Feasibility Study on One-Dimensional Dose Rate Distribution Measurement Using Fiber Noise Data from the Fiber-Optic Radiation Dose Rate Monitoring System

Abstract

Real-time dose-rate monitoring system under the high dose-rate situation is required for the decommissioning of the Fukushima Daiichi Nuclear Plants to remove the debris remaining inside the plants. We have proposed a dose-rate monitor consisting of a scintillator, over 100-m long optical fiber and CCD spectrometer. Some noises with a dominant-emission wavelength band of below 550 nm originating from the optical fiber itself must be separated from the scintillator emission light in 650-1000 nm, which is used as signal data, up to now. In this paper, we investigated if the noise region defined as below 550 nm is available for the position estimation of the hot spot through the fiber. The intensities of the noise emission or absorption band of such fiber-emission spectra are expected to depend on the hot-spot position through the fiber, and we demonstrated such dependence, “one-dimensional dose-rate distribution”, with a 20 m-long optical fiber and CCD spectrometer. Two types of optical fibers (High OH and Low OH) were tested under several length conditions of the fiber from the CCD spectrometer to 60Co source. The results of the emission spectra showed the intensity ratio of absorption to maximum intensity peak decreased as such length condition increased. We found that fiber noise is available for the position estimation for the hotspots (debris).