DOAN Manh Long
Nuclear Training Center, 140 Nguyen Tuan, Thanh Xuan, Ha Noi
Abstract: The In-vessel Melt Retention through Reactor Vessel External Cooling (so called IVR strategy) has been becoming an attractive accident management strategy for high power reactors such as AP1000, APR1400, VVER1000 … However, applicability of IVR for high power reactor has become more difficult than low power reactor like AP600 or VVER440 because of higher decay head and dependence of severe accident on each kind of scenario and individual reactor. Therefore, severe accident progression analysis for high power reactors is very important aspect for IVR study.
In the paper, the Station Blackout accident accompanied with IVR implementation has been analyzed for VVER1000/V320 reactor by using MELCOR code 1.8.6. Four SBO scenarios have been proposed for the study, among, two SBO scenarios with long-term high pressure showed that the failure of lower head occurred early due to high pressure and high temperature causing creep-rupture, and the external cooling only delayed the failure of lower vessel. Two others with short-term high pressure SBO by taking account the action of reactor vessel depressurization when temperature at core outlet (Tcoreoutlet) exceeds 650oC (923oK) as emergency operation procedures (EOPs) of VVER1000/V320 nuclear power plants, indicated that the failure of lower head lately occurred due to thermal load from hot debris according to creep-rupture mode, the external cooling only brought into play to delay the failure.
Keywords: VVER1000, SBO, IVR strategy, severe accident, MELCOR.