JPH01182795A - Nuclear reactor stopper - Google Patents

Abstract

PURPOSE:To achieve a higher scram responsiveness by providing an agitating means to mix a coolant which rises and flows into an introduction pipe from a control rod lower inner tube and a fuel rod lower guide tube. CONSTITUTION:A plurality of supports 18 are provided inside an introduction tube 16. An agitation blade 19 is fixed securely on each of the supports 18. Moreover, the blades 19 are so arranged in a spiral staircase as a whole by varying the height thereof for secure fixing. A cold coolant 24 flowing out of a control rod lower guide tube 20 and a large amount of hot coolant 23 flowing out of a fuel rod lower guide tube 21 are mixed with the blades 19 thoroughly in a spiral flow. Thus, a coolant in the uniform temperature state after the mixing can be made to flow and hit a Curie point electromagnet 10 thereby allowing a better scram responsiveness when an event requiring scram is induced with a rise in the temperature of the coolant for one reason or other.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor shutdown device for a fast breeder reactor, and in particular to a system for automatically shutting down a nuclear reactor when normal control rods do not operate. This invention relates to a nuclear reactor shutdown device suitable for

(Prior technology) In fast breeder reactors that use liquid sodium as a coolant, the output of nuclear fuel in the reactor core is controlled, and when reactor operation reaches a transient state, neutrons in the reactor are absorbed and reacted with nuclear reaction. Emergency stop operations are being carried out, and control rods are used for these operations.

This control rod is made up of a plurality of absorption pins installed in a trumpet tube whose upper and lower ends are supported by a lattice plate, and a gripping portion is formed at the top of the trumpet tube. These control rods are inserted into or withdrawn from the reactor core region to change the amount of neutron absorption and control the nuclear reactions in the reactor. When reactor operating conditions become transient, control rods are quickly inserted into the reactor core to stop the nuclear reaction. Rapid insertion is achieved by a nine control rod drive mechanism and gravity drop.

Conventionally, various types of control rod drive mechanisms and nuclear reactor shutdown devices have been proposed. Among these, we believe that a method of connecting control rods by directly magnetically attracting them with a magnet is more advantageous than other methods due to its simple structure and the fact that no mechanical action is required during the disconnection operation. is being received.

The 7th nuclear reactor shutdown device, which uses this magnet-based connection method,
As shown in the figure.

In the drawings, reference numeral 41 is a long cylindrical upper guide tube;
Inside this, an extension tube 42 is provided so as to be freely movable in the axial direction. Further, at the lower end of the extension tube 42, a Curie point electromagnet 43 is installed, which is a rod-shaped Curie point magnetic material with a coil wound around it. This Curie point electromagnet 4
3 is constantly attracted to the magnetic body at the upper end of the control rod 44 equipped with a neutron absorbing material. On the other hand, at the lower end of the upper guide pipe 41, a cylindrical introduction pipe 4 is provided with an outflow hole 45 at the upper part.
6 is connected and fixed. Further, in the core 49 below the introduction pipe 41, a fuel rod lower guide pipe 48 and a control rod lower guide pipe 47 are provided.

A coolant 50 flows upward in the fuel rod lower guide pipe 47, and a coolant 51 flows upward in the control rod lower guide rod 48.

According to the conventional nuclear reactor shutdown system having such a configuration, the sodium coolant 51 and the coolant 52 that have ascended through the lower fuel rod guide pipe 47 and the control rod guide pipe 48 are mixed in the introduction pipe 46 . Then, it rises further while mixing, and the outflow hole 4
5 and flows out of the introduction pipe 46.

On the other hand, when the temperature of the coolant 51, 52 rises abnormally and reaches the Curie temperature, which is the set value of the Curie point electromagnet 43, the Curie point electromagnet 43 loses its magnetism.

Due to this action, the adsorption force of the control rod 44 disappears, and the control rod 44 is automatically inserted and dropped into the reactor core, and a scram is performed.

(Problem to be Solved by the Invention) According to such a conventional nuclear reactor shutdown device, the coolant 51 flowing out from the fuel rod lower guide pipe 48 (normal outlet temperature 5
00 to 550° C.) is higher in temperature than the coolant 50 flowing out from the control rod lower guide tube 47 (usually outlet temperature 400° C.) and has a higher flow rate. Therefore, the static pressure of the coolant 51 decreases, and the flow of the coolant becomes closer to the high temperature coolant 51 side, and a laminar flow of low temperature and high temperature coolants exists at the upper part of the introduction pipe 46, and the two are mixed. is not done enough.

Further, a part of the mixed coolant hits the flow at the upper part of the introduction pipe 46 and after being reversed, flows back to the Curie point electromagnet 43. When the temperature of the coolant 50, 51 rises abnormally due to the flow of the coolant near the Curie point electromagnet 43, it takes a considerable amount of time for the Curie point electromagnet 43 to reach the Curie point and cut off the magnetic flux, resulting in a scram response. There was a point that there was not enough sex.

