Patent Number: 046559930
Section: summary

The invention relates to a method for locating defective fuel rod cladding tubes within fuel rod bundles combined to form complete fuel assemblies of water-cooled nuclear reactors, which includes moving probes equipped with at least one ultrasonic test head between the fuel rod cladding tubes, and placing a manipulator for moving the probes on parts of a device disposed within a fuel assembly storage pit. Such a method is known from the publication "Tagungsbericht der Jahrestagung Kerntechnik 1980" (Proceedings of the Annual Nuclear Engineering Meeting 1980), pages 827 to 831, of the Deutsche Atomforum e.v. (German Atomic Forum), Bonn, Germany. However, nothing is stated therein with respect to the interaction of the fuel assembly and the apparatus for locating the cladding tubes. Apparently, only the successful performance of the method of insonification was of interest therein. It is accordingly an object of the invention to provide a method and apparatus for locating defective fuel rod cladding tubes of water-cooled nuclear reactors which overcomes the disadvantages of the heretofore-known methods and devices of this general type, and with which the insonification method can be carried out simply and reliably. With the foregoing and other objects in view there is provided, in accordance with the invention, a method for locating defective fuel rod cladding tubes of a water-cooled nuclear reactor within fuel rod bundles combined to form complete fuel assemblies disposed in a water-filled fuel assembly storage pit, including a mooring, a carriage disposed on the mooring, a manipulator disposed on the carriage and having a water proof space disposed therein, driving elements of the manipulator disposed in the water proof space, probes disposed directly in the water of the pit and connected to the driving elements, at least one ultrasonic test head disposed on each of said probes, and a lifting device for holding the fuel assemblies, which comprises: centering a fuel assembly to be tested on the mooring with the lifting device, moving the carriage into a test position, and transmitting motion cycles of the driving elements in the water proof space to the probes in the water of the pit for moving the probes and the test heads between the cladding tubes. An advantage of this process is that the fuel assembly which is about four meters long is held reliably and always occupies a constant position relative to the carriage carrying the manipulator. Furthermore, an advantageous separation of the drive elements which must be accomodated in a water proof manner, and the desired probe motion, are obtained. Further in accordance with the invention, there is provided a method for locating defective fuel rod cladding tubes of a water-cooled nuclear reactor within fuel rod bundles combined to form complete fuel assemblies disposed in a water-filled fuel assembly storage pit, including a receiving container for receiving a fuel assembly to be tested, a bracket, a manipulator disposed on the bracket and having a water proof space disposed therein, driving elements of the manipulator disposed in the water proof space, probes disposed directly in the water of the pit and connected to the driving elements, and at least one ultrasonic test head disposed on each of said probes, which comprises: securing a fuel assembly to be tested in the receiving container in a vertical position, locking the manipulator in a test position on the bracket, and transmitting motion cycles of the driving elements in the water proof space to the probes in the water of the pit for moving the probes and the test heads between the cladding tubes. The combination of the manipulator with a conventional repair station permits acceleration of the fuel assembly exchange process and therefore leads to a gain in the availability of the nuclear power station. In accordance with another mode of the invention, there is provided a first slider in the water proof space connected to the driving elements, a first lever linkage in the water proof space connected to the first slider, a second lever linkage in the water of the pit connected to the first lever linkage, and a second slider connected to the second lever linkage, the probes being supported by the second slider, and the method includes moving the first slider linearily in X and Y-directions with the driving elements, converting the linear motion of the first slider into rotary motion with the first lever linkage, transmitting the rotary motion of the first lever linkage in the water proof space into linear motion in the water of the pit with the second lever linkage, and transmitting the same linear motion of the second lever linkage to the second slider. By taking these measures, the linear motion starting from the driving elements which are accomodated in a water proof manner, is transmitted to the probes to be moved in the water of the fuel assembly storage pit, with the interposition of a rotary motion and without causing sealing problems. In order to carry out the method there is provided an apparatus for locating defective fuel rod cladding tubes of a water-cooled nuclear reactor within fuel rod bundles combined to form complete fuel assemblies, the fuel assemblies being disposed in fuel assembly storage racks in a water-filled assembly storage pit, and the fuel assemblies having bases, comprising a mooring, a plurality of pins connected to the mooring and matchable to the dimensions of the upper surface of a storage rack for securing the mooring, a centering receptacle with a variable centering dimension disposed on the mooring for contacting the base of the fuel assembly on two opposite sides thereof, a carriage movable on the mooring between two