Fission-Product Transport and Retention in the PHTS Under Accident Conditions

Abstract

The current CANDU safety analysis methodology for predicting the release of radionuclides into containment is based on the bounding assumption that fission products released from the fuel go directly into containment. Allowing for FP retention in the PHTS will help achieve the following objectives: (1) improved estimates of doses to safety equipment in environmental qualification (EQ) analyses, (2) improved estimates of public and operator doses from an improved assessment of less volatile radionuclide behaviour, (3) improved ability to perform best-estimate safety analyses, (4) improved post-accident management plans from a better knowledge ofFP location, and (5) less restrictive exclusion area boundary (EAB) designs from better source term estimates. Two LWRfission-product behaviour codes, VICTORIA and SOPHAEROS, have been assessed for their ability to provide a CANDU PHTS FP transport and retention modelling capability. The assessment of VICTORIA and SOPHAEROS was conducted by comparing the features of the two codes with the requirements for CANDU PHTS fission-product transport software, and performing simulations representative of the Loss-ofCoolant Accident with additional Loss of Emergency Coolant Injection (LOCA/LOECI) and stagnation feeder break scenarios with both codes. Based on this assessment, SOPHAEROS is better suited for simulating fission-product transport and retention in the PHTSfor CANDU safety and licensing analysis, and VICTORIA should be retained to support more detailed calculations and R&D activities.