Review Reports on Wall Thickness Maintenance of Experimental Fast Reactor "JOYO" Secondary Pipe

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The reactor safety committee chairman of O-arai Engineering Center submitted review principles for the JOYO secondary pipe thickness maintenance condition, reflecting the secondary pipe break accident of Mihama power station No.3 of Kansai Electric Power Cooperation (9th. August 2004), A Specialist review committee for the JOYO secondary pipe thickness maintenance condition was established on 17th. August 2004. According the principles, the specialist committee reviewed following items based on explanations and documents of the Experimental Reactor Division, (1)Maintenance method of the secondary pipe thickness. (2)Maintenance and inspection results of the secondary-pipe thickness. Erosion-corrosion at inner wall of the JOYO secondary cooling loop pipe can hardly occur by the repetition of oxide formation, growth and peeling occurring in water environment, because the coolant of JOYO is not water but sodium. The maximum material loss in the secondary pipe is supposed to occur at the outer-surface of heat-transfer-pipe in the main air coolers due to contact of circulating air. Therefore, this committee paid attention to this portion for reviews. It was confirmed by the operator (Experimental Reactor Division) in periodical independent inspections that heat-transfer-pipe thickness was still larger than the minimum design value. Based on the carried review, the specialist committee has reported to the reactor safety committee that the maintenance method ((1)) was appropriate and the maintenance condition and inspection ((2)) were well for the secondary pipe.