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Two types of pure-silica-core fibers (one low-OH, Al-jacketed, one medium-OH, polyimide jacketed) suitable for use as sensing fibers for Raman-scattering-based temperature measurements in nuclear environments have been subjected to gamma and fission reactor irradiation tests. Spectral attenuation measurements were performed between 500 and 1500 nm with samples kept at room temperature, 80 and 300/spl deg/C. The Al-jacketed fiber was developed for use under ionizing radiation and showed lower loss compared with the polyimide-jacketed fiber at room temperature under gamma irradiation. Both fiber types showed similar spectra at room temperature with the main part of the loss originating from a band tail extending from the ultraviolet. Thermal bleaching of the radiation-induced defects was found to be effective in both fiber types. At 80/spl deg/C the loss in both fibers was compounded of a band at 625 nm together with the band tail from the ultraviolet, which now had a strength several times lower compared with room-temperature irradiations. At 300/spl deg/C, both fibers exhibited similar low-loss spectra, except for the band at 625 nm which reached levels of approximately /spl sim/2000 dB/km at an accumulated dose of 2.8/spl times/10/sup 4/ Gy(SiO/sub 2/). In light of the experimental spectral findings, selection of suitable Raman-distributed temperature sensors for nuclear plants can be made.

The heat and radiation resistant cable for the use on the liquid metal cooled fast breeder reactor (LMFBR) has been newly developed. Stainless steel sheathed mineral insulated type cable has been usually used in the vinicity of the primary cooling circuit of LMFBR because of the harsh environmental condition in this area. Sometimes, this type of cable causes problems for its inflexibility in terms of installation. This newly developed cable (named M. Flex cable) consists of inorganic materials such as mica and glass, and the heat and radiation resistant organic materials such as polyimide for the insulation and stainless steel wire braid for the protection layer. Such tests as gamma irradiation test up to total dose of 1.4 × 1010R, flexibility test, and other tests, have been performed and results show that M. Flex cable has been satisfactory for the LMFBR applicaltion. And also, these results implied the applicability of this cable to the other fields than nuclear plants.