Aging of a CANDU nuclear power plant affects various safety margins of the plant. Margin to fuel sheath dryout is one of the safety margins that have been detrimentally affected, leading to a reduced margin to dryout with time. If no proactive actions are taken, the plant will have to de-rate its operation at an earlier time. To postpone the de-rating, the Canadian nuclear Industry has taken multi-initiatives to restore, or partially restore the safety margins that have been eroded due to plant aging. One of the initiatives is modification/re-optimization of the current fuel design, in order to improve the fuel thermalhydraulic performance, i.e., to suppress fuel sheath dryout, whereby offset partially the erosion of margin to fuel sheath dryout.
In response to the initiative of fuel bundle modification, the Canadian Nuclear Safety Commission (CNSC) — the nuclear safety regulator — has set clear requirements and expectations and followed rigours processes and procedures for reviewing and licensing the modified fuel. This paper summarizes the fuel modification program in Canada, and the CNSC requirements, expectations, and review processes associated with licensing review of fuel modifications in Canada.