JPH0588797B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a self-actuated control rod drive mechanism that automatically inserts control rods into a reactor core in order to make an emergency shutdown of a nuclear reactor in the event of an abnormality. , a control rod drive that uses amorphous magnetic alloy as part of the magnetic circuit of the electromagnet that suspends and holds the control rod, and uses the fact that its saturation magnetic flux density decreases due to an abnormal rise in temperature to release and drop the control rod. It is about the mechanism.

[Prior Art] In general, fast reactors and the like are equipped with control rods that are inserted into the reactor core in the event of an abnormality, in addition to control rods for output control, in order to increase the reliability of reactor shutdown. The control rod drive mechanism that drives these starts operating in response to an external scram signal. As a result, reliability in the event of an emergency depends on an external scram signal generation mechanism, and the signal transmission path from the occurrence of an abnormality in the reactor to the scram becomes complicated, which poses problems in terms of reactor shutdown responsiveness and reliability. .

In order to solve these problems, a configuration has been proposed in which a temperature switch is installed inside the reactor and the control rods are directly driven by the signal from the temperature switch (for example, Japanese Patent Laid-Open No. 127493/1983).
(see publication). Here, the temperature switch used to detect abnormalities in the reactor uses a method to control the contacts on and off using the difference in thermal expansion between multiple dissimilar metals, and transmits the signal to the control rod holding mechanism. is configured to do so.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, the temperature switch is composed of a combination of dissimilar metals in which a tungsten rod is inserted into a stainless steel tube that is immersed in a coolant, and the lower end of the stainless steel tube and tungsten rod is The upper end of the joined tungsten rod contacts the movable contact. Due to the difference in thermal expansion between the stainless steel tube and the tungsten rod, the upper end of the tungsten rod moves up and down, causing the movable contact to come into contact with and separate from the fixed contact.

However, since the temperature switch is installed near the core, it is affected by irradiation and has reliability problems. Furthermore, since the tube is immersed in the coolant, a leak detector must be installed inside the stainless steel tube to detect whether or not the liquid coolant has entered, making the mechanism complicated.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, to be able to safely stop a nuclear reactor without relying on external operating force or signals, to have a simple structure, and to be able to control by self-operation. It is an object of the present invention to provide a self-actuated control rod drive mechanism that is equipped with a plurality of mechanisms for dropping the rod, thereby increasing reliability.

[Means for Solving the Problems] The present invention has a control rod and a control rod drive mechanism for driving the control rod up and down, and an electromagnet for attracting and holding the control rod in the control rod drive mechanism. It assumes the built-in configuration.

In order to achieve the above object, the electromagnet includes a central magnetic body, a coil wound around the central magnetic body, an outer magnetic body located outside the coil, and an outer magnetic body. It has a magnetic flange part whose upper end is connected to the central magnetic body, and the lower ends of the central magnetic body and the outer magnetic body are located in almost the same horizontal plane, and it is saturated when the coolant temperature becomes abnormally high. The structure is such that an amorphous magnetic alloy having magnetic properties that reduces magnetic flux density is used for either the central magnetic body or the outer magnetic body.

[Operation] During normal operation, the control rod is attracted and held by an electromagnet whose magnetic circuit incorporates an amorphous magnetic alloy that is a ferromagnetic material and has sharper magnetic properties than ordinary ferromagnetic materials. If an abnormality occurs in the reactor and the coolant temperature rises abnormally, the saturation magnetic flux density of the amorphous magnetic alloy will drop rapidly, the magnetic field formed by the electromagnet will be cut off, and the holding force will decrease, causing the control rod to release. being hit and falling. As described above, in the present invention, an abnormality within a nuclear reactor can be sensed as a physical phenomenon, and control rods can be directly driven by self-operation via various external controllers.

In the case of amorphous magnetic alloys, the Curie point is lower than the crystallization temperature, and by selecting the material and determining the operating temperature so that it will self-actuate due to a decrease in saturation magnetic flux density, control rods can be repeatedly operated without crystallization. A detachment operation can be performed.

