Developments of gaseous water, hydrogen and methane sampling system for environmental tritium monitoring

The atmospheric tritium concentration in or around a nuclear fusion facility must be measured, from the environmental safety point of view. The major chemical forms of atmospheric tritium are water, hydrogen and methane. We present an automatic sequential process for measuring each of these chemical forms, allowing reliable operation and saving much labor time. Water vapor is collected easily in a molecular sieve. The sampling method for hydrogen or methane is to oxidize the gas into water using a catalyst and to absorb the water in a molecular sieve. For hydrogen oxidization a Pt catalyst with an Al–Cr–Fe metal honeycomb is used because it is expected to have a small pressure drop and little memory effect from tritium contamination. For methane oxidization, a conventional Pd alumina catalyst is used. After sampling atmospheric tritium for a week, the water is recovered from the molecular sieves. The tritium concentration in the recovered water is measured with a low background liquid scintillation counter. The atmospheric tritium concentrations obtained by the automatic sampling system are consistent with the data of a manual sampling system.