A method of manufacturing a core of a core of nuclear fuel

 

(57) Abstract:

Usage: in the technology of rod cores of nuclear fuel dispersion type, consisting of grains of uranium oxide, uniformly distributed in the aluminum matrix. The inventive method comprises mixing a source powder of uranium dioxide and aluminum and molding the resulting mixture. The mixture is prepared portions for each core, and the pressing is carried out in two stages. The first stage is realized by pressing the workpiece at specific pressure of from 0.8 to 1.2 t/cm2in a conical matrix, the average diameter of 0.2 mm less than the average diameter of the conical matrix for the second stage. At the second stage, compressing the core size. Between the stages of pressing hold vacuum annealing the workpiece at a temperature from 600 to 620oC for 1.5-2.5 h In the result, you do not need the use of plasticizers improves the uniformity of the distribution of nuclear fuel in the core volume and simplifies the technology of molding core by eliminating machining. 7 C.p. f-crystals.

The technical field to which the invention relates

The invention relates is of the volumetric type, consisting of grains of uranium oxide, uniformly distributed in the aluminum matrix.

Art

The active zone of some channel of uranium-graphite reactors generated from fuel assemblies containing fuel elements, in which the fuel pole formed by the eyelets nuclear fuel. Block represents a core of nuclear fuel, with tight-fitting its aluminum shell. Geometrical dimensions of these cores suggest excess of its length L compared to the diameter D, in particular 3 times. Therefore, the manufacture of relatively long rod cores in contrast to the technology of production of fuel pellets having, as a rule, comparable values of L and D, is known difficulty.

The known method of manufacturing elongated cylindrical cores of uranium dioxide, including obtaining preliminary pressing of short elements (GB 1063598, G 21 3/62, 1967). Short parts of the nuclear fuel (pill) collected in the rod, which is placed in the induction coil. The magnitude of the electric current and its frequency in the induction coil is chosen such that the current induced in the rod, wysiwy short elements are soldered together in a monolithic rod, and nuclear fuel is sealed.

The method allows to obtain a sufficiently long cores of nuclear fuel. However, the structure of the fuel along its length inhomogeneous due to the presence of zones of fusing the original short elements.

Another type of rod manufacturing cores of nuclear fuel components is the method lies in the fact that the pre-formed into tablets of nuclear fuel from a mixture of powdered fuel and binder additives, which then is sintered (GB 1397014, G 21 C 3/62, 1975).

Thus obtained core can be a solid cylindrical or annular. The connection of tablets in a single element by sintering reduces the homogeneity of the composition of the fuel in places mates tablets. However, the pre-production of pressed pellets of nuclear fuel significantly complicates the process and increases the energy consumption during its implementation.

Therefore more adaptable to carry out the pressing of a single rod core, as, for example, in the production method of the fuel cores of granular nuclear fuel covered by a layer of deformable material: pyrocarbon, silicon carbide and histouy the entire length of the cavity pressing in the radial direction. Punches included with the matrix define the shape of the received items. More pressing to produce the opposite of the punches, moving axially in the cavity of the extrusion. The method allows production of long products, but the use of radial punches does not provide the necessary uniformity of the distribution of nuclear fuel over the length of the product. In addition, when the radial pressing on the surface of the product will remain free from defects in material (nodules) in places of contact of radial punches with a matrix that requires machining.

Obtaining long pellets of nuclear fuel by pressing two punches on the ends of the briquette can improve the quality of the products obtained through the use of a camera with an extending side surface (US 3949027, G 21 21/00). The angle of the walls of the chamber ranges from 0o6' to 1o30'. This method is quite simple, allows to obtain pellets of nuclear fuel for a one-time compression, which positively affects the structure of nuclear fuel by volume of the briquette. However, the method involves the use of a plasticizer is introduced into the original uranium dioxide powder.

The closest of tehnicheskaya nuclear fuel, including original mix powders of uranium dioxide and aluminum, and pressing the mixture in the matrix (RU 2091872, G 21 21/02, 1997). The method involves the use of liquid plasticizer, present in the mixture as a lubricant. When this liquid plasticizer is introduced into the mixture during the mixing process in individual portions in the form of spray and mixture is produced in a period of time sufficient to obtain a uniform distribution of fissile phase in non-dividing. By mixing a large amount of charge in it is always the heterogeneity of the distribution by volume of fissile material, because the mixture of heavier material always "drowning" in more light. Then perform hot pressing - calibration of the core to the desired density and size to use as lubrication products of the pyrolytic decomposition of organic matter.

