RU2262754C2 - Fuel assembly of a high-power channel nuclear reactor - Google Patents

Abstract

FIELD: nuclear power engineering.

SUBSTANCE: the invention may be used in nuclear reactors, in particular in the high-power channel nuclear reactors. The proposed assembly of these reactors is a framework with fuel elements, located in it. The framework has a central tube with the end grates and multi-tier system of spacers, fixed on the tube. This system is fabricated in the form of bent closed ships, skirting the fuel elements. The ships have the spacing bosses and are fastened between themselves. Besides, the fuel elements of internal and external rows contact with the ships, skirting them, in the places more than two. The external and internal rims, fastened with the ships, skirting the fuel elements, are the part of the multi-tier system of spacers. The ships and rims may be fastened between themselves with a shelf and may be fabricated from one sheet.

EFFECT: increased reliability of the fuel assemblies.

12 cl 28 dwg

Description

The invention relates to nuclear technology and can be used in the manufacture of fuel assemblies (FA) of nuclear reactors, especially for high-power channel reactors (RBMK).

Known fuel assemblies for nuclear reactors CANDU (Canada Deuterium Uranium). The arrangement of fuel elements (fuel elements) relative to each other in the fuel assemblies of the CANDU and RBMK reactors is organized according to the same principle. The fuel assemblies of the CANDU reactor are a frame containing end grids at the ends of the assembly and a spacer system that includes the frame grids and spacing protrusions on the shells of the peripheral fuel rods of the fuel assembly (see A. Dementiev, Nuclear Power Reactors, M .: Energoatomizdat, 1984, p. 64, 65).

However, this design is only possible for small fuel assemblies in which the fuel rods have sufficient bending stiffness. In RBMK and water-cooled power reactors of the WWER type, which use long fuel rods, the use of such a design can lead to burn-through of the claddings of fuel rods.

The closest in technical essence and achieved effect is a fuel assembly for RBMK (see ibid. P. 45, 47). A fuel assembly is a frame with eighteen fuel rods placed in it by two concentric annular rows. The frame is made in the form of a central pipe, with a spacer system and end grids fixed to it. In such a fuel assembly, all fuel rods are fixed at the same level of assembly height in the cells of the spacer grids.

This leads to the formation of narrow gaps between the cells, fuel rods and cell walls, and also, from the condition of minimal crowding of the coolant flow, limits the wall thickness of the cells of the spacing system. Narrow gaps contribute to the accumulation of reactor “garbage” circulating with the coolant at the spacing points of the fuel rods. “Garbage”, stuck in the spacer system of a fuel assembly, leads to the destruction of the cladding of the fuel rods according to the debris mechanism. The small thickness of the cell walls leads to an intensive increase in the concentration of hydrogen in the material of the spacer grids and to large stresses in the cell walls from the effects of vibrations and oxide film, which in turn causes their accelerated destruction and emergency condition of the fuel assembly. In addition, the spacing of the central and peripheral fuel rods at the same level along the height of the fuel assemblies does not contribute to the transverse flow of the coolant and, therefore, does not contribute to the intensive heat exchange between the fuel rods and the coolant, which is already difficult at the spacing points.

The technical task of the invention is to increase the reliability of fuel assemblies RBMK by reducing the accumulation of "garbage" in the spacing of the fuel rods and by increasing the reliability of the spacing of the fuel rods during operation.

This technical problem is solved in that the fuel assembly of a large channel power reactor is a frame in the form of a central pipe, on which end grids and a spacer system are fixed, made in the form of several tiers, with two concentric annular rows of fuel rods placed in them, with each tier spacing The system is made in the form of several curved tapes, each of which is connected to the adjacent one, and each fuel element contacts one of the tapes in at least two places.

In a particular embodiment, the fuel assemblies of the tape at the contact points with the fuel rods are provided with spacing protrusions.

