JPH0810262B2 - Control rod drive mechanism for nuclear power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to an electric control rod drive mechanism for a nuclear power plant capable of smoothly inserting and extracting a control rod and capable of being used for a long period of time. .

(Prior Art) Conventionally, as shown in FIG. 1, a control rod drive mechanism used in a nuclear power plant supports a control rod 3 inside a cylindrical body 2 projecting outside a reactor vessel 1. A seal ring for inserting the support cylinder 4 to cut off the reactor water and the control rod driving water
The control rod 3 was moved up and down by providing the control rod driving water.

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

By the way, in this electric control rod drive mechanism, since the hollow piston 14 is operated smoothly for a long period of time, in other words, the guide pins / rollers 17 to 25 are arranged so that the control rod 13 can be operated smoothly for a long period of time and accurately. Is installed.

As shown in FIG. 3, this pin / roller has a structure in which the pin 31 is fixed to the pin fixing portion 32 with a rotation stop, and the roller 33 rotates about the pin 31 as an axis.

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. Therefore, the pin is significantly worn by sliding friction with the hole surface of the roller.

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.

(Problems to be Solved by the Invention) As described above, a pin / coil-based alloy /
When the roller is used in the electric control rod drive mechanism for a nuclear power plant, wear products and corrosion products due to friction contain cobalt, and this is brought into the reactor by the cooling water of the electric control rod drive mechanism, which causes neutrons. Irradiation will produce cobalt-60, 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. In addition, when general metal materials are applied, the wear of the pins is particularly large, the control rod cannot be driven smoothly, and the diameter decreases so much that it is not possible to withstand the mechanical load and It cannot be used. Also the rollers are worn out,
So-called backlash occurs and it cannot be used for a long time.

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

[Structure of Invention]

(Means and Actions for Solving Problems) The present invention relates to a pin / roller combination mounted on an electric control rod drive mechanism, and as shown in one example in FIG. The electric control rod drive mechanism for a nuclear power plant is characterized in that at least the pin surface that makes sliding friction in contact with the hole surface of the roller is a nitride layer of the base, and the roller is metal.

Here, the reason for limiting the electric control rod drive mechanism according to the present invention will be described. The reason why the pin surface of the pin is the iron-based alloy and the pin surface that slides and frictions at least in contact with the roller hole surface is the nitride layer of the substrate is as follows. When the pins are made of ceramic, the pin base is made of metal because it has a small diameter and is easily broken when subjected to mechanical vibration or an impact force such as an earthquake.

Further, the reason why the pin base is made of an iron-based alloy is that nitriding is easy, the nitrided layer has excellent wear resistance in water, and the loss on wear is smaller than that of a cobalt-based alloy. Furthermore, when the pin is made of metal and the roller that slides and frictions in contact with the pin is nitrided, the pin and the roller are significantly worn,
This is because when both the pin and the roller are nitrided, the amount of wear of the roller is larger than that of the conventional cobalt-based alloy combination. The pin base is preferably stainless steel containing Cr.

Next, the reason why the roller is made of metal is that, as described above, when the pin is made of metal and the hole surface of the roller that makes sliding friction in contact with the pin is nitrided, both the pin and the roller have a large amount of wear. In both cases, the wear amount of the roller in the case of nitriding the surface is larger than that in the case of the conventional cobalt-based alloy combination, which is not suitable as the guide pin / roller combination.

(Example) As shown in Table 1, a roller and a pin were prepared, respectively, and a combination test was conducted.

The roller of Example 1 according to the present invention is an alloy commonly called Cormorloy, and a commercially available cast material was cut into a roller shape. The roller of the second embodiment is patent 11
The alloy No. 97149 was melted in a high-frequency induction melting furnace, cast, then cut, and then aged at 800 ° C. for 3 hours to obtain a roller. The roller of Comparative Example 1 is a cobalt-based alloy commonly referred to as stellite, which has been widely used for sliding members as a material having excellent wear resistance, and a commercially available cast material was cut into a roller shape.

