Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Patent
1992-08-28
1994-07-05
Walsh, Donald P.
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
376441, G21C 339
Patent
active
053274725
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of International Application PCT/DE91/00133, filed Feb. 20, 1991.
The invention relates to a boiling water reactor, having a pressure vessel, a steam turbine connected to the pressure vessel, at least one nuclear reactor fuel assembly and controllable absorber elements disposed in a reactor core in the pressure vessel, the fuel assembly including an elongated fuel assembly case with mutually parallel side walls laterally closing off the fuel assembly, an inlet end for liquid coolant and an outlet end for a liquid/steam mixture of the coolant, and fuel rods containing nuclear fuel and being disposed side by side and parallel to the case walls, the absorber elements being disposed outside the fuel assembly, the fuel rods being disposed in lengthwise rows and crosswise rows intersecting the lengthwise rows in such a manner that they reach through meshes of a grid extending practically at right angles to the side walls, and each four fuel rods disposed in two adjacent lengthwise rows and two adjacent crosswise rows forming one flow subchannel for the coolant, being parallel to the side walls. The invention also relates to a fuel assembly for the boiling water reactor.
The structures of fuel assemblies for boiling water reactors described above are conventional and are used in the invention as well. They are therefore part of the fuel assembly and the reactor of the invention. In the boiling water reactor core, the liquid coolant enters the fuel assembly case at a lower or inlet end and leaves it as a liquid/steam mixture at an upper or outlet end of the case.
Since an increasing proportion of the coolant, which simultaneously acts as a moderator, is in the form of steam in the upper part of the fuel assembly, the vertical flow in the reactor core must be channelled in such a way that sufficient moderator is present there as well. To this end, tubes for the liquid coolant (water tubes) can be used, which replace one or more fuel rods. Such a water tube may also have a larger cross section than an individual fuel rod, so that it extends over the cross section of a plurality of meshes in the grid, or it may have some other cross section (such as cross-shaped). The case walls also serve to channel the vertical flow and in particular must prevent coolant vapor from accumulating on the absorber elements because of an uncontrolled horizontal flow, which would interfere with the proper course and control of the reactions in the reactor
That kind of horizontal flow is even considered desirable for pressurized water reactors, because it brings about a temperature equalization between hotter and cooler regions of the fuel assembly and improves cooling.
Such a horizontal flow, which in a boiling water fuel assembly is largely suppressed by the case walls and in any event is kept away from the absorber elements between the fuel assemblies, can therefore be generated in a pressurized water fuel assembly by suitable baffles or vanes in the flow subchannels. Such vanes may be disposed at the ribs of spacers, which are necessary in any event to fix the mutual spacing of the fuel rods, or on the ribs of their own mixing grids, as is shown, for instance, in FIGS. 1 and 2 of German Published, Non-Prosecuted Application DE-OS 15 64 697. That produces a circular flow around the individual fuel rods by means of which all of the flow subchannels bordering a fuel rod communicate with one another. The superimposition of the individual circular flows then leads to horizontal flows, which pass transversely through the entire fuel assembly. The same circular flows also develop in the grid structures of pressurized water reactors as is shown in FIGS. 1, 8 and 9 of U.S. Pat. No. 4,224,107.
In German Published, Non-Prosecuted Application DE--OS 2 157 742, it is proposed that four vanes be disposed in propeller-like fashion in each flow subchannel of a pressurized away from the coolant flow, tapering and protruding obliquely from the wall of the water tube into the int
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Fromel Gustav
Kraemer Wendelin
Uebelhack Walter
Chelliah Meena
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Walsh Donald P.
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