The Phase 2 of the OECD/NEA Project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)" was established in mid-2015. The objectives were similar to Phase 1 of the project but with an extended analysis period of 3 weeks from the occurrence of the earthquake, the main focus on fission product behavior and releases to the environment and the comparison to various data including radiological data and results of backwards calculations of the source term.

Eight organizations of five countries (CRIEPI, IAE, JAEA and NRA, Japan; IRSN France; PSI, Switzerland; SNL, USA; VTT, Finland) submitted results of their calculated severe accident scenarios for Unit 3 at the Fukushima Daiichi site using different severe accident codes (ASTEC, MAAP, MELCOR, SAMPSON, THALES).

The present paper for Unit 3 describes the findings of the comparison of the participants' results against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on the status of the reactor pressure vessel, melt release and fission product release and transport. Unit 3 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized. The results for Units 1 and 2, and an overall summary are presented in separate papers.