JP2656337B2 - Reactor shutdown device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a reactor shut-down device for a fast breeder reactor, and particularly to a system for automatically controlling a reactor when a normal control rod does not operate. The present invention relates to an externally installed reactor shutdown device suitable for shutdown.

(Prior art) In a fast breeder reactor using liquid sodium as a coolant, the nuclear reaction is controlled by controlling the nuclear fuel output of the core and absorbing neutrons in the reactor when the reactor operation is in a transient state. An emergency stop operation is performed, and a control rod is used for these operations.

This control rod is composed of a plurality of absorption pins implanted in a trumpet tube whose upper and lower ends are supported by a lattice plate,
A grip portion is formed on the upper part of the trumpet tube. This control rod is inserted into or pulled out of the core region to change the amount of neutron absorption to control the nuclear reaction of the reactor. When the operation state of the reactor becomes transient, a control rod is rapidly inserted into the reactor core to stop the nuclear reaction. The quick insertion operation is performed by a control rod drive mechanism and gravity drop.

Conventionally, various types of control rod drive mechanisms and reactor shutdown devices have been proposed. Above all, the method of connecting the control rods by magnetically attracting them directly with a magnet is considered to be more advantageous than other types because of the structural simplicity and the fact that no mechanical operation is required in the contact / separation operation. Have been.

FIG. 4 shows a conventional reactor shutdown device of the coupling type using this magnet.

In the drawings, reference numeral 41 denotes a long cylindrical upper guide tube, in which an extension tube 42 is provided movably in the axial direction. At the lower end of this extension tube 42,
A Curie point electromagnet 43 in which a coil is wound around a bar-shaped Curie point magnet is provided. This Curie point electromagnet 43
Is always adsorbed to the magnetic material at the upper end of the control rod 44 provided with the neutron absorbing material. On the other hand, at the lower end of the upper guide tube 41,
A cylindrical introduction pipe 46 having two outflow holes 45 at a certain angle in the circumferential direction at the top is connected and fixed. A fuel assembly lower guide pipe 48 and a control rod lower guide pipe 47 are provided in a core 49 below the introduction pipe 46. A coolant 51 flows upward in the control rod lower guide tube 47, and a coolant 52 flows upward in the fuel assembly lower guide tube 48.

The introduction pipe 46 has a structure in which the coolant flowing out from the area of the control rods 44 and the six fuel assemblies surrounded by the fuel assembly lower guide pipe 48 around the control rods 44 is guided to the Curie point electromagnet 43. I have. In the introduction pipe 46, a thermocouple 53 for measuring the outlet temperature of the high-temperature coolant 52 flowing out of each fuel assembly, and a corresponding number of the thermocouples 53 in the introduction pipe 46, and Measurement line porous support 54
Is installed. On both sides of the measurement line porous support 54, a large number of outflow holes 55 arranged in a plurality of rows are provided so that the high-temperature coolant 52 from the core fuel assembly flowing out from the lower portion of the support 54 flows out efficiently. I have.

The upper portion of the measurement line porous support 54 is formed as a blind plate 56 in order to mix with the low-temperature coolant 51 from the control rod assembly. The support 54 has a structure that also protects the control rod 44 from a collision force against the vertical movement.

According to the conventional reactor shutdown device having such a configuration, the control rod lower guide tube 47 and the fuel assembly lower guide tube 48
Sodium coolant 51 and coolant 52 are
Mix within 46. Then, the liquid further rises while mixing, and flows out of the introduction pipe 46 via the outflow hole 45.

On the other hand, when the coolants 51 and 52 abnormally increase in temperature and reach the Curie temperature which is the set value of the Curie point electromagnet 43, the Curie point electromagnet 43 loses magnetism. By this action, the attraction force of the control rods 44 disappears, and the control rods 44 are automatically inserted into the core and dropped to perform scram.

