Sensitivity analysis of core slumping and alternative water injection in Fukushima Nuclear Power Plant Unit 3 accident

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

This study aims at identifying the modeling uncertainties and addressing the sensitivity parameters in Fukushima Daiichi Nuclear Power Station Accident (1F) Unit 3 with MELCOR 2.2 code. Sensitivity studies have been performed on the safety relief valve (SRV) functioning and alternative water injection (AWI) in Unit 3. With the current modelling assumptions in MELCOR, the best-reproduced RPV pressure history of 1F Unit 3 suggested that 6 SRVs should have been open during ADS operation and they remained open when the major core slumping took place at ca. 12:00 on March 13th (ca. 45:20 h after SCRAM). 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. The lower head failure timing is not necessarily positively correlated with the amount of water and overall dryout condition of the debris in the lower plenum.