JPS6322277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel assembly for a fast breeder reactor, and more particularly to a flow rate suppression mechanism for a peripheral subchannel.

FIG. 1 shows a cross-sectional view of a conventional nuclear fuel assembly. A nuclear fuel assembly for a fast breeder reactor consists of a large number of fuel elements 1 arranged in an equilateral triangular lattice and covered with wrapper tubes 2, so that coolant flows through the gaps between the fuel elements surrounded by the wrapper tubes 2. ing.

This coolant flow path can be divided into subchannels, which are virtual flow paths surrounded by fuel elements and wrapper tubes, and subchannel 3 at the periphery of the nuclear fuel assembly is inside. Since the flow path area is wider than that of the subchannel 4, and the coolant flows easily, the peripheral portion tends to be supercooled compared to the inside. Therefore, it has been required to suppress the flow rate of the coolant flowing through the peripheral subchannel 3 and increase the flow rate flowing through the inner subchannel 4, thereby making the heat removal ability uniform.

In order to solve this problem, the flow rate of the peripheral subchannel has conventionally been restricted by wrapping a thin wire around the outermost fuel element in one or two layers. However, this method of suppression has disadvantages such as an increase in the number of steps involved in assembling the fuel assembly, complication of product management, and an increase in the amount of radiation exposure during assembly. As another method, as shown in Figure 2,
There was also a method of restricting the flow rate by inserting a rod called a baffle rod 5 into the peripheral subchannel, but this method had the disadvantage that the flow vibration of the inserted rod would cause wear and damage to the fuel cladding tube. It was hot.

SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear fuel assembly that can uniformize heat removal capacity, prevent damage to fuel cladding tubes, and is easy to manufacture.

A feature of the present invention is that the baffle rod is constructed by fitting a plurality of short rods in the axial direction, and has means for fixing each of the divided short rods to the wrapper tube.

A nuclear fuel assembly which is a preferred embodiment of the present invention will be explained below with reference to FIGS. 3, 4 and 5.

In the conventional example shown in FIG. 2, a baffle rod is inserted into the peripheral subchannel, and the baffle rod is fixed to the lapper tube only at the upper and lower ends by welding. however,
In this embodiment, one baffle bar 5 is constructed by fitting a plurality of short bars 5A each having a triangular cross section in the axial direction. Each short rod 5A is
It has a hole 13 at the upper end and a protrusion 9 at the lower end. One protrusion 6 is provided on one surface of the short rod 5A, and this protrusion 6 is inserted into a hole 7 provided in the side wall of the wrapper tube 2. The protrusion 6 inserted into the hole 7 is fixed to the wrapper tube 2 by welding 8.
Therefore, fluid vibration of the short rod 5A can be prevented, and wear and damage between the fuel coatings of the fuel element 1 adjacent to the short rod 5A can be prevented. One protrusion 6 is provided on the short rod 5A, but this is because when multiple protrusions 6 are provided, there may be a dimensional mismatch between the protrusion 6 and the hole 7 due to errors in the accuracy of drilling into the tube 2. This is to prevent the occurrence of

Moreover, one baffle rod 5 is constructed by fitting the protrusion 9 of another short rod 5A arranged adjacently in the axial direction into the hole 13 of the short rod 5A.
By fitting the plurality of short rods 5A in this way, it is possible to absorb the dimensional error between the protrusions 6 and the holes 7 in the axial direction at this fitting part. can be easily fitted, and each short rod 5
Deformation such as twisting of A can be prevented.
When a single baffle bar is provided with a plurality of protrusions as in the conventional example shown in Fig. 2, and these protrusions are fitted into holes provided in the wrapper tube, the spacing between the protrusions and the holes must be carefully adjusted in advance. It is necessary to process with high precision,
It is difficult to manufacture. In the case of this embodiment, such a problem does not occur. FIG. 5 shows a state in which a baffle bar 5 consisting of a short bar 5A is attached to the side wall of the tuppan tube 2.

