JPH03243891A - Emergency reactor core shutdown mechanism - Google Patents

Abstract

PURPOSE:To improve the responsiveness, etc., by providing a reactor shutdown rod which has a storage chamber wherein a cooling material flows and a neutron absorber holding means whose lower end is opened, and making the cooling material flow out above abnormal temperature and floating the neutron absorber holding means. CONSTITUTION:A reactor stop rod trumpet tube 8 as the outer jacket of a back-up reactor shutdown rod forms the same hexagon with a reactor fuel assembly which is arranged at the periphery. The storage chamber 9 which is partitioned with a partition wall 10 with a communication hole 12, where liquid sodium as the cooling material runs, and a bottom plate 11 is provided at the lower part. The flow rate loss of the cooling material 13 is caused and the temperature of inert gas 7 in an internal cylinder 1 rises owing to the temperature rise of the cooling material, so that the gas expands. The cooling material 13 below the space of the gas 7 receives downward pressure and exits the internal cylinder 1 from the lower part to rise in the trumpet tube 8 to enter an upper plenum 14 from the communication hole 12. Consequently, the internal cylinder 1 becomes light and rises in the storage chamber 9. At this time, the neutron absorber 3 fitted to the lower part of the internal cylinder 1 moves to a reactor core fuel area 20 and absorbs neutrons to suppress the abnormal temperature rise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an emergency core shutdown mechanism of an abnormal temperature self-detection type that shuts down the core of a fast breeder reactor in an emergency.

[Conventional technology]

Conventionally, in fast breeder reactors, control rods are used to start, stop, and control the output of the reactor. The control rod has an adjustment rod and a backup reactor shutdown rod.The adjustment rod performs normal startup, shutdown, and output control, and in the event of an emergency shutdown, an emergency reactor shutdown system consisting of a system consisting of the adjustment rod and a system consisting of the backup reactor shutdown rod is activated. Working simultaneously, neutron absorbers are installed in the core fuel region to shut down the reactor.

FIG. 4 is an explanatory diagram of a nuclear reactor core in a conventional emergency core shutdown mechanism using backup reactor shutdown rods. In the figure, 20 is a core fuel region and 21 is a backup reactor shutdown rod.

As shown in the figure, a backup reactor shutdown rod 21 with a built-in neutron absorber is suspended above the core fuel region 20 by a control rod drive device (not shown), and an abnormal temperature rise in the core fuel region 20 is prevented. When this occurs, the backup reactor shutdown frame is disconnected from the control rod drive device and loaded into the core fuel region 20, decelerating and absorbing surrounding neutrons, suppressing the temperature rise in the core fuel region 20, and shutting down the reactor. stop immediately.

In this case, an electromagnetic clutch using an electromagnet or a permanent magnet having a cue temperature is used to hold the back-up reactor shutdown frame 21 in the control rod drive device, and the electromagnet is demagnetized by an emergency stop signal, or The permanent magnet is changed into a non-magnetic material due to an abnormal temperature rise exceeding the coolant temperature point, and the holding of the standby reactor shutdown frame 21 is released.

[Problem to be solved by the invention]

Conventionally, in order to stop a nuclear reactor in an emergency, a removable back-up reactor shutdown frame was attached to the control rod drive device.1. A back-up reactor shutdown frame containing a built-in neutron absorber is loaded into the core fuel area in response to an abnormal temperature rise or an emergency shutdown signal due to an abnormal temperature rise.

For those that hold the back-up reactor shutdown frame with an electromagnetic clutch, there is a need to maintain the soundness of measurement and control equipment during reactor operation and to prevent artificial inoperation, and it is necessary to use permanent magnets with a certain temperature. Those that retain the magnetic material have the disadvantage that it takes time to become non-magnetic and the responsiveness is poor.

Furthermore, the standby reactor shutdown frame, which is suspended from the control rod drive, is subject to lateral sway and may become disconnected from its connections, potentially resulting in malfunction.

