FR2560071A1 - DECANTATION PENDULUM CENTRIFUGE - Google Patents

Abstract

PENDULUM CENTRIFUGE FOR DECANTATION OF A LIQUID CONTAINING SOLID PARTICLES. THE CENTRIFUGE INCLUDES AN UPPER CYLINDRICAL PART 8A AND A LOWER PART 8B OF WHICH THE SIDE INTERNAL WALL 20 IS INCLINED. THE CONNECTION BETWEEN THE TWO PARTS 8A, 8B IS PROVIDED BY A CONICAL SURFACE 20. THE INCLINATION OF THE LOWER PART OF THE BOWL 8 AND THE TAPPING OF THE CONNECTION SURFACE 20 ARE SUCH AS AT A CERTAIN ROTATION SPEED OF THE BOWL 8, THE LIQUID AND PARTICLES INITIALLY CONTAINED IN THE LOWER PART ARE RAISED IN THE "CLARIFICATION" ANNULAR SPACE 28. APPLICATION TO NUCLEAR FUEL PROCESSING.

Description

The present invention relates to a centrifuge

pendular of decantation.

  More specifically, the present invention relates to a machine which allows to obtain the decantation of small particles suspended in a liquid by rotating the liquid in a centrifugation bowl, this bowl being

  attached to the lower end of a rotating shaft.

  It is known that in the reprocessing of fuel assemblies of nuclear reactors, the totality of operations

  1 of reprocessing, that is to say, in the recovery of activities

  still present in spent fuel assemblies,

  out of the reactor core, there are several operations.

  First of all, dismantling of the co-bustible assemblies, that is to say, their shearing in elements of reduced length. Each of these small elements therefore comprises a part of the irradiated fissile material, solid Fission products and a part of the protective sheath of

  the fuel assembly, which is usually made of zircon

  calloy. In a second step, the elements are dissolved. However, the sheaths and some particles do not go into solution and remain in suspension. It is for example small elements of the sheath which are thus in the form of "filings" and whose dimensions can range from a few microns to a few millimeters, There are 2; also solid insoluble fission products whose

  dimensions can range from less than a micron to a few

  cron. The second type of particles that remain suspended

sion is of course very radioactive.

  It is known that after this dissolution, this solution is extracted by chemical methods. fissile or non-existent products; it is reprocessing. However,

  presence of both types of insoluble products is very

  te for this extraction operation. On the one hand, insoluble products may accumulate and clog the extraction devices. On the other hand, among these solid particles, finely divided zircalloy presents risks of spontaneous ignition. Finally, insoluble fission products risk

  to create hotspots in the devices.

B 6589.3 GD

2 '2560071

  Therefore, it is planned between the phase of dis-

  solution and the extraction phase, a so-called

  to extract the particles as much as possible.

in suspension in the solution.

  Three types of solutions have already been proposed. We can first mention static decantation. In fact, this solution is unattractive because given the size of the particles, this operation actually allows only to remove the most important particles if we do not want to devote to this operation

  than a reasonable time. Another solution is filtration.

  The major disadvantage of this solution is that we have a

  fast filter cartridges.

  A third solution has also been used which consists in using a pendular centrifugal decanter. This solution consists in placing in a rotating bowl the solution containing the insoluble and to provide on the upper rim of the bowl a spill passage. Given the speed of rotation, the solid particles are pressed along the side wall of the bowl to form a 'cake' and the

  liquid comes out of the bowl through the spill passages. How-

  However, the disadvantage of prior art centrifuges and decanters lies in the subsequent processing of the "cake" of insolubles. In fact, after the centrifugation operation, this cake still retains a certain fraction of solution of fissile material or other material to be recovered. This is followed by a nitric acid rinsing phase of this cake. However, this rinse has some problems. On the one hand, it requires large flushing volumes which are therefore generators of

  additional quantities of liquid tributaries since the

  ration must be repeated several times. It is carried out in

  I am almost laminar and is therefore inefficient. It therefore requires large volumes of solution. In addition, this rinsing is more effective than the rinsing solutions have a density equal to or greater than that of the retention liquid to be removed. We are therefore limited in the choice of rinsing solutions.

