JP2007093520A - Fuel assembly for pressurized water reactor and its support grid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a support grid of a fuel assembly for a pressurized water reactor which has small flow resistance and can be easily provided vanes for deflection with a large stirring effect. <P>SOLUTION: The support grid of a fuel assembly for a pressurized water reactor keeps a circular tube or octagonal ferrule elements arrayed in nearly a rectangular grid. The vanes for deflecting cooling water around fuel rods in sub-channels formed by four ferrule elements adjacent to each other are attached by bridging the four ferrule elements. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a pressurized water nuclear fuel assembly and a supporting grid thereof, and more particularly, to a pressurized water nuclear fuel assembly provided with a deflection blade having a small flow resistance of cooling water and a large effect of deflecting cooling water. Concerning support grid.

  A fuel assembly and a support grid of a pressurized water reactor (hereinafter referred to as “PWR”) will be described with reference to the drawings. FIG. 1 is a diagram conceptually showing the main part of the fuel assembly as a whole and a state in which support grids and fuel rods are arranged and fixed in the fuel assembly. In FIG. 1, 90 is a fuel assembly, 91 is an upper nozzle, 92 is a lower nozzle, 93 is a support grid, 30 is a fuel rod, 35 is a thimble tube, and 10 is a horizontal plane. It is a lattice plate provided in the inner horizontal direction (left and right direction in the figure), and 20 is also provided in the vertical direction (in the actual arrangement, in the direction perpendicular to the horizontal direction in the horizontal plane, but in the figure, the so-called vertical direction). A lattice plate, 21 is a deflection blade, 95 is a frame material for an outer frame, and 96 is a weld nugget.

  1 is arranged in, for example, 17 × 17, the upper end is fixed to a support grid 93a integrated with the upper nozzle 91 via the thimble tube 35, and the lower end is fixed to the lower nozzle 92. It is a figure which shows notionally that the made fuel rod 30 is restrained while being supported by the support grids 93 at some points along the way. In the upper right diagram of FIG. 1, in each support grid 93, for example, 18 pieces each including a frame material for an outer frame are arranged in the horizontal direction and the vertical direction, and the grid plates 10 and 20 are arranged in vertical and horizontal lines (or FIG. 5 is a diagram conceptually showing a state in which fuel rods are arranged inside a mesh formed by crossing the frames 10 and 20 in the horizontal and vertical directions. The lower right diagram in FIG. 1 is a diagram conceptually showing a state in which the fuel rod penetrates the inside of the cell.

  The mesh portion will be described in more detail with reference to FIG. 2 is an enlarged view of a part of the upper right view of FIG. 1, and further conceptually shows the main part of the structure of the mesh portion, and also shows a view of the lower right view of FIG. 1 as viewed from above. It is also a diagram shown. In FIG. 2, 31 is a soft stop and 32 is a hard stop.

  As shown in FIG. 2, each support grid has grid plates 10 and 20 arranged in a horizontal and vertical direction like vertical and horizontal lines (or eyes) of a grid, and in a place where the grids intersect (grid points) in advance. Lattice plates in both directions are fitted using notches (not shown) formed in the lattice plates 10 and 20, and are assembled by being fixed by welding as necessary. For this reason, weld nuggets 96 are formed at the lattice points. In each support grid, a soft stop 31 on which a cylindrical fuel rod 30 acts elastically in each square cell formed by the two grid plates 10 and 20 in the horizontal and vertical directions. It penetrates in the up-down direction while being constrained via a hard stop 32 acting rigidly.

Further, the deflecting blade portions 21 provided in each square cell reverse the two trapezoidal protrusions formed on the upper end surface in the vicinity of the lattice points of the lattice plate 20 in the vertical direction, respectively. In this way, the coolant flowing from the lower side to the upper side of the fuel rod is deflected to improve the mixing and the cooling effect (Patent Document 1).
JP-A-5-172974

Under the strong demand for lower power generation costs in recent years, it is desirable to reduce the load of the cooling water pump. To that end, the flow resistance or pressure loss (hereinafter referred to as “ It is indispensable to reduce the “flow resistance”.
The flow path resistance of the cooling water by the support grid is generated by the collision between the lattice plate bottom surface and the cooling water and the friction between the lattice plate side surface and the cooling water. For this reason, the larger the flow rate of the cooling water, the larger the channel resistance.
By the way, between the upper and lower nozzles and the support grid, or between the upper and lower support grids, as shown in FIG. 3, subchannels are formed between the four fuel rods. In the subchannel shown in FIG. 3, the hatched 38 is near the surface of the fuel rod, and 39 is a location away from the fuel rod. Moreover, the part of the dotted line shown by 19 and 29 is a place where the grid plates 10 and 20 of the horizontal direction and vertical direction in a support grid are located.

