Tube Grid Cell

Abstract

A tube grid cell (2) for a fuel bundle (8) of a nuclear reactor. The tube grid cell (2) having the length (L), comprises a cell housing (10) which has, along the longitudinal axis A, a lower section (16), an upper section (18) and a middle section (20). The middle section (20) is provided with two pairs of support members (22) and a resilient member (24) configured to generate a resilient force in an inward radial direction, the resilient member is arranged at essentially equal distance from the support members (22), and positioned approximately (120) degrees apart from the support members seen along axis A. The upper section (18) and the lower section (16) have respectively a length L1 and L2 along axis A that is larger than 0.1 L and smaller than 0.3 L, and is provided with a solid housing wall, having an even thickness and no openings, indentations or protrusions.

Claims

1.-10. (canceled)

11. A tube grid cell for a grid assembly including a plurality of tube grid cells and intended to hold a plurality of elongated fuel rods in a fuel bundle in a nuclear reactor, the tube grid cell is cylinder-shaped, has an essentially circular cross-section and an elongated extension along a longitudinal axis A, and has a length L, and that axis A has an essentially vertical direction during normal use; the tube grid cell comprises a cell housing comprising a tubular housing wall defining a top opening and a bottom opening configured to receive a fuel rod, the cell housing comprises, along the longitudinal axis A, a lower section, an upper section and a middle section placed between the upper and lower sections; the middle section is provided with two pairs of support members each having a radially inward directed extension, one of said pairs is arranged close to an upper part of the middle section, and the other of said pairs is arranged close to a lower part of the middle section, the support members of each pair are arranged at a same plane being perpendicular to axis A and are positioned approximately 120 degrees apart seen along axis A, and the support members of one pair are arranged above the support members of the other pair, the middle section is further provided with a resilient member configured to generate a resilient force in an inward radial direction, the resilient member is arranged between said planes of the pairs of support members and at essentially equal distance from the planes of the support members, and positioned approximately 120 degrees apart from the support members seen along axis A, and characterized in that the upper section and the lower section have respectively a length L1 and L2 along axis A that is larger than 0.1 L and smaller than 0.3 L, i.e. 0.1 L<L1 (L2)<0.3 L, and is provided with a solid housing wall, having an even thickness and no openings, indentations or protrusions, except for optional welding members extending from the housing wall along axis A, wherein the solid housing walls of the upper and lower sections will improve lateral properties of the grid assembly which is made up of a plurality of tube grid cells welded together, and wherein the welding is performed at the upper and lower sections.

12. The tube grid cell according to claim 11, wherein the welding is performed by laser welding.

13. The tube grid cell according to claim 11, wherein each of the upper and lower sections is provided with a predetermined number of welding members structured for welding, when attaching neighbouring grid cells to each other.

14. The tube grid cell according to claim 13, wherein the welding is laser welding.

15. The tube grid cell according to claim 11, wherein each welding member is a protrusion extending from the housing wall along axis A.

16. The tube grid cell according to claim 11, comprising four or six welding members.

17. The tube grid cell according to claim 11, wherein said support members are provided with an open structure in the longitudinal direction along axis A allowing coolant to pass by.

18. The tube grid cell according to claim 11, wherein said support member has a bow-like shape in a plane perpendicular to axis A and is attached at each of its ends to an inner surface of the housing wall.

19. The tube grid cell according to claim 11, wherein the tubular housing wall of the middle section is provided with openings at positions where the support members and the resilient member are arranged.

20. A grid assembly comprising a plurality of tube grid cells according to claim 11.

21. A fuel bundle comprising at least two grid assemblies according to claim 20.

22. A nuclear reactor comprising at least one fuel bundle according to claim 21.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a side view schematically illustrating a tube grid cell according to an embodiment of the present invention.

[0028] FIG. 2 is a view along axis A schematically illustrating a tube grid cell according to an embodiment of the present invention.

[0029] FIG. 3 shows two perspective views of a tube grid cell according to an embodiment of the present invention.

[0030] FIG. 4 is a view from above of a tube grid assembly according to one embodiment with a triangular pitch between rods of the present invention.

[0031] FIG. 5 is a view from above of a tube grid assembly according to another embodiment with a square lattice arrangement of the present invention.

[0032] FIG. 6 shows a schematic illustration of a fuel rod bundle provided with grid assemblies according to the present invention.

