JPS63289489A - Self-action type nuclear reactor control rod - Google Patents

Abstract

PURPOSE:To enable the scramming of a reactor even when the temperature of a coolant rises, in addition to the time when the flow rate thereof lower, by retaining a control rod having a coolant passage cut-off valve allowed to counter the lowering of the flow rate of the coolant by a magnetic force of an electromagnet. CONSTITUTION:When the flow rate of a coolant lower, a neutron absorbing substance 1 in a control rod 2 drops spontaneously therethrough with a decrease in the buoyancy of a pressure fluid and inserted into a core area 13 to scram a reactor. At this point, with the same action, a coolant passage cut-off valve 14 drops to cut off a coolant passage, which increases the dropping effect of the absorbing substance 1. On the other hand, as the temperature of the coolant rises to exceed a Curie point temperature of an electromagnet 11 provided at the lower end of a drive rod 10, the body of the control rod 2 drops toward a core area 13 overcoming the retaining by the magnetic force with a decrease therein. Here, as there is no change in the flow rate of the coolant, the cut-off valve 14 floats up and with the passage opened, the coolant flows to make buoyancy of the pressure fluid action the absorbing substance 1 so that substance 1 is held at an upper part in the control rod 2. Thus, the absorbing substance is located at a position corresponding to the core area 13 thereby enabling the scramming of the reactor.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control rod for a nuclear reactor, and in particular to a control rod of a self-actuating type suitable for safely and reliably shutting down a fast breeder reactor when an abnormality occurs in the reactor. Regarding reactor control rods.

[Conventional technology]

Backup control rods in fast reactors are inserted into the reactor core to stop the reactor when the main control rods cannot be inserted into the reactor core. Generally, when a detector detects an abnormal event in a reactor, it is converted into an electrical signal and transmitted to the control rod drive device, and when the drive device is activated, the control rod is gripped.

Insertion into the reactor core begins when the ripper releases the control rod. Furthermore, control rods are generally operated from about 10rn above the core. For this reason, failures in mechanical equipment that control gripper operation can cause serious accidents for reactors, so back-up control rods are designed to prevent spontaneous scrams from occurring during abnormal reactor events without being affected by mechanical equipment failures. It is required to have a self-actuating function.

In the past, many proposals have been made to improve backup control rods in consideration of the above requirements in order to respond to abnormal events that may lead to particularly serious accidents, such as coolant flow rate drop accidents and reactivity insertion accidents. For example, in the case of a coolant flow reduction accident, the coolant is used as a pressurized fluid, and the pressure change caused by the change in flow rate is used to move a roughly spherical neutron absorbing material divided into multiple pieces up and down in the control rod guide tube. One example is a differential pressure control rod. An example of its structure is shown in FIG.

In FIG. 5, the coolant (pressurized fluid) flowing from the entrance nozzle 4 flows from the bottom to the top inside the control rod guide tube 16 and flows out from the upper outlet 6. Inside the control rod guide tube 16, there are upper and lower perforated partition plates 17 and 18, and a plurality of spherical neutron absorbing substances 1 are housed between the partition plates 17 and 18.

The neutron absorbing material 1 used has a specific gravity larger than that of the coolant flowing inside the control rod guide tube 16. During reactor operation, the specific gravity of the neutron absorbing material 1 is reduced by the pressurizing action of the coolant flowing from the bottom. Because the buoyancy force acts more than that, as shown in Figure 5 (a
), it floats above the outside of the core region 13. on the other hand,
When an abnormality occurs or the reactor is shut down, the buoyancy of the coolant drops below a predetermined flow rate, and the neutron absorbing material 1 spontaneously falls into the core region 13 due to its own weight and is inserted, as shown in Figure 5(b).
Deposits as shown in . This causes the furnace to scram.

In addition, as this type of technology, for example, Japanese Patent Application Laid-Open No. 56-16
No. 2087 is mentioned.

[Problem that the invention seeks to solve]

Originally, backup control rods are not affected by mechanical equipment failures, and are used in emergency situations in place of main control rods in response to abnormal reactor events, especially when coolant temperature rises due to a drop in coolant flow rate or a reactivity insertion accident. Ability to perform Scrum is required. However, although the method of the above-mentioned conventional example can cope with an accident in which the coolant flow rate decreases, there is a problem in that it does not have a function to scram the furnace when the coolant temperature rises.

In order to solve this problem, an object of the present invention is to provide a self-actuating control rod that can scram the reactor not only when the coolant flow rate decreases but also when the coolant temperature rises as an abnormal event in the reactor. It is in.

[Means for solving problems]

The above purpose is to install a control rod using a fluid pressure differential system, which has a coolant flow path cutoff valve that floats with pressurized fluid to cope with a decrease in coolant flow rate, at the lower end of the drive rod extending from the control rod drive mechanism. By providing an electromagnet with a single temperature point and using this magnetic force to attract and hold the control rod and suspending it, it is possible to respond even when the coolant temperature rises, and the purpose is achieved.

