Tritium concentration and diffusion in seawater discharged from Tokai Reprocessing Plant

Kokubun, Yuji ; Fujita, Hiroki; Nakano, Masanao ; Sumiya, Shuichi 

The Tokai Reprocessing Plant has reprocessed the total amount of 1,140 tons of spent fuels since 1977 to the end of fiscal year 2008. During the operation, radioactive liquid effluent has been discharged into the sea from the outlet of the pipeline stretching about 3.7 km from shoreline, after the discharge approval and discharged total amounts of 4.5 PBq of H to the sea. Therefore, since 1978, JAEA has sampled seawater around the outlet every month. Tritium concentrations in seawater were analyzed and measured using a liquid scintillation counter. All data were used to calculate the dilution factor which means the ratio of the H concentration in seawater to that in liquid effluent. The number of H concentrations below the detection limit was 9,079 (82.0%) and the number of those from the limit to 40 Bq/L (as quantification limit) was 1,964 (17.7%). The maximum concentration was 1,700 Bq/L at the point just above the outlet in 1979. Moreover, the dilution factors were ranged between 240 and 6,500,000. All the concentrations were confirmed to be those below 60,000 Bq/L of H concentration limit included in water decided by the law and that it were not concern of environmental safety.