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Draft Generic Technical Position:Interpretation & Identification of Extent of Disturbed Zone in High Level Waste Rule (10CFR60)
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Issue date:	06/20/1986
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DRAFT GENERIC TECHNICAL POSITION:

INTERPRETATION AND IDENTIFICATION 0F THE EXTENT OF THE DISTURBED ZONE IN THE HIGH-LEVEL WASTE RULE (10 CFR 60) 1

' Division of Waste Management Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission June 20, 1986 G

44 8607110472 WASTE 860703 PDR PDR WM-1

DZ DRAFT GENERIC TECHNICAL POSITION:

INTERPRETATION AND IDENTIFICATION OF THE EXTENT OF THE DISTURBE0 ZONE IN THE HIGH-LEVEL WASTE RULE (10 CFR 60)

June 30, 1985 Contents

1. 0 Introduction 2.0 Rationale behind the " disturbed zone" ,

3.0 Interpretation of the " disturbed zone" definition . -

4.0 Calculatio'n of the extent of the disturbed zone e

4.1 Stress redistribution 4.2 Construction and excavation 4.3 Thermomechanical effects 4.4 Thermochemical effects 4.5 Consideration of shafts and boreholes 4.6 Summary 5.0 Statement of Technical Position References l

Appendix A. Intrinsic Rock Properties Affecting Groundwater Travel Time l

Appendix B. Analyses of the Dissolution of Silica Near HLW Repositories l

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DZ Generic Technical Position on Disturbed Zone

1. 0 Introduction The NRC staff has established performance objectives for high level radioactive waste (HLW) repositories which include numerical performance criteria for the geologic setting and engineered barrier systems (10 CFR 60, Subpart E-Technical Criteria). One of these criteria, commonly referred to as the groundwater travel time criterion, is stated as follows:

"The geologic repository shall be located so that the '

pre-waste-emplacement groundwater travel time along the fastest path of likely radionuclide travel from the disturbed zone to the accessible environment' shail .be at 'least.1000 years or such.other travel time as may be approved or speci'fied by the Commission." (10 CFR 60.113(a)(2))

The " disturbed zone" cited in the above criterion is defined as:

"That portion of the controlled area the physical or chemical properties of which have changed as a result of underground facility construction or as a result of heat generated by the emplaced radioactive wastes such that the resultant change of properties may have a significant effect on the performance of the geolr3i c repository." (10 CFR 60.2)

The disturbed zone definition is intended to establish the inner boundary from

, which the groundwater travel time is determined. The evaluation of groundwater travel time is simplified by avoiding consideration of the effects of complicated and ill-defined processes related to the construction of the repository and the heat generated by the waste. .

Since publication c .'O CFR 60, studies (e.g. Chu et. al [1983]) have suggested l that the disturbed .e definition requires additional clarification by NRC.

In this paper, the disturbed zone concept is discussed, and guidance for identification of its extent is offered.

l .A second related draft generic technical position on application of the' l groundwater travel time criterion in repository' performance assessment and l licensing review has been prepared in conjunction with this draft generic L

DZ technical position. The generic technical position on ground water travel time discusses the concepts and methods of calculation of " pre-waste-emplacement groundwater travel time along the fastest path of likely radionuclide travel,"

as required by 10 CFR Part 60.

2.0 Rationale behind the " disturbed zone" The NRC staff considers that the waste isolation capabilities of the natural geologic setting in which an underground HLW waste facility is to be constructed constitute an important consideration in geologic HLW disposal.

The pre-waste-emplacement groundwater travel time performance objective was established by NRC to serve as a quantitative measure of the waste isolation potential of the natural geologic setting at the candidate repository site.

T e travel time criterion forms part of'a multiple,-barrier approach to HLW .

- isolation, which also incTudes numerical criteria for containment and release rates of HLW from the ergin,eered barrier s stem. As stated in 46 FR 35281, the g

Commission established t.ne 1000 year pre-emplacement groundwater travel time as one of three criteria which act independently of the overall performance to give confidence that the wastes will be isolated for the period during which they are most hazardous. Since ground water is considered to be the primary transporting mechanism for radionuclide migration from the geologic HLW facility, the pre-waste-emplacement groundwater travel time criterion was developed to provide a conceptually simple measure of the quality (in terms of HLW isolation capability) of this geologic setting.

The volume of the rock which contributes to isolation of HLW from the accessible environment clearly has its outer boundary at the accessible environment. For the inner boundary, the edge of the underground facility would at first seem a sensible choice. However, in establishing this inner boundary, there is good reason not to adopt the edge of the facility as the origin for travel time calcula.tions.

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First, the travel time criterion is intended to provide f,or natural barrier protection from HLW releases to the accessible environment, as part of the multiple-barrier appro'ach to HLW isolation. The'st'aff. considers,that the natural geologic barriers.at a given site'should not.be permitted to depend '

exclusively or predominately on'the favorable properties of the host rock dir.ectly adjacent to the underground faci.lity. The staff considers th'at an 1

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D7 acceptable retcdtory site would be one where the bulk of the surrounding geologic setting ccr. tributes to isolation of FLV.

Feccrd, the staff considers that credit tcyards the 1000-year pre-emplacement travel time should not be taken within that portion of the current ccriccic setting which right te substantially disturbed by construction of the facility or by the thermal effects of emplacement of HLW (irrespec+ive of the possible offsettirg benefits of err'r.eered barriers such as waste contair.ers and back#ill). Eecause of potential changes ir +Fe rcck croperties, the geolog.ic setting within this "distrrbed cne" may not be well represented by pre-emplacement properties and conditicrs erd thus it may be difficult to predict the contributions of this vclure c' rock to repository performance.

The disturbed zone was choser he ten rocrission as the starting peint for cetermining the crourdwater travel tire Fecc.tsc the.phy.sical and chemical processes which isob% +Pr veete are "especially dif'icult to understand in the area close tc the' er f aced waste because tFe area is physically and chemically disturtn' Fy 're heat aenerated hv those vestes. (46FR35280, 35281, July 8, 1981)" Therefore c pre-erplacement analysis based on existing

' conditions wi+ Fir this zone would ret supp!', an appropriate measure of the quality of the geolcgic tett:rg 'c" the purpose of assessirc future perforr.1crce. Tc avoid the uncertainties of cht.racterizing the rock very close

'e tFe emplaced waste, the " disturbed zcre" was de#ined and established es the inrer bcurdary fron whic h travel t1rre calculations are to be nade fer demerstrations of compliance with 10 CFR 60,113(ell?.). A typical disturbed zone is illustrated ir. Fig. 2.

This position considers only the cberges to the intrinsic properties; e.g.,

porosity anc perrreeb4'ity, of the rock. The ways in which changes to porosity and permeabili y rty affect groundwater travel tire are discussed in Appendix A. Thermally incucec tuoyancy is.not considered, because it is caused by changes to the prcperties of the water /e.g., dersity, viscosity) rather than

'Fr rcck. This interpretation is censistent with the Commission's intent as stated in the..supplementar,/ inferrration for the proposed co1'ornir.g emerdments te 10 CFF 60, 51 FR T CE, June 19, 1986. The'Ccmmission there sthtes:

"One potential + e' d e"ect which could alter local groundue.+er flow readitiern S tFe.r2; buoyancy .;f grounawater. Becew e buoyancy effects could extend over si;rificant cistances (see, e.g. , it.'Gorden and M.

