JPH049271B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a nuclear reactor shutdown device, and in particular, to a liquid metal cooled fast breeder reactor, which is suitable for reliably shutting down the reactor in the event of a reactor accident. Concerning nuclear reactor shutdown equipment.

[Technical background of the invention]

In general, power control and reactor shutdown of nuclear reactors, especially fast neutral breeder reactors that use liquid metals such as sodium as coolants, are performed using control rods containing a neutron-absorbing material such as boron or tantalum, which are implanted in the core support plate. This is done by inserting it between the book nuclear 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. For the above purpose, the device for driving the control rods is required to have stable operation and high reliability. The conventional drive device is installed at the top of the reactor vessel that houses the fuel assembly, and is fixed on a rotating plug that is installed in a part of the shield plug that isolates the surrounding air inside the reactor vessel. a control rod drive mechanism consisting of a drive part and an extension tube that extends through a rotary plug to connect the drive part and the control rods to the upper part of the reactor core area and connects with the control rods; The control panel is installed in the control room and generates electrical signals for driving the drive unit by automatic manual operation. 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. The drive housing 1 is fixed to the rotary plug 2 and is 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 7 is connected to 1 through plate 9.
The load cell 10 is coupled with a pair of load cells 10.
is connected to a hollow disc-shaped plate 11. Board 11
An electromagnet 12 and a cylinder 12a are coupled to the lower surface of the holder. The lower part of the cylinder 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.
is combined with 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 . Outer extension tube 14
The distal end of the inner extension tube 17 has a plurality of latch fingers 19 shaped like leaf springs to form a latch mechanism together with a finger rod 18 at the lower end of the inner extension tube 17.

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. Extension tube 17
is fixed to the top of the. 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 2 is installed at a position corresponding to the rotary plug 2.
1 is fixed to the top of the upper guide tube 3, 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 airtightly connected to an appropriate position of the outer extension tube 14. ing.
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 connected to the control rod 27.
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.

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.
4 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 according to the operation of the reverse operator by a preset logic circuit, and stops energizing the electromagnet 12. Electromagnet 1
When 2 is deenergized, the armature is separated and cylinder 1
It falls by the amount of the gap between it and the plate-like part 32 at the lower end of the part 2a. As a result, the inner extension tube 17 falls entirely, and the finger rod 18 falls to release the latch finger 19 from its restraint. The latch finger 19 then narrows inward 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 influence 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.

[Problems with background technology]

The control rod drive system, which is comprised of an electro-mechanical drive mechanism as typified by the control rod drive system described above, and a control panel equipped with sensors and electrical logic circuits, generally has sufficient reliability. , which can be expected to operate reliably and can be said to be sufficiently effective in ensuring the safety of nuclear reactors. However, when a very high level of safety is required as nuclear reactors become larger and more powerful, a reactor shutdown system that operates using a completely different method is introduced in addition to the conventional equipment. It is considered advantageous to do so. The reason for this is that the probability of a hypothetical situation in which the reactor protection system fails and cannot effectively shut down the reactor is reduced by the method used to increase the safety margin by multiplexing conventional equipment. This is because it is possible to reduce the amount more effectively by using another type of reactor shutdown device together than by using a reactor shutdown device of another type. For this reason, it is natural that a nuclear reactor shutdown system is desired that eliminates as much as possible common cause failures with conventional systems. As a means for this purpose, a nuclear reactor shutdown system is being researched in which an armature is provided on the top of the control element and the control element is directly held within the reactor vessel by an electromagnet.

However, such devices also have some drawbacks. One of these is that when connecting an electromagnet and an armature, if there is a relative shift in their central axes, there is a high possibility that the necessary holding force will not be obtained. The holding force generated by the electromagnet must be at least as strong as the force such as gravity applied to the control element, and the holding force must have redundancy, or a margin, in consideration of the frictional force during vertical movement and the force caused by fluid vibration. It is necessary to make it have. Considering the decrease in holding force due to misalignment of the center axis or increase in the gap length between the electromagnet and armature due to some reason, it becomes necessary to further increase the margin in the designed holding force, and if this is insufficient, errors during operation may occur. Undesirable failures such as scrams may occur. However, increasing the margin of holding force comes with certain difficulties. In other words, the size of the control elements, guide tubes, and extension tubes are all limited by their relationship with the surrounding fuel and upper core structure, and the horizontal dimensions of the electromagnets and armature are also subject to strong restrictions. It is. In particular, when the electromagnet and armature are to be coupled within the guide tube, the shape thereof must be smaller than the inner diameter of the guide tube. This limits the magnetic pole area, core cross-sectional area, and coil section cross-sectional area, making it difficult to provide a margin for holding force.

