Safety measure against tritium in the MLF muon target

For a high power proton driver like J-PARC, radiation safety is a crucial issue for stable and continuous operation. ³H is generated by a spallation process even in low-Z material such as Be, C which are generally applied not only to target materials but also to beam windows and other devices irradiated by high energy particles. In general, ³H diffuses easily in a material at high temperature, goes out to the surroundings environment and eventually increases the risk of an unexpected exposure. On the other hand, quantitative real-time monitoring of ³H in a big volume like exhaust gas from a facility is difficult because ³H emits only low-energy β-ray. Therefore, the treatment of ³H will be a key to facility operation. We developed a buffer tank system as a safety measure against ³H released from the muon production target to the beamline vacuum in MLF J-PARC. The system stores the exhaust gas from the beamline vacuum during the beam operation, and then exhausts the stored gas in a maintenance day after the radiation survey. This disables unexpected ³H release from the facility, and constructs the rigid RI control. (author)