RU2248053C1 - Nuclear fuel granule simulator - Google Patents

Abstract

FIELD: nuclear power engineering.

SUBSTANCE: proposed invention may be found useful for optimizing manufacturing process of dispersion-type fuel elements using granules of uranium, its alloys and compositions as nuclear fuel and also for hydraulic and other tests of models or simulators of dispersion-type fuel elements of any configuration and shape. Simulators of nuclear fuel granules of uranium and its alloys are made of quick-cutting steel alloys of following composition, mass percent: carbon, 0.73 to 1.12; manganese and silicon, maximum 0.50; chromium, 3.80 to 4.40; tungsten, 2.50 to 18.50; vanadium, 1.00 to 3.00; cobalt, maximum 0.50; molybdenum, 0 to 5.30; nickel, maximum 0.40; sulfur, maximum 0.025-0.035; phosphor, maximum 0.030; iron, the rest.

EFFECT: enhanced productivity, economic efficiency, and safety of fuel element process analyses and optimization dispensing with special shielding means.

1 cl, 3 dwg

Description

The invention relates to the nuclear industry and can be used to develop a technology for the production of dispersion type fuel rods in which uranium granules, its alloys and compounds are used as nuclear fuel, as well as for hydraulic or other tests of prototype or simulator dispersion type fuel rods of any configuration and shape.

It is known to use crushed grains of U-9% Mo alloy dispersed in a magnesium matrix as nuclear fuel (Samoilov A.G., Kashtanov A.I., Volkov BC Dispersion fuel elements. Vol. 2, M., Energoizdat, 1982, p. .159-161). However, the production of U-9% Mo alloy powder grains by crushing or mechanical grinding of the original ingots is a rather energy-intensive and labor-intensive process.

In recent years, interest in powders and granules from uranium and its alloys with Mo, Zr, Nb, Si, Os, Re and other elements has increased in connection with the international program for the non-proliferation of nuclear weapons by reducing the enrichment of nuclear fuel of dispersion fuel rods of research reactors for the content of uranium isotope - 235. If fuel enrichment by uranium isotope is reduced to 235 to values less than 20% by mass, in order to maintain the total amount of uranium in the fuel rod - 235 at a constant level, it is necessary to increase the concentration of total uranium in the fuel rod, or use as Fuel stve denser uranium compounds than those used to reduce the concentration (oxides, aluminides, silicides uranium). Since the limits for increasing the concentration of nuclear fuel in dispersion type fuel rods were exhausted (40-50% by volume), and the required amount of uranium - 235 was not brought to the required amount, it was proposed to use uranium compounds and its alloys with a density higher than fuel for dispersion fuel rods 17 g / cm ³ . Alloying elements are introduced into alloys in quantities sufficient to partially or completely stabilize the γ-phase, to reduce the interaction of fuel with the matrix and cladding material, and to reduce its swelling during operation of a fuel element in a reactor. The most commonly used dispersion fuel is obtained in the form of granule spheres with a size of less than 500 microns.

Known are granules of nuclear fuel from a uranium-molybdenum alloy and a method for producing them by centrifugal atomization of a melt from a rotating ingot electrode (ABAleksandrov, AAEnin and Tkachyov. Reduction of fuel enrichment for research reactors built-up in accordance with Russian (Soviet) projects. Transactions Oral Presentations and Posters ENS RRFM 2001, p. 127-131, 2001.), (R.Kh. Gibadullin, ADKarpin, Yu M.Pevchikh, VVPopov, VNSugonyaev, VMTroyanov. Examination of U-9% Mo alloy powder microstructure in its initial condition and after fuel pin fabrication. 6 ^th Internetional Topical Meeting on Research Reactor Fuel Management. Ghent, Belgium. March 17-20, 2002, pp. 193-196).

