The way to protect the core elements from destruction

 

(57) Abstract:

The invention relates to nuclear energy, namely technological ways of protecting the items in the active zones of nuclear reactors channel and frame type from destruction, and can be used to suppress the debris effect, fretting and local corrosion of the fuel elements (FE), fuel assemblies (FA), technological channels (TC). The technical result is achieved in that on the surface, or part of the surfaces of the fuel elements and/or assemblies, and/or TC cause the protective coating from a material with a hardness greater than the hardness of structural materials and their oxides contour of nuclear reactors. While on the surface put diamond-like coating. In addition, on the surface cause the carbides, nitrides or borides of metals. The surface may be diamond-like coating together with carbides, nitrides, borides of metals in various combinations. 3 C.p. f-crystals.

The method relates to the protection of the items in the active zones of nuclear reactors channel and frame type from destruction as a result of corrosion and mechanical abrasion by applying protective coatings. First of all to improve rprovides elements (Fe) of the active zone of the majority of Russian nuclear reactors made of an alloy of zirconium, 1% niobium on foreign reactors of zircaloy. In addition to zirconium alloys are alloys of aluminum and steel. Basically it is enough plastic having a low hardness materials. The fuel elements are combined in the fuel assemblies (FA) with grid spacers, which are made of steel or an alloy of zirconium. During operation of the fuel assemblies of various mechanical contamination of coolant, appearing in the circuit in the installation or repair work (metal chips, wire, welded hail, etc), as well as dispersed particles resulting from the corrosion of structural materials (corrosion products harder than the base metal), deposited or get stuck in the area of grid spacers. The pollutants while in the area of grid spacers under the influence of the coolant flow perform oscillatory motion and mechanical impact on the surface of the fuel elements (Fe). This breaks the protective oxide film, intensifying corrosion processes, and is also a purely mechanical wear thin shell Fe - debris-effect.

To solve this problem on a number of foreign reactors were installed mesh filters to remove mehanicheskaya (Strasser A. Experiments, Mechanisms and Management. 26-29 May 1992, Dimitrovgrad, Russia). Another solution measures are implemented to prevent contamination in the reactor when carrying out installation and maintenance work. Despite the implementation of these decisions, the main cause of the pressure loss of the fuel rods at the moment as foreign and Russian reactors is the debris effect. All activities aimed at reducing the probability of mechanical particles in the reactor core, but none of them solves the problem of combating the debris-effect in case of ingress of particles into the active zone and stuck them, usually in the spacer grid.

In the operation of the Assembly may occur some deformation processes in places of contact of the fuel rods in the clamping area, primarily in the spacer grids. Under the influence of the coolant flow is vibration of the fuel rods, resulting in a realized fretting (Smirnov A. C. D. Markov Century polenak B. C. and other Research into the causes depressurization of regular fuel of VVER and RBMK. Scientific-technical seminar "Modernization, improvement and improving the reliability of nuclear fuel for RBMK" S. 39-48. 25-27 October of coolant, under the influence generated oxidants processes are local corrosion as fuel, and technological channels (TC). The resulting zirconium oxide together with the corrosion products of steel structures of the circulation path passing through the active zone, lead to mechanical abrasion of the protective oxide layer on the surface of the fuel element.

These problems can be solved if to protect surfaces primarily membranes TVEL from abrasion under the influence of vibrations in the system shell Fe - dictaminara lattice (fretting corrosion) or in the system shell TVEL - mechanical particle stuck in the spacer grid (debris-effect), and there should be no contact of aggressive environment, which is the coolant when unrepressed radiolysis of water with the surface of the sheath of the fuel element.

These 3 problems can be solved by applying on the surface of the core constructs, such as fuel elements, fuel assemblies and TC of the protective coating.

There is a method of protection of fuel graphite block, made from a mixture of zirconium carbide, uranium carbide and graphite by coating of carbides of zirconium or niobium (U.S. Pat.RF 2066485, BI 25, 1996), but it pokrenuti - steel surfaces equipment contours nuclear reactor by applying a Nickel-phosphorus coating (prototype - authorship 1028091, BI 22, 1989 ), the coating has a hardness higher than the hardness of Zirconia, but this coating if the coating on the Zirconia surface has the disadvantage that it has with zirconium weak adhesion and irradiated at a neutron flux of Nickel forms of radioactive cobalt-58, which degrades the radiation environment of the reactor.

