HU214389B - Spacer grids for nuclear fuel elements - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to a spacer lattice for nickel heating elements, exemplary fuel bundle or fuel rods. The spacer is made up of a pair of intersecting and reciprocally bonded tubular cores of lattice strips (1a, 1b, 1c). The ribbons (1a, 1b, 1c) form a three-legged pipe spreader. The spaces (3) between the ribbons (1a, 1b, 1c) in their transverse cross-section are substantially regular hexagons separated by substantially equilateral triangles. ŕ

Description

The present invention relates to a spacer grille for nuclear fuel elements. Nuclear fuel elements may be rods or rods.

Such a grid is used in the nuclear industry to support a plurality of spaced-apart nuclear fuel rods or fuel rods that form a fuel assembly used in a nuclear power plant. The fuel is usually located in the outer housing of the rod or rod.

There are many types of spacer grids, but they are often complex to manufacture and control. For example, some cells forming a grid are, in some cases, fused along their lengths. Welding operations are not easy to perform and are very time consuming and therefore expensive.

U.S. Pat. No. 4,775,509 describes a spacer grid arrangement. In this arrangement, the trace rods are disposed between parallel plates disposed in different directions and at different spacings or levels along the geometric axis of the arrangement. Thus, the disk groups create a fraction of the contact required on the rod at each level along the geometric axis, and at the level the fragments add up to form the entire contact. This arrangement is complicated to manufacture and assemble, and the distance between the points of contact of the plates on the rod is not ideal.

GB 2081961A discloses a spacer grid arrangement in which two sets of mutually fixed plates form a square grid. Multiple rows of continuous, individually added ribbons, forming angled springs with two sets of plates, make it easier to hold the fuel rods between the thimbles on the inside of the grid plates. The production of individual bands forming springs is complicated and expensive to install. Such tapes consist of a large number of separate components prior to assembly. With the springs described, the belts have relatively large displacement bends and therefore the gripping force of the springs and the ends on the rod is not ideal.

The object of the present invention is to overcome the described drawbacks of known spacer grids.

According to the invention, this object is solved by a spacer grid of parallel ribbons for nuclear fuel elements, such as fuel rods and fuel rods, which are mutually intersecting and fixed to each other. The ribbons form three groups, and the spaces between the ribbons have substantially regular hexagons in their transverse cross-sections, which are separated by substantially equilateral triangles.

In this grid, the heating elements, fuel rods and fuel rods, are located in hexagonal spaces between the ribbons during use. Two or more grids can serve to hold the fuel assemblies in different positions along the length of the elements. The heating elements may be fuel rods or fuel rods, which are preferably long, straight cylinders of circular cross-section. The hexagonal spaces of the grid can be formed by frictional contact of each rod or rod with the inwardly directed ribbed surfaces forming the hexagon.

Preferably, the inwardly facing surfaces or selected portions of the tapes forming the individual hexagons, such as three of the six surfaces delimiting each hexagon, may have shapes that facilitate the holding of the fuel rod or fuel rod. Preferably, these shapes are all at substantially the same height as when the grid is assembled and holds the fuel rods. For example, every other surface of a given hexagon (e.g., the first, third, and fifth surfaces, if the surfaces are numbered in series) may have a thimble or a thimble and a spring such that the fuel rod or fuel rod held in the hexagon is pressed against the thimble the geometry axis of the fuel rod or fuel rod preferably coincides with the center of the hexagon.

The intersecting strips preferably form regular hexagonal spaces. The geometric arrangement of the lattice is such that every other side of the hexagon meets to form equilateral triangles with the sides of the hexagon between them. The area of each triangle is equal to (or nearly equal to) one-sixth the area of the hexagon. In this way, all the shapes formed by the sides of the hexagon meeting around each triangle are a six-pointed star around the hexagon. The triangular spaces suitably allow the refrigerant to flow in a direction parallel to the axis of the rods or rods when the grid and fuel rod or fuel rod assembly are in use.

