Analysis of carbon-14 and tritium in reactor stack gas

The analysis of gases from nuclear power stations include determination of tritium and 14C in several molecular forms. In this procedure, tritium water vapor is collected in a freeze trap, and 14C (as CO2) is collected by precipitation in bubblers. Water vapor, hydrogen, carbon dioxide, and methane gas carriers are added to a gas sample. The sample is drawn into the gas analysis system by means of a vacuum pump and is flushed through the system with purified air. HTO is collected in a freeze trap at -80C, and 14CO2 is precipitated as barium carbonate with freshly prepared barium hydroxide in a bubbler. Water mist from the bubblers is then removed from the gas stream as the sample passes through a silica gel spray trap. The gas is then passed through the catalytic oxidation chamber, which converts the remaining gaseous hydrogen and carbon compounds to water and carbon dioxide. The water is collected in a second freeze trap, and the CO2 is precipitated in a second bubbler. The precipitates are then transferred to glass vials and counted by liquid scintillation as a suspension. Minimum detectable levels for both 3H and 14C are 0.4 picocuries per sample for samples varying in size from 1 cc to 20 liters