A method of manufacturing a grid spacers for fuel assemblies

 

A method of manufacturing a grid spacers for fuel assemblies of stainless steel tubes intended for use in the nuclear industry. The method includes a heat treatment - anti-roll annealing. The last subject of the original thin-walled tubes before cutting them to length process for cells grid spacers under vacuum at a residual pressure and sufficient to improve the corrosion resistance of stainless steel time. Forming individual cells of the workpiece after cutting the tubes carry cold deformation of the order of 80-90% with a simultaneous increase of the yield strength and the tensile elastic characteristics while maintaining a high plasticity. After the contact spot welding cells to each other and to the rim of the heat grid spacers do not hold. Annealing of tubes is carried out at a temperature of 860-890oC for 40-45 minutes at a residual pressure of P=0.002 mm RT.article When the same pressure is conducted cooled to 100-120oWith further cooling. Improved quality of manufacturing grid spacers. 1 C.p. f-crystals, 2 Il.

The invention relates to atomic energy and can lowdelay assemblies of a nuclear reactor.

Known spacer grid (ETC) fuel Assembly (FA) water-water energetic reactor (WWER), made of stainless steel and assembled from individual curly cells welded together at points and bonded to the rim, containing in each cell internal ledges, durable, shrink-fixing passed through the cell fuel elements (Cartridges) and preventing radial movement under the influence of the coolant flow (see "Development, production and operation of fuel elements of nuclear power reactors". Edited by F. G. Reshetnikov, kN.1M.: Energoatomizdat, 1995, PL. 7.1 on pages 189 and S. 187).

The closest to the technical conditions and the achieved effect is a method of manufacturing grid spacers for fuel assemblies (see application 96103549/25 from 22.02.96, published in 13 Bulletin of inventions for 1998 , MPK G 21 3/34, 3/344, 21/00. A method of manufacturing a grid spacers for fuel assemblies) of austenitic stainless steels of the class, including mechanical forming individual cells, chemical processing, welding cells, chemical processing, welding cells in the lattice and thermal processing.

On ukazanyh gratings carry out defined by one end in the cell, and the other end of the support plate inserts, the material of the liners is chosen from a temperature coefficient of linear expansion greater than that of the material for cells. This is a consequence of the fact that the material of the cells was not prepared for the molding, i.e., was not enough plastic in the molding, which did not allow to observe the prescribed geometric dimensions of the cells and therefore required additional measures in the use of liners and the supporting plates with the corresponding temperature coefficients of linear expansion. The method of the prototype provided thermal processing of ready-grid spacers, which in stainless steel, which made the spacer grid, happen diffusion processes, the alignment chromium content in the cross section of the grain and the resulting structure of stainless steel in a stable state, i.e., increases the resistance of metal to intergranular and General corrosion (see the Materials of the atomic energy Commission, USA. Nuclear reactors III. Materials for nuclear reactors. Translation from English. Publishing house of foreign literature, M., 1956, 221).

The heat treatment of diffusion processes, the alignment constie stress the so-called "softening" of stainless steel, which is characterized by a low value of yield strength, low strength and high ductility. According to the requirements, each cell of the spacer grid should firmly with tightness record passed through its fuel rod in the fuel Assembly and to be sufficiently hardened at high plasticity, but otherwise these requirements can be broken already when assembling the fuel rod in the fuel Assembly. Proslavlennaya Assembly of the fuel element in the cell grid spacers or gap when working fuel assemblies in the reactor core of a nuclear reactor will cause the emergence of fitting-corrosion in places touch cladding with metal cells and destruction of TVEL (see "Development, production and operation of fuel elements of nuclear power reactors". Edited by F. G. Reshetnikov, kN.1. M.: Energoatomizdat, 1995, PL. 7.1 on pages 189 and S. 187).

An object of the invention is to improve the quality of manufacturing grid spacers, the quality of Assembly of the fuel assemblies and the reliability of their work in the core of a nuclear reactor.

