SENSITIVITY OF WIPP PERFORMANCE ASSESSMENT RESULTS TOREGULATOR-PRESCRIBED CHANGES
Todd R. Zeitler and Brad A. Day
Sandia National Laboratories
Address: 4100 National Parks Hwy. Bldg. A, Carlsbad, NM, 88220

Key words: performance assessment, transuranic waste, WIPP, regulatory

Abstract
The U.S. Environmental Protection Agency (EPA) requested of the U.S. Department of Energy (DOE) asensitivity study (CRA14_SEN4) of the current Waste Isolation Pilot Plant (WIPP) Performance Assessment(PA) model that incorporated several changes to the baseline WIPP PA model (CRA14), including: parameterchanges, use of an updated code, and a revised computational grid.
resulted in increased releases in all primary release mechanisms.

The modifications to the repository model

The impacts of each EPA-requested change to

CRA14 were analyzed with respect to each release mechanism in the CRA14_SEN4 study.

Overall, total

high-probability (P[Release>R] = 0.1) predicted mean releases from the repository were increased by about 15%,
which corresponds to a 0.6% reduction in the margin to the limit of 1. Total low-probability(P[Release>R] = 0.001) predicted mean releases were increased by about 107%, which corresponds to a 2.9%
reduction in the margin to the limit of 10. The upper 95% confidence level on the mean increased forhigh-probability and low-probability releases by 18 and 119%, respectively.

It is concluded that the

EPA-requested changes to the CRA14 result in increases to the predicted total releases from the repository.
However, releases calculated in the CRA14_SEN4 analysis remain below regulatory limits, demonstrating
continued compliance of the WIPP.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology andEngineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S.
Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
SAND2017-11969C.

1. Introduction
The Waste Isolation Pilot Plant (WIPP), located insoutheastern New Mexico, has been developed by the
U.S. Department of Energy (DOE) for the geologic(deep underground) disposal of transuranic (TRU)
waste. Containment of TRU waste at the WIPP isregulated by the U.S. Environmental Protection
Agency (EPA) according to the regulations set forthin Title 40 of the Code of Federal Regulations (CFR),
Part 191. The DOE demonstrates compliance withthe containment requirements according to theCertification Criteria in Title 40 CFR Part 194 bymeans of performance assessment (PA) calculations

performed by Sandia National Laboratories (SNL).
WIPP PA calculations estimate the probability andconsequence of potential radionuclide releases fromthe repository to the accessible environment for aregulatory period of 10,000 years after facility
closure. The models used in PA are maintained andupdated with new information as part of an ongoingprocess. Improved information regarding important
WIPP features, events, and processes typically results
in refinements and modifications to PA models andthe parameters used in them. Planned changes tothe repository and/or the components therein also
result in updates to WIPP PA models. WIPP PA

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanmodels are used to support the repository
recertification process that occurs at five-year
intervals following the receipt of the first waste
shipment at the site in 1999.
A sensitivity evaluation of the CRA-2014 PA(CRA14) has been requested by the U.S.
Environmental Protection Agency to investigate
potential regulatory compliance impacts associatedwith the following: 1) changes to certain sampled andconstant parameter values; 2) the use of an updated
version of the DRSPALL code; and 3) a correction to
the length of a panel closure representation in the
BRAGFLO grid (Zeitler 2016a, Zeitler and Day2016). The objective of the sensitivity analysis wasto evaluate the cumulative effects of these changes on
predicted releases from the repository during the
10,000-year regulatory period.
Modified parameters implemented herein wereused to satisfy an official request by the EPA for thissensitivity study. As such, the parameter values
modified for this analysis should not be interpreted as
being developed by SNL. The use of an updated
version of DRSPALL code (which corrects an error
in DRSPALL v. 1.21) and the correction of the lengthof the northern-most panel closure representation in
the BRAGFLO grid are supported by SNL. The
CRA14_SEN4 sensitivity analysis was performed
under AP-164, Analysis Plan for the 2014 WIPP
Compliance Recertification Application Performance
Assessment (Camphouse 2013).
2. Approach
The CRA14_SEN4 sensitivity study investigates
the impacts of parameter changes, the use of an
updated version of the DRSPALL code, and acorrection to the length of a panel closure
representation in the BRAGFLO grid. All of thesechanges are taken together for use in a single PA
calculation consisting of 3 replicates. The followingchanges to CRA14 inputs have been requested by the
EPA for CRA14_SEN4:
1.
Use newly-developed actinide solubility
uncertainty distributions for +III and +IV actinides
based on the Data0.FM1 WIPP thermodynamic
database (FM1 database) and the data sets selected by
the EPA.
2.
Use EPA-developed distribution for
GLOBAL:PBRINE parameter.
3.
Use BOREHOLE:TAUFAIL parameter
distribution with a new lower bound (EPA-directed).
4.
Use version 1.22 of the DRSPALL code.
5.
Use correct representative length ofnorthernmost set of panel closures.
6.
Set stoichiometric coefficients concerning
reactions of hydrogen sulfide with iron to zero
(EPA-directed).