In this embodiment, damage to the fuel cladding tube can be prevented by preventing fluid vibration of the baffle rod 5, and the flow rate of coolant in the nuclear fuel assembly can be made uniform by suppressing the flow rate of the peripheral subchannel. Moreover, the baffle rod 5 can be easily attached to the wrapper tube 2, and the manufacturing of the nuclear fuel assembly can be facilitated.

A sixth nuclear fuel assembly which is another embodiment of the present invention
This will be explained based on the diagram and FIG. 7. The baffle bar 5 of this embodiment is also constructed by fitting a plurality of short bars in the same way as in the previous embodiment. These short bars are not provided with protrusions 6. In this embodiment, the baffle rods 5, that is, each short rod, are fixed to the wrapper tube 2 by a holding plate 10, as shown in FIG. The holding plate 10 is fixed by inserting screws 11 into holes 7 provided in the wrapper tube 2. The holding plate 10 has a protrusion 12 formed into a triangular mountain shape. A plurality of short rods arranged in parallel on the inner surface of the gap 2 are inserted into triangular holes of the protrusion 12. The protrusion 12 of the presser plate 10 can also be made of a bent plate structure as shown in FIG.

When fixing the baffle rods with the presser plate 10, if the baffle rods are not divided and made to be approximately equal in length to the axial direction of the tube as in the conventional example shown in Fig. 2, multiple long and thin baffle rods can be arranged in parallel. It is extremely difficult to arrange these baffle rods on the rack tube with a presser plate. However, by configuring the baffle bar by fitting a plurality of short bars as in this embodiment, the baffle bar 5 is
This makes it extremely easy to fix and manufacture nuclear fuel assemblies. As mentioned above, damage to the fuel cladding tube can be prevented by preventing fluid vibration of the baffle rods 5, and the flow rate of coolant in the nuclear fuel assembly can be made uniform by suppressing the flow rate of the peripheral subchannel. This is similar to the embodiment.

According to the present invention, it is possible to prevent damage to the fuel cladding tube by preventing fluid vibration of the baffle rod, and to equalize the flow rate of coolant in the nuclear fuel assembly by suppressing the flow rate of the peripheral subchannel. Furthermore, the baffle rods can be easily attached to the lapper tube, making it easier to manufacture nuclear fuel assemblies.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional nuclear fuel assembly;
The figure is an enlarged cross-sectional view of the main part of a conventional nuclear fuel assembly having baffle rods, FIG. 3 is a partially broken perspective view of the main part showing an embodiment of the present invention, and FIG. FIG. 5 is a longitudinal sectional view of the main part of the embodiment of the invention in an assembled state, and FIG. 5 is an enlarged cross-sectional view of the main part of the embodiment of the invention.
Figures 6 to 8 are other embodiments of the present invention, in which Figure 6 is a perspective view of the holding plate holding the wrapper tube, Figure 7 is a perspective view showing the assembled state of the baffle bar, and Figure 8 is a perspective view of the holding plate. FIG. 7 is a perspective view showing another embodiment. DESCRIPTION OF SYMBOLS 1... Fuel element, 2... Rapper tube, 3... Peripheral subchannel, 5... Baffle bar, 6... Projection, 7... Hole, 8
...welding, 10...pressing plate.

Claims (1)

[Claims] 1. A plurality of fuel elements, a wrapper tube surrounding the outside of a bundle of these fuel elements, and a wrapper tube located between the fuel elements disposed at the outermost periphery and attached to the inner wall of the wrapper tube. A nuclear fuel assembly comprising a baffle rod, wherein the baffle rod is configured by fitting a plurality of short rods in the axial direction, and a means for fixing each of the divided short rods to the rapture tube. A nuclear fuel assembly comprising: 2. The nuclear fuel assembly according to claim 1, wherein the fixing means is a protrusion provided on the short rod, inserted into a through hole in the side wall of the wrapper tube, and welded to the wrapper tube. 3. The nuclear fuel assembly according to claim 1, wherein the fixing means is a holding means attached to the wrapper tube.