
particular TH model simulation is the evolution of liquid-water seepage flux, temperature, 
relative humidity (RH), and gas-phase air-mass fraction within the drifts as functions of time 
after repository closure. These are used directly as NFE performance measures in assessing total 
system performance. TH modeling also serves as the starting point for other process model 
calculations describing water chemistry, engineered-barrier performance, and radionuclide 
transport. These models compute distributions of temperature and flow velocity in the repository 
host rock, which are used with partially coupled models to evaluate whether more rigorous, fully 
coupled process models are needed. 
A recent issue of the Journal of Contaminant Hydrology focused on Yucca Mountain. Two 
articles, (Haukwa et al. 1999, p. 217-255 and Wu et al. 1999, p. 185-215) are descriptions of 
thermal hydrology, with emphasis on the MS. 
In this section, three TH conceptual models are described, some general TH results are 
presented, and detailed results are presented regarding application of these models for line and 
point spacing of waste packages, using the overall VA heat loading. 
Even with current computing resources, modelers have found that it is impractical to explicitly 
model a complex network of fractures or conduct full 3-D simulations on the scale of realistic 
spatial variability in the fracture system. As a result, several approximate approaches to 
modeling the naturally complex fracture system of Yucca Mountain have been developed. The 
three TH models described in greater detail below vary by the means in which flow through 
fractures is represented. 
The Equivalent-Continuum Model (ECM) assumes that the local matrix potential (water potential 
plus osmotic potential) is equal in the fractures and the adjacent matrix. Local thermodynamic 
equilibrium is assumed between the fractures and matrix. Composite functions are derived to 
describe the equivalent behavior of a single continuum and to define the relations between 
unsaturated hydraulic conductivity and liquid saturation and between matrix potential and liquid 
saturation (Klavetter and Peters 1986, for isothermal conditions, and Pruess et al. 1990 for 
non-isothermal conditions). The ECM does not treat fractures as discrete features; instead 
fracture-flow effects are averaged over the whole spatial domain. The ECM involves less 
computational effort than do other models described subsequently, because it uses a single 
continuum to represent the fractures and matrix. The assumption of local equilibrium between 
fractures and matrix is appropriate, if the liquid-phase flux in the fractures is sufficiently small 
(Buscheck et al. 1991, p. 313). Thus, the ECM is appropriate for modeling condensate drainage 
during periods of quasi-steady moisture movement in thermally driven models, but may be less 
well suited for modeling the early stages of repository heating, when the rate of thermally driven 
moisture reflux will be near its peak. The ECM assumptions are poorly suited for modeling the 
effects of transient boundary conditions (e.g., episodic infiltration events). This ECM approach 
has been applied in thermal-test analyses (see Section 3.6.1) with direct bearing on prediction of 
conditions in the near field and AZ: 
 Pretest analysis of the DST (Buscheck et al. 1997d, p. 15) 
 Posttest analyses of the Single Heater Test (SHT) (Buscheck et al. 1997c, Section 2.1) 
 Posttest analyses of the Large Block Test (LBT) (Hardin 1998, Section 3.4.3)

 2-16 
The Dual-Permeability Model (DKM) treats the matrix and the fractures as two distinct porous 
continua, with transfer terms to represent the mass and heat flux between them. Because the 
DKM does not assume capillary-pressure equilibrium between fracture and matrix continua, it 
can handle much larger liquid-phase fluxes than can the ECM without producing conditions near 
100 percent liquid saturation in the matrix. The DKM also allows thermodynamic 
disequilibrium between matrix blocks and the adjoining fractures, because of its capability to 
represent heat flow between these two continua. Because the DKM allows for gas-phase 
pressure disequilibrium between the matrix blocks and adjoining fractures, it can account for the 
way gas-phase pressure build-up in the matrix throttles (restricts) the rate of rock dryout. This 
throttling occurs early during the dryout period, when there is boiling in the rock matrix. It will 
persist if the matrix permeability is extremely small (e.g., matrix permeability is less than 
approximately 10 microdarcy) and the matrix blocks are large (e.g., greater than 3 m). 
Compared to the Discrete Fracture Model (DFM) described below, the DKM tends to 
overpredict gas-phase pressure build- up during the early stage of dryout in the rock matrix and, 
therefore, overpredicts the throttling of dryout during this period. For large matrix blocks, the 
DKM continues to overpredict throttling after the early dryout period (Hardin 1998, 
Section 3.3.3.2, p. 3-12). 
The DKM is more computationally intensive than is the ECM, but less intensive than the DFM 
described below. Typical transfer terms for heat and mass transfer between the fracture and 
matrix continua do not represent the diffusive nature of matrix imbibition in the matrix block. In 
other words, the DKM does not treat fractures as spatially discrete features; rather, the effects of 
fracture flow are distributed throughout the spatial domain. Consequently, the DKM 
underpredicts the fracture-to-matrix liquid flux during the early stages of matrix imbibition and 
thus tends to overpredict the magnitude of condensate drainage (shedding) around emplacement 
drifts. 
The DKM approach has been applied in DS TH models supporting TSPA-VA (DOE 1998, 
Volume 3, Section 3.2.1), with direct bearing on prediction of conditions in the NF/AZ. The 
DKM is applied to all the Line-averaged-heat-source Drift-scale Thermal-Hydrological (LDTH) 
model calculations used in the multi-scale TH modeling approach to predict NFE conditions for 
performance assessment (see Section 3.2.2.1). In this family of models, the fracture-to-matrix 
liquid flow is strongly influenced by the Fracture Matrix Interaction (FMX) parameter, which is 
specified for each hydrogeologic unit as a model input. This parameter varies between 0 and 1, 
and quantifies the fraction of the fracture surfaces that are wetted by the liquid phase. This 
fraction, together with a specified value for the fracture spacing, quantifies the interfacial flow 
area per unit volume of the rock matrix available for fracture-to-matrix liquid transfer. The FMX 
parameter for liquid-phase interaction accounts for channeling of flow as the liquid phase 
fingers through the fracture network. However, this factor probably under represents the 
wetted surface area of fractures that occurs during condensate drainage in TH models. Other 
approaches (Ho 1997), such as the Active Fracture Model (AFM) (Liu et al. 1998, pp. 2635 to 
2636), account dynamically for changes in the influence of condensate drainage on the FMX. In 
such approaches, the parameter that is analogous to FMX increases with the magnitude of liquid 
flux in the fracture continuum. Because repository decay heat will generally produce greater 
liquid flux than that which occurs at ambient conditions, and because condensate flow may be 
more ubiquitous than ambient percolation in fractures, this dynamic approach results in a larger 
value of the interaction factor where there is development of condensate flow. As the repository

 2-17 
heat output declines, thermally driven reflux decreases asymptotically toward the ambient 
percolation levels, and the interaction factor decreases to its previous value. The DS TH 
calculations supporting TSPA-VA assumed a constant value for FMX rather than the dynamic 
FMX approach. 
The DFM spatially discretizes the space occupied by the fractures and the matrix blocks, using 
finite-difference grid blocks (or elements). Because the location and morphology of individual 
fractures are not usually well known, their geometric characteristics are: (1) interpolated from 
field data, (2) randomly generated, or (3) represented using an idealized geometry. The third 
approach is commonly used (Buscheck et al. 1991, pp. 316 to 321; Nitao and Buscheck 1996, 
pp. 748 to 752; Kwicklis and Healey 1993, pp. 4091 to 4102; and Zimmerman and 
Bodvarsson 1996, pp. 433 to 438). The DFM is, by far, the most computationally intensive of 
the three approaches described here. Moreover, available data on the fracture networks may not 
justify using the DFM. The DFM more accurately represents fracture-to-matrix liquid flow and 
matrix-to-fracture gas flow, particularly at early time when the DKM tends to under-predict mass 
transfer between the fractures and matrix. The DFM has been used in modeling studies of 
episodic nonequilibrium percolation events (Buscheck et al. 1991, pp. 316 to 321) and analysis 
of the G-Tunnel heater test (Nitao and Buscheck 1996, pp. 748 to 752). 
The selection of an approach (ECM, DKM, or DFM) for representing FMX must weigh the 
trade-off between computational complexity and physical accuracy. Relevant factors include the 
magnitude of liquid flux in fractures, the size of the domain being modeled, and the scale over 
which predicted results are desired. The ECM is adequate for some scoping calculations. The 
DFM is probably not practical for repository-scale and mountain-scale calculations, but it can be 
used to determine phenomenological parameters needed for the DKM. The DFM can also be 
useful in interpreting the results of laboratory-scale experiments. Complementary use of these 
three approaches is an effective way of incorporating some of the effects of nonequilibrium 
fracture-matrix behavior at any practical scale of analysis. Each TH NFE model in 
Sections 3.2.3, 3.3, 3.4, and 3.6 used the DKM flow model. 
The TH models used in support of TSPA-VA are described in detail in the TSPA-VA (CRWMS 
M&O 1998b, Section 3.5). This section laid the technical foundation for the submodels and 
temperature correlations developed for the MSTHM as developed for and applied in the viability 
assessment TSPA and carried forward to the site recommendation TSPA. It also described the 
development of the mountain-scale TH models used to abstract the gas-phase flux and air mass 
fraction at the repository horizon before, during, and after repository heating. 
Submodels of different scale, flow processes, and dimensionality were used to approximate the 
physical processes associated with repository thermal loading. Mountain-scale submodels 
developed for TSPA-VA were used to describe repository edge effects (large scale processes), 
while DS models were developed to characterize waste package variability (small scale 
processes) for a point loaded repository design (see Section 3.2.3.3 in this PMR or CRWMS 
M&O 1999b, Section 3.5.3). The thermal-hydrologic submodel included a DKM representation 
for heat and fluid flow to capture the effects of thermally enhanced fracture flow towards or 
away from the repository drifts (see Figure 2-3) during early heating. The TH submodel also 
included uncertainty in infiltration rate and hydrologic fracture flow properties in order to 
determine the influence of the ground surface boundary conditions and hydrologic flow

 2-18 
properties on the in-drift variables used by TSPA. Future (wetter) climate states were also 
applied to the TH models as specified by the UZ F&T PMR (CRWMS M&O 2000f). 
The abstraction of the in-drift thermodynamic environment (e.g., waste package temperature and 
relative humidity) was based on the MSTHM results segregated into six repository subregions 
(CRWMS M&O 1998b, Figure 3-6). The abstraction TH results computed for each repository 
subregion were placed in bins (one set for the commercial waste another for the non-commercial 
waste) based on the time to reach a specified waste package relative humidity (85%) and the 
waste package temperature at times well after closure (5,000 years). Each bin may contain many 
waste packages that meet the specified criteria. Therefore, to reduce the amount of data to be 
analyzed by TSPA, a least-squares minimization is used to find the waste package closest to the 
mean relative humidity and temperature. The resulting abstraction (one time-history per bin with 
a maximum possible of 60 bins per repository subregion) is applied in the TSPA supporting 
models. 
The abstracted time-histories of gas flux and air mass fraction were developed for the repository 
center and edge regions and applied in the incoming gas and water chemistry models in the 
TSPA total system model. 
2.2.2 Past THC Modeling 
THC modeling work prior to the VA were reported in the Near-Field & Altered Zone 
Environment Report (Wilder 1997, Volume I, Sections 4.5 and 5.4) and the NF/AZ Models 
Report (Hardin 1998, Chapter 5). This previous wo uld focused on how water chemistry evolved 
within these zones over time on rock-water interactions that result in changed mineralogy, and 
on precipitates or salts left as the result of boiling and evaporation processes. This work was 
based on property set understanding, the conceptual designs and the hydrologic framework that 
existed at that time. All of these factors have since evolved and the specific results of those 
studies are not of direct value for the current design. However, they provided the framework for 
methodology development and model testing, as well as identified the issues that needed to be 
evaluated (e.g., hydrological property changes, mineral-cap formation, CO2 exsolution). 
As reported by Hardin (1998, Section 5.1.1, p. 2),  The AZ-water-composition model [was] 
used to estimate the concentrations of major chemical species in water that interacts with the host 
rock at ambient and elevated temperature along flow paths upgradient from the NFE. One of 
the models used included dual-permeability (DK) TH processes, and considered evaporation and 
condensation so that the results are applicable to 2-phase systems where liquid-phase chemistry 
is of interest. However, the models could accommodate only a few chemical components (e.g., 
silica) and were limited with respect to the representation of complex processes, such as boiling. 
The chemical components included the major and minor ions present in J-13 water as well as the 
silicate minerals. The components included: Na, Si, Cl, S, Ca, F, Mg, Li, Al, P and CO2 species. 
The gas phase composition was set to the ambient air composition with added water vapor (total 
pressure was allowed to vary). 
Results of this previous work (Hardin 1998, pp. 5-81 to 5-83) indicated that, although evolution 
of recharge water compared to the J-13 composition depends on several rate-limited reactions, it 
is consistent with Yucca Mountain mineral and meteoric water interactions. They also

 2-19 
concluded that sufficient silica could be mobilized by repository TH processes to plug fractures 
(for the properties and design analyzed, initial porosity of 3 x 10-4 [Hardin 1998, Table 3-7] 
30x less than used in Section 3.3). They concluded that minerals would accumulate where 
boiling occurs, predominantly at the bottom of the isothermal (heat-pipe) zone. Formation of a 
mineral cap above the emplacement drifts was predicted by those models for a broad range of 
conditions. This work did not include examination of the durability of the potential mineral cap 
from processes such as dissolution or seismic effects. While current models have reassessed this 
conclusion, the modeling work was valid for the conditions considered and helped to identify the 
need to evaluate this phenomena. Section 3.6.2 discusses the applicability of this work. 
Other uncoupled reaction-transport simulations reported by Hardin (1998, pp. 5-70 to 5-73) 
(assuming saturated fractures and no matrix interactions) showed that dissolution of calcite will 
occur rapidly, particularly during a transient period of increased CO2 fugacity, caused by 
evolution of CO2 from the rock during the first few years of heating. 
The THC modeling and abstraction, as applied to the viability assessment TSPA, are 
characterized in detail in the TSPA-VA (CRWMS M&O 1998c). The TSPA-VA NF 
geochemical environment is represented by time-dependent distributions of the gas and water 
compositions that interact with the waste package and waste form inside the potential repository 
emplacement drift. The parameters supplied to the total system model included the oxygen 
fugacity, the solution pH, the total dissolved carbonate, and the ionic strength of the water. 
These parameters were derived from a 13-component chemical system. The abstracted step 
change approximation for the time evolution of the four chemical parameters was based on the 
TSPA-VA thermal-hydrologic models. For each discrete time period, a batch calculation was 
performed with a geochemical model to determine the appropriate chemical composition of the 
groundwater during that time period based on the surrounding thermal-hydrologic conditions and 
the incoming composition of the groundwater reacting with iron oxides. The abstracted time 
periods were representative of repository center conditions. 
Since the VA, THC modeling of the Drift Scale and Single Heater Tests has explored water-gasrock 
reactions, including a variety of minerals (calcite, feldspars, clays, and zeolites, in addition 
to silica polymorphs), as well as gas-phase CO2 equilibration and transport (Sonnenthal 
et al. 1998, pp. 57 to 70; Tsang et al. 1999, pp. 4-1 to 4-74). These studies have further 
quantified effects of CO2 on water chemistry and on calcite dissolution and precipitation, as well 
as time- and space-dependent changes in mineralogy and water chemistry in a DK system. In 
particular, the models predict strong gravity drainage of condensate waters below drifts with 
greater calcite dissolution in these zones (Tsang et al. 1999, p. 4-46). 
The significance of uncertainties raised by past TC work is addressed in Section 3.6.4.2. 
2.2.3 Past THM Modeling 
Previous THM modeling efforts were focused on determining the impacts of TM on hydrologic 
and chemical aspects of the NFE. As was true for the TH and THC models, a discussion of the 
validity or usefulness of results from this previous modeling effort is contained in Section 3.6. 
However, some of the most useful results of the earlier work included insights into what needed

 2-20 
to be addressed by the models as well as assistance in the development and qualification process. 
The TM responses of most concern were: 
 the closing, opening and sliding of fractures that might impact permeability and thus 
flow of water through fractures 
 the impacts on chemistry as a result of formation of new surface area from fracturing 
 pressure dissolution, and precipitation of minerals in pressure-narrowed fractures 
 microfracturing that could affect drift stability, specifically the size of blocks that might 
fall, as well as to change the flow characteristics around the drifts 
 time-dependent (long-term, non-elastic creep) deformation behavior. 
This previous work was largely reported in the Near-Field and Altered-Zone Environment 
Report (Wilder 1997) and the Near-Field/Altered Zone Models Report (Hardin 1998). 
Previous modeling of mechanical impacts on hydrology focused on fracture impacts, because 
any changes in rock-mass permeability from TM effects can be attributed to the fractures. 
Changes to matrix permeability in response to stress and temperature are small (Hardin and 
Chesnut 1997). Moreover, the hydrologic behavior of a fractured rock mass is controlled by 
relatively few, well-connected fractures. 
THM modeling studies were also considered for the viability assessment TSPA (CRWMS 
M&O 1998b, Section 3.6.8). The approach taken for this weakly coupled process model was to 
develop a one-dimensional, mountain-scale, dual permeability model to assess the impact of 
normal stress driven changes in joint aperture, abstracted from a 2-D mountain-scale TM model, 
on percolation flux in the fractures below the repository horizon. Shear stress changes were not 
considered in the analysis. Aperture changes in regions of thermal-mechanical tension and 
compression were translated directly into corresponding changes in the hydraulic fracture 
aperture. This in turn affected the flow characteristics in the mechanically altered regions in the 
NF host rock. The thermal-mechanical alterations in fracture aperture were considered in five 
discrete time segments from initial emplacement to 750 years after waste emplacement. 
Subsequently, fracture hydrologic properties in the TH model changed from the initial unaltered 
state as a function of the same discrete time segments developed in response to thermalmechanical 
stresses. The thermal-hydrologic model simulation did not feed back temperature 
predictions to the TM model. That is, one-way coupling from TM to the TH model was assumed 
in this preliminary analysis. Fracture hydrologic properties in the TH model were altered at each 
discrete time increment with the zone of compression surrounding the potential repository 
horizon increasing with time, while the zone of tension above and below the horizon initially 
increased then decreased with time. The fracture hydrologic aperture was altered by a factor of 
two increase or decrease depending on the location of the zones of tension or compression, 
respectively. The fracture permeability, porosity, and van Genuchten alpha parameter were 
altered by change in fracture aperture. Parallel plate fractures were assumed in the analysis. It 
was found in the analysis that fracture liquid flow, matrix and fracture liquid saturation, and 
temperature were not drastically altered by normal stress changes to fracture aperture.

 2-21 
Laboratory studies (Bandis et al. 1983; Barton et al. 1985) have shown that greater hydrologic 
impact often results from shear displacement of fractures than from normal displacement. 
Permanent changes in hydrologic properties or flow paths can result from normal displacement, 
but they tend to be smaller than those caused by shear displacements. This has been observed in 
field studies (e.g., Wilder and Yow 1987). 
A one-dimensional TH analysis was included in the TSPA-VA Technical Basis Document 
(CRWMS M&O 1998d, p. 3-152 to 3-157). 
The results of thermal-mechanical simulations in the VA were coupled to TH simulations of the 
potential repository at Yucca Mountain. Past thermal-mechanical simulations (Mack et al. 1989) 
presented results that identified zones of altered rock where the fracture aperture either increased 
or decreased by a factor of two. These altered regions were used to update fracture properties at 
five discrete times (25, 50, 200, 250, and 500 years) during the TH simulation. The properties 
that were updated, as a result of the changes in fracture apertures, were fracture porosity, bulk 
fracture permeability, and fracture air-entry pressure (van Genuchten alpha parameter). 
Comparisons were made between altered and unaltered TH simulations during approximately 
1,000 years of heating. 
Results showed that the altered and unaltered simulations produced similar trends in fracture 
flow, liquid saturations, and temperatures. The fracture flow at and below the potential 
repository was increased by up to several orders of magnitude as a result of condensate drainage 
in both cases. However, in the altered case, the increased flow in the CHn persisted longer than 
in the unaltered case. It was postulated that the reduced apertures near the potential repository in 
the altered case allowed more water to be retained in the fractures because of higher capillary 
pressures. This subsequently produced larger fluxes through the fractures below the potential 
repository. The saturation profiles at 500 years of heating supported this hypothesis. In addition, 
the increased fracture flow was attenuated by 1,000 years of heating in both the altered and 
unaltered simulations. Finally, the temperature profiles at 500 years of heating revealed that 
natural convection was attenuated in the altered simulation because of reduced fracture apertures 
and, hence, fracture permeabilities near the potential repository. While the overall temperature 
distributions were similar between the altered and unaltered simulations, the temperatures in the 
altered simulation were slightly higher near the potential repository and more symmetric above 
and below the potential repository, indicating reduced convection in the compressed zones. 
Other more direct formulations are presented in Hardin (1998, pp. 4-33 to 4-35) for permeability 
changes associated with shear-slip and normal deformation. For permeability changes associated 
with shear-slip, the resultant change is a function of a scaling exponent (relating in smooth or 
rough fractures) and a shear offset term resulting from thermal stresses. As previously described, 
shear alterations tend to impact the horizontal fracture sets. For permeability changes associated 
with normal deformation, the resultant change is a function of the stress change perpendicular to 
the fractures, fracture spacing, the initial fracture aperture, and the rock-mass modules. Each of 
the models presented is driven by stress changes that result from an imposed temperature field. 
Previous modeling efforts recognized that permeability changes in the repository host rock were 
important ; however, no rigorous bases were available to analyze these effects. Models were

 2-22 
based on concepts such as the cubic law, Mohr-Coulomb slip criteria, idealized fracture stiffness, 
hypothetical scaling relations, and statistical assumptions. 
Preliminary calculations have estimated the effect of shear deformation on fracture permeability 
(Blair and Berge 1997). Potential zones of slip were predicted for vertical and horizontal 
fractures. Slip on fractures due to induced shear stresses, were expected to be limited to a few 
small zones that are within about one drift diameter of the drift wall. Because the design has 
changed, the significance of this past work is more in development of the techniques than in 
predicted performance. 
This work also supported model confidence building, and provided a basis for design and 
analysis of the in situ thermal tests (Section 3.6), as well as laboratory studies. The goal of the 
work was model confidence building. See Hardin (1998, Sections 4.3.4.4 and 4.4.2.2) for 
detailed description of these efforts. 
Using a continuum approach, Blair and Berge (1997) calculated that significant TM effects on 
permeability within the DST may extend to a distance of several tens of meters from the drift. 
They concluded that enhanced permeability is likely in regions of increased thermal-stress 
gradients, so that a region of increased permeability may accompany the thermal pulse as it 
travels outward from the heat source. The work reported in Section 3.5, which uses a distinct 
element approach, is a significant advance in realism of the calculations. 
Other laboratory work that has supported development of the THM models were reported by 
Martin et al. (1997) for laboratory experiments that investigated creep in Topopah Spring Tuff 
samples. The observed creep deformation was consistent with time-dependent crack growth. 
Blair and Berge (1995) have identified time-dependent, inelastic crack closure in response to 
stress that was oriented perpendicular to the cracks. 
The effect of radiation on the THM behavior of the rock is uncertain. The radiation field is 
expected to affect only rock exposed on the surface of excavated drifts and to penetrate only a 
few centimeters into the rock. If spalling occurs, the rubble will bulk-up and form a radiation 
shield. Blair et al. (1996) tested over 40 samples of Topopah Spring Tuff, TSw2, and found that 
radiation may have caused degradation of fracture-filling and cementing minerals, which are 
thought to be composed primarily of carbonates. This could affect long-term deformation of 
rock at the wall of the emplacement drifts. 
The significance of uncertainties raised by past TM work is addressed in Section 3.6.4.3. 
2.3 THERMAL HYDROLOGY AND COUPLED PROCESSES WORKSHOP 
SUMMARY 
An M&O workshop on thermal hydrology and coupled processes (THCPs) for performance 
assessment (PA) was held on March 24 and 25, 1999 in Albuquerque, New Mexico. The topics 
covered at the workshop were thermal effects on flow, thermal effects on emplacement-drift 
seepage, THM processes, THC effects, and LADS. The discussions resulting from the LADS 
studies included a dissemination of the details associated with the EDA-II. The goal of the 
workshop was to develop work plans that would address the remaining issues for study that 
require further understanding to support the next Total System Performance Assessment for Site

 2-23 
Recommendation (TSPA-SR). The results of this workshop and its analyses established the 
direction and scope for this PMR, the UZ F&T PMR, and the EBS PMR. 
The workshop was organized around issues for THCPs that had been raised in connection with 
the previous TSPA-VA and recently established criteria issued in the form of IRSRs by the NRC. 
Comments on the treatment of thermal-hydrology in TSPA-VA were received from the 
Performance Assessment Peer Review Panel, the NRC, the DOE through its Management and 
Technical Services contractor, and formal reviews of the TSPA-VA. In addition, some issues 
were identified internally with respect to TSPA-VA by the M&O. Criteria for acceptability of 
this component of TSPA in terms of a future LA have been issued by the NRC in the form of 
several IRSRs. In particular, the following IRSR documents were used to identify open issues 
for THCPs in TSPA: 
 Issue Resolution Status Report Key Technical Issue: Evolution of the Near-Field 
Environment, Revision 2 (NRC 1999a) 
 Issue Resolution Status Report Key Technical Issue: Thermal Effects on Flow, 
Revision 2 (NRC 1999b) 
 Issue Resolution Status Report Key Technical Issue: Total System Performance 
Assessment and Integration, Revision 1 (NRC 1998) 
 Issue Resolution Status Report Key Technical Issue: Repository Design and Thermal- 
Mechanical Effects, Revision 2 (NRC 1999c). 
The key or most important issues, as identified from comments on TSPA-VA (DOE 1998, 
Volume 3) and the above NRC IRSRs, formed the bases for discussions at the workshop. An 
additional mechanism to ensure completeness in the coverage of THCP topics for TSPA is the 
features, events, and processes (FEPs) screening and scenario-development approach (see 
Section 2.5). 
The issues presented at the workshop were discussed, modified, and agreed upon by the 
workshop participants. These issues are summarized below. Note that at the time of the 
workshops, the scope of the NFE had not been finalized in relation to other PMR topics, 
specifically the UZ F&T and EBS PMRs. Therefore, some of the issues discussed cover issues 
that are beyond the current scope of this PMR. 
Seepage issues centered on how seepage may enter the emplacement drift before, during, and 
after the thermal perturbation. The TSPA parameters of interest include both seepage fraction 
and seepage-volume flow rate. Of particular concern, is how a pulse of water (possibly driven 
by repository decay heat) may penetrate the heat-transfer zone surrounding the emplacement 
drifts. A discussion of how this process may be facilitated by heterogeneity was also considered 
by the participants at the workshop. At that time, it was decided that future sessions of the 
workshops would consider DS heterogeneity in the coupled-process models used to estimate the 
impact of the thermal period on drift seepage. For TSPA-SR, thermally enhanced percolation 
flux in the NF host rock above the crown of the drift is to be abstracted from the multiscale TH 
model. The abstracted percolation flux provides a direct input into the TSPA seepage model. As

 2-24 
indicated in Section 3.2.2.1, the multiscale TH model being used for TSPA-SR applies 
homogeneous fracture properties in the NF host rock. The EBS PMR also describes the 
multiscale TH model and in-drift results. 
For the issue of thermal effects on flow (TH processes), the participants decided that the impact 
of the overall heat pulse on mountain-scale (liquid-phase) flow fields below the repository 
horizon would be considered (now in the UZ F&T PMR, CRWMS M&O 2000f). (The focus 
was on below-drift locations, because for the EDA-II design, heat pipes above the drifts will be 
limited and shedding will increase flow below the drifts.) Previous TSPAs found that the 
thermal perturbation subsided after a few thousand years. However, these studies considered a 
higher areal mass loading (AML) than the repository design under consideration for site 
recommendation (CRWMS M&O 1999a, Table 6-3). For the critical time period of regulatory 
concern of 10,000 yr., the impact of the thermal perturbation would be considered using a 
reference repository design analogous to EDA II (CRWMS M&O 1999a, Table 6-3), base-case 
infiltration rates and climate states specified in the UZ F&T PMR (CRWMS M&O 2000f, 
Section 3.5), and appropriate conceptual flow models applied in a thermal-hydrological, 
mountain-scale model (CRWMS M&O 2000t). 
The issue of THM processes centered on how the thermal pulse would affect the vertical and 
horizontal fracture permeabilities, both on the scale of the drift and of the mountain. All 
mechanical effects were ignored in TSPA-VA, which was based on a simple 1-D abstraction that 
showed that mechanical effects did not alter fracture flow significantly below the repository (Ho 
and Francis 1998). The single heater test, the LBT, and the DST, all provide valuable 
information on the possible movement of fractures induced by thermal stresses. These tests can 
be used to validate rock-joint constitutive models. It was decided that the potential influence of 
adding mechanical effects to thermal-hydrology would be abstracted from a thermal-mechanical 
calculation (CRWMS M&O 2000d) and introduced into the TSPA models, if the effects are 
found to be significant. 
The issue of THC centered on how the thermal perturbation may drive chemical processes in the 
surrounding host rock and how this impacts seepage-water chemistry and gas-phase composition 
and flux at the emplacement-drift wall. Alterations of fracture hydrological properties above the 
emplacement drifts may also impact seepage fractions and seepage-volume flow rates. 
Discussions of THC processes included mineral-water reactions that alter host-rock properties, 
and result in different chemical components entering the emplacement drifts. Near-field host 
rock property alterations (e.g., by precipitation and dissolution reactions) provide the basis for 
how the in-drift physical and chemical environment evolves with time before, during, and after 
the thermal period. 
Each of the process-level models (TH, THC, THM seepage) used to characterize the coupled 
processes were discussed at the workshop in the context of the thermal tests ongoing at the ESF 
and other field-test results. The DST, SHT, and the LBT, all allow the opportunity for 
conceptual flow-model analysis (ECM or DKM), boundary-condition testing, and assumption 
testing related to flow-property specifications, initial conditions, and other important TH process 
issues. Personnel from the thermal testing activities were present at the workshop in order to 
specify ways that PA may potentially include thermal-testing results in process-level models and 
abstractions.

 2-25 
2.4 SUMMARY OF OTHER VIEWS AND ALTERNATIVE CONCEPTUAL MODELS 
The NFE involves complex coupling of thermal-hydrological-chemical-mechanical processes 
(THCM). Properly incorporating this complex coupling in fully-coupled models is very 
challenging and computationally demanding. Although progress is being made in developing 
more fully-coupled models, to date, most models applied to the NF have relied on various 
simplification approaches, including focusing on only one or two degrees of coupling (e.g., 
thermal-hydrological, or thermal-hydrological-chemical) with further simplifications as to how 
the coupling is reflected. For instance, if there is direct coupling between THC, a limited 
number of chemical species were commonly addressed, or simplifications of bounds on how the 
species are represented are incorporated into the models. Furthermore, the models commonly 
incorporate only forward coupling, such as considering the evolution of minerals under TH 
conditions, without coupling directly back into the TH analysis, specifically addressing 
permeability changes due to mineralogical changes. Therefore, iterative analyses are used to 
assess this interactive coupling. As a result, there are many different or alternative approaches 
that have been or could be applied to evaluations of the NFE. The basic tools available all rely 
on some combination of mass and energy conservation, as well as chemical interaction 
evaluations based on thermodynamic understanding of chemical species. However, the 
approaches to deal with the complexity of the coupling and the conceptualization of the 
processes can be quite different. 
As long as there is heat associated with the design, the kinetics and coupling of the THCM 
processes are very much dependent on repository design, emplacement modes and operational 
sequences (loading), as well as ventilation. These engineering factors have been evolving. 
Furthermore, understanding of the properties of Yucca Mountain have also been evolving. Many 
of the past analyses of the NF that can be compared to those reported in this PMR have used 
different inputs and parameters. Therefore, making direct comparisons between conclusions 
from the various approaches is not very useful. What is useful is to understand the differences in 
approach or fundamental assumptions. Rather than trying to compare the specific results or even 
details of the various alternatives, this report will review the conclusions of reviews of the 
modeling processes that have been used to analyze the NFE. Other views will then be discussed 
in this context. 
Although the processes are complexly coupled, for discussion purposes they will be grouped into 
essentially simply coupled processes related to thermal-hydrology, thermal-hydrology-chemistry, 
and thermal-mechanical processes. There is obvious coupling between these, but these single 
coupled processes facilitate discussion and reflect the simpler coupling that is often performed in 
iterative analyses. 
Alternative TH, THC, and THM models are described in the following Sections (Sections 2.4.1 
through 2.4.3). Section 2.4.4 summarizes the NFE-related issues developed by the TSPA Peer 
Review Panel. Section 2.4.5 summarizes the Expert Elicitation on NF/AZ Coupled Effects. 
Finally, Section 2.4.6 summarizes issues discussed in correspondence of the Nuclear Waste 
Technical Review Board and the NRCs Advisory Committee for Nuclear Waste (ACNW).

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2.4.1 TH Alternative Models 
The TH coupling of heat and mass transfer can be treated in a number of ways. For heat transfer, 
conduction models are the most straightforward, however; these fail to incorporate the coupling 
of heat transfer with moisture that can be dominant within the NFE. In regions where there is 
not active boiling or condensation, the conduction models can be used with confidence and are 
computationally less challenging. For the NFE, most of the approaches rely on TH models that 
include the impacts of latent and advective heat transfer. Different approaches to model the 
physical processes involving flow have included Equivalent Continuum, Discrete Fracture, and 
Dual Permeability (or porosity). For the NF, most of the analyses, including those reported in 
this PMR, have relied on DK (continuum) models with AFM to account for interactions between 
fractures and matrix. 
Different or alternative views regarding the TH coupled model approach also relate to the 
properties and to the approaches of how to treat the interaction between fracture and matrix. 
A peer review of the TSPA-VA (CRWMS M&O 1999c, p. 47) identified several concerns, if not 
alternative views. They noted that the use of van Genuchten model is not justifiable in the 
present context., because it ignores a number of processes, including: unstable nature of 
gravity-driven infiltration; hysteresis during episodic flow, small scale (sub-grid) heterogeneities; 
effects of connectivity of fracture and matrix continua; and effect of abrupt changes in properties 
on transport fluxes. Further, they note that the fracture-matrix factor, while reasonable and 
justified to account for a variety of processes for which the physics are not directly incorporated 
in the models, is devoid of convincing physical meaningThis is not satisfactory and reflects 
a lack of understanding of the actual physics of the process and, more generally, the lack of 
progress in the scale-up of two-phase flow in the fractured system 
The fracture-interaction factor reflects the observation that the contact area for interaction 
between water in fractures and the matrix is not the same as the fracture-surface contact area. 
There are both laboratory and field studies that support the understanding that flow in fractures 
does not occupy the entire fracture-system volume. Most of the studies, including laboratory 
studies, were under isothermal conditions, and many laboratory studies relied largely on artificial 
fracture studies (Nicholl et al. 1994; Liu et al. 1998). Currently, the model, called the AFM, uses 
a factor that varies as a function of saturation within the fracture. The AFM is intuitive, but is 
based essentially on inverse modeling to match saturation data from the field and not on a 
physical basis from laboratory studies, etc. (CRWMS M&O 2000f, Section 3.4.1.4.1). 
These issues are mainly related to the UZ F&T and are discussed in that PMR, as well as in the 
EBS PMR, where the multi-scale abstraction is discussed. However, the issues relate to the NF 
in that these are the models and approaches that are used to determine the TH coupling within 
the NF, and two-phase flow is a dominant process within the NFE. Also, directly related to the 
NF is their comment that the model approaches ignore differences between wetting and drying 
cycles. 
Some of the differences between views or approaches relate to the differences in design. During 
the TSPA-VA, the design did not include drip-shields. As a consequence, the peer-review panel 
(CRWMS M&O 1999c) comments included concerns about seepage being decoupled from the

 2-27 
TH. TH effects are considered for seepage within the UZ F&T PMR. Furthermore, a key 
assertion or basis of determinations of the impact of the NFE on performance is that the drip 
shield will perform its function throughout the period when the NFE is hot so that decoupling of 
processes regarding flow is justified. The impact of the NFE on flow is of concern only after the 
drip shields fail (CRWMS M&O 2000s). Therefore, the couplings that must be considered are 
those aspects of the NFE that cause permanent or long-lived changes to flow and transport 
(usually associated with coupling with chemistry or mechanics, not merely TH). Thus, one of 
the different approaches or views deals with whether the drip-shield lifetime projection is 
justified (the evaluations of drip-shield lifetime are discussed in the EBS and WPD PMRs). 
The NRC use of MULTIFLO models found performance to be dominated by variation of UZ 
parameters (Hughson and Green 1999). This implies that, although not the only source of 
uncertainty, the understanding and accounting for the natural-system heterogeneity is of primary 
importance in evaluating repository performance. This natural-system heterogeneity cannot be 
designed away, and is not addressed directly in the NFE models. Sensitivity studies have been 
done, but these assume that there is not spatial or temporal coupling of the impacts of 
heterogeneity on other parts of the system. Some work, as discussed below in this section, 
indicates that this assumption may not be valid and that the THC responses can be influenced by 
adjacent regions with significantly different natural or engineered properties. 
An additional alternative view deals with how well TH (as well as THC) processes are 
understood by the YMP. In a 1999 letter to DOE, the NWTRB expressed concern that elevated 
temperatures (particularly above the boiling point) increased uncertainty (Cohon 1999). They 
state, in part,  thermal loading has a larger effect than any other single design attribute.  
Unfortunately, the understanding of water mobilization and migration processes 
and effects during this initial high-temperature period is still far too limited to 
engender a reasonable degree of confidence. Some insight into 
thermal-hydrological response has been gained from in situ thermal tests. 
However, important results from the DST will not be available for several more 
years. 
In general, the cooler the repository, the lower the uncertainty about heat-driven 
water migration and the better the performance of waste package materials. 
Above this temperature, technical uncertainties tend to be significantly higher 
than those associated with below-boiling conditions. 
While this view is primarily focused on TH, it can be applied more generally to THC where 
elevated temperatures lead to higher chemical reaction rates and, thus, lower kinetic barriers to 
reaching equilibrium for all kinetically inhibited reactions. The implications for uncertainties is 
better made in the broader context, i.e., in Section 2.4.2, TH/THC Alternative Models. 
There are also differing views regarding the connectivity of the fracture system. As reported by 
Sagar et al. (1995, p. 4), there are questions regarding potential for pressure build-up that may 
suggest that fractures in a welded tuff are not well-connected and that gas pressures will in 
fact build up during the heating period. No thermal tests have been conducted to date within 
the Tptpll, where the majority of the potential repository would be located.

 2-28 
Another area of differing views relates to the potential for heat-pipe formation. Green 
et al. (1991, pp. 164 to 165) reporting on laboratory experiments and minimal analyses of glassbead 
experiments state Based on these analyses and observations. A heat-pipe process will 
occur only in the matrix block nearest the heat-generating source during the early stages after 
waste emplacement. Liquid water will only cross the fracture [to the next matrix block] when 
the moisture content of the matrix adjacent to the fracture is sufficiently high to cause the 
fracture to saturate. Prior to this, the matrix block on the heated side of the fracture will 
desaturate thus denying the heat-pipe process the return flow of liquid water necessary to 
continue. Other questions regarding heat pipes were raised by Manteufel et al. (1993, p. 577) 
where they conclude that heat pipes will be negligible because of the low matrix permeability. 
The field test results address these issues, but the issue is fracture-matrix-block-geometry 
specific (vertically continuous matrix blocks would not be bound by these effects for horizontal 
fractures) and therefore the issue remains to be address by tests in the Tptpll. 
One of the principal means to validate the YMP NFE models is comparison with results of field 
tests, particularly the Drift-Scale Test. Hughson and Green (1999) used model analyses 
supported by the MULTIFLO code to evaluate the DST. They raised the concern (Hughson and 
Green 1999, p. 1-5) that inadvertent and unmeasured loss of moisture through the bulkhead, 
which would not be experienced under repository conditions, may compromise the utility of the 
test. They noted that although the DST was designed to address model hypotheses, that 
additional uncertainty caused by heat and water mass loss through the bulkhead 
may render the DST an open system which can lead to increased modeling 
uncertainty. This modeling uncertainty can lead to increased uncertainty in 
performance assessments that are based on conceptual models evaluated and 
calibrated against the DST. 
While the increased uncertainty caused by losses across the bulkhead cannot be eliminated, 
nevertheless the test results have been useful in building model confidence (see Section 3.6 and 
CRWMS M&O 2000a). Based on data collected since that time, it is judged that the test is still 
useful for model validation, although there are uncertainties introduced by this moisture loss. 
In the discussion of coupling (Section 2.1), it was stated that TH processes are always strongly 
coupled in both directions. In an analysis by Manteufel et al. (1993, p. 581, Figure 2), the 
coupling is shown as primary in the T  H direction, but secondary in the H  T direction. 
The significance of uncertainties revised by alternative TH views is addressed in Section 3.6.4. 
2.4.2 TH/THC Alternative Models 
Because of the complexity of coupling when considering THC, there are even greater differences 
in approaches or views regarding this coupling. This is reflected in the TSPA-VA peer review 
comment Although the NFGE (near-field geochemical environment) models are logically 
constructed, there is little basis for accepting the results as indicative of repository behavior. The 
complexity of the models, the large uncertainties in parameter values, and the clearly coupled 
phenomena suggest that it is unlikely that the present NFGE model captures or usefully portrays 
the repository conditions in the near-field. (CRWMS M&O 1999c, p. 60).

 2-29 
As discussed in Sections 3.1.3 and 3.3, the analysis of THC processes for the DST used two 
approaches. One considered a relatively complete set of mineral assemblages and aqueous 
species needed to fully describe the NFE. The second included a less complex set of minerals 
and aqueous species. The analysis that included the less complex suite of minerals and aqueous 
species matched the CO2 and water pH data from the DST. If the models properly incorporate 
all physical processes, appropriate properties, details of the test, and accurate thermodynamic 
and kinetic data are available, then the model with more complex mineral assemblages would be 
expected to more closely match the data, but it did not. Possible reasons for this result, as 
discussed in Section 3.1.3 and 3.3, are uncertainties in rate parameters and thermodynamic 
properties, and the short duration of the test. 
As noted by Rosenberg et al. (1999, p. 7-8), limitations in THC modeling result, among other 
reasons, from limits in the geochemical data basis for high ionic strength solutions at elevated 
temperature. A modeler must presently choose a data file from several that are available. Each 
such file presently carries one of the following sets of limitations: 
1. Includes essentially all requisite chemical species, covers the necessary temperature 
range, but requires use of a thermodynamic activity coefficient model that is only valid 
for dilute solutions. 
2. Is valid for concentrated solutions, covers the necessary temperature range, but 
includes only some of the requisite chemical species. 
3. Is valid for concentrated solutions, includes most of the requisite chemical species, but 
is, limited to a temperature of 25C. 
4. Includes essentially all requisite chemical species, covers the necessary temperature 
range, and can be used for concentrated solutions, but many of the activity coefficient 
model parameters are estimates no t obtained from experimental measurement or a 
generally accepted estimation methodology. 
The difficulty arises in that modeling of concentrated solutions requires a host of additional data 
(e.g., Pitzer interaction parameters) that is not required to treat dilute solutions. To model a 
complex system, the required quantity of such data can easily dwarf the required quantity of 
standard state thermodynamic data (e.g., equilibrium constants). Pitzer parameters are required 
for most pairs and triplets of chemical species in the modeled system. 
In the THC model simulations for the DST and for predictions of THC processes accompanying 
waste package heating, completed dryout has occurred. Therefore, in these areas and in adjacent 
regions, the remaining liquids reached high ionic strengths. However, over much of the range of 
liquid saturation, and the regime of mineral dissolution and precipitation, the ionic strength of the 
modeled waters is quite low. The model results have shown that higher ionic strengths are 
reached only when liquid saturations are typically less than 1 percent and are, therefore, basically 
immobile (ignoring long-term changes in the local TH field) and less important to fundamental 
changes in seepage chemistry and permeability modification (Section 3.3). Water seeping into 
boreholes in the Drift Scale Test has been characterized by fairly low concentrations of aqueous 
species (CRWMS M&O 2000b, Section 6.2.7.3.1, Table 9).

 2-30 
The low saturation, high ionic strength regime is important for predictions of the final salts 
expected to be formed, especially within the EBS. If salts that formed in the NF during dryout 
have sufficiently different dissolution rates, their specific identities become more important once 
rewetting takes place during cooldown. In that case, the water compositions would most likely 
be dominated by dissolution of halides relative to sulfates, carbonates and silicates. Such 
behavior is not included in the current NF THC models. 
Murphy and Pabalan (1994, p. 3-38) note that there is an apparent discrepancy between 
dissolution-rate parameters determined in the laboratory and those deduced from field studies or 
natural-systems analyses. They point out the need to determine whether the kinetic models used 
should rely on near-equilibrium or far-from-equilibrium data, as some models do a better job of 
explaining one type of data than they do the other. They also point out the need to use consistent 
data sets. 
Kinetic data (e.g., rate constants and activation energies) are currently available for many 
important rock-forming minerals. Generally, these are obtained from mono-mineralic laboratory 
experiments (e.g., in systems comprised of a sample of a single mineral along with distilled 
water or a simple pH buffer solution). In the case of minerals, for which little or no kinetic data 
are available, reasonable (e.g., order of magnitude) estimates for rate constants can often be 
inferred by comparison to known data for similar minerals. The larger problem in dealing with 
mineral-water kinetics is the dependence of rates on reactive surface areas (rates are proportional 
to reactive surface areas). No simple, direct methods exist for the measurement of the reactive 
surface area of a mineral in an actual rock. Uncertainties in reactive surface areas may span 
several orders of magnitude. Plug-flow reactor experiments, using crushed quartz and 
devitrified-crushed Topopah Spring Tuff (Johnson et al. 1998), have been useful for refinement 
of reactive surface areas and other kinetic constraints. However, under unsaturated boiling 
conditions, the character of water-rock reactions may be different from saturated systems, and 
there are, as yet, not completely analyzed experiments that can be used to further refine the 
reactive surface areas and other aspects of mineral precipitation under boiling conditions. 
Reaction kinetics control the rate of approach to chemical equilibrium. The equilibrium state 
depends only on thermodynamic data. If a reaction approaches equilibrium rapidly on the time 
scale of interest, even relatively large errors in rate law parameters (including the reactive 
surface area) may not be significant to modeling the system. It may be proper to model such a 
reaction as approaching equilibrium instantaneously, thus, obviating the need for corresponding 
kinetic data. Reaction rates are accelerated by higher temperatures according to the Arrhenius 
activation energy principle. Thus, the consequences of uncertainties in kinetic data (including 
reactive surface areas) and even the need for such data tends to diminish at higher temperature. 
The Yucca Mountain Site Characterization Project (YMP) has changed the repository design to 
lower the temperatures, in an attempt to address the issue of additional uncertainty caused by 
vaporization and boiling process (CRWMS M&O 1999a), as noted in the preceding section on 
TH. A cooler repository could be produced by aging the waste before emplacement, by a longer 
period of ventilation after emplacement, or by emplacing the waste less densely. Such a 
repository would, by definition, produce less heat in a given volume of the repository system. 
This would generally result in lower maximum temperatures, reduced penetration of elevated 
temperature isotherms into the rock surrounding the drifts, reduced penetration of the boiling

 2-31 
zone into that rock, and less boiling overall. For a given amount of waste, the volume of rock in 
which boiling is occurring at any point in time is reduced as is the overall volume of rock in 
which boiling has occurred at any time in the thermal pulse period. From this, it can be inferred 
that any zone of significant rock/water alteration associated with higher temperatures and boiling 
would be confined closer to the drifts. The intensity of any such alteration at any given point in 
the rock would likely also be reduced. The possibility of significant feedbacks of rock/water 
interaction processes on the TH would almost certainly be lowered. Also, the formation of 
residual brine solutions and residual salt minerals would be consequently reduced. 
If the prediction of THC for a repository is viewed as a kind of Taylors series expansion about 
the ambient conditions, in which corrections are applied to the ambient model to account for the 
effects of processes associated with elevated temperatures, then it would seem that any 
uncertainties in these corrections (and hence the repository THC model) would be reduced by 
lowering the magnitudes of these corrections. In view of the preceding discussion, one might 
envision that the uncertainty in a given correction term is a constant fraction of the magnitude of 
that term, or perhaps even some fraction that increases with that magnitude. This intellectual 
framework suggests that TH/THC uncertainties would be most readily reduced by going to some 
type of cooler repository. This view is reinforced by consideration of the possibility that a 
sufficiently hotter repository might cross a threshold in terms of initiating some new, presently 
unaccounted-for process. 
It can be assumed that a cooler repository would be a more expensive repository due to larger 
footprint or longer operational period. The above argument needs to be carefully analyzed 
before the benefits of a cooler repository are accepted as compelling. First, the behavior of 
uncertainties may not actually follow the above conceptual model. Secondly, even if it does, it 
remains necessary to compare the uncertainties arising from the corrections with the 
uncertainties in the understanding of the ambient system. Certain aspects of that understanding 
are presently problematical. For the point in question, one would have to take the differences in 
the uncertainties for corrections of both a hotter and a cooler repository, and then compare that 
with the uncertainties in the ambient model. Thirdly, again even assuming the above behavior of 
uncertainties, the uncertainties in THC for a hotter repository may or may not make a critical 
difference to the final outcome of repository PA. 
Here further discussion will be directed only to the first point raised above: does the expansion 
about the ambient model give the correct picture about uncertainties as a function of how hot is 
the repository? That view may be too simple. First, the THC for a cooler repository may be 
more like the THC for a hotter repository than either is to the THC for the ambient system. 
Some boiling will occur even in any likely cooler repository. Moving from the ambient system 
to the cooler repository crosses two thresholds. There will be boiling even in a cooler repository, 
thus generating two-phase flow. There will also be attendant rock/water interaction driven by 
heating. Although this may be largely confined to a smaller volume of rock than in the case of a 
hotter repository, and it may be less intense as well, it is nevertheless centered about the most 
critical part of the repository, the drifts. What happens farther out into the rock may not have 
that much effect on repository performance. 
Second, at higher temperatures, uncertainties regarding rock/water interactions may actually 
decrease, as reaction rates are accelerated. The higher reaction rates will lower kinetic barriers to

 2-32 
reaching equilibrium and predictive modeling can rely more on thermodynamics (about which 
more is known) and less on kinetics (where reactive surface areas must be considered). Because 
of the higher reaction rates, the divergence of the system from equilibrium is smaller at higher 
temperatures and the length of time to get to equilibrium is smaller. Third, our general 
understanding of tuff/water interactions at higher temperatures (from various laboratory 
experiments and natural analogue studies) may even be somewhat better than that for such 
interactions at lower (here ambient) temperatures. This is due both to faster reaction rates, and 
also to the fact that much of the data was obtained in experiments that were, of necessity 
conducted at higher rather than lower temperatures (to shorten the experiment duration). 
A repository design that results in any elevation of temperatures will potentially increase the 
rates of mineral-water reactions. To a large extent, whether the repository temperatures at or 
near the drift wall are either above or below boiling will not remove the uncertainty introduced 
by the kinetics into the THC analyses. 
The geologic record (in general, not specific to Yucca Mountain) contains many examples of 
fully-filled fractures. Yet the fluid conductivity of a fracture can be substantially reduced by 
relatively little mineral precipitation, owing in part to the fact that the aperture width of a fracture 
is not constant but may vary substantially with position along a fracture. There is presently 
considerable uncertainty in how to relate the average degree of filling of a fracture to its ability 
to transmit water. This is one remaining problem in sorting out the question of a hotter versus a 
cooler repository. Another is a lack of general agreement on ambient fracture properties. 
Although a hotter repository might lead to a more significant reduction in the ability of existing 
fractures to transmit water, the larger magnitude of the thermal pulse, with its associated heating 
and cooling, might also lead to the formation or reactivation of fractures. Analyzing this 
possibility would require an even more involved THCM study. 
To a first approximation, the THC uncertainties remain the same with the lower repository 
temperatures, it is just a question of where in the system the processes occur. For above boiling 
conditions at the drift wall, the aqueous THC processes are minimized or no longer active, 
because at that location water would be removed from the system. Vapor THC processes may be 
present in this zone, but the mass of water in the vapor phase is limited and alteration is not 
expected to be significant. Beyond the region of rock that is above the boiling point, the same 
THC processes that would occur for a below boiling repository will take place. They will just 
occur at a different distance into the rock mass. If there is an extensive boiling region, there will 
be the addition of condensate, with different water chemistry, but there is no fundamental 
difference in the model and analysis of the THC processes. 
It is true that if the temperatures are above boiling there are additional uncertainties in the TH 
analyses that result from two-phase flow and from the potential differences in properties, such as 
imbibition, for vapor and elevated temperature fluids. However, for the unsaturated conditions at 
Yucca Mountain, there will be two-phase flow even at temperatures below the boiling point of 
water. At lower temperatures, the rate of mineral-water reactions may be slower but the twophase 
flow issues are still present. 
Murphy (1993, p. 118) estimated that, for a point located 75 m above the repository horizon of a 
potential repository at Yucca Mountain, temperatures would be in the 70C range for

 2-33 
approximately 4,000 yr. Under these conditions, he concluded that the temperature excursion 
is significant and chemical variations due to repository heating are likely to be significant. 
While this assessment was not for the EDA-II design and was addressing conditions above the 
drift, the temperatures and duration for the region considered by Murphy (1993) are similar to 
temperatures that will develop in pillar regions for EDA-II. 
One of the THC assumptions or inputs that is subject to alternate views is the relevant water 
chemistry used as input to TC and THC model simulations. Primarily, a water composition from 
the J-13 well in the same stratigraphic unit as the potential repository horizon has been used in 
TC simulations either directly or modified by evaporation or dilution. Compositions of several 
evolutions of J-13 water (concentrated, saturated, dilute, and acid-buffered) are shown in the 
Waste Package PMR (CRWMS 2000o, Table 3-2). Some previous coupled THC simulations for 
the DST (CRWMS M&O 2000b) and Single Heater Test (CRWMS M&O 1999d, Chapter 10) 
have used unsaturated zone pore water compositions because pore waters represent most of the 
in-situ water, and geochemical arguments suggest that water flowing in fractures is likely to have 
largely equilibrated with pore waters in the PTn hydrogeologic unit. Simulations of THC 
processes described in this PMR (Section 3.3) and the supporting AMR (CRWMS M&O 2000b) 
used pore water from the Tptpmn unit in the potential repository horizon from rock in the 
vicinity of the DST. The differences in view as to which water composition is appropriate for 
calculations of THC in the NFE reflect differences in view of the hydrological system and what 
the composition would be of water flowing in fractures under ambient conditions. (This is 
problematic because of the inability to collect water from fractures for chemical analyses.) The 
chemistry of the water collected from the DST, which had most likely flowed through fractures, 
indicates that the water was not a simple mixture of the condensed water and the pore water. 
The water reacted with silicate minerals and calcite in the thermal setting of the test. CO2 
fugacity is also an important chemical uncertainty in the THC models, since the acidity of 
seepage water can be affected by it (CRWMS M&O 2000b). 
As discussed in Section 3.3, model approaches have had to simplify the coupling in order to 
solve the problems. As noted by Hardin (1998, p. 8-12), The different THC simulation 
approaches have shown that conflicting results arise when simulations that consider only 
aqueous processes are compared with simulations that include boiling processes but do not 
incorporate a full set of chemical components and reactions. 
Another view, which on the surface may appear to be significantly different than that reported in 
this PMR, deals with the potential to plug fractures. Hardin (1998, Section 5, p. 82) concluded 
that sufficient silica would be mobilized by repository TH processes to cause significant local 
changes in fracture porosity. They postulated formation of a mineral cap above the 
emplacement drifts. Laboratory studies (Daily et al. 1987) have demonstrated fracture plugging. 
This is significantly different than conclusions reached in this PMR. These differences are 
potentially related to two fundamental changes in design and understanding that have taken 
place. The EDA-II design incorporates lower temperatures, so that the amount of water 
mobilized by the thermal pulse is reduced and, perhaps more fundamentally, the current estimate 
of fracture porosity is about 30x higher than used in earlier calculations. The current model also 
includes more components and physical processes than the earlier model.

 2-34 
A model proposed by Matyskiela (1997, pp. 1115 to 1118) suggests that silica precipitation in 
the rock matrix adjoining fractures will strongly reduce the permeability of the matrix, resulting 
in significantly decreased imbibition of percolating waters. The times for strong silica sealing of 
the matrix wall for a vitric tuff were five years for a solution having 350 ppm SiO2 and 105 yr. 
for a solution having 125 ppm silica (SiO 2). For a devitrified tuff, it was estimated that 
cristobalite dissolution followed by quartz precipitation would lead to a 1 mm-thick quartz 
fracture coating in about 30 yr. It is clear that several factors would immediately reduce the 
magnitude of the effects described by Matyskiela. First, the potential repository would be 
located in a devitrified tuff where the rates of reaction are orders of magnitude slower than for 
volcanic glasses. Second, the proposed model considered the system as fully saturated, 
maximizing the reactive surface area, the water available for reaction, and the diffusion 
coefficient. In an unsaturated system, only part of the fracture area would be contacted by water, 
so that the process would have to take place for much longer periods to actually affect a large 
part of the fracture surfaces. Third, it is considered by Matyskiela that the fracture water will 
have higher silica concentrations than matrix pore water, thus leading to a diffusion gradient into 
the matrix. However, no clear reason exists for the fracture water to have a higher silica 
concentration, because it originated as pure condensate (zero SiO 2) that has drained back toward 
the heat source, increasing its silica content through wall-rock reactions. Because the system is 
unsaturated, there is little driving force for convection, as in a single-phase hydrothermal system. 
A quantitative analysis of this problem was explored in Section 3.3 of this PMR and by Lichtner 
et al. (1999), who also questioned the interpretations and conclusions presented in the Matyskiela 
paper. 
2.4.3 THM Alternative Models 
The THM analyses have indicated that shear displacements can impact permeability, but that 
coupling to THC will not be strong since the additional surface area for reaction is not expected 
to be greatly increased. Reports on laboratory experiments of sheared rock (Mohanty et al. 1994, 
p. 258) have concluded that permeability changes due to shear displacements can be 
attributed primarily to the formation of fine materials. This would greatly increase the potential 
for coupling between TM and C. 
Further, Mohanty et al. (1994, p. 4-1) reported on experiments with Apache Leap Tuff, noted 
Forward and reverse normal stress showed a definite hysteresis in fracture permeability, with a 
similar trend being observed from mechanical aperture measurements. The THM calculations 
reported in this PMR have focused on shear displacements, because the normal displacements 
were assumed to be largely recoverable (elastic response) and resulting permeability changes of 
lesser magnitude than those associated with shear. However, the work of Mohanty et al. (1994) 
may indicate that normal stress displacements can not be ignored. 
As noted, many of the alternate approaches or views deal with how to simplify coupling. The 
THM models used in the NFE PMR have included simplifications in coupling TH to M. 
Other, more fully coupled THM approaches have also been developed. For example, work 
conducted in conjunction with the international Development of Coupled models and their 
validation against experiments in nuclear waste isolation program by countries developing 
repositories includes development of an analytical solution for coupled THM behavior by

 2-35 
Rehbinder (1995) and a study of THM behavior of sparsely fractured rock by Nguyen and 
Selvadurai (1995). In addition, Jiao and Hudson (1995) have presented a fully-coupled model 
for engineered systems in rock. Unfortunately, the simpler TH algorithms included in these 
saturated-zone simulations are not adequate for analysis of THM behavior in a partially 
saturated, fractured-rock mass. 
2.4.4 TSPA Peer Review Panel 
The TSPA Peer Review Panel (the Panel) was formed to provide a formal, independent 
evaluation and critique of the TSPA-VA for the potential high-level waste repository at Yucca 
Mountain. The objectives of the Panel were to describe the technical strengths and weaknesses 
of the TSPA-VA, and to provide suggestions for improvement. 
The Panel conducted a phased review over a two-year period to observe the development of the 
TSPA-VA and to review the completed TSPA-VA. During development of the TSPA-VA, the 
Panel submitted three interim reports with recommendations and comments on the process 
models, model abstractions, and draft documentation for the TSPA-VA. The Final Report Total 
System Performance Assessment Peer Review Panel (CRWMS M&O 1999c) includes the major 
points from the three interim reports, updated as appropriate, as well as new findings that the 
panel developed during its review of the TSPA-VA. Key issues described in the Final Report 
that are pertinent to this PMR are compiled in Appendix B. 
2.4.5 Expert Elicitation 
The Near-Field/Altered Zone Coupled Effects Expert Elicitation Project (CRWMS M&O 1998a) 
was established to help quantify the large uncertainties associated with thermal, hydrologic, 
mechanical, and chemical processes. The expert elicitation panel was tasked to consider how 
these processes occur, both temporally and spatially, and over what range of values the 
hydrological properties (for example, fracture permeability) may be influenced. 
The elicitation panel examined process models and experimental data on coupled processes from 
the single heater test. They considered THMC processes, potential changes to hydraulic 
interactions between fractures and the rock matrix, and effects of rockfall. Based on the results 
of the elicitation, the potential for thermally driven alteration of fracture properties (for example, 
permeability) fell within the range of the natural, spatial variability of the system. The net effect 
of combined THM and THC permeability changes would be to suppress convective heat transfer 
at the center of the repository block and increase lateral diversion of condensate on the downdip 
portion of the repository periphery. The panel concluded that the mechanical effects would tend 
to be reversible upon cooling, with the possible exception of horizontal changes in permeability 
caused by shear stress, but that chemical effects will be more permanent. The panel indicated 
that the FMX parameter used in the DK models might also be affected, because of chemical 
precipitation or dissolution. Although this effect may be permanent, the magnitude of such 
changes is uncertain. 
Appendix B includes a list of the key issues pertinent to this PMR that were reviewed and 
discussed by the panel members. A full description of the expert elicitation is provided by the 
NF/AZ Coupled Effects Expert Elicitation Project (CRWMS M&O 1998a).

 2-36 
2.4.6 Summary of Issues from Affected Organizations 
This PMR also addresses other key issues related to the NFE. These issues were identified by a 
review in the past two years of ACNW and Nuclear Waste Technical Review Board (NWTRB) 
meeting summaries and correspondence; Viability Assessment Volume 3, TSPA Peer Review 
Panel documentation; NRC comments on TSPA-VA; Expert Elicitation recommendations; 
licensing correspondence files for NRC; State and County correspondences; and issues noted by 
DOEs Management & Technical Support contractor. Appendix B provides a summary of key 
issues and describes how each issue is addressed in this PMR. 
Furthermore, by letter to DOE (Cohon 2000) the NWTRB expressed The Boards 
understanding is that current performance assessment models may not adequately describe the 
interaction of heat, water flow, chemical reactions, and mechanical disturbances with rocks near 
heated emplacement drifts. If this is the case, then sensitivity analyses could fail to identify 
coupled processes as principal factors. The Board recommends that DOE reexamine its 
evaluation of the importance of coupled processes in its identification of principal factor. 
2.5 FEATURES, EVENTS, AND PROCESSES 
The initial set of FEPs has been created for scenario development in the YMP TSPA by 
combining lists of FEPs identified as relevant to the YMP. This FEPs list consists of 
1,261 entries from the Nuclear Energy Agency working group, 292 FEPs from YMP literature 
and site studies, and 82 FEPs identified during YMP project-staff workshops. These FEPs are 
organized under 151 categories, based on NEA category headings, resulting in a total of 
1,786 entries in the YMP NFE FEPs AMR (CRWMS M&O 2000e, Section 1.2). The FEPs have 
been identified by a variety of methods, including expert judgment, informal elicitation, event 
tree analysis, stakeholder review, and regulatory stipulation. All potentially relevant FEPs have 
been included, regardless of origin. This approach has led to considerable redundancy in the 
features, events, and processes (FEP) list, because the same FEPs are frequently identified by 
multiple sources, but it also ensures that a comprehensive review of narrowly defined FEPs will 
be performed. 
Each FEP has been identified as either a primary or secondary FEP. Primary FEPs are those for 
which detailed screening arguments are developed. The classification and description of Primary 
FEPs strives to capture the essence of all the secondary FEPs that trace to the primary. 
Secondary FEPs are either FEPs that are completely redundant or that can be aggregated into a 
single Primary FEP. The resulting 310 primary FEPs have been assigned to associated PMRs. 
The assignments are based on the nature of the FEPs, so that the analysis and resolution for 
screening decisions reside with the subject-matter experts in the relevant disciplines. The 
resolution of other than system-level FEPs are documented in AMRs prepared by the responsible 
PMR groups. The assignment to the associated PMRs was made initially during a series of PA 
and PMR workshops. The initial assignment was then revised and now is consistent with the 
portion of the NF as covered in this PMR. There is overlapping, such that some FEPs are 
covered in more than one PMR. This section summarizes the screening decisions associated 
with the FEPs for the NFE PMR group. Details of the screening processes are documented in the 
NFE FEPs AMR (CRWMS M&O 2000e). Chapter 4 and Appendix D provide detailed mapping 
of NF related KTI subissues to this and other PMRs.

 2-37 
The scope of the FEPs screening is to identify treatment of primary FEPs affecting the NFE. The 
FEPs deemed potentially important to repository performance are evaluated, either as 
components for the TSPA or as separate analyses in the NFE FEPs AMR (CRWMS 
M&O 2000e). The scope for this activity involves two tasks, namely: 
Task 1: Identify which FEPs are considered explicitly in the TSPA (called included FEPs) 
and in which AMR report(s) these FEPs are addressed, 
Task 2: Identify FEPs not included in TSPA (called excluded FEPs) and provide justification 
for why these FEPs do not need to be a part of the TSPA model. 
Of the original list of FEPs, 26 have been identified as primary in relation to the NFE. These 
FEPs are best dealt with at the system level; do not fall within other PMRs; or are directly 
addressed by regulation, assumptions listed in the regulations, or in background information used 
in development of the regulations. 
NFE FEPs that are either fully or partially included in the TSPA-SR, based on the screening, are 
the following: 
 1.1.02.00.00: Excavation/construction (Section 3.5 includes effects on seepage) 
 1.1.02.02.00: Effects of pre-closure ventilation (Sections 3.2, 3.5) 
 2.1.08.01.00: Increased UZ water flux at repository (Sections 2.2.1, 3.2.3, 3.3, 3.5) 
 2.1.08.02.00: Enhanced influx (UZ F&T PMR) 
 2.1.08.03.00: Repository dry-out due to waste heat (Sections 3.2, 3.3) 
 2.1.08.10.00: Desaturation/dewatering of the repository (Section 3.2) 
 2.1.08.11.00: Resaturation of the repository (Sections 3.2, 3.3) 
 2.1.09.01.00: Properties of potential carrier plume in the waste and EBS (EBS PMR) 
 2.1.09.12.00: Rind (AZ) formation in waste, EBS, and adjacent rock (Sections 3.2, 
3.3) 
 2.1.11.01.00: Heat output/temperature in waste and EBS (Sections 3.2, 3.3, 3.4, 3.5) 
 2.1.11.02.00: Non-uniform heat distribution/edge effects in repository (Section 3.2) 
 2.2.07.10.00: Condensation zone forms around drifts (Sections 3.2, 3.3, 3.4) 
 2.2.07.11.00: Return flow from condensation cap/resaturation of dry-out zone 
(Sections 3.2, 3.3, 3.4)

 2-38 
 2.2.08.03.00: Geochemical interactions in geosphere (dissolution, precipitation, 
weathering and effects on radionuclide transport) (Sections 3.3, 3.4) 
 2.2.08.04.00: Redissolution of precipitates directs more corrosive fluids to container 
(Section 3.3) 
 2.2.10.06.00: Thermal-chemical alteration (solubility speciation, phase changes, 
precipitation/dissolution) THC input (Section 3.3) 
 2.2.10.10.00: Two-phase buoyant flow/heat pipes (Sections 3.2, 3.3, 3.4) 
 2.2.10.12.00: Geosphere dry-out due to waste heat (Sections 3.2, 3.3, 3.4) 
 2.2.10.13.00: Density driven groundwater flow (thermal) (SZ PMR). 
NFE FEPs that are not excluded or not fully included in the TSPA-SR, based on the screening, 
are the following: 
 1.1.02.00.00: Excavation/construction. Chemistry effects are excluded due to low 
consequence. The effects of chemistry due to coupled thermalhydrologic-
chemistry effects (which are included) are expected to be 
much larger than geochemical effects from boring or blasting. 
 1.2.02.01.00: Fractures. The effect of the alteration of fracture properties on transport 
are excluded due to low consequence, since transport times have been 
shown to be insensitive to fracture permeability. 
 2.1.08.01.00: Increased UZ water flux at repository. The effects of climate change 
resulting in increased water flux at the repository are included, but the 
section of the FEP relating to water rapidly cooling a waste package is 
excluded due to low consequence. The drip shield is expected to 
preclude water reaching the waste package during the thermal period. 
 2.1.09.12.00: Rind (AZ) formation in waste, EBS, and adjacent rock. The formation of 
a rind was included in the coupled THC model. These effects were 
found to be small and were not excluded, due to low consequence, in the 
TH models. 
 2.1.11.02.00: Non-uniform heat distribution/edge effects in repository. Both center 
and edge effects were included in the TH model. Thermal-mechanical 
effects on fractures around the drift were quantified based on a center 
location. TM effects on dose expected to be bounded by conservative 
implementation of seepage so are excluded from TH models base on low 
consequences (TBV). 
 2.2.01.01.00: Excavation and construction related changes in the adjacent host rock . 
Excavation related TM effects on dose expected to be bounded by

 2-39 
conservative implementation of seepage, so are excluded from TH 
models base on low consequences (TBV). 
 2.2.01.02.00: Thermal and other waste and EBS related changes in the adjacent host 
rock. TM effects on dose expected to be bounded by conservative 
implementation of seepage, so are excluded from TH models base on 
low consequences (TBV). 
 2.2.01.03.00: Changes in fluid saturations in the excavation disturbed zone. Initial 
fluid saturations are expected to be lower than ambient values due to 
ventilation during the pre-closure period. The initial saturations in the 
TH models were the ambient values. This FEP was excluded due to low 
consequences. Implementation of initial saturations will result in higherrate 
of earlier water flow onto waste packages than if lower initial 
saturations had been used as initial conditions. 
 2.2.06.01.00: Changes in stress (due to thermal, seismic or tectonic effects) change 
porosity and permeability of rock. TM effects on dose expected to be 
bounded by conservative implementation of seepage, so are excluded 
from TH models based on low consequences (TBV). 
 2.2.10.04.00: Thermal-mechanical alteration of fractures near repository. TM effects 
on dose expected to be bounded by conservative implementation of 
seepage, so are excluded from TH models based on low consequences 
(TBV). 
 2.2.10.05.00: Thermal-mechanical alteration of rocks above and below the repository. 
TM effects on dose expected to be bounded by conservative 
implementation of seepage, so are excluded from TH models based on 
low consequences (TBV). 
 2.2.10.06.00: Thermal-chemical alteration (solubility speciation, phase changes, 
precipitation/dissolution). Changes to hydrologic properties as a result 
of coupled THC processes were included in the THC model. The 
changes were found to be small and were excluded from the TH models 
due to low consequence. 
The approach used for this analysis is a combination of qualitative and quantitative screening of 
FEPs. The analyses are based on the criteria provided by the NRC in the proposed 10 CFR 
Part 63 (64 FR 8640) and by the EPA in the proposed 40 CFR Part 197 (64 FR 46976) to 
determine whether or not each FEP should be included in the TSPA. The criteria were: 
 Exclude on the basis of Low Probability if a FEP has less than one chance in 10,000 
of occurring during 10,000 yr. 
 Exclude on the basis of Low Consequence if omission of the FEP does not 
significantly change the expected annual dose.

 2-40 
For FEPs that are included in the TSPA, the TSPA Disposition includes a reference to the AMR 
that describes how the FEP has been incorporated into the process models that feed into the 
TSPA-SR abstraction. 
For FEPs that are excluded from the TSPA based on NRC or EPA criteria, the screening 
argument includes a summary of the basis and results that indicate either low probability or low 
consequence. As appropriate, screening arguments cite work done outside this activity, such as 
in other AMRs. If needed, a more detailed discussion is provided in the Analysis and Discussion 
section of the NFE FEPs AMR (CRWMS M&O 2000e). 
The FEPs screening analysis results for the 26 FEPs relevant to the NFE are summarized in 
Appendix C. The appendix, derived from the NFE FEPs AMR (CRWMS M&O 2000e, 
Table 3), shows the FEP number, FEP name and description, FEP screening decision 
(include/exclude) and basis for Exclude decision. The appendix also lists other PMRs that 
cover the FEP analysis, as appropriate.

 3-1 
3. PROCESS MODELS, ABSTRACTIONS AND CONFIDENCE BUILDING 
This chapter describes the relationship between the process-level models, model abstractions, 
and supporting analyses that address the NFE processes. The processes and/or sub models 
included are explained in terms of the conceptual models that provide the bases for the process 
models. In addition to the AMRs supporting the NFE Process Model Report (NFE PMR), this 
section also includes summary results of the field thermal tests and natural analogs applicable to 
understanding coupled thermal-hydrological-mechanical-chemical (THMC) processes. 
3.1 INTRODUCTION 
3.1.1 Overview Description and Results of Models and Abstractions 
The model components and analyses that support the NFE PMR include: 
 The Thermal Tests TH AMR (CRWMS M&O 2000a) has a primary purpose that relates 
to building confidence in the models that describe the thermal-hydrological (TH) 
processes in the potential repository system. The AMR tests various property sets, 
proposed for use in design and TSPA, to characterize the potential repository geologic 
setting. The AMR compares measurements from field tests to calculated temperatures 
and saturations using these property sets. Note that the evaluation of the TH property 
sets inherently involves the evaluation of the coupled thermal-hydrological processes 
that are both numerically-simulated and field measured. The report is discussed in 
Section 3.1.2 and summarized in Section 3.6. 
 The THC Process AMR (CRWMS M&O 2000b) discusses coupled THC processes. 
This AMR supports both this PMR and the UZ F&T PMR (and thus carries a second 
designation, U0110). The AMR focuses on the impact of coupled processes on fracture 
and rock hydrological property changes, and on mineral-water-gas reactions that drive 
changes to water and gas compositions within the NF that may enter potential drifts 
through fractures. The report is discussed in Section 3.1.3 and summarized in 
Section 3.3. 
 The Abstraction AMR (CRWMS M&O 2000c) provides the technical basis for the TSPA 
abstraction of THC processes. It abstracts the results of the THC Process AMR for use 
in TSPA. It also compares the TH results for process-level and abstracted TH and THC 
models. The report is discussed in Section 3.1.4 and summarized in Sections 3.4 
and 3.2.3.4. 
 The NFE FEPs AMR (CRWMS M&O 2000e) identifies and examines the effects of 
features, processes, and events that are related to the NFE on repository performance and 
provides the technical basis of evaluation of those FEPs. The report is summarized in 
Section 2.5. 
 The THM Calculation (CRWMS M&O 2000d) discusses the mechanical responses to 
the thermal pulse and the effects of the consequent fracture closure or opening on the 
hydrological properties of the rock mass. The report is summarized in Section 3.5.

 3-2 
The models and components that comprise the NFE model or analyses applied in TSPA-SR 
contain inherent uncertainties. Identification and propagation of parameter input and conceptual 
model uncertainty is required to correctly characterize the TSPA model. Input parameter and 
output variability are also contained in the models and components that make up the NFE models 
and analyses. Uncertainty and variability will be discussed in terms of each AMR used to 
support this PMR (see Table 3-1). 
Table 3-1. Uncertainty in Major AMRs used in the Near-Field Environment PMR 
Model/Analysis 
Component 
Input Parameter Uncertainty 
and Variability 
Conceptual Model 
Uncertainty 
Output Uncertainty and 
Variability 
Thermal Test 
AMR (CRWMS 
M&O 2000a; 
Section 3.6 in 
this PMR) 
Spatial variability (DST only) in 
calibrated DS hydrologic 
parameters; input parameter 
uncertainty with the use of 
multiple hydrologic and thermal 
property sets; heat loss through 
bulkhead 
DK model with and 
without interface-area 
reduction factor; dual 
permeability model-active 
fracture model (Liu et al. 
1998) using fracture and 
matrix continuum instead 
of discrete fractures 
Comparison of temperature 
variability at different locations 
in the tests (above boiling, 
below boiling at or near ends 
of drifts due to effects of 
bulkhead); the resulting 
uncertainty in temperature 
predictions (at different 
locations) based on multiple 
hydrologic and thermal 
property sets and two similar, 
but different, conceptual flow 
models 
THC Process 
AMR (CRWMS 
M&O 2000b; 
Section 3.3 in 
this PMR) 
Spatial variability in calibrated 
DS hydrologic parameters; 
temporal variability and 
uncertainty in temperature and 
precipitation (which is 
implemented in the model by 
three different climate states: 
present day, monsoonal, and 
glacial transition); duration of 
climate periods; uncertainty 
included in parameter 
calibration for different 
infiltration-flux cases; 
uncertainty in chemistry data 
(thermodynamic and kinetic 
data, chemistry of infiltrating 
water, different mineral 
assemblages); uncertainty in 
Tptpll property sets 
DK model-active fracture 
model (Liu et al. 1998); 
use of middlenonlithophysal 
(Tptpmn) 
parameters instead of 
lower-lithophysal (Tptpll) 
parameters 
Temporal and spatial variability 
of water and gas composition, 
as well as uncertainty from 
different infiltration-flux cases 
(including climate) and 
different mineral assemblages 
THC Abstraction 
AMR (CRWMS 
M&O 2000c; 
Sections 3.4 and 
3.2.3.4 in this 
PMR) 
Temporal and spatial variability 
of water and gas composition, 
as well as uncertainty from 
different infiltration-flux cases 
(including climate) and different 
mineral assemblages , which 
water chemistry is appropriate 
as input (pore water, perched 
water, J-13 etc.) 
DK model-AFM (Liu 
et al. 1998); use of four 
discrete geochemical 
periods to represent water 
chemistries and gasphase 
compositions 
Simplified description of 
temporal variability of water 
and gas composition for a 
single location; 
characterization of the 
temporal and spatial 
uncertainty and variability of 
TH quantities from two 
different process-level models 
(THC and TH-only)

 3-3 
Table 3-1. Uncertainty in Major AMRs used in the Near-Field Environment PMR (Continued) 
Model/Analysis 
Component 
Input Parameter Uncertainty 
and Variability 
Conceptual Model 
Uncertainty 
Output Uncertainty and 
Variability 
NFE FEP AMR 
(CRWMS 
M&O 2000e; 
Section 2.5 in 
this PMR) 
Spatial and temporal variability 
in infiltration (including climate); 
spatial variability in calibrated 
parameters; uncertainty 
included in parameter 
calibration for different 
infiltration-flux cases; temporal 
and spatial variability of water 
and gas composition, as well as 
uncertainty from different 
infiltration-flux cases and 
different mineral assemblages; 
spatial and temporal variations 
in temperature and hydrologic 
conditions 
Applicable conceptual 
model from process-level 
model that forms FEP 
basis 
Characterization (both 
qualitative and quantitative) of 
heat-driven uncertainties and 
variabilities in TH processes in 
the NF host rock and how they 
may affect repository 
performance 
THM Calculation 
(CRWMS 
M&O 2000d; 
Section 3.5 in 
this PMR) 
Spatial variability in mechanical 
properties 
Spatial variability in thermalmechanical 
properties. 
Spatial variability and 
uncertainty in joint properties. 
Uncertainty in situ stress 
conditions. 
Thermal Power input 
Coulomb-Slip model for 
shear fracture behavior 
Elastic model for rock 
matrix behavior 
Linear relation between 
fracture deformation and 
fracture permeability 
change 
Thermal model for infinite 
medium. 
Idealized fracture 
distribution. 
Temporal and spatial variability 
of stress 
Temporal and spatial variability 
of displacement. 
Temporal and spatial variability 
of permeability multiplier 
3.1.2 Thermal Testing AMR 
The Thermal Testing AMR (CRWMS M&O 2000a) compares experimentally measured 
quantities, such as host-rock temperature and liquid saturation, to simulation results from TH 
models specifically developed to estimate the TH processes that occur in the tested host rock as a 
result of controlled heat input. Temperature and liquid saturation measurements of varying 
duration and at different locations in the tests are compared to TH model simulation results. A 
number of comparisons are made for the host rock, both above and below the boiling point, in 
order to assess the ability of the TH models to reproduce the (simultaneous heat and fluid flow) 
processes that occur in regions of extreme changes in temperature or liquid saturation. 
In order to assess the ability of any TH model to reproduce the processes initiated by heat 
addition, the model must be equipped with appropriate flow properties and conceptual flow 
models. The flow properties govern the rate at which heat or fluid flows through the system and 
the conceptual flow model predicts how the distribution of temperature and liquid saturation 
evolve in time. The DS hydrologic flow properties developed by the UZ Flow and Transport 
(UZ F&T) model (CRWMS M&O 2000f, Section 3.6.4.1) to reproduce ambient conditions in the

 3-4 
mountain are also applied in the TSPA-SR models and abstractions that include the influence of 
repository heating (CRWMS M&O 2000g, Section 3.1). Since this is the case, it must be 
ensured that hydrologic properties developed to reproduce the ambient conditions of the 
mountain can also (approximately) reproduce the transient flow processes that result in the event 
of a thermal perturbation. The same is also true for the conceptual flow model. 
The DKM/AFM was developed to reproduce the ambient flow conditions of the mountain 
(CRWMS M&O 2000f, Section 3.4.1.4.1). This same conceptual flow model is also applied in 
the TSPA-SR models that include the thermal perturbation. An important question is whether 
hydrologic properties and conceptual flow models specifically developed for ambient flow 
conditions can be applied to models that include repository heating. The answer to this question 
only lies in direct comparison of experimentally measured quantities from the thermal tests to the 
results of the thermal test TH models that apply the same properties and conceptual flow models 
used in the TSPA-SR repository-heating models. Consequently, the TSPA-SR repositoryheating 
models, although conducted at spatial and temporal scales not amenable to experimental 
verification, are at least based on hydrologic properties and conceptual flow models successfully 
tested against the more reasonably scaled (both in time and space) thermal tests that include the 
transient nature of thermally induced flow processes. 
The comparison between experimentally measured data and TH model results, and the 
subsequent conclusions in the thermal AMR test indicate that application of the DS hydrologic 
property set, along with the flow model that uses the DKM and AFM, adequately reproduce the 
heat and fluid-flow processes initiated by a controlled thermal perturbation (CRWMS 
M&O 2000a, Sections 6.1, 6.2, and 7). Temperature comparisons between model and measured 
data at test locations, both above and below the boiling point, indicate that the hydrologic 
properties and DKM and AFM adequately represent the transient thermal response. 
Consequently, the DS hydrologic property set and DKM-AFM are deemed appropriate for use in 
TSPA-SR DS models used to represent the in-drift thermodynamic environment (e.g., 
temperature and relative humidity) and liquid- flow processes (e.g., rate of thermally enhanced 
fracture flow) in the host rock that influence seepage into the emplacement drift. 
3.1.3 The THC Process AMR 
The THC Process AMR (CRWMS M&O 2000b) calculates water chemistry and gas-phase 
composition in the NF host rock. The water at the drift wall that may seep into the emplacement 
drift during and after repository heating provides the geochemical boundary condition for the 
TSPA-SR model. Determination of the aqueous species and gas-phase concentrations that result 
from mineral precipitation and dissolution processes initiated by repository heating and mineralwater 
reactions requires a fully-coupled computer code that includes both mass and energy 
transfer, as well as the reactive-transport processes of a number of different mineral assemblages. 
Like the TH models described in the previous section, the DS THC model also requires 
appropriate hydrologic and thermal property inputs. Furthermore, it requires a working 
conceptual flow model that reasonably characterizes the processes initiated by a repository 
thermal perturbation. The THC model applies the DS hydrologic and thermal property set and 
the active-fracture conceptual flow model tested in the thermal test TH models. Since the model 
is used to estimate THC processes (e.g., evolution of water chemistry at the emplacement drift

 3-5 
wall) driven by repository decay heat, it must implement specifics related to repository design, 
such as emplacement-drift diameter, waste package and drip shield geometry, invert and backfill 
geometry, and waste package thermal-decay information (CRWMS M&O 2000b, Sections 4.1.1; 
4.1.7; 5, assumption A.1; 6.1.5.1). 
In addition to property, conceptual model, and repository-design inputs, the THC DS model 
requires parameters and conceptual models associated with reactive-transport processes. These 
include mineralogical data, initial water and gas chemistries, thermodynamic and kinetic data, 
transport parameters (e.g., diffusion of CO2), and kinetic-rate laws, including relationships for 
the reactive-surface areas (CRWMS M&O 2000b, Sections 4.1.2 through 4.1.6, and 6.1). The 
validity of the THC model and chemical-parameter inputs are based on measured results of the 
DST (CRWMS M&O 2000b, Section 6.2.7). 
The DS THC process-level model provides time-histories (at different locations in the NF host 
rock adjacent to the emplacement drift wall) of CO2, pH, Ca2+, Na+, SiO2, Cl, HCO3
, SO4
2, 
Mg2+, K+, AlO2
, HFeO2
, and F. The results are based on analysis of complex mineral 
assemblages as well as a simplified mineral assemblage. The complex mineral assemblage 
represents a relatively full set of minerals and aqueous species needed to describe more fully the 
chemistry of the NFE. In addition to including the minerals and species from the less complex 
mineral assemblage, the model also includes a wide range of alumino-silicates, such as feldspars, 
clays, and zeolites. The reduced set of species and minerals is specified to capture many of the 
basic aspects of the Drift Scale Test measured water and gas chemistries. Its mineralogy 
includes calcite, silica phases, and gypsum. It is found that general consideration of the less 
complex geochemical system in the THC model adequately represents the measured chemical 
evolution of the Drift Scale Test (DST) (CRWMS M&O 2000b, Section 7). However, 
refinement of these results will be necessary in the future, given the need to more fully and 
accurately represent the observed mineralogy in the models, and to honor the measured 
dissolution rates of mineral phases. 
In addition to the geochemical system-driven differences in water and gas-phase compositions, 
the differences in water and gas chemistry driven by infiltration rates are also incorporated in the 
THC DS model. Low, mean, and high infiltration-flux cases (including three climate states) in 
the DS THC model considered a 0.6 to 47 mm/yr. range in infiltration rates (CRWMS 
M&O 2000b, Table 12). Although not yet observed in the DST, rewetting periods in the model 
indicate an increase in CO2 gas and aqueous carbonate concentrations in the drift wall host rock. 
Rewetting periods are largely influenced by infiltration rates and climate histories. 
Abstraction of water chemistry and gas composition from the THC model, along with an analysis 
of TH-only and THC process-level model predictions of the important TH variables (e.g., hostrock 
temperature, fracture-liquid flux), is performed in the THC Abstraction AMR (CRWMS 
M&O 2000o). 
3.1.4 The THC Abstraction AMR 
The THC Abstraction AMR (CRWMS M&O 2000c) provides a simplified description of the time 
evolution of water and gas chemistry in the NF host rock. It also provides a detailed evaluation 
of process-level differences between the fully coupled THC and the TH-only models. The

 3-6 
evaluation is of the TH variables important for repository performance (e.g., liquid flux in hostrock 
fractures at the crown of the emplacement drift). The TH-only model used for comparison 
to the DS THC model is a 2-D submodel extracted directly from the draft multiscale TH model 
(CRWMS M&O 2000k, Section 6.3). Its infiltration boundary condition is altered to be 
consistent with the fully coupled DS THC model used in the evaluation analysis. 
The water chemistry and gas-phase composition abstraction provides a simplified overview of 
the process-level THC model results. The abstracted evolution of water chemistry and gas-phase 
composition in the NF host rock (CRWMS M&O 2000c, Section 6.1) is taken from the projected 
chemistry of water in fractures at the crown of the emplacement drift from detailed model 
analyses of THC (CRWMS M&O 2000b). The abstraction from the DS THC process-level 
model occurs in discretely simplified time periods: 
 Preclosure period (0 to 50 yr.) 
 Boiling period (50 to 1,000 yr.) 
 Transitional cool-down period (1,000 to 2,000 yr.) 
 Extended cool-down period (2,000 to 100,000 yr.). 
The detailed time-history results of the process-level THC model are simplified into a series of 
four discrete time periods as defined above. The abstraction provides a series of constant-value, 
geochemical periods that are used as in-drift geochemical TSPA boundary conditions. The four 
period, constant- value, THC abstraction includes five cations, six anions, pH, partial pressure of 
carbon dioxide, and the temperature during the abstraction boiling period used to re-equilibrate 
the condensate water with the carbon dioxide of the gas-phase adjacent to the emplacement drift. 
The impact of fracture dryout on water chemistry during the time period in which local host rock 
temperatures are at or above the boiling point of water, as characterized in the THC process-level 
model, is not used in the TSPA abstraction. Instead, the condensate water above the dryout zone 
is used as the water chemistry that may potentially enter the drift. Since the THC process model 
does not include fracture property heterogeneity, the condensate water above the dryout zone 
represents the water (chemistry) that could potentially seep through a heterogeneous fracture 
system (if included) thereby reaching the drift wall. Additionally, since the TSPA seepage 
model uses a value of percolation flux from a TH model, which is always greater than or equal to 
ambient percolation, a water chemistry calculation is required at all times. That is, seepage may 
occur (in the PA abstraction) even during the dryout period predicted by the 2-D process models 
that do not include repository edge cooling effects. 
Abstraction results focus primarily on the mean infiltration flux case (CRWMS M&O 2000c, 
Table 3). Limited uncertainty included in the THC model results of water and gas-phase 
chemistry is accounted for with three infiltration flux cases (low, mean, and high) and two 
different mineral assemblages (e.g., quantification of uncertainty in the reactive surface area is 
not included in the process-level model). The THC abstraction includes only the mean 
infiltration flux case, using the primary aqueous constituents from the less complex geochemistry 
and the trace constituents from the more complex geochemical system. Use of only the mean 
infiltration flux THC results in the abstraction is justified by an order of magnitude analysis 
based on ratios of individual concentrations taken between the low and the mean and the high 
and the mean flux cases (CRWMS M&O 2000c, Section 6.1.2). The use of condensate water 
chemistry, rather than an evolving fracture-water chemistry, such as concentrated J-13 water,

 3-7 
during the abstracted boiling period is determined to be appropriate, as this is the water most 
likely to seep into the drift due to the enhanced saturation in this zone. 
The THC Abstraction AMR also describes a detailed evaluation of process-level models that 
either include, or do not include, the fully coupled processes of thermal hydrology and reactive 
transport (CRWMS M&O 2000c, Sections 6.26.4). This evaluation is of the variables that 
characterize the TH performance of the repository and are important to TSPA in the overall total 
system description of the geologic system through time. Specifically, the evaluation is for 
potential differences in process-level model outcomes of host rock near the drift wall for: 
temperature, liquid saturation (both fracture and matrix), air mass fraction, fracture air flux, and 
fracture liquid flux. The results of this quantitative evaluation allows one to assess the relative 
importance of including a fully coupled reactive transport THC model when providing TSPA 
with the pertinent TH characteristics (defined above) used to determine performance of a 
geologic repository. A strict comparison of flux variables is not performed at the side and base 
of the drift-wall host rock due to differences in process-model boundary conditions applied at the 
drift-wall interface with the emplacement drift. Process-model evaluations are made at the 
crown of the drift where process-model conditions are the same. An analysis of this type is used 
to provide the necessary justification as to why a potential reduction in the numerical complexity 
of the problem (e.g., use of TH-only models instead of fully coupled THC models) does not 
negatively influence prediction of the overall TH performance of a potential geologic repository. 
Of course, if water chemical content and gas-phase composition are required, use of a fully 
coupled reactive transport code is necessary. However, if the TH variables used to characterize 
the NF host rock (percolation flux near the drift wall) or in-drift thermodynamic conditions 
(temperature and relative humidity) are required, the results of this analysis indicate that a THonly 
model will not result in unacceptable error by not including reactive-transport processes 
(CRWMS M&O 2000c, Section 6.3). 
In order to further quantify the impact THC processes may have on the TH variables used to 
predict repository performance, an evaluation of TH variables resulting from a fully coupled 
THC model that includes two different geochemical systems was also considered (CRWMS 
M&O 2000c, Section 6.2). This evaluation assessed whether the relative reaction rates of 
different mineral assemblages resulted in an appreciable alteration of hydrologic flow propertie s, 
which in turn translate to potential differences in predicted host-rock temperatures or liquid 
fluxes in fractures. It was found that the geochemical and reactive-transport alterations to the 
flow (and characteristic) properties (and how they alternatively occur for more or less complex 
geochemical systems) (CRWMS M&O 2000b, Section 7) are small, based on the 1 percent initial 
porosity and non-localized boiling front in the model. Given these assumptions, the hydrological 
changes are not enough to impact the fundamental properties of the geologic system (e.g., hostrock 
temperature adjacent to the emplacement-drift wall, and seepage) associated with repository 
heating processes. This holds true for the entire range of infiltration fluxes considered in the DS 
THC model analysis. 
One final evaluation in the abstraction AMR concerns the lack of influence of repository edge 
proximity in the results of a periodic, 2-D, DS model (either TH-only or fully coupled THC 
models). This analysis compares drift-wall temperature and liquid saturation from the THC 
model to the multiscale TH model that includes repository edges. The influence of lateral heat 
loss to rock masses surrounding the loaded repository is quantified in the multiscale TH model.

