A comparative simulation of severe accident progressions by CINEMA and MAAP5

Abstract

A newly developed code CINEMA is exercised for simulations of severe accident progressions in OPR1000 nuclear power plant. A Large Break Loss of Coolant (LBLOCA) and Station Black Out (SBO) initiated severe accidents are selected to cover a wide range of accident progression in terms of the system pressure, amount of core damage, and fission product release. The effects of mitigation actions by the operator are also considered. In parallel, independent simulations by the MAAP5 are carried out and the results are compared with those of CINEMA. Qualitative and quantitative comparisons are made for the sequence of events, the occurrence of RCS boundary failure, the amount of corium in the lower head, the amount of hydrogen generation, total release of CsI aerosols into the containment, and effectiveness of operator action for the stable cooling of molten corium in the reactor and containment. The overall trends were in the same direction but quantitative differences were observed. Major differences include the speed of heat up of the core, relocation of molten fuels into the lower head, the amount of hydrogen generation, the amount of pressurization due to the core slumping into the lower head filled with water, scrubbing of fission product aerosols by the containment spray, and the amount of CsI release into the containment. These comparative analyses helped to verify and validate the physical models and their implementation employed in CINEMA.