JPH0194291A - Control rod element - Google Patents

Abstract

PURPOSE:To improve a safety and a working efficiency, by decreasing the generation of a thermal stress caused by a difference in thermal expansion rates during a reactor scram. CONSTITUTION:With a clutching mechanism of a notched part 121 of a lower cap 116 and a notched part 122 formed at a lower end of an outer pipe 111a, and another clutching mechanism of a notched part 123 formed at an upper cap 115 and a notched 124 formed at an upper end of the outer pipe 111a a relative displacement caused by an axial and radial thermal expansion difference of the outer pipe 111a against an inner pipe 111b is absorbed. On the other hand, by making the inner pipe 111b and a spider 114 to be a fitting mechanism, a relative displacement along an axial and radial direction of the both parts caused by a thermal expansion, is absorbed. Thereby, the generation of thermal stress caused by a difference in thermal expansion and also the generation of a thermal strain is well prevented. Consequently, a integrity of a control rod element 106 and also a control rod 104 can be secured and its safety is much improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in control rod elements constituting control rods of nuclear reactors that use a gas such as helium as a coolant.

[Technical Background of the Invention] Generally, in a nuclear reactor, the nuclear fission reactivity of the reactor core is controlled by inserting and withdrawing control rods filled with neutron absorbers into the reactor core.

Therefore, the structure of the control rod will be explained with reference to FIGS. 4 and 5. Reference numeral 1 in the figure is a reactor core, and an insertion hole 2 is formed in this reactor core 1 . A control rod guide tube 3 is arranged above the insertion hole 2 . A control rod 4 is suspended by a wire rope 5 through this guide tube 3.

The control rod 4 has a configuration in which a plurality of control rod elements 6 are connected in the axial direction. Further, the control rod 4 has flexibility, and therefore has the advantage of having a large degree of freedom of insertion against bending of the control rod guide tube 3 and misalignment of the insertion hole 2.

Next, the configuration of the control rod element 6 will be explained in detail with reference to FIG. Reference numeral 11 in the figure is a double cylindrical cladding tube,
The outer tube portion is indicated by 11a, and the inner tube portion is indicated by 1.1b. A neutron absorber 12 is accommodated within the cladding tube 11 . Further, a spine 11 is arranged in the axial direction at the center of the cladding tube 11, and the cladding tube 11 is supported by the spine 13 via a spider 14 installed on the inner peripheral side of the upper end thereof. . Further, a plurality of control rod elements 6 are connected in the axial direction via this spine 13. Further, an upper cap 15 and a lower cap 1 are provided at the upper and lower ends of the cladding tube 11.
6 is welded. The reference numeral 17 in the figure is a guide ring, and the guide ring 17 prevents the control rod element 6 from swinging excessively with respect to the spine 13. Also code 18
is a plurality of guide fins installed at equal intervals in the circumferential direction,
These guide fins prevent the outer tube portion 11a from coming into direct contact with the insertion hole 2, thereby ensuring a coolant flow path. Furthermore, reference numeral 19 is a support member fixed to the spine 13, and the spider 14 is placed on this support member 19.

[Problems with background technology] According to the above configuration, there were the following problems.

In other words, during an emergency reactor shutdown (hereinafter referred to as scram),
When the control rods 4 are urgently inserted into the reactor core 1 at high speed, the outer tube portion 11a of the cladding tube 11 is heated due to high-temperature radiant heat received from the insertion hole 2 and heat conduction via the coolant, and the inner tube portion 11a is heated. A large temperature difference occurs between the tube portion 11b and the tube portion 11b. Due to the generation of such a temperature difference, thermal expansion occurs at the connecting portion between the outer tube portion 11a and the inner tube portion 11b, and more specifically, at the root portion between the upper cap 15, lower cap, 16 spreader portion 14 and the inner tube portion 11b. There is concern that thermal stress will occur due to the difference, and as a result, excessive plastic strain will occur in the cladding tube 11. This plastic strain occurs every time the above scram operation is performed,
There is a problem in that the loss of integrity of the cladding tube 11 causes the life of the control rod 4 itself to be significantly shortened.

[Object of the Invention] The present invention has been made based on the above points, and its purpose is to alleviate the thermal stress generated during scram,
The object of the present invention is to provide a control rod element that not only maintains the integrity of the cladding but also can significantly extend the life of the control rod itself.

