JP2002168983A - Method of manufacturing control rod for pressurized water reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence and progress of contact wear of a control rod for a pressurized water reactor. SOLUTION: The control rod 40 is composed of a cover pipe 7, upper and lower end plugs 9 and 11 respectively joined to upper and lower ends of the cover pipe 7, and a neutron absorber 13 and a spring 15 put inside the cover pipe 7. The method of manufacturing the control rod 40 is composed of assembly through processes of joining the upper end plug 9 to the cover pipe 7 by a weld 41, applying a coating 43 on outer circumferential faces of the weld 41 and the cladding tube 7, inserting the neutron absorber 13 and the spring 15 inside the cladding tube 7, joining the cladding tube 7 and the lower end plug 11 by a weld 45, and applying a surface coating 47 on outer circumferential faces of the lower end plug 11 and the weld 45.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod for a pressurized water reactor, and more particularly to a method for manufacturing the control rod.

[0002]

2. Description of the Related Art A control rod for a pressurized water reactor is generally constructed as shown in FIG.
It is used in the form of a control rod cluster as shown in FIG. To outline this structure, in FIG. 5, the control rod cluster 1
It comprises a spider 3 connected to a control rod drive and a plurality of control rods 5 each having an upper end connected to its radial vane. The structure of the control rod 5 will be described with reference to FIGS. 6 and 7. An upper end plug 9 and a lower end plug 11 are welded to the upper end and the lower end of a hollow cladding tube 7, and a neutron absorbing material is provided inside. 13 and a spring 15 are contained. As particularly shown in FIG. 7, the outer surface of the cladding tube 7 is provided with a chrome plating 17. The screw portion at the upper part of the upper end plug 9 is used for connection with the spider 3.

The control rod cluster 1 having the above-described structure is
The control rod 5 is used to be inserted into and removed from the control rod guide thimble of the fuel assembly constituting the core. FIG. 8 conceptually shows an example of the structure of such a fuel assembly. Referring to FIG. 8, the structure of the fuel assembly 20 will be outlined.
The upper nozzle 21 and the lower nozzle 23 are connected by a plurality of parallel control rod guide thimbles 25. A plurality of support grids 27 are fixed to the guide thimble 25 at intervals, and a plurality of fuel rods 29 are inserted and supported one by one in the plurality of grid openings. The core of a nuclear reactor is formed by loading a large number of such fuel assemblies 20 adjacent to each other.

In order to insert and remove the control rods 5 of the control rod cluster 1 into and from the core constituted by the fuel assemblies 20 as described above, a control rod driving device erected on the upper lid of a reactor vessel (not shown) is used. The control rod cluster guide tube structure shown in FIGS. 9 to 11 is used between the core and the top lid. In brief, the guide tube structure 35 is supported by an upper core plate 31 immediately above the core and an upper core support plate 33 further above. The outer circumference of the guide tube structure 35 is a cylindrical body 37 having a substantially square cross section, in which guide members 39a to 39j of control rods 5 called cards are provided at intervals in the vertical direction. During the rated output operation of the reactor, the control rod cluster 1 is almost lifted up and supported therein, so that the cards 39a to 39j
Contacts the control rod 5 and supports it from the side. The lower part of the guide tube structure 35 is called continuous and is particularly well shown in FIG. As shown in FIG. 10, a large opening is formed in the cylindrical body 37 in this portion, and a part of the coolant flowing as indicated by the white arrow flows outward through the opening. During the rated output operation, the lower end of the control rod 5 of the control rod cluster 1 is
0 is within the upper end.

[0005]

As described above, since the reactor coolant flows in the guide tube structure 35, the thin control rod 5 suspended and held in the guide tube structure 35 Subject to induced vibration, easily vibrates. The control rod 5 oscillating in this way contacts the guide support portion in the guide tube structure 35 and the inner surface of the guide thimble 25 in the fuel assembly 20 to be worn and progress. In the worst case, the occurrence and progress of such abrasion may result in the penetration of the cladding tube 7 of the control rod 5. Therefore, the outer surface of the cladding tube 7, which is liable to be damaged, is coated with chrome plating or the like. (See FIG. 7). Further, the thickness of the chrome plating on the lower part of the cladding tube 7 of the control rod 5 is appropriately changed, for example, the thickness is reduced in order to reduce interference with a dash pot formed on the lower part of the guide thimble 25. Is attached.

