JPH04250395A - Nuclear reactor shutdown device - Google Patents

Abstract

PURPOSE:To terminate the output of a reactor, and to suppress the output by automatically sending a neutron absorbing material to a reactor core when the temperature of the reactor is increased at the time of accident of the reactor. CONSTITUTION:When the output of a reactor is abnormally increased by some reasons, the temperature of a cooling material flown out from a fuel aggregate 33 is increased. The temperature of a heat sensitive plug 38 is immediately increased up to a melting point thereby, and a gas lead part 37 is opened, while the gas in a first container 34 is flown in the lead part 37 and is flown out into a second container 35, based on the pressure of the liquid column of a neutron absorbing material 42, and almost all of the absorbing material 42 is flown into the container 34 from the container 35, and the reactor can thus be stopped or the output is suppressed.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention relates to a nuclear reactor shutdown system, particularly a liquid metal cooled fast breeder reactor, which is capable of reliably shutting down a nuclear reactor or reliably reducing its output in the event of a reactor failure. Regarding reactor shutdown equipment.

0002

[Prior Art] Power control and reactor shutdown of nuclear reactors, particularly fast breeder reactors that use liquid metals such as sodium as coolants, are performed using control rods containing neutron-absorbing substances such as boron, which are installed in the core support plate. This is done by inserting it between multiple fuel assemblies. That is, control rod guide tubes are provided between the fuel assemblies with their axes parallel to these, and the control rods move up and down within these control rod guide tubes to control the reactivity of the reactor. The control rod drive device that drives each of the control rods described above is required to have stable operation and high reliability. In conventional fast breeder reactors, the control rod drive device is provided in the upper part of the reactor vessel that houses the reactor core.

[0003] The above-mentioned drive device includes a drive section fixed on a rotating plug provided on a shielding plug that closes an opening on the upper surface of the reactor vessel, and a drive section that connects the drive section and each control rod to extend through the rotating plug and extend above the reactor core area. It is equipped with a drive mechanism consisting of an extension tube that hangs down to the center, and this drive mechanism is controlled from a central control room to drive each control rod. The drive device also includes a control panel for issuing drive signals to the drive mechanism automatically or manually. Usually, the furnace output control and furnace shutdown by the drive unit are performed by electrical and mechanical means.

FIG. 7 is a schematic vertical sectional view of an example of a conventional control rod drive device. In this figure, the drive unit housing 1
is the upper guide pipe 3 hanging down from the rotating plug 2 into the furnace vessel.
are integrally combined with. A drive motor 4 is attached to the top of the drive unit housing 1, and the drive motor 4 is electrically connected to a control panel 6 via a cable 5. A ball screw 7 is concentrically connected to the output shaft of the drive motor 4, and a ball nut 8 is screwed onto the ball screw 7. This ball nut 8 has a disc 9,
It is connected to a hollow cylindrical body 11 via a load cell 10. An electromagnet 12 is housed in the hollow cylinder 11, and a small cylinder 12a fixed to the lower surface of the electromagnet is connected to the upper end of the outer extension tube 14 via a load cell 13. This outer extension tube 14 penetrates the rotary plug 2, projects into the reactor vessel, and hangs down to the vicinity of the upper end of a lower guide tube 16 provided in a reactor core 15 housed within the reactor vessel. An inner guide tube 17 is provided concentrically within the outer extension tube 14, and the lower end of the outer extension tube 14 and the lower end of a finger rod 18 connected to the lower end of the inner guide tube cooperate to form a latch mechanism. . In the figure, reference numeral 19 indicates a leaf spring-shaped latch finger formed at the lower end of the outer extension tube 14 to constitute the latch mechanism.

[0005] The electromagnet 12 is associated with a magnetically detachable armature 20, which is fixed to the top of the inner guide tube 17. Also,
A rotating plug 2 is provided between the upper guide tube 3 and the outer extension tube 14.
A biological shield 21 is fixedly provided at the top of the upper guide tube 3 at a position opposite to the upper guide tube 3 . Note that the outer extension tube 14
The appropriate axial position of the bellows 2 and the living body shield 21 are
2 is airtightly connected. In addition, the inner guide pipe 1
7 and the outer extension tube 14 are hermetically connected by bellows 23 at their appropriate positions.

An acceleration spring 25 is coupled to the stepped portion 24 of the outer extension tube 14 . This acceleration spring 25 is a coil spring that concentrically surrounds the outer extension tube 14, and its lower end is brought into contact with the head of the acceleration tube 26. The acceleration tube 26 concentrically surrounds the outer extension tube 14, and its lower end faces and abuts the handling head 28 of the control rod 27. Note that 29 in the figure indicates a damping spring supported by a stopper 30 provided at the lower part of the upper guide tube.

