Date: M

To:
From:

Technic a

QA Revi e

M anage m Subject:

1.0 Int
The W a develop e disposal U.S. En v the Cod e contain m means o f (SNL). radionuc 10,000 y informat i features, and the p therein a reposito r first was t WIPP w WIPP P A (CCA) o M ay 3, 201 2

WIPP Reco
R. Chris C a Michael G r Courtney G Dwayne C. Bill Thom p

a l Review:

e w:

m ent Revie w

Recommen Panel Clos u roduction
ste Isolatio n e d by the U

of transura n v ironmental P e of Federal m ent require m

f performan c

WIPP P A l ide release s ears after fa i on as part events, an d p arameters a lso result i n r y recertific a t e shipment aste panel c A regulator y o f 1996. P a 2

rds Cente r

a mphouse ( 6 r oss, WTS S u G . Herrick, S

Kicker, Th e p son, Golder
Ross Kirk e

Shelly Ni e

w : Janis Tro n

dations and u re Syste m D

n Pilot Pl a U .S. Depart m n ic (TRU) w a

P rotection A Regulation s m ents acco r c e assessme n A calculati o s from the r e cility closur of an ongo i d processes t

used in the m n updates to a tion proces at the site i n

c losures co m y complianc e a nel closure s 6 211)

u bcontracto r andia Natio n e S.M. Stoll e

Associates

e s

e lsen

n e

Justificatio n D esign Mod e

a nt (WIPP), m ent of E n a ste. Conta i A gency (EP A s (CFR), Pa r r ding to the n t (PA) cal c o ns estimat e e pository to t

e. The mo d i ng process. t ypically res u m . Planne d WIPP PA s that occu r n 1999.

m prise a fe a e demonstr a s are includ e

1 r n al Labs (6 2 er Corporati o

n s of Param e e led in the P

located i n n ergy (DOE ) i nment of T R A ) accordin g r t 191. The

Certificatio c ulations pe r e the pro b t he accessib l d els used in P

Improved u lts in refin d changes t o models. W r s at five-ye

a ture of the a tion since t h e d in the re p Oper a

2 11) o n

e ter Values f P CS-2012 P A

n southeast e

) for the g R U waste at g to the regu l

DOE dem o o n Criteria i n r formed by S b ability an d

l e environ m P A are mai n

informatio n n ements and

o the repos i W IPP PA m o

e ar intervals

repository t h e Complia n pository as a ted for the U.S. D e Sandia Co Defense Waste M a 4100 National Par k Carlsbad, New M e

f

or the Run- o A

e rn New M g eologic (de

the WIPP i s l ations set f o o nstrates co m

n Title 40 C S andia Nati o d conseque n m ent for a re g

n tained and u n regarding

modificati o i tory and/o r o dels are us e

following t

t hat has be e n ce Certific a a safety m e e partment of Ener g rporation a nagement Progra k s Highway e xico 88220

o f-Mine Sal t

M exico, has

ep undergr o s regulated b o rth in Title m pliance wi t C FR Part 1 9 o nal Labora t n ce of pot e g ulatory per i u pdated wit h

important W o ns to PA m r the compo e d to suppo r t he receipt o

e n represen t a tion Appli c e asure duri n g y by the

ms

t

been o und) b y the

40 of t h the 9 4 by t ories e ntial i od of h new W IPP m odels

nents r t the o f the

t ed in c ation n g the2 operational period. In particular, their presence in the repository is a means to protect workers from exposure to two potential hazards: 1) volat ile organic compounds that may be present in emplaced waste materials and 2) an explosion which has been hypothesized to occur from gas generation causing methane concentration in the wa ste panels to reach a su fficiently high level. Panel closures were not develope d to isolate radionuclides in the repository after closure. The DOE stated in the CCA (DOE 1996) that “The panel closure system was not designed or intended to support long-term repository performance.” Panel closures are included in WIPP PA models principally because th ey are part of the disposal system, not because they play a substantive role in inhibiting the release of radionuclides to the outside environment. The WIPP was certified to re ceive TRU waste in 1998. The 1998 rulemaking had several conditions, one of which involved the design of the panel closure system (PCS) implemented in the repository. The DOE presented f our design options in the CCA, and “The EPA based its certification d ecision on the condition that DOE implement the most robust design [referre d to in the CCA as “Option D”]. The Agency found the Option D design to be adequate, but also determined that the use of a Salado Mass Concrete- using brine rather than fresh waterwould produce concrete seal permeabilities in the repository more consistent with the values used in DOE’s performance assessment. Therefore, Condition 1 of the EPA’s certificati on requires DOE to implement the Option D PCS at the WIPP, with Salado Mass Concrete” (EPA 1998). The Option D panel closure system consists of three primary components: 1) a concrete block wall (the explosion wall), 2) open drift, and 3) a concrete monolith. The arrangement and dimensions of these components are illustrated in Figure 1.

Figure 1: A Schematic of th e “Option D” Panel Closure Extensive refinement to WIPP panel closur e modeling in PA has occurred since the implementation used in the CCA (Vugrin an d Wagner 2006). In the CCA and the PAVT (MacKinnon and Freeze 1997) that followed, regulatory compliance was demonstrated with a generic panel closure that was not Option D. Following certification of the WIPP in 1998, and the mandate that Option D be implemented as th e panel closure in WIPP, a PA was conducted in 2002 (Hansen 2002) with the aim of implementing an Option D panel closur e into the repository W a s te d is p o s a l O p e n D rift

