Efficacy assessment of independent severe accident mitigation measures in OPR1000 using MELCOR code |
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Authors: | Yongjae Lee Wonjun Choi |
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Affiliation: | 1. Department of Nuclear Engineering, Hanyang University, Seoul 04763, Republic of Korea;2. Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea |
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Abstract: | In-vessel and ex-vessel mitigation strategies have been revisited to improve the severe accident management (SAM) for operating nuclear power plants. Because independent mitigation measures tend to produce positive and adverse effects simultaneously, it is necessary to investigate the efficacy of individual measures by means of proper quantification. Thus, in the present study we investigated the overall efficacy of existing SA mitigation strategies prepared for the Optimized Power Reactor 1000 MWe (OPR1000) by means of MELCOR 1.8.6 code. The numerical evaluation showed that the Mitigation-01, feeding water into the steam generators, is the most effective among the other mitigations. In addition, Mitigation-02, reactor coolant system depressurization, could not mitigate the SA sufficiently when applied individually. Among the four ex-vessel mitigation strategies, execution of containment spray was effective in removing most of the aerosol fission product but also intensified hydrogen combustion by increasing the partial hydrogen pressure owing to steam condensation. Mitigation-07, operation of passive autocatalytic recombiners (PARs), could reduce the hydrogen concentration, though the catalytic reaction was predicted to increase the containment pressure. In conclusion, this study suggests that mitigation measures should be carefully selected, and that counteracting measures should be prepared to minimize potential adverse effects. |
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Keywords: | Severe accident OPR1000 accident management MELCOR effectiveness and adverse effects hydrogen risk Shapiro diagram |
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