JPH02222871A - Reactor shutdown equipment - Google Patents

Abstract

PURPOSE:To make a Curie-point magnetic member large in size, thereby to increase the attraction of an electromagnet and to improve reliability in respect to false scram and the like by providing an annular Curie-point magnetic member which is transferable from a position on the outer periphery of the electromagnet to a position above it. CONSTITUTION:When the temperature of a coolant rises extraordinarily and reaches a Curie point in a state wherein an electromagnet 38 is electrified and a control element is retained thereby through the intermediary of an armature 36, permeability is lowered by the action of a Curie-point magnetic member 103, the magnetic path (a) of the magnet 38 is interrupted, the attracting force thereof lowers, the armature 36 separates from the magnet 38, and the control element drops into a core under gravity. On the occasion, the member 103 is brought into direct contact with the coolant, while the coolant is introduced 106 into a gap G between the member and the magnet 38, and thus the heat of the coolant is propagated efficiently to the member 103. Therefore the rise in temperature is detected with high sensitivity and execution of a quick scram operation is enabled. At the time of start of a reactor, besides, only the magnet 38 is inserted into a guide tube 34 and the member 104 can be left on the tube 34. Therefore the member 103 can be made large in size, thus increasing the attraction of the magnet 38 and enabling prevention of false scram and the like.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor shutdown device, and in particular, to a nuclear reactor shutdown device that can reliably shut down a nuclear reactor in the event of a reactor accident in a liquid metal cooled fast breeder reactor. related to things.

(Prior art) In general, power control and reactor shutdown of nuclear reactors, especially fast neutron reactors that use liquid metal such as sodium as a coolant, are carried out by implanting control rods containing a neutron absorbing substance such as boron or tantalum in the core support plate. This is done by inserting it between multiple nuclear fuel assemblies. That is, a guide tube is arranged parallel to the fuel assembly in the longitudinal direction of the fuel assembly, and the reactivity of the reactor is controlled by moving the control rod up and down within the guide tube. The device that drives the control rods is required to have stable operation and high reliability.

Conventionally used drive devices are installed at the top of the reactor vessel housing the fuel assembly. This driving device includes a driving part fixed on a rotating plug of a shielding plug that closes the upper opening of the reactor vessel, and a rotating plug inserted to connect the driving part and control rods to the upper part of the reactor core area. It is equipped with a control rod drive mechanism consisting of an extension tube installed, and this drive mechanism is controlled from a central control room.

The drive device also includes a control panel for outputting a drive signal to the drive section automatically or manually. Normally, the operation for controlling the output of the drive unit and shutting down the furnace is as follows:
It is carried out by electrical and mechanical means.

Therefore, the configuration of a conventional control rod drive device will be explained with reference to FIG. In the figure, reference numeral 1 denotes a drive unit housing 1, and this drive unit housing 1 is connected to an upper guide tube 3 extending below the rotary plug 2. As shown in FIG. A drive motor 4 is provided at the top of the drive housing l, and the drive motor 4 is electrically coupled to a control panel 6 via a cable 5. A ball screw 7 is concentrically connected to the rotating shaft of the drive motor 4, and a pole nut 8 is screwed into the ball screw 7. This pole nut 8 is connected to a pair of load cells 10 via a plate 9, and this load cell 10 is connected to a hollow disc-shaped plate 11. An electromagnet 12 is accommodated in the hollow portion of the plate 11, and a cylinder 12a is coupled to the electromagnet 12. A load cell 13 is connected to the lower part of the cylinder 12a, and the lower part of the load cell 13 is connected to the outer extension tube 1.
It is combined with 4. The outer extension tube 14 is a lower guide tube 1 that passes through the rotary plug 2 and is provided in the core 15.
6, and its tip is the inner extension part 1.
A plurality of leaf spring-shaped latch fingers 19 are provided to form a latch mechanism together with the finger rods 18 of 7.
It becomes.