C o n cre te M o n o lith 7 .9 m 9 .1 m

E x p lo s io n W a ll 3 .7 m

40 m 2 .4 o r 2 .7 m

2 .4 m DRZ

DRZ O p e n D rift3 models used in WIPP PA, and to assess the im pacts of panel closur e design on long-term repository performance. Two panel closure cases were cons idered. The first was modeled upon the mandated Option D panel closure design. The second was the generic panel closure design implemented in the CCA and PAVT. Upon comple tion of the analysis, it was found that total normalized releases resulting from the two panel cl osure cases were nearly identical. Moreover, nearly identical distributions for each release co mponent were calculated in the two panel closure cases. A more granular representation of the Option D panel closure was developed during the 2002 – 2003 Technical Baseline Migration (TBM) PA . Upon completion of the TBM PA, it was found that the TBM and PAVT produced releases that are nearly iden tical, indicating that repository performance is not si gnificantly affected by changes in the panel closure properties (Dunagan 2003). The Option D panel closure representation developed during the TBM was used for the panel closure representation in the 2004 and 2009 Compliance Recertification Applications (CRA-2004 a nd CRA-2009, respectively). Panel closures are represented in PA by way of their material pr operties and spatial extent. Due to the regulatory time scale of 10,000 years for which regulatory compliance must be demonstrated, there are uncertainties associated with panel closure material properties. These uncertainties in material properties are incorp orated in PA. A material property with an associated uncertainty is assigned a distribution, and th is distribution is randomly sampled. This sampling process allows for repository performan ce to be quantified over a range of material conditions, as well as an analysis of performance sensitivity to changes in material properties. As briefly described above, numer ous studies have been conducte d to date, often by way of full PA analyses, to quantify the impact of changes in panel clos ure material propert ies on regulatory compliance. In addition, several PA analyses have been performed (Hansen 2002, Vugrin & Dunagan 2006, Camphouse et al 2011) with the aim of determining the impact of panel closure redesigns on repository performance. Regulatory compliance has been met in all PA analyses performed to date, including those that incor porated changes to panel closure modeling. Regulatory compliance has been repeatedly shown to be primarily insensitive to panel closure material properties. A future PA is planned that incorporates a new panel closure design into the current PA baseline established by the 2009 Pe rformance Assessment Ba seline Calculation (PABC-2009) (Clayton et al., 2010). The name given to this planned panel closure PA is PCS2012. The PCS-2012 will quantify impacts of a run- of-mine (ROM) salt panel closure design by comparing total normalized releases to t hose found in the PABC-2009 where Option D was implemented as the panel closure. Calculations and analyses have been performed to develop material properties to be used in the PCS- 2012, and are documented in DOE (2012) and Herrick (2012). This memorandum provides hydrologic and pore compressibility parameter values for the revised PCS in the PCS-2012 PA. Paramete rs are created as discussed in NP 9-2, Parameters . PCS-2012 parameters not listed in the memorandum will be equal to the values prescribed to them in the PABC-2009. In the di scussion that follows, material parameters and timings are developed to account for the fo llowing physical processe s and accepted rock mechanics principles:
1. Creep closure of the salt rock surrounding pa nel entries will cause consolidation of ROM salt emplaced in panel entries.4 2. Eventually, the ROM salt comprising the clos ures will approach a condition similar to intact salt. 3. As ROM salt reaches higher fractional densitie s during consolidation, back stress will be imposed on the surrounding rock mass leadin g to eventual heali ng of the disturbed rock zone (DRZ). 4. DRZ healing above and below the ROM salt panel closures will reduce DRZ porosity and permeability in those areas. A brief discussion of creep and reconsolidation of run-of-mine salt, and the DRZ healing that results, is the topic of the next section. 2.0 Creep and Reconsolidation of Run-of-Mine Salt 2.1 Creep Closure in Salt The ability of salt to deform w ith time, eliminate voids, and crea te an impermeable salt barrier around the waste was one of the principal reason s for locating the WIPP repository in a bedded salt formation. The creep closure process is a complex and interdependent series of events starting after a region within the repository is ex cavated, which creates a disturbance in the stress field. Stress relief results in some degree of brittle fracturing and the formation of a DRZ surrounding excavations in all deep mines. For the WIPP, the DRZ is characteri zed by an increase in permeability, and may ultimately ex tend a few meters from the excavated region. Stress relief generates deviator ic stresses in the host rock, causing salt to deform by creep processes and to move inward to fill the excavat ed void. This process of salt creep will continue until deviatoric stress is dissipated and the system is once again at stress equi librium (DOE 1996, Section 6.0.2.2 and Appendix PORSURF). Eventual ly, at equilibrium, deformation ceases, and the panel entry and any backfill (such as ROM sa lt) have undergone as much compaction as is possible by the weight of the rock above the repo sitory horizon. 2.2 Mechanical Behavior of Run-of-Mine Salt The mechanical behavior of ROM salt, which is also referred to as crushed salt, has been extensively studied and can be di vided into three basi c categories: elastic deformation, inelastic deformation, and failure (Callahan et al. 1995, S ection 2.4.1). The inelastic behavior can further be divided into time-independent (instantan eous compaction) and time-dependent (creep consolidation) deformation. A number of parameters or characteristics are expected to affect the mechanical behavior of crushed sa lt. These parameters include (but are not limited to) density (or porosity), grain size and grain size distribution, moisture content, impurity content (such as clay, anhydrite, etc.), temperature, stress state (i.e., co nfining pressure and stress difference), and time. Crushed salt is proposed as the main componentof the redesigned panel closure, and over time this crushed salt will be consolidated by the cr eep closure of the entry. Crushed salt is also proposed as one component of the shaft seal, and an assessment of the mechanical behavior of crushed salt is provided as pa rt of the WIPP shaft sealing system design (DOE 1996, Appendix SEAL). If salt reconsolidation is unimpeded by flui d pore pressures, the mate rial will eventually achieve extremely low permeabilities approachi ng those of the native Salado Formation. Developments in support of th e WIPP shaft seal system have produced confirming experimental results, constitutive material models, and construction methods that substantiate use of a salt5 column to create a low permeability seal component. Other advantages of the use of crushed salt for sealing systems is that as a replacement of the natural material in its original setting it ensures physical, chemical, and mechanical compatibility with the host formation. 2.3 Response of the Disturbed Rock Zone An underground excavation creates a disturbed zone in the surrounding ro ck. Microfracturing will occur in the rock adjacent to the drift wall, where confining stresses are low or nonexistent. The extent of the zone depends on the rock st rength and the prevailing stress state, which is depth dependent. In terms of WIPP repository applications, one of the most important features of salt as an isolation medium is its ability to heal previously damage d areas (Hansen 2003, Section 4.1). Damage recovery, or healing, arises when the magnitude of the deviatoric stress decreases relative to the applied mean stress. A decrease in deviatoric stress occurs as stresses approach lithostatic conditions, as would be the circumstance adjacent to the crushed salt barrier when it reaches a consolidated state. The healing mech anisms include microfracture closure and bonding of fracture surfaces. Microfractur e closure is a mechanical res ponse to increased compressive stress applied normal to the fractures, while bon ding of fracture surfaces occurs either through crystal plasticity, a relatively slow process, or pressure solution and redeposition, a relatively rapid process (Spiers et al., 1988). Evidence for healing has been obtained in laboratory experiments, small-scale tests at WIPP and th rough observations of field analogs (Hansen 2003, Sections 4.5, 4.6, and 4.9). 2.4 Impact of ROM Salt Reconsolida tion on Porosity and Permeability Numerical modeling conducted as part of shaft seal ing analyses provide s density of the compacted salt column as a function of depth a nd time. Many calculations comparing models for consolidation of crushed salt were performed to quantify performa nce of the crushed salt column in the shaft seal (DOE 1996, Appendix SEAL; Ca llahan et al. 1995; Brods ky et al. 1996). From the density-permeability relationship of reconsolidating crushed salt, permeability of the compacted salt seal component is calculated. In general, results show that the bottom of the salt column consolidates rapidly, achieving permeability of 1×10 -19 m 2 in about 50 years. By 100 years, the middle of the salt co lumn reaches similar permeability. Structural analysis calculations were developed to determine the fractional density of the crushed salt seal as a function of time and depth and, using these results, to determine permeability of the crushed salt as a function of time and depth (DOE 1996, Appendix SEAL, Section 7.4.2.1). The results of these calculations indicate that co mpacted salt will increase from its emplaced fractional density of 90% to a density of 95% approximately 40, 80, and 120 years after emplacement at the bottom, middle, and top of the shaft seal, respectively. Using the modified Sjaardema-Krieg creep consolidatio n model, the times required to fully reconsolidate the crushed salt to 100% fractional density are 70 years, 140 y ears, and 325 years at the bottom, middle, and top of the salt column, respectively. Based on these results, the desired fractional densities (hence, permeability) can be achieved over a substantial length of the compacted salt seal in the range of 50 to 100 years.Additio n and 5.1. 2 Section 5 flow pro damage a ROM sa l
3.0 R The DO E Conditio n WIPP. F reassess e easier to Accordi n revised d design o f feet of r u from on g emplace d as comp l the RO M permeab i

(a) P

(b) P n al details o n 2 . Based o n 5 .1.1, it is e perties indi s a nd heal is l t and the su r R evised Des i
E has submi t n 1 of the F F ollowing t h e d the engin e

construct a n n gly, the P C d esign for th e f the PCS, k n u n-of-mine ( g oing minin g d in a panel l etely as pr a M salt to co n

i lity.

anel closur e

anel closur e Fig u n the porosi t n the calcu l e xpected th a s tinguishabl e a time-dep e r rounding D ig n of the P C

t ted a plann e F inal Certi fi h e selectio n e ering of th e n d equally e C R submitt e e panel clos u n own as the ( ROM) salt w g operation s entry. The R a cticable. A n solidate to

e with 100 f e

e with 100 f e

u re 2. Sche m t y and per m l ations cite d a t a comple t e from natu r e ndent proc e D RZ will ret u

C S

e d change r e fi cation Rul e n of the Op t e panel clos u e ffective at p e d to EPA r u res be app r

Run-of-Mi n w ith b arrier s s at the WI P R OM salt w A fter emplac

a condition

e et of ROM s

e et of ROM s

m atic diagra m

6 m eability of R d above and t ely consoli d r al Salado s e ss; eventua l u rn to that o f

e quest (PCR ) e making for t ion D pan e u re and esta b p erforming r equested t h r oved for us e n e Panel Cl o s at each en d P P and may w ill be empl a

ement, cree p approachin

s alt betwee n

s alt betwee n

m

of the revi R OM salt a r

on in situ d ated ROM s alt. The a b l ly, the per m f intact salt.

