JP2008064464A - Fuel assembly for pressurized water reactor and its support grid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide swirl vanes with a low flow resistance and a high stirring effect for fuel rods positioned adjacent to a thimble tube liable to cause large output, having small thermal margin; and to provide a fuel assembly and its support grids for a pressurized water reactor with the swirl vanes disposed on the support grid. <P>SOLUTION: This fuel assembly for the pressurized water reactor has some or all swirl vanes adjacent to the thimble tube larger than swirl vanes not adjacent to the thimble tube, at least in some of the support grids. The area of the swirl vanes adjacent to the thimble tube in at least a part of the support grids is set more than 1.0 time and not more than 2.25 times of the area of the swirl vanes not adjacent to the thimble tube. The support grids for the fuel assembly are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel assembly for a pressurized water reactor, and in particular, a swirl vane installed on a support grid has a larger shape and size at a position adjacent to a thimble tube than a position not adjacent to the pressurized water reactor. About.

  A schematic overall structure of a fuel assembly for a pressurized water reactor is shown in FIG. In FIG. 1, 10 is an upper nozzle, 20 is a lower nozzle, 30 is a support grid, 30a is an uppermost support grid, 30b is a lowermost support grid, and 40 is a fuel rod, 50 is a thimble tube.

In the fuel assembly, the upper nozzle 10 and the lower nozzle 20 are fixed by a thimble tube 50. Further, the fuel rods 40 are arranged in, for example, 17 × 17, and the upper end portion thereof is fixed to the uppermost support grid 30a integrated with the upper nozzle 10, and the lower end portion thereof is also integrated with the lower nozzle 20. It is fixed to the lowermost support grid 30b, and is further elastically supported by several support grids 30 at some midpoints.
In the 17 × 17 arrangement of the fuel rods, the thimble tube 50 into which control rods, combustible poison rods, instrumentation devices, etc. are inserted is usually arranged instead of some fuel rods. It is.

For example, if the fuel rods are arranged in a 17 × 17 arrangement, the support grid 30 includes 18 grid plates in the horizontal and vertical directions, including the frame material for the outer frame, like vertical and horizontal lines (or eyes) on the grid. In the structure where they are arranged, they are fitted to each other at a place where they intersect (hereinafter referred to as “grid points”) and welded as necessary. A fuel rod or thimble tube passes through each grid formed by crossing the grid plates in the horizontal and vertical directions.
With reference to FIG. 2, the state in which the fuel rod or the thimble pipe penetrates the support grid will be described in detail. FIG. 2 is a view conceptually showing a portion where fuel rods and thimble tubes are adjacently penetrating through the adjacent grids of the support grid, as viewed from above.

  In FIG. 2, 31 is a lattice plate provided in the horizontal direction (horizontal direction in the figure) in the horizontal plane, and 32 is also the vertical direction (in the actual arrangement, a direction orthogonal to the horizontal direction in the horizontal plane, but in the figure, so-called It is a lattice plate provided in the vertical direction), 35 is a soft stop, and 36 is a hard stop.

  Reference numeral 60 denotes a blade (hereinafter, generally referred to as “swirling blade”) for turning the cooling water flowing from the lower side to the upper side by giving a horizontal (lateral) flow. Reference numeral 70 denotes a subchannel (cooling water passage) in which the cooling water swirls and flows from the bottom to the top as a whole. In FIG. 2, the sub-channel 70 is divided into four narrow flow paths by a cross-shaped partition plate formed by the lattice plates 31 and 32 in the horizontal direction and the vertical direction. It becomes one flow path.

The lattice plate 31 in the horizontal direction and the lattice plate 32 in the vertical direction are fitted to each other at lattice points, and are welded at positions opposite to the direction in which the swirl vanes are inclined.
Two soft stops 35 and two hard stops 36 are installed in each cell through which the fuel rod penetrates, and elastically support the fuel rod 40 that penetrates the inside of the cell.

