GB2553418A

GB2553418A - Fuel assembly mixing grid with flow deflector mixing vanes

Info

Publication number: GB2553418A
Application number: GB1710630.3A
Authority: GB
Inventors: Yu Wenchi; Li Weicai; Li Xianfeng; Wang Renjun; Nie Lihong; Chen Xiaoming; Pang Zhengzheng
Original assignee: China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd
Current assignee: China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd
Priority date: 2014-12-05
Filing date: 2015-11-30
Publication date: 2018-03-07
Anticipated expiration: 2035-11-30
Also published as: CN104485137A; CN104485137B; WO2016086809A1; GB2553418B; GB201710630D0

Abstract

A fuel component stirring-mixing lattice provided with fairing-type stirring-mixing vanes, comprising an outer band (10) and multiple inner bands (11). The multiple inner bands (11) intersect each other to form a grating structure. The grating structure is provided with multiple hollow grating units (110). The outer band (10) encloses the periphery of the grating structure and is fixed with the inner bands (11). The grating structure is provided with multiple stirring-mixing vanes (12). The stirring-mixing vanes (12) are extended into the grating units (110) and a surface of each of the stirring-mixing vanes (12) facing the interior of the grating units (110) is provided with a diversion groove (120). The fuel component stirring-mixing lattice is capable of reducing diversion of a coolant towards the left and right of the stirring-mixing vanes, thus restricting unordered fluid flow, providing a fairing effect, and ensuring an effect in which the stirring-mixing vanes increase the thermal headroom of a fuel component.

Description

(56) Documents Cited:

CN 204332387 U CN 102568632 A CN 001701392 A US 4039379 A

G21C 3/352 (2006.01)

CN 104485137 A CN 101752015 A TW 201023206 A (86) International Application Data:

PCT/CN2015/095902 Zh 30.11.2015 (58) Field of Search:

INT CL G21C

Other: VEN, CNKI, CNABS, CNTXT (87) International Publication Data:

WO2016/086809 Zh 09.06.2016 (71) Applicant(s):

China Nuclear Power Technology Research Institute Co., Ltd

Room 1502-1504,1506,15th Floor,

Shenzhen Science & Technology Bid., No.1001, Shangbu Road Middle, Futian District, Shenzhen, Guangdong, China

China General Nuclear Power Co. Ltd. (Incorporated in China)

17th - 19th Floor,

Shenzhen Science & Technology Bid., No. 1001, Futian District, Shenzhen, Guangdong, China (continued on next page) (54) Title of the Invention: FUEL ASSEMBLY MIXING GRID WITH FLOW DEFLECTOR MIXING VANES

Abstract Title: Fuel component stirring-mixing lattice provided with fairing-type stirring-mixing vanes (57) A fuel component stirring-mixing lattice provided with fairing-type stirring-mixing vanes, comprising an outer band (10) and multiple inner bands (11). The multiple inner bands (11) intersect each other to form a grating structure. The grating structure is provided with multiple hollow grating units (110). The outer band (10) encloses the periphery of the grating structure and is fixed with the inner bands (11). The grating structure is provided with multiple stirring-mixing vanes (12). The stirring-mixing vanes (12) are extended into the grating units (110) and a surface of each of the stirring-mixing vanes (12) facing the interior of the grating units (110) is provided with a diversion groove (120). The fuel component stirringmixing lattice is capable of reducing diversion of a coolant towards the left and right of the stirring-mixing vanes, thus restricting unordered fluid flow, providing a fairing effect, and ensuring an effect in which the stirring-mixing vanes increase the thermal headroom of a fuel component.

This international application has entered the national phase early

GB 2553418 A continuation (71) Applicant(s):

CGN Power Co. Ltd.

