Natural Analogue Synthesis Report Rev 00, ICN 02

TDR-NBS-GS-000027

May 2002

1. INTRODUCTION
1.1 PURPOSE OF REPORT AND LIMITATIONS
The purpose of this report is to present analogue studies and literature reviews designed to
provide qualitative and quantitative information to test and provide added confidence in process
models abstracted for performance assessment (PA) and model predictions pertinent to PA. This
report provides updates to studies presented in the Yucca Mountaiii Site Description (CRWMS
M&O 2000 [1519451, Section 13) and new examples gleaned from the literature, along with
results of quantitative studies conducted specifically for the Yucca Mountain Site
Characterization Project (YN1P). The intent of the natural analogue studies was to collect
corroborative evidence from analogues to demonstrate additional understanding of processes
expected to occur during postclosure at a potential Yucca Mountain repository. The report
focuses on key processes by providing observations and analyses of natural and anthropogenic
(human-induced) systems to improve understanding and confidence in the operation of these
processes under conditions similar to those that could occur in a nuclear waste repository. The
process models include those that represent both engineered and natural barrier processes. A
second purpose of this report is to document the various applications of natural analogues to
geologic repository programs, focusing primarily on the way analogues have been used by the
YMP. This report is limited to providing support for PA in a confirmatory manner and to
providing corroborative inputs for process modeling activities. Section 1.7 discusses additional
limitations of this report.
Key topics for this report are analogues to emplacement drift degradation, waste form
degradation, waste package degradation, degradation of other materials proposed for the
engineered bariier, seepage into drifts, radionuclide flow and transport in the unsaturated zone
(UZ), analogues to coupled thennal-hydrologic-mechanical-chemicaI processes, saturated zone
(SZ) transport, impact of radionuclide release on the blosphere, and potentially disruptive events.
Results of these studies will be used to corroborate estimates of the magnitude and limitation of
operative processes in order to build realism into conceptual and numerical process models used
as a foundation for PA in the representative case of postclosure safety.
1.2 DEFINITION OF ANALOGUE
Natural analogues refer to either natural or anthropogenic systems in which processes similar to
those expected to occur in a nuclear waste repository are thought to have occurred over long time
periods (decades to millenia) and large spatial scales (up to tens of kilometers). Analogues
provide an important temporal and spatial dimension to the understanding of processes not
accessible to laboratory experiments that may take place in a nuclear waste repository and
surrounding area. The use of analogy has been endorsed by the intemational nuclear waste
community as a means of demonstrating confidence in the operation of systems, components,
and processes related to nuclear waste disposal (e.g., publications of the Intemational Atomic
Energy Agency [IAEA] and the European Community's Natural Analogue Working Group).
"The role of a natural analogue should ... be to confirrn: (a) that the process is in fact something
which can or will occur in practice as well as in theory, and in nature as well as in the laboratory;
(b) where, when, and under what conditions it can occur; (c) that the effects of the process are
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those envisaged in the model; and (d) that the magnitude of the effects in terms of scale and time
are similar to those predicted for a similar set of conditions" (Chapman and Smellie 1986
[124323], p. 167).
1.3 ROLE OF NATURAL ANALOGUES IN PROCESS MODELS AND
PERFORMANCE ASSESSMENT
Natural analogues may be applied in a quantitative or a qualitative manner, depending upon the
purpose to which they are applied and upon the specific analogue. They can provide descriptive
information about the occurrence of various processes, or they may be able to constrain the
bounds of those processes. Natural analogues allow testing of the pertinence of individual
processes over geologic time and space scales, assessing the relative importance of various
processes, and gauging the effects of process coupling. For some processes (e.g., those that are
thermally coupled), natural analogues may be the only means of providing the required
understanding of long-term and large-scale behavior needed to provide scientific confidence in
process models for input to total system performance assessment (TSPA). Analogue
investigations may deterrnine the conditions under which the processes occur, the effects of the
processes, and the magnitude and duration of the processes.
Analogue information may also provide a body of data for testing codes and for validation of
conceptual and numerical models. Natural analogue infonnation may also be used to build
confidence in databases themselves. Because natural analogues can be used to evaluate the
validity of extrapolating from temporally limited field-scale experiments to longer time scales, or
to add confidence when extrapolating from laboratory and intermediate-scale experiments to
tests at larger spatial scales, they are uniquely suited to building confidence in process models. In
this manner, they are used as a means of model validation, or confi dence-bui I ding. Each of the
Process Model Reports (PMRs) that support Site Recommendation (SR) includes a section on
"validation" that in many cases utilizes natural analogue infonnation.
Less commonly, natural analogues may be used to assist and support the selection of scenarios
and to establish the probability of occurrence of selected scenafios. Natural analogues do not
reduce uncertainty per se; that is, the uncertainty bounds on a given parameter value may remain
unchanged. However, natural analogues can build confidence that the bounds are set
appropriately. Because some uncertainties are greater in natural analogues than at the site being
charactefized, infonnation from natural analogues should only be used in conjunction with other
inforrnation to evaluate consistency with laboratory and field data.
Comparison of model predictions with the results of natural analogue investigations will in
general only perrnit confirmation that the model takes into account the relevant processes in
appropriate ways. Validation of a predictive model by such comparison provides reasonable
assurance that the model reflects future behavior. This is the level of confidence required by 66
FR ([156671], p. 55804), which states, in 63.101(a): "Demonstrating compliance will involve
the use of complex predictive models that are supported by limited data from field and laboratory
tests, site-specific monitoiing, and natural analogue studies that may be supplemented by
prevalent expert judgment."
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1.4 ROLE OF NATURAL ANALOGUES IN LICENSE APPLICATION
The National Research Council endorsed the use of natural analogues as "natural test cases,
geological settings in which naturally occurring radioactive materials have been subjected to
enviromnental forces for millions of years" (National Research Council 1990 [100061], p. 27).
The Council's report indicates that natural analogues are essential for validating perfortnance
assessment models of geologic repositories over thousands or millions of years, as well as
forming the basis for communicating the safety of a deep geologic repository in terms the public
can understand. The Nuclear Waste Technical Review Board concurred in these
recommendations (NWTRB 1990 [126162], p. xiii).
In 66 FR ([156671], p. 55804, Section 63.101(a)(2)), the Nuclear Regulatory Commission
(NRC) has identified natural analogues as one way of demonstrating compliance with the
reasonable expectation that postclosure performance objectives will be met. As summarized in
Section 1 of this report, the NRC also specifies natural analogues as one method to provide the
technical basis for models in (66 FR [ 15667 1 ], p. 5 5 804). The content requirements for the license application (66 FR [156671], p. 55798, Section
63.21(c)(15)) specify natural analogue studies as one of the measures used to support analyses
and models that are used to assess performance of a geologic repository. In addition, the
technical criteria for a license a'pplication (66 FR [156671], p. 55804) specify the use of natural
analogue information as part of the demonstration of compliance with the performance
objectives of the disposal regulations. Further, the demonstration of the concept of multiple
barriers and the performance of complex engineered structures must include information from
natural and archaeologic analogs (66 FR [156671], p. 55805, Section 63.102(h)). The importance
of natural analogs in supporting performance assessment models is again included in the
requirements for performance assessment (66 FR [156671], p. 55807, Section 63.114(g)).
Ten agreements from the DOE-NRC technical exchanges and management meetings on key
technical issues (KTIs) include mention of analogues or information from analogue studies as
necessary to address the agreement item. As shown in Table I - 1, two KTI agreement items are at
least partially addressed by information in this report. A cross reference to this table is found in
the sections of this report that could provide information related to these KTIs.
1.5 CRITERIA FOR SELECTION OF ANALOGUES USED IN MODEL
VALIDATION
As pointed out by Pearcy and Murphy (1991 [157563]), the 10,000-year period required for
high-level waste isolation is a difficult period to approximate with natural analogues. For
instance, most ore deposits are on the order of a million to a billion years in age, whereas
anthropogenic sites (i.e., human made) are generally on the order of a few thousand years or less.
To be most helpftil in tenus of long-tenn processes relevant to a high-level waste repository, it
would be useful to find analogues with ages on the order of 1,000 to 1 million years.
Because no single site will be a perfect analogue to all ongoing and anticipated processes at
Yucca Mountain, focus is placed on identifying sites having analogous processes rather than total
system analogues. Nevertheless,. it is still worthwhile to attempt to match as many features and
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charactefistics as possible when identifying suitable analogue sites. An ideal analogue site to
long-term radionuclide transport at Yucca Mountain would have to satisfy the following
conditions: (1) a known source term, (2) a similar set of radionuclides, (3) well-characterized
with site data, (4) similar geologic conditions, (5) observable long-term conditions, (6)
identifiable boundaries of the system, and (7) a clear-cut process that can be decoupled from
other processes. It is most useful if the analogue has been in place for at least thousands of years,
so that the results of long-term behavior are observable. 
In addition to using natural analogues for long-term predictions, models must be able to explain
and match the transport times and pathways from contaminated sites that provide anthropogenic
analogues, such as Hanford, Washington; the Idaho National Engineering and Environmental
Laboratory (INEEL); and the Nevada Test Site (NTS). Anthropogenic analogue sites are a
challenge to constrain in models, because they often contain more than one contaminated source,
(sometimes with poorly identified source terms), have a complex mixture of radionuclides and
other contamiiiants, and often occur in highly heterogeneneous formations.
With respect to choosing different geochemical transport analogues, Chapman and Smellie (1986
[ 124323], p. 168) state the following:
The essentials to bear in mind when selecting analogues are as follows: (1) The
process involved should be clear-cut. Other processes which may have been
involved in the geochemical system should be identifiable and amenable to
quantitative assessment as well, so that their effects can be accountable. (2) The
chemical analogy should be good. It is not always possible to study the behavior
of a mineral system, chemical element or isotope identical to that whose
behaviour requires assessing. The limitations of this should be fully understood. 
(3) The magnitude of the various physicochemical parameters involved (P, T, Eh,
concentration, etc.) should be determinable, preferably by independent means. (4)
The boundaries of the system should be identifiable (whether it is open or closed,
and consequently how much material has been involved in the process being
studied). (5) The time-scale of the process must be measurable, since this factor is
of the greatest signficance for a natural analogue.
Care must be taken in selection of an appropriate analogue to represent correctly the process of
interest. For example, all uranium deposits are not categorically good analogues for stability of a
nuclear waste repository. Uranium deposits indicate the long-tenn stability of some geologic
environments, but some of the same ore deposits could be used to make arguments for massive
transport of radioactive materials over large distances by natural processes. Care must also be
exercised to exclude those analogues for which initial and/or boundary conditions are poorly
known and where important data, such as the source terrn, are poorly constrained and may not be
obtainable. A given site will usually only be analogous to some portion of a repository or to a
subset of processes that will occur in a repository. Furthermore, additional processes will have
occurred that are not charactefistic of the repository. Therefore, choices must be made to select
the processes of greatest relevance and the ability to isolate them for study. The long-term nature
of analogues introduces some limitations and uncertainties, but analogues can still be used
effectively if appropriate selection criteria are determined and applied.
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In the early 1990s, the U.S. Department of Energy (DOE)/YMP convened a panel of
intemational experts in natural analogues to provide guidance in selection and use of natural
analogues for implementation by the YMP. The Natural Analogue Review Group (NARG)
report recommended that natural analogues be process-oriented and "should address the issues
resulting from the perturbation of a natural system (the geologic site) by the introduction of a
technological system (the repository)" (DOE 1995 [124789], p. 2). The NARG was explicit in
stating that "one should clearly discriminate such studies from those which, following the
classical approach of earth sciences, are based on the comparative study of geological sites or
situations. In particular, all investigations normally part of site characterization, even when
considering comparisons with similar remote sites, such as (paleo)hydrology, etc., should not be
considered as natural analogue studies" (DOE 1995 [1247891, p. 2). The YMP has abandoned
that approach and now defines analogues in a more all-encompassing sense in order to avoid the
narrower definition.
1.6 SCOPE AND ORGANIZATION OF REPORT
This report considers a broad range of analogues that encompass both the engineered barriers and
natural system components of a geological repository at Yucca Mountain. In each section, the
conceptual basis for the process model is provided as a framework for discussion of relevant
analogue studies and examples. Next, examples of analogue studies relevant to the operative
processes in the conceptual models are presented. This is followed by an assessment of the
applicability of the information or conclusions derived from the analogue. The current repository
design approach (Section 2) and configuration of engineered baniers (Section 5) are provided as
the basis against which to identify relevant analogues for those systems. 
Section 3 presents
analogues related to drift stability. Section 4 provides qualitative corroboration of waste form
degradation processes. Section 6 presents examples of analogues for waste package corrosion
processes. Section 7 addresses analogues for engineered barrier components and processes.
Section 8 illustrates seepage into underground openings at sites with varying degrees of analogy.
Section 9 addresses unsaturated zone (UZ) flow processes, but is pfimarily concemed with Part I
of a modeling study using INEEL data. Part I of that study desciibes a flow model that was
calibrated using INEEL data and YMP modeling methods. The calibration parameter values
were then used in Part II of the study, which is described in Section 10 in a model of
radionuclide transport at INEEL. Section 10 also includes results to date of the Peiia Blanca field
study and literature examples of analogues related to UZ transport. Section 11 presents analogues
related to coupled processes, includes an extensive literature search for geothermal analogues,
and summafizes experimental work on drillcore from Yellowstone National Park. In addition,
Section I I presents the results of a field and modeling study for the Paiute Ridge coupled
processes analogue site and a literature study of thennal-hydrologic-mechanical (THM)
processes. Section 12 presents an analysis of uranium mill tailing data relevant to saturated zone
(SZ) transport and includes literature examples from selected sites. Section 13 uses parameters
measured after the Chemobyl nuclear accident to arrive at Biosphere Dose Conversion Factors
(BDCFs) that can be compared to those applied in the Yucca Mountain Biosphere Process
Model. Section 14 provides examples of the ways in which analogues have been used to support
conceptual models for volcanism and seismic hazard assessments and process models. Finally,
Section 15 discusses how the analogue inforination is applied, both for illustrative purposes and
in perfonnance assessments. The ways in which other countries have used analogues in
perfonnance assessment are summafized. The specific needs for analogue infonnation requested
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by YMP performance assessment are listed, and each of the analogues covered in the report is
mapped to its use in either conceptual model development, provision of data, or model
validation. In a few cases, topics are identified that could potentially increase confidence with the
use of natural analogues.
1.7 QUALITY ASSURANCE
This report provides corroborating information for the modeling of natural and engineered
barrier performance at Yucca Mountain. This report was developed in accordance with AP-
3.11Q, Technical Reports. Other applicable DOE Administrative Procedures (APs) and YMP-
LBNL Quality Implementing Procedures (QIPs) are identified in the Technical Work Plan
(TWP) Natural Analogue Studies for License Application (BSC 2001 [157535]). The Activity
Evaluation in the TWP (BSC 2001 [157535], Attachment I) graded the natural analogue work as
being non-Q and not subject to control under the DOE Office of Civilian Radioactive Waste
Management (OCRWM) Quality Assurance Requirements and Description (QARD) (DOE 2000
[149540]). All procedures followed were current revisions at the time of implementation.
The data collected under this study is corroborative and will not be used directly by Perfonnance
Assessment (PA) for licensing. This report will be used to support PA in a confirmatory manner
only. The TWP stipulates that all data generated by this work will be unqualified. However, data
that have been collected have been submitted to the YNV Technical Data Management System
(TDMS) in accordance with AP-SIII.3Q, Submittal and Incorporation of Data to the Technical
Data Management System. The TWP also exempts the natural analogue work from following
AP-SIAQ, Software Management. Procedures that were followed during the course of the work,
40 including AP-SIII.1Q, Scientific Notebooks, and AP-12.1Q, Control of Measuring and Test
Equipment and Calibration Standards are listed on the TWP. Scientific notebooks are used to
provide traceability to sample collection, data analysis, calculations, and modeling studies.
Input for this report consisted of a combination of existing information from natural analogue
sites reported in the literature and data collected for the.YMP. Literature data not developed by
the YMP are available for review through the Technical Information Center (TIC); data collected
by project personnel are available in TDMS; scientific notebooks (with relevant page numbers)
used in preparation of this report are listed in Table 1-2 and are available from the Records
Information System (RIS). Software referenced in this report is listed in Table 1-3. More detailed
discussion of software usage is provided in relevant scientific notebooks. Finally, this document
was developed to meet the deliverable criteria listed in Section 5 of the TWP (BSC 2001
[1575351).
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Table 1-1. KTI Agreements Addressed in This Report
Agreement
Number	Text of Agreement	Section of
This Report
KIA0204	Document that the ASHPLUME model, as used in the DOE performance	14.3
	assessment, has been compared with an analogue igneous system. (Eruptive
	AC-2). DOE agreed and will deliver calculation CAL-WIS-MD-00001 1 that will
	document a comparison of the ASHPLUME code results to observed data from
	the 1995 Cerro Negro eruption. This will be available to the NRC in January 2001.
	DOE will consider Cerro Negro as an analogue and document that in Eruptive
	Processes AMR (ANL-MGR-GS-000002). This will be available to the NRC in
	FY2002 (Eruptive AC-2). 
KUZ04071	Provide documentation of the results obtained from the Natural Analogues	3.2-3.4, 6.2,
	modeling study. The study was to apply conceptual models and numerical	8.2-8.4,
	approaches developed from Yucca Mountain to natural analogue sites with	10.3-10.5,
	observations of seepage into drifts, drift stability, radionuclide transport,	11.2-11.5
	geothermal effects, and preservation of artifacts. DOE will provide documentation
	of the results obtained from the Natural Analogues modeling study. The study
	was to apply conceptual models and numerical approaches developed from
	Yucca Mountain to natural analogue sites with observations of seepage into drifts,
	drift stability, radionuclide transport, geothermal effects, and preservation of
	artifacts. This will be documented in the Natural Analogues for the Unsaturated
	Zone AMR (ANL-NBS-HS-000007) expected to be available to NRC FY 2002.
I ne Natural Analogue bynthesis Report replaces the AMR in the provision of documentation stated in KUZ 0407
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Table 1-2. Scientific Notebooks
LBNL Scientific Notebook ID	YMP M&O Scientific	Responsible	Page Numbers	Citation
	Notebook ID	Individual
YMP-LBNL-AMS-NA-1	SN-LBNL-SCI-108-Vl	Simmons, A.	83-87,124-127,	Simmons 2002
			139-144	[157544]
YMP-LBNL-AMS-NA-2	SN-LBNL-SCI-108-V2	Simmons, A.	6-23	Simmons 2002
				(157578]
YMP-LBNL-AMS-NA-AU-2	SN-LBNL-SCI-186-Vl	Unger, A.	55-63	Simmons 2002
				[157578]
YMP-LBNL-DSM-ELS PD-2	SN-LBNL-SCI-190-V2	Dobson, P.	79-80	Simmons 2002
				[157578]
YMP-LBNL-AMS-NA PD-1 B	SN-LBNL-SCI-185-Vl	Dobson,P.	7-1	Simmons 2002
				[157578]
YMP-LBNL-AMS-NA PD-	SN-LBNL-SCI-185-Vl	Dobson,P.	RoII17	Simmons 2002
photos			Images 2 and 4	[157578]
N/A	SN-LANL-SCI-237-Vl	Murrell, M.	16	Simmons 2002
				[157578]
N/A	SN-LANL-SCI-215-Vl	Lichtner, P.	6-32,56-59,63,	Simmons 2002
			69-76,89-94,	[157578]
			100-104,107,	-
			110-112,117-118,
			128,130-131
N/A	SN-LANL-SCI-234-Vl	Lichtner, P.	16,20,22-24,26-33,	Simmons 2002
			61-68,75-76,83,	[157578]
			88-90
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Table 1-3. Software Codes Referenced in Text
Software Name	Version Number	Software Tracking
Number	Software Reference by
Section
ASHPLUME	V 1.4LV	10022-1.4LV-00	14.3
ASHPLUME	V 2.0	10022-2.0-00	14.3
CXTFIT	V 2.1	N/A 2	10.3.2.1, 11.4.7.1
DRKBA	V 3.3	10071-3.3-00	14.4
E03/6	V 7.2b	UCRL-MA-1 10662	11.2.12.1,11.3.5
FEHM	2.0	10031-2.00-00	10.3.1,10.3.6.1,
10.3.6.3,10.3.6.5
FLOTRAN	1.0	N/A	10.3.1,10.3.6.1,
10.3.6.3,10.3.6.4,
11.4.7,11.4.7.1,
11.4.7.2,
iTOUGH2'	V 4.0	N/A	9.3.3, 9.3.5, 9.3.6, 9.3.7,
9.5
Mathematica	V 4.1	N/A	10.3.6.4
TOUGH2	V 1.4	10007-1.4-01	11.3.5
TOUGHREACT	V 2.2	10154-2.2-00	11.3.5
TOUGHREACT	V 2.3	10396-2.3-00	11.3.5
UDEC	V 2.0	BOOOOOOOO-01717-
1200-30004	14.4
1
NOTE: 1 FOUGH2 with EOS9 and EOS7r modules
2 N/A signifies that the code is unqualified and it is currently not tracked by the Software
Configuration Management System.
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2.  REPOSITORY DESIGN SELECTION FOR SITE RECOMMENDATION
AND RELATION TO APPLICABLE ANALOGUES
2.1 INTRODUCTION
Studies of natural and anthropogenic systems can improve understanding and confidence in the
variables affecting the evaluation and operation of a selected repository design. The selection of
appropriate analogues to build confidence in repository design parameters should focus on the
variables affecting operational parameters rather than on a specific design for a potential Yucca
Mountain repository. The current design approach is flexible in that a wide range of thermal
operating modes is being examined. The flexible design approach is presented in Section 2.2.
The range of potential therrnal operating modes is described on the basis of three evaluated
scenarios in Section 2.3, while Section 2.4 presents design methods by which the thennal goals
can be achieved. Section 2.5 provides a basis for evaluating analogues to repository matefials
and processes that are discussed in subsequent chapters.
2.2 FLEXIBLITY IN DESIGN
Refining the design and operating mode of the potential monitored geologic repository at Yucca
Mountain has been an ongoing process since inception of the YMP. This iterative design process
has been focused on improving the understanding of how design features contribute to the
performance of a potential repository and to the uncertainty in that performance.
40 A pfimary design aspect has been the thennal load that will be generated by the repository.
Previous design concepts have considered higher-temperature operating modes, in which the
rock surrounding emplacement drifts exceeds the boiling point of water. More recently, to
maintain flexibility in design, the design process has evolved to examine the effects on the
repository over a wider range of thermal conditions. A flexible approach to design was
introduced in the Yucca Mountain Science and Engineeriiig Report (S&ER) (DOE 2001
[153849], Section 2.1.3). The design has flexible operating modes that can be adapted to
accommodate a waste stream with potentially evolving thermal charactefistics.
2.3 OBJECTIVES OF THERMAL OPERATING MODES
The current design concepts range from a lower-temperature operating mode to a higher-
temperature operating mode. For the lower-temperature mode, the objective is to keep the waste
package surface temperature below 85'C (DOE 2001 [153849], Section 2.1.2.3). 
In the higher-
temperature mode, the wall rock of the drift is above boiling temperature but the temperature is
controlled to prevent boiling fronts from coalescing in the rock pillars between the emplacement
drifts. Strategies that have been considered with regard to selecting the operating mode of the
repository are presented below.
2.3.1 Manage Boiling Fronts within the Rock Pillars
The higher end of the then-nal operating mode, presented in the Supplemental Science and
Perfonnance Analyses (SSPA) (BSC 2001 [155950], Table 2-1), assumes an average waste
package maximum temperature of -160'C. This mode preserves the capability of the rock mass
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to drain percolation flux through the repository horizon by preventing the boiling fronts from
coalescing in the rock pillars between the emplacement diifts. In this mode, the close spacing of
waste packages with thermally blended spent fuel inventories achieves a relatively uniform
distribution of rock temperatures along the drift, limiting potentially complex
thermal -mechanical effects resulting from a varying thermal gradient along the drift axis. This
operating mode would also meet a design requirement established to maintain the integrity of the
waste package cladding by not exceeding a temperature of 350'C, the temperature at which the
cladding loses its integrity.
2.3.2 Maintain Drift-Wall Temperatures Below Boiling
One lower-temperature objective is to keep all the rock in the repository below the boiling point
of water to reduce uncertainties associated with coupled thermal-hydrologic-chemical-
mechanical processes dtiven by the boiling of water (BSC 2001 [155950], Section 2.3.2). In the
higher-temperature operating mode described in the S&ER, the rock temperatures within the first
several meters outside the emplacement drifts exceed the boiling point of water for about a
thousand years.
2.3.3 Reduce Uncertainty in Corrosion Rates
The lower-temperature end of the range of thermal operating modes was defined by considering
the potential for reducing uncertainty in the raie of localized coffosion of Alloy 22 waste
package mateiial. At temperatures below about 85'C or relative humidity (RH) below 50
percent, the susceptibility of Alloy 22 to crevice corrosion is very low (DOE 2001 [153849],
Section 2.1.5, Figure 2-a). Operating the repository so that the temperature or relative humidity is
below this window of crevice corrosion susceptibility may increase confidence that corrosion
will not significantly reduce waste package service life.
2.4 MANAGING THERMAL OPERATING MODES
The temperature and relative humidity under which a repository would be operated for any
specified underground layout can be managed either singularly or through various combinations
of several operational parameters (DOE 2001 [1538491, Section 2.1.4) such as by:
Varying the thermal load resulting from the repository by managing the thermal output
of the waste packages
o Managing drift ventilation prior to repository closure
* Varying the distance between waste packages in emplacement drifts.
Figure 2-1 illustrates the variables affecting the thennal perfon-nance of the repository, from
waste fonns to emplacement drifts.
2.5 APPLICATION TO NATURAL ANALOGUES
Because of the flexible design approach, analogues must be considered in ten-ns of repository
40 design variables rather than attempting to match a specific design. The important variables are
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temperature of drift walls, presence or absence of a boiling front, dimensions and spacing of
40 drifts, absence of backfill, and ventilation. These variables affect drift stability (addressed in
Section 3), waste package and drip shield corrosion (discussed in Sections 5 and 6, respectively),
processes operative within the engineered barrier system (addressed in Section 7), and thermally
coupled processes affecting the host rock at the drift and mountain scales (covered in
Section 11).
40
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Source: DOE 2001 [1538491, Figum 24.
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ommo- 1~
=- VL. 1. -P1=.17
V.09M. =rdb."111
Figum 2-1. Variables Affedng ihe Thermal Performarme of Ihe Reposkory
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0 3. REPOSITORY DRIFT STABILITY ANALOGUES
3.1 INTRODUCTION
Section 2 provided background information on the current flexible design for a potential
repository at Yucca Mountain against which to discuss analogues for drift stability. The proposed
emplacement drift diameter is 5.5 m (18 ft) (DOE 2001 [153 849], Section 2.3. 1. 1). The ability of
underground openings to remain open and stable depends on a number of variables, including:
(1) rock strength; (2) the size, shape, and orientation of the opening; (3) orientation, length, and
frequency of fracturing; (4) effectiveness of ground support, and (5) loading conditions. There
are no exact analogues to the openings that would be created for a potential repository at Yucca
Mountain, but numerous examples demonstrate that both natural and man-made underg~ound
openings can exist for thousands of years in a wide variety of geologic settings, even with
minimal or no engineering. Analogue information is available for natural underground openings
(Section 3.2) and man-made excavations (Section 3.3). An analogue demonstrating thermal
effects on underground openings is presented in Section 3.4. Effects of ground shaking on
underground openings are mentioned in Section 3.4 and discussed in more detail in Section 14. 
Information found in Section 3.2, 3.3, and 3.4 may help to support arguments associated with
Key Technical Issue (KTI) KUZ0407 listed in Table I - 1.
3.2 NATURAL UNDERGROUND OPENINGS
Caves represent examples of natural underground openings. They are abundant, and in many
cases, it can be demonstrated that they have remained open for very long spans of time. The
oldest documented examples noted in this study are from the limestone fonnations of the
Guadalupe Mountains in New Mexico. Alunite is a mineral that forms on the floor of caves.
Undisturbed, uncovered alunite collected from the cave floors has been dated at 4.0-3.9 million
years (m.y.) for the Big Room at Carlsbad Cavems and at 6.0 to 5.7 m.y. for the upper level of
the nearby Lechuguilla Cave. Alunite from other nearby caves yields ages as old as 11.3 m.y.
(Polyak et al. 1998 [156159], p. 1919). Sections of the cave floors have blocks that appear to
have fallen from the ceiling; however, none of the dated caves has been closed by rockfall,
demonstrating the stability of most of these openings over millions of years. Because these
settings are common, they demonstrate stability for most of the openings for millions of years.
Many of these openings are as large or larger than those proposed for Yucca Mountain (Figure
3-1).
The San Antonio Mountain Cave in northem New Mexico is an example of a different geologic
setting in which an opening has remained open over a long period of time. This cave is a lava
tube in basalt from 3.4-3.9 million years ago (Ma) (Rogers et al. 2000 [154320], pp. 89-93). The
cave is more than 170 m long and generally several meters wide. In some places, the ceiling is
over 12 m high. The large size of the openings combined with abundant cooling fractures has
resulted in fallen blocks (generally less than3/4m in length and width) that cover about 30% of
the cave's floor. Several spots preserve a long record (up to I m.y.) of sedimentation, more than
400 cm thick, with no collapse (Rogers et al. 2000 [154320], Figure 5). Davis (1990 [144461], p.
338) notes that similar cave sediments in Europe date back 1.5 Ma, which suggests that long-
tenn stability of caves is a common feature.
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Most lava tubes are a few thousand to a few hundred thousand years In age. They are commonly
40 ellipsoidal to circular in cross section and several meters in diameter. Some of the most extensive
lava tubes are in the Undara region of Australia, where 190,000-year-old tubes reach 100 km in
length (Undara Experience 2001 [157515]). Figure 3-2a shows the interior of a lava tube in the
Undara region (with a person included in the photo for scale). Lava tubes are also common in
Hawaii (Figure 3-2b) and in the Cascade Range of Califomia, Oregon, and Washington, in lava
that is modem to a few thousand years in age. Most lava tubes exhibit areas of collapse where
the roof is thin, but large sections of open tunnel persist for long periods of time.
The maximum length of time that caves have stood open is usually not known, but the age dates
of datable biologic or archeologic materials found in many caves indicate that the caves have
remained open for extended periods of habitation without collapse. Some packrat middens found
in caves are thousands to tens of thousands of years old, and Davis (1990 [144461], p. 341)
reports that over 1,000 middens have been studied in cavems and rock shelters of the westem
United States. Stuckless (2000 [151957], p. 4-6) reports on several caves in limestone that
contain paintings that have been dated at 11,000 to 32,000 years old.
Kebara Cave in Mt. Cannel, Israel, is a very large opening (26 m long and 20 m wide, with a
ceiling up to 18 m high), and sediments accumulated on the floor of the cave yield ages as old as
50,000 years (Bar-Yosef et al. 1996 [157419], p. 305). Although the main portion of the cave
shows no sign of collapse, a terrace in front of the cave entrance was formed by collapse
sometime after 30,000 years ago (Bar-Yosef et al. 1996 [157419], p. 298). However, even this
collapsed section must have stood open for more than 20,000 years, because this section was the
entrance from before 50,000 until 30,000 years ago.
3.3 ANTHROPOGENIC OPENINGS
Anthropogenic, or man-made, underground openings do not provide as long a history as the
natural ones, but they may provide a closer analogy to a mined geologic repository. Here too,
there are abundant examples that exhibit considerable stability for hundreds to thousands of
years even with minimal engineering. The oldest examples are the Neolithic flint mines of
northem Europe and England. These were mined into chalk deposits in 3,000 to 4,000 B.C. At
one site in England, shafts that are 6 to 14 m deep access galleries that are 4 to 24 m in length
and are still open today (Crawford 1979 [157420], pp. 8-32).
Around 1,500 B.C., Egyptians began excavating tombs on the west bank of the Nile River,
across from Luxor. Over 100 tombs were excavated in bedded and jointed limestone (Figure 3-
3). The tombs were generally a few meters in length and width and about 2 m in height. Many
have pillars that were left for support in the larger rooms. Most of the tombs have incurred some
water damage to plaster and paintings on the walls and ceilings, but none seems to have suffered
collapse (Simmons 2002 [157578], SN-LBNL-SCI-108-V2, p. 7).
Mining of metallic ores has produced subterranean openings in a variety of rock types and often
in intensely altered or fractured rock. 
Unfortunately, many of the oldest examples have been
mined continuously or reopened in more modem times to mine remaining lower-grade ore. The
Laurion mines, about 40 km south of Athens, Greece (Figure 3-4), were first mined about 2,000
to 1,500 B.C., but were mined most actively from 600 to 300 B.C. (Shepherd 1993 [157425], p.
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75).  These silver and lead mines are in a gently dipping sequence of mica schists and marble,
with sulfides occurring along the contacts. Shafts 1.25-1.4 m by 1.5-1.9 m were sunk up to I I I
m deep (Shepherd 1993 [1574251, p. 17). Underground workings were 140 km in length; tunnels
averaged I m in width and 1.75. m in height (Shepherd 1993 [157425], pp. 17-18). Ore zones
were mined out by underhand stoping, which left large cavities a couple of meters high and a few
meters in diameter. Pillars of infeiior ore-grade rock supported these cavities. Removal of rock
from these pillars was punishable by death (Shepherd 1993 [157425], p. 25).
Bronze-age mining of metal also occurred at the Great Orme Copper Mine in Wales. Charcoal
recovered from the early workings dates at 1,000 to 2,000 B.C. In 1849, miners broke into a
cavem nearly 40 m long, which contained stone hammers, most likely from the Bronze Age. The
cavem, mined into limestone, had stood open for nearly 4,000 years (Llandudno Museum 1998
[1575261).
Underground mining was common during the Roman Empire, and the size and state of
preservation of the mines not destroyed by subsequent mining are fairly similar. Shepherd (1993
[157425]) and Davies (1935 [157421]) present locations and descriptions for most of these
mines. In addition to mining for metals, the Romans created large tunnels to transport water. For
instance, the aqueduct at Tresmines, Portugal, is 60 m wide, 80 m high and 480 m long; at Corta
das Coras, the tunnel is 100 m wide, 100 m high, and 350 m long (Shepherd 1993 [157425], p.
17).
Buddhist monks carved temples into caves in the fractured Deccan basalts of west-central India,
from approximately the second century B.C. until the tenth century A.D., with most excavated in
the late fifth or early sixth century A.D. (Behl 1998 [156213), pp. 27, 39). There are 31 caves at
Ajanta, India, carved along a 550 m long, horseshoe-shaped gorge of the Waghora River. Each
temple originally had steps carved into the rock leading up to it, but only Cave #16 still has a
vestige of steps. The monsoonal climate has destroyed the exterior stone structures exposed to
the elements, but subterranean openings have been well preserved in spite of the climatic effects.
Similar Buddhist caves, from the sixth through the tenth centuries A.D., are preserved at Ellora
and from the ninth century A.D. (Jain caves) at Sittanavasal, India (Behl 1998 [156213], p. 39).
The cross-sectional dimensions of most of the temples at Ajanta are larger than those proposed
for a mined geologic repository. For example, Cave #10 is 30.5 m x 12.2 m. Cave #2 has a
verandah of 14.10 m x 2.36 m, a main hall of 14.73 m x 14.5 m, and a shrine of 4.27 m x
3.35 m. Cave #16 has a verandah of 19.8 m x 3.25 m and a main hall of 22.25 m on a side with a
height of 4.6 m. In spite of these large sizes, there is no reported collapse. As in the case of the
Egyptian tombs, most of the Ajanta paintings appear to have suffered some water damage and
vandalism (Behl 1998 [156213], pp. 234-236).
During the second through eleventh centuries A.D., the Christians of Cappadocia, Turkey,
excavated underground cities and churches. One of these cities, Derinkuyu, covered
approximately 4 kM2 and had an estimated 15,000 to 20,000 inhabitants (Toprak et al. 1994
[157429), p. 54) during much of the first millennium A.D. As of 1994, eight levels of ancient
habitation had been discovered. Access to the underground cities was by way of narrow
passageways that could be closed by rolling a 1.5 m diameter millstone across the opening
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(Figure 3-5). The excavated rooriis were generally several meters across and more than 10 m
long.
The geology of Cappadocia (Toprak et al. 1994 [157429], pp. 8-11) is sin~filar to that of southem
Nevada (Sawyer et Al. 1994 [100075]). In both regions, the late Tertiary section is compos6d of a
thick sequence of silicic volcanic rocks. At Yucca Mountain, the host rock for the potential
repository is a densely welded, quartz latite ash-flow tuff that formed about 11.6 Ma, whereas the
underground cities of Cappadocia are situated in a partially welded, rhyolite ash-flow tuff that
formed about 4 to 9 Ma. The difference in welding at Yucca Mountain and the underground
cities of Cappadocia results in markedly different fracture density and engineering properties. 
Fracture density, which is a major variable contiibuting to underground collapse, is much lower
in the underground cities. Ground support, which would be carefully engineered at Yucca
Mountain, was nevet used in the underground cities. Thus, the fact that there has been no
collapse in the underground cities of Cappadocia during the past 1,500 to 1,800 years suggests
that excavations in tuff should be stable for long periods of time if undisturbed. Stability of
unsupported openings would be favored in tuffs of a low degree of welding and fracturing.
Churches were excavated into the tuff north of the underground cities at Goreme, in Cappadocia,
during the ninth to thirteenth centuries A.D. (Toprak et al. 1994 [157429], p. 53). All but one of
these show no evidence of collapse. The exception is a collapse of a cliff face that exposes part
of the inside of one church. The interior portions of the church are still in excellent condition,
and their painted walls and ceilings within are well preserved except for spallation and vandalism
(Stuckless 2000 [151957], p. 22).
Some of the underground openings excavated into the tuffs of Cappadocia are still used as
dwellings. There are at least two other places where underground excavations are still used as
dwellings. In Tunisia, 20 to 40 km south of the city of Gabes, ten underground villages, some of
which date back nine centun*es, are excavated in limestone (Golany 1983 fl57422], pp. 5-6).
The limestone is composed of poorly indurated layers approximately 2 m thick, which are e.asily
mined out, along with better indurated layers of similar thickness. Room sizes are typically 2 to
2.5 m on a side, with flat ceilings that may have a supporting column in the center. Similarly, in
northem China, thick deposits of slightly indurated loess exist, which could be easily excavated.
However, its intemal structure is such that loess can fonn vertical cliffs as much as 30 m in
height. The underground dwellings accommodate more than 10 million people, who farm the
land above their houses (Golany 1983 [1514221, p. 13).
Although all the examples given so far either lack ground support or utilize only unmined pillars,
examples do exist of wooden ground support. Around the beginning of the second century A.D.,
the Roman Emperor Hadiian mandated the use of wooden supports in all mines (Shepherd 1993
[157425], p. 25). Shepherd (1993 [157425], p. 26) provides a discussion of some examples, but
does not comment on the stability of openings that were shored up. 
Tombs in China provide a
different kind of example. Sixteen emperors from the Ming Dynasty (1368 to 1644 A.D.) were
buiied in tombs excavated in rock near Beijing. The earliest of the tombs has 32 sandalwood
pillars 1.17 m in diameter; dll are still intact and sturdy (Golany 1989 [157423], pp. 21-22).
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3.4 UNDERGROUND OPENINGS AFFECTED BY TEMPERATURE
The foregoing descriptions show that both natural and manmade underground openings maintain
stability well in an undisturbed setting. In fact, many of the examples given, as well as several
mines not discussed, have probably been subjected to significant seismic shaking. Further
discussion of seismic effects on underground openings is provided in Section 14.
The stability of underground openings~ can also be affected by temperature. An example of
thermal stresses causing rockfall around rock bolts in a heated area occurred at Linwood Mining
Company's limestone excavations (Simmons 2002 [157578], SN-LBNL-SCI-108-V2, pp. 7, 8).
Linwood has excavated limestone adjacent to the Mississippi River downstream from Moline,
Illinois, since World War I for processing in a kiln. The mine started as a surface quarrying
operation, but as excavation progressed, the mine was converted to an underground room and
pillar operation. The elevation of the underground workings is lower than the Mississippi River.
The company started venting the kiln exhaust underground in 1971 as part of a solution for
controlling dust emissions from the kiln (Simmons 2002 [157578], SN-LBNL-SCI-108-V2, pp.
7, 8). To do this, a 96-acre portion of the mine was nominally mined with 30 ft x 30 ft pillars 21
ft high. This portion was walled off from the active workings. Exhaust from the kiln is vented to
these workings at 400'F (204'C), leaving the dust behind for later collection.
The mining company adds bolts and mesh when a karstic depression is encountered, but
otherwise the mine is essentially unsupported. Perhaps for this reason, steel-bar rock bolts were
placed near the entry of the exhaust. After some period of venting, the rock near the exhaust vent
broke out, leaving the bolts that had been emplaced in the rock, with the bottom 5 feet or so of
the bolts surrounded by air. It was suggested that the surrounding rock had probably fallen out
because heat was transferred up the rock bolt faster than it was transferred through the rock,
which resulted in a thennal stress that caused failure for a rock with an unconfined compressive
strength of 18,000 psi (-125 MPa) (Simmons 2002 [157578], SN-LBNL-SCI-108-V2, pp. 7, 8).
3.5 SUMMARY
0
In Section 3, numerous examples are provided of the stability of natural and man-made
underground openings for millennia or longer under undisturbed conditions. However, an
inherent bias is reflected in the studies because of the difficulty of determining the relative
percent of openings that remain versus those that have collapsed. It is more difficult to evaluate
the cause of collapse of such openings, whether by human interference or natural causes. 
The
ability of underground openings to remain open and stable under ambient conditions depends on
a number of variables, including: (1) rock strength; (2) the size, shape, and orientation of the
opening; (3) orientation, length, and frequency of fracturing; and (4) effectiveness of gound
support. Radiometric dating of cave floor minerals at Carlsbad Cavems and Lechuguilla Cave
indicates that natural openings larger than those proposed for repository drifts at Yucca
Mountain have remained open for millions of years. Collapse of the roof of an opening tends to
occur where the fracture density is high and the overburden is thin, as is the case with some lava
tubes. Factors that contribute to the size of a block falling are fracture spacing, which in tum
depends on rock type and texture, and the size and shape of the opening.
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The oldest examples of stable man-made openings are Neolithic flint mines dating from 4,000 to
is 3,000 B.C. However, numerous Roman mines and some aqueducts remain intact that tended to
have been constructed of a similar size and now exhibit the same state of preservation. These and
other examples demonstrate that both natural and man-made underground openings can exist for
thousands of years in a wide variety of geologic settings, even with minimal or no engineering.
is
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0
NOTE: Aress such as this fuwe m obvkm mt blooks on the Owr of the
cavern w hoin in tM coiling from wNch blocks might hawi fallm.
Sou.w. 5mmons 2002 [1575781. SN-LSNL-SCI-108-V2, p. 6.
Figure 3.1. Photograph of Fairyland in Carlsbad Cavems. New Mexico
40
Soume: (a) Undara Experience 200111575151 -d
(b) USGS 2000 (1576171).
Figure 3-2. Photographs of (a) Lava Tube in Undara, AuMralia, and (b) Nahuku Lava Tube in Hawaii
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Nam,,l Arul.guc Syrffi-,, Rcp.,,
0
14,
Soume Simmons 2002 [1575781, SN-LBNL-SCI-108-V2, p, 6.
Figure 3-3. Photographs of the Nubian Limestone That Hosts the Tombs in the Valley of the Kings, Egypt
0
0
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NOTE: The roof,s formed by mica schist and the floor by marcle. Gmund support appears
to be modern because older reports make no mention of either mod or cement.
Source: G,Il 2001 [1575161.
Figure 3-4. Mined Out Cavern in the Laurion Mines, Greece

 

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0
Soume: Stuckless 2000 1151957], Figure 13. Figure 3-5. Photograph of a Rooin in the Underground City of Kaymakii, Turkey
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0 4. ANALOGUES TO WASTE FORM DEGRADATION
4.1 INTRODUCTION
Many variations of waste fonn types may be emplaced within a potential repository at Yucca
Mountain. However, most of the waste will be spent ftiel in the form Of U02, with the remaining
10% or so being encapsulated in borosilicate glass resulting from vitrification of defense high-
level nuclear waste. These waste forms are thermodynamically unstable under wet, oxidizing
conditions (DOE 2001 [153849], 4.2.6.1). For this reason, quantification of the degradation
modes and dissolution rates that detertnine the source terrn for perfonnance assessment is
extremely important.
Analogue studies may contribute to understanding long-term waste form degradation processes
through the record left behind in secondary minerals and groundwater. Many of the published
analogue studies of waste form degradation focus on dissolution of uranium under reducing
groundwater conditions. This is because most of the geologic waste disposal configurations of
other nations involve saturated, reducing conditions.  Sketches of the most important and well-
studied of these analogue sites were provided in Section 13 of the Yucca Mountain Site
Description (CRWMS M&O 2000 [151945]). As a whole, the sites with reducing groundwater
chemistry have limited applicability to conditions that would be expected to occur at a potential
Yucca Mountain repository, which is located in an unsaturated oxidizing environment. However,
in some instances, information from these analogue studies can still provide valuable insights
into the processes of waste fonn degradation. Section 4 relies to the extent possible on
information derived from oxidizing environments, but relevant information from examples in
reducing environments is included to illustrate general principles of waste form dissolution and
potential criticality.
Section 4.2 provides a conceptual basis for waste form degradation. Section 4.3 discusses
analogues r ' elevant to spent-fuel dissolution rates. Section 4.4 addresses the formation of
secondary minerals that may immobilize uranium and fission products. Section 4.5 briefly covers
radiolysis and Section 4.6 briefly covers nuclear criticality of the waste form. Section 4.7
summarizes studies of analogues to glass waste forms. Section 4.8 is a summary of the topics
discussed.
4.2 WASTE FORM DEGRADATION-CONCEPTUAL BASIS
4.2.1 Overview of Conceptual Basis . 
Although a few radionuclides such as cesium and
iodine may concentrate between the fuel and cladding during reactor operation, most of the
radionuclides will be incorporated within the various waste forms and cannot be released from
the waste package until the waste forms degrade.
Once the waste forms degrade, radionuclides as dissolved species and suspended particles may
be mobilized by advection or diffusion. Larger particles settle out of solution, or are filtered out
by trapping in small openings. Only after gross failure of the package will these larger pailicles
fall or wash out of the package. Particles in the colloid size range, however, can remain
suspended and may travel significant distances. The concentration of radionuclides associated
with colloids is lin-~ited by the colloid concentration and radionuclide carrying capacity of the
colloids (DOE 2001 [153849], Section 4.2.6.1). The concentration of dissolved species is limited
by the elemental solubility of the radionuclide within the local environment.
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4.2.2 Spent Fuel Dissolution in an Oxidizing Environment
Many laboratory studies attempt to measure parameters that can be used to determine the rate of
spent fuel dissolution under repository disposal conditions. These studies use either spent fuel
itself, uranium dioxide (as an analogue for spent fuel), or uraninite as a natural analogue.
Although the uraninite structure can accommodate some degree of oxidation, in highly oxidizing
aqueous environments uraninite is unstable and decomposes (Finch and Ewing 1992 [113030], p.
133). Secondary uranyl (U+6 )-bearing phases precipitate on the surface of the corroding
uraninite, and a iind of corrosion products forms. The impurities often contained in uraninite
affect its thermodynamic properties, the rate of uraninite alteration, and the composition of the
corrosion products (Finch and Ewing 1991 [105591], p. 392). Studies that have examined the
dissolution of uraninites under oxidizing conditions found that the dissolution rate was
diminished by the presence of thorium, lead, and rare-earth-element impurities in the uraninite
(Finch and Ewing 1992 [113030], p. 133). Compared to uraninite, spent fuel has a lower content
of these impurities (Finch and Ewing 1992 [127908], p. 466) and on this basis might be
considered to dissolve more rapidly.
Most of the uranium released to solution during the dissolution Of U02 combines with ions in
water to fonn secondary alteration phases. Both natural and experimental uranium systems
display a paragenetic sequence of mineral phase formation that is characterized by the following
general trend (Stout and Leider 1997 [100419], Section 2.1.3.5):
U02 => uranyl oxide hydrates =* alkali and alkaline-earth uranyl oxide hydrates =>
is uranyl silicates => alkali- and alkaline earth uranyl silicates + palygorskite clay.
Specifically, mineralization in the experimentally detennined paragenetic sequence of alteration
phases is:
U02 => dehydrated schoepite W03-2H20) ==> compreignacite K2(UO2)604(OH)6*8H20
+ becquerelite (Ca(U02)604(OH)6-8H20) => soddyite ((U02)2Si0462H20) =>
boltwoodite (K(H30)(UO2) Si04) + uranophane (Ca(U02)2Si2O7-6H20) + palygorskite
clay (Wronkiewicz et al. 1996 [102047], p. 94).
Thus, the uranyl oxide hydrates are common initial corrosion products of uraninite during
weatheiing. In the presence of dissolved silica, these early phases alter to uranyl silicates, most
commonly soddyite and uranophane. The phases that form depend on the chemical composition
of the waters With which the uraninite is in contact, which in tum depends on the mineralogy of
the surrounding host rocks and the oxidation potential of the hydrologic environment. The
experimentally deten-nined mineral sequence appears to be controlled by precipitation kinetics
and is nearly identical to secondary uranium phases observed during the weathefing of naturally
occurring uraninite under oxidizing conditions, such as that which occurs at the Nopal I uranium
deposit, Pefia Blanca, Mexico (Wronkiewicz et al. 1996 [102047], Figure 7). In laboratory U02
tests and in the natural uranium deposits at Nopal I, the alkali- and alkaline-earth uranyl silicates
represent the long-term solubility-limiting phases for uranium (Stout and Leider 1997 [100419],
Section 2.1.3.5). Furthermore, at Nopal I, uranium concentrations in groundwater and seepage
waters ranged from 170 parts per trillion (ppt) to 6 parts per billion (ppb) (Pickett and Murphy
1999 [110009], Table 2). The upper part of this range is similar to concentrations seen in filtered
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samples from spent fuel dissolution expefiments (Stout and Leider 1997 [100419], p. 2.1.3.5-4).
This added similarity increases confidence that the experiments and the natural analogue
reactions may simulate the long-term reaction progress of spent U02 fuel following potential
disposal at Yucca Mountain.
Uraninite usually contains radiogenic lead that has in-grown through time (Finch and Ewing
1992 [127908], p. 466). As a result, the early-formed Pb-poor uranyl oxide hydrates alter
incongruently to uranyl silicates plus radiogenic-Pb-enriched uranyl oxide hydrates, such as
curite (Pb2U5017 -4H20), that may serve to limit the mobility of uranium in nature (Finch and
Ewing 1992 [127908], p. 466). Curite may also play an important role in the fon-nation of uranyl
phosphates, which are significantly less soluble than the uranyl silicates and control uranium
solubility in many groundwaters associated with altered uranium ore (Finch and Ewing 1992
[127908], p. 465). In the absence of lead, schoepite and becquerelite are the common initial
corrosion products. The reaction path for the alteration of lead-free uraninite results in the
fonnation of uranyl silicates. Thus, the long-tenn oxidation behavior for ancient, lead-bearing
uraninite is different from that of young, lead-free uraninite, which is more similar to spent fuel.
Because the presence of lead effectively reduces the mobility of uranium in oxidizing waters, the
concentration of uranium in groundwaters associated with oxidized uranium ore deposits will
depend in part on the age of the primary uraninite (Finch and Ewing 1992 [113030], p. 133).
In summary, the paragenesis of uraninite alteration phases depends on the age of the piimary
uraninite, the mineralogy of surrounding host rocks, and on groundwater composition, pH, and
redox potential. In a general oversimplification, the progression of phases of uraninite alteration,
in the absence of radiogenic lead in-growth, will be to uranyl silicates, culminating in
uranophane in an oxidizing environment. Numerous compositional variations are caused by trace
elements present in the system. The composition of schoepite is often used to represent an
alteration product in models of spent fuel alteration, but this is an oversimplification, based on
observations in nature. As shown by Finch and Ewing (1992 [113030], p. 144), the formation of
intermediate-phase schoepite may be favored early during the corrosion of uraninite. Schoepite is
not, however, a long-term solubility-limiting phase for oxidized uranium in natural ground-
waters containing dissolved silica or carbonate (e.g., the type of groundwaters at Yucca
Mountain).
Despite the analogy between uraninite and spent fuel, there are important differences between
the two. For one thing, spent fuel is artificially eniiched in 235 U and contains nuclear fission
products that are not present in uraninite; in contrast, uraninite contains a higher proportion of
nonradiogenic trace element impurities. Also, the thermal history of spent fuel, unlike that of
natural uraninite, may cause lattice and structural crystallization defects in the spent fuel that are
not present in the uraninite. In addition, geologically old uraninite contains in-grown radlogenic
lead, which would not be found in younger uraninite or in spent fuel. Section 4.3 presents the
general dissolution path of uraninite, and by analogy spent fuel, under oxidizing conditions.
4.3 ANALOGUE STUDIES RELATED TO WASTE FORM DISSOLUTION RATES
The remaining issues of most relevance to the behavior of spent fuel in a repository that could be
addressed by natural analogues are dissolution and radionuclide release (Section 4.3),
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radionuclide retardation by secondary alteration products (Section 4.4), radjolysis (Section 4.5),
and criticality (Section 4.6).
4.3.1 Fission-Product Tracer Method
Rates Of U02 dissolution can be quantified by measuiing the amount of fission product released
from the uraninite and using this as a tracer. Concentrations of this tracer in the rock or in the
groundwater in the vicinity of the uraninite are proportional to the dissolution rate, assuming that
the tracer is released from the uraninite only by dissolution (Curtis 1996 [157497]; Curtis et al.
1994 [105270]; 1999 [110987)). The tracers used for this method are 99 Tc in rock, or its stable
daughter 99Ru, when technetium has decayed to insignificant amounts, and 129, in groundwater.
There are several uncertainties in the modeling and assumptions made in this approach, but some
consistency is apparent in the results obtained from different uranium orebodies when using the
same isotopic system. For example, using the 99Tc tracer at Oklo, Gabon, and at Cigar Lake,
Canada, provided average release rates of 1.5 x 10-6 per year and 1.1 x 10-6 per year,
respectively (Curtis 1996 [157497], p. 145). However, different rates are obtained when using
129 1 as a tracer. Applying this tracer at Cigar Lake provided release rates of between 9 x 1079 and
3 x IWO per year, which are 2 to 4 orders of magnitude less than the values obtained using the
99Tc tracer. 
Curtis et al. (1994 [105270]) used measurements of 99Tc, 1191, 139pU , and U concentrations in
rock from uranium deposits at Cigar Lake and Koongarra to estimate radionuclide release rates
from uranium minerals. At Koongarra, Australia, release rates appear to have been faster (le
per year; Curtis et al. 1994 [105270], p. 2234) than at Cigar Lake, where model-dependent
release constants from the uraninite bearing rocks were <5 x 10-8 per year (Curtis et al. 1994
[105270], p. 2234), producing small deficiencies of 99Tc, and larger ones of 129, . The inferred
differences in radionuclide release rates are consistent with expected differences in uranium
mineral degradation rates produced by the differing hydrogeochemical environments at the two
sites. In the Cigar Lake ore zone, low uraninite solubility in a reducing environment and small
water flux through impenneable rock would inhibit the rate of uraninite degradation and thus the
rate of radionuclide release. At Koongarra, higher mineral solubilities induced by higher
oxidation potentials, higher aqueous concentrations of carbonate and phosphate, and greater
water fluxes would be expected to produce higher rates of uranium mineral degradation. Curtis et
al. (1999 [110987], p. 284) note that the consistency Of 219pU/U and 99Tc/U ratios in bulk rock
suggests that the redistribution processes observed at Cigar Lake are highly localized and do not
result in large-scale losses or gains of these nuclear products from the deposit as a whole. The
fission product tracer method could be applied to water samples collected at Pefia Blanca
(Section 10.4). While this method clearly has potential for quantifying U02 dissolution under
natural conditions, the method has yet to be refined and differences between results for the two
tracers explained. Besides this fission product tracer method, there is no other technique for
quantifying directly long-term uraninite dissolution rates in natural analogue studies.
4.3.2 Dissolution of Oklo Uraninite
Application of the fission-product tracer method has not been reported for Oklo, but Oklo
provides a unique record of uranium and fission-product retention. Because parts of the Oklo
4D orebody achieved nuclear ciiticality as a result of highly enriched concentrations of 235U, Oklo
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uraninite contains significant quantities of fission products or their stable daughters, directly
equivalent to those present in spent fuel. In this regard, Oklo is unlike any other known uranium
deposit. A photograph of one of the reactor zones is shown in Figure 4-1.
There are, however, some differences between Oklo uraninite and spent fuel. For one thing, Oklo
contains lower concentrations of fission products than does spent fuel. Also the temperature of
reaction (400' to 600'C; for a discussion of temperatures, see Zetterstr6m 2000 ([1575011, p. 13)
and power density were somewhat lower than in a reactor, and the duration of criticality at Oklo
(on the order of 0.1 to 0.8 Ma; Louvat and Davies 1998 [125914], p. 140) was much longer than
the lifetime of reactor fuel. Recognizing these differences, several large-scale analogue
investigations have taken place at Oklo, and much relevant infon-nation has been obtained,
including semiquantitative infonnation on the fate of radionuclides contained in the orebody.
These analogue investigations (e.g., Louvat and Davies 1998 [125914]; Gauthier-Lafaye et al.
2000 [157499]) have revealed that when the Oklo reactor zones were cooling after periods of
criticality, some dissolution of the uraninite and elemental remobilization occurred. However, the
limited extent of this remobilization is indicated by the the fact that more than 90% of the
uranium "fuel" has remained in the same spatial configuration since criticality (Miller et al. 2000
[156684], p. 81). This implies that uranium has been almost fully retained within the uraninite
minerals. The disposition of some performance assessment-relevant elements and other elements
in the reactor zones at Oklo is provided in Table 4-1. The transuranic elements neptunium,
plutonium, and americium were all formed in situ within the uraninite during criticality, and their
stable daughters have also been retained due to their compatibility with the crystal chemical
structure of their host or in inclusions in the uraninite. Other radiogenic elements, which were
less compatible with the uraninite host (e.g., Cs, Rb, Sr, Ba) have been partially or totally lost by
diffusion from the uraninite. Some elements (e.g., Tc, Ru, Rh, Pd), however, migrated only short
distances and were totally retained within the clay matrix enclosing the reactors. Data for other
elements indicate clear deficiencies in the noble gases, halides, and lead (possibly resulting from
volatilization) and suggest that some minor loss from the system has occurred for other elements.
Because the reactions ended nearly two billion years ago, the short-lived radionuclides have
decayed to more stable daughter nuclides. Analysis of the behavior of these short-lived
radionuclides is problematic. According to Brookins (1978 [133930), p. 309), Pu, Np, and Am
were likely retained within the reactor, while Bi and Pb would have been redistributed locally
without substantial migration (Brookins 1978 [133930], p. 309). Most geochemical observations
at Oklo support these predictions to varying degrees. Curtis et al. (1989 [100438], p. 57)
conclude that the retention of fission products is related to their partitioning into uraninite or
secondary mineral assemblages. 
Those fission products that partitioned into the secondary
mineral assemblages were largely lost over time, pointing to the importance of small uraninite
grains in controlling the chemical microenvironment.
It is important to note that most of the observed uraninite alteration at Oklo occurred under
hydrothennal conditions. Little uraninite-groundwater interaction has taken place at present-day
ambient temperatures, except at the shallow Bangomb6 reactor zone (Smellie et al. 1993
[1266.45], p. 144). In summary, the Oklo natural analogue investigations indicate that the kinetics
Of U02 dissolution, either as uraninite or spent fuel, are exceedingly low under reducing
conditions expected in the near field of some repositories. While dissolution rates cannot be
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quantified readily from natural analogue data, the abundance of naturally occuning uraninite that
is nearly 2 billion years old at Oklo indicates its stability in the natural environment.
4.4 ANALOGUE STUDIES RELATED TO IMMOBILIZATION BY SECONDARY
MINERALS
Laboratory experiments have shown that U02 dissolution is accompanied by the fonnation of
secondary phases on the fuel surface and that these cor-rosion products can passivate further
dissolution (Wronkiewicz et al. 1996 [102047), p. 79). At the temperature and time scales of
laboratory experiments, these phases are amorphous. However, natural sites where uraninite
accumulations occur and where dissolution has taken place over long time periods could provide
insights into the structure and mineralogy of the secondary passivating phases, and indicate
whether they have been able to prevent further mobilization of radionuclides.
4.4.1 Shinkolobwe, Zaire
The 1,800 Ma Shinkolobwe uranium orebody in Zaire (at the time of study) was the subject of a
comprehensive investigation regarding the corTosion products of uraninite (Finch and Ewing
1991 [105591]). The Shinkolobwe deposit weathers under oxidizing conditions in a monsoonal-
type environment where rainfall is above I m per year, thus providing more aggressive
hydrochemical conditions than might be expected at a repository. At Shinkolobwe, the uraninite
is coarsely crystalline and lacks many of the impurities, such as thorium and rare earth elements,
found in other uranium deposits. This lack of impurities led Finch and Ewing (1991 [105591], p.
391) to suggest that the thennodynamic stability of the Shinkolobwe uraninite might closely
approximate spent fuel.
The deposit has been exposed at the surface since the Tertiary (< 60 million years), and extensive
weathering has altered or replaced much of the original uraninite. Uranium (VI) mineralization
occurs along fracture zones where meteoric waters have penetrated up to 80 m deep or more.
Uraninite crystals at Shinkolobwe are commonly surrounded by dense linds of alteration
minerals, mostly uranyl oxyhydroxides, as well as uranyl silicates and rutherfordine, a uranyl
carbonate (U02COO- Uranyl phosphates are also common within fractures throughout the host
rocks, but are rare or absent from corrosion iinds.
Uranyl minerals comprising the corrosion rinds that surround many uraninite crystals undergo
continuous alteration. This alteration occurs through repeated interaction with carbonate- and Si-
bearing groundwater combined with periodic dehydration of (especially) schoepite and
metaschoepite (Finch and Ewing 1991 [105591], p. 396). Such alteration occurs along small
(approx. 0.1 to I mm) veins within the corrosion iinds. There is a general decrease in grain size
as alteration proceeds, most commonly along veins. Schoepite, however, is not observed to re-
precipitate where in contact with dehydrated schoepite (Finch and Ewing 1991 [105591], p. 396).
Thus, while the formation of schoepite early during the corrosion of uraninite may be favored,
schoepite is not a long-term solubility-limiting phase for oxidized uranium in natural
groundwaters containing dissolved silica or carbonate (e.g., the type of groundwaters at Yucca
Mountain).
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Over 50 secondary uranyl phases were identified from the alteration of the uraninite. It was
concluded that uraninite transforms to Pb-U oxide hydrates and then to uranyl silicates if
sufficient silica is present in the system. Alteration of Proterozoic (-2400 to 700 Ma) uranium
deposits such as Shinkolobwe introduce the important Pb-bearing phases, such as curite, which
play a role in development of other stable phases in the system. Because of the very young age of
repository spent fuel, radiogenic lead would not be present at Yucca Mountain for helping to
immobilize spent-fuel elements.
4.4.2 Secondary Phases of Uranium Found at Nopal 1, Pefia Blanca
See Section 10.4 for a description of the Nopal I site. At Nopal I, uraninite occurs in rhyolite tuff
in a semi-arid environment, where it has been exposed to oxidizing groundwater conditions with
nearly neutral pH. Uranium was initially deposited as uraninite at Nopal I approximately 8 Ma
(Pearcy et al 1994 [100486], p. 729). Geologic, petrographic, and geochemical analyses indicate
that primary uraninite at Nopal I has been almost entirely altered to hydrated oxides and silicates
containing uranium in the oxidized (uranyl) forrn. Because of its young geologic age, the deposit
is low in radiogenic lead. The sequence of formation of uranyl minerals by alteration of uraninite
at Nopal I is shown in Figure 4-2 and is similar in many geologically young uranium deposits
located in oxidizing environments.
Leslie et al. (1993 [101714]) and Pearcy et al. (1994 [100486]) compared the alteration of
uraninite at Nopal I to laboratory experiments of degradation of spent nuclear fuel potentially to
be disposed of at Yucca Mountain, Nevada. They found that uraninite from the Nopal I deposit
should be a good natural analogue to spent nuclear fuel because long-term experiments on spent
fuel show alteration parageneses, intergrowths, and morphologies that are very similar to those
observed at Nopal I (Wronkiewicz et al. 1996 [102047]). Oxidation of the uraninite at Nopal I
has produced an ordered suite of minerals, first fonning schoepite, a uranyl oxyhydroxide,
followed by hydrated uranyl silicates, such as soddyite (Figure 4-2). Consistent with a high
calcium abundance in Nopal I groundwater, the dominant secondary uranium phase is
uranophane, a hydrated calcium uranyl silicate. Because of the abundance of calcite at Yucca
Mountain, uranophane would be a potential secondary phase there as well. In comparison,
laboratory expeiiments find that the general trend is to fonn mixed uranium oxides, followed by
uranyl oxhydroxides, and finally uranium silicates, mostly uranophane with lesser amounts of
soddyite (Wronkiewicz et al. 1996 [102047], p. 92). In addition, uraninite at Nopal I has a low
trace-element component (average of 3 wt%) that compares well with that of spent nuclear fuel
(typically < 5 wt% (Pearcy et al. 1994 [1004861, p. 730)). The young age of the Nopal I deposit
is another similarity to Yucca Mountain with respect to the absence of Pb-bearing secondary
phases.
4.4.3 Secondary Phases at Ok6lobondo
In the first detailed study of the Ok6lobondo natural fission reactor in Gabon, which corresponds
to the southem extension of the Oklo deposit (Figure 4-3), Jensen and Ewing (2001 [157500])
presented a history of uraninite alteration at that site showing complex mineralogical and textural
relationships. The Ok6lobondo reactor is the deepest of the 16 natural reactors (Figure 4-3). It is
situated at the base of a 2.5 m deep synform in the FA sandstone of the Francevillian Series. The
Ok6lobondo reactor zone (RZOKE) developed at the interface between overlying brecciated
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high-grade uranium-mineralized FA sandstone and underlying bitumen-rich black shale of the
FB Formation. RZOKE is relatively small (2.7 m wide and > 4 m long) and contains a - 55 cm
thick reactor core (Jensen and Ewing 2001 [157500], p. 32).
Ciiticality in RZOKE was facilitated by fixation and reduction of oxidized uranium by liquid
bitumen and precipitation of uraninite into a dense microfracture network in the FA sandstone.
The brecciation of the host rock may have been increased by overpressure created by the
accumulation of hydrocarbon gases during diagenetic maturation of oil introduced into the FA
sandstone. Chemical analyses and model estimates suggest that the ore grade at criticality at
RZOKE was on the order of 20 wt% uranium. Operation of the reactor caused extensive
dissolution of the FA sandstone and hydrothermal alteration of the black shale of the FB
Formation.  The sandstone dissolution was the major process that led to fon-nation of the 2.5 m
deep reactor synform and the high uranium concentrations L< 90 vol% uraninite) in the core of
RZOKE (Jensen and Ewing 2001 [157500], p. 59).
The mineral assemblage of RZOKE is comparable to that reported in the other Oklo reactor
zones, in that uraninite and Si-rich illite are the major phases in the reactor core, while chlorite
and illite are the major phases in the so-called argile de pile (reactor clays forming a halo around
the reactor zone). Galena (PbS) is also a major phase in the reactor zone. Minor coffinite (USi04)
and (U,Zr) silicates were also observed in addition to several accessory phases: e.g., titanium
oxides, La-bearing monazite, sulfides of Cu, Fe, Co, Ni, and Zn, and ruthenium arsenides. The
minor and trace elements include Th, Zr, Al, P, Ce, and Nd that seldom exceed concentrations of
0.1 oxide wt% (Jensen and Ewing 2001 [157500], p. 59). Figure 4-4 shows galena, illite, and
zircon embedded in a matrix of (U,Zr)-silicate in the center of the RZOK-E reactor core.
The acccessory (U,Zr)-silicate, phosphates, and ruthenium arsenides (+ Pb, Co, Ni, and S) were
of particular importance in secondary retardation of the fissiogenic isotopes (Jensen and Ewing
2001 [157500], p. 59). The (U,Zr)-silicate contains elevated concentrations of Zr02, Th02,
Ce203, and Nd203 as compared with the "unaltered" uraninite. This result suggests that the
fissiogenic 90Sr, Zr, Ce, and Nd, as well as the Th precursors, were efficiently retarded by the
(U,Zr)-silicate during their migration in the reactor zone. Lanthanide element fission products
may also have been retained in rare La-bearing monazite observed in the argile de pile of
RZOKE. Ruthenium arsenides incorporated fissiogenic Ru, probably including 99Ru, the
radiogenic daughter of 99Tc.
The presence of lead-uranyl sulfate hydroxide hydrate, anglesite, partial dissolution of uraninite
and galena, and the rapid oxidation of pyiite are evidence of a later shift toward oxidative
alteration conditions in and around the reactor zone. Hence, the slightly oxidizing deep
groundwaters at Ok6lobondo may have already reacted with the Ok6lobondo reactor zone.
4.5 RADIOLYSIS
Radiolysis is hydrolysis caused by radiation and results in production of charged species
(hydrogen and hydroxide ions) that may react to form more mobile species. Radiolysis can affect
both the waste form and the waste package. Because the waste canister is thinner than in
previous designs (CRWMS M&O 1999 [107292], Table 5-4), it is not self-shielded, so radiation
levels at the outside surface of the canister would be higher. 
However, it is not certain that
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radiolysis will be a problem. The effects of radiolysis in the Oklo ore deposit were discussed by
Curtis and Gancarz (1983 [1247851). They calculated the alpha- and beta-particle doses in the
critical reaction zones during criticality and the energy provided to the fluid phase by these
particles. This energy caused radiolysis of water and the production of reductants (H2) and
oxidants (02). The effect of these reductants and oxidants on the transport of radionuclides
within and outside the reactors has been difficult to quantify. Iron is most reduced in the samples
that show the greatest 235 U depletion. Curtis and Gancarz (1983 [124785], p. 36) suggested that
the reduction of iron in the reactor zones and oxidation of U (IV) in uraninite was
contemporaneous with the nuclear reactions and not a later supergene phenomenon of secondary
enrichment. Curtis and Gancarz (1983 [1247851, p. 36) suggested that radiolysis of water
resulted in the reduction of Fe (III) in the reactor zones and the oxidation of uranium.
Furthermore, the authors suggested that the oxidized uraniilm was transported out of the critical
reaction zones and precipitated through reduction processes in the host rocks immediately
outside the zones. The reduction processes likely involved organics or sulfides present in the host
rocks. However, if the host rocks around the natural reactor cores had not contained species
capable of reducing the oxidized uranium transported out of the cores, the uranium could have
been transported much further from the critical reaction zones. The important point is that, even
with intensive radiolysis, very little (only several percent) of the uranium in the natural reactors
was mobilized (Naudet 1978 [126123], p. 590).
Jensen and Ewing (2001 [157500], p. 59) noted a migration of Ce from reactor core to rim at
Ok6lobondo and suggested that this resulted from radiolysis taking place during reactor
operation. Cerium, particularly, showed indication of redistribution in the reactor zone, when
3+ 41
compared with Nd, in the uraninite rim. Because Ce can be oxidized to Ce , the difference in
the behavior of Ce as compared with Nd, results from oxidative alteration. The different
concentration of Ce in the uraninite rims, as compared with their cores across the reactor zone,
was produced during reactor operation, perhaps as a result of radiolysis.
4.6 CRITICALITY
The uranium deposit at Oklo, which was the site of naturally occurfing neutron-induced fission
reactions over 2,000 Ma, was used as a basis for reviewing conditions and scenalios that might
lead to nuclear criticality within and outside waste packages in the Swedish waste disposal
configuration (Oversby 1996 [100485]). The Swedish concept involves disposal in deep granite
with chemically reducing groundwaters, so the specific conditions are not relevant to those of
oxidizing environments. Yet in either oxidizing or reducing conditions, the combination of
simultaneous factors and probabilities required for criticality to occur seems very unlikely. For
criticality to occur, sufficient 239Pu and/or 235U would need to accumulate together with enough
water to allow for moderation of neutron energies. This would achieve a state where neutron-
induced fission reactions could be sustained at a rate significantly above the natural rate of
spontaneous fission. 
The chemical and physical conditions required to achieve nuclear criticality
at Oklo were used by Oversby (1996 [100485]) to estimate the amounts of spent fuel uranium
that would need to be assembled in a favorable geometry in order to produce a similar reactive
situation in a geologic repository. The amounts of uranium that must be transported and
redeposited to reach a critical configuration are extremely large in relation to those that could be
transported under any reasonably achievable conditions, even under oxidizing conditions. In
addition, transport and redeposition scenarios often require opposite chemical characteristics.
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Oversby (1996 [100485], p. vii) concluded that the likelihood of achieving a critical condition
caused by accumulation of a critical mass of uranium outside the canisters after disposal is nil,
provided that space ih the canisters is filled by low solubility materials that prevent entry of
sufficient water to mobilize uranium. Criticality caused by plutonium outside the canister could
be ruled out because it requires a series of processes, each of which has an increasingly small
probability. Criticality caused by uranium outside the canister would require dissolution and
transport of uranium under oxidizing conditions and deposition of uranium under reducing
conditions. There is no credible mechanism to achieve both oxidizing and reducing conditions in
the near-field repository host rock in the long ten-n, after decay of the majority of alpha-active
isotopes. Thus, the conditional probabilities required to achieve criticality caused by uranium
make the likelihood that criticality would occur vanishingly low.
4.7 NUCLEAR WASTE GLASS ANALOGUES
Among the natural volcanic glasses, basalt glasses are compositionally the most similar to
nuclear waste glasses (Lutze et al. 1987 [125923], p. 142). However, there are still substantial
compositional differences. Basalt glass and nuclear waste glass are similar in silica content,
alteration products, alteration layer morphologies, and alteration rates in laboratory experiments
(Grambow et al. 1986 [119228]; Arai et al. 1989 [123814]; Cowan and Ewing 1989 (124396]).
Basalt glass alteration has been studied in a number of environments including ocean-floor,
subglacial, hydrothermal and surface conditions (Grambow et al. 1986 [119228]; Jercinovic et al.
1986 [125289]; Byers et al. 1987 [121857]; Jercinovic and Ewing 1987 [144605]; Arai et al 1989
[123814]; Cowan and Ewing 1989 [124396]). Inferred alteration rates, as calculated from
alteration rinds, range from 0.001 gm (micrometers)/ 1,000 years to 30 gm/1,000 years (Arai et
al. 1989 [123814], p. 73).
Malow and Ewing (1981 [126058]) compared the thennal and chemical stabilities of two
borosilicate glasses and one glass ceramic to those of three rhyolitic glasses through a variety of
laboratory tests and observations of natural weathering. They concluded that natural glasses are
much more stable than waste-fonn glasses as a result of higher silica contents in the natural
glasses (74% versus 28 to 50% in waste-forin glasses). Tektites (nonvoicanic glass of
extraterrestiial or impact origin) range in age from _105 years to 35 Ma and rarely show signs of
alteration, dehydration, or devitrification (Lutze et al. 1987 [125923], p. 148). Their great
durability may be a result of their high silica and alumina (-30%) contents and their low (<4%)
alkali contents (Lutze et al. 1987 [125923], p. 152).
The compositions of the glasses utilized in natural analogue studies differ somewhat from
borosilicate glasses, and this makes a simple analogy dubious for quantitative purposes. lEgh
silica and alumina contents, along with low alkali contents and low water contents, are favorable
for long-tenn preservation. The dissolution rates measured on natural glasses are variable, but
always very slow. However, natural analogues cannot be used to provide a quantitative estimate
for the time at which devitrification will begin, or the rate at which it will proceed in the
repository environment. Natural glass studies do suggest that the rate of devitrification is too
slow for the process to be significant in the repository. These studies have not, however,
considered the effect of radiation. It might be possible to obtain relevant data on the radiation-
induced effects on glass durability by examining glasses that contain uranium oxides as
0 colorants, such as the "vaseline glass" produced in Germany and Bohemia in the 1800s (Miller et
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al. 2000 [156684], pp. 75-76). In all cases, the differences in chemistry between borosilicate
glass and natural and archeological glasses need to be considered when interpreting analogue
data. The qualitative evidence from analogues on natural and archeological glasses has added to
confidence that the glass degradation processes are well understood and has provided upper
bounding limits to the degradation rates.
4.8 SUMMARY AND CONCLUSIONS
The analogue sites located in chemically oxidizing environments are better analogues to
conditions expected to occur at Yucca Mountain than the more numerous sites located in
reducing environments. However, some examples from reducing environments may be
appropriate analogues for processes that would occur under repository conditions in either type
of chemical environment. Hence, both types of conditions were considered in studying the
processes relevant to waste form degradation. From the evidence presented in this section, the
main points are the following:
o The uranium alteration paragenesis sequence at Pefia Blanca is a good analogue to
alteration of uranium oxide spent fuel. The reaction path of alteration of spent fuel at
Yucca Mountain will be similar to that of geologically young, Pb-free uraninite, with
schoepite and becquerelite fonning as intermediate products followed by uranyl silicates.
9 Measurement of the concentration of fission products as tracers in rock and groundwater
surrounding uraninite provides a satisfactory approach to estimating natural dissolution
rates. This approach was tested at Cigar Lake and Koongarra under reducing and
oxidizing conditions, respectively, and the dissolution rate at Koongarra was found to be
more rapid. Use of the fission-product tracer method has not been reported for Oklo, but
other lines of evidence indicate that dissolution has been slight under reducing conditions
at Oklo over the past approximately 2 billion years. Whether deep oxidizing waters at
Ok6lobondo have increased the dissolution of uraninite as well as created an oxidized
suite of minerals is something that could be tested.
Secondary mineral fon-nation wa . s responsible for incorporating uranium at Shinkolobwe,
where 50 secondary uranium-beaiing phases could be identified. Because of the great age
of the Shinkolobwe uranium deposit, radiogenic lead-bearing phases played a role in
sequesteiing uranium. Lead would not play a role in secondary mineralization of younger
deposits, nor would it be present in spent fuel at Yucca Mountain. Other secondary
phases, particularly (U,Zr) silicates, formed stable phases at Ok6lobondo. Presumably
radiogenic lead was also present at Ok6lobondo, because of its approximately 2-billion-
year age.
It is uncertain whether radiolysis will be a potential problem around waste packages in the
current design scenatio (in which waste packages are not self-shielded). Under radiolysis
conditions occuning at the time of reactor criticality at Oklo, only several percent of
uranium was estimated to have been mobilized for transport from its original site, under
far more extreme conditions than those anticipated at Yucca Mountain. Likewise at
Ok6lobondo, radiolysis effects at the time of reactor operation appear to have been
9 confined to rare earth element migration from mineral core to rim. Because liquid water in
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contact with spent fuel is required for radiolysis to occur, the problem seems unlikely
under either higher- or lower-temperature operating modes for a potential repository at
40 Yucca Mountain. Cfiticality of spent fuel can be ttiggered by changes in pH as well as by reducing
conditions.  In the study examined, however, criticality was viewed from the standpoint of
redox conditions. Criticality of spent fuel, either within waste packages or by
reconcentration of uranium outside of the package, has a very low likelihood, because the
probability of certain processes required to achieve critical conditions occurring
simultaneously or sequentially renders certain conditions mutually exclusive.
9 Although natural glasses are somewhat different in composition from borosilicate nuclear
waste glass, studies of natural glass alteration indicate that glass waste forms will be stable
in a repository environment at Yucca Mountain. Higher stability is favored by higher
silica and alumina content and by lower alkali and water content of the glass. Analogue
studies have not considered radiation effects on glass over long time periods to confirm
expeiimental results showing that radiation has little effect on glass waste stability.
0
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0
0
Source: Blanc 1996 [157498]. p 111)
Figure 4 1 Photo of a Reactor Zone at the Oklo Natural Fission Reactor, Gabon
Nopal I Natural Analogue I Argonne Drip Experiments
		url-.11 (Syrlh.11~ UO,)

	L.dzyr,	S.Idy 11

3	lun-ho-
	11c

G-91, T- a ioo lob 3DO 400 500
n.. (-.)
Source Modified rom Murphy 2000 11574871, Figure 1,
Figure 4-2, Sequence of Formation of Uranyl Minerals by Alteration of Uraninite
I'DR NBS-GS 0900'7 REV 00 K-N 0 1 4F I April 2()02 1
NOTE: Vegetable matter in I-er center is in foreground, Man standing n lo,or aght-renter fo, scale

 