The requested changes to CRA14 are explained
below in detail. Additionally, in order to maintain agreater flexibility in prescribing material properties tospecific areas of the repository model in the future,
the CRA14_SEN4 sensitivity study uses the material
names
and
associatedgridmodifications
implemented
for
the
CRA14_SEN2
and
CRA14_SEN3 sensitivity studies (Day 2016, Day
and Zeitler 2016a); however, the material propertiesof those areas are set equivalent to those used in the
CRA-2014 PA.
2.1
Baseline PA Analysis
The most recent PA done to demonstrate WIPP
regulatory compliance is that performed for the
CRA-2014 (DOE 2014).
The CRA-2014 PA
considered four distinct cases with detailed
descriptions of the four cases considered in the
CRA-2014 PA found in Camphouse (2013) and asummary of results given in Camphouse et al. (2013).
The final of the four cases considered in the
CRA-2014 PA, identified as CRA14-0, is referenced
herein as CRA14 and utilized as the baseline analysis
for comparison with the sensitivity case called
CRA14_SEN4. All three replicates evaluated under
CRA14 are similarly run for CRA14_SEN4. Initial
seed values for LHS and CCDFGF calculations wereidentical to those used in CRA14.
2.2
Modified Parameters
The original parameters used for CRA14 and themodified parameters implemented for CRA14_SEN4
in response to the EPA request can be foundelsewhere (Zeitler and Day 2016).
2.2.1 Solubility Multipliers for Oxidation
State III and IV Models (SOLMOD3:SOLVAR
and SOLMOD4:SOLVAR)
As part of the EPA request for the CRA14_SEN4
analysis, the EPA has requested that actinide
solubility uncertainty distributions be recalculatedusing the FM1 database and an updated list ofreferences provided by the EPA (Zeitler 2016a).
Baseline actinide solubilities were identical to thoseused in CRA14. A separate analysis has been
performed in which new actinide solubility
uncertainties have been calculated (Xiong andDomski 2016).
The new analysis resulted in
updated cumulative distributions for actinide
solubility uncertainties, which are represented by the
SOLMOD3:SOLVAR (+III oxidation state) andSOLMOD4:SOLVAR(+IV
oxidationstate)
parameters.
Comparisons for the values of
SOLMOD3:SOLVAR and SOLMOD4:SOLVAR
that were sampled in the CRA-2014 PA andCRA14_SEN4 analyses are shown in Figure 2-1 andFigure 2-2. For SOLMOD3:SOLVAR, the sampledvalues for CRA14_SEN4 are generally higher than

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanthose for CRA14, while for SOLMOD4:SOLVAR,
the sampled values for CRA14_SEN4 are lower thanthose for CRA14.

Figure 2-1: Comparison of LHS sampled values of
the SOLMOD3:SOLVAR parameter for CRA14 andCRA14_SEN4 (300 sampled values for eachanalysis).

