JPH01217294A - Fuel rod spacer - Google Patents

Abstract

PURPOSE:To reduce pressure loss of coolant flow and improve the limit output of an fuel assembly by setting a conical projection in a lattice frame of a fuel rod spacer. CONSTITUTION:A lattice partition space 4 in which a fuel rod is inserted by a side frame 2 and a lattice frame 3 is formed to be a fuel spacer 1. Conical projections 5 extending upward and downward of a fuel spacer 1 are set on the crossing part of the lattice frame 3. The conical projections 5 form the peaks on the lines extending upward and downward of the crossing parts of the lattice frame 3 and is formed so as to make rills of the center part between the crossing parts. Elastic supporting fittings 6 supporting a fuel frame are jointed so as to sandwich the lattice frame 3 by both upper and lower ends thereof and slender streamline fixed projections 7 are set on the center of the lattice frame 2 and the side frame 2. Thus, since a sudden change of flow passage cross section in the neighborhood of the spacer is eliminated, pressure loss is reduced and liquid film breakage on the surface of the fuel rod is eliminated, the limit output of an fuel assembly can be improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a fuel rod spacer used to space and support a large number of fuel rods in a nuclear reactor fuel assembly; More specifically, the present invention relates to the above-mentioned fuel rod spacer for the purpose of increasing critical output and reducing pressure loss of coolant flow.

(Prior Art) FIG. 6 is a sectional view illustrating a fuel assembly of a conventional boiling water reactor. As shown in this figure, the fuel assembly 10 includes a plurality of fuel rods 14 (including water rods) arranged in a square lattice in a fuel channel 11 with both ends supported by upper tie plates 1 to 12 and lower tie plates 13, respectively. In order to prevent bending and vibration of the fuel rods 14, a plurality of fuel rod spacers 15 are provided in the axial direction between the upper tie plate 12 and the lower tie plate 13 to support the fuel rods at a distance. It has become.

The structure of the fuel rod spacer will be explained with reference to FIGS. 7 to 10.

FIGS. 7 and 8 are a plan view and a front view, respectively, of a fuel rod spacer. This spacer 20 is attached to the side frame 21
A fuel rod 14 is inserted into each shell 22, and a cooling space is provided in a substantially rectangular cylindrical space surrounded by the side walls of four adjacent shells 22. A cooling 44 passage 23 through which the material flows is formed. Each shell 22 is provided with an elastic support 24 and a fixing protrusion 25, by which the fuel rod 14 is elastically supported at a slight distance from the side wall of the shell 22.
A trapezoidal port 126 is secured to the outside of the fuel rod spacer 20 to support the fuel rod spacer 20 within the fuel channel. The constituent materials of these spacers are Zircaloy, which has low thermal neutron absorption, except that the elastic support member 24 is made of elastic Inconel material.

9 and 10 are a plan view and a partially cutaway front view of another fuel rod spacer. This spacer 30 is
A lattice frame 32 is provided in the side frame 31 to form a lattice compartment space 33, and the lattice frame 32 is provided with fixing protrusions 34 and elastic supports 35, which allow the grid frame 32 to be inserted into the lattice compartment space 33. This structure supports the fuel rods 14 at a distance. 36 is a lobe for supporting the spacer 30 within the fuel channel.

(Problems to be Solved by the Invention) Nowadays, it is desired to expand operational flexibility, such as automatic control of nuclear couplants and introduction of daily load following operation. In line with this demand, for example, in boiling water reactors, in order to further improve the thermal-hydraulic characteristics of the reactor core, development is underway to improve the safety of the reactor core, expand the thermal margin, and reduce core pressure loss. .

Here, if we focus on the core pressure loss, its breakdown is from the bottom to the top of the core: orifice pressure loss, lower tie plate pressure loss, spacer pressure loss, position pressure loss, upper tie plate pressure loss, and friction pressure loss and acceleration pressure loss are added. .

Of these pressure losses, the pressure loss occurring at the fuel rod spacer portion, that is, the spacer pressure loss, accounts for approximately 20%.

Therefore, reducing the spacer pressure loss greatly reduces the core pressure loss.

