Development of tritium monitor using hollow filament polyimide membrane

For preservation of the environment around high-energy accelerator facilities, it becomes more and more important to establish an effective technique for measurements of tritium released from the stacks and the beam-line tunnels. A new method for real-time and continuous monitoring of tritium has been proposed and developed using hollow filament polyimide membrane in our group. Tritium is a relatively long-lived isotope with half-life of about 12 years and emits only a low-energy beta ray, of which average energy is 5.7 keV. Tritium is formed in air mainly by spallation of oxygen and nitrogen in the tunnels. At the same time, the other radioisotopes such as 11C, 13N, 15O and 41Ar are also produced in the tunnels, and these short-lived radionuclides interfere direct measurements of tritium in air exhausted from the tunnels. Therefore the separation and enrichment of tritium from concomitant radioactive airbornes would be essential for continuous and real-time measurement of tritium. Among several methods of tritium separation, a hollow-filament type polyimide membrane is one of the most promising device because of its high separation efficiency with low cost, and the incorporation of this separation device to any practical detection systems is feasible due to its simplicity and compactness. In the present study, the experiments have been performed using a small membrane module system without tritium in order to investigate basic characteristics of the membrane for designing the system of real-time tritium measurements. Analytical methods of gaseous components were studied extensively, and a computer simulation for the gas separation was also performed. The preliminary results of gas separation obtained in the mixtures of H2 in Air and D2 in Air are presented as well as the design concept for the detection system using the membrane. The experimental results are discussed by comparing with the theoretical analysis. (author)