United States Nuclear Regulatory Commission

Office of Public Affairs

Washington, DC 20555

Phone 301-415-8200 Fax 301-415-2234

Internet:opa@nrc.gov

No. 96-167 FOR IMMEDIATE

RELEASE

(Friday, November 22,

1996)

NOTE TO EDITORS:

The Nuclear Regulatory Commission has received the four

attached reports from its Advisory Committee on Nuclear Waste

(ACNW). The reports, in the form of letters, provide comments

on:

-- A "road map" to the ACNW's recommendation for

establishing a time of compliance for the proposed high-level

waste repository at Yucca Mountain, Nevada.

-- Comments on coupled processes in the NRC high-level

waste prelicensing program.

-- Screening methodology for assessing prior land burials

of radioactive waste authorized under former regulations.

-- 1997 priority issues for the ACNW.

#

Attachments:

As stated
November 14, 1996

The Honorable Shirley Ann Jackson

Chairman

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

Dear Chairman Jackson:

SUBJECT: A "ROAD MAP" TO THE ACNW'S RECOMMENDATION FOR TIME SPAN

FOR COMPLIANCE OF THE PROPOSED HIGH-LEVEL WASTE

REPOSITORY AT YUCCA MOUNTAIN, NEVADA

Introduction

On June 7, 1996, the ACNW sent a letter to Chairman Jackson

laying out a procedure for establishing a time of compliance

(TOC) for the proposed high-level waste (HLW) repository at Yucca

Mountain, Nevada. This letter outlined a general two-part

approach in defining a compliance period for nuclear waste

facilities and recommended a site-specific approach to the Yucca

Mountain Repository compliance period that is based upon

scientific and technical insights gained from site studies. The

recommended approach deviates from the generic TOC established in

10 CFR Part 60, which the Committee found to be without strong

scientific basis, and also deviates from the peak dose compliance

period suggested in the report of the National Research Council,

"Technical Basis for Yucca Mountain Standards." As a result,

several questions have arisen regarding the ACNW's

recommendations, especially as related to implementing a TOC. To

answer these questions and improve understanding of the

advantages and limitations of the recommendations, the Committee

has prepared this brief explanatory memo, which provides a "road

map" to its proposal.

Time of Compliance - Definition and Problem

The TOC is the period of time over which the risk of adverse

consequences from a repository must comply with a specified

standard. Over this stipulated time span, the integrity of the

whole repository system must be maintained. In itself, the TOC

is not a measure of safety; rather dose (or risk) is the

appropriate indicator of safety for a repository. The TOC

specifies the minimum time span over which the repository system

must meet the dose limits.

The dilemma in developing a TOC is that the time span must be

sufficiently long to permit evaluation of potential processes and
2

events leading to the loss of integrity of the repository and

transport of radionuclides to the critical population. Yet the

period must be short enough that inherent uncertainties in

processes and events and in the biosphere and critical population

group, which will increase with time, will not invalidate the

results of the evaluation. Reasonable confidence must exist that

the

uncertainties in the reference calculation for the time span can

be identified and quantified in a probabilistic format.

The ACNW Recommendation

The Committee recommends a generic two-part approach for

determining the TOC. The first part involves determining the TOC

on a repository-specific basis, that is, on the basis of an

analysis using modeling, analogs, and experiments to specify the

time for release and transport of radionuclides to the critical

population group. This analysis considers site and waste

characteristics, site design, and engineered barriers. The TOC

must confirm the ability of the total repository system,

including the geosphere, to prevent radionuclides from reaching

the biosphere for a minimum of several thousand years.

The second part of the recommendation requires a point estimate

calculation of the time for the potential release of

radionuclides to reach peak dose. Performance assessment is used

to determine the magnitude of the dose at this time. Comparison

of the calculated peak dose with the standard will indicate

whether the repository performance complies and will identify

deficient performance factors that may require redesign or

reconsideration of the repository. This part does not require a

definitive measure of compliance in the sense of a numeric

evaluation between the standard and the calculated dose because

of the limitations in the calculations imposed by the breadth of

the uncertainties in processes and events.

