JPS6324748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pendulum centrifuge for decanting liquids containing solid particles.

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

As is known, when reprocessing nuclear reactor fuel assemblies, many operations are required to completely recover the actinides remaining in the spent fuel assemblies from the reactor core. is required. 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,
For example, if the pieces of the protective container are like filings and have different particle sizes from a few microns to a few millimeters, the fuel cladding and some of the particles do not dissolve but become 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, residual fission products and other products are extracted from the solution by chemical means, as is well known. This is a so-called treatment, but this extraction operation is extremely difficult due to the presence of the two types of insoluble products. For example, these insoluble products can accumulate and block the extraction equipment. Of these solid particles,
Finely ground Zircaloy is a risk of spontaneous combustion. Also, insoluble fission products can cause hot spots in the device.

Therefore, a clarification step is inserted between the lysis 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, which 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. Second
It's too much. The main drawback of this method is that the filter cartridge becomes clogged quickly.

The third method is to use a pendulum 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 because it 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 drainage liquid. This operation is carried out in substantially laminar flow conditions and is therefore less efficient and therefore requires large amounts of solution. Also,
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, thus limiting 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.

It is an object of the invention to provide a pendulum centrifuge for decanting liquids containing solid particles which does not have the drawbacks mentioned above.

According to the present invention, the object is to provide a biological shield having a through hole, a fixed outer container having an upper opening edge attached to one surface of the biological shield to cover the through hole, and one end portion of the fixed outer container. is suspended on the wall of the biological shield defining the through hole, and has a cylindrical extension protruding into the internal space of the outer container at the other end, and is aligned with the axis of the cylindrical extension. a vertical drive shaft inserted into the through hole of the plug member such that one end projects from the end face of the cylindrical extension toward the bottom of the outer container; , a cylindrical top portion surrounding the outer peripheral surface of the cylindrical extension to cooperate with the cylindrical extension to form a clearing annular space; a lower portion fixed at the center to the one end of the vertical drive shaft; and a rotating container having an inverted truncated conical connection part connecting the cylindrical top part and the lower part to form an annular passage communicating the internal space of the lower part and the annular fining space. , a first conduit means extending through the plug member and configured to introduce a liquid containing solid particles into the annular passage, and formed on the inner surface of the cylindrical top at a position facing the inner surface. a second tube means comprising a plurality of nozzles for squirting cleaning liquid onto the cake, and clarified liquid in said outer container spilling over an overflow lip formed at one end of said cylindrical top. and first means for withdrawing liquid remaining in the interior space of said lower part after the clarification operation performed prior to the cleaning operation;
a second means for extracting the liquid containing solid particles resulting from washing the cake with a washing liquid and remaining in the interior space of said lower part after the washing operation; stirring means fixed to the end face of the cylindrical extension to stir the cleaning liquid in the internal space of the cylindrical extension, the wall of the lower part continuous with the inverted truncated conical connection being oriented with respect to the axis. and the inverted frusto-conical connection has a generatrix inclined with respect to the axis, and the inclination of the inner surface of the wall of the lower portion and the generatrix with respect to the axis is , a liquid containing solid particles, which is determined such that when the rotating container rotates at a certain speed, the liquid and solid particles initially present in the internal space of the lower part flow into the fining annular space. This is achieved by a pendulum-shaped centrifuge for decanting.

The invention relates in particular to a pendulum centrifuge for decanting liquids containing solid particles which does not have the above-mentioned drawbacks. More specifically, the centrifuge of the present invention allows decantation to be performed with high efficiency. The centrifugal separator of the present invention is also configured to ensure subcritical placement and arrangement. Furthermore,
The cake washing operation is also carried out under much more favorable conditions, so that much smaller amounts of washing solution are needed to better extract residual fissile material in the cake.

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 Fig. 1 and Fig. 2.

In the embodiment of the centrifugal separator shown in these figures, a set of movable members is arranged below a biological shield 2 made of steel, for example. The shield is provided with a plug 4 as a removable plug member above the centrifuge main body.
has. The plug 4 is suspended from a wall defining a hole 100 as a through hole of the biological shield. The centrifuge includes an enclosure 6 as a substantially cylindrical fixed outer container suspended in the shield 2 and having a vent tube 96.
enclosed within. A centrifugal separator (generally designated 8) as a rotating vessel is fixed to a vertical drive shaft 10 whose tip passes through a vertical hole 12 as a through hole in the plug 4. The upper end 10a of the shaft 10 is held by a bearing 13 which provides a type of ball and inner and outer ring effect. The shaft 10 is connected to the shaft 1 of the electric drive motor 16 above the upper end 10a.
Connected to 4. Sealing means are also provided, such as by scavenging gas introduced via the pipe system 18.
The shaft 10 extends from the end face 4b of the downward extension as a cylindrical extension within the internal space 106 of the enclosure 6 in the direction of the bottom 105 of the enclosure 6.

