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t, . t ADVISOHV COMMillit ON NUCLt Ah WAbil9, [ WAf,HINGTON. O C. 205%

'%,, * ,o#**** May 17, 1991

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MEMORAllDUM FOR: James M. TaylorExec tive Director for Operations

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FROM: Raym E. raleExecutive Director, ACH

SUBJECT: 30Til ACNW MEETIllG FOLLOW-UP ITEMS

Based on discussions regarding inethods f or improving implementationand follow-up of AC11W recommendations, a summary of " Actions,Agreements, Assignments, and Requests" made during each AcilWmeeting is sent to your office following each meeting.

Attached is a summary of the " Actions, Agreements, Assignments,and Requests" made at the 30th ACllW Inceting , April 23-24, 1991,that deal with requests made of the NRC staf f or that are pertinentto NRC utaff activities.

Attachment:As stated

cc: 11 . L. Thorapson, EDOJ. L. Blaha, EDOS. J. Chilk, SECYE. L. Jordan, AEODR. M. Bernero, HMSST. E. Murley , 11RRE. S. Beckjord, RESA. L. Eiss, llMSS11. Pastis, NRRM. Weber, OCM/KCM. V. Federline, OCM/KCS. Bilhorn, OCM/KRJ. Kotra, OCM/JCR. R. Boyle, OCM/FR

LE31GliATED ORIGINAL

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SUMMARY OF ACTIONS, AGREEME!1TS , ASSIG!iMENTS, A!JD REQUESTS30TH ACNW MEETING - APRIL 23-24, 1991

REPORTS MilLli]21QEAl{DA

Individual _ancLCollective Docs Limits and Radiorluclide Releanse

Limits (Memorandum to Mr. Robert M. Bernero, Director, Of ficeof Nuclear Material Safety and Safegaards, dated April 29,1991. See Attachment 1.)

Consideration of Human Intrusion in the Licensina of a Hia}1-e

Level Waste Reposit2ry (Report to Chairman Carr, dated April29, 1991. See Attachment 2.)

program Plan for the Adv.iporv Committee on Nuclear WApfge

(Report to Chairman Carr, dated April 29, 1991. SeeAttachment 3.)

Draf t Staf f Technical Position on Underground Facility Design*Thermal Loads (Memorandum to Mr. B. J. Youngblood,--

Director, Division' of liigh-Level Waste Management, from Mr.Raymond Fraley, dated April 29, 1991. See Attachment 4.)

ljIGHLIGHTS OILMATTERS CONSIJ1ERED BY Tile COMMITIIE

1. Staf f Technical Engition on the Hich-Level Wan.t;p_leppgitoryDesion for Thermal Loadg

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The committee reviewed and commented on a draft NRC StaffTechnical Position (STP) on the High-Level Waste RepositoryDesign for Thermal Loads.

During the discussion, Dr. Moeller requested a catalog orlisting of all Staff Technical Positions pertaining to a high-level waste repository along with an index. Mr. JosephHolonich noted that the Division of High Level WasteManagement (HLWM) issues a quarterly products list thatincludes a list of all Staff Technical Positions issued. Heagreed to provide a copy for the members and to place Ms.Charlotte Abrams on the distribution list for future reports.

2. Individual vs. Colls.gt;ive Doses

In response to Chairman Carr's suggestion to Dr. Moeller thatthe Committee provide comments to the NRC staff, the Committeediscussed the advantages and disadvantages of using collectivedose criteria versus individual dose critoria and individualradionuclide release limits when determining risk posed to thepublic health and safety from a potential release from an HLWrepository. The Committee approved the memorandum noted aboveto Mr. Robert Bernero, NMSS, as background to a paper thatNMSS is preparing at the Commission's request.

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30th ACNW Meeting 2 |

April 23-24, 1991

3. Uncertaintion in Implementino the EPA's llLW RadiatioDProtection StaD51ard

The Committee was briefod on the revised draf t! pa aor on the" Staff's Approach for Dealing with Uncertatnties inImplomonting the EPA liLW Standards," 40 CFR Part 191. TheCommittoo and NRC staff favor different alternativoprobabilistic formats for the containment requirements inEPA's high-level wasto standards. I

In addition to going through the staff's draft item by item,the Committee agrood to issue a report on this subject duringits May 22-23, 1991 meeting.

!4. Leachina Resistance of Low-1evel Waste Forms4 ;

IThe Committee continued its discussion with the NRC staff on ;

a response to a recent Staf f Requirements Memorandum (SRM)concerning a proposed revision of Part 61 with regard to

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loaching resistance of the low-level wanto form. The NRCstaff responded to the member's questions and discussed 1

further issues that will need to be addresnod during the May22 23, 1991 ACNW meeting.

Dr. Steindler noted that the initial background informationreceived from the NRC staff did not provido sufficient in-depth information. The Committee indicated its nood foradditional specific information on safeguards already in theregulatory syston which provide protection against thepotential for groundwater contamination from LLW disposalsites. (A follow-up memorandum on this matter was sont toMr. James Taylor on May 10, 1991.)

5. ACNW Four-Month PlaD

The Committee prepared and issued to the Commission its four-month plan for the period May-August 1991.

6. ACNW Future Activities

The Committoo discussed its planned visit to the Center-

f_or Nuclear Waste Rqgulator_y ADalyses (CHWRA) in SanAntonio, Texas, scheduled for June 26-28, 1991. TheCommittee will bo briefed on the status of the SystematicRegulatory Analysis program and will receive an update'

on other activities of the Conter, such as PRA computercodes and tectonic modeling.

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30th \CNW Meeting 3

April 23-24, 1991

The Committee agreed to have a Workina Group on residual-

contamination clean-up criteria. Dr. Moeller will bethe Chairman. -

The Committee agreed to have a Workina Group on post--

closure monitorina of an IILW repository and other relatedlosues. The ACNW htaff will invite representatives fromEPA and NRC to brief the Committee on various aspectsassociated with post-closure monitoring. The date forthis necting is to be determined. Dr. Moeller has beententatively selected to be the Chairman.

The Committee agreed to have a Workina Group on an-

alternative _ probabilistic fornat for the containmentrequiremento in EPA's high-level waste standards. ThellRC staff has proposed that processes and eventspotentially affecting a repository could be divided into

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three categories (likely conditions, unlikely conditions,and very unlikely conditione) . Dr. Steindler will be the .Chairman.

