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 99Tc concentration and 99Tc/137Cs activity ratio were measured in the coastal waters off Aomori Prefecture, Japan, where a spent-nuclear-fuel reprocessing plant has begun test operation. The 99Tc concentrations in surface water ranged from 1.8 to 2.4 mBq/m3, no greater than the estimated background level. Relatively high 99Tc/137Cs activity ratios (10–12 × 10−4) would be caused by the inflow of the high-99Tc/137Cs water mass from the Japan Sea. There is no observable contamination from the reprocessing plant in the investigated area. The 99Tc concentration and the 99Tc/137Cs activity ratio in water column showed gradual decreases with depth. Our results implied that 99Tc behaves in a more conservative manner than 137Cs in marine environments.

► 99Tc concentration 99Tc/137Cs ratio in the coastal waters off Aomori, Japan.
► 99Tc concentrations in background level, but relatively high 99Tc/137Cs.
► 99Tc behaves in a more conservative manner than 137Cs in marine environments.