Variation of Tritium Concentration in Coastal Seawater Collected Along the Pacific Coast in Aomori Prefecture

A new nuclear fuel reprocessing plant in Aomori prefecture, Japan, began its reprocessing testing in March of 2006. During testing, tritium-contaminated wastewater was intermittently released into the coastal sea and diluted by the surrounding seawater. We measured tritium concentrations in seawater along the Pacific coast in the Aomori area to understand its temporal and geographical variation.

Coastal seawater samples were collected two or three times a year at four sites along the coast from 2006 to 2009. Samples were enriched by electrolysis up to a volume reduction factor of fifteen. Both tritium and deuterium concentrations were measured to calculate the samples' tritium concentrations.

Tritium concentrations obtained in this way were usually below 0.5 Bq/L, but they sometimes exceeded 1.0 Bq/L at the four sites on separate dates. From this result we estimate that the tritium-contaminated water is diluted by the coastal water current or by the stagnating water in the release area while it is discharged.