RU2255384C2 - Fuel assembly of water-moderated water-cooled power reactor - Google Patents

Abstract

FIELD: nuclear power engineering; nuclear-reactor fuel assemblies.

SUBSTANCE: each spacer grid of fuel assemblies has shaped supporting ribs symmetrically rounded-off on its edges abutting against corners of spacer-grid rims. Such design makes it possible to reduce nonuniformity of heat transfer in reactor core, to decrease resisting forces during emergency insertion of control rods, and to space apart fuel assemblies in core.

EFFECT: enhanced operating reliability and safety of nuclear reactor.

3 cl, 4 dwg

Description

The invention relates to nuclear energy and can be used at enterprises engaged in the assembly of fuel assemblies from fuel elements, mainly for nuclear water-cooled power reactors of the WWER-1000 type. At present, there is a widespread introduction of spacer grids for fuel assemblies made of zirconium alloys, promising in mechanical properties, radiation growth, and relaxation characteristics to increase energy production (see Nuclear Technology Abroad, 1990, No. 4, pp. 3-5) . In the process of manufacturing spacer grids, set and spot welding of curly cells from a zirconium alloy with each other with the formation of a field of curly cells, entering the typed field of curly cells into a hexagonal rim from a zirconium alloy and fixing it (see Development, production and operation of fuel elements of power reactors Book 1, edited by F.G. Reshetnikov, Energoatomizdat, 1995, p.198).

According to the requirements for the fuel assemblies in geometrical dimensions, the spacer grids, and there are fifteen of them in the fuel assembly located along the length of the fuel assembly through 250 mm each, must be made on strictly “turnkey” faces, i.e. 234 mm (see ibid., Pp. 184-185).

It is known that the core of a VVER-1000 nuclear reactor is composed of relatively tightly packed fuel assemblies that contain fuel elements with nuclear fuel with a gap of 2 mm between the fuel assemblies in the core of a nuclear reactor, which is necessary only for free installation and removal during the process overload (see B. A. Dementiev. Nuclear power reactors. M., Energoatomizdat, 1990, p. 31).

The closest in technical essence and the achieved effect is a fuel assembly of a nuclear water-water power reactor (see patent of the Russian Federation RU 2163036, IPC 7 G 21C 3/34, 21/00, from 05.04.1999, publ. 10.02.2001), including a bunch of fuel elements mounted vertically in the frame of the spacer grids mounted on tubular channels, a shank and a removable head, where each spacer grid is assembled from separate curly cells welded together at points fastened on the outside with a rim made of overt portions and forming channels for the coolant between the fuel elements and the walls of the cells, between cells and between cells and the peripheral rim provided with impingement coolant. It is known that curly cells made of zirconium alloy made of thin-walled tubes have fluctuations both in wall thickness and in diameter in accordance with TU. This leads to the fact that the collected field of cells welded together during welding of peripheral cells to the component parts of the rim either bends the rim face towards the field of cells, or bends the rim face to the outside of the cell field, both are undesirable, since the concave face the rim inside the cell field in the core of the nuclear reactor increases the gap between adjacent fuel assemblies, or narrows this gap, but the edges of the rim in the angle region practically do not change their size when assembling the spacer grid and welding an ode to the peripheral cells.

When a nuclear reactor is operating, an increased gap between the fuel assemblies in the core of a nuclear reactor can cause the fuel assembly to deform in this direction under the influence of temperature gradients and other circumstances characteristic of a nuclear reactor (see B. A. Dementyev. Nuclear power reactors. M., Energoatomizdat, 1990, p. 151). Significant deviations from normal operating conditions lead to additional, sometimes very large dynamic loads, as a result of which individual elements of the internals can be destroyed and bundles of fuel elements can be deformed (see also p. 281). The deformation of the bundles of fuel elements can also extend to the guide channels, which can cause jamming of the control and protection rods in them (see patent RU 2124238, section 3) and lead to an emergency.

In the well-known active zone of a nuclear water-water power reactor containing a lower support grid, on which fuel assemblies are installed that form an active zone spaced apart from above by a perforated shell of the protective tube unit, where each of the fuel assemblies contains a head, a shank, a bundle of fuel elements placed in spacing grids tightened by rims, the “turnkey” size along the edges of which is less than the step of placing fuel assemblies in the lower support grid by an amount mounting gap (see B. A. Dementyev. Nuclear power reactors, 2nd edition. M., Energoatomizdat, 1990, p. 42, Fig. 2.11). The mounting gap between the fuel assemblies is 2 mm (see B.A. Dementiev, p. 31). Remote lattices of fuel assemblies installed in the active zone of a nuclear water-water power reactor have a repeated lack of concavity or curvature of the rim faces, which distorts the “turn-key” size with an unchanged size of faces adjacent to the corners of the rim. The gaps formed by the concavity of the rim faces, summing up and redistributing during bending of the fuel assemblies during operation, create the prerequisite for increased deflections of the fuel assemblies.

