Abstract
After Fukushima Daiichi accident, the safety analysis of severe accident became one of the safety concerns in Taiwan. The emergency operating procedure (EOP) cannot cope with a multiple system failure situation under a severe accident since it is a "Symptom-basis" procedure. To deal with that, Taiwan Power Company built up a new strategy for Fukushima-like accident called Ultimate Response Guideline (URG). It is a very simple strategy with three main conditions: Loss of regular motor driven injection system, loss of all AC power and tsunami/earthquake warning. If two of three happen, the operating procedure will change from EOP to URG and start the main works by following the strategy. There are three main works in URG: Controlled-depressurization, line up low pressure injection water and prepare containment venting. In this study, MELCOR2.1 was used to calculate the cases of URG and checked the strategy reach the goal that prevents a severe accident or not. 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. An animation model of SNAP can also show the core degradation easily by using the results of MELCOR. There were three steps in this research. First, a model of Chinshan nuclear power plant (NPP) was built and compared the trend of some important results to MAAP5.0 in a case of SBO. Second, the MELCOR model was separated to two cases. One was the case with URG and the other was not. The results were compared to MAAP5.0, TRACE and PCTRAN and it seems the results of MELCOR were consistent with other codes. Finally, some sensitivity studies of depressurization and water injection rate were done by MELCOR2.1/SNAP. By the analysis of MELCOR, the strategy of URG successfully prevented Chinshan NPP from severe accident and kept the cladding temperature below 1088.7K. Also, the containment remained safety in the case using URG. The sensitivity studies showed that controlleddepressurization was better than fully-depressurization because the risk of cladding temperature rising was lower. The low pressure water injection rate should be higher than 150GPM (9.46kg/s) to prevent the temperature rising of cladding.