 3-8 
This is done by implementing a sequence of models that approximate edge heat- loss effects, with 
a mountain-scale model that incorporates the surrounding unheated rock masses, coupled with a 
variety of different DS models that produce the in-drift TH environment and processes occurring 
in the NF host rock surrounding the emplacement drifts (CRWMS M&O 2000k, Section 6.1). 
The results of the analysis indicate that edge proximity results in far cooler temperatures and 
higher liquid saturations in the host rock directly adjacent to the drift wall (CRWMS 
M&O 2000c, Section 6.4). Recall that the water chemistry in the condensate zone, developed 
above a dryout zone computed by a process model that does not include repository edge effects, 
is used with the TSPA seepage model that expects non-zero values for the percolation flux (used 
as an input to the seepage model) even during the peak temperature thermal period. 
3.1.5 Thermally Perturbed Percolation Flux in the Near-Field Host Rock 
The thermally perturbed percolation flux in the NF host rock is also considered in the THC 
abstraction covered in this PMR (Section 3.4), in the TH work summarized in Section 3.2.3, and 
in the thermal- test analyses (Section 3.6.1). Thermally enhanced liquid flux through fractures 
is a direct outcome of heat addition to the surrounding host rock. The process of enhanced 
fracture liquid flux is caused by increased host-rock temperatures with associated evaporation 
boiling of the fracture and matrix pore waters. Since the process-level models include a DK 
conceptual flow model, water vapor generated in the matrix is transported to the high 
permeability fractures (compared to the matrix) where it can flow away from the heat source 
primarily by pressure gradients or temperature-driven density gradients. When the vapor 
contacts a region of host rock at a lower temperature, the vapor in the fracture condenses on the 
fracture walls where it is either imbibed into the matrix or flows, driven by gravity, along the 
fractures. 
For vapor that condenses above the repository drifts, this condensate water in the fractures can 
flow back into the heated zone (if fracture orientations are towards the heated zone) or away 
from it (when orientations are away from the heated zone). When vapor condenses below the 
drifts, or to the sides of the drifts, the condensate in fractures would drain away from the heated 
zone (with exception of nearly horizontal fractures, which might allow flow towards the drifts). 
See Figure 2-3. 
For that part of the condensate that is imbibed, the water would move in response to gravity 
drainage and saturation- gradient diffusion (see Figure 2-3). For water imbibed above the drifts, 
both saturation-gradient diffusion and gravity drainage would be in the directions toward the 
drifts (heat zone). For water imbibed to the sides of the drifts, saturation- gradient diffusion 
would be towards the drifts, while gravity drainage would be downwards (essentially 90o from 
the saturation-gradient diffusion). The actual net movement would depend on the relative 
magnitudes of the two processes. It is estimated that saturation gradients will dominate. For 
condensate imbibed into the matrix below the drifts, saturation-gradient diffusion would be 
towards the drifts, while gravity drainage would be away from the drifts. 
Superimposed on this flow is the effects of vaporization of water within the heated zone. Any 
water returned to the heated zone would, unless percolation fluxes exceed volumes that can be 
vaporized per unit time, be revaporized and moved outward from the heated zone. Because only

 3-9 
part of vaporized water returns to the heated zone, there would be a net removal of water 
(excluding water introduced by way of percolation flux). 
Since this heat- mobilized water is in addition to the percolation water that is naturally present, 
the liquid flux is deemed enhanced. It is noted that the active- fracture parameters applied in the 
conceptual flow model (DKM) dictate the rate at which water in the fractures is conducted back 
into the matrix, and any water not calculated to be imbibed into the matrix is free to flow through 
the fracture. 
Of interest in this PMR is how the spatially dependent percolation flux at a specified location in 
the NF host rock (above the drift) varies in time after waste emplacement and how this increases 
the volume of water within the fracture, or matrix if imbibed, interacting with minerals in the 
rock or fracture coatings. Increased volumes of water will change the rock-water ratio, which 
affects the chemical equilibrium state. Further, the chemistry of this mobilized water will 
potentially be different than the water in pores or fractures that had not been thermally 
mobilized. 
Of interest to the UZ F&T and EBS PMRs is how this spatially and temporally-varying 
percolation flux drives the seepage-volume flow rate into the emplacement drifts, and the 
fraction of waste packages contacted by seeps, as discussed in the Abstraction of Drift Seepage 
(CRWMS M&O 2000l, Section 6.3.5). 
The percolation flux above the crown of the drift is obtained from the multi-scale thermalhydrologic 
model (described in Section 3.2.2.1) that includes different locations within the 
repository footprint (e.g., infiltration rate variability), three host rock units, and proximity to the 
repository edge, as described in the Multiscale Thermohydrologic Model AMR (CRWMS 
M&O 2000k, Section 6.6.13). The abstraction of the thermally-driven percolation flux into the 
TSPA model is described in CRWMS M&O (2000m, Sections 6.1 and 6.3.7). The abstraction 
by TSPA arranges waste package location-dependent results from the process-level model into 
infiltration-rate bin inputs for the TSPA models. The infiltration-rate bins defined by TSPA 
(CRWMS M&O 2000m, Sections 5.1, 6.2) are the following: 
 0  3 mm/yr 
 3  10 mm/yr 
 10  20 mm/yr 
 20  60 mm/yr 
 > 60 mm/yr. 
Each infiltration-rate bin provides percolation flux inputs for the TSPA seepage model. The 
waste package location-dependent information from the process model provides the in-drift (e.g., 
waste package temperature and relative humidity, etc.) and NF host rock (e.g., drift-wall 
temperature, percolation flux, etc.) data at 623 different locations within the repository footprint 
for three different infiltration-flux cases: low, mean, and high (CRWMS M&O 2000k, 
Section 6). Each of the 623 locations has associated with it a present-day, monsoonal, and 
glacial-transition climate state. The location-dependent data from the process model are 
arranged into an infiltration-rate bin (ranges defined above) by its glacial-transition climate. This 
is the climate state that is predicted to begin at 2,000 yr. after waste emplacement and persist for

 3-10 
times out to 106 yr., and is characterized by the highest mean and high infiltration rates of the 
climate scenarios considered. 
The infiltration-rate bins defined by TSPA are distributed over the repository footprint, as shown 
(for the low, mean, and high infiltration- flux cases) in Figures 3-1 through 3-3. The figures also 
indicate the location of the LDTH models (CRWMS M&O 2000k, Section 6.3.1). Each 
infiltration- flux case contains 623 location-dependent data results from the process-level model. 
Each result represents a different location in the repository footprint. The spatial location (or 
repository coverage) of each infiltration bin in Figures 3-1 through 3-3 places the 
location-dependent data into a range of infiltration rates for abstraction by TSPA. The individual 
numbers of location-dependent results for all three infiltration-flux cases are presented in 
Table 3-2. The table also includes the total repository-area fraction represented by each 
infiltration bin associated with an infiltration flux case. 
The (process model) data for percolation flux at selected distance above the crown of the drift are 
input into a TSPA model that characterizes the seepage-volume flow rate into the emplacement 
drift as a function of percolation flux. The selected height (5 m) is above the dryout zone at all 
times, for the location at which the THC abstraction was performed. Ongoing work may develop 
an abstraction in which percolation- flux sample height depends on other parameters. 
623 Low Glacial Infiltration Bin Locations 
231,500 
232,000 
232,500 
233,000 
233,500 
234,000 
234,500 
235,000 
235,500 
236,000
170,000 170,500 171,000 171,500 
Easting (m) 
0-3 mm/yr Bin 
3-10 mm/yr Bin 
TSw34 LDTH Models 
TSw35 LDTH Models 
1/4/00 
Source: CRWMS M&O 2000m, Figure 18 
Figure 3-1. The Location-Dependent Data in the Different 
Infiltration Bins for the Low Glacial Infiltration Map

 3-11 
623 Mean Glacial Infiltration Bin Locations 
231500 
232000 
232500 
233000 
233500 
234000 
234500 
235000 
235500 
236000 
170000 170500 171000 171500 
Easting (m) 
0-3 mm/yr Bin 
3-10 mm/yr Bin 
10-20 mm/yr Bin 
20-60 mm/yr Bin 
> 60 mm/yr Bin 
TSw34 LDTH Models 
TSw35 LDTH Models 
1/4/00 
Source: CRWMS M&O 2000m, Figure 19 
Figure 3-2. The Location-Dependent Data in the Different 
Infiltration Bins for the Mean Glacial Infiltration 
Map 
623 High Glacial Infiltration Bin Locations 
231,500 
232,000 
232,500 
233,000 
233,500 
234,000 
234,500 
235,000 
235,500 
236,000
170,000 170,500 171,000 171,500 
Easting (m) 
3-10 mm/yr Bin 
10-20 mm/yr Bin 
20-60 mm/yr Bin 
>60 mm/yr 
TSw34 LDTH Models 
TSw35 LDTH Models 
Source: CRWMS M&O 2000m, Figure 20 
Figure 3-3. The Location-Dependent Data in the Different 
Infiltration Bins for the High Glacial Infiltration Map

 3-12 
Table 3-2. Distribution of Process-Level Model Results within Infiltration Bins 
Low Infiltration Case 
Number of Location 
Dependent Entries in the Bin 
Repository Area 
Fraction (%) 
0-3 mm/yr. 368 59.7 
3-10 mm/yr. 255 40.3 
10-20 mm/yr. 0 0 
20-60 mm/yr. 0 0 
> 60 mm/yr. 0 0 
Mean Infiltration Case 
Number of Location 
Dependent Entries in the Bin 
Repository Area 
Fraction (%) 
0-3 mm/yr. 21 1.6 
3-10 mm/yr. 91 13.2 
10-20 mm/yr. 174 32.1 
20-60 mm/yr. 334 52.9 
> 60 mm/yr. 3 0.3 
High Infiltration Case 
Number of Location 
Dependent Entries in the Bin 
Repository Area 
Fraction (%) 
0-3 mm/yr. 0 0 
3-10 mm/yr. 14 1.2 
10-20 mm/yr. 98 13.4 
20-60 mm/yr. 318 54.8 
> 60 mm/yr. 193 30.6 
Source: CRWMS M&O 2000m, Table 5 
3.2 THERMAL-HYDROLOGICAL PROCESSES AND MODELS 
This section summarizes TH processes, TH models, and four case studies that use the models, 
including NF TH results for the SR design (EDA-II without backfill). 
3.2.1 Thermal-Hydrological (TH) Processes Affecting TH Behavior 
Under ambient conditions, liquid-phase flow in the repository host rock arises as a result of the 
infiltration of rainfall and snowmelt. Although most of the total fluid-storage capacity is 
contained in the matrix pores of this rock, the permeability in the matrix is very low. For the DS 
and MS base-case hydrological property sets (see CRWMS M&O 2000a; Section 4), the matrix 
permeability is as much as five and six orders of magnitude, respectively, less than that of the 
fractures in the repository host rock, and the percolation flux exceeds the unit gradient flow 
capacity of the matrix; consequently, fractures dominate liquid-phase flow. After the 
emplacement of radioactive waste, the thermally-driven transport of water vapor away from the 
heat source causes a redistribution of the pore fluids within a potentially large volume of rock. 
Depending on the thermal design of the repository, this volume can extend from the ground 
surface to some distance below the water table and over an area larger than the repository 
footprint. Water in the matrix pores evaporates, creating dryout zones around the emplacement 
drifts and condensation zones outside of the dryout zones. The generation of steam replaces air

 3-13 
within the boiling zone, reducing the gas-phase mass fraction of air to almost zero for a period of 
time. 
The initial movement of water vapor is within the matrix pores. Once the decay-heat-driven 
water vapor has entered a fracture network, the direction of flow is generally away from the heat 
source; however, if the fracture permeability is high enough, buoyant gas-phase convection can 
cause water vapor movement to be predominantly upward in the vicinity of the emplacement 
drifts. Depending on the thermal design of the repository and the fracture permeability, vapor 
flow within fractures occurs over length scales of several meters to hundreds of meters. 
Decay heat is transported away from the emplacement drifts (in the rock mass) by conductive 
and convective heat-transfer mechanisms. Thermal conduction is the dominant heat-transfer 
mechanism in the rock mass. Thermal radiation is the dominant heat-transfer mechanism within 
the open spaces inside the emplacement drifts; this applies particularly during the first several 
thousand years whe n temperatures in the drifts are relatively high. The transport of water vapor 
results in more efficient heat transport than does liquid-phase flow. Two important heat-transfer 
mechanisms involving the transport of water vapor and phase change (i.e., evaporation and 
condensation) are heat pipes and buoyant gas-phase convection. Heat pipes result from vapor 
transport away from the heat source, and gravity-driven and/or capillary-driven condensate flow 
back toward the heat source (i.e., refluxing). Buoyant gas-phase convection results from massdensity 
gradients driven by temperature gradients in the rock mass. Depending on the thermal 
design of the repository, this mechanism, which may occur at the DS and at MS, can increase the 
buildup of condensate above the repository. Buoyant gas-phase convection also contributes to 
heat transfer in the open spaces in the drifts. 
The thermal-hydrologic al behavior of the repository can be divided into three sequential periods: 
drying, steady state, and rewetting. The concept of these three periods is applicable over 
dynamically changing spatial regimes in addition to temporal regimes. At a given time, certain 
locations in the repository footprint may have already progressed to the rewetting regime, while 
other locations remain in the drying regime. During the drying and steady-state periods, liquidphase 
flux in the refluxing zone is greater than ambient local percolation flux. 
In the host rock, local thermal-hydrological behavior is dominated by location (inside or outside 
the zone of boiling temperatures). Therefore, the spatial and temporal extent of the boiling zone 
is very important. Although thermal- hydrologic al processes such as evaporation occur at belowboiling 
temperatures, the most important processes (i.e., refluxing and dryout) require that 
temperatures are at the boiling point of water. Note that the boiling temperature can be higher 
than the nominal boiling temperature (96C) at the repository horizon. The key aspects of the 
system are boiling-period duration and boiling-period temperatures (i.e., temperatures high 
enough to indicate superheated conditions or refluxing/heat-pipe conditions). 
Two important quantities influence the thermal- hydrological conditions within the emplacement 
drift: temperatures at the drift wall and the temperature gradient between the waste package and 
the drift wall. The likelihood of water seeping into the drift is strongly affected by whether 
temperatures at the drift wall are above the boiling point. If the local heat flux at the drift wall is 
greater than the product of the local liquid-phase flux and the heat of evaporation, water cannot 
steadily seep into the drift. If the converse is true, then steady seepage into the drift is possible.

 3-14 
The temperature gradient between the waste package and drift wall strongly affects how much 
lower the relative humidity (RH) on the waste package is than at the drift wall. 
Additional discussion of TH models is provided in the Multiscale TH & AMR (CRWMS 
M&O 2000k) and the UZ F&T PMR (CRWMS M&O 2000f). 
3.2.1.1 The Thermal-Hydrological Near-Field State: General Observations 
TH modeling is particularly critical to providing an overall indication of the TH state of the 
repository during the heating and cooling phases following repository closure. These phases can 
be combined broadly into the thermally disturbed period, followed by an indefinite period 
termed the final state during which temperatures are near-ambient (~30C). The thermally 
disturbed period which includes the drying, steady-state, and rewetting periods described in 
Section 3.2.1, results from the emplacement of waste packages. During the thermally disturbed 
period, which is predicted to last several thousand years, the thermal power density in the 
repository is high resulting in perturbations to the original, ambient thermal-hydrological state. 
Ultimately, the thermal perturbation vanishes, owing to the decay of the radioactive waste and 
the removal of heat by transport processes; this results in a final state of the repository 
environment that is expected to resemble the original ambient regime. Fluid redistribution and 
other important features of the thermally disturbed system are illustrated schematically in 
Figure 3-4 at the drift scale and in Figure 3-5 at the MS. 
This thermally driven transport of water and water vapor away from the heat source 
(TH behavior) causes a redistribution of the pore fluids. Each of the following processes 
described below (may) occur as a result of repository heat addition and thermally driven 
transport of water and water vapor in the geologic setting at Yucca Mountain. Previous TH 
models, either for site characterization or TSPA, have shown each of these processes, to varying 
degrees, as potentially important when considering decay heating from a potential repository 
located in the unsaturated zone at Yucca Mountain. The extent and duration of each process is a 
highly complex function of geologic characterization (e.g., rock formation layering, hydrologic 
and thermal properties, etc.), infiltration rate and future climates, conceptual flow model, and 
repository design. As such, the evolution of understanding and associated importance of a 
particular TH process was accomplished only through analysis of a number of different designs 
(for instance the VA point-loaded design, see Section 3.2.3.3) throughout each iteration of 
TSPA. The overall importance of each TH process described below and depicted schematically 
varies with repository design. As an example, for the VA design, the development of a 
coalesced dryout zone between emplacement drifts implied an impediment to condensate 
drainage between drifts during the thermal period. The ability of project models to ascertain this 
potential behavior allows site characterization and TSPA personnel to guide the design criteria 
for future TSPAs. Indeed, the ability of the models to ascertain this behavior in the VA design 
allowed the project to alter the SR design to include wider emplacement drifts in which dryout 
zone coalescence does not occur. 
 Dryout zones with liquid-phase saturation decreased from its initial value are created 
around the emplacement drifts. The relative humidity in dryout zones is also reduced, 
and, because the matrix potential is mathematically related to relative humidity via the 
Kelvin equation, the capillary suction potential will be much greater than ambient. The

 3-15 
vertical extent of the dryout zone increases with local decay-heat flux, distance from the 
repository edge, and decreasing percolation flux. For central locations away from the 
repository edge and percolation flux less than 5 mm/year, the vertical extent of dryout 
increases with repository depth below ground surface. This zone is yellow in Figure 3-4 
and red in Figure 3-5. 
 Condensation zones with liquid-phase saturation increase from initial values are created 
above and below the dryout zones. This zone is blue in Figures 3-4 and 3-5. 
 A region of reduced air mass fraction in the vapor phase is created. The generation 
of steam replaces air within the boiling zone, reducing the vapor-phase mass fraction of 
air almost to zero. This reduction will occur as long as boiling liquid water is present, 
whether or not rock dryout occurs. Decay heat flows away from the drifts by conductive 
and advective (also called convective) heat-transfer processes. For heat convection, 
latent-heat transport (due to boiling and condensation) is much more important than 
sensible-heat transport; consequently, the flow of water vapor results in much greater 
heat transport than does liquid-phase flow. The following two bullets describe the two 
primary mechanisms for gas-phase, advective heat transfer. 
 Heat pipes result when heat causes vaporization or boiling of water in matrix and 
fractures, with migration of the vapor away from the drifts into cooler regions where it 
condenses. The condensate then flows back towards the heat source due to gravity 
and/or capillary forces completing the heat pipe circuit. Because this mechanism 
requires either gravity-driven condensate flow in the fractures, or much slower 
saturation-gradient-driven matrix flow, heat pipes will primarily occur in zones with 
well-connected vertical fractures. Model results also indicate that the location of heat 
pipes is strongly affected by ambient percolation flux; high percolation flux 
(>10 mm/year) suppresses rock dryout and increases the tendency for heat pipes to form 
in the vicinity of drifts; low percolation flux (<5 mm/year) favors rock dryout and 
suppresses heat-pipe development near the drifts (Hardin 1998, pp. 3-7 and 3-8). 
 Buoyant gas-phase convection results from mass-density gradients driven by 
temperature gradients in the rock mass. Based on model results this mechanism is 
significant if the rock-mass bulk permeability is more than about 1 to 10 darcy and the 
fractures are ubiquitous and well-connected over large distances. This mechanism, 
which may occur at both DS and MS, can increase the build-up of condensate above the 
repository. (Because the SR design provides for efficient drainage through the pillars, 
additional saturation above the drifts due to bouyant gas-phase convection is likely to be 
negligible). Heat flow in the rock causes a temperature build-up in the EBS and NF. 
The temperature build-up depends strongly on the thermal-loading conditions imposed 
by emplacement of WPs. The overall repository thermal-loading conditions are best 
quantified using the AML, expressed in metric tonnes of uranium per acre (MTU/acre). 
Details of the heat output from individual WPs strongly influence NF TH behavior, 
particularly the TH conditions immediately adjacent to and within emplacement drifts, 
including conditions on the WP surfaces. Gas-phase, advective heat-transfer 
mechanisms increase the overall efficiency of heat transfer away from the drift; 
consequently, these mechanisms decrease NF temperature buildup. If heat pipes extend

 3-16 
from the boiling front all the way back to the repository horizon, NF temperatures 
cannot increase much above the nominal boiling point (~96C). If buoyant gas-phase 
convection (e.g., mountain-scale) is significant, NF temperatures will be decreased, 
particularly at the edges of the repository. A key issue (or hypothesis) to be resolved 
through field-scale thermal testing and analysis is the following: Does conduction 
dominate heat flow or do heat pipes and buoyant gas-phase convection significantly 
influence heat flow around emplacement drifts and in the repository as a whole? 
Source: Hardin 1998, Figure 3-2 
NOTE: Tb Refers to the Boiling Isotherm. Ventilation of the drifts during the preclosure period results in a 
significant amount of heat removal from the emplacement drift. Note that the majority of percolation and 
condensate drainage flux occurs in the fractures. 
Figure 3-4. DS Schematic Showing Decay-Heat-Driven TH Flow 
and Transport Processes Fracture Flow is Shown with 
Solid Arrows, Water Vapor Flow with Dashed Arrows, 
and Heat Flow with Oscillatory Arrows

 3-17 
Source: Hardin 1998, Figure 3-3 
Figure 3-5. Mountain-Scale Schematic Showing Decay-Heat-Driven TH Flow and 
Transport Processes that Influence Moisture Redistribution and the Moisture 
Balance in the UZ 
The preceding discussion concerns long-term transient changes in the UZ associated with the 
redistribution of water by evaporation and condensation. Because of the long expected lifetime 
of the engineered barriers, it is likely that radionuclide release and transport will occur after the 
thermally disturbed period, that is, in the final state of the mountain following the thermal pulse. 
Compared to the initial ambient conditions, the permeability distribution changes in the final 
state because of the associated saturation changes and changes due to coupled processes. Were it 
not for the coupled processes, in principle, the mountain would return to something resembling 
its initial state, except for the effects of climate change, after decay of the thermal pulse and 
rewetting of the dried-out regions. However, the TH disturbance will also generate TC and 
thermal-mechanical (TM) alteration of hydrological and transport properties, particularly in the 
fractures, in both the unsaturated and saturated zones. Some changes, such as normal 
deformation fracture closure that results from TM effects, may be temporary. However, shear or 
slip displacement along fractures as well as non-elastic normal closure will have permanent 
impact on permeability distribution within the NF. TC effects, such as the filling of fractures 
may also be irreversible such that changes are or the process dominated by very slow reaction 
rates such that they are limited by kinetics so that recovery takes extremely long time. It is 
possible that these changes are sufficiently significant enough to require inclusion in long-term 
calculations of repository performance. These issues are discussed further in Sections 2.2.2, 
2.2.4, 3.3, 3.4, and 3.5. 
Recall that each of the processes defined above apply to varying degrees to the base case 
repository design for TSPA-SR. Comprehensive insight of each TH process described in this

 3-18 
section (even those based on previous designs) was necessary in deciding which of these 
processes needed to be emphasized or mitigated by a strategic choice of design parameters 
specified for SR. The next section provides some of the important details of previous TH 
analyses for the VA and LADS repository designs. The importance of understanding the 
processes initiated by each of the previous designs led to the specification of many of the 
features and criteria developed for the SR repository design (e.g., an 81 meter emplacement drift 
spacing to allow condensate drainage during the thermal period). 
3.2.1.2 Key Factors Influencing Thermal-Hydrological Conditions in the NFE 
Thermal- hydrological conditions in the NFE (as well as in the EBS) are influenced by a number 
of key factors: 
 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 infiltration-flux 
cases considered in TSPA). 
 Repository-scale variability in and magnitude of 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 repository). 
 Dimensions and properties of the EBS components, such as the drip shield, engineered 
backfill and the invert. 
 WP-to-WP variability in heat-generation rate. 
 Repository-scale variability in overburden thickness. 
 Repository-scale variability in thermal conductivity (with an emphasis on the host-rock 
units). 
The influence of these factors is described in the MSTHM AMR (CRWMS M&O 2000k, 
Section 6.11). Sections 3.2.3.1 and 3.2.3.2 of this document discuss the influence of some of 
these factors on TH conditions in the NFE for the EDA-II design without and with backfill, 
respectively. 
3.2.2 Thermal-Hydrological Models 
The primary features that distinguish between various TH models involve: (1) dimensionality of 
the modeling domain, (2) dimensionality of the heat-source representation, and (3) representation 
of Fracture Matrix Interaction (FMX). With regards to modeling dimensionality, the two 
primary categories are drift scale and MS. DS TH models can be 1-D, 2-D, or 3-D. Mountainscale 
TH models are typically 3-D; however, symmetry assumptions are frequently used that 
result in mountain-scale TH models being effectively 2-D (note that such models can be 3-D at

 3-19 
the drift scale). With regards to heat-source representation, there are three primary categories: 
(1) smeared-heat-source, over a horizontal plane, (2) line-averaged-heat-source, along the axis of 
the emplacement drift, and (3) discrete-heat-source, representing the actual dimensions of the 
WPs and WP spacing. The line-averaged heat source category may be applied to the cross 
section of the WP or to the entire cross section of the emplacement drift. 
A summary of alternative conceptual models used to represent FMX is given in Sections 2.2.1 
and 2.4.1. All of the calculations described in Section 3.2.3 of this report used the DKM, 
together with the AFM. The DKM conceptualizes the fractured rock as having two interacting 
materials, one representing the matrix and one representing the fractures. The interaction 
between the fractures and the matrix is explicitly calculated from the local temperature and 
pressure differences, thus allowing local disequilibrium between fracture and matrix to be 
represented. The AFM accounts for the contact area between the fracture and the matrix, as well 
as the frequency of fractures. In the AFM, fracture flow may only occur through some of the 
fractures. The flux through a fracture is greater when it has higher saturation and, therefore, 
focusing flow through a portion of the fractures (i.e., to active fractures) maximizes flux and 
results in higher flow velocities through the mountain. 
NFE TH models used to date assume that the axial convection of heat (and moisture) by preclosure 
ventilation can be approximated by reducing the magnitude of the pre-closure heat 
source. During post-closure, axial convection is expected to be less significant, and it is not 
included in the models. In-drift convection (in a plane perpendicular to the drift axis) is treated 
at low resolution by some NFE TH models; more sophisticated treatment ma y be necessary for 
EBS calculations of moisture movement in the drifts. 
Ideally, a TH model of the repository would be fully 3-D at both mountain and drift scale. At 
MS, this model would represent the overall 3-D geometry of Yucca Mountain (including the 
topography of the ground surface and water table) and the engineered repository area, as well as 
the distribution of hydrostratigraphic units. At drift scale, this model would represent the 3-D 
geometry of the emplacement drifts, including details of the WPs, drip shields, and invert. This 
model would also represent the WP-to-WP variability of decay-heat generation and the areal and 
temporal distribution of infiltration flux throughout the repository area. 
The need for a multi-scale 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 repository (or mountain) scale. A single numerical model cannot readily 
incorporate the required range of scales, for locations throughout the repository, without 
involving an infeasible number (millions) of grid blocks. Two alternative approaches to the 
multi-scale prediction problem are combining a series of various scale models (Section 3.2.2.1) 
and a model that embeds a 3-D DS model with a relatively fine mesh into a 3-D mountain-scale 
model with a coarse mesh. (Section 3.2.2.2) 
3.2.2.1 Multi-scale Thermohydrologic Model 
Table 3-3 summarizes various TH models, as well as conduction (T) models. Several of these 
model types are process-level submodels for the MSTHM and others are abstracted models of 
the MSTHM.

 3-20 
Table 3-3. Summary of TH and T Model (or Submodel) Types, Including Those Used in the Multi-scale 
Thermal Hydrological Model 
Model 
Type Heat Source Dimensionality Process 
Type 
In-Drift 
Thermal 
Radiation 
Use in MSTHM 
SMT smeared 3-D mountain-scale T NA Process-model input 
SMTH smeared 3-D mountain-scale TH NA Process-model input1 
LMTH line-averaged 3-D mountain-scale TH yes MSTHM result2 
DMTH discrete 3-D mountain-scale TH yes MSTHM result2 
SDT smeared 1-D DS T NA Process-model input 
SDTH smeared 1-D DS TH NA Process-model input1 
LDTH line-averaged 2-D DS TH yes Process-model input 
DDT discrete 3-D DS T yes Process-model input 
DDTH discrete 3-D DS TH yes Model-abstraction testing1 
Source: Adapted from CRWMS M&O 2000k 
1 May be used in any potential future version of the multi-scale TH modeling approach 
2 Calculated with the MSTHM, see Figure 3-6) 
All models have an upper boundary that corresponds to the ground surface. Temperature, gasphase 
pressure, and relative humidity (or gas-phase air-mass fraction) are specified (as fixed 
values) at the upper boundary. Most of the TH models have a lower boundary that corresponds 
to the water table. The value of gas-phase pressure at the water table is established when the 
models are initialized at ambient conditions. The liquid-phase saturation at the water table is 
always 100%, while the temperature is a specified fixed value. The initialization model runs are 
continued until the temperature, liquid-phase saturation, gas-phase pressure, and gas-phase airmass 
fraction distributions in the model attain steady-state. 
The 3-D SMT model (Table 3-3) is a submodel used in the MSTHM calculations to determine 
the repository-scale variations in host-rock temperature resulting from the heat output from the 
entire inventory of 70,000 MTU of waste, including 63,000 MTU of CSNF and 7000 MTU of 
DHLW (vitrified high-level waste and DSNF WPs). The SMT model includes the influence of 
mountain-scale thermal-property distribution, the edge-cooling effect, which results from lateral 
heat loss at the repository edges, and the overburden-thickness distribution. (Overburden 
thickness is defined to be the depth of the repository horizon below the ground surface.) The 
SMT model domain extends from the ground surface to 1000 m below the present-day water 
table, and the lateral (adiabatic) boundaries are far enough away from the repository so that they 
do not affect repository temperatures. The temperature 1000 m below the water table is found by 
extrapolation, which is described in the Multiscale TH Model AMR (CRWMS M&O 2000k, 
Attachment XX). The extrapolation procedure assures the continuity of heat flux across the 
water-table boundary. 
The Mutiscale TH AMR (CRWMS M&O 2000k) describes the model used to provide NF and 
EBS conditions in the TSPA-SR. That AMR is based on a number of historical publications, 
including Hardin (1998). In Hardin (1998, Sections 3.2.2 and 3.5.2), the physical understanding 
of the NF and in-drift conditions is summarized based on numerous calculations, and results are

 3-21 
presented of a sensitivity study of waste package/drift spacing options and of hydrologic 
property sets. Section 3.2.3.3 is based on Hardin (1998). 
The MSTHM calculates results that are similar to those expected from a full-scale, 3-D 
mountain- and repository-scale model with DS resolution (i.e., millions of grid blocks). Given 
the number of required implementations of the calculation procedure for TSPA-VA performance 
measures, the multi-scale approach was developed to efficiently incorporate as much detail as is 
computationally feasible (the current MSTHM captures all relevant processes except mountainscale 
bouyant gas-phase convection). Submodels that comprise the current multiscale model 
(Figure 3-6) include: 
 Smeared-heat-source Mountain-scale Thermal conduction (SMT) models, can either 
be 2-D or 3-D (SMT in Figure 3-6). Because these models smear out the overall heat 
generation from the potential repository over the repository area, they cannot distinguish 
between conditions within (or close to) the emplacement drifts from those in the center 
of the rock pillar separating the drifts. Early attempts to represent 3-D mountain-scale 
heat flow used a 2-D axisymmetric disk-shaped representation of the repository area 
(Buscheck and Nitao 1994, p. 7). These models represent the influence of the edgecooling 
effect. The disk-shaped representation of the heat source has also been used in 
TH-model scoping calculations of large-scale in situ thermal tests (Buscheck 
et al. 1997c, Chapter 2). 
 Smeared-heat-source DS Thermal-conduction (SDT) models, are typically 1-D (SDT 
in Figure 3-6). These models cannot distinguish between conditions within (or close to) 
the emplacement drifts from those in the center of the rock pillar separating the drifts; 
neither can they represent the influence of edge cooling effects. 
 Line-average-heat-source Drift scale Thermal-Hydrological (LDTH) models, are 
typically 2-D or 3-D (LDTH in Figure 3-6). These models represent average conditions 
on the WPs (and other components in the drifts, such as drip shields). These models 
represent the 2-D distribution of conditions in the vertical plane orthogonal to the drift; 
therefore, they cannot distinguish between hotter and cooler WP locations; neither can 
they represent the influence of the edge-cooling effect. The H in the acronym 
indicates the submodel includes hydrological flow processes. 
 Discrete-heat-source, DS, Thermal-conduction (DDT) models, are always 3-D (DDT 
in Figure 3-6). These models discretely represent the 3-D geometry of the emplacement 
drifts, as well as WP-to-WP variability of decay-heat generation; therefore, they can 
distinguish between hotter and cooler WP locations. However, these models cannot 
represent the influence of the edge-cooling effect. These models were introduced 
relatively recently to TSPA and repository design analyses (Wilder 1996, Section 1.10; 
Buscheck et al. 1997e, pp. 1030-1034) and have also been used to model the DST 
(Buscheck et al. 1997d, Chapter 2). 
The Multi-scale Thermohydrologic Abstraction Code, MSTHAC (CRWMS M&O 2000k), is 
used to integrate the results from the SMT, SDT, and LDTH submodels to produce the MSTHM 
results, termed LMTH in Figure 3-6. (The LMTH is an intermediate output of the MSTHM). In

 3-22 
turn, the LMTH multi-scale results are combined with the DDT submodel results to produce the 
overall DMTH model results, the final output of MSTHM. (The software that combines the 
submodel results is termed MSTHAC, while the overall model is MSTHM.) 
Source: Derived from CRWMS M&O 2000k, Figure 1-1 
NOTE: The LMTH and DMTH models are combinations of results from feeder submodels. 
Figure 3-6. The Submodels of the Multi-Scale Thermal Hydrologic Model

 3-23 
It is useful to think of the LDTH submodel as the core submodel. For the TSPA-SR, these 2-D 
DS TH submodels are run for 31 locations spaced evenly throughout the repository area for 
several AML values (nominal value and lower) to represent the influence of edge-cooling 
effects. The LDTH submodel includes the hydrological processes and parameters (e.g., surface 
infiltration rates, H properties) used to describe a location, given specific coordinates within the 
repository. The remaining three submodels, which are conduction only, are required to account 
for the influence of 3-D mountain-scale heat flow and 3-D DS heat flow on DS TH behavior. 
The coupling of 3-D mountain-scale heat flow to 2-D DS TH behavior is accomplished with the 
SMT and the SDT submodels. The SMT is 3-D and includes the influence of thermal-property 
variation in the mountain, lateral heat loss at the repository edges, and overburden-thickness 
variation with location, assuming a uniform, planar (i.e., smeared) heat source throughout the 
repository area. The SMT calculates temperatures at 623 locations within the repository 
footprint. The SDT submodel is a 1-D (vertical) submodel, run at the same 31 locations and for 
the same AMLs as the LDTH submodels. To obtain the line-averaged drift-wall temperature 
(which is roughly equivalent to an average WP location), the relationship between the drift-wall 
temperature in the LDTH submodel and the smeared repository-plane temperature in the SDT 
submodel are interpreted to the 623 SMT locations and used to modify the temperatures in the 
SMT submodel, thereby resulting in an MSTHM drift-wall temperature that approximates the 
effects of the most important TH processes at DS and the geometry effects of mountain-scale. 
Because the SMT and SDT submodels both share the same smeared-heat-source approximation 
and thermal-conduction representation of heat flow, the relationship between the SDT submodel 
temperature and the LDTH submodel drift-wall temperature allows for the SMT submodel 
temperature to be corrected for both the influence of TH processes on temperature and for the 
influence of 2-D DS dimensionality (orthogonal to the axis of the drift). The SMT, SDT, and 
LDTH submodels all share a blended heat-generation history, which blends the heat-generation 
histories of the entire repository; hence, the heat-generation history is effectively that of an 
average WP. The DDT submodel is a 3-D DS submodel that includes individual WPs (with 
distinctive heat-generation histories) and accounts for thermal radiation in addition to thermal 
conduction between the WPs and drift surfaces. The drift-wall temperatures for an average WP, 
calculated with the combined use of the LDTH, SMT and SDT submodels, are then further 
modified to account for waste-package-specific deviations using the DDT submodel. This is 
accomplished by using the spatial variation of local temperatures at various point locations 
along the drift (such as on the drift wall, drip shield surface, and WP surface) and the 
corresponding line-averaged temperature in the DDT submodel. 
The MSTHM has been used to develop time-varying estimates of key NFE performance 
measures for locations throughout the entire repository for the VA (DOE 1998, Volume 3, 
Section 3.2) and is being used in the TSPA-SR (see Section 3.2.3.1). Performance predictions 
vary significantly for different locations in the repository, because of differences in the local 
hydrostratigraphy and local percolation flux. The performance measures include drift-wall 
temperature, WP temperature, and drift-air RH (relative humidity) at the WP surface. Multiscale 
methods use estimation procedures that are computationally fast enough to be conducted 
for many locations in the repository lay-out, and repeated for TSPA-VA sensitivity cases and 
alternative model exercises. This efficient method was also useful in conducting numerous THmodel 
calculations in support of the LADS (CRWMS M&O 1999a).

 3-24 
The measures in Table 3-4 were used by TSPA-VA (DOE 1998, Volume 3, Section 3.4.1.2) and 
TSPA-LADS (CRWMS M&O 1999a, Figure 5-11), and are currently being used by TSPA-SR to 
estimate WP corrosion rates, waste-form dissolution rates, and transport of radionuclides in the 
NFE. The use of conduction-only models will introduce small errors in the abstracted 
performance measures. The magnitude of these errors can be estimated by comparison of 
abstracted results with direct simulations. Where possible, conduction-only models are used to 
calculate temperature differences instead of absolute temperatures; this approach minimizes the 
abstraction errors. The TH performance measures (Table 3.A-b) were provided to TSPA-VA 
and TSPA-LADS for various combinations of repository location, heat production rates as 
determined by WP design and waste type (e.g., CSNF or defense high-level waste), WP spacing, 
sequencing of WP types in the emplacement drifts, and design options such as the line-load 
design or backfill. The TH performance measures were also provided for testing sensitivity of 
the TSPA-VA to variations in thermal and hydrological properties, distributions of infiltration 
flux, including the influence of climate change, conceptual models of FMX (e.g., comparing 
ECM with DKM results), and conceptual models of heat-flow conditions at the water table, (e.g., 
a fixed temperature vs. explicit representation of heat loss to the SZ). For the TSPA-SR, an 
expanded list of TH performance measures are being provided (Tables 3-5 and 3-6). 
Table 3-4. List of NFE and EBS TH Parameters Calculated with the MSTHM for the TSPA-VA and for 
the TSPA-LADS 
Location T RH Xair,gas Sliq qliq 
Rock above drift wall x X x x X 
Rock at drift wall X X x x x 
Drift above WP X 
WP surface X X 
Invert x X X X 
Measures calculated for TSPA-VA and TSPA-LADS are indicated by bold, uppercase X. Other measures also 
calculated by the approach are indicated by lowercase x. The measures are temperature (T), relative humidity 
(RH), gas-phase air-mass fraction (Xair,gas), liquid phase saturation (Sliq), and liquid-phase flux (qliq). 
3.2.2.2 Unsaturated-Zone Mountain-Scale TH Model 
The Mountain-Scale TH AMR (CRWMS M&O 2000t) documents the development of the MS 
Thermal-Hydrological (TH) model that evaluates the effects of heat on UZ flow and distribution 
of liquid and temperature over a period of 100,000 years. The issues addressed include the 
following: (1) extent of the 2-phase zone, (2) liquid and gas flux in near and far field, 
(3) moisture redistribution in the UZ, (4) temperature of drifts and pillars, (5) potential for flow 
and transport property change in the PTn and CHn, (6) TH effects on water table and perched 
water bodies, and (7) influence of climate and ventilation. While items (5) and (6) of the above 
are strictly far-field issues, all other items pertain to the NF environment.

 3-25 
Table 3-5. List of NFE and EBS TH Variables Calculated with the MSTHM at 623 Repository 
Subdomains for Backfill-Runs of the TSPA-SR 
TH Variable Drift-Scale Location 
NFE Parameters 
NFE rock (5 m above drift, and mid-pillar at repository horizon) 
Maximum lateral extent of boiling 
Upper drift wall (crown of the drift) 
Lower drift wall (below invert) 
Temperature 
Drift wall (perimeter average) 
Relative Humidity Drift-wall (perimeter average) 
Liquid-phase matrix saturation Drift wall (perimeter average) 
NFE host rock (5 m, 3 m, and 0.2 m above crown of drift) 
Liquid-phase flux 
Drift wall (crown, in matrix and in fractures) 
Gas-phase (water vapor) flux Drift wall (perimeter average) 
Gas-phase (air) flux Drift wall (perimeter average) 
Evaporation rate NFE rock 
EBS Parameters 
Drift wall (perimeter average) 
Backfill (crown) 
Drip shield (perimeter average and upper surface) 
WP (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-phase matrix saturation 
Invert (average) 
Drip shield (crown, upper surface average, and lower side at the base) 
Liquid-phase flux 
Invert (average) 
Gas-phase air-mass fraction Drip shield (perimeter average) 
Gas-phase pressure Drip shield (perimeter average) 
Drip shield (perimeter average) 
Invert (average) Capillary pressure 
Drift wall (crown, in matrix and in fractures) 
Gas-phase (water vapor) flux Drift wall (perimeter average) 
Gas-phase (air) flux Drift wall (perimeter average) 
Backfill (crown) 
Drip shield (crown and perimeter total) Evaporation rate 
Invert (total)

 3-26 
Table 3-6. List of NFE and EBS TH Variables Calculated with the MSTHM at 610 Repository 
Subdomains for No Backfill-Runs Rev 00 of the TSPA-SR 
TH Variable Drift-Scale Location 
NFE Parameters 
NFE rock (5 m above drift and along the entire repository horizon) 
Maximum lateral extent of boiling 
Upper drift wall (crown of the drift) 
Lower drift wall (below invert) 
Temperature 
Drift wall (perimeter average) 
Relative Humidity Drift-wall (perimeter average) 
Liquid-phase matrix saturation Drift wall (perimeter average) 
NFE host rock (5 m and 3 m above crown of drift) 
Liquid-phase flux 
Drift-wall (upper surface perimeter average in matrix & fractures 
Gas-phase (water vapor) flux Drift wall (perimeter average) 
Gas-phase (air) flux Drift wall (perimeter average) 
Evaporation rate NFE rock 
EBS Parameters 
Drift wall (perimeter average) 
Backfill (crown) 
Drip shield (perimeter average and upper surface) 
WP (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-phase matrix saturation 
Invert (average) 
Drip shield (crown, upper surface average, and lower side at the base) 
Liquid-phase flux 
Invert (average) 
Gas-phase air-mass fraction Drip shield (perimeter average) 
Gas-phase pressure Drip s hield (perimeter average) 
Drip shield (perimeter average) 
Invert (average) Capillary pressure 
Drift wall (crown, in matrix and in fractures) 
Gas-phase (water vapor) flux Drift wall (perimeter average) 
Gas-phase (air) flux Drift wall (perimeter average) 
Backfill (crown) 
Drip shield (crown and perimeter total) Evaporation rate 
Invert (total)

 3-27 
The mountain-scale TH model is deve loped based on the UZ model. It uses input parameters 
based on the Calibrated Properties AMR (CRWMS M&O 2000n), a spatially varying mean 
infiltration rate, with varying climates during the thermal-loading period. The simulations were 
performed using the average initial thermal load of 72.7 kW/acre, scale down by the natural 
decay curve over a total simulation period of 100,000 years. To account for ventilation, only 
30% of this heat is used for the first 50 years of emplacement. The TH model uses the 
mathematical formulation employed in the TOUGH2 family of codes (Pruess 1987, pp. 2-11; 
1991), the dual-continuum approach, and the van Genuchten capillary pressure and relative 
permeability relationships to describe the behavior of the UZ under thermal-loading conditions. 
This formulation is based on the traditional energy and mass conservation relationships. 
The embedded 3-D mesh approach was used in the UZ F&T PMR (CRWMS M&O 2000f, 
Section 3.12) with detailed discussion of the numerical gr ids in the Numerical Grids and 
Mountain-Scale TH AMRs (CRWMS M&O 2000w and 2000t). In addition to the 3-D 
submodels, two 2-D cross section analyses were performed. Six cases, two 3-D without drifts, 
one 2-D without drifts, and three 2-D with drifts (UZ F&T PMR, Table 3.12-1) were performed. 
Another, somewhat similar approach was used to evaluate the DST (CRWMS M&O 2000a). In 
this approach, a series of 24 vertical 2-D sections, orthogonal to the drift, were calculated with 
extremely refined grids around the drift. These cross-sections were then extended and merged 
into the third dimension. 
The MS TH modeling study uses both 2-D and 3-D submodels of the 3-D UZ flow model. This 
study shows that the available heat source and its distribution, as well as infiltration rates are the 
determining factors for boiling and re-wetting TH processes at the repository. With and without 
ventilation, two-phase heat-pipe conditions are developed in a region above the repository during 
10-100 years after emplacement. Dry-out conditions are predicted near the drifts, in both the 
fracture and matrix continua with drift temperatures exceeding 100oC for hundreds of years. 
With ventilation, temperatures rise to boiling conditions only in the immediate area of the drifts. 
The temperature in the pillars rises to 80-85oC. At early times (less than 100 years), thermally 
induced liquid flux up to two orders of magnitude larger than the ambient percolation flux is 
predicted to move toward the drying area due to capillary pressure gradient. However, this 
liquid flux is vaporized by the repository heat and does not reach the drifts. The model predicts 
that vertical flow crossing the pillars between the drifts generally continues at a rate close to the 
ambient percolation flux for most of the thermal loading period. In some locations the flow may 
be enhanced by condensate drainage for a period of several hundred years. The MS TH model 
predicts a nearly 30 to 35oC temperature increase at the water table to an average of 65 to 70o. 
At the top of CHn stratigraphic unit, the predicted maximum temperature rises to 75-80oC for a 
period between 2,000 and 7,000 years. This temperature is not high enough to induce sorption 
property changes. 
3.2.3 Thermal-Hydrological-Model Results 
Four case studies are described in this section. First, in Section 3.2.3.1, the detailed NFE TH 
results are presented for the current, no-backfill, SR design (using the MSTHM). Because these 
results are to be documented in an AMR ICN later than this PMR ICN, they are presented in 
detail here. Section 3.2.3.2 describes the MSTHM calculations of the initial SR design that 
included backfill. The final two subsections describe DS TH calculations that use the LDTH

 3-28 
model. Section 3.2.3.3 describes calculations used to support the philosophical shift in thermal 
design from mountain-scale dryout to maintenance of drainage in the pillars between the 
emplacement drifts. The LDTH submodels that were used in the MSTHM calculation were from 
the TSPA-VA. Section 3.2.3.4 describes a comparison of TH results from an LDTH submodel 
used in the TSPA-SR, a DS THC model, and a mountain-scale TH model. 
3.2.3.1 Multi-scale Thermohydrologic Model Calculations for the Site-Recommendation 
Design with No Backfill 
The Multiscale TH AMR (CRWMS M&O 2000k), described in Section 3.2.2.1, has been used to 
calculate temperature, liquid-phase saturation, relative humidity, evaporation rate, capillary 
pressure, and liquid fluxes in the NF rock, and temperatures, humidity, and liquid-phase flux and 
gas-phase flux in the emplacement drifts (DTN: LL000509112312.003). In this PMR, selected 
values and graphical distributions of parameters are presented for the NFE host-rock results. All 
calculations shown in this section pertain to the mean infiltration-flux case. 
3.2.3.1.1 Temperature 
Figure 3-7 shows the spatial distributions (over the repository footprint) of perimeter-averaged 
drift-wall temperature. Preclosure drift-wall temperatures stay below the boiling point, while the 
WP temperature climbs above the boiling point as it peaks around 15 yr. Shortly after 
ventilation ceases, peak drift-wall temperatures occur. Peak drift-wall temperatures are generally 
less than 150C. The edge-cooling effect is very evident thereafter, as temperatures around the 
repository edges are considerably less than at the repository center. Boiling at the drift wall 
ceases around 1,000 yr. 
Figure 3-8 shows the spatial distributions of temperature in the host rock 5 m above the crown of 
the drift. This vertical location reaches the boiling point at about 100 year and remains slightly 
above the boiling point for less than 300 year. 
Figure 3-9 shows the spatial distribution of temperature 7.39 m laterally away from the 
springline of the drift. This location in the pillar is about 20% of the distance in toward the 
midline of the pillar. This depth into the pillar never quite reaches the boiling point at any 
location in the footprint, assuring that condensate and percolation flux can readily shed between 
emplacement drifts. 
Figure 3-10 shows the temperature history at various locations in the NFE host-rock, as well as 
on the WP, for the geographical center of the repository and a location 27.5 m from the eastern 
edge of the repository footprint. The duration of boiling is considerably less at the edge 
(~100 year) than it is at the center of the repository. The temperature history 5 m above the 
crown of the drift is similar to that 7.39 m laterally away from the springline of the drift.

 3-29 
INTENTIONALLY LEFT BLANK 

 3-30 
DTN: LL000509112312.003 
Figure 3-7. Perimeter-Averaged Temperature on the Drift Wall for a 21-PWR 
WP for the Mean Infiltration-Flux Case for the Indicated Times 
(Page 1 of 2)

 3-31 
DTN: LL000509112312.003 
Figure 3-7. Perimeter-Averaged Temperature on the Drift Wall for a 21-PWR 
WP for the Mean Infiltration-Flux Case for the Indicated Times 
(Page 2 of 2)

 3-32 
DTN: LL000509112312.003 
Figure 3-8. Temperature 5 m above the Crown of the Drift in the Vicinity of a 21-PWR 
WP for the Mean Infiltration-Flux Case for the Indicated Times

 3-33 
DTN: LL000509112312.003 
NOTE: This location is about 20% of the distance in toward the midline of the pillar. This temperature is called Tpillar . 
Figure 3-9. Temperature 7.39 m Laterally away from the Springline of the Drift in the 
Vicinity of a 21-PWR WP for the Mean Infiltration-Flux Case for the 
Indicated Times

 3-34 
DTN: LL000509112312.003 
NOTE: The temperatures occur in the vicinity of a 21-PWR WP for the mean infiltration-flux case for the indicated 
times. 
Figure 3-10. Temperature History at the Indicated Locations at 
(a) the Geographical Center of the Repository and 
(b) a Location 27.5 m from the Eastern Edge of the 
Repository

 3-35 
Figure 3-11 shows the complementary cumulative distribution function (CCDF) for the peak 
temperature on WPs and on the drift wall, as well as showing the CCDF of the maximum lateral 
extent of the boiling point isotherm. The coolest WP location has a peak drift-wall temperature 
of about 115C, while the hottest WP location has a peak of about 147C. For the coolest WP 
location, the maximum lateral extent of boiling is about 6.5 m from the repository centerline, 
while for the hottest WP location, the maximum lateral extent of boiling is about 8.9 m. 
Therefore, between 78 to 84% of the repository horizon remains below the boiling point, which 
will assure that condensate and percolation flux can readily shed between emplacement drifts. 
3.2.3.1.2 Liquid-Phase Saturation and Relative Humidity 
Figure 3-12 shows the spatial distribution of relative humidity in the host-rock at the drift wall. 
Figure 3-13 shows the perimeter-averaged drift-wall liquid-phase matrix saturation history and 
relative humidity history at the center and edge of the repository. Minimum liquid-phase 
saturations are about 0.2 at the repository center and slightly greater than 0.2 at the repository 
edge. Minimum values of drift-wall relative humidity are about 25% at the repository center and 
about 40% at the repository edge. The differences between the center and edge locations result 
from the edge-cooling effect. Significant reduction in drift-wall liquid-phase saturation (relative 
to ambient conditions) persists for up to about 2000 yr. Significant reduction in drift-wall RH 
(relative to humid ambient conditions) persists for up to about 2000 yr. 
3.2.3.1.3 Evaporation Rate 
Figure 3-14 shows the evaporation-rate history at the crown of the drift for the repository center 
and edge. Immediately after ventilation ceases there is a sharp spike in evaporation rate as 
boiling commences in the host-rock around the drift wall. After this spike, the evaporation rate 
is close to zero at the repository center; a secondary sharp spike in evaporation rate occurs at the 
end of the boiling period (about 1,000 year). This spike results from the boiling front collapsing 
back into the emplacement drift. At the repository edge, there is no second spike because the 
boiling front never progresses very far away from the drift wall. Some time after the end of the 
boiling period the evaporation rate declines to relatively small values. 
3.2.3.1.4 Capillary Pressure 
Figure 3-15 shows the capillary-pressure histories in the fractures and in the matrix at the 
repository center and edge. Under ambient conditions, capillary pressure in the fractures is an 
order of magnitude less than that in the matrix. During the preclosure period, changes in 
capillary pressure are small, primarily arising as a result of the temperature dependence of the 
surface tension of water. Shortly after ventilation ceases and boiling and dryout occur in the host 
rock around the drifts, the magnitude of capillary pressure in the matrix rises abruptly, attaining 
values about three to four orders of magnitude larger than ambient values. As the rock rewets to 
ambient liquid-phase saturation conditions, the capillary pressure declines to ambient values.

 3-36 
DTN: LL000509112312.003 
NOTE: Uses the Mean Infiltration-Flux Case. 
Figure 3-11. (a) The Complementary Cumulative Distribution Function 
(CCDF) for the Peak Temperature on Waste Packages 
and for the Peak Perimeter-Averaged Drift-Wall 
Temperature. (b) The CCDF of the Maximum Lateral 
Extent of the Boiling Point (T = 96C).

 3-37 
DTN: LL000509112312.003 
NOTE: Contour labels and color bars indicate values. 
Figure 3-12. Perimeter-Averaged Drift-Wall Relative Humidity for a 21-PWR WP for the 
Mean Infiltration-Flux Case for the Indicated Times

 3-38 
DTN: LL000509112312.003 
NOTE: These conditions occur in the vicinity of a 21-PWR WP for the mean infiltration-flux case for the indicated 
times. 
Figure 3-13. Perimeter-Averaged Drift-Wall Liquid-Phase Matrix 
Saturation History (a) and Relative Humidity History 
(b) at the Geographical Center of the Repository and a 
Location 27.5 m from the Eastern Edge of the 
Repository

 3-39 
DTN: LL000509112312.003 
NOTE: These conditions occur in the vicinity of a 21-PWR WP for the mean infiltration-flux case for the indicated 
times. 
Figure 3-14. Evaporation Rate History in the Host Rock at the Crown of the Drift at 
the Geographical Center of the Repository and a Location 27.5 m 
from the Eastern Edge of the Repository 
3.2.3.1.5 Liquid-Phase Flux 
Figure 3-16 shows the spatial distribution of liquid-phase flux 5 m and 3 m above the crown of 
the drift. Figure 3-17 shows the spatial distribution of liquid-phase flux at the drift wall. 
Figure 3-18 shows the liquid-phase-flux history at 5 m and 3 m above the crown of the drift, as 
well as at the drift wall for a repository center and edge location. The increase in liquid-phase 
flux (above ambient values) is called thermally-enhanced percolation. 
At the repository center, the location 3 m above the crown of the drift experiences a very abrupt 
spike in liquid-phase flux just after ventilation ceases and boiling commences in the host rock 
around the drift. This primary spike is followed by a period of zero flux, which is then followed 
by a secondary spike (much smaller than the primary spike) that occurs shortly after boiling 
ceases. At the repository center, the location 5 m above the drift experiences a less abrupt spike 
in liquid-phase flux. Liquid-phase flux remains above ambient values until the end of the 
present-day climate (at 600 year); thereafter, the influence of thermally-enhanced percolation is 
swamped by the increased ambient percolation flux that results from the monsoonal and glacial 
climates.

 3-40 
At the repository edge, the duration of thermally-enhanced percolation flux (3 m and 5 m above 
the drift) is less than at the center of the repository. Percolation flux 3 m and 5 m above the drift 
returns to ambient values before the end of the present-day climate. At both center and edge 
locations, drift wall flux is low; the seepage model in the UZF&T PMR (CRWMS M&O 2000f) 
should be used for fluxes very near the drift wall. 
3.2.3.2 Thermal-Hydrological Results for the EDA-II Design with Backfill 
The Multiscale TH AMR (CRWMS M&O 2000k), described in Section 3.2.2.1, has been used to 
calculate temperatures, saturations, and liquid fluxes in the NF rock, and temperatures, 
humidities, and liquid fluxes in the emplacement drifts. In this PMR, selected values and 
graphical distributions of parameters are presented for the NF rock results. 
Figure 3-19 shows the spatial distributions of peak drift-wall temperature (in time) across the 
repository footprint, for low, mean, and high infiltration-flux spatial distributions. The highest 
temperatures are for the low infiltration flux, since the water acts as a heat sink. The peaks (in 
time and space) are about 205, 195, and 190C for the three infiltration-flux distributions. The 
temperatures are under the invert of the drifts. The 195C peak temperature of the mean 
infiltration case is comparable to the peak ~150C no-backfill drift wall temperature shown in 
Figure 3-7(d). The lower no-backfill temperature is averaged around the perimeter of the drift 
while the higher (backfill) design temperature is at the hottest location on the perimeter. The 
backfill design resulted in much higher downward heat flow (and temperature). 
Figure 3-20 shows the liquid flux 5 m above the crown of the emplacement drifts as a function of 
time. A series of snapshots show the distribution across the footprint, for the mean infiltration 
flux scenario. The highest flux at this location is about 60 mm/yr, about 30 years after the 
repository is closed. 
Figure 3-21 shows the liquid flux 0.2 m above the crown of the emplacement drifts as a function 
of time. A series of snapshots show the distribution across the footprint, for the mean infiltration 
flux scenario. The highest flux at this location is about 400 mm/yr, about 1 year after the 
repository is closed. 
Figure 3-22 shows the liquid flux history at two locations in the footprint (near the center and 
near the eastern edge). At the drift scale, fluxes are shown at 5 and 0.2 m above the crown. At 
both locations, the near-drift-wall experiences a very high pulse of flux almost immediately after 
ventilation ceases and the repository is closed. As the NF rock dries out, the near-wall flux is 
negligible; this is followed by a gradual return to ambient flux leve ls (with step increases at the 
assumed times of climate change). For the center location, the zero-flux duration is about 
300 years, and for the edge location, it is about 140 years. The center location also experiences a 
lesser-magnitude pre-closure flux peak at both the 0.2 and 5 m-depths into the rock, while the 
edge location does not.

 3-41 
DTN: LL000509112312.003 
NOTE: These conditions occur in the vicinity of a 21-PWR WP for the mean infiltration-flux case for the indicated 
times. 
Figure 3-15. Capillary Pressure History in (a) the Fractures and in 
(b) the Matrix Averaged Around the Perimeter of the 
Drift Wall at the Geographical Center of the Repository 
and a Location 27.5 m from the Eastern Edge of the 
Repository

 3-42 
DTN: LL000509112312.003 
NOTE: Contour labels and color bars indicate values. 
Figure 3-16. Liquid-Phase Flux 5 m and 3 m above the Crown of the Drift and in the 
Vicinity of a 21-PWR WP for the Mean Infiltration-Flux Case for the 
Indicated Times (Page 1 of 2)

 3-43 
DTN: LL000509112312.003 
Figure 3-16. Liquid-Phase Flux 5 m and 3 m above the Crown of the Drift and in the 
Vicinity of a 21-PWR WP for the Mean Infiltration-Flux Case for the 
Indicated Times (Page 2 of 2)

 3-44 
DTN: LL000509112312.003 
NOTE: Contour labels and color bars indicate values. 
Figure 3-17. Liquid-Phase Flux at the Upper Drift Wall in the Vicinity of a 21-PWR WP for 
the Mean Infiltration-Flux Case for the Indicated Times

 3-45 
DTN: LL000509112312.003 
NOTE: These conditions occur in the vicinity of a 21-PWR WP for the mean infiltration-flux case for the indicated 
times. 
Figure 3-18. Liquid-Phase Flux History at the Indicated 
Locations above the Drift at (a) the Geographical 
Center of the Repository and (b) a Location 
27.5 m from the Edge of the Repository

 3-46 
Source: CRWMS M&O 2000k, Figure 6-15 
NOTE: Contour labels and color bars indicate values. 
Figure 3-19. Peak Temperature on the Lower Drift Wall (Below the Invert) for the Low, 
Mean, and High Infiltration-Flux Cases

 3-47 
INTENTIONALLY LEFT BLANK

 3-48 
Source: CRWMS M&O 2000k, Figure 6-26 
NOTE: Contour labels and color bars indicate values. 
Figure 3-20. Liquid-Phase Flux 5 m above the Crown of the Drift for the Mean Infiltration Flux Case for 
the Indicated Times (Page 1 of 2)

 3-49 
Source: CRWMS M&O 2000k, Figure 6-26 
NOTE: Contour labels and color bars indicate values. 
Figure 3-20. Liquid-Phase Flux 5 m above the Crown of the Drift for the Mean Infiltration-Flux 
Case for the Indicated Times (Page 2 of 2)

 3-50 
Source: CRWMS M&O 2000k, Figure 6-27 
Figure 3-21. Liquid-Phase Flux 0.2 m above the Crown of the Drift for the 
Mean Infiltration-Flux Case for the Indicated Times (Page 1 
of 2)

 3-51 
Source: CRWMS M&O 2000k, Figure 6-27 
Figure 3-21. Liquid-Phase Flux 0.2 m above the Crown of the Drift for the 
Mean Infiltration-Flux Case for the Indicated Times (page 2 
of 2)

 3-52 
Source: CRWMS M&O 2000k, Figure 6-41 
Figure 3-22. Liquid-Phase Flux History at Indicated Drift-Scale 
Locations for the Mean Infiltration Flux Case at (top) the 
Geographic Center of the Repository, and (bottom) a 
Location 27.5 m from the Eastern Edge of the 
Repository

 3-53 
3.2.3.3 LDTH Calculations of Point and Line Loads 
This section reports the results of applying the LDTH submodel described in Section 3.2.2.1 as a 
tool to evaluate design options. This work was done as a sensitivity case for TSPA-VA, and led 
to more sophisticated calculation in support of LADS. As discussed in the LADS report 
(CRWMS M&O 1999a, Section 7.2), a design with excellent performance, such as the VA 
design, could be improved by reducing uncertainties in the effects of coupled processes on 
repository performance. The LDTH submodel was used to evaluate temperatures, saturations, 
and liquid fluxes that were used as surrogates for uncertainty evaluation. This section describes 
the results of trading drift spacing against waste package spacing, with constant inventory and 
repository area (i.e., AML). Other trade-off studies described in the LADS report included 
ventilation rate and duration, and different AMLs. The conclusion of LADS was that EDA-II 
(see the Introduction toChapter 2) met the uncertainty reduction goal by using a combination of 
these thermal-management techniques. 
Two-dimensional cross sectional TH models were used to calculate DS spatial distributions of 
temperature, liquid-phase saturation, relative humidity, liquid-phase flux, and air mass fraction, 
as functions of time. Two designs were compared: point-loading with 28 m drift spacing (and 
with spaces between WPs about the same as the length of the WPs), and line loading with 56.6 m 
drift spacing (and with only a small gap between WP ends). These results led to adoption of the 
EDA-II design, which uses line-loading with 81 m drift spacing (AML reduced from 85 to 
60 MTU/acre compared to VA) and preclosure ventilation. 
3.2.3.3.1 Model Inputs and Assumptions 
The surface location of the model was at the crest of Yucca Mountain, halfway between the 
northern and southern boundaries of the repository footprint and one-third of the way from the 
western to the eastern boundary. The nominal infiltration flux is 16.0 mm/year at this location 
(Flint et al. 1996). Mountain-scale lateral heat and mass flow are neglected in the model; the 
error introduced is thought to be small for locations near the center of the repository, but it is 
probably significant for the edges of the repository. 
The hydrostratigraphy used in the models is that reported within the UZ F&T PMR (CRWMS 
M&O 2000f). As noted in that PMR, the tuffs comprising Yucca Mountain are identified by 
lithostratigraphic name and by major and detailed hydrogeologic unit nomenclature. Table 3-7 
provides this nomenclature. The UZ Model Layer nomenclature and the properties of those 
layers were used in the TH models that will be reported in this PMR.

 3-54 
Table 3-7. Major Hydrogeological Unit, Lithostratigraphic Unit, Detailed Hydrogeological Unit, and UZ 
Model Layer Nomenclatures (adapted from CRWMS M&0 2000w, Table 10) 
Major 
Hydrogeological 
Unit Lithostratigraphic Unit 
Detailed 
Hydrogeological 
Unit 
UZ Model 
Layer 
Tpcr CCR, CUC tcw11 
Tpcp CUL, CW tcw12 
Tpcpv3 
Tiva Canyon 
welded (TCw) 
Tpcpv2 
CMW tcw13 
Tiva Canyon 
Tuff 
Tpcpv1 CNW ptn21 
Bedded tuff Tpbt4 BT4 ptn22 
TPY ptn23 
Yucca 
Mountain 
Tuff 
Tpy 
Bedded tuff Tpbt3 BT3 ptn24 
Pah Canyon 
Tuff 
Tpp TPP ptn25 
Bedded tuff Tpbt2 ptn26 
Tptrv3 
Paintbrush 
nonwelded (PTn) 
Topopah 
Spring Tuff Tptrv2 
BT2 
Tptrv1 TC tsw31 
Tptrn TR tsw32 
Tptrl TUL tsw33 
Tptpul 
Tptpmn TMN I tsw34 
Tptpll TLL tsw35 
TM2 (upper 213) tsw36 Tptpln 
TM1 (lower 1/3) tsw37 
Tptpv3 PV3 tsw38 
Tptpv2 PV2 tsw39 
Topopah Spring 
welded (TSw) 
Tptpv1 BT1 or 
BT1 a (altered)

 3-55 
Table 3-7. Major Hydrogeological Unit, Lithostratigraphic Unit, Detailed Hydrogeological Unit, and UZ 
Model Layer Nomenclatures (adapted from CRWMS M&0 2000w, Table 10) (Continued) 
Major 
Hydrogeological 
Unit Lithostratigraphic Unit 
Detailed 
Hydrogeological 
Unit 
UZ Model 
Layer 
BT1 or Bedded tuff Tpbt1 
BT1 a (altered) 
ch1 (vit, zeo) 
ch2 (vit, zeo) 
chi (vit, zeo) 
ch4 (vit, zeo) 
Calico Hills 
Formation 
Tac CHV (vitric) 
or 
CHZ (zeolitic) 
ch5 (vit, zeo) 
Bedded tuff Tacbt BT ch6 
Tcpuv PP4 (zeolitic) pp4 
Tcpuc PP3 (devitrified) pp3 
Calico Hills 
nonwelded (CHn) 
Prow Pass 
Tuff 
Tcpmd PP2 (devitrified) pp2 
Tcplc 
Tcplv 
Bedded tuff Tcpbt 
Tcbuv 
PP1 (zeolitic) PP' 
Tcbuc 
Tcbmd 
Tcblc 
BF3 (welded) bf3 
Bullfrog Tuff 
Tcblv 
Bedded tuff Tcbbt 
Tctuv 
BF2 (nonwelded) bf2 
Tctuc 
Tctmd 
Tctlc 
Not Available , tr3 
Crater Flat 
undifferentiated 
(CFu) 
Tram Tuff 
Tctlv & below Not Available tr2 
The following boundary conditions were used. The water table was considered to be a 
constant-property boundary with specified fixed temperature, liquid saturation, and gas pressure. 
The surface of the mountain was considered to be a constant-property boundary with specified 
fixed temperature and gas pressure. Because the imposed infiltration is the net of water influx 
and water vapor outflux, the relative humidity at the surface of the mountain was assumed to be 
100 percent; eliminating the need to explicitly calculate vapor flux near the surface. The 
temperature values at the water table and ground-surface boundaries were taken from the sitescale 
UZ flow model (Bodvarsson et al. 1997). At the water table, liquid-phase saturation is 
100 percent. The value of gas pressure at the ground surface was taken from the site-scale UZ 
flow model. The value of gas pressure at the water table is consistent with the value of gas 
pressure at the ground surface and the pressure profile of a static gas column from the ground 
surface to the water table.

 3-56 
Figure 3-23 is a vertical cross section, showing radiation connections, of the simplified (square) 
emplacement drift, orthogonal to the drift axis. By using periodic boundaries, the vertical plane 
through the centerline of the drift becomes a plane of symmetry (although care must be taken in 
the radiation connections across the plane) and, consequently, provides an adiabatic, no-flow 
boundary. The centerline of the pillar between drifts provides the other adiabatic, no-flow 
boundary in the x direction. The (later) LADS and SR calculations included round drifts with 
larger drift spacing. 
For the calculations shown here, the WP diameter was 1.67 m, and the emplacement drift 
diameter was 5.1 m. For earlier DS-model calculations for TSPA-VA, the WP diameter was 
assumed to be 1.85 m (Hardin 1998, Section 3.5.1.2). The invert, which is at the bottom of the 
drift, was assumed to occupy 16.6 percent of the drift cross section. As was demonstrated 
previously (Wilder 1996, Section 1.10.4 ), a circular WP in a circular drift can be accurately 
represented by a square WP in a square drift, provided that the respective circular and square 
cross sectional areas are equal. In the model, the WP dimensions are 1.445 m square, and the 
drift measures 4.52 m square. The invert was assumed to be filled with concrete, consisting of 
fractured and jointed matrix blocks. Heat flux from the WP sources is averaged over the length 
of the drifts and coupled to the drift surfaces primarily by radiant heat transfer. Thermal 
radiation is also accounted for between different locations on the drift surface. An efficient heattransfer 
mechanism distributes the heat flux uniformly to the perimeter surfaces of the 
emplacement drift. The drift-wall and drift-floor surfaces are assumed to be black-bodies 
(emissivity = 1), and the WPs have an emissivity of 0.8. This allows the use of a constant heatflux 
boundary condition at the drift perimeter. 
The initial conditions were set as follows: the value of gas pressure at the water table is 
established when the models are initialized at ambient conditions. The initialization model runs 
are continued until the temperature, liquid-phase saturation, gas pressure, and air-mass fraction 
distributions in the model attain steady-state distributions. 
The grid for the numerical calculations was established as follows: the DKM approximation is 
used in the LDTH submodel to represent fracture-matrix coupling. Because different properties 
are assigned to fracture elements and matrix elements, two grid blocks must be assigned to each 
spatial location, (i.e., twice as many as would be required to give the same spatial resolution with 
the ECM). Sixteen grid blocks are used in the x direction for the point-load design, and 18 are 
used for the line-load design. In the vertical direction, 80 grid-block layers are used to represent 
the hydrostratigraphy; thus, the point-load design requires 1,280 grid blocks, whereas the lineload 
design requires 1,440 grid blocks. 
Thermal and hydrological properties were established based on the base-case property set, using 
information from thermal testing and site-scale measurements.

 3-57 
Source: Hardin 1998, Figure 3-14 
NOTE: This diagram is a segment of the model domain; the full domain extends between mid-pillar locations and 
from the ground surface to the water table. 
Figure 3-23. Vertical Cross Section of the Emplacement Drift in the DDT and LDTH Model Showing the 
Thermal Radiation Connections Among the Surfaces in the Drift that are used in Thermal 
Simulations

 3-58 
3.2.3.3.2 TH Model Results for Line and Point Loading 
Figure 3-24 (a through l) shows contour plots around two drifts for temperature and liquid 
saturation in the x-z plane for point loading at t = 50, 100, 500, 1,000, 2,000, and 5,000 years, 
respectively. A single drift is shown in Figure 3-25 (a through l) for the line-load. The figure is 
representative of a line-loaded repository with a drift spacing of 56.6 meters as opposed to 
81 meters, which is the drift spacing utilized as the base case in TSPA-SR. 
For the line-load design (characterized by close waste package spacing and wide emplacement 
drift spacing), there is no significant dryout (<50 percent saturation) at the mid-pillar and the 
100C isotherm never coalesces between the drifts (Figure 3-25). However, for a point loading 
(Figure 3-24) design (characterized by waste package spacing on the order of emplacement drift 
spacing), the entire pillar (at 500 years) boils and pillar saturations are less than 60 percent 
(about 15 m below the repository horizon). The heat-flux density, which is greater by a factor of 
two along the line-load drifts, as compared to the point-load drifts, results in much higher 
temperature rise (and a much steeper temperature gradient) in the vicinity of the drifts than for 
point-loading. The line-loaded design is incorporated in the TSPA-SR model. The line-loaded 
drift contains very closely spaced waste packages (separation distance of 0.1 meters) which tends 
to concentrate the heat along the axis of the loaded drift. In the vicinity of the waste packages, 
closely spaced neighboring waste packages share heat with each other and along the drift wall 
causing locally higher temperatures within the loaded portion of the drifts. The thermal gradient 
along the axis of the drift is uniform due to a nearly uniform heat sharing between waste 
packages. The temperature gradient radially away from the waste package is much larger for the 
line-loaded design due to the local concentration of heat near closely spaced waste packages. 
The point-loaded drift contains a much wider waste package spacing. For this design, heat 
sharing between waste packages is far less prevalent and hence the axial thermal gradient is very 
non-uniform as one transitions along the drift when including waste package heat output 
variability. Since the heat output surrounding neighboring waste package is not as concentrated 
(e.g., not shared), local temperatures are much lower. Subsequently, the radial temperature 
gradient away from the waste packages is not as large as that developed in the line-loaded 
design. 
The key point from comparison of line and point loads at the common ambient fluxes and 
properties in this section is that the line load had the potential to dryout NF rock, while 
maintaining pillar drainage. In contrast, the point load had less NF dryout and a period of pillar 
blockage. 
These differences are subtle in Figures 3-24 and 3-25, but are more pronounced in the more 
widely spread drifts considered in LADS. The following more detailed observations were made 
about the TH behavior modeled in these and related calculations: 
 Liquid flux is much greater than percolation flux for early time (t =100-500 years), 
then gradually declines to the magnitude of percolation flux. 
 Liquid flux is insensitive to percolation flux for early time (less than 200 years). At 
100 years, liquid flux is nearly the same for all of the percolation flux cases considered. 
Therefore, when liquid flux is greatest (i.e., early time), it does not depend on the

 3-59 
magnitude of percolation flux. For later time (greater than 200 years), the magnitude of 
liquid flux increases with percolation flux. 
 Liquid flux above the drifts is the same for the point- and line-load designs. The 
magnitude of liquid flux depends only on the total heat flux available to mobilize water 
and not on how efficiently condensate sheds around the drifts. The more efficient 
condensate shedding for the line-load design results in less return flow of condensate to 
the drift from the previous refluxing cycle. The heat not required to repeatedly boil the 
condensate shed off to the sides is, in effect, excess heat that is available to mobilize 
additional water vapor from the rock matrix. Thus, the total return flow of condensate 
toward the drift comprises water from the previous refluxing cycle, plus water vapor that 
has just been mobilized from the rock matrix and condensed in the fractures. The only 
difference near the drifts between the point- and line-load designs is that a larger 
fraction (compared with the point load) of the heat for the line load is available for rock 
dryout, which allows the upper dryout front to advance more rapidly for the line load 
than for the point load. 
 The vertical length of the heat-pipe zone is less for the line load than it is for the 
point load at early time. For low percolation flux, the heat-pipe-zone length is also less 
for the line-load design at later times. The smaller heat-pipe-zone length for the lineload 
design arises from the more efficient condensate drainage between the line-load 
drifts, which results in less condensate build- up above the line-load drifts. 
 The vertical length of the heat-pipe zone increases with repository depth below the 
ground surface. 
 The tendency for dryout zone coalescence decreases with increasing percolation flux 
and is less for the line-load design than it is for the point-load design. 
It is stressed that the results illustrated in this section are not directly applicable to the TSPA-SR 
repository design and how it may evolve in time after the emplacement of heat generating wastes 
in the unsaturated zone at Yucca Mountain. However, the results and knowledge gained from 
TH analysis of previous repository designs provides a strong technical basis for project decisions 
made to mitigate and/or emphasize certain processes in the base case TSPA-SR design. 
Specifically, the knowledge gained from previous analyses allowed the specification of certain 
design criteria (for TSPA-SR) that would eliminate the processes associated with coalescence of 
dryout zones between emplacement drifts, thus limiting the ability of the system to allow 
thermally enhanced condensate drainage to occur between drifts. Based on this knowledge, the 
drift spacing is increased from the 28 meter spacing specified for the point-loaded VA repository 
design to an 81 meter spacing for the SR design. An increased drift spacing for TSPA-SR also 
serves to greatly lower the total thermal load (kW/acre at closure) of the repository when 
combined with a preclosure ventilation period. This reduces the host rock temperatures thereby 
decreasing or eliminating many of the TH processes discussed in this section. Specific TH 
results for the SR repository design (without backfill) are shown in detail in Section 3.2.3.1 in 
this PMR as well as in the Multiscale TH AMR (CRWMS M&O 2000k) and the In-Drift 
Environment AMR (CRWMS M&O 2000m, Section 6). Confidence in the TH NFE models is 
further discussed in Section 3.6.4.1.

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Source: Hardin 1998, Figure 3-17 
NOTE: Contour labels and color bars indicate values. 
Figure 3-24. Temperature and Liquid-Phase Saturation Distributions for Point 
Loading of 28 m-Spaced Drifts (Page 1 of 2)

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Source: Hardin 1998, Figure 3-17 
NOTE: Contour labels and color bars indicate values. 
Figure 3-24. Temperature and Liquid-Phase Saturation Distributions for Point 
Loading of 28 m-Spaced Drifts (Page 2 of 2)

 3-62 
Source: Hardin 1998, Figure 3-19 
NOTE: Contour labels and color bars indicate values. 
Figure 3-25. Temperature and Liquid-Phase Saturation Distributions for Line Loading of 
56.6 m-Spaced Drifts (Page 1 of 2)

 3-63 
Source: Hardin 1998, Figure 3-19 
NOTE: Contour labels and color bars indicate values. 
Figure 3-25. Temperature and Liquid-Phase Saturation Distributions for Line Loading of 
56.6 m-Spaced Drifts (Page 2 of 2)

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3.2.3.4 Comparison of Results from TH and THC Models 
In this section, the TH output variables used to describe the performance of a geologic repository 
with decay heating are compared using the 2-D DS THC model, a 2-D DS model extracted from 
the multiscale TH model, and the full MSTHM results that include repository edge effects. The 
resulting process model comparisons are for a repository design that includes 50 years of 
ventilation at 70 percent heat-removal efficiency, with backfill and drip-shield emplacement at 
repository closure. The specific analyses summarized in this section of the PMR are necessary to 
determine which process-level models of varying degrees of complexity can be used to address 
various process issues associated with repository heating. Quantities used by TSPA that are 
altered by repository heat-addition include the in-drift temperature and relative humidity, driftwall 
temperature, drift-wall liquid saturation, percolation flux in the NF host rock, and water and 
gas composition at the drift wall. This section focuses primarily on the coupled processes of 
reactive transport and thermal hydrology, and how these interact in the NF host rock. Arguments 
are made that some of the quantities of interest to TSPA do not need to be computed with a 
model that includes fully-coupled reactive transport with thermal hydrology. That is, a thermalhydrology 
model uncoupled from reactive transport is sufficient. This simplification allows one 
to neglect the additional mass-transport equations for individual species, as well as the chemical 
thermodynamics and kinetics associated with precipitation or dissolution reactions. 
Although also initiated by repository heating, mechanical processes occurring in the NF host 
rock are not included simultaneously with the processes described in this section. They are 
decoupled from the processes of chemistry and hydrology and described separately in 
Section 3.5 of this PMR. 
In the cases where water and gas compositions are required in the NF drift-wall host rock, fullycoupled 
reactive-transport models, including thermal hydrology, are required. Although 
uncertainties exist in how the reactive-transport model describes mineral-water chemical 
reactions in its process description (refer to Section 3.3.4), the chemical content of the water and 
gas can be obtained within the framework of the assumptions applied in the THC process model. 
The anion, cation, pH, and partial pressure of CO2 concentrations abstracted from the THC 
process model are fixed by reactive-transport assumptions and inputs, such as mineral reaction 
rate constants, activation energies, mineral reactive-surface areas, and mineral contents and 
compositions. Other assumptions and inputs associated with flow include infiltration flux and 
climate-state variability, along with the conceptual flow model used to describe heat and fluid 
flow. Of particular importance is how fluid-flow properties (such as fracture permeability) are 
altered in response to mineral-water chemical reactions. The THC process model assumes 
parallel-plane fractures of uniform aperture, relating changes in fracture porosity (which can 
increase when minerals dissolve or decrease when minerals precipitate) to subsequent changes in 
fracture permeability and capillary pressure. Consequently, the abstracted water chemistry and 
gas composition used by TSPA and summarized in Section 3.4 are applicable in the time periods 
shown and only for these assumptions that form the basis of the process model. Furthermore, the 
abstraction for TSPA, shown in Table 3-11 in Section 3.4 is valid only for the mean infiltration 
flux case (with climate change), but would require only a factor of 2 to 10 change in 
concentrations to account for the full range of infiltration-flux cases considered by other TSPA 
models (refer to Section 3.4.2.2).