The formation of increased gaps between the fuel assemblies leads to a local increase in the amount of moderator (water), as a result of which the energy release in the nearest fuel elements of the fuel assemblies will increase above the values allowed under reliable cooling conditions.

As already mentioned above, an increased gap between the fuel assemblies can cause deformation of the fuel assembly in this direction and deformation of both bundles of fuel elements and guide channels with jammed control and protection rods in them is possible.

An object of the invention is to increase the reliability and safety of a nuclear pressurized water reactor by reducing the unevenness of energy release in the core, reducing the resistance forces during emergency entry of the protection and control rods and spacing the fuel assemblies in the core relative to each other.

This technical problem is solved in that in a fuel assembly comprising a head, a shank and a bundle of fuel elements located in the spacer grids tightened by the rims, according to the invention, on the spacer grids of the fuel assembly on each face at the points adjacent to the corners of the rim, profile with symmetrical rounding support ribs with a “turnkey” dimension along the profile ribs with symmetrical rounding support ribs equal to the total “turnkey” size along the edges of the rim th grating and the total height profile with two symmetrical arcuate bearing ribs, equal to half the mounting gap between fuel assemblies to be installed in nuclear VVER active zone defined by the formulas:

L_м.з.,2H =

L _m .,

K _p = K _g + 2H,

where K _g - the size of "turnkey" along the faces of the rim of the spacer grid,

L _M.Z. - the size of the mounting gap between the fuel assemblies in the active zone of a nuclear reactor,

To _p - the size of the "turnkey" profile with symmetrical curvature of the support ribs,

2H - the total height of two profile with symmetrical curves of the supporting ribs.

Other differences are: the implementation on the faces adjacent to the corners of the rims of the spacing grids profile with symmetrical curves of the support ribs, inclined at an angle to the horizontal axis α = 5-85 °, forming a projection “X” on the vertical plane when combining two faces of the rims of the adjacent spacing grids fuel assemblies in the core of a nuclear reactor; the implementation on the faces adjacent to the corners of the rims of the spacing grids profile with symmetrical curves of the support ribs in the form of alternating angles on each face with the solution up and down, forming a projection “XX” on a vertical plane when combining two faces of the rims of adjacent spacing grids of fuel assemblies in the active zone nuclear reactor.

Such a design of support ribs profile with symmetrical curvatures on faces adjacent to the corners of the rim of the spacer grid will improve the reliability and safety of the nuclear water-water power reactor by reducing the unevenness of energy release in the core, reducing the resistance forces during emergency entry of protection and control rods and due to the spacing of fuel assemblies in the core of a nuclear reactor while maintaining the channels of the coolant flow between the fuel and assemblies in the core of a nuclear reactor, the mounting gap between the fuel assemblies and the reduced mounting gap between the profile with symmetrical curvature support ribs of each face of the spacer grids of the fuel assemblies in the core of the nuclear reactor.

The drawings show a fuel assembly of a nuclear pressurized water reactor, where:

figure 1 - fuel assembly;

figure 2 is a longitudinal section of a reactor with fuel assemblies;

figure 3 is a cross section of fuel assemblies in the active zone;

figure 4 - projection “X” profile with symmetrical rounding of the support ribs when joining two faces of the rims of the spacing grids;

figure 5 is a projection of "XX" profile with symmetrical curvature of the supporting ribs when joining two faces of the rims of the spacing grids.

The active zone of a nuclear water-water power reactor includes a lower support grid 1, on which fuel assemblies 2 are mounted, forming an active zone 3, spaced apart from above by a perforated shell of the protective tube unit 4, where each of the fuel assemblies 2 contains a head 5, a shank 6, a bundle of fuel elements 7 installed in the spacer grids 8, tightened by the rims 9. The “turnkey” size along the faces of 10 rims 9 “K _g ” is less than the step L of the placement of fuel assemblies 2 in the lower support grid 1 by magnitude L _m.z. mounting clearance

K _g = LL _m.s.

On the spacer grids 8 of the fuel assemblies 2 on each face 10, in the places adjacent to the corners 11, support ribs 12 with a “turn-key” size along the support ribs 12 with profile with symmetrical curves are made at an angle of 5-85 ° to the horizontal axis “K _p ” equal to the total “turnkey” size along the faces 10 of the rim 9 of the spacer grill 8 “K _g ” and the total height of 2H - two profile support ribs 12 with symmetrical curvatures equal to half of the mounting gap _L.m. between fuel assemblies 2 installed in the core 3 of a nuclear pressurized water reactor.

L_м.з.,2H =

L _M.Z. ,

K _{p =} K _g + 2H.

