Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo. Development of a high radiation resistant fiberscope (Joint research)

The radiation characteristics of image fiber and light guide fiber were evaluated to develop a high radiation resistant fiberscope for the fast reactor in-vessel observation. It is known that a pure silica core fiber has a high radiation resistance and radiation resistance is influenced with impurities in silica. Moreover it is necessary to change the clad material of the light guide fiber because that of the current light guide fiber is acrylate, which is weak against radiation. Hence the improved fibers consist of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad. As a result of a gamma irradiation test, we confirmed that OH inhibited the generation of the precursor by gamma irradiation. About the clad material, we confirmed that the transmission loss of the fluorine-doped silica clad fiber was smaller than that of the acrylate clad fiber. About the mechanical strength of a fiber, we confirmed that there was no weakening the strength of the fiber and no exfoliation of the coating from the glass. In this study, we discovered the fiber which consisted of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad had a high radiation resistance and it is possible to observe using this fiber under 200 degrees C after 5x105 Gy irradiation. (author)