(Incorporated in China)

24th Floor, Shenzhen Science & Technology Bid., No. 1001, Futian District, Shenzhen, Guangdong, China (72) Inventor(s):

Wenchi Yu Weicai Li Xianfeng Li Renjun Wang Lihong Nie Xiaoming Chen Zhengzheng Pang (74) Agent and/or Address for Service:

Mewburn Ellis LLP

City Tower, 40 Basinghall Street, LONDON, Greater London, EC2V 5DE, United Kingdom

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Fig. 8 Fig. 9

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Fig. 4 Fig. 11

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Fig. 12

FUEL ASSEMBLY MIXING GRID WITH FLOW DEFLECTOR MIXING

VANES

FIELD OF THE INVENTION [0001] The invention relates to reactor components, and more particular to a 5 fuel assembly mixing grid with flow deflector mixing vanes.

BACKGROUND OF THE INVENTION [0002] Fuel rods with certain amount arranged in a predetermined spacing (such as 15x15, 17x17. etc.) and formed to a bunch are called as a nuclear reactor fuel assembly which mainly includes a top nozzle, a bottom nozzle, a mixing grid (also called as a spacer grid), guide thimbles and fuel rods. Therein, the mixing grid for loading the fuel rods includes multiple inner straps and outer straps surrounding the inner straps. The multiple inner straps are orthogonally interlaced with one another to form a latticed grid structure with multiple grid cells.

[0003] As well known, chain reaction in nuclear reactors will produce large quantity of radioactive substances such as 1-131, Cs-137. For preventing these radioactive substances from being leaked out from the nuclear reactors in explosion accidents, Zirconium alloy shell, reactor press vessel and concrete contentment are configured outside the nuclear reactors. However, these means just are emergency safety measures acted for nuclear reactor accidents, while the important factors for preventing explosion accidents are to control the speed and the temperature of the chain reaction in the nuclear reaction, thus the water flow control of the light water in the fuel assembly that is acted as moderators and coolant is critical, and the mixing grid of the fuel assembly is significant to the water flow control of the light water.

[0004] To enhance the mixed flow of the coolant in the fuel assembly, mixing vanes are arranged on the inner straps to extend into the grid cells, as a result, the coolant flow from bottom to up to reach the mixing vanes will be diverted, cross-flow and eddies will be generated at downstream of the mixing grid to improve the flowability of the coolant thereby finally improving the thermal margin of the fuel assembly.

[0005] However, structures of the conventional mixing vanes have certain limitations, thus the effectiveness of improving the thermal margin is greatly reduced. As shown in Fig. 3, the conventional mixing vanes has a flat structure and is shaped like a triangle, when the coolant F flows upwards, the coolant will directly crash the flat surface of the mixing vane to divert and deflect, after the diversion and deflection, the upward remain coolant U are desired, while the dispersed coolant L and R toward the left and right directions along the surface of the mixing vane are undesired, which may weaken the upward coolant. That why the effectiveness of the mixing vanes for improving the thermal margin is degraded. Further, the dispersed coolant toward the left and right directions may interfere with the flow distribution and increase useless kinetic energy consumption.

[0006] Therefore, it is necessary to provide fuel assembly mixing grid to reduce the coolant flow diversions and improve the thermal margin.

SUMMARY OF THE INVENTION [0007] One objective of the invention is to provide fuel assembly mixing grid to reduce the coolant flow diversions and improve the thermal margin.

[0008] To achieve the above-mentioned objective, the present invention provides fuel assembly mixing grid with flow deflector mixing vanes, which comprises multiple outer straps and multiple inner straps, the multiple inner straps interlaced with each other to form a grid structure which is provided with multiple hollow grid cells, the multiple outer straps surrounding the grid structure and fixed to the inner straps, wherein the grid structure is provided with multiple mixing vanes each of which is extended towards the grid cell, and a surface of each mixing vane facing an interior of the grid cell is provided with a deflecting groove.

[0009] In comparison of the prior art, since the deflecting groove is configured on the mixing vane of the mixing grid, thus the surface of the mixing vane is not flat; further, as the deflecting groove is extended towards the interior of the grid cell, thus the coolant from bottom to up to reach the mixing vanes will be gathered by the deflecting grooves so as to guide more coolant to flow to the downstream of the mixing vanes, rather than directly crash the mixing vanes, thus the mixing length is increased. By comparison with the conventional flat-surface mixing vanes, the present invention can efficiently reduce the coolant flow diversions towards left and right directions of the mixing vanes and restrict disordered flow, thereby improving the effectiveness of the mixing vanes for improving the thermal margin of the fuel assembly.

