Method for manufacturing fuel assembly spacer grids

FIELD: nuclear power engineering; spacing apart fuel elements in reactor fuel assemblies.

SUBSTANCE: proposed method includes insertion of auxiliary inserts in assembly field holes designed for guide channels and central tube with desired inscribed circumference in each hole prior to spot welding of subchannels to join them together in assembled field; these auxiliary inserts have same diameter as guide channel and central tube and their temperature coefficient of linear expansion equals that of subchannel material; spot welding of subchannels to each other and to rim is effected while inserts are installed and upon heat treatment these inserts are removed.

EFFECT: enhanced quality and yield of spacer grids.

1 cl, 1 dwg

 

The invention relates to atomic energy and can be used in the fuel assemblies of nuclear reactors for the spacing of the fuel elements (FE).

A known method of manufacturing the spacer grid, which includes the manufacture of an alloy of zirconium, 1% niobium hexagonal rim and cells with internal protrusions, placement and fixation spot welded to each other and to the rim of cells with internal protrusions (see Bajamonti. Nuclear energy rectors, 11eedition, M., Energoatomizdat, 1990, p.44). The disadvantages of the method of manufacturing the spacer lattice of the zirconium alloy are:

- low elasticity of the projections of the cells are not capable when installing fuel elements sufficiently elastically deformed;

- the tendency of zirconium to coating and hardening (see metallurgy of zirconium, English, M., “Foreign literature”, 1959, str-163), that does not preclude any damage to the surface of zirconium sheath of the fuel element during Assembly FA;

- the internal stresses that occur when the spot welding cells among themselves, not preventing deformation and distortion of the cells in the spacer grid and therefore not exclude damage to the surface of a fuel rod during the pressing them into the cell.

A known method of manufacturing distancioni is the fact that the lattice of the zirconium alloy, includes the manufacture of an alloy of zirconium, 1% niobium hexagonal rim and cells with internal protrusions, placement and fixation spot welded to each other and to the rim of cells with internal protrusions (see Patent RU 2127001 on the application 97104685/25 from 27.03.1997, published 27.02.1999, Bulletin No. 6, MKI 6 G 21 C 3/34, “the Spacer grid TVs”). Known drawbacks of the known method and the method according to the patent 2127001.

In addition, because of the low elasticity of the above-mentioned protrusions of cells and applying surfaces of the fuel elements into the cells of the spacer grids of the tips of larger diameter than the diameter of a fuel rod as extensions of the walls of the cells, does not exclude the possibility of formation between the fuel rod and the wall of the cell gap, that during operation in a nuclear reactor, when the oscillations of a fuel rod in a possible gap may be destroyed zirconium sheath of a fuel rod (see “the metallurgy of zirconium”. Translation from English, M., “Foreign literature”, 1959, str), since zirconium is prone to corrosive corrosion, resulting from the abrasion of metal between the touching surfaces.

During the pressing of the fuel Rods in the cells of the spacer grids using cone dilator walls of the cells may occur displacement of the walls of the cell, deformation of neighboring cells and will not allow insertion of the fuel rod in the neighboring cake the spacer grid, as this could be damaged cell damage and destruction of the surface of the fuel element.

A known method of manufacturing the spacer lattice of the zirconium alloy, comprising manufacturing a hexagonal rim and cells with internal protrusions, placement and fixation spot welded to each other and to the rim of cells; according to the invention assembled spacer bars are annealed at a temperature, time and pressure sufficient to relieve internal stresses without oxidation of cells and the rim, and then reduce the temperature to a value sufficient to form a protective oxide film on the surface of the rim and the cells of the spacer grid, and further cooling leads to oxidative environment.

Other differences are: the annealing is carried out at t 580±15°C for at least 180 minutes at a residual pressure of 2×l0-3mm rtsora; the temperature was lowered to 500±20°C, and the formation of a protective oxide film are used as the oxidizing environment of atmospheric air (see Application 2000115190/06 (016048) from 13.06.2000, IPC 7 G 21 3/34, 21/00 “Method of manufacturing the spacer lattice of the zirconium alloy”, publ. 27.04.2002).

Performing annealing spacer grid with the above modes will allow you to relieve internal stresses from cells and rim distance is the dominant lattice, and air cooling from a temperature of 500°C to room temperature will form on the surface of the spacer grid oxide layer, increase in the hardness and strength due to oxygen, to increase the reliability and elastic properties of cells, reduce the effort of pressing them in fuel cells due to the exclusion of the factor setting between the touching surfaces of the fuel Rods and the cells of the spacer grids) when assembling the fuel Assembly and to prevent damage to the surface of the fuel elements.

It is known that in the spacer grid for a fuel Assembly of a nuclear reactor VVER-1000 cells under the fuel Rods 312, holes for the guide channels 18 and one hole for the Central pipe.

Hole guides the channels and under the Central tube does not contain cells and are formed by the walls of the cells located around the peripheral of each guide channel and a Central tube (see “Development, production and operation of fuel cell power reactors”. Book 1 edited Fgurative - M.: Energoatomizdat, 1995, p.184, table 7.1). In the process of manufacturing the spacer grids in the spring properties of the cells walls inscribed circle in the holes between cells under the guide channels and the Central tube hundred is ulitsa diameter less than the specified and you want to restore it to a specified Executive by means of burnishing. When donovani same deformation of cells around each guide channel and the Central pipe, lost center dimensions between cells and the incircle in the cells beneath the fuel Rods lose their size.

The closest in technical essence and the achieved effect is a method of manufacturing grid spacers for fuel assemblies of stainless steel or zirconium alloys (see Application 96103549/25 from 22.02.1996, IPC 6 G 21C 3/34, 3/344, 21/00, published in Bulletin of inventions No. 13 of 1998), including mechanical forming individual cells, chemical processing, welding cells in the lattice and thermal processing.

