JPS62132194A - Electric control-rod drive mechanism for nuclear power plant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an dynamic control rod drive mechanism for a nuclear power plant that allows smooth insertion and withdrawal of control rods and can be used for a long period of time.

[Technical background and problems of Hakumei]

As shown in FIG. 1, the control rod drive mechanism used in nuclear power plants includes a support cylinder 4 that supports the control rods 3 inside a cylinder 2 that protrudes from the outside of the reactor vessel 1. Seal ring 5 that is inserted and shuts off reactor water and control rod drive water
, 6 were provided, and the control rod 3 was moved up and down by supplying control rod drive water.

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

By the way, this electric control rod drive mechanism includes guide pins/rollers 17 to 25 in order to operate the hollow piston 14 smoothly for a long period of time, or in other words, to operate the control rod 13 smoothly and accurately for a long period of time. is installed.

As an example of this pin/roller is shown in FIG. 3, the pin 31 is fixed to a pin fixing part 32 with a rotation stopper,
The roller 33 has a structure that rotates around the pin 31.

In this case, the outer periphery of the pin 31 has sliding friction with the inner periphery of the roller 33, and the outer periphery of the roller has sliding friction with the hollow piston 1 in FIG.
4, the guide tube 17, and other parts cause rolling friction and wear.

For mechanical parts requiring wear resistance, such as in the case of pins/rollers, an alloy commonly called stellite containing approximately 50% cobalt is generally used.

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, so this is 'J1. @ It is brought into the reactor by the cooling water of the control rod drive mechanism, and becomes cobalt-60 by irradiation with neutrons, which increases the radiation dose rate of the nuclear power plant. Furthermore, if this cobalt-60 accumulates, there is a risk of increasing the amount of radiation exposure of workers during periodic inspections of nuclear power plants, which will also reduce the operating rate of the plant. Furthermore, when a general metal material is used, the wear is extremely large and the control rod cannot be smoothly driven for a long period of time.

Furthermore, such a shape is disadvantageous in that it is difficult to obtain dimensional accuracy and finishing accuracy for the outer diameter of the pin and the inner diameter of the roller, and that machining takes time.

[Purpose of the invention]

The present invention has been made in view of these points, and it not only allows for smooth insertion and withdrawal of control rods and allows for long-term use, but also suppresses the increase in the radiation 1 fit rate due to cobalt-60 and enables plant The purpose of the present invention is to provide a sleep control rod drive mechanism for a nuclear power plant, which improves the operating efficiency of a nuclear power plant.

[Summary of the invention]

In the pin/roller combination installed in the electric control rod drive mechanism, the roller 41 is a bearing, and the pin 42 has a rotation stopper in the pin attachment part 43, as shown in FIG. In the control rod drive mechanism, the control rod drive mechanism is characterized in that it has a fixed structure, and in the pin/roller combination, the ball or roller of the bearing, which is the roller 51, as shown in FIGS. 5 and 6, falls off. This control rod and drive mechanism is characterized in that the cover 52 that prevents this is a bearing connected to an outer ring or an inner ring of the bearing.

Here, the reason for the limitation of the electric control rod drive mechanism according to the present invention l
To explain further, the reason why we chose bearings for the rollers is that when the rollers are of integral construction as shown in Figure 3, the pins and the inner surfaces of the rollers slide against each other, causing wear and tear, making it difficult for the rollers to rotate smoothly and making it difficult to control the rollers. It becomes difficult to operate the rod with high precision, making it impossible to use it for a long period of time. In addition, if the wear is significant, the inner surface of the roller and the pin will seize and the roller will no longer rotate, causing the friction between the outer circumference of the roller, the outer circumference of the hollow piston, and the inner circumference of the guide tube to change from rolling friction to sliding friction, resulting in a coefficient of friction. The control rod was inserted as the motor rose significantly and a large torque was applied to the electric motor.

It becomes difficult to pull out.

However, when the roller is used as a bearing as in the present invention, the outer ring of the bearing rubs against the hollow piston, and the inner surface of the outer ring and the outer surface of the inner ring rub against the balls of the bearing or the roller. There is sliding friction between the inner surface of the inner ring and the pin, but the rolling friction coefficient is much smaller than the sliding friction coefficient, so there is almost no sliding wear between the pin and the bearing inner ring. Therefore, even after long-term use, the rollers rotate smoothly and the control rod can operate with high precision.

Note that the dimensional accuracy and finishing accuracy of the pin outer diameter and roller inner diameter are not required as much as in the conventional type, and processing is easy.

Also, the reason why a cover is attached to the inner or outer ring of the bearing to prevent the balls or rollers from falling off is to increase safety so that the balls or rollers of the bearing do not fly out even if torsional stress is applied to the bearing, which is a roller. It is.

Note that the pin attachment part and the bearing, which is a roller, are the seventh
If there is a gap as shown in the figure, the bearing (roller) or the pin may move in the axial direction, but in this case, it is sufficient to insert a spacer 61 as shown in Figure 7, and the outer diameter of this spacer can be changed. It may also be made larger to prevent the bearing balls or rollers from falling off.

〔Effect of the invention〕

As explained above, according to the electric control rod drive mechanism for a nuclear power plant according to the present invention, the frictional resistance and frictional wear of the pins/rollers are small, which occur when the reactor starts and stops and the output rises and falls. It has shown remarkable effects, such as being able to drive the control rods with high accuracy over a long period of time, and by improving the operating rate of the plant.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing a conventional hydraulic control rod drive mechanism, in which 1 is a reactor vessel, 2 is a cylinder, 3 is a control rod, 4 is a support tube, and 5 and 6 are seal rings. . FIG. 2 is a longitudinal sectional view showing an electric control rod drive mechanism according to the present invention, in which 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, and 16 is a Directional machines, 17-25 are bins/rollers. FIG. 3 is a sectional view showing an example of a pin/roller attachment part, and in the figure, 31 is a pin, 32 is a bottle fixing part, and 33 is a roller. FIG. 4 is a sectional view showing an example of the bin/roller mounting part of the electric control rod drive mechanism according to the present invention, in which 41 is a roller;
42 is a pin, 43 is a bottle attachment part. , J5, and 6 are cross-sectional views of the bin/roller mounting portion of the electric control rod drive mechanism according to the present invention, in which 51 is a roller, 52 is a cover, 53 is a pin, and 54 is a bin mounting portion. FIG. 7 is a cross-sectional view of the bottle/mouth-to-hole mounting part of the one-turn movement control rod movement mechanism according to the present invention, in which 61 is a bearing which is a roller, 62 is a spacer, 63 is a pin, and 64 is a bottle attachment part. Department.

Claims (2)

[Claims] (1) An electric control rod drive mechanism for a nuclear power plant, wherein the pin/roller combination installed in the electric control rod drive mechanism is a bearing. (2) An electric control rod drive for a nuclear power plant according to claim 1, wherein the cover that prevents the balls or rollers of the bearing from falling off is a bearing connected to the inner ring or outer ring of the bearing. mechanism.