JP4885607B2 - Control rod for pressurized water reactor - Google Patents

Description

  The present invention relates to a control rod for a pressurized water reactor, and more particularly to a control rod for a pressurized water reactor in which the tip portion thereof is plated for improving wear resistance.

  The control rod of the pressurized water reactor is inserted into a control rod introduction tube (thimble tube) in which the fuel rods are arranged in place of, for example, a part of the fuel assemblies arranged in 17 × 17. It has become. Furthermore, normally, when the reactor is rated (100%), it is pulled up to the top of the fuel assembly, leaving the tip (the tip when inserted into the fuel assembly, the bottom when in use). During partial load operation such as at night, a part of the fuel assembly is lowered to the place where the fuel is loaded, and when the fuel is stopped, the fuel assembly is completely inserted into the fuel rod introduction pipe. .

When pulled up to the top of the fuel assembly, most of the control rods except for the tip are inserted into the control rod cluster guide tube, and the top is supported by a spider assembly connected to the drive shaft. ing.
However, this region is where the coolant flowing upward in the fuel assembly flows into the reactor outlet nozzle, so the strength and direction of the coolant flow varies irregularly and violently. Also, the members such as the control rod cluster guide pipes around them vibrate irregularly and violently.

As a result, there is a risk that the control rod will rub against the surrounding members violently and damage the cladding tube that forms the outer surface of the control rod. If the cladding tube (hereinafter also simply referred to as “cladding tube”) is damaged, it is not very preferable from the viewpoint of operation of the nuclear reactor, ensuring safety, and the like.
For this reason, the outer surface of the cladding tube constituting the outer surface portion of the control rod is subjected to a surface treatment for fretting resistance, specifically, chromium plating within a required range (Patent Document 1). , 2 and 3).

  The chrome plating substantially covers the entire length of the cladding tube, and its thickness is about 30 μm except for the lower end portion, and the lower end portion is about 10 μm. That is, the control rod is quickly inserted into the reactor core in a free fall in an emergency, but at the final stage, the inner diameter of the lowermost part of the control rod introduction pipe of the fuel assembly is reduced to reduce the drop impact by the resistance of the cooling water. It is in line with what is.

The cladding tube has a length of about 4 m, a diameter of about 10 mm, and a wall thickness of about 0.5 mm. Therefore, the plating of the cladding tube is carried out by immersing it in the plating solution with the upper end plug side of the cladding tube welded only with the upper end plug facing down, and inserting an elongated cathode member inside the cladding tube, along the outer peripheral surface of the cladding tube. A plurality of types of complicatedly shaped anode bars are arranged (FIG. 5 of Patent Document 3).
Then, after the plating is completed and the cladding tube is filled with a neutron absorber or the like, the lower end plug is welded to the lower end of the cladding tube.
Japanese Utility Model Publication No. 3-91998 JP-A-11-153585 Japanese Patent No. 3692367

  However, as described above, there is a relationship with the plating method, and welding of the lower end plug and the lower end portion of the cladding tube is performed after plating. Therefore, the welding part and welding margin part of the lower end plug and the lower end part of the cladding tube are not plated. This is shown in FIG. In this figure, 10 is a cladding tube, 11 is its chromium plating layer, 19 is its welding allowance, 18 is a welding part, and 40 is a lower end plug. Even if there is an unplated portion in this way, the tip portion of the control rod is outside the control rod cluster guide tube, and thus it has been considered that such a configuration is sufficient in the past.

However, although it may be a lower end plug that does not have a neutron absorber and its mounting part, wear may occur due to contact with the upper part of the control rod introduction tube, so it is preferable not to have chrome plating. is not.
After welding the cladding tube and the lower end plug, plating with the same thickness so that it does not overlap with the already plated part with a thickness of 10 μm is extremely difficult because the length of the control rod is about 4 m. It is difficult, and it is difficult to perform thin plating again, because the chromium that has already been plated is oxidized.

  For this reason, it has been desired to develop a control rod in which the lower end plug and its mounting portion are subjected to surface treatment for fretting resistance such as chrome plating.

  The present invention has been made for the purpose of solving the above-described problems. The lower end plug, the outer end plug whose outer periphery has been subjected to a surface treatment for fretting resistance such as chromium plating, a cladding tube, It is divided into welded inner side end plugs, and the outer side end plugs and the inner side end plugs are fixed with screws or the like. The invention of each claim will be described below.