Weber, 'Ner-iscthermal Flow Modeling of the Hanford Site', available in the Public Document Pccc)'and because the Commission is propoc 4c to reduce the reyirun allowable distance to the accessible environment, it is

DZ particularly important to emphasize that the Commission did not intend such effects to serve as the basis for defining the extent of the disturbed zone. The Commission recognizes that such effects can be modeled with well developed assessment methods, and therefore were not the type of effects for which the disturbed zone concept was developed. Any contrary implication in our statement of consideration at the time the technical criteria were issued in final form (see 48 FR 28210) should be disregarded."

Seismic events, surface morphology changes, climate changes, and other-potential perturbations to existing hydrogeologic conditions need not be considered in evaluation of compliance with the pre-emplacement travel time criterion. The pre-waste-emplacement groundwater travel time, based on unperturbed conditions, provides a simpler and more easily quantifiable measure

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of the quality.of the geologic setting, in terms of groundwater flow,_than -

would a post-emplacement < criterion. The post-emplacement groundwater movement will also require evaluatio,n as part of a demonstration of compliance with the overall system standard (10 CFR 60.112).

In summation, the pre-waste-emplacement groundwater travel time criterion was established to gain a simple measure of the HLW isolation capabilities of the geologic setting based on existing conditions; the " disturbed zone" was subtracted from the " geologic setting" for this criterion for two reasons.

First, the zone di.rectly adjacent to the underground facility should not be depended upon to provide the major portion of natural barrier protection from HLW releases to the accessible environment. Second, the " disturbed zone" would not be well-characterized by pre-emplacement conditions and prediction of its

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contribution to the actual performance of the geologic setting might be difficult and uncertain. Therefore, assumption of existing properties within this zone for use in travel time calculations may not result in a reasonably conse,rvative measure of the HLW isolation capabilities of the geologic setting.

3.0 . Interpretation of the " disturbed zone" definition-

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Having clarified the intent of the groundwater travel time criterion and the

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" disturbed zone" concep't, the interpretation of the " disturbed zone" definition will 9 discussed. In the definition provided in S1.0, the disturbed zone is descrf.:ed as the zone of physical or chemical property changes resulting from underground facility construction or HLW heat generation that would

DZ 7-significantly affect the performance of the repository. A definition of the disturbed zone which includes completely the zone of increased temperatures and associated buoyancy effects, is likely to be quite extensive and in some cases might extend beyond the boundary of the accessible environment, thereby automatically violating the GWTT condition. These effects may have a significant impact on groundwater movement and radionuclide transport in terms of overall repository performance, and they must be accounted for in assessing total system compliance with the EPA Standard. However, the staff considers that the measure of the quality of the existing geologic setting, as a component of the multiple barrier system, need only be based on the pre-emplacement conditions outside of the disturbed zone, where the intrinsic properties of the rock remain unaffected by HLW heat generation or underground '

facility construction.

Limiting the dis'turbed. zone to the, zone of intrinsic rock property. changes -

which affect groundwater ' travel time can be construed as less comprehensive than the definition provided in 10 CFR 60.2. That is, it is possible that not all post-emplacement conditions outside of this zone will be identical to pre-emplacement conditions. For example, due to post-emplacement thermal buoyancy effects, the pre-emplacement travel time may not provide a completely accurate measure of actual post-emplacement performance. However, the pre emplacement groundwater travel time from the disturbed zone to the accessible environment is only meant to be an approximate measure of the l quality of the geologic setting, which provides a sensible and useful l performance criterion for both repository siting and licensing. Fur.ther, the actual post-emplacement performance, including post-emplacement groundwater flow paths and directions, must be 5ccounted for in assessments of compliance with the EPA Standard.

The movement of ground water through solid salt is not well understood at the present time, but such flow may be extremely slow or virtually non. existent. In such situations, tt. Jisturbed zone for salt should satisfy the consideration

'that the natural gec.ogic barrier at a given site not depend exclusively or predominately on the portion of the host rock directly adjacent to.the underground facility. -

In summati,on, the disturbed zone,used in p're emplacement groundwater travel time calculations is considered to be defined by the zone of significant changes in intrinsic ermeability and effective porosity caused by construction

DZ of the facility or by the thermal effects of the emplaced waste. The volume of the geologic setting which is not included in the disturbed zone, but which does change due to' waste emplacement or facility construction, may preclude identical pre- and post-emplacement conditions for assessments of compliance with the groundwater travel time criterion. However, the NRC considers that the pre-waste-emplacement groundwater travel time will still be an appropriate measure of the overall geologic setting performance for the purposes of licensing.

4.0 Calculation of the extent of the disturbed zone The particular processes that would require consideration in delineation of the '

disturbed zone, and the status of current investigations into these processes have been identified by the NRC Staff. Based on the technical and policy c'onsiderations d'escribed above, the,NRC Staff considers that the disturbed zone could theoretically be ca'lculated through evaluation of the spatial extent of changes in the intrinsic rock hydraulic properties caused by:

1) stress redistribution

2) construction and excavation

3) thermomechanical effects, and

4) thermochemical effects.

Each of these is discussed below. The analyses presented are not intended to be exact. Instead, they serve as approximations of complex coupled process behavior. The NRC Staff recognizes that the in-situ test facilities that may be constructed at many potential repository sites are likely to provide major advancements in our understanding of th.e complex process interactions governing changes in intrinsic rock hydraulic properties. However, the complex process interactions that would need to be considered in identifying the spatial extent of intrinsic p'ermeability and porosity changes have, in gdneral, not yet been sufficiently studir . 3 provide ready guidance in rigorously estimating their effect on the exter .i the disturbed zone at this time. Also, the general intent of the pre.. emplacement travel time performance objective, as discussed in S2.0, is to provide a relatively simple benchmark for the quality of the geologic setting. Therefore, the leve~ of rigor applied.in the following

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. analyses is considered to'be sufficient for the purposes of providing guidance for definiiig the disturbed zone in grou'ndwater travel time calculations.

DZ 9-The discussion below is based on current HLW facility designs, and considers only rock types currently under consideration for geologic repositories. If the adopted design is greatly altered from the design considered herein, or if rock types of greatly different mechanical or geochemical properties were to be considered, the guidance offered below may not apply directly. The limit of the disturbed zone then should be recalculated on a site-specific basis.

It should be noted that in an attempt to illustrate methods of identification of the extent of the disturbed zone, the impact of local geologic anomalies at specific sites has not been addressed. These types of features would have to be considered by DOE on a case by case basis in evaluations of the extent of the disturbed zone.

4.1 Stress redistribution ,

Rock permeability may be 'significantly altered in the region immediately -

surrounding repository penings as a result of stress redistribution. The extent of this region will depend on: (a) the rock characteristics (its mechanical properties, nature and extent of jointing and other discontinuities), (b) the in-situ (pre-construction) stress field; (c) the orientation and layout of the underground openings wi,th respect to the in-situ stress field; (d) the size and shape of openings; and (e) the proximity of openings to one another. The immediate vicinity around the opening is most affected by the presence of the opening. The effect gradually dies down and at a certain distance from the edge of the opening, the rock essentially continues to be in its pre-excavation condition. There are experimental results, predominately on small scale laboratory samples, relating permeability changes to stress changes. However, these results are site- and r,ock-dependent.

Therefore, there are no universal relationships which can be applied to all rocks under wide ranges of stress changes. A generic relationship between stress change and permeability change can be established by considering that for all practical purposes permeability will not change in the volume of rock

.3eyond the surface of no stress change. Therefore this boundary can be used to define the region.of no permeability change; i.e., the limit of the dis.turbed zone resulting from. stress redistribution.

