EVALUATION OF A SEVERE ACCIDENT MANAGEMENT STRATEGY FOR BOILING WATER-REACTORS - DRYWELL FLOODING

Flooding of the drywell has been suggested as a strategy to prevent re actor vessel and containment failure in boiling water reactors. To eva luate the candidate strategy, this study considers accident management as a decision problem (''drywell flooding'' versus ''do nothing'') an d develops a decision-oriented framework, namely, the influence diagra m approach. This analysis chooses the long-term station blackout seque nce for a Mark I nuclear power plant (Peach Bottom), and an influence diagram with a single decision node is constructed. The node probabili ties in the influence diagram are obtained from U.S. Nuclear Regulator y Commission reports or estimated by probabilistic risk assessment met hodology. In assessing potential benefits compared with adverse effect s, this analysis uses two consequence measures, i.e., early and late f atalities, as decision criteria. The analysis concludes that even thou gh potential adverse effects exist, such as ex-vessel steam explosions and containment isolation failure, the drywell flooding strategy is p referred to ''do nothing'' when evaluated in terms of these consequenc e measures.