Conventionally, coating such as chrome plating as described above has been applied before the control rod 5 is assembled, either in the state of the cladding tube 7 alone or after the cladding tube 7 and the upper end plug 9 are welded. According to this method, coating cannot be applied to the welded portion between the lower end plug 11 and the cladding tube 7.
For this reason, near the weld between the lower end plug 11 and the cladding tube 7,
In some cases, a portion to which no improvement in wear resistance has been imparted may remain. In addition, when the control rod 5 is assembled, even if the coating is applied after the cladding tube 7 and the lower end plug 11 are welded, abrasion resistance is partially provided near the welded portion between the upper end plug 9 and the cladding tube 7. The part which is not done will remain. Therefore, an object of the present invention is to manufacture a control rod,
It is an object of the present invention to provide a method for manufacturing a control rod for a pressurized water reactor, which can coat the outer surface including the cladding tube 7 and the welds at both ends thereof without any residue.

[0007]

According to the present invention, there is provided, in accordance with the present invention, a cladding tube, an upper end plug and a lower end plug respectively joined to an upper end and a lower end of the cladding tube, and The basic process of manufacturing a control rod composed of a neutron absorber and a spring to be put in is performed according to the following procedure. That is, the upper end plug or the lower end plug is fixedly joined to the upper end or lower end of the cladding tube by the first welding or the second welding, and thereafter, the neutron absorbing material and the spring are inserted into the cladding tube, Finally, a lower end plug or an upper end plug is joined and fixed to the lower end or the upper end of the cladding tube by the second welding or the first welding. Then, the coating on the outer peripheral surface of the cladding tube is performed as the first coating together with the outer peripheral portion of the region of the first or second welding performed in the first welding. The coating of the outer periphery of the region of the welding to be performed later is performed as a second coating, and the coating of the outer peripheral surface of the lower end plug is formed in the region of the second welding between the cladding tube and the lower end plug. Performed with coating. The coating of the outer peripheral surface of the cladding tube may be performed when the cladding tube is used alone.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same portions are denoted by the same reference numerals throughout the drawings, including the drawings related to the prior art. First, referring to FIG. 1, a cladding tube 7 is prepared (a),
The upper end plug 9 is joined and fixed to the upper end of the cladding tube 7 by welding 41 (b). Next, a coating 43 is applied around the welded portion between the upper end plug 9 and the cladding tube 7 and on the outer peripheral portion of the cladding tube 7.
The coating 43 may be chrome plating. The coating 43 is a part 4 corresponding to the conventional coating.
3a and the extension 43b, but no coating is applied to the joint between the cladding tube 7 and the lower end plug 11 (c).
Next, the spring 15 and the neutron absorbing material 13 are put into the cladding tube 7, and then the cladding tube 7 and the lower end plug 11 are joined and fixed by welding 45 (d). Finally, an additional surface coating 47 is applied to the outer peripheral surface of the lower end plug 11 and around the weld between the lower end plug 11 and the cladding tube 7 (e). In this way, the entire outer peripheral surface of the cladding tube 7 and the lower end plug 11 and the periphery of the welded portion of the upper end plug 9 are completely covered by the coating 43 and the surface coating 47, and the control rod 40 is completed. (F).

Next, a modification of the above embodiment will be described with reference to FIG. Explaining only the different part, the coating performed in the step c is only the part except the conventional construction part 43a, that is, the part corresponding to the dashpot. The coating of the dashpot-corresponding portion is performed in step e by including it in the surface coating 49 of the joint between the lower end plug 11 and the lower end plug 11 of the cladding tube 7. The control rod completed in this way is
The control rod 40 is the same as in the above embodiment. The thickness of the surface coating 49 is preferably smaller than that of the coating 43a in consideration of the insertability into the dash pot portion. In this embodiment, the coating is divided into the coating 43a and the surface coating 49, and the former is performed first, but the welding of the cladding tube 7 and the upper end plug 9 and the welding of the lower end plug 11 are performed. , The surface coating 49 is performed first, and finally the coating 43 is performed.
a may be performed.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 3, a cladding tube 7 is prepared (a),
The lower end plug 11 is joined and fixed to the lower end of the cladding tube 7 by welding 45 (b). Next, a coating 51 is applied to the outer peripheral surface of the cladding tube 7 excluding the periphery of the welded portion between the upper end plug 9 and the clad tube 7 and the outer peripheral surface of the welded portion 45 to the lower end plug 11. The coating 51 may be chrome plating (c). next,
A spring 15 and a neutron absorbing material 13 are put in the cladding tube 7,
Thereafter, the cladding tube 7 and the upper end plug 9 are joined and fixed by welding 41 (d). Finally, an additional surface coating 53 is applied around the weld between the upper end plug 9 and the cladding tube 7 (e). If the surface coating 53 is a two-stage coating as required, the abrasion resistance is improved. In this way, the entire outer peripheral surface of the cladding tube 7 and the lower end plug 11 and the periphery of the welded portion of the upper end plug 9 are completely covered with the coating 51 and the surface coating 53, and the control rod 50 is completed. (F).

