SBLOCA Analysis Using Modified MAAP4 Code through Semi-empirical CHF Correlation Application

The molten core configuration and thermal load analyses for the determined accident sequences and break areas of a cold leg in APR1400 PSA were performed using the MAAP4 code. As the break size increased, the starting time at which the molten core was relocated to the lower head and the reactor vessel failure time decreased while the debris crust thickness increased for the accident sequences 17, 22, and 23 in the SBLOCA event tree. The angular heat flux generally increased as the break size was increased. However, if the decay heat and ratio of total upward-facing heat transfer to decay heat from the debris are simultaneously greater than those for the other cases, the thermal load of the metal layer could be greater regardless of the break sizes. Furthermore, the difference between the average temperature of the metal layer and the temperature of the internal reactor vessel is also one of the uncertainties for a sideward heat flux from metal layer. Therefore, the sideward-facing heat flux from the metal layer could depend on the ratio of total upward-facing heat transfer to the decay heat, as well as the temperature difference between the average temperatures of the metal layer and inner vessel wall temperature