CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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### Contents

1 INTRODUCT ION ...................................................................................................... 4

2 METHODOL OGY ..................................................................................................... 5

2.1 Code Version .................................................................................................................. .. 6

2.2 Random Seed in the CCDFGF Control Files ................................................................... 6

2.3 Run Control ................................................................................................................... ... 6

3 ANALYSIS AND R ESULTS ..................................................................................... 7

3.1 Cuttings and Cavings Normalized Releases..................................................................... 7

3.2 Spallings Normalized Releases ...................................................................................... 12

3.3 Normalized Direct Brine Releases ................................................................................. 17

3.4 Normalized Transport Rel eases to the Culebra .............................................................. 22

3.5 Total Normalized Releases ............................................................................................. 24

4 SUMMARY ............................................................................................................. 28

5 REFERENC ES ....................................................................................................... 29CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 3 of 30 List of Figures

Figure 3-1: PC3R PA Replicate 1 Cutti ngs and Cavings Norm alized Re leases ...................................................... ...... 8 Figure 3-2: PCS-2012 PA Replicate 2 Cutti ngs and Cavings Norm alized Re leases .................................................. ... 8 Figure 3-3: PCS-2012 PA Replicate 3 Cutti ngs and Cavings Norm alized Re leases .................................................. ... 9 Figure 3-4: PCS-2012 PA Mean and Quantile CCDFs for Cu ttings and Cavings Normalized Releases, Replicates 1-3

.............................................................................................................................. ......................................................... 9 Figure 3-5: PCS-2012 PA Confidence Limits on Overall Mean for Cuttings and Cavings Normalized Releases ...... 10 Figure 3-6: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Cuttings and Cavings Releases . 10 Figure 3-7: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Cuttings and Cavings Volumes . 11 Figure 3-8: PCS-2012 PA Replicate 1 Spallings Normalized Releases ............................................................. ......... 13 Figure 3-9: PCS-2012 PA Replicate 2 Spallings Normalized Releases ............................................................. ......... 13 Figure 3-10: PCS-2012 PA Replicate 3 Spallings Norma lized Releases ............................................................ ......... 14 Figure 3-11: PCS-2012 PA M ean and Quantile CCDFs for Spallings Norm alized Releases, Re plicates 1-3 ............. 14 Figure 3-12: PCS-2012 PA Confidence Limits on Over all Mean for Spallings No rmalized Releases ....................... 15 Figure 3-13: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Sp allings Releases ................... 15 Figure 3-14: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Spalli ngs Volumes ...................................... 16 Figure 3-15: PCS-2012 PA Replicate 1 Normalized Direct Brine Rel eases ......................................................... ....... 18 Figure 3-16: PCS-2012 PA Replicate 2 Normalized Direct Brine Rel eases ......................................................... ....... 18 Figure 3-17: PCS-2012 PA Replicate 3 Normalized Direct Brine Rel eases ......................................................... ....... 19 Figure 3-18: PCS-2012 PA M ean and Quantile CCDFs for Normalized Direct Brine Releases, Replicates 1-3 ........ 19 Figure 3-19: PCS-2012 PA Confidence Limits on Overa ll Mean for Normalized Dir ect Brine Releases .................. 20 Figure 3-20: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Dire ct Brine Releases .............. 20 Figure 3-21: PCS-2012 PA and PABC-2009 Overall Mean CCDFs fo r Direct Brine Volumes ................................. 21 Figure 3-22: PCS-2012 PA an d PABC-2009 Replicate Means fo r Normalized Transport Rel eases to the Culebra ... 23 Figure 3-23: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Transport Releases to the Culebra .............. 23 Figure 3-24: PCS-2012 PA Replicat e 1 Total Normali zed Releases ................................................................ ........... 25 Figure 3-25: PCS-2012 PA Replicat e 2 Total Normali zed Releases ................................................................ ........... 25 Figure 3-26: PCS-2012 PA Replicat e 3 Total Normali zed Releases ................................................................ ........... 26 Figure 3-27: PCS-2012 PA Mean and Quantile CCDFs for Total Normal ized Releases, Rep licates 1-3 ................... 26 Figure 3-28: PCS-2012 PA Confidence Limits on Ov e rall Mean for Total Norm alized Rel eases .............................. 27 Figure 3-29: PCS-2012 PA and PA BC-2009 Overall Mean CCDFs for To tal Normalized Releases ......................... 27 Figure 3-30: PCS-2012 PA Primary Compone nts Contributing to Total Rel eases .................................................... . 28

