Estimation of Temporal Variation of Discharged Tritium from Port of Fukushima Dai-ichi Nuclear Power Plant: Analysis of the Temporal Variation and Comparison with released Tritium from Japan and Major Nuclear Facilities Worldwide

Abstract

We estimate the monthly discharge inventory of tritium from the port of Fukushima Daiichi Nuclear Power Plant (1F) from Jun. 2013 to Mar. 2020 using the Voronoi tessellation scheme, following the tritium monitoring inside the port that started in Jun. 2013. As for the missing period from the initial month, Apr. 2011 to May 2013, we calculate the tritium discharge by utilizing the ratio of tritium concentration to 137 Cs concentration in stagnant contaminant water during the initial direct runoff period to Jun. 2011 and the discharge inventory correlation between tritium and 137 Cs for the nextunknown continuous-discharge period up to May 2013. From all the estimated results over 9 years, we found that the monthly discharge inventory sharply dropped immediately after closing the seaside impermeable wall in Oct. 2015 and subsequently coincided well with the sum of those of drainage and subdrain etc. By comparing the estimated results with those in the normal operation period before the accident, we point out that the discharge inventory from the 1F port after the accident is not very large. Even the estimation for the year 2011 is found to be comparable to the maximum of operating pressurized water reactors releasing relatively large inventories in the number of digits. In the national level, the total domestic release inventory in Japan significantly decreased after the accident owing to the operational shutdown of most plants. Furthermore, 1F and even the total Japanese discharge inventory are found to be minor compared with those of nuclear reprocessing plants and heavy-water reactors on a worldwide level. From the above, we suggest that various scenarios can be 1 (国研) 日本原子力研究開発機構 システム計算科学センター 2 東京大学 大気海洋研究所 3 (国研) 日本原子力研究開発機構 原子力基礎工学研究センター 4 ㈱アトックス 5 (国研) 水産研究・教育機構 水産資源研究所 ＊ Corresponding author, E-mail: machida.masahiko＠jaea.go.jp 論 文(町田，他) 日本原子力学会和文論文誌( 2022) , Advance Publication by J-stage openly discussed regarding the management of tritium stored inside 1F with the help of the present estimated data and its comparison with the past discharge inventory.

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

“…The surface and subsurface seawater activities of 3 H varied from 0.08 to 0.29 Bq L −1 , which was higher than the estimated pre-Fukushima background of 0.07 Bq L −1 [ 70 ]. The peak concentrations, which were caused by the advection of the coastal current, were found north and south of the FDNPP seaport where ~0.2 Pbq of 3 H was cumulatively discharged directly into the sea [ 75 ]. The extended area offshore Fukushima was investigated again in June 2011.…”

Monthly Precipitation Collected at Hirosaki, Japan: Its Tritium Concentration and Chemical and Stable Isotope Compositions

“…Finally, nuclear facilities have released tritium into the environment during normal operations and as a result of accidents [4]. In Japan, the accident that occurred at the Fukushima Daiichi Nuclear Power Station in March 2011 released radioactive substances, some containing tritium, into the environment [5][6][7][8]. The released tritium deposited on the ground and the ocean through atmospheric dispersion and precipitation.…”