JPS63290990A - Shutdown device for nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent a decrease in holding power by intervention of foreign matter between an electromagnet which selectively attracts an armature fixed to the top end of a control element and said armature by forming rugged parts to at least either of the attraction faces of the armature and the electromagnet. CONSTITUTION:The armature 36 is attracted to the electromagnet 38 formed with the rugged parts 105, 105a, 104, 104a on the attraction face 101 when electric current is passed to a coil 41 by an energizing device 103. The coolant between both is displaced at this time to flow from the projecting parts 105, 105a toward the recesses 104, 104a and magnetic particles 106 are attracted into the recesses 104, 104a and, therefore, the generation of a spacing between the attraction faces 101 and 102 is obviated. Alternating magnetic fields different from the magnetic fields generated at the time of attraction are generated when the backward current is passed to the coil 41 by the device 103 after the armature 36 is detached by de-energizing the electromagnet. The particles 106 can be detached by decreasing the current value down to zero.

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, particularly fast neutron reactors that use liquid metal such as sodium as a coolant, are carried out by installing 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 nuclear reactor is controlled by moving the control rod up and down within the guide tube. The device for driving the control rods is required to have stable operation and high reliability. Conventionally used drives are installed at the top of the reactor vessel housing the fuel assembly. This drive device includes a drive part fixed on the rotating plug of the shielding plug that closes the upper opening of the reactor vessel, and a rotating plug inserted to connect the drive part and the 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 and a control rod drive mechanism, 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 output control of the drive unit and the operation for shutting down the furnace are performed 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, 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 1, 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 ball nut 8 is screwed into the ball screw 7. This ball nut 8 is connected to a pair of load cells 1o via a plate 9, and this load cell 10
is connected to a hollow disc-shaped plate 11. An N magnet 12 is accommodated in the hollow part of the plate 11, and a tube 12a is coupled to the electromagnet 12. A load cell 13 is connected below the 1m12a, and a lower portion of the load cell 13 is connected to an outer extension pipe 14.

The outer extension pipe 14 passes through the inside of the rotating plug 2 and extends through the core 1.
5, and its tip reaches above the finger rond 18 of the inner extension tube 17.
Together with this, there are a plurality of latch fingers 19 shaped like leaf springs to constitute a latch mechanism.

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 and the outer extension tube 14 form a double tube structure, and the inner extension tube 17 passes through a corresponding position of the rotary plug 2, and its tip becomes a finger iron 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 upper end of the bellows 22 are hermetically coupled, and the lower end of the bellows 22 is hermetically coupled to an appropriate position of the outer extension tube 14. Also, inner extension tube 1
Bellows 23 are provided at appropriate locations on each of the outer extension tube 7 and the outer extension tube 14, the ends of which are hermetically joined. An acceleration spring 25 is coupled to the stepped portion 24 of the outer extension tube 14, and the acceleration spring 25 is located outside the outer extension tube 14 and extends downward in the form of a coil spring. are in contact with. 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 two damping springs. The lower end of the damping spring 29 is supported by a spacing 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 bottles storing neutron absorbing material are bundled and housed in a protection tube. control rod 2
7 and the lower guide tube 16, an appropriate gap is provided.

According to the above configuration, during normal operation, the latch finger 19
A handling head 28 of the control rod 27 is engaged with the shoulder portion of the control rod 27, 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, the armature 20 is 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 head of the acceleration tube 26 which is restrained by the handling head 28 of the control rod 27. is in a compressed state. 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. This rotation of the drive motor 4 is converted into vertical movement by the ball screw 7 and ball 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 condition occurs in the plant due to some reason, such as a failure such as the lowest coolant flow, a rise in coolant temperature, or an increase in core neutron flux, the failure is detected by the sensor 31, and the detection signal is sent to the control panel. 6. Based on the detection signal, the control panel 6 outputs a scram command signal automatically or according to an operator's operation using a preset logic circuit, 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. As a result, the inner extension tube 17 falls entirely, and the finger rond 18 falls to release the latch finger 19 from being restrained. The latch finger 19 contracts inward due to the restoring force of the leaf spring, and as a result, 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. . A scram operation of the control rods is achieved by such operation.

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 reactor vessel. Also load cell 1
3 is used for the purpose of confirming the sound 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. This means that a hypothetical situation in which a reactor protection device fails and the reactor cannot be effectively shut down is less likely to occur than the conventional method of multiplexing devices to increase the margin of safety. This is because it is considered more effective to use other types of devices together.

In addition, 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. Reference numeral 33 in the figure is a control element, and this control element 33 is housed in a guide pipe 34 that is installed in the reactor core in parallel with the nuclear fuel assembly and allows a coolant to flow therein so as to be able to rise and fall. An extension rod 35 is connected to the top of the control element 33, and an armature 36 is connected to the upper end of the extension rod 35. The control element 33 is held by the armature 3 by an electromagnet 38 provided at the lower end of an extension tube 37 hanging from a shielding plug 39 which is the upper lid of the reactor vessel housing the reactor core.
This is done by adsorbing 6. 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 connected to a vertical movement drive device 40 fixed to the rotary plug 39, and this vertical movement drive device 40 performs a pulling operation of the control element 33 or a downward movement for resetting after disconnection. Ru. Note that a control device 43 is connected to the vertical movement drive device 40. Further, the reference numeral 44 in the figure is a dart pot, and the 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 or equivalent elongated object does not require mechanical movement in the separation operation during scramming of the control element, and at the same time there is no relatively complicated mechanism such as a latching mechanism, and an electromagnet is used. 3
The configuration is very simple since it is only necessary to selectively excite 8.