[0010] Preferably, a width of the deflecting groove is gradually expanded from a bottom of the deflecting groove to the outside. As a result, the coolant at two sides of the deflecting groove will be diverted to the deflecting groove by means of the tilted side walls and flow to the downstream, instead of dispersed towards the sides, thereby improving the flow deflection effect.

[0011] Specifically, a cross section of the deflecting groove is triangular, trapezoid, polygonal or arc.

[0012] Preferably, one end of the mixing vane is protruded from the inner strap, and another end of the mixing vane is bent and extended towards the grid cell.

[0013] Specifically, the deflecting groove is extended along a bending direction of the mixing vane. As a result, the coolant flow guided by the deflecting groove is ensured to follow the bending of the mixing vane thereby avoiding disordered flow and furthest increasing the mixing length.

[0014] Specifically, an angle between a vertical direction and the end of the mixing 5 vane that is bent and extended towards the grid cell is in a range of 0~90 degrees.

[0015] More specifically, an angle between the vertical direction and the end of the mixing vane that is bent and extended towards the grid cell is in a range of 20-80 degrees.

[0016] Preferably, the grid cells are installed with fuel rods, and a side of the mixing 10 vane that is close to the fuel rod is provided with a fairing edge that is matched to the fuel rod. In such a way, coolant flow leakage from a gap between the mixing vane and the fuel rod is efficiently reduced, thus more coolant can flow toward downstream along the bending direction of the mixing vanes, thereby improving the thermal margin of the mixing vanes.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] Fig. 1 is a partial perspective view of mixing grid according to one embodiment of the present invention;

[0018] Fig. 2 is a partial plane view of the mixing grid according to the present invention;

[0019] Fig. 3 is a schematic view of the mixing vanes showing the current direction around the mixing vanes;

[0020] Fig. 4 is a schematic view of the mixing vanes showing the bending direction; [0021] Fig. 5 is a cross section schematic view of the deflecting groove according to a first embodiment of the present invention;

[0022] Fig. 6 is a cross section schematic view of the deflecting groove according to a second embodiment of the present invention;

[0023] Fig. 7 is a cross section schematic view of the deflecting groove according to a third embodiment of the present invention;

[0024] Fig. 8 is a cross section schematic view of the deflecting groove according to a fourth embodiment of the present invention;

[0025] Fig. 9 is a cross section schematic view of the deflecting groove according to a fifth embodiment of the present invention;

[0026] Fig. 10 is a cross section schematic view of the deflecting groove according to a sixth embodiment of the present invention;

[0027] Fig. 11 is a cross section schematic view of the deflecting groove according to a seventh embodiment of the present invention; and [0028] Fig. 12 is a cross section schematic view of the deflecting groove according to an eighth embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS [0029] Preferred embodiments of the present invention will now be described with reference to the figures.

[0030] As shown in Fig. 1 and Fig. 2, the fuel assembly mixing grid with flow deflector mixing vanes according to the present invention includes multiple outer straps

10 and multiple inner straps 11. Specifically, the multiple inner straps 11 are interlaced each other to form a grid structure which is provided with multiple hollow grid cells 110, the multiple outer straps 10 surround the grid structure and fixed to the inner straps 11, the grid structure is provided with multiple mixing vanes 12 each of which is extended to the grid cell 110, and a surface of each mixing vane 12 facing an interior of the grid cell 110 is provided with a deflecting groove 120.

[0031] In an embodiment, the inner straps 11 are divided into two groups, each group of the inner straps 11 are parallel one another and spaced in predetermined intervals, and the two groups are orthogonally interlaced with one another to form the grid structure which is provided to be equipped with fuel rods or guide thimbles (not shown) which are cylindrical. Fig. 2 shows that the coolant in the mixing grid 1 is in the crossflow direction.