B 6589.3 GD

25600 71

  In addition, in the centrifuges of the prior art, there is no safe nuclear geometry, that is to say that in case of accidental plugging of the outlets, the configuration of the fissile material likely to be present can be critical. The present invention specifically relates to a

  pendulum centrifuge decantation that mitigates

  mentioned above. In particular, the centrifuge

  object of the invention makes it possible to obtain greater effi-

  settling capacity. In addition, the bowl of the centrifuge is such that a subcritical geometry is made. Finally, the operation of rinsing the cake is done under conditions

  much more favorable and which allow a better

  traction of fissile material remaining in this cake,

  requiring very small amounts of rinse solution.

  To obtain these results, the invention consists of

  a pendulum centrifuge for decanting a liquid

  holding solid particles; it is of the type comprising under a closure plug a biological protection slab, a fixed outer envelope suspended from the slab and in this envelope, a rotary bowl fixed by its bottom to the lower end of a vertical shaft for rotating, this tree

  passing through said stopper, said centrifuge is characterized

  characterized in that said bowl comprises a cylindrical upper part whose upper rim constitutes a discharge edge for said liquid and a lower part, the inner wall of the lower part being inclined with respect to the rotation shaft, connected on the one hand to the bottom of said bowl and on the other hand to. said upper part of the bowl by a very flared conical connecting surface, in that said plug comprises a cylindrical extension

  penetrating inside said upper part and delimiting

  placing with said cylindrical portion an annular space called "clarification" communicating through a passage of revolution

  with said lower part of the bowl, and in that it

  takes or less than a first insertion pipe through

  said plug and adapted to send said liquid to said step

B 6589.3 GD

4 - 2560071

  wise, a second tubing provided with nozzles able to send a liquid to the cylindrical wall of the upper part of the bowl, means for collecting in said envelope said clarified liquid which has crossed the discharge edge, means by siphon for extracting said liquid contained in the lower part of said bowl and means integral with said

  cork to create a stirring li.qui.de content in the-

  said lower part of said bowl when it is rotated, the conicity of said lower part of the bowl and that of the connecting surface being such that from a certain speed of rotation of the bowl, the liquid and the particles initially contained in the lower part

  go back into the annular space of "clarification".

  Preferably, the inner wall of the inferior part

  The upper bowl has a conical shape in its upper portion. In any case, the invention will be better understood in

  reading the following description of an embodiment

  of the invention given by way of non-limiting example. The

  description refers to the attached figures on which

  FIG. 1 shows a vertical sectional view of the centrifuge assembly in a first diametrical vertical plane, and FIG. 2 a vertical sectional view according to FIG.

  a second diametral plane substantially perpendicular to the first

mier.

  In the figures, there is shown an example of reali-

  The entire active parts of the centrifuge are placed beneath a slab 2 of biological protection, for example made of concrete. Above the centrifuge itself, this slab is constituted by a removable cap 4. The centrifuge is enclosed in a generally cylindrical envelope. 6 is suspended from the slab 2 and provided with a vent tube 96. The centrifuge lever bearing the general xéférérance 8 is fixed by its bottom on nn shaft rotational drive 10 through the iouch 4

B 6589.3 GD

  a vertical bore 12. At its upper end 10a, the shaft 10 is supported by a bearing 12 allowing a certain swiveling effect. This shaft 10 above its upper end 10a is connected to the shaft 14 of an electric drive motor 16. In addition, there are provided means for

  for example by sweeping gas introduced by a tubular

lure 18.

  The rotary bowl 8 comprises an upper part 8a of decantation and a lower part 8b provided with a bottom constituting a collection zone. The settling zone 8a is constituted by a cylindrical wall of diameter D1 while the inner wall 20 of the lower part 8b of collection is tapered. More precisely, this wall makes an angle of the order of 15 with the vertical direction, that is to say the

  direction of the axis of rotation 10. More generally, this half

  angle is between 10 and 20 degrees and preferably very close to 15 degrees. An annular portion of slightly conical connection 22 joins the lower part 8b and the

upper part 8a.