List of Tables

Table 1: PCS-2012 PA and PABC-2009 Statistics on the Overall Mean for Total Normalized Releases in EPA Units

at Probabilities of 0.1 and 0.001 ............................................................................................. ..................................... 24CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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### 1 INTRODUCTION

The Waste Isolation Pilot Plant (WIPP), locat ed in southeastern New Mexico, has been developed by the U.S. Department of Energy (DOE) for the geologic (deep underground) disposal of transuranic (TRU) waste. Containmen t of TRU waste at the WI PP is regulated by the U.S. Environmental Protection Agency (EPA) accord ing to the regulations set forth in Title 40 of the Code of Federal Regulations (CFR), Part 191. The DOE demonstrates compliance with the containment requirements according to the Certif ication Criteria in Ti tle 40 CFR Part 194 by means of performance assessment (PA) calculati ons performed by Sandia National Laboratories (SNL). WIPP PA calculations estimate the probability and cons equence of potential radionuclide releases from the repository to the accessible environment for a regulatory period of 10,000 years after facility closure. The models us ed in PA are maintained and updated with new information as part of an ongoing process. Improved information regarding important WIPP features, events, and processes typically results in refinements and modifications to PA models and the parameters used in them. Planned ch anges to the repository and/or the components therein also result in updates to WIPP PA mode ls. WIPP PA 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.

Waste panel closures comprise a repository feature that has been represented in WIPP PA since the original Compliance Certifica tion Application (CCA) of 1996. Panel closures are included in WIPP PA models principally because they are a pa rt of the disposal system, not because they play a substantive role in inhibiting the release of radionuclides to the outside environment. The DOE stated in the CCA (DOE 1996) that “The panel closure system was not designed or intended to support long-term repository performance.” The 1998 rulemaking that certified WIPP to receive transuranic waste placed c onditions on the panel closure design to be implemented in the repository. The mandated desi gn consists of a concrete block wall, an open drift section, and a concrete monolith, and was termed the “Option D” panel closure. Followingthe selection of the Option D design in 1998, the engineering of the panel closure has been reassessed, and a revised design has been establis hed that is simpler, cheaper, and easier to construct. The revised panel closure design, termed the Run-of-Mine Panel Closure System (ROMPCS), is comprised of 100 fe et of ROM salt with barriers at each end. The ROM salt is generated from ongoing mining operations at the WIPP and may be compacted and/or moistened as it is emplaced in a panel entry. The barriers c onsist of ventilation bulkheads, similar to those currently used in the pane ls as room closures.

The DOE has submitted a planned change request (PCR) to the EPA requesting that EPA modify

Condition 1 of the Final Certification Rulema king for 40 CFR Part 194 (EPA, 1998) for the WIPP. The PCR submitted to EPA requests that Condition 1 be changed, and that the ROMPCS design be approved for use in all panels (DOE, 2011). In support of this rulemaking change, a performance assessment has been completed that incorporates the ROMPCS design into the current PA baseline established by the 2009 Performance Assessment Ba seline Calculation (PABC-2009) (Clayton et al., 2010). The name given to this new panel closure PA is PCS-2012, and the plan for its executi on is detailed in AP-161 (Campho use 2012a). PCS-2012 PA results are compared to those obtained in the PABC-20 09 as a means to quantify potential impacts dueCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 5 of 30 to the panel closure redesign. This analysis p ackage consists of the CCDFGF component of the

PCS-2012 PA.



### 2 METHODOLOGY

The performance assessment methodology accommoda tes both aleatory (i.e. stochastic) and epistemic (i.e. subjective) uncertainty in its constituent models. Aleatory uncertainty pertains to

unknowable future events such as intrusion ti mes and locations that may affect repository performance. It is accounted for by the genera tion of random sequences of future events. Epistemic uncertainty concerns parameter values that are assumed to be constants and the

constants’ true values are uncertain due to a l ack of knowledge about the system. An example of a parameter with epistemic uncertainty is the perm eability of a material. Epistemic uncertainty is accounted for by sampling of parameter values from assigned distributions. One set of sampled values required to run a WIPP PA calculation is termed a vector. The performance assessment models are executed for three rep licates of 100 vectors, each vect or being a realization resulting from a particular set of parameter values. A sample size of 10,000 possibl e sequences of future

events is used in the calcula tions to estimate an exceedance probability of 0.001 (Helton et al. 1998). The releases for each of 10,000 possible sequences of future events are tabulated for each of the 300 vectors, totaling 3,000,000 possible sequences.

