SAND2003-3407 Unlim ited Release Printed Decem ber 2003



# The Disturbed Rock Zone at the Waste Isolation Pilot Plant

Francis D. Hansen Carlsbad Program s Group Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185-1395

Abstract The Disturbed Rock Zone constitutes an im portant geom echanical elem ent of the W a ste Isolation Pilot Plant. The science and engineering underpi nning the disturbed rock zone provide the basis for evaluating ongoing operational issues and their im pact on perform a nce assessm ent. Contem porary treatm e nt of the disturbed rock zone applied to the evaluation of the panel closure system and to a new m i ning horizon im proves the level of detail and quantitative elem ents associated with a dam a ged zone surrounding the repository openings. Technical advancem ent has been realized by virtue of ongoing experim e ntal investigations and international collaboration. The initial portion of this docum ent discusses the disturbed rock zone relative to operational issues pertaining to re-certification of the repository. The rem a ining sections

sum m a rize and docum ent theoretical and experim e ntal advances that quantify characteristics of the disturbed rock zone as applied to nuclear waste repositories in salt.

3

### Contents
1.0 Introduction

.......................................................................................... 7 2.0 Option D M odeling

............................................................................... 8
2.2 Background of Option D Panel Closure Anal y ses

............................................................. 10 2.3 Option D in the Technical Baseline Migration

..................................................................... 11 2.4 Preliminary Optio n D Assessment

......................................................................................... 16 

### 3.0 Clay G Evaluations

............................................................................ 17
3.1 Background of Clay G Anal y s es

............................................................................................. 17
3.2 Results of Cla y G Anal y s is

....................................................................................................... 19
3.3 Conclusions of Cla y G Anal yses

............................................................................................ 23 

### 4.0 Salt Damage Evaluations

.................................................................. 24
4.1 Principles of Salt Damage

........................................................................................................ 25 4.2 Hy drolo g ic Properti es of Damaged Salt

............................................................................... 26 4.3 Laboratory Studies of Salt Damage

....................................................................................... 27 4.4 Salt Damage Modeling

............................................................................................................... 30 4.5 Salt Damage Healing in Laboratory Studies

........................................................................ 31 4.6 Salt Damage Healing— In Situ Small Scale

........................................................................... 32
4.7 DRZ De lineation b y Sonic Velocity

....................................................................................... 33
4.8 Observ a tional Fracture Studies

.............................................................................................. 36 4.9 Full-Scale Field Analogs

.......................................................................................................... 39 

### 5.0 Summary

............................................................................................. 41
6.0 References

.......................................................................................... 42

4

### LIST OF TABLES

Table 1. D R Z Permeability used in the C CA and PAVT

.................................................. 9 Table A.1 Summary of Stre ngt h and Permeability Tests on

....................................... 51

5

### LIST OF FIGURES

Figure 1. Detail of PAVT and T B M grid and properties

...................................................... 12 Figure 2. Damage in the Floor of Panel 1, Room 2, August 21, 2001

.............................. 13 Figure 3. Stratigraphy near the Repos itory Hori zon (after Kreig, 1984)

........................... 14 Figure 4. Schematic of the Stratigraphy Surrounding the Raised and Unraised Sections of the Repository

................................................................................................................ 15 Figure 5. En Echelon DRZ Fracture Pattern to Clay G

....................................................... 19 Figure 6. Porosity Histories for Raised and Original Horizons Using Various Gas Generation Parameters

..................................................................................................... 20 Figure 7: Deformation of Raised Disposal Room Containing Waste with Time for f =0.0

............................................................................................................................... ................ 21 Figure 8: Anhydrite Shear Failure around the Raised Disposal Room with Time for f =0.0

............................................................................................................................... ................ 22 Figure 9: Disturbed Rock Zone around a Raised Dispos al Room with Time for f=0.0

.. 23 Figure 10. Stress States Known to Cause Dilation of WIPP Salt

....................................... 29 Figure 11. Permeability Versus Dilatant Volu metric Strai n for WIPP Salt

........................ 30 Figure 12. Damage Predicted Around a Typi cal WIPP Disposal Room 40 Years After Exc a vation (after Van Sambeek et al., 1993b)

.............................................................. 31 Figure 13. Layout of Holes for Room Q Alcove, with holes used for ultrasound measurements indicat ed in red

........................................................................................ 34 Figure 14. Same-hole measurements for adjacent holes, one in the left-hand wall (red) and in the corner (black)

................................................................................................... 35 Figure 15. Fractures and Apertures in Three WIPP Cores

................................................ 38 Figure 16. Fracture Apertures for DRZ Cores from WIPP and Asse

................................ 39 Figure 17. ALOHA2: Permeability Distri bution around the Bulkhead and Open Drift

.... 40 Figure A.1. Permeability of SMC, ESC, and MSC Concrete Specimens Versus Gas Pressure Difference

........................................................................................................... 52 Figure A.2. Cumulative Distribution Func tion for Permeability of SMC (after Repository Isolation Systems Department, 1996, WI PP Shaft Seal System Compliance Submittal Design Report, Appendix A)

........................................................................... 53

6

## 1.0 Introduction

The Disturbed Rock Zone (DRZ) is an im portant geom echanical elem ent of the W a ste Isolation Pilot Plant (W IPP). The DRZ was m odeled explicitly in the Com p liance Certif ication Application (CCA) and in the Perform a nce Assessm ent Verification Test (PAVT). On the basis of the perform a nce calculations, W I PP was certified by the U.S. Environm ental Protection Agency (EPA) as m eeting regulatory com p lian ce. Since the certification, the scientific understanding of the DRZ has progressed by virt ue of ongoing experim e ntal investigations, further evaluations of published research, and international collaborations. This paper reviews the considerable inform ation base on the DRZ and contrasts today’s understanding with the representation utilized for the com p liance determ ination. As docum ented subsequently, DRZ properties are bracketed m o re def i nitively today than at the tim e of the com p liance certif ication application, thereby m a king it possible to represent elem ents of the underground in a m o re realistic m a nner than represented heretof o re.
To begin the evaluation of the current W I PP operational fram ework in which DRZ issues are addressed, a lim ited discussion of DRZ evolution helps set the stage. The W I PP is situated in prim arily rock salt at a depth of 655 m e ters. Salt, being a plastic m e dium at this depth, exhibits a virgin lithostatic state of stress. Creation of underground openings perturbs the static equilibrium of the m i ned regions sufficiently to cause fracturing in rock proxim a l to the extracted m a terial. The DRZ com p rises the region near an excavation that experiences a change in hydrologic or

m echanical properties. The properties that typically define a DRZ include: (1) dilational deform ation ranging from m i croscopic to readily visible scales, (2) loss of strength evidenced by rib spall, f l oor heave, roof degradation and collapse, and (3) increased f l uid perm eability via connected porosity. The DRZ can play an im portant role in the geom echanical response of the W I PP underground, particularly where structures are pl aced to retard fluid flow in the repository. Although stress differences tend to decrease over tim e in a creeping m e dium , such as rock salt, fractures continue to grow and coalesce in an arching pattern around drifts and develop preferentially oriented parallel to the opening. As shown in photographs later in this report, the

m a nifestation of the DRZ can be observed today in several locations in the W I PP underground.

Treatm e nt of the DRZ is integral to the evaluati on of two features of the operating repository that have changed relative to the analyses supporting the initial certification:

• The Option D panel closure to be im plem ented as a condition of the certification, and,

• The operational change elevating the repository disposal room ceiling to Clay Seam G. These two considerations, which involve several geom echanical elem ents, will be referred to as Option D and Clay Seam G, respectively. In particular, construction of Option D will create conditions substantially different from those m odeled in the com p liance calculations. Nam e ly, the salt DRZ would heal around such a rigid m onolith and the anhydrite com p rising Marker Bed 139, a m a jor com ponent of the DRZ, beneath the current repository floor would be m i ned out. Raising the repository horizon by 2.43 m e ters to Clay G changes the structural setting by increasing the thickness of salt in the floor between the repository and MB 139 and decreasing the distance from the roof to overlying m a rker beds, such as Marker Bed 138. Construction of Option D within the raised repository setting is not addressed at this tim e.

7The prim ary m o tivation for developing this paper derives from the need to incorporate these two features in structural analysis of the underground setting and im plem ent the derivative inform ation into PA analyses. The EPA certified W I PP com p liance previously; however, incorporation of these operational features necessitated conceptual m odel m odifications and additional detail to the PA m odels. In anticipation ofthe scrutiny associated with recertification, the geotechnical aspects of Option D and Clay Seam G features are evaluated to ascertain deviations from the certified baseline. Technical docum entation dem onstrates and substantiates that these two changes can be adequately represented and understood and that they do not perceptibly change the PA cum u lative com p lem e ntary distribution function. In addition to evaluating these operational details, the broader context of a dam a ged rock in a salt repository will be reviewed and updated to include recent work at W I PP and within international repository
program s.
In preparation for the com p liance re-certification application, a prerequisite to the EPA deliberations includes assessm ent of advances in our knowledge of features, events and processes pertaining to W I PP. In technical ex changes between the DOE, EPA and stakeholders during the period between the com p liance determ ination and the re-certification application, ongoing technical assessm ent of the DRZ was di scussed periodically. Technical understanding of the DRZ has been recorded in reference literature, such as external publications, SAND docum ents published by Sandia National Laboratories, and biannual progress reports on repository investigations. This docum ent em phasizes present advances with respect to quantif ying characteristics of the DRZ and provides a literature review, both of which em phasize W I PP applications. This docum ent is m eant to provide com p rehensive docum entation and technical discussion of the DRZ relative to W I PP re-certification. In particular, the technical discourse em phasizes im provem e nt to our understanding of the DRZ at W I PP.

This docum ent provides a review and assessm ent of the Project’s understanding of the W I PP DRZ. Liberal reference will be m a de to a large am ount of available inform ation. The layout of this paper is an attem p t to be com p rehensive and system atic. Flow of the content begins with background inform ation, which contrasts previous and current treatm e nt of the DRZ in perform a nce assessm ent analyses. Then, treatm e nt of the two prim ary features—Option D and Clay G—will be addressed in Sections 2 and 3, respectively. Section 4 presents an overview of characteristics of the DRZ, which substantiate m a ny of the param e ters and m odeling treatm e nt of the DRZ. Section 4 reviews underlying theory and characteristics of the DRZ, and provides a

sum m a ry updating the understanding of the DRZ. The em phasis of the new treatm e nt is the DRZ itself, particularly the “salt” DRZ, but other elem ents of the underground, such as the concrete of Option D and fracture of the anhydrite, are involved in the analyses. These
geom echanical elem ents as represented in the baseline com p liance calculations and subsequent PA verification testing have been updated fo r re-certification calculations. The updated im plem entation is believed to represent an im provem e nt in accuracy, adequacy and validity of the m odeling em ployed for the initial certification. 

## 2.0 Option D Modeling

The PA calculation was conducted in 1996 (U.S. DOE, 1996) as part of the overall com p liance certif ication process established by the EPA in its radiation protection regulations (U.S. EPA,

81998). In 1997 the EPA required a PAVT to verify and evaluate the results of DOE’s CCA PA calculation. In their analysis, EPA addressed DRZ param e ter values and distributions. To support the upcom ing re-certification process, the technical baseline of the CCA and the PAVT was converged.

The table below sum m a rizes the DRZ param e ter changes m a de between the CCA and the PAVT. The grid used in CCA calculations im plem ented a DRZ of constant perm eability (10 -1 5 m 2 ) over a region 12 m e ters above and 2.23 m e ters below the disposal room s. The grid was continuous above panel closure system s, such that the sam e perm eability and thickness existed above and below the sim u lated panel closures. The PAVT changed the DRZ perm eability to a unif o rm distribution ranging from 10 - 19. 4 to 10 - 12. 5 m 2 . The geom etrical dim e nsions of the DRZ are the

sam e between the CCA and the PAVT. A consensus was reached that the PAVT perm eability values represented an acceptable range for purposes of those analyses and assum p tions pertaining thereto. Sandia National Laboratories reconciled all the param e ters used in the CCA and the PAVT and established a single param e ter baseline f o r the com p liance re-certif ication calculations (Hansen and Leigh, 2002).

Table 1. DRZ Permeability used in the CCA and PAVT.

DRZ Permeability Material ID's CCA Value Descri pti o n of Change for the PAVT Rati onal e

198 - DR Z_1/ prm x_l og 199 - DR Z_1/ prm y _l og 200 - DR Z_1/ prm z _l og -15 Lo g o f th e DRZ p e rm eab ility (m 2 ) was changed t o a uni form di st ri but i on rangi ng from -19.4
t o -12.5. Based o n g a s p e rm eab ility
t e st i ng of anhy dri t e cores from M B 139 (see W P O #30603 p. 2; W P O #32038; W P O #38367 p. 11)

The EPA docum ented their reasons f o r selecting PAVT DRZ perm eability distributions, which dif f

e red f r om the single perm eability value used in CCA calculations. Records f r om the W I PP Project Of f i ce (W PO) were used by the EPA to derive the recom m e nded PAVT perm eability range, which includes the CCA value near the m i d-range of PAVT distribution. The W P O records are listed in the table. Additional docum entation is cited in Sandia National Laboratories electronic database (PRAMVIEW ) . The DRZ param e ters now assem b led in PRAMVIEW are those selected by the EPA for the PAVT.

A brief review of the W P O docum ents supporting the PAVT DRZ values supports the m a gnitude and range of the PAVT values. W P O #32038 includes one data set com p rising 14 tests, which yields a perm eability range (log 10) from –12.5 to –21 m 2 . The other two W P O packages noted in the table include laboratory m easurem ents on Marker Bed 139 anhydrite. From a total of 42 anhydrite sam p les, a pressure-sensitive perm eability from (log 10) –16 to –21 m 2 was reported. Based on these data the range em ployed by the PAVT is appropriate.

