JPH0723915B2 - Electric control rod drive mechanism for nuclear power plant - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an electric control rod drive mechanism for a nuclear power plant capable of smoothly inserting / pulling out a control rod and capable of long-term use.

[Technical background and problems of the invention]

Conventionally, a control rod drive mechanism used in a nuclear power plant is, as shown in FIG. 1, inserted into a support cylinder 4 for supporting a control rod 3 inside a cylindrical body 2 protruding from the outside of a reactor vessel 1. Seal ring 5, 6 that shuts off the reactor water and control rod drive water
And the control rod 3 is moved up and down by supplying control rod driving water.

However, recently, from the viewpoint of effective use of fuel and highly accurate combustion control, a hollow piston that supports a control rod 13 inside a cylindrical body 12 that projects from the outside of a reactor vessel 11 as shown in FIG.
An electric control rod drive mechanism having a structure in which 14 is inserted and the control rod 13 is moved up and down by a motor 16 via a ball screw shaft 15 has begun to be developed.

By the way, this electric control rod drive mechanism has a hollow piston.
In other words, in order to operate 14 smoothly for a long time, in other words, control rod
Pins / rollers 17 to 25 for guiding are provided so that the 13 can be operated smoothly and accurately for a long period of time.

This pin / roller has a pin, as shown in FIG.
31 is fixed to the pin fixing portion 32 with a detent,
33 has a structure that rotates about the pin 31.

In this case, the outer peripheral portion of the pin 31 causes sliding friction with the inner peripheral portion of the roller 33, and the outer peripheral portion of the roller causes abrasion due to the outer peripheral portion of the hollow piston 14 shown in FIG.

Alloys commonly referred to as stellite containing approximately 50% cobalt are used for machine parts that require wear resistance, such as in the case of pins / rollers.

However, when a pin / roller made of a cobalt-based alloy is used in an electric control rod drive mechanism for a nuclear power plant, wear products and corrosion products due to friction contain cobalt, which results in cooling of the electric control rod drive mechanism. It is brought into the reactor by water and becomes a cobalt-60 by neutron irradiation, which will increase the radiation dose rate of the nuclear power plant. Further, the accumulation of this cobalt 60 may increase the radiation exposure of workers during the periodic inspection of the nuclear power plant, which in turn lowers the operating rate of the plant. Further, when a general metal material is applied, the wear is extremely large, and the control rod cannot be smoothly driven for a long period of time.

[Object of the Invention]

The present invention has been made in view of the above point, not only can the control rod be smoothly inserted and withdrawn, and can be used for a long period of time, as well as suppressing the increase of the radiation dose rate due to cobalt 60 in the plant. It is an object of the present invention to provide an electric control rod drive mechanism for a nuclear power plant with an improved operating rate.

[Outline of Invention]

The present invention is an electric control for a nuclear power plant having a structure in which a hollow piston supporting a control rod is mounted inside a cylindrical body protruding from the outside of a reactor vessel, and the control rod is moved up and down by an electric motor via a ball screw shaft. A rod drive mechanism, wherein the electric control rod drive mechanism is equipped with a pin / roller combination consisting of a pin fixed with a detent in the pin mounting portion and a roller that rotates about the pin. In the electric control rod drive mechanism for a nuclear power plant, the pin is made of ceramics, and the pin has a base body made of metal and at least the surface of the pin that makes sliding friction with the hole surface of the roller is covered with a nitride ceramic layer. is there. In the present invention, in the combination of pin / roller, FIG.
As shown in the figure, the roller 41 is a ceramic, and the pin 42 is characterized in that the base body having a detent is made of metal, and at least the surface of the pin that slides against the roller hole surface is covered with the nitride ceramic 43. To do.

Here, the reason for limiting the electric control rod drive mechanism according to the present invention will be explained. The reason why the roller is made of ceramic is that the roller is commonly known as stellite containing about 50% of cobalt which has been conventionally used as a wear resistant member of various devices. In the case of a so-called alloy, as described above, the products due to wear and the products due to corrosion are brought into the reactor by the cooling water, and the irradiation of neutrons turns them into cobalt 60 to increase the radiation dose rate of the nuclear power plant. In addition, it is difficult to obtain wear resistance equivalent to that of stellite with general metal materials. However, when the roller is made of ceramic, it does not contain cobalt and has better wear resistance than a metal material.

The reason why the pin used in combination with the roller has a structure in which the substrate is made of metal and at least the surface of the pin that causes sliding friction with the roller hole surface is covered with a ceramic, especially a nitride layer, is because the pin is made of a cobalt-based alloy. In addition, wear products and corrosion products are brought to the core by cooling water and neutron irradiation produces cobalt-60, which increases the radiation dose rate of the plant. This is because there is a large amount of wear due to friction, and when the entire pin is made of ceramic, the diameter of the pin is thin, so that it is easily damaged when an impact force such as mechanical vibration or an earthquake acts.

Example of Invention

As shown in Table 1, the friction plate corresponding to the roller is silicon nitride, and the indenter corresponding to the pin surface contacting the roller hole surface is commercially available Cr14%, W5%, Mo17%, balance Ni alloy (commonly known as Hastelloy C). , And a surface on which silicon carbide was generated by plasma PVD, and a surface on which silicon nitride powder was applied and baked in vacuum were prepared.

Then, as shown in FIG. 5, the friction plate 51 was reciprocated in the state of friction and indenter contact, and after sliding a predetermined sliding distance, the weight change of the indenter 52 before and after the test was measured. The sliding distance was 100 m, and the load applied to the indenter was 50 kg / cm ² atmosphere was room temperature water.

