JPH01182794A - Fuel rod spacer - Google Patents

Abstract

PURPOSE:To achieve a reduction in pressure loss and an increase in a limit output under vapor-liquid 2-phase fluid conditions by providing a spring fixed at a connecting portion of an internal wall of a cylindrical shell while a temple is formed at a non-connecting portion thereof. CONSTITUTION:A spacer 20 has a temple 24 convex inward formed at upper and lower ends of a part excluding a connecting portion of the internal wall of a shell 21. In addition, a spring 25 is provided as bonded on the internal wall surface at the connecting portion of the shell 21. A fuel rod 2 inserted into the shell 21 is elastically supported in compression with the temple 24 and the spring 25. With such an arrangement, the spacer 20 needs no groove for inserting a spring into the side wall of the shell 21 and has no groove as generated by the formation of a fixed stopper and hence, the flow of a coolant flowing into the shell 21 from the upstream side causes no turbulence. This can reduce a fluid resistance caused by a vapor bubble in a narrow space formed by the surface of the fuel rod and the interval wall of the shell 21 thereby achieving a reduction in a pressure loss and an increase in a limit output under vapor-liquid 2-phase fluid conditions.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a fuel rod spacer that supports a large number of fuel rods at a distance in a fuel assembly. Regarding the fuel rod spacer.

(Prior Art) Generally, the core of a boiling water reactor is loaded with a plurality of fuel assemblies arranged in a lattice pattern at equal intervals.
These fuel assemblies are constructed as shown in FIG. That is, a plurality of fuel rods 2 are housed in a rectangular tube-shaped channel box 1 with a square cross section, and the lower part of the fuel rod 2 is connected to a lower tie plate 3, and the upper part thereof is connected to an upper tie plate 4. Fixed. Coolant for extracting heat from the core flows upward in the channel box 1 through the lower tie plate 3 and flows above the upper tie plate 4.

The fuel rods 2 are elongated and have an outer diameter of, for example, about 10 mm and a total length of several meters. When installed in the channel box 1, a plurality of fuel rods 2 are spaced evenly in the radial direction by spacers 5. The fuel rods 2 are bundled at intervals, and the intervals between the fuel rods 2 and between the fuel rods 2 and the channel box 1 are set to be minute intervals of several millimeters. During reactor operation, the spacing between the fuel rods 2 and between the fuel rods 2 and the channel box 1 may deviate from the set value due to coolant flow, thermal expansion, etc., which may threaten safe operation.
Normally, as shown in Fig. 4, spacers 6 are interposed in multiple stages in the flow direction to maintain the above-mentioned distance, which forces the fuel rods to bend and suppresses the movement of the fuel rods. be.

The structure of a conventional fuel rod spacer is shown in FIGS. 5 to 8.

In FIG. 5, the fuel rod spacer 5 has a number of approximately cylindrical shelves arranged in a side frame 6, 8×8=
The 64 fuel rods are arranged in a square grid. That is, 64 approximately circular cylindrical shelves formed in exactly the same shape are arranged in an 8x8 square grid,
Since each shelf is connected to each other, the side walls of the four adjacent shelves form a substantially rectangular cylindrical coolant flow passage 10.
is formed. Each shelf is provided with a spring 8 and a fixed stopper 9, so that the fuel rod 2 inserted therein is elastically supported at a slight distance from each side wall.

Note that a trapezoidal lobe 11 is fixed to the outer surface of the side frame 6 to support the fuel rod spacer 5 within the combustion channel 1. Further, as the material for the fuel rod spacer 5, only an Inconel material with springiness is used for the spring 8, and a Zircaloy material with low thermal neutron 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. .

Here, if we focus on 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 to which friction pressure loss and acceleration pressure loss are added. . Among these pressure losses, the pressure loss occurring at the fuel rod spacer portion,
That is, the spacer pressure loss corresponds to about 20% of the total.

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

However, in the conventional fuel rod spacer, as shown in FIG. 7, a spring 8 (
(see Fig. 8) and a constricted fixed stopper 9 with the upper and lower ends of the shelf protruding inward.
The grooves 13 formed by forming the grooves 13 create a flow of coolant between the coolant flow section 10 and the inside of the shelf.

