JPS61226687A - Fuel rod spacer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a fuel rod spacer that supports a large number of fuel rods constituting a fuel assembly, and particularly relates to a fuel rod spacer that supports a large number of fuel rods constituting a fuel assembly. Regarding spacers.

[Technical background of the invention and its problems]

In general, in fuel assemblies for nuclear reactors, spacers are provided at multiple locations in the longitudinal direction to keep the fuel rods apart, to force the curvature of the fuel rods, and to reduce vibrations of the fuel rods due to the flow of coolant. I try to keep it in check.

Factors 9 to 13 show conventional fuel rod spacer structures. FIG. 9 shows a fuel assembly, in which a plurality of fuel rods 4 and water rods 5 are arranged and inserted into a fuel channel 1, with both ends held in an upper tie plate 2 and a lower tie plate 3, respectively. There is. A plurality of spacers 6 that align and support each fuel rod 4 are provided in the axial direction of the fuel rod 4 to ensure a coolant flow path.

10 and 11 show the structure of the fuel rod spacer 6 in detail. This fuel rod spacer 6 has a plurality of approximately circular shells 8 arranged in a side frame 7 in a connected manner.
It is formed so that X8-64 fuel rods are arranged in a square lattice. That is, 64 substantially cylindrical shells 8 formed in exactly the same shape are arranged in an 8 x 8 square grid, and a part of the side wall of each shell 8 is connected, and four adjacent shells are connected. A substantially rectangular cylindrical coolant flow passage 1 is formed by the side wall portion 8.
1 respectively. Each shell 8 is provided with a spring 9 and a fixed stopper 10, so that the fuel rod 4 inserted therein is slightly separated from each side wall portion and elastically supported.

Note that a trapezoidal lobe 12 that supports the fuel rod spacer 6 within the fuel channel 1 is fixed to the outer surface of the side frame 7. Further, as the material for the fuel rod spacer 6, only Inconel material with springiness is used for the spring 9, and Zircaloy material with low thermal neutral absorption is used for the other components.

Nowadays, there is a desire to expand operational flexibility, such as automatic control of nuclear couplers 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 efforts are underway to improve core stability, expand thermal margin, and reduce core pressure loss. ing.

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 tiebrate pressure loss, spacer pressure loss, position pressure loss, and upper tiebrate pressure loss, with the addition of friction pressure loss and acceleration pressure loss.

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

Therefore, reducing spacer pressure loss will significantly reduce core pressure loss.

However, in the conventional fuel rod spacer 6, as shown in FIG. 12, the side wall portion of the approximately circular shell 8 is l! fI is in a state of blockage. That is, only a spring 13 for inserting one spring 9 shown in FIG. 13 for fixing four fuel rods is provided. Therefore, no coolant flow occurs between the interior of the shell 8 and the coolant flow path 11 formed by the connecting portions of adjacent shells 8 and the four shells. Since the fuel rod 4 is inserted into the shell 8, the coolant flows through the narrow space f formed by the inner wall of the shell 8 and the surface of the fuel rod 4.
i5113 in the direction of arrow 16 in FIG. 11 (in the axial direction of the fuel rods 4).

On the other hand, during normal operation of the nuclear reactor, steam bubbles are generated from the surfaces of the fuel rods 4, and the inside of the fuel channel 1 is in a gas-liquid two-phase flow state of coolant and steam. And narrow space 1
3, the flow resistance of the coolant flow increases due to steam bubbles generated on the surface of the fuel rods 4. Therefore, the pressure loss characteristics under gas-liquid two-phase flow conditions are correspondingly lower.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, 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 flowability of the coolant under two-phase flow.

[Summary of the invention]

In order to achieve the above object, the present invention provides a large number of approximately circular shells for supporting fuel rod insertion inside a side frame, each of which has a portion of its side wall connected to each other, and the non-connected side wall of each shell. In a fuel rod spacer having a cylindrical coolant flow passage formed by a portion thereof, a coolant flow hole is provided in a non-contiguous side wall portion of the shell to communicate the coolant flow passage with a fuel rod insertion portion inside the shell. It is characterized by having been established.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 8.

In the fuel rod spacer 20 of this embodiment, 64 approximately circular cylindrical shells 21 into which fuel rods are inserted and supported are arranged in an 8×8 square lattice as in the conventional case, and the side wall of each shell 21 is A substantially square cylindrical coolant flow path 2 is formed by connecting a part of the shells 21 and by connecting a portion of the side walls of the adjacent four shells 21 that are not connected.
2 respectively.