The CCA and PAVT are docum ented, extensive, com p licated calculations, which underpin the

com p liance determ ination. In addition, the “record” includes reference docum ents of m a ny types, such as Technical Support Docum e nts (TSDs), and Com p liance Application Review Docum e nts (CARDS). These records were scrutin ized f o r their applicability to the DRZ m odel.

9A sum m a ry of the review of technical discussions existing in the records is included in this report (Appendix B).


### 2.2 Background of Option D Panel Closure Analy ses

In term s of PA, the m o st im portant DRZ param e ters are perm eability, porosity, and their extent. In the period since the com p liance application, W I PP personnel have re-exam i ned the DRZ

m odel, paying particular attention to im plem entation of Option D panel closure system s. Analysis Plan 087 (Hansen et al., 2002) describes the incorporation of the Option D closure into the existing BRAGFLO grid. The m i gration f r om the initial representations of the closures and DRZ to a m o re detailed analysis was called a Technical Baseline Migration (TBM). Detail is added to sim u late m o re closely the actual geom etry of the W I PP underground. Perm eability is a prim ary m odeling param e ter, theref ore a contrast will be drawn between treatm e nt of the DRZ for com p liance certification calculations, PA verification test calculations, and m o re recent calculations perform e d to reconcile param e ters, representations and conceptual m odels into a single baseline. The prim ary m o tivation to add detail to the BRAGFLO grid is to incorporate a

m o re realistic representation of the geotechnical issues attendant to Option D.

Im plem entation of Option D into the PA m odel necessitated additional detail within the BRAGFLO m e sh to capture the geotechnical interplay between the DRZ, the anhydrite m a rker beds and the concrete m onolith. The salt DRZ and the m a rker bed response are also integral to interpretation of the effects caused by raising the disposal horizon (see Section 3.0). Perspectives, background, and data will be provided to guide the argum ents toward the analysis being undertaken to evaluate incorporation of Op tion D panel closures into the PA calculations. Calculations underway for re-certification refine the detail of the repository and evaluate effects of the DRZ in concert with the panel closure Option D.

Perm eability values and geom etrical extent of the DRZ are based on observations, m easurem ents and an understanding of the m echanical response. The DRZ is also reversible in salt. W h en a rigid plug, such as the Option D panel closure concrete, is placed in a drift, the im pinging salt experiences a “back-stress”, which reduces stress differences. As the state of stress approaches equilibrium , existing m i crof ractures heal within the salt m e dium . Thus, the expectation is that the DRZ around an Option D panel closure would be m i nim a l at the tim e of construction and elim inated essentially im m e diately after the panel closure is com p leted. By contrast, the DRZ around room s filled with waste would continue to evolve as the country rock deform s into the open space of the room and then com p resses the waste stack. In a relatively short tim e (fewer than 100 years), however, the state of stress in th e salt around the waste room s will return to their original condition of no shear, and the DRZ around the greater areas of the waste room s would be largely healed as well. Im plications of DRZ healing and the underlying theory are discussed in Section 4.

Placem ent of a rigid structure within a drift, su ch as provided by the Option D concrete m onolith, will resist the inward flow of salt and locally return the state of stress to a condition that no longer produces a DRZ, rather conditions would favor healing of dam a ged salt. In addition, the DRZ is excavated prior to placem ent of the concre te structure. Therefore, consideration of the

10m odel for an Option D panel closure m u st include properties of the structure placed in the drift, particularly its perm eability, and properties of the surrounding rock. Characteristics of the Salado Mass Concrete (SMC) specified for the Option D closure are sum m a rized in Appendix A.

In the course of W I PP analyses, the DRZ proxim a l to the disposal room s and extending into panel entry drifts has been (and is proposed to be) represented in the following ways.

DRZ and panel closure in the CCA

. • DRZ perm eability was held constant at 10 -1 5 m 2

. • The DRZ extended 12 m e ters above and approxim a tely 2 m e ters below (bottom of Marker Bed 139).

• The panel closure was represented with a perm eability of 10 -1 5 m 2

. • Anhydrite fracture occurred when gas pressure approached lithostatic.

DRZ and panel closure in the PAVT

. • DRZ perm eability was sam p led f r om 10 - 19. 4 to 10 - 12. 5 m 2 with a m e dian perm eability of 10 - 15. 95 m 2

. • The DRZ extended 12 m e ters above and approxim a tely 2 m e ters below (bottom of Marker Bed 139).

• The panel closure was represented with a perm eability of 10 -1 5 m 2

. • The pressure-induced fracture m odel (designed for the anhydrite m a rker beds) was applied to the DRZ.

DRZ and panel closure in the TBM

• The PAVT perm eability distribution was applied to the vast m a jority of the DRZ.

• The DRZ extended 12 m e ters above and approxim a tely 2 m e ters below the disposal room s, however the DRZ residing above and below placem ent of the Option D concrete m onolith

assum e d a low perm eability.

• The panel closure concrete was represented with an appropriate perm eability distribution (10 - 17 to 10 -2 1 m 2 ), as discussed in Appendix A.

• The pressure-dependent fracture m odel was applied to the DRZ. Conceptually, fluid could access anhydrite m a rker beds and allow m i gration around the panel closure through Marker Bed 139 or propagate into overlying anhydrite seam s, which are underlain by thin clay

seam s. 

### 2.3 Option D in the Technical Baseline Migration

To im plem ent the various details required to m odel Option D and to prepare analyses for review by independent technical peers, Sandia em barked on an exercise called the TBM. The TBM grid refinem e nt represented Option D closures with SMC, the DRZ above and below disposal room s, and the DRZ above and below the Option D closure. SMC is Portland-cem ent concrete that is saturated with respect to NaCl (see Appendix A). Anhydrite characteristics rem a in the sam e as used in PAVT. Elem ents of the panel closure system are interrelated. For exam ple, the evolution of the DRZ is a function of stress stat e, which changes as salt creep redistributes the superincum bent loading. A rigid concrete m ono lith further affects the state of stress, which rapidly decreases the deviatoric stress com ponent and approaches equilibrium . Therefore,

11appropriate param e ter selection m u st include the coupled system . The sketches in Figure 1 illustrate the differences between the PAVT and the TBM grid. The accom p anying param e ters provide explicit refinem e nt to capture detail of the Option D panel closure system s that is not represented in the PAVT.



### 12 m

Was t e a r ea

Was t e a r ea k= 10

- 15 m 2 DR Z

DR Z

DR Z

DR Z 10

- 12.5 to 1 0

- 19.4 m 2

10

- 12.5 to 1 0

- 19.4 m 2 

### 12 m 10 -1 7 t o 2 x 10

- 21 m 2 

## PA V T

TB M

Figure 1. Detail of PAVT and TBM grid and properties.

Som e fundam e ntal issues with respect to treatm e nt of the DRZ were addressed as the m odels and grid were changed to accom m odate the details that Option D introduced. Analyses Plan AP-106 (Stein and Zelinski, 2003) defined the strategy. Som e of the deliberations are reviewed here. Previous analyses in the PAVT allowed fracture in the upper salt DRZ to provide a gas pathway for high repository pressures. Thereby, the PAVT analysis did not yield unrealistically high pressures in the repository. It is equally probabl e that the floor DRZ would allow flow to Marker Bed 139, which resides 1.4 m e ters below the repository horizon. Marker Bed 139 com p rises a

nom inally 1-m anhydrite layer that would not be expected to heal in the sam e m a nner as salt when it is dam a ged. Fractures around existing openings, such as shown in the photograph in Figure 2, evidence the nature of the dam a ge in the floor of the repository. Extensive floor heave was observed as room s in Panel 1 were reshaped to the original 4X10 m e ter rectangular cross section. Approxim a tely one m e ter of the floor was rem oved to re-establish the original height of 4 m e ters. Given the extensive dam a ge in the floor and that the rock com p rises anhydrite, it is probable that brine or gas flow to Marker Bed 139 is possible when high pressure is m odeled in the repository.

12Figure 2. Damage in the Floor of Panel 1, Room 2, August 21, 2001.

The situation gets a little m o re com p licated when the repository horizon is raised 2.4 m e ters to Clay Seam G. In the raised half of the repository, the distance through the lower DRZ from the repository floor downward to Marker Bed 139 will increase from 1.4 m e ters to approxim a tely 3.8 m e ters. This change m eans that fracturing associated with floor heave will likely be reduced in the raised part of the repository. The raised waste room s will have ready access to the Anhydrite “b” layer, which would now be excavated at the crown line of the raised waste room s. Anhydrite “b” is a thin (~6 cm -thick), layer that is present directly above Clay Seam G, as the stratigraphy near the repository illustrates in Figure 3. Because of the availability and likely connectivity to anhydrite seam s both above and below the repository horizon, it was deem ed appropriate to m odel potential fluid flow in both the upper and lower DRZ. In the event of high repository pressures it is equally likely that a fracture pathway would form (1) parallel to the roof of the repository via Anhydrite “b”, (2) vertically through the 2 m

- thick DRZ to Anhydrite A-- associated with Clay H, or, (3) into the floor to Marker Bed 139.

13Figure 3. Stratigraphy near the Repository Horizon (after Kreig, 1984).

The phenom enon of high-pressure opening of fractur es can be envisioned as hydrofractures that tend to open preferentially norm a l to the direction of the m i nim u m principal stress. To exam ine hydrofracture in m o re detail, field studies (W awersik and Stone, 1989) were re-evaluated. The results of hydraulic fracturing tests perform e d in W I PP salt, 3 to 100 m e ters from excavated

room s indicate that the pressures at which hydraulic fracturing is initiated, fall in the sam e range as hydrofracture tests perform e d in anhydrite Ma rker Beds 139 and 140 (W awersik et al., 1997). Fracture initiation pressures for the anhydrite tests ranged from 7.36 to 12.46 MPa with an average initiation pressure of 10.5 MPa. Fracture initiation pressures for the salt tests ranged from 4.14 to 17.24 MPa with an average initiation pressure of 11.98 MPa (W awersik and Stone, 1989). One im portant difference in the fracture behavior of intact salt is that because it is so im perm eable, fractures in W I PP salt will tend to stop at m o re perm eable anhydrite m a rker beds and change direction, m oving along the bed rather than fracturing across beds (W awersik et al., 1997). These data indicate that fractures in both m a terials will typically initiate at pressures below lithostatic and thus repository pressures significantly above lithostatic are unjustified and unexpected.

Because the data support the application of the fracture m odel to intact salt in addition to the

m a rker beds, calculations incorporated fracturing in both the upper and lower DRZ. Even in the parts of the repository that are not being raised to Clay Seam G, the test results support im plem enting the fracture m odel to both the upper and lower DRZ, considering the inherent uncertainty in exactly how the system will behave under possible near-lithostatic stresses. The im portant process that the fracture m odel sim u lates is the bleed off of very high pressures. W h ether these pressures bleed off through the upper or lower DRZ is not the salient point; rather, the im portant m odeling process is one of pressure relief. The param e ters used by the BRAGFLO fracture m odel and applied to the m a rker beds and the DRZ are justified, because they do not allow repository pressures to exceed lithostatic pressure significantly.

14Figure 4 com p ares the raised and unraised repository configurations in relation to the surrounding stratigraphy. In the grid used for com p liance re-certification, regions where the Option D panel closures intersect a m a rker bed are treated as isolated blocks of m a rker bed

m a terial. This representation is warranted for two reasons. First, the m a rker bed m a terial has a very sim ilar perm eability distribution (10 -2 1 to 10 -1 7 m 2 ) as the concrete portion of the Option D panel closures. Second, in the case of high pressures (near lithostatic) it is expected that fracturing m a y occur in the anhydrite m a rker beds and flow could go “around” the panel closures out of the 2-D plane considered in the m odel grid. In this case the flow would be through the

m a rker bed m a terial that is already allowed to fracture in the m odel. Therefore, treating these isolated cells as anhydrite m a rker bed m a terial is appropriate.

Figure 4. Schematic of the Stratigraphy Surrounding the Raised and Unraised Sections of the Repository

. Not to scale. (Stein and Zelinski, 2003)

One purpose of the grid change is to incorporate appropriate detail to represent Option D panel closures m o re accurately than either the CCA or the PAVT. As shown in Figure 1, the PAVT grid did not include detail associated with Option D, such as the m i ning to rem ove the local DRZ. The Option D panel closure system calls for rem oval of DRZ around the circum ference of the panel entry, and rem oves anhydrite Marker Bed 139 in the floor, as illustrated by the TBM grid shown in Figure 1. Details incorporated in the re-certification calculations include DRZ
perm eability as depicted and perm eability values of the SMC, a salt-based concrete included as part of the condition for Option D. Properties used for the salt-based concrete are sum m a rized in Appendix A.

Calculations im plem enting the refined grid were conducted to the point of assessing the repository saturations and pressures over the regulatory period of 10,000 years. W h en detail was

15added for the Option D elem ents, a com p lex variation of the pressures and saturations was observed. These calculations and the underlying m odeling rationale were provided to an independent peer review panel, which was em panelled consistent with requirem e nts of Title 40 Code of Federal Regulations (CFR) 1297. The peer review panel’s assessm ent of these conceptual m odel changes are sum m a rized in Section 2.4.


### 2.4 Preliminary Option D Assessment

During the spring of 2002, the DOE directed Sandia to m a ke a prelim inary calculation whereby Option D was m odeled within the PAVT grid sim p ly as a relatively tight plug. This prelim inary

assessm ent helped kick-start a re-design of the panel closure system . Results were provided to CBFO (Hansen, 2002). Assessing the im pact of an Option D panel closures on repository perform a nce was challenging because the CCA and the PAVT com p rise the regulatory baseline for W I PP certification. However, neither the CCA nor the PAVT explicitly represented Option D panel closures in the calculations. To provide a baseline for assessing the effects of changing the panel closure design, the DOE felt a PA that included Option D panel closures m u st be

com p leted and that the accepted PAVT grid be used.

