Miniature endoscope and method for the inspection of fuel elements

A device and a method for inspecting fuel elements of a nuclear reactor underwater are described. A remote controlled miniature endoscope forming part of an inspection device is introduced into the fuel element and the non-easily accessible parts of the fuel element located therein are inspected without having to disassemble the fuel element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown the construction of an apparatus 1 for inspecting a fuel element 3 . The inspection apparatus 1 substantially contains an endoscope 5 and a watertight, radiation-protected container 7 , which are carried by a mounting frame 9 . The mounting frame 9 is fixed to a position manipulator 11 , which is provided to move the endoscope 5 and the watertight container 7 up to the fuel element 3 . In this embodiment, the endoscope 5 has an intrinsically flexible end piece 13 B which is held in a center part 15 by a rigid part 17 , in this case a guide rail 17 . The endoscope 5 is coupled to the container 7 in a watertight manner via a flange 19 . The flange 19 is used to interchange the endoscope 5 and to couple it to devices accommodated in the watertight container 7 , which are described in more detail in FIG. 3 . For the purpose of inspection, the endoscope 5 , together with the watertight container 7 , is provided to be brought up to the fuel element 3 down to a water depth 21 via the manipulator 11 . All the necessary parts are accordingly protected against water and radioactive radiation 23 . The parts are at least an image receiving device 43 , an illumination device 45 ( FIG. 3 ) and at least one actuating motor 47 A, 47 B ( FIGS. 4, 5 ). The inspection apparatus 1 is therefore provided for the inspection of a region of the fuel element 3 , in particular a surface of a fuel rod 25 , or of another region of the fuel element 3 , for example a barely accessible region, as shown in FIG. 2 . A line 27 for controlling the endoscope 5 and the electrical power supply to the devices in the container 7 advantageously forms, in this embodiment, the single connection to a power supply device 29 and to a control device 31 ( FIG. 1 ). The latter are disposed, for example, at the rim of a fuel element storage basin of a nuclear reactor. Also advantageously disposed there is an image recording device and image display device 33 , so that the remote control of the endoscope 5 and the visual inspection of the same by service personnel can be performed from there. FIG. 2 shows two exemplary procedures for the inspection of barely accessible regions of the fuel element 3 , for example of a spacer 35 or of a bottom piece 37 . The inspection, for example, of a spacer cell 39 or a cell 47 of the bottom piece 37 is performed by the intrinsically flexible end piece 13 B of the endoscope 5 being bent into the corresponding cell 39 or 41 . Thus, for example, corroded surfaces can be made out or foreign parts can be found even in these barely accessible regions. FIG. 3 shows the endoscope 5 and the watertight, radiation-proof container 7 and also the devices accommodated in the container 7 in detail. It is again possible to see the lower part of the position manipulator 11 and of the mounting frame 9 which is fitted thereto and which carries the container 7 and the endoscope 5 . It is also possible to see, as in FIG. 1 , the line 27 for control and the electrical power supply, which leads upward to the control and power supply devices 31 , 33 , 29 above the water surface. In this embodiment, the endoscope 5 again has an intrinsically flexible end piece 13 B and in its center portion 15 is supported by the rigid part 17 . Furthermore, in this configuration, the endoscope 5 is coupled to the housing 7 via the flange 19 in order to interchange the endoscope 5 . The flange 19 is watertight, as is the container 7 , at least down to a depth of 10 m, advantageously down to at least 30 m. The flange 19 is also used to couple the endoscope 5 to the light source 45 , to the electronic image-receiving device 43 , an electronic camera 43 in this case, and to two actuating motors 47 B. The actuating motors 47 B are provided to bend the intrinsically flexible end piece 13 B of the endoscope 5 via a mechanical pulling device 51 B. For this purpose, the mechanical pulling device 51 B is connected to an endoscope objective 53 ( FIGS. 4, 5 ) at a front end 49 of the end piece 13 B of the endoscope 5 and is actuated via the actuating motors 47 B. A light guide 55 A for light leads away from the light source 45 . Together with a light guide 55 B for images, which opens into the electronic image receiving device 43 , the two light guides 55 A and 55 B are led as a bundle of individual fibers 57 as far as the endoscope objective 53 ( FIGS. 4, 5 ). In this way, the images supplied by the endoscope 5 are led to the electronic camera 43 and, the light discharged by the light source 45 is led to a front optical opening 59 ( FIG. 5 ) at the front end 49 of the end piece 13 B of the endoscope 5 . In addition to the container 7 , further protective apparatus or shields 61 ( FIG. 3 ) within the container 7 are used to shield against radioactive radiation 23 , to protect at least the light source 45 and the electronic camera 43 . A lead plate, for example, can be used as the shield 61 . Furthermore, the devices are disposed within the container in such a way that the most sensitive parts, the electronic camera 43 in this case, are located at the greatest distance from the radiation source, that is to say the fuel element 3 . As already mentioned, use is made here of, for example, of a xenon gas pressure lamp as the light source 43 , with a spectrum which is characterized by a temperature of about 6,000 Kelvin, that is to say similar to daylight. The transparent window belonging to the optical conductors 55 A, 55 B, 57 used to transmit the light from the light source 45 and the images to the camera 43 must accordingly be of a broadband configuration. Furthermore, cooling ribs 63 are preferably fitted to the housing 7 , at least in the vicinity of the light source 45 , and are used for better heat dissipation of the heat power produced by the light source 45 . According to the configuration in FIG. 3 , the guide rail 17 supports not only the center portion 15 of the endoscope 5 but, advantageously, also the fiber bundle 57 , continued in the housing, for the transmission of images and light. FIG. 4 shows, by way of example, an advantageous embodiment of an end piece 13 A of the endoscope 5 having an advantageous embodiment of an actuating device 67 A. The endoscope 5 with the end piece 13 A is enclosed by a rigid tube 69 , which is produced, for example, from metal or PVC material. In the embodiment shown in FIG. 4 , the endoscope 5 is closed at the front end 49 , but for this purpose contains a lateral optical opening 75 . Through the lateral optical opening 75 , light for illuminating a field of view 65 is intended to emerge, and through the opening 75 , the image produced by the endoscope 5 of a partial view, for example of the fuel element 3 , is intended to be picked up. Within the tube 69 , the bundle of individual optical fibers 57 is used for the transmission of both images and light. In this embodiment, use is further made of a lens 53 and a prism 73 as the endoscope objective. The lateral optical opening 75 functions as an objective aperture. If required, instead of the objective there may also be, for example, a zoom objective, in order to adjust the optical properties, such as depth of focus or enlargement of the endoscope 5 , in a variable manner. At another end of the endoscope 5 there is located the flange 19 , to be coupled to the watertight housing 7 . The flange 19 in FIG. 4 bears schematically illustrated lead throughs 58 for coupling the glass fiber bundle 57 , a mechanical pulling device 51 A inside and outside the watertight, radiation-proof housing 7 . In the embodiment of the mechanical pulling device 51 A illustrated in FIG. 4 , this is a rigid mechanical pulling device 51 A which, in the present example, is provided to rotate the end piece 13 A of the endoscope 5 with the endoscope objective 53 through an angle &thgr;. As FIG. 4 shows, the rotation about the axis of the rigid endoscope 5 through the angle &thgr; is effected by the actuating motor 47 A, as part of the actuating device 67 A. In this way, the field of view 65 of the endoscope 5 with a rigid, interchangeable end piece 13 A can be rotated, so that the viewing angle can substantially be varied by adjusting the rotational angle &thgr;. In a similar way, the actuating apparatus 67 A can also be used to tilt the rigid endoscope 5 . Given the aforementioned tilt by a tilting angle &thgr;, the viewing angle of the endoscope is likewise varied. FIG. 5 shows, by way of example, a beneficial embodiment of the endoscope 5 having the flexible, interchangeable end piece 13 B for the inspection of the fuel element 3 . A suitable actuating device 67 B for the flexible end piece 13 B is likewise shown. In this case, the flexible end piece 13 B is surrounded by a flexible hose 71 . This is preferably an intrinsically flexible PVC hose 71 or a metallic corrugated hose 71 . Furthermore, the endoscope 5 is closed off in a watertight manner by the hose 71 . In this embodiment, the flexible end piece 13 B carries at the front end 49 the front optical opening 59 . Through the optical opening 59 , the light led to the front end emerges, and the image produced by the endoscope 5 is picked up. The field of view 65 of the endoscope 5 with the flexible end piece 13 B therefore leads away from the front end of the endoscope. Disposed behind the front optical opening 59 of the endoscope 5 is the endoscope objective 53 , which is illustrated schematically here by a lens. This is followed by the bundle of individual glass fibers 57 , which are used for light guidance and image guidance. Also, guided in the intrinsically flexible hose 71 of the end piece 13 B of the endoscope 5 , in addition to the glass fiber bundle 57 , is the intrinsically flexible mechanical pulling device 51 B, which is fixed to the endoscope objective 53 . As opposed to the rigid mechanical pulling device 51 A, as illustrated in FIG. 4 , the flexible pulling device 51 B is used to bend at least the end piece 13 B of the endoscope 5 . It is therefore connected to the endoscope objective 53 at four points 56 to bend the end piece 13 B on all sides. The fixing points 56 are each located at one end of two Cartesian axes oriented at right angles to one another on the endoscope objective 53 . In a way similar to that shown in FIG. 4 , the flange 19 is also used in FIG. 5 to couple the endoscope 5 with the flexible end piece 13 B to the watertight, radiation-proof housing 7 or to interchange the endoscope 5 with the intrinsically flexible end piece 13 B. In addition, the flange 19 shown in FIG. 5 has suitable lead throughs 58 for coupling the glass fiber bundle 57 and the flexible mechanical pulling device 51 B to the devices inside the housing 7 . The advantageous configuration of the actuating device 67 B for the endoscope 5 with the flexible end piece 13 B is likewise illustrated schematically in FIG. 5 . In this case, the actuating device 67 B contains the flexible, mechanical pulling device 51 B to bend the end piece 13 B on all sides. The mechanical pulling device 51 B in this configuration contains four pull cords, preferably made of metal, of which in each case one pair is set by the actuating motor 47 B. Alternatively, configurations with two pull cords are also provided. The two cables of a pair are fixed to opposite sides of the endoscope objective 53 , in each case on one of the axes disposed in Cartesian fashion in relation to each other. If the cables of a pair are each adjusted by one of the two actuating motors 47 B by a distance S v and by a distance S h with respect to each other, this has the effect of tilting the objective about a horizontal or vertical axis, and this accordingly effects the bending of the end piece 13 B of the endoscope 5 . A further advantageous configuration of the inspection apparatus 1 for fuel elements is shown in FIG. 6 . The sketch shows the cross section of the intrinsically flexible end piece 13 B and, in schematic terms, the parts of an image production device 81 and of an illumination device 83 . The cross section of the end piece 13 B of the endoscope shows the intrinsically flexible endoscope sheath 71 and the cables 51 B, the light guides 55 A and the image conductors 55 B disposed along the endoscope axis, in section. Differing from the embodiments of the inspection apparatus previously shown, in particular of the endoscope 5 , an embodiment is illustrated here which, to bend the end piece of the endoscope on all sides, contains three cables 51 B and in which three separate glass fiber bundles serve as a light guide 55 A separate from the image conductor 55 B. The light guides 55 A are routed within the endoscope sheath 71 through the flange 19 (not shown here) as far as the light source 45 inside the container 7 . Accordingly, the image conductor 55 B is also routed to the image-receiving device 43 , likewise inside the housing 7 . The image receiving apparatus 43 is used to record an image 79 transmitted by the image guide 55 B. Likewise illustrated schematically in FIG. 6 is an eyepiece 77 , which is disposed between the image guide 55 B and image receiving device 43 and whose lens system is indicated schematically here by two lenses. Depending on the application, the eyepiece can advantageously be interchanged with a different eyepiece in order to optimize the field of view 65 , for example as regards the depth of focus or the focus. FIG. 7 shows, in schematic form, an exemplary procedure in the case of a method for the inspection of a region of the fuel element 3 , in this case the procedure for the inspection of the surface of fuel rods 25 inside the fuel element 3 . As already partly explained in FIG. 1 and FIG. 2 , for this purpose, the endoscope 5 with the intrinsically flexible end piece 13 A or 13 B carrying the endoscope objective 53 , together with the actuating device 67 A or 67 B, the illumination device 83 and the image production device 81 are brought up to the fuel element 3 under water. As shown in FIG. 7 , this can also be the endoscope 5 with a rigid end piece 13 A. In a second method step, the end piece 13 A is then guided up to a subregion 89 of the fuel element 3 in such a way that the subregion 89 comes into the field of view 65 of the endoscope 5 . This situation is recorded in FIG. 7 . The subregion 89 and further subregions 85 , which come into the field of view 65 of the endoscope 5 as a result of displacement of the end piece 13 A of the endoscope 5 along a vertical position 87 , using the position manipulator 11 , are then inspected in a third method step, the field of view 65 being illuminated by the illumination device 83 . FIG. 7 illustrates the rigid endoscope 5 with the optical aperture 59 at the front end. However, it is also possible for example for the rigid endoscope 5 with the lateral optical aperture 75 , as in FIG. 4 , to be used. In this case, as a result of rotation of the end piece 13 A of the rigid endoscope 5 , the viewing angle can be changed, which substantially predefines the direction of the field of view 65 , and thus the further subregions 85 of the fuel element can be inspected. In FIG. 8, a further beneficial alternative to the aforementioned third method step is shown schematically. In a similar way to the procedure explained previously, here the aforementioned third method step with the endoscope 5 with the intrinsically flexible end piece 13 B is sketched. Shown here is the inspection of the bottom piece cell 41 of the bottom piece 37 , which is not accessible to an inspection with the rigid endoscope 5 . However, since the endoscope 5 with the flexible end piece 13 B is used here, the barely accessible subregion 89 of the bottom piece is moved into the field of view 65 of the endoscope 5 by bending the end piece 13 B of the endoscope through an angle &phgr;. The further subregions 85 are subsequently moved into the field of view 65 of the endoscope 5 , and inspected, by curving and bending the end piece 13 B of the endoscope 5 by further bending angles &phgr;. In this case, the field of view 65 is illuminated by the illumination device 83 , not illustrated here.