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

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 3.5e4 s and it is compared to the results from the lumped parameter method.