JPH0352596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nuclear reactor shutdown device that can reliably shut down a liquid metal cooled fast breeder reactor in the event of an accident, for example.

[Technical background of the invention]

In general, power control and reactor shutdown in nuclear reactors, especially fast neutron breeder reactors that use liquid metals such as sodium as coolant, are performed using multiple control rods containing neutron absorbing substances such as boron or tantalum embedded in the core support plate. This is done by inserting it between the fuel assemblies. That is, the reactivity of the nuclear reactor is controlled by moving a control rod up and down within a guide tube fixed to a core support plate parallel to the longitudinal direction of the fuel assembly. With this control,
The device that drives the control rods is required to have stable operation and high reliability. A conventional control rod drive device is a drive unit that is fixed on a rotating plug that is installed at the top of a reactor vessel that houses fuel assemblies, and that is part of a shield plug that isolates the atmosphere inside the reactor vessel. and a control rod drive mechanism having an extension tube that extends through the rotating plug to connect to the control rods by passing through the rotating plug and connecting the control rods to the control rods; and a control panel that generates electrical signals for driving the drive section automatically or manually. Normally, the output control of the drive unit and the operation for shutting down the furnace are performed by electro-mechanical means.

FIG. 1 shows an example of a conventional control rod drive device. That is, the drive housing 1 is fixed to the rotary plug 2 and connected to an upper guide tube 3 passing through the rotary plug 2. A motor 4 is provided at the top of the drive housing 1, and the motor 4 is electrically connected to a control panel 6 via a cable 5. A screw 7 is concentrically coupled to the rotating shaft of the motor 4, and a ball nut 8 is threaded onto the screw 7. Ball nut 8 is plate 9
The load cell 10 is connected to a pair of load cell 10 via a hollow disc-shaped plate 11. An electromagnet 12 and a cylinder 12a are coupled to the lower surface of the plate 11. The lower part of the tube 12a is connected to a pair of load cells 13, and the lower part of the load cell 13 is connected to an outer extension tube 14. The outer extension tube 14 passes through the rotary plug 2 and extends above a lower guide tube 16 provided in the reactor core 15 . The tip of the outer extension tube 14 is connected to a plurality of latch fingers 1 in the shape of leaf springs to form a latch mechanism together with a finger rod 18 at the lower end of the inner extension tube 17.
It has become 9.

On the other hand, an armature 20 is provided below the electromagnet 12 which is electrically connected to the control panel 6, and is magnetically detachable. Inner extension tube 1
It is fixed to the top of 7. The inner extension tube 17 and the outer extension tube 14 form a double tubular shape, pass through a corresponding position of the rotary plug 2, and have a finger rod 18 at its tip that engages with a latch finger 19. In the gap between the upper guide tube 3 and the outer extension tube 14, a biological 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 biological shield 21 and the upper end of the bellows 22 are airtightly connected, and the lower end of the bellows 22 is connected to the outer extension tube 14.
are hermetically bonded in place. Furthermore, 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 coupled to the stepped portion 24 of the outer extension tube 14, and the acceleration spring 25 extends downward in the shape of an outer coil spring of the outer extension tube 14, and its lower end contacts the head of the acceleration tube 26. There is. The acceleration tube 26 is provided outside the outer extension tube 14, and 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 clearance is provided between the control rod 27 and the lower guide tube 16.

Next, an example of the operation of the conventional control rod drive device described above will be explained. During normal operation, the handling head 28 of the control rod 27 is engaged with the shoulder of the latch finger 19, as shown in FIG.
and the control rod 27 are connected. The inner surface of the latch finger 19 is restrained by a finger rod 18. At this time, the armature 20 is attracted to and in contact with the electromagnet 12 by magnetic force.
Further, the acceleration spring 25 has its upper end connected to the outer extension tube 1
The lower end of the accelerating tube head is restrained by the stepped portion 24 of No. 4 and the handling head 28 of the control rod 27, and is in a compressed state. To adjust the output of the core in this state, the control panel 6 is manually operated, or an automatic operation circuit in the tube transmits a forward or reverse rotation signal to the motor 4 to rotate the motor 4. This rotational movement is converted into vertical movement by the screw 7 and ball nut 8, whereby the control rod 27 is pulled out or inserted, and output adjustment is achieved.

