Evaluation of an IVR-ERVC strategy for a high power reactor using MELCOR 2.1

Abstract

The IVR-ERVC (In-Vessel Retention of molten corium through External Reactor Vessel Cooling) is an effective severe accident management strategy for reducing the possibility of a reactor containment failure by terminating the severe accident progress inside a reactor. However, the technical applicability and feasibility of the IVR-ERVC design for an advanced high-power reactor should still be validated considering the uncertainties of physical models, the initial conditions and assessment methodologies. In this paper, the severe accident progress of the APR1400 for a large break loss-of-coolant accident is analyzed using MELCOR 2.1 when the reactor cavity is fully flooded. The chronology of events, the thermal hydraulic behaviors and the core degradation behaviors are analyzed. As a result of the MELCOR calculation, a relatively large portion of particulate debris is relocated to the bottom of the lower head at the end of the debris-quench mode, preventing effective heat transfer to the ex-vessel wall. Because the lower head wall cannot be ablated by melting in the MELCOR, the in-vessel wall temperature is increased as compared to the melting point of the lower head. The heat flux is maximized at approximately 3.5e4s and it is compared to the results from the lumped parameter method.