BG66073B1 - Fuel assembly for a nuclear reactor - Google Patents

Abstract

The assembly is used in nuclear engineering, In particular for the structure of the elements of its rigid framework. The fuel assembly consists of head and rear parts connected to each other by guiding channels arranged in cells of spacer grids. Said guiding channels are rigidly connected to at least the end spacer grids. The height (h) of the spacer grids and the wall thickness delta of the cells thereof are selected in such a way that the quantitative characteristics thereof correspond to the calculated and-experimentally determined conditions. As a result the rigidity of the assembly is improved at transversal and longitudinal bending to increase an angular rigidity the pair û cells of spacer grid. The own bending of the fuel assembly in the sectors between the spacer grids and the free bending of the fuel assembly in non-homogenous neutron and temperature fields is reduced due the decreased tendency of an E635 alloy to radiation growth.

Description

Technical field

The invention is applicable in nuclear engineering and relates to the construction of hydro-nuclear power reactor fuel cassettes, in particular of the BBZR-1000 type, and in particular to the design of rigid skeleton elements.

BACKGROUND OF THE INVENTION

A fuel cartridge is known for containing a bundle of heat dissipating elements housed in cells of the spacer grids [A. Kramer, A Problem of Constructed Nuclear Reactors, M., Atomizdat, 1971, p. 198, fig. 7.2.2]. The rigidity and strength of this fuel cartridge is achieved through a hexagonal sheath that connects the head and tail of the cartridge. However, the presence of a sheath causes parasitic neutron capture in the core, which increases the linear heat load on the heat sinks at the expense of a forced increase in the pitch between the fuel cartridges.

Also known is a nuclear reactor fuel cassette comprising a hexagonal bundle of heat sink elements located in cells along the cassette of the spacer grids. [A. Kramer, A question on the design of nuclear reactors, M., Atomizdat, 1971, p. 204, FIG. 7.1.116]. The head and tail are joined by guide channels that move the rods with neutron-absorbing material. There is no sheath in this fuel cartridge, which reduces the clearance between adjacent fuel cartridges. This reduces the linear loads of the heat dissipation elements and the irregularity of the energy dissipation.

The lack of the sheath reduces the parasitic capture of neutrons, as well as the material consumption. However, the use of these cartridges in the units of the WWRP-1000 reactors shows that after three years of operation there is a distortion of the guide ducts due to the mechanical loading on the head which is folded to prevent the fuel cartridge from escaping under the influence of the coolant flow. . In addition, during the operation of the reactor, thermomechanical loading of the cassette structure generally occurs due to deformation of the heat-dissipating elements. These deformations are transmitted through the spacer bars, which is why they are also deformed. The relaxation of the elastic tension in the spacer grids, which are obtained by the placement of the heat dissipation elements and the guide channels in the grids, plays a major role in the expansion of the distortions of the fuel cartridges.

A significant reduction in the flexural stiffness of the combustion cartridge fundamentally alters the nature of its behavior in the core during prolonged operation: bends occurring in the combustion cartridge of complex spatial shape and deviations of the cartridge axes from the original position to a value that reaches the limit allowed, take into account the geometric possibilities of cartridge packaging in the core area, taking into account structural mounting loops. In this situation, large loops may appear between the peripheral heat sink elements of the adjacent curved cartridges. This disturbs the heat-technical reliability of these heat-dissipating elements as it can cause eruptions in them during the energy-release process. It should also be noted that angular anisotropy of bending stiffness is observed in the hexagonal designs of the fuel cartridges, especially those used in units with reactors BBZP1000 (bending stiffness in the angle from angle to angle). equals the wall-to-wall bending stiffness), with the cartridge bending rigidity in the tangential direction (relative to the center of the core) being less than its radial bending stiffness. The great freedom of movement in the tangential direction mainly results in swirling in the cores and, consequently, in the maximum distortion of the fuel cartridges in working conditions. There are experimental data showing that distortions in fuel cartridges are in the order of 20 µm. Such significant distortions of the fuel cartridges break initially