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In the cases where in-drift thermodynamic environment or NF percolation flux are concerned, it 
is argued in this section that recourse to a fully-coupled reactive-transport code with thermal 
hydrology is not necessary. TSPA can obtain the desired quantities (waste package temperature, 
drift-wall temperature, host-rock percolation flux, etc.) for abstraction purposes from a process 
model that includes thermal hydrology only. A thermal-hydrology model computes the flow of 
fluid and heat without physical alteration to fluid-flow properties by dissolution or precipitation 
mineral-water reactions. Since the TH-only model neglects chemical alteration to the flow 
properties, an evaluation (of the differences between THC and TH-only models) in both state and 
flow variables is presented in the THC Abstraction AMR (CRWMS M&O 2000c, Section 6.3) 
and summarized in this section. Primary focus of the PMR discussion is on how differences may 
occur in flow variables between models, since the changes in flow properties by dissolution or 
precipitation are neglected in the TH-only models. 
The result of the process-model evaluations described in Sections 3.2.3.4.1 and 3.2.3.4.2 indicate 
that the flow and state variables in the NF host rock are nearly identical for two different 
geochemical systems and are not appreciably different for models that may or may not include 
reactive transport (Section 3.2.3.4.2). The no-consequence conclusion of this process-model 
evaluation is primarily a result of the fracture porosities applied in the THC process model 
(1 percent) (CRWMS M&O 2000a, Table 5). For such initially large fracture porosities, the 
relative change in the fracture volume as a result of precipitation or dissolution is quite small. 
This results in little or no change in the fracture liquid or gas flows. For small initial porosity (as 
applied in TSPA-VA), reactive transport processes result in much larger changes in the flow 
variables, when compared to TH-only calculations, due to larger relative changes in fracture 
volume. 
In addition to providing an abstraction for water chemistry and gas-phase composition in the NF 
host rock, the THC Abstraction AMR (CRWMS M&O 2000c) also serves to illustrate the 
potential differences in the thermal-hydrologic response of a potential repository obtained from 
process models that either do or do not include reactive-transport processes coupled with the 
thermal-hydrologic processes that occur in response to repository heat-addition. An initial 
comparison is made with the DS THC model that includes fully-coupled reactive-transport 
processes for two mineral sets: complex and reduced. This evaluation compares drift-wall host 
rock temperature, liquid saturation, air mass fraction, gas flux in fractures, and liquid flux in 
fractures (CRWMS M&O 2000c, Section 6.2). The purpose of the TH variable comparison from 
the same process model that incorporates two different geochemical systems is to highlight that 
the resultant differences in the NF rock mineralogy only weakly influences the overall TH 
response of the geologic system. Another evaluation in the THC Abstraction AMR compares 
process-level models that incorporate the same boundary conditions and repository 
specifications, but may not include all of the fully-coupled processes in the rock that occur in 
response to heat-addition. 
A comparison of process-level models (TH-only vs. THC) is considered in the THC Abstraction 
AMR (CRWMS M&O 2000c, Section 6.3). Since the DS THC model described above has been 
developed independently of the TH-only model used to determine the in-drift thermodynamic 
environment (CRWMS M&O 2000k), a 2-D DS, TH-only model taken directly from the 
Multiscale TH AMR (CRWMS M&O 2000k, Section 6.3) is compared to the TH results of the 
2-D DS THC model developed in the THC Process AMR (CRWMS M&O 2000b). This

 3-66 
comparative analysis is used to determine whether (and how) reactive-transport processes 
occurring in the host rock as a result of repository heat-addition alter the fundamental TH 
properties of the geologic system (e.g., temperature, liquid flux in fractures, etc.). An evaluation 
of this type allows an assessment of the appropriateness of an abstraction of TH variables that 
describe the performance of a geologic repository from a process-level model that does not 
include the fully-coupled reactive-transport processes. (This is the approach used in the TSPA 
abstraction of the TH variables used to describe repository performance, since reactive-transport 
processes do not appreciably alter fracture flows.) 
A final comparison is made in the abstraction AMR (CRWMS M&O 2000c, Section 6.4). The 
DS THC model thermal-hydrologic results are compared to the multiscale TH model (CRWMS 
M&O 2000k, Section 6.1) results at the emplacement drift-wall. This evaluation provides an 
assessment of the extent of repository edge effects (and how this may affect the THC 
abstraction) on the TH variables obtained from DS models that incorporate no-flow lateral 
boundary conditions (e.g., do not include edge effects). Both the 2-D DS TH-only and THC 
models compared in Section 6.3 of the THC Abstraction AMR apply the no-flow boundary 
assumption on the lateral boundary conditions. 
3.2.3.4.1 TH Model 
The major TH model-set supporting this PMR is the MSTHM. One component TH submodel is 
a 2-D column model similar to the THC models described in Section 3.3. That is, essentially 2- 
D radial heat flow into the host rock with no flow boundaries at the pillar half-spacing. Another 
submodel in the MSTHM calculates the 3-D heat flow from a smeared heat source that is in the 
shape of the repository footprint. A third MSTHM sub model calculates the 3-D heat flow in a 
column that includes a set of discrete waste packages with a distribution of thermal powers that 
is consistent with the overall repository-wide distribution, based on the variability of the waste 
stream and the blend ing of hot and cold waste within individual waste packages. Two- and 
three-dimensional columns are calculated in a number of locations, edge and central, to capture 
the variability of geological conditions. 
The results of the MSTHM submodels are combined to capture the time- and space-dependent 
temperature and saturation distributions, including effects of the repository footprint edges, the 
distribution of geologic properties and ambient percolation flux, geometric effects at the drift 
scale, and the effects of variability in heat output of individual waste packages. 
The MSTHM submodels are implemented using the NUFT heat and mass transfer code 
(CRWMS M&O 2000k). As in the THC model described in Section 3.3, the 2-D DS submodels 
used in the MSTHM are also based on an active-fracture, DK conceptual flow model for matrix 
and fracture continua. 
The MSTHM submodels that calculate the space- and time-dependent temperatures, saturations, 
and percolation fluxes are used in the TSPA models. The TH models also calculate the spaceand 
time-dependent temperatures and relative humidities within the emplacement drifts, as 
described in the EBS PMR (CRWMS M&O 2000g, Section 3.1.4). These results are key inputs 
to performance of the engineered barriers (drip shields and waste packages), described in the

 3-67 
WPD PMR (CRWMS M&O 2000o) and the mobilization of radionuclides from breached waste 
packages, described in the WFD PMR (CRWMS M&O 2000ab). 
It is noted that this ensemble of TH models can be used to approximate the effects of waste 
package-edge proximity, variability in host rock in which heat is placed, variability in infiltration 
rate and climate-state, and variability in heat output for different waste package-types. The 
mineral-water reactio ns or ambient rock-stress alteration that proceed in the fractures or matrix 
in response to repository heat-addition are not included in these models. Therefore, flowproperty 
(and hence flow-rate) alterations by precipitation or dissolution reactions or tension and 
compression processes are not included in this modeling ensemble. Although an increase in 
model complexity occurs as a result of including, for instance, lateral heat losses due to 
surrounding unheated rock masses, the processes initiated by heat, other than thermal hydrologic 
processes, are not included. Since this is the case, an evaluation of neglecting these heat-induced 
processes in the TH models used by TSPA for abstraction is necessary. A comparison of THonly 
to THC processes is considered in the following sections. 
3.2.3.4.2 THC Model 
The THC models supporting this PMR are described in more detail in Section 3.3. 
In the results described below, the THC model is implemented at a location in the northeast part 
of the potential repository footprint, in which the repository horizon is located in the middle nonlithophysal 
geologic sub-unit (referred to as the Tptpmn or tsw34 sub-unit); this permits use of 
thermal and hydrologic properties as well as measured water chemistry and gas compositions 
obtained from the DST. 
The THC models account for 2-D heat and mass transfer within the drifts and in the surrounding 
rock, using separate continua in the rock to represent the connected network of fractures and the 
rock matrix in which the fractures reside. Movement of mass (liquid water, water vapor, and air) 
between the fractures and matrix is calculated using a submodel, termed an active-fracture 
DKM. This flow model specifies a means for fracture flow through the system. The THC 
models available for TSPA abstraction only include mineralogical-water reaction processes 
occurring in the host-rock matrix and fracture pore space; the chemical evolution of the 
emplacement drift is not included. Subsequently, the evolution of gas in the emplacement drift 
due to chemical (e.g., interaction of heat with backfill materials) or radiolitic processes is not 
included in the THC process model. 
The THC models include chemical reactions in selected geochemical systems. Two system are 
considered in the results described below. A Less Complex system includes H2O, H+, Ca2+, Na+, 
SiO2, Cl-, HCO3
-, and SO4
2- as main component species and all other aqueous species that can be 
derived from these components, together with CO2 gas and Calcite, Tridymite, "-Cristobalite, 
Quartz, Amorphous Silica, Glass, and Gypsum. 
A complex system includes H2O, H+, Na+, K+, Ca2+, Mg2+, SiO2, AlO2
-, HFeO2, Cl-, HCO3
-, 
SO4
2-, and F- as main component species and all other aqueous species that can be derived from 
these components, together with CO2 gas and Calcite, Tridymite, "-Cristobalite, Quartz, 
Amorphous Silica, Glass, Gypsum, Hematite, Fluorite, Goethite, Albite, Microcline, Anorthite,

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Ca-Smectite, Mg-Smectite, K-Smectite, Illite, Kaolinite, Sepiolite, Stellerite, Heulandite, 
Mordenite, and Clinoptilolite. 
This section compares the THC DS model (using the complex set of cations and anions listed 
above) to the Multiscale TH AMR (CRWMS M&O 2000k, Section 6.6). The multiscale model 
considers repository edge-cooling effects and WP thermal output variability, in addition to the 
thermal-hydrological processes considered by both models. The comparison focuses on the 
drift-wall temperatures and liquid saturations. For computational efficiency, the periodic lateral 
boundary conditions of DS models, such as the THC model, simulate a location at the center of 
an infinite repository. The limitations of this assumption are most pronounced near the 
repository edges, but can also influence temperatures at the repository center after enough time 
has passed. The results of this comparative analysis will provide TSPA with the basis to perform 
temperature-dependent alterations to the THC abstraction, so that edge effect cooling may be 
accounted for in the abstraction of aqueous species concentrations and gas phase compositions. 
3.2.3.4.3 The Influence of the THC Chemical Constituents on TH Parameters 
The TH output variables (gas flux, liquid flux, temperature, liquid saturation, and air mass 
fraction) are compared in this section, based on two implementations of the THC model, using 
the less detailed and more-detailed sets of chemical constituents (see Section 3.3.2.4). In 
particular, this comparative analysis evaluates how different geochemistry (e.g., including 
different mineral assemblages) may alter the TH variables associated with repository heating. 
The analysis uses the mean infiltration rate with climate change (as described in CRWMS 
M&O 2000b, Table 12) and compares conditions at the drift crown. 
The analysis (CRWMS M&O 2000c, Section 6.2) shows that the two geochemical systems result 
in nearly identical TH parameters at the drift crown. In each case, the calculations involving 
more minerals produced the same temperature, liquid flux, gas flux, air mass fraction, and liquid 
saturation as the calculations involving fewer minerals. Furthermore, this trend is true for the 
other drift-wall locations (side and base), as well as the other infiltration-flux cases (high and 
low). Therefore, the geochemical and reactive transport alterations to the flow (and 
characteristic) properties, as described in the THC Process AMR (CRWMS M&O 2000b, 
Section 6.1.6, Equations 16-19), are not enough to impact the fundamental properties of the 
repository system associated with heating processes (e.g., host-rock temperature adjacent to the 
emplacement-drift wall). This also holds true for the low and high infiltration cases considered 
in the THC Process AMR (CRWMS M&O 2000b, Table 12). 
The results in this section are based on a fracture porosity of about 1 percent. The results 
indicate that dissolution and precipitation would be inadequate to significantly alter fracture-flow 
capability. For a significantly smaller fracture porosity, the calculated amount of mineral 
precipitation could be enough to reduce fracture flow in the NF region above the drift. In 
addition, the limitations of continuum modeling do not permit the calculation to address 
concentration of precipitation in localized regions, which could potentially reduce fracture flow 
significantly, even when the overall porosity reduction is not large; these types of localized 
effects are well known in chemical engineering and biological systems. Ongoing work may 
address the localized effects. As indicated previously, chemical interaction of gas constituents

 3-69 
contained within the emplacement drift and how they may interact with the NF host rock are not 
included in the reactive-transport processes occurring in the NF host rock. 
3.2.3.4.4 Comparison of TH Parameters from the 2-D THC and 2-D TH-Only Models 
Both the THC and TH-only DS models use the same conceptual flow models (DKM/AFM). The 
TH DS model, as described in a line-averaged-heat-source, DS, Thermal-Hydrological (LDTH) 
submodel selected from the Multiscale TH AMR (CRWMS M&O 2000k, Section 6.3), is 
compared directly to the THC DS model. For consistent boundary conditions, the selected 
LDTH model location, l3c1, is near the stratigraphic location of the THC model (i.e., near the 
northeast section of the repository, located near borehole SD-9). See Figures 3-1 through 3-3 for 
LDTH column locations. Both models use periodic boundary conditions laterally (e.g., 
symmetry boundary along the drift centerline and a no-heat or mass-flow boundary at the pillar 
midpoint). Both also use similar (calculated) initial matrix saturations and identical 
infiltration-rate boundary conditions and climate-state changes. In the THC Abstraction AMR 
(CRWMS M&O 2000c), the l3c1 infiltration-rate boundary condition is altered from the 
Multiscale TH CRWMS M&O (2000k) to be consistent with the THC model. Finally, the timedependent 
heat-source thermal outputs are also identical. The DS models that apply a mean 
infiltration flux-case with climate changes at 600 and 2,000 years are used in this comparison. 
At both the crown and side of the drift wall, preclosure temperatures agree for the two models, 
within a degree or two. Between closure and 2,000 years, the THC model calculates higher 
temperatures than the TH model, up to 8oC. Because the THC temperatures are higher, the 
reaction kinetics will increase so that the THC analyses represent bound conditions. After 
2,000 years, until about 20,000 years, the THC model temperatures are up to 6oC lower than the 
TH model. The results of THC analyses for this period of time cannot be assumed to represent 
the bound case, since the temperatures (and thus kinetics) are lower. After 20,000 years, the two 
models produce identical temperatures, within a fraction of a degree (CRWMS M&O 2000c, 
Figures 8-9). The differences during the above boiling period are primarily due to the difference 
in the amount of water in the host rock-matrix at these locations near the drift wall. This is 
primarily driven by differences in implementation of the capillary-pressure curves in the models. 
In both models, at the crown of the emplacement drift, all of the water is driven out of the 
fractures during the above boiling period. However, both before and after boiling, the TH model 
calculates a few percent higher fracture saturation than the THC model (CRWMS M&O 2000c, 
Figure 11). This difference (which is calculated prior to the addition of heat, during the 
establishment of equilibrium initial conditions) is most likely due to subtle differences in how the 
AFM is implemented in the two models. Of particular importance is how the capillary pressure 
curve is treated at low fracture saturations (linearization or capillary pressure cut-off). 
Both models result in similar air compositions near the drift wall (CRWMS M&O 2000c, 
Figures 12 and 13). The gas flux in the fractures at the crown of the drift is similar between the 
two models during the preclosure period. During the above boiling and transition periods, the 
TH-only model predicts higher gas (air) fluxes than the THC model (CRWMS M&O 2000c, 
Figure 14). The difference in gas flux between models at this (crown) location during the boiling 
period is about two orders of magnitude lower in the fully coupled model. This difference is 
attributed largely to the extensive boiling zone developed in the THC model, but not present in

 3-70 
the corresponding TH-only model. During the boiling period in the THC model, a large amount 
of water is driven out of the matrix (vaporized), thereby decreasing the air mass fraction at this 
location during this time period. Subsequently, the air mass fraction from the THC model during 
boiling is somewhat lower than that from the TH-only model. As a consequence, the air flow 
near the crown of the drift during the boiling period in the THC model is primarily attributed to 
diffusion which occurs at a much lower rate than advection. After boiling, the models are in 
agreement to within about an order magnitude or less out to about 1x105 yr. The late time 
response is generally more important to TSPA since chemical environments associated with later 
times are more pertinent to EBS corrosion. Figure 3-26 (CRWMS M&O 2000c, Figure 15) 
shows the magnitude of the fracture liquid flux at the crown of the drift. Although the trends of 
the two models are similar, the liquid flux in the TH-only model is slightly greater at this 
location except for the early time spike shown in the figure. The differences in liquid flux at the 
side and at the base of the emplacement drift are largely driven by the no-flow boundary drift 
wall assumption made in the THC model (CRWMS M&O 2000b, Section 5, assumption C.1). 
This results in flow being diverted around the drift wall. The TH model allows water to cross the 
drift wall interface at locations in the emplacement drift where the backfill material contacts the 
drift wall. Consequently, at the drift base in the TH model, the percolation fluxes in the fractures 
will be larger, because water from the backfill drift-wall interface is not diverted around the drift 
opening (CRWMS M&O 2000c, Figure 16). 
The spike in the fracture-liquid flux shown in Figure 3-26 coincides with the time of repository 
closure (50 years). At the time of closure, repository ventilation ceases (all remaining waste 
package heat output is now available for host-rock heating), and backfill and drip shields are 
emplaced in the drifts. Enhanced liquid flow back to the crown of the drift occurs when water 
evaporated during the preclosure period condenses in the fractures (recall that 30 percent of the 
waste package heat was available for input into the surrounding host rock) immediately at the 
time of backfill emplacement. After about 20 years of ventilation, the heat removal rate by 
ventilation exceeds the waste form heat rate, and drift temperature decreases. At closure, 
ventilation ceases and backfill is added. During the time immediately following backfill (only 
for the first year after backfill), the drift-wall crown temperature drops slightly due to an 
increased resistance (represented by the low thermal-conductivity backfill) to heat flow between 
the waste package and the drift wall. When the backfill has been heated, drift wall temperatures 
begin to increase due to the lack of heat removal by ventilation. The drift wall rapidly increases 
in temperature (Figure 3-27) and the liquid flux is driven to zero (a few years after backfill).

 3-71 
Crown Liquid Flux, Mean Infiltration Parameter Set 
0.0E+00 
1.0E-06 
2.0E-06 
3.0E-06 
4.0E-06 
5.0E-06 
6.0E-06 
7.0E-06 
8.0E-06 
9.0E-06 
1.0E-05 
1 10 100 1,000 10,000 100,000 1,000,00 
0 
Time (years) 
Liquid Flux (kg/s/m 
2) 
THC Model 
TH-only Model 
Source: CRWMS M&O 2000c, Figure 15 
Figure 3-26. Host-Rock Fracture Liquid Flux at the Emplacement-Drift Crown 
20 
30 
40 
50 
60 
70 
80 
90 
100 
110 
120 
130 
1 10 100 1000 10000 100000 1000000 
Time (years) 
T (oC) 
Case 1 T Crown 
csnf_x21_y19 T DW U 
csnf_x22_y19 T DW U 
csnf_x23_y19 T DW U 
csnf_x24_y19 T DW U 
Source: CRWMS M&O 2000c, Figure 17 
NOTE: The multi-scale model used mean infiltration rate with climate change. The four csnf curves are the multiscale 
model results at four locations in the repository footprint. The Case 1 curve is from the THC model. 
Figure 3-27. Comparison of Drift Crown Temperatures Using the THC Model Multiscale TH Model

 3-72 
The small differences (<10%) in process-model predictions of fracture flux (both liquid water 
and air) at the crown of the drift are potentially attributed to reactive-transport processes 
occurring in the THC model and/or potential differences in model implementation of capillary 
pressure characteristic curves, which may alter the driving force for the fluxes. In regions of 
precipitation around the emplacement drift at the crown, potential permeability reductions caused 
by mineral precipitation in the fractures of the THC model could result in the reduced gas and 
liquid fluxes, when compared to the TH-only model (in which permeability remains unchanged 
after pore water boiling). If the conventional cubic law (Raven and Gale 1985) is used, a 
1 percent reduction in fracture aperture will cause a 3 percent reduction in fracture permeability. 
Relative permeability to water is a function of saturation. Fracture volume (aperture) changes, if 
water volumes remain constant, may result in increased fracture saturation. Thus, a 3% 
reduction in permeability may result in fluid flux reductions between zero and 3%. 
From Figure 3-26, the late-time ratio (10,000 years) of percolation flux from the THC model to 
the TH-only model is 0.94. This difference is of similar magnitude to the cubic law estimation 
of flux (permeability) changes due to aperture decreases. Subsequently, the reactive-transport 
processes and/or potential differences in characteristic curve implementation between models in 
the fracture medium causes a very slight reduction in the liquid-phase flux in the fractures. 
Therefore, as indicated previously when comparing state variables (e.g., temperature), either 
model is appropriate when predicting the TH flow variables used to determine the performance 
of the potential repository. 
Indeed, when the quantities of interest are the thermodynamic variables within the emplacement 
drift or the NF host rock percolation flux (e.g., temperature and relative humidity in the 
engineering barrier system components and percolation flux at the crown of the drift), the 
TH-only model is preferred since its computational complexity is far less than that of a fully 
coupled reactive transport model. However, if an assessment of the water chemistry and 
gas-phase composition is required, a fully coupled reactive transport model is needed. 
3.2.3.4.5 Comparison of Temperatures from the Multi-Scale TH Models with a 2-D 
Mountain-Scale Model 
The 2-D Mountain-Scale TH model described in Section 3.2.2.2 was used to calculate 
temperature along a north-south section through the repository. A typical result is shown in 
Figure 3-28 (CRWMS M&O 2000f, Figure 3.12-5b). The rock temperatures at 1,000 years are 
similar to the drift wall and pillar temperatures shown in Figures 3-7 and 3-8. The two models 
are complementary. The 2-D model captures mountain-scale convection spanning ~10 drifts (in 
the N-S direction only) not currently modeled in the MSTHM and is well suited to calculate 
pillar temperature where gradients are not as steep as at the drift wall. Its coarse zoning near the 
drifts results in an underprediction of drift wall temperature at the peak of the thermal pulse 
(earlier than shown in Figure 3-33). Conversely, in addition to more accurate peak drift wall 
temperatures, the MSTHM addresses a number of factors not included in the 2-D mountain-scale 
model, such as E-W edge and property effects and axial heat source variation.

 3-73 
Source: CRWMS M&O 2000f, Figure 3.12-5(b) 
Figure 3-28. Temperature Distribution Calculated at 1,000 Years in a 2-D Mountain-Scale TH Model 
3.2.3.4.6 Repository Edge Behavior 
The THC Process AMR does not include repository edge effects (e.g., lateral heat loss to 
unheated rock mass) since it implements periodic boundary conditions in its model formulation. 
This DS modeling assumption is generally more representative of the repository center where a 
particular emplacement drift is flanked on either side by additional heated drifts. An edge 
location is surrounded by unheated rock masses without drifts. Since it is postulated that edge 
heat loss due to the absence of neighboring heated drifts affects both the temperature and liquid 
saturation evolution at the boundaries of the potential repository, a comparison is made between 
process models that include varying complexity associated with repository edge heat losses. As 
discussed in Section 3.2.3.4.1, the multiscale TH model includes edge-heat loss in its 
formulation. Therefore, an assessment can be made as to the duration and influence of not 
including the edge effect in the 2-D model. The comparison of models is made at a location in 
the repository footprint in which the geologic stratigraphy and infiltration rate are nearly 
identical (e.g., infiltration rates are identical). Temperature and liquid saturation at the crown of 
the emplacement drift are compared. 
The edge-cooling effect results in dramatically lower temperatures in the multiscale TH model at 
the drift wall (CRWMS M&O 2000c, Figures 17-18). The drift-wall crown temperatures at this 
near-edge location are 30-40oC lower in the multiscale TH model, from about 200 to 800 yr.

 3-74 
Each of the potential repository footprint locations shown in Figure 3-27 indicates a variety of 
location-dependent results of an average drift wall temperature from the multiscale TH model 
near the THC model domain. Four different locations are specified from the multiscale TH 
model domain for comparison to the THC model. For example, location CSNF_x21_y19 T DW 
U represents a location-dependent result (stratigraphically) near the THC model domain for the 
upper drift wall adjacent to an average CSNF waste package. The peak temperature, which 
occurs between closure and 100 years, is about 10oC lower in the multiscale model, due to the 
repository edge-effect at this location. 
Corresponding differences in liquid saturation occur as well (CRWMS M&O 2000c, Figure 19). 
In the multiscale TH model, liquid saturation at the crown of the drift resaturates much more 
quickly (within a few centuries) than does the DS THC model (within a few millennia). This is 
primarily due to a lower maximum temperature and about 900 fewer years of temperatures above 
boiling at this location. 
The temperature comparison between a model that includes edge effects (multiscale TH model) 
to a model that does not (the THC model) illustrates how lateral heat loss influences the drift 
wall thermal conditions over time. Since the THC model was based on a borehole at a location 
near the edge of the potential repository (but the model applies periodic no-flow lateral boundary 
conditions, i.e., representative of the center repository), an assessment of the potential 
temperature and moisture conditions at the drift wall is made with this edge proximity 
comparison to determine if the duration of boiling obtained from the THC model may be 
overestimating the time at which the drift wall is dry. The result is that although the extent and 
duration of the boiling zone predicted by the THC model may be in direct response to a 
modeling assumption (e.g., periodic boundary conditions), the TSPA abstraction estimates the 
water chemistry at the drift wall during this boiling period by using the water chemistry obtained 
(from the DS THC model) in the condensate zone that develops above the boiling region. This 
approach minimizes the impact of the boundary conditions and ensures that an appropriate water 
chemistry is used. This compositional boundary condition is then applied during the abstracted 
boiling period in conjunction with other models to determine the in-drift geochemical 
environment at all potential repository locations. 
The abstraction of the condensate water composition applied at the drift wall during the boiling 
period is considered appropriate for the water that may potentially enter a heterogeneous fracture 
network and flow by gravity from the condensate zone to the drift wall (the location of the THC 
abstraction). This effective water composition at the emplacement drift wall during the boiling 
period is then coupled with the TSPA seepage model used to determine the volume flow rate of 
water into the drift in order to determine the quantity and chemistry of the water entering the 
emplacement drifts. This method is applied at all locations within the repository, center or edge, 
and is considered reasonable since the combination of different models (e.g., seepage model, 
THC model, and multiscale TH model) used to determine the physical and chemical environment 
within the drifts accounts for each of the different processes separately. 
Since the TSPA seepage model utilizes the percolation flux from a location in the multiscale TH 
model which is always greater than or equal to the ambient fracture percolation flux, a water 
composition (adjacent to the drift wall) is required from the THC model that tends to predict the 
development of an extended dryout zone, since the process of edge cooling is not included in its

 3-75 
model development. In order to provide the necessary water chemistry at the emplacement drift 
wall, the condensate composition above the dryout zone predicted by the THC process model is 
used as the composition of water that could potentially flow from the condensate zone to the drift 
wall. The TSPA models for the in-drift geochemical environment utilize location dependent 
temperatures and relative humidities from the multiscale TH model, as well as the seepage 
volume flow rate obtained as a function of the percolation flux computed from the multiscale TH 
model. As a consequence, the condensate water chemistry from the THC Process AMR, coupled 
with the appropria te location-dependent in-drift thermodynamic environment from the multiscale 
TH model provides for an approximate location-dependent (e.g., center and edge) geochemical 
result obtained from the abstracted in-drift chemical environment models. 
3.2.3.4.7 Conclusions of the TH Model Comparison 
As indicated by this process-model evaluation (Sections 3.2.3.4.3 and 3.2.3.4.4) of 
reactive-transport impact on TH performance of a potential geologic repository, either model is 
appropriate when predicting the TH state (temperature, liquid saturation) or flow variables 
(percolation flux) required by TSPA. Permeability reduction is approximately 3 percent, as 
described by parallel-plate (uniform-aperture) theory (CRWMS M&O 2000b, Equation 17). 
Figure 3-26 indicates a difference in liquid flux between models that can be explained by this as 
well as by potential difference in the driving forces in the models. As shown in the figures, the 
fracture liquid flow rates at the crown of the drift are nearly the same regardless of the 
model-type (THC or TH-only). It should be kept in mind that the results of this evaluation are a 
function of the initial fracture porosity used in the reactive-transport model. If the fracture 
porosity were to decrease, the chemically altered fracture permeability would be very different 
from the initial fracture permeability. 
Since the differences (in state and flow variables) between models used to describe the 
performance of a potential geologic repository are small, TSPA can accept TH variables (i.e., 
drift-wall temperature, percolation flux in the NF host rock, etc.) that describe the performance 
of a potential geologic repository from models of either type (THC or TH-only). Indeed, when 
the quantities of interest are thermodynamic variables within the emplacement drift or the NF 
host-rock percolation flux (e.g., temperature and relative humidity in the EBS components and 
percolation flux at the crown of the drift), the TH-only model is preferred since its computational 
complexity is far less than that of a fully-coupled reactive-transport model, and accounts for 3-D 
and edge effects. However, when an abstraction of the water chemistry and gas-phase 
composition is required, a fully-coupled transport-model is necessary and can be used to produce 
chemical boundary conditions for the TSPA model. It can do so since it has been shown not to 
produce inconsistent thermal-hydrologic results when compared to a TH-only model. 
3.3 DRIFT-SCALE THERMAL-HYDROLOGICAL-CHEMICAL PROCESSES AND 
MODELS 
The purpose of this section is to describe: (1)the conceptual model and input data for coupled 
thermal, hydrological and chemical (THC) processes; (2) the DST THC Model; and (3) the THC 
Process Model (termed the THC Seepage Model in the UZ F&T PMR). Abstractions done by 
Performance Assessment on the results of the THC Process Model are discussed in Sections 3.4 
and 3.2.3.4. The conceptual model for THC processes provides a comprehensive basis for

 3-76 
modeling the pertinent mineral-water-gas reactions in the host rock under thermal-loading 
conditions, as they influence the water and gas chemistry that may enter drifts over 100,000 yr. 
The purpose of the DST THC Model is to validate the conceptual model and input data by 
comparison of measured gas and water chemistry from the DST to the results of simulations. 
The purpose of the THC Process Model is to evaluate the effects of THC processes in the rock 
around emplacement drifts on the possible seepage-water chemistry, gas-phase composition, and 
the potential effects of THC processes on UZ flow and transport. This model was used to 
evaluate the effects of mineral dissolution and precipitation; the effects of CO2 exsolution and 
transport in the region surrounding the drift; the potential for forming zones of calcite, silica or 
other minerals; the resulting changes to porosity and permeability; and the potential effects on 
seepage. The THC Process Model and validation of the data and processes, using the DST data, 
are addressed in the THC Process AMR (CRWMS M&O 2000b). 
3.3.1 Thermal-Hydrological-Chemical Conceptual Model 
The THC conceptual model underlies the numerical simulations of THC processes in the DST 
THC Model and in the THC Process Model. The conceptual model must be able to describe 
processes involving liquid and vapor flow, heat transport, and thermal effects resulting from 
boiling and condensation, transport of aqueous and gaseous species, mineralogical characteristics 
and changes, and aqueous and gaseous chemistry. A conceptual model of reaction-transport 
processes in the fractured welded tuffs of the potential repository host rock must also account for 
the different rates of transport in very permeable fractures, compared to the much less permeable 
rock matrix (see for example, Steefel and Lichtner 1998, pp. 186-187). 
In addition to the unsaturated hydrological properties required to simulate THC processes in the 
UZ, the data necessary for evaluation of THC processes include the initial and boundary water 
and gas chemistry, the initial mineralogy, mineral- volume fractions, reactive-surface areas, 
equilibrium thermodynamic data for minerals, aqueous and gaseous species, kinetic data for 
mineral-water reactions, and diffusion coefficients for aqueous and gaseous species. The 
following sections describe the conceptual model for TH, geochemical, and coupled THC 
processes in the fractured tuffs. 
3.3.1.1 TH Processes 
TH processes in the fractured, welded tuffs at Yucca Mountain have been examined theoretically 
and experimentally since the early 1980s (Pruess et al. 1984; Pruess et al. 1990, 
pp. 1235 to 1248; Buscheck and Nitao 1993; pp. 418 to 448, Pruess 1997; Tsang and 
Birkholzer 1999; pp. 385 to 425, Kneafsey and Pruess 1998, pp. 3349 to 3367). A conceptual 
model showing the important TH processes occurring around a drift, as derived through these 
studies and through observations of the Single Heater Test and the DST (CRWMS M&O 2000a), 
is shown in Figure 3-34. The design shown here includes backfill; however, this conceptual 
model is not dependent on the presence of backfill. To summarize the processes depicted in the 
figure, heat conduction from the drift wall into the rock matrix results in vaporization and 
boiling, with vapor migration out of matrix blocks into fractures. The vapor moves away from 
the drift through the permeable fracture network by bouyancy, by the increased vapor pressure 
caused by heating and boiling, and through local convection. In cooler regions, the vapor 
condenses on fracture walls, where it drains through the fracture network either down toward the

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heat source from above or away from the drift into the zone underlying the heat source. Slow 
imbibition of water from fractures into the matrix, particularly with some disequilibrium in 
matrix and fracture capillary pressures due to limited interaction area and to fracture coatings, 
gradually leads to increases in liquid saturation in the rock matrix. Under conditions of 
continuous heat loading, a dryout zone may develop closest to the heat source, separated from 
the condensation zone by a nearly isothermal zone maintained at about the boiling temperature. 
Where this nearly isothermal zone is characterized by a continuous process of boiling, vapor 
transport, condensation, and migration of water back to the heat source (either by capillary forces 
or gravity drainage), this zone may be termed a heat pipe (Pruess et al. 1990, pp. 1235-1248). 
The design shown in Figures 2-1 and 2-2 includes backfill; however, this conceptual model is not 
dependent on the presence of backfill. A design change was made in January 2000 that removed 
backfill from the reference design. Qualitatitively, this change does not affect the THC 
processes occurring in the rock around the drifts; however, the absence of backfill will result in a 
slightly different temperature distribution at the drift-wall and different times of maximum driftwall 
temperature, maximum dryout and rewetting (compare Sections 3.2.3.1 and 3.2.3.2 for these 
changes). These different rates of heating may affect the time variation of water and gas 
chemistry around the drifts. 
3.3.1.2 Effects of TH Processes (Boiling, Condensation, and Drainage) on Water and 
Gas Chemistry and Mineral Evolution 
The chemical evolution of waters, gases, and minerals is closely coupled to the TH processes 
discussed in the Section 3.3.1.1. The distribution of condensate in the fracture system 
determines where mineral dissolution and precipitation can occur in the fractures, and where 
there can be direct interaction (via diffusion) between matrix pore waters and fracture waters. 
Figure 3-30 shows schematically the relationships between TH and geochemical processes in the 
zones of boiling, condensation, and drainage in the rock mass outside of the drift and above the 
heat source. 
One important aspect of the system is exsolution of CO2 from the liquid phase as temperature 
increases. The exsolution and transport of CO2 away from the boiling zone results in a local 
increase in pH and a decrease in pH in the condensation zone into which the vapor enriched in 
CO2 is transported. This has been documented in data collected from the DST and discussed in 
the THC Process AMR. The extent to which the pH is shifted depends strongly on the rates of 
mineral-water reactions, which can buffer the change in pH. Because the diffusivities of gaseous 
species are several orders of magnitude greater than of aqueous species, and because the 
advective transport of gases can be more rapid than that of liquids, the region where CO2 
degassing affects water and gas chemistry could be much larger than the region affected by 
transport of aqueous species.

 3-78 
Figure 3-29. Schematic Diagram of THC Processes Around a Potentially Heated Drift

 3-79 
Figure 3-30. Schematic Diagram Showing Relation Between TH Processes and THC Processes 
Effects of TH processes on water chemistry are varied and depend on the behavior of the 
dissolved species and its relation to mineral-water reactions. Conservative species (i.e., those 
that are unreactive and nonvolatile), such as chloride (Cl-), become concentrated in waters 
undergoing vaporization or boiling, but are absent from the vapor condensing in the fractures. 
Therefore, the concentration in the draining condensate waters is determined by mixing with 
fracture pore waters and interaction with matrix pore waters via diffusion. Concentrations of 
aqueous species, such as Ca+2, are also affected by calcite dissolution or precipitation as well as 
reactions involving Ca-bearing zeolites, clays, and plagioclase feldspar. 
Zonation in the distribution of mineral species may occur as a result of varied temperature effects 
on mineral solubility. The inverse relation between temperature and calcite solubility (compared 
to the silica phases, which are much more soluble at higher temperatures) may cause zonation in 
the distribution of these phases in the condensation and boiling zones (Figure 3-30). 
Precipitation of amorphous silica or another silica phase is likely to be confined to a narrower 
zone where evaporative concentration from boiling exceeds its solubility. Hence, calcite may 
precipitate in fractures over a broader zone of elevated temperature and where CO2 has degassed. 
Alteration of feldspars to clays and zeolites is likely to be most rapid in the boiling zone, because 
of their increased solubility (as well as dissolution and precipitation rates) at higher temperatures 
(Lasaga 1998, p. 66). In drainage zones, there may also be zonation in mineral alteration within 
the rock matrix adjacent to the fracture similar to that observed as a function of distance along

 3-80 
the transport path (Steefel and Lichtner 1998, pp. 186-199). At Yucca Mountain, there is no 
evidence for such zonation from the thermal tests, but it is implied from model results presented 
in the THC Process AMR (CRWMS M&O 2000b). The importance of mineral zonation patterns 
is that the spatial distribution of mineral alteration will influence the hydrological property 
changes that may occur. 
3.3.1.3 Effects of Infiltration and Climate Changes on THC Processes 
Early in the thermal history of the potential repository, much of the chemistry of the unsaturated 
zone (UZ) around drifts will be constrained by the chemistry of ambient fracture and matrix pore 
water, which may change in concentration as a result of boiling, by dilution with condensate 
water, or by mineral-water-gas reactions. Once the peak thermal period has subsided, 
percolating water mixes with any condensate water above the repository and eventually rewets 
the dryout zone. The composition of the percolating waters (before mixing) will likely be 
dominated by flow in fractures, which would be of meteoric-water composition modified by 
reaction with facture minerals. The degree of modification from meteoric composition depends 
on the velocity of flow, or more precisely the residence time of water in the fractures. While it 
has been assumed in this report that infiltrating water may be similar to that presently found at 
and above the repository as matrix pore water, no samples of percolating water have been 
obtained. The fraction of the percolation flux through the matrix is expected to be minor in 
comparison to the fraction through the fractures, and residence time in pores would allow 
interaction between rock and water to approach equilibrium. This would imply that the 
infiltrating water may be similar to that presently found above the potential repository as matrix 
pore water or more likely would reflect more dilute water. Implications are that analyses 
assuming pore-water composition should bound the precipitation of minerals, but may 
underestimate dissolution. Changes in percolation flux also affect the extent of mineral 
deposition and dissolution, because of changes in the flux of dissolved species to the region 
around drifts. For example, the greater the flux of Ca, the more calcite would be precipitated, at 
a given concentration. Higher percolation fluxes could increase the dissolution rates of minerals 
that are undersaturated in the fluid, because it can increase the degree to which the mineral is 
undersaturated. 
3.3.1.4 Hydrologic Property Changes in Fractures and Matrix 
Mineral precipitation and dissolution in fractures and matrix have the potential for modifying the 
porosity, permeability, and unsaturated hydrologic properties of the system. Because the molar 
volumes of minerals created by hydrolysis reactions (i.e., anhydrous phases, such as feldspars, 
reacting with aqueous fluids to form hydrous minerals, such as zeolites or clays) are often larger 
than the molar volumes of the primary reactant minerals, dissolution-precipitation reactions can 
often lead to porosity reductions. The extent of mineral-water reactions is controlled by the 
surface areas of the mineral phases in contact with the aqueous fluid, and the distribution of 
minerals in the fractures is heterogeneous. Therefore, changes in porosity and permeability 
caused by these processes may also be heterogeneously distributed. Other factors that may lead 
to heterogeneity in property changes are the distribution of liquid saturation in fractures, the 
proportion of fractures having actively flowing water, and the rates of evaporative concentration 
due to boiling, which may change the dominant mechanisms of crystal growth and nucleation.

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As summarized in the preceeding section, the conceptual model for THC processes incorporates 
a wide range of coupled physical and chemical processes. The following section deals with 
implementation of this conceptual framework into a quantitative numerical model. 
3.3.2 Modeling Approach, Assumptions, Inputs and Outputs 
The flow of information between various models and data sources, the DST THC Model and 
THC Process Model is presented in Figure 3-31. The DST THC Model takes its inputs from the 
DST TH Model (grid and power output) (CRWMS M&O 2000a), the Calibrated Properties 
Model (CPM)(CRWMS M&O 2000n), and numerous sources of geochemical data as discussed 
in the THC Process AMR (CRWMS M&O 2000b). Geochemical data include mineral 
abundances and compositions, and water and gas chemistry. The THC Process Model obtains its 
inputs from the CPM, geochemical data, the repository design, and the UZ Flow Model 
(CRWMS M&O 2000q). One key input is the fracture porosity of 1 percent in the Tptptm unit 
(CRWMS M&O 2000f, Section 3.6.3.2). Repository Design provides the drift geometry and 
drift spacing, and the thermal and hydrological properties of EBS components (such as the drip 
shields, waste packages, and invert) (CRWMS M&O 2000g). The UZ Flow and Transport 
Model (CRWMS M&O 2000f) provides the hydrogeologic layer boundaries and pressure and 
temperature boundary conditions. Results of sensitivity studies on mineral assemblages and 
conceptual model validation in the DST are used to guide development and analysis of the THC 
Process Model. Although direct numerical output from the DST THC Model is not used in the 
THC Process Model, understanding gained from simulations of the DST and comparison to 
measured data allow for a more focused approach in the THC Process Model calculations and 
analysis. Output data from the THC Process Model are water chemistries in fractures at the drift 
crown, side, and base (which are linked to seepage volumes in the UZ F&T PMR). The fracturewater 
chemistries are abstracted for use in TSPA and discussed further in Section 3.4. 
The following sections describe in more detail implementation of the conceptual model as a 
mathematical description of THC processes in the fractured tuffs. Data that form the basis of the 
DST THC and THC Process Model are also discussed. 
3.3.2.1 Dual-Permeability Model for Reaction-Transport Processes 
To treat separate yet interacting processes in fractures and matrix, the DKM (described in 
Section 2.2.1) was adopted for all aspects of the system (flow, transport, and reaction). 
Transport rates greater than the rate of chemical equilibration via diffusion necessarily lead to 
disequilibrium in water chemistry between fractures and matrix. This can lead to differences in 
dissolution and precipitation rates, and therefore the rate of change in porosity and permeability 
between the two media. Because the system is unsaturated and undergoes boiling, the transport 
of gaseous species is an important consideration. The model must also capture the differences 
between initial mineralogy in fractures and matrix and their evolution. In the dual-permeability 
method, each gridblock is separated into a matrix and fracture continuum, each of which is 
characterized by its own pressure, temperature, liquid saturation, water and gas chemistry, and 
mineralogy.

 3-82 
Figure 3-31. Model Diagram Relating Inputs and Outputs for the THC Process Model (labeled 
THC) and THC Drift Scale Test Model (labeled THC DST)

 3-83 
The fracture continuum is considered as separate from, but interacting with, the matrix 
continuum in terms of the flow of heat, water, and vapor through advection and conduction. 
Aqueous and gaseous species are transported via advection and molecular diffusion between 
fractures and matrix. It is assumed that the DK approach, with appropriate material and fracture 
properties and an appropriate discretization of time and space, is a sufficiently accurate 
approximation of the real world for the spatial scales of interest. The DK approach for modeling 
hydrologic processes in fractured porous media is also discussed in other sections of this PMR. 
This approach is validated by comparison of measured geochemical data to results of simulations 
presented in the THC Process AMR (CRWMS M&O 2000b), and is discussed in Section 3.6.4.2. 
The key observation that supports the DK approach is the strong disequilibrium between waters 
that have collected in hydrology boreholes in the DST and the matrix pore waters. The extent of 
the disequilibrium is captured by the model quite closely as judged by the pH and concentrations 
of other components. 
3.3.2.2 Active Fracture Model for Reaction-Transport Processes 
The AFM (Liu et al. 1998; CRWMS M&O 2000d, Section 6.4.5) has been used in many of the 
modeling studies described in this report. Because a major intent of the method is to modify the 
fracture-matrix area for the liquid phase as a function of liquid saturation, for consistency the 
AFM should also be used for calculation of the surface area of minerals on fracture walls in 
contact with the liquid phase. The reference saturation for the active- fracture concept is the 
residual liquid saturation, below which flow is considered to be absent. However, mineral-water 
reactions are expected to occur at all saturations above zero. Therefore, a modification of the 
AFM was implemented for mineral-water reactions, such that the reference saturation is taken as 
some arbitrarily small value (1 x 10-4), consistent with that implemented for mineral-water 
reactions and transport near conditions of complete dryout. This value is an approximate cut-off 
at which evaporative concentration increases the ionic strength of the residual pore water to 
values outside the range of the validity of thermodynamic relationships for dilute systems. 
3.3.2.3 Equilibrium and Kinetic Models for MineralWaterGas Reactions 
Mineral-water reactions are considered to take place under kinetic or equilibrium conditions. 
The methods used to express the kinetic and equilibrium reactions are described in the THC 
Process AMR (CRWMS M&O 2000b) and are similar to those described in Reed (1982) and 
Steefel and Lasaga (1994). Because the dissolution rates of many mineral-water reactions are 
quite slow, most phases were treated using pseudo-first-order reaction kinetics (CRWMS 
M&O 2000b, Table 4). Data for kinetic mineral-water reactio ns were derived from published 
experimental data. This assumption is likely reasonable (considering the uncertainties in the 
reactive surface areas) for most reactive transport calculations, except during the final stages of 
boiling where nucleation knetics may be more important. Gas species, such as CO2, were treated 
as ideal mixtures of gases in equilibrium with the aqueous solution. The validity of these 
methods to the problem are only known for particular cases; therefore, comparison of model 
results to data collected from thermal tests has been done.

 3-84 
3.3.2.4 Initial and Infiltrating Water and Gas Chemistry and Mineralogy 
The initial water chemistry for the DST THC Model and the THC Process Model was an average 
of measurements made of pore waters from Alcove 5, near the DST (CRWMS M&O 2000b, 
Section 6.1.2). This alcove is in the TSw hydrogeologic unit and represents in situ water in the 
NFE location under ambient conditions. The chemistry of this average water composition is 
given in Table 3-8. 
Table 3-8. TSw Pore Water Composition and CO2 Partial Pressure 
Parameter Units Concentration 
pH (at 25C) pH Units 8.32 
Na mg/L 61.3 
SiO2(aq) mg/L 70.5 
Ca mg/L 101 
K mg/L 8.0 
Mg mg/L 17 
Al mg/L 9.92x10-7 (1) 
Fe mg/L 6.46x10-8 (2) 
HCO3 (3) mg/L 200 
Cl mg/L 117 
SO4 mg/L 116 
F mg/L 0.86 
CO2 (gas) (4) Pa 85.2 
Source: CRWMS M&O 2000b, Table 3 
NOTE: (1) Calculated by equilibration with Ca-smectite at 25C. 
(2) Calculated by equilibration with hematite at 25C. 
(3) Total aqueous carbonate as HCO3
-, calculated from charge balance. 
(4) Calculated at equilibrium with the solution at 25C. 
The infiltrating water chemistry could be chosen from either the pore water chemistry in the UZ 
at or above the potential repository horizon or from a more dilute composition found in the 
perched water or saturated zone (e.g., J-13 water). The perched waters are much more dilute 
(e.g., lower Cl) than UZ pore waters (CRWMS M&O 2000r, Tables 6 and 8), and isotopic 
compositions (36Cl/Cl, 18O/16O, D/H, 14C) and Cl concentrations also suggest the presence of a 
large proportion of late Pleistocene to early Holocene water (Levy et al. 1997, p. 906; Sonnenthal 
and Bodvarsson 1999, pp. 107 to 108; CRWMS M&O 2000r, Table 9). It was assumed that the 
infiltrating water and the water in the fractures have the same chemical composition as the 
matrix pore water. The water chemistry is uncertain as indicated in Section 2.4.2. The sample 
chosen was collected in the TSw hydrogeologic unit at Alcove 5 near the DST, and its chemistry 
is listed in Table 3-8. Analyses of PTn pore waters (and some at the top of the TSw) and many 
Cl analyses of TSw pore waters are consistent with this interpretation (Sonnenthal and 
Bodvarsson 1999, pp. 140 to 141; CRWMS 2000r, Table 6). 
The minerals, aqueous and gaseous species, shown in Table 3-9 (denoted as more complex or 
complex), include the major phases found in fractures and the matrix in the TSw and others that

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are likely to occur under thermally perturbed conditions, based on their occurrence in deeper 
zeolitized units. Two sets of geochemical species were chosen, so the sensitivity to the mineral 
assemblage could be evaluated, and additional information could be obtained for PA 
abstractions. The other set of species (denoted as Less Complex Mineral Assemblage), 
represents a smaller set of species and minerals (calcite, gypsum, silica phases) that captures 
many basic aspects of the DST water and gas chemical evolution, such as the pH and gas-phase 
CO2 concentrations, but neglects Al, Fe, K, Mg, and F-bearing aqueous species and minerals. 
Simulations of the DST and the THC Process Model considered both geochemical cases. 
3.3.2.5 Relations for Mineral Reactive Surface Areas 
Reactive surface areas of minerals on fracture walls were calculated from the fracture-matrix 
interface area-volume ratio, the fracture porosity, and the derived mineral-volume fractions 
(CRWMS M&O 2000b, Section 6.1.5.1). The fracture-matrix interface areas and fracture 
porosities for each unit were taken from the DS calibrated properties set (CRWMS M&O 2000q, 
Section 6.2). These areas were based on the fracture densities, fracture porosities, and mean 
fracture diameter. The wall of the fracture is treated as a surface covered by mineral grains 
having the form of uniform hemispheres. 
Mineral surface areas in the rock matrix were calculated using the geometric area of a cubic 
array of truncated spheres that make-up the framework of the rock (CRWMS M&O 2000b, 
Section 6.1.5.2). Clay minerals are considered as coatings of plate-like grains. The grains 
forming the framework of the rock matrix are considered to be the primary high-temperature 
phases of the tuff (i.e., quartz, cristobalite, tridymite, and feldspars). The abundance of 
secondary phases (i.e., those that formed as alteration products or low-temperature coatings on 
the primary assemblage), such as clay minerals, is used to reduce the free surface area of the 
framework grains. 
3.3.2.6 Relations for Hydrological Property Changes 
Changes in porosity, permeability, and capillary pressure as a result of mineral precipitation and 
dissolution are treated in the THC Process AMR (Sections 6.1.6.2  6.1.6.3). Porosity changes in 
matrix and fractures are directly linked to the volume changes resulting from mineral 
precipitation and dissolution. Fracture permeability changes are approximated using the porosity 
change and an assumption of plane, parallel fractures of uniform aperture (Steefel and 
Lasaga 1994, p. 556). This simplification of the fracture geometry is used because it is not 
possible to predict the actual form and distribution of mineral precipitates at a very small scale. 
This is because of the complexities of the fracture geometry and the complex nature of mineral 
nucleation and growth under changing physical and chemical conditions. Thus, the permeability 
changes are approximate and apply to average conditions. However, these analyses reflect the 
trends, or overall magnitude of changes, that could be expected. Matrix permeability changes 
are calculated from changes in porosity, using ratios of permeabilities calculated from the 
Carmen-Kozeny relation (Bear 1988) and ignoring changes in grain size, tortuosity, and specific 
surface area. The Carmen-Kozeny equation has been used for many years to approximate the 
relation between permeability and porosity for packed spheres. In addition to changes in 
porosity, and changes in intrinsic saturated permeability as predicted by the Carmen-Kozeny 
relation, the retention characteristics of the fractures may also be altered. Jury et al. (1991,

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pp. 88-93) developed models for retention in soils as a series of capillary tubes. This model can 
be generalized to a series of parallel plates with varying size apertures. As rock deformations 
due to shear dilatancy occur, the fracture system will exhibit increased tendency to drainage or 
reduced tendency to retention that reduces fracture permeability. 
Table 3-9. Model Mineral Assemblage, Aqueous and 
Gaseous Species 
Species Minerals 
Aqueous: 
H2O Calcite 
H+ Tridymite 
Na+ a-Cristobalite 
K+ Quartz 
Ca+2 Amorphous Silica 
Mg+2 Hematite 
SiO2 Fluorite 
AlO2
- Gypsum 
HFeO2 Goethite 
HCO3
- Albite 
Cl- Microcline 
SO4
-2 Anorthite 
F- Ca-Smectite 
Mg-Smectite 
Gas: Na-Smectite 
CO2 K-Smectite 
Illite 
Kaolinite 
Sepiolite 
Stellerite 
Heulandite 
Mordenite 
Clinoptilolite 
Volcanic Glass 
Source: Complex Geochemical System; 
CRWMS M&O 2000b, Table 7 
Because of the exceedingly small initial matrix permeabilities of the welded Topopah Spring 
Tuff, simplification in the matrix relations is immaterial. If mineral precipitation caused very 
substantial changes in permeability, or the permeability of the fracture system was already very 
low, then it would be necessary to treat the relations between permeability changes and porosity 
changes more rigorously. If significant volumes of mineral precipitation were predicted, then 
back-coupling would need to be included in the analyses. Changing permeability and porosity 
also induces changes in the unsaturated flow properties of the rock. Therefore, the capillary

 3-87 
pressure is modified using the Leverett scaling relation (Slider 1976, p. 280). Through Leverett 
scaling, the capillary pressure then shifts to higher values as the permeability decreases, thus 
leading to greater suction. 
3.3.2.7 Basis for Numerical Code TOUGHREACT V2.2 
The geochemical module incorporated in TOUGHREACT V2.2 (STN: 10154-2.2-00) 
simultaneously solves a set of chemical mass-action, kinetic-rate expressions for mineral 
dissolution and precipitation, and mass-balance equations. Implementation of multiphase flow 
and heat transport for DK media is equivalent to TOUGH2 V1.4 (STN: 10007-1.4-01), which 
was used for other UZ flow calculations and TH calculations (CRWMS M&O 2000q) and for 
TH calculations of the DST (CRWMS M&O 2000a). TOUGHREACT V2.2 provides the extent 
of reaction and mass transfer between a set of given aqueous species, minerals, and gases at each 
gridblock of the flow model (Xu and Pruess 1998; Xu et al. 1998). Equations for heat, liquid and 
gas flow, aqueous and gaseous species transport, chemical reactions, and permeability and 
porosity changes are solved sequentially (Steefel and Lasaga 1994, p. 550). It is assumed that 
the physical properties of the gas phase are unaffected by changes in the partial pressure of CO2 
resulting from heating, calcite reactions, and gas-phase transport. This assumption is justified by 
the results of the DST THC Model and the THC Process Model runs, which show that the 
volume fraction of CO2 is generally less than 5 percent and always less than 10 percent 
(CRWMS M&O 2000b). 
3.3.3 THC Process Model 
The NFE may impact seepage if hydrologic properties change within the NFE. The assessment 
of TH effects on seepage is reported within the UZ F&T PMR (CRWMS M&O 2000f, 
Section 3.10.5) and the results are fed to the EBS PMR directly from the UZ F&T PMR and 
associated AMRs. The impacts on seepage are reported here in order to put the NFE results into 
context, and to identify the two-way coupling that exists between percolation flux and the NFE. 
This section describes the THC Process Model and the results of predictions of water and gas 
chemistry that may seep into drifts over the next 100,000 yr. This model also considers any 
changes in the hydrological properties as a result of mineral precipitation and dissolution. The 
overall abstraction results as used by TSPA are summarized in Table 3-10. 
3.3.3.1 THC Process-Model Description 
A THC Process Model incorporates elements of the EDA II (Wilkins and Heath 1999, 
Enclosure 2) to represent waste package heating over time, changes in heat load due to 
ventilation, the effective heat transfer within the drift, the addition of backfill after 50 yr, and 
THC processes (CRWMS M&O 2000b). This 2-D model incorporated the initial layering in 
hydrologic and thermal properties and mineralogy from the surface to the Calico Hills Formation 
zeolitic unit, along with different initial mineralogy and reactive surface areas in fractures and 
matrix (Figure 3-32). A number of cases were evaluated for different calibrated property sets, 
climate-change scenarios, and geochemical systems. The climate scenarios were constructed 
from average values of the present-day infiltration, monsoon and glacial-transition climates, 
along with the upper and lower bounds. These averages were calculated from about 30 TH

 3-88 
chimney models in the potential repository footprint. Predictions were presented of the water 
and gas chemistry that may enter the drifts for a period of 100,000 yr, including a pre-closure 
period of 50 yr with 70 percent heat removal by ventilation. 
3.3.3.2 TH Effects 
TH effects on liquid saturation and flow around drifts were investigated in the THC Process 
AMR (CRWMS M&O 2000b). The TH effects on liquid saturation and temperature around 
drifts are a function of the infiltration rate and initial liquid saturations calculated from steadystate 
simulations, using specific calibrated property sets (CWRMS M&O 2000n). Liquid 
saturations and temperature are shown around the drifts at 600 yr, which is approximately the 
time of maximum dryout extent for the three climate cases investigated (Figure 3-33). These 
climate cases considered three time periods (0-600, 600-2,000, and 2,000-100,000 yr) and 
different infiltration rates for each period (6/6/3, 6/16/25, and 15/26/47 mm/yr) for a lower, mean 
and upper bound, respectively (CRWMS M&O 2000b). The dryout zone is asymmetric around 
the drift as a result of the position of the waste package and backfill, and the effect of infiltration 
above the drift. The smaller dryout zone in the lowest infiltration case compared to the mean 
infiltration case is apparently the result of differing property sets rather than differences in the 
infiltration rate. Higher liquid saturations in the pillar region are a result of water diverting 
around the drift. 
3.3.3.3 Gas-Phase CO2 Evolution 
The CO2 evolution in the gas phase is a controlling factor for the pH and mineral-water 
reactions. Time profiles for gas-phase CO2 concentrations at three locations around the drift are 
shown in Figure 3-34 for the Less Complex (calcite-silica-gypsum) geochemical system. 
Carbon dioxide concentrations in fractures drop significantly during dryout and increase again 
during rewetting. The increase in CO2 concentrations in the gas phase during rewetting is likely 
a result of heating of these waters as they approach the drift wall, as suggested by the highinfiltration 
case showing the largest CO2 concentration after rewetting (near 12,000 ppmV). 
Another component of this increased CO2 concentration is the dissolution of calcite previously 
precipitated during heating and boiling of condensate and matrix pore water. The highest 
concentrations are similar to those observed during the DST, although rewetting has not taken 
place in the DST because it is still in the he ating phase. 
3.3.3.4 Water-Chemistry Evolution 
Chloride is a useful indicator of the extent of boiling or dilution, and interaction of condensate 
waters in fractures that are low in Cl with matrix pore waters having much higher chloride 
concentrations. Chloride concentrations are plotted in Figure 3-35 as a function of time at three 
locations around the drift. The gap in concentrations between about 75 and 1,000 yr. reflects the 
dryout period when no aqueous phase is present at the drift wall. Upon rewetting, chloride 
concentrations drop relatively quickly below 400 mg/L toward ambient values near 110 mg/L. 
There is no evidence of water with high concentrations of chloride at liquid saturations above 
residual saturation during the reflux period (after about 1,000 yr). Therefore, waters that are 
most likely to seep into drifts will not be significantly more concentrated in chloride than the 
ambient pore water.

 3-89 
Source: Adapted from CRWMS M&O 2000b, Figures 18 and 19 
NOTE: Topopah Spring Tuff Upper Lithophysal (tsw33), Middle Non-Lithophysal (tsw34), and Lower Lithophysal 
(tsw35) Units, and Blow-up Showing Discretization of In-Drift Design Components. 
Figure 3-32. THC Process Model Mesh Showing Hydrogeologic Units in Proximity of the Drift

 3-90 
Source: CRWMS M&O 2000b, Figure 26 
NOTE: (a) Low, (b) Mean, and (c) High (less complex system). Temperature (C) line contours are overlaid on the 
saturation color contours. 
Figure 3-33. Contour Plot of Modeled Liquid Saturations in the Matrix at 600 Yr (Near 
Maximum Dryout) for Three Climate-Change Scenarios 
Predicted pH and total aqueous carbonate concentrations (as HCO3
-) in fracture pore water are 
shown in Figures 3-36 and 3-37 for the calcite-silica-gypsum system. The calculated pH is 
generally higher for the Complex system results (approximate range 8.5 to 9.8; shown in the 
THC Process AMR [Figure 30]) than for the Less Complex system (approximate range 7 to 8.5). 
The composition of waters reaching the drift wall during rewetting were roughly neutral in pH 
(7.2 to 8.3) for the Less Complex system, and approximately 8.6 to 9.0 for the full geochemical 
system. Total aqueous carbonate concentrations are higher in the Complex system at the drift 
crown (maximum, after rewetting, near 10,000 mg/L for the low infiltration case) than in the 
calcite-silica-gypsum system (near ambient values of 200 mg/L after rewetting).

 3-91 
The pH-carbonate-CO2 data show different trends when aluminosilicates in the mineral 
assemblage are considered. The aluminosilicate reactions are sensitive to competing effects of 
infiltration rate and gas-phase CO2 diffusion relative to calcite dissolution and precipitation, 
feldspar dissolution, and calcium-zeolite precipitation. The dissolution of feldspars to form 
zeolites and clays directly affects the pH. For example, the dissolution of albite (Na-feldspar) to 
form kaolinite (clay) results in an increase in pH, as follows: 
2 NaAlSi3O8 (albite) + H2O + 2H+  Al2Si2O5(OH)4 (kaolinite) + 4SiO 2 + 2Na+ 
Feldspar dissolution also indirectly causes an increase in pH when Ca-rich zeolites precipitate, 
depleting calcium from solution and destabilizing calcite, as in the following reaction: 
2 NaAlSi3O8 (albite) + SiO 2 (aq) + CaCO3 (calcite) + H+ + 7H2O  
CaAl2Si7O18  7H2O (stellerite) + 2Na+ + HCO3
- 
As a result, simulations that consider aluminosilicate reactions generally yield higher pH and 
total aqueous carbonate concentrations and generally lower CO2 partial pressures than 
simulations with the Less Complex calcite-silica-gypsum system. Simulations of the DST show 
that results from the Less Complex system matches the observed pH, bicarbonate, and calcium 
more closely than the Complex system. However, over longer and more stable periods of reflux 
and boiling, the sys tem may trend toward the chemistry of the Complex system. 
3.3.3.5 Porosity and Permeability Changes and Assessment of Precipitation Cap 
Formation 
The calculated change in fracture porosity in the vicinity of the drift, at a simulation of 
10,000 yr., is shown in Figure 3-38 for the three climate scenarios and the Less Complex system. 
The maximum porosity reduction (negative in the plots) occurs for the high-infiltration case and 
is predominantly above the drift, adjacent to the tsw33 and tsw34 hydrogeologic unit contact. In 
all cases, the porosity change is relatively small (less than ~1 percent of the initial porosity) and 
mostly to smaller values. The porosity decrease results primarily from calcite precipitation (as in 
the DST simulations). In the full geochemical system, the fracture porosity change is similarly 
small, but is dominated by zeolite reactions. Because the fracture porosity changes are small and 
permeability changes are negligible, TH processes were not determined by this analysis to be 
significantly affected by mineral precipitation or dissolution. The analysis assumed that the 
porosity changes are uniformly distributed along the fracture surfaces. The models cannot assess 
fine structure changes (e.g., those that reflect variation in asperities). If mineral deposition is 
localized in smaller openings, they may have greater impact on permeability; this possibility is 
still being evaluated.

 3-92 
Source: CRWMS M&O 2000b, derived from Figure 29 
NOTE: The base location water chemistry does not consider effluent from the drift. 
Figure 3-34. Time Profiles of Modeled CO2 Concentrations in the Gas 
Phase in Fractures at Three Drift Wall Locations for 
Different Climate-Change Scenarios (Less Complex 
Calcite-Silica-Gypsum System) 
Fractures 
Crown 
0.1
1 
10 
100 
1000 
10000 
100000 
1 10 100 1000 10000 100000 
Time (yr) 
Concentration (ppmV) 
1 mm amb. 
0.6/6/3 mm 
6/16/25 mm 
15/26/47 mm 
CO2 Case 2 
Side 
0.1 
1 
10 
100 
1000 
10000 
100000 
1 10 100 1000 10000 100000 
Time (yr) 
Concentration (ppmV) 
1 mm amb. 
0.6/6/3 mm 
6/16/25 mm 
15/26/47 mm 
CO2 Case 2 
Base 
0.1 
1 
10 
100 
1000 
10000 
100000 
1 10 100 1000 10000 100000 
Time (yr) 
Concentration (ppmV) 
1 mm amb. 
0.6/6/3 mm 
6/16/25 mm 
15/26/47 mm 
CO2 Case 2

 3-93 
Source: CRWMS M&O 2000b, Figure 39 
NOTE: Numbers inside plot refer to liquid saturation at point shown, either just prior to complete dryout or at time of 
rewetting. Numbers outside plot refer to concentrations that are off-scale. 
Figure 3-35. Time Profiles of Modeled Total Aqueous Chloride 
Concentrations in Fracture Water at Three Drift-Wall 
Locations for Different Climate-Change Scenarios 
(Complex Mineral Assemblage)

 3-94 
Source: CRWMS M&O 2000b, Figure 31 
NOTE: Numbers inside plot refer to liquid saturation at point shown, either just prior to complete dryout or at time of 
rewetting. 
Figure 3-36. Time Profiles of the Modeled pH of Fracture Water at Drift- 
Wall Locations for Different Climate-Change Scenarios 
(Less Complex System)

 3-95 
Source: CRWMS M&O 2000b, Figure 33 
NOTE: Numbers inside plot refer to liquid saturation at point shown, either just prior to complete dryout or at time of 
rewetting. 
Figure 3-37. Time Profiles of Modeled Total Aqueous Carbonate 
Concentrations (as HCO3
-) in Fracture Water at Drift -Wall 
Locations for Different Climate-Change Scenarios (Less 
Complex System)

 3-96 
3.3.3.6 Zeolite and water table impacts 
An assessment was made of the potential impact on zeolite dehydration and water table chemical 
changes by considering the estimates of temperatures within those zones. However, THC 
coupled process model analyses were not performed to determine these potential impacts. 
The UZ F&T PMR (CRWMS M&O 2000f) reports that for the EDA-II design, the models 
estimate a maximum temperature of 70-75C at the top of the Calico Hills nonwelded unit 
(CHn), between 2,000 and 7,000 yr. This temperature range suggests minimal potential for 
temperature-induced mineralogical changes to occur within the zeolites of the nonwelded CHn 
hydrogeological unit (CRWMS M&O 2000f, pp. 280-281 and p. 287). Because the temperatures 
at the water table are of similar range, similar conclusions were drawn for the impact on rock 
units that include the saturated zone. 
3.3.4 Uncertainties and Limitations 
Many uncertainties exist in the thermodynamic and kinetic parameters used to describe mineral 
precipitation and dissolution. Limitations also arise under specific geochemical and/or physical 
conditions. For example, as the concentrations of dissolved solutes increase during boiling of 
pore water, the activity coefficients of the dissolved species may deviate significantly from one, 
and the ionic strength at which the models yield reasonable results is exceeded. Rapid boiling 
can also lead to mineral supersaturation outside the range of the pseudo-first-order kinetic 
models employed, which are generally reasonable under near-equilibrium conditions. Mineral 
precipitation may then be controlled by nucleation kinetics and other surface-energy-related 
phenomena. These uncertainties and limitations are generally difficult to quantify, because the 
models also introduce simplifications in the process of using these data, and the physical regimes 
under which the model breaks down may not be important for the overall dynamics of the 
system. Geochemical reactions are a strong function of temperature and the presence of water, 
which are better constrained than the rates of reaction and may control the spatial distribution, 
even if the exact quantities of the phases at a given time are uncertain. 
Relations between permeability changes and porosity changes are also highly uncertain. These 
uncertainties are difficult to quantify, because they depend on the detailed geometry of the pore 
space and throats; however, some methods have succeeded in quantifying this effect in 
diagenetically altered rocks (Ehrlich et al. 1991). Although these methods were developed for 
porous media and not in fractures, there may be some similarities because of the aperture 
variations in fractures. However, quantification of the effect of porosity reductions in fractures 
on the fracture permeability may be more uncertain.

 3-97 
Source: CRWMS M&O 2000b, Figure 42 
NOTE: (a) Low, (b) Mean, and (c) High. The red areas indicate the maximum decrease in porosity as a result of 
mineral precipitation. 
Figure 3-38. Contour Plot of Calculated Total Fracture Porosity Change at 
10,000 Yr for Three Climate-Change Scenarios (Less Complex) 
The model is also limited to the middle nonlithophysal unit of the Topopah Spring Tuff. 
Lithophysal units may exhibit different TH behavior that would change the interaction of 
fracture and matrix waters. Differences in the mineralogy of fractures and lithophysae could 
change the chemistry of the system somewhat, although the bulk-rock chemistry is very similar 
for all of the welded TSw units. The effective reactive surface area is more important than 
mineral abundances. More important than small differences in mineral abundances is the 
effective reactive surface area, which could be larger in lithophysal units because of the 
(a) greater abundance of vapor-phase minerals and (b) because of the interaction of waters 
flowing between fractures and lithophysae. 
These uncertainties do not, in general, limit the applicability of the models, because of the ability 
to calibrate effective reaction rates to fit the results of laboratory and in situ experiments (i.e., 
thermal tests). Some of the uncertainties inherent in the thermodynamic and kinetic data have 
been addressed by consideration of a simplified and a more complex mineral assemblage. 
Validation of the model by comparison to geochemical data from the DST provides the best 
degree of confidence building, and these comparisons have shown that the model is reasonable. 
Differences in the model results between the two geochemical systems, showing that the pH and 
CO2 concentration in the gas phase for the simpler system compares more favorably to data from 
the DST shows the model provides important bounds on reaction rates. The good agreement in 
pH reflects the role of calcite dissolution in moderating pH, which would be much lower (4 to 5)

 3-98 
given the elevated gas-phase CO2 concentrations in the condensate regions. Results from the 
more complete system yield a higher pH than in the measured waters from the DST, which is due 
to a greater calculated reaction rate for feldspars. Therefore, porosity reductions as a result of 
feldspars altering to clays and zeolites likely take place at rates less than that given by the model, 
giving an important upper bound. Over the longer time period of the potential repository, the 
system may tend toward the behavior of the complex system, in comparison to the thermal tests, 
where time of the interaction of condensate waters with minerals is short-lived and only the 
minerals with the largest reaction rates affect the chemistry significantly. 
3.3.5 Summary and Conclusions 
The conceptual model for THC processes provides a comprehensive basis for modeling the 
pertinent mineral-water-gas reactions in the host rock, under thermal- loading conditions, as they 
influence the water and gas chemistry that may enter drifts over 100,000 yr. Data are 
incorporated from the DS calibrated property sets, the UZ Flow and Transport Model, 
geochemical data (fracture and matrix mineralogy, aqueous geochemistry, and gas chemistry), 
thermodynamic data (minerals, gases, and aqueous species), data for mineral-water reaction 
kinetics, and transport data. Simulations of THC processes included coupling between heat, 
water, and vapor flow, aqueous and gaseous species transport, kinetic and equilibrium mineralwater 
reactions, and feedback of mineral precipitation and dissolution on porosity, permeability, 
and capillary pressure (hydrologic properties) for a DK (fracture-matrix) system. The effect of 
these coupled THC processes on the time evolution of flow fields in the UZ around drifts has 
been investigated for different climate-change scenarios, calibrated property sets, and initial 
mineralogy. Validation of the model was done by comparison of measured gas and water 
chemistry from the DST to the results of simulations using the DST THC Model. In particular, 
simulation results were compared to measured gas-phase CO2 concentrations and the chemistry 
of waters collected from hydrology boreholes during the test. 
Comparisons of water chemistry (pH) and CO2 concentrations in the gas phase from the DST 
indicate that a Less Complex set of aqueous species and minerals (calcite, silica phases, gypsum), 
but including gaseous CO2, can describe the general evolution of DST water quite closely. 
Including a wide range of aluminosilicates, such as feldspars, clays and zeolites yields 
information on additional species (i.e., Al, Fe, F), but their inclusion causes shifts in the water 
and gas chemistry that are more rapid than observed. These effects may be more important over 
longer time periods, leading to similar but less rapid changes (i.e., a slightly closer approach to 
equilibrium). However, over the time scale of the DST, the effective reaction rates and/or 
thermodynamic properties of these phases will clearly require some refinement. Section 3.6.4.2 
summarizes the use of field and laboratory data to validate THC models. 
The THC Process Model incorporates elements of the EDA II design to represent waste package 
heating over time, changes in heat load due to ventilation, effective heat transfer within the drift, 
addition of backfill after 50 yr, and THC processes in the unsaturated zone. A number of cases 
were evaluated for different calibrated property sets, climate-change scenarios, and geochemical 
systems. The THC Seepage simulations indicate that there may be an increase in the CO2 gas 
and aqueous carbonate concentrations around the drift during rewetting. The extent of the dryout 
zone and the time of rewetting were different for each climate history and calibrated property set, 
although the general character was unchanged. As in the DST THC simulations, notable

 3-99 
differences in the pH and CO2 concentrations appeared in the two geochemical systems. The 
composition of waters reaching the drift wall during rewetting were roughly neutral in pH (7-8.5) 
for the Less Complex geochemical system (without aluminosilicates) and approximately 8.69.0 
for the Complex geochemical system. The predicted pH and HCO3
- concentrations in the Less 
Complex geochemical system simulations are supported by data from the DST. However, the 
long-term evolution could trend in the direction of the Complex system chemistry, if the slow 
reaction rates of the aluminosilicates limit the changes in water chemistry that can be observed 
over the short heating time of the DST. Because the models are based on no-flow boundaries on 
the drift walls, no exchange of gas between the in-drift environment and the rock around the drift 
is considered within these analyses. The impact of this back-coupling to the THC models cannot 
be assessed, because the in-drift gas composition would be affected by ventilation, gas transport 
along drifts, and reactions with engineered materials within the drift. 
Even with the apparently overestimated reaction rates for the full mineral assemblage, the 
changes in porosity and permeability around drifts over 100,000 years were small (less than 
1 percent of the total fracture porosity), and, therefore, effects on flow and transport are 
considered negligible. Estimates of potential for plugging of fractures are very sensitive to the 
fracture porosity that is assumed. Estimates of potential plugging as reported in the 1998 time 
frame (Hardin 1998) were based on fracture porosities in the tsw33, 34, and 35 layers of 
1.05x10-4, 1.24x10-4, and 3.29x10-4 respectively, as shown on Table 310. The current estimates 
of potential plugging, which indicate plugging will be insignificant, are based on revised 
estimates of fracture porosities from gas tracer tests. The current estimates are approximately 
100 times greater than earlier estimates, as is shown on Table 310. Estimates of plugging have 
been consistent, when the porosity is considered, as discussed in Section 3.2.3.4 and 
Figure 3-100 in Section 3.6.2.2. Further, it should be noted that application of property values 
from the Tptmn to the entire repository footprint (as recommended in Section 5.4) introduces 
uncertainty that cannot be qualified without testing in the Tptll. 
Table 3-10. Comparison of Fracture Porosities Used in Analyses of Potential Fracture Plugging 
UZ Model Layer 
1998 Reported Fracture Porosity 
(Hardin, 1998) from RIB 
(MO9901RIB00044.000) 
Current estimates of Fracture 
Porosity 
(DTN: #LB997141233129.001) 
tsw 33 1.05x10-4 6.6x10-3 
tsw 34 1.24x10-4 1x10-2 
tsw 35 3.29x10-4 1.1x10-2 
The results of this section were abstracted for use in TSPA-SR, as discussed in Section 3.4. The 
thermal tests that are much of the basis of the NFE THC model are discussed in more detail in 
Section 3.6.1. Pertinent natural analogs are discussed in Section 3.6.2.2. Finally, the status of 
validation of the THC model is addressed in Section 3.6.4.2. 
3.4 THC MODEL ABSTRACTION 
The THC Abstraction AMR (CRWMS M&O 2000c) describes a THC abstraction, for the TSPA 
model, of the NF host rock water chemistry and gas-phase composition. It also provides an 
abstracted process- model analysis of potentially important differences in the thermal hydrologic

 3-100 
(TH) variables used to describe the performance of a geologic repository obtained from models 
that include fully coupled reactive transport with thermal hydrology and those that include 
thermal hydrology alone. Specifically, the motivation of the process-level model comparison 
between fully coupled thermal-hydrologic-chemical (THC) and thermal-hydrologic-only 
(TH-only) is to provide the necessary justification as to why the in-drift thermodynamic 
environment and the NF host rock percolation flux, the essential TH variables used to describe 
the performance of a geologic repository, can be obtained using a TH-only model and applied 
directly into a TSPA abstraction without recourse to a fully coupled reactive-transport model. 
Section 3.2.3.4 further addresses this issue. 
3.4.1 Inputs to the Abstraction 
Abstraction, as used in the context of the analysis described in the THC Abstraction AMR 
(CRWMS M&O 2000c), refers to an extraction of essential data or information from the processlevel 
model. The abstraction analysis reproduces and bounds the results of the underlying 
detailed process-level model. 
The DS THC process model developed in the THC Process AMR (CRWMS M&O 2000b) and 
discussed in Section 3.3 serves as the primary input used in the THC abstraction analysis. The 
THC model results are used to define the major (i.e., order-of-magnitude) changes to water and 
gas compositions resulting from thermally-driven coupled reactive transport in the geosphere. 
Specifically, the process model provides the basis for an abstraction of a time evolution of the 
aqueous water chemistry and gas-phase composition as obtained from an analysis that includes 
both a Complex mineral assemblage as well as a Less Complex mineral assemblage. In addition 
to including the minerals and species from the Less Complex mineral assemblage, the Complex 
set also includes a wide range of alumino-silicates, such as feldspars, clays, and zeolites. The 
Less Complex mineral set includes only calcite, silica phases, and gypsum. The Less Complex 
mineral assemblage applied in the THC process model is used to describe the general evolution 
of the DST. Since the Less Complex mineral assemblage represents the measured results of the 
DST more accurately than the complex set of minerals ; it provides the data input for abstraction 
of primary chemical species in the host-rock fracture water. The Complex mineral assemblage is 
used solely to abstract time-evolution data for the trace constituents that are not included in the 
Less Complex THC simulations. Although representing a more comprehensive set of 
components, the complex mineral assemblage results have additional uncertainty, because of: 
(1) larger uncertainty in the kinetic behavior of the additional phases, and (2) lack of additional 
mineralogic species that could affect some of the changes to major elements related to the 
carbonate subsystem (CRWMS M&O 2000b). The time-dependent abstraction THC data are 
used in the in-drift geochemical models developed for total system performance assessments 
(TSPA). 
One purpose of the THC modeling is to determine whether the values of the parameters in the 
Less Complex set change significantly when the additional cations and anions are included in the 
calculation. Another objective is to determine whether the chemical reactions have a significant 
effect on the hydrological parameters of the NF rock, such that seepage into the emplacement 
drifts could be affected. This section of the PMR summarizes how the THC results (described in 
Section 3.3) are abstracted for use in the TSPA models.

 3-101 
The THC models are implemented in the TOUGHREACT software package, which is one of the 
TOUGH family of heat and mass-transfer codes. As described in the UZ F&T PMR (CRWMS 
M&O 2000f, Section 1.3.2), the TOUGH family of codes is also used to calculate the 
hydrological property distribution in the mountain (using inverse modeling), the percolation flux 
distribution, and seepage into emplacement drifts. 
3.4.2 Abstraction of THC Results 
The results of the abstraction of water and gas composition for TSPA are given in Table 3-11. 
They provide boundary condition inputs for other in-drift geochemical models used by the TSPA 
model. The results in Table 3-11 shown below are abstracted from the process THC model 
described in Section 3.3. Consequently, they are constrained by the process-model assumptions 
and inputs. If, for example, the initial pore water composition used as input to the DS THC 
model, is only representative of the Topopah Spring Tuff middle nonlithophysal geologic unit 
(Tptpmn) and not the other host units, the abstraction may not be fully representative at 
repository locations other than the Tptpmn (initial pore waters used in the model are based on 
samples taken from the DST alcove, which is excavated in the Tptpmn). Under equilibrium 
conditions, the pore waters would reflect the interaction with the local mineral assemblage at that 
temperature and gas composition, which would create distinct waters within each rock unit. 
However, the mineral assemblages and their abundance within the potential repository units 
differ insignificantly and temperatures vary only minimally. This should not be construed to 
suggest that the pore water chemistry in the other units is fundamentally different than that of the 
Tptpmn, this was merely given as an example of the need to be aware of underlying assumptions 
or input when evaluating results of abstraction models. If the water chemistry is in equilibrium 
with the rock, given that the basic mineralogy is similar, then the water chemistry should be 
similar in all of the units. However, it cannot be ruled out that the chemistry might differ, the 
chemistry is not in total equilibrium. The point, as noted above, is that input uncertainties need 
to be recognized when considering the results of the abstractions. In this same vein, the 
abstraction results are valid only for the infiltration flux cases with climate change considered in 
the THC model (infiltration flux cases for low, mean, and high). 
3.4.2.1 Mean Infiltration Flux Case 
The THC abstraction of the mean infiltration flux (with climate change at 600 and 2,000 yr.) case 
is given in Table 3-11 (CRWMS M&O 2000c, Section 6.1.1). 
Table 3-11 represents the abstraction of water and gas compositions for the THC boundary 
conditions adjacent to the drift wall. Each of the time periods has a defined composition of gas 
and water that represent s those constituents that can enter into the drift during those times, based 
on the process-level THC models for the thermally perturbed geosphere. Four periods, 
preclosure, boiling, transitional cool-down, and extended cool-down are defined for use in 
TSPA-SR calculations. This provides roughly constant chemical conditions for the purposes of 
calculating in-drift processes for those representative time periods. The abstraction method 
reduces the coupling between the NFE and EBS models, allowing a larger degree of parallel 
work in developing the TSPA for the Site Recommendation.

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Note the abstracted temperatures listed in Table 3-11 are provided for reference only. Only the 
temperature in Boiling Period 2 will be used to calculate reequilibration of condensate with the 
CO2 gas composition. 
The abstraction includes both the Complex and Less Complex geochemical systems considered in 
the THC process model described in Section 3.3.2.4. For the constituents included in both 
chemical systems, (common constituents), major differences (factor of 10 or one log unit or 
more) are limited to Ca2+, Na+, and HCO3
. The other constituents contained in both 
geochemical systems, while not the same, are also not different by more than an order-ofmagnitude. 
The primary goal of the TSPA abstraction is to capture order-of-magnitude changes 
in species concentrations. Therefore, the smaller differences between common constituents 
would not be represented in the abstraction. In order to maintain consistency with the 
geochemical system that is most representative of the DST results, the constituents from the Less 
Complex system were chosen for abstraction. In the case of aqueous calcium, sodium, and 
carbonate, the primary differences result from the additional uncertainties associated with the 
kinetic representation of the Complex geochemical system (CRWMS M&O 2000c, 
Section 6.1.1). As in the case of the other common constituents, the abstraction for these three 
components also stems from the Less Complex system. 
The THC water chemistry and gas-phase composition abstraction represents the fracture waters 
impinging at the crown and sides of the potential emplacement drifts. The abstraction uses the 
detailed time-history results of the process-level THC model and discretizes them into four 
distinct geochemical periods for which compositional boundary conditions are provided for the 
potential in-drift geochemical environment for TSPA models. The abstraction compositional 
boundary conditions include constituents represented by five cations, six anions, and pH. In 
addition, this abstraction includes the partial pressure of carbon dioxide in the gas phase, in 
fractures adjacent to the potential drifts (and, during the abstraction boiling period, the 
equilibration temperature used for that gas with the condensate water composition). These 
boundary conditions to the potential drifts allow incorporation of time-varying, thermally 
perturbed water and gas compositions in the assessment of chemical interactions of the in-drift 
environment. 
Use of the abstracted THC process model results for the Less Complex mineralogy is based on 
the fact that it reproduces more accurately (than the Complex mineral set) the observed changes 
to water and gas compositions in the DST (see Section 3.3.3 of this report, and CRWMS 
M&O 2000b, Sections 6.1.7 and 6.2.7). This corresponds to using the mineralogic phase 
constraints represented in the Less Complex system to set the major-element composition of the 
water and gas. 
The first abstraction period defined goes from 0 to 50 year and represents the entire preclosure 
period. This is followed by the defined boiling period 2, during which the fractures are 
calculated to have zero saturation. The water that may enter the drift through these fractures 
would be that moving rapidly down from the condensate zone. This boiling period is followed 
by a transitional cooldown period from 1,000 to 2,000 years during which temperature is still 
high, but below boiling. Finally an extended cool-down period 4 is defined from 2,000 to 
100,000 years, over which temperatures return to ambient and water compositions change 
gradually.

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Table 3-11. THC Abstraction for the Mean Infiltration Rate Case with Climate Change 
Preclosure Boiling Transitional 
Cool-Down 
Extended 
Cool-Down 
Period 1 Period 2 Period 3 Period 4 
Parameter Abstracted Values Abstracted Values Abstracted Values Abstracted Values 
Time 0 - 50 yr. 50 - 1000 yr. 1000 - 2000 yr. 2000 - 100,000 yr. 
Constituents Considered in Less Complex Chemical System (calcite-silica-gypsum) 
Temperature, C 80 96 90 50 
log CO2, vfrac -2.8 -6.5 -3.0 -2.0 
pH 8.2 8.1 7.8 7.3 
Ca2+, molal 1.7E-03 6.4E-04 1.0E-03 1.8E-03 
Na+, molal 3.0E-03 1.4E-03 2.6E-03 2.6E-03 
SiO2, molal 1.5E-03 1.5E-03 2.1E-03 1.2E-03 
Cl

, molal 3.7E-03 1.8E-03 3.2E-03 3.3E-03 
HCO3

, molal 1.3E-03 1.9E-04 3.0E-04 2.1E-03 
SO4
2
, molal 1.3E-03 6.6E-04 1.2E-03 1.2E-03 
Additional Constituents Considered in the Complex (Full) Chemical System 
Mg2+, molal 4.0E-06 3.2E-07 1.6E-06 7.8E-06 
K+, molal 5.5E-05 8.5E-05 3.1E-04 1.0E-04 
AlO2

, molal 1.0E-10 2.7E-07 6.8E-08 2.0E-09 
HFeO2

, molal 1.1E-10 7.9E-10 4.1E-10 2.4E-11 
F

, molal 5.0E-05 2.5E-05 4.5E-05 4.5E-05 
Source: CRWMS M&O 2000c, Table 3 
During the second abstraction period, the boiling period, fracture saturation around the drifts is 
calculated to be zero in the THC process model results. The chemical composition of the 
condensate water calculated to be in the zone of highest saturation above the fracture dryout is 
used to represent the water that may flow rapidly through fractures during the boiling period. 
The composition of such water is given in Table 3-11 with the value of the partial pressure of 
CO2 in the gas surrounding the drift wall during that dryout time. The flux of such water would 
be at a minimum during this period, so the CO2 concentration at the drift wall can be used to 
represent the concentration at equilibrium with this water. This value is given in Table 3-11. 
Gas composition and associated boiling temperature should be used to equilibrate with the 
abstracted condensate water composition shown for this period in Table 3-11. This represents 
the abstracted water may flow rapidly down fractures into the dryout zone from the overlying 
condensate zone. 
The following should be noted for the abstraction shown in Table 3-11: 
 The first 50 years represents the repository preclosure period with 70 percent heat 
removal via ventilation. However, because the Performance Assessment only starts at 
closure, these values are not used and are only provided for completeness of the time 
span. It is emphasized that the values probably would not be representative of 
preclosure conditions, because the potential chemical effects of ventilation are not 
included in the process model.

