A critique of Canadian regulatory documents for tritium emissions from NPPs

The calculation of a set of Derived Release Limits or DRLs for radioactive species released to effluent streams from nuclear facilities in Canada is a licensing requirement imposed by the Canadian Nuclear Safety Commission (CNSC) to ensure that radiation doses to the public are kept below 1 mSv/year. All DRLs currently accepted by the CNSC for radionuclides in gaseous and waterborne effluent streams are calculated using computer codes that assume essentially constant emission rates and idealized dispersion conditions averaged over 1 year. This approach leads to unrealistic release limits that actually permit the release of a station’s entire inventory of tritium and therefore impose no meaningful restrictions on plant operations. In May 2024, through REGDOC-2.9.2, the CNSC proposed an alternative approach to setting radionuclide emission limits based on a facility’s Maximum Predicted Design Release Concentrations or MPDRCs that depend on a facility’s design and historical operational performance. Unfortunately, at the present time, the CNSC is yet to provide specific examples of how REGDOC-2.9.2 is to be implemented. Nevertheless, in this report a preferred approach is presented using previously reported Maximum Probable Emission Rates or MPERs , which takes into account the significant contribution to annual doses from non-routine spike emissions and leads to a more stringent, yet realistic and readily achievable, airborne tritium release limit of 2.5 × 10 15 Bq/yr.