The present invention is intended to solve the above problems, and has excellent reliability, coordination, and earthquake resistance, reduces the scale of measurement and control equipment related to emergency core shutdown, improves reliability, and reduces manufacturing and construction costs. The purpose is to provide an emergency reactor shutdown mechanism that can reduce the

[Means to solve the problem]

To this end, the emergency reactor shutdown mechanism of the present invention includes a reactor shutdown rod that has a storage chamber at its lower end into which coolant can flow, and an open lower end that is disposed within the storage chamber and contains an inert gas that holds a neutron absorber. A neutron absorber holding means is provided, and the coolant in the neutron absorber holding means is caused to flow out due to the expansion of the inert gas due to an abnormal temperature rise, and the neutron absorber holding means is levitated to move the neutron absorber into the reactor core fuel region. It is characterized by being moved.

[Effect]

In the emergency core shutdown mechanism of the present invention, an inert gas is placed in an inner cylinder that holds a neutron absorber such as boron in a storage chamber into which coolant can flow. This system pushes out the coolant inside the cylinder and uses the resulting levitation of the inner cylinder to move the neutron absorber to the core fuel area and shut down the reactor, making use of the physical phenomenon of thermal expansion of the gas space due to temperature rise. Therefore, the design becomes easier, and it becomes possible to diversify reactor shutdown methods and improve reliability and responsiveness.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a side view showing one embodiment of the emergency core shutdown mechanism according to the present invention, and FIGS. 2 and 3 are AA of FIG. 1, respectively.
' cross section and BB' cross section, 1 is an inner cylinder, 2 is a column, 3 is a neutron absorber, 4 is a storage container, 5 is a support rod, 6
is the lid, 7 is the inert gas, 8 is the reactor stop rod wrapper tube, 9 is the storage chamber, 1o is the bulkhead, 11 is the bottom plate, 12 is the circulation hole, 13 is the coolant, 14 is the upper blemish, 15 is the reactor core fuel assembly It is the body.

In the figure, the reactor shutdown rod wrapper tube 8 forming the exterior of the backup reactor shutdown frame has a hexagonal outer shape that is the same as the core fuel assembly 15 disposed around it. The lower part has one or more flow holes 1 through which liquid as a coolant 13 passes.
A storage chamber 9 is provided which is partitioned by a partition wall 1o and a bottom plate 11.

The partition wall 10 is attached at a position as will be described later.

The cylindrical inner cylinder 1 is longer than the core fuel area 2o so that it can move freely up and down into the storage chamber 9, and is provided with a lid 6 to create an airtight structure. Three fixed hollow columns 2 protrude and can be stably placed on the bottom plate 11. In addition, the inner cylinder 1
A hollow storage container 4 containing a neutron absorber 3 such as boron or hafnium is attached to the column 2 by a support rod 5 at the lower end thereof. Further, each of the above-mentioned components is made of stainless steel.

The partition wall 10 is located at a position such that when the inner cylinder 1 moves upward and the lid 6 comes into contact with it, the storage container 4 is at a height approximately at the center of the core fuel region 20, and the distance from the lid 6 is such that the storage container 4 is at a height approximately at the center of the core fuel region 20. It is provided at a position approximately equal to 1/2 of the height of the core fuel region 20.

This back-up reactor shutdown rod will be manufactured at a separate location. The method is to first create a vacuum inside the stop rod trumpet tube 8, insert an inert gas supply hose (not shown) through the flow hole 12 of the partition wall IO, and then pour the coolant liquid from above.
When sodium is added, the inside of the inner cylinder 1 is also filled with liquid sodium. When inert gas is supplied in this state, the upper part of the inner cylinder 1 is filled with the gas. Then, if you remove the hose, the IJum will cool and solidify. If the furnace is loaded with a reactor stop rod containing solidified sodium, the IJium will melt and become operational.

In the operating state, the neutron absorber 3 is located outside the core fuel region 20, and allows the reactor to operate normally without decelerating or absorbing neutrons from the core fuel assembly 15 around the reactor shutdown rod trumpet tube 8. I can do it.

