fuel assembly includes a plurality of control rod guide tubes 16 fixedly connected to the lower end fitting 18 and the perforated upper end plate 20 spacer grids 22 are welded to the guide tubes 16 and provide a support matrix for retaining a plurality of fuel rods 24 during operation of the reactor a coolant is pumped upward from below the support stand 12 up through perforations in the lower end plate 26 over the fuel rods 24 through the upper end plate 20 and out the upper alignment plate 14 through opening 28 the present invention provides an apparatus for holding the fuel assembly 10 down against the core support stand 12 to prevent the upward flow of the coolant from lifting the assembly off the stand in the preferred embodiment of the invention the fuel assembly 10 includes an actuating rod 30 movable with respect to the upper end plate 20 and the lower end fitting 18 the actuating rod 30 operates locking means 32 fig2 carried by the lower end fitting 18 whereby the assembly is locked to the shoulders 34 on the fuel alignment pins 36 formed as projections on the core support stand 12 fig2 shows the upper surface of the lower end plate 26 and fig1 and 2 show the relation of the lower end fitting 18 to the alignment pins 36 the posts 38 of the lower end fitting 18 rest on the base portion 40 of.