In the method prototype heat treatment grid spacers is performed with the set of one end of the cell, and the other end of the support plate inserts, the material for the inserts are selected temperature coefficient of linear expansion greater than that of the material for cells. The heat treatment of the value of the inscribed diameter of the cell is less than the diameter of the liner by 1-2%.

The disadvantages of the prototype method is:

in the welding process is inevitable internal stresses that occur when the spot welding cells to each other and not preventing deformation of the cells in the direction of free space, i.e. into the holes under the guide channels and the Central tube, the image of the bathrooms walls of cells around each guide channel and a Central tube;

the force of internal stresses in the cell after you enter them in inserts with a diameter of 1-2% larger than the diameter of the inscribed circle in the cell;

to increase the deformation of the cells in the direction of the holes under the guide channels and the Central hole of the pipe after installation of the cell liners with a coefficient of linear expansion greater than that of the material of the cell;

twice the productivity fall furnaces heat treatment due to a reduction in the efficiency of the oven due to the use of supporting liners plates;

is not excluded deformation 312 liners and the supporting plate with multiple heat treatments, which may cause damage to the cells of the spacer grids;

the method involves the installation of liners in the cell and does not provide for installation of inserts in the holes in the guide channels and the Central tube immediately before the heat treatment, and not before welding, which may increase stress and deformation of cells;

- increased the complexity of installation, removal 312 inserts in one grid.

An object of the invention is to improve the quality of manufacturing grid spacers, increase productivity and reduce labor intensity.

This technical problem is solved in that in the method of manufacturing a grid spacers DL the fuel Assembly stainless steel or zirconium alloys including mechanical forming individual cells, chemical processing, welding cells in the lattice and thermal processing using technological liners; according to the invention before spot welding cells between a typed field formed by the holes in the guide channels and the Central tube with a given inscribed circle in each hole in each hole injected technological liners, repeating the diameter of the diameter of the guide channel and the diameter of the Central pipe and having a temperature coefficient of linear expansion equal to the temperature coefficient of linear expansion of the material of the cell, carry out spot welding cells among themselves and with the rim in the presence of established technological liners forming the frame, warning deformation of cells in hole guide channels and the Central tube, and after the heat treatment process, the liners are removed.

This embodiment of the method of manufacturing the spacer grid will improve the quality of manufacturing through the use of technological liners installed in the openings of the guide channels and a Central tube, a warning deformation of cells in the direction of these holes when welding and heat treatment, to improve performance through the use of volume is ECI twice and reduce the complexity due to installation and removal 19 technological liners instead 312 on the prototype method.

The drawing shows a spacer grid for a fuel Assembly.

Spacer grid for a nuclear reactor VVER-1000 includes cell 1 mounted between a spot weld with the formation of the eighteen holes 2 under the guide channels (not shown) and a hole 3 under the Central tube (not shown) with a given inscribed circle 4 in each hole 2, 3.

In each hole 2, 3 introduced technological liners, repeating the diameter of the diameter of the guide channel or inscribed circle 4 holes 2, 3.

The rim 6 is fixed to the peripheral cells 1 spot weld.

A method of manufacturing the spacer grid is as follows. Cell 1 of zirconium alloy with 1% niobium or stainless steel with internal protrusions spread with the formation of the field of cells 1 with internal protrusions, formed holes 2, 3 inscribed circles and under 18 of the guide channels and the Central tube is injected liners 5 having diameters equal to the diameters of the guide channels and the Central pipe, and the temperature coefficients of linear expansion equal to the material cells 1, spot welding is fixed between the cell 1 and is subjected to degreasing, and then the field of cell 1 is fixed by spot welding to the rim 6 and is subjected to degreasing. Diest is ntivirus lattice is subjected to annealing at 580±15°C for at least 180 min at a residual pressure of 2× 10-3mm rtsora. The modes selected optimum and temperature increase above specified may result in warping the spacer grids, and the temperature reduction will not solve the technical problem. The temperature was lowered to 500±20°C and cooled in air to form on the surface of the spacer grid oxide protective film that protects against corrosion.

Modes are also selected optimal. After heat treatment and cooling process the inserts 5 are removed.

A method of manufacturing a grid spacers for the fuel Assembly, including mechanical forming individual cells, chemical processing, welding cells in the grid and heat treatment with the use of liners, characterized in that before spot welding cells between a typed field formed by the holes in the guide channels and the Central tube with a given inscribed circle in each hole in each hole injected technological liners, repeating the diameter of the diameter of the guide channel and the diameter of the Central pipe and having a temperature coefficient of linear expansion equal to the temperature coefficient of linear expansion of the material of the cell, carry out spot welding cells among themselves and with the rim in the presence of established technological liner is, forming the frame, warning deformation of the cells in the holes in the guide channels and the Central tube, and after the heat treatment process, the liners are removed.



 

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FIELD: nuclear engineering.

SUBSTANCE: proposed method primarily used for manufacturing spacer grids of VVER reactor fuel assemblies involves pre-compression of dynamometric clamp by welding gun electrodes prior to spot welding of shaped subchannels beyond subchannel field, evaluation of compression of welding gun electrodes by displacement distance of clamp jaws and force indicator readings, whereupon information about this compression force is processed in computer and passed to spatial displacement actuating mechanism of welding gun for conducting spot welding of shaped subchannels in assembled field when compression forces of electrodes comply with desired values or for ceasing spot welding when compression forces do not comply with desired values, this information being displayed on computer monitor.

EFFECT: enhanced quality of spacer grid manufactured by this method.

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FIELD: nuclear engineering.

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EFFECT: enhanced quality of spacer grid manufactured by this method.

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1 dwg

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