JPS63289487A - Nuclear reactor stopping apparatus - Google Patents

Abstract

PURPOSE:To prevent malfunctioning of a scram function due to an external force working on a control rod, by providing a universal coupling with an electromagnet retained on an extended tube. CONSTITUTION:A cover 17a is given the outline of a bottle and am neck part 17b thereof is inserted into an opening 21 of an extended tube 7b maintaining a clearance 22. Moreover, a nut 19a is screwed from inside of the extended tube 7 to put together an electromagnet 17 and the extended tube 7 forming a universal coupling 19. On the other hand, vibration or the like of the control rod 14 is transmitted to the electromagnet 17, while the universal coupling 19 is interposed between the electromagnet 17 and the extended tube 7, which especially allows lateral vibration of the electromagnet 17 to be absorbed by the clearance 22, making the vibration free from constraint by the extended tube 7. Therefore, a bending stress or the like become hard to occur in an attraction surface between the electromagnet 17 and a magnetic body 16 of the control rod 14 so that magnetic body 16 would not separate from electromagnet 17 eventually letting the control rod 14 drop by its own weight. The bottom of the cover 17a of the electromagnet 17 forms a convex in a truncated cone and is attracted fit in a concave of the upper end of the magnetic body to prevent a slide deviation of the attraction surface otherwise caused by vibration of the control rod 14, namely, the magnetic body 16.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a reactor shutdown device for a liquid metal cooled fast breeder reactor, and particularly relates to a nuclear reactor shutdown device for a liquid metal cooled fast breeder reactor, and particularly for an atomic reactor having a control rod holding mechanism using electromagnetic force. Regarding reactor shutdown equipment.

(Conventional technology) Generally, in a nuclear reactor, power is controlled by inserting and removing a control rod containing a neutron absorbing material into the reactor core, and in the event of an emergency such as an accident, the control rod is fully inserted into the reactor core to stop the reactor's output. It is designed to let you do so. However, in such an emergency, it is necessary to reliably stop the operation of the reactor, so for example, fast breeder reactors are provided with a reactor shutdown device that has a simple structure and can operate reliably. In other words, in this type of reactor, based on the scram signal output at the time of reactor abnormality,
A double safety measure is achieved by using both a reactor shutdown system that operates using external equipment such as a control rod drive mechanism, and an independent drop-type reactor shutdown system that operates independently without using such external equipment. is being taught.

In such a device, for example, as shown in FIG. 3, a reactor core 2 is housed in a reactor vessel 1 and covered with a shielding plug 3. A control rod drive mechanism 5 is provided in the core upper mechanism 4 that passes through the shielding plug 3. Control rod drive mechanism 5
As shown in detail in an enlarged view of FIG. 4, an extension tube 7 is inserted into the upper guide tube 6 so as to be able to rise and fall freely, and this extension tube 7 is driven up and down by a drive unit 8 provided outside the furnace. It has become.

On the other hand, a large number of trumpet tubes 9 and guide tubes 10 are vertically loaded in the core 2 in a predetermined arrangement. These trumpet tubes 9 and guide tubes 1O are supported by upper and lower core support plates 12.12 constituting the high-pressure plenum 11, and inside each trumpet tube 9 and guide tubes 10, there is a coolant flowing inside the high-pressure plenum 11. For example, liquid sodium flows in and flows through each tube from the bottom to the top. A core fuel 13 is contained in the trumpet tube 9, and a control rod 14 is inserted into the guide tube 10 so as to be movable up and down. The control rod 14 contains a neutron absorbing material 15 and has a magnetic material 16 at its upper end.

An electromagnet 17 that attracts the magnetic material 16 is attached to the lower end of the extension tube 7. Reference numeral 18 is a cable that supplies power to this electromagnet. Further, the electromagnet 17 is attached to the lower part of the extension tube 7 so as to be located near the upper opening 10a of the guide tube 10, that is, the outlet of the coolant, so that the coolant temperature is lower than that during normal reactor power operation. When the temperature rises abnormally and the temperature of the magnetic material of the electromagnet 17 reaches near its single point, a significant drop in magnetic force occurs, and the control rod 14 is separated from the electromagnet 17 to achieve an automatic scram. . In addition, in response to a pump trip, etc., power supply is stopped by a scram signal, the electromagnet 17 is demagnetized, and the control rod 14 is disconnected to achieve a scram.

