JPS6049271B2 - fuel rod spacer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel rod spacer that supports a large number of fuel rods installed in a fuel channel of a nuclear reactor in proper positions, and the present invention relates to a fuel rod spacer that supports a large number of fuel rods installed in a fuel channel of a nuclear reactor in a proper position. This invention relates to a fuel rod spacer that can be introduced into an outer frame.

Conventionally, this type of fuel rod spacer is constructed as shown in FIGS. 1 and 2.

This fuel rod spacer 1 is one of the elements constituting a plurality of fuel assemblies 4 that are replaceably installed in the core 3 of the nuclear reactor 2 shown in FIG. As shown in FIG. 4, each fuel assembly 4 supports a large number of fuel rods 5, 5 and one order rod 6 with an upper tie plate 7 and a lower tie plate 8, and supports a long cylindrical fuel assembly. Fuel spacers 1 are installed in the channel 9 at multiple locations in the longitudinal direction of the fuel rods 5.
, 1 are installed to support each fuel rod 5, 5 in an appropriate position. Each fuel rod spacer 1 has the first to
As shown in Figure 2, there are corner hands 14, 15, 1 at one end.
4 side hands 101 each having 6 and 17,
11, 12, and 13 are mutually connected to form a substantially square cylindrical outer frame 18, and a plurality of dividers 1 are installed in this outer frame 18.
9 and bars 20 are intersected to form a large number of substantially square fuel rod passages 21, 21.

S-shaped springs 22, 22 are formed in the portion of the debug 19 facing each fuel rod passage 21, and a square spring 23 having an outwardly protruding spring member 24 is formed at the intersection of the bars 20. , each side hand 10, 11, 1
Ropes 25, 25a are formed in the portions facing the fuel rod passages 21 of the 2nd and 1st rods 3, and the corner hands 14, 15,
A pair of spherical protrusions 26, 26 are formed on each of the protrusions 16, 17. The fuel rods 5, 5 inserted into each of the fuel rod passages 21 in the central part are elastically supported by two S-shaped springs 22, 22 and a spring material 24, respectively, and are inserted into the fuel rod passages 21 in the corner part. The fuel rods 5, 5 inserted into each fuel rod passage 21 are elastically supported by two spherical protrusions 26, 26 and the spring material 24, respectively, and the fuel rods 5, 5 inserted into each fuel rod passage 21 in the peripheral part , 5 are S-shaped springs 22, respectively.
It is elastically supported by spring members 24 and lobes 25. This fuel rod spacer 1 includes each corner hand 14,1
Large lobes 25a, 25a adjacent to 5, 16, 17
is brought into contact with the inner circumferential surface 27 of the fuel channel 9 and is supported at a proper position within the fuel channel 9. The fuel rods 5, 5, which are thus supported in proper positions within the fuel channel 9 by the fuel rod spacers 1, 1, are attached to the lower tie plate 8.
It is cooled by a coolant such as light water supplied into the fuel channel 9 through the nose-like piece 28 of the fuel.

That is, the coolant absorbs the thermal energy possessed by the fuel rods 5 while rising through the fuel rod passages 21, 21 and the gap 29 between the inner peripheral surface 27 of the fuel channel 9 and the outer frame 18. Cool the fuel rods 5,5. In order to prevent the fuel rods 5, 5 from burning out and to increase the critical power of the fuel rods 5, 5, the coolant supplied in the fuel channel 9 is applied to each of the fuel rods 5, 5. It is necessary to increase the cooling efficiency by placing it in contact with

When examining the distribution of the coolant within the fuel channel 9, it is found that the coolant tends to be concentrated near the inner peripheral surface 27 rather than the center of the fuel channel 9.

this is,! This is because the central portion is at a high temperature due to the nuclear reaction between the fuel rods 5, 5, whereas the inner circumferential surface 27 is at a low temperature, so that the coolant flows toward the inner circumferential surface 27 where the temperature is low. Therefore, a coolant flow rising along the inner circumferential surface 27 is formed in the gap 29 . In order to improve the cooling efficiency of the J fuel rods 5, it is sufficient to introduce a coolant flow along the inner circumferential surface 27 into the fuel rod spacer 1. However, the conventional fuel rod spacer 1 has an outer frame 18 as shown in FIG.
The lobes 25, 25a formed on the outer frame 18 are simply formed to bulge outward, so that the coolant flow 30 along the inner circumferential surface 27 is directed away from the outer frame 18. It cannot be introduced into 18.

