JPS6159288A - Driving mechanism of control rod - 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 a control body vJ mechanism, and particularly to an improvement of a control rod vJta structure suitable for fast breeder reactors.

[Technical background of the invention]

In general, in a liquid metal-cooled W-type fast breeder reactor that uses liquid metal, for example, liquid sodium, as a coolant, it is used to control the nuclear fuel output in the reactor core and to absorb neutrons in the reactor in the event of an abnormal situation within the reactor. It is well known that emergency shutdowns of nuclear reactions in reactor cores are carried out, and that control rods are used for these operations. This control rod has a plurality of absorption bottles loaded into a trumpet tube and supported by a lattice plate, and a gripping portion is formed at the top of the trumpet tube. Then, the nuclear reaction in the reactor is controlled by inserting or withdrawing the Illm rod configured in this way into the reactor core region to change the amount of neutron absorption. Furthermore, if an abnormal IS occurs in the reactor, the control rods are rapidly fully inserted into the reactor core to stop the nuclear reaction in the reactor.

Incidentally, the operation of inserting and withdrawing the control rods into the reactor core is performed by the control rod drive 1IIIR. Various types of conventional 1ltlJ m rod drive mechanisms have been proposed, but among them, one in which the control rods are connected magnetically directly using electromagnets is simple in structure and does not require mechanical movement in the disconnection operation. It is considered to be more advantageous than other methods in that it can be made unnecessary. However, in the control rod drive structure using such electromagnets, when an emergency shutdown of a nuclear reactor is required or a shielding plug is rotated for fuel exchange, the excitation current of the electromagnets is cut off and the control rods are disconnected. However, there is a possibility that an accident may occur in which the control rods cannot be disconnected in an emergency due to failures in the abnormality detection system, failures in the electric circuit for controlling the electromagnets, or even human interference. Therefore, in order to ensure that the reactor stops even if an accident like the one described above occurs, 'R1', which attracts the control rods,
A sealed container filled with a thermally expandable material that can be expanded and contracted in the axial direction is installed in the hollow part of one stone, and the control rod is separated from the electromagnet using the thermal expansion of the thermally expandable material inside the sealed container. A control rod drive mechanism has been proposed.

FIG. 3 and FIG. 4 are views showing an example of this, and in the drawings, reference numeral 1 partially shows a shielding plug that closes the upper opening of the reactor vessel (not shown). A through hole 2 is bored in this shielding plug 1, and a protection tube 3 is inserted through this through hole 2 into a reactor vessel (not shown). This protective tube 3 is suspended and supported by a fixed member 4, and its lower part is connected to a coolant, that is, liquid sodium 5 in the reactor vessel.
immersed within. Further, an extension tube 6 is inserted into the protection tube 3 so as to be movable up and down, and a nut 7 is attached to the upper end of the extension tube 6.

This nut 7 is connected to the motor (
It is threadedly engaged with a screw shaft 8 that rotates when the screw shaft 8 (not shown) rotates, and is moved up and down by the rotation of the screw shaft 8.

A hollow electromagnet 9 is attached to the lower end of the extension tube 6, and the control rod 1 is inserted into the guide tube 11 in the reactor core 10.
2 is held by suction. A magnetic body 13 is attached to the upper end of the handling head of the control rod 12, and the control rod 12 is attracted and held by the electromagnet 9 via the magnetic body 13. Further, a sealed container 15 filled with a thermally expandable material such as a liquid metal 14 is installed in the hollow portion of the electromagnet 9. A bellows 16 is built into the side wall of this sealed container 15, and it can expand and contract in the axial direction, but since the upper end of the sealed container 15 is fixed to the upper surface of the electromagnet 9, it can only expand and contract downward. It looks like this. Note that a coolant 5 is provided between the protection tube 3 and the extension tube 6.
A seal bellows 17 is interposed to prevent steam from leaking out of the furnace, and the upper end of the seal bellows 17 is connected to the biological shield 18, and the lower end is connected to the outer periphery of the extension tube 6. .

