Patent Number: 059057700
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a plurality of structural wells 4 which are fastened upright on a baseplate 2 in a storage framework for nuclear reactor fuel elements. An outer wall 10 of the storage framework is visible in a side view in the figure. The structural wells 4 are disposed on the baseplate in a checkered manner, so that the outer wall 10 is formed alternately by side walls of the wells and by edge plates 11 welded onto the these side walls. The side walls are identified by reference numerals 44 to 47 in FIG. 2 and will be explained in more detail below. Due to the checkered or checkerboard-type configuration of the structural wells 4, two structural wells adjoining one another diagonally in each case span interspaces 3 which have approximately the same cross-sectional area as the structural wells 4. Reinforcing slabs 14, which are provided with feet 16, are disposed on the baseplate 2. The feet 16 rest on foot slabs 18 disposed on a bottom 9 of the fuel element storage basin, which is not illustrated in any more detail in FIG. 1. The feet 16 are screwed into the reinforcing slabs 14 through the use of a coarse thread having a thread pitch of 6 mm. Clamping bolts 19 for bracing the feet 16 in the coarse thread are provided between the reinforcing slab 14 and the foot slab 18. The storage framework rests freely, without lateral fixing, on the bottom 9 of the fuel element storage basin. The structural wells 4 are connected to one another through the use of first and second connecting elements 20 and 26. A view of the side walls of the structural wells 4 disposed in a second row, which side walls are located behind the edge plates 11, is exposed in an upper right region of the figure. The first connecting elements 20 and the second connecting elements 26 can be seen alternately in a top view of their flat side and in a section through their narrow side, wherein in the first instance one half is concealed in each case by a structural well 4 located in front. In the example of FIG. 1, the lower first connecting elements 20 extend over an entire height a+b of the structural wells 4, that is to say over a lower region 6 and over an upper region 8. In order to make it possible for the second connecting elements 26 to be welded easily, they extend only in the upper region 8 over a length b which is less than 25% of the total height a+b of the structural wells 4. If the total height of the structural wells 4 is about 4.5 m, two connecting elements 26 having a length of between 300 mm and 500 mm are provided, in particular. The structural wells 4 are composed of austenitic steels qualified for use in nuclear power plants and are constructed as wells of approximately square cross section. The connecting elements are composed of a ductile austenitic steel having a low carbon content, particularly of less than 0.1%. The left-hand part of FIG. 1 illustrates a view of the side walls of the structural wells 4 disposed in the second row and of the spaces 3 located therebetween, over the entire height a+b of the structural wells 4. The side walls are located behind the edge surfaces 11. A guide strip 12 is located in the upper region 8 of the fuel element storage framework, at an end 8a of the structural wells 4 which is opposite the baseplate 2. The guide strip 12 runs parallel to the plane of the baseplate, on the outside of the structural well 4, that is to say on the side facing the interspace 3. A neutron-absorbing structure 1 which is located below this guide strip 12 in the interspace 3, is displaceable relative to the structural wells 4 and is composed of plates 7 made of boron-treated steel. Altogether, four such plates 7, 7a are disposed in an interspace 3. The plates extend largely over the entire height a+b of the fuel element storage framework and in each case run parallel to a side wall of the structural wells 4 surrounding the interspace 3. The plates 7, 7a have a plurality of projections over the entire height a+b. The plates 7, 7a, which in each case are perpendicular to one another, intermesh through the use of the projections. A self-supporting absorber well 15 is thereby formed from the plates 7, 7a. The absorber well is disposed within the interspace 3. According to FIG. 2, the structural wells in each case are disposed diagonally opposite one another, so that a checkered pattern is obtained. The figure illustrates an edge region of the storage framework at one corner. In the edge region of the storage framework, three structural wells 4 surround an interspace 3 which is closed relative to the outside through the use of an edge plate 11 and which, in addition to the structural wells 4, serves for receiving a non-illustrated fuel element in an intermediate position 5. An absorber well 15, composed of four plates 7, 7a made from boron-treated steel, is inserted into the interspace 3. Only one absorber well is illustrated for the sake of greater clarity. The