This assessm ent explicitly represented the Option D panel closures in the EPA-approved m odels of the repository, using the com putational grid and param e ter values that were used for the PAVT. However, the PAVT grid m a y be insufficiently detailed to capture all the im portant effects of the Option D panel closures. Subsequently Sandia conducted a second PA in which the com putational grid was revised to represent the panel closures m o re realistically. A

com p arison was m a de between the repository perform a nce with the Option D panel closures and the repository perform a nce as calculated using the PAVT grid. In general, results indicate that panel closure characteristics are unlikely to affect repository perform a nce significantly.

Peer review of conceptual m odels developed by the DOE f o r the W I PP is required by Title 40 CFR 194.27. To m eet this requirem e nt, the CBFO conducted a peer review of the three conceptual m odels that were changed in response to the Option D requirem e nt and to incorporate knowledge gained since the original conceptual m odels were developed. The peer review panel

exam ined the following conceptual m odels and their im plem entation:

• Disposal System Geom etry

• Repository Fluid Flow, and

• DRZ. The peer review process is a docum ented, critical review perform e d by peers who possess qualifications at least equal to those of the individuals who conducted the original work and independent of the work being done (Caporuscio et al., 2003). In m o st of their considerations the peer panel assessed the proposed changes against the existing im plem entation in the CCA or the PAVT. The panel concluded that the technical m i gration im plem ented for Option D was reasonable and adequate as sum m a rized from their report below:

Disposal System Geometry . W ith respect to the disposal system geom etry, the system characterized by the Option D concrete m onolith and the explosion wall led to proposed change in the grid geom etry since the existing grid block discretization was perceived to be too coarse for the representation of the specifics of Option D and the interrelated im pacts on the DRZ. The

16panel concluded that the geom etry retains the features of the original conceptual m odel and grid changes appear reasonable and sound.

Repository Fluid Flow . The panel also determ ined that the repository fluid flow conceptual

m odel was both reasonable and adequate for its intended purpose.

Disturbed Rock Zone

. The panel stated that the DRZ m odel represents a reasonable developm ent of the earlier alternatives. The m e thods and procedures used in the changed m odel are refinem e nts of the previous m odels, and m odulate the relationship between repository pressure, waste degradation and brine inflow in a m o re realistic and conservative way than preexisting

m odels, while integrating the influences of two design changes. The panel’s perception that excavation to Clay G is not a signif i cant change in concept will be explored in the f o llowing Section 3. 

## 3.0 Clay G Evaluations

This section sum m a rizes a series of structural calculations executed to exam ine possible effects of raising the W I PP repository horizon from the original design level upward 2.43 m e ters. These calculations allow evaluations to be m a de of various features involved with the conceptual

m odels im plem ented in W I PP PA. Notably this work addresses issues raised in an EPA letter to Carlsbad Field Office dated August 6, 2002. In the subject letter the EPA stated “ the conceptual model for the repository should reflect the change to raise the level of excavation to clay seam G. The conceptual change should be appropriately addressed in the modeling, if warranted ” (U.S. EPA, 2002). The Clay Seam G analyses included significant efforts to qualify the finite elem ent code SANTOS. The prim ary results involve the production of porosity surfaces for PA. These

com putations also allow evaluation of the DRZ behavior and anhydrite fracture. The calculations support the m odeling concepts used for the disposal area rock m e chanics. In addition, details of the geom echanical structural elem ents provide exam ples of appropriate
treatm e nt of these features in PA.


### 3.1 Background of Clay G Analy ses

Clay Seam G structural evaluations began with qualification of the finite elem ent code SANTOS, the finite elem ent code used for calculations supporting the original com p liance certification porosity surface. At the tim e of the CCA, this code was executed on a Cray J916 m achine. For the current analyses of Clay G the code was run on a Linux P4 Intel workstation. The first step in the requisite analyses was to replicate the CCA calculation of the porosity surface. These calculations verified that identical results can be obtained today, despite use of a new

com putational platform . Concom itantly, the verifi cation and validation test problem s were run to verify SANTOS functionality. The structural analysis m odels repository behavior of waste-filled disposal room s raised 2.43

m e ters above the present, or original, repository level. The DRZ evolution com p rises a fundam e ntal com ponent of this analysis. The goal of these analyses is to assess whether or not raising the repository to Clay Seam G has any significant im pact on the conceptual m odels used

17in PA. Results of these analyses provides an oppor tunity to review treatm e nt of the DRZ within the context of W I PP. The analysis period is 10,000 years after waste em placem ent. The calculations include

m echanical creep closure response of a filled disposal room in a m a nner em ployed for baseline calculations supporting the com p liance application. These calculations included construction of the three-dim e nsional porosity surfaces used for W I PP PA activities (Park and Holland, 2003). Thus, the prim ary output of Clay G structural cal culation pertains to developm ent of the porosity surface for PA.

The W I PP m a nagem e nt and operating contractor, W a shington TRU Solutions (W TS), gained concurrence of the DOE and EPA to raise the disposal room 2.43 m e ters above the present level. The elevation change m eans the roof of a disposal room would coincide with the Clay Seam G horizon and the floor would be separated fr om the underlying Marker Bed 139 by 3.81 m e ters instead of 1.38 m e ters (the existing separation in disposal Panels 1 and 2). The change in repository horizon was recom m e nded to ease ground control conditions. Fractures surrounding the existing horizon tend to coalesce in an arch, which m i m i cs the shear stress trajectories. These patterns can be seen in the underground today where the roof has been taken down along thelength of the East 140 drift (see Figure 5). The roof rock of the original horizon tends to decouple at Clay G, as exhibited by the shear fracture patterns. Underground operations personnel are currently obligated to provide roof support and m a intenance that they believe would be

m i nim i zed if the roof of the disposal room s is raised to Clay G. Raising the repository disposal horizon presents a different com b ination of lithologies intim ate to the disposal room than that of the com p liance baseline. Thus, it is necessary to evaluate the im pact of this proposed m i ning change.

18Figure 5. En Echelon DRZ Fracture Pattern to Clay G.

The analysis replicated results reported in “Final Disposal Room Structural Response Calculations, SAND97-0795” (Stone, C.M., 1997), which is the referenced baseline report for the CCA. Calculation procedures and data of S AND97-0795 were used in this analysis and the results of a new, current analysis were com p ared with the results of SAND97-0795. Therefore, the initial calculations replicate room pressure and porosity histories f o r various gas generation rates for a period of 10,000 years following excavation and waste em placem ent. 

### 3.2 Results of Clay G Analy s is

A recent report authored by Park and Holland (2003) provides the com p rehensive results of these structural analyses. A few notable exam ples of the analyses are provided here, with an em phasis given to the DRZ im plications. First the porosity hi stories for future states of the repository were replicated as shown in Figure 6. This figure plots porosity over tim e for representative gas generation factors and superim poses Clay Seam G results over the results obtained for the original repository horizon. In detail, m a ny such calculations were executed to obtain porosity surfaces, but this exam ple illustrates both replication of the previous results underpinning the CCA and the slight influence on these results that raising the repository horizon im parts to these baseline results. The CCA grid and m a terial properties were run and results overlay previous calculations by Stone (1997). Then the grid was m odified slightly to reflect elevation of the

19repository horizon by 2.43 m

, and the m odel was re-executed. Recall that the Stone calculations included gas generation with rates im posed by a factor f . In Figure 6 the Stone porosity results are reproduced for gas generation factors of 0.0 and 0.5. A com p arison is m a de to the porosity results derived from the new horizon at 2.43 m e ters upward. In term s of room closure operating in concert with gas generation, Figure 6 dem onstrates that the porosity surface for the upper horizon is identical, for all practical purposes, to the baseline porosity surface.

Figure 6. Porosity Histories for Raised and Original Horizons Using Various Gas Generation Parameters,.

The next series of f

i gures illustrates representative geom echanical results f r om Park and Holland (2003). In Figure 7 the original grid and deform ation over tim e are shown for the future without gas generation. The deform ed m e sh helps clarify the physical extent of deform ation. Over tim e the surrounding salt deform s over 2 m e ters into the disposal room com p ressing the waste inside. The anhydrite layers are dragged along with the salt, thus ensuring extensive fracturing within these m a rker beds. Figure 8 focuses on the anhydrite layers them selves, and shows the state of stress easily exceeds a Drucker-Prager failure criterion. Note the MSF represents the m a terial safety factor, which com p ares the existing state of stress to the Drucker-Prager criterion and MSF>1 denotes failure. Also note in Figure 8 that the state of stress difference would decrease over tim e and less of the anhydrite would reside in failed stress space. W h ereas salt has been shown to heal as the stress state approaches equilibrium (reducing deviatoric stress), anhydrite has not dem onstrated sim ilar healing characteristics.

200 y ear 1 0 y ears 2 5 y ears

r s ears ears 3 0 0 y e a 1 , 0 0 0 y 1 0 , 0 0 0 y

Figure 7: Deformation of Raised Disposal Room Containing Waste w i th Time for f =0.0.

210 y a r e 1 d a y ear

ears ears ears 1 y

1 0 y 1 0 0 y 1 0 , 0 0 0 y F a i l u r e C o n d i t i o n : M S F > 1

0 y a r

e a y ear

ears ears ears 1 0 , 0 0 0 y 1 0 0 y 1 0 y 1 d 1 y F a i l u r e C o n d i t i o n : M S F > 1

Figure 8: Anhy drite Shear Failure around the Raised Disposal Room w i th Time for f =0.0.

The above two figures show the dram atic deform ation involved with the waste repository room s. The prim ary m echanism of deform ation is salt creep, which ensues with dam a ge near the opening and without dam a ge further out in the form ation. Section 4 of this report will explore salt dam a ge evaluation in greater detail. These snapshots of the DRZ over tim e represent som e of the output of the Clay Seam G analyses. The DRZ m odel sim p ly relates stress invariants and

assum e s that dam a ge occurs based on the relation given in Figure 9. Thus the DRZ extends to its greatest dim e nsions relatively early in the repository regulatory period of 10,000 years. The report by Park and Holland (2003) contains several different situations for gas generation, and in all cases the DRZ vanishes early in repository history.

220 y ear 1 y ear 17 y ear s

50 y ear s 2 48 y e ar s 1 0 , 000 y ear s Undist urbed Zone:

1 2 27

. 0 I J

⋅ ≤ 0 y ear 1 y ear 17 y ear s

50 y ear s 2 48 y e ar s 1 0 , 000 y ear s Undist urbed Zone:

1 2 27

. 0 I J

⋅ ≤

Figure 9: Disturbed Rock Zone around a Raised Disposal Room w i th Time for f=0.0.



### 3.3 Conclusions of Clay G Analy ses

These calculations dem onstrate that changing the repository horizon upward 2.43 m e ters has no appreciable effect on the response of the underground relative to the com putations m a de for the CCA. This conclusion is drawn by first com p aring new results with the previous results that underpinned the com p liance application. The calculation procedures and input param e ters were consistent with SAND97-0795 (Stone, 1997). These analyses used the sam e code, SANTOS, that supported the com p liance calculations. A new validation and qualification of the software and hardware was assem b led, as required by Quality Assurance procedures.

Perform a nce Assessm ent . The hand-off to PA from the structural (finite elem ent) calculations takes the form of a porosity surface. The m odels include geom echanical response of the Salado stratigraphy, the waste m a terial, and gas generation in the disposal room s. The volum e change of the disposal room due to the salt creep is strongly dependent on the gas generation factor, f. The calculations used in the CCA were replicated and then repeated for grid changes appropriate for the new horizon to Clay Seam G. Because the CCA porosity surface calculated for the original horizon and the new porosity surface calculated for the raised room s are essentially identical, no changes to the porosity surface are recom m e nded to the com p liance re-certification calculations.

Disturbed Rock Zone. Calculations of the DRZ illustrate several interesting f eatures. First the propagation of the DRZ into the surrounding rock salt passes through Marker Bed 139 in the case of the original horizon (Park and Holland, 2003) and does not penetrate Marker Bed 139 in the case of the raised room , as shown above in Figure 9. Quantitatively, the extent of the DRZ can be sum m a rized as follows:

• In the case of the raised room , the m a xim u m thickness of DRZ is alm o st 6 m e ters above the room and 4 m e ters under the room

.

23• In the case of the original horizon, the m a xim u m thickness of upper DRZ is about 6

m e ters, while the lower DRZ extends 5.6 m e ters through Marker Bed 139.

In all m odels the DRZ grows until the creeping salt im pinges on the waste, at which tim e the stresses trend back toward equilibrium and the DRZ dim i nishes. In all the sim u lations, the DRZ disappears quickly relative to the regulatory period of 10,000 years. Anhydrite Fracture . The anhydrite m a rker beds sustain states of stress that prom ote failure. In addition, deform ation into the room by the m a rker beds is substantial. Therefore, fracture of the anhydrite in the proxim ity of the disposal room s is m o st probable and the strain (deform a tion) induced during room closure would ensure som e anhydrite fractures would exist in the proxim ity of the disposal room . The internal gas pressure of the room does not affect characteristics of the shear failure zone in the anhydrite layer. Deviatoric stress conditions becom e less severe over tim e, but the dam a ged anhydrite is not expected to heal in a m a nner expected of the salt DRZ.

Anhydrite m a rker beds reside in the proxim ity of the disposal room s, whether the room is at the original horizon or at the elevated horizon. Therefore, fractured anhydrite, possessing high
perm eability, resides intim ate to the def o rm ed room . High f l uid pressure that could develop in disposal room s would be expected to com m unicate readily and flow preferentially out the dam a ged m a rker beds. 

## 4.0 Salt Damage Evaluations

The first three sections of this report sum m a rize the current understanding of the geom echanical setting at W I PP, and the im plem entation of that state of knowledge against changes m a de to the repository since the initial com p liance determ ination. This section presents m u ch of the technical bases that buttress the choices m a de to address the changes. The discussion begins with first principles of the creation, evolution and attendant properties of the DRZ. The theory is expanded into laboratory test results, sm all-scale in situ experim e nts and full-scale analogs from industry experiences and international collaborations. These technical argum ents provide reasoning for the param e ter distributions and gr id refinem e nts selected for re-certification calculations, which m u st address changes to the underground as well as incorporate any advancem ent benefiting the collective state of knowledge. The ensuing discussion concentrates on rock salt dam a ge, m odeling, and properties, and provides objective evidence that the theory extends into practice sufficiently that the proposed analyses of the operating repository are reasonable and justified.

