Patent Number: 042467837
Section: summary

The invention relates to a measuring device for determining and checking the spring force of the resilient spacer projections that are set into spacer grids for nuclear reactor fuel assemblies and which push the fuel rods surrounded by each spacer mesh against, usually, two oppositely disposed rigid spacer projections. Nuclear reactor fuel assemblies generally include a multiplicity of fuel rods disposed parallel to each other which are held at the desired nominal distance from each other by spacer grids. These spacer grids, in turn, are normally constructed from crossed sheet metal webs. The meshes formed thereby surround one fuel rod each. For centering this fuel rod, resilient and rigid contact projections are provided in the respective mesh, where normally, as seen in the axial direction of the fuel rod, a resilient contact projection in one spacer wall is disposed opposite two rigid contact projections in the spacer wall parallel thereto. This method of centering not only permits easy insertion of the fuel rods into the spacer meshes but, during the operation of the reactor, also ensures maximum freedom from vibration of the fuel rods, around which the reactor coolant flows with high velocity. The resilient contact projections are of particular importance here. Their spring force, in addition to the accuracy of the physical dimensions, must be constant within narrow tolerances, so that the above-mentioned functions of the spacer grid remain assured, particularly with respect to the vibration behavior. The problem therefore arose to overcome the disadvantages associated with the previously used inaccurate and difficult to use measuring methods and to find a simple-to-operate measuring device to be used, on the one hand, during the manufacture of the spacer grids and, on the other hand, for checking spacer grids already subjected to reactor operation, which allows measurement and checking of the spring force of the resilient contact projections. It is therefore an object of the invention to provide a spring-force measuring device which overcomes the hereinaforementioned disadvantages of the heretofore known devices of this general type. With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for measuring the spring-force of resilient spacer projections set into spacer grids of nuclear reactor fuel assemblies to push fuel rods surrounded by spacer meshes against at least two oppositely disposed rigid spacer projections, comprising a force measuring plug having a diameter equal to the diameter of a fuel rod to be fixed in the spacer grid, and a flexible beam integral with the force measuring plug, the flexible beam, having a free end in contact with a first resilient spacer projection to be measured, and another end firmly connected to the force measuring plug and having at least one wire strain gage disposed thereon. In accordance with another feature of the invention, the flexible beam is formed by a stress-free slot formed in the force measuring plug. In accordance with a further feature of the invention, a second resilient spacer projection is disposed at a 10.degree. shift from the first resilient spacer projection in the spacer grid, said slot forming the flexible beam being formed step-like whereby the second resilient spacer projection contacts the force measuring plug and not the flexible beam. In accordance with a concomitant feature of the invention, the force measuring plug is hollow and has a lateral hole formed therein, the other end of the flexible beam being centered within the hollow force measuring plug, and including a pin disposed on the free end of the flexible arm extending radially through the lateral hole, the pin having a rounded end contactable with the first resilient spacer projection. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a spring-force measuring device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.