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Severe Accident Mitigation and Combustible Gases State of the Art Report

Abstract of the technical presentation presented at:
42nd Annual CNS Conference and the 47th Annual CNS/CNA Student Conference
June 4-7, 2023

Prepared by:
Samuel Gyepi-Garbrah, Altan Muftuoglu, Thambiayah Nitheanandan
Canadian Nuclear Safety Commission


The role of the Canadian Nuclear Safety Commission (CNSC) is to provide regulatory oversight of safe operation of CANDU nuclear power plants (NPPs) in Canada. One of the current regulatory issues drawing attention is the control of combustible gases during the ex-vessel phase of a severe accident. This issue is common to all reactor designs and international stakeholders. Therefore, practical guidelines, as well as fundamental basic physical principles governing the phenomenon of combustible gases and their mitigation are of particular interest to all international stakeholders, including the CNSC for safe regulation of NPPs. 

As part of CNSC’s international collaboration to maximize the benefit of lessons learned, operational experience and the dissemination of knowledge to identify potential mitigation measures of combustible gases in Containment of NPPs, a Task Group of international subject matter experts was formed to produce a combustible gases state-of-the-art report (SOAR) task group under the auspices of the Committee on the Safety of Nuclear Installations (CSNI) of the Nuclear Energy Agency (NEA).

The SOAR provided valuable state of the art information and updated knowledge on varying topics concerning combustible gases, including its behaviour during an accident, source term of the combustible gases, dispersion, key combustion phenomena, and its impacts on containment integrity when assessed using analytical models and tools. The report also contained guidance for future research and developmental areas to address the remaining knowledge gaps in the accident management of hydrogen and combustible gases in NPPs and Spent Fuel Bay (SFB) accidents. The report also took account of recent international collaborative projects and extensive research that have been performed since 2014.

This presentation will provide the highlights of the report with particular emphasis on how the compilation of such valuable piece of work and its application to the mitigation of combustible gas risk in present operating CANDU plants in Canada as well as to novel designs that will be regulated by the CNSC in the near future, including GE Hitachi’s BWRX-300 design.

In addition, it will further enhance the existing severe accident management (SAM) programs with respect to combustible gases since this topic gained international interest after the Fukushima Daiichi nuclear event. 

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

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