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RIC 2018 Session W20 Tom Wellock Presentation
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Issue date:	03/13/2018
From:	Thomas Wellock; NRC/SECY
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Quantifying Reactor Accident Risk: A History Panel W20: The Metamorphosis to a More Risk-Informed Regulator Tom Wellock NRC

Risk-Informed, Performance-Based

A New Paradigm

- Efficiency

- Safety Significant

- Relieve Regulatory Burden

PRAs: Significant Limitations

- Industry-NRC gap

- Methodology

- Data

- Peer Review

New Safety Issues NRC Chairman Shirley Jackson 2

Three Ds of the Deterministic Era

- Deterministic Design

- Design Basis Accidents

- Defense-in-Depth

Inherent Safety

Active Systems

Siting

Static Layers (containment) 3

4 WASH-1400 and the Roots of PRA

Methodology: Models and Goals in the 1960s

Regulatory Necessity

Political Necessity 5

Accident Modeling in the 1960s 6

Farmer Curve Chauncey Starr 7

New Safety Issues

Loss of Coolant and the China Syndrome

- ECCS

Anticipated Transient Without Scram

- Beyond the Design Basis Accident

- Need for regulatory risk expertise 8

AEC Under Siege

Anti-nuclear Movement

Environmental Protection Agency

- Class 9 accidents.

- Growing interest in risk

Congress Henry Kendall, UCS 9

WASH-1400: Positives

New tool for regulators

A spectrum of accidents

Core damage more likely but lower consequences 10

Small LOCA Event Tree from WASH-1400 11 WASH-1400: Negatives

Large error bands

Inappropriate comparisons to other risks

Some accidents not analyzed

Lacked adequate peer review

Lewis Committee (1978) 12

WASH-1400, Executive Summary 13 UCS Critique of WASH-1400 14

Three Mile Island and WASH-1400 Human factors and operations Severe accidents Safety systems other than ECCS TMI Control Room, March 1979 15

1980s: Beneficially Unfocused

- Beyond the Design Basis: ATWS, SBO, severe accidents

- Unresolved Questions: Generic issues, older plants

- Operating Reactors: Evaluating events

- New Reactors: Design certification

- Methodology: Industry PRAs and NUREG-1150

- Goals: Safety Goal Policy and Backfits 16

Toward Risk-Informed Regulation, 1990s Individual Plant Examinations Towers-Perrin Report Maintenance Rule PRA Policy Statement (1995) and Implementation Plan (1994) 17

References

Slide 2: U.S. NRC, An Evening with Dr. Shirley Ann Jackson, November 15, 1995, U.S. NRC ADAMS Main Library, ML003710152.

Slide 4: C.A. Bennett to A.B. Greninger, Evaluation of Probability of Disasters, HW-28767, July 20, 1953, DOE Public Reading Room Catalog, Accession #

D8451637.

Slide 6: P.A. Crosetti and R.F. Furrer, Comparative Reliability AnalysisK-Reactor Secondary Coolant System, DUN-4461 (Hanford, WA: Douglas United Nuclear, September 9, 1968), U.S. Department of Energy Opennet,,https://www.osti.gov/opennet/detail.jsp?osti-id=16413875; B.J.

Garrick, Reliability Analysis of Nuclear Power Plant Protective Systems, HN-190, May 1967, (Los Angeles: Holmes & Narver, May 1967); R.S. Hart and W.T. Harper, Final SNAPSHOT Safeguard Report, NAA-SR-10022(Rev.) (San Diego, CA:

Atomics International, March 20, 1965).

Slide 7: F.R. Farmer, Siting CriteriaA New Approach, Containment and Siting of Nuclear Power Plants, Proceedings of a Symposium, Vienna 3-7 April 1967 (Vienna: International Atomic Energy Agency, 1976) 322; Chauncey Starr, Social Benefit vs. Technological Risk, Science 165 no. 3899, September 19, 1969, 1232-38.

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References (cont.)

Slide 9: Archive of the Norfolk Charitable Trust, Sharon, MA.

Slides 11 and 13: U.S. NRC, Reactor Safety Study: An Assessment of Accident Risks in U.S. Commerical Nuclear Power Plants, WASH-1400 (NUREG-75/014) (DC:

U.S. NRC, October 1975).