JPH0273196A - Reactor shut-down device - Google Patents

Abstract

PURPOSE:To obtain sufficient attraction force and to surely disconnect a control element by providing a 1st magnetic member having high magnetic permeability and a 2nd magnetic member having high high-temp. strength to either or both of an electromagnet and armature. CONSTITUTION:The armature 5 has a blinded cylindrical outside pipe 13 in the outer peripheral part and top end part thereof and the top surface 13a is made into a disk shape to form an attraction surface. The bottom end thereof is integrally coupled to a connecting pipe 4 for connecting to the control element 2. The attraction force is proportional to the square of a magnetic flux and the sufficient attraction force is obtd. with adequate current if an electromagnet 8 and armature 5 are formed of such a high permeability material as pure iron. The residual magnetic forces after the disconnection of current is small and there are no hindrances in disconnection of the control element.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor shutdown device that shuts down a nuclear reactor by inserting a control element into the reactor core, and particularly relates to a nuclear reactor shutdown device that shuts down a nuclear reactor by inserting a control element into the reactor core. This invention relates to a nuclear reactor shutdown device that can reliably shut down a nuclear reactor in the event of a reactor accident in a fast breeder reactor.

(Prior art) In general, power control and reactor shutdown in nuclear reactors, particularly fast neutron reactors that use liquid metal such as sodium as a coolant, are carried out by implanting control rods containing neutron-absorbing substances such as boron and tantalum in the core support plate. This is done by inserting it between multiple nuclear fuel assemblies.

Conventionally, in this reactor control system, control rods are lifted up by engagement between latch fingers and finger rods at the lower end of long objects, but in the event of an accident, the engagement is released and the control rods are moved into the reactor core by their own weight. Something that makes it fall is used. This conventional nuclear reactor control device includes an electro-mechanical drive mechanism, a control panel equipped with sensors and an electrical logic circuit, and performs operational control by appropriately driving control rods.

This conventional device generally has sufficient reliability and can be expected to operate reliably. Therefore, it 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 the size and power of the reactor increases, a reactor shutdown system that operates by a completely different method is used in addition to the conventional equipment. It is considered advantageous to introduce

The reason for this is that the probability of a hypothetical situation in which a failure occurs in the reactor protection system and makes it impossible to effectively shut down the reactor occurs is reduced by increasing the safety margin by multiplexing conventional equipment. This is because the reduction can be made more effectively when another type of reactor shutdown device is used in conjunction with the reactor shutdown device. To this end, a reactor shutdown system is desired that eliminates common cause failures as much as possible with conventional systems.

Therefore, a system has been proposed in which the control rods are directly held using electromagnets.

This system is, for example, as shown in FIG. That is, the control element 2 that controls the operation of the reactor core 1
It is installed in parallel with the nuclear fuel assembly installed in the fuel assembly, and is housed in a guide tube 3 in which a coolant flows, allowing it to move up and down. An armature 5 is connected to the top of the control element 2 via an extension rod 4. On the other hand, an extension tube 7 is provided hanging from a rotary plug 6 serving as an upper cover of a reactor vessel (not shown) housing the reactor core 1, and an electromagnet 8 is provided at the end of this extension tube 7. It is being

The above-mentioned control element 2 is held by attracting the armature 5 with the electromagnet 8. Further, the upper part of the extension tube 7 is connected to a vertical movement drive device 9 fixed to the rotary plug 6, so that the control element 2 can be pulled out and lowered for reset after disconnection. . Further, the control circuit 9a is capable of electrically controlling the vertical movement drive device 9 and the electromagnet 8.

Using such a system has the following advantages: That is, unlike the latching mechanism used in the conventional system, the extension tube 7 or a corresponding elongated object does not require mechanical movement in the separation operation during the scram of the control element 2. At the same time, the structure is very simple because there is no relatively complicated mechanism such as a latch mechanism, and it is only necessary to de-energize the electromagnet. Therefore, the possibility of common cause failures with the conventional method can be significantly reduced. In addition, since the electromagnet is placed 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, and an automatic scram will occur. achieved.

By using a reactor control device with a significantly different scram operation principle in conjunction with a conventional system, the reactor can be shut down only by the scram operation of one of the two types of devices. , it becomes possible to significantly improve the safety of nuclear reactors.

(Problems to be Solved by the Invention) However, the above device also had the following drawbacks. That is, the magnetic member used in the electromagnet is required to have high magnetic permeability, soft magnetism, and high saturation magnetic flux density, and is also required to have sufficient high-temperature mechanical strength to support the weight of the control rod.

However, there has been a problem in that it is difficult to obtain suitable materials that can satisfy these requirements. For example, in the case of pure iron with good magnetic properties, high-temperature mechanical strength decreases at temperatures above 500°C. For this reason, using this as a strength member makes the design considerably difficult and may cause deformation of the electromagnet. On the other hand, various alloy steels with good high-temperature mechanical strength are
It has drawbacks in terms of magnetic properties, making it difficult to use as a core material. For example, low alloy steel has a saturation magnetic flux density almost equal to that of pure iron, but has low magnetic permeability. Therefore, in order to obtain the necessary magnetic flux density, it becomes necessary to increase the magnetomotive force of the coil, and as a result, within the limited shape of the electromagnet, the temperature of the coil due to the current increases, which is undesirable. Furthermore, since the residual magnetism is large in terms of soft magnetism, it has an adverse effect on the separation of the armature.