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 The values for abstraction period 3 correspond to the process-level model results at 
2,000 years. after initial waste emplacement. This is because, as soon as the drift-wall 
rock resaturates, the CO2 very rapidly approaches about 1x10-3 bars and the pH and 
water composition are taken consistently with this gas chemistry. A rapid transition 
occurs in the water and gas compositions from 1,000 to 2,000 yr. In this time span, the 
drift-wall temperature drops from above boiling to below boiling. Therefore, the THC 
process- level model results at 2,000 years first represent water and gas compositions at 
temperatures below boiling (since the precolsure period). This partial pressure of carbon 
dioxide and corresponding water compositions at the drift wall represent conditions just 
as the host-rock temperature drops below the boiling point of water at that location (e.g., 
at 2,000 years). 
 The 10,000-yr process-level model results are used for the abstraction values in the last 
period as a reasonable approximation of the water composition average for that whole 
period. This is due to the fact that the water composition does not change appreciably 
from 10,000 to 100,000 yr. For example, HCO-
3 and Ca2+ increase by less than a factor 
of 1.5 from 10,000 to 100,000 yr. These particular ions represent the largest change of 
all considered. All other concentrations vary even less from 10,000 to 100,000 years 
(CRWMS M&O 2000b, Figures 33 and 35). For instance, Na+, Cl-, and F- show no 
change during this time period (CRWMS M&O 2000b, Figures 37, 39, and 40). The 
CO2 concentration and pH also change, but very slightly during this period (CRWMS 
M&O 2000b, Figures 29 and 31). Other trace constituents accounted for in the 
abstraction are also nearly constant during this time period. 
The additional constituents taken from the results of the Complex chemical system are, in 
general, trace constituents compared to those taken from the Less Complex chemical system. 
Even though combination of these results may lead to discrepancies of the trace constituents that 
could be large in a relative sense, their contributions to the absolute uncertainties of the major 
constituents will remain small. Only potassium approaches the concentrations of the constituents 
taken from the less detailed chemical system, and even it is one to two orders of magnitude lower 
in concentration than the major cation species Ca+2 and Na+ included in the Less Complex system 
results. 
3.4.2.2 Low and High Infiltration-Flux Cases 
This section discusses and quantifies the THC conceptual uncertainty in these results due to the 
variability in infiltration that stems from uncertainty in the infiltration rate at Yucca Mountain. 
This aspect of uncertainty is based on comparison of the mean infiltration case results (used for 
the abstracted values given above) with those from both the low-and the high-infiltration flux 
cases representing the uncertainty in infiltration rate at Yucca Mountain. However, this provides 
an assessment of only part of the uncertainty within these results. Other aspects that contribute 
to uncertainty are related to the process model and include conceptual uncertainties about the 
initial water composition, specific mineral abundances and distributions, the effective surface 
areas of minerals and other kinetic parameter values for the phases (CRWMS M&O 2000b). In 
addition to these uncertainties in the chemical aspects of the model, all those for the hydrologic 
model of the system also apply. Because these parts of the system are highly non-linear, 
rigorous uncertainty quantification for all these aspects is not straightforward. That is why the

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validation activities for the process model (CRWMS M&O 2000b, Section 6.2.7) are a primary 
method for assessing the level of applicability of the results. 
Abstraction of uncertainty in the abstracted fracture-water compositions shown in Table 3-11 is 
based on the mean infiltration flux, low infiltration flux, and the high infiltration flux cases and 
uncertainty in the condensate-water compositions for these infiltration-flux cases (THC 
Abstraction AMR, Section 6.1.2). 
An estimate of uncertainty in the THC abstraction indicates that for most constituents the values 
calculated for the high- and low-infiltration cases are within about a factor of two of the 
mean-infiltration flux case used in the abstraction. The exceptions to this correspond primarily 
to those constituents evaluated for the period where the fractures are dry (saturation of zero). In 
almost all cases, this represents the inclusion of artifact water compositions that occur because 
the process-level THC calculation cut-off the solution chemistry either at the point the solution 
reaches a maximum of 2 molal ionic strength or the saturation reaches a minimum of 0.0001 
(CRWMS M&O 2000b, Section 6.3.5.2). Also, the three infiltration-flux cases (low, mean, and 
high) considered in the process model result in the different temperature histories for each 
mineral set. Variability in the temperature history leads to different rewetting times, potentially 
causing different water and gas compositions in the fractures when they resaturate. A dry 
fracture condition (CRWMS M&O 2000b, Figure 24) results in gaps in representation of 
reasonable, calculated fracture-water composition during that time (CRWMS M&O 2000b, 
Figures 31, 33, 35, 37, and 39), even though the gas composition calculation is continuous 
through this time (CRWMS M&O 2000b, Figure 29). In all cases, values that are different by 
more than an order of magnitude only occur for dissolved constituents during these situations. 
Even during those times, the water-chemistry values are different by more than one order of 
magnitude, but not by more than two orders of magnitude. As indicated, there is little meaning 
to the water composition as the fractures begin to dry (during the above-boiling period in the 
process-level model) because the water composition is fixed once fracture saturations are too 
low or ionic strength too high in the model. 
The differences in the rewetting process for the fractures is most pronounced for the CO2 gas 
compositions in the low climate history results compared to those for the mean climate history. 
The CO2 values from the low infiltration rate case are only about 2 to 5 percent of those for the 
mean climate, until about 10,000 years. This variation in gas composition is reflected in an 
increase of about 10 percent in the solution pH. This result appears to be driven primarily by the 
lower flux of water moving through the system for the low climate- history case. The liquid flux 
is both a major source of CO2 mass moving back to the drifts and a mechanism for heat removal. 
Both of these processes are enhanced for the higher infiltration-rate cases compared to the case 
for the low fluxes. 
For comparison of calculated condensate water-compositions (for period 2 in the abstraction) for 
the various infiltration histories, the only species for which results differ by more than an order 
of magnitude are the Mg and Al constituents, which for the low infiltration case are about 
8 percent and 6 percent, respectively, of their mean infiltration-rate case values. This represents 
only a small difference, because in all other cases the values are generally within a factor of two.

 3-106 
Given the observations from these comparisons, the abstracted water and gas compositions 
provided in Table 3-11 would only require about a factor of between two and ten to account for 
the variation in results from the other infiltration-flux cases. Using a factor of two to represent 
the standard deviation of such a distribution should encompass 95 percent of the variations that 
are meaningful, whereas using a value of 10 would conservatively encompass all of the 
meaningful variations within the uncertainty bands. 
As this variability is expected to be relatively small compared to that expected for changes 
driven by the in-drift evaporative processes accounting for higher concentration fluids and salt 
formation, it should not be necessary to explicitly incorporate this variability into a stochastic 
representation of the system until the larger variability of different conceptual processes is 
incorporated into this approach. 
3.5 THERMAL-HYDROLOGIC-MECHANICAL CALCULATIONS 
This section briefly describes the TM behavior of rock in the NFE and the coupling of this 
behavior with hydrologic processes. In particular, the influence of TM effects on fracture 
permeability is discussed. 
The stress field in the rock mass surrounding emplacement drifts in a potential repository at 
Yucca Mountain will be altered by excavation of drifts and by the heating and cooling cycle 
associated with emplacement of radioactive waste. The directions and magnitudes of the 
principal stresses will change significantly due to thermal loading, and then will return to 
near-ambient values during cool-down. Compressive stress will build up rapidly in the host 
rock, especially after the end of the ventilation period. The stress field will gradually decay as 
the temperature in the rock decreases. 
The proposed repository host rock is a fractured, densely welded, ash-flow tuff. These fractures 
are expected to deform as stress conditions evolve. Two types of fracture deformation will 
contribute to THM coupling: normal displacement perpendicular to the fracture plane, and shear 
displacement parallel to a fracture plane. 
Rock-mass permeability is an important TH property for assessment of repository performance. 
Because the rock has low matrix permeability, the rock-mass permeability is mainly associated 
with fractures, and fracture permeability is highly dependent on fracture deformation. 
In this section, the relationship of fracture deformation to fracture permeability is discussed, and 
a TM model for the rock mass surrounding an emplacement drift incorporates discrete fractures. 
Fracture deformation during various phases of the heating-cooling cycle is used to predict 
changes in rock-mass permeability. These changes can be coupled back to TH or THC models. 
In this section, a methodology for estimating TM effects on permeability is presented, using a 
distinct-element model that can capture the mechanical behavior of discrete fractures. Estimated 
permeability changes for selected times after waste emplacement, based on the EDA-II design 
(CRWMS M&O 1999a, Table 6-3; Wilkins and Heath 1999), are calculated using this method. 
In the distinct-element method, the rock mass is composed of an assembly of deformable blocks 
that are interfaced by discontinuities. In a distinct-element code (Itasca 1998), fractures in the 
rock mass are entered individually, and both normal and shear deformation are predicted for the

 3-107 
individual fractures. The example calculation discussed in this section uses fracture spacing 
appropriate for the middle non-lithophysal region of the repository. 
The effects of TM processes on fracture hydrologic properties are not directly incorporated in 
abstraction for TSPA-SR. Consequently, the effects of TM processes are screened out of TSPA 
based on low consequence (to be verified status by future calculations ). A range of uncertainty 
in fracture hydrologic properties is included in the TSPA seepage model that may potentially 
account for processes not directly included in TSPA (CRWMS M&O 2000l, Section 6.2.3). 
However, this range is not based on explicit information associated with TM effects on fracture 
properties. 
3.5.1 Approach to Coupling TM to TH Behavior 
Coupling of TM and TH behavior is principally through the temperature and permeability fields. 
At present, several sophisticated algorithms for predicting TH behavior in partially saturated 
fractured rock are available. Moreover, these sophisticated simulators, such as NUFT, are 
needed to capture the TH behavior, which controls the temperature field over long periods of 
time. However, these algorithms are also computationally complex and intensive, and have not 
been directly implemented into a fully coupled THM code. Accordingly, for this report, 
temperature distributions generated by TH simulators are approximated using the simpler 
(conduction-only, with a simplified heat source) thermal models currently incorporated into 
available TM simulators. The thermal-stress distributions associated with the approximated 
thermal field are analyzed using a conceptual model for fracture-permeability change in response 
to deformation. The changes in permeability are then fed back to the TH models for refinement 
of the TH simulations. 
3.5.2 Distinct-Element Calculation of TM Effect on Permeability  EDA-II Design 
A calculation to provide an estimate of bounds for TM effects on fracture permeability has been 
conducted and is documented in the THM Calculation (CRWMS M&O 2000d). One purpose of 
this estimate of bounds was to provide essential input to performance assessment analysis of the 
potential repository system. The method used in this calculation was to simulate the TM 
behavior of a region of fractured rock that surrounds a section of a long horizontal emplacement 
drift in the Topopah Spring Tuff at Yucca Mountain. 
The rock mass surrounding an emplacement drift is simulated in three dimensions as a 
rectangular prism 50 m wide by 60 m high by 30 m thick, defined as shown in Figure 3-39. A 
cylindrical drift 5.5 m in diameter is excavated through the region in the x direction and brought 
to stress equilibrium. This drift is horizontal, and oriented perpendicular to the narrow 
dimension of the region. The prism is intersected by three sets of fractures: one vertical set 
oriented parallel to the drift, one vertical set oriented perpendicular to the drift, and one 
horizontal fracture set. It should be noted that the drift orientation is consistent with that of the 
EDA-II design (CRWMS M&O 1999a, Table 6-3; Wilkins and Heath 1999), but the fracture 
orientations are based on field observations (Albin et al. 1997). Two fracture densities are used 
for each set of fractures, a low fracture density (0.1/m) for regions more than 15 m from the drift, 
and a higher fracture density (0.5/m) for regions within 15 m of the drift. This nested fracture 
density distribution was to facilitate computation of individual fracture movement. That is, the

 3-108 
available computational resources limited the number of fractures that could be included. These 
fracture densities are lower than those observed in situ, and lower than those used in thermalhydrologic 
modeling (CRWMS M&O 2000a), but are appropriate, as not all fractures are 
mechanically and hydrologically active in the field. Only active fractures are considered here, 
and work by Barton et al. (1997) presents convincing evidence that fractures that conduct fluids 
are fractures that are critically stressed in shear. Joint and rock-mass properties used in this 
calculation (CRWMS M&O 2000d) were taken from field and laboratory studies of rock and 
fracture behavior, such as those by Barton et al. 1985, and Olsson and Brown 1994. Stresses 
equivalent to the in situ stresses are imposed on the sides and top of the prism. The base of the 
prism is fixed in the vertical direction, but allowed to move in the horizontal directions. The 
model boundary conditions are intended to approximate in situ conditions and are similar to 
those used in previous thermomechanical modeling (Berge et al. 1998) and are based on field 
stress measurements. Fracture-deformation values estimated at a series of times are then used to 
compute permeability change in a cross section perpendicular to the emplacement drift. These 
values for permeability change at each time were then contoured. 
3.5.2.1 Thermal Field 
The commercial 3DEC (Itasca 1998) distinct-element code was used for the simulations. This 
model utilizes a weakly coupled approach to thermal mechanical analysis. The thermal field 
imposed by the emplacement of nuclear waste containers is simulated within the 3DEC code 
using a conduction-only thermal model that calculates temperatures in an infinite medium. The 
thermal model allows adiabatic and isothermal boundary conditions to be applied in the thermal 
formulation. This thermal model is used to compute temperatures at all gridpoints in the 
mechanical model of the problem being studied. The temperature change (from initial 
temperature) for each zone is used to calculate a stress change in each zone. This stress state is 
treated as an initial condition for the mechanical calculation, and the standard 3DEC mechanical 
calculation is used to reach equilibrium. 
The calculation is intended to evaluate rock behavior for a section of an emplacement drift 
within a potential nuclear waste repository. To do this, a block of rock is defined that includes a 
section of an emplacement drift. Within this block, a line heat source is used within the 
emplacement drift to simulate emplaced waste containers. To assure constant heat load along the 
section of simulated emplacement drift, the heat source extends approximately 30 m beyond the 
boundaries of the simulated block in both directions, as shown in Figure 3-40. The calculation is 
designed to simulate the EDA-II design; thus identical heat sources are placed at 81 m to the 
north and south of the tunnel heater array in the surrounding rock continuum, as shown in 
Figure 3-40. 
The thermal simulator incorporated into 3DEC is an isotropic uniform, conduction only model, 
and thus the estimated temperatures are expected to be elevated near the drift wall compared to 
those predicted using more sophisticated TH models that include cooling due to convection and 
latent heat (heat-pipes). Temperature distributions at several times after emplacement are given 
in the THM Calculation (CRWMS M&O 2000d). Overall, at locations more than a few meters 
away from the drift, the temperatures match those predicted using TH models well enough for 
use in this bounding calculation. Because the THM calculation is a bounding calculation, 
elevated temperatures near the drift wall are not an issue.

 3-109 
Figure 3-39. Simulated Rock Mass for TM Coupled Effects Showing 
Three Sets of Fractures and Two Fracture Densities for 
Each Set 
The thermal load of the model (see Figure 3-41) is based on the EDA-II design, in which 
ventilation is used to remove heat from the emplacement drift for the first 50 years after 
emplacement. The EDA-II design shows a spike in the pillar temperature starting at 50 years, 
when ventilation ceases, followed by slower cooling. 
A simple step function was used for the thermal power input (Figure 3-41). Power was supplied 
at a constant level of 460 watts for 50 years to simulate the ventilation phase, then raised to 
615 watts and held constant for another 100 years, then reduced to zero. This heating schedule 
produced temperatures similar to the maximum pillar temperature, but over a longer time, 
followed by a more rapid cooldown than TH calculations (Sections 3.2.3 and 3.3) with a more 
realistic source. Since the objective of the THM calculation is to calculate bounds for stresses 
and displacements, the faster cool down is appropriate as faster cooling produces higher stress 
gradients in the region around the drift than does cooling at a slower rate. These higher stress 
gradients in turn produce larger deformations in the NF rock. Moreover, the fast cool-down is 
more compatible with the assumption of a constant value of joint cohesion over the time span of 
the calculation. This is because fracture properties are thought to be time dependent Drift 
Degradation Analysis (CRWMS M&O 2000ac).

 3-110 
Source: CRWMS M&O 2000d, Figure 3 
NOTE: a. The heater array extends approximately 30 m beyond the boundaries of the mechanical model in both 
the + and  directions. 
b. Identical heat sources (dashed lines) are placed at 81 m to the north and south of the tunnel heater 
arrays. 
Figure 3-40. Schematic of Heater Layout for Simulation

 3-111 
Source: CRWMS M&O 2000d, Figure 4 
Figure 3-41. Thermal Power History for Simulation 
3.5.2.2 Fracture Deformation 
After non-heating equilibration to account for excavation effects, the numerical model was used 
to estimate stress and deformation values in the block at a series of times after emplacement. 
Both normal and shear deformation were predicted for multiple locations on each fracture face. 
Normal displacement is associated with changes in normal stress. Fractures stiffen readily as 
they close in response to normal compression, which limits the relative magnitude of the 
permeability change that can be produced. Several investigators have shown that increasing 
compressive stress across the apparent fracture faces causes a reduction in fracture aperture, and, 
to a first approximation, flow in a fracture is widely accepted to be related to the cube of the 
fracture aperture (Raven and Gale 1985, pp. 251-261). Heating the rock generally increases 
stress and thereby reduces the fracture aperture in proportion to fracture normal stiffness. If the 
average normal stress is maintained well below the intact rock strength, and if creep is not 
significant, fractures generally return to their previous aperture when unloaded (i.e., normal 
displacement is reversible). Fractures open in response to decreasing normal stress and 
eventually open at zero load. If fracture surfaces remain well aligned, and if shear displacement 
does not occur, fracture opening is also reversible. Fracture closing is expected during the

 3-112 
heating phase in response to thermal expansion of the rock mass. Fracture opening is expected 
during cooldown. 
The TM response of fractures may also include shear displacement along the face of the fracture. 
Moreover, field studies during the last few years (Barton et al. 1997) have shown convincing 
evidence that fractures that are critically stressed in shear, are likely to conduct fluids. In 
addition, experimental studies on laboratory samples have shown that fracture shear 
displacement can significantly increase fracture permeability and that the magnitude of change in 
permeability may be large. This is because even small shear displacements cause fractures to 
dilate, which mobilizes the surface roughness and decreases the spatial correlation or 
matedness of fracture surfaces. This opens up void space in the fracture and can greatly 
increase permeability with only a small change in normal aperture (Barton et al. 1985). 
The tendency for slip in response to shear stress is controlled by the frictional properties and 
geometry of the fracture surfaces, the hydraulic conditions within the fracture, the deformation 
history of the fracture, and the normal stress on the fracture. Frictional and geometrical 
properties are represented for all fractures in the host rock at Yucca Mountain by average 
property values that are similar to those used for analysis of drift degradation (CRWMS 
M&O 2000ac). Fractures in the host rock may be wet, but there will be no significant positive 
pressure head in the unsaturated zone. 
In the calculation of THM effects on permeability, the estimated joint-deformation values for a 
series of selected times are used to compute permeability change in a cross section perpendicular 
to the emplacement drift. 
3.5.2.3 Calculation of Permeability Change 
The distinct-element method was selected for this study because it allows discrete fractures to be 
simulated. Moreover, it is the only method that provides direct simulation of normal and shear 
displacement and other behavior on discrete fractures. When a distinct-element model is used 
for simulations, both normal- and shear-fracture deformations are computed directly. In this 
case, one approach for computing a change in fracture permeability is to define k0 as the initial 
fracture permeability and kt as the fracture permeability at time, t, due to TM effects. If df is 
defined as the magnitude of fracture displacement in mm (shear or normal), then a permeability 
multiplier, k , can be computed as the dimensionless ratio 
(mm) df ) mm / 10 ( 1 0  + = = k k k t 
Using this expression, shear deformation always produces an increase in permeability, while 
normal deformation will increase permeability if the fracture opens (df > 0) and will decrease 
permeability if the fracture closes (df < 0). This approach was used in the THM Calculation 
(CRWMS M&O 2000d). The calculated joint deformations were used to compute permeability 
changes in a cross section perpendicular to the emplacement drift. Maximum shear and normal 
deformation values were computed along an array of lines parallel to the drift, then projected 
onto a plane perpendicular to the drift. The displacements were then used to estimate 
permeability changes with the proportionality relationship given in the above equation. 
Moreover, while the model is generally symmetric about the mid-length of the heated region, the

 3-113 
permeability estimates are not expected to show well developed symmetry around this plane. 
This is because these estimates are based on 3-D displacement estimates that are projected onto a 
2-D plane, and because of small asymmetries in the 3DEC grid. 
The parameter k provides a straightforward linear approximation of permeability change as a 
function of deformation. This was made for several reasons. First, the relationship between 
shear slip and permeability change is poorly known. Second, use of the linear relation between 
permeability change and shear slip is consistent with the results of laboratory studies by Olsson 
and Brown (1993), who observed shear-induced fracture dilatancy and increased permeability 
with rotary shear slip, and by Esaki et al. (1999) who observed permeability increases of 1.2 to 
1.6 orders of magnitude for the first 5 mm of lateral shear slip. Assuming a linear relationship 
between slip and permeability, the results of Esaki et al. (1999) yield a permeability increase of 
between factors of 3 to 8 per mm of slip. Because this is a bounding analysis, a factor of 
10 permeability change per mm slip was used in the simulations. The combined effect of normal 
and shear deformation has not been considered, and will be addressed in future studies of 
coupled THM behavior. 
The same linear relationship for both normal and shear deformations was used for the bounding 
calculations. This approach is also consistent with numerical modeling work (CRWMS 
M&O 2000a), which found that increasing fracture permeability by two orders of magnitude, to 
simulate the opening of vertical fractures, was required to provide realistic predictions of 
temperatures in the LBT. Fracture opening displacements in the LBT were on the order of a few 
millimeters (Wilder et al. 1997). 
Finally, because it is assumed that all permeability change is due to deformation on fractures, it 
is the spatial distribution of fracture deformation that is of fundamental interest and this is 
independent of the relationship used to estimate the magnitude of changes. 
3.5.2.4 Results of Distinct-Element Calculation 
Results are presented as 2-D images of permeability multipliers, k , calculated from predicted 
values of normal and shear displacement of fractures. Stress gradients in the rock mass are 
directly related to temperature gradients due to thermal expansion of the rock. Given the 
thermal-loading regime presented in Figure 3-41, one time of interest is 55 years after 
emplacement, as this is five years after the end of ventilation, when thermal gradients in the rock 
are high. The greatest values for displacement at this time were computed for the plane 
perpendicular to the drift and were approximately 0.3 mm for normal (opening) displacements 
and 0.9 mm for shear displacements. 
Figure 3-42 shows an estimate of permeability change due to normal deformation of fractures at 
this time. The plot indicates the largest change in permeability at 55 yr after emplacement 
occurs within one drift-diameter of the drift wall. These include a decrease in permeability 
(multiplier values <1) in the ribs of the drift, and regions of increased permeability (multiplier 
values >1) above and below the drift. This is consistent with closing of vertical fractures in the 
drift rib as the rock tries to expand horizontally, and opening of vertical fractures above and 
below the drift. It is important to note that as described above, stress boundary conditions were 
used on the top and sides of the block in this simulation, and this influences the TM response.

 3-114 
These boundary conditions were used in the bounding calculation as they allow more movement 
than fixed boundaries. Moreover, despite this boundary condition, the magnitude of the 
predicted increase is relatively small (less than 2) and that a multiplier near one is estimated for 
much of the rock mass. This figure also shows that a slight increase in permeability is expected 
for horizontal fractures at distances greater than two drift-diameters. This is attributed to vertical 
thermal expansion of the rock in the near-drift region. Again, note that the predicted increase in 
permeability is small (<1.5x). 
Figure 3-43 is the 55-yr estimate of permeability change due to shear displacement. Shear 
displacement values at this time were a maximum of 0.9 mm in the plane perpendicular to the 
drift and 0.24 mm in the plane parallel to the drift. Figure 3-43 shows that after 55 years of 
heating, shear displacement may be expected to increase permeability as much as 3-6.5 in the 
region within one drift-diameter. Results in the THM Calculation (CRWMS M&O 2000d) show 
that this permeability enhancement was caused by the initial heating (0 year) and the additional 
heat at 50-55 years did not substantially change the permeability. 
Potential changes in fracture permeability are also important for evaluating repository 
performance at cooldown. Using the thermal regime shown in Figure 3-41, cooldown occurs at a 
time of 1,000 yr. Normal displacements were comp uted for the cooldown phase and maximum 
values were about 0.15 mm for planes both parallel and perpendicular to the drift. Estimated 
changes in permeability for normal deformation of the fractures at cooldown are shown in 
Figure 3-44. These results indicate that during cooldown, vertical fractures above the drift may 
open, increasing the permeability by a factor of two. 
The largest shear deformations (1.2 mm) were computed for both planes parallel and 
perpendicular to the drift at 1,000 yr. Figure 3-45 shows permeability multiplier values due to 
shear displacement at 1,000 yr. This figure shows that shear deformation on vertical fractures 
during cool down produces the maximum amount of permeability change, an order of magnitude 
above and below the drift, and increases in permeability by a factor of 5 may occur on vertical 
fractures at distances beyond two drift-diameters from the drift wall. 
3.5.3 Summary of Thermal-mechanical Models 
Results of this calculation indicate that the major TM effect on fracture permeability occurs 
during cooldown for both shear and normal deformation. 
These results indicate that shear deformation of fractures during cooldown of a potential 
geologic repository may cause permeability of the fractures in a region within two driftdiameters 
of a drift wall to increase in permeability by as much as an order of magnitude. 
Specifically, shear deformation on vertical fractures during cooldown produces the maximum 
amount of permeability change, and increases in permeability on the order by a factor of 5 may 
occur on vertical fractures at distances beyond two drift-diameters from the drift wall.

 3-115 
Source: CRWMS M&O 2000d, Figure 6(c) 
Figure 3-42. 55-year Estimate of Permeability Change Due to Normal Displacement 
Source: CRWMS M&O 2000d, Figure 6(c) 
Figure 3-43. Permeability Multiplier Values Due to Shear Displacement at 55 Years

 3-116 
Source: CRWMS M&O 2000d, Figure 5(g) 
Figure 3-44. Permeability Multiplier Values Due to Normal Displacement at 1,000 Years 
Source: CRWMS M&O 2000d, Figure 6(g) 
Figure 3-45. Permeability Multiplier Values Due to Shear Displacement at 1,000 Years

 3-117 
Results indicate that normal deformation of fractures may cause permeability to increase as well, 
but to a lesser extent than shear deformation. Closing of fractures during heating may cause 
permeability to decrease significantly within one drift-diameter of the drift wall. During 
cooldown, vertical fractures above the drift may open, increasing the permeability by a factor of 
two. It is important to note that the actual fracture permeability or hydraulic aperture is a 
function of displacements both parallel and perpendicular to the fracture wall. A quantitative 
description of how both types of fracture deformation affect flow in fractures has not yet been 
developed. Such a relationship might include a cubic term for normal deformation combined 
with an exponential term for shear deformation. 
It is important to note that as this is a bounding estimate, primarily concerned with fracture 
deformation, stress boundary conditions were chosen for the vertical sides of the model. This in 
effect provides a lower limit on normal stress across vertical fractures, thus making it easier for 
them to open and/or slip. Use of a roller boundary condition on the vertical sides to prevent 
lateral displacement at the mid-pillar would provide an upper limit on normal stress across 
vertical fractures with increasing temperature. That is, stress would build as the rock tries to 
expand in the lateral direction as temperature rises. Use of the roller boundary would provide an 
alternative distribution of permeability change. It is also important to note that Figures 3-29 to 
3-32 represent projections of 3 dimensional predictions projected onto a 2 dimensional plane. 
Thus, the symmetry normally associated with two dimensional calculations is not in evidence. 
Recall that the effects of TM processes on fracture hydrologic properties are not directly 
incorporated in abstractions for TSPA-SR. Consequently, the effects of TM processes driven by 
repository heating are screened out of TSPA based on low consequence (to be verified status 
by future calculations). 
3.6 VALIDATION OF NFE MODELS FOR USE ON YUCCA MOUNTAIN 
When discussing validation of models for use on Yucca Mountain, it is important to have a clear 
understanding of what is meant by a model, and the distinction between model and software 
validation. One definition of a model is A tentative description of a system or theory that 
accounts for all of its known properties. AP-3.10Q defines models similarly, A representation 
of a process, system, or phenomenon, along with any hypothesis required to describe the process 
or system or explain the phenomenon, often mathematically. In the strict sense of the word 
reflected by these definitions, much of the processes and software descriptions that are imbedded 
within various software codes are models. However, a general distinction can be made between 
models, which describe the system, including physical conceptualizations and all of the systems 
processes and interactions with other systems, and the software or codes used to perform the 
mathmatical or numerical manipulations needed to quantify this description. For purposes of this 
PMR, validation of models as discussed in this section refers to models that describe the system 
and its response, while software codes are considered to be the tools used to analyze the models. 
It is recognized that codes have embedded within the software a numerical description of 
submodels, however the submodels included within the coding of the software are validated as 
part of the code validation, as discussed in Appendix A for example. There is no distinction in 
building confidence, because confidence in the model also must addresses the submodels within 
the codes.

 3-118 
There are many different types of models, some conceptualizations of big systems, others are 
models of specific processes. The models to be validated can be grouped into a hierarchy of 
models often depicted as a pyramid with detailed mechanistic models at the base, with abstracted 
models in the middle, and overall models (TSPA) at the top (Figure 3-45). 
Figure 3-46. Hierarchy of Models 
This PMR discusses the detailed or mechanistic models and their abstractions. As noted in 
Section 1.4.2, there are three overall models that describe the NFE. These are the TH, THC, and 
THM models. For each of these models there are detailed or mechanistic models (e.g., the THC 
Process AMR) and abstracted models (e.g., the THC Abstraction AMR). Associated with the 
models are the inputs of properties from site characterization, as well as conceptual 
understanding of processes (e.g. fracture flow). All of these interactions must be considered in 
model validation efforts. The confidence building or validation efforts are based on testing the 
detailed models and therefore building confidence in the abstraction models that are based on the 
detailed models. This is necessary because the measurements against which models can be 
tested are usually of processes and results at the detailed level, not the abstracted level. The 
testing also provided a means of determining which property sets from the site characterization 
are appropriate for the various models. The relationship between the models in the hierarchy and 
the property and site characteristics inputs are shown on Figure 3-47. As noted, the models 
shown as process-level models are the ones that can be directly tested against field and 
laboratory tests. Table 3-12 lists the models of consideration for the NFE. The table indicates 
the general conditions and ranges over which model validation apples.

 3-119 
Figure 3-47. Hierarchy of NF Models and Relationship to Data Inputs and to TSPA

 3-120 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
Repository Models 
TH 
 Multi-Scale TH Model 
(MSTH) 
- SMT, thermal conduction  Thermal Conduction 
 Large Scale 
Repository Heat Source 
Constant T at ground 
surface & Constant T 
below UZ-SZ interface 
to 1,000 m 
Mountain-scale 
3-D 
Thermal 
conductivity 
NUFT DST, Geo-thermal 
Analogs 
- Line-average-heatsource, 
MS, TH 
 Fluid flow 
 Thermal Conduction 
 Radiation 
 Convection 
Constant T, Sliq, Pgas, 
& Xair,gas at ground 
surface, constant UZSZ 
interface 
Mountain-scale 
3-D 
DS property 
set; low, 
mean, & high 
infiltration 
NUFT, Conceptual result 
from the 
combination of the 
SMT, SDT, and 
LDTH submodels 
- Smeared-heat-source, 
drift scale, thermal 
conduction (SDT) 
 Thermal Conduction 
 Smear Heat Source 
Constant T at ground 
surface & WT 
Drift-scale (DS), 
1-D 
Thermal 
conductivity 
NUFT DST (wing heaters) 
- Line-average-heatsource, 
drift scale TH 
(LDTH) 
 Fluid flow 
 Thermal Conduction 
 Radiation 
 Convection 
 Average Discrete Heat 
Source 
 DKM Active Fracture 
Option 
Constant T, Sliq, Pgas, 
& Xair,gas at ground 
surface & WT 
Drift-scale, 2-D DS, calibrate 
hydrologic 
and thermal 
properties, 
low, mean 
and high 
infiltration 
NUFT DST (floor heaters) 
- Discrete-heat-source, 
MS TH 
 Fluid flow 
 Conduction 
 Convection 
Constant Sliq, Pgas, & 
Xair,gas at ground 
surface & WT; 
Constant T at ground 
surface & 1 Km below 
WT 
Mountain-scale 
3-D 
DS, calibrate 
hydrologic 
and thermal 
properties, 
low, mean 
and high 
infiltration 
NUFT, 
MSTHAC 
DST, Conceptual 
result from the 
combination of the 
SMT, SDT, LDTH, 
and DDT submodels 
- Discrete-heat-source, 
drift-scale, thermalconduction 
(DDT) 
 Conduction 
 Radiation 
Constant T at ground 
surface & WT 
Drift-scale, 3-D Thermal 
conductivity 
NUFT DST (drift heaters)

 3-121 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation (Continued) 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
 MS TH Models  Fluid flow 
 Thermal Conduction 
 Convection 
 Large Scale 
Repository Heat Source 
Constant T, constant 
gas pressure, constant 
Sliq 1,000 m below UZSZ 
interface, surface: 
RH, infiltration, T 
MS-2-D & multi 
2-D 
extrapolated to 
3-D 
Calibrated 
Hydrologic 
Properties, 
Thermal 
Properties 
TOUGH2 Geo-thermal 
Analogs 
DST 
- DKM with Active Fracture  Separate Fracture and 
Matrix Continua 
 Measure of Fracture 
Activity (hydraulically 
active fractures given by 
 
 Capillary Pressure for 
Active Fractures (fn of 
) 
 Liquid Relative 
Permeability for Active 
Fractures (fn of ) 
 Fracture and Matrix 
Interface Reduction 
Factor for Active 
Fractures (fn of ) 
(same as above) Valid for any 
dimension 
Calibrated 
Parameter for 
the Activity of 
connected 
fractures () 
NUFT, 
TOUGH2 
DST, SHT, LBT 
- DKM without Active 
Fracture 
 Separate Fracture and 
Matrix Continua 
 Fracture and Matrix 
Interface Reduction 
Factor as a Constant 
Value 
(same as above) Valid for any 
Dimension 
Calibrated 
Constant 
Value 
Reduction 
Term 
NUFT, 
TOUGH2 
SHT 
- ECM  Composite Continuum 
 Assumed Capillary 
Pressure Equilibrium 
between Fractures and 
Matrix 
(same as above) Valid for Any 
Dimension 
Thermal 
properties, 
hydrological 
properties, 
bulk 
permeability, 
moisture 
retention 
curves of 
porous media 
NUFT, 
TOUGH2 
SHT, G-Tunnel

 3-122 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation (Continued) 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
- DFM  Discrete fracture 
 Thermal conduction 
 Thermal convection 
 Fluid flow infractures 
Valid for any 
dimension 
Thermal 
conductivity 
Hydrological 
properties of 
fractures 
NUFT G-Tunnel 
THC 
Drift Scale Process Model Equilibrium and kinetics Constant T, Sliq, Pgas, 
& Xair,gas at ground 
surface & WT, pore 
water chemistry as 
initial condition 
Drift-scale, 2-D Limited and 
extended 
chemical 
species list 
TOUGHREACT 
DST 
THM
- Distinct element (allows 
for displacement along 
fractures) 
Stress and displacement of 
rock mass and fractures , 
thermal conduction 
Two cases: Fixed 
zero-displacement 
boundaries; constant 
applied stress at 
boundaries 
Drift scale, 
repository scale, 
or MS; 2-D and 
3-D 
Use same 
hydrologic 
and thermal 
properties as 
in NUFT 
modeling 
3DEC DST, LBT, SHT 
- Continuum (without 
fracture displacement) 
Stress and displacement of 
rock mass as porous 
medium, thermal 
conduction 
Two cases: Fixed 
zero-displacement 
boundaries; constant 
applied stress at 
boundaries 
Drift scale, 
repository scale, 
or MS; 2-D and 
3-D 
Use same 
hydrologic 
and thermal 
properties as 
in NUFT 
modeling 
FLAC DST, LBT, SHT 
TH FIELD TEST MODELS 
DST TH Model using DKM 
with AFM 
 Conduction and TH 
heat transfer 
 Interaction btw 
fractures and matrix 
 Line averaged heat 
source 
Surface conditions 
determine subsurface 
S&T 
Boundary @<100m 
horizontal, vertical at 
tsw34 contact 
conditioned to 1D 
initialization 
Multiple 2-D, 
extrapolated to 
3-D. 
DS and MS 
property sets, 
0<S<95% 
TOUGH2 DST: Compare to 
Measured 
Temperatures at 
various locations 
around the DST 
heat sources

 3-123 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation (Continued) 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
DST TH Model using DKM 
with AFM 
 Conduction and TH 
heat transfer 
 Interaction btw 
fractures and matrix 
 Line averaged heat 
source 
 
Measured saturations 
and temperatures at 
DST used to determine 
surface and WT 
conditions. 
Boundaries horizontal: 
250 - 300 m. 
Upper-mtn surface 
Lower-WT (constant T, 
p) 
2-D, 3-D DS and MS 
property sets, 
0<S<92% 
NUFT DST: 
Compare to 
Measured 
Temperatures at 
various locations 
around the DST 
heat sources 
LBT TH Model using DKM 
with AFM 
 Conduction and TH 
heat transfer 
 Interaction btw 
fractures and matrix 
 Line averaged heat 
source 
3x3x5 m heat flux 
horizontal boundaries, 
constant T top 
3-D DS and MS 
property sets 
NUFT LBT: 
Compare to 
Measured 
Temperatures at 
various locations 
around the DST 
heat sources 
Single Heater Test TH Model 
using DKM with AFM 
 Thermal Conduction 
 Thermal Convection 
 Thermal Diffusion 
 Liquid Flow in 
Fractures and Matrix 
(advection) 
 Gas Flow in Fractures 
and Matrix (advection 
and diffusion) 
 Fluid and Energy 
Transfer Between 
Fracture and matrix 
 Interface Area 
Reduction by Fracture 
Saturation of Active 
Fracture Network 
(this is not for the LBT) 
heat flux horizontal 
boundaries, constant T 
top 
3-D DS Property 
Sets 
TOUGH 2 
SHT: Compare to 
Measured 
Temperatures at 
various locations 
around the single 
heater test heat 
source

 3-124 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation (Continued) 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
Single Heater Test TH Model 
using DKM without AFM 
 Thermal Conduction 
 Thermal Convection 
 Thermal Diffusion 
 Liquid Flow in 
Fractures and Matrix 
(advection) 
 Gas Flow in Fractures 
and Matrix (advection 
and diffusion) 
 Fluid and Energy 
Transfer Between 
Fracture and matrix 
 Interface Area 
Reduction by Fracture 
Saturation of Active 
Fracture Network 
Discrete Heat Input 
onstant Property 
Boundaries (T, P, Sl), 
Insulation BC that 
allowed for heat flow 
according to the 
insulation thermal 
properties but did not 
allow for vapor flow, 
no-flow boundary to 
both heat and mass 
transfer 
3-D TSPA-VA 
Base Case 
Property Set 
Median Kb 
Property Set 
Measured 
Local to the 
SHT 
TOUGH2 SHT: Compare to 
Measured 
Temperatures at - 
various locations 
around the single 
heater test heat 
source 
Single Heater Test TH Model 
using DKM without AFM 
(same as above) Boundaries horizontal: 
52.5 - 62.6 m, 
adiabatic, imperm. 
Upper-mtn surface and 
WT: fixed T, P, 
S.liquid, RH 
3-D Kf 
9.84x10-10 m2 
Km 
4.07x10-18 m2 
Therm cond 
1.67 W/m-K 
dry, 2.1 W/m- 
K wet 
NUFT SHT 
Single Heater Test TH Model 
using ECM without AFM 
Thermal conduction 
Thermal diffusion 
Thermal convection 
Fluid flow in porous media 
Boundaries horizontal: 
52.5-62.6 m, adiabatic, 
imperm. 
Upper-mtn surface and 
WT: fixed T, P, 
S.liquid, RH 
3-D Kb 
1.22x10-13 m2, 
Kf 
9.84x10-10 m2 
Km 
4.07x10-18m2 
Therm cond 
1.67 W/m-K 
dry, 2.1 W/m- 
K wet 
NUFT SHT

 3-125 
Table 3-12. List of NFE Models, by Hierarchy, Showing Details Pertinent to Validation (Continued) 
Processes/ 
Equations 
Boundary 
Conditions Dimensionality 
Range of 
Material 
Properties 
Numerical 
Codes 
Used 
Validation 
ECM Equivalent Continuum Constant T, S.liquid 
outside heated zone 
2-D Grouse 
Canyon tuff 
measured 
properties 
predecessor 
code to 
NUFT 
G-Tunnel 
DFM Discrete Fracture Constant T, S.liquid 
outside heated zone 
2-D Grouse 
Canyon tuff 
measured 
properties 
predecessor 
code to 
NUFT 
G-Tunnel

 3-126 
There are essentially four TH process models. They are based on model approaches, and as 
shown on Figure 3-47 include the Dual Permeability Model (DKM) with and without inclusion 
of the AFM, the equivalent-continuum model (ECM), and the DFM. The DKM models treat the 
matrix and fractures as separate continua. The models provide for equilibrium between the two 
continua and the AFM allows adjustment to the amount of interaction between the continua. The 
ECM model treats the matrix and fractures as a single continuum with properties that reflect the 
bulk average (thus the name Equivalent Continuum). The DFM accounts for disequilibrium 
between the fractures and matrix. As such, it treats the fractures discretely and must, therefore, 
either address fractures as single fractures or as repeatable sets. In theory each fracture could be 
handled separately. However, this is not practical computationally nor based on limits from site 
characterization regarding individual fracture properties. Each of these models have been 
evaluated in field testing. However, the DKM with AFM is the model which has been more 
completely tested and therefore will be the focus of the validation discussion here. 
A number of simulations were conducted in support of the NFE PMR. The Thermal Test AMR 
included four thermal-hydrological models (one each for the LBT and SHT and two for the 
DST). The THC Process AMR also included a thermal-hydrological submodel as an integral part 
of the THC analysis. Finally, the MSTHM shared by the EBS PMR and the NFE PMR included 
a TH submodel. Each of these six models used a similar base case set of TH properties, although 
the sets have slightly different designators. For the purpose of determining the sensitivity of 
thermal and hydrological response of the field tests to selected thermal and hydrological 
properties, some of these models were run with modified TH property sets. Table 3-13 
summarizes the property sets used in each model. 
Two abstracted TH analyses (multi-scale and MS) as reported in this PMR are based on the 
DKM with AFM TH process model using the NUFT (LLNL 1999) and TOUGH2 (LBNL 2000) 
codes respectively. The first, discussed in Sections 3.2 and 3.6.4.1, is the multi-scale abstraction 
that uses the NUFT code as the analytical tool, and is reported in the THC Abstraction AMR. 
The second, discussed in Sections 3.3 and 3.6.4.2, was the TH part of the THC analysis, which 
relied on the TOUGH2 code for the numerical analyses or solutions, as reported in the THC 
Process AMR. These analyses were conducted under QA procedure AP-3.10Q. 
The THC process model (CRWMS M&O 2000b) includes both kinetics and thermodynamic 
submodels. The model utilizes the TOUGHREACT (LBNL 1999) code. Two model options 
were included, a complete mineral and chemical assemblage model and a model with a more 
limited suite of chemical and mineral assemblages. The validation status of these models is 
discussed in Section 3.6.4.2. The abstraction of the THC process model is discussed in detail in 
the Abstraction of Drift-Scale Coupled Processes (DSCP) AMR (CRWMS M&O 2000c). 
There are two basic THM models. The first is one that models the processes as being an 
inelastic continuum that uses various constitutive relationships (e.g. ubiquitous joint or compliant 
joint) to describe the deformation of blocks and joints. FLAC (Itasca 1996), is one code 
implementing the continuum model that has been used in reports. The other model is the 
Discrete Joint Model or Distinct Element Model which uses deformable (elastic or plastic) 
blocks and various constitutive relationships for the behavior. This model utilizes distinct block 
elements (thus the name) which allows displacements along fractures. The model validation

 3-127 
efforts discussed in this report were for the 3-D distinct element model with the 3DEC code. 
There are no THM abstraction models at this time. 
Table 3-13. Thermal-Hydrological Property Sets Used in TH Models in the NFE PMR 
Base Case (CRWMS M&O 2000f, TH Property Set from UZ Flow and Transport Model) 
Thermal Test AMR (CRWMS M&O 2000a) 
SHT 
(TOUGH2): DS 
DST (TOUGH2): 
DS/AFM-UZ99 
DST (NUFT): 
DS 
LBT (NUFT): 
DS 
THC Process 
AMR 
(CRWMS 
M&O 2000b): 
Inputs from 
the CPM 
(CRWMS 
2000n) 
Multiscale TH 
Model AMR 
(CRWMS M&O 
2000k): DS 
Sensitivity Cases (CRWMS M&O 2000a) 
TSPA-VA: TH 
Property set 
from Total 
System 
Performance 
Assessment - 
Viability 
Assessment 
Case 
DKM-TT99: Dual 
Permeability 
(matrix and 
fracture) property 
set from the 
thermal test region 
MS Property 
Set: only the 
bulk fracture 
permeability 
differs from 
base case 
MS Property 
Set: only the 
bulk fracture 
permeability 
differs from 
base case 
Single Heater 
Test Median 
Bulk 
Permeability 
(Median kb): 
Based on Air-k 
measurements 
from SHT 
MS Local 
Thermal 
Conductivity: 
Different 
thermal 
conductivity 
from MS 
property set 
MS Local 
Thermal 
Conductivity: 
Different 
thermal 
conductivity 
from MS 
property set 
Conduction 
Only: 
Hydrologic 
properties not 
included 
Conduction 
Only: 
Hydrologic 
properties not 
included 
MS Higher 
Fracture 
Permeability): 
Higher bulk 
fracture 
permeability by 
two orders of 
magnitude 
Source: Modified from CRWMS M&O 2000a, Table 3. 
Validation of the process models was performed by comparison of model results with field and 
laboratory tests, as specified in AP-3.10Q, Section 5.3b. The results of the field tests are 
discussed in the Thermal Test, also prepared under controls of AP-3.10Q. This section discusses 
the results of comparisons of the models with those field-test results. There is repetition in that 
each model will be compared to essentially the same set of results from the field tests.

 3-128 
Validation of models (perhaps more appropriately described as confidence building) is provided 
by first building an understanding of the processes to be modeled through a combination of 
laboratory and field experiments, as well as considerations of basic principles, and then by 
testing these models. 
The assessment of the performance of a high- level nuclear waste geological repository requires 
prediction of the performance of waste package materials, and the flow and transport 
characteristics of radionuclides from the emplacement drifts to the accessible environment. 
Those predictions require information regarding the THCM conditions within the emplacement 
drift and the region between the drifts and the accessible environment, as functions of time and 
space. Model analyses are needed in order to predict the THCM conditions in a repository for its 
entire life span. Test data are needed to enhance confidence of those model analyses. 
A series of tests have been designed and conducted in order to build confidence in the models 
and the parameters used as inputs to those models. These tests were designed to address 
geometric-scale issues, as well as issues of rates of NF processes and representative geologic 
units. Table 3-14 summarizes the scale and purposes of the tests. 
The testing program thus included core-sized laboratory tests to determine property values, and 
to determine physical processes for laboratory samples that were mostly focused on processes in 
matrix or single fracture and typically of relatively short duration. Advantages of the laboratory 
tests include the ability to control laboratory conditions. 
The second scale of tests were block or bench-scale test on blocks of about 1 m x 1 m x 0.5 m 
size. These tests allowed the response to be tested on both single and multiple fractures, as well 
as larger matrix sized. These tests provided for longer duration, with stresses applied to the faces 
of the block, with somewhat diminished boundary controls. 
The third scale test was conducted on a large-block (3 m x 3 m x 4.5 m) excavated on an outcrop 
at Fran Ridge (see Figure 3-48). This LBT was of sufficient size to include at least 100 fractures 
and allowed processes of THMC to be tested, including interconnections of fracture systems. 
The boundaries did not include stress, nor active controls on heat losses. They did include 
insulation and monitoring of heat loss from the sides of the block and temperature control of the 
top. This test was of sufficient size to provide for longer duration testing with heat-flux rates 
somewhat comparable to possible repository rates. Due to its surface location, the test was not 
intended to simulate the actual responses expected in YM. Rather, it was to identify coupled 
processes, and test conceptual models of those processes in a representative rock mass.

 3-129 
Table 3-14. Test Strategy 
Scale Description Purpose 
Core Core up to 1 ft. 
Hrs. to days 
(some long-term) 
Property Measurements 
Matrix Processes 
Single-Fracture Processes 
Limited Model Testing 
Bench 1 ft. to 1 m blocks 
Outcrop 3 to 5 m block, ~ 2 yr. 
Multiple Fracture Processes 
Fracture Interconnectivity Phenomena 
Coupled Processes 
Small in situ 
Heater 
Up to ~ 100 m2, ~ 1 yr. Site characterization 
In Situ Hydrothermal/Geochemical/Geomechanical Responses 
Large in situ 
Heater 
Up to 1,500 m2, ~ 8 yr. Scaling Effects, Natural Heterogeneity Impacts 
Internal Drifts Repository-Scale Monitoring 
50  200 yr. 
Performance Confirmation 
Analogs 
10,000 years 
Large-Scale 
Long-Term Coupled Effects 
Modified From: NWTRB 1992 Denver 
The fourth scale of tests was in situ, small and large-scale tests performed underground in one of 
the lesser host rock units. These tests (SHT and DST) allowed testing of physical processes and 
models under in situ conditions and included sufficient size to test multiple fractures and 
interconnections. The SHT involved a smaller rock region than the DST, and included only a 
single heater. Thus, the temporal and spatial scale was not sufficient to allow all coupled 
processes to be tested at scales representative of a potential repository. However, the duration of 
the SHT allowed sufficient volume of rock to be elevated in temperature to consider THC 
effects, and the test successfully captured mobilized water in instrument boreholes. The test also 
measured in situ rock thermal and mechanical properties for the first time in the repository 
setting. 
The DST is a large-scale (1,500 m2) and long-duration (four years heating, four years cooling) 
test in which the heating rate, size of the test and duration allow THC coupling to be tested at 
appropriate scales. 
The size of the DST provides for an assessment to be made of heterogeneity effects on THC 
responses. Three measurement arrays perpendicular to the DST axis, in addition to longitudinal 
measurements, provide for this assessment. 

 3-130 
Source: CRWMS M&O 2000a, Figure 10. 
Figure 3-48. Photograph of Large Block Test Site

 3-131 
As depicted in Table 3-14, Repository-Scale monitoring is the ultimate test of performance 
against which models must be judged. These tests will be based on monitoring the response to 
actual emplaced waste, where the scale issues will be addressed directly. However, the duration 
of the response monitored, even at repository scale, will be very short, perhaps 50-200 yr, in 
comparison to the period of active evolution of the NFE (1,000 to 10,000-yr). 
Therefore, even repository monitoring can provide testing or confidence in only part of the 
temporal regime covered by the models. 
Testing of the models ability to accurately predict performance over these large time frames can 
only be provided by comparisons with geologic analog sites, where the duration of THCM 
processes are appropriate for repository time-scales. 
Natural analogs provide opportunities for testing models and building understanding of thermally 
coupled processes by assessing data from fossil hydrothermal systems, by observing ongoing 
processes in geothermal fields, and by using data from geothermal systems to test and build 
confidence in numerical modeling codes, and in thermodynamic and kinetic databases. 
1) The challenge is first to find analogs that are sufficiently representative of the 
repository processes and characteristics that conclusions are not misleading. Murphy 
and Pabalan (1994, pp. 4-28) point out as an example of this challenge that the 
variations in temperature for the repository environment are relatively short duration 
compared to metamorphic or major hydrothermal systems, but. long duration 
compared to most volcanic or hybabyssal systems. 
2) Second, the challenge is to find analogs for which the geologic history, 
(environmental conditions with time) and processes are well understood. 
If analogs meeting these criteria are found, they can provide confidence building in the long-term 
prediction capability of the models. 
Because the actual coupled processes are no longer active, except for the analogs such as 
hydrothermal or geothermal fields, the analyses are based on interpretations of the minerals 
present and fracture systems present, which are essentially the permanent or long- lived effects of 
the coupled processes. This section focuses on the field-scale tests and natural-analog analyses 
that are used to build confidence in the models. The laboratory tests used to develop the models 
and provide property values for use in the models are covered in the individual model AMRs, 
and in past reports (e.g., Hardin and Chestnut 1997; Hardin 1998). 
The field validation tests are described below in Section 3.6.1 in order of scale, following the 
general philosophy depicted in Table 3-14. The natural-analog studies are then discussed in 
Section 3.6.2. Section 3.6.3 discusses several laboratory scale tests. Finally, Section 3.6.4 
summarizes the validation status of the TH, THC, and THM models. 
3.6.1 Model Confidence Building through Field Thermal Testing 
The ESF thermal tests and the LBT will be used to help specify appropriate conceptual flow 
models, thermal perturbations to hydrological flow properties, coupled-process data

 3-132 
specifications, and assessments of implementation of ambient-flow hydrologic properties in 
thermally driven models. Thermal-hydrological simulation of the field thermal tests were 
conducted using both MS and Multi-Scale models, utilizing the DS property set and/or the 
mountain-scale property set, from the UZ F&T Model for comparative analyses with the 
measured data from the tests. 
Three field thermal tests are being, or have been, conducted to provide data for enhancing the 
confidence of the model analyses. Those tests are the LBT at Fran Ridge, the Single Heater Test 
(SHT) and the DST. Both SHT and DST are conducted at Alcove 5 of the ESF. A detailed 
description of the LBT can be found in LBT Status Report (Wilder et al. 1997, Section 2 and 4). 
A detailed description of the SHT can be found in Single Heater Test Status Report (CRWMS 
M&O 1997a, Section 3). Finally, the detail description of the DST can be found in Drift Scale 
Test Design and Forecast Results (CRWMS M&O 1997b, Section 3). A brief description of 
these tests will be provided here to facilitate discussion of the test results. 
The primary purposes of these field thermal tests are to provide data regarding the coupled 
TMHC processes, so that they can be used to build confidence in the TH model, the THC model, 
and the THM model, which will be used to predict the performance of a repository (CRWMS 
M&O 1997a, p. 1-1; CRWMS M&O 1997b, p. 1-1; and Wilder et al. 1997, pp. 3-4). It was 
understood that the test regions of these tests are relatively small compared with the size of the 
potential repository, and that the major part of the potential repository will not reside in the rock 
unit in which these tests were conducted. Therefore, the primary purpose of these tests was not 
for testing the properties of the host-rock unit of much of the potential repository, but rather to 
gain understanding of the processes that may occur in a repository. Then the processes can be 
modeled with the appropriate property sets determined for the potential repository. 
A primary objective of these tests was to determine whether the conceptual and mathematical 
models properly account for the important physical processes and phenomena, and to gain 
understanding of the processes that may occur in a repository. The tests were designed to 
accomplish this objective by identifying the hypotheses and postulations of how the NF system 
would respond to emplacement of waste, specifically from the heat generated by the waste, and 
then designing the tests to monitor the responses hypothesized. 
Beyond testing hypotheses, the tests also provide data by which it can be determined whether 
any important physical processes were overlooked in the conceptual and mathematical models or 
improperly emphasized. Once assurance is gained that the models properly incorporate the 
important physical processes, then confidence in their ability to predict repository performance is 
increased. Once model confidence is established and properties are obtained, the appropriateness 
of the PA calculations can be established through use of measured and inversely-modeled 
property sets for specific locations in the potential repository. Thus, the second objective of the 
field tests is to provide a means to test the inversely-modeled property sets for use in the 
repository performance models. 
The host rock for all three field thermal tests: the LBT, the Single Heater Test and the Drift 
Scale Test is the middle nonlithophysal unit of the Topopah Spring welded tuff unit (TSw). 
However, the repository emplacement area will be located in three units of the Topopah Spring 
welded tuff. These are described, in downward sequence, as the middle nonlithophysal

 3-133 
(Tptpmn), the lower lithophysal (Tptpll), and the lower nonlithophysal (Tptpln) units. In both 
the VA design and the EDA-II design, a majority (approximately 70%) of the emplacement area 
will be in the lower lithophysal unit. The characteristics of the three TSw layers differ primarily 
because of the nature and abundance of lithophysae and the nature and frequency of fracturing. 
Though the physical and chemical coupled processes are universal and independent of the 
geological units, the different fracture and lithophysal properties of the lower lithophysal unit 
may give rise to thermal-hydrological (TH) behavior that differs from that observed in the LBT, 
SHT, and DST. In order to have confidence in our ability to predict the TH response of the 
potential repository to heating, a thermal test in the lower lithophysal unit is being designed. 
The ESF Main Drift is largely in the Tptpmn with only the upper part of the Tptpll exposed near 
the South Ramp. Consequently, the database on the Tptpmn, compared to that of Tptpll and 
Tptpln, is extensive, having been derived both from surface-based drilling and observations, 
mapping, and testing in the ESF. The recent excavation of the Enhanced Characterization of the 
Repository Block (the Cross Drift) has provided access to all three Topopah Spring units. 
Mapping along the Cross Drift shows that in the nonlithophysal units, the density of fractures up 
to several meters in length is high, whereas in the lithophysal unit, there are few fractures that are 
longer than one meter, though density of fractures less than one meter appears similar to that of 
the middle nonlithophysal unit. Further, lithophysal cavities of size ranging from 15 cm to 
100 cm abound in the lower lithophysal unit. While the mapping of the Cross Drift is complete, 
hydrological tests to characterize the Tptpll are still in their initial phase. The tests in progress 
include monitoring downward water movement from injection boreholes in Alcove 8 in the 
Cross Drift to the ESF cross-over point in Niche 3; the investigatio n of seepage threshold in 
Niche 5; and systematic characterization of seepage characteristics in boreholes at 30-m 
intervals. 
The Cross Drift Thermal Test (CDTT) is currently being designed to begin construction in the 
Tptpll at the start of FY2001. The main objectives of CDTT is to investigate the premise that 
heat-mobilized pore water will shed/drain between emplacement drifts to below the repository 
horizon, and to test the premise that liquid water can penetrate through zones/regions at or above 
boiling temperature. The design uses five (5-meter-long) heaters installed in parallel boreholes 
and is patterned to test the pillar drainage concept for the EDA-II design. Numerical modeling 
for the design of CDTT makes use of the currently available Tptpll properties based on surface 
based boreholes. Data from hydrological testing of the Tptpll in the Cross Drift will be 
incorporated in the predictive modeling of the CDTT as they become available. 
The field-thermal test data included in this PMR have been referenced in the following two 
AMRs: THC Process AMR (CRWMS M&O 2000b) and Thermal Test AMR (CRWMS 
M&O 2000a). This PMR summarizes the field-thermal test data and the THMC processes that 
those data represent. 
3.6.1.1 Large-Block Test 
The primary purpose of the LBT was to investigate the coupled TMHC processes in a controlled 
one-dimensional heating condition so that the test results can be readily compared with model 
calculations. Comparison of the test results with model calculations will enhance the confidence 
of the model. The description of the LBT can be found in Large-Block Test Status Report

 3-134 
(Wilder et al. 1997). A free-standing 3 x 3 x 4.5 m square column of Topopah Spring Tuff was 
isolated at the outcrop at Fran Ridge, Nevada. The rock-type of the block was the same as the 
middle non-lithophysal unit of the Topopah Spring tuff in the potential repository horizon in 
Yucca Mountain. Preconstruction characterization and pre-test scoping model calculations 
indicated that the fracture characteristics, bulk permeability, the initial moisture content, and the 
size of the block are suitable for testing the coupled TMHC processes. During the construction, 
small blocks of the rock adjacent to the large block were collected for tests in the laboratory. 
The mineralogical composition of the small blocks, especially the secondary minerals in the 
fractures, will serve as a baseline of mineralogy. The mineralogical baseline can be used to 
investigate the chemical processes due to heating. Fractures in the block were mapped on the 
five exposed surfaces and in boreholes. Five heaters were installed in the block to form a 
horizontal heater plane at about 2.743 m from the top. Instruments were installed in boreholes to 
measure temperature, gas pressure, relative humidity, moisture content (using neutron logging), 
and deformations. In addition, instruments installed on the block-surface include electrodes for 
electrical-resistance tomography, fracture gauges, and resistance-temperature devices (RTD) to 
monitor the near-surface temperature gradients. Labeled native microbes were introduced into 
the heater holes and two vertical holes in the block so that their survivability and migration could 
be studied. Four observation holes were constructed near the bottom of the block to conduct 
qualitative observations of fracture flows and microbial migrations. Coupons of candidate waste 
package materials were placed at designated locations within the block. The four vertical sides 
of the block were coated with a moisture-barrier layer, then covered with three layers of 
insulation: (from inside outward, Ultratemp boards, fiberglass, and reflexic). Water vapor was 
allowed to leave the block through the top. A heat-exchange unit was installed on the top to 
control the top temperature. Wilder et al. (1997, Section 4.0) plotted the location of the 
boreholes in the LBT (Figure 3-49). 
The heaters were energized to full power (450 W each) on February 28, 1997 (CRWMS 
M&O 2000a, Section 6.1.4). The temperature on the top was allowed to rise until it reached 
60C, then the heat-exchange unit was turned on to maintain the 60 temperature at the top of the 
block. When the temperature near the heater horizon reached 140C, the heater-power was 
adjusted to keep the temperature between 135 and 140C. The heating phase of the LBT was 
terminated on March 10, 1998, and monitoring of the LBT was terminated on September 30, 
1998 (CRWMS M&O 2000a, Section 6.1.4). Cores have been collected after the test. Analyses 
of the post-test cores for assessing the effects of heating on the mechanical, hydrological, and 
mineralogical characteristics of the rock are still on-going. 
A small part of the LBT results has been included in the Thermal Test AMR for comparing with 
model predictions (CRWMS M&O 2000a, Sections 6.2.4, 6.4.4, and 6.5.4). The bulk of the 
LBT results are presented here to facilitate discussions of the TMHC processes. 
3.6.1.1.1 Temperature Distribution in the Block 
The temperature in the block was measured along two vertical holes (TT1 and TT2) and seven 
horizontal holes (NT1 through 4 and WT1 through 3). In each hole, the temperature was 
measured every 20 cm. Only a small part of the measured temperature data will be shown in this 
report to facilitate discussions. The sensors in the two vertical boreholes, located nearest to the 
heater horizon, were designated TT1-14 and TT2-14, for the TT1 and TT2 boreholes,

 3-135 
respectively. Figures 3-50 and 3-51 show the highest temperature, measured along the two 
vertical holes, TT1 and TT2 respectively, as a function of time for the entire test history. The 
downward spikes at 552 hour, 1,036 hour, 3,802 hour in both figures were due to short periods of 
power outages. Those short power outages did not have significant impact on heating of the 
block. The heaters were turned off on March 10, 1998 (8,999.5 hour). The temperature at 
TT1-14 was about 15C greater than that at TT2-14. This was probably due to two causes: 
(1) TT2 was closer to the edge of the block than TT1, and therefore influenced more by heat loss 
from the block, and (2) due to the difference in total depth of the two vertical holes, TT2-14 is 
8.2 cm below the heater horizon, whereas TT1-14 is 2.1 cm below. The temperature drop at 
TT1-14 at 2,525 hour and the subsequent temperature fluctuations at both TT1-14 and TT2-14 
(8 cm below heater plane) were probably caused by thermal-hydrological events, which will be 
discussed later. 
Figures 3-52 and 3-53 show examples of temperature variations along the horizontal RTD holes 
NT3 and WT3. The data gap in the curves for 9/10/97 and 10/24/97 was due to malfunction of 
RTD#6 in WT3. Sensor number RTD#14 was located at about 12.8 cm from the collar in each 
of the horizontal holes. This is one of the reasons why the temperature at RTD#14 was lower 
than the others in the same hole, as shown in those figures. RTD#1 in each one of the horizontal 
holes was located at about 30.5 cm from the opposite block surface. The temperatures in WT3 
show greater heat loss at the block surfaces than that in NT3. It is generally true that the 
temperature variation in an east-west horizontal hole was greater than that in a north-south hole. 
Nevertheless, temperatures in the horizontal holes show that the block was heated fairly 
one-dimensionally.

 3-136 
Source: Wilder et al. 1997 
NOTE: The first letter for each hole refers to the collar location (top, west, etc.). The second letter refers to the hole 
function: Temperature, Neutron logging, Hydrology, Observation, Mechanical, REKA (thermal properties), 
Biology, and electrical-resistance tomography (ERT) (saturation). Heater holes are EH. The holes are also 
color coded. 
Figure 3-49. LBT Instrument Holes

 3-137 
Source: Modified from CRWMS M&O 2000a, Figure 67 
Figure 3-50. Temperature Measured in Borehole TT1-14 of the LBT as a Function of Elapsed Time 
DTN: LL970803004244.036 
Figure 3-51. Temperature Measured in Borehole TT2-14 of the LBT as a Function of Elapsed Time 
TT1-14 of the Large Block Test. 
0 
20 
40 
60 
80 
100 
120 
140 
160 
0 100 200 300 400 500 600 
Days of Heating (2/28/97 - 9/30/98) 
Temperature (C) Temperature (C) 
TT1-14 
0 
20 
40 
60 
80 
100 
120 
140 
0 100 200 300 400 500 600 
Days after Start of Heating (2/28/97 - 9/30/98) 
TT2-14

 3-138 
3.6.1.1.2 Boiling of Pore Water 
Temperature measured just below the heater plane by sensor RTD-TT1-14 is shown in 
Figure 3-50. The relatively flat region at a temperature of about 97C in TT1-14 between 922 
and 1,127 hours (Figure 3-50) was probably caused by the balance of energy from the heaters 
and the energy required to evaporate pore water in proximity to RTD TT1-14. In TT2-14 (8 cm 
below the heater plane Figure 3-51), the relatively flat temperature occurred between 1,907 and 
2,647 hours, at a temperature of about 98C. If the flat temperature-time curve was indeed 
caused by evaporation, the longer duration of the flat temperature region at TT2-14 may be 
caused by either a greater amount of pore water to be evaporated or a slightly slower heating rate 
at TT2-14 than at TT1-14. Hole #TT2 is closer to the edge of the block than #TT1; therefore, 
greater heat loss in the block-sides may have caused the slower heating rate at the RTDs in TT-2. 
The temperature at which the flat temperature-time curve occurs relates to the boiling point of 
water. The measured temperatures from the RTDs at those two locations were accurate to within 
0.1C. These results indicate that the boiling point of the pore water at TT1-14 was greater than 
that at TT2-14 by about 1C (97C vs. 98C). The difference in the boiling point of water may 
be due to several factors, including differences in the transmittal of barometric pressure, the 
suction potential of the pores, the difference in ionic concentration in the pore water, or possibly 
different fracture spacing. Based on the Steam Table (Keenan et al. 1969), the boiling point of 
pure water at the elevation of the LBT is 96.6 C. The boiling point of the water in the block, 
inferred by the measured temperature, was slightly greater than that of pure water. This is 
probably due to the suction potential in the pores, and the ionic concentration in the water. 
DTN: LL970803004244.036 
Figure 3-52. Snapshots of the Temperature in NT3 of the LBT at the 
Location of each RTD Sensor in the Borehole 
0.00 
20.00 
40.00 
60.00 
80.00 
100.00 
120.00 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 
RTD Sensor Number 
Temperature (C) 
9/10/97 (196 days) 
10/24/97 (210 days) 
6/5/97 (100 days) 
2/27/97 (-1 day)

 3-139 
DTN: LL9708030041244.036 
Figure 3-53. Snapshots of the Temperature in WT3 of the LBT at the Location 
of each RTD Sensor in the Borehole 
3.6.1.1.3 Thermal-Hydrological Processes 
The sudden drops of temperature at TT1-14 at 105 days (6/13/97) and 186 days (9/2/97), as 
shown in Figure 3-50, and at TT2-14 at 186 days, as shown in Figure 3-51, and the subsequent 
temperature fluctuations, were probably caused by thermal-hydrological processes. Some 
examples of the temperature data affected by the thermal-hydrological events on 6/13/97 and 
9/2/97 are shown in Figures 3-54 and 3-55, respectively. Figure 3-54 shows the temperatures 
measured at TT1-13 (18 cm above the heater plane) to TT1-17 (62 cm below the heater plane) 
between the 100 and 133 days. During the event, all of the temperatures converged to around the 
boiling temperature of the pore water, then the temperatures rose and the fluctuation started. At 
the onset of the event at 105 days, the above-boiling location experienced a rapid temperature 
drop to the boiling point. Nearly below-boiling locations increased temperature to the boiling 
point (TT1-17), indicative of heat transferred to this zone, possibly by hot water or vapor. 
Examining the temperature measured at other locations in TT1 indicates phenomena similar to 
those shown in this figure. The influence of this event reached to TT1-8 (118 cm above the 
heater plane). It appears that the temperature changes were related to hydrological processes, 
and the temperature fluctuations were caused by condensate refluxing. However, the causes of 
this thermal-hydrological event are not clear. The thermal-hydrological event and the 
subsequent temperature fluctuations may have been caused by rain water that infiltrated into the 
block, or the releasing of overheated water within the block. It was reported that a weather 
station about 5 km southeast of Fran Ridge registered rain on 6/13/97, but there was no direct 
measurement of precipitation at Fran Ridge during that time. 
0 
20 
40 
60 
80 
100 
120 
140 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 
RTD Sensor Number 
Temperature (C) 
9/10/97 (196 days) 
10/24/97 (210 days) 
6/5/97 (100 days) 
2/27/97 (-1 day)

 3-140 
Although the initiating event may have been rapid, temperatures persisted at near-boiling for 
about 16 days indicating persistence of water that moved to these locations. Then, initia lly-hot 
locations returned to their initial temperatures over a four week period, with a large amount of 
temperature fluctuation during the recovery, possibly due to rapid movement of the last residual 
water from place to place. 
Figure 3-55 shows the temperatures measured at TT1-10 (78 cm above the heater plane) to 
TT1-14 (2 cm below the heater plane) from 186 to 192 days. Similar to the earlier event shown 
in Figure 3-54, the temperatures converged to the boiling point of water, held steady for some 
time, and then returned to pre-event temperatures over a period of time, with fluctuating 
temperatures during the recovery period. For this event, the durations of the hot temperature and 
recovery periods were only a few days each. 
Examining the temperature measured at other locations for the September 2, 1997 event indicates 
that the temperatures decreased rapidly and simultaneously, and then converged to the boiling 
point of water. The influence of this event reached to the TT1-11 sensor location 58 cm above 
the heater plane. One of the causes of this event was clearly related to rain. It rained hard at 
Fran Ridge the night before this event. The fact that all of the measured temperatures along TT1 
show a decrease in temperature at the onset of this event is also indicative of the influence of rain 
water on this event, and again, the temperature fluctuations were probably caused by condensate 
refluxing. The external rainwater may have influenced this event in two ways: (1) it triggered 
this event, and (2) it supplied enough water to sustain a condensate refluxing for about 2 days. 
The time period in which the temperatures stayed at the boiling point of water was about 2 weeks 
for the June 13, 1997 event, but only about 2 days for the September 2, 1997 event. This 
difference was probably due to more available heat in the block to evaporate the water more 
quickly, because more insulation was added to the block surfaces at about 125 days. It is also 
possible that the matrix of the block during the September 2, 1997 event had been dried out more 
than that during the June 13, 1997 event or that less water was involved in the event. The 
vertical extent of the disturbance was also less for the second event.

 3-141 
DTN: LL970803004244.036 
Figure 3-54. Temperatures at Several RTDs in TT1 Show Fluctuations 
Due to a Thermal-Hydrological Event on June 13, 1997 
90.00 
100.00 
110.00 
120.00 
130.00 
140.00
186 187 188 189 190 191 
Days after Start of Heating 
Temperature (C) 
TT1-14 
TT1-13 
TT1-12 
TT1-11 
TT1-10 
DTN: LL970803004244.036 
Figure 3-55. Temperatures at Several RTDs in TT1 Show the Fluctuations 
Due to a Thermal-Hydrological Event on September 2, 1997 
80 
90 
100 
110 
120
100 104 108 112 116 120 124 128 132 136 
Days after Start of Heating 
Temperature (C) 
TT1-13 
TT1-14 
TT1-15 
TT1-16 
TT1-17

 3-142 
3.6.1.1.4 Moisture Distribution 
Moisture distribution in the block was measured by two methods: ERT and neutron logging. 
The electrode configuration is shown in Figure 5 of Wilder et al. (1997). Figure 3-56 shows 
some examples of the ERT images in the East-West vertical plane of the LBT. The East-West 
vertical plane passes the middle of the block. The four columns of images represent ERT 
measurements on four dates. The three rows of images represent resistivity ratio, temperature, 
and saturation ratio, respectively. The resistivity is a function of both temperature and 
saturation. When the temperature field is independently measured, the resistivity ratio and 
temperature can be used to deduce the spatial distribution of saturation (the third row). In 
Figure 3-56, the resistivity ratio and the saturation ratio are with respect to the baseline data 
obtained before heating was started, on February 28, 1997. The heaters were turned off on 
March 10, 1998. The ramp-down of heater power was started on October 6, 1997, in order to 
keep a constant temperature in the block. So, the first three columns of the images in 
Figure 3-56 show the ERT obtained during the final stage of the heating period, when the block 
temperature was almost constant. The saturation-ratio images on November 19, 1997 and 
January 23, 1998 (the third row in Figure 3-56) show a dryout region at the heater horizon 
(centered at about 2.74 m from the top), and extended vertically near the west side of the block. 
The vertical dry zone may be related to one of the high-angle major fractures near the west side 
of the block (Wilder et al. 1997, Figure 2-10). There were no other major features in the 
saturation distribution, except one localized small region in each image, which shows increased 
moisture content. The saturation-ratio image on February 24, 1998 and March 19, 1998 seems to 
indicate that the dryness in the previous dryout zones was decreasing. However, there was no 
significant change in the moisture content in other locations. Field measurements indicate that 
due to the dryness on the block surface, the quality of the signals in the later ERTs was not as 
good as the earlier ones. Therefore, the apparent rewetting in the dryout zones may not be very 
reliable. 
Neutron logging was conducted in five vertical holes and ten horizontal holes (six from the 
North side and four from the West side), as described in Wilder et al. (1997, Figures 4-1, 4-2, 
and 4-5). The data from one of the vertical neutron holes are presented below as an example of 
the variation of moisture distribution in the LBT due to the heating. 
Figures 3-57 and 3-58 show the difference of volume-fraction water content as measured along 
neutron hole TN3 on various days of heating. TN3 was the vertical neutron hole located closest 
to the middle of the block (Wilder et al. 1997, Figure 4-1). The zero volume-fraction water in 
these two figures means no difference from the pre-heat baseline data. These two figures clearly 
show development of a dry-out zone. The neutron data from other vertical neutron holes were 
similar to those shown here. The drying seemed to start in an area slightly below the heater 
horizon, which is about 2.74 m from the top. The maximum drying region then gradually 
extended below the heater horizon in most of the holes. In TN5, the maximum drying area 
extended above the heater horizon. In TN1 the maximum drying region extended both below 
and above the heater horizon. These variations may be caused by the heterogeneity in the block, 
however, they are relatively minor compared to the intensity and extension of the drying zone. 
All of the neutron data along the vertical holes show that the width of the drying zone and extent 
of drying virtually did not change between the 334th and 361st days of heating. The 
absolute-volume-fraction moisture content in the driest region was about 0.85 to 1 percent.

 3-143 
DTN: LL980913304244.072 
Figure 3-56. Temperature and the Electrical-Resistance Tomograph of an 
East-West Cross Section of the LBT 
In summary, both ERT and neutron logging show that the heating created a significant dry out 
zone in the block. The width of this dryout zone ranged from 1.5 to 1.7 m. The ERT shows a 
localized vertical dryout region extend ing to the upper part of the block. This is not shown by 
the neutron data, probably due to the lack of a vertical neutron hole in that part of the block. 
Within the dryout zone, the drying could only reduce the moisture content to about 1 percent 
volume-fraction. 
The labeled (double-drug resistant) native microbes were found in observation holes, about 
1.5 m below the heater holes, during the heating phase of the LBT. This is an indication that 
microbes may have survived the heat, and liquid water flow below the heaters was able to 
facilitate the migration of the microbes. It is emphasized that this observation serves as an 
indication only because the microbial investigation was scoping in nature, and therefore, was 
non-Q.

 3-144 
DTN: LL980919304244.075 
Figure 3-57. Difference Volume-Fraction Water in TN3 of the LBT as a 
Function of Depth, up to 103 Days of Heating 
DTN: LL980919304244.075 
Figure 3-58. Difference Volume-Fraction Water in TN3 as a Function of 
Depth, from 103 to 565 Days of Heating 
-0.08 
-0.07 
-0.06 
-0.05 
-0.04 
-0.03 
-0.02 
-0.01
0 
0.01 
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 
Depth from Top, m 
Fraction Volume Water 
11 days 
25 days 
48 days 
60 days 
74 days 
88 days 
103 days 
-0.08 
-0.07 
-0.06 
-0.05 
-0.04 
-0.03 
-0.02 
-0.01
0 
0.01 
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 
Depth from Collar, m 
Fraction Volume Water 
130 days 
334 days 
361 days 
411 days 
437 days 
473 days 
501 days 
538 days 
564 days

 3-145 
3.6.1.1.5 Deformations in the Block 
Deformations within the block were measured by multiple-point borehole extensometers 
(MPBXs), for bulk displacements within the block, and fracture gauges, for deformations across 
fractures on the block surfaces (Wilder et al. 1997, p. 19). Overall block deformations near the 
heater plane was closely correlated with temperature as shown in Figure 3-59. The MPBX 
measurements showed that the block experienced expansion in the upper half during the heating 
phase of the test. The surface fracture-gauge measurements showed that during the 
June 13, 1997 thermal hydrological event (Wilder et al. 1997, and Section 3.6.1.1.3 of this PMR) 
the horizontal fracture near the top of the block (at about 30 to 60 cm below the top) experienced 
opening of about 0.094 to 0.11 mm at the northern and eastern sides, and a 0.058 mm shear 
displacement on the western side. Those deformations may have changed the hydrological 
properties of the block. 
DTN: LL970803104244.037 
Source: CRWMS M&O 2000a, Figure 67 
NOTE: Temperature sensor TT1-14 was located approximately in the center of the block, near the heater plane. 
Anomalies in the temperature at 2250 and 4400 hours were associated with weather disturbances and may 
indicate refluxing in the fractures. MPBX anchor WM2-4 monitored horizontal deformation approximately 
3 m above the base of the block. 
Figure 3-59. Thermal and Deformation History for the Large Block Test 
0 
50 
100 
150 
0
0.5 
1
1.5 
2
2.5 
3 
-2000 0 2000 4000 6000 8000 10000 12000 14000 
TT1-14 WM2-4 
Temperature (C) 
Displacement (mm) 
Hours of Heating 
Displacement 
Temperature

 3-146 
3.6.1.1.6 Microbial Studies 
The transport of bacteria in the LBT was also studied (Lin et al. 1998a). Two bacterial species, 
Bacillus subtilis and Arthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural 
mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and 
rifampicin, were selected from these species by laboratory procedures. The double-drug 
resistant bacteria, which could be thus distinguished from the indigenous species, were injected 
into the five heater boreholes of the large block hours before heating was initiated. The 
temperature, as measured 5 cm above one of the heater boreholes, rose slowly and steadily over a 
matter of months to a maximum of 142C. Samples were collected from the boreholes that were 
approximately 5 ft below the injection points. Double-drugresistant bacteria were found in the 
collection boreholes nine months after injection. Surprisingly, they also appeared in the heater 
boreholes where the temperature had been ~ 140C throughout much of the test. These bacteria 
appear to be the species that were injected. The number of double-drugresistant bacteria that 
were identified in the collection boreholes increased with time. An apparent homogeneous 
distribution among the observation boreholes and heater boreholes suggests that a random 
motion could be the pattern that the bacteria migrated in the block. These observations indicated 
the possibility of rapid bacterial transport in a thermally perturbed geologic setting. 
3.6.1.1.7 Post-Test Thermal-Mechanical Analysis 
Post-test characterization activities for the LBT consisted primarily of drilling/coring to provide 
boreholes and samples for post-test characterization of the block, and laboratory testing and 
analysis of core samples collected by the drilling/coring activity. A post-test analysis of rock 
mechanical properties was conducted in order to determine if elevated temperatures and high 
thermal gradients may have induced grain boundary scale microcracks in the tuff. This effect 
was expected to me the most pronounced near the borehole heaters where conditions were most 
extreme. Thermal micro cracking would contribute to the mechanical degradation of the rock, 
leading to a loss of compressive strength and a reduction in elastic modulus. A loss of 
mechanical strength in the rock surrounding nuclear waste canisters would have adverse 
consequences for repository performance. The purpose of this work was to ascertain if 
measurable mechanical degradation resulted around at least one of the heater boreholes during 
the LBT. Two suites of twelve samples were collected. One suite, consisting of cores from one 
of the heater boreholes, was never exposed to elevated temperatures. The other suite, taken from 
overcore of the same borehole, experienced the highest temperatures and thermal gradients 
attained during the LBT. 
Results showed that no statistically significant differences in dry density, ultrasonic velocity, 
compressive strength or Youngs modulus between the thermally-cycled overcore and nonthermally 
cycled heater core suites. The dry densities, ultrasonic velocities, uniaxial 
compressive strengths, and elastic moduli obtained for these specimens are also similar to those 
obtained for Topopah Spring tuff in other laboratory studies. No evidence was found that the 
tuff specimens were damaged in the LBT.

 3-147 
3.6.1.1.8 Model Analysis of the Large Block Test Results 
The DKM with Active Fracture using the NUFT code was used to analyze the temperature and 
neutron data from the LBT (CRWMS M&O 2000a, Section 6.1.4). Both the DS property set and 
the mountain-scale property set were used in the analyses. The purpose of the model analyses 
was to identify a property set that would give a better prediction of the measured data. As 
mentioned before, the LBT was for understanding processes, not for testing properties. It was 
concluded from the comparison that both the DS property set and the mountain-scale property set 
provided generally good predictions of the measured temperature. Figure 3-60 (CRWMS 
M&O 2000a, Figure 65) shows one example of the comparison. The DS property set had a 
better statistical fit than the mountain-scale property set, as shown in Figure 3-61 (CRWMS 
M&O 2000a, Figure 66). Both property sets were able to capture the major characteristics of the 
measured temperature variations with time and space. Figure 3-62 (CRWMS M&O 2000a, 
Figure 67) shows one example of the comparison using the drift-scale property set. This means 
that the DKM model was able to simulate the processes that affected the measured temperatures. 
The model, using the DS property set, was able to capture the shape of the volume-fraction water 
versus depth curves measured by neutron logging quite well. But neither property set could 
predict the extent of drying, nor the increase of water content outside the drying zone, as 
illustrated by Figures 3-63 and 3-64 (CRWMS M&O 2000a, Figures 68 and 101). Again, from 
the simulation of processes point of view, the DKM/AFM did well on the moisture distribution 
in the LBT. As expected, the model could not simulate the two thermal-hydrological events as 
discussed in Section 3.6.1.1.3 which were likely caused by localized events (in one or more 
fractures). 
3.6.1.1.9 The LBT Summary 
The LBT performed as designed. The heating of the block was close to the designed onedimensional 
heating. A uniform dryout zone was created at the heater horizon. The moisture 
distributions above and below the dryout zone varied, probably due to the heterogeneity of the 
block. Refluxing of condensates, due to boiling at the heater horizon, were illustrated by the 
temperature fluctuations. The water, which was involved in at least one of two observed thermal 
hydrological events was supplied by rain. Monitoring and labeled mircobes placed at the heater 
horizon indicate that the microbes may have survived the heat, and that liquid water flow below 
the heaters was able to facilitate the migration of the microbes. The microbes were found in the 
observation holes, about 1.5 m below the heater holes, during the heating phase of the LBT. 
There was some indication of coupling between block deformation and thermal-hydrological 
processes. The DKM/AFM calculated the processes that governed the general temperature and 
moisture distributions. Analyses of the posttest cores are still on-going. The results from the 
post test analyses are expected to provide insight to chemical processes in the LBT. At that time, 
some assessments of the coupled THCM processes can be performed.

 3-148 
Source: CRWMS M&O 2000a, Figure 65 
NOTE: The y-axis, Z(m), is the distance below the top of the block. 
Figure 3-60. Simulated Temperature Profile Along Borehole TT1 in the LBT Computed Using the DS 
and MS Rock Property Data Set, Compared to Measured Data

 3-148 
Source: CRWMS M&O 2000a, Figure 65 
NOTE: The y-axis, Z(m), is the distance below the top of the block. 
Figure 3-60. Simulated Temperature Profile Along Borehole TT1 in the LBT Computed Using the DS 
and MS Rock Property Data Set, Compared to Measured Data

 3-149 
Source: CRWMS M&O 2000a, Figure 66 
NOTES: 1. The property sets tested were the Drift Scale (DS) set used in TSPA-SR calculations, a MS set with higher 
fracture permeability, a second MS set with still higher fracture permeability, a third MS set with a narrower range 
of thermal conductivity dependence on saturation, and a conduction-only (CON) set that does not track mass 
transfer. 
2. The three statistical measures (averaged over all sensors within a given range) are the root mean square 
difference (RMSD) which indicates the scatter in the data, the mean difference (MD) which indicates trends (bias) 
between measured and calculated temperatures, and normalized absolute mean difference (NAMD), which 
indicates scatter in the data normalized to the total amount of heating. 
3. The three columns are averaged over all temperature sensors, all above-boiling sensors (at each 
plotted time), and all below-boiling sensors, respectively. 
Figure 3-61. Statistical Measures for LBT Thermal Analyses

 3-150 
Source: CRWMS M&O 2000a, Figure 67 
Figure 3-62. Simulated Versus Measured Temperature Histories for Sensors TT1-14 
(Top) and TT1-19 (Bottom) in Borehole TT1 of the LBT. The DS Property 
Set was Used in the Simulation. 
Temperature (oC) 
Temperature (oC) 
Simulated 
Measured 
Simulated 
Measured

 3-151 
Source: CRWMS M&O 2000a, Figure 68 
NOTE: The y-axis, Z(m), is the distance below the top of the block. 
Figure 3-63. Liquid-Saturation Profile Along Borehole TN3 for the LBT. The DS 
Property Set was Used in the Simulation

 3-152 
Source: CRWMS M&O 2000a, Figure 101 
NOTE: The y-axis, Z(m), is the distance below the top of the block. 
Figure 3-64. Comparison of Liquid Saturation Along Borehole TN3 in the LBT for 
the DS and MS Rock Property Data Sets 
4. LIQUID 5. LIQUID 
6. LIQUID 
Simulated (MS) 
Simulated (DS) 
Simulated (MS) 
Simulated (DS) 
Simulated (MS) 
Simulated (DS)

 3-153 
3.6.1.2 Single Heater Test 
This section includes experimentally determined data from the SHT (CRWMS M&O 1999d). 
This section will describe the SHT and explain how the data derived from the test have been 
used to help specify appropriate conceptual flow models, thermal perturbations to hydrologicflow 
properties, coupled-process data specifications, and assessments of implementation of 
ambient-flow hydrologic properties in thermally driven models. 
The primary purpose of the SHT was to investigate the thermal- mechanical responses of the rock 
mass caused by heating from a single heater in a borehole. The objectives of the SHT was to 
provide data and information on the rock-mass thermal and TM properties, preliminary 
information on coupled thermal- hydrolo gical -chemical- mechanical (THCM) response, and 
preliminary information on ground support and rock interaction at elevated temperatures 
(CRWMS M&O 1996, p. 2-1). The test design and the borehole layout were focused on 
providing data for the TM responses. Boreholes for monitoring water saturation and other 
coupled THCM related responses were located so that interference with the TM measurements 
was avoided. 
The borehole layout of the SHT is shown in Figure 3-65 and Table 3-15 (CRWMS M&O 1999d, 
Figure 3-2 and Table 3-1). In the SHT, the temperature was measured by thermocouples in 
seven thermocouple holes (TMA-TC-1 to -7) and by resistance thermal devices in four neutron 
holes (TMA-NEU-1, TMA-NEU-3, TMA-HYD-1, and TMA-HYD-2); the rock-mass 
displacements were measured in four MPBX boles (TMA-MPBX-1 to -4) and two optical 
MPBX holes (TMA-OMPBX-1 to -2); ERT was conducted in four ERT holes (TMA-ERT-1 to 
--4); hydrological measurements and sampling were conducted in TMA-NEU-2 and 
TMA-NEU-4. The SHT was also used to test the methodology of using chemical sensors in the 
Science and Engineering Associates Membrane In-situ Sampling Technology (SEAMIST) 
system for in situ chemical monitoring. The SEAMIST system was installed in TMA-CHE-1 
and TMA-CHE-2. 
The following instruments and boreholes were used to measure data fo r the TM responses, 
mechanical properties of the rock mass, and ground support and rock interaction: 
thermocouples, MPBXs, borehole jack, rock bolt with load cell, and tape extensometers. 
Neutron logging, ERT, relative humidity and gas-phase pressure (in packer holes), and chemical 
sensors (in SEAMIST holes) were used to measure data for the coupled thermal-hydrologicalchemical 
(THC) responses. Candidate waste package material coupons were also placed in the 
packer holes. The test block in the SHT was bounded by the observation Drift, Thermomechanical 
Alcove, and Thermo-mechanical Alcove Extension in Alcove 5 of the ESF 
(CRWMS M&O 1997a, Figure 3-1). The test block was heated by a 4-kW heater from 
August 26, 1996 till May 28, 1997. The block was cooled naturally after the heater was turned 
off on May 28, 1997.

