A review of tritium radioisotope in Fukushima waters, Japan

Tritium radioisotope (H-3 or T) with a half-life of 12.32 years was released to the atmosphere in the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident prompting tritium monitoring efforts in Fukushima waters. Tritium in precipitation has been measured monthly from 2012 accumulating a decade-long record in Namie Town [1] and the Fukushima Prefectural Government sampled river, lakes, dam reservoir, and coastal sites twice per year for direct tritium measurements [2]. Since the FDNPP anthropogenic tritium was measured at several coastal sites influencing natural background tritium, which is a cosmogenic radionuclide traced as a water molecule (HTO), a combined time-series of both anthropogenic and natural tritium in precipitation was required for the transit times interpretation using the atmospheric FDNPP release tritium simulation [3]. In October 2023, tritium measurements at several Fukushima city headwater catchments indicated natural background levels and tritium-tracer was useful for estimating water transit times and volume in the subsurface [4]. While tritium is a useful tracer to estimate water transit times in Fukushima, the continuation of tritium monitoring is needed to disentangle natural levels with the ongoing tritium-related FDNPP activities such as the tritiated water discharge from the FDNPP site.  References: [1] Yamada R., Hasegawa, H., Akata, N., et al. (2024) Temporal variation of tritium concentration in monthly precipitation collected at a Difficult-to-Return Zone in Namie Town, Fukushima Prefecture, Japan. Environmental Science and Pollution Research (5): 7818–7827. https://doi.org/10.1007/s11356-023-31652-9[2] Fukushima Revitalization Portal Site (2024). https://www.pref.fukushima.lg.jp/site/portal/[3] Gusyev, M., Cauquoin, A., Igarashi, Y., et al. (2024) Anthropogenic and natural tritium radioisotope in terrestrial water cycle of Fukushima, Japan, EGU General Assembly 2024, Vienna, Austria, EGU24-17332, https://doi.org/10.5194/egusphere-egu24-17332.[4] Cauquoin, A., Gusyev, M., et al. (2025) Modeling tritium release to the atmosphere during the Fukushima Daiichi Nuclear Power Plant accident and application to estimating post-accident water system transit times, Japan, Environmental Science and Pollution Research, https://doi.org/10.1007/s11356-025-35919-1