Monitoring of Airborne ¹⁴C Discharge at RI Facilities: a Comparison of Collection and Oxidation Methods

Abstract

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.