JPS6333676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealing device for sodium or cover gas in a control rod drive device of a sodium-cooled fast neutron nuclear reactor (fast reactor).

In the above-mentioned fast reactor, sodium is used as a coolant, and the upper part of the sodium liquid level is filled with a cover gas that prevents the rise of sodium vapor. It is necessary to seal the sodium vapor or cover gas.

Figure 1 shows the bellows of the coarse adjustment rod drive mechanism (hereinafter referred to as
It is called CRD bellows. ) is shown. The CRD bellows 7 is provided with an inner guide ring 3 and an outer guide ring 4 to prevent excessive expansion and contraction of the control rod during constant driving. A large number of inner guide rings 3 are arranged above and below to surround the control rod drive shaft extension tube 5. The upper and lower ends of the inner guide ring 3 are provided with protruding rings 6 that protrude outward, and an outer flange 8 protrudes from the center. This inner guide ring 3 is partially cut away at the upper and lower sides to form cut portions 12, and the cut portions 12 are provided at three locations on both the upper and lower sides. The outer guide ring 4 is arranged so as to surround the upper and lower ends of the inner guide rings 3 that are vertically adjacent to each other, and has a protrusion ring protruding inwardly at the upper and lower ends so as to engage with the protrusion ring 6 of the inner guide ring 3. In addition, a flange 8 protrudes outward from the central portion. Each flange 8 of the inner guide ring 3 and the outer guide ring 4 is connected by each bellows 2.

The uppermost inner guide ring 3 can be hooked onto a fixing ring 10 fixed to the base 1.
The lowermost inner guide ring 3 can be hooked onto a drive ring 11 fixed to the control rod drive shaft extension tube 5. The bellows 2 at the top end is fixed to the base 1, and the bellows 2 at the bottom end is fixed to the drive ring 11.
The bellows 2 achieves sealing. FIG. 2 shows a detailed structural diagram of the inner guide ring 3 and the outer guide ring 4.
When manufacturing the CRD bellows 7, the inner guide ring 3 and the outer guide ring 4 are assembled alternately, and the single bellows 2 is welded to the flange 8 of the guide ring between them. The ring 3 is provided with a notch 12. According to the design example of the conventional rough adjustment rod,
There are ten inner guide rings 3 and ten outer guide rings 4 as described above, and during a scram, these fall while repeatedly colliding with each other in a complicated manner.

Figure 3 shows the analysis results of the dynamic behavior (time-displacement) of the CRD bellows 7 when the CRD bellows 7 is scrammed at a speed of approximately 2300 mm/s. It can be seen that the displacement is constrained. From Figure 3, 11 from the bottom
The th mass point (inner guide ring 3) and the 12th mass point from the bottom
Figure 4 shows the temporal change in the distance to the second mass point (outer guide ring 4), and the temporal change in the aperture strain of the bellows 2 connected to the outer guide ring 4. is shown in Figure 5. The sudden rise in the strain between the guide rings in Figure 4 is caused by the fact that the displacement of the upper guide ring is restrained sequentially, and as a result, after the outer guide ring 4 collides with the inner guide ring 3 at high speed, , it can be seen that the bellows 2 vibrates with a large amount of strain. This is due to the inertial force of the bellows 2 caused by the sudden restriction of displacement of the outer guide ring 4.

If such a large amount of strain occurs in the bellows 2 and the scram is repeated, fatigue cracks will occur in the bellows 2, increasing the possibility of breakage. There have been a few actual cases of bellows breakage accidents in control rod drive mechanisms, and this is a serious problem that can lead to accidents in which cover gas inside the reactor leaks out of the reactor vessel.

The purpose of the present invention is to reduce the inertial force of the bellows caused by the collision of the guide ring, reduce the amplitude of vibration of the bellows after the collision of the guide ring, reduce the amount of distortion, and prevent damage to the bellows. There is a particular thing.

