Three Dimensional Modeling And Application About The Core For SBLOCA In PWR

As a typical design basic accident of the PWR,the consequences of SBLOCA includes the decrease of pressure caused by the reduction of coolant,the deterioration of core cooling,the leakage of coolant into the containment and the potential radioactive leakage to the outside of the factory.Generally,the RELAP5 computer code is used to analyze the SBLOCA,however,this program only provide the point reactor kinetics to model the behavior of core,the local void effect can't be well feed back to the cross-section of adjacent fuel assembly after accident,so the peak cladding temperature obtained can't represent the real situation very well.In this paper,the RELAP5-3D computer code is used to analyze the SBLOCA.The nodal reactor kinetics is used to model the behavior of core,in which the simulation of the void effect is realized by a second order polynomial,and the local void is fed to the cross-section of adjacent fuel assembly in time.When the variation range of void fraction is huge,and the void fraction exceeds the fitting range of the second order polynomial,this polynomial is no longer applicable.Therefore,the void effect is fitted piecewise and the void effect is simulated by different second order polynomials in different void fraction,thus realizing the modeling of void effect in the whole void fraction range.The sensitivity analysis of different segmentation schemes is done and the appropriate segmentation plan is screened out.After modeling the SBLOCA of PWR based on nodal reactor kinetics by piecewise fitting,the model is used to analyze and calculate the accident consisted of shut-down failure accident and SBLOCA.In the case of the SBLOCA overlay the failure of shut-down rod and the safety injection system,the peak cladding temperature will exceed the suitable range of the RELAP5-3D,so the subsequent calculation is calculated by MELCOR which is used for the analyzing of serious accidents in reactor,the data produced by RELAP5-3D are collected and processed,and then written into the MELCOR input file,finally the results are compared with the results which are obtained by MELCOR code separately.Then the two methods of serious accident analysis are used to analyze the entry condition of serious accident management guidelines and verifying the effectiveness of serious accident management.The results show that the peak cladding temperature obtained by the model which is based on nodal reactor kinetics is obviously lower than the result which is calculated by the model based on point reactor kinetics.When the nodal reactor kinetics is used,the SBLOCA overlying the failure of shut-down and safety injection system will exceed the applied range of RELAP5-3D.The timing accident sequence calculated by RELAP5-3D/MELCOR is later seriously than the results of the MELCOR code alone.After management measures are taken,the consequences of accident are significantly alleviated.