Probabilistic risk assessment study of a CANDU 600

The paper summarizes the methodology, phenomenology and results relevant to the assessment of severe events in a CANDU 600 station. The station design being analysed is a CANDU 600 currently operating in Canada. This evaluation includes event frequency and fission product release assessments but does not include dose assessments, so that the information is equivalent to a level 2 PRA. The study has shown that the predicted frequency for core melt in a CANDU is fairly low (4.6x10-6 events/year). This is due in large part to the heavy water moderator which acts as a heat sink, prevents UO2 melting and maintains core geometry for many events which could otherwise turn into a core melt. The consequences for most core melts will be limited to the release of a fraction of noble gases and organic iodides. Other isotopes will be condensed or dissolved in the containment atmosphere and will, after some time, end up in the pool of water in the basement, unavailable for release. The frequency and consequences of less likely, more severe core melt sequences are also discussed in the paper and shown to be small contributors to public risk. (author). 9 refs, 2 figs, 1 tab