Performed on the faces of 10 rims 9 spacing grids 8 profile with symmetrical rounding ribs 12 will allow you to distance the fuel assemblies over their entire height in the active zone of a nuclear reactor and to solve the technical task to improve the reliability and safety of a nuclear water-water power reactor by reducing the uneven energy in the active zone, reducing the resistance forces during emergency entry of the protection and control rods and due to the distance, the heat their assemblies over their entire height of the core of a nuclear reactor while maintaining coolant flow channels between the fuel assemblies in the core of a nuclear reactor.

The execution on the faces 10 adjacent to the corners 11 of the rims 9, profile with symmetrical rounding of the support ribs 12 in the form of angles 13 alternating on each face with the solution up and down, forming a projection “XX” on a vertical plane when two faces 10 of the adjacent rim 9 are aligned lattices 8 of fuel assemblies 2 in the core 3 of a nuclear reactor, will allow in the manufacture of spacer grids 8 to exclude the orientation of the rims 9 depending on the direction of the angles 13 of the support ribs 12, and when placing the fuel x assemblies 2 in the active zone 3 of a nuclear reactor reliably distance the fuel assemblies 2 relative to each other without their rotation and displacement.

The nuclear reactor includes control and protection rods 15 suspended from the drives 14, guides of the fuel assemblies 2 included in the channels 16, coolant inlet pipes 17 and coolant outlet pipes 18 from the nuclear reactor body 19.

The core of a nuclear reactor operates as follows. When the fuel assemblies 2 are installed on the lower support grid 1 in the core 3, the support ribs 12, formed with symmetrical curves, made at an angle of 5-85 ° to the horizontal axis, form a projection “X” on a vertical plane when two faces 10 rims 9 of the spacing grids are combined 8 fuel assemblies 2, and support ribs 12, profile with symmetrical curves, made in the form of angles 13, alternating on each face 10 adjacent to the corners 11 of the rim 9 with the solution angles up and down, form a projection onto the vertical the “XX” plane when combining two faces 10 of the rim 9 of the spacer grids 8 over the entire height of the fuel assemblies 2 and exclude the possible deflection of the fuel assemblies 2 before contact with adjacent fuel assemblies 2. In this case, the “turn-key” dimension is along the profile edges with symmetrical roundings 12

“K _p ” = K _g + 2H, where

L_м.з., а К_г=L-L_м.з., т.е.2H =

L _M.Z. , and K _g = LL _m.s. , i.e.

×2; Н=0,5, К_г=234 мм2H =

× 2; H = 0.5, K _g = 234 mm

K _p = 234 + 2 × 0.5; To _p = 235 mm.

The fuel assemblies 2 in the core 3 are spaced apart from above by a perforated shell with a protective tube block 4, and the fuel assemblies 2, containing a head 5, a shank 6, a bundle of fuel elements 7, are spaced apart by profile ribs 12 or supporting ribs in the form of angles thirteen.

The protection control rods 15 with actuators 14, which are included in the channels 16 of the guides of the fuel assemblies 2, are placed in the upper position and the coolant is supplied through the nozzles 17, and the coolant is discharged through the nozzles 18 from the housing 19.

A decision has been made to carry out support ribs with symmetrical curves on spacing grids of fuel assemblies and to use them in a nuclear reactor.

Claims (3)

1. The fuel assembly of a nuclear water-water power reactor, comprising a head, a shank, a bundle of fuel elements placed in the spacer grids tightened by rims, characterized in that on the spacer grids of the fuel assembly on each face in places adjacent to the corners of the rim are made profile with symmetrical roundings, support ribs with a turnkey size along profile support ribs with symmetrical roundings equal to the total turnkey size along the edges of the rim guide lattices and the total height profile with two symmetrical arcuate bearing ribs, equal to half the mounting gap between fuel assemblies to be installed in nuclear VVER active zone defined by the formulas:

K _p = K _g + 2H, where To _g - the size of the "turnkey" along the faces of the rim of the spacer grid; L _M.Z. - the size of the mounting gap between the fuel assemblies in the active zone of a nuclear reactor; To _p - the size of the "turnkey" profile with symmetrical rounding support ribs; 2H is the total height of two profile with symmetrical rounded supporting ribs. 2. The fuel assembly according to claim 1, characterized in that on the faces adjacent to the corners of the rims of the spacer grids, support ribs with profile with symmetrical curves are made with a slope at an angle α = 5-85 ° to the horizontal axis, forming a projection X on a vertical plane when combining two faces of the rims of adjacent spacer grids of fuel assemblies in the core of a nuclear reactor. 3. The fuel assembly according to claim 1, characterized in that on the faces adjacent to the corners of the rims of the spacing grids, profile ribs are made with symmetrical curvatures in the form of alternating angles on each face with the solution up and down, forming a projection XX on a vertical plane at combining two faces of the rims of adjacent spacer grids of fuel assemblies in the core of a nuclear reactor.

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