Implementation of the Recommendation

The enclosed flow chart provides a road map for implementing the

Committee's recommendation on TOC for the proposed HLW repository

at Yucca Mountain. Implementation flows from the top of the

chart downward. The process is based on input provided by the

site characterization, the engineering design of the repository,

the waste characteristics, and the design of the waste

containment. Part #1 involves determination of the TOC and

evaluation of the repository in terms of the specified standard.

Part #2 also is a requirement but does not involve a numerical

evaluation. It is an advisory component, not a de facto

regulation.
3

The implementation process should be defined in the regulation,

but the actual TOC need not be specified. The time span only can

be determined when the site characterization and repository

design are completed.

The steps in the implementation of the TOC are indicated on the

flow chart:

Input

1) Site characterization, the engineering design of the

repository, the waste characteristics, and the waste containment

design provide input to the first part of the TOC. The

engineering, waste characteristics, and waste containment are

subject to redesign, depending on the results of the performance

evaluation for the TOC. In addition, it may be necessary to

further investigate specific components of the natural setting as

a result of

the assessment of the performance and the range of uncertainties

in the performance of the repository.

Part #1

2) Analysis of the input characteristics using empirical and

theoretical modeling, analog studies, and results from laboratory

and in situ experiments will determine the anticipated time for

release and transport of radionuclides to the critical population

group on the basis of the defined reference biosphere. The

critical population group and the reference biosphere should be

delineated in the regulation. Note that this time is not the

ground water travel time, but, tying it to the dose standard, it

is the time for transport of radionuclides from the repository to

the critical population group. This time should be based for

example on the peak dose or the beginning of the decrease from

the peak dose of the most mobile (i.e., high-solubility,

low-retardation) radionuclides such as 129 I and 99 Tc that are

anticipated from possible leakage of the repository.

3) A base-level TOC is required to eliminate the consideration of

a low-integrity repository system. If the anticipated TOC is

less than a few thousand years (e.g., ~3 x 10 3 years) the

repository is rejected or the engineered system and waste

containment are redesigned to increase time for release and

transport of radionuclides to the critical population.

4) If the calculated time is greater than a few thousand years,

total systems performance assessment is used to compare
4

repository performance with the anticipated Yucca Mountain

standard (40 CFR Part 197).

5) If comparison of the calculated performance with the standard

shows that the repository performance is deficient, the

repository should be rejected or redesigned. However, if the

repository performance complies with the standard at the TOC the

repository evaluation process should continue with Part #2.

Part #2

6) The performance assessment analysis used in Part #1 to

establish the TOC should be continued until peak dose is obtained

and repository performance should be evaluated at that time. The

uncertainties in the system should be identified and quantified

in a probabilistic format on the basis of the best available

information, and their effect should be determined through

bounding calculations.

7) If the comparison of the calculated performance shows that at

the time of peak dose the repository is significantly deficient,

for example, an order of magnitude or more, compared to the

anticipated standard, the major sources of the deficiency should

be identified and possible remedial actions designed and

carried out. If these actions are not possible or ineffective

the repository may be rejected. However, if the bounding

calculations indicate that the repository complies with in an

order of magnitude of the standard, the proposed repository

performance is deemed acceptable.

Sincerely,

/s/

Paul W. Pomeroy

Chairman, ACNW
5

November 8, 1996

The Honorable Shirley Ann Jackson

Chairman

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

Dear Chairman Jackson:

Subject: COMMENTS ON COUPLED PROCESSES IN THE NRC HIGH-LEVEL

WASTE PRELICENSING PROGRAM

SUMMARY

The Advisory Committee on Nuclear Waste (ACNW) is impressed by

the progress that the NRC staff and the Center for Nuclear Waste

Regulatory Analyses (CNWRA) have made in developing a strong

program to study potential coupled processes at the site of the

proposed repository at Yucca Mountain, Nevada. Furthermore, we

are pleased with the plans for integrating coupled processes

among the vertical slice investigations of key technical issues

(KTIs). The Committee has provided observations and suggestions

to strengthen NRC's approach to coupled processes.

