Patent Number: 042467837
Section: description

Referring now to the figures of the drawing and first, particularly to FIG. 1 thereof, it is seen that a spacer mesh of a spacer includes walls 1, 2, 3 and 4, which represent sections of crossed, upright webs. In these mesh walls are disposed resilient contact projections 5 as well as rigid contact projections 6. There is further shown the position of a fuel rod 20, which rests against the rigid contact projections 6 and slightly deforms the resilient contact projections 5, elastically. To ensure operationally secure clamping of the fuel rods 20 in the spacer meshes, the resilient contact projections 5 must supply definite contact pressures. In the conventional devices used up to now, the spring forces have been checked by indirect measurement and the clearance between the springs and the rigid contact projections (inscribed mesh diameter) was determined by limit or go-no go plug gages. The permissible range of this clearance was determined empirically. It was found, however, that this testing method is too inaccurate and is inherently full of uncertainties. Thus, the spread of the spring forces is not determined, the measurement of the clearance depends on the inspector and the spring force actually present cannot be determined; only its range of force can be given. The measuring device according to the invention, which is shown in the embodiment examples of FIGS. 2 and 3, serves for measuring these spring forces and thereby, the spring characteristic as well. The embodiment of FIG. 2 has no friction-dependent, mechanically movable parts. In addition, it is small and handy and can be handled separately from the indicating device. This device therefore also has little weight, so that from this aspect as well, interference with the measurement results is avoided. An added advantage is that this device can be placed into the spacer grid in any position, i.e., in the vertical position as well, so that canting the meauring device in the spacer mesh due to its own weight is therefore impossible. In FIG. 2, two rigid contact projections 6 are attached to the mesh wall 2 and a resilient contact projection 5 is attached to the mesh wall 1. For measuring the spring force of the projection 5, the measuring device includes a ground plug 11, the diameter of which corresponds exactly to that of the fuel rods 20 which are to be inserted into the spacer meshed. This plug is further provided with a slot 12 as in FIG. 2, for instance, by electron-beam machining or spark erosion, so that a flexible beam 13 remains. At the transition to the solid part of the plug 11, this flexible beam 13 is provided with at least one wire strain gage 17 which is connected through an amplifier 15 to a suitable indicating device 16. This, however, is within the state of the art, so that details are not shown for the sake of clarity. The plug 11 is fastened to a heat-insulating handle 14 which serves simultaneously, as shown, as a stop against the spacer grid, so that the point of contact between the spring or resilient contact projection 5 and the flexible beam 13 is thereby always accurately fixed. The slotting 12 of this flexible beam 13 is formed so that the contact point 18 of a resilient contact projection 5, not shown, which is shifted 90.degree. in the spacer mesh, comes to lie on the solid part of the plug 11 and therefore cannot falsify the indication. The measurement principle of this device is based on the fact that due to the contact of the resilient projections 5 with the flexible beam 13, the latter is slightly bent, This bend is in turn picked up electrically by the wire strain gage 17 and is made visible at the indicating device 16 through the amplifier 15 and an interposed conventional measuring bridge, not shown. The calibration of this device is very simple, since only the flexible beam 13 needs to be loaded with known forces at the contact point with the resilient contact projection 5. It has been found that this measuring device permits very reliable operation, and the measuring of the individual springs in the spacer meshes is accomplished very quickly. Since the handle 14 of the plug 11, through which the measuring leads are also brought out, is constructed as heat insulation, no falsification of the measured values through heat transfer from the operator to the measuring device proper is possible either. Since the plug 11 must always have the same diameter as the fuel rods 20 being used, it is necessary to have plugs 11 with the proper dimensions available for measuring different spacer geometries. These plugs can be made so that they are exchangeable in the handle 14 and with respect to the electronic evaluator by means of a mechanical coupling. Contrary to FIG. 2, the embodiment example according to FIG. 3 shows a hollow plug 21, in the interior of which the flexible beam 22 is fastened at one end. Wire strain gages 17 are again attached in the vicinity of this fastening point and the measuring lines are brought out through the non-illustrated handle which is similar to the handle 14 shown in FIG. 2. A radial pin 23 which protrudes to the outside through a hole 24 in the plug 21 is attached to the free end of this flexible beam 22 for making contact with the resilient projection 5. This embodiment is better protected against external influences than that according to FIG. 2. It can also be sealed, for instance, by means of an elastic rubber substance, so that it can also be used, for instance, under water. To further illustrate this device, it should be mentioned that the plug 11 or 21, respectively, has a diameter in the order of 10 mm, corresponding to the diameter of the fuel rods. The flexure of the flexible beam 13 or 22, respectively, at the point where the spring makes contact is in the order of 16 .mu.m. Instead of the wire strain gages, other force transducers can, of course, also be used, such as the piezoelectric type, for example. In conclusion, it should be mentioned that a measuring device of this kind can be used in all spacer types in which springs serve for centering fuel rods. The plugs 11 and 21, respectively, then only need to be adapted to the respective spacer geometry. Such measuring devices of course, can logically also be used for measuring the spring force in other equipment outside the field of nuclear power plant engineering, where a simple and reliable control of resilient parts is likewise required.