In particular, the present invention has a structure in which the control rod body does not move when the coolant flow rate decreases, and only the built-in neutron absorbing material falls and moves inside the control rod, and the position where this material is deposited becomes the core region. be.

[Effect]

According to the configuration of the present invention, when the coolant flow rate decreases, due to the decrease in the buoyancy of the pressurized fluid, the neutron absorbing substance in the control rod overcomes the buoyancy of the pressurized fluid and spontaneously falls within the control rod and is inserted into the core region. , scram the furnace. At this time, the coolant flow path cutoff valve falls by the same action and blocks the coolant flow path, thereby increasing the effect of the neutron absorbing material falling. on the other hand,
When the coolant temperature rises to below the temperature of the cue of the electrode stone installed at the lower end of the drive rod, the magnetic force of the electromagnet decreases, making it impossible to attract and hold the control rod, causing the control rod body to fall toward the core area. . At this time, since there is no change in the coolant flow rate, the coolant flow cutoff valve floats up and the flow path is open, allowing the coolant to flow, and the buoyancy of the pressurized fluid continues to act on the neutron absorbing material. Therefore, it is held in the upper part of the control rod, and since this position corresponds to the core region, the reactor can be scrammed.

〔Example〕

Next, an embodiment of the self-actuating nuclear reactor control rod according to the present invention will be described.

FIG. 1 is a sectional view showing the configuration of one embodiment, and shows a case where the coolant is flowing at the rated flow rate. In Figure 1, a plurality of approximately spherical neutron absorbing materials 1 are built into the main body of the control rod 2, and are normally installed in a high-pressure plenum when coolant is flowing at the rated flow rate during reactor startup and operation. 3 through the entrance nozzle 4 and exits from the upper outlet 6 at the upper end of the lower guide tube 5. Due to the buoyancy of the coolant, the coolant floats in the upper part of the control rod 2 as a block. It goes without saying that the hole diameter of the coolant flow path flowing in and out of the control rod 2 is smaller than the spherical diameter of the neutron absorbing material 1.

The control rod 2 is provided with a connecting rod 7 that passes through the inside and extends upward. The connecting member 8 provided at the upper end is connected to the magnetic force (attractive force) of an electromagnet 11, which is provided at the lower end of a drive shaft 10 in an upper guide tube 9 extending from a control rod drive device (not shown) or the like, and has a single point at a certain arbitrary temperature. ) and is connected to the electromagnet 11, whereby the main body of the control rod 2 is lifted and held within the lower guide tube 5. At this time, the control rod 2 is in a position where the upper surface of the control rod 2 is in contact with the lower surface of the stopper 12 provided above inside the lower guide tube 5, as shown in FIG. The location of the mass of neutron absorbing material 1 is in the core region 13.
It is higher up. In addition, the connecting rod 7 is provided with a coolant flow path cutoff valve 14, which floats up due to the buoyancy of the coolant, as shown in FIG. If it is flowing, it floats above the stopper 12. As the material for the neutron absorbing substance 1, a substance having a large neutron absorption cross section and a specific gravity greater than that of the coolant, such as B2O (boron carbide), is recommended. Further, the control rod 2 and the coolant flow path shielding valve 14 are also made of a material that has a higher specific gravity than the coolant and is corrosion resistant to the coolant, such as stainless steel or Nilacel metal. Although not shown, the electromagnet 11 is excited by passing a current through a wire 15 from a power source such as a control rod drive device provided above the upper guide tube 9. The magnetic force (holding force) decreases when the flow of coolant decreases.
Alternatively, even if the control rod is stopped, the control rod 2 is adjusted so as to maintain the total weight of the control rod 2 which contains the neutron absorbing material 1 and is equipped with the connecting rod 7, the coolant flow cutoff valve 14, and the like. The connecting member 8 at the upper end of the connecting rod 7 is made of a material that is easily attracted to a magnet, such as a nickel metal, and the electromagnet 11 is made of an iron-nickel alloy.

That is, when the control rod 2 according to the present invention is not held by the electromagnet 11, its total weight is adjusted so that it overcomes the buoyancy and falls even when the coolant is flowing at the rated flow rate.

In the above configuration of the present invention, when the coolant is flowing at the rated flow rate, the heat generated in the core region 13 can be removed by the coolant without any problem.