Next, still another embodiment of the present invention will be described with reference to FIG. In FIG. 4, a cladding tube 7 is prepared (a), and a coating 61 is applied to the outer peripheral surface of the cladding tube 7 alone (b). As the coating 61, chrome plating may be used, but the outer peripheral surfaces of the scheduled welds at both ends are not coated. Next, the upper end plug 9 is fixed to the upper end of the cladding tube 7 by welding 41, and a spring 15 and a neutron absorbing material 13 are put into the cladding tube 7 (c). Thereafter, the cladding tube 7 and the lower end plug 11 are joined and fixed by welding 45 (d).
Finally, additional coatings 63 and 65 are applied around the weld 41 between the upper end plug 9 and the cladding tube 7, the weld 45 between the lower end plug 11 and the cladding tube 7, and the outer peripheral surface of the lower end plug 11 (e). . By doing so, the cladding tube 7 and the lower end plug 11
Is completely covered by the coating 61 and the additional coatings 63 and 65, and the control rod 60 is completed (f).

[0012]

As described above, according to the present invention,
Cladding in which the control rods may contact the control rod cluster guide tube structure and the fuel assembly guide thimbles during use;
Since the outer peripheral surfaces of the upper end plug and the lower end plug, including the welded portion, are coated with chrome plating or the like without leakage, the occurrence and progress of abrasion are suppressed, and the service life thereof is increased.

[Brief description of the drawings]

FIG. 1 is a process diagram of a method according to an embodiment of the present invention.

FIG. 2 is a process diagram of a modification method in which a part of the method according to the embodiment of FIG. 1 is modified.

FIG. 3 is a process diagram of a method according to another embodiment of the present invention.

FIG. 4 is a process chart of a method according to still another embodiment of the present invention.

FIG. 5 is a shortened elevational view showing a control rod cluster in a state where a control rod to which the present invention is applied is used.

FIG. 6 is a schematic vertical sectional view showing the structure of a conventional control rod.

FIG. 7 is an enlarged plan sectional view taken along line VII-VII in FIG. 6;

FIG. 8 is a partially cutaway perspective view of a fuel assembly with which the control rod of the present invention is used.

FIG. 9 is a conceptual diagram of a control rod cluster guide tube structure used together with the control rod of the present invention.

10 is a partially enlarged elevation view showing a part of FIG. 9 in an enlarged manner.

11 is a plan sectional view taken along line XI-XI in FIG.

[Explanation of symbols]

 7 Clad tube 9 Upper end plug 11 Lower end plug 13 Neutron absorbing material 15 Spring 40 Control rod 41 Welding 43 Coating 45 Welding 47 Surface coating

Claims (4)

[Claims] 1. A control rod comprising a cladding tube, an upper end plug and a lower end plug respectively joined to an upper end and a lower end of the cladding tube, and a neutron absorbing material and a spring to be put in the cladding tube. Fixing the upper end plug to the cladding tube by first welding, applying a first coating to an outer peripheral surface of the first welding and an outer peripheral surface of the cladding tube, and placing the neutron in the cladding tube. After inserting the absorber and the spring, the cladding tube and the lower end plug are joined and fixed by second welding, and then a second coating is applied to the outer peripheral surface of the lower end plug and the outer peripheral surface of the second weld. A method for manufacturing a control rod for a pressurized water reactor, comprising the steps of: 2. The control rod for a pressurized water reactor according to claim 1, wherein a coating on an outer peripheral surface of the cladding tube close to the second welding is included in the second coating. Method. 3. A method for manufacturing a cladding tube, an upper end plug and a lower end plug respectively joined to an upper end and a lower end of the cladding tube, and a control rod composed of a neutron absorbing material and a spring put in the cladding tube. After the cladding tube and the lower end plug are joined and fixed by a first welding, a first coating is applied to an outer peripheral surface of the cladding tube, an outer peripheral surface of the lower end plug, and an outer peripheral surface of the first welding. After inserting the neutron absorbing material and the spring into the cladding tube, the cladding tube and the upper end plug are joined and fixed by a second welding, and then a second welding is performed on the outer peripheral surface of the second welding. 2. A method for manufacturing a control rod for a pressurized water reactor, comprising: assembling through a step of applying a coating. 4. A method for manufacturing a cladding tube, an upper end plug and a lower end plug respectively joined to an upper end and a lower end of the cladding tube, and a control rod comprising a neutron absorbing material and a spring to be put in the cladding tube. A first coating is applied to the outer peripheral surface of the cladding tube except for portions near both ends to be welded, and the upper end plug is joined and fixed to the cladding tube by first welding, and the neutron is inserted into the cladding tube. After inserting the absorber and the spring, the cladding tube and the lower end plug are joined and fixed by second welding, and then the outer peripheral surface of the lower end plug, the outer peripheral surface of the second welding, and the first A method for manufacturing a control rod for a pressurized water reactor, comprising: assembling through a step of applying a second coating to the outer peripheral surface of the welding of (1).