An armature 20 is provided below the electromagnet 12 so as to be magnetically attachable and detachable, and is fixed to the top of an inner extension tube 17 provided inside the outer extension tube 14 with a suitable gap. The inner extension tube 17 forms a double tube structure with the outer extension tube 14, passes through the corresponding position of the rotary plug 2, and its tip becomes a finger rod 18 that engages with the latch finger 19. . In the gap between the upper guide tube 3 and the outer extension tube 14, an ecological shield 21 is fixed to the top of the upper guide tube 3 at a position corresponding to the rotary plug 2. The lower end of the ecological shield 21 and the bellows 22
The upper end is hermetically coupled, and the lower end of the bellows 22 is hermetically coupled to an appropriate position on the outer extension tube 14. or,
Bellows 23 are provided at appropriate locations on the inner extension tube 17 and the outer extension tube 14, respectively, with both ends hermetically joined.

An acceleration spring 25 is attached to the stepped portion 24 of the outer extension tube 14.
The acceleration spring 25 is located outside the outer extension tube 14, has a coil spring shape, extends downward, and has its lower end in contact with the head of the acceleration tube 26. Accelerator tube 26
is provided on the outside of the outer extension tube 14 , its lower end is in contact with the handling head 28 of the control rod 27 , and the lower surface of its upper end is supported by a damping spring 29 . The lower end of the damping spring 29 is supported by a stopper 30 fixed near the lower end of the upper guide tube 3.

The control rod 27 has a structure in which a plurality of absorption pins containing a neutron absorption material are bundled together and housed in a protection tube. An appropriate gap is provided between the control rod 27 and the lower guide tube 16.

According to the above configuration, during normal operation, latch finger 1
A handling head 28 of the control rod 27 is engaged with the shoulder of the control rod 9, and the outer extension tube 14 and the control rod 27 are connected. The inner surface of the latch finger 19 is constrained by the finger rod 18. At this time armature 20
are attracted to and in contact with the electromagnet 12 by magnetic force. Further, the acceleration spring 25 has an upper end restrained by the stepped portion 24 of the outer extension tube 14, and a lower end restrained by the control rod 2.
It is in a compressed state as it is restrained by the head of the acceleration tube 26 which is restrained by the handling head 28 of No. 7. When controlling the core output in such a state, the control panel 6 is manually operated (or the automatic operation circuit in the panel is used) to output a forward or reverse rotation signal to the drive motor 4. Rotate. The rotation of the drive motor 4 is converted into vertical movement by the ball screw 7 and the pole nut 8, whereby the control rod 27 is pulled out and inserted, and output adjustment is achieved. Note that the reference numeral 31 in the figure is a sensor.

By the way, if an abnormal state occurs in the plant due to some reason, such as a failure such as a decrease in the coolant flow rate, a rise in the coolant temperature, or an increase in the core neutron flux, the failure is detected by the sensor 31, and the detection signal is sent to the control ff16. transmitted to. The control panel 6 automatically outputs a scram command signal using a preset theoretical circuit based on the detection signal or according to an operator's operation, and stops energizing the electromagnet 12. When the electromagnet 12 is deenergized, the armature 20 is separated and falls by the gap between it and the plate-shaped portion 32 at the lower end of the cylinder 12a. Along with this, the inner extension tube 17 falls entirely, so the finger rod 18 falls and releases the restraint of the latch finger 19. The latch finger 19 contracts inward due to the return force of the leaf spring, and as a result, the control rod 27 rapidly moves toward the lower guide tube 16 under the force of gravity and the spring force of the acceleration spring 25 transmitted to the acceleration tube 26.
Fall inside. Through this operation, a scram operation of the control rod 27 is achieved. Bellows 22 and bellows 23
is used for the purpose of enabling the axial movement of the outer extension tube 14 and the inner extension tube 17 and isolating the atmosphere inside the reactor vessel. Further, the load cell 13 is used for the purpose of confirming the healthy operation of the control rod drive mechanism.

