The NEA benchmark study of the accident at the Fukushima Daiichi NPP

In November 2012, the NEA, under the aegis of the Committee on the Safety of Nuclear Installations (CSNI), initiated a joint research project called the Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF). Objectives of this project include supporting Fukushima Daiichi decommissioning by analysing accident progression and the current status of the reactors, such as fuel debris distribution in the reactor pressure vessels and primary containment vessels in preparation for fuel debris removal. A second objective of the project is to improve SA (severe analysis) codes through comparisons with data from the Fukushima reactors. So as to enhance communication between analysts and those involved in decommissioning activities, participants in the project have been discussing the remaining uncertainties in relation to understanding the accident and the data needs from the viewpoint of the analysts. Since the accident sequences at the Fukushima Daiichi site include a wide range of phenomena, a phased approach is being applied in this benchmark exercise while awaiting more detailed information on debris examination and other factors. This article provides an overview of the project (scope, input data and boundary conditions, participants (from eight countries), analytical approach - common case and best estimate case) as well as an outline of the project's next phase (BASF phase 2) that begins in June 2015