Abstract: A device for relieving thermally induced stresses developed in a nuclear fuel assembly during reactor heatup is disclosed herein. The device generally comprises a stress relieving fastener capable of connecting a fuel assembly top nozzle, which may be stainless steel, to a threaded stud, which may be Zircaloy. The stud is attached to a fuel assembly channel. The fastener includes a threaded nut having a deformable portion for relieving thermally induced stresses developed in the stud by the differential thermal expansion of the top nozzle and stud. In a first embodiment of the nut, the deformable portion comprises a circumferential, deformable ridge which is substantially recessed from the marginal edge of the nut and which is disposed on the bottom most surface of the nut. The ridge contacts the top nozzle when the nut threadedly engages the stud. A second embodiment of the nut is similar to the first embodiment except that the deformable ridge is disposed flush with the marginal edge of the nut.

Abstract: A tool (30) for facilitating insertion or removal of a C-shaped spring clip in a burnable poison rod, or the like, includes an outer member (38) secured to a front handle (32) and an inner member (40) extending through the outer member and the front handle which is connected to a coaxial rear handle (34). The handles (32, 34) are interconnected for relative rotation by means of a set screw (64) and circumferential groove (56). The distal ends of the inner and outer members (38, 40) are notched to receive the spring clip and engage it for compression. Provided between the handles (32, 34) is a locking and release assembly (42) and an adjustable positioning ring (58) by which the spring clip can be compressed, locked in compressed condition for insertion, and then released in the desired position before withdrawing the tool.

Abstract: A nuclear fuel rod and a device for use within the rod cladding to maintain the axial position of the fuel pellets stacked one atop another within the cladding. The device is initially of a smaller external cross-section than the fuel rod cladding internal cross-section so as to accommodate loading into the rod at preselected locations. During power operation the device responds to a rise in temperature, so as to permanently maintain its position and restrain any axial motion of the fuel pellets.