The control rod drive system with this configuration has sufficient reliability and can be expected to operate reliably, but as nuclear reactors become larger and have higher output, a very high degree of safety is required. is required, and it is being considered to introduce nuclear reactor shutdown equipment that operates by completely different means into conventional equipment. In order to reduce the probability of a hypothetical situation in which a nuclear reactor protection device fails and the reactor cannot be effectively shut down, it is necessary to multiplex conventional devices and increase safety margins. This is because it is considered more effective to use other types of devices together than to increase the amount of energy. Furthermore, in this case, there is a demand for a device that eliminates as much as possible the causes of failure common to conventional devices.

Therefore, the idea is to directly hold the control rods using electromagnets. This will be explained with reference to FIG. In the figure, reference numeral 33 is a υ control element, and this control element 3
B is installed in the reactor core 15 in row f with the nuclear fuel assembly, and is housed in a guide tube 34 through which a coolant flows, allowing it to move up and down. An extension rod 35 is connected to the top of the control element 33;
An armature 36 is coupled to the upper end of the extension rod 35. The control element 33 is held by adsorbing the armature 36 with an electromagnet 38 installed at the lower end of an extension tube 37 that hangs down from three shielding plugs that form the upper lid of the reactor vessel housing the reactor core 15. It will be done. The electromagnet 38 is composed of an iron core 42 and a coil 41 embedded in the iron core 42. By energizing the coil 41, a magnetic force is generated, and the armature 36 is attracted by this magnetic force. The upper part of the extension tube 37 is
It is connected to a vertical movement drive device 40 fixed to the shielding plug 39, and the vertical movement drive device 40 performs a pulling operation of the control element 33 or a lowering operation for resetting after disconnection. Note that the vertical movement drive device 40 is connected to a control device 43. Further, in the figure, reference numeral 44 is a dashpot, and reference numeral 45 is a support plate.

When the control rod drive device with the above configuration is adopted, there are the following advantages. That is, unlike conventional latching mechanisms, the extension tube 35 or a corresponding elongated object does not require mechanical movement in the separation operation during scramming of the control element 33, and at the same time does not require a relatively complex mechanism such as a latching mechanism. The configuration is very simple because there is no need to selectively excite and de-energize the electromagnet 38. Therefore, common causes of failure with conventional types of devices can be significantly reduced. or,
Since the electromagnet 38 is placed in a coolant, if the temperature of the magnetic material used for the iron core 42 and armature 36 of the electromagnet 38 reaches near its Curie point due to an abnormal temperature rise of the coolant, the electromagnet 38 will automatically shut down. Significant magnetic force reduction is achieved and automatic scram is achieved. In this way, reactor shutdown devices with largely different scram operation principles are used in conjunction with conventional systems, so that only one of the two types of devices can achieve reactor shutdown through scram operation. This makes it possible to significantly improve the safety of nuclear reactors.

(Problems to be Solved by the Invention) In such a conventional nuclear reactor shutdown device that scrams the control element 33 by utilizing changes in magnetism at the Curie point of a magnetic material, the electromagnet 38 during normal operation of the nuclear reactor is It is necessary to make the adsorption force sufficiently large (to prevent this scram), and to make the adsorption force sufficiently small when the coolant temperature rises abnormally to ensure that scram can be achieved. To do this, it is first necessary to sufficiently increase the magnetic flux obtained by the electromagnet 38 during normal operation, but it is necessary to increase the magnetic flux obtained by the electromagnet 38 during normal operation.
For example, the saturation magnetic flux density of a magnetic material with a Curie point of about 600°C at a normal operating temperature of about 550°C is significantly lower than that of iron, etc., making it extremely difficult to design a material with sufficient characteristics. be. Especially when starting up a nuclear reactor,
Since it is necessary to insert the electromagnet 38 at the position of the armature 36 in the guide tube 34, the outer diameter of the electromagnet 38 is limited, and there is a major problem in that it is not possible to secure the necessary magnetic flux by increasing the cross-sectional area of the magnetic circuit. There's a problem.

