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CNSC Technical EOC Tools for Accident Assessment and Prognosis

Abstract of the technical presentation presented at:
2nd International CNS Conference on Fire Safety and Emergency Preparedness for the Nuclear Industry
September 17–20, 2017

Prepared by:
Thuy Nguyen
Canadian Nuclear Safety Commission


During a reactor nuclear emergency, the Reactor Safety Group (RSG) of the Canadian Nuclear Safety Commission’s (CNSC) Emergency Operations Centre (EOC) performs an independent assessment/diagnosis of the reactor state and predicts the potential release characteristics (fission product source term evaluation) into the environment. This independent assessment and prognosis of the accident are critical inputs for the offsite preparation and response activities (i.e., federal, provincial and international organizations).

The RSG uses a fission products barrier assessment approach as a roadmap to assess the status of the fission products barriers (diagnosis) and their forecasted statuses (prognosis) in order to quickly characterize the actual and/or possible release characteristics. This approach is adapted from the internationally known IRSN 3D/3P methodology for pressurized water reactors. For emergency response purposes, CANDU reactors can be considered to have four main barriers to prevent/reduce the release of fission products into the environment (i.e., fuel sheath, primary heat transport system, calandria vessel and containment). Hence the CANDU methodology has been named the CANDU 4D/4P methodology.

To support the CANDU 4D/4P accident assessment and prognosis process, the RSG uses a suite of in-house-developed tools to promptly assess the fission barriers status and the timing of possible release(s) into the environment. This toolset includes the CANDU 4D/4P tool grid, the CNSC technical EOC assessment tool, the CNSC accident handbook, the Computational Hydrogen Assessment Tool (CHAT) and the CNSC source term calculation tool, VETA. The RSG is also able to perform MAAP-CANDU simulations, as required, to support the accident diagnosis and prognosis.

In this presentation, the CANDU 4D/4P accident assessment and prognosis methodology and the supporting tools that the RSG uses to confirm the reactor state and predict the release characteristics of a CANDU accident domestically and internationally will be discussed.

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