Therefore, common causes of failure with conventional types of devices can be significantly reduced. Furthermore, since the electromagnet 38 is placed in the coolant, if the temperature of the magnetic member used in the magnetic circuit of the electromagnet 38 and the armature 36 reaches near the single point due to an abnormal temperature rise of the coolant, the electromagnet 38 will automatically shut down. Automatic scram is achieved with a significant magnetic force drop. By using reactor shutdown equipment with largely different scram operation principles in conjunction with conventional systems, reactor shutdown can be achieved by only scram operation of one of the two types of equipment. It becomes possible to significantly improve the safety of nuclear reactors.

However, even with this configuration, there are the following problems. In other words, if a foreign object is present between the attracting surfaces of the electromagnet 38 and the armature 36, a gap will be created between the electromagnet 38 and the armature 36 when the armature 36 is attracted, and it will be difficult to hold the control element 33. It becomes difficult to secure the holding force. The holding force by the electromagnet 38 must be at least comparable to the force of gravity, etc. applied to the control element 33, and a margin should be given to the holding force in consideration of the frictional force of vertical motion or the force caused by fluid vibration. It is necessary to In this case, when taking into account the reduction in holding force due to an increase in the gap between the suction surfaces, it is necessary to provide an even larger margin. This is because if this is insufficient, undesirable failures such as erroneous scrams during operation may occur. On the other hand, there are certain difficulties in securing the above margin. That is, the control element 33, the guide tube 34, and the extension tube 37 are all limited in size due to their relationship with the surrounding fuel or the upper core mechanism, and therefore the shapes of the electromagnet 38 and the armature 36 are also limited. It is from. Furthermore, if the coupling operation between the electromagnet 38 and the armature 36 is to be performed within the guide tube 34, there are particularly severe restrictions on the shape. As described above, there is a large limit to securing a margin for the holding force.

(Problems to be Solved by the Invention) As described above, in the conventional configuration, it is expected that foreign matter will be interposed between the attracting surfaces of the electromagnet and the armature, and a gap will be generated between the two during attracting. Therefore, there is a problem that a large margin must be given to the holding force, and there is also a problem that there is a large limit due to physical reasons in the structure of increasing the size of the electromagnet to ensure the holding force. It was developed based on these points, and its purpose is to effectively prevent the increase in the gap caused by the presence of foreign matter between the electromagnet and the armature, thereby ensuring a margin for holding force. It is an object of the present invention to provide a nuclear reactor shutdown device that can reduce the amount of energy used.

[Structure of the Invention] (Means for Solving the Problems) That is, the nuclear reactor shutdown device according to the present invention is arranged in a reactor core in a reactor vessel, a coolant flows inside the reactor vessel, and 1I
A guide tube through which the III control element is inserted and removed, an armature fixed to the upper end of the control element, and an elevator suspended from the shielding plug that closes the upper opening of the reactor vessel and arranged on the upper surface side of the shielding plug. an extension tube that is raised and lowered by a mechanism; an electromagnet that is fixed to the lower end of the extension tube and selectively attracts the armature; an excitation mechanism that excites the electromagnet; and an uneven part on the attraction surface of at least one of the armature and the electromagnet. The formation of In is defined as In.

(Function) In other words, by forming an uneven portion on at least one of the contact surfaces of the electromagnet and the armature, the coolant interposed between the electromagnet and the armature is pushed away from the convex portion to the concave portion. This system generates a flow of coolant to collect foreign matter that has entered between the electromagnet and the armature in the recess, thereby suppressing the creation of a gap between the electromagnet and the armature due to foreign matter.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. It should be noted that the same parts as in the prior art are denoted by the same reference numerals and the explanation thereof will be omitted. In the figure, reference numeral 101 is an attraction surface of the electromagnet 38, and reference numeral 102 is an attraction surface on the armature 36 side. The adsorption surface 101 on the electromagnet 38 side has an annular convex portion 105, an annular concave portion 104, an annular convex portion 105 from the outer circumferential side.
a1 and a concave portion 104a are formed, and convex portions 105 and 105a are formed in a smooth curved shape. Further, the annular recess 104 is located directly below the coil 41. With this configuration, foreign matter (magnetic particles) that has entered between the electromagnet 38 and the armature 36 is removed from the recess 104.
and 104a, and the adsorption surface 10 due to the foreign matter 106
This suppresses the formation of a gap between 1 and 102. Further, the reference numeral 103 in the figure is an excitation device, and this excitation device 103
can change the direction of the current flowing through the coil /41.