Theoretical stress districutions are estatilished in the . literature (Hoek and Brown'[1980]) for various opening shapes, with different orientations to in situ stress fields.- The rock media are idealized for simplicity, i.e.' ttle l

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DZ r t.citr: 1s assun.ed to be isotropic, htmcger. ecus, and is assumed te beFeve ir: c lirearly elastic fashion. Fcrther, these sclutions are ger.eral'y fcr +ve dirrersicr cl cases. The distance to the contour of no stress change from the edge of the opening will vu ty ce ncing on the size atid shape cf ttc crening and its crier.ttticii tu the stress field. For a circular or semicircular opening, a reaseratie estinate ct this distance for the ideclizec' case will be about three diameters. Fcr c rioncircular opening, a reasonable estimate is roughly five t1rres the height in most cases.

The anisotrcpy of rock (jointing, Leccirs places, directional differerces in trecFanical properties, e c., its a significant effect on the stress i

distribution. This anisotropy causes a shift in the stress redistribution (Goodman [1980]) and the'cci.tcur ct no . stress change can te 4 to 5 diarreters away, frem tte wy. ci the opening. A thiro important ccnsideration in stre.ss .

distribution is the extert ci rcck fracturing (Cuates '['.9 T . Geodman [1980])

and subsequent yielc'irr ,' :lc cl . This yielaing, again, char.gss the stress oridici.c ofic at tects the redistributicr ir, the rrck mass.

Taking the envelcre c' ttc aLove stress distributions for a reasonable range of anticipated it c ccr.citicns, the nc-stress-chcrce centour could be somewhat ccr.servatively estimated in mary ccses tc be about 5 diameters Tor circular c per. i t.. . or ; tmes the cper.it.g heirbt fer rcrcircular openings. However, s1te-specific intirmation must be UH li ec it, oraer to gain a realistic estimate of the disturbec :cr.r. extert for a given si te.

There will be openires cf mtny sizes in the repository. The size will range from 1 to ;G meters ter a majority of the oper.ir.cs Ncr a schematic of a layout ci sore repository openings. see Figure 1). based on distances descritec in the ilterature for hotogeneous, isotrcpic, and linearly elastic tecic, and taking into consiceration the ef.fects of best rcck cnisctropy, in-situ stress conditions, and frat *.cr re arc' yielding, it is estimatec that the cisturbed i

zct e caused by stress recistr1LLticn for the simplified exartple described above

- r cy etterc' tc. a distance of 5' diameters, er 5 to' 50 meters, from the edge of J.e openirg depending cy the operirc size.

The ngchanical proper w , v. La'.' r'.d cre'significantly different frcm other rocks, ano therefort, <' separa.te discussion is warrar.tec. ' A unique feature of l

sal; is its cbi*; tc creep into excavated oper.ingc cver perioc's that eitend from a few years tc hur creds c' years depending on the specific salt, its

DZ depth, prevailing stresses, and other geologic anomalies. Salt in the immediate vicinity of underground excavations undergoes elastic plastic deformation and quickly goes into the creep phase. Numerous reports exist on excavations in salt that closed completely in a span of tens of years. This closure is expected to occur in a salt geologic repository in which the creep will be accelerated by the heat generated by the stored nuclear waste.

A second important difference between salt and other rocks is the applicability of the concept of groundwater flow and permeability. Traditional concepts of groundwater flow through porous media and jointed rocks are not applicable.to pure salt. However, changes in permeability for the flow of brine or gas will occur as a result of excavation, stress redistribution, and creep. DOE must consider these changes on a site-specific basis in order to evaluate compliance with the EPA Standard. .

It should be noted that m'any geologic anomalies have been reported (Kupfer, 1979) in and around salt mines. These include shear zones in and around salt domes, gas pockets, and brine cavities. Gas pockets have extended up to 100 meters above the excavation and gas blowouts and brine migration are known to have occurred. This GTP is generic in nature and thus does not account for these site-specific features in salt and other media, which would have to be considered on a case-by-case .,csis.

The opening sizes discussed abovt wan those of the final completed excavation, and not the design dimer- ; . Large overbreaks can occasionally occur during excavations of undergrm e .enings.resulting in the actual dimensions being significantly greater t . ne design dimensions. This potential problem can be minimized by using controlled blasting techniques and other ccnstruction methods. The extent-to which the openings themselves may alter their position within salt media should be considered by 00E in delineating the boundaries of the disturbed zone in salt media.through time. It is not known at this time whether the potential for post-emplacement gas bl.owouts or post-emplacement creep of th'e salt will be a significant consideration i'n this regard.

4.2 Construction and excavation The z~e of permeability change.because of. construction-induced effects is usually. smaller than that due to stress redistribution (with perhaps the exception"of massive unjointed rocks), and depends on: (1) the inethod of

a:s DZ excavation (blasting or boring); and (2) the type or rock and its degree of discontinuities. The extent of porosity and permeability changes caused by dewatering of the facility should also be considered on a site-specific basis.

It is reported in the literature that the extent of damage due to controlled blasting rarely exceeds one to one and a half meters away from the excavated openings. Furthermore the zone of altered permeability is estimated to be within half the opening diameter from the edge of the opening (Kelsall et. al.

[1982]). Tunnel (and shaft) boring, on the other hand, produces smooth walls and normally results in little change in permeability of the surrounding rock.

Therefore, a 50 meter distance from the edge of the opening established as the minimum distance to the boundary of the disturbed zone resulting from stress redistribution might also conservatively cover the effects of construction induced changes in rock permeability.

4.3 Thermomechanical effects The emplacement of nuclear waste in the host rock and the subsequent heat generation may result in a significant change in permeability in the region immediately surrounding the waste emplacement holes. Thermal stresses can create new cracks and open or close existing joints, therefore resulting in a permeability change. Far from the waste, thermal stresses may cause uplift and eventual subsidence effects. The resulting permeability changes may be more significant in salt than in hard rocks due to salt creep and a relatively high coefficient of thermal expansion. Thermal stresses and joint displacements are generally calculated using appropriate numerical models. These models require several input parameters such as the expected temperature range, the existing stress field, and rock thermal and mechanical properties (e.g., thermal conductivity, thermal coefficient of expansion, heat capacity, compressive strength, joint mechanical characteristics). One such study (Johnstone et. al.

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[1984]), using a finite element model for thermomechanical analysis of four different host rocks at the Yucca Mountain site in southern Nevada, showed

. joint movement (sl - opening, or both), and signi.ficant associated change in permeability, at one diameter from the edge of the opening after 100 years.

The above study noted that these model predictions of joint movement resulting from the thermal effects of. waste emp.lacement were likely to be conservative.

This conclusion was based on comparisons between model predictions (without the thermal feature) and uncerground.observati'ons of the joint movements in '

existing excavations,near the site.

i DZ Experimental assessment (Daeman et. al. [1983]) of change in rock permeability as a result of heat application has shown that for several granites and gneisses tested (up to 2 meter cubes), permeability increases with temperature because of thermal cracking. However, confining pressure can strongly reduce permeability increases caused by heat. In a repository environment, this could mean that the permeability increase at or close to the repository wall will largely diminish as confining pressure increases in the surrounding rocks. In jointed rock, some or all of the thermal expansion may be absorbed by the closure of microcracks and joints resulting in overall reduction in both the permeability and thermal stresses.

Despite the modeling efforts and the laboratory and in-situ testing work '

available in the literature, the temperature-stress and temperature permeability relationships are difficult to quantify, especially for large volume's of rock mas's. Con.sidering the above. discussion, the disturbed zone which covers the eff'ect of stress redistribution and construction might in many cases also be expected,to include the zone of significant thermomechanical effects on permeability. However, DOE should demonstrate this on a site specific basis.

