RU2256243C2 - Nuclear reactor fuel assembly - Google Patents

Abstract

FIELD: nuclear power engineering.

SUBSTANCE: supporting ribs of fuel assembly bottom nozzle are droplet-shaped in cross-section and are made in the form of two coaxially disposed rings secured to bottom nozzle so that they are abutting against bottom end of lower spacer grid.

EFFECT: enhanced operating reliability and improved hydrodynamic characteristics of fuel assembly.

1 cl, 4 dwg

Description

The invention relates to nuclear energy and can be used in enterprises manufacturing fuel assemblies (FA) for nuclear reactors of the WWER type.

Known fuel assemblies of a VVER-440 nuclear reactor, including a beam of fuel elements (fuel elements) installed in a frame of hexagonal spacing grids mounted on a central tubular channel fixed together with fuel rods with a lower end in the lower grid, a shank connected to the lower grid using adapters fixed in the corners of this lattice, a cover in the form of a hexagonal tube covering the entire bundle of fuel rods connected at one end to the shank, a head fixed to the other end by a cover, and elements printing the fixing of fuel elements in the lower lattice (see B. Dementyev, Nuclear Power Reactors: a textbook for universities, 2nd edition, revised and expanded. M .: Energoatomizdat, 1990, pp. 31-35).

In the known fuel assembly from the axial up-down movement, the fuel rods are fixed in the lower lattice with their lower caps placed in its corresponding cells. As an element that prevents the axial movement of the fuel rods relative to the lower lattice down, an annular ledge is used on each lower plug above the upper end of this lattice.

The axial movement of the fuel rods relative to the lower lattice up is limited by means of a cotter pin located in the groove made on the lower end of this lower lattice along the entire row of cells for the lower plugs of the fuel rod and passed through the holes in each lower plug at the level of the groove for the cotter pin. The number of cotter pins corresponds to the number of rows of fuel rods in a fuel assembly. Both ends of each cotter pin are fixed to the side face of the lower grill. The central pipe channel used to place measuring instruments in the fuel assemblies is fixed with its tip in the lower grill with the same fastening as the fuel rods. The disadvantage of this fuel assembly is the high complexity of its manufacture due to manual operations on orienting each fuel rod with holes in the plugs towards the cotter pin, splinting through holes in the lower plugs of each fuel rod and fixing the cotter pins with welding. These operations are not automated.

Known fuel assemblies for a VVER-1000 nuclear reactor, including a bunch of fuel rods installed in a frame of hexagonal spacer grids mounted on tubular channels, are mounted together with fuel rods with lower plugs in the lower grill, a shank connected to the lower grill using adapters fixed in the corners of this gratings, the head and the elements that secure the fuel rods in the lower grating (see ibid., p. 41-45). This fuel assembly, in addition to the central one, has a number of tubular channels used to place control rods in them.

The fuel elements are fixed in the lower lattice in the same way as in the fuel assemblies described above. The shank is equipped with a system of supporting ribs for the lower lattice, which are adjacent to its lower end, and the head is mounted on the upper tubular channels protruding from the fuel rod bundle for the control rods. This fuel assembly has the same drawback as the fuel assembly described above, but more pronounced, since it has almost three times as many fuel rods, therefore, the higher laboriousness of the cotter pin assembly operation when fixing the fuel rod bundle in the lower grating. In addition, both fuel assemblies are non-separable, which creates certain difficulties when replacing one or several fuel assemblies in fuel assemblies, and the grooves on the lower ends of the cotter pin grids placed perpendicular to the coolant flow can cause unpredictable vibration of the fuel assemblies and damage to welding of the lower plug to the fuel assembly .

Known fuel assembly of a nuclear reactor, mainly VVER, including a beam of fuel elements mounted in a frame of spacer grids mounted on tubular channels, mounted together with fuel elements, lower plugs in the lower grid equipped with adapters, a shank with supporting ribs attached to the adapters of the lower gratings, a head mounted on the upper ends of the tubular channels, and elements that secure the lower plugs of the fuel elements s at the bottom of the lattice (see. Russian Patent RU 2079170 of 30.05.95 of, published 10.05.97, IPC 6 G 3/32).

