JPH0611590A - Control rod for pressurized water reactor - Google Patents

Abstract

PURPOSE:To obtain a control rod for a pressurized water reactor which is improved in wear of outer surface in all potential region of touching the guide card of control rod guide tube during the use in a pressurized water reactor and can attain long life. CONSTITUTION:A control rod 10 for a pressurized water reactor is constituted by containing neutron absorber 12 inside a clad tube 11 cladded for almost whole length of outer surface with wear resistive metal layer and sealing with welding, the both ends of the clad tube with an upper end plug 14 and a lower end plug 15. Then, the outer surface in predetermined region including at least the junction 16 of the upper end plug 14 and the clad tube 11 is cladded with a wear resistive metal layer.

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.

[0002]

2. Description of the Related Art A control rod in a pressurized water reactor is hung at the lower end of a control rod drive shaft that is elevated by a control rod drive device at the top of the reactor to form a cluster. Since it is a long thin rod with an outer diameter of about 4 m and an outer diameter of about 10 mm, it has a plurality of stages of stainless steel plates with a thickness of about tens of mm in the control rod guide tube provided on the upper core plate of the core. It is guided by penetrating a guide hole provided in a guide card (plate), and is inserted into a control rod guide thimble in the fuel assembly below the guide hole.

A control rod cluster (RCC) in a conventional pressurized water reactor has a structure in which the upper ends of a plurality of control rods are fixed to a common support generally called a spider, and are suspended and supported. Since it is a small diameter rod, it easily shakes and vibrates.Therefore, the RCC is configured to suppress the wear of the control rod cladding due to the contact with the inner wall of the hole of the guide card due to the vibration of running water when used in the furnace. For each control rod, for example, a cladding tube coated with an outer surface of wear-resistant metal such as chrome plating is used.

A typical example of a conventional control rod for a pressurized water reactor is shown in FIG. In the figure, a neutron absorbing material 22 and a plenum spring 23 are housed inside a cladding tube 21, and upper and lower ends of the cladding tube are welded and sealed by an upper end plug 24 and a lower end plug 25 at welded portions 26 and 27, respectively. There is. The outer surface of the cladding tube 21 is plated with chrome for almost the entire length before assembly, but the coating range is less than the entire length where the non-plated portions B and C for end plug welding are left at both ends. Region A.

The reason why the structure is such that the non-plated portions B and C are left is due to circumstances in the process of assembling the control rod. That is, in the conventional process of assembling the control rod of this type, the lower end of the cladding tube 21 having the area A previously coated with the outer surface of the chrome is attached to the lower end plug 2 at the end of the non-plated portion C.
5, the neutron absorbing material 22 and the plenum spring 23 are inserted into the inside, and then the upper end of the cladding tube 21 is sealed with the upper end plug 24 by welding at the end of the non-plated portion B. However, in order to ensure the welding soundness of the welded portions 26, 27 of the end plugs, the non-plated parts B, C was required, and as a result, the non-plated portion remained in the finished control rod in the vicinity of the joint with the end plugs at both ends of the cladding tube.

[0006]

In the conventional control rod for a pressurized water reactor, the non-plated portion remains at the joint with the end plugs at both ends of the cladding tube as described above. The non-plated portion B of the joint portion of the control rod often faces the inner wall of the hole of the guide card when the core power is adjusted, for example, when the control rod is inserted or withdrawn in a stepwise manner. When running water vibration is generated, the outer surface of the cladding tube is abraded due to contact with the inner wall of the guide card hole, and the outer surface of the cladding tube is worn or thinned. As a result, the life of the control rod may be shortened.

Therefore, it is an object of the present invention to improve the wear resistance of the outer surface over the entire area of the control rod guide tube that may come into contact with the guide card when used in a pressurized water reactor, and A control rod for a pressurized water reactor capable of achieving a longer life is provided.

[0008]

A control rod for a pressurized water nuclear reactor according to the invention described in claim 1 has a neutron inside a cladding tube whose outer surface is coated with a wear-resistant metal layer over substantially the entire length. In a control rod that accommodates an absorbent and welds and seals the upper and lower ends of the cladding tube with an upper end plug and a lower end plug, respectively, a predetermined region including at least a joint between the upper end plug and the cladding pipe The above-mentioned problems are achieved by adopting a constitution in which the outer surface of the above is covered with the wear resistant metal layer.

Further, in a control rod for a pressurized water reactor according to a second aspect of the present invention, the outer surface including the joints between the upper end plug and the lower end plug and the cladding pipe is continuous with the wear resistance. The above-mentioned problems are achieved by adopting a structure of being covered with a metal layer.

[0010]

In the control rod for a pressurized water nuclear reactor of the present invention, basically, the outer surface of the cladding tube including the joint with the upper end plug over a predetermined region is coated with a wear-resistant metal layer such as chromium. ing. This covering area is an area covering almost the entire length of the covering tube except for the lower part where there is almost no chance of face-to-face wear with the inner wall of the hole of the guide card in the control rod guide tube when used in the furnace. , By covering this area with a wear-resistant metal layer, the wear-resistant metal layer prevents wear thinning of the non-plated portion of the cladding tube near the joint with the upper end plug, which has been a conventional problem. Is
The longer life is achieved.

