JPS61291052A - Pendulum type centrifugal separator for decantation - 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 pendulum centrifuge for decantation.

More particularly, the present invention relates to an apparatus for decantating a liquid in which small particles are suspended by rotating it in a centrifugal separator fixed to the lower end of a drive shaft.

As is well known, when reprocessing nuclear reactor fuel assemblies,
Many operations are required for reprocessing, a process that completely recovers the actinides remaining in the spent fuel assembly from the core.

First, the fuel assembly is pulverized into small pieces, for example by shredding. Each piece will contain a portion of the irradiated fissionable material, a portion of the solid fission products, and a portion of the fuel assembly protection vessel (usually made of Zircaloy). Next, these small pieces are dissolved, and for example, small pieces of the protective container are
In the case of particles having various particle sizes ranging from several microns to several millimeters, such as tltng), the fuel cladding and some of the particles do not dissolve but are suspended. There are also other insoluble solid fission products that can have particle sizes ranging from less than one micron to several microns. Suspended particles such as the latter are of course highly radioactive.

After the dissolution operation, as is well known, (residual fission products and other products are extracted from the solution by chemical means. This is the so-called treatment, but this extraction operation is Extremely difficult. For example, these insoluble products can accumulate and block the extraction equipment. Among these solid particles, finely ground Zircaloy poses a risk of spontaneous combustion. Also, the insoluble fission products can create hot spots in the equipment. can occur.

Therefore, a clarification step is inserted between the dissolution step and the extraction step in order to recover the maximum amount of particles suspended in the solution.

Three types of clarification methods have already been proposed. The first is static decantation, but this is not very effective. This is because the particles are so small that only the largest particles can be removed using this method, even if a reasonable amount of time is taken. The second is filtration. The main drawback of this method is that the filter cartridge becomes clogged quickly.

The third method is to use a pendulum-hole decantation centrifuge. In this method, an insoluble matter-containing solution is introduced into a container having an overflow passageway in the upper end. The rotational speed forces the solid particles against the side walls of the container, forming a cake, and the liquid flows out of the container via the overflow passage. However, prior art decantation centrifuges have drawbacks in subsequent treatment of the insoluble cake. The cake is washed with nitric acid, which still contains some solution of fissile material or other material to be recovered after centrifugation, but this washing presents several problems. That is, since this operation has to be repeated many times, a considerable amount of cleaning liquid is required, resulting in an increase in the amount of drained liquid. This operation is carried out in substantially laminar flow conditions and is therefore inefficient and therefore requires large amounts of solution. Still, the efficiency of this cleaning process increases when the density of the cleaning solution is greater than or equal to the density of the residual liquid to be removed, which limits the range of cleaning solution choices.

Additionally, prior art centrifuges lack reliable core-aware arrangements. That is, if a situation occurs where the exit is blocked, the accumulation of existing fissile material may reach a critical level.

The invention particularly relates to a pendulum centrifuge for decantation which does not have the above-mentioned drawbacks. More particularly, the centrifuge of the present invention allows decantation to be carried out with high efficiency. The centrifugal separator of the present invention is also configured to ensure subcritical placement and arrangement. Moreover, the cake cleaning operation is also carried out under much more favorable conditions, so that the residual fissile material in the cake can be better extracted with a very clean cleaning solution.

That is, the present invention includes a plug constituting a biological shield, a fixed outer container is suspended below the plug, and the outer container holds a rotating container whose tip is fixed to the lower end of a vertical drive shaft passing through the plug. A centrifugal separator for decanting liquids containing solid particles of the type, wherein the rotating vessel has an upper cylindrical part with a cylindrical edge constituting an overflow edge for the liquid and is inclined with respect to the drive shaft. a lower part having an inner wall surface connected to the bottom of the rotary vessel and also connected to the upper part of the rotary vessel through a very wide conical connecting surface, the plug being inserted into the upper part of the rotary vessel; an elongated cylindrical extension which cooperates with the upper cylindrical part to define an annular fining space which communicates with the lower part of the rotating vessel via an annular passage; a first insertion tube system configured to pass through the plug and introduce liquid into the passageway; a two-pipe system, means for collecting clarified liquid in the outer vessel after the liquid has crossed the overflow edge, siphon means for collecting liquid from the lower part of the rotating vessel, and liquid in the lower part of the rotating vessel as it rotates; and means fixed to the plug for stirring, the conical shape of the lower part of the rotary container and the conical shape of the connecting surface being initially present in the lower part when the rotary container rotates at a specific speed. The centrifugal separator is characterized in that the liquid and particles float and flow into the annular clarification space.