However, in conventional fuel spacers, the axial length of each shell or lattice compartment space is the same, so the area A of the coolant flow path formed along the axial direction of the fuel assembly as shown in FIG. The pressure decreases and increases rapidly by about 20% at the end of the spacer, which causes pressure loss due to expansion and contraction of the flow path. Furthermore, the protrusions provided on the spacer for supporting the fuel rods disturb the flow of coolant within the spacer, further increasing pressure loss. In general, the lattice frames have openings that communicate with adjacent lattice spaces for installing elastic supports, which create lateral flows within the spacer, thereby increasing pressure losses in the spacer.

On the other hand, in normal operation of a boiling water reactor, the coolant is steam -
Water flows through the assembly in a two-phase flow state, with 2/2 of the axial direction
At a distance of 3 to 3/4, the flow pattern is such that liquid flows in the form of a film on the surface of the fuel rods, and vapor flows in the space between the fuel rods with droplets. Therefore, even in a steam-hydraulic phase flow state, the fuel rods are stably cooled with liquid. However, the first
As shown in FIG. 2(b), in the spacer part that becomes an obstacle to the flow, the liquid film 37 is thinned because the vapor flow suddenly changes direction or generates a vortex at the part where it collides with the lattice frame 32. This causes a sudden temperature rise in the cladding tube, which is thought to be due to disappearance or separation of the liquid film on the upstream side of the spacer. 12(a) is a partially enlarged view of the lattice type spacer shown in FIG. 9, and FIG. 12(b) is a partially enlarged view of the lattice type spacer shown in FIG.
) is a longitudinal sectional view taken along the line A-A, showing the state of coolant flow.

Such an increase in humidity in the cladding tube has a negative effect on the health of the fuel, so in core design, the maximum output that reaches this temperature increase is called the limit output, and it becomes the output limit value of the fuel assembly.

As described above, since the fuel spacer has a large effect on the pressure loss and critical output of the fuel assembly, improvements in this respect are desired.

The present invention has been made in response to the above problems, and an object of the present invention is to provide a fuel rod spacer that can reduce the pressure loss of the coolant flow and improve the critical output of the fuel assembly. be.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention forms a lattice compartment space by side frames and a lattice frame, and supplies fuel to the lattice compartment space by projections and elastic supports provided on the lattice frame. The present invention relates to a fuel rod spacer in which rods are supported at a distance, wherein the lattice frame is provided with chevron-shaped protrusions whose cross-sectional area gradually decreases toward the upstream and downstream sides of the coolant.

(Function) Since the fuel rod spacer of the present invention has chevron-shaped protrusions on the lattice frame whose cross-sectional area gradually decreases toward the upstream and downstream sides of the coolant, changes in the cross-sectional area of the axial flow path near the spacer are prevented. It becomes gentler, and there is no sudden increase or decrease in the flow path as in the conventional spacing. Therefore, the pressure loss due to the spacer is reduced compared to the conventional case. In addition, the cooling (A flow) becomes smoother and the generation of vortices is reduced, so there is no separation of the liquid film and the limit output is improved.

Incidentally, in the present invention, the above-mentioned effects can be roughly improved by forming the lattice frame, the elastic support, and the projections into shapes as shown in the following embodiments.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a fuel rod spacer illustrating an embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a longitudinal sectional view taken along line A--A in FIG. 2.

As explained in these figures, the fuel rod spacer 1 of the present invention has a side frame 2 and a lattice frame 3 forming a lattice compartment space 4 into which the fuel rods are inserted, as in the conventional case. A chevron-shaped protrusion 5 extending upward and downward of the spacer 1 is provided at the intersection thereof. As shown in FIG. 3, this chevron-shaped protrusion 5 has a shape that forms an apex on the vertical extension line of the intersection portions of the lattice frame 3, and a valley at the center between the intersection portions. , the cross-sectional shape at the intersection is cross-shaped. The cross-sectional area of this chevron-shaped protrusion 5 gradually decreases toward the tip. In addition, side frame 2
has a square shape with rounded corners, and a trapezoidal lobe 8 is installed to support the spacer within the channel box.