In the fuel assembly prototype of the lower plugs of the fuel elements, the lower ends are previously dissected in the longitudinal direction into two equal parts before assembly, and when assembling the fuel assembly, these equal parts are separated to the sides behind the lower end of the lower grill, for example, by upsetting them on a conical mandrel. The fuel assembly according to patent 2079170 eliminates the disadvantages of the known fuel assemblies in terms of complexity by eliminating the pinning of the fuel rods, automating the fastening of the plugs of the fuel rods in the lower lattice and it becomes possible to replace one or more fuel rods, i.e. such a fuel assembly can be called as a variant of a collapsible fuel assembly. However, it was not taken into account that performing additional milling operations on each plug to dissect the end of the plug into two parts increases its manufacturing cost, the thickness of one part being 1.5 mm, which does not exclude its bending, damage at the stage of manufacture and transportation. When a fuel rod is pressed through 15 spacer grids and one lower grille during assembly of a fuel assembly, damage to the dissected parts of the lower plug during the assembly of the fuel assembly is possible. Damage to the dissected parts of the lower plug during precipitation on the mandrel is not ruled out. A fuel rod with a broken, at least one part, goes into marriage.

It is known that VVER-type nuclear reactors operate at temperatures of 270-330 ° C of coolant and a pressure of 10-20 MPa with a coolant supply from the bottom up of the core (see Development, production and operation of fuel elements of power reactors. Book 1, M .: Energoatomizdat. , 1995, p. 14, §1.2), which does not exclude the axial displacement of the fuel rod from bottom to top in the fuel assembly and pushing it out of the cell of the lower lattice. In addition, the diluted parts of the lower plug of the fuel rod create additional resistance to the flow of coolant. If we take into account that the ends of the lower plugs are placed in the cells of the lower lattice with a gap, then unpredictable vibration of the fuel rods and the destruction of the weld of the fuel rod shell with the lower plug can occur, since zirconium is prone to corrosive corrosion resulting from oscillations even at very small amplitudes (see Metallurgy of zirconium. Translation from English. Foreign Literature Publishing House, M., 1959, p. 298).

When assembling fuel assemblies, to prevent damage to the lower dissected parts of the lower plugs of the fuel elements when they are pressed through the cells of fifteen parallel-mounted spacer grids, polymer tips were previously installed on the dissected part of the lower plug before mounting. Pressing the fuel rod through the cells of the spacer grids was carried out with the tips forward to the bottom of the grid. Before the lower lattice, the pressing was stopped to remove the tips, and then the TVEL was pressed with the lower part of the lower cap into the cell of the lower lattice, where behind the lower end of the lower lattice, the dissected part of the lower cap was deposited on the mandrel. Stopping the press-fitting reduced the assembly performance of the fuel assemblies, and manual removal of the tips in front of the lower grill and the burning of the dissected part of the plug increased labor costs and increased the cost of manufacturing fuel assemblies.

The closest in technical essence and the achieved effect is a fuel assembly of a nuclear reactor, mainly of the WWER type, including a bunch of fuel elements installed in a frame of spacer grids mounted on tubular channels, fixed together with fuel elements with lower plugs in the lower grid equipped with adapters, a shank with support ribs attached to the adapters of the lower grill, a head mounted on the upper ends of the tubular channels, and elements providing fastening of the fuel elements in the lower lattice, made in the form of at least one puklevka on the cell walls from the side of the lower end of the lower lattice in the direction of the lower part of the lower cap placed in the cell, repeating the shape of the cell and the annular band on the lower part of the lower cap, fixing the pupple in the place of their contact, and the end face of the lower part of the lower plug is made hemispherical. Chamfers are made on the walls of each cell for the lower part of the lower plug of the fuel element along the generatrix from the side of the lower end of the lower lattice, and the annular girdle on the lower part of the lower plug is made fixing this shape at the point of contact with the marking with the opening angle of the annular girdle larger than the opening angle without chamfers on the cell (see Patent RU 2174718, IPC 7 G 21 C 3/32, priority December 28, 1999, publ. October 10, 2001. The fuel assembly of a nuclear reactor).