For a random variable, the complementary cumula tive distribution functi on (CCDF) provides the probability of the variable being greater than a particular value. By regulation, performance assessment results are presented as a distribution of CCDFs of releases (U.S. EPA 1996). Each

individual CCDF summarizes the likelihood of releases across all futures for one vector of parameter values. The uncertainty in paramete r values results in a distribution of CCDFs.

Releases are quantified in terms of “EPA units”. Releases in EPA units result from a normalization by radionuclide and the total inventory. For each radionuclide, the ratio of its 10,000 year cumulative release (in curies) to its release limit is calculated. The sum of these

ratios is calculated across the set of radionuc lides and normalized by the transuranic inventory (in curies) of α -emitters with half-lives greater than 20 years. Mathematically, the formula used

to calculate releases in terms of EPA units is of the form

ܴ ൌ 10 ൈ 1 ଺ ݏ݅݁ݎݑܿ

ܥ ෍ ܳ ௜
ܮ ௜ ௜

where R is the normalized release in EPA units. Quantity Q i is the 10,000 year cumulative release (in curies) of radionuclide i . Quantity L i is the release limit for radionuclide i , and C is

the total transuranic i nventory (in curies) of α -emitters with half-lives greater than 20 years.

Mean and quantile CCDFs are calculated to compare the distributions of CCDFs among replicates and to demonstrate sufficiency of sa mple size. At each value of normalized release R on the horizontal axis, the CCDFs for a single replicate define 100 values of probability. Forming the arithmetic mean of these 100 probab ilities yields the mean probability that the

release exceeds R . The curve defined by the mean probabilities for each value of R is the meanCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 6 of 30 CCDF. The 10 th and 90 th quantile CCDFs for a particular replicate are determined from the

sorted order of the 100 CCDFs f ound for that replicate.

The overall mean CCDF is computed as the arithme tic mean of the three mean CCDFs from each replicate. Confidence limits are computed about the overall m ean CCDF using the Student’s tdistribution, the mean CCDFs from each replicat e, and the standard error based on the three replicate means. Confidence lim its as they are implemented in PA are defined vertically about the mean, rather than horizontall y. An artifact of this conventi on is that lower confidence limits can sometimes assume negative values, which ca nnot be plotted on a logarithmic scale. When this occurs, the resulting lower conf idence curve appears incomplete.

CCDF curves and statistics are generated usin g the CCDFGF_Analysis database utility. A description of this utility can be found in Kirchner (2010). A DVD containing the data loaded into this utility result ing from PCS-2012 PA and PA BC-2009 CCDFGF calculations, and subsequent SigmaPlot plots, are included as an attachment to this document.

2.1 Code Version

PRECCDFGF version 1.01 and CCDFGF version 5.02 were used for the PABC-2009 and the

PCS-2012.

2.2 Random Seed in the CCDFGF Control Files

One of the features that the CCDFGF control file initializes is the random number generator in the code. Setting the random number seed in th e control file determines the sequence of pseudorandom numbers used by CCDFGF. This sequence of numbers affects several stochastic parameters, such as the drilli ng location, depth, and type of plugging pattern, utilized when CCDFGF simulates the drilling of boreholes at the surface of the WIPP repository.

For the PCS-2012 PA, the same random seeds fo r CCDFGF were used as in the PABC-2009. This was done to allow a vector by vector compar ison of the results of the PCS-2012 PA to those

obtained in the PABC-2009. As the random seed s used to initialize the sampling of the epistemic parameters were unchanged in th e PCS-2012 PA and the PABC-2009, any differences between the analyses can be attributed solely to the changes in parameters and geometry used in

those calculations. Random seeds used in the PCS-2012 PA calculations are specified in the files CCGF_AP161_CONTROL_Rr.inp, where r = 1, 2, 3. These files are located in CMS library LIBAP161_CCGF.