Figure 2-3: Comparison of LHS sampled values of
the GLOBAL:PBRINE parameter for CRA14 andCRA14_SEN4 (300 sampled values for eachanalysis).
2.2.3 Effective Shear Strength for Erosion(BOREHOLE:TAUFAIL)
For the CRA14_SEN4 sensitivity study, the EPA
has requested the use of a revised distribution for the
BOREHOLE:TAUFAIL
parameter.
The
BOREHOLE:TAUFAIL parameter is a sampledparameter that represents the shear strength of waste.
The lower end of the uniform distribution waschanged from 2.22 Pa to 1.60 Pa as specified by the
EPA (Zeitler 2016a). A comparison of the values
sampled in CRA14 and CRA14_SEN4 is shown in
Figure 2-4.
Because the lower end of the
distribution is only slightly lowered for
CRA14_SEN4, sampled values are only slightly
lower than those used in CRA14.

Figure 2-2: Comparison of LHS sampled values of
the SOLMOD4:SOLVAR parameter for CRA14 andCRA14_SEN4 (300 sampled values for eachanalysis).
2.2.2 Probability that Drilling Intrusion in
Excavated Area Encounters Pressurized Brine(GLOBAL:PBRINE)For the CRA14_SEN4 sensitivity study, the EPA
has requested the use of a revised distribution for the
GLOBAL:PBRINE parameter (Zeitler 2016a). The
GLOBAL:PBRINE parameter is a sampled parameterthat represents the probability that an inadvertent
human drilling intrusion intersecting the repository
also intersects pressurized brine. A comparison of
the values of GLOBAL:PBRINE that were sampled
in CRA14 and CRA14_SEN4 is shown in Figure 2-3.
The
EPA-requested
distribution
ofthe
GLOBAL:PBRINE parameter is given in the form of
a cumulative distribution, while the distribution usedin CRA14 was parameterized as a normal distribution.
The range of values sampled from the CRA14_SEN4
distribution encompasses that from CRA14, but
predominantly consists of values higher than thoseused in CRA14.

