RU2523676C1 - Nuclear reactor fuel assembly - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: nuclear reactor fuel assembly has a head, a tail, a bundle of cylindrical fuel elements and guide channels located in spacer grids, and aligning elements made in spacer grid cells. At least part of the aligning elements in contact with the spacer grid is made on casings of the fuel elements at places where the spacer grids are located. In a particular design of the fuel assembly, on at least part of the outer surface of the casings of the fuel elements there are wall-mounted heat exchange intensifiers, the projection height over the surface of the casings of which is less than the projection height of the aligning elements.

EFFECT: longer operating life and higher thermal efficiency of the nuclear reactor fuel assembly.

2 cl, 3 dwg

Description

The invention relates to nuclear technology and can be used in fuel assemblies of water-cooled nuclear reactors.

Known fuel assembly of a water-cooled energy reactor [RF Patent No. 2192051 "Fuel Assembly". Declared 10/26/1993, published 10/27/2002]. The device uses fuel elements with a smooth cylindrical surface, the centering of which in the cells of the spacer grids is provided by the presence of centering elements. Centering elements are part of the distance grid.

A disadvantage of the known technical solution is the damage to the cladding of a fuel rod as a result of fretting corrosion caused by the presence of rubbing pairs “cladding of a fuel rod - spacer grid”. Damage to the shell leads to the release of radioactive products into the coolant, an increase in dose loads for personnel, and to early unloading of the unburnt fuel assembly.

Closest to the technical nature of the claimed technical solution is the fuel assembly of a nuclear reactor [Application WO 96/19811 "Fuel Assembly and a spacer grid for a nuclear reactor". Declared December 21, 1994, published June 27, 1996]. The fuel assembly contains a head, a shank, a bunch of fuel rods and guide channels located in the spacer grids. The alignment of smooth cylindrical fuel rods in the cells of the spacer grids is provided by the presence of centering elements with the formation of friction pairs “cladding of the fuel rod - spacer grid”.

A disadvantage of the known technical solution is damage to the cladding of a fuel rod as a result of fretting corrosion caused by the presence of rubbing pairs “cladding of a fuel rod - a spacer grid” and a reduced heat transfer rate of the fuel rods.

The objective of the proposed technical solution is to eliminate these drawbacks, namely, eliminating damage to the cladding of the fuel rods and increasing the heat transfer of the fuel rods.

The technical result consists in increasing the resource and thermal efficiency of the fuel assembly of a nuclear reactor.

To eliminate this drawback in a fuel assembly of a nuclear reactor containing a head, a shank, a bundle of cylindrical fuel elements and guide channels located in the spacer grids, and centering elements made in the cells of the spacer grids, at least a portion of the centering elements in contact with distance grid, run on the shells of the fuel elements in the locations of the distance gratings.

In particular cases of the implementation of the fuel assembly of a nuclear reactor, it is proposed that at least part of the outer surface of the shells of the fuel elements carry wall-mounted heat transfer intensifiers, the height of the protrusion of which above the surface of the shell is less than the height of the protrusion of the centering elements.

The invention is illustrated by figures 1-3, where the following notation: 1 - spacer grid; 2 - inelastic centering element; 3 - the shell of the fuel element; 4 - fuel tablet; 5 - elastic centering element.

The fuel assembly of a nuclear reactor contains a head, a shank, a bunch of cylindrical fuel elements and guide channels located in the spacer grids, and centering elements made in the cells of the spacer grids.

At least part of the centering elements in contact with the spacer grid is made on the shells of the fuel elements in the locations of the spacer grids.

In particular cases of performing a fuel assembly of a nuclear reactor, but at least on a part of the outer surface of the shells of the fuel elements, wall heat transfer intensifiers are made, the height of the protrusion of which above the surface of the shells is less than the height of the protrusion of the centering elements.

The figure 1 shows an example of the alignment of the fuel rod using inelastic centering elements 2, made in the form of fixed ribs on the shell of the fuel element 3, and an elastic centering element 5, mounted on the cell wall of the square spacer grid 1.

The figure 2 shows an example of the alignment of the fuel rod using an elastic centering element 5, mounted on the shell of the fuel element 3.

The figure 3 shows an example of the alignment of the fuel element using an elastic centering element 5 made on the shell of the fuel element 3, and an inelastic centering element 2 made in the form of a ring (solid or perforated) and mounted on the cell wall of the square spacer grid 1.

