JPH0326995A - Drive mechanism of control rod for fast breeder - Google Patents

Abstract

PURPOSE:To allow the mechanism to make exchange work of an electromagnet easy by dividing a iron core part of an electromagnet into a lower iron core and an upper iron core detachably engaged with the lower iron core to detachably mount a coil part on the upper iron core so as to provide the upper iron core on the lower end of an inside tube. CONSTITUTION:An electromagnet 21 consists of a coil part 28 and an iron core part 27, which is divided into a lower iron core 29 fixed on an extension tube 27 and an upper iron core 30 detachably engaged with the lower iron core 29. A projection part 55 detachably engaged with a recess part 34 is provided on the upper iron core 30 to support on the lower end of an inside tube 36 in an extension tube 20 through a support shaft 37 so as to detachably hold the coil part 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a control rod drive mechanism used in a fast breeder reactor.

(Prior art) Control rods used in liquid metal cooled fast breeder reactors are made up of a plurality of neutron absorption bins housed in a wrapper tube, and are volatilized into the core area by a control rod drive mechanism. It is designed to control the nuclear reactions in the reactor core by being pulled out. Additionally, if an abnormal situation occurs within the reactor, the control rod drive mechanism rapidly inserts the control rods into the core region to bring the reactor to an emergency shutdown.

The control rod drive mechanism that drives such control rods is as follows:
Various methods have been proposed in the past, but among them, the magnetic method, which magnetically attracts and holds the control rod with an electromagnet, has a simple structure and is easy to operate mechanically in the disconnection operation during scram. It is considered to be more advantageous than other methods in that it does not require

A conventional magnetic control rod drive mechanism is shown in FIG. In the figure, liquid sodium 11 is contained in a reactor vessel (not shown) and a reactor core 12 is provided, and a lower guide pipe 1 from which control rods 13 are volatilized is provided in the reactor core l2.
4 is provided. Further, a through hole I6 is formed in the shielding plug 15 that closes the upper opening of the reactor vessel, and an upper guide pipe 17 is inserted into the reactor vessel through this through hole 18.

The guide pipe 17 is connected to a cylindrical housing I8 installed on the shielding plug 15 via a flange portion 19, and an extension pipe 20 is provided inside the upper guide pipe 17 and the housing 18. There is. An electromagnet 21 is provided at the bottom of the extension tube 20, and the control rod 13 is attracted and held by the electromagnetic force of the electromagnet 21.

In addition, the control fillH! A magnetic body 22 that is attracted to the electromagnet 2t is provided at the upper end of the electromagnet 2t.

Further, a nut 23 is provided at the upper part of the extension tube 20, and a screw shaft 24 is screwed into this nut 23. This screw shaft 24 is connected to a motor (not shown) installed at the top of the housing l8, and the rotation of this motor moves the nut 23 and the extension tube 20 in the axial direction of the screw shaft 24, causing the electromagnet 2l to move. The control rod 13 that has been attracted is raised and lowered. During a scram, the power to the electromagnet 21 is cut off, and the electromagnetic force of the electromagnet 21 is lost, so that the control rod 13 falls into the reactor core 12 due to gravity. In addition, the upper guide pipe 17
A neutron shield 26 connected to the extension tube 20 via a bellows 25 is provided inside the neutron shield 26 .

(Problem to be Solved by the Invention) By the way, the electromagnet 21 of such a control rod drive mechanism is composed of an iron core and a coil that constitute a magnetic path, and when the coil is energized, the control rod 13 is moved by the magnetic force generated in the iron core. It is designed to be magnetically attracted.

For this reason, if a failure such as coil breakage or insulation deterioration occurs during reactor operation, control rod l3 cannot be held.
It is necessary to stop operation and replace the coil. However, in the past, when replacing the coil of the electromagnet 21, the entire control rod drive mechanism had to be removed and replaced, which required sodium cleaning after removal and disassembly of the electromagnet, which required a lot of labor to replace the electromagnet. It took time.

The present invention was made by focusing on these problems.
An object of the present invention is to provide a control rod drive mechanism for a fast breeder reactor that allows easy replacement of electromagnets.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention provides an extension tube that attracts and holds a control rod by the electromagnetic force of an electromagnet, and is screwed into a screw shaft connected to a motor. In a control rod drive mechanism for a fast breeder reactor in which a control rod is moved up and down by moving it in the axial direction with a nut, an iron core part of the electromagnet is removably fitted into a lower iron core fixed to the extension tube. The coil portion of the electromagnet is detachably attached to the upper core, and the upper core is provided at the lower end of an inner tube that is removably provided within the extension tube.

(Function) In the present invention, by pulling out the inner tube provided in the extension tube out of the reactor, the upper core and coil portion of the electromagnet can be taken out without disassembling the entire control rod drive mechanism.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 5.

In FIG. 1, liquid sodium 11 is housed in a reactor vessel (not shown) and a reactor core 12 is provided, and a lower guide pipe 1 into which a control rod L3 is inserted and extracted is provided in the reactor core 12.
4 is provided. Further, a through hole 16 is formed in the shielding plug I5 that closes the upper opening of the reactor vessel, and an upper guide W17 is inserted into the reactor vessel through this through hole 1G.