The flow velocity in this subchannel is reduced near the fuel rod surface 38 due to friction with the fuel rods and is increased at a location 39 away from the fuel rods. However, as is apparent from FIG. 3, the grid plates 10 and 20 of the support grid are positioned above the central portion away from the fuel rods and on the side where the cooling water flows. As a result, the cooling water collides with the bottom surface of the grid plates 10 and 20 of the support grid located on the downstream side at a high speed, and the flow path resistance increases. Furthermore, at this time, in the lattice plate coupling structure as shown in the lower right of FIG. 1, the cooling water collides at the intersections of the upper and lower two points at the lattice points of each stage, and the flow path resistance also increases from this surface. To do.
Further, in the place where the weld nugget 96 for firmly fixing the lattice plates 10 and 20 in both directions at the lattice points is formed, the flow path resistance further increases.
Further, the deflection blade portion is preferable in terms of generating a deflection flow if the shape is large, but if it is too large, the flow passage resistance is further increased because the deflection blade portion is located at a location where the flow velocity of the channel central portion 39 is large. It will be.

On the other hand, if these measures are taken, if the coolant flow rate is slowed or the deflection vanes are made smaller, the cooling capacity of the coolant will be reduced this time, and there will be inconveniences in terms of ensuring the safety of the reactor. It can happen.
In addition, as shown in the lower right diagram of FIG. 1, a window is formed on the side surface of the lattice plate to reduce the area where friction is generated, and the flow resistance has been reduced accordingly. Since the collision with the cooling water occurs in the upper part of the window, the effect is limited.
For this reason, it has been desired to develop a support grid having a low flow resistance, and particularly to develop a support grid that has a small flow resistance but is easy to provide a deflection blade having a large stirring effect.
It has also been desired to develop a fuel assembly having such a support grid.

  The present invention has been made for the purpose of solving the above-described problems. The support grid has a structure in which a ferrule element such as a circular tube is fitted, and four vane members for deflection are provided. It is designed to be installed across the space formed by the individual ferrule elements. Hereinafter, the invention of each claim will be described.

The invention described in claim 1
A support grid for a fuel assembly for a pressurized water reactor, in which circular or octagonal tubular ferrule elements are arranged in a substantially square lattice pattern.

In the invention of this claim, since the support grid is formed by arranging circular or octagonal ferrule elements (members, hereinafter referred to as “elements”) in a substantially square lattice pattern, Since the supporting grid member is not arranged in the central portion in the sub-channel, that is, the place where the cooling water flows at a high speed, or even if it is arranged, the flow resistance of the cooling water is reduced.
Further, since each ferrule element is manufactured integrally, and there is a margin in strength, it is possible to make the thickness smaller than the thickness of the lattice plate and shorten it in the flow direction. As a result, the flow resistance is also reduced from these aspects.

It should be noted that the ferrule element is not a polygon of 9 or more but a circular or octagonal tube because it is easy to manufacture. The non-hexagonal element is as small as possible in the center of the subchannel. This is to prevent a part from being located.
Here, “arranged in a substantially square lattice” means that a large number of ferrule elements are arranged on the same plane with their openings directed in the vertical direction, and the overall planar shape is substantially square. Point to. In addition, “almost” means that some irregularities occur in the outer peripheral portion, and in addition, the ferrule element is not arranged in the place where the thimble tube is located, and instead a fixing or connecting member is installed. Refers to that.

The invention according to claim 2 is a support grid of the fuel assembly for a pressurized water reactor,
A vane member for deflecting cooling water around the fuel rod in a subchannel formed by the four ferrule elements adjacent to each other is attached across the four ferrule elements. It is a support grid of a fuel assembly for a pressurized water reactor.

