News Release Article from  Canadian Nuclear Safety Commission

Archived - CNSC releases draft study for public review: Study of Consequences of a Hypothetical Severe Nuclear Accident and Effectiveness of Mitigation Measures

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June 4, 2014 - Ottawa

The Canadian Nuclear Safety Commission (CNSC) has released for public review its draft study entitled Study of Consequences of a Hypothetical Severe Nuclear Accident and Effectiveness of Mitigation Measures.

The study is in response to the Commission’s request to assess the consequences and possible preventative mitigation of a hypothetical severe nuclear accident to address concerns raised during public hearings on the environmental assessment (EA) for the Darlington Nuclear Generating Station refurbishment project.

The study focuses on the assessment of health impacts of a hypothetical, unlikely scenario of a severe nuclear accident. Various scenarios were assessed, where radioactive releases happen without full consideration of multiple safety systems at Canadian nuclear power plants. Had all of the Fukushima Task Force enhancements been fully considered in the study, the likelihood of a severe accident would have been practically eliminated.

The study concludes that in the unlikely event of a radioactive release, there would be no detectable increased risk of cancer for most of the population, with the exception of a theoretical increase in childhood thyroid cancer risk. The result is not unexpected given the sensitivity of a child’s thyroid gland to radiation. The findings suggest that further consideration is needed in how children are considered as part of nuclear emergency planning.

The study is available for public comment until August 29, 2014. Copies may be requested and comments can be submitted through

The CNSC regulates the use of nuclear energy and materials to protect the health, safety and security of Canadians and the environment; to implement Canada’s international commitments on the peaceful use of nuclear energy; and to disseminate objective scientific, technical and regulatory information to the public.

Quick facts

  • The Study of Consequences of a Hypothetical Severe Nuclear Accident and Effectiveness of Mitigation Measures is being presented to the Commission as an information item at the June 19, 2014 public meeting.
  • The study is theoretical and does not reflect the state of enhanced readiness of Canadian nuclear power plants, the operators or responsible authorities to be able to address a severe accident.
  • Canadian nuclear power plants are regulated and designed to minimize risk to the public and the environment. Many conservative assumptions had to be made to allow for the examination of a severe accident.
  • A severe accident represents a beyond-design-basis accident involving significant core degradation or significant fuel degradation in the spent fuel pool (also called the irradiated fuel pool). The modelled accident in this study is in the range of a probability of occurring of 1 in 10,000,000 (10-7).
  • It is very likely that the doses modelled in this study are overestimated as a result of conservative assumptions made about the progression of the accident (i.e., no credit for safety enhancements) and about the human health risk assessment (i.e., overestimation of dose due to modelling as opposed to direct measurements).
  • The results of this study provide insights that are useful for the purposes of emergency planning and response.

Additional links

CNSC Integrated Action Plan on the Lessons Learned from the Fukushima Daiichi Nuclear Accident

Record of Proceedings for the Darlington Refurbishment Project EA


Aurèle Gervais
Media and Community Relations
Canadian Nuclear Safety Commission

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