The guide tube t7 is connected via a flange portion 19 to the control rod drive mechanism housing t8 installed on the shielding plug I5, and an extension tube 20 is provided in the upper guide tube 17 and the control rod drive mechanism housing 1s. It is provided. An electromagnet 21 is provided at the bottom of the extension tube 2G, and the control rod I3 is attracted and held by the electromagnetic force of the electromagnet 21. Note that a magnetic body 22 is provided at the upper end of the control rod 13 to attract the electromagnet 2l.

Further, a nut 23 is provided at the upper part of the extension tube 20, and a screw shaft 24 is screwed into this nut 23. This screw shaft 24 is connected to a motor (not shown) installed at the top of the control rod drive mechanism nozzle / housing 18, and the rotation of this motor causes the nut 23 and extension tube 20 to move in the axial direction of the screw shaft 24. Move and electromagnet 2l
The control rod l3, which is attracted to the rod, is raised and lowered. During scram, the power to the electromagnet 21 is cut off, and the electromagnetic force of the electromagnet 21 is lost, causing the control rod l
3 falls into the core l2 by gravity. Furthermore, an extension pipe 20 and a bellows 25 are installed inside the upper guide pipe l7.
A neutron shield 26 is provided which is connected via the neutron shield 26 .

The electromagnet 2l is composed of an iron core part 27 and a coil part 28, as shown in FIG. It is divided into an iron core 30.

The lower core 29 includes a cylindrical outer core 31, an inner core 32 provided inside the outer core 3l, and a connecting member 33 made of a non-magnetic material that connects the inner core 32 and the outer core 3l. A recess 34 for centering is formed at the upper end of the inner core 32.

On the other hand, the upper core 30 has a protrusion 35 that removably fits into the recess 34, and is supported via a support shaft 37 at the lower end of an inner tube 38 that is removably provided in the extension tube 20. . A spring 38 is incorporated in the lower part of this support 1dl37, and the spring force of this spring 38 presses the upper iron core 30 against the lower iron core 29 to bring it into close contact. Note that a coil portion 28 is detachably held in the upper core 30.

A flange 39 is provided at the upper part of the inner tube 3B. This flange 39 includes a flange 40 provided on the upper part of the extension tube 20 and a flange 4 to which the nut 23 is fixed.
These flanges 39. 40. By disassembling 41, the inner tube 3
6 can be pulled out from the extension tube 20. Note that the flanges 39, 40. are provided at the bottom of the control rod drive mechanism housing l8. An opening 42 for disassembling 41 is formed and is normally sealed by a flange 43.

In the control rod drive mechanism constructed in this manner, when replacing the coil portion 28 of the electromagnet 2l, first remove the flange 43 as shown in FIG. 3, and open the opening 42 of the control rod drive mechanism housing l8. . Next, after setting the stopper 44 to prevent the extension pipe 20 from falling between the shielding plug l5 and the flange 40 through the opening 42, the bolted flanges 39, 40. Disassemble 41. Then, as shown in FIG. 4, the control rod drive mechanism housing l8
Remove the shielding plug i5 from the inner tube 3G and extend the inner tube 3G to the extension tube 20.
pull it out.

When the inner tube 36 is pulled out from inside the extension tube 20 in this way,
As shown in FIG. 5, the upper core 30 is separated from the lower core 29 and the coil section 28 provided in the upper core 30 can be taken out of the reactor, so the coil section 28 can be removed without disassembling the entire control rod drive mechanism. 28 exchanges can be made.

Next, a second embodiment of the present invention is shown in FIGS. 6 and 7. This embodiment has a main coil 28a and a spare coil 28b on the upper core 30, and has the same structure as the first embodiment described above except for the above points.

Note that in this embodiment, when the main coil 28a is disconnected, a switching circuit (not shown) switches the energization to the main coil 2.
8a to the spare coil 28b.

[Effects of the Invention] As explained above, in the present invention, by pulling out the inner tube provided in the extension tube, the coil portion detachably provided in the upper iron core can be taken out of the furnace.
Even if the coil portion of the electromagnet is disconnected, the coil can be replaced safely and easily without disassembling the entire control rod drive mechanism.

[Brief explanation of drawings]

1 to 5 show a first embodiment of the present invention, FIG. 1 is a sectional view showing the schematic structure of the control rod drive mechanism, FIG. 2 is a sectional view showing the structure of the electromagnet, and FIG. 3 is a sectional view showing the structure of the electromagnet. 5 are explanatory diagrams of the operation of the same embodiment, FIGS. 6 and 7 are sectional views showing a second embodiment of the present invention, and FIG. 8 is a sectional view showing a conventional control rod drive mechanism. 1l...liquid sodium, 12...core, 13...
- Control rod, l4... Lower guide tube, l5... Shielding plug, 17... Upper guide tube, 18... Housing, 20... Extension tube, 21... Electromagnet, 23... Nut, 24... Screw shaft, 27... Iron core portion, 28... Coil portion, 29... Lower iron core, 30... Upper iron core, 3B... Inner tube.

Claims (1)

[Claims] The extension tube holds the control rod by attraction using the electromagnetic force of the electromagnet.
In a control rod drive mechanism for a fast breeder reactor in which a control rod is moved up and down by moving it in the axial direction by a nut screwed into a screw shaft connected to a motor, an iron core part of the electromagnet is connected to a lower iron core fixed to the extension tube. an inner tube that is divided into an upper core that removably fits into the lower core, and a coil portion of the electromagnet is removably attached to the upper core, and the upper core is provided in the extension tube so that it can be pulled out. A control rod drive mechanism for a fast breeder reactor, characterized by being installed at the lower end of the control rod.