JPH0324261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in centrifugal separators including centrifugal clarifiers and extractors having a cylindrical bowl at the lower end of a suspended, cantilevered drive shaft. .

[Technical Background of the Invention] The technical background will be explained below using a centrifugal clarifier as an example.

In nuclear fuel reprocessing plants, after dissolving spent nuclear fuel in nitric acid, U (uranium) and Pu are removed from the solution.
(plutonium) is extracted and recycled for use. In this reprocessing process, the insoluble residue generated when the fuel is dissolved is harmful in the U and Pu extraction process, so it is necessary to remove the insoluble residue from the solution using a centrifugal clarifier prior to extraction.

From the point of view of clarification performance, a cylindrical centrifugal clarifier as shown in Fig. 1 is suitable for this type of centrifugal clarifier. Since the rotary shaft drive mechanism 8 and the bearings 3 and 4 of the rotary shaft support mechanism are configured with a bowl 7 that performs a clarification action at the bottom, the rotary shaft 5 needs to be long, and the radiation level is extremely high below the shielding wall 1. It is impossible to provide a support mechanism at the bottom of the rotating shaft 5 because of the high height.

[Problems with the background art] In order to improve the performance (throughput, degree of clarification) of this type of clarifier, it is necessary to increase the circumferential speed of the bowl 7, which reduces the material strength of the bowl 7 and the vibration of the rotating shaft. It is essential to take this into consideration, and the wall thickness of the cylindrical portion of the bowl 7 must be increased in terms of material strength, which forces the lower end of the shaft to be heavier. On the other hand, from the viewpoint of vibration, the rotating shaft support mechanism shown in FIG. 2 (however, this figure shows a centrifugal extractor) is suitable.
The reason for this can be explained with reference to FIG. 2 as follows.
A bearing 3 that enables rotation around the axis of the rotating shaft,
A part of the housing 21 containing the 4 is spherical 22
By making it possible to move like a pendulum around the spherical center point A of the housing part 21,
In addition, by holding the housing part 21 with a spring 23 and a damper 24 whose constants can be arbitrarily selected, the critical speed of the shaft system, for example, a subcritical speed that does not exceed the low-order critical speed of the rotating shaft, is taken into account, and earthquake-resistant design is taken into consideration. can do.

However, a more reliable structure with better earthquake resistance was desired.

[Object of the Invention] The present invention was made in view of the above circumstances, and its purpose is to provide a suspended centrifuge that can maintain safety in the event of an earthquake or when unexpected vibrations are applied. It's about doing.

[Structure of the Invention] The centrifugal separator for nuclear fuel reprocessing according to the present invention is characterized by having a fixing device that restrains a movable housing housing a rotating shaft supporting bearing in the event of an abnormality.

[Effects of the Invention] According to the present invention, it is possible to provide a centrifuge that is safe even when an earthquake occurs or when unexpected vibrations are applied, and has radiation shielding and earthquake resistance.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG.

A rotating shaft 5 having a bowl 7 below has bearings 3 and 4.
The bearing is supported by a housing 21 that accommodates the bearing, and since the housing 21 has a spherical surface 22, it has a structure that allows pendulum movement around point A in the figure.

In the present invention, the displacement of the rotating shaft is measured by a non-contact displacement meter 3.
3, and when the displacement exceeds the allowable value, the plurality of hydraulic cylinders 3 attached to the frame 2
1 presses the housing part 21 from above, and rotates the rotating shaft 5
The structure is such that the housing 21, which moves with the swing of the vehicle, can be fixed. In addition, if the abnormal vibration subsides, the displacement meter 3
3, the hydraulic cylinder drive device 32 operates to release the lock.

With the main structure 29, when an earthquake occurs, seismic motion (force) is transmitted to the centrifuge from the shielding wall 1 on which the centrifuge is installed, causing the rotating shaft 5 to vibrate, but before the rotating shaft 5 and the shielding wall 1 come into contact. The housing 21 is fixed and the rotating shaft 5 is supported by a very stiff spring, and the rotating shaft 5 and the housing 21 vibrate together, but the vibration amplitude (displacement) can be made smaller than when the housing 21 is not fixed. realizable. Therefore, the gap between the shielding wall 1 and the rotating shaft 5 can be reduced, and it is possible to design a centrifuge that combines radiation shielding and earthquake resistance.

The reason for this is explained qualitatively as follows. As shown in Fig. 4, in this type of shaft system, as the rigidity of the spring 23 in Fig. 2 or 3, the so-called spring constant K, increases, the critical speed increases, and the rotational speed increases with a constant spring constant. and passing the dangerous speed limit multiple times. However, if the critical speed (rotational speed) to be passed is high, the amplitude of the rotating shaft when passing the critical speed becomes large, or the force acting on the bearings 3 and 4 becomes large. Since it is necessary to pass the speed, it is preferable to reduce the spring constant. Therefore, with a relatively small spring constant K ₁ as shown in Fig. 4, the first-order critical speed
It is common practice to pass W ₁₁ and set the rotation speed W _A below the secondary critical speed W ₂₁ as the rating.

Further, the constant C of the damper 24 shown in FIGS. 2 and 3 is taken into consideration, and the rotational shaft amplitude when passing the first-order critical speed is determined and organized using a computer, as shown in FIG.
The solid lines indicated by A ₁ , . . . , A ₄ in Fig. 5 are equal amplitude lines when passing the critical speed, and represent a tendency for the amplitude to become smaller from A ₁ to A ₄ . Therefore, for the above phenomenon, a design in which K is small and C is large is preferable.

On the other hand, the displacement of the rotating shaft when an earthquake occurs is expressed as K and C as described above.
The broken lines B ₁ , B _{2 .} . . B ₄ in FIG. 4 are obtained using a computer as parameters and smoothly show equal displacement lines.
Here, the magnitude relationship of displacement becomes smaller from B ₁ to B ₄ .

As described above, it has been found that it is better to increase C in order to reduce the rotating shaft amplitude and displacement when passing through a critical speed and during an earthquake. However, the desired size of C
In reality, this is not possible, and this is why we have come up with the present invention. In the present invention, as can be understood from FIG.
It is possible to operate at K and C corresponding to in the figure during ascending and descending speeds or during normal times, and to set the K and C corresponding to , that is, large K, at abnormal times to reduce the earthquake response displacement.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view schematically showing the main parts of a centrifugal clarifier for nuclear fuel reprocessing, Fig. 2 is a longitudinal sectional view schematically showing the main parts of a centrifugal extractor for nuclear fuel reprocessing, and Fig. 3 is a longitudinal sectional view schematically showing the main parts of a centrifugal clarifier for nuclear fuel reprocessing. FIGS. 4 and 5, which are cross-sectional views showing one embodiment of the present invention, are diagrams shown for explaining the present invention. DESCRIPTION OF SYMBOLS 1... Shielding wall, 2... Frame, 3, 4... Bearing, 5... Rotating shaft, 7... Bowl, 31... Hydraulic cylinder, 32... Hydraulic cylinder drive device, 33
...Displacement meter.

Claims (1)

[Claims] 1. A part of the housing that houses a bearing that supports the rotating shaft is a spherical seat, and the housing is movably fixed to a frame with a spring and a damper, and a cylinder is provided at the lower end of the rotating shaft that is supported by a cantilever. A centrifugal separator comprising a displacement meter for observing displacement of a rotating shaft and a housing fixing device attached to the frame, and a function of operating the fixing device in response to a signal from the displacement meter. .