2.3 Run Control

Run control, including code versions used and descriptions of code sequencing used to obtain

CCDFGF results in the PCS-2012 PA, is documented in Camphous e et al. (2012c). PCS-2012 PA results generated by code CCDFGF have file names CCGF_AP161_Rr.OUT, where r (the replicate number) equals 1, 2, or 3. These f iles are located in CMS library LIBAP161_CCGF under class AP161-0. PABC-2009 results ge nerated by CCDFGF have file namesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 7 of 30 CCGF_PABC09_Rr.OUT, and are located in CMS library LIBPABC09_CCGF under class

PABC09-0.



### 3 ANALYSIS AND RESULTS

Results obtained from PCS-2012 PA calculations are broken out in subsections for each component of release. At the conclusion of th e subsection for each release component, results obtained for the PCS-2012 PA are compared to those found in the PABC-2009. Normalized releases for cuttings and cavings are discussed in Subsection 3.1. Spallings releases are presented in Subsection 3.2. Results found for dire ct brine releases are discussed in Subsection

3.3. New calculations for normalized transport releases through th e Culebra were not performed as part of the PCS-2012 PA. BRAGFLO scenar io S6-BF is used by PA code PANEL to

determine the radionuclide source term to the Culebra. BRAGFLO scenario S6-BF results

obtained in the PCS-2012 PA ar e virtually identical to thos e calculated in the PABC-2009 (Camphouse 2012b). Consequently, the radionuclide source term to the Culebra is unaffected by the change of the panel closure design from Option D to the ROMPCS. There have been no updates to the Culebra flow model, e.g. updated tran smissivity fields, sin ce the completion of the PABC-2009. As a result, it is reas onable and appropriate to incor porate Culebra transport results

calculated in the PABC-2009 into the PCS-2012 PA.

Total normalized releases are shown in Subsection 3.5.

3.1 Cuttings and Cavings Normalized Releases

The change in panel closure design from Option D to the ROMPCS has no impact on cuttings and cavings releases. PA code CUTTINGS_S cal culates cuttings and cav ings release volumes, as well as spallings volumes. Spallings release volumes are potentially impacted by the panel closure redesign, and so are calculated as part of the PCS-2012 PA. As a result, cuttings and cavings releases are also calculated, even though they are identical to those obtained in the

PABC-2009.

PCS-2012 PA cuttings and cavings releases are pr esented in this section and subsequently compared to results obtained in the PABC-2009. Figure 3-1, Figure 3-2, and Figure 3-3 contain PCS-2012 PA cuttings and cavings re lease CCDFs for replicates 1, 2, and 3, respectively. Mean and quantile CCDF distributions fo r the three replicates are show n together in Figure 3-4. As seen in that figure, the mean and quantile CCD Fs obtained for the three replicates are nearly coincident. Figure 3-5 contains the 95 percent confidence limits about the overall cuttings and cavings mean. As is clear in that figure, the confidence limit is very tightly contained about the mean at all probabilities.

For the sake of reference, overa ll means of cuttings and cavings releases calculated in the PCS2012 PA and the PABC-2009 are plotted simultaneous ly in Figure 3-6 and Figure 3-7. As seen in those figures, cuttings a nd cavings releases and volumes obtained for both analyses were identical as no changes were made to the unde rlying models or parameters used in their calculation for the PCS-2012 PA (Kicker 2012).CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 8 of 30 Figure 3-1: PCS-2012 PA Replicate 1 Cu ttings and Cavings Normalized Releases

Figure 3-2: PCS-2012 PA Replicate 2 Cu ttings and Cavings Normalized ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 9 of 30 Figure 3-3: PCS-2012 PA Replicate 3 Cu ttings and Cavings Normalized Releases

Figure 3-4: PCS-2012 PA Mean and Quantile CCDFs for Cutti ngs and Cavings Normalized Releases, Replicates 1-3CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 10 of 30 Figure 3-5: PCS-2012 PA Confidence Limits on Overall Mean for Cuttings and Cavings Normalized Releases

Figure 3-6: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Cuttings and Cavings ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 11 of 30 Figure 3-7: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Cuttings and Cavings VolumesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 12 of 30 3.2 Spallings Normalized Releases