In the invention of this claim, the blade member is mounted in a subchannel formed by the four fuel rods and slightly above the upper end of the ferrule element. For this reason, from the aspect of the position where the blade member is attached and arranged, there is no change or the same as the conventional attachment position of the blade member. However, conventionally, there is a lattice plate below the blade member (on the upstream side of the cooling water) that has a cross shape and is relatively long in the flow direction. Then, there is no such thing under the blade member. This means that when attention is paid to one blade member, the downstream support grid also has no lattice plate. Therefore, the cooling water deflection provided by the upstream blade body is not rectified and weakened by the lattice plate of the downstream support grid. As a result, the effect of deflecting the cooling water by the blades becomes more efficient, the flow resistance is greatly reduced, and the cooling effect of the fuel rod located on the downstream side is increased.
In addition, the blade | wing part of a blade member may be installed in the somewhat downstream side of the ferrule element.

  As the material of the deflection blade, Inconel 600, SUS304, and SUS316 are preferable in view of bending resistance and high heat resistance, and Zircaloy is preferable in view of non-absorption of neutrons.

The invention according to claim 3 is a support grid of the fuel assembly for a pressurized water reactor,
The blade member has two blade bodies formed above the base, the base is mounted across four ferrule elements, and the two blade bodies are bent in opposite directions to each other. Is a supporting grid of a fuel assembly for a pressurized water reactor.

In the invention of this claim, the two (or two) blade bodies are bent in opposite directions, so that a deflection flow is generated around the entire periphery of the fuel rod. Further, since the base portion is provided, the attachment to the central portion of the channel formed by the four ferrule elements is facilitated.
The width and length of the blade body are (2 ^1/2 P−D) / 5 mm, where P is the fuel rod pitch and D is the outer diameter of the fuel rods, because of the effect of imparting deflection and flow path resistance. Therefore, the plate thickness is preferably about 0.1 mm to 1.0 mm in terms of strength and flow resistance reduction.
Moreover, especially when manufacturing separately from a ferrule element, since a shape is simple and it only needs to cut and bend the board | plate material of a material, a manufacturing process becomes easy.
Further, the base part of the blade member only blocks the cooling water flow only once, and the flow path resistance can be reduced also from this surface.
In addition, the blade part may be equipped with a short one for each channel for each channel, and the blade part is integrated through the vertical or horizontal direction of the support grid, so that a large number of blade parts are provided on the upper part of one thin plate. It may be formed.
Moreover, deflection and flow path resistance due to the blade at each support grid (pressure loss due to deflection) may be the same for convenience of manufacture and the like, vanes at the level of the middle of absolutely heat generation increases due to the interior of the furnace The deflection may be increased by increasing the bending or twisting of this, or since the deflection has already been given on the upstream side of the cooling water, there may be some changes such as the reverse on the downstream side.

The invention according to claim 4 is a support grid of the fuel assembly for a pressurized water reactor,
The blade member is formed with a blade portion via a constriction portion above the base portion, the base portion is mounted across four ferrule elements, and the blade portion is formed by twisting the constriction portion to form a blade. This is a support grid for a fuel assembly for a pressurized water reactor.

In the invention of this claim, since the blades are twisted, the deflection effect of the cooling water is good.
Further, particularly when manufactured separately from the ferrule element, the shape is simple, and the process is facilitated because the plate material is simply cut out and bent.
In addition, the width and length of the blade portion are preferably about (2 ^1/2 P−D) / 5 mm to about four times that in view of the effect of imparting deflection and the flow path resistance. Here, the meanings of P and D are the same as described above.

  The invention according to claim 5 is a fuel assembly for a pressurized water reactor, wherein the support grid according to any one of the above inventions is provided.

In the invention of this claim, since the support grid according to any one of the above inventions is provided, the fuel assembly for a pressurized water reactor has a low flow resistance and a sufficient margin for cooling the fuel rods. .
In addition, if at least one support grid of the invention is provided, it corresponds to the invention of this claim.