Another problem is that electromagnets are used in high-temperature sodium baths, which are extremely harsh conditions for electrical products, and it is expected that failures such as coil breakage and ground faults may occur. . If such a failure occurs, the reactor will inevitably be shut down and the utilization rate of the plant will be impaired.

Yet another problem is the aforementioned problem of increased gap length between the electromagnet and the armature. If the surface roughness of the attracting surfaces of the electromagnet and armature becomes significant, or if foreign matter gets between them, the effective gap length will increase, which may significantly reduce the holding force. This may lead to an erroneous scram while driving.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned 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 are as described below. One of these is to isolate the coil part in a sealed case to protect it from high-temperature sodium, and to fill the coil case with inert gas, and also to have a gas system to supply inert gas. In addition, it is necessary to provide a means for detecting damage to the coil case.
In addition to this, in order to provide a larger magnetomotive force within the space allowed for the coil, the coil wire should be coated around the conductor with an inorganic insulating layer. Furthermore, in order to minimize the space taken up by the coil case, a part of the coil case is made up of an iron core and a yoke.

Further, other means used in the present invention are as follows.

The electromagnet consists of multiple coils so that the electromagnet can function even if some of the coils are damaged. Also, at least one of the plurality of coils is used as a magnetic flux detection coil, so that changes in magnetic flux due to the gap value between the electromagnet and the armature or other causes can be detected.

[Embodiments of the invention]

An embodiment of the nuclear reactor shutdown device according to the present invention will be described below with reference to FIGS. 2 to 6.

In FIG. 2, the same parts as in FIG. 1 are denoted by the same reference numerals, and explanations of overlapping parts will be omitted.

That is, the biological shield 21 and the bellows 22 are connected to the upper guide tube 3 inserted through the rotary plug 39, and the extension tube 27 is inserted into the biological shield 21 and the bellows. Extension tube 2
The upper end of the rotary plug 29 is connected to a vertical movement drive device 40 placed on the upper end surface of the rotary plug 29 . The vertical movement drive device 40 is electrically connected to the control panel 6 via the cable 5 and is also connected to the gas supply device 41 via the piping 43. Gas supply device 4
1 is electrically connected to a control panel 6 provided outside the furnace vessel. Note that a leak detector 42 is provided within the gas supply device 41. In addition, the extension tube 37
An electric line 44 is disposed inside, and is connected to an electromagnet 38 connected to the lower end of the extension tube 37.
The control element 33 is inserted into the lower guide tube 16 , and the lower part of the lower guide tube 16 rests on the core grid plate 34 . The lower guide tube 16 is installed so as to be inserted into the reactor core. The control element 33 is housed in a guide pipe 16 that is installed in parallel with a nuclear fuel assembly (not shown) installed in the reactor core 15 and allows a coolant 50 to flow therethrough, so that the control element 33 can be moved up and down. An armature 36 is connected to the top via an extension rod 35. The control element 33 is held by an electromagnet 38 installed at the lower end of an extension tube 37 that hangs down from a rotating plug 39 that serves as the upper lid of the reactor vessel housing the reactor core.
This is done by suctioning the armature 36 by means of a screw. The upper part of the extension tube 37 is a rotating plug 39
The control element 33 is connected to a vertical movement drive device 40 fixed to the control element 33, so that the control element 33 can be pulled out and lowered for reset after separation.

