Applications of plastic scintillator fibers for the decommissioning of nuclear facilities

Morishita, Yuki   ; Abe, Tomohisa ; Sasaki, Miyuki ; Yamada, Tsutomu*; Nakasone, Takamasa*; Sanada, Yukihisa   

Accurate and rapid measurement of beta surface contamination is essential during the decommissioning of nuclear facilities. However, conventional Geiger Muller (GM) survey meters have limited detection areas and cannot measure contamination inside piping, resulting in significant labor and measurement inefficiency. In this study, we developed several plastic scintillation fiber (PSF) based detectors designed for wide-area surface monitoring, in-pipe contamination measurement, and drainage-channel monitoring. The PSF enables radiation detection along its entire length, allowing large-area scanning and insertion into narrow spaces. For surface measurements, a 10-m PSF arranged in a zigzag configuration was mounted under a cart, enabling efficient mapping of beta contamination over asphalt floor surfaces in Fukushima (demonstration up to 5 m 5 m). For piping applications, thin and flexible PSF probes were developed, enabling direct insertion into pipes with an inner diameter of 8 mm and achieving detection limits below the regulatory threshold of 4 Bq/cm; within one minute. Additionally, a waterproof PSF system was developed for monitoring radioactive contamination in drainage channels and successfully detected temporal fluctuations, including rainfall-induced increases in radioactivity. Overall, the developed PSF systems provide practical, versatile, and highly efficient alternatives to conventional survey meters for contamination monitoring in nuclear decommissioning environments.