Natuml Analogue Synthesis Repon
0
t 1-2 OXCLOopmpit
3-6
7'
FB o4u- --z-
An.Wi..d
FA -d-
Ah- b-
.... . ..
o Reactor
Soume: Gauthisr~Lafaye 1996 (157542], Figum 4.
Figure 4-3. Schematic Cross Section Showiing Depth of Okdlobondo Natural Fission Reactor in Relation
to other Oklo Reactors
NOTE: The (U,Zr)-Si1lcate Is the medium gmy colored matdx mineml In which the other
minerWs am encased.
Sourm: Jonmn and Ewing 2001 [157500], Figum 110.
Figure 4-4. Aggregate of (U,Zr)-SI1Icate, Ziroon, Galena, and lllite in the Center of the Ok6lobondo
Reactor Core (RZOKE) I
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Natural Analogue Synthesis Report
0
0
Table 4-1. Elemental Distribution within Uraninite, Inclusions, and Clays for Elements in the Reactor
Zones at Oklo
Element	Uraninite	Inclusions	Clays	Migration
Cs				x
Rb				x
Sr				x
Ba				x
Mo		x		x
Tc		x	x
Ru		x	x	?
Rh		x	x	?
Pd		x	x	?
y	x		x
Nb	?	?
Zr	x	x	x
Te		x
REE	x		x
Ce		x
Pb	x	x		x
Bi		x
Th	x		x
u	x		x
Np	?	x
Pu	x		x
NOTE: REE-rare earth elements
Source: Miller et al. 2000 [156684], Table 4.2 (summarized from Blanc 1996 (157498]).
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Natural Analogue Synthesis Report
0 5. CURRENT ENGINEERED BARRIER SYSTEM DESIGN
5.1 INTRODUCTION
Section 5 provides a context for Engineered Barrier System (EBS) analogues that are discussed
in Sections 6 and 7. This section summarizes the key components of the EBS system and
describes the materials proposed to be used in the construction of these components. Finally, the
key processes that are expected to occur during the operational life span of the EBS are
described.
5.2 EBS COMPONENTS
The EBS currently planned for the potential Yucca Mountain repository (Figure 5-1) consists of
three main components: (1) diip shield, (2) emplacement drift invert, and (3) waste package
(DOE 2001 [153849], Section 2.4). Because they will affect the performance of the EBS,
materials included within the waste forms and used in the construction of the emplacement drifts
also are considered in the evaluation of the EBS. 
The following summary of the components of
the EBS system is based upon Sections 2.4 and 3 of the Yucca Mountain Science and
Engineering Reporl (S&ER) (DOE 2001 [153849]).
5.2.1 Drip Shield
The drip shield is designed to serve as a protective barrier, for the length of emplacement drifts,
that will divert water dripping from the drift walls, thus minimizing direct dripping onto the
waste packages. The drip shield has the added function of protecting the waste package from
rock falls from the drift perimeter. These functions require that the drip shield assembly is both
highly resistant to corrosion and has the structural strength to withstand rock falls.
The drip shield consists of three separate elements: the drip shield, supporting structural
members, and stands (or "feet") upon which the shield assembly rests (Figure 5-2). Current
design plans call for the drip shield to be manufactured from 15 mm (0.6 in.) thick Titanium
Grade 7 plates for long-ten-n corrosion resistance. The structural members will be constructed
using Titanium Grade 24, which has greater strength than Titanium Grade 7. Alloy 22 (see Table
5.2) will be used for the feet, preventing direct contact between the titanium structural members
and the carbon steel beams of the invert.
5.2.2 Drift Invert
The drift invert is designed to form a stable, level platform along the base of the emplacement
drift on which the waste package and drip-shield assemblies will be placed. The invert as
cuffently planned (DOE 2001 [153849], Section 2.4. 1) consists of two components: a steel invert
structure and a crushed-tuff invert ballast.
The steel invert structure needs to provide sufficient support for all expected pre-closure
activities for up to 300 years and must also keep the waste packages in a horizontal position for
10,000 years after closure. The steel structure consists of transverse and longitudinal support
beams, which serve to transfer the weight of the waste package and drip shield (along with any
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Natural Analogue Synthesis Report
needed emplacement and maintenance equipment during the initial phases of operation) to the
bedrock (Figure 5-3). Gantry rails, needed to transport the waste packages and drip shields into
the tunnel, will be placed along the margins of the support beam structure. Guide beams will be
used (if considered necessary to mitigate movement resulting from seismic events) to secure the
waste package emplacement pallets and the drip shield assembly. The current design calls for the
invert support and guide beams to be manufactured of ASTM A 572/A 572M steel, which was
chosen to provide sufficient strength for the emplacement drift environment. The gantry rail will
be made of ASTM A 759 carbon steel (DOE 2001 [1538491, Section 2.4. 1. 1).
The invert ballast is designed so that moisture present in the emplacement drift will drain directly
into the surrounding rock without flowing along the base of the drift. Crushed tuff, produced by
crushing material obtained during the excavation of the emplacement drifts, would be used as the
primary ballast material. The ballast will be placed around the steel invert beams, to a level just
below the top of the support beams, so that the waste package pallets and drip shields rest on the
support beams and not on the ballast. The ballast material will be compacted so that no
significant settling will occur over time. The crushed tuff -should not be affected by heating
related to emplacement of the waste packages. Transport of radionuclides within the crushed tuff
is expected to be dominated by diffusive transport, thus serving to retard any potential release of
radionuclides into the surrounding host rocks (DOE 2001 [153849], Section 2.4.1.2).
5.2.3 Waste Package
The waste package assembly is designed to securely contain high-level radioactive wastes and
serve as the primary element to the EBS. 
The waste package system consists of two main
components: a waste package emplacement pallet and a sealed, corrosion-resistant waste
package canister (Figure 5-4).
The waste package emplacement pallets are designed to support the waste package canisters in a
horizontal position and facilitate line-loading of the waste packages. Current plans call for the
pallets to be manufactured from plates of Alloy 22 (a mateiial highly resistant to corrosion) with
support tubes fabricated from Stainless Steel Type 316L (DOE 2001 [153849], Section 2.4.3.1).
The V-shaped design will allow the pallets to be used for all waste package canisters.
A number of distinct waste package designs have been developed to accommodate the different
waste fonns generated from boiling water and pressuiized water reactors, excess weapons
matelial, high-level waste, and DOE and naval spent nuclear fuel (Figure 5-5). All of these waste
package designs contain a number of important components that are needed to meet performance
criteria. The performance criteria (DOE 2001 [153849], Section 3.4.1) are as follows:
 Strength
 Resistance to corrosion and microbial attack
 Predictable materials behavior
Compatibility with waste package and waste form materials
Ease of fabrication
Proven perforinance record
Favorable heat transfer properties
Utility in shielding and preventing criticality.
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Natural Analogue Synthesis Report
Table 5-1 lists the major waste package components for commercial spent nuclear fuel waste
4D packages, the composition of each component, and the component function(s).
The different materials chosen for the constructio ' n of the waste package system are based on the
functional requirements for each component. Key properties include resistance to corrosion and
cracking caused by thermal, mechanical, and chemical processes; preservation of the structural
integrity of the waste package system; conduction of heat away from the wa.ste forms; and the
ability to prevent ciiticality from occuning. A brief description of each of the main types of
materials incorporated in the current design (DOE 2001 [153849], Section 3) is given below.
5.2.3.1 Corrosion-Resistant and Structural Materials
Alloy 22 was selected for the outer barrier of the waste package because of its resistance to
corrosion under conditions of high temperatures and low humidity and under all low-temperature
conditions, its similar thennal expansion coefficient to stainless steel, and because it can be
welded more easily than can titanium. The chemical composition of Alloy 22 is given in Table
5-2. Stainless Steel Type 316NG was chosen for the inner cylinder of the waste package because
of its relative strength, compatibility with Alloy 22, and its affordability. The chemical
composition of Stainless Steel Type 316NG is given in Table 5-3.
5.2.3.2 Other Waste Package Materials
A variety of other materials will be used in the fabrication of the waste package assembly (DOE
2001 [153849], Section 3.2.2.1). These include Neutronit A 978 (borated 316 stainless steel) or
SA 516 Grade 70 carbon steel plates, boron carbide rods with Zircaloy cladding used for control
of criticality within the waste package container, and aluminum shunts (SB-209 6061 T4) to
assist in heat transport away from the waste form. The waste package will encompass the waste
forrn materials described in Section 5.2.4.
5.2.4 Waste Form Components
The waste forms for disposal at the potential Yucca Mountain repository include spent fuel from
commercial power reactors and that owned by the U.S. Department of Energy, solidified high-
level radioactive waste, and plutonium waste from excess nuclear weapons. All waste must be in
solid form and must not contain flammable or chemically reactive materials. The waste forms
will contain fuel rods constructed out of Zircaloy and stainless steel as well as a variety of
radioactive waste types, including uranium metal, uranium oxide, uranium dioxide, radioactive
borosilicate glass, and plutonium encased in ceramic pellets (DOE 2001 [153849), Section 3).
Analogues to waste form materials and their degradation are discussed in Section 4.
5.2.5 Emplacement Drifts
While the emplacement drifts are not considered a component of the engineered barrier system,
the materials used in their construction could significantly affect the EBS performance. 
The
emplacement drifts contain a variety of materials that are used to help maintain the integrity of
the drift after excavation. The ground support system, designed to stabilize the emplacement
drift, includes W6X20 rolled s teel ring beams (steel sets), tie rods, welded wire fabric, rock bolts,
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Natural Analogue Synthesis Report
and cementitious grout used to secure the rock bolts in place (DOE 2001 [1538491, Section
2.3.4.1.2. 1). Analogues relevant to emplacement drift components are discussed in Section 7.
5.3 PROCESSES AFFECTING EBS PERFORMANCE
Numerous processes and event scenarios have been identified and considered in designing the
EBS (DOE 2001 [153849], Sections 2.4 and 3.1). These can be grouped into four major
categories: structural, thermal, chemical, and nuclear criticality. The structural events evaluated
involve scenafios (such as mishandling of the packages, seismic events, or rock falls) that would
result in the waste package being physically disturbed by an impact that could potentially result
in breaching the sealed waste packages. Thermal processes include changes in physical and
chemical properties associated with heating caused by radioactive decay of the waste forms, such
as thermal expansion and cracking, as well as the effects of heat transfer properties. Chemical
processes such as corrosion and chemical reaction of the different materials could also result in
breaching of the sealed waste packages and subsequent release of radionuclides into the
surrounding environment. Special attention has been placed on the design of the waste packages
and composition of the waste forms to prevent the radioactive waste from achieving criticality. 
The selection of the different materials used in construction of the EBS components has been
made to ensure the long-term structiiral, thennal, and chemical integrity of the waste packages
and to prevent the waste forms from going critical.
While the properties of all of the materials selected for the EBS design have been extensively
tested and deten-nined in the laboratory, the long-term performance of these materials under the
predicted temperature, humidity and chemical environment for the potential Yucca Mountain
repository has not been experimentally confirmed. Natural analogues for similar materials found
in the natural environment can be used to validate long-term performance models for the EBS.
The following sections (6 and 7) provide descriptions of natural analogues for waste package
materials and for processes that might take place within the EBS.
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Natural
0
0
StIN
Brac
(Typ
Lon
Sur
(Tyl
3antry Rail Cap
Nate and Runway
3eam
of Rail
B.Ilmt
c,..N - T. S-
CW Rg
Soume: DOE 2001 ([1538491, Figure 2-71).
Figure 5-1. Cross Sntion of Emptacement Drift with EBS Componenis
0
TDR-NBS-GSM0027 REV 00 ICN 01 5F] April 2002 1
5.5 m Diameter Emplacement Ddft

 

N-, l Symh-, R,p,l
0
7itanium Shield -4
Lifting PI :!::.
Source DOE 200 1 ([153849], Fqua 2-73)
Fig u re 5-2, Schematic View of Drip Shield Assembly with Drip Shield, Support Members, and Feet
4D
0
Sourue DOE 2001 ([1538491 Figure 2 72)
Figure 5-3. Perspective View of Steel Invert Structure in Emplacement Drift
TDR NBS-GS 000027 RlFV 00 ICN W 5F 2 Apnl 2()02 1

 

Natural
0
Source DOE 2001 ([1538491, modified fmm Figund 3-1),
Spent Nud- Foal
Dip Shield
Co os,on-Resistant
15 - Titanion, Grade 7
Walte Palkage Oute, Ba e,
Cormsion-Res,stant Alloy 22
Waste package Inner Laye,
S r,ct,ral Renforoemerit
Stainless Steel Type 316NO
Figure 5-4. Cross Section of Waste Package, Emplacement Pallet, and Drip Shield
0
NOTE PWR = Press,ri,ed Water Rlart.,; DHLW = Defense High-Le,el Radtoactive Wastil BWR - Boiling
Water Reactor; and SNF = Spent Nuclear Fuel. Source: DOE 2001 ([153849], Figure 2-77),
Figure 5-5. Schematic View of Dtfferent Waste Packages in Emplacement Drift
TDR NBS GS-000027 REV 00 ICN 0 1 5F-3 April 2002
Waste package
C.Un Steel En.placernern Pallet
Dlifi 1-1 Alloy 22 Stainless steel
Type 316L

 

Natural Analogue Synthesis
Table 5-1. 
Commercial Spent Nuclear Fuel Waste Package
0
Component	Composition	Function
Outer barder and lids	Alloy 22	Protect against corrosion
Support ring	Alloy 22	Hold inner cylinder in place
Inner structural shell and lid	Stainless Steel Type 316NG	Provide structural integrity
Waste package fill gas	Helium	Heat conductor, with need to be
		compatible with spent fuel
Fuel tubes for internal basket	Carbon steel (SA 516 Grade 70)	Hold fuel assemblies in place and
		provide structural strength and
		conduct heat away from cladding
Interlocking plates for internal	Carbon steel (SA 516 Grade 70)	Provide structural strength to
basket		maintain fuel geometry and
		prevent criticality
Neutron absorber materials for	Neutronic A 978 (borated 316	Prevent criticality, provides
internal basket	stainless steel)	structural strength and conduct
		heat away from waste form to
		walls of waste package
Thermal shunts for internal	Aluminum alloy (SB-209 6061 T4)	Transfer heat from waste form to
basket		walls of waste package
Structural guides for internal	Carbon steel (SA 516 Grade 70)	Provide structural strength to hold
basket		basket structure in place and
		prevent criticality, conduct heat to
		walls of waste package
Control rods	Boron carbide with Zircaloy
I	Provide long-term criticality
	cladding	control
Source: DOE 2001 [153849], modified from Table 3-9, Sections 3.1 and 3.2.2.
Table 5-2. Chemical Composition of Alloy 22
Element	Composition (wt 0/6)
Nickel	50 to 63
Chromium	20.0 to 22.5
Molybdenum	12.5 to 14.5
Iron	2.0 to 6.0
Tungsten	2.5 to 3.5
Cobalt	2.50 (max)
Manganese	0.50 (max)
Vanadium	0.35 (max)
Silicon	0.08 (max)
Phosphorus	0.02 (max)
Sulfur	0.02 (max)
Carbon	0.015 (max)
Source: DOE 2001 [153849], modified from Table 3-12.
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Natural Analogue Synthesis Report
Table 5-3. Chemical Composition of Stainless Steel Type 316NG
0
0
Element	Composition (wt %)
Iron	61 to 71
Chromium	16.00 to 18.00
Nickel	11.00 to 14.00
Molybdenum	2.00 to 3.00
Manganese	2.00 (max)
Silicon	0.75 (max)
Copper	0.50 (max)
Cobalt	0.10 (max)
Vanadium	0. 1 (max)
Nitrogen	0.06 to 0. 10
Titanium	0.05 (max)
Tantalum and Niobium	0.05 (max)
Aluminum	0.04 (max)
Phosphorus	0.030 (max)
Carbon	0.020 (max)
Bismuth + Tin + Arsenic + Lead +Antimony + Selenium	0.02 (max)
Sulfur	0.005 (max)
Boron	0.002 (max)
Source: DOE 2001 [153849], modified from Table 3-13.
0
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Natural Analogue Synthesis Report
6. WASTE PACKAGE DEGRADATION ANALOGUES
6.1 INTRODUCTION
This section desctibes the use of natural analogues to evaluate the long-term performance of
metals used in the fabrication of waste packages for storage of high-level radioactive waste. Key
concems for the waste package materials (described in Section 5) include the possible
degradation and corrosion of metals caused by mechanical stress, hostile physical and chemical
environments, and metallurgical factors. The primary degradation and corrosion issues expected
for Yucca Mountain include elevated temperature and humidity, and contact with seepage water
that could have corrosive chemistry. A number of different analogues were previously discussed
in Chapter 13 of the Yucca Mountain Site Description (CRWMS M&O 2000 [151945], Section
13.3.5); those analogues applicable to the waste materials desciibed in Section 5 are briefly
summarized below. Additional analogue examples are discussed in more detail in the following
subsections.
The long-term stability of the waste package materials is directly related to repository
environmental conditions. Preservation of delicate archaeological materials, including metals,
appears to be enhanced by their location in an and or semi-arid unsaturated environment
(CRWMS M&O 2000 [151945], Section 13.3.4). Mummified remains 4,000 to 8,000 years in
age were recently discovered in shallow buiial pits in the high Andes Mountains of Chile. The
Dead Sea scrolls were preserved in caves along the shores of the Dead Sea for over 2,000 years.
All of these artifacts have survived millennia, and their preservation is attributed in part to being
in aiid to semiarid unsaturated environments (Winograd 1986 [127015], p. 8).
Metal analogues, involving both naturally occurring and archaeological objects, were also
described in the Yucca Mountain Site Description (CRWMS M&O 2000 [151945], Section
13.3.5). A cache of Roman iron nails was recovered after almost 1,900 years of burial in
Scotland (Miller et al. 1994 [126089], pp. 114-119). Corrosion of the outermost nails formed a
protective rust rind, serving to create a more reducing (and thus more stable) environment for the
innennost nails. Using a variety of iron archaeological artifacts, Johnson and Francis (1980
[125291], Fig. 3-1) calculated general corrosion rates of 0.1 to 10 ~tm/yr for most of the artifacts
under a range of environmental conditions. Iron meteoiites often have poorly constrained
exposure histories, but differential corrosion of different mineral phases can be used to estimate
relative resistance to corrosion, suggesting that Ni-iich phases (taenite and schreibersite) are
more stable than Fe-rich phases (Johnson and Francis 1980 [125291], p. 4.23). Copper-beaiing
archaeological artifacts, such as sunken and buried bronze cannons, can also be used to estimate
general corrosion rates over extended (hundreds to thousands of years) periods of time. These
metal analogues, while differing in chemical composition from the waste package films, provide
important insights into the way different metals survive corrosion over long time periods, and
illustrate the importance of passive films.
Most of the metals being considered for use in the waste packages at a potential Yucca Mountain
repository consist of alloys that do not occur naturally and are not present in the archaeological
record (see Tables 5-1 to 5-3). However, the long-term behavior of metals with similar
compositions that are present either as minerals or as man-made objects can be used to build
TDR-NBS-GS-000027 REV 00 ICN 01 6-1 April 2002

 

Natural Analogue Synthesis Report
confidence in long-term perfonnance models of the waste package materials. Analogues to long-
term behavior of metals related to waste package materials are described in Section 6.2.3.
Information found in Section 6.2 may help to support arguments associated with Key Technical
Issue (KTI) KUZ0407 listed in Table I - 1.
6.2 NATURAL ANALOGUE STUDIES OF CORROSION
This section will discuss new work on some of the natural analogues previously summarized in
Chapter 13 of the Yucca Mountain Site Description (CRWMS M&O 2000 [151945]), as well as
present information on examples not previously discussed in the Site Description.
6.2.1 Environmental Factors Related to Corrosion
Knowledge of the in-drift physical and chemical environment at Yucca Mountain is critical in
predicting the long-term perfonnance of waste packages and the EBS. Processes such as the
evaporation and condensation of water, precipitation and dissolution of salts, seepage and mass
transport of materials into the drift environment, and the abundance, compositions, and reactions
between solid, liquid, and gas phases will affect the physical and chemical integrity of waste
packages and other EBS components.
One of the key attributes of the potential Yucca Mountain repository is its location within the
unsaturated zone, thus reducing the amount of water that can come into contact with waste
packages. Previous reviews of natural analogues of caves within the unsaturated zone have
demonstrated that very old archaeological artifacts can be preserved in such environments
(CRWMS M&O 2000 [151945], Section 13.3.4). Hundreds of wooden and reed fragments of
dart and arrow shafts (dated between 3,300 to 9,300 years B.P.) have been recovered from
Pintwater Cave in southem Nevada (Buck and DuBarton 1994 [157438], pp. 228, 239). These
delicate items were collected from the limestone cave floor and in a test pit excavated within
eolian sediments lining the floor of Pintwater Cave (Buck and DuBarton 1994 [157438], p. 226),
and their preservation suggests that they were not subjected to prolonged exposure to water.
However, as shown in the following example, the maintenance of a stable microclimate is a
critical feature in making caves suitable for long-term preservation.
The Altamira cave, located in northem Spain, is the site of Paleolithic cave paintings (Sanchez-
Moral et al. 1999 [157382]). Since the discovery of the prehistoric cave art in 1879, significant
degradation of the cave paintings has occurred, leading to the cave being closed to the public in
1977. The cave was reopened in 1982 with fixed limits on the number of visitors. Continuous
monitoring of the Altamira cave microclimate within Polychromes Hall (a cave chamber with
famous polychromatic paintings) during 1997-1998 determined that increases in temperature (A
= +0.25'C) and C02 concentrations (A = +500 ppmv) resulted directly from the presence of
visitors in the cave (Sanchez-Moral et al. 1999 [157382], p. 78).
Sanchez-Moral et al. (1999 [157382]) used these data to estimate effective calcite corrosion rates
for both the baseline and modified (visitor-related case) cave conditions. They predicted that the
visitor-induced temperature increase (resulting from radiation of body heat) will greatly increase
the amount of water condensation occurring on the cave walls and ceiling. The elevated PC02
(partial pressure of carbon dioxide) conditions caused by human respiration, combined with the
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Natural Analogue Synthesis Report
higher amounts of condensation, were predicted to result in visitor-induced cor-rosion rates (314
mm 3 /yr) in Polychromes Hall that are 78 times higher than the baseline (no visitor) case
0
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Natural Analogue Synthesis
(Sanchez-Moral et al. 1999 [157382], p. 78). As noted by visual observation and modeling, the
relatively minor changes in temperature and PC02 at Altamira had a significant impact on
deterioration of the cave art. Thus, the corrosion-resi stance properties of waste package mateiials
at Yucca Mountain need to be evaluated for all possible variations in environmental conditions
during the postclosure period.
One critical factor affecting the chemical integlity of the waste packages is the potential
development of hypersaline fluids within emplacement drifts at Yucca Mountain. Such fluids
could be generated by evaporative concentration of dissolved salts in pore waters in the near-drift
environment caused by heating, or by dissolution of previously formed salts in the dryout zone
around the drift by downward percolating condensate waters and/or surface infiltration. The
amount and salinity of water in contact with waste packages depend on a number of factors,
including evaporation, condensation, temperature, and fluid flux rates into the emplacement
drifts (Figure 6-1).  Conceptual and numerical models of these processes suggest that fluid
compositions within the emplacement drifts may be highly variable over time (Walton 1994
[127454], pp. 3483-3486).
To constrain models involving the generation of hypersaline fluids at Yucca Mountain,
Rosenberg et al. (2001 [154862]) conducted a series of experiments at sub-boiling temperatures
(75-85'C) to evaluate the evaporative chemical evolution of pore water from the unsaturated
zone and of well water from the saturated zone at Yucca Mountain. Synthetic solutions of these
two fluid types were evaporated, with samples collected and analyzed after approximately 100
and 1,000 x evaporative concentration and evaporation to dryness (Table 6-1). A number of
different minerals formed from complete evaporation of these waters, including amorphous
is silica, aragonite, calcite, halite, niter, smectite, thermonatrite, tachyhydrite, and gypsu'm. The
groundwater (obtained from the J-13 well at Yucca Mountain) composition evolved into a high
pH, sodium carbonate-bicarbonate biine resulting from the precipitation of calcium-magnesium
carbonate, while the UZ pore-water composition evolved into a near-neutral pH, sodium-
potassium-calcium-magnesium-chloride-nitrate brine resulting from the precipitation of gypsum.
Different fluid chemistry may develop under higher temperature (boiling) conditions as a result
Of C02 degassing, which could have an important impact on the pH of the evolved fluids. These
experimental results provide a data set against which to compare brines from analogue sites that
have interacted with metals in a natural environment.
Hypersaline fluids, such as those encountered at the Salton Sea geothermal field (Table 6-2),
have been observed to aggressively corrode many steel compositions (McCright et al. 1980
[157384], pp. 646-648). Carbon steel drill casings initially used in geothermal production wells
at the Salton Sea field experienced general corrosion rates as high as 25.4 mnVyr, with even
higher localized corrosion rates observed (Pye et al. 1989 [157385], p. 260). These rates are
much higher than the rates of 10-40 gm/yr obtained by Ahn and Soo (1995 [10475 1 ], p. 475) for
corrosion tests of A216-Grade WCA low-carbon steel in concentrated synthetic groundwater
solutions. The differences in corrosion rates likely result from: (1) differences in steel
compositions; (2) higher temperatures for the Salton Sea fluids (232-315'C) than that those used
for the corrosion experiments (80-150'C); and (3) much higher salinities for the Salton Sea
brines (150,000-300,000 ppm TDS) relative to the synthetic experimental biines (7,455 ppm
TDS). Corrosion problems at the Salton Sea were successfully mitigated through the use of a
corrosion-resistant titanium alloy (see Section 7.2.1). The current diip shield design for Yucca
TDR-NBS-GS-000027 REV 00 ICN 01 6-3 April 2002 1

 

Natural Analogue Synthesis Report
Mountain (see Section 5.2.1) calls for the use of titanium because of its corrosion-resistant
properties.
Another concem for waste package materials is the possible evaporative concentration of minor
dissolved constituents, such as arsenic, lead, and mercury, that could enhance corrosion (BSC
2001 [1559501, Section 7.3.1.3.4; [157151], Appendix E, Section 3.1.2). The hypersaline Salton
Sea brines have significant concentrations of arsenic (8 ppm) and lead (66 ppm). However,
groundwaters in the vicinity of Yucca Mountain have only trace amounts of lead, with a median
concentration of 9 ppb (Lee 2001 [155241]; Perfect et a]. 1995 [101053]). Two samples of J-13
well water from Yucca Mountain were analyzed for lead, with one sample yielding a value of 3
ppb, while the other was below detection (BSC 2001 [155950], Section 7.3.1.3.4; Perfect et al.
1995 [1010531). Lead concentrations in groundwater at Yucca Mountain may be limited by
precipitation of lead in the fon-n of carbonate, oxide, or sulfide minerals, or by sorption onto
mineral surfaces (BSC 2001 [155950], Section 7.3.1.3.4, [157151], Appendix E, Section 3.1.2).
Evaporative concentration of water in the near-drift environment at Yucca Mountain could result
in higher lead concentrations. However, even a 1,000-fold increase in lead concentration in J-13
water would still only result in a brine with -3 ppm lead, over 20 times lower than the
concentrations observed in Salton Sea biines. Thus, the very low concentrations of lead in
groundwater at Yucca Mountain greatly reduce the risk that lead (and other trace metals) could
pose to the chemical integiity of the waste packages.
6.2.2 Passive Film Formation
The formation of passive films has a significant impact on the corrosion-resistant properties of
metals and metal alloys (BSC 2001 [1559501, Section 7.3.4). Passive films are stratified coatings
consisting of an inner oxide layer and an outer layer of hydroxide or oxyhydroxide (Macdonald
1992 [154720], pp. 3434-3437; Marcus and Maurice 2000 [154738], pp. 145-152]. The inner
layer fonns a corrosion banier, while exchange occurs within the outer layer of the passive film.
These films act as semiconductors or insulators, thus reducing the rate of metal dissolution
ttiggered by an electrochemical potential between a metal and its surrounding electrolyte
solution.
The Delhi iron pillar is a 1,600-year old metal artifact (Figure 6-2) that has withstood exposure
to the atmosphere with only relatively small amounts of corrosion. Study of the rust layer coating
the pillar reveals the presence of crystalline iron hydrogen phosphate hydrate and amorphous
iron oxyhydroxides and magnetite (Balasubramaniam 2000 [157383], pp. 2115-2116). The low-
porosity crystalline phosphate phase forms a passive film around the pillar, serving to protect it
from further corrosion (Figure 6-3). Balasubraminiam (2000 [157383], pp. 2112-2115)
interpreted the presence of -0.25 wt% phosphorous and fine slag particles in the iron to be
ciitical to the development of the corrosion-resistant layer.
6.2.3 Naturally Occurring Metals as Natural Analogues
Josephinit"osephinite, a naturally occurring Ni-Fe-Co metal-bearing rock consisting of the
minerals Ni3Fe (awaruite), andradite gamet, FeCo (wairuite), and minor to trace amounts of
Ni6Fe4 and CaO-2FeO (calciowiistite), is a possible natural analogue for Ni-Fe alloys (similar to
Alloy 22, which is a Ni-Cr-Mo-W alloy) proposed for the Yucca Mountain waste packages. The
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type locality of josephinite is the Josephine Ophiolite, a -150 million-year-old serpentinized
ultramafic body in Oregon, where it occurs within serpentine veins and as coarse metallic
nuggets in nearby placer deposits (Dick 1974 [154749]). Josephinite was interpreted by Dick
(1974 [154749], p. 297) to be a product of hydrothermal alteration and serpentinization of
peridotite. Josephinite and awaruite are very stable rock and mineral phases, as evidenced by
their survival for millions of years with only minor amounts of oxidation. Because of this long-
lived stability, these ordered Ni-Fe-Co metals (Bassett et al. 1980 [157531]) have been proposed
as alloys in constructing containers for the storage of high-level radioactive waste (Bird and
Ringwood 1980 [157397]; 1982 [157398]; 1984 [157396]).
Relatively unaltered masses of metal that are predominantly Ni3Fe (with small inclusions of
Ni3As) were discovered in 1999 within harzburgite in the Josephine Ophiolite and as eroded
blocks up to -3 kg (Bird 2001 [157514]). Preliminary Pb and Os isotopic analyses of these new
samples suggest that the josephinite metal did not form as an alteration product of the Josephine
Ophiolite, but instead may represent xenoliths within the serpentinite body that have a deep-
mantle origin (Bird 2001 [157514]). 
The josephinite nuggets have alteration rims comprised of Fe304 (magnetite, with maghemite)
and NiFe204 (trevorite). Some samples of josephinite contain the high-temperature phase taenite
(a disordered Ni-Fe metal) in addition to awaruite (BSC 2001 [155950], Section 7.3.2.4.2). Phase
relation studies of the Fe-Ni system suggest that taenite is not stable below -350'C, and that a-
Fe, pure Ni, and awaruite are the stable phases for this system at ambient temperatures (Botto
and Morrison 1976 [154716], p. 264). The persistence of taenite for millions of years suggests
that low-temperature phase change rates for taenite are exceedingly slow (BSC 2001 [155950],
Section 7.3.2.4.2). X-ray photoelectron spectroscopic analysis of a josephinite placer sample
from the'Josephine Ophiolite (Figure 6-4) revealed that while both iron and nickel are oxidized
on the surface, nickel remains in reduced (metallic) form at depths of 2 nm and greater (analyzed
to a depth of 120 nm), indicating that the bulk sample has not undergone significant amounts of
oxidation (BSC 2001 [157151], Appendix E, Section 3.3.2, Table 1). Because of its high nickel
concentrations, the longevity of josephinite indicates that nickel alloys will have long-term phase
stability. While josephinite does not contain the molybdenum and tungsten that serve as
stabilizing elements in Alloy 22 passive films, its ability to resist corrosion provides confidence
that Alloy 22 will remain passive under potential repository conditions (BSC 2001 [157151],
Section 3.3.2, Appendix E).
Chromite Analogues for chromium are considered because of the chromium content of Alloy
22 (Table 5.2). Chromium occurs in minerals in the form of chromite (FeCr204) and chromium
spinel (Mg(Cr,AI)204). These Cr-bearing minerals are typically found in mafic and ultramafic
rocks. Elevated concentrations of chromium in groundwaters in the Leon-Guanajuato valley of
central Mexico have been attributed to weathering and alteration of chromite from ultramafic
rocks of the Sierra de Guanajuato that have been interpreted to be Jurassic in age (Robles-
Camacho and Annienta 2000 [157386], pp. 172-173, 178-181). The San Juan de Otates
pyroxenite unit consists of pyroxenite and serpentinized peridotite, harzburgite, and wehrlite.
Discrete concentrations of ilmenite and chromite occur within these rocks, and form subrounded
masses in outcrop. Chromite is typically found as subrounded crystals, often with exsolution
borders of magnetite.
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A variety of ultramafic rock samples from the Sierra de Guanajuato, with total chromium
contents ranging from 55 to 4115 ppm, were leached with acid to evaluate the susceptibility of
the rocks to weathering and subsequent release of chromium (Robles-Camacho and Annienta
2000 [157386], pp. 173-181). The laboratory acid treatment was designed to examine (over a
much shorter time scale and under much more acidic conditions that found in the field) the
effects of weathering resulting from interaction of oxygenated, C02-rich groundwater with
chromium-bearing minerals (Robles-Camacho and An-nienta 2000 [157386], pp. 174-177). The
leachate from Cr-rich serpentinite samples yielded the highest concentrations (up to 274 mg
Cr/kg rock), suggesting that they have the greatest potential to release chromium. SEM analysis
of samples examined after leaching suggests that dissolution occurred along magnetite
exsolution borders of chromite grains (Figure 6-5). Total chromium contents of groundwater
samples collected from wells, streams, and reservoirs near the ultramafic rocks range up to
0.0149 mg/L. The Ca-Mg-HC03 composition of these waters is consistent with interaction with
serpentinized ultramafic rocks. 
The study does not provide information on the rates of chromite
weathering, but it does indicate that chromite exsolution borders are susceptible to chemical
attack. This observation is analogous to localized corrosion and pitting observed in metals along
structural defects.
6.3 SUMMARY
1. The survival of metal archaeological artifacts over prolonged periods of time is related
to the corrosion-resistant properties of metals and metal alloys, the development of
protective passive film coatings with the onset of coffosion, and the location of artifacts
in arid- to semi-arid environments. Such features can be used in the selection of
materials and design configuration to enhance the durability of waste packages at
Yucca Mountain.
2. Archaeological examples, such as the Altamira cave, illustrate how environmental
changes can significantly affect corrosion behavior. A wide variety of environmental
conditions is expected to occur in the near-drift environment at Yucca Mountain duling
the lifespan of the repository. The introduction of heat-generating waste packages and
EBS materials into drifts will perturb the existing physical and chemical system at
Yucca Mountain. The materials used for the waste packages (and the rest of the EBS)
need to withstand the predicted adverse changes in environmental conditions.
3. Small volumes of concentrated brines could develop in the near-drift environment as a
result of evaporation and later dissolution of precipitated salts in the dryout zone with
rewetting. Bgh-salinity fluids pose a significant cor-rosion hazard to carbon steel, as
seen at the Salton Sea geothermal field, but the use of titanium alloys can effectively
minimize this hazard.
4. The survival for millions of years of the naturally occuning ordered Ni-Fe alloy found
in josephinite (with only relatively minor amounts of surface oxidation) indicates that
this material is highly resistant to oxidation and other forms of corrosion that occur in
its geologic environment. While the composition of this metal differs from Alloy 22 (in
that it does not contain Cr, Mo, and W), it does provide evidence that a similar alloy
0 can remain passive over prolonged periods of time.
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5. The potential instability of chromium-bearing materials is illustrated by the observed
natural release (under ambient conditions) of chromium from chromite in the Sierra de
Guanajuato ultramafic rocks. Corrosion appears to be concentrated along exsolution
fims, analagous to structural defects on metal surfaces. While the chromite has
undergone some alteration, it has survived for over 140 m.y. (since Jurassic time).  The
corrosion behavior of this chromium oxide mineral may differ from that of the
chromium-bearing metal alloys (Section 5) that are currently slated for use in the
construction of the waste package.
0
0
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Ilquid water and soluble
salts influx rate
condensation "Vaporation
% ~/_l
wetted area
Soume: Walton 1994 1127454], Figum 3.
Figure 6-1. Processes Affecting Fomation of High-Salinity Fluicls on Wwte Package Surface
0
0 Figure 6-2. The Coffosion-Resistant Iron Pillar at Delhi
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Soume: Satasubrarnaniam 2000 [157383). Figum 1.

 

NLtu,Ni
WEATHERING SIEEL
---col
ACi,QNc,P
"Y'
DEL.. PON PILLAR
- F'oo
1- F-P
FIDGH
7,75771-7177-P, IHID)
NOTE: Iron hydmgen phosphate hydmte layer on Delhi imn pillarforms a
protective, lmpermeabie coating that retards fulher corrosion.
40 Source: Balasubnamaniarn 2000 (157383], Figum 7,
Figure 6-3. Schematic Showing Development of Rust Coating on Mild Steel, Wealhering Steel, and Delhi
Iron Pillar
NOTE: Metallic-looking areas mre analyzed
using X-my photoelectmn spectroscopy.
Source BSC 2001 [157151 ],Appendix E, Figure 3.
Figure 6-4. iosephinite Sample Used for Surface Analysis Study
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0
NOTE: Whfte dm around chrornits in (Ib) reffeds dissoludw of axsolution border amrtd chrornits.
Smw. Robles-Camwho and Arrnlenta20001157386], Figums5 ends.
Figure 6-5. Chrornite, Grains in Serpengnfte Before (a) and After (b) Acid Leaching
0
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le
Table 6-1. Composition of Synthetic Yucca Mountain Waters (mg/L) from Unsaturated and Saturated
Zones and Their Evaporated Compositions
	Synthetic
J-1 3 water	"l 57 X"
J-1 3 water	11956 X"
J-1 3 water	Synthetic
UZ water	"62 X"
UZ water	"1243 X"
UZ water
Na	45.2	5,288	43,302	8.56	477	6,223
K	5.2	593	4,701	4.00	268	2,644
Mg	2.1	1.2	0.13	11.8	550	5,546
Ca	5.8	0.06	27.3	57.3	1,713	15,643
SI02	10.4	1,040	----	10.4	503	541
HC03	105	4,410	24,255	20.3	9.9	<45
S04	18.5	2,109	13,209	83.9	1,544	2,098
ci	7.2	814	5,047	76.6	4,259	52,165
N03	7.9	1,035	5,483	10.7	592	....
F	2.3	237	1,622	2.16	38	<542
TDS	209.6	15,527	97,646	285.7	9,954	-85,000
pH	8.07	10.18	----	7.55	7.65	6-6.5
NOTE: TDS calculated as sum of dissolved solids.
Source: Rosenberg et al. 2001 [154862], Tables 2 and 4.
0 Table 6-2. Typical Salton Sea Geothermal Well Brine Composition
Component	Concentration
PPM	Component	Concentration
PPM
Na	49,800	Ba	100
K	12,840	B	301
Mg	80	Cu	7
Ca	24,000	Fe	708
Si02	658	Pb	66
C02	125	Li	177
S04	22	Mn	785
ci	126,700	Rb	62
NH3	339	Sn	402
As	8	Zn	287
1	5	Br	68
pH	5.8	H2S	90
		TDS	261,800
Source: Pye et al. 1989 [157385], Table 1.
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0 7.'ENGINEERED BARRIER SYSTEM ANALOGUES
7.1 INTRODUCTION
This section descfibes the use of natural analogues to evaluate the long-term performance of
materials used in the construction of the Engineered Barrier System (EBS) and how these
materials may affect radionuclide transport. The primary functions of the EBS components are
to: (1) protect the waste package from physical and chemical degradation resulting from
processes such as seepage, corrosive fluids, and rock fall; and (2) retard any potential transport
of radionuclides from the emplacement drift in the event of waste package failure. Key concems
for the EBS materials (described in Section 5) include the possible degradation and corrosion of
metals resulting from mechanical stress, hostile physical and chemical environments, and
metallurgical factors. Another important perfonnance parameter is the effect of EBS materials on
flow and transport of fluids and dissolved solids into and out of the emplacement dfifts.
Important issues relating to EBS performance include the degradation of materials caused by
corrosive fluids, radiation, thennal and physical stresses, and microbial attack, as well as the
effects of sorption and colloids on radionuclide transport. A number of analogues were
previously discussed in Section 13 of the Yucca Mountain Site Description (CRWMS M&O
2000 [151945]); these analogues are briefly summarized below. Additional analogue examples
are discussed in more detail in the following subsections.
Three main issues relating to the EBS were discussed in detail in the natural analogues chapter of
the Yucca Mountain Site Description (CRWMS M&O 2000 [151945], Section 13.3): (1) metal
analogues (native metals and archaeological artifacts) in the evaluation of corrosion resistance;
(2) cements and alkaline plumes to determine the impact of high pH fluids on EBS mateiials,
surrounding host rock, and radionuclide transport; and (3) the effects of radiolysis on the
integrity of waste package materials. A biief summary of earlier work on metal analogues is
presented in Section 6 and thus will not be repeated here.
Under the current EBS design, cementitious material is expected to be present in only minor
amounts (as grout for rock bolts) in the near-drift environment. The durability of cements over
time has been documented by Gallo-Roman cements that are over 1,500 years old (Thomassin
and Rassineux 1992 [157439], p. 137). Cementitious mortar from Hadrian's Wall (-1,700 years
old) in England (Figure 7-1) has the same calcium silicate hydrate phases found in modem
Portland cement, and still possesses excellent strength and stability (Miller et a]. 2000 [156684],
p. 131). The potential development of hyperalkaline fluids resulting from interaction of water
with cementitious mateiial could affect radionuclide transport and reduce the stability of EBS
materials. Two areas with hyperalkaline fluids were described in the earlier review of natural
analogues (CRWMS M&O 2000 [151945), Section 13.3.6): the Semail ophiolite in Oman, and
the Maqarin area in Jordan. Serpentinization reactions in the Semail ultramafic rocks have
resulted in the generation of reducing, hyperalkaline (pH = 10-12) Na-Cl-Ca-OH fluids, with
associated minerals brucite (Mg(OH)2) and portlandite (Ca(OH)2). The Maqalin analogue site
(also discussed in Section 7.3.1) contains a suite of naturally formed cement minerals, including
portlandite. High pH (12-13) fluids emanate from these rocks as a result of reaction of
groundwater with the cement phases. These analogue sites have been used in the development of
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numerical models to predict water-rock reactions and resulting fluid compositions under similar
conditions (McKinley et al. 1988 [126077]; Chambers et al. 1998 [157549]).
Chemical decomposition resulting from radiation (radiolysis) was also examined in the Yucca
Mountain Site Description (CRWMS M&O 2000 [151945], Section 13.3.7). This process was
studied at the natural reactor site at Oklo (in Gabon), where high radiation doses were interpreted
to have led to radiolysis of water and redox reactions involving the surrounding rocks (Curtis and
Gancarz 1983 [124785]). Similar reactions within the waste package assembly could lead to
decomposition of the waste packages and release of radionuclides. However, since the waste
loads are configured so that they will not approach criticality and the waste package design
excludes free water, the amount of radiolysis that might occur at the potential Yucca Mountain
repository should be much less than Oklo (see also Section 4 of this report). Section 7.2
describes analogues for EBS materials and Section 7.3 describes analogues for EBS processes.
7.2 ANALOGUES FOR EBS MATERIALS
7.2.1 , Analogues for the Titanium Drip Shield
Coffosion caused by saline fluids has been identified as a potential hazard to the integrity of
waste packages (see Section 6.2.1 for discussion). The drip shield assembly is designed to
protect the waste packages from physical and chemical degradation resulting from events such as
rock falls, seepage, and saline fluids. The current drip shield design calls for corrosion-resistant
titanium. Titanium metal does not occur in nature, nor in the archaeological record, so other
40 proxies need to be used to assess its long-term resistance to corrosion.
The Salton Sea geothermal field in Califomia is characterized by hypersaline (15-30 wt% TDS)
brines that have caused significant corrosion and scaling problems (Pye et al. 1989 [157385],
p. 259). A series of corrosion tests led field operators to select Beta-C titanium (Ti-3AI-8V-6Cr-
4Mo-4Zr) for the fabrication of corrosion-resistant production casing (Pye et al. 1989 [157385]).
Four tests were conducted over a period from 256 to 833 days, involving installation of ftill-size
Beta-C titanium tubulars in geothermal production wells, resulting in no visible pitting corrosion
in two of the tests, little or no change in hydrogen content, and no significant degradation in
mechanical properties (Pye et al. 1989 [157385], pp. 262-263). In the 833-day test, localized
corrosion was observed, occurring at a rate of 7 mils/yr (178 pm/yr); this was interpreted to have
occurred in an area where surface contamination had not been completely removed at the start of
the test. Local corrosion was observed along 2 of the 48 casing joints in the fourth test; this
coffosion was also interpreted to be the result of pre-existing surface contamination.
A longer-tenn evaluation of the corrosion behavior of titanium-bearing materials can be obtained
by examining the stability of naturally occurring titanium minerals. Titanium is present as a
major constituent in a number of refractory accessory minerals commonly found as a minor
phase in igneous rocks and in heavy mineral concentrates in sediments. These minerals include
sphene (titanite) (CaTiSi04(0,OH,F)), rutile (Ti02), ulv6spinel (Fe2TiO4) and ilmenite (FeTi03).
The Canadian nuclear waste disposal concept includes a metallic titanium container surrounding
spent fuel. The corrosion resistance of titanium arises from its passivation in aqueous solutions
0
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by the formation of a protective layer containing rutile (Cramer 1994 [157537], pp. 8-10). At the
Cigar Lake uranium deposit in Saskatchewan, Canada, rutile is present within the uranium ore
and has persisted unchanged for over a billion years i-n reducing groundwaters, under
hydrothertnal conditions, and in a radiation field. While rutile and other titanium-bearing
minerals are oxides, and thus do not share the same physical properties as metals, their general
resistance to alteration reflects the stable nature of titanium-bearing materials.
7.2.2 Analogues for the Invert Ballast
The nonwelded Calico Hills Formation and portions of the Paintbrush Tuff at Yucca Mountain
are possible analogues for processes, such as sorption and ion exchange, that would affect the
transport of radionuclides within the crushed tuff invert ballast. The relative lack of fractures in
these tuffs results in fluid flow occurring in the tuff matrix, resulting in overall slower fluid flow
and transport in these units caused by the lack of fast flow pathways, similar to what is predicted
for the crushed tuff invert. Because of the presence of zeolites and/or smectite in the nonwelded
tuffs, extensive ion exchange occurs between pore waters and the tuffs (Vaniman et al. 2001
[157427]). The zeolitic tuffs are significantly enriched in cations such as Ca2+, Mg2+ , and Sr2+,
and depleted in Na+ and K+ (Figure 7-2); thus, waters are interpreted to have complementary
(opposite) enrichments and depletions (Vaniman et al. 2001 [157427], pp. 3420-3423). This ion-
exchange process would have a major impact on radionuclide transport, with species such as 90Sr
being effectively immobilized by this process. However, the current design for the invert ballast
(DOE 2001 [153849], Section 2.4.1.2) uses crushed tuff derived from the repository interval
(welded, devitrified Topopah Spring Tuff), which has only minor amounts of zeolites and clays
(Vaniman et al. 2001 [157427], Figure 2). As a result, the ion exchange and sorption capacity of
the crushed tuff invert ballast should be significantly lower than that observed in the nonwelded
tuffs at Yucca Mountain. The crushed tuff invert would have high effective grain surface areas,
which would favor sorption of species onto mineral surfaces, thus serving to retard radionuclide
transport. The effects of fluid flow on radionuclide retardation in ash flow tuff can also be evaluated
through an anthropogenic analogue. At Los Alamos National Laboratory, radionuclide-bearing
liquid wastes were discharged from 1945 to 1967 into gravel- and cobble-filled absorption beds
(approximately 6 m x 37 m) built on outcrops of moderately welded rhyolite ash now tuff
(Figure 7-3) (Nyhan et al. 1985 [157447], p. 502). Large amounts (corresponding to a depth of
20.5 m) of tap water and radioactive effluent were added to one of the absorption beds (Bed 1) in
1961 to evaluate radionuclide mobility. The site was revisited in 1978, when profiles of Pu and
24'Am were measured in a series of 30.5 m deep boreholes drilled through two of the absorption
beds (Bed I and Bed 2) and into the underlying ash flow tuff (Nyhan et al. 1985 [157447], p.
502). This study revealed that the bed where water and effluent had been added in 1961 (Bed 1)
exhibited higher water saturations, along with significantly more radionuclide migration ou ' t of
the absorption bed and into the underlying tuff (Figure 7-4), than the bed where no additional
fluid had been added during this test (Bed 2).  Plutonium and 24'Am were not detected beyond
11.28 m below the bottom of Bed 2, whereas 0.3 to 5,1% of the plutonium and 3.0 to 49% of the
americium inventory were present within the depth interval of 11.28-27.13 m for Bed I (Nyhan
et al. 1985 [157447]), p. 506). Elevated concentrations of radionuclides were observed to occur
within lower permeability intervals of the tuff. The radionuclide concentrations of fracture
fillings were similar to those of adjacent tuff samples, suggesting that fractures did not enbance
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radionuclide transport under unsaturated conditions and generally acted as barfiers to unsaturated
zone (UZ) flow (Nyhan et al. 1985 [1574471, pp. 504-505, 508). These results suggest that
radionuclide mobility was triggered by flushing of the absorption beds with large volumes of
fluids. The volume of the column of fluid used in the Los Alamos test is equivalent to the
amount of percolating surface water expected to flow through Yucca Mountain over a timespan
of 2,000 to 4,000 years (assuming an infiltration rate of 5 to 10 mm/yr (Flint et al. 2001
[156351], p. 26), and thus represents an illustration of the effects of flushing on radionuclide
mobility. However, this example does suggest that the ability of the invert ballast at Yucca
Mountain (as well as the underlying welded tuffs) to retard radionuclide migration will depend in
part on the amount of water flowing through this interval. Both of the analogue examples
described are also relevant to processes controlling radionuclide transport in the UZ at Yucca
Mountain (see Section 9).
7.3 NATURAL ANALOGUES FOR EBS PROCESSES
The physical and chemical conditions for the near-field area around the emplacement drifts at
Yucca Mountain are predicted to undergo changes over time. These changes would result from
coupled then-nal-hydrologic-chemical (THC) processes, such as boiling, condensation,, fluid flow
and transport, and mineral dissolution, alteration, and precipitation (BSC 2001 [154677]). THC
processes are also expected to occur within the EBS, and could lead to degradation of the EBS
components, resulting in the release and transport of radionuclides away from the EBS. Natural
analogue studies for some of the processes expected to impact the EBS system, such as the
generation of alkaline plumes resulting from interaction of water with cementitious material and
the effects of colloids on radionuclide transport, are described below.
7.3.1 Natural Analogues for Development of Alkaline Plumes from Cement
The presence of naturally occurring cement minerals and associated hyperalkaline groundwaters
at Maqarin, Jordan, has been used as a natural analogue for examining the effects of
hyperalkaline waters (e.g., Khoury et al. 1992 [1256771; Smellie 1998 [126633]). The Maqafin
site consists of interbedded bituminous limestones and marls that have been locally thermally
metamorphosed from spontaneous combustion of the bitumen, resulting in the calcination of
limestone and formation of cement minerals, including portlandite. Water interacting with
portlandite has resulted in the formation of highly alkaline (pH = 12.5) groundwaters and the
precipitation of minerals such as ettringite and thaumasite at ambient temperatures (Figure 7-5).
Initial geochemical modeling efforts resulted in model predictions of dissolved selenium and
uranium concentrations that were several orders of magnitude higher than those observed in the
field (Linklater et al. 1996 [108896], p. 67). A multicomponent reactive transport model that
incorporated mixed equilibrium and kinetic reactions was applied to simulate rock alteration
mineralogy and fluid chemistry changes for discrete fractures in the Maqarin system (Steefel and
Lichtner 1998 [156714]). These simulations predict the formation of hydrated calcium sulfate
and silicate minerals, such as ettringite and tobermorite, which were observed in the field
(Khoury et al. 1992 [125677], p. 122), and also reproduced measured fluid pH values. 
The
simulations suggest that mineralization caused by interaction of the hyperalkaline plume with
surrounding rocks may result in both reduction of matrix porosity and fracture sealing. Fractures
at the Maqarin site have complex mineralogy and textures that suggest that they have undergone
repeated sealing and reopening over time. The relative rates of matrix and fracture mineralization
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(and associated reduction in permeability) will significantly affect the mobility of the alkaline
plume, and thus the transport of associated radionuclides.
The development of large hyperalkaline plumes and associated alteration and transport are not
expected to occur at Yucca Mountain. The amount of cementitious material expected to be
present in the potential repository (in the form of grout around rock bolts in the emplacement
drifts) is much less than what is observed at Maqarin. The fluid pH of the near-field environment
thus will be buffered by tuff rather than by portiandite, resulting in less alkaline pH conditions
(DOE 2001 [153849], Section 4.2.3.3.3). The Maqarin natural analogue is important to consider
in illustrating the effects of alkaline fluids on water-rock processes, and thus constraining EBS
design parameters (through minimization of the use of cement) and coupled process models. The
ability of the multicomponent reactive transport simulations to reproduce observed water-rock
interactions for the alkaline plumes at Maqarin provides confidence that similar THC modeling
efforts at Yucca Mountain predict reactive chemistry and transport processes that are expected to
occur over time.
7.3.2 Natural Analogues for Colloidal Transport of Radionuclides
Colloids can facilitate radionuclide transport (Figure 7-6) if they are: (1) present in sufficient
quantities, (2) mobile, and (3) can bind radionuclides (Wieland and Spieler 2001 [157442],
p. 511). Naturally occurring colloids are ubiquitous in groundwaters; sampled by Kingston and
Whitbeck (1991 [113930], pp. 26, 57) (mainly from central and southem Nevada) have dilute
colloid concentrations ranging from 0.28-1.35 mg/L), and ferric oxide and oxyhydroxide
colloids can also be generated through degradation of structural steel present in EBS materials.
Filtration of Fe-bearing colloids has been documented in some environments. For instance,
groundwaters in the Pogos de Caldas area, Brazil, typically have low concentrations (<I mg/L)
of colloids (Miekeley et al. 1989 [126083], pp. 838, 840-841; 1991 [127199], pp. 35, 49). Most
of the colloids there are composed of iron and organic species. Only minor amounts of uranium
are associated with colloids, but greater amounts of thorium and rare earth elements are
transported in the colloidal fraction. The results of the colloid studies at Poqos de Caldas
(Miekeley et al. 1989 [126083], p. 841; 1991 [127199], p. 58) suggest that radionuclide and other
trace-element transport by colloids does not play a significant role in the geochemical processes
of weathering, dissolution, and erosion of these ore deposits. One reason for this could be
filtration of material which traps colloids in pore throats and narrow fractures (Smellie et al.
1989 [126636], p. 868). The colloidal mateiial acts as an efficient and largely irreversible sink or
trap for many elements (especially if they are immobile), but needs to be taken into account in
equilibrium thermodynamic modeling of radionuclide speciation. The point of this example is
that the iron'-bearing colloids that may fon-n in the Exploratory Studies Facility could be
beneficial in complexing with uranium and could be retained effectively in the EBS by filtration.
7.4 SUMMARY
The highly corrosive-resistant nature of titanium has been demonstrated by long-term
experiments conducted on a range of metal alloys in wells at the Salton Sea geothennal field.
The commercial use of titanium alloys in production casings over the past decade at the Salton
Sea has greatly alleviated severe corrosion problems that were previously experienced resulting
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Natural Analogue Synthesis
from exposure of conventional steel casing to the hot, hypersaline geothermal biines. This
lb anthropogenic example supports the selection of titanium alloys for the construction of a
corrosion -resistant drip shield for the EBS.
Mineralogic and geochemical analysis of tuffs in the UZ at Yucca Mountain indicates that the
presence of zeolite and clay minerals greatly enhance cation exchange, thus serving to retard the
transport of some radionuclides. While the proposed matelial (devitrified welded tuff) for the
invert ballast in the current design does not have high concentrations of these minerals, the high
surface area of crushed tuff will retard radionuclide transport through absorption. The Los
Alamos example of actinide absorption in a gravel bed provides qualitative evidence of
retardation at the contact between an invert-like material and underlying bedrock.
The presence of cementitious mateiials can potentially lead to the development of alkaline
plumes, resulting in corrosion of waste package materials, alteration of surrounding host rocks,
and possible enhancement of radionuclide transport. Because the use of cementitious material in
the EBS and its environs is restricted to grout for securing rock bolts in the emplacement drifts,
hyperalkaline conditions are not expected to develop at Yucca Mountain. However, through
reactive transport modeling of the Maqarin site, it has been demonstrated that a model can
reproduce the same suite of cement minerals, hyperalkaline water compositions, and pH that
were found in the field, thus building confidence in use of such a model for analogous conditions
at other sites.
The Poqos de Caldas analogue illustrated that iron-beating colloids may retard the transport of
uranium and other spent-fuel components by forming colloids that are then filtrated from
suspension at short distances. Degradation of steel structural elements in the EBS could
conceivably contiibute to this process.
0
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Natural Analogue Synthesis Repon
0
, wi
Soume: Miller et al. 2000 (1566B4], Figure B10.2.
Figure 7-1. Portion of HadriaWs Wall in England. Showing Strength and Stablifty of Roman Mortar after
1.700 Years
0
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Natural Analogue Synthesis Report
0
is
(a) .,,ph -- tw- . ugo lwm anh) coo (wm anh)
Y 25 54 75 .2 0.6 1.4 1 2 3
0~ . . . . I I ~ I I .
100
S
200
.8
300
400
P- P-
nonwmftd
sr W9 W-h) (b) ... zeclims 4wm) Mn?0 (wt% mh) KgO (wr% anh) Ftb (pW9 anh)
1000 zm rophy zs so 74 1 3 5 3 6 7 100 200
T~
r-p-
QTCF

Tq.p.h
apd"
07c,
cwiw
low
b.ddw
ft-
P- ca

iz

100
20
400
PI-P-.
no.-wd
Goo
P- P- I
QTCF
n....Mw
Twwo
CMIC.
mom
NOTE: Shaded bars represent corresponding compositions of unzeolitized precursor tuffs. Symbols (Q = quartz, T
= teidymite, C = cristobalite, F = feldspar) indicate devitdfication minerals in welded tuff intervals. UZ-SZ line
marks location of water table. Chemical abundances are normalized to anhydrous (anh) compositions.
Source: Vaniman et aL 2000 [1574271, Figure 4.
Figure 7-2. Stratigraphic Section of Drill Hole UE-25 UZ#16, with Abundance of Zeolites Plofted versus
(a) Alkaline Earth and (b) Alkali Constituents
Source: Nyhan et al. 1985 [157447], Figure 1.
Figure 7-3. Cross Section of Absorption Bed for Disposal of Radioactive Liquid Wastes, Area T, DP West
Site, Los Alamos National Laboratory
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	Natural Analogue Synthesis Report

		Plutonium ooncentration (Sq/kg)
		100 IODO 10000 100000 IOOODOO 100 1000 10000 100000 1000000
			Absorption bad IL
UN	------
			.........
I
P~' M

obble
		UI)	Cobble				EAyer
			IAYCV
Hole I
				Hole 2
.
.
			.
.......... .. ..........		Ho" 2 Abswption bed 2
			x .............
l
				Ha
e I

				...........
............
		cv-
. ...................

				Minimum		Minimum
				sawtivity
Of		serwtivity
Of
				Aridyds RJ		Anab'sis
	(a)
		Americium concentration (Bq/kg)
		to 100 1000 10000 100000 1000000 io ioo tooo ioooo tooooo ioooooo
			Absorption bed I
.............
				.........
				. .
			Cobble
Cobbie
			EAyer	LAyer
Absorption bed 2
.......
			...
............ ............. z
..............
............
...................
........ ..
				........ . Haie I
			to
Hole 2
		to
			Holc 2
		E

C-i	cv
Minimum	MinimuTn
			Sensitivity
af	Sendtivitv
			-	of
			A..IyU
Analysis
		oj
r)
	(b)
	Source:	Nyhan et al. 1985 [157447], Figures 2 and 3.
	Figure 7-4.	Concentrations of Plutonium (a) and Americium-241 (b) within and beneath Absorption Beds
		1 and 2, Area T, DP West Site, Los Alamos National Laboratory (1978)
0
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Natural Anaiotyue Synthesis Report
Vein IS mm thick
mmw 2 mm
altcmtion zone
calcite -7 1
.'.'BROWN ALTFJMD ZONE GREY-COLOURED MARL
thin.
thaunmtc otaer litnit of brown
bands alteration bands
;ZZ ettringite pmetrates
Wte 1~ wWkock edge
etfti4ite microve ins
highly aftered
mad indusions 0 10 20 30 40 so 6.0 70 so
nun from fracture edge
Source: Steefel and Lichtner 1998 [156714], Figure 6.
Figure 7-5.  Fracture Mineralization and Wall Rock Alteration at C353 Site, Maqarin, Showing the
Presence of Hydrated Calcium Silicate and Sulfate Phases Thaumasite and Eftringite
Porous rock matrix . , Np
op
Radionuclide
N n N
P'racture
CoHoid
l'orous rock matrix 0
NOTE: N = dissolved radionuclides in fracture,
GN = radionuclides on fracture surface,
N,= radionuclides bound to mobile colloids,
ciim = radionuclides sorbed on immobile colloids,
Np = dissolved radionuclides in pores of rock matrix,
ap = radionuclides sorbed on rock matdx.
Source: modified from Jen and Li 2001 [157463), Figure 1.
Figure 7-6. Schematic Illustration of Radionuclide Transport in a Fractured Rock
0
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Natural Analogue Synthesis Report
0 8. NATURAL ANALOGUES FOR SEEPAGE
8.1 INTRODUCTION
This section examines several different types of qualitative and quantitative natural analogues for
seepage, taken from caves, lava tubes, tombs, rock shelters, and buildings that were investigated
since publication of the FY 01 Supplemental Science and Performance Analyses [SSPA], Volume
I : Scientific Bases and Analyses (BSC 2001 [155950]). It considers the role of the
hydrogeologic setting of underground openings on seepage and the effect of relative humidity. It
evaluates a number of candidate settings that have been suggested as analogues and demonstrates
why they are or are not considered appropriate as seepage analogues. It also examines the
question of the preponderance of evidence of preservation of seepage analogues. In this section,
the term infiltration is used for precipitation that is not lost by runoff, evaporation, or
transpiration, and seepage is used for that portion of the infiltration within the unsaturated zone
(UZ) that enters tunnels or other underground openings. For reference, current precipitation at
Yucca Mountain is about 190 mm/yr (DOE 2001 [153849], Section 4.2.1.2.1), with future rates
predicted to be 269 to 529 mm/yr (BSC [155950], Table 3.3.1-5). Infonnation found in Sections
8.2, 8.3, and 8.4 may help to support arguments associated with Key Technical Issue (KTI)
KUZ0407 found in Table 1-1.
8.2 GEOLOGIC EXAMPLES
Seepage is mainly govemed by the capability of individual fractures to hold water by capillary
forces, and by the permeability and connectivity of the fracture network, which enables water to
be diverted around a drift or underground opening. Both properties determine the effectiveness
of the capillary barrier in diverting flow and thus reducing seepage rates below the prevailing
percolation flux. Percolation is the downward or lateral flow of water that becomes net
infiltration in the UZ. The physical properties of water, together with the hydrologic properties of
rock, lead to the prediction that much of the infiltrating water in the UZ will be preferentially
diverted around openings, such as tunnels, at the potential mined geologic repository at Yucca
Mountain. The percentage of infiltration that can become seepage decreases as infiltration
decreases, and at low infiltration rates (<5 mni/yr) and most permeabilities, no seepage occurs
(DOE 2001 [153849], Section 4.2.1.4.2). Two natural analogue studies confirm the prediction
that most infiltration does not become seepage.
In a two-year study at Kartchner Cavems, Axizona, yearly precipitation ranged from 288 mm to
607 mm, and averaged 448 mm/yr (Buecher 1999 [154295], pp. 108-109). This was similar to
the long-term average at two nearby stations. Estimates of seepage into the cave by three
methods based on infiltration and precipitation measurements ranged from 4.3 mm/yr to 12.4
mm/yr, with an average of 7.9 mm/yr (Buecher 1999 [154295], p. 110). Thus, less than 2% of
the available moisture became seepage. This low seepage occurs even though the cave, which
covers an area of approximately 350 m (N-S) by 550 m (E-W), is cut by more than 60 mapped
faults (Jagnow 1999 [154296], p. 49 and Figure 3).
The cave at Altamira, Spain, was monitored for 22 months by Villar et al. (1985 [145806]). The
volume of water flowing from 9 of 14 "significant drips" was measured, and an average total
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Natural Analogue Synthesis Report
seepage of 7 liters/mo was reported. This volume is estimate'd to represent about 80% of the total
seepage (Stuckless 2000 [151957], p. 6), which would biing the total seepage rate up to almost 9
liters/mo. Villar et al. (1985 [145806], Figure 4) also measured the average rainfall. Based on the
data from Villar et al. (1985 [145806], Figure 4) the average annual rainfall was calculated to be
approximately 1152 mm/yr or 1152 liters/yr/m 2 (Simmons 2002 [157544], p. 144). The average
evapotranspiration was calculated as approximately 660 mm/yr (660 liters/yr/m 2), which results
in an average net infiltration of about 480 mm/yr (480 liters/yr/m 2) . The area of the painted cave
2
studied was reported as 150 m , which would result in a monthly volume of infiltration water of
about 6,000 liters/mo above the footprint of the area studied in the cave (Simmons 2002
[157544], pp. 143-144). As was the case at Kartchner Cavems, the rock is obviously fractured
(Figure 8-1). Nonetheless, less than 1% of the infiltrating water seeped into the cave. The fact
that the paintings have not been bleached or dissolved near the fractures suggests that little water
has seeped in along fractures during the last 14,000 yrs, which is the age of the paintings
(Stuckless 2000 [151957], p. 8).
Both of these examples are from limestone caves in fractured karst terrain. It follows from these
examples that UZ flow would be dominated by fracture flow, just as it is at Yucca Mountain.
Both caves are much closer to the surface than a potential repository at Yucca Mountain, and
therefore, there is a much greater probability for fractures to communicate directly betw'een the
underground opening and the surface, thereby facilitating seepage. At the caves, a pulse of water
enters at peak saturation, whereas at the potential repository horizon the amplitude of the water
pulse is attenuated because of the damping effect of the PTn (BSC 2001 [155950], Section
3.3.3.1). This damping effect yields lower average saturations that are less conducive to seepage.
At both Altamira and Kartchner Cavems, precipitation exceeds current rates at Yucca Mountain
and those predicted for future climates as well. Thus, the observational data from these natural
analogues support the conclusion that seepage into a potential repository at Yucca Mountain
would be a very small percentage of the percolation flux, which will therefore result in a very
small volume of water entering drifts.
8.3 ARCHEOLOGICAL EXAMPLES
The long-ten-n quantitative hydrologic studies such as those cited above are not common, but
there is abundant qualitative evidence that openings in the UZ divert much infiltration, thereby
protecting fragile and easily destroyed items. The examples that follow are from both natural and
man-made underground openings and include preservation of both anthropogenic and biological
materials. The examples chosen are representative and are not meant to constitute an exhaustive
listing.
The oldest and perhaps the best known examples of preservation of anthropogenic items within
the UZ are the Paleolithic cave paintings of southwestem Europe. The Paleolithic cultural period
lasted from 750,000 to 15,000 years ago. There are dozens of caves with paintings (Stuckless
2000 [151957], Figure 1); the oldest of those authenticated is the recently discovered cave of
Chauvet, France (Figure 8-2). The cave is located in a subhumid region, with reported
precipitation totals within the region ranging from 580 to 780 mm/yr (Stuckless 2000 [151957],
p. 3). The Chauvet cave paintings depict animals that are now extinct, such as mammoths, and
other species that no longer live in Europe, such as rhinoceroses (Chauvet et al. 1996 [152249]),
0 which attest to a much different paleoclimate from the climate at present. The paintings in the
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French caves were made largely with oxides of iron and other minor constituents (Leroi-Gourhan
Is 1982 [156454] p. 105; Ruspoli 1987 [1562231, pp. 192-193). Charcoal or manganese oxide was
commonly used for black. Neither the iron and manganese oxide nor charcoal would be expected
to survive long in the presence of abundant oxidizing water. This is evidenced by a painted block
that fell from a painting of a bull at Lascaux, France, and lay painted side down on the damp
floor. Although the block fit back into the painting, it had lost all evidence of paint (Breisch 1987
[156456], p. 286).
Well-preserved Paleolithic art is common only in the caves of southem Europe, but examples of
late Paleolithic and, more commonly, Neolithic art from the Neolithic cultural period that began
about 10,000 B.C. are known throughout the world. Stuckless (2000 [151957]) provides a
summary and references for paintings in Africa, South America, North America, and Asia. In
most of the world, painted rock shelters are more common than painted caves, which
demonstrates that even a few meters of overhang can protect fragile art from infiltration water
(Stuckless 2000 [151957], p. 9).
In addition to paintings, caves have preserved fragile artifacts such as the 14,000-year-old clay
bison in a cave near Tuc d'Audoubert, France (Stuckless 2000 [151957], Figure 3). Some caves
are located in zones of such low percolation flux that they have little, if any, measurable seepage
flux. This supports another part of the UZ flow model in which seepage is predicted to decrease
with a decrease in infiltration. Caves in Israel provide an example of this, where cloth, ivory,
reed mats, and many bronze items have been preserved in a nearly perfect state (Schick 1998
[156641], Color Plates 3.7-3.9; Ozment 1999 [155058], pp. 74-75). These date from about 3,800
B.C., and although the climate is currently drier than that at Yucca Mountain, the preservation
40 demonstrates that the lack of water allows even easily destroyed items to endure for long peliods
of time and suggests that the predicted zero seepage at low infiltration rates is likely corTect.
Relatively dry caves are common throughout the southwestem United States. Because of the
dryness, pollen and other delicate plant and animal materials have been preserved for tens of
thousands to hundreds of thousands of years (Davis 1990 [1444611; Rogers et al. 2000 [154320])
in caves and lava tubes, respectively. In fact, Davis (1990 [144461], p. 338) notes that dryness in
caves is ciitical to preservation of biotic remains. That such preservation is common is supported
by the fact that over 1,000 packrat middens have been studied throughout semi-arid to arid North
America, and some of these are older than 40,000 yrs (Davis 1990 [144461], p. 341). The
middens are cemented with diied uiine, which would dissolve readily in water. Nonetheless, the
middens older than about 20,000 yrs (some of these were found near Yucca Mountain) have
survived much wetter past climates, similar to those predicted for the future climate at Yucca
Mountain, indicating that over a long period of time, little seepage has entered the openings
where middens were found.
Underground openings in the UZ have been excavated by early civilizations, but these examples
are generally much younger than those from natural systems. Nevertheless, they also provide
evidence of the robust protection provided against the effects of water. In addition, these
anthropogenic examples broaden the range of geologic settings that can be examined as
analogues for a potential repository at Yucca Mountain.
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Man-made underground openings include the Egyptian tombs across the Nile River from Luxor.
These were excavated in limestone approximately 3,500 to 3,000 years ago. As noted in Section
8.2, this host rock is hydrologically similar in fracturing and low matiix porosity to the welded
tuffs of Yucca Mountain. Although the climate is somewhat drier than that at Yucca Mountain,
precipitation events have been strong enough to cause mud flows within the Valley of the Kings
(Weeks 1998 [154297], pp. 10, 11). Seepage into the tombs is indicated by small areas of
spallation of plaster, which can be seen in many tombs for both areas of wall and ceilings (Figure
8-3), but evidence of dripping, such as efflorescence or stalactitic formations, seems to be
lacking.
Buddhist monks carved several temples into basalt flows at Ajanta, India, between the second
century B.C. and the tenth century A.D. (Behl 1998 [156213], p. 27, 39). Water flow within the
basalts would, as at Yucca Mountain, be dominated by fracture now. The interiors of the temples
are painted. The paintings were done on a plaster that consisted of mud, rock dust, and vegetable
fiber. The climate at Ajanta is monsoonal, such that the precipitation (800 mm/yr), which is more
than four times that at Yucca Mountain (Section 8.1), falls in four months (Stuckless 2000
[151957], p. 19). Nonetheless, many of the paintings are well preserved, except for small areas of
spallation (Figure 8-4).
The Chiistians of Cappadocia, Turkey, excavated underground cities and churches during the
second through eleventh centuiies A.D. The geology here is similar to that of southem Nevada in
that the bedrock is a thick sequence of silicic volcanic rocks. Visits to the underground cities and
churches produced no evidence of dripping from the ceiling, but evidence for flow down a wall
was found where a fracture intersected the wall (Stuckless 2000 [151957], p. 22). As with the
Egyptian tombs and Buddhist temples, some of the church paintings showed evidence of
spallation (Figure 8-5).
The caves at Carlsbad Cavems, New Mexico have stood open for as much as I I m.y. (Polyak et
al. 1998 [156159], p. 1919). During that time, seepage occuffed as evidenced by stalactites,
stalagmites, and flowstone. Today, only a small percentage of the seeps are active in spite of an
average precipitation of approximately 500 mm/yr. This is more than twice the amount cuffently
observed at Yucca Mountain and larger than that predicted for likely future climates. 
In addition to showing that most infiltration does not become seepage, natural analogues
demonstrate that much of the seepage that does occur stays on the walls rather than dripping into
the openings. Figures 8-2 and 8-3 show evidence of water flow down walls. Figure 8-6 shows the
soot-covered wall and ceiling of a kitchen excavated in the tuffs of Goreme (Cappadocia region),
Turkey. The soot deposited along the fracture in the ceiling has been bleached out, presumably
because of infiltrating oxygenated water. Stalagtitic deposits that might indicate dripping water
do not exist, but the removal of soot below the fracture on the wall would have to be caused by
some flow of water down the wall.
Perhaps the best analogue for water that might seep into the tunnels at Yucca Mountain can be
seen at Building 810 in the Denver Federal Center, Colorado (Figure 8-7a). The roof of this
building is constructed of a series of arches called barrels. Each represents a segment of a
cylinder with a diameter of 25 ft, the same diameter as the Exploratory Studies Facility (ESF) at
0 Yucca Mountain. As shown by the white efflorescent salt deposits, water has seeped through the
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Natural Analogue Synthesis Report
roof over the loading dock along fractures in the concrete and then flowed on the underside of
the roof, until it either evaporates or reaches the vertical sections along the sides of the barrels,
wherd it can drip. The undersurface shown in Figure 8-7b is smoother than much of the ESF
tunnel, and thus it may be more effective in diverting seepage to the walls. In contrast, the
roughness of the ESF walls may cause asperities that could focus drips. Nonetheless, it
demonstrates how seepage could be directed in the tunnels.
8.4 EVALUATING THE ANALOGUES
Although there are many examples of Paleolithic and Neolithic art preserved in caves, questions
persist about whether an equal or perhaps even larger number of paintings have been completely
destroyed. Null evidence is difficult to evaluate, but a few lines of evidence suggest that
paintings have not been totally destroyed in caves where they may have once existed.
First, if paintings had been completely destroyedin some caves, or even parts of caves, one
would expect most, if not all, localities to exhibit either a spectrum of preservation from largely
destroyed to fully preserved paintings. Altematively, there should be an explanation for the
binary distribution. A vaiiety in the degrees of preservation of cave art was not found in the
current literature search, either within individual caves or in the body of literature as a whole. A
cave at Palomera in Burgos, Spain, like the cave at Cosquer, has had some paintings removed by
water while others are in good condition. This cave, which has paintings dated at 10,950 +/- 100
to 11,540 +/- 100 B.P. (Corchon et al. 1996 [156636], pp. 41-44), has at times had a stream
flowing in it that has left organic debris plastered to heights of several meters on the walls. The
flooding is younger than the paintings and has apparently destroyed the paintings to the height of
the flooding. Lascaux provides anothet example where one gallery has had over 90% of the
paintings removed by wind abrasion (Breisch 1987 [156456], p. 286).
Second, areas where paintings would be least likely to survive, such as drip sites in the ceiling or
flow channels on the walls of caves, have probably been the loci of flow for thousands of years.
Early man would likely have avoided these areas, because they were too wet to paint. Exceptions
to this hypothesis are known. For example, one painting on the ceiling at Chauvet is partly
covered by stalactitic calcite (Chauvet et al. 1996 [152249], p. 47). Some paintings have thin
coatings of calcite caused by evaporation of thin films of water. Finally, the shear number of painted caves and the number of paintings in some of the caves
argues for. a high degree of preservation. In France and Spain alone, there are more than 1 , 50
painted caves (Ruspoll 1987 [156223], p. 18). Grand (1967 [156218], p. 28) reports over 2,188
paintings of animals in 110 caves.
In the case of rock shelters, some observational data correlate with preservation or destruction. In
sandstone shelters in India, the roots of banyan trees have been noted to provide a preferential
path for water across a painting. The part of the painting exposed to water has been encrusted
with calcium deposits, "while leaving another part of the same figure-untouched by water-
unscathed" (Neumayer 1983 [156221], p. 6).
Not all underground openings provide appropriate analogues. The previous examples of caves
and underground openings were all <100 m from the surface. The, Mission Tunnel through the
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Natural Analogue Synthesis Report
Santa Ynez Mountains near Santa Barbara, Califomia, is closer in depth (200 to 670 m from the
surface) to the potential mined geologic repository (300 m depth), as compared to the previous
examples. The Mission Tunnel exhibits rapid response to precipitation events and large amounts
of see page flux (1.23 million m 3 /yr; Boles 1999 [156635]). Unfortunately, quantitative
measurements have not been made, so the percentage of infiltration that becomes seepage is
unknown. However, the apparently large amounts of seepage into the Mission Tunnel are caused
by flow paths that are within nearly vertical, highly transmissive, fractured sandstone units
(Boles 1999 [156635]). Furthennore, at least some part of the flow could be from grdundwater
seeps below the water table (Boles 1999 [156635]). Thus, the hydrogeology for this potential
analogue is drastically different from that for the potential repository at Yucca Mountain, where
the hydrologic units are gently dipping and few through-going fractures have a hydrologic
connection with the surface.
Mitchell Cavems, located on the eastem slope of the Providence Mountains in the East Mojave
National Preserve, Califomia, may also be a potential location for study of seepage. The cavems
are found at an elevation of 1,341 m (4,400 ft; Pinto 1989 [156638], p. 6) in a wedge of Pennian
limestone (approximately 300 Ma; Norris 1999 [156637], p. 10). The limestone layers are
upended, folded, and highly fractured by intrusion of younger Jurassic quartz monzonite
(approximately 160 Ma; Miller et al. 1991 [156458], Plate 1).
The larger of the caves accessible to the public, Tecopa, exhibits soda straw features, which are
hollow stalactites in early stages of development. Tecopa, however, is a drier cave than the other
publicly accessible cave, El Pakiva, and is said to be aging. Because Tecopa has two entrances, it
is more influenced by the surface environment than El Pakiva cave, which tends to dry out more
quickly after a rainfall. 
Approximately 10 drip locations were observed to begin a few days after
a rainfall. All but one of these are in El Pakiva Cave, which is less than 30 m (100 ft) from ihe
surface (Simmons 2002 [157544], pp. 124-125).
The speleothems are nearly inactive under present climate conditions; there are no continuous
seeps. The caves respond rapidly after a rainfall. Dripping can be observed to last from a variety
of locations up to 28 days after a heavy rainfall (Simmons 2002 [157544], p. 126). Mean annual
precipitation measured at the cavems is 18.6 cm (Stein and Warrick 1979 [156642], p. 12).
Because the fractured limestone in which Mitchell Cavems are situated has rapid communication
with the ground surface along fracture flow paths after a rainfall, and because there is a
considerable bedrock catchment basin above the caves that would enduce seepage, they are not
an ideal analogue to the conditions expected at Yucca Mountain. Instead, Mitchell Cavems may
provide an intermediate analogue between the cave at Altamira, Spain, where very little water
has seeped along fractures, and the Mission Tunnel, Califomia, which experiences heavy flow
along numerous surface-intersecting pathways.
8.5 SUMMARY OF SEEPAGE ANALOGUES
One important variable for preservation in underground openings is relative humidity. It is
obvious that if relative humidity in the drift is kept below 100% by ventilation, then seepage of
liquid water would be reduced or completely suppressed. Most caves are close to but below
100% humidity (e.g., Kartchner RH=99.4 % (Buecher 1999 [154295], p. I 11); Altimira RH=9.8
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Natural Analogue Synthesis Report
+/- 2% (Breisch 1987 [156456], p. 290; Quindos 1987 [156640], p. 555)). These caves are
naturally ventilated; thus, the amount of seepage in these caves would be expected to be low.
This would also be true at Yucca Mountain while ventilation is maintained.
This section has examined several different types of qualitative and quantitative natural
analogues. The findings support the hypothesis that most of the infiltrating water in the UZ is
diverted around underground openings and does not become seepage. The analogues show that
this is true even for areas with much greater precipitation rates than that at Yucca Mountain.
Although examples exist where large amounts of seepage can be observed (e.g., the Mission
Tunnel and Mitchell Cavems), the hydrogeologic setting is significantly different from that at
Yucca Mountain, and thus, these are not appropriate analogues. However, for all of the
analogues that show some seepage, at least some of the seepage that enters underground
openings does not drip, but rather flows down the walls. In the few instances where dripping has
been noted in settings that are analogous to Yucca Mountain, the drips can be attributed to
asperities in the surface of the roof and ceiling of the opening. Whether water flows on walls or
drips depends on conditions affecting drop formation and drop detachment (e.g., surface tension,
roughness angle, saturation). 
Thus, by analogy at Yucca Mountain, although most water would
flow around emplacement drifts, the small amount of seepage that would occur would primarily
flow down tunnel walls. In the few instances where dripping may occur, it would be expected to
be attributable to asperities in the tunnel ceilings.
0
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Natural Analogue Synthesis Repon
1*
40
Soume: Stucklm 2000 (1519571, p. 8.
Figure 8-1. Painted Bison from the Ceiling of the Caw at Attamira, Spain
9
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NOTE: Th.'m Is no apparwt watw damage near ftactums thmugh both ft im oxide and chamoal portiom
of the 14,000-year-old painfing,

 

Nawrai Analogue Synthesis Report
0
0
Figure 8-2. 32,000-.year-old Painted Auroches and Horses from Chauvet Cave
0
TDR-NBS-GS-000027 REV 00 ICN 01 SF-2 April 2002 1
NOTE Although them is evidence of water flow down the wall, in genami, them Is still good presentation.
Source: Chauvat etal. 19961152249], Figure 49 (used vAth pemission of the French Ministry OfAnfiquity).

 

N,lu,ul A,i Synth-, Rcp.,,
0
o Ak
w

OLA,
0,

4
NOTE: Thatom b shows no evidence of ddpping from the ceiling. but plaster on the wall has been damaged
by moisture and some of the paint shows evidence of water running down the wall The tomb was
excavated in limestone about 1,400 B,C,
Source Simmons 2002 [1575441, p, 141.
Figure 8-3. The Painted interior of the Tomb of Sennefer
9
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APT'l 2002 1

 

N,ii.ml Anolhgu, Sy rh~,i, R, p
0
0
NOTE The hexagonal column is flom the second century B.C
Source Bahl 1998 [1562131, p. 42
Figure 8-4, Painting from the Underground Alanta Temple in India Is Fairly Well Preserved in Spite of
Its Age and the Wet Climate
T.1 11.1-Cl-I.1111121 11111111 ICI III i Ap,I 2002

 

Natural Analogue Synthesis Repon
0
NOTE: Th' perfectly preserved painting on the left was painted in the eleventh century A.D. The paintng on the
right shows damage fmm vandals and from spallation of the plaster.
Source: Stuckless 2000 [151957], p, 23.
Figure B-5. Frescoes on the Ceiiing and Walls of the Karanlik Church at Goreme, Turkey, Show
Varying Degrees of Preservation, but No Evideme of Dripping frm the Ceiling
0
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Natural Analogue Synthesis Repon
0
0
NOTE: T e kitchen was ex-ated into ash flow tuft and was pmbably in use until the twelfth century A D.
The s ot has been mmmed adjwent to t'e fracture in the ceiling, ponibly by oxidati.n. Flow has
occurred dcwn the well, as evidenced by removal of some of the soot below the fracture.
Source: Stuckless 2000 (1519571, p. 24.
Figure 8-6. Photograph ald Drawing of a Fracture in the Blackened Wall and Ceiling of a Kitchen in a
0 Subterranean Monastery at Goreme, Turkey
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Natural
iij, A'.
e
NOTE. Water has seeped aiong joints in the concrete, but mther than drippingT it has fl-cl along the
curvature of the roof.
Source: Simmons 2002 [1575441, p 142.
Figure8-7. Photograph ot Building 810 in the De-er Federal Center, Colorado (a), and Close-up of the
Underside of the Roof over the Loading Dmk (b)
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0 9.  ANALOGUES FOR UNSATURATED ZONE FLOW
9.1 INTRODUCTION
The conceptual and numerical modeling methodologies for the unsaturated zone (UZ) at Yucca
Mountain are applicable to other sites, including Apache Leap (Arizona), Box Canyon (Idaho),
Rainier Mesa (Nevada), and other semi-arid sites in fractured rock. These and other examples are
presented in Natural Analogs for the Unsaturated Zone (CRWMS M&O 2000 [141407]) and in
the Yucca Mountain Site Description (CRWMS M&O 2000 [151945], Sec. 13). Analogues for
climate and infiltration processes are presented in the Yucca Mountain Science and Engineering
Report (S&ER) (DOE 2001 [153849], Table 4-5). Analogues for UZ flow and seepage processes
are listed in the S&ER (DOE 2001 [153849], Table 4-6). In general, these analogues contribute
to providing confidence in the understanding of paleoclimatic conditions, the bounds on various
climate models, the efficacy of a UZ in isolating nuclear waste, the occurrence of very limited
seepage in the UZ, and limited fracture-matrix interactions.
Section 9 presents results of a quantitative analogue investigation that had the objective of
utilizing related data sets gathered at the Idaho National Engineering and Environmental
Laboratory (IN-EEL) to test the dual-permeability approach of the Yucca Mountain UZ flow
model at another site in an attempt to match results of field tests, thus building confidence in the
UZ modeling approach. This section also presents a number of possible locations and
configurations for testing the drift shadow zone concept in analogous settings and conditions.
9.2 UZ FLOW MODEL
The UZ flow model is described in Unsaturated Zoiie Flow and Transport Model Process Model
Report (UZ PMR) (CRWMS M&O 2000 [151940]) and in the S&ER (DOE 2001 [153849],
Section 4.2.1). Available site data are used to provide infiltration and percolation flux
distributions and hydrologic properties. The model accounts for the occurrence of perched water
and the effects of the PTn unit and fault zones on flow in the UZ.
Upper bound limits on infiltration rates and percolation fluxes at Yucca Mountain are estimated
based on multiple approaches, including analyses of chloride and chloiine-36 isotopic ratios,
calcite deposition, and the occurrence of perched water. The analysis of chloiide data indicates
that the average percolation rate over the model domain at Yucca Mountain is about 4.6 mm/yr.
Analysis of calcite deposition gives infiltration rates of 2 to 20 mm/yr in the vicinity of borehole
USW WT-24. To match perched water occurrences, three-dimensional model calibrations
require that the present-day infiltration rate be greater than I mnVyr, with an upper limit of about
15 mm/yr (DOE 2001 [153849], Section 4.2.1.3.2). Infiltration and flow pattems at Yucca
Mountain are summarized below.
Rainfall for the modem mean climate is about 190 mm/yr (7.5 in/yr) resulting in average steady-
state net infiltration of 4.6 mnVyr (0.18 in/yr, DOE 2001 [153849], Table 4-11). The net
infiltration is episodic, with a significant amount infiltrating only every few years. There is large
spatial variability of infiltration, with most water infiltrating on ridge-tops and in the upper
reaches of washes where there is little alluvial cover. Fracture flow dominates in the Tiva
Canyon welded hydrogeologic unit (TCw), transmitting water rapidly through the TCw to the
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Natural Ana
underlying Paintbrush tuff nonwelded hydrogeologic unit (PTn). Flow through the PTn is
primaiily matrix flow with most of the fast flow occurring via faults, although this represents
only a very small fraction of the total flow.

