OVERVIEW OF THE 1994 CHRONIC HT RELEASE EXPERIMENT AT CHALK-RIVER

Trace amounts of tritiated hydrogen (HT) were released continuously to the atmosphere at Chalk River Laboratories over the 12-day period 199 4 July 27 to August 8. Scientists from eight institutions in four coun tries took extensive air, soil and vegetation samples to study the dyn amics of tritiated water (HTO) and organically-bound tritium (OBT) for mation, and the environmental concentrations of these compounds at ste ady-state. The short-term HT air concentrations varied strongly in tim e and space over the test area, but the variation decreased rapidly as the averaging time increased. HTO concentrations in soil, vegetation and air built up gradually over time but they fluctuated substantially with ambient meteorological conditions, particularly rainfall. OBT co ncentrations in plants increased throughout the period. HTO concentrat ions were at or near steady-state at the end of the release, but OBT l evels were continuing to rise.