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Enclosure

August 2015

BRAGFLO Sensitivity Study Request 

Effect of Creep Closing Non-Waste Areas on the 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 would

affect the CRA-2014 WIPP PA calculations. The current CRA 2014 inputs for room porosity and 

permeability were derived using analyses conducted in the mid-1990s and based on a FEP 

screening for FEP DR-3. The results of the FEP screening analysis indicated modeling the timevarying 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 modified1and a much larger experimental area is planned. In addition, modifications to the 

WIPP 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 of 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 these 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 gathered 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 

depicted in Figure 2. 

 

1 Some of the issues EPA raises in this sensitivity study related to the impact of creep closure on the DRZ and the 

open rooms are also raised in EPA’s Technical Support Document (S. Cohen and Associates, 2013) assessing the 

impacts of creep closure on DOE’s parameterization of the run-of-mine -alt panel closure design.
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Figure 1. The WIPP North Experimental Room dimensions (in meters) during the mid-1980’s.

Then, as now, numeric instabilities arise when the vertical and horizontal edges of the model 

cells begin to overlap. Because of these limitations Morgan’s simulations went only to 200 years, 

the time when the model cells representing opposing room faces began to contact one another. 

These limitations still provide enough information to assess when an empty room will approach 

the time to final end-point porosity/closure. 

Morgan provided a curve of the calculated initial room closure volume reduction 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 porosity 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. 

Extrapolating 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. 
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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).
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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 

and 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. For FEP DR-3, the time-varying permeability of an 

empty room was calculated as a function of room porosity (page 69, Vaughn et. al, 1995) and 

expressed in Equation 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 particular analysis. Room 

permeability will be derived using Equation 1. The 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 following information summarizes 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-Waste Rooms 

1. Porosity - From -5 to 0 years. Use the same porosity as in the CRA 2014. 

For the two following time periods use 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) 

Assumptions

The rooms furthest north in the repository were closed in the late 1990s and early 2000s, 

and some of these rooms were backfilled. From the 1990s to the anticipated final 

repository closure in 2035, approximately 40 years will have passed.
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 Assume 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 creep closure will have begun in the remaining 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 repository 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 porosities 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 closed over 60 years with a porosity reduction 

from 80% to 40 %. Averaging these non-waste area porosities results in an 

effective non-waste 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. The 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)

Assumptions

Applying the aforementioned non-waste area closure dates and conclusions, at 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. At 200 years a 2% effective porosity is equivalent to 

a volume loss of 98%. 
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 The average composite non-waste room volume loss over the 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 average 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 nonwaste room area porosities will be at least 2% and approaching 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 increased by

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 porosities 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 slightly 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 value 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 rooms may consist of large void spaces while they 

are creep closing for a large portion of the 200 year closure period, it is assumed 
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they will not behave as a porous medium. 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 effect and should be the same sampled values as those 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. Brief summaries 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 fracture 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 MPa. Fracture healing 

occurred in both types of fractures and resulted 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—

100o C and over 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 has been investigated by research 

conducted at the Utrecht University2by Houben, Speirs, and Grupa 2011 (reported in 

SAND2012-1245). This work indicates 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 compress and ultimately 

heal. The other, and less commonly known mechanism, is due to surface energy iontransport driven healing. In surface energy healing salt ions are transported from large

fractures along hygroscopic brine films and precipitated in smaller fractures. For this 

process migration and precipitation of salt ions in fracture openings will eventually fill 

open fractures, reduce and eventually close fractures and fracture networks. Predicted 

modeled times to completely fill DRZ micro-fractures are within 250 years. Because it 

 

2 Note, the DRZ is referenced as Excavated Disturbed Zone in the European community. 
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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 occur. 

In summary, the 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 compression. The creep closure process will produce rigid bodies in the empty rooms due 

to roof-fall, floor-heave and rib exfoliation producing 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 forming a rigid body that 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, it is assumed the end 

point porosity for the DRZ adjoining 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 

permeability for intact halite (1 OM >S_HALITE). 

3. Two-phase flow –

500 to 10000 years –It 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 flow is expected to have a role in both 

gas and brine moving through these pore networks. At 500 to 10000 years assign the 

same two-phase flow properties as those 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 closure 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.
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Table of Parameter Values to Be Used for BRAGFLO Sensitivity Study –Impact of Creep 

Closing Non-Waste Areas

The 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 values to be given to the DRZ adjoining the non-waste rooms. 

Porosity and Permeability of Non-Waste (Experimental and Operations) Areas 

Time – years Porosity Derived Perm1 m2 Log k - m2

-5 – 0 1 (N/A) Same as CRA 2014

0-502, 3

0.502 4.12E-13 -12.40

50-2002 0.182 3.75E-15 -14.43

200 to 10,000

1/2 STD5greater than 

sampled porosity for 

intact halite

1 OM6greater than 

sampled 

permeability for 

intact halite

1 OM6greater 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 room closure times from 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 SAND92-0427.

4. From Morgan memo 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

200 to 10,000 Same as sampled values for intact halite

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

Time – years Porosity Derived Perm m2Log k m2

-5 – 500 Same as CRA 2014 Same as CRA 2014 Same as CRA 2014

500 to 10,000

Same as sampled 

porosity for intact 

halite1

1 OM greater than

sampled 

permeability for 

intact halite

1 OM greater than

sampled 

permeability for 

intact halite

Two Phase Flow Properties DRZ

200 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.
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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 2nd 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 Waste 

Isolation Pilot Plant (WIPP) During Damage Evolution and Healing. Sandia National 

Laboratories, Albuquerque, NM. SAND98-0417C

S. Cohen and Associates (SCA). Review 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 Consolidation 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.