JPH0238000B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to the core of a boiling water nuclear reactor.

[Technical Background of the Invention] Fig. 1 shows a nuclear fuel assembly for a boiling water reactor, and this nuclear fuel assembly consists of a fuel bundle 2 in which fuel rods 1 are arranged in a lattice pattern, and a channel box 3 surrounding the fuel bundle 2. The main part is composed of these.

The fuel bundle 2 is supported by an upper tie plate 4 and a lower tie plate 5, and the spacing between the fuel rods 1 is maintained constant by spacers 6. A fastener 7 and a pad 8 are arranged on the upper part of the channel box 3, and a handle 9 is formed at the upper end. and fuel bundle 2
The channel box 3 that surrounds it is made of a long tube made of Zircaloy, for example, and has the following functions.

(1) By forming isolated coolant flow paths for each nuclear fuel assembly, the flow rate of coolant flowing within the nuclear fuel assembly is ensured.

(2) Forms a guide surface when inserting and withdrawing control rods between nuclear fuel assemblies.

(3) Ensure the rigidity of the nuclear fuel assembly and facilitate its handling.

And this channel box 3 is conventionally the second
As shown in the drawings and FIG. 3, members 10a and 10b each having a U-shaped cross section are butt-welded 11 to each other.

FIG. 4 shows a state in which such a nuclear fuel assembly 12 is housed in a reactor core, and each corner of a control rod 13 having a cross-shaped cross section is connected to a sheath 15 connected to a tie rod 14 at a constant interval. A channel box 3 is provided. Furthermore, sheath 15
A neutron absorption rod is inserted inside. Note that the reference numeral 16 indicates an upper lattice.

[Problems with the Background Art] However, in the nuclear fuel assembly 12 configured as described above, it is known that when the nuclear fuel assembly 12 is inserted into a reactor core and used for a long period of time, the channel box 3 is bent.

Conventionally, the bending of this channel box 3 was
It was thought that this was caused by the distribution of fast neutron flux inside the nuclear reactor, but very recent research has revealed the configuration of Channel Box 3 when it was manufactured and the metallurgy of irradiation growth associated with fast neutron irradiation when used inside the reactor. It was revealed that the difference based on the physical difference was the main cause, and the influence of the fast neutron flux distribution was relatively small.

That is, FIGS. 5 and 6 show the bending of the channel box 3. In the channel box 3 in which the members 10a and 10b having a U-shaped cross section are butt welded together, the butt welded part 11 is bent. The side where 11 does not exist is deformed in the direction of arrow A in the figure, for example, as shown by the two-dot chain line in FIG. This is due to the difference in the elongation (irradiation growth) of the members 10a and 10b due to the in-reactor irradiation of fast neutrons based on the slight metallurgical differences between the members 10a and 10b, which have a U-shaped cross section and are located on the left and right sides of the figure, respectively. This is because the bending occurs approximately in proportion to the amount of fast neutron irradiation, that is, the burnup of the nuclear fuel assembly. At this stage, it is not clear whether the channel box 3 bends in the left or right direction when irradiated with fast neutrons.

FIGS. 7 and 8 show the state when such a channel box 3 is inserted into the reactor core. In the channel box 3a, which is disposed at the bottom of the figure and has a butt welded part 11 in the vertical direction, ,
You can expect each to turn in the same direction, in opposite directions, and in directions where one chases and the other runs away. For example, when the channel boxes 3a are deformed in opposite directions, the sheath 15 of the control rod 13 becomes sandwiched between the two channel boxes 3a, as shown in FIG. The width of the water gap necessary for running becomes narrower, which may impede the insertion and removal of the control rod 13. As a result, in the worst case, the safe shutdown of the nuclear reactor may be impaired.

[Object of the Invention] The present invention has been made in response to the conventional situation, and an object thereof is to provide a reactor core that can always maintain the width of the water gap in which the control rods run at an appropriate value.

[Summary of the Invention] That is, the present invention provides a nuclear fuel assembly constructed by accommodating fuel rods in a channel box formed by butt-welding members each having a U-shaped cross section, and each of the control rods having a cross-shaped cross section. In a reactor core configured such that each channel box is arranged at a corner, the direction of the butt weld of each of the channel boxes is the same as the direction of the butt weld of two other channel boxes adjacent to each other via the control rod. This is a reactor core characterized by being arranged in different directions.