The invention described in claim 1
Of the cladding tube and the end plug connected by welding without appearing on the outer peripheral surface, at least all of the side surfaces of the cladding tube that contact the cooling water and the outer peripheral surface of the connecting portion of the cladding tube and the end plug Is a control rod for a pressurized water reactor that has been subjected to a surface treatment for fretting resistance,
The bottom end plug
The upper side is inserted into the cladding tube from the lower end of the cladding tube, the lower side is an insertion portion welded to the inner peripheral surface side of the lower end surface of the cladding tube, and the lower end center of the insertion portion is directed downward. An internal end plug having a male thread portion provided, and
The outer peripheral surface on the upper side forms a cylindrical surface continuous with the outer peripheral surface side of the lower end of the cladding tube, and the outer side on which the male screw portion is screwed downward from the upper end center on the upper side A control rod for a pressurized water reactor characterized by comprising an end plug.

In the control rod for a pressurized water reactor according to the present invention, the fretting resistance is improved because all the side surfaces are subjected to a surface treatment for fretting resistance.
The “side surface” refers to a portion that forms a cylinder of a cylindrical control rod. For this reason, it is included in this invention even if the surface treatment for a fretting resistance is not given to the front-end | tip part which does not have a fear of fretting.
Further, “being subjected to surface treatment for fretting resistance” includes selecting a material having a material having excellent fretting resistance in addition to performing a pure surface treatment such as chrome plating.

The control rod for a pressurized water reactor according to this claim divides the lower end plug attached to the lower end of the cladding tube into an inner end plug and an outer end plug, and the inner end plug is an inner peripheral surface of the lower end surface of the cladding tube. The outer end plug is attached to the outer peripheral side of the inner end plug with a screw. For this reason, since it is not necessary to weld the outer surface of a cladding tube, it becomes possible to give a fretting-proof process to a lower end prior to welding. Similarly, the end plugs on the outer side do not need to be welded except for the stoppers around the screw, so that fretting-resistant treatment is applied to areas where surface fretting may occur prior to welding. It is possible to manufacture with a material having excellent fretting resistance regardless of the degree of difficulty.
The upper and lower sides of the cladding tube and the like are based on actual use.
In use, the male screw of the inner side end plug and the female screw of the outer side end plug are firmly screwed in, and are further prevented from rotating as necessary.

Invention of Claim 2 is the said control rod for pressurized water reactors,
The pressurized water reactor control rod is characterized in that welding between the lower side of the insertion portion and the inner peripheral surface side of the lower end surface of the cladding tube is laser welding or electron beam welding.

  Since laser welding or electron beam welding is used, the inner peripheral surface side and the outer surface side of the insertion portion of the inner end plug are securely sealed even if the thickness of the cladding tube is as thin as about 0.5 mm. And it becomes easy to weld without adversely affecting the fretting processing portion or the like on the outer peripheral surface of the cladding tube.

  In the present invention, since the outer peripheral surface on the upper side of the external end plug is subjected to surface treatment for fretting resistance, the fretting resistance of the lower end plug is improved. In addition, since it is not necessary to consider fretting resistance as a material, it is possible to select a metal that is easy to machine or a metal that is compatible with the cladding tube.

The invention according to claim 3
Of the cladding tube and the end plug connected by welding without appearing on the outer peripheral surface, at least all of the side surfaces of the cladding tube that contact the cooling water and the outer peripheral surface of the connecting portion of the cladding tube and the end plug Is a control rod for a pressurized water reactor that has been subjected to a surface treatment for fretting resistance,
The lower end of the cladding tube is narrowed so that its diameter becomes smaller,
The bottom end plug
An insertion portion inserted into the cladding tube from the lower end of the cladding tube, and a cylindrical surface continuous with the outer peripheral surface side of the lower end of the cladding tube in a state where the insertion portion is inserted into the lower portion of the cladding tube, and an upper end An inner end plug having a flange portion that is butt welded to the lower end surface of the cladding tube, and a male screw portion in which a male screw is erected downward at the center of the lower end of the collar portion;
A portion that has been narrowed to reduce the diameter of the lower end of the cladding tube is inserted on the inner peripheral side, and a cylindrical surface that is continuous with the portion that has not been narrowed to reduce the diameter of the lower end of the cladding tube is formed on the outer peripheral side. A control rod for a pressurized water reactor, comprising: an outer-side end plug having a cylindrical portion to be formed and a female screw portion in which a female screw into which the male screw portion is screwed is formed at the center.

  Also in the invention of this claim, the lower end plug attached to the lower end of the cladding tube is divided into an inner side end plug and an outer side end plug, and the inner side end plug is attached to the inner peripheral surface side of the lower end surface of the cladding tube by welding. As in the first aspect of the invention, the sealability is secured and the outer end plug is attached to the outer peripheral side of the inner end plug with a screw. However, the difference is that the lower end of the cladding tube is squeezed and the outer end plug is fitted on the outer periphery thereof. For this reason, even with Tig welding that does not require special equipment, the attachment of the lower end plug is sufficiently stable.

Invention of Claim 4 is the said control rod for pressurized water reactors,
A control rod for a pressurized water reactor, wherein the butt welding between the outer peripheral surface of the upper end of the flange portion of the inner end plug and the lower end surface of the cladding tube is laser welding, Tig welding or electron beam welding It is.

  The invention of this claim corresponds to the invention of claim 2 that specifically defines the preferred type of welding in the invention of claim 1, and specifically defines the preferred type of welding in the invention of claim 3. is there.

  In the present invention, since the lower end plug and the cladding tube near the mounting portion thereof are chrome-plated, damage due to fretting of the lower end plug of the control rod and the cladding tube near the mounting portion is further less likely to occur.

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(First embodiment)
This embodiment is manufactured by dividing the lower end plug into an inner end plug and an outer end plug, inserting the cylindrical insertion portion of the inner end plug into the lower end surface of the cladding tube, and Are welded to the inner peripheral surface of the lower end of the cladding tube.

Hereinafter, the control rod for a pressurized water reactor according to the present embodiment will be described with reference to FIG.
In FIG. 1, 10 is a cladding tube of the control rod, 11 is a chromium plating layer on the outer surface, and 12 is a lower end surface of the cladding tube 10. Reference numeral 20 denotes an inner end plug of the lower end plug, 21 denotes an insertion portion thereof, 22 denotes a lower end surface thereof, and 28 denotes an external thread portion thereof. 30 is an external end plug of the lower end plug, 31 is a chromium plating layer on the outer surface thereof, 32 is an upper end face thereof, 33 is an internal thread portion, and 39 is a detent. Reference numeral 40 denotes a lower end plug in which the inner end plug 20 and the outer end plug 30 are integrated.

In addition, in (1) to (4) in FIG. 1, portions that are clearly identified as the same portion are complicated, and thus are not appropriately denoted by reference numerals.
In addition, as described above, the upper and lower sides of the control rod are based on the state in which the control rod is actually loaded. For this reason, not only in FIG. 1 but also in other drawings, the right is the top and the left is the bottom.

A manufacturing procedure will be described.
As shown by (1) in FIG. 1, a stainless steel cladding tube 10 having a chromium plating layer 11 formed on the outer surface is attached to the inner side of the lower end plug from the lower end to the inside as indicated by a thick arrow. The insertion part 21 of the end plug 20 is inserted.
As shown in FIG. 1B, the insertion is performed so that the lower end surface 12 of the cladding tube 10 and the lower end surface 22 of the insertion portion 21 are flush with each other. Next, only the inner side of the lower end surface 12 of the cladding tube 10 and the outer peripheral side of the lower end surface 22 of the insertion portion 21 are laser-welded to firmly fix the cladding tube 10 and the insertion portion 21, and the cladding tube 10 is completely To seal. The part painted black is the part melted by laser welding.

Here, since laser welding is used, precise welding is possible. Further, since welding of the lower end surface 12 of the cladding tube 10 is only on the inner side, the chrome plating layer 11 on the outer surface has no adverse effect.
Further, burrs or the like generated on the lower end surface after the welding must be polished and flattened, but since this is also laser welding, minimal effort is required.
Note that the inner diameter of the cladding tube 10 and the outer shape of the insertion portion 21 are made the same by precision machining, thereby preventing a change in the outer dimension of the cladding tube 10 due to the insertion of the insertion portion 21, and further, the cladding tube 10 during welding. And the insertion portion 21 move relative to each other to prevent the occurrence of displacement, enabling welding in which only the inside of the thin cladding tube 10 and the outer periphery of the insertion portion 21 are deeply melted only in the length direction of the cladding tube. . The tip of the insertion portion 21 is slightly rounded to facilitate insertion.

