Fuel assembly

In a fuel assembly, a fuel rod spacer comprises an outer frame capable of being contained in a channel box, a great number of cells connected with each other and arranged in a raw in the outer frame and having a plurality of inward protrusions, and springs disposed to the walls of the cells in adjacent with each other for urging fuel rods to the side of the inward protrusion. A coolant guide is formed at a portion of the cell so as to direct the flow of coolants to the fuel rod. Centrifugal force is applied by the coolant guide to the coolant stream in the spacer, and droplets having greater weight than steams are scattered to the periphery to be blown to the surface of the fuel rod. The thickness of the liquid membrane on the surface of the fuel rod can be increased to prevent burning loss of the fuel rod and increase the critical power. That is, thermal margin is improved and reactor power is increased by forming a bent portion bent on the side of a region of great flow rate and deforming a portion of a cell so as to direct the stream of the coolants toward the fuel rod. (N.H.)