JPH01288795A - Control rod for gas cooled nuclear reactor - Google Patents

Abstract

PURPOSE:To suppress the generation of a plastic strain on a cladding tube of control rod elements and to contrive to keep the integrity of a control rod, by fitting upper and lower ends of an outer tube inbetween the outer edges of upper and lower caps of the tube. CONSTITUTION:A cladding tube 103 is constituted with an outer tube 104, an inner tube 105, and an upper and a lower caps 106 and 108 which are inserted at both upper and lower end of a ring space formed between the two tubes. The cladding tube 103 houses a neutron absorber 108 in the ring space, and is fixed to a spine 102 through a spider 109. In this configuration, both upper and lower ends of the outer tube 104 are fitted to an outer edges of both upper and lower caps 106 and 107, by fitting each other but not by welding method. This fitting structure allows thermal expansions along both an axial and an outward radial directions. Therefore, even if control rods are quickly inserted into a reactor core for an emergency shut down of a reactor, the thermal expansion of the outer tube 104 caused by a temperature difference between the outer tube 104 and the inner tube 105, is absorbed, and the generation of a plastic deformation caused by a thermal stress can be avoided.

Description

Detailed Description of the Invention [1-1 of the Invention (Industrial Application Field) The present invention relates to a gas-cooled nuclear reactor used in a gas-cooled nuclear reactor such as a high-temperature gas reactor using helium gas as a coolant. Regarding control rods for type nuclear reactors, in particular, it is possible to allow thermal expansion of the outer tube part constituting the cladding tube of the control rod element in the axial and radial directions outwards, and between the outer tube part side and the inner tube part side. This method prevents the occurrence of thermal stress at the connecting part of the member connecting the outer tube section and the inner tube section due to the difference in thermal expansion of the tubes, thereby preventing the occurrence of plastic strain, thereby extending the life of the control rod elements and, ultimately, the control rods. Concerning what is possible to achieve.

(Prior Art) 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.

By the way, there are various kinds of control rods, and for example, in a high-temperature gas reactor of a gas-cooled nuclear reactor, a control rod having a configuration as shown in FIG. 3 is employed. Reference numeral 1 in FIG. 3 is a reactor core, and an insertion hole 2 is formed in this core. A control rod guide tube 3 is installed above the insertion hole 2 . The control rods 4 are placed in the core 1 within this control rod guide tube 3.
It is arranged so that it can be inserted and pulled out. The control rod 4 has a plurality of control rod elements 5 connected in the axial direction via spines 6, and a wire lobe 7 is connected to the control rod element 5 located at the uppermost end. A control rod drive mechanism (not shown) is connected via this wire lobe 7.

The control rod 4 having the above structure is flexible and has a certain degree of freedom, so it can sufficiently cope with bends in the control rod guide tube 3 or the insertion hole 2. I can do it.

Next, the above control will be explained with reference to FIG. FIG. 4 is a sectional view showing the configuration of the control rod element 5, and reference numeral 11 in the figure is a cladding tube. This km
As shown in the figure, the tube 11 has a double cylindrical shape, and includes an outer tube section 12, an inner tube section 13 disposed on the inner circumferential side of the outer tube section 12, an outer tube section 12, and an inner tube section 13. An upper cap 14 is fitted over the upper end of the annular space formed by the outer tube section 12 and the inner tube section 13. There is. A hollow cylindrical neutron absorber 17 is provided in the annular space.
is filled. The outer tube part 12, the inner tube part 13, the cap 14, and the lower cap 15 are welded to each other, and the welded parts are indicated by symbols a, b, and C in the figure.

Further, as already mentioned, the plurality of control rod elements 5 are connected via the spine 6, and in this case, each control rod element 5 is connected via the spider 16 integrally provided at the upper part of the inner tube section 13. It is fixed to the '-2 spine 6. The inner peripheral end of the spider 16 is welded to the spine 6 (the welded portion is indicated by d in the figure).