The task on which the invention is directed, is the suppression of the debris-effect, fretting and local corrosion of the fuel elements, fuel assemblies and TC made of zirconium and its alloys, which ultimately will increase the reliability of a nuclear reactor by reducing the probability of destruction of the core elements due to corrosion and mechanical abrasion.

For this method of protection of core elements, in particular of fuel elements, fuel assemblies and technological channels, from destruction, namely, that on the surface, or a portion of the surface of fuel elements, and/or fuel assemblies, and/or technological channels are coated with material which tori.

On the surface of the diamond-like coating is applied.

In addition, on the surface cause the carbides, nitrides or borides of metals.

The surface may be diamond-like coating together with carbides, nitrides, borides of metals in various combinations.

In order to achieve the objectives of the coating should have the following properties:

1 - hardness and wear resistance of the coating should be less than similar properties of particles that can appear in the loop;

2 is a cross - section of the neutron absorption of the coating material should be commensurate with the absorption of neutrons structural material of a fuel rod, fuel Assembly or TC, or the contribution to the absorption of neutrons of this coverage must be comparable with the absorption of neutrons oxide film of corrosion products present on the surface of the fuel elements and the other, provided that the coating material does not perform other functions, such as the alignment of the energy release at the height of the zone;

3 - the coating material should not be activated with the formation of long-lived radionuclides from the hard emission spectrum;

4 - the coating should have good adhesion to the material of the fuel elements, fuel assemblies or TC and not break down during the operate is of Arbidol, nitrides, borides of metals with high hardness.

For comparison, we give the microhardness of zirconium, aluminum, steel microhardness of the proposed coatings (according to works:. Panchenko, E. C., Skakov Y. A., creamer B. I. In the book. Laboratory of metallography. Ed. by B., Lifshitz. Ed. Metallurgy, Moscow, 1965.

Long D. I. , Olshansky, E. D., Ryazantsev E. P. Obtaining diamond-like carbon films and application. Conversion in mechanical engineering. 1999 vol.3-4 (34-35), S. 119-122. Baryshnikov, M. C., Dubrovin the Karelian Isthmus is the Generalization of the results of post-irradiation studies of uranium-zirconium fuel rods. Paper presented at the conference. RIAR, Dimitrovgrad, 2000).

Material Microhardness kg/mm2< / BR>
Aluminum cast - 37,0

Aluminum deformed 25,0

then annealed at 40oC for 4 h, unpolished

Steel 10, base metal - 161

Steel 45, base metal - 191

Steel EI - 825 - 965

Carbide zirconium - 2836 - 3480

The titanium carbide - 2850 - 3390

Tungsten carbide-zirconium - 2700 - 2733

Tungsten carbide - 3000 - 3400

The boron carbide - 3700

Carbide vanadium - 2400 - 2800

Bored titanium - 3400

Bored zirconium - 2200

The Nickel-phosphorus coating - 500 - 550

Diamond-like coating is BR>
Diamond-like coating has good adhesion, high abrasion resistance, the film is not processed even with diamond paste, high surface quality. These coatings also have excellent chemical resistance, not react with acids and alkalis.

To reduce internal stresses in the creation of a relatively thick diamond-like films (5-20 μm), it is advisable to make a joint application of diamond-like films with carbides, nitrides, borides of metals, for example, is highly compatible with diamond-like film of silicon carbide.

The application of coatings with high hardness and corrosion resistance, and above all the application of diamond-like coatings, and borides, nitrides and carbides of metals will allow to solve problems of wear and corrosion of equipment and circuit elements of power plants and nuclear power plants.

1. The way to protect the core elements, in particular, fuel elements, fuel assemblies and technological channels from destruction, characterized in that on the surface or a portion of the surface of fuel elements, and/or fuel assemblies, and/or technological channels are coated with a material with mi the century

2. The method according to p. 1, characterized in that on the surface of the diamond-like coating is applied.

3. The method according to p. 1, characterized in that on the surface cause the carbides, nitrides or borides of metals.

4. The method according to p. 1, characterized in that on the surface of the diamond-like coating is applied together with carbides, nitrides, borides of metals in various combinations.

 

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