DE2840590A1 - NUCLEAR REACTOR - Google Patents

Description

DR. BERG DIPL.-ING. STAPF DIPL.-ING. SCH7 / ABS DR. DR. SANDMAIR

PATENTANWÄLTE PO Box 86 0245 8000 Munich 86

284059Q

Lawyer file 29 I \ 5H
IR September 197P

United Kingdom Atomic Energy Authority, 11 j Charles II Street, London SWlY 4QP, United Kingdom

Nuclear reactor

viimii / H 909813/0973

r (089) 911272 Telegrams: Bank accounts: Hypo-Bank Munich 4410122850

«» 273 BERGSTAPFPATENT Munich (BLZ 70020011) Swift Code: HYPO DE MM

»« 274 TELEX: Bayer Vereinsbank Munich 453100 (BLZ 70020270)

9 * 3310 0524560 BERG d Postscheck Munich 65343-808 (BLZ 70010080)

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The invention relates generally to a nuclear reactor, but more particularly to nuclear fuel subassemblies for liquid metal cooled Fast breeder nuclear reactors.

In known metal-cooled fast breeders, such as those known from DE-OS 25 57 910, the fuel arrangement has a plurality of slim fuel elements or rods over which a coolant made of liquid metal, such as sodium, flows. As a practical matter, the fuel assembly is divided into a plurality of interchangeable sub-assemblies which are elongate and comprise a plurality of fuel rods enclosed by a jacket which is provided with a headed attachment. The subassemblies are regularly arranged side by side and each is cantilevered by a mandrel at the lower end which is inserted into a support structure for the fuel assembly. The jackets have tubular sleeves with a hexagonal cross-section and have relatively thin walls to reduce neutron absorption. During operation of the nuclear reactor, the pressure of the coolant flow through the subassemblies expands the shrouds, the expansion usually being an elastic deformation. After prolonged exposure to radiation, the jacket does not return to its original shape due to thermal expansion and radiation hardening. The expansion in cooperation with bending due to voids created by fast neutrons flows

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the subassemblies in the fuel assembly with each other jam. This makes it very difficult to take them out when changing fuel. To account for the expansion and bending To carry, it has been necessary to provide considerable spacing between the sub-assemblies, but large spacing leads to Vibrations and instabilities of reactivity in the fuel arrangement. It has been recognized that a certain radius every corner of the jacket reduces the elastic deformation and a further reduction could be achieved by increasing the radius can be achieved, but unfortunately corners with increased radii can only be achieved at the expense of one or more fuel rods may be provided at the corners of the hexagonal bundle and a reduced use of fuel is not desirable.

The invention therefore provides a hexagonal jacket for a Nuclear fuel subassembly that has increased resistance to expansion across the surfaces and improved Liquid metal-cooled fast breeder, in which vibrations of the sub-assemblies and reactivity instabilities are reduced are.

According to the invention, a nuclear fuel off arrangement A plurality of spaced apart fuel rods within a tubular jacket, wherein the cross-section of the jacket has a closed shape with six straight main sides in a hexagonal arrangement, the main sides

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are connected by secondary sides that are straight or convex in an 'alternative configuration to the center of the shape are. In another aspect, the invention resides in a nuclear fuel subassembly having a plurality of spaced apart located fuel rods within a tubular jacket with a substantially hexagonal cross-section, but where the Corners are replaced by flat sides or radii, the convex surfaces of which are arranged inwards towards the jacket. Just Adjacent sides of the cross section of a shell of a nuclear fuel subassembly according to the invention have the effect that they '' Shorten the length of the main sides and thereby the deflection decrease due to the load from the coolant pressure, and for this reason the resistance to expansion is a Mantle increased over the surfaces by making the straight main and secondary sides of the cross-section of the same length, so that the jacket approximates more of a (circular) cylindrical shape. As regards the illustration, the term "length" refers to the main sides of the closed shape that goes through limiting the cross-section of the shell means the same as "width" with reference to the flat surfaces or sides of the elongated mantle.

Secondary sides, the cross section of a jacket of one according to the invention Nuclear fuel off subassembly, and in particular those which are convex towards the center of the cross-section, increase the strength of the corners of the mantle and increase about it in addition, resistance to expansion. . . ,

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Although there is a jacket for a fuel subassembly according to the invention it is necessary to have some of the fuel rods normally in a hexagonal bundle with them Dimensions are provided to omit, it has been found that the sub-assemblies according to the invention in FIG Fuel assemblies can be used with a smaller distance from one another, which, because of the reduced expansion, besides the reduction of the vibration and the reactivity instability, it also allows a fuel assembly to contain more fuel subassemblies than a fuel assembly same dimensions in a conventional nuclear reactor. Accordingly, the invention resides in a liquid metal cooled fast breeder of the type in which the nuclear fuel assembly comprises a plurality of closely spaced elongated fuel subassemblies which stand side by side on a support assembly, and each subassembly is a bundle of spaced apart Having fuel rods within a tubular jacket in which the cross-section of the jacket is closed Outline with 6 straight main pages, which are arranged in a hexagonal arrangement, the main pages by minor pages that are straight or, in an alternative shape, convex to the center of the outline.

