A high reliability fuel assembly with coordinated flow control

Abstract

The present invention relates to the field of nuclear fuel technology, and specifically discloses a high-reliability fuel assembly with coordinated flow control, including a lower tube seat, a skeleton, an upper tube seat, and fuel rods, guide tubes, and instrument tubes inserted into the skeleton, which are sequentially arranged along the flow direction of the coolant; the lower tube seat is a low-outlet lateral flow lower tube seat; on the lower tube seat connecting plate, there are a number of space-through slender flow channels with a width less than the fuel rod spacing and axial bending; the outlets of the surrounding flow channel areas of the space-through slender flow channels located on the outer periphery of the lower tube seat connecting plate are higher than the outlets of the middle flow channel areas located in the middle of the lower tube seat connecting plate, so as to reduce the lateral flow of the outlets between assemblies. The present invention carries out a coordinated and innovative design of the fuel assembly as a whole, and ensures a high thermal safety margin of the fuel assembly.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear fuels, and in particular relates to a coordinated flow-controlled high-reliability fuel assembly. Background Art

[0002] Fuel assemblies are the core components of nuclear power plants. They operate in a harsh water chemical environment with high temperature, high pressure, high flow rate and strong radiation. Their performance directly affects the economy, safety and reliability of nuclear power plants. The core indicators of safety include the breakage rate and thermal safety margin of nuclear fuel assemblies, which are closely related to the flow field in nuclear fuel assemblies. High safety is the goal that nuclear fuel innovation design continues to pursue.

[0003] Regarding nuclear fuel failure, according to the IAEA report "Review of Fuel Failures in WaterCooled Reactors", grid-to-rod fretting has long been the number one factor leading to fuel rod failure, and it mainly occurs in the first grid area. The main reason is that there is a large lateral flow at the entrance of the fuel rod bundle, which causes a large vibration at the lower end of the fuel rod.

[0004] Regarding the thermal safety margin of nuclear fuel assemblies, the critical heat flux is its core technical indicator, which means that when the local power density of the fuel assembly is higher than the critical heat flux, the local temperature of the nuclear fuel assembly will rise sharply, resulting in local burnout failure and radioactive substances breaking through the first safety barrier. According to existing research, the critical heat flux is closely related to the flow field of the fuel rod accessories, and is strongly affected by the positioning grid structure design, rod bundle irradiation deformation, etc. It is also closely related to the monitoring feedback of the temperature field and flow field in the core.

[0005] In addition, according to the operating experience of nuclear power plants, if the lateral flow at the outlet of the nuclear fuel assembly is large, it is easy to cause wear of the control rod cladding and the fuel assembly guide tube in the control rod assembly.

[0006] The above phenomena are all related to the flow field design of the fuel assembly. The upstream flow field has a significant impact on the downstream flow field, and its impact area is closely related to the hydraulic diameter. Therefore, it is urgent to propose a new design of the fuel assembly structure based on the overall flow field control of the fuel assembly to improve the thermal safety performance of the fuel assembly. Summary of the invention

[0007] The present invention aims to provide a high-reliability fuel assembly with coordinated flow control, with the goal of reducing the lateral flow at the inlet and outlet of the fuel rod bundle and enhancing the coolant mixing in the near-wall area of ​​the fuel rod and improving the critical heat flux density. The fuel assembly with the lower tube seat, upper tube seat, grid and fuel rod as the core is collaboratively and innovatively designed as a whole to achieve overall coordination of the flow field of the fuel assembly.

[0008] The technical solution of the present invention is as follows:

[0009] A coordinated flow control high reliability fuel assembly, wherein a lower tube seat, a frame, an upper tube seat, and a fuel rod, a guide tube, and an instrument tube inserted into the frame are sequentially arranged along the coolant flow direction;

[0010] The lower tube seat is a low-outlet lateral flow lower tube seat; on the lower tube seat connecting plate, there are provided a plurality of space-through slender flow channels with a width less than the fuel rod spacing and axial curvature; the outlets of the space-through slender flow channels in the surrounding flow channel areas located on the periphery of the lower tube seat connecting plate are higher than the outlets of the middle flow channel areas located in the middle of the lower tube seat connecting plate, so as to reduce the lateral flow at the outlets between components.

[0011] An inlet chamfer is processed at the inlet end of the elongated flow channel that passes through the space to reduce flow resistance.

[0012] The upper tube seat is a low-outlet transverse flow upper tube seat, which is composed of an upper tube seat connecting plate, an upper tube seat enclosure fixed on the edge of the upper tube seat connecting plate, and an upper tube seat frame plate fixed on the upper tube seat enclosure plate; the upper tube seat enclosure plate is provided to reduce the transverse flow between the upper tube seats, and the frame plate through holes are opened on the upper tube seat frame plate to reduce the flow resistance.

[0013] An upper tube seat water flow hole group is processed on the upper tube seat connecting plate, and the upper tube seat water flow hole group is distributed in a central rotational symmetry and an axisymmetric manner on the upper tube seat connecting plate, with densely arranged curved through holes in the middle and parallel arranged straight holes around, and chamfers are provided on the upper and lower parts of the holes; upper tube seat connecting holes are opened at corresponding positions of the upper tube seat connecting plate, the guide tube and the instrument tube, and the upper tube seat water flow holes near the upper tube seat connecting hole are distributed in a rotational symmetry and an axisymmetric manner with the upper tube seat connecting hole as the center.

[0014] The upper tube seat is equipped with a variable stiffness low relaxation plate spring clamping system to reduce the clamping load during the operation of the fuel assembly.

[0015] The skeleton comprises a structural mixing grid, the guide wings of which are arranged on the inner strips and the outer strips and smoothly bent toward the inner side of the fuel rod grid element; the inner strip guide wings are projected to cover the grid element corners, and the projected edges are in the shape of an arc concentric with the fuel rods, thereby guiding the coolant at the grid element corners to flow around the fuel rods to achieve strong diversion.

[0016] The skeleton also includes a pure structural grid and a pure mixing grid; wherein the pure structural grid is arranged at both ends of the turbulent flow field of the fuel rod, only positions the fuel rod, has no flow guidance function, and is not provided with flow guidance wings; the pure mixing grid is arranged between the structural mixing grids with insufficient flow guidance function, plays a role in enhancing the flow guidance, and does not position the fuel rod.