Figure 2-4: Comparison of LHS sampled values of
the BOREHOLE:TAUFAIL parameter for CRA14
and CRA14_SEN4 (300 sampled values for eachanalysis).
2.2.4 Stoichiometric
Coefficientsfor
Sulfidation
Reactions(REFCON:STCO_31,
STCO_32, STCO_35, STCO_36, STCO_43,
STCO_46)
As part of the EPA request for the CRA14_SEN4
analysis, the EPA has requested that the chemistry
reactions used in BRAGFLO, in which hydrogensulfide (H2S) interacts with iron, be eliminated.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Elimination of the sulfidation reactions isaccomplishedbysettingtheappropriate
stoichiometric coefficients to zero. Reactions 3 and
4 in the chemistry model implemented in the
BRAGFLO code include H2S (WIPP PA 2012).
Reaction 3 represents Fe(OH)2 sulfidation andreaction 4 represents metallic Fe sulfidation (seereaction equations below).
Fe(OH)2(s) + H2S(g) → FeS(s) + 2 H2O(l).
(BRAGFLO chemical reaction 3)
Fe(s) + H2S(g) →FeS(s) + H2(g),(BRAGFLO chemical reaction 4)
By removing these two reactions from the
BRAGFLO chemistry model, the expected impact on
PA calculations is that less hydrogen sulfide gas will
be consumed and less water will be produced in thewaste areas.
The stoichiometric coefficients for reactions 3 and
4 are represented by parameters REFCON:STCO_3x
and REFCON:STCO_4x (where x ranges from 0 to 9
and represents one of ten compounds considered in
the BRAGFLO chemical reactions), respectively.
Of the twenty stoichiometric coefficients used todefine reactions 3 and 4, fourteen had a value of zeroin the CRA14. In order to comply with the EPA
request for CRA14_SEN4, the following six
coefficients were set to zero: STCO_31, STCO_32,
STCO_35, STCO_36, STCO_43, and STCO_46(Zeitler and Day 2016).
2.3
Use of Updated Version of DRSPALL
One of the requests from the EPA for
CRA14_SEN4 is that DRSPALL v. 1.22 be used.
When DRSPALL v. 1.22 was developed, in order tocorrect an error found in DRSPALL v. 1.21, acomplete set of official DRSPALL calculations(including three replicates of 100 vectors each) was
run using a current set of PA parameters as input(Kirchner et al. 2015). Results for DRSPALL v.
1.22 calculations were compared with those from v.
1.21 and documented in an impact assessment report(Kicker et al. 2015). Because PA parameter inputs
for the DRSPALL code have not changed since those
calculations were performed, and because the
DRSPALL code does not rely on the output of any
other code for its input, DRSPALL v. 1.22 was not
rerun for CRA14_SEN4. Instead, the DRSPALL v.
1.22 output results from the calculations described in
the impact assessment were used as input to the
CUTTINGS_S code in CRA14_SEN4 calculations.
2.4
Modified Length of Northern Panel
ClosureThe proposed repository panel closures aremodeled in BRAGFLO as three separate panel
closure areas. The “northernmost” panel closurearea separates the operations area from the “north restof repository” (NROR) waste area, the “middle”
panel closure separates the NROR from the “south
rest of repository” (SROR), and the “southernmost”
panel closure separates the SROR from the waste
panel. The CRA14_SEN4 sensitivity study request(Zeitler 2016a) is consistent with that for the
CRA14_SEN3 sensitivity study (Zeitler 2016b) andnotes that the northernmost panel closure in the
BRAGFLO grid should represent the length of twopanel closures, 60.96 m. The CRA14 PA used alength of 30.48 m for the northernmost panel closure.
The correction to the BRAGFLO grid has been madehere.
As part of the EPA completenessdetermination for CRA-2014, the issue of the lengthof the northernmost panel closure was broached by
the EPA (EPA 2015). A PA calculation was done to
examine the impact of doubling the length of thenorthernmost panel closure and negligible changes tothe pressures and saturations in the waste areas were
found (Zeitler 2015, DOE 2015).
2.5
Modified BRAGFLO Material Map
The code BRAGFLO is the WIPP PA code used tomodel brine and gas flow in and around therepository. The current disturbed rock zone (DRZ)
above and below the operations and experimental(OPS/EXP) areas is modeled as the same material
representing the DRZ above and below the waste
areas. For the CRA14_SEN3 sensitivity study,
EPA-requested parameter changes for DRZ
properties above and below the OPS/EXP areas andthe PCS required a change to the BRAGFLO material
map in order to implement the requested parameterchanges specific to those areas. The BRAGFLO
grid and material map that incorporates the requested
OPS/EXP area and PCS property changes has beencorrespondingly modified. This modification to thegrid is an extension of that made for the
CRA14_SEN2 sensitivity study (Day 2016). Thechanges in the BRAGFLO grid and material map thatwere implemented for CRA14_SEN3 have been kept
for CRA14_SEN4. The modified grid separates thematerial in the DRZ, located above and below the
OPS/EXP area and the PCS, so that they may betreated separately from the DRZ above and below thewaste areas of the repository. The new material
regions for the DRZ above and below the OPS/EXP
and PCS areas as well as the pre-existing material
regions for the PCS and OPS/EXP areas are thus
available for any future parameter modifications.
Although the BRAGFLO grid changes made here are
the same as those made for the CRA14_SEN3
sensitivity study, material property values for thoseregions are the same as those used for the CRA14
analysis. The modified grid has been kept for
flexibility in potential future parameter changes.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan3. Results
Results for all release mechanisms are now
presented and compared to those obtained in the CRA
2014 PA (CRA14). Results are discussed in termsof overall means. Overall means are obtained byforming the average of all realizations. In WIPP PA,
a replicate consists of 100 calculated realizations.
Three replicates are used to generate results for
CRA14 and CRA14_SEN4. Means and statistics
presented for the analyses are also calculated over all
three replicates. The impacts of the requested
modifications to CRA14 results include changes toall of the primary release mechanisms: cuttings andcavings, spallings, direct brine releases, and releases
from the Culebra. Plots of releases for individual
release mechanisms include lower and upper 95%
confidence intervals on the means, as well ascomparisons with results from CRA14. A summaryof critical means and lower and upper confidence
limits for individual release mechanisms at
probabilities of 0.1 and 0.001 is presented in Section
3.5.
3.1
Cuttings and Cavings Releases
Cuttings and cavings releases are minimallyincreased due to the EPA requested modifications to
CRA14 inputs (Figure 3-1). The reduction in thelower bound of the BOREHOLE:TAUFAIL
parameter distribution resulted in the sampling oflower values of waste shear strength (Figure 2-4).
The use of slightly reduced shear strength values
resulted in minimally increased cavings releases forborehole intrusions into the repository that intersect
waste.

