Probability Analysis for External Reactor Vessel Cooling Effectiveness under Severe Accident

There are many uncertainties in severe accident phenomena which affect the effectiveness of External Reactor Vessel Cooling （ERVC） measurement. The uncertainties of In-Vessel Retention （IVR） issue are analyzed based on Risk-Oriented Accident Analysis method, and the probability distribution of ERVC effectiveness is obtained. The calculation results using VTA sampling program show that if the melt pool in lower head achieves final bounding state, the success probability of core debris IVR is over 99% for 8 kinds of severe accident sequences, supposing a postulated severe accident occurs in Chashma-2 Nuclear power plant and ERVC is performed successfully.