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

Abstract

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/ Al 2 O 3 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 313 K 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 ½s À1 ¼ 5:59 Â 10 7 Â SV½h À1 Â exp À 67:7 ½kJ/mol R g T ;where the space velocity range was from 600 to 7,200 h À1 .

Development of Pt/ASDBC catalyst for room temperature recombiner of atmosphere detritiation system

“…The experimental flow-through system is shown in Fig. 1 [5]. The 12 m 3 tritium tank made of 316 stainless steel was prepared not to fluctuate the tritium concentration fed to the catalytic reactor.…”

“…Pt/ASDBC catalyst is more hydrophobic than SDBC due to the intended incorporation with hydrophobic alkyl-groups in the molecular structure. A feature of Pt/ASDBC catalyst was intended large and fine mesopores considering that pore diffusion is generally the rate-controlling step of hydrogen oxidation over catalyst at more than 373 K [5]. In the light of the feature, application of Pt/ASDBC catalyst to the isotope exchange reaction between hydrogen and water vapor has also been investigated.…”

Change in activity of catalysts for the oxidation of tritium during a fire event

“…The activity of HTO trapped in the HTO Trap 2 was determined with a liquid scintillation counter. The numerical procedures for evaluating the overall reaction rate constant were similar as previously described elsewhere [2,3].…”

“…The catalyst temperature was controlled by a heater wrapped the RTR/LTR with a PID temperature controller. The catalyst temperature in the RTR/LTR was directly monitored with a thermocouple [2]. Humidity in the effluent produced by tritium oxidation reaction in the RTR/LTR was measured with the hygrometer in the rear of the reactor.…”

“…A combined catalytic reactor and water absorber system has been applied to control the tritium release into the environment as low as reasonably achievable [1]. The oxidation performance of tritium both with hydrophobic Pt-catalysts for a room temperature reactor and with hydrophilic Pt-alumina catalysts for a low temperature reactor operated near 423 K has been systematically demonstrated [2,3]. The overall reaction rate constant for tritium oxidation with those catalysts was determined as a function of space velocity, hydrogen concentration in carrier, catalyst temperature, and water vapor concentration in carrier.…”