[0032] One end (proximal end) of the mixing vane 12 is protruded from an upper edge of the corresponding inner strap 11 and extended upwards, and the other end (distal end) of the mixing vane 12 is bent and extended towards the interior of the corresponding grid cell 110. More specifically, the projection of the distal end of the mixing vane 12 along the flowing direction of the coolant is located within the projection of the grid cell 110. The bend of mixing vane 12 means the mixing vane 12 is inclined towards the grid cell 110 relatively to the vertical direction. Preferably, the mixing vane 12 may have a certain curvature and gradient at the extending direction itself, and the actual shape of the mixing vane 12 can be designed according to the actual demands, which is well known to the person skill in the art. In addition, any two adjacent mixing vanes 12 are extended toward the individual grid cell 110, that is, every mixing vane 12 is arranged for a corresponding grid cell 110. Of course, the amount of the mixing vanes 12 is not limited.

[0033] As shown in Fig. 4, an angle Θ between a vertical direction and the end of the mixing vane 12 that is bent and extended toward the grid cell 110 (that is the angle between the vertical direction and the mixing vane 12) is in a range of 0~90 degrees. Preferably, the angle is in a range of 20-80 degrees.

[0034] Specifically, the deflecting groove 120 is extended along the bending direction of the mixing vane 12 and follows the bending of the mixing vane 12, thus the coolant flow guided by the deflecting groove 120 is ensured to follow the bending of the mixing vane 12 thereby avoiding disordered flow and furthest increasing the mixing length.

[0035] As another embodiment of the present invention, the end of the mixing vane extending to the grid cell 110 is provided with an arc notch that is matched to the external profile of the fuel rod. The arc notch has a fairing edge that is arc, and the curvature of the fairing edge is matched to the circumferential curvature of the corresponding fuel rod. In such a way, coolant flow leakage from a gap between the mixing vane 12 and the fuel rod is efficiently reduced, thus more coolant can flow toward downstream along the bending direction of the mixing vanes 12, thereby improving the thermal margin of the mixing vanes 12.

[0036] As shown in Figs. 5~11, the width of the deflecting groove 120 is gradually expanded from the bottom of the deflecting groove 120 to the outside, that is, the bottom of the deflecting groove 120 has a narrower width than that of the opening of the deflecting groove 120, in such a way, it’s beneficial to guide the coolant to flow to the deflecting groove 120 along two sides of the deflecting groove 120. Alternatively, the cross section of the deflecting groove 120 can be triangular, trapezoid, polygonal or arc. [0037] Fig. 5 shows the first embodiment of the present invention, the bottom wall of the deflecting groove 120 is in a gradual V-shape, and the deflecting groove 120 has two side walls one of which is perpendicular to a surface of the mixing vane 12 where the deflecting groove 120 is formed, and another of which is tilted to this surface with a tilting direction from outside to inside, thereby ensuring the opening of the deflecting groove 120 is wider than the bottom.

[0038] Fig. 6 shows the second embodiment of the present invention, difference between the instant embodiment and the first embodiment is that, both of two side walls of the deflecting groove 120 are titled to the surface of the mixing vane 12 where the deflecting groove 120 is formed.

[0039] Please refer to Fig. 7, the bottom wall of the deflecting groove 120 according 5 to the third embodiment of the present invention includes two portions, one of which is titled to said surface of the mixing vane 12, and another of which is parallel to said surface. The deflecting groove 120 also has two side walls that are the same with that in the first embodiment.

[0040] As shown in Fig. 8, the deflecting groove 120 according to the fourth embodiment has a cross section in an isosceles triangle shape.

[0041] As shown in Fig. 9, the deflecting groove 120 according to the fifth embodiment has a cross section in an isosceles trapezoid shape, that is, the deflecting groove 120 has a bottom wall that is parallel to the surface of the mixing vane where the deflecting groove 120 is formed, and two side walls that are tilted from outside to inside.