According to the above configuration, for example, when the control rod 4 is inserted into the reactor core 1 at high speed in order to make an emergency shutdown of the reactor (so-called scram operation), the outer tube portion 12 of the cladding tube 11 of the control rod element 5 is inserted. It is heated by radiant heat from the wall surface of the hole 2, heat transfer via the coolant, etc., and a large temperature difference occurs between it and the inner tube part 13. Due to the generation of such a temperature difference, the connecting portion between the outer tube section 12 and the inner tube section 13, for example, the upper cap 14
Thermal stress due to the difference in thermal expansion occurs at the connection portion between the lower cap 15, the spider 16, and the inner tube portion 13, and as a result, there is a possibility that plastic strain may occur in the cladding tube 11. This is particularly noticeable at welds a, bSc, and d. That is, since the material strength is not stable in the welded part and its vicinity, it is expected that plastic strain will be concentrated. Scram operations are often performed during reactor operation, and if plastic strain occurs in the yi cladding 11 each time, the lifespan of the cladding 11, the control rod elements 5, and even the control rods 4 themselves will be affected. This will shorten the period.

(Problems to be Solved by the Invention) In this conventional configuration, plastic strain repeatedly occurs in the cladding tube of the control rod element, which impairs the integrity of the control rod element and, in turn, the control rod. The present invention was made based on these points, and its purpose is to suppress the occurrence of plastic strain in the cladding tube of the control rod element, thereby improving the soundness of the control rod element and, ultimately, the control rod. An object of the present invention is to provide a control rod for a gas-cooled nuclear reactor that can maintain its properties.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the control rod for a gas-cooled nuclear reactor according to the present invention includes an outer tube portion, and a control rod arranged at intervals on the inner circumferential side of the outer tube portion. Inner pipe section. The upper cap is fitted over the upper end of the annular space formed by the outer tube and the inner tube, and the lower cap is fitted over the lower end of the annular space formed by the outer tube and the inner tube. A control rod configured by connecting a control rod element to a spine via a spider and having a cladding tube including a cap and a neutron absorber housed in the annular space of the cladding tube, the outer tube The part is installed with its upper and lower ends engaged with the outer circumferential edge of the upper cap and the outer circumferential edge of the lower cap, respectively, and in a free state within a predetermined range outward in the axial and radial directions. It is characterized by the fact that

(Function) In other words, the upper and lower ends of the outer tube portion are not welded to the outer circumferential edges of the upper cap and the outer circumferential edges of the lower cap as in the conventional case, but are attached in an engaging relationship. The engagement structure is designed to allow thermal expansion of the outer tube portion in the axial direction and outward in the radial direction.

Therefore, even if the control rods are inserted into the reactor core at high speed in order to bring the reactor to an emergency shutdown, plastic deformation will not occur as in the conventional method. In other words, even if the outer tube is heated and a large temperature difference occurs between the inner tube and the inner tube, the outer tube is free to move outward in the axial and radial directions, so the heat will be absorbed. Expansion is effectively absorbed, thereby reliably preventing the generation of thermal stresses and thereby plastic deformation. The life of the control rod elements and thus of the control rods is thus significantly extended.

(Example) An example of the present invention will be described below with reference to FIG. It should be noted that the same parts as in the prior art are denoted by the same reference numerals and the explanation thereof will be omitted, and the basic structure of the control rod 4 will be explained with reference to FIG. 3.

FIG. 1 is a sectional view showing the configuration of a control rod element 101,
The control rod is constructed by connecting a plurality of control rod elements 101 via spines 102.

The configuration of the control rod element 101 will be explained first. First, reference numeral 103 in the figure is a cladding tube, and this cladding tube 103 consists of an outer tube section 104, an inner tube section 105 disposed at an interval on the inner circumferential side of the outer tube section 104, the outer tube section 104, and an outer tube section 104. Pipe part 10
upper caps 10 and 6 fitted over the annular space formed by 5; the outer tube portion 104 and the outer tube portion 105;
It consists of a lower cap 107 with a corrugated bottom at the bottom of an annular space formed by. A hollow cylindrical neutron absorber 108 is accommodated in the annular space.

The cladding tube 103 is fixed to the spine 102 via a spider 109. The spider 109 has a cylindrical portion 110 through which the spine 102 passes, and this cylindrical portion 11.
0, and a flange 111 provided on the outer peripheral side. A key 112 is provided in the cylindrical portion 110, and a key groove 113 is formed in the spindle 102.

The spider 109 transfers the key 112 to the spine 102.
By engaging the keyway 113 of the spine]02
Fixed. In addition, a plurality of ribs 114 are provided radially on the flange portion 111, and a plurality of coolant channels are formed, and the inner peripheral side of the cladding tube 103 is also cooled through these coolant channels. distribute materials.

Further, a steadying ring 115 is installed below the spider 109 and inside the inner tube section 105. This steady rest ring 115 is composed of a cylindrical portion 116 fixed to the spine 102 and a flange portion 117 extending outside of the cylindrical portion 116. The cylindrical part 116
A key 118 is formed on the side, and a key groove 119 is formed on the side of the spine 102. Steady rest ring 115
is fixed to the spine 102 by engaging the key 118 in the keyway 119.

