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Tritium dynamics in soils and plants at a tritium processing facility in Canada

Abstract of the technical paper/presentation presented at:
International Conference on Radioecology and Environmental Radioactivity
September 7–12, 2014

Prepared by:
Steve Mihok
Canadian Nuclear Safety Commission


The dynamics of tritium released as tritiated water (HTO) have been studied extensively with results incorporated into environmental models. The dispersion of tritiated gas (HT) and rates of oxidation to HTO have mainly been studied under controlled conditions, with few studies under natural conditions. To support the improvement of regulatory models, a garden was set up near a tritium processing facility in Pembroke for experimental studies. Soils and plants were sampled for HTO and organically bound tritium (OBT), along with day-night monitoring of tritium in air. The experimental design included a plot of natural grass, contrasted with grass and garden produce grown in topsoil in barrels under different irrigation regimes. The three irrigation regimes were: rain only, low-tritium tap water, and high-tritium water. This design provided a range of conditions with contrasts in initial tritium activity in soils, and major tritium inputs from air versus water.

Air monitoring indicated that the plume was only occasionally present for sustained periods during working hours; i.e. daylight
(HT > HTO). Mean ambient air averaged 3.3 Bq/m3 HT and 4.7 Bq/m3 HTO. Native soils retained a historical signature of a high OBT:HTO ratio (19.5); there was little formation of OBT in barrel soils during this work.

Plants irrigated with high-tritium water had OBT:HTO ratios near 1, as expected from current models (1.0, beans/potatoes, 1.4, sod). In contrast, plants exposed to low amounts of tritium in rain and air, or supplemented by low-tritium tap water had a very high OBT:HTO ratio. Although some OBT:HTO ratios were higher than expected, doses from ingestion of produce remained well below the public dose limit of 1 mSv per year.

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