The rollers of Comparative Examples 2 and 3 are commercially available austenitic stainless steels commonly referred to as XM-19, which are cut into a roller shape and then are fed with ammonia gas and ammonia decomposition gas at a flow rate of about 10 / min. The entire surface was nitrided by heating at ℃ ± 5 ℃ for 40 hours.

The roller of Comparative Example 4 was obtained by cutting a solution-treated material from a commercially available nickel-base precipitation hardening alloy commonly called Inconel 718, and then aging it to obtain a roller. In addition, Example 1,
The metal structure of the roller of No. 2 was a structure in which precipitates were crystallized, but no precipitate was crystallized in the rollers of Comparative Examples 2 to 4.

Next, the pins of Examples 1 and 2 and Comparative Row 3 are commercially available XM.
Austenitic stainless steel called -19, after cutting into a pin shape, while flowing ammonia gas and ammonia decomposition gas at a flow rate of about 10 / min in the same manner as in the rollers of Comparative Examples 2 and 3, the temperature was changed to 580 ° C ± 5 ° C. The surface was heated for nitriding. The nitride layer had a thickness of about 100 μm.

The pin of Comparative Row 1 is a cobalt-based alloy commonly referred to as "Hanes Alloy" which has been widely used as a sliding member as a material having excellent wear resistance, and a commercially available forged material is cut into a pin shape. The pins in comparative rows 2 and 4 are commercially available, commonly known as 13-8Mo.
After being forged into a pin shape by cutting from a forged material called PH steel, it was aged.

The shape of the roller is 15 mm in outer diameter and 6.08 to 6.116 in hole diameter.
Mm, thickness 8 mm, pin shape is outer diameter 5.991-6.0
Mm, length 24 mm.

In the test, as schematically shown in FIG. 4, the roller 41 and the pin 42 were mounted on the holder 43 in a combination as shown in Table 1, and the roller was applied to the mandrel 44, which is a wear partner, with a predetermined load. After the training, the mandrel was rotated. The test load was 5Kg and 10Kg, the atmosphere was room temperature pure water, the wear sliding distance was 4,280.3m, and the mandrel peripheral speed was 30mm / sec and 3500mm.
/ sec was combined to measure the amount of wear of the roller and pin before and after the test.

 The test results are also shown in Table 1.

As is clear from Table 1, in Examples 1 and 2 according to the present invention, compared to Comparative Example 1, which is a combination of cobalt-based alloys that has been widely used as a wear-resistant member in the past, both the pin and the roller wear amount. It can be seen that there is little, and excellent characteristics are exhibited.

Further, Comparative Example 3 which is a combination in which both the pin and the roller are nitrided is Comparative Example 1 which is a combination in which a cobalt-based alloy is used.
Compared to, the amount of wear with the pin is small, but the amount of wear of the roller is
Further, in the case of Comparative Example 2 in which the roller was nitrided and the pin was made of metal as it is, the amount of wear of both the pin and the roller was larger than that of Comparative Example 1 which was a combination of cobalt-based alloys, and both were used as the pin / roller for the electric control rod drive mechanism. In addition to the fact that it was found to be unsuitable, it was found that in Comparative Example 4 in which both the pin and the roller were not surface-nitrided, they were not suitable for use because both the pin and the roller were significantly worn.

〔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 THE 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, 5 and 6 are seal rings, 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, 15 is a ball screw shaft, 16 is an electric motor, 17-
25 is a pin / roller, 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. The nitride layer of the pin base, 44 is the pin fixing part, FIG. 5 is a diagram showing the abrasion test method, 51 in the figure is a roller,
52 is a pin, 53 is a holder, 54 is a rotating cylinder, and W is a load.

Claims (1)

[Claims] 1. A guide pin / roller combination mounted on a control rod drive mechanism for a nuclear power plant, comprising:
A nuclear power generation characterized in that the pin has a base body made of an iron-based alloy, and at least the pin surface that slides and rubs in contact with the hole surface of the roller is a nitride layer of the base body, and the hole surface of the roller is a metal. Control rod drive mechanism for plants.