Tritium determination in natural water samples in Fukushima from 2022 to 2023 using an ultra-low-level tritium counting system

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident created large stockpiles of tritium containing cooling water, which is to be gradually released into the Pacific Ocean, gaining attention from surrounding countries, environmental groups, and local residents concerned with the possibility of increasing tritium concentrations in the water and food cycle. Establishing baseline concentration levels and monitoring tritium immission values are important for assuring public safety, providing data for scientific research and risk communication. Tritium concentrations in the environment are very low; therefore, tritium measurements require enrichment in order to estimate the radiation exposure from drinking water intake and provide information on the water cycle. Natural water samples were collected at Tomioka Town located south of the FDNPP. Samples were distilled, enriched by electrolysis, and re-distilled using an improved SPE method to preconcentrate tritium to measureable levels. Tritium concentrations were determined by a low-background liquid scintillation counter. The observed tritium concentrations were relatively low, rainwater had a mean and SD value of 0.40 ± 0.13 Bq/L, and freshwater samples showed similar concentrations, while brackish coastal water samples were below 0.13 ± 0.02 Bq/L. The observed tritium concentrations in this study are considered safe as effective doses based on annual drinking water intake; however, continous monitoring is necessary to assure public safety.