Transmission and mechanical characteristics of an image fiber under gamma-ray irradiation at high temperature

In the nuclear industries, a visual inspection is required to confirm the i ntegrity of the facilities and components. Recently, a silica-based image f iber has been used for visual inspection in the nuclear facilities. As the emphasis on visual inspection increases, an image fiber which can function in harsh environments, such as under high dose rate, narrow spaces and high temperature is required. It is thus necessary to study the transmission an d mechanical characteristics of a silica-based image fiber exposed to gamma -ray irradiation and elevated temperatures. We investigated the transmissio n loss characteristics and mechanical strength under gamma-ray irradiation at high temperature with the objective of identifying the causes of deterio ration of the image fiber. The induced loss of the transmission in the visi ble wavelength region was caused by E' center and NBOHC (non-bridging oxyge n hole center), and their annealing effect by thermal energy was confirmed. We believe that a high radiation resistant image fiber can be realized by improving its manufacturing condition, since it was identified that there w as close relation between the induced loss of transmission and the thermal history of the glass material during melt-fused process of image fiber manu facturing. The mechanical characteristics were also investigated. The mecha nical strength decreased by the deterioration of the primary coating. A sec ondary coating resistant to heat and radiation contributes to maintaining m echanical strength of the image fiber.