Preferably, the inner wall surface of the lower part of the rotating container has a conical upper part.

The present invention will be explained in more detail below by giving non-limiting specific examples based on the attached drawings (Flg, 1, Ftg, 2).

In the embodiment of the centrifugal separator shown in these figures, two sets of movable members are arranged below a biological shield 2 made of steel, for example. The shield has a removable plug 4 above the centrifuge body. The centrifuge is enclosed in a generally cylindrical enclosure 6 which is suspended in the shield 2 and has a vent tube 96. The centrifuge vessel (generally designated 8) is secured to a drive shaft 10 whose tip passes through a vertical hole 12 in the plug 4. The upper end 10a of the shaft 10 is held by a bearing 13 which provides a kind of ball and inner and outer ring effect.

shirt) 10 is an electric drive motor 1 above the upper end 10&
6 is connected to the shaft 14 of No. 6.

A sealing means is also provided, such as by scavenging gas introduced via the blue line 18.

The rotating container 8 has an upper part 8a of a decantation vessel and a lower part 8b having a tip forming a connection area with the upper part. The upper region 8a for decantation consists of a cylindrical wall of diameter DI, whereas the inner wall 20 of the lower or collecting reservoir 8b is conical. More specifically, this wall surface forms an angle of approximately 15° with respect to the perpendicular, ie, with respect to the direction of the rotation axis 10. Generally, this half-angle has a value between 10 and 20°, preferably very close to 15°.

The lower part 8b and the upper part 8a are connected to each other via an annular connecting part 22 having a slightly circular Φ1 shape.

As mentioned above, the inner surface 2 of the lower part 8b
However, if the upper part is inclined with respect to the perpendicular in the vicinity of the connecting part 22, it is not necessary to form it into a conical shape. This elevated surface portion 20 may be, for example, a paraboloid, in which case the plane tangential to this paraboloid satisfies the above-mentioned angular conditions. An annular plate 24 is arranged at the upper end of the upper part 8a.

The plug 4 has a downward extension 4a within the rotating vessel upper part 8a. The JJl'Iin of the upper part 8a comprises, for example, four radial fins 9. The outer wall 26 of the extension 4a cooperates with the side wall of the upper part 8a to define a cleaning wedge-shaped space 28. The annular space 28 communicates via a hollow channel 30 with the interior of the row-side enclosure 6 and below via an annular channel 32 with a collection area 34 defined by the lower container part 8b.

The outer enclosure 6 communicates with the square annular passage 30 by means of a chair-shaped buttful 35 defined therein by an outer overflow space 36,! 1 m, a collection space 38 inside a baffle 35.

The blue line 40 communicates with the lower end of the annular overflow space 36. A drain pipe system 41 communicates with the lower end of the collection space 38. The collection area 34 is located on the inner wall surface 54 of the lower part 8b.
It has a cylindrical baffle 52 which cooperates with it to define an overflow region 56.

The region 56 has a passage 58 passing through the lower end of the lower portion 8b and connecting the overflow region 56 and the collection space 38.
has.

The blue line 42 passes through the lower part 4a of the plug 4 and
It passes through the bottom surface 4bK. A flow deflector 44 is arranged at the lower end of the blue line 42, by means of which the liquid flowing in the tube 42 is directed in the direction of the annular passage 32. The other end of the blue line 42 is connected to a withdrawal hole line 46 for supplying the liquid to be decanted.

