Junichi Taniuchi

Room-Temperature Reactor Packed with Hydrophobic Catalysts for the Oxidation of Hydrogen Isotopes Released in a Nuclear Facility

A room-temperature reactor packed with hydrophobic catalysts for the oxidation of hydrogen isotopes released in a nuclear facility will contribute to nuclear safety. The inorganic-based hydrophobic Pt catalyst named H1P has been developed especially for efficient oxidation over a wide concentration range of hydrogen isotopes at room temperature, even in the presence of saturated water vapor. The overall reaction rate constant for hydrogen oxidation with the H1P catalyst in a flow-through system using a tritium tracer was determined as a function of space velocity, hydrogen concentration in carriers, temperature of the catalyst, and water vapor concentration in carriers. The overall reaction rate constant for the H1P catalyst in the range near room temperature was considerably larger than that for the traditionally applied Pt/Al2O3 catalyst. Moreover, the decrease in reaction rate for H1P in the presence of saturated water vapor was slight compared with the reaction rate in the absence of water vapor due to the excellent hydrophobic performance of H1P. Oxidation reaction on the catalyst surface is the rate-controlling step in the range near room temperature and the rate-controlling step is shifted to diffusion in a catalyst substratum above 313K due to its fine porosity. The overall reaction rate constant in the range near room temperature was dependent on the space velocity and hydrogen concentration in carriers. The overall reaction rate constants in the range of 1;000=T greater than 3.2 correlated to k overall[s−1] = 5.59 × 107 × SV[h−1] × exp (−67.7 [kJ/mol]/RgT), where the space velocity range was from 600 to 7,200 h−1.

Hydrophobic Platinum Honeycomb Catalyst to be Used for Tritium Oxidation Reactors

Abstract We have developed two types of hydrophobic platinum honeycomb catalyst to be used for tritium oxidation reactors. One is the hydrophobic platinum catalyst on a metal honeycomb. The other is the hydrophobic platinum catalyst on a ceramic honeycomb made of silicon carbide. The activity of these catalysts was evaluated with tritium. The effects of hydrogen concentration (0.02 to 1000 ppm) and water concentration (100 or 22000 ppm) in the gaseous feed on the activity were investigated. The fine platinum particles around a few nanometers significantly improve the catalytic activity for the oxidation tritium at a very small concentration. The hydrogen concentration in the gaseous feed slightly affects the overall reaction rate constant for hydrogen oxidation. Due to the competitive adsorption of hydrogen and water molecules on platinum surface, the overall reaction rate constant has the bottom value at the hydrogen concentration of 100 ppm with the dry feed gas. We have experimentally confirmed the activity of these honeycomb catalysts is as good as that of granular hydrophobic catalyst. The results support the hydrophobic honeycomb catalysts can be used for tritium oxidation reactors.