EA041297B1 - SPACING AND MIXING GRILLE OF FUEL CARTRIDGE OF NUCLEAR POWER REACTOR - Google Patents

Description

The invention relates to the field of nuclear industry, specifically to the design of spacer mixing grids for fuel assemblies of nuclear reactors.

A spacer grid is known (RU2127001, G21C3/34, 02/27/1999), having a hexagonal rim, in which cells of a tetrahedral, pentahedral and hexagonal shape are connected to the rim and to each other, made of zirconium tape, provided with protrusions and notches. The cells are connected to each other by weld points on each face.

The disadvantage of this design is the occurrence of fuel elements in the cells of the spacer grid with great effort. Because of this, the probability of damage to the fuel elements increases, since the diameter of the inscribed circle between the four points formed by the protrusions in the lattice is somewhat smaller than the diameter of the fuel element itself. The presence of various types of cells in the grating complicates the process of manufacturing the grating and leads to an increase in the cost of production of the spacer grating.

A known design of the mixing grid with the arrangement of fuel elements according to the triangular pattern (RU2389091, G21C3/344, 10.05.2010), consisting of cells. The cells are in the form of tubes of variable cross section, while the upper and lower parts of the cells are in the form of polyhedrons, whose faces adjoin each other.

The disadvantage of this design is the lack of operational reliability of the lattice and the complexity of manufacturing technology.

The closest in technical essence to the proposed grid structure is a hexagonal spacer grid with a triangular package of fuel elements (RU2399968, G21C3/32, 27.04.2010). The grating has three groups of plates parallel to each other within the group. In this case, the plates of different groups intersect with each other, the displacement between the plates belonging to any two groups is 60°. The plates are fixed in the lattice between the inner and outer shells, having corresponding holes for the plates.

One group of plates is provided with slots on both sides to fix the three groups of plates together and to stiffen the entire structure.

The disadvantage of this design is the choice of a non-optimal shape of the inner shell in the form of a hexagon, which complicates the installation of the central displacer inside it, and the sides of the inner shell touch a number of fuel elements located near the displacer, which can lead to a decrease in the efficiency of heat removal from the fuel elements.

The objective of the claimed invention is to create a more advanced design of the spacer mixing grid, which will guarantee a rigid structure of the geometry of the fuel bundle, and will also have an additional function of mixing the flow and thereby ensure heat transfer intensification through the use of special mixing blades, slots and bends.

EFFECT: ensuring the geometric stability of the fuel bundle, homogenizing the temperature field of the flow in the cross section of the fuel cassette, intensifying heat transfer in the fuel bundle, eliminating stagnant coolant flow zones in the cross section of the cassette and increasing the margin to the heat transfer crisis, which, in turn, increases thermal reliability fuel cassette and the core as a whole.

The technical result is achieved by the fact that in the spacer grid with a triangular package of fuel elements, taken as a prototype, and consisting of three groups of intersecting plates enclosed between two shells, the shape of the inner shell was changed to a dodecahedron, additional stiffening ribs were installed in the corners of the outer shell, the design plates of the outer shell is changed by adding diagonal slots, on the ends of two groups of plates located between the inner and outer shells, mixing blades of two types of profile shape are installed, and in one of the two selected groups of plates, which has the largest width, triangular bends are additionally made. The essence of the technical solution is illustrated by drawings, where in Fig. 1 - cross section of the spacer mixing grid;

in fig. 2 - plate of the outer rim of the spacer mixing grid;

in fig. 3 - development of the inner shell of the spacer mixing grid;

in fig. 4 - general view of the inner shell;

in fig. 5 - orientation of the plates of the spacer mixing grid relative to the fuel element;

in fig. 6 - wide plate with perforation and mixing blades;

in fig. 7 - diagram of the bend of the mixing blades and triangular bends on a wide plate;

in fig. 8 - narrow plate with mixing blades;

in fig. 9 - scheme of the bending of the mixing blades on a narrow plate.

The spacer mixing grid, the cross section of which is shown in (Fig. 1) is a set of plates of three types 1, 2, 3, parallel to each other within the same type, located in the inter-fuel space and enclosed between the outer 4 and inner 5 shells.