[0042] As shown in Fig. 10, the deflecting groove 120 according to the sixth embodiment has two tilted bottom walls and two tilted side walls, and the bottom walls and the side walls have greater tilt than that in the second embodiment, and the length of the bottom walls is shorter, while the length of the side walls is longer. By this token, the depth of the deflecting groove 120 is increased to bring a better flow diversion effect.

[0043] As shown in Fig. 11, the deflecting groove 120 according to the seventh embodiment has a bottom wall in a smooth arc shape.

[0044] Please refer to Fig. 12, the deflecting groove 120 according to the eight embodiment is similar to that in the sixth embodiment, difference is that, the deflecting groove 120 in the sixth embodiment is extended from the top of the mixing vane 12 to the bottom of the mixing vane, while the deflecting groove here is extended from the top to bottom, and further to the inner straps 11, so as to improve the flow diversion effect. As understood, the other deflecting grooves 120 in the other embodiments also can be configured to extend to the inner straps 11.

[0045] By this token, shapes and sizes of the deflecting groove 120 according to the present invention are not limited, only if the deflecting groove 120 is configured at a side that is faced to the interior of the grid cell 110 and extended along the flow direction of the coolant, thereby acting the flow diversion effectiveness.

[0046] It should be explained that, the improvement of the present invention is aimed 10 at configuring the deflecting groove 120 on the mixing vane 12, it’s not claimed for the specific shape of the mixing vane 12 and the tilt of the mixing vane 12. Figs. 5~11 just show the shape of the deflecting groove 120, but not the whole shape of the mixing vane 12. The structures of the mixing vane 12 mentioned in the above embodiments are just for better explanation, which is not limited to the deflecting groove 120.

[0047] In comparison of the prior art, since the deflecting groove 120 is configured on the mixing vane 12 of the mixing grid 1, thus the surface of the mixing vane 12 is not flat; further, as the deflecting groove 120 is extended towards the interior of the grid cell 110, thus the coolant from bottom to up to reach the mixing vanes 12 will be gathered by the deflecting grooves 12 so as to guide more coolant to flow to the downstream of the mixing vanes 12, rather than directly crash the mixing vanes 12, thus the mixing length is increased. By comparison with the conventional flat-surface mixing vanes, the present invention can efficiently reduce the coolant flow diversions towards left and right directions of the mixing vanes 12 and restrict disordered flow, thereby ensuring the effectiveness of the mixing vanes for improving the thermal margin of the fuel assembly.

[0048] While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention.

Claims

1. A fuel assembly mixing grid with flow deflector mixing vanes, comprising multiple outer straps and multiple inner straps, the multiple inner straps interlaced with

5 each other to form a grid structure which is provided with multiple hollow grid cells, and the multiple outer straps surrounding the grid structure and fixed to the inner straps, wherein the grid structure is provided with multiple mixing vanes each of which is extended towards the grid cell, and a surface of each mixing vane facing an interior of the grid cell is provided with a deflecting groove.

2. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 1, wherein a width of the deflecting groove is gradually expanded from a bottom of the deflecting groove to the outside.

15

3. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 2, wherein a cross section of the deflecting groove is triangular, trapezoid, polygonal or arc.

4. The fuel assembly mixing grid with flow deflector mixing vanes according to

20 claim 1, wherein one end of the mixing vane is protruded from the inner strap, and another end of the mixing vane is bent and extended towards the grid cell.

5. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 4, wherein the deflecting groove is extended along a bending direction of the

25 mixing vane.

6. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 4, wherein an angle between a vertical direction and the end of the mixing vane that is bent and extended towards the grid cell is in a range of 0~90 degrees.

7. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 6, wherein an angle between the vertical direction and the end of the mixing vane that is bent and extended towards the grid cell is in a range of 20-80 degrees.

10

8. The fuel assembly mixing grid with flow deflector mixing vanes according to claim 1, wherein the grid cells are equipped with fuel rods, and a side of the mixing vane that is close to the fuel rod is provided with a fairing edge that is matched to the fuel rod.