JPH0117560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod drive mechanism that drives control rods arranged in the upper part of a reactor core.

Figure 1 shows a conventional boiling water reactor.
Inside the reactor pressure vessel 1, there is provided a reactor core 3 made up of a large number of fuel assemblies 2, a steam separator 4 above it, a steam dryer 5 above it, and a lid 6 at the upper end of the pressure vessel 1. It is blocked. In addition, the inside of the pressure vessel 1 is filled with water 7 as a coolant to a predetermined level, and the water boiled by the nuclear reaction in the reactor core 3 is separated into steam and water in a steam separator 4, and the steam that rises further. is dried by the dryer 5 and exhausted from the main steam pipe 8 as a turbine drive source. After the turbine is driven, the condensate is again supplied into the reactor pressure vessel 1 as a coolant.

Further, inside the pressure vessel 1, a large number of control rods 9 having a neutron absorption function are provided at the lower part of the reactor core 3, and at the bottom of the pressure vessel 1, a control rod drive mechanism 10 for driving these control rods 9 up and down is provided. is provided.

Therefore, the control rod 9 is driven by the control rod drive mechanism 10.
When the nuclear reactor is raised and inserted into the reactor core 3, the nuclear reaction in the reactor core 3 is suppressed and the reactor output is reduced.
When the control rods 9 are lowered and withdrawn from the reactor core 3, the nuclear reaction is accelerated and the reactor output is increased.

The control rod drive mechanism 10 has a relatively gentle construction and can be inserted and removed in order to prevent sudden changes in nuclear reactivity during normal reactor operation, and can be inserted and removed in a relatively gentle manner so as not to cause sudden changes in nuclear reactivity during normal reactor operation. In order to rapidly reduce the pressure and bring the reactor to an emergency stop, it is necessary to be able to insert the control rods 3 very quickly.

By the way, due to the structural characteristics of a boiling water reactor, the control rods 9 are inserted from the bottom of the pressure vessel 1 into the core 3.
High-pressure water is generally used as the drive source for the control rod drive mechanism 10. By applying pressure to the piston connected to the control rod 9 from the lower surface side, the control rod 9 is inserted into the piston. However, in this case,
Since the control rod 9 must be inserted by rising against gravity, if the drive source is lost in an emergency situation, it is predicted that the emergency insertion operation of the control rod will not be performed. Further improvement in reliability was desired.

Generally, a control rod drive mechanism is provided with a collect finger to prevent the piston connected to the control rod from falling due to its own weight, but in the conventional control rod drive mechanism, the collect finger is attached to the drive piston. It is located on the outside,
Since the drive piston is held at an appropriate height by engaging the collect finger with a notch provided on the outer circumferential surface of the drive piston, there is no need to secure a space between the cylinder and the piston to accommodate the collect finger. This resulted in a disadvantage that the cylinder had a large diameter.

The present invention was developed based on these circumstances, and its purpose is to make it possible to place the control rods at the top of the reactor core, thereby preventing the loss of the driving source in the event of an emergency shutdown of the reactor. In order to improve safety, the control rod is inserted by gravity even in cases where the cylinder has a small diameter. The object of the present invention is to provide a control rod drive mechanism that can be reduced in size or size.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 2 and 3.

FIG. 2 shows a schematic configuration of a boiling water reactor, in which the core shroud 12 inside the reactor pressure vessel 11
The core 1 is composed of a large number of fuel assemblies 13.
4. A steam separator 15 is provided above it, and a steam dryer 16 is further provided above it, and the upper end of the pressure vessel 11 is closed with a lid 17. Also, pressure vessel 1
The inside of the reactor 1 is filled with water 18 as a coolant to a predetermined level.The water boiled by the nuclear reaction in the core 14 is separated into steam and water by a steam separator 15, and the steam that has risen is sent to a dryer. Dry at 16,
The condensed water is discharged from the main steam pipe 19 as a turbine driving source, and the condensed water after driving the turbine is supplied back into the reactor pressure vessel 11 as a coolant.

Further, inside the pressure vessel 11, a large number of control rods 20 having a neutron absorption function are provided at the top of the reactor core 14, and at the bottom of the pressure vessel 11, a control rod drive mechanism 21 for driving these control rods 20 up and down is provided. is provided.