) to the EP A

40 CFR P a e l closure d e b lished a re v

its operatio n h at Conditi o e in all pane o sure Syste m d (Figure 2 ) be compac t a ced to all s a p closure o f g intact sal t

n two ventil a

n a ventilati o

sed panel cl o r e provided observation s

salt-filled d b ility of sal t m eability o f

A requesting

a rt 194 (EP A e sign in 19 9 v ised design n al-period i s o n 1 be cha n

ls (DOE, 2 0 m

(ROMPC S ) . The RO M t ed and/or m a lt surfaces ( f the panel e t , with low p

a tion bulkhe a

o n bulkhead

osure desig n in Sections s as descri b d rift will ac h t to recover f the consoli

that EPA m A, 1998) f o 9 8, the DO E which is si m s olating fun c n ged, and t 0 11). The r e S ), comprise M salt is gen e

m oistened a s ( back, walls , e ntries will c p orosity an d

a ds

& explosio n

n

Concrete block wall 5.1.1 b ed in

hieve from dated

m odify

o r the E has m pler,

c tion. t hat a e vised

s 100 e rated s it is

, etc.) c ause d low

n wall7 The barriers will consist of ventilation bulkheads, similar to those currently used in the panels as room closures (Figure 3). The ventilation bu lkheads are designed to restrict air flows and prevent personnel access into waste- filled areas during the operational phase. In Panels 1, 2, and 5, where explosion walls fabricated from concre te blocks have already been emplaced in the panel entries, an explosion wall is the inbye barri er and a ventilation bulkhead will be the outbye barrier, as shown in Figure 2b. The emplacement scheme for the ROM salt will be finalized once in situ testing has been completed. It is expected that the final empl acement scheme will involve some degree of inplace compaction, with or without added moisture (moisture may be added because it accelerates the consolidation of the crushed salt). The emplacement technique and/or strategy is not important to long-term repository performance. In particular, th e uncertainty in the final panel closure emplacement strategy is not a result of consideration of long-term panel closure characteristics. Panel closures are emplaced in the repository to protect workers during the operational phase of the facility. Emplacement uncer tainty is due to curre nt lack of operational experience in constructing/emplaci ng this type of closure system . The method used will be based on consideration of various operational variables. Cost, efficiency, short-term effectiveness, dust control, and other factors will all play into the final emplacement scheme. A range of possible emplacement strategies are be ing assumed in the PCS-2012 to develop panel closure materials, properties, and timings represen tative of all potential emplacement strategies. At one end of the range is emplacement of dr y ROM salt without any initial compaction. The uncompacted porosity of ROM salt is assumed to be 35%, based on several sources. Callahan and Devries (1991, Section 4.1 and Ta ble 2-2) define the initial density of crushed salt as about 65% of intact density, based on data from (Sjaardema and Krieg, 1987) and (Weatherby, 1989). This initial density corresponds to an initial por osity of approximately 35% for the crushed salt. Recent work on backfill compaction in the German repository program also assumes an initial backfill porosity of 35% (Rot hfuchs and Wieczorek, 2010). The uncompacted ROM salt is therefore assumed to have an in itial porosity of 35%, equivalent to a fractional density of 65%. At the other extreme, the ROM salt may be emplaced in compacted layers that are wetted with a small amount of moisture to enhance the initial emplacement density and short-term consolidation. The average porosity of the compacted layers is estimated to be greater than 20%, based on engineering judgment. The values of th e hydrologic and mechanical parameters for the PCS-2012 PA are intended to enco mpass both of these extremes.The RO M at the re p small a m chemica l the repo s the host r 4.0 M o A new P b etween design o f used for in the P C closure i m modeled b e modi f Option D
The RO M years to 2 panel cl o Figure 3. T
M salt is che p ository ho r m ount of m o l ly similar t o s itory. The m r ock and wi t

o delin g Ap p P A baseline

the PABC

f the PCS. M the PABC- 2 C S and the d m plemente din the PCSf ied slightl y D

. M PCS prop e 2 00 years, a o sure mode l T ypical desi g mically co m r izon and b e o isture. The o the iron- ba m aterials in t t h the mater i

p roach for P

was establi s

- 2009 and t h M ore speci fi 2 009, but w i d isturbed ro c d in the PA B

2012 is 100 y to accoun t

e rties will b n d from 20 0 l ing underta k g n of a vent i

m patible wit h e cause it ha s

sheet meta l a sed metals i t he redesign e i als already i
P CS-2012 P A

s hed by the h e PCS-20 1 fi cally, the P i th new pro p c k zone dir e B C-2009 is 4

feet (30.48 t for the re d

b e based on 0 years to 1 0 k en in the 2

8 i lation bulk h
h the host ro c s no additiv e l in the ven t i n the wast e e d PCS will i n the repos i
A
PABC-200 9 1 2 PA will P CS-2012 P A p erties for t h e ctly around 4 0 meters l o meters) lon g d uction in l e

three time p 0 ,000 years. 2 006 PCS P h ead that bl o

c k because i es, except f t ilation bul k e and waste c

therefore be i tory.

9 (Clayton e be a direct A will use t h h e materials

the PCS. N o ng (Figure g . The PAB e ngth of th e

periods: fro This is a re f P A (Vugrin o cks the pan e i t is mined f r f

or the poss i k head has s m c ontainers t h e chemicall y

e t al., 2010)

consequen c t he BRAGF L that repres e N ote that th e

1) while th e B C-2009 BR A

e ROMPC S

m 0 to 100 f inement to t and Dunag a e l entry

r om the hos t i ble additio n m all mass a h at are alre a y compatibl e

. The differ e c e of the r e L O grid tha t e nt the RO M e Option D p e redesigne d A GFLO gri d S as compar

years, fro m t he granular a n 2006) a n t rock n of a a nd is a dy in e with

e nces e vised

t was M salt

p anel d PCS d will r ed to

m

100 r ity of n d the2011 PC to conso l the proc e approxi m as PCS_ T years. S i material s The ven t These bu creep cl o This wal l through n conditio n spalling the salt. I under in c 1.2 to 1. 5 layer of b inch beh i 3R PA (Ca m l idate the R O e ss to heal f r m ately 200 y

T 1 for the f i i milarly, th e s DRZ_PCS

_ t ilation b ul k u lkheads are o sure of the p l is inspecte d n umerical m n of the fre e o r slabbing I n contrast, t c reasing loa d 5 inches an d b ricks that h i nd the free s

Figure 4. S u m phouse et a O M salt occ u r actures in t h ears. The R O i rst 100 yea r e DRZ dir e

_ T1, DRZ_ P
k heads are d e

not expect e p anel entrie s d on a regul a m odeling (e. g e face in Pa n

of the conc r t he plastic p r d due to sal t d quite cons i h ave becom e s urface.

u rface spall i a l 2011). T h u rs over a p h e DRZ sur r O M salt wil l r s, PCS_T2 f e ctly above P CS_T2, an d

e signed to p e d to remai n s . The expl o a r basis, an d g . RockSol, n el 1 d urin g r ete blocks a r operties on creep. The i stent. The r o e detached a

i ng at the ba s

Panel 1 du r

9 h ree time pe r

rimary time r ounding th e l therefore b f

or 100 to 2 and below d DRZ_PC S

p rovide isol a n intact 100 y o sion wall is d the anticip a

2006). Fi g g February 2 a s a result o the ROMP C thickness o o d in Figur e a nd pushed o

s e of the ex p r ing Februa r r iods are ap p scale of ap p e PCS occu r e represent e 00 years, a n

the ROM S _T3.

a tion only d u y ears after r also design e a te d conditi o g ures 4 and 5 2 012. The e o f the loadi n C S will allo w f the slabs s e 5 is ancho r o ut by the f o

p losion wall r y 2012 p ropriate b e c p roximately r s over a lo n e d by three m n d PCS_T3 f

salt will b e

d uring the o p r epository c l e d for the o p o n of the wa l 5 present p h e xplosion w a n g caused b y w it to reco n s hown in Fi g r ed by a nu t o rmation of

in the intak e c ause the pr

100 years, w n ger time sc a m aterials, de n f

or 200 to 1 0 e represent e

p erational p e l osure beca u p erational p e l l is also ass h otographs o a ll shows s u y inward cr e n solidate an d g ure 4 is typ i t resting on a

a crack ab o

e drift of ocess w hile a le of n oted 0 ,000 e d by

e riod. u se of e riod. essed o f the u rface e ep of d heal i cally a thin o ut anFi g

Numeric the rib c emplace m out; ho w not be s i b ehavior significa n analysis during t h through explosio n 5.0 P C
As disc u this clos u ROM sa l as the R surroun d permeab i the surr o values f o ROM sa l g ure 5. Surf a

al stress an a ontacts will m ent (Rock s w ever, it is e x

gnificant st r of concret e n t impact o n of material h e initial 1 0 t he closure n wall will b
S Paramet e

u ssed in Sec t

u re will ca u l t will appr o R OM salt r e d ing rock m a

i lity. These p o unding DR Z o r a complet e l t and for th e a ce spalling

a lysis of the

be in a co n s ol, 2006, Fi x pected that r uctures aft e e . The ve n n long-term properties f 0 0 year pe r system wil l b e minimal.