4.4 Thermochemical effects 4 The perturbation to the geochemical environment caused by the heat generated by the high-level waste, and by the introduction of the mined facility and engi-neered barriers into the geologic environment, is the driving force for chemi-cal reactions that can occur in the geological system. The extent of the perturbation depends on 1) thermal load of the repository, 2) thermal conduc-tivity of the surrounding rock, 3) degr.ee to which the engineered system is ;

chemically out of equilibrium with the surroundings 4) mobility of components within the system and 5) the stability of pre emplacement minerals. ,

Changes in mineral , amblages caused by the thermochemical perturbation could "af.fect both the che .31 and physical ability of the host rock to retard radionuclides. However,.by defining the disturbed zone in solely hydro. logical-terms, thermochemical ef fects to be considere.1 in quantifying the extent of. .the disturbed zone involve only those reac*. ions that either change the volume of

. solids (M,

0) or redist'ribute the solids in the repository system.

These reaclions include dissolution and' alteration of pre-emplacement minerals, and precipitation o'f secondary minerals. 'The change in volume of th'e' solids

DZ results in a change in the porosity and possibly permeability of the host rock.

R9 distribution of solid material, on the other hand, results in porosity in-creases in one portion of the repository and decreases in another. The relationship between intrinsic permeability and porosity has been discussed previously in 63.0. The net effect on the flow may be favorable or unfavorable. It is demonstrated in Appendix B that even if the effect is unfavorable, it will be small and may on this basis generally be ignored.

A change in porosity or permeability of the host rock may result if pre emplacement minerals undergo alteration due to increased temperature and/or altered groundwater composition. Commonly the solids that are involved in water / rock interactions in crystalline rocks are glass, silica phases, clays, zeolites, feldspars and micas. The silica phases include quartz, cristobalite, tridymite and amorphous silica. The cl,ays generally include smectite and

, illite; zeolites are clinoptilolite, mordenite and analcime. Reactions -

involving these phases cah result in either increases or decreases in solid volume (V ). For example, under hypothetical repository conditions, the hydrolysi$ofalkalifeldspar 3KAISiq80 + 2H = W $I 3 910(OH)2 3

+ 02 + 2[

orthocTase muscovite quartz 3

results in a decrease in solid volumes (aV = -43 cm ), whereas, the conversion s

of anorthite to clinoptilolite CaAi.,Si28 0 + SSiO 2+6H0=CaAlSi918 j 2 7 "20 anorthitu quartz Ca-clinopt1Tolite 3

increases solid volumes (AV = 98 cm ). Large uncertainties in volume changes resultfromreactionsinvolhingphaseswhosemolarvolumesarevariable.

Smectite, a common secondary mineral found in the fractures of crystalline rocks, is notorious for volume changes due to variation in water content. Den-l

-ities of smectites can vary from 2 to 3 g/cc (Deer, et al., 1966).

Dehydration reactions may also result in a net change in porosity of'the host

. rock. Dehydration of hydrous minerals can occur in the region s.urrounding the.

..anisters where temperatures are greatest. This will be of particular

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impor'tance in a repository located in the vadose' zone. Dehydration could occur' at temperatures as low as 85 C, e.g. , zeolites such as mordenite and

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DZ clinoptilolite can react to form analcime, producing a reduction in molar volume of the solids. Such reactions may have an adverse affect on the permeability of the host rock, if the hydrous minerals occur in a significant amount in these regions.

Dissolution and re precipitation of minerals under repository conditions may exhibit a profound effect on the ability of the host rock to transmit fluids.

The system Si0 - H 0 can be used as an example. This simple system is chosen toillustrate$hechemicalprocessesinarepositorybecausethermodynamicand kinetic data are well established and significant amounts of silica are present in two of the sites being considered for nuclear waste disposal. A sample generic analysis of the extent and effects on porosity of silica dissolution is presented in Appendix B. Based on these generic calculations, silica dissolution is not expected to be significant beyond the previously-discussed mechanically-disturbed zone distance. It is apparent,,however, that the

- distance to the edge of tile thermochemically disturbed z'one is strongly dependent on the therma', loading of the repository and the groundwater flux in the host rock. These factors would have to be considered carefully for any site specific analyses.

While the silica-water system is not to be used as the only basis for establishing the extent of mineralogical effects to the host rock, the type of analysis presented here, i.e. the use of a simple, one-dimensional mass transfer model, is recommended to determine the effect of repository induced conditions on mineral stability and'hence porosity. It is recognized that each '

site may have multiple-component reactions which could have a significantly different result from a simple two-component system. For that reason, we recommend that 00E perform chemical analyses on a site-specific basis, having fully characterized the hydrological, mineralogical and chemical data of the system to the. point where they have sufficient confidence to determine the extent of significant thermochemical changes at a given site. These calculations will roughly indicate the suitability of the suggested fifty-meter minimum dis'turbed zone distance in encompassing the zone of thermachemical changes at th.e given site.

4.5 Consideration of Softs and Surface Boreholes In th U GTP, shafts, inclines and surface boreholes are considered to be exc:uded from the disturbed zone. The NRC Staff recognizes that'the rock.

DI immediately surrounding all openings will be disturbed to some extent, and may become a flow path connecting the repository to the accessible environment.

This effect may be mitigated by following careful excavation techniques, and through installation of effective shaft and borehole seals. The performance of these seals should be assessed as part of the overall performance assessment of the repository system. The performance objectives explicitly state that "the geologic setting shall be selected and the engineered barrier system and the shafts, boreholes and their seals shall be designed" to assure compliance with EPA Standards (10 CFR Part 60.112). However, the groundwater travel time criterion is intended to provide a representative measure of the effectiveness of the geologic setting far from the buried waste as a barrier to radionuclide transport, and not of the overall quality of the repository system. Therefore, a discussion of the disturbed zone around the boreholes and shafts is beyond the scope of this GTP, although it should be considered in overall repository

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performance assessment. ,

4.6 Summary <

The NRC Staff considers that establishment of generic and easily evaluated guidance on the disturbed zone is desirable in order to allow for the demonstration of compliance with the groundwater travel time criterion (10 CFR 60.113(a)(2)) consistent with NRC's intent in the criterion and in the overall multiple-barrier approach to HLW isolation. Based on the information provided above, it appears that a distance of five opening diameters from any underground opening, excluding surface shafts and surface boreholes, would be a reasonably conservative distance for the extent of the mechanically-disturbed zone in some cases. Given current conceptual designs for underground HLW facilities, this would imply a distance of roughly fifty meters from the underground openings. The limit of one process (silica dissolution) contributing to the thermochemically disturbed zone, based on a simplified evaluation, appears to-be less than the above-stated mechanically-disturbed distance from the underground facility. However,.the thermochemically,

~

disturbed fo.ne at a site should be calculated on a site- and design-specific basis, taking into account the hydrochemical, ge' ochemical, hydrologic and thermal conditions for each site. The impact o.f each of the four. processes li.sted on page 8 should'be considered by DOE on a site- and design-specific basis

DZ In this paper, a detailed interpretation of the " disturbed zone" has been presented, and sample calculations have been performed, which provide guidance to 00E in establishing the surface from which to calculate pre-waste-emplacement groundwater travel times for repository sites. It must be noted that post-waste emplacement groundwater flow paths and velocities must be evaluated by 00E in demonstrations of compliance with the overall system standard (10 CFR 60.112).

