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Fig. 2-12 Comparison of images taken with a conventional periscope, and the new, heat and radiation resistant, periscope

Remote handling tools are necessary for the inspection and maintenance of activated equipment in the vessel of an experimental fusion reactor like ITER. One such tool is a periscope for the observation of the inside of the reactor. We needed new technology to develop a periscope, longer than 15 m, which works at high temperatures under intense irradiation. We have developed a lead (Pb) glass including cerium oxide, and a silicon glass including hydroxide, for use in a lens which is resistant to high radiation doses. A periscope has been built using a combination of these glass lenses. We have also developed a support mechanism to automatically compensate for the expansion and contraction caused by the temperature changes. At high radiation doses (10 kGy/h), under which it is impossible to make observations using a normal periscope, the new periscope gives clear views even after 4,000 hours of operation (Fig. 2-12). There is no reduction in the accuracy of the optical axis, and no change in the focal quality. This technology will have spin-off benefits in a wide range of fields.

Reference K. Obara et al., Development of In-Vessel Viewing and Metrology System, Purazuma Kaku Yugo Gakkai-Shi, 73 (1), 42 (1997).

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