Local Flow Blockage Experiments in 37-Pin Sodium Cooled Bundles with Grid Spacers

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M.Uotan*; Haga, K.*; Kikuchi, Y.*; M.hori*

M.Uotan*; Haga, K.*; Kikuchi, Y.*; M.hori*

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A series of out-of-pile experiments were conducted on local temperature rises due to non-heat generating blockages in 37-pin bundles. In the central blockage experiment, the central 24 subchannels of the bundle were blocked with a 5 mm thick stainless-steel plate at up-stream end of a grid spacer. The blocked area was 27% of the total flow area. In the edge blockage experiment, a stainless-steel plate blocked 39 subchannels of a 1/2 edge part of the cross-sectional area. In both cases of the central and the edge blockage, the pin surface temperature attained a local peak in the grid spacer behind the blockage and decreased with the distance from the blockage. The mass exchange rate and the coolant residence time in the wake rigions were evaluated from the observed temperature rises. The mass exchange rate per unit interface area behind the edge blockage agreed fairly well with that behind the central blockage. The dimensionless coolant residence time was found independent of Reynolds number except in the low number range, and the value obtained in the edge blockage experiment was about 2.4 times as much as that obtained in the central blockage experiment. when experimental results were extrapolated to the reactor condition, an edge blockage of more than 30% might cause local boiling in the wake region, while a central one would not cause local boiling in any blockage ratio less than 60 %. The temperature rises in the blocked grid spacer were also discussed.