JPS6353493A - Control-rod drive mechanism - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION (Objective of the Invention) (Field of Industrial Application) The present invention relates to a control rod drive mechanism incorporated in a boiling water nuclear reactor.

(Prior Art) The schematic structure of a boiling water reactor is shown in FIG. 11. As shown in a partial cross-sectional view, a large number of fuel assemblies are loaded in a reactor pressure vessel 1 to form a reactor core 2. ing.

A large number of control units 2111 and 3 are inserted at predetermined intervals from below into j1υ of this fuel assembly. This control rod 3, II
Insert it into the reactor core 2 by the drive mechanism (hereinafter referred to as CRD) 4, and then pull it out and set its set position.
Reactor output by adjusting the living room) li''1112
11 will be carried out.

The above CR[)4 is a control rod drive Jfji 1M housing (
It is inserted into the CRD housing (hereinafter referred to as the CRD housing) 5 from below and fixed therein. A hollow piston is accommodated in the CRD 7I so as to be able to rise and fall freely, and the control rod 3 and the hollow piston are integrally connected by a connecting member provided at the top of the hollow screw 1-.

CRD4 performs relatively slow insertion and withdrawal operations (shim operations) of control rods 3 to adjust the reactor output to a predetermined state during 3F'7; To stop the furnace, line 41a, II fl
It has the function of i-1 for rapid insertion (scrum movement 1'l) of ll-3.

Generally, shim movement (Yudenri) is performed by Iso-bori J, and scram movement is performed by hydraulic drive.

In other words, when the shim operates (1, 7 drive the motor 6, transmit its rotational motion to the ball screw shaft 8 via the drive shaft 7, and the ball nut screwed into the ball screw 4!j 8!~ 9 is moved up and down.As a result, the a,+ control rod 3 supported and connected to the hollow piston 10 is inserted into the reactor core 2 or moved out of the bow 11.

On the other hand, during scram operation, high-pressure water is injected into the CRDJ from a water pressure A1 control unit (LI CU ), not shown, through the insertion pipe 11 and through the insertion flow path 13 roughly formed inside the outer peripheral flange 12 of the CRD 4. The high-pressure water pressurizes and pushes up the lower surface of the hollow piston 19, thereby providing a mechanism for inserting the control rod 3 into the reactor core 2 at high speed.

Furthermore, even when the operation is stopped, a portion of the high-pressure water passes through the insertion flow path 13 and is supplied to the CRD 4 to cool the seal portion of the hollow piston 1o.

In this way, CR plays an important role in controlling the output of nuclear reactors.
D is designed so that the function can be maintained even if the insertion pipe 11 breaks. That is, C.R.D.
A check valve 14 is disposed in the insertion passage 13 formed in the outer peripheral flange 12 of No. 4, and the check valve 14 is configured to prevent reactor water from flowing out from the ceiling.

In the conventional check valve 14, as shown in FIG. 6, a retainer 16 for vertically movably holding a ball 15 serving as a valve body is installed in the insertion channel 13 via an O-ring 17. A communication opening 18 is bored in the side circumference of the retainer 16. High-pressure water for scram and cooling water for CRD cooling are fed through the insertion pipe 11, from the retainer 16, through the communication opening 18, and into the CRD 4 via the insertion channel 13.

Next, when the external pressure suddenly decreases due to a rupture (fIi, etc.) of the insertion pipe 11, the reactor water in the CRDJ flows backward through the insertion channel 13 and begins to flow outside.However, due to the action of this flow, the ball 15 Since the pressure on the top surface is lower than the pressure on the bottom surface, the ball 15 floats up and comes into close contact with the opening part 19 of the retainer 16, blocking the flow path of the reactor water. Reactor water 020 is drilled to communicate with the inside, and when the insertion pipe 11 is broken, the pressure inside the furnace acts on the ball 15, and the assisted ball 15 is pushed into the valve seat opening 19.
By tightly tightening the CRD 4 hollow screw l~
This prevents the driving water and reactor water on the lower surface side of the reactor 10 from flowing backwards and flowing outside.

