JPH0412296A - Reactor stop device - Google Patents

Abstract

PURPOSE:To independently stop a reactor by providing a control rod driving mechanism which is placed above a guide tube and supports an attracting material of a latch mechanism grasping an upper stop part of an extended tube by an electromagnet and an earthquake detector which turns on/off the power source of the electromagnet. CONSTITUTION:When the operation of a reactor is urgently stopped because of the occurrence of earthquake or the like, an electromagnet 6 is demagnetized by a scram signal. When the electromagnet 6 is demagnetized, an attracting member 17 is detached from the electromagnet 6, and a link mechanism 16 holding an inside extended tube 11 is opened. The extended tube 11 is dropped by this opening to push out a finger rod 13 downward. Then, a latch finger 3 has the diameter reduced and is disengaged from a handling head 15 to drop a control rod 14 into a core. Since the spring force of a compressed acceleration spring 20 acts downward in an acceleration tube 18 in this case, the drop speed of the control rod 14 is accelerated by the acceleration tube 18, and the control rod 14 is quickly inserted into the core.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is a nuclear reactor shutdown device that operates in the event of an abnormality such as an excessive earthquake occurring in a fast breeder reactor, etc., and stops the output of the nuclear reactor. Regarding.

(Prior Art) Nuclear reactors are designed to control output by inserting and removing control rods containing neutron absorbers into the reactor core.

In the event of an emergency such as an accident, these control rods are fully inserted into the reactor core to stop the reactor's output. In such an emergency, it is necessary to reliably stop the operation of the nuclear reactor, so a reactor shutdown device that has a simple structure and can operate reliably is required.

(Problems to be Solved by the Invention) This type of device is a reactor shutdown system that operates using external equipment such as a control rod drive mechanism based on a scram signal output when a reactor is abnormal, and a reactor shutdown system that operates using external equipment such as a control rod drive mechanism. There is an issue in which double or triple safety measures must be taken by using an independent drop-type reactor shutdown system that operates independently without using a system.

The present invention has been made to solve the above problems, and has a simple structure, can operate reliably, and is reliable and can operate independently of other reactor shutdown systems using drive mechanisms etc. Our goal is to provide a high quality nuclear reactor shutdown system.

[Object of the Invention] (Means for Solving the Problems) The present invention provides a guide tube installed vertically in a furnace, a control rod inserted into the guide tube so as to be able to rise and fall freely, and a control rod located above the guide tube. A drive unit installed outside the reactor inserts and pulls out the control rods through the inner and outer extension tubes of the double-tube structure, and the adsorbent of the latch mechanism that grips the upper stops of these extension tubes is moved using electromagnets. and an earthquake detector installed near the upper end of the drive unit that turns on and off the power to the electromagnet. A conical receiver with a lowered center is always held in a section, and when the steel ball is located at the center of the receiver, the receiver can be used to hold the switch knob of a limit switch located in a hole provided in the center of the section. When the steel ball is off center and the switch knob is released from being pressed, the switch is turned off.
It is characterized by being configured so that.

(Operation) Under normal conditions, the electromagnets are excited and the control rod drive mechanism inserts or withdraws the control rods into the reactor core to control the output.

During a scram, the scram cutoff switch is activated by the scram signal, demagnetizing the electromagnets, and dropping the control rods into the reactor core to perform a scram. If a failure occurs in the circuit that outputs the scram signal during an earthquake and a scram is not performed, the steel ball that presses the limit switch knob built into the earthquake detector installed near the top of the drive unit will move. When the knob is released and the limit switch is turned off, the electromagnet is demagnetized and scram operation can be performed.

This kind of scram is performed independently in the event of a large earthquake, regardless of electrical signals such as the scram signal, so in the unlikely event that other reactor shutdown systems, such as a reactor shutdown system that scrams based on the scram signal, do not function normally. Even if the system does not operate, the control rods can be reliably dropped and scrammed, resulting in a safe reactor shutdown system.

(Example) An example of a nuclear reactor shutdown device according to the present invention will be described with reference to FIGS. 1 to 3.

The scram type control rod drive mechanism generally used in fast breeder reactors includes a gas pressure acceleration type and a spring acceleration type. In the gas pressure acceleration method, gas pressure is constantly applied to the extension rods that transmit acceleration force and vertical motion to the control rods, and this gas pressure is used to rapidly insert the control rods into the reactor core during scram. The spring acceleration method uses a compressed spring as a means of applying acceleration force to the control rods, and uses the spring force of the springs to rapidly insert the control rods into the reactor core during scram.

