| 摘要 |
A BWR fuel assembly having an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, and a hollow central water cross extending through the outer flow channel and composed of respective pairs of spaced apart sheet members interconnected together at their outer and inner ends so as to define an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly and to the outer channel so as to divide the array of fuel rods into a plurality of fuel rod subassemblies, includes features which improve structural and hydraulic characteristics as well as CHF characteristics. The features which improve structural and hydraulic characteristics relates to closures in the form of perforated plates connected across the bottom and top ends of the sheet members of the water cross. The plates have respective holes sized so as to limit the outlet of the water cross to an open area less than the open area of its inlet so as to distribute hydraulic losses between its inlet and outlet in a way which maintains a positive pressure gradient in the subcooled moderator flow through the water cross inner flow channel relative to the coolant/moderator flow through the fuel rod subassemblies in the outer flow channel. The features which improve CHF characterisitcs relate to a series of holes defined at the same axial height in the sheet members of the water cross nearer to the top outlet ends than the bottom inlet ends of the adjacent fuel rod subassemblies for supplying a portion of the subcooled moderator flow from the inner flow channel in the water cross to the outer flow channel surrounding the fuel rods.
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