As a variant of the latter design, it is possible that the spacer grid itself is composed of ring sleeves with an external diameter equal to the pitch of the fuel rods in the fuel assembly. In this case, the cell wall of the spacer grid will play the role of the inelastic centering element. In this case, the inelastic centering element 2 shown in FIG. 3 is not needed.

As can be seen from the drawings shown in figures 1-3, the rubbing pair in these structures is the "centering element-spacer grid". The shell of the fuel element is not involved in friction, which reduces the likelihood of fretting corrosion and, accordingly, reduces the likelihood of damage to the shell.

The presence of centering elements on the cladding creates a gap between the cladding and the spacer grid that is sufficient to accommodate wall-mounted heat transfer intensifiers on the outer surface of the cladding that do not impede the pulling of fuel rods through the cells of the spacer grids in the manufacture of fuel assemblies.

The optimal shape, material and size of the centering elements, the shape, material and size of the wall mounted intensifiers made depends on the type of reactor, the type of spacer grid, the manufacturing technology of the fuel assembly, the conditions of its operation in the core and are determined on the basis of standard strength and heat-hydraulic calculations, experimental studies.

To perform centering elements and wall intensifiers, known technological processes of soldering, rolling, gas-dynamic spraying of metals, etc. can be used.

According to statistics, among the mechanisms of fuel damage at the US PWR between 2000 and 2008. 77% is lattice-fuel fretting [Experience in operating fuel in PWR reactors (Review of materials from the Top Fuel 2009 conference, Paris, France, September 6–10, 2009). Nuclear Technology Abroad, 2010, No. 6, p. 3-11].

The proposed technical solution - the placement of inelastic 2 or 5 elastic centering elements on the cladding of the fuel rod 3 allows to eliminate the conditions of fretting corrosion and thereby increase the life of the fuel assemblies, and wall intensifiers make it possible to significantly increase the heat transfer coefficient from the fuel rod to the coolant and, as a result, thermal fuel assembly efficiency.

An example of a specific implementation of the device.

The fuel assembly of the nuclear reactor has a square cross-section with a side of 21.5 cm, contains 264 fuel rods with an external radius of 9.5 mm, 24 channel guides and a central tube placed in the cells of square spacing grids with a pitch of 12.6 mm. The height of the active part of the fuel rod is 366 cm. At this height there are 6 spacing grids, each 4 cm high. The wall thickness of the spacer grid 1 is 0.5 mm.

The implementation of the invention in accordance with figure 1 involves the presence of an elastic centering element 5, fixed by resistance welding in the cells of the spacing grid 1. The thickness of the resiliently centering element is 0.3 mm, its shape is shown in the drawing of figure 1. On the cladding of the fuel rods in the area of the spacing grids using gas dynamic spraying [Alkhimov A.P., Klinkov SV., Kosarev V.F., Fomin V.M. Cold gas-dynamic spraying. Theory and practice. - M., Fizmatlit, 2010], 4 inelastic centering elements 2, each 20 mm long, protruding 1.5 mm above the surface of the shell, were made. To intensify heat transfer on the shells of the fuel elements along the height of their active part, wall-mounted intensifiers were made using gas-dynamic spraying in the form of ring-shaped protrusions 0.4 mm high, 3 mm wide with a step of 10 mm. Such intensifiers can increase the heat transfer coefficient up to 2 times, compared with smooth shells [Kalinin E.K., Dreitser G.A., Yarkho S.A. Intensification of heat transfer in the channels. 3rd ed., Revised. and add. - Engineering, 1990]. At the locations of the spacing grids, wall intensifiers are absent.

Claims (2)

1. A fuel assembly of a nuclear reactor containing a head, a shank, a bunch of cylindrical fuel elements and guide channels placed in the spacer grids, and centering elements made in the cells of the spacer grids, characterized in that at least part of the centering elements in contact with spacing grids, made on the shells of the fuel elements in the locations of the spacing grids. 2. The fuel assembly of a nuclear reactor according to claim 1, characterized in that at least on a part of the outer surface of the shells of the fuel elements, wall heat transfer intensifiers are made, the height of the protrusion of which above the surface of the shells is less than the height of the protrusion of the centering elements.

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