FIG. 1 is a sectional view showing a control rod drive mechanism in a nuclear reactor shutdown system using a spring acceleration method, and FIG. 1 is representative of the explanation. Reference numeral 1 in the figure is a guide tube inserted into the reactor vessel by penetrating the upper cover 2 of the reactor vessel (not shown). Inside the guide tube 1, there is provided an outer extension tube 4 having a latch finger 3 whose diameter can be freely expanded at its lower end and whose upper end is held by an extension tube latch finger 5. The extension tube latch finger 5 is integrally provided at the lower end of a magnet holder 7 having an electromagnet 6 incorporated therein, and is adapted to move up and down within the guide tube 1 together with the magnet holder 7. A drive motor 8 is provided at the top of the guide tube 1 to rotate a ball screw 9. A nut 11 connected to the upper end of the magnet holder 7 via a connecting member 10 is screwed into the ball screw 9.
It is designed to move up and down by the rotation of the ball screw 9.

That is, the extension tube latch finger 5 and the magnet holder 7 are configured to move up and down within the guide tube 1 as the nut 11 moves.

An inner extension tube 12 is slidably inserted into the outer extension tube 4. At the lower end of this inner extension pipe 12 is an outer extension pipe 4.
A finger rod 13 is provided which enlarges the latch finger 3 so that it engages the inner surface of a handling head 15 provided at the upper end of the control rod 14. The upper end of the inner extension tube 12 is introduced into the magnet holder 7 and held by a link mechanism 16 provided within the magnet holder 7. One end of this link mechanism 16 is connected to an adsorption member 17 that is adsorbed and held by the electromagnet 6.
By separating from the inner extension tube 12, the inner extension tube 12 is opened.

An acceleration tube 18 is provided on the lower outer periphery of the outer extension tube 4. The lower end of the accelerating tube 18 is in contact with the upper end surface of the handling head 15, so as to apply acceleration force to the control rod 14. That is, a plurality of acceleration springs 20 are installed in a compressed state between the acceleration tube 18 and the spring bearing protruding from the inner circumferential surface of the guide tube 1, and the acceleration tube 18 The spring force of the spring 20 is used to apply acceleration force to the control rod 14. The upper end of the acceleration spring 20 is fixed to the spring receiver 19, and only the lower end is free. The upper end of the acceleration tube 18 is a large-diameter stopper portion 18a, and this stopper portion 18a comes into contact with an annular dashpot portion 22 provided on the inner circumferential surface of the guide tube 1 to reduce the amount of movement of the acceleration tube 18. is now regulated. In the figure, reference numerals 23 and 24 indicate stopper portions that respectively restrict the amount of movement of the outer extension tube 4 and the inner extension tube 12. An earthquake detector 32 having the following configuration is provided near the upper end of the drive motor 8.

That is, as shown in FIGS. 2 and 3, the earthquake detector 32 has a steel ball 25. It consists of a limit switch 26 and a casing 27 surrounding these. A cable 28 for feeding power to the electromagnet 6 is connected to the limit switch 26 to turn on/off the electromagnet 6.

A switch knob 29 for operating the limit switch 26 is normally inserted from below into a hole 3I penetrating downward at the center of the casing 27, which has a conical receiver with a depressed center part 30. Moreover, this switch knob 29 has a receiving part 30.
It is pushed downward by the steel ball 25 placed on top, and the switch is turned off.

The steel ball 25 has enough weight to push the switch knob 29 downward. The limit switch 26 is turned on when the steel ball 25 moves from the center of the receiving part 30.
It is configured so that The steel ball 25 has geometric dimensions such that the receiver does not come off the part 30 completely even after the switch knob 29 is released, and the receiver returns to the center of the part 30. It is formed. Also,
The sensitivity of the motion depending on the magnitude of the earthquake can be adjusted by appropriately adjusting the inclination angle of the support portion 30, the size of the steel ball 25, etc.

In the reactor shutdown system having the earthquake detector 32 configured as described above, the drive motor 8 moves the control rods 14 up and down during normal operation of the reactor. That is, when the drive motor 8 is driven to rotate the ball screw 9, the nut 1
1 moves up and down in accordance with the direction of rotation of the ball screw 9, and together with this, the extension tube latch finger 5 and the magnet holder 7 move up and down within the guide tube 1. This extension pipe latch finger 5
As the magnet holder 7 moves up and down, the outer extension tube 4 and the inner extension tube 11 holding the control rod 14 move up and down, causing the control rod 14 to move up and down. As a result, control rod 1
4, the amount inserted into the reactor core (not shown) changes, and the output of the reactor is controlled.