In the above configuration, when controlling the output of the nuclear reactor, the rotation of a motor (not shown) is transmitted to the screw shaft 8, and the nut 7 converts this into vertical movement of the extension tube 6 to move the control rod 12 up and down. As a result, the control rods 12 are inserted into or withdrawn from the reactor core 10, and the amount of neutron absorption changes. Further, if an abnormal situation occurs in the furnace, the excitation current of the electromagnet 9 is interrupted by a scram signal. Along with this operation, an abnormal temperature rise occurs in the reactor vessel due to an accident in the reactivity of the core or an accident when the flow rate of the coolant decreases, and the liquid metal 14 in the sealed vessel 15 expands rapidly. This causes the bellows 16 to extend downward, increasing the distance between the electromagnet 9 and the control rod 12. When this interval A increases, the attractive force acting on the control rod 12 decreases significantly even if the electromagnet 9 is not excitation-blocked, and the control rod 12
[It is separated from the electromagnet 9 and falls naturally, suppressing the reactivity within the reactor core 10 and stopping the operation of the reactor.]

In this way, the control rod drive rod section where the sealed container 15 is installed in the hollow part of the electromagnet 9 and the control rod 12 is separated by utilizing the thermal expansion of the liquid metal 14 filled in the sealed container 15 is 'I41.
This has the advantage that even if one stone 9 is not demagnetized due to a failure in the electric circuit or the like, the reactor can be automatically stopped in response to the situation without any human intervention.

[Problems with background technology]

However, in such a control rod drive structure, a certain amount of thermal expansion force of the liquid metal 14 is required to separate the control rod 12 from the electromagnet 9. There were drawbacks such as the need to seal in a large volume of liquid metal 14 under high pressure and the need to make a portion of the tongue of the sealed container strong. In addition, such a control rod drive mechanism uses the attraction force (adsorption force of the electromagnet 9) acting on the control PJ 112 and the liquid gold Jilli1 required for separation.
Another disadvantage was that it was difficult to adjust the thermal expansion force of No. 4.

[Purpose of the invention]

The present invention has been developed based on the above circumstances, and its purpose is to provide a system with a simple structure that allows the control rods to be immediately disconnected in response to an abnormal temperature rise in the reactor without any manual operation. It is an object of the present invention to provide a highly safe control rod drive mechanism with excellent reliability in disconnection operation in an emergency.

(Summary of the Invention) In order to achieve the above object, the present invention includes a diaphragm installed in the upper opening of a sealed container, and the operation of the diaphragm opens and closes a switch contact of an electromagnet.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are diagrams showing the main parts of a control rod section 111tl structure which is an embodiment of the present invention, and FIGS.
The same parts as those in the figure are given the same reference numerals.

In this embodiment, a diaphragm 19 is disposed at the upper opening of the sealed container 15 inserted into the hollow part of the electromagnet 9. A rod 20 is located at the center of the upper surface of this diaphragm 19.
The upper end of the rod 2o projects upward through a through hole 22 formed in a plate-shaped stopper 21 fixed to the upper surface of the sealed container 15 so as to sandwich the diaphragm 19 therebetween. Furthermore, contact springs 24a and 24b are attached to the lower inner surface of the extension tube 6 via an insulator 23. Cables 25 for supplying magnet power are connected to these contact springs 24a and 24b, respectively, and are normally in contact with each other to supply excitation current to the electromagnet 9. Note that the upper end of the rod 20 is in contact with the lower surface of the contact spring 24b.

Next, the effect will be explained. First, when controlling the output of the nuclear reactor, as described above, the rotation of the motor (not shown) is transmitted to the screw shaft 8, and this is converted to the vertical movement of the extension tube 6 by the nut 7, and the control rod 12 is moved vertically. control rods 12 to core 1
Insert or withdraw it into 0. In addition, if the temperature inside the furnace rises abnormally, the liquid metal 14 in the sealed container 15
expands and the bellows 16 tries to extend downward, but since the IIJI rod 12 is attracted by the electromagnet 9 below the bellows 16, the thermal expansion force of the liquid metal 14 is applied to the bellows 1.
It acts on the diaphragm 19 earlier than 6.

