JPS6223275B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to control rods for boiling water nuclear reactors.

The control rod of a boiling water reactor (hereinafter referred to as BWR) has an appearance as shown in Figure 1A. That is, a handle 2 is provided at the upper end of an upper structure member 1 having a cross-shaped cross section, and wings 3 are formed below the upper structure member 1. The wing 3 has a tie rod 4 having a cross-shaped cross section as shown in Fig. 1B.
A U-shaped sheath 5 is attached radially to the
Inside each U-shaped sheath 5, absorption rods 6, which are shown enlarged in FIG. 1C, are arranged side by side. The absorption rod 6 has a structure in which a stainless steel tube 7 is filled with boron carbide (B ₄ C) powder 8, which is a neutron absorbing substance. The lower part of the wing 3 in which the absorption rod 6 is housed is a lower structural member 9, and a speed limiter 10 having a circular cross section is connected to the lower part of the lower structural member 9.

Control rods having such a configuration are moved in and out of the nuclear reactor to control the operating state of the reactor. Therefore, used control rods have strong induced radioactivity as a result of being irradiated with a strong neutron field for a long period of time, and must be stored in a specific location and shielded from radiation. For this reason, conventionally used control rods have been stored upright on a control rod stand 11 in a fuel storage pool with the speed limiter 10 portion facing down, as shown in FIG. 2A.
That is, since the cross section of the speed limiter 10 portion is circular, the control rods cannot be brought closer to each other than they are in contact with each other, and the storage space cannot be used efficiently.

Furthermore, when used control rods are stored upright in a fuel storage pool, the upper ends of the control rods are placed closest to the water surface. However, since the induced radioactivity of the upper end of the control rod, particularly the superstructure member 1, is higher than that of the lower end, the control rod must be submerged to a position considerably below the water surface.
In other words, it is necessary to increase the depth of the storage pool accordingly, and the utilization efficiency in the depth direction of the pool is not necessarily high.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control rod for a boiling water reactor that can make more effective use of a pool.

In the first invention of the present case, a cuttable spacer is interposed between the lowermost end of each absorption rod housed in the control rod and the lower structure material, and thereby the speed limiter portion having a circular cross section is connected to the control rod. This objective is achieved by having a structure that can be separated from other parts of the body. That is, the cut-off section having a cruciform cross section can be stored in the control rod stand 12 with the wing sections overlapping each other as shown in FIG. 2B, and the conventional control rod shown in FIG. Storage space can be used much more effectively than storage.

In addition, in the second invention of the present case, a cuttable spacer is interposed between the lowermost end of each absorption rod housed in the control rod and the superstructure material, and thereby the superstructure material with high induced radioactivity is This objective is achieved by allowing the parts to be separated and stored by cutting. That is, the other part of the control rod, which has relatively weak radioactivity, can be placed close to the water surface, and the pool can be effectively utilized in the depth direction.

The present invention will be explained in detail with reference to Examples below.

FIG. 3, in which the same parts as in FIG.
B shows the vicinity of the upper end of the control rod, and B shows the vicinity of the lower end of the control rod.

In the present invention, a spacer 31 is provided on the lower surface of the upper structure 1 to fit into each U-shaped sheath 5 and terminate near the tie rod 4. Further, a similar spacer 32 is provided on the upper surface of the lower structure 9 connected to the speed limiter 10, and each absorption rod is connected to the spacer 3.
It is supported between 1 and 32.

Incidentally, a window hole 33 that opens at the lower surface position of the spacer 31 is provided in the upper end portion of each U-shaped sheath 5 on the tie rod 4 side.

The control rod of the present invention having the above structure can be cut at the intermediate portion of the spacer as shown by dotted lines AA and BB in FIGS. 3A and 3B, respectively.

As described above, according to the present invention, the speed limiter portion of the control rod can be stored separately, so that the storage space for the control rod can be saved. In addition, if the upper end including the superstructure material can be separated and stored by cutting as in this example, there is no need to place the upper end of the control rod, which has particularly strong induced radioactivity, at the position closest to the water surface. Therefore, other parts of the control rod that have relatively weak radioactivity can be placed closer to the water surface, and the pool can be used more effectively.

Note that when the upper structural member 1 is separated after cutting, the handle 2 for hanging support provided on the upper structural member 1 will also be removed, but the U
Since the lower remaining portion of the spacer 31 after cutting is exposed through the window hole 33 provided in the letter-shaped sheath 5, a hanging tool (not shown) or the like is hung over the remaining portion of the spacer 31 through the window hole 33. If you use this as an auxiliary handle, you can easily transport it into the pool.

Note that when a conventional control rod is separated into its upper end, intermediate portion, and lower end, the upper structure, For example, the lower structure is indicated by dotted line C-
It must be cut either at the locations shown by C and DD, or near their inner ends, for example at the locations indicated by dotted lines EE and FF. However, in the case of the former method, the cutting length is long and the cutting operation takes a long time. Furthermore, in the latter case, since the absorption rod must be cut, there is a risk that the cutting device may be damaged by the boron carbide. Furthermore, the high-pressure He gas inside the absorption rod may cause the boron carbide powder inside to scatter explosively during cutting. In contrast, in the present invention, a spacer is interposed between the absorption rod end and the inner end surfaces of the upper and lower structures, and the control rod is cut at the position of this spacer, so the above problem is completely eliminated. be done.

Note that the spacer used in the present invention can take various forms. FIG. 5 shows some of these, and shows a side view and a sectional view of the spacer, respectively. Of these, Figure A shows the spacer with the upper and lower parts separated from the original, and Figure B
In the figure, a protrusion is provided on the spacer and the protrusion is used as a cutting point, and in C and D of the same figure, a recess is used as a cutting place. Since the spacer portion located below the cut plane AA and above the cut plane B-B becomes a portion that supports the absorption rod after cutting, it is preferable to perform spot welding between the spacer portion and the U-shaped sheath.

[Brief explanation of the drawing]

1A is a perspective view of a control rod according to an embodiment of the present invention, FIG. 1B is a cross-sectional view of the control rod, FIG. 1C is a cross-sectional view of an absorption rod housed in the control rod, and FIG. A
3 is a plan view showing the absorption state of a conventional control rod, FIG. 3B is a plan view showing the absorption state of the control rod of the present invention, and FIGS. 4A and 4B are longitudinal sectional views of a conventional control rod, and FIGS. 5A to 5D are side views and sectional views of a spacer that can be used in the present invention. DESCRIPTION OF SYMBOLS 1... Upper structure material, 6... Absorption rod, 9... Lower structure material, 31, 32... Spacer.

Claims (1)

[Claims] 1. A control rod for a boiling water reactor, characterized in that a cuttable spacer is interposed between the lowermost end of each absorption rod housed in the control rod and a lower structural member. . 2. A control rod for a boiling water reactor, characterized in that a cuttable spacer is interposed between the lowermost end of each absorption rod housed in the control rod and an upper structural member.