Long-term analysis of 14CO2 measurement using mid-IR cavity ring-down spectroscopy for nuclear power plants

Carbon-14 (C-14) is a radioactive isotope that is easily combined with living organisms and has a long half-life time, requiring continuous monitoring. In a nuclear power plant, it is necessary to monitor the concentration of C-14 generated during the power generation process, and strict management is required, especially in the case of carbon-14 dioxide (14CO2) emitted to the outside as stack gas. In this study, a concentration measurement system of 14CO2 using a mid-infrared (mid-IR) range cavity ring-down spectroscopy (CRDS) system was established. In the mid-infrared region, carbon dioxide (CO2) has a strong absorption spectrum centered at a wavelength of 4.6 μm. This strong absorption allows for the measurement of CO2 content with high sensitivity. To evaluate system performance, we measured 12CO2 absorption spectrum that is close to 14CO2 absorption. The measured sensitivity was 50 ppt with 1000 s averaging based on noise equivalent sensitivity and long-term operation analysis was performed over 2 h for use in actual nuclear power plants. This technology will a be promising alternative to liquid scintillation counting (LSC) which is currently used for C-14 measurement in nuclear power plants.