We want to emphasize the following recommendations:

(1) Performance assessment needs to have a more prominent role

in guiding the prioritization of coupled processes studies.

(2) The NRC should revise its decision to not participate in

DECOVALEX, a multidisciplinary international program

dedicated to the Development of Coupled Models and their

Validation against Experiments.

(3) The coupled processes studies are "data starved." Changes

are needed in the program to rectify this situation.

(4) The modeling studies in thermal-hydrological (TH) processes

need to be expanded.

(5) Greater attention is needed on near-field chemistry, with

particular emphasis on thermal-hydrological-chemical (T-H-C)

processes that affect contaminant release and transport.
6

INTRODUCTION

In February 1996, we communicated our recommendations and

suggestions on the "Revised Prelicensing Program Strategy for the

U.S. Nuclear Regulatory Commission High-Level Waste Repository

Program ('Vertical Slice Approach')" and the NRC staff's plans

for resolving KTIs dealing with the proposed high-level waste

(HLW) geologic repository at Yucca Mountain, Nevada. In that

letter, we made suggestions for improving the strategy and

investigation of the KTIs, but we were, and continue to be,

supportive of the work of the NRC staff in this regard. We see

this program as an excellent response to maintaining a

prelicensing program focused on critical issues in the face of

limited resources. In our February 1996 letter we expressed our

concern that within the specified strategy and program, it was

unclear if the issue of in situ thermal-mechanicalhydrological-chemical (T-M-H-C) coupled processes was moving

toward resolution. This letter provides further comments on that

concern.

Construction of the proposed repository will perturb the stress

pattern in Yucca Mountain, thus resulting in mechanical

deformation of the surrounding rock and the emplaced HLW will

cause a significant heat pulse to the rock. The resulting thermal

and mechanical effects are interrelated and may significantly

affect the movement of water and the nature of related hydrologic

properties, as well as the chemical processes acting on the

waste, canisters, and surrounding engineered and natural

materials of the repository. These coupled processes may have an

important impact on the performance of the repository over the

course of its history. The algorithms used in modeling the

performance of the repository system are influenced strongly by

the analytical descriptions of the various coupled relationships

among physical and chemical phenomena. The Committee is

concerned that the "vertical slice" approach to the KTIs could

lead to neglect of interaction of phenomena and their resulting

modifications of parameters and processes. To evaluate the

current validity of this concern, the ACNW reviewed the status of

the investigation of coupled processes by the NRC staff and the

integration of these activities among and within KTIs through a

working group on T-M-H-C coupled processes at the 85th meeting of

the Committee. Comments were made by representatives of the NRC

staff, the CNWRA, Lawrence Berkeley Laboratory, the U.S.

Geological Survey, the Department of Energy (DOE), academia, and

private industry.

The Committee learned of the significant progress in the T-M-H-C

coupled processes investigations and was impressed by studies

being performed by the NRC and CNWRA. Effort has been put into

the related KTI investigations and the integration of elements of

the coupled processes among the KTIs. Below are our observations
7

and suggestions regarding coupled processes, which should focus

future activities on the potentially most critical elements.
8

TECHNICAL OBSERVATIONS AND SUGGESTIONS

I. General

(1) The NRC staff, with the support of the CNWRA, has developed

a strong program for studying the impact of selected coupled

processes on the performance of the potential repository at

Yucca Mountain. This is especially true in T-H coupled

processes, which have been ranked consistently as high

priority in reviews of both the NRC's and the DOE's

programs.

(2) A key to coupled processes studies and the development of

supporting data is understanding their overall importance to

repository performance. The Committee is pleased to see the

increasing role of performance assessment (PA) in this

regard. It is critical that the PA activity be used to

provide the necessary insights and understanding of physical

processes to maximize the return on investment of

investigative resources. The Committee looks forward to the

increased use of PA to guide the scope of analysis and

research activities.

