JPH03165298A - Reactor shutdown device - Google Patents

Abstract

PURPOSE:To improve the responsiveness with the abnormal temp. rise of coolants and to assure the scram of a reactor by providing a bimetal switch which detects the temp. of the coolants flowing out of a lower control rod guide pipe and a lower fuel rod guide pipe. CONSTITUTION:The bimetal switch 51 operates to turn off and an electromagnet 40 loses its magnetic force when the temp. of the coolants 52, 53 is increased by a certain cause to exceed the set temp. of the bimetal switch 51. The control rod 43 is detached from the electromagnet 40 in this way and is inserted into the reactor core by gravity fall, by which the scram of the reactor is executed. Namely, the low-temp. coolant 52 flowing out of the lower control rod guide pipe 54 and a large volume of the high-temp. coolant 53 flowing out of the lower fuel assembly guide pipe 55 are eventually press attached, right after the outflow to the bimetal switch 51 installed in the lower part of a measuring wire support 49. The responsiveness with the abnormal temp. rise of the coolants 52, 53 is improved and the scram of the reactor is assured.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor shutdown device that is applied to, for example, a fast breeder reactor, and is used for emergency shutdown of nuclear reactor operation. This invention relates to an improvement in a nuclear reactor shutdown system in which a control rod is detached from a drive part and inserted into a reactor core by an electromagnetic switching action based on temperature detection.

(Prior art) Conventionally, in nuclear reactors such as fast breeder reactors that use sodium as a coolant, for example, it is necessary to control the output of nuclear fuel in the core or to absorb neutrons in the reactor when the reactor operation reaches a transient state. Operations are carried out to emergency stop the nuclear reaction, and control rods are used for these operations.

Control rods are usually connected at their upper ends to vertically movable rods that are vertically introduced into the core of a nuclear reactor from above through an upper guide tube, and are driven up and down by a control rod drive mechanism. It controls the nuclear reaction in a nuclear reactor by changing the amount of neutrons absorbed by inserting or withdrawing them into the reactor.

When reactor operation becomes transient, control rods are quickly inserted into the reactor core to stop the nuclear reaction. Rapid insertion is achieved by a control rod drive mechanism and gravity drop.

Various control rod drive mechanisms and reactor shutdown devices have been proposed so far. In particular, control rods in which control rods are attracted to and connected to rods using electromagnets tend to be used more frequently due to their simple structure and easy approach and separation operations, and various developments have been made. There is.

FIGS. 4 and 5 show a nuclear reactor shutdown device using Curie point electromagnets as an example of such an electromagnetic coupling configuration.

The upper opening of the reactor vessel is closed by a shielding plug 1. A long cylindrical upper guide tube 3 is inserted into a through hole 2 provided in the shielding plug 1 along the vertical direction. This upper guide tube 3 is fixed to the shielding plug 1 by a flange portion 4 provided at its upper end. A housing 5 is connected to the upper end of the upper guide tube 3, and a motor for driving a control rod (not shown) is mounted on the top of the housing 5. On the other hand, the lower end of the upper guide tube 3 is immersed in liquid sodium 6, which is a coolant for the nuclear reactor.

Furthermore, an extension tube 7, which is a rod for driving a control rod, is inserted into the upper guide tube 3 so as to be movable in the vertical direction. A nut 8 is fixed to the upper part of the extension tube 7, and this nut 8 is screwed onto a screw shaft 9 rotated by the aforementioned motor. An electromagnet 10 is installed at the lower end of the extension tube 7.

Then, a control rod lower guide tube 20 provided in the reactor core 11
A control rod 13 is inserted therein so as to be movable up and down, and the upper end of the control rod 13 is made of a magnetic material. This control rod 13 is electromagnetically connected by an electromagnet 10 of the extension tube 7.

The electromagnet 10 is, for example, a Curie point electromagnet, and has a configuration in which a coil is wound around a rod-shaped Curie point magnetic material.

When the drive unit (not shown) rotates, the nut 8 rotates through the screw shaft 9, which causes the extension tube 7 to rotate.
and the control rod 13 move up and down in unison.

Note that a neutron shield 14 is arranged above the upper guide tube 3, and this neutron shield 14 has a bellows 15 attached to the extension tube 7.
This isolates the reactor sodium atmosphere from the upper mechanism of the control rod drive mechanism.

Further, an introduction pipe 16 having the same diameter for introducing a coolant is integrally connected to the lower end of the upper guide pipe 3. This introduction pipe 16
Inside, thermocouples 17 for measuring the outlet temperature of the high-temperature coolant flowing out from the fuel assembly and measurement wire supports 18 corresponding to the number of thermocouples 17 are installed. This measurement line support 18 is provided with a large number of outflow holes 19 arranged in a plurality of rows so that high temperature coolant from the core fuel assembly can flow out efficiently. In addition, the upper end of the measurement line support 18 is
A blind plate is used to facilitate mixing with the low-temperature coolant flowing out from the control rods. In addition, this measurement line support 1
8 also serves to protect the control rod 13 from collision forces caused by its vertical movement.