e rs

t ion 2.0, th e u se consoli d o ach a cond i e aches high e a ss leading p rocesses a n Z are discu s e set of hyd r e DRZ direc t at the top c o Panel 1 du r

concrete ex p n dition of p l gures 7 and the spalling e r the initial n tilation bul k

performan c f

or the PCS r iod after r e l be throug h

e salt rock s u d ation of R O i tion equiva l e r fractiona to healing n d their effe c s sed in Sect i r ologic para m t ly above a n

10 o rner of the e r ing Februar y
p losion wall l astic yield

10). No lo n and yield w 100 year ti m k heads and c e of the pa n

and the D R e pository cl h the DRZ s

u rrounding t O M salt e m l ent to intac t l densities, of the DR Z c t on porosi t i on 2.0. Th i m eters and t h n d below the e xplosion w a r y 2012.
l has demon s with an un y n g term stre s w ill be progr e

m e perio d , d explosion w n el closure s R Z surroun d osure, the p s o any infl u

t he panel e n m placed in p

t salt. Duri n

a back str e Z and a red u

t y and per m i s section o f h e pore co m PCS. a ll in the int

s trated that t y ielded core s s analyses h e ssive, and t d ue to the b w alls will t h s and are n o d ing the PC p rimary po t u ence from t

n tries is cre e p anel entrie s n g the cons o e ss will be u ction in D m eability of t

f this mem o m pressibility ake drift of

t he free fac e by 7 years h ave been c a t hat the wall s rittle, non-p h erefore ha v o t included i

S. Additio n t ential flow t he bulkhe a

e ping close d s . Eventuall y o lidation pr o

imposed o n D RZ porosit y

t he ROM sa l o randum pr o

parameter f o e s and

after a rried s will p lastic v e no i n the n ally,

path a ds or

d , and

y the o cess, n the y and l t and o vides o r the11 5.1 Hydrologic and Pore Compressibil ity Parameters for the ROM Salt 5.1.1 Porosity of ROM Salt Estimates of the consolidation process have been made in a series of cal culations (Herrick 2012) carried out using JAS3D (Blanford et al., 2001; DOE, 2012, Figures 4 through 7) with the Sjaardema and Krieg (1987) model for crushed salt, modified with a deviatoric creep compaction response (Stone, 1997). Separate calculations were performed fo r initial emplacement porosities of 20%, 25%, 30%, and 35%, which correspond to in itial fractional densities of 80%, 75%, 70%, and 65%, respectively. These calculations show c onsolidation to a porosity of 5% in 65 years from an initial porosity of 20% and in 152 year s from an initial porosi ty of 35%. The results from the JAS3D calculations during the first 150 years are summarized in Table 1 as a function of time and initial emplacement porosity.

Table 1. Porosity predicted by JAS3D for ROM salt in a panel en try as a function of time and initial emplacement porosity Time After Emplacement (Years) Porosity 0 20% 25% 30% 35% 50 6.6% 10.3% 14.6% 18.7% 100 1.9% 4.2% 7.3% 10.7% 150 1.0% 1.2% 2.9% 5.2% During the first time period, from 0 to 100 years, the data in Table 1 show th at the porosity of the ROM salt decreases rapidly. In orde r to represent this time varying porosity in a way suitable for long-term performance assessment calculations, it is reasonable to define the range of porosity of the ROM salt at the midpoint of this time interval, 50 years. The porosity range for the first 100 years is then 6.6% to 18.7%, base d on the second row of data in Table 1. This range explicitly accounts for the uncertainty in initial emplacement porosity for the ROM salt. For the time period from 100 to 200 years, the poro sity range is 2.5% to 7.5%, with an expected or mean porosity of 5%. The lower limit for the por osity range, 2.5%, is essentially the same as the lower limit of porosity from the JAS3D calcu lations at 100 years, 1 .9% (see Table 1). The upper limit for the porosity range, 7.5%, is less than the maximum porosity from the JAS3D calculations at 100 years, which is 10.7% (see Table 1); however, the JAS3D calculation for ROM salt with an initial porosity of 35% pred icts a porosity of 7.5% by 126 years after emplacement. The value of 7.5% as an upper limit is also consistent with the magnitude of the porosity range for intact halite. That is, the magnitude of the porosity range from 100 to 200 years is 7.5% - 2.5% = 5%, approximately equal to the magnitude of the observed porosity range for intact salt, which is 5.19% - 0.1% = 5.09% (DOE 2009, Appendix PA, Parameter 17; Ismail 2007). Finally, the mean porosity, 5%, is consiste nt with the JAS3D pred ictions at 100 years, which have a porosity range of 1.9% to 10.7% at 100 years afte r emplacement (see the 3rd row of data in Table 1).
A number of sources corroborate the use of a reduced upper limit, 7.5% rather than 10.7%, during the second time period. Hurtado et al. ( 1997) carried out a numb er of consolidation12 estimates for the proposed crushed salt component of the shaft seals. The proposed crushed salt component of the shaft seals wi ll consist of mined WIPP crushed salt, dynamically precompacted with added moisture to a porosity of 10%. Calcul ations of the consolida tion of this component due to creep closure of the shaft indicate that the crushed salt will be at an essentially intact condition (a fractional density approaching 1) wi thin 100 years at a depth of 515 m and within 60 years at a depth of 600 m (Hurtado et al. 1997, Fi gure 2-3). Additional calculations by Callahan (1999) show consolidation results for different crushed salt models at depths of 430 m, 515 m, and 600 m, indicating similar results to Hurta do et al. (1997). Callah an and DeVries (1991) conducted calculations on the closure of disposal rooms backfilled with crushed salt that show closure to essentially intact de nsity in about 25 years. Collectiv ely, these alternate calculations imply that a mean porosity of 5% and an uppe r limit of 7.5% by 100 years after emplacement are reasonable and conservative values. The consolidation process will continue after 200 years, particularly for ROM salt that is emplaced dry with minimal compaction. This is accounted for by assigning a third time period, 200 to 10,000 years, during which consolidation of the ROM salt will continue and achieve a porosity similar to that of intact sa lt regardless of the emplacement strategy. In situ observations from the BAMBUS II project at the Sigmundshall mine in Germany indicat e consolidation of a crushed salt slurry to essentially an intact condition w ithin tens of years (B echthold et al., 2004, Figure 2.57). Consolidation to an es sentially intact condition is also confirmed by observations at the Rocanville mine, where a consolidated salt plug was emplaced after a water inflow, and has been effective in sealing off a hydrostatic gr oundwater pressure of about 1200 psi (8.3 MPa) (Van Sambeek et al., 1995). The state of the int act halite at WIPP therefore provides an analog for the long-term consolidated state of ROM salt in a panel entry. Table 2 summarizes the values for porosity of the ROM sa lt as a function of time.
The values in Table 2 indicate that there is a significant overlap between the porosity ranges for the 100 to 200 year and the 200 to 10,000 year time periods. Mo re specifically, the 2.5% to 5.19% porosity range is included in both time peri ods, although this range represents the lower end of the porosity range from 100 to 200 years and the upper end of the porosity range from 200 to 10,000 years. This representation is very re asonable because the consolidation process will continue after 200 years, particularly for ROM sa lt that is emplaced with minimal compaction, and because the JAS3D predictions show that th e rate of consolidation decreases significantly after 100 years, making an overlap in the porosity range likely to occur as porosity decreases to in situ values. Table 2. Porosity of the ROM salt during three time periods

