Abstract: A thimble tube cap for replacing conventional thimble tube plugs (18) within thimble tubes (10, 110) of a nuclear reactor fuel assembly is fixedly mounted within a holddown assembly base plate (126) so as to cover the upper end of its associated thimble tube (110) fixedly mounted within the fuel assembly top nozzle adaptor plate (114). An axial through-bore (148) is provided within each cap for controlling the volume flow rate of coolant through the thimble tube (110). Each thimble cap includes a disc-shaped base portion (142) and an upstanding shaft portion (144) integrally formed therewith, an annular ledge or shoulder portion (146) being defined therebetween.

Abstract: A method of welding tabs projecting outwardly from grip straps in a fuel assembly grid to a control rod guide thimble positioned in a cell in the grid including providing a weld guide having openings therein which receive dimples on the strap when the weld guide is placed in a cell adjacent to the cell containing the control rod guide thimble. THe weld guide includes an opening which falls into alignment with a tab so that when a welding gun electrode is placed through the opening and into contact with a tab, the other electrode is automatically centered on its tab thus permitting accurate spot welding of the parts. To make a second spot weld on the same tab but at a point outwardly from the first spot weld, a second weld guide having an opening therein displaced a greater distance from a reference point on the weld guide, is placed in the same cell and the welding process repeated.