Further, a coolant flow path is formed in the flange portion 117, and the coolant is introduced into the inner peripheral side of the cladding tube 103. The steady rest ring 115 having such a structure prevents the cladding tube 103 from swinging.

Next, the outer tube part 104, the inner tube part 105, and the upper cap 106
, the coupling structure of the lower cap 107, etc. will be explained. First, a flange portion 120 that projects outward is formed at the lower end of the inner tube portion 105, and a stepped engagement portion 121 is formed on the outer peripheral edge of this flange portion 120. On the other hand, a stepped engagement portion 122 that engages with the stepped engagement portion 121 is formed on the inner peripheral edge of the lower cap 107, and the inner tube portion 105
and the lower cap 107 are the stepped engaging portions 121 and 12.
2 by engaging with each other.

Further, a stepped engagement portion 123 is formed on the outer peripheral edge of the lower cap 107.

The upper end of the inner tube portion 105 is reduced in diameter to form a stepped engagement portion 124.
is formed. On the other hand, the inner circumferential edge of the upper cap 106 is extended downward to form an engaging portion 125, and this engaging portion 125 engages with the stepped engaging portion 124 from above. Further, a stepped engagement portion 126 is formed on the outer peripheral edge of the upper cap 107. The stepped engagement portion 126 of the upper cap 106 and the lower cap 105
The outer tube portion 104 is disposed between the stepped engagement portion 123 and the stepped engagement portion 123 . As is clear from the figure, the outer tube part 10
4 has a degree of freedom in the axial direction, and also has a degree of freedom in the radial direction as a button. This aims to maintain the integrity of the control rod 4. That is, when the control rods 4 are inserted into the reactor core 1 at high speed in order to make an emergency shutdown of the reactor, the outer tube section 104 is heated by radiant heat from the wall of the insertion hole 2, and the inner tube section 105 side is heated. There is a large temperature difference between them, which causes a difference in thermal expansion. Conventionally, the configuration was incapable of absorbing this difference in thermal expansion, resulting in large thermal stress and resulting plastic strain in welded parts. On the other hand, in the case of this embodiment, as already explained, thermal expansion in the axial direction and radial outward thermal expansion of the outer tube portion 104 is allowed, so a large The generation of thermal stress and the resulting plastic strain are reliably prevented.

The inner tube portion 105 engages the lower end surface of the stepped engagement portion 124 with the flange portion 11 of the spider 109 from above. Further, a key hole 127 is continuously formed in the stepped engagement portion 124 of the inner tube portion 105 and the engagement portion 125 of the upper cap 106, and a key 128 is inserted into this key hole 127.

A plurality of guide fins 129 are attached at equal intervals in the circumferential direction on the outer peripheral surface of the lower part of the outer tube section 104. These guide fins 129 prevent the outer tube portion 104 from coming into direct contact with the insertion hole 2 of the core, and actively form a coolant flow path.

The operation will be explained based on the above configuration.

First, the control rod 4 according to the present embodiment 1J is placed in the control rod guide tube 3, and its upper end is connected to the control rod drive mechanism via the wire rope 7. The control rod drive mechanism adjusts the insertion and withdrawal of the control rods 4 into the reactor core 1 to control the output of the reactor.

Note that when assembling the control rod element 101, first the inner tube part 10 is assembled.
The lower cap 107 is assembled into the lower part of the housing 5 via the stepped engagement parts 121 and 122. Next, the outer tube part 104 is assembled into the lower cap 107 via the stepped engagement parts 123 and 122. In this state, the neutron absorber 108 is inserted, the upper cap 106 is fitted, and the key 128 is inserted into the key hole 127.

Next, the stepped engagement portion 124 of the inner tube portion 105 is attached to the spider 109.
The control rod element 101 is attached to the spine 102 by placing it on the heel 111 of the control rod element 101 .

Now, in the event of an emergency shutdown of a nuclear reactor, control rods are inserted into the reactor core at high speed. At that time, according to conventional control rods, large plastic deformation occurs in, for example, welded parts.
There was a risk that the integrity of the control rods would be compromised. On the other hand, in the case of this embodiment, there is no such concern, and the integrity of the control rod 4 is reliably maintained. This point will be explained in detail below.