all impact repository pressure at the time of intrusion.
Changing the northernmost panel closure length has
been shown to be minimally impactful on waste panelpressures and saturations and not impactful on
releases (DOE 2015).
The impact of removing sulfidation from thechemistry model has not been previously examined,
but is shown here to slightly increase pressures anddecrease saturations in the waste areas by comparing
BRAGFLO results from CRA14, CRA14_SEN4, andthe analysis done by DOE (2015). In the waste
panel, there is little to no impact of the northernmost
panel closure length on pressures and saturations.
When the northernmost panel closure length ischanged (lengthened) and sulfidation is removed in
CRA14_SEN4, waste panel pressures are increased
and brine saturations decreased—the increased
pressure and decreased brine saturation can therefore
be attributed to the removal of sulfidation.
Increased pressure and gas volumes in the waste
panel are consistent with reduced gas consumption
associated with removing sulfidation reactions.
Decreased brine saturation and brine volume in thewaste panel are consistent with reduced waterproduction associated with removing sulfidation
reactions.
The shifting of the GLOBAL:PBRINE parameter
distribution to generally higher values for
CRA14_SEN4 leads to an increased number of
intrusions into pressurized brine below the repository,
which typically leads to increased pressure in thewaste areas and therefore increased spallings. The
impact of changing the GLOBAL:PBRINE
distribution has not been examined independently ofother changes.
An increase in spallings releases has been shown
previously when DRSPALL v. 1.22, which hascorrected an error in DRSPALL v. 1.21, is used
(Kicker et al. 2015). Overall, spallings releases are
increased with the application of all of the EPA
requested changes, as compared to CRA14 results(Figure 3-2).

Figure 3-1: Confidence Interval on Overall Mean
CCDFs for Cuttings and Cavings Releases: CRA14
and CRA14_SEN4
3.2
Spallings Releases
Spallings releases are a function of repository
pressure at the time of intrusion. Increases inpressure necessarily translate to increased spallings
release volumes. Changes to the northernmost panel
closure length, the chemistry model (i.e., removal of
sulfidation), and the GLOBAL:PBRINE parameter

Figure 3-2: Confidence Interval on Overall Mean
CCDFs for Spallings Releases: CRA14 andCRA14_SEN4

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan3.3
Releases from the Culebra
Transport releases through the Culebra and acrossthe land withdrawal boundary are impacted by theamount of brine released to the Culebra, as well as
actinide solubilities. Brine flows up the intrusion
borehole obtained in CRA14_SEN4 are slightly
decreased compared to those obtained in CRA14.
Consequently, volumes of brine flowing up to theCulebra are slightly decreased, which is attributed tothe modification to the northernmost panel closureand the removal of sulfidation (i.e., the only twochanges in CRA14_SEN4 that could potentially
impact BRAGFLO results).
Additionally, the change to the GLOBAL:PBRINE
distribution leads to increased waste panel pressures
following intrusion into pressurized brine below therepository (as discussed above for spallings releases),
which tends to increase releases to the Culebra.
The differences in actinide solubilities between
CRA14 and CRA14_SEN4 also contribute to releases
from the Culebra. In general, increased solubilities
lead to increased releases from the Culebra.
However,
becausesampledvaluesof
SOLMOD3:SOLVAR have increased and those for
SOLMOD4:SOLVAR have decreased, it is possiblethat the combined impacts of the solubility changes
are to increase or decrease releases from the Culebra.
The overall impact of the solubility changes on
releases from the Culebra is dependent on the relative
impacts due to the +III and +IV solubilities. The
isolated impact of the solubility uncertainty changes(i.e., apart from all of the other changes made for
CRA14_SEN4) has not been investigated. Overall,transport releases through the Culebra and across theland withdrawal boundary are slightly increased
compared to results calculated for CRA14 (Figure3-3). At very low probabilities (P[Release>R] <0.0003), releases from the Culebra are decreased.