The conventional control rod drive device having the above structure operates as follows. That is, during normal operation of the nuclear reactor, the handling head 28 of the control rod 27 is engaged with the finger rod 18 and the latch finger 19, and the control rod 27 is connected to the outer extension tube 14. At this time,
Armature 20 is attracted by electromagnet 12. Further, the acceleration spring 25 has its upper end brought into contact with the stepped portion 24 of the outer extension tube 14, and its lower end brought into contact with the head of the acceleration tube 26 which is brought into contact with the handling head 28 of the control rod 27.
maintained in a compressed state. In such a state, a forward or reverse rotation signal is given to the drive motor 4 by human operation of the control panel 6 or a command from the automatic operation circuit inside the panel. For example, this forward or reverse rotation is converted into linear motion by the ball screw 7 and ball nut 8 and transmitted to the control rod 27, which can be moved up and down. This vertical movement allows the control rods 27 to be inserted into and removed from the reactor core 15, thereby adjusting the output during normal operation.

However, if an abnormal condition occurs in the plant for some reason, such as a decrease in coolant flow rate, a rise in coolant temperature, or an increase in core neutron flux, the sensor 31 placed inside the reactor vessel An abnormality is detected, and the detection output is transmitted to the control panel 6 via the cable 5a. The control panel 6 receives the detection output, automatically issues a scram command (operator's operation depending on the case) using a preset logic circuit, and stops energizing the electromagnet 12. When the electromagnet 12 is deenergized, the armature 20 is separated and falls by the distance from the plate-shaped portion 32 at the lower end of the small cylindrical body 12a. Along with this, the inner guide tube 17 falls entirely, so that the finger rod 18 also falls and the restraint on the latch finger 19 is released. Due to its elasticity, the latch finger 19 contracts inward and moves away from the handling head 28 of the control rod 27, and the control rod 27 receives the force of gravity acting on itself and the spring force of the acceleration spring 25 transmitted via the acceleration tube 26. As a result, the reactor core 1 rapidly falls through the lower guide tube 16.
5 will be rapidly inserted. This causes the reactor to scram.

[0009]

[Problems to be Solved by the Invention] Although the conventional control rod drive device with the above configuration has sufficient reliability and can be expected to operate stably and reliably, As nuclear power generation progresses and the number of installed nuclear reactors increases,
Even higher levels of safety are now required,
Consideration is being given to introducing a nuclear reactor shutdown device that operates by means other than the conventional devices described above.

The present invention has been made based on the above-mentioned circumstances, and in the conventional control rod drive device, if the mechanical deformation of the control rod, lower guide tube, extension tube, etc. exceeds a certain level, the control rod cannot be inserted. One of the objectives is to provide a nuclear reactor shutdown device that can function even when large mechanical deformations occur, taking into account the fact that smooth operation is not possible due to interference.

[0011] Furthermore, in consideration of the fact that in conventional control rod drive devices, if there is a failure in electrical components such as logic circuits or sensors in the control panel, the control rod drive device may not be able to start operation, Another object of the present invention is to provide a nuclear reactor shutdown device capable of shutting down a nuclear reactor even in the event of a major failure. [Structure of the invention]

0012

[Means for Solving the Problems] The nuclear reactor shutdown system of the present invention comprises a first container provided between fuel assemblies constituting a reactor core and filled with a liquid neutron absorbing material and gas; a second container provided outside the upper core region and communicated with the first container through a communication portion opening near the inner bottom surface of the first container and filled with a liquid neutron absorbing material and gas; An opening is opened in the gas space in the upper part of each of the two containers to communicate the first container and the second container, and a part of the opening is closed with a temperature-sensitive plug made of a metal that melts when the temperature inside the furnace exceeds a set value. It is characterized by having a gas conduction part.

[0013]

[Operation] In the nuclear reactor shutdown device of the present invention having the above configuration,
During normal reactor operation, due to the presence of inert gas inside the first vessel, there is only a small amount of neutron absorbing material at the bottom of the first vessel, and most of it is in the second vessel when the pressure is balanced. It is maintained.

[0014] When the temperature of the core rises abnormally for some reason, the temperature of the coolant also rises rapidly, and the temperature of the temperature-sensitive plug installed in the gas communication section immediately rises and melts, opening the gas communication section. . As a result, the pressure caused by the height of the liquid column of the neutron absorbing material causes the inert gas in the first container to be pushed out into the second container through the gas communication part, and the neutron absorbing material passes through the communication part into the first container. Flow in until it is filled. As described above, the temperature increase during a reactor failure automatically pumps a large amount of neutron absorbing material into the core region.