(Problems to be Solved by the Invention) Generally, the attraction force of a magnet has a large resistance to a tensile force load acting perpendicularly to the attraction surface. However, the resistance force against loads such as bending and twisting is small, and it is possible to separate the suction surfaces with a relatively small load.

However, since the electromagnet 17 in the above-mentioned device is located near the coolant outlet and the coolant is introduced from the high-pressure plenum 11, there is a considerable flow velocity.

Therefore, the adhesion surfaces of the electromagnet 17 and the control rod 14 are subjected to loads such as bending and twisting due to fluid forces such as hydrodynamic vibrations, as well as vibrations themselves, and there is a risk that the electromagnet 17 and the control rod 14 may be separated.

This is when the control rod 14 is scrammed even though there is no cause such as input of a scram signal or abnormal rise in coolant temperature, resulting in a malfunction. In order to release the scram caused by this malfunction and restore the reactor to normal operation, it is necessary to investigate various causes of the scram and confirm that the cause is not due to some kind of abnormality. These investigations and confirmations require a very long time, leading to a decrease in the operating rate of the reactor or an increase in operating costs.

An object of the present invention is to provide a nuclear reactor shutdown device that prevents malfunctions of a scram mechanism caused by external forces applied to control rods.

[Structure of the invention]

(Means for Solving the Problems) In the present invention, an electromagnet that can be raised and lowered by being guided by an extension tube provided in a control rod drive mechanism, and a magnetic body fixed to the upper end are attracted to the electromagnet. The nuclear reactor shutdown device has a control rod that hangs down and can be inserted into and removed from a guide tube installed in the reactor core, and is equipped with a universal joint that locks an electromagnet to an extension tube.

(Function) Even if a control rod held by an electromagnet vibrates during normal operation of a nuclear reactor, for example due to the behavior of the coolant in which it is immersed, this vibrational force will be suppressed. Since it is absorbed by the universal joint, there is no stress that would cause the attraction surface between the control rod and the electromagnet to separate. Therefore, the nuclear reactor shutdown function is prevented from malfunctioning due to causes other than the original scram operation in which the control rods are dropped by actively losing the attraction force of the electromagnets and the reactor is shut down.

(Example) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a sectional view showing a main part of an embodiment of the present invention.
In FIG. 1, an extension tube 7 installed in a fast breeder reactor has a closed inner side at a lower end forming a spherical shape 7a, and an opening 21 is provided in the center thereof. An electromagnet 17 for attracting the control rod 14 to the extension tube 7 is attached as follows.

An electromagnet 17 consisting of an iron core 1.7e and a coil 17c wound around the core 1.7e is covered on the outside by a cover 17a made of a non-magnetic metal such as stainless steel. This cover 17a has an approximately block-shaped outer shape, and its neck portion 17b
is inserted into the opening 21 of the extension tube 7 with a certain gap 22 in between. A male thread is provided on the outside of the neck portion 17b,
A nut 19a is screwed into the extension tube 7 from the inside thereof, whereby the electromagnet 17 and the extension tube 7 are connected by forming a universal joint 19. It is more convenient if the bottom surface of the nut 19a has a shape that matches the spherical shape 7a inside the lower end of the extension tube 7. A cable 18 connected to the coil 17c is inserted through the neck portion 17b and is sealed with a sealing material 17d.

Further, the corner portions of the bottom surface of the cover 17a are cut obliquely over the entire circumference, and have a shape in which truncated cones are connected.

A magnetic body 16 is fixed to the upper end of the control rod 14, and the upper end has a concave shape that matches the truncated cone shape of the bottom surface of the cover 17a.

Next, the effect of this will be described.