On the other hand, in the event of an emergency shutdown of the nuclear reactor due to an earthquake or the like, the electromagnet 6 is demagnetized by a scram signal. When the electromagnet 6 is demagnetized by the scram signal, the attraction member 17
is detached from the electromagnet 6, and the link mechanism 16 holding the inner extension tube 11 is opened. By opening this link mechanism 16, the inner extension tube 11 falls, and the finger rod 13
push downward. As a result, the latch finger 3 is reduced in diameter and released from engagement with the handling head 15, allowing the control rod 14 to fall into the reactor core. Further, in this case, since the spring force of the compressed acceleration spring 20 is acting downwardly on the acceleration tube 18, the falling speed of the control rod 14 is accelerated by the acceleration tube 18. As a result, control rod 1
4 will be rapidly inserted into the reactor core.

Normally, the electromagnet 6 is energized, and the control rod drive mechanism inserts or withdraws the control rod 14 into the reactor core.
Perform output control. During a scram, a scram cutoff switch is activated by a scram signal to demagnetize the electromagnet 6, and the control rod 14 is dropped into the reactor core to perform a scram. If a failure occurs in the circuit that outputs the scram signal during an earthquake and a scram is not performed, the steel ball 25 pressing the knob 29 of the limit switch 26 built into the earthquake detector 32 installed near the top of the drive unit When the knob 29 is moved, the push-in of the knob 29 is released, the limit switch 2G is turned off, and the electromagnet 6 is demagnetized so that a scram operation can be performed. This type of scram is performed independently, independent of electrical signals such as scram signals, during large earthquakes, so other atoms
Even if a reactor shutdown system, for example, a reactor shutdown system that scrams based on a scram signal, does not operate normally, the control rod can be reliably dropped and scrammed, and a safe reactor shutdown system can be obtained.

Moreover, the earthquake detector 32 used in the nuclear reactor shutdown device of this embodiment includes a limit switch 26, a steel ball 25, and a housing 2.
7, which have the advantage of simple structure and reliable operation. Therefore, it is extremely effective as a backup for other reactor shutdown systems, and can significantly improve the safety of the reactor. The present invention can of course be applied to output adjustment rods that adjust the output by arbitrarily adjusting the vertical position of the control rods using the drive unit, and can also be applied to power adjustment rods that do not have such an output adjustment function and only have a reactor shutdown function. It can also be similarly applied as a safety rod.

[Effects of the Invention] According to the present invention, in a nuclear reactor shutdown system in which a scram cutoff switch is actuated by a scram signal to demagnetize an electromagnet and scram, a scram occurs due to a failure in the circuit that outputs the scram signal, especially during an earthquake. If this is not done, a limit switch is activated by the movement of a steel ball installed near the drive unit, which automatically cuts off the power to the electromagnet.

Therefore, it can operate as an independent drop type reactor shutdown system independent of other reactor shutdown systems, and high safety and reliability can be obtained as a multiple safety device. Furthermore, since the detector consists of a limit switch and a steel ball, it has a simple structure and reliable operation, and can easily return after a scram.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment of the nuclear reactor shutdown system according to the present invention, FIG. 2 is a vertical cross-sectional view partially showing the normal state of the earthquake detector in FIG. 1, and FIG. It is a longitudinal cross-sectional view showing the moving state of steel balls of the same earthquake detector during an earthquake. 29... Switch knob 30... Conical receiver is part 31... Hole 32... Earthquake detector (8733) Agent, patent attorney Yoshiaki Inomata (and others)
1 person) 6... Electromagnet 12... Inner extension tube 16... Link mechanism 17... Adsorption member 25... Steel ball 26... Limit switch 27... Housing 28... Cable

Claims (1)

[Claims] A guide tube installed vertically inside the furnace, a control rod inserted into the guide tube so as to be able to rise and fall, and a drive section located above the guide tube and installed outside the furnace to extend the inside and outside of the double tube structure. Inserting and withdrawing the control rods through the tubes and turning on and off the power to the control rod drive mechanism, which uses electromagnets to support the adsorption members of the latch mechanism that grips the stops at the top of these extension tubes. and an earthquake detector provided near the upper end of the drive unit, and the earthquake detector always holds a steel ball located at the center of the housing with a conical receiver with a downwardly centered center, If the steel ball is located in the center of the receiving part, the switch knob of the limit switch located in the hole provided in the center of the receiving part is recessed to turn the switch "on", and the steel ball moves off the center and the switch is turned on. A nuclear reactor shutdown device characterized in that the switch is configured to be turned off when the knob is released.