Severe Accidents in A Nuclear Power Plant Severe Accident Analysis of Steam Generator Tube Rupture Postulated for The OPR1000 Using MELCOR

Abstract

Abstract – Since the Fukushima accident occurred in 2011, many researches related to severe accident analysis have been performed experimentally and numerically. As well, many experimental and analytical activities have been performed in Korea to investigate the thermal-hydraulic response of the Korean Optimized Power Reactor (OPR1000) against the postulated severe accidents such as Small Break Loss of Coolant Accident (SBLOCA), Station Black Out (SBO), Total Loss of Feed Water (TLOFW), and Steam Generator Tube Rupture (SGTR), to mention a few. While the first three accidents are expected to result in the generation and transportation of the radioactive nuclides within the containment building as a consequence of the core damage and subsequent reactor pressure vessel (RPV) failure, the latter accident scenario may be progressed with possible direct release of the radioactive nuclides to the environment by bypassing the containment building. Thus it is of significance to investigate the SGTR accident with a sophisticated severe accident code. In this study, a base case of the SGTR accident was analyzed using the MELCOR 1.8.6 code. Onset of cladding oxidation, fuel cladding melting, molten core relocation, RPV failure were predicted without application of any in-vessel severe accident management strategies such as steam generator feed water injection (Mitigation 1), reactor coolant system (RCS) depressurization (Mitigation 2), RCS coolant injection (Mitigation 3). With the aforementioned unrealistic assumption (i.e., no mitigation strategy is applied), current MELCOR calculation shows that primary coolant may be released into the secondary steam generator and contained radioactive nuclides can be released into the environment upon opening of Main Steam Safety Valve (MSSV) installed in the steam generator. While most of the aerosols are retained in the RCS and containment building, most of Xe gas can be released into the environment unless any mitigation strategy is applied. For the future work, it is necessary to investigate effect of application of in-vessel strategies on the effectiveness and adverse effects on the behavior of nuclear power plant.