Mitigation of radiation load by trapping of tritium in off-gas during dry-processes

Although tritium gas is produced a small amount comparing to the other fission products, it should be controlled for long half-life, high residence time, high isotopic exchange rate and ease of assimilation into living matter. A demand for lengthening the life time of disposal site needs treatment of spent nuclear fuel to reduce the volume of high level radwaste. This study is for trapping the tritium gas during dry processes carried out in oxygen condition, having a potential of exposure into operators and environment. The experiments were performed into two different hydrogen concentration ranges, i.e. 1000 - 9000 ppm of high range of hydrogen concentration and 25 - 100 ppm of low range of hydrogen concentration. At high range of hydrogen concentration, H₂O conversion ratio at 400degC indicated above 98% up to 7000 ppm, and 100% at 450degC. All the results of H₂O conversion ratio at the low range of hydrogen concentration are represented close to 99%. Converted H₂O vapor was adsorbed at the Molecular sieve close to 100%. More than 98% of H₂O conversion ratio was attained up to 4 cm/s of linear gas velocity, whereas over 99% for the low range of hydrogen concentration. Some catalytic effect of ability of conversion hydrogen into H₂O on stainless steel was studied. (author)