JPH068883B2 - Self-actuated control rod drive mechanism - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a self-actuated control rod drive mechanism for automatically inserting control rods into a core for emergency shutdown of a nuclear reactor when an abnormality occurs, and more particularly, In an electromagnet for suspending and holding a control rod, a temperature-sensing magnetic body forming a part of its magnetic circuit is installed directly above the fuel assembly.
The present invention relates to a self-actuated control rod drive mechanism in which the temperature of coolant from a fuel assembly can be directly sensed to improve the response of control rod disconnection.

[Prior Art] In order to improve the reliability of reactor shutdown, the reactor is equipped with control rods for power control, which are inserted into the core when an abnormality occurs. The control rod drive mechanism that drives them starts operating in response to an external scrum signal. Therefore, the reliability in an emergency depends on the external scrum signal generation mechanism, and the signal transmission path from the occurrence of abnormalities in the reactor to the scrum becomes complicated, so there was a problem in the reliability of the reactor shutdown.

Therefore, a self-actuated control rod drive mechanism has been proposed in which an electromagnet for magnetically attracting and holding the control rod is provided in the control rod drive mechanism, and a temperature sensing magnetic alloy is incorporated into at least a part of its magnetic circuit.

An example of such a self-actuated control rod drive mechanism is shown in FIG. The prior art is composed of an electromagnet 12 that magnetically attracts and holds the control rod 10, a motor 14 for vertically moving the electromagnet 12, a ball screw 16, a drive shaft 18, and the like. Details of the electromagnet 12 are as shown in FIGS. 7A and 7B. The electromagnet 12 includes a coil 20, an upper magnetic core 22 around which the coil 20 is wound and which has a flange portion, a temperature sensing magnetic body 24 hung downward from the outer periphery of the flange portion of the upper magnetic core 22, and the control rod 10. And a lower magnetic core 26 attached to the upper end of the.

During normal reactor operation, the control rod 1 magnetically attracted and held by the electromagnet 12 as shown in FIGS. 6 and 7A.
0 is pulled up and held by a driving device such as a motor 14. If an accident such as a stick of a cooling system circulation pump occurs in the reactor, the fuel assembly 2
The heat removal capacity for cooling 8 decreases, and the temperature of the coolant flowing in the fuel assembly 28 rises sharply as compared with the temperature during normal operation. An abnormal rise in the temperature inside the furnace is detected by the temperature sensing magnetic body 24, which changes from a ferromagnetic body to a non-magnetic body. Therefore, the magnetic circuit of the electromagnet 12 is cut off at the temperature sensing magnetic body 24 and the magnetic attraction is lost, so that the electromagnet is disconnected and the control rod 10 falls to stop the reactor as shown in FIG. 7B.

In the prior art, the coolant from the fuel assembly 28 is supplied to the electromagnet 12
In order to lead to the temperature sensing magnetic body 24, a cooling material flow conduit 32 is provided at the lower end of the upper guide tube 30.

[Problems to be Solved by the Invention] However, in the above structure, it takes a considerable time for the high-temperature coolant that has exited the fuel assembly 28 to reach the temperature-sensitive magnetic body 24 of the electromagnet 12 (8 There is a drawback that the responsiveness until detecting an abnormality in the furnace is poor.

Further, since the high temperature coolant from the fuel assembly 28 and the low temperature coolant passing near the control rod 10 mix inside the coolant flow conduit 32, the high temperature coolant from the fuel assembly 28 is transferred to the electromagnet 12. There was also a problem of lack of reliability because there was no guarantee that it would reach it reliably.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to enable the temperature of a coolant from a fuel assembly to be directly sensed by a temperature sensing magnetic body of an electromagnet, and to reliably and quickly detect an abnormality in a furnace. It is an object of the present invention to provide a self-actuated control rod drive mechanism that enables the reliability and increases the reliability without the need to consider uncertain phenomena such as coolant flow.

