A risk-informed perspective on deterministic safety analysis of nuclear power plants

An abstract of the technical paper presented:
2009 International Congress on Advances in Nuclear Power Plants
(ICAPP 09 – paper 9448)
Tokyo, Japan
May 10–14, 2009

Prepared by:
Pak T. Wan
Canadian Nuclear Safety Commission (CNSC)
Ottawa, Ontario, Canada

Abstract

In this work, the deterministic safety analysis (DSA) approach to nuclear safety is examined from a risk-informed perspective. One objective of safety analysis of a nuclear power plant is to demonstrate via analysis that the risks to the public from events or accidents that are within the design basis of the power plant are within acceptable levels with a high degree of assurance. This nuclear safety analysis objective can be translated into two requirements on the risk estimates of design basis events or accidents:

• the nominal risk estimate to the public must be shown to be within acceptable levels
• the uncertainty in the risk estimates must be shown to be small on an absolute or relative basis
  

The DSA approach combined with the defense-in-depth (DID) principle is a simplified safety analysis approach that attempts to achieve the above safety analysis objective in the face of potentially large uncertainties in the risk estimates of a nuclear power plant by,

• treating the various uncertainty contributors using a stylized conservative binary (yes-no) approach
• applying multiple overlapping physical barriers and defense levels to protect against the release of radioactivity from the reactor
  

It is shown that by focusing on the consequence aspect of risk, the previous two nuclear safety analysis requirements on risk can be satisfied with the DSA-DID approach to nuclear safety.

It is also shown the use of multiple overlapping physical barriers and defense levels in the traditional DSA-DID approach to nuclear safety is risk-informed in the sense that it provides a consistently high level of confidence in the validity of the safety analysis results for various design basis events or accidents with a wide range of frequency of occurrence. It is hoped that by providing a linkage between the consequence analysis approach in DSA with a risk-informed perspective, greater understanding of the limitation and capability of the DSA approach is obtained.

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