Patent Number: 041893476
Section: description

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there are shown graphite blocks 1 to 8, disposed in a horizontal plane, and assembled to form a side wall sector of a nuclear reactor vessel which is bounded on two sides by radial parting lines that are not in contact with the adjacent side wall sectors. Toward the pebble bed of numerous fuel spheres 9, provided in the interior of the vessel, this side wall sector is bounded by two surfaces inclined convexly to one another, which are formed by the blocks 1, 3, 5 and 7. Toward the outside, this side wall sector is likewise bounded by two surfaces that are inclined convexly to one another, which are formed by the blocks 2, 4, 6 and 8 and are braced through rolling planes 10 and rolling elements 11 against two rolling planes 12 and 13 which are inclined concavely to one another. Actually, these rolling elements 11 are not spheres but cylindrical rolling elements which, however, act in principle like spheres between two planes. The forces exerted by the pebble bed on the blocks 1, 3, 5 and 7 can be considered, grossly simplified, as acting perpendicularly on the respective surface, even if force directions locally deviating somewhat from the perpendicular are to be expected due to the friction between the fuel spheres 9 and the wall. In the case of the rolling elements 11, on the other hand, it can be assumed that the respective bearing forces are transmitted only perpendicularly to the rolling plane. All in all, the external forces acting upon a side wall sector have the effect that this body, since it cannot absorb any appreciable tensile forces, is held together in the horizontal direction under all operating conditions and is pushed against a fixed point 14 which is located at the intersection of the outer rolling plane thereof. Since the friction at the rolling elements 11 is very much lower than the friction in the boundary surfaces between the pebble bed and the side wall sector, the angle .beta. between the two outer rolling planes can be selected so that it is considerably smaller than the angle .alpha. between the two inner boundary surfaces. In a non-illustrated vertical section of a base sector, the forces originating from the pebble bed and the support act in a manner similar to those acting in the configuration of FIG. 1 i.e. so that also the base sector is held together and is forced into a defined position. In FIGS. 2 and 3, the reactor vessel, shown without cover and without pebble bed, is formed by a total of twelve sectors 20, with parting lines or gaps 21 therebetween. Each of these sectors 20 is made up of numerous blocks, for example, of graphite, and is bounded in the region of the base against the pebble bed in gable roof-shaped fashion with a radial ridge 22 which declines towards the center of the reactor. The blocks which are immediately adjacent to the subsequent pebble bed have numerous vertical, parallel ducts or channels, through which the reactor coolant is conducted, in a manner not otherwise described in detail, to a collecting channel or manifold 24. In the center of the reactor base, a cone-like body 25 with the apex thereof pointing upwardly is disposed. It is similarly constructed of individual blocks and has a polygonal parting line or gap 26 opposite the sectors 20 surrounding it. This cone-like body 25 serves to conduct the fuel spheres away from the center and toward the discharge channels 27, indicated by broken lines, and from there to several discharge tubes 28. The side wall 29, which is likewise constructed of numerous blocks, also has, in direction toward the pebble bed, two boundary surfaces inclined toward each other in gable-roof-fashion with a vertical ridge 30. Toward the outside, the side wall 29 is braced, through rolling bodies disposed in separate cages 31, against a metallic polygonal ring 32, through which numerous vertical ducts 33 pass for cooling purposes. This polygonal ring 32 rests on cylindrical rolling bodies 34 and, when heated, travels outwardly together with the side wall sector 29 and the base sector. The base sectors 20 are supported on separate rolling bodies 35 which are shown in FIG. 6 and described in detail hereinafter. From FIG. 3 it is apparent, however, that these rolling bodies 35 are disposed in planes that ascend or slope upwardly toward the center of the reactor, so that the base sectors 20 are forced outwardly against the polygonal ring 32 by their own weight and the weight of the pebble bed which will subsequently rest thereon. The central cone-like body 25 rests on rolling bodies 36 which, as shown in detail in FIG. 6, are disposed in rolling planes declining or falling off toward the center of the reactor. This body 25 is thereby held uniformly together toward the center by its own weight and due to the weight of the pebble bed resting thereon. This body 25, in fact, also has radial and annular parting lines, however, they are always closed, in contrast with the side wall sectors and the base sectors 20. In FIG. 4, respective pairs of cylindrical rolling bodies 40 which are provided with an annular slot, rest on a plate 41 which has a ridge 42 for guiding these rolling bodies 40. On the two lower rolling bodies 40, there is disposed a middle plate 43 which has ridges 42 on the underside and on the upper side thereof which are transposed 90.degree. to one another. Thereabove, again two upper rolling bodies 40 are disposed which are offset 90.degree. relative to the lower rolling bodies and support an upper plate 44 which is also provided with a ridge 42 similarly engaging in the annular slot of the rolling bodies 40. In the illustrated position of FIG. 4, this roller or antifriction bearing is freely movable in horizontal direction and has as an advantage over rolling spheres which are disposed between two planes, that the contact surface and, therefore, the load capacity is greater. If one wishes to dispose such roller or antifriction bearings in vertical planes, as is intended in the invention of the instant application, these rolling bodies must be guided in a conventional manner by gears which mesh with appropriately shaped