Online monitoring of tritium in water using uncladed plastic scintillating fibers

The present study focuses on applying uncladed plastic scintillation fiber for an online tritium monitor in water. Initially, the hydrophilicity of the fiber surface was enhanced with atmospheric pressure cold plasma, resulting in increased surface roughness and a reduction in water contact angle. Then, the uniformity of liquid flow within the fiber array was examined using the COMSOL simulation software while varying fiber spacing. A fiber spacing of 0.5 mm was found to be adequate for achieving uniformity of liquid flow. Finally, three types of flow cells were prepared based on differences in surface hydrophilicity and space between fibers, and these flow cells were used to assess online measurement performance for tritium in water. The results demonstrated that optimizing the surface hydrophilicity of the fibers contributed to an increase in count rate and reduced response time within the flow cell while adjusting the space between fibers improved the uniformity of liquid flow. The optimized flow cell yielded a radiation background count of approximately 400 cpm, an effective measurement volume of 100 mL, a detection efficiency of about 0.0139 %, and the minimum detection limit reached 16 Bq/mL when the measurement duration was 1 h (as the tritium water flow stabilized). These findings indicated that the system can monitor tritium online in nuclear wastewater and, importantly, has the potential to become a practical detection tool with further optimization. Moreover, the experiment provided valuable data on the count rate and energy spectrum during the flow of the scintillation fiber flow cell-from the inflow of tritium water to stabilization, through the evacuation of tritium water, to the rinsing with pure water. The analysis and interpretation of these data offered insights for developing and optimizing similar instruments in the future.