The centrifuge further comprises a tube 60 having a free end near the bottom of the lower part 8b. This blue line 60 passes through the plug 4a and constitutes one arm of the siphon 62. Siphon 62 also has a second arm 64. This siphon will be explained in detail later.

Operation is actually made more reliable by having two siphon devices. In this case two reserve siphons may be provided.

As shown in the accompanying drawing (FIG. 2), the centrifuge also includes a blue line 7o for removing cake.

The blue system 70 has a plurality of nozzles 72 that protrude toward the side wall of the cylindrical upper portion 8a of the container. A tube 74 is also provided that extends to near the bottom of the lower portion 8b. A blue line 76 also passes through the plug 4 to clean the O/M flow area 56.

As an example, the upper part 8a has a diameter D! of 900+1111!
has. The rotating vessel is made of titanium and therefore has a lower density and therefore can have a larger diameter for a given rotational speed. In this way a diameter is obtained that is comparable to the prior art and thus the decantation effect is improved.

This centrifuge operates as follows. During the actual decantation, the solution is conveyed through the tubing 42 after the vessel has started rotating at the rated rotational speed. Due to the rotation and the presence of the deflector 44, liquid flows into the clarification annular space 28. The b+z particles (X point P) are pressed against the wall surface of the upper part 8.a to form a cake. Due to the centrifugal action, the liquid overflows through the passage 30 into the overflow space 36 .

In this way the liquid is clarified. That is, suspended residual particles are almost completely removed. The clarification solution exits via tubing 40. After clarifying an amount of solution corresponding to a predetermined tonnage, the container 8 is stopped by natural deceleration. The cake remains attached to the side walls of the upper part 8a. The liquid falls into the collection area 34. The solution, which may contain cake fragments, is discharged by a siphon 62 upstream of the clarification assembly. This solution can be recycled.

As mentioned above, the cake formed on the side wall 8a must be washed in order to completely extract the solution remaining therein. This process is carried out by the following operations: A nitric acid solution is ejected from a nozzle 72 using a tubing 70. In the embodiment shown, the amount of solution required for this purpose is less than the volume of the fining annular space.

This removal operation causes the sludge to fall into the collection area 34 where it is preferably suspended by low speed alternating rotation of the container 8 by the drive motor 16. Very effective cleaning is achieved because the lower end of the siphon tube 60 acts as an agitator. After the mixing operation, increase the rotational speed of the container to the rated speed. The liquid and the solid are contained in the conical wall surface 20 of the lower part 8a.
The water floats up to the surface and flows into the annular fining processing space 28.

This levitation occurs at speeds well below the rated speed. Once the cake has reformed, the centrifuge is stopped, preferably by natural deceleration. The wash solution falls to the bottom of the lower part 8b and is recirculated upstream of the clarification assembly. Repeat this washing operation many times.

It is clear that the use of such a snowmaking and cake cleaning method provides greater efficiency than prior art devices, even with a reduced number of cleaning operations. Of course, if the number of cleaning operations is small, the amount of drained liquid is also small.

After washing, the particles are collected in collection area 34, forming a particle-enriched suspension. further introducing a cleaning solution into the container;
The region 34 is emptied by continuing to stir the solution by slow rotation of the container.

The supplied solution overflows into the oatsmer flow region 56 and then into the collection space 38 .

Once the concentration of the suspension has decreased sufficiently, a second siphon, identical to siphon 62, is used to drain the solution.

Siphon 62 is started by piston 80.

This piston is placed in a chamber 82 provided in the plug 4 and blocked by a small plug 84. Piston chamber 80B is fixed to small plug 84. The piston body includes a plate 80b fixed at one end to a small plug 84 and at the other end to a circular plate 80c. A control rod 80d is fixed to the plate 80c. This rod 80d passes through the small plug 84 and is driven by a motor 86. The piston chamber 80a has a passage 80f.
is connected to the siphon 62 via. As rod 80d rises, a negative pressure is created within chamber 80e, resulting in the siphon being activated. Although other conventional starting devices may of course be used, the device of the present invention has many advantages. First, because all the seals are static, the bellows 80b provides extremely high sealing performance. Second, even if the siphon is damaged, the siphon assembly can be removed by moving the small plug 84 upward.

