JPH0317595A - Control rod drive mechanism - Google Patents

Abstract

PURPOSE:To improve the soundness of each member of the title mechanism by engaging the first upper guide to a control rod guide tube base and by connecting the first guide to the second upper guide, so as to be able to move freely. CONSTITUTION:An upper guide is divided into the first upper guide 24a and the second upper guide 24b, and a spring 29 is placed between them. The guide 24a is attached to an inner upper most end of a CRD (control rod drive mechanism) housing 5 and is engaged to a CR guide tube base 23a, by rotating. On the other hand, the guide 24b is fixed to each guide 24a and an outer tube 21 by keys 30 and 31, through the spring 29. For the outer tube 21, a whole spring constant can be selected by providing grooves on an outer surface part of the tube. In this case, a much greater energy absorption can be realized by selecting a groove depth at a thin thickness part of the groove, not so as to become the weakest point in its strength, and a travelling distance of the guide 24b can be increased as well and therewith a dash-pot effect of the spring 29 can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a control rod drive mechanism used in boiling water nuclear reactors and the like.

(Prior Art) Generally, in a boiling water nuclear reactor, a control rod drive mechanism provided at the bottom of a reactor pressure vessel inserts and removes control rods into the reactor core to control reactor output.

That is, as shown in FIG. 3, a large number of horizontal control rod drives 2 are provided at the bottom of the reactor pressure vessel 1 of a boiling water reactor.
A control rod 3 connected to the top of the control rod drive mechanism (hereinafter abbreviated as CRD) 2 is inserted into or withdrawn from the reactor core 4 to control the reactor output.

FIG. 4 shows this conventional CRD2. In the figure, a long control rod drive mechanism housing (hereinafter abbreviated as CRD housing) 5 penetrates and is fixed to the lower end of a reactor pressure vessel 1.

This CHD housing 5 is attached with a mounting bolt 22.
The HD 2 is fixed to the CRD housing 5, and an outer tube 21 and a guide tube 13 are fixed to the inside of the CRD housing 5 in this order. An electric motor 6 is attached to the lower end of the outer tube 21 via the lower cylindrical portion 18 and the motor bracket 5a. This electric motor 6 drives the control rod 3 to be inserted and removed, and the rotation of its rotation start shaft 7a is transmitted via a gear device 8 to a rotation transmission shaft 7b.

The upper end of this rotation transmission shaft 7b is connected to the drive screw 9 by means of a key. This drive screw 9 is formed in a length that reaches from the lower end to the upper end of the control rod drive mechanism housing 5, and a nut 12 is screwed onto this drive screw 9. This nut l2 has a roller 1 attached to its outer periphery.
5 is engaged with a groove 14 formed on the inner surface of the guide tube 13 to prevent rotation, and is raised or lowered by forward and reverse rotation of the drive screw 9. A long hollow piston 10, which is placed on the outside of the drive screw 9, is placed on the nut 12 so as to be able to move toward and away from the nut 12. This hollow piston 10 is formed in such a length that it protrudes from the top into the reactor pressure vessel 1 from the coupling spout loa at the upper end that connects the control rod when the nut 12 is at the lowest position. In addition, the hollow piston {0 is prevented from rotating by engaging a roller 15 attached to its lower end with Sl4, and is further engaged with a window (not shown) formed in the guide tube {3 to prevent the hollow piston {0 from rotating. A latch L9 is provided to prevent the item 10 from falling. Also, inside the II1 control rod drive mechanism housing 5, there is a lower flange thereof, an outer tube 2
Water (purge water) is always filled through the inlet 1B provided in this order to the guide tube 1 and the guide tube 13, and this water passes through the gap between the hollow piston 10 and the labyrinth seal 17 and enters the reactor pressure vessel 1. There is an influx.

Normal insertion and withdrawal of control rods by the control rod drive mechanism 2 formed in this manner is performed as follows.

That is, by rotating the electric motor 6 in the forward and reverse directions, the drive screw 9 is rotated in the forward and reverse directions, and the nut 12 is raised or lowered. Then, the hollow piston IO placed on the nut l2 by its own weight moves up and down together, and the control rod 3 connected to the upper end of the hollow piston IO via the coupling sbad lOa is moved to the control rod guide tube 23. It is inserted into and withdrawn from the reactor core 4 through the .

On the other hand, when rapid insertion of the $+1 2lIl rod 3 is required, high pressure water flows from the inlet 16 into the control rod drive mechanism housing 5.
The hollow piston lO is supplied below the hollow piston 10 in the interior and rests on the nut 12 only by its own weight.
is separated from the nut 12 and rapidly moves upward, rapidly inserting the control rod into the reactor core 4. The lower end of the latch 19 then engages the lower edge of the window (not shown) and the hollow piston lO
prevent the fall of

After that, when the hollow piston 10 is lowered again by the electric motor 6, the drive screw 9 is rotated in the insertion direction, and the nut 12 and the hollow piston 10 are brought into contact with each other, thereby returning the latch l9 inward and securing it to the window. is released, and then the drive screw 9 is rotated in the withdrawal direction to lower the hollow piston 10.

In the rapid insertion of the control rod, the hollow piston 10 and the control rod 3 are decelerated at the end of the stroke, and the CRD
In order to reduce the impact force on the housing 5 and the reactor pressure vessel 1, a large number of disc springs 25 as a buffer mechanism are provided above the control rod drive mechanism 2. As a result, the hollow piston 10 and the control rod 3 with a certain inertia force act on the throttle 2.
6 and compressing a large number of disc springs 25.