There is a method allows to obtain a finned tubular fuel elements with a relatively low thickness of the core. When using this method for manufacturing a solid rods it is necessary to significantly increase the tonnage, which in turn will lead to increased friction on the boundary of the core -" the middle part of the core at the bilateral and the lower part of the core in a one-sided pressing. Moreover, high values of pressure on the side wall of the matrix lead to so effective adhesion of the core material that supressive core becomes impossible. In addition, the presence of plasticizer in the mixture reduces the chemical purity of the core and increases its porosity. The introduction of the plasticizer increases the number of technological operations and increases energy consumption.

The invention

The present invention is the creation and development of a method of manufacturing a rod cores of nuclear fuel with improved manufacturability, lower energy consumption and increased output of finished products.

The solution of this problem can be obtained new technical results, which consists in eliminating the need for the use of plasticizers, the increase in the uniformity of distribution of nuclear fuel in the volume of the core and the simplification of the molding core by eliminating machining.

These technical results are achieved by the fact that in the method of manufacturing a rod cores of nuclear fuel comprising a mixture of original powders dioxide uratowanie carried out in two stages, in the first stage is realized by pressing the workpiece at specific pressure of from 0.8 to 1.2 t/cm2in a conical matrix, the average diameter of 0.2 mm less than the average diameter of the conical matrix for the second stage, in which the pressing core size, and after the first stage of pressing hold vacuum annealing the workpiece at a temperature from 600 to 620oC for 1.5 to 2.5 hours.

A distinctive feature of the present invention is as follows. In the manufacture of a mixture of the original powder charge weighed grains of uranium dioxide powder and aluminum required for forming only one core, which provides a guaranteed content of fissile material in each core and increases the uniformity of its distribution in the volume of the core. However, in the absence of a plasticizer mixture, which reduces the porosity of the core, forming the core in a single operation is impossible, because the amount of core experiencing significant stress, preventing uniform distribution of pressure on the volume of the core. Therefore, after the first stage of compression, which is formed by the workpiece hold vacuum annealing sahampati in the workpiece material and direct it to the final pressing rod core. The lower limit of the annealing temperature is due to the fact that at temperatures below 600oWith the volume of the workpiece contains a significant number of stressed zones. When the annealing temperature above 620oWith the possible loss of form or melting of the preform core. The lower value of the range of time of annealing due to the need to fully warm up the entire structure of the workpiece and removing it stresses. Annealing over 2.5 hours is impractical, because the positive changes in the structure of the workpiece practically does not, it only increases the energy consumption. The range of the specific pressure in the first stage selected for the following reasons. When the value of the specific pressure of less than 0.8 t/cm2it is impossible to obtain the structure of the workpiece, which can be used for annealing and final pressing, because the material is insufficiently compacted. When the value of the specific pressure of more than 1.2 t/cm2supressive procurement of a matrix is difficult. In addition, compression of the workpiece at the first stage produces a conical matrix with smaller dimensions than the dimensions of the matrix used in the second stage of compression. Therefore, the strain in the matrix at the second stage of compression is carried out as in the final pressing of the core is carried out in size, receiving in the end, the finished product that does not require machining. The process of pressing the core size is carried out at specific pressures from 4.5 to 5.0 t/cm2and stop when reaching the core size of the specified length.

Information confirming the possibility of carrying out the invention.

The described method of manufacturing a rod cores of nuclear fuel can be illustrated by the following examples.

Example 1. Source components: aluminium powder and nibs uranium dioxide. Take a sample of aluminium powder mass 203,1 g and uranium dioxide mass 102,1, Provide individual mixture components of the mixture in the mixer type "drunken barrel for 15 minutes, after which the mixture is poured into the matrix of a press tool. The working surface of the matrix is pre-lubricated with a manually kerosene-oleic acid mixture. At the first stage receiving the workpiece by the method of double-sided pressing at specific pressure of 0.8 t/cm2. The pressing operation is carried out in a conical matrix with taper 6'. The resulting blank has the following dimensions defined by the geometry of the press tool and the weight of backfill (average diameter: 33,7 mm, the height is with the following temperature-time regimes:

- rise of temperature 600oC for 2 hours;

the extract at a temperature of 600oC for 2.5 hours;

- cooling to a temperature of 20oC for 2 hours (cooling rate 290oC/hour).