Mr. Fraley noted that review of the first Reculatory-

Guide for implementing the new 10 CFR Part 20 (Standardsfor Protection Against Radiation) will be scheduled forJuly. ( Advanced copies of three guides wcre received onApril 25, 1991, for the ACRS and ACNW to begin theirrespective reviews. Members will be sont a copy ofRegulatory Guide 8.N8, Assessing External Doses fromAirborne Radioactive Materials to begin their review. )

The committee requested a briefing on the Oak Ridae-

Study, " Mortality Among Workers at OhP Ridge NationalLaboratory -- Evidence of Radiation Effects in Follow-Up Through 1984" by the principa' investigators as wellas representatives of the National Institutes of IIcalth.This meeting will be scheduled as time permits.

! The Committee agreed not to schedule briefings on the-

decommissioning of the Hanford Production Reactors andin-place vitrification. The Committee also stated thatfurther review of the LLW Uniform Shinnina Manifest bythe Committee was not necessary (an August high priority

| item per memorandum to Raymond Fraley from-James Blaha,| dated April 5, 1991). i

Appendix A summarizes the proposed items for future meetings of theCommittee and related Working Groups. This list includes itemsproposed by the Commissioners and NRC staff as well as ACNWmembers,

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30th ACNW Meeting 4April 23-24, 1991

APPENDIX A. FUTURE AGE!1DA

(Tentab1veAgenda)31st ACNW Committeo Meeting May 22-23, 1991

EPA HLW Repository Standards (Workina Draft #3) The Committee-

will be briefed on Working Draf t #3 of the Environmental ProtectionAgency's 40 CFR Part 191, liigh-Level Waste Repository Standards,if available.

Leachina Resistance of LLW Waste FqrJ2 The Committee will-

continue its discussion on a response to a recent StaffRequirements Memorandum (SRM) concerning a proposed revision 01Part 61 with regard to leaching resistance of the low-level wasteform and groundwater protection requirements.

Uncertainties in Imnlementina t))e EPA!s HLW lladiation ProtectionEtandard The Committee will continue discussions which address-

dealing with uncertainties associated with impicmenting the EPA IILWrepository standards.

Workina Groun Report on Intearation of Geenhysics into siteCharactpriff tion ,pf a flich-_ Level Wa1}te Renository The Working-

Group Cnairman will report on the importance and advantage of, andpotential results from, geophysical testing methods as thosemethods apply to the identification of possibly adverse conditionsat an IILW site.

State of South Carolina The Committee will be briefed by-

representatives of the State of South Carolina on theimplementation of its Agreement State Program.

| Trin Reports The Committee will hear from members who attended-

the Second Annual International liigh-Level Radioactive WasteManagement Conference and members who participated in the fieldtrip to Lunar Crater.

| Dinital Data Set The Committee will be briefed on a digital-

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data set prepared for the Yucca Mountain Site.

Committee Activities The Committee will discuss anticipated and-

proposed Committee activities, future meeting agenda, andorganizational matters, as appropriate. The members will alsodiscuss matters and specific issues that were not completed duringprevious meetings as time and availability of information permit.

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30th ACNW Meeting S

April 23-24, 1991

Working Group Hectings

Exnert Judament in Performatig_e Assessment of a Geologic RepositoryJune 18-19, 1991, 7920 Norfolk Avenue, Bethesda, MD , 8:30 a.m.,

The Working Group will continue the examination ofRoom P-110 -

methods for eliciting expert judgment. The meeting will focus onthe actual mechanics of clicitation. This includes questions onwho will identify and select the experts, as well as how theselected experts are trained and how their opinions are aggregated,iluman intrusion will serve as the reference example in relating theclicitation process to a real and useful application. Participantswill include normative experts, as well as 11RC and DOE staff andconsultants involved with Yucca Mountain and WIPP.

The Working Group willGeoloqic Daling (Date 'to be determined) -

review and discuss the problems and limitations associated with thevarious quaternary dating methods to be used in site character-12ation of an llLW repository.

Residual Contamination Clean-up Criteria (Date to be dctormined)The Working Group will review, discuss and make recommendations-

regarding the clean-up criteria and clean-up levels forunrestricted use at contaminated sites that are or have been underNRC license.

Egst-closure mod 11pIlng (Date to bc determined) The Working-

Group will discuss post-closure monitoring of an IILW repository andother related issues. The ACHW staff will invite representativesfrom EPA and NRC to brief the Committee on various aspectsassociated with post-closure monitoring.

Alternative Probabilist;.ic Format for the Containment ReauirementaThe Workingin EPA's HLW Standards (Date to be determined) -

Group will discuss the division of the processes and events (likelyconditions, unlikely conditions, and very unlikely conditions) thatpotentially affect a repository.

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Attachment 1+ r+ m <,f" * UN11LD S1 Alf S

g h h; V, /; i,' 'i g NUCLEAR REGULATORY COMMISSION

3 - s Auv404Y COMM01ti ON NOCil AH W Abitb[ f W A $mNG TON. D C .W$

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April 29, 1991

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Mr. Robert M. Bernero, DirectorOffice of Nuclear Material Safety

and SafeguardsU.S. Nuclear Regulatory CommissionWashington, DC 20555

Dear Mr. Bernero:

SUBJECT: INDIVIDUAL AND COLLECTIVE DOSE LIMITS AND RADIONUCLIDERELEASE LIMITS

The Advisory Committee on Nuclear Waste has been developingcomments, thoughts, and suggestions relative to individual andcollective dose limits and radionuclide release limits. Since weunderstand that your staff is reviewing those same topics, wewanted to share our thoughts with you. In formulating thesecomments, we have had discussions with a number of people,including members of the NRC staff and Committee consultants. TheCommittee also had the benefit of the documents listed.Basic Definitions

As a basic philosophy, individual dose limits are used to placerestrictions on the risk to individual members of the public dueto operations at a nuclear facility. If the limits havo beenproperly established and compliance is observed, a regulatoryagency can be confident that the associated risk to individualmembers of the public is acceptable. Because the determination ofthe dose to individual members of the public is difficult, theInternational Commission on Radiological Protection (ICRP) hasdeveloped the concept of the " critical group" and recommends thatit be used in assessing doses resulting from environmentalreleases. As defined by the ICRP, a critical group is a relatively l

homogeneous group of people whose location and living habits areI'such that they receive the highest doses as a result o'f radio- -

nuclide releases. The group may be real (in which case theiractual habits may be knewn or predicted) or hypothetical (in whichcase their habits may be adatmed,- based on observations of similargroups).

