Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
1999-07-15
2002-10-29
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
C376S441000, C376S438000, C376S448000
Reexamination Certificate
active
06473482
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a spacer of a fuel assembly for a light-water cooled nuclear reactor, according to European Patent Application 0 027 203 A1, corresponding to U.S. Pat. No. 4,578,239. The invention also relates to a spacer of such a fuel assembly with a pair of springs held on a common web, according to U.S. Pat. No. 3,679,546.
In fuel assemblies which are subjected to a strong cooling water flow, fuel rods that are set into powerful vibrations are therefore laterally supported in meshes of grid-shaped spacers, in order to damp those vibrations, exclude mechanical damage and hold the rods at a distance apart which is technically safe thermally. Those spacers frequently have square meshes which are formed from crossed webs and contain springs that laterally support fuel rods respectively inserted in the meshes.
A spacer formed of crossed webs is known from U.S. Pat. No. 3,679,546, in which each fuel rod of a mesh is supported by a spring formed of a long sheet-metal strip that extends parallel to a center line of the fuel rod. That sheet-metal strip has an approximately C-shaped longitudinal section with a resilient or sprung central part which merges at the top and bottom (in relation to the center line direction of the fuel rod) through the use of a convex curvature into end strips that extend along and are supported by the inside of a web forming the mesh, facing toward the fuel rod. Assembly slots extending transverse to the fuel rods are respectively associated with the two end strips and the ends of the end strips are bent in such a way that they reach through the assembly slots and are still in contact with the back of the web.
In the working position, each spring is located approximately in the center of a mesh side. The spring can be displaced laterally (i.e. along the slots) from the operating position into an assembly position. The assembly slots merge at that position into enlarged cross-sectional areas so that the bent ends of the end strips can be inserted in or extracted from the enlarged cross-sectional areas.
In order to prevent an unintentional displacement, the convex curves of the springs are configured as protrusions which, in the operating position, protrude into corresponding recesses on the upper edge and lower edge of the web but which, for assembly and dismantling, have to be bent away from the wall of the web.
Particular spring materials are necessary in order to produce the spring force necessary for optimum support of the fuel rods. However, those materials frequently have a high absorption for neutrons which are necessary in the reactor in order to maintain nuclear fission. Although relatively little material is necessary for those known springs, the spring forces which are necessary can only be achieved by special materials.
A spring is known from European Patent Application 0 527 244 A1 (corresponding to U.S. Pat. No. 5,311,564) which likewise has a C-shaped cross section but is configured as a “diagonal spring”. In other words, it does not protrude into the mesh from a side surface of the mesh and at right angles to the web but instead diagonally from a corner of the mesh at which two webs cross. For that purpose, arms (end strips) of the C-shaped spring have long straps extending at right angles to the fuel rods on both sides and the two straps are formed practically into the shape of a right-angle triangle which can be inserted in the corner of the mesh. All of the straps pass through corresponding assembly openings in one of the two webs. They are held in the assembly openings of that one web and are in contact with the other web.
As compared with the spring of U.S. Pat. No. 3,679,546, it is in fact an advantageous feature that two such diagonal springs can be combined to form a double spring which protrudes into adjacent corners of two meshes located side by side. However, the way in which the springs are fastened to the mesh walls does not, in both cases, permit two such springs to be disposed in the center of a web in such a way that the two springs protrude into two adjacent meshes from the common web.
It is shown in European Patent Application 0 027 203 A1 that a fastening of straps on the rims of the end strips, similar to European Patent Application 0 527 244 A1, is also suitable for one spring which is held on a web in the center between two corners of a mesh. That spring has the features of the prior art mentioned initially above.
Those fastening straps require a relatively large amount of material which can be disadvantageous with respect to the neutron absorption as well as the natural frequency of the vibrating springs.
A similar spring with two end strips, which respectively engage in slots of a web on each side through the use of profiled sections but with which less material is required for the straps, is also presented in International Publication No. WO 94/09495, corresponding to U.S. Pat. No. 5,539,792. That spring is not associated with structural limitations with respect to the shape of the spring. Instead, the fastening is so flexible that the spring shape can be matched to the respective requirements of the reactor. In particular, therefore, the C-shape known from other documents can also be retained. However, the use of that fastening principle does not appear to be suitable for spring pairs in which the springs of the pair respectively protrude in opposite directions into the meshes, on a common web between two adjacent meshes.
It is also a disadvantage that the springs for those structures are relatively loosely seated in the openings in which their end strips are seated because it has to be easy to insert them during assembly. However, they should not be able to fall out even when no fuel rods have as yet been inserted, in the ready-for-use condition. In addition, during operation of the reactor, they should not be shaken by the cooling medium flow to such an extent that mechanical damage to the springs or the fuel rods can occur.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a spacer with specially fastened springs for fuel assemblies of nuclear reactors, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which the springs have a retention on a web of the spacer that involves little material, leaves a choice of a favorable shape of the springs practically unlimited and is seated as well as possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a spacer of a fuel assembly for a light-water cooled nuclear reactor, comprising:
webs crossing each other to form meshes for inserting fuel rods having center line directions, the webs having snap-in openings formed therein, the webs having assembly openings formed therein with substantially slot-shaped opening parts having ends with edges, the assembly openings having enlarged opening parts each leading from a respective one of the substantially slot-shaped opening parts in parts of the webs, and the webs having inner surfaces facing toward the fuel rods;
a plurality of springs each held in one of the assembly openings in one of the webs, the springs having an operating position and an assembly position offset laterally relative to the operating position, and the springs having a spring force;
each of the springs having a resilient central part facing toward a fuel rod, the central part having a top and a bottom relative to the center line direction, and the central part having end strips each extending substantially parallel to a respective one of the webs and adjoining a respective one of the top and bottom; each
of the end strips having two lateral rims each extending parallel to the center line direction and bent away from a fuel rod about the center line direction;
profiled sections each seated on a respective one of the rims of the end strips, the profiled sections having inner parts respectively supported on the inner surface of a respective one of the webs i
Carone Michael J.
Greenberg Laurence A.
Locher Ralph E.
Richardson John
Stemer Werner H.
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