JPS5928693A - Control rod drive mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a control rod drive mechanism suitable for fast breeder reactors.

[Technical background of the invention and its problems]

In fast breeder reactors that use liquid sodium as a coolant, the output of the nuclear fuel in the reactor core is controlled, and in the event of an abnormal situation within the reactor, operations are carried out to absorb neutrons in the reactor and emergency stop the nuclear reaction. It is well known that control rods are used for these operations.

This control rod is made up of a plurality of absorption pins implanted in the trumpet bone, whose upper and lower ends are supported by a lattice plate, and a gripping portion is formed at the upper part of the trumpet tube.

These control rods are inserted into and withdrawn from the reactor core region to change the amount of neutron absorption and control the nuclear reactions in the reactor.

If an abnormal situation occurs in the reactor core, control rods are rapidly inserted into the reactor core to stop the nuclear reaction.

Rapid insertion is performed using a control rod drive mechanism and gravity fall, but there are limitations in the time required for insertion, the number of insertions, and the structure or material of the control rod or core.

Furthermore, when exchanging fuel in a nuclear reactor, it is necessary to disconnect the control rod drive mechanism and move the reactor upper mechanism with the control rods fully inserted into the reactor core region.

Therefore, a means to confirm complete insertion and removal of the control rod is required.

Conventionally, various types of control rod drive mechanisms have been proposed. Among these, a method in which the control rods are connected directly by magnetic attraction using magnets is considered to be more advantageous than other methods in terms of structural simplicity and the ability to eliminate the need for mechanical movement in disconnection operations. .

FIG. 1 is a schematic cross-sectional view of the main parts of a typical conventional magnet direct connection type control rod drive mechanism.

In the figure, reference numeral 1 partially indicates a shielding plug (not shown) that closes the upper opening of the reactor vessel.
8 is fixed via the 7 rank portion 18a.

The upper part of the upper guide tube 18 is connected 1° to the housing 4, and a motor (not shown) is mounted on the top thereof. On the other hand, the lower part of the upper guide tube 18 is immersed in the coolant of the reactor vessel, that is, the liquid sodium 5.

Further, an extension tube 6 is inserted inside the upper guide tube 18, and a nut 7 is fixed to the upper part of the extension tube 6.
is screwed into and connected to a screw shaft 8 which rotates with the rotation of the motor.

A magnet 10 is installed at the lower end of the extension tube 6.
The control rods 9 in the lower guide tube 24 implanted in the reactor core 22 are attracted and connected. Therefore, when the motor of the drive section is rotated, the screw shaft 8 rotates, and the nut 7, extension tube 6, and control rod 9 move up and down together.

In the case of sudden reactor shutdown in the control rod drive mechanism described above, the control rods 9 are separated by cutting off the excitation current of the magnet 10, but there is a limit to the speed at which they can be inserted into the reactor core 22 by gravity acceleration alone. , there is also a problem with the reliability of inserting control $9.

Therefore, an acceleration mechanism such as a gas cylinder and spring is required, but with the magnetic coupling method, the size of the magnet for connecting the control rods is limited due to the space constraints of the reactor, and the control rod retention force is compromised. There is a problem in that it is very difficult to provide a mechanism.

[Purpose of the invention]

The present invention has been made to solve the above problems,
We provide a highly reliable control rod drive mechanism that can shorten control rod insertion time, allow the bushing rod to completely push the control rod into the core, and even allow for accelerated insertion even if some friction occurs inside the guide tube during insertion. It's about doing.

[Summary of the invention]

That is, one aspect of the present invention is a control rod drive mechanism in which a control rod is inserted into a reactor core by separating the control rod from the extension tube during a scram using an extension tube having a nut screwed into a screw shaft rotated by a motor and fixed to the upper end thereof. An acceleration shaft operated by a spring or a gas cylinder is provided, and in a steady state, the acceleration shaft is held by a magnet installed in the extension tube, and the force of the acceleration shaft does not act directly on the magnet to ensure control rod retention, and the scram It is a control rod drive mechanism that can sometimes ensure control rod insertion.

[Embodiments of the invention]

Hereinafter, one embodiment of the control rod drive mechanism according to the present invention will be described in detail with reference to FIG.

FIG. 2 is an enlarged view of the inner portion of the extension tube of the control rod drive mechanism according to the present invention.

In FIG. 2, only essential parts of the present invention are shown, and parts common to those in FIG. 1 are designated by the same reference numerals.

Figure 2a shows the control rod connected to the extension tube and pulled out.

A control rod 9 is connected to the lower part of the extension tube 6 via a first magnet 10.

A second magnet 11 is provided at the top of the extension tube, and this magnet 11 attracts and holds an acceleration shaft 14 provided inside the extension tube 6.

A stop bar 16 is attached to the acceleration shaft 14, and compresses and holds the spring 15 between it and a seat 13 provided inside the extension tube 6.

In this state, the lower end of the acceleration shaft 14 is separated from the top of the control rod, so that the force of the acceleration shaft 14 does not act on the control rod 9.

The stopper 16 has a plurality of claws 19 protruding from its outer periphery, which pass through long holes 17 cut in the extension pipe 6 and are engaged with the stopper 20 of the upper guide pipe during scram. .

When scramming the control rod 9, when the power circuits of the magnets 10 and 11 are cut off at the same time, the control rod 9 and the acceleration shaft 14 are simultaneously released, and the acceleration shaft 14 accelerates the control rod 9 by the repulsive force of the spring 15. will be inserted.

Figure 2 shows the state after the scram.

The control '+IP-9 is completely inserted into the reactor core 22, and the acceleration +11+14 is stopped when the claw 19 on the outer periphery of the stopper 16 comes into contact with the stopper 20 and shock absorber 21 provided at the lower part of the upper guide tube 18. are doing.