Now, if an abnormal state occurs in the plant due to some reason, such as a failure such as a decrease in coolant flow rate, a rise in coolant temperature, or an increase in core neutron flux, the failure will be detected by the sensor 31 installed in the reactor, and the signal will be used to control It is transmitted to board 6. Control panel 6
generates a scram command signal automatically or in accordance with a reverse operation by a preset logic circuit, and stops energizing the electromagnet 12. Electromagnet 12
When the armature is deenergized, the armature is separated and the tube 12
It falls by the amount of the gap between it and the plate-like part 32 at the lower end of a. As a result, the inner extension tube 17 falls entirely, and the finger rod 18 falls, releasing the latch finger 19 from its restraint. The latch finger 19 then narrows inwardly due to the restoring force of the leaf spring and disengages from the handling head 28 of the control rod 27. The control rod 27 rapidly falls through 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 .

Through the above steps, the scram operation of the control rods is achieved. The bellows 22 and the bellows 23 are used for the purpose of allowing the outer extension tube 14 and the inner extension tube 17 to move in the axial direction and isolating the atmosphere inside the furnace vessel. Further, the load cell 13 is used for the purpose of confirming the healthy operation of the control rod drive mechanism.

A control drive device consisting of an electro-mechanical drive mechanism, typified by the control rod drive device as described above, and a control panel equipped with sensors and electrical logic circuits generally has sufficient reliability. It can be expected to operate reliably and can be said to be sufficiently effective in ensuring the safety of nuclear reactors. However, if a very high level of safety is required as the size and power of the reactor increases, it is advantageous to introduce a reactor shutdown device that operates by a completely different means in addition to the conventional device. It is believed that The reason for this is that the probability of a hypothetical situation in which the reactor protection system fails and it becomes impossible to effectively shut down the reactor occurs is lower than with conventional systems that increase the safety margin by multiplexing devices. This is because the reduction can be more effectively achieved when a different type of reactor shutdown device is also used. To this end, it is natural that a nuclear reactor shutdown system is desired that eliminates as much as possible common cause failures with conventional systems.

For this purpose, systems in which control rods are directly held using electromagnets have been recently studied.
This is, for example, as shown in FIG. The control element 33 is a guide pipe 3 provided in parallel with the nuclear fuel assembly installed in the reactor core and through which a coolant flows.
4, and an armature 36 is connected to the top thereof via an 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 a shield plug 39 that serves as the upper lid of the atomic vessel housing the reactor core. It is done. The upper part of the extension tube 37 is connected to a vertical movement drive device 40 fixed to the rotary plug 39, so that the control element 33 can be pulled out and lowered for reset after disconnection. . Using such a system has the following advantages: Unlike conventionally used latch mechanisms, the extension tube or equivalent long object does not require mechanical movement in the separation operation during the scram of the control element, and at the same time there is no relatively complicated mechanism such as a latch mechanism, and an electromagnet is used. The configuration is very simple, as all you need to do is de-energize. Therefore, the possibility of common cause failure with the conventional type can be significantly reduced. Additionally, since the electromagnet is immersed in the coolant, if the temperature of the magnetic material reaches near its Curie point due to an abnormal temperature rise in the coolant, a significant drop in magnetic force will automatically occur, causing an automatic scram. is achieved. In this way, reactor safety can be significantly improved by using a reactor shutdown device with a significantly different scram operation principle in conjunction with a conventional system so that reactor shutdown can be achieved through scram operation alone. becomes.

[Problems with background technology]

However, such conventional devices also have some drawbacks. In other words, one of them is that if a foreign object gets caught in the joint surface of the electromagnet and the armature, or if one or both of the joint surfaces becomes rough for some reason, the gap value between the electromagnet and the armature will change. . This has a severe negative effect on the magnetic circuit, and if the magnetomotive force of the coil is constant, the magnetic flux will greatly decrease and the holding force will be insufficient, making it easy to cause erroneous scrams due to vibration force or friction.
In extreme cases, it becomes impossible to lift the control elements, making it impossible to operate the reactor. This problem of gap value changes is caused by the strong magnetic force of the electromagnet during operation or by the residual magnetism that exists even during periods of rest, especially when fine particles of magnetic materials such as iron are suspended in the surrounding coolant. It is thought that there is a high possibility that this occurs due to adsorption. The holding force by an electromagnet must be at least comparable to the force of gravity applied to the control element, and there must be a margin in the holding force in consideration of the frictional force during vertical movement and the force due to vibrations caused by fluid force and other factors. It is necessary to make it have. Furthermore, considering the decrease in holding force due to the change in the gap value mentioned above, it becomes necessary to further increase the margin in the designed holding force, and if this is insufficient, undesirable failures such as erroneous scrams during operation may occur. There is a risk.

