Record of 3H and 36Cl from the Fukushima nuclear accident recovered from soil water in the unsaturated zone at Koriyama

Ohta, TomokoFifield, KeithPalcsu, LaszloTims, StevePavetich, StefanMahara, Yasunori2024-11-122024-11-122045-2322https://hdl.handle.net/1885/733724465The opportunity to measure the concentrations of 3H and 36Cl released by the Fukushima nuclear accident in 2011 directly in rain was lost in the early stage of the accident. We have, however, been able to reconstruct the deposition record of atmospheric 3H and 36Cl following the accident using a bore hole that was drilled in 2014 at Koriyama at a distance of 60 km from the accident. The contributions of 3H and 36Cl from the accident are 1.4 × 1013 and 2.0 × 1012 atoms m−2 respectively at this site. Very high concentrations of both 3H (46 Bq L−1) and 36Cl (3.36 × 1011 atoms L−1) were found in the unsaturated soil at depths between 300 and 350 cm. From these, conservative estimates for the 3H and 36Cl concentrations in the precipitation in the ~ 6 weeks following the accident were 607 Bq L−1 and 4.74 × 1010 atoms L−1, respectively. A second hole drilled in 2016 showed that 3H concentrations in the unsaturated soil and shallow groundwater had returned to close to natural levels, although the 36Cl concentrations were still significantly elevated above natural levels.T his work was supported by JSPS Grants-in-Aid for Scientific Research (Kakenhi Grant Numbers, 24686098, 17K07024, 20H02674), Ichimura Foundation for New Technology and YESSA (Yanmar shigenjunkan zaidan). We are deeply grateful to Dr. Leonard I. Wassenaar and Takuya Matsumoto, the IAEA and ATOMIKI staff for their technical support and Prof. Tamotsu Kozaki, Hokkaido University, for the financial support for the collection of the sediment cores in Fukushima in 2016, and Central Research Institute of Electric Power Industry for f inancial support for drilling of observation well in 2019. The Heavy Ion Accelerator Facility (HIAF) at ANU is supported by the National Collaborative Research Infrastructure Strategy (NCRIS) of the Australian Governmentapplication/pdfen-AU© 2023 The authorshttp://creativecommons.org/licenses/by/4.0/Record of 3H and 36Cl from the Fukushima nuclear accident recovered from soil water in the unsaturated zone at Koriyama202310.1038/s41598-023-46853-y2024-01-21Creative Commons Attribution licence