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Reactor Risk Reference Document

Author	US NRC
Date
Classification	3.01.0.20/05 (UNITED STATES - SAFETY)
Front

EXECUTIVE SUMMARY

1. Introduction

The Reactor Risk Reference Document, NUREG-1150, provides the results of major 
risk analyses for five different U.S. light-water reactors (Surry, Zion, Sequoyah, 
Peach Bottom, and Grand Gulf) using state-of-the-art methods. The broad base of 
probabilistic risk information contained in this document is intended to provide a 
data base and insights to be used in a number of regulatory applications. It is 
anticipated that these regulatory actions will include (1) implementation of the NRC 
Severe Accident Policy Statement, (2) implementation of NRC safety goal policy, 
(3) consideration of the NRC Backfit Rule, (4) evaluation and possible revision of
regulations or regulatory requirements for emergency preparedness, plant sitting, 
and equipment qualification, and (5) establishment of risk-oriented priorities for 
allocating agency resources. This report has been published in draft form. Since 
estimates of severe accident likelihoods, consequences, and risk and their use in 
regulation are important subjects, public comment is sought on the quality and format 
of the information and how best to present it for use in the regulatory process.

For the plants analyzed, this document describes (1) the major factors related to 
internally initiated events (excluding fires, flood, and earthquakes) that contribute to 
severe core damage, (2) the frequencies and related uncertainty ranges of severe core 
damage events, (3) the major factors and severe accident phenomena that could lead 
to containment failure (and particularly early containment failure), (4) the conditional 
probabilities and uncertainty ranges of early containment failure, (5) the consequences 
and risks of severe accidents, including the sensitivity of these risks to factors such 
as evacuation or sheltering measures, (6) comparisons of the risks with NRC safety 
goals, and (7) cost and risk-reduction analyses of plant-specific measures that could 
reduce risk from severe accidents.

In the period directly following the Three Mile Island accident in 1979, the NRC 
began a major effort to review existing U.S. plant designs and identify potential risks 
to the public from those reactor accidents that would be beyond the coverage of 
present licensing design basis events. As a result, the TMI Action Plan (NUREG-0660 
and NUREG-0737) was developed, and eventually numerous modifications to U.S. 
light-water reactor plant designs and operating procedures were made. In addition, 
major programs were begun to reassess the role that severe accident issues should 
have in NRC's regulatory process. These programs were related to the development 
of an appropriate regulatory policy, a set of decision criteria, and an expanded data 
base on severe accident lfke11hoods, phenomena, and risks.

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