During reactor operation, coolant 22,23 flows upward through the control rod lower guide tube 20 and the fuel assembly lower guide tube 21. The normal exit temperature of the coolant 23 flowing out from the fuel assembly lower guide pipe 21 is 500 to 550°C, which is higher than the normal exit temperature of 400°C of the coolant 22 flowing out from the control rod lower guide pipe 20. And the flow rate is fast. The coolant 22 , 23 that has flowed out is guided by the introduction pipe 16 to the electromagnet 10 , further rises while being mixed, and flows out of the introduction pipe 16 through the outflow hole 17 .

If the temperature of the coolant 22, 23 rises abnormally and reaches the Curie temperature, which is the set value of the Curie point electromagnet, the electromagnet loses its magnetism. Due to this action, the adsorption force of the control rod 13 disappears,
The control rods 13 are dropped and inserted into the reactor core by their own weight, and a reactor scram is performed.

(Problem to be Solved by the Invention) According to such a conventional nuclear reactor shutdown device, the coolant 23 (constantly outlet temperature 500 to 550°C) flowing out from the fuel assembly lower guide pipe 21 flows through the control rod lower guide pipe. The temperature is higher than that of the coolant 22 flowing out from the coolant 20 (constant outlet temperature of 400° C.), and the flow rate is faster. Therefore, the static pressure of the high-temperature coolant 23 decreases, and the coolant flow state is such that the low-temperature coolant 22 flows toward the high-temperature coolant 23 side, and a laminar flow of low-temperature and high-temperature coolants occurs at the upper part of the introduction pipe 16. There is a possibility that the two may not be sufficiently mixed. Further, a part of the coolant comes into contact with the upper part of the introduction pipe 16 and after being reversed, flows back into the electromagnet 10 section. Due to the flow of coolant near the electromagnet 10,
When the temperature of the coolant rises abnormally, it takes a considerable amount of time for the electromagnet to reach its Curie point and interrupt the magnetic flux, and there is a possibility that sufficient scram response cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a nuclear reactor shutdown device that has good responsiveness to abnormal temperature rise of the coolant and can reliably scram the reactor. .

[Structure of the invention]

(Means for Solving the Problems) A nuclear reactor shutdown device according to the present invention includes a vertically movable rod vertically introduced into the core of a nuclear reactor from above via an upper guide pipe, and a lower end of the upper guide pipe. a fuel assembly lower guide tube disposed coaxially in the fuel assembly lower guide tube; a control rod lower guide tube coaxially disposed inside the fuel assembly lower guide tube; and a control rod whose upper end is removably connected to the lower end of the rod via an electromagnet, and the electromagnet detects the increase in temperature of the low-temperature coolant flowing upward from the control rod lower guide tube. In the nuclear reactor shutdown system that detaches the control rods by demagnetizing the control rods, a bimetallic switch is disposed inside the upper end of the upper guide tube as a means for detecting an increase in temperature of the low-temperature coolant. .

(Function) According to the present invention, first, low-temperature coolant flows out from the control rod lower guide pipe, and high-temperature large amount coolant flows out from the fuel rod lower guide pipe as an upward flow, and is guided into the introduction pipe. A bimetallic switch installed on a support is placed at the bottom end of this inlet pipe, so even if the coolant temperature rises abnormally for some reason, the bimetallic switch is activated immediately, and the electromagnet is activated. The control rod loses its magnetic flux and separates from the lower end of the extension tube, causing a scram.

(Example) Hereinafter, an example of a nuclear reactor shutdown device according to the present invention will be described with reference to FIGS. 1 to 3.

Figure 1 is a sectional view showing the entire reactor shutdown system, Figure 2 is an enlarged view of a part of Figure 1, and Figure 3 is the
■It is a line sectional view.

The upper opening of the reactor vessel is closed by a shielding plug 31 . Through hole 32 provided in this shielding plug 31
A long cylindrical upper guide tube 33 is inserted along the vertical direction. This upper guide tube 33 is fixed to the shielding plug 31 by a flange portion 34 provided at the upper end. A housing 35 is connected to the upper end of the upper guide tube 33,
Although not shown, a motor for driving the control rod is mounted on the top of the housing 35. On the other hand, the lower end of the upper guide tube 33 is immersed in liquid sodium 36, which is a coolant for the nuclear reactor. Furthermore, an extension tube 37, which is a rod for driving a control rod, is inserted into the upper guide tube 33 so as to be movable in the vertical direction. A nut 38 is fixed to the upper part of the extension tube 37, and this nut 38 is screwed onto a screw shaft 39 rotated by the aforementioned motor. An electromagnet 40 is installed at the lower end of the extension tube 37.

A control rod lower guide tube 42 provided in the reactor core 41
A control rod 43 is inserted therein so as to be movable up and down, and the upper end of the control rod 43 is made of a magnetic material. This control rod 43 is electromagnetically connected to the extension tube 37 by an electromagnet 40.

