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Overview of CNSC EOC Technical Tools Supporting Accident Prognosis

Abstract of the technical presentation presented at:
IAEA Consultancy Meeting
Vienna, July 23–25, 2019

Prepared by:
Mohamed E. Shawkat
Canadian Nuclear Safety Commission


This presentation provides an overview of the process the CNSC uses in its Emergency Operations Centre (EOC) to assess a nuclear emergency in a CANDU nuclear power plant (NPP) and perform an accident prognosis to estimate any potential releases to the environment. The presentation outlines CNSC’s emergency response mandate and EOC activation levels, then discusses the four fission product barriers in CANDU reactors and the possible core damage states in the event of a postulated unmitigated severe accident. The main tools used in CANDU NPP accident prognosis are then reviewed, with focus on the roadmap used to organize the prognosis tools into a systematic approach known as the 4D/4P Grid. The structure and main features of the 4D/4P Grid are explained as well as the supporting tools used to provide 4D/4P Grid inputs and outputs. The presentation also illustrates the general approach used by the CNSC EOC which produces best-estimate and credible worst-case prognoses and their corresponding radioactive source terms. The difference between these two source terms is monitored continuously to evaluate the NPP operator’s station actions. Ideally, the best-estimate source term is expected to diverge, or at least remain constant, below the credible worst-case source term. The presentation also describes the structure of the CNSC’s Nuclear Emergency Organization and the Reactor Safety Group responsible for accident assessment and prognosis. The presentation concludes with a summary of the main exercises used to test the prognosis process and the CNSC’s efforts to improve the 4D/4P Grid interface to make Grid input/output handling more effective.

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