This technical problem is solved in that in the method of manufacturing a grid spacers for fuel assemblies of tubes, NKU, welding of cells in the grid and heat treatment, according to the invention heat treatment - anti-roll annealing is subjected to the original thin-walled tubes before cutting them to length process for cells grid spacers under vacuum at a residual pressure, temperature and time sufficient to increase the corrosion resistance of stainless steel, stress-relief, low yield strength, low strength and high ductility, forming individual cells of the workpiece after cutting the tubes carry cold deformation of the order of 80-90% with a simultaneous increase of the yield strength, elastic strength characteristics while maintaining high plasticity, and after the contact spot welding cells to each other and to the rim of the heat grid spacers are not conducted.

Another difference is that the annealing of tubes is carried out at a temperature of 860-890oC for 40-45 minutes at a residual pressure of P=0.002 mm RT.art., then carried out at the specified residual pressure cooled to 100-120oWith further cooling.

The proposed method allows on stage before cutting the tubing into shapes to give it such mechanical properties,x, to improve the quality of manufacturing grid spacers.

Heat treatment of the tubes before cutting into blanks and forming with subsequent cold deformation will give the cell such properties, which are incorporated in the requirements fixing them Rods with tightness, which allows high-quality Assembly FA.

When cold - forming cells experiencing stress, work hardening, resulting in increased strength and elastic properties of characteristics of cells and, in General, achieved the goal of the project.

Spot welding is a process that takes place in fractions of a second, may not affect the structural condition of the stainless steel, because of the passage of the diffusion processes of redistribution of the composition of the solid solution required a significantly longer period of time and it does not reduce the corrosion resistance, require stabilizing annealing. Carrying out annealing, ETC in this case is undesirable operation, reducing the mechanical properties of the product.

In Fig. 1 shows a method of manufacturing a grid spacers for the fuel assemblies.

In Fig. 2 presents a drawing of the spacer grating stainless is emitting Assembly includes the following items: 1. Long stainless steel tube.

2. Measuring procurement of cells from stainless steel.

3. Cells from stainless steel.

4. Rim stainless steel.

5. Contact spot welding.

The method is as follows.

Long tube 1 stainless steel is subjected to a stabilizing annealing at a temperature of 860-890oC for 40-45 minutes at a residual pressure of P=0.002 mm RT.art., then produce cooling at the specified residual pressure up to a temperature of 100-120oWith further cooling.

Annealing can improve the corrosion resistance of stainless steel to produce stress relief, to provide a low value of yield strength required strength and high ductility. The tube 1 is subjected to the cutting-to-length workpiece 2, which is subjected to cold deformation of the order of 80-90% in cell 3 with a simultaneous increase of yield strength and elastic characteristics while maintaining a high plasticity. Carry out a chemical treatment and the contact spot welding 5 cells 3 each other and to the rim 4 of stainless steel. Heat treatment of the finished grid spacers do not hold. The parameters are optimal. Any excess Ilir>1. A method of manufacturing a grid spacers for fuel assemblies of tubes stainless austenitic steels, including mechanical forming individual cells, chemical processing, welding cells in the grid and heat treatment, wherein the heat treatment is stabilizing annealing is subjected to the original thin-walled tubes before cutting them to length process for cells grid spacers under vacuum at a residual pressure, temperature and time sufficient to increase the corrosion resistance of stainless steel, stress-relief, low yield strength, low strength and high ductility, forming individual cells of the workpiece after cutting the tubes carry cold deformation of the order of 80-90% with a simultaneous increase of the yield strength, elastic strength characteristics while maintaining high plasticity, and after the contact spot welding cells to each other and to the rim of the heat grid spacers are not conducted.

2. The method according to p. 1, characterized in that the annealing of tubes is carried out at a temperature of T=860-890C for 40-45 minutes at a residual pressure of P=0.002 mm RT.art., then carried out at the specified mod is

 

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