[0017] The guide wings of the structural mixing grid and the pure mixing grid have a radius of 2-10 mm bent toward the inner side of the fuel rod grid element; multiple openings are provided on the inner strips and outer strips of the structural mixing grid, which are inner strip flow holes and outer strip flow holes, respectively, to enhance the lateral flow in different grid elements.

[0018] At least one structural mixing grid is arranged in the high power area; if two or more structural mixing grids are arranged, the distance between two adjacent structural mixing grids is 200~700mm, and 1~2 pure mixing grids can be added in between.

[0019] The fuel rod is a low-irradiation deformation fuel rod, which is composed of a zirconium alloy cladding with creep resistance and low-irradiation growth characteristics, a fuel core block, and an end plug, which is filled with an inert gas; the pressure of the inert gas is balanced and iteratively designed according to the external pressure of the fuel rod, the gas storage volume, the creep characteristics of the cladding and the fuel rod burnup, and the maximum value is selected under the condition that the hot internal pressure of the fuel rod does not exceed the external pressure.

[0020] The active section of the fuel rod is composed of: uranium dioxide pellets, plutonium dioxide pellets or uranium-plutonium mixed oxide pellets, or pellets containing gadolinium or boron or erbium or dysprosium, or a combination of the above pellets; or other compounds of uranium, plutonium, thorium and other fissile nuclides, or compounds or mixtures containing gadolinium or boron or erbium or dysprosium and other neutron poison nuclides, or a combination of the above compounds or mixtures;

[0021] Among them, the isotopes of fissile nuclides account for 1~10%; the mass content of compounds or mixtures of neutron poison nuclides is 0~12%.

[0022] The average grain size of the pellets in the active section of the fuel rod is greater than 30 μm.

[0023] The fuel rod also includes a fuel positioning structure, which is a spiral spring, a radial spring or other elastic structure for compensating for the thermal expansion difference of the active section.

[0024] The material of the cladding is a zirconium-tin-niobium series zirconium alloy, and the weight percentage is: Sn: 0.50%-1.20%, Nd: 0.60%-1.25%, Fe: 0.05%-0.55%, and the balance is Zr and impurities.

[0025] The surface of the zirconium-tin-niobium series zirconium alloy is tightly covered with a corrosion-resistant and high-temperature resistant chromium coating.

[0026] The guide tube is a zirconium alloy tube with a constant outer diameter and an inner neck; or a "tube in tube" combination consisting of an outer tube with a constant wall thickness and an inner tube with a constant wall thickness sleeved on its inner lower part, with a rod drop overflow hole opened on the outer tube near the upper end of the inner tube.

[0027] The guide tube is made of creep-resistant, low-growth zirconium-tin-niobium zirconium alloy, and the outer tube wall thickness is ≥0.55 mm. When a batch of guide tubes are assembled on the same fuel assembly, the diameter and wall thickness of the batch of guide tubes are different due to processing tolerances, and the guide tubes with larger diameters and wall thicknesses are arranged on the periphery of the fuel assembly.

[0028] The space-through slender flow channel is symmetrical on the left and right sides and has opposite bending directions, and an outlet straight flow section with a length of ≥3mm is provided at the outlet end.

[0029] The instrument tube is a temperature-measurable instrument tube, which is arranged on a 12-foot fuel assembly running at 5m / s. 22 small holes with a diameter of 3mm are opened on the instrument tube at a height of 3 to 4m from the lower surface of the active section of the fuel rod; the temperature measuring instrument or other core measuring instruments are inserted from the upper part of the instrument tube.

[0030] The remarkable effects of the present invention are:

[0031] (1) The present invention achieves a high thermal safety margin for fuel assemblies. The whole flow field of the fuel assembly is coordinated and controlled by using the inlet tube seat to guide the flow uniformity, the middle grid to stir and control the flow, and the outlet tube seat to reduce pressure and guide the flow, so that the coolant is evenly distributed and the "low-temperature" coolant at the corner of the grid element is guided to flow around the "high-temperature" fuel rod, which significantly improves the mixing degree of the cold and hot coolants and reduces the local hot spot temperature. Compared with the domestic fuel assemblies currently in service, the coolant mixing effect is improved by 25%. The test data obtained based on the critical heat flux density test of the fuel assembly proves that its average heat flux density is increased by about 5%. The guide fins of the outer strips of the grid are matched in height and the bent ends are buried in the gap between the fuel rods without protruding from the outer surface of the grid. The inner strip ends support the welded guide fins, which improves the mixing uniformity between the fuel assemblies and ensures that no hooking occurs in the test of the lateral 500N extrusion force, eliminating the interference phenomenon of the unloading grid hooking, and the structure is stable.

[0032] (2) The lower tube seat structure of the present invention does not generate obvious lateral flow. Compared with the prior art, the average lateral flow velocity is reduced by 5%. At the same time, the comprehensive filtration efficiency exceeds 87%, and the foreign matter capture efficiency reaches 32%. Compared with the domestic fuel assemblies currently in service, the probability of foreign matter abrasion, which accounts for the highest proportion of fuel rod damage, can be reduced by more than 40%, and the effect of preventing foreign matter capture is good.

[0033] (3) The present invention realizes the thermal safety monitoring feedback of the fuel assembly. By setting up a temperature-measurable instrument tube, a temperature sensor can be placed in it to continuously measure the temperature of the coolant (the coolant has been mixed evenly by the strong guide grid) entering the instrument tube from the radially evenly distributed water holes online in real time, so as to know the actual thermal safety margin of the fuel assembly, and provide feedback to the operation to guide the optimization of the operation strategy.

[0034] (4) The present invention achieves the maintenance of safety margin under strong load of fuel assembly. High-strength zirconium-tin-niobium zirconium alloy is used as cladding material and guide tube material, combined with "tube-in-tube" guide tube, welded guide fins for the end support of strips in the grid, high-rigidity tube seat and other structural reinforcement measures. Through the mechanical test of fuel assembly, it is proved that its pressure-bending stiffness (pressure-bearing state throughout the life of the reactor) is 25% higher than that of domestic fuel assemblies in service, meeting the seismic resistance requirements of 0.3g extreme ground motion, and achieving no reduction in safety margin after strong loads such as earthquakes.

