Fueda, KazukiKazukiFuedaTakami, RyuRyuTakamiMinomo, KentaKentaMinomoMorooka, KazuyaKazuyaMorookaHorie, KenjiKenjiHorieTakehara, MamiMamiTakeharaYamasaki, ShinyaShinyaYamasakiSaito, TakumiTakumiSaitoShiotsu, HiroyukiHiroyukiShiotsuOhnuki, ToshihikoToshihikoOhnukiLaw, Gareth T.W.Gareth T.W.LawGrambow, BerndBerndGrambowEwing, Rodney C.Rodney C.EwingUtsunomiya, SatoshiSatoshiUtsunomiya2026-01-022026-01-022022-04https://www.scopus.com/pages/publications/85122805035?inwardhttps://scholars.lib.ntu.edu.tw/handle/123456789/734965Boron 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.Boron-lithium isotopesCesium-rich microparticleFukushima Daiichi Nuclear Power PlantRe-criticalitySecondary ion mass spectrometryjournal article10.1016/j.jhazmat.2022.128214