1

Enclosure August 2015 BRAGFLO Sensitivity Study Request Effect of Creep Clos ing Non

- Waste Areas on t he WIPP CRA 2014 PA

The information herein provides input values to be used to perform a set of BRAGFLO calculations to determine how, if at all, modeling creep
- closure of the non
- waste areas w ould affect the CRA

- 2014 WIPP PA calculations. The current CRA 2014 inputs for room porosity and permeability were derived using analys es conducted in the mid

- 1990s and based on a FEP screening for FEP DR

- 3

. The result s of the FEP screening analysis indicated modeling the time

varying closure of the non

- waste areas did not impact PA results. Now, approximately 20 years later, substantial changes in the repository design have occurred , waste panel closure seals have been modified 1 and a much larger experimental area is planned . In addition, modifications to the W IPP numerical grid during subsequent CRA PAs have been made

. As a result of these changes the EPA would like to have a re

- evaluation of FEP DR

- 3 to see if time

- varying properties of the
non
- waste areas would affect repository performance

. A brief summary o f the room closure modeling efforts to be used in this sensitivity study follows. Early Work Early in the project’s history WIPP field scientists conducted numerical model predictions on room closure rates based on their field experiments . Data from the se early field experiments were used as inputs in simulations of closure rates for both filled and empty waste rooms
. Specific ‘empty

- room’ closure rate calculations were based on in

- situ conditions (i.e. no heat added to the room) using closure data gathere d from experimental Room D. Room D is located on the far right side of the diagram in Figure 1. Results from these calculations were provided in a 1987 memo from Harold Morgan to D.E. Munson and the memo was included as an Appendix in Butcher et al. 1993 ( pages A

- 67 thru A

- 84). Morgan’s memo indicated that an empty room will creep close to a room porosity of approximately 22 % by 100 years. A porosity of 2% was predicted to occur at ~ 195 years, the modeled room shape at closure from Morgan’s memo is depic ted in Figure 2.

1 Some of the issues EPA raises in th is sensitivity study related to the impact of creep closure on the DRZ and the open rooms are also raised in EPA ’ s T echnical S upport D ocument (S. Cohen and Associates, 201 3) assessing the impacts of creep closure on DOE ’ s par ameterization of the run

- of

- mine

- alt panel closure design.2

Figure 1. The WIPP North Experiment al Room d imensions (in meters) during the mid
- 1980 ’s.

Then, as now, n umeric instabilities arise when the vertical and horizontal edges of the model cells begin to overlap. Because of these limita tions Morgan’s simulations went only to 200 years, the time when the model cells representing opposing room faces began to contact one another. Th ese limitations still provide enough information to assess when an empty room will approach the time to final end

- point porosity/closure. Morgan provide d a curve of the calculated initial room closure volume reduc tion with respect to time, given in Figure 3 of this memo. Figure 3 indicates at 44 years the room has a porosity of ~ 50% (0.5), at 100 years room poro sity is ~ 22% (0.22), and at 195 years an empty room will be almost fully closed. Given further creep closure compression of the room , it is reasonable to assume that soon after 200 years the room volume porosity will approach an asymptotic value. Extrapol ating on the Figure 3 curve it appears the room porosity would be reduced to ~ 1% (0.01) around 210 years. A porosity of 1% (0.01) is within the upper range of expected values for intact halite porosity.3

Figure 2. From Butcher and Mendenhall, SAND92
- 0427, (Morgan Memo , page A
- 76 )

Figure 3. Empty Room volume reduction calculations due to creep closure. From Butcher and Mendenhall, SAND92
- 0427, (Morgan Memo, page A
- 77 )
.4

For this sensitivity exercise , predicted room porosities for specified time periods will be based on the Morgan curve illustrated in Figure 3. For simplicity sake, the room porosity will be estimated from the Morgan curve for only 2 time periods. These time periods are 0 to 50 years
a nd 50 to 200 years

