Comparative Study Of Key Models For MELCOR And MAAP Containment Phenomena In Severe Accidents

At present,the code simulation is one of the important methods of the research of severe accident.As a serious accident,MELCOR code and MAAP code can the overall analysis of reactor system.But the code which use different types of model have different simulation results when the plant have a serious accident.Existing research mainly focused on the comparison on the process and the core of the accident and lack of comparison of containment phenomena and models.Therefore,it is necessary to compare the difference of containment results between the two codes in the case of a serious accident at a nuclear power plant,and to further compare and analyze important containment models.In this paper,MELCOR and MAAP are used to model the AP1000 nuclear power plant which is the third generation of passive pressurized water reactor.The severe accident caused by a small break in the heat pipe section is selected for simulation.The containment simulation results of the two codes are compared to analyze the reasons for the difference in simulation results.On this basis,this article selects the appropriate benchmark problem to further compare three important containment models which include non-condensable gas wall condensation model,aerosol deposition and hydrogen combustion model.This paper also combine the two codes to calculate wall total heat transfer coefficient,total deposition rate as well as the flame propagation speed and so on.The comparison results show that the failure time of lower head calculated by MAAP code is earlier than that calculated by MELCOR code.The pressure values calculated by MELCOR code are higher than those calculated by MAAP code.The Cs I aerosol deposition quality and hydrogen mole fraction simulated by MELCOR code are lower than those simulated by MAAP code.The containment models used by MELCOR and MAAP successfully simulate wall condensation,aerosol deposition,and hydrogen combustion,but there are some differences in the calculated values due to the different models used.Both codes have their own advantages.The model used by the MAAP code is more suitable for wall condensation with noncondensable gases,while the model used by the MELCOR code is more suitable for aerosol deposition and hydrogen combustion.In addition,Herranz’s wall condensation model and the correlation of flame speed used by the CONTAIN code are more applicable to this situation than the models used by MELCOR and MAAP.