5.0 Statement of Technical Position It is the position of the NRC staff that the disturbed zone may be considered to be 1) defined by the zone of substantial thermo-hydro-chemical-mechanical '

changes in intrinsic permeability and effective porosity caused by underground facility construction or by HLW heat generation and 2) should at least include

the portion of the host rock directly adjacent.to the underground facility i' order that a proper measu're of the quality of the geologic setting far from the buried waste may be obtained through the application of the groundwater travel time criterion. NRC considers that, based on consideration 2) above, a disturbed zone of five diameters for circular openings, 5 opening heights for noncircular openings, or fifty meters, whichever is largest, from any underground opening, excluding surface shafts and boreholes, may be the minimum appropriate distance for use in calculations of compliance with the pre-waste-emplacement groundwater travel time criterion (10 CFR 60.113(a)(2)).

The disturbed zone at a given site may, however, extend further than this distance depending on the site and design characteristics. The extent of the disturbed zone should be calculated,by DOE on a site-specific basis. These site-specific analyses should account for the effects of heterogeneities in.the geologic system, local geologic anomalies,.the magnitude of likely groundwater flux, magnitude of areal thermal loading of the repository, the geochemical and hydrochemical characteristics of the site, and changes in the facility configuration through time.

' Investigators calcu ating the extent of the disturbed zone for use in 10 CFR 60.113(a)(2) groundwater travel time calculations should be prepared to support

~

this finding through documented technical evaluation. I.f the investigators.

believe that the hydrogeology of the site. indicates that some of the recommendations. in this . guidance . document do not need to be satisfied, oi' alternative methodologies are appropriate,~dequate a technical evalua'tions'must be documented support'ing the differing ap'proach.

DI

References:

Braithwaite, J.W. , and F.B. Nimick, "Effect of Host-Rock Dissolution and Precipita' tion on Permeability in a Nuclear Waste Repository in Tuff,"

SAND 84-0192, 1984.

Chu, M.S., N. R. Ortiz, K. K. Wahi, R. E. Pepping, and J. E. Campbell, "An Assessment of the Proposed Rule (10CFR60) for Disposal of High-Level Radioactive Wastes in Geologic Repositories", Vol. I, NUREG/CR-3111, U.S.

Nuclear Regulatory Commission, June, 1983.

Coates, D. F, " Rock Mechanics Principles", Mines Branch Monograph 874, '

Department of Energy, Canada, 1970.

Daemen, J. J. K. , et, al ,. " Rock Mass Sealing - Experimental Assessment of Borehole Plug Performance *', NUREG/CR-3473, September,1983.

Deer, W.A., R.A. Howie, and J. Zussman, "An Introduction to the Rock-forming Minerals," John Wiley and Sons, Inc., New York, 1966.

Goodman, R. E., " Introduction to Rock Mechanics", John Wiley & Sons, New York, 1980.

Hoek, E. and Brown, E. T. , " Underground Excavation in Rock", The Institution of Mining and Metallurgy, London, England, 1980.

Jaeger, Charles, " Rock Mechanics and Engineering", Cambridge University Press, London, 1972. .

Johnst6ne, J. K. , R. R. Peters, and P. G. Gnirk, " Unit Evaluation at Yucca Mountain, Nevada Test Site: Summary Report an'd Recommendation," Sandia National Laboratori , SAND 83-0372, June 1984.

Kelsall, P.C. , J.B. Case and C.R. Chabaness, "A Preliminary Evaluation, of the .

Rock . Mass. Disturbance Resulting from shaf t, T.:nnel, or Borehole Excavation."

Technical Report ONWI-411. prepared bp )'Appolonia Consulting Engineers, Inc.

,for Office of Nuclear Waste Isolati.on, Battelle Memoria1 Institute, Columbus, 0hio, November, 1982. ,

6

+

DZ 19 -

Kupfer, D. H., " Problems Associated with Anomalous Zones in Louisiana Salt Stocks, USA," Fifth International Symposium on Salt- Northern Ohio Geological Society, 1979.

Stagg, K. G. and Zienkiewicz, 0.C , " Rock Mechanics in Engineering Practice",

John Wiley & Sons, London, 1968.

4 ?

t

= .

l l

3 l

_ /

,/

n y "

a L /

~

Storage Hole L -

/

Host Rock

' (Y rr fr '2

} r '

Host Rock '

Waste Pipckage/

/-

Placement Room Crown u

l 3m f i 1r I Og

6m

i lGilPI 1 - An example of repository layout showinctions and velocities which may be affected by

' post-emplacement prxesses such as fluid buoyancy, will'however need to be considered in assessment of compliance with the overall system standard (10 CFR 60.112).. ,

For a given medium,.there is likely to be'a relationship between an increase in

. effective porosity and an increase in intrinsic permeability. For example, relationships such as laminar flow betwesn parallel plates and in granular

02 materials indicate that permeability increases roughly to the cube of the porosity. Therefore, the effects on velocity or travel time to a change in one of these parameters is likely to be offset to a degree by the effects to the corresponding change in the other. The media under consideration generally have small effective porosities. Thus small decreases in porosity can be expected to cause larger decreases in intrinsic permeability. Conversely, an increase in total porosity is likely to cause a larger associated increase in intrinsic permeability. In the case of the disturbed zone caused by the precipitation of solids, the relationship is likely to be even further esaggerated because precipitation will occur predominantly along the interconnected flow paths. Therefore, the sensitivity of intrinsic perreability to small changes in total porosity is expected to be, if anything, increased if one substitutes effective porosity for total porosity, particularly when considering chemical precipitation and dissolution.

r a.... . . . . . . . . . .,.,

C is ,ve.$ .. a.: i u. n '..S t.. ' '.".* ?. ".N *o :. (. ". . .' '..A SEAR HLW REFOSITCRIES