plates 7, 7a are essentially planar and in each case run parallel to the side walls of the structural wells 4, 4b surrounding the interspace. Side walls 44 to 47 are outwardly beaded, so that the plates 7, 7a bear against the side walls, with the result that the position of the absorber well 15 within the interspace 3 is fixed. Moreover, sufficient space is provided at edges 42a, 42b of the structural wells 4 for the planar plates 7, 7a to engage in one another, i.e. to intermesh. FIG. 2 also illustrates how an absorber well 15 with beaded plates 7b or with planar plates 7c having spacers 13a is disposed in a structural well 4. Since the largely planar plates 7, 7a have bearing contact at least at particular points, the inner region of the interspace 3 is free for receiving a non-illustrated spent fuel element. As already explained with regard to FIG. 1, the structural wells 4 have guide strips 12 at their upper end 8a. The guide strips 12, only two of which are illustrated, run parallel to the side walls 44 to 47 and face into the interspace 3. The side walls 44 to 47, as well as side walls 44a to 47a and 44b to 47b of the structural wells 4, 4a, 4b in each case are outwardly beaded, so that a clear width c of the structural wells coincides approximately with a clear width g of the interspaces 3. The widths correspond in each case to the fuel elements to be stored and may amount to between 140 mm and 380 mm. The structural wells and side walls are designated in general by reference numerals 4 and 44 to 47 and in particular by reference numerals 4a, 4b and 44a to 47a, 44b to 47b. The structural wells 4 are connected to the structural wells 4 located opposite them through the first and second connecting elements 20 and 26. In each case two side walls 44a and 45a of a well 4a which form a common longitudinal edge 42a are assigned two side walls 47b and 46b of the diagonally opposite well 4b which form a common longitudinal edge 42b. The first connecting element 20 has the shape of a plate strip and connects the side wall 44a of the well 4a to that side wall 46b of the well 4b which is approximately parallel thereto. The second likewise strip-shaped connecting element 26 connects the side wall 45a of the well 4a to the side wall 47b of the well 4b. The first connecting element 20 has high rigidity in the directions indicated by a double arrow 30 and running parallel to the flat side of the first connecting element 20. The second connecting element 26 has high rigidity in a direction 36 running approximately perpendicularly to the direction 30. An approximate right angle .alpha. between these two directions 30 and 36 preferably amounts to between 70.degree. and 90.degree.. It can be seen in the figure that the first and second strip-shaped connecting elements 20 and 26 do not run exactly parallel to or perpendicularly to the outer wall 10 and the side walls 44a, 45a, 46b and 47b, but in each case rest on surfaces of the side walls 44a, 45a, 46b and 47b at an acute angle .beta. shown in FIG. 5. An offset S1 in an x direction and an offset S2 in a y direction between the structural wells 4a and 4b is thereby compensated. The offset is necessary in the region of the longitudinal edges 42a and 42b. The direction of the offset S1 is parallel to the x axis and the direction of the offset S2 is parallel to the y axis of a right-angled system of coordinates x-y which is oriented with its two axes parallel to the walls 44, 46 and 45, 47 of the structural wells 4. This offset S1, S2 is canceled again by the outwardly beaded side surfaces 44a, 44b to 47a, 47b of the structural wells 4a and 4b, so that the clear width c of the structural wells virtually coincides with the clear width g of an interspace 5a or of an intermediate position 5. By virtue of the outwardly beaded surfaces of the side walls 44 to 47 of the structural wells 4, these side walls 44 to 47 are set back in the region of their longitudinal edges 42, as is seen from a center point of the interspace 3 which is surrounded by them, so that the risk of the connecting elements welded on there possibly catching on a fuel element during loading and unloading of the structural wells 4 or of the intermediate locations 5 is virtually ruled out. In FIG. 5, the offsets S1, S2 are shown separately and enlarged in a position vector diagram, wherein a resulting position vector S that is equal to a distance or gap between the two longitudinal edges 42a, 42b is obtained. A width d of the strip-shaped first and second connecting elements 20 and 26 amounts to about 10 to 30%, of the clear width c of a structural well 4, which is 60 mm in the example. The wall thickness of the connecting elements 20, 26 is preferably 50% to 90% of the wall thickness of the structural wells 4. In the exemplary embodiment shown in the figure, a wall thickness of the connecting elements 20, 26 of about 1.5 mm is provided for a wall thickness of the structural wells 4 of 2 mm. FIG. 3 illustrates