The dose to individuals within the critical group is assumed to be-

that recei.ved by a typical member of the group. The purpose ofthis approach is to ensure that members of the public do not

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receive unacceptable exposures while, at the same time, ensuringthat decisions on the acceptability of a practice are not preju- |idiced by a very small number of individuals with unusual habits. q

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11 the number of people being exposed is large, the question oftenarises as to how to quantify the societal impact of the individualexposures. The collective dose concept was developed for express-ing that impact in a quantitative manner and, as it is anumerical expression of the summed doses to a given,such,population.

In many respects, placing limits on total radionuclide _ releasesfrom a nuclear facility is comparable to placing a limit on itstotal societal impact. In other words, placing a limit on thequantity of a given radionuclide that can be released is equivalentto placing a limit on the total societal impact that the facilitycan exert. This was the basis used by the U.S. EnvironmentalProtection Agency (EPA) in setting release limits for a high-levelradioactive waste repository, and it relates directly to EPA'sbasic criterion that the number of health effects should not exceed1,000 during the first 10,000 years.

Underly_ing_Assus tions

Although it is generally accepted that the dose received by an...djvidual is a reasonable expression of the associated risk, itis questionable whether the collective dose is a true measure ofthe societal impact of the aggregate of exposures to individualmemberc of a population. Implicit in the concept of collectivedose in the assumption that the linear hypothesis is correct, thatis, that there is a linear (non-threshold) relationship between thetotal dose to a population group and the associated health impacts.

In many ways, application of the collective dose concept leads toa paradox. At high doses and high dose rates where the riskcoefficients are best known, the concept of collective dose cannotbe applied since the dose-response curve is nonlinear; at low dosesand low dose rates where linearity between dose and the associatedhealth effects is assumed to apply, the risk coefficients are farless certain. This leads to additional restrictions in theapplication of the collective dose concept, as follows:

The exposed population must be well known with respect to size*

and possibly age, sex, and temporal distributions. ;

The exposure pathways must be characterized for the population*

at risk.

Individual contributions to the collective dose must consist*

only of doses to the whole body, or to specific organs ortissues for which stochastic risk coefficients are known.

s h o r t ,'. a p p l i c a t i o nIn of the collective dose concept requires ~

detailed knowledge of the exposed population and the radiationdoses to its members. The collective dose concept is valid forrepresenting the collective risk only if both of these factors can

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Mr. Robert M. liernero 3 April 29, 1991

be described and quantifled, and it should be used for riskassessments only if the associated uncertainties are aufficientlysmall that the calculated collective dose itself is within anacce}) table range of uncertainty. In addition, it is important tonote that a high individual risk to a small number of people isnot necessarily the same as a low individual risk to a large numberof people j

this reaso,n,even though the collective dose may be the same. For ;expressions of societal risk in terms of collectivedose should always include detailed data not only on the number of ,

peopic exposed, but also on the number of people receivingexposures within each dose range. Although collective donc can beused as a surrogate for societal risk, its 1/.terpretation requirescare.

Truncation of Collective Dose _Calculgt.igng

on a theoretical basic, there is no justification for excluding theapplication of the linear hypothesis to the eva3uation andinterpretation of the societal impact of low doses and low dose4

rates on population groups. This hypothesis, in fact, has beengenerally accepted by the scientific community, including organiza-tions such as the National Council on Radiation Protection andMeasurements (NCRP) and the ICRP, as a valid basis for (stimatingthe stochastic risks associated with low doses of ionizingradiation. If one accepts this observation, calculations ofcollectivo doses should include the doses to all individuals withinthe population group, regardless of how small the associated dosesand/or dose rates may be. At the same time, however, it isimportant to recognize that there may be cogent reasons for notincluding within collective dose calculations extremely low dosesto-individual members of a population group. Several approachesthat have been proposed and/or applied to justify such omissionsare discussed below.

Following the concept that certain risks to individual members ofthe population are negligible, the NCRP has recommended (under whatit defines as the concept of a " Negligible Individual Risk Limit")that annual doses to individual members of the population that areless than 0.01 mSv (1 mrem) Le excluded from collective dosecalculations. In interpreting this recommendation, howev'er, it isimportant to understard the underlying principle on which it wasbased. Informal discussions with representatives of the NCRPrevealed that truncation in this case was considered to beacceptable from the standpoint of societal liapact, because theburden on society represented by any additional cancers amongpeople receiving exposures in this donc rate range would notnecoscitate any additional medical facilities. Another approachfor truncation that has been informally suggested by representa- .

tives of the NCRP is that it might be permissible to discard acollective dose (calculated on the basis of extremely low doserates to members of an exposed population) provided that the

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fW Robel t 11. Dernero 4 April 29, 1993

associated collective dose would not be entiruated to result in oneadditional cancer.

Variationu in the dose rates from natural background radiation.~acces have been proposed as another basis on whi'ch to truncatocollectivo dose calculations. The contribution to collective dosefrom natural sources is large relative to that from many artificialsources. Consequently, it is of ten difficult to measure in ameaningfully quantitative manner very low dose rates to individualmembers of the population that arine from artificial sources.Thus, although there may be no biological basis for excluding verylow dose rates from collective dose calculations, there isjustification for excluding them on a statistical basis because ofthe uncertainties in the associated calculations.[Leterminations of Compliance With Standards

from the previous discussion, it f ollows that the establishinent oflimits on the concentratior, of individual radionuclides in variousenvironmental inedia (e.g., air and water) is coinparable to thewtablishment of dose limits for individual members of thepopulation. Likewise, the placement of limits on total radio-nuclide releases from a nuclear facility is comparable to theectablishment of limits on the ascociated permittuible collectivedoses to the affected population. In terim of the determinationof compliance with a set of standards, it is readily possibic toineacure the concentrations of individual radionuclides in variousenvironmental media, and it is similarly possible to estimate theassociated doses to individual mornbors of the population. Incontrast, estimates of the total releases of radionuclides from anuclear iacility would require not only knowledge of the concentra-tions of individual radionuclides in all environmental media, butalso the determination of the rate of movement (transport) of eachradionuclide (including the evaluation of site-specific pathways)within all such inedia from the facility to the accessible environ-ment. Similar uncertainties would accompany estimates of theassociated collectivo doses.Summarv

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In summary, the Committee offers the following statements on thebenefits of the application of various limits for determining thepublic health risks associated with nuclear operations.1. Individual dose limits can be used to limit the risks toindividual members of a population group.2. Collhetive dose limits can be used to limit the societal ~

impacts of doses to a large nuinber of individuals. Theaccuracy of collective dose as a measure of societal rick,however, depends on the validity of the linear (non-threshold)

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Mr. Robert M. Bernero S April 29, 1991

hypothesis in accessing the stochastic offects of ionizingradiation.

