Fuel assembly and fuel spacer

Abstract

In a fuel assembly having fuel rods inserted into regularly arranged cells of a fuel spacer which keeps the fuel rods correctly spaced from one another and has spacer elements disposed in a plurality of stages in the longitudinal direction of the fuel rods, the fuel spacer comprises vanes formed on the cells in such a manner that each vane is bent from a cut formed in a part of the side wall of the cell. The vanes obliquely project into the corresponding spaces between adjacent fuel rods and allow a coolant flowing through the spaces and forming two-phase flows to generate swirling flows toward the fuel rods. The fuel spacer may alternatively comprise either thin-walled cylinders having built-in vanes or spiral vanes, which are fixed to the spacer that has not been subjected to any direct machining. Also disclosed is a fuel assembly provided with any of the above-described fuel spacers. The arrangement of the present invention enables, while assuring a sufficient strength for maintaining fuel rods in their correct position, the transfer of heat from the fuel rods to the coolant to be promoted so as to raise the allowable power level of the fuel assembly, and enables the void ratio to be lowered so as to increase the reactivity.