Tritium Concentration of Inland Water at Rokkasho Village, Aomori Prefecture

Abstract

This study adds new data points for 2024 to the existing time series of tritium concentrations in inland water in Rokkasho Village, Aomori and evaluate its relevance for environmental safety. Rokkasho has hosted major nuclear facilities, including nuclear power plants and a nuclear fuel reprocessing facility, and been considered a candidate site for a fusion facility in Japan. Since tritium is both a fuel for fusion and a waste product from nuclear reprocessing, background concentration data is essential for environmental monitoring during future operations. The most recent measurements in this area were conducted by Hasegawa et al. in 2006 during final testing of the nuclear fuel reprocessing facility with actual fuel and now are outdated. In this study, water samples were collected from 10 sites in October 2024. Tritium concentrations were measured using low-level tritium counting method with a commercially available solid polymer membrane enrichment system. Tritium concentration ranged from 0.21 to 0.37 Bq L⁻¹ and the mean value is 0.29 ± 0.06 Bq L⁻¹, which is lower than previously reported in Rokkasho. Based on this mean concentration, the estimated internal dose was 3.84 × 10⁻⁶ mSv year⁻¹ which is negligible compared with the public dose limit (1 mSv year⁻¹). These results indicate that the background tritium levels remain very low, and continuous monitoring is important to provide reliable baseline data for future environmental assessments.