66073 Blurred core geometry results in changes in energy release and thermal-hydraulic characteristics of the core.

To eliminate these negative factors in the combustion cartridge and to ensure its stable behavior, which means that the cartridge is not distorted in working conditions for 4-5 years, it is necessary to:

- to provide guaranteed bending rigidity values for longitudinal bending fuel cartridges by introducing longitudinal elements that do not displace relative to the spacer grilles during the service life;

- to ensure a greater value of the flexural bending rigidity of the transverse bending by reducing in working conditions the individual bending of the bars or other longitudinal elements in the sections between the spacers while increasing the rigidity of the rotation of the rods or longitudinal members in the cells of the spacer grids.

The aforementioned conditions are met by the closest in technical nature and the resultant nuclear reactor cassette comprising a head and a tail connected by guide channels placed in cage cells spaced apart from each other along the cassette [RU 2093906, G 21 C 3 / 30,20.10.97]. In the construction of the known fuel cassette, additional stiffeners are introduced - longitudinal pins that extend from the lower support grille to the upper spacer grille and are welded externally at six corners to each spacer grille. The rigid connection of the winkles with the spacer grilles provides a substantial increase in the stiffness of the fuel cartridge relative to the longitudinal bending, regardless of the relaxation of the elastic tightenings in the rod system of the fuel cartridge. The spatial shape of the winkles has a very high value of the intrinsic moments of inertia, which ensures sufficient rigidity of the structure in the transverse bending of the fuel cartridge. In addition, the inability of the winkles to rotate against the axis of the spacer grilles at the locations of their interconnections further helps to increase the rigidity of the fuel cartridge.

However, the known fuel cartridge has the following disadvantages:

- the metal intensity of the structure increases, which leads to deterioration of the neutron-physical characteristics of the core;

- the heat dissipation from the angular and peripheral heat dissipating elements deteriorates;

- the technology of the production of the combustion cartridge is complicated, as additional angular elements appear, the volume of welding and control activities increases;

- the possibilities for visual inspection during the construction and during inspection during the period of operation are reduced.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a fuel cassette of a low-energy-intensive nuclear reactor with increased stability during operation in extended-cycle fuel cycles without accumulating unacceptable bends.

In solving this problem, new technical results are obtained, which consist of the following: the stiffness of the combustion cartridge is increased in the case of transverse and longitudinal folds, the angular stiffness in the pairs "guide channel - cell of the spacer grate" is increased, its own bending is reduced of the fuel cartridge in the sections between the spacer grids and the free bending of the fuel cartridge in nonuniform neutron and temperature fields due to the reduced tendency of alloy 3635 to radiate growth.

These technical results are achieved by the fact that in the nuclear reactor combustion cassette (comprising a head and a tail connected by guide channels placed in the cells of the spacer grids, spaced apart from each other along the cassette, the guides channels are rigidly connected to at least the front spacers) the height h of the spacers and the thickness of the cell walls of the spacer cells are chosen such that their quantitative value and satisfy the condition:

66073 Bl

(h ϊ \ and ^with 'I _to 20 | / wn]) _< 0.25 [«m] _>

where:

fh ^f h ° \ 20 (t / i], \ 2fit] bB ₀ + B _{x 20} j _mm j ¹ - ^{5 +} ^ [20 (^] where:

h - height of spacer grille, mm;

