Study On Assessment Of Severe Accident Models For PWR Based On Comparison And Parameters' Sensitivity Analysis

SCDAP/RELAP5 and MAAP4 codes are the widely used severe accident analysis computer codes. SCDAP/RELAP5 is a mechanical analysis code, and MAAP4 is a fully integrated code. SCDAP/RELAP5 code contains more mechanistic models than MAAP4 code. In this thesis, SCDAP/RELAP5/MOD3.1 and MAAP4.0.3 computer codes are used to investigate the severe accident induced by large break loss of coolant accident and station blackout accident, postulated at DYBAY Nuclear Power Plant, and the applicability and discrepancies are identified for models of both codes.For severe accident induced by large break loss of coolant accident, the calculation results of two codes are similar in terms of water level in pressurizer and pressure in pressurizer. When the RPV is failed, the results of elevation of debris bed in low head of two codes are also very similar. There are main discrepancies in various timings of phenomena, which include timing of start of core uncovery and timing of slumping to low head. Plots show that MAAP4 code calculated results have a substantial delay in the complete voiding of the core. Furthermore in this thesis, it is found that the weakness of rupture model which is used in two codes is that the model may not effectively calculate the damage fraction of low head structure in low pressure core melting accident. Damage fraction of low head calculated by SCDAP/RELAP5 MOD3.1 code for large break loss of coolant accident validates the conclusion. Because of models of instrument penetration tubes in low head, MAAP4 code can avoid this question.