Patent Number: 047175303
Section: summary

The invention relates to a process and a device for the remote underwater monitoring of a small-size component of a nuclear reactor, to check the state of the connection between this component and a structure, in which it is arranged in an almost inaccessible position. In nuclear reactors, such as pressurized-water which are nuclear reactors, there are small-size components which are located inside complex structures in almost inaccessible positions, and it is consequently difficult to monitor them. Furthermore, after remaining in the reactor for a certain period of time, these structures are contaminated by radioactive products, and it is necessary to monitor them and repair them by remote control and under water. Some small-size components in the internal equipment of a nuclear reactor may perform an extremely important function, and for reasons of safety, it is necessary to ensure that these components are perfectly intact. It is necessary, at all events, to make sure, when the nuclear reactor is being maintained, that it is impossible for any component inside the vessel to come loose from the structure to which it is fastened. As regards the upper internal equipment of the nuclear reactor, comorising in particular the set of guide tubes for the control rods of the reactor, the lower part of the guide tubes has centering pins which are intended to position themselves in holes provided in the upper plate of the reactor core. These centering pins are very important, because they determine the position of the guide tube for the control rods in relation to the assembly, into which the control rods will be introduced, and consequently the alignment of the control rods and guide tubes of this assembly. During the maintenance work carried out on the shutdown reactor, one of the operations involves extracting the upper internal equipment from the vessel and placing it on a stand located in the reactor pool, so that it can be checked and repaired. In particular, the state of the centering pins of the guide tubes and of the nuts fastening them to the lower flange of the guide tube is checked by introducing a television camera into the central part of the guide tube, to bring it as far as the base of the tube and level with the centering pins. The nuts of the pins, which project above the lower flange of the tube, can then be seen, and a check can be made to ascertain that they are present and perpendicular to the flange. However, even if the shank of the guide pin, on which the nut is screwed, is broken inside the flange, the nut can still remain in a correct position on the flange of the guide tube. A simple visual inspection does not always make it possible to check the state of the connection between the centering pin and the flange of the guide tube. The object of the invention is, therefore, to provide a process for the remote underwater monitoring of a small-size component of a nuclear reactor, to check the state of the connection between this component and a structure, in which it is arranged in an almost inaccessible position, this process making it possible to determine, in all instances, whether the connection between the component and its structure has been destroyed because of a fracture. To achieve this purpose, a means of injecting water at a pressure higher than 40 MPa and in the form of a straight jet of a diameter less than 3.times.10.sup.-3 m is introduced into the structure immersed in water, in the vicinity of the component to be monitored, the injection means is directed towards the component to be monitored, water is injected under pressure in such a way that the jet reaches the component, and the position of the component after the action of the jet is monitored by a televisual means. The invention also relates to a device for carrying out the monitoring process.