Appearance of Unit 1 and 2 reactor buildings at Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings (June 2022). Photo: Japan Nuclear Regulation Authority

The FACE project is a constructive and integrative extension of already completed projects (BSAF, PreADES and ARC-F) related to the Fukushima-Daiichi accident analysis and the preparation of the fuel debris retrieval operations. Based on the Japanese needs and expected needs of project partners, the FACE project is implemented with the following general objectives:

• refining the interpretation of the Fukishima-Daiichi accident scenarios including the effects of accident management measures in consistency with insights obtained from plant investigations;
• clarifying current capabilities and directions to further improvement of modelling for severe accident progression;
• interpreting the results of analysis for uranium-bearing particles collected on-site and determining suitable hot laboratory analysis techniques and procedures for future application to fuel debris analyses;
• maintaining communication channels between Japanese organisations and international partners to share data, information and expertise towards the resolution of Fukushima-Daiichi plant decommissioning and dismantling (D&D) related issues and improvement of reactor safety in various countries.

Three main scopes of work are proposed in light of the general objectives. The first scope is in-depth discussions and analyses for accident progression in the damaged units and related fission product (FP) behaviour and hydrogen (H₂) combustion. This scope considers technical issues identified in recent Fukushima-Daiichi plant investigations, which are far from previous knowledge, and the quantification of uncertainties in severe accident modelling (melt progression, Molten Corium Concrete Interaction (MCCI), FP and H₂ issues) taking into account uncertainties in boundary conditions such as the rate of alternative water injection and leakage from the containment vessels. It is also important to maintain flexibility on the choice of technical tasks based on newly obtained insights from ongoing and future on-site investigations.

The second scope is related to the characterisation of uranium-bearing particles and the establishment of techniques for future fuel debris analysis for D&D. Scope 2 includes a study on the plausible mechanisms for the formation of uranium-bearing particles collected on-site. This will contribute to the understanding of the progression of the accident and which fuel debris analysis technology and evaluation methods may be most useful. An international round-robin analysis activity with debris simulants is also included in this scope.

Data and information obtained from activities associated with the Fukushima-Daiichi plant investigation are collected by Japanese organisations and shared with the project partners in the third scope. This is a continuation of one of the tasks initiated in the ARC-F project with an expansion of the information contributed.

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