2022 Annual Meeting

Presentation information

Oral presentation

III. Fission Energy Engineering » 304-1 Thermal Hydraulics, Energy Conversion, Energy Transfer, Energy Storage

[1E01-07] Severe Accident 1

Wed. Mar 16, 2022 10:00 AM - 12:00 PM Room E

Chair: Kenichi Tezuka (IAE)

10:15 AM - 10:30 AM

[1E02] Estimation of the In-Depth Debris Status of Fukushima Unit-2 and Unit-3 with Multi-Physics Modeling

(12)Evaluation of debris-relocation history to the pedestal in Fukushima-Daiichi Units 2 and 3

*Ikken Sato1, Akifumi Yamaji2, Masahiro Furuya2, Yuji Ohishi3, Xin Li2, Hiroshi Madokoro1 (1. Japan Atomic Energy Agency, 2. Waseda University, 3. Osaka University)

Keywords:severe accident of a nuclear reactor, decommissioning of Fukushima-Daiichi NPP

Based on the analysis of plant data during the accident transient, the results of the internal investigation, and various analysis evaluations, the behavior of fuel debris relocation to the pedestal in Units 2 and 3 was evaluated.
From the results of the internal investigation, it is understood that the material relocated to the pedestal includes, ①“preceding runoff-like material" presumably consisting mainly of molten metal,②"debris-like material number 1“ presumably with an intermediate viscosity like that of wet concrete , and ③“debris-like material number 2” with high viscosity presumably consisting mainly of oxides.
Based on the results of computer model simulation and data analysis, it was estimated that ① and ② relocated to the pedestal in Unit 2 in about 2 hours, and ① to ③ in Unit 3 in about 7 hours.
Based on post-accident muon measurements and analysis of temperature data during the accident transient, it is estimated that oxide debris mainly remained in the pressure vessel in Unit 2, whereas most fuel debris containing oxides relocated to the pedestal in Unit 3.