The present invention has been made in view of the above points, and is a nuclear reactor shutdown system in which a control element is directly lifted by an electromagnet. By improving the characteristics, it is possible to provide a nuclear reactor shutdown device that is highly reliable and can be used for a long period of time without repair.

[Structure of the invention]

(Means for Solving the Problems) The present invention has been made to solve the above problems, and includes a method for lifting the control element by attracting an armature provided at the upper end of the control element with an electromagnet. In the developed nuclear reactor shutdown device, either one or both of the electromagnet and the armature,
A first magnetic member with high magnetic permeability and a second magnetic member with high temperature and high strength.
The structure includes a magnetic member.

(Function) In the present invention, since one or both of the electromagnet and the armature includes the first magnetic member having high magnetic permeability, sufficient magnetic flux density can be obtained with an appropriate current. At the same time, the residual magnetic force after the current is cut off can be reduced. In addition, since it has a second magnetic member with high temperature and high strength, the load can be transmitted by this second magnetic member, reducing the force applied to the first magnetic member which does not have sufficient high temperature mechanical strength. be able to.

Therefore, sufficient suction force can be obtained, the control element can be reliably separated, and sufficient mechanical strength and durability can be obtained.

(Example) Examples of the present invention will be described below with reference to FIGS. 1 to 4. Note that the same reference numerals are given to the parts having the same configuration as those of the conventional example, and the explanation thereof will be omitted.

FIG. 1 is a partial sectional view showing only the armature 5 and electromagnet 8 provided in the control element 2 in FIG.

The electromagnet 8 includes a cylindrical outer tube 10 on its outer periphery. The outer tube 10 has its upper end integrally connected to the extension tube 7, and its lower end is provided with a reduced diameter section 10a, and the lower surface 10b of this reduced diameter section 10a forms part of the suction surface. The material for the outer tube 10 is low alloy steel, such as chrome steel,
A material with excellent high-temperature mechanical strength and high saturation magnetic flux density, such as chrome-molybdenum steel, is used. As the chromium molybdenum steel, one containing about 2.25% chromium and about 1% molybdenum is used. A cylindrical excitation coil 11 is provided inside the outer tube 10, and this excitation coil 11 has its lower outer periphery connected to the reduced diameter portion 10a of the outer tube 10.
The lower surface 11a thereof is fitted onto the inner periphery of the reduced diameter portion 10a, and the lower surface 11a thereof is aligned with the lower surface 10b of the reduced diameter portion 10a. In addition, the outer tube 10
An iron core 12 is disposed inside the excitation coil 11 in a portion other than the excitation coil 11 so as to surround the upper surface, inner peripheral surface, and outer peripheral surface of the excitation coil 11.

This iron core 12 is formed so that its outer peripheral surface has almost no gap with the inner peripheral surface of the outer tube 10.

Further, the lower surface 12a of the iron core 12 is the lower surface 10b of the outer tube 10.
, are formed to coincide with the lower surface 11a of the excitation coil 11, and form part of the attraction surface.

As the material for the iron core 12, a material with high magnetic permeability and saturation magnetic flux density, such as pure iron, is used. For example, pure iron with a purity of 99% or more is used. In addition, outer tube 1
0 and the iron core 12 are fixed with bolts 17.

The armature 5 includes a bottomed cylindrical outer tube 13 on its outer periphery and upper end, and its upper surface 13a is disk-shaped to form a suction surface. Further, its lower end is integrally connected to a connecting pipe 4 for connecting to the control element 2. An iron core 14 is provided inside the outer tube 13,
The upper surface and outer peripheral surface of the iron core 14 are in close contact with the outer tube 13 with almost no gap. The same materials as the outer tube 10 and the iron core 12 are used for the outer tube 13 and the iron core 14, respectively. Further, the outer tube 13 and the iron core 14 are connected with bolts 15,
Further, the iron core 14 is supported by a disc spring 16 to reduce the impact during scram.

Next, the functions and effects of this embodiment will be explained with reference to FIG. 2.

Consider a case where the electromagnet 8 and the armature 5 are not composed of an outer tube and an iron core, but are made of the same material. First, when the electromagnet 8 and the armature 5 are made of a material with high magnetic permeability such as pure iron, the relationship between the excitation current and the magnetic flux on the attraction surface is as shown in FIG. 2(a). The solid line shows the state when a current is first applied to the coil, and the broken line shows the characteristics when the current is reduced after reaching saturation.