-t-::.:: den Tre ::tential for etssslutten Of mineeais in the re:k is a :nsicerati:n in tre
esi;- Of mi;n ievel ; eel:;+: -aste ee:: sit:rtes. Dissolutten of the rect
ale enlaege ::rcuits f:e the :assage of water, increastng the flux tnrcugn tee re::stt:ry a-: tre ::tenttal fer,migrati:n of raciceuclices from the waste.'
0:nversely. : e:1:i ta"-- a' -*=erals Otssolves from cee area could :1ug.
-:vits in ae:t e- I*ea'. ine : resent analysis :ensicers as a worst case only tre regtce -rere tre-e .:;1: :e ir rease flow cause0 :y cissolution.
5111:a is a : - ee -+recal in ost of tre r::A ty:es currently unter Its presence in these re:ks
nsiceration ey CCE as geologic re:ository ecia.
eas le: to : r:e ns that trere mtgn: ce a signift: ant change in :orosity cause:
y *ne 04 55:1.*'** Of sill:a in the fI:=ing gr0e*:=ater. A auMerical et*eet ert =as :evise: whtCn m3uld test this Py :t"ests for *y:iCal to .
aservative : Cec'**:es et:ecte: " ear MLW re:Csit: ries. Inis re: Ort ces *i:es tre numerical es
e*t at: its results, at: tPe 1-:act of the results On t?e .
cefiniti:n of tre ? st.-:e: 2:se. T e to:r ';ues ces rtte: -t;nt :e useful fc-
?
s j
.v-- r - . - , _ ~ %-., . . . , , - , _ , ,,,_..,_,._y_ _ , . _ , _ . . . - - _ _ . _ , , , , , _ . _ , _,.,, _ _,m., ..._--,.,m , . _ , _ , ,,,,._,..,,-.,,.____r_ , , . , , _ . . _ , . _ _
t 3...... ,.
(
evaluatin; dissolut'en of :tner ty:es of -f recals. Out ea:n :ase sr:.;: :e
asicere: :are'ul'y.
Ces:r': t:a of t~e -eat T*a s'er *:cel ine seat transfer -:cel nas :een taken frce Ref. 1. Tre re:: sit:ry is assure
te a 1919 -e:ta.*;ular :iate :a-aI?el : tre surface Of the earth Iccated in a saturate: ecium as se:=n in Fig. 1. West tra9sfer is considered t: te
tally ty ::re.:tt:n in ::nstant :Per al ecu tivity and neat ca:acity.
int s assu-btien is 'justifie: in most cases te:ause Peat transfer y (1 =ii; ge:uec.atea til al : :eatainly te smaller inan cencuetive Feat transfer.
Tre cases f:e 1945 assu : t:n are : resented in Ref.1. Tne effects of : nase
Parges are als: ei:e:te: :: ce ce;11;4:le.
-est is ein; ge*e-ate: cy 10 year Ole s:ent fuel, uniformly distet:utec acr ss t?e area Of tre -e: sitory, Coefficients of tre eeat transfer recel are given in Tatie 1.
0 4
g ..
m e. . s . . . . . .. .
3 t
Table 1 - Fara-eters of Recesit:ry w del l
P l
Re::stt:ry it gte. : 600 ? '
! 4e: sttery =icts = '.200 -
Centn of re::stt *y telc- es-tn's surfa:e = 1200 m 7 -
C:efft:1 eat f weat Tea sfer, A = 7.25 a 10 joules /(m yr *:) !
a 4 3 J
heat ca:a:ity of -7:k, C. = 2.77 s 1C" f:ules(m *:) ~
-i 2
Initial Heat 1:40, 03 ( t) = 1.11 m 10* j:ules /(s yr) 7 Greur:.ater flux, U = 1 ete*/ year a
i A-: tert 'e :erata-e, I, *I= 30*C, 5080 .
t Ceesity ot 44:s. = = . 1 ge/::
i T-ans::-t w::el G canc ater is ~assa e: :: ce saving in a straign llee tnreugn a thin streas t.:e at a flus 0 ete-s/ years, as sn:.4 in Fig.1. 7be stream tu:e is alignec t
te, re of :== -ay5:
1. Parallel to tre i asts (e rt::rtal) passing snecugn the :: int y = 0,

1,. Or e
I e
d s
F i
---e . , < v _ , , , ,.-n, - - , - - - - . ~ - - . , - - . - > - - - , .,-n-, ---n, , ,. -
r,e,..--,m,,.---, -r-n- ~~m.,--n.,w, ,-w.-.----,,--n, ,.-,r ,a ,
2. Darallel to tre : atis (vertt:al), :a551 ; tne: ;n tre : 5-; , = g, i = C.
t*:n Of t: e ceter- e: :y : e ea.
e : erat re at:P; i."e St-eam t. e 15 a '.s.
tran5fte ~::ti.
A *a55 O&ll*~e "a t*e 5e- eat Of *.=e steea?. *,,te of P:55 Secti:n A , a5 SP wn i n ;i g . 2 f *:". t 10 m
an '5 ese: : ceveI:p t*e relati:N5Nf: f:P the 0155:Iuti:n O # StCa: .
9
a55 Of StI'*4 eate***; at a : U&C at (
<1s *a55Of5Ca'ea.'*;at t
at : UaC t*at at 4*1 Pa ge ir as5 :d 5:lic Silica tn tire at : SM (3) 4 A O g
. , g k h$ !"e 0*';'*al $1'i:1 9455 in t*e Se;" eat. W ;
(1)
"g
A a 't
="e'e a 's ;'4 C e a s ' t ., Of tre 5t't:a
DRAR The Change of ::r sity at a :: -t +s tre e':re:
w:w, =; (;/ ) (10/ >i) :t' (5)
#*
00th t"e : nOu:*ing A*O It is asss'e: tr&* si03 wil'( Oe "e O=e:
a:*-::a .:t*ag : res '* **e 7::A. 50 tPe *3Pge in either tot &I Or effe:tfwe
e:sity 03* Oe et resse: ) ;*?5 *3t' .

e*!*3ti;' Of sil':A '" =4ter Can Oe des riOed Oy &n I"e f*w1IiO*'w?
e :tr':al -e'att: s-4: ('e' .): s = :: (3 . - i . -'T)
'esite- (6)
=" eft ? 'a *.*e its:'.te te" erat.*e ceJ'ees (elvin. And 4 O. And : Are t C effi ients are given in
-staats =**:- Ce:ea: 09 tre solic si ':a :aase.
Ta:le ? 'er sewe-ai :Fases of silt:a.
tRAFT 2ti e 2 - 0:effi:ients 'n 5:1.otlity E:;ati:n f:r ::.r Stii:a : ases
*s. at
a. 3A-). 30>
."35e .& O. .O . ~b *3 * *a a *
A. w* ..s3
t.0

t. . .: :. 1 ..
w.A . .. . . .. 3 ). a * **
.' 02 . .* - .5 9
w... t ?. 9 J.*1 4 1. .* j'. .. 4 w.r ,< ,a.... . . h s ... t i
.... - n w *tTJ.O *. ,3 1 ,0"3 . A 2..3 1 lu. - 5 Ott&- ..OOw ,
t w., .1.... . 3 . . +. . e 4 t- 3 * ** 3.. , .. :
*~
.::a s.*3 1 ....t.. v.. A. . t. a. 1 .w . . ..w . .
d q..i..... vt..... .. . . . .
*e
eat **2*S'e*

Cel =&$ fun *0 OeweI O* te*:e*At.*e5 at 00 tat 5 AIO*i t'e ST*e&5 tuOf ff0m t* es Of 1 00 '.0.000 years. Tire -as :alculatec :n a I:31*tt*Mic 5:4It
- * , *n 0*0e" 10 t&Le tPe : *0ttt0*5 Over 4 =1:e #3*ie
#. ' * $ *. .* *. .* e
4 .4.,
3..... 3.......... e .e..e*A*..'re
. . y**3.**.f**. 15 et *. ". e 5 5ed. .* y *.
e
3......
. ... .. . U .
cifference between two ::! Pts. E;uatten (5) in solve: fo r aM/ Wg in ti.e at
ints -40.ay :et.ee t*e te :erature ::ints using tne tra:a::ical rule: e
(:-a:)= () (7) - ( AM/M)) g.. (a*/*,). g - (LA /2ata) (f .. ( ) - f ,q(:-a )) g g wrere f g( t ) = ( 0, , ,(t) - 0,(t)) e' 3 The ::r:entrati :n
s ass. e t: ce ceter-ice: ty tre e:uilibrium :: efficient:
C,(t) =0.05:09 ( (I(s.:)) . (S) , i t
.rece e :: sta-- q. i:09 is a ::nverst:n fact:r frem moles / liter to ;-/mi. *:cel 'esults Tre ::el -as ran 'Or tre n:rt::ntst an: vertical streas tutes using a flux of ; eter ;er year an a ti-e limit of 10.000 years. The a-: lent te :erature .as tasen :: :e 30'0 an: 50*C. Tee ance:ncus stit:a mase was use: as tre case .
51 eral Oe:adse it is t"e *0st solutle f3PS. ar: .ill result 19 the *0st
a. In C nservative Dreci:ti:" Sesults Of these *uns are s* =n in Eigs. 3 ac f
*Se hori* ".tal strea? * :e Ase sr.:Wn In Eig. 3. *Pe *atinuS C urs IJse t0 the u:streae et;e ;* e e: sit:"y. I*e Deat values of aM/"; are i
a:: :st atel y 0 :::s a : : .0637 for T, = 30'0 an: 50*C res:ectively. P
, _ - , - , . . ....m.. - - - - - . ,- _y ...r--_ . , . . _ . ..-.--,c-%.-m-- y--.,,. . , . - -
DRAFT 2.v s.-::... .. . 4 No silica wculd cissolve :=estream of tre re:: sit ry :en:er, x = 0, :e:ause , Tr* te ;erature are trerefore selubility will ce:rease Oeyecc this cint.
-e e1 . uld re:t:: re:f:itati:n of an e:ual amount of dissolvec sili:a
.cstream fre.m tre re: stt:ry :enterliae Oe:ause of symmetry an tre The : resent analysis ::nservatively eieluces assue:tien of e:uiliertum.
tenttal :1.gging Of ::rcuits :y : rect:itatec silica.
Ir see vertical stream :.:e case sn:=n +n :ig. 4, Ne maximum iM/M O 0"U*I - eter/ year ::;urs at Ne intersection aftn :ne re::sitory place, and is at:ut ine 0.C005 anc 0.:005 for : e cases of TO = 3C C anc 50'C res:ectively. vertical strea- tu:e : ees sligr. ly f*:m tre heri: ental case :ecause the f'unes ?ay te .:-ar er ::=rware, are tre te :erature is not symmetrical arcund An increase in ar: tent tre : lane : :
,

