Overview and outcomes of the OECD/NEA benchmark study of the accident at the Fukushima Daiichi NPS (BSAF), phase 2 – Results of severe accident analyses for unit 2

This is the second paper in a series of 3 in which results of severe accident analyses for Unit 2 of Fukushima Daiichi are presented, gained in phase 2 of the OECD/NEA project “Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)”. Nine organizations of six countries (CNL Canada; CRIEPI, IAE, JAEA and NRA Japan; IRSN France; KAERI Korea; NRC/DOE/SNL U.S. and VTT Finland) submitted results of their calculated severe accident scenarios for Unit 2 of Fukushima Daiichi using different severe accident codes (ASTEC, MAAP, MELCOR, SAMPSON, THALES-KICHE). The present paper describes the findings of the comparison of the participants’ results for Unit 2 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. Unit 2 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized.