Patent Number: 
Section: description

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 6 thereof, there is shown a reactor core, indicated by the reactor pressure vessel 64 together with the fuel elements 65, 66. The reactor core is located below a water level 60 of a reactor pool 61 which is connected to a storage pool 63 via a channel 62. A loading machine 70 is movable through the use of a carrying structure 67. This loading machine carries a hollow mast divided into two parts 71, 72 which are provided parallel to one another and which are movable relative to one another in a horizontal plane and which contain their own devices for gripping, raising and lowering. These devices are illustrated symbolically in each case as a cable assembly with lifting drum 74 and with a hook 73 as a gripper. In a first step A, the loading machine is brought over the reactor core and two fuel elements 65, 66 are simultaneously or successively gripped and raised into the parts 71, 72 of the mast. If the fuel elements are closely adjacent to one another, the two mast parts are preferably in a first end position 70a, in which they form a hollow mast open at the bottom, but virtually closed laterally. It will be assumed, here, that the fuel elements are subsequently to be inspected visually and, in this case, to be rotated. This is illustrated by position 70b: the spacing of the two mast parts together with the fuel elements 65, 66 is increased and at least one mast part is rotated into a longitudinal axis. In this position, each individual fuel element can be lowered and be inspected outside the mast. In order to transport the fuel elements into the storage pool 63, preferably the first end position 70a of the two mast parts is resumed (Step C). The loading machine can be moved into this position through the water-filled channel 62 quickly and without putting the fuel elements located in its mast at risk (Step D). When the loading machine is brought over the storage rack 75 in the storage pool 63, a relative movement of the two mast parts causes their mutual spacing to be enlarged to the extent desired for their storage (Step E). Finally, in their other end position 70c (wide position), the fuel elements are lowered again, that is to say they are removed from the mast (Step F). In principle, a step sequence A, E, D, F is also possible. In the same manner, two fuel elements may also be moved out of the storage rack into the reactor core, in which case a reduction in the relative spacing takes place between the first step (raising of the fuel elements out of the storage rack into the two mast parts) and the last step (lowering of the fuel elements into the reactor core). Since the fuel elements are often slightly bent in the reactor pressure vessel, fuel elements can often be drawn out of the reactor core or inserted into the reactor core only when they are at the same time rotated. It may happen, for example, that an irradiated fuel element which is still usable and is temporarily set down in the storage rack has to be rotated through xe2x88x9290xc2x0, +90xc2x0 or 180xc2x0 (Step B in the diagram of FIG. 6). FIG. 1 is a diagrammatic illustration of a loading machine for handling of fuel elements. This loading machine has essentially a movable bridge 1, such as is installed in reactor buildings. In the following, a pressurized water reactor will in particular be considered here. The direction of movement of the bridge 1 leads into and out of the plane of the drawing sheet. A trolley 2 is located on the bridge. This trolley 2 is movable in the geodetically horizontal direction at right angles to the bridge 1. Located on this trolley 2 is an operating platform (not illustrated) from which the loading machine can be operated. Furthermore, a guide mast 3 is mounted rotatably about its mid-axis on the trolley 2. A centering bell 4 is located in the guide mast 3. Within this centering bell 4 there is a double gripper which has an outer fuel element gripper 5 and an inner control element gripper 6. Above a frame 2.1 of the trolley 2 are located lifting mechanisms 7 which are provided on a lifting mechanism linkage 7.1 connected to the guide mast 3. FIG. 2 is a cross sectional view of the guide mast 3, together with the centering bell 4 located in the guide mast 3 and with two fuel elements 8a, 8b. The guide mast 3 is divided in the vertical direction at the points 3.1. In other words, the guide mast is composed of two halves 3a, 3b of a tube divided in the axial direction. The centering bell 4 has a rectangular cross section and is divided vertically at the points 4.1 according to the division of the guide mast 3. Each of the portions 4a, 4b of the centering bell 4 is dimensioned in such a way that a fuel element Sa, 8b can be received in it. For a stable guidance of the centering bell 4 in the guide mast 3, the guide mast has angle irons 3.2 along its longitudinal direction. Angle irons 3.2 located diagonally opposite one another carry a roller guide 3.3. Guide wheels 4.3 configured as rollers engage with sufficient slip into these roller guides 3.3. The axes of rotation of these guide wheels 4.3 are perpendicular to the surface of the angle irons 3.2 which carries the roller guide 3.3. The guide rollers 4.3 are mounted on a virtually trapezoidal appendage 4.2 of the centering bell 4, the appendage largely overcoming the spatial distance between the centering bell wall and the angle iron 3.2. Located opposite these virtually trapezoidal appendages 4.2 are further trapezoidal appendages 4.4 of the centering bell 4. On their side adjacent to the angle iron 3.2, these appendages 4.4 have running rollers 4.5, the axis of rotation of which is oriented parallel to the adjacent surface of the angle iron 3.2. A running roller 4.6, which rolls directly on the inner wall of the guide mast 3, is in each case mounted on the outer wall of the centering bell 4, on the two remaining free outer sides of the centering bell 4. The fuel elements 8a, 8b or 8 (FIG. 3) are received in each part 4a, 4b of the centering bell 4 through the use of fuel element grippers 5 not illustrated in FIG. 2. In this case, each of the two centering bell halves is provided with a fuel element gripper 5 (FIG. 3). One of these fuel element grippers 5 is supplemented by a control rod gripper 6 provided inside the fuel element gripper 5, to form a so-called double gripper according to Published German Patent Application DE 17 64 176. Reference is made to DE 17 64 176 with regard to details of the double gripper. The double gripper has essentially two functional elements, specifically a fuel element gripper 5 and a control element gripper 6 provided concentrically in the fuel element gripper 5. The basic configuration of the double gripper is explained below in context with the function of the double gripper: In order to extract a fuel element 8 from the reactor core or a fuel element storage rack, or else extract a control element 9 from a fuel element 8, first the entire gripping configuration is brought into a position above the respective fuel element with the aid of the bridge 1 and the trolley 2. The centering bell 4 is then lowered until its lower edge assumes a position just above the fuel element 8. When a fuel element 8 is extracted from a reactor core, the centering bolts 4.7 of the centering bell 4 engage into corresponding bores in the fuel element heads of the fuel elements adjacent to the respective fuel element 8. Exact positioning of the fuel element gripper 5 and of the control element gripper 6 is brought about in this way. At the same time, the centering bell is held in its position in the mast in such a way that its weight does not act on the fuel elements which are located geodetically below it. The fuel element gripper 5 is subsequently lowered until it latches with its gripping latches 5.1 into the fuel element head of a fuel element 8. The fuel element 8 held by the fuel element gripper 5 is then lifted upward and moved into the centering bell 4 with the aid of a lifting mechanism 7 and a double cable 7.2. A control element can also be extracted from a fuel element 8 in a similar way. For this purpose, after the centering bell 4 has been moved down, the fuel element gripper 5 is interlocked in an upper position in the centering bell, so that it cannot move down to the fuel element 5. The control element gripper 6 is subsequently lowered until, with a control element gripper head, it grips the head of a control element contained in the fuel element 8. The control element gripper 6 catches with the control element by using the gripper latches contained in the fuel element gripper head. The control element is then drawn out of the fuel element 8 into the centering bell 4 by the raising of the control element gripper 6 via a lifting mechanism 7 and the double cable 7.2. After either a fuel element 8 or a control element has been received in the centering bell 4 in this way, the centering bell 4 itself is drawn upward and moved into the guide mast. The fuel element 8 or the control element can then be moved horizontally in the reactor space. The other half of the centering bell 4 is equipped with a simple fuel element gripper in the manner of that described. For the transport of fuel elements and control elements in the reactor space, it is usually sufficient for only one of the two grippers in the centering bell 4 to be configured as a double gripper. It is, of course, also possible for both grippers in the centering bell 4 to be configured as double grippers. Since fuel elements are positioned very close to one another in the reactor core, but, on the other hand, a given space remains between the individual fuel elements in the fuel element storage rack, it is necessary to have the possibility of varying relative to one another the position of the two fuel elements transported through the use of the device described. The same need arises when a visual check of the fuel elements is to be carried out. In order to allow a change in the position of the fuel elements 8a, 8b relative to one another, the guide mast 3 is divided vertically at the points 3.1 and the centering bell 4 is likewise divided vertically at the points 4.1. As illustrated in FIGS. 4a-4c, each half 3a, 3b of the guide mast 3 and the corresponding half 4a, 4b of the centering bell 4 are equipped with a lifting mechanism 7a, 7b. The guide mast halves 3a, 3b, together with their internal fittings, such as the centering bells, halves 4a, 4b and grippers, and their associated lifting mechanisms 7a, 7b, are movable horizontally on the trolley 2. It is also sufficient, however, if only one of the two guide mast halves is movable on the trolley 2 and the other half is fixed. The movement device for the two guide mast halves is indicated in FIG. 1 by a guide 2xe2x80x3 which is movable in the x-y direction and in which wheels 2xe2x80x2 for rotating the structure 2.1 are guided. Rotation of the fuel elements 8b about their own axis thereby becomes possible at the same time. For this purpose, the guide mast halves are moved through the use of the guide 2xe2x80x3 until the mid-axis of the transported fuel element is congruent with the axis of rotation. When the rotary shield then executes a rotational movement, the fuel element, together with the associated guide mast half, the centering bell half and the gripper, is corotated. The possible angles of rotation amount, in this case, to +90xc2x0, xe2x88x9290xc2x0 and 180xc2x0. In order to avoid that the structures or installations on the guide mast, in particular the lifting mechanisms, do not collide during the rotational movement, it may be necessary that the horizontal movement exceeds that distance which is required to provide sufficient spacing between the two transported fuel elements for placing these fuel elements into a fuel element storage rack. In order to increase the handleability of the loading machine, the transported fuel elements can be moved toward one another again after rotation has taken place. The operation just described is illustrated diagrammatically in FIGS. 4a-4c and 5a-5c. Thus, FIGS. 4a-4c show the first lifting mechanism 7a and the second lifting mechanism 7b, together with the two transported fuel elements 8a and 8b which are moved apart (and, with them, also the guide mast halves 3a, 3b and centering bell halves 4a, 4b). At the same time, the fuel element 8b has been rotated through 180xc2x0 along its mid-axis in the rotary position A. The fuel element 8b, together with its lifting mechanism 7b and the associated guide mast half and also with the centering bell half, have subsequently been moved back toward the other fuel element 8a into position B indicated in FIG. 4. A similar procedure was performed in FIGS. 5a-5c. Here, after the fuel elements 8a and 8b, together with the associated guide mast half 3 and centering bell half 4, were moved apart, the fuel element 8b was rotated through 90xc2x0 about the longitudinal axis of the fuel element 8b (Position Axe2x80x2) and thereafter moved back again in the direction of the fuel element 8a (Position Bxe2x80x2). In both cases, the fuel elements 8a, 8b, which were in the narrow position in the core (FIG. 2), are oriented again, with sides parallel to one another, in the wide position (Position B in FIGS. 4a-4c, Position Bxe2x80x2 in FIGS. 5a-5c), the spacing of the fuel elements corresponding to the spacing which they must have, for example, in the fuel element storage rack, on a test stand for inspection, maintenance or repair or when they are to be reinserted into the reactor pressure vessel. However, their orientation relative to one another is different. The situation may arise where a fuel element has been bent during the operation of the reactor and cannot readily be removed from the formation it forms with the adjacent fuel elements or inserted into the formation. However, removing and inserting becomes possible when the fuel element is rotated through +90xc2x0, xe2x88x9290xc2x0 or 180xc2x0. Such faults in which the vertical movement of the fuel element is impeded by obstacles can be detected if the lifting mechanism is mounted on a platform having a weight measuring device which signals both an improper decrease in weight (the fuel element sits on an obstacle) and an increase in weight (the fuel element is detained) during the vertical movement. Moreover, it may be advantageous if the fuel element can be rotated at the workplace so that it can be inspected, attended to or worked on from different sides. For an inspection, the trolley 2, together with the guide mast halves fastened to it and with the elements held therein, is moved over the new workplace and the transported fuel elements or transported control elements can be lowered out of the guide mast 3. For this purpose, the centering bell halves are detained in the moved-up position via fastening devices in the guide mast, while the fuel element gripper 5 moves downward and thus frees the fuel element 8 for inspection. A visual inspection of the transported control element may also be carried out in a corresponding way, in that the centering bell 4 and the fuel element gripper 5 are held in a moved-up position via locking devices, while the control element gripper moves downward and thus frees the control element 9. These operations are illustrated in detail in DE 17 64 176. In the loading machine described, the fuel element 8 or control element 9 can be moved out of the centering bell 4 and the guide mast 3 in that the fuel elements 8 and control rods 9 can be individually moved out downward, even when the loading machine is equipped with two fuel elements 8 or with one fuel element 8 and one control element 9. Even in positions in which they are moved apart and which correspond to FIGS. 4a-4c and 5a-5c, fuel elements 8 or control elements 9 can be moved independently of one another out of the centering bell half held high in the guide mast half and can be examined. Through the use of the loading machine illustrated in the exemplary embodiment, two fuel elements or one fuel element and one control element can be handled simultaneously. It is also possible, however, to configure the loading machine in such a way that a plurality of fuel elements, for example four fuel elements, can be handled simultaneously. For this purpose, it is necessary to divide the guide mast and centering bell into four in a similar way to the exemplary embodiment. The handled fuel elements then result in a bundle of two times two fuel elements. It is then necessary, correspondingly, that, for a mutual relative movement, the fuel elements be either movable horizontally in the horizontal direction or be movable at an angle of 45xc2x0 with respect to the dividing planes of the guide mast 3. In all cases, it is possible that the loading machine handles a number of fuel elements or control elements, which is below the capacity of the loading machine.