Unlike the conventional latch mechanism, the reactor shutdown device described above does not require any mechanical movement of the extension tube 37 or an equivalent long object during the separation operation during the scram of the control element 33, and at the same time does not require any mechanical movement compared to the latch mechanism. The structure is very simple because there is no complicated mechanism and it is only necessary to deenergize the electromagnet 38. Since the electromagnet 38 is immersed in the coolant 50, if the temperature of the magnetic material reaches near its Curie point due to an abnormal temperature rise in the coolant 50, a significant drop in magnetic force will automatically be realized. Automatic scrum is achieved.

Note that the leak detection device 42 is connected to the gas supply device 41.
It connects from the piping 43 to the extension pipe 37 via the vertical drive device 40 to the electromagnet 38, and detects leaks in the gas system.It detects changes in gas pressure, flow rate, etc., and is based on a principle that is not particularly limited. It is something that works. This leak detection signal is transmitted to the control panel 6. Further, the electric line 44 is constituted by a plurality of conductive wires corresponding to the number of coils in the electromagnet 38, and supplies current and transmits signals to and from the control panel 6.

FIG. 3 is an enlarged cross-sectional view of the electromagnet 38 in FIG. 2.

In the example shown in FIG. 3, the electromagnet 38 has a plank-type structure, and the coil 45 is positioned so as to be wound around the inner core 46, and is housed in a coil case 47. The coil case 47 has a cylindrical part 48 on a part of its upper surface through which the electric circuit 44 passes, and is connected to the extension tube 37, which has a sealed structure and is connected to the space inside the coil case 47.
This and the vented space 49 within the extension rod 35 are isolated from the surrounding coolant sodium 50.
The space 49 is filled with an inert gas such as Ar or He supplied from the gas supply device 41 shown in FIG. 3, and preferably the gas pressure is higher than the pressure of the coolant sodium 50. It is now maintained automatically. The coil wire 51 is taken out from the inorganic insulating sleeve 5 inside the cylindrical part 48.
2, is guided into the extension tube 37, and is supported by the extension tube 37 via an insulating sleeve 53.

The armature 36 is made entirely or partially of a magnetic material with a suitable Curie point temperature so that the control element 33 can be automatically disconnected from the electromagnet 38 by the Curie point effect when the surrounding sodium temperature rises abnormally. Preferably, the periphery thereof is coated with hard chrome plating or the like.

4A, 4B, and 4C are cross-sectional views of the structure of the coil wire 51 used in the coil 45. FIG. FIG. 4A shows a cable in which a conductor 54 is protected by a metal sheath 55, and an insulating layer 56 is formed by filling the gap with powder such as MgO, which is usually called an MI cable. In FIG. 4B, a central conductor 57 made of copper is protected by an outer conductor 58 made of heat-resistant and oxidation-resistant metal such as nickel, and the outermost layer is made of SiO ₂ , MgO,
An insulating layer 5 is formed by coating with an inorganic material such as Al ₂ O ₃ .
6 was formed. In FIG. 4C, a copper conductor 59 is preferably plated with Ni, and then an insulating layer 56 is formed in the same manner as in B, and preferably has a rectangular shape. Figure 4 A, B, and C can all be used in the nuclear reactor shutdown system of the present invention, but C is the most advantageous when trying to obtain a large holding force with a limited shape due to the design of the electromagnet. So Ha becomes the most disadvantageous. This is because the ratio of the conductor's cross-sectional area to the overall cross-sectional area is very small, and the allowable current per total cross-sectional area is small. This is because by having a rectangular shape, it is possible to eliminate the invalid space when used as a winding wire, and B shows an intermediate property.

By the way, the atmosphere in which each of the cables shown in Fig. 4 A, B, and C can be used is as follows. That is, it can be used even in high temperature sodium due to the protection of the metal sheath 55. Although B is preferably used in a high-temperature inert gas, it can also be used in a high-temperature atmosphere by protecting the outer conductor 58. However, the insulating layer 56 is destroyed in high-temperature sodium, so it cannot be used. Even if the surface of the conductor 59 is plated with Ni, the central conductor 59 will be oxidized during long-term use, so it is considered that reliability is low not only in high-temperature sodium but also in high-temperature air. However, if the conductor 59 is made of Ni, it can be used even in high-temperature air, but in this case an increase in electrical resistance is unavoidable.