Furthermore, the fixed stopper 9 causes disturbances in the flow of coolant inside the shelf. These factors increase spacer pressure loss. Furthermore, since a portion of the coolant that has flowed into the shelf flows out through the grooves 12 in the side wall of the shelf, there is also the problem that it does not effectively cool the fuel rods 2.

(Problems to be Solved by the Invention) The present invention was made in view of the above circumstances, and it is necessary to reduce the pressure loss of the coolant flow and improve the coolant fluidity under two-phase flow. The purpose is to provide a fuel rod spacer that can be used.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a fuel rod spacer in which a number of cylindrical shells for supporting insertion of fuel rods are provided in a side frame in a connected manner. The above object has been achieved by providing a fixed spring in the connected portion of the inner wall of the shaped shell and forming dimples in the non-connecting portion of the inner wall.

(Function) As described above, the fuel rod spacer of the present invention is provided with a spring fixed to the connecting portion of the inner wall of the shell with an adjacent shell, and roughly forms dimples in the unconnected portion of the inner wall of the shell. I decided to keep it, so
There is no longer a groove in the side wall of the shell that allows the coolant to flow between the inside of the shell and the coolant flow path as in the conventional case. Therefore, the coolant flowing inside the shell does not cause turbulence as in the conventional case.
Spacer pressure loss can be reduced. In addition, the coolant is used without waste for cooling the fuel rods, so the limit output can be improved.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

The fuel rod spacer 20 of this embodiment has a cylindrical shell 21 that supports the fuel rods inserted therein, as well as an outer frame 21, as in the conventional case.
The coolant flow passage 23 is formed by a substantially rectangular cylindrical space surrounded by the side walls of four adjacent shells 21. Inwardly projecting dimples 24 are formed at the upper and lower ends of the portions that are not the connecting portions, and springs 25 are roughly fixed to the inner wall surfaces of the connecting portions of the shell 21. The fuel rod 2 inserted into the shell 21 is elastically supported by the dimple 24 and the spring 25.

Since the spacer 20 of this embodiment is configured in this way, there is no groove for inserting a spring in the side wall of the shell 21 or a groove formed by forming a fixed stopper.
Therefore, the flow of coolant flowing into the shell 21 from the upstream side does not flow between the inside of the shell and the coolant flow path and become turbulent, unlike in the conventional case.

Therefore, flow resistance due to steam bubbles in the constriction 26 formed between the surface of the fuel rod 2 and the inner wall of the shell 21 can be reduced, and pressure drop characteristics under gas-liquid two-phase flow conditions can be improved.

Further, since the inside of the shell 21 and the coolant flow passage 23 are isolated from each other, the rectifying effect of the coolant can be increased, and the coolant flowing into the shell 21 is used to cool the fuel rods 2. Since it is used without waste, it has the effect that the marginal output can be improved.

[Effects of the Invention] As described above, according to the present invention, pressure loss under two-phase flow conditions can be reduced and the limit output can be increased. Due to this effect, it is also possible to reduce the capacity of the coolant-driven pump.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 show an embodiment of the fuel rod spacer of the present invention, and are a plan view, a front view, and a perspective view, respectively. Figure 4 is a perspective view of a conventional fuel assembly;
5 and 6 are respectively a plan view and a front view of a conventional fuel rod spacer, FIG. 7 is a perspective view of the shell in FIG. 5, and FIG. 8 is a perspective view of the spring in FIG. 5. 2...Fuel rod 20...Fuel rod spacer 21...Cylindrical shell 22...Side frame 23...Coolant flow passage 24...Demple 25...Spring agent Patent attorney Nori Chika Ken Yudo Daishimaru Kano Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A fuel rod spacer comprising a plurality of interconnected cylindrical shells for supporting fuel rod insertion inside a side frame, in which a spring fixed to the interconnected portion of the inner wall of the cylindrical shells is provided, and A fuel rod spacer characterized in that dimples are formed in non-connecting portions of the inner wall.