[0035] (5) The present invention achieves the maintenance of safety margin under high fuel consumption. The creep-resistant and low-growth zirconium-tin-niobium zirconium alloy is used as the cladding material and guide tube material, combined with large-grain fuel, "tube-in-tube" guide tube, variable stiffness leaf spring clamping system, low pressure drop grid and tube seat and other structural load reduction and enhancement measures, so as to achieve low irradiation growth, small creep deformation, small bending deformation, strong containment capacity, safe and reliable geometric structure, and no reduction in safety margin under high fuel consumption of fuel assembly.

[0036] (6) The present invention achieves high safety under accident conditions of fuel assemblies. The creep-resistant zirconium-tin-niobium zirconium alloy is used as the cladding material, which improves the structural stability of the fuel rods under accident conditions, thereby maintaining the stability of the coolant flow channel, ensuring the rapid removal of residual heat, and improving the ability to cope with accident conditions. Tightly covering the surface of the creep-resistant zirconium-tin-niobium zirconium alloy with a corrosion-resistant and high-temperature coating reduces the corrosion rate of the cladding, reduces the temperature of the cladding and fuel pellets compared to before the coating, improves the safety margin under accident conditions, and can delay the zirconium-water reaction, with good accident resistance.

[0037] (7) The present invention achieves high economic efficiency of fuel assemblies and nuclear power plants. The fuel rod burnup designed according to the present invention can reach 62GWd / tU, the refueling cycle can reach 18-24 months, and the fuel rod design control breakage rate is less than 10 -6 It has the characteristics of high fuel consumption, long refueling cycle and low breakage rate. It can reduce the number of fuel assemblies and the number of refueling times, improve the availability of nuclear power plants, and bring excellent economic benefits to nuclear power plants.

[0038] (8) The present invention realizes high-quality batch manufacturing of fuel assemblies. The unique fuel assembly process and mechanical batch manufacturing method, such as the guide tube "expansion welding combination method", the space slender flow channel forming method, the skeleton three-layer welding method, the low-friction rod drawing method and the guide tube reverse drawing method, are adopted to ensure the high fuel consumption, high safety and high reliability of the fuel assembly of the present invention, and improve the stability of product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the structure of the fuel assembly of the present invention;

[0040] Figure 2 This is a schematic diagram of the fuel rod structure of the present invention;

[0041] Figure 3 This is a schematic diagram of the fuel assembly skeleton structure of the present invention;

[0042] Figure 4 This is a schematic diagram of the overall structure of the structural mixing grid of the present invention;

[0043] Figure 5 It is a schematic diagram of the spring structure of the present invention;

[0044] Figure 6 A schematic diagram of the inner strip flow holes of the structural mixing grid of the present invention;

[0045] Figure 7 It is a schematic projection diagram of the inner strip guide wing of the structural mixing grid of the present invention;

[0046] Figure 8 This is a schematic diagram of the outer strip structure of the structural mixing grid of the present invention;

[0047] Fig. 9 It is a schematic diagram of the inner strip structure of the structural mixing grid of the present invention;

[0048] Fig.10 It is a partial schematic diagram of the assembly of the inner and outer strips of the structural mixing grid of the present invention;

[0049] Fig.11 This is a schematic diagram of the structure of the instrument tube of the present invention;

[0050] Fig.12 This is a schematic diagram of the structure of the lower tube seat of the present invention;

[0051] Fig.13 This is a schematic diagram of the slender flow passage that passes through the space of the lower tube seat of the present invention;

[0052] Fig.14 This is a schematic diagram of the guide tube structure of the present invention;

[0053] Fig.15 It is a schematic diagram of the overall structure of the upper tube seat of the present invention;

[0054] Fig.16 It is a schematic diagram of the structure of the upper tube seat connecting plate and the frame plate of the present invention.

[0055] In the figure, 1. fuel rod; 2. structural mixing grid; 3. guide tube; 4. instrument tube; 5. lower tube seat; 6. upper tube seat; 7. pure structural grid; 8. pure mixing grid; 101. cladding; 102. end plug; 103. fuel pellet; 104. fuel positioning structure; 201. inner strip; 202. outer strip; 2011. inner strip guide wing; 2012. inner strip spring; 2013. inner strip rigid convex; 2014. support structure; 2015. inner strip guide wing projection surface; 2016. inner strip flow hole; 2021. outer strip short guide wing; 2022. outer strip high guide wing; 2023. outer strip rigid convex; 2024. outer strip flow hole; 301: Outer tube; 302: inner tube; 401: coolant exchange hole of instrument tube; 402: instrument cooling hole; 403: throttling hole of instrument tube; 501: lower tube seat connecting plate; 502: lower tube seat support leg; 503: lower tube seat enclosure; 504: lower tube seat connecting hole; 505: space through slender flow channel; 5011: rib; 5012: blade; 5051: outlet straight section; 5052: inlet chamfer; 5053: surrounding flow channel; 5054: middle flow channel; 601: upper tube seat connecting plate; 602: upper tube seat enclosure; 603: upper tube seat frame plate; 604: clamping system; 6011: upper tube seat connecting hole; 6012: upper tube seat water flow hole group; 6031: frame plate through hole. DETAILED DESCRIPTION

[0056] Hereinafter, the term "include" or "may include" used in various embodiments of the present invention indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present invention, the terms "include", "have" and their cognates are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the presence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0057] In various embodiments of the present invention, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the words listed at the same time. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0058] The expressions (such as "first", "second", etc.) used in various embodiments of the present invention may modify the various constituent elements in various embodiments, but may not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing an element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of various embodiments of the present invention, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0059] It should be noted that if it is described that one component element is “connected” to another component element, the first component element may be directly connected to the second component element, and a third component element may be “connected” between the first component element and the second component element. Conversely, when one component element is “directly connected” to another component element, it can be understood that there is no third component element between the first component element and the second component element.

[0060] The terms used in various embodiments of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present invention. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used herein (including technical terms and scientific terms) have the same meaning as the meaning generally understood by those of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as the terms defined in the dictionary generally used) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in various embodiments of the present invention.

[0061] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. Example 1

[0062] like Figure 1 As shown, this embodiment discloses a coordinated flow control high reliability fuel assembly, which is obtained by loading fuel rods 1 into a skeleton.

[0063] like Figure 2 As shown, the fuel rod 1 is formed by a zirconium alloy cladding 101 and an end plug 102 having creep resistance and low irradiation growth characteristics, in which an active section of fuel containing fissile nuclides, a fuel positioning structure 104 and a heat-conducting gas of appropriate pressure are sealed and welded, so that the structure of the fuel rod 1 is stable during irradiation and the safety margin is not significantly reduced.