In the second stage, compressing the core size was carried out in a conical matrix of larger size (average diameter of the matrix in the working area of more than 0.2 mm, the average diameter of the matrix in the working area on the first stage of compression). The specific pressure was 5.0 t/cm2. Before the second stage of the extrusion press tool also smeared kerosene-oleic acid mixture. After pressing, received a core with dimensions not exceeding defined: diameter 34,05 mm, height 98,1 mm, a porosity less than 2%.

Next, the core is aimed at hypobromide in a solution of nitric, phosphoric and acetic acid for 5 minutes. After chemical treatment was performed degassing core modes, similar to the conditions of annealing.

The finished core is fed to the seaming in the aluminum shell.

Example 2. The mass of the original batches, mixture, preparation of press tool, the mode of heating to the annealing temperature, honorable and degassing in Pitesti 24%) dimensions: diameter 33,7 mm, height 124,5 mm, annealed at a temperature of 620oC for 1.5 hours. Cooling was performed with a speed of 310oWith/hour.

After the second stage of compression obtained core with the following parameters: diameter 33,9 mm, height 98,0 mm, a porosity less than 2%. The pressing force on the second stage was of 4.75 t/cm2.

Example 3. The mass of the original batches, mixture, preparation of press tool, the mode of heating to the annealing temperature, honorable and degassing as in example 1. Pressing the first stage was performed with a specific pressure of 1.2 t/cm2. The resulting material (porosity 23%) dimensions: diameter 33.8 mm, height 124 mm, annealed at a temperature of 610oC for 2 hours. Cooling was performed at 320oWith/hour.

After the second stage of compression obtained core with the following parameters: diameter 34,0 mm, height 98,0 mm, a porosity less than 2%. The pressing force on the second stage was 4.5 t/cm2.

Thus, the described method allows to obtain cores pressing into the given size without the use of plasticizers, which significantly reduces the complexity of the process.

Reducing the number of technological operations, due to the absence is for drinking, preparing fuel blocks. Furthermore, the lack of use of the plasticizer in the mixture simplifies the processing of the defective items.

1. A method of manufacturing a rod cores of nuclear fuel, including the original mix powders of uranium dioxide and aluminum and pressing the mixture in a matrix, characterized in that the mixture is prepared portions for each core, and the pressing is carried out in two stages, with the first stage is realized by pressing the workpiece at specific pressure of from 0.8 to 1.2 t/cm2in a conical matrix, the average diameter of 0.2 mm less than the average diameter of the conical matrix for the second stage, in which the pressing core size, and after the first stage of pressing hold vacuum annealing the workpiece at a temperature from 600 to 620oC for 1.5-2.5 hours

2. The method according to p. 1, characterized in that the extrusion is carried out in a conical matrix with an angle of taper from 5' to 7'.

3. The method according to p. 1 or 2, characterized in that the pressing rod core size is carried out at specific pressures from 4.5 to 5.0 t/cm2.

4. The method according to p. 1, or 2, or 3, characterized in that before pressing hold blur is the fact that after annealing the workpiece is cooled with a cooling rate of from 280 to 320oWith/hour.

6. The method according to p. 1, or 2, or 3, or 4, or 5, wherein the vacuum annealing is carried out at the magnitude of the vacuum is not worse 510-3mm RT. Art.

7. The method according to p. 1 or 2 or 3 or 4 or 5 or 6, characterized in that the pressing rod core size is held vacuum degassing at a temperature of from 600 to 620oC for 1.5-2.5 hours

8. The method according to p. 1 or 2 or 3 or 4 or 5 or 6 or 7, characterized in that the vacuum degassing is carried out at the magnitude of the vacuum is not worse 510-3mm RT. Art.

 

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FIELD: atomic power engineering.

SUBSTANCE: device has welding chambers having apertures for inputting covers for pressurization, which concurrently are output apertures of heat-conductive elements, welding chambers electrodes, power source, transporting module for transverse product feed, common control system with blocks for parallel and serial connection, device for forming a break in secondary contour. Welding chambers are placed in parallel to each other at distance from each other, determined from formula S=t(m k+1), where S - distance between chambers axes, t - step of transport module, k - number of chambers in device equal to number of steps of transporting module in each singular step thereof, m - any integer starting from one, and control systems connected through parallel connection block to working tools of device of same names, and through block for serial connection to welding force drive and to device for forming break in secondary contour of power source, as well as to power source connected in parallel to welding chambers electrodes.

EFFECT: higher efficiency.

4 cl, 1 dwg

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