Lateral flow occurs in the PTn.
Episodic flow into the Topopah Spting welded hydrogeologic unit (TSw) is damped by the PTn
to the extent that flow can be considered steady-state at the boundary to the TSw. However, at or
near major faults, episodic flow may still persist through the F'Tn. Fracture flow dominates in the
TSw because this unit is densely welded and highly fractured; additionally, within some subunits
of the TSw, the low-penneability matrix is incapable of transmitting the percolation flux
estimated to be moving through the unit. Fracture flow in the potential repository horizon, which
intersects the Topopah Spring middle nonlithophysal, lower lithophysal and lower
nonlithophysal stratigraphic units, is estimated to range from 84 to 94 percent of the total water
flow.
Water drainage in the potential repository unii[s is expected to be good, owing to the generally
high fracture pen-neability (-10-" to 10-10 M2 [10-10 to 10-9 ft2]) (DOE 2001 [153849], Section
4.2.1.2.5). Evidence for fast or preferential flow is seen at the potential repository horizon,
primarily near major faults. It is estimated that the fast component of flow is less than a few
percent of the total flow.
9.3 THE SUBSURFACE DISPOSAL AREA AT THE IDAHO NATIONAL
ENGINEERING AND ENVIRONMENTAL LABORATORY AS AN ANALOGUE
FOR TESTING YUCCA MOUNTAIN MODELING APPROACHES
This section discusses modeling of UZ flow and tracer tests at INEEL. Modeling of UZ transport
at this site is discussed in Section 10. Section 9.3.1 provides infonnation on the geologic and
hydrologic setting of the Radioactive Waste Management Complex (RWMC) at INEEL as
background for a flow modeling study in Section 9.3.2 and a radioactive transport model in
Section 10.3. Further discussion compaiing similaiities and differences between INEEL and
Yucca Mountain is found in Section 10.3.5.
9.3.1 Background
Between 1952 and 1986, approximately 180,000 m 3 of transuranic and low-level radioactive
mixed wastes, containing about 9.5 million curies of radioactivity, were buried in unlined
trenches and pits in shallow sediment above basalt flows at the INEEL in the 144,100 m 2
Subsurface Disposal Area (SDA) of the Radioactive Waste Management Complex (RWMC)
(Cecil et al. 1992 [156256], p. 709). Included with these buried wastes were approximately
334,000 liters of transuranic-contaminated mixed-waste sludges that were absorbed on calcium
silicate and placed in 55-gallon steel drums (Rawson et al. 1991 [156439]). Since 1970,
transuranic wastes have been stored in containers placed above ground on asphalt pads in a part
of the RWMC known as the transuranic disposal area. Subsurface disposal of radioactive waste
at the SDA is planned to continue until at least 2003 (Lockheed Idaho Technologies Company
1995 [156430]). Environmental monitoring beneath the SDA in both the unsaturated and
saturated zones has resulted in positive detections of americium, plutonium, and other waste
products that have migrated from the SDA (Dames and Moore 1992 [157409], pp. 73-74;
Becker et al. 1998 [157407], pp. 4-36 to 4-37), thereby raising concems about the long-tenn
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Natural Analogue Synthesis Report
water quality of the Snake River Plain Aquifer (SRPA), the piincipal source of potable
groundwater in the area. Effort is underway to evaluate the long-term risk posed to the aquifer by
past waste-disposal practices (Magnuson and Sondrup 1998 [156431]; Becker et al. 1998
[1574071) and to determine the necessity of potentially costly remedial strategies, including
exhumation and redisposal of the buried waste.
9.3-1.1 Geologic and Hydrologic Setting
The geologic and hydrologic setting of the RWMC has been described in a series of reports by
the U.S. Geological Survey (USGS) and the U.S. Department of Energy (DOE) and its
contractors (e.g., Rightmire and Lewis 1987 [156440]; [156441]; Magnuson and Sondrup 1998
[156431]). The top of the surficial sediment in which the wastes are buiied is approximately 175
to 180 m above the regional water table. The thick UZ beneath the SDA contains 13 individual
basalt flows ranging in thickness from less than I m to 17 m and averaging about 5 m in
thickness (Knutson et al. 1990 [107839], p. 21).  The individual basalt flows can be subdivided
into four zones, with varying amounts of rubble, vesicles, and fractures, and grouped on the basis
of the presence of three major sedimentary interbeds. Three sedimentary interbeds at 9 m, 34 m,
and 73 m have been used to subdivide the basalts into A-, B-, C-, and D-group basalts;
coffespondingly, the 9 m, 34 m, and 73 m interbeds are altematively known as the A-B, B-C, and
C-D sediment layers (Figure 9.3-1).
Annual precipitation at INEEL ranges from 13 to 36 cm/yr, with an average of 20 cm/yr. About
30 percent of the annual precipitation typically occurs as snow (Barraclough et al. 1976
[156426], p. 45). Chlorine-36, tritium, and neutron-logging data from a series of shallow
boreholes diilled just outside the northem boundary of the SDA provided estimates of
background infiltration rates for undisturbed soils of 0.36 to 1.1 cm/yr (Cecil et al. 1992
[156256], p. 709). Infiltration rates within the SDA have been estimated to be higher than the
background infiltration rates because of the drifting and accumulation of snow within the SDA.
Based on neutron-probe measurements of soil moisture changes for the years 1994 to 1995 and
weather data extending back to 1952, Martian (1995 [156432], pp. 32-36) estimated that the
spatially and temporally variable infiltration rates within the SDA have averaged between 6 and
10 cm/yr since 1952. Only two of the seventeen neutron-probe boreholes were located in the
soils within the trenches; therefore, moisture content changes and infiltration rates through the
trench fill are not as well characterized as the areas between the trenches. In addition, the SDA
has been flooded three times (1962, 1969, and 1982) as a result of the local accumulation of
overland flow associated with rapid snowmelt (Vigil 1988 [157416], p. 1, 8). Estimates have
been made of the amounts of water that infiltrated (Vigil 1988 [157416]) and which areas of the
SDA were flooded (Magnuson and Sondrup 1998 [156431], Figures 2-17). The average depths
of the infiltrated water in the flooded areas in the SDA were estimated by Magnuson and
Sondrup (1998 [156431], Tables 2-3) to be 0.17 m in 1962, 0.12 m in 1969, and 0.08 m in 1982.
Perched water has been encountered by boreholes within the SDA at depths that correspond
roughly to the tops of the sedimentary interbeds (Rightmire and Lewis 1987 [156441], pp. 43-
45, Figure 10). Rightmire and Lewis (1987 [156441], p. 45) proposed a hypothesis that the
source of at least some of the perched water was actually infiltration from spreading areas,
located about 1.7 km to the southwest of the SDA. This infiltration migrated laterally in the UZ
along and across the interbeds. Water is diverted from the Big Lost River into these spreading
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Natural Analogue Synthesis Report
areas during peiiods of high flow (>14 m 3/S) to minimize flooding to downstream areas. Support
for the hypothesis that the deeper perched water beneath the SDA originated from- the spreading
areas seemed to Rightmire and Lewis (1987 [156441], p. 65) to be provided by delta-deuterium
(81)) and delta oxygen-18 (8180) data. The 8D and 8180 values of the deep perched water
indicated little evidence for evaporation compared to shallow perched water or to groundwater
from the regional aquifer, a relation that Rightmire and Lewis (1987 [156441]) considered to be
consistent with their hypothesis that the deep perched water originated from the rapid infiltration
(and minimal evaporation) of large amounts of water through the spreading areas. For a
comparison of the hydrologic settings of INEEL and Yucca Mountain, see Section 10.3.5. 1.
9.3.1.2 Surficial Sediments and Sedimentary Interbeds
The surficial sediments consist of the undisturbed areas between the waste trenches and the
trench backfill, which is a mixture of excavated material. In some cases, the trenches and pits
were oiiginally excavated down to the top of the uppermost basalt layer; however, in these cases
a sediment buffer ranging in thickness from 0.67 to 1.0 m was placed in the trench between the
waste and the underlying basalt (Rawson et al. 1991 [156439]).
9.3.1.2.1 Mineralogy
The predominant minerals in surficial sediments and sedimentary interbeds are quartz,
plagioclase with the composition of labradorite, pyroxene (probably augite), potassium feldspar,
clay, and calcite (Rightmire and Lewis 1987 [156441], p. 11). The percentage of clay is higher
and the percentages of plagioclase, potassium feldspar, and pyroxene are lower in the surficial
sediments compared to the sedimentary interbeds. 

Calcite is often 10% or more by weight of the
surficial material and sedimentary interbeds (Rightmire and Lewis 1987 [156441], p. 26), with
much higher percentages of calcite present locally.
The 9 m interbed (A-B Sediment Layer) contains some organic-lich paleosols, with the organic
material possibly introduced by infiltrating water, as well as a red color (due to the oxidation of
ferrous iron derived from minerals in the nearby basalts). The 34 m interbed (B-C Sediment
Layer) also contains a dark-brown organic-rich soil hoiizon and caliche, amorphous silica, and
Ca-smectite. The 73 m interbed (C-D Sediment Layer) has a red color resulting from iron
oxyhydroxides throughout its entire thickness (Rightmire and Lewis 1987 [156441], pp. 24-28).
A study of the clay mineralogy of the surficial sediment, the sedimentary interbeds, and fill
material of fractures in the basalt indicated that the dominant clay species are illite, followed by
mixed illite/smectite, and finally, kaolinite plus chlorite (Rightmire and Lewis 1987 [156441],
Table 8). The smectite that is present is mainly a calcium smectite (Rightmire and Lewis 1987
[156441], p. 40).
9.3.1.2.2 Geochendcal Properties
Four measurements of the cation exchange capacity (CEC) of the surficial sediments ranged
from 11 to 27 meq/100 g, with an average of 19 meq/100 g (Rightmire and Lewis 1987
[156441], Table 5). There was no apparent correlation between the CEC and the clay content of
the sediments. The CEC of the interbed sediments is highly variable (0.9 to 36 meq/100 g) and
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Natural Analogue Synthesis Report
appears to be related to the percentage of the expandable layer clays present as either pure
smectite or mixed illite/smectite (Rightmire and Lewis 1987 [1564411, pp. 33-34). 
The distribution coefficient (Kd) values of various radionuclides are given for the surficial
sediments, sedimentary interbeds, and basalts in Table 9.3-1 (Dicke 1997 [157410], Table 1).
The Kd values were measured using composite samples from the interbed sediments and crushed
basalts with the fines removed. The reported values for Am, Cs, Co, Hg, Pu, Sr, Tc, and U were
based on site-specific data, with values for other elements estimated from the literature or by
analogy with chemically similar elements (Dicke 1997 [157410], pp. 10-11). In cases where
literature values were used, the data were screened to remove those values obtained using water
compositions very dissimilar to that of water that is present in the UZ beneath the SDA. Data
from the literature were also adjusted to reflect differences in the amount and type of clays
present in the test mateiial and in the surficial and interbed sediments (Dicke 1997 [157410], p.
5). The data indicate higher Kd values for the sediments, possibly because of a greater amount of
reactive minerals, such as smectite, in the sediments. Because the interbed sediments were
combined in a single sample, there is no basis for estimating how the sorptive properties vary
among the interbeds.
9.3.1.2.3 Unsaturated Zone Matric Potentials
A summary of the matric potentials measured beneath the SDA in the surficial sediments and
sedimentary interbeds using tensiometers, heat-dissipation probes, and gypsum blocks was
presented by McElroy and Hubbell (1990 [156433]). In the surficial sediments, the shallowest
measurements ranged between about -0.2 and -1.3 bars, reflecting seasonal wetting and drying
is cycles. The deepest measurements taken from near the sediment/basalt interface were near 0
bars, indicating near-saturated conditions. Hydraulic gradients vaiied over time, ranging between
upward and downward flow within the upper 1.2 to 3.3 m of the sediment profile, depending on
the location of the borehole, but were consistently downward beneath this range of depths.
The equilibrium matric potentials within the 9 m, 34 m, and 73 m interbeds were between -1.4
and -0.3 bars. In general, wetter conditions existed at the tops of the interbeds compared to the
bottoms, and hydraulic gradients across the interbeds were greater than unity.
9.3.1.2.4 Unsaturated Zone Gas Cheniistry
Soil gas samples taken from a 0.3 to 0.76 m depth in the surficial sediment at a site
approximately I I miles from the SDA were reported by Rightmire and Lewis (1987 [156441 ],
Table 12). 

The data from this site may be representative of conditions at the SDA prior to its
development as a waste disposal area. The chemistry of the soil gas samples closely resembled
the chemistry of air, except for C02(g), whose concentration in the soil gas was several times
higher than in the atmosphere. The logarithm of carbon dioxide partial pressure (log PC02) and
the delta carbon-13 value (813C) of the C02(g) were observed to vary seasonally and with depth
in the soil zone. Rightmire and Lewis (1987 [156441], p. 59) concluded that log PC02 values
(expressed as bar) of -2.84 to -3.04, and 813C values of -15.5 to -19.6 per mil were characteristic
of shallow soil zone gas in late spring, summer, and early autumn, and that log PC02 values of
-2.97 to -3.09, and 813C values of -16.4 to -17.2 per mil were characteristic of shallow soil zone
0 gas in early spiing. Snow melt in early spring has been hypothesized to be the principal source of
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Natural Analogue Synthesis Report
recharge at the SDA (Rightmire and Lewis 1987 [156441], p. 59). A comparison of the
geochemical settings of INIEEL and Yucca Mountain is presented in Section 10.3.5.2.
9.3.2 Modeling the Large-Scale Aquifer Pumping and Infiltration Test at INEEL
Regional and local-scale Large-Scale Aquifer Pumping and Infiltration Test (LPIT) models were
developed as a goal of this work to address issues related to the fate and transport of
radionuclides from the RWMC. Modeling activities related to this work were documented in
Simmons (2002 [157578], SN-LBNL-SCI-186-VI, pp. 17-21). A companion study that used
sonie of the'same data sets to investigate radionuclide retardation is presented in Section 10.3. A
location map of the RWMC and SDA sites within INEEL is provided in Figure 9.3-2.
Statistically significant radionuclide concentrations have been measured as deep as 43 m (140 ft)
and possibly deeper (Becker et al. 1998 [157407], pp. 4-23 to 4-39) beneath the SDA in core
samples from a sedimentary interbed. This is thought to be a consequence of the SDA having
been flooded in 1962, 1969, and 1982 (Section 9.3.1.1), when infiltrating water may have
initiated subsurface migration of the plutonium-contaminated waste. The migration pathway is
suspected to be vertically downward through the unsaturated basaltic lava flows and then
laterally on the low permeability (silt, clay) interbeds as ponded-water conditions develop.
Lateral transport of the radionuclides is suspected to have been enhanced by water infiltrating
from the spreading area (Figure 9.3-2), causing ponded-water conditions at a scale significantly
larger than the SDA. The fate and transport of radionuclides at the regional scale involves the
RWMC, the spreading area, and the inferred saturated zone pathway potential that radionuclides
would take from beneath the RWMC to the INEEL boundary (Magnuson and Sondrup 1998
[156431]).
Migration of radionuclides from the RWMC is dependent upon the mechanisms controlling
unsaturated flow of infiltrating water. It is also dependent upon the fate and transport of
radionuclides within the infiltrating water as it flows through the undulating fractured basaltic
lava flows and sedimetary interbeds beneath the SDA. To address these issues, the LPIT was
conducted in the summer of 1994 to mimic the intennittent flood events observed at the SDA.
The test was located approximately 1.43 km south of the RWMC within the same geological
units (Figure 9.3-2). Details conceming the location, design, implementation, and data sets
collected duiing the LPIT are summarized in Dunnivant et al. (1998 [156402]). 

 Magnuson (1995
[156404]) developed a numeiical model to simulate the highly transient water infiltration and
ponding conditions that existed during the LPIT, as well as transport of the conservative
selenium (75 Se) tracer introduced in the infiltrating water. The modeling approach involved
detennining parameters controlling unsaturated and saturated flow and transport in the fractured
basalt and sedimentary interbeds. The model was calibrated to ponded water hydrographs and
75Se breakthrough curves within the ponded water measured during the LPIT.
The goal of the new modeling presented in Section 9.3.2 was to build confidence in the modeling
approach used for UZ process modeling at Yucca Mountain by compaiing simulations to results
of the LPIT. To achieve the goals of this work, both regional and local-scale LPIT models were
developed. These models were based upon the work of Magnuson (1995 [156404]) and
Magnuson and Sondrup (1998 [156431]). The sequence of model development was first to use a
local-scale LPIT model (Figure 9.3-2) to determine a set of hydrological parameters by
simultaneous calibration to multiple hydrographs, while using a dual -permeability representation
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Natural Analogue Synthesis Report
of the basalt fracture and matrix continua. These parameters would represent the large-scale
properties of the lithological units affected by the field-scale LPIT test as used in the dual-
permeability approach rather than local-scale heterogeneities influencing individual hydrographs.
Calibration of the model to the LPIT hydrographs and 75 Se breakthrough curves is important
from the perspective of the work conducted in support of the potential Yucca Mountain
repository. This is because it tests confidence in the dual-permeability approach, which is also
used to represent flow and transport processes that are anticipated to occur in the tuff fracture
and matrix continua at Yucca Mountain. The next step in the sequence of model development
was to use hydrological parameters obtained from the LPIT_ calibration to simulate the fate and
transport of radionuclides from the SDA in the regional model. The dimensions of the regional
model are shown in Figure 9.3-2. Results presented here are limited to the LPIT analysis.
9.3.3 Conceptual and Numerical Model
The LPIT consists of a 183 m diameter infiltration pond that was constructed by removing
surficial soil to build a 1.5 m high earthen benn. The floor of the infiltration pond was highly
uneven, with approximately 80% of the basin floor consisting of a thin layer of soil overlying the
basalt, while the remaining 20% consisted of exposed and elevated basalt. The water depth in the
infiltration pond ranged from 0.3 m to 2 m (Dunnivant et al. 1998 [156402], p. 950). The area
beneath the infiltration pond that was instrumented and influenced by the LPIT test consists of
three separate basalt flows (the A, B, and C basaits) with a laterally continuous dense clay
sedimentary interbed between the B and C basalts. No sedimentary interbed was found between
the A and B basalt flows at the LPIT site.
The three-dimensional model (3-D) made to represent the region influenced by the LPIT used a
radial coordinate approach consisting of 20 spokes evenly spaced at 18 degree intervals. The
centroids of the elements are shown in plan view in Figure 9.3-3a, which shows contours of the
elevation of the top of the B-C interbed. A radial coordinate approach was used because during
the LPIT, the infiltrating water was observed to pond on the B-C interbed. 

 It was expected to
flow radially away from the perimeter of the infiltration pond, with flow controlled by the
topography of the B-C interbed. Lateral flow caused by ponding on the B-C interbed was
detected in wells located on the B, C and E iings (Figure 9.3-3a) at several locations (Burgess
1995 [1564011). The perimeter of the LPIT model was located sufficiently far from the E ring to
remove any influence of boundary conditions. The surface of the B-C interbed is irregular and is
crudely approximated by the plan-view discretization shown in Figure 9.3-3a. Note that this
discretization does not place the centroid of a node at the exact position of a well where a
specific hydrograph was measured and therefore at the exact elevation of the B-C interbed. This
approximation was adopted because of constraints in model size required to achieve reasonable
calibration times.
Figure 9.3-3b shows a vertical E-W cross-sectional cut through the center of the model. This
figure shows the undulating thickness of the A and B basalts and the B-C interbed. The centroids
of the elements are shown in cross section in Figure 9.3-3b, indicating significant mesh
refinement at the interface between the B basalt and B-C interbed. Grid refinement exercises
necessitated 0.02 m thick elements at this interface to obtain a convergent solution to the physics
of water ponding on top of the B-C interbed, while simultaneously imbibing and infiltrating
through it. In total, 28 elements were used to discretize the domain in the vertical direction.
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Natural Analogue Synthesis Report
Figure 9.3-3b also shows the steady-state water saturations in the fracture continuum calculated
using a background infiltration rate of 0.01 m/yr (Cecil et al. 1992 [156256], p. 713). Simulation
results indicate that the silt/clay-like nature of the surficial sediments and B-C interbed retain a
higher water saturation than the basalt fracture continuum.
Unsaturated flow was simulated using iTOUGH2 with the EOS9 module, which solves
Richards' equation, while 75 Se transport was simulated using the EOS7r module. The mesh was
constructed using a dual -permeability representation for the basalt fracture and matrix continua,
while the surficial sediments and B-C interbed were simulated as a single matrix continuum. The
dual-penneability grid is used in an analogous manner to that used in simulating site-scale
unsaturated flow at Yucca Mountain (Barenblatt et al. 1960 [156255]; Pruess and Narasimhan
1985 [101707]; Bandurraga and Bodvarsson 1999 (1039491). Within the context of the dual-
permeability approach, various methods are proposed to reduce the interfacial area between the
fracture and matrix continua, and hence the degree to which they interact. They range in
complexity from a constant scaling factor (Bandurraga and Bodvarsson 1999 [103949]) to the
"active fracture" model of Liu et al. (1998 [105729]). The constant scaling factor approach was
adopted for this study to reduce the interfacial area between the basalt fracture and matrix
continua. 

This simplification was adopted given the transient nature of the LPIT test and because
the "active fracture" model has anly been validated for steady-state flow within the site-scale
Yucca Mountain model.
The background infiltration rate prescribed to all surface nodes inside the infiltration pond is
shown on Figure 9.3-4. The rate was calculated as part of a water management system and water
balance analysis by Starr and Rohe (1995 [156400]). Additional boundary conditions for
is simulating unsaturated flow within the LPIT model include the sides of the model, which were
assigned to be impermeable boundaries, while the bottom of the model is prescribed as a
constant-water-pressure condition. For the LPIT transport model, 2 Ci of 75 Se was added to the
infiltration pond water (approximately 31,650 m 3 ) and allowed to infiltrate into the fractured
basalt from Day 6 to Day 17. The mass fraction of 75 Se in the infiltrating water was nonnalized
to i x io-1, given the linear nature of the advection-dispersion equation describing transport of
the conservative 75 Se tracer and the lower limits on the convergence tolerance of the Newton and
iterative sparse matrix solver schemes (approximately I X 10-6) . This scaling is evident in Figure
9.3-8.
9.3.4 Hydrological Parameter and Perched Water Hydrograph Data
Perched water hydrograph data were collected at 17 locations as presented in Burgess (1995
[1564011). These were collected in wells located primarily on the A, B, and C rings (see labeled
symbols in Figure 9.3-3a) and with the screen located at the B basalt-B-C interbed interface.
Hydrographs were not observed at all locations because of difficulties in completing the wellat
this interface. Of the 17 hydrographs, six were selected for the calibration effort.  Results of
numerical tests indicated that inversion using the full 3-D LPIT model containing all 17
hydrographs was too computationally intensive; therefore, a wedge of nodes on radial spokes of
342'-0'-l8'-36' was extracted to calibrate simultaneously to hydrographs in wells B04NI I,
C04CIl, B06NII, and C06C11. This set of hydrographs was chosen for calibration because it
0 contained two of the three C-ring hydrographs and matched B- and C-ring wells on the same
radial angle. Although well B05011 contained an observed hydrograph and was within this
TDR-NBS-GS-000027 REV 00 ICN 01 9-8 April 2002 1

 

Natural Analogue Synthesis Report
wedge, it was not used during the inversion in order to act as a control to test the predictive
capability of the calibrated parameter set. The hydrograph at well B08NII was also
independently used as part of a separate calibration to yield a parameter set to test for significant
differences between calibrated parameters across the region influenced by the LPIT. The six
hydrographs introduced here will be presented in Section 9.3.6, along with calibration results.
Selenium-75 breakthrough curves within the ponded water were collected at nine locations, as
presented in Burgess (1995 [156401]). Of the nine breakthrough curves, the B04NII and
C04CII data were selected for calibration because they were within the 342'-0'-18'-36'
submodel described above. Furthen-nore, they have matching B and C ring wells on the same
radial angle.
Hydro logical parameters relevant to the fractured basalt and sedimentary interbed stratigraphy at
the LPIT site were identified in a literature survey to constrain the calibration procedure. These
parameters are listed in Table 9.3-2. 

 Because none of the laboratory analysis was done on cores
obtained specifically from the LPIT site, only the mean, maximum, and minimum values were
used to cover the range over which they may be expected to vary for lithological units in the
LPIT area. The relevant parameters include the basalt matrix continuum permeability, kB~m; and
porosity, 4m (Knutson et a]. 1990 [107839], p. 3-93); the B-C interbed matrix continuum
penneability, kBcm; porosity, OB(~~m; residual water saturation, S,,,Bcm; and van Genuchten
capillary pressure parameters aBcm and MBCM (McElroy and Hubbell 1990 [156433]). The
properties of the B-C interbed vary significantly because this unit was observed to vary in
lithology from a fine silt to clay (McElroy and Hubbell 1990 [156433]). Fracture spacing for the
basalt was set to 2.6 m for the entire thickness of the basalt units (Grossenbacher and
0 Faybishenko 1997 [107832]).
All relevant unsaturated flow parameters in the hydrological model are listed in Table 9.3-3.
Flow parameters shown in Table 9.3-3 but not discussed in this section were not measured from
cores taken at INEEL in the fractured basalt-sedimentary interbed stratigraphy, they were
instead based on previous INEEL modeling work conducted by Unger et al. (2000 [1563981).
Selenium-75 transport parameters such as the dispersivity and tortuosity of the basalt and B-C
interbed were not measured as part of prior laboratory or field investigations. Therefore, it is
assumed that 75 Se does not undergo either molecular or hydrodynamic dispersion over the 60-
day time frame.of the LPIT. Hydrodynamic dispersion of the 75 Se breakthrough curves will
occur instead because of imbibition between the basalt fracture and matrix continua.
9.3.5 Hydrograph Calibration Results
Initial manual calibration indicated that the six most sensitive parameters controlling the
calibration of the LPIT model to the hydrographs were the basalt fracture-matrix continua
interfacial area constant-scaling factor ABFm, the basalt fracture continuum pennability kBF, the
basalt matrix continuum permeability kom, the B-C interbed matrix continuum permeability kBcm,
the B-C interbed van Genuchten capillary pressure parameters aBcm and MBCM. The basalt
fracture and matrix continua porosities were not sensitive parameters controlling calibration.
This is because imbibition of the infiltration front from the basalt fracture continuum to the
matrix continuum controlled its downward advection rate rather than the porosity, because of the
0 initial dry conditions present at the site. This is shown on Figure 9.3-5, which depicts the water
saturation in the fracture and matrix continua at 35.5 days. At this point, ponding of water is well
TDR-NBS-GS-000027 REV 00 ICN 01 9-9 April 2002 1

 

Natural Analogue Synthesis
developed on the B-C interbed and significant quantities of water have been imbibed into the
matrix continua within the migration path of the infiltration front.
Parameter estimation dufing calibration was performed by iTOUGH2 using a Levenberg-
Marquardt algotithm. Five parameters were included for estimation: kBF, kBm, kBcm, aBCM and
MBCM. Parameter ABFM was manually adjusted because changes to this parameter required
rebuilding the mesh. Initial manual adjustment indicated that a value of ABFM = 0-01 provided the
best fit to the data when using a Brooks-Corey relative penneability curve, which was also
observed by Unger et al. (2000 [156398], p. 14). A van Genuchten relative permeability curve
was not used in this study because it caused excessive numerical difficulties when simulating
ponding because of its steep gradient at water saturations approaching unity. 

Figure 9.3-6 shows simultaneous calibration results to hydrographs B04N 11, C04C 11, B06N 11,
and C06C I I using the 342'-O'-l 8'-36' submodel extracted from the full 3-D LPIT model. This
model will be referred to hereafter as the "2-D model," while the entire LPIT model will be
referred to as the "3-D model." The symbols in Figure 9.3-6 represent water pressure and
indicate ponded-water elevation within the fracture continuum of the B basalt on top of the B-C
interbed, where reference atmospheric gas-phase pressure is 85 kPa. Calibration was performed
to a subset of the data points shown in Figure 9.3-5 that were chosen to be more evenly spaced in
time to prevent biasing the calibration to regions where the data were collected more frequently.
Calibration parameters were obtained by setting ABFM = 0-01, while the sensitivity of the other
five calibration parameters to ABFM was detennined by doubling it to ABFM = 0.02 and then by
halving it to ABFM = 0.005. Parameters obtained from the JTOUGH2 calibration are provided in
Table 9.3-3.
Comparison of calibrated parameters obtained with ABFM = 0-01 indicates that the estimated
basalt matrix permeability is almost equal to the mean shown in Table 9.3-2, the B-C interbed
pen-neability is just above the minimum observed value, and the B-C interbed van Genuchten
parameters are also near the mean of the values in Table 9.3-2. Although the data in Table 9.3-2
were not obtained from the LPIT site, their close correspondence to the estimated parameters
does build confidence in the ability of the LPIT model to yield a spatially averaged set of
hydrological parameters to fit the hydrographs. Comparison of calibrated parameters for the
three different values of ABFM indicates that the basalt fracture continuum permeability remains
constant at kBF = 3 x 10-10 rw and is insensitive to ABFM over the range tested. The basalt matrix
continuum permeability increases by a factor of 2.51 as ABFM is halved, and decreases by a factor
of 2.51 as ABFm is doubled. This indicates that basalt fracture-matrix imbibition is an impoiiant
process controlling calibration, with ABFm and kBm adjusting themselves proportionately to
maintain the same amount of flow into the matrix continuum. Interpreting the response of the
B-C interbed parameters to variations in ABFM iS considerably more difficult, except that MBCM
reaches (and was constrained during calibration by) the maximum observed value for ABFM -
0.005, thereby reducing confidence in the physical relevance of the calibration values. In general,
given the standard deviation of the estimated parameters, no significant difference exists within
two standard deviations between the three parameter sets listed in Table 9.3-4.
The full 3-D LPIT model was used to detennine the effect of having reduced the mesh size to
the four radial angles of 3420-0'-180-36' to calibrate to the four hydrographs shown in Figure
9.3-6. The greatest deviation occurs for hydrographs B06N11 and C06CI I because the former is
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Natural Analogue Synthesis Report
situated in a local depression, while the latter is situated on a local mound in the elevation of the
B-C interbed, as shown on Figure 9.3-3a. Therefore, plan-view grid refinement is necessary to
obtain increased numerical convergence for parameters listed in Table 9.3-4. The physical
relevance of the converged parameters would still be limited by the sparse distiibution of points
prov iding information on the elevation of the B-C interbed.
The full 3-D LPIT model was also used to determine how well the calibrated parameters
matched the control hydrograph B05011 that was located within the 2-D submodel, as well as
hydrograph B08NI I that was located outside of the 2-D submodel. Figure 9.3-7a shows that the
3-D model successfully modeled the control hydrograph, thus building confidence in the
physical relevance of the estimated parameters. Figure 9.3-7b shows that when the 3-D model is
used to simulate -the B08NI I hydrograph using parameters from Table 9.3-4, the predictive
capacity of the estimated parameters diminishes. B08NI I is the only hydrograph shown because
it exhibited the worst fit of the hydrographs located outside of the 2-D submodel. 

An additional
2-D submodel at a radial angle of 2880 was extracted from the 3-D LPIT model to calibrate to
the B08NI I data. Calibration was performed with ABFM = 0-01 only; the results are shown on
Figure 10.3-7b, with the final calibrated parameters listed in Table 9.3-5. Analysis of the
parameters in Tables 9.3-4 and 9.3-5 indicates that for ABFM = 0.01, the mean estimated values
for kBF and kBm are significantly different at two standard deviations, while values for kBcm, aBcm
and MBcm are not. This implies that at the field scale of the LPIT expeliment there is greater
heterogeneity in the hydrological properties of the basalt than of the B-C interbed.
9.3.6 Selenium (75 Se) Calibration Results
The six parameters identified for the hydrograph calibration were also used to perfonn a joint
calibration on the hydrograph and 75 Se data for wells B04NI I and C04C 11. The objective of this
calibration effort was to determine whether parameters estimated using both flow and transport
data are significantly different than those estimated using flow data alone.
Figure 9.3-8 shows joint hydrograph and 75 Se results for observation wells B04N 11 and C04C I I
using parameters estimated from the flow calibration (see Table 4, ABFM = 0.01). Two numerical
difficulties were identified during calibration that prevented completion of the iTOUGH2
calibration. First, iTOUGH2 with the EOS7r module did not provide a sufficiently robust flow
simulation in comparison with the EOS9 module while simulating water ponding on the B-C
interbed. Repeated failure of the Newton iteration caused an excessive number of timesteps,
ultimately resulting in an accumulation of numerical mass-balance errors within the 75 Se mass
conservation equation. This resulted in nonmonotonic behavior of the 75 Se mass-fraction curves
(as shown on Figure 9.3-8a), making parameter estimation with iTOUGH2 impossible. These
mass-accumulation errors are not evident in the water mass-conservation equation, as shown by
Figure 9.3-8b.
Transport simulation results show that 75 Se mass fractions reached source values of I X 10-3,
which are fifteen times greater than peak values observed in the field for B04N 11. The tail of the
simulated 75 Se breakthrough declines much more rapidly than observed in the field. This
discrepancy does not result from the omission of molecular diffusion between and within the
fracture and matrix continua of the dual-permeability mesh, because upstream-weighting of the
0 advective mass-fraction terms in the discretized mass-balance equations in iTOUGH2 will
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Natural Analogue Synthesis
introduce significantly more numerical dispersion than would be observed by molecular
diffusion alone. Any numerical dispersion would be a product of the coarse grid discretization of
the dual -permeability mesh, as well as the highly advective flow fields simulated during the
infiltration tests. Given that the general shapes of the simulated breakthrough curves are
incorrect, it is suggested that while the dual -permeabi I ity conceptual model can be used to
simulate unsaturated flow, it may not adequately capture the physics of conservative transport in
fractured basalt. Wu et al. (2001 [156399]) suggest that a triple-continuum conceptual model
involving an interconnected matrix continuum, large-scale fracture continuum, and a small-scale
fracture continuum may provide a better representation of transport. In this case, it is assumed
that the small-scale fractures would retain sufficient 75 Se to retard its advection, decrease peak
breakthrough values, and cause significant tailing of the breakthrough curves. Mass transfer of
75 Se from the large-scale fracture continuum into the small-scale fracture continuum would be
primarily driven by molecular diffusion, which depends upon the concentration gradient of 75 Se
(Liu et al. 2000 [154579]). 

 Resolving the concentration gradient would require multiple
interconnected nodes to represent the small-scale fracture continuum over a very fine
(millimeter) scale. Although testing of the triple-continuum conceptual model would only require
rebuilding a new mesh, successful calibration of this conceptual model in iTOUGH2 is
contingent upon a more robust flow simulation and removal of the mass-accumulation errors
seen in the radionuclide conservation equations.
9.3.7 Conclusions of LPIT Analogue Study
The study of UZ flow at the RWMC was chosen because INEEL is somewhat analogous to
Yucca Mountain in hydrogeology. Average precipitation is similar at both sites, although
infiltration is higher at INEEL. Perched water occurs in the UZ at both sites. Rock at both sites
consists of a fractured porous media - basalt at INF-EL and rhyolitic ash-flow tuff ai Yucca
Mountain.  At both sites lateral flow plays a role in diverting flow, whereas the dominant now
paths are along fracture pathways. Fracture-filling minerals consist of clays and calcite at both
sites. Although the two sites differ in significant ways (see Section 10.3.5), their similarities
made it worthwhile to test modeling approaches of UZ flow (and also radionuclide transport in
the UZ, as presented in Section 10) at Yucca Mountain with INEEL data.
Hydrographs of ponded water and 75 Se breakthrough curves measured dufing the LPIT test
conducted at INEEL were analyzed to deterrnine parameters controlling unsaturated flow and
transport. Analysis of this data involved building a numerical model using iTOUGH2. The
numerical model was constructed to conform to the lithological units at the LPIT site, which
consisted of surficial clay-like sediments undeflain by fractured basalt flows (the A, B, and C
basalts) with a clay-like sedimentary interbed (B-C sediment layer) situated between the B and C
basaits. The numerical model involved deterinining parameters controlling unsaturated and
saturated flow and transport in fractured basalt, using a dual-permeability modeling approach
that has been extensively employed to simulate flow and transport at Yucca Mountain.
Six parameters were identified to be most sensitive in controlling the calibration of the LPIFF
model to the observed hydrographs. These included the basalt fracture-matrix interfacial area,
the basalt fracture and matrix continua perrneabilities, the B-C interbed penneability, and van
Genuchten capillary pressure a and m values. Simultaneous calibration to hydrographs B04NI 1,
C04CII, B06N11, and C06CII using iTOUGH2 yielded parameters that were consistent with
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Natural Analogue Synthesis Report
the range in values seen in data obtained from cores drilled near the LPIT site. Joint calibration
to hydrograph and 75 Se data in wells B04NII and C04CII was unsuccessful because of
numerical difficulties. Preliminary results indicated that while the dual -permeabi I ity conceptual
model can be used to simulate unsaturated flow, it does not adequately simulate conservative
transport in fractured basalt. This is because the matrix continuum needs to be significantly
refined relative to the dual -permeability approach to resolve molecular diffusion caused by the
concentration gradient between the fracture and matrix continua. This conclusion is especially
significant to the site-scale Yucca Mountain model, in which, the dual -pen-neabi I i ty approach is
used extensively to simulate both unsaturated flow and transport in fractured tuff. The dual-
permeability approach provides conservative estimates of peak concentrations and arrival times
by underpredicting the mass transfer of conservative (i.e., nonsorbing) tracers from the fracture
to the matrix continua. 

Parameters estimated by the calibration are inherently spatially averaged over the region sampled
by the downward-advecting infiltration front and laterally migrating ponded water. This region
starts from directly beneath the infiltration pond and covers the radial area of the four
hydrographs. These parameters were able to predict the control hydrograph that was located
within the spatially averaged region, but were unable to predict hydrograph B08NII, located
outside of this region. Independent calibration to hydrograph B08NII indicated that the basalt
properties showed significantly greater vaiiability than the B-C interbed properties. This implies
that the field-scale heterogeneity limits the volume to which the spatially averaged basalt
parameters can be assigned relative to the B-C interbed parameters. This may in part result from
the fractured-porous dual-continuum nature of the basalt in comparison to the porous single-
0 continuum nature of the B-C interbed.
9.4 DRIFT SHADOW ANALOGUES
The phenomenon of flow diversion around a cavity was investigated for a general homogeneous
porous medium by Philip et al. (1989 [105743]). The key feature of this phenomenon with
respect to the transport of dissolved or colloidal mateiial from the drift is that flow velocities in a
zone beneath the drift are slower than unaffected flow velocities away from the drift (Figure 9.4-
1). In particular, the flow velocity at the base of the drift is exactly zero. According to this
conceptual model, the zone beneath the drift was also found to have lower water saturation than
the undisturbed zone. This region of reduced flow velocity and water saturation beneath the drift
is known as the drift shadow.
For a quasi-linear representation of the hydrogeologic properties, Philip et al. (1989 [105743], p.
18) found that the extent of the drift shadow is a function of a characteristic sorptive length scale
and the drift radius. The shape of the drift shadow is govemed by the ratio of the dlift radius to
the sorptive length scale. The ratio of the drift radius to the sorptive length scale is a measure of
the relative importance of gravitational forces compared with the capillary forces that define
flow pattems around the drift.
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9.4.1 Caves
The drift shadow phenomenon cannot be accurately tested in the underground facility at Yucca
Mountain because the natural system has been greatly perturbed by the heavy use of construction
water for dust control and by the large volumes of air exhausted every day. Furthermore, the
underground facility probably has not yet come to equilibrium with the undisturbed host rock.
Complicating matters is the fact that detection of a drift shadow zone has never been documented
for either natural or anthropogenic openings--conceivably ancient underground tombs and
features could lie above a dfift shadow zone. However, naturally occurring caves provide an
opportunity to test for a drift shadow zone beneath an opening in the UZ. Limestone caves are
hydrologically similar to the welded tuffs at Yucca Mountain because, in both cases, flow occurs
primarily along fractures. 

Furthermore, caves have had sufficient time to establish hydrologic
equilibrium. The Carlsbad, New Mexico, region is ideally suited for such a study because the
large number of caves in the region allows for selection of a cave that closely matches the
physical characteristics of a potential mined geologic repository. Caves that are known to receive
direct surficial runoff should be eliminated from consideration. The cave chosen for study should
be as large as or larger than proposed repository emplacement drift cross sections, currently
approximately 5 m in diameter. The roof of the cave should be below the zone of surface
influence, currently estimated as 6 m. Ideally, the cave should be readily accessible to light
drilling equipment and should be sited so as to accommodate a small meteorological data station.
The small cave approximately 800 m southeast of Boyd's Waterhole and northwest of Carlsbad,
New Mexico (on the Azotea Peak 71/2-minute topographic quadrangle map) appears to meet the
necessary criteria.
The site should be amenable to standard tracer or infiltration tests. The infiltration tests would
push the system out of hydrologic equilibrium by applying enough water to the surface above the
cave to establish dripping into the cave. The tracers would be dyes or biodegradable tracers that
would be used in an attempt to define flow paths.
9.4.2 Tunnels or Mine
Conceivably, an environmental tracer analysis could be used to demonstrate the presence of a
drift shadow. An old mine in an and region would be an ideal location, especially if its history
dated back 100 years or so. Another possibility would be an old railroad tunnel or other tunnel,
such as the Never-Sweat Tunnel (for ore haulage) at Apache Leap, Aiizona, and the nearby
mine. Chlorine-36 could be used as one possible example of an environmental tracer with a pulse
input occurring -50 years ago. If the mine drift is older than 50 years, it is possible that cores
collected at present adjacent to the drift would contain the bomb-pulse signal, while cores
collected below the drift would not. In a nearby, much younger drift, it would be expected that
there would be essentially no difference in 36CI signal above and below the drift. Chlorine-36 is
not the only possible tracer that could be used; the ideal tracer would be without background
from the rock, such as an artificial environmental tracer.
9.5 CONCLUSIONS
Hydrographs of ponded water and 75Se breakthrough curves measured during the LPIT test
conducted at INEEL were analyzed to determine parameters controlling unsaturated now and
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Natural Analogue Synthesis Report
transport. Analysis of this data involved building a numerical model using iTOUGH2 in a dual-
permeability modeling approach, an approach that has been extensively used to simulate flow
and transport at Yucca Mountain.
Six parameters were identified to be most sensitive in controlling the calibration of the LPIT
model of unsaturated flow in fractured basalt. These included the basalt fracture-matrix
interfacial area, the basalt fracture and matrix continua permeabilities, the B-C interbed
pen-neability, and van Genuchten capillary pressure aand m values. Simultaneous calibration to
hydrographs using iTOUGH2 yielded parameters that were consistent with the range in values
seen in data obtained from cores drilled near the LPIT site. 

Preliminary results indicated that
while the dual-perineability conceptual model can be used to simulate unsaturated flow, it may
not adequately capture the physics of conservative transport in fractured basalt. This conclusion
is relevant to the site-scale Yucca Mountain model, in which the dual-permeability approach is
used extensively to simulate both unsaturated flow and transport in fractured tuff.
Parameters estimated by the calibration are inherently spatially averaged over the region sampled
by the downward-advecting infiltration front and laterally migrating ponded water. The region
starts from directly beneath the infiltration pond and covers the radial area of the four
hydrographs. The basalt properties showed significantly greater variability than the B-C interbed
properties. This implies that the field-scale heterogeneity limits the volume to which the spatially
averaged basalt parameters can be attributed relative to the B-C interbed parameters. This may in
part be due to the fractured-porous dual-continuum nature of the basalt in comparison to the
porous single-continuum nature of the B-C interbed.
Finally, natural caves and man-made openings such as mines and tunnels may be suitable
locations for testing the drift shadow concept, particularly if those sites have existed long enough
to establish hydrologic equilibrium.
9
TDR-NBS-GS-000027 REV 00 ICN 01 9-15 April 2002 1

 

NaTural Arial,gue Syrith-s Repmt
F SLrflcial Sonimert
Clay Layer
A B=ff
A-3 Sediment Loyef
8 Basoft
B-C SedimenT Lcryer
C Bmalt
C D Sediment LcM
D Bcsolt
Source: Simmons 2002 [157578]r SN-I-SNL-SCl-l0&V2, p, 8
Figure 9.3 1. Schematic Stratigraphic Sequence illustrating the Relationsh[p between Basalt Flows and
Sediment Layers
0
Ele flon
iZ
i~141
11- .1- r1u.
E-Ing (m)
Source Simmons 2002 1157578], SN-LBNL-SCI-186-Vl p, 58
Figure 9.3-2, Plan View of Regional Model with Contours of the Ground Surface Eievation
FDR-NBS-C.S-(")027 REV 00 ICN 01 9F- I April 2002

 

Natural Analog= Synthesis R"
0
, Zl-
-5
(a) E-*v (.)
medn-
seems
claaaft-
Radlus I.)
(b)
NOTE: In (a) ' ft wtrolds of the alemnts m indimted a black dots md the
wall. b~ md dots
Sou": Simmms 20021157578), SN-LBNL-SCI-IMVI, p. 59
Figure 9.3-3. (a) Top of B-C lnterbed Elevabon wfth Centrolds of Elements In Plan View As Well As the
Location of All Hydrographs Used in this Analysis. (b) East-West Cross-Secfional View
Showing the Steady-State Water Saturation in the Fracture Continuum
TDR-NBS-GS-OD0027 REV 00 ICN 01 9F-2 April 2002

 

Natural Analogue Synthesis Report
0
0
0.14
0.13---
0.12
0.11
0. 1
0.09
E
,-, 0.08
0.07
0.06
0
0.05
0.04
0.03
z
0.02
0. 0 1
0 F- I I I I I I I I I I I I I I I I I I I I I I I I
0 10 20 30 40 50 60
Time (days)
Source: Simmons 2002 [157578], SN-LBNL-SCI-186-Vl, p. 60.
Figure 9.3-4. Infiltration Rate Observed by Starr and Rohe (1995 [156400]) during the LPIT Using a
Water Balance Analysis
TDR-NBS-GS-000027 REV 00 ICN 01 9F-3
April 2002 1

 

N,i,-I SIr,,h,,,, Roi
dirnts, M
A b-It r 7
.2
C b ... H
1
J~l
Radius (m)
(a)
s
-dioxi
rll
11
rll
A .i
A?
lur
Cb ... It
Radius (m)
(b)
Source. Simmons 2002 [1575781, SN-LBNL-SCI-186-VI, p. 61
Figure 9 3-5 Water Saturation in the (a) Fracture and (b) Matrix Continua at 35.5 Days after the Start
of the LPIT
T.1 NIII-11 1)(111027 IFI (11) 111111 9F-4 April 2002

 

Natuml Analogue Synthesis Repon
0
0
(b)
0004 B04N11 Cil
[ C04-
92
87M
(c)
		U
		J
%

		.

on ID"		P I
j,
	870w	-
0.02 ID
a
so,
aaow
~
o.o2 2.
woo B06N11
aw. -
C06C1 1
j,
87000
a6cGO j i "
o lo x m v
Time (days) Time (days)
NOTE: Symbols represent field data vvith mfewce atmospheric gn phase pressure equal to 135 kPa.
Lin" represent mlibmtion maults using the 2-D submodel and the full 3-D LPIT model With
varying AAFm values (0.01, 0.005, 0.02).
Source: Simmons 2002 fl 575781, SN-LBNL-SCI-186-VI, p. 62. 

Figure 9.3-6. Ponded Water Hydrographs in Wells B04NI 1.  C04C1 1, B06NI 1 and C06CI I
TDR-NBS-GS-000027 REV 00 ICN 01 9F-5
April 2002 1

 

0
N,t,,,,,l Aral,,gue S~ -the- Rep-
(a)
(b)
B08N1 1
Time (days) Time (days)
NOTE Symbols represent hydograph data h,le lines repmsent model results.
Souce Simmons 2002 1157578]r SN-LBNL SCI-186-Vl, p. 63.
Figure 9.3-7. (a) Predictive Model Results for Control Hydrograph B05011 and (b) Calibration Model
Results for Hydrograph B08N1 1
(b)
to
.-I C04CI 1
f- -611
-CD4 I
KI.
-se
-'s
2,
i... - B0501 1
p
-0,0
Time (days) Time (days)
S-rc. S-m.m, 2002 [1575781, SN-LBNL-SCI-1 86-Vl, p, 63,
Figure 9,3-8. Jcint (a) "Se Breakthrough and (b) Hydrograph Calibralion Results for Welis BOW 1
and C04C1 1
IlIlI-lI.S-.I-.0()21 REV d0 lIN 1), 9F-6 April 2002

 

Natural AnuioSue Synthcsim Repon
0
0
No SeepagO
$.u-: DOE 2001 [153949], Figure 4-116.
0
Figure 9.4-1. Schematic Diagram of Diffusion Barriers in Invert and Drift Shadow Zone
TDR-NBS-GS-000027 REV 00 ICN 01 917~7 April 2002 1

 

Natural Analogue Synthesis Report
0
0
Table 9.3-1. Distribution Coefficient (Kd) Values for Sorption of Contaminants on INEEL Sediments
	Kd Values (mL/g) and Range
Element	Surficial Sediments	lnterbeds	Basalt
Am	No data	450 (450 to 1, 100)	70 (70 to 280)
Co	No data	1, 148 (1,148 to 3,912)	11 (111 to 54)
Cs*	950 (589 to 1,253)
(75 to 225)	2,228 (2,228 to 3,255)	39 (39 to 44)
Pu	7,800 (7,800 to 22,000)	5,100 (5,100 to 7,900)	70 (70 to 130)
Sr*	24 (23 to 26)
(8.3 to 16.6)
50 (35 to 52)	42 (42 to 63)
155 (110 to 186)	6 (6 to 13)
(1.1 to 2.7)
Tc	0	0	0
u	No data	3.4 (3.4 to 9)	0.2 (0.2 to 5.2)
Hg	972 (236 to 1,912)	176 (72 to 673)	(9.2 to 87)
NOTE: *Different Kd values for Cs and Sr are from different authors cited by Dicke (1997 [157410], Table 1).
Source: Dicke 1997 [157410], Table 1.
Table 9.3-2. Basalt and B-C Interbed Parameters Collected by Laboratory Analysis of Core Samples
Property	Samples	Mean	Maximum	Minimum
kE~M [M2]
43
'2.24.1 0-l'	0-14
9.48xl	16
lxlo-
OBM 1-1	50	"19.2	43.2	5.2
kscm Im 2	15	t4.21 X10-14	6.86x10-12	1.15x10-17
OBM 1-1	15	'0.530	0.629	0.424
S.rBcm [A	15	'0.183	0.376	0.038
aBcm [Pa-']	15	'7.95xlO-'	5.025xlO -4	1.938xlO-'
MBcm H	15	'0.4	0.86	0.23
tgeometric mean
*arithmetic mean
Source: Simmons 2002 [157578], SN-LBNL-SCI-1 86-Vl, p. 55.
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Natural Analogue Synthesis Report
9
0
Table 9.3-3. Basalt and B-C Interbed Parameters Used in the LPIT Model

Parameter	Value
	basalt fracture	basalt matrix	B-C interbed
k. = ky = k~ [M)	From calibration	From calibration	From calibration
0 H	0.01	19.2	0.53
S-, H	0.01	0.1	0.183
a [Pa-1]	5-1 0-3	5xlO-'	From calibration
m H 1	0.5 1	0.25	From calibration
Source: Simmons 2002 [157578], SN-LBNL-SCI-186-Vl, p. 55.
Table 9.3-4. Parameters Estimated during Calibration to Hydrographs B04NI 1, C04C1 1, BOW 1 and
C06C1 1
Param	ABFM = 0-01	ABFM 0.005	ABFM = 0.02
.	Mean	std. dev.	Mean	std. dev.	Mean	Std. dev.
IkBF	3.27.10-"	0.0701	3.13-1 0-l'	0.0553	3.44.10-'0	0.0759
tkBm	2.51.10-15	0.395	6.31 X10-15	0.197	lxlo-15	0.381
tkBCM	5.01xlO-17	1.51	6.31xlO-17	0.538	1.26xlO-"	0.848
t aBCM	X,0-4	1.23	4.07xlO-'	0.465	X,0-4	0.852
MBCM	0.28	0.341	0.86	0.718	0.67	1.08
tmean permeability values are in [m 2 ] while standard deviation is in [loglo M2]
tmean aBcm values are in [Pa-1] while standard deviation is in [logio Pa-1]
Source: Simmons 2002 [157578], SN-LBNL-SCI-186-Vl, p. 56.
Table 9.3-5. Parameters Estimated during Calibration to Hydrograph B08N1 1
Parameter	Mean	std. dev.
kBF	7.05x10-10 [M)	0.0553 [loglOM2]
kBM	7.94xlO-14 [M2]	0.162 [loglOM2]
kBcm	2.51xlO-16 [M)	0.342 [log, o M)
CCBCM	6.31 x 10-5 [Pa'l	0.690 [logio Pa-I
MBCM	0.48	0.527
Source: Simmons 2002 [157578], SN-LBNL-SCI-186-Vl, p. 56.
0
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Natural Analogue Synthesis Report
10. 

ANALOGUES TO UNSATURATED ZONE TRANSPORT
10.1 INTRODUCTION
This section presents updates on two recent studies examining transport of radionuclides in
unsaturated zone (UZ) conditions. The first is a study of migration of radionuclides at the Idaho
National Engineering and Environmental Laboratory (INEEL) with the objective of explaining
mechanisms responsible for detection of concentrations of neptunium and uranium in monitoring
wells below the water table. The second study presents results of analyses and modeling of
uranium systematics at Pefia Blanca, Mexico, based on water sampling campaigns in 2000 and
2001. Additional insights derived from natural analogues in Steenkampskraal, South Africa, and
Koongarra, Australia, on the significance of colloid transport in the UZ are also presented.
Previous studies have indicated that fractures act as both transport pathways and places of
retardation at a number of the analogue sites. This was shown in Yucca Mountain Site
Description (CRWMS M&O 2000 [151945], Section 13) through analogues from Pefia Blanca,
Mexico; Akrotiri, Greece; and volcanic tuff-hosted uranium deposits in northem Nevada. At
Nopal I (Peiia Blanca), uranium has been transported relatively small distances, essentially
completely along fractures, and has been sorbed or precipitated onto fracture-coating Fe-oxides
and calcites. Colloidal transport of uranium was shown to be minimal at another analogue site in
Koongarra, Australia, where filtration of colloids appears to be effective. The YMP total system
perfonnance assessment (TSPA) assumes no colloid filtration, an assumption that may be
unnecessarily conservative. Data available for the Yucca Mountain Site Description also
indicated that the geochemical system at Nopat I restricted actinide mobility in the UZ and that
by analogy the tuffs at Yucca Mountain should have similar retentive properties and impede the
mobility of oxidized uranium. Additionally, clays found in fractures and vitrophyres at Yucca
Mountain may also be effective in retarding migration of radionuclides. This conclusion can be
drawn from examination of the clay haloes (5-30 cm thick) surrounding ore deposits at Oklo,
Gabon, and Cigar Lake, Canada, which have been shown to be effective in retarding the
migration of uranium away from the source (CRWMS M&O 2000 [151945], Section 13.5).
Radionuclide migration experiments under unsaturated conditions have also been completed in a
30 cm block of Calico Hills nonwelded tuff from the Busted Butte test facility near Yucca
Mountain. This type of study could be thought of as a self-analogue to migration in the Calico
Hills nonwelded unit under Yucca Mountain. Elution profiles showed that relative to an ideal
conservative tracer (tritiated water), transport of Tc04- was approximately 15% faster, but that
Np02+ was retarded by a factor of 3 (Vandergraaf et al. 2001 [155042]). These findings fall
within the range of retardation coefficients determined from tuff column expenments (Triay et
al. 1996 [101024], Appendix A). Retardation of 22 Na , 60Co, and 137CS was higher than for
neptunium in the Calico Hills block experiments, and this agreed qualitatively with
experimentally determined batch sorption coefficients for these isotopes (BSC 2001 [155950], p.
11 -46). The analogues discussed in this section focus primarily on processes occurring at INEEL
and Pefia Blanca as potential analogues for radionuclide transport in the UZ at Yucca Mountain.
Information found in Sections 10.3, 10.4, and 10.5 may help to support arguments associated
with Key Technical Issue (KTI) KUZ0407 listed in Table 1-1.
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10.2 TRANSPORT IN THE UZ AT YUCCA MOUNTAIN
The evaluation of possible radionuclide transport from the potential repository to the
groundwater in the saturated zone (SZ) is key to assessing the performance of the potential
repository. 

In the event of such waste mobilization and migration away from the potential
emplacement drifts at Yucca Mountain, the rate of radionuclide transport through the UZ is
determined by the percolation flux and by the hydrologic properties and sorptive properties of
the tuff units. Water carrying radionuclides may percolate vertically through fractured tuff units,
or it may be laterally diverted around low-permeability horizons (particularly where perched
water occurs) to fault zones. Diffusion, sorption, and dispersion processes would retard the
movement of radionuclides. Each of these processes potentially affects the distribution and
concentration of radionuclide particles at the water table.
The transport of aqueous and colloidal radionuclide species can occur in both fracture and matrix
continua, with exchange between continua (fracture-matiix interaction) resulting from advective
and/or diffusive processes, as well as sorption in the matrix. The flow pathways are determined
by the characteristics of hydrogeologic units, faults, and perched water.
These characteristics control the extent of downward versus lateral flow, fracture-matrix
interaction, and the partitioning of flow between fractures and the rock matrix. Fractures and
faults can be fast flow paths, with diffusion into the matrix and sorption to the rock being the
important processes for radionuclide retardation.
The concentration of radionuclides and their daughter products are diminished according to their
radioactive decay rates, the extent of sorption onto the solid phase, and dilution as a result of
mixing and dispersion. The effects of advective flow processes, sorption of solutes or filtration of
colloids, matrix diffusion, hydrodynamic dispersion, and radioactive decay are important factors
that play varying roles of significance in slowing the movement of radionuclides through the UZ.
10.3 INEEL AS A POTENTIAL ANALOGUE FOR RADIONUCLIDE TRANSPORT AT
YUCCA MOUNTAIN
10.3.1 Background
Section 10.3 presents a preliminary hydrologic and geochemical transport model for americium
(Arn), cesium (Cs), neptunium (Np), plutonium (Pu), strontium (Sr), and uranium (U) in the UZ
beneath the Subsurface Disposal Area (SDA) of the RWMC at R'MEL. The geologic,
hydrologic, and geochemical bases for the model were summarized in Section 9.3. Section 10.3
uses these bases to develop a conceptual model of flow and transport beneath the SDA. A series
of numeiical models have been developed that test various aspects of the conceptual model. The
computer codes FLOTRAN and FEEM were used to develop models for flow and radionuclide
movement in the surficial sediments in and beneath the waste pits. Measurements of radionuclide
concentrations made duiing the drilling of shallow monitoring holes in and near the waste
trenches (Humphrey and Tingey 1978 [157491]; Rightmire and Lewis 1988 [156442]) provide a
basis for evaluating the model. Flow and radionuclide transport in the UZ beneath the SDA is
simulated, and the results are compared to available field data.
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Natural Analogue Synthesis Report
10.3.2 Column Experiments
10.3.2.1 Description of Experiment
Column experiments and associated batch tests to measure values of the equilibiium disttibution
coefficients (Kd) and the reaction-rate coefficients for the sorption of americium-241 ( 241 Am),
cesium-137 (137CS), cobalt-60 (60CO), strontium-90 (90Sr), uranium-233 (233U), and plutonium-
239 (239pU) were carried out at Clemson University and INEEL (Newman 1996 [156434)). The
experiments included columns of crushed basalt (> 0.25 mm size fraction), mixed interbed
sediments (< 0.25 mm size fraction), and intact basalt cores taken from the same boulder that
provided the crushed basalt. In the first phase of the experiments, the steady, saturated flow of
synthetic water with a composition (Table 10.3-1, Section 10.3.5.2) similar to groundwater at
INEEL was established in the columns. A spiked solution containing tritiUM (3 H) and one or
more of the radionuclides of interest was input with the synthetic water for a duration equivalent
to about one pore volume and then was flushed with about 200 pore volumes of the unspiked
synthetic water. 

The breakthrough curves of tiitiUM (3 H) were fit with the advection-dispersion
equation, as implemented in the computer code CXTFIT (Parker and van Genuchten 1984
[126526]), to demonstrate the absence of preferential flow during the expefiments and estimate
dispersion coefficients for the material in the columns (Newman 1996 [156434], Appendix E).
CXTFIT also was used to fit the advection-dispersion equation to the breakthrough curves for
each of the radionuclides. These fits provided estimates for the retardation coefficient R,:
R, =(I+ PbKd (Eq. 10-1)
0
where pb is bulk density (g/cm 3 ) and 0 is porosity. The Kd values for each combination of
radionuclide and column material were then calculated from fitted R values. CXTFIT also
includes a variation of the equilibrium advection-dispersion model known as the two-site/two-
region model that accounts either for (1) the presence of both equilibrium and nonequilibrium
sorption sites or (2) the presence of mobile and immobile water. The advection-dispersion model
and the two-site/two-region model were fitted to the radionuclide breakthrough curves, as
appropriate, to estimate R and parameters that account for the transfer of radionuclides between
the mobile and immobile water.
10.3.2.2 Results of Experiments
Results for the columns containing crushed basalt (Newman 1996 [156434], Table 6, Appendix
F) showed that most of the radionuclide mass (except for 233U) was substantially retarded
compared to the water. Recovery of the input radionuclide mass was less than 100% for 60co
(-69%), "Sr (-50%) , 23lpU (-33%), and 23 'Am (-10%), indicating that the unrecovered fraction
had a retardation factor greater than 200 (Newman 1996 [156434], p. 28).  Two-site/two-region
models fit to the breakthrough curves of 90Sr, 131CS , and 233U generally resulted in better fits to
the data than the equilibiium advection-dispersion model; recovery was insufficient to appV the
two-site/two-region model to the remaining radionuclides. A fraction of the "Co (-3%), ' 'Am
(9 to 13%), and 23lpU (10 to 55%) in the column studies exhibited early breakthrough compared
with most of the mass of these radionuclides. Fits of the equilibrium advection-dispersion
TDR-NBS-GS-000027 REV 00 ICN 01 10-3 April 2002 1

 

Natural Analogue Synthesis Report
equation to the breakthrough curves for this so-called enhanced mobility fraction resulted in
retardation factors of between 1.5 and 2 (Newman 1996 [1564341, Table 6). Possible
explanations for the existence of the enhanced mobility fraction included (1) the sorption and
transport of these radionuclides on colloids such as Si02, (2) the formation of neutral or
negatively charged complexes involving these radionuclides and carbonate, and (3) kinetically
limited sorption. Related experiments demonstrated that the enhanced mobility fraction Of 239pU
increased with total alkalinity and the mobile fraction of 24'Arn increased with flow rate
(Newman 1996 [156434], Figures 15 and 16). However, no definite conclusions regarding the
specific causes for the enhanced -mobility fraction were made. Batch studies done to evaluate the
equilibration time between various radionuclides and crushed basalt showed that the
equilibration time for 60CO was not longer than radionuclides lacking an enhanced mobility
fraction (such as 90Sr and 137CS) (Newman et al. 1996 [156434], Table 8). The data from the
batch tests for 24'Arn indicated equilibrium behavior, and data for 239pU were not reported.
Results from column studies of the interbed material (Newman 1996 [156434], Table 7,
Appendix F) indicated much higher sorption of all radionuclides in the interbed material
compared to the crushed basalt. The percent recovery for 233U was over 90% but less than 4% for
all other radionuclides. Although their retardation factors must be over 200, which is the number
of eluted pore volumes following introduction of the spiked solution, exact retardation factors
could not be calculated for radionuclides other than 233U. In spite of the large retardation of most
of the mass, a small (< 1%), highly mobile fraction of 60CO, 2"Am, and 239pU was observed to
break through within the first five displaced pore volumes (Newman 1996 [156434], Section
3.1.2, Figures 11, F- 10 to F- 13, and F- 17 to F- 19).
Other experiments conducted as part of the Clemson University and INEEL studies demonstrated
that:
(1) 10 to 90% of the water in the intact basalt cores may be immobile, based on the fit of
the two-site/two-region model to breakthrough curves of bromide (Newman 1996
[156434), Table 14);
(2) Kd values for 90Sr estimated from column studies of crushed basalt were similar under
saturated and unsaturated conditions (Newman 1996 [156434], pp. 68-69); and
(3) Kd values for 237CS, 60CO, 90Sr, and 233 U estimated from batch experiments and column
experiments were generally similar, suggesting the applicability of Kd values
measured from batch tests to field conditions with much different sediment/water
ratios (Newman 1996 [156434], p. 62, Table 13).
10.3.3 Distribution of Radionuclides beneath the Surficial Sediments at the SDA
Several radionuclides, including 238 Pu, 239'24lpU, 21'Arn , 60CO, 131CS, and 90Sr, have been found
sorbed to rocks and interbed sediments beneath the surficial sediments at the SDA. 

 The locations
where radionuclide activities were at least three times greater than the detection limits are noted
on maps showing the locations of all deep wells in Figure 10.3-1. These maps are based on a
recent data compilation by the USGS (2000 [157415], Tables 3-10a, b, and c), which itself is
based on earlier work by Dames and Moore (1992 [157409]). Each map shows the radionuclides
TDR-NBS-GS-000027 REV 00 ICN 01 10-4 April 2002 1

 

Natural Analogue Synthesis Report
present in different depth intervals, each of which contains either the 9 m, 34 m, or 73 m interbed
(see Section 9.3.1.1). Note that not all of the wells shown in Figure 10.3-1 have been sampled, so
that well locations with no indicated radionuclides are a mixture of true nondetections and
unsampled wells.
The maps in Figure 10.3-1 locally have some lateral and vertical consistency with regard to
radionuclide distributions. For instance, closely spaced wells DO-2, 79-2, and TW-1 contain
238 Pu, 239,24OpU, and 24'Arn at multiple depth intervals. Similarly, well 93 containS 24 'Am and 90Sr
at two different depth intervals (Figures 10.3-2a and 10.3-2b). Elsewhere, however, different
radionuclides are present at different depths in a given borehole or different radionuclides are
present at the same depths in nearby boreholes, making simple interpretations of these
radionuclide distributions difficult. The erratic distribution of these radionuclides may be related
to complex flow and transport behavior, including preferential and lateral flow, or to cross
contamination during dtilling (USGS 2000 [157415]).
Because a complete list of sample locations is not available, it is not known whether the absence
of radionuclide detections in Figure 10.3-1 reflects the true absence of radionuclides or simply
the absence of samples from those locations. Therefore, although it can be stated confidently that
radionuclides are present in the deep subsurface of the SDA, the exact distribution of these
radionuclides is uncertain. Qualitatively, however, it is possible to anticipate some of the factors
that would be expected to influence the distribution of sorbed radionuclide activities in the
subsurface, even if these factors are poorly characterized at present. These factors are (1) the
distribution and strength of contaminant sources within the SDA; (2) the distribution of
infiltration within the SDA; (3) heterogeneity in fracture properties within the basalt layers; (4)
40 the sorptive properties of the rocks and sediments themselves; (5) the thicknesses of the surficial
sediment and sedimentary interbeds; and (6) the orientations of rock/sediment interfaces.
The distribution and strength of the radionuclide sources within the SDA are the subjects of
ongoing study at INEEL, and it is likely to be an important control on the observed radionuclide
distribution, based on models of nonradiological contaminants at the SDA (Magnuson and
Sondrup 1998 [156431]). The models indicated that the observed distribution of these
nonradiological contaminants was at least as sensitive to uncertainty in source-term strength as to
uncertainty in hydrologic parameters, and a similar sensitivity to source strength could
reasonably be expected for the radioactive contaminants as well.
Temporally averaged infiltration rates have been estimated within the SDA (Magnuson and
Sondrup 1998 [156431]), based on a study by Martian (1995 [156432]) that used neutron probe
moisture logs from 17 boreholes within the SDA and historic data on the nature of the spring
thaw to calibrate surficial sediment properties and estimate time-varying drainage from the
surficial sediments into the underlying basalts over a 42 yr period. Although there is uncertainty
associated with these estimates, the analyses that generated the estimates were as complete as
can be expected, and it is unlikely that future analyses will be able to reduce this uncertainty.
Heterogeneities within individual basalt flows are known to exist (Knutson et al. 1990 [107839))
and indicate that the brecciated upper and lower margins may be the most porous and permeable
parts of the basalt flows. This conceptual model has suggested to some (Rightmire and Lewis
1987,[156441]) that the basalt penneability is highly anisotropic, with higher permeability in the
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Natural Analogue Synthesis Report
subhorizontal direction. Beyond this general conceptual model, however, very little is known
about the details of the permeability disttibution in the basalts beneath the SDA. 

It is unlikely
that the permeability variations resulting from fractures in the basalts would ever be known in
sufficient detail to be able to explain the contaminant distribution, if indeed these permeability
variations are the controlling factor.
The thickness of the surficial sediments and the sedimentary interbeds is a possible control on
the distribution of radionuclides, because flow through the sediments is through the porous
matrix rather than the fractures and the sediments have a much higher porosity and water content
than the basalts. Therefore, assuming that flow is primarily vertical, effective porosity between
the land surface and any depth largely depends on the thickness of the sediments within that
depth interval. Radionuclide migration is expected to be most rapid where the surficial sediments
and sedimentary interbeds are thin or absent.
If contrasts in the hydrologic properties of rocks and sediments beneath the SDA cause water to
flow laterally along the interfaces between these layers, the orientation of these interfaces may
indicate the areas toward which water and contaminants are moving. Lateral flow is possible
both when the vertical flux greatly exceeds the vertical hydraulic conductivity of the least
permeable layers, and at lower fluxes, when capillary baniers delay or prevent the entry of water
moving through fine-grained layers into underlying coarse-grained layers (Montazer and Wilson
1984 [100161]). As discussed below, contour maps of these interfaces exist and can be used to
infer flow directions if lateral flow along these interfaces were to occur.
Of all the factors cited above that are likely to influence radionuclide transport at the SDA,
is perhaps the best known are the thickness and orientations of the major hydrostratigraphic units.
Contour maps of the thickness of the sedimentary units and the orientations of the upper surfaces
of each hydrostratigraphic layer, including the basalt groups, were created using SURFER
(V. 7.0) and data from Magnuson and Sondrup (1998 [156431], Table 2-1) as shown in Figures
10.3-2 to 10.3-11. Unfortunately, the possible relation between the radionuclide distributions
shown in Figure 10.3-1 and the layer thicknesses and orientations shown in Figures 10.3-2 to
10.3-11 have been difficult to identify because of uncertainty in the actual extent of the
contamination and in other factors likely to influence transport.
10.3.4 Perched Water
The distribution of perched water within the SDA was examined to deten-nine if it could provide
some indication of flow paths and evidence for the possible stratigraphic and topographic
controls on its occurrence. Perched water has been observed at many locations within the SDA
along the surficial sediment/basalt interface, where seasonal water levels have been monitored in
several wells and boreholes (Hubbell 1993 [157412], p. 2-6; 1995 [1574131, p. 2). Hydrographs
of this shallow perched water showed strong seasonal effects, with the highest perched water
levels occurring after the spring snow melt. Perched water at the surficial sediment/basalt
interface has been found in topographically low areas (MS-03, MS-04, pit 9 wells 1, 2, 3, and 6,
and possibly W-06 and NAT-06; see Hubbell 1993 [157412), Figure 1; 1995 [157413], Figure I
for well locations), but higher elevation areas were not monitored, so the role of topography is
unclear. Perched water at the surficial-sedimentlbasalt interface has also been found in
structurally low areas at the surficial sediment/basalt contact (Acid pit well 4 and NAT-16).
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However, most of SDA is in a structurally low area along surficial sediment[basait contact
(Figure 10.3-4), so the SDA as a whole may be receiving subsurface lateral flow from the
adjacent areas.
Deep perched water has been found consistently in a number of wells within the SDA (Hubbell
1993 [1574121; 1995 [157413]). The wells that contain perched water, the average depth to the
top of the perched water, and the perched water elevations are shown in Figure 10.3-12. Wells in
which perched water is found at or above the B-C interbed are listed in blue, whereas wells with
deeper perched water are listed in red. A comparison of perched water locations shown in Figure
10.3-12 with the contour maps shown in Figures 10.3-2 to 10.3-11 indicates the following: (1)
wells D-10, 92, 93-02D, and 8802D are in topographically low areas (Figure 10.3-2); (2) wells
92, 93-02D, and 78-1 are at structurally low areas in the surface of the uppermost (A) basalt
(Figure 10.3-4); (3) wells with perched water at the B-C interbed (77-2 and 78-1) are at locations
where the A-B interbed is absent (Figure 10.3-5); (4) only well 93-02D is at a structurally low
point in the top of the B-C interbed (Figure 10.3-8); and (5) only well 93-02D is at a structurally
low point in the top of the C-D interbed. 

 These observations, summarized in Figure 10.3-12,
suggest that the topography, the orientation of the surficial sedimentlbasait interface, and,
possibly, the absence of the A-B interbed may deterinine where perched water is found at the
SDA.
10.3.5 On the Use of INEEL as a Potential Analogue for Radionuclide Transport at
Yucca Mountain
The following sections discuss the similarities and differences between various facets of the
hydrogeology and geochemistry at Yucca Mountain and the SDA of INEEL. The motivation for
this compaiison is to evaluate the potential use of the SDA as an analogue for radionuclide
migration from a potential repository at Yucca Mountain through the UZ at some time in the
distant future.
10.3.5.1 Comparison of Hydrogeologic Settings
There are several similarities in the general hydrogeologic settings that recommend the use of the
SDA as an analogue for Yucca Mountain. First, both sites are presently relatively arid. Average
annual precipitation is approximately 200 mm/yr at INEEL (Rawson et al. 1991 [156439),
p. 478) and 190 mm/yr at Yucca Mountain (DOE 2001 [153849], Table 4.11).  The relatively low
precipitation rates and high evaporative demand result in estimated net infiltration rates of
approximately 10 mm/yr for undisturbed soils near the SDA (Cecil et al. 1992 [156256], p. 711),
whereas steady-state deep infiltration rates at Yucca Mountain are estimated to be between I and
12 mm/yr (Flint et al. 2002 [157411 ]), averaging 4.6 mnVyr (DOE 2001 [153 849], Table 4.11),
depending on the local topographic setting.
The second similarity exists in the hydrostratigraphic settings of the sites and their anticipated
effect on water movement through fractures. In the UZ at INEEL, fractured basalts altemate with
relatively thin, unconsolidated sedimentary layers (Rightmire and Lewis 1987 [156441]). At
Yucca Mountain, relatively unfractured, nonwelded tuffs altemate with fractured, welded tuffs
(Scott et al. 1983 [101156]). At both sites, water is expected to move from fractures into the
40 porous matrix and back into fractures as it percolates downward through the fractured layers,
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into the unconsolidated sedimentary material or nonwelded tuffs, and back into fractured layers
(Montazer and Wilson 1984 [100161]; USGS 2000 [1574151). The details of water movement
across the boundaries between these layers may have implications for the formation of perched
water, lateral flow, fingering through the porous material, and flow focusing in fractures
underlying the porous layers.
The third similarity is the presence of perched water at both sites, some of which may have
migrated laterally beneath the present or proposed waste-disposal areas from adjacent areas.
Perched water beneath the SDA may have resulted from the diversion of water from the Big Lost
River during periods of high flow into spreading areas located I to 2 km southwest of the SDA
(Rightmire and Lewis 1987 [156441], pp. 40-41, 60-65). At Yucca Mountain, perched water
beneath the northem part of the proposed repository area may have originated, in part, from
water that had infiltrated in the northem part of Yucca Mountain and moved southward along
low-permeability layers at depth (Wu et a]. 1999 [117167], pp. 163, 176). At both sites, an
understanding of the source and cause of the perched water is important for what it may imply
about the magnitude of recharge at the disposal areas and for predicting the pathways that waste
may take to the SZ.
Finally, both sites have potential flow-focusing mechanisms. According to one possible
conceptual model (USGS 2000 [157415], pp. 2.8-2.10), perched water flowing laterally above or
through the sedimentary interbeds at the SDA may be funneled into areas where the interbeds are
absent, resulting in the accelerated movement of water and waste compared to areas where the
interbeds are present. Additionally, there is the potential for water in the interbeds to flow toward
low points along the irregular lower contacts between the sedimentary interbeds and underlying
basaits, thereby focusing flow into the basalts in these areas. At Yucca Mountain, lateral flow
along stratigraphic contacts may divert water laterally until it is redirected downward by faults or
by other discontinuities in the interface between the diverting layers (Montazer and Wilson 1984
[100161], pp. 47-52). Additionally, fault zones mapped at the surface narrow with depth through
the PTn (Day et al. 1998 [101557], Plate 2), a factor that could tend to focus water flow through
the PTn. In the deep subsurface at Yucca Mountain, most recharge may reach the water table
along faults or by moving laterally along perched layers (Flint et al. 2002 [157411]). 

 Both
potential recharge mechanisms at Yucca Mountain would tend to concentrate flow and mix water
that has flowed through different areas.
Certain dissimilarities that exist between the hydrogeologic settings at the SDA and Yucca
Mountain must be taken into account when radionuclide migration in the UZ at the SDA is used
as an analogue for how radionuclides could migrate in the UZ at Yucca Mountain. First, in spite
of the similarity in precipitation rates and long-term recharge rates of the sites, recharge rates at
the SDA site have increased considerably since the SDA was constructed. The drifting of snow
within the SDA and its melting during subsequent spring thaws are estimated to cause a net
infiltration at the SDA of between 60 and 100 mnVyr, with an estimated long-term spatial
average of 85 mm/yr (Martian 1995 [156432], pp. 31-36). Additionally, the SDA has been
flooded three times because of the collection of surface runoff in the topographically low areas
fon-ned, in part, by the compaction of backfill in the waste pits and trenches. The three flood
events of 1962, 1969, and 1982 are estimated to have resulted in the infiltration of 365 mm of
water, or the equivalent of about 36 yr of natural infiltration, over the site (Magnuson and
Sondrup 1998 [15643 1 ], Table 2-3). Thus, a great deal more water has actually been available to
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mobilize waste at the SDA than is estimated to be available at Yucca Mountain under present
climate conditions or at the SDA under undisturbed conditions.
A second dissimilarity between the two sites is in the fracture pattems in the basalts at the SDA
and the welded tuffs at Yucca Mountain. At the SDA, fracture densities are greatest along the
brecciated margins and least in the dense interiors of the individual basalt flows (Knutson et al.
1990 [107839], p. 119; Rightmire and Lewis 1987 [156441], p. 41), suggesting that horizontal
penneability may be much larger than the vertical permeability in the basalts. Anisotropy of this
type in the basaits, like the presence of the sedimentary interbeds, would enhance lateral flow in
the UZ. At Yucca Mountain, the generally steep dips of fractures in the Topopah Spring Tuff are
likely to favor a high vertical to horizontal permeability ratio in that unit, a hypothesis supported
by air-injection and pneumatic pressure-wave analysis (Rousseau et al. 1999 [1020971, p. 76).
High vertical to horizontal anisotropy in the Topopah Spring Tuff would tend to promote more
vertical drainage than might be expected at INEEL. However, beneath the densely welded part of
the Topopah Spring Tuff, welding changes and stratified mineral alteration zones also effectively
create a high horizontal -to-vertical permeability ratio in the deeper units, so conditions at Yucca
Mountain become more similar to those at the INEEL site at depth.
A third distinction between the hydrogeologic settings at Yucca Mountain and INEEL is that
fractures in the basalts are often filled with sediments, including authigenic calcite and clay, and
detrital clay, silt, and sand that probably washed into the fractures when individual flows were
exposed at the land surface (Rightmire and Lewis 1987 [156441], pp. 22-24). Besides providing
additional surface area for radionuclide sorption within fractures, the presence of sediment in the
fractures at INEEL reduces the likelihood of sheet or film flow within the fractures. Sheet and
film flow could be inferred to take place in some fractures at Yucca Mountain, based on the
observation that mineral coatings have been deposited preferentially on the footwall of dipping
fractures (Paces et al. 1998 [107408], p. 37)
10.3.5.2 Comparison of Geochemical Settings
This section compares the overall geochemical settings of Yucca Mountain and the SDA at
INIEEL, including mineralogy and water and gas compositions.
The rocks beneath the SDA are tholeiitic and alkali olivine basalts. The dominant minerals in the
basalts are olivine (F050 to Fogo), plagiociase (average An65), clinopyroxene, minor magnetite,
and illmenite (Rightmire and Lewis 1987 [156441], p. 10). The interbedded sedimentary material
was deposited by rivers and streams draining the surrounding mountains, as well as in lakes that
fonned when lava flows dammed these streams (Rightmire and Lewis 1987 [156441], p. 11).
Eolian deposits are also present. 

 Mineralogically, the interbedded sedimentary material consists
of quartz, plagioclase, potassium feldspar, clinopyroxene, olivine, chlorite, clays (illite,
illite/smectite, and kaolinite, in order of abundance), and amorphous silica. Calcite-rich and iron-
oxide coated horizons exist in the interbeds (Rightmire and Lewis 1987 [156441], pp. 11, 20-
24). As mentioned previously, fractures are often filled with sediment and have deposits of
calcareous clay.
In terms of their bulk composition, the rocks at Yucca Mountain are classified as rhyolitic and
quartz-latitic tuffs. The vitric nonwelded tuffs are composed of sodium- and potassium-rich glass
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(Broxton et al. 1987 [102004], Table 3; Vaniman et al. 1996 [105946], Table 1-7). The interiors
of thick welded tuffs have devitrified to quartz and feldspar. Phenocrysts include plagiociase
(Anjo to An30), potassium feldspar, biotite [Mg/(Mg+Fe) = 35 to 70%] (Vaniman et al. 1996
[105946], Figure 1.22), and quartz, with trace amounts of homblende, pyroxene, and magnetite.
Major alteration products include smectite, zeolites, silica, and calcite in the rock matrix
(Vaniman et al. 1996 [105946], Section 4), and opal, calcite, smectite, zeolites, manganese
oxide, and hematite deposited along fracture walls (Vaniman et al. 1996 [105946], Section 5.5).
One factor likely to influence the transport of actinides at the SDA, and potentially at Yucca
Mountain, is the dissolved inorganic carbon (DIC) concentration of the groundwater. The DIC of
the groundwater is a function of the carbon dioxide partial pressure of the gas in the recharge
environment and of the extent to which calcite or other carbon-bearing minerals have been
dissolved along the flow path. The DIC of groundwater affects the migration of radionuclides
because of the tendency for U, Pu, and other actinides to form aqueous complexes with
carbonate (C032-) ions (Langmuir 1997 [1000511, pp. 495-530). The formation of neutral or
negatively charged aqueous complexes reduces the proportion of the actinides that ate present in
solution (as positively charged ions that tend to sorb to the rock as a result of ion exchange or
surface complexation reactions), thus enhancing the mobility of the radionuclide in groundwater
(Langmuir 1997 [10005 1 ], pp. 537-538).
Calcite is present in the soils and along fractures in the UZ at Yucca Mountain (Paces et al. 1998
[107408]), and in the surficial sediments, sedimentary interbeds, and fractures in the basalts at
INEEL (Rightmire and Lewis 1987 [156441], pp. 21, 31, 33). The natural background carbon
dioxide partial pressures of gases in the UZ at Yucca Mountain (Yang et al. 1996 [100194),
Figure 18) and at INEEL (Rightmire and Lewis 1987 [15644 1 ], p. 55) are similar (109 PC02 (bar)
= -3.0), and the natural background oxygen partial pressures at the two sites are approximately at
atmospheric levels (109 P02 (bar) = -0.7). However, the decomposition of buried organic wastes at
the SDA may have caused local, and presumably temporary, increases in the carbon dioxide
partial pressure, as indicated by calculated 109 PC02 for soil water that are much greater than -3.0
(see below). The same processes may have locally reduced log P02 at the SDA, but no
measurements are presently available. In summary, although the background compositions of
gases in the UZ at INEEL and Yucca Mountain are similar, the oxidation of buried organic
matter at the SDA may have caused local unsaturated zone gas compositions to be substantially
different than the gas compositions that exist at Yucca Mountain today.
The chemistry of selected unsaturated zone pore and perched water, and regional groundwater
from Yucca Mountain and the SDA, is given in Table 10.3-1. The data for these wells show that
the groundwater from the SDA has higher concentrations of most major species except for
dissolved silica. Speciation calculations show that the water samples from Yucca Mountain are at
or slightly below saturation with calcite and have values Of 109 PC02 (bar) between -3.17 (UZ-14
CHn) and -2.41 (WT-3); water samples from the SDA are all slightly supersaturated with calcite
and have values Of 109 PC02 (bar) between -3.03 (well 92) and -2.52 (W02). 

At Yucca Mountain, clays, zeolites, and iron- and manganese-oxide coatings that exist in rock
pores and fracture walls could sorb radionuclides and slow their migration (Vaniman et al. 1996
[105946), Section 4). Clays and iron-oxide coatings are ubiquitous in the surficial sediments,
sedimentary interbeds, and sediment-filled fractures in the basalts at RSTEEL (Rightmire and
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Lewis 1987 [156441]). At both Yucca Mountain and INEEL, the dominant clays are smectites
(Vaniman et al. 1996 [105946], Section 5.5.6) or mixed illite/smectite (Rightmire and Lewis
1987 [156441], Table 5); generally, the cation exchange capacity of the clays increases with the
percentage of expandable smectitic clay layers. In terms of sorbing substrates, zeolites are more
prevalent at Yucca Mountain (Bish and Chipera 1989 [101195]), and iron oxides more prevalent
at INIEEL, because of the presence of abundant iron in the basalts.
There appears to be more organic matter at the SDA than at Yucca Mountain. In addition to the
organic matter mixed with the radioactive waste (Rawson et al. 1991 [156439], p. 478;
Magnuson and Sondrup 1998 [156431], p. 4-48), the sedimentary interbeds at the SDA contain
organic-iich paleosols (Rightmire and Lewis 1987 [156441], p. 27). Organic matter has the
potential to facilitate the movement of radionuclides by forming anionic organic complexes with
little tendency to sorb on rock surfaces (Langmuir 1997 [10005 11, pp. 523-524).
10.3.5.3 Other Challenges and Benerits of Using INEEL as an Analogue for Radionuclide
Transport
Several challenges exist if the SDA is used as an analogue for radionuclide transport. The first
challenge is that the source terms for various radionuclides are uncertain. The source tenn
reflects the mass of the radionuclide buried in the SDA, its solubility in the existing
hydrochemical environment, and its rate of release from any encapsulating medium.  Recent
attempts to model the observed movement of nonradioactive contaminants beneath the SDA
have shown that model results are as sensitive to the assumptions about the poorly known source
teryns as they are to the expected uncertainty in subsurface transport parameters (Magnuson and
Sondrup 1998 [156431], p. 6-2).
The second challenge that the SDA poses as an analogue site is that there has been a lack of
consensus on the significance of low-level concentrations of radionuclides in pore and perched
water and groundwater beneath the SDA. Many suspected detections of radionuclides have been
either near the detection limit, found to be less than the detection limit when resampled, were
irreproducible in samples that were split and analyzed by different laboratofies, or deemed
unlikely to be true detections because of the absence of other radionuclides that should have been
present along with the "detected" radionuclide (USGS 2000 [157415], Chapter 4). Even when
there has been agreement that the radionuclide is present at statistically nonzero concentrations
in the subsurface, there have been questions as to whether or not the contamination was brought
into the deeper subsurface during drilling. In summary, there is no well-defined distribution or
plume of radionuclides in the deep subsurface that can be used to calibrate geochemical transport
models of radionuclides at the field scale.
A third challenge for the potential use of the SDA as an analogue site is that it is
hydrogeologically complex. As discussed above, flow through the basaits may depend on local
fracture pattems or on details of the configuration of the basalt/interbed interface that may never
be known in detail sufficient to make detenninistic predictions with confidence. Also, there is
uncertainty in the UZ percolation flux because of past flooding events at the SDA and possible
lateral migration of water in the deep UZ from nearby water-spreading areas (Magnuson and
Sondrup 1998 [15643 1 ), pp. 6-3, 6-4). Predictions of radionuclide transport are therefore subject
0 not only to uncertainty in geochemical processes and parameters but also to a great deal of
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complexity in hydrologic processes. Ideally, a site chosen as an analogue for geochemical
processes at Yucca Mountain would exist in a very simple, well-understood hydrologic
environment, so that the geochemical processes and parameters could be clearly identified. I
In spite of these limitations as an analogue site, the SDA has produced a great deal of site data,
and many analyses have been done of both the hydrologic and geochemical environment at the
site. 