[0064] like Figure 3 As shown, the framework is composed of a guide tube 3 and an instrument tube 4 which are sequentially connected from bottom to top to a lower tube seat 5, a plurality of structural mixing grids 2 and an upper tube seat 6, and the distance between two adjacent structural mixing grids 2 is 200-700 mm.

[0065] like Figure 4 , 5 As shown, the structural mixing grid 2 is composed of inner strips 201 with springs 2012 and / or rigid convexities 2013 which are inserted into each other and then surrounded by outer strips 202 with springs and / or outer strip rigid convexities 2023; the grid element formed by the intervals between the inner strips 201 and the outer strips 202 is used to place the fuel rods 1, the guide tubes 3 or the instrument tubes 4, and the guide wings which are smoothly bent into the grid element are arranged at the coolant outflow end of the strip fuel rod grid element position to guide the coolant mixing flow to reduce the hot spot temperature and thus improve the safety.

[0066] The guide tube 3 is a zirconium alloy tube with a constant outer diameter and an inner neck, or a "tube in tube" assembly consisting of a straight tube of constant wall thickness sleeved on the lower inner side of another straight tube of constant wall thickness, so as to achieve rapid control rod drop and hydraulic buffering at the end of the stroke to reduce the impact load and ensure rod drop safety.

[0067] like Fig.11 As shown, the instrument tube 4 is a temperature-measurable instrument tube, which is connected to the lower tube seat 5, several structural mixing grids 2 and the upper tube seat 6 from bottom to top. In addition to the conventional instrument cooling holes 402 and the instrument tube throttle holes 403, the instrument tube coolant exchange holes 401 are opened at the hot section position of the instrument tube 4 corresponding to the higher heating power of the fuel assembly, so that the coolant at the hot section position enters the instrument tube 4 to achieve the temperature measurement of the fuel assembly and track the operating safety margin of the fuel assembly. The instrument tube 4 is arranged to run on a 12-foot fuel assembly at 5m / s. 22 small holes with a diameter of 3mm are opened on the instrument tube 4 at a height of 3~4m from the lower surface of the active section of the fuel rod 1; the temperature measuring instrument or other core measuring instruments are inserted from the upper part of the instrument tube 4.

[0068] like Fig.12 As shown, the lower tube seat 5 includes a lower tube seat connecting plate 501, a lower tube seat support leg 502 and a lower tube seat enclosure 503, and a guide surface is arranged on the inner side of the lower tube seat support leg 502; the lower tube seat connecting plate 501 is provided with a lower tube seat connecting hole 504 corresponding to the position of the guide tube 3 and / or the instrument tube 4, and a plurality of multi-layer transverse discontinuous structures with a width smaller than the fuel rod spacing are arranged between the lower tube seat connecting holes 504, and an axially curved space-through slender flow channel 505 is formed through cross-layer connection, which has the function of evenly distributing the flow rate, and can block and capture foreign matter in the coolant flowing through, avoid abrasion and damage caused by foreign matter and reduction of safety margin, and improve the safety and reliability of the fuel assembly. Example 2

[0069] This embodiment further optimizes the space-through slender flow channel 505 of the lower tube base 5. The space-through slender flow channel 505 is formed by orthogonally clamping multiple groups of parallel ribs 5011 and multiple groups of parallel blades 5012. On the blades 5012, a convex structure with the same direction is provided in the middle position of the two rows of fuel rods 1. The convex structure makes the flow channel bend along the axial direction to change into a spatial curved surface structure, which plays a role in blocking and capturing foreign matter in the coolant flowing through, which can avoid abrasion damage or reduction of safety margin caused by foreign matter, and improve the safety and reliability of the fuel assembly.

[0070] Preferably, the blade 5012 has a thickness of 0.1-2 mm, a height of 5-20 mm, a raised structure radius of 2-10 mm, and a spacing of 1-5 mm.

[0071] like Fig.13 As shown, the space-through slender flow channel 505 is symmetrical on the left and right sides and has opposite bending directions. An outlet straight section 5051 is provided at the outlet end. The length of the outlet straight section 5051 is ≥3mm to reduce the lateral flow at the outlet of the lower pipe seat. An inlet chamfer 5052 is processed at the inlet end of the space-through slender flow channel 505 to reduce flow resistance.

[0072] The outlet of the surrounding flow channel 5053 area of ​​the space-through elongated flow channel 505 located at the periphery of the lower tube seat connecting plate 501 is higher than the outlet of the middle flow channel 5054 area located in the middle of the lower tube seat connecting plate 501, and the height difference is ≥1mm, so as to reduce the lateral flow at the outlet between the lower tube seats of the assembly. According to the CFD numerical analysis results, compared with the existing fuel assembly lower tube seat structure, the internal lateral flow at the outlet position of the lower tube seat 5 of this embodiment is reduced by 4.8%, the lateral flow between the lower tube seats is reduced by 2.3%, and the drag coefficient is reduced by 2.6%. Example 3

[0073] The present embodiment further optimizes the structural mixing grid 2 in the fuel assembly, and the structural mixing grid 2 is composed of 2×(N-1) inner strips 201 with springs and / or rigid convexities, which are inserted into each other to form an (N-1)×(N-1) arrangement, and then surrounded by an outer strip 202 with springs and / or rigid convexities. The inner strips 201 and the outer strips 202 are spaced to form N×N grid elements, wherein N×NM fuel rod grid elements are used to place fuel rods, and M non-fuel rod grid elements are used to place guide tubes 3 or instrument tubes 4; guide vanes can be provided at the coolant outflow end of the strip fuel rod grid element position. The spring can be punched directly on the strip, or it can be made of a separate material and then stuck on the strip, and the rigid convexity can be punched on the strip. Figure 6As shown, the inner strip rigid protrusion 2013 includes flow holes 2016 on both sides, and the shape of the holes is long strip or circular, which facilitates the lateral flow of the coolant and enhances the mixing. In a single fuel assembly, 2 to 20 grids are arranged along the axial direction of the fuel rod 1. The guide wing of the structural mixing grid 2 is smoothly bent into the fuel rod grid element, and the bending radius is 5mm. After the inner strip guide wing 211 is bent, the inner strip guide wing projection surface 2015 covers the grid element corner, and the projection edge is in the shape of an arc concentric with the fuel rod 1, as shown in FIG. Figure 7 As shown in A in the middle, the "low temperature" coolant at the grid cell corner is guided to flow around the "high temperature" fuel rod 1 by multiple bending to minimize the hot spot temperature and improve safety. The inner strip guide wing 2011 is formed by two bendings, and the distance between the horizontal baselines of the two bends is 3mm.