24

### 4.1 Principles of Salt Damage

Sim ilar to underground structures sited in other geologic m e dia, excavation of an opening, such as a drift, disposal room or shaft at the W I PP alters the virgin state of stress (i.e., σ 1 ≈ σ 2 ≈σ 3 ) that exists in the rock salt. The rock zone proxim a l to the opening experiences deviatoric (or shear) states of stress ( σ 1 > σ 2 > σ 3 ) after excavation. Because of the stress-concentrating effect of the opening itself, the deviatoric stresses are highest in the rock salt near the opening, especially near abrupt changes in opening geom etry (e.g., corners), and decrease rapidly with distance from the opening. In addition to opening geom etry and spatial position, other factors affecting the m a gnitude of the induced deviatoric stress include local geology (e.g., hom ogeneous versus layered m e dia) and depth of the opening below ground surface because, absent tectonic influences, the stress m a gnitude is approxim a tely proportional to depth. Because salt is a creeping m e dium , the stress differences are m a xim i zed upon excavation, and decrease thereafter.

In salt, deviatoric states of stress activate three deform ation processes: (1) elastic, (2) inelastic viscoplastic flow, and (3) inelastic dam a ge-induced flow 1 . Elastic deform ations occur instantaneously (tim e-independent) in response to changes in stress state, while the two inelastic

m echanism s are tim e-dependent, which gives salt its well-known creep characteristics. Inelastic flow m odels usually include stress and tem p erature term s, but the flow rate also depends on factors such as stress history and relative hum idity.

Viscoplastic flow of salt has been well characterized for W I PP applications. Much of the m o st pertinent literature derives from W I PP research and developm ent (e.g., Munson, 1979; Carter and Hansen, 1983; Munson and Dawson, 1984) but the W I PP history of salt deform ation benefits from international collaboration (e.g., Langer, 1984; W a llner, 1984; Aubertin et al., 1991; Cristescu and Hunsche, 1992, to nam e a few). Plastic deform ation occurs by dislocation m o tion within the salt lattice. The various dislocation m echanism s of concern to repository sciences are also well docum ented and include dislocation m u ltiplication, glide, cross slip, and clim b. Because viscoplastic flow is an isochoric or incom p ressible process, it does not induce dam a ge to the salt m a trix. In salt, dislocation m echanism s are activated by virtually all deviatoric stress states regardless of the m a gnitude of the applied m ean stress (average of the three principal stresses). The physics and the m a them atics are well established for m odels that represent viscoplastic flow.

In contrast to viscoplastic flow, dam a ge-induced flow in salt is less well understood. Dam a ge only occurs when the deviatoric stresses are relatively high com p ared to the applied m e an stress and is m a nifested through the tim e-dependent initiation, growth, and coalescence of

m i crofractures. Modeling approaches have been suggested for the m i crofracturing process, with lim ited success. For exam ple, predictions of dam a ge space for W I PP applications seem to represent what is witnessed in the underground in a qualitative sense. Indeed, point-wise geophysical m easurem ents often validate the general sense of the dam a ge m odel. However, a

m odel f o r spatial and tem poral dam a ge evolution that includes prediction of perm eability is not yet available to salt repository sciences.

1 Som e tim es referred to as stress-induced dam a ge.

25In term s of W I PP repository applications, one of the m o st im portant features of salt as an isolation m e dium is its ability to heal previously dam a ged areas. Dam a ge recovery is of ten referred to as healing in geom echanics parlance. Healing arises when the m a gnitude of the deviatoric stress decreases relative to the applied m ean stress. A decrease in deviatoric stress occurs as stresses approach lithostatic conditions, as would be the circum stance adjacent to a rigid inclusion such as Option D panel closures . The healing m echanism s include m i crofracture closure and bonding of fracture surfaces. Microfr acture closure is a m echanical response to increased com p ressive stress applied norm a l to the fractures, while bonding of fracture surfacesoccurs 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 experim e nts, sm all-s cale tests at W I PP and through observations of natural analogs as described later. Healing the salt DRZ can readily restore dam a ged salt to a low perm eability as discussed in Section 4.5.

The discussion of salt behavior and deform ation processes around W I PP openings lead to the following general observations about the DRZ:



## • Microfracturing of the salt initiates im m e diately upon excavation of the openings and continues with tim e.


## • Microfracture density and growth rates are highest near the opening and decrease with distance away from the opening



## • Fracture growth in the DRZ will be anisotropic with f r actures aligning parallel to the

m o st com p ressive stress (the m o st com p ressive stresses are typically aligned parallel to the free surfaces of the openings).



## • Over tim e, m acrof racturing will lead to salt f a ilure including f l oor heave, roof f

a lls and rib slabbing and spalling.



## • Salt dam a ge is reversible. Rigid panel closures placed in W I PP openings will create a nearly hydrostatic state of stress in the DRZ adjacent to the inclusion.


### 4.2 Hy drologic Properties of Damaged Salt

Most geologic m e dia, including salt, contain natural porosity in the form of interconnected channels and isolated inclusions. Fluid flow th rough such m e dia is necessarily constrained to the interconnected porosity. In pure W I PP salt, the natural porosity is on the order of 1 percent or less and not well connected. In argillaceous W I PP salt, the porosity is m a rginally higher and fluid flow has been observed, although at very low rates (Beauheim and Roberts, 2002). The porosity of W I PP salt is f illed with brine containing dissolved gases, principally nitrogen. Because salt creeps, pore pressures in the brine-filled pores would be expected to approach lithostatic. At the depth of the repository, the lithostatic pressure has been established at 14.9 MPa.

The porosity of the salt in the DRZ is higher than in the surrounding virgin rock because of the dilation induced by m i crofracturing, as explained above. Peach (1991) studied the effects of salt dilation using percolation theory and found that sm all levels of dilation (as little as 0.05 percent)

26were sufficient to develop an interconnected pore network that form ed prim arily along grain boundaries. Furtherm ore, perm eability through this network was found to be proportional to ( ε dv ) 3 , where ( ε dv ) is the dilatant volum etric strain equivalent to ∆ V/V with ∆ V and V representing the change in volum e due to dilation and the initial volum e, respectively. Assum i ng a dilatant strain of 0.5 percent (a value that could easily occur in the DRZ), the 0.05 threshold strain, and the Peach proportionality, the perm eability within the DRZ could increase by at least three orders of m a gnitude. As shown later, Pfeifle et al. (1998) conducted perm eability tests on W I PP salt specim e ns that had been deform ed in the laboratory to volum etric strains of the order of 0.5 percent and estim ated perm eabilities that ranged from 10 -1 5 to 10 -1 4 m 2 , at least seven orders-of-m a gnitude higher than observed in the field by Beauheim and Roberts (2002) for virgin argillaceous salt em phasizing the extrem e sensitivity of W I PP salt perm eability to sm all dilatant volum etric strains.

Utility of this sim p le m odel is com p licated by the anisotropy of dam a ge in the field. As will be shown throughout this section, fractures in salt develop with preferential orientation with respect to the stress state. As clearly shown in Figures 2 and 5, fractures in situ are generally parallel to the drift and perpendicular to the m i nim u m principal stress. Perm eability along the fractures, parallel to the drif t would be m u ch higher than perm eability perpendicular to the drif t. The anisotropic nature of f

r actures and the sensitivity to dam a ge (i.e., the perm eability increases by orders of m a gnitude with relatively low levels of dam a ge) are two features that com p licate developm ent of a dam a ge/perm eability relationship f o r f i eld applications.

Because of the sensitivity between salt perm eability and dilation, the DRZ is expected to exhibit high perm eability im m e diately adjacent to the W I PP openings and decrease away from the opening in direct relation to the level of induced dam a ge and deviatoric stresses. The

m i crofracturing will also relieve the pore pressu re in the DRZ. At the free surface of the opening, the pore pressure will be atm o spheric, while at depth the pore pressure will be on the order of 14.9 MPa. This pressure gradient through the DRZ will release brine into the opening. The pore pressure in the salt som e distance beyond the DRZ m a y be lower than 14.9 MPa because the alteration of the stress field resulting from the excavation m a y relieve som e stress acting on the isolated brine-filled pores even though the change in stress is not sufficient to induce dam a ge. Because healing processes reduce porosity, perm eability is expected to decrease when hydrostatic states of stress activate healing pr ocesses, particularly in the vicinity of rigid panel closures.


### 4.3 Laboratory Studies of Salt Damage

Laboratory studies provide the m o st readily attainab le setting f o r testing m a terial properties. The

m a terials of interest to the Option D panel closure system include intact salt, dam a ged salt, saltbased concrete and anhydrite. The geom echanical calculations being conducted in support of W I PP re-certif ication activities have added detail in the representation of salt dam a ge (and healing) and salt-based concrete m a terials. Both elem ents are m o re representative of actual conditions than previously m odeled in the CCA calculations. Laboratory characterization of salt dam a ge and healing is sum m a rized in the following section and discussion of salt-based concrete properties is found in Appendix A, Section 4.6 and Section 4.9.

27Extensive research has been conducted in the laboratory to determ ine both the deform ational and hydrological behavior of W I PP salt. Early work focused on the characterization of the elastic and inelastic viscoplastic flow properties of salt (e.g., Hansen and Mellegard, 1977; W a wersik and Hannum , 1979, Hansen and Mellegard, 1980; Se nseny, 1986; Mellegard and Pfeifle, 1993). Most of the early studies provided param e ters for the W I PP creep m odel. This m odel is popularly known as the Munson-Dawson (1984) Model, or M-D Model. In fact the author (Munson) called the m odel the M-D Model to denote m ultim echanism

- d eform a tion. The constant-volum e creep behavior of the underground m odeled by M-D was validated against large-scale therm o m echanical experim e nts. This background inform ation was available for the use in the PA and the com p liance certification application.

The phenom ena associated with salt fracture were m a de obvious from observations in the W I PP underground (Section 4.6) and geophysical m easurem ents (Section 4.7). Despite an acknowledged im portance of salt dam a ge to the W I PP repository, the DRZ was given a rather rudim e ntary treatm e nt in the com p liance calculations . As preparations are being m a de for the recertification of regulatory com p liance, additional sophistication is brought to the treatm ent of the DRZ. A large am ount of the data available to quantify DRZ properties derives from laboratory studies that were perform e d to param e terize the M-D m odel. Eventually, system atic studies of salt fracture were undertaken in the laboratory. Based on field observations, experim e nts, and theory, salt dam a ge is reversible. Therefore, consideration of the salt DRZ includes its creation, growth, and properties, as well as the conditions under which the DRZ would heal. The properties of the DRZ provide the crux of the m odeling issues for the Option D panel closures.

Van Sam b eek et al. (1993a) re-exam i ned the extensive creep data existing from years of experim e nts on salt. Their hypothesis was that dam a ge could be assessed because volum etric strain and principal stresses are carefully controlled test param e ters. Stress states that led to dilation were defined in term s of stress invariants rather than individual stress com ponents because the stress com ponents for one type of test could not be com p ared directly with the stress

com ponents of another type of test. The two stress invariants selected were the first invariant of the traditional Cauchy stress tensor, I 1 , and the second invariant of the deviatoric stress tensor, J 2
. These invariants are related to m ean (or confining) stress and deviatoric stress, respectively, and are defined as follows:

3 2 1 1 3 σ σ σ σ + + = = m I



## ( ) ( ) ( ) 

# [ ] 2 / 1 2 1 3 2 3 2 2 2 1 2 / 1 2 6 1 ⎭ ⎬ ⎫ ⎩ ⎨ ⎧

− +

− +

− = σ σ σ σ σ σ J

where σ m is the m ean stress and σ 1 , σ 2 , and σ 3 are the three principal stress com ponents for a particular type of test. Using these definiti ons, Van Sam b eek et al. (1993a) plotted the stress states (in term s of invariants) that both did a nd did not induce dilation in W I PP salt as shown in Figure 10. In addition, laboratory data for Avery Island, Louisiana, dom al salt were plotted, as

m a ny experim e nts had been conducted on Avery Island salt over the years. As shown, a clear delineation in the I 1 – J 2 stress space exists between conditions that cause dilation and those that do not regardless of the type of salt or type of test considered. Van Sam b eek et al. (1993a)

28suggested an em pirical relationship to divide d ilating stress states from non-dilating stress states and expressed this em pirical relationship as follows:

1 2 27

. 0 I J =

This relationship is of ten ref e rred to as the stress-invariant m odel and is used to predict dilational states of stress for W I PP salt.

Figure 10. Stress States Know n to Cause Dilation of WIPP Salt

.

Storm ont (1990) and Pfeifle et al. (1998) conduc ted laboratory tests on W I PP salt to correlate
perm eability with dam a ge level expressed as dilatant volum etric strain. Figure 11 provides the results of these two studies and shows that perm eability changes by nearly 10 orders-of

m a gnitude from less than 10 -2 1 m 2 to m o re than 10 -1 2 m 2 corresponding to changes in dilatant volum etric strain (or porosity) of up to 4 percent. These data are consistent with the range in
perm eability used in the PAVT.

291E

- 2 2 1E

- 2 1 1E

- 2 0 1E

- 1 9 1E

- 1 8 1E

- 1 7 1E

- 1 6 1E

- 1 5 1E

- 1 4 1E

- 1 3 1E

- 1 2 1E

- 1 1

0 0

. 0 1 0

. 0 2 0

. 0 3 0


### D ila t a n t V o lu m e t r ic S t r a inInstrinsicPermeability(m2)

. 0 4 P f ei f l e et al , 1 9 9 8 S t or m o n t , 199 0

Figure 11. Permeability Versus Dilatant Volumetric Strain for WIPP Salt.