However, increasing the margin of holding force comes with certain difficulties. That is, the control elements, guide tubes, and extension tubes are all limited in size by the relationship of the surrounding fuel to the upper core structure. Therefore, the shape of the electric circuit of the electromagnet, the magnetic circuit, and the engaging surface between the electromagnet and the armature are also subject to strong restrictions. In particular, when attempting to perform these coupling operations within the guide tube in order to limit relative misalignment between the electromagnet-side engaging surface and the armature-side engaging surface, there are severe restrictions on the shape. Therefore, it is difficult to provide a margin for the holding force, and if the design prioritizes the holding force, excessive current may be applied especially to the coil section.
There are drawbacks that may reduce reliability and service life. In addition, in environments such as high-temperature sodium used as a coolant, there is a phenomenon of self-fusion of the contact surfaces, and if the material that makes up the contact surfaces is not selected appropriately, there is a risk of impairing the reliability of armature disconnection. Ta.

[Purpose of the invention]

The present invention has been made to solve the above technical problems, and its purpose is to provide a nuclear reactor shutdown device in which control elements are directly held by highly reliable electromagnets.

[Summary of the invention]

The means used to achieve the above object in the present invention include a guide tube provided in parallel with the fuel assembly installed in the reactor core, a control element provided in the guide tube so as to be movable up and down, and a control element for controlling the control element. In a nuclear reactor shutdown device comprising an armature fixed to an upper part, and an electromagnet that is provided so as to be able to be attached to the armature and hangs down from a lid of a container accommodating the reactor core, a coupling surface of at least one of the electromagnet and the armature, and The spacer is fixed in the gap between the inner magnetic pole and the outer magnetic pole of the electromagnet, and the projected area of the contact area of the spacer when the electromagnet and armature are coupled is smaller than the magnetic pole area of the electromagnet, and the magnetic pole surface of the electromagnet does not contact the armature. This is a unique nuclear reactor shutdown device.

Briefly explaining the present invention, a spacer made of a non-magnetic material is provided on the attraction surface of the electromagnet and the armature to prevent direct contact between the magnetic pole surface of the electromagnet and the armature, and the spacer surface when the electromagnet attracts the armature. The purpose of this is to make the area of contact at the magnetic poles significantly smaller than the area of the magnetic poles.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 and 4.

FIG. 3 is a longitudinal sectional view showing the electromagnet and armature in the main part of the nuclear reactor shutdown device according to the present invention. Since the overall configuration other than the electromagnet and armature is the same as that shown in FIG. 2, the explanation of the duplicated parts will be omitted. That is, the relative positions of the armature, guide tube and electromagnet in FIG. 3 are such that the control element is separated from the electromagnet and its lower end lands on the guide tube dosspot. Further, the electromagnet is shown inserted by a vertical movement drive mechanism up to just above the armature in order to be coupled to the armature. A suspended electromagnet 38 is fixed to the lower end of the extension tube 37. The central axis of the electromagnet 38 is hollow 38a, and a position detection sensor 41 is fixed thereto. A reflector 42 is formed in the center of the upper surface of the armature 36, and reflects the ultrasonic waves emitted from the position detection sensor 41. By detecting this signal with the position detection sensor 41, the position of the control element can be detected. It's becoming like that. A handling head 43 is provided at the upper part of the guide tube 34, and this
It is possible to engage an exchange device, not shown, for exchange of the guide tube 34 and the control element. Further, the electromagnet 38 and the armature 36 on the inner surface of the handling head 43 are guided so that their respective central axes have appropriate dimensions so as not to cause excessive relative displacement when coupled. The spacer 44 is fixed so as to be embedded in a ring-shaped portion between the inner magnetic pole 45 and the outer magnetic pole 46, and is fixed to the magnetic pole surface 47.
This allows the spacer surface 48 to protrude by an appropriate amount. The spacer 49 is fixed so as to be embedded in the armature 36 with a positional relationship such that it comes into contact with the spacer 44 when the armature 36 is coupled, and its upper surface protrudes from the upper surface 50 of the armature by an appropriate dimension. A plurality of spherical protrusions 51 are formed.

Fig. 4 is a plan view to facilitate understanding of Fig. 3, and Fig. 4 A is a plan view of the electromagnet A-A in Fig. 3.
FIG. 4B shows the armature seen from the direction A, and FIG. 4B shows the armature seen from the direction B--B in FIG.