Direct brine releases (DBRs) require sufficientwaste panel pressure and brine saturation in order tooccur. The repository pressure near the drilling
location must exceed the hydrostatic pressure of thedrilling fluid, which is specified to be 8 MPa in WIPP
PA. The brine saturation in the intruded panel must
exceed the residual brine saturation of the waste, asampled parameter in WIPP PA. The changes to the
CRA14 analysis that have been implemented for the
CRA14_SEN4 sensitivity analysis result in slightly
increased waste region pressure and very slightly
decreased waste region brine saturation.
The change to the GLOBAL:PBRINE distribution
results in increased intrusions into pressurized brine
below the repository, which increases pressures andsaturations in waste areas—the net result of thischange is increased direct brine volumes.
Additionally, the changes to actinide solubilities
impact actinide concentrations in DBR releases. In
general, increased solubilities lead to increased DBR
releases. However, because sampled values of
SOLMOD3:SOLVAR have increased and those for
SOLMOD4:SOLVAR have decreased, it is possiblethat the combined impacts of the solubility changes
are to increase or decrease DBRs. The overall
impact of the solubility changes on DBRs isdependent on the relative impacts due to the +III and+IV solubilities.
The isolated impact of thesolubility uncertainty changes (i.e., apart from all of
the other changes made for CRA14_SEN4) has notbeen investigated. The net result of all of thechanges introduced in CRA14_SEN4 is an increase
in DBRs at all probabilities (Figure 3-4).

Figure 3-4: Confidence Interval on Overall Mean
CCDFs for Direct Brine Releases: CRA14 andCRA14_SEN4

Figure 3-3: Confidence Interval on Overall Mean
CCDFs for Releases from the Culebra: CRA14 andCRA14_SEN4
3.4

Direct Brine Releases

3.5
Total Releases
Total releases are calculated by totaling thereleases from each release pathway: cuttings andcavings releases, spallings releases, DBRs, andtransport releases (there were no undisturbed releases
to contribute to total release).
CRA14_SEN4
CCDFs for total releases obtained in replicates 1, 2,
and 3 are plotted together in Figure 3-5. The overallmean CCDF is computed as the arithmetic mean of

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

the mean CCDFs from each replicate. A confidence
interval is computed about the overall mean CCDF
using the Student’s t-distribution and the mean
CCDFs from each replicate. Figure 3-6 shows 95%
confidence intervals about the overall mean for
CRA14 and CRA14_SEN4.
Mean CCDFs of the individual release mechanismsthat comprise total normalized releases are plotted
together in Figure 3-7, as well as the CRA14_SEN4
total release overall mean. As seen in that figure,total normalized releases obtained for CRA14_SEN4
are dominated by cuttings and cavings releases and
DBRs.
Contributions to total releases fromspallings and Culebra transport are not dominant,although spallings and Culebra transport releases
have been increased in comparison to CRA14.
Overall means for total normalized releases
obtained for CRA14 and CRA14_SEN4 are plotted
together in Figure 3-6. Overall, total normalized
releases increase from CRA14 to CRA14_SEN4 due
to increases in all contributing release components.
Total normalized releases increase at low
probabilities (below 0.1) from CRA14 to
CRA14_SEN4 principally due to increased DBRs.
A comparison of the statistics on the overall mean for
total normalized releases obtained for CRA14 andCRA14_SEN4 is now made. At a probability of 0.1,
values obtained for the mean total release and upper
95% confidence interval for CRA14_SEN4 areincreased in comparison to CRA14 (15 and 18%,
respectively). At a probability of 0.001, the mean
total release and upper 95% confidence level arehigher for CRA14_SEN4 in comparison to CRA14(107 and 119%, respectively).