There is a method of producing spherical granules from uranium and its alloys, which consists in the fact that uranium and alloying materials are loaded into a crucible, melted by electric arc or induction heating, the melt is fed to a rotating disk and sprayed in an inert gas atmosphere under the action of centrifugal force. The composition of the spherical granules obtained by this method is as follows: uranium base, about 4-9 mass% Q and about 4 mass% X, where Q is Mo, Nb, Zr, and X is selected from Mo, Nb, Ru, Pt, Zr, Si , Ir, Rd, W, Ta at Q ≠ X (US Patent No. 5978432 dated 02.11.1999, MKI G 21 C 3/60 with priority dated 04.17.1998, Patent of the Republic of Korea (South Korea) No.98- 15783).

Croup and spherical granules obtained by the above methods are used as dispersion nuclear fuel in the fuel rods of research reactors. Increasing the load of dispersion fuel in the fuel rod matrix, the use of spherical fuel instead of grains require experimental work on the development of technological modes, such as

- mixing of spherical granules with a powder of the matrix material (aluminum, its alloys or magnesium);

- pressing mixtures;

- rolling or extrusion of blanks in the shell;

- hydraulic tests of fuel rods when changing their design, as well as a number of other studies and improvements.

It is not always advisable to use spherical granules of nuclear fuel from uranium and its alloys for these purposes, since the products obtained are usually sent for processing. In addition, working with radioactive materials imposes a number of limitations, both organizational and safety. All these restrictions reduce the number and increase the time of experiments and experimental work. For initial research, you can use granules simulators - substitutes for nuclear fuel. So, in (TCWiencek and IGProkofiev. Low-Enriched Uranium-Molybdenum Fuel Plate Development. To be presented at the 2000 International Meeting on Reduced Enrichment for Research and Test Reactors / October 1-6, 2000, Las Vegas, Nevada, USA, p. 273-284) spherical particles of tungsten are used as a simulator of uranium-molybdenum spheres.

The theoretical density of tungsten is close to the density of uranium and its alloys, therefore, spherical granules of tungsten require fractional composition as nuclear fuel, can be used to develop mixing and loading the mixture into a mold, study the process of separation of spherical granules and matrix powder of aluminum, magnesium and their alloys . However, pure spherical tungsten powder, with a particle size close to that of U-Mo alloy granules i.e. less than 160 microns, is also quite an expensive material, since a special high-temperature technology for its production is required and the machining of cores of fuel element simulators with tungsten granules is difficult due to the fact that tungsten is a hard metal.

The objective of the invention is the replacement of spherical granules of nuclear fuel from uranium, its alloys and their simulators from tungsten during experimental work and development of technological modes and structural elements, to less expensive, affordable and safer granules.

The problem is solved by using spherical granules of known materials, such as high-speed steels having the following chemical composition, wt.%: Carbon from 0.73 to 1.12; manganese and silicon not more than 0.50; chrome 3.80 to 4.40; tungsten from 2.50 to 18.50; vanadium from 1.00 to 3.00; cobalt not more than 0.50; molybdenum from 0 to 5.30; nickel not more than 0.40; sulfur not more than 0.025-0.035; phosphorus is not more than 0.030, the rest is iron.

Spherical granules from high-speed steels are obtained by centrifugal electric arc spraying of a rotating ingot electrode or by gas spraying of a melt. So, for example, spherical granules from high-speed steel PR-10R6M5 (GOST 19265-73 rods and strips from high-speed steel. Technical conditions. Ed., Standards, 1986) are produced according to technical conditions (Technical conditions 14-1-3851-84. High-speed steel powder) and are used for the manufacture of cutting tools by powder metallurgy methods.

Figure 1 shows the surface morphology of spherical granules of high-speed steel PR-10R6M5.

Figure 2 shows the surface morphology of the spherical granules of the alloy U-9% Mo.

Figure 3 shows a section: a spherical granule made of high-speed steel, grade PR-10Р6М5-1, in a matrix of aluminum alloy - 3, simulating the process of interaction of a fuel rod matrix of an aluminum alloy with the formation of Me _x Al _y - 2 intermetallic compound.

The morphology of the surface of the granules of high-speed steels is identical to the morphology of the surface of the granules of uranium-molybdenum alloys.