The shape of the outer casing, and thus the enclosed shape of the bars or rods held by the lattice, is determined by the shape of the cavity in the reactor core, in which the entire assembly (i.e., the lattice and rods or rods supported by the lattice) The grid itself may be surrounded by an outer wrapping tape, which may itself be hexagonal or, alternatively, square.

The strips forming the hexagonal spaces of the grid preferably have end tongues at one or both intersecting edges (i.e., edges perpendicular to the geometric axes of the hexagonal spaces), which facilitate the welding of the strips. Additional end tongues may be provided on the first ribbon, forming a step and thereby allowing the refrigerant to be mixed when used in the nuclear reactor. For this latter purpose, the tongues preferably have agitator blades on the downstream side of the grid (i.e., the side further downstream of the flow of refrigerant). Such blades increase the swirling of the refrigerant stream as the refrigerant flows through the grid. This improves the heat transfer capacity of the refrigerant.

The ribbons described can be linked in the same way as in the UK the egg tray grids used to pack eggs in an egg box. Preferably, the tapes of the present invention have a plurality of regular spacings 2

EN 214 389 Β, which allow the tapes to be far apart and interconnected. For example, these gaps can be formed alternately at the top and bottom edges of the tapes in one band group and only at one edge of the tapes in the other two band groups. In either case, the slits are inwardly directed toward the center of the web, preferably perpendicular to the longitudinal axis of the web. Preferably, the length of the slits is slightly more than 0.5 W, where W is the average depth of the tape, which does not include the side tabs protruding from the edges of the tape. This gap length ensures that the assembled strips are properly connected. The gaps can pass through the tongues, if any. Preferably, the width of the slits is slightly larger than the thickness of the strips so that the strips fit snugly into the slots. There may be additional gaps in the tapes that do not extend to the edges of the tapes. These additional slots further facilitate the flow of refrigerant during operation. Preferably, the additional gaps are parallel to the first gaps. The aforementioned springs, if any, may be formed by extruding the straps between said further gaps.

The spacer grid according to the invention is preferably simpler to manufacture than the known spacer grid and is inherently more rigid in structure. This results in better contact with the fuel rods to be retained. Since the tapes are not bent, the original strength of the tape is retained. This eliminates the problems of bending the tape. The associated tapes are held together by the mutual friction forces. The welded joints between the strips may be formed at the side edges of the strips where the edges intersect. However, these joints are easy to form due to the accessibility of the welding sites and require only a small amount of welding material since they do not have to be cut to length between the ribbons. In order to increase the strength, further welds may be made at some or all of the ribbing cuts, at the upper or lower edges. The belts of the present invention do not need to assemble as many components as before.

In the nuclear reactor, the refrigerant moves from the bottom of the fuel assembly to the top of the fuel assembly and discharges to the heat exchangers. It is desirable that the fuel assembly slightly reduce the refrigerant pressure so as to minimize the pressure of the refrigerant passing through the reactor core. The refrigerant pressure is always reduced to a certain extent each time it comes into contact with the spacer grid of a heating element. The grid according to the invention represents only one bar of barrier thickness for the refrigerant and therefore causes minimal pressure drop. This allows you to maximize reactor efficiency.

The capture of fission-free (parasitic) neutrons is also minimized. This, together with minimizing pressure drop, reduces the cost of the reactor fuel cycle.

The following is a summary of the features and advantages of the lattice according to the invention. This grille has a very solid and rigid structure and can be formed with a simple Coupler assembly. The groove placement pattern ensures easy manufacturing. The number and position of welding sites is minimized, which reduces manufacturing costs. Grids can be made of low neutron capture material (such as Zircalloy 4 alloy). The amount of material used for the lattice is minimized, which reduces the capture of non-fissionable neutrons. The spring load of the heating elements in the grille is easily adjustable. The size of the fuel elements does not increase due to irradiation in the reactor. The grilles provide a suitable support for the heating elements during transport and handling. Grids minimize refrigerant pressure, although refrigerant mixing vanes can be used where necessary.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a spacer and support grid for a nuclear fuel rod, a

Figure 2 is a side view of the strip used in the grid of Figure 1, a

Figure 3 is a sectional view taken along line III-III of the strip of Figure 2, a

Figure 4 is a sectional view taken along line IV-IV of the strip of Figure 2;

Figure 5 is a side view of another embodiment of the belt used in the grid of Figure 1, a

Figure 6 is a sectional view taken along line VI-VI of Figure 5, a

Figure 7 is a sectional view taken along line VII-VII of the strip of Figure 5.