### 4.4 Salt Damage Modeling

The investigations of dam a ge evolution are international issues. The W I PP science advisor (Sandia National Laboratories) has a long-standi ng collaboration with peers in European salt
program s, m o st notably with the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR). Salt researchers at the BGR have led developm ent of a constitutive relationship between dilatancy and perm eability (e.g., Hunsche and Schulze, 2000; Cristescu and Hunsche, 1998). Their experim e nts and theory show that dilatancy (also called volum e change or dam a ge) is linearly increasing with creep deform ation under dilatant conditions and decreasing or healing with tim e in the com p ressive dom ain. This collaborative research is continuing. As noted by the Peer Review Panel (See Section 2.4) in their deliberations constitutive models based on measurement of the influence of creep damage on hydrologic properties may be feasible in the future, but such models are not expected to indicate that the changed model has failed to conservatively bound repository performance (Caporuscio et al., 2003)

. The stress-invariant dilatancy m odel has been used in structural calculations for approxim a tely 10 years and rem a ins a viable tool for engineer ing purposes and can be coupled with num erical analyses to predict disturbed or dam a ged zone s around a typical waste disposal room , as shown in Section 3.2. Figure 12 depicts the disturbed zone in term s of a dam a ge factor, D , 40 years after excavation. In the region corresponding to D > 1, the stress states fall within the dilational zone, while in the region corresponding to 0.8 < D < 1.0, the stress states rem a in in the isochoric zone (non-dilating zone) but are very near the dilational lim it expressed by the stress-invariant

m odel. As shown, the dam a ged zone or DRZ (D > 1) extends away from the room approxim a tely 3 m e ters or m o re after 40 years of unobstructed closure.

30Figure 12. Damage Predicted Around a Ty pical WIPP Disposal Room 40 Years After Excavation (after Van Sambeek et al., 1993b).

The stress-invariant m odel described above can be used to predict the extent of the DRZ around openings in salt but quantif ies neither the level of dam a ge nor the increase in perm eability associated with the DRZ. Based on the theoretical discussions provided above, the salt nearest an opening is expected to undergo the greatest dam a ge and, as a corollary, will also experience the greatest increase in perm eability. Salt farther from the opening undergoes m u ch less dam a ge and, as a result, experiences a m u ch sm aller change in perm eability.



### 4.5 Salt Damage Healing in Laboratory Studies

In laboratory tests Costin and W a wersik (1980) , Brodsky (1990) and Pfeifle and Hurtado (1998) have shown that the dam a ge evolution process in salt is reversible through crack closure and healing. In the Costin and W a wersik study, a series of short-rod fracture toughness strength tests were perf orm e d to determ ine the tensile load required to initiate and propagate f r actures in W I PP salt. The fractured test specim e ns were subsequently subjected to healing hydrostatic

com p ressive stresses ranging from 10 to 35 MPa, and then retested in a second series of fracture toughness tests after healing tim es of varying length. The study showed that the healed specim e ns regained from 70 to 80 percent of their initial fracture toughness strength.

Using the well-known correlation between wave velocity and crack developm ent in geologic

m a terials, Brodsky (1990) used com p ressional ultrasonic wave m easurem ents to study crack initiation, propagation and healing of W I PP salt. In general, velocity decreases with increases in

31rock dilation and increases in response to crack closure and/or porosity reduction. Microcracks were introduced into W I PP salt specim e ns during constant strain-rate triaxial com p ression tests conducted at low confining pressure. After speci fied dam a ge levels were induced, hydrostatic

com p ressive stresses of 5, 10, or 15 MPa were applied to the dam a ged specim e ns to prom ote healing. During both the loading and healing stages of the tests, ultrasonic wave transducers

were m ounted directly on the test specim e ns to m onitor wave velocity parallel and perpendicular to the m a xim u m principal com p ressive stress. During loading, wave velocity parallel to the

m a xim u m principal stress decreased 1 to 2 percent, while velocity perpendicular to the m a xim u m principal stress decreased by as m u ch as 10 percent. In contrast, velocity m easurem ents m a de during healing (or f r acture closure) increased, with the rate of increase depending on the initial level of dam a ge and the m a gnitude of the applied hydrostatic stress. The rate of increase in the wave speeds was slower for the m o re highly dam a ged specim e ns and this finding was attributed to shear offsets along the fractures. Rates of increase in velocity were ordered with respect to hydrostatic stress with higher rates corresponding to the higher hydrostatic stress levels applied during healing. Velocity recovery generally occurred within a few days.

Pfeifle and Hurtado (1998) studied salt healing through a series of gas and brine perm eability tests conducted on dam a ged W I PP salt specim e ns subjected to com p ressive hydrostatic stresses of 1, 5, 10 and 15 MPa. Dam a ge was initially introduced through constant stress creep tests conducted at low confining pressure. The dam a ged specim e ns were then loaded hydrostatically to prom ote healing and perm eability m easurem ents were m a de as a f unction of tim e. Perm eability decreased as a function of tim e with larger decreases corresponding to higher hydrostatic stress levels and specim e ns saturated with brine rather than gas. In som e tests, perm eability decreased by nearly two orders-of

- m a gnitude in less than 30 days. The
perm eability data were used to estim ate healing tim e constants that could then be used to predict the tim e required f o r com p lete healing. Based on their results, com p lete healing requires several hundreds of years at very low hydrostatic stress states (1 to 5 MPa), but is of the order of only a few years for higher hydrostatic stress states (i.e., 10 and 15 MPa).


### 4.6 Salt Damage Healing— In Situ Small Scale

The laboratory data for salt dam a ge characteristics, healing and salt-based concrete properties are all germ ane to the DRZ issues, particularly as applied for Option D panel closures. However, im plem entation of closures at W I PP involves m u ch larger scales and uncertainties associated with up-scaling properties. This section presents additional inform ation regarding the DRZ and seal m a terial perform a nce in situ

. A series of sealing experim e nts in the W I PP underground were executed over a ten-year period from 1985 to 1995. Series A and B are particularly relevant to panel closures, as they com p rised vertical (A) and lateral (B) placem ent of salt-based concrete. Many technical publications on the Sm all Scale Seal Perform a nce Test (SSSPT) program have been prepared and are sum m a rized in Finley and Tillerson (1992). Series A and B utili zed nine em placem ent holes located in the floor of the D Room Alcove and in the west rib of R oom M. The seal m a terial was an expansive-salt concrete developed by W a terways Experim e nt Station (W akeley and W a lley, 1986).

32All nine salt-based concrete seals perform e d well (Knowles and Howard, 1996). The larger (91-

cm diam eter) horizontal seals are m o st closely an alogous to panel closures, and are described in

m o re detail here. The concrete was pum ped into form s and was not vibrated (Storm ont and Howard, 1986). The seal system consists of the seal m a terial, the seal/host rock interface, the zone of rock im m e diately surrounding the seal, and the far-field host rock. The seals were tested for gas and brine perm eability from 1985 to 1987 a nd again from 1993 to 1995. The tests did not provide inform ation regarding the flow paths of the test fluid, so the calculated system
perm eability represents a com posite fluid barrier presented by all com ponents of the seal system

. Gas perm eability determ ined in 1985-1987 ranged from 10 -1 7 to 10 -2 0 m 2 and im proved to 10 -1 9
to 10 -2 3 m 2 when re-tested between 1993-1995. Additi onal geophysical and petrographic studies conducted in concert with the flow testing of the concrete seals (Knowles et al., 1998) provided evidence that the dam a ge existed on both sides of the concrete plug. Therefore, the rigid concrete inclusion provided the requisite back stress to heal the extant DRZ.



### 4.7 DRZ Delineation by Sonic Velocity

A considerable body of geophysical investigative work has been com p leted in the W I PP underground in the period since the initial certification (Holcom b , 1999, Hardy and Holcom b, 2000, Holcom b and Hardy, 2001). In m o st investigations, Holcom b and co-workers delineated the W I PP DRZ as a function of depth orthogonal to a drift wall and along vertical and horizontal paths parallel to the wall. In one cam paign, they m easured velocity in holes oriented at angle to the walls. The borehole array and the transducer assem b lies allow m easurem ent of elastic wave velocities necessary to detect the anisotropy of cr acking associated with the DRZ. Velocity and attenuation of elastic waves in the salt are a f unction of the density of cracks, as is the
perm eability.

Cross-hole and sam e -hole velocity m easurem ents give a consistent picture of the DRZ around the Q room access drift. The DRZ is well developed at m i d-height on the rib, extending into the rock 2 m e ters and possibly as m u ch as 4 m e ters. Near the back and floor, the DRZ is shallow (1

m e ter or less) or not detectable. Com p ressional m ode (P) waves in sam e -hole m easurem ents are

m o st sensitive to the DRZ because of favorable orientation of particle m o tion perpendicular to the cracking. Changes in V P as large as 22 percent were observed for P waves propagating perpendicular to the drift axis at room m i d-height.

Open cracks and loosened grain boundaries decrease elastic m oduli and therefore, elastic wave velocities. The effect on elastic wave velocities is strongest for cracks oriented perpendicular to the particle m o tion induced by the wave. Thus the physical extent of the disturbed zone can be determ ined by propagating elastic waves through successive portions of the form ation until an undisturbed zone is reached, as indicated by a cons tant velocity with increasing depth from the rib. Cracking responsible for the disturbed zone is expected to vary as a function of distance from the walls of the Room Q alcove and to depend on the position of the m easurem ent path relative to the back, floor and corner.

Cross-hole m easurem ent paths were nom inally one m e ter long, while the sam e -hole

m easurem ents all had the sam e fixed path length of 33 cm . Figure 13 shows the arrangem e nt

33and nam i ng schem e for the m easurem ent holes, QGU30, QGU31, ... QGU41. Travel tim e

m easurem ents were m a de using the technique com m only used for laboratory determ inations of sound speed in rock; a sound pulse was applied to the rock at a known tim e and place and, after traveling through the rock, was received by a transducer at a known distance. The travel tim e and distance com b ine to give the average velocity over that path.

The m o st recent work com p leted at W I PP probed twelve holes cored in the Room Q alcove corner (see Figure 13). Two rows of holes, 1 and 3 counting f r om the top, were in halite, while rows 2 and 4 were in argillaceous salt. Each hole was 10.16 cm (4 inches) in diam eter, 6+

m e ters deep and as nearly horizontal as possible. Hole locations were chosen to sam p le the m a p units present (labeled halite and argillaceous in Figure 13), and also the expected variation in dam a ge around the corner.

4

4 4 4 4 4 4 4 4 Q A L C O VE S O UT HE AST CO R N E R BO RE HO L E S

TE R R Y MACDO NALD & WE S DEYO NG E

SANDI A NATI O N AL LABO RAT O R I ES, D EPT

. 6 8 2 1 DRZ CHAR. TEST PLAN

04 / 1 0/ 0 0

( HALITE)

(A RGILLACE OUS) 4 4 4

( ARGI LLACEOUS) ( HALITE)

FL O O R ( S O U THEAST CO R N ER) BACK

( M ARKER BED) QGD 30 QGD 31

QGD 32 QGD 33

QGD 34 QGD 35

QGD 36 QGD 37 QGU 30 Q G U 3 1 QGU 3 2

QG U 3 3 Q GU 34 QGU 3 5

QGU 3 6 Q G U 3 7 QGU 3 8

QGU 3 9 Q G U 4 0 QGU 4 1

Figure 13. Lay out of Holes for Room Q Alcove, w i th holes used for ultrasound measurements indicated in red. Other holes indicated are for proposed hydrological studies.

Sonic velocities can be m easured vertically and horizontally across holes, resulting in 9 sets of

m easurem ents f o r vertical paths and 8 horizontal paths in planes parallel to the corner walls. In addition, twelve sam e -hole m easurem ent sets were com p leted. Typical sam e -hole, P-wave results are shown in Figure 14. The DRZ of less than 2 m e ters developed along the wall (red dots) is typical for W I PP openings. The unique aspect of these m easurem ents is the lack of DRZ

34in the zone directly outside the room corner. As seen in Section 4.8, the dam a ge fracture orientations also reflect stress states along the walls toward the corner.

7

0 1 2 3 4 5 6 7 Depth (m) 0VP(km/sec) 4 4. 5

QG U 3 6 -

- > Q G U 36

, P

co lu mn 1 4 4.5

QG U 37

- - > Q G U 3 7
, P

Figure 14. Same-hole measurements for adjacent holes, one in the left-hand w a ll (red) and in the corner (black).

Results show that velocity at depths greater than about 1 m e ter vary from the m ean by less than 0.5%, which is close to the attainable accuracy. Sim ilarly constant velocities are observed in the other paths through halite. In contrast, V P along paths in the “argillaceous” halite layers variesby several percent even at depths beyond the DRZ. All four data sets for the horizontal crosshole V P m easurem ents m a de in halite layers indicate a constant velocity as the m easurem ent depth approaches 6 m e ters. Two data sets show clear evidence of a disturbed zone extending in about one m e ter. Little or no evidence for a DRZ was found in the other two m easurem ents in halite. In contrast to horizontal paths, dam a ge m easured along vertical paths is less extensive, reaching shallower depths and producing sm aller changes in V P . The general pattern of dam a ge is sim ilar and slightly asym m e tric, with greatest dam a ge observed in the upper portion of the left wall and the lower portion of the right wall.

Previous work (Holcom b and Hardy, 2001) in the access drift leading into the Q room alcove, showed a sim p ler pattern of DRZ developm ent and a m o re extensive dam a ged zone. In the access drift, where the geom etry is essentially 2-dim e nsional, the DRZ was observed to be best developed at m i d-height of the drift and to extend as m u ch as two m e ters. The com p lexity

35observed in the corners reflects the influence of the 3-dim e nsional geom etry on the stress state and subsequent developm ent of the DRZ.

