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

• Published in: Journal of hazardous materials Vol. 428; p. 128214
• Main Authors: Fueda, Kazuki, Takami, Ryu, Minomo, Kenta, Morooka, Kazuya, Horie, Kenji, Takehara, Mami, Yamasaki, Shinya, Saito, Takumi, Shiotsu, Hiroyuki, Ohnuki, Toshihiko, Law, Gareth T.W., Grambow, Bernd, Ewing, Rodney C., Utsunomiya, Satoshi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2022
• Subjects: Boron-lithium isotopes; Cesium-rich microparticle; Fukushima Daiichi Nuclear Power Plant; Re-criticality; Secondary ion mass spectrometry; Cesium-rich microparticle; Re-criticality; Secondary ion mass spectrometry; Fukushima Daiichi Nuclear Power Plant; Boron-lithium isotopes
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2022.128214

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. [Display omitted] •Radioactive Cs-rich microparticles containing B were released from Fukushima Daiichi.•Boron–Li isotopes indicate partial volatilization of control rods in the reactors.•The amount of B remaining in the reactor should prevent re-criticality.