[0074] The above design improves the coolant mixing effect by an average of about 25% (part of the numerical analysis data is shown in Table 1 below). The test data obtained based on the critical heat flux density test of the fuel assembly proves that its average heat flux density is improved by about 5%.

[0075] Table 1 Comparison of coolant mixing effect test data

[0076]

[0077] The outer strip guide wing has a high-low configuration, so as to guide the coolant to mix and flow, reduce the hot spot temperature and thus improve safety: when the cross-flow direction generated by the guide wing is the same as that of the inner strip 201, a high guide wing H1 with a size of 6-10 mm is used; when the cross-flow direction generated by the guide wing is opposite to that of the inner strip 201, a short guide wing H2 with a size of 2-6 mm is used. For example, when the cross-flow direction generated by the outer strip guide wing is the same as that of the inner strip 201, an outer strip high guide wing 2022 with a size of 8 mm is used, and when the cross-flow direction is opposite, an outer strip short guide wing 2021 with a size of 3 mm is used. At the same time, the outer strip rigid convex 2013 has outer strip flow holes 2024 on both sides, and the shape of the hole is a long strip or a circle, such as Figure 8 As shown, the outer strip guide wing is matched in height and the bent rear end is buried in the gap between the fuel rods without protruding from the outer surface of the structural mixing grid 2, which improves the mixing uniformity between the fuel assemblies and ensures that no hooking occurs in the test of the lateral 500N extrusion force, eliminates the grid hooking interference phenomenon during unloading, and the structure is stable. Fluid mechanics analysis is carried out on the high and low matching design of the outer strip guide wing, and the mixing uniformity between the grids is improved by about 10%. Example 4

[0078] This embodiment further optimizes the structural mixing grid 2 in the fuel assembly. The spring is directly punched on the strip, arranged along the axial direction of the fuel rod, and contacts the fuel rod through a streamlined slightly concave arc surface. Fig. 9As shown, the inner strip spring 2012 is designed as a bridge-type spring, the inner strip rigid convex 2013 is designed as a buckle-type rigid convex and other diversion structures, and diversion structures such as chamfers are added to the inflow end of the inner strip 201, and combined with matching measures such as increasing the coordinated spacing, the coolant is better guided to gather at the corners of the gate element with the guide wing projection at the upper end, while reducing the degree of turbulence when the fluid reaches the guide wing.

[0079] like Fig.10 As shown, support structures 2014 whose shapes match those of the outer strip guide wings are provided at the contact positions between the two ends of the inner strip 201 and the outer strip guide wings, so that the outer strip guide wings lean against the support structures 2014; the top end of the support structure 2014 can be fixed to the inner side of the outer strip guide wings it supports by welding or the like as an integral structure, so as to avoid structural deformation during the operation of the fuel assembly and reduce the safety margin. Example 5

[0080] This embodiment further optimizes the lower tube seat 5 in the fuel assembly. The through slender flow channel of the lower tube seat connecting plate is composed of a group of parallel blades arranged orthogonally with a small spacing, which are clamped by two layers of parallel rib assemblies with the same center distance as the fuel rod center distance of 12.6mm; a protrusion structure with the same direction is set on the blade between the two rows of fuel rods. The protrusion causes the slender flow channel to bend axially and change into a spatial curved surface structure, which plays a role in blocking and capturing foreign matter in the coolant. The blade height is 18mm, the protrusion ball radius is 8mm, and they are neatly and symmetrically arranged at a spacing of 2mm. A spatial curved surface flow channel for filtering foreign matter is formed between the two parallel protrusions on two adjacent blades. Foreign matter filtration test data show that the comprehensive filtration efficiency of the lower tube seat exceeds 87%, which is 9 percentage points higher than the 78% of the domestic fuel assemblies in service. Example 6

[0081] The present embodiment further optimizes the fuel rod 1 in the fuel assembly. The creep-resistant zirconium alloy cladding 101 is a zirconium-tin-niobium series zirconium alloy, and the weight percentage is Sn: 0.50%-1.20%, Nd: 0.60%-1.25%, Fe: 0.05%-0.55%, and the balance is Zr and impurities. It has good strength, so that the structure of the fuel rod 1 is stable during the irradiation process, and the safety margin is not significantly reduced.

[0082] The active section is composed of uranium dioxide pellets, or uranium dioxide pellets containing gadolinium / erbium, or a combination thereof; it can also be composed of uranium dioxide pellets, or boron-coated uranium dioxide pellets, or a combination thereof; it can also be composed of plutonium dioxide pellets, or plutonium dioxide pellets containing gadolinium / erbium, or a combination thereof; it can also be composed of uranium-plutonium mixed oxide pellets, or uranium-plutonium mixed oxide pellets containing gadolinium / erbium, or a combination thereof; it can also be composed of other uranium, plutonium, thorium and other fissile nuclides, or compounds / mixtures containing gadolinium / erbium / dysprosium and other neutron poison nuclides, or a combination thereof. The isotope proportion of fissile nuclides is 1% to 10%. The pellets are prepared into single crystal or large-grain fuel pellets with an average grain size greater than 30μm to improve the pellet irradiation stability and reduce fission gas release. The mass content of the compound / mixture of neutron poison nuclides is 0%~12%, which can provide diversified means for regulating the heat flux density of the fuel rods to support safety margin control.

[0083] The fuel positioning structure 104 is a spiral spring, a radial spring or other elastic structure that can compensate for the thermal expansion difference of the active section to achieve reliable positioning of the fuel active section during operation.

[0084] The heat-conducting gas is high-purity helium with good heat conductivity and does not react with the fuel pellets 103 and the cladding 101. The gas pressure is designed in a balanced iterative manner according to the coolant pressure, gas storage volume, cladding creep performance and burnup, and the maximum value is selected under the condition that the operating internal pressure at the end of 95% of the fuel rods' life is not greater than the external pressure, so as to reduce the creep effect caused by the pressure difference, thereby stabilizing the fuel rod structure during the irradiation process and not significantly reducing the safety margin.