delta - the thickness of the cells forming cells of the spacer grids, in mm, as for the 8 grids C _o = 39.17, A _o = 5.563, A1 = -3.482, A ₂ = 1.332, B _o = 2.245, B1 - -4.500 , В ₂ = 6.072, В ₃ = -3.128, В ₄ = -0.620, for the 9 lattices С _о = 22.74, А _о = 4.988, Al - -2.985, А ₂ = 1.119, В _о = 2.225, В, = -4.005, В ₂ = 5.145, В ₃ = 2.595, В ₄ = -1.113, for the 10 lattices С _о - 13.06, А _о = 4.481, А, = -2.568, А ₂ = 0.932, В _о = 2.203 , B, = -3.568, B ₂ = 4.324, B ₃ = -2.127, B ₄ = -1.510, for the 11 lattices C _o = 8.84, A _o = 4.138, A] = -2.281, A ₂ = 0.811, At _D = 2.170, C ₍₌ -3.250, B ₂ = 3.752, C ₃ = -1.814, B _{4 to -1675,} the 12 lattices C _o = 6.90, and _o - 3.895, a] = -2.088, and ₂ = 0.732, Βθ = 2.126, B, = -3.042, B ₂ = 3.400, B ₃ = -1.623, B ₄ = -1.695, for the 13 lattices C _o = 5.73, A _o = 3.697, A] = -1.937, A ₂ - 0.667, B _o = 2.068, B] = -2.910, B ₂ = 3.199, B ₃ = -1.505, B ₄ = -1.651, for the 14 lattices C _o = 4.70, Αθ = 3.526, A] = -1.813, A ₂ = 0.614, Βθ = 2.003, B, = -2.815, B ₂ - 3.062, B ₃ = -1.422, B ₄ = -1.575, for the 15 lattices C _o = 3.78, A _o = 3.356, A! = -1.684, A ₂ = 0.560, Βθ = 1.940, B! = -2.722, B ₂ = 2.928, B ₃ = -1.336, B = -1.490.

A distinctive feature of the present invention is the rigid connection of the guide channels with at least the front ones, but preferably with all spacer bars, which precludes the sliding of the guide channels towards the cells of these bars. In this case, the total bending stiffness of the combustion cartridge upon irradiation is increased as ^{+ +>>} (b ( ¹ - ⁵ ) ^{+ b,} ( ^b ^ ^_1 4 ') is the constant component in the bending stiffness of the cartridge, which, component, is equal to the stiffness of the coupled guide duct structure, where the heat dissipation elements may cease to play the role of a coupled multipart system and, when slid into the cells of the spacer gratings, may contribute to the overall bending rigidity of the cartridge. connected multi-beam , and as a plurality of independent rods, which is much smaller in magnitude.Improve the stiffness of the fuel cartridge as a whole and ensure the stability of the fuel cartridge so that the grooves formed between the cartridges do not exceed the value limit is possible. from the point of view of achieving the permissible energy intensity of the heat dissipating elements and the thermotechnical reliability of the core, can only be fulfilled if the condition is fulfilled:

h D (S r

In addition, the aforementioned design-experimental expression relates the amount of spacer grids to their characteristic parameters, in which the stresses occurring in the spacer grids and caused by the axial forces appearing at bending at the fixing points of the guiding channels do not exceed the permissible values.

It is recommended that the guide ducts be made of alloy 3635 and the spacer bars are made of alloy 3110 or preferably 5

66073 Bl reading - from alloy 3635.

Guide channels can be

Exemplary embodiment and operation of the invention firmly coupled to at least the front spacer grilles directly or by means of intermediate sleeves arranged in the respective cells of the spacer grilles. It is preferable to connect the guide channels with the distance grilles symmetrically with respect to the longitudinal axis of the guide channel on the two front parts of the distance grilles with a distance of not more than 0.15 h from the front of the distance grille.

The rigid connection of the guide ducts with at least the front spacer bars may be made by spot welding.

It is most rational to use 18 guide channels 12 to 14 mm in diameter.

Explanation of the annexed figures

Best preferred embodiment of the invention

The nuclear reactor fuel cassette consists of a head 1 and a tail 2 connected by guide ducts 3. The guide ducts 3 are located in cells 4 of the spacer lattice 5 located at a certain distance from each other along the cartridge. Typically, the guide ducts, which are 18 in number, pass through the cells symmetrically arranged around the central duct 15 ⁶ - In other cells of the spacer grilles 5 are located the heat dissipation elements 7. The spacer grilles 5 together with the guide ducts 3 form a rigid structure of the fuel cassette. as guides in more detail the invention is illustrated in the 20 appended figures, where:

Figure 1 is a general view of a fuel cartridge;

