Evaluation of corium behavior in the lower plenum of the reactor vessel during a severe accident

Corium behavior in the lower plenum of the reactor vessel during a severe accident is very important, because this affects the failure mechanism of the lower spherical reactor vessel and the thermal load to the outer reactor vessel under the IVR-ERVC (in-vessel corium retention through external reactor vessel cooling). A detailed analysis of the in-vessel melt progression during a SBLOCA (small break loss of coolant accident) without the SI (safety injection) of the APR (advanced power reactor) 1400 was conducted to determine the corium mass in the lower plenum upon a reactor vessel failure using the SCDAP/RELAP5 computer code. GEMINI code analyses were conducted to determine the final thermodynamic states of the melt compositions using the SCDAP/RELAP5 results. The heights of the metallic and oxide layers are 1.46 m and 0.46 m, respectively. Finally, the corium behavior in the lower plenum of the reactor vessel under the IVR-ERVC was analyzed using the ASTEC (accident source term evaluation code) computer code. A two layer corium formation of the lower oxide and the overlying metallic layers was analyzed. The corium temperature, the lower head vessel temperature, and the final reactor vessel geometry in the lower plenum under the IVR-ERVC were estimated for the APR1400.