Dam a ge along the m easurem ent path contributes to velocity decrease, which is a signature of the DRZ. Thus the constant V P observed in the alcove corner along vertical paths indicates that no point from ceiling to floor has experienced signifi cant dam a ge in the form of cracks that could decrease the speed of a com p ressional wave propagating vertically. Cracks oriented perpendicular to the direction of propagation are m o st effective in decreasing V P ; in this case, horizontal cracks would be m o st ef f

ective. Thus it appears that little or no horizontal cracking has occurred near the bisecting plane of the corner, at any depth, even 12 years after excavation. A m e ter away, the stress state is sufficiently different that V P in the vertical direction is decreased, indicating som e horizontal, or at least non-vertical, cracking did occur. Near the floor and ceiling the DRZ was less pronounced than in sim ilar zones closer to the m i d-height of the

room . Dam a ge was clearly anisotropic, with the m a xim u m decrease in V P being observed in directions m o re nearly perpendicular to the walls. This f its with the assum p tion that the DRZ is the result of cracks opening in the direction of m i nim u m com p ressive stress. In previous work, velocity m easurem ents typically indicate a DRZ extending in about 2 m e ters. An exception to that rule was found in the AIS (Hardy and Holcom b, 2000) where the DRZ only extends 0.5 to 1

m e ters. In the corner of the Room Q alcove the DRZ only extended in about 1 m e ter and there

were m a ny areas that did not appear to be dam a ged.

It is expected that the current results will be useful to other studies of the long-term deform ation characteristics of salt. The data delineate the DRZ as a function of depth from the alcove corner and as a function of the varying stress state around a rectangular alcove corner cross-section. The significance of the results lies in the length of tim e the DRZ has had to develop (approxim a tely 12 years), the geom etrical com p lexity of the alcove corner, which will allow a

m o re rigorous test of m odels than is possible in sim p ler geom etries. Understanding the tim edependent changes in dam a ge, and thus perm eability, as the DRZ develops is im portant because these properties affect sealing and PA m odels of underground openings at the W I PP.

Previous work had exam ined the DRZ in sim p le ge om etries, typically a room wall or a long drift. More recent work is an extensive look at what happens in the corner of a room , an area deliberately chosen for its com p lexity. As expected, the pattern of dam a ge was found to be m o re

com p lex than in the sim p ler geom etries previously studied. Two features were unexpected: dam a ge did not extend in nearly as far as in the previous studies, and along the bisecting axis of the corner, no DRZ at all was observed.



### 4.8 Observational Fracture Studies

The W I PP site itself provides an underground research setting that has been exploited to quantify spatial and tem poral characteristics of the distur bed rock zone. In concert with the work of Holcom b and coworkers as sum m a rized in the previous section, we have continued petrofabric analyses of salt core recovered from the sonic velocity holes. To com p lem e nt these studies, international partners provided cores from the Asse Mine of interest to their program s. Together, these cores avail an opportunity to assess the nature of dam a ged core from the proxim ity of

36underground openings in salt workings. In this section we present petrophysical evidence of the structural state of the DRZ and excavation disturbe d zone cores drilled f r om two dif f

e rent sites.

The com p rehensive m i crostructural exam inations that include fracture, free dislocation density and subgrain boundaries have been subm itted to the European Union for publication with their sponsored research on salt repositories. However, the relevant observations concern the

m a nifestation of dam a ge, which is described and quantified in term s of fractures. In addition to salt cores from W I PP, sam p les were provided by Germ an colleagues from the ALOHA II Project (W ieczorek and Zim m e r, 1999), and from the Northern Test Drift B of the Germ an Therm a l and Structural Dem onstration Experim e nt (TSDE) Test Field. The TSDE was conducted at the Asse Mine, near Braunschweig, Germ any, by Gesellschaft fur Anlagen- und Reaktorsicherheit m b H (GRS). BAMBUS II (Backfill and Material Beha vior in Underground Salt repositories) is the post-f acto evaluation of the TSDE, and addresses the behavior of the DRZ, as well as backf ill

m a terial within a geologic repository for heat-generating radioactive waste in rock salt. Fracture analyses entail petrographic fracture m a pping; crea tion of thick sections to investigate fracture densities, f r acture apertures, f r acture angles and th e spatial distribution of f

r actures. For the m o st part scanning electron m i croscopy (SEM) was used to capture and quantify the im ages.
A larger suite of observational studies (Chapin and Hansen, 2002) focused on m i crostructural analyses of seven salt cores: (1) W I PP Core QGU14 (6.07 m ) , (2) W I PP Core QGU36 (7.33 m )

, (3) W I PP Core QGU39 (2.25 m ) , (4) Asse Mine Core DJ-V (6.97 m ) , (5) Asse Mine Core HD-V (6.83 m ) , (6) TSDE Core VVS-A-Mi4 (0.72 m ) , and (7) TSDE Core VVS-D1-Mi4 (0.77 m )

. The dim e nsions in parentheses indicate the lengths of the cores referenced from the opening or drift face in which the cores were recovered. As can be seen, m o st cores extend from a free surface to a considerable depth into the country rock. The TSDE cores were selected from the near field of the heater experim e nt. These core s exhibited little fracturing, despite being adjacent to a free surface. The associated elevated tem p erature gave rise to therm a lly activated def o rm ational processes, thereby m i nim i zing the brittle m a nif e stations of f

r acture.

The geology of W I PP QGU14 and QGU36 are sim ila r; both com p rise elongate, coarse, clear halite and m i nor am ounts of anhydrite. W I PP QGU39 derives from the so-called “argillaceous” salt zone. All W I PP core was obtained by dry drilling (horizontally) through the inside rib of the 4-m high repository drif t. W I PP Core QGU14 was drilled norm a l to the rib at m i d-height, whereas cores QGU36 and QGU39 were recovered f r om boreholes drilled into the corner of the Q-Room access drift at an angle of 45 ° –50 ° to the inside rib faces. The Germ an cores derive from lined and unlined portions of 80-year-old drifts in the Asse research m i ne, at a depth of 700

m e ters (see Section 4.10). The TSDE cores were extracted from the Asse Mine’s Northern Drift B, at the 800-m level as part of ongoing international collaborations.

37Of the seven cores studied, three cores were analyzed over their entire length at a shallow distance into the rib: (1) W I PP Core QGU39 (2.25 m ) , (2) TSDE Core VVS-A-Mi4 (0.72 m )

, and (3) TSDE Core VVS-D1-Mi4 (0.77 m ) . The four rem a ining cores, W I PP Cores QGU14 (6.07 m ) and QGU36 (7.33 m ) , as well as the ALOHA II Cores DJ-V (6.97 m ) and HD-V (6.83

m ) were analyzed differently. The com p lete first m e ter of each core was exam ined, and then subsequent f r acture analyses were perf orm e d at 1-m intervals until the core length was exhausted. For display purposes Figure 15 plot s the fracture distribution for the W I PP cores alone. Of the 744 fractures m easured in the thr ee W I PP cores, only two fractures at a depth of greater than 2 m e ters have m easured apertures wider than 125 μ m

. In all the cores m easured, fracture apertures are predom inantly wider proxim a l to the rib face (at approxim a tely 0.1 m e ters and 1.25 m ) . Cores QGU36 and QGU39 were oriented nearly 45 o to the drift face. The

m easured f r acture angles qualitatively oriented parallel to the drif t wall, and thus could be categorized as stress induced fractures and clearly not coring dam a ge. Fracture angles closest to the rib face lie subparallel to the rib face for both cores; at approxim a tely 60 ° to the core axis in QGU36 and approxim a tely 50 ° in core QGU39. At approxim a tely 2 m

, the fracture angles in both cores have rotated essentially norm a l to the core axis. Results of the fracture analyses of the W I PP, ALOHA II and TSDE salt cores are presented in Figure 16.

0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0

0 1 2 3 4 5 6 7 8 

### D i s t ur be d R o c k Z o ne F r a c t u r e An a l y s e s : WI PP Re pos i t o ry C o r e s QGU14, QGU3 6 an d QGU3 9

W I

P P C o re QG U 1 4 W I

P P C o re QG U 3 6 W I

P P C o re QG U 3 9FractureAperture(microns)



### Di s t ance from R i b Fac e (m )

Figure 15. Fractures and Apertures in Three WIPP Cores.

r a t h e r s u r p r i s i n g r e s u l t i s t h a t t h e f r a c t u r e d i s t r i b u t i o n s a n d f r a c t u r e a p e r t u r e s b e t w e e n t h e A ALOHA II Cores DJ-V and HD-V were found to be sim i l a r

. O n e w o u l d h y p o t h e s i z e t h a t core obtained from behind the rigid tunnel lining (details given in Section 4.9) would have

com p letely healed the f r actures. Perm eability m easurem ents showed that perm e a b i l i t y w a s

38reduced behind the liner, despite the presence of fractures m easured in the cores. Except for a few wide fractures m easured proxim a l to the rib wa ll in core DJ-V, there does not appear to be a large disparity between fracture density and fracture aperture as a function of depth between either the ALOHA II lined (DJ-V) and unlined (HD- V) drift sam p les. Fracture distributions and fracture apertures are sim ilar for both TSDE cores and m i nim a l com p ared to the unheated cores. A com p arison of all seven cores is presented in Figure 16. The highest density of fractures is observed closest to the rib walls, at an approxim a te distance < 2 m e ters. Fracture apertures at a depth of 2 m e ters or greater are predom inantly < 100 μ m w i d e

.

0 1 2 3 4 5 6 7 8 0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0 

### DRZ a n d E D Z F r ac tur e A n a l y s es: W I P P a n d G e r m a n R e po sito ry Co r e s

W I

P P Co re QG U 1 4 W I

P P Co re QG U 3 6 W I

P P Co re QG U 3 9 AL O H A I I C o re DJ

- V AL O H A I I C o re HD -V TS D E C o r e V V S

- A- M i 4 TS D E C o r e V V S

- D1

- M i 4



### Di st ance from R i b Fac e (m )FractureAperture(microns)

Figure 16. Fracture Apertures for DRZ Cores from WIPP and Asse

h e m i crostructural analyses perform e d on cores reveals that the distribution of fractures is T higher and that fracture apertures are wider proxim a l (approxim a tely < 2 m e t e r s ) t o t h e r i b f a Fracture apertures existing at a depth of 2 m e ters or greater are predom inantly c e s

. < 100 μ m w i d e

. A clear, though qualitative relationship defining the DRZ exists between velocity and dam a ge. Sonic velocity increases as dam a ge decreases and the shapes of the curves are inversely proportional. It would appear that the DRZ exists as deep as 2 m e t e r s i n t h e c l e a n z o n e s near the rib m i d h e i g h t , a n d t o a r e l a t i v e l y l e s s e r e x t e n t n e a r t h e f l o o r , n e a r t h e b a c k a n d n e a r t h e

corners. o f s a l t



### . 9 F u l l

- S c a l e F i e l d A n a l o g s

a l t d a m a ge healing has been dem onstrated in the laboratory and in 1-m

- scale field tests on W I PP salt. Field evidence of dam a ge healing on a large scale has not been dem onstrated within 

### 4

S

39the conf ines of W I PP. Indeed, in the world this type of inf o rm ation is sparse. The Germ a n s have published an excellent exam ple of healing around a rigid enclosure. This case study is known as ALOHA (Untersuchungen zur Auflockerungeszone um Hohlräum e im Steinzalzgebirge). These investigations were conducted in the Asse salt m i ne near Braunschweig, Germ any (W ieczorek and Zim m e r, 1999).

The in situ perm e a b i l i t y t e s t s w e r e c o n d u c t e d o n t h e 7 0 0

- m level of the Asse salt m i ne, where a

a s t s t e e l b u l k h e a d w a s p l a c e d i n a d r i f t d u r i n g t h e 1 9 2 0 ’ s

. T e s t s w e r e c o n d u c t e d i n o p e n

n d a c sections of the drif t and behind the steel liner. Perm eability m a gnitudes are diagram e d i n F i g u r e 17. As can be readily ascertained, the perm e a b i l i t y t e s t s e v i d e n c e h e a l i n g o f t h e D R Z a r o u rigid structure, at a depth com p arable to W I PP. T h e e x t e n s i o n a n d t h e h y d r a u l i c p r o p e r t i e s o f t h e DRZ around a drift were investigated by m eans of gas and liquid injection testing.

10 m -1 5 2 10 m -1 6 2 10 m -2 1 2 10 m -2

0 2 10 m -1 9 2 10 m -1 8 2 10 m -1 7 2 P

e

r m e

a

b

ili ty 1. 5

1. 3 1. 5 8. 0 5. 0

7. 0 9. 0 1. 8
5. 7

1. 0 Bu l k h

e

a

d O p

e

n

D

r if

t

Figure 17. ALOHA2: Permeability Distribution around the Bulkhead and Open Drift.

C o

o t h c o n s t r u c t i o n a n d p e r f o r m a nce. The m o st pertinent experience noted during a

y e r m a n et al.,

e s e a l n c r e t e b u l k h e a d s p l a c e d i n C a n a d i a n p o t a s h m i nes also provide im portant case studies for b reconnaissance in 1994 occurred in the PCS Rocanville potash m i ne. Additional analog observations regarding Canadian bulkheads and othe r c a s e s t u d i e s a r e r e p o r t e d i n E 1995. The experience at the Rocanville m i ne is particularly illum i n a t i n g b e c a u s e c o n c r e t construction was perform e d quickly, and success was critical to survival of the m i ne itself. This successful deploym ent of a drift seal constructed of brine-based concrete is analogous to panel closure construction at the W I PP.

