Development of an in-vessel severe accident analysis code MID AC

The Module In-vessel Degradation severe accident Analysis Code (M1DAC) is developed by Xi'an Jiaotong University to meet the domestic demand of software autonomous scheduling. The whole processes of in-vessel severe accident can be analyzed by the code with credible results. The code is composed of five main modules: the core early behavior module, the core degradation module, the debris bed module, the RPV melt behavior module and the thermal hydraulic module. These modules are combined with each other and can simulate almost all the severe accident phenomena in the vesseL The core early behavior module contains models for phenomena as the core heat up after the core exposure, the cladding oxidation reaction, the cladding ballooning, the fuel-cladding interaction and other related phenomena. Core degradation module can calculate the core melt and relocation process in the core. A new candling model is developed to determine the behavior of melting material outside the fuel rods, inc hiding the melt flow and freeze. The debris bed module can be used to analyze the process of the formation and cooling of the debris both in the core and lower plenum. RPV melt behavior module treats the heat transfer of the corium pool to the lower head and determines the property of the in-vessel retention of the corium. The thermal hydraulic module is well developed to interact with all the other modules and combine them to a uniform MIDAC code. A preliminary validation of the code with TMI-2 accident has already been done and the simulation results show good agreement with the real plant data.