Patent Number: 045432333
Section: description

DETAILED DESCRIPTION The overall function of load pads is illustrated by FIGS. 1 and 2. In FIG. 1, a fuel assembly 1 is shown having a duct 2, this example being a six sided fuel assembly 1 and duct 2. In a section of the fuel duct 2, generally above the active fuel region of fuel assembly 1, one or more load pads 3 are installed. Each face of duct 2 has at least one pad 3, unless the fuel assembly happens to be located in a core position, especially the core perimeter, at which position external faces may not bear on adjacent assemblies and load pads 3 may not be required. FIG. 2 illustrates how load pads 3 bear on one another. A beveled surface 4 (see FIG. 3) may be provided to facilitate movement of fuel assembly 1 up and down during installation and removal from the reactor. Beveled surface 4 eliminates or minimizes edge 5 upon which obstructing interference can occur. Load pad 3 has a small groove 6 machined around the circumference of a stem 7 (refer to FIGS. 3 and 4). A spirally wound retaining ring 8 is assembled into machined groove 6. A plurality, preferably four oval slots 9 are machined through the flat pad portion; these slots 9 just nick the circumference of stem 7. Duct wall 10 has a hole 12 machined nearly through it; the hole 12 diameter is slightly larger than the diameter of load pad stem 7. A groove 11 is machined into the wall of hole 12 which will be aligned with groove 6 in stem 7. Also milled into duct wall 10 are oval slots 13 to match those slots 9 milled into the pad. Load pad 3 is installed into duct wall 10 by means of a special tool (see FIGS. 5, 6 and 13). This tool has fingers 14 which drop through slots 9 in the load pad 3 and around ring 8 in its free state. By utilizing a cam action, fingers 14 are then moved toward the center of pad 3, compressing ring 8 to a diameter slightly less than that of stem 7. Load pad 3 is then positioned into hole 12 of duct wall 10 with the tool holding ring 8 compressed. The cam action of the tool is then reversed allowing ring 8 to expand into groove 11 of duct wall 10. The tool is then removed. The spirally wound retaining ring 8 now engages both groove 11 in duct wall 10 and groove 6 in load pad stem 7, locking the two together. When installed, the forces which are applied between ducts 2 in the reactor are distributed over duct wall 10 by the broad surface of pad 3. Retaining ring 8 only has to prevent load pad 3 from falling away from duct 2. There are no appreciable forces in the direction and ring 8 has the capability of withstanding over 1000 pounds force. There are no conceivable forces that may break ring 8 into pieces, however, even if this were possible, a minimum of three breaks would be necessary before load pad 3 could be disengaged from duct wall 10, thus an inherent redundancy is provided. A feature of this design is that it allows inspection of ring 8 engagement through holes 9. If a problem exists, load pad 3 can be removed through the use of the tool and the problem corrected. The presence of hole 12 in duct wall 10 tends to weaken the duct, especially if load pads 3 on each face of the duct are located at a common elevation. To minimize this weakening effect, load pads on different faces of the duct may be located at different elevations. This requires a potentially complicated core loading plan because the load pads on adjacent faces must abut, and must therefore be at the same elevation. Slots 13 in duct wall 10 are shown in the drawings to extend only partially through duct wall 10 such that no coolant flow through these holes occurs. If load pad 3 is located above the active fuel region of the fuel assembly, it may be desired to machine slots 13 completely through duct wall 10 thus allowing coolant flow to pass outside the duct via slots 13 and 9. See FIG. 14. Once installed, load pad 3 as shown in the drawings is free to rotate, which will cause a loss of alignment between slots 9 and 13. Such rotation can be prevented by a variety of methods, including a pin and hole arrangement between duct wall 10 and load pad 3. FIGS. 7 through 10 are design drawings bearing dimensions relative to a preferred embodiment. The geometric shape of load pad 3 need not be circular but could obviously be of many shapes. The geometry of pad stem 7 and hole 12 also need not be circular, although a circular geometry here is appropriate to the use of ring 8. Substitution for ring 8 by other mechanical attachment means makes other geometries feasible.