40The Rocanville bulkhead was constructed in halite, f o llowing water inf l ow f r om an overlying

a q u i f e r

. A c o n c r e t e b u l k h e a d w a s d e s i g n e d t o c ontain the inflow and prevent additional inflow
t o t h e m i ne. A “tem porary” bulkhead located 120 ft from the face (point of inflow) was d d

e

i t s

v e r w h e l m ing success. These factors dem onstrate that basic salt concrete is i g h l y i m perm eable and construction m e thods need not be overly elaborate to be successful.

s

r y

r f i e l d t e s t s

. T h e f a c t t h a t s a l t m i nes creep closed is well known. Ancient sections of the

d i s

h e t r e a t m e nt of operational changes at the W I PP that include the

g t e c h n i c a l c o n s i d e r a t i ons. The flow of the docum ent is chronological

o m the com p liance certification, through the perform a nce assessm ent verification, to the

ent

r r e d
t o

n t

l l o w e d t h e C C A

. A t t h e s a m e tim e, the DRZ m odel was updated to depict m o re accurate

. i n constructed, and has functioned perfectly since its em placem e n t i n 1 9 8 5

. T o t a l h y d r o s t a t i c h e a is m o n i t o r e d b y v a r i o u s a c c e s s e s t h r o u g h t h e b u l k h e a d

. D e s i g n a n d c o n s t r u c t i o n o f t h e b u l k h e a t o o k o n l y a f e w w e e k s , a n d t h e c o n d i t i o n s f o r t h e c o n s t r u c t i o n w e r e l e s s t h a n i d e a l

. D e s p i t these factors, the bulkhead has resisted water pressures approaching 10 MPa and has not leaked since construction. This does not dem onstrate th at the DRZ developed and then healed, but does dem onstrate a f u ll-scale salt-based concrete bulkhead in salt that is im perm eable to a f u ll hydrostatic head.

The principal reason this case study is so im portant to the future panel closure at W I P P i s sim p l i c i t y a n d i t s o h

The m o st relevant analogs to the case at hand include sim ilar scale, setting, tim e and m a t e r i a l s a the W I PP Option D Panel Closure. Tim e repres ents one elem e n t b e y o n d t h e r e a c h o f l a b o r a t o

o Hallstatt salt m i ne have preserved holdings dating from the Late Iron Age (500 B.C. to 0), including an unfortunate Celtic m i ner encapsulated in salt, whose “fully preserved body...was found in the Hallstatt salt m i ne” (DHP-Design, 2003)

. T h e f a c t t h a t s a l t c a v i t i e s c r e e p c l o s e

w e l l r e c o g n i z e d

. T w o p e r t i n e n t a n a l o g s p r e s e n t e d h e r e i l l u s t r a t e t h a t o n a l a r g e s c a l e , r i g i d inclusions tend to heal dam a ged salt and when functioning in tandem with salt provide essentially im perm eable barriers.



## 5.0 Summary

This docum e n t p r e s e n t s t disturbed rock zone am o n f r technical m i gration of the baseline in preparation for the re-certification calculations. Inform ation within this report provides justification and reasonableness for the DRZ m odel in Salado f l ow calculations, param e ters, and level of detail that will represent m a jor changes experienced in the W I PP underground, nam e ly, incorporation into perform a n c e a s s e s s m calculations 1) the EPA m a ndated Option D panel closure and 2) the advent of raising the repository horizon 2.43 m e t e r s t o C l a y G

. I n c o r p o r a t i o n o f t h e s e c h a n g e s , w h i c h h a v e o c c u since the original com p l i a n c e c e r t i f i c a t i o n f i v e y e a r s a g o , r e q u i r e d a d d i t i o n a l d e t a i l b e a d d e d the analysis schem e and that im provem e n t t o o u r u n d e r s t a n d i n g o f t h e D R Z b e i n c l u d e d t o reflect m o re accurately the actual conditions experienced in the W I P P n u c l e a r w a s t e r e p o s i t o r y

. These changes, particularly the Option D conditi o n o f t h e c e r t i f i c a t i o n , r e p r e s e n t e d s i g n i f i c a departure from the analyses run for the original com p liance PA and the verification test that f

o geom etries and properties of the DRZ. The operational reality of m i ning to Clay G was evaluated in term s of room closure and the resulting porosity, which in turn is sam p l e d i n P A

41Details of the Clay G analyses also provided insi g h t t o t h e l o c a l b e h a v i o r o f t h e D R Z e v o l u t i and devolution and the distortion of the anhydrite layers near the disposal room s. This inform ation supports the analytical treatm e nt of t h e O p t i o n D p a n e l c l o s u r e a n d i t s i n c o r p o r a t i o into the Salado flow conceptual m odel. The updated m odeling approaches and the concepts for the DRZ were subjected to independent peer re v i e w i n a c c o r d w i t h r e g u l a t o r y p r o c e d u r e found to be acceptable.

The rest of this docum ent provides a sum m a ry of technical inform ation pertaining to the DRZ and em p h a s i z e s k n o w l e d o n

n

s a n d

g e p e r t a i n i n g t o W I PP that m i ght change the m e thods im plem ented in

r e v i o u s a n a l y s e s

. C a l c u l a t i o n s s h o w t h a t prediction of the one-way evolution of the DRZ

o f

l t

h e

t o a s s e s s v a r i o u s o f f i c i a l p o s i t i o n s o n t h e D R Z a s a m a tter of “record”. Places within

e r e c o r d t h a t m e ntion the DRZ are listed in Appendix B. Contents of this docum ent and its

B

. L a d a n y i

. 1 9 9 1

. “ U n i f i e d V i s c o p l a s t i c M o d e l f o r t h e I n e l a s t i c

e s , ” Mechanics of Materials . Vol. 11, no. 1, 63-82.

s . SAND90- 7076. Albuquerque, NM: Sandia National Laboratories.

B r o d s k h e

, N M : S a n d i a N a t i o n a l Laboratories. p replicates observations in the W I PP underground. The size and shape of the DRZ around an opening based on a stress invariant criterion are sim ilar to the size and shape derived from s o n i c velocity studies and from m i croscopy of core dam a ge. The m odel output does not provide
perm eability directly, but the trend and m a gnitude of perm eability around W I P P o p e n i n g s a r e understood in considerable detail. For W I PP applications, the high perm eability in zones near the skin of a room is of little consequence. On the other hand, over estim ation of t h e e x t e n t the DRZ could im part signif i cant f i ctitious ef f

ects, if m odeled im properly. Healing of the DRZ—entom b m e nt of the waste—is a f a r m o re im portant concept to PA. Eventually DRZ evolution will reverse as the creeping salt approaches equilibrium with the disposal room

c o n t e n t s

— a c o n d i t i o n t h a t c o u l d a r i s e q u i c k l y i f a r i g i d p a n e l c l o s u r e w e r e c o n s t r u c t e d

. S a healing will ensue and the technical bases, f r om theory to practice, f o r this f a c t a r e g i v e n i n t

m a in text.

A review of the com p liance supporting docum ents and the com p liance subm ittal itself was perform e d
t h references include all the significant advancem ents pertaining to the DRZ and sufficient technical justification for m odel and param e ter changes proposed for W I PP re-certification.


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49Appendix A: Salt-Based Concrete

Salt-based concrete constitutes the m a jor engineered m a terial in the Option D panel closure design. Because the behavior of the salt DRZ depends upon interaction with the concrete

m onolith, characteristics of the salt-based concrete are essential f o r incorporation into the analyses. Portland cem ent concrete has exceptionally low perm eability and is widely used f o r hydraulic applications. Salt-based concrete, such as the SMC specified for the Option D closure, is essentially Portland cem ent concrete with the m i xing water saturated with respect to NaCl. Salt-saturated concrete has been used successfully as a seal m a terial in potash and salt m i ning applications. Salt-based concrete has received less attention than ordinary Portland cem ent (OPC) concrete, however several specific investigations provide a com p arison between saltbased and OPC concrete. Upon hydration, unfractured concrete is nearly im perm eable, having a
perm eability of less than 10 -2 0 m 2 . From laboratory and field experim e nts, it has been dem onstrated that salt-based concrete possesses engineering properties sim ilar to OPC concrete. And, salt-based concrete is com p atible with the salt m i ne environm ent.

The following text establishes perform a nce expectations for the SMC used in the Option D panel closure construction. It is included in this docum ent as an appendix to the DRZ discussion, because the analysis necessary for PA involves a system com p rising intact salt, dam a ged salt, and the concrete m onolith. Properties of salt-based concrete are established in the laboratory, in scale-m odel field tests (Section 4.6) and at the full scale (Section 4.9).

Pfeifle et al. (1996) conducted tests on two salt-based concretes: (1) SMC and (2) cured concrete recovered from the shaft plug of an existing salt m i ne (referred to as MSC concrete). The SMC was specifically designed for use in the W I PP shaft sealing system and was tailored to have lim ited shrinkage and to be com p atible with W I PP salt through the addition of salt to the m i xing water (W akeley et al., 1994). The MSC concrete was originally placed as a shaft plug in a

com m e rcial salt m i ne located near the St. Lawrence seaway and consisted of two types of

m i xtures, MSC(1) and MSC(2). The MSC(1) conc rete com p rised a typical 27.6 MPa (4,000 psi) design batch using coarse and fine (sand) aggregates and Type I/II cem ent. The water for the MSC(1) was m i xed with salt in a truck to produce a saturated brine before the solid com ponents were added to the batch. MSC(2) concrete com p rised a sand/cem ent m i x that was placed in the shaft by trem ie line under 70 m e ters of water. Granular salt was added to this batch to form brine during m i xing.

Table A.1 sum m a rizes the strength and perm eability testing conducted on the SMC and MSC cores. Figure A.1 plots perm eability as a f unction of the gas pressure dif f

e rence applied during the perm eability testing of the SMC and MSC specim e ns as well as ESC specim e ns, which are described further in the discussion of sm all-scale seal perform a nce tests (Section 4.6). The
perm eability of the SMC was typically of the order of 10 -2 1 m 2 , while the perm eability of the MSC was approxim a tely four orders-of-m a gnitude higher, i.e., 10 -1 7 m 2 . This difference in
perm eability was attributed to two f actors: (1) the stringent design requirem e nts established to lim it fluid flow through the W I PP SMC shaft sealing com ponents and (2) the lim ited quality control used in the placem ent of the MSC concrete under extrem e conditions (i.e., placem ent under water). The perm eability of the ESC from the SSSPT (Section 4.6) is approxim a tely

5010 -1 9 m 2 , which f a lls between the perm eability f o r the SMC and MSC tests. The strengths of the two types of concrete are com p arable, and increase appreciably when confined.

Table A.1 Summary of Strength and Permeability Tests on SMC and MSC Concrete Specimens.

Specimen I.D. Permeability (m 2 ) Confining Pressure

(MPa) Stress Difference At Failure (MPa) Elastic Modulus, E (GPa) Poisson’s Ratio, ν

Salado Mass Concrete 40SM4-19/2- 1/1 2 × 10 -2 1 – 8 × 10 -2 1 0 4 4

. 2 3 6

. 3 0

. 1 9

32SM4-25/1- 1/1 – 5 75.8 30.5 0.20

40SM4-11/2- 1/1 9 × 10 -2 2 1 0 8 0

. 5 3 6

. 7 0

. 3 5

40SM4-2/1- 1/1 – 1 5 1 1 1

. 4 3 2

. 2 0

. 2 0

MSC Shaft Concrete MSC/D-1 4 × 10 -1 7 – 10 × 10 - 17 0 6 0

. 2 1 8

. 3 0

. 1 5

MSC/O-2/2 2 × 10 -1 7 – 4 × 10 -1 7 0 4 5

. 3 2 2

. 6 0

. 2 3 MSC/K-2/2 2 × 10 -1 7 – 4 × 10 -1 7 0 5 6

. 4 3 2

. 8 0

. 1 7

511. E

- 2 1 1. E

- 2 0 1. E

- 1 9 1. E

- 1 8 1. E

- 1 7 1. E

- 1 6 1. E

- 1 5

0. 2 0

. 3 0. 4 0

. 5 0. 6 0

. 7 0. 8
G a s P r essu r e D i f f er en ce ( M P a )Permeability(m2) S M C C onc r e t e E S C C onc r e t e M S C( 1 ) & M S C ( 2 ) C o n c r e t e

Figure A.1. Permeability of SMC, ESC, and MSC Concrete Specimens Versus Gas Pressure Difference.

52The perm eability of salt-based concrete was m easured in the Sm all Scale Seal Perf orm a nce Test (SSSPT) for a decade and corroborated by laboratory m easurem ents. From these tests, values and ranges of concrete perm eability have been developed. For PA calculations, perm eability of SMC seal com ponents is treated as a sam p led variable, for which the probability distribution function is plotted in Figure A.2.

Figure A.2. Cumulative Distribution Function for Permeability of SMC (after Repository Isolation Sy stems Department, 1996, WIPP Shaft Seal Sy stem Compliance Submittal Design Report, Appendix A).

53Appendix B: DRZ Issues Addressed in the CCA

The disturbed rock zone was addressed in several com p liance docum ents. Because these references com p rise the basis for the EPA com p liance determ ination, a review of the disturbed rock zone discussions as they exist in the com p liance record is appropriate. The conceptual

m odel im plem ented at the tim e of the com p liance subm ittal has been advanced in certain ways, as discussed in the m a in paper. Modest research effort has continued in the underground at the repository horizon as well as collaborative research on the international frontier. Based on recent inform ation obtained since the CCA coupled with historical inform ation, the current understanding and description of the DRZ differ som e what from the concepts put forward in the CCA. A word search on DRZ was conducted for the CCA and supporting docum ents. The following reference sections of the CCA were exam ined in preparation of the DRZ discussions in the m a in text to ensure consistency between the CCA baseline and the current discussions of the DRZ. These docum ents are identified below and a brief evaluation or sum m a ry is provided. Thus, the bases of the DRZ considerations in the CCA have been reviewed in preparation of this

m e m o randum

. The Compliance Application: Section 2.2.1.3 Hydrology of the Salado: sum m a rizes hydraulic tests in salt and anhydrite. Measured perm eabilities are all lower than 10 -1 8 m 2 . Other discussion acknowledges that flow observations are com p lex.

Section 3.2 Repository Conf iguration: states that the panel closure system “will prevent f u rther developm ent of the DRZ in panel entries.” W h en the Option D panel closure is constructed, this
statem ent should be m odified to include the f act that the DRZ would be m i ned out and any existing DRZ would heal shortly thereafter.

Section 3.3.1.3.2 Clay Colum n s: clay colum n s tiffness is sufficient to heal fractures, thus

rem oving the DRZ.