(3) We understand the continued need to reassess the allocation

of HLW funding in the face of shrinking resources. However,

the Committee is concerned about NRC's withdrawal from

Phase II of the multidisciplinary international program

DECOVALEX. The Committee sees the results of the DECOVALEX

project to date as meaningful to the NRC HLW program. The

testing of mathematical models and computer codes for

predicting the effects of coupled processes, which is the

aim of the project, is a most critical aspect of the study

of coupled processes. In the tasks outlined for the

continuing project, a variety of models and codes, developed

largely independently by investigators in several countries,

will be tested against each other and against experimental

results from international nuclear waste test facilities.

Although these test sites will not duplicate exactly the

proposed unsaturated-tuff geologic repository at Yucca

Mountain, the results should be useful in the NRC scoping

studies and testing of models and codes. For these reasons,

the Committee urges the staff to reverse its decision to

withdraw from the DECOVALEX project.

(4) The coupled processes studies of the NRC and the CNWRA

appear to be "data starved." The primary emphasis of the

studies has been on developing models and related codes.

This is an important element of the program but is only one

of the necessary ingredients to bringing the program to

fruition. The termination of the HLW research program in

this topic apparently has reduced access to experimental and
9

geologic analog information useful in validating the models

and codes and in providing bounding data. This is true over

a range of processes but is especially important to thermal

processes and their effect on properties and other

processes. In the face of this problem, both the NRC and

the CNWRA should make specific efforts to obtain all

relevant data from the DOE and its contractors. Further,

the Committee believes that there is important information

to be gained from studies of current and ancient geologic

regions, with thermal anomalies for which data are

available. For example, existing data from the Nevada Test

Site operations may be useful. Also, the Committee has

learned of recent studies on the properties, chemistry

(mineralogy), and mechanical characteristics of rocks

similar to those at Yucca Mountain surrounding an igneous

intrusion in the Nevada Test Site. This and similar analogs

are potentially a valuable source of T-H-M-C information.

Limitations on data from thermal testing are exacerbated by

the current timing of the thermal tests being conducted and

organized by the DOE at Yucca Mountain. The high thermal

inertia of the rock precludes significant acceleration of

the studies. Currently, the single heater test in the

Exploration Study Facility and the large block test will

provide thermal input before the DOE's Viability Assessment

(VA), but these tests will not give the bulk properties of

Yucca Mountain. The plan is to obtain these properties from

the drift scale thermal tests, but data from this test will

not be available in time for the VA decisions. Furthermore,

it is unclear how the results of these tests will be used to

evaluate alternative models for describing thermally induced

phenomena in highly fractured rock. The NRC should consider

how these data limitations will affect their response to the

DOE's VA.

II. Specific

(1) The Committee concurs with the emphasis placed by the NRC

staff on the T-H coupled processes, but we note that in the

CNWRA's assessment of the importance of post-closure

processes, the combination of T-H processes on chemical

processes is deemed most important. We agree with this

conclusion because of the potential effect on release,

transport, and retardation of radionuclides. However, we

note only limited, albeit important, attention directed to

the chemical portion of the coupled processes equation.

Studies are largely limited to model and code development

using simplified matrix mineralogy (chemistry). We believe

greater attention is warranted on near-field,

contaminant-related chemistry, for example, the effect of
10

temperature on the chemistry of glasses, of sorption of

radionuclides by zeolites and other minerals, of redox

changes, and so on. We encourage scoping studies to

determine the potential impact of temperature and hydrology

on chemistry as this will affect NRC decisions that have to

be made in the near term related to the VA. For example,

mineral precipitation and dissolution may profoundly alter

the rock permeability in the near-field region. The

required thermodynamic data at elevated temperatures

currently are inadequately known and the effects of such

attributes as grain size and fracture filling on chemical

reactions need clarification.

(2) The NRC and the CNWRA note potential shortcomings in the

Equivalent Continuum Model (ECM), which is the current focus

of T-H studies. Of critical concern is the effectiveness of

the ECM in predicting flow through fractured rock and the

possible development of the "heat pipe" associated with the

thermal pulse caused by the decaying HLW. The DOE Peer

Review Team on Thermohydrologic Testing and Modeling also

identifies potential shortcomings. The Executive Summary of

the DOE report states that the ECM quantitative predictions,

particularly where they impact design of the underground

structures, should be accepted with a great deal of caution.