positions, a manipulator disposed on the carriage, the manipulator having a supporting base plate and a cover hood defining a water proof space therebetween, driving elements disposed in the water proof space, means connected to the driving elements and passing through the base plate for converting linear motion of the driving elements into rotary motion, probes disposed directly in the water of the storage pit and connected to the motion converting means, and at least one ultrasonic test head disposed on each of the probes, for insertion between the cladding tubes. In accordance with another feature of the invention, the mooring includes a base plate having T-shaped slots formed therein, and the pins are in the form of sliding blocks movable and lockable in the slots. Therefore, the matching of the bolt spacings to different storage rack constructions is provided in a simple manner. In accordance with a further feature of the invention, the mooring includes another base plate and the centering receptacle includes an abutment fastened to the other base plate, an eccentric shaft opposite the abutment, a rocker disposed on the shaft for moving the shaft by remote control, and a stop disposed on the shaft for limiting motion of the shaft. Besides the variability of the centering receptacle, a particular advantage is seen in the fact that the highest point of the eccentricity cannot be exceeded because of a stop. In accordance with an added feature of the invention, the centering receptacle includes a guide and jaws movable along the guide in opposing directions. In this way, the opening of the centering receptacle can be better adapted to different fuel assembly dimensions. In accordance with an additional feature of the invention, the mooring includes another base plate and tracks fastened to the other base plate for guiding the carriage, the first-mentioned base plate of the manipulator having dowel pins protruding outwardly therefrom, the dowel pins being screwed into dowel holes formed in the other base plate, and including a remote control linkage and/or a hydraulic/pneumatic cylinder for moving the carriage. In accordance with again another feature of the invention, there are provided means connected to the manipulator for admitting compressed air to the water proof space raising the pressure of the water proof space above the water pressure in the storage pit, and means connected to the manipulator for indicating a leak in the water proof space. This is done so that no water can penetrate into the water proof space of the manipulator through leaky supply lines. In accordance with again a further feature of the invention, the motion converting means includes a flange passing through and bolted to the base plate of the manipulator, a hollow shaft with a free end and a solid shaft with a free end both being coaxial with the flange, a first lever connected to one of the free ends in the water proof space, a second lever connected to the other of the free ends outside the water proof space, a third lever articulatingly connected to the first lever, a fourth lever articulatingly connected to the second lever, the first and third levers forming a lever linkage in the water proof space in the form of a mirror-symmetrical parallelogram with a first fixed point or fulcrum in the water proof space, the second a fourth levers forming another lever linkage outside the water proof space in the form of another mirror-symmetrical parallelogram with a second fixed point or fulcrum outside the water proof space, a first slider connected to the first fixed point for executing linear driving motions, and a second slider connected to the second fixed point carrying the probe. Due to the coaxial disposition of the hollow and the solid shafts, the magnitude of the error in the transmission of the motions is kept small. In accordance with again an added feature of the invention, there are provided two ball bushing spindles connected to the first slider for moving the first slider, and two stepping motors each being connected to a respective one of the spindles. The carriage which forms the fixed point or fulcrum of the lever linkage disposed in the water proof space is moved by two ball bushing spindles and the stepping motors. The travel distances given by the stepping motor are thereby transmitted without play. In accordance with a concomitant feature of the invention, there is provided a force pickup associated with the second slider for protecting the probes against run-on motions thereof. There is also provided another apparatus for locating defective fuel rod cladding tubes of a water-cooled nuclear reactor within fuel rod bundles combined to form complete fuel assemblies disposed in a water-filled fuel assembly storage pit, the fuel assemblies having bases, comprising a receiving container holding a fuel assembly to be tested in a vertical position, the container having a lower edge, the cladding tubes associated with the base of the fuel assembly having a portion thereof protruding beyond the lower edge of the container, a bracket attached to the storage pit, a manipulator locked on the bracket in a test position, the manipulator having a water proof space disposed therein, driving elements disposed in the water proof space, probes disposed directly in the water of the storage pit and connected to the driving elements, and at least one ultrasonic test head disposed on each of the probes for insertion between the cladding tubes at the portion of the cladding tubes protruding beyond the lower edge of the container. 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 method and apparatus for locating defective fuel rod cladding tubes of water-cooled nuclear reactors, 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.