The present invention has been made in consideration of these points, and provides a reactor shutdown device that can sufficiently increase the suction force during normal operation of the reactor and greatly improve reliability against erroneous scrams, etc. The purpose is to provide.

[Structure of the invention]

(Means for Solving the Problems) A first aspect of the present invention is a means for achieving the above-mentioned object, in which the control element is disposed in the core of the reactor vessel, through which a coolant flows and a control element is inserted and removed. a guide tube, an armature fixed to the upper end of the control element, and an extension tube that hangs from a shutoff plug that closes the upper opening of the reactor vessel and is driven up and down by a lifting mechanism disposed on the upper surface side of the shutoff plug. an electromagnet fixed to the lower end of the extension tube for selectively attracting the armature; an excitation mechanism for exciting the electromagnet; In a nuclear reactor shutdown device comprising a Curie point magnetic member installed so as to lose the holding force of the electromagnet and come into direct contact with the coolant in the reactor, the Curie point magnetic member is formed into an annular shape and the electromagnet is The movement between the outer periphery position and the upper position of the electromagnet is set to J, and when the Curie point magnetic member is located on the outer periphery of the electromagnet, a required gap is formed between it and the electromagnet. Features.

Further, a second aspect of the present invention provides, as a means for achieving the above object, a guide tube which is arranged in a reactor core in a nuclear reactor vessel, through which a coolant flows and into which a control element is inserted and removed; an armature fixed to an upper end; an extension tube that hangs from a shielding plug that closes the upper opening of the reactor vessel and is driven up and down by a lifting mechanism disposed on the upper surface side of the shielding plug; and a lower end of the extension tube. an electromagnet that is fixed to the armature and selectively attracts the armature; an excitation mechanism that excites the electromagnet; and an excitation mechanism that is provided on the electromagnet and causes the electromagnet to lose its holding force when the furnace temperature reaches a preset temperature. In a nuclear reactor shutdown device comprising a Curie point magnetic member installed so as to be in direct contact with the coolant in the reactor, a part of the control element or inside the guide tube,
The present invention is characterized in that a position support mechanism is provided that presses and urges the armature to project upward from the top of the guide tube.

(Function) In the nuclear reactor shutdown device according to the first invention of the present invention,
The Curie point magnetic member is formed in an annular shape and is movably arranged between a position on the outer periphery of the electromagnet and a position above the electromagnet. Therefore, at reactor startup, it is possible to leave the Curie point magnetic member on the top of the guide tube and insert only the electromagnet into the guide tube, and the outer diameter of the Curie point magnetic member is limited to the inner diameter of the guide tube. It is possible to increase the adsorption force during normal operation to prevent erroneous scrams and the like. In addition, when the Curie point magnetic member is located on the outer periphery of the electromagnet, a required gap is formed between the Curie point magnetic member and the electromagnet, so the coolant flows into this gap,
It becomes possible to quickly detect a temperature rise in the coolant and perform a scram operation.

Further, in the nuclear reactor shutdown device according to the second aspect of the present invention, in the normal state, the armature is in a state of protruding upward from the top of the guide tube due to the suppressing force of the position support mechanism. Therefore, there is no need to insert an electromagnet into the guide tube, and there are no dimensional restrictions on the Curie point magnetic member. Therefore, it is possible to sufficiently increase the suction force during normal operation to prevent erroneous scrams and the like. Further, the armature is pushed by a gripper or the like of the exchanger to resist the suppressing force of the position support mechanism and sink into the guide tube. Therefore, there is no problem when replacing the control element together with the guide tube.

(Example) Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 to 3.

