Insights on in-vessel core degradation behavior from sensitivity analysis of Fukushima Daiichi Nuclear Power Plant Unit 3 by MELCOR

Li, X. ; 佐藤 一憲 ; 山路 哲史*

Li, X.; Sato, Ikken; Yamaji, Akifumi*

With the current modeling assumptions in MELCOR, the best estimate conditions for RPV pressure history of Unit 3 suggested that 6 Safety Relief Valves (SRVs) could have remained open when the major core slumping is assumed to occur at ca. 45:20 h (ca. 12:00, March 13) with 50 to 80 tons of water inventory in the lower plenum. The current analysis also suggested that the efficiency of the AWI to the reactor core could have been only 15 percent as of reported by TEPCO estimated amount of water discharged by fire engines with the current modeling conditions if debris dryout was assumed to have occurred at around ca. 54:00 h (20:40 h, March 13th). As for lower head failure, there is still large uncertainty in predicting lower head failure time with Larson-Miller creep rupture model in the current MELCOR modeling.