Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Patent
1998-03-12
1999-04-20
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
376440, G21C 332
Patent
active
058964363
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a nuclear fuel assembly for a light-water nuclear reactor, and more particularly a boiling water reactor. The fuel assembly comprises a bundle of elongated elements which are retained and fixed by a plurality of spacers arranged in spaced relationship to each other along the bundle. The spacers comprise a plurality of cells for mutually fixing the elongated elements. A structure comprising elongated elements retained by spacers is referred to as a bundle. The ends of the bundle are retained at the bottom and at the top, respectively, by a bottom tie plate and a top tie plate, respectively. In certain boiling water reactor assemblies, the bundle is divided into four orthogonal sub-bundles and the lower and upper parts, respectively, of each sub-bundle, which are arranged in the fuel assembly, are retained by a bottom tie plate and a top tie plate, respectively. The bundle and the sub-bundles, are surrounded by a fuel channel. A coolant is adapted to flow from below and up through the normally vertically arranged fuel assembly and, during a nuclear reaction, to cool the fuel rods arranged in the assembly.
During, for example, inspection of the fuel or at a certain burnup stage, when the positions and/or orientations of the bundles or the sub-bundles are to be changed, the bundle or the sub-bundles is/are to be lifted out of the surrounding fuel channel. To achieve this lifting operation, a bottom tie plate or a lifting plate is normally arranged so that a member may engage this plate and then release the bundle or the sub-bundles from the fuel channel. In certain cases, a handle is provided for the fuel assembly for lifting and handling the entire fuel assembly. With the aid of this handle, an entire bundle can also be released from the fuel channel. In those cases where sub-bundles are to be inspected, for example, the handle is detached before the sub-bundles are released from the fuel channel.
BACKGROUND OF THE INVENTION
The design of the top tie plate or the top tie plates of the fuel assembly is very important for the performance of the fuel assembly. When coolant flows upwardly through the fuel assembly, it is important that the coolant be subjected to as low a pressure drop as possible. A low pressure drop in the fuel assembly is favorable for the stability properties of the fuel assembly. A low pressure drop also results in an increase of the capacity in the pumps which provide the fuel assembly with coolant, as well as an increase of the flexibility during operation of the reactor. Further, it is important that the top tie plate or the top tie plates be designed for lifting a bundle or four sub-bundles out of the fuel assembly.
FIG. 1 shows a prior art fuel assembly 1 for a boiling water reactor, and FIG. 3 shows in a view from above a prior art top tie plate 5a for a sub-bundle. Extra long fuel rods 3a, which partially extend above the top tie plate 5a, are adapted to run through two of the openings in the top tie plate 5a. The two extra long fuel rods 3a are fixed to the bottom tie plate 6 and are each provided, at the upper side of the top tie plate 5a, with a nut 8. The other rods 3 rest on the bottom tie plate 6 and make contact with the lower side of the top tie plate 5a by means of a helical spring 9 arranged around the respective end plugs 10 of the rods 3. The helical springs press the top tie plate 5a against the nuts 8, whereby the nuts 8 limit the maximum distance between the top and bottom tie plates 5a, 6. The two extra long fuel rods 3a are arranged in a tensile-force-transmitting connection between the top and bottom tie plates 5a, 6 while at the same time they limit the maximum distance between the top and bottom tie plates 5a, 6.
The top tie plate 5a is designed to receive a handling tool in a respective handling opening 11 located adjacent to the openings for the extra long rods 3a. The handling tool is passed through the top tie plate 5a by way of the handling openings 11, whereupon they are adapted to engage bars 5c at the res
REFERENCES:
patent: 4560532 (1985-12-01), Barry et al.
patent: 4684501 (1987-08-01), Lui
patent: 4753774 (1988-06-01), Taleyarkhan et al.
patent: 5323434 (1994-06-01), Lorek et al.
ABB Atom AB
Wasil Daniel D.
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