K. "Munakata

S. Kanjo

S. Yamatsuki

T." Uda

Y. Asakura

Y. Yokoyama

National Institute for Fusion Science (NIFS-Repository)

§2. Development of Catalyst for Oxidation of Tritium in Room Air Munakata, K., Yokoyama, Y., Kanjo, S., Yamatsuki, S. (Interdisciplinary Graduate School of Engineering Sci-ences, Kyushu University), Asakura, Y., Uda, T. (National Institute for Fusion Science) The catalytic oxidation and adsorption is the most conventional and reliable method for removing tritium that is accidentally released into the working area of fusion power plants. This air-cleanup system, which consists of catalyst and adsorption beds, should be the last barrier to the emission of tritium to the environment, and thus its design is an important issue for the safety of the fusion power plants. The catalysts used for oxidizing tritium (HT, T2) and tritiated methane (CH3 T) plays a key role in the air-cleanup system, and thus it is necessary to select or develop effective catalysts to oxidize such tritium species. In our previous work, the authors developed a catalyst, which consists of Pt and a MS4A adsorbent and tested its performance. This cataly::,t was designed and prepared to directly capture oxidized HT and CH3 T into its substrate (MS4A) through adsorption and isotope exchange reactions. However, its oxidation performance was not satisfactory. This time, the authors tried to improve the oxidation performance of such catalysts. In this work, several fabrication techniques were tested to improve the catalytic performance. A MS3A adsorbent was used for the catalyst substrate. A Pd solution was used in the fabrication of catalysts. The experiments were performed using a packed bed reactor. About I g of each catalyst was placed in the reactor. An Argon gas containing -------1000 ppm of H2, '""'--'I 000 ppm of CH4 and '"'-'20 % of 0 2 was introduced to the reactor. The values of SV (reciprocal of residence time) range from 17,000 to 22,000 h- 1; each catalyst was tested under the almost same condition. The temperature of the reactor was raised stepwise from ambient temperature to 400 °C. At each temperature, the conversions of H2 and CH4 were measured under steady state conditions. Figures I, 2 and 3 show the conversions of H2 and CH4 over various catalysts. H2 was almost completely oxidized at 150 oc over the catalysts (a)-a reference commercial Pd catalyst. CH4 was almost completely oxidized at 400 oc over this catalyst. However, the conversion of H2 was only 30 % at I 50 oc over the catalyst (b), which was developed in the previous work. Moreover, the conversion of CH4 was only I 0 % even at 400 °C. This result suggests that the catalyst developed in the previous work is not effective for oxidation of tritium species especially at lower temperatures. However, H2 was almost completely oxidized even at 100 oc over the catalysts (c), which is the catalyst developed in this work. Comparison with the result for catalyst (b) suggests that the catalytic performance is considerably improved. Additionally, it was also found that the oxidation performance for CH4 is low. Thus, there is a possibility that this catalyst can be used in a monitoring system of environmental tritium, which requires selective oxidation of HT and CH3T. 100 80 ~ 60 0 .E 1: 0 -~ 40 ;> 1: 0 u 20 0 0 80 ~ 0 60 ·.c r: 1: 0 .§ 40 ~ 1: 0 u 20 0 0 g]/ ~/ I I H2:114lppm 2 CH, 1138ppm • 02:22.17% Frow rate:380 cc/min (SV=21700 hr· ' ) j I Amount of catalyst: 0. 72g Bed diameter: 8.4mm Bed height: 19nun Bed volume: 1. 1 cc Bed density: 0 .69g!cc • I 100 200 300 400 Temperature [0C] Fig. 1 Conversions of H2 and CH4 over (a) 0.3%Pd/Al20 3 catalyst (G-68C) Fig. 2 Conversions of H2 and CH4 over (b) 0.5%Pt/MS4A catalyst ~ H2 1331.2 ppm CH, 1268.3ppm ' 02 22 .29% Flow rate : 392 cc/min (SV 16689.4 hr.1) Amount of catalyst : 0.83 g Bed heigh t: 50 mm • Bed vol ume : 1.41 cc Bed dens ity : 0.589 glee 100 200 300 400 Temperature [0C] Fig. 3 Conversions of H2 and CH4 over (c) 0.5%Pd/MS3A catalyst 273 

Development of Catalyst for Oxidation of Tritium in Room Air

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