The lower melt (melting) temperature when producing granules from high-speed steels relative to tungsten, as well as the content of a small number of expensive components, such as tungsten and molybdenum, make granules available for use as imitators of nuclear fuel granules.

As a rule, in the manufacture of dispersion type fuel rods, aluminum, magnesium and their alloys are used as the matrix of the fuel core of the fuel rod. The temperature regimes of their processing and the fuel elements themselves do not exceed 600 ° C and, as a rule, are in the range 360h500 ° C.

Spherical granules from “high-speed steel” alloys proposed as simulators of nuclear fuel up to a temperature of 600 ° C are resistant to oxidation in air for a long time, do not form an oxide layer that is subject to shedding or interaction with the matrix and cladding material of fuel elements.

At the same time, with a long exposure time of more than 5 hours at a temperature of more than 500 ° С, the material of granules of simulators, as well as the material of granules from uranium and its alloys, begins to interact with the material of the fuel core and shell, that is, with aluminum or aluminum-based alloys forming their intermetallic compounds of type Me _x Al _y . Thus, it is possible to observe a change in the volume of a fuel rod or its components in the same way as in the case of the interaction of uranium and its alloys with aluminum.

Example 1. Figure 3 shows the use of nuclear fuel pellets as an simulator in an aluminum alloy matrix when heating the fuel core simulator at a temperature of 600 ° C for 6 hours, commercially available spherical granules from high-speed steel grade PR-10R6M5 having the following chemical composition, wt.%: carbon 0.82-0.90, manganese and silicon not more than 0.50; chrome 3.80-4.40; tungsten 5.50-6.50; vanadium 1.70-2.10; cobalt not more than 0.50; molybdenum 4.80-5.30; nickel not more than 0.40; sulfur not more than 0.025-0.035; phosphorus is not more than 0.030, the rest is iron.

1 - a simulator of nuclear fuel - spherical granules of alloy 10R6M5;

2 - Me _x Al _y intermetallic layer formed as a result of the interaction of spherical granules of 10Р6М5 alloy with an aluminum alloy, simulating the interaction of nuclear fuel with a matrix and shell material; 3 - aluminum alloy.

The presence of elements such as tungsten and molybdenum in the granules of high-speed steels makes these granules radiopaque against the background of the cladding of a fuel rod and a matrix of aluminum and its alloys, that is, it allows X-ray control of their distribution in the matrix matrix of the fuel simulator.

It should be borne in mind that uranium and its alloys with Mo, Zr, Nb, W, Ta, Si, Ru, Rd have different hardness depending on the content of the listed components in them, as well as on the preparation methods and heat treatment modes. So, the hardness of the U-Mo alloy of 8% (mass) can vary from 280 to 620 kg / mm ² when the processing temperature changes from 300 to 600 ° C and the exposure time at these temperatures from 0.1 to 1000 hours, and the hardness of the alloy U -Mo 10% (mass) processed at the same temperature-time characteristics is from 300 to 560 kg / mm ² .

The hardness of granules made of alloys of high-speed steels selected as nuclear fuel simulators can be changed to the hardness required as that of granules of nuclear fuel, changing the temperature-time regimes of preliminary heat treatments. For this, granules from high-speed alloys are subjected to quenching or tempering.

Example 2. Raising the heating temperature of the granules of the P6M5 alloy from 500 ° C to 860 ° C, followed by slow cooling at a speed of 50 ° C / h, the hardness of the material of the granules varies from 975 to 340 kg / mm ² .

Thus, the use of a pellet simulator instead of nuclear fuel pellets will allow research and development of TVEL technology without equipment with special protection, more economically, efficiently and safely.

Claims (1)

The use of granules from alloys of high speed steel composition: carbon from 0.73 to 1.12; manganese and silicon not more than 0.50; chrome 3.80 to 4.40; tungsten from 2.50 to 18.50; vanadium from 1.00 to 3.00; cobalt not more than 0.50; molybdenum from 0 to 5.30; nickel not more than 0.40; sulfur not more than 0.025-0.035; phosphorus is not more than 0.030 wt.%, the rest is iron, as imitators of granules of nuclear fuel from uranium and its alloys.

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