a cross section through a storage framework in a similar way to FIG. 2, with like parts being designated by the same reference symbols. The structural wells 4 are formed from planar plates which merge into one another at the edges, in each case with a rounding. The structural wells 4 can be produced particularly simply. Structural wells 4 located diagonally opposite one another in each case are connected to one another in a mechanically stable manner through the use of a connecting element 20, with adjacent connecting elements 20 being extended in two different directions. The directions form an angle of 70.degree. to 90.degree.. An absorber well 15 composed of releasably intermeshed plates 7 in each case is disposed in the interspaces 3. The plates 7 run largely parallel to the side walls 44 to 47 of the structural wells and have edge beads 13, with which they bear against the respective side wall 44 to 47. The plates 7 may also be planar and may be spaced from the side walls 44 of the structural wells through corresponding spacers 13a shown in FIG. 2, so that the plates 7 engage in one another, i.e. intermesh, in the region of the longitudinal edges 42a seen in FIG. 2. As a result, the position of the absorber well 15 in the interspace 3 is fixed, and the absorber well 15 affords a sufficiently large amount of space for receiving a spent fuel element. According to FIG. 4, first connecting elements 22 extend only in the lower region 6 of the structural wells 4 and do not reach as far as their top edge. These first connecting elements 22 likewise have a pointed or tapered shape at their free end projecting into the well interior, in order to prevent them from catching on the fuel elements during loading while using the first connecting elements 22. The second connecting elements 26 have a tapered or pointed shape at their end facing away from the end surface of the structural wells 4, in order to likewise avoid catching on the fuel elements during unloading. FIG. 5 not only serves to explain the offsets S1, S2, but also shows an advantageous configuration with cross-shaped second connecting elements 28 that are welded to mutually confronting surfaces of the side walls 44a, 45a and 46b, 47b of the structural wells 4a and 4b. It can be seen in the figure that, in this exemplary embodiment too, the respective flat sides of the cross-shaped second connecting element 28 run at an acute angle .beta. to the surfaces of the side walls 44a, 45a, 46b and 47b of the structural wells 4a and 4b). Since the second connecting elements 28 are disposed only in the upper region of the storage framework, they may be mounted at a later stage from above. The cross-shaped connecting elements 28 may be welded in, as separate pieces of the length b (as seen in FIG. 1), between the structural wells 4 from above. However, they may also be obtained by welding the first connecting elements 20, which run through over the height a+b and are slotted at the top according to FIG. 5, to the second connecting elements 26 disposed there, or by welding short second connecting elements in two longitudinally divided halves onto slotted first connecting elements of the length a+b. The invention is characterized by a fuel element storage framework for spent fuel elements of a nuclear power plant, in which the storage framework has structural wells that stand vertically on a baseplate and are disposed in a checkered manner. A neutron-absorbing structure, which is preferably an absorber well, is provided in the interspaces formed between the structural wells disposed in a checkered manner. Alternatively, the absorber well may also be inserted directly into a structural well. Placing a respective absorber well in the interspace and in the structural wells also makes it possible to store fuel elements having a relatively high radioactive radiation capacity, since two absorber layers (plates) are disposed one behind the other. This absorber well is composed of four intermeshed plates and is displaceable within the interspace relative to the structural wells, thus ensuring that the absorber well does not have a load-bearing function. The absorber well can therefore be produced from a boron-treated steel without any problem at all. A storage framework thus produced has a separation of load-bearing components, namely the structural wells, from the neutron-absorbing components, namely the absorber wells, with the result that separation is also achieved during the production of the different components and this production can thereby be carried out especially simply. In particular, the structural wells can be produced from known steels on a large scale. The interspaces between the structural wells are preferably dimensioned in such a way that, even after an absorber well has been inserted, there is sufficient room in the interspace for receiving a spent fuel element, so that a compact storage device for the space-saving storage of fuel elements is provided.