JPH01239497A - Self-operation type control rod drive mechanism - Google Patents

Abstract

PURPOSE:To lower the ambient temp. of the coil of an electromagnet and to safely shut down a nuclear reactor without depending on the operating force from the outside by installing the above-mentioned coil above a shielding plug and providing a magnetic attraction part to the bottom end of a drive shaft. CONSTITUTION:A control rod 14 is moved upward and downward by operating a drive motor 28 to make output adjustment at the time of ordinary operation of the nuclear reactor. The coolant temp. in the reactor rises when abnormality such as flow rate loss of the coolant arises during the reactor operation. The saturation magnetic flux density of magnetic members 36a, 36b drops sharply and the members change from ferromagnetic materials to paramagnetic materials when the temp. rise exceeds the Curie point of said members. The magnetic path is, therefore, automatically opened even if the energization to the coil 30 is continued. The attraction force between magnetic attraction members 40a, 40b and a magnetic handling head 10 is lost and the handling head 10 is automatically disconnected. The control rod 14 is then dropped and the reactor is shut down.

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. , an electromagnetic coil that suspends and holds the control rod is installed above the shielding plug, and
This relates to a control rod drive mechanism that uses a temperature-sensing magnetic material in a part of the magnetic circuit, and releases and drops the control rod by utilizing the decrease in its saturation magnetic flux density due to an abnormal rise in coolant temperature.

[Prior Art] In order to improve the reliability of reactor shutdown, nuclear reactors 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. 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, leading to problems in terms of response and reliability when shutting down the reactor. .

In order to solve these problems, a configuration has been proposed in which a temperature switch is provided in the reactor and the control rod is directly driven by the signal from the temperature switch (for example, see Japanese Patent Application Laid-open No. 127493/1983).
As a temperature switch for detecting an abnormality in the furnace, a method is adopted in which a contact point is controlled on and off by utilizing the difference in the amount of thermal expansion of a plurality of different types of metals.

However, with this technology, since the temperature switch is installed near the reactor core, it is susceptible to radiation and ray irradiation, which poses a problem in terms of reliability. In addition, since the tube is immersed in the coolant, a leak detector must be installed inside the stainless steel tube to detect whether or not liquid coolant has entered the tube, making it mechanically complex.

Therefore, as a solution to this problem, an electromagnet is installed in the control rod drive mechanism to magnetically attract and hold the control rods, and at least a part of the magnetic circuit is equipped with an electromagnet that can be used when the coolant temperature becomes abnormally high. A self-actuating control rod drive mechanism incorporating an amorphous magnetic alloy with a reduced saturation magnetic flux density was proposed (see Japanese Patent Application Laid-open No. 19593/1983).
Here, the electromagnet is attached to the lower end of the drive shaft that drives the control rod up and down.

[Problems to be Solved by the Invention] In the self-actuating control rod drive mechanism of the conventional configuration as described above, the electromagnet (coil and magnetic circuit) for releasing and dropping the control rod when the coolant temperature rises abnormally is All are located in the coolant inside the reactor.

When the nuclear reactor is a fast reactor that uses metallic sodium as a coolant, the temperature of the coolant sodium is as high as about 200 to 600°C. Therefore, the electromagnet coil must also be able to withstand such high temperatures.

However, if the coolant temperature is relatively low, it will struggle and the 600
A highly reliable coil that can be used for long periods at temperatures as high as ℃ is still under development. Therefore, the above-mentioned prior art is currently not applicable to nuclear reactors that use particularly high-temperature coolants.

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 use high-temperature metals. It is an object of the present invention to provide a highly reliable self-actuated control rod drive mechanism that can be fully used in nuclear reactors that use sodium as a coolant.

[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 is incorporated in the control rod drive mechanism. The system is based on a self-actuated control rod drive mechanism in which at least a portion of its magnetic circuit uses a temperature-sensitive magnetic material whose saturation magnetic flux density decreases when the coolant temperature abnormally increases.

In order to achieve the above object, in the present invention, the electromagnet coil is installed above the shielding plug, a magnetic adsorption part is provided at the lower end of the drive shaft, and the magnetic circuit of the electromagnet is connected at the upper end and connected at the lower end. The structure includes a magnetic member that is open and vertically disposed so as to surround the drive shaft, and the magnetic adsorption section.