3. Collective dose calculations are representative of societalrisk only if certain conditions are satisfied; namely, theexposed population is defined and characterized with respectto size, age, and sex; the distribution of doses to individualrnembers of the population is within a limited range; theexposure pathways have been characterized for the populationat risk; and individual contributions to the collectivo doseconsist only of doses to the whole body, or to specific organsor tissues for which stochastic risk coefficients have beenadopted.

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4. Techniques for ineasuring the concentrations of individualradionuclidos 'in various environmental Inedia, and forestimating the associated dose rates to individual members ofthe population, are readily available, and cornpliance withsuch limits can be deterinined. In contrast, the measurementsthat would be required to actermite the total releases ofindividual radionuclidos from a nuclear facility and estima-

itionc of the associated collectivo dose to all cffsit.epopulation groups would be difficult.

!5. Given the general acceptance of the linear hypothesic,, thereis no biological basis on which to truncate calculations ofcollective doses. Nonetheless, regulators must recognize thatestimates of dose rates from artificial radiation sources,that represent onl a few percent of those from naturalradiation sources, ycarry with them large uncertainties and

! relatively little aggregate risk. Such uncertainties may wellserve as a basis for truncating collective dose calculationsat very low done rates without adverse impacts on estimatesof the associated risks.

We trust that these comments will be helpful. We plan to reviewand comment on your report regarding this subject when it becomesavailable, consistent with the snM dated April 18, 1991.

Sincerely,

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Dade W. MoellerChairman

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Et11:D dla.G :International Commission on Radiological Protection, "19901. Recommendations of the International Commincion on Radiologi-cal Protection," Publication 60, Annals of the ICRP (1991).

2. 11ational Council on Radiation Protection and'Hensurements," Recommendations on Limits f or D:posure to Ionizing Radia-tion," Report 11o. 91 (1987).

3. 11ational Radiological Protection Board, " Radiological

Protection Objectivos for the Land-based Disposal of SolidRadioactive Wastes." Concultative Document. 11RPB-H27 9,

March 1991." Possibilities and Limits of the Application of the collective4.Done." A Recommendation of the Radiological ProtectionCommicsion (SSl') . Bunde s anzc ig er , 110. 126a, July 198S.

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Attachment 2'

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. s utalt n s1 Alt t,

[ i, 4 NUCLLAR Rf GULATORY COMMISSION, g :Q [ W AbtilNGT OfW D C 20'M,

s c Anmoin couvan t oN two t an unt;8 ,e

-y***** April 29, 1991

The lionorable l'enneth M. Carr i

ChairmanU.S. 11uclear Regulatory CommissionWashington, D.C. 20555

Dear Chairman Carr:

SUITJ ECT: COliS1DEPJsTIoli OF liUlGli IllTRUSIO!J 114 Tile LICEliSIliG OF AIIIG|l-LEVEL WASTE REPOSITORY

In its report to you dated May 1, 1990, the Committee recommendedthat the U.S. Environmental Protection Agency (EPA) standards for,

the disposal of high-level radioactive waste be revised to permit,

the application of a separate approach for evaluating the potentialinpacts of human intrusion. Mr. Floyd L. Galpin, Chief, WasteManagement Standards Branch, Of fice of Radiation Programs, EPA, hanrequested that the Committee provide additional comments andelaboration regarding this subject. This letter is in response tothat request.

One approach for evaluating human intrusion in the case of thegeologic repository would be to apply techniques similar to thoseused by the 11RC staff in assessing the threat of sabotage atnuclear power plants. In evaluating this threat, tht liPC uses adeterministic rather than a quantitative probabilistic approach.The IJRC approach recognizes the inherent uncertainties associatedwith the application of quantitative probabilistic techniques inassessing an issue of this nature.

The enclosed paper summarizes the 11RC approach in the treatmentand evaluation of the sabotage threat at nuclear power plants, andit addresses the issue of human intrusion as treated in the EPAstandards. The paper was prepared by Mr. Steven E. Mays (ACRS/ACNWFellow) at the request of the Committee. It has been discussedwith members of the 11RC staff, and it is being provided to you forpossible forwarding to Mr. Galpin. '

Sincerely,

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Dade W. Moeller, ' , Chairman .

Enclosure:An stated

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COMi' Alt 1!;O!J 01 'J i. clita l gu r f. j o3t

AS SI:S S 114G 14UCLLAlt l'OW L l< l'!.ht47l'ItOTECTIOli AG AI!1ST SAILOTACI: Af4D

li1Gil11VIL WASTE (llLW ) ht!'os } Tol< yI'llOTECTIOli AGAllisT )!UMAIJ I f4TP US 1014

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Steven E. Mayr.ACitS / ActIW rellow

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A})r i 1 1991

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A14TidicT

Human actions have the potential to bypave the protective f eat uret that minimiro*

the likelrhood of releaoe of radioactive material to the environ tierit irom nuclearpower plants or a geologic high level waute tilLW) reposit or y , sabot age ofnuclear power planto and human intrusion irato a geologic repository are exanpleo'of acts of commission that the IGC atM EPA respectively havet concluded requirespecific regulations. This paper compares the uno of probabilistic techniqueo

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by the two agencion in dealing with these acto of commisolon. The NRC chose adeterministic approach f or assoceing the itopact of sabotage on power plants andlimited the use of probabilistic techniques to qualitative asecucments of theadequacy of licensee-security plane. EPA chose to require treatment of humanintrunion quantitatively as an explicit part of the performance assoccmentrequired for licensing a geologic HLW repository.

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CUMI'AH1S014 OF TFClifflQUl:S FORAESL$S114G fJUCLI:AH POW 1:H }'LAtiT

PHOTI:CTION AGAll4ST SABOTAGE Af4D111G11 LEVI:L WASTl: (llLW) kEPOSITORY

PROTFCTION AGAlliST 11UMAfJ INTHUSION

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iINTRODUCTIO!4

14uelear power planto have engineered f eatures and proposed HLW repositories haveengineered and geologic features that serve to limit the likelihood of releaseof radioactive material to the environment. In the case of nuclear power planto,several engir;oered barriers exist including the fuel cladding, the reactorcoolant system boundary, and the containment. For spent f uel at a nuclear plant,the barriers include the fuel cladding and the alent fuel pool (or dry cackstorage at some locations). For a HLW repository the proposed barriere includethe fuel cladding, the containere for the opent fuel, and the geologicalf ormation (analogous to the reactor containment).