Moreover, INEEL as an institution is highly motivated to collect additional data and
perform additional analyses, so that some of the uncertainty discussed in the preceding sections
will undoubtedly be reduced at some time in the future. The SDA does not serve as a typical
analogue in the sense that it can provide clear, unambiguous, and widely accepted explanations
for radionuclide migration that indicate the expected behavior of radionuclides at Yucca
Mountain. However, examination of the SDA site by the Yucca Mountain Site Characterization
Project (YMP) is useful in that it provides additional opportunities to test models similar to those
that have been or will be developed for Yucca Mountain. To better understand which lessons the
scientific community (including regulatory agencies and oversight groups) have learned from the
SDA is truly relevant to the YMP.
10.3.6 The SDA Modeling Study
The overall purpose of the models developed as part of this study is twofold. First, it is important
for INEEL to understand the processes that resulted in the apparent migration of radionuclides to
the deep UZ. Only then can they determine if the causes for mobilization and transport of
radionuclides continue to exist, or if recent improvements at the site have eliminated the
conditions that led to the earlier mobilization of the waste. In particular, if the radionuclides
present in the deep subsurface could have been transported there only because of past flooding
(and the potential for future flooding has been eliminated by ben-n construction, drains, or other
mechanisms), then the likelihood for continued or renewed mobilization of radionuclides at the
SDA may be small. Conversely, if radionuclide migration has resulted from flow-focusing
processes that are caused by permanent geologic features of the site, or from geochemical
conditions that are likely to persist for a long time, the continued or renewed transport of
radionuclides becomes more likely.
For the YMP, it is important to understand if the processes that resulted in the apparent migration
of radionuclides at the SDA are present or will be present at Yucca Mountain in the future. If
radionuclide transport at the SDA has been facilitated by flooding events or geochemical
conditions at the SDA (such as the co-burial of radionuclides and chelate-forrning organic
chemicals) that are unlikely to exist at Yucca Mountain, then radionuclide migration at the SDA
becomes no more than a cautionary waming to "do no hann" to Yucca Mountain by
inadvertently altering its natural hydrologic or geochemical state. Altematively, if radionuclide
migration at the SDA is the result of hydrologic or geochemical processes that are or will be
common to both sites, numeiical transport models of the SDA may have substantial transfer
value to the YMP in ten-ns of experience and understanding gained. In any case, modeling
radionuclide transport at the SDA provides the possibility to actually test model predictions
against reality, a possibility that is lacking at Yucca Mountain.
0
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10.3.6.1 General Strategy for the Calibration of Radionuclide Transport Models at the
SDA
In view of the uncertainties in the hydrologic system, the radionuclide source term, and even in
the distribution of radionuclides in the field environment at the SDA, two radionuclide transport
models were developed: (1) a shallow one-dimensional model extending a few meters from the
waste buiial pits to the top of the underlying basalt and (2) a deep two-dimensional model
extending from the ground surface to the water table beneath the SDA. The purpose of the
shallow model is to identify the transport parameters of the sediments through ttial-and-error
matches of the model to the measured radionuclide concentrations beneath the waste burial pits.
This model requires assumptions about the local infiltration rate as well as other transport
parameters, but because the measured profile does not extend into the fractured basaits, it is
relatively simple hydrologically. The first mod~l was used to simulate the transport of
radionuclides in the surficial sediments beneath the waste-disposal pits. Field studies (Humphrey
and Tingey 1978 [157491]; Rightmire and Lewis 1988 [156442]; Rawson et a]. 1991 [156439]),
provided measurements of radionuclide concentrations in a relatively simple hydrologic setting
that did not directly involve flow in the fractured basaits. The effects of assumptions regarding
source-term inventory and of hydrologic property contrasts were explored in this group of
simulations.
The deeper two-dimensional model is restricted to transport of a single tracer. The results of the
model were qualitatively compared to measurements of matfic potential, observations of perched
water, and the distributions of radionuclides and other contaminants in the interbed sediments,
perched water, and the Snake River Plain Aquifer. 

The overall purpose of the two-dimensional
model is to identify combinations of rock hydrologic and geochemical properties that could have
allowed the deep migration of radionuclides through the basalt layers and interbedded sediments.
The fully coupled, nonisothennal, two-phase flow and reactive transport computer codes
FLOTRAN (Lichtner 2001 [156429]) and FEHM (Zyvoloski et al. 1997 [100615]) were used for
the modeling studies.
10.3.6.2 Numerical Simulations of Water Flow and Conservative Tracer Transport
Single- and dual-permeability models of water flow and conservative tracer transport were based
on a highly schematic representation of the UZ beneath the SDA. The purpose of these schematic
models was to investigate the conditions under which radionuclides might have reached the B-C
and C-D interbeds at depths of approximately 34 and 73 m, respectively. The flow domain for
these models extends 60 m in the horizontal direction and from land surface to slightly below the
water table at a depth of approximately 180 m. A background infiltration rate of 1 cm/yr (Cecil et
al. 1992 [156256], p. 711) was used to establish steady flow conditions in these models and was
maintained at land surface outside the waste-disposal area throughout the transient peliod,
assumed to span the last 50 years. Within the 12 m wide waste disposal area, the flux was
increased to 8 cnVyr at the start of the transient part of the simulations, reflecting the increase in
infiltration rates that are estimated to have occurred at the SDA because of disturbances to the
natural conditions following construction of the SDA in 1952 (Magnuson and Sondrup 1998
[156431], pp. 1-5, 1-7). Additional amounts of water (Table 10.3-2) were applied over ten-day
periods 10, 17, and 30 yr into the transient part to represent flood events that occurred at the
SDA in 1962, 1969, and 1982 (Magnuson and Sondrup 1998 [15643 1 ], Table 2-3).
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10.3.6.3 Results of Single-Continuum Models
40 In the single-continuum models, only the fracture-continuum properties of the basalts and the
matrix-continuum properties of the surficial sediments and sedimentary interbeds are represented
(Table 10.3-3). Shown in Figure 10.3-13 is a comparison of the saturation profile for the single
continuum obtained using the computer codes FLOTRAN and FEIBI with a numerical solution
of Richards equation obtained from Mathematica (Wolfram 1991 [157417]). As can be seen
from the figure, excellent agreement is obtained for the two codes, as well as good agreement
with the Mathematica solution. The slight offset between FEI-IM and FLOTRAN can be
attributed to differences in the discretization approach used in the codes.
The saturation calculated using the single-continuum model at the end of the 50 yr transient
period (2002) is shown in Figure 10.3-14. No significant lateral changes in simulated saturation
are present resulting from the higher infiltration rates associated with the waste disposal area in
the central part of the model domain. McElroy and Hubbell (1990 [156433], p. 362) reported
capillary pressures of 0.2-1.3 bars in the surficial sediments and 0.3-1.3 bars in the 9 m, 34 m,
and 73 m interbeds. McElroy and Hubbell (1990 [156433], p. 363) also reported that conditions
were wetter at the tops of the sedimentary interbeds than at the bottoms, a condition that is also
present across the interbeds in the simulation results (see also Figure 10.3-13).
The relative tracer concentrations (concentration relative to input concentration) at the end of the
50 yr transient petiod are shown for the upper 80 m of the model domain in Figures 10.3-15a and
b for constant and pulse infiltration, the latter representing the flooding events listed in Table
10.3-2. Shown in Figure 10.3-16 is the tracer concentration for both FLOTRAN and FEHM for
constant infiltration and pulsed infiltration using FLOTRAN along the centerline of the
computation domain. The tracer is applied with unit concentration within the waste-disposal area
in the central part of the model domain. Outside this region, a concentration of 10-3 is applied.
An initial concentration of 10-8 is assumed. 

 The model results indicate that a small fraction of a
conservative solute could migrate from shallow waste-disposal pits to the 73 m interbed within
50 years, given the infiltration rates and rock properties assumed in this model. The pulse release
leads to a somewhat greater penetration depth.
10.3.6.4 Results of Dual-Permeability Models
In the dual-permeability models, the basalt fracture-continuum properties and the sediment
matrix-continuum properties are the same as in the single-continuum models and, additionally,
the basalt matrix-continuum properties and sediment fracture-continuum properties are included.
The FLOTRAN code requires that dual-permeability models have a fracture continuum
throughout the model domain, but it is unlikely that the unconsolidated sedimentary layers
actually contain fractures. Ideally, then, the fracture continuum in th-e sedimentary layers would
be defined in such a way that it transmits negligibly small amounts of water and does not affect
the saturations or capillary pressures in the matrix continuum of the same sedimentary layer or in
the fracture continuum of the adjacent basalts. Therefore, the fracture-continuum properties and
fracture-matrix interaction terms in the sedimentary layers (see note to Table 10.3-3) were
chosen to ensure that the water flow rates, saturations, and capillary pressures of the sedimentary
layers in the dual-permeability models were nearly identical to the flow rates, saturations, and
0 capillary pressures of the sedimentary layers in the single-continuum models. This was done by
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assigning a low volume to the fracture continuum in the sedimentary layers and making the
fracture-matrix interaction term large enough to result in the.equivalent continuum limit of the
dual-continuum rhodel. Hydrodynamic equilibrium between the fracture and matrix continua in
the sedimentary layers is maintained and dominated by the properties of the matrix continuum.
The approach was verified by comparing the saturation of the matrix continuum in the dual-
permeability model with the saturation of the sedimentary layers of the single-continuum model,
in a one-dimensional steady-state model with infiltration rate of I cm/yr (Figure 10.3-17). Also
shown is the numerical solution to Richards equation obtained using the software code
Mathematica (Wolfram 1991 [157417]) for the single-continuum case. Saturation of the
sedimentary layers in the two models is nearly identical.  As expected, saturation of the fractLire
continuum of the basalt layers in the dual-permeability model is slightly less than that of the
basalt layers in the single-continuum model, because a small part of the nux in the dual-
permeability model moves through the basalt matrix. In the upper parts of the individual basalt
now units, the fracture continuum and matrix continuum are not in capillary-pressure
equilibfium, probably because the large reduction in the fracture-matrix surface area (0.01) limits
water flow from the fractures into the matrix. However, capillary-pressure equilibrium is re-
established with depth within the flow unit as water flows from the fractures into the matrix.
The simulated saturation profiles for the fracture and matrix continua of the dual -permeability
model are shown in Figure 10.3-18 after an elapsed time of 50 years for constant infiltration.
Matrix saturations in the basalts are much higher than fracture saturations throughout the model
domain because the assumed moisture retention characteristics allow the matrix to retain more
water at high capillary pressures than the fractures. The fracture and matrix continua are in
approximate capillary-pressure equilibrium above the 73 m interbed, but, similar to the results of
the one-dimensional steady-state dual-pen-neability model (Figure 10.3-17), the matrix capillary
pressures just below the 73 m interbed correspond to drier conditions (have higher capillary
pressures) than in the adjacent fractures. Gradually, as water flows from the fractures into the
matrix, capillary-pressure equilibrium between the two continua is re-established with increasing
depth below the 73 m interbed.
The relative tracer concentrations at the end of the 50 yr transient period are shown for the upper
80 m of the fracture and matrix continua in Figure 10.3-19 for the case of constant infiltration.
The fracture-continuum relative concentrations (Figure 10.3-19a) are slightly less than the
concentrations of the sing] e-continuum model at the same location (Figure 10.3-15a) because
some of the tracer has moved into the basalt matiix in the dual-permeability model. The
additional storage provided by the basalt matrix prevents the tracer from arriving at the 73 m
interbed in the dual-permeability model. 

However, tracer is present in the 9 m interbed at a
relative concentration of 0.06 and in the 34 m interbed at a relative concentration of 0.03, despite
the much lower concentrations or absence of the tracer in the overlying basalt matrix (Figure
10.3-19b). Clearly, the tracer distribution in the matrix continuum of the A-B and B-C interbeds
reflects the transport of tracer almost exclusively through the fractures of the basalt units.
It should be noted that in the single-continuum models, the basalt layers used the properties listed
for the A, B-, C-, and D-basalts. In the dual-permeability models, these property values were
used for the fracture continuum in the appropriate layer, and "basalt matrix" properties were used
for the matrix in all basalt layers. All layers (including sedimentary layers) in the dual-
permeability model were assumed to have cubic matrix blocks 1 m on a side and a bulk fracture
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porosity of 0.01. Fracture-continuum properties of the sedimentary layers were assumed to be the
same as those given for the matrix in Table 10.3-2. In the basalt layers, the effective
fracture-matrix area calculated from the block dimensions was reduced by a factor of 0.01 based
on model calibration results of the large-scale infiltration test (Section 9.3). In the sedimentary
layer, the fracture-matrix area was increased by a factor of 100 to ensure hydrodynamic
equilibrium between the fracture and matiix continua. The equivalent continuum permeability
was twice that given for the interbed matrix permeability.
10.3.6.5 Flow and Transport Simulations with Dipping, Discontinuous Layers
The previous simulations in Sections 10.3.6.3 and 10.3.6.4 have considered an idealized
hydrostratigraphy for the SDA in which layers are horizontal and of uniform thickness. In
contrast, structural contour and isopach maps (see Section 10.3.3) indicate that the SDA is
located in an area where the surficial-sediment[basalt interface is relatively low and where the
interbeds have variable thicknesses and dips. To examine the effect that departures from the
idealized stratigraphy of the previous case might have on flow and transport beneath the SDA,
investigators created a model with the computer code FEIB4 that considers the structural
depression in the A-basalt beneath the SDA and treats the 9 m and 34 m interbeds as dipping
discontinuous layers (Figure 10.3-20). The C-D interbed is horizontal with uniform thickness, as
in the previous calculations.
The FEHM model is based on a single-continuum representation with the same hydrologic
properties as used in the previous single-continuum models (Table 10.3-3). The FEHM model
has a constant vertical node spacing of 0.5 m and horizontal node spacing of 1.0 m. In this
model, the pulses of water associated with flooding events are not.used; instead, the flux in the
central 12 m of the model domain was increased to 10 cm/yr during the 50 yr transient peliod to
implicitly account for these events. This led to slightly more water being introduced into the UZ
than in the previous models for the last 50 yrs (5 m for this model compared with the 4.61 m of
water introduced for the cases with flood events).
For a steady-state uniform infiltration rate of I cm/yr, flow-lines calculated by particle tracking
in FEHM indicate that the clay layer at the base of the surficical sediment strongly focuses flow
toward low areas in this layer beneath the hypothetical SDA, at the center of the model domain
(Figure 10.3-21). The interbeds also divert water laterally along their upper surface, but the
amount of offset for the flow lines is less than 5 m at any interbed. Because water Dow is focused
by the slope of these layers, wetter conditions exist at low points in the clay layers and where the
interbeds tenninate, even when infiltration rates are uniform. (Note that water potentials were
calculated by subtracting a unifonn air pressure of 1 bar from the calculated water pressure; a
water potential of 0 bars indicates saturated conditions. 

)
Saturations calculated at the end of the 50 yr transient period, in which 10 cm/yr of infiltration
was applied in the central 12 m of the flow domain, indicate that the basalts are wettest below the
ends of the overlyinginterbeds (Figure 10.3-22). Tracer concentrations near the water table at the
end of the 50 yr transient period are highest where the 34 m interbed has focused water flow
(Figure 10.3-3). Peak tracer concentrations at the water table are about 0. 12 compared to peak
concentrations of about 0.05 for the case with unifon-n, horizontal layers. Although slightly more
water was applied in the case with discontinuous layers, the pattem of saturation (Figure 10.3-
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22) and tracer concentrations (Figure 10.3-23) suggests that part of the early breakthrough is
caused by some water flowing around rather than through the high-porosity interbeds. Also, flow
40 rates are relatively high where flow is focused by the dipping, discontinuous layers.
10.3.6.6 Reactive Transport Calculations
In this section, vertical radionuclide transport through the surficial sediment zone in the SDA is
investigated. Using representative soil-zone water and Pco,, along with surface site density,
cation exchange capacity, and mineralogy of the soil zone, sorption profiles for 241AM' 238PU,
137CS , and 90Sr were calculated and compared with field observations. The resulting model
calibration predicts a high retardation factor for Np and essentially no retardation for U.
10.3.6.6.1 Sorption Reactions: Surface Complexation and Ion Exchange
Both surface complexation reactions and ion exchange are included in the description of
sorption. The radionuclides americium and plutonium take part in surface complexation
reactions, and cesium takes part in ion exchange. Strontium is involved in both sorption
processes. The generic fonn of surface complexation reactions can be written as
x m v ma A <=* Ama (Eq. 10-2)
a + Ylj ik i k
where X' denotes the surface site of type cc, A an aqueous primary species, Akm' the sorbed
m i
surface complex, and v" the stoichiometric coefficient matrix. This description neglects the
ik
role played by the counter ion and therefore does not conserve charge separately within the
aqueous and solid phases whenever the surface complex is charged. It is presently unknown what
effect this inconsistency may have on predicting retardation- and changes in solution chemistry,
such as pH (Lichtner 1996 [101409], pp. 57-59). Ion exchange reactions have the form
z X A + ZiAj <-* zjX_ A + z Aig (Eq. 10-3)
i Zi i ~j i i
where X,.A refers to the sorbed cation. These reactions conserve charge ligorously in both
~' i
aqueous and solid phases, unlike the representation used for surface complexation reactions.
Sorption reactions for surface complexation included in the model calculations are listed in
Table 10.3-4 along with corresponding selectivity coefficients. The data were taken from Zavaiin
and Bruton (2000 [156443] and 2000 [156444]). Cations taking part in ion exchange reactions
are listed in Table 10.3-5, along with their selectivity coefficients. The data were adapted from
generic values given in Appelo (1996 [156425]).
Generally, sorption reactions involve multiple sorption sites associated with different mineral
surfaces. Two distinct philosophies have been articulated in the literature (Davis et al. 1998
[154436]) for modeling sorption reactions. 

 One approach is to develop a detailed model based on
the specific minerals present in the sorbing medium. This approach has the advantage of being
more mechanistically based and having the potential capability of incorporating changes in
mineral abundances on sorption. Its primary disadvantage is the extensive amount of data
required as input parameters to the sorption model. An altemative approach is based on the bulk
properties of the porous medium. This approach is more phenomenological, but has fewer data
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requirements. It is based on direct measurements of bulk properties such as cation exchange
capacity (CEC) and surface site densities. In this report, the bulk approach is used, employing a
multisite description of surface complexation reactions and a single-site representation of ion
exchange reactions.
For a dilute aqueous solution, retardation of a particular primary species is derived from the
distribution coefficient K D , defined as the ratio of total sorbed to total aqueous concentration of
that species
Rj =I+Ko
The distribution coefficient is given by the expression
(Eq. 10-4)
D= I maE.a +Ki oTj ~:kma Vjk k (Eq. 10-5)
involving a sum over surface complexation and ion exchange isothenns, where --" refers to the
k
sorbed concentration of surface complex Ak", and "E'j refers to the ion exchange isotherm. The
quantity Tj represents the total aqueous concentration of the subscripted species.
Sorption reactions used for surface complexation include the surface sites: >FeOH, >SiOH,
2+>AlOH, and >Ca . Unknown is the appropriate site density to use in the calculations. The site
concentration associated with the mth mineral, denoted by n' [mol/dm 3], can be expressed as a
is a 2
product of a number of factors involving the intrinsic mineral site density (77' [# sites/nm
a
mineral concentration (pno. [kg/dM3]), and mineral specific surface area (A fm2/kg]). Thus,
the site concentration can be calculated from
M= I 'nA. g, 0. (Eq. 10-6)
n,, - 17a
NA
where NA denotes Avogradro's number, the intrinsic site density is denoted by i7a, and the
specific surface area is represented by A,,,.
Retardation caused by ion exchange is proportional to the CEC of the exchanging medium and
the bulk rock density. The conventional definition of the CEC is in units of meq/100 g solid. A
more useful quantity is mole equivalents of exchange sites per bulk volume of porous medium,
denoted by the symbol (o. The two quantities are related by the porosity and grain density of the
porous medium
w = Q - 0) pCEC (Eq. 10-7)
where p, denotes the grain density and 0 the porosity. Retardation is proportional to co and,
thus, to the product of the bulk density and the CEC.
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10.3.6.6.2 Model Simulations
Calculations were performed in one dimension with a constant infiltration Darcy flow rate of 10
cm/yr, a porosity of 50%, and an average saturation of 0.58 (Magnuson and Sondrup 1998
[156431], p. 4-8, Table 4-2). Radioactive decay was not included in the simulations. 

 An aqueous
diffusion coefficient of 10-5 CM2/S with a tortuosity of 0.294 taken from Magnuson and Sondrup
(1998 [15643 11, Table 4-2, p. 4-8) for the surficial sediment layer was used in the simulations.
The injection fluid composition is listed in Table 10.3-6. The fluid composition is taken from
Well 99 corresponding to perched water as listed in Table 10.3-1. The pH was adjusted to give
equilibrium with calcite, which otherWise would have been supersaturated by one log unit. This
adjustment resulted in a reduction in the reported pH of 8.4 to 7.59. The redox state of the fluid is
not given in Table 10.3-1. As discussed below, to obtain a simultaneous fit to the concentration
profiles for plutonium and americium, it was necessary to invoke reducing conditions. The initial
fluid composition was set to be the same as the injection fluid, with the exception of the
radionuclide concentrations: plutonium, americium, cesium, uranium, and neptunium, which
were set to small values (10-20 mol/L) and strontium, which was given the value of 5 x 10-1 6
mol/L to fit the minimum observed strontium value. It was not determined how much of the
strontium profile resulted from nonradioactive strontium that was naturally occurring. The
calculated 109 PC02 = -2.18, which is quite high, presumably resulted from decomposition of
organic matter in the waste and soil zones.  As can be seen by inspection of Table 10.3-6,
carbonate complexes play an important role in speciation of americium and uranium and less so
for neptunium. Plutonium exists primafily in the IV oxidation state in the form of the complex
Pu(OH)4-
The observed sorbed concentration profiles were fit by adjusting the surface site densities and the
injected radionuclide concentrations. Site densities >FeOH, >AlOH, and >SiOH were adjusted to
fit the observed profiles. The >Ca 21 site density was arbitrarily set to 10-4 mol/L. The resulting
site densities used in the simulations are listed in Table 10.3-7.
Speciation results of the injection fluid for the amount sorbed for different radionuclides
participating in surface complexation are presented in Table 10.3-8, in which the contiibution to
the distribution coefficient is listed for each surface site. It can be seen that plutonium contains
contributions from sorption sites >FeOH and >AlOH, whereas ameficium is primafily sensitive
to site >AlOH and to a lesser extent site >Ca. There were no data available for uranium and
neptunium. The distribution coefficients are much smaller than those reported by Dicke (1997
[157410]) as listed in Table 9.3-1.
An entirely different result is obtained under oxidizing conditions. 

In this case, both plutonium
and americium are strongly sorbed to >FeOH, with americium several orders of magnitude
greater compared to plutonium. Because under oxidizing conditions plutonium is not sorbed to
any other sites, it is not possible to fit the plutonium and amelicium profiles simultaneously
under these conditions.
Generic values for the ion exchange selectivity coefficients (see Table 10.3-5) were taken from
Appelo (1996 [156425]). The CEC was varied to fit the cesium profile. A value of 0.02 mol/kg
was obtained. This value is at the lower limit of the reported CEC range for the surficial
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sediments of 0.27 to 0.02 mol/kg (Rightmire and Lewis 1987 [156441], Table 5). The strontium
profile was predicted by the model without any additional fitting.
The resulting fit to the data is shown in Figure 10.3-24, corresponding to advection and
diffusion. The obtained fit does not capture the observed decrease in plutonium concentration at
depth of approximately I m. This discrepancy could be a result of several factors, including
heterogeneity, lateral flow, and the possibility of the presence of the contact between the clay
and basalt layer that occurs at this depth. Other species also indicate a slight increase in
concentration at this depth.
10.3.7 Discussion
Several interpretations of radionuclide transport in the surficial sediment zone are possible. One
is that lateral flow occurred, sweeping out part of the radionuclide plume. The thickness of the
stratigraphic layers is highly irregular, and the possibility exists that flow occurred along the
interface between the clay layer and the surficial sediment layer. Another possibility is that a
catastrophic or sudden release of a pulse of fluid, caused by a flooding event, released a pulse of
radionuclides that propagated downward with reduced retardation, due to kinetic effects caused
by fast flow rates. For this situation, the data are interpreted as background flow (or diffusion)
producing the Lipper monotonically decreasing profile with depth. The lower portion of the
profile, where the concentration is increasing was the result of a sudden flow event. Presumably,
according to this interpretation, the peak lies at a still greater depth below that at which the data
were collected.
The model calculations predict retardation factors for neptunium and uranium that are seen to be
orders of magnitude higher compared to the other radionuclides. This result would indicate that
very little movement of neptunium and uranium should be observed. No values for these
radionuclides were reported that could be taken as consistent with their predicted high
retardation. 

Finally, although it was necessary to assume reducing conditions for fluid coming from the SDA,
it is not expected that such conditions would persist at greater depths because of the partially
saturated conditions that are present there, leading to oxidizing water.
10.3.8 Conclusion
The main conclusion to be drawn from this study is that INEEL presents a far wetter
environment than that of Yucca Mountain. This increase in infiltration is manifested in higher
infiltration at the SDA and flooding events that could have resulted in enhanced radionuclide
migration beneath the SDA. Focused flow resulting from the undulating topography of the basalt
flows and sedimentary interbeds would be expected to exacerbate the situation, leading to even
greater distances of radionuclide migration, as demonstrated in the modeling exercises.
It was found that to fit observed radionuclide concentrations in the surficial sediment layer,
reducing conditions were required. Otherwise, it was not possible to fit the observed profiles of
both americium and plutonium simultaneously. Note that although detailed waste compositions
are not currently known, there is significant organic matter in the waste that is not inconsistent
with the assumption of reducing conditions. However, as noted above, such conditions are not
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Natural Analogue Synthesis Report
expected to prevail at greater depths, where the system would be expected to be oxidizing. The
is calculated profiles did not capture the increase in concentration observed at greater depth near
the base of the surficial sediment layer. To further test and validate model predictions, continuity
of data at greater depths beneath the SDA would be needed along with site-specific data for
surface complexation site densities.
10.4 RADIONUCLIDE FLOW AND TRANSPORT STUDIES AT PERA BLANCA,
MEXICO
10.4.1 Objectives
The goal of these studies is to construct a three-dimensional conceptual model of the transport of
uranium and radiogenic daughter products at Pefia Blanca, Mexico (Technical Work Plan for
Natural Analogue Studies for License Application (BSC 2001 [157535], p. 4)). A three-
dimensional model will extend the previous work at Pefia Blanca that was limited to collection of
data for exposed planar surfaces. The model will also address whether there has been preferential
flow/drainage downward through fractures or if there has been a net flux of uranium off-site. To
accomplish this, three wells will be diilled at the site to obtain core samples from within and
beneath the uranium ore body and to collect water samples from beneath the ore body. The core
and water samples will be analyzed using a variety of techniques to support development of the
conceptual model of transport at Pefia Blanca. The conceptual model will then be tested using
numerical methods employed by the UZ Flow and Transport Model to build confidence in
understanding UZ transport at a potential Yucca Mountain repository.
0 10.4.2 Background
In the 1970s, the Pefia Blanca region, approximately 50 km north of Chihuahua City, was a
major target of uranium exploration and mining by the Mexican govemment. Since that time the
Nopal I uranium deposit has been studied extensively because it is a good analogue for
evaluating the fate of spent fuel, associated actinides, and fission products at a geologic
repository in unsaturated volcanic tuff. Previous studies associated with Pefia Blanca as well as a
geologic desciiption of the site were reviewed in Natural Analogs for the Unsaturated Zone
(CRWMS M&O 2000 [141407]). Biiefly, the Nopal I uranium deposit at Pefia Blanca represents
an environment that closely approximates that of the potential high-level radioactive waste
repository at Yucca Mountain, Nevada, in the following ways:
0 Climatological I y: both are located in semi-arid to and regions
0 Structurally: both are parts of a basin-and-range horst structure composed of Tertiary
rhyolitic tuffs overlying carbonate rocks
Hydrologically: both are located in a chemically oxidizing, UZ 100 m or more above
the water table
Chemically: the alteration of uraninite to secondary uranium minerals at Nopal I may
be similar to the eventual fate of uranium fuel rods in a potential geologic repository
like Yucca Mountain.
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10.4.3 Previous Radionuclide Transport Studies at Peiia Blanca
Studies of uranium-series disequilibria within and around uranium deposits can provide valuable
information on the timing of actinide mobility and hence the undisturbed stability of a potential
repository over the geologic time scales associated with the required lifetime of the facility.
Previous studies at Pefia Blanca dealing with bulk samples and fractures have focused on the
extent and timing of uranium-series mobility or transport at this site, and have been summarized
in Natural Analogs for the Unsaturated Zone (CRWMS M&O 2000 [141407]). Some of these
studies reported open-system behavior, suggesting mobility of uranium and its daughter
products. 

 In contrast, previous uranium-series thermal ionization mass spectrometry (TIMS)
work at Nopal I (CRWMS M&O 2000 [141407], pp. 89-90) found closed-system behavior,
suggesting very limited mobility in fracture-filling material for uranium. Briefly, the TIMS
results indicated that the uranium (235, 238), thorium, and protactinium in the fracture-filling
minerals have remained stable for more than 300 ka at Nopal 1.
Pickett and Murphy (1999 [1100091) presented measurements of U-Th isotopic composition and
concentration in various water samples collected near the Nopal I uranium deposit duting
relatively wet conditions (see 1995 collections in Table 10.4-1). The observed uranium and
thorium concentrations generally correlate with concentrations of major cations and anions and
total conductivity, which may reflect evaporation-dilution or rock dissolution effects on all of
these species. Thoiium and uranium concentrations also correlate strongly with each other,
which is surprising given the expected differences in solution chemistry and potential solubility
controls for these two elements. Pickett and Murphy (1999 [110009], p. 812) interpreted these
concentrations in the context of solubility control by various uranium silicate minerals
(haiweeite, soddyite) and thorianite. They found that the perched water is close to solubility for
haiweeite, a calcium uranyl silicate mineral. All of the other waters are undersaturated with
respect to uranium mineral phases. However, all of the waters are supersaturated with respect to
thorianite, which is attributed to the presence of colloidal thorium in the <0.2 ~tm fraction of
these samples. The occurrence of undersaturation for uranium and supersaturation for thorium
indicates that radionuclide transport in the UZ may be controlled by kinetic factors such as
evaporation, rock dissolution, and colloid formation, which complicate the interpretations based
on thermodynamic (solubility) considerations. The incorporation of kinetic factors will be
discussed below with respect to the generalized radioisotope transport model of Ku et al. (1992
[1099391).
10.4.4 Ongoing Work at Nopal I
As previously summarized, prior work at Peha Blanca contrasts the long-term stability of
uranium and thorium in fractures against the ongoing dissolution of uranium by surface waters,
as evidenced by elevated uranium concentrations and 234U/238U in adit seepage waters. The net
flux off-site is not well constrained other than by the 8  5 m.y. age of the primary uranium
mineralization at Nopal 1 (Pearcy et al. 1994 [100486], p. 729). Current (2002) work is discussed
in the following subsections.
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10.4.4.1 Drilling
The goal of current work (BSC 2001 [157535], p. 4) is to extend geochemical studies to the third
dimension by drilling wells at Nopal 1. Work is now underway to drill one borehole through the
uranium ore deposit to a depth of approximately 200 m. The borehole is planned to penetrate the
SZ to at least 20 m, and core will be collected during diilling. In addition, two additional wells
will be drilled at approximately +50 m and -50 m from the borehole. Monitoring wells will be
installed to sample ground water on a quarterly basis.
10.4.4.2 Surface Water Sampling
The work of Pickett and Murphy (1999 [110009]) has been extended to include water samples
collected at Nopal I during the dry season. Samples were collected in February 2000 and March
2001 (Simmoris 2002 [157544], pp. 86-87). These data provide new infonnation on temporal
and seasonal variations at the site (see Section 10.4.4.4). 

As with the previous work, samples are
of three different types: (1) perched water trapped in an old borehole about 20 m outside the
deposit, (2) seep water obtained from an old adit approximately 8 m below the +10 m surface
(see Figure 10.4-1), and (3) a groundwater sample located in the regional carbonate aquifer 1.3
km southeast of the deposit. In addition, data has been collected from an old mining camp well
located about 0.6 km southeast of the deposit.
These new data, along with the 1995 data from Pickett and Murphy (1999 [110009]), are detailed
in Table 10.4-1. In many cases, the new data show higher uranium concentrations ratios than the
results from Pickett and Murphy for samples collected during the wet season. This could result
from longer fluid/rock interaction times or from greater evaporation. A portion of the collection
system is shown in Figure 10.4-2. The water is collected in plastic sheets, in which it remains
until sampled. Although the adit is comparatively cool and damp, evaporation could greatly
influence the uranium concentrations.
Stable isotope data were obtained for some of these adit samples to evaluate the effects of
evaporation on the uranium concentrations.These data are shown in Figure 10.4-3. When water
evaporates, the isotopic composition of the resulting vapor will be shifted to lower values of
8180 , and the residual water will be shifted to higher values on a plot of 8D versus 8180 . The
stable isotope data for AS-5 (from a water well) and AS-6 (from a diill hole into a perched water
horizon) have significantly lower values than other samples.  They fall on the Global Meteoric
Water Line (GMWL) and probably represent the average composition for the precipitation at the
site. The adit samples all lie much higher on this plot. Of these, AS-2, AS-3, and AS-4 all fall
significantly to the left of the GWNEL and may represent atmospher ic water vapor that has
diffused into the adit and condensed in the cooler, underground environment, followed by some
peiiod of evaporation in the collection system. AS-1 lies on the GMWL, but probably does not
represent a rainwater sample, because it is relatively high for meteoric water at this latitude; it is
closer to the opening of the adit and may represent a more evaporated version of cluster AS-2,
AS-3, and AS-4. The evolution of stable isotopes for the adit samples appears to have at least
three components: (1) evolution of vapor from GMWL, (2) modification by water/rock
interaction, and (3) evaporation in the adit collection system. A simpler approach planned for
evaluation is to nonnalize the uranium data to chloride or bromide concentrations.
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10.4.4.3 Radioisotope Transport Modeling
A model based on naturally occurring uranium and thorium-series disequilibria is being tested
for characterization of the in situ migration of actinide nuclides in and around the Nopal I
uranium deposit. Estimates can then be made of the rates of sorption-desorption, hence
retardation factors, and dissolution-precipitation of the isotopes over a range of time scales, in
both the SZ and UZ. Such information is vital to testing or validating perfonnance assessment
models for geologic nuclear waste disposal.
Current models utilizing uranium- and thorium-sen'es disequilibria for radioisotope transport in
geologic systems are primarily based on the steady-state flow assumption (Ku et al. 1992
[109939], pp. 639,640). 

 These models, while elucidating the behavior of radioisotopes in the
phreatic zone, may not sufficiently constrain the isotope transport in unsaturated vadose layers
where the concentration and transport behavior of radioisotopes are often govemed by nonsteady
conditions. During the past year, the uranium-series transport model of Ku et al. (1992 [109939])
has been extended to include the nonsteady-state situations. Free of the steady-state assumption,
this new, generalized radioisotope transport model has the two important features of being
applicable to both the SZ and UZ, and providing simultaneous constraints on the behavior of
radioisotopes in dissolved, colloidal, sorbed, and solid pools of a groundwater system.
The model makes the following assumptions: (1) in natural water-rock systems, radionuclides
reside in four "pools"--dissolved, colloidal, sorbed, and solid-with the colloidal pool being
treated as a mobile particle pool; (2) radionuclides in the sorbed and colloidal pools are in first-
order sorption equil-ibrium with those in the dissolved pool; (3) radionuclides in the solid pool
are transferred to the dissolved pool through dissolution and cc-recoil, whereas those in the
dissolved pool are incorporated into the solid pool through precipitation.
The data in Table 10.4-1 have been analyzed using this model. In contrast to the then-nodynamic
modeling of Pickett and Murphy (1999 [1100091), this model provides a means to characterize
kinetically controlled radionuclide transport at Peiia Blanca. The uranium data from the 1995
wet-period measurements are shown in Figure 10.4-4.
As predicted by the model, a linear relationship exists between 234U/238U and 1/238U in waters
collected from the vadose zone near the Nopal I uranium deposit (Figure 10.4-4a), due to a-
recoil-induced 234U enrichment in the water. The one sample from the carbonate aquifer (SZ)
shows a much lower 234U/238U ratio, perhaps caused by prolonged interaction with old calcites in
the aquifer, allowing uranium exchange between rock and solution to mask the effect of 234U
enrichment in the water. Using the model as well as the slope and intercept from Figure 10.4-4a,
the relative input rates of uranium from solids to the solution through dissolution and (x-recoil
can be detived. The 234U (x-recoil rate for the adit fluids is calculated to be -9 dpnVUyr. The
dissolution rates are -8.3 dpm/Uyr for 238U and 234U (or 47 x 10-9 mol/LJyr for 238U and 2.6
X 10-12 mol/Uyr for 234U).
The model also allows deten-nination of the fluid transit time (,rw) in the UZ. Because of the short
transit time of water in the UZ, 238U concentrations increase linearly with increasing rw (Fig.
10.4-4b). Meanwhile, the ~234U/238U ratio decreases rapidly with increasing rw and very high
234U/238U ratios can occur when the water has a very short transit time in the UZ. It is estimated
TDR-NBS-GS-000027 REV 00 ICN 01 10-24 April 2002 1

 

Natural Analogue Synthesis Report
that the transit time for the seep water that infiltrated into the Level +00 adit 8 m below the
surface is about 6-29 days; for the perched water at 10.7 m depth in an old borehole, the transit
time is about 0.4-0.5 years. The large values of rw for the perched water may reflect the long
residence time of water in the borehole. Note that because water at different sites may have
different pathways, the value of rw itself does not provide information on possible connections
between the perched and seep waters sampled. In conclusion, although the water transit time in
the UZ is quite short, significant dissolution of uranium may have occurred in a low-water flux,
high-uranium concentration setting near the Nopal I uranium deposit.
10.4.4.4 Seasonal Variability of Uranium Dissolution Rate in UZ
To assess temporal variations in the transport of uranium in the UZ, samples of perched and adit
seep waters were collected during the dry winter season in late February 2000 and again in early
March 2001. 

The results are plotted in Figure 10.4-5a. Compared with samples collected during
the September wet season of 1995, many of these new measurements show much higher 238 u
concentration and lower 234U/211U, suggesting increased uranium dissolution and/or lower a-
recoil associated 234 U enrichment rates during the dry season. The low humidity during the dry
season may have also enhanced evaporation, causing higher uranium concentrations in the
waters sampled.
The data collected during the winter dry season depart considerably from the linear relationship
between 234U/238U and 1/238U predicted by the model for the wet season of 1995 (Figure
10.4-5a). Such a departure could result from: (1) high and vaiiable evaporation under low
humidity conditions and (2) incomplete flushing associated with low rainfall during the dry
season. Linear regressions on data for the perched and adit seep waters collected during March
2001 give a 234U a-recoil rate (AP,) of -5.7 dpm/l-/yr. Compared to the -9 dpnVUyr for the wet
season, this lower a-recoil rate estimate may reflect incomplete flushing of waters through the
vadose layers during the dry season. Dissolution rates of uranium are estimated to be about 24
dpnVUyr for 238U and 234U (or 136 x 10-9 mol/L/yr for 238U and 7.5x10-12 MOI/Uyr for 234U).
These rates are about three times higher than those in the wet season, possibly suggesting a
favorable physiochemical condition (e.g., increased oxygenation) for uranium dissolution during
dry periods. In this context, it should be noted that the samples collected 15 m from the adit
entrance show 234U/211U values lower than secular equilibfium, which suggests dissolution of
material previously preferentially depleted in 234 U by a-recoil effects.
Note in addition that large variations in the 238U concentration and 234U/238U ratio were also
found in samples collected from the SZ during the dry season (Figure 10.4-5b). While no clear
correlation between 238U and 234U/238U iS seen, the plots suggest that both the decreased water
infiltration flux and the increased uranium dissolution rates in the vadose zone may contribute to
the higher dry-season uranium concentrations in the SZ. Observations such at these may have
important implications for the effects of climate change on the long-tenn stability of uranium in
the environment.
10.4.5 Work in FY02
Although the data and modeling discussed above provide useful preliminary data for uranium
transport at Pefia Blanca, spatial dependence and the net flux of uranium transport from the
TDR-NBS-GS-000027 REV 00 ICN 01 10-25 April 2002

 

Natural Analogue Synthesis
deposit via groundwater cannot be thoroughly evaluated without higher resolution sampling of
any potential groundwater uranium plume in the vicinity of the deposit. This will be
accomplished through the drilling program at Nopal I (BSC 2001 [157535], pp. 4-5).
In addition to the core and fluid samples from the borehole and wells, the perched, seep, and
aquifer waters from the sites previously sampled will be resampled (see above). Where adequate
234 238 232
samples can be obtained, isotopes will be measured of uranium ( U and U), thoiium ( Th,
230 Th, 228Th, and 234 Th), radium ( 226 Ra, 228 Ra), polonium ( 210 Po) and lead (210 Pb) in the fluid
samples. Radioactive disequilibria in sorbed phases will also be studied, using leaching methods
on the core samples. Since it may be difficult to collect enough fluids from the UZ for all of the
proposed measurements, data on the sorbed phases should provide an altemative way to assess
the radionuclide transport in the UZ.
The U-series modeling effort will be extended to the thorium and radium isotopes.
Measurements of polonium and lead isotopes will be applied to the Th model to further evaluate
the role of colloids in the transport of these nuclides. 

Modeled results on uranium transport may
be affected by the evaporative concentration in UZ fluids. To coffect for this possible bffect, the
chlofide or stable isotope measurements made on water samples from the UZ will be compared
with those on rainwater. Model sensitivity and validity will be tested, and ways to evaluate the
uncertainties of model parameters will be sought. Results from the Pefia Blanca analogue study
will be provided for testing the UZ process model.
10.5 OTHER TRANSPORT ANALOGUES
10.5.1 Steenkampskraal
The Steenkampskraal monazite mine, located about 100 km south of Vaalputs, South Aflica,
provides an example of colloidal transport of radionuclides in the UZ (Figure 10.5-1).
Steenkampskraal is a licensed low-level waste radioactive-waste disposal site in South Africa
that is being considered as a potential high-level waste disposal site. Steenkampskraal is the
richest monazite ore body in the world. From 1952 to 1963 it was the world's leading producer
of thorium and rare earth elements (REE), with total production estimated at 50,000 metlic tons
of monazite concentrate, containing 45 wt % REE oxides, 4% thorium oxide, and 600 ppm
uranium oxide (Jarvis et al. 1997 [157489], p. 12). Monazite and fluorapatite together constitute
approximately 80% of the ore mass, along with minor sulfides, oxides, and silicates. Locally, the
ore shows enrichment of Fe/Ti oxides. The mine is situated within the granulite facies high-
temperature zone of the Namaqualand Metamorphic Complex, where model U-Pb ages of the
mineralization are given as 1180 +40 Ma (Jarvis et al 1997 [157489], p. 12).
A characterization study was undertaken to investigate the degradation of monazite and apatite
and to assess the extent of uranium, thorium, and REE transport away from the piimary ore body
under in situ conditions. One of the main objectives of the study was to evaluate the role of
colloids in promoting the mobilization and retardation of trace metals. The average rainfall in the
area is 70 mm/yr (Jarvis et al. 1997 [157489], p. 15). Upper sections of the mine experience
permanently unsaturated conditions. The steady-state level of the water table is 50 m below the
surface when pumping is stopped. The pH of the waters ranges from 7.3 to 8.4 (Jarvis et al. 1997
TDR-NBS-GS-000027 REV 00 ICN 01 10-26 April 2002 1

 

Natural Analogue Synthesis Report
[157489], p. 21). Analyses of waters collected from boreholes indicate supersaturation by 2 to 3
orders of magnitude with respect to amorphous uranium W02) and thorium (Th02) phases.
There is a marked fractionation between light and heavy REEs, with the heavier elements
strongly enriched in the aqueous phase (Figure 10.5-2). The heavy REEs show a greater
tendency for complexation and a greater affinity for mineral surfaces (Jarvis et al. 1997
[157489]), suggesting association with colloidal particles. Given the degree of fractionation
exhibited by the lanthanide series elements (REEs), finely comminuted monazite cannot
represent the dominant colloidal phase. 

 Extensive leaching and alteration of the original
mineralogy must have occurred and has resulted in a phase or phases containing proportionally
more uranium, thorium, and REE than the parent. A similar phenomenon has been observed at
other localities where monazite weathering is accompanied by preferential loss of uranium and
thorium (Jarvis et al. 1997 [157489], p. 16).
Results of the study indicate that the monazite deposit behaves as a partly open system,
especially where monazite disseminated in its silicate matrix is exposed to oxidizing surface and
groundwaters along fractures and stratigraphic discontinuities, such as the contact between
overburden and bedrock. Under these conditions, there is evidence that colloids in the infiltrating
water act as vectors for the transport of thorium, uranium, and REE. This evidence includes very
high concentrations of uranium and thorium and fractionation between the heavy and light REE
in samples taken from boreholes. Final results of this study are not yet available, but the
information to date indicates that both the Steenskampskraal and Nopal I sites are open systems
with respect to thorium, with colloidal transport being the main transport mechanism. Both sites
are similar to Yucca Mountain with respect to unsaturated, oxidizing conditions. This suggests
that should thorium escape waste packages emplaced at Yucca Mountain, it would likely be
transported by colloids, unless attenuated by filtration.
10.5.2 Koongarra
The Koongarra uranium deposit at Alligator Rivers, Australia is found at the steeply tilted
contact between Proterozoic sandstone and schist (CRWMS M&O 2000 [151945], Section 13).
The ore body is located in a shallow unsaturated environment that is subject to seasonal
fluctuations of monsoons.  Payne et al. (1992 [124812]) investigated the role of colloids in
transport of uranium in the dispersion fan of the weathered zone above the ore body. The colloids
and particles included clay minerals, particularly kaolinite, and chlorite, along with fine quartz
grains. Iron was present as particle coatings, and in a separate colloidal fonn. The amount of 238U
associated with colloids ranged up to 6.5%, whereas the amount of 230Th associated with colloids
ranged from 10% to 85%. However, 21OTh was associated to a much greater extent with larger
particles, which are unlikely to be mobile in natural groundwaters. The high 22'Th/2"Th ratio
was high in some fractions, indicating that 227 Ac could be present as colloids. Overall, however,
there was little colloidal material in these groundwaters, with only iron, uranium, thorium, and
actinium showing a significant association with colloids (Payne et al. 1992 [124812], p. 481).
10.6 CONCLUSIONS
The hydrogeologic and geochemical setting at Pefia Blanca is closely analogous to that at Yucca
Mountain, as described in Section 10.4.2 and in CRWMS M&O 2000 [141407]. While the
TDR-NBS-GS-000027 REV 00 ICN 01 10-27 April 2002

 

Natural Analogue Synthesis Report
hydrogeologic and geochemical features at INEEL are less similar to Yucca Mountain, of the
contaminated anthropogenic sites initially considered for study, INEEL provided the closest
similarity in that it occurs in a fractured porous medium with perched water zones and units of
varying permeability. It provided the additional advantage of data sets that included
radionuclides, which strengthen model testing aspects of the analogue study. Radionuclide
transport in the surficial sediment zone at the RWMC can be interpreted in a number of ways. 

One is that lateral flow occurred, sweeping out part of the radionuclide plume. The thickness of
the stratigraphic layers is highly irregular, and the possibility exists that flow occurred along the
interface between the clay layer and the surficial sediment layer. This would be in keeping with
the hypothesis of Nimmo et al. 2001 [154458]). Another possibility is that a catastrophic or
sudden release of a pulse of fluid caused by a flooding event released a pulse of radionuclides
that propagated downward with reduced retardation, owing to kinetic effects in tum caused by
fast flow rates. Presumably, according to this interpretation, the concentration peak lies at a still
greater depth below that at which the data were collected.
The model calculations predict retardation factors for neptunium and uranium that are seen to be
orders of magnitude higher compared to the other radionuclides. This result would indicate that
very little movement of neptunium and uranium should be observed. No values for these
radionuclides were reported that could be taken as consistent with their predicted high
retardation.
In comparison to Yucca Mountain, the wetter environment at INEEL is manifested in higher
infiltration at the SDA and flooding events that could have resulted in enhanced radionuclide
migration beneath the SDA. Focused flow, resulting from the undulating topography of the
basalt flows and sedimentary interbeds, would be expected to exacerbate the situation, leading to
even greater distances of radionuclide migration, as demonstrated in the modeling exercises. The
UZ Flow and Transport Model at Yucca Mountain considers a range of infiltration rates that are
then used to bound the range of percolation flux. Because the PTn has a damping effect on flow
to the TSw, it is unlikely that the enhanced transport scenario proposed in the INEEL modeling
study would occur at Yucca Mountain.
At Nopal 1, the evolution of stable isotopes for the adit samples appears to have at least three
components: (1) evolution of vapor from the GMWL, (2) modification by water/rock interaction,
and (3) evaporation in the adit collection system. A simpler approach planned for evaluation
shortly is to normalize the uranium data to chloride or bromide concentrations. It is estimated
that the transit time for the seep water that infiltrated into the Nopal I Level +00 adit 8 m below
surface is about 6-29 days, and for the perched water at 10.7 m depth in an old borehole, the
transit time is about 0.4-0.5 years. The large values of -rw for the perched water may reflect the
long residence time of water in the borehole. It should be noted that as water at different sites
may have different pathways, the value of -rw itself does not provide information on possible
connections between the perched and seep waters sampled. In conclusion, although the water
transit time in the UZ is quite short, significant dissolution of uranium may have occurred in a
low-water flux, high-uranium concentration setting near the Nopal I uranium deposit. If analyses
from future sampling campaigns confirm that transit time is short in the UZ at Nopal 1, then the
implications would need to be considered for the similar low-water flux environment at Yucca
0 Mountain.
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Natural Analogue Synthesis Report
Compared with samples collected during the September wet season of 1995, many of the new
measurements in late February 2000, and again in early March 2001, show much higher 238u
concentration and lower 211U/211U, suggesting increased uranium dissolution and/or lower cc-
recoil-associated 234 U enrichment rates during the dry seasons. 

The low humidity during dry
seasons may have also enhanced evaporation, causing higher uranium concentrations in the
waters sampled.
The data collected during the winter dry seasons of 2000 and 2001 depart considerably from the
linear relationship between 234 U/ 238 U and 1/ 238 U predicted by the model for the wet season of
1995 (Figure 10.4-5a). Such a departure could be caused by: (1) high and variable evaporation
under low humidity conditions, and (2) incomplete flushing associated with low rainfall during
the dry season. The uranium dissolution rates are about three times higher than those in the wet
season, possibly suggesting a favorable physiochemical condition (e.g., increased oxygenation)
for uranium dissolution during dry periods.
Large variations in the 238U concentration and 234U?38U ratio were also found in samples
collected from the SZ during the dry season. Both the decreased water infiltration flux and the
increased uranium dissolution rates in the vadose zone may contribute to the higher dry-season
uranium concentrations in the SZ. Observations such at these may have important implications
for the effects of climate change on the long-term stability of uranium in the environment.
As a final point, colloid transport appears to be an important factor for migration of thorium in
one open unsaturated system, Steenkampskraal, but not in another, Nopal 1. Both systems have
similar hydrologic conditions to those at Yucca Mountain, although the rock type is different at
Steenkampskraal. At Koongarra, another unsaturated but seasonally fluctuating system, colloid
transport takes place but is a minor mechanism of uranium transport. Because seasonal
fluctuations in uranium dissolution have been discovered at Nopal 1, it would be useful to
investigate the possibility of colloid transport in that system. A more informed understanding of
the implication for colloid transport in the UZ at Yucca Mountain could then be had and could be
used to evaluate whether TSPA assumptions that disregard colloid filtration are appropriately
conservative.
9
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Naa.,.l
101
0
z
Eastirig, in feet
Source: Simmons 2002 [1575781, SN-LANL-SCI-234-VI, p. 61 ~
Figure 10.3-1a. Map of SDA and Deep Wells Showing Location of Radionuclide Concentrations
Greater Than Three Times Detection for Depth lntewals to the 9 m Interbed
z
-- - - - - - - - - -
Easting, in feet
Soume! Simmons 2002 (157578], SN-LANL.SCI-234-Vl. p, 61,
Figure 10.3-lb. Map of SDA and Deep Wells Showing Lmation of Radionuclide Concentrations Great.,
Than Three Times Detection for Depth linteivals to the 34 m Interbed
TDR-NBS GS-IXXX)27 REV (X) ICN 02 ]OF-] May 2002 1

 

Natural Analogta, Synthesis Report
0
0
0
z
- - - - - - --- - - -
Easdng, In feet
Source: Simmons 2002 (157578], SN-LANL-SCI-234-Vl, p. 62,
Figure 10.3-1c. Map of SDA and Deep Wells Shomng Lmation of Radionuclide Concentrations
Greater Than Three Times Detwtion for Depth lntemals to the 73 m lnterbed
gt12
.12
z
= 2
-IM sat
Easdng, In feet
Soume; Simmons 2002 [1575781, SN-LANL-SCI-234-Vl, p. 63.
Figure 10.3-2. Ground Surface Elevation in the Vicinity of the SDA
TDR-NBS-GS-000027 REV 00 ICN 0 1 1 OF-2
April 2002 1

 

Natural Analogue Synthesis Report
~-n
z I
0 12 1 14
c.
Easting, in feet
Source: Simmons 2002 [1575781, SN-LANL-SCI-234-VI, p, 64.
Figure 10.3-3. 

 Surficial Sediment Thickness in the Vicinity of the SDA
ID IN
8
4-
A*-
J.
z 0
+=,=
4p
Eastng, in feet
Source: Simmons 2002 [157578], SN-LANL.SCI-234-VI, p. 64.
Figure 10.3-4. Elevation of Top of Basalt Flow A in the Vicinity of the SDA
TDR-NBS-GS-000027 REV 00 ICN D I IOF-3 Aprii 2002

 

Natural Analogue Sy,thesis Report
01
14
2
Z.
z
4
4
4::' .
.n. o
Easfing, in feet
Source. Simmons 2002 [1575781, SN LANL-SCI-234-VI, p. 65,
Figure 10.3-5. Elevation of Top of AB Interbed in the Vicinity of the SDA
41.
es-
cfi
o
z
1 24
Easbng, in feet
Source: Simmons 2002 (1575781, SN-LANL-SC)-234-Vl, p, 65,
Figure 10.3~6. Thickness of AB Interbed in the Vicinity of the SDA
TDR-NBS-GS-O(X)027 REV 00 ICN 01 1 OF-4 April 2002 1

 

Natuml Analogue Synthesis Repon

%

rD

z

- -	- - - -- - - - -
	Easbng, In feet
Souxe: Sirrmcma 2002 [157578], SN-LANL.SCI-234-Vl, p. 66.
Figure 10.3-7. Eleva	tion of Top of B Basalt in the Vicinity of the SDA

		7
	7
F
	0
z
1 %v

0.	.
*4

	Easting, In feet
	Source: Simmons 2002 [1575781, SN-LANL.SCI-234-Vl, p. 66.
	Figure 10.3-8. Elevation of Top of BC Interbed in the Vicinity of the SDA
TDR-NBS-GS-000027 REV 00 ICN 01 IOF-5 April 2002 1

 

Natural Analogue Synthesis Repon
Is
io.
z
Eastng, In feet
Source: Simmons 2002 (1575781, SN-LANL-SCI-234-Vl, p. 67.
Figure 10.3-9. Thickness of SC Interbed in the Vicinity of the SDA

		- - - - - - - - - -
Easdng, In feet
	Soume: Simmons 2002 [157578], SN-LANL-SCI-234-VI, p. 67.
		FigurelO.3-10. Elevation of Top of C Basalt in the Vicinity of the SDA
TDR-NBS-GS-000027 REV 00 ICN 01 1 OF-6 April 2002 1

 

Natural Anloga Synttmis Report

		4M

	Essfirig, in feet
	Source: Simmons 2002 (1675781, SN-LANI.-SCI-23441, p. $8.
	Figure 10.3-11. Elevation of Top of CD tnterbed in the Vicinity of the SDA

	a- se0e MWKM i-MW MMIN -20~' - 21M 20000 XWOOs W-
Essfing, in %M
	Source: Simmns MM [157US], SN-LANL-SCI-234-Vl, p. 75.
	Figum 10.3-12. Depths and Elevations of Perched Watw in the Vicinity of the SDA
0
TDR-NBS-GS-000027 REV 00 ICN 01 IOP-7 April 2002 1

 

Natural Analogm Synthesis Repon
0
OA
.... H [.1
So.rce: Sirrm.rut 2002 [1575781. SN-LANL-SCI-234-Vl, p. 16.
Figure-10.3-13. Comparison of Steady-State Saturation Profiles for FEHM and FLOTRAN for Single-
Continuum Simulation
0
0
TDR-NBS-GS~000027 REV 00 ICN 0 1 IOF-8 April 2002 1

 

Natml Analog= Synthmis Report
0
02
0.5
0.4
03
02
0.1
0
Source: Simmons 2002 [1575781, SN-LANL-SCI-234-Vl, p. 20.
Figure 10.3-14. Liquid Saturation for the Single-Cwtinuum Simulation
0
0
TDR-NBS-GS-000027 REV 00 ICN 01 IOF-9 April 2002 1
DISTANCE DW

 

Nutu,s)
0
1.-:,
0.8
0 1
0 1
0.01
Source: Simmons 2002 [1575781, SN-LANL-SCI-234-Vl, p. 23. 

Figure 10.3-15a. No"alized Tracer Concentration after 50 Years for the Single-Continuum Model with
Constant Release
Os gs
N.
0.5
.4
N',
0.01
Sou"' Simmons 2002 (157578], SN-LANL-SCI-234-Vl, p. 23,
Figure 10.3-15b. Normalized Tracer Concentration after 50 years for the Single-Continuum Model with
Pulse Release
TDR-NBS-GS-000027 REV 00 ICN 01 IOF-10 April 2002
DigrANCE M
DlirrANCE rrrd

 

Natural Analogue Syntheiis Repon
08
ot
02

DEM1.]
Sou"e: Simmons 2002 (157578], SWLANL~SCI.23441, p. 24.
Figure 10.3-17. Comparison of Steady-State Saturation Profiles for Single- and Dual-Continuum
Simulations
07
as
OA
03
02
O'l
DEP7141,al
NOTE: Also Shom is the Pulse Release using FLOTRAN.
'9.o,ce: Simunors 2002 [1575781, SN-LANL-SCI-234-VI, p. 24.
Figure 10.3-16.  Com parison of FEHM and FLOTRAN for Normalized Tracer Concentration after 50 Years
fo, 'he Single-Continuum Model with Steady Releme at the Center of the Injection
Reg,on
TDR-NBS-GS-000027 REV 00 ICN 01 [OF-I I April 2002 1

 

Natmal Analogue Synftsis Ritixm
02
0.7
03
05
0.4
03
02
0.1
a
Sw": Sirnmons 2002 [157578], SN-LANL.SCI-234-Vl, p. 26.
Figure 10.3-1 aa. Liquid Satumtlon for Fractum Continuum
0
03
0 .7
as
CA
0.4
03
0.2
0.1
a
Souros: Sim- 2002 [1575781, SN-LANL-SCI-234-VI, p. 26.
Figure 10.3-18b. Liquid Saturefion for Matrix Corytlnuum
0
TDR-NBS-GS-000027 REV 00 ICN 0 1 IOF-12 Apil 2002 1
DigrANCE M
DigrANCE OW

 

Natural Analogue Synthesis Reeort
0
~O gs
N,
O.s
0 .4
0
0.01
Source: Smmons 2002 (1575781, SN-LANL-SCI-234.Vl, p. 27.
Figure 10.3-19a. Normalized Tmcor Cc,ncentratlon for Fracture Continuum
0
'T
V,
N
es
0.4
0
0.01
Soums: SIMMOM 2002 (1575781, SWI-ANI.-SCI-23441, p. 27.
Figure 10.3-19b. Normalized Trwer Concentration for Matrix Continuum
40
TDR-NBS-GS-000027 REV 00 ICN 01 [OF-13 April 2002 1
DISTANCE bd
DIGTANCE &W

 

Nataal Analogue Synthesis Repon
0
x,in mme
0
Source: Simmns 2002 [157578), SN-LANL-SCI-234-Vl, p. 76.
Figure 10.3-20. Hydrostrafigraphy
I
.0.01
41
44A
X, in niatm
NOTE: Armm indicate panicle-tracking ffm lines.
Source: Stnurions 2002 [1675781, SN-LANL-SCI-234-Vl, P. 83.
Figure 10.3-21. Steady-State Water Potentials
TDR-NBS-GS-000027 REV 00 ICN 01 [OF-14 April 2002 1

 

Natural Analogm Synthesis Repon
40
ol
03
,4
02
a .1
0
X, In memo
Source: Simmons 2002 [1575781, SN-LANL-SCI-234-VI, p. 88. 

Figure 10.3-22, Liquid Saturation at 50 Yeam
0
03
'A
0.
ol
0.1
X. In riveme
SO- Simmons 2002 (1575781, SN-LANL-SCI-234-Vi, p. 89.
Figum 10.3-23. Nomalized Tracer Cmcentration at 50 Yeam
0
TDR-NBS-GS-000027 REV 00 ICN 01 IOF-15 April 2002 1

 

Naturai Analogue Synthesis Report
0
6

iol-	0.1 mly
101-
	A.
101-

10-
10-
10-1-
0 0 OL75 LOO L25 1.50 L75 2.00
DEP7H C.]
Scv..: S,rnrn- 2002 [157578], SN-LANL.SCI-234-Vl, p 30.
FigurelO.3-24. Compa(tson of Field Data for Sorption of Cs, Pu, Am, and Sr for a Fiow Velocity of 0. 1
mlyr through the Surficial Sediment
0
0
TDR-NBS~GS-000027 REV 00 ICN 01 1 OF- 16 April 2002 1

 

Natural
0
0
North
I
IN
Peiia Bi
Adit)'cheim
5 meters
DTN: LB0202PBANALOG.001 (157610]
Figure 10.4-1. Schematic of Level +00 Adit Sampling Locations
0
TDR-NBS~GS-000027 REV 00 ICN 0 1 IOF-i7 April 2002 1

 

Natural Ar,,Iogue Syrihe- Repon
0
0 Figure 10.4-2. Photo of Samplirg Locations A, B, and C in the Nopal 1 +00 Adit
0
TDR-NBS.GS~O(X)027 REV 00 ICN 0 1 IOF-18 April 2002 1
DTN: LB0202PBANALOG.001 [157610]

 

N,(.,,il Amfl,,g- Snlh,,,, Ripin,
20
0
-20
o
-40
-60
-80
AIS-4 (3.1)
AS-3 (4.4) 0 smow
4111111111,
AS-2 (36 9)
.!QP .	AS-1 (67.5)
.
r
. ~C
e.,O Sample
I
z	Location
AS-1
j	12 m from adit entrance on +00 level
AS-2	1 5 m from adit entrance
AS-3	23 m from adit entrance
,z- -6(6-0) AS-4	8.5 m into north part of adit
AS-5 (6.5) AS-5	Perched water from borehole at + 10 level
AS-6	Abandoned mining camp supply well
-10 -5 0 5
DTN LB0202PBANALOG001 [1576101
NOTE Aiso shown is the p-am, of ne, global meteoric water line and SMOW (Standard Meal
Oic- Wat.O
Figure 10.4-3. Plot of 6D versus 6"0 for water samples collected (black circles) from Pena Blanda
during February 2000
0
I DR-NBS GS-000027 REV 00 ICN 01 [OF 19 April 2002 1

 

Natural Analogue Synthesis Report
0
0
0
6 .. . I P.. I. .... 1. ... I . .. I I .... 1. 1. 1. 6
(a)
5
5 An
4
4
CP 3
.01,
3
)IN 0 wbonataquar 9 2
o BH12pwd-ed
m acit seep water
2
lb- X 7
7
Pr/Pd = 0.4
10,
loe
tof ... I .... I .... I .... I , , I
6
5
4
3
2
0 2 4 6 8 0.0 0.1 0.2 0.3 0.4 0.5 0.6
1/[238U) (dpm/L)" rw (y)
NOTE: The dashed line in (a) delineates the positive linear correlation for waters sampled from
the UZ. Its slope and intercept can be used to dehve Pr (input from recoil) and Pd (input
from dissolution) by the model. (b) shows a rapid decrease of 234U/238U to a relatively
constant level within a couple of weeks after the water enters the UZ. The IOW 234U/238U
activity ratio of 1.39 in the carbonate aquifer as shown in (a) requires a PWPd ratio of about
0.4, about three times smaller than that in the UZ. 

(dpm/L)" values calculated from data in Table 10.4-1, using half-lives of 234 U and 238U.
Source: Modified from Pickeft and Murphy 1999 [110009], Figure 15.
Figure 10.4-4. (a) 234U/238U Activity Ratio vs. Reciprocal 238U Activity in Nopal I Waters and (b) 234U/238U
Activity Ratio (solid lines) and 238U Concentration (dashed line) as a Function of Water
Transit Time (z~j in the UZ
TDR-NBS-GS-000027 REV 00 ICN 01 1 OF-20
April 2002 1

 

Natural Analogue Synthesis
is
6
5
4
co
3
C%I 2
1
0
(a)
0
<> - wet season
-*---dry season
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 8 9
K>4
TT... .... I .... J.-I
(b) o wet seaso
o dry seawn
1/[238U] (dpm/L) -1
0
0
NOTE: Solid and dashed lines in (a) are linear regressions for samples collected during the dry
(February 2000 and March 2001 collections) and wet (August - September of 1995)
seasons, respectively. Dissolution of uranium is higher during the dry periods.
Source: Data values calculated from data in Table 10.4-1, using half-lives of 234 U and 238U.
FigurelO.4-5. 234U/238U Activity Ratio vs. Reciprocal 238U Activity in Nopal I Waters from (a) UZ and (b)
sz
TDR-NBS-GS-000027 REV 00 ICN 01 1 OF-21
April 2002 1

 

N-ul A-h,guc Sy,-ill-, R,,p I
0
0
Zi	ABWE

BOTSWANA

NAMIBIA
D

LES,

URBAN

CAPE TOWN

Source: Ja-el al. 1997 [1574891, Figure 1.
Figure 10.5-1. Lmation of Steenkampskraal, South Africa
40
TDR-NBS-GS-000027 REV 00 ICN 0 1 IOF-22 April 2002 1

 

Natural Analogue Synthesis Report
0
0
(a)
I
7
0.1
0.01 1
La Ce Pr Nd
10
0.1
r-
ED
Sm Eu Gd Th Dy
SK"S
__C3__=5
0.01 1
La Ce Pr Nd
Sm Eu Gd Th Dy
Source: Jarvis et al. 1997 [157489], Figures 3 and 4.
Figure 10.5-2. (a) Shale-normalized REE Paftern for Steenkampskraal Monazites and (b) REE
Distribution for Groundwater Samples Normalized to Average Steenkampskraw Monazite
TDR-NBS-GS-000027 REV 00 ICN 01 1 OF-23 April 2002

 

C)
1~
t'i
C)
0
0
Table 10.3-1. Chemical Characteristics of Selected Samples of Pore Water, Perched Water, and Groundwater
from Yucca Mountain and the Subsurface Disposal Area of INEEL
is
Location	Temp.		Ca	Mg	Na	K	ci	S04	HC03	Si02	F	N03	Data
	(OC)	pH	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	Source
Yucca	UZ- 14 pore water	28*	8.7	1.2	0.2	155	-	16	14	160	72.0	-	4	A
Mountain	(CHn)
	UZ-14 perched	25*	7.8	31	2.5	35	4.1	7.0	24.2	146.4	40.7	-	17.1	B
	water
	WT-3 saturated	31.8	7.6	11.2	1.0	49.0	3.9	6.0	18.3	138.5	56.0	2.3	5.7	c
	zone	I											I
INEEL	Borehole W02	5 to	8.1	46.1	15	188	1.5	27	133	508	-	0.2	-	D
	Lysimeter WOL01	10*	1						1		1
	Well 92 perched	13.5	8.4	29	17	120	12	81	64	290	22	0.4	-	E
	water
	(10/29/76)
	RWMC	13	8.1	45	15	9.0	2.8	13	27	180.4	28	0.2	3.0
	production well
	saturated zone
NOTE: *estimated temperature
Sources: A = Yang et al. 1996 [100194], Table 3, sample UZ-14/1563.6-1563.8/upl,2,3.
B = Yang et al. 1996 [100194], Table 6, sample UZ-14D.
C = DTN: GS980908312322.008 [145412].
D = Dicke 1997 [157410], Table 5.
E = Rightmire and Lewis 1987 [156441], Table 13, sample of 10/29/1976. 

F = USGS 2000 [157415], Table 4-2.
~0
CD
liz
0
a

 

Natural Analogue Synthesis Report
0
Table 10.3-2. Additional Water Inputs to the Waste-Disposal Area Due to Flooding
	Infiltration Rate	Total Equivalent Depth of
Year	(mlday)	Infiltrating Water (m)
1962	1.66 x 10'	0.166
1969	1.24 x 10'	0.124
1982	7.49 x 10-3	0.075
Source: Magnuson and Sondrup 1998 [156431], Table 2-3.
0
0
Table 10.3-3. Hydrologic Properties Used in the One- and Two-Dimensional Single-Continuum and
Dual-Permeability Models
Layer	Depth	Porosity	Permeability	Residual	Pore-size	Air Entry
				Saturation,	Distribution,	Parameter, a
	(m)		(M)	Swr		(Pa-')
Surficial sediments	0-5	0.50	6.8 x 10-13	0.194	0.401	1.642 x 10-4
Clay layer	5-6	0.05	1.0 x io-11	0.246	0.273	1.817 x 10-4
A-basalt	6-9	0.01	2.5 x 10-12	0.010	0.500	4.094 x 10-4
AB (9 m) interbed	9-10	0.57	1.0 x 10-11	0.246	0.273	1.817 x 10-4
B-basait	10-34	0.01	2.5 x 10-12	0.010	0.500	4.094 x 10'
BC (34 m) interbed	34-36	0.48	4.0 x 10-"	0.083	0.273	3.270 x 10-4
C-basait	36-73	0.01	2.5 x 10-12	0.010	0.500'	4.094 x 10-4
CD (73 m) interbed	73-76	0.57	4.0 x 10-15	0.246	0.273	1.817 x 10-4
D-basait	76-180	0.01	2.5 x 10-12	0.010	0.500	4.094 x 10-4
Basalt matrix		0.14	5.0 x 10-17	0.066	0.322	3.917 x 10-5
NOTE: A and aare pore-size distribution and air-entry parameters in the van Genuchten (1980 [100610]) moisture
characteristic functions (see Lichtner 2001 [156429]).
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 22.
TDR-NBS-GS-000027 REV 00 ICN 02 1 OT-2 May 2002

 

Natural Analogue Synthesis
Table 10.3-4. Sorption Reaction Stoichiometry and Parameter Values for a Nonelectrostatic Description
4D of Surface Complexation Reactions
0
		Surface Complex Reaction			log K	z
		Iron oxide
>FeO-	1 >FeOH	-1 H+				8.930	-1
>FeOH2'	1 >FeOH	1 H+				-7.290	1
>FeOAm'	1 >FeOH	-1 H+	1 Am ..			-1.240	2
>FeOAm(OH)2	1 >FeOH	-3 H+	1 Am ...	2 H20		15.29	0
>FeOHPuO'	1 >FeOH	1 H+	1 PU02'	-0.25 02(aq)	-0.5 H20	-2.010	2
>FeOHPU02	1 >FeOH	-1 H+	1 PU02+	-0.25 02(aq)	0.5 H20	6.210	0
>FeOHPU02+	1 >FeOH	1 PU02+				-4.790	1
>FeOHPuO3-	1 >FeOH	-2 H+	1 PU02+	1 H20		10.66	-1
>FeOHU03	1 >FeOH	-2 H+	1 U02++	1 H20		3.050	0
>FeOHU02'	1 >FeOH	1 U02++				-6.630	2
>FeOHNP02+	1 >FeOH	1 NP02+				-4.320	1
>FeOHNpO3-_	1 >FeOH	-2 H+	1 NP02+	1 H20		11.26	-1
>FeOSr+	I >FeOH	-1 H+	1 Sr++			5.3	-1
>FeOSrOH	1 >FeOH	-2 H+	1 Sr+,+	1 H20		14.14	-1
		Aluminosilicate
>Sio-	1 >SiOH	-1 H+				7.200	-1
>SiOPUO+	1 >SiOH	2 H+	1 PU02+	--0.25 02(aq)	--0.5 H20	2.600	1
>SiOPU02	1 >SiOH	-1 H+	1 PU02+			6.430	0
>SiOPU03H-	1 >SiOH	-2 H+	1 PU02+	1 H20		14.80	-1
>SiOU03H	1 >SiOH	-2 H+	1 U02'	1 H20		5.180	0
>SiOU03-	1 >SiOH	-3 H+	1 U02'			12.35	-1
>SiONP02	1 >SiOH	-1 H+	1 NP02+			3.720	0
>SiONP03H-	1 >SiOH	-2 H+	1 NP02+ -	1 H20		12.16	-1
>SiOAm++	1 >SiOH	-1 H+	1 Am ..			-0.7	2
>SiOAmO	1 >SiOH	-3 H+	I Am ..	1 H20		14.20	0
>AIO-	1 >A1OH	-1 H+				9.730	-1
>AIOH+	1 >A1OH	1 H+				-8.330	1
>AIOPuO+	1 >A1OH	1 PU02+	-0.25 02(aq) -0.5 H20		-1.03	1
>AIOPU02-	1 >A1OH	-2 H+	1 PU02+	-0.25 02(aq)	0.5 H20	16.85	-1
>AIOPU02	1 >A1OH	1 PU02+				3.090	0
>AIOU02+	1 >A1OH	-1 H+	1 U02'			-3.130	1
>AlONpO2	1 >A1OH	-1 H+	1 NP02+			4.670	0
>AIONP03H-	1 >A1OH	-2 H+	1 NP02+	1 H20		14.26	-1
>AIOAm++	1 >AlOH	-1 H+	1 Am..			-2.490	2
		Calcite
>PU02+	1>Ca'	-1 Ca++	I PU02+			-1.850	1
>U02'	1 >Ca'	-1 Ca++	1 U02'			-5.120	2
>NP02+	1>Ca'	-1 Ca'	1 NP02+			-2.350	1
>AmC03+	1>Ca'	-1 Ca++	-1 HC03-	-1 H+	1 Am++-+	-1.587	1
>Sr'+	1 >Ca++	-1 Ca'	1 Sr++			1.750	1
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vi, P.29.
TDR-NBS-GS-000027 REV 00 ICN 01 IOT-3 April 2002 1

 

Natural Analogue Synthesis Report
40
Table 10.3-5. Ion Exchange Selectivity Coefficients and Fitted Cation Exchange Capacity (CEC)
Cation	Selectivity Coefficient
Na+	1 .
cs'	12.5
Sr4,+	2.857
K+	5.
Mg++	2.
Ca'	2.5
	CEC (mol/kg solid)
	0.02
NOTE: Selectivity coefficients modified from
Appelo 1996 [156425], pp. 197.
Source: Simmons 2002 [157578], SN-LANL-SCI-
234-VI, p. 28.
4D
TDR-NBS-GS-000027 REV 00 ICN 01 IOT-4 April 2002 1

 

Natural Analogue Synthesis Report
0
0
0
Table 10.3-6. Composition of Injected Fluid
Table 10.3-6a.  Primary Species Properties
Species	Moiality	Total
Concentration	Activity Coeff.	Species Activity
Ratio/H+	Constraint
Ca ++	6.7143 x 10'	7.2355 x 10-4	6.7444 x 10-'	1.1936 x 10'	1 total
K +	3.0692 x 10-4	3.0692 x 10'	8.9884 x 10-'	4.0415	1 total
Mg ++	6.3025 x 10-4	6.9944 x 10'	6.8849 x 10-'	1.1908 x 10'	1 total
Na~	5.2197 x 10-3	5.2197 x 10-3	9.0166 x 10-'	5.2721	1 total
ci-	2.4696 x 10-3	2.4706 x 10-3	8.9884 x 10-'	-1.0162 x 101	-1 charge
S04 -2	5.9941 x 10-4	6.6627 x 10-4	6.5908 x 10-'	-1.8331 x 101	1 total
HC03-	4.4631 X 10-3	4.7528 x 10'	9.0166 x 10-'	-9.9048	1 total
F	1.9919 X 10-5	2.0154 x 10-5	9.0027 x 10-'	-1.2255 x 101	1 total
Si02(aq)	3.6615 x 10-4	3.6615 x 10-4	1.0000	-3.4363	1 total
H +	2.7897 x 10-8	2.0345 x 10-4	9.1373 x 10-'	0.0000	3 calcite
Al...	3.5938 x io-17	5.5068 x 10-10	4.4062 x 10-'	6.2189	3 K-feldspar
Fe++	1.0078 x 10-"	1.6446 x 10-11	6.7444 x 10-'	4.1123	3 goethite
Sr++	4.7300 x 10-13	5.0000 X 10-13	6.6693 x 10-1	2.7837	1 total
PU02+	9.9671 X 10-15	4.0000 x 10-9	9.0166 x 10-1	-6.4470	1 total
U02++	1. 1940 x 10-17	1.11 io x io-IO	6.6305 x 10-1	-1.8141	1 total
NP02+	7.1760 x 10-"	1. 1150 x 10-'0	9.0166 x 10-1	-2.5897	1 total
Am...	7.5783 x 10-14	2. 0000 x 10-"	4.0148 x 10-'	9.5429	1 total
Cs+	4.0000 x 10-13	4.0000 X 10-13	8.9736 x 10-'	-4.8435	1 total
02(aq) 7	1 .2611 x 10 -48	-1.0030 x 10-9	1.0000	-4.7899 x 10'	402(g)
Solution conditions:
Temperature: 25.OOC Ionic strength: 1.0087 x 10-2 Solution density: 0.99780 g/CM3
pH: 7.5936 pe: 1.931 Eh: 1.1430 x 10-1 V
Charge balance: -q = -6.3071 X 10-16
Computational parameters:
Boundary condition: type 1 Iterations: 5
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 31.
TDR-NBS-GS-000027 REV 00 ICN 02 1 OT-5 May 2002

 

Natural Analogue Synthesis Report
0
0
Table 10.3-6 continued. Composition of Injected Fluid
Table 10.3-6b. Properties of Complexes
Complex	Molailty	Activity Coeff.	Species Activity/H+	log K
C02(aq)	2.25165 x 10'	1.0000	-3.6475	6.3414
MgS04(aq)	4.43159 x 10-'	1.0000	-4.3534	2.4125
CaS04(aq)	2.25424 x 10'	1.0000	-4.6470	2.1004
CaHC03+	2.23075 x 10-5	0.90166	2.9029	1.0429
MgHC03+	2.08899 x 10'	0.90166	2.8744	1.0329
C03-2	1.12691 x 10-'	0.66305	-20.057	-10.325
CaC03(aq)	7.00620 x 10'	1.0000	-5.1545	-7.0088
MgC03(aq)	3,01655 x 10--'0	1.0000	-5.5205	-7.3562
mgci+	7.76285 x 10-7	0.90166	1.4445	-0.13865
OH-	4.44777 x 10-7	0.90027	-13.906	-13.991
CaCl+	2.22229 x 10-7	0.90166	0.90124	-0.70039
MgF+	1.92570 x 10-7	0.90166	0.83903	1.3486
CaF+	4.28435 x 10-8	0.90166	0.18632	0.67736
Pu(OH)4(aq)	3.99990 x 10-'	1.0000	-8.3980	-13.920
CaOH+	2.78300 x 10 -9	0.90166	-1.0010	-12.850
A102-	5.49982 x 10-"	0.90166	-16.814	-22.879
CaC12(aq)	4.95545 x 10-'0	1.0000	-9.3049	-0.65346
U02(CO3)3-4	5.83351 x 10-"	0.18815	-40.452	-9.4530
U02(CO3)2 -2	5.18682 x 10-11	0.65908	-25.394	-3.7613
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 90.
TDR-NBS-GS-000027 REV 00 ICN 02 1 OT-6 May 2002

 

Natural Analogue Synthesis Report
0
0
Table 10.3-6c. Mineral Saturation Indices
Mineral	Saturation Index	log K
Dolomite	1.16594	-2.52402
Hematite	9.59704 x 10-'	1.68702 x 101
Quartz	5.69305 x 10-'	4.00565
Chalcedony	2.98104 x 10-'	3.73444
Goethite	0.00000	7.95526
Calcite	0.00000	-1.85424
K-feldspar	0.00000	2.94216 x 10-'
Pu(OH)4	-1.57462 x 10-1	-5.67951
Magnesite	-4.62767 x 10-'	-2.29848
Si02(am)	-7.16385 x 10-'	2.71996
Kaolinite	-1.70898	-6.79726
Gibbsite	-1.77543	-7.75591
Muscovite	-1.90002	-1.35668 x 101
Gypsum	-2.27448	4.47292
Beidellite-Ca	-2.29087	-5.56815
Sepiolite	-3.72692	-3.04075 x 10'
Brucite	-4.47379	-1.62984 x 101
Magnetite	-5.38525	6.50570
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 32.
Table 10.3-6d. Gas Compositions
Gas	log Partial Pressure	Pressure (bars)	log K
02(g)	-45.00	1.0000 X 10-45	2.8993
C02(g)	-2.180	6.6104 x 10-3	7.8092
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 32. 

TDR-NBS-GS-000027 REV 00 ICN 02 IOT-7 May 2002

 

Natural Analogue Synthesis Report
Table 10.3-7. Fifted Surface Complexation Site Densities
Site	Concentration (mol/bulk dM3)
>FeOH	4.0 x 10-7
>AIOH, >SiOH	5.0 x 10'
>Ca++	1.0 x io,
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 28.
Table 10.3-8. Contribution of Radionuclides to Surface Complexation Sites
0
0

Component Site	Mineral Kd
(dm'/dM3)	Retardation:
I + Kd
% Adsorbed
Sr++	>FeOH	5.9996 x 10-'
	>SiOH	0.0000
	>AIOH	0.0000
	>Ca++	4.9530 x 10'
Total of all sites:	6.4949 x 10-'	1.0001	6.4945 x 10-'
PU02+	>FeOH	2.3473 x 10'
	>SiOH	1.7024 x 10-11
	>AIOH	3.4754 x 10'
	>Ca++L	7.0217 x 10'
Total of all sites:	5.8227 x 10'	5.9227 x 10'	9.8312 x 10'
U02++	>FeOH	4.4734 x 10-2
	>SiOH	1.1785 x 10'
	>AIOH	5.7571 x 10'
	>Ca++	4.1468 x 10-6
Total of all sites:	5.1674 x 10'	1.0517	4.9135
NP02+	>FeOH	7.7954 x 10'
	>SiOH	7.5785 x 104
	>AIOH	7.5055 x 10'
	>Ca++	5.7351 x 10'
Total of all sites:	7.5785 x 104	7.5786 x 104	9.9999 x 101
Am...	>FeOH	4.9624 x 10-1
	>SiOH	3.9129 x 10-1
	>AIOH	2.8157 x 10'
	>Ca++	4.0926
Total of all sites:	3.3137 x 10' i	3.4137 x 101	9.7071 x 10'
Source: Simmons 2002 [157578], SN-LANL-SCI-234-Vl, p. 33.
TDR-NBS-GS-000027 REV 00 ICN 02 1 OT-8
May 2002

 

8
3
16
0
C)
t')
0
0
0
Table 10.4-1. Measurements of U-Th Isotopic Composition and Concentration in Various Water Samples Collected near the Nopal I Uranium
Deposit
Sampling Location	Sample ID	Collection Date	U (ppb)	(+/-)
N	234U,211U
atom ratio
(X 10-)	(+/-)
N	BD
(%0)	S"O
(%0)	Notes
Perched water from
borehole at +10 level	BH12W95-5	August 1995	4.79	0.20	119.66	0.18
	BH12W95-11	September 1995	5.77	0.25	120.86	0.14
	AS-5	25 February 2000	5.73	0.19	156.75	0.10	-64	-9.3
	030701 2001	7 March 2001	10.40	0.19	112.59	0.11
8.5 m into north part of
adit at +00 l
l	ADIT95-6	September 1995	0.20	2.4	278.40	0.16
eve	AS-4	25 February 2000	2.87	0.30	121.15	0.25	-1	-2.8
	030701-02	7 March 2001	1.20	0.24	142.05	0.20			E in Figure 10.4-1
23 m from adit entrance	ADIT95-9	September 1995	0.89	0.54	156.16	0.11
	AS-3	February 2000	4.03	0.19	64.61	0.18	-7	-3.6
	030701-03	7 March 2001	26.96	0.18	64.36	0.10			D in Figure 10.4-1
15 m from adit entrance	AS-2	25 February 2000	36.92	0.19	51.53	0.16	-7	-3.4
	030701-04	7 March 2001	16.49	0.28	50.51	0.40			C in Figures 10.4-1, 10.4-2
12 m from adit entrance	AS-1	25 February 2000	68.46	0.19	58.21	0.14	-11	-2.5	B in Figures 10.4-1, 10.4-2
5 m from adit entrance	030701-05	7 March 2001	13.01	0.23	56.14	0.20			A in Figures 10.4-1, 10.4-2
Abandoned mining camp
supply well	AS-6	25 February 2000	2.53	0.25	64.93	0.30
Pogos Ranch	WVW95-03	September 1995	0.17	2.8	76.02	0.22			Well
	AS-7	25 February 2000	0.27	1.0	140.00	1.0	-61	-8.7	Holding Tank
	F030701-06 1	7 March 2001	5.71	0.19	111.69 1	0.10 i			Holding Tank
Source: 1995 samples from Pickeft and Murphy 1999 [110009], Table 11.
2000 and 2001 samples from Simmons 2002 [157578], SN-LANL-SCI-237-Vl, p. 16; SN-LBNL-SCI-108-Vl, pp. 86, 87.
z
CD

 

Natural Analogue Synthesis Report
11. ANALOGUES TO THERMALLY COUPLED PROCESSES
11.1 INTRODUCTION
Numerous igneous-intrusion contact zones have been examined with the objective of
understanding chemical reactions and migration of elements away from the heated contact zone,
as well as understanding thermal-hydrologic-chemical (THC) effects. A number of these studies
are described in CRWMS M&O (2000 [141407]; 2000 [151945], Section 13), as summarized by
the following.
The effects of shallow (<500 m) magmatic intrusions into unsaturated host rocks can be quite
different from effects associated with deeper hydrothermal systems. Deeper, saturated
hydrothermal systems may display evidence that a large-scale hydrothermal cell was established
(Brookins 1986 [109877], p. 337). In contrast, both the Banco Bonito study (Stockman et al.
1994 [117820], p. 88) and the Grants Ridge basalt intrusion study (WoldeGabriel et al. 1999
[110071], p. 409) indicate that the effects of high-temperature (-850'C; Stockman et al. 1994
[ 117820], p. 88) intrusions into these unsaturated environments appear to have been slight, to
have been limited to within 10 m or so of the contacts, and to show no evidence of fluid-driven
convective. heat transfer or pervasive hydrothermal alteration of the country rock. These field
studies, along with the Paiute Ridge field studies (see Section 11.4), provide limiting high-
temperature-case natural analogues for evaluating THC processes resulting from the heat
released by the decay of radioactive waste in an unsaturated environment.
4D A good analogy for understanding future water-rock interactions at the mountain scale is the
fossil hydrothermal system at Yucca Mountain itself Most zeolitic alteration occurred 13 to 11.6
Ma, at about the same time as tuff emplacement (Bish and Aronson 1993 [100006], p. 148).
After formation of the major zeolitic horizons, deep-seated hydrothermal activity persisted until
about 10 Ma. This activity was evidently limited to temperatures of 90-100T, because at
prolonged exposure to temperatures greater than 90T, the sorptive zeolites clinoptilolite and
mordenite are altered to the nonsorptive minerals analcime plus quartz and/or calcite, and this
transformation did not occur.
Section I I reports analyses conducted since CRWMS M&O 2000 [141407] of THC and
thermal-hydrologic-mechanical (THM) natural analogue studies. Section 11.2 presents the
results of an extensive survey of geothennal literature for the purpose of obtaining insights from
coupled processes operating in geotherrnal fields. Section 11.3 then provides a detailed
examination of THC processes relevant to the Yucca Mountain drift-scale system, observed at
the Yellowstone, Wyoming, geothermal field. Section 11.4 presents results of a field
investigation and modeling study of evidence left in a fossil hydrothermal system at Paiute
Ridge, Nevada. Next, examples are given in Section 11.5 of evidence for THC effects on
transport. Section 11.6 reports THM effects to a potential repository from a number of settings
with analogous conditions. 