In this way, there is a tendency for coil wires to choose an atmosphere that is more advantageous in terms of dimensional constraints due to the design. Therefore, maintaining the atmosphere of the coil part as an inert gas as in the present invention is effective in meeting dimensional constraints and reliability. It is easy to understand that it is effective for improving

For example, when using coil wires as shown in FIG. If the pressure is kept higher than that, the inert gas will only leak into the surrounding sodium, and the electromagnet 38 will not become unusable immediately. This leak is detected by the leak detection device 42 shown in FIG. 2 and displayed on the control panel 6. If the amount of leak becomes excessive,
Maintenance or replacement can be carried out during the next outage period, avoiding negative effects that reduce plant utilization. Such a sealing method using a coil case is effective in improving reliability even in the case of a coil wire as shown in FIG. 4A, since it can provide double protection from sodium. Note that claim 4 of the present invention does not particularly limit the shape of the wire, and if the configuration is the same, it is included in the scope of the claim.

FIG. 5 shows another example of forming a coil cover.

In this example, the coil 45 is sealed by a coil cover 60, an inner core 46, an outer core 61, and a yoke 62.
is combined with Each of these parts is welded to maintain airtightness. It is easily understood that this arrangement provides an advantage in terms of space compared to the case of the coil case 47 shown in FIG.

FIG. 6 is a system diagram illustrating an example of claims 5 to 7 of the present invention, and schematically shows an electrical system of an electromagnet. The electromagnet 63 is provided with a plurality of excitation coils 64 on one or more iron cores 65, and at least one detection coil 6.
It is equipped with 6. These coils are connected to extension tube 6
7. Connected to the control panel 6 by an electric path 69 passing through the vertical movement drive section 68. Inside the control panel 6 are a power source 70 that supplies current to each exciting coil 64 and a failure detection device 71 that detects ground faults and disconnections in the exciting coils.
is provided, and if the excitation coil 64 is damaged, the supply of current is stopped to prevent the damage from expanding. On the other hand, the detection coil 66 converts the magnetic flux excited in the iron core 65 into an electric signal,
The signal is transmitted to magnetic flux detector 72. Magnetic flux detector 7
The magnetic flux signal detected by 2 is transmitted to the magnetic flux stabilizer 73, and the magnetic flux stabilizer 73 transmits a signal to the power source 70 to change the excitation current value so as to reach a preset target magnetic flux value, The target magnetic flux value can be obtained by feedback.
However, the power supply 70 is equipped with a protection device in advance to prevent excessive current from being generated. These feedbacks may also be provided by the driver monitoring the magnetic flux display and manually adjusting the current.

First of all, the present invention uses multiple excitation coils. Even if one coil is damaged, by providing an appropriate margin of holding force, the control element will immediately scram and the utilization rate of the plant will be improved. It is possible to avoid failures that cause deterioration. Furthermore, by installing a detection coil and detecting the magnetic flux, it is possible to monitor the magnetic flux within the iron core. In particular, it is possible to detect and excite a drop in magnetic flux due to an increase in the gap between the electromagnet and armature or damage to some excitation coils. It is possible to supplement the holding force by changing the current.

〔Effect of the invention〕

The effects of the present invention are as follows.

In a nuclear reactor shutdown system in which a control element is directly lifted by an electromagnet, the electromagnet can securely hold the control element, and the possibility of a malfunction resulting in a loss of plant utilization is significantly reduced.

Furthermore, since a large holding force can be obtained within the limited dimensions of the electromagnet, the reactivity value of each control element can be designed to be large, which is advantageous in terms of core economy.

In addition, it prevents the deterioration of the insulation and conductive properties of the electromagnet coils, improving the lifespan and reliability of the electromagnets, and eliminating the need to immediately shut down the reactor even if an electromagnet malfunctions during reactor operation. It is possible to continue operation while maintaining the normal scram function until at least the next outage period, and changes in holding force can be estimated with high accuracy, so there is always sufficient margin for holding force. On the other hand, by giving an excessive margin, it is possible to prevent the time required for separation during scram from becoming excessively long.