. Of interest is what would be the appropriate room permeability for the porosity time periods derived from the Morgan analysis . A relationship between room porosity and permeability was used in the 1995 FEP screening exercise. F or FEP DR

- 3 , the time

- varying permeability of an empty room was calculated as a function of room porosit y (page 69, Vaughn et. al, 1995) and expressed in E quation 1 given below.
k = a f ^n

a = 1.00E

- 11 f = porosity
n 4.6
Equation 1. Empty room permeability as a function of porosity, page 69, Vaughn et. al, 1995. The Agency believes using the same relationship between room porosity and permeability as that used by the 1995 FEP screening team is appropriate for this particu lar analysis . R oom permeability will be derived using Equation 1

. T he porosity for the time periods of 0

- 50 years and 50

- 200 years , determined from the Morgan curve, will be the input porosity values. The follow ing information summarize s the steps used to derive the permeability and porosity parameter values to be assigned to the non
- waste rooms (presumed empty) for this BRAGFLO sensitivity calculation. Flow Properties for the Non
- W aste R oom s 1. Porosity

- From

- 5 to 0 years . Use the same porosity as in the CRA 2014. For the two following time periods u se the empty room closure dates and the creep closure
curve for the empty rooms provided in SAND92

- 0427 (page A 77; Figure 3 above) to determine room porosities

.

a. 0 to 50 years

–

porosity, 50 % (0.50 )
Assumption s T he rooms furthest north in the repository were closed in the late 1 990s and early 2000 s , and s ome of these rooms were backfilled. From the 1990s to the anticipated final repository closure in 203 5 , approximately 4 0 years will have passed

.5  As sume that creep closure will have begun 40 years prior to final repository closure in 50% of the empty non
- waste areas

.

 Assume it will take 10 years for the repository to be completely decommissioned , and that c reep closure will have begun in the remaini ng 50% of the empty rooms 10 years before final repository closure ( decommissioning includes sealing of all the shafts and subsequent testing once sealed, and permit requirements completed with all regulatory agencies )

. Therefore, the time when the reposit ory is considered to be closed, at time ‘0’ for PA considerations, half of the non

- waste areas will have been closed for approximately 40 years with a porosity of about 50%, and the other half will have been closed for at least 10 years, with a porosity of about 80%. Averaging these non
- waste area porosit ies results in an effective
non
- waste area porosity of 65% at time zero.

 At 50 years after repository closure , half of the non

- waste rooms will be assumed to have closed over 90 years with a porosity reduction from 50% to 30%. The remaining rooms will have creep clos ed over 60 years with a porosity reduction from 80% to 40 %. Averaging these non

- waste area porosities results in an effective non

- wa ste area porosity of 35% at 50 years.
In summary the ‘ composite ’ porosity of all waste rooms will have dropped from 65% at time 0 to 35% 50 years later. Th e average effective non

- waste area porosity in the time period from 0 to 50 years is therefore 50%.

b. 50 to 200 years

–

porosity, 18 % ( ~0. 02) Assumption s A pplying the aforementioned non

- waste area closure dates and conclusions , a t 50 years after repository closure the average non

- waste area will have an effective porosity of 35 %

. At 200 years after repository closure all non

- waste rooms will have been closed for at least 210 years. An effective porosity needs to be estimated between these two endpoints times. Looking at the two non

- waste panel clusters (i.e., those areas that will have been closed for at least 50 years prior to repository decommissioning and those closed just prior to) separately the following room closure assumptions are adopted:

 At 50 years a 35% effective composite porosity is equivalent to a volume loss of 65%

.  From the Morgan curve the room porosity at 200 years after repository closure will be at least 2% and approaching an asymptotic value of 1% for all non

- waste rooms. A t 200 years a 2% effective porosity is equivalent to
a volume loss of 98 %.6  The average c omposite non

- waste room volume los s over th e 50

- 200 year time period is ~ 82% and the equivalent average room porosity is 18%. In summary the ‘composite’ porosity of all waste rooms will have dropped from 35% at 50 years to at least 2% at 200 years. The av erage volume loss over this time period is 82% and the equivalent average room porosity from the Morgan curve is 18%.