In FIG. 3, reference numeral 34 denotes a guide tube having a handling head 34a at the top. ing. A control element (not shown) is housed in the guide tube 34 so as to be able to rise and lower. An extension tube 35 is connected to the top of the control element. 36
is installed. And this armature 36 is
As shown in FIGS. 1 and 3, it is magnetically attached to an electromagnet 38 provided at the lower end of the extension tube 37.

The electromagnet 38, as shown in FIGS. 1 to 3,
It is composed of an iron core 42 and a coil 41 embedded in the iron core 42. A cover 102 made of non-magnetic metal is installed around the coil 41, and a cover 102 made of a non-magnetic metal is installed at the lower end of the cover 102. Pole piece 42 made of magnetic material such as alloy steel
A is installed. When the armature 36 is attracted to the electromagnet 38, the magnetic pole piece 42a forms part of a magnetic path together with the armature 36 and the like, as shown by the broken line arrow a in FIG.

As shown in FIGS. 1 and 2, an annular Curie point magnetic member 103 is disposed on the outer periphery of the first coil 41.
As shown in FIG. 3 and FIG. 3, the locking piece 10 provided on the extension tube 37 is movable between the outer peripheral position of the electromagnet 38 and the upper position of the electromagnet 38.
4 and the Curie point magnetic member 103
Due to the urging force of 05, it is positioned at the outer periphery of the electromagnet 38.

As shown in FIG. 2, this Curie point magnetic member 103 has a plurality of coolant introduction grooves 106 formed in the circumferential direction, and the Curie point magnetic member 103 is located on the outer circumference of the electromagnet 38. , a required gap G is formed between the electromagnet 38 and the electromagnet 38. and,
The coolant introducing groove 106 allows the Curie point magnetic member 1 to
A large number of thin parts are formed in 03, and the gap G
As a result, the coolant flows between the electromagnet 38 and the electromagnet 38.

The Curie point of the Curie point magnetic member 103 is lower than that of the iron core 42 and armature 36 made of iron or low alloy steel, and the normal operating temperature of the nuclear reactor (500 to 500
50°C), specifically, for example, 60°C.
The temperature is around 0℃.

Next, the operation of this embodiment will be explained.

As shown in FIG. 1, when the electromagnet 38 is energized and the control element 33 is held through the armature 36, if there is an abnormal temperature rise in the reactor, a scram operation is automatically performed. Ru. That is, when the temperature of the coolant rises abnormally and reaches the Curie point, the Curie point magnetic member 10
3, the magnetic permeability decreases, and the magnetic path a of the electromagnet 38
is cut off, and the attraction force by the electromagnet 38 is reduced. As a result, the armature 36 separates from the electromagnet 38 and the control element 33 falls into the reactor core due to gravity.

By the way, the Curie point magnetic member 103 is in direct contact with the coolant and has a plurality of coolant introduction grooves 106.
A thin wall portion is formed by providing the electromagnet 3.
8 is formed, the coolant sufficiently contacts the Curie point magnetic member 103, and the heat of the coolant is efficiently transmitted to the Curie point magnetic member 103. Therefore, the temperature rise of the coolant can be detected with high sensitivity, and rapid scram operation is possible.

On the other hand, when the nuclear reactor is started up, the inlet armature 36 shown in FIG. 3 is in a state of being recessed into the guide tube 34. In this state, when the electromagnet 38 is lowered to a position directly above the armature 36 for coupling with the armature 36, the Curie point magnetic member 103 is placed on the handling head 34a of the guide tube 34, and only the electromagnet is handled. It is inserted into the head 34a. In this state, the armature 36 is attracted by the attraction force caused by the magnetic flux generated in the magnetic path shown by broken lines and arrows in FIG. 3 due to excitation. For this reason, the handling head 34a
is made of a magnetic material such as low alloy steel or magnetic stainless steel.

In this way, the outer diameter of the Curie point magnetic member 103 can be increased without being limited by the inner diameter of the guide tube 34, and even when the coolant introduction groove 106 is formed, the magnetic path cross-sectional area can still be made larger than before. be able to.