Furthermore, since the probability of common cause failure occurring between the conventional type and the nuclear reactor shutdown device according to the present invention is low, by designing a nuclear reactor that uses both in combination, the reactor can be shut down by operating only one of them. The safety of nuclear reactors will be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view schematically showing a conventional control rod drive device, FIG. 2 is a vertical cross-sectional view schematically showing an embodiment of a nuclear reactor shutdown device according to the present invention, and FIG. 2 is an enlarged longitudinal cross-sectional view of the electromagnet in FIG. 2, FIG. 4 is a sectional view showing three examples of the electromagnet coil wire in FIG. 3, and FIG. 5 is an enlarged view of another example of the electromagnet in FIG. 2. 6th longitudinal sectional view shown as
The figure is a system diagram showing the electrical system of the electromagnet in FIG. 2. 1... Drive housing, 2... Rotating plug, 3... Upper guide tube, 4... Motor, 5... Cable, 6... Control panel, 7... Screw, 8... Ball nut, 9,
DESCRIPTION OF SYMBOLS 11...Plate, 10, 13...Load cell, 12...Electromagnet, 12a...Cylinder, 14...Outer extension tube, 15...Reactor core, 16...Lower guide tube, 17...Inner extension tube, 18
...Finger rod, 19...Latch finger,
20... Armature, 21... Biological shield, 22,
23...Bellows, 24...Stepped part, 25...Acceleration spring, 26...Acceleration tube, 27...Control rod, 28...Handling head, 29...Damping spring, 30...Stopper, 31...Sensor, 32...Plate-shaped part, 33 ...Control rod, 34...Core lattice plate, 35...
Extension rod, 36...armature, 37...extension pipe, 3
8... Electromagnet, 39... Rotating plug, 40... Vertical drive device, 41... Gas supply device, 42... Leak detection device, 43... Piping, 44... Electric circuit, 45... Coil,
46...Inner core, 47...Coil case, 48...Cylinder part, 49...Space, 50...Sodium, 51...Coil wire, 52, 53...Insulating sleeve, 54...
Conductor, 55... Sheath, 56... Insulating layer, 57... Center conductor, 58... Outer conductor, 59... Conductor, 60... Coil cover, 61... Outer core, 62... Yoke, 63
...Electromagnet, 64...Exciting coil, 65...Iron core, 66
...Detection coil, 67...Extension tube, 68...Vertical movement drive section, 69...Electric circuit, 70...Power source, 71...Failure detection device, 72...Magnetic flux detector, 73...Magnetic flux stabilizer.

Claims (1)

[Scope of Claims] 1. A guide tube provided in parallel with a nuclear fuel assembly installed in a reactor core, a control element provided within this guide tube so as to be movable up and down, and an armature fixed to the upper part of this control element. an extension tube that is attached to the armature and hangs down from the lid of the container that houses the core; an electromagnet that is fixed to the lower end of the extension tube; and an electric circuit that applies an exciting current to the electromagnet. A nuclear reactor shutdown device characterized in that an electromagnetic coil is isolated from the reactor coolant in a sealed coil case, and the inside is filled with an inert gas. 2. The atomic coil case according to claim 1, wherein the coil case of the electromagnet is connected to a gas system that supplies an inert gas to the inside thereof, and the gas system is equipped with a leak detection device. Furnace shutdown device. 3. The nuclear reactor shutdown device according to claim 1 or 2, wherein the coil case of the electromagnet is partially composed of an iron core and a yoke. 4. Claim 1 or 2, characterized in that the wire used in the electromagnet coil is made of an electrical conductor coated with an inorganic insulating layer and is not provided with a metal protective sheath. nuclear reactor shutdown equipment. 5. The nuclear reactor shutdown device according to claim 1, wherein the electromagnet includes a plurality of coils. 6. Claims characterized in that each of the coils of the electromagnet is equipped with a failure detection device that detects disconnection and ground fault, and the energization of only the failed coil is cut off, while the other coils continue to be energized. A nuclear reactor shutdown device according to item 5. 7. The nuclear reactor shutdown device according to claim 5, wherein at least one of the magnet coils is used as a magnetic flux detection coil and is equipped with a magnetic flux detection device.