c. 200 to 10 , 000 years
. Extrapolating on the Figure 3 curve it appears the all non

waste room area porosities will be at least 2% and appro aching an asymptotic value of about 1% (0.01) at about 210 years

. A non

- waste area porosity of about 1% (0.01) at 200 years is within the sampled range for halite porosity. Based on the Morgan analysis, and for computational simplicity, assume at 200 years the end

- point porosity of the empty rooms has been reached and is slightly larger than that of intact halite. Therefore, the non

- waste area porosity for the time period of 200 to 10,000 years will be the sampled porosity for intact halite but increase d b y 1/2 the standard deviation for intact halite porosity (~0.0078), 1⁄2 STD >S_HALITE

. Assumption Stress

- induced creep on the closed non
- waste area will further reduce the porosity to values below 1 % (0.01). After approximately 200 years these lower porosit ies will approach an asymptotic value. This value will be similar to that of intact halite porosity. Because the room corners may not compress to the porosity of bedded salt (as indicated in Figure 2) assume ‘final creep closed’ room porosity will be slig htly greater than intact halite.

2. Permeability

a. 0 to 50 years

– Use Equation 1, permeability as a function of porosity , provided in the Vaughn, Lord, MacKinnon ( 1995, pg. 69) FEP DR

- 3 analysis, and assume the
room porosity is 50 % ( as explained in the text above )

. b. 50 to 200 years

- Use Equation 1, permeability as a function of porosity, provided in the Vaughn, Lord, MacKinnon ( 1995, pg. 69) FEP DR

- 3 analysis, and assume the room porosity is 18 % (as explained in the text above)

.

c. 200 to 10000 years

– Use the sampled permeability va lue for intact halite but increase it by 1 order of magnitude (1 OM >S_HALITE)

. 3. Two

- phase Flow Properties

a. 0

– 200 years

– Because the room s may consist of large void space s while they are creep closing for a large portio n of the 200 year closure period, it is assumed7 they will not behave as a porous medi um
. Therefore two

- phase flow will not occur during this time period. b. 200 to 10000 years

- It is assumed that the non

- waste rooms will have closed to the final end

- point porosity and permeability values reflective of porous media. Void space will no longer be continuous and inter

- connected. Once closed , rooms will behave as porous media , and gas and brine flow will be impeded by limited pore networks. Therefore, two

- phase flow properties for the non
- waste areas will be in e ffect and should be the same sampled values as th ose for intact halite

. Flow Properties to Be Used for the DRZ Adjoining the Non
- Waste Rooms Numerous studies support the supposition that the DRZ will heal within a few hundred years after creep closure begins and back pressures are applied . The healing process is due to multiple mechanisms. B rief summar ies of a few of these studies are given below.

a. Pfeifle and Hurtado (1998) report stress induced fractures will heal within several hundred years when hydrostatic stresses of 1

- 5 MPa are imposed on them; fracture healing will occur within a few years when imposed stresses are increased to 10 and 15 MPa.
b. The IT Corporation (1987) conducted f racture healing permeability tests on longitudinal

- tension and sawtooth fractures that were both dry and moistened , tests were conducted at confining pressures between ~ 3.5 MPa to 20 MP a
. Fracture h ealing occurred in both types of fractures and result ed in endpoint permeabilities within an order of magnitude of pre

- damage values.

c. Costin and Wawersik (SAND80

- 0392) conducted short

- term tests for fracture healing under confining pressures ranging between 10

– 35 MPa at temperatures between 22

— 100 o C and ov er various lengths of time. The majority of specimens healed to within 70

– 80 % of original strength (i.e., mechanical properties)

. d. More recent work of DRZ micro

- fracture healing ha s been investigated by research conducted at the Utrecht University 2 by Houben, Speirs, and Grupa 2011 (reported in SAND2012