In the present invention, since the support grid has a structure in which ferrule elements such as circular tubes are arranged, the support grid is not located at a place where the cooling water flows at a particularly high speed, so that the flow resistance of the support grid is reduced. The load on the cooling water pump is also reduced.
In addition, since the thin deflection blades are provided in a place where the flow is fast, a large deflection effect can be obtained with a small flow path resistance.

  Hereinafter, the present invention will be described based on the best mode. In addition, this invention is not limited to the following embodiment. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(First embodiment)
In this embodiment, a tubular ferrule element is used. The support grid will be described below with reference to the drawings. FIG. 4 is a diagram conceptually showing a main part of the support grid according to the first embodiment of the present invention. In FIG. 4, 40 is a circular ferrule element, and 95 is a frame material for the outer frame. The support grid of the present embodiment is arranged so that the tubular ferrule elements 40 are arranged in a row in the horizontal direction, for example, 17 pieces in the horizontal direction, 17 pieces in the vertical direction in the same manner, and 289 in total form a square. An outer frame material 95 for bundling the entire ferrule element is provided on the outer periphery. The ferrule elements 40, the ferrule elements 40, and the frame material 95 for the outer frame are fixed by fitting or contact welding to form an integral support grid.

A fuel rod (not shown) passes through the ferrule element 40 from below to above. The support while restraining the fuel rod by the ferrule element 40 includes an elastic restraint band formed by punching the side surface of the ferrule element, a separately attached spring, a soft stop, a hard stop (all not shown), etc. Made through.
For convenience of explanation, the above description has been made assuming that ferrule elements are arranged at all positions. However, in places where there are other elements such as thimble tubes, the ferrule elements are not attached, and the four ferrules around them are not attached. For example, a bridging material (not shown) for connecting the elements may be provided.
In this support grid, a relatively thick member constituting the support grid is not located at the center of the subchannel formed by being surrounded by four fuel rods. For this reason, channel resistance decreases.
In the drawing, no window is formed on the outer peripheral side wall of the ferrule element 40. However, depending on the design conditions and operating conditions of each PWR, the convenience of mounting work such as a spring for supporting and restraining the fuel rod, the flow path It may be formed in order to further reduce the resistance.

(Second Embodiment)
This embodiment differs from the previous embodiment in that an octagonal tubular ferrule element is used.
FIG. 5 conceptually shows how each fuel rod 30 is supported and restrained by the inner wall of an octagonal tubular ferrule element via a soft stop 31 and a hard stop 32 in the present embodiment. FIG. 5 corresponds to FIG. 2 used for the description of the background art. Therefore, the description of the support and restraint of the fuel rod 30 is omitted.

Next, a structure for supporting and restraining a thimble tube having a diameter larger than that of the fuel rod will be described with reference to FIG. In FIG. 5, 35 is a thimble tube, 36 is a bridging material, and 50 is an octagonal tubular ferrule element. The ferrule element is not provided at the position where the thimble tube 35 passes, and the thimble tube passes through the support grid as it is, but the thimble of the two bridging members 36 connecting the four ferrule elements 50 around the thimble tube 35 is provided. The shape of the side surface facing the tube 35 is such that the thimble tube 35 is sandwiched from opposite directions. As a result, the thimble tube 35 is supported and restrained while also fixing the ferrule element 50.
Note that a spring or the like may be attached to the four surrounding ferrule elements 50 on the thimble tube 35 side, and the thimble tube 35 may be supported and restrained by the spring force.
In addition, a spring may be attached to the bridging member 36 and held.

(Third embodiment)
The present embodiment relates to a deflection blade. Conventionally, the deflection blades are formed integrally with the lattice plate, but in the present invention, they are manufactured separately from the ferrule elements 40 and 50. Hereinafter, this embodiment will be described with reference to FIG. In FIG. 6, reference numeral 70 denotes a blade member, reference numeral 71 denotes a base portion thereof, and reference numerals 72 and 73 denote blade bodies formed so as to protrude in a trapezoidal shape on the upper side thereof. As shown in the upper left diagram of FIG. 6, the blade member 70 has two blade bodies 72 and 73 bent in opposite directions, and in this state, as shown in the lower diagram of FIG. Both ends of 71 are sandwiched between two ferrule elements 40 and fixed. For this reason, it arrange | positions so that the space formed by four ferrule elements 40, ie, a subchannel part, may be straddled, and this produces big deflection | deviation in the cooling water between four surrounding ferrule elements.

