RU2715387C1 - Separation and mixing grid of nuclear reactor fuel assembly - Google Patents

Abstract

FIELD: nuclear physics and equipment.

SUBSTANCE: invention relates to design of mixing separation grids for fuel assemblies of nuclear reactors. Intermixing separation grid consisting of plates mutually perpendicular in two planes, forms cross-section channels of square cross-section of grid with fixed at the center of intersection of plates on side of inlet and outlet of heat carrier spacer spring elements – rings. At ends of plates deflectors are located, one edge of which is located at base of plates intersection, and the other in cross section is limited by the shape of spacer elements with allowance for margin to touch in cross section, which is necessary for installation of second row of spacer elements on the side of heat carrier outlet.

EFFECT: high uniformity of distribution of the temperature field in the cross-section of the channel, high intensity of heat exchange on the surface of fuel elements, which increases stock before the crisis of heat exchange.

1 cl, 6 dwg

Description

The invention relates to the field of nuclear engineering, specifically to designs of mixing spacing grids for fuel assemblies of nuclear reactors. Remote lattices provide fixing and the set step of arrangement of fuel elements among themselves. The distance between the core elements remains unchanged throughout the life of the fuel assembly due to rigid fixation in the cells of the spacer grid. To equalize the thermohydraulic characteristics of the coolant, as well as to ensure the uniformity of the temperature field of the cross section of the cartridge, mixing lattices are used, which include special elements - petals, which create a turbulization of the coolant flow and its mixing in the inter-space, providing the necessary intensification of heat transfer.

Known mixing spacer grid containing cells made in the form of a perforated shell, forming in cross section a curved shape obtained by stamping a workpiece at four corner points inside the cell (US6816563, G21C3 / 344, 09.11.2004). In this design, the cells are interconnected by welding and externally pulled together by a rim. On the cells on both sides of the mixing spacer grid, spherical spacing protrusions are made, as well as mixing blades formed by a straight cut on the cell shell and bending its free part.

The disadvantage of this design is the insufficient stiffness of the cells, necessary to prevent displacement of the fuel element during operation, which is justified by the presence of perforations in the shell, forming elastic elements that do not have the required stiffness. Another drawback is the requirement for precision manufacturing of stamped blanks to ensure guaranteed contact of the elements using spot welding, which in turn is characterized by a large amount of work and complexity in the automation of the process.

Known mixing spacer grid containing cells formed by perpendicular mutually intersecting plates, in which the spacing elements are made, which are bent, mirror-shaped relative to the center of the plate, plate strips angled in the longitudinal axis inside the cell, at the free end of which are bead elements (US9620250 , G21C3 / 352, 04.11. 2017). In this design, on the plates, in addition to the four lateral ones, bent plate elements are made - intensifiers located on the end part of the plates on the outlet side of the coolant, designed to mix the flow. In turn, cuts are made at the edges of the four lateral plates, the free part of which is bent into the grating, designed to prevent damage to the intensifiers in the collision of two mixing distance gratings.

The disadvantage of this design is the high clutter of the channel, due to the large area covered by the distance elements. Another drawback is the high complexity of the manufacturing and assembly process, which is caused by a large number of stamping elements and the heterogeneity of the spacing elements on the plates, depending on the specific position of the plate in the assembly.

 The closest in technical essence and the achieved result to the present invention is a spacer grid containing cells formed by perpendicular intersecting plates, at the edges of which bent blades are made at the outlet of the coolant flow, designed to mix the coolant (EP2929539B1, G21C3 / 356, 11/01/2017). In this design, the spacing of the fuel elements is carried out by tubular spring elements of square section located at the center of intersection of the plates, for which special grooves are made in them.

The disadvantage of this design is the large length of the grooves for the plug-in spacer element, which reduces the bending stiffness of the cells and the rigidity of the overall structure as a whole. Also, the large length of the spacing elements creates a large hydraulic resistance and is characterized by a large friction force when pushing the fuel elements at the time of assembly.

The objective of the invention is to create a more advanced design of elements that intensify heat transfer, and their mutual orientation in the channel of the heat assembly, taking into account the design features of the spacing of the fuel elements.

The technical result is a more uniform distribution of the temperature field in the cross section of the channel, an increase in the intensity of heat transfer on the surface of the fuel elements, which in turn allows you to increase the supply before the heat transfer crisis.

The technical result is achieved by the fact that a mixing spacer lattice, consisting of plates mutually perpendicular in two planes, forms cross-section channels of a square cross-section of the lattice with spacing spring elements fixed in the center of intersection of the plates on the inlet and outlet sides of the coolant; deflectors are located at the ends of the plates, one edge of which is located at the base of the intersection of the plates, and the other in the cross section is limited by the shape of the spacing elements, taking into account the margin until touching in the cross section, which is necessary to install the second row of spacing elements from the coolant outlet side.

To increase the critical heat flux in the channels of thermal assemblies, as a rule, they seek to increase the intensity of the following phenomena: intracellular vortex formation and intercellular mixing. To form a large-scale long-lived vortex in the center of each cell, the four deflectors at the base of the intersection of the plates are oriented in such a way that the bending direction of the deflectors has one direction in a circular axis. To increase the intensity of intercellular mixing, a convective flow is created, formed when the deflectors flow around the flow, oriented in such a way that two deflectors on the same plate are located opposite to each other in the cell, and there is no deflector in adjacent cells in the direction of the deflected flow, but deflectors located on the perpendicular plates in cross section, occupy the same area as adjacent cells. To assemble this mixing lattice, in particular, fixing the spring elements from the outlet side of the coolant, a margin of up to touching d between the outer edge of the deflector and the inner side of the annular spring element in the cross section of the flow channel of the coolant is provided.

The essence of the invention is fully disclosed graphically in the drawings:

FIG. 1 - plug-in spacer element in the General Assembly;

FIG. 2 - cell fuel assembly;

FIG. 3 - transverse projection of the plate;

FIG. 4 - mixing spacer grid with 2 deflectors per cell;

FIG. 5 - mixing spacer grid with 4 baffles per cell;

FIG. 6 - profiles of deflectors for various bending angles.

The mixing distance grid consists of intersecting perpendicular plates (1), (2) (Fig. 1), interconnected in specially made grooves (3) (Fig. 3), made up to the middle of the plate (Fig. 3), forming cells ( 4) (Fig. 2) the shape of the square in cross section. Also on both sides of the plate (figure 3) has grooves of square cross-section (5) for installation and cellular spacing elements - rings (6) fixing the fuel elements (7) having a margin to touch d.

Figure 4 shows a mixing distance grid with deflectors (8) oriented in such a way that in the cell (9) two deflectors (10) are on the same plate oppositely directed to each other, and in adjacent cells (11) in the direction of the deflected flow deflectors (12) are absent.

Figure (5) shows a mixing distance grid with deflectors (13), the bending direction has one direction along the rotary axis (14).

Fig. 6 shows deflector profiles for an angle of 25 degrees (15) and 30 degrees (16), the geometry of which is determined by the internal shape of the spring element (6).

Claims (1)

A mixing spacer grid consisting of plates mutually perpendicular in two planes, characterized in that it forms cross-section channels of a square cross-section of the grid with spacing spring elements fixed in the center of the plate intersection from the coolant inlet and outlet sides - rings; deflectors are located at the ends of the plates, one edge of which is located at the base of the intersection of the plates, and the other in the cross section is limited by the shape of the spacing elements, taking into account the margin until touching in the cross section, which is necessary to install the second row of spacing elements from the coolant outlet side.

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