Delegates during the fifth FACE project meeting at the ANL office in Illinois, United States.
The FACE (Fukushima Daiichi Nuclear Power Station Accident Information Collection and Evaluation) project’s US partners hosted the fifth project meeting at Argonne National Laboratory in Lemont, Illinois (United States) on 23-25 September 2024. For the occasion, 90 experts from 23 organisations, 12 countries and the European Commission gathered to discuss advances in investigations and analyses of the accident and remaining knowledge gaps.
During the meeting, Japanese partners presented recent investigation results that reduce uncertainties in the understanding of the accident progression, including insights obtained from primary containment vessel (PCV) drone investigations.
Regarding accident progression, participants provided updates on: analyses of gas phase iodine formation from contaminated water; analyses based on smear samples taken from the FDNPS unit 2 reactor building; experimental activities related to possible combustible gas distributions that led to the unit 3 reactor building explosion; efforts to reduce uncertainties in simulating fission product release (using forward accident progression simulations and backward simulations based on radiation measurement data); and activities to reduce uncertainties in simulating molten core concrete interaction (MCCI) phenomena. With respect to MCCI activities, participants provided results from analyses supporting MCCI benchmark calculations and efforts to quantify the composition and thermal properties of a unit 1 concrete sample.
In addition, experts shared updates on accident analysis considering thermal stratification and data obtained from water level reduction efforts, formation mechanisms of U-bearing particles found in PCVs, and efforts (using prototypic debris and debris from the Three Mile Island Unit 2 accident) to quantify the amount and behaviour of radioactive particles generated by candidate cutting methods during retrieval activities. Progress was reported on the round-robin debris analysis activities (RRDAA). Several participants have received the simulant debris and started or completed their analyses. A RRDAA symposium will be held in conjunction with the next FACE meeting to share the experience gained in debris analysis results from different laboratories.
Experts also reviewed remaining major knowledge gaps identified through Fukushima Daiichi accident analyses. These relate to the understanding of the vessel ruptures and ex-vessel phenomena and of the sequence of events responsible for the radioactive releases. Experts agreed that results of investigations and analyses should be discussed in the future with the perspective of proposing accident management enhancements in operating and future reactors. These discussions will continue at the next project meeting, to be held in Daejeon, Korea, in May 2025.