e:ause of :ne ge:tre- al gractent. t te :eeature Of 208: cause enly at ut a 2:*. increase in -animus cissolution, n;=ever, se tne gee:Permal gradient, wnten is en :ne cecer cf 5'C cer 10C0 eters cule not affe:: :ne results signift:ar'.ly.
!c :: n cases, :tssolutten is cirectly pr::ce:1:nal :: tre greue: water flui.
An 'n rease in *** flux :: 10 eter/ year (3.2 x 10' m/se ) wcule trerefere tacrease :ne .aut u- 1* *,v :: 0.007 anc 0.006 fer tre r ri: ental anc sertt:al st'eam tutes res ect.veIf, ' T F 9
, , . , , , ~ , - - - -,-,-e . . _ - - - - , - - - -- - - - - - - - - -
. . . . . , . . . . . . . . . . . w 3
54 :! f fiec
del Tae eesults of ne :cel :-esente at ve indicate t at silica cissoluti:n is greatest =rere tre te :erature g*acient is stee:est, .nien is at the interface between tre re:ository aac tre serr:ua cia; ec:k. In accitten, the :eas cissolutten calculatec f:r tne n:rt:crial anc vertical stream tutes eee r:ugnly e:aal, even :n:ugn tne ee:: sit:*y -as re: resented as a thin plate heri:antal to tne eartn's surface. These c servations lead to the devele:sent of a si :le* :cel ht:5 :an te usec for cui:( esti-ates of the maximum ciss=1ution. C:nstcer t e :ase of tae vertical stream tute, with-flew along tre : amis. By a::1ying'tne emain rule, tne encontration gracter.t in Ec. 5
an :e -ewettten:
30/3: = (10/37) (37/3:) (9) 1 l E;uation (5) te:o es 1 w/w0* I *} ( ' o
'er an infinite hert::*tal : lane source, ::ncu: tve neat flui away fac- tne a::er and 1 =e* su 'a:es of tne re:osit:ry is 2A 3T/3:, nere i'is tre ther-al
rcu: tvity
e ::e1 assu es :ne-t:al ecutlitetum, so C = 0.C6009 ( as state: Oy E:. 3- Ire *ef:re:
...=s. ::... . . . .
DRAFT
. r.m .
aC/ai = 0.C6:09 ></37 (11) If .e assu e trat 3(/)T :an :e re:resente: :y an average value $ in E:. 6: 5(?) = ( a</37) , - (12) anc tee e<:re taser :uts::e :f : e 1,teg-at, E:. 13 te:: es (13) aM/M g = 0.060C9 U 5(I)/(2 sk) / 2i 3I/1: Ot' = 0.060C9 U $(I) Q(t)/2nk e
.aere Q(t) is t~e teat:ad, ; ules, integrateh to ti e t per square eeter of re: sitory (1:0) 1-ei. *re ::effi:ie-t 1 :29 :e cert'.e: ty cifferentiating E;. 6, anc is snewn in Fig.5 for a :-:rcas silf:a. Note inat 5 :Nanges Oy less than a fa:: r of 2 te: ween 300 a-: 373.1 'K, which is witnin :ne en:ectec :erating tee:eratures of :lannec ML'd re::sitories. Taking S cutsi e of ne integral woulc no ~e-ef:re lea: :: a g-eat error. ine irtegrate: Peat loac can te expressec as * (14) = 0., f( t )
t
.nere 00 tt tP' 1"'t 8' '"rf*E' nt t0'C'. joules /(- 'yr) and f(t)/.z(0/CO} . ~ ';el. ~~e fu :t':9 f(t} 's t :.e ;-a:-4:aily *e sig. 6 fer.10 year cic s: eat a
4 4
2. .s s. ::.....a . . .

e. t.
E:uati:n 13 is conservative te:ause it ::asicers only ice stee:est te :erature gracient. The tree-41 gracient is als: animi:ec :e:ause Feat traasfer is
nsice-e: in only one :t ension r.ics fails :: ase seat less :er:e-ci:a'ar ::
a tre : amis into a:::unt. A ::rservati.e value of $ mus ce :nesen, n: evee. soggestec value of i -nt:n nas teen sne-n :: give conservative results is I~(*() = (i nv - 100 )/2 a 273.1 (15) ere i, is :ne a- tent e :erature at ne en::sitory level, "C. a . Inis ::el src.ic ce a::lica:le :: nort:Ontal flows as well, since the stitca
tssolution f*a::1ces : rect :e: fe:m tre nu erical ::els of tre crevious secti:n gave e:.;r.l> e:ual results 'er tre .ertical anc heri::ntal cases.
Eia-ele e -es: sit ry Oresente in t*e :-evi:us sectt:n (Table 1). Zalculate Censicer 0" *
*~ O' #"5' '
1*/"O #' 5:lution 4 Tre ee:*ese-tat'.e te :e stare Ites etween a-ste-: anc D 111ng:
DRAFT s...<%=...... . . . . T = (3C8 - ICO*C)/2 - 273.1 = 333.1*(
"r:: Fig. 2 $ = 5.55 10 ' :les/ liter *<
(a) f:r = ;;0; yea-s, f-em Fig. 5 f(t) = 119, 50:
~5 3
/w, = ( 1. 0 5 95 10 i 11:10 119 i 0 060:9 = 5.Sx10"#
a ,
;i . 3.3 i <.3:i.;.'
e (c) f:r
= ;;.000 years, f(t) = 275, se: -3 iw!*.. = '. 32 10 ,
Ine *esult at 10,:00 . ears is at at ::u:le tne ciss:lutten predictec ey tne
~
a. eei:al : ei Of t e :*evicus se:: ten. Tee largest :iscre:ancy is prota 1y causec ey t~e ::ase wat**e encice af l. Figure 7 se ws tne time ce:encent te cerature rise a: ve a-etent at tne re:: sit:ry center Orecictec ey sne
-. erical te :e-atare :cel, incicating trat the average temperature is Orc:stly O':asice-atly less tnan 333.1
K. The a:proxi. ate soluti:n is reas:ca le ::asiceeir;