The electromagnet 40 is, for example, a Curie point electromagnet, which has a configuration in which a coil is wound around a rod-shaped Curie point magnetic material.

When a motor (not shown) serving as a drive unit is rotated, the nut 38 is rotated via the screw shaft 39, thereby causing the extension tube 37 and the control rod 43 to move up and down together.

Note that a neutron shield 44 is arranged above the upper guide tube 33, and this neutron shield 44 is connected to the extension tube 37 via a bellows 45, whereby the reactor sodium atmosphere and the control rod drive mechanism upper mechanism are connected to each other. is being quarantined.

Further, an introduction pipe 46 of the same diameter for introducing a coolant is integrally connected to the lower end of the upper guide pipe 33.

This introduction pipe 46 is provided with a coolant outflow hole 47 arranged to surround the control rod 43, and inside this introduction pipe 46,
A plurality of measurement line supports 49 having an abbreviated cross section and facing each other are provided on the upper part of the fuel assembly 48 . A measurement line 50 is supported within the corner of the measurement line support 49, and a bimetal switch 51 is provided at the lower end portion of the inner surface of the measurement line support 49 close to the measurement line 50. The bimetal switch 51 is responsive to the temperature of the coolant and turns off when the temperature exceeds a set temperature, thereby releasing the power circuit to the electromagnet 40 via the measurement line 50 and demagnetizing it. Note that the upper end 49a of the measurement line support 49 is a blind plate to promote mixing with the low-temperature coolant flowing out from the control rod. Further, this measurement line support 49 also serves as protection from collision force caused by vertical movement of the control rod 43.

In the configuration of such an embodiment, during reactor operation,
A low temperature coolant 52 flows out from the control rod lower guide pipe 54, and a large amount of high temperature coolant 53 flows out from the fuel assembly lower guide pipe 55. The low-temperature coolant 52 and the high-temperature coolant 53 flow into the introduction pipe 46 and, when rising, contact the bimetal switch 51 provided at the lower end of the measurement line support 49.
It flows out from the outflow hole 47. At this time, under normal operating conditions, the temperature of the coolant 52 and 53 is lower than that of the bimetal switch 5.
The set temperature has not been reached to turn it off.

However, if the temperature of the coolant 52, 53 rises for some reason and exceeds the set temperature of the bimetal switch 51,
The bimetal switch 51 is activated and turned off, and the electromagnet 4
0 loses magnetic force. As a result, the control rod 43 is connected to the electromagnet 40.
It is separated from the reactor, inserted into the reactor core by gravity fall, and a reactor scram is performed.

Therefore, according to this embodiment, the low temperature coolant 52 flowing out from the control rod lower guide pipe 54 and the fuel assembly lower guide pipe 5
A large amount of high-temperature coolant 53 flowing out from the measuring line support 49 comes into contact with the bimetal switch 51 installed at the bottom of the measurement line support 49 immediately after flowing out, so that the scram response can be improved.

〔Effect of the invention〕

As described above, according to the nuclear reactor shutdown device according to the present invention,
A bimetal switch is installed to detect the temperature of the coolant flowing out from the control rod lower guide tube and the fuel rod lower guide tube at a suitable position, so any abnormal rise in coolant temperature can be promptly detected and magnetic flux loss of the electromagnet can be prevented. The control rods can be detached reliably and quickly, and the effects include improved responsiveness to abnormal temperature rises of the coolant and reliable reactor scram.

[Brief explanation of the drawing]

FIG. 1 is an overall sectional view showing an embodiment of a nuclear reactor shutdown device according to the present invention, FIG. 2 is an enlarged view of a part of FIG. 1,
3 is a sectional view taken along line mm in FIG. 2, FIG. 4 is an overall sectional view showing a conventional example, and FIG. 5 is an enlarged view of a part of FIG. 4. 33... Upper guide pipe, 36... Liquid sodium (coolant), 40... Electromagnet, 41... Core, 42...
・Control rod lower guide tube, 43... Control rod, 46... Introductory tube, 49... Measurement line support, 50... Measurement line,
51... Bimetal switch, 52.53... Coolant.

Claims (1)

[Claims] A vertically movable rod vertically introduced into the core of a nuclear reactor from above through an upper guide pipe; a fuel assembly lower guide pipe disposed coaxially at the lower end of the upper guide pipe; A control rod lower guide tube disposed coaxially inside the lower body guide tube, and a control rod lower guide tube provided inside the control rod lower guide tube so as to be movable up and down, the upper end of which is connected to the lower end of the rod via an electromagnet so as to be able to move toward and away from the control rod. In a reactor shutdown system, the electromagnet detects an increase in temperature of the low-temperature coolant flowing upward from the control rod lower guide tube and demagnetizes the control rod to detach the control rod. A nuclear reactor shutdown device characterized in that a bimetallic switch is disposed inside the lower end of the upper guide tube as a means for detecting an increase in temperature of the coolant.