[0015]

[Embodiment] FIG. 1 is an enlarged vertical cross-sectional view of main parts of a first embodiment of the present invention in a normal operating state of a nuclear reactor, and FIG. 2 is a vertical cross-sectional view of the first embodiment when a reactor failure occurs. .

In these FIGS. 1 and 2, the core 15
Between the fuel assemblies 33 constituting the
A container 34 is provided, and a second container 35 containing a neutron absorbing material 42 is provided at the upper end of the container 34 . The first container 34 and the second container 35 are communicated with each other by a tubular communicating portion 36 that extends from the bottom of the second container 35 to near the bottom of the first container 34 . Furthermore, the second container 35
It hangs down from the upper side of the fuel assembly 33 and partially penetrates the inside of the second container 35 via the vicinity of the coolant outlet of the fuel assembly 33 to form the first container 3.
A gas conduction section 37 is connected to the upper surface of 4.

[0017] Of this gas conducting portion 37, the fuel assembly 33
A temperature-sensitive plug 38 made of a metal having an appropriate melting point of, for example, about 600° C. and whose details are shown in FIGS. 3 and 4 is provided near the coolant outlet. This temperature-sensitive plug 38 has a coolant outlet temperature of, for example, 500 during normal operation.
It becomes a solid at temperatures around 0.degree. C., and keeps the gas conducting portion 37 closed as shown in FIG. Also, 38a
38b is a heater, and 38b is a thermocouple, which are provided for testing the function of the temperature-sensitive plug 38 by heating it. In addition,
The first container 34 is generally located within the region of the reactor core 15, and the second container 35 is disposed above the reactor core 15.

As shown in FIG. 1, a tube body 39 is integrally disposed below the first container 34, and the lower end of the tube body 39 is supported by a core support plate 40. Also, the first container 35
passes through the shielding plug 49 and is coupled to the support member 41 fixed thereto. A thermal expansion absorption mechanism 50 is disposed on this support member 41.

Further, the first and second containers 34 and 35 have a shielding plug 49 inserted therein.
, 35 is provided with a liquid level detector 43 for detecting the liquid level of the neutron absorbing material 42 within the neutron absorbing material 42 . Note that the neutron absorbing material 42
As the liquid level detector 4, a neutron absorbing material with a melting point of 200 °C or less, such as lithium or indium, is used.
For No. 3, an inductive type that allows continuous measurement is recommended. In addition, the material for the temperature-sensitive plug 38 has a melting point of 550 to 600.
Various alloys with a temperature of around 30°F are suitable, and candidates include various brazing materials (silver solder). In this embodiment, a pipe 44 is provided so that the internal pressure of the second container 35 can be controlled from the outside, and is connected to a gas pressure control device 45.

[0020] If the coolant flow rate decreases during reactor operation due to some reason, such as a failure of the circulation pump, or if the reactor output increases abnormally, the coolant flowing out from the fuel assembly 33 temperature increases. For this reason,
The temperature of the temperature-sensitive plug 38 also rises immediately and reaches the melting point.
As shown in FIG. 4, the gas conduction section 37 is opened, and based on the pressure caused by the liquid column of the neutron absorbing material 42, the gas in the first container 34 flows through the gas conduction section 37 in the direction of the arrow in FIG. 2
At the same time, almost all of the neutron absorbing material 42 flows from the second container 35 into the first container 34, as shown in FIG.
The situation will be as shown in .

As described above, due to the temperature rise in the event of a reactor failure, a large amount of neutron absorbing material 42 is automatically fed into the region of the reactor core 15, making it possible to shut down the reactor or suppress the output, thereby allowing the reactor to continue operating. can be kept safe.

This embodiment also has another effect. That is,
When the temperature of the coolant flowing out from the fuel assembly 33 rises, the gas inside the gas conducting portion 37 expands, and subsequently the neutron absorbing material 42 also expands. As a result of these expansions, a portion of the neutron absorbing material flows into the first vessel 34 even before the temperature-sensitive plug 38 melts, making it possible to suppress the core output.

Note that the gas pressure control device 45 controls the first and second containers 3 of the neutron absorbing material 42 before and during reactor operation.
General equipment such as valves and pressure regulators are used to adjust the pressure inside the second container 35 as necessary in order to maintain a pressure equilibrium state that ensures appropriate distribution within the second container 35. It is not explained in detail because it consists of Furthermore, the soundness of the device can also be confirmed by manipulating the pressure in the same manner before starting the reactor and checking changes in the liquid level detected by the liquid level detector 41. Furthermore, by monitoring the liquid level during reactor operation, leakage of the neutron absorbing material can be detected and the health of the reactor can be confirmed. In addition, the first container 34 and the second container 35 of the embodiment are supported by the core support plate 40 by the pipe body 39, and their positions in the core region are stable, and the thermal expansion absorption mechanism 50 is provided. , so that its position does not change even if the temperature changes.

