| 摘要 |
PURPOSE:To eliminate any moving parts and also to improve effectiveness of a spectro-shift operation by providing a variable orifice mean of which pressure loss coefficient depends on a flow rate of passing-through coolant, to an opening through which a part of effective flow being formed at a side wall of lower tie-plate leaks out to an outside of channel box. CONSTITUTION:A leak hole, for leaking out a part of effective flow of reactor core coolant to a gap zone, is provided on a surface 2 of lower tie-plate 4, and a variable orifice 11 is provided at the leak hole position. The orifice 11 is a round bar 31 attached to a ring 30 and the coolant flows through a gap 32 of the orifice. Accordingly, no moving part exists there. A boundary layer being formed on the surface of the round bar 31 during the coolant flows through the gap 32, splits from the surface of the round bar 31, at an outlet of the gap 32. This splitting position and an extent of splitting zone at a down- stream side of the position varies accordingly to a flow rate of the coolant which flows through the gap 32. Moreover, the splitting zone causes pressure loss at the place. In other words, the orifice 11 has a function to change the pressure loss of the orifice according to a Reynolds number of the orifice by utilizing a splitting phenomenon of the boundary layer.
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