  In fact, as already indicated, it is not necessary for the inner wall of the lower part 6b to be conical. It suffices that the upper part of this wall in the vicinity of the connecting portion 22 is

  inclined relative to the vertical axis. For example, this portal

  the wall could be a paraboloid. In this case, it is the planes tangent to this surface that would check the angle conditions. Finally, the upper edge of the game

  upper 8a is mLuniuni of an annular plate 24.

  It should be noted that the plug 4 is extended at its lower part 4a inside the upper portion 8a of the rotary bowl. This wall 8a is provided with radial fins 9. There are four for example. The side wall 26 of the extension 4a of the plug defines with the lateral wall 8a of the rotary bowl an annular clearance space 28. It is

  important to note that this annular space 28 is in common

  by an annular upper passage with the inte-

  envelope 6 and that, on the other hand, it communicates

B 6589.3 GD

  its lower part, by an annular passage 32 with the collection zone 34 defined by the lower part of the bowl 8h. A ferrule 35 integral with the envelope 6 separates the envelope 6 into an external discharge space 36 communicating with the passage 30 and a collection space 38 internal to the ferrule 35.

  bulestone 40 emerges at the lower end of the space

  Similarly, a discharge pipe 41 opens into the bottom of the space 38. It should be added that inside the zone 34 of collection, there is a cylindrical shell 52 which defines with the inner wall 54 of part 8b a

  overflow zone 56. This is equipped with a 58

  pouring the bottom of the lower part 8b, which brings into

  munication the overflow space 56 with region 38.

  We also find, crossing the lower part

  4a of the plug 4, a tubing 42 opening into the underside

  4b of the cap 4. This tubing 42 is extended by a deflector 44 which directs the liquid passing through the pipe 42

  towards the annular passage 32. At its other end; tubular

  lure 42 is connected to a retractable feed pipe 46 of

in liquid to be decanted.

  Inside the centrifuge, there is also a pipe 60 whose free end is close to the bottom of the

  the lower part 8b, this tubing 60 passing through the

  chon 4a and constituting one of the branches of a siphon 62 whose other branch is referenced 64. This siphon will be described more

in detail later.

  In reality, there are two identical siphon devices

  ticks to ensure operation. There can be two

siphons in 'reserve'.

  In the figures, it can be seen that the centrifuge also comprises a pipe 70 for unclogging the cake which is provided with nozzles 72 directed towards the side wall of the cylindrical portion 6a of the rotary bowl. There is also a pipe 74 whose end opens near the bottom of the lower part 8b. Finally, there is a tubing 76 which also passes through the plug 4 and serves to wash the zone of

too full 56. -

B 6589.3 GD

  By way of example, it can be indicated that in its upper part 8a, the rotating bowl has a diameter D equal to 900 mm. In addition, this bowl is made of titanium, which allows through this decrease in density to have a larger diameter bowl for the same nominal speed of rotation.

  This increase in diameter compared with centrifuges

  of the prior art, allows, all things being equal,

  improve their stopping power, that is to say the efficiency of

city of decantation.

  The operation of the centrifuge is as follows: during the actual decantation operation, the solution is sent via the tubing 42 after the bowl has been rotated at its nominal operating speed. Under the effect of the rotation and thanks to the presence of the deflector 44, the liquid

  enters the annular settling zone 28. The

  suspended particles are pressed on the wall 8a (these particles are symbolized by the crosses P] thus forming the cake.The liquid under the centrifugal effect leaves by the

  passage 30 and flows into the zone 36.

  So, the solution is clarified, that is to say

  that it contains practically no more particles in sus-

  sension. This clarified solution exits through the tubing 40.

  After clarification of the volume of solution corresponding to

  tonnage set, we stop the bowl 8 by natural slowdown.

  The cake remains glue on the side wall 8a of the bowl. The liquids fall into the collection space 34. This solution is siphoned off and may contain fragments of

  "cake" upstream of the clarification for recycled hearth ul-

  térieurement. As already indicated, the "cake" that has formed on the side wall 8b must be rinsed to extract the solution that is still retained. To perform this operation, the following operations are performed using the tubing 70, nitric solution is injected through the nozzles 72 to cause declogging of the cake. This requires in the embodiment shown a volume of

  solution less than the volume of the clarification ring.