Human actions such as sabotage or human intrueion have the potential to bypassthe f eaturco that limit the likelihood of release of radioactive material to theenvironment. Ebile the_ intent of t hn,_ participant _e and the_ .naturf 9.Lt hene two?cilnne ru'e dif f erm1L __ euch event e aie dif ficult to EDAlYIf by _ rrobab}jitti.igifShulcues at1d at leert cabot e.co ie noLyo t rest ed. .. .Thijt.,miper exnt.iingt._ihrrytent that_1he_,1gp_ agencies uce probabi1ir,tl.q_.1rchnicupp to requl21R.prQ1RI11QDLE2!!L.1h20e RE1R ._of _ C9mm,Liggion. I t _. igLng.t int ended .to ecrgAtp_,1ht phy11ngkartat hemt: elves _ nor to sta13 that the anPl9ach puagested here ifL.1h2 Midil_yffd onL.he subins k

lThe NRC and EPA have regulationa '2 requiring licensees to demonstrate theirability to maintain the integrity of the featuren against certain acts ofcommission. In the case of nuclear power plants, phyoical security requirementsfor protection against sabotage are contained in 10 CFR 73.55. For a HLWrepository, the EPA requiremento for human intrusion (H2) are contained in anappendix to 40 CFR 191.

While both agencies recognize the potential for human actions to bypace theseprotective features, the use of probabilistic technig en in the licensing andregulatory process in vastly dif ferent. Briefly stated, the EPA regulationerequire a quantitative probabilistic analysis (called a perf ormance assesement)of the performance of the protective features of a repository over a ,10,000 yearperiod. Thin assessment must ine lude human intrusion scenarios explivitly. TheNRC approach with respect to sabotage at nuclear power planto, on the otherharid, eschewa quantitative probabilistic criteria in f avor of a determinitticevaluation supported by qualitative use of probabilistic analysen.

The purpose of this paper is to compare the methods used by the NRC and EPA toregulate protection from sabotage at reactors and inadvertent human intrucionat a potent,ial HLW repository. The paper specifically addrococo the use of (orthe lack of.) probabilictic techniques in their regulations and applications. ~

while there may be concerno regarding the olmilarity of the events themselves(and therefore the applicability of comparing the typen of regulation) and

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unet her vit her agency hau come ulon t he ultimat e met hodology f or regulating them,this paper compat es t he regulatione and applicatione ppdelnintnMymLrl.It in f or t he reader t o determine the applicability of t here t echniquen to thesegulation of protection against oabotage at reactors and human intruelon at allLW t epoci t ory.

I HOHAhlLISTIC TECilll3 QUES 'i

In any discussion of probabilictic analysis, definitions are import ant. Sincethe terms used by the two agencien dif f er comewhat, it la necennary to definethe terrno in this paper with respect to the two agency's terms.

The EPA regulatione require, as a licensing condition for a HLW repository, a* performance assessment * of any potential site. The EPA has set release lirnitsfor various radionuclidea and constructed a probabilistic criteria that theperformance assessment needs to satisfy. Specifically, the asceenment rnust

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analyse a variety of scenarion that could result .i n release of radioactivematerial to the envirotunent and calculate a complementary cumulative distributionfunction (ccDF) that shows the likelihood of releases to be 1)olow the EPA'cprobabilistic limite. In . nuclear power plant probabilictic riek accocementlanguage, this is known as a * risk curve *. This paper will une the termo CCDPand risk curve synonymously,

for nuclear power plants, risk curves are a quantitative part of the processxnown no pab&bilictic risk asseecment (P}G) or probabiliotic s;af ety assentment(PSA;. Thus, the performance ansessment of the EPA requiremente le analogousto a PRA for a nucleer plant. The elements of a PRA needed to generate a riskcurve are a set of initiating events, a model of the plant respones to theseevent.a (event trees and fault trees), and a model of the consequences of thevarious pequences derived f rom the modele. Figure 1 shows the three majorelements of a PRA along with its equivalent element from a perfortnance asoceamentrequired by the EPA. .The PRA risk curve is generated by propagating datadistributions for the initiating events, plant response modela, and consequencemodels to arrive at a distribution for each of the undesired sequences in theinodels. A distribution le derived for the sum of the sequence distributions andthe risk curve (CCDP) for the result is produced. The equivalent elements ofan EPA performance annessment are scenario development, HLW containment behaviormodele, and transport modele. Distributions are propagated through thesemathematical models, in a manner similar to the PRA methodo (although themathematical models f or containment and transport are much different from the

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event /f ault tree rnodele of PRA) . The combination of the resulting dl,etributionsis used to produce the CCDP for cornparison to the EPA requiremente.'

SABOTAGE VERSUS HUMAN INTRUSION

i As noted before, both the NRC anc' the EPA recognized the potential for humanactions to adversely impact the protective features of a nuclear power plant orpotential HLW repository. The inethod for dealing with these two similar iocur eis vartly 8,i f f erent . *

liuman actions that adversely impact the performance of protective features areIl y

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gerwa ally chagacterited by the I RA connurity at either act s of omission or actoof conolosion ''. Acts of omission are cases where a Inqui.rt(Latllan _. door r,p1acty t. Acts of conniscion are cues where actions occur that adversely impact

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the protectivo f eaturou in upite of the f act that the M11nn.,_1AE11her_remiredpor deg1rd .

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This paper characterizoo sabotage and human intrusion as ciramples of acts ofconois sion. While the intent of the participante in both cases to drasticallydifferent as is the phyelcal nature of the actione, probabilistic analysis ofacts of conenisolon le the same. current PRA practice excludes acts of commissionirom the quantitative process due to the inability to calculate either the'

f requency of such acts or their ef f ects on the protective f eatures. This papercompares the NRC use of probabilistic analysis techniques for regulating ,

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protection f rom sabotage to the E.9A tequirenents for probabilistic analysis ofhuman intrusion for a geological repository. It is not intended to equate the

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actions themselves.

; I;RC Approach to sabotage

The liRC chose a deterministic, rather than a quantitative probabilistic app 4oach,for dealing with sabotage. In fact, even with the current maturity of TRA (ascompared with the emerging perf ormance assectment techniques), the NRC has notused a rack curve as a licensing criteria for any plant, rnuch less for the subsetof events that would include sabotage.