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

[Structure of the invention]

(Means for Solving the Problems) The nuclear reactor shutdown device of the present invention includes a cylindrical upper guide pipe, an inlet pipe provided with an outflow hole at the upper part, and fixedly installed at the lower end of the upper guide pipe. This upper guide tube and the introduction tube are provided with an extension tube movable in the axial direction, a Curie point electromagnet fixedly installed at the lower end of the extension tube, and a neutron absorbing material, the upper end of which is a Curie point electromagnet. A control rod made of a magnetic material that can be attracted and detached, a control rod lower guide tube provided around the control rod below the introduction tube, and a fuel rod lower guide tube provided around the control rod lower guide tube. The reactor shutdown device is characterized in that the introduction pipe is provided with a stirring means for mixing the coolant flowing out from the control rod lower guide pipe and the fuel rod lower guide pipe.

(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 large amount of low temperature and high temperature coolants are mixed by the stirring means inside the introduction pipe, and flow out from the outlet hole. Therefore, when the temperature is uniform, cooling (A) flows directly into the Curie point electromagnet.If the temperature of the coolant rises for some reason and reaches the Curie point, the Curie point electromagnet loses its magnetic flux and the control rod moves to the lower end of the extension tube. A scrum is held after leaving the group.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall schematic diagram of a first embodiment of the present invention.

In the drawings, reference numeral 1 denotes a shielding plug, which closes an upper opening of a reactor vessel (not shown). A long cylindrical upper guide tube 3 is inserted into a through hole 2 provided in the shielding plug 1, and further fixed to the plug 1 by a flange portion 4 provided on the upper guide tube 3. The upper part of the upper guide tube 3 is connected to the housing 5, and a motor (not shown) is mounted on the top of the housing 5. On the other hand, the lower part of the upper guide tube 3 is immersed in liquid sodium 6, which is the coolant of the nuclear reactor. Further, an extension tube 7 is inserted into the upper guide tube 3 so as to be movable in the axial direction, and a nut 8 is fixedly installed in the upper part of the extension tube 7, and this nut 8 is attached to a screw shaft 9 rotated by a motor. It's screwed in. In addition, a Curie point electromagnet 1 is attached to the lower end of the extension tube 7.
Furthermore, a control rod 13 that is movable in the axial direction is provided in the control rod lower guide tube 20 implanted in the core 11, and its upper end is connected to the Curie point electromagnet 1.
0 magnetically connected. Therefore, when the drive motor is rotated, the screw shaft 9 rotates and the nut 8,
The extension tube 7 and the control rod 13 move up and down together.

The neutron shielding body 14 installed above the upper guide tube 3 and the extension tube 7 are connected by a bellows 15 to isolate the reactor sodium atmosphere from the upper mechanism of the control rod drive mechanism.

Furthermore, the lower end of the upper guide tube 3 has an outflow hole 17 in the upper part.
An introduction tube 16 is provided.

Additionally, an extension pipe 7 and a control rod 13 are provided in this introduction pipe 16.
A stirring blade 19 is fixed to a support 18 provided around the .

FIG. 2 is a partial cross-sectional view of the vicinity of the Curie point electromagnet 10 according to this embodiment, FIG. 3 is a view from the ■-■ arrow direction, and FIG.
It is an IV-IV arrow expanded view in a figure. Upper guide tube 3
A cylindrical introduction pipe 16 is attached to the lower end of the tube, and an outflow hole 17 is provided at the upper end as a coolant outflow path. A plurality of supports 18 are provided inside this introduction tube 16. On one side of this support 18, an introduction pipe 1 is provided.
A plurality of rectifying holes 22 are provided in the axial direction through which the coolant flowing between the support 6 and the support 18 can flow out.

Furthermore, one L-shaped stirring blade made of an obtuse angle formed by two planes is fixed for each of the 181 support members with a part of the corner facing upward (so that it has an inverted shape). Further, the stirring blades 19 are arranged at different fixed heights so that the stirring blades 19 are arranged in a spiral step shape as a whole inside the introduction pipe 16.

On the other hand, in the core 11 below the introduction pipe 16, a cylindrical control rod lower guide tube 20 and a fuel rod lower guide tube 21 are arranged around it. A sodium coolant 24 and a coolant 23 are flowing upward in the control rod lower guide tube 20 and the fuel rod lower guide tube 21 .