PCS-2012 PA spallings releases are presented in this section and subsequently compared to results obtained in the PABC-2009. Figure 3-8, Figure 3-9, and Figure 3-10 contain PCS-2012 PA CCDFs for spallings releases. Mean and quant ile CCDF distributions for the three replicates are shown together in Figure 3-11. As seen in that figure, the 10 th percentiles for each replicate have releases sufficiently small as to not appear at all on the chosen axes. Moreover, the mean CCDF for each replicate beco mes larger than the 90 th percentile as releases increase. The large number of vectors with very sma ll spallings releases causes the distribution to be heavily rightskewed. This results in a mean that exceeds the 90 th percentile as releases increase. Figure 3-12 contains the 95 percent confidence limits about the spallings mean. In total, 38 % of the replicate 1 vector, 47 % of the replicate 2 vector s and 41 % of the replicate 3 vectors in the PCS2012 PA showed non-zero spallings releases

To facilitate comparisons of spallings releases calculated in the PCS- 2012 PA to those obtained in the PABC-2009, overall mean and volume CCDFs obtained in these two analyses are plotted simultaneously in Figure 3-13 and Figure 3-14. As seen in those figures, the PCS-2012 PA CCDF curves shown in Figure 3-13 and Figure 3- 14 show increases in spallings releases and volumes when compared to PABC-2009 results. Spallings volumes, a nd their associated releases, are a function of reposit ory pressure. A pre ssure increase in an intruded waste panel typically corresponds to an increa se in spallings volumes. As nothing was changed regarding the waste inventory used in the PABC-2009 and the PCS-2012 PA, an increase in spallings volume results in an associated increase in spallings releases. The ROMPCS design implemented in the PCS-2012 PA has slightly lower long-term pe rmeabilities (on average) than the Option D closures implemented in the PABC-2009. For intrus ion scenarios that invo lve an encounter with a pressurized brine region below the repository, the reduction in closure permeability resulted in an increase in pressurization of the waste panel for a period of time following the intrusion. This increase in pressure translates directly to increases in PCS-2012 PA spallings volumes and releases as compared to the PA BC-2009 results. For intrusion sc enarios that do not involve an encounter with a region of pressu rized brine below the repository, the mean average pressure in the intruded waste panel was higher in the PCS- 2012 PA as compared to the PABC-2009. This increase in pressure also yields increases in spallings volumes and their associated releases. Increased pressure in repository waste areas is responsible for the in creases seen in PCS-2012 PA spallings volumes and releases as compar ed to the PABC-2009 results (Kicker 2012).CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 13 of 30 Figure 3-8: PCS-2012 PA Replicate 1 Spallings Normalized Releases

Figure 3-9: PCS-2012 PA Replicate 2 Spallings Normalized ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 14 of 30 Figure 3-10: PCS-2012 PA Replicate 3 Spallings Normalized Releases

Figure 3-11: PCS-2012 PA Mean and Quantile CCDFs fo r Spallings Normalized Re leases, Replicates 1-3CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 15 of 30 Figure 3-12: PCS-2012 PA Confidence Limits on Overall Mean fo r Spallings Normalized Releases

Figure 3-13: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Spallings ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 16 of 30 Figure 3-14: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Spallings VolumesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 17 of 30 3.3 Normalized Direct Brine Releases

PCS-2012 PA normalized direct brin e releases are presented in th is section and subsequently compared to results obtained in the PABC- 2009. Figure 3-15, Figure 3-16, and Figure 3-17

contain PCS-2012 PA CCDFs for D BRs. Mean and quantile CCDF distributions for the three replicates are shown together in Figure 3-18. Figure 3-19 contains th e 95 percent confidence

limits about the DBR overall mean. As seen in Figure 3-19, the overall mean and its lower/upper 95% confidence limits are well below acceptable release limits.

To facilitate comparisons of DBRs calculated in the PCS-2012 PA to those obtained in the PABC-2009, overall mean and volume CCDFs obtai ned in these two analyses are plotted together in Figure 3-20 and Figur e 3-21. As seen in Figure 3-20, the CCDF curve obtained for direct brine releases shows greater mean probab ilities in the PCS-2012 PA for the majority of

release values.

