JPH0514235Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention is a burnable poison rod (bar) that plays a role in suppressing excess reactivity at the initial stage of fuel combustion and extending the life of the fuel in a nuclear reactor. (Nable Poison Stick).

[Conventional technology]

The conventional burnable poison rod, as shown in Figure 8,
A glass tube (for example, borosilicate glass) 3 containing a burnable poison (for example, boron) with a spacer tube 2 inserted in the center is housed inside a mantle tube (commonly known as BP tube) 1 made of stainless steel. , end plugs 4 and 5 are welded and sealed to the upper and lower ends of the mantle tube 1, respectively.

The spacer tube 2 serves to reinforce stress against bending of the glass tube 3, and when the glass tube 3 is broken, the broken portion 3a of the glass tube 3 moves in the radial direction of the glass tube 3, as shown in FIG. It has a flange 2a at the bottom so that it follows the glass tube 3 and descends when the burnable poison rod enters the furnace.

Further, the glass tube 3 and the spacer tube 2 are individually movable in the axial direction for the following reason.

Since the burnable poison rod is hung vertically in the reactor, even if it is hung upward from its original position, the glass tube 3 and spacer tube 2 will fall relative to the mantle tube 1, Must be in the correct position.

If the glass tube 3 and spacer tube 2 are not free to some extent, when inserting the end plugs 4 and 5 into the end of the mantle tube 1, the glass tube 3 and spacer tube 2 will act as resistance and the end plugs 4 and 5 will not be completely inserted. It may not be possible to insert the

We want to reduce the number of components of the burnable poison rod as much as possible.

[Problems to be Solved by the Invention] However, in the conventional burnable poison rod, the glass tube 3 and the spacer tube 2 are in a completely free state as described above. Therefore, when the glass tube 3 is broken into two halves as shown in FIG. 10, the glass tube 3
The upper part 3b and the lower part 3c of the first
There is a concern that the gap G may occur between them due to relative rotation in the circumferential direction as shown in Fig. 1. If this occurs and a gap G occurs, the presence of the gap G will cause a localized output peak of the fuel, which is undesirable from the viewpoint of the soundness of the fuel.

Even if the glass tube 3 is broken, from the above point,
Although it is thought that the possibility of gap G occurring is small, it is desirable to eliminate predicted nuisance factors in advance.

[Means for solving the problem]

In this invention, a glass tube into which a spacer tube having a flange at the lower end is inserted is housed in an outer tube.
In addition, in a burnable poison rod with end plugs attached to the upper and lower ends of the mantle tube, a spacer tube that protrudes above the glass tube containing the burnable poison is placed at the upper end of the spacer tube to raise the glass tube relative to the spacer tube. The above-mentioned problem is solved by providing a rise prevention part that prevents the above problem.

[Effect]

At the upper end of the spacer tube that protrudes above the glass tube, a part to prevent the glass tube from rising is installed to restrict the movement of the glass tube, which causes the glass tube to break into multiple pieces vertically, and each of the broken glass tubes to be Even if a relative circumferential rotational force is applied to the parts, the glass tube will not rotate and rise, causing a gap.

〔Example〕

Figures 1 to 3 show an embodiment of this invention, and this burnable poison rod is constructed by inserting a glass tube 13 into which a spacer tube 12 having a flange 12a at the bottom is inserted into a stainless steel jacket tube. 11, and end plugs 14 and 15 are attached to the upper and lower ends of the mantle tube 11, respectively. The glass tube 13 is movable in the axial direction relative to the mantle tube 11, and the spacer tube 12 has its upper end 12b protruding above the glass tube 13, but this basic structure is different from that of a conventional burnable poison stick. are the same.

In this invention, as mentioned above, the upper end 12b of the spacer tube 12 is provided with the rise prevention part A of the glass tube 13. In the case of this embodiment, the upper end 12b of the spacer tube 12 is It crosses over and expands outward to be larger than the inner diameter of the glass tube 13 to form a rise prevention section A.