[Means for Solving the Problems] The present invention has a control rod and a control rod drive mechanism for driving the control rod up and down, and an electromagnet for adsorbing and holding the control rod is incorporated in the control rod drive mechanism. It is premised on a self-actuated control rod drive mechanism in which at least a part of the magnetic circuit uses a temperature sensing magnetic body whose saturation magnetic flux density decreases when the coolant temperature rises abnormally.

In order to achieve the above-mentioned object, in the present invention, the upper guide tube is provided with a ferromagnetic arm protruding laterally, and the ferromagnetic arm holds the temperature sensing magnetic material just above the top of the fuel assembly, A magnetic circuit is formed by the inner electromagnet body and the outer ferromagnetic material.

Here, the electromagnet body includes a coil, an upper magnetic core around which the coil is wound and has a flange portion, and a lower magnetic core located at the upper end of the control rod. The upper magnetic core is attached to the lower end of the drive shaft. The configuration.

Further, preferably, a vertically movable electromagnet lifting pipe made of a ferromagnetic material is provided between the upper guide tube and the electromagnet body so that the control rod can be vertically moved or pulled up after the control rod is separated. . A part of the pipe is made of a non-magnetic material so that the magnetic circuit can be opened and closed depending on the relative position to the electromagnet body.

In addition, the ferromagnetic arm has a two-tiered structure, a temperature sensing magnetic body is connected between the tip ends of the ferromagnetic arm, and a skirt is hung from the base end of the lower ferromagnetic arm toward the upper end of the control rod guide tube for control. The cold coolant passing through the rod may be directed to the electromagnet body.

[Operation] In the present invention, a conventional coolant flow conduit diverging at the lower end of the upper guide tube is not used, but instead, a ferromagnetic arm is laterally extended, and the ferromagnetic arm causes the temperature-sensing magnetic material to burn. Since it is configured to be held just above the top of the assembly, the coolant discharged from the fuel assembly rises as it is and reaches the temperature sensing magnetic body, so that it is not necessary to consider uncertain phenomena such as flow. Therefore, the response time required for the high temperature coolant to reach the temperature sensing magnetic body is very short, so that the excellent response can be obtained and the operation reliability is also improved.

The operation of the electromagnet holding the control rod is basically the same as in the prior art. In a normal state, the temperature sensing magnetic body exhibits ferromagnetism, and the magnetic force lines generated by the coil current pass through the magnetic circuit and magnetically attract the magnetic core at the upper end of the control rod by the magnetic attraction portion to hold the control rod. If an electromagnet lifting pipe made of a ferromagnetic material is provided outside the electromagnet body, the control rod driving mechanism can drive the control rod up and down in the attracted state.

When an abnormality occurs in the reactor and the coolant temperature rises abnormally, the saturation magnetic flux density of the temperature sensing magnetic body is rapidly reduced, the formed magnetic circuit is cut off, and the adsorption holding force is lost.
Therefore, the control rod is released and falls freely, stopping the reactor.

[Embodiment] FIG. 1 is an explanatory view showing an embodiment of a self-actuating type control rod drive mechanism according to the present invention, FIG. 2A is an enlarged explanatory view of the main part thereof, and FIG. It is a III arrow line view.

As shown in FIG. 1, the control rod 10 having a neutron absorber inside is suspended by an electromagnet 42. Electromagnet 4
2 is located at the lower end of the drive shaft 18 and is vertically movable by the motor 14, the ball nut 16, and the like.

As shown in detail in FIG. 2, the electromagnet body includes a coil 43, an upper magnetic core 44 around which the coil 43 is wound and which has a flange portion above, and a lower magnetic core 45 located at the upper end of the control rod. Composed of.

The feature of the present invention is that the upper guide tube 30 is provided with the ferromagnetic arms 46 and 47 that project laterally.
The point is that the temperature sensing magnetic body 48 is held right above the top of the fuel assembly 28 by 47, and a magnetic circuit is constituted by the inner electromagnet body and the outer ferromagnetic body.