In this embodiment, an electromagnet 38 and an armature 36
When the spacers 44 and 51 are coupled together, the protrusions of the spacers 44 and 51 come into contact, and an appropriate gap is maintained between the magnetic pole surface 47 and the armature top surface 50. Therefore, even if foreign matter is adsorbed to either or both of the magnetic pole surface 47 and the armature upper surface 50, and even if impurities are deposited, the gap can be prevented from widening. Furthermore, since these surfaces do not come into direct contact with each other, surface roughness does not occur on each other's surfaces, and changes in the effective value of the gap can be prevented. Furthermore, in the present invention, since the spacer 44 is embedded between the inner magnetic pole 45 and the outer magnetic pole 46, there is no change in the magnetic pole area compared to when no spacer is provided, and therefore the attraction force is reduced by providing a gap. The negative effects can be minimized because only the effects caused by The spacer 44 and the spacer 49 are made of a metal that has low magnetic permeability at the operating temperature, and the protruding surfaces of the spacers 44 and 49 are made of a metal that is difficult to self-fuse in high-temperature sodium and is hard to cause surface roughness due to contact. It is formed. Hard alloys such as colmonoy and stellite are known as metals that meet these conditions.

In the above embodiment, by providing the spacer 44 in the gap between the inner magnetic pole 45 and the outer magnetic pole 46,
Since the spacer can be introduced without changing the magnetic pole surface area, the negative effect on the magnetic circuit can be minimized, and it has the effect of fixedly supporting the coil 52, as well as reducing the generation of excessive stress caused by reducing the contact area. It can be prevented. That is,
Compared to the case where the entire magnetic pole surface is in contact, a large stress that is inversely proportional to the contact area is generated in the spacer.
The problem of increased stress applies to the spacer itself as well as to the members supporting the spacer. For example, JP-A-55
-37959 publication describes an example in which a protrusion is provided on the armature magnetic pole surface, but in this case, if the attraction force is large, the protrusion itself will be deformed, so even if the protrusion is made of hard metal, the protrusion attachment part on the armature magnetic pole surface It will transform. In general, only a limited number of magnetic pole materials can be used from the viewpoint of magnetic properties, mechanical strength is low, and the gap formed by the spacer or protrusion is at most 1 mm or less, so this problem is important. In this embodiment, the spacer is supported by a ring-shaped support surface, so that the support area is wide and the thickness of the spacer can be increased, so that deformation does not occur even with a large adsorption force. Further, since the spacer 44 has low magnetic permeability at the operating temperature, leakage magnetic flux in this portion is also extremely small, and a decrease in magnetic force can be prevented. Also spacers 44, 49
The magnetic force on the surface is very small compared to the magnetic pole face 47 and the armature surface 50, so it does not attract magnetic particles in the coolant, and since these surfaces are made of hard alloy, they are not affected by surface roughness. It can be prevented. Furthermore, since the contact surfaces on these surfaces are small compared to the magnetic pole surface 47, the probability of foreign objects being caught is significantly reduced. Although the surface pressure of these contact surfaces during adsorption is higher than that of the contact at the magnetic pole face 47, the reliability of scram separation is rather high because the contact surfaces are made of a metal that does not easily cause self-fusion. things become possible. This reduces the need to consider issues such as self-fusion and surface roughness when considering the materials of the electromagnet's iron core and armature, and allows the selection of materials with better magnetic properties and other required properties. It has the effect of making it possible.

5 and 6 are for explaining other embodiments of the present invention. FIG. 5 is a vertical cross-sectional view of only the electromagnet part which is the main point of the invention, and FIG. Plan view, FIG. 6B is a plan view of the armature in FIG. 5.

In FIG. 5, the magnetic pole surface 47 and the armature upper surface 50 have a conical shape, and are automatically aligned when the armature 36 is coupled to prevent relative displacement of the coupling surfaces. A ring 53 is provided in the gap between the inner magnetic pole 45 and the outer magnetic pole 46.
is embedded. Spacer 54 is ring 53
A plurality of them are provided radially on the surface of the inner magnetic pole 45, and these are formed by a method such as thermal spraying. Further, the spacer 49 is formed on the weight surface of the armature 36 by a method such as thermal spraying. In this embodiment, the alignment when the electromagnet 38 and the armature 36 are coupled is performed by the spacers 54 and 49 sliding in contact with each other, so that the magnetic pole surface 47,
Surface roughening and galling of the upper surface 50 of the armature can be prevented. Regarding materials and other effects,
Since it is similar to the embodiments shown in FIGS. 3 and 4, the explanation thereof will be omitted.