As shown in FIG. 1 (3), the external thread plug 33 of the external end plug 30 of the lower end plug is applied to the external thread section 28 erected in the center of the lower end surface of the insertion section 21, and the external end plug 30 is shown in the figure. As shown by the rotation arrow, the male screw portion 28 of the inner end plug 20 is screwed into the female screw portion 33 inside as shown by the thick arrow in the figure.
As shown in FIG. 1 (4), when the outer side end plug 30 is completely turned, the upper side end surface 32 becomes the lower end surface 22 of the insertion portion 21 of the inner side end plug 20 and the lower end surface 12 of the cladding tube 10. Close to. Further, the upper part of the outer peripheral surface of the outer end plug 30 and the lower part of the cladding tube 10 are continuous cylinders, and the outer peripheral side surface of the lower part of the cladding tube is all covered with a chromium layer.

Next, the lower end (front end) of the male screw portion 28 and the lower end of the female screw portion 33 are welded to form a rotation stop 39, whereby the attachment of the lower end plug 40 to the cladding tube 10 of the control rod is completed. Accordingly, (4) in FIG. 1 is also a diagram showing a completed state.
As a result, as shown in FIG. 2, the tip portion of the control rod and the vicinity thereof are all covered with the chromium plating layers 11 and 31.
In the present embodiment, electron beam welding may be used instead of laser welding.

(Second Embodiment)
The present embodiment is characterized in that, when compared with the first embodiment, the lower end portion of the control rod cladding tube is narrowed down and inserted into the external end plug.
Hereinafter, the control rod for a pressurized water reactor according to the present embodiment will be described with reference to FIG. In FIG. 3, 10 is a cladding tube of the control rod, 11 is a chromium plating layer, 15 is a narrowing portion at the lower end of the cladding tube of the control rod, and 16 is a lower end surface of the narrowing portion 15. 25 is an insertion part of the inner side end plug 20 of the lower end plug 40, 26 is the collar part, 27 is the upper end surface of a collar part, 28 is an external thread part. Reference numeral 33 denotes an internal thread portion of the external end plug 30 of the lower end plug 40, 31 denotes a chromium plating layer on the outer surface, and 36 denotes a cylindrical portion. Note that, in (1) to (4) of FIG. 3, the reference numerals are omitted as appropriate.
The narrowing portion 16 has a slightly smaller outer diameter in the range of about 5 mm to 10 mm from the end.

A manufacturing procedure will be described.
As shown in (1) of FIG. 3, the lower end of the stainless steel cladding tube 10 is narrowed down to reduce the diameter. In addition, in this part, in order to narrow down easily, the chromium plating layer is not formed in the outer surface. The insertion portion 25 of the inner side end plug 20 of the lower end plug is inserted into the narrowed portion 15 having a smaller diameter and thus a smaller inner diameter as indicated by a thick arrow.

As shown in FIG. 3B, the upper end surface 27 of the flange portion 26 of the inner side end plug 20 and the lower end surface 16 of the narrowed portion 15 of the cladding tube 10 are brought into contact with each other and joined by Tig welding. The blackened area in the figure is the melted part.
Here, since it is Tig welding, it is possible to perform sufficiently precise welding without special equipment.

  Note that the inner diameter of the narrowed portion 15 of the cladding tube 10 and the outer shape of the insertion portion 25 are made the same by precision machining, thereby preventing a change in the outer dimension of the narrowed portion 15 due to insertion of the insertion portion 25 and further welding. Occasionally, the cladding tube 10 and the insertion portion 25 of the inner end plug 20 are moved relative to each other to prevent displacement, and the outer periphery of the thinned narrowing portion 15 and the collar portion 26 is reliably welded. .

As shown in FIG. 3 (3), the external thread end portion 33 of the lower end plug is applied to the external thread portion 28 erected at the center of the lower end surface of the flange portion 26, and the outer peripheral surface of the flange portion 26 is The outer end plug 30 is inserted into the inner peripheral surface of the cylindrical portion 36 as shown by a rotation arrow in this state, and the male screw portion 28 of the inner end plug 20 is inserted with a thick arrow into the female screw portion 33 inside thereof. Screw in as shown.
As shown in FIG. 3 (4), when the outer end plug 30 is completely turned, the outer peripheral surface on the upper side of the cylindrical portion 36 is continuous with the outer peripheral surface of the portion where the cladding tube 10 is not narrowed. A cylindrical surface that is flush with no step is formed. The outer peripheral surface on the upper side of the cylindrical portion 36 of the outer end plug 30 and the outer peripheral surface of the portion where the cladding tube 10 is not narrowed are both covered with a chromium layer. As a result, the outer peripheral surface of the continuous cylindrical surface, that is, the outer peripheral surface of the control rod is all covered with the chromium layer.