The rotating container 8 has an upper part 8a as a cylindrical top for performing decantation, and a lower part 8b having a tip forming a connection area with the upper part. Upper area 8 for decantation
a consists of a cylindrical wall of diameter D ₁ , whereas the inner wall 20 as the second inner surface of the lower or collecting part 8b is conical. More specifically,
This wall surface is perpendicular to the axis of the downward extension 4a,
That is, it forms an angle of approximately 15° with respect to the direction of the rotation axis 10.
More 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 interconnected via a slightly conical annular connection part 22 as a frustoconical connection part. The lower part 8b includes a bottom part 101 fixed to the drive shaft 10 and a bottom part 101 fixed to the drive shaft 10.
01 and a wall portion 102 connected to the wall portion 102. bottom 1
01 and the wall 102 define an internal space 103.

As mentioned above, the inner wall surface 20 as the inner surface of the lower part 8b does not need to be conical as long as its upper part is inclined with respect to the perpendicular in the vicinity of the connecting part 22. This wall portion 20 may be, for example, a paraboloid, in which case the tangential plane to this paraboloid satisfies the above-mentioned angular conditions. An annular plate 24 serving as an overflow edge is arranged at the upper end of the upper part 8a.

The plug 4 has a lower extension 4a as a cylindrical extension in the upper part 8a of the rotary container. Upper part 8a
The wall surface 104 as the inner surface includes, for example, four radial fins 9. The outer wall 26 as the outer peripheral surface of the extension part 4a cooperates with the side wall of the upper part 8a to define an annular fining space 28 as a fining annular space. The annular space 28 has an upper annular passage 30
It communicates with the interior of the outer enclosure 6 via an annular channel 32 and below with a collection area 34 defined by the lower container part 8b. The outer enclosure container 6 has a container-shaped buttful 35 fixed thereto.
is divided into an outer overflow space 36 communicating with the upper annular passage 30 and a collection space 38 inside the baffle 35 . A pipe system 40 as collection means for clarified liquid 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 has a cylindrical buffle 52 as a cylindrical internal buffle which cooperates with the inner wall surface 54 of the lower part 8b to form an overflow area 56. The region 56 has a passage 58 passing through the lower end of the lower portion 8b and connecting the overflow region 56 with the collection space 38. Cylindrical buttuful 5
The upper end of 2 forms a top free portion 109.

A pipe system 42 as a first pipe means passes through the lower part 4a of the plug 4 and communicates with the bottom surface 4b as an end surface of the plug 4. At the lower end of the tube system 42 a flow deflector 44 is arranged, 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 tubing 42 is connected to a retractable tubing 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 pipe system 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 becomes reliable in practice 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 tube system as a second tube means for removing cake. The pipe system 70 includes a plurality of nozzles 7 that protrude toward the side wall of the cylindrical upper portion 8a of the container.
It has 2. A tube 74 is also provided that extends to near the bottom of the lower portion 8b. A line of tubing 76 also passes through the plug 4 to clean the overflow area 56.

By way of example, the upper part 8a has a diameter D ₁ of 900 mm. 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. This larger diameter than in the prior art provides, other factors being equal, a greater ability to immobilize suspended particles, thus improving the decantation effect.

This centrifuge operates as follows. During the actual decantation, the solution is conveyed through the line 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 suspended particles (point x P) are pressed against the wall of the upper part 8a 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 is collected in the collection area 34
fall inside. A solution that may contain pieces of cake is
It is evacuated by a siphon 62 as the first means upstream of the finer assembly. This solution can be recycled.

As previously mentioned, the cake formed on the sidewall 8a must be washed to completely extract the solution remaining therein. This process is performed by the following operation. To remove the cake, pipe line 7
The nitric acid solution is jetted out from the nozzle 72 using 0. In the embodiment shown here, the amount of solution required for this purpose is less than the volume of the clarification annular space.

This removal operation removes the sludge from the collection area 34.
, where it is preferably suspended by low-speed alternating rotation of the container 8 by the drive motor 16. Since the tube 107 as a stirring means attached to the downward extension 4a to surround the lower end of the tube 60 as the first siphon leg of the siphon operates as a stirrer,
Very effective cleaning takes place. After the mixing operation,
Gradually increase the rotational speed of the container to the rated speed. Liquids and solids float along the conical wall 20 of the lower part 8a and flow into the annular clarification 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 device 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. Region 34 is emptied by introducing more cleaning solution into the container and continuing to stir this solution by slow rotation of the container.
The supplied solution overflows into the overflow area 56 as an overflow space and then into the collection space 3
8. When the concentration of the suspension is sufficiently reduced, the second
Drain the solution using a siphon.