The implementation of the fastening elements in the lower lattice in the form of a pair: an annular girdle on the lower part of the lower stub and a bump or puff on the cell walls of the lower grating, repeating in cross section the annular girdle with a hemispherical end face of the lower part of the lower stub allow:

- to increase the reliability of fastening of fuel elements in the lower fuel assembly lattice due to the reliable coupling of the pair: beetle - belt and, accordingly, increase the reliability of operation of fuel assemblies in a nuclear reactor;

- reduce labor costs and increase productivity, which will generally reduce the cost of manufacturing fuel assemblies by eliminating the use of tips in assembling fuel assemblies;

- reduce the cost of manufacturing the lower plugs by performing only turning operations during the manufacture, cancel milling and drilling operations and reduce the cost of manufacturing the entire fuel assembly;

- ensure the safety of personnel and not expose personnel to irradiation in the manufacture of fuel assemblies with mixed fuel by pre-attaching the shank to the lower grill, eliminating the operation of removing the tips from the lower plugs of the fuel rod in front of the lower grill and transferring the assembly of the fuel assemblies to unmanned technology;

- to assemble fuel assemblies in a non-separable version and a collapsible version when performing a chamfer on the walls of the cells of the lower lattice from the side of its lower end and, accordingly, performing a reciprocal ring belt on the lower part of the lower plug, repeating the cross-section with a bevel with a chamfer.

However, in the heat-generating assemblies-analogues and in the heat-generating assembly-prototype, the fastening of the plugs of the guide channels and the fastening of the lower plugs of the fuel elements is carried out in the lower grill, which is a supporting element for the entire fuel assembly.

The shank in the analog fuel assemblies and in the prototype fuel assembly is equipped with support ribs on which the lower lattice is supported by the lower end (see B. A. Dementyev. Nuclear power reactors. M .: Energoatomizdat, 1990, p. 44 fig. 2.13 ; Patent RU 20799170, figure 2; Patent RU 2174718, claims).

With an upward flow of coolant from a temperature of 270 ... 330 ° C and a pressure of 10 ... 20 MPa in the core of a nuclear reactor, deformation of the lower lattice of the fuel assembly is not ruled out, which can lead to a change in the flow cross sections between the fuel elements. The difference in the sizes of the flow sections leads to deviations in the flow rate and the coolant velocity. And if we take into account that the energy release and heat load of the fuel element do not depend on the flow rate of the coolant, then this inevitably leads to deviations of both heating of the coolant itself and temperature differences in the cross section (see B. A. Dementyev. Nuclear power reactors. M .: Energoatomizdat , 1990, p. 150 ... 151).

The same thing happens with possible hydraulic reamers in the shank of the fuel assembly due to the support ribs creating hydraulic resistance.

An object of the invention is to increase the reliability of operation of a fuel assembly in the core of a nuclear reactor and to improve its hydrodynamic characteristics.

This technical problem is solved in that in the fuel assembly of a nuclear reactor, mainly of the type of pressurized water reactor, comprising a bundle of fuel elements installed in a frame of spacer grids mounted on tubular channels, fixed together with the fuel elements with lower plugs in the lower grid equipped with adapters, a shank with supporting ribs attached to the adapters of the lower grill, a head mounted on the upper ends of the tubular channels, and an element nt fastening of fuel elements in the lower grill; according to the invention, the supporting ribs of the shank of the fuel assembly are made in the section of a droplet of a prominent shape in the form of two coaxially arranged rings fixed to the shank adjacent to the lower end of the lower lattice, while at the ends of the plugs of the tubular channels located in the holes of the lower lattice, they are made aligned with the ends of the plugs of the hole with a threaded connection with mating fasteners with mating thread, located coaxially to each tubular channel in the housing of the support ribs of coaxially spaced EC, and the fastening of the central part of the lower grill to the shank is carried out by a screed above the indicated fasteners with threaded connections in the holes of the ends of the lower plugs of the tubular channels.