 Finally, Section 11.7 summarizes what can be leamed about THC and
THM coupled processes relevant to a potential high-level waste repository at Yucca Mountain.
Information found in Sections 11.2 through 11.5 may help to support arguments associated with
KTI KUZ 0407 listed in Table 1 - 1.
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11.2 GEOTHERMAL ANALOGUES TO YUCCA MOUNTAIN THERMAL-
HYDROLOGIC-CHEMICAL PROCESSES
11.2.1 Objectives
The goal of Section 11.2 is to demonstrate the utility of geothermal systems as natural analogues
for . processes that are expected to occur in the potential Yucca Mountain repository. The primary
objective of Section 11.2 is to use geothen-nal systems as natural analogues for illustrating
coupled processes that impact permeability, fluid flow, and chemical transport. The introduction
to this section notes some of the key THC processes observed in geothen-nal systems, and how
these processes might impact the potential Yucca Mountain repository. A summary of key
components of geothermal systems is then presented, followed by a description of the potential
Yucca Mountain repository and a discussion of limitations of geothermal analogues for the
Yucca Mountain system. The main body of this report consists of descriptions of geothennal
analogues for each of the key THC processes identified. This is followed by a discussion of how
these processes could impact the total site performance. Finally, suggestions are made for
additional work that would further extend the use of geothermal systems in the validation and
confin-nation of Yucca Mountain models. The initial stages of a literature survey identified the
Yellowstone geothermal system as particularly relevant for the Yucca Mountain system. Detailed
analysis of core samples from Yellowstone was conducted to supplement previous studies of the
Yellowstone geothennal system. The results of this work are described in detail in Section 11.3
of this report.
11.2.2 Introduction
Geothennal systems can be used as a natural laboratory for examining many of the coupled THC
processes expected for the potential nuclear waste repository at Yucca Mountain, Nevada
(Simmons and Bodvarsson 1997 [126511 ]; CRWMS M&O 2000 [141407]). Key processes that
are expected to occur in the potential high-level nuclear waste repository at Yucca Mountain,
such as boiling and condensation and mineral dissolution and precipitation, and their effects on
pen-neability, fluid flow, and radionuclide transport, can be observed in many geothermal
systems. Piior use of geothermal systems as natural analogues has focused on the verification of
geochemical models (e.g., Meijer 1987 [101345]; Apps 1995 [154615]; Bruton et al. 1995
[ 117033]). However, active and fossil geothermal systems can also yield important insights into
the consequences of processes such as boiling, condensation, fluid mixing, and water-rock
interaction associated with fluid flow in mattix and fractures (Figure 11.2-1). These systems
allow observation of the effects of processes over much longer time scales than are possible in
laboratory or field testing, and provide a benchmark for coupled process modeling.
Characterization of the effects of water-rock interaction (such as mineral precipitation and
dissolution) on matrix and fracture permeability in geothen-nal systems can then be used to
estimate potential changes in fluid flow resulting from the thermal impact of storing high-level
nuclear wastes in fractured ash flow tuffs.
This study builds upon an earlier review of geothermal systems as natural analogues (Simmons
and Bodvarsson 1997 [126511 ]; CRWMS M&O 2000 [141407]). This study expands the scope
of the earlier review by including additional THC processes that are observed in geothermal
systems and incorporates the results of new geothen-nal studies as part of a literature review. 
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Because no single geothermal analogue is suitable for all elements of Yucca Mountain, the
geothermal analogues are used to evaluate the effects of individual THC processes, with multiple
geothermal examples examined for each process of interest.
11.2.3 Similarities between Geothermal Systems and Yucca Mountain
There are many similarities between geothermal systems and an anthropogenic (man-made)
hydrothermal system that would be created by the emplacement of high-level nuclear waste. 
 For
most geothermal systems, intrusion of magma at shallow crustal levels results in high heat flow
and the formation of a convective hydrothennal system with associated water-rock interaction. In
the anthropogenic system, heat-generating nuclear waste would induce changes in the ambient
system. Both types of systems are subjected to coupled THC processes (Table 11.2-1) such as
conductive and advective heating, fluid flow and chemical transport through matrix and
fractures, boiling and condensation, and mineral dissolution and precipitation. These processes
can result in important changes in the fluid flow properties of the rocks surrounding the heat
source over time.
The use of geothermal systems as natural analogues for THC processes is most applicable for the
higher temperature (above boiling) operating mode, because many of the processes mentioned in
Table 11.2-1 would have little effect on a cooler, sub-boiling repository. These processes will
have a greater impact in the near-field area, where the effects of heating (and associated THC
processes) are expected to be most pronounced. For all cases, the magnitude of the effects of
many THC processes (such as boiling, condensation, mineral dissolution, and precipitation) is
envisioned to be significantly reduced at Yucca Mountain as a result of the much lower
40 anticipated fluid and thenTial flux rates than those observed in active geothermal systems. Key
differences between geothermal systems and Yucca Mountain are described in Section 11.2.7.
However, geothennal systems provide well-constrained examples of how THC processes can
modify important hydrogeologic properties (such as porosity, perrneability, and sorptive
capacity) that would affect the total system performance of a geologic high-level radioactive
waste repository.
11.2.4 Key Physical Components of Geothermal Systems
Prior to providing detailed evaluation of geothermal systems of natural analogues, it is
worthwhile to examine the key components of these systems. While geothermal systems are
found in a vaiiety of geologic and tectonic environments and have many different characteristics,
they all share a number of common traits. These include: (1) heat source, (2) fluids, (3),
penneable flow paths, and (4) impermeable boundaries. Another important feature present in
many vapor-dominated geothermal systems is a heat pipe, consisting of a boiling zone and
condensation zone. Each of these features is discussed below.
11.2.4.1 Heat Source
Most active geothermal systems have magmatic heat sources, consisting of shallow intrusions
that provide a high-level heat source for periods ranging from 100,000 to over 1,000,000 years.
These intrusive bodies also supply magmatic components (such as water, C02, S02, and HCI)
that often control the chemistry of the reservoir fluids. For example, the granitic pluton
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underlying The Geysers geothermal field in Califomia was emplaced around 1.2 Ma (Dalrymple
et al. 1999 [1563741, pp. 293-297), serving as a long-lived heat source for the still-active
geothermal field. The Krafla and Ndmafjall geothermal fields, located along the Mid-Atlantic
Ri ft Zone in Iceland, are much younger systems, where recent ongoing volcanic activity (1975-
1984) led to the injection of magma into an existing geothermal well bore (Larsen et al. 1979
[155885]).
11.2.4.2 Fluids
Geothermal energy is extracted from local thermal anomalies in the earth's crust through the
withdrawal of heated fluids. These fluids have a number of origins: connate (formation) waters,
surface (meteoric) waters, juvenile (magmatic) waters, and seawater. The relative amounts of
these fluids depend greatly on the geology and tectonic environment, the groundwater hydrology,
the local climate, and the size and composition of the cooling and degassing intrusive heat
source. The origin and abundance of these fluid types in geothermal systems can be determined
through isotopic and geochemical study of fluid compositions (e.g., Giggenbach 1997 [156338];
Kennedy and Truesdell 1996 [156339]; Arn6rsson 1995 [156321]).
11.2.4.3 Permeable Flow Paths
The development of a convecting geothermal reservoir (and the successful exploitation of such a
resource) depends on the presence of high-permeability pathways. Many geothermal reservoirs
are hosted by rocks with low matrix penneabilities, resulting from either intrinsically low
pen-neabilities (i.e., intrusive igneous rocks and welded ash flow tuffs) or from hydrothennal
alteration. 

 The presence of a high-permeability fracture network in many geothermal systems
allows for the heated fluids to flow convectively within the reservoir. Such pen-neable fracture
networks may be generated by faulting occuning within tectonically active areas (Moore et al.
2001 [156320]; Forster et al. 1997 [1563551).
11.2.4.4. Impermeable Seals
The longevity of a geothermal resource depends on the presence of an impenneable cap above
the reservoir. Without such a cap, heated fluids would buoyantly rise to the surface, rapidly
dissipating the heat of the source. This impermeable barrier may result from a pre-existing low-
permeability formation, but often develops as a result of extensive argillic alteration occurring at
temperatures of 100-200T. Lateral penneability barriers along the margins of geothermal
systems can form by precipitation of retrograde solubility minerals, such as anhydrite and calcite,
from descending (and heating) fluids along the margins of a geothennal system (Allis and Moore
2000 [156316], p. 215).
11.2.4.5 Heat Pipes
Geothen-nal heat pipes have been described for a number of vapor-dominated geothermal
systems (Ingeblitsen and Sorey 1988 [1375371; Allis and Moore 2000 [156316]). In a
geothermal heat pipe (Figure 11.2-1), water boils at the heated (lower) end, and water vapor
migrates to the cooler region where it condenses and the heat of vaporization is released. The
condensed water then flows back to the heated end by gravity or capillary forces. The region
within the heat pipe will be at a nearly uniform temperature near the boiling point of water. The
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condensate water will be undersaturated with respect to the host rock minerals and will begin to
dissolve constituents from the rock and gases locally present. Some of the water containing the
dissolved constituents will flow through the fractures back down towards the heat source. Water
flowing back towards the heat source will boil again, precipitating the formerly dissolved solids.
The repeated dissolution and precipitation will affect fracture perineability by locally widening
apertures where dissolution takes place, or narrowing apertures where precipitation occurs.
The heat-pipe features observed in geothermal systems have also been demonstrated in smaller-
scale laboratory experiments. A heat-pipe reactor was built using tuff chips from Yucca
Mountain and operated for 30 days (Rimstidt et al. 1989 [142190]). In the top region
(condensation zone), etching and dissolution were observed. In the center region, few indications
of dissolution or precipitation were observed. In the bottom region, extensive precipitation was
observed with silica, iron oxyhydroxides, stilbite, and possibly clays fonning. A layer of rock
grains tightly cemented with amorphous silica formed at the face of the heater; this
mineralization would result in reduced pen-neability. Similar heat-pipe features were also
observed in the column tests reported in Lowry (2001 [157900]).
11.2.5 Characteristics of the Potential Yucca Mountain Repository
The potential nuclear waste repository is sited within a section of crystal-poor, devitrified,
moderately to densely welded Topopah Spring tuff that forms part of a 1,000 m (3,300 ft) thick
section of 11-14 Ma ash flow tuffs at Yucca Mountain (CRWMS M&O 1997 [100223], Figure
35). 

 The repository horizon is overlain by 300 m (980 ft) of nonwelded to densely welded tuff,
and underlain by a sequence of nonwelded to densely welded Miocene ash flow tuffs, older
Tertiary volcanic and sedimentary rocks, and Paleozoic dolomites. The repository would be
located within the unsaturated zone (UZ), 350 m (1,150 ft) above the regional water table
(Figure 11.2-2). The potential repository is located in fractured unsaturated host rock with very
low matrix permeability. The combination of low matrix permeability and unsaturated rock helps
keep water from waste packages, thus retarding unwanted processes such as corrosion of the
waste packages, dissolution of the waste materials, and transport of radionuclides to local
aquifers. Fluid flow along high-permeability fractures may, however, result in seepage.
The higher-temperature operating mode (BSC 2001 [155950], Section 2.3) consists of a drift
spacing of 81 m (266 ft), with drip shields, line load waste packaging, and 50 years of drift
ventilation after the waste has been emplaced. These design attributes (see also Section 2 of this
report) are used to minimize seepage onto the waste containers, limit peak temperatures in the
drifts, and reduce the likelihood of the development of coalescing boiling zones, thus permitting
drainage to occur in the pillar regions between the drifts. For the higher-temperature operating
mode, maximum temperatures of around 120'C are predicted for the drift wall (BSC 2001
[155950], Section 4.3.5.3.3), with temperatures greater than 100'C predicted to persist in the
waste package and near-field for 1,000-2,000 years. Other design possibilities also under
consideration include a lower-temperature operating mode in which the maximum temperature at
the drift wall will never exceed 85'C (BSC 2001 [155950], Section 3.2.5).
The near-field repository environment is predicted to undergo two distinct phases resulting from
the then-nal loading: dryout and rewetting. Dryout is predicted to occur as the waste packages
transfer their heat to the surrounding enviromnent. The size of the dryout zone will vary with
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time and may extend up to 13 m (43 ft) away from the drift walls, depending on waste package
configuration (BSC 2001 [154677], Section 6.4.5.1). Duiing the dryout phase, liquid water will
be converted to water vapor, which will effectively displace air from this zone. This is important
because the oxygen necessary for many corrosion reactions will be present only in low
concentrations. As the heat output from the waste package diminishes with time, dryout zones
are predicted to gradually undergo rewetting from reflux Of C02-replenished condensate and
ambient percolation. The rewetting will be accompanied by an influx of air back into the near-
drift environment as temperatures drop below the local boiling point and slowly approach
ambient (pre-repository) then-nal conditions (BSC 2001 [154677], Section 6.6.5).
Subsurface fluid flow for the Yucca Mountain area is controlled by the penneability and
unsaturated hydraulic properties of the Miocene ash flow tuff sequence. Densely welded sections
of the tuff have very low matrix pen-neabilities, and fluid flow through these sections is
controlled by faults and fractures. Nonwelded tuffs have significantly higher matrix
permeabilities and fewer fractures, and thus matrix flow appears to be the dominant process in
these sections. These differences in matrix and fracture permeability as a function of welding
(Figure 11.2-3) are characteristic of ash flow tuff deposits (Winograd 1971 [156254]). 

 The
potential repository is located within a densely welded devitrified tuff (Figure 11.2-2), and thus
bulk permeability for this horizon is controlled by fractures.
Fracture permeability depends on a variety of fracture characteristics, including fracture
orientations relative to the regional stress field, fracture density and spacing, fracture apertures,
and the presence or absence of mineralization within the fractures. Field permeability
measurements have been made at the Yucca Mountain Exploratory Studies Facility (ESF) to
evaluate the variability of permeability and identify controlling factors. The matrix penneability
of the welded Topopah Spring tuff (TSw) is 3 to 6 orders of magnitude lower than the fracture
penneability (LeCain 1997 [100153], pp. 28-29), so fluid flow within this formation should be
highly focused along fractures.
11.2.6 Time Scales of Geothermal Processes
Time scales of processes expected to occur in a geologic nuclear waste repository are compared
with processes that occur in geothennal systems shown in Table 11.2-2. Because of these very
long and variable time scales, it is not possible to create a scale model of a potential nuclear
waste repository, study all of these processes for a short while, and then extend this knowledge to
real repository future behavior. Laboratory and field-scale studies have been conducted and
others are currently underway to study some of these processes for the purpose of model
validation. Computer-based numerical modeling is being used to interpret and extend these
results within a framework of well-understood physical laws and data.  The same processes
expected to occur at a geologic high-level nuclear waste repository at Yucca Mountain have been
occurring over the long-ten-n in geothennal systems, making the study of geothermal systems
highly relevant to the long-tenn understanding of possible repository behavior.
11.2.7 Lindtations of Geothermal Analogues
It is important to note several important differences between most geothermal analogues and the
potential Yucca Mountain repository:
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The potential Yucca Mountain repository is located within unsaturated rocks, while most
geothermal systems have saturated conditions. While the repository may develop locally
saturated areas (such as the condensation zone), this difference should result in reduced
water-rock interaction for the then-nally loaded repository system. Convective liquid flow
will not develop under unsaturated conditions, and thus thermal and fluid fluxes for the
Yucca Mountain system will be significantly lower than those found in high-temperature
geothermal systems. Advective transport will still occur within the fracture network, and
thus chemical transport rates could be fairly rapid along the fast flow paths within the UZ
at Yucca Mountain. Several natural analogues that have experienced elevated
temperatures under unsaturated conditions (Banco Bonito, New Mexico, and Paiute
Ridge intrusive complex, Nevada) exhibit very little hydrotherrnal alteration resulting
from the heat pulse event (Stockman et al. 1994 [117820]; Lichtner et al. 1999 [121006];
and Section 11.4 of this report).
o Liquid-dominated geothermal systems have increasing hydrostatic pressures with depth,
reflecting the presence of a hydrostatic column. Boiling within a geothermal system at
depth thus occurs at progressively higher temperatures (following the boiling point-depth
curve). Because Yucca Mountain is an unsaturated system, fluid pressures will typically
not exceed atmospheric pressure, and thus boiling should occur at temperatures around
96'C throughout the system.
The higher-temperature operating mode for the potential Yucca Mountain repository is
predicted to have an areally restricted and short-lived (1,000-2,000 yrs) higher
temperature (>IOO'C) pulse, thus limiting the time when boiling and condensation
processes could occur. In addition, because of the unsaturated nature of the Yucca
Mountain system, dryout zones should develop around the high-temperature repository
drift areas, also serving to reduce the potential impact of water-rock interaction.
9 For the lower-temperature operating mode, drift-wall temperatures will never exceed
boiling point values, and thus precipitation of dissolved species resulting from boiling
will not occur. Some increase in the concentration of dissolved species may result from
evaporation in this case. The lower predicted temperatures in this operating mode will
also result in less extensive water-rock interaction, with reduced amounts of mineral
alteration, dissolution, and precipitation.
0 Speciation and transport of dissolved species may be affected by the redox state of the
system. Geothen-nal systems are typically somewhat reducing in nature (as evidenced by
the presence of H2S rather than S02 in most geothermal fumarolic gases), whereas the
Yucca Mountain system is expected to be more oxidizing (owing to the presence of
atmospheric oxygen in the gas phase). This difference in oxidation state could affect the
transport and precipitation of chemical components with multiple oxidation states (such
as Fe 2+/Fe 3+ and U4+/LJ6+), but should not significantly impact the behavior of important
sealing species such as silica.
9 Gas compositions of geothennal systems differ significantly from that predicted for
Yucca Mountain, which lacks a magmatic fluid component. 

While both systems will
contain C02 and air, most geothermal systems also contain significant amounts of sulfur-
  11-7 

 

 
bearing gases (typically H2S) that can lead to the development of acidic fluid
compositions when oxidized.
11.2.8 Geothermal Examples of Heat and Fluid Flow
Many geothermal systems worldwide have been the subject of heat and fluid flow studies. Fluid
flow in geothermal systems is controlled in part by thennal buoyancy effects, chemically
controlled density contrasts, and channelized flow resulting from pen-neability baniers. Drilling
of exploration and production wells in developed geothermal fields facilitates the collection of
downhole temperature and pressure data. Production flow and tracer tests also permit the
detennination of fonnation pen-neability and fluid flow paths and rates. Reservoir simulation
models have been widely used along with such data to predict future heat and fluid flow behavior
in commercial geothermal reservoirs under production (e.g., Bodvarsson et a]. 1993 [138618];
Steingrimsson et al. 2000 [156686]; also see Section 11.2.8.2). The ability of these models to
accurately forecast changes in reservoir behavior provides confidence that similar models
developed for Yucca Mountain will reasonably simulate future repository performance. Two
aspects of heat and fluid flow in geothermal systems are discussed in detail below. The first topic
is the role of faults and fractures in providing high-perimeability pathways for fluid flow within
the convecting geothennal reservoir. The second topic is the use of numerical models to create
natural-state models and to simulate the effects of production and reinjection on geothennal
reservoirs.
11.2.8.1 Fracture-Dominated Fluid Flow
Many geothermal systems have reservoir rocks with relatively low matrix permeabilities, but
high overall fonnation permeability caused by the presence of a high-permeability fracture
network (Bodvarsson and Witherspoon 1989 [156337], p. 3). For some systems, this network is
dominated by a few large-scale faults that control both the location of surface thermal features as
well as fluid flow in the subsurface. Several examples of these geothermal systems are described
below.
Dixie Valley, Nevada
The Dixie Valley geothermal field is located along the active Stillwater normal fault, in an area
of high regional heat flow in the Basin and Range province of Nevadd. The production wells are
targeted to intersect strands of this fault at depth. Interference and tracer tests conducted in this
field demonstrate that the high-permeability wells are well connected by a high-pen-neability
fracture network. In a tracer test at Dixie Valley, three tracer combinations were introduced into
three wells (Adams et al. 1989 [156348), pp. 215-217). Pre-test modeling based on the porous
medium approximation identified seven well pairs that were expected to show tracer
breakthrough. Only one well produced tracer, identifying a connected fracture network between
the injection site and the producing well. The minimum velocity (based on a straight line
between injection and the producing well) for the tracer front was 5 M/hr, and the minimum
velocity for the tracer peak was 1.4 m/hr. As part of another investigation at Dixie Valley, a
series of four tracer tests was performed (Rose et al. 1998 [156341]). Tracers were introduced in
pulses in target injection wells located in the southem and central portions of the field.

The
0 tracers were detected only in a cluster of seven wells located between the injection wells. The
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amount of short-circuiting between the wells differed for each injection well, with one of the
40 wells having a much shorter residence time than the others, indicating heterogeneity in the
fracture network. Breakthrough curves presented by Rose et al. (1998 [156341], Figure 2) can be
used to calculate tracer-front minimum velocities ranging from about 0.7 to 3 M/hr (average =
1.6 m/hr) and peak minimum velocities ranging from about 0.4 to 0.8 m/hr (average = 0.6 m/hr).
Silangkitang, Indonesia
The Silangkitang geotherinal field is one of several geothermal systems located along the Great
Sumatran fault zone. The main thermal features are located along surface traces of this major
stiike-slip fault (Gunderson et al. 1995 [156361], p. 691). Exploration wells drilled directionally
to penetrate the main trace of the fault encountered extremely high fluid flow rates within the
fault zone (Gunderson et al. 2000 [1563101, Figure 4, pp. 1184-1185). In contrast, nearby
vertical wells that do not intersect the fault have very low fon-national penneabilities, thus
underscoring the importance of the fault in providing high-permeability flow paths. Higher
temperatures and increased alteration were encountered near the fault, which serves as an upflow
zone for this geothennal system (Moore et al. 2001 [1563201, pp. 1190-1191).
Wairakei, New Zealand
The Wairakei geothennal field is located in the Taupo Volcanic Zone, a tectonically active area
that has been the site of voluminous Quatemary volcanism. Normal faults cutting the area appear
to be the piimary conduits for high-volume fluid flow. Grindley (1965 [154663]) identified three
groups of wells based on their relative deliverabilities. Wells intersecting faults have very high
permeabilities (>I darcy) that cannot be precisely quantified because of a lack of pressure
drawdown during production tests. Wells drawing on reservoir storage have pronounced
drawdown, with calculated permeabilities ranging from 5-30 millidarcies. Nonproductive wells
typically intersect hydrothermally cemented rocks with intrinsically low (<I millidarcy)
permeabilities. The intensely altered, impermable rocks serve to protect the producing reservoir
from cold water encroachment. Tracer tests conducted at Wairakei (Jensen and Home 1983
[156643], Table 1) suggest minimum flow velocities along fractures that are as high as 38 m/hr.
These flow velocities result from high-pressure gradients within the system; similar gradients are
not expected for Yucca Mountain.
Relevance to Yucca Mountain
These geothermal examples show the importance of high-penneability fractures in the
circulation of geothen-nal fluids. Numerous nonnal faults (i.e., Solitario Canyon, Bow Ridge,
Dune Wash, Drill Hole Wash, Pagany Wash, Sever Wash, Sundance, Ghost Dance) have been
identified at Yucca Mountain, but little is currently known about their permeability (BSC 2001
[155950], Section 3.3.4.5.1). 

If these faults are pen-neable, then they could serve as fast fluid
flow paths for infiltrating surface waters reaching the repository level, as well as pathways for
dissolved radionuclide transport from the waste packages down to the water table.
The presence of bomb-pulse tritium and 36CI in water samples collected from core samples from
the potential repository horizon within Yucca Mountain suggests that fault and fracture pathways
have expeiienced relatively fast rates of fluid flow (Fabryka-Martin et al. 1997 [1001451). Based
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on these results, minimum fluid-flow velocities calculated using a distance of 300 m (distance
from the surface to the sampled areas) and a maximum time of 50 years (first generation of
bomb-pulse tritium and 36 Cl) are on the order of 0.0007 m/hr; these rates are much slower than
those observed in geothermal fields. Because the bomb-pulse tracer flow rate estimate is poorly
constrained, a number of fluid flow experiments have been conducted along faults within the
ESF at Yucca Mountain with the goal of obtaining better estimates of flow velocities. A series of
in situ flow tests was conducted in Alcove 4 between two boreholes 1.07 m apart that intersected
a minor normal fault (Salve and Oldenburg 2001 [157316], Figure 8, p. 3049). Measured flow
velocities along the fault ranged from 0.08-0.58 m/hr. In another test between Alcove 8 and
Niche 3, the time (-840 hr) between water release and the onset of seepage along a fault that
intersects both the main drift and cross-drift tunnels (Figure 11.2-4) and the distance between
these two areas (-25 m) can be used to calculate a flow velocity of about 0.03 m/hr (Salve et al.
2001 [156848]). The measured fluid velocities from these field experiments are significantly
higher than those obtained from the bomb-pulse data and may reflect the need for surface
infiltration rates to be high enough to initiate and sustain fracture flow (Flint et al. 2001
[156351], pp. 19-21, 24, 25).
The percolation flux at Yucca Mountain is much lower than the fracture flow rates described
above. The percolation flux depends on the magnitude and spatial distribution of surface
infiltration rates, as well as other factors, such as the presence of fast flow paths and lateral
diversion within low-permeability intervals. Present-day infiltration rates are estimated to vary
from 0-8 0 mm/yr, with an average value of about 5-10 mm/yr, for the potential Yucca Mountain
repository block area (Flint et al. 2001 [15635 1], pp. 22-23). Thus, it is critical to understand the
role of faults and fractures at Yucca Mountain and how these features could serve to accelerate
and/or focus fluid flow within the potential repository.
11.2.8.2 Heat and Fluid Flow Simulations for Geothermal Systems
Numerical simulation of geothermal fields has been perfonned successfully for more than three
decades. The Code Comparison Study (Molloy 1981 [156407]) evaluated several geothermal
simulators with six test problems. The codes tested all performed reasonably well, indicating that
the physics of the test problems were correctly represented. Numerical simulation of geothermal
fields has proved to be of great economic importance in aiding geothermal companies to
understand where to drill and to predict production capacity (Simmons and Bodvarsson 1997
[ 126511 ]). In a recent examination of geothennal simulations, more than 100 field simulations
have been carried out worldwide since 1990 using a variety of simulators (O'Sullivan et al. 2001
[156353]).
Over the decades of geothermal reservoir simulation, a robust modeling process has been
developed. The process includes data collection and evaluation, conceptual model development,
numerical model design, natural-state modeling, history matching, prediction, and postauditing.
Each step is dependent on the preceding steps, and thus changes in any preceding step require
modifications in all subsequent steps. 
In the first step, all available data are evaluated. 

The data may be from several sources, including
flow tests, well logs (temperature, lithology, electrical resistivity), fluid chemistry, self-potential
surveys, measurements on core samples, topography, location and flow rates from hot springs
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and fumaroles, seismic data, precision gravity surveys, and other techniques. The data evaluation
may be performed by individuals from many disciplines, yielding a conceptual model that is
typically distilled into a few plan- and cross-sectional schematics providing an understanding of
how the reservoir works.
The numerical model is constructed to resemble the conceptual model. Region size, glidblock
sizes, boundary conditions, fluid chemistry, and equations of state are selected and parameters
are assigned for each gridblock. The first step in model calibration is natural-state modeling. In
natural-state modeling, the numeiical model is tested by placing a heat source into the system at
some time in the past (usually thousands to millions of years ago) and running the model forward
to obtain a match with current measurements. If an adequate match is not obtained, parameters
are altered within reason and the process is repeated. Many iterations are often required, and this
procedure may be partially automated (White et al. 1997 [156340]; Bullivant and O'Sullivan
1998 [144410]; Finsterie 1999 [104367]). The importance of field features may be identified in
this step, often leading to inferences of fluid inflows and faults.
The second step in model calibration is history matching, which can be perfonned when fluids
have been produced from the geothermal system. In history matching, the field perturbation
(caused by fluid extraction) is modeled, with the results compared to field measurements
(temperature, pressure, enthalpy, brine composition). Again, parameters are adjusted until a
reasonable match is obtained. Since natural-state modeling is performed for long time frames and
history matching over significantly shorter time frames (years to decades), different types of
parameters can be inferred. In natural-state modeling, parameters such as penneability are
inferred. In history matching, storage-type parameters like porosity are inferred. Changes in
parameters at any stage require verification in earlier stages. Calibration of a model using both
natural-state modeling and history matching is a significant milestone in the creation of a viable
reservoir model and becomes increasingly difficult as the amount of data increases.
Upon completion of successful natural-state modeling and history matching, the model is used
for predictive purposes. Geothermal fields are modeled for a variety of reasons, but generally to
devise a strategy for energy extraction. These models are generally evaluated and updated when
development is planned. 

Few postaudits of geotherinal field models have been published (post
audits of two fields were found in the literature), although model perfortnance is often monitored
and demonstrated. The postaudit of Olkaria East Geothermal Field, Kenya (Bodvarsson et al.
1990 [136384], pp. 399-407) showed that the field-wide decline in steam rate agreed very well
with predictions. A well-by-well comparison identified adequate predictions for 75% of the
wells. Many of the wells for which prediction was inadequate had limited production when the
initial model was constructed, and thus there was insufficient history on which to base the
predictions for these wells. In a postaudit of the Nesjavellir Field, Iceland, Bodvarsson et al.
(1993 [138618]) evaluated predictions made with a 1986 model for pressure decline and
enthalpy changes. Acceptable agreement was reported between modeled and measured data
(Figure 11.2-5), particularly considering that the prediction time (6 years) was longer that the 1-
3 yr calibration period. A second audit was perfonned of the Nesjavellir geothermal system
(Steingrimsson et al. 2000 [156686]) because the model underestimated enthalpy decline in some
wells. Recalibration led to slight changes in the conceptual model within the producing region of
the reservoir. The new model matched well data better, but the larger-scale reservoir
performance predictions remained unchanged.
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The geothermal industry relies heavily on the use of models, and at many fields several
generations of models have been used. Beginning in the early 1980s, UNOCAL developed and
maintained 3-D models of U.S., Philippine, and Indonesian geothermal fields (e.g., Williamson
1992 [156613]; Strobel 1993 [156614]; Murray et al. 1995 [1566121). The Wairakei geothen-nal
field (New Zealand) has been modeled since the late 1960s, including many types of models and
levels of complexity (OSullivan et al. 1998 [154567]). The Kawerau geothermal field (New
Zealand) has also been extensively modeled for more than a decade (White et al. 1997
[156340]). These models have been upgraded over time as new information, codes, and
techniques became available. The accumulated longevity of the models at a particular field
indicates a significant degree of confidence in geothermal reservoir modeling.
Application to Yucca Mountain
There are a number of similarities and differences between modeling geothermal reservoirs and
modeling the potential high-level nuclear waste repository at Yucca Mountain. The volume and
number of dimensions modeled at Yucca Mountain are similar to those employed fot geothermal
reservoir modeling. The number of gridblocks in Yucca Mountain models ranges from hundreds
to millions. The time scale for Yucca Mountain THC coupled process models is similar to the
time scales of natural-state geothennal modeling, but significantly exceeds the time scale of
history-matching reservoir models used to predict future reservoir behavior. 

The temperature and
pressure conditions expected at Yucca Mountain are well within the range observed and modeled
for geotherinal reservoirs.
The aims of modeling geothermal fields and modeling Yucca Mountain are different.
Geothen-nal reservoirs are generally modeled to optimize energy extraction for economic gain.
To that end, fluid extraction and injection rates, enthalpy, and the number and location of
replacement wells are n-eeded. Modeling for the potential Yucca Mountain repository is
performed to desciibe the environment within the repository drifts and to assess the potential for
release of the emplaced radionuclides and their fate. Data collection at Yucca Mountain to
constrain these models has been extensive; however, much of it is related to small-scale
measurement and requires scaling to be adequately represented in the numerical models.
Repository performance depends on: (1) the amount of water that may seep into the repository,
(2) the temperature and humidity near the waste packages, and (3) the ability of the natural
system to sorb and retain radionuclides possibly escaping the repository (Bodvarsson et al. 1999
[120055], pp. 3, 5). As understanding geothen-nal systems requires modeling at vaiious scales
(i.e., well scale, zone scale, and field scale), so modeling for Yucca Mountain requires modeling
at multiple scales (drift scale, mountain scale), but in addition requires an understanding at
smaller scales, because flow on smaller scales may impact repository performance.
Prediction time frames for geothermal fields range from 10-50 years. It is generally accepted in
the geothermal-modeling community that predictions for a well-studied geothermal field are
valid only for a time scale on the order of magnitude of the history-matching data (Bodvarsson et
al. 1993 [138618]), because of uncertainties in assigning parameters to the model. It is not
realistic to collect history-matching data for a 10,000-year period of model confidence for the
thennal system at Yucca Mountain. Tests applying thermal perturbations to Yucca Mountain are
planned for as long as eight years. Because of this, the modeling effolis for the potential
repository have investigated potential behavior for a large range of possible conditions, including
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higher and lower percolation fluxes resulting from climate changes, different heat loads, and
different waste package arrangements. Sensitivity analyses have been performed for a variety of
model parameters (Bandurraga and Bodvarsson 1999 [103949]).
Modeling for the Yucca Mountain repository has benefited greatly from the foundation produced
from the robust modeling techniques developed in geothennal modeling. Wu et a]. (1999
([ 11716 1], pp. 186-188) reviewed many of the earlier thennal -hydrologic (TH) modeling efforts.
These coupled, multiphase, multicomponent models simulate the flow and distribution of
moisture, gas and heat at Yucca Mountain for use in predicting current and future conditions in
the UZ. For example, Tsang and Birkholzer (1999 [137577]) used a 3-D coupled TH numerical
model to predict the results of the Single Heater Test at Yucca Mountain. They obtained good
agreement between measured temperatures and model results, and the simulated dryout and
condensation zones were consistent with radar tomography and air-permeability data. 

More recent Yucca Mountain modeling efforts (e.g., BSC 2001 [154677]) have utilized the
TOUGHREACT code (Xu and Pruess 2001 [156280]), which couples reactive chemistry and
transport to the TOUGH2 code used to create many of the TH models. The coupled THC models
incorporate heat and fluid flow, chemical transport, kinetic and equilibrium mineral-water
reactions, and coupling between mineral dissolution and precipitation, porosity, and permeability
for a fracture-matrix system. Three heater tests have been performed (the Large Block Test, the
Single Heater Test, and the still-active Drift-Scale Test [DST]) to allow assessment of the
numerical models. These tests provide data (for validation of Yucca Mountain numerical
models) that are analogous to production data used for history-matching exercises performed on
geothermal reservoir models. The duration of these thermal-perturbation tests is short relative to
the time scale of the potential repository, with the DST having a four-year heating phase
followed by a planned four-year cooling phase. These thennal tests have been used to validate
the THC model by comparing measured gas and water chemistry from the DST to the results of
simulations obtained using the DST THC model (BSC 2001 [1546771). The THC model captures
the observed changes in pH, Ca, Cl, and C02 concentrations over time for areas that have
different therrnal histories, and is consistent with the results of TH modeling (BSC 2001
[154677], Sections 6.2.7 and 6.2.8).
Simulations of the anticipated system at Yucca Mountain have been performed using coupled-
process modeling to assess THC effects on seepage and fluid flow within the near-field
environment (BSC 2001 [154677]). Fracture porosity reductions in the near-field environment
resulting from the precipitation of calcite and silica are predicted to be less than 3% (for the
homogeneous model; higher fracture porosity reductions of 5% were obtained for heterogeneous
fracture permebility models), and thus only minor changes in penneability and fluid flow caused
by THC processes are expected to occur (BSC 2001 [155950], Section 4.3.6.4.2). Similar to
postaudit reviews of geotheniial reservoir models, Yucca Mountain models should be regularly
updated, as new data become available, to maximize their effectiveness as a repository
management tool.
11.2.9 Cheniical Transport in Geothermal Systems
The transport of chemical species in geothermal systems is intimately linked to advective fluid
flow. Chemical constituents of geothermal fluids are commonly used to infer deep reservoir
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temperatures, identify sources of fluids (such as magmatic, meteoric, connate, and condensate
waters), and monitor important processes such as injectate breakthrough and influx of ground
waters into producing portions of geothermal reservoirs. Because fluid velocities are rapid (and
often faster than chemical reequilibration rates) within most geothermal systems, the chemistry
of reservoir fluids sampled at surface thennal features can be used to estimate reservoir
conditions. For example, chloride springs found at many geothermal systems are typically
derived in large part from deep reservoir fluids. The chemical compositions of geothermal waters
are commonly used to determine reservoir temperatures using a variety of silica and alkali
geothermometers (Foumier 1991 [105419]). Natural and introduced chemical tracers are used to
monitor fluid velocities, estimate flow paths, examine fracture-matrix interaction, and identify
the sources of fluids within geothermal systems. The presence of hydrotherrnal minerals along
veins and fractures in fossil geothermal systems is evidence for chemical transport (and
subsequent mineralization) in these systems.
11.2.9.1 Geothermal Tracer Tests
For conservative tracers (such as iodine and chloride), tracer travel time represents the flow rate
of advecting fluid within the geothennal reservoir. Tracer tests at Dixie Valley and Wairakei
(previously summarized in Section 11.2.8. 1) indicate minimum tracer velocities ranging from 0.7
to 38 m/hr. In some Japanese fields, tracer retums have been observed at rates of up to 100 M/hr,
indicating high-conductivity fractures. Observed tracer speeds in the Hatchobaru field are as high
as 80 m/hr (Home 1982 [156362], p. 501).
4o Naturally occurring tracers are commonly used in geothermal fields to evaluate important
processes such as heat flow, groundwater influx, and reinjectate breakthrough. Measurements of
the total amounts of chloride and boron (nonreactive components that are often magmatic in
oiigin) associated with surface feature discharges have been used to estimate heat flow values of
geothen-nal systems (e.g., Foumier et al. 1976 [156817]; Sorey and Lewis 1976 [156809]). 

Because reinjected fluids have higher chloride contents than produced fluids (due to the
concentration of chloride in the liquid phase resulting from the removal of steam), the arrival of
reinjected waters in production zones can be detected and monitored by tracking chlofide
contents of production well brines. Chloride generally behaves in a conservative fashion (it is
nonsorbing and is not involved in mineral precipitation, except in very saline water), and thus
generally reflects the effects of mixing and boiling only.
Bulalo, The Philippines
Tracer tests conducted at the Bulalo geotherinal field have been used to monitor the dispersal of
injected fluids within the reservoir, track the influx of groundwater influx, and identify high-
pen-neability flow paths (Villadolid 1991 [156656]). Changes in chloride contents and fluid
enthalpies were used in production wells to identify the contribution of reinjected fluids in
production wells. Elevated concentrations of tritium were interpreted to indicate zones where
downflux of groundwater along perrneable flow paths occurred. Rapid increases in magnesium
concentrations following acid stimulation in neighboring wells were used to identify fast flow
paths between wells.
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11.2.9.2 Application to Yucca Mountain
Gravity-driven fracture flow is predominant through the fractured units with low matrix
permeability at Yucca Mountain. Chemical transport accompanying percolation flux and
associated seepage into cavities over time is evidenced by the precipitation of calcite and opal
along fracture and cavity surfaces. Textural observations and fluid inclusion, isotopic, and
geochronologic data on the coatings suggest that these secondary minerals were deposited from
infiltrating meteoric water under unsaturated conditions (Whelan et al. 2001 [154773], p. 6).
Using an equilibiium evaporation model to predict calcite and opal precipitation associated with
seepage into lithophysal cavities, Marshall et al. (2000 [151018], p. 4) calculated that the total
seepage volume over the past 10 million years (m.y.) is approximately 5 x 104 times greater than
the volume of secondary calcite precipitated over the same time period at Yucca Mountain. This
model assumes that all water is calcite-saturated, and no significant dissolution of calcite has
occurred. The seepage flux estimated from this model (4 x 10-6 MnVyr (Marshall et al. 2000
[151018], p. 5)) may be used to calibrate predicted rates of seepage into drifts for numerical
models (e.g., Birkholzer et al. 1999 [105170]) as well as provide insights relating to chemical
transport rates and mechanisms at Yucca Mountain.
A key factor affecting chemical transport at Yucca Mountain involves possible interaction
between minerals and dissolved constituents. The effects of ion exchange are demonstrated by
the marked difference in strontium concentrations of perched waters in the Topopah Spring and
Calico Hills tuffs. The strontium contents of perched waters in the UZ-14 and WT-24 boreholes
(that sample the strati graphical I y higher Topopah Spiing tuff) range from 169-240 ppm
(Sonnenthal and Bodvarsson 1999 [117127], Table 3). Much lower strontium concentrations (3-
11 ppm) were measured for perched waters from the SD-7, SD-9, and NRG-7A boreholes in the
Calico Hills tuff. The lower strontium values from these samples were interpreted by Sonnenthal
and Bodvarsson (1999 [117127], pp. 119-120) to result from ion exchange between the perched
waters and Ca-rich zeolites, which are abundant in the Calico Hills tuff (see Figure 7-2). These
zeolite-rich tuffs form an important part of the geologic barrier inhibiting radionuclide transport
from the repository down to the water table at Yucca Mountain.
11.2.10 Geothermal Examples of Boiling and Dryout
Many geothermal systems have localized boiling zones resulting from upward flow of high-
enthalpy fluids, or from depressurization induced by geotherinal production. Dryout zones (areas
where fluids have boiled to dryness) are much less common, and typically are associated with the
transition between liquid-dominated to steam-dominated geothermal systems. The effects of
boiling on fluid chemistry, mineral precipitation, and reservoir permeability have been
documented for a number of natural-state and producing geothermal systems. 

Dryout zones are
more transient features, and thus are more difficult to charactelize. However, as discussed in
Section 11.2.10.2, detailed study of cores from the Karaha-Telaga Bodas geothermal field
provides some insights as to how these zones develop and their significance. Summaries of some
relevant geothermal examples of boiling and dryout are presented below.
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11.2.10.1 Boiling in Geothermal Systems
Boiling is a common phenomenon in high-enthalpy geothermal systems. Many of these systems
have high-temperature (~!100'C) thermal features (boiling hotsprings and superheated fumaroles)
resulting from the depressuiization of high-enthalpy fluids ascending to the surface. Localized
boiling within the reservoir can also occur as a result of production of geothennal fluids, which
decreases reservoir pressure. The process of boiling results in increased concentrations of
dissolved constituents in the residual liquid phase, as well as the partitioning of volatile species
(such as C02) into the gas phase. These changes often lead to the precipitation of phases such as
amorphous silica and calcite. Several examples of the observed effects of boiling in geothen-nal
systems are given below.
Waiotapu, New Zealand
The Waiotapu geothermal system is the largest of the 20 major geothennal systems located in the
Taupo Volcanic Zone on the North Island of New Zealand (Hedenquist 1991 [156315]). Surface
thermal features include fumaroles and associated acid sulfate springs along the flanks of dacite
cones, and numerous chloride, acid-sulfate and mixed composition hot springs located in
Waiotapu Valley. The chloride springs represent the liquid component of the hot (~!230'C)
reservoir fluid that feeds these surface features.
Champagne Pool, one of the largest of the chloride springs at Waiotapu, has a surface
temperature of 75'C (Hedenquist 1991 [156315], Table 1, pp. 2756, 2758-2764). It derives its
name from the outgassing Of C02 near the surface, thus giving it the appearance of champagne.
The elevated chloride contents of this feature (1,898 ppm) suggest that it has experienced
minimal dilution from meteoric fluids. The effects of boiling and evaporation on the waters from
this feature can be seen by the isotopic enrichment in deuterium and 180 resulting from the loss
of vapor. The dissolved silica concentration of 445 ppm is much higher than the equiliblium
solubility concentrations of both quartz and amorphous silica at the pool temperature, and results
from the processes of boiling and cooling of a hot (~!230'Q reservoir fluid as it ascends to the
surface. An extensive silica sinter deposit suffounds this therinal feature, and similar deposits are
common for many of the other chloride springs at Waiotapu.
Cerro Prieto, Mexico
Localized aquifer boiling occurs in the shallow two-phase reservoir at Cerro Pfieto (Truesdell et
al. 1984 [156350]). Boiling increases the total dissolved solids (TDS) concentrations in the
residual liquid through steam production, but also causes a decrease in fluid temperatures, thus
reducing the solubility of most mineral phases. The increase in dissolved silica concentrations
and decrease in silica solubility often results in the precipitation of silica polymorphs.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Boiling
also results in the partitioning Of C02 into the gas phase, thus causing pH to increase and calcite
to precipitate.
Large decreases (up to 70%) in discharge rates from wells located in the boiling zone at Cerro
Prieto (Figure 11.2-6) have been interpreted to result from the precipitation of quartz and calcite,
which decreased permeability for these zones (Truesdell et al. 1984 [156350], Table 2, p. 226).
0
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This interpretation is supported by the observed decrease in silica and bicarbonate contents of the
produced fluids of these wells with time.
Relevance to Yucca Mountain
For the higher-temperature operating mode at Yucca Mountain, a heat pipe may form above the
repository when temperatures reach boiling. Water originally stored in the rock matrix, combined
with water infiltrating from the surface, would boil near the margins of the heated drifts and
migrate (as vapor) to cooler suffounding areas, where condensation would occur. Similar to the
cases mentioned above, boiling will lead to increases in the concentration of dissolved species in
the residu'al liquid phase, resulting in supersaturation and subsequent precipitation of phases such
as amorphous silica.
The impact of boiling on mineral precipitation at Yucca Mountain should be significantly less
than that observed in most geothermal systems because of the restricted area where boiling
would occur, the much smaller quantities of fluid involved, and the lower initial concentrations
of dissolved silica. A simple calculation using the matrix porosity, saturation, and pore-water
silica concentrations and fracture volume can be made to estimate the maximum amount of silica
that could potentially precipitate in adjoining fractures (Simmons 2002 [157578], SN-LBNL-
SCI-190-V2, p. 79). Assumptions for this model include a matrix porosity of 10%, a matrix fluid
saturation of 90%, a silica pore-water concentration of 70 mg/L, and a fracture volume of the
rock of 0.5%. Also assumed is that with boiling, the water and associated dissolved silica are
completely transferred from the matrix pore space into the fractures, where the water is
subsequently boiled to dryness so that all of the dissolved silica precipitates as amorphous silica.
For a 1 m 3 block of rock undergoing this process, that would correspond to a matrix water
volume of 90 L and a dissolved silica amount of 6.3 g. The fracture volume for this block would
be 5 L, and using a density of 2100 g/L for amorphous silica, the volume of amorphous silica
available for precipitation is thus equivalent to 0.003 L. This corresponds to 0.06% of the
available fracture volume. This very minor reduction in fracture porosity would result in a
negligible reduction in fracture penneability.
Another bounding calculation can be made by estimating the amount of silica precipitation
resulting from transport of additional dissolved silica to the boiling zone resulting from
continued influx of infiltrating water from the surface 3 (Simmons 2002 [157578], SN-LBNL-SCI-
190-V2, p. 80). This calculation uses the same I m block as a starting point, with a fracture
volume of 0.5%, a fluid infiltration rate of 5 mm/yr, a fluid composition of 70 mg SiO2AL, and
assumes that: (1) all infiltrating water is focused into the fractures and (2) all of the water
entering this zone from above undergoes complete boiling, resulting in the precipitation of
dissolved silica as amorphous silica. For a boiling zone duration of 1,200 years, this translates
into an infiltration fluid volume of 6000 L with a coffesponding silica amount of 420 g. Using
the density and fracture volumes given above, this corresponds to 4% of the available fracture
volume. This simplistic bounding calculation is meant to illustrate the potential for fracture
sealing at Yucca Mountain. Migration of the boiling front with time at Yucca Mountain would
result in a larger area with reduced porosity and permeability, but with smaller average
reductions. Variability in fracture apertures could lead to sealing of small aperture fractures and
focussing of flow into larger aperture fractures. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  A fracture sealing experiment conducted in a
block of ash flow tuff and accompanying numefical simulations demonstrate that similar
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amounts of total fracture sealing could result in large (up to two orders of magnitude) reductions
in permeability in the case where mineralization is highly focused (BSC 2001 [155950], Section
4.3.6.7.4).
One factor that could significantly increase the amount of silica precipitation in the fracture zone
is the transport of additional dissolved silica to the boiling zone through reflux of fluids
associated with a heat pipe. The return of condensed vapor that has dissolved silicate minerals
back into the boiling zone could effectively transport significant amounts of silica into the
fractures of the boiling zone. However, it is difficult to quantify the impact of this process. THC
coupled-process modeling of the near-field environment, using a homogeneous fracture-
permeability model, predicts that porosity reduction caused by precipitation of silica and calcite
will be less than 3% over the 100,000-year simulation of the higher-temperature operating mode
(BSC 2001 [155950], Section 4.3.6.4.2). This fairly small change relative to geothermal systems
is in part due to the much lower fluid fluxes and lower temperatures expected at Yucca
Mountain.
Boiling would not occur for the lower-temperature operating mode at Yucca Mountain.
Moderately elevated temperatures (-80'C) around the drift area for this case would lead to
higher amounts of evaporation, and thus result in higher concentrations of dissolved constituents
in the'remaining fluids in the area around the heated drifts. However, the amount of silica
precipitation calculated above for the higher-temperature operating mode would be much
reduced for the lower-temperature operating mode. THC simulations performed for the near-field
environment for the lower-temperature operating mode predict that less than 1% porosity
reduction will occur, because amorphous silica will remain undersaturated except in areas
adjacent to the drift wall, where substantial evaporation will take place (BSC 2001 [155950],
Section 4.3.6.5).
11.2.10.2 Dryout Zones in Geothermal Systems
Dryout is less common than boiling in geotherrnal systems, because most systems are liquid-
saturated, and thus always contain some water. However, dryout zones do occur in steam-
dominated geothermal systems, and evidence of these zones in such a system is presented in the
summary below. 
Karaha-Telaga Bodas, Indonesia
The Karaha-Telaga Bodas geothermal system, located on the island-of Java in Indonesia, consists
of a horizontally zoned reservoir with an upper condensate layer, an intermediate vapor-
dominated zone, and an underlying deep liquid-dominated zone (Allis et al. 2000 [156317],
Figures 4 and 5, pp. 220-221). Mineralogic and fluid inclusion studies of core samples from the
T-8 corehole reveal a complex history, with calcite and quartz (after chalcedony) veins present at
shallower depths, and veins containing epidote, actinolite, albite and quartz (after chalcedony)
present in deeper samples (Moore et al. 2000 [156319], pp. 260-262). The precipitation of
chalcedony (revealed by botryoidal textures) at elevated temperatures is unusual (Figure 11.2-7)
and is interpreted to result from extreme silica supersaturation resulting from decompressional
boiling (Moore et al. 2000 [156319]). The abundance of vapor-rich inclusions in the vein
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minerals is consistent with this model. Many of the hydrothermal minerals are coated with scale
(consisting of Ti- and K-bearing phases along with iron chloride, and halite) with desiccation
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cracks (Figure 11.2-8). These minerals are thought to have formed as a result of dryout (Moore et
al. 2000 [156319], pp. 260-261). The youngest fluid inclusions, associated with scale-coated
anhydrite, have extremely high salinities (31% NaCl equivalent), and Moore et al. (2000
(156319], pp. 262-263) interpreted that the inclusions and scale formed as a result of condensate
boiling to dryness. The high solubility of the chloride minerals suggests that the rocks containing
the scale have not been subjected to rewetting after they were formed. 

Relevance to Yucca Mountain
Dryout is predicted to occur in the rock mass around the potential repository drifts at Yucca
Mountain (for the higher-temperature operating mode) as the waste packages transfer their heat
to the surrounding environment. The size of the dryout zone will vary with time and may extend
up to 13 m away from the drift walls (as previously mentioned in Section 11.2.5), depending on
the waste package configuration (BSC 2001 [154677], Section 6.4.5.1). During the dryout phase,
liquid water will be converted to water vapor, which will effectively displace air from this zone.
This is important because the oxygen necessary for many corrosion reactions will only be present
in low concentrations. As the heat output from the waste package diminishes with time, dryout
zones will gradually undergo rewetting from influx of condensate and precipitation infiltration as
temperatures drop below the local boiling point. The rewetting process will be accompanied by
an influx of air (BSC 2001 [154677], Section 6.6.5).
In the dryout zone near repository drifts, water will be driven from the pore space in the rocks.
The rock in the potential repository has a porosity of about 10%, which is about 90% filled with
water in the natural condition (90% water saturation). This water is expected to be an important
source of circulating water near the repository. Heating of the matrix rock, even to temperatures
below boiling, may cause dryout in fractures. As the rock mass heats following waste
emplacement, the volume of the dryout zone may increase to include regions formerly altered in
the heat pipe. Mineralogic changes expected in this region will include precipitation of minerals
in fractures (see discussion above), dehydration of naturally present sorbing clay minerals,
carbonate mineral decomposition, and deposition of minerals on fracture faces from liquid driven
from the rock.
With rewetting of the dryout zone, some of the more soluble mineral salts are likely to be
redissolved. This could initially result in the formation of fairly saline fluids that could cause
corrosion problems with the waste package in the drift. However, with continued seepage into
the former dryout area, the resulting fluids will become increasingly more dilute. Dryout will be
much less pronounced for the lower-temperature (sub-boiling) operating mode.
11.2.11 Geothermal Examples of Condensation and Mineral Dissolution
The processes of condensation and mineral dissolution and their effects can also be detected in
many geothermal systems. Condensation of upflowing steam, when it comes into contact with
cooler meteoric waters in the shallow portions of geothennal systems, results in the production
of steam-heated waters (e.g., Hedenquist 1991 [1563151, pp. 2756-2757). These dilute fluids
often have fairly distinct chemical compositions and often reflect the effects of the gas phase
accompanying the steam. Waters that receive an influx Of C02 are typically bicarbonate fluids,
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Whereas those interacting with H2S become acid-sulfate waters. The acid-sulfate waters are often
associated with acid-sulfate alteration, where feldspars readily alter to kaolinite. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Mineral dissolution is not as readily evident in geothermal systems, but can be detected in core
samples. At The Geysers geothermal field, corroded faces of quartz crystals found in
hydrothermal veins indicate that these crystals underwent partial dissolution prior to being coated
in later chalcedony (Moore et al. 2000 [156318], Figure 9, pp. 1722-1723). Similar dissolution
features are also observed for calcite. These textural features (Figure 11.2-9) are interpreted to
represent dissolution resulting from the downward percolation of condensate near the site of
condensation in the upper portion of a vapor-dominated heat pipe (Moore et al. 2000 [156318],
Figure 11, pp. 1731-1732).
11.2.11.1 Relevance to Yucca Mountain
Condensation and dissolution are processes that are likely to occur at Yucca Mountain. A tuff
dissolution experiment was conducted to simulate mineral dissolution by condensate water in
fractured tuff (Kneafsey et al. 2001 [154460]). Deionized water containing dissolved C02 was
flowed through a column containing crushed Topopah Spring tuff at a temperature of 94'C. The
reacted water exiting the column was regularly collected and analyzed. The experiment achieved
a pseudo-steady-state flow composition after I I days. Silica (92 ppm) was the dominant
dissolved consituent. A similar plug-flow reactor expeiiment (using higher temperature
conditions) was conducted by Johnson et al. (1998 [101630]), and a series of unsaturated
nonisothennal vertical column tests were conducted by Lowry (2001 [157900]). These
experiments demonstrate the ability of condensate waters to dissolve (and subsequently
is transport) significant quantities of dissolved constituents. As mentioned in the discussion on
boiling, reflux of condensate fluids containing dissolved silica could serve as an impoilant source
for the generation of fracture-plugging minerals precipitated at the boiling front.
11.2.12 Geothermal Examples of Mineral Alteration and Precipitation
Mineral alteration and precipitation are ubiquitous in geotherinal fields. The nature and extent of
alteration depends on a variety of factors, including temperature, initial rock mineralogy, initial
water and gas chemistry, fluid/rock ratios, and the rock surface area exposed to fluids. Many
geothermal systems show a series of mineral assemblages that corresponds to different
temperature and fluid chemistry regimes (e.g., Muffler and White 1969 [156650]; Arn6rsson
1995 [1563211). Mineral alteration and precipitation can significantly affect porosity,
permeability and sorptive properties (at least locally) of both matrix and fractures, resulting in
the sealing of former fluid flow pathways.
Precipitation of new minerals in vugs, pore spaces, and fractures can occur when fluids reach
supersaturation with respect to dissolved constituents. The rate of precipitation is often
controlled by kinetic processes, and thus is highly dependent on factors such as nucleation sites
and temperature. Supersaturation can be caused by processes such as boiling, cooling, heating (in
the case of minerals with retrograde solubility, such as anhydrite and calcite), degassing, and
mixing of two distinct fluids. The effects of boiling have previously been discussed, so this
section will focus on the other processes mentioned.
9
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11.2.12.1 Hydrothermal Alteration and Seal Formation in Geothermal Systems
Imperial Valley
The effects of water-rock interaction have been studied at a number of geothermal fields (Salton
Sea, East Mesa, Heber, Brawley, Cerro Prieto, and the Dunes) within the Imperial Valley (e.g.,
Muffler and White 1969 [156650]; Schiffman et al. 1985 [154644]; Cho et al. 1988 [154599]). 

 
 
 Elders (1987 [154632]) examined the Salton Sea geothermal field as a potential natural analogue
for evaluating processes related to radioactive waste storage. One of the features examined was
the impact of water-rock interaction and mineralization on fluid flow and solute transport. While
primary lithology plays a major role in the distribution of permeability and porosity within the
field, processes such as compaction and hydrothennal alteration have significantly modified
these rock properties. Carbon ate-cemented sandstones form the primary caprock for the Salton
Sea geothermal system, and represent the first of four distinct mineralogic zones related to
hydrothermal alteration. Within this sealed zone, calcite cement fills up to 50% of the pore space,
resulting in very low matrix permeabilities for this interval (Elders and Cohen 1983 [157502], p.
100). Matrix permeability appears to favor horizontal fluid flow, as low permeability shale
interbeds serve as barriers to vertical fluid flow. Fractures provide fluid flow pathways that can
cut across these lithologic barriers. Complex sequences of fracture mineralization observed at the
Salton Sea indicate that fractures have been episodically opened and sealed throughout the life of
the geothermal system (Elders 1982 [154602] pp. 63-64).
Silica sealing has been documented at the Dunes geotherinal system (Bird and Elders 1976
[154601], Figure 3, p. 289). An exploration well drilled at this prospect (DWR No. 1) has a depth
of 612 m, with a maximum temperature of 104'C. Fluids sampled from this well are NaCl brines
with up to 4,000 ppm TDS. Seven distinct zones of sandstones and conglomerates have
undergone intensive silicification, which significantly reduced porosity and permeability. These
silicified zones (Figure 11.2-10) are located in what originally were the most permeable strata
within the sedimentary section. Silicification appears to be most intense near the upper portions
of these units, immediately below low-penneability shale interbeds. The silicified zones have
mineral assemblages of quartz + adulaiia + hematite and quartz + adularia + pyrite, reflecting
enrichments of silica and potassium to these zones caused by mass transfer accompanying
hydrothennal alteration. Brittle fractures developed in the silicified zones. The precipitation of
silica is thought to be caused by the lateral migration of hot brine to a cooler environment.
Smectite and kaolinite have reacted with potassium-rich biines to fonn adularia.
Wairakei Geothermal Field, New Zealand
Fluid chemistry and mineralogy data from the Wairakei field were used to test the EQ3/6
geochemical modeling codes and the GEMBOCHS thermodynamic databases (Bruton 1995
[100105]). Water and gas compositions obtained from well samples were used to reconstruct
reservoir fluid compositions, and these fluid compositions were used as input for the EQ3/6 code
to calculate equilibrium mineral assemblages. 

 These calculated assemblages were then compared
to the observed downhole mineralogy for these wells to help identify which thermodynamic
datasets produced the best match between the observed and calculated mineralogy. Lower
temperature portions of the reservoir exhibit similar mineralogy (including zeolites such as
0 mordenite, clinoptilolite, stilbite, and dachiardite) to that observed in the Yucca Mountain tuffs.
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Natural Analogue Synthesis Report
Vein mineral assemblages contain fewer phases than those found associated with the matrix.
Bruton (1995 [100105], p. 18) inferred that the fracture, vein, and vug minerals are the product
of a fluid-dominated system, whereas the more complex matrix alteration mineralogy results
from high rock-water ratios.
Medicine Lake Geothermal Field, California
The Quatemary Medicine Lake volcano in northem Califomia is host to a high-temperature
geothermal system. Exploratory drilling has revealed that the geothermal reservoir is capped by
hydrothermally altered rock rich in smectite-group swelling clays that fonn a barrier to fluid flow
(Hulen and Lutz 1999 [154600], pp. 217, 219). Glassy dacitic to rhyolitic tuffs and pumiceous
lavas have been strongly altered to smectites, calcite, zeolites, quartz, potassium feldspar,
hematite, and pyrite. This argillic alteration mineral assemblage also fills fractures and vugs, and
forms a hydrologic barrier between a shallow, cool groundwater zone and a deeper, hot
geothermal reservoir.
Fossil Systems
Fossil hydrothermal systems also demonstrate the impact that water-rock interaction has on
pen-neability. Figures 11.2-11 and 11.2-12 illustrate variations in permeability for interbedded
siliceous diatomite and pumiceous tuff from northem Japan (Chigira and Nakata 1996 [156349],
Figure 2, Table 1; Chigira et al. 1995 [156364], pp. 75-76). An andesite dike intruded these
bedded rocks, inducing a hydrothennal system that resulted in the alteration of the tuffs and
diatomite, thereby reducing permeability up to four orders of magnitude.  While the initial
temperatures immediately adjacent to the dike probably approached those of the andesite magma
(-1000'C), conductive and convective heat transfer resulted in a significantly lower temperature
(<150'C) alteration assemblage (opal-CT, quartz, and several zeolite minerals) near the heat
source (Nakata et al. 1998 [156365], p. 334).
11.2.12.2 Scale Formation in Geothermal Reinjection
Reinjection of geothermal water is necessary in many fields because of the need to dispose of
produced water and maintain reservoir pressure, The precipitation of minerals can pose a serious
problem in the reinjection of geothermal fluids. Reinjection occurs following energy extraction,
thus the resulting geothermal fluid has been cooled and concentrated (owing to steam extraction)
from its oiiginal, in-reservoir condition. This often results in silica concentrations exceeding
saturation values, causing scale fonnation in reinjection pipelines, wells, and the receiving
formation (Corsi 1986 [156344], pp. 839-840).
Silica behavior in geothermal environments has been studied in great detail (Bohlmann et al.
1980 [156363]; Weres and Apps 1982 [156644]; Rimstidt and Bames 1980 [101708]), but the
scaling behavior of a particular geotherinal fluid is still difficult to predict. This is because traces
of contaminants can significantly affect the rate of silica polymerization and deposition
(Mroczek and McDowell 1990 [156342], p. 1619). Additionally, quantitative data on other
factors such as pH, temperature, and supersaturation may not be known for the conditions for
which one desires to predict. Reduction in the ability to inject these fluids has been noticed at
several geothermal fields (for example, Hatchobaru and Otake, Japan) (Home 1982 [156362];
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Natural Analogue Synthesis Report
Itoi et al. 1984 [156347]) and is considered a delicate problem with reinjection (Stefdnsson 1997
[156343]).
Otake Geothermal Field, Japan
In an effort to understand silica precipitation in the Otake geothermal field, Japan, an extensive
research effort was undertaken including field-scale reinjection, laboratory expeiiments, and
numeiical modeling. In the field, Itoi and colleagues (Itoi et al. 1987 [1563461, pp. 541-542;
1989 [156345], pp. 153-155) injected geothermal waters into two wells over 656 days. 
 
 
 
 The 120-
162'C waters were extracted and cooled to temperatures between 50 and 80'C to cause silica
supersaturation ratios between 2 to 3.2, and were reinjected. Over the course of the experiments,
the permeability of the two wells declined unsteadily to 4% and 0.35% of their initial values,
respectively (Figure 11.2-13). Under the conditions 3 of the injection, the volume of silica, if all
precipitated, would have been about 170 and 196 m for the two wells. Borehole televiewer and
caliper logs indicated that little of the total mass of injected silica was deposited in the well
bores; however, the well screens were strongly fouled by silica scale.
Of interest in the Otake geothermal field is the likely occurrence of formation sealing, over both
gradual and punctuated temporal intervals, probably resulting from the plugging of narrow
fracture and pore apertures. Yet, there are significant differences between this reinjection study
and the potential anthropogenic system at Yucca Mountain. First, supersaturation ratios at Yucca
Mountain will only be high near the boiling front. In the field experiments at Otake, the
supersaturation ratios were controlled by cooling the water, resulting in the entire reinjected
volume being supersaturated with respect to silica. Supersaturation in the Yucca Mountain
system will be controlled either by boiling off water as water approaches the drifts, or by cooling
as water flows away from the repository below the drifts. Second, water flow rates will be much
lower at Yucca Mountain. Flow at Otake is hydraulically saturated, and large volumes of water
were reinjected into the wells over the test duration. Flow at Yucca Mountain will be
hydraulically unsaturated with a flow rate many orders of magnitude less than at Otake,
considering the spatial scale of the experiment at Otake. Permeability at Otake was dramatically
reduced as a result of silica precipitation from injection of large (5 x 105 M) volumes of water
into each well over the test duration (Itoi et al. 1989 [1563451, pp. 153-155). If we assume that
this water affects a spheiical shell 50 m in diameter within the reservoir, this provides a fluid flux
of several m/yr, which is three orders of magnitude larger than expected fluxes at Yucca
Mountain (order of ten mm/yr) (Flint et al. 2001 [15635 1 ], pp. 22-23).
Laboratory experiments were run to evaluate perrneability changes caused by silica precipitation
using water from the Otake geothennal field. In these experiments, geothermal water at about
92'C was run through a column (50 cm x 5 cm diameter) of 2 mm aluminum beads or rock
particles (Itoi et al. 1984 [156347] pp. 301-302; 1986 [156352], p. 229). Silica was deposited
primarily in the top 10 cm of the column. Specific deposits of silica (defined as the ratio of silica
weight to bead weight) of less than 0.02 caused a two-orders-of-magnitude permeability
decrease. These results were compared to the drilling of a replacement injection well next to a
fouled well at the Hatchobaru Geothermal Field, Japan. The new well had the same injectability
as the original old well, indicating that silica precipitation is occurring near the source.
0
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Natural Analogue Synthesis Report
Reinjection at New Zealand Geothermal Fields
4D A variety of studies of silica precipitation from geothermal waters fTom the Taupo. 

Volcanic
Zone has been performed (Mroczek and Reeves 1994 [156360]; Mroczek and McDowell 1990
[156342]; Mroczek 1994 [154621]; Carroll et al. 1998 [124275]). Field experiments conducted at
several of the geothermal fields in this area measured scale deposition rates under different
process conditions in pipes, open channels, and gravel beds to detennine the conditions under
which the scaling could be tolerated in piping, wells, and reinjection aquifers. Data were
collected at the Rotokawa well RK4, Ohaaki wells BR20, BR22, BRI 1, and Wairakei well 61.
Geothennal fluid, being pretreated to the proper initial condition by cooling, aeration, and
flashing, was then flowed through packed beds or pipes, and the amount of silica deposited was
measured, generally by weighing.
The main conclusions drawn from the field studies are: (1) silica deposition occurs prior to the
beginning of polymerization when all the silica is present as monomers; (2) only a small fraction
of total silica deposits as scale, such that the total silica concentration is relatively unchanged; (3)
deposition remains constant or increases with increasing fluid residence time; (4) deposition rates
from lower-temperature, low-silica and poorly buffered Wairakei water exposed to the
atmosphere were up to more than an order of magnitude higher than unaerated water; however,
aeration had little effect on Ohaaki BR22 water; (5) nucleation appears slow in nonhomogeneous
nucleation systems, but once started, scale will continue to grow rapidly; (6) scale appeared to be
denser and deposition rates lower at higher velocities; (7) deposition onto clean iron pipes
decreases after some time, presumed to be after the surface is uniformly coated with silica, and
deposits fonned at higher temperature were tougher and more adherent than those fon-ned at
lower temperatures. I
11.2.12.3 Application to Yucca Mountain
The potential effects of fracture mineralization on fluid flow have already been discussed in the
section on boiling. Other potential impacts to consider include alteration and precipitation of
hydrothermal minerals that would impact the sorptive pr6perties of the Yucca Mountain
unsaturated zone and affect transport of fluids below the drift areas.
Below the potential repository, regions containing zeolites are present. Zeolites are hydrous
secondary minerals that are well known for having sorptive properties. Heating of the zeolites
may cause dehydration or transformation to phases (such as the less-sorptive zeolite analcime)
that will reduce the sorptive capacity of the subrepository horizons. The zeolites at Yucca
Mountain were formed by diagenetic alteration of vitric tuff in response to a magmatically
induced therrnal pulse (Broxton et al. 1987 [1020041, pp. 107-108). The increase in temperature
caused by waste emplacement could result in the formation of additional zeolites in the vitric
tuffs below the potential repository horizon. Because of heat conduction, the temperatures will
decrease with distance from the repository. Many dissolved components, such as silica, decrease
in solubility as the temperature decreases. However, the precipitation of amorphous silica below
the potential repository is expected to be limited in extent (BSC 2001 [155950], Section
3.3.6.3.2).
0
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Natural Analogue Synthesis Report
11.2-13 General Observations and Conclusions
Geothermal systems illustrate a variety of THC processes that are relevant to Yucca Mountain.
They include advective and conductive heating, fracture-dominated fluid flow, chemical
transport, boiling and dryout, condensation, and mineral alteration, dissolution, and precipitation.
Some of the more pertinent observations made regarding these processes are listed below:
Fluid flow in low-permeability rocks (such as the welded ash flow tuffs found at Yucca
Mountain) is controlled by interconnected fractures. Alteration in low-permeability rocks
is typically focused along fracture flow pathways. Only a small portion of the fracture
volume needs to be sealed in order to retard fluid flow effectively. At Yucca Mountain,
fluid flow and low-temperature water-rock interaction over the past 10 m.y. have resulted
in the precipitation of minor amounts of opal and calcite on fracture and lithophysal
cavity surfaces. 

More extensive water-rock interaction may occur in fractures in the near
field if a heat pipe is generated after waste emplacement occurs.
The main sealing minerals in geothermal systems are silica polymorphs (amorphous
silica, chalcedony, cristobalite, and quartz), swelling clays (smectite and saponite),
zeolites, anhydrite, and calcite. These minerals typically form an impermeable cap above
the high-temperature geothermal reservoir where convective fluid flow occurs. The main
minerals predicted to precipitate in the near field of the potential Yucca Mountain
repository are amorphous silica and calcite.
9 Sealing can occur in geothermal systems over a relatively short time frame (days to
0 years). Precipitation of minerals can be tiiggered by a variety of processes, including
boiling, water-rock interaction, heating and cooling of fluids, and fluid mixing. Mineral
solubilities, reaction rate kinetics, and the flux and chemistry of circulating fluids control
the rates and volumes of mineralization. The unsaturated conditions, lower temperatures,
and much lower' fluid flow rates predicted for the Yucca Mountain system in comparison
to geothermal systems, should result in less extensive water-rock interaction than is
observed in geothennal systems. Current THC models for Yucca Mountain (BSC 2001
[155950], Section 4.3.6.4.2) predict that significant fracture sealing in the near field is
unlikely.
0 Fractuiing and sealing occur episodically in geothermal systems. Different generations of
fracture mineralization indicate that there are multiple pulses of fluid flow, recording
distinct temperature conditions and fluid compositions, throughout the lifespan of a
geothennal system. Most mineralization at Yucca Mountain is predicted to occur soon
after waste emplacement (1,000 to 2,000 years), when temperatures would reach boiling
(for the higher-temperature operating mode) above the emplacement drifts. The absence
of boiling for the lower-temperature operating mode would result in reduced amounts of
fracture mineralization.
o The effects of processes such as boiling, condensation, dissolution, and precipitation for
the higher-temperature operating mode for Yucca Mountain will be most significant in
the near-field environment. Changes in permeability and porosity are expected to be
relatively minor at the mountain scale, where thermal perturbations will be reduced; this
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Natural Analogue Synthesis Report
also applies to the lower-temperature (sub-boiling) design. Relatively small changes in
zeolite concentrations (<1% volume) were predicted within the nonwelded zeolite-
bearing Paintbrush and Calico Hills tuffs resulting from precipitation and dissolution
reactions (BSC 2001 [155950], Section 3.3.6.3.2), and thus the sorptive properties of the
potential repository would not be greatly modified.
TH reservoir models have been effectively used for many producing geothermal systems
to model initial state conditions and to predict changes in field perfonnance resulting
from production and injection activities. The successful use of these models provides
confidence that they can be applied to predict fluid and heat flow at Yucca Mountain.
Incorporation of chemical reactions and transport processes into these models has not
been done extensively for geothennal systems.
THC coupled-process modeling approaches used at Yucca Mountain can be validated by
applying the technique to a number of wel I -constrained geothermal systems. A simplified
model of a portion of the Yellowstone geothen-nal system is currently under construction.
The goal of these simulations will be to reproduce the observed variations in alteration
mineralogy, porosity, and permeability and to demonstrate the effects of THC processes
on fluid flow and chemical transport.
Detailed reviews of selected geothermal systems improve understanding of fluid flow in
fractured rocks, the timing and episodicity of alteration, and the effects of alteration on
permeability. 

A number of geothermal systems hosted by rhyolitic ash flow tuffs such as Long
Valley, Califomia (Mariner and Willey 1976 [156811]; Flexser 1991 [156815]; Sorey et al. 1991
[156816]), and Baca, New Mexico (Hulen and Nielson 1986 [156813]; White 1986 [156814];
Goff et al. 1992 [156808]; Goff and Gardner (1994 [156812]) have been the subject of earlier
studies of core and fluid samples.  Further examination of the zonation, distribution, and ages of
alteration minerals, and porosity and penneability variations as a function of degree of welding,
alteration, and fracture intensity, can serve as additional validation of THC models. To construct
an integrated time/temperature/fluid composition/alteration history of these systems, it may be
necessary to supplement existing information with new fluid inclusion data, penneability and
porosity measurements, and radiometiic age determinations. In the next section, a detailed
review of the Yellowstone geothermal system is presented, with attention focused on silica
mineralization and sealing, geochemical modeling, and their relevance to the Yucca Mountain
system.
11.3 YELLOWSTONE AS A NATURAL ANALOGUE FOR THC PROCESSES
11.3.1 Introduction and Objectives
The Yellowstone geothermal system has previously been utilized as a natural analogue for Yucca
Mountain (CRWMS M&O 2000 [141407]). During the course of the current review of
geotherrnal natural analogues (Section 11.2), Yellowstone was identified as a particularly useful
example of a number of important THC processes of interest. The Yellowstone geothen-nal
system has reservoir rocks very similar in mineralogy and chemistry to rhyolitic tuffs found at
Yucca Mountain. Important processes such as boiling, mineral dissolution and precipitation, and
0 changes in penneability caused by self-sealing have been documented at Yellowstone. An added
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Natural Analogue Synthesis
benefit is the availability of rock and fluid samples collected from surface and subsurface
locations (see Section 11.3.5). In addition to reviewing the existing body of literature on
Yellowstone, permeability and porosity vaiiations were also studied in two Yellowstone
coreholes (Dobson et al. 2001 [154503]; [154547]).
In this section, several aspects of the Yellowstone geothen-nal system are reviewed in the context
of coupled THC processes. These include: (1) observed changes in surface thermal feature
chemistry and associated mineralization; (2) a study of the role of lithology and alteration on
porosity and permeability in the reservoir rocks of the Yellowstone geothennal system; and (3)
fhe validation of water-rock geochemical modeling through study of fluid chemistry and
alteration mineral assemblages. The objective of thi's review is to illustrate how such processes
can affect fluid flow behavior, and ultimately, apply these observations to the potential Yucca
Mountain repository.
11.3.2 Introduction to the Yellowstone Geothermal System
Yellowstone National Park is the site of one of the largest active geothennal systems in the world
(Figure 11.3-1), with hundreds of thermal features located both within and outside of the 0.6 Ma
Yellowstone caldera (Foumier 1989 [156245], p. 16). The Yellowstone volcanic center has had
three major caldera-forming ash flow tuff eruptions (at 2.0, 1.3, and 0.6 Ma); these eruptions
have been interspersed with lesser eruptions of lavas and tuffs that are predominantly rhyolitic in
composition (Hildreth et al. 1984 [1562481, pp. 8339-8350; Christiansen 2001 [1567391, pp.
G11-G68). While the most recent eruptive activity at Yellowstone occurred at about 70 ka, the
high heat flow at Yellowstone suggests that magma currently underlies much of the Yellowstone
caldera.
Studies of the active hydrothermal features at Yellowstone suggest that the geothermal system
consists of two distinct reservoirs: a liquid-dominated reservoir in the westem portion of the
caldera and a steam-dominated system in the eastem portion (Foumier 1989 [156245], p. 17).
The chemistry of chlofide-tich waters sampled from the Upper, Midway, Lower, West Thumb,
Shoshone, and Norris Geyser Basins indicates that the reservoirs feeding these features have
temperatures ranging from 180 to 325'C, with a fairly dilute (<2,000 ppm TDS) neutral chloride
brine (Foumier 1989 [156245], pp. 18-20; Foumier et al. 1992 [156247], p. 1289).
The U. S. Geological Survey drilled 13 research core holes in Yellowstone National Park in
1967-1968, with the objectives of detennining the temperature and pressure gradients and
describing the nature of water-rock interaction at the Yellowstone geothermal system (White et
al. 1975 [154530], Table 3, pp. 1-2). 

These holes range in depth from 66-332 m, with most
holes having depths of 150 m. Pressure and temperature measurements were made as the drilling
progressed, with additional pressure and temperature surveys conducted in most wells after
completion. The highest measured temperature (237.5'C) was obtained at the bottom of the
deepest hole; most of the wells have maximum temperatures of 165-200'C. Continuous core
samples collected from each well were subsequently subjected to detailed mineralogic study to
characterize the primary lithologies and the alteration phases formed by water-rock interaction.
0
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Natural Analogue Synthesis Report
11.3.3 Silica Mineralization at Porkchop Geyser
Numerous studies at Yellowstone have focused on hydrothermal silica sealing and its effect on
permeability (Keith et al. 1978 [106316]; Sturchio et al. 1986 [156253]; Foumier et al. 1991
[156246]). Mechanisms for silica precipitation include: (1) cooling of silica-saturated waters; (2)
mixing of fluids with different chemistries and temperatures; and (3) boiling. Silica sinter is a
commonly observed trait of many of the thennal features at Yellowstone National Park.
Porkchop Geyser, located in the Norris Geyser Basin, provides a natural laboratory to evaluate
rapid changes in permeability due to amorphous silica sealing caused by boiling (Foumier et al.
1991 [156246] pp. 1118-1119).
Porkchop Geyser has been the subject of chemical monitoring for over 50 years. Early changes
in flow characteristics were attributed to the 1959 magnitude 7.5 Hebgen Lake earthquake,
which caused many observed changes in thermal activity throughout Yellowstone (Marler 1964
[156249]). Since the earthquake, flow properties of this thermal feature have evolved from a
quiescent hot spiing (1960-1971) to an infrequently geysering pool (1971-1985) to a perpetually
spouting geyser (1985-1989). The geyser eruption height increased significantly (from 6-9 m to
20-30 m) immediately preceding a small hydrothermal eruption that occurred on September 5,
1989. This eruption consisted of a single blast that formed a crater measuring 13.9 by 11.7 m
(Figure 11.3-2), suffounded by ejecta blocks of siliceous sinter (Foumier et al. 1991 [156246],
p. 1115). Some of the ejected sinter blocks (Figure 11.3-3) had coatings (up to I cm thick) of
clear to translucent botryoidal masses of silica; a few of these masses were still pliable shortly
after the eruption, suggesting that the amorphous silica formed as a colloidal coating on
subsurface cavity walls just piior to eruption.
The observed temporal changes in flow properties were accompanied by systematic changes in
the chemistry of the Porkchop Geyser fluids (Figure 11.3-4). Sodium-potassium-calcium (NKC)
geothen,nometry temperatures increase with time from 214'C in 1961 up to 273'C a few months
prior to the hydrothermal eruption (Foumier et al. 1991 [156246], Figure 4, Table 1, pp. 1116-
1118). These increases in calculated reservoir temperatures are accompanied by increasing silica
concentrations (from 420 ppm in 1961 to 741 ppm in 1989). No colloidal silica was either
detected by observation (via the presence of an opalescent color to the water) or by analysis
(compaiison of colorimetric and total silica measurements) piior to the time that the thennal
feature became a perpetual geyser. While the lack of standing water precluded such
measurements during the time when Porkchop Geyser was a perpetually spouting feature (1985
to 1989), the presence of colloidal silica during this time can be inferred from posteruption
conditions. The boiling water partially filling the eruption crater has an opalescent color, and
18% of the total silica measured on January, 1990, consisted of colloidal silica.
The above observations were interpreted by Fournier et al. 

(1991 [156246], p. 1118-1120) to
reflect changes in the upflow water chemistry and in the amount of boiling occurring during
upflow. The increasing NKC geothermometry temperatures since 1961 suggest that the waters
for this feature were derived from an increasingly hotter source with time. The higher silica
contents are probably caused by both the higher fluid source temperatures and the increased
amounts of boiling occurring during upflow. Deposition of amorphous silica triggered by the
increased silica concentrations would result in decreased permeability within the flow channels
and contribute to increased pressures below constrictions present in the fluid pathways. Fluid
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Natural Analogue Synthesis Report
overpressures probably led to the rupturing of the sinter throttle at the mouth of the geyser,
resulting in a rapid depressurization of the shallow part of the geyser plumbing, causing
immediate boiling that tiiggered the hydrothermal explosion.
11.3.3.1 Comparison with Yucca Mountain
While the amounts of heat and fluid flow at Yellowstone are orders of magnitude greater than
those expected for Yucca Mountain, the link between boiling, increased silica concentrations,
and resulting precipitation of amorphous silica can still be applied to the Yucca Mountain
system. Under the higher-temperature operating mode, where boiling temperatures are predicted
to persist in the near-diift environment for 1,000 to 2,000 years, dissolved solids will precipitate
as dryout occurs (BSC 2001 [154677], pp. 146-171). The amount and composition of minerals
precipitated by dryout depends in part on the flux of fluids into the dryout front and the
composition of these fluids. Development of a heat pipe above the emplacement drifts at Yucca
Mountain could lead to increased fluid flow and chemical transport into the dryout area.
Measured concentrations of dissolved silica in heated waters (26.5-51.7'C) collected from
hydrology boreholes around the Yucca Mountain Drift-Scale Test (DST) are up to two times
those of unheated porewater compositions (BSC 2001 [154677], Table 9). While the DST fluid
concentrations (up to 139 ppm Si02) are still significantly lower than those observed for
Porkchop Geyser (741 ppm), they demonstrate how heating can lead to increased silica
concentration that ultimately results in the precipitation of amorphous silica. Sustained reflux of
silica-bearing fluids into fractures within the dryout zone at Yucca Mountain could ultimately
.lead to plugging of high-permeability flow channels, thus changing fluid flow paths in the near-
drift area. These changes could persist with time, so that when the near-drift area cools below
4D boiling temperatures, seepage into the drifts is restricted to flow along unsealed fractures with
larger apertures. Because of the unsaturated nature of the Yucca Mountain system, fluid
overpressures will not develop, and thus hydrothennal explosions such as the one observed at
Porkchop Geyser do not need to be considered for Yucca Mountain.
11.3.4 Silica Sealing at Yellowstone
Mineral dissolution and precipitation and associated changes in permeability resulting from
water-rock interaction have been observed in a number of geothennal systems (Grindley and
Browne 1976 [154531]; Foumier 1985 [154614]). One of the best examples of self-sealing is
recorded in the subsurface hydrothennal mineralogy observed in Yellowstone drill cores (White
et al. 1975 [154530], pp. 20-22). Keith et al. (1978 [106316], pp. A24-A25) present a summary
of hydrothermal alteration studies conducted on cores from two scientific drilling locations in the
northem part of the Upper Geyser Basin, located about 3 km northwest of Old Faithful Geyser.
These drill holes are separated by only 130 m and have similar stratigraphies, but have
significantly different temperature and pressure profiles. Keith et al. (1978 [1063161, pp. 