[0085] In a single fuel assembly, the fuel rods with active section height H are arranged in a square shape of N×NM. The diameter of the fuel rods is D and the center distance is L, wherein 100mm≤H≤6000mm, 3≤N≤25, 1≤M≤50 and M≤N×N / 4, 3mm≤D≤15mm, and 4mm≤L≤20mm. Example 7

[0086] The present embodiment further optimizes the fuel rod 1 in the fuel assembly. The creep-resistant zirconium-tin-niobium zirconium alloy cladding of the fuel rod comprises, by weight percentage, Sn: 0.68-0.75, Nb: 0.75-1.00, Fe+Cr: 0.10-0.50, Fe / (Nb+Fe): 0.20-0.35, Cu or Bi: 0.01-0.10, Si or S: 0.002-0.01, O: 0.06-0.15, C: less than 0.008, N: less than 0.006; the remainder is Zr and impurities, and the fuel rod has good mechanical properties, creep resistance and low radiation growth characteristics, so that the structure, shape and size of the fuel rod are stable during the irradiation process, and the safety margin is not significantly reduced.

[0087] The good properties of the fuel rods have been confirmed by commercial in-pile irradiation of more than 60,000 fuel rod cladding tubes, and the burnup depth of the completed irradiation has reached 57GWd / tU, including: the structure is intact after four 18-month long cycle irradiation in a million-kilowatt nuclear power unit; the thermal creep rate at 400℃ and 130MPa is less than 2.4×10 -5 / h, and the creep rate after irradiation at 400℃ and 130MPa is less than 2.2×10 -6 / h; the creep rate at 850℃ and 40MPa is less than 5.6×10 -3 / s; after being oxidized at 1204℃ for more than 17% and quenched, it still maintains plasticity; the irradiation growth is less than 0.55%, so that the axial size of the fuel rod is stable during the irradiation process and the safety margin is not significantly reduced.

[0088] The fuel rods 1 are arranged in a 17×17-25 square, with a diameter of 9.5 mm, an active section height of 12 feet, 14 feet, 4.2 m or 2.15 m, and a center distance of 12.6 mm. They have good power and coolant distribution uniformity and mutual matching, supporting good safety. Example 8

[0089] This embodiment further optimizes the fuel rod 1 in the fuel assembly. The surface of the creep-resistant zirconium-tin-niobium zirconium alloy cladding of the fuel rod is tightly covered with a corrosion-resistant and high-temperature resistant chromium coating to improve the corrosion resistance and high-temperature oxidation ability of the zirconium alloy cladding and improve safety. Example 9

[0090] This embodiment classifies and optimizes the layout of the grids in the fuel assembly according to the different requirements of the different axial positions of the fuel assembly. According to the axial position and temperature distribution of the grids in the fuel assembly, they can be divided into pure structural grids 7, structural mixing grids 2 and pure mixing grids 8. The pure structural grids 7 are arranged at the two ends of the fuel assembly where the power is low and the flow field is turbulent. They only position the fuel rods, have no diversion function, and do not set diversion wings; the structural mixing grids 2 are arranged in the middle of the fuel assembly, and play the role of positioning the fuel rods and diversion at the same time; the pure mixing grids 8 are arranged between the structural mixing grids 2 with insufficient diversion function, usually in the high temperature area of ​​the active section, and play the role of enhancing diversion, without positioning the fuel rods. The pure mixing grids 8 can be arranged or not arranged between the two structural mixing grids 2 as needed; the spacing of the pure mixing grids 8 matches the coolant flow rate, which is the distance at which its diversion function disappears or is insufficient. Through the reasonable arrangement and spacing setting of the grids, the coolant cross-mixing flow of the entire length of the fuel assembly is guided to reduce the hot spot temperature and thus improve safety.

[0091] Preferably, the grid is specifically arranged axially in the 12-foot fuel assembly as 2 pure structural grids 7, 6 structural mixing grids 2 and 3 pure mixing grids 8, the spacing between the pure structural grid 7 and the adjacent structural mixing grid 2 is 400-650 mm, preferably 522 mm, and one pure mixing grid 8 is arranged between the 3rd to 6th structural mixing grids 2 from bottom to top.

[0092] Preferably, the 14-foot fuel assembly is specifically arranged axially as 2 pure structural grids 7, 8 structural mixing grids 2 and 4 pure mixing grids 8, the spacing between the pure structural grids 7 and the structural mixing grids 2 is 400 mm to 650 mm, and the preferred value is 516 mm, and one pure mixing grid 8 is arranged between the 4th to 8th structural mixing grids 2 from bottom to top. Example 10

[0093] like Fig.14 As shown, the present embodiment further optimizes the guide tube 3 in the fuel assembly, and the "tube in tube" guide tube is prepared by an "expansion welding combination method" of first expanding the inner tube 302 on the inner lower part of the outer tube 301 and then welding the two layers of tubes to the end plug as a whole, so as to reduce the difficulty of the manufacturing process; the outer tube 301 is provided with a rod drop overflow hole at a position above the upper end of the inner tube 302; the expansion spacing and the spacing between expansion and welding meet the requirements that the inner tube 302 and the outer tube 301 are theoretically not in contact when the guide tube is subjected to the maximum axial load, so as to achieve appropriate structural strength and reduce the number of expansions; the outer diameter of the outer tube 301 is as large as possible and optimally coordinated with the cooling of the surrounding fuel rods, and the inner diameter of the inner tube 302 is as small as possible and optimally coordinated with the control rod drop; a cold assembly process can be selected to minimize the initial gap requirement and thereby increase the inner tube wall thickness and improve the structural strength.

[0094] Preferably, the guide tube material is the creep-resistant, low-growth zirconium-tin-niobium series zirconium alloy, and the wall thickness of the outer tube 301 is ≥0.55 mm. When a batch of guide tubes are assembled on the same fuel assembly, the diameter and wall thickness of the batch of guide tubes are different due to machining tolerances. The guide tubes with relatively larger diameters and wall thicknesses are arranged at the periphery of the fuel assembly, thereby improving the rigidity and avoiding deformation of the fuel assembly during irradiation operation to reduce the safety margin. Embodiment 11