Therefore, the attraction force of the electromagnet 38 is increased, and erroneous scrams and the like can be completely prevented.

4 and 5 show a second embodiment of the present invention, in which a Curie point magnetic member 103 is fixed to the outer periphery of an electromagnet 38, and the attraction position of the armature 36 and the electromagnet 38 is on the guide tube 34. A control element 33 is disposed within the guide tube 34 so as to be above the handling head 34a of the
A position support mechanism 107 that presses and urges the is provided.

That is, as shown in FIG. 4, a Curie point magnetic member 103 is fixed to the outer circumference of the electromagnet 38, and its outer diameter is
In order to increase the magnetic flux and increase the attraction force, it is formed to have a larger diameter than the handling head 34a of the guide tube 34.

On the other hand, a guide tube 34 in which the control element 33 is housed so as to be able to rise and fall freely.
As shown in FIG. 4, a position support mechanism 107 consisting of a support member 108 and a spring 109 is provided at the inner lower end of the control element 33, and the control element 33 is constantly pressed by the pressing force of this position support mechanism 107. As a result, the armature 36 protrudes above the handling head 34a of the guide tube 34 in a normal state. This armature 36 is connected to a changing device 110 as shown in FIG.
When replacing the control element 33 using the gripper mechanism 111, it is pushed into the guide tube 34 and allows the gripper mechanism 111 to engage with the handling head 34a.

In the figure, the reference numeral 112 is a dashpot provided at the lower end of the position support mechanism 107, and the reference numeral 113 is a flow path hole as a flow path for allowing the coolant to flow into the guide tube 34.

Next, the operation of this embodiment will be explained.

As shown in FIG. 4, when the electromagnet 38 is energized to hold the control element 33 through the armature 36 and pull it out above the reactor core, if there is an abnormal temperature rise in the reactor, automatic A scrum operation is performed. That is, when the temperature of the coolant abnormally rises and reaches the Curie point, the magnetic permeability decreases due to the action of the Curie point magnetic member 103, the magnetic path a of the electromagnet 38 is interrupted, and the attraction force by the electromagnet 38 decreases. As a result, the armature 36 separates from the electromagnet 38 and the control element 33 falls into the reactor core due to gravity.

By the way, since the Curie point magnetic member 103 is in direct contact with the coolant and the heat is efficiently transferred, the humidity of the coolant can be detected with high sensitivity, making it possible to perform a quick scram.

Furthermore, when the control element 33 falls due to a scram and is seated, the impact is absorbed by the dashbot 112 and the spring 109, and the rebound due to the elastic reaction force of the spring 109 is caused by the dashbot 112 moving in the reaction direction. Since this also acts, damping is absorbed and it is possible to prevent problems such as the control element 33 springing up after being seated.

Furthermore, since the Curie point magnetic member 103 can be made larger,
A large magnetic flux is obtained, the adsorption force is increased, and erroneous scrams do not occur even if there is mechanical or fluid vibration.

Furthermore, the armature 36 is retracted into the guide tube 34 when pressed by the gripper mechanism 111, so when replacing the control element 33 with the replacement device 110, the gripper mechanism 111 is engaged with the handling head 34a by the same operation as in the past. can be combined.

FIG. 6 shows a third embodiment of the present invention.
In place of the position support mechanism 107 in the embodiment, a position support mechanism 117 configured by incorporating a support member 118 integral with the seat 101 and a spring 119 into the extension tube 35 is used.

Even with this configuration, the same effects as in the second embodiment can be expected, and the position support mechanism ]-17 can be made smaller because it is not necessary to suppress and support the control element 33.