In another particular embodiment of the fuel assembly, the ribbons enveloping the outer row of fuel elements consist of several fragments.

In another particular embodiment of the fuel assembly, adjacent ribbons of each tier are arranged with a step of not less than the width of the ribbon in height.

In another particular embodiment of the fuel assembly, at least a portion of the tiers of the spacer system is provided with an external rim with which tapes are enveloped around the outer row of fuel elements.

In another particular embodiment of the fuel assembly, the outer rim and adjacent tapes are placed with a height step of at least the width of the tape or rim.

In another particular embodiment of the fuel assembly, spacer protrusions are formed on the outer rim to secure the fuel rods.

In another particular embodiment of the fuel assembly, the spacing protrusions are formed in the form of beakings, corrugations or bends.

In another particular embodiment of the fuel assembly, the ribbons enveloping the fuel rods of the outer row are made with petals for fixing the fuel rods of the inner row.

In another particular embodiment of the fuel assembly, the ribbons enveloping the fuel rods of the inner row are attached to the central pipe.

In another particular embodiment of the fuel assembly, at least a portion of the tiers of the spacer system is provided with an inner rim that is fixed to the central pipe and connected to ribbons enveloping the fuel rods of the inner row.

In another private embodiment, the fuel assembly of the tape is made with petals for turbulization of the coolant flow.

This design, in comparison with any previously known designs of an 18-rod assembly, allows, with less oppression of the coolant flow, to double the wall thickness of the spacer system and, therefore, halve the concentration of hydrogen in its material that accumulates during operation. In addition, tensile stresses in the fuel assembly spacing system are significantly reduced, which, in turn, in structures made of zirconium alloys will complicate the formation of radial hydrides and, therefore, will significantly delay the start of destruction of the spacing system during fuel assembly operation. This removes the obstacle to the use of zirconium alloys as a material for spacing systems of RBMK fuel assemblies, which will significantly increase the efficiency of RBMK and the durability of fuel assemblies. The increase in the area of the holes for the flow of coolant in the spacing of the fuel rods and the decrease in a number of options of the wetted surface of the spacer system, along with the stepwise arrangement of the strips and the rim, reduces its clogging with "garbage", contributing to debris. In addition, the formation of the elements of the spacing system from a whole sheet, incorporated in some particular versions of the proposed design, allows the use of welded joints only on the rims, which, in turn, increases the reliability of the fuel assemblies.

The essence of the invention is illustrated by drawings.

Figure 1 shows the cross-section of an 18-rod fuel assembly of a nuclear reactor with a spacer system without rims directly attached to the central tube of the fuel assembly. The tapes of the spacer system are fastened directly to each other along the widest edges.

Figure 2 presents the sheet billet tape envelope of the fuel rods of the outer row.

Figure 3 presents the sheet blank of the tape envelope of the fuel rods of the inner row, with technological protrusions formed at one of its ends for fastening the tapes on the central pipe.

Figure 4 presents a fragment of the spacing system shown in figure 1.

Figure 5 shows a cross section of an 18-rod fuel assembly of a nuclear reactor with a spacer system that does not have rims and is directly attached to the central fuel assembly pipe. The tapes of the spacer system are fastened to each other along the ribs. The spacing protrusions on the tapes are made in the form of bends of tapes, bellows and corrugations.

Figure 6 presents the sheet blank tape, envelope of the fuel rods, cut from a whole sheet.

Figure 7 presents the sheet blank tape, envelope of the fuel rods, consisting of two fragments.

On Fig presents a sheet blank tape, envelope of the fuel rods, consisting of three fragments.

In Fig.9 presents a fragment of the spacer system depicted in Fig.5.

Figure 10 shows a cross section of a fuel assembly of a nuclear reactor, the spacing system of which has an external rim attached along the widest edges to a tape enveloping the fuel rods of the outer row. Spacing protrusions are formed on the rim.

11 shows a portion of a spacer system with an external rim consisting of individual fragments.