Further, the bottom surface of the lower portion on the inner peripheral side of the cylindrical portion 36 and the lower end surface of the collar portion 26 are in a state of being in contact with each other.
Next, the lower end (front end) of the male screw portion 28 and the lower end of the female screw portion 33 are welded to form a rotation stop 39, whereby the attachment of the lower end plug 40 to the cladding tube 10 of the control rod is completed. Therefore, (4) in FIG. 3 is also a diagram showing a completed state.
As a result of the above, also in the present embodiment, as shown in FIG. 2, the tip portion of the control rod and the vicinity thereof are all covered with the chromium plating layer.

It is a figure which shows the manufacture procedure of the principal part of the control rod for pressurized water reactors of the 1st Embodiment of this invention, and a completion state. It is a figure which shows the mode of the chromium plating layer of the front-end | tip part of the control rod for pressurized water reactors concerning this invention. It is a figure which shows the manufacturing procedure and completion state of the principal part of the control rod for pressurized water reactors of the 2nd Embodiment of this invention. It is a figure which shows the mode of the chromium plating of the front-end | tip part of the control rod for pressurized water reactors of a prior art.

DESCRIPTION OF SYMBOLS 10 Cladding pipe 11 Chromium plating layer 12 Lower end face 15 of a covering pipe The narrowing part 16 of the lower end part of a covering pipe The lower end face 18 of a narrowing part Welding part 19 Welding allowance part 20 25 Insertion part 26 Collar part 27 Upper end face 28 of the collar part Male thread part 30 External end plug 31 of the lower end plug Chrome plating layer 32 Upper end face 33 Female thread part 36 Cylindrical part 39 Detent 40 Lower end plug

Claims (4)

Of the cladding tube and the end plug connected by welding without appearing on the outer peripheral surface, at least all of the side surfaces of the cladding tube that contact the cooling water and the outer peripheral surface of the connecting portion of the cladding tube and the end plug surface treatment for fretting is a pressurized water reactor control rods which are subjected to,
The bottom end plug
The upper side is inserted into the cladding tube from the lower end of the cladding tube, the lower side is an insertion portion welded to the inner peripheral surface side of the lower end surface of the cladding tube, and the lower end center of the insertion portion is directed downward. An internal end plug having a male thread portion provided, and
The outer peripheral surface on the upper side forms a cylindrical surface continuous with the outer peripheral surface side of the lower end of the cladding tube, and the outer side on which the male screw portion is screwed downward from the upper end center on the upper side A control rod for a pressurized water reactor comprising an end plug . 2. The pressurized water reactor control rod according to claim 1 , wherein welding between the lower side of the insertion portion and the inner peripheral surface side of the lower end surface of the cladding tube is laser welding or electron beam welding. Of the cladding tube and the end plug connected by welding without appearing on the outer peripheral surface, at least all of the side surfaces of the cladding tube that contact the cooling water and the outer peripheral surface of the connecting portion of the cladding tube and the end plug Is a control rod for a pressurized water reactor that has been subjected to a surface treatment for fretting resistance,
The lower end of the cladding tube is narrowed to such a diameter is reduced,
The bottom end plug
An insertion portion inserted into the cladding tube from the lower end of the cladding tube, and a cylindrical surface continuous with the outer peripheral surface side of the lower end of the cladding tube in a state where the insertion portion is inserted into the lower portion of the cladding tube, and an upper end An inner end plug having a flange portion that is butt welded to the lower end surface of the cladding tube, and a male screw portion in which a male screw is erected downward at the center of the lower end of the collar portion;
A portion that has been narrowed to reduce the diameter of the lower end of the cladding tube is inserted on the inner peripheral side, and a cylindrical surface that is continuous with the portion that has not been narrowed to reduce the diameter of the lower end of the cladding tube is formed on the outer peripheral side. A control rod for a pressurized water reactor, comprising: an outer end plug having a cylindrical portion and a female screw portion in which a female screw into which the male screw portion is screwed is formed at the center. The pressurized water according to claim 3 , wherein the butt welding between the outer peripheral surface of the upper end of the flange portion of the inner side end plug and the lower end surface of the cladding tube is laser welding, Tig welding or electron beam welding. Control rod for type reactor.

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