In the following, the construction of a liquid metal-cooled fast breeder and a fuel subassembly in which the invention is implemented is shown as an exemplary embodiment

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described. Reference is made to the drawings, because of their great clarity and clarity is expressly pointed out with regard to the disclosure.

Show it

FIG. 1 shows a section of a nuclear reactor structure;

Figure 2 is a side view of the structure of a fuel subassembly ;

FIG. 3 shows a cross-section of a shell for a structure of a fuel subassembly, on an enlarged scale Scale;

FIG. 4 shows a cross section of a jacket for a further construction of a fuel subassembly and

FIG. 5 shows part of a cross section of a shell for a second further construction of a fuel subassembly .

FIG. 1 shows a liquid metal-cooled fast breeder with a fuel assembly 1 which is immersed in a tank 2 made of liquid sodium as a coolant in a primary vessel. The primary vessel is from the roof of the security

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heitsgewölbes 4 is suspended and there is a plurality of Coolant pumps 5 and heat exchangers 6 are provided, wherein only one of the pumps and one of the heat exchangers is shown. The fuel assembly 1 mounted on a support structure is located with the heat exchangers in a core tank 8j while the pumps 5, which supply coolant to the grating, are arranged outside the core tank 8. The core or fuel assembly 1 has a plurality of subassemblies protruding upwardly from the grate in close juxtaposition and the fuel assembly is of a cylinder 7a to provide a perimeter border. Control rods 9 and instrumentation 10 penetrate the roof of the vault.

The subassemblies as shown in Figure 2 each have a central fuel section 11, an insert section 12 at the lower end, and a neutron shield section 13 at the upper end. The fuel section has a bundle of elongated fuel rods I ¹ I, which are surrounded in a tubular jacket 15 of essentially hexagonal * cross-section. The rods are supported within the shell at their lower ends by a grid 16 and are stiffened along their length by honeycomb-shaped cell grids 17. The insert portion at the lower end has a mandrel 18 for engaging sockets in the nuclear fuel support structure 7 and has openings 19 through which coolant from inside the structure

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can flow. The upper section 13 is made of solid steel and has a tubular part which has an outlet for Forms coolant flow and a head for lifting.

The tubular jacket 15 in Figure 3 has a generally hexagonal cross-section, but with the 'corners of the hexagon are replaced by narrow flat sides, i.e. the cross-section of the shell has an outline of six straight main sides 15a, which are arranged in a hexagonal arrangement, and the main sides are shortened by Secondary pages that are currently connected. A conventional hexagonal subassembly with the same dimensions over the flat sides and with relatively sharp edges or corners would contain a bundle of 271 fuel rods, but in In the described subassembly, it is necessary to remove three fuel rods from each of the six corners, which is therefore a Bundles of only 253 fuel rods result. However, because of the increased stiffness of the jacket, the expansion is so reduced that that the sub-assemblies can be placed closer together in the fuel assembly and additional sub-assemblies can be added to keep fuel consumption without increasing the overall dimensions of the fuel assembly. Accordingly, by providing small spaces between the sub-assemblies, vibration becomes unö; reactivity instability reduced and it can be achieved overall a profit in fuel use.

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In the first modified fuel subassembly shown in Figure H, sides 15a and 15b of the jacket cross-section are of equal length, thus forming a tubular jacket with 12 sides of equal width. The cross-section of the shell approximates a rigid (circular) cylindrical shape, while maintaining the shape of a hexagonal cross-section suitable for close packing.

In the second alternative fuel subassembly, the is shown in Figure 5, the secondary sides 15b of the jacket cross-section are convex to the center of the cross-section, so that the stiffness of the corners of the shell further increases the resistance to expansion.

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Claims (2)

DR. BERG DIPL.-ING. STAPF DIPL.-ING. SCH7 / ABS DR. DR. SANDMAIR PATENTANWÄLTE Postfach 860245 · 8000 Munich 86 Lawyers' files 29 patent claims: 1. Nuclear fuel subassembly having a plurality of spaced apart fuel rods within a tubular jacket, characterized that the cross section of the jacket (15) has a closed contour with six straight lines Main pages (15a) in a hexagonal arrangement and that the main pages by secondary pages (15b) that are straight or, in an alternative shape, convex to the center of the outline. 2. nuclear fuel subassembly according to claim 1, characterized in that the Minor sides (15b) of the closed outline are straight and the same length as the main sides (15a) to have. Liquid metal cooled fast breeder of the type in which the fuel assembly has a plurality of in close proximity spaced elongated fuel subassemblies extending up side by side from a support structure protrude, has, and wherein each subassembly has a multi- [(089) 988272 telegrams: »U ö O I O / U O /« 3 bank accounts: Hype-Bank Munich 4410122850 988273 BERGSTAPFPATENT Munich (BLZ 70020011) Swift Code: HYPO DE MM 988274 VIT / VTTT / M TELEX: Bayer. Vereinsbank Munich 453100 (bank code 70020270) 983310 vx-LX / UO ₅₂₄₅₆₀ BERGd Postscheck Munich 65343-808 (bank code 70010080) number of spaced apart fuel rods within a tubular jacket, characterized in that the cross-section des Fanteis (15) has a closed outline with six straight main sides (15a) arranged in a hexagonal arrangement are arranged, and that the main pages are connected by secondary pages (15b), the straight or, in a alternative shape, convex to the fit of the outline. 909813/0973