U.S. Team Measurements During the June 1987 Experimental HT Release at the Chalk River Nuclear Laboratories, Ontario, Canada

In June 1987, an experiment was performed at the Chalk River Nuclear Laboratories in Ontario, Canada, to study the oxidation of HT in the environment. The experiment involved a 30-minute release of 3.54 TBq (95.7 Ci) of HT to the atmosphere at an elevation of one meter. The HTO/HT ratios were shown to slowly increase downwind (∼ 4 × 10⁻⁵ at 50 meters to almost 10⁻3 at 400 meters) as conversion of HT takes place. For several days after the release, HTO concentrations in the atmosphere remained elevated. Freeze-dried water from vegetation samples was found to be very low in HTO immediately after the release suggesting a very low direct uptake of HTO in air by vegetation. The free-HTO concentration in vegetation increased during the first day, peaking during the second day (about 1.5 − 3.0 × 10⁴ Bq/L at 50 meters from the source) and decreasing by the end of the second day. The organically bound tritium continued to accummulate during the period following exposure (about 400 Bq/kg dry weight at 50 meters after two days).