AGHCF gaseous-effluent tritium sampling system: design considerations and performance testing results

Performance testing results involving the operation of a gaseous-effluent tritium sampling system are provided. A system description, including design improvements made over the course of several years of operation, is also presented. The sampling technique is based on using ethylene glycol bubblers for collecting tritiated water entrained as vapor in a nitrogen purge gas from a hot cell facility. Tritiated gas is converted to water vapor using a high temperature copper oxide bed; newly-formed water molecules are readily collected in a second set of ethylene glycol bubblers. For a single bubbler containing 20 mL of ethylene glycol, the tritium collection efficiency was determined to be 98.3%. To optimize performance and to minimize the volume of mixed waste generated, tests were performed to evaluate variations in the collection efficiency as a function of sorbent volume. For purposes of comparison the performance of water-filled bubblers was also evaluated. With two water bubblers connected in series the overall collection efficiency was quite satisfactory at 95.4%, although appreciable water losses were evident. The bed oxidation efficiency for tritiated gas was evaluated over a range of temperatures; at a catalyst bed temperature of 350 degrees C nearly all the gas was converted to water vapor. System memory effects were assessed by measuring the amount of residual contamination present in the bubblers after purging the sampling system for a week offline. Contamination problems arising from previous sampling periods were inconsequential. The overall uncertainty associated with the total quantity of tritium discharged to the environment based on the results of the performance testing was estimated to be +/-24% at the 95% confidence level.