(Problems to be Solved by the Invention) In the conventional reactor shutdown device, the coolant 52 flowing out of the fuel assembly lower guide pipe 48 (normally at an outlet temperature of 500 to 5) is used.
50 ° C) and the coolant 51 flowing out of the control rod lower guide tube 47
(Usually outlet temperature 400 ° C)
In the lower part of the low-temperature coolant 51,
The flow is approaching the 52 side.

However, from the vicinity of the intermediate portion of the introduction pipe 46, the low-temperature and high-temperature coolants 51 and 52 flow as a mixed flow to the upper part of the introduction pipe 46, and flow out of the outflow hole 45 to the outside. A part of the mixed coolant becomes a stagnant or reversed flow at the upper part of the introduction pipe 46.
In particular, in the angular direction where there is no outflow hole 45, the flow velocity is slower than in the side where there is the outflow hole 45, and as a result, the flow has a temperature distribution that varies in the circumferential direction of the Curie point electromagnet 43. In the case of such a flow having a variation in the temperature distribution, when the coolants 51 and 52 abnormally rise in temperature, the Curie point electromagnet 43 reaches the Curie point and cuts off the magnetic flux for a considerable time. And there is a problem that the scrum response is not sufficient.

Therefore, in order to mix the low-temperature coolant 51 and the high-temperature coolant 52 by swirling flow, a method of installing a plurality of guide vanes on the support 54 has been proposed, but the guide vanes are arranged in a fluid. Therefore, not only the flow resistance increases, but also the flow force vibration of the guide blade becomes a problem, which is not practical.

The present invention has been made in consideration of such points,
It is an object of the present invention to provide a reactor shutdown device which has good responsiveness to an abnormal temperature rise of a coolant and can quickly and surely scram a reactor.

[Configuration of the invention]

(Means for Solving the Problems) According to the present invention, as a means for achieving the above object, a cylindrical upper guide tube whose lower end is immersed in a sodium coolant, and fixed to a lower end portion of the upper guide tube. An inlet pipe, two outlet holes provided at a top end of the inlet pipe at a predetermined angle in a circumferential direction, and a high-temperature coolant flowing through the upper guide pipe and the inlet pipe and flowing out of each fuel assembly A thermocouple for measuring the outlet temperature, a measurement line perforated support that is installed in the introduction pipe corresponding to the thermocouple and functions as a flow stopper without obstructing the flow of the coolant, and the upper guide pipe and the introduction pipe. An extension pipe internally disposed movably in the axial direction, a Curie point electromagnet fixed to a lower end of the extension pipe, a control rod having an upper end magnetically attached to the Curie point electromagnet, and the introduction pipe Control rod provided on the outer periphery of the lower control rod A reactor shutdown device including a lower guide tube and a fuel assembly lower guide tube provided on an outer peripheral portion of the control rod lower guide tube,
The inlet pipe has an umbrella shape having a top connected to a position connecting the upper ends of the two outlet holes, and a guide plate for guiding the coolant that has risen in the inlet pipe to each outlet hole is provided. I do.

(Operation) In the reactor shutdown device according to the present invention, a low-temperature coolant flows from the lower control pipe of the control rod, and a large amount of high-temperature coolant flows from the lower guide pipe of the fuel assembly into the lower part of the inlet pipe and mix. Is done. The mixed coolant flows in the introduction pipe as an ascending flow.

By the way, in the introduction pipe, an umbrella-shaped guide plate having a top connected to a position connecting the upper ends of both outflow holes is provided, so that the coolant rising in the introduction pipe may stay in the introduction pipe. Instead, it is smoothly guided to each outlet and discharged to the outside. Therefore, there is no coolant stagnation area around the Curie point electromagnet, and therefore, the temperature distribution around the Curie point electromagnet becomes uniform. Therefore, if the coolant temperature rises to the Curie point for some reason, the Curie point electromagnet loses magnetic flux in a short time, the control rod is quickly disconnected from the extension pipe, and scram is performed. .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a reactor shutdown device according to the present invention. In the figure, reference numeral 1 denotes a shielding plug, and the shielding plug 1 closes an upper opening of a reactor vessel (not shown). ing.