Therefore, as shown in the figure, the coolant flow 30 cannot be effectively used for cooling, and the amount of the coolant flow 31 flowing around the outer periphery of the fuel rods 5 is small. Therefore, when conventional fuel rod spacers are used, the cooling efficiency of the fuel rods is low, and the limit output of the nuclear reactor is also low as shown by the broken line A in FIG. 7. The present invention eliminates the above disadvantages, allows the coolant flow along the inner peripheral surface of the fuel channel to be guided into the outer frame, increases the cooling efficiency of the fuel rods, and increases the critical power of the reactor. The purpose is to provide a fuel rod spacer that can

As shown in FIG.
A coolant introduction path 32 is provided to guide the coolant into the outer frame 18.

This coolant introduction path 32 connects a portion of the outer frame 18 to the inner circumferential surface 2.
7, and its lower end is opened to allow a coolant flow 30 to flow therethrough.
The present invention will be described in more detail below with reference to the embodiments shown in FIGS. 8 to 14.

8 to 11 show an embodiment of the present invention, in which lobes 25, 25a formed on the outer frame 18 are used to create a coolant introduction path 3.
2 was formed.

The lobes 25, 25a of this embodiment are formed at a portion of the outer frame 18 in the axial direction.

The large lobe 25a adjacent to each corner hand 14, 15, 16, 17 brings the back of the bulge into contact with the inner circumferential surface 27 of the fuel channel 9, as shown in FIG. An opening 33 is formed by cutting the lower end of the lobe 25a and bending it outward until it abuts the inner peripheral surface 27.
2 is formed. On the other hand, the small lobe 25 has a first
As shown in FIG.
7 to form an opening 33a, and this opening 33a and the inside of the lobe 25 form a coolant introduction path 32. 12 to 14 show another embodiment of the present invention, in which the lobes 25, 25a are formed in a size that reaches the lower end of the outer frame 18 in the axial direction, and a coolant introduction path 32 is provided.

The large lobe 25a is formed so that its spine 35, which abuts against the inner circumferential surface 27 of the fuel channel 9, reaches the lower end of the outer frame 18, as shown in FIGS.

Therefore, the lower end of the lobe 25a has a chevron-shaped opening as shown in FIG. 15, and a coolant introduction path 32 is formed by this chevron-shaped opening and the inside of the lobe 25a. The small lobe 25 has a lower end 36 that is continuous with the back and bulges out until it reaches the inner circumferential surface 27, forming a similar chevron-shaped opening at the lower end. A coolant introduction path 32 is formed by this chevron-shaped opening and the inside of the lobe 25 . Next, the operation of the present invention will be explained.

As the coolant flow 30 ascends along the inner peripheral surface 27 of the fuel channel 9 and reaches the fuel rod spacer 1, each lobe 2
The coolant flows into the numerous coolant introduction passages 32, 32 through the openings 33, 33a of the coolant 5, 25a or the chevron-shaped openings.