A24-
A25) interpret the contrasts in wellhead pressures at equivalent depths to indicate horizontal self-
sealing resulting from hydrothennal alteration. Vertical pressure gradients found in the wells also
suggest the presence of low-permeability flow baniers.
To detennine the nature and extent of self-sealing at Yellowstone, lithologic and alteration
descriptions, matrix permeability measurements, and fracture and vein characterization were
conducted on core samples from the Y-5 and Y-8 boreholes (Dobson et al. 2001 [1545471, pp.
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283-287; [1545031). The Y-5 well, located in the Midway Geyser Basin, penetrates a thick
section of Lava Creek rhyolite ash flow tuff that varies in texture from nonwelded to densely
welded, with vapor-phase cavities present in some sections (Figure 11.3-5). The Y-8 core hole,
located in the Upper Geyser Basin, has a more complex stratigraphy, consisting of voicaniclastic
sediments, perlitic rhyolitic lava, and nonwelded pumiceous ash flow tuff (Figure 11.3-6). Both
of these wells have an upper conductive gradient that changes into a nearly isothen-nal (-170'Q
section at depths of 55-80 m (Figure 11.3-7). Detailed descriptions of the alteration mineralogy
of both of these cores are presented in Keith et al. (1978 [106316], Figure 4, pp. A13-A24) and
Keith and Muffler (1978 [152663], Figure 2, pp. 392-398).
Variations in porosity and permeability (Figures 11.3-8 and 11.3-9) correlate with lithology,
degree of welding, and alteration (Dobson et al. 2001 [154547], pp. 285-286; [154503]). Perlitic
rhyolitic lava samples have low porosities (mean of 10%) and very low matrix permeability
values, as most samples were below the 0.1 millidarcy (md) detection limit of the
mini permeameter. Voicaniclastic sediments typically have intermediate porosities (mean of
27%) and high penneabilities (>100 md), but silicified sediments have much lower
permeabilities and a 50% reduction in porosity. Nonwelded pumiceous tuff samples from the Y-
8 well have very high porosities (mean of 53%) and intennediate perrneability values that range
from 0.54-78.1 md (median value of 5.4 md). Nonwelded to weakly welded ash flow tuffs from
the Y-5 well have intermediate porosities (mean of 34%) and penneabilities ranging from 5.57-
1190 md (median value of 177 md).  Moderately to densely welded tuffs have greatly reduced
porosities (mean of 15%) and very low matrix permeabilities (0.002-18.5 md, with a median
value of <0.1 md). The large difference in matrix permeability between nonwelded and densely
welded tuffs is similar to that reported by Winograd (1971 [156254], Figure 5, p. 999).
Fractures observed in the Yellowstone core samples have a number of different origins, relating
to the cooling of volcanic units, regional volcanic and tectonic processes, and hydrothermal
activity. The distribution of veins and fractures in the Yellowstone cores (Figures 11.3-10 and
11.3-11) is correlated with texture and lithology (Dobson et al. 2001 [154547], pp. 286-287;
[154503]). Veins and fractures are most abundant in the more densely welded tuffs, which have
an average of about 5 fracture/vein features per meter of core over the studied interval (17.7-
84.7 m for the Y-5 core). 

These fractures range from planar to irregular to hackly in form and
have dips ranging from subhorizontal to near-vertical, and many of the fractures probably
originated as joints forrned duiing cooling of the tuff after emplacement (Winogad 1971
[156254], Figure 4, p. 997). The above correlation between fracture frequency and degree of
welding is consistent with the observed fracture distribution at Yucca Mountain, where fractures
are more abundant in welded Topopah Spring tuff (0.81-4.36 fractures/m) than in the nonwelded
Paintbrush tuff (0.46-0.97 fractures/m) (CRWMS M&O 2000 [145771], Table 6).
In the Y-8 core, the perlitic rhyolitic lava has abundant, randomly oriented veiniets and
microveinlets that form a stockwork configuration. In contrast, the volcaniclastic sediments and
nonwelded to weakly welded tuffs have very few veins and fractures. Fracture and vein apertures
range from <0.5 mm up to 20 mm. While most of the fractures observed in the core samples
appear to be effectively sealed by mineralization, the presence of euhedral secondary mineral
phases such as mordenite, analcime, and bladed calcite indicates that some fractures, veins, and
vugs were open to fluid flow and may still serve as open pathways.
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Several zones of hydrothermal breccia (Figure 11.3-12) were observed in the cores (Dobson et
al. 2001 [154547]; [1545031). The breccia zones typically consist of a discrete, near-vertical vein
that broadens upward and contains angular clasts of wall rock up to 5 cm in diameter that form a
jigsaw texture in a brownish-red silica, montmorillonite, and Fe-oxide/hydroxide matrix. These
breccias, found within the densely welded tuff, represent transient conduits of high fluid flow
that are formed by the explosive release of overpressure in the underlying geothermal reservoir,
and are subsequently sealed by supersaturated gedthermal fluids (Grindley and Browne 1976
[154531], pp. 379-381). Numerous hydrothen-nal explosion craters have been identified at
Yellowstone (Muffler et al. 1971 [156250], pp. 723-724), and a small hydrothen-nal eruption
was observed in 1989 at Porkchop Geyser (Foumier et al. 1991 [156246], pp. 1114-1116). This
type of eruption will not occur at Yucca Mountain, because the prevailing unsaturated conditions
will preclude the pressure buildup required for this to occur.
Most fluid flow in the Yellowstone geothermal system is associated with high-permeability
features, namely the matrix of high-permeability lithologies and open veins and fractures. While
the initial permeability distribution is controlled by lithology, subsequent hydrothermal alteration
has clearly modified both matrix and fracture penneability (Figure 11.3-13). Hydrothermal
alteration resulted in the reduction of matrix permeability and focusing of flow along fractures,
where multiple pulses of fluid flow and self-sealing have occurred.
Hydrothermal self-sealing appears to have generated the existing permeability banier that
delineates the top of the convecting geothermal system at Yellowstone. A steep increase in
wellhead pressure observed during drilling between 49.7 (0.55 barg [bar gauge]) and 55.2 m (2.0
barg) in the Y-8 well suggests that a major low-permeability zone is located between these
4D depths within the lower part of the volcaniclastic section (White et al. 1975 [154530], Table 5,
pp. 18-22). The fluid responsible for this pressure increase probably entered the borehole
immediately below the low-permeability silicified interval at 51.7-54.0 m and above the contact
with the perlitic rhyolitic lava at 55.2 m. This depth also marks the transition between a steep
conductive therinal gradient observed above and a near-isothermal section that extends to the
well bottom. The presence of bladed calcite near this interval and elevated 8.180 values of
hydrothermal quartz suggest that the silica sea] may have formed in response to transient boiling
events associated .~,ith depressurization (Sturchio et al. 1990 [154524], Table 1, pp. 30-34).
Silicification is not the only type of hydrothermal alteration that has affected fluid flow in the
Yellowstone geothermal system. 

The presence of abundant clay minerals (montmorillonite and
celadonite) and zeolites (clinoptilolite, mordenite, and analcime) as replacement minerals and in
void spaces also probably reduced the matrix penneability for all of the rock units studied.
Dissolution and replacement of obsidian likely led to localized increases in porosity and
permeability, especially within the volcaniclastic sediments.
Hydrothennal sealing can occur fairly rapidly. Most of the USGS core holes at Yellowstone
were partially or completely plugged by mineral precipitation within 25 years of having been
drilled (Foumier et al. 1993 [154527], p. 33). However, the timing and duration of the
mineralization observed in the Y-5 and Y-8 cores are not well constrained. Uranium-Thorium
disequilibrium dating of Biscuit Basin rhyolite samples from the Y-8 core (Sturchio et al. 1987
[154525], pp. 2029-2030) suggests that uranium was mobilized and added to the rock around 19
ka. Subsequent hydrothennal alteration that decreased permeability (and thus ended uranium
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Natural Analogue Synthesis Report
mobility) in this unit is more recent. A radium disequilibrium study of hot spring waters at
Yellowstone (Clark and Turekian 1990 [156780], p. 179) suggests that the mean water-rock
reaction time (involving congruent rock dissolution and release of radium) in the high-
temperature reservoir is 540 years, with a maximum calculated reaction time of 1, 150 years.
The presence of multiphase veining in the Yellowstone cores suggests that there have been
multiple episodes of fluid flow and self-sealing. A commonly observed vein assemblage for the
perlitic rhyolitic lava is an outer band of celadonite, followed by chalcedony, and with most
recent precipitation of mordenite. The sequential deposition of these phases indicates that there
were progressive changes in fluid chemistry and/or temperature with time that resulted in this
paragenetic sequence.
11.3.4.1 Comparison with Yucca Mountain
These observations from the Yellowstone geothennal system can be used to evaluate the coupled
THC models developed for Yucca Mountain to predict whether, and in what time scale,
permeability changes resulting from water-rock interaction could cause self-sealing at Yucca
Mountain. While the Yellowstone system and the potential Yucca Mountain repository share
many of the same THC processes, the effects of the processes are expected to differ significantly
because of large differences in scale between the two systems, with much less extensive water-
rock interaction predicted for the potential Yucca Mountain repository (Table 11.3-1).
Sturchio et al. (1987 [154525], p. 2029) estimate a conservative formational velocity of 1,500
m/yr (4.8 x 10-5 m/s) for the liquid-dominated, convecting Yellowstone geothermal system,
about four to five orders of magnitude higher than those predicted for Yucca Mountain.
Significantly higher fluid flow velocities occur along fractures, as evidenced by the high fluid
discharge rates observed at many of the hot springs and geysers at Yellowstone. The initial heat
flux value (67.7 kW/acre or 16.7 W/m 2 ) estimated for the higher-temperature operating mode at
Yucca Mountain (BSC 2001 [155950], Section 3.3.5.4) is about one-third the calculated value
(46 W/M2) for the Firehole River drainage basin, where the Y-5 and Y-8 coreholes are located
(Christiansen 2001 [156739], p. G52). However, the heat flux for Yucca Mountain will decline
steadily with time as radioactive decay progresses, so that elevated temperatures at Yucca
Mountain will not be sustained in the near-field environment beyond several thousand ye.ars.
The dissolution, transport, and precipitation of silica are highly dependent on system
temperature, mineralogy, and liquid flux rate, as well as on whether boiling occurs. Rates of
silica dissolution and equilibrium silica concentrations in geothermal fluids at Yellowstone are
significantly higher than those predicted for Yucca Mountain because of the higher temperatures
(170' to 2400C) encountered in the Yellowstone system (White et al. 1975 [154530], Table 3). 

Downhole water samples from the Y-7 and Y-8 wells have silica concentrations of 364 and 290
mg/L, respectively (Sturchio et al. 1989 [154529], p. 1028), more than three times greater than
those predicted for the Yucca Mountain system (Kneafsey et al. 2001 [154460], Table 1) and
more than twice the maximum measured value (139 ppm) of waters collected from higher-
temperature intervals in the Drift-Scale Test (BSC 2001 [154677], Section 6.2.7.3.2). The rate of
silica precipitation and concomitant permeability reduction depends not only on the rate of fluid
flow, but also on processes such as boiling, cooling, and fluid mixing that result in silica
supersaturation and subsequent mineralization. The presence of discrete zones of silicification at
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Yellowstone suggests that the processes controlling mineralization are restricted both spatially
and temporally.
11.3.5 Geochemical Modeling at Yellowstone
Meijer (1987 [101345]) reviewed four active hydrothermal systems (Newberry, Long Valley,
Valles, and Yellowstone) hosted in tuffaceous rocks within the U.S. to select the system that best
reflects the predicted geochemical and hydrologic behavior of the Yucca Mountain repository.
Meijer (1987 [101345], p. 7) developed the following screening criteria:
 Host rocks are tuffaceous with zeolitic alteration
 Presence of an active hydrothermal system
 Availability of core samples with characterized subsurface alteration mineralogy.
 Availability of chemical analyses of then-nal waters
 Availability of geologic and hydrologic data.
Based on these criteiia, Meijer (1987 [101345], p. 10) selected the Yellowstone geothermal
system as the best analogue case for Yucca Mountain.
Detailed studies of the downhole mineralogy at Yellowstone (e.g., Honda and Muffler 1970
[106045]; Keith et al. 1978 [106316]; Keith and Muffler 1978 [152663]; Bargar et al. 1981
[156244]; Bargar and Beeson 1984 [156241]; 1985 [156243]) show that a valiety of secondary
minerals are present. The observed hydrothennal mineralization includes the following phases:
silica polymorphs (quartz, opal-CT, chalcedony, a-cristobalite), zeolites (clinoptilolite,
mordenite, analcime, laumontite, heulandite, dachiardite), sheet silicates (montmorillonite, illite,
chlorite, celadonite, kaolinite, lepidolite), carbonates (calcite, siderite, rhodochrosite), Fe-Mn
oxides/hydroxides, pyrite, fluorite, adularia, albite, and minor accessory phases. The distribution
and abundance of these minerals appears to be controlled by fluid and rock compositions and
temperature.
Several therinal water compositions have been identified for the Yellowstone system on the basis
of fluid samples collected from surface features and wells (Foumier 1989 [156245], pp. 18-20).
Deep thennal waters have low sulfate and high chloride contents, and are near-neutral to slightly
alkaline. Steam condensate waters have low chloride and high sulfate contents, and are acidic.
Meteoiic waters have low TDS contents and are similar to the waters currently found at Yucca
Mountain.
Meijer (1987 [101345]) used reported fluid compositions and the EQ3/6 geochemical codes
(Wolery 1979 [156741]) to calculate mineral assemblages for a fixed temperature. EQ3 speciates
the dissolved constituents and calculates saturation indices for minerals, and EQ6 selects and
precipitates phases to bring the fluids back to equilibrium conditions. A number of water samples
were used for the geochemical modeling, including a sample with the highest silica content
collected from Biscuit Basin that was chosen to represent the deep thermal water composition.
Predicted mineral assemblages include silica polymorphs (chalcedony or cristobalite), zeolites
(leonhardite or K-clinoptilolite), clays (Ca-nontronite, Ca-saponite)  calcite and talc. These
assemblages are similar to those found in the Yellowstone cores. Meijer attributed discrepancies
between the predicted and observed mineralogies to: (1) some of the early-formed mineral
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Natural Analogue Synthesis
phases not being in equilibrium with the cuffent fluids; and (2) the use of inappropriate
thermodynamic data for some of the mineral phases, such as zeolites.
One important observation made from the core samples from Yellowstone is that the effects of
hydrothermal alteration on welded devitiified tuffs for temperatures less than 170'C (and where
the geothermal fluids are not acidic) appear to be relatively minor. 

From this observation, Meijer
(1987 [101345], p. 48) concluded that the thermal pulse at Yucca Mountain would have only
minor effects on the host rocks, limited to transport and redeposition of silica and precipitation of
clays and zeolites in fractures, cavities, and the groundmass.
However, the key factor affecting fluid flow through the welded tuff repository horizon at Yucca
Mountain is not the degree of alteration, but whether or not fluid flow through fractures is
enhanced or restricted by mineral dissolution or precipitation.  Meijer's study validates the use of
geochemical modeling to predict changes in fluid and rock chemistry resulting from water-rock
interaction, but it does not address how alteration of the Yellowstone cores might impact the
overall permeability structure of the host rocks.
Comparison with Yucca Mountain
Recent geochemical modeling for the Yucca Mountain system (BSC 2001 [154677]) employs a
more dynamic approach that couples heat and fluid flow with geochemical transport and
reactions and resulting changes in porosity and permeability. The TOUGHREACT simulators
(Versions 2.2 and 2.3) incorporate reactive chemistry and transport into the framework of the
TOUGH2 Version 1.4 code, which simulates multiphase flow of gas and fluids together with
tracer and heat transport through porous and fractured geologic media (Pruess 1991 [100413]).
The TOUGliREACT code allows for the selection of kinetic or equilibrium thermodynamics to
be used for mineral dissolution and precipitation, and it has several permeability law options
available to relate porosity changes to changes in pen-neability. Simulations of fluid and heat
flow and changes in permeability and porosity resulting from water-rock interaction were
conducted for the near-drift region of the potential Yucca Mountain repository (BSC 2001
[154677]). The results of these simulations (conducted for thennal loads where boiling
conditions persist for 1,000-2,000 years) suggest that only small changes in permeability and
porosity will occur in the near-dfift area (resulting from the precipitation of amorphous silica and
calcite), and that these changes will not have a significant effect on repository performance.
The approach used for these simulations was validated through the modeling of the Yucca
Mountain DST results (BSC 2001 [154677]) and by simulating a series of dissolution and
precipitation experiments conducted using Topopah Spring tuff samples (BSC 2001 [155950],
Section 4.3.6.7.4). These simulations were able to successfully predict observed changes in fluid
and gas chemistry, mineral precipitation, and associated changes in porosity and pen-neability
over the duration of these expeiiments.
11.3.6 Discussion and Conclusions
The Yellowstone geothennal system serves as a natural laboratory for studying a variety of
important THC processes. The presence of abundant thermal features, such as Porkchop Geyser,
afford the unique opportunity to track changes in fluid chemistry and temperature over time and
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Natural Analogue Synthesis Report
observe associated changes in mineral precipitation and reservoir permeability. Detailed studies
of alteration mineralogy using continuous core samples from research holes drilled at
Yellowstone reveal a detailed history of water-rock interaction. Observed variations in rock
lithology, texture, and degree and nature of hydrothermal alteration can be used to identify
correlations with vafiations in porosity and permeability. Densely welded tuffs have very low
matrix permeabilities, but have more abundant fractures than nonwelded tuffs. A permeability
sea] encountered in the Y-8 core results from the precipitation of abundant secondary silica,
which has greatly reduced the porosity and permeability of several intervals of volcaniclastic
sandstones. Silica precipitation at Yellowstone results from both cooling and boiling processes,
which serve to raise silica concentrations to above saturation levels. Geochemical modeling of
fluid compositions has been used to successfully predict observed alteration mineral assemblages
at Yellowstone.
THC processes are expected to have a much smaller effect on hydrogeological properties at
Yucca Mountain than what is observed at Yellowstone, because of unsaturated conditions, lower
temperatures, and much lower fluid fluxes that will result in less extensive water-rock
interaction. Development of a heat pipe above emplacement drifts at Yucca Mountain under the
higher-temperature operating mode could lead to increased chemical reaction and transport in the
near field. Dissolved silica concentrations in waters from boreholes around the Yucca Mountain
DST (with water boiling under heat-pipe conditions near 95'C) are up to two times those of
ambient pore waters. 

Reflux and boiling of silica-bearing fluids within the near field at Yucca
Mountain could cause fracture plugging, thus changing fluid flow paths. THC simulations
conducted to date for the potential Yucca Mountain repository suggest that only small reductions
in fracture porosity (1-3%) and pen-neability (<I order of magnitude) will occur in the near field
as a result of amorphous silica and calcite precipitation (BSC 2001 [155950], Section 4.3.6.4.2).
These predicted changes in hydrogeological properties should not significantly affect repository
perfonnance.
11.4 PAIUTE RIDGE-A NATURAL ANALOGUE FOR THC COUPLED PROCESSES
11.4.1 Introduction
In addition to active geothermal fields described in Sections 11.2 and 11.3, sites of "fossil"
hydrothennal alteration can be useful analogues to illustrate THC processes at Yucca Mountain.
An example of this type of natural analogue is the Paiute Ridge intrusive complex, located on the
northeastem boundary of the Nevada Test Site (NTS), Nye County, Nevada. The complex
consists of late Miocene basaltic dikes and sills intruded into a panially saturated Rainier Mesa
tuff and pre-Calico Hills Formation tuffaceous host rocks. The intrusions were emplaced at an
estimated paleodepth of about 200 m, similar to the depth of the potential repository. The
tuffaceous host rock surrounding the intrusions was hydrothermally altered to varying extent,
depending on the distance from the intrusions (Matyskiela 1997 [100058], pp. 1115, 1117;
Lichtner et al. 1999 [121006], p. 8).
Natural analogues provide a means of investigating the geologic processes characteristic of the
potential repository (which take place over long time spans) and validating coupled-process
models used to predict multicomponent flow, transport, and chemical reactions. The Paiute
Ridge intrusive complex provides useful physical and chemical data for understanding the
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influence of heat released from the repository on the tuff host rock and for THC modeling studies
of the repository. Many other such intrusive complexes exist at the NTS and elsewhere that could
provide an extensive data set for understanding and predicting the behavior of the potential
Yucca Mountain repository.
To model mineral alteration processes properly in the highly fractured tuff host rock, mineral
concentrations and associated surface areas in fractures and rock matrix must be distinguished,
and kinetic rate constants-including nucleation kinetics associated with the transformation of
metastable phases-must be known. In addition, mineral alteration may result in significant
changes to hydrologic and transport properties such as permeability, porosity, and tortuosity of
the repository host rock. Fon-nation of mineral alteration zones on the scale of millimeters to
centimeters could strongly affect the hydrologic properties of the repository host rock. As shown
in Sections 11.2.12 and 11.3.4, fractures could become filled with silica minerals, forming a low-
permeability zone, or cap rock, above the repository. Altematively, the rock matrix bordering
fractures could become sealed, thus reducing or preventing matiix imbibition and creating fast
pathways for infiltrating water to reach the repository. Regardless of whether mineral alteration
in the repository host rock is considered beneficial or detrimental to the integrity of the
repository, potential changes in physical and chemical properties of the host rock create
significant uncertainty in performance assessment models.
11.4.2 THC Coupled Processes Associated with a Yucca Mountain Repository
The tuffaceous host rocks at Yucca Mountain are composed primarily of volcanic glass (absent
in the devitrified repository host units), silica polymorphs (cristobalite, tridymite, and opal-CT),
feldspars, zeolites, clays, and calcite (Broxton et a]. 1987 [102004], Table 2). An important
question is to ascertain whether and at what rate this metastable assemblage will revert to a
thermodynamically stable configuration as a result of heat introduced by the repository. This
transfonnation can be accelerated with the addition of heat in the presence of liquid water in an
otherwise closed system. Uncertainty exists in estimating the impact that heat produced by the
decaying nuclear waste will have on the repository's performance over time (Lichtner et a]. 1999
[121006], Section 6).
It is important to distinguish between changes in the near-field environment that take place in a
closed system and changes resulting from fluid fluxes as a consequence of the heat generated
from radioactive decay. 

For the higher-temperature operating mode, heat pipes may form above
the repository drifts. Heat pipes (Section 11.2.4.5) are characterized by counterflow of liquid and
vapor, with evaporation taking place at one end of the heat pipe and condensation of water vapor
at the other, resulting in degassing Of C02 and a consequent increase in pH and purging of
oxygen (Lichtner and Seth 1996 [1007711, pp. 3-140 to 3-141). Liquid water in the condensate
zone is relatively dilute with reduced pH and chloiide concentrations compared to the ambient
groundwater composition. Within the heat-pipe zone, temperature is near boiling at atmospheric
pressure. Salts are expected to form in the dryout zone where complete evaporation takes place.
High salinities could result during the rewetting phase of the dryout zone, depending on the rate
at which liquid water comes in contact with the deposited salts. This then-nal period is expected
to last for, at most, several thousand years with relatively low liquid fluxes (Lichtner and Seth
1996 [100771]; Hardin 1998 [100350], Figures 5-20 to 5-23; BSC 2001 [154677], Figures 70,
7 1, pp. 121-13 1).
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Scenarios based on THC simulations range from little or no alteration to extensive alteration with
the formation of a silica cap above the repository and alteration of feldspars, silica polymorphs,
and glass to zeolites and clay minerals (Hardin 1998 [100350]; Whitbeck and Glassley 1998
[156452]; Nitao 1998 [117880]; BSC 2001 [154677]). The strong-alteration scenario could result
in significant changes in porosity and permeability of the repository host rock that would affect
its performance. The strong-alteration scenario represents a less probable case, because it
assumes extremely small fracture porosity, and must occur over relatively short time spans
(1,000-2,000 years) and at relatively low temperatures (-95-100'C). At such low temperatures,
nucleation kinetics can inhibit certain reactions, such as precipitation of quartz, zeolites, or clays.
As a consequence, there exists significant uncertainty as to which reactions will actually take
place, and if so, at what rate. Generally, silicate minerals react relatively slowly at low
temperatures, requiring geologic time spans (>10,000 yr) before significant alteration can take
place.
Typically, THC calculations are performed using various forms of the dual-continuum model
(DCM) to distinguish between fracture and matrix flow systems. The different DCMs are
distinguished by the number of matrix nodes and their connectivity (Lichtner 2000 [156428]).
Although fracture apertures used in DCMs can be on the order of millimeters or less, matrix
block sizes are generally quite large-on the order of a meter to half a meter or larger-govemed
by the fracture spacing. Employing a DCM with a single matrix node of this size associated with
each fracture node, it would be virtually impossible to describe processes taking place in the rock
matrix at the millimeter to centimeter scale. DCMs that discretize the rock matrix are
computationally intensive, and for this reason have not been used extensively in THC models
0 applied to the Yucca Mountain repository.
11.4.3 Criteria for Selecting an Intrusive Body as a Natural Analogue for THC Processes
Several critefia should be satisfied for an intrusive body to serve as a natural analogue for THC
processes at a potential Yucca Mountain repository. These ciiteria should include the following:
The intrusive should be of sufficient size to produce enough heat to sustain boiling
conditions for time spans of several thousand years. Typically, dikes and sills with widths
greater than approximately 30 m (98 ft) will be required.
0 The intrusive should be emplaced above the water table. 

Ideally, the host rock in which the intrusive is emplaced should be a volcanic tuff with
compositional and physical properties similar to the Topopah Spring tuff at Yucca
Mountain.
For the Paiute Ridge intrusive complex to serve as a natural analogue for the Yucca Mountain
repository, it is beneficial to demonstrate that the time-temperature-saturation history
surrounding an intrusive sill is similar to that predicted for the repository. The amount of heat
stored in the intrusion is directly proportional to its width. Typical widths in the Paiute Ridge
intrusive complex vary from tens to hundreds of meters. The typical emplacement temperature of
a basaltic intrusion is approximately 1,000-1,200'C. This temperature is considerably higher
than the maximum temperature of about 120'C estimated for the repository (BSC 2001
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Natural Analogue Synthesis Report
[155950], Section 4.3.5.3.3), and thus, the region very near to the intrusion cannot be expected to
correspond to repository conditions. However, farther away from the intrusion, the temperature
is expected to be buffered at the boiling temperature of water at atmospheric pressure. In this
region, evaporation and condensation processes should be very similar to those encountered in a
Yucca Mountain repository. Very likely, heat-pipe effects could have occurred with counter flow
of liquid and vapor that were similar to those predicted to occur above and below the repository.
The Paiute Ridge intrusive complex satisfies the first two criteiia; however, the tuff host rock in
which it has intruded coffesponds to the Rainier Mesa tuff and not the Topopah Spring tuff (see
below).  The Rainier Mesa tuff has different chemical and physical properties compared to the
Topopah Spring tuff. The Rainier Mesa tuff at Paiute Ridge consists of nonwelded vitric
rhyolitic tuff (Simmons 2002 [157578], SN-LANL-SCI-215-VI, pp. 90-94), whereas the
Topopah Spring unit proposed for the repository horizon is a densely welded devitfified rhyolitic
tuff. Because of this difference in welding, important physical properties, including fracture and
matfix porosity and permeability and capillary properties, are different. The mineralogy is also
different-the Rainier Mesa tuff contains abundant glass, compared to the devitrified,
microcrystalline matrix of the welded Topopah Spring tuff. As a consequence, chemical
alteration, as well as wetting and drying characteristics, can be expected to be different. Even so,
given the difficulty in finding an exact analogue to the repository host rock, the Paiute Ridge
complex can provide answers to many questions associated with THC processes at a potential
repository.
11.4.4 Paiute Ridge Intrusive Complex as a Natural Analogue
0 11.4.4.1 Paiute Ridge Geologic Background
The study site is located about 40 km northeast of Yucca Mountain along the northeastem part of
the Nevada Test Site (NTS), Nevada (Figure 11.4-1). The shaliow (-200 m depth) Paiute Ridge
complex consists of late Miocene (8.7 Ma) alkali basalt that was intruded into massive and
bedded middle Miocene Calico Hills Fonnation, Paintbrush, and Timber Mountain Group tuffs
(Byers and Bames 1967 [101859], p. 2; Perry et a]. 1998 [144335], p. 5-42). According to Crowe
et al. (1983 [100972], p. 265), the basaltic intrusions are confined to a series of gently tilted fault
blocks that are within a north-northwest-trending graben system of 15-20 km length (9.3-12.4
mi) and 4-8 km (2.5-5 mi) wide. Most of the faulting predates the basaltic intrusion in this area. 

For further details, the reader is referred to Lichtner et al. (1999 [121006]).
Fieldwork was conducted at Paiute Ridge for this study to characterize changes in tuff
mineralogy, texture, and chemistry resulting from emplacement of the basaltic intrusions. While
some variability in these properties may be attributed to pre-existing compositional, mineralogic,
and textural zonation of the tuff (Broxton et al. 1989 [100024]; Mills et al. 1997 [157570]) and to
low-temperature alteration associated with cooling of the ash-flow sheet and water-rock
interaction since the tuff wds deposited at 11.6 Ma, many of the changes in texture, degree of
alteration, and whole-rock chemistry observed in the Rainier Mesa tuff samples described in
Section 11.4 can be directly related to the proximity of these samples to the basaltic sill contact
(Lichtner et al. 1999 [121006]; Matyskiela 1997 [100058]). Similar types of field relations were
also observed at the Grants Ridge basalt intrusion (WoldeGabriel et al. 1999 [110071]). The goal
0 of the studies described in Section 11.4 was to identify and characteiize the changes in rhyolitic
  11-38  1

 

Natural Analogue Synthesis Report
tuff host rock caused by a thermal pulse analogous to the emplacement of waste packages within
the potential repository at Yucca Mountain. The field observations were then used to constrain
numeiical simulations of the Paiute Ridge system (Section 11.4.7).
11.4.4.2 Field Studies
A reconnaissance field study focused on examining contact relations between basaltic sills,
dikes, and plugs, as well as the volcanic tuff country rock. The field area consists of shallow-
level intrusions exposed at Slanted Buttes and the valley to the east toward Carbonate Ridge
(Lichtner et al. 1999 [121006], Section 3.1, pp. 4-7). Seventeen individual contact regions were
investigated. Seven of these regions were within and around the Papoose Lake Sill, a region also
studied by Matyskiela (1997 [100058]). Two of these regions were sites of detailed sampling.
The field studies focused on evaluating the possible effect of basaltic intrusions on the physical,
mineralogical, and chemical characteristics of the volcanic tuff. The volcanic tuff was examined
in the field for changes clearly related to contact metamorphic effects. The contact relations were
found to vary with the type and thickness of the basaltic intrusion. As a result, the hydrothermal
alteration is more extensive adjacent to thicker sills as compared with thinner dikes.
The most significant chemical and mineralogical alteration was associated with basaltic sills.
Contact relations above, beneath, and adjacent to sills were observed on the southem flanks of
the Slanted Buttes and at the Papoose Lake Sill. In the latter case, it was possible to observe
volcanic tuff above the sill. Alteration was less evident adjacent to dikes compared with sills.
This result may have been a consequence of the subvertical contact geometry, but was probably
also affected by the relatively narrower aspect of the dikes compared with the sills, resulting in
shorter-lived thermal events. 

Dikes were observed in two locations, on the southem and eastem
flanks of Slanted Buttes, and at the Papoose Lake Sill (Figure 11.4-1, Locations B and 0). A
volcanic plug along the southem part of Slanted Buttes, which is probably the source for the
dikes and offshoot sills at Paiute Ridge, was also examined (Figure 11.4-1, Location C). This
plug showed the most significant physical interaction with the host tuff. The outcrop around the
plug allowed direct observations of the contact, demonstrating plastic defonnation of the tuff,
brecciation along the contact zone, and stoping of the host tuff into the basalt flow.
Unfortunately, the determination of the occurrence of alteration at a distance from the plug was
not possible because of poor exposure and talus cover.
A variety of alteration features is readily observable adjacent to contacts. These features include
the following:
Fusion of tuff adjacent to contact with basalt. The tuff is transformed to a dense, glassy
erosion-resistant mass adjacent to contact with larger intrusions.
0 Formation of altered anastomosing opal vein zones (Figure 11.4-2). The tuff engulfed by
these veins is altered in color, texture, and degree of induration. The veins are found both
as isolated features and as complex structures that completely infiltrate the rock. In
places, the center of the veins retains open fractures that may be lined with late-stage opal
deposits.
0
  11-39 

 

Natural Analogue Synthesis Report
 Development of silica-iich veins that penetrate the tuff with relatively little obvious
alteration of the matrix. These veins may be traceable for many meters.
 Development of pipe-like alteration features. Silica-cored pipes (circular features) cross
the tuff, producing concentric alteration halos. These features occur on the scale of a
meter or two.
Milky-white opal deposits along fractures. These appear to be late-stage deposits along
open surfaces.
Calcite-filled fractures widespread in the basaltic sill and adjacent altered tuff (Figures
11.4-3 and 11.4-4).
These alteration features are common and are particularly well developed adjacent to the sills
observed in the area. In regions lacking outcrop, altered tuff can still be identified in weathered
rock fragments scattered as float. 

Two sites were selected for detailed sampling and assessment of the alteration geometry of the
host tuff and the intrusive body (Table 11.4-1). These were the westem limb of the Papoose Lake
Sill (Figure 11.4-1 (Location H), Figure 11.4-5, and transect 7 of Matyskiela (1997 [100058]))
and an exposure beneath a sill exposed on the southem part of Slanted Buttes (Figure 11.4-1,
Location B). Most of the analytical work was conducted on samples collected from the Papoose
Lake Sill and the adjacent host tuff. Hydrothennal alteration features are highlighted in the
following sections, demonstrating significant changes above, adjacent to, and beneath the
40 intrusive bodies. In all cases, the alteration effects diminish with distance from the contact.
11.4.4.3 Contact Metamorphic and Hydrothermal Features at Paiute Ridge Intrusive
Complex
11.4.4.3.1 Alteration Adjacent to Papoose Lake Sill
The Papoose Lake Sill is approximately 27 m (90 ft) wide and trends N17E at the site of detailed
investigation (Figure 11.4-5 and Location H in Figure 11.4-1). The exposure represents a vertical
contact with the ' adjacent fused (vitrophyre) Rainier Mesa tuff along the westem edge of the sill.
The base of the sill is not exposed here and the host rock above the sill is partially eroded. The
basalt along the contact is characterized by vertically jointed plates that are about an inch wide
and oriented parallel to it. In contrast, the basal contact between the sill and the host rock as
observed in other locations is mainly represented by horizontally jointed narrow plates (e.g., the
southem part of Slanted Buttes, Figure 11.4-1, Locations B and E). A few feet from the contact,
the Papoose Lake Sill is massive. Detailed descriptions of the samples mentioned in Section
11.4.4.3 are found in Table 11.4-1 (Simmons (2002 [157578], SN-LANL-SCI-215-VI, pp. 7-32,
90-94).
The basalt is generally sparsely vesicular with amygdules and veinlets of calcite. A sample
(LANL# 3547) collected along the contact is purplish gray, fine grained, and sparsely porphyritic
with partially altered pyroxene phenocrysts. The vitrophyre zone (i.e., fused volcanic tuff)
adjacent to the contact varies in thickness from 0.5 to 2.1 m (1.5 to 7 ft) along strike of the
  11-40 

 

Natural Analogue Synthesis
contact. It is generally black, glassy, and foliated with rare opal nodules, silica and calcite veins,
and veiniets of reddish opaline tuff. Alteration of the tuff was investigated adjacent to the sill.
Two vitrophyre samples (LANL# 3548 and 3549) separated by 8.2 m (27 ft) were collected
along strike, 0.9 and 1.4 m (3 and 4.5 ft) west of the contact zone. The vitrophyre sharply
transitions to a reddish, strongly indurated baked tuff several feet in width. A sample (LANL#
3550) was collected about 0.5 m (1.5 ft) west of the vitrophyre. It is porphyritic with quartz and
plagioclase phenocrysts in a partially devitrified glassy matfix. 

The baked tuff grades to a
nonwelded, pinkish, and weathered tuff (LANL# 3551) that crops out about 1.7 m (5.5 ft) west
of the vitrophyre. The pink, weathered tuff sample occurs along the eastem edge of a narrow
anastomosing opal vein zone. The 8 cm (3 in) wide pinkish orange opal veins (LANL# 3552 and
3554) trend north to south parallel to the sill contact. The host tuff (LANL# 3552 and 3553)
engulfed by the opaline vein zone is pinkish and forms resistant knobs protected by the
surrounding veins (Figure 11.4-2).
These anastomosing veins are found as close as 2.4 m (8 ft) from the contact. In places, the vein
centers are open and contain white opal. The veins pinch and swell and wind around remnant
knobs of tuff. They occur singly and as infiltrating masses. The veins are less common with
distance from the contact and were not observed beyond about 14 m (45 ft). At 6.7 m (22 ft) west
of the vitrophyre, the tuff (LANL# 3555) is altered. In the altered tuff, pumice clasts and the
matrix appear to be totally silicified. In contrast, a sample collected about 0.12 m (0.4 ft) from
LANL# 3555 is partially altered, and the pumice clasts are glassy. At 14 m (45 ft) from the
contact, opal veins and veinlets are sparse. However, the moderately welded host tuff (LANL#
3557) is partially altered and contains glassy pumice clasts. Silica and calcite replacements occur
side by side in the matrix (Figure 11.4-4).
Between 15 and 61 m (50 and 200 ft) from the contact, the nonwelded and unaltered tuff is
friable and vitric and contains large pumice fragments. Naffow fractures contain calcite in some
places, but no other alteration features were evident in cavities and/or vesicles (Figure 11.4-6).
These contact relations represent the most complete record of alteration at close proximity to the
intrusive bodies in the study area.
11.4.4.3.2 Alteration Patterns above the Papoose Lake Sill
Although well-preserved sections were not found above the sill, abundant evidence of pervasive
alteration was observed in the overlying Rainier Mesa tuff. In some places, the alteration
appeared more intense in tenns of density of veining or discoloration and silicification of the
host tuff. Several samples (LANL# 3560-3565) were collected above the sill between the
westem and eastem limbs, directly east of the detailed sampling section at Papoose Lake (Figure
11.4-1, Locations 1, J, K, N, 0, and P; Table 11.4-1). 

Because of poor exposure in the westem
half of the overlying tuff, most of the samples were collected closer to the eastem limb. More
samples (LANL# 3538-3545) were also collected above the Papoose Lake sill at location K,
about 490 m (1,600 ft) northeast of the main sampling location (Location H) along the westem
limb of the sill (Figure 11.4-1). At Location K, the exposed sill is about 15 m (50 ft) wide. The
degree of alteration is similar to Location H, represented by dense anastomosing opal veining
that is about 7.6 m (25 ft) wide. However, unlike the sill contact with the tuff at Location H, no
vitrophyre or fused tuff was noted near the opal veins above the sill at Location K. The Location
K area is not completely exposed, and thus a vitrophere zone that is obscured by talus may exist
  11-41  1

 

Natural Analogue Synthesis Report
in this area. Although the thickness of the veined zone is unknown, it is located about 45 m (150
ft) to the east of the exposed sill margin. The opal veins above the sill are generally oriented
N20W, slightly different from the N-S trend noted adjacent to the sill at Location H.
11.4.4.3.3 Alteration Patterns beneath a Sill
The contact zone of a sill was examined in a gully located on the SW flanks of Slanted Butte
(Figure 11.4-1, Locations A and B). The contact relations below the sill are generally well
exposed and alteration pattems can be observed. The basaltic sill dips about 55' to the south. The
sill is about 7.6 m (25 ft) thick at the point of investigation. The basalt is purplish gray, coarsely
vesicular, and includes trains of fine vesicles. Amygdules filled with calcite and opal are
common.  Large altered mafic phenocrysts are also present. The basalt along the contact exhibits
a thin chilled margin, consisting of horizontally jointed (with respect to the sill) and narrowly
spaced plates along the contact with the underlying tuff. In contrast, at the Papoose Lake Sill in
the northem part of Paiute Ridge, vertically jointed plates characterize the sill margin. These
features clearly delineate the nature of the contact between the basaltic intrusions and the tuff
host rocks. The country rock tuff units are pre-Rainier Mesa tuff and belong to the Wahmonie
Formation and Crater Flat Group (Table 11.4-2). Two samples (LANL# 3570 and 3571) were
collected from the contact and the top part of the sill (Figure 11.4-1, Location B). The pinkish
tuff along the contact with the basalt does not form a foliated vitrophyre (as was noted at the
Papoose Lake Sill in the northem part of the Paiute Ridge area), but exhibits a dense, coarse-
grained granite-like texture, possibly as a result of slow cooling. 

Incipient mineral layering is
noted within the fused tuff directly beneath the sill. About a foot beneath the contact, the tuff
(LANL# 3572) grades from coarser to fine-grained crystalline material. This resistant contact
zone extends for 1.2-1.5 m (4-5 ft) below the basalt. Unlike the sections sampled in the northem
part of the Paiute Ridge area, there are at least five tuff units beneath the sill that are cut by a
dike finger that is vertically wedged along a fault into the underlying tuff sequence. The fault
zone is extensively altered to clay. Two tuff samples (LANL# 3573 and 3574), collected about
1.3 m (4.4 ft) beneath the contact, are generally nonwelded. A moderately welded, light gray tuff
(LANL# 3575-3578) that contains brown and dark lithic fragments occurs about 4.6 m (15 ft)
beneath the sill. At 6.4 m (21 ft) beneath the sill, the same unit (LANL# 3576 and 3577) contains
multiple layers of white to reddish orange opal veins and veinlets mostly parallel to bedding and
to lithologic contacts.
These opal veins are of different character than those observed at the Papoose Lake Sill section.
They consist of white siliceous cores surrounded by a discoloration halo in some places and no
observable halo in other places. They occur parallel to the sill-tuff contact and are about an inch
in thickness.
These fractured veins pinch and swell along strike and mostly occur in a 0.6 m (2 ft) wide zone.
About I m (3.4 ft) below the vein zone, the tuff (LANL# 3578) is nonwelded and contains no
opal veins. A white crystal-rich tuff crops out about 11 m (35 ft) beneath the sill. It is coarse
grained with pumice clasts and abundant feldspar, quartz, and biotite phenocrysts. On the south
side of the dike that wedges down into the underlying tuff, the crystal-rich tuff is intruded by a
0.12-0.46 m (0.4-1.5 ft) wide opal vein that is 4.9 m (16 ft) beneath the sill. The vein trends
obliquely to the tuff-sill contact and is traceable for more than 30 m (100 ft). this vein strikes
  11-42  1

 

Natural Analogue Synthesis Report
N-S and dips 65' to the east. In addition, siliceous pipes occur about 4.6 m (15 ft) below contact.
They are well-indurated and characterized by a white core and circular reddish halo.
11.4.5 Original Depth of Intrusions
Paleozoic limestone, quartzite, and shale unconformably underlie middle Miocene tephra of the
Timber Mountain and Paintbrush tuffs and older undivided tuff units at the Paiute Ridge study
area (Byers and Bames 1967 [101859]; Perry et al. 1998 [1443351). The Tertiary tuffs at the
northem and southem study areas were extensively intruded by shallow late Miocene basaltic
dikes, sills, and plugs. 

A light pinkish brown tuff (LANL# 3539) collected from a 7.6 m (25 ft) wide, densely
veined zone about 46 m (150 ft) from the westem edge of a sill northeast of the Papoose Lake
Sill is sparsely porphyiitic with plagioclase, albitic sanidine, quartz, biotite, and minor amounts
of homblende and clinopyroxene. Secondary minerals of silica, calcite, and minor clay replaced
the matiix. These secondary minerals also occur in cavities and along fractures as veiniets,
aggregate crystals, and radiating spherules, ranging in width from 25-105 gm. At Papoose Lake
Sill (Location H), east of the main outcrop, a number of Rainier Mesa tuff samples collected
above the sill are strongly indurated, moderately altered, and contain similar phenocryst
assemblages. Secondary minerals of opal, calcite, and zeolite replaced the matrix and also occur
in cavities and fractures. Shard fragments and p umice clasts are totally replaced by secondary
silica.
Similar physical (e.g., color, hardness, welding, veining) and mineralogical (silica, zeolite,
calcite) alteration pattems are noted in the basalt and host tuff samples collected from the main
section adjacent to the Papoose Lake Sill. The basalt along the contact is fine grained, vertically
jointed with uniformly spaced plates, purplish gray, and sparsely vesicular with minor calcite
and/or opal amygdules. The altered basalt is porphyritic with plagioclase and sparse mafic
minerals that are altered to reddish brown spots. The matrix is dominated with microlites and
microcrystalline aggregates of pyroxene. Secondary calcite, silica, clays, and perhaps zeolites
occur as veiniets and crystal aggregates in cavities and along fractures. The veinl ets pinch and
  11-44  1

 

Natural Analogue Synthesis Report
swell and range in width from 90 to 135 ltm. Some cavities or mineral pseudomorphs are
partially filled with abundant microcrystalline aggregates of epidote and calcite (Figure 11.4-3).
Three main alteration zones were identified in the tuff near the basaltic intrusion: (1) a vitrophyre
zone immediately adjacent to the sill contact, (2) a baked zone, and (3) an altered zone
characterized by opal veining. The host tuff adjacent to the basaltic sill contact was fused and
transfonned to a foliated, perlitic vitrophyre with opal amygdules and silica veinlets. The
phenocryst assemblage in the vitrophyre is similar to the overlying tuff. Secondary silica
deposits, represented by overgrowth around phenocrysts up to 27 jAm wide and veiniets that are
27 Rm to 0.28 mm wide, are commonly noted parallel and transverse to welding fabric. Away
from the contact, the intensity of alteration transitions from the 2.1 m (7 ft) wide vitrophyre at
the contact to a baked interval and then to a 7.6 m (25 ft) wide zone that is characterized by
dense, anastomosing opal veining (Figure 11.4-2). The tuff samples are sparsely porphyritic with
variable degrees of welding. In one of the samples (LANL# 3554), the phenocrysts are
segregated and fonn bands of crystals represented by quartz, plagioclase, sanidine, and minor
biotite and homblende. 

Based on reconstructed topography above the sills and dikes, it was
suggested that the intrusive bodies were emplaced a few hundreds of meters from the
paleosurface (Valentine et al. 1998 [119132], p. 5-29, Figure 5.16; Ratcliff et al. 1994 [106634],
p. 413). This assumption is consistent with the presence of abundant vesicles along the edges of
the sills and dikes, the localized nature of the contact metamorphic effects adjacent to the sill,
and minimal amounts of hydrothermal alteration along the contacts (Valentine et al. 1998
[ 119132], pp. 5-41 to 5-44, 5-5 1).
However, based on detailed field observations of contacts between the intrusive bodies and host
tuffs throughout the study area, it appears that the sills and dikes started at deeper levels close to
the plugs and eroded centers and migrated up section into shallow levels away from the central
part of the intrusive complex. For example, the sills generally branch out from major dikes and
intruded into pre-Rainier Mesa tuff units in the southem part, whereas the Papoose Lake Sill in
the north intruded into the Rainier Mesa tuff. This observation is corroborated by subsurface
stratigraphic data from several drill holes (Figure 11.4-1) along the eastem part of Yucca Flats,
which provide information about the type and thicknesses of the major tuff units deposited in the
basin adjacent to Paiute Ridge during the Miocene (Drellack and Thompson 1990 [156446], pp.
1-11). The thicknesses of the tuff units encountered in these diillholes can be used to estimate
the original thicknesses of the corresponding units that crop out in the adjacent Paiute Ridge area
(Figure 11.4-1; Table 11.4-2). 1
According to the subsurface stratigraphic infon-nation, the major tuff units intersected in the
upper part of the Yucca Flats drill holes consist of the Timber Mountain Group (i.e., Rainier
Mesa tuff and Rainier Mesa tuff vitrophyre), the Lower Wahmonie Formation, and the Crater
Flat Group in descending stratigraphic order. The Ammonia Tanks tuff at the top of the Timber
Mountain Group, the Paintbrush Group, and the Calico Ilills Formation units were not defined in
the drill holes (Drellack and Thompson 1990 [156446]). Using the thicknesses of the different
tuffs in the drill holes (from the surface to the top of the Rainier Mesa vitrophere unit), it is
estimated that the late Miocene basaltic magma was intruded into a shallow environment of
about 200 m depth.
Infonnation on the degree of alteration of the tuffs encountered in the drill holes can be used to
help differentiate between alteration caused by the basaltic sills from more regional alteration
events. According to the Yucca Flats drill hole data (Table 11.4-2), pervasive zeolitization
(interpreted to predate the intrusion of the basaltic sills) occurs in the lower half of the subsurface
sequences, typically below the Rainier Mesa tuff unit. The presence of zeolites (such as
clinoptilolite and chabazite; see Table 11.4-3) in Rainier Mesa tuff samples adjacent to the sill
  11-43  1

 

Natural Analogue Synthesis
contact (and above the regional zone of pervasive zeolitization) was thus attributed to
hydrothermal alteration res-ulting from the sill intrusion.
11.4.6 Laboratory Methods and Results
Thin sections were prepared of almost all of the samples for petrographic descriptions, using
optical and scanning electron microscopic techniques. Selected samples from the host tuff and
basaltic sill in the Papoose Lake area were processed for bulk chemical and mineralogical
analyses. Additional major-element glass chemistry was obtained for most of the tuffs selected
for bulk analysis, using an electron microprobe. Most of the tuff samples selected for analysis
were collected adjacent to the sill at Location H.
11.4.6.1 Petrographic Results
The mineralogical and chemical characteristics of the alteration are keys to understanding the
conditions of hydrothermal processes'. Petrographic observations identify opal and calcite
veining associated with some of the alteration features (Simmons 2002 [157578], SN-LANL-
SCI-215-VI, pp. 89-94). Calcite appears rather abundant in some sections. The vitrophyre found
adjacent to the basalt contact contains significant volcanic glass and is largely free of hydrous
mineral alteration. Some interesting observations were made of the anastomosing veins from the
Papoose Lake Sill locality.
Preliminary petrographic examination of samples of Rainier Mesa tuff systematically collected at
intervals from the contact zone to about 61 m (200 ft) west of the sill indicate variable physical
and mineralogical alterations (Figure 11.4-1, Location H). Compaiison of two tuff samples from
above the sill collected at different distances from the sill outcrop (Figure 11.4-1, Locations K
and N) indicated that the intensity of alteration above the sill decreases away from the sill
margin. 

Consistent with the petrographic results,
the basalt from the contact and those tuffs collected within 14 m (45 ft) from the sill contain
abundant secondary minerals dominated by clinoptilolite (Table 11.4-3). Although petrographic
analysis reveals calcite and silica in the basalt, smectite was the only secondary mineral
identified by XRD analysis. Despite clay-like alteration noted petrographically in most of the
altered tuffs, the XRD results show only vaiiable amounts of opal, tridyrpite, cristobalite,
clinoptilolite, and chabazite in the various tuff samples.
11-4.6.3 Geochemical Results
Aliquots of powdered samples were used for major and trace element analyses using a Rigaku
3064 wavelength dispersive X-ray fluorescence (XRF) (Simmons 2002 [157578], SN-LANL-
SCI-215-VI, pp. 63, 69-76). Analysis and statistics of the unknown samples are based on a
model that uses intensities for 21 standard rocks. To assess whether the major and trace element
variations of the tuff samples are genetic or a result of hydrothermal alteration related to the
basaltic intrusion, major and trace element concentrations of bulk-rock samples were plotted
against distance from the sill (Figures 11.4-7 and 11.4-8). An average Rainier Mesa rhyolitic tuff
composition reported by Broxton et al. (1989 [100024]) is plotted with these data for
comparison. A discussion of the ma . or and trace element vaniability and its origin is presented in
Section 11.4.6.4.
0 111.4.6.4 Discussion
Field and analytical results suggest that the Paiute Ridge basaltic dikes and sills intruded into at
least two different tuff units, the Rainier Mesa tuff of the Timber Mountain Group and older
bedded tuffs from the Lower Wahmonie Fonnation and Crater Flat Group that mostly crop out in
the southem part of the study area. Generally, the host tuffs in the southem part of the study area
are thin, mostly bedded, and crop out along gullies. Those outcrops in the northem part are
massive, nonwelded, and occur mostly along ridge tops. Most of the analytical results were
obtained on samples collected from the Papoose Lake Sill area at Locations H, N, and K (Figure
11.4-1). These tuffs are pinkish, sparsely porphyritic, variably welded, massive, and generally
contain abundant pumice clasts. For example, a light pinkish brown tuff from above a sill at
Location K contains plagioclase (30%), quartz (32%), sanidine (38%), and minor amounts of
blotite, homblende, and clinopyroxene. According to Byers et al. (1976 [104639]), mafic
phenocrysts such as homblende, clinopyroxene, biotite, plagioclase, and Fe-Ti oxides are
common in the upper part of the Rainier Mesa tuff, and sanidine generally contains
cryptoperthite fims. A vitrophyre (fused tuff) and a nonwelded tuff collected at Location H
adjacent and at 61 m (200 ft) from the Papoose Lake sill, respectively, also have similar
phenocryst assemblages with diagnostic albitic rims on sanidine, which is a characteristic feature
of alkali feldspars in the Rainier Mesa tuff (Byers et al. 1976 [104639], p. 42).
Depending on proximity to the sill, vaiiable degrees of alteration related to the intrusion are
recorded in the tuff units. For example, the transformation of the nonwelded Rainier Mesa tuff to
vitrophyre, hardening and discoloration resulting from baking, and the prevalence of
  11-46 

 

Natural Analogue Synthesis Report
anastomosing opal veins within 12 m (40 ft) of the sill are macroscopic physical modifications
related to the sill. However, such features are not uniformly apparent at all the contacts studied
during the field investigation. At Location H of the Papoose Lake Sill area, the 12 m (40 ft) wide
alteration aureole adjacent to the sill progressively changes from a 2.1 m (7 ft) wide vitrophyre at
the contact to a comparable size of baked interval, and to a 7.6 m (25 ft) wide opal veining zone. 

However, such systematic alteration is not fully developed at Location K above the sill. There,
hardening of the tuff and a 7.6 m (25 ft) wide opal vein zone are developed 46 m (150 ft) east of
the westem edge of the sill. At Location B in the southem part of the study area, the pre-Rainier
Mesa tuff units are exposed beneath the sill and the alteration features are different from those
noted at Locations H and K. The tuff directly beneath the sill was transformed into a granitic-like
granular-to-fine-grained rock, suggesting slow cooling, following the fusion of the tuff. In
contrast, the vitrophyre observed at location H represents a fused Rainier Mesa tuff that chilled
rapidly adjacent to the sill. The type of the stratigraphic units and the nature of the fused tuff
along the contact (e.g., vitrophyre or granular) suggests that the level of intrusion was deeper in
the southem part compared with those sills and dikes along the northem boundary of the basaltic
intrusive complex. In the southem part, multiple opal veins, ranging in thickness from a few
inches to about a foot thick are present within 6 m (20 ft) below the contact. The opal vein zone
(:0.5 m or 25 ft wide) noted adjacent and beneath the sills at Locations B and H (Figure 11.4-1)
represent mass silica mobilization from altered tuff within the hydrothermal aureole. Although
other low-temperature secondary minerals are closely associated with opal, no systematic
zonation is apparent from the effect of the basaltic intrusion. The anastomosing opal veins
engulfed vaiiable sizes of tuff clasts that are partially affected by these veins. Although there was
voluminous mobilization of silica along fractures created during the basaltic intrusion,
subsequent fluid flow was probably significantly reduced because of the impenneable opal veins.
The alteration zone occurred at close proximity and parallel to the basaltic sill (:514 m or 45 ft),
likely creating a barrier between the intrusion and the outer tuff units.
Petrographic examination of samples from hydrothermal alteration zones at Locations H and K
revealed other secondary features related to the intrusions. Silica, calcite, zeolite, and clay
materials are present as veinlets along fractures, as clusters in cavities and matrix, and as
overgrowths around feldspar and quartz phenocrysts. These features appear to contain abundant
zeolite (clinoptilolite) and show precipitation layering within the veins (Figures 11.4-6a and
11.4-9b). The figures show a tabular crystal of zeolite overgrowing a second layer of zeolite
having a scalloped or rounded morphology.
The presence of zeolite as multiple generations within fractures and cavities of the altered tuffs
suggests that zeolites in addition to silica were deposited by hydrothermal alteration associated
with the basaltic intrusion. However, older zeolitzed tuffs are present in the southem part of
Paiute Ridge and in the lower half of the subsurface units intersected in the drill holes along the
eastem part of Yucca Flats (Table 11.4-2; Drellack and Thompson 1990 [156446], pp. 60, 64,
66, 68-69; Valentine et al. 1998 [119132], p. 5-46, 5-55, Table 5.3). The silica and calcite
veinlets that range in width from microns to millimeters and in length to several millimeters also
fonned during this process. The pumice clasts and the glassy matlix of the tuffs from the
alteration zone are mostly devitrified and/or totally replaced by calcite and silica. 

A basalt
sample from the contact at Location H is also moderately altered. The rock is purplish gray and
contains clay, calcite, epidote, and silica along fractures and in cavities.
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Natural Analogue Synthesis Report
Published Rainier Mesa tuff chemical data from the lower part of the unit (Quinlivan and Byers
is 1977 [156450], Table 6; Broxton et al. 1989 [100024], Table 3) are correlative to the major and
trace element concentrations of the tuff samples from Locations H, K, and N in the northem part
of Paiute Ridge. This observation is also consistent with the petrographic results. Physical,
mineralogical, and chemical variations noted in some of the Paiute Ridge samples collected from
the hydrothermal aureole beneath, adjacent, and above the basaltic sills are attiibuted to the
intrusions.
Localized chemical variations are noted in the host tuffs adjacent to the basaltic sills. Variations
in major and trace element contents are more pronounced in samples collected near the contact
(Figures 11.4-7 to 11.4-8). For less mobile components such as Ti02, A1203, total iron, Nb, and
Zr, little variation is observed throughout the suite of samples, with most variability occurring
within a zone that extends 30-40 feet from the sill contact. While silica appears to be mobile (as
observed by the presence of opal veins), the actual range of observed silica concentrations for all
of the analyzed tuff samples is fairly small (74-81% Si02, nonnalized to anhydrous
compositions). Significantly more variability is observed for the more mobile alkali and alkaline
earth elements (Na, K, Rb, Ca, Sr). Most of the variability for Na, K, and Rb occurs within 30 ft
of the sill contact, suggesting that the original tuff compositions were modified by hydrothennal
alteration resulting from the sill intrusion. However, the distribution of Ca (and Sr to a lesser
degree) is much more scattered. The measured CaO concentrations of the tuff samples (ranging
from 0.5 to 5.6% CaO, normalized to anhydrous compositions) are generally higher than the
average Rainier Mesa rhyolitic tuff composition (0.52 wt.%) of Broxton et al. (1989) [100024]
(Table 3). The observed increase in CaO contents is in part caused by the presence of vafiable
amounts of secondary calcite in the tuff samples. The calcite may originate from two separate
events, one being the intrusion of the sill, while the other would be low-temperature precipitation
of calcite from infiltrating groundwater over millions of years. One of the samples collected
about 122 m (400 ft) above the sill at Location 0 (LANL# 3560) has higher Fe203, MgO, CaO,
Sr, Zr, and Ba concentrations. This, may reflect a difference in the bulk rock composition
resulting from the presence of lithic fragments within the tuff (Simmons 2002 [1575781, SN-
LANL-SCI-215-VI, p. 25).
As shown in Table 11.4-3, abundant clinoptilolite with minor chabazite fonned from the
alteration of glass within the contact aureole of the basaltic sill at Papoose Lake Sill. Hydrolysis
of volcanic glass, resulting in higher alkalinity and increased silica and alkali ion to hydrogen
activity ratio in pore fluids, provided the necessary environment for the fonnation of zeolite (Hay
1978 f 105967], pp. 135-136; Broxton et al. 1987 [102004], pp. 91, 93). 

A documentation of the mass- and
heat-conservation equations in the dual-continuum model used in FLOTRAN, and their relation
to the equivalent-continuum formulation, is presented in Simmons 2002 ([157578], SN-LBNL-
SCI- I 08-V2, pp. 17-2 1).
Equation-of-state properties used in FLOTRAN for pure water were derived from the IFC
(Intemational Formulation Committee) (1967 [156448]). Constitutive relations must be provided
as ftinctions of pressure and/or temperature for the density, viscosity, saturated vapor pressure
curve, intemal energy, and enthalpy of pure water.  The reported validity of the equation of state
properties lies in the range of pressure p and temperature T. 0 < p < 165.4 x 105 Pa (165.4 Bars),
and 0 < T < 800'C (IFC 1967 [156448], p. 1, Figure 2). Although this is satisfied for pressure, it
is not satisfied for the temperature range needed to describe the intrusion. However, as
demonstrated in Table 11.4-4, the calculated properties are quite close to the measured values
reported by Haar et al. (1984 [105175], Table 3) at the maximum temperature of interest.
0
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Natural Analogue Synthesis
In the scoping calculations that follow, a one-dimensional (I-D) model was considered of a
is semi-infinite medium representing the host rock in contact with the intrusion (Figure 11.4-10).
This approach is a simplified model in which the effects of gravity and surface infiltration are
neglected. By symmetry, only half of the dike width need be modeled. A 30 m wide completely
dry intrusion with an initial temperature of 1,200'C is assumed to be emplaced instantaneously
into unsaturated tuff at ambient temperature and pressure.
Rock properties and initial and boundary conditions used in the calculations for the equivalent
continuum model are listed in Table 11.4-5. The values used for density, specific heat, and
thermal conductivity for basalt are typical for basalts as listed in Drury (1987 [156447], p. 107).
Very small values for porosity and permeability of basalt were chosen to simulate an essentially
impenneable intrusion. The "tuff' values are representative of the nonwelded Paintbrush tuff
(PTn) at Yucca Mountain (approximately analogous to the nonwelded tuffs at Paiute Ridge). (It
should be noted that the host rock at Papoose Lake Sill is now believed to be composed of
Rainier Mesa tuff, which had not been established at the time these calculations were
performed.) Values for van Genuchten parameters (fracture/matrix equivalent continuum) are
means for PFn values in Wu et al. (1997 [156453], Table A-1). Then-nal properties of tuff are
from Francis (1997 [127326], Table B-1). Values for density and porosity are from Peters et al.
(1984 [1219571, Table A-2). 

Saturation values ranging from 0.4 to 0.6 are observed for the PTn
at Yucca Mountain, and corresponding calibrated model values were taken from Robinson et al.
(1997 [100416], Table 5.2). Because of the extreme dryout conditions produced by the high
temperature of the intrusion, the results are sensitive to the cutoff used to evaluate the
characteristic curves near the residual saturation.
11.4.7.2 Dual- Continuum Model Calculations
Several cases are considered with varying coupling strength between fracture and matrix
continua. Values for the fracture-matiix area factor of cyfm = 10-6, 10-4, 10-2 , and 102 are compared
and contrasted. Results are shown in Figures 11.4-11 to 11.4718 for fracture and matrix
temperature and saturation as functions of distance for various times indicated in the figures.
Boiling and condensation fronts propagate into the country rock as indicated by the 100'C
isothenn and changes in saturation. Liquid water is stable only for temperatures below the
boiling point, coffesponding to approximately 100'C at atmospheric pressure. In the figures,
boiling occurs at the leading edge where saturation increases from zero. The boiling front is
followed by condensation further away from the intrusion, where both saturation and
temperature return to ambient conditions. In the intervening region, the temperature is buffered
at the boiling temperature of 100'C. In this region, a heat pipe is present with counterflow of
liquid and gas. High flow rates of liquid towards the contact are a consequence of capillary
suction, as the country rock is dried out from heat released from the intrusion. At early times,
liquid flow rates are on the order of 1,000 m/yr, with gas flow rates several orders of magnitude
higher.
As can be seen from the figures, fracture and matrix saturations are very different, even for
strong coupling between fracture and matrix, in order to preserve equality of the capillary
pressure between the two continua. For crfn = 100 (shown in Figures 11.4-11 and 11.4-12), the
dual-continuum results agree with the equivalent-continuum model. Fracture and matrix
temperatures are identical, and saturations obey Equations 11-19 and 11-26 in Lichtner (2001
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Natural Analogue Synthesis Report
[156429]). With the fracture volume fraction F-f = 0.01, fracture porosity of = 1, and matrix
porosity 0 .. = 0.47, it follows that the equivalent continuum porosity 0, =_ 0", and the equivalent
continuum saturation s, =_ s,,, the matrix saturation. The fracture saturation follows from
Equation 11-26 (Lichtner 2001 [156429]). As can be seen from the figures, fracture and matrix
temperatures become significantly different from one another only in the extreme case of very
weak coupling strength with (yf. = 10-6 . For weaker coupling, the fracture network cools
sufficiently to sustain liquid water at the intrusion-host rock interface for times up to one year, as
shown in Figure 11.4-19. 

It should be noted that
a more detailed desciiption of the chemical system is required to distinguish between the
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Natural Analogue Synthesis Report
different chemical compositions of the basaltic intrusion and the tuff host rock; however, this
level of detail was not attempted in this preliminary study. Fast kinetics were assumed with
reaction rates close to local equilibrium. The value for the saturation cutoff used in the
calculation was 0.001. Figure 11.4-20 shows the volume fraction of amorphous silica in the
fracture at different times for the case of af,,, = 10-2 . As the boiling front propagates into the host
rock, silica precipitates from solution in the fractures. The source of silica is derived from the
matrix upstream where dissolution of amorphous silica occurs (not shown). This result appears to
be consistent with field observations at the Papoose Lake Sill.
11.4.7.3 Discussion
Although the field observations for mineral alteration are not inconsistent with the
dual-continuum model predictions, there still remain a number of puzzling features. First, the
close confinement of the alteration of the tuff host rock to zones adjacent to the intrusion is
difficult to understand. This is the region that would be expected to be dry over the long term
until the system cooled and rewetting took place. Whether the alteration could have occurred
during the relatively rapid and transient passage of the boiling front as it swept through the host
rock is still unresolved. It would appear difficult, however, to explain the extent of alteration of
the matrix as caused by such a short-duration, transient event. Unfortunately, alteration of the
matrix is not properly desciibed by the dual-continuum connected-matrix model used here. A
better approach would appear to be the dual-continuum disconnected-matrix fon-nulation, which
was beyond the scope of the present study.
A second puzzling feature is the sporadic appearance of alteration along the contact rather than a
Is more unifonn appearance, as modeling would predict. This feature could have several
explanations. One is that nucleation kinetics were involved, and in most places, the reactions
simply did not take place, although they were then-nodynamically favored. This could be a result
of low permeability and porosity values present in portions of the tuff (especially those that were
fused) which would thus restiict the amount of water that could interact with the rock. Another
possibility is that dehydration reactions of the basaltic dike released volatiles that reacted with
the tuff host rock. Additionally, the host tuff may have had variable physical and chemical
properties prior to the intrusion of the sill that might have resulted in non-uniform alteration.
Sensitivity analyses would help improve future models of the Paiute Ridge system. 

A number of
the model input parameters are uncertain, and a sensitivity analysis would be useful to determine
which parameters have the most impact on model results. In this regard, it should be emphasized
that, for example, the van Genuchten parameters used for the intrusion and tuff country rock
were not based on field measurement but were geneiic values that are approximate at best. The
initial saturation condition of the tuff host rock plays an important role in moistOre and heat
redistribution, but is difficult, if not impossible, to know saturation values at the time the
intrusion was emplaced.
11.4.8 Conclusions of Paiute Ridge Study
Magmatic intrusions in tuffaceous rock above the water table offer a unique opportunity to study
conditions analogous to the potential Yucca Mountain high-level nuclear waste repository
following emplacement of waste. The Paiute Ridge intrusive complex in partially saturated tuff
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Natural Analogue Synthesis Report
appears to offer a possible natural analogue site. A new result of this study is that the Papoose
Lake Sill apparently intruded into Rainier Mesa tuff, and the resulting hydrothermal process was
characterized by low-temperature alteration of glass to clinoptilolite and opal. The key
observations of this study suggest that:
9 The intrusion generally occurred at shallow levels and decreased in depth away from the
central intrusive complex.
The basalt along the contact is sheeted into narrow vertically or horizontally jointed
plates, depending on whether the host tuff is exposed adjacent to or beneath the sill.
0 Variable cooling pattems (e.g., glassy or crystallized fused tuff) occurred as noted along
the intrusive contact.
Alteration of nonwelded tuff to clinoptilolite and opal is similar to that observed in
diagenetic processes at Yucca Mountain.
o Fractured zones in the tuff created by the basaltic intrusion were sealed by extensive
silica remobilization during hydrothermal processes, resulting in low-porosity, highly
indurated tuffs adjacent to the intrusive body.
Hydrothennal alteration was confined to a narrow zone close to the contact zone, as
indicated by major and trace element chemical data.
Field observations at the Paiute Ridge intrusive complex and results from laboratory analysis of
altered and unaltered tuffs illustrate the intensity of hydrothermal alteration and extent of THC
processes associated with thennal perturbation of rhyolitic ash flow tuffs. The secondary mineral
assemblages are similar to those present at Yucca Mountain, and the presence of these minerals
in the tuff at Paiute Ridge indicates the extent of the alteration. The pervasive anastomosing opal
veins an,d associated secondary minerals (e.g., clinoptilolite, calcite, ciistobalite) appear to have
reduced matrix or fracture permeability in the immediate vicinity of the basaltic intrusion. The
observed mineral zonations can be used to evaluate coupled process models. The widespread
opal veins along fracture-matrix margins provide a means for evaluating porosity/permeability
relationships and descriptions of fracture-matrix interaction employed in THC codes.
Preliminary results were presented for a one-dimensional THC dual-continuum model of the
interaction of country rock with heat released from an intrusive complex emplaced above the
water table.  A simplified chemical system was considered involving precipitation and dissolution
of amotphous silica. Results demonstrated the possibility of fonning opal-filled veins with the
source of silica derived from the matiix of the host rock. However, because of the irregularities
caused by kinetic barrier effects associated with reaction of glass, it is important to compare and
contrast a number of different natural analogue sites to be able to derive general conclusioris
regarding mineral alteration and, specifically, the effect of heat generated by a potential
repository in tuff at Yucca Mountain.
Finally, an unexplained observation of this study is the proximal confinement of alteration of the
tuff host rock to the intrusion. Additional modeling studies, and analytical data such as isotopes,
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Natural Analogue Synthesis Report
would elucidate the mechanisms responsible for the observed alteration pattems. 

A more
extensive treatment of chemical processes, combined with the dual-continuum disconnected
40 matrix fonnulation of the dual-continuum model, would allow for discretization of the rock
matrix, thus resulting in more representative simulation results.
11.5 ANALOGUES TO THC EFFECTS ON TRANSPORT
The Marysvale hydrothermal uranium-molybdenum ore deposit in Utah has been evaluated as a
natural analogue for evaluating the effects of water-rock interaction and radionuclide transport.
Depletions in igneous rock 8180 values were interpreted to result from exchange with circulating
meteoric waters (Shea and Foland 1986 [1566721, p. 281). The largest 18 0 depletions were
observed along an intrusive contact, where enhanced fluid flow was thought to have occurred.
Uranium mineralization related to the hydrothermal event associated with the intrusion appears
to be concentrated along faults and fractures (Shea 1984 [156673], p. 327). Uranium is pfimarily
concentrated in uranium-bearing mineral phases, such as uraninite and coffinite, but is also found
associated with sericite and chlorite along zones of microfracturing. The observed distribution of
uranium was interpreted to be due to both bulk-flow and diffusion-transport processes, with most
transport (and subsequent deposition) occurring within the fracture network.
Wollenberg et al. (1995 [157467]) used gamma-ray spectrometry and fission-track radiography
to examine the 16cation and abundance of uranium and thorium in tuffaceous rocks
encompassing hydrothermal systems at the Long Valley caldera, Califomia, and the Valles
caldera, New Mexico. In the lateral flowing hydrothermal system at the Long Valley caldera,
where temperatures range from 140-200T, uranium is concentrated to 50 ppm with Fe-rich
mineral phases in brecciated tuff fragments. In the vapor zone of the Valles caldera's
hydrothermal system (temperature -100T), the concordance of high uranium, low Th/U, and
decreasing whole-rock oxygen-isotope ratios suggests that uranium was concentrated in response
to hydrotherrnal circulation when the system was formerly liquid-dominated. In the underlying
present-day liquid-dominated zone (temperature to 210'Q, up to several tens of parts per million
uranium occurs with pyrite and Fe-oxide minerals, and in concentrations to several percent with
a Ti-Nb-Y rare-earth mineral.
In the Valles caidera's outflow zone, uranium is also concentrated in Fe-rich zones, as well as in
carbonaceous-rich zones in the Paleozoic bedrock that underlies the Quatemary tuff. Thoiium,
associated with accessory minerals, predominates in breccia zones and in a mineralized fault
zone near the base of the Paleozoic sedimentary sequence. Relatively high concentrations of
uranium occur in springs representative of water recharging the Valles caldera's hydrothermal
system. By contrast, considerably lower uranium concentrations occur in hot waters (>2200C)
and in the system's outflow plume, suggesting that uranium is being concentrated in the hotter
part of the system. The Long Valley and Valles observations indicate that uranium and radium
are locally mobile under hydrotherrnal conditions, and that the reducing conditions associated
with Fe-rich minerals and carbonaceous mateiial are important factors in the adsorption of
uranium and its attenuation in water at elevated temperature. The Valles and Long Valley studies
provide evidence for at least localized mobility of uranium and its daughters in tuff and
underlying sedimentary rocks at temperatures comparable to those expected in a nuclear waste
repository environment.
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Natural Analogue Synthesis Report
11.6 ANALOGUES TO THM EFFECTS
11.6.1 Insights from Field Tests
Results of heater tests conducted at the NTS in granite and tuff and at the Stripa Swedish
underground laboratory in granite showed a decrease in fracture permeability as a result of
thermal expansion. The Climax spent fuel test at the NTS was conducted in a 426 m deep shaft
in granite. During the three-year test, temperatures in the monitored region of the rock mass
reached 80'C (Hardin and Chesnut 1998 [1500431, pp. 4-1 to 4-3). 

No significant changes in
mineralogy or microfracturing occurred as a result of heat or irradiation. Monitored permanent
displacements were on the order of 0.1-1 mm (Hardin and Chesnut 1998 [150043], p. 4-3). The
sense of displacement was consistent with the regional extensional tectonic regime.
Four heater experiments were conducted in G-tunnel, within Rainier Mesa, NTS. In the heated-
block test, rock-mass mechanical and thermomechanical properties were measured in tuff under
controlled therrnal and stress-loading conditions. The block was subjected to maximum
temperatures ranging from 76-145'C, and equal biaxial stresses with magnitudes up to 10.6 MPa
(Zimmerman et a]. 1986 [138273], pp. vii-ix). The penneability of a single, near-vertical fracture
was measured. The largest changes in pertneability were associated with excavation of the block,
when the apparent perrneability increased from 76 to 758 microdarcies. Subsequent compressive
loading decreased the permeability but did not completely reverse the unloading conditions, and
the apparent permeability ranged from 252-332 microdarcies over a stress range of 3.1-10.6
MPa (Hardin and Chesnut 1998 [150043], p. 4-6). Increased temperature under biaxial
confinement decreased the fracture aperture, lowering the apparent permeability from 234 to 89
microdarcies duiing h'eating.
In addition to full-scale heater tests that investigated short-term near-field effects from thermal
loading, a time-scaled heater test was also performed at the Stripa underground laboratory to
investigate the long-term thermomechanical response to thertnal loading (Robinson 1985
[157445]). In the full-scale and time-scale heater tests, heat flow was not affected by fractures or
other discontinuities in the granitic rock mass. Thermoelastic deformation of the rock mass was
nonlinear and less than predicted. Fracture closure in response to thermal expansion was
confirmed by observation of diminished water inflow to the heater and instrument boreholes
(Nelson et al. 1981 [150092], pp. 78-80) and by increased compressional wave velocity during
heating (King and Paulsson 1981 [157444], p. 699).
11.6.2 Krasnoyarsk
Krasnoyarsk-26 (K-26) is an underground facility in south-central Siberia where nuclear power
has been generated by three underground reactors for approximately four decades, with a
byproduct of weapons-grade plutonium.. The power generated by these reactors is used to
provide heat, electricity, and hot water for the city of Zheleznogorsk. Although K-26 differs from
Yucca Mountain in geology and hydrologic regime, with K-26 located in saturated, fractured
Archean-Proterozoic gneisses, it is the longest "heater test" on record, with a 40-year record of
thermal measurements.
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Natural Analogue Synthesis Report
A schematic of the underground workings is shown in Figure 11.6-1. The depth of the
underground workings has not been reported precisely, but is estimated to be at -200-300 m
is below the surface in saturated bedrock (Gupalo 2001 [1574711, p. 9). Large sources of heat are
present. in the P-2 and P-4 underground workings, where air temperatures reach 60-65'C
(Gupalo 2001 [157471] p. 15). Based on temperatures measurements in 125 boreholes around
the heat sources over 30 years, the dynamics of the rock-mass heating have been obtained. 

The
maximum temperature of the rock is 63'C. The 300C isotherm is established at a distance of
30 m from the heat sources (Gupalo 2001 [157471], pp. 52, 83).
Facilities at B-3 and B-4 were constructed for "technological works" in 1960, but they have not
been used. This makes it possible to monitor coupled processes in both types of underground
facilities, those that have and have not been impacted by heat. The dimensions of the chambers
containing the heat source are approximately 20 m wide x 60 m long x 40 m in height (Gupalo
2001 [157471], pp. 24, 83; 1999 [157470], p. 9). All chambers have a 1.6 m thick concrete
lining.
The geologic conditions of the P-2, P-4, B-3, and B-4 facilities are quite different. Chamber P-2
is located in the footwall of a steeply dipping zone of cataclasis and is surrounded by schistose
zones. Chambers P-4 and B-4 are located in fractured gneiss (Gupalo 2001 [157471], p. 15).
The convergence of underground chamber walls as a result of manmade disturbances has been
small over the 40-year lifetime of the facility. The largest values of convergence were measured
in chamber P-2, where convergence ranged from 16.9-21.5 mm. In chamber P4, maximum
convergence of walls is half that of P-2. In B-4, maximum convergence of walls amounted to
is 1.55 mm, one order of magnitude les's than the heated facilities in P-2 and P-4. Approximately
similar heat sources operate in P-2 (T = 45T) and P-4 (T = 620C), such that their impact on the
host rock is similar. The increased defon-nation in P-2, as compared to P-4, is attributed to the
unfavorable mining and geologic conditions, compared to the rock mass in pillars surrounding
chamber P-4 (Gupalo et a]. 1999 [157470], p. 45).
According to the velocity of ultrasonic waves measured from logging seven boreholes, three
zones of deformation can be distinguished in the rock mass: (1) a zone of concrete lining (0.0-
1.6 m) and adjacent rock layer with high disturbance level (1.6-2.0 m); (2) a zone of contour
rock layer of intermediate disturbance (1.6-2.0 m); (3) the undisturbed rock mass (over 4.0 m)
(Gupalo et al. 1999 [157470], p. 80). The vertical component of convergence was determined to
be. 2.1 mm (+0.09 mm/yr from 1976 to 1998). (Gupalo 2001 [15747 1 ], p. 80).
The effect of therinal loads on rock-mass deformation was found to be significant in the
disturbed zone. Within a homogeneous rock mass, convergence of chamber walls over a 40-year
observation period was 1.0 mm in the absence of thennal impacts, but dislocations increased 8 to
10 times under increased temperature effects (Gupalo 2001 [15747 1 ], p. 8 1). 

There is a clear temperature-related effect of the underground facilities on fracture-vein waters.
The area of enhanced temperatures of underground water reaches 38-70 m above the roof of the
workings, and maximum recorded temperatures of the underground waters is 36'C. (Gupalo
2001 [157471], p. 83).
0
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Natural Analogue Synthesis Report
Although the K-26 example is more analogous to preclosure conditions rather than postclosure
performance at Yucca Mountain, it provides an example of relative thermomechanical stability
under sub-boiling conditions in a more heterogeneous rock mass than that found at Yucca
Mountain. It also provides a test case that compares a thermomechanically disturbed regime to
one that is merely mechanically disturbed in the same rock mass, to determine the thermal
component of disturbance.
11.6.3 THM Insights from Geothermal Fields
During the 1970s and 1980s, The Geysers geothermal region was rapidly developed as a site of
geothermal power production. The likelihood that this could cause significant strain within the
reservoir, with corresponding surface displacements, led to a series of deforrnation monitoring
surveys from 1973 to 1996, For the period 1980-1994, peak volume strains occurred in excess of
5 x 10-4. Changes in reservoir steam pressures were well correlated with volume strain and
contraction of the reservoir (Mossop and Segall 1999 [157466), p. 29,113).
Seismicity has been induced by oil and gas production in areas where pore pressures have
decreased, in some cases by several tens of MPa (Segall and Fitzgerald 1998 [1574641, p. 117).
Induced earthquakes are also common in geothen-nal fields, such as The Geysers, where strong
correlations between earthquake activity and both steam production and condensate injection,
have been observed. Stress measurements within hydrocarbon reservoirs show that the least
horizontal stress decreases with declining reservoir pressure, as predicted by poroelasticity.
Production-induced stressing may promote frictional sliding on pre-existing faults. However, it is
not expected that this magnitude of stress would occur at Yucca Mountain.
Studies of hydraulic fracturing experiments in hot dry rock suggest that under thermal
conditions, mechanical stresses in the rock at Yucca Mountain will occur along preexisting
fracture zones and will develop in the direction of maximum principal stress. The Mjoli hot dry
rock site in Yamaga ta, Japan, was the site of hydraulic fractunng experiments in 1988 that were
accompanied by microseismic events (Sasaki 1998 [157465], p. 171). The microseismic events
were thought to have been caused by shear failures induced by high pore-fluid pressures
occurring on planes of weakness in the rock surrounding the main hydraulic fracture. The
experiment indicated a migration of the induced microseismic events that eventually distributed
along a vertical plane, with the strike of seismicity nearly parallel to the direction of the
maximum principal stress. The vertical oiientation and east-west strike of the seismic events are
essentially coplanar with the caldera ring-fault structure in the southem portion of the I-Iijiori
Caldera.  This indicates that a preexisting fracture zone was being reopened and developed in the
direction of maximum principal stress.
11.7 SUMMARY AND CONCLUSIONS
Geothennal systems illustrate a variety of THC processes that are relevant to Yucca Mountain.
They include advective and conductive heating, fracture-dominated fluid flow, chemical
transport, boiling and dryout, condensation, and mineral alteration, dissolution, and precipitation.
Yellowstone and other geotherTnal systems in welded ash flow tuffs or other low-perrneability
rocks indicate that fluid flow is controlled by interconnected fractures. Alteration in low-
penneability rocks is typically focused along fracture-flow pathways. 

Only a small portion of the
  11-57  1

 

Natural Analogue Synthesis
fracture volume needs to be sealed in order to retard fluid flow effectively. At Yucca Mountain,
fluid flow and low-temperature water-rock interaction over the past 10 m.y. have resulted in the
precipitation of minor amounts of opal and calcite on fracture and lithophysal cavity surfaces.
The main minerals predicted to precipitate in the near field of the potential Yucca Mountain
repository are amorphous silica and calcite, which are also commonly found as sealing minerals
in geothermal systems.
Sealing in geothermal fields can occur over a relatively short time frame (days to years).
Precipitation of minerals can be triggered by a vafiety of processes, including boiling, water-rock
interaction, heating and cooling of fluids, and fluid mixing. The unsaturated conditions, lower
temperatures, and much lower fluid-flow rates predicted for the Yucca Mountain system in
compaiison to geothermal systems, should result in less extensive water-rock interaction than is
observed in geothennal systems.
Fracturing and sealing occur episodically in geothermal systems. Different generations of
fracture mineralization indicate that there are multiple pulses of fluid flow, recording distinct
temperature conditions and fluid compositions, throughout the lifespan of a geothennal system.
Most mineralization at Yucca Mountain is predicted to occur soon after waste emplacement
(1,000-2,000 yr), when temperatures would reach boiling (for the higher-temperature operating
mode) above the emplacement drifts.
The effects of processes such as boiling, condensation, dissolution, and precipitation on the
higher-temperature operating mode for Yucca Mountain will be restricted to the near-field
environment. Silica precipitation at Yellowstone results from both cooling and boiling processes,
which serve to raise silica concentrations to above saturation levels. Geochemical modeling of
fluid compositions has been used to successfully predict observed alteration of mineral
assemblages at Yellowstone.
As shown in Section 11.3, THC processes are expected to have a much smaller effect on
hydrogeological properties at Yucca Mountain than on those observed at Yellowstone. However,
development of a heat pipe above emplacement drifts at Yucca Mountain under a higher-
temperature operating mode could lead to increased chemical reaction and transport in the near
field. Reflux and boiling of silica-bearing fluids within the near field at Yucca Mountain could
cause fracture plugging, thus changing fluid-flow paths. THC simulations conducted to date for
the potential Yucca Mountain repository suggest that only small reductions in fracture porosity
(1-3%) and perrneability (<1 order of magnitude) will occur in the near field as a result of
amorphous silica and calcite precipitation (BSC 2001 [155950], Section 4.3.6.4.2). Changes in
pen-neability, porosity, and sorptive capacity are expected to be relatively minor at the mountain
scale, where thermal peilurbations will be minimal; this also applies to the lower-temperature
(sub-boiling) design. These predicted changes in hydrogeological properties should not
significantly affect repository perforinance.
Magmatic intrusions in tuffaceous rock above the water table, such as the Paiute Ridge intrusive
complex studied in Section 11.4, offer a unique opportunity to study conditions analogous to the
predicted postclosure repository conditions at potential Yucca Mountain. The Papoose Lake Sill
intruded into Rainier Mesa tuff, and the resulting hydrothennal effects were characterized by
  11-58  1

 

Natural Analogue Synthesis Report
low-temperature alteration of glass to clinoptilolite and opal, similar to those present at Yucca
Mountain. 