Figure 3-5: Total Normalized Releases, Replicates
R1, R2, and R3, CRA14_SEN4

Figure 3-6: Confidence Interval on Overall Mean
CCDFs for Total Normalized Releases: CRA14 andCRA14_SEN4

Figure 3-7: Comparison of Overall Means for
Release Components of CRA14_SEN4
4. Summary
The application of EPA-requested modified
parameters has been incorporated into a sensitivity
analysis (CRA14_SEN4) and compared to the mostrecent PA done in support of WIPP recertification(CRA14). A minimal increase in cuttings andcavings releases was found due to a change to the
BOREHOLE:TAUFAIL parameter distribution.
Spallings releases were increased as a result of a
combination of changes to the northernmost panel
closure length and GLOBAL:PBRINE parameter
distribution, as well as a correction to the DRSPALL
code and removal of sulfidation from the chemistrymodel.
Total releases from the Culebra wereincreased as a result of a combination of changes tothe northernmost panel closure length, actinide
solubility uncertainties, and GLOBAL:PBRINE
parameter distribution, as well as removal of
sulfidation from the chemistry model. Direct brinereleases were increased as a result of a combinationof changes to the GLOBAL:PBRINE and actinide
solubility
uncertainties.
Overall,total
high-probability (P[Release>R] = 0.1) predicted
mean releases from the repository were increased byabout 15%, which corresponds to a 0.6% reduction in
the margin to the limit of 1. Total low-probability(P[Release>R] = 0.001) predicted mean releases wereincreased by about 107%, which corresponds to a
2.9% reduction in the margin to the limit of 10. The
upper 95% confidence level on the mean increased
for high-probability and low-probability releases by
18 and 119%, respectively. It is concluded that the
EPA-requested changes to the CRA14 result inincreases to the predicted total releases from therepository, but with those increased releases, theCRA14_SEN4 analysis continues to demonstrate that
WIPP complies with the regulatory limits.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan5. References

Brush, L.H., and P.S. Domski. 2013. Uncertainty
Analysis of Actinide Solubilities for the WIPP
CRA-2014 PA. Analysis Report, February 22,2013 ERMS 559278. Sandia National Laboratories,
Carlsbad, NM.
Camphouse, R.C. 2013. Analysis Plan for the 2014
WIPP Compliance Recertification Application
Performance Assessment. Sandia National
Laboratories, Carlsbad, NM. ERMS 559198.
Camphouse, R., D. Kicker, S. Kim, T. Kirchner, J.
Long, B. Malama, T. Zeitler. 2013. Summary
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Application
Performance
Assessment. Sandia National Laboratories,
Carlsbad, NM. ERMS 560252.
Day, B. 2016. Operations and Experimental Area
Sensitivity Study. Sandia National Laboratories,
Carlsbad, NM. ERMS 565918.
Day, B. and T. Zeitler 2016. Panel Closure System
Sensitivity Study. Sandia National Laboratories,
Carlsbad, NM. ERMS 566725.
DOE (U.S.Department of Energy), 2009. Title 40
CFR Part 191 Compliance Re-Certification
Application for the Waste Isolation Pilot Plant,
DOE/CBFO. U.S. Department of Energy, Waste
Isolation Pilot Plant, Carlsbad Field Office,Carlsbad, New Mexico.
DOE (U.S. Department of Energy). 2014. Title 40
CFR Part 191 Compliance Recertification
Application for the Waste Isolation Pilot Plant.
DOE/WIPP-14-3503. U.S. Department of Energy,
Waste Isolation Pilot Plant, Carlsbad Field Office.
Carlsbad, NM.
DOE (U.S. Department of Energy). 2015.
Response to Environmental Protection Agency
Letters Dated December 17, 2014 and February 27,
2015
Regardingthe2014Compliance
Recertification Application. U.S. Department ofEnergy, Waste Isolation Pilot Plant, Carlsbad Field
Office. Carlsbad, NM. ERMS 563433.
U.S. Environmental Protection Agency (EPA).
2015. Letter correspondence dated 2/27/16 from
Jonathan Edwards, EPA, to Jose Franco, CBFO,
Subject: [title not supplied] (Second Set of EPA
Completeness Comments on the CRA-2014).
Sandia National Laboratories, Carlsbad, NM.
ERMS 563410.

Kicker, D., C. Herrick, and T. Zeitler. 2015.
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6th East Asia Forum on Radwaste Management Conference
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