Parameter Time Period Assumed Porosity Notes PCS_T1:POROSITY 0 to 100 years 6.6% to 18.7% Assumes ROM salt is emplaced with an initial porosity of 20% to 35%. An initial porosity of 35% represents no compaction during emplacement. PCS_T2:POROSITY 100 to 200 yrs 2.5% to 7.5% 2.5% to 7.5% is cons istent with the JAS3D calculations and is conservative relative to alternate computational predictions from several sources. PCS_T3:POROSITY 200 to 10,000 yrs 0.1% to 5.19% Assumes that the porosity of crushed salt after 200 years is equal to the porosity for intact halite.13 5.1.2 Permeability of ROM Salt Laboratory experiments on consolidated cores of crushed salt confirm that the intrinsic permeability of crushed salt decreases as the fractional density of the cores increases (Hurtado et al. 1997, Figure 2-1). This observation is corroborat ed by other experiments on the behavior of crushed salt under similar conditions to WIPP (C ase et al., 1987; Zhang et al., 2007); although the cores tested by Zhang et al. (2007) are for sa lt from the Asse mine and some of the core tested by Case et al. (1987) is for salt from Av ery Island, the overall be havior of the crushed material is expected to be similar. The general observations from testing of crushed salt cores are that: (1) intrinsic permeability decreases as th e fractional density increases (or as the porosity decreases), (2) crushed salt cores with added mois ture generally have lower values of intrinsic permeability than dry cores, and (3) cores of crushed salt with smaller grain sizes generally have lower values of intrinsic permeability than cores with larger grain sizes. The first and third observations are generally valid for all granular materials, while the second observation specifically relates to the microstructure of the salt cores and require s further explanation. At equivalent fractional densit ies, dry consolidated salt core s are more permeable than wet consolidated salt cores because of the difference in the mechanism causing consolidation. Under dry conditions, the effective consolidation me chanism is crystal plasticity, while under wet conditions the effective consolidation mechanism is pressure solution/r edeposition (Hurtado et al. 1997, page 2-7; Case et al., 1987, Section 4). Pressure solution/redeposition under wet conditions generally produces higher consolida tion rates and more deformation than crystal plasticity under dry conditions, leading to lowe r measured permeability for wet consolidated salt than for dry consolidated salt at equivalent fr actional densities (Hurta do et al. 1997, Figure 2-1; Case et al., 1987, data for Test 3 in Figure 1). During the first time period, from 0 to 100 years, the porosity of the ROM salt varies from 6.6% to 18.7% (see Table 2). Table 3 summarizes permeability data for cores of crushed salt that are relevant to the maximum porosity of 18.7%. The data are from three sources: Hurtado et al. (1997), Case et al. (1987), and Zhang et al. (20 07). Hurtado et al. (1997) summarizes data from (Brodsky 1994) and (Brodsky et al., 1996) for wet and dry cores, respectively. The permeability data from the three sources are remarkably c onsistent and provide a basis for defining the maximum permeability as approximately 10 -12 m 2 at a porosity of 18.7%. Table 3. Permeability data for core s of crushed salt at 18.7% porosity

Source Porosity Permeability (m 2 ) Notes (Brodsky et al., 1996), summarized in Table 2-1 of (Hurtado et al., 1997) 17.8% 4.11×10 - 13 m 2 For dry WIPP salt at fractional density of 0.822 (porosity of 17.8%). This co re has the greatest porosity of the data in (Brodsky et al., 1996) and (Brodsky 1994). Case et al., 1987, Figure 1 18.7% 1×10 - 13 m 2 to 2×10 -12 m 2 For dry WIPP salt with 0.9 mm and 10 mm maximum grain sizes (Tests 1 and 2) and for moistened WIPP salt with 20 mm maximum grain size (Test 3). Zhang et al., 2007, Figure 4 18.7% 2×10 - 13 m 2 to 1×10 -12 m 2 For dry Asse salt cores with maximum grain size of 32 mm.14 At the minimum porosity value of 6.6% during th e first 100 years after f acility closure, the measurements have a wide range of permeability because of the microstructure of the cores. Table 4 has the measured values that are rele vant to a porosity of 6.6%. The gas permeability data for dry cores at 6.6% are relatively consistent from the three sources, falling within a permeability range of 10 -15 m 2 to 10 -14 m 2 . The brine permeability from Case et al. (1987) is lower than the brine permeability from Hurtado (1994), which may be caused by the maximum grain size for the cores. Test 3 from Case et al. (1987, Table 1) has a maximum grain size of 20 mm, while the maximum grain size of ROM WI PP salt was measured at 1.5 inches (38 mm) (Pettigrew and Associates, 1993), or almost twice as large as the crushed salt for Test 3. Cores with finer grain sizes are expected to have lowe r permeability than cores with larger grain sizes, which may explain the observed difference in permeability from different sources. Table 4. Permeability data* for cores of crushed salt at 18.7% porosity

Source Porosity Permeability (m 2 ) Notes (Brodsky et al., 1996) & (Brodsky, 1994), summarized in Table 2-1 of (Hurtado et al., 1997) 6.61%

6.67% 4.95×10 - 15 m 2

2.14×10 -19 m 2 For dry WIPP salt at a fractional density of 0.9339 (porosity of 6.61%)(Brodsky et al., 1996) For wet WIPP salt at a fractional density of 0.9333 (porosity of 6.67%)(Brodsky 1994) Case et al., 1987, Figure 1 6.6%

6.6% 1×10 - 15 m 2 to 1×10 -14 m 2

1×10 -21 m 2 to 1×10 -20 m 2 For dry WIPP salt with 0.9 mm and 10 mm maximum grain sizes (Test 1 and Test 2) For wet WIPP salt with 20 mm maximum grain size (Test 3). Zhang et al., 2007, Figure 4 18.7% 1×10 - 14 m 2 For dry Asse salt cores wi th maximum grain size of 8 mm. *Data on fractional density and permeability from (Brodsky, 1994 ) and (Brodsky et al., 1996) are reproduced with the same number of digits in (Hurtado et al., 1997, Table 2-1) to facilitate identification of specific measurements in the data sets. The range of permeability for performance assessm ent should encompass the range of laboratory measurements shown in Tables 3 and 4. At a porosity of 18.7%, the maximum permeability is approximately 10 -12 m 2 . At a porosity of 6.6%, the brine permeability from Hurtado et al. (1997) is about 2×10 -19 m 2 . The brine permeability data from Case et al. (1987) are not used here because the maximum grain size for Test 3, 20 mm, is somewhat smaller than the measured maximum grain size for WIPP salt, 38 mm. We ther efore determine that the permeability of the ROM salt should be sampled from a log-uniform distribution, [2×10 -19 m 2 , 10 -12 m 2 ], during the first time period, from 0 to 100 years. During the second and third time periods, the perm eability of consolidated ROM salt is based on the experimental measurements of consolidated WIPP salt cores summarized in Hurtado et al. (1997) and further documented in additional Sandia documents (Brodsky, 1994; Brodsky et al., 1996; Ahrens and Hansen, 1995). This analysis us es the brine permeability data from Brodsky (1994) for two reasons. First, the salt cores ar e based on ROM salt from the WIPP and provide a consistent data set for defining permeability as a function of porosity. Second, the fractional densities of the salt cores measured by Brodsky (1994) have a range of 0.8953 to 1.0051 1 (porosity of 10.47% to ~ 0%, resp.), which encomp ass the porosity range of interest during the second and third time periods (see Table 2). The alternate data sets are either sparsely populated

1 A fractional density greater than 1 may imply uncer tainty in the assumed density of intact salt.15 at the porosities of interest duri ng the second and third time periods or are based on crushed salt with finer grain sizes than ROM salt from the WIPP. The permeability data from Brodsky (1994) are re presented as a functio n of porosity through a two-step relationship: (1) a least squares fit to the permeability data as a function of fractional density, and (2) a normal distributi on that represents the residuals of the data about the least squares fit. This approach captures the mean variability of permeability with porosity and represents the uncertainty in the data set. Figure 6 shows the least squares fit to the data from (Brodsky, 1994). Figure 7 is a quantile-quantile pl ot showing that a normal distribution provides a good representation of the residual s of the individual data points about the least squares fit. (The closeness of the individual points to the st raight line in Figure 7 indicates the goodness of fit by a normal distribution.) This normal distribu tion has a mean of 0.0 a nd a standard deviation of 0.86. The parameters for the normal distri bution are determined by the data, without adjustment or expert judgment. Given the limite d number of data points from Brodsky (1994), the normal distribution will be truncated at plus or minus two standard deviations. The relationship between porosity and permeab ility can be mathematically written as:

, 5353

. 1 ) 1 ( 187

. 21 ) log( 

    e k (1)

, 10 10 ) log(   e k k k e 

  (2)

where k e is the expected value of permeabil ity from the least squares fit,  is the sampled value of porosity, k is the final value of permeability, and  is the sampled value of a normal distribution with a mean of 0, a standard deviation of 0.86, and trunc ated at ±2 standard deviations.