This embodiment of the fuel assembly will allow the tubular channels to be fixed directly to the shank, to remove the load from the lower grate to which these tubular channels were previously attached, and to transfer the load from the lower grate to a more massive shank, while fixing the lower grate to the shank not only through adapters with an external side of the fuel assembly, but also the central part of the lower lattice with its screed to the drop-shaped support rings in cross section, which will increase the reliability of operation of the fuel assembly in the active onet of a nuclear reactor and will improve its hydrodynamic characteristics.

The drawings show a fuel assembly, where

Figure 1 - General view of the fuel assembly;

Figure 2 is a fragment of the mounting of the shank to the lower grill;

figa - supporting ribs of the shank and fixture tubular channels (top view);

figb - supporting ribs of the shank and fixture tubular channels in the context;

Figure 4 is a fragment of the mounting of the tubular channels, the lower lattice to the supporting ribs.

The fuel assembly of a nuclear reactor, mainly of the WWER type, includes a bunch of fuel elements 1 mounted in a frame of spacer grids 2 mounted on tubular channels 3, mounted together with the fuel elements with lower plugs 4 (Fig. 2) in the lower grid 5 equipped with adapters 6 , a shank 7 with supporting ribs 8, attached to the adapters 6 of the lower lattice 5, the head 9, mounted on the upper ends of the tubular channels 3, and the elements that secure the fuel elements 1 in the lower grill 5 (not shown).

The supporting ribs 8 of the shank 7 of the fuel assembly are made in a drop-shaped cross-section in the form of rings 10, 11 coaxially located fixed to the shank 7, adjacent to the lower end of the lower lattice 5, while at the ends of the plugs 12 of the tubular channels 3 located in the holes 13 of the lower lattice 5 made pine end caps 12 holes 14 with a threaded connection with mating fasteners 15 with mating threads, located coaxially to each tubular channel 3 in the housing of the supporting ribs 8 - coaxially located rings 10, 11.

The fixture of the Central part of the lower lattice 5 to the shank 7 is carried out by a coupler above the indicated fasteners 15 with threaded connections in the holes 14 in the ends of the lower plugs 12 of the tubular channels 3.

The fuel assembly is assembled as follows.

Assemble the frame from the spacer grids 2, tubular channels 3, the lower grill 5 and the shank 7.

The central part of the lower grill 5 with a coupler in the holes 13 of the lower grill 5 with fasteners 15 with threaded connections in the holes 14 at the ends of the plugs 12 of the tubular channels 3 is fixed to the supporting ribs 8 by the support rings 10, 11 of the shank 7.

The fuel elements 1 are pressed through the spacer grids 2 and the lower plugs 4 are fixed in the lower grill 5.

From the outside, the shank 7 is fixed through an adapter 6 to the lower grill 5, and in the upper part, the head 9 is fixed to the tubular channels 3.

The downward movement of the tubular channel 3 is prevented by the support element 16 of the plug 12, which rests on the upper end of the lower grill 5, and the fastening element 15 of the fastening of the channel 3 to the support rings 10, 11 prevents the movement of the tubular channel 3 upward.

Claims (1)

The fuel assembly of a nuclear reactor, mainly a pressurized water reactor, including a bundle of fuel elements mounted in a frame of spacer grids mounted on tubular channels fixed together with fuel elements with lower plugs in a lower grid equipped with adapters, a shank with supporting ribs attached to lower lattice adapters, a head mounted on the upper ends of the tubular channels, and fastening elements of the fuel elements in neither bottom grating, characterized in that the supporting ribs of the shank of the fuel assembly are made in a drop-shaped cross-section in the form of two coaxially arranged rings fixed to the shank adjacent to the lower end of the lower grate, while at the ends of the plugs of the tubular channels located in the holes of the lower grate coaxial to the ends of the plugs of the hole with a threaded connection with mating fasteners with a mating thread, located coaxially to each tubular channel in the housing of the support ribs coaxially distributed false rings and fastening the central portion to the lower grating coupler shank carried aforementioned fasteners with threaded connections in holes of the lower ends of the stubs of tubular channels.

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