E Summary of the Invention In other words, a control rod element according to the present invention includes a spider fixed to a spine extending in the axial direction, an upper cap integrally attached to the outer peripheral side of the spider, and an outer peripheral end of the upper cap. an outer tube portion disposed such that a first engaged portion formed at the upper end portion is engaged with a first engaging portion formed at the outer tube portion; A lower cap is disposed such that a second engaged portion formed on the outer circumferential end is engaged with the retaining portion, and a neutron absorber is integrally attached to the lower cap and is disposed on the inner circumferential side of the outer tube portion. The invention is characterized by comprising an inner tube section which is arranged in a wide-spread manner to accommodate the spider, and whose upper end is fitted into the spider.

In other words, by making the connection between the outer tube part and the upper cap, and the outer tube part and the lower cap into an engaging structure that allows displacement in the axial and radial directions, and by making the inner tube part and the spider into a fitting structure. , for example, absorbs the thermal expansion of each member during scram, suppresses the generation of thermal stress due to the difference in thermal expansion between the outer tube and the inner tube, and the difference in thermal expansion between the inner tube and the spider, thereby reducing plastic strain. The aim is to extend the life of control rods by suppressing the occurrence of

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a longitudinal sectional view of a control rod element 106 constituting a control rod 104 according to this embodiment, and reference numeral 111 in the figure indicates a cladding tube. The cladding tube 111 is composed of an outer tube portion 111a and an inner tube portion 111b, and has a double cylindrical shape. In addition, a pellet-shaped neutron absorber 1 is provided inside the cladding tube 111.
12 are accommodated. A lower cap 116 having an annular disk shape is continuously formed at the lower end of the inner tube portion 111a. Further, the corners are formed with curvature to prevent stress concentration. Above lower cap 1
At the outer peripheral end of 16, there is a cutout step portion (second engaged portion) 121.
is formed over the entire circumference in the circumferential direction. This notch step 1
21 has its lower part cut out. On the other hand, a cutout step portion (second engagement portion) 122 that engages with the cutout step portion 126-1 is formed along the entire circumferential direction at the lower inner peripheral edge of the outer tube portion 111a. This cutout stepped portion 122 has a shape with an upper portion cut out. In addition, the inner tube part 111
The upper end of b is formed into a straight tube shape. The outer cylindrical portion 114a of the spider 114 is fitted into this upper end. An upper cap 115 is continuously formed on the upper part of the outer cylinder part 114a. A notch step portion (first engaging portion) 123 is formed at the outer circumferential end of the upper cap 115 and has a shape in which the upper portion is notched. A notch step portion (first engaged portion) 124 formed at the upper end portion of the outer tube portion 111a and having a shape in which a lower portion thereof is notched is engaged with the notch step portion 123. An engagement structure between the cutout step 121 of the lower cap 116 and the cutout step 121 formed at the lower end of the outer tube portion 111a, and the engagement structure between the cutout step 123 formed in the upper cap 115 and the cutout step 123 formed at the upper end of the outer tube portion 111a. cutout step 1
24, it absorbs the relative displacement due to the difference in thermal expansion in the axial and radial directions of the outer tube portion 111a with respect to the inner tube portion 111b, and the inner tube portion 111b and the spider 1
14, the relative displacement in the axial and radial directions caused by the difference in thermal expansion can be absorbed.

Conventionally, these connections were made by welding.

Further, the neutron absorber 112 is placed on the lower cap 116. That is, 1 m of the neutron absorber 112 is supported by the above two engagement structures. The two engaging parts are configured to sufficiently withstand the weight of the neutron absorber 112, and as shown in FIG. 3, the outer tube part 111a and the inner tube part 11
1b, the engagement is maintained in a sound state even if a relative displacement occurs between the two and 1b.

This also applies to the fitting structure between the inner tube portion 111b and the spider 114.

Next, the spider 114 will be further explained. The spider 114 consists of the outer cylinder 114a and an inner cylinder 114b located on the inner peripheral side of the outer cylinder 114a. 1
The support member 119 is fixed to the spine 113 by inserting the inner insertion hole 114C into the spine 113.
is placed on top. Note that the outer cylinder 114a and the inner cylinder 114
b is integrated with the rib plate 114d via a plurality of rib plates 114d.

Further, the reference numeral 117 in the figure is a guide ring, and the reference numeral 1
18 is a guide fin. These guide rings 117
The functions of the guide fins 118 are as described above.

