HT to HTO conversion and field experiments near Darlington Nuclear Power Generating Station (DNPGS) site

•Value of the deposition velocity measured using an exposure chamber was on average 1.1 × 10−4 m s−1.•A number of candidate soil bacteria that may be contributing to the HT to HTO conversion in soil were identified.•The total fraction of oxidized HT was estimated up to 2.4% of the tritium released to the air.

The Canadian input parameters related to tritiated hydrogen gas (HT) used in tritium dose models are currently based on experiments performed at the Chalk River Laboratories (CRL) site in 1986, 1987 and 1994. There is uncertainty in how well other sites experiencing atmospheric HT releases are represented by these data. In order to address this uncertainty, HT to HTO conversion factors were evaluated at different locations near the Darlington Nuclear Power Generating Station (DNPGS) site using various experimental approaches. These were D2 gas exposure chamber experiments, atmospheric tritium measurements, and HTO and OBT measurements in vegetation and soil. In addition to these field experiments, chamber experiments were conducted using HT gas on field soil samples. The suggested Canadian input parameters for atmospheric tritium releases estimate the total fraction of HT oxidized in air and in soil, at the site, to be up to a maximum of 2.4%. Based on the more limited data obtained near DNPGS in early spring, this fraction would likely be closer to 0.5%. The result suggests that current parameters provide a conservative estimate for the DNPGS site.