The present invention provides an axial air resistance plate near the collision of the guide ring to apply viscous resistance to the guide ring in order to reduce the guide ring speed before the collision of the guide ring and reduce the amount of distortion of the bellows. It is something. Therefore, since the speed of the guide ring at the time of a collision can be suppressed, the inertial force of the bellows is reduced, the amount of distortion can be reduced, and damage to the bellows can be prevented.

Examples will be described below.

FIG. 6 shows the structure of an embodiment of the present invention, and the same parts as in FIG. 2 are given the same numbers. The differences in this structure from FIG. 2 are as follows.
That is, a vertically long air resistance plate 9 is attached along the vertical edge of the notch 12 and continues with the protrusion ring 6, and the air resistance plate 9 protrudes in the direction of the outer guide ring 4. Air pockets 13 are formed between the guide rings. The arrows in FIGS. 2 and 6 indicate the direction of gas flow between the guide rings.

In the guide ring of the CRD bellows 7 having such a structure, when the lower inner guide ring 3 collides with the upper outer guide ring 4 in FIG. However, the flow path of the gas attempting to flow out is blocked by the air resistance plate 9, and the viscous resistance of the gas increases. The speed at which the inner guide ring 3 collides while experiencing such viscous resistance is smaller than that without the air resistance plate, and therefore the inertia of the bellows 2 coupled to the inner guide ring 3 is reduced. Power will also decrease. As a result, the amplitude of vibration of the bellows 2 becomes smaller, and the amount of distortion can be reduced.

During scram, the CRD bellows 7 has a large distortion amplitude as shown in Figure 5, and especially the CRD
At the bottom of the bellows 7, the distortion due to the reflected waves is superimposed and the distortion increases as shown in FIG. decreases.

The air resistance plate 9 is attached to a protruding ring 6 with a plate thickness of 3 mm, but since it will not collide with the upper and lower guide rings, it is only necessary to attach plates with a thickness of about 0.2 mm by welding, and the weight of the entire guide ring is reduced. The increase is small.

Although the air resistance plate 9 is attached to the inner guide ring 3 in the above embodiment, it may be attached to the protrusion ring 6 of the outer guide ring 4. However, attaching the air resistance plate 9 to both the inner guide ring 3 and the outer guide ring 4 is a CRD
The procedure for manufacturing the bellows 7 is difficult.

As described above, the bellows of the control rod drive mechanism device of the above embodiment can suppress the speed at the time of collision of the guide ring, so the amount of distortion of the bellows can be reduced, and damage to the bellows can be prevented. can.

[Brief explanation of the drawing]

Figure 1 is a bellows structural diagram of the coarse adjustment rod drive mechanism.
Fig. 2 is a structural diagram of the guide ring, Fig. 3 is a diagram showing the behavior of the bellows, Figs. 4 and 5 are diagrams showing temporal changes in the bellows, and Fig. 6 is a structural diagram of an embodiment of the present invention. be. DESCRIPTION OF SYMBOLS 1...Base, 2...Bellows, 3...Inner guide ring, 4...Outer guide ring, 5...Control rod drive shaft extension tube, 6...Protrusion ring, 7...
CRD bellows, 8...flange, 9...air resistance plate, 12...notch, 13...pocket.

Claims (1)

[Claims] 1 A plurality of inner guide rings on the upper and lower sides surrounding the middle of the control rod drive shaft extension tube have notches from the middle to the upper and lower ends, protruding rings protruding outward at the upper and lower ends, and protruding rings protruding outward in the center part. The outer guide ring has a protruding flange, and the outer guide ring is placed in a position to surround the upper and lower parts of each of the inner guide rings that are vertically adjacent to each other. In the control rod drive device, the control rod drive device has a shape having a protrusion ring protruding from the center portion, and a flange protruding outward from the central portion, and each flange of the inner and outer guide rings is connected by a bellows. At least one of both guide rings is provided with a vertically long plate as an air resistance plate that is arranged so as not to interfere vertically with the protrusion ring of the other guide ring and protrudes in a direction to close the gap between the inner and outer guide rings. A control rod drive device characterized by: