抄録
Much interest in severe accident research has been attracted since Fukushima accident, which indicates that severe accident could possibly happen although the probability is extremely low. Although many researches have been conducted in severe accident progression simulation and emergency condition analysis, it is still necessary to do some research on emergency conditions of severe accident that have not been sufficiently analyzed. In this paper, a 50mm small break loss of coolant accident (SBLOCA) in cold leg along with station blackout (SBO) initiated severe accident was simulated using MELCOR code. The model which was built for this study consists of 46 control volumes (27 in primary loop, 17 in secondary loop, 1 in containment and 1 in environment) and 52 flow paths. Before the calculation, steady state was achieved in order to check the model. Main parameters of the model were compared with that of nuclear power plant (NPP). Relative error was acceptable, so the model could be used to simulate the accident. Based on the accident scenario, high pressure safety injection (HPSI) and low pressure safety injection (LPSI) were assumed to be lost because of loss of on-site and off-site power, as well as main feed water and auxiliary feed water of the steam generators. The accumulator is the only emergency cooling coolant source, since it is passive. The calculation ended with failure of lower head, and the response of the containment was not studied. Emergency condition progression of the accident was obtained, including start of uncover of the active core, start of zirconium-water reaction, failure of fuel clad and failure of the lower head. Thermalhydraulics response of reactor was analyzed. In future work, research on emergency condition of other severe accidents could be conducted.