racks, so that they do not travel downwardly. FIG. 5 illustrates how the base sectors 20 are supported on numerous column-shaped rolling bodies 35, and the inner, cone-like body 25 is supported on numerous rolling bodies 36. In addition, FIG. 5 shows the location of the cylindrical rolling bodies 34 for supporting the polygonal ring illustrated in FIGS. 2 and 3. In FIG. 6, the column-shaped rolling bodies 35 and 36 have, at the respective upper and lower ends thereof, curved rolling surfaces which have a common center of curvature and are supported above and below on inclined but, in themselves, planar rolling surfaces 37 and 38. The displacement paths of the parts supported on rolling bodies 35 and 36 are so small that the contact points of the rolling bodies 35 and 36 with the upper and lower bearing surfaces always remain within the respective spherical or curved rolling surface thereof, and the column-shaped rolling bodies 35 and 36, therefore, cannot topple over. Holders 39 are, nevertheless provided, primarily during assembly to minimize the possibility of toppling. It is of particular importance that all of the rolling bodies 35 belonging to one base sector 20, are disposed in two planes which, on the one hand, are inclined toward one another valley-like and, on the other hand, ascend toward the center of the reactor. In this manner, this base sector is held together in itself and is forced outwardly against the polygonal ring 32. Since the rolling bodies 35 are supposed to permit movements in the respective rolling plane, they must be defined by two spherical surfaces with a common center of curvature. The rolling bodies 36, on the other hand, which support the central, cone-like body 25, may have cylindrical end surfaces, also with a common center of curvature, since this cone-like body 25 can only expand or contract in radial direction. FIGS. 7 to 9 show diagrammatically another embodiment of the invention in a gas-cooled pebble bed reactor with a cylindrical core vessel of about 12 m diameter and 10 m height, which has a funnel-shaped base and a central cone having an upwardly directed apex disposed therein. With a temperature difference i.e. increase, of about 1000.degree. C., the diameter of such a base of graphite would have to expand about 60 mm if no special measures were taken. In FIGS. 7 and 8, the cylindrical core vessel 51 contains a bed of numerous fuel spheres 52. The base of the vessel 51 is formed of an outer, funnel-shaped part 53 and an inner, conical part 54 with an annular gap 55 therebetween. As is evident from FIG. 7, the funnel 53 and the cone 54 are constructed of numerous blocks, of which several, stacked on top of one another, form a respective column which is supported on a rolling body 56 that, together with other rolling bodies 56, is supported on plates 57 and 58 which, in turn, rest on a horizontal, flat base 61 through the intermediary of foundations 59 and 60. The cylindrical side walls of the core vessel are constructed from the inside to the outside thereof, successively, of a layer of graphite blocks 62 acting as a reflector, a layer, for example, of carbon blocks 63 acting as insulation, and an outer polygonal wall of metallic elements 64 which are bolted together and are cooled from the outside. Since the temperature and, therefore, also the dimensions of this outer polygonal wall change only little, it can be considered as a fixed abutment or bracing for the blocks of the funnel 53 which, upon becoming heated, move radially toward the center of the vessel, on the one hand, and vertically upwardly into the pebble bed, on the other hand. Upon cooling down, these blocks, due to their own weight and the weight of the pebble bed resting thereon, move back again on the inclined plates 8 in radial direction toward the fixed outer abutment. In contrast, the blocks of the inner cone 4, when heated up, expand in radially outward direction, on the one hand, and also upwardly into the pebble bed, on the other hand. Upon cooling down, these blocks travel back again radially toward the center due to their own weight and due to the weight of the pebble bed pushing on their inclined surfaces. In this manner, the blocks of the funnel 53, as well as the blocks of the cone 54 are stressed only in compression. In FIG. 8, there are again shown both the cone 54 built of the multiplicity of columns of blocks 70, 71 and 72, as well as the outer funnel 53 built of the multiplicity of columns of blocks 73, 74 and 75 which, respectively, form segment-shaped or annular segment-shaped groups. Between adjacent columns of the inner core 54, parting lines or joints but no expansion gaps are provided because the blocks thereof are all forced toward the center due to their own weight. Between the block 70 of the inner core 4 and the block 73 of the outer funnel 53, an annular expansion gap 55 is provided, which is supposed to remain in existence even at the highest possible temperature. Between the block 73 and the radially adjacent block 77, there is likewise provided an expansion gap 78 extending in radial direction, whereas, on the opposite side of the block 73 along the adjacent block 79, in fact, a parting line or joint is provided, but no expansion gap. FIG. 9 shows, with the same reference numerals applied to like parts as in FIGS. 7 and 8, how the annular or ring segments of the outer funnel 53, that are constructed of a multiplicity of column of blocks, are mounted through roller bearings 56 on the planar base 61. It is apparent therein how the weight of the blocks per se and the weight of the bed of fuel pebbles 52 disposed thereon, hold together the blocks of a ring segment in horizontal direction. It is also readily apparent that the inclincation of the plane above the blocks is opposite to the inclination of the roller planes below the blocks, but does not have the same angle of inclination with respect to the horizontal. While the inclination at the upper side of the blocks is determined by the flow characteristics or behavior of the fuel pebbles, the inclination at the underside of the blocks must be selected to be only so great that the friction in the roller bodies is overcome.