The Executive Summary also states the following:

The main computational codes. . .have undergone

extensive development and verification. The next step

in their use, however, should involve investigations,

primarily in underground tests, where the efficacy of

ECM can be carefully examined. Given the apparent

limitations of the ECM, further application of these

models would appear to be inappropriate without such

confirmation.

We encourage the CNWRA to expand its studies of T-H to

include testing the ECM models and codes through studies of

current and ancient geothermal regions. These geologic

analogs, at a minimum, should identify the effects and

relative importance of the principal processes.

(3) We encourage studies of T-H-C processes between the

repository and the location of the critical group. We

understand that a study has been initiated at the CNWRA to

study hydrological chemical (H-C) effects in the Calico

Hills formation, which is rich in cation exchange minerals.

We believe this and related studies are warranted. The

staff needs to be aware of nonreversible processes in the

near field, such as thermal effects on permeability, and

their impact upon far-field processes.
11

(4) The program to study the effect of natural disruptive

processes, for example, igneous activity, was not the

subject of our current review. Nonetheless, we were pleased

to learn that the study of the effect of natural disruption

of the repository is included in future plans for coupled

processes investigations by the NRC.

(5) We believe it is important to conduct scoping studies to aid

in the assessment of the potential effects from coupled

processes that are not deemed important on the basis of

literature review. Specifically, we suggest that scoping

calculations be performed to address the concerns regarding

"indirect flow" processes or "Onsager processes."

(6) We believe the mechanical aspects of the T-H-M-C processes

are less problematic than the other components, and, thus,

at this time, related studies can be minimized or

eliminated.

III. Related Issues

(1) Our original concerns about the investigation of coupled

processes in the "vertical-slice" approach to key issues

during the prelicensing studies by NRC were focused on the

integration among the various processes. We are pleased

that the NRC management has proceeded beyond the KTI dealing

with Total Systems Performance Assessment and Integration by

developing a management integration task force. We

congratulate the staff on this action, which goes a long way

toward alleviating our concern. This "top-down" approach

has many advantages. Nonetheless, we encourage the staff at

all levels to be sensitive to the need to communicate across

discipline and KTI boundaries and thus to implement

integration meaningfully and in a timely manner. In

addition, we encourage management to continue support of the

Integration Task Force in the important studies leading to

decisions at the time DOE completes its VA process and in

the years beyond the VA in the prelicensing and licensing

periods.

(2) We have referred to many of the coupled processes

investigations as "data starved." Resource limitations

mandate limited opportunity for experimentation and field

studies, and, thus, this lack of data is likely to remain

unremedied, without special efforts on the part of

management. We believe joint programs with other nations

that have parallel interests are a worthwhile investment.

In addition, every effort must be made to apply the

considerable data collected by DOE and its contractors to

the NRC programs. Furthermore, we suggest that important

data on critical coupled processes problems exist in
12

peer-reviewed journals and industrial and government

literature. Management should work toward developing a

climate that fosters using these low-cost data in the NRC

program.

(3) The Staff is encouraged to be sensitive to the developing

DOE strategy for waste emplacement in the repository so that

the potential effects on thermal loading are included in

scoping and sensitivity studies as part of the coupled

processes program. Because of limited thermal testing at

the time of the VA, the NRC should evaluate the impact of

these studies at that time and develop strategies for

minimizing their impact. Limitations imposed by an

incomplete understanding of thermal properties and processes

because of restricted in situ testing even in the post-VA

period remains a possibility that needs to be considered by

the NRC.

We believe the NRC staff has a strong program to examine the

importance of coupled processes and trust that these suggestions

will be helpful in further focusing the program.

