Comparison of Severe Accident Results by Using MAAP5 and MAAP4 Codes

Abstract

MAAP5 (Modular Accident Analysis Program Rev. 5.0.0), developed by Fauske & Associates, Inc.’s (FAI) based on the MAAP4 code, is a severe accident analysis code. It is a computer program capable of simulating the response and mitigation actions of light water reactor nuclear power plants (NPPs), including advanced boiling water reactor (ABWR) during severe accident. A specific loss of all core cooling accident sequence, LCLP-PF-R-N, based on Final Safety Analysis Report (FSAR) of Lungmen (ABWR) NPP, was selected as a based case and simulated by the MAAP5 and MAAP4 codes. The MAAP5 and MAAP4 parameter files for Lungmen NPP were established based on Lungmen NPP design data and the MAAP5 and MAAP4 users’ guides. The main severe accident phenomena and the fission product release fractions associated with the LCLP-PF-R-N sequence were simulated. The purpose of this paper is to compare the analysis results of LCLP-PF-R-N sequence calculated by MAAP5 and MAAP4 codes. The two codes give similar results for important phenomena during the accidents, including core uncovery, core support plate failure, debris relocation to the lower plenum, vessel failure, passive flooder opens, containment overpressure protection system (COPS) activation, noble gases and volatile species (like CsI) release to environment, except for the amount of hydrogen production in core. MAAP5 predicts a greater amount of hydrogen production in core than that of MAAP4. This is because MAAP4 predicts earlier reactor pressure vessel (RPV) depressurization than that of MAAP5. That results in earlier steam exhaustion and oxidation reaction termination in core than those of MAAP5. This paper successfully demonstrates the severe accident of Lungmen NPP, and analysis results can provide useful information for the MAAP5 and MAAP4 users.