In this embodiment, the upper and lower ferromagnetic arms 46 and 47 are provided at intervals corresponding to the flange portions of the upper and lower magnetic cores to form a magnetic circuit as shown by the broken line in FIG. The ferromagnetic arms 46 and 47 and the temperature sensing magnetic body 48 are provided in six directions so as to project above the six fuel assemblies arranged so as to surround the control rod guide tube 50. (See Figure 3).

An electromagnet lifting pipe 52 is located between the upper guide tube 30 and the electromagnet body. The electromagnet raising / lowering pipe 52 is vertically movable, and most of it is made of a ferromagnetic material, but the lower part thereof is made of a non-magnetic material 53. The height of the non-magnetic body 53 is substantially equal to the distance between the base ends of the upper and lower ferromagnetic arms 46 and 47.

In the above-described embodiment, the ferromagnetic arms 46 and 47 extend toward the adjacent six fuel assemblies and the temperature sensing magnetic bodies 48 are provided respectively, but it is not always necessary for all six fuel assemblies to be ferromagnetic. There is no need to extend the arm, and two or three bodies may be used.

The electromagnet raising / lowering pipe 52 is for raising / lowering the electromagnet main body together with the control rod. An example of the vertically movable structure is shown in FIG. A screw portion 60 is provided at the upper end of the pipe 52 and is screwed with the large gear 61. The large gear 61 meshes with the small gear 62 and is rotationally driven by the motor 63. Therefore, when the small gear 62 is rotated by the motor 63, the large gear 6 is rotated.
1 rotates, and the electromagnet lifting pipe 52 moves up and down.

Next, the operation of the self-actuated control rod drive mechanism configured as described above will be described with reference to FIG. FIG. A shows a normal operation state of the nuclear reactor, and shows a state in which the control rod is magnetically attracted and held by the electromagnet 42. The temperature-sensing magnetic body 48 exhibits ferromagnetism because the temperature of the coolant that rises through the fuel assembly is low, and a magnetic circuit as shown by the broken line in the figure is formed, and the lower magnetic core 45 is adsorbed and held.

If an abnormality occurs in the reactor for some reason and the temperature of the coolant passing near the fuel assembly rises abnormally, the temperature sensing magnetic body 48 changes from ferromagnetic to non-magnetic. Therefore, the magnetic circuit is cut off, the magnetic attraction force in the electromagnet 42 is lost, and the control rod falls due to its own weight as shown in FIG.
This will shut down the reactor.

The procedure for pulling up the dropped control rod is as shown in FIGS. First, the electromagnet raising / lowering pipe 52 is lowered (see FIG. C). Next, as shown in FIG. 6D, the drive shaft 18 is lowered to bring the lower end of the upper magnetic core 44 into contact with the lower magnetic core 45. In this state, since the electromagnet raising / lowering pipe 52 located outside the electromagnet body is made of a ferromagnetic material, the magnetic circuit is closed and the control rod can be magnetically attracted. Therefore, the control rod can be pulled up by raising the drive shaft 18 as it is. Then, the upper and lower flange portions of the electromagnet body are pulled up to positions corresponding to the upper and lower ferromagnetic arms (see FIG. E). Finally, by pulling up the electromagnet lifting pipe 52, the initial state as shown in FIG. 5A can be restored.

When the skirt portion 70 is hung vertically from the base end of the lower ferromagnetic arm 47 toward the control rod guide tube 50 as in the embodiment shown in FIGS. 1 to 4, the low temperature cooling flows out from the control rod assembly. It is possible to prevent the material from flowing to the temperature sensing magnetic body 48 side, and also to guide the low temperature coolant to the electromagnet main body and to cool the coil 4
3 can be cooled.

In one electromagnet, it is desirable that a plurality of temperature sensing magnetic bodies simultaneously rise in temperature and shut off the magnetic circuit.
However, if the magnetic path cross-sectional area of the ferromagnetic arm is set to the minimum value that the control rods can hold across the multiple arms, the control rod will operate if only one of the temperature sensing magnetic bodies detects an abnormal temperature rise. It can also be configured to fall.