The blade member 70 is manufactured separately from the ferrule element 40. For this reason, the shape of the blades can be optimized, and the thickness and length of the flow direction (vertical direction) can play its role without being damaged or deformed by the flow of cooling water. As long as it can be set to the minimum necessary value (in the past, since a part of the lattice plate was used, the shape and thickness of the plate were limited due to the lattice plate). For this reason, the channel resistance is further reduced.
In addition, although the blade member 70 shown in FIG. 6 is of a type that is attached to each channel, each blade member 70 extends from one outer frame frame of the support grid to the other outer frame frame facing each other. A pair of blade bodies may be formed corresponding to the channel.

(Fourth embodiment)
The present embodiment relates to the shape of a deflection blade. Hereinafter, the present embodiment will be described with reference to FIG. In FIG. 7, reference numeral 80 denotes a blade member, 81 denotes a base portion thereof, 82 denotes a blade lower portion formed by protruding in a semicircular shape on the upper side thereof, and 83 denotes a half-upside down portion above the blade lower portion 82. The blade portion is formed in a circular shape, and 84 is a constricted portion. In this blade member 80, as shown in the left and right views of FIG. 7, the blade portion 83 is twisted from the constricted portion 84, and in this state, both ends of the base portion 81 have two ferrule elements 40 respectively. It is sandwiched between and fixed.
The reason why the lower blade portion 82 is formed above the upper end of the ferrule element is to eliminate the influence of the ferrule element and increase the cooling water deflection effect.

In a fuel assembly, it is a figure showing notionally a mode that a support grid and a fuel rod are arranged and fixed. It is a figure which shows notionally that a fuel rod is supported and restrained in the conventional support grid. In the conventional support grid, it is a figure which shows notionally a mode that the lattice plate of a downstream is located in the center part in the subchannel surrounded by four fuel rods. It is a figure which shows notionally the structure of the principal part of the support grid of the 1st Embodiment of this invention. It is a figure which shows notionally the state which is restraining, supporting the principal part of the support grid of the 2nd Embodiment of this invention, and a fuel rod. It is a figure which shows notionally the element which attaches the blade | wing member as the 3rd Embodiment of this invention in the subchannel enclosed by the four ferrule elements. It is a figure which shows the principal part of the blade member as the 4th Embodiment of this invention.

Explanation of symbols

10 Lattice plate (lateral direction)
20 Lattice plate (vertical direction)
21 Blade (conventional technology)
30 Fuel rod 31 Soft stop 32 Hard stop 35 Thimble tube 36 Bridging material 38 Subchannel 39 near fuel rod Subchannel 40 in the center Circular ferrule element 50 Octagonal ferrule elements 70, 80 Blade member (Embodiment)
71, 81 Blade member bases 72, 73 Blade body 82 Blade lower portion 83 Blade portion 90 Fuel assembly 91 Upper nozzle 92 Lower nozzle 93 Support grid 93a Support grid (integrated with upper nozzle)
95 Frame material 96 for outer frame Welding nugget

Claims (5)

  A supporting grid for a fuel assembly for a pressurized water reactor, comprising circular or octagonal ferrule elements arranged in a substantially square lattice pattern.   A vane member for deflecting cooling water around the fuel rod in a subchannel formed by the four ferrule elements adjacent to each other is attached across the four ferrule elements. The support grid of the fuel assembly for pressurized water reactors of Claim 1.   The blade member has two blade bodies formed above the base, the base is attached across four ferrule elements, and the two blade bodies are bent in opposite directions. A supporting grid for a fuel assembly for a pressurized water reactor according to claim 1 or 2.   The blade member is formed with a blade portion via a constriction portion above the base portion, the base portion is attached across four ferrule elements, and the blade portion is formed by twisting the constriction portion to form a blade. The supporting grid for a fuel assembly for a pressurized water reactor according to claim 1 or 2, A fuel assembly for a pressurized water reactor, wherein the support grid according to any one of claims 1 to 4 is provided.

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