In the PCS-2012 PA, intrusion scenarios that invol ve drilling into a pre ssurized brine region underneath the repository exhibited an increase in the average pressure in the intruded waste panel when compared to the PABC-2009 results for a period of time following the intrusion (Malama 2012). Additionally, an increase in m ean waste panel brine saturation was found for this type of intrusion (Malama 2012). The combin ation of an increase in waste panel pressure

and brine saturation leads to an increase in DBR volumes, as well as a greater number of nonzero brine volume vectors for PCS-2012 PA compared to PABC-2009 (Camphouse 2012b). For intrusion scenarios that do not involve drilling into a pressurized brine region underneath the repository, there is an increase in mean waste panel pressure accompanied by a small decrease in brine saturation for the PCS-2012 PA compared to the PABC-2009 (Malama 2012). This results

in an increase in maximum DBR volume for the PCS-2012 PA. This increase in pressure of the intruded panel as compared to the PABC-2009 impact ed the number of DBR realizations used to calculate the DBR release tables (Malama 2012) . The total number of nonzero DBR volumes increased from 2,999 in the PABC-2009 to 3,182 in the PCS-2012 PA, an increase of 183

realizations with a nonzero D BR volume (Malama 2012). For undi sturbed conditions, the longterm mean waste panel pressure and brine pressure also incr eased from the PABC-2009 to the PCS-2012 PA. The is due to the implementation of the ROMPCS design, which allows greater brine flow into the waste panel than the Opti on D design, resulting in greater gas generation and thus mean waste panel pressure (Camphouse 2012b).

However, despite the greater number of nonzero DBR volumes found in the DBR analysis (Malama 2012), the number of nonzero DBR rele ase vectors found in the CCDFGF analysis

remains the same from the PABC-2009 to the PC S-2012 PA. The increase in mean DBR releases

is due to increased releases in only a few vectors, and is not attr ibuted to an overall increase in releases for a majority of vectors (Kirchner 2012). Additional evidence of the influence of a few vectors on the DBR volumes is found in Figure s 5-1 to 5-10 of the PCS-2012 PA DBR report (Malama 2012), which show that the DBR volume distribution skews toward higher volumes only for the high end of the distribu tion. The final result is an in crease in mean probabilities for the PCS-2012 PA compared to the PABC-2009 fo r the majority of DBR release values.

The overall mean CCDF curves for direct br ine volumes obtained in the PCS-2012 PA and the PABC-2009 are shown together in Figure 3-21. Fo r probabilities less than about 0.1, the meanCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 18 of 30 DBR volume increased, most likely due to the incr ease in waste panel pre ssure observed in the Salado flow modeling results as compared to the PABC-2009. The increase in the number of

realizations with a no nzero DBR volume combined with th e increase in the maximum DBR volumes found in the Salado flow modeling re sults (Camphouse 2012b) explain the differences

observed in the CCDF DBR volume curves obtained in the PABC-2009 and the PCS-2012 PA.

Figure 3-15: PCS-2012 PA Replicate 1 Normalized Direct Brine Releases

Figure 3-16: PCS-2012 PA Replicate 2 Normalized Direct Brine ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 19 of 30 Figure 3-17: PCS-2012 PA Replicate 3 Normalized Direct Brine Releases

Figure 3-18: PCS-2012 PA Mean and Quantile CCDFs for Normalized Direct Brine Releases, Replicates 1-3CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 20 of 30 Figure 3-19: PCS-2012 PA Confiden ce Limits on Overall Mean for Normalized Direct Brine Releases

Figure 3-20: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Normalized Direct Brine ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 21 of 30 Figure 3-21: PCS-2012 PA and PABC-2009 Ov erall Mean CCDFs for Direct Brine VolumesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 22 of 30 3.4 Normalized Transport Releases to the Culebra

PCS-2012 PA normalized transport releases to th e Culebra are discussed in this section and compared to those seen in the PABC-2009. These results are included prim arily as a means to validate the expectation that th e proposed changes to the PCS investigated in the PCS-2012 PA have minimal impact on Culebra transport releases.

Replicate means obtained in the PCS-2012 PA and the PABC-2009 for normalized transport

releases to the Culebra are show n together in Figure 3-22. As s een in that figure, the means obtained in the two analyses fo r each replicate are identical. Overall means of transport releases

to the Culebra obtained in the PCS-2012 PA an d the PABC-2009 are shown together in Figure 3-23. As is evident from that figure, there is no difference in the overall mean of transport

releases to the Culebra obtained in the two analyses. The indi vidual replicate means and the overall mean of transport releases to the Cule bra are primarily unaffected by the panel closure design changes implemented in the PCS-2012 PA. As a result, it is reasonable to conclude that normalized transport releases from the Culebr a be primarily unchanged as well, since nothing was changed in the Culebra transport m odel from the PABC-2009 to the PCS-2012 PA.CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 23 of 30 Figure 3-22: PCS-2012 PA and PABC-2009 Replicate Means for Normalized Transport Releases to the Culebra