(Problems to be Solved by the Invention) However, in the check valve of the conventional structure described above, when the insertion pipe rupture time is small and the outflow of reactor water i) is small,
Since the lifting force acting on the ball is small, the ball does not float up and there is a problem in that the valve seat opening of the check valve cannot be completely closed. Therefore, it is necessary to collect the leaking reactor water in the drain funnel and reprocess it, which has the drawback of requiring a large amount of cost.

The present invention was devised to solve the above-mentioned problems, and even if the CRD insertion pipe breaks, it can minimize the leakage of reactor water to the outside, and improve the leakage prevention ability. The object of the present invention is to provide a control drive system incorporating a reverse valve with high reliability.

(Structure of the invention) (Means for solving the problems) Control rod drive according to the present invention); Part 1 is a control rod drive structure in which a hollow piston connected to an 11 control rod is housed so that it can be freely lowered. An outer peripheral flange is fixed to the lower part of the housing, and a check valve is arranged in the insertion flow path formed within the outer peripheral flange.
This check valve prevents the flow of reactor water in the event of a rupture of the insertion pipe.
The reversal valve is characterized by comprising a valve body that opens and closes the insertion channel, and a spring that constantly presses the valve body against a valve seat provided in the insertion channel.

(Function) The check valve built in the control rod drive structure of the present invention is
The valve element that opens and closes the insertion flow path is always pressed against the valve seat by the spring force of the spring, and the scram high-pressure water and CRD cold 741 water that are sent through the insertion pipe are under pressure. It acts on the valve body, pushes the valve body apart against the spring force of the spring, and flows into the CRD.

On the other hand, if the insertion pipe breaks, the valve body assisted by the bubbling force instantly comes into close contact with the valve seat and blocks the insertion flow path, thereby minimizing the amount of outflow of reactor water.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of a CRD according to the present invention, and is a sectional view showing an enlarged portion of a check valve.

Outer flange 1 fixed to the lower part of the CRD housing 5
2, and a check valve 14 is disposed in an insertion passage 13 formed inside this outer peripheral flange 12.

The check valve 14 is composed of a valve body 21 that opens and closes the insertion passage 13, and a spring 23 that always presses the valve body 21 against a valve seat 22 provided in the insertion passage 13.

Further, a retainer 16 that accommodates the valve body 21 and guides the vertical movement of the valve body 21 is inserted into the insertion channel 13 through a ring 17.
ni&? ? has been done. A communication opening 18 is provided on the side surface of the retainer 16.

In the first embodiment, the valve body 21 has a spring 23
is constantly pressed against the valve seat 22 by the spring force of the insertion channel 1.
3 is closed. During normal operation u, 1, the small hj of CRD cold lJI water fed from the insertion pipe is due to its pressure.
The valve body 2 is pushed down 2'i1 against the force, and flows into the ID4 through the communication opening 18 and the insertion channel 13.

On the other hand, when d3 is in the scrum, i! "l!i Pressure water is rapidly injected, and the valve body 21 f;1 is pushed down greatly,
High-pressure water flows into the lower surface side of the hollow piston 10 in the CRD 4 through the communication 111018, and the control rod 3 is urgently inserted into the reactor core.

In addition, if the insertion pipe 11 is ruptured, there is a risk that the drive EJJ water and reactor water in the CRD 4 will flow back into the rupture part due to the action of the reactor internal pressure. Since the valve body 21 instantly comes into close contact with the valve seat 22 formed on the retainer 16 and closes the insertion flow path, C.
It is possible to prevent driving water and reactor water from flowing backward from inside the RD 4 to the fractured portion and flowing out to the outside.

In addition, the valve body 21 opens slightly when CRl) cold 7,1+ water passes through it. The response time until the complete closure 11 of the man flow path is short, and the outflow of reactor water m can be suppressed to a minimum.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the second embodiment, 0'! 1 Perforation III where CRD cold IJl water bypasses the check valve at the valve seat part of the check valve in box 131
The feature is that the hole 24 is provided. This pore 24 is bored so as to bypass the valve body 21 and communicate the primary side flow path and the secondary side insertion flow path of the valve body 21.

In the ti4 configuration of the second Jinoura example above, the small hole 24 that bypasses the valve body 21 is installed, so the CRD
Cold uI irrigation, t, co (7) lff1 hole 2 /1
woa') Injected into CRD 4. therefore,
During normal operation, the valve body 21 is in close contact with the valve seat 22.

