Development of New MHI LOCA Analysis Code: MCOBRA/RELAP5-GOTHIC

Mitsubishi Heavy Industries, Ltd. (MHI) has developed the safety analysis code system, MCOBRA/RELAP5-GOTHIC, for large break LOCA, small break LOCA and containment integrity analyses of PWR. The code system contains three codes, MCOBRA code, M-RELAP5 code and GOTHIC code. MHI implemented some models and correlations to MCOBRA and M-RELAP5 code to improve prediction of important phenomena of LOCA event. MHI conducted a lot of analyses for separate effect tests and integral effect tests to confirm the applicability of the MHI’s safety analysis code to LOCA key phenomena, like core heat transfer, DNB, entrainment, break flow, counter-current flow limitation (CCFL), core froth level, and so on. The code model uncertainties are quantified to calculate core heat transfer break flow rate, loop seal phenomena; heat transfer in steam generators, and so on. The results show that the code system can predict the key phenomena well and can calculate LOCA event scenario. Consequently, it is confirmed that the new code system is applicable to the LOCA licensing analysis.