As shown in Fig. 1, the grid is formed by a series of ribbons la which, in a first direction, intersect a series of ribbons lb and are connected thereto. The second row of lb bands runs in a second direction, which makes an angle of 120 ° with the first direction. The first row of ribbons la also intersects the row of ribbons down which goes in a third direction. This third direction has an angle of 120 ° with the first and second directions. The bands la, lb and le may be made of high-strength machinable metal with adequate neutron capture capacity. Examples of such metals are stainless steel or Zircalloy alloy.

Between the ribbons 1a, 1b and down, hexagonal spaces 3 are provided for holding fuel rods or fuel rods (not shown) and triangular spaces 5 are formed between hexagons 3. The spaces 5 facilitate the flow of refrigerant between the fuel rods during operation.

On the side walls of the strips la there are formed thimbles 7a which extend inwardly and abut the hexagonal spaces 3. The side walls of the lb strips are provided with thimbles 7b which also extend inwardly and abut the hexagonal spaces 3.

The springs 9, formed as inwardly curved ribbons, are provided on the side walls of the ribbons la, which are inwardly facing and bounded by the hexagonal spaces 3.

HU 214 389 Β

The entire configuration of the hexagons and triangles formed by the bands la, lb and down is bounded by an outer hexagonal ribbon. On the inwardly facing walls of the outer strip 10 there are thimbles 12 similar to thimbles 7a where the ribbon 10 is parallel to the ribbons la and lb and the springs where the ribbon 10 is parallel to the down ribbons.

2-4. FIG. 1A shows one of the types of tapes, the down tapes, from which the grid of FIG. 1 is formed. The length of each strip is selected according to the position occupied by the strip in the lattice in the enclosing hexagonal envelope formed by the strip. (The need for tapes of different lengths is evident from the arrangement of the tapes shown in Figure 1). The same is true with the bands la and lb.

As shown in Figure 2, the pattern of the down ribbon consists of P-division repeating units. Each unit in the sample has two large tongues 11 and two small tongues 13 which serve as welding points at the upper edge of the down band. The tongues 11 and 13 are arranged alternately along the upper edge. For each second tongue 13, denoted as tongue 13a in Fig. 2, tongue 13a passes through tongue 13a which is perpendicular to the longitudinal axis of ribbon 1c (i.e., geometric axis IV-IV in Fig. 2). If necessary, the tongues serving as mixing vanes can be bent into areas which will form triangular spaces 5 in the alternating pattern of Figure 1 along the length of the down belt. Each slot is substantially directed toward the center of the down band, i.e. line IV-IV, which is approximately half the average width of the down band (ignoring the extra width represented by the tongues at the edges of the down band). As opposed to the small tongues 13 at the upper edge of the strip, the tongue has small tongues 17 at the bottom edge which also allow welding. For every other 17 languages, designated 17a, a gap 19 passes through 17a. The slot 19 is parallel to the slot 15. Each of the slots 19 is substantially oriented towards the center of the strip 1c. The slots 15 and 19 alternate along the length of the down ribbon.

As shown in Figures 3 and 4, in the down strip, between the alternating pairs of slots 15 and 19 (i.e., between the first, third, fifth, etc., but not between the second, fourth, sixth, etc., slice pairs) 9 springs are formed. This ensures that the springs 9 are formed at the locations containing the hexagonal spaces 3. The positions of the springs 9 are flush with the alternating large tongues 11. The springs 9 are formed between two slots 21 formed in the down belt, which do not extend to the edges of the down belt. The springs 9 have curved portions which are formed such that the strip is perpendicular to its plane,

2.

