A new type of tritium-in-air monitor for fusion reactors

Abstract

A real-time tritium-in-air monitor is described which uses flow-through air proportional counters as the detector. The counters need no counting gas other than the sampled air, and they construct a low background system with an anti-coincidence shielding technique. Using background compensation, the monitor allows separate detection of tritium from β- and γ-backgrounds which might appear in fusion reactor environments. In addition, α-background from radon and its daughter nuclides is eliminated by pulse height discrimination. The present monitor can detect tritium activities in air less than 5 μCi/m3, i.e. the maximum permissible concentration, with a measuring time of 30 s under γ-background with an exposure rate of 10 mR/h or β-background from other radioactive gases than tritium with a concentration level of some 200 μCi/m3. The monitor also has a wide range up to 0.1 Ci/m3 of tritium concentration. The monitor could be used effectively to monitor tritium in work locations of fusion reactors and related facilities.