THE JET HYDROGEN-OXYGEN RECOMBINATION SENSOR -A SAFETY DEVICE FOR HYDROGEN ISOTOPE PROCESSING SYSTEMS

摘要

Fusion vacuum systems for processing of deuterium and tritium pose safety hazards by formation of potentially explosive mixtures in case of air inleakage. Early detection of such hazards is essential for the safety of process equipment for fuel purification and recycling. Having established the fact that conventional oxygen monitors do not work well in hydrogen atmospheres at low pressures, we developed a sensor compatible with this duty. It is based on the detection of the oxygen-hydrogen reaction heat in a differential thermoelectric calorimeter, using a proprietary AECL wetproof catalyst for promoting the recombination reaction and semi-conductor thermopiles for detection. Operating at room temperature, the sensor provides signals in excess of 1mV for explosive hydrogen-air mixtures at pressures as low as 1mbar. The differential principle employed suppresses erroneous signals originating from hydrogen sorption/desorption heat on the catalyst. The design and performance of these sensors will be described in detail. Two of the sensors have been installed on the main forevacuum lines of the JET device to provide unambiguous alarms in case of air inleakeage. A previously developed (batch processing) oxygen detector reacting a sample in a vessel at 77K by means of a hot platinum filament (-900K) will then be used for exact quantitative assessment of the combustible mixture. Depending on the result, a suitable safe process route will be selected.