Figure 6. Least squares fit to brine permeability measurements for WIPP crushed salt y = ‐ 21.187x + 1.5353 R2 = 0.3222

‐ 22 ‐ 21 ‐ 20 ‐ 19 ‐ 18 ‐ 17

0.88 0.9 0.92 0.94 0.96 0.98 1 1.02Log10(Permeability[m2])

Fractional Density Brine Data (Brodsky 1994) Linear Fit16 Figure 7. Quantile-quantile plot of the data residuals relative to th e linear fit and of the predicted residuals for a normal distribution with mean of 0.0 and standard deviation of 0.86 The following algorithm for representi ng the values of PCS_T1:PRMX_LOG, PCS_T2:PRMX_LOG and PCS_T3:PRMX_LOG in PA should be used: 1. The value of PCS_T1:POROSITY is sample d from a uniform distribution, [6.6%, 18.7%], in each realization. 2. The permeability [m 2 ] of ROM salt from 0 to 100 years, PCS_T1:PRMX, is sampled from a log-uniform distribution, [2×10 -19 m 2 , 10 -12 m 2 ], in each realization. The values of PCS_T1:PRMY and PCS_T1:PRMZ are set equal to PCS_T1:PRMX. 3. For each realization, the value for PCS_ T2:POROSITY between 100 and 200 years is sampled from a uniform distribution with a minimum of 0.025 and a maximum of 0.075. The value for PCS_T3:POROSITY between 200 and 10,000 years is sampled from a uniform distribution with a minimu m of 0.001 and a maximum of 0.0519. 4. Calculate the expected values of the log 10 ( k e ), the logarithm of th e expected permeability, using Equation (1) with the sampled values of PCS_T2:POROSITY and PCS_T3:POROSITY. 5. Sample a normal distribution (mean of zero, sta ndard deviation of 0.86) that is truncated at ±2 standard deviations and calculate th e final value of the permeability, k, using Equation (2). This ca lculation is performed twice, once for 100 to 200 years, and a second time for 200 to 10,000 years. This samp ling is performed on ce per realization. ‐ 2.5 ‐ 1.5 ‐ 0.5 0.5 1.5 2.5

‐ 2.5

‐ 1.5

‐ 0.5 0.5 1.5 2.5ResidualofLog10(K[m2])fromLinearFit

Residual for a Normal Distribution17 6. The values of PCS_T2:PRMX, PCS_T2:PRMY, and PCS_T2:PRMZ are set equal to the value of k for the second time period. Th e values of PCS_T3:PRMX, PCS_T3:PRMY, and PCS_T3:PRMZ are set equal to the value of k for the 200 to 10,000 year time period. Figure 8 shows the range of perm eability as a function of fracti onal density for this algorithm. Table 5 presents numerical values of the mini mum, and maximum permea bility from 0 to 100 years, from 100 to 200 years, a nd from 200 to 10,000 years based on this approach. For the latter two time periods, the mean permea bility is based on the sampled va lue of porosity (between 0.025 and 0.075 for 100 to 200 years, a nd between 0.001 and 0.051 9 for 200 to 10,000 y ears), as defined by the least squares fit (Equation (1)). The minimum and ma ximum permeabi lity values correspond to -2 and +2 standard deviations on the normal distribution, respectively (Equation (2)). The 2.5% to 5.19% porosity range is included in both the 100 to 200 year and the 200 to 10,000 year time periods (see discussion in Section 5.1.1), and represents the lower end of the porosity range from 100 to 200 years and the upper end of the porosity range from 200 to 10,000 years. This provides an overlap in the permeability ranges for these two time periods, although the effect is mitigated by sampling the uncertainty in the data about the least squares fit in Figure 8. With this algorithm, the calculated permeability value for 200 to 10,000 years may be greater than the calculated perm eability value for 100 to 200 years. This is not a reasonable outcome, so the permeability value for 200 to 10 ,000 years should be sampled so th at it is never greater than the permeability value for 100 to 200 years.

Figure 8. Variation of permeability with fractional density, based on the least squares fit and a normal distribution with a mean of 0. 0 and a standard deviation of 0.86

‐ 22 ‐ 21 ‐ 20 ‐ 19 ‐ 18 ‐ 17 ‐ 16 ‐ 15

0.88 0.9 0.92 0.94 0.96 0.98 1 1.02Log10(Permeability[m2])

Fractional Density (= 1 ‐  ) Brine Data (Brodsky 1994) ±1 Standard Deviation ±2 Standard Deviations Linear Fit18 Table 5. Permeability of the ROM salt during three time periods
Parameter(s) Porosity Fractional Density Minimum a, b Permeability Maximum a, b Permeability PCS_T1: PRMX_LOG, PRMY_LOG, PRMZ_LOG 6.6% to 18.7% 0.825 to 0.933 -18.7 (2×10 -19 m 2 ) -12 (1×10 -12 m 2 )

PCS_T2: PRMX_LOG, PRMY_LOG, PRMZ_LOG 0.025 0.975 -20.8 (1.44×10 -21 ) -17.4 (3.96×10 -18 ) 0.075 0.925 -19.8 (1.65×10 -20 ) -16.3 (4.55×10 -17 ) PCS_T3: PRMX_LOG, PRMY_LOG, PRMZ_LOG 0.001 0.999 -21.4 (4.46×10 -22 ) -17.9 (1.23×10 -18 ) 0.0519 0.9481 -20.3 (5.34×10 -21 ) -16.8 (1.47×10 -17 )

a Each cell has the log( k [m 2 ]) and the corresponding value of k in parentheses. b Minimum corresponds to -2 standard deviations below the least squares fit; maximum corresponds to +2 standard deviations above the least squares fit. The permeability values in Table 5 and Fi gure 8 are reasonable and appropriate and are supported from several viewpoints:

 From 0 to 100 years, the crushed salt is assigned a permeability range of 2×10 -19 m 2 to 10 -12
m 2 , representative of the combined test results from Hurtado et al. (1997), Case et al. (1987), and Zhang et al. (2007) for loosely consolidated ROM salt.

 From 100 to 200 years, the pe rmeability range in Table 5 en compasses a wide range of possible outcomes, from a mi nimum permeability of 1.44×10 -21 m 2 to a maximum permeability of 4.55×10 -17 m 2 . This range will produce a range of hydrologic responses for the ROM salt, from very “tight ” to much “looser” in terms of brine and gas flows across the closure. This wide range has been chosen because of the uncertainties in emplacement of the ROM salt.

 From 200 to 10,000 years, the permeability range in Table 5 represents the response of fully compacted salt, with a mi nimum permeability of 4.46×10 -22 m 2 and a maximum permeability of 1.47×10 -17 m 2 . This range of values is purposefully greater than the range for intact halite in PA, which is 10 -24 m 2 to 10 -21 m 2 . The consolidation mechanisms for moistened versus dry crushed salt are different and can lead to different degrees of interconnected porosity and permeability for a give n effective porosity. In this situation, the very low permeability of intact salt may not be attained for thousands of years by the ROM salt.