FIG. 2 is an embodiment of node A of FIG. 1 in section; 25 is a second embodiment of node A of FIG. 1 in section.

the conduit 3 is firmly connected to the front spacer grilles or, preferably, to all spacer grilles

5. The height h of the spacer grids and the thickness 5 of the cell walls of the spacer grids shall be chosen so that their numerical values meet the condition:

Λ Ί * Ί l <20 (mm) J ^ 0.25 [tt] _?

where:

B ~ wc + b _}

ί h -1.5 + Λ ^f h -1.5 ₄ 20 (mm) 20 (mm) J ί ^h -1.5 + B _d ί *, -1.5 ^ 20 [mm] ^ 20 [mm] J

h - height of the spacer grille, mm;

delta - the thickness of the elements forming the cells of the spacer grid, as for the 8 grids C _o = 39.17, A _o = 5.563, A! = 3.482, А ₂ = 1.332, В _о = 2.245, В, = -4.500, В ₂ = 6.072, В ₃ = -3.128, В ₄ = -0.620, for the 9 lattices С _о = 22.74, А _о = 4.988 , А, = -2.985, А, = 1.119, В _о = 2.225, В, = -4.005, В ₂ = 5.145, В ₃ - -2.595, В ₄ = -1.113, for the 10 lattices С _о = 13.06, A _o = 4.481, A, = -2.568, A ₂ = 0.932, B _o = 2.203, V, - -3.568, ₅ θ

B ₂ = 4.324, B ₃ = -2.127, B ₄ = -1.510, for the 11 lattices С _о = 8.84, А _о - 4.138, Aj = -2.281, А ₂ = 0.811, В _о = 2.170, Bj = - 3.250, B ₂ = 3.752, B ₃ = 1.814, B ₄ = -1.675, for the 12 lattices С _о = 6.90, А _о = 3.895, А, = -2.088, А ₂ = 0.732, В _о = 2.126, В , = -3.042, В ₂ = 3.400, В ₃ = -1.623, В ₄ = -1.695, for the 13 lattices С _о = 5.73, А _о = 3.697, А! = 1.937, A ₂ = 0.667, B _o = 2.068, Bj = -2.910, B ₂ = 3.199, B ₃ = -1.505, B ₄ = -1.651, for the 14 lattices C _o = 4.70, A _o = 3.526, Aj = -1.813, A ₂ = 0.614, B _o = 2.003, B ₁ = -2.815, B ₂ = 3.062, B ₃ = -1.422, B ₄

66073 Bl = -1.575, for the 15 lattices С _о = 3.78, А _о = 3.356, А, = -1.684, А ₂ = 0.560, Βθ = 1.940, В, = -2.722, В ₂ = 2.928, В ₃ = -1.336, B ₄ = -1.490.

The cell shape can be accomplished in any known manner. The spacer grilles 5 and the guide channels 3 are preferably made of zirconium alloy 3635; alloys 3636 and 3110 can be combined: NK of alloy 3635 and DR of alloy 3110.

The guide channels 3 are rigidly connected to the spacers by means of the intermediate bushings 8, which are housed in the respective cells of the spacer grids. The rigid joint 9 of the guide channels with the spacer grilles is made with 15-point welding, for example, with electrocontact welding. The rigid connection of the guide ducts with the spacer grilles is symmetrically symmetrical with respect to the longitudinal axis of the spacer channel by the two front 20 parts of the spacer grate at a distance of not more than 0.15 h from the spacer grille front. In this situation, the bending strength of the guide ducts is significantly increased. 25

Industrial applicability

The combustion cassette can be manufactured in industrial conditions, and this is best done in hydropower nuclear reactors, especially type BBZR-1000, when designing the elements of the rigidly coupled skeleton of the cassette.

The combustion cartridge can be manufactured using any equipment designed for these purposes and it is not necessary to develop new machines and accessories in principle.