In this way, in the vicinity of the spacer of this embodiment, since the chevron-shaped protrusions 5 whose cross-sectional area decreases upward and downward are installed on the lattice frame 3, the cross-sectional area of the coolant flow path in the axial direction within the spacer The change becomes gradual, and the cross-sectional area of the flow path changes without rapid increase or decrease as shown in FIG. Therefore, the pressure loss caused by the rapid increase and decrease of the cross-sectional area of the flow path as in conventional spacers is reduced, and the liquid film on the surface of the fuel rods is prevented from breaking, so that the limit output is improved.

In this embodiment, as shown in FIG. 2, elastic supports 6 and fixing protrusions 7 for supporting fuel rods on the lattice frame 3 are installed at the center of the lattice frame 3.

As shown in FIG. 3, this elastic support 6 consists of a striped part 6a and a leg part 6b. They are joined so that they can slide. The tips of the leg portions 6b and the tips of the lattice frame 3 are cut into blades to reduce flow resistance. On the other hand, the fixing protrusion 7 has an elongated streamlined shape, and its axial direction coincides with the flow direction of the coolant. The fixing protrusion 7 is also provided on the side frame 2.

In this way, the elastic supports 6 are joined at both the upper and lower ends of the lattice frame 3 so as to sandwich the lattice frame 3, so there is no need to provide an opening in the lattice frame for attaching the elastic supports as in the conventional case, and the spacer The pressure loss due to the occurrence of lateral flow within the tank is eliminated, and the pressure loss is greatly reduced. Further, since the fixed protrusion 7 has a streamlined shape, turbulence in the coolant flow due to the fixed protrusion is reduced, and pressure loss is reduced.

The flow of the coolant inside the spacer is as shown in FIG.

That is, compared to the flow in the conventional spacer (see FIG. 12(b)), the flow in the spacer becomes smoother, and the flow of steam toward the fuel rods is reduced. In addition, since the generation of vortices is eliminated, the thinning of the liquid film 9 on the surface of the fuel rod is alleviated.
Breaking of the liquid film is reduced.

[Effects of the Invention] As explained above, since the fuel rod spacer of the present invention has the above-mentioned chevron-shaped protrusions on the lattice frame, sudden changes in the flow passage area near the spacer are eliminated, and pressure loss is reduced. Decrease. Furthermore, the liquid film rupture on the fuel rod surface is eliminated, and the limit output of the fuel assembly is improved.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a fuel rod spacer illustrating an embodiment of the present invention, Figure 2 is a plan view of the fuel rod spacer in Figure 1, and Figure 3 is taken along line A-A in Figure 2. A vertical cross-sectional view of Hayabusa, FIG. 4 is a diagram explaining the fuel rod spacer near △ in FIGS. 1 to 3, and FIG. 6 is a cross-sectional diagram explaining the structure of a fuel assembly of a conventional boiling water reactor. 7 and 8 are a plan view and a front view, respectively, of a conventional fuel rod spacer, FIG. 9 and 10 are a plan view and a front view, respectively, of another conventional fuel rod spacer, and FIG. 11 is a plan view and a front view, respectively, of a conventional fuel rod spacer. Figure 12 is a diagram showing the change in axial coolant flow path area when fuel rod spacers are used. Figure 12 is a diagram explaining the influence of conventional fuel rod spacers on coolant flow. (a) is Figure 9. A partially enlarged view of
(b) is a diagram showing the state of coolant flow in a cross section taken along line A-A in figure (a). DESCRIPTION OF SYMBOLS 1... Fuel rod spacer, 2... Side frame 3... Lattice frame, 4... Lattice section space 5... Chevron projection, 6... Elastic support 6a... Elastic support Bullet portion 6b...Leg portion 7 of the elastic support device...Fixing protrusion, 8...Lob 14...Fuel rod agent Patent attorney Noriyuki Chika Kenichi Figure 1 2 Figure 3 Figure 4 Figure 5 ■ Figure 6 Figure 7 Figure 9 Figure i0

Claims (1)

[Claims] (1) A fuel rod spacer in which a side frame and a lattice frame form a lattice compartment space, and fuel rods are supported at a distance in the lattice compartment space by protrusions and elastic supports provided on the lattice frame. A fuel rod spacer characterized by being provided with a chevron-shaped protrusion whose cross-sectional area gradually decreases toward the upstream and downstream sides of the coolant.