- 1245). This work indicate s DRZ healing will occur due to multiple mechanisms. The more commonly understood mechanism is due to back pressure imposed on fracture openings by a rigid body causing them to c ompress and ultimately heal. The other, and less commonly known mechanism , is due to surface energy ion

transport driven healing. In surface energy healing salt ions are transport ed from large fractures along hygroscopic brine films and precipitat e d in smaller fractures. For this process m igration and precipitation of salt ions in fracture openings will eventually fill open fractures , reduce and eventually close fracture s and fracture networks. P redicted modeled time s to completely fill DRZ micro

- frac ture s are within 250 years. Because it

2 Note, the DRZ is referenced as E xcavated D isturbed Z one in the European community.8

is assumed small amounts of brine will be present in the DRZ due to seepage from both the anhydrite layers and clays within the halite , surface energy healing of micro fractures due to ionic transport of salts may occ ur. In summary, t he above studies and reports indicate the DRZ adjoining the non

- waste areas should heal within a few hundred years after repository closure

. The dominant process will be compress ion

. The creep closure process will produce r igid bodies in the empty room s due to roof

- fall, floor

- heave and rib exfoliation produc ing rock

- debris. The rock

- debris will partially fill the open rooms. Creep closure will cause all the drift faces to compress on the rock

- debris form ing a rigid body tha t will exert backpressures onto the adjacent DRZ. 3 Additionally, surface energy ion

- transport from brine seepage may also cause DRZ healing.
Based on the room closure curves , and the cited experimental studies , i t is a ssume d the end point porosity for t he DRZ adjoin ing the non

- waste areas will be reached at approximately 500 years. The assigned values for DRZ properties adjoining the non

- waste area for two time periods are given below.
1. Porosity

– a. 0 to 500 years

– use the same values adopted in the CRA 2014. b. 500 to 10000 years

– use the sampled values for intact halite

. 2. Permeability

– a. 0 to 500 years

– use the same values adopted in the CRA 2014

. b. 500 to 10000 years

– use one order of magnitude (1 OM) greater than the sampled permeabilit y for intact halite (1 OM >S_HALITE). 3. Two

- phase flow

–

500 to 10000 years

– I t is assumed the final end

- point porosity and permeability values for the DRZ will transition from those for fractures and micro

- fractures to those for porous media. Therefore, two

- phase f low is expected to have a role in both gas and brine movin g through these pore networks. At 500 to 10000 years assign the same two

- phase flow properties as th ose sampled for the intact halite

.

3 Creep closure back pressures will heal the DRZ, similar to the rigid body formed by run

- of

- mine salt in the panel closure drifts that will heal the panel closu re DRZ. However, it will take more years for the creep closure process to compress the loose rock

- debris in the non

- waste area to a rigid body than the run

- of

- mine salt. Consequently, the adjoining non

- waste room DRZ will take longer to heal than the DRZ near the panel closures.9

Table of Parameter Values t o Be Used for BRAGFLO Sensitivity Study

– Impact of Creep Closing Non
- Waste Areas T he table below summarizes the time

- frames and values to be used to represent non

- waste room permeability , porosity and two

- phase flow parameter for this sensitivity study . The table also provides parameter v alues to be given to the DRZ adjoining the non

- waste rooms.

Porosity and Permeability of Non

- W aste (Experimental and Operations) Areas

Time
– years Porosity Derived Perm 1 m 2 Log k

- m 2

- 5

– 0 1 (N/A) Same as CRA 2014 0

- 50 2, 3 0.50 2 4.12E

- 13

- 12.40 50

- 2 00 2 0. 18 2 3.75 E

- 1 5

- 14.43

2 00 to 10,000 1 /2 STD 5 greater than

sampled porosity for i ntact halite 1 OM 6 greater than sampled permeability for intact halite 1 OM 6 greater than sampled

permeability for intact halite 1

. From 1995 FEP Screening (Vaughn , Lord, MacKinnon ERMS 230798) , Permeability varying w/ porosity , Page 69

