Abstract
After Fukushima event, researchers did lots of safety analysis and procedure improvement of the nuclear power plants (NPPs) in Taiwan. The procedures such as emergency operating procedures (EOPs) cannot cope with the multiple failures like ELAP accident. Some methods for such accidents were developed, such as Ultimate Response Guideline (URG) and FLEX. In this study, the phenomena of ELAP accident in Kuosheng NPP were calculated by MELCOR2.1/SNAP. By this calculations, the phenomena in ELAP accident can be shown and help the development of emergency procedures for multiple failures accidents. In this research, the latest version MELCOR2.1 was used and combined with Symbolic Nuclear Analysis Package (SNAP). In this combination, MELCOR was used with a graphical user interface (GUI) that users can easily modify any detail of the model. It can also show the detail results and phenomena through an animation model. There were four main steps in this research. First, the MELCOR model of Kuosheng NPP was built. The steady-state results of this model were compared to TRACE and the Kuosheng NPP data. Second, a case of ELAP was calculated by MELCOR2.1/SNAP. In this case, RCIC was set to be failed for a more conservative result. The results before core damage were compared to the thermal-hydraulic code, TRACE. TRACE is a code developed by U.S.NRC and lots of benchmark was already done for thermal-hydraulic calculations before. The thermal-hydraulic calculations for the severe accident codes such as MELCOR were always been questioned. So in this research, the thermal-hydraulic calculations before core damage were compared to TRACE for checking the MELCOR model of Kuosheng was good for use. Third, the MELCOR results after core damage were discussed in detail, such as hydrogen explosion, containment overpressure, debris relocation, radionuclides movement, etc. Finally, some sensitivity studies such as containment spray were done by MELCOR. In this study, the MELCOR2.1 results were consist with the TRACE results at the important thermal-hydraulic parameters such as water level, Reactor Pressure Vessel (RPV) pressure, cladding temperature. The MELCOR calculations showed that in the ELAP case of Kuosheng NPP, the water level dropped to top of active fuel (TAF) at 28.5 min. The cladding temperature rose to 1088K at 57.5 min. The fuel cladding started candling at 72.8 min. Several hydrogen burns happened inside the containment starting at 75 min. This study showed the important phenomena during an ELAP accident of Kuosheng NPP. The results can help NPP safety analysis and emergency procedure improvement in a beyond design basis accident