Sincerely,

/s/

Paul W. Pomeroy

Chairman, ACNW
13

November 20, 1996

The Honorable Shirley Ann Jackson

Chairman

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

Dear Chairman Jackson:

SUBJECT: SCREENING METHODOLOGY FOR ASSESSING PRIOR LAND BURIALS

OF RADIOACTIVE WASTE AUTHORIZED UNDER FORMER 10 CFR

20.304 AND 20.302

During its 87th meeting, October 22-23, 1996, the Advisory

Committee on Nuclear Waste (ACNW) reviewed staff plans relevant

to the decommissioning of sites in which radioactive waste had

been buried as authorized under former 10 CFR 20.304 and 20.302.

In addition to receiving information on the history and

background leading to the development of the screening criteria

to be promulgated in a branch technical position (BTP), the ACNW

was briefed on related agency rules and information notices. The

BTP, which was not available for ACNW review during its 87th

meeting, will be finalized when more directly related field

experience is obtained and public and licensee comments are

evaluated.

These screening criteria are directed at potentially hundreds of

onsite, non-reactor burial locations that will require an

evaluation or screening process to determine if further

remediation is required. The NRC staff has prepared a simple,

conservative three-step method to evaluate the risk from these

burial sites:

1. review burial records,

2. estimate the dose from ingestion of the total inventory in

groundwater (a conservative approach), or

3. estimate the dose to a resident farmer from all pathways.

If the estimated dose from Step 2 or Step 3 is less than 100

mrem/yr, no further site work is required, and the site can be

released for unrestricted use. The ACNW agrees with the NRC

staff approach.

The ACNW offers the following comments and recommendations:
14

1. The NRC staff does have a responsibility to assure itself

through independent audits and reviews that the risks are

reasonably assessed. These reviews are especially important

where, for example, the burials may include greater than

anticipated inventories of uranium; disposed wastes that

contain isotopes, such as chlorine-36, which at the time of

disposal were not perceived to be a significant problem;

the location and distribution of wastes are imprecisely

recorded (or, in some instances, unrecorded).

2. In those situations requiring review and approval of the NRC

staff prior to final site decommissioning, the staff must be

certain that the risks and contributors to the risks are

understood, and should not rely only on an assessment of how

the input parameters were either measured or calculated.

3. We concur with the staff's position that licensees not be

allowed to use Step 3 of the BTP screening process for

isotopes with atomic numbers of 88 or higher due to the lack

of confidence in the dose equivalent factors in the current

version of NUREG-1500, "Working Draft Regulatory Guide on

Release Criteria for Decommissioning: NRC Staff's Draft for

Comment," August 1994.

The ACNW recognizes the benefit in providing a simple, relatively

straightforward approach to resolving the problems extant from

these past burials. We note that this issue might provide the

Commission with an opportunity to advance its risk-informed,

performance-based decision-making process. The ACNW anticipates

further discussions on this specific issue with the NRC staff as

the staff completes its evaluation of public comments and gains

applicable field experience. Further, the ACNW intends to

explore the compatibility of various screening criteria and

methodology currently used by the NRC in the decommissioning

process.

Sincerely

/s/

Paul W. Pomeroy

Chairman, ACNW

Reference:

Draft Branch Technical Position, "Screening Methodology for

Assessing Prior Land Burials of Radioactive Waste Authorized

Under Former 10 CFR 20.304 and 20.302," October 1996.
15
16

November 20, 1996

The Honorable Shirley Ann Jackson

Chairman

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

Dear Chairman Jackson:

SUBJECT: 1997 PRIORITY ISSUES FOR THE ADVISORY COMMITTEE ON

NUCLEAR WASTE

CRITERIA FOR PRIORITIZATION

The Advisory Committee on Nuclear Waste (ACNW) has adopted and

implemented criteria for assigning priorities to issues it will

consider. Priorities are assigned and updated annually on the

basis of the criteria presented below. Of course, priorities are

subject to change at any time on the basis of the needs of the

Commission and developing events.

The overarching criterion for assigning priorities to issues is

the protection of the public, workers, and the environment from

any adverse effects of the management of nuclear waste,

especially in regard to disposal facilities.