. 2

. An estimate using r oom cl osure times f rom SAND92

- 0427, Memorandum, H.S. Morgan to D.E. Munson , Page A

- 77

. 3

. A simplified value based on ranges depicted in Morgan memo in SAND92

- 0 427

. 4

. From Morgan mem o extrapolated porosity out to 500 years for simplification purposes 5. STD

- standard deviation 6 . OM

- Order of magnitude

Two Phase Flow Properties Non

- Waste (Experimental and Operations) Areas 2 00 to 10,000 Same as sampled values for intact halite

DRZ Porosity and Permeability Adjoining Non
- W aste (Experimental and Operations ) Areas

Time
– years Porosity Derived Perm m 2 Log k m 2

- 5

– 500 Same as CRA 2014 Same as CRA 2014 Same as CRA 2014

500 to 10,000 Same as sampled porosity for i ntact halite 1 1 OM greater than

sampled permeability for intact halite 1 OM greater than

sampled permeability for intact halite Two Phase Flow Properties DRZ 2 00 to 10,000 Same as sampled values for intact halite

1. If this value is greater than the value from the previous time period, then the previous value will be retained.10

References: Butcher, B.M., and F.T. Mendenhall 1993. Memorandum from H.S. Morgan to D.E. Munson

. A Summary of the Models Used for the Mechanical Response of Disposal Rooms in the Waste Isolation Pilot Plant with Regard to Compliance with 40 CFR 191, Subpart B. SAND92

- 0427, Appendix A, p. A67

- 105. Sandia National Laboratories, Albuquerque, New Mexico

. Costin, Larry S. and W.R. Wawersik. 1980. Crack Healing Of Fractures in Rock Salt. SAND80

- 0392. Sandia National Laboratories, Albuquerque, NM (cited in SAND2003

- 3407). IT Corporation 1987. Laboratory Investigation of Crushed Salt Consolidation and Fracture Healing , Battelle Memorial Institute. Office of Nuclear Waste Isolation, National Technical Information System, Accession Number, DE87005487 ( Report to Sandia National Laboratories, Albuquerque, NM). Pfeifle, Thomas W. and Hurtado, L. D. 1998. Permeability of Natural Rock Salt From the Waste Isolation Pilot Plant (WIPP) During Damage Evolution and Healing

. Sandia National Laboratories, Albuquerque, NM. SAND98

- 0417C Hansen, Frank D. 2012

. Presentation by Maartje, H., C. Speirs, J. Gurpa, 2011. Microphysical Modelling of EDZ Healing , in 2 nd US/German Workshop on Salt Repository Research, Design and Operation , Chapter One Proceedings
. SAND2012

- 1245C
. Sandia National Laboratories, Albuquerque, New Mexico

. Pfeifle, Thomas W. and Hurtado, L. D. 1998. Permeability of Natural Rock Salt From the Was te Isolation Pilot Plant (WIPP) During Damage Evolution and Healing

. Sandia National Laboratories, Albuquerque, NM. SAND98

- 0417C S. Cohen and Associat es (SCA). R eview of DOE ’ s Planned Change Request to Modify the WIPP Panel Closure System 2013 (November 20 ). Vienna, VA: SCA. Vaughn, Palmer, Lord, MacKinnon 1995, ERMS 230798 , Record of FEP Screening Work

. FEP ID # DR

- 2 Capillary Action (Wicking) Within the Waste , FEP ID # DR

- 3 Dynamic Consolidation of the North End and Hallways , FEP ID # DR

- 6 Brine Puddling in the Repository Due to Heterogeneities , FEP ID # DR

- 2 Capillary Action (Wicking) Within the Waste , FEP ID # DR

- 7 Permeability Varying the Co nsolidation in the Closure Regions , FEP ID # S

- 6 Dynamic Alteration of the Disturbed Rock Zone/Transitions Zone , 15 page preface material, 125 pages of text.