Abstract
After Fukushima Daiichi accident, the safety analysis of severe accident became one of the safety concerns in Taiwan. In recent days, both MELCOR and MAAP were the main used codes for nuclear reactor severe accident in Taiwan. These two codes can both calculate the phenomenon happen in the late reactor severe accident, like core meltdown, hydrogen generation and fuel debris penetrations, etc. The main MELCOR used in Taiwan now was an earlier version and in the ASCII code mode (Coding with text file) which is not always easily to be understood by a beginner of the code. 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 combine some other applications like AptPlot for output drawing and DAKOTA for uncertainty analysis. There were three main steps in this research. First one is to establish the MELCOR2.1/SNAP model of Chinshan (BWR/4) nuclear power plant (NPP). This model included 22 control volumes of lower plenum, core, separator, dryer, drywell, wetwell, reactor building and environment, etc. The components of Fuel Dispersal, Cavities and Radionuclide were also built in. Second, a steady-state test was calculated by MELCOR to check the model. After the steady state calculations, the model of MELCOR2.1/SNAP will next used for a transient situation. Finally, the Chinshan NPP model was set to a situation of SBO to simplify the control system. After the model was built, the SBO calculation of this model was done and compared to the results of MAAP5.0 and MELCOR1.8.5. The results of this MELCOR2.1/SNAP model fit the MAAP results well at the main outputs we concerns in the severe accident. In addition, a Chinshan NPP spent fuel pool SBO model was also built by MELCOR2.1/SNAP and the output of cladding temperatures, water level also fit the results from MAAP calculations. The comparisons of MELCOR spent fuel pool and some other thermalhydraulic codes like TRACE and CFD were also done in this research.