Claims (9)

Claims A nuclear reactor fuel cassette having a head (1) and a tail (2) connected by guide channels (3) which are located in cells (4) of spacers (5), spaced a certain distance apart on the other, characterized in that the guide channels (3) are firmly connected to at least the front spacer grilles, and the height h of the spacer grilles (5) and the thickness of the cell walls (4) of the spacer grilles are selected such that their numerical values meet the condition: r ^h Ί -o / 20 (m / n), hours δ 0.25 [mm] <1.0, where: _a = J + d [—— 1.5 ^ + 4 (: ^ -; -! ⁵ \ 20 (mm]) \ 20 [m7i] J & = c ₀ + d [—— \ 20 (ot] —1.5 + .¾ -1.5 ^f h _k 20 (mm) -1.5 + ό ₄ -------- 1.2; 0.25 (mm] J 'where: h - height of the spacer grille, mm; delta - thickness of the elements that form the cell of the spacer grid, mm, as for the 8 grids C _o = 39.17, A _o = 5.563, A, = -3.482, A ₂ = 1.332, Βθ = 2.245, B! = -4.500, B ₂ = 6.072, B ₃ = -3.128, B ₄ = -0.620, for the 9 grids C _o = 22.74, A _o = 4.988, A, = -2.985, A ₂ = 1.I9. At _D = 2.225, B = -4.005, B ₂ = 5.145, C ₃ = 2.595, B = -1.113 ₄ to 10 bars _Co = 13.06, a = _o 4481, a] = -2.568, _A2 = 0.932, Βθ = 2.203, B, = -3.568, B ₂ = 4.324, B ₃ = -2.127, B ₄ = -1.510, for the 11 lattices C _o = 8.84, Αθ = 4.138, Aj = -2.281, A ₂ = 0.811, Βθ = 2.170, B] = -3.250, B ₂ = 3.752, B ₃ = -1.814, B ₄ = -1.675, for the 12 lattices С _о = 6.90, 66073 Bl A _o = 3.895, A, = -2.088, A ₂ = 0.732, B _o = 2.126, B, = -3.042, B ₂ = 3.400, B ₃ = -1.623, B ₄ = -1.695, for the 13 lattices C _o = 5.73, A _o = 3.697, Aj = -1.937, A ₂ = 0.667, B _o = 2.068, B _] = -2.910, B ₂ = 3.199, B ₃ = -1.505, B ₄ = -1.651, for 14- those lattices C _o = 4.70, A _o = 3.526, A ₁ = -1.813, A ₂ = 0.614, B _o = 2.003, B, = -2.815, B ₂ = 3.062, B ₃ = -1.422, B ₄ = -1.575 , for the 15 lattices C _o = 3.78, A _o = 3.356, A] = -1.684, A ₂ = 0.560, B _o = 1.940, Bj = -2.722, B ₂ = 2.928, B ₃ = -1.336, B ₄ = -1,490. A fuel cartridge according to claim 1, characterized in that the guide channels (3) are made of alloy 3635. Fuel cartridge according to claim 1, characterized in that the spacer grilles (5) are made of alloy 3635 or alloy 3110. Fuel cartridge according to claim 1, characterized in that the guide channels (3) are firmly connected to at least the front spacer grilles (5) by means of intermediate bushings (8) housed in the respective cells (4) of the spacer grilles. 5. A fuel cartridge according to claim 1, characterized in that the rigid connection (9) of the guide ducts (3) to the spacer grilles (5) is arranged symmetrically with respect to the longitudinal axis of the spacer channel by the two ends of the spacer grille. Fuel cartridge according to claim 1, characterized in that the rigid connection (9) of the guide channels (3) to the spacer grilles (5) is positioned on the front side of the spacer grate at a distance of not more than 0.15 hours. Fuel cartridge according to claim 1, characterized in that the rigid connection (9) of the guide channels (3) to the spacer bars (5) is made by spot welding. A fuel cartridge according to claim 1, characterized in that the number of guide channels (3) is 18. Fuel cartridge according to any one of the preceding claims, characterized in that the diameter of the guide ducts (3) is selected in the range of 12 to 14 mm.