FIG. 3 shows the configuration of the control rod drive mechanism 21, in which reference numeral 22 denotes a cylindrical control rod drive mechanism housing to which the lower surface of the bottom wall of the reactor pressure vessel 11 is attached. The upper end opening of this housing 22 communicates with the inside of the pressure vessel 11, and the annular water supply pipe connector 23 is attached to the lower end opening. Further, a cylindrical cylinder 24 is provided upward from the inner circumferential edge of the upper end of the connecting body 23, and a hollow drive piston 25 is disposed inside the cylinder 24 and slides against the inner circumferential surface of the cylinder 24. It is housed to move up and down. The drive piston 25 has an annular lower part and a cylindrical body 26 at the upper part. A rod 27 is connected to the upper end of the cylindrical body 26, and this rod 27 passes through the reactor core in the reactor pressure vessel 11 from below and extends to the upper part of the reactor core. are connected. Moreover, the space between the outer circumferential surface of the cylindrical body 26 and the inner circumferential surface of the upper end of the cylinder 24 is maintained liquid-tight. Further, a guide tube 28 is introduced into the drive piston 25 through its lower end opening. This guide tube 28
is configured to guide the piston 25 in the vertical direction by sliding the inner circumferential surface of the piston 25 on the outer circumferential surface. The lower outer circumferential surface of the guide tube 28 and the inner circumferential surface of the water supply pipe connecting body 23 are kept liquid-tight, and the lower end of the guide tube 28 is connected to the lower end of the connecting body 23 via a fixing plate 29. Fixed. And the above guide tube 28
An inner tube 30 is introduced into the interior of the guide tube 28 by passing through the center of the fixing plate 29 and the lower end opening of the guide tube 28 .

A collet receiver 31 is formed at the upper end of the guide tube 28, and a guide cap 32 is formed further above the collet receiver 31. A collect finger 35 is formed at the outer circumferential end of the guide cap 32, and the collect finger 35 normally expands in diameter outward in the radial direction and has a plurality of holes provided on the inner circumferential surface of the drive piston 25 at equal intervals in the axial direction. It engages with one of the notches 36 (only one is shown in the figure) to prevent the drive piston 25 from falling. A release claw 33 is housed in the collet receiver 31 so as to be movable up and down, and the release claw 33 is normally urged downward by a compression spring 34. When the pressure of the driving water, which will be described later, acts from below, it rises against the biasing force of the compression spring 34 to reduce the diameter of the collect finger 35, thereby releasing the engagement between the collect finger 35 and the notch 36. .

The water supply pipe connection body 23 has a water supply nozzle 3 at the time of insertion.
7 and a water supply nozzle 38 at the time of withdrawal are provided. Water supply pipes (not shown) are connected to these water supply nozzles 37 and 38, respectively, and high-pressure water as a driving source is supplied thereto.

The water supply nozzle 37 during insertion communicates with the inside of the guide tube 28 through a water passage 39 formed at the lower end of the guide tube 28, and into the cylinder 24 through an orifice 40 provided at the upper end of the guide tube 28. It communicates with the upper surface side space of the piston 25 in the guide tube 28, and also communicates with the lower surface side space of the release claw 33 in the collet receiver 31 through an orifice 41 provided at the upper end of the guide tube 28, and these water supplies. The nozzle 37, the water passage 39, the space inside the guide tube, the orifice 40, and the space on the upper surface of the piston inside the cylinder 24 constitute a pressurized flow path for inserting the control rod. Incidentally, an orifice 42 is provided at the lower part of the cylindrical body 26 to communicate the inner and outer surfaces of the cylindrical body 26. Further, a thin tube 43 is formed in the water supply pipe connection body 23 to communicate the water supply nozzle 37 during insertion with the inner space of the control rod drive mechanism housing 22 .

On the other hand, during extraction, the water supply nozzle 38 communicates with the space on the lower surface of the piston 25 in the cylinder 24 through a plurality of shock absorption holes 44 having a small cross section. A pressurized flow path is configured.

In addition, 45 in the figure is a shock absorbing spring arranged on the inner bottom surface of the cylinder 24.

Next, the operation of this embodiment will be explained.

First, the control rod insertion operation for reducing the reactor power during normal operation is performed by supplying high pressure water from the insertion water supply nozzle 37. That is, when high-pressure water is supplied from the water supply nozzle 37 during insertion, the high-pressure water flows into the guide tube 28 through the water passage 39 as shown by the solid line arrow in FIG. The release claw 33 is compressed by the spring 34.
rise against the urging force of As a result, the release claw 33 reduces the diameter of the collect finger 35 inward in the radial direction, releases the engagement between the collect finger 35 and the notch 36, and allows the drive piston 25 to fall. Furthermore, the high-pressure water that has flowed into the guide tube 28 flows through the orifice 40 into the upper space of the drive piston 25 in the cylinder 24 and pressurizes the drive piston 25 from the upper surface. The control rod 20, which is connected to the piston 25 via the rod 27, is also lowered and inserted into the reactor core. Further, when the drive piston 25 moves downward in this way, the water existing in the space on the lower surface side of the piston 25 is absorbed into the plurality of shock absorption holes 44.
After that, the water is discharged from the water supply nozzle 38 during extraction.
When the control rod 20 is inserted to the desired position and the supply of high-pressure water is stopped, the release claw 33 is returned downward by the compression spring 34, and the collect finger 35 is also returned outward to the predetermined notch 36. The piston 25 is engaged again to restrict the falling movement of the piston 25.