Hydrothen-nal alteration was confined to a narrow zone close to the contact zone. The
40 pervasive anastomosing opal veins and associated secondary minerals (e.g., clinoptilolite, calcite,
cristobalite, etc.) appear to have reduced matrix or fracture permeability in the immediate
vicinity of the basaltic intrusion.
The widespread opal veins along fracture-matrix margins provide a means for testing and
validating porosity/permeability relationships and desciiptions of fracture-matfix interaction
employed in THC codes. Preliminary results of a one-dimensional THC dual-continuum model
of the interaction of country rock with heat released from an intrusive complex emplaced above
the water table demonstrated the possibility of forming opal-filled veins with the source of silica
derived from the matrix of the host rock. However, because of the irregularities caused by kinetic
barrier effects associated with the reaction of glass, it is important to compare and contrast a
number of different sites to be able to derive general conclusions regarding mineral alteration
and, specifically, the effect of heat generated by a potential repository in tuff at Yucca Mountain.
Examples provided in Section 11.5 indicate that the observed distribution of uranium resulting
from hydrothennal conditions at Marysvale was a result of advective transport and diffusion,
with most transport-subsequent precipitation of uranium occurring within the fracture network.
This observation was also bome out at portions of the Long Valley and Valles calderas. The
latter two studies also provided evidence for at least localized mobility of uranium-series
radioisotopes at temperatures more comparable to those expected under higher-temperature
thermal-loading conditions in a nuclear waste repository environment.
THM effects at Yucca Mountain (Section 11.6) are expected to be less extreme than those
operating in geothennal fields where microseismicity is detected. Although rock type,
hydrogeology, and design configurations differ from those at Yucca Mountain, the closest
analogue identified so far is K-26, which is particularly relevant to lower-temperature design
scenarios. Although the 40-year record of experiments should be interpreted cautiously with
respect to extrapolation to long time periods, thermomechanical effects, such as drift
convergence, might be in the same range of magnitude (on the order of a few mm) as that at
Krasnoyarsk for the preclosure period.
0
  11-59  1

 

Natural
0
NOTE: Similar proutesses include boiling and condensation, advactive liquid flow, mineral dissolution and
preop'tation, 'i'i'g' recharge (percolation), and heat conduction. A heat p[pe is depicted on the
right side of the geothermal system, showing counterounart rqu,d and .por flow resulting from
bolling and Condensation.
Source: Left figure adapted from Bod,,arssion and Witherspoon (1989 [156337]), bght adapted from
CRWMS M&O (2000 [1519401).
Figure 11.2-1. Comparison oi Processes in Geothermal (Left) and Anthropogenic (Right) Thermal
Systems Created by Emplacing Heat-Generating Nuclear Waste in an Unsaluraied
Fractured Rock Mass
is
TDR-NBS-CS-000027 REV 00 ICN 01 1 ll`~I April 20102 1
Cua-- H- S.-

 

Natural Analoguc Synthesis Rcport
0
T,a Canyon (TC.)
Paintbwsh Tuft (PTn)
Topopah Spring (TSw)
Calico Hills (CHa)
Cmter Flat (CFu)
eV
(b)
Yu- Crew
Bxehole SD-6
01500- Ghost
e Danm
'41)(3 - Solitsul. Bomhole fault Dune
Canyo Wash
fault
E 1300
1200 Tc-w
o iioo
o
E 1000 TS
/CM
n (molkic)
800 /6.Hn(,Ir.,, o
0 .25 .50 . 5 1.0
DiSt- (krn)
.Z.-002
NOTE: In both (a) and (b), the water table is indicated by a blue cl-ward-pointing tdangle.
Source: CRWMS M&O 2GOO (1519401, Figure 3.2-1.
Figurell.2-2. Schematic Diagram (a) and Cross Section (b) of the Yucca Mountain Lfthology and
Topography, Imiuding Surface Features and Major Geologic Strata
TDR-NBS-GS-MM27 REV 00 ICN 01 1 IF-2  1

 

Natural Analogue Synthesis Report

fCET		PeRogill MATRtX
PERMEABILITY
		percmt)
180-
		>50
	LFAKY AQVITARO	13
Is
		- M
10'
		33

120-		10' 17 10' Is
r

I.-	In
	WELDED TUFF AQUIrEM
	itromminibi(dr ca~

-	lntltd by No ey and	-10-
80	Wanda" ="I	o-18 io-17
	.
ftsaum pe Ity
5 ~ 10*11 - 5 . 10, ff? 

I
~l
		l
tEAKV oLQUIITARD I I lio"s
> 50 1 \~
r- 67-1
TRANSITIONAL CONTACT WJBSLE ZONE
laeTweep, ZONES OF WELDING
ZOW OF NO VIELOtNG
- ----------- - ------- ----------
ZONE CW PAR71AL WELDING
M
PRIMARY AND SECONDARY
JOINTS
-------------- ----------
ZONE OF. DEMSt WELDING
------ - - - ----------------
ZONE OF PARTIAL IWCLDIWG
-- - - - - - - - - - - - - - - - ---
ZONE OF 140 WELDI"G
- ---------
BEDDED
"E OF PARTIA
;EC
TUrr
F--'-'-fl
L'?N0;HrSAL*A," D MIAROLITIC
CAV, ICS [Or atl, eAaggwratwdl
NOTE: While zones of dense welding have intrinsically low matrix permeabilities, these zones also have
much more abundant fractures, resulting in higher overall permeability than nonwelded (and
unfractured) tuff.
Source: Generic profile modified from Winograd (1971 [156254], Figure 5).
Figurell.2-3. Typical Variations in Permeability and Porosity in Welded and Unwelded Ash Flow Tuff
0
  1 IF-3  1

 

Natural
0
0
0
ECRB Cross
Tptpul
~Fp-tp--
TDR-NBS-GS-000027 REV 00 ICN 0 1 1 IF-4  1
NOTE: Water is introduced into the fault in Alcove 8 and collKted in and near Niche 3.
Soume: Modified from BSC 2002 (157606], Figum 2.
Figure-11.2-4. Schematic Diagram of Flow Test at Yuma Mountain

 

Natural Analogue Synthesis Report
0
0
90
U. 3
1982 1984 1 M 1988 1990 1992
'nme /years)
NOTE: Flow rates are slightly greater and enthalpy is slightly less than predicted by the 1986 model from
1988 to 1992.
Source: Steingrimsson et al. 2000 [156686], p. 2904.
Figurell.2-5. Comparison between Predicted and Observed Flow Rates and Enthalpies for Well 6 of
the Nesjavellir Geothermal Field (Iceland)
240		xo
220
6 2W	t.t.1
M-5	9 2W
u	M-31
so
		gm	% .-,t
140		x
'0 , 20		so
loo
	A	X
so	0
%	100
oo
40		so

90	WHP
13	14 ?S 76 77 78 79 80 Of 02 83 64	73	74 7s 76 77 78 79 OD 91 82 Oll 84
	YEAR		YEAR
0
NOTE: Well M-31 experienced near-well boiling with abundant mineral deposition. Cleaning well M-31 in
1981 yielded a short-lived increase in production. WHP = well head pressure.
Source: Truesdell et al. 1984 [156350], p. 227.
Fi gure 11.2-6. Comparison of Production between Wells M-5 and M-31 at the Cerro Prieto Geothermal
Field
TDR-NBS-GS-000027 REV 00 ICN 02 1 IF-5
May 2002 1

 

Natural Analoguc Synthesis Repon
0
NOTE: Th' botryoidal lemure of the quartz indimtes that it was deposited as chalcedony or amorphous
stlica, and that this dopmition occurred at 300'C due to rapid decompression. qtz = quanz,
q t~(chal) = chalcedony, py = pydte, wt = wbmlite, and ep = epidote
Source: Moore et aL 2000 11563191, p. 261.
is Figure 11.2-7. Photmicrograph of Fracture Minerals in the Karaha-Telaga Bodas System, Indonesia
NOTE: Titanium- Mch wale coats anhydhte and fine needles of acfinolite. The wale is peeling off the top of
the crystal.
Soume: Moore et al. 2000 [156319], p. 260.
Figure 11.2-8. 

Scanning Electron Microscope Backscattered Image of Fracture Minerals in the
Karaha-Telaga Bodas System, Indonesia
  1 IF-6  1

 

Natural Analogue Synthesis Report
0
seal
Vent
quartz
calcite
0 liquid
0
0 level
c steam
~6 vaporization
0 condensate
0
NOTE: In A, quartz and calcite are deposited as the result of boiling possibly due to depressurization in the
system. Initially, the rock is too hot for condensation to occur. In B, the top portion of the vein has
cooled sufficiently so that condensation occurs. Steam from below migrates through the vein until it
reaches the cooler rock where condensation occurs. Corrosion of quartz and calcite occurs near
the site of condensation. In C, subsequent lowering of the water table (indicated by the arrow) due
to venting results in quartz and calcite deposition due to condensate boiling. Mineral deposition
.may also occur as condensate reaches the lower, superheated region, and in the liquid-dominated
portion of the vein.
Source: Moore et al 2000 [156318], p. 1731.
Figure 11.2-9. Schematic Illustration Showing the Transition from a Liquid Dominated System to a
Vapor-Dominated System, Showing only a Portion of the Vein
0
TDR-NBS-GS-000027 REV 00 ICN 02 1 IF-7 May 2002 1

 

Natural Analogue Synthesis Report
0
THERMAL PROFILE DUNES DWR No. I
	STRATIGRAPHY
BOREHOLE
TEMPERATURE (*C)
40 50 60 70 Bo 90 100 :J
				WATERTAKE
50-
	LEGEND			4
100-				2
	LITHOLOGY
	= DELTAIC SAtJD
150-
	EN INTERBEDDEO SANDS,			trw
ou.
	SILTS.  AND SHALES
200-				n
X C,
	DUNE' GRADED SAND
SEQUENCES			j -x
LLJ 250-	CHANNELFILL CONGLOMERATES			-
				w
LLI
00
.3
-
	SILICIFIEO SEDIMENTS
350-
a-
w
400-
450-
500-
550-
600-1
NOTE: The silicified regions are identified in the right column by cross hatching.
Source: Bird and Elders 1976 [154601], p. 286.
Figure 11.2-10. Temperature Profile and Lithology of Borehole DWR No. 1 at the Dunes Geothermal
System, California
0
  11 F-8  1

 

Natural Analog= Syntheiis Report
9
smedte rich
20m h."
= diatomite (opal-A mn.)
Im Poroelanke (opal-CT zone)
po-l-Re (quart.
and.site
pumice tuff
NOTE: The diatomite ms altemd to pomelanite and chert as a rftult of a hydrothemal systenn iriduced by
the intrusion of an aridesite dike. The thickn"ws of the porcelanite and chen layers range from 20
cm to 20 m (po"lanite) and 5 m to 20 m (Cheri).
Source: Chigim and Nakata 1996 (1563491, p~ IS.
Figure 11.2-11. Schematic of Lfthology near Borehole A in the Miocene lwaya Formatim, Japan
0
TDR-NBS-GS-000027 REV 00 ICN 0 1 11 F-9  1

 

Natural Analo
2D
40
11
Too
120
A ht
0
I.W7 IS-05 I.E-M I.E.04
P.-dAll (.WQ
NOTE: Alteradw mimW porcetanits hu a eirrdiar parmeabiHty to the original diatomlte, but the chort Is far
less, panneable
Soumw. 

 Data hvn Chigim wd Nakata 19M (1 56M], p. 11.
Figure 11.2-12. Pemeabirtty Profile of Samples alotV Borehole A in the MWcerte lwaya Formation, Japan
0
MR-NB"S-000027 REV 00 ICN 01 lmio '~pdl 2m 1

 

Natural Analogue Synthesis Report
0
0
is
1.0
0.8
70.6
50.4
0.2
- - go ~ I - . - ,
le oc :01< -c ~.K so -c
0 R-1
0 0 0 0 00 CPO 0 0
0
1 0 , 0 0 1 0. CD?01,
0
1.0
0.8
50.6
1-1
50.4
0.2
100 200 300 400 500 600 700
TIME (doysi
- so *C w 60 'C- 50 *C
0
R-2
0
000
0 0 Cbo 0 0
? 00pa
0 100 200 300 400 500 600 700
TIME ldaysl
NOTE: The temperatures indicate the temperature of the injected water. The permeability-thickness
product (kh) in Well R-1 decreased from 224 darcy-m to 0.79 darcy-m over 624 days. In Well R-2,
the permeability-thickness product decreased from 91 darcy-m to 5 darcy-m over 637 days.
kh = permeability-thickness product
koh = initial permeability-thickness product
Source: ltoi et al. 1987 [156346], pp. 543-544.
Figure 11.2-13. Reduction in Permeability in Wells R-1 and R-2 over the Duration of a Reinjection
Experiment
 
I IF-I I
April 2002 1

 

Natural Analogue Synthesis Report
I*
f
OOKM H
HSB
IkNh~,A Gc~ lic
4% ractur CH Dome
m
io
LB
ma
0 Dome
u a
;? VVT
SB4
HLB
act
0 10 20 40 km
~O ~O
NOTE: Areas abbreviated as follows: BC = Black Creek, CH = Crater Hills, GC = Grand
Canyon, HLB = Hart Lake Basin, HSB = Hot Springs Basin, JC = Joseph's Coat
Hot Spring, MH = Mammoth Hot Spdngs, NB = Nords Geyser Basin, LB = Lower
Geyser Basin, MB = Midway Geyser Basin, UB = Upper Geyser Basin, SB
Shoshone Geyser Basin, MV = Mud Volcano, WT = West Thumb, WS
Washburn Hot Springs, YL = Yellowstone Lake.
Source: Fournier 1989 [156245], Figure 2.
Figure 11.3-1. Map of Yellowstone National Park, with Outline of 0.6 Ma Caldera Rim
0
  1 IF-12  1

 

Natural Analogue Synthesis ReporL
0
NOTE: Large sinter blocks had been elected by 1989 explosion. The pool has an opalescent color,
indicating presence of colloidal silica (photo by R. Fournier, USGS~.
Source, Simmons 2DO2 (1575781, SN-LBNL-SCI-1 85-Vl. p. 7-1.
0
Figu re 11.3-2. Porkchop Geyser (J uly 199 1 )
Source: Simmons 2002 [157578], SN-LBNL-SCI-185-VI, P. 7-1,
Ftgure 11.3-3. Block from 1989 Porkchop Geyser Eruption, with Gelatinous, Botryotdat Silica Coating
Outer Margins and Cavities (photo from T.E.C. Keith, USGS)
TDR-NBS-GS-00(YD27 REV 00 ICN 0 1 1 IF- ir, 
DTN. L80201YSANALOG.001 (1575691
DTN LB0201YSANALOG.001 11575691

 

Natuml Analogue Synthesis Repon
0
280 8DO
NKC (C)
270 Si02 (ppm) 750
260 700
co
1.
250 650
-R 'o 600
240
E 2
230 550
z
to
220 , 5DO
2
210 450
200 400
Ywr
NOTE: Change inflow behavior interpreted to be linked to precip,tation ofamorphous silica, resulting
in the clogging of flow channels.
Source: Foumier et al. 19911156246], p. 1116. 

Figurell.3-4. Changes in Calculated Sodium-Potassium-Calcium (NKC) ReseNoir Temperatures and
Silica Concentrations for Waters Sampled from Porkehop Geyser
0
TDR-NBS-GS-000027 REV 00 ICN 02 1 IF-14 May 2002 1

 

Natural Analogue Synthesis Repon
Y-5 Can Log
e'uffiologyWeldintg u D'stription
a 0 3 1.,
0
H-kl.d W denady
-kl,dL-C-k.h
n- tIff
SAHMONE-Co -
Fired tuffw.
eaditonds.
D.-IY welded L-
C-k hfli
D~gr.. f.eldig 0 - -,Id.d, I - -ldy
welded,2- --derately welded, 3 - dm,elywelded.
VP - .P-ph..
DTN: LB0201YSANALOG.001 [157569]
Source: Dobwn et al. 200111545471, Ftgum 2.
Figurell.3-5. Simpiffied Geologic Log of the Y-5 Core
0
  1 IF-15 ApTil 2002 1

 

Natural Analogue Synthesis Repon
Y-8 Care Log
e,LM.l.UAh"o-. D.s*ti-
0 0 4
0
VOLCANICUMIC
SAKDSTONF
V.1-icleatic-dato.
RHYOLrM PdW,
rhyohte kw
PUNECEOUSTUFF
Pa- -ekld
thyahte wh flow tiff
Alt..ti- 0-
DTN: LB0201YSANALOG.001 (157569]
Soume: Dobwn et a]. 2001 [154547], Figum 3.
Figure-11.3-6. Simplified Geologic Log of the Y-8 Core
0
  1 1F- 16  1

 

Natural Analogue Synthesis Repon
40
. . ..........
Y y
E
Y::
DTN: LB0201YSANALOG.001 [1575691
NOTE: Vertiml bars at left indicate studied wre-depth intewals, Tempemture and pressure data fmm
White et ai. 1975 [154530).
Source: Dobson et al. 2001 [154547], Figum 1.
Figurell.3-7. Downhole Temperature (Solid Lines) and Wellhead Pressure Variations (Dotted Lines) in
the Y-5 and Y-8 Wells

	I P.-

DTN: L80201YSANALOG.001 [1575691
NOTE: W= moderately to densely welded tuff, NW = nonwelded to "akly welded tuff. The 0.1 md values
represent the lower detwtion limit for minipeneability measurements; wtual values are lower,
Soume: Dobsor et al. 2001 (154547], Figure 4.
0 Figurall.3-8. Porosity and Pemeability Variations in the Y-5 core
TDR-NBS-GS-000027 REV 00 ICN 02 1 IF-17 May 2002 1

 

Natural
10
v V.I.,
4
75
DTN: LB0201YSANALOG.001 (157569)
Soume Dobson et al. 2001 (154547], Figure 5.
Figure 11.3-9. Porosity and Permeability Variations in Ihe Y-8 Core
40
VIi- & Flftt..a 12.5 . -.1
o 10 20 sa
2o
2~
30 NW
35
-1y w-
41
art
70
71
tio
.s
DTN: LB0201YSANALOG.001 [157569]
NOTE: W= moderately to densely welded tuff, NW = nonmided to weakly welded tuff
Source: Dobson et al. 2001 [1545471, Figum 6.
Figure 11.3-10. 

Veins and Fractures in the Y-5 Core
  1 IF-18  1

 

Nraural
	-,,a, &
a	F- / 2.5
	45 M

		sifi-

	so

DTN: L80201YSANALOG.001 (1575691
Soume: Dobson et al. 2001 [154547], Figum 8.
Figure 11 ~3-1 1. Veins and Fractures in the Y-8 Core
0
DTN L80201YSANALOG,001 [1575691
NOTE: C.-dth,.4.4cm. Permeability talues of welded tuff clast (A) and matrix (B) am both below the
minipeneameter d.taoton limit (0. 1 md).
Source: Dobson et al. 2001 [1545471, Figure 7.
Figure 11.3-12. Hydrothermal Breccia from the Y-5 Core at 47.7 m (156.5 feet)
TDR-NHS-GSAKXX)27 REV 00 ICN 02 1 IF-19 May 2(X)2

 

Natuial Analogue Synthesis Report
0
Y-8, 155.91 Y-8, 159.2' 1 oun
Permeabiltty = 1030 md Permeability = 16.9 nod
Porosily = 29.2% Porosity = 15.0%
DTN: LB0201YSANALOG.001 1157569]
NOTE, Stlicification of the sample from 159.2' has resulted in a 50% reduction in porosity (change in
abundance of blue epoxy denoting porosity) and decmase in permeability of nearly two orders of
,nagmi
Source: Simmons 2002 [157578]. SN-LBNL-SCI-185-Vl, Roll 17, Photos 2 and 4~
Figure 11.3-13. Photomicrographs of Volcaniclastic Sandstone Unit from Y-8 Core
0
  11 F-20  1

 

Natural Analogue Synthesi.s Repon
0
0
E
Iz
NOTE: Sampling sections, labeled mth single ieners, md ddil holes, which all start vgth U, are indicated on the
Ight and left sides of the figure, respectwilly. The strafigraphic units of the drift holes am given in Table
11.4-2.
Soume: Simmons 2002 [157578] SN-LANL-SCI-215-Vl, p. 6.
Figure 11.4-1. Lmation Map of the Paiute Ridge Basaltic Intrusion Complex in the Nevada Test Site
0
TDR-NBS-GS-000027 MV 00 ICN 01 11 F-21  1

 

Natural Analogue Symhesis Repoo,
I*
NOTE: These veins are within 8 ft (2.4 m) fmm the basaltic intrusion contact adjacent to the Papoose Lake
Slll in the northem paa of Paiute Flidge. The vein zone is about 25 ft (7.6 m) wide.
Source: Simmons 2002 (1575781; SN-LANL-SCI-215-Vl, p44, Figure 16B.
Figurell.4-2. Anastomosing Opal Veins Adjacent to Papoose Lake Sill
49
TDR-NBS-GS-OOW27 REV 00 ICN 01 11 F-22  1

 

N,t,r,l Anal,gue Sy,theii, Repon
0
"'A
NOTE: Calcit-vems along fractures and cavitlee wd epidote grains in cavities am present in the
phIll.icrograph of basalt (LANL# 3547) (view is 170 x 255 pm).
Srurce: Simmons 20021157578), SN-LANL-SCI-215-VI, p. 130.
Figurell.4-3. Photornicrograph of Basalt from the Contact Zone of the Papwse Lake Sill in the
Northern Part of Paiute Ridge
0
  11 F-23  1

 

N;uu,"I SYi'll""' R'l'-
0
Source: Simmons 2002 [1575781, SN-LANL-SCI-215-Vl, P, 131~
Figure 11.4-4. 

Photomicrograph oi Altered Rainier Mesa Tuff
0
0
TDR NBS-GS-(X)0027 REV 00 ICN 01 1 tF-24  1
NOTE This sample (LANLN 3557) was collmled 43 ft (131 m) from the Papoose Lake S'll
contact, Bnghter patches of silica (left) and calcite (nght) sepamted by opaque
material replace the vitric matux (,ie, is 70 x 110 pm).

 

Na-A Amilk,g,c Syrthe,i, Rep,,rt
0
PROO-3-15-7
PROO-3-15-5
PROO-3-15-6
-u
-u
PROO-3-15-13

PROO-3-15-8
		00-3-15-3
0

0

		p ROO-3-15-1
I

NOTE: Map not to scale; compiled fmm field notes; see Table 11.4-1 for sample descnptions and
measured distances fmm sill margin.
Source: Simmons 2002 [157578], SN-LSNL-SCI-108-V2, p. 23.
Figure-11.4-5. Schemalic Map of Lmation H, Papoose Lake Basaltic Sill, Paiute Ridge, Nevada Test
Site
0
TDR~NBS-GS-000027 REV 00 ICN 01 11 F-25
April 2002 1

 

N,it-l A,,,I,g,, Synth-, Rep-I
0
j Lee
J,
W,
4t
" P
NOTE: This samp~e of nonwelded Rainier Mesa Tuff (LANL# 3559) was collected 200 ft (61 m) fmm the
basait'c si[ contact. It is apparent that the vesfcles are devoid of smondary mmeals from
dev trification after deposition or fmm the hydrothemal F-ess miated to the basaltic intr-on.
Source: Simmons 2002 [157578]; SN-LANL-SCI-215-Vl, p. 101.
Figure 11.4-6. Scanning Electron Microscope Image of Vesicles in Nonwelded Rainier Mesa Tuff
0
TDR-NBS-C,S-(X)0027 REV 00 ICN 01 11 F-26  1

 

Naturai Analogm Synthesis Repon
0

NOTE: These variation diagmms use data in feet for distwce and m% for Na2O, K20. A1203,
CaO. SiO~ TiO2, and Fe2O3 of tuff samples fmm the northem part ot Paiute Ridge. Major-
element contents am calcul ted to 100% volatile free. Total lmn reported as Fe203. Line
indicates average cmpmition of Rainier Mesa rhyolitic tuff mported by Broxton et al.
( 1 989 1100024]. Table 3).
Soume: Simmons 2002 11575781; SN-LANL-SCI-215-Vl, pp. 63, 69-76.
Figurell.4-7.  Variation Diagrams of Distame Versus Na2O, K20, A1203, CaO, S102, TIO2, and Fe203
0
TDR-NBS-GS.00(X)27 REV 00 ICN 02 1 IF-27
May 2002 1

 

Natwal Analorue Synthesis Report
I*
m
M
2M
im
im
N
100 400 WO
(ft)
280:
2Q j
200:
in
so
40
0
0 iw m 3DO 400 500
Distan. (ft)
0
0 -
0 iw 200 300 WO
OhMance (ft)
700
m
wo
ie
im'
o
0 loo ZO WO 40D 500
Dislan- (ft)
NOTE: The" variation diagrarns use date in fftt for distance vemus Pprn for Zr, Rb, Nb, wd Sr of taff
earnples fmm the northem part of Paiute Ridge. 

Une incflmtft mmge cornposibon of Rainier
Mea. rhyollfio tuff reported by Broxton at al. (1989 [1000241, Table 3).
Soume: Simmom 200211676781; SN-LANL.SCI-21 5-Vl, pp. 63, 69-76.
Figurell.4-8. Variation Diagrarnsof Distanm Vemus Zr, Rb, Nb, and Sr
0
  IIF-28
Aprii 2M 1

 

Natural Analogue Synthesis Repon
0
0
Figure 11.4-ga. Tabular Crystal of Clinoptilolfte Overgrowth on a Second Layer of Clinoptilolite with
Scalloped or Serrated Edges (LANL# 3552)
40
TDR-NBS-GS~000027 REV 00 ICN 0 1 1 IF-29  1
NOTE: 500prnscal.
Soume: Simmons 2002 [1575781; SN-LANL-SCI-215-Vl, p. 128.

 

Natuml Analogue Synthesis Report
0
Soume: Simmons 2002 1157578]; SN-LANL-SCI.215.Vl, p. 100.
Figure 11.4-9b. Scanning Electron Microscope Image of Ctinoptilolite Crystal Aggregates in a Cavity of
Rainier Mesa Tuff
TDR-NBS-GS~O(K)027 REV 00 ICN 01 11 F-30  1
NOTE: This mmple of Rainier Mesa Tuff (LANL# 3550) wascollected 8.5 ft (2.6 m) from the Papoose
by clinoptilolite
Lake Sili contact in the northern part of Paiute Ridge, It is appamnt that the cavity is panially filled

 

Nawrat Analogue Synthesis Report
0
mm lOff
=016C 30 OC
V2 E16*ace x
NOTE: This diagram of ft halfspace, cornputal,wal dmain indicates the
inidW tompmtum of the Intmsion of thickness L and tuff mntry roulk
for a one-cilmensionai simulafim perpendicular to the intrusion.
Swrce: Smm" 2002 [1575781, SN-LBNL-SCI-1 DS-V2, p. 22.
Figure 11.4-10. Schematic Diagmm of the Haff-apace Computational Domain
(a) 1200 . .................... .

000
O'S
y - - -
W.M.
Z
- . .. . .....	y
4, .- -
1 oy
m
St.	1000 y
20D
1	1 0 100
DISTANCE E.,
(b) = ." i, lwwTempwatoe
ODO	Fracture 0.5 y

T	1 y
1 0 y

a. 400
200
1	10 100
DISTANCE 1.1
NOTE: 43~m= 102
SOU- Simmons 2002 [1575781; SN-LANL.SCI-216-Vi, p. 112.
Figure 11.4-11. Matrix (a) and Fmct re (b) TeMperatUre Profiles as a F ... tim of Distance at the
Indicated Times for tuhs Dual-Continuum Model with Strong Fracture-Matdx Coupling
  llr-31 Apfil 2002 1

 

Natuml Analogue Synthesis Report
(a) , - na'.1 Sava.-
0 mian, a 11 yy
Y,
1.00 y
10 100
DISTANCE
0,31
. -
z 0 5 y
0 0,25
100,
1000 y
0.1
4-
0
'o IN
DiSTANCE fmi
NOTE: 10'
Soume; Simmons 2002 [157578); SN-LANL-SCI-215.Vl, p. 112,
Figure 11.4,12. Matrix (a) and Fracture (b) Saturation Profiles as a Function of Distance at the Indicated
Times for the Dual-Cwtinuum Model with Strong Fracture-Matrix Coupling
0
TDR-NBS-GS-000027 REV 00 ICN 0 1 1 IF-32 Aplil 2002 1

 

Not-I
000
ly
Boo
la,
Boo
ly
............................... .
o
I io IN
DISTANCE [.1
..........
ow F.O.. 0 5 - ------- -
I yy
800 to
600 100Y ----
Q0 10, . ........
No
0
IN
DiSTANCE [,o)
NOTE: ot- 10'
Soume: Simmons 2002 [1575781; SN-LANL.SCI-215-Vl, p. 111
Figure 11.4-13. Matrix (a) and Fracture (b) Temperature Profiles as a Function of Distance at the
0 Indicated Times for the Dual-Continuum Model with Moderate Fracture-Matrix Coupling
0
TDR-NBS-GS-000027 REV 00 ICN 0 1 11 F-33  1

 

Natural
(a) _h".1 Sanuna-
08 M."', OS
y
y
0.6
ZY . ....... ............
'o 100
DISTANCE
0.35
z y
0.3
0 025 1 y
- IOY
0. Imy
IOODY
0 0 , I
0.05
0
1 10 im
DISTANCE (.1
NOTE: - 10'
Source: Simmons 2DO2 (157578]; SN-LANL-SCI-21 541, p. 111. 

Figure 11.4-14. Matrix (a) and Fracture (b) Saturation Pmfiles as a Furiction of Distance at the Indicated
0 Times for the Dual-Continuum Model with Moderate Fracture-Matrix Coupling I
0
TDR-NES-GS-000027 REV 00 ICN 01 1 IF-34 April 2OC12 I

 

Natural Analogue Synthesis Report
(a) :X0
rowl T
MWAX 0. 1 y
, y
_775-77 'GY
600 looy
201 - ----------
0 ----
10 100
DISTANCE[.)
(b)
= ............
OOD Fmd- 0.5 y
800 c, Y,
600 OOY
400 zy
21 ... . ... ..... .....
0 ----------
10 100
DISTANCE [.1
NOTE: m-10"
Source: Simom 2002 [1575781; SN-LOkNL-SCI-215-Vl, p. 110.
Figure 11.4-15. Matrix (a) and Fracture (b) Tempwature Profiles as a Functim of Distanos at the
0 Indicated Times for the Dual-Confinuum Model with Weak Fracture-Matrix Coupling
0
  1 IF-35 April MM I

 

Natural Analogue Synthesis Report
(a) ,	--,
-
	r

0.4
o .2
o
	io ioo
	DISTANCE [.1
0.35
0.3
0 '25
z 0,5 ..........
------- ----- ------ ----
o.,
0',
0.05
. .......... .
0 , - F_
im
DISTANCE 1,,3
NOTE: 10'
SOUMO: Simmons 2002 (157578]; SWILANIL-SCI-21541, p. 110.
Figure 11.4-16. Matrix (a) and Fracture (b) Saturation Profiles as a Function of Distance at the Indicated
0 Times for the Dual-Continuum Model with Weak Fracture-Matrix Coupling
0
  11 F-36  1

 

Natural Analogue Synthesis Repon
.0 Tllpl~-,, - - -
	o 5 1

6oo	loo
Qo	Iwo y
---------
200	------
o
	io ico
	D ISTANC E J,]
(b)
"I , Idd T-1.1-
F-I's M y
I y
80D 1) ,
6w I oo y
Q. 1way
----------
2M
o 7 7 7
io ioo
DISTAIIGE I.]
NOTE: o-10'
Source: Simmons 2002 [1575781: SN-LANL-SCI-215-VI, p 107.
Figure 11.4-17. Matrix (a) and Fracture (b) Temperature Profiles as a Function of Distance at the
0 Indicated Times for the Dual-Continuum Model with Very Weak Fracture-Matrix Coupling
0
TDR-NBS-GS-000027 PEV 00 ICN 01 1 IF-37  1

 

Natural Analogw Synthesis Repon
ka)
~tn, 0.5 y
I y
0.6 10, t/ Iv,
0.
1000 v
c:
10 IDD
DISTANCE
0.35
0.3 -I'FW S.,..d-
-tmre 0.5 y
2y
0.25 , y
0 0 , .2
0
DISTANCE (.1
NOTE:
Source: Simmons 2002 (157578]; SN-LANL-SCI-215-Vi, p. 107
Figure 11.4-18. Matrix (a) and Fracture (b)Saturation Profiles as a Functim of Distance at the Indicated
0 Times for the Dual-Continuum Model with Very Weak Fracture-Matrix Coupling I
0
TDR-NBS-GS-000027 REV 00 ICN 0 1 1 IF-38  1

 

Natural Analogue Synthesis Repon
o,6
1-6 omi ooi I im
n,e ~l
Source: Simmons 2002 [1575781: SN-LAN L-SCI-21 5-V 1, p. 11 S.
Figu re 11. 4-19. Fracture Saturation as a Function of Time at the Boundary between the I ntrus,on and
Country Rmk for Differenl Fracture-Matrix Coupling Strengths
40
0
0.10
0.08		TIME f I Ef.=0.01
y
0.06		-0.01
0.1
		0
.1
		,
0.04		-10
0.02-
o4	--
u b 10 15 7 30 35 40 45 50 55 60 65 70 75 0
DISTANCE [m]
NOTE: u-10'
Soume: Simmons 2002 [1575781; SN-LANL-SCI-215-Vl, p. 117.
Figure 11.4-20, Fracture Volume Fraction of Amorphous Silica Precipitation as a Function of Distance for
Various Times with Moderate Fracture-Matrix Coupling
  11 F-39 

 

Natural Analotpx Synthesis Repon
0
71i
To
85,\
Legend
Diabase dyke
Porphyritic dyke
BioMe gneisses
Crushing zone
Soume: Gupalo ot a]. 1999 (1574701, Figum 2.16.
Figure 11.6-1. Schmatic of the Underground Workings at Facility P-4 at K-26, Siberia, in Cross Section
0
  1 IF-40
April 2002 1

 

Natural Analogue Synthesis
0
0
Tablell.2-1. THC Processes in Geothermal Systems and Their Applicability to Yucca Mountain
THC process	Geothermal system	Geothermal	Applicability to	Potential impact to
	component	examples	Yucca Mountain	repository
				pertcrrmance
Advective	Heat transfer within	Nearly ubiquitous:	Would only occur very	Could result in
heating	convecting geothermal	examples include	locally in high-	localized zone of
	reservoir: develop	Yellowstone	temperature (>1000C)	enhanced water-rock
	near-isothermal	(Wyoming), Salton Sea	design (within heat	interaction and
	vertical thermal profiles	(Califomia), Wairakei	pipe)	chemical transport
		(New Zealand)
Conductive	Heat transfer within	Nearly ubiquitous:	Main mechanism of	Heating leads to more
heating	low-permeability and	examples include hot	heat transfer at Yucca	rapid chemical
	unsaturated portions of	dry rock resources,	Mountain (unsaturated	reactions. Thermal
	geothermal systems	upper portions of San	conditions)	expansion of rocks
		Vicente (El Salvador),		could alter fracture
		Amatitian (Guatemala)		permeability
Fracture-	Fluid flow in fractured	Silangkitang	Main mechanism for	Could permit rapid
dominated fluid	reservoir rocks with	(Indonesia), Dixie	fluid flow within welded	movement of fluids
flow	low matrix permeability	Valley (Nevada), Los	ash flow tuffs at Yucca	along fast flow paths
		Azufres (Mexico)	Mountain	(evidenced by bomb-
				pulse tdtium)
Chemical	Advective and diffusive	Ubiquitous. Well-	Advective transport	Potential mechanism
transport	transport of dissolved	documented tracer	within fractures, and	for movement of
	constituents in fluids.	tests for many	advective and diffusive	radioactive waste
	Tracer tests used to	geothermal systems,	transport between	matedals from
	determine fluid flow	including The Geysers	fractures and matdx	repository
	paths and rates.	(Califomia), Dixie
		Valley (Nevada), Coso
		(Califomia),
		Awibengkok
		(Indonesia)
Boiling	Development of two-	Occurs in most high-	Would only occur in	Would create dryout
	phase and steam	temperature liquid-	high-temperature	zone around drift for
	zones in geothermal	dominated geothermal	design near drift walls	high-temperature
	systems due to	systems with	for limited time	design, and could lead
	depressudzation and	production, e.g.,		to development of heat
	heating	Awibengkok		pipe. Fracture
		(Indonesia), Coso		permeability could be
		(Califomia), and		modified by
		occurs naturally in		precipitation caused by
		steam-dominated		boiling.
		systems, e.g., The
		Geysers (California),
		Karaha-Telaga-Bodas
		(Indonesia). 

		
		
Dryout	Occurs during	Documented for The	Would only occur in	Dryout zone would
	transformation from	Geysers (California),	high-temperature	prohibit seepage into
	liquid-dominated to	Karaha-Telaga-Bodas	operating mode near	drift for early stages of
	steam-dominated	(Indonesia)	drift walls for limited	high-temperature
	geothermal system		time	operating mode. Would
				lead to precipitation of
				dissolved solids in area
				that could be
				redissolved as cooling
				and rewefting
				occurred.
  1 IT-1  1

 

Natural Analogue Synthesis Report
0
41
0
Tablell.2-1. THC Processes in Geothermal Systems and Their Applicability to Yucca Mountain
(Cont.)
THC process	Geothermal system	Geothermal examples	Applicability to Yucca	Potential impact to
	component		Mountain	repository performance
Condensation	Occurs during	Observed in many	Would mainly occur in	Condensation above
	transformation from	geothermal systems	high-temperature	drift could lead to
	liquid-dominated to	where rising gas and	design above drift	recycling of fluids, thus
	steam-dominated	steam is cooled and	areas for limited time;	resulting in a higher
	geothermal system,	mixes with near-	can also occur in low-	volume of fluids
	and in upper levels of	surface meteoric fluids,	temperature design,	passing through near-
	geothermal systems	resulting in	but at a reduced level	field area. This could
	where rising vapor	development of		also result in localized
	contacts cooler	bicarbonate and acid-		zones of near-
	meteoric waters	sulfate springs.		saturation conditions
		Documented for		and increase water-
		Yellowstone		rock interaction.
		(Wyoming), Wairakei		Condensation could
		(New Zealand),		also take place in the
		Waiotapu (New		drift, resulting in
		Zealand)		dripping on waste
				packages.
Mineral	Occurs typically in	Difficult to document,	Would occur primarily	Mineral dissolution
dissolution	condensation zones, or	but observed at The	where condensation	associated with
	where acid fluids are	Geysers (Califomia)	occurs	condensation zone
	present	and Karaha-Telaga-		could lead to local
		Bodas (Indonesia)		increases in porosity
				and permeability.
Mineral	Occurs in numerous	Ubiquitous.  Degree	Alteration and	Alteration could lead to
alteration and	portions of geothermal	and type of	precipitation likely to	changed sorption
precipitation	systems, especially in	mineralization depends	be confined to near-	properties (zeolite and
	zones with abundant	on rock and fluid	field environment,	clay formation).
	fluid flow that have	compositions, water-	where boiling and	Precipitation of silica
	undergone heating	rock ratios, and	increased fluid flux	minerals and calcite in
		temperature. Boiling	occur. These effects	fractures could locally
		can result in significant	may be negligible for	reduce permeability, or
		mineralization.	low-temperature	lead to focussed flow
		Alteration mineralogy	design.	within a few larger
		well-characterized at		fractures.
		Wairakei (New
		Zealand), Salton Sea
		(Califomia),
		Silangkitang
		(Indonesia), Krafla
		(Iceland)
Source: Simmons 2002 [157578], SN-LBNL-SCI-108-V2, pp. 14-15.
  1 IT-2  1

 

Natural Analogue Synthesis Report
0
0
0
Table 11.2-2. Estimated Process Time Scales for Potential Repository and Geothermal Reservoirs
Process	Repository
Time Scale (yr)	Geothermal Reservoir
Time Scale (yr)
Duration of heating (magma or nuclear
waste)	1000S	10,000S
Dryout	1 00s to 2,000	10,000S
Fast-path flow from ground surface to
repository or geothermal system	10's	los
Water recycling in "heat pipe" (cyclic
liquid-vapor counterflow)	<<1	ls to los
Intermittent flow events	<<<1	<<<1
Physical changes due to dissolution and
precipitation	<1 to 1,000s	<1 to 10,000S
Mineralogic changes	<1 to 1,000S	<1 to 10,000S
Climate change	10,000S	10,000S
Source: Simmons 2002 [157578], SN-LBNL-SCI-1 0842, p. 15.
Table 11.3-1. Comparison of Yellowstone and Yucca Mountain Systems
	Potential Yucca Mountain
Repository	Yellowstone Geothermal System
Boiling zone temperatures	-950C	92-2700C
Si02 in fluids	<200 ppm	200-700 ppm
Duration of boiling conditions	<11,200 yr (high T)
0 years (low T)	~1 5,000 yr
Fluid-flow conditions	Unsaturated	Saturated
Estimated fluid flux	i o-I to i o-11 M/S	4.8 x 10,5 M/S
Estimated heat flux	16.7 W/M2 (in near-field area
around waste packages)	46 W/M2 (Firehole River Drainage Basin)
1.7 W/M2 (Yellowstone Caidera)
Source: Simmons 2002 [157578], SN-LBNL-SCI-1 0842, p. 15.
  1 IT-3  1

 

Natural Analogue Synthesis Report
Table 11.4-1. Samples, Lithologic Types and Descriptions, and Measured and Estimated Distances of
0 Tuff Samples from a Basaltic Intrusion
0
0

Sample Number	Distance to
Contact (ft)
[m)
Lithology
Sample Description
Adjacent and west of Papoose Lake Sill
PROO-3-15-1 (LANL# 3547)	Contact	Basalt	Purplish gray, fine grained, platy, and altered
PROO-3-15-2 (LANL# 3548)	4.5 [1.4]	Vitrophyre	Fused tuff, glassy, foliated, and 7 ft (2.1 m) wide
PROO-3-15-3 (LANL# 3549)	3.0 [0.9]	Vitrophyre	Fused tuff, glassy, foliated, and contains silica
veinlets
PROO-3-15-4 (LANL# 3550)	8.5 [2.6]	Baked tuff	Hardened, pinkish orange, and devitrified
PROO-3-15-5 (LANL# 3551)	12.5 [3.8]	Tuff	Partially welded, cavernous, and pinkish orange
PROO-3-15-6 (LANL# 3552)	15.5 [4.7]	Opal vein	3" wide, NS trend parallel to contact, and reddish
PROO-3-15-7 (LANL# 3553)	15.5 [4.7]	Tuff	Within opal vein zone, pinkish, contains few opal
nodules
PROO-3-15-8 (LANL# 3554)	12.5 [3.8)	Opal vein	N20E trend, crystalline, variable thickness, cuts
nonwelded tuff
PROO-3-15-9 (LANL# 3555)	29 [8.8]	Tuff	Altered, silicified, pinkish and fine grained
PROO-3-15-10 (LANL# 3556)	29.4 [9.01	Tuff	Nonwelded, collected within silicified zone, pinkish
PROO-3-15-11 (LANL# 3557)	43 [13.1]	Tuff	Nonwelded, cut by few opal veins, pinkish
PROO-3-15-12 (LANL# 3558)	82 [25]	Tuff	Nonwelded, pinkish, pumice-rich
PROO-3-15-13 (LANL# 3559)	200 [61]	Tuff	Nonwelded, pinkish, friable, pumice-rich, and
cavernous
Above and east of Papoose Lake Sill
PROO-3-14-2 (LANL# 3538)	-150 [46]	Tuff	Pale pink tuff cut by opal veins, dark red halo,
pumice clasts
PROO-3-14-3 (LANL# 3539)	-150 [46]	Tuff	Same as LANL# 3538 with thicker veins and
alteration
PROO-3- 14-4 (LANL# 3540)	-150 [46]	Tuff	Same tuff with pumice clasts and nodule
PROO-3-14-5 (LANI_# 3541)	-150 [46]	Tuff	Same tuff with corroded pumice clasts and devitrified
PROO-3-14-6 (LANL# 3542)	-150 (46]	Opal vein	1 cm wide in a similar tuff, contains fresh pumice
clasts
PROO-3-14-7 (LANL# 3543)	-150 [46]	Tuff	Same tuff with dense pumice
PROO-3-14-8 (LANL# 3544)	-150 [46]	Tuff	Same tuff with thick opal veins
PROO-3-14-9 (LANL#3545)	> 150 [46]	Tuff	Tuff east of opal vein zone, gray, no veins, pumice
less distinct
PROO-3-15-14 (LANL# 3560)	-400 [122]	Tuff	Nonwelded, matrix silicified, few opal veins, reddish
brown
PROO-3-15-15 (LANL# 3561)	-400 [122]	Tuff	Nonwelded with nodules, pumice-dch, grayish,
cavernous
PROO-3-15-16 (LANL# 3562)	-500 [152]	Tuff	Dark reddish orange, nonwelded, fdable, massive
  1 IT-4  1

 

Natural Analogue Synthesis Report
0
0
0
Table 11.4-1. Samples, Lithologic Types and Descriptions, and Measured and Estimated Distances of
Tuff Samples from a Basaltic Intrusion (Cont.)
Above and east of Papoose Lake Sill (continued)

PROO-3-15-17 (LANL# 3563)	720 [220],
60.0 [183]
west of
dike
Tuff
Moderately welded with opal nodules, grayish

PROO-3-15-18 (LANL# 3564)	695 [212),
38.5 [11.7]
west of dike
Tuff
Moderately welded with opal nodules, orangish

PROO-3-15-19 (LANL# 3565)	660 [2011,
3.0 [0.9]
west of dike
Fusedtuff
Fused with fiamme and nodules, pinkish brown
Beneath sill (Figure 11.4-1, Section B)
PROO-3-16-1 (LANL# 3570)	Top part of
sill	Basalt	25 ft (7.6 m) thick, sparsely porphyritic, amygdules
PROO-3-16-2 (LANL# 3571)	Contact	Basalt-tuff	Platy basalt, fused granular tuff, no vitrophyre
PROO-3-16-3 (LANL# 3572)	1 [0.3]	Tuff	Pinkish gray, medium grained, partially fused
PROO-3-16-4 (LANL# 3573)	4.4 [1.3]	Tuff	Nonwelded, bedded, coarse, and crystal-rich
PROO-3-16-5 (LANL# 3574)	4.4 [1.3]	Tuff	Fine grained, pinkish gray, tilted 200S
PROO-3-16-6 (LANL# 3575)	15 [4.6]	Tuff	Moderately welded, light gray, contains lithics
PROO-3-16-7 (LANL# 3576)	21 [6.4]	Opal vein	2 ft (0.6 m) wide, fractured, orange and white veins
PROO-3-16-8 (LANL# 3577)	30.8 [9.4)	Opal vein	Host tuff fractured, same as LANL# 3576
PROO-3-16-9 (LANL# 3578)	34.2 [10.4]	Tuff	Nonwelded, light gray, and contains lithics
PROO-3-16-1 0 (LANL# 3579)	35 [10.7]	Tuff	Crystal-rich, coarse, pumice-rich, matrix-free
PROO-3-16-11 (LANL# 3580)	16 [4.9]	Opal	0.4-1.5 ft (0.1 to 0.5 m) thick, N-S trend, dips 650E,
(98 ft) (30 m) long
PROO-3-16-12 (LANL#3581)	8 [2.4]	Tuff	Host tuff for the (98 ft) (30 m) long opal vein
Source: Simmons 2002 [157578], SN-LANL-SCI-215-Vl, pp. 13-27, 90-94.
  1 IT-5  1

 

-9
C)
lp
C)
C>
z
C)
61
0 0
Table 11.4-2. 

 Subsurface Stratigraphic Information from Drill Holes along the Eastern Part of Yucca Flats Adjacent to Paiute Ridge
0
	Drill Holes: Interval Thickness
I (m)
and Depth to the Tops of Formations
D (m)
Stratigraphic Units	,
,
,
(upper one third of
i	U 3mk	U 7at	U 7bg	U 7bh	U 7bk	U 7bm	U 7bo	UE7h	UE 7m	U 7x
sect
on)
	I	D	I	I D	I	D	I	D	I	D	I	D	I	D	I	D	I	D		D
Qal

(Ota)	65.5		82.3		48.8		54.9		41.1		92.4		138.7		51.8		61		67.1
Tma Ammonia Tanks	none	None	none	none	29	48.8	21.3	54.9	none	none	none	none	none	none	18.3	51.8	none	none	none	none
Tmab Bedded Ammonia	none	N

Tanks		one	none	none		70.1		68.6	none	none	none	none	none	none		62.5	none	none	none	none
Tmr Rainier Mesa	56.4	65.5	21.3	82.3	67.1	77.7	48.8	76.2	54.9	41.4	95.1	92.4	47.2	138.7	82.3	70.1	94.5	61	73.2	67.1
Tx Rainier Mesa/
(TmdfT
24.4
121.9
35.1
103.6
3g
144.8
39
6
125
38
1
96
59
4
1187
1
39
6
185
9
4
6
152
4
39
6
155
4
~
73
1
14U
Vitrophyre
a)							.		.		.	-	.	.	.	.	.	.	t
.
Tpc Tiva Canyon	nd	nc	nd	nd	nc	nd	nd	nd	nd	nd	nd	nc	nd	nd	nc	nd	nd	nd	na	nc
Tpt Topopah Spring	nd	nc	nd	nd	nc	nd	nd	nd	nd	nd	nd	nc	nd	nd	nc	nd	nd	nd	nd	nc
Tac Calico Hills	nd	nc	nd	nd	nc	no	no	na	nc	na	nd	nd	nd	nd	nc	nd	nd	nd	nc	nc
TW Lower Wahmonie	24.4	146.2	21.3	138.7	1U	176.8	19.8	164.6	2M	134.1	18.3	246.9	15.2	225.6	1 8.'~
1
157
21.9
195.1
nc
nc
Tc Crater Flat	56.
5
j	170.7	51.1	160	43.2	195.1	82.3	184.4	44,	155.4	80.8	265.2	51.8	240
-	59.	175.3	51.2	217	nc	nc
Tcb Bull Frog
n	nd	n	nd	nc	nd	nd	nj	nc		nj	nd	nd	1	nj		nl	nd
Surface elevation

(m)		1297.8		1336.6		1337.5		1338.7		1333.5		1291.7		1319.2		1338.7		1315.2		1328.9
Drill hole depth (m)		381		460.4		396.2		396.2		376.4		472.4		609.6		780.6		587		533.4
Depth to pervasive

zeolitization (m) I		281.9
I	182.9
I
I	167.1
,
157
-1	198.1		243.1		262.1
1
1	1,92.1		240.~
MI
NOTE: nd means "not defined." Values in bold-type indicate depth to Rainier Mesa Vitrophere Unit.
Source: Drellack and Thompson 1990 [156446], pp. 60, 64, 66, 68-69,118, 122,124,126-127.
z

 

~q
C)
z
12
0
0
0
Table 11.4-3. Quantitative Mineral Abundances by XRD for Selected Tuff Samples Adjacent to Papoose Lake Sill in the Northern Part of Paiute
Ridge

Sample	Smec-
tite	Clino-
ptilote	Chab-
azite	Tridym
mite	Crist-
obalite	Opal-
CT	2ndary i
Quartz'
K-Spar	Plogio-
clase
Glass	Hem-
atite	Blo-
tite	Horn-
blende
Augite	Cal-
cite
Total
PROO-3-15-01, LANL# 3547	18.5	-	-	-	-	-	-	8.1	52.8	-	3.0	2.1	-	16.5	-	101.0
PROO-3-15-02, LANL# 3548	-	-	0.8	0.9	0.4	-	5.7	1.0	8.2	79.8	-	0.2	-	-	-	97.1
PROO-3-15-03, LANL# 3549	-	-	1.0	3.4	0.9	-	3.7	3.5	13.9	75.2	-	0.5	-	-	-	102.0
PROO-3-15-04, LANL# 3550	-	-	-	1.4	1.9	-	3.6	3.2	11.4	75.4	-	0.2	-	-	-	97.1
PROO-3-15-05, LANL# 3551	1	-	- 1	-	-	-	5.3	4.7	7.5	82.8	0.3	1.5	-	-	-	102.2
PROO-3-15-06, LANL# 3552	-	55.9	-	-	1.0	27.7	2.4	7.0	5.6	-	-	0.1	-	-	-	99.6
PROO-3-15-07, LANL# 3553	-	2.8	-	-	- 1	-	2.9 1	8.3	8.0 1	71.8	0.2	2.7	-	-	4.5	101.3
PROO-3-15-08, LANL# 3554	-	26.5	-	-	-	18.7	22.7	13.5	16.9	-	-	0.4	0.1	-	-	98.8
PROO-3-15-09, LANL# 3555	-	64.6	-	-	0.9	23.5	2.3	4.6	8.3	-	-	0.1	-	-	-	104.3
PROO-3-15-10, LANL# 3556	-	6.8	4.6				4.5	6.4	6.4	65.5	0.1	0.9	-	-	2.9	98.2
PROO-3-15-1 1, LANL# 3557	-	3.8	-				7.3 1	5.1	8.4	74.5	-	1.5	-	-	1.3	102.0
PROO-3-15-12, LANL# 3558	-	-	-				3.6	2.9	6.5	84.7	0.1	0.4 1	-	-	-	98.1
PROO-3-15-13, LANL# 3559	0.1	-	-				3.8	3.9	7.1	85.2	0.2	11.4 1	-
NOTES: Mineral abundances are in weight percent - means "not detected"
Source: Simmons 2002 [157578]; SN-LANL-SCI-215-Vl, p. 59.

 

Natural Analogue Synthesis
0
10
0
Table 11.4-4. Comparison of Equation of State Properties of Pure Water at 1,200QC
p
(bars)	Density
(kg/M3)	Enthalpy
(kJ/kg)	tnergy
(kJ/kg)	Viscosity
(JApa S)
	FLOTRAN	HGK	FLOTRAN	HGK	FLOTRAN	HGK	FLOTRAN	HGK
1	0.14709	0.14708	5,131.03	5,150.0	4,451.18	4,470.1	40.66
5	0.7356	0.7354	5,130.4	5,149.2	4,450.7	4,469.4	40.89
10	1.4714	1.4710	5,129.7	5,148.2	4,450.1	4,468.4	41.18
NOTES: The comparison is between Haar et al. (1984 [105175]) (the HGK columns) and the equation of state used
by FLOTRAN based on the International Formulation Commiffee of the Sixth lntemational Conference on
Properties of Steam (IFC 1967 [156448]) with the reported range of validity of 0 < p < 165.4 x 105 Pa (165.4
Bars) and 0 < T < 800'C.
Source: Simmons 2002 [157578]; SN-LANL-SCI-215-Vl, pp. 102-103.
  1 IT-8 

 

Natural Analogue Synthesis Report
Table 11.4-5. Basalt and Tuff Hydrothermal-Model Parameters for Fracture (f) and Matrix (m)
0 and Dual-Continuum Parameters Used in the THC Simulations
0
0
Property	Symbol	Units	Mafic Intrusion	Tuff Host Rock
Fracture Permeability	kf	m 2	2.74 x 10-9	2.74 x 10-9
Matrix Permeability	km	m 2	1.0 X 10-20	4.66 x 10-"'
Fracture Porosity	Of		1.0	1.0
Matrix Porosity	Om		0.05	0.47
Rock Density	Pr	kg M,3	2,830	2,410
Specific Heat	CP	J kg-1 K-'	1,010	1,100
Thermal Conductivity	C-wei	J m-1 s-1 K'	1.93	0.61
Thermal Conductivity	Cdry	J m-1 s*1 K,	1.93	0.61
Gaseous Diffusivity	D	m 2 S'l	2.13 x 10's	2.13 x 1 o-5
Temperature Exponent	0		1.8	1.8
Tortuosity	T		1.0	1.0
Residual Saturation	Sr		0.04	0.04
van Genuchten Parameter	at	Pa-'	8.92 x 10-4	8.92 x 10-4
van Genuchten Parameter	am	Pa-1	4.15 x 10-5	4.15 x 10*5
van Genuchten Parameter	Xf		0.449	0.449
van Genuchten Parameter	xm		0.327	0.327
Initial Temperature	TO	!2C	1,200	30
Initial Saturation	A 0		0.0	0.4
Dual Continuum Parameters
Fracture Volume Fraction	ef		0.01	0.01
Matrix Block Size	/M	m	0.5	0.5
Frature-Matrix Area Factor	Crfm		100	0.1
Source: Simmons 2002 [157578]; SN-LANL-SCI-215-Vl, p. 104.
  1 IT-9  1

 

Natural Analogue Synthesis Report
0 12. ANALOGUES TO SATURATED ZONE TRANSPORT
12.1 INTRODUCTION
This section discusses analogues to transport in a saturated environment under oxidizing
conditions, such as that at Yucca Mountain. Most of the analogue sites studied to date in
saturated environments occur in rock types dissimilar to the saturated zone (SZ) at Yucca
Mountain, e.g., fractured crystalline granite or gneiss, or sandstone. However, some aspects of
these systems have attributes or demonstrate processes that warrant attention with respect to
Yucca Mountain and are included in this section. Section 12.1 briefly summarizes the main
conclusions of past Yucca Mountain Site Characterization Project (YMP) analogue studies with
respect to SZ transport. Section 12.2 provides a background by describing the SZ flow system at
Yucca Mountain.  Section 12.3 is a study of transport plumes formed from uranium mill tailings
at selected sites in the westem United States, and the relevance of this information to saturated
transport in alluvium at Yucca Mountain. Section 12.4 provides examples from analogues of
matrix diffusion and colloid transport in the SZ. The main ideas and conclusions are presented in
Section 12.5.
12.1.1 Insights into SZ Transport from Previous Analogue Studies
Some of the processes relevant to radionuclide transport at saturated sites were discussed in
Yucca Mountain Site Description (CRWMS M&O 2000 [151945], Section 13.4:3). The main
points of those discussions are summarized here. 

Filtration of particulate matter is an efficient process at Poqos de Caldas (CRWMS
M&O 2000 [151945], Section 13.4.3.3). The colloidal matelial acts as largely
irreversible sinks for many immobile elements, such as thorium and rare-earth
elements.
The redox front at Pogos de Caldas provided direct evidence of the operation of flow
channeling in fractures and solute transport in the rock matrix as the key controls on the
shape and movement of the redox front. The very slow, diffusion-dominated movement
of the redox front plays a significant role in retarding many trace elements (CRWMS
M&O 2000 [1519451, Section 13.4.3.3; Romero et al. 1992 [157573], pp. 471-472).
Pogos de Caldas also highlighted the importance of amorphous phases in suspension or
as coatings on rock as the principal sorptive surfaces for many trace elements in
solution (CRWMS M&O 2000 [151945], Section 13.4.3.3). Some of the fixing
processes appeared to be irreversible over long time scales, compared to reversible
sorption used in Perfon-nance Assessment (PA) models. Sorption onto fracture coatings,
particularly calcite, also efficiently retards uranium transport in fractures at Palmottu
(CRWMS M&O 2000) [151945], Section 13.4.3.3).
The Chemobyl study (CRWMS M&O 2000 [151945], Section 13.4.3.3) showed that
pathways of rapid groundwater contamination around Chemobyl may not be directly
connected to the pathways of near-surface zones of preferential flow.
  12-1 

 

Natural Analogue Synthesis Report
Other analogues were mentioned as multiple lines of evidence in FY 01 Supplemental Science
and Perforinance Analyses, Volume 1: Scientific Bases and Analyses (BSC 2001 [155950],
Section 12.4). Using Yucca Mountain as a self-analogue, it was possible to interpret groundwater
hydrochemical data to estimate flow paths in the vicinity of Yucca Mountain (BSC 2001
[155950], Section 12.4.1). These estimated flow paths were shown to be consistent with flow
paths predicted by the site-scale SZ flow model.
The initial phase of investigation of the Uranium Mill Tailing Remedial Action (LTWRA) sites
discovered that some fraction of the total inventory of uranium Mill tailings appears to be
transported as a nonsorbing to weakly sorbing species under oxidizing conditions (BSC 2001
[155950], Section 12.4.2). This supported the TSPA-SR treatment of uranium as weakly sorbing
(BSC 2001 [1559501, Section 12.4.2).
12.2 HYDROGEOLOGY AND FRACTURE MINERALOGY OF THE SATURATED
ZONE
The water table near the proposed Yucca Mountain repository block is currently at an elevation
of approximately 730 m, more than 300 m below the proposed repository horizon (DOE 1998
[100548], Section 2.2.4). Water infiltrating the unsaturated zone (UZ) becomes recharge to the
regional flow system. Water moves generally southeast beneath the (UZ) site before flowing
south out of the volcanic rocks and into the thick valley fill of the Amargosa Valley. The
hydraulic gradient is very low (-0.0001; Fridrich et al. 1994 [100575], p. 138) downgradient
from Yucca Mountain, so that travel time of groundwater may be long. Near Yucca Mountain,
volcanic rocks up to several thousand meters thick overlie the Paleozoic and older rocks of the
region (DOE 1998 [100548], Section 2.2.4.1). Their hydrologic properties change substantially
over short distances, which produces a complex hydrogeology. The volcanic-rock section
becomes thinner to the south and is a lesser component of the saturated zone flow system in
southem Amargosa Valley, where the major aquifer consists of Quatemary-Tertiary
heterogeneous valley-fill deposits.
The dominant regional aquifer is the Paleozoic carbonate aquifer, consisting of marine
limestones, dolomites, and minor clastic sediments thousands of meters thick. 

In the vicinity of
Yucca Mountain, the carbonate aquifer is not tapped as a source of groundwater because of its
great depth (DOE 1998 [100548], Section 2.2.4.1).
Luckey et al. (1996 [100465], pp. 18-20) divided the volcanic rocks below the water table into
four hydrogeologic units. From top to bottom, these are the upper volcanic aquifer, the upper
volcanic confining unit, the lower volcanic aquifer, and the lower volcanic confining unit. The
upper volcanic aquifer is composed of the Topopah Spring Tuff, which occurs in the UZ near the
repository, but is present beneath the water table to the east and south of the potential repository
and in Crater Flat. The upper volcanic confining unit includes the Calico FBIls Formation and the
uppermost, unfractured part of the Prow Pass Tuff in areas where they are saturated. The lower
volcanic aquifer includes most of the Crater Flat Group (Luckey et al. 1996 [100465] pp. 18-20),
and the lower volcanic confining unit includes the lowermost Crater Flat Group and deeper tuffs,
lavas, and'flow breccias. The upper volcanic aquifer underlying Yucca Mountain is generally
productive and provides groundwater for the site. The main distinction between SZ volcanic
aquifers and confining units is that the aquifers tend to be more welded and contain more
  12-2  1

 

Natural Analogue Synthesis Report
permeable fractures than the aquitards. However, alteration of the nonwelded tuffs to zeolites
and clays, which reduces permeability, is more pronounced at depth. The increase of pressure
with depth also reduces fracture perineability, such that the overall tendency is toward decreased
permeability with depth, even in aquifers.
The chemistry of SZ waters beneath Yucca Mountain (Oliver and Root 1997 [100069]) reflects
processes that affected these waters as they flowed to the Yucca Mountain area from recharge
areas to the north (McKinley et al. 1991 [116222]). In general, they are dilute sodium
bicarbonate waters that are neutral to mildly alkaline and mildly oxidizing. Similarities between
the composition of SZ waters in the recharge areas north of Yucca Mountain and those beneath
Yucca Mountain suggest that water compositions primarily reflect water-rock interactions in the
recharge areas (DOE 1998 [100548], Section 2.2.4.3).
After reaching the water table, flow continues generally to the southeast away from the potential
repository. The majority of saturated flow occurs in zones with enhanced permeabilities caused
by fractures. Retardation processes such as sorption, matrix diffusion, and dispersion would also
function in the SZ. Water may contact sorbing zeolites in the Calico Hills Formation and Prow
Pass Tuff, and, as in the UZ, fracture minerals may have a significant effect on both flow and
transport.
Fracture-filling minerals in the SZ include smectite, manganese oxide minerals, hematite, quartz,
opal-CT, calcite, and clinoptilolite and mordenite, the same zeolites that characterize the altered
rock matiix below the water table (Carlos et al. 1995 [101326], pp. 8-12). Laboratory
expefiments have shown that fractures containing smectite, manganese oxides, and calcite have
particular affinity for plutonium retention (DOE 1998 [100548], Section 2.2.5.2). 

Thus,
analogues related to transport through saturated, oxidizing environments need to consider the
role of fracture-filling minerals such as these in retarding the migration of radionuclides.
12.3 URANIUM MILL TAILINGS
12.3.1 Purpose and Approach
This section summarizes pertinent inforrnation on the transport of uranium and other constituents
of interest in alluvial aquifers at UMTRA sites. The YNV is particularly interested in the
dispersion characteiistics of the contaminant plumes and in the retardation behavior of
constituents, such as uranium, that are found in nuclear waste to be emplaced in a repository.
The scope of Section 12.3 is limited to a review of the subsurface transport behavior of uranium
and other constituents of interest at UMTRA sites. All UMTRA sites have been evaluated to
identify those sites appropriate for more detailed analysis. The emphasis here is on the transport
behavior of uranium and other constituents in alluvial deposits. This is because the potential
transport pathways from Yucca Mountain to the accessible environment pass through alluvium
and because there are no UMTRA sites with bedrock similar to the volcanic rocks at Yucca
Mountain.
The approach is to evaluate the UMTRA sites in terms of aquifer materials, hydrologic
characteristics, and groundwater chemistry. Those sites that are closest in hydrologic and
  12-3 

 

Natural Analogue Synthesis Report
chemical characteristics to the alluvium downgradient from Yucca Mountain and for which
41 sufficient data are available for detailed transport analysis are considered in more detail.
12.3.2 Background
The UMTRA Project was authorized by Congress in 1978 to clean up 24 inactive uranium ore
processing sites (DOE 1996 [154693]). Currently, there are 20 UMTRA Project sites in the
continental United States, located mostly in the westem states (Figure 12-1). Many of the sites
are located in the Rocky Mountain states of Colorado (seven sites), Utah (three sites), Wyoming
(two sites), New Mexico (two sites), and Idaho (one site). Sites are also located in Arizona (two
sites), Oregon (one site), and Texas (one site) (DOE 2000 [157603]).
Most of the sites consisted of a uranium processing mill with associated waste streams and ore
and tailings piles. The ore and tailings piles were situated directly on surface soils. Rain and
siiow melt percolated through the piles, leaching uranium and other constituents, before entering
the underlying shallow groundwater systems. The LTMTRA Project has monitored the
concentrations of radionuclides and other contaminants in shallow groundwaters beneath and
downgradient from these sites for 15 to 20 years. The information obtained provides useful
insight on the fate and transport of uranium and related ore constituents in shallow aquifers. The
infon-nation obtained on transport in alluvial aquifers could be particularly useful in the
development of models and calculations for radionuclide transport in shallow alluvial aquifers
down gradient from Yucca Mountain.
4D 12.3.3 Selection of Analogue Sites
The magnitude of operations at the valious UMTRA sites was quite variable. Sites such as Grand
Junction, Rifle, and Naturita in Colorado had large operations that resulted in large tailings piles.
Operations at Cannonsburg in Pennsylvania and Spook in Wyoming were much smaller, with
correspondingly smaller tailings piles. Other sites were in between these two groups in tenns of
magnitude of operations and size of the tailings piles. 

The magnitude of the operation is
important in this discussion, because the magnitude of the site-characterization activities
undertaken by the UMTRA Project was generally proportional to the magnitude of the operation
at a given site. To be useful to the Yucca Mountain Project, detailed site-characterization data are
required on the flow and transport systems at these sites. Only a limited number of UMTRA sites
have been investigated in sufficient detail to be of use as analogues to the transport of uranium
and other constituents of interest in the alluvial part of the Yucca Mountain flow system.
The history of operations at the various sites was also quite variable. Operations at the Old Rifle
site started as early as 1924. Most of the sites started operation in the mid to late 1950s and
ended operations in the early 1960s to early 1970s. During the 1980s and 1990s, the tailings piles
located at the 24 sites were either capped in place or removed to another location and
encapsulated. Therefore, the tailings piles were sources of contaminants for subsurface transport
for, at most, 30 to 70 years.
The ores processed at the various locations contained other chemical elements besides uranium
and its daughter products. These elements included vanadium, arsenic, selenium, manganese,
molybdenum, barium, and other trace metals. Most of these ore "byproducts" ended up in the
  12-4 

 

Natural Analogue Synthesis Report
tailings piles. In addition, chemicals used in processing the ore were also dumped on the tailings
piles. Important among the latter were sulfuric acid, nitric acid, ammonium hydroxide, and
is organic complexing agents. While the mills were in operation, rain and melted snow infiltrated
into the uncovered tailings piles and leached constituents from the tailings. Liquid spills or leaks
from site operations also infiltrated into the subsurface. These spill, leak, and leach solutions
have since percolated downward through the subsoils and sediments beneath the sites and
reached groundwater, forming plumes of contaminants in shallow aquifers.
Those UMTRA sites where the most extensive subsurface characterization and groundwater
monitoring activities were performed are of the most interest to the YMP. The transport of
contaminants in groundwater is controlled by numerous site-specific factors. Part of the value of
UMTRA sites as analogues, therefore, is the site-specific infonnation they can provide on the
factors that control the transport behavior of important constituents such as uranium. Other
parameters used to screen sites for more detailed discussion include the hydrogeology and
hydrology of the shallow aquifers, and groundwater chemistry. 
The intent was to select sites with
alluvial aquifers and low-ionic-strength groundwaters.  The sites chosen for detailed discussion in
this report are the Gunnison and New Rifle sites in Colorado.
12.3.3.1 Gunnison, Colorado, UMTRA Site
The following discussion is based primarily on infon-nation presented in the Final Site
Observational Work Plan for the UMTRA Project Gunnison Site (DOE 2001 [156666]) and
"Groundwater Hydrology Report" Attachment 3 of Remedial Action Plan and Site Design for
Stabilization of the Inactive Uranium Mill Tailings Site at Gunnison, Colorado, Final (DOE
1992 [1546921). The Gunnison processing site is located adjacent to the city of Gunnison in
Gunnison County, Colorado, on a drainage divide between the Gunnison River and Tomichi
Creek in the Gunnison River valley (Figure 12-2). Uranium was processed at the site from 1958
to 1962. Approximately 719,000 yd 3 (550,000 M) of contaminated material including tailings
were originally present on 68 acres (28 hectares). Between 1992 and 1995, the contaminated
material was moved to the Gunnison disposal site, approximately 6 mi (10 km) from the
processing site.
The processing site was located on floodplain alluvium between the Gunnison River and
Tomichi Creek. The site is about 0.4 mi (0.6 km) east of the Gunnison River and 0.4 mi (0.6 km)
west of Tomichi Creek (Figure 12-2). It is bounded on the west by small ston-n drainage ditches
and on the south and west by irrigation ditches. The climate at the site is semi-arid, with an
average annual precipitation of 10.5 in. (27 cm), of which approximately half is contributed by
snowfall (DOE 2001 [156666], Section 3.1). The average depth to groundwater beneath the site
is 5 ft (1.5 m). The uppennost (unconfined) aquifer at the site is in the floodplain alluvium of the
Gunnison River and Tomichi Creek. These alluvial deposits extend to at least 110 ft (34 m)
beneath the processing site. The aquifer is recharged from rain, snowmelt, the Gunnison River,
Tomichi Creek, and seasonal irrigation ditches around the site. The groundwater flows southwest
at an average velocity of 270 ft (82 m) per year. Groundwater from beneath the site discharges
into the Gunnison River and Tomichi Creek (DOE 1992 [154692], pp. 18-20).
Tailings seepage has contaminated the alluvial groundwater beneath and downgradient from the
processing site. Sulfuric acid was used extensively in ore processing at the site (DOE 1992
  12-5 

 

Natural Analogue Synthesis Report
[154692], p. 23). Because sulfate is a conservative constituent (i.e., is not retarded) in oxidizing
groundwaters, it can be used to delineate the maximum extent of movement of site-related
contaminants in groundwater. 

A sulfate plume has been delineated that originates at the site and
extends approximately 7,000 ft (2,000 m) in a southwesterly direction (Figure 12-3). Even
though the plume intersects, and possibly flows beneath, the Gunnison River, sulfate is
conservative relative to uranium at this site. The inferred areal shape of the plume suggests only
limited lateral dispersion over most of the length of the plume. A lateral pinching of the plume is
also inferred by its shape. Borehole lithology logs show a local variation in unit thicknesses close
to the narrowing of the plume. Here, the uppermost sand and gravel unit is about twice its
thickness in adjacent boreholes and appears to fill a paleochannel cut into the underlying clayey
sand and gravel unit (DOE 1992 [154692], p. 16). The highest concentration contours of both the
sulfate and uranium plumes (DOE 1992 [154692], pp. 31, 35, Figures 12-3, 12-4) are tied to a
water analysis from this location. Therefore, the widths of the plumes may be locally constrained
by geohydrologic variations in the subsurface alluvial deposits. Interpretations of plume shape
must be tempered by the fact that the number of sampling points available to construct the plume
map was limited. The maximum concentrations of sulfate in groundwaters along the length of
the plume show only limited variation (715-378 mg/Q. This suggests that downgradient dilution
of contaminants originating at the processing site is limited.
A uranium plume has also been delineated in association with the Gunnison site (Figure 12-4).
The inferred plume has a shape and lateral extent very similar to the inferred sulfate plume
(Figure 12-3). The similar shapes of the two inferred plume maps suggest that the narrow shape
of the uranium plume is locally controlled by geohydrologic variations in the alluvium, described
above, and not directly related to chemical conditions in the alluvial aquifer. For example, the
possibility that lower uranium concentrations outside the inferred plume could simply reflect
more reducing conditions that lead to the removal of uranium from groundwater is not supported
by the data. The similarity in the lengths of the infeffed uranium and sulfate plumes suggests that
at least some of the uranium originating from the site may have been transported with little or no
retardation. However, the groundwater concentrations of uranium decrease more rapidly with
distance from the site than the sulfate concentrations. One possible explanation for the different
concentration gradients is that the source ten-ns increased with time. Another possible
explanation is that the travel time for uranium was longer than the travel time for sulfate (i.e.,
that uranium was retarded to some degree). Laboratory data on sorption coefficients for uranium
on alluvium from this area support the latter interpretation. 

The sorption coefficient values
obtained for two alluvium samples were 1.70 and 5.24 mUg (DOE 2000 [156666], Table 4-7).
Note that dilution alone is not a likely explanation for the decreasing uranium concentrations
downgradient, because sulfate concentrations do not decrease proportionately downgradient.
In summary, the groundwater data for the Gunnison site yield several conclusions that may be
significant with regard to radionuclide transport in alluvium at the Yucca Mountain site. To the
extent that the hydrology of the alluvial aquifers at the Gunnison site and Yucca Mountain are
comparable, the Gunnison data suggest that: (1) lateral dispersion may be very limited
downgradient, (2) dilution may not be a significant process over the transport distance in
alluvium, and (3) uranium may be only slightly retarded by interaction with aquifer materials.
0
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Natural Analogue Synthesis Report
12.3.3.2 New Rifle Site, Rine, Colorado
The Rifle UMTRA site is located along the Colorado River approximately 90 miles (144 km)
east of Grand Junction, Colorado. The Rifle site actually consists of two separate sites, known as
"Old Rifle" and "New Rifle." The Old Rifle site is located approximately 2.3 mi (3.7 km)
northeast of the New Rifle site (Figure 12-5). The New Rifle site has been studied in greater
detail and is for this reason the subject of this summary. The discussion in this section is based
primarily on the Final Site Observational Work Plan for the UMTRA Project New Rifle Site,
Volumes I and 2 (DOE 1999 [154687]).
The New Rifle site processed uranium and vanadium ores from 1958 to 1984. The site is located
within the broad alluvial floodplain of the Colorado River (Figure 12-6). The New Rifle site
occupied much of the width of the Colorado River floodplain in a north-south direction
(approximately 3,000 ft) (500 m), with the iiver located on the southem portion of the floodplain.
The ore storage areas were located in the eastemmost (upgradient) portion of the site, whereas
the tailings pile was located in the westem portion of the site. The mill and other buildings were
located between the tailings pile and the ore storage areas. Approximately 3.5 million yd 3 (2.7
million m 3) of contaminated material were present on 238 acres (96 hectares) at the site. The
transfer of this contaminated material to a disposal cell was completed in 1996.
The climate in the Rifle region is semi-arid, with an average total annual precipitation of I I in.
(28 cm) of which approximately one third is contributed by snowfall (DOE 1999 [154687],
Section 3.2). The New Rifle site is underlain by 20-30 ft (6-9 m) of alluvium deposited by the
Colorado River (DOE 1999 [154687], Section 5.1.2.2). Unconfined groundwater is present at the
base of the alluvium at a depth of 5-10 ft (1.5-3 m) below the ground surface. In general,
groundwater flows west-southwest in the alluvium and in the underlying bedrock (DOE 1999
[154687], Section 5.2.2). The alluvial deposits north of the river pinch out approximately 4 mi
(6.4 km) to the southwest of the site (Figure 12-5). 

The alluvium is underlain by the Tertiary
Wasatch Fon-nation. The weathered upper few feet of the underlying Wasatch Formation also
contain unconfined groundwater. Semiconfined and confined groundwater occurs in interlayered
sandstone, siltstone, and claystone beds deeper in the Wasatch Formation. The hydraulic gradient
in the deeper Wasatch Formation is upward (DOE 1999 [154687], Section 5.2.3). The major ion
composition of waters in the unconfined aquifer is quite variable, largely because of seepage of
contaminants from site operations. The downgradient groundwaters in the alluvial aquifer are
primarily sodium-calcium sulfate waters. Upgradient (background) groundwaters tend to be of
the sodium-calcium bicarbonate-sulfate-chloride type, similar to river waters and of much lower
ionic strength than downgradient groundwaters (DOE 1999 [154687], Section 5.3.3).
Processing operations at various locations on the site have resulted in the seepage of
contaminants into the alluvial aquifer and the upper Wasatch Fonnation. The major sources of
contaminated seepage were the mill and other processing buildings and vats, vanadium and
gypsum ponds, evaporation ponds, and the tailings pile (Figure 12-6). The degree to which
contaminants have migrated from various source areas on the site has been investigated with an
extensive monitoring program that has been in place since 1985. Monitoling wells have been
used to obtain water levels and water samples from the alluvial aquifer and from the Wasatch
Fonnation. Monitoring wells that intersect the Wasatch Formation are located within -0.25 mi of
the operations area. The proximity of the uranium source term to the underlying bedrock aquifer
  12-7  1

 

Natural Analogue Synthesis Report
with the upward hydraulic gradient and the disturbed nature of the UMTRA sites are two
conditions that would not be analogous to transport at Yucca Mountain.
The locations of the monitoring wells are shown in Figure 12-7. The site-related inorganic
constituents most prevalent in the alluvial aquifer include ammonia, calcium, nitrate,
molybdenum, selenium, sulfate, and uranium. Of these constituents, the transport behavior of
uranium and selenium are of interest to the Yucca Mountain Project. Nitrate and sulfate are
potentially of interest as conservative constituents, to trace the maximum extent of movement of
contaminants from the site. However, the existence of reducing conditions in various wells
downgradient from the site calls into question the use of nitrate as a conservative constituent.
Organic constituents such as kerosene were also released to the alluvial aquifer, particularly in
and around the processing buildings and vats.
An estimate of the average extent of movement of contaminants from the site, without
accounting for dispersion, can be obtained by calculating the distance groundwater could have
traveled from the site since operations were initiated in 1958. 

The estimate is obtained using the
following equation for the average linear groundwater velocity, V, (Fetter 2001 [156668],
p. 125):
vx = - K/ne(dh/dl), (Eq. 12- 1)
where K is the hydraulic conductivity, ne iS the effective porosity, and dhldl is the head gradient.
The average hydraulic conductivity for the New Rifle site is reported as 114 ft/day (0.040 cm/s)
(DOE 1999 [154687], Section 5.2.2) was derived for the alluvial aquifer based on pump tests.
The effective porosity was specified as 0.27. Based on water-level measurements taken in 1998,
the average gradient was found to be 0.0030. Substituting these values into the equation yields
the following linear groundwater velocity:
vx = (-114 ft/day)/0.27(0.0030) = 1.27 ft/day
A linear groundwater velocity of 1.27 ft/day (0.4 m/day) over a period of 40 years (1958-1998)
leads to an estimated travel distance of 18,506 ft (5.64 km).
Because the site operations covered most of the alluvial terrace in a north-south direction and
because most of the contamination is in the alluvial aquifer, significant lateral dispersion of
contaminated groundwater is precluded by the decreasing width of the alluvial deposits in the
downgradient direction. However, the magnitude of the source term for different contaminants
may have varied over the site. For example, uranium processing facilities were located in the
northem portion of the site. Therefore, uranium concentrations might be expected to be highest
in groundwater beneath this portion of the site. In fact, well 655, located near the noilhem end of
the site fence shown in Figure 12-7, has the highest uranium concentrations in any of the wells
sampled in the 1998 and 1999 sampling rounds (DOE 1999 [154687], p. 5-56). The absence of
similarly high concentrations in downgradient wells suggests the operation of some dispersive
process. In addition to lateral dispersion, vertical advective dispersion of contaminants in the
alluvial aquifer may also occur. However, the saturated thickness of the alluvial deposits is only
10-20 ft (3-6 m) (DOE 1999 [154687], p. 5-19). Furthermore, the hydraulic gradient in the
underlying Wasatch Fonnation is upward. These observations suggest that vertical advective
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Natural Analogue Synthesis Report
dispersion of contaminants in the alluvial aquifer would be limited, but dilution may be an active
le process.
The use of sulfdric acid in processing ores at the site [inferred to be common practice (Merritt
1971 [156670], p. 29)] would have resulted in seepage to the vadose zone with high
concentrations of sulfate. The highest measured concentrations were observed in samples taken
in the first two years of the monitofing program.  The available data suggest that sulfate
concentrations in groundwater beneath and downgradient of the site have generally been
decreasing since approximately 1986, consistent with the fact that processing operations at the
site ended in 1984. Analyses of groundwater samples from (background) wells in the Wasatch
Formation located across the Colorado River and upgradient from the site indicate that these
waters have lower sulfate concentrations than waters from the alluvial aquifer but substantially
higher chloride concentrations. This suggests the S04 2-/Cl- ratio may be useful in identifying
groundwaters contaminated by site operations. 

Groundwaters from wells at background locations
(DOE 1999 [154687], Appendix C) show that S04 2-/Cl- ratios in the Wasatch Formation are less
than 2.0, with most less than 0.5. Water samples from the Colorado River have S04 2-/Cl- ratios in
the range of 0.75 to 0.85. As shown in Figure 12-8, most water samples from wells located on
the site have S04 2-/Cl- 2 ratios in the range of 10 to 20. This ratio decreases with distance
downgradient. The S04 -/Cl- ratio retums to near-background values at wells 220 and 172, the
wells farthest downgradient. Thus, the maximum distance contaminants appear to have traveled
from the site, based on the S04 2-/Cl - ratio of alluvial goundwater samples, is approximately
19,000 ft (5.8 km). This is similar to the maximum travel distance of 18,506 feet (5.64 km)
calculated for groundwater based on hydraulic parameters.
The observed decreases in the S04 2-/Cl - ratios (Figure 12-8) and S04 2- concentrations (6,000 to
2,000 mg/L) in alluvial groundwater with increasing distance downgradient suggests that these
waters are progressively diluted with waters that have low S04 2-/Cl- ratios and low S04 2-
concentrations. Because there is an upward hydraulic gradient in the Wasatch Forination (DOE
1999 [154687], p. 5-27) and because Wasatch Formation groundwaters from upgradient wells
have low S04 2-/Cl- ratios (< 0.5) and low sulfate concentrations (< 500 mg/L), the diluting waters
most likely come from the Wasatch Formation.
Measured uranium concentrations show a pattem similar to that observed in the S04 2-/Cl - ratio
data. Upgradient alluvial wells located on the eastem portion of the site have uranium
concentrations between zero and 0.05 mg/L (Figure 12-9). Wells located near the former
uranium processing buildings on site have the highest uranium concentrations of all water
samples (0.4-0.5 mg/Q. Note that waters with these uranium concentrations are undersaturated
with respect to solid uranyl phases, as calculated by Jove Colon et al. (2001 [157472], p. 13, 14),
for groundwater compositions typical of the New Rifle site. Uranium concentrations in alluvial
groundwaters decrease downgradient and reach the 0.05 mg/1L (background) level between
10,000 and 15,000 ft (3-4.6 km) downgradient (Figure 12-9). Thus, it appears uranium has not
traveled downgradient as far as sulfate, although the exact travel distance is difficult to quantify
because background values show such a large range (0-0.05 mg/L). The uranium "plume length"
based on the 1998 sampling data (3-4.6 km) is considerably greater than the I km length
proposed by Jove Colon et al. (2001 [157472], p. 24) as the "steady-state" length for uranium
plumes in groundwater systems (i.e., the length at which uranium concentration in monitoring
wells remains fairly constant). In fact, there is no evidence in the New Rifle data that the
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Natural Analogue Synthesis Report
uranium migration rate has decreased significantly with time, contrary to the conclusions reached
by Jove Colon et a]. (2001 [157472], p. 24). 