The operation will be explained based on the above configuration. First, core power control is performed by controlling the control rods 104 in the core 1 by a control rod drive mechanism (not shown).
This is done by controlling the insertion and withdrawal of the If a scram signal is output for some reason, a scram operation is performed and the control rods 104 move to the core 1.
It is urgently inserted into the body at high speed. During this scram, the control rod 104 receives high-temperature radiant heat through the wall surface of the insertion hole 2 and is heated to a high temperature by heat conduction through the coolant. As a result, both the outer tube portion 111a and the inner tube portion 111b thermally expand, but there is a difference in thermal expansion between the two, and the outer tube portion 111a expands more. This is as described above. Such a difference in thermal expansion occurs significantly in the axial direction, but of course also occurs in the radial direction. At this time, in the case of the control rod 104 according to this embodiment, such a difference in thermal expansion can be effectively absorbed, and the outer tube portion 111a and the inner tube portion 111
The health of not only the control rod 1b but also the control rod 104 is maintained reliably. In other words, the outer tube part 1118, the inner tube part 11 lb, the upper cap 115, and the lower cap 116 are connected by an engaging structure in two places, and this is not a fixed structure that is merely engaged, but in the axial direction. and can absorb relative displacement in the radial direction. Further, the inner tube portion 111b and the spider 114 are connected by fitting, and thus also absorb relative displacement in the axial direction. As a result, the control rod element 106 is in the state shown in FIG. At that time, both the pipe portions 111a and 111
The engagement relationship between the two engagement portions is not released due to the relative displacement of b, and the coupling relationship is reliably maintained.

According to this embodiment, the following effects can be achieved. That is, the outer tube portion 111a and the upper and lower caps 115
．． 116 is connected to the notched step portions 121 and 122.12.
3 and 124, the difference in thermal expansion between the outer tube section 111a and the inner tube section 111b is absorbed, and the inner tube section 111b and the spider 114
Since the relationship between the inner tube portion 111b and the inner tube portion 111b is a mere fit, the difference in thermal expansion between the inner tube portion 111b and the spider 114 is also effectively absorbed. Therefore, no thermal stress is generated due to the difference in thermal expansion during scramming, and no plastic strain is generated. Therefore, it is possible to maintain the soundness of the control rod element 106 and, by extension, the control rod 104, to improve safety, and to extend its life. Due to such an extended life, the number of replacements of the control rods 104 can be reduced, which is extremely effective in improving the plant operating rate.

Note that the present invention is not limited to the above-mentioned embodiments, and the shapes of each engaging portion and locking portion may be any shape as long as they can absorb relative displacement in the axial direction and radial direction, and various shapes may be used. Conceivable. Furthermore, for the upper cap and the lower cap, for example, connecting portions may be left at a plurality of locations in the circumferential direction, and the portions between may be cut out. In this case, the thermal stress generated at the root portion can be further reduced.

[Effects of the Invention] As detailed above, according to the control rod element according to the present invention,
It is possible to effectively reduce the generation of thermal stress caused by the difference in thermal expansion during scram, suppress the generation of plastic strain, maintain the integrity of the control rod, and extend its life, resulting in improved safety. The effects are great, including not only improvement but also the ability to improve the plant's operating rate.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing one embodiment of the present invention.
The figure is a longitudinal sectional view of the control rod element, Figure 2 is a sectional view of the control rod element before displacement, Figure 3 is a sectional view of the control rod element after displacement, and Figure 4 is a diagram showing the entire control rod. , FIG. 5 is a longitudinal sectional view of a conventional control rod element. 104... control w rod, 106... control rod element, 111
...Claying tube, 111a...Outer tube part, 111b...
Inner tube part, 112... Neutron absorber, 113... Spine, 114... Spider, 115... Upper cap, 116... Lower cap, 121... Notch step part (second cover) Engagement part>, 122... Notch step part (second engaging part). 123... Notch step part (first engaging part), 124...
Notch step portion (first engaged portion). Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] A spider fixed to a spine extending in the axial direction, an upper cap integrally attached to the outer circumferential side of the spider, and a first engaging portion formed at the outer circumferential end of the upper cap. an outer tube portion disposed to engage the formed first engaged portion; and a second engagement portion formed at the outer peripheral end of the outer tube portion, and a lower cap disposed to engage the engaged portion; and a lower cap integrally attached to the lower cap and arranged concentrically to accommodate a neutron absorber on the inner peripheral side of the outer tube portion, and an upper end portion thereof. and an inner tube portion fitted into the spider.