HT and HTO in the Environment at Chalk River

The release of tritium into the public environment from heavy water reactor operations at Chalk River Nuclear Laboratories is about 0.1% of the Derived Release Limit which is based on internationally accepted standards. A mean discharge of 500 TBq/a of HTO vapour to the atmosphere has resulted in concentrations in precipitation at the plant boundary of 74 Bq/L. (1 TeraBq = 10¹²Bq = 27 Ci). A dilution factor of 6 × 10⁷ m³/s is observed. Measurements of HTO in tree leaf moisture and integrated snow cores serve to delineate the dispersal plume. Measured discharges of liquid HTO to local surface and groundwaters totaling 147 TBq/a agree reasonably well with amounts observed in the Ottawa River. Preliminary measurements have shown that minor amounts of HT are being released to the atmosphere from the Chalk River facilities.