In addition, the swirl vane 60 provided on the upper part of each square cell through which the fuel rod 40 penetrates has two trapezoidal shapes for each cell formed on the upper end surface in the vicinity of the lattice point of the lattice plates 31 and 32. Are projected in opposite directions. FIG. 3 shows this state three-dimensionally. By this bending, the cooling water flowing from the lower side to the upper side of the outer periphery of the fuel rod is swirled to achieve good mixing and increase the cooling effect (Patent Document 1).
Since the thimble tube 50 does not generate heat, the swirl vanes 60 where the thimble tube 50 penetrates are attached so as to be directed away from the thimble tube 50 and directed toward the fuel rod 40. .
The horizontal (horizontal) width and the vertical length of the swirl vane are about 1.4 times (1.4P-D) / 5mm, where P is the fuel rod pitch and D is the diameter, The thickness is about 0.1 mm to 1 mm.

If the swirling effect of the cooling water by the swirling blade is small, the fuel rod is not sufficiently cooled, and in the worst case, a boiling transition (nuclear boiling) occurs, which may lead to a rapid rise in the temperature of the fuel rod and eventually to burning. For this reason, various inventions have been made in order to further exert the effect of the swirl vanes that give the swirl to the coolant that flows from the lower part to the upper part of the outer periphery of the fuel rod to achieve good mixing and increase the cooling effect (patents) Reference 1).
JP-A-5-172974

However, if the swirling blades are too small, the swirling effect of the cooling water is reduced, and if they are too large, the swirling effect is sufficient, but the flow resistance increases, and the load and power consumption of the cooling water circulation pump increase. . For this reason, it is set to an appropriate size in consideration of these lengths, and in the current pressurized water reactor, the length in the flow path direction is about 10 mm and the width is about 5 mm.
However, the demand for reducing the power generation cost for pressurized water reactors in recent years has become increasingly severe.
For this reason, with respect to the swirl vanes, there is an increasing demand for a swirl efficiency of the cooling water that is even better and that the flow path resistance is low.

In addition, the demand for safety for nuclear power generation has become increasingly severe in recent years. However, as described above, since the proper effect of swirl blades is closely related to the safety of fuel rods, the swirl imparting effect is more than present. Therefore, it is desired to develop a swirl vane that can exhibit a cooling effect and contribute to safety.
In addition, development of a fuel assembly having a support grid on which such swirl blades are installed is desired.

  The present invention has been made for the purpose of solving the above-described problems. In at least some of the support grids, the swirl blades installed on the support grid of the fuel assembly are swirled at positions adjacent to the thimble pipes. The shape and dimensions of the blades are larger than the swirl blades at positions not adjacent to the thimble tubes. The invention of each claim will be described below.

The invention described in claim 1
In at least some of the support grids, a part or all of the swirl blades adjacent to the thimble tube are made larger than swirl blades not positioned adjacent to the thimble tube. Fuel assembly.

  Although cooling water has entered the thimble tube, the neutron moderating effect by the water is very large. Therefore, the neutron spectrum in the vicinity of the thimble tube is soft and easily absorbed by uranium 235. As a result, the output of the fuel rod at the position adjacent to the thimble pipe tends to increase as compared with the fuel rod at the position not adjacent to the thimble pipe, and as a result, the amount of heat generation tends to increase. For this reason, the fuel rods at positions adjacent to the thimble tubes tend to have severe thermal conditions.

  Also, since the thimble tube is larger in diameter than the fuel rods, the subchannel surrounded by one thimble tube and three fuel rods has a broken channel compared to the subchannel surrounded by four fuel rods. The area is small, and the thermal condition of the fuel rod located adjacent to the thimble tube is severe from this surface.

  However, in the fuel assembly according to the present invention, in at least some of the support grids, the swirl vanes attached to the support grid are positioned adjacent to the thimble pipe and not positioned adjacent to the thimble pipe. The area, shape, and dimensions are larger than those. As a result, the effect of imparting swirling to the cooling water is increased, and the cooling water swirls strongly by that amount, and further, mixing and stirring are increased, and the cooling effect of the fuel rod is increased. As a result, the fuel rod at the position adjacent to the thimble tube is sufficiently cooled even if the output is larger than the fuel rod at the position not adjacent to the thimble tube. In addition, since the ratio of the swirl vanes at such positions is small, the adverse effect on the flow path resistance due to the enlarged swirl vanes is slight.

  Here, “a part or all of the swirl blades adjacent to the thimble tube” means a swivel located on the thimble tube side and the anti-thimble tube side of the four apexes (lattice points) of the mesh through which the thimble tube passes. It means a part of or all of the swirling blades or swirling blades that swirl the cooling water in the subchannel surrounded by one thimble tube and three fuel rods.

