Thermal Safety Analysis Of Pressure Vessel In The Core Melt Accident

As we all know nuclear power is one of the most potential clean energy in the world. Itshows unique advantage compared with thermal power and other clean power. Even though, ithas one important drawback which is that it’s safety has always being concerned in nuclearpower field. Actually since the first nuclear power plant had been built the nuclear technologyis being mature and it’s safety is obvious. But the human beings’ confidence to nuclear powershacked once more after the Fukushima nuclear accident happened. So, the problem of thesafety of nuclear reactor is the key issue which is the restrict of the development of nuclearpower.The nuclear reactor had been designed as three barriers to prevent the diffusion of theradioactive material, and from inside to outside they are: fuel cladding, primary loopboundary and containment. The pressure vessel is the equipment in which, the reactor core isplaced, meanwhile it bears a high operating pressure, and it plays a crucible role in the secondbarrier. It will be greatly damaged when the core melt accident happened.In this paper, the pressure vessel fusion ablation course is studied, which is caused bymelting core materials at the core melt accident when the PWR nuclear reactor lose watercoolant. The stratified heat transfer model of melting core materials in the lower head hasbeen established, and the two dimension thermal conductivity differential equation also hasbeen established. The temperature field in the lower head of pressure vessel wall wascalculated. Temperature evolvement of lower head wall in a certain time after accident wasgot, and the course of pressure vessel wall fusion ablation and the temperature increasing ofthe pressure vessel wall by using of Fortran programming with numerical calculation. Theresults are helpful to investigate of accident development and provide useful evidence topredict and monitor the dangerous hot spots. It also proposes proper advise to prevention andremission countermeasure at core melt accident.One of the important imposing in this paper is that we use moving boundary model todeal with the boundary problem creativity under the calculation of fusion ablation of pressure vessel at unsteady state in the core melt accident. The conclusion is that region of the fastestdecrease thick of pressure vessel wall is the part of which contact with oxide melting pool.The reason is that the heat flux from oxide melting pool to pressure vessel changed with theangel, and the larger of the heat flux, the fast increased of the wall temperature, so more of themelting rods. The thinnest of the pressure vessel wall is only2centmeters after the accidenthappened15000s, it is at the point of, near the interface between metallic meltinglayer and oxide melting pool. That is this area is the dangerous area. The pressure vessel wallis probably failure if we do nothing cooling measure to the core. These conclusions areprovide well evidence to investigate the development course of the core melt accident and topredict and monitor the dangerous hot point. Meanwhile it also provide reference for the coremelt accident prevention and remission measures.