A typical embodiment of the invention provides a means for selectively inserting and withdrawing one or more fuel rods from a fuel element cellular grid structure. The transverse stubs on one side of a long, thin bar are turned through 90 DEG to extend across the gap between mutually perpendicular grid structure plates. The extreme ends of these stubs engage the adjacent portions of the associated plates that form part of the grid cells. Pressing the stubs against the plate portions through the application of appropriate force in a longitudinal direction relative to the bar deflects the engaged plates through a sufficient distance to enable fuel rods to be inserted into, or withdrawn from, respective cells. After rod insertion, the force applied to the bar is released to enable the plates to relax and engage the fuel rods. The bars are rotated once more through 90 DEG and withdrawn from the grid structure. A similar procedure is employed to withdraw fuel rods from the grid structure.
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