2014 年 49 巻 1 号 p. 39-44
The Japan Atomic Energy Agency has conducted a monthly monitoring of airborne 14C discharge at the forth research building (RI facility) of the Tokai Research and Development Center. In the current monitoring, 14C, which exists in various chemical forms in airborne effluent, is converted into 14CO2 with CuO catalyst and then collected using monoethanolamine (MEA) as CO2 absorbent. However, this collection method has some issues on safety management because the CuO catalyst requires a high heating temperature (600℃) 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 14C discharge, we examined collection methods that use different CO2 absorbents (MEA and Carbo-Sorb E) and oxidation catalysts (CuO, Pt/Alumina and Pd/ZrO2). The results showed 100% CO2 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 CO2 collection because of its high volatile nature. Among the oxidation catalysts, the Pd/ZrO2 showed the highest oxidation efficiency for CH4 at a lower temperature.