Importance of Simultaneous Combustion of Tritium and Hydrocarbons by Detritiation System in a Fire Event at Nuclear Fusion Facility

A detritiation system (DS) is required to remove tritium from the atmosphere of a nuclear containment in any extraordinary situations. Realization of a DS that does not require heating of a catalyst reactor for tritium oxidation and frequent switching operation of adsorption columns for tritiated vapor collection will greatly contribute to the improvement of fusion safety. Concerning the catalyst reactor, it has been demonstrated that tritium can be oxidized at room temperature without any heating by the developed hydrophobic catalyst. To achieve a high tritium conversion efficiency for detritiation, it has already been revealed that suppression of production of tritiated hydrocarbons by hydrogenation reactions as side reactions of tritium oxidation in a catalyst reactor is the key issue to be solved. We have to pay special attention to ethylene among hydrocarbons because ethylene is easily tritiated by reaction of hydrogenation. In this study, complete combustion of ethylene at room temperature in the catalyst reactor is proposed as a measure to suppress the formation of tritiated hydrocarbons. Catalytic combustion characteristics of hydrocarbons were obtained, and the change in the ignition temperature by a change in each design parameter of the catalyst was demonstrated. Concerning noble metal species, platinum is superior to palladium due to less susceptibility to water vapor. The smaller the particle size of noble metal is, the higher the activity is, but because it is more susceptible to water vapor, the particle size of noble metal can be optimized. It was suggested that there is an optimum value for the pore size of the catalytic support.