Overview and Outcomes of the OECD/NEA Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station

The Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) project, run by the Organisation for Economic Co-operation and Development/Nuclear Energy Agency, was established in November 2012. The primary objectives of this benchmark study are to estimate accident progression and status inside the nuclear reactors, including the distribution of fuel debris, and consequently, to contribute to the decommissioning activity at the Fukushima Daiichi nuclear power plant. Altogether, 17 organizations from eight countries calculated the thermohydraulic behavior inside the three reactors for the time span of about 6 days from the occurrence of the earthquake with their severe accident integral codes. Since many boundary conditions are unknown for the accident, those necessary for the calculation were discussed and determined by the participants.

The results submitted were compared on coolant level change, hydrogen generation, initiation and progression of melt in fuel bundle and control blade, failure of reactor pressure vessel, distribution and composition of molten and solidified materials, and progression of the molten core–concrete interaction. Finally, the current estimates of the accident progression and status inside the reactors were summarized together with the still remaining uncertainties and data needs as the output from the project.