 3-154 
Source: Adapted from Figure 3-2 of CRWMS M&O 1999d 
Figure 3-65. Borehole Layout for the Single Heater Test 
OBSERVATION 
DRIFT 
THERMOMECHANICAL 
ALCOVE 
EXTENSION 
CROWN CROWN 
A A 
Heater 
Rock bolt load cell 
THERMOMECHANICAL 
ALCOVE 
EXTENSION OBSERVATION 
DRIFT 
THERMOMECHANICAL ALCOVE 
REFERENCE ONLY 
(NOT TO SCALE) 
CROSS-SECTION A-A 
38 
39 
38 
39 
38 
39 
38 
39 
23 
21 14 
19 
22 
20 
24 27 
15 36 37 
37 16 36 
3129 2830 
11 
3 8 2 96 
12 
1 
10 4 
40 
41 
40 
41 
40 
41 
40 
41 
25 26 
36 37 17 
7,18 
13 5 
10 8
12 
11
2 
9
4
6 
39 
19 
20, 21 
22, 23 
14 
38 
39 
38 
36 3 
31 
6 37 
29 
36 33 32 
34 
37 
41 
40 
7
13 
41 
5
40 
26,27 
15,16,17,18 
Heater 
Thermal 
Mechanical 
Hydrological 
Chemical 
LEGEND: Boreholes 
24,25 
28 
12 
11 
1 3

 3-155 
Table 3-15. Borehole Numbers, Types, and Locations for the Single Heater Test 
Collar Coordinates Bottom Coordinates Borehole 
Number 
Borehole 
Identification 
Primary 
Purpose x y z x y z 
Orientation 
Degree 
Length 
meters 
1 ESF-TMA-H-1 Heater 0.01 0.04 -0.03 0.00 6.97 -0.01 0.5 7.00 
2 ESF-TMA-MPBX-1 
MPBX - Rock 
Mass 
Displacement 
0.18 0.08 0.27 0.14 6.99 0.28 0.5 7.00 
3 ESF-TMA-MPBX-2 
MPBX - Rock 
Mass 
Displacement 
-0.62 0.23 0.21 -0.62 7.25 0.25 0.5 7.00 
4 ESF-TMA-MPBX-3 
MPBX - Rock 
Mass 
Displacement 
0.75 0.10 1.24 0.78 7.00 1.29 0.5 7.00 
5 ESF-TMA-MPBX-4 
MPBX - Rock 
Mass 
Displacement 
6.43 3.50 -0.11 0.40 3.50 -0.21 0.5 6.20 
6 ESF-TMA-OMPBX-1 Optical MPBX 1.19 -0.05 0.28 1.21 11.99 0.13 -0.5 12.00 
7 ESF-TMA-OMPBX-2 Optical MPBX 6.20 6.49 -0.17 0.30 6.45 -0.27 -0.5 6.20 
8 ESF-TMA-TC-1 Thermocouple -0.18 0.15 0.28 -0.27 7.85 0.34 0.0 8.00 
9 ESF-TMA-TC-2 Thermocouple 0.63 0.06 0.21 0.62 8.15 0.26 0.0 8.00 
10 ESF-TMA-TC-3 Thermocouple -0.75 0.23 1.26 -0.71 8.05 1.31 0.0 8.00 
11 ESF-TMA-TC-4 Thermocouple -0.02 0.03 -0.69 -0.09 5.49 -0.77 0.0 8.00 
12 ESF-TMA-TC-5 Thermocouple 0.00 0.16 0.65 -0.04 6.84 0.68 0.0 8.00 
13 ESF-TMA-TC-6 Thermocouple 6.26 5.49 -0.01 1.87 5.46 -0.04 0.0 6.20 
14 ESF-TMA-TC-7 Thermocouple -6.59 3.46 -0.01 -0.34 3.43 -0.02 0.0 6.20 
15 ESF-TMA-NEU-1 Neutron Probe & 
Temp 
6.10 4.29 0.33 -1.60 4.28 2.74 17.0 8.50 
16 ESF-TMA-NEU-2 Hydrology 6.19 4.30 0.04 1.14 4.32 0.71 7.5 5.50 
17 ESF-TMA-NEU-3 Neutron Probe & 
Temp 6.16 4.30 -0.45 -1.78 4.31 -1.47 -7.0 8.50 
18 ESF-TMA-NEU-4 Hydrology 6.17 4.29 -0.22 1.51 4.28 -0.28 -0.5 5.00 
19 ESF-TMA-BJ-1 Borehole Jack -6.55 5.52 -0.14 -0.34 5.51 -0.07 0.5 6.20 
20 ESF-TMA-CHE-1 Chemistry - 
SEAMIST -6.64 4.91 -0.66 -1.51 4.93 -0.77 -0.5 5.00 
21 ESF-TMA-CHE-2 Chemistry - 
SEAMIST 
-6.59 5.01 -0.01 -1.06 5.10 0.63 7.5 5.50 
22 ESF-TMA-HYD-1 Neutron Probe & 
Temp 
-6.60 4.43 -0.66 -1.56 4.39 -0.74 -0.5 5.00 
23 ESF-TMA-HYD-2 Neutron Probe & 
Temp 
-6.57 4.43 0.00 -1.31 4.42 0.65 7.5 5.50 
24 ESF-TMA-ERT-1 
Electrical 
Resistivity 
Tomography 
-6.56 3.89 0.12 -0.41 3.82 6.28 45.0 8.70 
25 ESF-TMA-ERT-2 
Electrical 
Resistivity 
Tomography 
-6.57 3.91 -0.13 -0.29 4.07 -6.22 -45.0 8.70 
26 ESF-TMA-ERT-3 
Electrical 
Resistivity 
Tomography 
6.25 3.89 -0.36 1.15 3.85 -5.71 -45.0 8.70 
27 ESF-TMA-ERT-4 
Electrical 
Resistivity 
Tomography 
6.25 3.90 0.36 0.38 3.97 6.29 45.0 8.70 
28 ESF-TMA-RB-1 Rock Bolt w/ 
Load Cell 
0.14 0.05 -0.38 0.26 4.21 -0.38 0.0 4.00

 3-156 
Table 3-15. Borehole Numbers, Types, and Locations for the Single Heater Test (Continued) 
Collar Coordinates Bottom Coordinates Borehole 
Number 
Borehole 
Identification 
Primary 
Purpose x y z x y z 
Orientation 
Degree 
Length 
meters 
29 ESF-TMA-RB-2 Rock Bolt w/ 
Load Cell 
-0.23 0.00 -0.35 -0.18 4.22 -0.42 0.0 4.00 
30 ESF-TMA-RB-3 Rock Bolt w/ 
Load Cell 0.59 0.10 -0.31 0.60 4.03 -0.35 0.0 4.00 
31 ESF-TMA-RB-4 Rock Bolt w/ 
Load Cell 
-0.68 0.13 -0.29 -0.59 4.18 -0.23 0.0 4.00 
32 ESF-TMA-RB-5 Rock Bolt w/ 
Load Cell 
0.14 -5.37 -0.39 0.06 -9.47 -0.41 0.0 4.00 
33 ESF-TMA-RB-6 Rock Bolt w/ 
Load Cell 
-0.20 -5.45 -0.42 -0.21 -9.45 -0.42 0.0 4.00 
34 ESF-TMA-RB-7 Rock Bolt w/ 
Load Cell 
0.59 -5.49 -0.30 0.64 -9.60 -0.36 0.0 4.00 
35 ESF-TMA-RB-8 Rock Bolt w/ 
Load Cell -0.64 -5.38 -0.31 -0.73 -9.43 -0.45 0.0 4.00 
Source: Table 3-1 of CRWMS M&O 1999d 
Note: Borehole Coordinates are Referenced to a 0,0,0 Coordinate Located at the Center of the Collar for the Heater Borehole. 
3.6.1.2.1 The Single Heater Test Results 
A listing of data obtained from the Single Heater Test can be found in the SHT Final Report 
(CRWMS M&O 1999d, Section 2.3). 
The chemical sensors in the SEAMIST system did not work as expected. Only the discussion of 
test results that are related to the NFE and AZ are summarized below. Detailed discussion of the 
test results can be found in the SHT Final Report (CRWMS M&O 1999d). 
MPBX measurements in the SHT were made in directions both parallel and perpendicular to the 
heater. During the test, MPBX instruments oriented parallel to the heaters registered mostly 
expansion of the rock mass. The MPBX perpendicular to the heater registered compression 
movement at the beginning of heating, followed by expansion after about 40 to 50 days of 
heating. Figure 366 (CRWMS M&O 1999d, Figure 9-5) presents data for MPBX-2 which 
measured deformation parallel to the heater at a distance of 0.69 m from the heater. Gaps in the 
data are due to power outages that occurred during the SHT. The data show general extension 
between all pairs of anchors during the heating period, with exception of anchors 4 and 5, which 
show compression near the end of heating phase. These measurements are consistent in form 
with predicted values (using the FLAC computer code) for this location shown in Figure 367 
(CRWMS M&O 1999d, Figure 9-6). Comparison of these two figures shows that the measured 
displacement values are consistently lower than the observed displacements. Cooldown data 
show a few minor jumps that may be associated with stick-slip behavior on a fracture. The data 
indicate that the rock has a lower coefficient of thermal expansion, and lower stiffness than 
measured for lab samples.

 3-157 
NOTE: No data collected from about day 100 to about day 150 due to a blown fuse in the signal conditioner for the 
LVDTs. 
Figure 3-66. Displacement History for ESF-TMA-MPBX-2 (Corrected for Rod Thermal 
Expansion; Extension Positive) 
Source: CRWMS M&O 1999d, Figure 9-6 
Figure 3-67. Pretest Predicted MPBX-2 Anchor-to-Anchor Displacement History Relative 
to the Borehole Collar

 3-158 
Figure 3-68 shows that both ERT and neutron logging measured significant drying in a region 
that was at least four times larger than the region where the temperature was greater than the 
boiling point of water (CRWMS M&O 1999d, Figures 8-45 and 8-65). The temperature in the 
neutron holes, where significant drying had occurred, was below 90C (CRWMS M&O 1999d, 
Figures 7-18 and 8-65). The ERT also showed some increase in moisture content in regions 
below the heater hole. About 17 liters of water was collected from zone 4 in Hole 16 
(TMA-NEU-2), one of the two packer holes. Hole 16 was drilled from the Thermal-mechanical 
Alcove Extension toward the heater hole with a upward inclined angle of about 7.5. The end of 
this hole was about 1 m above and 1.14 m to the side of the heater hole. Zone 4 was the last 
zone in Hole 16, counted from the collar. Therefore, this zone, which was about 2 m in length, 
was at a radial distance of at least 1.5 m from the heater (CRWMS M&O 1999d, Figure 7-36). 
At the end of the heating phase of the SHT, the boiling-point isotherm reached a radial distance 
of about 1 m from the heater. When water was collected from Hole 16, the water-producing 
zone was beyond the boiling region, therefore in the condensation region. This zone was about 
2 m from the heater hole (CRWMS M&O 1999d, Figure 3-2). The chemical composition of the 
water indicated that the water was more diluted than J-13 water and pore water of the Topopah 
Spring Tuff, except for the concentration of calcium. The calcium composition in the 
Borehole 16 water was about the same as in the J-13 water. Also, the pH value in the Hole 16 
water ranged from 6.2 to 6.9, which was lower than the 7.4 for the J-13 water (CRWMS 
M&O 1999d, Table 4-1). One of the interpretations of the chemical characteristics of the Hole 
16 water is that the pore water in the rock mass near the heater hole was evaporated, condensed 
in the outer and cooler region, then flowed along fractures into Hole 16. On its way to Hole 16, 
the condensed water interacted with minerals on the fracture surfaces to pick up calcium, and 
generate greater CO2 partial pressure, which lowered the pH in the water (CRWMS 
M&O 1999d, Section 4.1.7). Air-permeability measurement by cross-hole injection between 
Hole 16 and 18 (TMA-NEU-2 and - 4) indicated reduced permeability during heating. For 
example, the permeability near zone 4 in Hole 16 decreased from 1.10 x 10-14 m2 (preheat) to 
2.58 x 10-15 m2 (on 2/4/97) (CRWMS M&O 1999d, Table 8-3). After cooling, the air 
permeability in these holes increased by factors ranging from 0.2 to 3.5 orders of magnitude of 
the pre-heat values (CRWMS M&O 1999d, Table 8-5). Increases in water saturation and/or 
reduced fracture aperture may have caused this reduction in air permeability during heating. The 
displacement measurements in the SHT, using MPBX, did not generate information suitable for 
inferring coupling between the TM responses and TH responses.

 3-159 
Source: CRWMS M&O199d, Figure 12.1, BAB0000000-01717-5700-00005, Rev 00 
Figure 3-68. Synthesis of ERT and Neutron Logging Measurements of the Single Heater Test 
Wetting 
Regions 
Drying Interval for water 
collection 
Note: Sampling interval for water samples is

 3-160 
3.6.1.2.2 Model Analysis of the Single Heater Test Results 
Part of the SHT results (Single Heater Test Final Report, CRWMS M&O 1999d) were compared 
to model results in the Thermal Test AMR. The model used constant temperature, pressure and 
saturation boundaries at three locations far from the heater and insulation boundaries to simulate 
the insulated but occupied access drifts. Since the experiment was symmetric around a vertical 
plane through the heater, only half of the heated rock was modeled. The DKM model, using 
TOUGH2 with dual permeability active fracture modeling and the DS property set, was used. 
TSPA-VA and Median kb property sets were used for analyses, along with the DS property set 
(CRWMS M&O 2000a, Section 6.3.1). The Median kb property set is a local hydrologic 
property set representative of the measurements taken at the actual single heater test location. 
The temperature data measured in three of the thermocouple boreholes (TMA-TC-1A, 
TMA-TC-4A, and TMA-TC-5A) and the temperature as a function of the radial distance from 
the heater were compared (CRWMS M&O 2000a, p. 40). The Thermal Test AMR conclusion 
was that the simulated temperature in the SHT matched the trend of the measured temperature 
data (CRWMS M&O 2000a, p. 73). As shown in Figures 3-69, 3-70, and 3-71 (Figures 15, 16, 
and 17 of the Thermal Test AMR), the temperature matches indicate that the active- fracture, DK 
model adequately represents the thermal-hydrological processes of the SHT. In some locations, 
the median kb property set (CRWMS M&O 2000a, Table 4) represents the SHT temperatures 
better than the other two property sets as shown in Figures 3-72 and 3-73 (CRWMS 
M&O 2000a, Figures 77 and 79). The Thermal Test AMR used statistical measures to assess 
agreement between simulated and measured temperatures (CRWMS M&O 2000a, 
Section 6.2.1.2). Root-mean-square difference (RMSD, MD, and normalized absolute mean 
difference (NAMD) were the statistical measures used in the AMR. The statistical assessment of 
the property sets for the SHT temperatures are shown in Figure 3-74 (CRWMS M&O 2000a, 
Figure 18).

 3-161 
Source: CRWMS M&O 2000a, Figure 15 
Legend = Red is measured data, black is simulated data. 
Figure 3-69. Comparison of the DKM/TOUGH2 Simulation Using the Drift-Scale 
Property Set and the SHT Measured Temperatures at Thermocouple 
Location TMA-TC-4A-6 (73 cm below the heater center) 
Source: CRWMS M&O 2000a, Figure 16 
Legend: Red is measured data, black is simulated data. 
Figure 3-70. Comparison of the DKM/TOUGH2 Simulation Using the Drift-Scale 
Property Set and the SHT Measured Temperatures at Thermocouple 
Location TMA-TC-5A-7 (66 cm above the Heater Center) 
20 
30 
40 
50 
60 
70 
80 
90 
100 
110 
120 
0 50 100 150 200 250 300 
Time (days from heater activation) 
20 
40 
60 
80 
100 
120 
140 
0 50 100 150 200 250 300 
Time (days from heater activation)

 3-162 
Source: CRWMS M&O 2000a, Figure 17 
Legend: Red line is lateral direction simulated data, green line is upward direction simulated data, blue line is 
downward direction simulated data, and red squares are measured data. 
Figure 3-71. Comparison of the DKM/TOUGH2 Simulation Using the 
Drift-Scale Property Set and the SHT Temperatures 
Measured Radially Around Heater Mid-Length 
Source: CRWMS M&O 2000a, Figure 77 
Legend: Blue is simulated data with DS property set, green is simulated data with TSPA-VA property sets, brown is 
simulated data with median bulk permeability, red is measured data. 
Figure 3-72. Comparison of Three SHT DKM/TOUGH2 Simulations (Property Sets: 
DS, Median kb, and TSPA-VA) and Measured SHT Temperatures at 
Thermocouple Location TMA-TC-1A-7 
20 
40 
60 
80 
100 
120 
140 
160
0 1 2 3 4 5 6 7 
Radial Distance from Heater (m) 
TMA-TC-1A-7 
20 
40 
60 
80 
100 
120 
140 
160 
180 
0 50 100 150 200 250 300 
Time (days from heater activation)

 3-163 
20 
40 
60 
80 
100 
120 
140 
0 50 100 150 200 250 300 
Time (days from heater activation) 
Source: CRWMS M&O 2000a, Figure 79 
Legend: Blue is simulated data with DS property set, green is simulated data with TSPA-VA property sets, brown is 
simulated data with median bulk permeability, red is measured data. 
Figure 3-73. Comparison of Three SHT DKM/TOUGH2 Simulations 
(Property Sets: DS, Median kb, and TSPA-VA) and 
Measured SHT Temperatures at Thermocouple Location 
TMA-TC-5A-7

 3-164 
Source: CRWMS M&O 2000a, Figure 18 
NOTES: 1. The property sets tested were the Drift Scale (DS) set used in TSPA-SR calculations, the TSPA-VA set 
with higher fracture permeability but lower fracture porosity, and the Median Kb set with lower fracture 
permeability and porosity and a narrower range of thermal conductivity dependence on saturation. 
2. See Note 2 of Figure 3-56 for descriptions of the statistical measures. 
3. See Note 3 of Figure 3-56 for sensor group descriptions. 
Figure 3-74. Statistical Measures for SHT Thermal Analyses

 3-165 
3.6.1.2.3 SHT Summary 
The TM displacement measurements in the SHT generated good information of the effect of 
heating on bulk deformation of the rock mass. The SHT generated interesting information about 
the coupled THC in a heated rock mass, even though it was not designed particularly for that 
purpose. The test confirmed the process that heat drives water away in vapor form. The water 
vapor appears to have condensed when it reached cooler regions. Further, it appears that the 
condensed water may have traveled through fractures. Rock-water interaction between the 
condensed water and mineral coating on fracture surfaces can occur within a relatively short 
period of time, in the order of months. The Thermal Test AMR conclusion was that the simulated 
temperature in the SHT, from the DKM active- fracture modeling using TOUGH2 and the DS 
property set, matches the trend of the measured temperature data well. The drift scale property 
set and the median kb property set matched the measured temperature values better than the 
median TSPA-VA set (CRWMS M&O 2000a, Section 6.3.1). 
Important coupled processes observed from the SHT include: 
 Dryout of rock occurred in regions below the boiling-point temperature. The region of 
drying exceeded that of the region where temperatures were greater than the 
boiling-point temperature by more than four times 
 Moisture increased below the heater (presumably due to condensation) 
 Chemical composition of water sampled was consistent with the concept of evaporation, 
condensation, and flow along fractures 
 Low pH in the sampled water is probably caused by excess CO2 generation from rockwater 
interaction during flow along fractures 
 Air permeability measurements noted reduced permeability during heating in regions 
outside of the dryout zone, and increased permeability after the rock had cooled. 
These changes in permeability are possibly the result of mobilization, during the thermal 
period, of water from the dryout zone with condensation of that water in the fractures 
outside of the dryout zone. This increased saturation in fractures would reduce the 
relative permeability of air within the fractures. After cooling, as the increased fracture 
saturation in the condensate zone dissipated, the relative permeability to air would 
increase. 
Another possible reason for the changes in air permeability are changes in fracture 
aperture that resulted from the mechanical responses to the increased temperatures. As 
the rock expanded during the thermal pulse, the fracture apertures would decrease, thus 
decreasing the permeability. After cooling, the rock deformations would decrease so 
that the apertures would return to preheating conditions, with an accompanying increase 
in permeability.

 3-166 
 The conceptual and mathematical model simulates temperatures consistent with 
measured temperatures. 
 The Thermal Test AMR was focused on TH responses and therefore did not report 
mineralogical change in the SHT due to the heating. Posttest cores and over-cores were 
obtained from the SHT block. Detail descriptions of the mineralogical analysis of the 
post-test cores and over-cores can be found in Single Heater Test Final Report (CRWMS 
M&O 1999d). The analysis of the post-test cores for the mineralogical change is 
summarized below. 
Calcite, gypsum, and opal-A were identified as the principal alteration products of the 
SHT. These minerals were observed on pretest borehole surfaces and in natural 
fractures adjacent to the boreholes (from post-test over-cores). The distribution and 
textural attributes of the mineral deposits in a borehole within the condensation zone 
may be most compatible with mineral precipitation during the post-test cooldown 
period. The amounts of secondary minerals available from post-test overcores 
(producing annular samples) were minimally adequate to identify the mineralogic test 
products. Given the combined limitations of time constraints on posttest analysis and 
availability of suitable core, a 3-D distribution of mineral deposition could not be 
established. Such a database could test whether attributes of mineralogy or mineral 
textures correlate with the geometry of the dryout, condensation, and reflux zones. 
There are indications that the mineralogical products of the SHT may reflect an 
influence of materials introduced during drilling operations. Introduced materials such 
as gypsum could alter the sulfate budget of the water and rock system. The magnitude 
of this influence is probably small, but additional documentation would be required to 
increase confidence in this assessment. Existing geochemical models of the test do not 
account for introduced materials that may participate as reactants or catalysts. (CRWMS 
M&O 1999d, Section 6.4.10). 
3.6.1.3 Drift Scale Test 
The DST was designed to collect data on coupled THCM processes in an in situ DS setting, and 
to test conceptual and mathematical model understanding, specifically the hypotheses of the 
processes. Although the DST was designed to test processes and process models at the 
repository horizon, it also considered the conceptual repository design at the time of the DST 
planning. This goal of understanding heat-driven coupled processes is not directly linked to a 
specific repository design and does not require replication of potential repository conditions, 
geometries, and heating rates, nor is such replication practical in limited-duration field test. The 
fundamental nature of the DST is to test conceptual process models in the system and the ability 
to model quantitatively the systems response to those processes. Once confidence is developed 
in the coupled-process models, they can be applied to a range of repository designs. Therefore, 
although the test was focused on a VA design rather than the EDAII design, the testing of 
physical processes is judged to be applicable. The detailed description of the objectives and 
design of the DST can be found in DST Design and Forecast Results (CRWMS M&O 1997b, 
Sections 2 and 3). A brief summary of the DST will be given here to facilitate discussion of the 
test results. The drift configuration of the DST consists of an Access/Observation Drift (AOD),

 3-167 
Connecting Drift (CD), and Heater Drift (HD). The AOD connects with the main ESF Tunnel at 
about 2.88 km from the North portal of the main Tunnel. The HD is about 47.5 m in length, 
starting from a thermal bulkhead that is located near its intersection with the CD. The heat 
source in the DST includes nine canister heaters lined up on the floor of the HD, and 25 wing 
heaters on each side of the HD. Each of the nine canister heaters is about 4.7 m in length and 
1.7 m in diameter. Each of the 50 wing heaters is about 10 m in length. Each of the wingheaters 
is placed in a horizontal wing- heater hole, which is 11.5 m in length, and was drilled into 
the sidewall of the HD at about 0.25 m below the springline. The total power of the nine canister 
heaters and the wing heaters are about 68 kW and 143 kW, respectively. Each wing heater 
consists of two sections of heating elements. The outer (further away from the HD) heating 
element has a rated power output of about 1.719 kW; the inner section has a power of about 
1.145 kW. 
The borehole layouts for the DST are shown in Figures 3-75, 3-76, and 3-77. Temperature is 
measured in RTD holes that are arranged radially from the HD (CRWMS M&O 1997b, 
Figure 3-3 and Table 3-1, Holes 133, 134, 137144, 158165, 168, 169, and 170175). In 
addition, temperature is also measured in two longitudinal neutron-RTD holes (CRWMS 
M&O 1997b, Figure 3-1, Hole 79 and 80) that are parallel to the HD, at about 3.5 m above the 
midpoint of the wing- heater plane. The ERT is conducted in vertical planes parallel to the HD, 
and in two vertical planes perpendicular to the HD from the AOD, at 4.57 and 24.69 m from the 
bulkhead. Neutron logging is conducted in two sets of holes from the AOD. Each set of neutron 
holes (five holes) forms a fan-shape vertical plane perpendicular to the HD, with three holes that 
extend above the HD, and two holes that extend under the HD. The two neutron-hole sets are 
located at 6.4 and 26.52 m from the bulkhead. Gas-sampling ports and water-absorbing pads are 
installed in the SEAMIST system in two sets of Chemistry holes, which were drilled from the 
AOD. Similar to the neutron holes, each set of the Chemistry holes forms a fan-shaped vertical 
plane perpendicular to the HD, with three holes extending above the HD, and two holes 
extending under the HD. The two Chemistry hole sets are at 8.23 and 28.35 m from the 
bulkhead. Four packers with gas-injection and sampling capabilities were installed in two sets of 
Hydrology holes, which were drilled from the AOD. The arrangement of the Hydrology holes is 
the same as the SEAMIST holes. The two sets of Hydrology holes are located at 10.06 and 
30.18 m from the bulkhead. In addition, two more hydrology holes were drilled from the AOD 
at 44.8 m from the bulkhead, with one extending above the HD, and one extending below the 
HD. The displacement in the rock mass is measured by MPBX in the MPBX holes. Those are 
Hole #42, 43, 44, 81, 82, 147, 148, 149, 150, 154, 155, 156, 157, 178, 179, 180, 181, 187, and 
188, as shown in the DST Design and Forecast Results (CRWMS M&O 1997b, Table 3-1 and 
Figure 3-1). In situ thermal conductivity and thermal diffusivity are measured in the three 
REKA holes (Hole #151, 152, and 153) at 17.37 m from the bulkhead. All of the 
instrumentation holes, except the MPBX holes, were sealed by cement grout, packers, or 
SEAMIST. The effect of the thermal-hydrologically open MPBX holes on the coupled THCM 
processes to be tested in the DST will have to be assessed. The heaters in the DST were 
energized on December 3, 1997. The test is now in the third year of its four-year heating phase, 
then the heaters will be turned off to start a natural cooling phase, which is planned to last for 
another four years.

 3-168 
Source: CRWMS M&O 2000a, Figure 4
Figure 3-75. Plan View of the DST

 3-169 
Source: CRWMS M&O 2000a, Figure 5 
Figure 3-76. Cross Section (A-A) Parallel to the Heated Drift in the DST

 3-170 
Source: CRWMS M&O 2000a, Figure 6 
Figure 3-77. Cross Section (B-B) Orthogonal to the Heated Drift in the DST 
3.6.1.3.1 The Drift Scale Test Results 
Because the test is ongoing, any discussion of the THCM processes inferred from the test results 
is preliminary. The temperature and the moisture distribution data of the DST were analyzed and 
included in the Thermal Test AMR (CRWMS M&O 2000a). The water chemistry and gas 
chemistry data of the DST were analyzed and included in the THC Process AMR (CRWMS 
M&O 2000b). The analyses of the DST data conducted for the Thermal Test AMR focus on 
comparison of the measured temperature and moisture distribution simulated by DKM with 
133, 
137 
135, 
145 
47 
52 
57 
149 
144 147 148 
138 
45,48 
53 
58 
54 
59 
49 
79 81 80 82 
140 
42,43,44 
139 
Wing Heater 187,188 Wing Heater 
46,51 
56 
61 
142 140 
136,146 
150 
134,141 
Heated 
Drift 
Observation 
Drift 
Wing Heaters 
Thermal 
Mechanical 
Hydrological 
Chemical 
LEGEND: Boreholes 
55 
50 
60

 3-171 
AFMs using TOUGH2 and NUFT codes with the objective of identifying a property set that 
yields the best temperature and saturation predictions. 
The Thermal Test AMR analyses are summarized in Section 3.6.4.1. In addition to property-set 
evaluations, and discussions of the DST temperature profile and evaluation reported in the 
Thermal Test AMR, this report examines the processes that can be inferred from the DST results. 
Those processes are boiling of pore water, movement of moisture, effect of the bulkhead on 
measured results, and drying of rock mass. 
Inspection of the temperature data can provide several insights into the TH processes. When 
conduction dominates or is the only heat-transfer mechanism, heat flow is a function of 
temperature gradients and thermal conductivity of the medium. Therefore, at any point within 
the DST, the response should show increases in temperature with time, with the slope of the 
increase decreasing with time. However, there are three TH-related processes that can impact 
that general response. The first is conduction, which is sensitive to the 25 to 40 percent, is a 
difference between wet- and dry-rock thermal conductivity (CRWMS M&O 2000a, Tables 4 
and 5). The thermal conductivity decreases once rock has become dry. The second condition is 
the heat capacity of the rock mass changes with its moisture content. Decreasing moisture 
content of the rock mass will decrease its heat capacity. The total effect of these two is that, as 
the rock within the region of a sensor dries out, the slope of the temperature-time curve may 
increase. The third effect is that vaporization or boiling of water requires energy. This will 
result in temperatures approaching the boiling point of water and remaining at that temperature 
until the water has been removed from that region of rock mass. On a plot of temperature as a 
function of time, this will cause a flattening of the slope of the temperature curve at the boiling 
point temperature. 
Whether there is a flattening of the curve or merely an inflection point, it is a function of how 
long water remains in proximity of the sensor. The amount of inflection also depends on 
whether water remains in the rock until the boiling point is reached, or if the evaporation rate 
increases sufficiently that the rock mass becomes dry prior to reaching the boiling point of water. 
The evaporation rate depends, among other factors, on the suction potential and the permeability 
of the rock mass near the temperature sensor. If water remains in the system until the 
temperature reaches boiling, there would be a flattening of the temperature curve, with the curve 
remaining at the boiling point until the water was removed. If much of the water were removed 
prior to the temperature reaching boiling, there would be a very short period of time at which the 
temperature would remain at the boiling point. Depending on how short this period was, the 
result could be an inflection at the boiling point, but not a flattening that extended for any length 
of time. If the water had been entirely removed from the system prior to the region reaching the 
boiling point, the temperature response would not change as the temperatures reached and then 
passed the boiling point temperature. 
With these principles in mind, data from the DST can be inspected to determine whether a 
distinction can be made regarding the physical processes that occurred. Two arrays of sensors 
are considered. These are fan arrays of boreholes 23 m from the bulkhead and 12 m from the 
bulkhead. As shown on Figures 3-75, 3-76, and 3-77, an array of 8 boreholes were installed at 
each of these locations to monitor responses in those locations. For simplicity, the comparisons 
were made for half of each array, assuming that the results will be symmetrical. The boreholes

 3-172 
considered for the array 23-m from the bulkhead consist of holes 158 to 162. These boreholes 
were drilled from the HD with borehole 158 drilled vertically upward, borehole 159 drilled 45 
upward, borehole 160 drilled horizontally toward the AOD, borehole 161 drilled 45 downward, 
and borehole 162 drilled vertically downward, thus forming a fan of boreholes oriented at 45s 
from each other, with a common apex. The array considered at 12 m was a similar fan array 
consisting of boreholes 137 (vertical upward), 138 (45 upward), 139 (horizontal), 140 
(45 downward) and 141 (vertical downward). 
All of the figures of temperature in this section are based on the temperature data in the TDMS, 
as listed in the Thermal Test AMR (CRWMS M&O 2000a, Table 8). Figures 3-78 and 3-79 
show the temperatures measured at a depth of about 2 m from the collar in the five Holes #137 to 
141 and 158 to 162, respectively, as a function of time (days) since heating commenced. The 
purpose of presenting those figures is to show boiling of the pore water as measured from 
different orientations with respect to the HD. Boiling of pore water and reflux or influx water at 
the temperature sensors are illustrated as a flat temperature-time curve, at about the boiling point 
of water, about 96C in the DST. Different profiles would indicate different interactions with 
water, non-uniform porosity and saturation or thermal conductivity, or the effects of different 
temperature gradients. Consider first, the monitored temperatures from the array at 23 m from 
the bulkhead where end effects should be minimal. All of the holes show either flattening or 
inflection of temperature with time at the boiling point temperature (Figure 3-79). The least 
amount of flattening was exhibited in borehole 159, which is oriented 45 upward. The most 
well defined flattening (boiling) occurred in borehole 160, which was horizontal. This flattening 
lasted for about 35 days. If the data are accurate for borehole 158 (temperature plot is less 
uniform around 450-500 days), this vertical borehole exhibited the longest duration of impact of 
boiling or flattening. The array at 12 m indicates a similar response, but the horizontal borehole 
(hole 139) shows less well-defined flattening, and the 45 upward borehole shows no flattening, 
not even an inflection. Because flattening indicates the presence and boiling of water, and not all 
boreholes exhibited the same response, there are either physical processes that are not uniform in 
all of the boreholes or the rock is not uniform in properties and/or saturation. Because the 
pattern of differences is similar for the two fan arrays, it appears that more than property 
differences must be considered. 
By inspecting the plots, hypotheses can be made as to why the boreholes responded differently. 
It should be noted that the fracture system is dominated by vertical fractures. For the region of 
rock sampled by the vertical upward boreholes, water that was vaporized would likely move up 
the fractures as vapor, then condense and return along the same fracture back to the area of the 
sensor. This is essentially a gravity driven heat-pipe as discussed in Section 3.2.1. This would 
explain the nearly 70 to 120 day cycle of boiling of water in vertical boreholes 137 and 
158, respectively. It is unlikely that there was sufficient water in the pores of the rock to 
maintain boiling effects for nearly 100 days and, if so, there should have been a similar volume 
of water to cause similar boiling effects in the 45-upward boreholes. For other than purely 
vertical boreholes, the moisture migration is potentially more complex. Water vapor will 
migrate either in response to pressure or density (buoyancy). Further, the water that is vaporized 
will be water within the matrix (the fractures are essentially drained, except during episodic 
percolation events). Within the matrix, vaporization will cause pressure gradients. The overall 
direction of vapor migration within matrix blocks in response to this pressure would be radially

 3-173 
outward from the heat source. Buoyancy will cause vertically upward migration. It is unlikely 
that two-phase flow would impede vapor flow, unless the pores are nearly saturated. A 
differential between the dried portion of the matrix and the saturated portion can not be 
eliminated, but is not expected to be a dominant process. The largest impact on the migration 
direction for vapor is the presence (or lack) of fractures. If the matrix blocks are not too large, 
and the fracture permeabilities are greater than about 10 millidarcies, pressure buildup in the 
matrix will not be large enough to throttle evaporation. 
DTN: MO9807DSTSET01.000, MO9810DSTSET02.000, and MO9906DSTSET03.000. 
Figure 3-78. Temperature at a Depth of 2 m from Collar of Holes #137 To 141 as a 
Function of Elapsed Time 
Given these complexities, it can nevertheless be generalized that pressure gradients dominate the 
movement of vapor in the matrix and thus water vapor will tend to be driven radially away from 
the heat source. Therefore, water vaporized around the sensor of the 45-upward fracture would 
be driven (essentially) radially outward through the matrix and upward from the point it entered 
into the fractures. As water condensed, it would tend to drain vertically downward. Thus, the 
behavior of the vertical and 45-upward sensors could be expected to be potentially different and 
the data does indicates this. Furthermore, the horizontal boreholes, particularly borehole 160, 
showed well-defined impact of boiling that lasted for approximately 35 days. However, these 
boreholes are close to the wing heaters. Water vaporized in this region would tend to be driven 
perpendicular to the heaters through matrix and then vertically in fractures. Thus, it is likely that

 3-174 
the horizontal boreholes are exhibiting effects of reflux. The difference in boiling between 
Holes 139 and 160 may be caused by localized heterogeneous hydrological properties and/or by 
the effect of the bulkhead. 
A similar conclusion regarding boiling can be drawn for the 45-downward inclined holes. For 
these regions, the water removed as vapor would tend to migrate through the matrix, radially 
away from the heat source, if vapor was driven by pressure. Within fractures, buoyancy 
dominated, the vapor would tend to migrate vertically. Thus, either the fracture system is 
sufficient to allow buoyancy to dominate so that reflux can occur or the vapor would be driven 
by pressure radially away from the sensor, where boiling was occurring, and then condensate 
would drain vertically and not return to the sensor area. If reflux dominates, the responses would 
be similar to those observed in the vertical borehole. If pressure redistribution dominates, the 
condensate contribution to maintaining temperatures at the boiling point would be reduced or 
eliminated. However, it is likely that sensors would be subjected to a combination of refluxing 
of water from the sensor location as well as influx of water condensate driven from rock regions 
above the sensor. This might explain the flattening, noted particularly in borehole 140 where it 
occurred for approximately 60 days. Because these sensors are located below the wing heaters, 
it is possible that water from above was migrating and causing boiling effects similar to those 
seen by the horizontal-hole sensors. The difference between the 45 down and the horizontal 
regions may also be influenced by the plane heat source of the DST created by the wing heaters.

 3-175 
DTN: MO9807DSTSET01.000, MO9810DSTSET02.000, MO9906DSTSET03.000 
Figure 3-79. Temperature at a Depth of 2 m from Collar of Holes #158 to 162 of 
the DST as a Function of Elapsed Time 
The vertical downward boreholes are more problematic. Water vaporized would tend to move 
downward through the matrix and fractures, in response to pressure gradients. Vapor movement 
in the fractures would be expected to be upward by buoyancy. However, any vapor that moved 
upward would move into hotter regions, and therefore would not condense. Thus, refluxing by 
gravity drainage would not be anticipated. Saturation-gradient liquid return through the matrix, 
described in Section 3.2.1 as saturation- gradient matrix- flow (the classic heat-pipe mechanism) 
would be the only reflux mechanism. Water influx from rock above would be the only other 
likely source for water returning to the sensor region. If the saturation gradient were the waterreturn 
mechanism, any vapor lost through upward migration (either pressure within matrix or 
buoyant in fractures) would cause a continual diminishing of volume of water available for 
return. However, the vertical downward holes exhibit a similar response to the vertical upward 
oriented boreholes, at least for the 137, 141, and 162 boreholes. If the vertical-upward responses 
were the result of reflux, a similar response with flattening to be exhibited by the vertically 
downward boreholes, where the water vapor that was displaced below the sensor and condensed 
would drain in the same vertical downward direction away from the sensor. As noted, it is 
possible to have heat-pipe effects in which water is returned within the matrix itself by way of 
saturation gradients, in the classic heat-pipe effect. However, if this were the case and matrix 
reflux was the major contributor to the boiling effects observed, all of the boreholes should have 
shown similar behavior, unless the hydrologic properties of the matrix was not uniform among 
those boreholes. Another possibility is that water was continuously supplied to the sensor in

 3-176 
Hole 141 and 162, either from below via a larger-scale convection cell or from drainage from 
regions above. 
Figure 3-80 shows the temperature measured at about 0.4 m from the collar of 10 vertical holes 
drilled from the HD, as a function of distance from the bulkhead. Five of those holes (#133, 137, 
158, 168, and 170) were in the crown of the HD; the other five (#134, 141, 162, 169, and 173) 
were in the invert of the HD. There was no temperature sensor at depth shallower than 1.5 m 
from collar in Hole 141. The temperature value for Hole #141 was projected using the thermal 
gradient established by other measurements between the depth of 0.4 m and 1.5 m from collar. 
Figure 3-80 shows the thermal effect of the bulkhead. The temperature measured in the crown of 
the HD showed no effect of the bulkhead in that the temperature gradient from borehole 158 was 
approximately 1.3C/m towards either end of the drift. However, the effect of the bulkhead 
seems to be significant for temperatures in the invert. The gradient toward the end of the drift is 
similar to that in the crown. However, the gradient towards the bulkhead was nearly double 
(2.3C/m) that measured in the crown and towards the far-end invert. 
DTN: MO9807DSTSET01.000, MO9810DSTSET02.000, MO9906DSTSET03.000 
Figure 3-80. Temperature at About 0.4 m from the HD Wall in All Vertical 
Temperature Holes of the DST, as a Function of Distance from the 
Bulkhead 
Figure 3-81 shows temperature snapshots along Hole #80, which was parallel to the axis of the 
HD at about 3.5 m above the midpoint of the wing- heater plane. The bulkhead is at 0 m in the 
horizontal axis of the plot. Similar to the water-content data shown in Figure 3-82, the measured 
temperatures in the rock above the heaters showed no effect of the bulkhead. The temperature in

 3-177 
Hole 80 showed some episodic fluctuations, at a depth range of 16 to 24 m, and a trend of 
decreasing temperature at a depth range of 32 to 36 m. The borehole video in this hole showed 
an extended fracture zone between 33.9 and 34.8 m depth. The temperature fluctuations may be 
related to vapor or gas movement in fractures. 
Source: Adapted from CRWMS M&O 2000a, Figure 50 
Figure 3-81. Temperature Snapshots along Hole #80 of the DST, as a Function of 
Distance from the Bulkhead

 3-178 
DTN: LL990708904243.033 
Figure 3-82. Difference Volume-Fraction Water in Hole #50 of the DST, as 
a Function of Depth from Collar 
The drying of the rock mass in the DST, as monitored by ground-penetrating radar (GPR), ERT, 
and neutron logging, is discussed in the Thermal Test AMR (CRWMS M&O 2000a, 
Figures 6-35, 6-50 to 6-56). There are five figures in the Thermal Test AMR showing moisture 
distribution in the DST measured by GPR and ERT (CRWMS M&O 2000a, Figures 33, 53 to 
56). Those figures show that moisture distribution varied with time and location, with respect to 
the HD and the Wing Heaters. It is difficult to draw conclusions regarding the vertical symmetry 
of the drying and wetting regions with respect to the heat source. For example, Figure 3-83 
(CRWMS M&O 2000a, Figure 56) shows a more extended dry region below the wing heater. 
But Figure 3-84 (CRWMS M&O 2000a, Figure 33) seems to show a wetter region at a distance 
greater than 3 m below the inner wing heater than at the same distance above. 
Some plots of neutron data are included to illustrate the local drying process, and spatial 
variability of the drying. Figures 3-82 and 3-85 show four snapshots of the volume water 
fraction difference, as measured by neutron logging in Boreholes 50 and 67, respectively. 
Boreholes 50 and 67 are in about the same configuration in the DST, refined below the heated 
drift and wing heaters from the observation drift, except that Borehole 50 is much closer to the 
bulkhead than Borehole 67 (6.4 m and 26.5 m, respectively) (CRWMS M&O 1997b, Figures 3-2 
and 3-3). Drying started in Borehole 67 several months before that in Borehole 50. This may be 
related to the thermal evolution of the DST, influenced by the bulkhead. The drying region in 
Hole 67 was still expanding at the end of 18 months of heating, but the drying in this hole 
seemed to have reached maximum, which represented a decreased water content equal to about 
0.16 percent of the volume of the rock mass. Figure 3-86 shows that drying in Borehole 68, 
which was at the same location as Borehole 67, but declined 6 more, started even later. 
Figure 3-86 illustrates that in regions further away from the heaters, the drying had been more 
uniform along hole 68. Figure 3-87 shows the drying along Borehole 80, which was parallel to 
the HD at about 3.5 m above the mid point of the wing-heater plane. The drying in this hole was 
-0.2 
-0.18 
-0.16 
-0.14 
-0.12 
-0.1 
-0.08 
-0.06 
-0.04 
-0.02
0 
0.02 
0 5 10 15 20 25 30 35 40 
Depth from Collar, m 
fraction Volume Water 
3/16/98 
6/23/98 
12/1/98 
6/3/99

 3-179 
accompanied by localized increase of moisture content. It is possible that this might be related to 
heat-pipe effects. The high water content region between 40 and 50 m from the collar was 
associated with the temperature fluctuation shown in Figure 3-81. 
Source: CRWMS M&O 2000a, Figure 56 
NOTE: Measured ERT-derived water saturation ratio (at 558 days) for the longitudinal cross-section through the 
HD axis (top) and transverse cross-section OD#5 (Boreholes 62, 63) (bottom). 
Figure 3-83. Comparison of Distributions of Measured and Simulated (NUFT) Water 
Saturation at 547 Days for the DST, Using the DS Property Set

 3-180 
Source: CRWMS M&O 2000a, Figure 33 
NOTE: The observation drift is just to the left of the figure, where the borehole lines would converge. 
Figure 3-84. Tomogram Showing Saturation Change from Pre-Heat Ambient 
Values Derived from a Cross-Hole Radar Survey Taken in January of 
1999 (~13 months of heating) in the Plane of DST Boreholes 64-68 
Vertical Distance 
25 
20 
15 
10 
5
0
-5 
-10 
-15 
Horizontal Distance (m) 
-0.7 -0.4 -0.1 0.2 
Changes in Saturation 
25 
20 
15 
10 
5
0
-5 
-10 
-15 
-30 -25 -20 -15 -10 -5 0 5 10 
-30 -25 -20 -15 -10 -5 0 5 10

 3-181 
Difference fraction volume water, with respect to the 2/98 
measurements, in Hole #67 of the DST as a function of depth. 
-0.2 
-0.18 
-0.16 
-0.14 
-0.12 
-0.1 
-0.08 
-0.06 
-0.04 
-0.02
0 
0.02 
0 5 10 15 20 25 30 35 40 
Depth from Collar, m 
d3/18/98 
d6/23/98 
d11/20/98 
d6/2/99 
DTN: LL990708904243.033 
Figure 3-85. Difference Volume-Fraction Water in Hole #67 of the DST, as 
a Function of Depth from Collar 
Difference fraction volume water, with respect to the 2/98 
measurements, in Hole #68 of the DST as a function of depth. 
-0.18 
-0.16 
-0.14 
-0.12 
-0.1 
-0.08 
-0.06 
-0.04 
-0.02
0 
0.02 
0 10 20 30 40 
Depth from collar, m 
D3/18/98 
D6/22/98 
D11/20/98 
D6/2/99 
DTN: LL990708904243.033 
Figure 3-86. Difference Volume-Fraction Water in Hole #68 of the DST, 
as a Function of Depth from Collar

 3-182 
Difference fraction volume water, with respect to the 2/98 measurements, in Hole #80 of 
the DST as a function of depth. 
-0.18 
-0.17 
-0.16 
-0.15 
-0.14 
-0.13 
-0.12 
-0.11 
-0.1 
-0.09 
-0.08 
-0.07 
-0.06 
-0.05 
-0.04 
-0.03 
-0.02 
-0.01
0 
0.01 
0.02 
0.03 
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 
Depth from Collar, m 
D3/12/98 
D6/25/98 
D12/3/98 
D6/10/99 
DTN: LL990708904243.033 
Figure 3-87. Difference Volume-Fraction Water in Hole #80 of the DST, as a Function of Depth 
from Collar 
The measured CO2 concentration in the DST after 12 months and 15 months of heating showed 
high values above and below the heaters, and the CO2 concentrations after 15 months of heating 
were greater than that after 12 months of heating (CRWMS M&O 2000b, Figure 8). Four water 
samples were collected from hydrological Holes 60 and 186 between December 11, 1998 and 
January 26, 1999. The chemical composition of those water samples, along with that of the pore 
water of Topopah Spring Tuff, are shown in the THC Process AMR (CRWMS M&O 2000b, 
Table 9). The waters that were collected from the hydrological holes are generally more dilute 
(lower Cl- and SO4
2-) and have lower pH than the initial pore water. The aqueous silica 
concentrations are similar to or much higher than in the pore water, indicating that the collected 
waters were not simply a mix of the pore water and pure condensate water. The water from a 
hotter interval (60-3) had a greater pH and SiO2 concentration than from a cooler interval 
(186-3). This trend is consistent with the evolution of pure condensate water. The concentration 
of HCO3
- is lower in 60-3 relative to 186-3. This is also expected because of the greater 
temperature in 60-3 (CRWMS M&O 2000b, p. 65). 
3.6.1.3.2 Model Analyses of the DST Results 
In the Thermal Test AMR (CRWMS M&O 2000a), the measured temperature and moisture 
content data of the DST were compared with the simulated data from the TOUGH2 and NUFT 
models, using the following property sets: the DS property set, mountain-scale property set, and 
DKM-TT99 property set. Statistical measures, such as root-mean-square-error, mean-error, and 
normalized-absolute-mean-error, were used to compare the fitness of the property sets to the

 3-183 
measured temperature data. Sensitivity analyses were conducted to assess the effect of certain 
parameters on the predicted temperature and moisture content. 
The Thermal Test AMR (CRWMS M&O 2000a) results indicated that the temperatures predicted 
by the DKM model with TOUGH2 simulations were in good agreement with the measured ones. 
There are three figures in the Thermal Test AMR showing the measured DST temperature 
profiles and those simulated by the DKM/AFM using TOUGH2, and the Drift Scale property set. 
Figure 3-88 (CRWMS M&O 2000a, Figure 21) illustrates one example of the comparison. 
There are a few minor differences between the measured and the simulated temperatures. The 
simulation under-predicted the temperature in the two horizontal holes (Hole 139 and 143). This 
is probably caused by smearing of the data from the wing heater source in the simulation. The 
simulation over-predicted the temperature near the heater-drift wall. This may imply that the 
model did not adequately represent heat losses in the test block. Another difference between the 
measured and simulated temperatures is the temperature signature of the boiling processes (heatpipe 
effect). Figure 3-89 (CRWMS M&O 2000a, Figure 83) shows one example of the 
TOUGH2 simulation, using property set DKM-TT99. This property set seems to represent the 
heat-pipe effect better than the DS/AFM-UZ99 property set (CRWMS M&O 2000a, Section 
6.3.2.2). The statistical comparison between the measured temperature and that simulated 
temperatures using TOUGH2 is in good agreement, as shown in Figure 3-90 (CRWMS 
M&O 2000a, Figure 25). For the NAMD of the sensors below 97C, the DKM-TT99 property 
set seems to be better than that of the DS/AFM-UZ99 property set. 
The DKM/AZ TOUGH2 simulation using the drift-scale property set (DS/AFM-UZ99) was also 
used in the Thermal Test AMR to compare the measured to simulated temperature evolution in 
the DST. (CRWMS M&O 2000a, Figures 22-24). Figure 3-91 (CRWMS M&O 2000a, 
Figure 22) is presented as an example of the comparison of this temperature evolution. 
Generally, the predictions agree with the measured ones reasonably well. However, the model 
seems to have under-predicted the temperature, except during the time when the measured 
temperatures showed boiling. The model results did not show the boiling signature. 
The DST temperatures simulated by the DKM model using NUFT and the DS property set, were 
reported in the Thermal Test AMR (CRWMS M&O 2000a, Figures 35 to 56). Figure 3-92 
(CRWMS M&O 2000a, Figure 43) shows good comparison of the measured and simulated 
temperatures as a function of distance from the centerline of the HD in vertically-upward hole 
137. The temperatures in horizontal-hole 160 simulated by NUFT also compare well with the 
measured results, as shown in Figure 3-93 (CRWMS M&O 2000a, Figure 46). Similar to the 
DKM TOUGH2 simulation (Figure 3-91), the DKM NUFT simulation also did not capture the 
boiling signature. A statistical evaluation indicates that NUFT simulations are apparently not as 
good as the TOUGH2 simulations, as shown in Figure 3-94 (CRWMS M&O 2000a, Figure 51). 
Possible causes for the differences in performance of the DKM model using NUFT and 
TOUGH2 may include the difference in the drift shape and model domain size. NUFT used a 
rectangular drift shape and model domain that extended from 267 m below the HD to 321 m 
above the HD (i.e. from the ground surface to the water table). TOUGH2 used a circular drift 
shape and a model domain that extended 100 m above the HD and 150 m below the HD. 
They may also result from the difference in how the boundary conditions and property sets were 
used in the models. The TOUGH2 simulations used the boundary conditio ns to determine

 3-184 
saturation for use in the model whereas the NUFT simulations used the measured saturations to 
determine the boundary conditions. 
Source: CRWMS M&O 2000a, Figure 21 
NOTE: The DS/AFM-UZ99 properties were used in the simulation. 
Figure 3-88. Measured (top) and DKM/TOUGH2 Simulated (bottom) DST 
Temperatures, as a Function of Distance of Sensor Locations from 
Borehole Collars in RTD Boreholes 137-144, after 18 Months of Heating 
0 5 1 0 1 5 2 0 2 5 
D ista n c e from B o re h ole C o lla r (m ) 
2 0 
4 0 
6 0 
8 0 
1 0 0 
1 2 0 
1 4 0 
1 6 0 
1 8 0 
2 0 0 
2 2 0 
Temperature (oC) 
1 37 (0 o ) 
1 38 (4 5 o ) 
1 39 (9 0 o ) 
1 40 (1 3 5 o) 
1 41 (1 8 0 o) 
1 42 (- 1 3 5o ) 
1 43 (- 9 0 o) 
1 44 (- 4 5 o) 
B o re h ole 
# 
R ad ia l 
D irec tio n 
0 5 1 0 1 5 2 0 2 5 
D ista n c e from B o re h ole C o lla r (m ) 
2 0 
4 0 
6 0 
8 0 
1 0 0 
1 2 0 
1 4 0 
1 6 0 
1 8 0 
2 0 0 
2 2 0 
Temperature (oC) 
1 3 7 ( 0 o) 
1 3 8 ( 4 5o ) 
1 3 9 ( 9 0o ) 
1 4 0 ( 1 35 o ) 
1 4 1 ( 1 80 o ) 
1 4 2 ( -1 3 5 o) 
1 4 3 ( -9 0 o) 
1 4 4 ( -4 5 o) 
Bo reh o le 
# 
R a d ia l 
D ire ctio n

 3-185 
Source: CRWMS M&O 2000a, Figure 83 
Figure 3-89. DKM/TOUGH2 Simulated Temperatures along RTD 
Boreholes 137-144 after 18 Months of DST Heating 
0 5 10 15 20 25 
Distance from Borehole Collar (m) 
20 
40 
60 
80 
100 
120 
140 
160 
180 
200 
220 
Temperature (oC) 
137 (0o) 
138 (45o) 
139 (90o) 
140 (135o) 
141 (180o) 
142 (-135o) 
143 (-90o) 
144 (-45o) 
Borehole 
# 
Radial 
Direction

 3-186 
Source: CRWMS M&O 2000a, Figure 25 
NOTES: 1. The property sets tested were the Drift Scale (DS/AFM-UZ99) set used in TSPA-SR calculations and 
the DKM-TT99 set which has higher fracture permeability, lower fracture porosity, and a narrower range 
of thermal conductivity dependence on saturation. 
2. See Note 2 of Figure 3-61 for descriptions of the statistical measures. 
3. See Note 3 of Figure 3-61 for sensor group descriptions 
Figure 3-90. Statistical Measures for DST DKM/TOUGH2 Thermal Analyses

 3-187 
Source: CRWMS M&O 2000a, Figure 22 
NOTE: The DS/AFM-UZ99 properties were used in the simulation. 
Figure 3-91. Measured (top) and DKM/TOUGH2 Simulated (bottom) DST 
Temperatures, as a Function of Time at Selected Sensor 
Locations in Borehole 160 (Horizontal, near the Wing Heaters) 
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 
T im e ( d a y s) 
2 0 
4 0 
6 0 
8 0 
1 0 0 
1 2 0 
1 4 0 
1 6 0 
1 8 0 
2 0 0 
2 2 0 
Temperature (oC) 
39
1 7 
2 3 
3 3 
4 4 
5 5 
R T D # 
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 
T im e (da y s) 
2 0 
4 0 
6 0 
8 0 
1 0 0 
1 2 0 
1 4 0 
1 6 0 
1 8 0 
2 0 0 
2 2 0 
Temperature (oC) 
391
7 
2 3 
3 3 
4 4 
5 5 
R T D #

 3-188 
Source: Adapted from CRWMS M&O 2000a, Figure 43 
Figure 3-92. Comparison of DKM/NUFT Simulated and Measured 
Temperatures from the DST, Along Borehole 137 
(Vertical-Upward) at (a) 12 Months and (b) 18 Months

 3-189 
Source: CRWMS M&O 2000a, Figure 46 
Figure 3-93. Comparison of DKM/NUFT Simulated and Measured Temperature 
Histories for Sensors No. 2, 5, 10, 40, and 67 Over 18 Months of 
Heating in Borehole 160 (Horizontal, near the Wing Heaters) for the 
DST, Using the DS Property Set 
0 
20 
40 
60 
80 
100 
120 
140 
160 
180 
200 
220 
0 100 200 300 400 500 600 
Time (Days) 
Temperature (oC) 
Measured 
Sensor #2 
Sensor #5 
Sensor #10 
Sensor #40 
Sensor #67 
Simulated 
Sensor #2 
Sensor #5 
Sensor #10 
Sensor #40 
Sensor #67 

 3-190 
Source: CRWMS M&O 2000a, Figure 51 
NOTES: 1. The property sets tested were the Drift Scale (DS) set used in TSPA-SR calculations, MS set with 
higher fracture permeability, a second Mountain Scale (MSLK) set with a narrower range of thermal 
conductivity dependence on saturation, and a conduction-only (CON) set that does not track mass 
transfer. 
2. See Note 2 of Figure 3-61 for descriptions of the statistical measures. 
3. See Note 3 of Figure 3-61for sensor group descriptions 
Figure 3-94. Statistical Measures for DST DKM/NUFT Thermal Analyses

 3-191 
The DKM/TOUGH2 simulations showed that the calculated temperatures of the fractures are 
practically the same as in the nearby matrix, implying that, for all practical purposes, the matrix 
and fracture are in thermal equilibrium (CRWMS M&O 2000a, Section 6.2.2.1). The 
DKM/TOUGH2 simulations also showed that the temperature distribution was not very sensitive 
to the thermal conductivity values over the range considered. The thermal conductivity values in 
the DS property set and the DKM-TT99 property set were both within an acceptable range, based 
on comparison of measured data and calculated temperatures (CRWMS M&O 2000a, 
Section 6.3.2.2). For the hydrological processes, the comparison between the measured and 
calculated water saturation was more qualitative. Qualitatively, the moisture distribution 
calculated by the DKM model (using NUFT) agreed with that measured by ERT, especially after 
one year of heating (CRWMS M&O 2000a, Figures 53 to 56). One example of the comparison 
is shown in Figure 3-83 (CRWMS M&O 2000a, Figure 56). The TOUGH2 calculation of water 
saturation in the matrix was in general agreement with the neutron data of the DST in the region 
below the heaters, as shown in Figures 3-95 and 3-96 (CRWMS M&O 2000a, Figures 34 and 
59). The simulated distribution of saturation also qualitatively agrees well with the GPR results, 
as shown in Figures 3-95 (CRWMS M&O 2000a, Figure 33). In the region above the wing 
heaters, the predicted saturation in the matrix was greater than that measured by neutron logging 
(CRWMS M&O 2000a, Figures 34 and 61). The DKM/TOUGH2 model results showed that the 
DKM-TT99 property set seemed to have better predicted measured air-permeability, based on 
saturation changes in the fractures. However, both property sets used the DKM/TOUGH2 model 
simulation are considered to have predicted results that were within acceptable limits of the 
measured data from the DST (CRWMS M&O 2000a, Section 6.2.2.3). It should be noted that 
the model analyses using TOUGH2 assumed that the measured air-permeability changes were 
solely due to changes in water saturation in fractures. Fracture permeability is very sensitive to 
changes in the fracture aperture. The fracture aperture in a heated rock mass can be changed due 
to thermal expansion and slips along fractures. Coupling of TM calculation results to TH 
simulations is ongoing.

 3-192 
Source: CRWMS M&O 2000a, Figure 34 
NOTE: The x- and y-axes are the horizontal and vertical distances from the drift centerline. The hydrology 
boreholes converge at the observation drift, just beyond the upper left edge of the figure. 
Figure 3-95. TOUGH2 Simulated Matrix Liquid Saturation in the Plane of DST 
Boreholes 64-68. After 12 Months of Heating, Using the DS/AFM-UZ99 
Properties 
-20.0 -10.0 0.0 10.0 20.0 
x [m] 
-10.0 
0.0 
10.0 
z [m] 
0.20 0.50 0.80 0.90 0.92 0.94 0.96 0.98 1.00 
Matrix Liquid Saturation 
65
66 
67 
64 
68

 3-193 
Source: CRWMS M&O 2000a, Figure 59 
Figure 3-96. Fraction-Volume of Water Content in DST Boreholes as Measured by Neutron Logging 
Boreholes 64 to 68 for Nominal Heating Duration of 12 Months 
In the THC Process AMR (CRWMS M&O 2000b) THC model calculations using 
TOUGHREACT were conducted to analyze evolution of the measured gas phase CO2 and the 
chemistry of the water. Two sets of chemical components and mineral assemblages were used in 
the simulations: Complex and Less Complex. The Complex geochemical system was a full 
set, including the major solid phases (minerals and glass) encountered in the geologic unit at 
Yucca Mountain. The Less Complex geochemical system was a subset that excluded aluminum

 3-194 
silicate minerals (CRWMS M&O 2000b, Section 6.1.7). Model calculations of the Less 
Complex set predicted the locations of high CO2 concentration and the range of the CO2 
concentration reasonably well. The Less Complex set model calculations also predicted the 
evolution of CO2 concentration, in the first 9 to 12 months of heating, quite well. However, in 
the later months of heating the model predictions were not as good, except for measurements in 
the third packed-off region of Borehole 74 (Interval 74-3), which is bounded by the nodes, as 
shown in Figure 3-97 (CRWMS M&O 2000b, Figure 10). The apparent lower CO2 
concentration at 20 months of heating, as shown in Figure 397(b), may be due to a 6-day power 
outage that occurred about 1 month before the measurement. The greater than predicted CO2 
concentration in Borehole Intervals 76-3 and 78-3 may be due to drying of the gas phase when 
the gas sample was collected (CRWMS M&O 2000b, Section 6.2.7.2). The More Complex set 
model predicted similar locations for the CO2 concentration as the Less Complex set. However, 
for the More Complex set, model-predicted CO2 concentration values were much less than those 
of the Less Complex set model. 
The chemical compositions of four water samples, collected from hydrology Boreholes 60 and 
186 on December 11, 1998 and January 26, 1999 (CRWMS M&O 2000b, Section 6.2.7.3.1), are 
shown in Table 3-16. The water samples collected during the test were obtained from zones that 
were hotter than the temperatures given for the samples, because water temperatures were 
measured after collection and they had cooled substantially. Both intervals are located in the 
zone below the wing heaters. Borehole Interval 186-3 is lower and probably cooler than 
Borehole 60-3. Borehole 60 is located approximately in the same location as Borehole 77, and 
borehole 186 corresponds to about the position of Borehole 78. 
Waters that were collected from the hydrology boreholes at elevated temperatures are generally 
more dilute (lower Cl and SO4) and lower in pH than the initial pore water. Aqueous silica 
concentrations are similar to or much higher than in the pore water, indicating that these waters 
are not simple mixtures of pore water and pure condensate water. Some clear trends in water 
chemistry of the condensate waters in both intervals over time are increases in pH and SiO 2 (aq) 
concentration, and a drop in Ca. A similar trend for pH and SiO 2 (aq) exists between the 
boreholes, where the hotter interval (60-3) has a higher pH and SiO 2 (aq) concentration than the 
186-3 interval at each time. The concentration of HCO3 is also lower in 60-3 relative to 186-3 as 
expected from the higher temperature of 60-3. Other relationships are less obvious. 
The modeled pH of condensate waters in fractures (Figure 3-98) compares favorably with those 
collected from the hydrology boreholes (Table 3-16). As in the measured data collected at two 
times before the borehole intervals dried out, the model results show the effect of increasing pH 
with time and with increasing temperature in areas greater than 60C. Therefore, in a given 
zone, the pH in the fractures first starts to drop because of steam condensation; then once the 
temperatures increase, so that the rate of evaporation and mineral-water reactions (and loss of 
CO2) are greater than the rate of addition of water (and CO2) via condensation, then the pH rises. 
Some of the processes that could explain the water chemistry of samples collected in the 
hydrology boreholes include: mixing of pure condensate water with fracture pore waters, 
equilibration of condensate waters with matrix pore waters via molecular diffusion, reaction of 
condensate waters with fracture-lining minerals, and mineral precipitation due to reaction, 
boiling, temperature changes, or pH changes. The higher silica concentration in the waters

 3-195 
collected in January compared to those collected in December, relative to chloride and the initial 
pore water silica concentration, is consistent with dissolution of a silicate phase, rather than 
increased concentration by boiling. However, concentrations of K, Mg, and Na are higher than 
what would be expected by dilution of original pore water (as evidenced by the low chloride 
concentrations). Therefore, the silicate phases that dissolved must have been some combination 
of cristobalite, opal, feldspar, clays or zeolites, rather than just a single silicate-phase. The drop 
in Ca over time is consistent with calcite precipitation, which would be expected as the 
condensate waters were heated further and underwent CO2 degassing, resulting in an increase in 
pH. 
Table 3-16 Measured Concentrations in TSw Pore Water from Alcove 5 and Chemistry of 
Water Taken from Hydrology Boreholes 
Parameter Units Pore Water(1) 60-3(2) 
(12/11/98) 
60-3(2) 
(1/26/99) 
186-3(2) 
(12/11/98) 
186-3(2) 
(1/26/99) 
Temperature C 25 26.5-49.6 51.7 34.3-34.8 Unknown 
pH 8.32 6.92 7.4 6.83 7.2 
Na mg/l 61.3 20.3 19.1 17 25.9 
SiO2 (aq) mg/l 70.5 115.5 139 58.2 105.5 
Ca mg/l 101 13.9 5.9 20.2 2.92 
K mg/l 8.0 7.8 4.1 3.9 5.9 
Mg mg/l 17 3 1.2 5.7 6.3 
Al mg/l 9.92x10-7 (3) n.d. (< 0.06) n.d. (< 0.06) n.d. (< 0.06) n.d. (< 0.06) 
HCO3 (3) mg/l 200 n.a. 41 n.a. 116 
Cl mg/l 117 20 10 19 23.3 
SO4 mg/l 116 30.8 13.5 26.2 21 
DTN: LL990702804244.100. 
NOTES: (1) Average of porewater analyses ESF-HD-PERM-1 (30.1'-30.5') and ESF-HD-PERM-2 
(34.8'--35.1'). DTN: LL990702804244.100. 
(2) Calculated by assuming equilibration with Ca-smectite at 25C. 
(3) Total aqueous carbonate as HCO3, calculated from charge balance. 
n.a.=not analyzed, n.d.=not detected 
The model results also predicted precipitation of calcite in the fractures above and to the margins 
of the heaters, with some dissolution of calcite below the wing heaters. In the matrix, the models 
predicted a uniform region of calcite precipitation in the dryout zone. However, the change of 
either fracture or matrix porosity due to the precipitation and dissolution of calcite was no more 
than 0.1 percent, and the effect on the changes in permeability and capillarity was negligible 
(CRWMS M&O 2000b, Section 6.2.7.5). It should be noted that the change in fracture 
permeability is not just the result of porosity change due to mineral precipitation and dissolution. 
Laboratory studies of fracture healing indicate that smoothing of the fracture asperities by 
dissolution and precipitation can effectively change the permeability (Daily et al. 1987, p. 7861). 
Most fractures in an underground rock mass are under compressive stresses. Decreases in 
fracture roughness allow fractures to close under compressive stresses, and fracture permeability 
may be significantly reduced. Therefore the mechanical effects should be considered in 
assessing the THCM processes.

 3-196 
Source: CRWMS M&O 2000b, Figure 10 
Figure 3-97. Comparison of Modeled CO2 Concentrations (Less Complex) in 
Fractures and Matrix Over Time to Measured Concentrations in 
Boreholes (a) Borehole Interval 74-3 at Nodes Above and Below (upper 
left); (b) Borehole Interval 75-3 (upper right); (c) Borehole Interval 76-3 
(lower left); and (d) Borehole Interval 78-3 at Nodes Near Center and 
End (lower right).

 3-197 
Source: CRWMS M&O 2000b, Figure 13 
NOTE: Results are for the Less Complex Geochemical Sys tem. 
Figure 3-98. Distribution of pH and Temperature at 12 Months (Fracture 
13a, Matrix  13b) and at 20 Months (Fracture  13c, 
Matrix  13d) 
3.6.1.3.3 Summary of the DST 
After 18 months of heating, the DST had heated the rock mass such that boiling of pore water, 
drying of pore water, changing of the CO2 concentration, and changing of the chemistry of the 
water had occurred. Along with boiling of the pore water, heat-pipe effects may have occurred 
in regions above the heaters. Both the TOUGH2 and NUFT models predicted the temperature, 
and saturation reasonably well. The Thermal Test AMR TH model analyses showed that 
temperature distribution in a repository is not very sensitive to the values of thermal conductivity

 3-198 
used in the models. This indicates that very high confidence is justified when using the thermal 
conductivity of the rock mass to predict average temperature distributions. The comparison of 
measured and simulated temperature distributions in those model analyses was focused on the 
statistics of the mean temperatures. Detailed analysis of spatial and temporal temperature 
variations provided insight into the processes of moisture movements and variations, including 
possible convection at a scale greater than the size of the drift. Investigation of more localized 
phenomena of boiling and drying, in specific fractures, for example, is on-going. The THC 
model using TOUGHREACT code provided reasonably good predictions of the variation of CO2 
concentration due to heating, boiling, drying, thought to be associated with local heterogeneity in 
the rock and fracture systems. This is because the models are designed to simulate large scale 
behavior, and are not expected to predict localized behavior. The bulkhead seemed to have some 
effects on temperature distribution, variation of CO2 concentration in the HD, and, possibly the 
spatial variations of drying. The test is ongoing and is in the third year of a four-year heating 
phase that will be followed by a four-year cooling phase. Understanding of the THCM processes 
is expected to improve as the test progresses and more data are available. 
3.6.2 Confidence Building through Use of Natural Analogs 
As noted in the Section 3.6 introductory material, validation of models is accomplished by 
testing at various scales. Natural analogs provide the opportunity to test the models at very large 
spatial scales and at temporal scales consistent with the long duration of the coupled processes 
that would be present in a repository. This section on use of natural analogs will discuss the 
confidence building in the models that results from, or might result from, the study of natural 
analogs. The confidence building efforts have proceeded roughly in progression with scale, that 
is the smaller scale tests of shorter duration are more mature or complete than the larger scale 
tests, which were based upon the previous work at smaller scales. Of all of the scales of testing, 
the natural analogs studies are the least mature, and therefore much of the discussion will 
identify the processes that can be addressed by specific analogs, and to some extent the 
observations are discussed. For this and other reasons, that will be discussed, natural analog 
studies are most useful in providing qualitative data against which the model processes can be 
judged rather than the quantitative data typical from other testing. As an example, Table 3-7 lists 
coupled process components within TSPA under the column called Yucca Mountain Issues. The 
analog processes that can be observed at geothermal sites, along with the sites identified that 
exhibit those processes, are listed on the table. Because the geothermal analogs address 
components of the TSPA, these analogs provide validation of TSPA models more directly than 
the smaller scale tests that more effectively provide validation of the detailed process models, as 
was discussed in Section 3.6 introductory material. This section also discusses analogs of the 
TH and THC process models and the confidence obtained from those studies.

 3-199 
Table 3-17. Application of Geothermal Field Information as Analogs to Coupled Processes Anticipated at 
a Potential Yucca Mountain Repository (CRWMS M&O 2000p, Table 6-13) 
Yucca Mountain 
Issue 
Geothermal 
Analog Potential Sites Possible Approach 
Multiphase Flow 
(liquid, vapor, gas) 
Multiphase 
Flow (liquid, 
vapor, gas) 
All Numerical Modeling, Conduct and 
Review Geothermal Post Audits 
Hydrologic 
Properties 
Hydrologic 
Properties 
Kamojang (Indonesia), Tianjin 
(China), Wairakei (New Zealand), 
Oguni (Japan), Sumikawa (Japan) 
Numerical Modeling 
Preferential Flow Preferential 
Flow 
Wairakei (New Zealand), The 
Geysers (CA), Dixie Valley (NV), 
East Mesa (CA), Cerro Prieto 
(Mexico) 
Numerical Stochastic Modeling, 
Evaluate Geothermal Tracer Study 
Results 
Fracture Network 
Permeability 
Fracture 
Network 
Permeability 
All Modeled Fractured Sites, e.g. 
Cerro Prieto (Mexico), Krafla 
(Iceland), Matsukawa (Japan), 
Sumikawa (Japan), Olkaria (Kenya), 
Krafla (Iceland), Wairakei (New 
Zealand), Geysers (CA), Kamojang 
(Indonesia), Larderello (Italy) 
Reservoir Model Calibrations Used 
FMX FMX Yellowstone (WY), Long Valley 
(CA), Olkaria (Kenya), Fenton Hill 
(NM), Dixie Valley (NV) 
Field and Laboratory Experiments, 
Evaluate Geothermal Tracer Study 
Results 
Heat Pipes, Boiling 
and Condensation 
Heat Pipes, 
Boiling and 
Condensation 
The Geysers (CA), Kamojang 
(Indonesia), Matsukawa (Japan), 
Larderello (Italy) 
Numerical Modeling to Extend 
Measurements 
Mineral Precipitation 
and Dissolution 
Mineral 
Precipitation 
and 
Dissolution 
Larderello (Italy), Dixie Valley (NV), 
Wairakei (New Zealand), 
Broadlands (New Zealand), Long 
Valley (CA), Yellowstone (WY) 
Laboratory Experiments, Analog 
Site Investigation, Numerical 
Modeling 
Self-Sealing Caprocks The Geysers (CA), Kamojang 
(Indonesia), Matsukawa (Japan), 
Larderello (Italy), Cerro Prieto 
(Mexico), Reykjanes (Iceland) 
Core Sample Evaluation, Water 
Chemistry Evaluation, Numerical 
Modeling 
Mineral Alteration Mineral 
Alteration 
Wairakei (New Zealand), 
Broadlands (New Zealand), Dixie 
Valley (NV), Yellowstone (WY) 
Core Sample Evaluation, 
Numerical Modeling 
Thermo-Hydro- 
Mechanical Effects 
Subsidence, 
Flow 
Changes 
Wairakei (New Zealand), Bulalo 
(Philippines), Krafla (Iceland) 
Numerical Modeling

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Table 3-18. Similarity of Analog Sites to Yucca Mountain 
Similar Water 
Chemistry Similar Geology 
Similar Alteration 
Mineralogy 
Larderello (Italy)  possibly 
Yellowstone (WY)    
Fenton Hill (NM)  
Dixie Valley (NV)  
Wairakei (New Zealand)    
Broadlands (New Zealand)    
Long Valley (CA)   possibly 
The ideal analog would be similar in all respects to a potential repository at YM. It is not 
practical to find an analog that simultaneously matches spatial, temporal, mineralogical, heat 
flux, stress conditions and hydrological characteristics of a potential repository. Therefore, a 
series of analogs were identified that can provide information on TH and THC processes. In 
addition, a number of geothermal analogs have been investigated as potential sites against which 
models could be tested (see Tables 3-17 and 3-18). Although all analog sites essentially exist 
because of THC processes, the analogs have been divided into those that provide evidence for 
testing TH coupling and those that provide evidence for THC coupling. Three analog sites are 
discussed as TH analogs: The Eldora Stock in Colorado, the Alamosa River Stock in Colorado, 
and Grants Ridge in New Mexico. Four sites are discussed as analogs for THC processes. These 
are: Yucca Mountain, Banco Bonito obsidian flow in New Mexico, Grants Ridge in 
New Mexico, and Paiute Ridge in Nevada (Nevada Test Site). No analog sites have been 
identified for THM. 
3.6.2.1 Thermohydrological Analogs 
In early studies, elemental migration across the 2-m-wide contact zone around the Eldora Stock 
in Colorado was investigated as an analog to elemental transfer in a crystalline repository during 
heating by waste canisters (Brookins 1986; Wollenberg and Flexser 1986). Oxygen- isotope data 
showed a distinct contrast between the 60 Ma quartz monzonite stock and the Precambrian 
metamorphic country rock, which Wollenberg and Flexser (1986) interpreted to indicate a lack 
of convective hydrothermal cooling. No systematic uranium enrichment or depletion that could 
be related to distance from the contact was detected (Wollenberg and Flexser 1986), but data 
were insufficient to ascertain whether uranium mineralization occurred before or after 
emplacement of the stock. 
In contrast to the Eldora stock, intrusion of the Alamosa River, Colorado stock, a monzonite 
body that intruded tuffaceous and andesitic volcanic rocks about 30 million years (Ma) ago 
(Brookins 1984), appears to have established a large-scale convecting hydrothermal system 
(Brookins 1986). Alteration of the tuffs is observable to 60 m from the contact, with the 
occurrence of calcite intergrown with the rock matrix, chlorite and sericite, quartz overgrowths, 
and epidote (Wollenberg and Flexser 1986). The contact itself contains a dense intergrowth of 
epidote, sphene, and fine hematite-filled fractures. Uranium occurs in sphene, but is otherwise 
absent from the contact (Wollenberg and Flexser 1986). Concentration gradients of Cs, Th, and

 3-201 
Co in the tuff increase toward the contact, but other trace elements show no indication of 
migration between the stock and the tuff (Wollenberg and Flexser 1986). 
The influence of a shallow basaltic intrusion into pyroclastic deposits at Grants Ridge, New 
Mexico, was studied by WoldeGabriel et al. (1999). At this location, a 2.6-Ma basalt plug 
intruded into 3.3-Ma nonwelded, pumice-rich, compositionally homogeneous, rhyolitic tuff and 
volcaniclastic sediments. A 10-m wide aureole characterized by color variation, contact 
welding, brecciation, partial melting, and stopping developed around the 150-m wide basalt plug. 
Despite the high-temperature basaltic intrusion, there was no evidence in the country rock of 
pervasive hydrothermal circulation and alteration that could have been caused by extensive fluiddriven 
convective heat transfer. 
3.6.2.2 THC Analogs 
A good analogy for understanding future repository behavior is the fossil hydrothermal system at 
Yucca Mountain itself (Bish and Aronson 1993). Detailed mineralogical examination of Yucca 
Mountain tuffs showed that most zeolitic alteration occurred about 13 to 11.6 Ma, at about the 
same time as tuff emplacement. After formation of the major zeolitic horizons, deep-seated 
hydrothermal activity persisted until about 10 Ma. This activity was limited to temperatures of 
90 to 100oC, the zeolite stability limit; at prolonged exposure to temperatures greater than 90oC, 
the sorptive zeolites clinoptilolite and mordenite are altered to analcime plus quartz and/or 
calcite. 
Conceptual models for mineral evolution at Yucca Mountain (Carey et al. 1997) suggest that the 
most likely mineralogical reactions caused by repository heating would include dissolution of 
volcanic glass and precipitation of clinoptilolite, clay and opal-CT; dissolution and precipitation 
of silica polymorphs (cristobalite, opal-CT, tridymite, and quartz); alteration of feldspars to 
clays; and, finally, reactions involving calcite and zeolites. Figure 3-99 illustrates 
paleotemperatures that were inferred from mineralogical data in several drillholes at Yucca 
Mountain. Measured present-day temperature profiles are shown for comparison. 
As can be noted, the temperatures projected to be typical of the NFE for 1000s of years are those 
represented by the G-2 core at about 1,100 m-depth and G-1 core at about 1,600 m-depth. There 
are no depth dependencies determined for the mineralogy, and therefore the repository horizon 
shown on the figure is not of direct relevance to the analog comparisons. However, it provides 
insight into the thermal gradients that are projected to exist, in comparison with existing 
gradients. The paleothermal gradient most comparable with projected repository thermal 
gradients are those of G-1 at approximately 1,500 m-depths. It can be seen from the figure that 
present-day temperatures in drillhole G-3, which is within the repository block, compare closely 
to inferred paleotemperatures. In contrast, increasingly higher paleotemperatures are inferred for 
drillholes G-1 and G-2, which are closer to the center of the Timber Mountain caldera source of 
eruption (G-2 being the farthest north). Figure 3-99 shows mineral and glass abundance and clay 
mineralogy from GU-3/G-3 drill core that were used to infer the paleotemperatures. Similar 
mineral abundance diagrams for G-1 and G-2 drill core indicate northward progression of an 
increasing abundance of clays and zeolites, along with decreased abundance of glass. This is in 
keeping with the reactions stated above.

 3-202 
Thermodynamic modeling results indicate that the stability of various zeolites is a function of 
silica activity, temperature, aqueous sodium concentration, and the mineralogy of silica 
polymorphs. Increasing temperature or sodium concentration causes the alteration of zeolites to 
other phases. Kinetic effects are, however, important in assessing the significance of 
thermodynamic and natural analog study conclusions. Kinetic data suggest that saturated 
conditions are necessary for notable progress in these reactions, as discussed by Carey et al. 
(1997). Therefore, under ambient conditions the reactions are likely to proceed more slowly in 
the Yucca Mountain unsaturated zone (excluding perched-water zones) than below the water 
table. Similarly, the persistence of opal-CT below the water table indicates that silica reaction 
kinetics at Yucca Mountain are slower than laboratory studies would suggest (Carey et al. 1997). 
However, if prolonged boiling occurred in saturated tuffs, significant progress in all these 
reactions could occur. The thermal design of the repository would limit the occurrence of 
temperatures above 100oC to the Topopah Spring welded unit, and to the region immediately 
surrounding the drifts. The current EDA-II design scenario includes sufficient drift spacing to 
allow temperatures between drifts to remain below boiling (CRWMS M&O 1999a). 
The contact between the Banco Bonito obsidian flow and underlying Battleship Rock Tuff in a 
steep-walled canyon on the southwest rim of the Valles Caldera, New Mexico, provides an 
analog for THC in an unsaturated environment. This site has been the focus of a number of 
analog studies (Krumhansl and Stockman 1988; Stockman et al. 1994). The Banco Bonito flow 
filled a steep-walled canyon cut in the Battleship Rock Tuff about 400 ka (thousands of years 
ago). Present hydrologic conditions are unsaturated. The obsidian, initially at temperatures of 
850oC, heated the porous tuff in the canyon walls to 150-350oC for decades, and, according to 
models, vaporized much of the pore water and caused refluxing of water. Contact effects include 
a reddish baked zone extending tens of feet into the tuffs. Krumhansl and Stockman (1988) 
found that Cs and Rb showed little variation with distance from the contact, whereas Th, Ta, Hf, 
Co and rare-earth elements showed slight concentration trends; however, it is possible that these 
trends may have predated the obsidian flow. Stockman et al. (1994) observed no evidence of 
trends in trace element migration at the contact; however, water and Cl are depleted near the 
contact, whereas F is slightly enriched toward the contact. No evidence of hydrothermal 
alteration was noted, suggesting that the area was unsaturated at the time of contact.

 3-203 
Source: Modified from CRWMS M&O 1998a, pp. F6.1-75, 76 
NOTE: (a) Illustrates paleotemperatures inferred from mineralogical data in drill holes USW G-3, G-2, and G-1 along 
with present-day temperature profiles. (b) Compares mineral and glass abundance in drill-core USW 
GU-3/G-3 determined by x-ray powder diffraction. 
Figure 3-99. Yucca Mountain Mineralogy, an analog for potential Mineral Alteration 
The Valles analog site presents several interesting features. First, the Battleship Rock Tuff is 
very homogeneous in major and trace-element composition, such that it would be possible to 
detect distinct elemental differences caused by heating at the contact. Second, there is no 
hydrothermal overprint that could blur the effect caused by deposition of the obsidian flow.