Next, the control rod withdrawal operation for increasing the nuclear power output is performed by supplying high pressure water from the water supply nozzle 38 during withdrawal. That is, when high-pressure water is supplied from the water supply nozzle 38 during withdrawal, the high-pressure water flows into the lower surface side space of the drive piston 25 in the cylinder 24 through the shock absorption hole 44 as shown by the dotted line arrow in FIG. 2
5 is pressurized from the bottom side, the piston 25 rises, and together with this, the control rods 20 also rise, and the reactor core 3
A pull-out operation is performed. Also, during this control rod withdrawal operation, water existing in the space on the upper surface side of the drive piston 25 passes through the guide tube 28 through the orifice 40, further passes through the water passage 39, and is discharged from the water supply nozzle 37 during insertion. . When the control rod 20 is pulled out to the desired position and the supply of high pressure water is stopped, the collect finger 3
5 is engaged with a predetermined notch 36, the control rod 2
0 stops.

In addition, when an emergency shutdown of the nuclear reactor is required, it is sufficient to supply water at a higher pressure to the insertion water supply nozzle 37. In addition to strongly pressurizing the drive piston 25 from the upper surface side,
The gravity of the control rod 7 and the control rod 20 acts in the insertion direction, resulting in a rapid insertion operation.

In addition, in the unlikely event that the driving source (for example, high-pressure water) is lost when an emergency shutdown of the nuclear reactor is required, the water supply nozzle 38 can be opened to the atmosphere at the time of withdrawal, so that the gap between the upper surface side and the lower surface side of the drive piston 25 can be removed. The differential pressure of the control rod 20 increases rapidly, and in addition, the gravity of the drive piston 25, rod 27, and control rod 20 acts in the insertion direction, so the control rod 20 can be fully inserted quickly and safety can be ensured. can.

With the above configuration, since the rods 27 penetrate the reactor core from below and extend to the upper part of the reactor core, it becomes possible to arrange the control rods 20 in the upper part of the reactor core. Even if high-pressure water as a driving source is lost when a stop is required, the control rod 20 will be inserted by gravity.
Safety can be improved. Further, the drive piston 25 has a hollow shape, and the collect finger 35 is provided inside the cylindrical body 26, so that
It is not necessary to secure a large space between the cylinder 24 and the piston 25, and therefore the diameter of the cylinder 24 can be reduced, and the entire control rod drive mechanism can be made smaller.

As detailed above, according to the control rod drive mechanism according to the present invention, since the rod connecting the control rod and the drive piston extends to the upper part of the reactor core,
It became possible to place control rods at the top of the reactor core,
This allows the control rods to be inserted into the reactor core in the direction of gravity, and even if the drive source is lost during an emergency reactor shutdown, the control rods can be inserted by gravity, improving safety and reliability. is planned. Furthermore, by providing the collect finger inside the drive piston, the diameter of the cylinder can be reduced, and the overall size can be reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic sectional view showing a conventional example of a reactor pressure vessel section, Figs. 2 and 3 show an embodiment of the present invention, and Fig. 2 is a schematic sectional view of a nuclear reactor pressure vessel section. It is. DESCRIPTION OF SYMBOLS 11... Reactor pressure vessel, 14... Reactor core, 20... Control rod, 21... Control rod drive mechanism, 24... Cylinder,
25... Drive piston, 27... Rod, 33...
Release claw, 35...Collection finger, 36...Notch, 37...Water supply nozzle upon insertion, 38...Water supply nozzle upon withdrawal.

Claims (1)

[Claims] 1. A control rod drive mechanism housing that is provided at the bottom of the reactor pressure vessel and is hollow and has a closed lower end opening; a rod that is inserted through the core and whose upper end is connected to a control rod located at the top of the reactor core; a cylinder that is housed in the control rod drive mechanism housing; a hollow drive piston having a cylindrical body; a guide tube inserted into the drive piston from below and fixed to the cylinder; A collect finger that prevents the drive piston from falling and holds the drive piston at an appropriate height by engaging with any one of a plurality of notches formed in the axial direction on the inner circumferential surface of the drive piston, and the guide. It is housed in a collet receiver formed below the collet finger of the tube so as to be able to rise and lower, and is normally biased downward by a spring, so that when the pressure of driving water is applied from below, it resists the biasing force of the spring. a release claw that ascends to reduce the diameter of the collect finger inward in the radial direction to release the engagement between the collect finger and the notch; A pressurized flow path for inserting a control rod that communicates with the space on the upper surface side of the drive piston, a pressurized flow path for withdrawing the control rod that communicates with the space on the lower surface side of the drive piston from the outside of the control rod drive mechanism housing, and A control rod drive mechanism comprising: a release pawl flow path formed at a lower end of the release pawl for causing pressurized water supplied into the guide tube to act on a lower end surface of the release pawl.