Experimental Results of JAERI (Japan Atomic Energy Research Inst.) in the Canadian HT (Tritium Gas) Field Release Study of June 10, 1987

摘要

A tritium gas (HT) release study was performed in Chalk River Nuclear Laboratories, Ontario, Canada, on June 10, 1987. About 3.5 x 10/sup 12/ Bq (96 Ci) of HT gas was released to an experimental field over 30 minutes from an outlet placed at 1 m height from the ground surface. From measurements of air, soil and pine needle samples collected during the extended period of 5 days after initiation of the HT release, the following findings were obtained. HT gas was deposited in the soil through diffusion into the soil and conversion to HTO by microbial activity therein. The concentration ratio of HTO to HT in the air during the release period tended to increase with downwind distance and was 4.1 x 10/sup -4/ at 400 m. Soil measurements showed that HT gas was deposited in the soils as HTO, mostly in the top 5 cm soils and its deposition velocities to the soils ranged from 1.6 x 10/sup -4/ to 3.0 x 10/sup -4/ m/s. A low deposition velocity of <1.0 x 10/sup -5/ m/s was measured for the silty loam with low microbial activity. The deposition velocities for the coarse sands were comparable to those for the very fine sandy loam. The deposition velocities for resuspended HTO to the silty loam, ethylene glycol and water were 2.4 x 10/sup -2/, 1.5 x 10/sup -2/ and 2.3 x 10/sup -2/ m/s, respectively. Pine needle measurement showed that HT deposition was negligible as compared with HTO deposition. Due to deposition of air HTO, the tissue-free-water-tritium concentration increased with time and reached a peak concentration in 5 hours. This fact suggested that vapor exchange between air and vegetation was an important process. Uptake of HTO by roots was seen from about 50 hours after the end of the HT release. (ERA citation 14:023105)