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Canadian Approach to Defence in Depth, Design Extension Conditions and Severe Accident Management

Abstract of the technical paper presented at:
Technical Meeting on Current Approaches in Member States to the Analysis of Design Extension Conditions for New Nuclear Power Plants – IAEA Vienna, Austria
March 19–23, 2018

Prepared by:
Noreddine Mesmous
Canadian Nuclear Safety Commission


This presentation summarizes Canadian Nuclear Safety Commission (CNSC) requirements and guidance on design and analysis of new reactor facilities to address design extension conditions (DEC). The presentation focuses on the interrelation of DEC with defence-in-depth (DiD) principles and severe accident management (SAM) needs. The presentation is based on the following CNSC regulatory documents:

  • REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants, May 2014
  • REGDOC-2.3.2, Accident Management, September 2015
  • REGDOC-2.4.1, Deterministic Safety Analysis, May 2014
  • REGDOC-2.4.2, Probabilistic Safety Assessment (PSA) for Nuclear Power Plants, May 2014

DiD is to ensure overlapping provisions are applied to all organizational, behavioural, and design-related safety and security activities. Both accident management, including SAM, and emergency preparedness and response form part of DiD. DEC have the safety objectives of preventing severe core damage, mitigating accident consequences, and protecting containment integrity as long as possible.

In summary, DEC are introduced in Canada to ensure that overlapping design and procedural provisions are available to:

  • address plant-specific accident challenges including severe accident challenges
  • strengthen levels 3 and 4 DiD for severe accident prevention and Level 4 DiD for severe accident mitigation
  • provide design features that help ensure safety goals are met and accident management objectives and strategies are achieved
  • prevent significant releases of radioactive materials

To obtain a copy of the abstract’s document, please contact or call 613-995-5894 or 1-800-668-5284 (in Canada). Please provide the title and date of the abstract.

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