Sensitivity and Uncertainty Analysis of Molten Corium-Concrete Interaction (MCCI) for ALWR During Severe Accident

Abstract

Molten corium-concrete interaction is an important phenomenon in the late phase of severe accident, threatening the integrity of containment and might causing potential large release of radioactivity. A sensitivity and uncertainty analysis of MCCI under severe accident of a 1000 MW advanced light water reactor (ALWR) was performed with ASTEC (MEDICIS) [1], a lumped parametric integral severe accident code developed by IRSN. Several representative phenomena were screened out referenced by EURSAFE severe accident Phenomena Identification and Ranking Table (PIRT) [2], including debris bed formation, layer configuration, heat sources, and convective heat transfer correlation. Related input parameters, sensitivity coefficients, and modeling options in ASTEC code were selected, such as convective correlations, layer stratifications, initial layer compositions, and the potential ranges of these parameters were identified. A simple sampling method was used to analyze the independent effect of each parameter/model. Key parameters were chosen to evaluate the impact of sensitivity parameters to the MCCI process. A large break loss of coolant accident scenario, where in-vessel melt retention is invalid is simulated as an initial event. The results emphasize the importance of layer configuration and fission product partition. However, it should be emphasized that analysis results may be quite uncertain due to the limitation of the physical models and the adequacy or validity of the selected range of input variables.