Abstract
Abstract A periscope-type viewing system has been chosen as a reference of the ITER in-vessel viewing system due to its wide viewing capability. According to the ITER research and development program, development of a radiation hard periscope has been conducted by the Japan Home Team in collaboration with the JCT. As an intermediate stage, a sub-scaled radiation hard periscope with a length of 6 m was fabricated and irradiated at a dose rate about 10 kGy h –1 . In this periscope, three types of radiation hard lenses made of alkaline barium glass, lead glass containing CeO 2 and OH doped synthetic quartz were adopted on the basis of the irradiation experiments on various glasses. The irradiation test results of the sub-scaled periscope show no degradation of the viewing performance up to the accumulated dose of 50 MGy, while a standard-type (non-radiation hardness) periscope becomes invisible after 2 h irradiation. Based on this, a full-scale radiation hard periscope with a length of 15 m was fabricated and tested. As a result, it has been verified that the developed 15-m-long periscope has sufficient viewing capability and the focal adjusting mechanisms are capable of accommodating thermal expansion due to high temperature operation up to 250°C.
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