JPS5814086A - 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 The present invention relates to a control rod drive device for a fast breeder reactor, and more particularly to a control rod drive device equipped with a control rod damping device during scram.

A control rod drive device for fast breeder reactors is a device that inserts or withdraws control rods into the reactor core in high-temperature fluid (liquid sodium). In the case of rapid shutdown of the reactor, the control rods are caused to fall at an angular velocity (scram) into the reactor core to stop the reactor operation.

During this rapid fall, the control rod must fall a predetermined stroke (height approximately 100,100 degrees) within a predetermined time, and the control rod will have a large falling speed in the final stage.

Therefore, if it is stopped quickly, an extremely large impact force will be generated.

Various shock absorbers have been developed to alleviate this impact force. As an example, a conventional scram shock absorber for a control rod drive device includes a cylindrical dash ram and a dash pot that fit into each other and utilize fluid restriction. FIGS. 1 and 2 are diagrams showing the structure of a conventional control rod drive device comprising a dash ram and a dash pot.

An upper guide tube 2 is supported on the upper part of the guide tube support plate 1. A dashpot 3 is provided inside the upper guide tube 2 and is integrated therewith. A dash ram 4 is inserted into the interior of this dash pot 3, and this dash ram 4 can move back and forth in the axial direction. The lower end of this dash ram 4 is integrally connected to a drive extension shaft 5, and a gripper 6 is attached to the lower end of this drive extension shaft 5.
is provided. The dash ram 4, drive extension shaft 5, and gripper 6 are guided by a guide portion 7 formed at the lower end of the dash pot 3 and driven in the vertical direction.

Further, a latch rod 8 for opening and closing the claw of the gripper 6 is built into the center axis of the drive extension shaft 5 and the dash ram 4.

The gripper 3 grips the two ends of the control rod 9 and connects the control rod 9 with the drive extension shaft 5. This control rod 9 is inserted into a lower guide tube 10, and the lower end of the control rod 9 is connected to a control rod dashpot 1 provided at the lower part of the lower guide tube 10.
1 is inserted. Note that the dashpot 11 and the lower guide tube 10 are integrally fixed by another support part (not shown). ! An entrance nozzle section 12 is attached to the lower end of the lower guide tube 10, and liquid sodium is forced to flow into the lower guide tube 10 from the lower part of the entrance nozzle section 12. This liquid IJum has the function of cooling and assisting in shock absorption in the event of a control rod falling. In addition, the dashpot 11 and the lower guide pipe 1
0 is placed in the hot fluid (liquid sodium) of the reactor core.

Next, the operation of the above conventional example will be explained. As shown in FIG. 1, the dash ram 4 has a cylindrical shape, and when the dash ram 4 plunges into the dash pot 3, the fluid inside the dash pot 3 is throttled to reduce the impact force when the vehicle stops. At this time, the lower end of the control rod 9 enters the control rod dashbot 11, and the impact force upon stopping is also buffered here, but the impact between the dashram 4 and the dashpot 3 is first buffered. Since the dimensional relationships are maintained, the control rod dashbot 11 has the role of buffering only the control rod 9 itself. The object of the present invention is the dash ram 4 and the dash pot 3, which are shock absorbers provided on the upper side.

By the way, the smaller the diameter gap between the dash ram 4 and the dash pot 3, the greater the buffering effect.
If this gap is small, a slight misalignment between the two causes the disadvantage that the dash ram 4 collides with the dash pot 3 when the dash ram 4 enters, as shown in FIG. This results in a metal-to-metal collision, and an extremely large impact force is applied to both metals, potentially resulting in damage to both. The impact force caused by the dash ram 4 colliding with the dash ram 4 at the entrance of the dash pot 3 has a negative effect on the reactor core and the control rod drive device itself. Therefore, in order to avoid a collision between the dash ram 4 and the dash pot 3, if the gap between them is widened, the buffering effect will be reduced, and in the final stage, the bottom of the dash ram 4 will be too close to the bottom of the dash pot 3. They will collide with each other due to the impact force. It is also possible to provide a guide over the entire stroke in order to prevent misalignment between the two, but in this case it is not preferable because the falling speed becomes slow and it becomes impossible to obtain a predetermined scram time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control rod drive device that smoothly absorbs shocks during control rod scrams.

