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Understanding and Verification of Severe Accident Mitigation Actions

An abstract of a technical paper presented at:
2014 Pacific Basin Nuclear Conference
Vancouver, Canada
August 24–28, 2014

Prepared by:
Quanmin Lei, Peter Devitt, Corey French, Alexandre Viktorov
Canadian Nuclear Safety Commission
Ottawa, Ontario


Implementing countermeasures or actions to mitigate the consequences of a severe accident, should one occur at a nuclear power plant, is an essential part of severe accident management to reduce radiological risks to the public and environment. These actions, together with the technical basis (a set of severe accident management strategies and enabling instructions), are developed and documented in station-specific severe accident management guidelines (SAMGs). Speeding up the implementation of the existing SAMG program for each Canadian nuclear power plant is one of the CNSC’s action items in light of the lessons learned from the Fukushima nuclear accident.

To evaluate the adequacy and usability of the SAMGs, Canadian Nuclear Safety Commission staff have initiated several activities. These include a desktop review of SAMG documentation, evaluation of SAMG implementation through exercises and interviews with station staff, and verification of SAMG actions.

This paper focuses on the verification of SAMG actions. The objectives of the verification are twofold: to understand the SAMG-specified mitigation actions, and to check their feasibility under accident conditions. The understanding comes from obtaining insights into specific steps of execution of an action that may require operators to use the available equipment and material resources (e.g., power, water, instrument air, etc.). The feasibility check includes ascertaining the positive and negative effects of the action for the time periods and environmental conditions under which the action is being carried out. The severe accident computer code MAAP4-CANDU is used as a tool in this verification.

This paper describes the methodology used in the verification of SAMG actions and some results obtained. The key findings from such a verification exercise can help identify gaps to improve SAMGs and to help the technical support centre staff make recommendations during severe accident management.

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