Siphon 62 is started by piston 80. This piston is placed in a chamber 82 provided in the plug 4, and is blocked by a small plug 84 as a small plug member for a biological shield. The upper space of the cavity 108 provided in the plug 4 is closed by a small plug 84. piston chamber 80
a is fixed to the small plug 84. The piston body includes a bellows 80b as a deformable metal bellows fixed to a small plug 84 at one end and a circular plate 80c as a plate at the other end. 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 80 in a T-shaped connection.
It is connected to the siphon 62 via f. Rod 8
As 0d rises, a negative pressure is created in the chamber 80e, which results in the siphon starting. piston 80
constitutes the means for initiating the extraction action of the siphon, and motor 86 and control rod 80d constitute the means for moving plate 80c. Although other conventional starting devices may of course be used, the device of the present invention has many advantages. Firstly,
Since the seals are all static, the bellows 80b
This provides extremely high sealing performance. Second, if the siphon is damaged, the siphon assembly can be removed by moving the small plug 84 upwards.

As shown in FIG. 1, a second arm 64 as a second siphon leg of the siphon extends from the intermediate chamber 80 into a starting receptacle 90 having a tip 90a. Tube 92 is used to supply starting container 90 with sufficient inert solution to start the siphon. A third 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 present invention has a subcritical alignment mainly because the central space is occupied by the plug extension 4a. Moreover, decantation can be carried out more effectively. Furthermore, the amount of solution required for the cake washing operation is low, and therefore the amount of waste liquid is also low. These operations may be performed using a dilute nitric acid solution, a solution that will not ignite the Zircaloy particles.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the centrifugal separator of 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... Centrifuge container, 22... Annular connection part, 28... Annular space for clarification, 44... Deflector, 62, 94... Siphon, 72... nozzle, 80... piston, 80b... bellows.

Claims (1)

[Scope of Claims] 1. A biological shielding body having a through hole; a fixed outer container having an upper opening edge attached to one surface of the biological shielding body to cover the through hole; a cylindrical extension suspended from the wall of the bioshield defining the hole and having a cylindrical extension projecting into the interior space of the outer container at the other end, a through-hole aligned with the axis of the cylindrical extension; a plug member having a hole; a vertical drive shaft inserted into the through hole of the plug member such that one end projects from the end face of the cylindrical extension toward the bottom of the outer container; a cylindrical top part surrounding the outer peripheral surface of the cylindrical extension to cooperate with the fining annular space, a lower part fixed at the center to the one end of the vertical drive shaft; , a rotating container having an inverted truncated conical connection portion connecting a cylindrical top portion and a lower portion to form an annular passage communicating an internal space of the lower portion with the clarification annular space; and a stopper member. a first conduit means extending through the annular passageway and configured to introduce a liquid containing solid particles into said annular passage; and at a portion facing the inner surface of the cylindrical top, a cleaning liquid to be applied to a cake formed on said inner surface. a second tube means comprising a plurality of nozzles for ejecting clarified liquid in said outer container that spills over an overflow lip formed at one end of said cylindrical top; means and
a first means for extracting the liquid remaining in the internal space of the lower part after the clarification operation performed prior to the cleaning operation; a second means for withdrawing liquid remaining in the interior space of the lower part afterward; and said end face of the cylindrical extension for stirring the cleaning liquid in the interior space of the lower part when the rotating container is rotated. a stirring means fixed to the inverted frusto-conical connection, the wall of the lower part continuous with the inverted frusto-conical connection having an inner surface inclined with respect to the axis; has a generatrix inclined with respect to the axis, and the inclination of the inner surface of the wall of the lower part with respect to the axis and the generatrix is such that when the rotating container rotates at a particular speed, the inner surface of the lower part A pendulum centrifuge for decanting a liquid containing solid particles, in which the liquid and solid particles initially present in the space are determined to flow into a clarification annular space. 2. The centrifugal separator according to claim 1, wherein the inner surface of the lower wall of the rotating container is conical. 3. A centrifugal separator according to claim 2, wherein the angle between the axis and the inner surface of the wall of the lower part is between 10° and 20°. 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 rotary vessel is provided with a cylindrical internal buffle having a top free edge, which cylindrical internal buffle surrounds the drive shaft and defines an overflow space within the interior space of the lower part of the rotary vessel. A centrifugal separator according to any one of claims 1 to 4 forming the claim. 6. Each of the first and second means comprises a siphon, the siphon being T-shaped with a first siphon leg extending into the interior space of the lower part of the rotating container and penetrating a portion of the closure member. a second siphon leg connected to the first siphon leg by a connected connection and opening into a container outside the outer container; and means for initiating an extraction operation of said siphon. A centrifugal separator according to any one of claims 1 to 5. 7. said starting means comprises a piston including a chamber connected to said T-shaped connection;
the chamber has a deformable metal bellows;
One edge of the bellows is fixed to the wall of the chamber and the other edge is fixed to the periphery of a plate, which plate is connected to means for moving the plate along the axis of the chamber. A centrifugal separator according to claim 6. 8. Claims in which the piston is arranged in a cavity formed in the plug member and closed by the biological shielding plug member, and the piston is suspended from the biological shielding plug member. The centrifugal separator according to paragraph 7.