  In addition, “at least some of the support grids have part or all of the swirl vanes adjacent to the thimble pipes” means that the temperature of the cooling water passing through the support grid below the fuel assembly is compared. Therefore, even a fuel rod located near the thimble tube may have a sufficient thermal margin. Moreover, since the neutron density becomes low in the vicinity of the thimble tube for the burnable poison rod, there may be a thermal margin as well. For these reasons, there may be a case where only the swirl vanes at positions adjacent to some thimble pipes of some support grids are enlarged, but these cases are also included in the present invention.

  There has also been proposed a support grid having a structure in which a ferrule structure is adopted instead of a lattice plate by a lattice plate in the elastic support portion of the fuel rod, and swirl vanes are attached so as to straddle between the ferrules. Even in this case, as long as the swirl vane at a position adjacent to the thimble tube is larger than the swirl vane at a position not adjacent to the thimble tube, the present invention is included in the present invention.

Invention of Claim 2 is the said fuel assembly for pressurized water reactors,
The area of the swirl vane at a position adjacent to the thimble tube in the at least part of the support grid is more than 1.0 times and not more than 2.25 times the area of the swirl blade at a position not adjacent to the thimble tube. This is a fuel assembly for a pressurized water reactor.

  In the invention of this claim, the area of the swirl vane in the position adjacent to the thimble tube in the at least some support grid is 1.0 times the area of the swirl vane in the position not adjacent to the thimble tube of the support grid. Since it is a range that does not exceed 2.25 times, the cooling water in the channel around each fuel rod is swirled according to the output of the fuel rod, and the flow resistance of the entire swirling blade is reduced. An appropriate cooling effect can be obtained while suppressing the increase.

Invention of Claim 3 is the said fuel assembly for pressurized water reactors,
In the 2 to 4 support grids from above, the area of the swirl vane at a position adjacent to the thimble tube is more than 1.0 times and not greater than 2.25 times the area of the swirl blade at a position not adjacent to the thimble tube. This is a pressurized water nuclear reactor fuel assembly.

  In the invention of this claim, the area of the swirl vane at the position adjacent to the thimble tube of the support grid of 2 to 4 pieces (2 to 4 stages, and the second piece is particularly severe) from the top which is thermally severe, Since the area of the swirl vane at a position not adjacent to the thimble tube exceeds 1.0 times and does not exceed 2.25 times, the cooling effect is increased only at thermally severe points, and the increase in overall flow resistance is minimized. Therefore, the effect of the invention of claim 1 is further exhibited.

The invention according to claim 4
A fuel assembly for a pressurized water reactor, wherein a part or all of the swirl blades adjacent to the lattice passing through the thimble tube are made larger than the swirl blades located not adjacent to the lattice passing through the thimble tube It is a support grid for the body.

  The invention of this claim is obtained by capturing the invention of claim 1 from a support grid.

The invention according to claim 5 is a support grid of the fuel assembly for a pressurized water reactor,
Pressurized water characterized in that the area of the swirl vane at a position adjacent to the grid through which the thimble pipe passes is 1.0 to 2.25 times greater than the area of the swirl blade at a position not adjacent to the grid through the thimble pipe It is a support grid of a fuel assembly for a nuclear reactor.

  The invention of this claim is obtained by capturing the invention of claim 2 from the support grid.

The invention according to claim 6 is a support grid of the fuel assembly for a pressurized water reactor,
The area of the swirl vane at a position adjacent to the lattice passing through the thimble pipe is mounted at 2 to 4 positions from above the fuel assembly, and the area of the swirl vane at a position not adjacent to the lattice passing through the thimble pipe is 1.0. It is a support grid of a fuel assembly for a pressurized water reactor characterized by exceeding twice and not exceeding 2.25 times.

  The invention of this claim is obtained by capturing the invention of claim 3 from the support grid.

  In the present invention, since some or all of the swirl vanes located adjacent to the thimble pipe are larger than the swirl vanes located not adjacent to the thimble pipe, the fuel rod tends to have a large output because it is adjacent to the thimble pipe. The cooling water flowing around is sufficiently swirled, and the fuel rods at such positions are cooled well. In addition, since the ratio of the swirl vanes at such positions is small, the adverse effect on the flow path resistance due to the enlarged swirl vanes is slight.