For example, the drive shaft is made of a non-magnetic material, and the magnetic member vertically disposed so as to wrap around the drive shaft is composed of a pair of temperature-sensing magnetic materials having an arcuate cross section and facing each other. It is desirable that the structure is slidable relative to the section.

[Operation] In the present invention, since the electromagnetic coil is installed above the shielding plug rather than in the coolant, the ambient temperature is relatively low, and there is no need to particularly consider high temperatures. Therefore-
It can also be used with electromagnetic coils for boat fishing.

During normal operation, the temperature-sensing magnetic material exhibits ferromagnetism, and the magnetic flux generated by the coil current passes through the magnetic circuit, and the magnetic attraction section magnetically attracts the magnetic handling head at the upper end of the control rod. Hold. Therefore, in this state, the control rod can be driven up and down by the control rod drive mechanism.

When an abnormality occurs in the nuclear reactor and the coolant temperature rises abnormally, the saturation magnetic flux density of the temperature-sensing magnetic material rapidly decreases, the previously formed magnetic path is cut off, and the attraction and retention force is lost. This releases the control rods and allows them to fall freely.

As described above, in the present invention, an abnormal rise in the coolant temperature of a nuclear reactor can be sensed as a physical phenomenon, and the control rods can be directly driven by self-operation without using various external controllers.

[Embodiment] Fig. 1 is an explanatory diagram showing an embodiment of the self-actuating type control rod according to the present invention. Each figure shows the state in which the control rods are released. In addition, the main part of the present invention is shown in FIG.
The mm-m cross section is shown in FIG.

As shown in FIG. 1A, a control rod 14 having a magnetic handling head 10 on the top and a neutron absorber 12 inside.
is located above the control rod 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 2o and an electromagnet 22, which are provided so as to pass through the upper guide tube 18, and are supplied with excitation current from a power source through a cable (not shown), and the excited electromagnet 22 is It is configured to hold the control rod 14 by attracting the magnetic handling head 1o.

The drive shaft 20 is made of a non-magnetic material, and 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 a drive motor 28. During normal operation of the nuclear reactor, the control rod 14 is moved up and down by operating the drive motor 28 to adjust the output. If some kind of abnormality occurs in the reactor and the temperature rises, the control rod holding mechanism is self-activated, and as a result, the control rods 14 are separated and dropped by gravity as shown in Figure 1, stopping the reactor.

Now, the feature of the present invention is that the electromagnet 22 in the control rod holding mechanism
It is in the configuration of In the present invention, the coil 30 is connected to a shielding plug 32.
located on the top surface of A magnetic circuit is provided so as to penetrate the shielding plug 32 from near the installation position of the coil 30 and reach the coolant 34, and at least a portion of the magnetic circuit has a temperature sensing sensor whose saturation magnetic flux density decreases when the coolant temperature abnormally rises. Magnetic materials are used.

In this embodiment, as shown in detail in FIGS. 2 and 3, the magnetic circuit includes a pair of magnetic members 36a and 36b that are vertically disposed along the drive shaft 20 so as to wrap around the drive shaft 20, and an upper part of the magnetic members 36a and 36b. and the upper connecting part 38 that connects the non-magnetic drive shaft 2.
A pair of arc-shaped magnetic adsorption parts 4 provided at the lower end of 0
The configuration has 0a and 40b. The magnetic members 36a and 36b vertically disposed so as to surround the drive shaft 20 have an arcuate cross section and a long elongated shape along the outer peripheral surfaces of the magnetic attraction parts 40a and 40b, and are made of a temperature-sensitive magnetic material. The magnetic adsorption parts 40a and 40b can be slid relative to each other. The coil 3o is connected to each magnetic member 36a at the upper surface of the shielding plug 32 as described above.

36b, respectively. Magnetic member 36a
, 36b is, for example, an amorphous magnetic alloy or the like, and has the property that its saturation magnetic flux density sharply decreases when the temperature reaches a certain temperature (Curie point) or higher. Here, a material whose Curie point corresponds to the abnormal temperature of the reactor coolant is selected.