The liRc e.pproach recognized the inherent uncertaintico and lack of data for; quantifying the nature of or the probability of a sabotage event, It also

recognized the dif ficulty in assessing the damage a potential cabotage eventwould have tan the operation of the engineered features for limitinq the release>

| of radioactive material. In other words, quantifying sabotage initia ting eventsand their effects on plant systems was impractical.

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The NRC conducted studies to assess the threat level that plante would berequired to address in their security plans. Their rulos ,b,6 recognized that1

a graded approach to sabotage protection at nuclear lower plants (in comparisonwith nuclear weapons facilities or weapone grade material facilities) wasappropriate. After determining the threat level that security plans mustaddress, the NRC regulations specify the types of plant equipmcnt that require

- protection and tht level of protection required. For nuclear power plarits,10CTR73.5L specifies general performance objectives and requirements for theplant's physical security organization, physical barriero, access,, detection,and connunications. *

This approach is similar to other NRC actions, such as regulatione dealing withthe spectrum of loss of coolant accidents (LOCAs) that emergency core cooling

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systems must be capable of mitigating. None of the sabotage regulations requirequantitative analyses such as risk curves as a basis for acceptance. However,probabilistic techniques have played an important role in the NRC reviews oflicensee security programs.

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The NBC has used fault tree modele as one tool f or annessing t he ef f ectivenessof security programs. Fault tree tr $dels f or almost every plant in the United

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* t atou have been pr epar ed by t he 148C. The Inodels dif f er f r om typical PRA modelsby.vartue of the f a c t. that the vital equipment locations are included in thenedels. In a PkA, the fault tree models4 at e reduced by computer algorithms toproouco minimal cut rets. *1his qualitative analysis is necessary bef ore data

| distributions can be propagated to produce a distribut ion for the system f alluteprobability that eventually is part of t he input to the risk curve (CCDF) . Forevaluating security programs, the location information included in the modelsis used to produce minimal eut eets containing impatiga inf ormation instead ofthe actual vital equipment.

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In addition, the fault tree models provide qualitative results thtt show the '

minimum number of areas that must be protected to ensure that the plant can be jj brought to a hot shutdown condition. This kind of qualitative information)provides the NRC with a list of areas that can provide for safe plant!

shutdownin the event of a specific sabotage scenario. jj

EPA Approach to lluman Intrusion |;

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In contract to the NHC, the EPA has chosen to include human intrusion (HI) inthe quantitative analysis of perf ormance assessment. In f act, the EPA not only

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requireu that H2 be considered, but alto specifies how H2 affects are to be '

ralculated.I

The EPA specifles a drilling density assumed to occur over a 10,000 year period.Further, the EPA allows no credit for active institutional controls beyond 100years after repository closure. The EPA also states that passive institutionalcontrols cannot be assumed to be a successful deterrent to a potential intruder.

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To date, several attempts at developing and applying performance assessment7methodologies to potential repository systems have beer, made ' 8''. In each case,

the H1 scenario has dominated the CCDF. In each caoe where the CCDF curvdeintersected the EPA requirements of part 191.13, removal Of H2 from the CCDFwould eliminate the conflict. Figures 2 and 3 show CCDFs f rom studies along with

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the impact of HI on the numerical results.

| COMMENTARYl

Probabilistic techniques can be important tools in the regulatory arena. Theproducts of probabilistic techniques can either be qualitative or quantitativein nature. The ability to use quantitative probabilistic technique,s is highlydependent on the availability of data, the uncertainties in the data, and theuncertaintlee in the processes.

| The dearth of data relating to sabot. age events along with the uncertaintiesassociated with the range of potential sabotage events and their impacts onengineered features led the NRC to chose a deterministic rnothod for regulatinglicensee acticos relating to physical plant protection in 20 CFR 73.55. The |Nhc usco qualitative probabillr. tic techniques as one measure of the ef fectiveness

|of licensev', programs. '-

The EPA has decided to require development of a quantitative probabilistic|

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.m i n i o in thu form of a risk curve covering repository performance over a30.000 year period au the bacle for licensing a geologic HLW repoult ory .Tarotment of human intrusion is required au part of thin analysin and the EPAo t andard r4 s.pecif y t hat it must be included quantit atively. Whether this analynicchould be quantitative, howevcr, appears to be in quertion, hea tont: for(xcluding human intruolen f rom the quantitative analyclo follow.

tCurrent PRA techniques have conciderable dif ficulty quantif ying human actions.The actions that PRAo try to include are those whero operatoro fail to followrequired actione (typleally known as acts of omission). Actn of commission (suchas cabotage or actions that operators might take that bypass engineered f eatureswhen there is no compelling reason to take the action at all) are routinelyexcluded f rom quantitative risk assessments for nuclear power plants. The reasonto oireple. No one has produced a reliable method for predicting either thefrequency or- the effects of euch actions. Qualitative methods using -|probabiliotic techniques exist (such as confusion matrices and other tools) thatcan . help to identify potential interactions, but none of thoce claim to beecmprehensivo even in the, qualitative sense. Analyzing acts of commission overa 10,000 year time f rame as required in the case of a geologic HLW repositorywould be even more difficult..

Except human intrusion, the EPA guidelines in 40CFR191 do not specify eit herthe f resquency of the scenarios that could adversely affect the protective-teatures nor do they specif y the ability of these features to withetand thepotential scenario. Rather, the EPA requires, that the analyses provide*reasonabic expectation, based on performance assessments that the cumulative

,releases of radionuclides to the accessible environment for 10,000 years afterdisposal f rom all significant processes and events. . '' have less than a one in

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ten enance of exceeding the values in Table 1 of the rule and less than a one,chance in 1,000 of exceeding ten times the Table 1 valucc.

Fcr human intrusion, the EPA provides guidance on the frequency of the event,3

diaallows any consideration of active inctitutional controls, and declares thatpassive controls can never be used to eliminate HI from consideration. Thisappears to be ditierent irom the other parts of the analyses that snake up thequantitative risk curve. Limited performance assosoment activition to date haveindicated that the prescribed method of analyzing HI 1cado to CCDro that exceedthe EPA requiremento.

The EPA regulatione do not addrost t he potential impact of human int. .tsion fors1 ternate means of disposal compared to the deep geological HLW repoqitory. HLWalready exists and the only method currently approved for storing HLW is spent-fuel pools or dry cask storage. Potential human intrusion leading to releasesf rom these storage f acilities over a 10,000 year period (or from some other meansof disposal not addressed by the regulations) might be greater than that allowedfor a deep geological repository.