[0095] like Fig.15 , 16As shown, this embodiment further optimizes the upper tube seat 6 in the fuel assembly. The upper tube seat 6 is composed of an upper tube seat connection plate 601, an upper tube seat enclosure plate 602 fixed to the edge of the upper tube seat connection plate 601, and an upper tube seat frame plate 603 fixed to the upper tube seat enclosure plate 602. The upper tube seat connection plate 601 is provided with an upper tube seat connection hole 6011 for installing the guide tube 3 and the instrument tube 4, and an upper tube seat water flow hole group 6012. The upper tube seat water flow hole group 6012 is centrally symmetrical and axially symmetrically distributed, with densely arranged curved through holes in the middle and parallel straight holes arranged around. Chamfers are set on the upper and lower water flow holes, showing the comprehensive characteristics of high flow and low pressure drop, high rigidity and low stress, and high symmetry and average flow, which can avoid uneven outlet flow field or deformation leading to reduced safety margin. The upper tube seat enclosure plate 602 is provided to reduce the lateral flow between the upper tube seats 6, and the frame plate through holes 6031 are provided on the upper tube seat frame plate 603 to reduce the flow resistance. Example 12

[0096] This embodiment further optimizes the upper tube seat 6 in the fuel assembly. The upper tube seat 6 is equipped with a variable stiffness, low relaxation, high stability leaf spring clamping system 604 for clamping and positioning the fuel assembly in the stack, so as to reduce the clamping load of the fuel assembly during operation, improve the structural stability of the fuel assembly under high burnup, and avoid deformation leading to a reduction in safety margin. Embodiment 13

[0097] This embodiment further optimizes the fuel assembly. The fuel assembly is composed of 264 fuel rods 1, 24 guide tubes 3, 1 temperature-measurable instrument tube 4, 11 layers of grids, 1 upper tube seat 6 and 1 lower tube seat 5 and their connection structure, arranged in a 17×17 square, the diameter of the fuel rod 1 is 9.5 mm, the height of the active section is 12 feet, and the center distance of the fuel rod 1 is 12.6 mm. Through the arrangement of the fuel rods 1 and the setting of the grid structure, the coolant cross-flow of the entire length of the fuel assembly is guided to reduce the hot spot temperature and thus improve safety.

[0098] The fuel rod 1 has a fuel consumption of up to 62GWd / tU. Tests and in-core applications show that the thermal safety margin of the fuel assembly used in the Hualong One and other active cores is greater than 15%, meets the 0.3g extreme ground motion seismic requirements, has a refueling cycle of 18 to 24 months, has an irradiation growth of less than 0.3%, a bending deformation to assembly length ratio of less than 0.1%, and a fuel rod design control breakage rate of less than 10 -6 . Embodiment 14

[0099] This embodiment discloses a fuel assembly assembly method: one end of the guide tube 3 and the instrument tube 4 passes through a plurality of structural mixing grids 2 in sequence, and then the other end is pulled back through the lowest structural mixing grid 2 and then installed on the lower tube seat 5, and the guide tube 3, the instrument tube 4 and the structural mixing grid 2 are fixedly connected; the lower tube seat 5 is removed, and the fuel rods 1 with the surface coated with water-soluble lubricant or pyrolysis fat and other measures to reduce the friction coefficient are pulled into the grid elements of the structural mixing grid 2 in batches; the upper tube seat 6 is installed and the lower tube seat 5 is reinstalled to form a fuel assembly.

[0100] The guide tube 3 is a "tube in tube" guide tube, which is prepared by an "expansion welding combination method" of first expanding the inner tube to the inner lower part of the outer tube and then integrally welding the two layers of tubes to the end plug.

[0101] The smooth bending of the guide wing of the structural mixing grid 2 is obtained by stamping and forming with a mold to improve manufacturing efficiency. The inner strip guide wing of the structural mixing grid 2 is formed by Q bending, wherein the first bending is along the first horizontal baseline of the upper edge of the inner strip, or along the first oblique baseline at an angle of 10-20° with the first horizontal baseline; the distance between the horizontal baseline of the Qth bending and the Q-1st bending is 2-5mm; the distance between the oblique baseline of the Qth bending and the Q-1st bending is 2-5mm; the angle of the Qth bending is smaller than the angle of the Q-1st bending, and continuous Q bending guides the coolant intermixing flow to maximize the reduction of hot spot temperature and thus improve safety.

[0102] The lower tube seat 5 is realized by additive manufacturing methods such as brazing or printing to ensure manufacturing efficiency and economy.

[0103] The zirconium-tin-niobium series zirconium alloy cladding 101 of the fuel rod 1 is processed by cryogenic technology and delivered in a completely recrystallized state to ensure good mechanical properties and corrosion resistance. Embodiment 15

[0104] This embodiment further optimizes the fuel assembly. The fuel assembly can be used together with a control rod assembly with M-1 control rods to better flatten the power level in the fuel assembly, achieve a higher safety margin and also achieve a higher assembly burnup. Example 16

[0105] The core formed by the fuel assembly described in any of the above embodiments can be specifically arranged into 177 cores and 157 cores according to 15×15, into 193 cores according to 16×16, into 241 cores according to 17×17, into 121 cores according to 14×14, and into 57 cores according to 9×9.

[0106] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A coordinated flow control high reliability fuel assembly, characterized in that: A lower tube seat (5), a frame, an upper tube seat (6), a fuel rod (1), a guide tube (3), and an instrument tube (4) inserted into the frame are sequentially arranged along the coolant flow direction; The lower tube seat (5) is a low-outlet transverse flow lower tube seat; a plurality of space-through elongated flow channels (505) having a width smaller than the fuel rod spacing and being axially curved are provided on the lower tube seat connection plate (501); the outlets of the surrounding flow channels (5053) located on the outer periphery of the lower tube seat connection plate (501) of the space-through elongated flow channels (5055) are higher than the outlets of the middle flow channels (5054) located in the middle of the lower tube seat connection plate (501), so as to reduce the outlet transverse flow between components; The skeleton comprises a structural mixing grid (2), wherein the guide wings of the structural mixing grid (2) are arranged on the inner strip and the outer strip and are smoothly bent toward the inner side of the fuel rod grid element; the projection (2015) of the inner strip guide wing covers the grid element corner, and the projection edge is in the shape of an arc concentric with the fuel rod (1), thereby guiding the coolant at the grid element corner to flow around the fuel rod (1) to achieve strong diversion; The skeleton also includes a pure structural grid (7) and a pure mixing grid (8); The pure structural grid (7) is arranged at both ends of the fuel rod (1) where the flow field is turbulent, and only positions the fuel rod (1), has no flow guidance function, and is not provided with flow guidance wings; the pure mixing grid (8) is arranged between the structural mixing grids (2) with insufficient flow guidance function, and plays a role in enhancing the flow guidance, but does not position the fuel rod (1); The guide wings of the structural mixing grid (2) and the pure mixing grid (8) are bent toward the inner side of the fuel rod grid element at a radius of 2 to 10 mm; multiple openings are provided on the inner strip (201) and the outer strip (202) of the structural mixing grid (2), namely the inner strip flow holes (2016) and the outer strip flow holes (2024), so as to enhance the lateral flow in different grid elements; At least one structured mixing grid (2) is arranged in the high power area; if two or more structured mixing grids (2) are arranged, the distance between two adjacent structured mixing grids (2) is 200-700 mm, and 1-2 pure mixing grids (8) can be arranged therebetween.

