Research On Heat Transfer Of Passive Containment Cooling System Based On MELCOR

The containment is the last barrier for nuclear power plants to prevent the leakage of radioactive materials.Once the containment is damaged,it will cause a large amount of radioactive materials to leak out and bring huge harm to the environment.The function of the passive containment cooling system(PCS)is to reduce the temperature and pressure of the containment after a break accident to ensure the integrity of the containment.The integrated serious accident analysis code MELCOR is a second-generation risk assessment code developed by the Sandia National Laboratory(SNL)commissioned by the US Nuclear Energy Regulatory Commission(NRC).It is one of the important tools for the current nuclear safety review and independent verification calculation of serious accidents in my country.In this paper,MELCOR2.2 code has been used to establish PCS model to calculate the physical state of containment under the Main Steam Line Break(MSLB)accident,for steel containment.The short-term and long-term effects of various sensitive parameters on the thermal parameters of containment are analyzed,and the superposition of two adverse factors,PCS flow reduction and liquid film coverage reduction,were further discussed to the integrity of containment.The results show that MELCOR code can quickly and accurately simulate the thermal hydraulic phenomena of PCS and containment system;the peak pressure of containment is sensitive to the initial temperature of heat sink,heat transfer area of heat sink,water film coverage,PCS flow rate,break position and PCS delay time.The water film coverage and PCS flow rate have great influence on the containment depressurization rate in the later stage of the accident.Under MSLB accident or DECLG accident,the severe conditions of spray flow reduction(as low as 33%)caused by blockage of spray water outlet pipe and water film coverage reduction(as low as 35%)caused by superposition of water distributor failure will not lead to short-term overpressure risk of containment.