〔Effect of the invention〕

As explained above, the first aspect of the present invention has a structure in which the Curie point magnetic member can move between the outer peripheral position of the electromagnet and the upper position of the electromagnet. There is no need to insert it into the holder, making it possible to increase its size. Therefore, the suction force during normal operation can be sufficiently increased, and reliability against erroneous scrams and the like can be greatly improved. In addition, when the Curie point magnetic member is located on the outer periphery of the electromagnet, a required gap is formed between the electromagnet and the heat of the coolant is efficiently transferred to the Curie point magnetic member, resulting in a rapid Scrum becomes possible.

Further, in the second aspect of the present invention, the armature is made to protrude above the top of the guide tube due to the suppressing force of the position support mechanism, so that the Curie point magnetic member and the electromagnet are inserted into the guide tube. It is possible to adsorb the armature without having to do so.

Therefore, it is possible to increase the size of the Curie point magnetic member and greatly improve reliability against erroneous scrams and the like. Furthermore, since the armature is pushed into the guide tube by being pressed by the grip mechanism of the exchanger, it does not pose a problem when exchanging the control element.

[Brief Description of the Drawings] Fig. 1 is a cross-sectional view of main parts showing a nuclear reactor shutdown device according to a first embodiment of the present invention, Fig. 2 is a cross-sectional view taken along the line ■-n in Fig. 1, and Fig.
The figure is a diagram equivalent to Figure 1 showing the state at the time of reactor startup, Figure 4 is a sectional view of main parts showing the reactor shutdown device according to the second embodiment of the present invention, and Figure 5 is the state at the time of control element replacement. FIG. 6 is a diagram equivalent to FIG. 5 showing a nuclear reactor shutdown device according to the third embodiment of the present invention, and FIG. 7 is a diagram equivalent to a conventional nuclear reactor shutdown system having a mechanical control rod drive device. FIG. 8 is a sectional view showing a conventional nuclear reactor shutdown device having an electromagnetic control rod drive device. 33... Control element, 34... Guide tube, 37... Extension tube, 38... Electromagnet, 103... Curie point magnetic member, 107.117... Position support mechanism, 108°1
18...Support member, 109.119...Spring, G.
··gap.

Claims (1)

[Scope of Claims] 1. A guide tube disposed in the core of the reactor vessel through which a coolant flows and into which a control element is inserted and removed; an armature fixed to the upper end of the control element; An extension tube that hangs down from a shutoff plug that closes the upper opening of the furnace vessel and is driven up and down by a lifting mechanism arranged on the upper surface side of the shutoff plug, and an extension tube that is fixed to the lower end of the extension tube and selectively adsorbs the armature. an electromagnet, an excitation mechanism that excites the electromagnet, and an excitation mechanism provided on the electromagnet so that when the temperature inside the furnace reaches a predetermined temperature, the holding force by the electromagnet is lost and the electromagnet comes into direct contact with the coolant inside the furnace. In a nuclear reactor shutdown device comprising an installed Curie point magnetic member, the Curie point magnetic member is formed in an annular shape and is disposed so as to be movable between an outer peripheral position of the electromagnet and a position above the electromagnet, and A nuclear reactor shutdown device characterized in that a required gap is formed between the electromagnet and the electromagnet when the device is located on the outer periphery of the electromagnet. 2. A guide tube disposed in the core of the reactor vessel through which a coolant flows and a control element is inserted and removed, an armature fixed to the upper end of the control element, and an upper opening of the reactor vessel. an extension tube that hangs down from the shielding plug to be closed and is driven up and down by a lifting mechanism disposed on the upper surface side of the shielding plug; an electromagnet that is fixed to the lower end of the extension tube and selectively attracts the armature; An excitation mechanism that excites, and a Curie point magnet installed in the electromagnet so that when the temperature in the furnace reaches a predetermined temperature, the electromagnet loses its holding force and comes into direct contact with the coolant in the furnace. A nuclear reactor shutdown device comprising: a position support mechanism that is provided in a part of the control element or inside the guide tube and presses and biases the armature to protrude upward from the top of the guide tube; A nuclear reactor shutdown device characterized by: