Volatilization of B4C control rods in Fukushima Daiichi nuclear reactors during meltdown: B-Li isotopic signatures in cesium-rich microparticles

Kazuki Fueda; Ryu Takami; Kenta Minomo; Kazuya Morooka; Kenji Horie; Mami Takehara; Shinya Yamasaki; Takumi Saito; Hiroyuki Shiotsu; Toshihiko Ohnuki; Gareth T W Law; Bernd Grambow; Rodney C Ewing; Satoshi Utsunomiya

doi:10.1016/j.jhazmat.2022.128214

Volatilization of B₄C control rods in Fukushima Daiichi nuclear reactors during meltdown: B-Li isotopic signatures in cesium-rich microparticles

J Hazard Mater. 2022 Apr 15:428:128214. doi: 10.1016/j.jhazmat.2022.128214. Epub 2022 Jan 4.

Authors

Affiliations

¹ Department of Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
² National Institute of Polar Research, 10-3 Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan; Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI), Shonan Village, Hayama, Kanagawa 240-0193, Japan.
³ National Institute of Polar Research, 10-3 Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan.
⁴ Faculty of Pure and Applied Sciences and Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
⁵ Nuclear Professional School, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan.
⁶ Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4, Shirakata-shirane, Tokai-Mura, Naka-Gun, Ibaraki 319-1195, Japan.
⁷ Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
⁸ Radiochemistry Unit, Department of Chemistry, University of Helsinki, A.I. Virtasen aukio 1, 00560 Helsinki, Finland.
⁹ SUBATECH, IMT Atlantique, CNRS-IN2P3, the University of Nantes, Nantes 44307, France.
¹⁰ Department of Geological Sciences and Center for International Security and Cooperation, Stanford University, Stanford, CA 94305-2115, USA.
¹¹ Department of Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. Electronic address: utsunomiya.satoshi.998@m.kyushu-u.ac.jp.

PMID: 35042164
DOI: 10.1016/j.jhazmat.2022.128214

Abstract

Boron carbide control rods remain in the fuel debris of the damaged reactors in the Fukushima Daiichi Nuclear Power Plant, potentially preventing re-criticality; however, the state and stability of the control rods remain unknown. Sensitive high-resolution ion microprobe analyses have revealed B-Li isotopic signatures in radioactive Cs-rich microparticles (CsMPs) that formed by volatilization and condensation of Si-oxides during the meltdowns. The CsMPs contain 1518-6733 mg kg^-1 of ¹⁰⁺¹¹B and 11.99-1213 mg kg^-1 of ⁷Li. The ¹¹B/¹⁰B (4.15-4.21) and ⁷Li/⁶Li (213-406) isotopic ratios are greater than natural abundances (~4.05 and ~12.5, respectively), indicating that ¹⁰B(n,α)⁷Li reactions occurred in B₄C prior to the meltdowns. The total amount of B released with CsMPs was estimated to be 0.024-62 g, suggesting that essentially all B remains in reactor Units 2 and/or 3 and is enough to prevent re-criticality; however, the heterogeneous distribution of B needs to be considered during decommissioning.

Keywords: Boron-lithium isotopes; Cesium-rich microparticle; Fukushima Daiichi Nuclear Power Plant; Re-criticality; Secondary ion mass spectrometry.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Cesium
Cesium Radioisotopes
Fukushima Nuclear Accident*
Japan
Nuclear Power Plants
Radiation Monitoring*
Volatilization

Substances

Cesium Radioisotopes
Cesium