RU2351028C2 - Method of making triple-layered tubular fuel elements - Google Patents

Abstract

FIELD: physics, nuclear physics.

SUBSTANCE: invention relates to nuclear energetics and can be used in the manufacture of triple-layered tubular fuel elements with a dispersion type core. Method of manufacturing triple-layered tubular fuel elements involves putting a work piece of the fuel core from uranium dioxide into a cover from an aluminium alloy, calibration, combined hot pressing, thermal processing and, at least one draw process. Uranium dioxide is dispersed in the aluminium matrix. Tempering is used for thermal processing. Tempering includes heating at a temperature of 350-440°C for a period of 5-30 minutes followed by cooling in air. Tempering is carried out before each drawing passage.

EFFECT: increase in the quality of fuel elements, prevention of cracking of the cover and core, gives them elasticity.

3 dwg

Description

The invention relates to nuclear energy and may find application in the manufacture of three-layer tubular fuel elements (fuel elements) with a dispersion type core. Fuel elements of this type are made in the form of pipes of circular or multifaceted cross-section, consisting of an inner working layer — a core and a two-sided protective sheath made of a corrosion-resistant material, for example, an aluminum alloy.

A known method of manufacturing a three-layer tubular fuel elements (Sokursky Yu.N. Uranus and its alloys. M: Atomizdat, 1971, p. 421-423), including the placement of the core blank in the shell, calibration, joint hot pressing, drawing and heat treatment. Heat treatment includes heating to 480 ° C, holding for 1-1.5 hours and cooling in air.

The disadvantage of this method is the low quality of the fuel rods due to the unstable thermodynamic state of the aluminum alloy of the cladding and aluminum matrix, which leads to grain growth and further natural aging and cracking of the cladding.

The closest in technical essence and the achieved result is a method - a prototype of the manufacture of three-layer tubular fuel elements according to the patent of the Russian Federation No. 2223561, IPC 7 G 21 C 21/10, 2004, including the placement of a core blank made of uranium dioxide dispersed in an aluminum matrix in aluminum alloy shell, calibration, joint hot pressing, drawing and heat treatment at a temperature of 420-460 ° C for 2-2.5 hours and cooling in an oven at a temperature and speed of 30 ° C / hour.

The disadvantage of this method is that it can only be used for the manufacture of fuel elements with a volumetric fuel content in the core of up to 17% vol. At a higher fuel content in the core, the proportion of aluminum in the matrix decreases, therefore, the plastic properties of the core decrease, which leads to rupture of the core and shell during drawing.

The present invention is aimed at achieving a technical result, which consists in improving the quality of the rod fuel elements with any fuel content in the core.

To obtain the specified technical result in the proposed method for the manufacture of three-layer tubular fuel elements, which includes placing a billet of a fuel core made of uranium dioxide dispersed in an aluminum matrix in an aluminum alloy shell, calibration, joint hot pressing, heat treatment and at least one drawing, according to the claims, quenching is used as heat treatment, including heating the resulting assembly of the fuel element at a temperature 350-440 ° C for 5-30 minutes and subsequent cooling in air, and hardening is carried out before each drawing passage.

Carrying out heating in the indicated temperature range and in this time interval allows to achieve ductility of both the core material and the sheath material.

The increase in heating time for more than 30 minutes and temperatures above 440 ° C leads to grain growth and an increase in the hardness of the shell material and the core matrix material. This, in turn, leads to a decrease in the quality of fuel elements.

Structural stresses in the metal resulting from previous deformations, such as stamping and drawing, are not removed if the heating temperature is below 350 ° C and the holding time is less than 5 minutes.

Hardening before each drawing pass is necessary to increase the tensile strength of the shell metal and the matrix in comparison with the applied deformation forces.

The proposed method is carried out in the following sequence.

A core blank made of uranium dioxide dispersed in an aluminum matrix is placed in an aluminum alloy shell, calibrated and co-pressed. After that, the three-layer pipe is subjected to heating at a temperature of 350-440 ° C for 5-30 minutes, and then cooled in air. After hardening, drawing is carried out.

Example 1

A blank of a core of uranium dioxide dispersed in an aluminum matrix is placed in an aluminum alloy shell. The fuel content in the core is 16% vol. The three-layer assembly, consisting of an aluminum shell and a core, is calibrated, then the heated three-layer assembly is subjected to joint hot pressing and a three-layer tube is obtained. The three-layer pipe is heated at a temperature of 400 ° C for 20 minutes and cooled in air to room temperature. After cooling in air, a three-layer pipe is subjected to a drawing operation. Depending on the required profile of a three-layer pipe: circle, hexagon, square, the number of drawing passes can be from one to five. Before all subsequent drawing operations, the pipe is heated at a temperature of 400 ° C for 20 minutes, and then cooled in air to room temperature. The finished three-layer pipe is subjected to instrument radiometric and radiographic control. Instrument radiometric and radiographic control did not detect any cracks, tears of the core and shell. The macrostructure of the shell is fine-grained, as shown in figure 1.

Example 2

A blank of a core of uranium dioxide dispersed in an aluminum matrix is placed in an aluminum alloy shell. The fuel content in the core is 34% vol.

The sequence of operations, temperature and time modes are the same as in the first example.

Instrument radiometric and radiographic inspection of defects on the core and the shell was not found. The macrostructure of the shell is fine-grained, as shown in Fig.2.

Example 3

A blank of a core of uranium dioxide dispersed in an aluminum matrix is placed in an aluminum alloy shell. The fuel content in the core is 34% vol. The sequence of operations remains the same as in the first and second examples, and the heating temperature of the three-layer pipe is 480 ° C and the exposure time is 1 hour. Then the pipe is cooled in air.

After the drawing operation, the instrument radiometric and radiographic control showed defects on the core and tears on the shell. The grain size increased with increasing heating temperature and increasing the exposure time, which is associated with collective recrystallization, see figure 3.

Thus, a universal method for manufacturing three-layer tubular fuel elements is proposed. The optimal temperature-time regimes of heat treatment of three-layer pipes are proposed. Under these conditions, the effect of natural aging of the matrix in the ceramic-metal product is excluded, which is positively reflected in further operations associated with plastic deformation of the shell material and the ceramic-metal core. The method allows to improve the quality of the fuel rods, to prevent cracking of the shell and core.

Claims (1)

A method of manufacturing a three-layer tubular fuel elements, including the placement of a fuel core blank of uranium dioxide dispersed in an aluminum matrix in an aluminum alloy shell, calibration, joint hot pressing, heat treatment and at least one drawing, characterized in that as a heat treatment use hardening, including heating at a temperature of 350-440 ° C for 5-30 minutes and subsequent cooling in air, while hardening is carried out before each passage of drawing.

Images