However, when the coolant flow rate decreases, the present invention takes action as follows. That is, in FIG. 1 described above, when the coolant flow rate decreases, the buoyancy of the coolant decreases, and as a result, the neutron absorbing material 1 and the coolant flow path cutoff valve 14 overcome the buoyancy of the coolant and fall of their own accord. On the other hand, since the control rod 2 itself does not change the magnetic force of the electromagnet 11, it is held connected to the electromagnet 11 via the connecting member 8, and does not move at all. Therefore, the position where the neutron absorbing material 1 falls and accumulates is in the core region 13 as shown in FIG. 2, thereby making it possible to scram the reactor. In addition, the coolant flow cutoff valve 14 is connected to the stopper 12.
The neutron absorbing material 1 falls as if inserted into the reactor and blocks the flow of the coolant, thereby promoting the fall of the neutron absorbing material 1 and shortening the scram time of the reactor.

On the other hand, if the coolant temperature rises due to abnormal heat generation in the furnace, etc., the measures to be taken are as follows. In Figure 1 above,
When the coolant temperature rises, the temperature of the coolant at the upper outlet 6 of the lower guide pipe 5 rises, and this temperature exceeds the set Curie point temperature of the electromagnet 11 (generally around 600°C).
The magnetic force of the electromagnet 11 decreases rapidly. For this reason,
The electromagnet 11 is no longer able to attract and hold the entire control rod 2 connected to the connecting member 8 and below, and spontaneously separates it and causes it to fall. FIG. 3 shows the state after the fall, in which the control rod 2 has fallen to the lower end within the lower guide tube 5. In this case, as shown in FIG. 3, the connecting member 8 is adjusted so that the coolant flow cutoff valve 14 is pushed into the stopper 12 and stopped at a position where it is not inserted. For this reason, the coolant flow cutoff valve 14 floats due to the buoyancy of the coolant and is in a position where the coolant flow path is secured, so that the flow of the coolant is not changed at all. That is, neutron absorbing substance 1
The buoyant force of the cold electrode material remains unchanged as in the state shown in FIG. This position is located in the core area 1 as shown in Figure 3.
3, which allows the furnace to scram. In addition, since the flow of the coolant is ensured, the effect of cooling the furnace by the coolant is maintained, and cooling of the abnormally high temperature section can be promoted. The control rod 2 that has fallen to the lower end of the lower guide tube 5 pushes the drive rod 10 downward, and when the lower surface of the electromagnet 11 comes into contact with the upper surface of the connecting member 8, the electromagnet 11 is energized and the connecting member 8 , and then pull it out to the top and return it to the position shown in Figure 1.

In the above embodiment, the connecting rod 7 is inserted through the control rod 2 to the lower end thereof. This is aimed at increasing the mechanical strength of the control rod 2 as a whole and reducing the eccentricity of the control rod 2 on its axis. Alternatively, the connecting rod 7 may be joined at the upper end of the control rod 2 without penetrating the inside thereof. As a result, the amount of neutron absorbing material 1 contained in the control rod 2 can be increased.
When using this, the size of the control rod 2 body can be made more compact. Furthermore, the scram capability with one control rod can be increased.

The above description describes the case where the present invention is applied to a fast reactor that uses sodium as a coolant, but it goes without saying that the present invention can also be applied to a nuclear reactor that uses water or gas as a coolant. Although such embodiments have been described, it will be obvious that many modifications and changes may be made within the scope of the invention.

〔Effect of the invention〕

As explained above, according to the present invention, a control rod using a fluid pressure differential method is suctioned and held using an electromagnet having a single point at a certain temperature, and when the coolant flow rate decreases, a plurality of approximately spherical shapes in the control rod The neutron-absorbing material is caused to fall spontaneously by the buoyancy reduction effect of the coolant and is moved to the reactor core area, the reactor is scrammed, and when the coolant temperature rises, the holding force of the control rods is reduced using the spontaneous reduction of the magnetic force of the electromagnets. The action causes the rod to fall spontaneously and scram the reactor, and has the effect of being able to cope with the above-mentioned two abnormal events in the reactor, which were lacking in conventional fluid differential pressure control rods.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram of one implementation of a self-actuating nuclear reactor control rod according to the present invention, FIG. 2 is an explanatory diagram showing a state when the coolant flow rate decreases in the embodiment shown in FIG. 1, Figure 3 is an explanatory diagram showing the state when the coolant temperature rises,
FIG. 4 is a cross-sectional configuration diagram of another embodiment, and FIG. 5 is a cross-sectional configuration diagram of a conventional fluid differential pressure type self-actuating nuclear reactor shutdown rod. DESCRIPTION OF SYMBOLS 1... Neutron absorption material, 2... Control rod, 5... Lower guide tube, 7... Connection rod, 8... Connection member, 9...
・Upper guide tube, Figure 1, Figure 1, page 3, page 41, sEjJ

Claims (1)

[Claims] 1. In self-actuating reactor control rods, a fluid pressure differential method that levitates multiple approximately spherical neutron-absorbing materials deposited on the outer upper part of the core by the action of pressurized fluid flowing in from the bottom is also used.
A self-actuating nuclear reactor control rod characterized in that the nuclear control rod is held by the magnetic force of a magnetic material.