A long tubular upper guide tube 3 is inserted into a through hole 2 provided in the shield plug 1, and is fixed to the shield plug 1 by a flange portion 4 provided in the upper guide tube 3. The upper part of the upper guide tube 3 is connected to a housing 5 as shown in FIG. 1, and a motor (not shown) is mounted on the top of the housing 5. On the other hand, as shown in FIGS. 1 and 2, the lower part of the upper guide tube 3 is immersed in liquid sodium 6 which is a coolant of a nuclear reactor.

As shown in FIG. 1, an extension pipe 7 is inserted and arranged inside the upper guide pipe 3 so as to be movable in the axial direction, and a nut 8 is fixedly mounted on the upper part of the extension pipe 7. The nut 8 is screwed into a motor-driven screw shaft 9.

As shown in FIGS. 1 and 2, a Curie point electromagnet 10 is provided at the lower end of the extension tube 7, and the upper end of a control rod 13 described later is magnetically attached to the Curie point electromagnet 10. And is driven by an extension tube 7.
That is, by activating the motor of the drive unit, the screw shaft 9 rotates, and the nut 8, the extension pipe 7, and the control rod
13 move up and down as one. As shown in FIG. 1, the control rod 13 is inserted into the control rod lower guide tube 12 implanted in the core 11 so as to be movable in the axial direction.

A neutron shield 14 is installed on the upper part of the upper guide tube 3 as shown in FIG. 1. The neutron shield 14 and the extension pipe 7 are connected by a bellows 15 and are connected to the reactor sodium atmosphere. The control rod drive mechanism is separated from the upper mechanism.

1 and FIG.
As shown in the drawings, a tubular introduction pipe 16 is connected, and an upper end of the introduction pipe 16 has a predetermined angle in a circumferential direction as shown in FIGS. 1 to 3. Two outflow holes
17 are provided respectively.

Also, the second inside of the upper guide tube 3 and the introduction tube 16
As shown in the figure, a measurement line 18 composed of a thermocouple for measuring the outlet temperature of the high-temperature coolant flowing out of the fuel assembly is arranged so as to surround the extension pipe 7 and the control rod 13,
An L-shaped measurement line support 19 that supports the measurement line 18 at the inner corner portion is provided inside the introduction pipe 16.
There are 18 anti-skids. As shown in FIG. 2, a large number of outflow holes 20 are formed on both sides of the measurement line support 19 so as not to hinder the flow of the coolant. A blind plate 21 for promoting the mixing of the two is integrally provided.

As shown in FIGS. 1 and 2, a guide plate 22 is provided inside the upper end of the introduction pipe 16 for smoothly guiding the coolant rising in the introduction pipe 16 to the outflow hole 17. ing.

This guide plate 22, as shown in FIGS. 2 and 3,
In order not to hinder the vertical movement of the extension pipe 7 and the control rod 13, it has a donut disk shape having a hole at the center, and the plate surface is connected to the top of the two outflow holes 17 by the top. It has an umbrella shape. The coolant that has risen in the introduction pipe 16 flows along the lower surface of the umbrella-shaped guide plate 22, is smoothly guided to the outflow holes 17, and is discharged to the outside.

On the other hand, the core 11 below the inlet pipe 16 is
As shown in the figure, a cylindrical control rod lower guide tube 12 is provided, and on the outer peripheral portion of the control rod lower guide tube 12,
A fuel assembly lower guide tube 24 is provided. And, in these two guide tubes 12, 24, a coolant 25, of liquid sodium,
26 flows upwards.

 Next, the operation of the present embodiment will be described.

A low-temperature coolant 25 flows out of the control rod lower guide tube 12, and a large amount of high-temperature coolant 26 flows out of the fuel assembly lower guide tube 24. These two coolants 25 and 26 are mixed and flow into the introduction pipe 16 and rise in the introduction pipe 16. Eventually, it flows out of both outflow holes 17 to the outside.

