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Effect of containment systems and (early) mitigation on fission product release

Abstract of the technical presentation presented at:
2018 International Severe Accident Management Conference (ISAMC–2018)
October 15–18, 2018

Prepared by:
Altan Muftuoglu
Canadian Nuclear Safety Commission


Following the events at Fukushima, beyond-design-basis accident (BDBA) analysis became the focus of interest for nuclear industry in evaluating the ability of a design to restore or maintain the safety functions of a plant and eventually to reduce and/or mitigate the consequences of a BDBA. In line with this interest, this presentation focuses on the effect of mitigation strategies on accident progression and source term for a generic CANDU-6 reactor for two BDBA scenarios.

The MAAP-CANDU 5.00 code is used to determine the progression, timing and magnitude of the fission product release fractions to the containment and to the environment during these major-event scenarios.

The analyses are performed for a station blackout (SBO) and for a large loss-of-coolant accident, coincident with the loss of emergency core cooling (LLOCA/LOECC) as reference cases where, for each scenario, there is no operator intervention and only a limited number of safety systems are credited.

Later on, Severe Accident Guide-1 (SAG-1) and Severe Accident Guide-2 (SAG-2) mitigation strategies with corresponding sensitivity analyses are performed to compare the effect of the mitigation strategies with the reference (unmitigated) cases. Accident progression times and magnitude of releases (source term) are presented for each case parametrically and, for each scenario, the results are compared to, and discussed with respect to, their specific sensitivity cases. Finally, the conclusions of the simulations are discussed and presented.

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