Analysis of high pressure in-vessel melt progression using SCDAP/RELAP5/MOD3 computer code

High-pressure in-vessel melt progressions of a typical PWR (Pressurized Water Reactor) have been analyzed using the SCDAP/RELAP5/MOD3.3 computer code. The total Loss Of Feed Waters (LOFW) to steam generators with/without intentional RCS depressurization using the safety depressurization system and the Station BlackOut (SBO) have been estimated from transient initiation to reactor vessel failure. The CDAP/RELAP5/MOD3.3 results have shown that the pressurizer surge line had failed before reactor vessel failure, which results in a rapid decrease of RCS pressure in the high-pressure sequences of the LOFW and the SBO transients. In all high-pressure transients, approximately 80-90 % of the core material was melted and relocated to the lower plenum of the reactor vessel at the time of reactor vessel failure. The LOFW with intentional RCS depressurization using the safety injection system prevents failure of the pressurizer surge line and results in actuation of the safety injection tanks. At the time of reactor vessel failure, approximately 40-60 % of the fuel rod cladding was oxidized in the LOFW and the SBO transients of the typical PWR