ASSESSMENT ON DIRECT DEBRIS INTERACTION AT HIGH PRESSURE MELT EJECTION SCENARIO IN LEVEL 2 PSA

摘要

Advanced Boiling Water Reactor (ABWR) has multiple safety features to prevent core damage and mitigate the accident progression. Failures of all injection systems to the reactor (ECCS, alternative injection systems, mobile injection systems) could cause a core melt accident and the Reactor Pressure Vessel (RPV) failure. If large amount of debris particles are deposited on the structures in the containment such as access tunnel, hatches, and Vacuum Breakers (V/Bs), it may result in containment failure or Suppression Pool (S/P) bypass due to the direct heating from the corium. This is defined as Direct Debris Interaction (DDI) in this paper. The phenomenon is introduced in the containment event trees of internal events at power Level 2 Probabilistic Safety Assessment (PSA) for an ABWR and sensitivity analyses and source term analyses are performed in this paper. As a result, the contribution of DDI to total Containment Failure Frequency (CFF) is not significant for the ABWR even if the conservative DDI probability is assumed.