Thermodynamic analysis for the three-layered melt pool during the severe accidents in the APR1400

For precise evaluations of the coolability through the External Reactor Vessel Cooling (ERVC) during a severe accident, the melt pool configuration should be accurately defined. The melt pool configurations inside the lower head of the reactor vessel affect the initial thermal load to the vessel and play a key role in determining the integrity of the reactor vessel. In this study, thermodynamic analyses were performed to examine the final melt pool configuration during the severe accidents in the APR1400. As the representative accident scenarios, Large Break Loss of Coolant Accident (LBLOCA), Medium Break Loss of Coolant Accident (MBLOCA), Small Break Loss of Coolant Accident (SBLOCA), Station Black Out (SBO), and Total Loss of Feed Water (TLFW) were selected. The initial melt pool conditions, such as melt mass and melt pool temperature etc., were calculated using the SCDAP/RELAP5/MOD3.3 code. The thermodynamic analyses were performed using the GEMINI code. Combined with the GEMINI code calculations and a peer review of the RASPLAV/MASCA experimental results, the final melt pool configurations were determined for the major accident scenarios of the APR1400. Density evaluation graph was developed for the precise examination of the melt pool layer inversion. The thermodynamic analyses results address the possibility of a melt pool layer inversion in the APR1400 accident sequences. (author)