ML20211A623

Discusses Site Variability in Large,Early Release Frequency as Risk Acceptance Criterion Derived from Individual Early Fatality Quantitative Health Objective

ML20211A623
Person / Time
Issue date:	09/19/1997
From:	Seale R Advisory Committee on Reactor Safeguards
To:	Shirley Ann Jackson, The Chairman NRC COMMISSION (OCM)
Shared Package
ML20211A627	List: ML20211A623 ML20211A641 ML20211A657
References
ACRS-R-1723, FACA, NUDOCS 9709240316
Download: ML20211A623 (3)

Text

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NUCLEAR REGULATORY COMMISSION y

ADVISORY COMMITTEE ON REACTOR SAFEGUARDS o

WASHINGTON, D. C. 20684 September 19, 1997

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The Honorable Shirley Ann Jackson Chairman U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

SITE-TO-SITE VARIATION IN RISK-BASED REGULATORY ACCEPTANCE CRITERIA FOR PLANT-SPECIFIC APPLICATION OF SAFETY GOALS In the Staff Requirements Memorandum dated May 27,

1997, the Commission requested that the ACRS determine the change in core damage frequency (CDF) and large, early release frequency (LERF) from site-to-site when these lower-tier criteria are derived from the individual early fatality quantitative health objective (OHO).

In response to this Commission request, during the 443rd and 444th meetings of the Advisory Committee on Reactor Safeguards, July 9-11 and September 3-5,

1997, we discussed the plant-specific application of NRC Safety Goals and derivation of subsidiary criteria.

These criteria would be used in determining the acceptability of proposed changes to the licensing basis.

During the discussions, we had the benefit of the documents referenced.

This report discusses the site variability in LERF as a

risk-acceptance criterion derived from the individual early f atality QHO. The bases for the conclusions and recommendations in this report are provided in the attached studies.

We addressed the CDF criterion in our April 11, 1997 report.

Variability in LERF Criteria Derived from the Safety Goal Individual Early Fatality OHO In support of preparing our response to the Commission's request, 4

an ACRS Senior Fellow performed a study (Attachment 1) to answer the following questions:

e Is there sufficient site-to-site variability in the site characteristics important to individual early f atality risk to f'J)I warrant site-specific determination of lower level acceptance criteria - e.g.,

LERF?

e can this range of variability be evaluated and bounded?

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.f Can generic criteria or site-specific criteria be determined 9

using simplified approximate methods?

4 The range of variability in individual early fatality risk due to the site-to-site variations-in the parameters important to individual early f atality_ risk, such as site-to-site population distribution, wind direction frequency distribution, exclusion zone size, and meteorology record, was evaluated for all U.S.

plant sites and was found to be relatively small (a variation of a factor of 4).

This study has been independently reviewed, and although the reviewers had different opinions on some of the details of the

analysis, all of the reviewers concurred with the overall conclusion on the magnitude of the variability.

Since this variability is much less than the magnitude of uncertainties associated with the probabilistic risk assessment (PRA) calculation of the LERF, this study cor.cluded that the site-to-site variability in individual early fatality risk is insufficient to warrant development of site-specific LERF criteria.

Hence, a single LERF a

criterion can be determined on a generic basis. This is consistent with the approach used by the staff in the draft Regulatory Guide DG-1061, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Current

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Licensing Basis."

We believe that the information provided in the study can be used to bound the variability of site-specific LERFs.

Adecuacy of Individual Risk Metric 5

In addition to the individual risk metric, DG-1061 contains deterministic considerations that include other risk parameters -

one of which is " siting factors."

A second study, which was performed by an ACRS Senior Fellow (Attachment 2), noted that one such siting factor, site population density, is a robust indicator of total (societal) early fatality risk.

Consequently, we recommend that the consideration of siting factors, mentioned in DG-1061 only in passing, be given much greater visibility and prominence as part of the decision making process.

Conclusions and Recommendations We have determined that there is insufficient site-to-site variability in the f actors that influence individual early f atality risk to warrant site-specific differences in the LERF subsidiary criterion, 4

i Large site-to-site. variations.in the population density result in large variations in total early fatality risk.

We recommend that f

this robust indicator of societal risk be made more explicit and 4

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prominent in the criteria to be used in assessing plant-specific changes to the current licensing basis.

Sincerely, n

.+y R. L. Seale Chairman

References:

i 1.

Memorandum dated May 27, 199'i, from John C. Hoyle, Secretary, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Staff Requirements Meeting with the ACRS, May 2,

1997, Commissioners' Conference Room.

l 2.

Report dated November 18, 1996, from T.

S.

Kress, Chairman,

ACRS, to Shirley Ann

Jackson, Chairman,

NRC,

Subject:

Plant-Specific Application of Safety Goals.

3.

Report dated April 11, 1997, from R. L. Seale, Chairman, ACRb, 1-to Shirley Ann Jackson, Chairman, NRC,

Subject:

Risk-Based Regulatory Acceptance Criteria for Plant Specific Application of Safety Goals.

j 4.

U. S. Nuclear Regulatory Commission, NUREG/CR-2239, " Technical Guidance for Siting Criteria Development," Prepared by Sandia National Laboratories, December 1982.

Attachments:

l 1.

Memorandum dated June 27, 1997, from R.

Sherry, Senior ACRS Fellow to ACRS Members,

Subject:

Considerations for Plant-

Specific, Site-Specific Application of Safety Goals and Definition of Subsidiary criteria.

2.

Memorandum dated June 11, 1997, from R. Sherry, Senior ACRS Fellow to ACRS Members,

Subject:

Consideration of Societal 4

Risk in Plant-Specific, Site-Specific Application of Safety Goals and Definition of Subsidiary Criteria.

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