5-7. 1A shows how lb strips are used in the lattice of FIG. The la bands are the same as the lb bands. The lb bands also have a pattern of repeating units of P division. Within each unit, each unit has two small tongues 23 similar to tongues 13a at the upper edge of the lb strip, and slots 25 similar to slots 15 pass through tongues 23 substantially toward the center of the lb band. In this case, there are two 25 slots per P division unit, and the slots 25 pass through each of the 23 languages (not just every other language as in Figure 2). At the lower edge of the strip lb, there are tongues 27 similar to the tongues 13 of Fig. 2, in contrast to the tongues 23. In this case, rings 29 are formed by pressing the lb in the center of the lb. (The density of these is one per repeating unit, so that the rings 29 are located in the areas that will form the hexagonal spaces 3).

The density of the slots 25 in the strips 1 a is different from the density of the slots 19 in the down strips (Fig. 3), since it depends on the configuration of the grid assembly. It allows easy installation and connection of the tapes in different places of the grid.

In use, the tapes 1a, 1c and 1c are joined using a positioning device to form the grid of Figure 1. When installing the grid, the tapes la are first inserted into the positioning device (not shown) and the tapes 1c are inserted into these tapes at the slots. The bands la are then inverted and rotated by 120 ° to fit into the slots in the down bands and the other bands lb. The slots 25 in the lb bands and the corresponding slots in the bands la receive the down bands, and the slots 15 and 19 in the down bands receive the bands la and lb. The tongues 13 and 17 on the ribbons down, the tongues 23 and 27 on the ribbons lb and the corresponding tongues on the ribbons la make it easier to join the ribbons by spot welding at their edges.

For use, the nuclear fuel rods or rods of Figure 1 and the grids are assembled in a known manner. The rods or sticks in a given group are held in a suitable position by a suitable arrangement of the lattices. The entire assembly thus formed fits into the nuclear reactor nucleus through the hexagonal shape of the lattice.

During operation, the large tongues 11 (Fig. 2) serve as a refrigerant agitator blade in the reactor core as described above.

If mixing vanes are not used, then all three groups of belts used in the grid can be the same, which reduces production costs.

Claims (9)

PATENT CLAIMS A spacer grid for nuclear fuel elements, such as fuel rods or fuel rods, consisting of mutually intersecting and interconnected groups of parallel ribbons, characterized in that the ribbons form three groups and have a transverse transverse cross-section (3) in the space between the ribbons. equilateral triangles separate. HU 214 389 Β Spacer grid according to claim 1, characterized in that nuclear fuel elements are arranged in the hexagonal spaces (3) between the strips (1a, 1b and down). Spacer grid according to claim 1 or 2, characterized in that the strips (1a, 1b and down) or the surfaces or selected portions forming the hexagonal spaces (3) have shapes formed thereon or therefrom which facilitate the heating elements. compliance. Spacer grid according to claim 3, characterized in that the shapes are formed by springs (9,14) and rings (7a, 7b, 12, 29). Spacer grid according to any one of the preceding claims, characterized in that it is surrounded by a hexagonal or square outer wrapping grid strip (10). Spacer grid according to one of the preceding claims, characterized in that the strips (1a, 1b, le) forming the hexagonal spaces (3) have tongues (11,13,13a, 17, 17a, 23, 27) at one or both of the intersecting edges. there are some 5 making welding of the strips (1a, 1b, 1c) and mixing refrigerant in a nuclear reactor easier. Spacer grid according to any one of the preceding claims, characterized in that it is regular in the strips At intervals there are gaps (15,19,23,25) which allow the tapes (la, lb, le) to be interconnected and the width of these gaps is slightly larger than the thickness of the tapes (la, lb, le), so that tapes (la, lb, down) fit snugly into the slots 15 (15,19,23,25).