As shown in FIG. 1, it is used to supply a starting container 90 with sufficient inert solution to start the second arm of the siphon. A second siphon 94 is used to drain this solution.

As is clear from the above description, the centrifuge of the invention has many advantages over those of the prior art. The centrifugal separator of the invention is subcritical in alignment mainly because the central space is occupied by the plug extension 4a. It also allows decantation to be carried out more effectively. Furthermore, the amount of solution required for the cake cleaning operation is small (
Therefore, there are fewer fireflies in the drainage fluid. These operations may be performed using a dilute nitric acid solution, a solution that will not ignite the Zircaloy particles.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a centrifugal separator according to the present invention along a first vertical radial plane, and FIG. 2 is a longitudinal sectional view of the centrifugal separator along a second radial plane substantially perpendicular to the first vertical radial plane. It is a diagram. 2... Biological shield, 4... Plug, 6... Enclosure container, 8... Centrifugation container, 22... Annular connection part,
28...Annular space for clarification, 44...Deflector, 62.94...Siphon, 72...) Zuru,
80°° Bi'stone, 8Qb...Bellows.

Claims (8)

[Claims] (1) A rotating container including a plug constituting a biological shield, with an outer enclosure fixed under the plug suspended, and a rotary container having a tip fixed to the lower end of a vertical drive shaft passing through the plug. A pendulum centrifuge for the decantation of liquids containing solid particles of the type in which an enclosure retains a cylindrical upper part with a cylindrical end defining an overflow edge for the liquid; a lower part having an inner wall surface inclined with respect to the axis and connected to the bottom of the rotating vessel and also connected to the upper part via a very wide conical connecting surface, the plug being connected to the bottom of the rotating vessel; having a cylindrical extension projecting into the section;
This extension cooperates with the cylindrical upper part to define a clarification current space, which space communicates with the lower part of the rotary vessel via an annular passageway, the device passing through the plug and into the passageway containing liquid. a first insertion tube system configured to introduce liquid, and a second tube system including a plurality of nozzles configured to direct liquid to the cylindrical wall of the upper portion of the rotating vessel.
a system of tubing, means for collecting clarified liquid in the outer vessel after the liquid has crossed the overflow edge, at least two sets of siphon means for collecting liquid from the lower part of the rotating vessel, and rotation of the rotating vessel; and means fixed to the plug for stirring the liquid in the lower part of the container,
The slope of the lower part of the rotating vessel and the conical shape of the connecting surface cause liquid and particles originally present in the lower part to float up and flow into the fining annular space when the rotating vessel rotates at a certain speed. A centrifugal separator characterized by being determined as follows. (2) The centrifugal separator according to claim 1, wherein the inner wall surface of the lower part of the rotating container is conical. (3) The half angle of the apex of the conical wall surface is 10 to 20°
The centrifugal separator according to claim 2, characterized in that the centrifugal separator is between. (4) The centrifugal separator according to any one of claims 1 to 3, wherein the rotating container is made of titanium. (5) The lower part of the rotating vessel has a cylindrical internal baffle with an upper free end, the baffle surrounding the shaft and defining an overflow space for the lower part inwardly. The centrifugal separator according to any one of paragraphs 1 to 4. (6) a first siphon arm in which the siphon means protrudes into the lower part of the rotating container and passes through a portion of the plug;
Claims 1 to 5 characterized in that it has a second arm connected to the first arm by a shaped connection and communicating with a container outside the stationary container, and starting means.
The centrifugal separator according to any of paragraphs. (7) the starting means comprises a piston including a chamber connected to a T-shaped siphon, the chamber having a deformable metal bellows, one end of which is fixed to the wall of the chamber and the other end of the piston with a plate; 7. A centrifuge according to claim 6, characterized in that the plate is connected to means for moving it along the axis of the chamber. (8) The piston is disposed in a cavity provided in the plug and closed by a small bioshielding plug, and the piston chamber is suspended from the small plug. The centrifugal separator according to paragraph 7.