DETAILED DESCRIPTION

[0033] The tube grid cell, and also the grid assembly and fuel bundle, will now be described in detail with references to the appended figures. Throughout the figures the same, or similar, items have the same reference signs. Moreover, the items and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

[0034] With references to FIGS. 1 and 2 the tube grid cell 2 will now be described in detail. The tube grid cell 2 is structured to be mounted in a grid assembly 4 (see FIGS. 4-5) including a plurality of tube grid cells and intended to hold a plurality of elongated fuel rods 6 in a fuel rod bundle 8 (see FIG. 6) in a nuclear reactor. The tube grid cell 2 is cylinder-shaped, has an essentially circular cross-section and an elongated extension along a longitudinal axis A, and has a length L, and that axis A has an essentially vertical direction during normal use.

[0035] The tube grid cell comprises a cell housing 10 defining a top opening 12 and a bottom opening 14 (see FIG. 3) configured to receive a fuel rod 6 (see FIG. 4).

[0036] The cell housing 10 comprises, along the longitudinal axis A, a lower section 16, an upper section 18 and a middle section 20 placed between the upper and lower sections. The lower and upper sections may be symmetrically arranged with regard to the middle section as presented on FIG. 3.

[0037] The middle section 20 is provided with two pairs of support members 22 each having a radially inward directed extension, one of said pairs is arranged close to an upper part of the middle section 20, and the other of said pairs is arranged close to a lower part of the middle section 20.

[0038] The support members 22 of each pair are arranged at a same plane being perpendicular to axis A and are positioned approximately 120 degrees apart from each other, and the support members 22 of one pair are arranged above the support members 22 of the other pair.

[0039] The middle section 20 is also provided with a resilient member 24 configured to generate a resilient force in an inward radial direction to support a fuel rod. The resilient member is arranged between said planes of the pairs of support members and at essentially equal distance from the planes of the support members 22. The resilient member 24 is positioned approximately 120 degrees apart from the support members seen along axis A. The resilient member may have shape of a leaf spring attached to the housing wall and displaying an arcuate shape inwards. When a fuel rod 6 is inserted in the grid cell, see the mid cell of FIG. 4, the resilient member 24 is structured to urge the fuel rod inwards in a radial direction against the support members 22.

[0040] The upper section 18 and the lower section 16 have respectively length L1 and L2 along axis A that is larger than 0.1 L and smaller than 0.3 L, i.e. 0.1 L<L1(L2)<0.3 L. In one embodiment L1 and L2 are equal. Furthermore, the upper and lower sections are provided with a solid housing wall, having an even thickness and no openings, indentations, or protrusions.

[0041] The solid housing walls of the upper and lower sections will improve lateral properties of the grid assembly which is made up of a plurality of tube grid cells welded together. The welding is performed at the upper and lower sections, e.g. by laser welding.

[0042] According to one embodiment, each of the upper 18 and lower sections 16 is provided with a predetermined number of welding members 26 structured for welding when attaching neighbouring grid cells to each other. Preferably, each welding member is a protrusion extending from the housing wall along axis A.

[0043] Preferably, the tube grid cell 2 comprises four or six welding members.

[0044] If four welding members 26 are provided at each upper 18 and lower 16 sections, the tube grid cells advantageously are arranged in the grid assembly as illustrated in FIG. 5, in a square lattice.

[0045] If instead six welding members 26 are provided at each upper 18 and lower 16 sections, the tube grid cells advantageously are arranged in the grid assembly as illustrated in FIG. 4, in a triangular array.

[0046] Note that in FIGS. 4 and 5 only a minor part of a grid assembly are shown.

[0047] According to an embodiment the support members 22 are provided with an open structure in the longitudinal direction along axis A allowing coolant to easy pass by. Preferably, the support member has a bow-like shape in a plane perpendicular to axis A, and is attached at each of its ends to an inner surface of the housing wall.

[0048] According to still another embodiment, the tubular housing wall of the middle section is provided with openings at positions where the support members and the resilient member are arranged (see e.g. FIG. 3).

[0049] The present invention also relates to a grid assembly 4 comprising a plurality of tube grid cells 2 as defined above. The plurality of tube grid cells are advantageously arranged in a triangular array (see FIG. 4) or in a square lattice (see FIG. 5).

[0050] Furthermore, the present invention relates to a fuel bundle assembly 8 comprising at least two grid assemblies 4 arranged to firmly hold a bundle of fuel rods 6. An exemplary fuel bundle 8 is schematically illustrated in FIG. 6 that comprises four grid assemblies.

[0051] The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.