 3-204 
Based on a detailed mineralogical, chemical, and isotopic study, Stockman et al. (1994) 
concluded that, overall, the effects of heating in this unsaturated environment appeared to have 
been slight and were limited to the tuff nearest the contact. Some evidence existed for 
devitrification and migration of volatile elements in the tuff within 10 m of the contact, but 
variations in major and trace-element chemistry were small and difficult to distinguish from the 
natural variability of these elements in the rock. Apart from devitrification, the principal 
mineralogic change in tuff near the contact was the development of feldspar-silica linings on 
voids in the pumiceous tuff matrix; no significant development of zeolites was found. It was not 
possible to map paleoisotherms from the heating event, but Stockman et al. (1994) developed a 
model to predict the temperatures in the obsidian and tuff as a function of time. The model 
predicts the movement of a boiling front several tens of meters into the tuff over several hundred 
years and is relatively insensitive to assumed saturation. 
The Grants Ridge site, discussed previously as a TH Analog (Section 3.6.2.1), provides 
additional information regarding THC processes. WoldeGabriel et al. (1999) found that the 
proportion of volcanic glass, volatile species, Fe, and some trace-element and rare-earth element 
contents in the host rocks were somewhat depleted at the contact of the intrusion. In contrast, the 
degree of devitrification and potassium content were higher along the contact. The authors 
postulated that vapor-phase expulsion of elemental species could have been responsible for the 
minor depletion of elements during devitrification of the silicic glass at near-solidus temperature 
related to the basaltic intrusion. 
The WoldeGabriel et al. (1999) study performed finite-difference numerical modeling to model 
the Grants Ridge intrusion as a dry, conduction-dominated system and compared its results with 
those of an analytical solution, and with the heat-and mass-transfer code FEHM (Zyvoloski et al. 
1992, 1997). Modeling results, which agreed well with geochemical and mineralogical data, 
indicated that contact welding of the host rocks apparently occurred at temperatures > 700oC 
under a density-driven lateral load of approximately 1 MPa, corresponding to the observed depth 
below the former ground surface of ~100 m. Other physical changes in the host rock, 
represented by partial devitrification and color changes, apparently occurred at temperatures of 
500 to 600oC, which probably persisted for up to 55 yr. after emplacement of the basaltic plug 
(WoldeGabriel et al. 1999). Because devitrification is generally enhanced by the presence of 
aqueous fluids, the abundance of volcanic glass within a short distance (~10 m) from the plug is 
consistent with the authors inference that the plug intruded into an unsaturated environment. 
Although no apparent hydrothermal alteration was recognized in the contact zone, this field 
study and others like it provide an upper temperature bound natural analog to evaluate the effects 
of heat from decay of radioactive waste. Results of these types of studies are also important for 
performance assessment of basaltic-magma intrusions into or close to a potential repository 
environment. Field and laboratory data from the analog study can also be used to build 
confidence and to calibrate models of such processes within similar physical and chemical 
environments. 
The Paiute Ridge area of the Nevada Test Site analog provides insights regarding alteration of 
glass and potential to plug pores. Late Miocene basaltic magma intruded a sequence of 22 to 
11 Ma tuffs in a single magmatic pulse (Lichtner et al. 1999). The intrusions formed as dikes, 
sills, and lopoliths. The original depth of the intrusions was on the order of 150 to 250 m (Crowe 
et al. 1983). A contact aureole ~3 m-wide surrounds the intrusions. Matyskiela (1997) studied

 3-205 
alteration surrounding one intrusion, the 50 m-wide Papoose Lake sill, in proposing the Paiute 
Ridge intrusive complex as a natural analog for THC processes at Yucca Mountain. 
Matyskielas (1997) analysis was based on a pure heat-conduction model. Matyskielas (1997) 
model results indicated maximum temperatures in the tuff host rock of 550oC and cooling times 
ranging from 10 to 400 yr. Matyskielas (1997) major finding was alteration of glass shards to 
cristobalite and clinoptilolite within 60 m of the intrusion. He interpreted the alteration as 
hydrothermal in origin, resulting from emplacement of the intrusion (although he never 
conclusively demonstrated that the alteration post-dated the intrusion). Most significant was 
Matyskielas (1997) observation of complete filling of pore spaces with silica at fracture-matrix 
interfaces, thus creating open conduits for infiltrating fluid flow along fractures. 
Matyskiela (1997) estimated enhanced fracture flow to be as much as five-times ambient 
conditions. This appears to be the opposite behavior to formation of a silica cap, as predicted by 
recent simulations conducted for Yucca Mountain (Hardin 1998, pp. 5.57 to 5.58) in which 
fractures would become filled with quartz or chalcedony, thus inhibiting further flow. It is also 
not consistent with calculations reported in this PMR that show very minor changes in 
permeability due to THC processes. This analog provides insight into the extent to which a 
fracture can be filled by the silica contained in matrix pore water. Figure 3-100 shows that, for a 
given matrix porosity, the degree of sealing of the fracture depends on the fracture volume 
fraction and the particular silica polymorph that precipitates (Lichtner et al. 1999). This analysis 
is predicated upon the assumption that, as pore fluid in the matrix is brought into equilibrium 
with respect to a particular silica polymorph (e.g., amorphous silica) at boiling conditions, the 
matrix fluid boils and escapes into the surrounding fracture network. As the fluid vaporizes, its 
released silica content precipitates in fractures. Lichtner et al.s (1999) two-phase numerical 
simulation results suggest that at distances of tens of meters from the larger of the Paiute Ridge 
intrusions that they studied (width > 39 m), prolonged boiling conditions were established for 
times on the order of several thousands of years. The analysis shown in Figure 3-100 represents 
a limiting case and is dependent on all pore water flashing to steam in the fracture. Amorphous 
silica, with its higher solubility, gives the largest fracture filling, followed by chalcedony and 
quartz. For complete sealing of the fracture, a very small fracture-volume fraction is necessary. 
Moderate filling could represent fracture coatings that armor the fracture.

 3-206 
Source: Derived from Lichtner et al. 1999, Figure 10 
NOTE: A volume fraction of one represents complete filling of the fracture, assuming that the fracture was initially 
open. Dashed vertical lines use fracture volumes from Hardin (1998). Solid vertical lines use fracture 
volumes from CRWMS M&O 2000a, Table 5. 
Figure 3-100. Volume of Silica Polymorphs Precipitated in Fracture as a 
Function of Volume Fraction for a 10 Percent Matrix Porosity 
The dashed vertical lines shown on the figure reflect values of fracture porosity used in the 
calculations reported in Hardin (1998, Table 3-7). As indicated for those porosities, if the fluid 
equilibrium was with amorphous silica, the fracture porosity would be completely filled for the 
tsw33 and 34 hydrostratigraphic units, and 50 percent filled in the tsw35 unit. For fluid 
interactions with quartz and chalcedony, the fracture filling would be approximately 20 and 
30 percent respectively. In contrast, the current estimates of fracture porosity (CRWMS 
M&O 2000a, Table 5) are plotted as solid lines. Note that fractures with these porosities would 
not fill and that even fluid interactions with amorphous silica would produce virtually no 
reduction in porosity. 
3.6.3 Summary of Laboratory Tests 
The laboratory tests that may play significant roles in the understanding of the THCM processes 
are those dealing with TH and THC processes. Some of those laboratory test results may have 
already been incorporated in the complex TH and THC models, such as the NUFT DKM model 
and TOUGH2 DKM model. 
3.6.3.1 Hydrological Properties 
First, variations associated with temperature changes have been found to be much less than 
variations between samples in matrix permeability of the Topopah Spring welded tuff (Lin and 
Daily 1988; Hardin and Chesnut 1997, Section 2.10). Second, no enhancement in vapor 
diffusion was observed in Topopah Spring tuff core samples (Wildenschild, et al. 1998). Finally, 
the wetting/drying hysteresis typically observed in saturation vs. water potential functions at 
ambient temperature was reversed at 90C and was virtually nonexistent at 78C (Lin and 
Roberts 1996).

 3-207 
3.6.3.2 Chemical and Transport Properties 
First, investigation of spiked J-13 water at temperatures as great as 100C indicated that Pu 
solubility decreased, but U, Np, and Am solubility remained the same or increased 
(Nitsche 1991). Carbonate complexes appeared to be important to the solubility of U, Np, and 
Am at elevated temperature (Wruck and Palmer 1997). Second, changes in the composition of 
water in contact with the tuff were moderate at temperatures as great as 150C, with slight 
alteration of the tuff over a few months. At higher temperatures, similar alteration products were 
produced, but reaction rates increased significantly. Accelerated experiments on crushed tuff at 
temperatures greater than 150C produced more extensive alteration, including metastable 
phases (Hardin and Chesnut 1997, Section 2.10). Finally, zeolites could have a significant effect 
on the heat and water balance where they are abundant because zeolite dehydration requires 
more energy than evaporation of water on a molar basis (Bish 1995; Bish et al. 1996; Carey and 
Bish 1996). Zeolite hydration is apparently reversible (at dehydration temperatures as great as 
215C for clinoptilolite), so complementary effects are expected during repository cool-down 
(Hardin and Chesnut 1997, Section 2.10). 
3.6.3.3 Laboratory-Scale TH Processes 
Fracture healing experiments have shown (Figure 3-101) that flowing hot water or steam will 
significantly reduce fracture permeability, and the effect is strongest at temperatures greater than 
90C (Lin and Daily 1989; Lin et al. 1995). Observations reported in the literature can be 
explained by three mechanisms: 
1. Dissolution of fracture asperities by flowing water and consequent aperture reduction 
under the influence of confining stress, 
2. Dissolution/precipitation reactions that clog porosity by redistributing silica or by 
creating alteration products with greater molar volume, and 
3. Heating the rock matrix, which causes flow of matrix pore water toward fractures 
where the pressure is lower and evaporation or boiling occurs, clogging fractures or 
matrix porosity.

 3-208 
0
5 
10 
15 
20 
0
1
2
3
4
5
6 
0 1600 3200 4800 6400 
permeability 
Confining pressure 
Permeability (x 10-15m2) 
Confining Pressure (MPa) 
0
5 
10 
15 
20 
0
50 
100 
150 
200 
0 1600 3200 4800 6400 
permeability 
temperature 
Permeability (x 10-15m2) 
Temperature (C) 
Elapsed Time (Hours) 
Source: Lin et al. 1995 
NOTE: Temperature and confining pressure variation during the test series are plotted for comparison. 
Figure 3-101. Permeability of a Single Fracture in a Core Sample of 
Topopah Spring Welded Tuff, Which Varied as a 
Function of Time and Exposure to Flowing Water

 3-209 
Fracture flow and matrix imbibition laboratory studies (Roberts and Lin 1997; Lin et al. 1998b) 
have physically demonstrated the relationship between fracture-matrix coupling in welded tuff 
(Figure 3-102). Results indicate that under some conditions it is difficult for water to penetrate 
the boiling region, but that water can penetrate this region under certain circumstances, for 
example, sufficient hydraulic head and sufficient flow rate. Fracture flow stopped or slowed 
significantly when a region of porosity higher than the surrounding matrix was encountered. 
Rapid evaporation events were frequently observed, and pressure pulses from those events were 
observed in glass fracture models and in a hanging column of water at an appreciable distance 
compared to the physical size of the events. 
Source: Lin et al. 1998b, Figure 5 and 6 
NOTE: Thermal gradient is indicated between the figures , ranging from 80C at the top to 148C at the bottom. The 
difference between these two experiments was the height of the water column, 0.26 (left) and 0.46 (right) m 
respectively. The difference in head was large enough to force flow through the boiling region in the right 
image. 
Figure 3-102. Difference X-Ray Radiography Images of 7.2 (Left) and 
0.67 (Right) Hours after Flow was Initiated 
Flow channelization visualization experiments (Geller et al., 1996) showed that fracture flow in 
response to constant boundary conditions can be unsteady and associated with intermittent 
rivulets that snap off and reform periodically (Figure 3-103). These ambient-temperature 
experiments demonstrated that parallel plate fractures and epoxy casts of natural fractures can 
produce unsteady, episodic fracture flow in response to constant upstream boundary conditions. 
Similar flow can be expected in the fractures of a heat-pipe zone. These data have important 
qualitative/conceptual implications for FMX, especially in areas of the fracture traversed by the 
unsteady flow and where the contact time available for matrix imbibition or chemical reactions is 
limited.

 3-210 
Source: Geller et al. 1996, Figure 19 
NOTE: Fracture Aperture Varies in Zones, and the Middle Zone has the Largest Aperture. The right side of each 
snapshot is the bottom of the flow cell, and that bottom edge is inclined 30 degrees from the horizontal with 
the right end higher. Snapshots (a) through (h) are a time sequence. The snapshots have been cropped to 
show only a small part of the upper and lower zones. 
Figure 3-103. Physical Model of Water Flow in an 
Unsaturated Fracture Consisting of Parallel 
Plates of Acrylic Plastic 
Physical models of heat pipes have been studied in fracture thermal-hydrology visualizations 
(Kneafsey and Pruess 1997; 1998). Conditions were examined (e.g., fracture saturation, 
temperature difference, and fracture dimensions) that support heat-pipe development. Heat pipes 
were observed in parallel plate fractures containing obstacles, heat sources, and vents, and using

 3-211 
fluids with low boiling points. Film flow as well as meniscal flow were observed to produce 
heat pipes (Figure 3-104). Unsteady rivulet-flow behavior, analogous to episodic fracture flow 
at ambient temperature, was observed (Geller et al. 1996). Rapid evaporation events occurred 
when islands of fluid became superheated and suddenly boiled, constituting another 
mechanism for unsteady flow with the potential to rapidly disperse solute. A few of these 
observations were repeated with a half-cast model incorporating welded tuff as one fracture wall. 
With this kind of mechanism, there is the potential for large-scale episodic reflux flow into 
emplacement drifts. The thermal-hydrological event on June 13, 1997 in the LBT 
(Section 3.6.1.1.3) could be related to this kind of mechanism. 
Source: Adapted from Kneafsey and Pruess 1998, Figure 5 
NOTE: Experiment 9: T bath = 42.4C. 
Figure 3-104. Pentane Visualization (Left) and Temperature Distribution (Right) Showing a Heat Pipe

 3-212 
3.6.4 Summary of Model Validation and Confidence Building 
The following three sections discuss the validation status of TH, THC, and THM process 
models, respectively. Each section is based on available site specific data (Section 3.6.1), 
process models (Sections 3.2, 3.3, and 3.5), historical work (Section 2.2) and alternative views 
(Section 2.4). Sections 3.6.4.1 through 3.6.4.3 discuss in some detail the model validation status 
of individual models. See Chapter 5 for a higher level summary discussion of NFE model 
validity. 
3.6.4.1 Validation of TH Models 
This section discusses the validation or confidence building efforts related to the TH models. 
The confidence building consists of both checking that the codes used to do the mathematical 
manipulations can be relied on (usually referred to as code validation), and on assessing that the 
overall models (including conceptual models, embedded physics, assumptions, boundary 
conditions used, property sets and codes selected) applications are appropriate for the analyses of 
Yucca Mountain conditions and performance. The validation of the codes is discussed in 
Appendix A. The latter assessment (appropriateness of overall modes) as discussed here was 
provided by comparisons of model results with field and laboratory studies. 
The following applications or studies that demonstrate appropriateness of TH models are 
examined for YMP calculations: 
 The AMR that presents comparisons of the DST and LBT field data with fully 3-D 
model calculations, using two different DKM material-property sets 
 Comparison of field results with TH calculations of the G-Tunnel test 
 Comparison of field results with TH calculations of the SHT 
 Simulation of vadose-zone tritium transport at the Lawrence Livermore National 
Laboratory Site 
 Code-testing for QA qualification 
 Early verification and benchmark testing of the code 
3.6.4.1.1 TH Model Confidence Building based on non-Yucca Mountain Cases 
This section examines the performance track record of model studies using the NUFT and 
TOUGH2 codes (Nitao 1993, Pruess 1991) and documents the rigorous testing and wide range of 
applications work that build confidence in both the codes and in ability to model TH responses 
applying these codes in the modeling of multiple problems or cases. Confidence in the ability to 
model these processes using the NUFT and TOUGH2 codes to simulate thermohydrologic 
processes in porous and fractured media has increased significantly since initial testing of the 
codes and modeling of YM. As noted, Appendix A will include discussion of qualification of 
the codes themselves.

 3-213 
An international cooperative project was established for theoretical and experimental studies of 
coupled thermal, hydrologic, and mechanical processes in hard (crystalline) rock. This project is 
called DECOVALEX and is described by Jing et al. (1995). In this work, different mathematical 
models and computer codes were used to study problems of interest to geologic disposal of 
nuclear waste. In particular, eleven codes were evaluated; these included both 2-D and 3-D 
finite-element codes in which the rock was modeled as a porous-fracture medium and a 2-D 
discrete-element code in which the rock was modeled as discrete deformable block assemblages. 
Much of the work done for DECOVALEX is documented in a special issue of the International 
Journal of Rock Mechanics (Stephansson 1995). 
As part of the DECOVALEX program, two intercode benchmark comparisons were performed. 
The benchmark test BMT1 considered a large-scale (kilometer-scale) mass of rock as described 
by Millard et al. (1995). The benchmark problem BMT2 involved a system of nine blocks of 
intact, hard rock separated by two pairs of soft fractures, as described by Chan et al. (1995). For 
each of these exercises, both finite-element and distinct-element methods were used. Chan et al. 
(1995) found that, for the BMT2 test, heat convection significantly affects the distribution of 
temperature, thermal stresses, and displacements, and that the predominant coupled effect is 
fracture closure caused by thermal expansion of the rock-blocks. Results for DECOVALEX also 
indicate that, for tests BMT1 and BMT2, the different modeling techniques produced very 
similar results. This indicates that use of the continuum codes is adequate for study of host-rock 
behavior for a Yucca Mountain repository. 
Another study used a physical model to simulate waste emplacement for evaluating a nuclear 
waste disposal concept in Japan. The large-scale laboratory test involved heating and flow 
testing, and was simulated with a software code that includes vapor-flow processes (Borgesson 
and Hernelind 1995). The test was performed using a partially saturated buffer material 
surrounding a simulated waste package in a hollow cylinder of rock. The calculations resulted in 
a prediction of void ratio, temperature, water saturation, pore pressure, and effective stress. The 
calculations were coupled THM; the hydrologic and thermal results compared well with the 
experiment, but the prediction of mechanical response did not. The 3-D finite-element model 
THAMES underestimated the experimental measurements of temperature in the buffer material 
(Ahola et al. 1994a and 1994b). 
For another field-scale experiment, FLAC 2-D (Itasca Consulting Group Inc., 1996) was used to 
model heat and water flow through a 50 m x 50 m block of fractured granite (Israelsson 1995). 
Stress-induced permeability changes were limited to one order of magnitude, and fractures were 
assumed to be randomly oriented, thus allowing use of the continuum approach in FLAC. 
3.6.4.1.2 Large Block Test 
The results of DKM with active fracture model using NUFT were compared with temperature 
and liquid-phase saturation fields measured in the block. Temperature histories at selected 
sensor locations and temperature profiles along selected boreholes were graphically compared 
with model results. Liquid-phase saturation profiles, measured along boreholes by neutron 
probe, were also compared with corresponding field profiles. Graphical comparisons were done 
for liquid-phase saturation.

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A statistical goodness-of-fit analysis was performed to compare model and field temperatures at 
all sensor locations in the block. Three statistical measures of goodness-of-fit were used, the 
root-mean-squared difference (RMSD), MD, and normalized-absolute-mean-error between 
measured and simulated temperatures. 
Two different rock property data sets were used in the calculations: the DS data set and the MS 
data set. Hydraulic and thermal properties of the tsw34 unit of these property sets were used in 
model calculations, because the hydrogeologic unit of the LBT area is equivalent to the tsw34 
model unit (Tptpmn) of the site-scale UZ flow model. The main difference between the DS and 
MS properties for the tsw34 unit is a higher fracture permeability of 1.70 x 1011 m2 for the MS 
versus 2.76 x 1013 m2 for the DS. 
Results of this comparative analysis using the DS and MS data sets contribute to the validation of 
the NUFT code and underlying models to simulate the thermal hydrological process in a 
repository. Specifically: 
 Model results using both rock-property data sets, DS and MS, show very good 
agreement with field temperatures 
 Model results obtained using the DS data set show slightly better agreement with the 
field temperatures than simulation results obtained using the MS data set 
 Both data sets slightly over-predict temperatures, particularly in and adjacent to the 
heater horizon, but the degree of over-prediction is less for the DS data 
 The RMSD for the DS data set, computed at six times from 30 days to 400 days, varied 
from 3.7C to 8.7C 
 The RMSD for the MS data set, computed at six times from 30 days to 400 days, varied 
from 4.3C to 8.8C 
 The MD for both the DS and MS is generally positive, confirming the slight 
overprediction of temperature observed in the graphical comparisons 
 The dryout zone modeled using the DS data is in good agreement with the dry out zones 
measured by neutron probe; the model dryout develops slower, but later catches-up with 
the field zone 
 The dryout zone modeled using the MS data property set is significantly larger than the 
zones modeled using the DS property set and zones measured by neutron probe 
The LBT was conducted in the tsw34 unit of the Topopah Spring tuff that outcropped at Fran 
Ridge. The rock properties of the test block were neither expected, nor required, to be identical 
to those of the potential repository horizon at Yucca Mountain. The purpose of the LBT was not 
to test property sets, but to test the capability of models in representing the coupled THCM 
processes. However, testing the capability of models to analyze THCM processes for the 
potential repository requires a property set that is at least representative of the properties at

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Yucca Mountain in order to conduct appropriate model validation. If the property set that 
provided the best (or at least a good) match between the simulated and measured results from the 
LBT is also the one that provides an appropriate match for other field tests, then the LBT model 
validation procedure will not only build confidence in the models themselves, but also add 
confidence in use of that property set to evaluate the performance of the overall potential 
repository. 
The focus of the LBT was on TH model capability testing, with some THM and THC testing, but 
these latter were not the main focus of the test. The DK TH models, using both DS and MS 
property sets and using the NUFT code to make the numerical analyses, were able to predict the 
temperatures in the LBT well. This enhances confidence that the DKM/AFM TH model has the 
ability to properly represent the heat transfer mechanisms in a potential repository, and therefore 
has the ability to properly predict temperatures in the near field. 
The DK TH model, using the DS property set in NUFT code, predicted the moisture distributions 
in the LBT well. The DK TH model did not match the moisture distributions as well when using 
the MS property set. This does not necessarily imply that the use of MS property sets is 
inappropriate for use in calculations of the potential repository responses. It indicates that the 
moisture distributions are somewhat sensitive to the property sets, and using properties that 
represent averages of many units do not match the data as well as when using the properties that 
are specific to the unit of the test. In some respects this enhances the confidence in the models 
ability to discriminate between the property sets. It also enhances confidence that property 
measurements of specific units can be appropriately utilized, but indicates the need to use care in 
selecting the most appropriate property set. Because the tsw34 unit is not representative of the 
major portion of the potential repository, the DS property set should not be automatically 
selected as representative of the potential repository. 
The matching of moisture distributions enhances confidence that the TH model has the ability to 
properly represent water flow, evaporation, and condensation in a potential repository. The fact 
that the DS property set did well in this test case enhances confidence that it is appropriate for 
use in predicting moisture distributions in the near field of a potential repository within the tsw34 
unit. It also enhances confidence that once properties are determined for the units representing 
the remainder of the potential repository, the models will be appropriate for use in predicting 
moisture distributions within these units. 
3.6.4.1.3 Single Heater Test 
The SHT was one phase of the field-scale thermal-testing program of the Yucca Mountain Site 
Characterization Project. The SHT Final Report (CRWMS M&O 1999d) describes the test in 
more detail. The primary purpose of the SHT was to study the TM behavior of the densely 
welded, non-lithophysal Topopah Spring Tuff at the ESF. The SHT was also used as a shakedown 
for testing thermal-hydrologic-chemical-mechanical processes in situ, testing that will be 
conducted in the Drift Scale Test. 
In the SHT, a line-heat source 5 m-long was placed in a pillar and used to heat the pillar for 
approximately nine months. The thermal field was relatively cylindrical about the line-heat 
source. The heater was turned-off after nine months of heating, and the rock mass was

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monitored during the cool-down for another nine months, until May 28, 1997, when the test was 
terminated. 
Thermal neutron-logging was used to monitor moisture content in four boreholes during the 
SHT. Neutron-logging data and analysis presented here indicated drying of the rock mass during 
the heating phase of the test. Neutron-logging results were in good agreement with ERT results. 
The degree of drying seemed in good correlation with temperatures in the rock. ERT and 
neutron-logging data indicated drying in regions of rock that reached 60C and more. 
The TH behavior during the heating and cooling stages of the SHT was analyzed with the DKM 
AFM using the NUFT code. Two different conceptual models for FMX were considered: the 
ECM, which assumes equilibrium between the fracture and matrix continua, and the DKM that 
accounts for disequilibrium processes between the fracture and matrix continua. All of the 
models in this study included the influence of vapor and heat flow along the heater borehole. 
The DKM model predicted temperatures that were in excellent agreement with the observed 
temperatures throughout the heating stage of the SHT. The ECM model agreement was not as 
good: it predicted lower temperatures, but a more extensive dry-out region, than did the DKM 
model. Both the ECM and DKM models predicted a pronounced cold-trap effect in the heater 
borehole. Vapor and latent heat flowed from the heated interval of the heater borehole to the 
cool end of the heater borehole adjacent to its collar, where the vapor condensed, resulting in 
focused condensate drainage and a local increase in liquid saturation in the matrix. The cold-trap 
effect efficiently transferred heat along the heater borehole toward the TM alcove. The cold-trap 
effect is a potentially important mechanism influencing TH behavior in emplacement drifts. 
For the SHT, the comparison of the predicted and the measured moisture distributions was not 
discussed in the Thermal Test AMR (CRWMS M&O 2000a). The following summary of the 
predicted and measured moisture distributions is extracted from SHT Final Report (CRWMS 
M&O 1999d). Due to the nature of the measured moisture distribution data, only qualitative 
comparisons between the simulated results and the measured data are possible. 
 The simulation of the moisture distribution in the SHT using the TOUGH2 DKM 
qualitatively agreed well with the data from GPR and air-permeability measurements. 
The model predicted that, at the end of the heating, drying had extended to a radial 
distance of about 1.2 m from the heater. In cooler regions, the vapor condensation at the 
fracture walls resulted in an increase of liquid saturation in both fractures and the matrix. 
At 3 months of heating, strong downward drainage flux in the fractures was observed 
below the heater. The rock matrix was drier above the heater than below. GPR data 
showed, at 5 months of heating, a drier region close to the heater and a wetter region 
about 1 m away from the heater. The GPR data at 7 and 9 months showed a further 
drying near the heater, but no significant changes in the regions beyond the 1-m radius. 
After 3 months of heating, the measured air permeability in the predicted condensate 
regions decreased by factors of 2 to 4, compared to the preheat values. This decrease in 
the air permeability was likely due to increased water saturation in the fractures 
(CRWMS M&O 1999d, Section 8.7.3.1). The TOUGH2 ECM model was also used for 
sensitivity analyses of the SHT. It was conc luded that DKM is better suited to

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realistically represent thermal-hydrological processes in the SHT than ECM (CRWMS 
M&O 1999d, Section 8.7.3.3.2). 
 The simulated moisture distribution in the SHT using the NUFT DKM model was in 
good qualitative agreement with the neutron logging data. The radial extent of the dryout 
zone predicted by the NUFT ECM model was less than that measured by neutron 
logging. The NUFT DKM model calculated a condensate-shedding zone that was to the 
sides and below the dry-out zone, which was qualitatively consistent with the liquidphase 
saturation changes measured by the ERT. The ECM model calculated a 
pronounced condensation zone that was vertically symmetrical about the heater axis; this 
was inconsistent with the liquid-phase saturation changes measured by ERT. The SHT 
was not sensitive to the magnitude of percolation flux (CRWMS M&O 1999d, 
Section 8.8.7). 
3.6.4.1.4 Drift Scale Test 
The results of DKM Active Fracture model with NUFT calculations were compared with 
temperature fields measured in the DST. Temperature histories at selected sensor locations, and 
temperature profiles along selected boreholes were graphically compared with model results. 
Figure 3-105 shows a graphical comparison for a typical thermal sensor. A statistical goodnessof-
fit analysis was performed to compare model and field temperatures at all sensor locations in 
the field. Three statistical measures of goodness-of-fit were used, the RMSD, MD, and 
normalized-absolute-mean-difference (NAMD) between measured and simulated temperatures. 
Two different rock-property data sets were used in the calculations: the DS data set and the MS 
data set. Hydraulic and thermal properties of all hydrogeologic units along a stratigraphic profile 
through the DST test area were used in the model calculations. However, the HD and wing 
heaters are located in the tsw34 unit; therefore, tsw34 and its immediate neighbors tsw33 (above) 
and tsw35 (below) were expected to have greatest influence on rock temperature and liquid 
saturation.

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Source: CRWMS M&O 2000a, Figure 96 
Figure 3-105. Comparison of DKM Simulated (NUFT) and Measured Temperature Histories 
for Sensor #10 in Borehole 160 (Horizontal, Near the Wing) for All Property Sets 
in the DST 
Graphical comparisons of model-temperature profiles and temperature histories with field data 
show very good agreement, except at locations adjacent to the heat sources. Some over 
prediction of temperature, up to about 16 percent, was observed adjacent to the HD and in the 
wing-heater areas. In general, the comparison between the simulated and measured temperatures 
is poor for all sensors located very close to the heated drift at small times (less than 100 days). 
This is at least partially the result of the computational grid spacing being too coarse to resolve 
the large temperature gradients generated near the heat sources at early times. At later times, in 
excess of 1 year, the results improve significantly as the temperature profiles smooth in space. 
Agreement between model and field temperatures was better in the sub-boiling zones than in 
above-boiling zones. Better agreement in the sub-boiling zones indicates that heat flow is 
dominated by conduction and that the value used for wet thermal conductivity (0.92 W/mCC) is 
reasonable. 
The RMSD, MD, and NAMD between the simulated and measured temperatures were selected 
as measures of the goodness-of-fit of the simulated values to the field values. These results, like 
the graphical comparisons discussed earlier, show good agreement between model and field 
Measured Data 
DS 
MS 
MSF 
CON

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temperatures. For the Drift-Scale data set, the RMSD above 97C is generally two to three times 
higher than the RMSD below 97C (1216C compared to 67C) and at times greater than 
182 days, it does not vary significantly with time. Also, for the Drift-Scale data set, the MD 
shows that temperature is generally over-predicted by the model at large times for temperatures 
both above and below 97C. As with the LBT, model results using the DS data set are in slightly 
better agreement with field temperatures than results obtained with the MS data set. 
3.6.4.1.5 G-Tunnel 
Nitao and Buscheck (1996) used the ECM TH model with NUFT to analyze the thermohydrologic 
flow in variably saturated, fractured, welded tuff for the Prototype Engineered Barrier 
System Field Tests (PEBSFT) in G-Tunnel at Yucca Mountain. Post test analyses were also 
conducted using the DFM TH model with NUFT. The PEBSFT (Ramirez 1991) were conducted 
to evaluate the applicability of measurement techniques, numerical models, and procedures 
developed for large-scale field tests at Yucca Mountain. The primary objective of the tests was 
to provide the basis for determining whether tests planned for Yucca Mountain had the potential 
to be successful. The PEBSFT was conducted prior to the current QA program and as such can 
not be used directly. However, the results can be used to corroborate experimental results from 
the ESF tests. 
The tests were performed in a section of the tunnel referred to as the G-tunnel Underground 
Facility. The Small-Diameter Heater Alcove and the Rock-Mechanics Incline bounded the test 
block. A 30.5 cm (12 in.) horizontal heater-emplacement borehole was drilled to a depth of 
10.7 m. A 3 m long heater element was placed inside the borehole with its midpoint positioned 
at 8.5 m from the collar. The heater power-level was maintained at about 3.2 kW for 128 days. 
The power was then ramped down to zero over a 67 day period. Rock temperature, moisture 
content, and other hydrothermal variables were monitored in twelve instrumentation boreholes. 
All instrumentation boreholes were grouted after drilling. The highest borehole-wall temperature 
measured was 242C. 
The test was modeled using the ECM and the DFM approaches. For the ECM, local 
thermodynamic equilibrium is assumed between the matrix and fractures within a representative 
elementary volume. The ECM is actually a single-continuum model with composite 
characteristic curves derived as a function of bulk-averaged liquid saturation in the matrix and 
fractures. For the DFM, the matrix and fractures are separated into distinct spatially discretized 
domains, which can represent disequilibrium between the matrix and fractures. 
Good agreement was observed between model and field temperatures for histories at the lower 
borehole wall, and at points 0.55 m below and 2.4 m above the heater axis. The best agreement 
was apparently obtained for 280 and 524 mm fractures. The 1,048-mm case shows some 
over-prediction of field temperatures, possibly because buoyant gas-phase convection was 
over-predicted. 
The rock matrix dry-out volume, measured by neutron probe, was reasonably well predicted by 
both the DFM and ECM models. The neutron measurements also showed preferential drying 
along the fractures, which was observed in the results of both models.

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3.6.4.1.6 TH Model Validation Conclusions 
The heating and cooling stages of the SHT were modeled by ECM and DKM TH models with 
the NUFT code, using the December 1997 TSPA-VA base-case hydrologic parameter set, which 
was modified to include the field measurements of bulk permeability in the SHT area. Two 
different conceptual models for FMX were considered: the ECM, which assumes equilibrium 
between the fracture and matrix continua, and the DKM that accounts for disequilibrium 
processes between the fracture and matrix continua. For the DKM-model calculations, two 
different approaches for representing the FMX were considered: a fixed-FMX approach and a 
dynamic-FMX approach. For the ECM-model calculations, two different western boundaries 
were considered: one that placed the western boundary at the eastern wall of the TM alcove and 
one that placed the western boundary 33 m to the west of the western wall of the TM boundary. 
Unlike earlier TH models of the SHT, all of the models in this study included the influence of 
vapor and heat flow along the heater borehole. This modeling study resulted in the following 
observations and conclusions: 
 The DKM model predicts temperatures that are in outstanding agreement with the 
observed temperatures throughout the heating stage of the SHT. 
 The DKM predicts higher temperatures in the superheated, dry-out zone than does the 
ECM model, primarily because the DKM model predicts a substantial gas-phase 
pressure increase in the matrix blocks, whereas the ECM model assumes gas-pressure 
equilibrium between the matrix and adjoining fractures. The gas pressure increase 
predicted by the DKM model causes the saturated temperature (which is the boiling 
temperature at the local pressure) to increase well above the nominal boiling point 
(96C). 
 The ECM model predicts temperatures that are in good agreement with the observed 
temperatures in the sub-boiling region of the SHT during the heating stage. In the 
superheated, dryout zone, the ECM model predicts temperatures that are lower than the 
observed temperatures during the heating stage. 
 For the DKM model, the predicted radial extent of the dryout zone is in good, qualitative 
agreement with the neutron-probe measurements of liquid-phase saturation change. For 
the ECM model, the radial extent of the dryout zone is less than that predicted by the 
DKM model (and is somewhat less than that indicated by the neutron-probe 
measurements). 
 The DKM model predicts a condensate-shedding zone that is to the sides and below the 
dry-out zone, which is qualitatively consistent with the measurements of liquid-phase 
saturation change made with ERT. 
 The ECM model predicts a pronounced condensation zone that is vertically symmetrical 
about the heater axis; this is inconsistent with the measurements of liquid-phase 
saturation change made with ERT.

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 The SHT cannot distinguish between alternative conceptual models of the FMX factor. 
Both approaches result in the same outstanding agreement with observed temperatures, 
and both approaches predict the same distribution of liquid saturation in the matrix 
continua. 
 The models with an extended western boundary predict temperatures that are in better 
agreement with the observed temperatures than are those predicted by the model with 
the western boundary located at the eastern wall of the TM alcove. 
 All of the models underrepresented heat loss to the TM alcove, resulting in predicted 
temperatures being greater than observed temperatures in the vicinity of the TM alcove; 
this over-prediction increases as the distance to the TM alcove decreases. The cause for 
this over-prediction is the manner in which heat flow in the TM alcove is treated. Had 
thermal radiation from the warmer to cooler wall surfaces in the TM alcove been 
accounted for in the SHT models, the cooling rate on the eastern TM alcove wall would 
have been much greater, resulting in lower predicted temperatures in the vicinity of the 
TM alcove. 
3.6.4.2 Validation of THC Models 
The current understanding of the effect of coupled THC processes on the Near Field is based on 
various experiments from small- scale to field-scale (see Table 3-14), modeling of water-rock 
reactions (Hardin, 1998; Johnson et al. 1998), coupled modeling of water-gas-rock reactions 
(Lichtner and Seth 1996, pp. 133 to 142; Hardin, 1998; Sonnenthal et al. 1998; Tsang et al. 1999; 
CRWMS M&O 2000b), and observations of zeolitization due to higher-temperature alteration 
that took place early in the history of the tuffs (see Section 3.6.2). 
Although a few water samples were collected from the Single-Heater Test, that were mildly 
acidic to near neutral in pH and moderately dilute, data on gas chemistry were lacking and the 
test was too short for significant alteration to have taken place. Most of the quantitative data on 
coupled THC processes in the Near Field have come from the ongoing Drift-Scale Test, which 
has yielded water samples in several hydrology boreholes above and below the heaters. Gas 
samples have been collected in numerous borehole intervals around the test and approximately 
quarterly since heating was initiated in December 1997. In general, water compositions have 
been similar to, but not as dilute, as those collected from the Single Heater Test, with pH values 
in the Drift Scale Test ranging approximately from just above 6 to nearly 8. The gas chemistry 
exhibits large regions of increased CO2 concentrations that have been attributed to exsolution, 
gas transport, and calcite dissolution. Significant shifts in stable carbon, oxygen and hydrogen 
isotopic ratios (CRWMS M&O 2000b) have been attributed to isotopic fractionation 
accompanying boiling, vapor transport, and condensation. 
Lab and field experiments have provided insight and data pertaining to the effects of THC 
processes on the chemistry of water and gases, but for the most part there is only indirect 
evidence for mineral dissolution and precipitation. Increased silica concentrations relative to 
chloride (a generally conservative species) have indicated significant reaction of silicates as 
shown in Table 3-16 (CRWMS M&O 2000b, Table 9). The modeling presented in Section 3.3 
has indicated only minor changes in porosity as a result of mineral precipitation and dissolution.

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Such small changes in hydrologic properties are consistent with a return to higher air 
permeability after boiling zones dried-out in the DST (CRWMS M&O 2000a). The first two 
years of the test were generally in a heating-up phase, and during the following two years a more 
stable boiling zone should persist and be more conducive to localized mineral precipitation. 
Modeling of coupled THC processes (CRWMS M&O 2000b, Section 3.2) has indicated that 
calcite and silica polymorphs are the dominant dissolving and precipitating mineral phases, with 
feldspars, clays, and zeolites modifying the water composition, and pH to a lesser extent. The 
model results that were based on a relatively complete geochemical system produced shifts in pH 
to somewhat higher values than those observed in the Drift Scale Test, indicating that the model 
most likely overestimated the effective reaction rates for these phases. Thus, if the DST water 
chemistry is representative of the long-term water compositions accompanying the thermal 
period of the potential repository, then the modeling results may be viewed as an upper limit to 
the effect of these phases on system behavior. Modeling of the water and gas composition in 
fractures in the Near Field was shown to also depend on the infiltration rate. 
Data from the field tests and associated modeling suggest the following general characterization 
of the NF THC processes: 
 Exsolution of CO2 by heating and boiling of predominantly matrix pore water will result 
in an expanding zone of elevated CO2 concentrations (1 to 2 orders of magnitude above 
atmospheric levels) 
 Accompanying the zone of increased CO2 will be an area of higher fracture-liquid 
saturation due to condensation, and pH values of water less than the ambient porewater 
(~ pH 8.3, but generally not lower than about 6) 
 Strong drainage of lower pH condensate water in fractures will result in calcite 
dissolution 
 Enhanced precipitation of calcite, amorphous silica, and possibly zeolites will be 
localized above and to the sides of the drifts 
 Overall changes in fracture porosity and permeability will be minor, although some 
fractures could be more tightly sealed than others 
 Waters that reach the drift during the early stage of rewetting will not be strongly 
elevated in salts, because of rapid dissolution and strong dilution, but may have 
increased carbonate and silica concentrations. 
3.6.4.2.1 Summary of THC Model Validation Using Tests 
The DS THC Model has been extensively validated by comparison of gas and water geochemical 
data collected during the DST, as discussed in Section 3.6.1.3 and described in detail in the THC 
Process AMR (CRWMS M&O 2000b). These comparisons include gas-phase CO2 
concentrations as a function of time and space, the pH of waters collected in boreholes, and 
general observations on changes in concentrations of Cl and other aqueous species. The model

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can thus be considered valid for its intended use, which is to interpret data for the SRCR. For 
LA, DST cooling data will be available to more extensively validate the model. 
The DST is the second underground thermal test being performed in the ESF at Yucca Mountain, 
Nevada. The purpose of the test is to evaluate the coupled thermal, hydrological, chemical and 
mechanical processes that take place in unsaturated fractured tuff over a range of temperatures 
from approximately 25C to 200C. The heaters were activated in December 1997 and are 
planned to run for four years followed by a four year cooling period. 
The thermal tests provide the only field-scale experiments that have produced seepage under 
thermally perturbed conditions. Numerous samples of water have been collected from several 
borehole intervals during the DST, and previously a few samples were collected in the Single 
Heater Test (CRWMS M&O 2000a). 
Simulation of DST THC processes provides an important validation test for the THC conceptual 
models and input data used in the THC Seepage Model for a much longer time-scale. 
Geochemical input parameters have not been calibrated to measured data collected during the 
DST and therefore the DST THC Model simulations are an independent test of the conceptual 
model and input data used also in the THC Seepage Model. Detailed analysis of THC processes 
in the DST and validation tests are presented in the THC Process AMR (CRWMS M&O 2000b). 
This validation process involves examination of areas of modeled fracture drainage compared to 
locations where water was collected during the test, the comparison of CO2 concentrations 
collected from sampled gases, and comparison of the chemistry of waters collected from 
boreholes over time. These validation exercises are continuing as more data is collected from the 
DST and the models are improved to represent the physical and chemical processes more 
accurately. The following section compares modelling results to measured CO2 concentrations 
collected from boreholes. Brief descriptions of the evolution of water chemistry and mineralogy 
follow. 
3.6.4.2.1.1 Gas-Phase CO2 Evolution 
In the first test, CO2 concentrations measured in gas samples taken from boreholes during the 
DST are compared to simulation results using the DST THC Model. It is very important to 
properly simulate evolving gas-phase CO2 concentrations, because they strongly control the pH 
of condensate waters, are sensitive to temperature, and CO2 transport is sensitive to the fracture 
hydrologic properties. CO2 also affects HCO3
- concentrations in fracture waters, which are 
important for the in-drift geochemical environment. Modeled distributions of CO2 
concentrations and temperature in fractures and matrix are shown after 6 and 20 months of 
heating (which are also times for which CO2 measurements are available) in Figure 3-106 for the 
calcite-silica-gypsum geochemical system (Less Complex). At both times, and in both fractures 
and matrix, a halo of increased CO2 concentrations appears centered approximately at the 60C 
isotherm. Over the 14-month period, between 6 months and 20 months, the halo increases 
considerably in extent and magnitude. Areas close to the HD that have dried-out and are at 
above-boiling temperatures show a decline to much lower CO2 concentrations. 
To evaluate how the model predicts the time-evolution of CO2 concentrations in the gas phase, 
measured CO2 concentrations from intervals that were repeatedly sampled from February 1998

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to August 1999 (20 months) are compared to model results for the same times. Figure 3-106 
shows the time-evolution of CO2 concentrations in borehole intervals 74-3, 75-3, 76-3, and 78-3 
(see Figure 3-106 for locations of borehole intervals). In borehole interval 74-3, there were only 
grid nodes above (cooler side) and below (hotter side) the interval, and therefore results from 
both nodes are plotted to see if they bracket the measured compositions. In borehole 
interval 78-3, two locations (center and end) were chosen, because of the strong thermal gradient 
across this region. The comparison shows that the simulations generally follow the trends in 
measured CO2 concentrations. Two exceptions are when a known heater power- loss occurred 
(around 19 months; see slope change in 74-3 and 75-3 at 20 months) or when the samples were 
at boiling temperatures and were nearly all water vapor (instead of air), and had much of the 
water condensed-out during sampling (76-3 and 78-3, largest peaks). In the latter case, the 
modeling results should diverge from the measured data, because they reflect the CO2 
concentration in the full water vapor-air mixture. This effect is discussed in the THC Process 
AMR (CRWMS M&O 2000b, Section 6.2.7.2).

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NOTE: Temperature Contours are Superimposed. OD refers to the Observation Drift (adapted from CRWMS 
M&O 2000b, Figures 5 and 6). Contour labels and color bars indicate values. 
Figure 3-106. Simulated CO2 Volume-Fractions in Fractures and Matrix, After 6 and 
20 Months of Heating, During the Drift-Scale Test (Less Complex case) 
3.6.4.2.1.2 Water Chemistry Evolution 
The modeled chemistry of waters in fractures is shifted from an initial pH of about 8.3 to 6.5, 
and is captured as changes in time and space. The lowest modeled pH values are in the region of 
highest gas-phase CO2 concentrations. The shift in pH in the modeled fracture water is similar to 
that observed in the water collected from hydrology boreholes at the same times and in the 
expected regions during the DST (CRWMS M&O 2000b), which were also areas of high 
gas-phase CO2 concentrations. Chloride concentrations in waters collected from hydrology 
boreholes are considerably more dilute (a factor of 5 to 10) than the matrix pore water, which 
was also predicted by the modeling. The good aggreement between simulation and measurement 
for pH and chloride indicates that the degree of communication between fractures and matrix in 
the simulation is appropriate. Stronger communication in the simulation would predict higher 
pH and higher chloride than measured in the samples. Other species, such as Ca and Si, show 
similar trends in the modeled fracture-water compositions compared to measured water 
compositions. These trends indicate increasing silicate mineral dissolution and calcite

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precipitation, as condensate waters undergo heating (CRWMS M&O 2000b, p. 72). Additional 
information on water chemistry can be found in the THC Process AMR (CRWMS M&O 2000b). 
3.6.4.2.1.3 Mineralogical Changes 
In the model simulations, calcite is the major phase forming in the zone above the heaters, 
although the abundances are exceedingly small. Secondarily, amorphous silica also precipitates, 
but is much less abundant compared to calcite. No direct observation of the precipitation or 
dissolution of calcite has been found, because the DST is ongoing; however, trends such as 
decreasing Ca in water found in boreholes with increasing temperature, pH and silica 
concentrations are strongly suggestive of calcite precipitation as shown in Table 3-16 (CRWMS 
M&O 2000b, Table 9). Fracture porosity changes in the DST simulations are very small after 
20 months of simulation (on the order of 0.01 percent) and follow closely the area of calcite 
precipitation (CRWMS M&O 2000b, Figure 17). Such small changes likely have no measurable 
effect on the hydrologic properties of the rock. More data are being collected from the DST, 
including 14C concentrations in gas-phase CO2 and hydrogen, carbon, oxygen, strontium, and 
uranium isotopic measurements that will allow for more careful testing of the DST THC Model. 
3.6.4.2.2 Corroborative Evidence 
Data collected from the DST over the next several years will include water and gas chemistry, 
and eventually samples of rocks around boreholes. These data will be invaluable in testing of the 
models developed to predict long-term repository performance. No other data can be used to 
directly corroborate the model, because of the uniqueness of the system. However, studies from 
natural analogs have been useful in analyzing aspects of the Yucca Mountain THC performance, 
as discussed in Sections 3.6.2 and 3.6.4.4. 
3.6.4.3 Validation of TM and THM Models 
The TM and THM behavior of rock in the near field has been simulated using two fundamentally 
different techniques (e.g. the continuum and distinct-element techniques). The continuum 
technique simulates a rock mass as a continuous body with properties that may vary from place 
to place, while the distinct-element technique simulates the rock masses a collection of 
independent blocks separated by individual fractures. For problems involving coupled behavior 
in partially saturated, fractured rock, these two types of simulators are generally weakly coupled 
to the TH models, via temperature and permeability parameters. This is because the thermal and 
fluid-flow capabilities in TM models are generally much less sophisticated than for the TH 
models, and because simulation of TM response in a rock mass requires a much different grid 
than is generally used for TH response. This is especially true in the case of the discrete-element 
model in which blocks of rock move independently. The coupling between TH and TM is 
generally done by first computing a temperature field using the TH model and passing this 
temperature field to the TM model. The TM model predicts a deformation or change in stress, 
which causes a change in permeability, which is passed back to the TH model. 
The T results of TH portions of the THM models are compared with results from TH models 
discussed in Section 3.2.4, the validation of which is discussed in Section 3.6.4.1. No separate

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model validation or confidence building exercise was performed for the TH portions of the THM 
models. The temperature fields are what are coupled to the mechanical models. 
The TM model validation or confidence building is provided mainly by comparisons with field 
tests. Confidence building of the TM models in a non-YM specific context was provided by an 
assessment of various model approaches made as part of the international cooperative 
DECOVALEX project. As noted by Ahola et al. (1994a and 1994b), there is good agreement 
among the predicted temperatures and displacements, and lesser agreement among the predicted 
stresses and fluid fields. However, as they point out, validation requires comparison to actual 
field data. 
The YMP approach is consistent with the above observation in that one of the primary means of 
model validation for the TM models has been comparison of measured and computed 
displacements for the field-scale thermal tests, including the LBT, the SHT and the DST. 
Additionally, a large number of laboratory tests have been conducted on samples ranging from a 
few mm to 0.5 m in scale. The laboratory tests have provided essential data on rock properties 
and insight into the coupled THM behavior of the rock under well-controlled conditions. 
The field-scale thermal tests provide deformatio n data mainly via displacement measurements 
using MPBX instrumentation. These instruments are installed in boreholes and provide 
measurement of displacement along the axis of the borehole. Thus, they are essentially a line or 
point measurement and, when used in an array, can provide deformation data for a test block. 
These data can then be used to compute rock-mass thermal expansion, and can sometimes 
indicate movement on fractures. MPBX instrumentation has also been used in conjunction with 
plate-loading apparatus to provide information on the deformation modulus at a scale containing 
numerous fractures. Comparison of deformation from different tests and from different sections 
of a field test can provide an assessment of how the heterogeneity of the rock mass affects TM 
properties. These field tests have also provided data on the temperature dependence of 
mechanical properties. 
Stress measurements can also be used in TM model validations. A few Goodman Jack stress 
measurements were made in association with the SHT. However, these measurements did not 
provide useful information on the stress field in the rock during this test and were not further 
considered. 
Laboratory tests on cores and small-block samples have provided data on mechanical properties 
of rock and rock fractures. In particular, a few tests on fractures have been conducted, including 
fracture properties such as friction angle, fracture stiffness, and fracture cohesion on samples on 
a scale up to 0.5 m. It is important to note that some of these properties are difficult or 
impossible to measure in the field. A few tests designed to characterize fracture flow at elevated 
temperature and stress conditions have also been conducted, and results of these can be used to 
gain confidence in model simulations. 
3.6.4.3.1 TM analysis of the Large Block Test 
The LBT was conducted on a rectangular block of near-surface fractured rock exposed (via 
excavation) at Fran Ridge. Deformation of the block at a scale of 1 mm and above was

 3-228 
monitored using MPBX instrumentation. Overall block deformations near the heater plane was 
closely correlated with temperature as discussed in Section 3.6.1.1. A series of pretest 
simulations of the TM behavior of the LBT were performed using a continuum model. 
Comparison of the observed and simulated profiles indicates that the predicted deformation 
below the heater plane has the same direction as the observed deformation, but the magnitude of 
displacement is over predicted (Blair and Wood, 1998). This may indicate that the value of 
thermal expansion used in the model was too large, and more recent field measurements confirm 
this. Above the heater plane the predicted and observed profiles diverge dramatically. The 
predicted profile shows a decrease in horizontal deformation with height that can be associated 
with the vertical thermal gradient imposed on the block. However, the observed horizontal 
deformation continues to increase with height and is independent of the thermal profile above the 
heater plane. Moreover, MPBX data from boreholes in the upper portion of the block show that 
most of the deformation occurs in discrete vertically oriented zones (Wilder, et al. 1997). This is 
attributed to opening of vertical fractures in this upper region. This result indicates that the LBT 
is more suitable for simulation using the distinct element technique. Efforts are ongoing in the 
use of a distinct element model to simulate the LBT. This model is based on the drift scale 
distinct element model discussed in Section 3.5. 
3.6.4.3.2 TM Analysis of the Single Heater Test 
The SHT is described in Section 3.6.1.2. MPBX instrumentation was installed both parallel and 
perpendicular to the heater in this test. During the test MPBX instruments oriented parallel to 
the heater registered mostly expansion of the rock mass, while the MPBX oriented perpendicular 
to the heater registered compression movement at the beginning of the heating, followed by 
expansion after about 40 to 50 days of heating. The SHT was simulated with a continuum TM 
model. Comparison of the MPBX data along the heater with and model simulations shows good 
correspondence during the test, although the measured displacements tend to be smaller than the 
pretest model predictions by about 20 percent during the heating cycle. However, several 
aspects of the SHT deformation data were not adequately simulated by the model. These 
primarily included localized offsets of anchors that were of opposite sense to the continuum 
predictions. 
Results indicate that the coefficient of thermal expansion measured in the field is about 50% 
lower than values measured on core samples in the laboratory. The general trendsfrom the 
initial compression, followed by general extension, and ending with the sharp extension after the 
heater is deenergizedare consistent between both laboratory data and model predictions. 
3.6.4.3.3 TM Analysis of Drift Scale Test. 
The DST is described in Section 3.6.1.3. MPBX data, for two locations above the center of the 
heated drift, have been most extensively analyzed. These correspond to locations approximately 
4 m into the rock above the crown of the drift. Comparison of observed and simulated 
deformations show good agreement for both sets of comparisons in terms of trend and 
magnitude. Further analysis of the DST deformation is underway using both continuum and 
distinct element techniques.

 3-229 
A plate loading test was also conducted in conjunction with the DST. This test applied 
horizontal load to opposite sides of a niche in the DST Alcove in order to determine the 
deformation modulus of the rock mass. Results showed that the heated side had a Youngs 
modulus of approximately 40 GPa, while the cool side had a modulus of approximately 12 MPa. 
This result was unexpected, but may be due to the proximity of the cool side. Additional plate 
loading tests are planned for this location, and further analysis of this result is underway. 
3.6.4.3.4 Coupled Analysis 
Much of the work on hydromechanical behavior of fractures has focussed on normal deformation 
of fractures and the cubic law. Recent work by Barton et al (1997) provides convincing evidence 
that shear deformation of fractures plays an important role in their hydromechanical behavior. 
Initial efforts to integrate shear deformation into THM analysis for YMP used the approach 
presented by Berge et al. 1998 in which a continuum model was used to predict zones where 
shear deformation could be expected on fractures of a given orientation. This approach was used 
to simulate the SHT and the DST and was applied to emplacement drift geometry in the 
Near-field Altered-Zone Models Report (Hardin 1998). 
This analysis was difficult to verify, given the data available from the field tests. For instance, 
the analysis of the DST indicates zones of increased permeability in areas where no 
instrumentation had been placed. 
These initial analyses were in 2-D for cross sections perpendicular to heat sources. Berge et al 
(1998) did a 3-D calculation using this approach for an emplacement drift analysis and found 
that the 3-D problem slip was predicted in some locations in the direction parallel to the drift. 
This technique has a serious limitation in that it only calculates where slip might occur, but does 
not indicate the amount of slip, nor does it provide for stress relaxation after slip, nor for dilation 
and other aspects of shear deformation. Subsequently, analysis using the distinct element 
method has been initiated as discussed in Section 3.5. 
Section 3.6.4.3.1 discussed the observed deformation of the LBT. These results have been used 
to inform a thermal-hydrological simulation of the LBT. In this calculation, a Dual Permeability 
Model (DKM) was used to simulate the temperature history of the LBT. One set of simulations 
utilized the YMP MS data set. Figure 3-107 shows that for this calculation, calculated and 
observed temperatures agree very well during the first 25 days of heating, but the model 
overpredicts temperatures during the period from 25 to 225 days (dotted line in Figure 3-107). A 
second model calculation was made that attempted to incorporate the opening of fractures. For 
this calculation, the fracture permeability used in the model was increased at Day 125 to simulate 
fracture opening. The solid line in Figure 3-107 shows the results. These results indicate that 
increasing the fracture permeability reduce the predicted temperature to values much closer to 
those observed in the test.

 3-230 
DTN: LL00031430242.094 
Source: CRWMS M&O 2000a, Figure 67 
Figure 3-107. Comparison of Two Simulations with Temperatures Measured During the 
Large Block Test. Increasing Fracture Permeability at 122 Days Causes 
Temperatures to Drop to Values Closer to Those Observed. 
It appears that the opening of fractures and associated increase in fracture permeability caused an 
increase in the amount of heat and vapor transported out of the portion of the block above the 
heaters, thus lowering the temperature. This provides an example of how thermal mechanical 
effects may influence thermal hydrologic behavior in a fractured rock mass. More refined 
calculations are underway. 
3.6.4.3.5 Summary of TM and THM Validation 
Validation of TM models is in the preliminary stage. The main avenue of validation of TM 
calculations to date has been through comparison of calculated deformation to line displacement 
measurements, and reasonable agreement has been found between continuum calculations and 
selected observations of deformation for the underground tests. However, more robust data 
describing field deformation is needed to improve confidence in the THM simulations. 
Moreover, observations made at the LBT indicate that a distinct-element approach is needed to 
accurately simulate the test. Deformation data for the SHT and DST also show behaviors that 
are not readily simulated using continuum models. These behaviors include localized extensions 
or contractions detected by a particular MPBX anchor that are not detected by adjacent anchors.

 3-231 
Validation of THM simulations using either the continuum or discrete element models is also in 
initial stages. THM continuum calculations have been done for the SHT (CRWMS M&O 
1999d) and DST (Blair et al, 1997) as discussed above. 
These studies indicate that pursuit of an alternative modeling approach is warranted for 
simulation of the TM and THM behavior of rock in the Near Field Environment. This 
alternative is the drift scale distinct element model as described in Section 3.5. This model 
provides for the inclusion of discrete fractures, and can predict localized fracture deformation in 
both normal and shear modes. Application of this model to the field scale thermal tests is 
ongoing. 
3.6.4.4 Summary of Validation from Analog Studies 
Two analogs, Eldora and Grants Ridge, show different hydrothermal convection. Eldora 
indicates there was a significant large scale (at least 60m) convecting hydrothermal system, 
whereas at Grants Ridge there was no evidence of pervasive hydrothermal convection. The 
Eldora stock developed under saturated conditions that are not representative of YM. Therefore, 
the Grants Ridge analog results, which indicates no pervasive hydrothermal convection, would 
be expected to be the better analog for NFE. 
The analogs for THC processes also vary. The Yucca Mountain self analog suggests potential 
for hydrothermal development of mineral suites dominated by analcime and illite/smectite and 
minor calcite and clinoptilolite (based on trends shown on Figure 3-99(b) that show other 
minerals dropping out with depth-temperature). 
The Banco Bonito, Valles and Grants Ridge show minimal (10 m) hydrothermal alteration, 
which is interpreted to be due to unsaturated conditions at the time of contact. This is consistent 
with THC model results. 
Finally, analysis of the Paiute Ridge indicate that THC analyses of fracture plugging (mineral 
cap), have been consistent with this analog study.

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 4-1 
4. RELATIONSHIP TO NRC ISSUE RESOLUTION STATUS REPORTS 
The NRC has indicated it plans to structure its review of issues that are subjects of Process 
Model Reports (PMRs) around the NRCs KTIs and Issue Resolution Status Reports (IRSRs). 
This chapter of the PMR describes how the acceptance criteria in the IRSRs relevant to the 
NFE PMR have been addressed. 
4.1 SUMMARY OF THE KEY TECHNICAL ISSUES 
As part of the review of site characterization activities, the NRC has undertaken an ongoing 
review of information on Yucca Mountain site characterization activities to allow early 
identification and resolution of potential licensing issues. The principal means of achieving this 
goal is through informal, prelicensing 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 prelicensing issue resolution on those topics most critical to postclosure 
performance of the potential geologic repository. These topics are KTIs. Each KTI is 
subdivided into a number of subissues. The KTIs are: 
 Activities Related to Development of the Environmental Protection Agency (EPA) 
Standard 
 Container Lifetime and Source Term 
 ENFE 
 Igneous Activity 
 Radionuclide Transport 
 Repository Design and Thermal Mechanical Effects 
 Structural Deformation and Seismicity 
 Thermal Effects on Flow (TEF) 
 Total System Performance Assessment and Integration (TSPAI) 
 Unsaturated Zone (UZ) and Saturated Zone (SZ) Flow Under Isothermal Conditions. 
Identifying KTIs, integrating their subissues into a risk informed approach, and evaluating their 
significance for postclosure performance help ensure that NRCs attention is focused on 
technical uncertainties that 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 understanding future

 4-2 
repository safety. The IRSRs are the primary mechanism that the NRC staff uses to provide 
feedback to the DOE on the status of the KTI subissues. IRSRs focus on NRC acceptance 
criteria for issue resolution and the status of issue resolution, including aspects of agreement or 
disagreement. IRSRs also communicate comments or questions from the NRC staff. Open 
meetings and technical exchanges between NRC and DOE, provide additional opportunities to 
discuss issue resolution, identify areas of agreement and disagreement, and develop plans to 
resolve any disagreements. 
Additional issues include those identified by the Performance Assessment Peer Review Panel, 
the ACNW, the Total System Performance System Assessment - Viability Assessment 
(TSPA-VA), the Near-Field Expert Elicitation, and others, as described in Section 2.4 of this 
document. Generally these concerns are closely related to the KTI subissue acceptance criteria. 
4.2 RELATIONSHIP OF THE NEAR-FIELD ENVIRONMENT PMR TO THE KTIs 
The following sections describe the KTIs and the subissues relevant to the NFE PMR. 
Table 4-1 lists the KTIs that contain subissues relevant to the NFE PMR. The relevant subissues 
are shown in italics. Appendix D lists the acceptance criteria relevant to the NFE PMR and 
provides a description of the PMR approach. In many cases, a given PMR may only partially 
address acceptance criteria. For acceptance criteria relevant to the NFE PMR that are addressed 
in more than one PMR, cross-references to other PMRs are provided. For all ENFE IRSR 
acceptance criteria, pointers to this and other PMRs that contain details relevant to ENFE IRSR 
acceptance criteria are provided in Table 4-2.

 4-3 
Table 4-1. Issue Resolution Status Report/Key Technical Issues Related to the NFE PMR 
Issue Resolution Status Report/Key 
Technical Issues Subissues* 
ENFE Effects of Coupled THC Processes on Seepage and Flow 
Effects of Coupled THC Processes on the Waste Package 
Chemical Environment 
Effects of Coupled THC Processes on the Chemical Environment 
for Radionuclide Release 
Effects of Coupled THC Processes on Radionuclide Transport 
Through Engineered and Natural Barriers 
Coupled THC Processes Affecting Potential Nuclear Criticality in 
the Near-Field (Addressed in Topical Report) 
Thermal Effects on Flow (TEF) Is the U.S. Department of Energy TH testing program, including 
performance confirmation testing, sufficient to evaluate the 
potential for thermal reflux to occur in the near field? 
Is the U.S. Department of Energy TH modeling approach 
sufficient to predict the nature and bounds of thermal effects on 
flow in the near field? 
Does the U.S. Department of Energy Total System Performance 
Assessment (TSPA) adequately account for thermal effects on 
flow? 
Repository Design and Thermal-Mechanical 
Effects 
Implementation of an Effective Design Control Process Within The 
Overall Quality Assurance Program 
Design of the Geologic Repository Operations Area for the effects 
of seismic events and direct fault disruption 
Thermal-Mechanical Effects on underground facility design and 
performance 
Design and long-term contribution of repository seals in meeting 
postclosure performance objectives 
Total System Performance Assessment and 
Integration (TSPAI) 
System description and demonstration of multiple barriers 
Scenario analysis 
Model abstraction 
Demonstration of the overall performance objective 
*Subissues relevant to the NFE PMR are shown in italics 
The definition of the NFE includes the in-drift environment and the immediately surrounding 
host rock. This PMR describes models used to evaluate the rock part of the NFE, and the EBS 
PMR (CRWMS M&O 2000g) describes models used to evaluate the in-drift part of the NFE. 
The ENFE KTI (NRC 1999a) subissues are addressed in various PMRs. Table 4-2 provides a 
correlation between the ENFE KTI subissues and the PMRs that address them. The remainder of 
this chapter and Appendix D of this PMR provide detailed explanations describing how the 
acceptance criteria relevant to the Near-Field Environment PMR have been addressed.

 4-4 
Table 4-2. PMRs Related to ENFE Issue Resolution Status Report/Key Technical Issue Subissues 
NRC Key Technical Issue - Evolution of the 
Near-Field Environment Subissues Process Model Reports Addressing Subissue 
Effects of Coupled THC Processes on Seepage 
and Flow 
Unsaturated Zone Flow and Transport 
Engineered Barrier System Degradation, Flow and 
Transport 
Near Field Environment 
Effects of Coupled THC Processes on the Waste 
Package Chemical Environment 
Engineered Barrier System Degradation, Flow and 
Transport 
Near Field Environment 
Effects of Coupled THC effects on the Chemical 
Environment for Radionuclide Release 
Unsaturated Zone Flow and Transport 
Engineered Barrier System Degradation, Flow and 
Transport 
Effects of Coupled THC Processes on 
Radionuclide Transport Through Engineered and 
Natural Barriers 
Unsaturated Zone Flow and Transport 
Engineered Barrier System Degradation, Flow and 
Transport 
Near Field Environment 
Coupled THC Processes Affecting Potential 
Nuclear Criticality in the Near-Field 
Criticality is addressed in a Topical Report and supporting 
documents 
4.2.1 Evolution of the Near-Field Environment 
The objective of the ENFE KTI (NRC 1999a) is to assess all aspects of the evolution of the 
near-field geochemical environment that have the potential to affect performance of the proposed 
repository. The near-field geochemistry will be perturbed from ambient conditions by variations 
in temperature and pressure associated with the heat production of the waste, introduction of 
foreign materials into the mountain, variations in fluid flow, and consequent chemical reactions. 
Coupled thermal-hydrologic-chemical (THC) and thermal-chemical processes can cause changes 
in parameter values and conceptual models used in various modules of performance assessment 
computer codes. The consequent effects on performance from the ENFE are expressed as the 
results of coupled processes. 
4.2.1.1 ENFE IRSR Subissue 1 
This subissue is entitled The Effects of Coupled THC Processes on Seepage and Flow. The 
acceptance criteria in this section are designed to ensure that coupled THC effects on the 
quantity and chemistry of seepage into drifts are adequately estimated and that they are 
appropriately considered in assessments of repository performance. Important factors affecting 
seepage and flow include: groundwater flux, fracture density and physical properties, presence 
or absence of fracture coatings, rock heterogeneity, moisture content, existence of fast pathways, 
and fluid-density gradients. 
Chapter 3 of this PMR describes the process-level models, model abstractions and supporting 
analyses that address the near-field environment processes. Section 3.3 describes the models 
used to evaluate the potential effects of coupled THC processes on permeability and porosity 
within the NFE, which are then used in evaluations of UZ flow and transport. Temporal and

 4-5 
spatial variations of properties or conditions used were consistent with the Unsaturated Zone 
Flow and Transport (UZ F&T) PMR (CRWMS M&O 2000f). In addition, spatial and temporal 
variations in conditions that arise from the emplacement of waste and the EBS were considered. 
Sections 3.2.3 and 3.4 of this PMR describe the abstraction of the models used to evaluate the 
potential effects of coupled THC processes on properties within the NFE that might impact 
seepage chemistry and UZ flow and transport in TSPA. 
Seepage and flow are also covered in the UZ F&T PMR (CRWMS M&O 2000f). The NFE 
PMR contributes information to the UZ F&T PMR (CRWMS M&O 2000f) relative to 
permanent changes to the permeability and porosity structure. Changes can occur due to 
mechanical closure or opening of fractures during the period when thermal processes might 
mobilize water. However, assessments of drip-shield lifetime (CRWMS M&O 2000o, 
Figure 3-84) indicate no seepage through the drip shield that would allow water to contact the 
waste packages for a period of time that exceeds the period during which thermal mobilization of 
water might occur. Therefore, mechanical impacts on flow of water during this period are not of 
primary importance. 
THC couplings under consideration for the engineered systems are covered in the EBS PMR 
(CRWMS M&O 2000g), and the Waste Form Degradation (WFD) PMR (CRWMS 
M&O 2000ab). THC couplings for the natural system are covered by both the UZ F&T PMR 
(CRWMS M&O 2000f) and this PMR. 
4.2.1.2 ENFE IRSR Subissue 2 
This subissue is entitled Effects of Coupled Thermal-Hydrologic-Chemical Processes on the 
Waste Package Chemical Environment. The acceptance criteria in this section are designed to 
ensure adequate consideration of coupled THC processes affecting the waste package chemical 
environment in the assessment of repository performance. The EBS PMR (CRWMS 
M&O 2000g) discusses work performed that is related to the majority of the acceptance criteria 
described in this subissue. The NFE PMR has only a secondary role in resolution of this issue. 
It addresses property changes that might impact the chemistry of water within the unsaturated 
zone that seeps into the drifts. These property changes are input to the unsaturated zone 
analyses. The results, the chemistry of water seeping into drifts, are input to the EBS PMR 
(CRWMS M&O 2000g). 
THC interactions between the natural and engineered systems are primarily covered within the 
EBS and UZ F&T PMRs (CRWMS M&O 2000g and 2000f). The EBS and WPD PMRs 
(CRWMS M&O 2000g and 2000ac) determine the chemistry of fluids that result from THC 
couplings between the drift and waste package materials. They also provide the water chemistry 
information to the unsaturated zone to analyze effects on flow and transport. The EBS and 
WPD PMRs (CRWMS M&O 2000g and 2000ac) report the evaluations of the resulting 
chemistry, the waste package chemical environment, and report on the associated abstractions. 
They also provide the descriptions of assumptions, approximations, simplifications, and 
abstractions used in those assessments. The UZ F&T PMR (CRWMS M&O 2000f) provides the 
descriptions of models used in establishing seepage water chemistry, and reports the seepagewater 
chemistry that is used as input to the EBS and WP models.

 4-6 
Section 3.3 of this PMR addresses models used to evaluate the potential effects of coupled THC 
processes on near-field chemical properties. These models provide the framework (or inputs) for 
the UZ F&T and EBS PMRs (CRWMS M&O 2000f and 2000g) to evaluate THC coupled 
processes at the DS, predict flow and transport behavior for specified thermal- loading conditions, 
and predict the chemistry of waters and gases entering the emplacement drifts. Sections 3.2.3 
and 3.4 describe the abstraction of the models used to evaluate the potential effects of coupled 
THC processes on changes in mineralogy and deposition of salts. 
4.2.1.3 ENFE IRSR Subissue 3 
This subissue is entitled The Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
the Chemical Environment for Radionuclide Release. The acceptance criteria in this section are 
designed to ensure adequate evaluation of the chemical environment for radionuclide release and 
ensure that coupled THC processes affecting this chemical environment have been appropriately 
considered in the assessment of repository performance. 
Slow rate of release of radionuclides from the waste form has been identified as a key factor for 
meeting the objective of acceptably low annual doses to a person living near the site 
(NRC 2000). Radionuclide release rates and solubility limits constitute one of the NRC key 
elements of subsystem abstraction for a performance assessment. Radionuclide release from 
waste forms and from the EBS will depend on the chemical environment, which will be 
conditioned by coupled THC processes. The chemical environment for radionuclide release 
must be adequately evaluated and coupled THC processes must be appropriately considered. 
Acceptance criteria addressed by this subissue are described by the EBS and WFD PMRs 
(CRWMS M&O 2000g, 2000ab, and 2000ac). There are no models of coupled effects on 
radionuclide release covered in this PMR. 
4.2.1.4 ENFE IRSR Subissue 4 
This subissue is entitled The Effects of Coupled Thermal-Hydrologic-Chemical Processes on 
Radionuclide Transport through Engineered and Natural Barriers. The acceptance criteria in 
this section are designed to ensure adequate evaluation of the effects of coupled THC processes 
on the transport of radionuclides through engineered and natural barriers, and ensure that these 
effects have been appropriately considered in the assessment of repository performance. 
Radionuclide concentration-reduction during transport through engineered and natural barriers is 
considered a key performance attribute of the proposed repository (NRC 2000). Distribution of 
mass flux between fracture and matrix, and retardation of radionuclides in fractures in the UZ 
and in the SZ constitute three of the NRC key elements of subsystem abstraction for performance 
assessment. Coupled THC processes affect each of these abstractions. 
Radionuclide transport issues are reported primarily in the UZ F&T PMR (CRWMS 
M&O 2000f). The EBS, WFD, and WPD PMRs (CRWMS M&O 2000g, 2000ab, and 2000ac) 
provide input to UZ analyses relative to the chemistry of water, and the amount and form of 
radionuclides released from the drifts. As such, this subissue is discussed principally in the 
UZ F&T PMR (CRWMS M&O 2000f) with some discussion in the EBS, WFD, and 
WPD PMRs.

 4-7 
The NFE PMR discusses issues of precipitation and dissolution of minerals within the fracture 
system of the near-field, which could affect transport of radionuclides through this region. The 
calculation of these effects remains to be completed. The effects of the effluent chemistry, as 
described in the EBS, WFD, and WPD PMRs, are included in UZ transport calculations 
described in the UZ F&T PMR. 
4.2.2 Thermal Effects on Flow (TEF) 
The objective of the TEF KTI (NRC 1999b) is the estimation of temperature, moisture content, 
and humidity at the waste package surface, and estimation of temperature and thermally driven 
water flux with respect to the transport of radionuclides from failed waste packages. 
Redistribution of moisture driven by heat may result in extended periods of dryness in the 
proposed repository. Redistribution of moisture driven by heat could result in channeling 
moisture toward the waste package. It is necessary to understand the spatial and temporal effects 
of the thermal load on liquid-phase and gas-phase fluxes, and resultant effects on temperature 
and relative humidity of the waste package environment at the proposed repository, to have 
confidence in predictions of containment and long-term waste isolation. 
4.2.2.1 TEF IRSR Subissue 1 
This subissue relates to the sufficiency of DOEs thermohydrologic testing program to provide 
information used to verify conceptual models that DOE will use to evaluate thermally-driven 
flow in the near field. Subissue 1 asks, 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? The acceptance criteria in this section are designed 
to critically evaluate the sufficiency of the thermohydrologic testing program to provide 
information needed to verify conceptual models used to predict thermally driven flow in the 
near-field (NRC 1999b). 
Section 3.6 of this PMR describes the thermal tests, including the Single Heater Test (SHT), the 
DST, and the LBT. These tests were designed specifically to test thermal-hydrological (TH) 
process models. The LBT and DST were based on the VA design, and therefore tested reflux for 
that design. While repository design changes have occurred, this testing remains applicable to 
testing the conceptual and numerical models that describe refluxing. As described in 
Section 3.6, a specific goal of the LBT was observation of condensate refluxing above a boiling 
zone. Also, the Updated In Situ Thermal Testing Program Strategy (CRWMS M&O 1997c) 
states that the LBT was intended to address the need for information on drainage and reflux by 
fracture flow. The LBT has been completed and the results, including refluxing of condensates, 
are described in Section 3.6.1.1 of this PMR. 
4.2.2.2 TEF IRSR Subissue 2 
This subissue relates to the sufficiency of DOEs thermohydrologic modeling approach 
(process-level models) to predict thermally-driven flow in the near- field. Subissue 2 asks, 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? The acceptance criteria in this section

 4-8 
are designed to critically evaluate the sufficiency of the thermohydrologic modeling approach 
(process-level models) to predict thermally-driven flow in the near-field (NRC 1999b). 
This PMR provides input to coupled process-induced changes in the parameters used in those 
analyses. Sections 3.2.3, 3.3, 3.4, and 3.5 address the drift-scale coupled-process models and 
abstractions used to evaluate those parameter changes. TH analysis and modeling in this PMR 
are described in Sections 3.2.3 and 3.6 and the supporting Thermal Test AMR (CRWMS 
M&O 2000a). This subissue is also addressed in the UZ F&T and EBS PMRs (CRWMS 
M&O 2000f and 2000g). 
4.2.3 Repository Design and Thermal-Mechanical Effects 
The primary issue of the Repository Design and Thermal-Mechanical Effects (RDTME) KTI 
(NRC 1999c) is the adequacy of design, construction, and operation of the geologic repository 
operations area, including seals for the shafts and boreholes, to meet the preclosure and 
postclosure performance objectives, taking into consideration the long-term thermal-mechanical 
(TM) processes. 
Consideration of the time-dependent TM coupled response of a jointed rock mass is central to 
repository design and necessary for performance assessment (PA) at the Yucca Mountain site. 
Consequently, that is the focus of both the preclosure and postclosure elements of this KTI. 
Design for adequate postclosure performance requires an understanding of the TM response of 
the jointed rock mass over an anticipated compliance period of 10,000 yr. Long-term TM 
response is anticipated to influence hydrological properties in the vicinity of the emplacement 
drifts, waste package degradation, radionuclide release within the EBS, performance of seals, 
and flow into and out of the emplacement drifts. 
The RDTME IRSR Subissue 3 has three important components: (i) stability of the underground 
excavations with regard to safety during the preclosure period, waste retrievability, and potential 
adverse effects on emplaced wastes; (ii) effect of seismically induced rockfall with respect to 
waste package performance; and (iii) changes in emplacement-drift geometries and hydrological 
properties surrounding emplacement drifts due to TM perturbation of the rock mass. All of these 
components have broad design and performance implications. 
Section 3.5 of this PMR describes the results of thermal-hydrological-mechanical (THM) 
calculations performed to estimate bounds on changes in fracture permeability in rock 
surrounding emplacement drifts. The results of these calculations are input to UZ F&T PMR 
(CRWMS M&O 2000f). Drift stability, rock fall and drift geometries are all covered in the 
EBS PMR (CRWMS M&O 2000g). This PMR considers changes in rock- mass properties, 
specifically hydrologic properties, as a result of THM. 
4.2.4 Total System Performance Assessment and Integration (TSPAI) 
The objective of the TSPAI KTI (NRC 2000) is to describe an acceptable methodology for 
conducting performance assessments of repository performance and using these assessments to 
demonstrate compliance with the overall performance objective and requirements for multiple 
barriers. The acceptance criterion applicable to this PMR is described in the following section.

 4-9 
4.2.4.1 TSPAI IRSR Subissue 1 
This subissue focuses on the demonstration of multiple barriers and includes: (i) identification of 
design features of the EBS and natural features of the geologic setting that are considered 
barriers important to waste isolation; (ii) descriptions of the capability of barriers designed to 
isolate waste; and (iii) identification of degradation, deterioration, or alteration processes of 
engineered barriers that would adversely affect the performance of natural barriers. Acceptance 
criteria addressing multiple barriers will be developed and issued in Revision 3 of the 
TSPAI IRSR. 
Subissue 1 also addresses transparency and traceability of the analyses. The acceptance criteria 
describe staffs expectation of the contents of DOE=s TSPA and the supporting documents. They 
focus on those aspects of the TSPA that will allow for an independent analysis of the results. 
This PMR was carefully structured to be complete, clear, and consistent. Reviews of this 
document included checks for completeness, clarity and consistency. Descriptions are provided 
of process models and, if appropriate, model abstractions including summaries of data and 
assumptions used to construct models. The PMR and supporting AMRs provide descriptions of 
the basis for decisions and assumptions made during the abstraction process. In addition, data 
and parameters used in the development of the AMRs are clearly identified and details regarding 
the pedigree of data are provided. 
4.2.4.2 TSPAI IRSR Subissue 2 
This subissue focuses on the attributes of an acceptable methodology for identifying, screening, 
and selecting features, events and processes (FEPs) for inclusion in the total system performance 
assessment (TSPA). 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 into the TSPA. This is a key factor in ensuring completeness of 
the TSPA. The acceptance criteria described in this subissue are applicable to every PMR that 
contains an AMR describing FEPs. 
As described in Section 2.5, a systematic method was applied to identify and screen FEPs for 
NFE. 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.

 4-10 
INTENTIONALLY LEFT BLANK

 5-1 
5. SUMMARY AND CONCLUSIONS 
The NF is the part of the UZ that is subjected to the influence of heat from waste such that 
significant alterations of the hydrological, mechanical, and mineralogical properties may occur. 
Physically, the NF includes the emplacement drift and the engineered components in the drift 
that are normally called the EBS. In the process model reports (PMRs), the EBS is treated 
separately from the NF. In terms of the thermal-hydrological-chemical-mechanical (THCM) 
processes of a potential repository, the EBS, the NF, and the unsaturated zone (UZ) are 
intimately coupled. The UZ will provide the initial and boundary conditions for the NF. The NF 
in turn provides boundary conditions, such as the impacts on seepage of water into the drift, to 
the EBS. On the other hand, the EBS provides the heat source to the NF. During the heating 
phase of a repository, the NF will affect the UZ by moving moisture into it. And during the 
heating phase, convection cells may connect the EBS, the NF and the UZ together. During the 
cooling phase, the UZ may feed some of the moisture back to the NF. The thermal-hydrologicalchemical 
conditions within the EBS are strongly influenced by the NF. The introduced materials 
and their corrosion products in the EBS can chemically change the transport properties in the NF. 
And the transport of any radionuclides that may be released from waste packages, from the EBS 
to the accessible environment, will pass through the NF. The relationship among the PMRs that 
deal with those three components of a repository is discussed in the sections below. 
5.1 THE UZ FLOW AND TRANSPORT INPUTS AND THE NFE MODELS 
There are two AMRs in this PMR that dealt with flow and transport modeling. Those AMRs are 
the Thermal Test AMR (CRWMS M&O 2000a) and the THC Process AMR (CRWMS 
M&O 2000b). Both AMRs used the DK model with the active-fracture submodel, as described 
in the Conceptual and Numerical Models for UZ Flow and Transport AMR (CRWMS 
M&O 2000h). The DS property set developed in the UZ F&T was used throughout the analyses 
(CRWMS M&O 2000f, Section 3.6.4.1). The AMRs that feed this PMR and the UZ F&T PMR 
use the same geologic framework, infiltration rates, and the climate states in modeling the THC 
processes. There was minor difference in treating the initial water-saturation condition in the 
rock mass of the DST among the two model analyses in the Thermal Test AMR, with the NUFT 
analysis using the measured 92 percent as the initial water saturation of the tsw34 (CRWMS 
M&O 2000a, Table 4-3), and the TOUGH2 analysis using a 1-D column model to calculate the 
initial water saturation in the tsw34 (94 to 95 percent) (CRWMS M&O 2000a, p. 50). 
5.2 THE REPOSITORY DESIGN INPUTS AND THE NFE PMR 
The TTTH AMR and the DST part of the DSCP AMR deal with analysis of the thermal field test 
results, therefore no repository design inputs were considered in the models. The THC Seepage 
part of the DSCP AMR took repository design inputs in its model. Among the design inputs, 
two time-periods of the repository design were considered: (1) a 50-yr. preclosure period during 
which 70 percent of the heat released by the waste packages is removed by ventilation, and 
during which there is no drip shield and backfill, and (2) a postclosure period following the preclosure 
period and extending to 100,000 years, during which a drip shield and backfill are 
installed above the waste packages, and no heat is removed by ventilation. Other design inputs 
of the TSPA-SR, Rev. 0, Basecase design were incorporated (CRWMS M&O 2000b, p. 27 and 
Figure 1).

 5-2 
5.3 THE EBS INPUTS AND THE NFE PMR 
At the current stage of the coupling between this PMR and the EBS PMR, it is mostly forward 
coupling. The AMRs, especially the Water Distribution and Removal AMR (CRWMS 
M&O 2000u), the Physical and Chemical Environment AMR (CRWMS M&O 2000v), and the 
Thermohydrology AMR (CRWMS M&O 2000k), of the EBS PMR modeled the NFE in order to 
calculate the THC within the EBS. The inputs from the NFE TH model were included in those 
AMRs. The EBS AMRs include calculated in-drift processes to determine environmental 
conditions at the engineered barriers. These calculations included components of the EBS, such 
as the drip shield, backfill, invert, and waste packages; the emplacement drift layouts in a 
repository; waste package layout within an emplacement drift; and heat output of waste 
packages. These components were also used to determine the heat source for the NFE models. 
A back-coupling from the EBS PMR to the NFE PMR would require considering the effect of 
the TMHC conditions in the EBS on the THC in the NF. For example, corrosion products from 
the introduced materials, including the waste packages, in the EBS may change the hydrological 
and chemical properties of the rock mass below the invert of a drift. Another example is water 
that seeps from the crown of a drift and flows through components in the EBS may have very 
different chemical properties than the water in the rock mass above the drift. This water may 
enter the rock mass below the drift via the drift invert. Those back-couplings from the EBS to 
the NFE have not been established. It is possible that the effect of back-coupling on the NFE is 
secondary. 
5.4 VALIDITY OF COUPLED PROCESS MODELS FOR THE NEAR-FIELD 
ENVIRONMENT 
The NFE evolves in response to highly coupled THCM processes. These processes are often 
coupled in complex ways that include back-coupling of process interactions. The interactions 
are largely caused by the introduction of heat to the system by the emplacement of waste. 
Therefore, the coupling of processes that contribute to the evolution of the NFE, and thus the 
NFE, are dependent on the design and operational features of the repository. The analyses 
summarized in this PMR were performed using the EDA-II design. The analyses were 
performed by considering coupling between processes such as thermal-hydrological, without 
including full or direct coupling of all of the THCM processes within the same model. The 
results of the TH, THC, and THM models will be summarized in this section. In addition, 
although a rigorous evaluation of the fully coupled THCM processes is not available, a 
discussion included presenting the synthesis of fully coupled THCM that can be derived from the 
TH, THC, and THM evaluations. Finally, this section discusses the level of confidence that has 
been established for the models, as well as the conclusions based on those models. This latter 
discussion will rely on the results of ongoing in situ thermal tests, and their use for model 
validation and property-set determinations, as reported in this PMR. 
To support the following discussion, the interaction-matrix approach is used to conceptually 
identify the coupling of processes in the NFE. This approach assists in discussing the results of 
the models and shows how those results were extended to consider THCM implications. The 
interaction matrix shown on Figure 5-1 identifies the key components of the NFE process models 
(thermal-hydrologic-chemical-mechanical), along the diagonal, and the interactions of processes

 5-3 
are shown off-diagonal. Along the left-hand side of this matrix are examples of the types of 
property inputs needed by the models and along the top are examples of the site characteristics 
needed by the models. This matrix does not attempt to show all components and all couplings, 
rather it focuses on the key parameters, components, and processes that are discussed in this 
PMR. Forward-coupling is shown to the right of the diagonal, and back-coupling is shown to the 
left of the diagonal. 
Because TH couplings are the basis for all of the other couplings, the TH model results will be 
discussed first. The major issues that are addressed by the TH part of the NFE PMR are the 
temperatures and moisture-distribution changes (saturation and water movement) within the 
NFE. 
As shown on the interaction matrix, Figure 5-2, the first part of the TH model is the 
determination of the thermal response. As noted in the matrix, the thermal response model 
determines temperatures based on inputs of design and repository information, along with the 
thermal properties coupled with the hydrologic model, which determines moisture distributions 
based on the thermal input. As shown in the interaction matrix, the TH model includes a 
forward-coupling from the thermal response to the moisture conditions and then is back-coupled 
to the thermal response. This coupling is actually included in a single TH model and associated 
codes. However, it is shown explicitly here to distinguish it from the thermal response models 
that consider only conductive heat transfer. 
The TH model temperature predictions for the NFE, at about 600 years after emplacement and 
for the mean- infiltration case, are summarized in Figures 3-7 through 3-11 (Multi-scale TH 
model without backfill), and in Figure 3-28 (THC model with backfill). The temperatures at 
600 years in Figure 3-28 represent maximum temperatures because assumed climate change 
results in infiltration increases after 600 yr. Waste heat decreases with time. The maximum 
temperature for the crown of the drift occurs at about 100 yr. 
TH models predict above-boiling temperatures extending approximately 10 meters into the rock 
of the NFE. Temperatures are elevated to approximately 90C, extending about 30 meters above 
the drift. The temperature distributions are not symmetrical around the drift. The boiling 
temperature only extends above the drift about 5 meters, but extends below the drift nearly 
13 meters. This is illustrative of the interactive coupling between the effects of waste placement 
in the drift, and of the effects of hydrologic response on the temperatures. (Two detailed models 
were used in the NFE to determine the TH response. These were the TH models included in the 
multi-scale abstraction and the TH parts of the THC models. The THC model did not consider 
the details of convection, radiation etc. within the drifts. The abstraction models were based on 
the multi-scale models that included these details. The multi-scale models are described within 
the EBS PMR. The TH results of the two model approaches were compared in Section 3.2.3.4 
and found to be fairly consistent).