The above object of the present invention is to provide a guide part at the lower end of the dashpot, form a guide part that engages with the guide part on the drive extension shaft, and guide the drive extension shaft just before the dashpot enters the dash ram. This is achieved by a configuration in which the dash pot and the dash ram are centered by engaging the guide portion at the lower end of the dash pot.

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 3 and 4 are cross-sectional views showing essential parts of an example of a control rod drive device according to the present invention. However, similar or identical components to those in FIGS. 1 and 2 are indicated using the same reference numerals.

A guide portion 7 is formed at the lower end of the dashpot 3, which is integrally attached to the upper guide tube 2. The drive extension shaft 5 connected to the lower part of the dash ram 4 inserted into the dash pot 3 is still engaged (sliding contact) with the guide part 7 formed at the lower part of the dash pot 3. A drive extension shaft guide portion 13 is provided for centering the dashpot 3 and the dash ram 4.

By the way, the positional relationship between the guide part 7 and the drive extension shaft guide part 13 is as shown in FIG. The relationship is such that the point passes through the guide part 7 and comes to the position d where the dash ram 4 and the dash pot 3 are centered. Because of this relationship, as shown in FIG. 4, when the dash ram 4 falls scram from above, the drive extension shaft guide portion 13 provided on the drive extension shaft 8 first hits the lower end of the dash board I.3. The dash ram 4 and the dash pot 3 enter the guide part 7 provided in the
After that, the Dalashiram 4 rushes into the dashpot 3.

According to this embodiment, the dash ram 4 is connected to the dash pot 3.
Immediately before entering the shaft, the guide section 7 and the drive extension shaft guide section 13 align the two, and then the shaft enters the shaft.
The dash ram 4 is prevented from colliding violently with the inlet of the dash pot 3, the dash ram 4 smoothly enters the dash pot 3, and the liquid sodium in the dash bot 3 is compressed and squeezed to control the scram. It has the effect of cushioning the impact of the rod drive device. Since the dash ram 4 and the dash pot 3 are centered, the diameter gap between them can be reduced, and a large buffering effect can be obtained.

As is clear from the above description, according to the present invention, a guide section is provided at the lower part of the dashpot and the drive extension shaft, and by centering the two immediately before the dash ram enters the dashpot, the control rod It is possible to provide a control rod drive device that smoothly buffers the impact during scram.

[Brief explanation of drawings]

Figure 1 is a longitudinal sectional view showing a conventional control rod drive device equipped with a control rod shock absorber; FIG. 3 is a longitudinal cross-sectional view showing a main part of an embodiment of the control rod drive device according to the present invention, and FIG. 4 is a vertical cross-sectional view showing the state immediately before the dash ram of FIG. 3 enters the dashpot. be. 2... Upper guide pipe, 3... Dashpot, 4...
- Dash ram, 5... Drive extension shaft, 6... Gripper, 7... Guide section, 9... Control rod, 10... Lower cavity inner tube, 11... Control rod dashpot , 13・
...Drive extension shaft guide part.・zu- Agent Patent Attorney Takahashi Meishaku Year 3

Claims (1)

[Claims] 1. It has a control rod impact force mitigation device whose main components are a dash ram connected to the reactor control rod by a drive extension shaft and a dash pot into which this dash ram enters, and is installed inside the reactor core. In a control rod drive device that inserts and pulls out control rods, a guide part that surrounds the outer periphery of the drive extension shaft is provided at the bottom of the dash pot, and the dash ram engages with this guide part to cause the dash ram to open the dash board! - A control rod drive device characterized in that a guide portion for centering both of them immediately before entering is provided on the outer periphery of the drive extension +1qll.