In addition, when this type of material crystallizes, it expands rapidly and its electrical resistance drops sharply, so by making use of these changes in physical properties to separate the control rods, it is possible to control the movement associated with crystallization. By positioning it as a backup, a more effective and reliable control rod drive mechanism can be realized. That is, by incorporating an amorphous magnetic alloy into either the central magnetic body or the outer magnetic body of the electromagnet, only one of them expands rapidly during crystallization, pushing down the magnetic handling head at the upper end of the control rod, thereby causing A gap occurs in the magnetic circuit and the control rod is separated.

Embodiment Figure 1 is an explanatory diagram showing an embodiment of the self-actuating control rod drive mechanism according to the present invention, in which figure A shows a state in which a control rod is held by suction, and figure B shows a state in which the control rod is released. Each state is shown below.

A control rod 14 having a handling head 10 made of a magnetic material at the top and a neutron absorber 12 inside.
is located above the lower guide tube 16 in the reactor core and is held by a control rod holding mechanism. The control rod holding mechanism consists of a drive shaft 20 inserted through the upper guide tube 18 and an electromagnet 22 attached to the lower end of the drive shaft 20, and is supplied with current from a power source via a cable (not shown). and excited electromagnet 2
2 attracts the magnetic handling head 10 and holds the control rod 14.

A ball nut 24 is attached to the upper part of the drive shaft 20, the ball nut 24 meshes with a ball screw 26, and the upper end of the ball screw 26 is connected to the drive motor 2.
It is connected to 8. During normal operation of the reactor, the control rods 1 are activated by operating the drive motor 28.
4 to adjust the output. If any abnormality occurs in the reactor, the control rod holding mechanism will self-activate.
As a result, the control rod 14 is separated and falls by gravity, stopping the reactor as shown in Figure B.

The feature of the present invention is that the electromagnet 22 of the control rod holding mechanism
The advantage is that at least a portion of the magnetic circuit incorporates an amorphous magnetic alloy that has a characteristic that the saturation magnetic flux density decreases when the coolant temperature becomes abnormally high.

For example, as shown in FIG. 2, the electromagnet 22 includes an iron core 30 located at the center, a coil 32 wound around the core, and an amorphous magnetic alloy made of an amorphous magnetic alloy that covers the outside of the coil 32 and has an upper end connected to an iron core flange portion 30a. It consists of a cylindrical body 34, and the cylindrical body 34
This is a structure in which the lower end surface of the iron core 30 and the lower end surface of the iron core 30 are located in substantially the same horizontal plane. The coil 32 has a power supply 3
Power is supplied from 6.

When an amorphous magnetic alloy reaches a certain temperature (Curie point) or higher, its saturation magnetic flux density decreases rapidly. Here, a material is selected such that the temperature at which the saturation magnetic flux decreases corresponds to the abnormal temperature inside the nuclear reactor.

The state during normal operation is as shown in Figure 2.
The coil 32 is energized from the power source 36, and the iron core 30,
A magnetic circuit is constituted by a cylindrical body 34 made of an amorphous magnetic alloy and a handling head 10 made of a magnetic material, and a control rod is attracted and held therein. During reactor operation, if an abnormality such as loss of coolant flow rate occurs, the coolant temperature within the reactor increases. Along with this, the temperature near the electromagnet 22 also rises. When this temperature rise reaches an abnormal value, the saturation magnetic flux density of the amorphous magnetic alloy constituting the cylindrical body 34 rapidly decreases, changing from a ferromagnetic material to a paramagnetic material. As a result, the magnetic circuit opens, the attraction force is lost, the handling head 10 is separated, the control rod falls as shown in FIG. 3, and the reactor is shut down.

Basically, this is how the reactor is shut down when an abnormality occurs. Even if the control rod is not separated due to a drop in the saturation magnetic flux density of the amorphous magnetic alloy for some reason, this device operates the following backup mechanism to ensure that the control rod falls. .

When the temperature of the nuclear reactor further increases and reaches the crystallization temperature of the amorphous magnetic alloy, the amorphous magnetic alloy crystallizes, causing rapid expansion. That is, as shown in FIG. 4, the cylindrical body 34 undergoes rapid thermal expansion and pushes the handling head 10 downward. As a result, a gap G is formed between the iron core 30 and the handling head 10, and the control rod is surely dropped.