The attraction force is proportional to the square of the magnetic flux, and the case shown in FIG. 2(a) provides the best magnetic characteristics, and a sufficient attraction force can be obtained with an appropriate current. Furthermore, the residual magnetic force after the current is cut off is small, so there is no problem in disconnecting the control element. However, as explained above, the high-permeability material does not have sufficient high-temperature mechanical strength, so it deforms due to mechanical fatigue or creep, making it difficult to use for a long period of time.

Figure 2(b) shows the case where low alloy steel is used in place of the material in Figure 2(a); the example shown is 2.25% chromium,
This is an example of chrome molybdenum steel containing 1% molybdenum. The meanings of the solid lines and broken lines are the same as in FIG. 2(a).

In this case, since the magnetic permeability is low, the attraction force will be too small when compared with the same current, for example A. Therefore, it becomes necessary to increase the current, which is difficult to implement. Further, even if the attracting force is obtained by increasing the current, the reliability in disconnecting the control element decreases because the residual holding force is large.

FIG. 2(c) shows the case of this embodiment, in which the material of the iron core is the same as that of FIG. 2(a), and the material of the outer tube is the same as that of FIG. 2(b). In this case, the characteristics will be intermediate between those in FIG. 2(a) and FIG. 2(b), but since most of the magnetic circuit is made of the same material as in the case of FIG. 2(a),
The characteristics are close to those shown in FIG. 2(a), and a sufficient attraction force can be obtained even with a current of A, and the residual magnetic force can be made relatively small.

Thus, in the above embodiment, the electromagnet and the armature are made of pure iron, which has high magnetic permeability and saturation magnetic flux density, and chrome steel or chrome-molybdenum steel, which has excellent high-temperature mechanical strength and high saturation magnetic flux density. Because of the structure, a sufficient magnetic flux density can be obtained with an appropriate current, and therefore a sufficient adsorption force can be obtained, and the residual magnetic force can be made relatively small, thus improving the reliability of disconnection of the control element. be able to.

In addition, the iron core 12 of the electromagnet 8 is connected to the reduced diameter portion 10a of the outer tube 10.
while engaging and holding the iron core 1 of the armature 5.
4 is surrounded and held by the bottomed cylindrical outer tube 13, so the weight of the control element 2 is equal to the outer tube 13 and the outer tube 10.
As a result, the heat is transmitted to the extension tube 7 and is not applied to the iron cores 12 and 14, which do not have sufficient high-temperature mechanical strength. Therefore, iron core 12
．． 14 can be suppressed from deformation and deterioration caused by creep deformation and high-temperature fatigue, and the electromagnet and armature can be used for a long period of time.

Next, FIG. 3 shows another embodiment of the present invention. In this embodiment, a magnetic gap is added to a part of the magnetic circuit shown in FIG. 1 to reduce the residual attraction force. iron core 12
The lower surface 12b of the inner part of the excitation coil 11 is placed at a higher position than the lower surface 10b of the outer tube 10, so that even when the electromagnet 8 and the armature 5 are in close contact with each other, a gap 18 exists in the attraction surface. FIG. 4 explains the effect of the embodiment of FIG. 3. The broken lines in FIG. 4 are the same as in FIG. 2(C), and the solid lines are for the embodiment in FIG.

The arrows indicate cases in which the current is increased and cases in which the current is decreased. While the residual magnetic flux in the case where there is no air gap is B, in the case of the embodiment shown in FIG. 3, the residual magnetic flux decreases to C due to the magnetic resistance due to the presence of the air gap. Therefore, the residual attraction force when the current is cut off is reduced, thereby eliminating the adverse effects of using low-alloy steel as part of the magnetic circuit, and making it possible to ensure reliability in disconnecting the control element.

In the above embodiment, the gap 18 between the iron core 12 and the iron core 14 is used as the magnetic gap provided in a part of the magnetic circuit, but there is no need to limit it to this. A gap may be provided in other parts of the electromagnet 8 and the armature 5.

〔Effect of the invention〕

As explained above, the present invention has the advantage that sufficient suction force can be obtained, the control element can be reliably separated, and sufficient mechanical strength and durability can be obtained. is obtained.

[Brief explanation of the drawing]

1 to 4 are diagrams showing one embodiment of the present invention, in which FIG. 1 is a longitudinal cross-sectional view thereof, FIG. 2 is a diagram showing the relationship between current and magnetic flux, and FIG. 4 is a diagram showing another embodiment of the present invention, FIG. 4 is a diagram showing the relationship between current and magnetic flux showing the effect of FIG. 3, and FIG. 5 is a diagram showing a conventional nuclear reactor shutdown device. 2... Control element, 5... Armature, 8... Electromagnet, 10... Outer tube, 12... Iron core, 13... Outer tube, 14... Iron core. Applicant's Representative Sato -Yu Figure Figure 9; Circle Figure

Claims (1)

[Claims] In a nuclear reactor shutdown device configured to lift an armature provided at an upper end of a control element by attracting the control element with an electromagnet, one or both of the electromagnet and the armature have high magnetic permeability. A nuclear reactor shutdown device comprising a first magnetic member and a high-temperature, high-strength second magnetic member.