Section 3.3.1.5.1 DRZ Behavior: discusses DRZ healing as accounted for in the Shaft Seal Design.

Section 3.3.2 Panel Closure System : again notes that the PCS would prevent the existing DRZ f r om increasing in perm eability. Option D would change this position. Also, this section notes that the panel concrete would not degrade to a condition that is m o re perm eable than the DRZ.

Section 6.0.2.2 Undisturbed Perform a nce: presents argum ents for DRZ healing around the
concrete com ponents. In the absence of elevated pressure in the repository, salt creep would also eventually result in substantial com p action of the waste.

Section 6.4.3.1 Creep Closure: discusses creep closure and developm ent of the porosity surface.

Section 6.4.4 This section discusses the Shaf t Seal System (from Appendix SEAL) and its representation in BRAGFLO.

54Section 6.4.5 The Salado: discusses m odeling interbeds and fracturing.

Section 6.4.5.1 Im pure Halite: begins by noting that gas will not f l ow in halite.

Section 6.4.5.2 Salado Interbeds: identifies the distinct anhydrite interbeds m odeled in BRAGFLO (MB 138, MB 139, and anhydrite layers a and b). MB 139 and anhydrite a and b are included within the DRZ. The DRZ is extended to reach MB 138 “because of uncertainty in the extent and properties of the DRZ and the associ ated long-term isolation of MB 138 from the repository.” The extent of the DRZ as m odeled in the CCA and PAVT is m u ch larger than practical observation, geophysical m easurem ent, and m odeling would suggest.

Section 6.4.5.3 DRZ: states that PA approxi m a tes the effects of the DRZ conservatively by extending it from MB138 to MB 139, thus creating a perm anent high-perm eability region that does not significantly im pede flow between the repository and affected interbeds. Table 6-17 lists the DRZ param e ter values as discussed in the m a in CCA text. The DRZ representation has been m odified for the re-certification calculati ons to include Option D closures. Therefore,
perm eability near the Option D closure has been assigned values consistent with the best available inform ation since the CCA.

Section 6.4.7.1.1 Direct Brine Release During Drilling: presents arbitrarily assum e d DRZ f o r pillars.

Section 6.4.10.1 Disposal System Flow and Transport Modeling (BRAGFLO and NUTS): discusses start-up perm eabilities, constant perm eabilities and other initial conditions, such as gas reaction rates.

Section 6.5.4 Uncertainty: basically states that PCS and DRZ are assigned perm eability of 10 - 15 m 2

. Section 7.2 Monitoring: states that “Mon itoring the DRZ hydrologic properties would not provide relevant inf o rm ation of verif y assum p tions used in PA; theref ore, they will not be

m onitored during the operational period nor during the postclosure period.” This statem ent was presum ptuous, as ongoing evaluation of DRZ provide s m o re realistic appreciation of the DRZ than reflected in the CCA.

Section 7.2.3.1 Geom echanical Monitoring Program : counterm a nds the previous statem ent by acknowledging “...geotechnical m easurem ents will be useful to detect deviations in ...DRZ developm ent.

Section 9.3.1.1 Adequate Models: “concludes that the present DRZ m odel is adequate to be im plem ented in perform a nce calculations.”

Section 9.3.1.2.2.3 Third Peer Review Panel Concern-Repository Fluid Flow: presented and discussed the issue stated as “Consolidation of the waste, panel seals, and repository disturbed rock zone (DRZ) over tim e would result in lower perm eabilities f o r these regions.” The ef f

ects

55of dynam i c perm eability of the DRZ were m odeled and “results in com puted releases to the accessible environm ent that are essentially equivalent to the baseline case. In addition, dynam i c alteration of the DRZ/TZ has an insignif i cant e ffect on waste room conditions relevant to blowout cuttings, and spalling releases.”

Section 9.3.1.2.8.3 Third Peer Review Panel Concerns: revisits direct brine release owing to penetration into the DRZ.

Appendices Appendix SOTERM 7.1.2 Use of Brine End Mem b ers: Material here is of no consequence to DRZ considered in the repository horizon.

Appendix SEAL (contains 210 call outs of DRZ): Discussion in Appendix SEAL concerns the shaft seal system . In the design and analysis of the shaft system , the DRZ was incorporated into the analysis in considerable detail. The shaft seal design thoroughly accounted for the DRZ, as noted by the EPA com m e nts found in other sections; however, the DRZ near the disposal room s is com p licated by the horizontal stratigraphy and the size and shape of openings.

Appendix MASS.2.4 CM Developm ent (1982 to Present): The m odeling concept for panel closures and an “im p erfectly healed DRZ” are noted here.

Appendix MASS.3.1 Darcy’s Law: Not applicable for DRZ discussions.

Appendix MASS.13.0 Salado: Flow in the Salado is m odeled to occur through interbeds that intersect the DRZ. The conceptual m odel for Salado fluid flow has prim ary interactions with three other conceptual m odels. The interbed fracture conceptual m odel allows porosity and
perm eability of the interbeds to increase as a f unction of pressure.
Appendix MASS Table 1.0 General Modeling Assum p tions: Modeling assum p tions for various
treatm e nt of the DRZ are listed in this table. First, the shaft is surrounded by a DRZ, which heals with tim e. The DRZ is represented through the perm eabilities of the shaft system itself, rather than as a discrete zone. Second, panel closures are m odeled with the sam e properties as the surrounding DRZ. Third, the perm eability of the DRZ is constant and higher than intact Salado. Fourth, excavation and waste em placem ent result in partial drainage of the DRZ. The treatm e nt of

the shaf t within the BRAGFLO m odel will be sim p lif ied f o r purposes of the re-certif ication PA.

Appendix MASS.13.4 Flow in the Disturbed Rock Zone: Along with Section 6.4.5.3 this text presents the basic treatm e nt of the DRZ in CCA calculations. The conceptual m odel im plem ented in the PA uses values f o r the perm eablility and porosity of the DRZ that do not vary with tim e. A screening analysis exam ined an alternative conceptual m odel for the DRZ in which perm eability and porosity changed dynam i cally in response to changes in pressure (Vaughn et al., 1995). The Vaughn et al. report im plem ented a fracturing m odel in BRAGFLO for the DRZ. This fracturing m odel is identical to the existing anhydrite interbed alteration

m odel. They concluded that the DRZ fracture m odel yielded results “essentially equivalent” to those with the DRZ constant. Treatm e nt of anhydrite fracture and the interplay with the DRZ is

56being treated in som e detail in the re-certif ication calculations and changes to the conceptual

m odels for Salado flow were subjected to P eer Review consistent with 40 CFR 194.27 and NUREG-1297.

Appendix PAR 11 Log Intrinsic Perm eability—All Clay Shaf t Materials: This section discusses how the DRZ perm eability was incorporated into the m odel elem ent f o r the clay shaf t seal

com ponent.

Appendix PAR 9 Log Intrinsic Perm eability—Asphalt: This section discusses how the DRZ
perm eability was incorporated into the m odel elem ent for the asphalt shaft seal com ponent.

Appendix PAR 12 Intrinsic Perm eability-Shaft Disturbed Rock Zone: Along with param e ters 9 and 11, this discusses in situ m easurem ents m a de on the Air Intake Shaft (Dale and Hurtado, 1998) and in Room D (Knowles and Howard, 1996).

Appendix PAR Tables PAR-2 and PAR-3: These tabl es are identical and list seal m a terials and DRZ extent. This inf o rm ation is not applicable to treatm e nt of the DRZ in the repository.

Appendix PAR Tables PAR-6: This table provi des perm eabilities of various anhydrite layers (MB 139, MB 140 and anhydrite b).

Appendix Peer Conceptual Models: Section 3.7 Disturbed Rock Zone. As noted in the text (Section 2.3) the updated treatm e nt of the DRZ com p rised a portion of the independent peer review process.

Technical Support Documents TSD 23 Section 1.3.24 Disturbed Rock Zone Con ceptual Model: here the EPA was not satisf i ed with DOE’s assum p tion that the perm eability of the DRZ rem a ined constant with tim e. Consequently, this param e ter was treated as a variable in the EPA m a ndated PA verif i cation test.

TSD 23 Section 3.3 198 DRZ_1-PRMX_LOG:DRZ Perm eability

Compliance Application Review Documents CARD 23 Section 4.4.9.1 DOE’s Im plem entation of the Salado Interbeds Conceptual Model in CCA

CARD 23 Section 1.3.25.1 DOE’s Model Description

CARD 23 Table 2.3.1 Alternative CM’s Seriously Considered for PA

CARD 23 Section 4.4.7.1 DOE’s Im plem entation of the Salado Conceptual Model into CCA

CARD 23 Section 4.4.11 Shaft and Shaft Seal CM

CARD 23 Section 4.4.12 Disturbed Rock Zone (DRZ) Conceptual Model

57CARD 23 Section 7.3.2.3 Salado CM CARD 14 Section 14.B.4 DOE Methodology and C onclusions, Rustler, Dewey Lake, and Santa Rosa Form ation Hydrology

CARD 14 Section 14.E.4 DOE Methodology and Conclusions

CARD 14 Section 14.E.5 EPA Com p liance Review

PAVT W P O#46674 Rev. 1. Sum m a ry of EPA Mandated PAVT

58Di st ri but i on Li st

Federal Agencies

US Departm e nt of Energy (1) Of f i ce of Civilian Radioactive W a ste Mgm t

. Attn: Deputy Director, RW -2 Forrestal Building W a shington, DC 20585

US Departm e nt of Energy (7) Carlsbad Field Office Attn: I. Triay G. Basabilvazo S. Casey D. Mercer R. Nelson R. Patterson Mailroom P.O. Box 3090 Carlsbad, NM 88221-3090

US Departm e nt of Energy Office of Environm ental Restoration and W a ste Managem e nt Attn: P. Bubar, EM-20 Forrestal Building W a shington, DC 20585-0002

US Departm e nt of Energy Office of Environm ental Restoration and W a ste Managem e nt Attn: Mary Bisesi/Lynne Sm ith, EM-23 W a shington, DC 20585-0002

US Environm ental Protection Agency (1) Radiation Protection Program s Attn: B. Forinash ANR-460 W a shington, DC 20460 Boards

Def e nse Nuclear Facilities Saf e ty Board Attn: D. W i nters 625 Indiana Ave. NW , Suite 700 W a shington, DC 20004

State Agencies

Attorney General of New Mexico P.O. Drawer 1508 Santa Fe, NM 87504-1508

Environm ental Evaluation Group (2) Attn: Library 7007 W yom ing NE Suite F-2 Albuquerque, NM 87109

NM Environm ent Departm e nt (1) Secretary of the Environm ent 1190 St. Francis Drive Santa Fe, NM 87503-0968

NM Bureau of Geology & Mineral Resources 801 Leroy Place Socorro, NM 87801

Laboratories/Corporations

Battelle Pacif i c Northwest Laboratories Battelle Blvd. Richland, W A 99352

Los Alam os National Laboratory Attn: B. Erdal, INC-12 P.O. Box 1663 Los Alam os, NM 87544

W a shington TRU Solutions (3) Attn: Library, GSA-214 P.O. Box 2078 Carlsbad, NM 88221

Distribution List – Page 1 of 3National Academ y of Sciences W I PP Panel

National Academ ies Attn: Barbara Pastina (1) Com m ittee on W I PP Board on Radioactive W a ste Managem e nt 500 Fifth Ave NW ; Keck 634 W a shington, DC 20001

Universities

University of New Mexico Geology Departm e nt Attn: Library 141 Northrop Hall Albuquerque, NM 87131

Libraries

Governm e nt Inform ation Departm e nt Zim m e rm an Library MSC05 3020 University of New Mexico Albuquerque, NM 87131-0001

New Mexico Junior College Pannell Library Attn: Earl Dye 5317 Lovington Highway Hobbs, NM 88240

New Mexico State Library Attn: L. Canepa 1209 Cam i no Carlos Rey Santa Fe, NM 87507

New Mexico Tech Joseph R. Skeen Library 801 Leroy Place Socorro, NM 87801

Distribution List – Page 2 of 3Foreign Addresses

Francois Chenevier (2) ANDRA Parc de la Croix Blanche 1-7 rue Jean Monnet 92298 Chatenay-Malabry Cedex FRANCE

Com m i ssariat a L’Energie Atom ique Attn: D. Alexandre Centre d’Etudes de Cadarache 13108 Saint Paul Lez Durance Cedex FRANCE

Bundesanstalt fur Geowissenschaften und Rohstoffe Attn: M. W a llner Postfach 510 153 D-30631 Hannover GERMANY

Bundesm inisterium fur Forschung und Technologie Postfach 200 706 5300 Bonn 2 GERMANY

Gesellschaft fur Anlagen und Reaktorsicherheit (GRS) Attn: B. Baltes Schwertnergasse 1 D-50667 Cologne GERMANY

Dr.-Ing. Klaus Kuhn TU Clausthal Institut f u r Bergbau Erzstr. 20 D-38678 Clausthal-Zellerfeld GERMANY

Distribution List – Page 3 of 3Dr. Susum u Muraoka Nuclear Material Control Center Tokai-Mura, Ibaraki-Ken, 319-11 JAPAN

Nationale Genossenschaft fur die Lagerung Radioaktiver Abf a lle (2) Attn: NAGRA Library Hardstrasse 73 CH-5430 W e ttingen SW ITZERLAND

AEA Technology Attn: W

. R. Rodwell 424-4 Harwell Didcot, Oxfordshire OX11 OQJ UNITED KINGDOM Internal

MS Org. 0701 6100 P. B. Davies 0731 6800 823 Library (2) 0771 6800 D. Berry 1395 6820 P. E. Shoem a ker 1395 6821 D. Kessel 1395 6822 M. Rigali 1395 6820 F. Hansen (4) 1395 6820 W I PP Library (10)

9018 8945-1 Central Technical Files 0899 9616 Technical Library (2)

Distribution List – Page 4 of 3