The operation will be explained based on the above configuration. First, during normal operation, the coil 41 is energized by the excitation device 103 to generate a magnetic attraction force, and the armature 36 is attracted to the electromagnet 38 by the magnetic attraction force, and the control element 33 is connected to the extension tube 2.
It is held at 7.

Also, at that time, when the electromagnet 38 is attracted, 101 and Armadure 3
It is in substantially close contact with the suction surface 102 of No. 6.

Next, the nuclear reactor is to be stopped, but in this case, the excitation device 103 cuts off the current supply to the coil 41. Thereby, the adsorption of the armadure 36 by the electromagnet 38 is released, and the control element 33 is rapidly inserted into the reactor core by gravity.

In this series of operations, the magnetic particles in the coolant are attracted to the electromagnet 38 by the action of an external magnetic field generated by the energization of the coil 41 during normal operation or by the magnetism remaining in the electromagnet 38 and armature 36 when the reactor is shut down. Part of it is attracted to the surface 101 and the attraction surface 102 of the armature 36 .

Conventionally, the electromagnet 38 and the armature 3 were
This means that there will be a gap between 6 and 6.
In the case of this embodiment, the following effects are achieved. That is, when current is applied to the coil 41 by the excitation device 103, the armature 36 is attracted to the electromagnet 38. At this time, the coolant between the two is pushed away and the convex portion 105,105a is removed from the concave portion 104.
．． A coolant flow occurs in the direction of 104a. The flow of the coolant causes the magnetic particles 106 to collapse into the recesses 104 and 104.
It is collected in a and adsorbed there. Therefore, even if the armature 36 is attracted to the electromagnet 38, there will be no gap between the two attraction surfaces 101 and 102.

Next, the effect of releasing the magnetic particles 106 attracted to the recesses 104 will be explained. After cutting off the power to the electromagnet 38 and removing the armature 36, the excitation device 103 causes a current to flow in the opposite direction to the coil 41. This generates an alternating magnetic field different from that during adsorption, and by reducing the current value to zero, the attached magnetic particles 106 are detached. Therefore, the magnetic particles 106 are not deposited in the recess 104.

It goes without saying that even if this configuration of flowing a reverse current and decreasing the current is applied to conventional electromagnets and Armasure as is, the effect of removing the attracted magnetic particles can be exhibited.

According to this embodiment, the following effects can be achieved.

(1) First, the magnetic particles 106 are interposed between the electromagnet 38 and the armature 36, so that no gap is created between 101 and 102 when the two are attracted. Therefore, there is no need to provide a large margin in the holding force in anticipation of the occurrence of a gap, and the gap can be dealt with with sufficient margin within the physical constraints.

■Also, since the convex portion 105 has a smooth curved shape,
A coolant flow is effectively generated toward the four parts 104, and the magnetic particles 106 can be effectively collected in the recesses 104.

■Also, by applying a current in the opposite direction to the coil 41 by the excitation device 103, the magnetic particles 106 adsorbed to the recess 104
Since the magnetic particles 106 can be reliably removed, deposition of the magnetic particles 106 in the recesses 104 can also be effectively prevented.

■In this way, the reliability of the stopping device using the electromagnet 38 has been greatly improved, and by using this device in combination with the conventional ramming type device, a configuration that uses devices with different failure causes can be realized with high reliability. The reliability of reactor shutdown can be greatly improved.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, the number and shape of the uneven portions may be varied, and the uneven portions may be formed only on the armature side or on both the armature and the electromagnet attraction surfaces. Of course it's a good thing.

[Effects of the Invention] As detailed above, according to the nuclear reactor shutdown device according to the present invention, it is possible to effectively prevent a decrease in the holding force due to the generation of a gap due to the presence of foreign matter between the electromagnet and the armature. As a result, there is no need to provide an unnecessarily large margin for the holding force, and the reliability of the device is greatly improved, which has great effects.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are diagrams showing one embodiment of the present invention.
The figure is a front view of the electromagnet and armature, Figure 2 is a front view of the electromagnet and armature showing the release of magnetic particles, and Figure 3 is a front view of the electromagnet and armature.
4 and 4 show conventional examples, FIG. 3 is a sectional view of a mechanical control rod drive device, and FIG. 4 is a sectional view of an electromagnetic control rod drive device. 36... Armature, 37... Extension tube, 38...
・Electromagnet, 40... Vertical movement drive device, 101, 102
...Adsorption surface 104, 104a...recess, 105.1
05a...Protrusion. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A guide tube arranged in the reactor core in the reactor vessel, through which 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 that closes the shielding plug and is raised and lowered by a lifting mechanism arranged on the upper surface side of the shielding plug; an electromagnet that is fixed to the lower end of the extension tube that selectively attracts the armature; A nuclear reactor shutdown device comprising: an excitation mechanism that excites; and an uneven portion formed on an attracting surface of at least one of the armature and the electromagnet. (2) The nuclear reactor shutdown device according to claim 1, wherein the convex portion of the uneven portion is formed in a smooth curved shape. (3) The nuclear reactor shutdown device according to claim 1, wherein the excitation device is capable of changing the direction of the current flowing through the electromagnet.