According to such a first embodiment, the control rod lower guide tube 20
The low temperature coolant 24 flows out from the fuel rod lower guide pipe 21.
A large amount of high-temperature coolant 23 flows out. The low-temperature coolant 2″4 and the high-temperature coolant 23 flow into the introduction pipe 16,
When rising, the stirring blade 19 creates a swirling flow. By becoming this swirling flow and passing through the rectifying hole 22,
During the upward flow, the high temperature coolant 23 and the low temperature coolant 24 mix. The temperature is in the opposite direction, the flow hits the Curie point electromagnet 10, and flows out from the outflow hole 17.

At this time, under normal operating conditions, the temperature of the coolant after mixing has not reached the Curie point of the Curie point electromagnet 10. However, if the temperature of the coolant rises for some reason and reaches the Curie point, the Curie point electromagnet 10 loses its magnetism and loses its magnetic force. As a result, the control rod 13 is separated from the Curie point electromagnet 10 and inserted into the reactor core 11 by falling due to gravity, and a scram is performed.

According to the first embodiment, the control rod lower guide tube 20
Low-temperature coolant 24 flowing out from the control rod lower guide tube 21
A large amount of high temperature coolant 23 flowing out from the support material 1
A stirring blade 19 fixedly installed at 8 creates a swirling flow, and sufficient mixing can be achieved.

Therefore, the coolant having a uniform temperature after mixing can be applied to the Curie point electromagnet 10. For this reason, when the temperature of the coolant rises for some reason and an event that requires scramming occurs, the scram response can be improved.

Next, a second embodiment is shown in FIGS. 5 and 6. FIG. 5 is a sectional view of the second embodiment, and FIG. 6 is a partial perspective view thereof. In the drawings, reference numeral 31 is an introduction pipe similar to the first embodiment;
A control rod 32 is provided in the center thereof. A plurality of screw propeller-shaped stirring blades 33 are fixedly installed inside the introduction pipe 31 and around the control rod 32.
As a whole, they are arranged in a spiral staircase shape inside the introduction pipe 31. Furthermore, a hole 3 is provided at the tip of each stirring blade 33.
4 is provided, and a thermocouple 35 is inserted through this hole and supported.

As described above, according to the second embodiment, since the stirring blade 33 is directly fixed to the introduction pipe 31, unnecessary support material can be omitted. Therefore, the swirling effect of the coolant is improved, and the mixing ratio of the high-temperature coolant and the low-temperature coolant can be improved, so that the scram reactivity can be improved.

〔Effect of the invention〕

As described above, according to the present invention, the low-temperature coolant flowing out from the control rod lower guide tube does not flow directly to the Curie point electromagnet, but the high-temperature and low-temperature coolants swirl around the Curie point electromagnet and mix. You can hit the trail. Therefore, the time from when the temperature of the coolant abnormally rises to when the magnetic body reaches the Curie point and cuts off the magnetic flux can be made shorter than in the past. Further, by promoting the mixing of high and low temperature coolants, it is possible to eliminate temperature non-uniformity in the circumferential direction and axial direction of the Curie point electromagnet, and at the same time, improve elasticity. Because of this, the reliability of the nuclear reactor shutdown device can be increased.

[Brief explanation of the drawing]

Fig. 1 is an overall sectional view of the first embodiment of the present invention, Fig. 2 is a partially enlarged sectional view thereof, Fig. 3 is a view taken along the ■-■ arrow in Fig. FIG. 5 is a cross-sectional view showing a second embodiment of the present invention, FIG. 6 is a partial perspective view thereof, and FIG. 7 is a cross-sectional view of a conventional reactor shutdown device. . 3... Upper guide pipe, 6, 23.24... Coolant, 7
...Extension tube, 10...Curie point electromagnet, 11...
・Reactor core, 20... Control rod lower guide tube, 13.32...
・Control rod, 21...Fuel rod lower guide tube, 16.31・
...Introduction tube, 17... Outflow hole, 18... Support material, 19.33... Stirring blade. Applicant's agent Mr. Sato Figure 1! f) 2 Figure 5 Figure 6 Figure 6 S) Q) w

Claims (1)

[Claims] A cylindrical upper guide pipe partially filled with sodium coolant, an introduction pipe with an outflow hole provided at the upper part and fixedly installed at the lower end of the upper guide pipe, and an axial direction inside the upper guide pipe and the introduction pipe. An extension tube movably installed in the extension tube, a Curie point electromagnet fixed to the lower end of the extension tube, a neutron absorbing material, and an upper end made of a magnetic material capable of attracting and detaching from the Curie point electromagnet. In a nuclear reactor shutdown device comprising a control rod, a control rod lower guide tube provided around the control rod below the introduction tube, and a fuel rod lower guide tube provided around the control rod lower guide tube. , inside the introduction tube,
A nuclear reactor shutdown device characterized in that a stirring means is provided for mixing coolant flowing upward from the control rod lower guide tube and the fuel rod lower guide tube.