Research On Temperature Field Of The Reactor Pressure Vessel Lower Head For IVR Calculation In Core-molten Severe Accident

In-Vessel Retention (IVR) is an important and crucial method for preventing andmitigating the consequences of severe accident. Temperture Field of Reactor PressureVessel in Steady state and unsteady state conditions is obtain with External Reactor VesselCooling(ERVC),and these data can calculated thermal stress,which provide the parameters forvessel wall structure creep failure. Details are as follows:(1) According to the theory of core melt retention, in a serious core melt accident,considering the hierarchical structure of core melt, the metal melt layer collector effects andso on, and take use of the core melt cooling computation module to determine the critical heatflux of wall and the temperature distribution of the saturated cooling water of outer wall.(2) On the basis of the core melt cooling model, the heat flux distribution the core meltpass to the wall is calculated in the lower head in different angles. Compared with thecalculation results of the United States and other countries, The result indicates a perfectportability which confirms the rationality of the model in this article and provides accurateboundary conditions for the research of core melt retention strategy.(3) Reactor pressure vessel wall temperature node equations is established in the help ofthe numerical discrete mechanism after considering the reactor pressure vessel wall physicalparameters vary with temperature, the cooling of the outer wall water and so on, and then useMATLAB to solve the corresponding steady-state temperature distribution according toGauss-Seidel iteration method. From the thermal load point of view, it is safety to implementthe external reactor cavity cooling core melt retention strategy. It is found that the wall melt isthe most serious in the junction of the hierarchical structure.(4) When calculating the transient temperature distribution, the explicit differencemethod is used to deduce the control equation of the reactor pressure vessel wall temperaturenode on the basis of numerical discretization, and solve the temperature distribution of thedifferent time which provides parameters for further development of the pressure vesselstructure integrity failure analysis. According to the transient temperature distribution of thereactor pressure vessel, the influence of the time step and space step on calculation results, how the wall temperature distribution changes with the angle and how the node temperaturechanges over time is considered separately. Next the research of the reactor pressure vessellower head structure failure criteria is conducted in serious accidents, including the creepcaused by machinery and thermal load, stress analysis, structural integrity analysis.