Impact of CANDU Emissions on Tritium Levels in the Great Lakes

Abstract

A concentration-time model has been developed to estimate the relative contributions of cosmogenic, weapons fallout and CANDU tritium emissions from OPG Nuclear Generating Stations to the Great Lakes tritium inventories. Tritium input to the lakes is from tritium in precipitation, water vapour exchange, drainage from lake watersheds and direct input from CANDU reactors. Removal is by outflow from the lakes, evaporation and radioactive decay. Lakes Huron and Ontario are the only two Great Lakes which receive direct inputs from CANDU reactors and are therefore of particular interest. Estimated relative contributions of cosmogenic, residual weapons testing fallout and CANDU tritium to 1999 lake tritium inventories are 6, 30 and 64% for Lake Huron and 8, 27 and 65% for Lake Ontario. Projections are that the contribution of CANDU tritium to Lakes Huron and Ontario tritium inventories will increase to 80% and the residual tritium fallout from historic weapons testing will decline to 10% by 2025. Lakes Huron and Ontario tritium concentrations are currently approximately 7 Bq/L; three orders of magnitude lower than the Ontario drinking water standard. These concentrations are projected to decline to 5 Bq/L by 2025. The decline is primarily due to the continued decay and outflow of residual weapons fallout tritium.