As a result, as also shown in Table 1, Comparative Example 1 had a friction loss of 14.8 mg / cm ² , whereas Example 1 and Example 2 had a very low friction loss of 1 mg / cm ² or less. It has excellent wear resistance, and when mounted on a control rod drive mechanism, it does not generate cobalt 60, and it can be seen that the control rod can be inserted and pulled out stably for a long time.

In the pin / roller combination according to the present invention, the roller may be not only silicon nitride but also silicon carbide, zirconium oxide, alumina, aluminum nitride, or the like.

Further, as a method of forming a ceramic layer on the surface of the pin that makes sliding contact and friction with at least the inner surface of the roller hole of the pin, not only plasma PVD and diffusion bonding in the examples but also general industrial methods such as CVD, thermal spraying or substrate It may be an oxide layer obtained by oxidizing a metal.

The base metal of the pin preferably has a high hardness, and an iron-based or nickel-based precipitation hardening alloy is preferable.

Example 2 in Table 1 was prepared as follows.

After setting the sample in the chamber and evacuating the chamber, titanium chloride was introduced as a carrier gas and nitrogen gas was introduced to adjust the pressure in the chamber to about 1 torr. Next, plasma discharge was performed to generate titanium nitride on the surface of the sample. (The thickness of the produced titanium nitride was about 2 μm.) Next, after the chamber was evacuated to a vacuum, silicon chloride was introduced as a carrier gas and methane gas was introduced, and then plasma discharge was performed to introduce silicon carbide onto the sample surface. Was generated.

(Note that the thickness of the silicon carbide was about 3 to 4 μm).

The TiN layer as the base layer has good bondability with a ceramic layer such as SiC.

[Other Embodiments of the Invention]

As shown in Table 2, the friction plate corresponding to the roller is made of silicon nitride, and the indenter corresponding to the pin surface in contact with the roller hole surface is C0.06% or less, Si1.0% or less, Mn4-6%, Ni11 .5 ~ 13.5
%, Cr20.5 to 23.5% Mo1.5 to 3.0%, Nb + Ta0.1 to 0.3, N0.
2 to 0.4%, V 0.1 to 0.3%, an alloy commonly called XM-19 consisting of balance iron and incidental impurities and C0.05% or less, Si0.
1% or less, Mn 0.1% or less, Ni7.5 to 8.5%, Cr12.25 to 13.27%,
An alloy called PH13-8Mo, which is composed of Mo2.0-2.5%, AC0.9-1.35%, N0.01% or less, and balance iron and incidental impurities, and those whose surfaces are nitrided were prepared.

Further, commercially available Cr14%, W5%, Mo17% and the balance Ni alloy (commonly known as Hastelloy C) were also prepared.

Then, as shown in FIG. 5, the friction plate 51 was reciprocated in a state where the friction plate and the indenter were in contact with each other, and after sliding a predetermined sliding distance, the weight change of the indenter 52 before and after the test was measured. .
The sliding distance was 100 m, and the load applied to the indenter was 50 kg / cm ² in room temperature water.

As a result, as shown together in Table 1, Comparative Examples 1 to 3
Wear loss is 10 mg / cm ² or more, while the wear loss of Examples 1 and 2 is 2 mg / cm ² or less, which is very small and has excellent wear resistance. When it is done, it can be seen that the control rod can be inserted and pulled out stably for a long time without the generation of cobalt 60.

The nitriding treatment was performed as follows.

After setting the sample in the nitriding device, while flowing ammonia gas and ammonia decomposition gas at a flow rate of about 10 / min,
The sample was heated to 580 ° C ± 5 ° C for 40 hours to form a nitride layer on the surface. (The gas decomposition rate was about 75%).

〔The invention's effect〕

As described above, according to the electric control rod drive mechanism for a nuclear power plant according to the present invention, it is possible to reduce the frictional resistance and frictional wear of the pin / roller that accompanies the start / stop of the reactor and the rise / fall of the output. In addition, the control rod can be driven with high accuracy in a stable manner for a long period of time, and the plant operating rate can be improved, which is a remarkable effect.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a conventional hydraulic control rod drive mechanism. In the figure, 1 is a reactor vessel, 2 is a cylinder, 3 is a control rod, 4 is a support cylinder, and 5, 6
Is a seal ring, and FIG. 2 is a longitudinal sectional view showing an electric control rod drive mechanism according to the present invention. In the figure, 11 is a reactor vessel, 12 is a cylinder, 13 is a control rod, 14 is a hollow piston, and 15 is a ball screw. Shaft, 16 is an electric motor, 17 to 25 are pins / rollers, and FIG. 3 is a sectional view showing an example of a pin / roller mounting portion.
In the drawing, 31 is a pin, 32 is a pin fixing part, 33 is a roller, and FIG. 4 is a sectional view showing an example of a pin / roller mounting part according to the present invention. In the figure, 41 is a roller, 42 is a pin, and 43 is a pin. Ceramic layer, 44 is a pin fixing part, Fig. 5 is a diagram showing a wear test method, in which 51 is a friction plate, 5
2 is an indenter.

Continuation of the front page (56) References JP-A-58-33182 (JP, A) JP-A-58-172585 (JP, A) JP-A-55-161050 (JP, A)

Claims (1)

[Claims] 1. An electric motor for a nuclear power plant having a structure in which a hollow piston supporting a control rod is mounted inside a cylindrical body projecting outside the reactor vessel, and the control rod is vertically moved by an electric motor via a ball screw shaft. A control rod drive mechanism, wherein the electric control rod drive mechanism is equipped with a pin / roller combination consisting of a pin fixed with a detent in the pin mounting portion and a roller rotating about the pin, An electric control rod drive mechanism for a nuclear power plant, characterized in that the roller is made of ceramic, and the pin has a base body made of metal and at least a surface of the pin that makes sliding friction with the hole surface of the roller is covered with a nitride ceramic layer. .