Figure 3-23: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Transport Rele ases to the CulebraCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 24 of 30 3.5 Total Normalized Releases

Total normalized releases for PCS-2012 PA are pr esented in this section and subsequently compared to results obtained in the PABC-2009. Total releases are calculated by forming the summation of releases across each potential re lease pathway, namely cuttings and cavings releases, spallings rel eases, direct brine releases, and tr ansport releases. PCS-2012 PA CCDFs for total releases are presented in Figure 3-24, Figure 3-25, and Figure 3-26 for replicates 1, 2, and 3, respectively. Mean and quantile CCDF dist ributions for the three replicates are shown together in Figure 3-27. Figure 3-28 contains the 95 percent confidence limits about the overall mean of total releases. As seen in Figure 3- 28, the overall mean for normalized total releases and its lower/upper 95% confidence limits are well below acceptable release limits. As a result, the panel closure design and repository configur ation changes investigated in the PCS-2012 PA do no result in WIPP non-compliance with the c ontainment requirements of 40 CFR Part 191.

PCS-2012 PA and PABC-2009 overall mean CCDFs fo r total releases are shown together in Figure 3-29. As seen in that figure, the overa ll mean CCDFs obtained in the two analyses are nearly identical for release values less than ap proximately 0.1 EPA units. For releases greater than 0.1 EPA units, the CCDF curv e obtained in the PCS-2012 PA is higher than that found in the PABC-2009. This increase corresponds primarily to the differences found for direct brine releases between the two analyses as discussed in Section 3.3 and illustra ted in Figure 3-20. The differences found for spallings may slightly af fect the total CCDF curve as well (Section 3.2, Figure 3-13). PCS-2012 PA cuttings and cavings results are unchanged from those found in the PABC-2009. The panel closure design change inve stigated in the PCS-2012 PA has an impact

on the overall mean of total releases from the PABC-2009 to the PCS-2012 PA due to the changes in direct brine releases calcu lated in those anal yses (Figure 3-30).

A comparison of the statistics on the overall mean for total normalized releases obtained in the

PCS-2012 PA and the PABC-2009 can be seen in Table 1. At a probability of 0.1, values

obtained for mean total releases has increased from 0.09 to 0.10 for the PCS-2012 PA. At a probability of 0.001, the increase in DBRs seen at that probability in the PCS-2012 PA results in an increase in the mean total release by approxima tely 0.41 EPA units. An increase is seen in the 95% confidence limit when compared to the PABC-2009 results, while the 90 th percentile

remains the same. An increase in the mean to tal release accompanied by no change to the 90 th
percentile value is additional evidence that only a few vectors have significantly increased

releases.

Probability Analysis Mean Total

Release 90 t h

Percentile Lower

95% CL Upper

95% CL Release

Limit

0.1 PCS-2012 PA 0.10 0.17 0.10 0.10 1

PABC-2009 0.09 0.16 0.09 0.10 1

0.001 PCS-2012 PA 1.51 1.00 0.33 2.81 10

PABC-2009 1.10 1.00 0.37 1.77 10

Table 1: PCS-2012 PA and PABC-2009 Statistics on the Overa ll Mean for Total Normalized Releases in EPA Units at

Probabilities of 0.1 and 0.001CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 25 of 30 Figure 3-24: PCS-2012 PA Replicat e 1 Total Normalized Releases

Figure 3-25: PCS-2012 PA Replicat e 2 Total Normalized ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 26 of 30 Figure 3-26: PCS-2012 PA Replicat e 3 Total Normalized Releases

Figure 3-27: PCS-2012 PA Mean and Quantile CCDFs for Total Normalized Releases, Replicates 1-3CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 27 of 30 Figure 3-28: PCS-2012 PA Confid ence Limits on Overall Mean for Total Normalized Releases

Figure 3-29: PCS-2012 PA and PABC-2009 Overall Mean CCDFs for Total Normalized ReleasesCCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 28 of 30 Figure 3-30: PCS-2012 PA Primary Compon ents Contributing to Total Releases