An umbrella-shaped guide plate 22 is arranged inside the upper end of the introduction pipe 16. Therefore, the coolants 25 and 26 that have risen in the introduction pipe 16 are smoothly guided along the lower surface of the guide plate 22 to the top 23 without stagnating in the introduction pipe 16 or generating a reverse flow. It is discharged to the outside through the outflow hole 17. That is, the high-low mixed coolant 2 entering the introduction pipe 16
5 and 26 flow in the introduction pipe 16 in a layered manner and
It flows smoothly around and flows out from both outflow holes 17 to the outside as it is.

Here, under normal operating conditions, the coolant 25, 26
Does not reach the Curie point of the Curie point electromagnet 10, and therefore, the upper end of the control rod 13 is magnetically attached to the Curie point electromagnet 10.

On the other hand, the temperature of the coolant 25, 26 rises for some reason,
When the Curie point electromagnet 10 reaches the Curie point, the magnetism of the Curie point electromagnet 10 is lost and the magnetic force is lost. As a result, the control rod 13 is separated from the Curie point electromagnet 10, is inserted into the core 11 by gravity, and scram is performed. At this time, the coolant 25, 26 around the Curie point electromagnet 10 is provided by the guide plate 22.
Since the temperature distribution is uniform without variation, the time until the Curie point electromagnet 10 reaches the Curie point and the magnetic flux is cut off is shortened, and the scrum response can be improved.

〔The invention's effect〕

As described above, according to the present invention, an umbrella-shaped guide plate having a top portion at a position connecting the upper ends of both outflow holes is provided in the introduction pipe, and the cooling material that has risen in the introduction pipe is subjected to both guide plates by this guide plate. Since it is guided smoothly to the outflow hole and allowed to flow out, the flow of the coolant in the introduction pipe becomes laminar and the temperature distribution around the Curie point electromagnet does not fluctuate,
The temperature of the coolant in the inlet pipe can be made uniform. Therefore, the scrum response can be improved, and the reliability of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a reactor shutdown device showing one embodiment of the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 is II in FIG.
FIG. 4 is a cross-sectional view taken along the line I-III, and FIG. 4 is a cross-sectional view showing a conventional reactor shutdown device. 3 ... upper guide tube, 7 ... extension tube, 10 ... Curie point electromagnet, 11 ... core, 12 ... control rod lower guide tube, 13 ... control rod, 16 ... introduction pipe, 17 ... outflow Hole, 18 ... Measurement line, 19
…… Measurement line support, 22 …… Guide board, 23 …… Top, 24…
... fuel assembly lower guide tube, 25, 26 ... coolant.

Claims (1)

(57) [Claims] 1. A cylindrical upper guide tube having a lower end immersed in a sodium coolant, an inlet tube fixed to a lower end portion of the upper guide tube, and a predetermined angle in a circumferential direction at an upper end portion of the inlet tube. A thermocouple that is inserted into the upper guide pipe and the inlet pipe to measure the temperature of the high-temperature coolant outlet flowing out of each fuel assembly, and a thermocouple in the inlet pipe. A measurement line porous support that is installed as a work and functions as a steady rest for the flow of the coolant without obstructing the flow of the coolant, an extension pipe movably arranged in the axial direction inside the upper guide pipe and the introduction pipe, and A Curie point electromagnet fixed to the lower end of the extension pipe, a control rod whose upper end is magnetically attached to the Curie point electromagnet, and a control rod lower guide pipe provided on the outer periphery of the control rod below the introduction pipe. , A fuel rod provided on the outer peripheral portion of the control rod lower guide tube. In the reactor shutdown device including the assembly lower guide tube, the coolant flowing upward in the introduction tube is formed into an umbrella shape having a top connected to a position connecting the upper ends of the two outflow holes. A reactor shutdown device comprising a guide plate for guiding a hole.