 5-4 
Source: Modified from Wilder 1997, Figure 1-5 
Figure 5-1. Interaction Matrix Showing Coupling of NFE Processes

 5-5 
Source: Modified from Wilder 1997, Figure 4-1 
Figure 5-2. Interaction Matrix Showing TH Coupling

 5-6 
The TH model is also used to determine the hydrologic response to the thermal regime. The 
elevated temperatures cause redistribution of moisture such that the saturation within both 
fractures and matrix are changed within the NFE. The NFE model predictions for 600 years, as 
shown on Figure 3-28, define a zone where saturation is decreased from the original ambient 
saturation. A zone of 10 percent or less saturation extends for approximately 20 m below the 
drift and 18 m horizontally from the drift. This zone extends less than 10 m above the drift. 
On the TH interaction matrix (Figure 5-2), the back-coupling indicates that the effects of latent 
heat and heat-pipes, and of saturation changes (not shown on the figure) are fed back into the 
thermal model. One of the TH characteristics of the coupling is the difference between thermal 
conductivity of saturated and dry rock; this coupling is reflected in the forward- and 
back-coupling shown on the interaction matrix. 
The third diagonal entry (RH) on the TH interaction matrix (Figure 5-2) is not covered within the 
NF PMR, but is part of the TH model shared by the NFE and EBS PMRs. It will not be 
discussed here. 
The next coupled model is the THC model. The major issues that are addressed in the THC 
model for the NFE are changes in hydrologic properties due to dissolution or precipitation of 
minerals, or due to rock-water interaction, and deposition of salts or other minerals that might 
impact the chemistry of percolating water. 
As noted on the THC interaction matrix (see Figure 5-3), the water chemistry must first be 
determined. To determine the evolving water chemistry, the ambient chemistry must first be 
determined. The chemistry of percolating (ambient) water is determined and reported within the 
UZ F&T PMR (CRWMS M&O 2000f). This ambient chemistry determination is fed from that 
PMR to the NFE and EBS PMRs and associated AMRs water chemistry is determined by the 
THC model, as reported in the Drift Scale Coupled Process Model AMR (CRWMS 
M&O 2000b). As noted in Section 3.3.2.4, the THC model uses as an input the ambient water 
chemistry determined in the UZ F&T PMR studies. The model also uses geoche mical properties 
databases of thermodynamic and kinetic or rate properties for chemical species. From these 
inputs, coupled with the temperature and saturation conditions determined in the TH submodels, 
the THC model calculates the evolution of water chemistry with time. 
The chemistry, as calculated, is then abstracted along with TH and other coupled processes as 
reported within the Abstraction of DSCP AMR (CRWMS M&O 2000b). The results of these 
analyses are reported in Table 3-11 for the four time periods considered (0-50 years, 
50-1,000 years, 1,000-2,000 years, and 2,000-10,000 years). As can be observed, the 
constituents in the water at the drift-wall decrease over the period from 50 to 1,000 yr. This 
may be partially an artifact of drying of this region that removes the water. Most of the chemical 
constituents return to values that are similar to those prior to closure of the repository at 50 yr. 
This implies that there are not long-term perturbations in water chemistry, with the possible 
exception of the bicarbonate ion (HCO3
-) and Silica (SiO 2). Figure 3-29 shows that there is a 
significant drop in CO2 concentrations in fractures during drying. The THC seepage simulations 
indicate that there may be an increase in CO2 gas and carbonate concentrations around the drift 
during rewetting. The pH of the water drops during the period from closure until around 
10,000 years, when the pH begins to slowly return to higher values.

 5-7 
Source: Modified from Wilder 1997, Figure 4-9 
Figure 5-3. Interaction Matrix Showing THC Coupling

 5-8 
The issue of changes to hydrologic properties (due to the next diagonal element, dissolution and 
precipitation, on the interaction matrix [Figure 5-3]) was determined in the THC model based on 
the interaction of constituents in the water with the rock and in response to temperatures. 
Specifically, the models determined dissolution and precipitation of minerals that would change 
the porosity and permeability of the fracture system. The temperature-dependent solubilities of 
calcite and silica, in particular, are of interest. 
The model results indicate that fracture porosity changes primarily due to calcite precipitation 
and that the change is relatively small (less that 1 percent of the initial porosity). Calcite 
deposition is expected to occur over wider zones than silica deposition. Therefore, a decrease of 
porosity due to calcite is not likely to occur in a very narrow zone. These analyses, and a cubic 
law to relate aperture to permeability, suggest that reduction in permeability due to mineral 
deposition within fractures would be negligible, less than the range of permeability within YM. 
The back-coupling for changes in hydrologic properties are shown on the interactive matrix 
(Figure 5-3) in the changed hydrologic properties that feed to the hydrologic response model, 
which forward-feeds volume of water to the dissolution and precipitation model and back-feeds 
to the thermal response model. As can be seen, the coupling becomes much more involved. The 
THC model accounts for this coupling by off-line feedback between mineral dissolution and 
precipitation, and porosity, permeability and capillary pressure changes. It was noted that silica 
precipitation is subordinate to calcite. 
The final aspect of concern for the NFE is that of the geomechanical responses and how these 
couple to other processes within the NFE. The THM coupled model essentially uses thermal 
response models to determine the temperatures with time. Those temperatures are then coupled 
to rock deformation and resulting stress responses. On the THM interaction matrix (Figure 5-4) 
this is the box at the upper right-hand corner. Although other geomechanical coupling (i.e., 
water impacts on crack growth) exist, they were considered of secondary importance to the 
deformations. Based on the calculated deformations, impacts on permeability were assessed. 
After 55 years, representing the highest heating gradient period, it was found that permeability 
increases of about 40 percent might be experienced above the drifts, due to normal deformations 
that would be expected to be reversible as the rock cooled, and increases from 3 to 6.5 times 
pre-heat values due to shear displacements. There are no established constitutive relationships to 
combine the effects of decreased permeability from both types of deformations. The increases 
will be at least equal to those related to the shear deformations. After 1,000 years, the 
permeability increases, due to normal deformations, to approximately twice the pre-emplacement 
value in the regions above the drifts, and to about a 40 percent increase in the pillar areas. 
However, there is projected to be about an order of magnitude increase in permeability above 
and below the drift due to shear displacements at 1,000 yr. 
The back-coupling of these permeability changes into the NFE models should be as shown on 
the interaction matrix. However, the models are not fully coupled at this time. Back-coupling 
could be assessed by inputting the results into the property sets used in the hydrologic model and 
then repeating the calculations. This has not been done to date.

 5-9 
Figure 5-4. Interaction Matrix Showing THM Coupling

 5-10 
The THCM responses can be assessed to some degree by comparison to the results of the THC 
model. The THC model includes the backfeeds from the C to the TH models. The results of the 
THC model indicate a small decrease in permeability (about 3 percent) above the drifts. This is 
of similar magnitude, but opposite direction, as the projected increases (about 40 percent) from 
the normal-deformation geomechanical responses. Thus, for regions above the drift, it can be 
concluded that the coupled effects, if including the normal-deformation components, would 
cancel-out. However, it is not known whether the much larger increased permeability from the 
shear deformations would then cause sufficient differences in the TH responses that the THC 
responses would be impacted. As shown in Figures 3-40 and 3-41, the regions of maximum 
potential for THM permeability enhancement are zones extending about 10 m above and below 
the drifts, with less of a potential increase along a horizontal plane extending through the drift 
centerline. The very minimal changes from THC (see Figure 3-33) indicate less than 1 percent 
decrease in permeability in a horizontal region about 15 to 18 m above the drift. 
While these changes may suggest the potential for focusing flow towards the drifts, the 
heterogeneity of permeability is greater than the range of change projected and, furthermore, the 
fracture permeability is sufficient to support drainage through the pillar areas. Therefore, 
although there is still some uncertainty, it is not suggested by these analyses that restrictions to 
downward percolation would cause diversion from the pillar regions of the repository. 
Percolation from the regions above the drifts would continue regardless of any changes in 
permeability from the THM and THC effects. Extension of both simulations and testing to the 
lower tsw35 hydrogeologic unit (Tptpll) in which most emplacement drifts will be located is 
ongoing. 
5.5 MODEL CONFIDENCE 
The TH model capabilities to accurately predict temperatures have consistently been 
demonstrated, at least for the overall temperature fields that develop. This demonstration has 
included both laboratory and field studies. When temperatures are below boiling, the conduction 
only models are appropriate and the physics is well understood. Confidence in temperature 
predictions beyond the zone of boiling is quite high, with the principal uncertainty related to the 
property determinations of thermal conductivity and the natural heterogeneity of the system. 
When hydrological processes are considered (either boiling or convective movement of moisture 
that impacts heat) confidence is reduced. The major issues are not the physical understanding of 
the hydrological parameters; the issues are the property uncertainty (thermal conductivities of 
wet and dry rock are different), the heterogeneity of the ambient system, and the potential 
heterogeneity of thermal responses. For instance, the amount of drying that occurs is a function 
of the porosity and permeability of the rock matrix, and of the fracture spacing and connectivity, 
all of which can vary spatially. Since no model will be able to fully or directly account for this 
heterogeneity, a statistical approach will be needed. To date, the TH models have been quite 
accurate in predictions of TH responses in the thermal tests, with local spatial and temporal 
exceptions. Therefore, confidence in the TH model predictions of temperature is considered 
quite high. 
The TH model predictions of hydrologic responses (second diagonal box on interaction matrix, 
Figure 5-4) is also relatively high. In addition to the heterogeneity issues, there are some 
uncertainties in the range of hydrologic properties. For instance, the imbibition curves show

 5-11 
hysteresis for wetting versus drying cycles. As noted in Section 2.4, there are different views as 
to the applicability of the van Genuchten model and the AFM, which could be viewed as 
conceptual uncertainty. However, in spite of these uncertainties, the TH models have generally 
accurately predicted both the magnitude and trends in hydrologic responses of field tests, such as 
the SHT, LBT, and DST. Therefore, while confidence is not as high for the hydrologic response 
parts of the TH models as for the temperature response parts, the confidence is nonetheless high, 
particularly in the tsw34 hydrogeologic unit (Tptpmn) in which the DST is being conducted. 
As the THC interaction matrix (Figure 5-3) illustrates, the THC models are coupled to the TH 
models. As a result, the uncertainties for the THC models include not only the uncertainties of 
the chemical parts, but the uncertainties already discussed for the TH models. There are 
additional uncertainties related to the input data, as well as the geochemical models. As noted in 
Section 2.4, there are limited thermodynamic data available on chemical species at high 
concentrations and elevated temperatures. This introduces uncertainties for the model analyses 
that apply to regions close to the boiling or evaporation fronts. In the areas where the TH models 
predict saturations that exceed 10-20 percent, the ionic concentration due to water removal 
should not be a problem. The natural heterogeneity of the mineralogy may cause local 
uncertainties. Likewise, the effects of engineered heterogeneities, especially repository edge 
effects, may impact the thermal regime, which would couple to create some uncertainties. 
The THC responses in field studies have not been as widely studied as the TH responses. 
However, there has been agreement between model predictions and measurements in the DST. 
For instance, in the DST, the simulations of CO2 concentrations have the same trend as the 
measured concentrations. This indicates that the process model is reflecting the physical 
processes appropriately. The magnitudes of the simulated values did not match as well, which 
probably reflects not only the difficulties in accurately accounting for heterogeneity but also the 
challenges in obtaining accurate measurements. The water-chemistry simulations indicated 
lowered pH in the region of the highest gas-phase CO2 concentrations (Section 3.3.3.3). This 
shift in pH is similar, both temporally and spatially, to that measured from water collected from 
boreholes in the DST. Further, chloride concentrations from water collected from those 
boreholes was 5 to 10 times more dilute than the pore water, which was also predicted by the 
models. In addition, trends of other species, such as Ca and Si, were similar in model results and 
measurements. Samples are not available for direct comparison of mineralogical changes 
predicted to those observed. However, trends in water chemistry provide evidence of the 
mineralogy trends. The chemistry determined from water samples from boreholes in the DST 
show decreasing Ca with temperatures, and the pH and silica concentrations are suggestive of 
calcite precipitation, as was simulated. 
Thus, there is confidence in the THC model ability to predict the responses, although there is less 
confidence in the magnitudes predicted. The confidence in the THC results is somewhat less 
than that for the TH-only models. 
The THM models are less mature than the TH or THC models. There are limited data available 
to build confidence in these models, since most of the data are from laboratory studies. 
Therefore, the projections from the THM models must be considered as giving trends and 
identifying areas of potential impacts, but the magnitudes of the projections cannot be given very 
high confidence. The primary effect of the uncertainty in THM model response is a potential

 5-12 
variability in fracture permeability, with an increase of up to an order of magnitude in an already 
large value. The consequence of such a permeability increase on seepage is expected to be small 
due to the high initial permeability. Therefore, because the primary THM coupling effect is 
through permeability changes, the effect of THM uncertainty on overall performance is not 
expected to be significant. 
Uncertainties and limitations have been described in each of the AMRs that support the 
NFE PMR. The specific uncertainties are listed in Table 3-1. These uncertainties are related to 
thermal test measurements, property inputs, conceptual flow models, and boundary conditions 
that vary both in time and space. A discussion of the most important uncertainties, and how they 
affect TSPA, are discussed with potential advice to TSPA as to how these can be accommodated 
in the models that provide the abstractions. 
There are measurement uncertainties associated with measurements of temperature and liquid 
saturation acquired from the LBT, SHT, and DST. The quantitative analysis of measured 
uncertainty is a function of the instrumentation and how it is used to measure a specific quantity. 
Uncertainty in measurements involves more than just the instrument, and therefore assessment of 
uncertainty must be based on the experience of those who design experiments and specify the 
instrumentation with which to take measurements. 
The measured results (e.g., temperature at some radial distance from the heat source) are 
compared to TH model simulations, which try to characterize the processes initiated by heat. 
Uncertainties also exist in the model simulations. The important ones include property 
specifications, boundary conditions, and the conceptual flow models used to approximate the 
processes caused by thermal perturbation. These directly impact TSPA specifically, since it 
must provide an abstraction, to a total system model, of data obtained from a repository heating 
model that provides information over large space dimensions and long time intervals. The 
thermal tests provide information over a variety of different spatial scales for various lengths of 
time (both much less than that of the potential repository itself). However, the measured thermal 
tests provide TSPA the ability to test (against a controlled thermal perturbation) the thermal and 
inverse-modeled hydrologic property sets and the conceptual flow models used in the process 
models that are the basis of the abstractions. 
The advice provided to TSPA resulting from the thermal tests is an analysis of different 
hydrologic property sets and conceptual flow models. A number of property sets and flow 
models are compared to measured data, because of the inherent uncertainty contained in each. 
Ranges of results are obtained from the TH simulations and compared to experimentally 
measured results of temperature and liquid saturation. An assessment is made as to the best fluid 
processes initiated by a controlled thermal perturbation (e.g., LBT, SHT, and DST), and hence 
should be applied to the TSPA models used to approximate repository heating. The result is the 
following: TSPA can build confidence in the property sets and conceptual flow models used in 
the TH models for abstraction, since they have been tested and verified against a quantifiable and 
understood thermal transient. 
The process models discussed in the NFE PMR contain many of the uncertainties previously 
described (e.g., conceptual flow model, hydrologic properties, etc.). These uncertainties are 
characterized and understood by comparison to measured TH results from the LBT, SHT, and

 5-13 
DST. Many of the process models also contain potential limitations based on the assumptions 
applied to the inherent processes they characterize. The THC DS model contains uncertainties 
associated with: 
 thermodynamic and kinetic parameters used to describe precipitation and dissolution 
 reaction processes for dissolved solutes that occur at elevated temperatures 
 fracture and matrix mineralogy 
 initial water and gas chemistry 
 reactive mineral surface area 
 correlation used to modify permeability change as a function of porosity change 
 water and gas composition changed by infiltration flux 
These model limitations and uncertainties are evaluated with THC model comparisons to the 
measure data from (pH and aqueous carbonate) the DST. It was shown that the less complex 
geochemical system used as input in the THC model is supported by the measured results of the 
DST. Since this is the case, confidence is built in the model such that many of the uncertainties 
listed above produce water and gas compositions obtained by a model that are reasonably 
supported by an experiment. Therefore, the advice to TSPA is that the THC process-level model 
contains inherent uncertainties and limitations in the processes that it described, yet it reasonably 
approximates the measured results of an experiment that establishes a controlled heat input into a 
geologic formation. The same geologic formation that will house part of the repository wastes. 
However, TSPA must not only apply the THC model to present-day infiltration rate conditions at 
the location of the thermal tests, but also apply its results to different repository locations, 
infiltration rates, and future climate states. These, at this time, have no experimental backing 
associated with model confidence building. Since the DST model has been benchmarked with a 
degree of success against an evolving and understood heating process (the DST), its results are 
extended to other repository locations, infiltration fluxes, and future climate states. These results 
are uncertain due to the uncertainties mentioned above and how they may be different for other 
locations or geologic sub-units; however, the uncertainty in water and gas composition is 
quantified for varying infiltration flux and future climate states, and found to be usually less than 
an order-of-magnitude different than the expected-value case. Therefore, it is reasonable to 
apply the expected-value water and gas composition abstraction over the entire infiltration flux 
scenario (low, mean, and high). 
One final assessment is required to advise TSPA as to the potential changes in fracture flow 
properties as a result of the reactive-transport processes that, at elevated temperatures and in the 
presence of water, initiate precipitation or dissolution of minerals in a geologic system. TSPA 
abstracts from a variety of process-level models. Some contain the coupled process of reactive 
transport with thermal-hydrology, others do not. Since TSPA abstracts from both model types, 
an assessment is required to determine whether the simplified models (TH-only) may inherently 
be neglecting processes that should be included. The evaluation considers both state and flow 
variables that are typically used to describe the performance of a geologic repository. Based on 
these comparisons and the calculation that reactive transport does not appreciably change the TH 
results that would be obtained from a TH-only model, it is recommended that TSPA select the 
process model that fits their needs. If the in-drift or near-field host rock thermodynamic and 
fracture-flow environment is to be determined without specification of a geochemical boundary

 5-14 
condition, it is recommended that a TH-only model be applied. It is computationally less 
rigorous and results in approximately the same TH response as obtained from a model that 
includes more processes in its formulation. If geochemical boundary conditions are needed, a 
fully coupled model must be applied to the abstraction. 
5.6 CONCLUSION 
Although there are uncertainties and issues of heterogeneities in properties, the overall binary 
coupling between thermal, hydrological, chemical, and mechanical processes in the near-field 
environment is understood, as discussed above. Ternary coupling among these processes has 
been investigated experimentally and computationally with good agreement. Simultaneous 
coupling of all four types of processes has not yet been addressed, but multiple combinations of 
ternary couplings have been investigated. Based on these considerations, THCM processes are 
not inconsistent with the treatment of repository performance in TSPA. Ranges of parameters 
are used in TSPA to account for uncertainty and investigate the sensitivity to specific processes 
and events. Ongoing work will further reduce these uncertainties and increase confidence in 
coupled-process models that must predict responses over geologic time scales. 
Table 3-1 identifies uncertainties associated with TH, THC and model abstractions. The TH 
model uncertainties can best be addressed by use of conservative parameter values to bound the 
natural heterogeneity. The model uncertainty is within acceptable bounds, based on comparisons 
with field tests (Section 3.6). It appears that use of multiple models, perhaps with more 
representative grids to represent drifts, will address the model uncertainties. The uncertainties 
regarding property sets for Tptpll cannot be resolved until property data and testing within the 
Tptpll is performed. Lacking that information, use of properties from the Tptpmn for the entire 
repository footprint is the most defensible approach, since the property sets have been tested 
against field results. 
In summary, the treatment of coupled processes in TSPA is considered adequate for its intended 
use for site recommendation.

 6-1 
6. REFERENCES 
6.1 DOCUMENTS CITED 
Ahola, M.P.; Chowdhury, A.H.; Hsiung, S.M.; and Philip, J. 1994a. Comparison of Coupled 
Thermal-Mechanical-Hydrological Analyses of a Fractured Rock Mass. High Level 
Radioactive Waste Management, Proceedings of the Fifth Annual International Conference, 
Las Vegas, Nevada, May 22-26, 1994. 4, 2492-2499. La Grange Park, Illinois: American 
Nuclear Society. TIC: 210984. 
Ahola, M.P.; Ofoegbu, G.I.; Chowdhury, A.H.; and Hsiung, S-M. 1994b. Thermo-Hydro- 
Mechanical Coupled Modeling: Big-Ben Experiment, TC3 DECOVALEX - Phase III. 
CNWRA 94-021. San Antonio, Texa s: Center for Nuclear Waste Regulatory Analyses. 
TIC: 215628. 
Albin, A.L.; Singleton, W.L.; Moyer, T.C.; Lee, A.C.; Lung, R.C.; Eatman, G.L.W.; and Barr, 
D.L. 1997. Geology of the Main Drift - Station 28+00 to 55+00, Exploratory Studies Facility, 
Yucca Mountain Project, Yucca Mountain, Nevada. Denver, Colorado: Bureau of Reclamation 
and U.S. Geological Survey. ACC: MOL.19970625.0096. 
Baca, R.G. and Magnuson, S.O. 1990. Independent Verification and Benchmark Testing of the 
UNSAT-H Computer Code, Version 2.0. EGG-BEG-8811. Idaho Falls, Idaho: EG&G Idaho. 
TIC: 247840. 
Bandis, S.C.; Lumsden, A.C.; and Barton, N.R. 1983. Fundamentals of Rock Joint 
Deformation. International Journal of Rock Mechanics and Mining Sciences & Geomechanics 
Abstracts, 20, (6), 249-268. Oxford, United Kingdom: Pergamon Press. TIC: 224201. 
Barton, C.A.; Hickman, S.; Morin, R.; Zoback, M.D.; Finkbeiner, T.; Sass, J.; and Benoit, D. 
1997. Fracture Permeability and Its Relationship to In Situ Stress in the Dixie Valley, Nevada, 
Geothermal Reservoir. Proceedings from Twenty-Second Workshop on Geothermal Reservoir 
Engineering, January 27-29, 1997. 210-215. Stanford, California: Stanford University. 
TIC: 237673. 
Barton, N.R.; Bandis, S.; and Bakhtar, K. 1985. Strength, Deformation, and Conductivity 
Coupling of Rock. Joints. International Journal of Rock Mechanics and Mining Sciences and 
Geomechanics Abstracts, 22, (3), 121-140. New York, New York: Pergamon Press. 
TIC: 217135. 
Bear, J. 1988. Dynamics of Fluids in Porous Media. New York, New York: Dover Publications. 
TIC: 217568. 
Berge, P.A.; Wang, H.F.; and Blair, S.C. 1998. Estimated Bounds on Rock Permeability 
Changes from THM Processes. UCRL-ID-131492. Livermore, California: Lawrence 
Livermore National Laboratory. ACC: MOL.19981109.0302.

 6-2 
Bish, D.L. 1995. Thermal Behavior of Natural Zeolites. Natural Zeolites '93: Occurrence, 
Properties, Use, Proceedings of the 4th International Conference on the Occurrence, Properties, 
and Utilization of Natural Zeolites, June 20-28, 1993, Boise, Idaho. Ming, D.W. and 
Mumpton, F.A., eds. Pages 259-269. Brockport, New York: International Committee on 
Natural Zeolites. TIC: 243086. 
Bish, D.L. and Aronson, J.L. 1993. Paleogeothermal and Paleohydrologic Conditions in Silicic 
Tuff from Yucca Mountain, Nevada. Clays and Clay Minerals, 41, (2), 148-161. Long Island 
City, New York: Pergamon Press. TIC: 224613. 
Bish, D.L.; Carey, J.W.; Levy, S.S.; and Chipera, S.J. 1996. Mineralogy-Petrology Contribution 
to the Near-Field Environment Report. Milestone Report LA3668. Los Alamos, New Mexico: 
Los Alamos National Laboratory. ACC: MOL.19971111.0588. 
Blair, S.C. and Berge, P.A. 1995. Uniaxial Compression Behavior of Small Blocks of Welded 
Tuff. UCRL-JC-122733. Livermore, California: Lawrence Livermore National Laboratory. 
ACC: MOL.19960501.0273. 
Blair, S.C. and Berge, P.A. 1997. Geomechanical Properties of Topopah Spring Tuff at the 0.5- 
m Scale: Preliminary Results of Compression Tests at Elevated Temperature. UCRL-ID- 
125089. Livermore, California: Lawrence Livermore National Laboratory. TIC: 236600. 
Blair, S.C. and Wood, S.A. 1998. Geomechanical Observations During the Large Block Test. 
High-Level Radioactive Waste Management, Proceedings of the Eighth International 
Conference Las Vegas, Nevada, May 11-14, 1998. Pages 769-771. La Grange Park, Illinois: 
American Nuclear Society. TIC: 237082. 
Blair, S.C.; Berge, P.A.; and Wang, H.F. 1997. Bounding Models for Estimating Changes in 
Fracture Permeability Due to Thermo-Mechanical Stresses in Host Rock Surrounding the 
Repository, 1: Permeability Changes Estimated for the Heated Drift Test. Milestone SPLF2M4. 
Livermore, California: Lawrence Livermore National Laboratory. ACC: MOL.19980107.0411. 
Blair, S.C.; Kelly, J.M.; Pine, O.; Pletcher, R.; and Berge, P.A. 1996. Effect of Radiation on the 
Mechanical Properties of Topopah Spring Tuff. UCRL-ID-122899. Livermore, California: 
Lawrence Livermore National Laboratory. ACC: MOL.19961021.0132. 
Bodvarsson, G.S.; Bandurraga, T.M.; and Wu, Y.S., eds. 1997. The Site-Scale Unsaturated 
Zone Model of Yucca Mountain, Nevada, for the Viability Assessment. LBNL-40376. Berkeley, 
California: Lawrence Berkeley National Laboratory. ACC: MOL.19971014.0232. 
Borgesson, L. and Hernelind, J. 1995. DECOVALEX I - Test Case 3: Calculation of the Big 
Ben Experiment - Coupled Modelling of the Thermal, Mechanical and Hydraulic Behaviour of 
Water-Unsaturated Buffer Material in a Simulated Deposition Hole. SKB Technical Report 
95-29. Stockholm, Sweden: Swedish Nuclear Fuel and Waste Management Company. 
TIC: 224376.

 6-3 
Brookins, D.G 1984. Geochemical Aspects of Radioactive Waste Disposal. New York, 
New York: Springer-Verlag. TIC: 206675. 
Brookins, D.G. 1986. Natural Analogues for Radwaste Disposal: Elemental Migration in 
Igneous Contact Zones. Chemical Geology, 55, 337-344. Amsterdam, The Netherlands: 
Elsevier. TIC: 246170. 
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. 
Buscheck, T.A. and Nitao, J.J. 1993. Repository-Heat-Driven Hydrothermal Flow at Yucca 
Mountain, Part I: Modeling and Analysis. Nuclear Technology, 104, (3), 418-448. La Grange 
Park, Illinois: American Nuclear Society. TIC: 224039. 
Buscheck, T.A. and Nitao, J.J. 1994. The Impact of Buoyant, Gas-Phase Flow and 
Heterogeneity on Thermal-Hydrological Behavior at Yucca Mountain. UCRL-JC-115351. 
Livermore, California: Lawrence Livermore National Laboratory. ACC: NNA.19940524.0012. 
Buscheck, T.A.; Nitao, J.J.; and Chesnut, D.A. 1992. The Impact of Episodic Nonequilibrium 
Fracture-Matrix Flow on Geological Repository Performance. Proceedings of the Topical 
Meeting on Nuclear Waste Packaging, Focus '91, September 29-October 2, 1991, Las Vegas, 
Nevada. 312-323. La Grange Park, Illinois: American Nuclear Society. TIC: 231173. 
Buscheck et al. 1997a. Not Used. 
Buscheck et al. 1997b. Not Used. 
Buscheck, T.A.; Shaffer, R.J.; Lee, K.H.; and Nitao, J.J. 1997c. Analysis of Thermal- 
Hydrological Behavior During the Heating Phase of the Single-Heater Test at Yucca Mountain. 
Supplemental Submission to Deliverable SP9266M4. Livermore, California: Lawrence 
Livermore National Laboratory. ACC: MOL.19980109.0241. 
Buscheck, T.A.; Shaffer, R.J.; and Nitao, J.J. 1997d. Pretest Thermal-Hydrological Analysis of 
the Drift-Scale Thermal Test at Yucca Mountain. Livermore, California: Lawrence Livermore 
National Laboratory. ACC: MOL.19980507.0359. 
Buscheck, T.A.; Nitao, J.J.; and Ramspott, L.D. 1997e. Near-Field Thermal-Hydrological 
Behavior for Alternative Repository Designs at Yucca Mountain. Scientific Basis for Nuclear 
Waste Management XX, Symposium held December 2-6, 1996, Boston, Massachusetts. 
Gray, W.J. and Triay, I.R., eds. 465, 1029-1036. Pittsburgh, Pennsylvania: Materials Research 
Society. TIC: 238884. 
Carey, J.W. and Bish, D.L. 1996. Equilibrium in the Clinoptilolite-H2O System. American 
Mineralogist, 81, 952-962. Washington, D.C.: Mineralogical Society of America. 
TIC: 233145.

 6-4 
Carey, J.W.; Chipera, S.J.; Vaniman, D.T.; and Bish, D.L. 1997. Three-Dimensional 
Mineralogic Model of Yucca Mountain, Nevada. Milestone SP32B5M4, Rev. 1.1, Draft R0. 
Los Alamos, New Mexico: Los Alamos National Laboratory. ACC: MOL.19980520.0170. 
Chan, T.; Khair, K.; Jing, L.; Ahola, M.; Noorishad, J.; and Vuillod, E. 1995. International 
Comparison of Coupled Thermo-Hydro-Mechanical Models of a Multiple-Fracture Bench Mark 
Problem: DECOVALEX Phase I, Bench Mark Test 2. International Journal of Rock 
Mechanics and Mining Sciences & Geomechanics Abstracts, 32, (5), 435-452. Oxford, United 
Kingdom: Elsevier Science. TIC: 235730. 
Cohon, J.L. 1999. Comments on the Process for Selecting the Repository Design Letter from 
J.L. Cohon (U.S. Nuclear Waste Technical Review Board) to L.H. Barrett (DOE/OCRWM), 
July 9, 1999. ACC: MOL.20000412.0786. 
Cohon, J.L. 2000. Comments from the Nuclear Waste Technical Review Board January 2000 
Meeting Letter from J.L. Cohon (U.S. Nuclear Waste Technical Review Board) to I. Itkin 
(DOE/OCRWM), March 20, 2000. ACC: MOL.20000412.0787. 
Crowe, B.; Self, S.; Vaniman, D.; Amos, R.; and Perry, F. 1983. Aspects of Potential 
Magmatic Disruption of a High-Level Radioactive Waste Repository in Southern Nevada. 
Journal of Geology, 91, (3), 259-276. Chicago, Illinois: University of Chicago Press. 
TIC: 216959. 
CRWMS M&O 1996. Test Design, Plans and Layout Report for the ESF Thermal Test. 
BAB000000-01717-4600-00025 REV 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19970114.0166. 
CRWMS M&O 1997a. Single Heater Test Status Report. BAB000000-01717-5700-00002 
REV 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19980416.0696. 
CRWMS M&O 1997b. Drift Scale Test Design and Forecast Results. BAB000000-01717- 
4600-00007 REV 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19980710.0155. 
CRWMS M&O 1997c. Updated In Situ Thermal Testing Program Strategy. B00000000- 
01717-5705-00065 REV 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19990526.0296. 
CRWMS M&O 1998a. Near-Field/Altered Zone Coupled Effects Expert Elicitation Project. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19980729.0638. 
CRWMS M&O 1998b. 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.

 6-5 
CRWMS M&O 1998c. 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 1999a. License Application Design Selection Report. B00000000-01717-4600- 
00123 REV 01 ICN 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990908.0319. 
CRWMS M&O 1999b. Work Package Planning Summary for the Near Field Environment 
Process Model Report FY 00 WP #1401213NM1 and 891213NU1 Revision 00. WPP-MGRMD-
000024. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19991021.0080. 
CRWMS M&O 1999c. Final Report Total System Performance Assessment Peer Review Panel. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990528.0155. 
CRWMS M&O 1999d. Single Heater Test Final Report. BAB000000-01717-5700-00005 
REV 00 ICN 1. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000103.0634. 
CRWMS M&O 2000a. Thermal Tests Thermal-Hydrological Analysis/Model Report. ANLNBS-
TH-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000505.0231. 
CRWMS M&O 2000b. Drift-Scale Coupled Processes (DST and THC Seepage) Models. MDLNBS-
HS-000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0523. 
CRWMS M&O 2000c. Abstraction of Drift-Scale Coupled Processes. ANL-NBS-HS-000029 
REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000525.0371. 
CRWMS M&O 2000d. Calculation of Permeability Change Due to Coupled Thermal- 
Hydrologic-Mechanical Effects. CAL-NBS-MD-000002 REV 00. Las Vegas, Nevada: 
CRWMS M&O. URN-0438 
CRWMS M&O 2000e. Features, Events and Processes in Thermal Hydrology and Coupled 
Processes. ANL-NBS-MD-00004 REV 00. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20000602.0053. 
CRWMS M&O 2000f. Unsaturated Zone Flow and Transport Model Process Model Report. 
TDR-NBS-HS-000002 REV 00. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20000320.0400. 
CRWMS M&O 2000g. Engineered Barrier System Degradation, Flow, and Transport Process 
Model Report. TDR-EBS-MD-000006 REV 00. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20000324.0558. 
CRWMS M&O 2000h. Conceptual and Numerical Models for UZ Flow and Transport. MDLNBS-
HS-000005 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0526.

 6-6 
CRWMS M&O 2000i. Site Recommendation Subsurface Layout. ANL-SFS-MG-000001 
REV 00. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0220 
CRWMS M&O 2000j. Not Used. 
CRWMS M&O 2000k. Multiscale Thermohydrologic Model. ANL-EBS-MD-000049 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000609.0267. 
CRWMS M&O 2000l. Abstraction of Drift Seepage. ANL-NBS-MD-000005 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000322.0671. 
CRWMS M&O 2000m. 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 2000n. Calibrated Properties Model. MDL-NBS-HS-000003 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0520. 
CRWMS M&O 2000o. Waste Package Degradation Process Model Report. TDR-WIS-MD- 
000002 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000620.0346. 
CRWMS M&O 2000p. Natural Analogues for the Unsaturated Zone. ANL-NBS-HS-000007 
REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0524. 
CRWMS M&O 2000q. UZ Flow Models and Submodels. MDL-NBS-HS-000006 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990721.0527. 
CRWMS M&O 2000r. Analysis of Geochemical Data for the Unsaturated Zone. ANL-NBSHS-
000017 REV 00. Las Vegas, Nevada: CRWMS M&O. Submit to RPC URN-0048 
CRWMS M&O 2000s. Repository Safety Strategy: Plan to Prepare the Postclosure Safety Case 
to Support Yucca Mountain Site Recommendation and Licensing Considerations. TDR-WISRL-
000001 REV 03. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000119.0189. 
CRWMS M&O 2000t. 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 2000u. Water Distribution and Removal Model. ANL-EBS-MD-000032 
REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000504.0303. 
CRWMS M&O 2000v. Physical and Chemical Environment Abstraction Model. ANL-EBSMD-
000046 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000523.0155. 
CRWMS M&O 2000w. Development of Numerical Grids for UZ Flow and Transport 
Modeling. ANL-NBS-HS-000015 REV 00. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19990721.0517.

 6-7 
CRWMS M&O 2000x. Near-Field Environment Process Model Report(PMR). TDP-NBS-MD- 
000011 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000310.0353. 
CRWMS M&O 2000y. 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 2000z. Performance Confirmation Plan. TDR-PCS-SE-000001 REV 01. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000302.0312. 
CRWMS M&O 2000aa. Subsurface Facility System Description Document. SDD-SFS-SE- 
000001 REV 00. Volume I. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20000221.0712. 
CRWMS M&O 2000ab. Waste Form Degradation Process Model Report. TDR-WIS-MD- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000403.0495. 
CRWMS M&O 2000ac. Drift Degradation Analysis. ANL-EBS-MD-000027 REV 00. 
Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000107.0328. 
CRWMS M&O 2000ad. Emplacement Drift System Description Document SDD-EDS-SE- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000121.0119. 
CRWMS M&O 2000ae. Backfill Emplacement System Description Document. SDD-BES-SE- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000210.0074. 
CRWMS M&O 2000af. Subsurface Ventilation System Description Document. SDD-SVS-SE- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000217.0221. 
CRWMS M&O 2000ag. Ground Control System Description Document. SDD-GCS-SE- 
000001 REV 00. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.20000221.0711. 
Daily, W.; Lin, W.; and Buscheck, T. 1987. Hydrological Properties of Topopah Spring Tuff: 
Laboratory Measurements. Journal of Geophysical Research, 92, (B8), 7854-7864. 
Washington, D.C.: American Geophysical Union. TIC: 226512. 
DOE (U.S. Department of Energy) 1988. Site Characterization Plan Yucca Mountain Site, 
Nevada Research and Development Area, Nevada. DOE/RW-0199. Nine volumes. 
Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive Waste 
Management. ACC: HQO.19881201.0002. 
DOE (U.S. Department of Energy) 1998. Total System Performance Assessment. Volume 3 of 
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.19981007.0030.

 6-8 
DOE (U.S. Department of Energy) 2000. Quality Assurance Requirements and Description. 
DOE/RW-0333P, Rev. 9. Washington, D.C.: U.S. Department of Energy, Office of Civilian 
Radioactive Waste Management. ACC: MOL.19991028.0012. 
Ehrlich, R.; Etris, E.L.; Brumfield, D.; Yuan, L.P.; and Crabtree, S.J. 1991. Petrography and 
Reservoir Physics III: Physical Models for Permeability and Formation Factor. AAPG Bulletin, 
75, (10), 1579-1592. Tulsa, Oklahoma: American Association of Petroleum Geologists. 
TIC: 246294. 
Esaki, T.; Du, S.; Mitani, Y.; Ikusada, K.; and Jing, L. 1999. Development of a Shear-Flow 
Test Apparatus and Determination of Coupled Properties for a Single Rock Joint. International 
Journal of Rock Mechanics and Mining Sciences, 36, 641650. New York, New York: Elsevier 
Science. TIC: 247483. 
Flint, A.L.; Hevesi, J.A.; and Flint, L.E. 1996. Conceptual and Numerical Model of Infiltration 
for the Yucca Mountain Area, Nevada. Milestone 3GUI623M. Denver, Colorado: U.S. 
Geological Survey. ACC: MOL.19970409.0087. 
Geller J.T.; Su G.; and Pruess K. 1996. Preliminary Studies of Water Seepage Through Rough- 
Walled Fractures. LBNL-38810. Berkeley, California: Lawrence Berkeley National 
Laboratory. URN-0454. 
Green, R.; Martin, R.; Svedeman, S.; and Dodge, F.T. 1991. Nonisothermal Laboratory and 
Numerical Experiments Results. Proceedings of Workshop V: Flow and Transport Through 
Unsaturated Fractured Rock - Related to High-Level Radioactive Waste Disposal, Held at 
Radisson Suite Hotel, Tuscon, Arizona, January 7-10, 1991. Evans, D.D. and Nicholson, T.J., 
eds. NUREG/CP-0040, 161-168. Washington, D.C.: U.S. Nuclear Regulatory Commission. 
TIC: 207128. 
Hardin, E.L. 1998. Near-Field/Altered-Zone Models Report. UCRL-ID-129179 DR. 
Livermore, California: Lawrence Livermore National Laboratory. ACC: MOL.19980504.0577. 
Hardin, E.L. and Chesnut, D.A. 1997. Synthesis Report on Thermally Driven Coupled 
Processes. Milestone SPL8BM4. Livermore, California: Lawrence Livermore National 
Laboratory. ACC: MOL.19980107.0356. 
Harrison- Giesler, D.J.; Morissette, R.P.; and Jardine, L.J. 1991. Yucca Mountain Site 
Characterization Project Waste Package Plan. UCRL-JC-106161. Livermore, California: 
Lawrence Livermore National Lab. ACC: NNA.19920529.0030. 
Haukwa, C.B.; Wu, Y.S.; and Bodvarsson, G.S. 1999. Thermal Loading Studies Using the 
Yucca Mountain Unsaturated Zone Model. Journal Of Contaminant Hydrology, 38, (1-3), 217- 
255. New York, New York: Elsevier Science Publishers. TIC: 244160.

 6-9 
Ho, C.K. 1997. Models of Fracture-Matrix Interactions During Multiphase Heat and Mass 
Flow in Unsaturated Fractured Porous Media. ASME International Mechanical Engineering 
Congress and Exposition, Dallas, Texas, November 16-21, 1997. FED-Vol. 244, 401-412. 
New York, New York: American Society of Mechanical Engineers. TIC: 241082. 
Ho, C.K. and Francis, N.D. 1998. Coupled Thermo-Hydro-Mechanical Simulations of the 
Potential Repository at Yucca Mountain. High-Level Radioactive Waste Management, 
Proceedings of the Eighth International Conference, Las Vegas, Nevada, May 11-14, 1998. 
Pages 113-115. La Grange Park, Illinois: American Nuclear Society. TIC: 237082. 
Hughson, D. and Green, R. 1999. Evaluation of Thermal-Hydrological Model Concepts, Data, 
and U.S. Department of Energy Thermal Test Results-Status Report. San Antonio, Texas: 
Center for Nuclear Waste Regulatory Analyses. TIC: 247537. 
Israelsson, J. 1995. DECOVALEX I - Bench-Mark Test 3: Thermo-Hydro-Mechanical 
Modelling. SKB Technical Report 95-30. Stockholm, Sweden: Swedish Nuclear Fuel and 
Waste Management Company. TIC: 223944. 
Itasca Consulting Group 1996. FLAC, Fast Lagrangian Analysis of Continua, Version 3.3. Four 
Volumes. Minneapolis, Minnesota: Itasca Consulting Group. TIC: 236418; 236419; 236420; 
236421. 
Itasca Consulting Group 1998. 3DEC, 3 Dimensional Distinct Element Code, User's Guide, 
(Version 2.00). Minneapolis, Minnesota: Itasca Consulting Group. TIC: 247503. 
Jiao, Y. and Hudson, J.A. 1995. The Fully-Coupled Model for Rock Engineering Systems. 
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 32, 
(5), 491-512. Oxford, United Kingdom: Elsevier Science. TIC: 235731. 
Jing, L.; Tsang, C.F.; and Stephansson, O. 1995. DECOVALEX - An International Co- 
Operative Research Project on Mathematical Models of Coupled THM Processes for Safety 
Analysis of Radioactive Waste Repositories. International Journal of Rock Mechanics and 
Mining Sciences & Geomechanics Abstracts, 32, (5), 389-398. Oxford, United Kingdom: 
Elsevier Science. TIC: 235918. 
Johnson, J.W.; Knauss, K.G.; Glassley, W.E.; DeLoach, L.D.; and Thompson, A.F.B 1998. 
Reactive Transport Modeling of Plug-Flow Reactor Experiments: Quartz and Tuff Dissolution 
at 240C. Journal of Hydrology, 209, 81-111. Amsterdam, The Netherlands: Elsevier 
Science. TIC: 240986. 
Jury, W.A.; Gardner, W.R.; and Gardner, W.H. 1991. Soil Physics. 5th Edition. New York, 
New York: John Wiley & Sons. TIC: 241000. 
Keenan, J.H.; Keyes, F.G.; Hill, P.G.; and Moore, J.G. 1969. Steam Tables, Thermodynamic 
Properties of Water Including Vapor, Liquid, and Solid Phases. New York, New York: John 
Wiley & Sons. TIC: 246766.

 6-10 
Klavetter, E.A. and Peters, R.R. 1986. Estimation of Hydrologic Properties of an Unsaturated, 
Fractured Rock Mass. SAND-84-2642. Albuquerque, New Mexico: Sandia National 
Laboratories. TIC: 202727. 
Kneafsey, T.J. and Pruess, K. 1997. Preferential Flow Paths and Heat Pipes: Status Report 
Second Quarter FY 1997. Milestone SPL6A3M4. Berkeley, California: Lawrence Berkeley 
National Laboratory. ACC: MOL.19971125.0196. 
Kneafsey, T.J. and Pruess, K. 1998. Laboratory Experiments on Heat-Driven Two-Phase Flows 
in Natural and Artificial Rock Fractures. Water Resources Research, 34, (12), 3349-3367. 
Washington, D.C.: American Geophysical Union. TIC: 247468. 
Kotra, J.P.; Lee, M.P.; Eisenberg, N.A.; and DeWispelare, A.R. 1996. Branch Technical 
Position on the Use of Expert Elicitation in the High-Level Radioactive Waste Program. 
NUREG-1563. Washington, D.C.: U.S. Nuclear Regulatory Commission. TIC: 226832. 
Krumhansl, J.L. and Stockman, H.W. 1988. Site Selection Criteria and Preliminary Results 
from the Valles Caldera Natural Analog Study. Proceedings of Workshop IV on Flow and 
Transport Through Unsaturated Fractured Rock-Related to High Level Radioactive Waste 
Disposal, December 12-15, 1998 Tucson, Arizona. Pages 249-276. Tucson, Arizona: 
University of Arizona. TIC: 247519. 
Kwicklis, E.M. and Healey, R.W. 1993. Numerical Investigation of Steady Liquid Water Flow 
in a Variably Saturated Fracture Network. Water Resources Research, 29, (12), 4091-4102. 
Washington, D.C.: American Geophysical Union. TIC: 226993. 
Lasaga, A.C. 1998. Kinetic Theory in the Earth Sciences. Princeton, New Jersey: Princeton 
University Press. TIC: 246279. 
LBNL (Lawrence Berkeley National Laboratory) 1999. Software Code: TOUGHREACT V2.2. 
V2.2. SUN. STN: 10154-2.2-00. URN-0365. 
LBNL 2000. Software Code: TOUGH2 V1.4. V1.4. STN: 10007-1.4-01. 
LLNL (Lawrence Livermore National Laboratory) 1999. Software code: NUFT . V3.0.1s. Sun 
SPARC, UNIX OS. 10130-3.0.1s-00. URN-0394. 
LLNL 1999. Software code, MSTHAC. V6.2. STN: 10290-6.2-00. URN-0455. 
Lee, K.H.; Kulshrestha, A.; and Nitao, J.J. 1993. Interim Report on Verification and Benchmark 
Testing of the NUFT Computer Code, October 1993. UCRL-ID-113521. Livermore, California: 
Lawrence Livermore National Laboratory. TIC: 235555.

 6-11 
Levy, S.S.; Fabryka-Martin, J.T.; Dixon, P.R.; Liu, B.; Turin, H.J.; and Wolfsberg, A.V. 1997. 
Chlorine-36 Investigations of Groundwater Infiltration in the Exploratory Studies Facility at 
Yucca Mountain, Nevada. Scientific Basis for Nuclear Waste Management XX, Symposium 
held December 2-6, 1996, Boston, Massachusetts. Gray, W.J. and Triay, I.R., eds. 465, 901-908. 
Pittsburgh, Pennsylvania: Materials Research Society. TIC: 238884. 
Lichtner, P.C. and Seth, M. 1996. Multiphase-Multicomponent Nonisothermal Reactive 
Transport in Partially Saturated Porous Media. Proceedings of the 1996 International 
Conference on Deep Geological Disposal of Radioactive Waste, September 16-19, 1996, 
Winnipeg, Manitoba, Canada. Toronto, Ontario, Canada: Canadian Nuclear Society. 
TIC: 233923. 
Lichtner, P.C.; Keating, G.; and Carey, B. 1999. A Natural Analogue for Thermal-Hydrological- 
Chemical Coupled Processes at the Proposed Nuclear Waste Repository at Yucca Mountain, 
Nevada. LA-13610-MS. Los Alamos, New Mexico: Los Alamos National Laboratory. 
TIC: 246032. 
Lin, W. and Daily, W. 1988. Hydrological Properties of Topopah Spring Tuff Under a Thermal 
Gradient Laboratory Results. UCRL-96926. Livermore, California: Lawrence Livermore 
National Laboratory. ACC: NN1.19881027.0006. 
Lin, W. and Daily, W.D. 1989. Laboratory Study of Fracture Healing in Topopah Spring Tuff- 
Implications for Near Field Hydrology. Livermore, California: Lawrence Livermore National 
Laboratory. ACC: NNA.19900711.0241. 
Lin, W. and Roberts, J. 1996. Laboratory-Determined Hydrologic Properties and Processes. 
Chapter 2 of Near-Field and Altered-Zone Environment Report. Wilder, D.G., ed. UCRL-LR- 
124998. Volume II. Livermore, California: Lawrence Livermore National Laboratory. 
ACC: MOL.19961212.0122. 
Lin, W.; Wilder, D.; Blair, S.; Daily, W.; Gdowski, G.; Glassley, W.; Lee, K.; Meike, A.; 
Ramirez, A.; Roberts, J.; Ruddle, D.; Wagoner, J.; Watwood, D.; Williams, T.; and Carlson, R. 
1998a. The Large Block Test of the Exploratory Studies Facility Thermal Tests. High-Level 
Radioactive Waste Management, Proceedings of the Eighth International Conference, Las 
Vegas, Nevada, May 11-14, 1998. Pages 49-51. La Grange Park, Illinois: American Nuclear 
Society. TIC: 237082. 
Lin, W.; Roberts, J.J.; and Wildenschild, D. 1998b. A Report on Laboratory Scale Thermally- 
Coupled Processes Experiments. UCRL-ID-129843. Livermore, California: Lawrence 
Livermore National Laboratory. ACC: MOL.19981123.0401. 
Lin, W.; Roberts, J.J.; Glassley, W.E.; and Ruddle, D. 1995. The Effect of Rock-Water 
Interaction on Permeability. UCRL-JC-119574. Livermore, California: Lawrence Livermore 
National Laboratory. ACC: MOL.19960416.0275.

 6-12 
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. 
Mack, M.G.; Brandshaug, T.; and Brady, B.H. 1989. Rock Mass Modification Around a Nuclear 
Waste Repository in Welded Tuff. NUREG/CR-5390. Washington, D.C.: U.S. Nuclear 
Regulatory Commission. TIC: 229166. 
Manteufel, R.D.; Ahola, M.P.; Turner, D.R.; and Chowdhury, A.H. 1993. A Literature Review 
of Coupled Thermal-Hydrologic-Mechanical-Chemical Processes Pertinent to the Proposed 
High-Level Nuclear Waste Repository at Yucca Mountain. NUREG CR-6021. Washington, 
D.C.: U.S. Nuclear Regulatory Commission. TIC: 207771. 
Martin, R.J.; Noel, J.S.; Boyd, P.J.; and Price, R.H. 1997. Creep Properties of the Paintbrush 
Tuff Recovered from Borehole USW NRG-7/7A: Data Report. SAND95-1759. Albuquerque, 
New Mexico: Sandia National Laboratories. ACC: MOL.19971017.0661. 
Matyskiela, W. 1997. Silica Redistribution and Hydrologic Changes in Heated Fractured Tuff. 
Geology, 25, (12), 1115-1118. Boulder, Colorado: Geological Society of America. 
TIC: 236809. 
Millard, A.; Durin, N.; Stietel, A.; Thoraval, A.; Vuillod, E.; Baroudi, H.; Plas, F.; Bougnoux, 
A.; Vouille, G.; Kobayashi, A.; Hara, K.; Fujita, T.; and Ohnishi, Y. 1995. Discrete and 
Continuum Approaches to Simulate the Thermo-Hydro-Mechanical Couplings in a Large, 
Fractured Rock Mass. International Journal of Rock Mechanics and Mining Sciences & 
Geomechanics Abstracts, 32, (5), 409-414. Oxford, United Kingdom: Elsevier Science. 
TIC: 235740. 
Mohanty, S.; Chowdhury, A.H.; Hsiung, S-M.; and Ahola, M.P. 1994a. Single Fracture Flow 
Behavior of Apache Leap Tuff Under Normal and Shear Loads. San Antonio, Texas: Center for 
Nuclear Waste Regulatory Analyses. TIC: 247817. 
Mohanty, S.; Pickens, A.; and Kana, D. 1994b. Single-Fracture Permeability Under Normal 
and Shear Displacement of Natural Rock Joint. EOS Transactions , 75, (44), 258. Washington, 
D.C.: American Geophysical Union. TIC: 247737. 
Murphy, W.M. 1993. Geochemical Models for Gas-Water-Rock Interactions in a Proposed 
Nuclear Waste Repository at Yucca Mountain. Proceedings of the Topical Meeting on Site 
Characterization and Model Validation, Focus '93, September 26-29, 1993, Las Vegas, Nevada. 
La Grange Park, Illinois: American Nuclear Society. TIC: 102245. 
Murphy, W.M. and Pabalan, R.T. 1994. Geochemical Investigations Related to the Yucca 
Mountain Environment and Potential Nuclear Waste Repository. NUREG/CR-6288. 
San Antonio, Texas: Southwest Research Institute. TIC: 227032.

 6-13 
Nataraja, M.S. and Brandshaug, T. 1992. Staff Technical Position on Geologic Repository 
Operations Area Underground Facility Design - Thermal Loads. NUREG-1466. Washington, 
D.C.: U.S. Nuclear Regulatory Commission. ACC: NNA.19921030.0049. 
Nguyen, T.S. and Selvadurai, A.P.S. 1995. Coupled Thermal-Mechanical-Hydrological 
Behaviour of Sparsely Fractured Rock: Implications for Nuclear Fuel Waste Disposal. 
International Journal of Rock Mechanics Mining Sciences & Geomechanics Abstracts, 32, (5), 
465-479. Oxford, United Kingdom: Elsevier Science. TIC: 235741. 
Nicholl, M.J.; Glass, R.J.; and Wheatcraft, S.W. 1994. Gravity-Driven Infiltration Instability in 
Initially Dry Nonhorizontal Fractures. Water Resources Research, 30, (9), 2533-2546. 
Washington, D.C.: American Geophysical Union. TIC: 243493. 
Nitao, J.J. 1993. The NUFT Code for Modeling Nonisothermal, Multiphase, Multicomponent 
Flow and Transport in Porous Media. Eos, 74, (43), 313. Washington, D.C.: American 
Geophysical Union. TIC: 226135. 
Nitao, J.J. and Buscheck, T.A. 1996. Discrete-Fracture Modeling of Thermal-Hydrological 
Processes at Yucca Mountain and the LLNL G-Tunnel Heater Test. Scientific Basis for 
Nuclear Waste Management XIX, Symposium held November 27-December 1, 1995, Boston, 
Massachusetts. Murphy, W.M. and Knecht, D.A., eds. 412, 747-758. Pittsburgh, Pennsylvania: 
Materials Research Society. TIC: 233877. 
Nitsche, H. 1991. Basic Research for Assessment of Geologic Nuclear Waste Repositories: 
What Solubility and Speciation Studies of Transuranium Elements Can Tell Us. Scientific 
Basis for Nuclear Waste Management XIV, Symposium held November 26-29, 1990, Boston, 
Massachusetts. Abrajano, T., Jr. and Johnson, L.H., eds. 212, 517-529. Pittsburgh, 
Pennsylvania: Materials Research Society. TIC: 203656. 
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 1999a. 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 1999b. 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. 
NRC 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 1999d. Nuclear Regulatory Commission Meeting. Meeting Summary. Rockville, 
Maryland: Nuclear Regulatory Commission. TIC: MOL.19990406.0198.

 6-14 
NRC (U.S. Nuclear Regulatory Commission) 2000. Issue Resolution Status Report Key 
Technical Issue: Total System Performance Assessment and Integration. Rev. 2. Washington, 
D.C.: U.S. Nuclear Regulatory Commission. TIC: 247614. 
NWTRB (U.S. Nuclear Waste Technical Review Board) 1992. Minutes, NWTRB Full Board 
Meeting, Denver, Colorado, July 7-8, 1992. TIC: 210563. 
Olsson, W.A. and Brown, S.R. 1993. Hydromechanical Response of a Fracture Undergoing 
Compression and Shear. International Journal of Rock Mechanics, Mining Sciences & 
Geomechanics Abstracts, 30, (7), 845-851. New York, New York: Pergamon Press. 
TIC: 234100. 
Olsson, W.A. and Brown, S.R. 1994. Mechanical Properties of Seven Fractures from Drillholes 
NRG-4 and NRG-6 at Yucca Mountain, Nevada. SAND94-1995. Albuquerque, New Mexico: 
Sandia National Laboratories. ACC: MOL.19941007.0081. 
Paperiello, C.J. 1999. U.S. Nuclear Regulatory Commission Staff Review of the U.S. 
Department of Energy Viability Assessment for a High-Level Radioactive Waste Repository at 
Yucca Mountain, Nevada. Letter from C.J. Paperiello (NRC) to L.H. Barrett (DOE), June 2, 
1999, with enclosures, U.S. Nuclear Regulatory Commission's Staff Evaluation of U.S. 
Department of Energys Viability Assessment and Letter from B.J. Garrick (NRC Advisory 
Committee on Nuclear Waste) to S.A. Jackson (NRC), dated April 8, 1999. 
ACC: HQO.19990811.0007; HQO.19990811.0008. 
Pruess, K. 1987. TOUGH User's Guide. NUREG/CR-4645. Washington, D.C.: U.S. Nuclear 
Regulatory Commission. TIC: 217275. 
Pruess, K. 1991. TOUGH2-A General-Purpose Numerical Simulator for Multiphase Fluid and 
Heat Flow. LBL-29400. Berkeley, California: Lawrence Berkeley Laboratory. 
ACC: NNA.19940202.0088. 
Pruess, K. 1997. On Vaporizing Water Flow in Hot Sub-Vertical Rock Fractures. Transport 
in Porous Media, 28, 335-372. Amsterdam, The Netherlands: Kluwer Academic Publishers. 
TIC: 238922. 
Pruess, K.; Tsang, Y.W.; and Wang, J.S.Y. 1984. Numerical Studies of Fluid and Heat Flow 
Near High-Level Nuclear Waste Packages Emplaced in Partially Saturated Fractured Tuff. 
LBL-18552. Berkeley, California: Lawrence Berkeley Laboratory. TIC: 211033. 
Pruess, K.; Wang, J.S.Y.; and Tsang, Y.W. 1990. On Thermohydrologic Conditions Near 
High-Level Nuclear Wastes Emplaced in Partially Saturated Fractured Tuff: 1. Simulation 
Studies with Explicit Consideration of Fracture Effects. Water Resources Research, 26, (6), 
1235-1248. Washington, D.C.: American Geophysical Union. TIC: 221923. 
Ramirez, A.L., ed. 1991. Prototype Engineered Barrier System Field Test (PEBSFT) Final 
Report. UCRL-ID-106159. Livermore, California: Lawrence Livermore National Laboratory. 
ACC: NNA.19910711.0047.

 6-15 
Raven, K.G. and Gale, J.E. 1985. Water Flow in a Natural Rock Fracture as a Function of 
Stress and Sample Size. International Journal of Rock Mechanics and Mining Sciences & 
Geomechanics Abstracts, 22, (4), 251-261. Oxford, United Kingdom: Pergamon Press. 
TIC: 235724. 
Reed, M.H. 1982. Calculation of Multicomponent Chemical Equilibria and Reaction Processes 
in Systems Involving Minerals, Gases, and an Aqueous Phase. Geochimica et Cosmochimica 
Acta, 46, 513-528. New York, New York: Pergamon Press. TIC: 224159. 
Rehbinder, G. 1995. Analytical Solutions of Stationary Coupled Thermo-Hydro-Mechanical 
Problems. International Journal of Rock Mechanics and Mining Sciences & Geomechanics 
Abstracts, 32, (5), 453-463. Oxford, United Kingdom: Elsevier Science. TIC: 235725. 
Roberts, J.J. and Lin, W. 1997. X-Ray Radiography of Fracture Flow and Matrix Imbibition in 
Topopah Spring Tuff Under a Thermal Gradient. International Journal of Rock Mechanics and 
Mining Sciences and Geomechanics Abstracts, 34, (3/4), 482. [London], Great Britain: Elsevier 
Science. TIC: 237400. 
Rosenberg, N.D.; Knauss, K.G.; and Dibley, M.J. 1999. Evaporation of J13 Water: Laboratory 
Experiments and Geochemical Modeling. UCRL-ID-134852. Livermore, California: Lawrence 
Livermore National Laboratory. TIC: 246322. 
Sagar, B.; Bagtzoglou, A.C.; Green, R.T.; and Stothoff, S.A. 1995. Measurement and 
Modeling of Flow Through Unsaturated Heterogeneous Rock in the Context of Geologic 
Disposal of Nuclear Waste. Proceedings of the ASME Heat Transfer and Fluids Engineering 
Divisions: Presented at the 1995 ASME International Mechanical Engineering Congress and 
Exposition, November 12-17, 1995, San Francisco, California. HTD Vol. 321, FED Vol. 233, 
271-284. New York, New York: American Society of Mechanical Engineers. TIC: 247816. 
Slider, H.C. 1976. Practical Petroleum Reservoir Engineering Methods, An Energy 
Conservation Science. Tulsa, Oklahoma: Petroleum Publishing Company. TIC: 247798. 
Sonnenthal, E.; Spycher, N.; Apps, J.; and Simmons, A. 1998. Thermo-Hydro-Chemical 
Predictive Analysis for the Drift-Scale Heater Test. Milestone SPY289M4. Version 1.1. 
Berkeley, California: Lawrence Berkeley National Laboratory. ACC: MOL.19981130.0132. 
Sonnenthal, E.L. and Bodvarsson, G.S. 1999. Constraints on the Hydrology of the Unsaturated 
Zone at Yucca Mountain, NV from Three-Dimensional Models of Chloride and Strontium 
Geochemistry. Journal of Contaminant Hydrology, 38, (1-3), 107-156. New York, New York: 
Elsevier. TIC: 244160. 
Steefel, C.I. and Lasaga, A.C. 1994. A Coupled Model for Transport of Multiple Chemical 
Species and Kinetic Precipitation/Dissolution Reactions with Application to Reactive Flow in 
Single Phase Hydrothermal Systems. American Journal of Science, 294, (5), 529-592. 
New Haven, Connecticut: Kline Geology Laboratory, Yale University. TIC: 235372.

 6-16 
Steefel, C.I. and Lichtner, P.C. 1998. Multicomponent Reactive Transport in Discrete 
Fractures: I. Controls on Reaction Front Geometry. Journal of Hydrology, 209, 186-199. 
Amsterdam, The Netherlands: Elsevier Science B.V. TIC: 247524. 
Stephansson, O. 1995. Introduction. International Journal of Rock Mechanics and Mining 
Sciences & Geomechanics Abstracts, 32, (5), 387. Oxford, United Kingdom: Elsevier Science. 
TIC: 236217. 
Stockman, H.; Krumhansl, J.; Ho, C.; and McConnell, V. 1994. The Valles Natural Analogue 
Project. NUREG/CR-6221. Washington, D.C.: U.S. Nuclear Regulatory Commission. 
TIC: 246123. 
Tsang, Y.W. and Birkholzer, J.T. 1999. Predictions and Observations of the Thermal- 
Hydrological Conditions in the Single Heater Test. Journal of Contaminant Hydrology, 38, 
(1-3), 385-425. New York, New York: Elsevier. TIC: 244160. 
Tsang, Y.W.; Apps, J.; Birkholzer, J.T.; Freifeld, B.; Hu, M.Q.; Peterson, J.; Sonnenthal, E.; and 
Spycher, N. 1999. Single Heater Test Borehole Perspective. LBNL-42537. Berkeley, 
California: Lawrence Berkeley National Laboratory. ACC: MOL.20000331.0665. 
Wildenschild, D.; Roberts, J.J.; Hardin, E.; and Lin, W. 1998. Experimental Tests of 
Enhancement of Thermal Vapor Diffusion in Topopah Spring Tuff. UCRL-JC-128747. 
Livermore, California: Lawrence Livermore National Laboratory. ACC: MOL.19990118.0060. 
Wilder, D.G. 1997. Technical Bases for EBS Design. Volume I of Near-Field and Altered-Zone 
Environment Report. UCRL-LR-107476, Rev. 1. Livermore, California: Lawrence Livermore 
National Laboratory. ACC: MOL.19980107.0365. 
Wilder, D.G. and Yow, J.L., Jr. 1987. Geomechanics of the Spent Fuel Test - Climax. UCRL- 
53767. Livermore, California: Lawrence Livermore National Laboratory. 
ACC: NNA.19900110.0337. 
Wilder, D.G., ed. 1993. Preliminary Near-Field Environment Report. UCRL-LR-107476. Two 
volumes. Livermore, California: Lawrence Livermore National Laboratory. 
ACC: NNA.19920501.0002. 
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. 
Wilder, D.G.; Lin, W.; Blair, S.C.; Buscheck, T.; Carlson, R.C.; Lee, K.; Meike, A.; Ramirez, 
A.L.; Wagoner, J.L.; and Wang, J. 1997. Large Block Test Status Report. UCRL-ID-128776. 
Livermore, California: Lawrence Livermore National Laboratory. ACC: MOL.19980508.0727.

 6-17 
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 EDA II Requirements and Guidelines for Implementation of EDA II. 
ACC: MOL.19990622.0126; MOL.19990622.0127; MOL.19990622.0128. 
WoldeGabriel, G.; Keating, G.N.; and Valentine, G.A. 1999. Effects of Shallow Basaltic 
Intrusion into Pyroclastic Deposits, Grants Ridge, New Mexico, USA. Journal of Volcanology 
and Geothermal Research, 92, 389-411. Amsterdam, The Netherlands: Elsevier Science. 
TIC: 246037. 
Wollenberg, H.A. and Flexser, S. 1986. Contact Zones and Hydrothermal Systems as 
Analogues to Repository Conditions. Chemical Geology, 55, 345-359. Amsterdam, The 
Netherlands: Elsevier Science B.V. TIC: 246171. 
Wruck, D.A. and Palmer, C.E.A. 1997. Analysis of Elevated Temperature Data for 
Thermodynamic Properties of Selected Radionuclides . Milestone SPL4B2M4. Livermore, 
California: Lawrence Livermore National Laboratory. ACC: MOL.19980109.0250. 
Wu, Y-S.; Haukwa, C.; and Bodvarsson, G.S. 1999. A Site-Scale Model for Fluid and Heat 
Flow in the Unsaturated Zone of Yucca Mountain, Nevada. Journal of Contaminant 
Hydrology, 38, (1-3), 185-215. New York, New York: Elsevier. TIC: 244160. 
Xu, T. and Pruess, K. 1998. Coupled Modeling of Non-Isothermal Multi-Phase Flow, Solute 
Transport and Reactive Chemistry in Porous and Fractured Media: 1. Model Development and 
Validation. LBNL-42050. Berkeley, California: Lawrence Berkeley National Laboratory. 
TIC: 243735. 
Xu, T.; Pruess, K.; and Brimhall, G. 1998. An Improved Equilibrium-Kinetics Speciation 
Algorithm for Redox Reactions in Variably Saturated Subsurface Flow Systems. LBNL-41789. 
Berkeley, California: Lawrence Berkeley National Laboratory. TIC: 240019. 
Younker, J.L. 1999. Question from Nuclear Waste Technical Review Board Regarding 
Variable Hydrologic Properties in Subunits of Potential Repository Emplacement Horizon. 
Letter from J.L. Younker (M&O) to Dr. S.J. Brocoum and R.E. Spence (DOE), May 11, 1999, 
LV.NS.JLY.05/99-020, with enclosure. ACC: MOL.19990520.0184. 
Zimmerman, R.W. and Bodvarsson, G.S. 1996. Effective Transmissivity of Two-Dimensional 
Fracture Networks. International Journal of Rock Mechanics and Mining Sciences & 
Geomechanics Abstracts, 33, (4), 433-438. Oxford, United Kingdom: Pergamon Press. 
TIC: 245649. 
Zyvoloski, G.; Dash, Z.; and Kelkar, S. 1992. FEHMN 1.0: Finite Element Heat and Mass 
Transfer Code. LA-12062-MS, Rev. 1. Los Alamos, New Mexico: Los Alamos National 
Laboratory. ACC: NNA.19910625.0038.

 6-18 
Zyvoloski, G.A.; Robinson, B.A.; Dash, Z.V.; and Trease, L.L. 1997. Users Manual for the 
FEHM Application  A Finite-Element Heat- and Mass-Transfer Code. LA-13306-M. 
Los Alamos, New Mexico: Los Alamos National Laboratory. TIC: 235999. 
6.2 CODES, STANDARDS, REGULATIONS, AND PROCEDURES 
64 FR 46976. 40 CFR 197: Environmental Radiation Protection Standards for Yucca Mountain, 
Nevada; Proposed Rule. Readily Available 
64 FR 67054. 10 CFR Parts 960 and 963. Office of Civilian Radioactive Waste Management; 
General Guidelines for the Recommendation of Sites for Nuclear Waste Repositories; Yucca 
Mountain Site Suitability Guidelines. Readily Available 
64 FR 8640. Disposal of High Level Radioactive Wastes in a Proposed Geologic Repository at 
Yucca Mountain. Readily Available 
AP-2.13Q, Rev. 0, ICN 1. Technical Product Development Planning. Washington, D.C.: U.S. 
Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: MOL.19991115.0230. 
AP3.10Q, Rev 2, ICN 2. Analyses and Models. 
AP-3.11Q, Rev. 0, ICN 1. Technical Reports. Washington, D.C.: U.S. Department of Energy, 
Office of Civilian Radioactive Waste Management. ACC: MOL.19991130.0149. 
AP-3.12Q, Rev 0, ICN 2. Calculations. Las Vegas, Nevada: ACC: MOL.20000620.0068. 
AP-3.15Q, Rev. 1, ICN 1. Managing Technical Product Inputs. Washington, D.C.: U.S. 
Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: MOL.20000218.0069. 
AP-SIII.2Q, Rev 0, ICN 2. Procedure for Qualification of Unqualified Data and the 
Documentation of Rationale for Accepted Data. Las Vegas, Nevada. 
ACC: MOL.20000217.0150. 
QAP-2-0, Rev. 5. Conduct of Activities. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19980826.0209. 
6.3 SOURCE DATA, LISTED BY DATA TRACKING NUMBER 
LL000314304242.094. NUFT Calculation LBT Sensitivity Calcs. Submittal date: 03/28/2000. 
LL000509112312.003. TSPA-SR MULTISCALE TH RESULTS (E0120) MEAN 
CALCULATIONS USING DRIFT SCALE PROPERTY SET. Submittal date: 05/18/2000. 
TBV.4713. 
LL970803004244.036. Data on Temperature of the Large Block Test (LBT). 
Submittal date: 08/08/1997.

 6-19 
LL970803104244.037. Data on Displacement of the Large Block Test (LBT). 
Submittal date: 08/08/1997. 
LL980913304244.072. Data Submission Report for Electrical Resistance Tomography Results 
Obtained During the Large Block Test FY98. Submittal date: 09/24/1998. 
LL980919304244.075. Neutron Logging Activities at the Large Block Test (LBT). 
Submittal date: 09/30/1998. 
LL990702804244.100. Pore Water Data. Submittal date: 7/13/1999. URN-0458. 
LL990708904243.033. Drift Scale Test (DST) Neutron Logging Data Report. 
Submittal date: 07/29/1999. 
MO9807DSTSET01.000. Drift Scale Test (DST) Temperature, Power, Current, Voltage Data 
for November 7, 1997 through May 31, 1998. Submittal date: 07/09/1998. 
MO9810DSTSET02.000. Drift Scale Test (DST) Temperature, Power, Current, Voltage Data 
for June 1 through August 31, 1998. Submittal date: 10/09/1998. 
MO9906DSTSET03.000. Drift Scale Test (DST) Temperature, Power, Current, and Voltage 
Data for September 1, 1998 through May 31, 1999. Submittal date: 06/08/1999.

 6-20 
INTENTIONALLY LEFT BLANK

 
APPENDIX A 
STATUS OF TH MODELS IMPLEMENTED BY THE NUFT COMPUTER CODE



 A-1 
A.1 TH MODEL TESTING USING NUFT 
NUFT is an integrated suite of software for numerical solution of a conceptual model of thermal 
and isothermal flow and transport in porous media, with application to subsurface contaminant 
transport problems. The code simulates the coupled transport of heat and multiple 
multicomponent fluid phases in porous and fractured media. The medium may be modeled as a 
single porous continuum, an equivalent porous continuum, or multiple continua consisting of 
porous and fractured media. Components may be volatile. Grid systems may be Cartesian or 
cylindrical, with one, two, or fully three-dimensional configurations possible. The active 
fracture concept (Liu et al. 1998) is one of the options available for handling fluid flow with the 
DKM. 
A validation test plan was prepared as is required by the Software Activity Plan for qualification 
and certification of NUFT Version 3.0s. The Integration Test Case Suite consists of 
twenty-seven test cases. The cases are identified as bmrk001 through bmrk018, vsam1 through 
vsam6, and verif01 through verif03. The problems are one-, two-, or fully three-dimensional, 
solved using the Cartesian coordinate system. The code was tested by benchmarking against 
NUFT 2.0s or by comparison with analytical solutions. All benchmarking problems were earlier 
benchmarked against the VTOUGH code. 
The test cases are generally two-phase and two-component problems that may be thermal or 
isothermal. The phases are liquid and gas, and the components are water and air. Air is treated 
as a pseudo-component with averaged properties. In some problems, it was necessary to isolate 
a physical process for examination by turning off other processes. For example, vapor diffusion 
and liquid flow are turned-off to examine code performance in modeling gas flow driven by 
pressure gradients. In other problems, multiple processes are addressed. 
The goal with bmrk001 through bmrk017 is to test the TH models treatment of specific 
hydrologic and thermal processes that are central to nuclear-waste isolation at Yucca Mountain. 
In some cases, a single process is isolated and examined, while in others, two or three process are 
examined. All bmrk problems are 1-D. 
The codes restart capability is tested using bmrk018. This test case is identical to bmrk001, 
except that execution is stopped at an earlier time and a restart file printed. The restart file is 
then used to prescribe initial conditions for a restart run. 
The vsam test cases for NUFT, vsam1 through vsam6, are one- and two-dimensional problems 
taken from the TOUGH manual. These problems were used in testing the TOUGH code, and 
later, in the qualification of VTOUGH and NUFT 2.0. Like the bmrk problems, the vsam 
problems examine many of the thermo-hydrologic processes that are important to nuclear waste 
disposal at the proposed repository site in Yucca Mountain. However, vsam2 through vsam6 
address more practical problems that examine multiple interacting processes, in 1-D and 2-D. As 
with the bmrks, the code was tested by benchmarking against NUFT 2.0s. 
The capability of NUFT to accurately solve three-dimensional problems was tested using 
verif01. This test problem addresses heat conduction in a rectangular parallel pipe. The 
numerical solution was compared with an analytical solution.

 A-2 
Radiant heat transfer was included in verif03 and the NUFT nested-mesh option in verif02. 
Active fracture simulation is addressed in verif04, evaporative flux in verif05, and the dual 
permeability option is tested in verif06. 
A.2 HISTORICAL TH MODEL TESTING 
Lee et al. (1993) presented preliminary verification and benchmark testing of NUFT. In this 
initial phase of model testing, seven one-dimensional fluid flow and thermal energy transport 
problems were solved. The primary objective was to examine model applicability for general 
field and laboratory problems. 
The term verification implies checking of the governing equations of the mathematical model 
to ensure that they have been properly programmed, and that the numerical solution algorithm 
works as intended. Code verification was performed by making direct comparisons between 
NUFT simulation results and known analytical or semi-analytical solutions of appropriate 
problems. 
Analytical and semi-analytical solutions are available for only a limited range of problems of 
interest, often with highly simplifying assumptions. Therefore, verification does not necessarily 
imply a fully debugged code, but suggests that the main program of the code and its frequently 
used subroutines are functioning adequately. 
In order to test the performance of the code on real or hypothetical field and laboratory problems 
for which analytical solutions were not available, code calculations were directly compared with 
well-established codes that had been previously tested. Benchmarking is used here to imply this 
kind of code-to-code comparison using test problems that are more realistic and are of practical 
interest. A relative or comparative validity is established if the results of such a code 
intercomparison show some acceptably low deviation. Through benchmarking, the credibility of 
a well-established code in solving some specific type of problem can be transferred to another 
code. 
The test problems were selected from a report on the verification and benchmark testing of the 
UNSAT-H computer code (Baca and Magnuson 1990). 
The test problems are classified as isothermal and thermal. The seven problems solved comprise 
four isothermal and three thermal problems. A brief description of each of them follows: 
1. VI-1. Philips Solution for a Vertical Column. This first isothermal test case is a 
verification problem addressing vertical unsaturated flow in a laboratory soil column. 
It requires simulation of the rapid movement of a wetting front driven by gravity and 
capillary forces. This test is a direct check of the computational accuracy of the code 
in the solution of Richardss equation. 
2. BI-1. Vertical Flow in a Laboratory Soil Column with Ponding. This is a benchmark 
problem addressing vertical flow in a relatively dry laboratory soil column under 
ponded conditions. The problem is similar to VI-1, except a constant pond ing height 
is maintained at the upper boundary. This problem tests the capability of the model to 
handle strong nonlinearities and high-pressure gradients. The NUFT simulation

 A-3 
results are compared with the results from three other codes: INSAT-H, FLASH, and 
TOUGH. 
3. BI-2. Infiltration in a Stratified Vadose Zone. This benchmark problem addresses 
infiltration in a thick, relatively dry, multilayered vadose zone located in a semiarid 
environment. The simulation deals with moisture movement through desiccated soils 
of highly variable hydrologic properties. It is assumed that the system is initially at 
steady state, receiving recharge at a constant rate. The recharge rate is then drastically 
reduced, and the response of the system, as it adjusts to the new recharge rate and 
eventually approaches a new steady state, is simulated. This type of problem is 
usually difficult to solve numerically, and provides a good test of the codes numerical 
solution technique. NUFT is benchmarked against UNSAT-H. 
4. BI-3. Partially Saturated Flow in Basalt. This problem requires simulation of 
unsaturated flow through a layered field site. The site considered is the vadose zone 
beneath the Radioactive Waste Management Complex of the Idaho National 
Environmental and Engineering Laboratory . The geology consists of surficial 
sediments underlain by flows of vesicular and massive basalt (Baca and 
Magnuson 1990). This test case will evaluate the model performance in simulating 
flow at field site using data obtained from laboratory and filed measurements. NUFT 
is benchmarked against UNSAT-H. 
5. VT-1. Heat Conduction with Sinusoidal Boundary Conditions. This nonisothermal 
problem presents a direct test of the ability of the code to solve the energy equation for 
purely conductive heat transfer with a time-varying temperature boundary condition. 
The system is a homogeneous soil column at a uniform initial temperature and a 
sinusoidal boundary temperature. Fluid flow is turned-off to prevent convective heat 
transfer. The problem simulates the temperature distribution observed in soil, 
including diurnal temperature fluctuations. Simulation results from NUFT are 
compared with the closed- form analytical solution. 
6. VT-2. Heat Conduction with Constant Heat Flux. This problem tests the ability of the 
code to solve the energy equation for purely conductive heat transfer with a constant 
heat-flux boundary condition. As with VT-1, the system is a homogeneous soil 
column at a uniform initial temperature, with fluid flow turned-off to prevent 
convection. NUFT results are compared with the closed- form analytical solution. 
7. BT-1. Thermal History of a Vadose Zone. This verification problem is based on field 
studies of soil temperatures at Idaho National Environmental and Engineering 
Laboratory (Baca and Magnuson 1990). The objective is to simulate the soil 
temperature history. The geology consists of surficial sediments and basalts. The 
system is simplified to two soil layers, each with homogeneous thermal properties. 
The surface boundary condition reflects seasonal temperature changes. The simulation 
results from NUFT are compared to results from UNSAT-H. 
In this initial phase of verification and benchmark testing, the NUFT code was used to solve 
seven 1-D unsaturated-flow and heat-transfer problems. Three verification and four

 A-4 
benchmarking problems were solved. Verification was performed by making direct comparisons 
between NUFT simulation results and known analytical or semianalytical solutions. Benchmark 
testing was done by comparing NUFT simulation results with the results from well-established 
and previously tested codes, using field and laboratory problems for which analytical solutions 
are not available. 
In the verification testing, agreement was observed between NUFT results and the analytical 
solutions. In the benchmark testing, results of code intercomparison were satisfactory. 
From these testing results, it was concluded that the TH model and NUFT code were ready for 
application to the types of unsaturated-flow and heat-transport problems addressed here. 
Additional code testing is ongoing including, multidimensional problems with chemicaltransport.

 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, 
AND PMR APPROACH FOR RESOLUTION



 B-1 
APPENDIX B 
7. ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION 
This appendix was developed from a review of the TSPA Peer Review Panel (Budnitz et al. 1999), the NF/AZ Coupled Effects Expert 
Elicitation (CRWMS M&O 1998a) and correspondence and reports of the Nuclear Waste Technical Review Board and the NRCs 
Advisory Committee for Nuclear Waste. 
Source Description of Issue PMR Approach 
Performance 
Assessment Peer 
Review Panel 
(PA PRP) 
(Budnitz 1999) 
Concerning coupled processes and the data and 
models that support them, the Panel believes that it 
may be beyond the capabilities of current analytical 
methodologies to analyze system of such scales 
and complexity. For this reason, the effects of 
coupled processes can probably be best dealt with 
through a combination of bounding analyzes and 
engineered features designed to minimize the 
effects of such processes. 
The EDA-II design provides for minimization of the effects through reduction in 
temperatures of the drift wall. 
The effects of coupled processes are modeled, as discussed in part, in Section 3.3 
and 3.4 of this PMR based on ranges of properties and climates. Section 3.3 
describes the models used to evaluate the potential effects of coupled THC 
processes on permeability and porosity within the NF. Section 3.4 describes the 
abstraction of the models used to evaluate the potential effects of coupled THC 
processes on UZ flow and transport. The confidence in coupled-process models is 
based on on-going field tests, which indicate that these models are generally 
appropriate. 
The effects of coupled processes are also described in other PMRs. The THC 
couplings under consideration for the engineered systems are included in the EBS 
Degradation, Flow, and Transport PMR (CRWMS M&O 2000g), the Waste 
Package Degradation PMR (CRWMS M&O 2000o), and the Waste Form 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural system 
are included in both the UZ F&T PMR (CRWMS M&O 2000f) and this PMR. 
PA PRP 
(Budnitz 1999) 
The coupled effects and their absence from the 
TSPA-VA are a significant cause of concern to the 
Panel. In the opinion of the Panel, the assumptions 
made in the TSPA-VA that the effects of THC 
activities will be short-lived and can be neglected 
are not warranted. 
The effects of coupled processes are modeled, in part, in Section 3.3 and 3.4 of 
this PMR. Section 3.3 describes the models used to evaluate the potential effects 
of coupled THC processes on permeability and porosity within the NF. Section 3.4 
of this PMR describes the abstraction of the models used to evaluate the potential 
effects of coupled THC processes on UZ flow and transport. The conclusions from 
these analyses were that THC effects for the EDA II design were not significant 
and therefore, can be neglected regardless of their duration. 
The effects of coupled processes are also described in other PMRs. The THC 
couplings under consideration for the engineered systems are included in the EBS 
Degradation, Flow, and Transport PMR (CRWMS M&O 2000g), the Waste 
Package Degradation PMR (CRWMS M&O 2000o), and the Waste Form 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural system 
are included in both the UZ F&T PMR (CRWMS M&O 2000f) and this PMR.

 B-2 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
PA PRP 
(Budnitz 1999) 
The Panel believes that there are some complicating 
factors in analyzing the thermal processes that need 
further attention. The Panel suggested testing the 
abstraction methodology against the DST. 
One of the objectives of the DST, as discussed in detail in the Thermal Test AMR, 
was to evaluate the impact of differing property sets and their impact on model 
results. Section 3.6 of this PMR describes the thermal tests, including the SHT, 
LBT, and the DST. Section 3.4 describes the abstraction of the models used to 
evaluate the potential effects of coupled THC processes on unsaturated zone flow 
and transport. The Thermal Test AMR (CRWMS M&O 2000q, Chapter 1) 
describes how a comparative analysis is performed of measurements from the 
thermal tests to results from the numerical simulations. These form the bases for 
the conclusions presented in the AMR. 
PA PRP 
(Budnitz 1999) 
Although the effects of thermal-mechanical 
interactions have not been included in the TSPA-VA, 
the Panel believes that they cannot be neglected. 
This PMR considers changes in hydrological properties because of THM. 
Section 3.5 of this PMR describes the results of THM calculations performed to 
estimate bounds on changes in fracture permeability in rock surrounding 
emplacement drifts. The results of these calculations are input to the UZ F&T PMR 
(CRWMS M&O 2000f). 
PA PRP 
(Budnitz 1999) 
A substantial part of fundamental scientific work on 
the relevant geochemical processes and conditions 
remains to be done. The Panel emphasizes their 
concern that this work be completed; however, given 
the magnitude of the experimental programs 
required, they suspect much will be lacking at the 
time of LA. 
Design changes implemented after TSPA-VA and incorporated in the EDA II 
design include reduced temperatures in the rock, a drip shield, different waste 
package design/materials, and a different ground support system. This reduces 
the need for studies, although it does not eliminate it. Furthermore, as described 
below, field studies continue. Section 3.6 of this PMR describes the thermal tests, 
including the SHT, the DST, and the LBT. The thermal testing program is 
designed for a duration that extends beyond the LA submittal date. This is 
required because of the temporal and geometrical scales needed to be somewhat 
representative of the repository conditions. However, the testing program will be 
sufficiently complete to allow testing of the conceptual and numerical models of the 
thermal heating period and with information from LBT and SHT, the cool down 
period can be represented, although testing will be incomplete. DOE is in the 
process of designing a Performance Confirmation program that will allow additional 
testing and model confidence-building to occur throughout the licensing process.