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Claims (3)

In the corners of a regular hexagon formed by the outer shell, stiffening ribs 6 are installed, made in the form of rectangular plates, having a length equal to the length of the rim of the outer shell. Thanks to the stiffening ribs, the positioning of the corner fuel elements 7 is carried out, their rigid fixation inside the grate and the strength of the structure of the grate itself increases. The outer shell 4 consists of plates placed in the form of a regular hexagon. Each plate shown in (Fig. 2) is provided with rectangular grooves 8 for attaching plates 1, 2, 3, as well as perforation 9, made in the form of rectangular slots rotated at an angle of 25° and with a width less than slot 8, and designed for additional flow turbulence in the peripheral fuel cassette area. The end parts of the plates (Fig. 2) of the outer shell are provided with protrusions 10 so that the plates are aligned with the absence of transverse displacement. The inner shell 5 (Fig. 3, 4) is a plate bent into a dodecagon to facilitate the installation of the central displacer, as well as to reduce cross-sectional crowding. The inner shell is provided with rectangular grooves 11 for fixing plates 1, 2, 3, which provide spacing of fuel elements. On (Fig. 3) are presented in the form of dotted lines the place of bending 12 of the plate of the inner shell 5. Plates 1, 2, 3 (Fig. 1), located between the outer and inner shells 4, 5, intersecting, form cells of two types: free cells 13, made in the form of triangles and not occupied by fuel elements 7, and regular cells 14, made in the form of irregular hexagons, in which fuel elements 7 are installed and reliably positioned for the entire period of operation of the fuel cartridge. Moreover, the plates 1, 2, 3 are located at three levels, so that the fuel element 7 touches only the plate of one of the levels (Fig. 5). Plates 1, 2, 3 located between the outer and inner shells 4, 5 are divided into three groups. The first group - wide plates 1 (Fig. 6, 7). On the plates 1 assigned to the first group, grooves 15 are made for fixing obliquely arranged plates 2, 3 and forming free and regular cells 13, 14 (Fig. 1). The plates of the first group have a perforation 16, and the corners 17 formed by the perforation are bent at an angle of 20°. The layout of the slots is shown in (Fig. 6), and the directions for bending the corners are shown in (Fig. 7). Bent corners 17 located on a wide plate 1 on the same line running parallel to the fuel elements 7 are directed in one direction. Bent corners 17 have the function of additional turbulence of the coolant inside the grate. On the side ends of the plates, protrusions 18 are made (Fig. 6, 7) for attaching the plates between the outer and inner shells 4, 5. At the end of the wide plate 1 (Fig. 6, 7), located on the exit side of the grate, mixing blades 19, 20 are installed, of two types shown in (Fig. 6, 7). The first type of blade 19 has a trapezoidal profile with a bend inside the free cell 13 at an angle of 30°. The shape of the bend of the mixing blade 19 is shown in (Fig. 7). The second type of blade 20 is asymmetric, on the one hand there is a cutout made to maintain a margin before contact with the fuel element 7. The mixing blade 20 is located in the cells in which the fuel elements 7 are located. The blade 20 is bent at an angle of 30 ° towards the fuel element 7 The shape of the fold of the mixing blade 20 is shown in (FIG. 7). Mixing blades 19, 20 and the plates on which they are located are a single body. The second group of plates - narrow plates 2 (Fig. 8, 9), rotated relative to wide plates 1 at an angle of 60°. They are inserted into the grooves of 15 wide plates 1 located on the exit side of the grate. The shape of the narrow plates 2 is shown in (Fig. 8, 9). On the narrow plates 2 there are mixing blades having a shape, bending angles and layout similar to the blades 19, 20 located on the wide plate 1. The third group of plates - narrow plates 3, located at the entrance to the grate, have a shape similar to the shape of the second group of plates (narrow plates 2), but without mixing blades. Narrow plates 3 are inserted into wide plates 1 in the corresponding grooves 15. Relative to wide plates 1, this group of plates is also rotated by 60°, but in the other direction. The wide plates 1 are fixed between the outer and inner shells 4, 5 due to the protrusions 18 at the ends of the plates (Fig. 6, 7) and rectangular slots 8 in the outer shell and rectangular slots 11 in the inner shell. Narrow plates 2, 3 are fixed by fastening them in grooves 15 (Fig. 6, 7) located on wide plates 1 and in rectangular slots 8 in the outer shell and in rectangular slots 11 in the inner shell. CLAIM A spacer mixing grid consisting of three rows of plates enclosed between the outer and inner shells, characterized in that the outer shell and one of the rows of plates are provided with perforations of various shapes to provide additional flow turbulence, -