FIG. 5 is a longitudinal sectional view of the second embodiment of the present invention at the time of reactor failure. In this embodiment, the valve 46 disposed on the pipe 44 connected to the second container 35 is electrically controlled by the control panel 6, and various sensors 51 (not shown) control the flow rate and temperature. When an abnormality such as the above is detected, the logic circuit inside the control panel 6 is configured to open the valve 46. As a result, high pressure gas is sent into the second container 35 from a gas pressure supply source (not shown) through the valve 46, and the neutron absorbing material 42 is immediately
Most of the liquid flows into the first container 34, resulting in the state shown in FIG. In this case, such an operation is possible before the temperature-sensitive plug 38 melts, but in the unlikely event that the above operation cannot be performed due to a failure in the logic circuit or valve, the operation shown in the first embodiment may be performed. The purpose of reactor shutdown can be achieved by the operation based on the melting of the temperature-sensitive plug 38. Further, with such a configuration, it is also possible to use the device for output control during normal operation. In this way, in the second embodiment, it is possible to stop the nuclear reactor using a plurality of methods, and reliability can be improved.

FIG. 6 shows a third embodiment of the present invention. In this embodiment, a temperature-sensitive plug 52 is installed on the inner side surface of the second container 35. A coolant side outlet 47 is provided on the upper side of the adjacent fuel assembly 33, and the coolant flows through the temperature-sensitive plug 52 as shown by the arrow in the figure. is the same as the second embodiment. Furthermore, because of this action, the reactor shutdown device can be housed in a relatively narrow space, making installation, removal, and other handling easier. Since it can be placed closer to the core region than in the example, the temperature of the temperature-sensitive plug part rises more quickly in the event of a reactor failure, and the responsiveness of the reactor shutdown system can be improved.

[0026]

As is clear from the above explanation, in the reactor shutdown system of the present invention, when a reactor malfunctions, for example, the coolant flow rate decreases due to a malfunction of the circulation pump, etc.
If the temperature of the core increases due to an abnormal increase in the output of the core for some reason, the system automatically shuts down without any external operation or the operation of conventional electrical safety circuits. As neutron absorbing material is fed into the reactor core,
In the event of a nuclear reactor failure, the output of the reactor can be reliably stopped and suppressed. Furthermore, since it is possible to easily check whether the above-mentioned functions are sound or not, it is possible to provide a highly reliable nuclear reactor shutdown device. Furthermore, since it can be used in conjunction with a conventional control rod drive device, the nuclear reactor shutdown function in the event of a failure is provided twice, and the safety of the nuclear reactor can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a nuclear reactor shutdown device according to an embodiment of the present invention during normal operation.

FIG. 2 is a longitudinal sectional view showing the reactor shutdown device shown in FIG. 1 at the time of an accident.

FIG. 3 is an enlarged sectional view of the temperature-sensitive plug shown in FIG. 1.

FIG. 4 is an enlarged sectional view showing the operating state of the temperature-sensitive plug shown in FIG. 3 at the time of an accident.

FIG. 5 is a vertical sectional view showing the nuclear reactor shutdown device according to the second embodiment of the present invention at the time of an accident.

FIG. 6 is a vertical cross-sectional view showing a nuclear reactor shutdown device according to a third embodiment of the present invention during normal operation.

FIG. 7 is a vertical cross-sectional view showing a conventional example of a nuclear reactor shutdown device.

[Explanation of symbols]

33... Fuel assembly 34... First container
35...Second container 36...Communication part 37...Gas conduction part 38, 52...Temperature-sensitive plug 38a...Heater 38b...Thermocouple
42...Neutron absorber 51...Sensor

Claims (1)

[Claims] Claim 1: A first fuel cell provided between fuel assemblies constituting the reactor core and containing a liquid neutron absorbing material and a gas inside.
a second container, which is provided outside the core region above the first container, communicates with the first container through a communication portion that opens near the inner bottom surface of the first container, and seals a liquid neutron absorbing material and gas; , which opens into the gas space in the upper part of each of the first container and the second container, connects the first container and the second container, and has a part of the metal that melts when the temperature in the furnace rises above a set value. 1. A nuclear reactor shutdown device characterized by having a gas communication part closed with a temperature-sensitive plug using a thermosensitive plug.