Application of optical fiber sensors to nuclear plants

Abstract

The utilization of optical fibers for sensing devices in nuclear facilities was pointed out to have a big problem due to the radiation induced loss. The feasibility of Raman Distributed Temperature Sensor (RDTS) has been studied. Calibration methods for the radiation induced errors have been demonstrated and their long term applicability has been examined experimentally. The principle of RDTS was illustrated, and the Raman scattered light due to spontaneous Raman scattering in optical fibers was pointed out to be consisting of two components, namely, Raman Stokes and Raman anti-Stokes components. Two calibration methods have been studied for the application of RDTS systems to nuclear power plant. One was for the calibration method using two thermocouples, and the other was for that based on the loop arrangement. In order to check the feasibility of the calibration method based on the loop arrangement, an experiment using a Co-60 gamma source has been carried out, and that of the calibration method has been demonstrated. The effects of the long term irradiation and the feasibility of the calibration methods using two thermocouples have been investigated by the experiments at the experimental fast reactor, JOYO. It was found that at the place where the radiation induced loss along the optical fiber is uniform, the calibration method using two thermocouples can be applied to nuclear plants.

原子力施設において検出器として光ファイバを利用する場合には、放射線誘導損失に起因する大きな問題を有していることを指摘した。ラマン分散型温度センサ(RDTS)の実現可能性を研究した。放射線誘導誤差に対する較正法を実証し、較正法の長期適用性を実験的に調査した。RDTSの原理を図示し、光ファイバ内の自発ラマン散乱に起因するラマン散乱光は2種の構成要素、すなわち、ラマン・ストークスとラマン・反ストークスから成ることを指摘した。原子力発電所へのRDTSシステムの適用について2種類の較正法を研究した。2つの熱電対を用いた較正法、およびループ配列に基づく較正法である。ループ配列に基づく較正法の実現可能性を調べるため、Co-60ガンマ線源を用いて実験を行い、この較正法の実現可能性を実証した。長期照射の影響と2熱電対を用いた較正法の実現可能性を実際の常陽実験高速炉で実験して検討した。光ファイバに沿って放射線誘導損失が均一な所では、2熱電対を用いた較正法は原子力発電所に適用可能であることが分かった。