2. A coordinated flow control high reliability fuel assembly according to claim 1, characterized in that: An inlet chamfer (5052) is processed at the inlet end of the space-penetrating elongated flow channel (505) to reduce flow resistance.

3. A coordinated flow control high reliability fuel assembly as claimed in claim 1, characterized in that: The upper tube seat (6) is a low-outlet transverse flow upper tube seat, which is composed of an upper tube seat connecting plate (601), an upper tube seat enclosure plate (602) fixed to the edge of the upper tube seat connecting plate (601), and an upper tube seat frame plate (603) fixed to the upper tube seat enclosure plate (602); the upper tube seat enclosure plate (602) is provided to reduce the transverse flow between the upper tube seats, and the frame plate through hole (6031) is opened on the upper tube seat frame plate (603) to reduce the flow resistance.

4. A coordinated flow control high reliability fuel assembly as claimed in claim 3, characterized in that: An upper tube seat water flow hole group (6012) is processed on the upper tube seat connection plate (601). The upper tube seat water flow hole group (6012) is distributed on the upper tube seat connection plate (601) in a rotationally symmetrical and axially symmetrical manner, with densely arranged curved through holes in the middle and parallelly arranged straight holes around, and chamfers are provided on the top and bottom of the holes. Upper tube seat connection holes (6011) are opened on the upper tube seat connection plate (601) at corresponding positions of the guide tube (3) and the instrument tube (4), and the upper tube seat water flow holes near the upper tube seat connection hole (6011) are distributed in a rotationally symmetrical and axially symmetrical manner with the upper tube seat connection hole (6011) as the center.

5. A coordinated flow control high reliability fuel assembly as claimed in claim 4, characterized in that: The upper tube seat (6) is equipped with a variable stiffness low relaxation leaf spring clamping system (604) to reduce the clamping load of the fuel assembly during operation.

6. A coordinated flow control high reliability fuel assembly as claimed in claim 1, characterized in that: The fuel rod (1) is a low-irradiation deformation fuel rod, which is composed of a zirconium alloy cladding (101) with creep resistance and low-irradiation growth characteristics, a fuel core block (103), and an end plug (102), which is filled with an inert gas; the pressure of the inert gas is designed through balanced iteration according to the external pressure of the fuel rod, the gas storage volume, the creep characteristics of the cladding, and the fuel rod burnup, and the maximum value is selected under the condition that the hot internal pressure of the fuel rod does not exceed the external pressure.

7. A coordinated flow control high reliability fuel assembly as claimed in claim 6, characterized in that: The active section of the fuel rod (1) is composed of: uranium dioxide pellets, plutonium dioxide pellets or uranium-plutonium mixed oxide pellets, or pellets containing gadolinium or boron or erbium or dysprosium, or a combination of the above pellets; or other compounds of uranium, plutonium, thorium and other fissile nuclides, or compounds or mixtures containing gadolinium or boron or erbium or dysprosium and other neutron poison nuclides, or a combination of the above compounds or mixtures; Among them, the isotopes of fissile nuclides account for 1~10%; the mass content of compounds or mixtures of neutron poison nuclides is 0~12%.

8. A coordinated flow control high reliability fuel assembly as claimed in claim 7, characterized in that: The average grain size of the pellets in the active section of the fuel rod (1) is greater than 30 μm.

9. A coordinated flow control high reliability fuel assembly as claimed in claim 6, characterized in that: The fuel rod (1) further comprises a fuel positioning structure (104), wherein the fuel positioning structure (104) is a spiral spring, a radial spring or other elastic structure capable of compensating for the thermal expansion difference of the active section.

10. A coordinated flow control high reliability fuel assembly according to claim 9, characterized in that: The material of the cladding (101) is a zirconium-tin-niobium series zirconium alloy, and the weight percentage is: Sn: 0.50%-1.20%, Nd: 0.60%-1.25%, Fe: 0.05%-0.55%, and the balance is Zr and impurities.

11. A coordinated flow control high reliability fuel assembly according to claim 10, characterized in that: The surface of the zirconium-tin-niobium series zirconium alloy is tightly covered with a corrosion-resistant and high-temperature resistant chromium coating.

12. A coordinated flow control high reliability fuel assembly as claimed in claim 1, characterized in that: The guide tube (3) is a zirconium alloy tube with a constant outer diameter and an inner neck; or a "tube-in-tube" combination consisting of an outer tube with a constant wall thickness and an inner tube with a constant wall thickness sleeved on its inner lower part, with a rod drop overflow hole being provided on the outer tube near the upper end of the inner tube.

13. A coordinated flow control high reliability fuel assembly according to claim 12, characterized in that: The guide tube (3) is made of a creep-resistant, low-growth zirconium-tin-niobium series zirconium alloy, and the outer tube wall thickness is ≥0.55 mm. When a batch of guide tubes (3) are assembled on the same fuel assembly, the diameters and wall thicknesses of the batch of guide tubes vary due to machining tolerances, and the guide tubes (3) with larger diameters and wall thicknesses are arranged at the periphery of the fuel assembly.

14. A coordinated flow control high reliability fuel assembly as claimed in claim 1, characterized in that: The space-through elongated flow channel (505) is symmetrical on the left and right sides and has opposite bending directions, and an outlet straight flow section (5051) with a length of ≥3 mm is provided at the outlet end.

15. The coordinated flow control high reliability fuel assembly according to claim 1, characterized in that: The instrument tube (4) is a temperature-measurable instrument tube, arranged on a 12-foot fuel assembly running at 5 m / s, and 22 small holes with a diameter of 3 mm are opened on the instrument tube (4) at a position 3 to 4 m above the lower surface of the active section of the fuel rod (1); a temperature measuring instrument or other core measuring instrument is inserted from the upper part of the instrument tube (4).

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