Vertical distributions of 99Tc and the 99Tc/137Cs activity ratio in the coastal water off Aomori, Japan

Using a sector-field ICP-MS the vertical distributions of the Tc-99 concentration and Tc-99/Cs-137 activity ratio were measured in the coastal waters off Aomori Prefecture, Japan, where a spent-nuclear-fuel reprocessing plant has begun test operation. The Tc-99 concentrations in surface water ranged from 1.8 to 2.4 mBq/m(3), no greater than the estimated background level. Relatively high Tc-99/Cs-137 activity ratios (10-12 x 10(-4)) would be caused by the inflow of the high-Tc-99/Cs-137 water mass from the Japan Sea. There is no observable contamination from the reprocessing plant in the investigated area. The Tc-99 concentration and the Tc-99/Cs-137 activity ratio in water column showed gradual decreases with depth. Our results implied that Tc-99 behaves in a more conservative manner than Cs-137 in marine environments. (C) 2011 Elsevier Ltd. All rights reserved.