September 2015

The Study of Consequences of a Hypothetical Severe Nuclear Accident and Effectiveness of Mitigation Measures was done to assess the consequences and possible preventative mitigation of a hypothetical severe nuclear accident in Canada. It addresses concerns raised during public hearings in December 2012 on the environmental assessment for the Darlington Nuclear Generating Station refurbishment project.

In June 2014, the draft study was released for public consultation and presented to the Commission. Following the consultation period, the CNSC addressed and incorporated Commission feedback and comments from over 500 submissions from the public, government and other organizations. Certain study assumptions and language were clarified, and information was added on a number of topics such as reactor behaviour, emergency response decisions, risk acceptability, and comparisons to effects from the Fukushima accident. In some cases, dose and risk results were updated, using a statistical approach more consistent with how dose modelling would be done in an actual emergency. These changes did not alter the conclusions of the report.

A subsequent update was presented to the Commission in March 2015. The study was published on CNSC’s website in both languages in September 2015, in advance of Part 2 of the Darlington relicensing hearing being held in November 2015.

Some of the severe accident scenarios predicted doses that are comparable to the actual doses measured at Fukushima. 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 an increase in childhood thyroid cancer risk. The result is not unexpected given the sensitivity of a child’s thyroid gland to radiation. The findings emphasize the continued importance of considering sensitive receptors (i.e., children) in emergency planning, such as KI pill administration.

Read the study (PDF): Study of Consequences of a Hypothetical Severe Nuclear Accident and Effectiveness of Mitigation Measures