However, although the probability is extremely low, if we assume that the throttle 26 or the disc spring 25 cannot fully perform its castle speed function, a larger load will be applied than under normal conditions.

(Problems to be Solved by the Invention) The present invention has been made in view of the above, and provides control that further improves the health of each member by reducing the impact force at the end of the stroke even when the deceleration function is lost. The purpose is to provide a dedicated drive mechanism 2.

The deceleration function during scram in the control rod drive mechanism constructed in this way will be explained.

The hollow piston IO, which is rapidly inserted by high-pressure water, hits the stop piston 27, compresses the coil spring 28, and moves upward. At this time, the magnet at the tip of the steel ribbon connected to the stop piston 27 is pulled up, and a scram produces a signal that the ribbon has been completely inserted. The stop piston 27 then hits the throttle 26 and is decelerated by compressing the disc spring 25.

The above is a case where the normal speed function is working, but below, a case where the speed function does not function sufficiently will be explained. Stop piston 27 or throttle 26 during scram
If it moves upward even slightly, a hydraulic damper effect can be expected due to the flow of water filling the interior. In the most severe case, it is stipulated that these also do not move. In this case, the buffer mechanism is completely rigid. The hollow piston 10 rapidly inserted by high-pressure water hits the stop piston 27. Stop piston 27, throttle 2
6 does not move, the load is directly transmitted to the outer tube upper guide 24. The outer tube upper guide 24 transmits the load to the outer tube 2l via the key, deforming (stretching) the outer tube 21.
let This results in the absorption of inertial energy. When the outer tube 2l extends, the upper guide 24 moves upward to compress the coil spring 28 and discharge the water therein through the gap in the upper guide 24. This gap is made narrow in advance, and water is discharged through it at high speed, creating a dashpot effect and functioning as a hydraulic damper.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a cylindrical piston that is rapidly inserted into the reactor core during scram, and a cylindrical piston that is disposed at the upper end of the cylindrical piston and is coupled to a control rod. A coupling, a guide tube for guiding the cylindrical piston, an outer tube provided outside the guide tube and having a lower end connected to a flange, and a buffer groove provided above the guide tube. In the control rod drive mechanism consisting of The guide engages the control rod guide tube base and
The second upper guide is movably connected to the upper guide of the outer tube, and the second upper guide is fixed to the outer tube.

(Function) In the control rod drive I1 structure configured in this way, even if the deceleration mechanism such as a disc spring does not operate and cannot perform its full function, the inertia force is transmitted to the outer tube, By absorbing energy through its elongation, CH
Reduces impact force on D housing, reactor pressure vessel, etc.

(Embodiment) FIG. 1 is a top sectional view showing an embodiment of the $I1 drive m structure of the present invention, and FIG. 2 is an explanatory view showing an enlarged view of the main part thereof. As shown in FIGS. 1 and 2, the upper guide 24 is divided into a first upper guide 24a and a second upper guide 24b, with a spring 29 interposed between them. The first upper guide 24a is attached to the upper end inside the CHD housing 5 as in the conventional case, and is engaged with the CR guide tube base 23a by rotation. On the other hand, the second upper guide 24b is connected to the key 30 with the spring 29 interposed therebetween. 3
1 are fixed to the first upper guide 24a and the outer tube 2l, respectively. Ki-3 located below
1 is fixed with no clearance, whereas the key 30 disposed above has a clearance equal to or less than the compression margin of the spring 29. The spring 29 connects the first upper guide 24a and the CR guide tube base 23.
This is to make the engagement of point (a) more complete, and a slight compressive load is applied to the installation side.

The outer tube 2l basically has a circular tube shape, but by providing a groove on the outer periphery, it is possible to select the overall spring constant. In this case, by setting the depth of the groove so that the thin part of the groove does not become the weakest point in terms of its strength, it is possible to absorb more energy and increase the moving distance of the upper guide 24b.
This makes it possible to increase the dashpot effect of the engine and contribute to the deceleration force.

〔Effect of the invention〕

As explained above, the control rod drive mechanism of the present invention has a plurality of deceleration means, and even if any of the deceleration functions is insufficient, it has the ability to increase speed and further alleviate the impact force. This makes it possible to further improve reliability.

[Brief explanation of the drawing]

Fig. 1 is a top vertical sectional view showing an embodiment of the control rod drive mechanism according to the present invention, Fig. 2 is an explanatory diagram showing the main parts of Fig. 1 on an enlarged scale, and Fig. 3 is a conventional boiling water type atom FIG. 4 is a side view showing a partially cutaway furnace, and FIG. 4 is a schematic vertical cross-sectional view showing a conventional example of a control rod drive mechanism. 2... Control rod drive mechanism 5... Control rod drive mechanism housing 10... Hollow piston 17... Labyrinth seal 2l... Outer tube 23... Control rod guide tube base 24... Upper guide 24a...first upper guide 24b...
・Second upper guide 25...Disc spring 29...Spring 31...Key

Claims (1)

[Claims] A cylindrical piston that is rapidly inserted into the reactor core during a scram, a coupling disposed at the upper end of this cylindrical piston and coupled to a control rod, a guide tube that guides the cylindrical piston, and an outside of this guide tube. In the control rod drive mechanism, the control rod drive mechanism includes an outer tube whose lower end is connected to a flange, and a buffer mechanism disposed above the guide tube. a set of upper guides with springs interposed therebetween, the first upper guide engaging the control rod guide tube base and movably connected to the second upper guide. , this second
A control rod drive mechanism, wherein the upper guide is fixed to the outer tube.