 After 100 years, the range of pe rmeability in Table 5 is simila r to the permeability range for material DRZ_PCS in the PABC-2009, which is 2×10 -21 m 2 to 1×10 -17 m 2 (Clayton et al. 2010), as discussed in Section 5.2 of this memorandum. The ranges of permeability after 100 years are therefore consistent with the e xpected response for a healed DRZ above and below a panel closure, as represented in PABC-2009.19 5.1.3 Residual Brine Saturation and Resi dual Gas Saturation of ROM Salt The residual gas saturation is the degree of ga s saturation necessary to create an incipient interconnected pathway for a porous material to be permeable to gas. The residual gas saturation for all materials in the original shaft seal mode l, including crushed salt, was defined for the CCA (DOE, 1996, Appendix PAR, Parameter 14). The residual gas satura tion was based on a literature review for consolidated geologic materi als, concrete, and asphalt, and on professional judgment. Similarly the residual brine saturation fo r all shaft seal materials, including crushed salt, was defined for the CCA based on a litera ture review and on prof essional judgment (DOE, 1996, Appendix PAR, Parameter 15). The residual br ine saturation and resi dual gas saturation of the ROM salt in the PCS will use the same distri butions as the corresponding parameters for the crushed salt component of the shaft seals. Th ese distributions are summarized in Table 6.
Table 6. Residual brine saturation and re sidual gas saturation of the ROM salt Parameter Distribution PCS_T1:SAT_RBRN PCS_T2:SAT_RBRN PCS_T3:SAT_RBRN Cumulative distribution: Probability Value 0.0 0.0 0.5 0.2 1.0 0.6 PCS_T1:SAT_RGAS PCS_T2:SAT_RGAS PCS_T3:SAT_RGAS Uniform distribution: Minimum value: 0.0 Maximum value: 0.4 5.1.4 Relative Permeability Model and Capillary Pressure Model for ROM Salt Several two phase flow models have been impl emented in the BRAGFLO code, and the values of the parameters RELP_MOD and CAP_MOD define the relative permeability model and the capillary pressure model for a material, respec tively. Most materials mapped to the BRAGFLO grid use a modified Brooks-Corey model for relative permeability, with the exception of the anhydrite Marker Beds and Anhydrite Layers a and b (DOE, 2009, Table PA-4), which switch between the Brooks-Corey and Va n Genuchten models for relati ve permeability. The two phase flow model for the ROM salt will also use the modified Brooks-Corey model, which corresponds to relative permeability model number 4 (i.e., RELP_MOD = 4) (DOE, 2009, footnote to Table PA-4) and use capillary pressure model numb er 2 (i.e., CAP_MOD = 2), which has a fixed maximum capillary pressure. The choice of these models is independent of the timing of the consolidation process. Table 7 summarizes these values. Table 7. Relative permeability model and cap illary pressure model for the ROM salt Parameters Value PCS_T1:RELP_MOD PCS_T2:RELP_MOD PCS_T3:RELP_MOD 4 (a modified Brooks –Corey model) PCS_T1:CAP_MOD PCS_T2:CAP_MOD PCS_T3:CAP_MOD 2 (fixed maximum capillary pressure)20 5.1.5 Other Two Phase Flow Parameters Table 8 identifies seven parameters for the rela tive permeability and capillary pressure models for the ROM salt. All WIPP PA materials us e the same values for KPT, PC_MAX, and PO_MIN. The crushed salt materials and concrete-r elated materials for the original shaft seal model use the same values and distributions for the COMP_RCK, PCT_A, PCT_EXP, and PORE_DIS parameters shown in Ta ble 8. The values or distributi on in Table 8 will be used for the ROM salt, independent of the time period. Table 8. Two phase flow parameters for the ROM salt

Parameter Description Type Value COMP_RCK Bulk Compressibility Constant 8.0x10 - 11 Pa - 1 KPT Flag for permeability determined threshold Constant 0.0 (dimensionless) PO_MIN Minimum brine pressure for capillary model KPC=3 Constant 1.01325×10 5 Pa PC_MAX Maximum allowable capillary pressure Constant 1×10 8 Pa PCT_A Threshold pressure linear parameter Constant 0.56 Pa PCT_EXP Threshold pressure exponential parameter Constant -0.346 (dimensionless) PORE_DIS Brooks-Corey pore distribution parameter Cumulative distribution Probability V alue 0.0 0.11 0.5 0.94 1.0 8.1

5.2 Hydrologic and Pore Compressibility Parameters of the DRZ Surrounding the ROMPCS 5.2.1 Porosity and Permeability of the DRZ Initially it is expected that the DRZ around the PCS will be no different from that around the disposal rooms, since there will be only very sm all back stress from the consolidating ROM salt. Calculations for closure of pane l entries and consolidation of th e ROM salt have been performed for two bounding cases: (1) ROM salt that is emplaced and compacted to 20% porosity (80% fractional density), and (2) ROM sa lt that is emplaced without compaction to 35% porosity (65% fractional density) (Herrick 2012). The results of these calculati ons demonstrate that the time dependent backstress does not become appreci able until approximately 200 years after emplacement. While the back stress is low, the state of the DRZ surrounding the PCS will be similar to the state of the DRZ surrounding the dis posal rooms, and it is appropriate to maintain the same ranges of DRZ porosity and DRZ pe rmeability above and below the PCS as those around the disposal rooms during the first 200 y ears. Thus, the porosity of DRZ surrounding the PCS lies between 0.0039 and 0.0548 for the firs t 200 years (i.e. the same porosity range prescribed for material DRZ_1 in the PABC- 2009). The permeability of the DRZ surrounding the PCS has a range of 10 -12.5 m 2 to 10 -19.4 m 2 for the first 200 years.After 20 shown i n rapidly u For exa m

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l22 Figure 10. Vertical back stress on the roof of the panel entry for ROM salt with an initial emplacement porosity of 35% (fracti onal density of 65%) (Herrick 2012) Given the values of back stress calculated for closures with some degree of emplaced compaction, and the rapid increase of stress even for the most extreme case of salt that is emplaced without compaction (see Figure 10), the back stress is expect ed to heal the DRZ directly above and below the ROMPCS, reducing its porosity and its permeability. It is then appropriate to assume that the porosity a nd permeability of the DRZ after 200 years will be equivalent to the state of the DRZ surrounding the Option D panel closure in the PA for CRA2009 (DOE, 2009, Appendix PA) and in the PABC- 2009. The porosity of the DRZ directly above and below the Option D pa nel closure in the PA for CRA-2009 and in the PABC-2009 has a minimum value of 0.0039 and a maximum value of 0.0548 at all times. The permeability of the DRZ directly above and belo w the Option D panel closure has a minimum value of 2×10 -21 m 2 and a maximum value of 1×10 -17 m 2 (DOE, 2009, Appendix PA, Sections PA-4.2.8.2 and PA4.2.8.3). We have chosen that these ranges be used for the DRZ surrounding the ROMPCS after 200 years. Table 9 summarizes the ranges for poros ity and permeability for the DRZ directly above and below the ROMPCS. The selected porosity for the DRZ directly above a nd below the PCS is constant at all times. After 200 years, it is reasonable to expect that the heal ing of the DRZ caused by increasing back stress will reduce the DRZ porosity. A redu ction in DRZ porosity should have minimal impact on the PCS-2012 PA because sensitivity cal culations have demonstrated that PA results are insensitive to the porosity of a panel closure, and by extensio n to the porosity of the DRZ directly above and below the ROMPCS (DOE 2012, Response to EPA Question 1.2b).23 Table 9. Porosity and permeability of the DRZ surrounding the PCS Parameter Value Notes DRZ_PCS_T1:POROSITY DRZ_PCS_T2:POROSITY DRZ_PCS_T3:POROSITY 0.0039 to 0.0548 Same range in the PA for CRA-2009 and the PABC-2009 as for the DRZ (material DRZ_1) around disposal rooms at all times. DRZ_PCS_T1:PERMEABILITY DRZ_PCS_T2:PERMEABILITY 10 - 19

. 4 m 2 to 10 -12.5 m 2 Same permeability range in the PA for CRA2009 and PABC-2009 for the DRZ (material DRZ_1) surrounding disposal rooms from 0 to 200 years. DRZ_PCS_T3:PERMEABILITY 2×10 - 21 m 2 to 1×10 -17 m 2 Same permeability range in the PA for CRA2009 and PABC-2009 for the DRZ_PCS above and below the Option D panel closures after healing of the DRZ. 5.2.2 Two Phase Flow Parameters for Materials DRZ_PCS_T1 and DRZ_PCS_T2 During the first 200 years, while th e back stress is low, the stat e of the DRZ surrounding the PCS will be similar to the state of the DRZ surrounding the disposal rooms, and it is appropriate to maintain the same values for two phase flow pa rameters for the DRZ directly above and below the ROMPCS as those for the DRZ around the dispos al rooms. Table 10 identifies the values for the two phase flow parameters and th eir sources during the first 200 years. 5.2.3 Two Phase Flow Parameters for DRZ_PCS_T3 After 200 Years After 200 years, the back pressu re from the consolidated ROM salt is expected to heal the fractures in the DRZ directly a bove and below the PCS. In this state, the DRZ above and below the consolidated ROM salt is ex pected to have similar propert ies to the DRZ above and below the Option D monolith in the PA for the CRA -2009 and the PABC-2009. Therefore, the two phase flow parameters for the DRZ directly ab ove and below the ROM sa lt shall be assigned the same values and distribution as the DRZ_PC S in the PA for CRA-2 009 or the PABC-2009. Table 11 identifies the values for the two phase flow parameters and their sources after 200 years.24 Table 10. Two phase flow parameters for the DRZ directly above and below the ROMPCS during the first 200 years Parameter Description Value Source DRZ_PCS_T1:SAT_RBRN DRZ_PCS_T2:SAT_RBRN Residual brine saturation 0.0 DOE, 2009, Table PA-3 for material DRZ_1 DRZ_PCS_T1:SAT_RGAS DRZ_PCS_T2:SAT_RGAS Residual gas saturation 0.0 DOE, 2009, Table PA-3 for material DRZ_1 DRZ_PCS_T1:RELP_MOD DRZ_PCS_T2:RELP_MOD Relative permeability model number 4 (modifiedBrooksCorey model) DOE, 2009, Table PA-4 for material DRZ_1