Other criteria applied in the prioritization process are listed

below:

ˇ NRC’s strategic plan, including trends and directions in

regulatory practice, such as the adoption of a riskinformed, performance-based method of regulation and

decision-making

This criterion for establishing priorities includes the

consideration of the Commission’s own thinking and judgment

concerning nuclear waste issues. In particular, it includes

a clear understanding of the Commission’s view of what the

priorities are. However, the ACNW does not restrict the

issues to only those of immediate concern to the Commission.

ˇ The strategy and activities of licensees and applicants

Special emphasis should be placed on the Department of

Energy’s (DOE's) licensing strategy and activities,

including the program plan, the site characterization
17

program, and the performance assessment for the proposed

Yucca Mountain repository. The idea is that priorities are

dependent not only on the regulatory process but also on the

intentions of the licensee and applicant.

ˇ The scientific and technical basis of information supporting

the safety and performance assessments of nuclear waste

disposal facilities, including the quality and level of

technical expertise involved

The importance of an issue is clearly dependent on the

quality of the supporting information, such as basic data,

and the analyses performed.

ˇ The timeliness of the advice provided by the ACNW with

respect to effective decision-making in the regulatory

process

The licensing process involves the systematic and

incremental development of information. Timely regulatory

decision-making depends strongly on an effective match of

information development and regulatory involvement.

The application of these criteria has resulted in the following

priority issues, not listed in order of importance. It should be

pointed out that not all of these issues will be considered. In

the final analysis, current events will determine the course of

our reviews.

PRIORITY ISSUES

1. Regulatory Framework

The ACNW will continue to focus on the framework for highlevel waste disposal. Environmental Protection Agency (EPA)

standards (40 CFR Part 197) and NRC's conforming regulations

are scheduled for development. The ACNW will monitor the

interaction between the EPA staff and the NRC staff as they

consider these standards and regulations. In 1997 DOE will

provide for agency and public comment, their HLW siting

regulation (10 CFR Part 960). The ACNW will review and

comment on the DOE document. Subissues under this topic are

the following: regulatory time of compliance, consideration

of the critical group and reference biosphere, and whether

consideration should be given to risk discounting as an

element of a standard. We will consider the defense-indepth philosophy, the use of subsystem requirements, and the

treatment of uncertainty.
18

2. Waste Isolation Strategy

The ACNW will monitor and comment on DOE's final Waste

Isolation Strategy and the NRC staff's response to this

document, once these become available. The Waste Isolation

Strategy document is expected toward the end of 1996 from

the DOE. This issue will focus on the source term and will

consider container design. As part of this review, we will

examine the NRC staff's Key Technical Issues (KTI) effort

and its interface with the DOE's Waste Isolation Strategy.

3. Viability Assessment and Site Characterization

The DOE is scheduled to complete the viability assessment

(VA) of the Yucca Mountain repository site in 1998. The

principal objective of the VA is to address the major

unresolved technical questions and the technical and

economic feasibility of constructing and operating a

geologic repository at the Yucca Mountain site. The ACNW

will review DOE's conclusions and the NRC staff's review of

the VA. The ACNW will also be able to determine if the KTI

process (the basis of the staff's review effort) will

produce sound regulatory decisions. The ACNW will provide

advice to the Commission and guidance to the staff on site

characterization and analysis activities related to DOE's

studies and NRC's KTIs.

4. Repository Design

The ACNW will continue to focus its attention on the

repository design, including thermal loading issues.

Additional details of the design will be developed as part

of the viability assessment determination, but will not be

finalized. The ACNW has unresolved concerns on coupled

thermal-hydrological-mechanical-chemical processes and will

continue to evaluate progress in this area. Other design

elements that could affect the overall behavior of the

repository, due to their effects on overall system

chemistry, are concrete tunnel liners and iron from steel

sets and fuel canisters. The ACNW will evaluate the

adequacy of models that have been developed to predict

repository behavior. Issues such as retrievability and

canister design would be considered under this topic. The

ACNW will examine the proposed location of the repository

within Yucca Mountain and the impact that the repository

"foot print" will have on the facility design.

