Manufacturability evaluation of the triple wall SG tubes

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In order to evaluate the manufacturability of the triple wall tubes for the steam generators (SGs), which are designed for the simplified secondary sodium loop, various specifications of the triple wall tubes were constructed. We used SUS316 steel and evaluated the manufacturability of the 12Cr tubes, since it was estimated to be difficult to fabricate the ribs even on the SUS316 thin tubes. The following results were obtained from these results; (1)It was estimated that a thin wall tube made from 12Cr steel could be manufactured for the practical plant design, (2)The two kinds of the separate tubes, which had the spiral ribs and the straight ones and were installed between the inner and the outer tubes, were manufactured by the drawing-tube method. Those with ringed ribs were also manufactured by welding of ringed spacers, (3)It was estimated that 0.4mm height for the spiral ribs and the straight ones was almost limiting height in case of 1mm tube thickness, and the drawing-tube process did not affect the tube strength and the tube tolerances, and (4)The assembling loads of the inner tubes, the separate ones and outer ones were estimated to become the reasonable loads for the practical size of triple wall SG tubes. Triple wall SG tubes for vibration tests were designed and manufactured.They were made up of four kinds of ribes (spiral rib, straight rib, ringed rib and straight rib with narrow gap). In this study, the vibration tests were also planned for examining the actual behaviour of the triple wall SG tubes.