The state during normal operation is as shown in FIG. 1A and FIG. 2. The coil 30 is excited by energizing it from a power source (not shown), and a closed magnetic path consisting of the magnetic member 36a, the upper connecting portion 38, the magnetic member 36b, the magnetic attraction member 40b, the handling head 10, and the magnetic attraction member 40a is formed. configured. As a result, the control rod 14 is held by suction. If the drive shaft 2o is raised in this state, the control rod 14 is pulled up and the reactor enters the operating state.

Now, in the unlikely event that an abnormality such as loss of coolant flow rate occurs during nuclear reactor operation, the coolant temperature within the reactor will rise. Along with this, the temperature of the magnetic material forming the magnetic circuit also rises. When this temperature rise exceeds the Curie point of the magnetic members 36a, 36b, their saturation magnetic flux density drops rapidly and they change from ferromagnetic to paramagnetic. Therefore, even when the coil 30 continues to be energized, the magnetic path opens naturally, and the attraction force between the magnetic attraction members 40 a, 40 b and the magnetic handling head 10 is lost, causing the handling head 10 to automatically move. The control rods 14 fall as shown in FIG. 1B, and the reactor shuts down.

When the control rod 14 falls and the reactor is shut down, the temperature inside the reactor also decreases. The temperature inside the furnace is the magnetic member 36a.

When the temperature drops below the Curie point of 36b, those members return to ferromagnetism again. Drive shaft 20 by drive motor 28
and magnetic adsorption parts 40a, 40 attached thereto.
b is lowered to the magnetic handling head IO on the top of the discount 14, and further the magnetic member 36 is lowered by another drive device (not shown).
When a and 35b are lowered to form a closed magnetic path, the control rod 14 can be attracted and held again, and the control rod 14 can be pulled up to a predetermined position by each of the aforementioned drive devices.

Although a preferred embodiment of the present invention has been described in detail above, the present invention is not limited to only such a configuration.
The magnetic attraction member may be made of a temperature-sensitive magnetic material,
A magnetic handling head may be constructed of such temperature sensitive magnetic material. Further, the configuration of the magnetic circuit can be modified in various ways other than those described above.

[Effects of the Invention] As described above, the electromagnetic coil for attracting and holding the control rods is installed above the shielding plug, so the ambient temperature of the coil is relatively low. Even when the coolant temperature is high, as in the above case, there is no need to pay special consideration to the high temperature, and it can be easily realized because an electromagnetic coil that can be used on a boat can be used. This also has the effect of increasing the reliability of the system and improving maintainability.

Furthermore, since the present invention is basically a self-actuating type that can directly stop the reactor without relying on external operating force or signals, the overall system configuration is simplified and there is no possibility of failure of external mechanisms. It is possible to avoid a decrease in reliability due to such factors and a decrease in responsiveness due to the complexity of the signal transmission path, and has the effect of extremely increasing safety.

[Brief explanation of the drawing]

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 main parts thereof, and Figure 3 is a cross-sectional view taken along line mm. be. DESCRIPTION OF SYMBOLS 10... Magnetic handling head, 14... Control rod, 20... Drive shaft, 22... Electromagnet, 30... Coil, 32... Shielding plug, 34... Coolant, 36
a. 36b...Magnetic member, 38...Upper connecting portion, 40a
. 40b...Magnetic adsorption part. Figure 1 8 “-□

Claims (1)

[Claims] 1. It has a control rod and a control rod drive mechanism that drives the control rod up and down, and an electromagnet for attracting and holding the control rod is built into the control rod drive mechanism. In at least a portion of the magnetic circuit, a temperature-sensitive magnetic material whose saturation magnetic flux density decreases when the coolant temperature rises abnormally is used, the coil of the electromagnet is installed above the shielding plug, and the magnetic circuit is installed at the lower end of the drive shaft. A self-actuating type characterized in that the magnetic circuit of the electromagnet is connected at the upper end and is open at the lower end, and has a magnetic member and the magnetic attraction part that are vertically arranged so as to wrap around the drive shaft. Control rod drive mechanism. 2. The drive shaft is made of a non-magnetic material, and the magnetic member vertically disposed so as to wrap around the drive shaft is made of a pair of temperature-sensing magnetic materials that have an arcuate cross section and are placed opposite each other. 2. A self-actuated control rod drive mechanism according to claim 1, wherein said control rod drive mechanism is movable relative to said control rod drive mechanism.