5. Low-Level Radioactive Waste (LLW) Disposal

In December 1995, the ACNW commented on SECY-95-201 in which

the NRC staff listed three options for NRC's LLW program
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(eliminate, reduce, or keep the status quo). In July 1996,

the ACNW produced a report titled "Elements of an Adequate

LLW Program," which suggested that, as a minimum, the

current program be retained. Our advice is consistent with

the Commission's preliminary preferred option in Direction

Setting Issue Paper 5. Agreement State programs and the

progress of compacts and individual States in developing new

disposal facilities remain an issue with ACNW. We remain

concerned about the final disposal strategy for mixed wastes

and will continue to monitor developments. The ACNW will

continue its review of an NRC staff Branch Technical

Position on Low-Level Waste (LLW) Performance Assessment and

the related time of regulatory compliance associated with

LLW disposal.

6. Decommissioning

The ACNW continues to have a strong interest in waste

disposal issues related to decommissioning. In the past,

the ACNW has advised the Commission on streamlining the Site

Decommissioning Management Plan (SDMP) and on the lessons

learned from decommissioning the Pathfinder power plant.

The ACNW anticipates commenting further on the use of

performance assessment in determining priorities for cleanup

in SDMP sites. We have several concerns in this area,

including residual levels of contamination, mixed waste,

greater-than-Class C waste, and consistency of screening

criteria and methodology.

7. Expert Judgment in Regulatory Decision Making

The ACNW issued a report in August 1996 on the NRC's Branch

Technical Position (BTP) on Expert Elicitation in the HighLevel Radioactive Waste Program. In its advice on the BTP,

the ACNW identified four areas of concern: (1) the

selection of subject matter experts and participation of the

experts in refining the problem definition, (2) aggregation

of the results, (3) interpretation of the results, and (4)

application of expert elicitation. The ACNW will continue

to monitor the application of the BTP to specific expert

elicitations being conducted by DOE and on the generic

applications of the BTP guidance.

8. Risk-Informed and Performance-Based Regulation

The ACNW expects to support an effort designed to help move

the agency from deterministic regulations toward riskinformed and performance-based regulation. The goal is to

link adequate assurance of safety more closely with the

regulations. Our effort will consider practices in other

nations that are implementing risk-informed and performance-
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based regulations. Efforts toward risk harmonization with

the EPA will be considered.

9. Performance Assessment (PA)

The ACNW will continue to monitor DOE's total system

performance assessment (TSPA) and review the staff's

Iterative Performance Assessment Program including NRC's

audit review of TSPA. We will continue to consider whether

PA is being used to its full advantage in prioritizing

issues. The ACNW will investigate the treatment of

uncertainty in the use of bounding analyses. Uncertainty

analyses are important in determining the adequacy of site

characterization and abstracting geologic information for PA

models. The ACNW will continue to monitor progress in

these areas, and will comment on the advisability of the NRC

staff producing a separate guidance document on the

treatment of uncertainty.

10. Uranium Mill Tailings

The ACNW will review NRC regulations pertaining to uranium

mill tailings. Considerations will include a determination

of the risk and practical remediation methods such as the

stabilization of tailings piles and groundwater protection

monitoring in the vicinity of the tailings pile, as well as

radon emissions control. We are interested in the impact on

NRC regulations of (1) the current Congressional requirement

for perpetual government custody of tailings sites and (2)

the EPA standards for the cleanup of uranium and thorium

mill sites after permanent closure.

11. Interim Surface Storage Facilities for Spent Fuel

The ACNW will address NRC concerns with a central interim

HLW storage facility. We will identify issues that need

consideration in surface HLW facilities, including handling

operations, cask requirements, comparative risk of various

options, and alternatives to dry storage.

We look forward to discussing this 1997 list of priority issues

with you and the other Commissioners in the near future. We

would welcome any comments and suggestions regarding additions,

deletions, or changes in emphasis that you might wish to make.

Sincerely,

/s/

Paul W. Pomeroy

Chairman, ACNW
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