In normal nuclear reactor operating conditions, the control rods 14 are connected to coils 1 that are energized from an appropriate power source through a cable 18.
The extension tube 7 is attracted by the electromagnet 17 excited by the magnet 7c, and is adjusted up and down to be maintained at a constant insertion position determined by the operating state of the reactor.

The controller 14 vibrates and shakes at a high frequency under the influence of the flow of coolant in a guide tube (not shown) into which it is inserted. These vibrations or shaking are directly transmitted to the electromagnet 17, but the electromagnet 17 and the extension tube 7
A universal joint 19 is interposed between the electromagnet 17 and the magnetic body 16 of the control rod 14, so that the lateral vibration of the electromagnet 17 is absorbed by the gap 22 and is not restrained by the extension tube 7. Bending or torsional stress is less likely to occur on the attracting surface, and even though the attracting force of the electromagnet 17 exists, the magnetic body 16 will not separate from the electromagnet 17 and the control rod 14 will not fall due to its own weight.

In addition, the bottom of the cover 17a of the electromagnet 17 forms a convex part in the shape of a truncated cone, which fits into the recess at the upper end of the magnetic body 16 and is attracted to it, so even if the control rod 14, that is, the magnetic body 16 vibrates, No sliding displacement of surfaces occurs. Further, when the control rod 14 that has fallen as a result of the loss of the magnetic force of the electromagnet 17 due to normal scram operation is attracted by bringing the electromagnet 17, which has been re-energized again after the scram factor has been restored, close to the electromagnet 17, for example, the electromagnet 17
An appropriate mutual positional relationship can be easily obtained, such as by aligning the centers of the control rods 14 and attracting them.

Furthermore, in the present invention, in addition to the above-described embodiment, as shown in FIG. The neck portion 17b of the electromagnet 17 may be located at the center of the opening 21 of the extension tube 7, and the centripetal force of the spring 2o may be used, for example, when the control rod 14 is separated. Since the position of the electromagnet 17 with respect to the extension tube 7 can be kept constant, mutual alignment can be easily performed when the excited electromagnet 17 is brought close to the separated control rod 14 and attracted.

In addition, in the above-described example, a universal joint is provided between the extension tube 7 and the electromagnet 17, but this is also provided between the control rod 14 and the magnetic body 16.
It may be provided in between.

〔Effect of the invention〕

According to the invention, the control rod held by the electromagnet is
Even though the coercive force of the electromagnet is maintained, it is possible to prevent malfunctions in which the coolant separates from the electromagnet and falls due to fluid force such as hydrodynamic vibration of the coolant or shaking caused by an earthquake, causing a scram of the reactor. The present invention provides a highly reliable nuclear reactor shutdown device that eliminates scrams caused by malfunctions and their investigation and recovery work, and has the effect of improving the operating rate of nuclear reactors.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main parts of one embodiment of the present invention, FIG. 2 is a sectional view showing the main parts of another embodiment of the invention, and FIG. 3 is a sectional view schematically showing a fast breeder reactor. , FIG. 4 is an enlarged cross-sectional view of the main part of FIG. 3. 2... Core 5... Control rod drive mechanism 7.
... Extension tube 10 ... Guide tube 14 ... Control rod 16 ... Magnetic body 17 ... Electromagnet
19...Universal joint 20...Spring agent Patent attorney Rule Chika Ken Yudo Daishimaru Kendai 1 Figure 2 Figure 3
Figure 4

Claims (1)

[Claims] 1. An electromagnet that can be raised and lowered by being guided by an extension tube provided in a control rod drive mechanism, and a magnetic body fixed to the upper end of the control rod is attracted to the electromagnet and hangs down into the reactor core. What is claimed is: 1. A nuclear reactor shutdown device comprising a control rod that can be inserted into and removed from an installed guide tube, the device comprising a universal joint for locking the electromagnet to the extension tube. 2. The nuclear reactor shutdown device according to claim 1, wherein the magnetic body and the electromagnet are attracted by a contact surface whose mutual positional relationship is uniquely determined by engagement between a concave portion and a convex portion. 3. The nuclear reactor shutdown device according to claim 1, wherein the universal joint is provided with alignment means.