Tritium concentrations of natural waters in Rokkasho-mura

There are two types of lakes in the vicinity of the nuclear fuel cycle faci lities in Rokkasho-mura. One is a brackish lake, Obuchinuma Lake, and the o ther is a freshwater lake, Takahokonuma Lake. Tritium concentrations in Obu chinuma Lake had a good negative correlation with salinity at any sampling point and period. We consider that the water of Obuchinuma Lake has been on ly slightly influenced by precipitation depending on the ratio of seawater and river water of the Futamata River. Tritium concentrations in Takahokonu ma Lake ranged from 0.6 to 1.5 Bq.l(-1), and were higher than that in preci pitation in Rokkasho-mura. Tritium concentration in rivers flowing into the lakes ranged from 0.7 to 2 Bq.l(-1). and were higher than that in the prec ipitation. It is assumed that ground waters with higher levels of tritium i nflow into the rivers.