[Effects of the Invention] The present invention is configured such that the upper guide tube is provided with the ferromagnetic arm protruding laterally as described above, and the ferromagnetic arm holds the temperature sensing magnetic material just above the top of the fuel assembly. Therefore, it is possible to significantly reduce the time required for the coolant discharged from the fuel assembly to reach the temperature sensing magnetic body, and it is possible to significantly improve the response of the control rod disconnection.

Further, in the present invention, it is not necessary to consider an uncertain phenomenon such as a flow because the coolant flow conduit for guiding the coolant from the fuel assembly to the temperature sensing magnetic body as in the prior art is not used, and the cooling from the fuel assembly is eliminated. Since the material temperature can be directly sensed, the reliability and reliability of operation are improved.

In particular, the provision of the skirt has the effect of preventing the high temperature coolant from the fuel assembly from reaching the main body of the electromagnet, and cooling the coil with the low temperature coolant passing through the control rod.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a self-actuating type control rod drive mechanism according to the present invention, FIG. 2 is an enlarged explanatory view showing a main part thereof, and FIG. 3 is a III-III arrow view thereof. FIG. 4 is an explanatory view showing a vertical movement mechanism of the electromagnet lifting pipe, and FIGS. 5A to 5E are operation explanatory views of the self-actuated control rod drive mechanism according to the present invention. Further, FIG. 6 is an overall configuration diagram showing an example of a conventional technique, and FIGS. 7A and 7B are operation explanatory diagrams of the electromagnet. 10 ... Control rod, 12, 42 ... Electromagnet, 18 ... Drive shaft, 2
0, 43 ... Coil, 22, 44 ... Upper magnetic core, 24, 48
... temperature sensing magnetic body, 26, 45 ... lower magnetic core, 30 ... upper guide tube, 46 ... upper ferromagnetic arm, 47 ... lower ferromagnetic arm, 50 ... control rod guide tube, 52 ... electromagnet lifting pipe, 53 ... non-magnetic material, 70 ... skirt part.

Front Page Continuation (72) Inventor Makoto Saito, 4002 Narita-cho, Oarai-cho, Higashi-Ibaraki-gun, Ibaraki Prefecture, Reactor and Nuclear Fuel Development Corp., Oarai Engineering Center (56) References: 63-31395 (JP, U)

Claims (5)

[Claims] 1. A control rod and a control rod drive mechanism for moving the control rod up and down. An electromagnet for adsorbing and holding the control rod is incorporated in the control rod drive mechanism. In at least a part of which a temperature sensing magnetic body whose saturation magnetic flux density decreases when the coolant temperature abnormally rises is used, a ferromagnetic arm protruding laterally is provided in the upper guide tube, and the temperature is controlled by the ferromagnetic arm. A self-actuated control rod drive mechanism, characterized in that a sensing magnetic body is held immediately above the top of a fuel assembly, and a magnetic circuit is formed by an inner electromagnet body and an outer ferromagnetic body. 2. The electromagnet body comprises a coil, an upper magnetic core around which the coil is wound and which has a flange portion, and a lower magnetic core located at the upper end of the control rod, the upper magnetic core being the lower end of the drive shaft. The self-actuating control rod drive mechanism according to claim 1, mounted on a. 3. The self-actuated control rod drive mechanism according to claim 1, wherein an electromagnet lifting pipe made of a ferromagnetic material and movable up and down is provided inside the upper guide tube. 4. A self-actuated control rod drive according to claim 3, wherein a part of the electromagnet lifting pipe is made of a non-magnetic material, and the magnetic circuit can be opened and closed by the relative position to the electromagnet body. 5. The upper and lower ferromagnetic arms are located at the lower end of the upper guide tube, a temperature-sensitive magnetic material is connected between the distal ends of the upper and lower guide arms, and a skirt portion is suspended from the base end of the lower ferromagnetic arm. The self-actuating control rod drive mechanism according to claim 1.