On Fig presents a cross section of a fuel assembly of a nuclear reactor, in the spacer system of which the outer rim is formed by a tape connected along the ribs (with a ledge equal to the width of the tapes) with a tape enveloping the fuel rods of the outer row. Spacing protrusions are formed on the rim. A part of the tape envelope of the outer row fuel rods is formed in the form of symmetrically spaced spacing petals, and spacing protrusions are also formed on the petals.

On Fig presents a sheet blank of a fragment of this spacer system with formed beakings and corrugations.

On Fig presents a fragment of the spacing system of the fuel Assembly shown in Fig.

On Fig presents a fragment of the spacer system of the fuel assembly, similar to that shown in Fig, but with the displacement of the tapes and the rim relative to each other along the axis of the fuel assembly with a ledge equal to twice the width of the tape.

On Fig presents a cross section of an 18-rod fuel assembly of a nuclear reactor, in the spacer system of which the outer rim is formed by tapes connected on both sides (with a step) with two tapes symmetrically located relative to the rim, enveloping the fuel rods of the outer row. At the tapes enveloping the fuel rods of the outer row, spacing petals are formed. Moreover, part of the petals connect the outer row tapes, and spacing protrusions are formed on the rim, petals and profiled tapes.

On Fig presents a side view of a fragment of the fuel Assembly, the cross section of which is presented in Fig.16.

On Fig shows the cross section (at different levels) of the fragment of the fuel assembly shown in Fig. In the plane of sections only elements of the spacing system are shown.

At levels "a" and "and" are located both the tape envelope of the inner row of fuel rods, and the petals of the tape envelope of the outer row of fuel rods.

At levels "b" and "h" are the junction of the ribbons enveloping the inner and outer rows of the fuel rods, and the spacing petals of the ribbon enveloping the outer row of the fuel rods.

At levels "c" and "g" there are ribbons enveloping the outer row of fuel rods.

At the levels "g" and "e" are the junction of the rim with tapes, enveloping the outer row of fuel rods and spacing the petals of these tapes.

At level "d" is the rim.

On Fig presents a sheet blank with extruded beetles and corrugations of the spacing assembly system, which is shown in Fig.16, 17.

On Fig presents a fragment of the spacer assembly system shown in Fig.16, 17.

On Fig presents a cross section of a fuel assembly of a nuclear reactor, in which the arrangement of the fuel rods is typical for RBMK and in which the outer rim of the spacer system is formed by tapes connected to the ledge with a tape enveloping the fuel rods of the outer row. Puklevki, corrugations and sections of profiled tapes are directed at an angle to the central axis of the lattice.

On Fig presents a sheet blank of the tier of the spacer system with extruded beetles and corrugations.

On Fig presents a fragment of the spacer assembly system depicted in Fig.21.

On Fig presents a cross section of a fuel assembly of a nuclear reactor, in which part of the tape spacer system, envelope the fuel rods of the outer row, is formed in the form of spacer lobes. Puklevki are formed on the petals and ribbons. Spacer tapes are attached to the rim. The tapes of the spacer system are attached to the outer and inner rims, and the edges of these tapes are formed in the form of petals twisted and / or angled to the central axis of the spacer grid.

On Fig presents a sheet blank tapes of tiers of this spacer system with extruded beetles and corrugations.

On Fig presents a fragment of the spacer system depicted in Fig.24.

On Fig presents a side view of the spacer system fragment of the fuel assembly shown in Fig.24, and a section:

- AA on the system tapes, enveloping the inner row of fuel rods, and the inner rim;

- BB on the tape system envelope the outer row of fuel rods, and the outer rim.

On Fig presents a cross section of an 18-rod fuel assembly of a nuclear reactor, in which two fuel rods of the inner row and two peripheral are located on each of the 3 axes passing through the center of the assembly. On the outer rim, pieces of spacer tape are welded onto which spacer tabs are formed.

The fuel assembly contains end grids and a spacer system, which are curved closed and fastened together at least in several places of the tape 1 (Fig. 1, 4, 5, 9-21, 23, 24, 26-28), mounted on the central pipe 2 (Fig. 1, 5, 10, 12, 16-18, 21, 24, 27, 28) of the fuel assembly. The tapes span the fuel rods 3 (FIGS. 1, 5, 10, 12, 16-18, 21, 24, 28) by means of the spacing projections 4 on them (FIGS. 1, 4, 5, 9-16, 18-28), located at an angle of 120 ° to each other relative to the axis of the fuel rod fixed by them. Tapes enveloping the outer row of cells are attached along the widest edges to the outer rim 5 (Fig. 10, 24, 27, 28), to fragments of the outer rim 6 (Fig. 11) or along the edges to ribbons forming the outer rim 7 (Fig. .12-23), and / or their ends are bonded to each other.

The distance lobes 8 (FIGS. 12-20, 24-27) are part of the tapes 1 and can be formed at the edges of the tapes. Individual sections 9 (Fig.21, 23) of the tapes can be tilted with respect to the axis of the fuel assembly. In the center, there may be an inner rim 10 (FIGS. 24, 27) fastened with tapes enveloping the inner row of fuel rods, and also these tapes can be fastened together. At the edges of the tapes can be formed turbulent petals 11 (Fig.24-27). The outer rim or rim fragment may be provided with spacing elements. The distance elements can be made in the form of a wave-like tape 12 attached to the rim directly (Fig.24, 28), or the rim can be made with distance elements (Fig.10-20). The fuel rod 3 is spaced by the elements 12 and the protrusions of the tapes.

In most of the described private construction options of the fuel assembly, the fuel elements located in the center can be spaced at different levels than the fuel elements located on the periphery near the rim (Figs. 5-28). Ribbons without petals and ribbons with petals are formed from one sheet (Fig.6, 9-28). In some embodiments, the tape and rim preform is formed from a single sheet by notches or slots with a slot width of up to twice the tape width (Figs. 12-23).

Large than doubled tape width, the width of the slots leads to a decrease in the rigidity of the spacing system, which, in turn, can lead to its unacceptable deformations during assembly overloads. Welding or soldering places in most design options are located only on the rims and ends of the spacing tapes, which increases the durability of the entire spacing system compared to the standard design, and also increases the manufacturability of the fuel assembly as a whole (Figs. 5-28). The proposed fuel assembly can be manufactured using any known technology on known equipment using simple equipment.

The proposed RBMK fuel assembly is equipped with ribbons 1 that are attached to the central pipe 2 directly (Fig. 1, 5, 10, 12, 16-18, 21, 28) or through the inner rim 10 (Fig. 24, 27), and can also be attached to the outer rim 5 (Fig.10, 24, 27, 28), to fragments of the outer rim 6 (Fig.11) or made together with the outer rim 7 (Fig.12-23).

In the proposed fuel assembly, the spacing system using the petals 8 formed on the tapes, which are part of the tapes (Figs. 12-20, 24-27), spacers 4 (Figs. 1, 4, 5, 9-16, 18-28) and spacing elements located on the rims or fragments of the rim (Figs. 10-20, 24, 27, 28), spans fuel rods 3 at a given distance from each other more reliably than in existing fuel assemblies, preventing them from being bent and pushed out of place throughout FA operation time.