To expand the upper end 12b of the spacer tube 12,
Usually, a suitable jig is used, but the specific processing method is arbitrary, including whether or not a jig is used.

The advantage of this embodiment is that the number of parts does not increase, and after inserting the spacer tube 12 into the glass tube 13, it can be processed by assembling the actual product.
As shown in the figure, a spacer tube 12 and a glass tube 13
Even if there is an error in the length, the error can be easily absorbed and the desired purpose achieved.

FIG. 4 shows a modification of the first embodiment, in which a stainless steel washer 16 is fitted onto the upper end 12b of the spacer tube 12. As shown in FIG. In this way, the glass tube 13 will not be damaged when the upper end 12b of the spacer tube 12 is expanded.

FIG. 5 shows another embodiment of this invention, in which the rise prevention part A of the glass tube 13 is formed by caulking the upper end 12b of the spacer tube 12 into a flat plate shape, thereby curing a part of the periphery of the upper end 12b. It is formed to extend over the glass tube 13. This example also has the same advantages as the first example, and the washer 16 can be used like the one in FIG. 4.

Note that the spacer tube 12 and the glass tube 13 expand due to the heat during irradiation, but even if the glass tube 13 is restrained by the flange 12a and the rise prevention part A, the linear expansion coefficient of the spacer tube 12 is smaller than that of the spacer tube 12. Since the coefficient of linear expansion is greater than that of the glass tube 13, no problem will occur.

[Effect of idea]

As explained above, the burnable poison stick of this invention has a rise prevention part formed at the upper end of the spacer tube that projects above the glass tube, which restricts the movement of the glass tube and prevents the glass tube from rising relative to the spacer tube. Since the glass tube is configured to prevent this, even if a situation occurs where the glass tube is cracked vertically and subjected to rotational force in the circumferential direction, the glass tube will not move upward and create a gap. Therefore, the occurrence of local fuel output peaks due to the occurrence of gaps can be prevented, and the integrity of the fuel can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of a burnable poison rod according to this invention, FIG. 2 is a cross-sectional view showing the relationship between the glass tube and spacer tube of the burnable poison rod of FIG. 1, FIG. 3 is a plan view of the same, FIG. 4 is a cross-sectional view of the glass tube and spacer tube showing an example in which a washer is used, FIG. 5 is a plan view of the glass tube and spacer tube showing another embodiment, and FIG.
FIG. 7 is a front view showing the processing state of the upper end of the spacer tube when the glass tube is short, FIG. 8 is a front view showing the processing state of the upper end of the spacer tube when the glass tube is long, and FIG.
The figure is a cross-sectional view of a conventional burnable poison rod, Fig. 9 is a cross-sectional view showing the state where the middle part of the broken glass tube has moved in the radial direction of the glass tube because the spacer tube has not been inserted, Fig. 10 is a front view of the glass tube and spacer tube showing the state where the glass tube of the conventional burnable poison rod has been broken into upper and lower parts, and Fig. 11 is a front view showing the state where the upper glass tube in Fig. 10 has risen by rotating 180 degrees relative to the lower glass tube, creating a gap. 11 ... outer jacket tube, 12 ... spacer tube, 12a
......flange, 12b...upper end, 13...glass tube, 14, 15...end plugs, A...rise prevention part.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A glass tube containing a burnable poison into which a spacer tube with a flange is inserted at the lower end is housed in an outer tube, and end plugs are provided at the upper and lower ends of the outer tube. A burnable poison rod, which is attached to each of the burnable poison rods, is provided with a rise prevention part for preventing the glass tube from rising relative to the spacer tube at the upper end of the spacer tube projecting above the glass tube. (2) The burnable poison rod according to claim 1, wherein the rise prevention portion is formed by expanding the entire circumference of the upper end of the spacer tube onto the glass tube. (3) The rise prevention portion is formed by crushing the upper end of the spacer tube and extending a part of the periphery above the glass tube.
Burnable poison sticks as described in Section.