ts stepi tet ty.
54:nt #1:an:e :' 5':a Oisselutt:n Silica cissolutice t 'a:-ease the Octestty ac: nycrauli: con:2:tivity of ne saturatec *:ct, t e-e:,
creasteg tee gacun water flux ter:uge Ne affecte:
ORAFT 2 ...
, n. ,: . . , : ; . . , ,, . . . . . . , . . . ..
region. For an ecual value of 1*/.80' "0C " '" '"I 'I Y 5**II 20"05IIY "0"Id te m:re greatly affecte: than r00k witn large iattial por:sity. A reas: atle estimati:n Of the 1 ::rtan:e of silica cissolution can te ace y
nsicering tne :ase of a res: sit:ry witn :ne tare minimum s:ecificattens of a 100 year travel ti e aa: cistance :: tne a::essible envir:n er; cf 2000 eters n:rt::etally. Sin:e tne ::-e vel::ity is tne flux civice: y the effective

r:sity, travel ti e t.'cistan:e L. Initial effective scrosity n0 3"U "' U are relate: y tne foi!: trg e:uati:n:
Cla. = . t = 2000 ete s/100 years (16) v Ecuati:n is e:utres t'at tre nycrault: gra:ient reeains constant. .nien is
nservative s acer the ete:umstar:es cf a 10:al increase in the hycraulic concu:tivity.
Tre enange ia tre effe:tive : rosity relative :: tre initial effective ::r:sity e, can ce cert.e: f- s Ec. 13: v
= (UC f(t) = $(i) = 0.05009)/2r,aAw (17) an/n0 = (a*/"3)/en. 3
A
,....s............ RAW ,,
le f:r 0:nservatively assuming :ne sa-e ::ncitions as in 15e crevicus exa 10,C00 years, an/r v3 = (2003 i 5.35=10'I 2.41:103 = 275 0 C6CC9) = 0.C27 7 100 x 2 = 2.2 = 7.25:10 The effe::ive : r:sity f:r tre :resert case tnerefore w:ule enange less tnan 2% cver a 10,000 year :ert: . Tre :er eattlity of a low-:orestty medium anc thus roviding the g-:un:-ater flus . uic te Or :Ortional to tne orosity cuted. trat tre cycra.I': ;ra ie'a 3 ::5er re;ersies remain the same: AU/ L' = 1 - ( 1 - :-/ ,) 2 = 0.CSI (18) v The flus sne:ugn :Se affe:te: area =cul: therefore increase by at:ut B cercent in :ne rescat ena-:le. Tne a::ve aralysis is censeevatt.e for tre follcwing reasons: all times, with no
1. E:utittet.m :etween water and stit:a ts assumec a'
- ::nsideration given :: tre rates of dissolutien, wnich coulc de limittr; in sese'ctrcumstances;
2. "Me Ost 507.0 e ':r- Of stitta was as'sumec; 1
.-..w.- .-- .::.<7.- . . . . . , , -
te tne
3. A kncwn conservative value Of the solu:tlity ::ef fi tent -as use:
cissolution ?::ei; 4 ine six lif f e: ::el :.eresti ates isselution an: ::nsicees Only its nfgrest value;
5. wi-? se s:e:if':ati: s :n travel 11 e an: Oistaa:e :: :ne a::essi:le envirce-eat were use: :: estimate tne ratto U/nO; -
The analysts for **:-ease: fl = Assu.es that tne mycrault gra 1ent 6. criv4rg e 'i: ss : nstant =neras a ic al increase in Mycrauli 0050s:t1.4 ty -ig t :ause tne gractent ce Oe:-esse: (i.e., tne fle= rate ay te ::-tr:I'e: Oy tre resistaate to fle= else=rere); and
7. Ine :lectage of ficw in areas nere silica is being rect:itated is cet taten fnte a : vet.
In a:Cition, ?.ineral alteratice may in so.-e cases
'ead to ar 1-trease in volume ever tra uralte-e: -ire-al. '0"'
f ne iM/M O I"O~ -
"""' "I ~00' I *~ I " "5'#' ' #"I "' " ' -easona:le 1000 3.. ; :.-:-ater travel ti e, less ina- a 0.5*. increase in flux .ck': :e reci:tec. ' ese esults s e gene' sliy sa::crte: by Otner st.:ies.
e.;., ;ef.3.
a ...< s.. :: c . . .a. ,, C:nt!usions Tne 1 : rtan:e Of ne cissolutice. of silica to the integrity Of a re:0 sit:ry
,as ex:lorec witn several st :le cels. TPe m:cels assu ec ::ncu:tive neat transfer only, anc tra ;-curewater =45 ai=ays saturatec with silica at a a,
ncentrati:n cete--'re: ty an e :irical ' unction of te :erature. Tre 9axi ciss lutt:n rati: :::.ree: ae-e te :e-ature gracients were g-eatest anich was at tre ec;es of tre re::sti:ry, anc =ere cire: ly Orc ortional to the greurc-ater flui. .
Ine 1 :criance f tre silica cissolutton was ceterminec fer a censervative case
! a re:cstt: y :a-ely eetteg tre e:utre ents of grouncwater travel time anc etstance :: tre a::essi:le envie:r.ent. C:sservative coef ficients were used in a ::nservative, st :lifie: -ecel t: *ecict inat effective poresity would Mere increase ey less inan 3*. anc grcunewater fium ey 8% cver 10,000 years.
It reasona:le estt-ates of ne coefficients inci: ate euen smaller increases. can te gene-ally c:n:!uced frem inese resu'ts that increased Ocresity :ausec Oy a silica cissolutt:9 15 not 4 -ajor ::nsiceration te tne trans:cet of gr u cwater chracionuclicesnearageoldgicHLWre:: sit:ryinasaturatec00rcustecium. Ints may ect recessa-i~f te tPe *ase f r cissolution or :hase :nange Of other
-**erals, F:= eve * (
tw** In tre :ase Of si'* a if the circumstan:ts were
p...... T. . . .. DRAFT ,
.i -
It will te ne:essary t: ract: ally different from tnese use: for tre exa :le).
erfor. an analysis fer :trer ty:es of minerals en a case-cy-case cast s. *ne te:-ni: es e :Ic>ec in tnis re: Ort ay te useful for einer minerals, es:e:ially if t e crarge in '"O'"'" 0"00'55 00' I'0 OY
*/*0 OY O'55#I"*IO" 0" te :erature g acient al:ne. ..: s-r.c -- :.; 2:::s a.g =.
1. "Aralytt:41 *:ce'.':r Re:0 sit:ry Te cerature," R. Cocell, Attachment ts w e o, 00:e * ! :: s a::, w a y 4, 1934

2. J. D. Ri sti:t aae u. L. Barnes, "ine (inetics of silica =ater eactt:ns," Geo mi-ica et Cas-centmica Acta Vol. 44, op 1633 to 1699,
.: 0.
3. J.W. Seattn-atte, ~.S. Nimick, "Effect of dest-Ro:s Otsselution anc a s.: Tear waste Re: stt:ry '- Taff", SANO34-0192, Deeciottatten i Sarcia Natt: cat .4::ratory. A1:uawercue, N.M., Sect. 1934 6
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Y z ! i i r i ! n l U FIGURE 1 REPOSITORY WITH VERTICAL AND HORIZONTAL STREAM TUBES L I C C; _3 C; C; . 3 C i-2 . i-2 I 8
I l 8
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i i-3. 2 il i - 1/ 2 ll i-1/2 g i-3/2 ll i-2 i-1 i i-1 i-2 ( FIGURE 2 STREAM TUBE TRANSPORT MODEL ! I
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ML20202C901

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