The surface of the cladding tube in the vicinity of the joint between the cladding tube and the lower end plug is located below the position of the guide card in the control rod guide tube even when the control rod cluster is most pulled out in the in-furnace operating condition. Since it is normal, there is no problem even if the unplated part remains, but as long as it is in the reactor as a control rod cluster, the upper core plate under the control rod guide tube or the upper nozzle of the fuel assembly etc. Regarding the control rod that may come into contact with the structure portion, it is preferable that the surface of the cladding tube near the joint with the lower end plug is also coated with the wear-resistant metal layer.

[0012]

1 shows a structure of a control rod 10 for a pressurized water nuclear reactor according to an embodiment of the present invention with a part of its length omitted. In FIG. 1, a neutron absorbing material 12 and a plenum spring 13 are housed inside a cladding tube 11, and upper and lower ends of the cladding tube are welded and sealed at upper and lower end plugs 14 and 15 at welded portions 16 and 17, respectively. ing. The outer surface of the cladding tube 11 is plated with chrome, leaving a non-plated portion E at the lower end, and covering the region D over almost the entire length beyond the joint by welding with the upper end plug 14. The thickness of this outer chrome plating coating layer is usually 30 ± 10 μm
The degree is enough.

FIG. 2 shows the appearance of a control rod cluster constructed by using the control rod 10 having such a structure. In FIG. 2, a plurality of control rods 10 are attached to a spider 18 serving as a common support at the upper ends thereof and are hung and supported to form a control rod cluster for one fuel assembly.
This control rod cluster is arranged so that the upper end of the spider 18 is connected to the lower end of the control rod drive shaft so as to be movable up and down in the control rod guide tube in the furnace. Each control rod is designed to be inserted and removed.

The control rod according to this embodiment is assembled in the following manner, for example, by slightly changing the manufacturing process of the conventional control rod. That is, a cladding tube not yet coated with a wear-resistant metal outer surface is prepared, and first, the upper end thereof is sealed by welding the upper end plug 14. Then, the outer surface of the cladding tube including the welded portion 16 with the upper end plug, which may come into contact with the guide card (the area D), is coated with a wear resistant metal layer by chrome plating or the like. After this is washed and dried, the neutron absorber 12 and the plenum spring 13 are loaded inside, and the end of the lower non-plated portion E is sealed by welding the lower end plug 15.

As described above, in the control rod of the present embodiment, the end plug welding process in the conventional control rod manufacturing process is performed from the upper end plug first, and the plating process of the wear-resistant metal coating on the outer surface of the cladding pipe is performed. It can be manufactured with a slight change in the order of steps, such as after welding the end plugs.

The control rod of the present invention is not limited to the one manufactured in the order of assembling described above. For example, the upper end plug is welded by using a cladding tube in which the region A is previously chrome-plated as in the conventional case. After that, additional chrome plating is applied to the area B so that both plating layers are continuous, or if necessary, finally the lower non-plated portion E is also chrome plated so that the plating layers are continuous. May be.

When a continuous plating layer is formed in the regions D and E, the welding and sealing of the upper and lower end plugs to the non-plated coating pipe is performed first, and the assembled control rod is connected to the upper end plug at the final stage. Substantially the entire length including the welded portion 16 may be immersed in the plating bath, and the entire lower end plug may be covered with the wear-resistant metal layer up to the neck portion of the control rod.

[0018]

As described above, according to the present invention,
When used in a pressurized water reactor, it is possible to obtain a control rod whose outer surface is coated with a wear-resistant metal layer over the entire area where it may come into contact with the guide card in the control rod guide tube. It is possible to provide a control rod having a super long life and excellent wear resistance under all operating conditions including stepping operation.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration of a control rod for a pressurized water reactor according to an embodiment of the present invention with a part of the length omitted.

FIG. 2 is an explanatory view showing the appearance of a control rod cluster configured by using a control rod for a pressurized water nuclear reactor according to an embodiment of the present invention with a part of the length omitted.

FIG. 3 is an explanatory view showing a configuration of a typical example of a conventional control rod for a pressurized water reactor, with a part of the length omitted.

[Explanation of symbols]

 10: control rod 11: cladding 12: neutron absorber 13: plenum spring 14: upper end plug 15: lower end plug 16: upper welded part 17: lower welded part 18: control rod cluster

Claims (2)

[Claims] 1. A neutron absorber is housed inside a cladding tube whose outer surface is coated with a wear-resistant metal layer over substantially the entire length,
In a control rod for a pressurized water reactor in which the upper and lower ends of the cladding tube are welded and sealed by an upper end plug and a lower end plug, respectively, a predetermined region including at least a joint between the upper end plug and the cladding pipe A control rod for a pressurized water nuclear reactor, characterized in that the outer surface thereof is covered with the wear resistant metal layer. 2. The outer surface including the joints between the upper end plug and the lower end plug and the coating pipe is covered with the continuous wear-resistant metal layer. Control rod for pressurized water reactor.