If the amount of inert gas 7 is adjusted so that when the coolant 13 reaches an abnormal temperature, for example, 600°C, the inner cylinder 1 will rise inside the reactor shutdown ring wrapper tube 8 due to the buoyancy caused by the expansion of the inert gas. During normal operation, the upper plenum 14 of the reactor stop rod trumpet tube 8
When the temperature of the storage container 3, that is, the neutron absorber 3
is below the core fuel region 20. However, if a loss of coolant flow occurs due to an abnormality in the primary main circulation pump, etc., the temperature of the coolant at the core outlet will rise abnormally, causing the core fuel assembly 15 around the reactor shutdown rod pumper pipe 8 to Due to heat transfer from
The temperature of the inert gas 7 in the inner cylinder 1 rises and expands. As a result, inert gas? The coolant 13 under the space is subjected to downward pressure and comes out from the lower part of the inner cylinder l, rises inside the reactor shutdown rod damper pipe 8, and comes out from the circulation hole 12 into the upper plenum 14.) <. Therefore, the inner cylinder 1 is light and has a storage compartment 9.
rise within. At this time, the neutron absorber 3 in the storage container 4 attached to the lower part of the inner cylinder l moves to the core fuel region 20, absorbs neutrons, suppresses abnormal temperature rise, and shuts down the reactor. In this case, a rough calculation that ignores the buoyancy of sodium, the weight of boron, the weight of the hollow support, and the buoyancy with respect to the weight of the inner cylinder shows that if the thickness of the inner cylinder is approximately 0.05 cm and the density is 10 g/Crl, then the weight of the inner cylinder is is approximately 3 kg, and the height of the gas column required to levitate this inner cylinder is approximately 4 kg.
It is 5cm. In addition, the inner cylinder 1 may be a long cylinder having one or more circulation holes for the coolant 13 at the bottom without supporting the bottom plate 11 with the struts 2, and may be placed directly on the bottom plate 11.
It may also have a polygonal shape. Needless to say, this emergency reactor shutdown mechanism is reusable.

〔Effect of the invention〕

As described above, according to the present invention, when an abnormal temperature occurs, an emergency shutdown of the reactor is performed due to the physical phenomenon of thermal expansion of the inert gas due to the temperature rise of the coolant at the core exit, but only the temperature change at the core exit pressure in the reactor due to damage to the primary main circulation system, including failure of the primary main circulation pump, such as pressure changes in the upper plenum, such as high pressure when the main circulation pump is operating and low pressure when it is stopped. It has the effect of providing an immediate response even when the temperature decreases.

In addition, since it is a self-detection type, it can improve safety and reliability without causing malfunctions due to abnormalities in measurement and control equipment or human causes. Therefore, it is possible to improve earthquake resistance.

[Brief explanation of drawings]

FIG. 1 is a side view showing one embodiment of the emergency core shutdown mechanism according to the present invention, and FIGS. 2 and 3 are AA of FIG. 1, respectively.
FIG. 4 is an explanatory diagram of a nuclear reactor core part of an emergency core shutdown mechanism using a conventional back-up reactor shutdown rod. 1... Inner cylinder, 2... Support column, 3... Neutron absorber,
4...Storage container, 5...Support rod, 7...Inert gas, 8...Furnace stop rod trumpet tube, 9...Storage chamber, 13
...Coolant, 15...Core fuel assembly, 20...
Core fuel area, 21...Backup reactor shutdown rod.

Claims (4)

[Claims] (1) A reactor shutdown rod that has a storage chamber at its lower end into which coolant can flow, and a neutron absorber holding means that is open at the lower end and contains an inert gas that holds the neutron absorber and is placed inside the storage chamber. In case of an emergency, the coolant inside the neutron absorber holding means is caused to flow out due to the expansion of inert gas due to an abnormal temperature rise, the neutron absorber holding means is levitated, and the neutron absorber is moved to the core fuel area. Core shutdown mechanism. (2) The emergency core shutdown mechanism according to claim 1, wherein the neutron absorber holding means comprises a cylindrical body with an open bottom end. (3) The emergency core shutdown mechanism according to claim 1, wherein the neutron absorber holding means is supported by a support on the bottom plate of the stop rod. (4) The emergency core shutdown mechanism according to claim 1, wherein the upper partition wall forming the storage chamber has coolant flow holes.