Taking the maximum distance traveled by uranium as 13,000 ft (Figure 12-9) and the maximum
distance traveled by sulfate as 18,000 ft (Figure 12-8), an estimated retardation factor (Rt) for
uranium of 1.38 (i.e., 18,000/13,000) is obtained. Using the retardation equation (Freeze and
Cherry 1979 [1011731, Equation 9.14)
R, = (1+ PbKd (Eq. 12-2)
0
where Pb is the dry bulk density in g/cm 3 and ~ is the porosity, we can solve for the sorption
coefficient (Kd),
Kd = (R, - 1)0 (Eq. 12-3)
Pb
Using values for the dry bulk density (Pb) and porosity given for the alluvial aquifer in DOE
(1999 [154687]), we obtain the following result for the uranium sorption coefficient (Kd):
Kd = (1.38 - 1)0.25/1.52 = 0.06 mUg.
Batch-sorption coefficient measurements for uranium using alluvial materials from the New
Rifle site and a synthetic groundwater show a range of coefficients from -0.3-1.4 mUg, with an
average value of 1.0 mLJg (DOE 1999 [154687], Table 4-6). The Kd calculated here falls within
that range, but is lower than the mean average value. This difference may be partly accounted for
by the fact that the calculated Rt is based on what may be closer to the maximum, rather than the
average, distance traveled by uranium; therefore, the calculation yields a lower Kd.
It is possible also that some uranium could have been transported downgradient as part of a
colloidal phase (including microbes). Such colloidal transport could carry the uranium at
essentially the velocity of groundwater. As part of the Nye County Early Waming Drilling
Program, several monitoring wells have been installed down gradient of the potential repository
at Yucca Mountain. Colloid transport is being studied through analyses of groundwater samples
collected from these wells (Kung et al. 2001 [157604]).
Selenium has been detected only in groundwaters from wells located within the boundaries of the
oiiginal New Rifle site. There is no evidence of significant downgradient transport. This is
probably a result of the combined effects of a smaller source tenn and higher sorption
coefficients measured for selenium in contact with sediments from the alluvial aquifer (DOE
1999 [154687], pp. 5-41, 5-42).
In summary, the data available on uranium transport at the New Rifle LTMTRA site suggest that
dilution in the alluvial aquifer is a significant process downgradient from the site and that the
sorption of uranium on alluvial sediments also occurs.
0 -
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Natural Analogue Synthesis Report
12.3.3.3 Summary and Conclusions of UMTRA Study
An evaluation of data available for 24 UMTRA sites determined that only a few of these sites are
potentially useful in the evaluation of transport of radionuclides in the alluvial portion of the
Yucca Mountain flow system. Most of the sites are of limited use either because they are situated
in a hydrogeologic setting different from Yucca Mountain or because there is insufficient
infon-nation available to perform an adequate evaluation of transport behavior. There are enough
data available for the Gunnison and New Rifle sites to perform a useful analysis. The
conclusions derived from an analysis of the Gunnison site are (1) that a fraction of the uranium
ofiginating at the site is transported in the alluvial aquifer at a rate similar to the rate at which a
conservative constituent is transported, and (2) there is little evidence for dispersion of
contaminants in the downgradient direction. For the New Rifle site, the main conclusions are (1)
that dilution is a significant process in the downgradient direction and (2) that uranium is
transported at a slower rate then conservative constituents, although a fraction of the uranium
traveled almost as far. The conclusions regarding uranium transport distances relative to
conservative constituents must be tempered somewhat by uncertainties regarding the potential
presence of unidentified complexing agents, such as organic matefials, that could fon-n colloids
and enhance uranium transport. An additional note of caution attaches to the use of laboratory
batch-defived Kd values for the prediction of large-scale field transport, because the two
parameters are conceptually and numefically different.
12.4 OTHER SATURATED ZONE ANALOGUES
12.4.1 Uranium Retardation under Oxidizing Conditions
Studies of the weathered zone overlying the Coles thll, Virginia, uranium deposit indicate that
the natural attenuation of uranium in oxidizing environments may occur in groundwaters with
low dissolved carbonate/phosphate ratios (Jerden and Sinha 2001 [157474]). At the Coles Hill
site, uranium concentrations are buffered to values <20 ppb due to the precipitation of low-
solubility U(Vl) phases. 

The attenuation mechanism involves the transfonnation of U(IV)
coffinite, the primary ore, to U(VI) phosphate minerals. Above the water table in the soil zone,
where phosphate minerals are rare, uranium is primarily associated with an aluminum phosphate
of the crandallite mineral group and with phosphorous sorbed to ferric hydroxide mineral
coatings. Expeiiments demonstrated that the transformation of U(IV) to U(VI) assemblages
could occur in less than two months, given high enough phosphate levels. Model predictions
agreed with the field observations: for oxidizing systems with relatively low dissolved
carbonate/phosphate ratios, uranium may be immobilized by secondary uranium phosphate
precipitation and sorption processes. It is unlikely that low dissolved carbonate/phosphate ratios
would occur in bedrock aquifers at Yucca Mountain, but if use of phosphate-containing fertilizer
contaminates the alluvial aquifer in Amargosa Valley, the carbonate/phosphate ratio could be
lowered, making this a more analogous situation for Yucca Mountain.
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Natural Analogue Synthesis Report
12.4.2 Matrix Diffusion
0 12.4.2.1 El Berrocal
El Beffocal is an area approximately 100 km southwest of Madrid, Spain. The El Berrocal
granite fonns a large hill and contains a number of small, vein-hosted uranium ore bodies, one of
which was the focus of analogue investigations (Figure 12-10). The El Berrocal granite has a
uranium content that averages 16 mg/kg, with primary uranium occurring as accessory uraninite
dispersed in the granite matrix (De ]a Cruz et al. 1997 [157473], pp. 82-83). Post-emplacement
hydrothennal alteration mobilized some of the uranium, thorium, and rare-earth elements from
the granite and redeposited them in a 2-m-wide, steeply dipping quartz vein more than I Ma
(Rivas et al. 1998 [126287], pp. 15-16). Erosion and weathering exposed the vein-hosted
mineralization, causing further elemental mobilization and transport. The groundwaters contain
moderate to low concentrations of uranium (4 x 10-9 to 8 x 10-6 M) (De ]a Cruz et al. 1997
[ 157473], p. 8 1; this converts to 9.52 x 10-4 to 1.9 rng/L). Carbonate complexes are the dominant
species in oxidized zones and U(IV) hydroxides in reduced zones. The general behavior of
uranium can be accounted for by the kinetic control of the dissolution of the source tenn and
solubility controlled by coprecipitation processes.
The multinational El Berrocal project had the objective of investigating these present-day, low-
temperature processes, as well as the processes responsible for elemental retardation in the
granite. In particular, the study investigated uranium mineral stability, degradation, and
dissolution; uranium solubility and speciation; matrix diffusion in the rock adjacent to fractures,
and colloidal transport of radionuclides. Study activities included blind predictive testing of
geochemical codes and databases. The results of the project indicated that mobilized uranium
and thoiium tended to be associated by sorption and coprecipitation with certain fracture-coating
minerals, notably iron oxyhydroxides and calcite. Enrichment of uranium by a factor of up to 6
was observed, and up to 3 for thorium, relative to the unaltered granite (Miller et al. 2000
[156684), p. 201). Considerable effort was made to understand these coprecipitation processes in
order to improve then-nodynamic models and databases for perfon-nance assessment (Section 15).
12.4.2.2 Matrix Diffusion Comparison Studies
The Palmottu, Finland, site in saturated, fractured gneisses and migmatites was the location of a
matrix diffusion study. Radionuclide concentration profiles from a fracture in the rock matrix
were examined in several different drillcores (Blomqvuist et al. 1995 [124640]). Alpha-
autoradiography showed the distribution of radionuclides decreasing from the fracture surface
into the rock matrix. 

Based on the findings of three drillcore samples, the profile of decreasing
radioactive content could be traced >100 mm into the rock (Blomqvist et al. 1995 [124640],
pp. 64-65). The radionucides were associated with clay particles and iron oxyhydroxides that
had formed from alteration of feldspar and biotite grains. Selective leaching experiments showed
that most of the radionuclides that had diffused into the rock matrix were only loosely bound to
the iron-rich phases. In some samples, activity correlated to microfractures indicated that fluid
flow was channelled even at the microscopic level, whereas in another sample diffusion was
predominantly along grain boundaries. This supports the hypothesis that physical disruption
around a fracture may enhance transport into the rock matrix (Blomqvist et al. 1995 [124640],
pp. 27, 60, 63, 64).
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Natural Analogue Synthesis Report
A comprehensive investigation of matrix diffusion processes compared granite samples from a
number of locations: the El Berrocal natural analogue site, Spain; the Stripa test mine, Sweden;
40 the Whiteshell Underground Research Laboratory (LJRL), Canada; and the Grimsel Test Site,
Switzerland (Heath 1995 [157478]). Each sample was taken from close to a hydraulically active
fracture, cut to provide a series of slices parallel to the fracture, and charactefized in detail. For
all samples, the region of enhanced uranium mobility correlated with the zone of microstructural
alteration in the rock adjacent to the fractures. The actual depth of enhanced uranium mobility
varied from site to site; for instance, enhanced uranium mobility extended 35 mm in the shallow
El Berrocal granite, but 50 mm in both the altered and unaltered URL granite. 
Interpretation of the El Berrocal core sample data indicated the following: not only was matrix
diffusion limited to the first few tens of millimeters of rock adjacent to the fracture surface, but
also within the rock matrix the mobilized uranium was associated with secondary phases and
located in microfissures along grain boundaries (Heath 1995 [157478], p. 51). There was a very
good correlation between the distlibution of the mobilized uranium, the redox conditions, and the
isotopic disequilibrium. Heath (1995 [157478], p. 51) concluded from a combination of all of the
data that a complex combination of matrix diffusion and chemical interaction had occuffed
between the rock and the mobile phases, rather than matrix diffusion alone. From this
conclusion, Heath suggested the possibility that retardation processes that rely on matrix
diffusion mechanisms may make little overall contribution to performance in a crystalline rock
mass. However, the data from El Berrocal provide good evidence that, once radionouclides
migrate into the rock matrix from the flowing fracture, they are effectively immobilized
irrespective of the process involved.
12.4.3 Colloidal Transport in the SZ
Colloids are ubiquitous in all groundwaters (McCarthy 1996 [157479], p. 197). However, in
deep crystalline rocks with a stable geochemical system, the colloid populations are low, -25
pg/L. In contra'st, shallow aquifer systems generally appear to have the largest colloid
populations, even in the absence of geochemical stability. Enhanced colloidal populations occur
in all rock types where there is some hydrogeochemical perturbation to the system. For example,
in fractured granitic systems, colloid populations are 20 to 1,000 times higher in groundwaters
affected by inputs of surface water or in hydrothermal zones with large temperature and pressure
gradients, compared to stable hydrogeochemical systems (Degueldre 1994 [101128]).
The uptake and transport of radionuclides by colloids has been investigated in several analogue
studies of natural systems with enhanced radionuclide content: Cigar Lake, Canada (Vilks et a].
1993 [108261]); Alligator Rivers, Australia (Seo et al. 1994 [157480], p. 75); El Berrocal, Spain
(Rivas et al. 1998 [126287]); and Pogos de Caldas, Brazil (Miekeley et al. 1992 [106762]). In
most of these studies, it was found that some proportion of the total uranium, thoiium, and rare-
earth elements in the groundwater was associated with the colloids. 

This proportion was higher
for thoiium than for uranium because of thorium's lower solubility in most groundwaters. The
rare earths generally show an affinity for colloids interrnediate between uranium and thorium
(Miekeley et al. 1992 [106762], pp. 429, 434).
Unambiguous evidence from natural systems indicating colloidal transport over long distances is
rare. The only known example suggesting transport on the kilometer scale is at Menzenschwand,
  12-13 

 

Natural Analogue Synthesis
Germany, where the Ti:Mg ratio and rare-earth-element composition of the natural colloids
differed from that of the host granite but were similar to that of a neighboring gneiss several
kilometers away and upgradient (Hofmann 1989 [125081], pp. 925-926). However, the flow
system at Menzenschwand is not representative of a natural system, because it is perturbed by
the presence of a uranium mine with associated fast flow.
Many analogue studies suggest that colloid transport in natural systems is significantly restiicted.
For instance, at Cigar Lake, the uranium and radium contents of colloids in the ore and the
surrounding clay zones are significantly higher than in colloids from the sandstone host rock,
indicating that the clay is an effective barrier to colloid migration (Vilks et al. 1993 [108261]).
Similar results at Alligator Rivers and Morro de Ferro also suggest that colloids have a limited
capacity for migration, because the concentrations of colloid-bound radionuclides outside the
orebodies are relatively low (Miekeley et al. 1992 [106762], pp. 420, 432-433).
Colloid concentrations of 0.8-6.9 mg/L for particles greater than 30 nm were observed in two
wells on Pahute Mesa at the Nevada Test Site (NTS) (Buddemeier and Hunt 1988 [100712], p.
537). One well was inside the Cheshire experimental site, and the second, a water well, was 300
m away. Tritium, krypton, strontium, cesium, antimony, cobalt, cerium, and europium were
detected in pumped water from the water well. All of the cobalt, cesium, and europium were
associated with colloids in samples from both locations. Buddemeier and Hunt (1988 [100712],
p. 537) maintained that the presence of colloidal radionuclides outside the cavity indicates
radionuclide transport as colloids.
In another study at the NTS (Kersting et al. 1999 [103282], p. 56), isotopic ratios of plutonium
were used to fingerprint the source of plutonium detected in monitoring wells with a specific
underground nuclear test, suggesting that the plutonium migrated a distance of 1.3 km.
Plutonium has a tendency to strongly sorb to tuff minerals, which would retard its transport.
Thus the observed presence of colloids in waters at the NTS and the observed association of
plutonium with colloids were interpreted to indicate that radionuclide transport was expedited by
colloids.
A similar conclusion was reported by Tiiay et al. (1997 [100422], p. 172) to explain the transport
of plutonium and americium away from a low-level waste site in alluvial sediments at Mortandad
Canyon at Los Alamos, New Mexico. These radionuclides were detected at depths of 30 m in
monitofing wells in unsaturated tuff up to 3.4 km downgradient from the waste disposal site
(Buddemeier and Hunt 1988 [100712], p. 536). The migration reportedly took place over a
peliod of 30 years (Buddemeier and Hunt 1988 [100712], p. 536). 

Because sorption studies
involving the alluvial sediments suggested that plutonium and americium should be relatively
immobile, the observed movement of radionuclides was reported by Triay et al. (1997 [100422],
p. 172) to suggest that the transport of plutonium and americium through alluvium resulted from
association with highly mobile colloids.
These observations lend support to the concept that radionuclide transport in the far field can be
facilitated by colloids, but so far no natural analogue studies have been able to quantify the
importance of this process.
0
  12-14 

 

Natural Analogue Synthesis
12.5 CONCLUSIONS
UMTRA StLdy: Only a few of the UMTRA sites are potentially useftil in the evaluation of
radionuclide transport in the alluvial portion of the Yucca Mountain flow system. Most of the
sites are of limited use either because they are situated in a hydrogeologic setting different from
Yucca Mountain or because there is insufficient infonnation available to perform an adequate
evaluation of transport behavior. Enough data were available for the Gunnison and New Rifle
sites to perform a useftil analysis. The conclusions derived from an analysis of the Gunnison site
are: (1) a fraction of the uranium originating at the site is transported in the alluvial aquifer at a
rate similar to the rate at which a conservative constituent is transported, and (2) there is little
evidence for lateral dispersion of contaminants in the downgradient direction. For the New Rifle
site, the main conclusions are: (1) dilution is a significant process in the downgradient direction,
and (2) uranium is transported more slowly than conservative constituents. The conclusions
regarding uranium transport rates relative to conservative constituents must be tempered by
uncertainties regarding the potential presence of unidentified complexing agents.
Difftision: Matrix difftision in crystalline rock is generally limited to only a small volume of rock
close to fractures, but even a small volume can make a significant difference in radionuclide
retardation.
SoMtion onto fractures: Comparison of the results from a number of analogue study sites shows
that similar sorption behavior is seen at many locations in crystalline rocks. For example,
uranium and rare earth elements are frequently associated with calcite and iron oxyhydroxides.
However, because it is often impossible to define in detail the paleohydrological history of a site,
it is difficult to identify the unique effects of recent low-temperature retardation events. This is
possibly the reason for the anomalous observations at El Berrocal related to limited observed
uranium sorption on iron oxyhydroxides.
Although several natural analogue studies have demonstrated the effect of sorption and
precipitation processes on fracture surfaces, none has been able to distinguish clearly between
these processes or to provide quantitative data on retardation with respect to transport of trace
elements in natural waters. However, these studies do highlight which phases are most active,
and they provide useftil information on the effect of interaction between solutes and the rock
surface.
Colloid transport: In most studies of natural systems, it was found that some portion of the total
uranium, thorium, and rare-earth elements in the groundwater was associated with colloids.
Unambiguous evidence from natural systems indicating colloidal transport over kilometer-scale
distances is limited to a few reports. Observations from such places as Los Alamos and the NTS
lend support to the concept that radionuclide transport in the SZ can be facilitated by colloids,
but so far no natural analogue studies have been able to quantify the importance of this process.
0
TDR-NBS-GS-000027 REV 00 ICN 02 12-15 May 2002 1

 

Natural Analogue Synthesis Report
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0 10 20
MILES
Source: DOE 2001 [156666], Figure 1 -1.
Figure 12-2. 

 For the groundwater-contamination scenario, annual doses are
estimated by multiplying radionuclide concentrations in groundwater by the corresponding
BDCFs. For the disruptive event scenario that results in a surface-contaminated source term, the
doses are obtained by multiplying surface-activity concentration of a radionuclide by the
corresponding BDCF (CRWMS 2000 [151615], Section 3.1.4).
13.3 USING CHERNOBYL DATA FOR EVALUATING BIOSPHERE PATHWAYS OF
RADIONUCLIDES
13.3.1 Relevance of Chernobyl Information
Information about the distifibution of radionuclides in the biosphere following the Chemobyl
Nuclear Power Plant (ChNPP) reactor explosion in April 1986 is a valuable source of data for
testing environmental transport models (Hoffman et al. 1996 [156616]; Konoplev et al. 1999
[156624]). The 1986 Chemobyl accident resulted from an explosion of the Fourth Reactor Unit
of the ChNPP. Figure 13.3-1 shows the location of the ChNPP in the territory of Ukraine. The
ChNPP accident resulted in contamination by a variety of radionuclides (89 Sr, 'OSr, "Zr, 9'Mo,
103 Ru, 106 Ru, 134CS, 137CS, 141 Ce, 144 Ce, 154EU, 155 Eu , 238PU, 239 pU, 210pU, 241 Pu, etc.) of large areas
of the fonner USSR and the globe (Baryakhtar 1997 [156953], p. 35; Kashparov 2001 [156819],
p. 11). Research into many environmental and health effects of the Chemobyl accident has
become a major intemational enterprise aimed at understanding long-tenn transport processes
and effects of exposure to radioactivity. A significant amount of data has been collected for the
past 16 years about the distribution and accumulation of radioactive materials in different parts
of the biosphere after the Chemobyl accident, including the main exposure pathways and
mechanisms of radioactive contamination of the environment and the population. These data
represent a valuable source of infon-nation to improve confidence in conceptual models of
exposure pathways and processes.
13.3.2 Objective and Approach
Because direct observation of the actual outcome of the Biosphere Process Model scenalios will
not be possible for many years, if ever (CRWMS M&O 2000 [151615], Section 3.2.3), one of
the approaches to building confidence in biosphere models is to use inforination obtained from
natural and anthropogenic analogue sites. As part of the model validation activities to improve
biosphere models for both the groundwater-release and the volcanic-release scenarios, the Yucca
Mountain Project is interested in measurements at specific locations to aid in selection of input
data for models of specific environmental processes.
The objective of Section 13.3 is to review infonnation from the Chemobyl accident regarding the
exposure pathways, inputs to risk assessment, and distribution * of radioactive contaminants in the
biosphere, to determine its potential relevance for the Yucca Mountain Biosphere Process Model.
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Natural Analogue Synthesis
In particular, information was collected on the specific environmental processes of radionuclide
transfer and resuspension, which could be used to improve confidence in the modeling of Yucca
Mountain environmental processes. Major monographs and numerous articles were reviewed in
English, Russian, and Ukrainian scientific and professional joumals, magazines, and proceedings
of intemational conferences and symposia.
Taking into account the difference in climatologic and environmental conditions of Chemobyl
and Yucca Mountain, this survey presents a broad picture of the environmental pathways of
radionuclides in the biosphere. Radiation doses resulting from Chemobyl are presented as a
means of illustrating the types of data available related to stated needs of the Yucca Mountain
Biosphere Department, including the following:
 Radionuclide transfer from soil to plants via root uptake, soil to plants via atmospheric
resuspension, and animal fodder to animal food products
 Removal of contaminants via erosion and leaching
 Inhalation of resuspended contaminants deposited on the ground
 Radionuclide accumulation in soils and plants under irrigation using contaminated water
 The ecological half-life of radionuclides in soils and plants.
13.3.3 Chernobyl Accident and Main Exposure Pathways
This section provides background for later discussion by describing the Chemobyl location,
climate, and soil conditions; and the accident in terins of its explosion characteiistics, radiation
release, principal pathways, and types of particles released.
13.3.3.1 Location, Climate, and Soil Conditions
The ChNPP exclusion zone is located in the central part of the Ukrainian Polessye physiographic
province. The term "exclusion zone" refers to an area surrounding the site that was sealed off as
an institutional control to prevent further access after the accident. Immediately after the
accident, the exclusion zone was established within the radius of 30 km from the ChNNT.
However, as more measurements of the level of contamination over a larger territory were made,
the boundary of the exclusion zone was adjusted to prevent access to highly contaminated areas.
Its total area within the Ukrainian borders, except for part of the Kiev reservoir, is 2,044 km 2
(Shestopalov 1996 [107844], p. 3).
The Chemobyl region has a humid climate, with mild, short winters and a warm summer.
Average annual precipitation ranges from 550 to 750 mm/yr. 

The relief consists of slightly
undulating plains and ridges, and irregularly located bogs. The relatively dense network of
Pripyat and Dnieper River tributaries forins boggy valleys of moderate relief. Approximately
50% of the land in the exclusion zone is covered by forest, 30% by arable farm land, and the
remaining 20% by urban areas, marshlands, and water bodies (Shestopalov 1996 [107844], p.
22). The soils are relatively homogeneous, with mostly podsols and peaty podsols (soils of
forested, temperate climates) as the topsoil layer in the exclusion zone.
9
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13.3.3.2 Type of Explosion and Amount of the Radionuclide Release
The initial explosion at Chemobyl was a steam explosion (Baryakhtar et al. 2000 [157504],
pp. 12-13; Tarapon 2001 [156920], p. 95). The total amount of radionuclides released by the
accident into the environment expressed in becquerels (Bq) was approximately I I X 1018 Bq
(expressed in curies [Cil this would equal 3 x 108 Ci), while approximately 6 x 10, 7 Bq (1.6 x
1W CO of long-lived radionuclides remained in the destroyed reactor. (Note that I Ci = 3.7 x
1010 Bq). The kinetic energy released from the accident has been estimated to be equivalent to
30-40 tons of trinitrotoluene (TNT) (Bar'yakhtar et al. 2000 [157504], p. 13). This was the
highest single release of radionuclides into the global environment, with contamination
calculated to be equivalent to that of a 12 Mt (megaton) nuclear explosion (Bar'yakhtar et al.
1997 [156953], p. 224).  No other nuclear accident approaches the dimensions of the Chemobyl
disaster in ten-ns of radiological release, acute radiation health effects, and socioeconomic and
psychological impact (Baryakhtar et al. 2000 [157504], p. 9).
The Chemobyl accident released approximately 2,000 Ci of isotopes of 239, 240pU into the
atmosphere (Bar'yakhtar et al. 2000 [157504], Table 2.5.1; Bondarenko 1998 [156952], p. 13,
15). This amount of radiation is comparable to about 0.5% of the total global fallout of these
isotopes from nuclear weapons testing from 1945 to 1963 (Bondarenko 1998 [1569521, p. 13;
Bondarenko et al. 2000 [156593], p. 473). The activity of plutonium isotopes, distributed outside
the 30 km exclusion zone, was 1,344 Ci, or 5 x 1013 Bq. The specific activity of a-emitting
isotopes of plutonium was calculated to be 1.5 x 1013 Bq/t (Bondarenko 1998 [156952], p. 23).
13.3.3.3 Principal Pathways
The initial explosion and heat plume at Chemobyl cartied volatile radioactive materials up to 1.5
km (0.93 miles) in height, from where these materials were transported over large distances by
prevailing winds (Figure 13.3-2). About a quarter of the total released radioactivity entered the
atmosphere during the first day after the accident. By the fifth day, the release had decreased
approximately sixfold, because of mitigation effoils at the ChNPP. The radionuclides that
escaped into the atmosphere then migrated and settled in different areas, causing radioactive
contamination of living things. Crops, vegetables, grasses, fruits, milk, dairy products, meat, and
eggs were contaminated with radionuclides. The most severe radioactive contamination of fields,
rivers, tributaiies, canals, drainage ditches, and agricultural lands occurred in the Pripyat and
Dnieper iiver basins that surround the ChNNP.
As part of the cleanup effort after the Chemobyl accident, approximately 8 x 1015 Bq of high-,
medium-, and low-level radioactive waste (in mostly solid fonn, such as construction parts,
concrete, and soils) were accumulated and stored at more than 800 intelim storage and disposal
places in the region (Poyarkov 2000 [157503], pp. 1-2; Kukhar' et al. 2000 [157506]).
Infiltration through unlined waste storage and disposal sites has caused leaching of contaminants,
so these sites provide the current localized source term for soil and groundwater contamination
(Shestopalov and Poyarkov 2000 [157507], pp. 146-147). 

Figure 13.3-3 illustrates the principal pathways for radionuclides enteiing the biosphere through
terrestrial and aquatic ecosystems after the Chemobyl accident.
0
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Natural Analogue Synthesis Report
13.3.3.4 Types of Particles Released
Two main types of radioactive particles were released from the damaged reactor: (1) a fuel
component of finely dispersed fuel particles, containing elements of low volatility, such as
cenum, zirconium, barium, lanthanum, strontium, and the actinides; and (2) a condensed
component that formed when gases of nuclides (such as iodine, tellulium, cesium, and a lesser
amount of strontium and ruthenium) that were ejected during the nuclear fuel fire, condensed on
different surfaces (e.g., ground, buildings, and trees-Kashparov 2001 [156819], pp. 11-12). Fuel
particles settled primarily on the land surface near the ChNNP zone (Kashparov 2001 [156819],
pp. 24, 26).
Hot particles formed from both fuel and condensed components, including particles of uranium
dioxide (a few tens of Am in diameter or smaller) made of fuel fused with the metal cladding of
the fuel rods and fuel mixed with sand or concrete (Loshchilov et al. 1991 [125894]; NEA 1995
[1566321, p. 53). Hot particles have an activity concentration exceeding 105 Bq/g (Bar'yakhtar
1997 [156953], p. 235). Chemobyl hot particles behaved differently from nuclear bomb particles
and Chemobyl gaseous and aerosol forms (Zheltonozhsky et al. 2001 [156630], p. 151). For
example, Chemobyl hot particles (1) did not contain activation products such as 60CO; (2)
contained 125 Sb and 144Ce, which are absent in atomic bomb hot particles; (3) contained a larger
fraction Of 137CS than that in nuclear bombs; (4) had a ratio of 154 Eu/ 155 Eu about 10 times greater
than that in atomic bomb particles and about 200 times than that in fusion bomb particles; (5)
have a lower radiation of uranium and neptinium than that from fusion bombs; and (6) had a
lower plutonium content than that in the fusion bombs (Zheltonozhsky et al. 2001 [156630], pp.
156-159). After nuclear weapons testing, over 90% of the activity of 90Sr and 137CS was present
in water-soluble and exchangeable forms in global fallout, but after the Chemobyl accident, the
fraction of exchangeable forms of 90Sr and 137Cs in the near-ChNNP zone in 1986 was less than
25% of their activity in a fallout, and the remaining activity was caused by nonexchangeable
fonns of these radionuclides associated with fuel particles (Kashparov 2001 [156819], p. 27).
90Sr, 106 Ru, 134CS, 137CS, '44Ce, and 147Pm contiibuted to the total P-activity of hot particles (Papp
et al. 1997 [124806], p. 951). Isotopes of actinide elementS 238pU, 239PU, 24OpU, and 242CM
contributed mostly to the total (x-activity of hot particles. The surface density of hot particles was
about 1,600 per M2 in downtown Kiev (Papp et al. 1997 [124806], p. 951). Hot particles were
detected not only on the surface, but they also migrated in soils to depths of about 0.5 m
(Gudzenko 1992 [107835], p. 2), as detected in the fall of 1987 (Gudzenko et al. 1990 [125020],
p. 122).
The released fuel particles that entered the atmosphere are categorized by relative size into large
(tens to several hundred Arn) and small particles (median radius of 1.5-3.5 gm). The large fuel
particles were formed from the fragmentation of the fuel at high temperatures during the initial
phase of the accident. The large particles were primarily deposited within a 5 km zone around
the damaged reactor. Small fuel particles consisted of unoxidized uranium dioxide (Bar'yakhtar
et al. 2000 [157504], pp. 21-22). Note that hot particles <10 gm in size can be inhaled into the
lungs (Loshchilov et al. 1991 [125894], p. 47).
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Natural Analogue Synthesis
13.3.4 Soil Contamination
This section provides an overview of the distribution of soil contamination resulting from the
Chemobyl accident and characteristics of actinide element migration in soils.
13.3.4.1 Lateral Distribution of Soil Contamination
The prevailing wind directions and velocities that occurred immediately after the Chemobyl
accident established the contaminant fallout trajectories (see Figure 13.3-2). The surface
deposition of contaminants is affected mainly by local wind pattems and rain conditions existing
at the time of the accident. Therefore, the surface contamination resulting from the Chemobyl
accident is extremely irregular over very large areas. The contaminated spots range in size from a
few square meters to more than a thousand square kilometers (Shestopalov 1996 [1078441, p.
14). The data on air transport of contaminants demonstrate the important role of the local spatial
and temporal pattems in the wind direction and the need for estimating both the source strength
and the lateral distribution of contaminants in numerical models (Goldman et al. 1987 [156820]). 

The area of highest concentration Of 137CS is the "Westem finger," which extends almost in a
straight line westward from the ChNPP. The plume is 1.5 to 5 km wide; for a distance of <70 km
the concentration of 137Cs along its axis decreases from >10,000 Ci/km 2 (3.7 x 105 kBq /M2) to 10
Ci/kM2 (3.7 x 102 kBq /M2) . Because of the local wind pattem, the "Southem finger" splits into
five separate tracks and has the highest concentrations of 90Sr and actinides. The pattem of the
widespread "Northem finger" was likely fonned by deposition with rain. The "South-West
fingei" has the most complex, vortex-like shape (Shestopalov 1996 [107844], pp. 13-14).
The results of large-scale soil sampling on a regular giid of about I km (radius of 36 km) are
shown on two maps of 90Sr and 137CS contamination in Figure 13.3-4. The difference in
distribution pattems for 90Sr and 137CS is caused by different processes of precipitation for these
radionuclides: 90Sr was ejected with fuel particles and precipitated mainly in the near ChNNP
zone, while 137CS was contained in the condensed component, which moved and precipitated
further away from the ChNPP (Kashparov 2001 [156819], pp. 24-26). These maps were used to
estimate the total contents of radionuclides on the ground surface of the 30 km exclusion zone
(without the reactor site and the radioactive waste disposal sites), which showed that initial
estimates of the contamination were overestimated. For example, the content of 90Sr is estimated
to be approximately 810 TBq (8.1 X 1014 Bq) for the Ukrainian territory, which is 3 to 4 times
lower than previous estimates (Kashparov et al. 2001 [157400], p. 295).
13.3.4.2 Vertical Distribution of Radionuclides in Soils
Silant'ev et al. (1989 [126508], p. 224), Isaksson and Erlandsson (1998 [156617], p. 150), and
Likar et al. (2001 [156627], Figure 2) detennined that, overall, the concentration of radionuclides
in the soil profile decreases exponentially with depth to a depth of approximately 3 cm. In the
exclusion zone, the downward velocity of migration of 137 Cs ranged from 0.4 to 0.7 cm/yr in the
first years after the accident, and then dropped to 0.2 cm/yr (Bar'yakhtar 1997 [156953], p. 247).
Vertical migration of uranium and plutonium in soils is limited to the topsoil layer, because these
radionuclides were released as hot particles that are more or less stable in the near-surface
weathered zone. Table 13.3-1 shows that about 99% of plutonium accumulated within the top 2
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Natural Analogue Synthesis Report
cm soil layer. This table also shows that the ... U/ ... U ratio remained unchanged below a depth
of 3 cm. Figure 13.3-5 shows measurable quantities of actinides (plutonium, americium and
40 curium) in soil to a depth of 4.5 cm, in spring 1994, in the Kopachi village, located a few
kilometers from the ChNNP (Mboulou et al. 1998 [156628]). Figure 13.3-6 shows the actual and
predicted distribution of activities with depth for 90Sr, 131CS, and 239pU. The total activity of all
these radionuclides is mostly in the upper 3 cm layer. 

Radionuclide releases from hot particles present an additional source of soil contamination,
causing the concentration of mobile 137CS in soils to reach a maximum 1.5 to 2.5 years after the
accident and concentration of 90Sr to reach a maximum 6 to 15 years after the accident
(Bar'yakhtar 1997 [156953], p. 243). The decrease in 137CS concentration in soils in the exclusion
zone by about 25%-50%, as observed 10 years after the accident, was caused by several factors
(Shestopalov 1996 [107844], p. 14): (1) natural radioactive decay of I 37CS (about 20%); (2)
partial washout of the soil surface layer from elevated areas and slopes; (3) soil decontamination;
and (4) migration deeper than 20 cm from the soil surface along the zones of preferential flow. A
secondary contamination by 137Cs affected many areas, such as local soil depressions, edges of
marshes, and reservoir banks, where 1 37CS concentration increased by a factor of 2 to 10, and
locally up to 50 to 250 times. Concentration Of 137CS in the exclusion zone reached 50,000 to
150,000 CAM2, which is 5 to 15 times greater than that in soils in the so-called "Red Forest"
around the ChNPP, where intense radioactivity caused leaves to lose chlorophyll and tum red.
13.3.4.3 Characteristics of Migration of Actinides in Soils
Within the European part of the forrner Soviet Union, the plutonium content in soils after the
Chemobyl accident varies from 10 to 3,700 Bq/m 2 (Lebedev et al. 1992 [125854), p. 516). The
typical content of 219, 24OpU in Ukraine soils is 70 Bq /M2 (Bondarenko et al. 2000 [156593], p.
473). The determination of the isotopic composition of plutonium, and especially the ratio 238PU/
239,21lpU, is important to assess the source of soil contamination. For example, for the global
fallout, this ratio is typically from 0.03 to 0.05. However, in Chemobyl soil samples, this ratio
varied from 0.25 to 0.35, which corresponds to the ratio of about 0.3 in spent fuel (Lebedev et al.
1992 [1258541, p. 517). In contrast to the radioactive gases and relatively mobile radionuclides
such as iodine and cesium, isotopes of plutonium, ameficium, and other actinides are associated
with fuel particles.
Bondarenko (1998 [156952]) and Bondarenko et al. (2000 [156593]) presented the results of an
I 1-year investigation (1986-98) of the migration of long-lived (x-emitting transuranic (TRU)
elements in ecologic chains and the human body. The accumulation of TRU elements in plants
showed significant variability, depending on the type of soil, vegetation, and presence of
microbial activity. The ratio of concentrations of TRU elements in plants valies within several
orders of magnitude among the isotopes of each element. The main pathways for the entrance of
TRU elements in the human body are ingestion of food and water, and inhalation (Bondarenko
1998 [156952], Section 5; Bondarenko et al. 2000 [156593], pp. 473-474). Migration of TRU
elements that accumulated in hot particles begins as hot particles are broken down.
Thus, near-surface soil contamination by 90Sr, "'C, and TRU elements is widespread within a
large area around Chemobyl, but vertical distribution of contaminants is mostly limited to depths
of several centimeters. This creates favorable conditions for the atmospheric resuspension and
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Natural Analogue Synthesis Report
secondary deposition, as described in Section 13.3.5, of hot particles and radionuclides attached
to soil particles as a result of wind erosion.
13.3.4.4 . Technetium in Soils
At present, there are only limited dat'a on concentration of 99Tc in the environment caused by the
ChNPP accident. Uchida et al. (1999 [156945]; 1999 [156925]) presented results of 99Tc
measurements in soil samples collected within three forest sites around Chemobyl in 1994 and
1995. 

Two sites were located 28.5 km and 26 km to the south, and one site is 6 km to the
southeast of the ChNPP.  The 99Tc concentration was determined by inductively coupled plasma
mass spectrometry after its chemical separation from the soil sample. Concentrations of 99Tc in
these soil samples ranged from 1.1 to 14.1 Bq/kg at a depth of 6-9 cm, which is one to two
orders of magnitude higher than those under background conditions. The regression function
describin the change of the 99Tc concentration with distance is 99Tc concentration =
4.88 x R- P77 1, where "Tc concentration on the ground is in GBq/km 2 (Note: I GBq = 109 Bq)
and the distance R is in kilometers from the ChNPP (Uchida et al. 1999 [156925], p. 2,764).
The most stable fonn of technetium under aerobic conditions is Tc(VII), Tc04-, which is
characterized by high mobility in soils and availability to plants. Under anaerobic conditions and
increased soil-water saturation (for example, under inigation), Tc04 could be transformed to a
lower oxidation state of Tc(IV), to Tc sulfide forms, or to organic bound forms, which are
insoluble and will adsorb and accumulate in soilg with time (Tagami and Uchida 1999 [156923],
pp. 963-964).
0 13.3.5 Erosion and Atmospheric Resuspension of Radionuclides
After the Chemobyl release ended, atmospheric resuspension of radionuclides became a
secondary source of contamination, which affected people in areas that were not exposed to the
original release (Garger et al. 1996 [156602], p. 18). The main cause for the resuspension of
radionuclides is wind erosion of soil. The average annual soil erosion in Ukraine from 1987 to
1990 due to spring winds was I t/ha (tons/hectare) (Prister et al. 1991 [156824], p. 74), which,
for topsoil with a density of 1.3 g/cm 3, corresponds to soil loss of 8 x 10-3 cm/year. Erosion led to
the total (spring and fall) annual removal of 0.7 x 105 Bq/ha of 137CS from soils, with a
concentration activity of I X 103 Bq/kg (Prister et al. 1991 [156824], Table 7).
Resuspension of radionuclides with dust driven by wind is especially hazardous in agricultural
areas. The resuspension of particles with 137Cs increases after the tillage of agricultural lands
from background conditions of 0.7 Bq (m 2 /day) to 10 Bq (M2 /day) (Loshchilov et al. 1991
[156828], p. 64). For rural areas in Ukraine with 3 different agricultural activities, the
concentration of dust in air ranged from 0.3-203 mg/m for a soil moisture content of 3-20%
(Loshchilov et al. 1991 [156823], p. 199, Table 1). The maximum concentration of dust in
samples collected from air stirred up by agricultural machinery in the Ukraine was 4,000 mg/m 3
during potato planting (Anokhova and Krivtsov 1991 [156829], p. 206).
In the topsoil layer, radionuclides are attached mostly to small soil particles that are less than
1 gm in diameter (Loshchilov et al. 1991 [156823], p. 198). Therefore, the specific activity of
small soil particles exceeds that for largest particles (0.1-1 mm; Anokhova and Yfivtsov 1991
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Natural Analogue Synthesis Report
[156829], p. 206). For example, for 134CS the specific activity of small particles exceeds that of
large particles by a factor of 12.7, for 1 37Cs by a factor of 9. 1, for 9OSr by a factor of 7.4, and for
238+239+240pu by a factor of 19.2 (Anokhova and Krivtsov 1991 [156829], Table 2, p. 208). The
specific radioactivity of resuspended dust particles (<10 [Lm) increases by a factor of 10
compared to that in soils, from which these particles were originated (Loshchilov et al. 199i
[156823], p. 200).
One of the main parameters characterizing the atmospheric resuspension of radionuclides is the
resuspension factor. The resuspension factor is defined as the ratio between the airbome (Bq/m 3 )
and surface (i.e., <1 cm depth) concentration (Bq/M2) of a radionuclide in question. According to
Bondarenko et al. 

(2000 [156593), pp. 474-475), the resuspension factor in 1998 ranged from
0.34 x 100-17 x 10-10/m. This value is_ in agreement with the range of resuspension factors
(from 1.4 x 10-'O/m for 137Cs and I x 10 H/m for 239,240pu) determined in 1998 by Rosner and
Winkler (2001 [156629], pp. 11, 17). The resuspension factor was higher at the earlier stage after
the accident. For comparison, in the Yucca Mountain Biosphere Process Model, the
resuspension-factor mean value is 8.3 x 10-"/m (CRWMS M&O 2000 [151615], Section
3.2.4.1.3).
Kashparov et al. (2000 [156622]) investigated the resuspension and redistribution of
radionuclides at various distances from fires occurring in areas previously contaminated by the
.Chernobyl accident and outside the 30 km ChNPP exclusion zone. They determined that the
resuspension factor for the active phase of a fire was as high as 10-7_10-8/M (Kashparov et al.
2000 [156622], p. 288). The dose coefficient from the radioactive aerosol inhalation was
estimated to be 1.5 x 10-8 Sv (1 Sv = 100 rem), which provides less than 1% of the total dose
resulting from inhalation and extemal radiation (Kashparov et al. 2000 [156622], p. 296). This
value for the dose coefficient was obtained for a one-year period following a single intake of
radionuclides due to a fire (Kashparov et al. 2000 [156622], p. 297). Equivalent dose is the
quantity obtained by multiplying the absorbed dose (the quantity of energy imparted by radiation
to a unit mass of matter such as tissue, measured in Sl (Intemational System of Units) units in
grays, Gy, or rad) in a body organ or tissue by a factor representing the effectiveness of the type
of radiation causing harm to the organ or tissue (NEA 1995 [156632], p. 60). Effective dose is
the weighted sum of the equivalent doses to the various organs and tissues, multiplied by
weighting factors reflecting the differing sensitivities of organs and tissues to radiation (NEA
1995 [156632], p. 59). In Sl units, equivalent dose is measured in sieverts (Sv). The whole-body
(intemal and extemal) dose (i.e., total effective dose equivalent [TEDE]) limit for a radiological
worker is 5 rem/year (DOE 1994 [104736], p. 2-6, Table 2-1). The presence of (X-emitting
radionuclides (in the 30 km zone)- causes a considerable increase in inhalation dose during forest
fires, which can exceed extemal exposure doses (Kashparov et al. 2000 [156622], p. 297).
Thus, measurements and modeling investigations indicated that radionuclide resuspension could
become a source of both extemal and inhalation radiation doses for people, depending on the
distance from the release. The size distribution of resuspended particles is important in
determining inhalation (i.e., lung) dose.
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Natural Analogue Synthesis Report
13.3.6 Groundwater Contamination
This section examines the extent of groundwater contamination resulting from the Chemobyl
accident and the type of radionuclides involved.
The largest source of radionuclide contamination of groundwater is from about 800 radioactive
waste disposal sites within the Chemobyl exclusion zone. Another large, local source of
contamination is the Chemobyl cooling pond (Shestopalov and Poyarkov 2000 [157507],
p. 146). Radionuclides dispersed over large areas can migrate to the water table through and
around casings of boreholes and in colloi-dal and dissolved states in percolating water from the
vadose zone. 

Field investigations showed a lack of correlation between 1 37CS Soil concentration
and its travel time to the water table (Gudzenko et al. 1991 [107834], p. 3), indicating that soil
contamination is not a major source of groundwater contamination.
Before the Chemobyl accident, the depth to the water table around the ChNPP was
approximately 6 to 8 m and was controlled by several drainage systems. Since 1986, some
drainage systems have been abandoned, so that the water table has risen, creating a potential
instability for the remaining structure of the ChNPP. Subsequently, several countermeasures,
such as the construction of a vertical drainage system and an impenneable underground vertical
wall, allowed the water table to decline to previous depths.
The highest 90Sr concentrations of groundwaters (102-104 Bq/L) were measured in water samples
taken at inteiim radioactive storage sites near the ChNPP (Table 13.3-2). By 1995-1996, an
increase in the 90Sr and 137CS concentrations by 2-3 orders of magnitude, in comparison with
pre-accident conditions, occurred in the upper section of groundwater within the inner part (5-10
km) of the exclusion zone. At the same time, radionuclide concentration in the groundwater and
the artesian aquifer are below the maximum pennissible concentration. Despite a low level of
current contamination of the artesian aquifer in the Eocene deposits, which is the source of
potable water within the exclusion zone, it is predicted that groundwater contamination will
increase over the next few decades (Shestopalov and Poyarkov 2000 [157507), p. 141).
The presence of 134CS in groundwater and the increase of 90Sr concentration by two orders of
magnitude (from 4-400 mBq[L) confirm that radionuclides from Chemobyl reached
groundwater at 50 to 70 m depths over five years (1987-1992) (Bar'yakhtar 1997 [156953], p.
254). Cs-137 and 90Sr contamination was detected in the Cretaceous aquifer at depths of 80 to
120 m within the 30 km zone 22 months after the accident (Gudzenko 1992 [107835], p. 5).
Elevated concentrations of 90Sr and 137CS OCCUrred at substantial distances from the ChNPP plant
in all aquifers down to 200-300 m (Table 13.3-3).
Given these findings, groundwater contamination by 90 Sr and 137CS, caused by leakage from
radioactive waste disposal sites within the Chemobyl exclusion zone, cooling pond, and
migration through casings of boreholes to depths below 120 m, is expected to influence all
nearby aquifers. However, the risk associated with the use of contaminated groundwater water
for water supply is marginal, as compared to extemal radiation and inhalation doses (see
Sections 13.3.7 and 13.3.9).
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Natural Analogue Synthesis Report
13.3.7 Using Contaminated Water for Irrigation and Water Supply
The Dnieper River water is used for irrigation of more than 1.8 million hectares in Ukraine,
involving the tenitoiies from Kiev in the north to Crimea in the south (Berkovski et al. 1996
[156592], p. 39). Figure 13.3-8 shows the concentration of radionuclides in water from six
reservoirs along the Dnieper River used for inigation. In the southem Ukraine, which has a semi-
and climate and a depth to the water table of 50-70 m, irrigation water is taken mostly from
canals extending from the Dnieper River reservoirs. About 50% of the land is used to plant
fodder crops, eventually leading to the contamination of meat and milk products, and about 10%
is used to plant vegetables (Berkovski et al. 1996 [156592], p. 39). The water loss into the
subsurface on irrigated lands and from irrigation canals accelerates migration of the radioactive
elements from crops, soil surface, and surface water sources into the vadose zone and
groundwater. The amount of radionuclides migrating into the subsurface depends on the quality
(pH and chemical composition) of the irrigation water and soils, soil structure, depth to water
table, and evapotranspiration, as well as the type of irrigation.
Table 13.3-4 illustrates that the concentrations Of 137CS in grains, grass, and vegetables grown on
lands that were irrigated with contaminated Dnieper River water exceeded by a factor of 2-6
those in crops irrigated using uncontaminated water, while the concentrations in irrigation water
increased by a factor of 2-4 (Perepelyatnikov et al. 1991 [156822], p. 112, Table 5). The
increase in the concentration observed during inigation confinms the concept of a buildup factor
in soils. 

Table 13.3-5 indicates that the accumulation of radionuclides on irrigated lands occurred to
depths of at least 10-20 cm. An example is data on the disttibution of 137Cs and 90Sr in soils
irrigated using contaminated water in the southem Ukraine (Perepelyatnikov et al. 1991
[156822]). After the rice harvest in 1988, irrigation caused an increase in the I 37CS concentration
in the 0-0.5 cm topsoil layer by 58% compared to that on unirrigated (bare) lands. In the'0.5-2
cm layer, its concentration increased by 14-19%. For the same time period, the 90Sr
contamination increased by a factor of -2 (from 18-35 mCi/kM2) in compaiison with that of bare
soil (i.e., without vegetation and irrigation). The accumulation Of 137CS -and 90Sr in soils caused
the concentration of these radionuclides in rice to increase. For example, in the first harvest after
the accident in 1986, the 137CS concentration increased by a factor of 1.6 compared to 1985
concentrations. The 90Sr concentration began to increase in 1987, and it increased by a factor of
1.3 compared with 1985 values. However, in the southem Ukraine, concentrations had not
reached levels detected in 1972, from global fallout generated by nuclear testing
(Perepelyatnikov et al. 1991 [156822], pp. 110, 112, Table 4).
Using the average concentrations of 117Cs and 90Sr in the 20 cm soil layer obtained after three
years of rice irrigation (last column of Table 13.3-5) and concentrations in bare soils (third
column of Table 13.3-5) assuming that the preaccident concentration is equal to that of bare
soils, the following buildup factors are obtained: for "'Cs, 0.48/0.37 = 1.3 (for three years), or
approximately 10% per year; and for 9'Sr, 116/60 = 1.97 (for three years), or approximately 32%
per year. It is expected that the radionuclide buildup factor in soils under irrigation will change
with time, depending on the processes of leaching and ecological decay of radionuclides.
0
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Natural Analogue Synthesis Report
Thus, irrigation with contaminated water in the southem Ukraine'leads to the accumulation of
radionuclides in both the topsoil layer and in crops. The data obtained in Ukraine qualitatively
confirm the concept of a radionuclide buildup factor in irrigated soils; this concept is employed
in the Yucca Mountain Biosphere Process Model.
13.3.8 Leaching and Transfer Coefficients
This section discusses the dissolution rate, leaching parameters, soil-plant transfer of
radionuclides, and radionuclide accumulation in fish and livestock.
13.3.8.1 Dissolution Rate and Leaching Parameters
Hot particles exposed at the surface were oxidized, which caused superficial cracking of the
particles and increased their surface area, which in tum led to higher dissolution rates.  The
dissolution rates for nonoxidized and oxidized fuel particles (U02,,,) differ with acidity of the
solution (Kashparov et al. 2000 [156623], p. 232). The dissolution rate V for fuel particles
depends on the soil pH according to the formula (Bar'yakhtar et al. 2000 [157504], p. 32):
V=ax job pH gm/yr (Eq. 13-1)
where coefficients a = 14.45 and b = -0.431 for weakly oxidized particles, and a = 4.59 and b =
-0.234 for strongly oxidized fuel particles. This fonnula was used to describe radionuclide
leaching from fuel particles for pH from 4 to 6. Kashparov et al. (2000 [1566231, p. 232, Figure
4), who studied dissolution kinetics of Chemobyl fuel particles over a pH range from 3 to 9,
determined that the dissolution rate is minimal in a neutral medium, while it increases in both
acidic and alkaline media.
A study of concentrations of Chemobyl radionuclides in Neuherberg, Germany, was carried out
by Rosner and Winkler (2001 [156629]). They detennined that the annual mean concentrations
in air and annual deposition to ground decreased for 90Sr, 137CS, 23gpU , and 239,24OpU froM jUly
1986 to 1998. Figure 13.3-9 shows an-nual mean values of radionuclide concentrations in air
(gBq /M3), specific activities in air dust (Bq/g), and radionuclide ratios in air (Bq/Bq) at Munich-
Neuherberg since 1985. 

The air-dust concentration (gg/m 3) iS shown in this figure for
comparison.
The leaching coefficient is defined as a parameter characterizing the downward movement of
radionuclides dissolved in percolating waters (CRWMS M&O 2001 [152517), p. 6) and is
calculated as part of the total mass of the radionuclide leached from a soil layer per unit of time
(CRWMS M&O 2001 [152517], Section 5.1, Equation 1).
The leaching coefficient for 90Sr determined using I Chemobyl data varies significantly from
3 x 10-2 -3.1 Llyr (Bar'yakhtar 1997 [156953], p. 240). For comparison, the leaching coefficient
for 90Sr used in the Yucca Mountain biosphere process model is 4.47 x 10-2 L/yr (CRWMS
M&O 2000 [151615], Table 3-7), which is near the lower limit of the Chemobyl range. The
dissolution rate of uranium reached 2.2 x 10-2 LJyr using Chemobyl data (Baryakhtar 1997
[156953], p. 241).
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Natural Analogue Synthesis Report
The release of radionuclides from solid particles into the soil is govemed by the diffusion
process (Sobotovich and Dolin 1994 [156821], p. 57). Given the diffusion coefficients for 90 Sr
(1.3-2.1 X 10-16 CM2/S) and "'Cs (2.5-4.8 x 10-IICM2/S) , about 65-80% of 90Sr will become
mobile in 10 years, and only 20-30% of 137CS will become mobile over the same time
(Sobotovich and Dolin 1994 [1568211, p. 59, 60).
Smith et al. (2000 [156906], p. 141) hypothesized that the "fixation" process of radionuclides
controls the amount of cesium in soil water and therefore its availability to terrestrial biota. The
decline in 1 37CS mobility and bioavailability over the first few years after fallout is most likely
controlled by slow diffusion of 137CS into the soil's illitic clay mineral lattice. However, the
sorption-desorption process may be reversible for 137CS, in which case the ecological half-life
increases towards its physical half-life decay rate of 30.2 years. Smith et al. (2000 [156906],
p. 141) showed a two-component exponential decline model for the 1 37 Cs decline in vegetation,
water, and fish.
13.3.8.2 Soil-Plant-Food Transfer of Radionuclides and Food Contandnation
Two main mechanisms control radionuclide transfer to plants: (1) direct deposition on plant
surfaces from atmospheric resuspension of contaminated soil and from inigation with
contaminated water, and (2) the root uptake of radionuclides. For example, immediately after the
Chemobyl accident, when aerosol particles accumulated only on the outer bark of trees, the
radioactivity of leaves of some trees in the streets of central Kiev in 1986 varied from 70,000-
400,000 Bq/kg (Bar'yakhtar 1997 [156953], pp. 260, 261). At that time, inner tissues of trees and
roots did -not pick up contamination. Radioactivity of the outer bark of trees decreased in 5-6
years after the accident, while the activity in wood and inner bark increased because
contaminants migrated through the root systems. According to Prister et al. (1991 [157548], p.
146) root uptake became significant the second year after the accident. Bulgakov and Konoplev
(2000 [156699], p. 776), who reviewed the existing infon-nation on root uptake and modeled root
uptake by pine trees within the Chemobyl exclusion zone, stated that the radionuclide
concentration at the bottom of the root system is the same as in the most contaminated part of the
topsoil layer, and the radiocesium transfer from the root's exchangeable complex into the above-
surface part of the plant is relatively rapid. For grass, this takes one day. Radionuclide migration
from roots into tree trunks is limited by diffusion and convective radionuclide transfer from the
soil into the roots. 

The soil-to-plant transfer factor (or concentration ratio) is defined as the ratio of radioactivity
concentration in the edible part of the plant (Bq/kg) to the radioactivity concentration in soil
(Bq/kg). This factor is also tenned the accumulation factor by Bar'yakhtar (1997 [1569531, p.
270). Table 13.3-6 compares the soil-to-plant-transfer factors for different radionuclides in the
Yucca Mountain Biosphere Process Model with those in Chemobyl. The range of these factors
for each element depends on many processes affected by the type of elements and soil properties,
plant species, concentration of nutrients and carrier elements in soils, moisture content, acidity of
soils, and meteorological and climatic conditions.
The soil-plant transfer processes are not important for short-lived radionuclides, such as 131j,
because they essentially decay before being taken up by plant roots. The transfer of radionuclides
from soils to plants is limited to long-lived radionuclides. However, the soil-plant transfer is a
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Natural Analogue Synthesis Report
predominant pathway for cesium and strontium to appear in pasture and/or fodder, and
subsequently in meat and milk, thus becoming part of the exposure pathway. Table 13.3-7
summarizes the values of the cesium soil-to-fodder transfer coefficients, depending on the soil
pH and types of agricultural products. This table shows that transfer factors for 137CS vary
significantly (several orders of magnitude) depending on types of soils and plants, because of the
effects of microbiological activity in soils (metabolism and decay of microorganisms), and in the
presence of different complex-forming ligands (Bondarenko 1998 [1569521, pp. 28-3 1).
A plausible explanation for the observation in Table 13.3-7 that transfer coefficients are higher in
natural grasses than in other fodder types could be the following. The transfer coefficients
depend on the diffusion of radionuclides into the root system. Natural grasses grow on
undisturbed soils with better contact between the soils and roots, which increases the diffusion of
radionuclides into grasses. In contrast to undisturbed soils, cultivated soils do not have as good
contact with the roots, which reduces diffusion of radionuclides into the plants. At the same time,
cultivated soils experience more significant weathering and resuspension of radionuclides by
wind. Furthennore, application of fertilizers to cultivated soils and soil-plant microbiological
activity may immobilize radionuclides.
The effective meadow-vegetation transfer coefficient for 90Sr is of the same order of magnitude
as in alfalfa, and is shown in Figure 13.3-10. Accumulation Of 137CS in vegetables (cucumber and
tomato) is higher than in wheat and com (see Table 13.3-4). Accumulation Of 137CS in some
meadow grasses depends on the type of soils and increases in wet soils (Shestopalov and
Poyarkov 2000 [157507], Table 5.6.3). The data given in this figure can be used to estimate that
the transfer coefficient for 90Sr increased from 1 X 10-3_1 X 10-2 m2/kg from 1988 to 1994. This
increase can be explained by the fact that 90Sr, which settled on soils, is gradually transformed
into a soluble form and thus absorbed by plants. 

Bruk et al. (1998 [156600], p. 178) detennined that during the first five to six years after
deposition, the ' 37CS concentration in vegetables and animal agricultural products decreased with
an environmental half-life period of 0.7-1.5 years (i.e., the length of time required for 1/2 of the
radioacting to decay in situ). Thereafter, beginning from 1990-1991, no significant variation of
the 137CS content in food products was found, and the values of the transfer factors for this
radionuclide in the main types of food (milk, potatoes) for rural inhabitants were close to those
obtained in the pre-accident period (1980-1985), based on the global origin. Reduction of the
137CS content in produce was most rapid during the early years after the accident, as intensive
countenneasures were applied at that time. Half-life periods for 1 37CS content in milk (the basic
dose-forming product) and other products for the most contaminated areas in Russia amounted to
1.6-4.8 years, depending on the type of countermeasures used. Half-life pefiods of the decrease
in the 137CS content in other types of agricultural products (grain, potato) were within the range
of 2-7 years. Ivanov (2001 [156818], pp. 65-66) approximated the dynamics of the transfer
coefficient for 137CS in the chain soil-plant by a function
y = a exp(-bt) + (I -a) exp(-ct) (Eq. 13-2)
where y is the transfer coefficient normalized to the maximum transfer coefficient, t is the time
(in years), and a, b, and c are parameters that depend on the type of soil and plants: a = 0.76-
0.94, b = 0.44-1.38, and c = 0.038-0.17 (Ivanov 2001 [156818], p. 67, Table 5). According to
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Natural Analogue Synthesis Report
Ivanov (2001 [156818], Table 6), the ecological half-life Of 137CS in agricultural plants vaiied in
terms of averaged values from 0.42 (first period) to 22.1 (second period) years, depending on the
type of soils. Figure 13.3-11 presents the dynamics of the transfer coefficient for 137CS in
meadow grass.
Zhdanaova et a]. (2000 [156951], p. 64) determined that interaction between biota and
micromycetes fungi destroyed hot particles after the Chemobyl accident. They detennined two
mechanisms responsible for these processes: (1) microbial metabolic activity; and (2) mechanical
destruction by mycelial overgrowth of radioactive particles. From this, it follows that these
processes may also decrease the half-life of radionuclides in the environment, compared with
physical half-life values. Therefore, the use of physical values of the half-life of radionuclides
gives conservative estimates of radionuclide migration in the Yucca Mountain Biosphere Process
Model.
Based on an extensive experimental and modeling study of transfer factors for mushrooms, wild
animals, benies, meat, and milk in different regions of Ukraine, Belarus, and Russia, Jacob and
Prohl (1995 [156864], p. 110) determined that a peroral (oral) dose is higher than that from the
extemal radiation. They applied several models in calculating transfer coefficients in the chain
soil-->plants-4food-4human body. The soil-milk transfer coefficient ranges from less than I to
2
20 Bq/L per kBq/m .
Table 13.3-8 presents concentrations of 137CS in the pasture, milk and meat, and their daily
uptake (Richards and Hance 1996 [157613]). These concentrations are used to calculate transfer
40 coefficients using the following fonnula (CRWMS M&O 2000 [152435], Table 1)
Transfer coefficient = Concentration in meat or milk / Intake
For Chemobyl, the meat and milk transfer coefficients are 1.6-2.0 x 10-2 day/kg and 6.4-8.0 x
10-3 day/L, respectively. For the Yucca Mountain Biosphere Process Model, the beef and milk
transfer coefficients are 5 x 10-2 day/kg and 8 x 10-3 day/L, respectively (CRWMS M&O
[151615], Table 3-14). 

Thus, the Yucca Mountain meat transfer coefficient exceeds that
determined for Chemobyl, and the Yucca Mountain milk transfer coefficient is essentially the
same as that for Chemobyl.
13.3.8.3 Radionuclide Accumulation in Fish
Smith et al. (2000 [1569061) measured 137Cs activity concentrations in terrestrial vegetation at
seven sites, in lake water, and in mature fish in Cumbria, LTK. They determined that 117CS froM
the 1986 Chemobyl accident has persisted in freshwater fish for much longer than was initially
expected because of the so-called "fixation" process of cesium in soil. They concluded that the
effective ecological half-life in young fish, water, and terrestrial vegetation has increased from
values of 1-4 years measured dufing the first five years after Chemobyl to 6-30 years
determined since 1990. Jonsson et al. (1999 [156620]) measured cesium in nearly 4,000 fish,
taking samples 2-4 times every year in a Scandinavian lake contaminated by Chemobyl fallout.
The estimated half-life of cesium concentration in fish was 0.3-4.6 years. Jonsson et al. (1999
[156620]) found that the decline in cesium was initially rapid for three to four years and then
became much slower. About 10% of the initial peak radioactivity declined with a half-life of 8-
  13-16  1

 

 
22 years. Smith et a]. (2000 [157433]) determined the bioaccumulation factor of different fish in
ten lakes of Belarus, Russia, and Ukraine from 1-232 km from Chemobyl from 6-11 years after
the accident. They determined that the bioaccumulation factor for I 37Cs ranged from 82-14,424
Ukg for different lakes and types of fish (Smith et al. 2000 [157433], Table 2). The
bioaccumulation factor used in the Yucca Mountain Biosphere Process Model for freshwater fish
for 137CS is 2,000 Llkg (CRWMS M&O 2000 [151615], Table 3-15), which is within this range.
The Yucca Mountain recommendation for the bounding value of the bioaccumulation factor is
15,000 L/kg (CRWMS M&O 2000 [152435], Table 14), which agrees with the maximum value
determined by Smith et al. (2000 [157433], Table 2). Smith et al.  (2000 [157433], p. 360) used
the term concentration factor, which is the same as the bioaccumulation factor for the Yucca
Mountain Biosphere Process Model.
13-3.8.4 Livestock Uptake
Livestock uptake represents radionuclide transfer to animal food products. The 137CS transfer
coefficients to cattle, milk, and meat in Ukraine from 1987-1993 are different for sbils with
different soil pH values (Baryakhtar 1997 [156953], Table 1.5.4). In 1993, radionuclide
concentration in beef from collective farrns, where fodder was produced on arable soils, ranged
from 20-71 Bq/kg. 

At the same time, the radionuclide concentration in meat from private fanns
ranged from 75-520 Bq/kg, and in wild animal meat, it ranged from 504-1,540 Bq/kg
(Bar'yakhtar 1997 [156953], p3. 370-371). In the Rivne region of Ukraine, the transfer factor for
beef ranged from 0. 16-0.59 m /kg for collective farms, and ranged from 1-1.7 m2/kg for private
farms. The difference between the collective and private farms can be explained by the fact that
countenneasures were undertaken on collective farms.
Empirical data from the leaching and transfer coefficients summarized in Section 13.2.8 show
that the initial dissolution of hot particles exposed to the atmosphere increases the concentration
of radionuclides, which then decreases with time. The ecological half-life of radionuclides in
soils, plants, and foodstuff is less than physical values for radionuclides. Diffusion and
absorption processes are limiting factors for radionuclide transfer in soils. Radionuclide transfer
to a plant depends on two main mechanisms: (1) direct deposition on the plant surfaces from
resuspension of contaminated soil particles or from irrigation with contaminated water, and (2)
the root uptake of radionuclides, which is limited by diffusion and convective transport from the
soil to the root.
13.3.9 Human Receptor Exposure
This section defines the Chemobyl human receptors and critical groups, gives examples of
human exposure pathways and BDCF calculations, and presents the radiation doses from
plutonium.
13.3.9.1 Chernobyl Human Receptors and Critical Groups
For risk-assessment purposes, the critical group for Chemobyl was selected to be individuals
who were bom in the year of the accident and who will live in the same contaminated location
for 70 years (IAEA 1991 [156750], p. 207). Exposute of the population was from two main
pathways: (1) the radiation dose to the thyroid as a result of the concentration of radioiodine and
  13-17  1

 

 
similar radionuclides in the gland, and (2) the whole-body dose caused largely by extemal
irradiation mainly from radiocesium (NEA 1995 [156632], p. 30). About 80% of the lifetime
dose was accumulated in the first ten years after the accident (Los'and Poyarkov 2000 [157508],
p. 194). A group of people that can be considered to include the reasonably maximally exposed
individual includes pregnant women, fetuses, and school children (Lazjuk et al. 1995 [156626],
p. 71). The risk of radiation for these people is correlated with the level Of 137CS contamination,
because 137CS iS the most significant contributor to intemal and extemal doses (see Section
13.3.9.2).
Doses received by the public are different for rural populations, including agricultural workers
and "come-backers" living within the highly contaminated exclusion zone, and urban
populations. Doses have varied with time since the Chemobyl accident.
13.3.9.2 Human Exposure Pathways
Exposure pathways to the populace resulting from the Chemobyl accident occurred through (1)
extemal irradiation from radioactive materials deposited on the ground from the radionuclide
fallout or accumulation from irrigation water, and (2) intemal irradiation caused by inhalation of
airbome materials and ingestion of contaminated foodstuff. Table 13.3-9 presents an example of
the typical types of data for the city of Bragin, Belarus, and includes the following categories of
data:
Population (number of children and total inhabitants)
Deposition density of 137CS and 90Sr
Exposure rate
Concentration in foods
Consumption rate of foods
Intemal dose.
This table also illustrates changes in the radionuclide concentration with time in different types
of foods and actual intemal doses in different population groups.
The dose received by the rural population makes up the bulk of the collective dose. Collective
dose is the total dose over a population group exposed to a given source and is represented by the
product of the average dose to the individuals in the group, multiplied by the number of persons
comprising the group-for example, person-sievert (Sv) (NEA 1995 [156632], p. 59). Between
1986 and 1996, the rural population received 77% of the collective total effective dose. From
1986 to 1996, the mean annual collective effective intemal dose was 65% versus 35% for the
extemal dose for the rural areas (Los' and Poyarkov 2000 [157508], p. 186). In the urban areas,
the main source of the intemal dose was inhalation, while in the rural, agricultural areas, the
intemal dose consisted of both inhalation and ingestion of radionuclide particles. 

About 95% of the contribution to extemal and intemal doses to the rural population was by I 37cS
(Los' and Poyarkov 2000 [157508], p. 185). Based on Chemobyl investigations, the dose
received by the public from TRU elements would be several dozen to several hundred times
smaller than that from strontium and cesium over the 70-year period following the accident.
Table 13.3-10a shows that the effective dose for the rural population is higher than that for the
  13-18 

 

 
urban population, because people in rural areas spent more time outdoors. The effective dose
decreased rapidly for the first year after the accident, and then slowly until 1996. Table 13.3-10a
4D presents changes in the effective dose of extemal radiation from 137CS with time. These values, if
expressed in mrem/yr per pCi/M2 (Table 13.3-10b), can be compared with BDCFs from extemal
radiation for the Yucca Mountain Disruptive Event Scenario model. The annual value of
I ltSv/(kBq/m 2) corresponds to 3.7 x 10-6 mrem/yr per PCi/M2.
Table 13.3-10c presents the BDCFs from the Yucca Mountain disruptive event scenaiio
(CRWMS M&O 2001 [152536], Tables I I and 13). Figure 13.3-12 shows that the calculated
Yucca Mountain and observed Chemobyl BDCFs for 1 37Cs are within the same order of
magnitude for both minimum and maximum values. (To relate BDCF values using the method
presented above to potential contamination at Yucca Mountain, the BDCF units reported in
Table 5-17 of CRWMS M&O (2000 [151615)) have to be converted from mrem/yr per pCi/L to
mrem/yr per PCi/M2 . Assuming that the wetted zone due to potential irrigation is I cm thick and
the volumetric moisture content is 10%, 1 mrem/yr per pCi/L is equivalent to I mrem/yr per
PCi/M2.)
Table 13.3-11 shows maximum 137CS concentrations (kBq /M2) in soils producing an intemal
radiation dose of I mSv/yr (100 mrem/year). The total radiation dose of 100 mrem/year is the
annual permissible limit for the general public (DOE 1994 [104736], p. 2-6). The corresponding
BDCFs for the intemal radiation were calculated from the forinula
BDCF = Intemal radiation dose / Radionuclide concentration activity of soil
which is based on the BDCF definition given in CRWMS M&O (2000 [151615], Section
3.1.4.1). Because the Yucca Mountain model uses BDCFs in mrem/year per PCi/M2' the
concentrations in pCi/m 2 (Columns 4 and 5 of Table 13.3-11) were first calculated using the
conversion factors I kBq = 27,027 pCi, and then the corresponding BDCFs (Columns 6 and 7 of
Table 13.3-11) were calculated from the formula
BDCFs = 100 mrem/year / Concentration in soil (pCi/m. 2)
Because Table 13.3-11 presents maximum 137CS concentrations to obtain the annual dose of I
mSv (I mSv = 100 mrem), BDCFs calculated are minimal. These can be compared to BDCFs
derived for both disruptive and nondisruptive contamination event pathways at Yucca Mountain
as shown in Figure 13.3-13. For Chemobyl loamy soils, which have properties closer to Yucca
Mountain soils than other types of soils, the BDCF is 1.25 x 10-5 mrem/yr per PCi/M2 for tilled
soils. This value is two to ten times higher than the minimal BDCFs for the Yucca Mountain
disruptive contamination scenario. This difference occurs because contaminated groundwater is
not taken into account when calculating BDCFs for the disruptive event scenario for Yucca
Mountain (CRWMS M&O 2000 [151615], Section 3.3.2), while the use of contaminated
groundwater contiibuted to the intemal dose obtained after the Chemobyl accident.
(Contaminated groundwater for the Yucca Mountain biosphere is included in dose calculations
perfonned in the TSPA model once the radionuclide concentrations are estimated.) The critical
group pathway analyses and sensitivity studies conducted for Yucca Mountain showed that the
BDCF values for most radionuclides were dominated by only two consumption rates: water and
leafy vegetables (CRWMS M&O 2000 [151615], Section 3.1.2.3). In contrast, Chemobyl data
  13-19  1

 

Natural Analogue Synthesis
showed that drinking groundwater was an insignificant contiibutor to the human dose (Bugai et
al. 1996 [156596]). However, milk and milk products contributed significantly to the human
dose (Table 13.3-12), more so than would be true for the Yucca Mountain clitical population,
because the consumption of milk products in Ukraine [the average is 0.18-1.5 LJday in different
regions (Bar'yakhtar 1997 [156953], Table 1.3.9-1.3.11)] is much higher than that in the United
States. (The average used in the Yucca Mountain Biosphere Process Model is 0.011 Uday
(CRWMS M&O 2000 [151615], Table 3-16)). More importantly, the short-lived. radionuc I ides
associated with the Chemobyl accident are far more significant contributors to human dose.
The IAEA (1991 [156750], Part E, pp. 222-237) estimated extemal and intemal doses based on
(1) direct measurements and (2) dose calculations in settlements located within the area with
137CS concentrations exceeding 550 kBq/m' (>15 Ci/kM2) . Figures 13.3-13a indicates that a 137CS
body concentration has a log-normal distribution across the population. Different dietary
restrictions or habits (such as eating large quantities of forest mushrooms, an example relevant to
Yucca Mountain in principle only) could cause variable body concentration distributions
between different settlements. Figures 13.3-13b shows a significant scatter of data for the age-
dependent distribution Of 137CS.
Commercial fishermen on the Kiev reservoir, who consumed 360 kg/yr of fish in 1986, received
4.7 x 10-4 and 5 x 10-3 Sv from 90Sr and 137CS , respectively (Berkovski et al. 1996 [156592], p.
41), i.e., the dose ratio of cesium to strontium was 10.6. The predicted contributions to the
collective effective dose resulting from irrigation, municipal tap water, and fish for members of
the general public for over 70 years following the ChNPP accident are shown in Table 13.3-13.
The predicted contribution of 90Sr to the collective dose resulting from the use of Dnieper water
is 80% (Berkovski et al. 1996 [156592], p. 42). Figure 13.3-14 presents the contribution of 90Sr
and 137CS in different components of food-chain pathways to averaged effective intemal dose for
Kiev in 1993. The contribution of radionuclides through the dfinking-water pathway is different
in different areas. For example, the drinking-water pathway contiibution for the people of Kiev
was about 6% of the total radiation dose; for the people of the southem Ukraine, it was 14% to
34% (Voitsekhovich et al. 1996 [156921], Figure 7).
Bugai et al. (1996 [156596]) estimated health risks caused by radionuclide migration to
groundwater and compared these risks with risks from exposure to radioactive contamination on
the ground surface. They determined that the estimated health risk to hypothetical, self-sufficient
residents in the 30 km exclusion zone is dominated by extemal and intemal ir-radiation from
137CS, caused mainly by ingestion of agricultural products. The estimated risk caused by drinking
contaminated groundwater is approximately an order of magnitude lower. Strontium-90
migration via groundwater to surface water used in downriver population centers shows that
groundwater can potentially only marginally contribute to the offsite radiological lisk. 

Bugai et
al. (1996 [156596), pp. 13-14) calculated the annual committed effective doses caused by
consumption of 90Sr-contaminated water, using an ingestion dose conversion factor of 3.9 x 10-5
mSv/Bq, deterniined by the Eckerman et al. (1988 [101069], Section III) formula. Committed
effective dose equivalent is the resulting dose committed to the whole body from radionuclides
absorbed intemally over a 50-year period (DOE 1994 [104736], p. 2-3). Berkovski et al. (1996
[156592], p. 42) determined that consumption of drinking water in 1986 by the populace in the
  13-20  1

 

Natural Analogue Synthesis
Kiev region led to the maximum individual annual committed effective doses of 1.7 x 1 0-5 and
le 2.7 x 10-5 Sv from 90Sr and 137Cs, respectively.
13.3.9.3 Radiation Doses from Plutonium
An effective dose equivalent was used to assess the risk of inhalation of hot particles,
accumulated on lungs from the Chemobyl accident, as a function of the distance between
particles and (x and P-radiation (Loshchilov et al. 1991 [156823], pp. 198, 202). The risk of lung
cancer calculated based on the assumption of uniform distribution of radioactivity exceeds that
calculated for a point source by a factor of two to three.
The most hazardous particles are those containing plutonium, which can contribute up to 40% of
radioactivity in dust (Anokhova and Krivtsov 1991 [1568291, p. 206). Calculations showed that
the inhalation doses for agricultural laborers working on truck platfon-ns are greater than extemal
doses, and the Pu concentration exceeded the acceptable limit by an order of magnitude
(Anokhova and Krivtsov 1991 [156829], pp. 209, 212). In the Yucca Mountain Biosphere
Process Model for the disruptive event scenafio, the sum of fractions of plutonium-238, -239,
and -240 would exceed the contribution of other radionuclides (CRWMS M&O 2000 [151615],
Table 3-23), as was observed at Chemobyl.  Breathing air containing such high concentrations of
plutonium for two months can lead to its accumulation in bones in concentrations exceeding the
annual permissible limit (Anokhova and Krivtsov 1991 [156829], p. 209).
The main pathways for plutonium intake resulting from the Chemobyl accident are inhalation
(which has been treated as an acute intake since 1986), uniform oral intake from food products,
and inhalation of resuspended dust particles. Bondarenko et al. (2000 [156593], p. 475)
calculated that the transfer factor of plutonium into grass is 0.3 x 10-3 (Bq/kg)/(Bq /M2 ), and it
could be as low as 0.15 x 10-6 (Bq/kg)/(Bq/M2 ) due to the superficial contamination of grass.
They also detennined that the "soil-diet" transfer coefficient nonnalized to unit contamination
density is 1.2 x 10-7 (Bq/kg)/(Bq/M2). In this calculation, Bondarenko et al. (2000 [156593], p.
475), assumed that the "soil-diet" transfer coefficient is 2.4 x 10-5 (Bq/kg)/(Bq /M2); the soil
density is 2 g/CM3; radioactivity is unifon-nly distiibuted within the top 10 cm soil profile;
2
plutonium concentration in soils is 3,700 Bq/m , which is typical for the southeastem peiiphery
of the exclusion zone; initial fallout particles of I ~trn in diameter, precipitating on inert soil
pailicles, form agglomerates 5 gm in diameter; rural inhabitants spend one-third of the day
outdoors; and the averaged resuspension coefficient is 10-9 /m.
Bondarenko et al. (2000 [1565931, pp. 476-477) also presented data on the content of cc-emitting
isotopes of plutonium in the human skeleton. They found that the average plutonium content in
25 samples was 4.9 x 10-2 Bq for regions contaminated at the level of 20 mCi/kM2 (740 Bq /M2). 

Table 13.3-14 presents the calculated content of cc-emitting plutonium isotopes in the human
skeleton in 1998 and compares these data with global fallout. This table indicates that the
Chemobyl data exceeded that resulting from global fallout by 2.5-9.2 times.
13.4 SUMMARY AND CONCLUSIONS
Section 13.3 reviewed infonnation from the Chemobyl accident regarding the exposure
pathways, distribution of radioactive contaminants in the biosphere, and inputs to risk assessment
  13-21  1

 

 
that may be relevant to future revisions of the Yucca Mountain Biosphere Process Model.
Despite the difference in climatic conditions and the accident/potential-exposure scenarios for
Chemobyl and Yucca Mountain, respectively, the Chemobyl data serve as a source of
information to improve the confidence in a conceptual model of exposure pathways and process
models. As part of the biosphere-model validation for both groundwater release and volcanic
release scenarios, the YMP is interested in measurements that could represent input data in
validating models for specific environmental processes, as listed in Section 13.2. The main
conclusions that can be drawn from Chemobyl with respect to these processes and parameters
are described below.
Radionuclide transferfrom soil to plant via root uptake (see Section 13.3.8.2). Cesium migration
from soils to grasses is relatively rapid. The radionuclide migration from roots into the tree
trunks is limited by diffusion and advective radionuclide transfer from the soil (Bulgakov and
Konoplev 2000 [156699]). Root uptake became a significant contributor to the food chain in the
second year after the accident (Prister et al. 1991 [157548], p. 146).
Radionuclide transfer from soil to plants via atmospheric resuspension, including deposition of
resuspended material on plant surfaces (see Section 13.3.5). Resuspension of radionuclides by
wind-driven dust is an important factor after the tillage of agricultural lands, increasing the
resuspension by more than an order of magnitude. Resuspended material is likely to settle on
plant surfaces, thereby increasing their contamination. The Chemobyl data on hot-particle
dispersal and dust transport showed that radionuclides attach to dust particles and move as
combined particles. Aspects of models of atmospheric contaminant dispersal, radionuclide
fallout, radionuclide resuspension, and particle-size distiibutions developed by Garger et al.
(1999 [1514831), Goldman et al. (1987 [156820]), and Kashparov et al. (2000 [156622]) may be
relevant to building confidence in a model for radionuclide resuspension resulting from a
volcanic eruption through a potential Yucca Mountain repository.
Radionuclide transferfrom animal food to animal products (see Sections 13.3.8.2 and 13.3.8.4).
These data could be used in assessing the Yucca Mountain models for meat and milk
contamination. Environmental half-life periods of decay Of 137CS content in milk and agricultural
products were shorter than those initially expected. 

Renioval of cotitaminants via erosion and leaching (see Sections 13.3.5 and 13.3.8.1). The
average annual topsoil erosion in Ukraine from 1987 to 1990 contributed to the annual removal
of 0.7 x 105 Bq/ha of 137CS from soils (Piister et al. 1991 [156824], Table 7). As a result of
biochemical and physical-chemical processes, hot particles have been significantly dissolved by
now, and radionuclides have been transferred to soils (Kashparov 2001 [156819], p. 37). The use
of physical values of the half-life of radionuclides gives conservative estimates of radionuclide
removal from soils in the Yucca Mountain Biosphere Process Model.
Inhalation of resuspended contamination material originally deposited on the ground (see
Sections 13-3.5 and 13.3.9.3). The most hazardous particles associated with the Chemobyl
accident are those containing plutonium, which can contribute up to 40% of radioactivity in the
dust (Anokhova and Krivtsov 1991 [156829], p. 206). The inhalation doses for agricultural
laborers are greater than the extemal doses, with the plutonium concentration exceeding the
0 acceptable limit by an order of magnitude.
  13-22  1

 

 
Radioiiuclide accumulation in soils and plants under irrigatioti using contaminated water (see
Section 13.3.7). Inigation using contaminated water creates radioactive contamination of both
irfigated soils and agricultural products (Perepelyatnikov et al. 1991 [156822]; Bondar et al.
1991 [1568461). The increase in the concentration of radionuclides in soils during irfigation in
the southem Ukraine, where environmental conditions are more similar to those at Yucca
Mountain than are those in the Chernobyl vicinity, confirms the concept of a radionuclide-
buildup factor used in the Yucca Mountain Biosphere Process Model.
In summary, results of the Chemobyl literature survey suggest that soil type influences the
ecological half-life of radionuclides in the biosphere, both in regard to soil bioaccumulation
factors and advective and diffusive transport properties that limit radionuclide transfer to plant
roots. With respect to rural populations, agricultural methods-including irrigation and tillage-
and crop types play an important role in resuspension of radionuclides. Resuspended material is
likely to increase the contamination of plant surfaces. Resuspended radionuclides would increase
the inhalation dose for agricultural workers, which would be particularly significant for
plutonium associated with the Chemobyl accident.
Chemobyl data include both the relatively short-lived isotopes of iodine, cesium, and strontium,
and long-lived transuranic elements such as plutonium and americium. Amonp the long-lived
radionuclides of interest to Yucca Mountain, and not present at Chemobyl, are '29 1, 227 Ac, 232 U,
233u, 237 Np, 243 Am '21 OPb , 23 'Pa , 226 Ra , 230Th, and 242pU (CRWMS M&O 2000 [151615), Sections
3.3.1 and 3.3.2).
Numerous data collected for the past 15 years about the distribution and accumulation of
radioactive materials in different parts of the biosphere after the Chemobyl accident, including
the main exposure pathways and mechanisms of radioactive contamination of the environment
and the population, can be used to build confidence in Yucca Mountain conceptual and
numerical models. They can also be used to enhance models for long-term transport processes
and radiation doses associated with possible exposure to radioactive material in the vicinity of
the potential nuclear waste disposal site at Yucca Mountain. For the potential groundwater-
contamination scenario at Yucca Mountain, radionuclide-contaminated water, which is to be
used as the source of drinking water, irrigation, animal watering, and domestic uses, is expected
to increase the likelihood of ingestion uptake of radionuclides by humans. Chemobyl data on the
atmospheric distribution of contaminants, their fallout, and redistfibution in soils and plants may
be considered an anthropogenic analogue for the potential release of radionuclides caused by a
volcanic eruption at Yucca Mountain, accompanied by atmosphelic dispersal of contaminants
into the environment through ash fallout on the land surface. 

 Calibration and Alignment of the Siemens Diffractometers. Los
Alamos, New Mexico: Los Alamos National Laboratory. ACC: NNA. 19920430.0207.
LANL-EES-DP-56, R4. Brinkman Automated Grinder Procedure. Los Alamos, New Mexico:
Los Alamos National Laboratory. ACC: MOL.19980626.0230.
16.3 SOURCE DATA, LISTED BY DATA TRACKING NUMBER
145412 GS980908312322.008. Field, Chemical, and Isotopic Data from Precipitation
Sample Collected Behind Service Station in Area 25 and Ground Water Samples
Collected at Boreholes LTE-25 C #2, LTE-25 C #3, USW UZ-14, LJE-25 WT #3, UE-
25 WT #17, and USW WT-24,10/06/97 to 07/01/98. Submittal date: 09/15/1998.
  16-52 

 

 
157569 LB0201YSANALOG.001. Permeability and Porosity Measurements of Core
0 Samples from Core Samples at Yellowstone National Park. Submittal date:
01/25/2002.
157610 LB0202PBANALOG.001. Stable Isotope Analyses of Pena Blanca Waters.
Submittal date: 02/12/2002.
16.4 OUTPUT DATA, LISTED BY DATA TRACKING NUMBER
N/A
0
0
  16-53  1