DRZ_PCS_T1:CAP_MOD DRZ_PCS_T2:CAP_MOD Capillary pressure model number 1 (capillary pressure is unbounded) DOE, 2009, Table PA-4 for material DRZ_1 DRZ_PCS_T1:KPT DRZ_PCS_T2:KPT Flag for permeability determined threshold 0.0 Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T1:PO_MIN DRZ_PCS_T2:PO_MIN Minimum brine pressure for capillary model KPC=3 1.01325x10 5 (Pa) Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T1:PC_MAX DRZ_PCS_T2:PC_MAX Maximum allowable capillary pressure 1.0x10 8 (Pa) Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T1:PCT_A DRZ_PCS_T2:PCT_A Threshold pressure linear parameter 0.0 DOE, 2009, Table PA-3 for material DRZ_1 DRZ_PCS_T1:PCT_EXP DRZ_PCS_T2:PCT_EXP Threshold pressure exponential parameter 0.0 DOE, 2009, Table PA-3 for material DRZ_1 DRZ_PCS_T1:PORE_DIS DRZ_PCS_T2:PORE_DIS Brooks-Corey pore distribution parameter 0.7 DOE, 2009, Table PA-3 for material DRZ_1 Table 11. Two phase flow parameters for the DR Z directly above and be low the ROMPCS after 200 years Parameter Description Value Source DRZ_PCS_T3:SAT_RBRN Residual brine saturation 0.0 DOE, 2009, Table PA-3 for material DRZ_PCS DRZ_PCS_T3:SAT_RGAS Residual gas saturation 0.0 DOE, 2009, Table PA-3 for material DRZ_PCS DRZ_PCS_T3:RELP_MOD Relative permeability model number 4 (modifiedBrooksCorey model) DOE, 2009, Table PA-4 for material DRZ_PCS

DRZ_PCS_T3:CAP_MOD Capillary pressure model number 1 (capillary pressure is unbounded) DOE, 2009, Table PA-4 for material DRZ_PCS DRZ_PCS_T3:KPT Flag for permeability determined threshold 0.0 Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T3:PO_MIN Minimum brine pressure for capillary model KPC=3 1.01325x10 5 (Pa) Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T3:PC_MAX Maximum allowable capillary pressure 1.0x10 8 (Pa) Stein, SNL, ERMS 520524, Table 2 DRZ_PCS_T3:PCT_A Threshold pressure linear parameter 0.0 DOE, 2009, Table PA-3 for material DRZ_PCS DRZ_PCS_T3:PCT_EXP Threshold pressure exponential parameter 0.0 DOE, 2009, Table PA-3 for material DRZ_PCS DRZ_PCS_T3:PORE_DIS Brooks-Corey pore distribution parameter 0.7 DOE, 2009, Table PA-3 for material DRZ_PCS25 6.0 Summary
The DOE has submitted a planned change reques t to the EPA proposing that a revised panel closure design be approved for use in all WIPP wast e panels. Panel closures are emplaced in the WIPP to protect workers during the operational phase of the facility. They are represented in PA because they are a significant physical featur e of the repository. Long-term repository performance has been repeatedly shown to be insensitive to pane l closure material properties. The revised panel closure design proposed by the DOE is compri sed of 100 feet of run-of-mine salt with barriers at each end. A performance assessment named the PCS-2012 PA is planned to quantify regulatory compliance impacts resultin g from the incorporation of the new closure design in the repository. PA ma terials, properties, and timings are developed to allow for modeling of the revised panel closure system in the PCS-2012. These parameter choices are reasonable values that will adequately repres ent the PCS within PA, and are based on sound science, modeling, and external data sources where available. 7.0 References Ahrens, E.H., and F.D. Hansen. 1995. Large-Sc ale Dynamic Compaction Demonstration Using WIPP Salt: Fielding and Preliminary Results. Sa ndia National Laboratories. Albuquerque, NM. SAND95-1941. Bechthold, W., E. Smailos, S. Heusermann ,T. Bolli ngerfehr, B Bazargan Sabet, T. Rothfuchs, P. Kamlot, J Grupa, S. Olivella, and F. D. Hansen. 2004. Backfilling and Sealing of Underground Repositories for Radioactive Wast e in Salt (BAMBUS II Project) : final report. European Commission, Directorat e General for Research, Of fice for Official Publications of the European Communities. Call No: EUR 2062 1 EN. Showcased in Research for Europe: Successful EUfunded projects by the Directorate General for Research. Blanford, M.L., M.W. Heinstein, and S.W. Ke y. 2001. JAS3D: A Multi-Strategy Iterative Code for Solid Mechanics Analysis User’s Instruc tions, Release 2.0. Sandia National Laboratories. ERMS 552358. Brodsky, N.S., 1994. Hydrostatic and Shear Consolidation Tests With Permeability Measurements on Waste Isolation Pilot Plant Crushed Salt. Sandia National Laboratories. Albuquerque, NM. SAND93-7058. Brodsky, N.S., F.D. Hansen, and T. Pfeifle. 1996. “Properties of Dynamically Compacted WIPP Salt.” Proceedings of the 4th Intern ational Conference on the Me chanical Behavior of Salt, Montreal, Quebec, Canada, June 17-18, 1996. Sandia National Laboratories. Albuquerque, NM. SAND96-0838C. Callahan G.D. and K.L. DeVries. 1991. Analyses of Backfilled Transuranic Wastes Disposal Rooms. Sandia National Laboratories. SAND91-7052.26 Callahan, G.D., M .C. Loken, L.L. Van Sambeek, R. Chen, T.W. Pfeifle, J.D. Nieland, and F.D. Hansen. 1995. Evaluation of Potential Crushed- Salt Constitutive Models. Sandia National Laboratories. Albuquerque, NM. SAND95-2143. Callahan, G.D. 1999. Crushed Salt Constitutive M odel. Sandia National Laboratories, SAND98- 2680. Camphouse, R.C., Clayton, D.J., Kicker, D.C., and Pasch, J.J. 2011. Summary Report for the AP-151 (PC3R) Performance Assessment, Revision 1. Sandia National La boratories, Carlsbad, NM. ERMS 555489. Case, John B., Peter C. Kelsall, and James L. Withiam. 1987. Laboratory Investigation of Crushed Salt Consolidation. 28 th US Symposium on Rock Mechanics, Tucson, Arizona, 29 June – 1 July 1987. 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 , Revision 1. Sandia National Laboratorie s. Carlsbad, New Mexico, ERMS 553039. Costin, L.S. and W. R. Wawersik. 1980. Creep H ealing of Fractures in Rock Salt. Sandia National Laboratories. SAND80-0392. 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). 2004. Title 40 CFR Part 191 Compliance Recertification Application for the Waste Isolation Pi lot Plant. DOE/WIPP 2004-3231, 10 vols. U.S. Department of Energy, Carlsbad Field Office. Carlsbad, NM. DOE (U.S. Department of Energy). 2009. Ti tle 40 CFR 191 Parts B and C Compliance Recertification Application. DOE/WIPP-09-3424. Carl sbad Field Office. Carlsbad, New Mexico. DOE (U.S. Department of Energy), 2011. Pane l 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. DOE (U.S. Department of Energy), 2012. Respons e to First Set of EPA Questions to DOE, December 22, 2011

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. Sandia National Laboratories Internal Me morandum to B. M. Butcher, Division 6332, Albuquerque, NM. Zhang, Chun-Liang, Tilman Rothfuchs, and Johannes Droste, 2007. Post-tests on thermomechanically compacted salt backfill. The Mechanical Behavior of Salt – Understanding of THMC Processes in Salt, Wallner, Lux, Minkley and Hardy, Jr., Editors.