Budi Rohman; Bapeten. Simulation ofdirect containment heating (DCH) phenomenon for B WR 5 Mark II reactor containment vesselhad been performed for the purpose of PSA level 2 study. The accident was assumed to follow asequence with combination of failure on High Pressure Core Spray System and the failure ofmanual depressurization of the reactor coolant system leading to core melt-down. The meltingcore then collapses into the bottom head of the pressure vessel. If the bottom head could notwithstand the increasing thermal and pressure loads released by the melts, it would result in thebreak of the bottom head and subsequent ejection of the core debris to the surface of reactorcavity. During this process, steam containing core debris is then transported to the drywell andcontainment atmosphere as well as to suppression pool where condensation takes place.Various modes of heat transfer, including radiation, conduction, and convection, and masstransfer take place during this process. The release of such a large amount of heat source couldresult in increasing pressure of containment atmosphere. The increase in temperature andpressure loads to the containment could be enhanced by metal-water reaction iftf1.e temperaturereaches the ignition point of this reaction.The simulation assumed release fractions of core debris from reactor vessel to thecavity of 0 %,10 %, 50 %, and 100 %. The temperature and pressure of the containmentatmosphere reach maximum values of 3380 K and 0.726 MPa respectively for the assumedrelease fraction of core debris of 50 %. This pressure is still below the design pressure of thistype of containment, i,e. 0,78 MFa,Kevwords: core melt, BWR 5 Mark-II, containment heating, temperature, pressure.