The increased reliability of the proposed design of fuel assemblies with a spacer system made of zirconium alloys is ensured by the fact that the ratio of the surface area of the walls of the spacer system to the volume of its material is significantly less than that of a fuel assembly with spacer grids made of especially thin-walled pipes. At the same rate of surface oxidation and, correspondingly, the same stream of hydrogen going into the material of the tapes through a unit area of their surface, the accumulation of hydrogen in a unit volume of the material of the tapes is much less. In addition, the stresses from the tensile action of the formed oxide film and the vibrational effects of the fuel rods on the ribbons will be much less, since the ribbons, due to their greater thickness, have a cross-sectional area of the wall and a moment of resistance much higher than that of the cell wall. A decrease in hydrogen concentration will delay in time, and possibly prevent the formation of hydrides in the walls of the spacer system during operation. Reducing tensile stresses, on the one hand, reduces the likelihood of hydrides forming the most dangerous radial orientation, and on the other hand, as is known, reducing tensile stresses always reduces the likelihood of product failure. Consequently, the operating time of a fuel assembly before the destruction of its spacer system will increase significantly. In addition, an increase in the average area of the holes in the spacing points in the fuel assemblies loaded with fuel rods and a decrease in the total length of the walls of the spacer system along with a two-stage arrangement of tapes reduces the clogging of the fuel assemblies with “garbage” in the coolant, which will reduce the debris of the fuel rods. Therefore, the reliability of fuel assemblies increases significantly. When the flow of heat transfer medium onto the spacer system ", the presence of spacing projections 4 located at an angle to the central axis of the grate and, accordingly, the direction of flow of the heat transfer medium, sections of tapes 9, turbulent lobes 11 and distance elements (Figs. 21-23) lead to turbulence of the heat transfer stream and, consequently, improved heat removal from the surface of the fuel rods.The angle of inclination to the axis of the fuel assembly of the turbulent protrusions and elements, puppets, corrugations and sections of the profiled tape should not exceed 60 ° due to ozhnosti cavitation.

Thus, the reliability of the RBMK fuel assembly is increased by increasing the reliability of its spacer system and reducing the likelihood of destruction of the claddings of fuel rods by the debris mechanism.

Sources of information

1. B. A. Dementyev "Nuclear Power Reactors", p. 64, 65. M.: Energoatomizdat. 1984 year

2. Ibid., Pp. 45, 47.

Claims (12)

1. The fuel assembly of a high-power channel nuclear reactor (RBMK), which is a framework in the form of a central pipe, on which end grids and a spacing system are made, made in the form of several tiers, with two concentric annular rows of fuel rods placed in them, characterized in that each tier of the spacing system is made in the form of several curved tapes, each of which is connected to the adjacent one, and each fuel rod contacts at least two places with one of the tapes. 2. The fuel assembly according to claim 1, characterized in that the tapes at the points of contact with the fuel rods are equipped with spacing protrusions. 3. The fuel assembly according to claim 1, characterized in that the ribbons enveloping the outer row of fuel rods consist of several fragments. 4. The fuel assembly according to claim 1, characterized in that the adjacent tapes of each tier are placed with a step in height of not less than the width of the tape. 5. The fuel assembly according to claim 1, characterized in that at least part of the tiers of the spacer system is provided with an external rim with which tapes are enveloped that envelope the outer row of fuel elements. 6. The fuel assembly according to claim 5, characterized in that the outer rim and adjacent tapes are placed with a step in height not less than the width of the tape or rim. 7. The fuel assembly according to claim 5, characterized in that spacing protrusions are formed on the outer rim for fixing the fuel rods. 8. The fuel assembly according to claim 2, characterized in that the spacing protrusions are formed in the form of bellows, corrugations or bends. 9. The fuel assembly according to claim 1, characterized in that the tape envelope of the fuel rods of the outer row is made with petals for fixing the fuel rods of the inner row. 10. The fuel assembly according to claim 1, characterized in that the tape envelope of the fuel rods of the inner row are attached to the Central pipe. 11. The fuel assembly according to claim 1, characterized in that at least a portion of the tiers of the spacer system is provided with an inner rim that is mounted on a central pipe and connected to ribbons enveloping the fuel rods of the inner row. 12. The fuel assembly according to claim 1, characterized in that the tape is made with petals for turbulence of the coolant flow.

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