Operation during scrum (same as the J first embodiment. Also,
If the insertion pipe 11 is ruptured, the valve body 21 will be more firmly attached to the valve seat 22, but there is a drawback that a small amount of reactor water will flow back through the pores 24. However, by making the drilled pore 24 a dedicated flow path for CRD cold IJ water, a phenomenon occurs when CRD cold IJ water passes between the valve body 21 and valve 22. It is possible to prevent an accident in which the body 21 intermittently shoots the valve seat 22 against the valve seat 22.

Next, a third practical example of the present invention will be explained with reference to FIG.

In the third embodiment, the valve body of the check valve of the first embodiment is replaced with a disk 2.
5, and this disk 25 is rotatably supported at its upper edge by a pin 26. Further, a spring 23 is interposed to constantly press the disk 25 as a valve body toward the valve seat 22. NaJ'3, disk 2
5 can sufficiently land on the valve seat 22 due to its own weight, the spring 23 may be omitted.

In the above configuration, the disc 25 is always pushed against the valve seat 22 by its own weight or by the spring 23.
Closely attached to. When high-pressure scram water or CRD cooling water flows in, the disk 25 tilts in the opening direction in response to the flow rate and pressure.

On the other hand, if the insertion pipe 11 breaks, the disk 25 instantly moves to f? due to the decrease in the primary side pressure of the disk 25.
- Firmly adheres to the seat 22. Therefore, it is possible to effectively prevent the driving water and reactor water in the CRD 4 from flowing backward and flowing out from the fractured portion.

〔Effect of the invention〕

As explained above, in the II Illll dynamic drive mechanism of the present invention, the valve body of the built-in check valve is constantly pressed against the valve seat by the spring force, and the insertion flow path is almost closed. Therefore, even if the insertion pipe breaks, it is possible to instantly prevent reactor water from flowing out. Additionally, even if the insertion pipe is partially ruptured and only a small amount of reactor water flows out, the valve body can instantly shut off the insertion pipe and minimize the amount of reactor water flowing out. . In addition, the 4M structure is simple and the ability to close the flow path is strengthened by the spring force, so the operational reliability is greatly improved compared to the conventional control drive mechanism.

Fig. 3 is a sectional view showing the third practical example of the present invention, Fig. 4 is a partial sectional view of a boiling 113 water reactor, and Fig. 5 is a conventional control! 6th sectional view showing the structure of the v-carrying drive mechanism.
The figure is a partially enlarged sectional view of the check valve J5 in FIG. 5.

1... Reactor pressure vessel, 2... Reactor core, 3... Control rod, 4... Control rod drive type (1°4<CRD), 5...
・・CRD housing (CRD housing), 6...
Electric motor, 7... Drive shaft, 8... Ball screw shaft, 9...
・・Ball nut, 10・Hollow bislin, 11・
...Insertion piping, Go2...Outer flange, 13...Insertion channel, 14...Check valve, 15...Ball, 16...
... Retainer, 17... O-ring, 18... Communication opening, 19... Valve seat opening, 20... Reactor water inlet, 21
...valve body, 22...valve seat, 23...spring,
2/1...pore, 25...disc, 26...pin.

Applicant's agent H. Hisa / Figure Figure 3 Easy 42 Must be 5 times

Claims (1)

[Claims] 1. An outer flange is fixed to the lower part of the control rod drive mechanism housing in which a hollow piston connected to the control rod is movably raised and lowered, and a check valve is installed in the insertion flow path formed in the outer flange. The control rod drive mechanism is equipped with a check valve that prevents reactor water from flowing out in the event of a rupture in the insertion pipe.
The control rod drive mechanism is characterized in that the check valve is composed of a valve body that opens and closes the insertion channel, and a spring that constantly presses the valve body against a valve seat provided in the insertion channel. 2. The control rod drive mechanism according to claim 1, wherein the check valve has a pore that bypasses the valve body and communicates the primary side insertion passage and the secondary side insertion passage of the valve body. 3. The control rod drive mechanism according to claim 1 or 2, wherein the valve body is constituted by a disk whose end edge is rotatably supported by a pin.