On-site irradiated fuel inspection in PWR plant

During the second annual inspection of Mihama Unit No.1 from March 1973, irradiated fuels were inspected on site by visual and sipping equipments. Visual inspection was performed with binocular, underwater TV and periscope. For the sipping inspection, combined wet/dry method was adopted because of its reliability and sensitivity which is very similar to NOK's method in Switzerland. The equipment consists of fuel chamber, gas circulating system and measuring system. Fuel is immersed in water in the fuel chamber. Nitrogen gas is circulated through the fuel chamber and gas sampler in order to have fission gas (Xenon-133) entrained in Nitrogen. Samples gas was analyzed by single and multi-channel analyzers which were set up to integrate the counts for energy range from 50 keV to 100 keV. Multi-channel analyzer was used to display energy spectrum between 0 keV and 975 keV. About 5 weeks after shutdown, the measurements gave adequate sensitivity. The basis for determining ''leaker'' is the increase in count rate well beyond the background. (auth.)