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CONCLUSIONS

Human actiot,u have the potential to adversely af f eet the protective systems that *

limit the release of radioactive material to the environment. The NRC and EPAhave chosen vastly dif f erent ways to deal with ruch actions in their regulationc

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* c t- nuclear powe r plant o and HLW reponitories.

%e L' A hus opted f or a quantitative, probabilictic analysin tha' inclu2en humanr

2 nt rucion as one of its partc. The EPA guidelinen specif y the f requency of theH1 evento and the offectiveneco ;f controlo to prevent intrusion for theanalycis. No cuch opecification of frequencies or effectiveness of engineeredcyctoma for othet scenarios is stipulated, s

The I;RC has opted f or a determinictic approach for plant security. In a n.et hodsitnilar to their :.reat.aent of design basis evento, the NFC has specified a threatlevel that security plans must account for. The NRC requires identification ofvital equipment and the areas encortpas s ing vital equi w nt. Probabilicticttechniques are used internally ;> the NRC ctaf f to produce qualitative resultcthat support the evaluation of the (t f ectiveness of licensee security programs.Quantitative risk curves are not a licensing requirement for this ionue. Infact, the NRC does not have any licensing criteria that require a risk curvecomparison to a numerical standard.

This paper addrecses the methods that the NRC and the EPA use to regulateprotection from cabotage at reactors ac? inadvertent human intrusion at apotential HLW repository. While there may be concerns regarding the similarityof the events themselves (and theref ore the applicability of comparing the typeco; regulation) and whether either agency has come upon the ultimate methodologyf or regulating them, thic paner compares the regulations and applications ao theynLrrent3v_exiet. It 1.s for the reader to determine the applicability of thesetechniques to the regulation of protection against sabotage at reactoru and humanintrusion at a HLW repository.

REFERENCES

1. Code of Federal Regulations, Title In, Part 73, Physical Protection ofP! ants and Materials.

2. Code of Federal Regulations, Title 40, Part 191, Environmental Standardsfor the Management and Diaposal of Spent Nu''9ar Fuel, High-Level andTransuranic Radioactive Wastes.

3. NUREG/CR-2300, PRA Proceduren Guide.

4. NUREG/CR-1278, Handbook of Human Reliability Analysis with pmphasis enNuclear Power Plt t Applications. '

5. NUREG-0800, Standard Review Plar., Chapter 13.6 Physical Se ;urity.C. USNRC Review Guidei.ir.e 17, Definition of Vital Areas and Equipment.7.

NUREG / CR-4 510 ( S AND86-0121 ) , Ascessing Ccmpliance With the EPA High-LevelWaste Standard: An Overview.

.

SANDi$ presentation, 2 5th ACNW nieeting t ranscript , October 24, 1990.6.

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'9. NRC s t a f' t precentation,. 25t h ACIN meeting t ranneript, OctoW!r 25, 1990.10- CAO lloport to CongresD, Security a t. Nuclear ' I' owe r~ Plants- At nest'

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Inadequato, April 7, 1977,

12. Gho iteport to 11RC Chairman, Additional Improvemento peoded in l'hysicalSecurity at liucioar_ Power Plants, July 13, 1983. 't

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PROBABILISTIC RISK ASSESS!iENT ELEMENTSi.

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PLANT CONSEQUENCE ~| !

INITIATING MODEL ANALYSIS RISE '

EVENTS >>>> (EVENT TREES >>>> (SOURCE TEPli >>>> CUP 3/E-ANALYSIS & FAULT TREES) AND RELEASE) ;

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PERFORMANCE ASSESSME?iT _ ELEJiENTS,

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ANTLYSIS >>>> ANALYSIS >>>> (NEAR FIELD >>>> CCDF | !

& FAR FIELD)

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Figure 1. Comparison of PRA and PA Elements fI

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SUMMED NORMAUZED RELEASES R

CCDF f or the Example plotted with EPA contaitunent. requirement.

Figure 3.SANDIA Report SAND 86-0123 -(NUREG/CR-4 510)overview of Assessing compliance with10 CFR 191

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llorchole Iill Potesli) and Hydreolic Conductivity

o e s t..e t ine in t 5 A c c+ionment nequoenient1CC -- t a

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Conditional CCDF curves shoving sensitivity to variations inborehole plus porosity and hydraulic conductivity (Andersone t al. , 19 90) . * Expected * and *least favorable" value's fordeteriorated borehole plus porosity and hydraulic conduc.tivity are shovn. "Mo s t f avorable* value s , corresponding tothe properties of the reposltory seals plot off. scale.e

Curves assume intrusion scenario El occurs. Curves verecalculated usin6 the preliminary nodeling systen de scribedin Marietta et al, (1989) and cannot be used to judge cou.

.pliance or nonce::pliance because all significant scenarios**are not included, crucial nodels and data

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are t: i s s i n g, , sur-face releases are cuitted, and the Standard has beenvacated. They si:: ply ce a sure nodeling sens i t ivi t y to varia-tions in the test isrcneters. ;

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,p%. Attachment 3e *v N UNITLD STATES'. .: N'.

gj, } 5 NUCLEAR REGULATORY COMMISSION[ 5Aovisom coMMmt r ON NOCLE AR WASICgg ,/ W ASHINGTON, D C. M%

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April 29, 1991

The Honorable Penneth M. CarrChairman

nU.S. Nuclear Regulatory commissionWashington, D.C. 20555

Dear Chairman Carr:

SUBJECT:PROGRAM PLAN FOR THE ADVISORY COMMITTEE ON NUCLEAR WASTE

This is our fifth response to your memorandum of November 6, 1989,in which you requested that the Advisory Committee on Nuclear Waste(ACNW) provide a program plan at four-month intervals. This plancovers the period May-August 1991. We hope you will find this aconvenient avenue for us to share information on our proposedupcoming activities and for you to provide feedback on issues onwhich the Commission wishes us to focus our efforts.In preparing this program plan, we have considered the list of,pcific technical issues of particular interest to the Commission,requests of individual Commissioners, the EDO's list of proposed

agenda items for the ACRS and the ACNW, the NRC's Five-Year Plan,and items of particular interest and/or concern to the Committee.The priorities proposed are based on information provided byrepresentatives of NMSS, NRR, RES, and the EDO office, as well asour own interpretation of the subject in relation to our activitiesas a' Committee and our input into the regulatory process.