FIG. 5 shows yet another example of a backup mechanism, in which the control rod is released by utilizing the decrease in electrical resistance accompanying the crystallization of an amorphous magnetic alloy. An electrode 38 is embedded within the amorphous magnetic alloy and connected in parallel with the coil 32. The coil 32 is designed to attract and hold the control rod during normal operation.
At the same time, the cylindrical body 34 made of amorphous magnetic alloy is also energized. The voltage and current values applied to the coil 32 are set so as not to be too large to a value that allows the control rod to be attracted and held. When the temperature inside the furnace rises abnormally and the amorphous magnetic alloy crystallizes, its electrical resistance rapidly decreases. As a result, more current flows to the amorphous magnetic alloy side, and conversely, the current to the coil side decreases. As a result of this change, the holding power of the electromagnet decreases and it is no longer able to attract and hold the control rod, causing the control rod to fall and shutting down the reactor.

As described above, the present invention uses an amorphous magnetic alloy as a part of the electromagnet components.
This is significantly different from the conventional self-actuated control rod drive mechanism, which operates by reducing the saturation magnetic flux density.

It operates by rapid expansion due to crystallization.

It operates due to the rapid decrease in electrical resistance associated with crystallization.

A plurality of operation methods can be provided. Even if this operation is not performed and the control rod does not fall, the control rod can be reliably dropped and the reactor can be stopped by the operation of and/or. Note that once an amorphous magnetic alloy has crystallized, it is impossible to use it again under the same conditions, but in general, the Curie point of an amorphous magnetic alloy is much higher than the crystallization temperature (although it varies depending on the material, it is usually (100℃ or more), so if the material is selected and the operating temperature is determined so that it operates by reducing the saturation magnetic flux density, the electromagnet can be used repeatedly without crystallization. In other words, if the operation associated with crystallization is regarded as backup, it can be used more effectively.

Although a preferred embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited to only such a configuration. The amorphous magnetic alloy may be incorporated into the magnetic circuit on the center side,
Various modifications are possible.

[Effects of the Invention] As described above, the present invention incorporates an amorphous magnetic alloy into a part of the magnetic circuit of the electromagnet for attracting and holding the control rod, and when the coolant temperature becomes abnormally high, the control rod is Because the control rod drive mechanism itself is equipped with a function to detect abnormalities within the reactor (abnormal rise in temperature), it can directly control the reactor without relying on external operating force or signals. This simplifies the system configuration and prevents deterioration in reliability due to failures in external mechanisms and poor responsiveness due to complication of signal transmission paths, resulting in extremely high safety. There is a certain effect.

Additionally, since it is equipped with multiple mechanisms that detect abnormalities and self-actuate to drop the control rods, it also has the effect of being more reliable than conventional self-actuating control rod drive mechanisms.

[Brief explanation of drawings]

Figures 1A and B are explanatory diagrams showing one embodiment of the self-actuating control rod drive mechanism according to the present invention, Figure 2 is an explanatory diagram showing the structure of the electromagnet, and Figure 3 is the saturation magnetic flux of the amorphous magnetic alloy. An explanatory diagram showing the state in which the control rods are released due to a decrease in density, Figure 4 is an explanatory diagram showing the state in which the control rods are released due to thermal expansion due to crystallization, and Figure 5 is an explanatory diagram showing the state in which the control rods are released due to thermal expansion due to crystallization. FIG. 10... Handling head made of magnetic material, 14...
Control rod, 22... Electromagnet, 30... Iron core, 32... Coil, 34... Cylindrical body made of amorphous magnetic alloy, 3
6...power supply, 38...electrode.

Claims (1)

[Claims] 1. It has a control rod and a control rod drive mechanism that drives the control rod up and down, and the control rod is installed in the control rod drive mechanism.
In the case where an electromagnet is incorporated for adsorption and holding by a magnetic handling head at the upper end, the electromagnet includes a central magnetic body, a coil wound around the central magnetic body, and an outer magnetic body located outside the coil. a magnetic flange portion that connects the upper end of the outer magnetic body to the central magnetic body, and the lower ends of the central magnetic body and the outer magnetic body are located in substantially the same horizontal plane, and the central magnetic body or the outer magnetic body A self-actuating control rod drive mechanism characterized in that an amorphous magnetic alloy whose saturation magnetic flux density decreases when the coolant temperature becomes abnormally high is used for either one of the mechanisms.