Severe accident analysis of TMI-1 seal LOCA scenario using MELCOR 1.8.2

The pump seal LOCA scenario for Three Mile Island Unit 1 Nuclear Power Plant is analyzed using the NORC's MELCOR 1.8.2 Code. This scenario was a major contributor to containment failure for the LOCA group as a result of the IPE Level 2 analysis which was done using EPRI's MAAP3B code. The main purpose of this paper is to see if conclusions would have been different with regard to the impact of this scenario on containment performance had MELCOR been used instead of MAAP3B. The major areas addressed were in-vessel and ex-vessel phenomena. For the in-vessel part, three major stages of a severe accident were investigated, namely (1) thermal-hydraulic behavior before core uncovers; (2) core heatup, relocation, and hydrogen generation; and (3) lower head failure. For the ex-vessel part, the following were addressed: (1) Corium-concrete interaction; (2) containment failure; and (3) source term release. It is shown that the same conclusions are made with regard to containment performance and its impact on Level 2 results