The spring 15 is in an extended state, and the lower end of the acceleration shaft 14 is located a little away from the control rod 9.

FIG. 2C shows the state in which the control rod 9 and the extension pipe 6 are connected after the scram.

The extension tube 6 has descended to the vicinity of the reactor core 22, and the magnet 10 at the lower end is in contact with the control rod 9.

The top armature 12 of the acceleration shaft 14 is a magneto-soto 11
Fish by contacting.

At this time, the magnet 11 is slightly pushed up by the acceleration shaft 14, and the spring 23 is slightly compressed.

At this time, the difference in length between the extension tube 6 and the acceleration shaft 14 due to thermal expansion is canceled out by the amount of compression of the spring 23.

〔Effect of the invention〕

As described above, according to the present invention, even in a control rod drive mechanism in which the control rods are directly connected using magnets, an acceleration force by a spring can be applied to the control rods. Gives a large acceleration force. Therefore, the control rod can be reliably inserted into the reactor core, and the insertion time can be shortened.

That is, the acceleration shaft 14 separates the control rods 9 from the core 22.
Since the control rod 9 is pushed in until it is completely inserted into the core 22, the control rod 9 can be inserted reliably even if the frictional resistance between the control rod 9 and the lower guide tube 24 increases due to deformation of the core 22 due to thermal deformation, swelling, etc.

Further, an acceleration mechanism section is provided on the stiffener plug 1, and the stopper 2 inside the upper guide tube 18 is connected to the stopper 16.
If a reed switch or the like is installed at 0, it will be possible to confirm the disconnection and insertion of control rods, which will significantly improve the safety of the reactor.

In addition, with the magnetic coupling method, due to space constraints within the reactor, the size of the magnet for connecting the control rods is limited, and it is extremely difficult to provide an acceleration mechanism due to the conflict with the holding force of the control rods. there were.

In contrast, by providing the magnet that holds the force of the acceleration spring according to the present invention, it is possible to prevent the force for accelerating the insertion of the control rod from being applied to the control rod connecting magnet when the control rod is connected. The holding force of the rod-connecting magnet can be made to have some leeway.

Furthermore, even if the control rod connecting magnet cannot be released due to a failure in the power supply circuit in an emergency, demagnetizing the acceleration mechanism holding magnet will apply the acceleration force to the connected control rods, thereby increasing the holding force of the control rod connecting magnet. scrum becomes possible because it exceeds the limit.

[Other embodiments of the invention]

The present invention is not limited to the embodiment described above, but has other embodiments as shown in FIGS. 3 and 4.

In each figure, the same parts as in FIG. 2 are denoted by the same reference numerals, and explanations of overlapping parts will be omitted.

FIG. 6 shows a simplified structure of the control rod drive mechanism in FIG. 2.

That is, the part above the stopper 16 of the acceleration shaft 14 and the seat 13 of the extension tube 6 of the embodiment shown in FIG. 2 are omitted, and the magnetite 11 is changed to the position of the seat 13 shown in FIG. 12 is an integral type fixed to the stopper 16, and this embodiment has the advantage that the overall length of the acceleration mechanism is shortened.

In this embodiment, not only a spring 23 is provided at the upper end of the magnet 11, but also a spring 15 is interposed between the magnet 11 and the armature 12.

FIG. 4 shows an example in which the present invention is applied to a fluid floating type control rod 1 drive mechanism, in which a piston 25 is provided on the control rod 9.

The fluid floating type control rod in this embodiment has a lower guide tube 24.
In a steady state, the pressure of the fluid flowing through the piston 25K acts on the piston 25K, so that it floats until it comes into contact with the extension tube and then stops.

At the time of scram, by activating the acceleration mechanism based on the present invention at the same time that the fluid pressure acting on the piston 25 disappears, the control rod 9 can be inserted at an accelerated rate by being pushed in with the acceleration shaft 14, and the control rod can be inserted more quickly. You can insert it into the reactor core.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view schematically showing a conventional control rod drive mechanism, and FIG. 2 is a control rod 1WD Ti! control rod according to the present invention! FIG. 6 is a vertical cross-sectional view showing one embodiment of the I+ mechanism, in which a shows the steady state, b shows the scram, and C shows the recombination after the scram, and FIGS. 6 and 4 show other embodiments of the present invention. FIG. 3 is a vertical cross-sectional view showing examples. 1... Shielding plug 2... Through hole 4... Housing 5... Liquid sodium 6... Extension tube 7... Nut 8... Screw shaft 9... Control rod 10... First magnet 11... Second magnet 12... Armature 13... Seat 14... Acceleration shaft 15... Spring 16... Stopper 17... Long hole 18... Upper part Guide tube 19...Claw 20...Stopper 21...Shock absorber 22...Furnace core 23...Spring 24...Lower guide tube 25... Piston attorney Patent attorney Kazutoshi Figure 1 Figure 2vA Figure 3 Figure 4

Claims (1)

[Claims] 1. The control rod is moved up and down by an extension tube whose upper end is fixed with a nut screwed into a screw shaft rotated by a motor. During a scram, the control rod is separated from the extension tube and the control rod itself is moved into the reactor core. In the control rod drive mechanism inserted into the extension tube, an acceleration shaft operated by a spring or a gas cylinder is provided in the extension tube, and in a steady state, the acceleration shaft is held by a magnet provided in the extension tube. mechanism. 2. The control rod drive mechanism according to claim 1, wherein an armature is connected to the upper end of the acceleration shaft, and the armature is held by a magnet. 3. The control rod drive mechanism according to claim 1, wherein a spring is provided at the upper end of the magnet.