SIMULATION OF FARO L-28 AND L-31 TESTS TO ASSESS MOLTEN JET FRAGMENTATION MODELING IN MAAP

摘要

In the framework of severe accident analysis, Molten Fuel-Coolant Interaction (MFCI) is a major issue of concern for safety analysis regarding in- or ex-vessel melt retention (IVR and EVR) and corium coolability. As melt is relocated in the lower head or in the reactor pit, it may interact as a high-temperature jet with the remaining water. Fragmentation of a corium jet falling into water is of particular interest since it influences accident progression and consequences. MAAP (Modular Accident Analysis Program) is an integral code used to simulate the response of pressurized water reactors to severe accident sequences. The present study aims at assessing the relevance of jet fragmentation modeling in MAAP based on FARO L-28 and L-31 tests simulation. These MFCI experiments, conducted with prototypical melt composition and under realistic accident conditions, provide consistent information on the underlying phenomena. Calculation results are consistent with experimental measurements. Computed pressure and temperature levels as well as debris size are predicted within the correct order of magnitude. Furthermore, a sensitivity analysis has been conducted to evaluate the impact of some input parameters on jet fragmentation mechanism. This study has led to suggest improvements of jet fragmentation modeling in MAAP such as implementing new correlations describing jet fragmentation, improving the evaluation of debris size or of heat transfer between melt and the surrounding environment.