This program plan is based on the current best estimates of workoutput by the DOE, EPA, NRC staff, and their consultants andcontractors, as well as our own estimates of-how to deal with theseissues effectively. In addition to the full Committee meetingsnoted, Working Group meetings will be _ held as - necessary tofacilitate full Committee review and action. There may be somerevisions to this plan associated with the completion of NRC staff,applicant,

and/or contractor studies and reviews as well as otherschedule problems beyond our control.iFull Committee meeting dates for this period are tentativelyscheduled as follows:

31st Meeting May 22-23, 1991-

32nd Meeting - June 20, 199133rd Meeting - July 24-26, 199134th Meeting August 28-29, 1991-

The . Commi.ttee anticipates considering the topics listed below ~

during this four-month period.

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The lionorable 1:enneth M. Carr 2 April 29, 1991

lia Y ??-2L _1991

e The Committee will be briefed on Working Draft #3 of theEnvironmental Protection Agency's 40 CFR Part q93, liigh-LevelWaste Repository standards, if tvailable. (Iligh Priority)

The Committee may continue discuitsions which address dealing*

with uncertainties in implementing the EPA liigh-Level WasteStandards. (High Priority)

* The Committee will hear a report from its Working GroupChairman on a recent meeting concerning Integration ofGeophysics into Site Characterization of a liigh-Level WasteRepository. (Medium)

e The Committee will be briefed by representatives from heState of South Carolina on the implementation of its agreementstate program. (Medium Priority)

* The Committee will discuss information obtained by membersfrom attendance at the Second Annual International liigh-LevelRadioactive Waste Management Conference and a field trip toLunar craters. (Medium Priority)

The Committee will be briefed on a digital data set preparede

for the Yucca Mountain site. (Medium Priority)|

e The Committee will be briefed on research sponsored by theDepartment of Energy related to site characterization. Anoverview of this research is sought. (Iligh Priority)

June 20, 1991

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The Committee will respond to a Staff Requirements Memorandume!

concerning the need for revision to 10 CFR Part 61 as it|.

relates to low-level waste form leachability and groundwaterprotection requirements. (High Priority)

The Committee will hear a report by a member on a rec nt visit, e

to the West Valley Demonstration Project. (Medium Priority)The meeting with the Commission which was scheduled for thee

June ACliW meeting has been tentatively deferred to July bySECY. This meeting may still be scheduled for the June ACNWmeeting if appropriate Commissioners can be available.

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1he lionorable Kenneth M. Carr 3 A}7ril 29, 1991

03tly_2322fb_11Mll

eThe Committee will meet with the Commissioners to discussitems of mutual interest. (liigh Priority) %

The Committee will review and comment on an NRC staff report*

that discusses exemptions to 10 CFR Part 20 that allow sewerdis};osal f or certain waste streams. (liigh Priority)

Listing of Facilities and Structures in One Document. Thee

Committee will review and comment on a proposed rule dealingwith record keeping for modifications and procedures madeduring decommissioning. This rulemaking is in response to aCongressional request. (High Priority)

The Committee will review and comment on the first of the two*

groups of draf t Re,gulatory Guides implementing the revised 10CFR Part 20, Standards for Protection Against Radiation.(High Priority)

e The Committee will discuss its recent trip to and meeting atthe Center for Nuclear Waste Regulatory Analyses. (MediumPriority)

The Committee will discuss and report on how expert judgmente

will be used in conducting performance assessments used inthe licensing of high-level and low-level waste repositories.(High Priority)

August 28-29, 1993

e The Committee will invite the State of Nevada to present asummary and discussion of the State's review and comments onDOE's Site Characterization Plan and related Study Plans.(High Priority)

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e The Committee will invite DOE to present a summary anddiscussion of the DOE responses to comments by EPA} NRC andState of Nevada on the Yucca Mountain Site CharacterizationPlan. (High Priority)

eThe Committee will review and comment on the NRC staff'sTechnical Position on Investigations to Identify PaultDisplacements and Seismic Hazards. (Medium Priority)

* The . Committee will hear a presentation on the proactive -procjram for HLW. This involves planned rulemakings,guidelines, and technical position in support of the HLWprogram. (High Priority)

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The lionorable 1 enneth M. Carr 4 April 29, 1991

e The Committee will hear a report from its Working Group onQuaternary Dating Methods. (Medium Priority)

The Committee will review and comment on the staff's analysise

of the benefits and limitations of using collectivo dose andindividual dose approaches as the basis for establishingstandards f or a high-level waste repository. (High Priority)

Unschedu3ed Discussions: (Will be considered as documents and timebecome available.)

The Committee will be briefed on the NRC HLW staf f's positione

on penetration of the Calico Hills tuff. (High Priority)

The Committee plans to invite a representative from AECL toe

discuss Canada's high-level waste standards. (Low Priority)

e The Committee will be briefed on the staff's review of theExploratory Shaft Alternatives Study and the Surface BasedTesting Prioritization study. The studies are being preparedby DOE. The Committee will review these studies whenavailable. (High Priority)

The Committee will be briefed by EPA on their adoption of a*

revised Hazard Ranking System used in assessing the threatassociated with the release or potential release into theenvironment of hazardous chemicals and/or radioactivematerials. (Low Priority)

* The Committee will be briefed by the NRC staff on a recenttechnical meeting on the Alligator River Analogue Project.This project is designed to investigate the Koongarra uraniumore body, a natural analogue to a high-level waste repository.(High Priority)

The Committee will discuss an alternative probabilistic format*

for the containment requirements in EPA's high-level wastestandards. Processes and events potentially affecting arepository would be divided into three categories (likelyconditions, unlikely conditions, and very unlikelyconditions). (High Priority)

* The Committee will discuss issues related to post closuremonitoring of a high-level waste repository. (High Priority)

* The . Committee will discuss a recent report concerning .Mortality Among Workers at Oak Ridge National Laboratory.

* The Committee will discuss and make recommendations oncriteria for the cleanup of sites contaminated with residual

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The Ilonorable Kenneth M. Carr 5 April 29, 1991

3evel of radioactivity (e.g., natural uranium, deplettduranium, thorium, etc.).

This list represents our best estimate of the , topics to beconsidered through August 1991. If you or'' your fellow.Commissioners have additional items to suggest or proposed changesin priorities, please let us know.

Sincerely,

n

e

Dade W. Moellerj Chairman

cc: Commissioner RogersCommissioner CurtissCommissioner RemickSamuel J. Chilk, SECYJames M. Taylor, EDO

i

Robert M. Bernero, NMSS

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