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Regulatory Consideration of Environmental Degradation in Licensing Light Water Small Reactors in Canada

Abstract of the presentation presented at:
The 21st Conference on Environmental Degradation of Materials in Nuclear Power Plants
August 6–10, 2023

Prepared by:
X. Wei, K. Kirkhope, and A. Bounagui
Canadian Nuclear Safety Commission


The Canadian Nuclear Safety Commission is currently undergoing licensing review for a light water small reactor (BWRX 300) that is being proposed to be built in Canada. The ASME Boiler and Pressure Code Section III Division 1 is being proposed to be used for the design and construction of the nuclear systems and components of these reactors. However, while Division 1 has a wide scope; it does not cover some unique technical aspects of a few specific reactor components and it does not cover deterioration that may occur in service because of corrosion, radiation effects, or the instability of materials. For example, ASME chemical composition limits for reactor pressure vessel material (SA 508) are 0.2% for copper, 0.025% for phosphorus, and 0.025% for sulfur, which are too high to prevent embrittlement of reactor pressure vessels under neutron irradiation. In the US, this is addressed in the NRC’s supplementary regulatory requirements to protect the vessel's integrity. Therefore, supplementary technical requirements to the ASME codes, especially with respect to environmental degradation, may eventually need to be developed in CSA standards or CNSC regulatory documents to ensure the safety and reliability of the light water reactor to be built in Canada.

This presentation identifies gaps in the code that are related to environmental degradation.  These include irradiation embrittlement of reactor vessels; failure control of mechanical connections; thermal aging control of weld metal; cold working and contamination control of stainless steels; and control of the use of sensitized stainless steel, nickel-chromium-iron alloys, and cast austenitic stainless steels. The presentation will also discuss in-service aging management considerations and how the regulatory requirements in foreign countries (or in other foreign codes) address these identified environmental degradation issues. The information may be considered or referenced during the development of CSA standards or CNSC regulatory requirements for light water reactors.

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