End state of debris in the units 1-3 of Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings. Photo: Japan Atomic Energy Agency
The Preparatory Study on Analysis of Fuel Debris (PreADES) project was initiated in December 2017 for 3 years as one of the near-term projects proposed by the Senior Expert Group on Safety Research Opportunities Post-Fukushima (SAREF). The main objective of the project was to support preparing nuclear fuel debris retrieval operations from the three reactors which underwent core melt down at the Fukushima Daiichi Nuclear Power Station (FDNPS). PreADES was established to collect experience, knowledge and methods for retrieval and characterisation of fuel debris from core melt down accidents. Experience with real debris from past major accidents (Three Mile Island unit 2 (TMI-2) and Chernobyl unit 4), core melt-down testing (e.g. Phebus FP tests, molten corium concrete interaction (MCCI) tests) and with relevant simulant debris was capitalised. Preliminary analyses conducted on first debris collected during forensic investigations at FDNPS, so-called uranium-bearing particles, also served expanding the knowledge base on expected fuel debris characteristics.
The project addressed three tasks.
The first task was a joint effort to establish expected fuel debris location, distribution and characteristics in the three units where core melt down and relocation occurred based on knowledge collected from past accidents (e.g. TMI-2 and Chernobyl-4) and analyses conducted on the Fukushima-Daiichi accident (e.g. expected damaged state as calculated in the OECD/NEA BSAF project). Maps of debris’ distribution and debris characteristics at different locations have been proposed for the end state of fuel debris in the three damaged units of the FDNPS. A table presenting expected debris characteristics at different locations in the damaged units was also created, summarising expected composition, mechanical and thermal properties of debris at different locations. These elements (maps of fuel debris distribution and table of debris characteristics) constitute a preliminary basis that could guide fuel debris retrieval operations.
The second task was to identify and analyse risks and challenges related to fuel debris retrieval operations, considering potentials for re-criticality, for dispersion of radioactivity (loss of containment), for loss of cooling, for personal radiation exposure and issues related to sampling analysis methods, facility demands, transportation, accounting, and hot testing facilities. The task also aimed at providing preliminary plans for fuel debris analysis with priorities to support safe fuel retrieval operations and safe decommissioning of the damaged reactor. Considerations such as cost, availability and timing of decommissioning work were included. These plans can be used to guide establishment in the future of more consolidated fuel debris retrieval and analysis plans for starting fuel retrieval operations. Finally, a review of available techniques and facilities for FDNPS fuel debris sample preparation and analyses was made and capabilities of various techniques and guidance sheets for hot samples characterisation were tabulated.
The third task was to establish an international collaborative framework for continuing activities to prepare fuel debris retrieval operations. The organisations who participated in PreADES proposed to pursue with tasks devoted to deepen the characterisation of collected U-bearing particles and the analysis of their formation in relation to the accident progression and aimed at organising an international round-robin analysis exercise between laboratories equipped for hot samples analysis on representative simulant fuel debris.
Canada, European Commission, France, Japan, Korea, Sweden, Switzerland and the United States
December 2017 - December 2021
EUR 275 K