The JET hydrogen-oxygen recombination sensor-a safety device for hydrogen isotope processing systems

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 1 mV for explosive hydrogen-air mixtures at pressures as low as 1 mbar. The differential principle employed suppresses erroneous signals originating from hydrogen sorption/desorption heat on the catalyst.