Abstract
A new method was developed to assess the probabilistic effectiveness of severe accident management, including decision-making errors (DME), operation errors, and unavailability of accident management equipments (UOE). This method was applied to evaluated the risk decreasing effect at a typical 4-loop PWR plant with a dry containment vessel, and analyzed the sensitivity of DME and UOE.
As a result, (1) after the preparation of accident management, the containment failure frequency was 1.0×10-8 (1/reactor year), and the risk decreased by 77%. In this case, it was shown that phase II accident management has 89% of risk decreasing effect to the containment failure modes concerned, and has sufficient effectiveness. (2) The results of the sensitivity study on DME revealed that the increase in risk due to a high-dependence cognition condition was about 4%, and the increase in risk due to loss of the double-check function in an organization was about 20%. (3) The results of the sensitivity study on UOE revealed that low pressure injections and recirculation systems were the most important in preventing containment failure. When the average time taken to repair the accident management equipment was tripled, the risk increased by about 13%. (4) This assessment method can be shown the positive/negative effect of accident management strategy clearly by using a logic operation formula, and is suitable when a third-party review is required.