〔Effect of the invention〕

The effects of the present invention are as follows. In reactor shutdown equipment that uses electromagnets to directly lift control elements, the electromagnets ensure reliable holding.
The possibility of damaging plant utilization due to scram malfunctions is significantly reduced. Moreover, the tolerance of the design holding force of the electromagnet requires consideration of the gap value and eccentricity in the state in which the electromagnet and armature are coupled, but by implementing the present invention, it is possible to reduce the margin. This makes it possible to reduce the surplus holding force when the joints are joined without any foreign matter intervening on the joint surfaces, and the residual holding force during scramming can be reduced, making it possible to perform more reliable scramming. Further, in the present invention, the contact surface when the armature and the electromagnet are coupled becomes the spacer surface, so that the magnetic pole and the magnetic material portion of the armature do not come into contact with each other. Therefore, by selecting the material of the spacer, it is possible to sufficiently prevent self-fusion, galling, and abrasion, improve the reliability of coupling and disconnection, and reduce the adverse effect on the magnetic circuit due to the introduction of the spacer.

In addition, the reactor shutdown system according to the example of the present invention has a lower probability of occurrence of a common cause failure than the conventional example, so in a reactor that uses both the conventional example and the example of the present invention, only one of the operations will cause the reactor to react. The safety of nuclear reactors is significantly improved by designing them so that they can be shut down.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view schematically showing a conventional control rod drive device, Fig. 2 is a longitudinal cross-sectional view schematically showing a conventional electromagnet holding type reactor shutdown device, and Fig. 3 is a vertical cross-sectional view schematically showing a conventional control rod drive device. A vertical sectional view showing an enlarged portion of an electromagnet in an embodiment of a nuclear reactor shutdown device, FIG. 4 A and B are a plan view showing the electromagnet and armature of FIG. 3, and FIG. FIG. 6 is a longitudinal cross-sectional view showing an enlarged portion of the electromagnet in the embodiment, and FIG. 6 is a plan view showing the electromagnet and armature of FIG. 5. 1...Drive unit housing, 2...Rotary plug,
3... Upper guide tube, 4... Motor, 5... Cable, 6... Control panel, 7... Screw, 8... Ball nut, 9, 11... Plate, 10, 13... Load cell, 12, 38 ...Electromagnet, 12a...
Cylinder, 14... Outer extension tube, 15... Core, 16...
...Lower guide tube, 17...Inner extension tube, 18...Finger rod, 19...Latch finger, 2
0, 36... Armature, 21... Biological shield, 22, 23... Bellows, 24... Stepped portion,
25...Acceleration spring, 26...Acceleration tube, 27
... Control rod, 28, 43 ... Handling head, 29 ... Damping spring, 30 ... Stopper, 31 ... Sensor, 32 ... Plate-shaped part,
33... Control rod element, 34... Guide tube, 35...
Extension rod, 37...Extension tube, 39...Rotary plug,
40... Vertical movement drive device, 41... Position detection sensor, 42... Reflector, 44, 49, 54
... Spacer, 45 ... Inner magnetic pole, 46 ... Outer magnetic pole, 47 ... Magnetic pole surface, 48 ... Spacer surface, 50 ... Armature upper surface, 51 ... Protrusion, 52 ... Coil, 53 ... Ring.

Claims (1)

[Scope of Claims] 1. A guide tube provided in parallel with a fuel assembly installed in a reactor core, a control element provided within this guide tube so as to be able to rise and fall freely, and an armature fixed to the upper part of this control element. and a nuclear reactor shutdown device including an electromagnet that is installed to be able to be attached to the armature and is suspended from a lid of a container that houses the reactor core,
A spacer is fixed on at least one coupling surface of the electromagnet and the armature and in the gap between the inner magnetic pole and the outer magnetic pole of the electromagnet, and when the electromagnet and armature are coupled, the projected area of the contacting part of the spacer is larger than the magnetic pole area of the electromagnet. This nuclear reactor shutdown device is small in size and is characterized by the fact that the magnetic pole face of the electromagnet does not come into contact with the armature. 2. The nuclear reactor shutdown device according to claim 1, wherein the magnetic pole surface of the electromagnet has a conical shape, and a plurality of spacers for at least one of the electromagnet and the armature are provided radially. 3. A patent claim characterized in that the spacer has excellent self-fusion resistance and is made of a non-magnetic material, or has low magnetic permeability compared to the iron core material of the electromagnet, or is made of a hard alloy with a low saturation magnetic flux density. A nuclear reactor shutdown device according to any one of the first and second items.