| Summary: | 碩士 === 國立清華大學 === 核子工程與科學研究所 === 102 === In this study, the MELCOR input deck of Kuosheng Nuclear Power Plant is developed based the the plant data as specified in the MAAP5 input deck and calculation sheets of the plant, which are provided by Institute of Nuclear Energy Research. The plant is deployed with two Boiling Water Reactors (BWR VI) designed by General Electric and enclosed in Mark III containment. A high pressure station blackout (SBO) sequence of the plant is simulated using MELCOR and MAAP5. The results of the simulations are compared to assess the differences of these two codes. The comparisions are concentrated on the timing of major events, thermal hydraulic response of reactor coolant system and containment, debris relocations from one region to another, hydrogen production, in-vessel and ex- vessel release and environmental releases of radionuclides.
The differences of the simulation results are very significant due to the differences in the severe accident phenomenological models adopted by these two codes. The amount of hydrogen generation within the reactor pressure vessel as predicted by MELCOR is 921 kg and that as predicted by MAAP5 code is 76 kg. Nevertheless, the amount of hydrogen production during molten core concrete interaction as predicted by MELCOR and MAAP5 code is 1,382 kg and 2,016 kg, respectively. The extent of in-vessel and ex-vessel releases of radionuclides as predicted by these two codes is also very different. In environment release, there are several fission products that MELCOR is bigger than MAAP5, including Cs, I, Te, Ru, Mo, Nb, U, Sn; And other fission products such as Xe, Ba, Zr, La, Ce, Cd, MAAP5 is larger than MELCOR.
In the study, sensitivity study is performed to assess the impact of depressurization on the failure mode of reactor vessel bottom head. In a high pressure SBO sequence, the vessel failure is caused by the stress and strain produced in a high pressure environment. In a low pressure SBO sequence, the failure of vessel is caused by the melting of instrumentation tubes.
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