First, when the control rod 4 is inserted into the core 1 at high speed, the outer tube part 1
04 is heated by radiant heat from the wall of the insertion hole, a large temperature difference occurs between the outer tube section 104 side and the inner tube section 105 side. A large difference in thermal expansion occurs between the two sides. This thermal expansion difference occurs both in the axial direction and in the radial direction, but is particularly noticeable in the axial direction. At this time, in the case of this embodiment, since the outer tube portion 104 is configured to be freely axially and radially outward, its thermal expansion is effectively allowed. Therefore, the occurrence of large thermal stress and the resulting plastic strain are reliably prevented, and control rod elements,
In turn, the integrity of the control rods is reliably maintained.

In addition, in the case of this embodiment, the outer tube part 104 is not only configured to be free to move outward in the axial and radial directions, but also to connect the outer tube part 104 with the upper cap 106 and the lower cover 107, as well as to connect the outer tube part 104 with the upper cap 106 and the lower cover 107. The coupling between the tube part 105 and the upper cap 106 and the lower cap 106 and the coupling between the inner tube part 105 and the spider 109 are all realized by an engagement structure,
The welded area, where conventionally plastic strain was concentrated, has been made into a sharper structure. In each engagement structure, the difference in thermal expansion between the members is effectively absorbed. In particular, the inner tube portion 105 and the spider 109 are not integrated as in the past, and the stepped engagement portion 124 of the inner tube portion 105 is connected to the spider 109.
It is simply placed on the flange 111 of No. 9. Therefore, the difference in thermal expansion between the inner tube portion 105 and the spider 109 is effectively absorbed, and the generation of thermal stress and thereby plastic strain is effectively prevented.

According to this embodiment, the following effects can be achieved.

(1) First, according to this embodiment, it is possible to prevent the occurrence of plastic strain in each control rod element 101 and maintain its soundness. As a result, the control rod element 101 as well as
The lifespan of control rods can be significantly extended.

This is achieved by first cutting the welded parts and then assembling the entire body with an engaging structure.In particular, the outer tube part 104 is configured to have a free configuration in the axial direction and outside in the diametrical direction so that its thermal expansion can be absorbed. This is because the relationship between the inner tube portion 105 and the spider 109 is not integrated as in the conventional case, but is assembled in an engaging relationship that can absorb the difference in thermal expansion between them.

(2) Furthermore, since the integrity of the control rods is maintained, their functions are also reliably maintained, which improves the safety of the nuclear reactor.

■Furthermore, as the lifespan of the control rods has been extended, the frequency of replacing control rods has been reduced, which not only eliminates the time and effort required for replacement work, but also improves plant availability. be able to.

Next, a second embodiment will be described with reference to FIG.

In this second embodiment, a guide 131 is provided on the upper surface side of the spider 109, and the guide 131 guides the inner tube portion 104 to determine its position with respect to the spider 109.

[Effects of the Invention] As detailed above, according to the control rod for a gas-cooled nuclear reactor according to the present invention, the occurrence of plastic strain in the cladding tube of the control rod element is suppressed, and the life of the control rod element and ultimately of the control rod is reduced. The effects are great, such as being able to extend the time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a control rod element according to a first embodiment of the present invention, FIG. 2 is a sectional view of a control rod element according to a second embodiment,
Figures 3 and 4 are diagrams used to explain the conventional example.
The figure is a sectional view of a control rod, and FIG. 4 is a sectional view of a control rod element. 1... Reactor core, 2... Insertion hole, 3... Control rod guide tube, 4... Control rod, 7... Wire lobe, ]01.
...Control rod element, 102...Spine, 103...
Cladding tube, 104... Outer tube part, 105... Inner tube part, 1
06... Upper cap, 107... Lower cap,
108...neutron absorber, 109...spider. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] an outer tube part, an inner tube part arranged at intervals on the inner circumference side of the outer tube part, an upper cap fitted over the upper end of an annular space formed by the outer tube part and the inner tube part, and the outer tube. A control rod element comprising a cladding tube consisting of a lower end cap fitted onto the lower end of an annular space formed by a section and an inner tube section, and a neutron absorber housed in the annular space of the cladding tube. In the control rod, each of which is connected to a spine via a spider, the outer tube part has its upper and lower ends engaged with the outer peripheral edge of the upper cap and the outer peripheral edge of the lower cap, respectively. 1. A control rod for a gas-cooled nuclear reactor, characterized in that the control rod is attached to the axially and radially outwardly in a state capable of absorbing thermal expansion within a predetermined range.