Due to the thermal expansion effect of this liquid metal 14, the diaphragm 19
pushes the contact spring 24b upward via the rod 2o, and places the switch contact 26 between the contact springs 24a and 24b. As a result, the N magnet 9 becomes demagnetized, and the control rod 12 is separated from the 78 magnet 9 and falls into the guide tube 11 in the reactor core 10, causing an emergency shutdown of the reactor. Furthermore, even if the switch contact 26 cannot be separated due to fusion, etc., once the diaphragm 19 moves to a certain position, its movement will be restrained by the stopper 21, so that the thermal expansion force of the liquid gold YA14 will be applied to the hero 16 side. The control rod 12 can be separated even if the electromagnet 9 remains in an excited state by the extension operation of the rod 0-16 as in the conventional case.

According to this embodiment, the diaphragm 19 is installed at the upper opening of the sealed container 15, and the diaphragm 19 turns on the magnetic power source before the thermal expansion force of the liquid metal 14 in the sealed container 15 acts on the bellows 16. Since it is released, a double safety structure is provided, and the reliability of the disconnection operation in an emergency is improved. In addition, in the present invention, if the electromagnet 9 is equipped with a detection part that interrupts the magnetic circuit according to the temperature of the coolant, for example, a Curie single point material 27, it will be possible to eliminate the conventional sensors and human operations. It also provides a better safety measure by automatically detecting coolant temperature and shutting down the furnace without having to rely on it.

〔Effect of the invention〕

As explained above, according to the present invention, there is a protection tube inserted into the reactor vessel through a shielding plug, an extension tube inserted into the protection tube so as to be movable up and down, and a A nut attached to the upper end, a screw shaft screwed into the nut and rotated by the rotation of the motor, a hollow electromagnet attached to the lower end of the extension tube to attract and hold the upper end of the control rod, and this electromagnet. an axially expandable sealed container provided in a hollow part and filled with a thermally expandable substance;
A diaphragm attached to the upper part of the sealed container that protrudes and collapses due to the thermal expansion of the thermally expandable material, and a means for opening and closing the switch contacts of the electromagnet in accordance with the operation of the diaphragm are provided, thereby eliminating the need for manual operation. It is possible to provide a highly safe control III drive mechanism that can immediately disconnect the control rod in response to an abnormal temperature rise in the reactor without adding any additional pressure, has a simple structure, and has excellent reliability in disconnection operation in an emergency.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show control II which is an embodiment of the present invention.
Figure 1 is a cross-sectional view of the control rod being attracted to the electromagnet, Figure 2 is a cross-sectional view of the control rod being separated from the electromagnet, and Figure 3 is a diagram showing the main parts of the drive mechanism. 4 is a cross-sectional view showing an example of a conventional control rod drive mechanism, and FIG. 4 is an enlarged cross-sectional view showing the section ■ in FIG. DESCRIPTION OF SYMBOLS 1... Shielding plug, 3... Protection tube, 6... Extension tube, 7... Nut, 8... Screw shaft, 9... Electromagnet, 14... Liquid gold a<thermal expansion sexual substances〉, 15...
- Sealed container, 16... bellows, 19... diaphragm, 20... Orad, 21... stopper, 24a,
24b...Contact spring, 26...Switch contact. Applicant's agent Patent attorney Takehiko Suzue Figure 1 s2

Claims (1)

[Claims] A protection tube inserted into the reactor vessel through the shielding plug, an extension tube inserted into the protection tube so that it can move up and down, a nut attached to the upper end of the extension tube, and this nut. a screw shaft that is screwed into the shaft and rotates with the rotation of the motor, a hollow electromagnet that is attached to the lower end of the extension tube and holds the upper end of the control rod by suction, and A sealed container filled with a substance that can be expanded and contracted in the axial direction, a diaphragm attached to the upper part of the sealed container that protrudes and collapses due to thermal expansion of the thermally expandable material, and a switch contact of the electromagnet according to the operation of the diaphragm. A control rod drive mechanism characterized by comprising means for opening and closing.