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

A swirl vane according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a plan view conceptually showing the characteristics of the swirl vane according to the embodiment of the present invention. In FIG. 4, 61 is a swirl blade attached adjacent to the thimble tube, and 62 is a swirl blade attached at a position not adjacent to the thimble tube. Reference numeral 71 denotes a subchannel (a region surrounded by one thimble tube and three fuel rods) around the thimble tube, and 72 denotes a subchannel surrounded by four fuel rods. 4 is the same location as shown in FIG. 2, but the swirl vane 61 at a position adjacent to the thimble tube is made larger than the swirl blade 62 at a position not adjacent to the thimble tube.

  Specifically, the length and width of the swirl vane 61 at positions adjacent to the thimble tube are 12 mm and 6 mm, respectively, and the length and width of the swirl vane 62 at positions not adjacent to each other are 10 mm and 5 mm, respectively. For this reason, the swirl vane 61 at a position adjacent to the thimble tube is approximately 40% larger in area than the swirl vane 62 at a position not adjacent to the thimble tube.

  Therefore, in the subchannel 71 surrounded by the thimble tube and the three fuel rods, the projected area in the flow direction of the swirl blade is larger than in the subchannel 72 surrounded by the four fuel rods, Accordingly, the cooling water is swirled and the agitation is increased, and the cooling effect is increased.

  FIG. 5 shows the influence of the increase or decrease in the projected area ratio on the critical heat flux ratio (DNB ratio) with reference to a swirl blade having a certain shape and size. The horizontal axis in FIG. 5 is the projected area ratio, and the vertical axis is the critical heat flux ratio. FIG. 5 shows that the critical heat flow rate ratio monotonously increases as the projected area ratio increases. For this reason, it can be seen that if the swirl vane adjacent to the thimble tube is made larger, the thermal margin of the fuel rod at the position adjacent to the thimble tube increases accordingly.

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 top view which shows notionally the mode of the location where the fuel rod is elastically supported by the lattice board in a support grid. It is a figure which shows notionally a mode that the turning blade | wing is formed in the conventional support grid. It is a figure which shows notionally the characteristic of the turning blade | wing of embodiment of this invention. It is a figure which shows notionally the influence which the increase in the projected area ratio of a rotary blade has on the increase in the critical heat flux ratio of a fuel rod.

Explanation of symbols

10 Upper nozzle 20 Lower nozzle 30 Support grid 30a Top support grid 30b Bottom support grid 31 Grid plate (lateral direction)
32 Lattice plate (vertical direction)
35 Soft stop 36 Hard stop 40 Fuel rod 50 Thimble tube 60 Swirling blade 61 Swirling blade (adjacent to the thimble tube)
62 Swivel blade (not adjacent to thimble tube)
70 Subchannel 71 Subchannel 72 around the thimble tube Subchannel surrounded by four fuel rods

Claims (6)

  In at least some of the support grids, a part or all of the swirl blades adjacent to the thimble tube are made larger than swirl blades not positioned adjacent to the thimble tube. Fuel assembly.   The area of the swirl vane at a position adjacent to the thimble tube in the at least part of the support grid is more than 1.0 times and not more than 2.25 times the area of the swirl blade at a position not adjacent to the thimble tube. The fuel assembly for a pressurized water reactor according to claim 1.   In the 2 to 4 support grids from above, the area of the swirl vane at a position adjacent to the thimble tube is more than 1.0 times and not greater than 2.25 times the area of the swirl blade at a position not adjacent to the thimble tube. The fuel assembly for a pressurized water reactor according to claim 1.   A fuel assembly for a pressurized water reactor, wherein a part or all of the swirl blades adjacent to the lattice passing through the thimble tube are made larger than the swirl blades located not adjacent to the lattice passing through the thimble tube Body support grid.   The area of the swirl vane at a position adjacent to the lattice passing through the thimble tube is more than 1.0 times and not greater than 2.25 times the area of the swirl blade at a position not adjacent to the lattice passing through the thimble tube. Item 5. A support grid for a fuel assembly for a pressurized water reactor according to item 4. The area of the swirl vane at a position adjacent to the lattice passing through the thimble pipe is mounted at 2 to 4 positions from above the fuel assembly, and the area of the swirl vane at a position not adjacent to the lattice passing through the thimble pipe is 1.0. The supporting grid for a fuel assembly for a pressurized water reactor according to claim 4, wherein the supporting grid exceeds 2 times and does not exceed 2.25 times.

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