 B-3 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
PA PRP 
(Budnitz et al. 1999) 
Given this level of complexity, the Project staff 
should consider the degree to which they can expect 
to successfully model the NFE. There is 
considerable experience within the geochemical 
community in modeling equally complex systems 
(e.g., geothermal systems, natural analogue studies, 
studies of trace element behavior in natural 
systems). Even if critical parameters were well 
defined (e.g., incoming gas and water 
compositions); it would still be a formidable task to 
model the NFGE. 
Design changes implemented after TSPA-VA and incorporated in the EDA II 
design include reduced temperatures in the rock, a drip shield, different waste 
package design/materials, and a different ground support system (CRWMS 
M&O 1999a, Table 603; and Wilkins and Heath 1999). This reduces the need for 
studies, although it does not eliminate it. Furthermore, field studies continue. The 
effects of coupled processes are modeled, in part, in Sections 3.3 and 3.4 of this 
PMR. Section 3.3 addresses models used to evaluate the potential effects of 
coupled THC processes on UZ flow and transport. Section 3.4 describes the 
abstraction of the models used to evaluate the potential effects of coupled THC 
processes on UZ flow and transport. These models provide the framework to 
evaluate THC coupled processes at DS, predict flow and transport behavior for 
specified thermal loading conditions, and predict the chemistry of waters and gases 
entering the emplacement drifts. 
The effects of coupled processes are also described in other PMRs. The THC 
couplings under consideration for the engineered systems are described in the 
EBS Degradation, Flow, and Transport PMR (CRWMS M&O 2000g), the Waste 
Package Degradation PMR (CRWMS M&O 2000o), and the Waste Form 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural system 
are described in both the UZ F&T PMR (CRWMS M&O 2000f) and this PMR. 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, Section 
6.5)* 
Conceptual model of flow 
Differences have been found between results using 
the DK flow model and the equivalent-continuum 
flow model. The DK model allows for greater 
mobility of water in fractures, which has a great 
effect on modeled condensate build-up and 
drainage. A related flow issue, which could be 
important to thermal hydrology, is channelized flow, 
especially in discrete fractures. Such flow could 
greatly increase the spatial variability in the results 
by increasing the range of water flow rates 
contacting individual waste packages. 
A description and treatment of DK models and ECMs is provided in the Thermal 
Test AMR (CRWMS M&O 2000q). As described in that AMR, flow of liquid, gas, 
and heat in the rocks for the model domain occurs in both the fractures and rockmatrix 
of the model domain. The fractures and rock-matrix are conceptualized as 
two separate, overlapping continua. This conceptual model is referred to as the 
DK model. The assumption that the fractures form a continuum for flow is 
consistent with fracture-mapping data, borehole videos, and interference airpermeability 
data obtained from the DST test block. An AFM has been 
incorporated to address issues of channelized flow. The UZ F&T PMR (CRWMS 
M&O 2000f) and EBS Degradation, Flow, and Transport PMRs (CRWMS 
M&O 2000g) include detailed descriptions of the conceptual flow models and their 
justifications. The thermal testing program provides data from which to determine 
model appropriateness. In general, it is found that the DK model, which includes 
an AFM, is able to match the field results. The DK model represents the trends of 
the processes occurring in the host rock during a thermal perturbation better than 
the ECM using the same hydrological properties. 
* The VA synthesized issues raised by internal and external parties, without attribution of the source of each issue

 B-4 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Coupled processes 
A potentially important shortcoming of the thermalhydrological 
calculations is the lack of coupling to 
thermal-mechanical and thermal-chemical 
processes. These issues have been addressed to a 
limited extent (see Section 3.3.1), but the full range 
of possible (or even likely) behaviors has not been 
analyzed. The Near Field Environment Expert 
Elicitation will aid in considering these issues, but it 
was not completed until after the TSPA-VA analyses 
were finished. Therefore, implementing the 
recommendations from the expert elicitation remains 
to be done. 
Design changes implemented after TSPA-VA and incorporated in the EDA II 
design include reduced temperatures in the rock, a drip shield, different waste 
package design/materials, and a different ground support system. This reduces 
the need for studies, although it does not eliminate it. Furthermore, field studies 
continue. 
The coupling of THC to TM and TC processes has been investigated and is 
described in Chapter 3 of this PMR. The Thermal Test AMR (CRWMS 
M&O 2000q) describes both the DST and LBT. The purpose of the DST is to 
evaluate coupled thermal, hydrological, chemical, and mechanical processes that 
take place in unsaturated, fractured tuff over a range of temperatures from 
approximately 25BC to nearly 100BC. The scale of the DST allows investigation of 
the NFE and associated coupled thermal, hydrological, chemical, and mechanical 
processes on an emplacement-drift scale. In addition, the objective of the LBT was 
to create a planar, horizontal region of boiling in fractured-welded Topopah Spring 
tuff, to observe coupled THMC behavior in a block representative of the repository 
horizon rock. 
See Section 2.4.5 of this PMR for a summary of the NFE expert elicitation. 
Recommendations from the NF expert elicitation were not used directly, because 
the expert-elicitation recommendations were already bounded by the NF seepage 
abstraction. 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Thermal alterations of hydrological properties 
Thermal alterations of flow and thermal-hydrologicalchemical 
or thermal-hydrological- mechanical 
alterations of hydrological properties are potentially 
important. In the current TSPA structure, these 
effects fall under the thermal-hydrology component, 
but thermal-hydrological effects could be more 
closely coupled with mountain-scale UZ flow and 
transport, if necessary. 
The UZ F&T PMR (CRWMS M&O 2000f) addresses the effects of coupled THC on 
seepage and flow. In addition, Section 3.3 of this PMR addresses models used to 
evaluate the potential effects of coupled THC processes on UZ flow and transport. 
* The VA synthesized issues raised by internal and external parties, without attribution of the source of each issue

 B-5 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Thermal response of different hydrogeologic units 
The single heater test and the heated drift test are 
both located in the Topopah Spring middle 
nonlithophysal hydrogeologic unit. However, in the 
current repository design most of the emplacement 
drifts are in the Topopah Spring lower lithophysal 
unit, with some drifts in the middle nonlithophysal 
unit and others in the lower nonlithophysal unit. 
Confidence in the models would be enhanced by 
obtaining thermal response data in the other two 
units. 
The Project has never maintained that the thermal testing program in the Topopah 
Spring middle nonlithophysal hydrogeologic unit was totally representative of the 
entire repository horizon (Younker 1999). Nonetheless, the thermal testing 
program in the Topopah Spring middle Nonlithophysal hydrogeologic unit provides 
significant benefit to understanding coupled processes and thermal-mechanical 
properties of the Topopah Spring welded tuff. 
The recent completion of the ECRB cross drift through the Lower Lithophysical 
hydrogeologic unit offers the capability to extend thermal testing to the rock type in 
which most repository drifts will be located. The NWTRB recently questioned the 
general applicability of results from the DST. In response to these questions, 
several lines of evidence were reviewed and analyzed (Younker 1999). It was 
concluded that the hydrological properties in all three subunits of the Topopah 
Spring welded tuff are sufficient to induce drainage of moisture flux that would be 
mobilized by the thermal pulse in a design concept that maintains pillars that are 
below boiling. The Thermal Test AMR (CRWMS M&O 2000q) describes the 
thermal tests. As described in that AMR, although the DST block is located in the 
Topopah Spring middle nonlithophysal stratigraphic unit (tsw34) at Yucca 
Mountain, stratigraphic units both above and below tsw34 are also included in the 
model domain of the DST. 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Thermal-mechanical-chemical coupling 
Coupled models would benefit from incorporation of 
more details of drift materials, both their physicalmechanical 
evolution and chemically-induced 
changes to the hydrological properties of the 
engineered materials. These aspects would 
improve the description of water flow and 
radionuclide transport pathways and allow for 
development of more specific NFGE scenarios. 
The THC couplings under consideration for the engineered systems are addressed 
in the EBS Degradation, Flow, And Transport PMR (CRWMS M&O 2000g), the 
Waste Package Degradation PMR (CRWMS M&O 2000o), and the Waste Form 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural system 
are addressed in both the UZ F&T PMR (CRWMS M&O 2000f) and the NFE PMR. 
However, design changes have mitigated many of the concerns related to drift and 
engineered materials. The drift design no longer uses concrete liners and invert 
materials , and therefore the evolution of water chemistry associated with 
cementaceous materials is mitigated. 
* The VA synthesized issues raised by internal and external parties, without attribution of the source of each issue

 B-6 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Conceptual model of the NFGE 
The updated NFGE model could consider such 
topics as: 
Heterogeneity of water composition flowing through 
the fracture system and interacting with the drift 
environment 
Explicit CO2 evolution from water and minerals 
coupled to the gas flow in the thermal-hydrological 
system 
Explicit coupling of flow and geochemical reactions 
Section 3.3 of this PMR addresses models used to evaluate the potential effects of 
coupled THC processes on UZ flow and transport. This includes a complete 
description of the pertinent description of the mineral-water processes in the host 
rock and their effect on the NFE. The model is used to evaluate the effects of 
mineral dissolution and precipitation, the effects of CO2 exsolution and transport in 
the region surrounding the drift, the potential for forming calcite, silica or other 
mineral assemblage precipitation caps, and the resulting changes to porosity, 
permeability and seepage. Water chemistry evaluation and the heterogeneity of 
water composition flowing through the fracture system and interacting with the drift 
environment are addressed in Section 3.3.4. 
These topics are also addressed in the UZ F&T PMR (CRWMS M&O 2000f) and 
EBS Degradation, Flow, And Transport PMR (CRWMS M&O 2000g). 
TSPA-VA (CRWMS 
M&O 1998b, 
Volume 3, 
Section 6.5)* 
Consideration of All Significant Features and 
Processes in the Performance Assessment 
Modeling assumptions should be consistent across 
different process models, unless there is a 
defensible technical rationale. 
The AMRs that document assumptions have been subjected to thorough 
interdisciplinary reviews to help ensure consistency among assumptions made in 
more than one document about a given parameter. In addition, the PMRs 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. 
NF Expert Elicitation 
(CRWMS 
M&O 1998a) 
Thermal-Mechanical 
Assess the mechanical stability of the host rock in 
the NFE, where rock-mass failure can cause linear 
collapse, leading to rockfall into the emplacement 
drifts. Describe the processes in the thermal 
evolution of the repository, that will contribute to NF 
mechanical stability, both during the period of 
increasing or stable elevated temperature, and 
during cool down. Consider changes, if any, that 
would occur solely from thermal and thermalmechanical 
causes. 
This issue is discussed in the EBS Degradation, Flow, and Transport PMR 
(CRWMS M&O 2000g). Furthermore, design changes, specifically the addition of 
a drip shield and potential changes regarding backfill and drift orientation, minimize 
these impacts. This PMR considers changes in rock mass properties, specifically 
hydrological properties, because of THM. Section 3.5 of the NFE PMR describes 
the results of THM calculations performed to estimate bounds on changes in 
fracture permeability in rock surrounding emplacement drifts. The results of these 
calculations are input to UZ F&T PMR (CRWMS M&O 2000f). The results will also 
be input to the EBS Degradation, Flow, and Transport PMR (CRWMS M&O 2000g) 
for evaluation of impact on drift stability. 
* The VA synthesized issues raised by internal and external parties, without attribution of the source of each issue

 B-7 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
NFEE (CRWMS 
M&O 1998a) 
Thermal-Hydrological-Chemical 
Assess the impact of dissolution and precipitation in 
reflux zones, on fracture porosity and permeability 
above the emplacement drifts, and in pillars 
between drifts where drainage occurs in thermalhydrological 
simulations conducted for the TSPA-VA 
base case. Describe the changes, if any, that would 
occur solely from these chemical causes, both 
during the period of maximum thermal-hydrological 
activity before the reflux zone begins to contract, 
and during the cool down. 
Assess the impact of mineral alteration (to 
secondary forms with different physical hydrological 
properties) on fracture porosity and permeability 
above the emplacement drifts and along pathways 
where drainage occurs in thermal-hydrological 
simulations conducted for the TSPA-VA base case. 
Describe the changes if any, that would occur solely 
both during the period of maximum thermalhydrological 
activity before the reflux zone begins to 
contract, and during cool down. 
Assess changes in fracture-matrix coupling that may 
result from reflux activity. Describe the location, 
intensity, and irreversibility of such changes. 
Assess multiple effects from dissolution and 
alteration, and from thermal and thermal-mechanical 
processes, on the porosity, permeability, and 
mechanical stability of fracture pathways for 
drainage below the emplacement drifts. 
Assess the durability of any fracture porosity and 
permeability changes caused by dissolution and 
precipitation, or by mineral alteration, as the host 
rock cools. Consider redissolution of precipitates 
and mechanical adjustment of the rock mass during 
cooling. Identify any processes that are likely to 
dominate the long-term hydrological response of the 
rock mass. 
These issues are addressed in both the UZ F&T PMR (CRWMS M&O 2000f) and 
this PMR. Section 3.3 of this PMR addresses models used to evaluate the 
potential effects of coupled THC processes on hydrological properties while the 
UZ F&T PMR (CRWMS M&O 2000f) addresses impact of these changes on UZ 
flow and transport. These models provide the framework to evaluate THC coupled 
processes at DS, predict flow and transport behavior for specified thermal-loading 
conditions, and predict the chemistry of waters and gases entering the 
emplacement drifts. This includes a complete, pertinent description of the mineralwater 
processes in the host rock and their effect on the NFE. The model is used to 
evaluate the effects of mineral dissolution and precipitation, the effects of CO2 
exsolution and transport in the region surrounding the drift, the potential for forming 
calcite, silica or other mineral assemblage precipitation caps, and the resulting 
changes to porosity, permeability and seepage. Dissolution and precipitation are 
the primary impacts on FMXs. 
Section 3.5 of this PMR addresses models used to evaluate TM effects on 
permeability.

 B-8 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
NFEE (CRWMS 
M&O 1998a) 
Uncertainties in the near field need to be addressed. THC couplings for the natural system are addressed in both the UZ F&T PMR 
(CRWMS M&O 2000f) and this PMR. The THC couplings under consideration for 
the engineered systems are addressed in the EBS Degradation, Flow, And 
Transport PMR (CRWMS M&O 2000g), the Waste Package Degradation PMR 
(CRWMS M&O 2000o), and the Waste Form Degradation PMR (CRWMS 
M&O 2000ab). The UZ F&T PMR addresses the effects of coupled THC on 
seepage and flow. Section 3.3 of this PMR addresses the drift-scale coupled 
process models used to evaluate the potential effects of coupled THC processes 
on properties within the NFE, which are then used in evaluations of UZ flow and 
transport. Temporal and spatial variations of properties or conditions used in this 
PMR were consistent with the UZ F&T PMR (CRWMS M&O 2000f). In addition, 
this PMR considered spatial and temporal variations in conditions that arise from 
the emplacement of waste and the EBS. This information was based on the multiscale 
abstraction reported in the EBS Degradation, Flow, and Transport PMR 
(CRWMS M&O 2000g), as well as in the THC Abstraction AMR (CRWMS 
M&O 2000c) and the NFE FEPs AMR (CRWMS M&O 2000e) that support this 
PMR. 
NFEE (CRWMS 
M&O 1998a) 
NF chemical effects on the flow regime are not 
addressed in the PA and neither are temporal 
changes in NF chemistry. 
Section 3.3 of this PMR describes the models used to evaluate the potential effects 
of coupled THC processes on permeability and porosity within the NF. Section 3.4 
describes the abstraction of the models used to evaluate the potential effects of 
coupled THC processes on UZ flow and transport. Temporal and spatial variations 
of properties or conditions used in this PMR were consistent with the UZ F&T PMR 
(CRWMS M&O 2000f). In addition, this PMR considered spatial and temporal 
variations in conditions that arise from the emplacement of waste and the EBS. 
THC couplings for the natural system are addressed in both the UZ F&T PMR 
(CRWMS M&O 2000f) and this PMR. The THC couplings under consideration for 
the engineered systems are addressed in the EBS Degradation, Flow, And 
Transport PMR (CRWMS M&O 2000g), the Waste Package Degradation PMR 
(CRWMS M&O 2000o), and the Waste Form Degradation PMR (CRWMS 
M&O 2000ab). The UZ F&T PMR (CRWMS M&O 2000f) addresses the effects of 
coupled THC on seepage and flow. 
Results of THC analyses indicate that impact on flow is likely not to be significant. 
Section 3.3 of this PMR describes the models used to evaluate the potential effects 
of coupled THC processes on permeability and porosity in the NF. Section 3.4 
describes the abstraction of the models used to evaluate the potential effects of 
coupled THC processes on UZ flow and transport. Temporal and spatial variations 
of properties or conditions used in this PMR were consistent with the UZ F&T PMR 
(CRWMS M&O 2000f). In addition, this PMR considered spatial and temporal 
variations in conditions that arise from the emplacement of waste and the EBS.

 B-9 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
NRC Letter dated 
June 2, 1999 
(Paperiello 1999) 
The data and models used in the VA to calculate the 
quantity and chemistry of water dripping on waste 
packages are inadequate to describe the process 
and extent of potential dripping under ambient and 
thermally-altered conditions. 
The UZ F&T PMR (CRWMS M&O 2000f) addresses the effects of coupled THC on 
seepage and flow. The EBS Degradation, Flow, and Transport PMR (CRWMS 
M&O 2000g) describes the potential for seepage to contact waste packages. 
Section 3.3 of this PMR addresses the drift-scale coupled process models used to 
evaluate the potential effects of coupled THC processes on properties within the 
NFE, which are then used in evaluations of UZ flow and transport. The parameter 
values used in this PMR were the values either provided by the UZ F&T AMRs 
(CRWMS M&O 2000f) or used in their evaluations. 
NRC Comments on 
TSPA-VA 
(Paperiello 1999) 
The importance of characterizing the thermal 
perturbations to UZ flow fields during the heating 
phase and considering coupled thermalhydrological-
chemical-mechanical processes in PAs 
was raised in letters to DOE. 
Section 3.3 of this PMR addresses the drift-scale coupled process models used to 
evaluate the potential effects of coupled THC processes on properties within the 
NFE, which are then used in evaluations of unsaturated zone flow and transport. 
The parameter values used in this PMR were the values either provided by the 
UZ F&T AMRs (CRWMS M&O 2000f) or used in their evaluations. 
Section 3.6 of this PMR describes the thermal tests, including the Single Heater 
Test, the DST, and the LBT. The Thermal Test AMR (CRWMS M&O 2000a, 
Chapter 1) describes how the properties (and conceptual flow models) used to 
estimate in-drift thermodynamic environment and flow processes are compared to 
experimentally determined thermal-hydrological results.

 B-10 
APPENDIX B 
ISSUES IDENTIFIED BY REVIEW GROUPS, AND PMR APPROACH FOR RESOLUTION (Continued) 
Source Description of Issue PMR Approach 
NRC Letter dated 
June 2, 1999 
(Paperiello 1999) 
Another issue is the appropriate role of data 
collected during performance confirmation, relative 
to data available at the time of construction 
authorization. 
Section 3.6 of this PMR describes the thermal tests, including the SHT, the DST, 
and the LBT. The thermal testing program is designed for a duration that extends 
beyond the LA submittal date. This is required because of the temporal and 
geometrical scales needed to be somewhat representative of the repository 
conditions. However, data available at the time of construction authorization 
should be sufficiently complete to allow testing of the conceptual and numerical 
models of the thermal heating period. With the information from LBT and SHT, the 
cool down period can also be represented, although testing will be incomplete. 
DOE is in the process of designing a Performance Confirmation program that will 
allow additional testing and model confidence building to occur throughout the 
licensing process. 
NRC Meeting 
3/16/99 
(NRC 1999d) 
The DOE recognizes the chemical complexity of the 
near field, but the VA provides inadequate treatment 
of it. The chemical complexity of the NF needs to be 
addressed. 
The effects of coupled processes are modeled, in part, in Section 3.2 and 3.3 of 
this PMR. Section 3.3 describes the models used to evaluate the potential effects 
of coupled THC processes on permeability and porosity within the NF. Section 3.4 
of this PMR describes the abstraction of the models used to evaluate the potential 
effects of coupled THC processes on UZ flow and transport. 
The effects of coupled processes are also described in other PMRs. The THC 
couplings under consideration for the engineered systems are addressed in the 
EBS Degradation, Flow, and Transport PMR (CRWMS M&O 2000g), the Waste 
Package Degradation PMR (CRWMS M&O 2000o), and the Waste Form 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural system 
are addressed by both the UZ F&T PMR (CRWMS M&O 2000f) and this PMR. 
The NFE THC models are being improved to reduce uncertainty in water chemistry 
and effects on hydrological properties that can affect seepage.

 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES



 C-1 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES 
This appendix lists NFE FEPs. The process for developing and screening the FEPs is described 
in Section 2.5 of this PMR. 
FEP Number FEP Name and Description Screening 
Decision 
Screening 
Basis 
PMR 
1.1.02.00.00 Excavation/Construction. 
Excavation-related effects include changes to 
rock properties. 
Fracture effects 
Included/ 
chemistry 
effects excluded 
Meets all 
criteria/low 
consequence 
EBS 
UZ F&T 
1.1.02.02.00 Effects of pre-closure ventilation. 
Controls the extent of the boiling front. 
Condensation of moisture as a result of 
ventilation onto a waste package should not 
occur during the preclosure period since the 
ventilation air is expected to be relatively dry 
and the air-flow rate will be high. 
Include Meets all criteria EBS 
1.2.02.01.00 Fractures. 
Generation of new fractures and re-activation of 
preexisting fractures may significantly change 
the flow and transport paths. Newly formed and 
reactivated fractures typically result from 
thermal, seismic, or tectonic events. 
Exclude Low 
consequence to 
dose (TBV) 
UZ F&T 
SZ 
DE 
2.1.08.01.00 Increased unsaturated water flux at the 
repository. 
Extremely rapid influx could reduce 
temperatures below the boiling point during part 
or all of the thermal period. 
Include climate 
change/ 
exclude water 
quenching 
waste package 
Meets all 
criteria/Low 
consequence to 
dose 
UZ F&T 
EBS 
2.1.08.02.00 Enhanced influx (Philips drips). 
A mechanism for focusing unsaturated flow to 
an underground opening and producing local 
saturation. 
Include Meets all criteria UZ F&T 
EBS 
2.1.08.03.00 Repository dryout due to waste heat. 
The zone of reduced saturation migrates 
outward during the heating phase (about the 
first 1,000 years) and then migrates back to the 
containers as heat diffuses throughout the 
mountain and the radioactive sources decay. 
Include Meets all criteria NFE 
UZ F&T 
2.1.08.10.00 Desaturation or dewatering of the repository. 
Dewatering of rock at Yucca Mt occurs 
because of ventilation and because of 
repository heating. The UZ is unsaturated and 
resaturation (reentry of water to an equilibrium 
partial saturation) has a meaning different from 
that for a repository beneath the water table. 
Include Meets all criteria NFE 
UZ F&T

 C-2 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES (Continued) 
FEP Number FEP Name and Description Screening 
Decision 
Screening 
Basis 
PMR 
2.1.08.11.00 Resaturation of the repository. 
During resaturation (and sealing) of the 
repository, flow directions are different and the 
hydraulic conductivity is different. The 
conceptual flow models used in the process 
level thermal-hydrological models allowed rock 
matrix and fracture elements to resaturate as 
the repository cooled. 
Include Meets all criteria EBS 
2.1.09.01.00 Carrier plume forms in reestablishment of flow 
system and carries signature of repository 
(temp, pH, and solutes). 
It is likely that the flow system is reestablished 
before radionuclides are mobile. This 
reestablished flow system, which can be a 
locally saturated system (fracture flow) or a UZ 
flow system, carries the signature of the 
repository (e.g., pH, T, dissolved constituents, 
etc) and is termed the carrier plume 
Include Meets all criteria EBS 
2.1.09.12.00 Rind (altered-zone) formation in waste, EBS, 
and adjacent rock. 
Thermal-chemical processes alter the rock 
forming the drift walls mineralogically. These 
alterations have hydrological, thermal and 
mineralogic properties different from the current 
country rock. 
Included in THC 
model, but 
Excluded from 
TH models 
Low 
consequence to 
dose 
EBS 
2.1.11.01.00 Heat output/temperature in waste and EBS. 
Decay heat is a major issue in design. High 
loading density is intended to be part of the 
waste isolation scheme. Temperatures in the 
waste and EBS will vary through time. 
Include Meets all criteria EBS 
WF 
2.1.11.02.00 Non-uniform heat distribution/edge effects in 
repository. 
Temperature inhomogeneities in the repository 
lead to localized accumulation of moisture. 
Uneven heating and cooling at repository edges 
lead to non-uniform thermal effects during both 
the thermal peak and the cool-down period. 
Include/ 
exclude TM 
effects 
Meets all 
criteria/TM low 
consequence to 
dose (TBV) 
NFE 
UZ F&T 
2.2.01.01.00 Excavation and construction-related changes in 
the adjacent host rock. 
Stress relief, leading to dilation of joints and 
fractures, is expected in an axial zone of up to 
one diameter width surrounding the tunnels. 
Exclude Low 
Consequence to 
dose (TBV) 
UZ F&T

 C-3 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES (Continued) 
FEP Number FEP Name and Description Screening 
Decision 
Screening 
Basis PMR 
2.2.01.02.00 Thermal and other waste and EBS-related 
changes in the adjacent host rock. 
Changes in host-rock properties result from 
thermal effects or other factors related to 
emplacement of the waste and EBS, such as 
mechanical or chemical effects of backfill. 
Properties that may be affected include rock 
strength, fracture spacing and block size, and 
hydrological properties such as permeability. 
Exclude Low 
consequence to 
dose (TBV) 
2.2.01.03.00 Changes in fluid saturations in the excavation 
disturbed zone. 
During repository construction and operation, 
the near-field will partially desaturate, and the 
local hydrological regime may be disturbed. 
After backfilling, groundwater reenters host rock 
zones that were partially desaturated during the 
operational phase. 
Exclude Low 
consequence to 
dose 
2.2.06.01.00 Changes in stress (due to thermal, seismic, or 
tectonic effects) change porosity and 
permeability of rock. 
Even small changes in the fracture openings 
can cause large changes in permeability. The 
rock deforms according to the rock stress field. 
Changes in the groundwater flow and in the 
temperature field can change the stress acting 
on the rock, which in turn, can change the 
groundwater flow. However, it is estimated that 
the overall dose will not be sensitive to these 
permeability and flow path changes. 
Exclude Low 
consequence to 
dose 
DE 
2.2.07.10.00 Condensation zone forms around drifts. 
Repository design will affect the scale at which 
condensation caps form (over waste packages, 
over panels, or over the entire repository), and 
the extent to which shedding will occur as 
water flows from the region above one drift to 
the region above another drift or into the rock 
between drifts. 
Include Meets all criteria UZ F&T 
2.2.07.11.00 Return flow from condensation cap/resaturation 
of dryout zone. 
When the rocks have cooled enough, there is a 
return flow toward the drifts from the 
condensation cap as a plume of unsaturated 
flow. 
Include Included in 
process models 
used in TSPA 
UZ F&T

 C-4 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES (Continued) 
FEP Number FEP Name and Description Screening 
Decision 
Screening 
Basis PMR 
2.2.08.03.00 Geochemical interactions in geosphere 
(dissolution, precipitation, weathering and 
effects on radionuclide transport). 
Effects on hydrological flow properties of the 
rock, radionuclide solubilities, sorption 
processes, and colloidal transport are relevant. 
Kinetics of chemical reactions should be 
considered in the context of the time scale of 
concern. 
Include Meets all criteria UZ F&T 
SZ 
2.2.08.04.00 Redissolution of precipitates directs more 
corrosive fluids to container. 
This FEP concerns chemical precipitation 
plugging pores during heating and dissolution of 
the plugs during cooldown. When the pores 
open, the corrosive water is released and drains 
into the drift. 
Include Meets all criteria EBS 
UZ F&T 
2.2.10.04.00 Thermal-mechanical alteration of fractures near 
repository. 
Heat from the waste causes thermal expansion 
of the surrounding rock, generating 
compressive stresses near the drifts and 
extensional stresses away from them. The 
zone of compression migrates with time. 
Exclude Low 
consequence to 
dose (TBV) 
UZ F&T 
2.2.10.05.00 Thermal-mechanical alteration of rocks above 
and below the repository. 
Thermal-mechanical compression at the 
repository produces tension-fracturing in the 
PTn and other units above the repository. 
These fractures alter UZ flow between the 
surface and the repository. Extreme fracturing 
may propagate to the surface, affecting 
infiltration. Thermal fracturing in rocks below 
the repository affects flow and radionuclide 
transport to the saturated zone. 
Exclude Low 
consequence to 
dose (TBV) 
UZ F&T 
2.2.10.06.00 Thermal-chemical alteration (solubility 
speciation, phase changes, precipitation and 
dissolution). 
Changes in the groundwater temperature in the 
far-field, if significant, may change the solubility 
and speciation of certain radionuclides. This 
would have the effect of altering radionuclide 
transport processes. Relevant processes 
include volume effects associated with silica 
phase changes, precipitation and dissolution of 
fracture-filling minerals (including silica and 
calcite), and alteration of zeolites and other 
minerals to clays. 
Exclude except 
for THC input to 
some geochemical 
models 
Low 
consequence to 
dose (TBV) 
UZ F&T 
SZ

 C-5 
APPENDIX C 
NEAR-FIELD ENVIRONMENT FEATURES, EVENTS, AND PROCESSES (Continued) 
FEP Number FEP Name and Description Screening 
Decision 
Screening 
Basis PMR 
2.2.10.10.00 Two-phase buoyant flow and heat pipes. 
A heat-pipe consists of a system for transferring 
energy between a hot and a cold region, using 
the heat of vaporization and movement of the 
vapor as the transfer mechanism. Two-phase 
circulation continues until the heat source is too 
weak to provide thermal gradients required to 
drive it. Alteration of the rock adjacent to the 
drift produces may include dissolution that can 
maintain the permeability necessary to support 
circulation. 
Include Meets all criteria UZ F&T 
2.2.10.12.00 Geosphere dryout due to waste heat. 
Repository heat evaporates water near the 
drifts. The zone of reduced saturation migrates 
outward during the heating phase (about the 
first 1,000 years) and then migrates back to the 
containers as heat diffuses throughout the 
mountain and the radioactive sources decay. 
The extent and degree of dry-out depends on 
design and on the loading strategy for 
emplacement. 
Include Meets all criteria NFE 
UZ F&T 
2.2.10.13.00 Density-driven groundwater flow (thermal). 
The distribution of temperature within the 
crystalline basement is expected to be 
correlated with a distribution of groundwater 
density. Variations in density provide a driving 
force for groundwater flow. Density-driven flow 
is expected at Yucca Mountain, but with heat 
supplied by the repository. Based on the 
geothermal gradient and depth to the basement 
rocks, there is not likely to be any significant 
thermal contribution from the deep rocks. 
Include Meets all criteria SZ

 C-6 
INTENTIONALLY LEFT BLANK

 
APPENDIX D 
ISSUE RESOLUTION STATUS REPORTS, SUBISSUES, 
TECHNICAL ACCEPTANCE CRITERIA, AND PMR APPROACH



 D-1 
APPENDIX D 
ISSUE RESOLUTION STATUS REPORTS, SUBISSUES, 
TECHNICAL ACCEPTANCE CRITERIA, AND PMR APPROACH 
This appendix was developed from an analysis of the NRCs KTIs for the ENFE (NRC 1999a), Thermal Effects on Flow 
(NRC 1999b), Repository Design and Thermal-Mechanical Effects (NRC 1999c), and Total System Performance Assessment and 
Integration (NRC 2000). The table shows the location in YMP PMRs where each acceptance criterion applicable to the NFE is 
addressed. 
NRC Acceptance Criteria PMR Approach and Section Reference 
IRSR: EVOLUTION OF THE NEAR-FIELD ENVIRONMENT 
SUBISSUE 1 - EFFECTS OF COUPLED THC PROCESSES ON SEEPAGE AND FLOW 
Data and Model Justification Acceptance Criteria 
1 - Available data relevant to both temporal and spatial variations in conditions 
affecting coupled THC effects on seepage and flow were considered. 
Section 3.3 of the NFE PMR describes the models used to evaluate the 
potential effects of coupled THC processes on permeability and porosity within 
the NFE. The THC Process AMR (CRWMS M&O 2000b) describes how 
available data relevant to both temporal and spatial variations in conditions 
affecting coupled THC effects are considered. In addition, Section 3.10 of the 
UZ F&T PMR (CRWMS M&O 2000f) documents the abstraction of coupled THC 
effects for TSPA, based on the process modeling results presented in the same 
section. 
2 - DOEs 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 seepage and 
flow. 
Section 3.3 of the NFE PMR describes the models used to evaluate the 
potential effects of coupled THC processes on permeability and porosity within 
the NFE. This information is contained in the THC Process AMR (CRWMS 
M&O 2000b) that describes how available data relevant to both temporal and 
spatial variations in conditions affecting coupled THC effects are considered. In 
addition, the UZ F&T PMR (CRWMS M&O 2000f) summarizes available data 
used to establish initial and boundary conditions for the evaluation of THC 
effects on seepage and flow in the near field.

 D-2 
NRC Acceptance Criteria PMR Approach and Section Reference 
5 - If the testing program for coupled THC processes on seepage and flow is 
not complete at the time of LA, or if sensitivity and uncertainty analyses indicate 
additional data are needed, DOE will identify specific plans to acquire the 
necessary information as part of the performance confirmation program. 
All of the information needed to support the LA will be complete prior to the LA. 
Arguments presented in the LA will be based on testing and analysis conducted 
before LA and considered in the licensing review. Testing contained in the 
performance confirmation program is confirmatory. The performance 
confirmation program addresses coupled THC effects associated with the rock 
mass cooling response, coupled process testing, and seepage testing under 
heated environments during the pre-emplacement period. Longer term testing 
for seepage and NF THC testing and monitoring around selected emplacement 
drifts and under simulated postclosure conditions is also addressed. Testing of 
the in-drift environments is included as well. See the Performance 
Confirmation Plan (CRWMS M&O 2000z, Sections 5.3.1.2, 5.3.1.4, 5.3.1.5, 
5.3.2, and Appendix G). 
Acceptance Criteria within this sub-element addressed by other PMRs include: 
3  UZ F&T, EBS 
4  UZ F&T 
See Table 4.3-1 of the UZ F&T PMR and Appendix A of the EBS PMR 
(CRWMS M&O 2000f and 2000g) for additional information regarding these 
acceptance criteria. 
Data Uncertainty and Verification Acceptance Criteria 
1 - Reasonable or conservative ranges of parameters or functional relations 
were used to determine effects of coupled THC processes on seepage and 
flow. Parameter values , assumed ranges, probability distributions, and 
bounding assumptions are technically defensible and reasonably account for 
uncertainties. 
Section 3.3 of this PMR addresses the DSCP models used to evaluate the 
potential effects of coupled THC processes on properties in the NFE, which are 
then used in evaluating UZ flow and transport. The parameter values used in 
this PMR were the values either provided by the UZ F&T AMRs or used in their 
evaluations. Section 3.10.3 of the UZ F&T PMR (CRWMS M&O 2000f) 
discusses ranges in the characteristics of the natural system that were used to 
evaluate the effects of THC processes on seepage and flow, and the rationale 
for these ranges. 
2 - Uncertainty in data due to both temporal and spatial variations in conditions 
affecting coupled THC effects on seepage and flow were considered. 
Section 3.3 of this PMR addresses the DSCP models used to evaluate the 
potential effects of coupled THC processes on properties in the NFE, which are 
then used in evaluations of UZ flow and transport. Temporal and spatial 
variations of properties or conditions used were consistent with the UZ F&T 
PMR (CRWMS M&O 2000f). In addition, spatial and temporal variations in 
conditions that arise from the emplacement of waste and the EBS were 
considered. This information was based on the multi-scale abstraction reported 
here, as well as in the THC Abstraction AMR (CRWMS M&O 2000c) and the 
NFE FEPs AMR (CRWMS M&O 2000e) that support this PMR. Section 3.10.6 
of the UZ F&T PMR (CRWMS M&O 2000f) discusses the uncertainty in data 
affecting THC coupled processes on seepage and flow.

 D-3 
NRC Acceptance Criteria PMR Approach and Section Reference 
4 - The initial conditions, boundary conditions, and computational domain used 
in sensitivity analyses involving coupled THC effects on seepage and flow were 
consistent with available data. 
Sensitivity analyses will be included in TSPA-SR. 
5 - DOEs performance confirmation program should assess whether the 
natural system and engineered materials are functioning as intended and 
anticipated with regard to coupled THC effects on seepage and flow. 
All of the information needed to support the LA will be complete prior to the LA. 
Arguments presented in the LA will be based on testing and analysis conducted 
before LA and considered in the licensing review. Testing contained in the 
performance confirmation program is confirmatory. The performance 
confirmation program addresses coupled THC effects associated with the rock 
mass cooling response, coupled process testing, and seepage testing under 
heated environments during the pre-emplacement period. Longer term testing 
for seepage and NF THC testing and monitoring around selected emplacement 
drifts and under simulated postclosure conditions is also addressed. Testing of 
the in-drift environments is included as well. See the Performance Confirmation 
Plan (CRWMS M&O 2000z, Sections 5.3.1.2, 5.3.1.4, 5.3.1.5, 5.3.2, and 
Appendix G). 
Acceptance Criteria in this sub-element addressed by other PMRs include: 
3  UZ F&T 
See Table 4.3-1 of the UZ F&T PMR (CRWMS M&O 2000f) for additional 
information regarding this acceptance criterion. 
Model Uncertainty Acceptance Criteria 
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 the 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 DS THC models considered a large group of minerals, including calcite and 
hydrous calcium alumino-silicates, such as zeolites and smectite that occur 
naturally in the fracture and matrix. These are listed in Table 3-11 of 
Section 3.4 of this PMR and in the DS THC AMR (CRWMS M&O 2000b). The 
THC couplings under consideration for the engineered systems are also 
addressed in the EBS PMR (CRWMS M&O 2000g) and the Waste Form (WF) 
Degradation PMR (CRWMS M&O 2000ab). THC couplings for the natural 
system are addressed by both the UZ F&T PMR (CRWMS M&O 2000f) and the 
NFE PMR. However, much of this issue has been mitigated by design 
changes, which no longer incorporate use of concrete liners and invert 
materials. Thus, the major potential source of hyperalkaline fluids no longer 
exists. The UZ F&T and EBS PMRs (CRWMS M&O 2000f and 2000g) also 
discuss aspects of this Acceptance Criterion.

 D-4 
NRC Acceptance Criteria PMR Approach and Section Reference 
3 - Alternative modeling approaches consistent with available data and current 
scientific understanding were investigated, and their results and limitations were 
appropriately considered. 
Section 3.4 of this PMR describes the abstraction of the models used to 
evaluate the potential effects of coupled THC processes on properties within 
the NFE that might impact UZ flow and transport. The THC Abstraction AMR 
(CRWMS M&O 2000c) describes how a comparison of the thermal hydrologic 
variables , obtained from a DS THC model that implemented two different 
geochemical systems, was performed. The comparison highlighted that the 
differences in mineralogy only weakly influence the overall TH response of the 
geologic system. 
Model approaches and alternative model approaches for THC impacts on flow 
and transport are discussed in Section 3.10.7 of the UZ F&T PMR (CRWMS 
M&O 2000f). This acceptance criterion is also discussed in the EBS PMR 
(CRWMS M&O 2000g, Sections 3.1.1 and 3.1.2). 
Acceptance Criteria in this subelement addressed by other PMRs include: 
2 - UZ F&T, EBS 
4 - UZ F&T, EBS 
See Table 4.3-1 of the UZ F&T and Appendix A of the EBS PMR (CRWMS 
M&O 2000f and 2000g) for additional information regarding these acceptance 
criteria. 
Model Verification Acceptance Criteria 
1 -The mathematical models for coupled THC effects on seepage and flow are 
consistent with conceptual models based on inferences about NFE, field data 
and natural alteration observed at the site, and expected engineered materials. 
The mathematical models for coupled THC processes on seepage and flow are 
consistent with conceptual models and were developed based on data collected 
from the site, including the area around the in-situ thermal tests and borehole 
data. Section 3.3 and 3.4 of this PMR describes the process-level models, 
model abstractions , and supporting analyses that address the NFE processes. 
The THC Process AMR and THC Abstraction AMR (CRWMS M&O 2000b and 
2000c) that support development of this section describe the inputs and 
assumptions that underlie the modeling. 
Section 3.10 of the UZ F&T PMR (CRWMS M&O 2000f) summarizes the 
mathematical models used to evaluate coupled THC effects on seepage and 
flow. Rev. 0 of this PMR addresses the effects of THC on property sets. 
However, back-coupling with EBS PMR (CRWMS M&O 2000g) to consider 
expected engineered materials impacts on NFE properties was not included. 
Therefore, the effects of flow out of the drifts were not addressed in Rev. 0 of 
the NFE PMR. 
This acceptance criterion is also discussed in Appendix A of the EBS PMR 
(CRWMS M&O 2000g).

 D-5 
NRC Acceptance Criteria PMR Approach and Section Reference 
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 are compared with 
different mathematical models to judge robustness of results. 
Section 3.4 of this PMR describes the abstraction of the models used to 
evaluate the potential effects of coupled THC processes on NFE properties, 
which were considered in the UZ flow and transport PMR. The THC 
Abstraction AMR (CRWMS M&O 2000c) provides detailed descriptions of the 
inputs and assumptions used in the model abstraction. Chapter 5 of this PMR 
states that the assumptions described in detail in the THC Process AMR 
(CRWMS M&O 2000b) are applied in the THC Abstraction AMR. The processlevel 
model evaluation describes assumptions that are appropriate, because 
they are based on the calculation of mineral water reactions, the transport of 
aqueous and gaseous species, and the conceptual models that are used to 
describe the chemical and physical systems. It also provides a comparison of 
thermal-hydrologic variables obtained from a DS THC model that implemented 
two different geochemical systems. A comparison across process-level models 
(TH-only and THC) is also described in the AMR. In addition, results from a 
2-D, DS, TH-only model are compared to the TH results of the 2-D DS THC 
model described in the THC Process AMR (CRWMS M&O 2000b). Finally, the 
DS THC model TH results were compared to the multiscale TH model results in 
order to determine the extent of edge effects. These comparisons demonstrate 
robustness of results. Section 3.6 of this PMR discusses the validation of NFE 
models . 
Models with accompanying assumptions and approximations used to evaluate 
impacts of THC on seepage and flow are discussed primarily in the 
UZ F&T PMR (CRWMS M&O 2000f). Abstractions in the UZ F&T PMR 
(CRWMS M&O 2000f, Section 3.10) were derived from the underlying process 
models described in the UZ F&T PMR (CRWMS M&O 2000f). This acceptance 
criterion is also discussed in Appendix A of the EBS PMR (CRWMS 
M&O 2000g). 
Acceptance Criteria within this sub-element addressed by other PMRs include: 
2  UZ F&T, EBS 
See Table 4.3-1 of the UZ F&T PMR and Appendix A of the EBS PMR 
(CRWMS M&O 2000f and 2000g) for additional information regarding this 
acceptance criterion.

 D-6 
NRC Acceptance Criteria PMR Approach and Section Reference 
Integration Acceptance Criteria 
1 - DOE has considered all the relevant FEP. The abstracted models 
adequately incorporated design features, physical phenomena, and couplings, 
and used consistent and appropriate assumptions throughout. 
Section 2.5 of this PMR describes the treatment and documentation of primary 
FEPs affecting thermal hydrology and coupled process phenomena that impact 
the NFE. This section describes the process used to ensure that FEPs are 
categorized as either included or excluded. Included FEPs are directly 
represented in the process models and abstractions and are discussed in the 
PMR sections corresponding to the specific models. Section 3.4 describes the 
abstraction of the models used to evaluate the potential effects of coupled THC 
processes on UZ flow and transport. The THC Abstraction AMR (CRWMS 
M&O 2000c) provides descriptions of the inputs and assumptions used in the 
model abstraction. 
The UZ F&T PMR (CRWMS M&O 2000f) contains a discussion of FEPs 
impacting seepage and flow. This acceptance criterion is also discussed in 
Appendix A of the EBS PMR (CRWMS M&O 2000g). 
2 - Models reasonably accounted for known temporal and spatial variations in 
conditions affecting coupled THC effects on seepage and flow. 
Sections 3.3 and 3.4 of this PMR describes the process-level models, model 
abstractions and supporting analyses that address the NFE processes. The 
THC Process AMR and THC Abstraction AMR (CRWMS M&O 2000b and 
2000c) that support development of this section describe the inputs and 
assumptions that underlie the modeling. The DS THC used average conditions 
and temperature profiles for seven cases to address the variation in natural 
system effects. 
The UZ F&T PMR (CRWMS M&O 2000f) and ISM PMR (CRWMS M&O 2000y) 
discuss the spatial variations in properties and conditions that occur in the 
natural system that have impact on the NF. This acceptance criterion is also 
discussed in Appendix A of the EBS PMR (CRWMS M&O 2000g).

 D-7 
NRC Acceptance Criteria PMR Approach and Section Reference 
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 could include activities, such as independent 
modeling, laboratory or field data, or sensitivity studies. 
Section 2.1 of this PMR describes the process of analysis used to determine 
which couplings need to be considered in PA, and which were excluded, and 
the technical justification for that determination. Section 2.1 identifies and 
describes the weak couplings as second or third order effects for the NF 
processes. Weak coupled processes may be neglected in the initial 
calculations as second or third order effects this reduces the computer 
computational effort required to compute coupled problems. Sections 3.3 and 
3.4 describe the process level models, model abstractions and supporting 
analyses that address the NFE processes. The THC Process AMR and THC 
Abstraction AMR (CRWMS M&O 2000b and 2000c) that support development 
of this section describe the inputs and assumptions that underlie the modeling. 
Detailed descriptions and justification are provided for the basis for each 
assumption. The Repository Safety Strategy (RSS) describes the factors that 
contribute strongly to performance (CRWMS M&O 2000s). Coupled processes 
are described in the RSS as factors that do not contribute strongly to 
performance. 
It should also be noted that Section 2.5 of this PMR describes the FEPs 
included in this PMR. The NFE FEPs AMR (CRWMS M&O 2000e) supporting 
this section 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. 
The coupling of THC to seepage and flow is described in the UZ F&T PMR 
(CRWMS M&O 2000f). This acceptance criterion is also discussed in 
Appendix A of the EBS PMR (CRWMS M&O 2000g).

 D-8 
NRC Acceptance Criteria PMR Approach and Section Reference 
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. 
This PMR addresses the process of changes to properties that would need to 
be considered within the UZ F&T PMR (CRWMS M&O 2000f). Sections 3.3 
and 3.4 describe the process-level models, model abstractions and supporting 
analyses that address the NFE processes. The THC Process AMR and THC 
Abstraction AMR (CRWMS M&O 2000b and 2000c) that support development 
of this section describe the inputs and assumptions that underlie the modeling. 
Detailed descriptions and justifications are provided for the basis for each 
assumption. In addition, the THC Abstraction AMR (CRWMS M&O 2000c) 
provides explanations, documentation and justification for simplifications used 
in the abstractions described in that AMR. 
Modeling of seepage and flow, as well as abstractions of those models, is 
discussed in the UZ F&T PMR (CRWMS M&O 2000f). The UZ F&T PMR 
(CRWMS M&O 2000f, Section 3.10.11) documents the basis for the abstraction 
of coupled THC effects on seepage and flow. This acceptance criterion is also 
discussed in Appendix A of the EBS PMR (CRWMS M&O 2000g). 
Programmatic Acceptance Criteria 
1 - Data and models were collected, developed, and documented under 
acceptable quality assurance (QA) procedures. 
Activities associated with development of this PMR and its related AMRs were 
determined to be subject to the quality assurance program as described in the 
Quality Assurance Requirements and Description (QARD) (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 - Deficiency reports concerning data quality on issues related to coupled THC 
effects on seepage and flow were closed. 
The NFE PMR has been prepared according to AP-3.10Q and AP-3.15Q to 
address quality assurance deficiency issues. At the current time, the data used 
for the analyses and models are obtained from controlled sources that are 
undergoing qualification, and will be closed after completion of data qualification 
entries. 
This acceptance criterion is also discussed in Appendix A of the EBS PMR 
(CRWMS M&O 2000g).

 D-9 
NRC Acceptance Criteria PMR Approach and Section Reference 
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. 
Expert elicitations regarding seepage and flow were conducted in both the UZ 
and NF aspects . Expert elicitations associated with development of this PMR 
were determined to be subject to the quality assurance program as described in 
the QARD (DOE 2000) document. Appendix C of the QARD and implementing 
procedures for expert elicitation were developed using the guidance provided in 
NUREG-1563 (Kotra et al. 1996). Section 2.4.5 of this PMR addresses expert 
elicitation regarding parts of the elicitation that relate to the NFE. Refer to that 
section for a description of how expert elicitation was used. For a complete 
discussion, refer to the UZ F&T PMR (CRWMS M&O 2000f). 
SUBISSUE 2  EFFECTS OF COUPLED THC PROCESSES ON THE WASTE PACKAGE CHEMICAL ENVIRONMENT 
Data and Model Justification Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS 
2  EBS 
3  EBS 
4  EBS 
5  EBS 
6  EBS 
7  EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding these acceptance criteria. 
Data Uncertainty and Verification Acceptance Criteria 
1  EBS 
2  EBS 
3  EBS 
4  EBS 
5  EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding these acceptance criteria.

 D-10 
NRC Acceptance Criteria PMR Approach and Section Reference 
Model Uncertainty Acceptance Criteria 
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 the TH effects on gas and water 
chemistry. 
The THC interactions between the natural and engineered systems are 
primarily addressed in the EBS and UZ F&T PMRs (CRWMS M&O 2000g and 
2000f). This PMR addresses property changes that might impact the chemistry 
of water in the UZ that seeps into the drifts. These property changes are input 
to the UZ analyses. The results, the chemistry of the water seeping into drifts, 
are then input to the EBS PMR (CRWMS M&O 2000g). The EBS and WPD 
PMRs (CRWMS M&O 2000g and 2000ac) report the evaluations of the 
resulting chemistry. 
Likewise, the WP and EBS PMRs (CRWMS M&O 2000o and 2000g) determine 
the chemistry of fluids that result from THC couplings between the drift and 
waste package materials. They also provide the water chemistry information to 
the UZ to determine its effect on flow and transport. In this PMR, no analyses 
were made of the impact of chemistry of water exiting drifts on the hydrologic 
and chemical properties of the NF. The effects of the effluent chemistry are 
included in UZ transport calculations described in the UZ F&T PMR (CRWMS 
M&O 2000f). 
Section 3.3 addresses models used to evaluate the potential effects of coupled 
THC processes on NF chemical properties. These models provide the 
framework (or inputs) for UZ and EBS to evaluate THC coupled processes at 
DS, predict flow and transport behavior for specified thermal-loading conditions, 
and predict the chemistry of waters and gases entering the emplacement drifts.

 D-11 
NRC Acceptance Criteria PMR Approach and Section Reference 
3 - DOE provided a reasonable description of the mathematical models 
included in its analyses of coupled THC effects on waste package chemical 
environment. The description should include a discussion of alternative 
modeling approaches not considered in its final analysis and the limitations and 
uncertainties of the chosen model. 
The EBS PMR (CRWMS M&O 2000g) and the WPD PMR (CRWMS 
M&O 2000o) report the efforts to evaluate waste package chemical 
environment. The EBS PMR (CRWMS M&O 2000g, Section 3.1.2) presents 
alternative models for fully coupled THC modeling and also discusses modeling 
limitations and uncertainties. The UZ F&T PMR (CRWMS M&O 2000f) provides 
the descriptions of models used in establishing seepage-water chemistry and 
reports seepage-water chemistry that is used as input to the EBS and Waste 
Package models. The NFE PMR provides an assessment of the changes in 
mineralogy and deposition of salts etc. that would affect the seepage-water 
chemistry. 
Section 3.3 of this PMR addresses models used to evaluate the potential 
effects of coupled THC processes on mineralogy and/or salt depositions within 
the NF zone. Section 3.4 describes the abstraction of the models used to 
evaluate the potential effects of coupled THC processes on those chemical 
factors. The THC Abstraction AMR (CRWMS M&O 2000c) describes how the 
abstraction results in a number of simplified time-histories of mineral alterations 
or formations and/or depositions. 
Acceptance Criteria in this sub-element addressed by other PMRs include: 
2 - EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding this acceptance criterion.

 D-12 
NRC Acceptance Criteria PMR Approach and Section Reference 
Model Verification Acceptance Criteria 
3 - Abstracted models for coupled THC effects on waste package 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 
are compared with different mathematical models to judge robustness of 
results. 
The EBS and WPD PMRs (CRWMS M&O 2000g and 2000ac) report the waste 
package chemical environment and report on the associated abstractions. The 
EBS and WPD PMRs (CRWMS M&O 2000g and 2000ac) provide the 
descriptions of assumptions, approximations simplifications and abstractions 
used in those assessments. The UZ F&T PMR (CRWMS M&O 2000f) reports 
similar information for models used to determine seepage-water chemistry. The 
NFE PMR provides the description of assumptions and approximations used in 
models to assess the changes in mineralogy and deposition of salts etc. that 
would effect the seepage-water chemistry. 
Section 3.4 describes the abstraction of the models used to evaluate the 
potential effects of coupled THC processes on changes in mineralogy and 
deposition of salts etc. The THC Abstraction AMR (CRWMS M&O 2000c) 
provides detailed descriptions of the inputs and assumptions used in the model 
abstraction. It also provides a comparison of thermal-hydrologic variables 
obtained from a DS THC model that implemented two different geochemical 
systems. A comparison across process-level models (TH-only and THC) is also 
described in the AMR. In addition, results from 2-D, DS, TH-only models are 
compared to the TH results of the 2-D DS THC model described in the THC 
Process AMR (CRWMS M&O 2000b). Finally, the DS THC model TH results 
were compared to the multiscale TH model in order to determine the extent of 
edge effects. 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS 
2  EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding this acceptance criterion. 
Integration Acceptance Criteria 
1 - DOE has considered all the relevant FEP. The abstracted models 
adequately incorporated important design features, physical phenomena, and 
couplings, and used consistent and appropriate assumptions throughout. 
The determination of features, events and processes important to an 
assessment of the waste package chemical environment is contained in the 
EBS and WPD PMRs (CRWMS M&O 2000g and 2000ac). No evaluation of 
these FEPs was made as part of this PMR.

 D-13 
NRC Acceptance Criteria PMR Approach and Section Reference 
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 can include activities such 
as independent modeling, laboratory or field data, and sensitivity studies. 
The determination of which THC couplings were to be considered and how to 
address them was made in the EBS and WPD PMRs (CRWMS M&O 2000g 
and 2000ac). 
This PMR considered couplings that impacted changes in physical and 
chemical parameters of the NF. As such, it merely discussed those couplings 
that impacted the NF directly. Chapter 3 describes the process level models, 
model abstractions and supporting analyses that address the NF environment 
processes. The AMRs that support development of this section describe the 
inputs and assumptions that underlie the modeling. Detailed descriptions and 
justifications are provided for the basis for each assumption. 
4 - Where simplifications for modeling coupled THC effects on Waste Package 
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. 
This PMR had no direct feeds to performance assessment in this aspect. The 
EBS and WPD PMRs (CRWMS M&O 2000g and 2000ac) discuss the 
performance assessment efforts for this aspect. 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1 - EBS 
2 - EBS 
3 - EBS 
4 - EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding this acceptance criterion. 
Programmatic Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS 
2  EBS 
3  EBS 
See Appendix A of the EBS PMR (CRWMS M&O 2000g) for additional 
information regarding these acceptance criteria.

 D-14 
NRC Acceptance Criteria PMR Approach and Section Reference 
SUBISSUE 3 - EFFECTS OF COUPLED THC PROCESSES ON THE CHEMICAL ENVIRONMENT FOR RADIONUCLIDE RELEASE 
Data and Model Justification Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
4  WF and EBS 
5  WF and EBS 
6  WF and EBS 
7  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria. 
Data Uncertainty and Verification Acceptance Criteria 
Acceptance Criteria within this sub-element addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
4  WF and EBS 
5  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria. 
Model Uncertainty Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria.

 D-15 
NRC Acceptance Criteria PMR Approach and Section Reference 
Model Verification Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria. 
Integration Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
4  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria. 
Programmatic Acceptance Criteria 
Acceptance Criteria in this sub-element addressed by other PMRs include: 
1  WF and EBS 
2  WF and EBS 
3  WF and EBS 
See Table 4.2-1 of the WFD PMR and Appendix A of the EBS PMR (CRWMS 
M&O 2000ab and 2000g) for additional information regarding these acceptance 
criteria.

 D-16 
NRC Acceptance Criteria PMR Approach and Section Reference 
SUBISSUE 4 - EFFECTS OF COUPLED THC PROCESSES ON RADIONUCLIDE TRANSPORT THROUGH ENGINEERED AND NATURAL BARRIERS 
Data and Model Justification Acceptance Criteria 
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. 
Radionuclide transport issues are reported in the UZ F&T PMR (CRWMS 
M&O 2000f). The UZ F&T PMR (CRWMS M&O 2000f, Section 3.10) describes 
how relevant data were incorporated into the modeling. The EBS, WF, and 
WPD PMRs (CRWMS M&O 2000g, 2000ab, and 2000ac) provided input to UZ 
analyses relative to the chemistry of water and the amount and form of 
radionuclides released from the drifts. As such, this subissue is discussed 
principally in the UZ F&T PMR (CRWMS M&O 2000f) with some discussion in 
the other listed PMRs. There was no discussion within this PMR of this 
subissue. 
2 - DOEs 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 near field. 
The evaluation of coupled THC processes in the UZ F&T PMR (CRWMS 
M&O 2000f, Section 3.10) considered site characteristics in establishing initial 
and boundary conditions for conceptual models and simulation of coupled 
processes. This PMR calculated THC effects that could affect transport, but 
application of the results has not been completed. The chemistry of the 
effluent, as described in the EBS, WP, and WFD PMRs, is considered in 
transport by the UZ F&T PMR. 
7 - If the testing program for coupled THC processes on the chemical 
environment for radionuclide release from the EBS is not complete at the time 
of LA, 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. 
All of the information needed to support the LA will be complete prior to the LA. 
Arguments presented in the LA will be based on testing and analysis conducted 
before LA and considered in the licensing review. Testing contained in the 
performance confirmation program is confirmatory. The performance 
confirmation program addresses coupled THC effects associated with the rock 
mass cooling response, coupled process testing, and seepage testing under 
heated environments during the pre-emplacement period. Longer term testing 
for seepage and NF THC testing and monitoring around selected emplacement 
drifts and under simulated postclosure conditions is also addressed. Testing of 
the in-drift environments is included as well. See the Performance Confirmation 
Plan (CRWMS M&O 2000z, Sections 5.3.1.2, 5.3.1.4, 5.3.1.5, 5.3.2, and 
Appendix G).

 D-17 
NRC Acceptance Criteria PMR Approach and Section Reference 
Acceptance Criteria in this subelement addressed by other PMRs include: 
3  EBS, UZ F&T 
4  EBS 
5  EBS 
6  EBS, UZ F&T 
See Appendix A EBS PMR and Table 4.3-1 of the UZ F&T PMR (CRWMS 
M&O 2000g and 2000f) for additional information regarding these acceptance 
criteria. 
Data Uncertainty and Verification Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS, UZ F&T 
2  EBS, UZ F&T 
3  EBS, UZ F&T 
4  EBS, UZ F&T 
5  EBS, UZ F&T 
See Appendix A of the EBS PMR and Table 4.3-1 of the UZ F&T PMR 
(CRWMS M&O 2000g and 2000f) for additional information regarding these 
acceptance criteria. 
Model Uncertainty Acceptance Criteria 
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 the precipitation and dissolution of 
oxides and hydroxides on fracture surfaces, illitization of smectite, and 
recrystallization of zeolites to analcime, which could affect sorption 
characteristics. 
The UZ F&T PMR (CRWMS M&O 2000f) reports the issues related to zeolites 
and other minerals related to sorption characteristics. The NFE PMR discusses 
issues of precipitation and dissolution appropriate to the NF minerals within the 
fracture system of the NF. The effects of NF property changes on transport 
remain to be evaluated. The effluent chemistry, described in the EBS, WP, and 
WFD PMRs, is considered in the UZ F&T PMR. 
Acceptance Criteria in this subelement addressed by other PMRs include: 
2  EBS, UZ F&T 
3  EBS, UZ F&T 
See Appendix A of the EBS PMR and Table 4.3-1 of the UZ F&T PMR 
(CRWMS M&O 2000g and 2000f) for additional information regarding these 
acceptance criteria.

 D-18 
NRC Acceptance Criteria PMR Approach and Section Reference 
Model Verification Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS, UZ F&T 
2  EBS, UZ F&T 
3  EBS, UZ F&T 
See Appendix A of the EBS PMR and Table 4.3-1 of the UZ F&T PMR 
(CRWMS M&O 2000g and 2000f) for additional information regarding these 
acceptance criteria. 
Integration Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS, UZ F&T 
2  EBS, UZ F&T 
3  EBS, UZ F&T 
4  EBS, UZ F&T 
See Appendix A of the EBS PMR and Table 4.3-1 of the UZ F&T PMR 
(CRWMS M&O 2000g and 2000f) for additional information regarding these 
acceptance criteria. 
Programmatic Acceptance Criteria 
Acceptance Criteria in this subelement addressed by other PMRs include: 
1  EBS, UZ F&T 
2  EBS, UZ F&T 
3  EBS, UZ F&T 
See Appendix A of the EBS PMR and Table 4.3-1 of the UZ F&T PMR 
(CRWMS M&O 2000g and 2000f) for additional information regarding these 
acceptance criteria. 
SUBISSUE 5 - COUPLED THC PROCESSES AFFECTING POTENTIAL NUCLEAR CRITICALITY IN THE NEAR-FIELD 
Subissue 5 acceptance criteria are not addressed in PMRs. Criticality is 
addressed in a Topical Report and in supporting documents.

 D-19 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
Programmatic Acceptance Criteria 
1 - DOEs 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 PMR and its related AMRs were 
determined to be subject to the quality assurance program as described in the 
QARD (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. The NFE PMR provides input on changed conditions that could 
impact flow. This subissue is also addressed in the EBS PMR (CRWMS 
M&O 2000g), with supporting information from the NFE PMR. 
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 (Kotra et al. 1996) or other acceptable approaches. 
This PMR provides input on changed conditions that could impact flow. 
Therefore, this subissue is mainly addressed in the UZ F&T PMR (CRWMS 
M&O 2000f), with supporting information from this PMR. Expert elicitations 
associated with development of this PMR were determined to be subject to the 
quality assurance program as described in the QARD (DOE 2000) document. 
Appendix C of the QARD and implementing procedures for expert elicitation 
were developed using the guidance provided in NUREG-1563 (Kotra 
et al. 1996). Section 2.4.5 addresses expert elicitation. Refer to that section for 
a description of how expert elicitation was used.

 D-20 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
Technical Acceptance Criterion 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. 
TH processes affecting flow and transport are in the UZ F&T PMR (CRWMS 
M&O 2000f). This PMR reports the in situ and field thermohydrologic testing 
The EBS PMR (CRWMS M&O 2000g) reports quarter-scale testing at the Atlas 
Test Facility. Associated laboratory testing is reported in each of these PMRs. 
In this PMR, Section 3.6 describes the thermal tests, including the (SHT), the 
DST, and the (LBT). These tests were designed specifically to test the TH 
processes. While subsequent repository design changes have occurred, this 
testing remains applicable to testing the conceptual and numerical models. The 
Thermal Test AMR (CRWMS M&O 2000a) describes how the properties (and 
conceptual flow models) used to estimate in-drift thermodynamic environment 
and flow processes are compared to experimentally determined thermalhydrologic 
results. The thermal tests provide measured temperature and liquidsaturation 
data obtained from a known thermal perturbation. These data help 
make it possible to assess whether the hydrologic properties developed for 
ambient conditions alone can also reproduce the extent of the transient flow 
processes driven by a thermal perturbation. 
2 - Thermohydrologic tests are designed and conducted with explicit 
consideration of TH, thermal-chemical, and hydrologic-chemical couplings. 
This PMR reports the in situ and field thermohydrologic testing. The EBS PMR 
(CRWMS M&O 2000g) reports quarter-scale testing at the Atlas Test Facility. 
Associated laboratory testing is reported within each of these PMRs. 
Section 3.6 describes the thermal tests, including the LBT and the DST. 
Section 6.1 of the Thermal Test AMR describes the objectives of the LBT. The 
objective of the LBT was to create a planar, horizontal region of boiling in a 
block of fractured TSW, to observe coupled thermal-hydrological-mechanicalchemical 
(THMC) behavior in a representative rock unit. The heating duration 
of the test was designed to provide a sufficient length of time for THC 
processes to develop. 
The THC Process AMR (CRWMS M&O 2000b) describes the DST. The 
purpose of the DST is to evaluate the coupled thermal, hydrological, chemical, 
and mechanical processes that take place in unsaturated, fractured tuff over a 
range of temperatures from approximately 25C to nearly 200C.

 D-21 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
3 - Thermohydrologic tests are designed and conducted at different scales to 
discern scale effects on observed phenomena. 
The testing program discussed in Section 3.6 was designed to continue the 
testing at different scales. The scale dimension was extended from laboratory 
scale (core samples) to bench scale (small block tests) to the LBT and SHT and 
then to the large scale DST. Section 3.6 provides a description of the thermal 
tests. The SHT, DST, and LBT are all different scale tests. The SHT is a small 
to intermediate sized field test. The DST is geometrically more complex and 
larger scale than the SHT or LBT. The scale of the DST allows investigation of 
the NFE and associated coupled thermal, hydrological, chemical, and 
mechanical processes on an emplacement-drift scale. The size of the LBT was 
chosen so that the block of rock to be heated was large enough to contain 
several fractures, but small enough so that boundary conditions and rock 
heterogeneity could be adequately controlled and/or characterized. 
This subissue is also addressed in the EBS PMR (CRWMS M&O 2000g) 
4 - Thermohydrologic tests are designed and conducted for temperature ranges 
expected under repository operating conditions. 
The DST was designed to be consistent with the designs being considered. 
Section 3.6 describes the thermal tests, including the DST. As described in 
Section 3.6 of this PMR and in the THC Process AMR (CRWMS M&O 2000b, 
Section 6.2), the purpose of the DST is to evaluate the coupled thermal, 
hydrological, chemical, and mechanical processes that take place in 
unsaturated, fractured tuff over a range of temperatures from approximately 
25C to nearly 200C. The planned temperatures for the DST are consistent 
with an 85 MTU thermal load. Current design decisions may lower the driftwall 
peak temperatures. However, the overall rock temperatures are expected to be 
representative, unless there is a significant lowering of the MTU loading in the 
repository. 
This subissue is also addressed in the EBS PMR (CRWMS M&O 2000g)

 D-22 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
5 - Thermohydrologic tests are designed and conducted to determine if water 
refluxes back to the heaters during either the heating or cool-down phases of 
the tests. 
Two of the field tests reported in this PMR were specifically designed to look at 
reflux issues. The LBT was designed to maximize the conditions under which 
refluxing could occur. The temperatures were maintained at the surface to a 
point that would allow for condensation within the rock, and the heater 
temperatures were maintained above boiling. The wing heaters in the DST 
were also designed to create conditions that would be favorable to condensate 
buildup (or more correctly to create a thermal barrier that could potentially 
impair condensate drainage, and thus allow for both reflux and thermal 
perching of condensate) by creating a horizontal plane above the boiling point 
approximately 1/3 of the way up on the block and by maintaining below boiling 
temperatures on the top of the block. 
Section 3.6 describes the thermal tests, including the DST and LBT. The LBT 
was an integrated test and many different types of data were collected. A 
specific goal of the LBT was observation of condensate refluxing above a 
boiling zone. Also, the Updated In Situ Thermal Testing Program Strategy 
(CRWMS M&O 1997c) states that the LBT was intended to address the need 
for information on drainage/reflux by fracture flow. 
This subissue is also addressed in the EBS PMR (CRWMS M&O 2000g) 
7 - Thermohydrologic tests are designed and conducted to account for all mass 
and energy losses/gains in the model system. 
As discussed in Section 3.6, the LBT had controlled or monitored side 
boundaries to account for all mass and energy losses/gains. These boundaries 
consisted of an impermeable membrane glued to the side-rock surface to 
prevent loss of water mass through the sides , with insulation and heat-flux 
monitoring outside the membrane to account for the energy losses/gains. 
Further, there was a temperature control system installed at the top of the block 
to maintain constant surface temperature. The power input from this system 
was monitored. There were no controls on water mass-movement through the 
top and bottom of the block, although measurements were made below the 
block. 
As also discussed in Section 3.6, the DST was heavily monitored to account for 
mass and energy losses within the measurement sections. There was only 
partial control or accounting for energy losses from the ends, as discussed in 
the Thermal Test AMR (CRWMS M&O 2000a). Evaluation of impacts of heat 
and moisture losses in the DST concludes that test is acceptable and heat 
losses do not invalidate the test. 
This subissue is also addressed in the EBS PMR (CRWMS M&O 2000g)

 D-23 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
8 - Thermohydrologic tests are designed and conducted such that the model 
environment is sufficiently characterized so that the level of uncertainty in 
property values does not result in unacceptable uncertainty in thermal test 
interpretation. 
One of the objectives of the DST was to evaluate the impact of different 
property sets and their impact on model results. Section 3.6 describes the 
thermal tests, including the SHT, LBT and the DST. Chapter 1 of the Thermal 
Test AMR describes how a comparative analysis is performed of 
measurements from the thermal tests to results from the numerical simulations. 
These form the bases for the conclusions presented in the AMR. Section 6.2 of 
the Thermal Test AMR describes the results of the comparative analyses in 
sufficient detail to conclude that the environment is sufficiently characterized, so 
that the level of uncertainty in property values does not result in unacceptable 
uncertainty in thermal-test interpretation. Evaluation of impacts of heat and 
moisture losses in the DST concludes that losses do not invalidate the test. 
9 - Thermohydrologic tests are designed and conducted such that accuracy in 
the measurement of the test environment saturation is sufficient to discern the 
relative ability of different conceptual models to represent the TH processes in 
heated partially saturated, fractured porous media. 
Section 3.6 of this PMR describes the thermal tests, including the SHT, the 
DST, and the LBT. The Thermal Test AMR (CRWMS M&O 2000a) compares 
model results using a number of property sets to measured temperature and 
liquid saturation data obtained from a known thermal perturbation for 
comparison. The AMR provides a comparison of simulated and measured 
water saturation distributions to determine the accuracy of NFE and EBS TH 
models. The LBT and DST were performed at saturation ranges that are 
representative of that expected for the repository (from nearly 95% for DST to 
near-total desaturation or dryout). 
Technical Acceptance Criterion 2 
Thermohydrologic test results from other sites and programs have been 
analyzed and applied, as appropriate, to the Yucca Mountain site. 
Section 3.6 of this PMR addresses thermohydrologic test results from 
G-Tunnel, an unsaturated site similar to Yucca Mountain in rock type (welded 
tuff, Grouse Canyon) and initial saturation (approximately 85%).

 D-24 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
Technical Acceptance Criterion 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. 
All of the information needed to support the LA will be complete prior to the LA. 
Arguments presented in the LA will be based on testing and analysis conducted 
before LA and considered in the licensing review. Testing contained in the 
performance confirmation program is confirmatory. The performance 
confirmation program addresses thermal-hydrologic effects on unsaturated 
zone flow and seepage into emplacement drifts during the pre-emplacement 
period, including assessment of the thermal hydrologic response of rock mass 
and cooling and seepage testing under heated environments . Longer term 
testing for seepage and NF THC testing and monitoring around selected 
emplacement drifts and under simulated postclosure conditions is also 
addressed. Testing of the in-drift environments is included as well. See the 
Performance Confirmation Plan (CRWMS M&O 2000z, Sections 5.3.1.2, 
5.3.1.4, 5.3.1.5, 5.3.2, and Appendix G). 
SUBISSUE 2 - IS THE U.S. DEPARTMENT OF ENERGY TH MODELING APPROACH SUFFICIENT TO PREDICT THE NATURE AND BOUNDS OF 
THERMAL EFFECTS ON FLOW IN THE NEAR FIELD? 
Programmatic Acceptance Criteria 
1 - DOEs thermohydrologic modeling analyses were developed and 
documented under acceptable QA procedures. 
Activities associated with development of this PMR and its related AMRs were 
determined to be subject to the quality assurance program as described in the 
QARD (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. TH modeling is contained in this PMR scope (Sections 3.2, 3.3, 
3.4, and 3.6) and two of its supporting AMRs, Thermal Test AMR and THC 
Abstraction AMR (CRWMS M&O 2000a and 2000c). This subissue is also 
addressed in the EBS PMR (CRWMS M&O 2000g).

 D-25 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
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 (Kotra et al. 1996) or other 
acceptable approaches 
TH modeling is contained in this PMR scope (Sections 3.2, 3.3, 3.4, and 3.6) 
and two of its supporting AMRs, Thermal Test AMR and THC Abstraction AMR 
(CRWMS M&O 2000a and 2000c). This subissue is also addressed in the UZ 
F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). Expert elicitations 
were determined to be subject to the quality assurance program as described in 
the QARD (DOE 2000) document. Appendix C of the QARD and implementing 
procedures for expert elicitation were developed using the guidance provided in 
NUREG-1563 (Kotra et al. 1996). 
Section 2.4.5 addresses expert elicitation. Refer to that section for a 
description of how expert elicitation was used. 
Technical Acceptance Criterion 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. 
TH modeling is contained in this PMR scope (Sections 3.2, 3.3, 3.4, and 3.6) 
and two of its supporting AMRs, Thermal Test AMR and THC Abstraction AMR 
(CRWMS M&O 2000a and 2000c). This subissue is also addressed in the UZ 
F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). This PMR provides 
input to coupled-process-induced changes in the parameters used in those 
analyses. Section 3.3 addresses the drift-scale coupled-process models and 
abstractions used to evaluate those parameter changes. 
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. 
TH modeling is contained within this PMR scope (Sections 3.2, 3.3, 3.4, and 
3.6) and two of its supporting AMRs, Thermal Test AMR and THC Abstraction 
AMR (CRWMS M&O 2000a and 2000c). This subissue is also addressed in the 
UZ F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). This PMR provides 
input to coupled-process-induced changes in the parameters used in those 
analyses. Section 3.3 addresses the coupled process models and abstractions 
used to evaluate parameter changes within the NF that might effect the results 
of the TH analyses.

 D-26 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
Technical Acceptance Criterion 3 
Coupling of processes has been evaluated using a methodology in accordance 
with NUREG-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. 
TH modeling is contained within this PMR scope (Sections 3.2, 3.3, 3.4, and 
3.6) and two of its supporting AMRs, Thermal Test AMR and THC Abstraction 
AMR (CRWMS M&O 2000a and 2000c). This subissue is also addressed in the 
UZ F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). This PMR 
discusses the evaluation of coupled process effects on the conditions or 
parameters (e.g., porosity and permeability) that are input to the TH models. 
This acceptance criterion is also addressed by the EBS PMR (CRWMS 
M&O 2000g). See Appendix A of the EBS PMR for additional discussion. 
Technical Acceptance Criterion 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. 
TH modeling is contained in this PMR scope (Sections 3.2, 3.3, 3.4, and 3.6) 
and two of its supporting AMRs, Thermal Test AMR and THC Abstraction AMR 
(CRWMS M&O 2000a and 2000c). This subissue is also addressed in the UZ 
F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). See Table 4.3-1 and 
Appendix A of the referenced PMRs for additional discussion. 
Technical Acceptance Criterion 5 
ECMs 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 
ECM produces a conservative effect on calculated overall performance. 
TH modeling is contained within this PMR scope (Sections 3.2, 3.3, 3.4, and 
3.6) and two of its supporting AMRs, Thermal Test AMR and THC Abstraction 
AMR (CRWMS M&O 2000a and 2000c). This subissue is also addressed in the 
UZ F&T and EBS PMRs (CRWMS M&O 2000f and 2000g). This PMR 
discusses issues dealing with THC effects on properties or with model 
confidence building. Chapter 3 addresses process models and abstractions. 
As described in that section, ECM models are not used in DS THC models. 
The only models used are DK models. 
This acceptance criterion is also addressed by the US F&T and EBS PMRs 
(CRWMS M&O 2000f and 2000g). See Table 4.3-1 and Appendix A of the 
referenced PMRs for additional discussion.

 D-27 
IRSR: THERMAL EFFECTS ON FLOW 
SUBISSUE 1 - IS THE U.S. DEPARTMENT OF ENERGY TH TESTING PROGRAM, INCLUDING PERFORMANCE CONFIRMATION TESTING, 
SUFFICIENT TO EVALUATE THE POTENTIAL FOR THERMAL REFLUX TO OCCUR IN THE NEAR FIELD? 
Technical Acceptance Criterion 7 
Results of process-level models have been verified by demonstrated 
consistency with results/observations from field-scale, thermohydrologic test. In 
particular, sufficient physical evidence should exist to support the conceptual 
models used to predict thermally driven flow in the near field. 
Chapter 3 addresses process model confidence building or verification through 
comparisons with field tests. As described in that section, the DST THC model, 
constructed for the DST, is used to predict THC processes prior to and during 
the DST. Measured data from the DST are used to evaluate the conceptual 
and numerical models. Results from DST THC simulations were compared to 
measured gas-phase CO2 concentrations, and the chemistry of waters collected 
from hydrology boreholes during the test. The results of these comparisons 
provide indication of consistency with results and observations from field-scale 
thermal tests. 
This acceptance criterion is also addressed by the UZ F&T and EBS PMRs 
(CRWMS M&O 2000f and 2000g). See Table 4.3-1 and Appendix A of the 
referenced PMRs for additional discussion.

 D-28 
IRSR: REPOSITORY DESIGN AND THERMO-MECHANICAL EFFECTS 
SUBISSUE 3: THERMAL-MECHANICAL EFFECTS ON UNDERGROUND FACILITY DESIGN AND PERFORMANCE 
Component 1: Thermal-Mechanical Effects on Design of the Underground Facility 
7 - The thermal-mechanical design and analyses make use of appropriate 
constitutive models that represent jointed rock mass behavior under prolonged 
heated conditions. These models are tested as appropriate (verified, validated, 
and calibrated) to the extent practicable 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.) 
All of the information needed to support the LA will be complete prior to the LA. 
Arguments presented in the LA will be based on testing and analyses 
conducted before LA and considered in the licensing review. Testing contained 
in the performance confirmation program is confirmatory. The performance 
confirmation program addresses thermal-mechanical effects on the rock mass 
during the pre-emplacement period. Additional longer-term measurements 
associated with rock mass monitoring are identified for selected emplacement 
drifts during the pre-closure period and are included in testing of the proposed 
simulation of the postclosure environment. See the Performance Confirmation 
Plan (CRWMS M&O 2000z, Sections 5.3.1.5, 5.3.2, and Appendix G). 
8 - Both drift- and repository-scale models of the underground facility are used 
in thermal-mechanical 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. 
This is addressed in the EBS PMR (CRWMS M&O 2000g). 
10 - Time sequences of thermal loading used in thermal-mechanical design and 
analyses are clearly defined. 
This is reported in the EBS PMR (CRWMS M&O 2000g). For purposes of THC 
and the THM calculation in this PMR, related to hydrology, the thermal loading 
and repository design inputs are provided in Sections 3.2, 3.3 and 3.5, 3.6. 
NFE and EBS TH calculations currently assume simultaneous emplacement of 
all waste, and run cases for various preclosure periods ranging from the first to 
last drift preclosure heat duration.

 D-29 
IRSR: REPOSITORY DESIGN AND THERMO-MECHANICAL EFFECTS 
SUBISSUE 3: THERMAL-MECHANICAL EFFECTS ON UNDERGROUND FACILITY DESIGN AND PERFORMANCE 
Component 3: Thermal-Mechanical Effects on Flow into Emplacement Drifts 
1 - Approved quality assurance, control procedures, and standards, were 
applied to collection, development, and documentation of data, methods, 
models, and codes. 
Activities associated with development of this PMR and its related AMRs were 
determined to be subject to the quality assurance program as described in the 
QARD (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. However, this subissue is primarily addressed in the EBS PMR 
(CRWMS M&O 2000g). 
2 - If used, expert elicitation is conducted and documented in accordance with 
NUREG-1563 or other acceptable approaches. 
This subissue is primarily addressed in the EBS PMR (CRWMS M&O 2000g). 
Expert elicitations were determined to be subject to the quality assurance 
program as described in the QARD (DOE 2000) document. Appendix C of the 
QARD and implementing procedures for expert elicitation were developed using 
the guidance provided in NUREG-1563 (Kotra et al. 1996). 
4 - Changes in hydrological properties (e.g., fracture porosity and permeability) 
due to thermally induced ground movements are estimated taking into account 
the uncertainties in the context of their impacts on performance. 
Section 3.5 describes the results of THM calculations performed to estimate 
bounds on changes in fracture porosity and permeability in rock surrounding 
emplacement drifts. Ongoing work is expected to reduce uncertainties in THM 
results.

 D-30 
IRSR: TOTAL SYSTEM PERFORMANCE ASSESSMENT AND INTEGRATION 
SUBISSUE 1  SYSTEM DESCRIPTION AND DEMONSTRATION OF MULTIPLE BARRIERS 
Transparency and Traceability of the Analysis 
TSPA Documentation Style, Structure, and Organization 
Criterion T1 - Documents and reports are complete, clear, and consistent. The NFE PMR was carefully structured to be complete, clear, and consistent. 
Reviews of the draft document included checks for completeness, clarity and 
consistency. 
Criterion T2 - Information is amply cross-referenced. The NFE PMR and supporting AMRs contain ample references to data sources, 
codes, assumptions, and conclusions. 
Features, Events, and Processes Identification and Screening 
Criterion T1 - The screening process by which FEPs were included or excluded 
from the TSPA is fully described. 
Section 2.5 of this PMR summarizes the FEPs process. Appendix C of this 
PMR presents the results for the NFE FEPs including excluded and included 
FEPs and the rationale for these decisions. 
Criterion T2 - Relationships between relevant FEPs are fully described. Section 2.5 of this PMR describes the relationship between primary and 
secondary FEPs. The NFE FEPs AMR (CRWMS M&O 2000e) provides 
additional documentation. 
Abstraction Methodology 
Criterion T1 - The levels and method(s) of abstraction are described starting 
from assumptions defining the scope of the assessment down to assumptions 
concerning specific processes and the validity of given data. 
For each model in the NFE PMR, descriptions are provided of process models 
and, if appropriate, model abstractions. The description includes a summary of 
data and assumptions used to construct models. The AMRs describing the 
models and the abstracted models provide additional details regarding data and 
assumptions. 
Criterion T2 - A mapping (e.g., a road map diagram, a traceability matrix, a 
cross-reference matrix) is provided to show what conceptual features (e.g., 
patterns of volcanic events) and processes are represented in the abstracted 
models, and by what algorithms. 
The NFE PMR and supporting AMRs provide descriptions of the basis for the 
decisions and assumptions that were made during the abstraction process. 
Criterion T3 - An explicit discussion of uncertainty is provided to identify which 
issues and factors are of most concern or are key sources of disagreement 
among experts. 
The NFE PMR provides a discussion of uncertainties and limitations for the 
major process models included in the report. The AMRs describing the 
abstracted models provide additional details regarding uncertainties and 
limitations.

 D-31 
Data Use and Validity 
Criterion T1 - The pedigree of data from laboratory tests, natural analogs, and 
the site is clearly identified. 
Section 1.5 of this PMR describes the quality assurance requirements applied 
to the development of this PMR. Chapter 4 of the AMRs describing the models 
clearly identifies data and parameters used in the development of the AMRs 
and provides additional details regarding pedigree of data. 
Criterion T2 - Input parameter development and basis for their selection is 
described. 
The NFE PMR discusses input parameter development and the basis for using 
the parameters. Chapter 4 of the AMRs describing the models provide 
additional details regarding input parameter development and the basis for input 
selection. 
Criterion T3 - A thorough description of the method used to identify 
performance confirmation program parameters [has been developed]. 
The Performance Confirmation Plan (CRWMS M&O 2000z) specifically 
addresses the methodology for identifying and selecting parameters that are 
important to performance based upon TSPA sensitivity analyses and the 
repository safety strategy. Methods used to collect information for each 
parameter will be described by the performance confirmation plan or relevant 
supporting documents to support the LA. Performance confirmation test 
selection and rationale is also described in the plan based upon the significance 
of the parameter being measured, and the ability of the test to distinguish 
construction, emplacement, or time dependent changes in the parameter 
significant to performance. 
Assessment Results 
Criterion T1 - PA results (i.e., the peak expected annual dose within the 
compliance period) can be traced back to applicable analyses that identify the 
FEPs, assumptions, input parameters, and models in the PA. 
The TSPA-SR summarizes features, processes, conceptual models, and their 
implementation into the TSPA. This discussion will be based in part on 
information provided by the NFE PMR. 
Criterion T2 - The PA results include a presentation of intermediate results that 
provide insight into the assessment (e.g., results of intermediate calculations of 
the behavior of individual barriers) 
TSPA-SR provides performance analysis results for the total system and will 
include intermediate results for the components of the system. 
Code Design and Data Flow 
Criterion T1 - The flow of information (input and output) between the various 
modules is clearly described. 
TSPA-SR provides a description of information flow between component 
models including couplings between information and data, conceptual and 
process-level models, and abstracted models. 
Criterion T2 - Supporting documentation (e.g., users manuals, design 
documents) clearly describes code structure and relationships between 
modules. 
TSPA-SR describes the TSPA code and provides a reference to supporting 
documentation such as the users guide.

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SUBISSUE 2 - SCENARIO ANALYSIS 
Identification of an Initial Set of Processes and Events 
1 - 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. 
Section 2.5 describes the FEPs in this PMR. The NFE FEPs AMR (CRWMS 
M&O 2000e) supporting this section 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 matter experts. In addition, the AMR describes development of the 
FEPs database, including a description of the FEPs process in sufficient detail 
to demonstrate the comprehensiveness of the database. 
Classification of Processes and Events 
1 - DOE has provided adequate documentation identifying how its initial list of 
processes and events has been grouped into categories. 
Section 2.5 of this PMR describes the FEPs in this PMR. The NFE FEPs AMR 
(CRWMS M&O 2000e) supporting this section 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. The AMR also describes development of the FEPs database, 
including identifying and classifying relevant FEPs. 
2 - Categorization of processes and events is compatible with the use of 
categories during the screening of processes and events. 
Section 2.5 describes the FEPs applicable to this PMR. The NFE FEPs AMR 
(CRWMS M&O 2000e) supporting this section provides documentation and 
justification for screening arguments and TSPA dispositions. Documentation is 
maintained of all mapping of FEPs into primary and secondary categories. The 
PMRs and AMRs describe the categorization of processes and events in 
sufficient detail to determine that events are not narrowly defined and that the 
categorization of processes and events is compatible with the use of categories 
during the screening of processes and events . 
Screening of Processes and Events 
1 - Categories of processes and events that are not credible for the Yucca 
Mountain repository because of waste characteristics, repository design, or site 
characteristics are identified and sufficient justification is provided for DOEs 
conclusions. 
Section 2.5 describes the FEPs in this PMR. The NFE FEPs AMR (CRWMS 
M&O 2000e) supporting this section 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.

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2 - The probability assigned to each category of processes and events not 
screened based on criterion T1 or criterion T2 is consistent with site 
information, well documented, and appropriately considers uncertainty. 
Section 2.5 describes the FEPs in this PMR. The NFE FEPs AMR (CRWMS 
M&O 2000e) supporting this section 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 which appropriately 
considered uncertainty. 
3 - DOE has demonstrated that processes and events screened from the PA on 
the basis of their probability of occurrence, have a probability of less than one 
chance in 10,000 of occurring over 10,000 years. 
Section 2.5 describes the FEPs in this PMR. The NFE FEPs AMR (CRWMS 
M&O 2000e) supporting this section 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 one chance in 10,000 of 
occurring over 10,000 years (proposed 10 CFR 63.114) (64 FR 8460). 
4 - DOE has demonstrated that categories of processes and events omitted 
from the PA on the basis that their omission would not significantly change the 
calculated expected annual dose, do not significantly change the calculated 
expected annual dose. 
Section 2.5 describes the FEPs in this PMR. The NFE FEPs AMR (CRWMS 
M&O 2000e) supporting this section 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. 
Formation of Scenarios 
1 - DOE has provided adequate documentation identifying: (1) whether 
processes and events have been addressed through consequence model 
abstraction or scenario analysis and (2) how the remaining categories of 
processes and events have been combined into scenario classes. 
TSPA 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 nominal scenario, which is simulated by the base case model described 
in the TSPA documentation. Disruptive scenarios are constructed from 
expected FEPs and combinations of disruptive FEPs. Section 2.5 describes the 
FEPs addressed in this PMR. The PMRs provide descriptions of process-level 
models, model abstractions, and supporting analyses in sufficient detail to 
conclude that processes and events have been addressed through 
consequence model abstraction or scenario analysis and that the remaining 
categories of processes and events have been combined into scenario classes .

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2 - The set of scenario classes is mutually exclusive and complete. TSPA provides documentation and justification for screening arguments and 
TSPA dispositions. In addition, TSPA describes development of the FEPs 
database, including a description of the construction and screening of 
scenarios . Taken together, the entire set of PMRs and TSPA will provide NRC 
staff with sufficient documentation to evaluate whether the set of scenario 
classes is mutually exclusive and complete, and whether expected FEPs are 
addressed either through model abstraction or through incorporation into 
scenarios. 
Screening of Scenario Classes 
1 - 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 DOEs conclusions. 
TSPA 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. 
2 - The probability assigned to each scenario class is consistent with site 
information, well documented, and appropriately considers uncertainty. 
TSPA provides justification for screening arguments and TSPA dispositions. 
Probability estimates for scenario classes are based on analyses similar to 
probabilities assigned for individual FEPs. 
3 - Scenario classes that combine categories of processes and events may be 
screened from the PA on the basis of their probability of occurrence, provided: 
(i) the probability used for screening the scenario class is defined from 
combinations of initiating processes and events and (ii) DOE has demonstrated 
that they have a probability of less than one chance in 10,000 of occurring over 
10,000 years. 
TSPA 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 one chance in 10,000 of occurring over 10,000 years 
(64 FR 67054). 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, the NFE FEPs AMR (CRWMS M&O 2000e) 
describes the development of the FEPs database, including a description of 
screening and specifying scenarios for TSPA analysis. 
4 - 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. 
TSPA 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, the NFE FEPs 
AMR (CRWMS M&O 2000e) describes the development of the FEPs database, 
including a description of screening and specifying scenarios for TSPA analysis.