### 4 SUMMARY

Total normalized releases calculated in the PC S-2012 PA remain below their regulatory limits. As a result, the panel closure design and reposito ry configuration change s investigated in the PCS-2012 PA do not result in WIPP non-compliance with the containment requirements of 40 CFR Part 191. Cuttings and ca vings releases and direct brin e releases are the two primary release components contributing to total releases in the PC S-2012 PA. Cuttings and cavings

releases are identical to those calculated in the PABC-2009. Changes in total releases are primarily attributed to changes calculated in di rect brine releases from the PABC-2009 to the

PCS-2012 PA. Increases are observed in PCS-2012 PA spallings releases as compared to the PABC-2009, but these differences are comparatively minor and do not have a significant impact

on the overall total norm alized releases f ound in the PCS-2012 PA.CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 29 of 30 

### 5 REFERENCES

Camphouse, R.C. 2012a. Analysis Plan for the 2012 WIPP Panel Closure System Performance Assessment A-161, Revision 0. Sandia National Laboratories, Carlsbad, NM. ERMS 557726.

Camphouse, R.C. 2012b. Analysis Package for Sa lado Flow Modeling D one in the AP-161 (PCS-2012) Performance Assessment. Carlsb ad, NM, Sandia National Laboratories. ERMS

558204

Camphouse, R.C, D.C. Kicker, T.B. Kirchner, J.J. Long, B. Malama, and T.R. Zeitler. 2012c. Summary Report and Run Control for the WIPP P anel Closure System Performance Assessment

. Carlsbad, NM: Sandia National Laboratories. ERMS 558226.

Clayton, D.C., Camphouse, R. C., Garner, J. W., Ismail, A. E., Kirchner, T. B., Kuhlman, K. L., and Nemer, M. B.. 2010. Summary Report of th e CRA-2009 Performance Assessment Baseline

Calculation. Sandia National Laboratorie s. Carlsbad, New Mexico, ERMS 553039.

DOE (U.S. Department of Energy). 1996. Title 40 CFR Part 191 Compliance Certification Application for the Waste Isolation Pilot Plant. DOE/CAO-1996-2184. U.S. Department of Energy, Waste Isolation Pilot Plant, Carlsbad Area Office. Carlsbad, NM.

DOE (U.S. Department of Energy), 2011. Panel Closure System Design, Planned Change Request to the EPA 40 CFR Part 194 Certificati on of the Waste Isolation Pilot Plant. U.S. Department of Energy, Carlsbad Fiel d Office. Carlsbad, New Mexico.

EPA (U.S. Environmental Protection Agency). 1998. Criteria for the Certification and

Re-Certification of the Waste Isolation Pilot Plants Compliance with the 40 CFR Part 191 Disposal Regulations: Certifi cation Decision; Final Rule, Federal Register , Vol. 63, No. 95, pp. 27353-27406. U.S. Environmental Protection Agency, Office of Air and Radiation, Washington, D.C.

Helton, J. et al. 1998. Uncertainty and Sensitiv ity Analysis Results Obtained in the 1996 Performance Assessment for the Waste Isolation Pilot Plant. Sandia National Laboratories, Albuquerque, NM. SAND98-0365.

Kicker, D.C. 2012. Analysis Package for Cuttings, Cavings, and Spallings: Panel Closure System Performance Assessment (PCS-2012 PA). Sandi a National Laboratories, Carlsbad, NM.

Kirchner, T. 2010. Sensitivity of the CRA-2009 Performance Assessment Baseline Calculation

Releases to Parameters. Sandia Nationa l Laboratories, Carlsbad, NM. ERMS 552960.

Kirchner, T. 2012. Sensitivity of the AP-161 (P CS-2012) PA Releases to Parameters. Sandia National Laboratories, Carlsbad, NM.CCDFGF Analysis Package for the AP-161 (PCS-2012) Performance Assessment

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Page 30 of 30 Malama, B. 2012. Analysis Package for Direct Brine Releases: 2012 Panel Closure System Performance Assessment (PCS-2012 PA). Sandia National Laboratories, Carlsbad, NM. ERMS

558226.

U.S. Environmental Protection Agency (EPA ). 1996. 40 CFR Part 194: Criteria for the

Certification and Recertification of the Waste Isolation Pilot Plant’s Compliance with the 40 CFR Part 191 Disposal Regul ations; Final Rule. Federa l Register, Vol. 61, 5223-5245.