Fundamental Research on pretreatment process for Kr-85 recovery system

In the separation of radioactive rare gas from off-gas stream by cryogenic distillation systems, impurities such as nitrogen oxides, oxygen and hydrocarbons must be removed by a pretreatment process. In this study, an oxygen-hydrogen recombination reactor was employed for the simultaneous removal of oxygen and nitrogen oxides in off-gas. The removal of these impurities and the formation of ammonia were studied with palladium and ruthenium as catalysts. The concentrations of oxygen, nitrogen oxides, and ammonia at the outlet of the reactor were determined by galvanic cell method, Nessler's spectrophotometric method, and chemiluminescent method, respectively. The affects of catalysts, temperature, and space velocity on the efficiencies of the removal of these impurities have been examined under various experimental conditions. The experimental results show that it is necessary to choose the space velocity of less than 5,000 hr-1, and that palladium is more useful than ruthenium. It was also found that the conversion ratio of nitrogen oxides to ammonia increased in the presence of water. (Aoki, K.)