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Report No.

Monitoring of airborne $$^{14}$$C discharge at RI facilities; A Comparison of collection and oxidation methods

Ueno, Yumi; Koarashi, Jun; Iwai, Yasunori; Sato, Junya; Takahashi, Teruhiko; Sawahata, Katsunori; Sekita, Tsutomu; Kobayashi, Makoto; Tsunoda, Masahiko; Kikuchi, Masamitsu

The Japan Atomic Energy Agency has conducted a monthly monitoring of airborne $$^{14}$$C discharge at the forth research building (RI facility) of the Tokai Research and Development Center. In the current monitoring, $$^{14}$$C, which exists in various chemical forms in airborne effluent, is converted into $$^{14}$$CO$$_{2}$$ with CuO catalyst and then collected using monoethanolamine (MEA) as CO$$_{2}$$ absorbent. However, this collection method has some issues on safety management because the CuO catalyst requires a high heating temperature (600$$^{circ}$$C) to ensure a high oxidation efficiency and the MEA is specified as a poisonous and deleterious substance. To establish a safer, manageable and reliable method for monitoring airborne $$^{14}$$C discharge, we examined collection methods that use different CO$$_{2}$$ absorbents (MEA and Carbo-Sorb E) and oxidation catalysts (CuO, Pt/Alumina and Pd/ZrO$$_{2}$$). The results showed 100% CO$$_{2}$$ collection efficiency of MEA during a 30-day sampling period under the condition tested. In contrast, Carbo-Sorb E was found to be unsuitable for the monthly-long CO$$_{2}$$ collection because of its high volatile nature. Among the oxidation catalysts, the Pd/ZrO$$_{2}$$ showed the highest oxidation efficiency for CH$$_{4}$$ at a lower temperature.



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