Scale, mainly consisting of magnetite, flows on the secondary side of steam generators (SGs), causing the formation of concentrations of impurities on the tubesheet (TS), increasing the fouling of tube heat transfer, and blocking the broached egg crates (BEC) on the tube support plates (TSP). Accumulation of scale on the tubesheet forms environment in which impurities are highly concentrated on the tubes. And we have experienced tube degradation, in the past, from the concentration of impurities in feed water. The concentration of scale accumulation on the tubesheet is caused by the dry and wet phenomenon, etc. In Japan, the first tubesheet sludge lancing, via water jets, to prevent tube damage, was done at the Mihama-2 plant in 1975. And that is why this pile sludge becomes hard depending on time, removal made an effort toward removal with CECIL* (in bundle cleaning system) us very difficulty. However, sludge remained in localized areas, it had possibility of concentration. So that we improve the CECIL in these a purpose of removal, and we improved removal performance of the device. This paper introduces the improvement in sludge removal performance.
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