The shell 21 has four side frames 23 arranged on each of the four sides.
is located inside. The fuel rods 4 are elastically supported under pressure by springs 24 fixed to the inner wall surface of each shell 21 and constricted fixed stoppers 25 that project the upper and lower ends of each shell 21 inward.

The shell 21 includes four corner shells 2 arranged at four corners.
1a and 24 side shells 21b arranged on the four sides
and 36 internal shells 21c arranged inside. Each shell has a substantially circular cross section;
It is connected to adjacent shell-side members 23 at four locations indicated by reference numerals 26, and coolant flow passages 22 are formed by non-adjacent side wall portions 27.

In this thing, the side wall portion 27 of each shell has a fourth
As shown in the figure, a large number of slit-shaped coolant flow holes 29 are provided.

Note that the shape and number of the coolant flow holes 29 may be any as long as they allow steam bubbles generated inside the shell 21 to flow out to the coolant flow path 22. Therefore, as shown in FIG. 5 or 6, the coolant flow holes 29 may be rectangular or circular, and the number thereof is not particularly limited.

In such a configuration, by providing coolant flow holes 29 in the side wall portion 27 of the approximately circular cylindrical shell 21, the fuel rods 4 inserted into the shell 21 can be cooled as shown in FIG.
The vapor bubbles generated on the surface of the shell can flow out into adjacent coolant flow passages 22 formed by four shells, as shown by arrows 30. Therefore, flow resistance due to steam bubbles in the narrow gap 31 formed between the surface of the fuel rod 4 and the inner wall of the shell 21 can be reduced. That is, pressure drop characteristics under gas-liquid two-phase flow conditions can be improved.

The ratio of the pressure drop gradient under two-phase flow conditions to the pressure drop gradient under single-phase flow conditions containing only the liquid phase (referred to as the two-phase flow multiplication coefficient) is a quantity that represents the pressure drop characteristics under two-phase flow conditions. . FIG. 8 shows the two-phase flow multiplication coefficient for the total flow rate of the gas phase m flow rate. As shown in the figure, compared to the conventional two-phase flow multiplication coefficient shown by the broken line B, in the case of the present invention, the two-phase flow multiplication coefficient can be reduced as shown by the solid line A.

i! 2! In other words, the pressure loss under two-phase flow conditions is reduced, so the capacity of the coolant-driven pump can be reduced, and the quantity of the fuel spacer itself can be kept small.
Neutron absorption will also be small.

〔Effect of the invention〕

As described above, according to the fuel rod spacer according to the present invention,
By providing a coolant flow hole in a non-contiguous part of the shell that forms a coolant flow path to communicate the coolant flow path with the fuel rod insertion part inside the shell, vapor bubbles generated on the surface of the fuel rod can be reduced. Since it is made easier to flow out into the coolant flow path, pressure loss can be reduced under two-phase flow conditions.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the entire spacer, FIG. 2 is a front view of the spacer, and FIG. 3 is a side frame. 4 is a perspective view of the shell, FIGS. 5 and 6 are perspective views showing shell modifications, FIG. 7 is a schematic diagram showing the flow of coolant, and FIG. 8 is a two-phase flow diagram. Characteristic diagrams showing the relationship between layer magnification and quality, Figures 9 to 13 show conventional examples, Figure 9 is a vertical view of the fuel assembly, Figure 10 is a plan view of the fuel rod spacer, Figure 11 The figure is a front view of the spacer, Figure 12 is a perspective view of the shell, and Figure 13 is a perspective view of the spring. This is an R diagram. 4...Fuel rod, 20...Fuel rod spacer, 21...
- Shell, 22... Coolant flow path, 23... Side frame,
24...Spring, 26...Connection part of side wall part,
27... Disconnected portion of side wall portion, 29... Coolant distribution hole. Applicant's agent Hisashi Hatano 1 Figure 2 Figure 3 Figure 7 (-1 Bunny) Figure 9 Certain 12th Figure 13

Claims (1)

[Claims] 1. A large number of approximately circular shells for supporting the insertion of fuel rods are provided inside the side frame, with part of the side wall connected to each other, and the non-connected side wall portion of each shell In a fuel rod spacer formed with a cylindrical coolant flow passage, a coolant flow hole is provided in a non-connecting side wall portion of the shell to communicate the coolant flow passage with a fuel rod insertion portion inside the shell. A fuel rod spacer characterized by: 2. The fuel rod spacer according to claim 1, wherein the coolant flow holes are slit-shaped. 3. The fuel rod spacer according to claim 1, wherein the coolant flow holes are square holes or circular holes.