[Embodiment of the Invention] The details of the present invention will be described below with reference to an embodiment shown in the drawings.

FIG. 9 shows a reactor core according to an embodiment of the present invention. In the figure, reference numeral 17 indicates a fuel rod 1 placed in a channel box 3 formed by a butt-welded portion 11 of members 10a and 10b having a U-shaped cross section. It shows a nuclear fuel assembly that is housed and configured. These nuclear fuel assemblies 17 are arranged at each corner of a control rod 13 having a cross-shaped cross section, and constitute a reactor core. and channel box 3 that constitutes the nuclear fuel assembly 17.
The direction of each of the butt welds 11 is different from the direction of the butt welds 11 of the other two channel boxes 3 adjacent to each other via the sheath 15 of the control rod 13.

That is, in the nuclear fuel assembly 17 located at the upper right and lower left of the figure, the channel box 3
The butt welds 11 are formed in the vertical direction, and in the channel boxes 3 of the nuclear fuel assemblies 17 arranged at the upper left and lower right of the figure, the butt welds 11 are arranged in the left and right direction. ing.

In the core configured as described above, the channel box 3 of each nuclear fuel assembly 17 is deformed in the direction of arrow A in the figure, so that the sheath 15 of the control rod 13 is The adjacent channel boxes 3 are no longer deformed in the direction of the sheath 15 through the control rod 13.
It is possible to secure a sufficient width of the water gap for the vehicle to run.

That is, in general, the bending of the channel box 3 is 2 to 3 at the end of combustion of the nuclear fuel assembly 17.
When the channel boxes 3 arranged on both sides of the control rod 13 sandwich the control rod and bend in a direction to narrow the water gap, the water gap of the control rod 13 decreases by 4 to 6 mm due to this bending. control rod 1
There is a risk that the control rods 13 and the channel box 3 will come into contact with each other, but in the core configured as described above, there is only a risk that the channel box 3 on one side will bend in the direction of reducing the water gap, and the control rod 13 and the channel box 3 may come into contact with each other. Contact with box 3 can be completely eliminated.

FIG. 10 shows another embodiment of the present invention,
In this embodiment, butt welds 11 are formed in the horizontal direction in the channel boxes 3 at the upper right and lower left in the figure, and butt welds 11 are formed in the vertical direction in the channel boxes 3 at the upper left and lower right in the figure. .

In the core of this embodiment, the same effects as in the embodiment shown in FIG. 9 can be obtained.

[Effects of the Invention] As described above, according to the core of the present invention, it is possible to always ensure a sufficient width of the water gap in which the control rods run, and the contact between the control rods and the channel boxes of the nuclear fuel assemblies is completely prevented. can be prevented. As a result, the control rods can be inserted and removed reliably, and the safety of the reactor can be improved.

[Brief explanation of drawings]

Figure 1 is an external view of a nuclear fuel assembly, Figure 2 is an external view of a channel box, Figure 3 is a cross-sectional view of Figure 2, and Figure 4 is a core containing control rods and nuclear fuel assemblies. The top view, FIGS. 5 and 6 are explanatory diagrams showing the bending of the channel box, and FIGS.
8 and 8 are explanatory diagrams showing the bending of the nuclear fuel assembly inserted into the reactor core, FIG. 9 is a top view showing the core of one embodiment of the present invention, and FIG. 10 is another embodiment of the present invention. FIG. 2 is a top view of an example reactor core. 1...Fuel rod, 3...Channel box, 1
1...Butt welding part, 13...Control rod, 17...
...Nuclear fuel assembly.

Claims (1)

[Claims] 1 A nuclear fuel assembly is constructed by accommodating fuel rods in a channel box made by butt welding U-shaped members in cross section, and is arranged at each corner of a control rod having a cross-shaped cross section. In the reactor core, the direction of the butt welds of each of the channel boxes is arranged in a different direction from the direction of the butt welds of two other adjacent channel boxes via the control rod. The core of a boiling water reactor.