The coolant flowing into each coolant introduction path 32, 32 is transferred to the outer frame 1.
8 and joins the main flow of coolant flowing around each fuel rod 5,5. Due to this confluence, as shown in Figure 6,
The flow rate of coolant flow 31 around the fuel rods is increased, increasing the cooling effect. Additionally, along with this merging, turbulence occurs in the mainstream of the coolant, promoting gas-liquid mixing between the coolant and the vapor bubbles generated by the nuclear reaction on the surface of the fuel rods, and making the gas-liquid mixture even more uniform. As a result, the heat transfer surface of the fuel rod 5 is prevented from being covered only with the gas phase, and cooling can be performed by effectively utilizing the liquid phase portion, that is, the coolant. Furthermore, the coolant flow flowing along the inner circumferential surface 27 is disturbed when passing through the coolant introduction path 32, and after passing through the fuel rod spacer 1, some of the coolant is located around the coolant. It flows in the direction of the fuel rod 5 and cools the fuel rod 5. In this way, according to the present invention, the cooling efficiency is increased, so that the critical output of the nuclear reactor becomes higher than that of the conventional reactor, as shown by the solid line B in FIG. In addition to forming the outer frame to bulge as in the above embodiment, the coolant introduction passage may be formed by fixing a curved pipe to the outer peripheral surface of the outer frame, or
It can be formed by providing a tongue piece reaching the inner drawing 27 at the lower end of the outer frame.

Further, the shape of the outer frame may be cylindrical or the like. In this way, the fuel rod spacer of the present invention is configured so that the coolant flow along the inner circumferential surface of the fuel channel is guided into the outer frame and directly participates in cooling the fuel rods, resulting in high cooling efficiency. ,
It is possible to prevent the heat transfer surface of the fuel sheath from being partially covered with steam bubbles, prevent burnout of the fuel sheath from occurring, and increase the critical output of the reactor.

Furthermore, the operating margin of the nuclear reactor is expanded, and the reactor has the effect of increasing the power density of the reactor.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing a conventional fuel rod spacer, Fig. 2 is a stair sectional view taken along the line ■-■ in Fig. 1, Fig. 3 is a longitudinal sectional view showing the core structure of a nuclear reactor, and Fig. 4 is 5 is a schematic sectional view showing the flow of cooling material using a conventional fuel rod spacer; FIG. 6 is a view similar to FIG. 5 using the fuel rod spacer of the present invention; Fig. 7 is a characteristic diagram showing the relationship between the flow rate of the coolant in the fuel assembly and the critical output of the reactor, and Figs. 8 to 11 show an embodiment of the present invention. 9 is a partial plan view, FIG. 10 is a sectional view taken along line X-X in FIG. 9, FIG. 11 is a sectional view taken along line MM in FIG. 9, and FIGS. The twelfth example shows the example of
The figure is a partial front view, Figure 13 is a cross-sectional view taken along the line x■-X■ in Figure 12, Figure 14 is a cross-sectional view taken along the line x■-X■ in Figure 12,
FIG. 5 is a partial bottom view of the outer frame showing the opening of the coolant introduction path. DESCRIPTION OF SYMBOLS 1...Fuel rod spacer, 5...Fuel rod, 9...Fuel channel, 18...Outer frame, 25
, 25a... Lobe, 27... Inner peripheral surface of fuel channel, 29... Gap, 30...
... Coolant flow along the inner peripheral surface of the fuel channel, 32
......Coolant introduction path, 33,533a...
Opening.

Claims (1)

[Scope of Claims] 1. An outer frame having a size to be installed in a fuel channel with a gap between it and the inner peripheral surface of the fuel channel, and an outer frame having a size that is installed inside the fuel channel with a gap between the frame and the inner circumferential surface of the fuel channel, a fuel rod spacer having a coolant introduction passage for guiding a flowing coolant flow into the outer frame. 2. The coolant introduction path bulges out a part of the outer frame until it comes into contact with the inner circumferential surface of the fuel channel, and the coolant flow flowing along the inner circumferential surface at the lower end of the bulged portion flows into the bulged portion. The fuel rod spacer according to claim 1, characterized in that the fuel rod spacer is formed with an opening for inflow. 3. The fuel rod spacer according to claim 2, wherein the bulging portion is a rope formed into a bulge on the outer frame. 4. The fuel rod spacer according to claim 3, wherein the rope is formed at a part of the outer frame in the axial direction. 5. The fuel rod spacer according to claim 3, wherein the lower end of the rope reaches the lower end of the outer frame, and the opening of the coolant introduction path has a chevron shape.