B 6589.3 GD

  Under the effect of this unclogging, the sludge falls into the lower zone 34 where they are held in suspension by preferably alternating rotations at low speed of the bowl 8, obtained by controlling the motor 16. The lower ends of the siphoning pipes 60 Play the role of agitators. This gives a very good rinsing. After this stirring operation, the bowl is gradually rotated at its nominal speed. The liquids and solids rise along the conical wall 20 of the lower portion 8b of the bowl until the assembly is found in the annular space

  28, this rise occurring at a distance of

  much lower than the nominal speed. After the

  reconstitution of the cake, the centrifuge is stopped,

  natural slowdown. The rinsing solution falls to the bottom of the lower part 8b, it is recycled upstream of the clarification, that is to say at the inlet of the tubing 42. It is repeated

  rinsing operations several times.

  It is understandable that thanks to this device and this process

  In addition to rinsing the cake, the number of rinses can be limited while ensuring a much better efficiency than the devices of the prior art. As the number of rinses is limited, it is understood that the amount of effluents as well

created is also limited.

  When the rinsing is complete, the particles get

  found in the collection area 34 by constituting a sus-

  pension with high concentration of particles.

  To evacuate it, we continue to supply solution

  rinse the bowl while maintaining the agitation of the solution.

  slow rotations of the bowl. The charged solution overflows into the overflow zone 56 where it passes into zone 38. When the concentration of the suspension has

  sufficiently diminished, we use a second siphon identi-

  trap siphon 62 to evacuate the solution.

  The siphons 62 are primed using a piston referenced 80. This piston is housed in a chamber 82 arranged

  in the plug 4 and closed by a small plug 84. The chamber

  80a of the piston is fixed on the plug 84. The piston itself is constituted by a bellows BOb fixed with a

B 6589.3 GD

  part on the slug 84 and, secondly, on a circular plate 80c, a control rod 80d is fixed on the plate 84. It passes through the small plug 84 and is driven by a motor 86. The piston chamber 80 is connected to the siphon 82 by a passage 80f. We understand that by raising the. rod 80d is created a depression in the 80th chamber, which causes the boot siphon. Of course, we could

  use other conventional priming devices. How-

  However, it should be noted that this device has important advantages. On the one hand, the bellows 80b ensures a very good

  sealing since there are only static seals.

  On the other hand, in case of damage on the siphon, we see that by lifting the small plug 84 can extract the entire siphon. It is also seen in Figure I that the second branch 64 of the siphon enters an intermediate chamber provided with a bottom 90a to the priming pot. A driving 92

  allows to introduce into the pot 90 the volume of inactive solution.

  necessary to prime the siphon. A second siphon 94

23 allows the output of the solution.

  It follows from the foregoing description that the

  centrifuge object of the invention has many

  avanteges compared to centrifuges of the prior art.

  On the one hand, it has a subcritical geometry due in particular, the filling of the central space by the extension 4a of the plug. On the other hand, it ensures better settling. Finally, the rinsing operations of the cake require only a small volume of solution, which decreases the amount of liquid effluents produced, These operations can be carried out with solutions

  diluted nitrates therefore not presenting any risk of

zircalloy particles.

B 6589.3 GD

  Eqg99 l (9) loq np eJneTJqJUT aTeJed a; Tpel ap uosTeu $ [or $, the uo $; Se -eqoJ ua sTw; his To- $ nteo anbsJol loq 4Tpnp (q]) eanaTJ -gauT aelqed a; Ipel suep nuaquoo apTnbîI np uo $ 3e; 2Be aun Jaq.om xnod (t) uoqanoq qTpnp saaJepT [os suaiow sap 4a (9) [oq; pnp aJnaaUT aFzaed el suep nua; uoo apînbTI 4pal aj.erçxa inod uoqdTs jed suafiow ap selqwasua xnap 0O

  suTow no 'UawaSJaeap ap pioq al T4qoueJ e Tnb gTJTeloo.

