A study of the man-made radioactivity in the Ottawa and St. Lawrence Rivers, Canada

Abstract

The contribution of nuclear sites and fallout to aquatic radioactivity in the St. Lawrence-Ottawa Rivers system in eastern Canada is presented for different periods between 1958 and 1987. The concentrations of fission and activation products, generated by the Chalk River Nuclear Laboratories (CRNL) located along the Ottawa River, are given for the 1975–1987 period. The transit times of the radionuclides in the rivers from the CRNL to the Ottawa-Hull, Montreal Islands and Quebec City areas have been estimated to vary between 23 and 42, 32 and 52, and 42 and 62 days, respectively. The concentrations of fission products resulting from fallout due to weapons' testing by the People's Republic of China and Chernobyl have been determined for the 1977–1987 period. These results show also that the impact of Chernobyl was equivalent to that of a small nuclear weapon detonated in the troposphere. The results also show that thaws of the rivers in February and April 1981, respectively, after the 1 MT Chinese thermonuclear explosion of 16 October 1980, gave rise to a large increase in the concentrations of fallout fission products (from ∼10 to ∼290 Bq m −3). These latter results have been used to estimate the concentrations of fallout fission products in the regular spring thaws of the 1958–1977 period following the thermonuclear explosions in the northern hemisphere; estimated highs of ∼20 Bq l −1 were reached in the springs of 1962 and 1963.