  ITP apTnbTI rTpal addolaeAua aTpel suep JTlTlenoaJ jnod suasow sep 'loq np (e8) ajnalnadns a; jTed el ap enbTip -UTlio ToJed el SJeA apTnblT a Jaeo ^ Us? se9de tZ) sesnq ap aTunw (O_] eaJnlnqnq aswTxnep aun '(tZ] Se2ssed; Tpel SJsA Sz apTnbI bTpeIP Jofioua Ue a (b) uoqonoq.Tpal. ues2sA -eg1 (EZ) Uo; onpoiJup ean [nqnq eJaTwSJd aun suTow ne puaedwoo alla, nb ao us 4a '(q9) aBnaBJ, & up aB ed BTpel DBoae (Z) aJTeInuue aSessed a jed quenblunwwoo uol; - = e0JTJeto ap # 4TP (8Z) alTelnuue aoedsa a (eg) anbTip OZ -uTI [ o etched a4Tpel oae; ue; 3wTgp 4a (teg9) aJnafTjdns eT4ed a4Tpel ap JnafTJqUTTl V ueaqpugd (eb) enbT.p -uTIo 4uaBwe2uoloJd aejodwoo (b) uoqonoq TFpal anb

  ao us' agseAg SJ4 (ZZ) enbîuoo uaWapioooeJ ap aej.

  -Jns aun jed loq np (eg) ainea1gdns a; jed a; pele; Jed S9 aJ; nep qa (g) loq 4Fpnp puo. Appeals were made by the President of the United States of America, and he had been elected by the President of the United Nations, and had been appointed to the Board of Directors by a four-year-old committee, who had been serving with him for a year and a half. [o ewJo. ep (eg) a.nat.zdns eT; .ed a 01

  aoooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

  (f) uoqonoq; Fpal 4uesa ^ eBA; (0) aaqJe; so uol4eqoJ ua asTW ap (01) 3eo ^ 4JBA if one, pAJneaJg &uT; waxa, l? puo & uos Jed 9xl & (g). e4oiJ loq a '(9) addoleAua e; ao suep qe (Z) allep el senpuadsns axT S (9) BuJaBxa addoleAus aun' (Z) aubTaololq uoT4oa; oad ap allep Sun quewJas (t) uoqonoq a snos 4ueqJodwoo adfi np 'sapfios his [noTqed sap 4euue4uoo apTnbTI a, p

  uoTelueopu Sp p ajTeInpuad esnasn & riJ u3 '-

SNOIIV3ION3A3

tiL oo9sz 01

LLOOQ9S

  and the conicity of the connecting surface (20) being such that at a certain speed of rotation

  of the bowl, the liquid and the particles contained in

  tially in the lower part go back into the annular space of "clarification" (28). 2. Centrifuge according to claim 1, characterized in that said inner wall (20) of

  said lower portion of the bowl is tapered.

  Centrifuge according to claim 2, characterized in that the half-vertex at the top of

  said conical wall is between 10 and 20 degrees.

  4. Centrifuge according to any one of

  Claims I to 3, characterized in that said bowl

(8) is made of titanium.

  5. Centrifuge according to any one of

  Claims I to 4, characterized in that

  lower portion (8b) of the bowl internally comprises a cylindrical ferrule (52) with a free upper edge, surrounding the shaft (10) and defining internally

  an overflow space (56) for said lower portion

  pool. 6. Centrifuge according to any one of

  Claims I to 5, characterized in that

  means by siphon consist of a first siphon branch (60) immersed in said lower part (8b) of the bowl and partially passing through said cap

  (41 in a second branch (80d) connected to the first

  first by a tee, and opening into an outside pot

  said envelope, and means for priming.

  Centrifuge according to claim 6,

  characterized in that said priming means

  are in a piston (80) having a chamber (80e) connected to the tee (80f) of said siphon and in this chamber a deformable metal bellows (80b) whose one edge is integral with the wall of the chamber and the other

B 6589.3 LW

  edge is secured to the periphery of a plate (80c) connected to means for moving said plate according to

the axis of said chamber.

  8. Centrifuge according to claim 7, characterized in that said piston (80) is housed in a cavity formed in said plug (4), said cavity being itself closed by a small plug (84) of biological protection, said chamber (80th) of the piston

  being suspended from said small plug (84).

B 6589.3 LW