CA2049466A1 - Process and installation for the treatment of solid particle agglomerates suspended in a liquid, in order to obtain a heterogeneous mixture able to flow in long ducts without causing deposits - Google Patents

Abstract

DESCRIPTIVE ABSTRACT

During their reprocessing, irradiated nuclear fuels are sheared and then dissolved in a hot nitric solution, which is then settled in a clarifier (10). According to the invention, the dissolving fines collected at the bottom of the clarifier are broken up before being transferred to a vitrification site. For this purpose the fines are passed to a transfer tank (16) and then made to flow in a loop (20) comprising a pump (24) and a dilacerating device (26).
The transfer to the vitrification site then takes place by passing through an e.g. ultrasonic fines screening machine or sifter (30).
The dilacerating device (26) can be of the ultrasonic type, the venturi tube type, or of the type having a venturi tube and baffle system. A prior dilaceration can take place within the clarifier (10) .

Fig. 1.

Description

Process and installation for the treatment of solid ~artiele ag~lo-merates suspended in a liquid9 in order to obtain a heterogeneous mixture able to flow in lon~ ducts without cau~ing depo~it~.

DESCRIPTION.

The invention relates to a process for proce~sing agglomerates in solid particle form suspended in a liquid, in order to break or divide them up and in this way obtain a heterogeneous mi~ture able to flow in ducts or pipes of considerable length without any depos-ition risk. This process is more particularly applicable to the reprocessing of irrsdiated nuclear fuels, following the cutting up of the latter, their dissolving in a nitric solution and their settling in a clarifier. The invention also relates to an installa-tion for performing this process.

In particular when it iR necessary to displace in long ducts liquids containing solid particles, the latter tend to agglomerate with one another and form heaps in areas ~here turbulent flow conditions are not ensured. Due to the agglomeration, these heaps te~d to form heaps ha~$ng a density lower than that of the particles forming them. The agglomeration mechanisms are not well known, but the bonds invol~ed are~mainly of two types, namely chemical bonds which, when the said bonds are broke~, do not re-form in rapid manner and Van Der Walls-t~pe bonds~which, when broken, can rapidly re-form.

The treatment proce~s according to the inYention makes it possible to break these bonds by utilizing the characteristics of the equi-pment used. This process is more particularl~ applicable to thetreatment of agglomerates~of fines encountered in the reprocessing of irradiated nucleàr fuel~.

urlng their reprocessing, the irradiated~nuclear fuels are cut up and then dissolred in hot nitric solutions. Following the : ~ ~

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dissolving operation, solid products called shells are obtained and which are constituted by fuel can fragments and nitric solutions containing agglomerates of solid particles ha~ing a limited grain size and known as fines. These solid psrticle~ are based on zircon-ium, molybdenum, ruthenium and other metals from the structure ofthe fuels.

Before being passed to extraction co:Lumns of the solvent, the nitric dissolving solutions are settled in a clarifier, e.g. constituted by a centrifugal, swinging settling tank. Thi3 clarifier makes it possible to separate the clear nitric solutions to be passed to the extraction columns from the fines which are then in the form of sludges or solutions of varying thickness and agglomerated to a varying e~tent.

In ~iew of their Yer~ high radioacti~it~, the fines must be incor-porated in a glass ~atri~ with the fis d on products resulting from the e~traction processes. For this purpose the~ are transferred from the clarifier to the ~itrification site by transfer pipes.
On the ~itrification site, the said pipes issue into storage tanks, where the solutions of fines are continuously stirred for nuclear safety reasons, e.g. using pulsing mea~s.
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Such an installation suffers from numerous disadYantages. Firstl~, the fines are abr~sive particles which, with increasing size) brin8 about ever gr~ater wear of the pipes, particularly in their curved parts.
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In addition, when the fines are formed from highl~ agglomerated particles, they tend to be deposited in the pipes, particularl~
:; in ehe ~on-turbulent areas or where there are surface roughnesses.After a certain time, plugs are formed~ w~lch cause stoppages in ; the inwardly cur~ed parts of the pipes. This constitutes 2 difficult problem, becauee the unblocking of the pipes requires inter~ention B 10505 GP~

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in cells where man is no~ allowed access. Moreover, in view of the difficulties encountered in modelling the behaviour of fine~, it is ~ery difficult to successfully ~odify the installations and parameters such as the flow rate, the pressure drops in the pipes, etc., in order to pre~ent the formation of such plugs.

Moreover, the presence of agglomerates in the solutions of fines also tends to lead to the said agglomerates bein8 deposited in the bottom of storage tanks located on the vitrification site. As a result the operation of the pulsing means used for stirring the solutions of fines is disturbed, which is agaln an important dis-advantage, in view of the difficulties encountered in intervening within the tanks.

The invention specifically ~ims at a process and an installation making it possible to treat in a simple manner agglomerates of solid particles suspended in a liquid, such as the dissol~ing fines obtai-ned during the reprocessing of irradiated nuclear fuel~, in order to break up the agglomerates before said particles flow in long -ducts or pipes, e.g. in order to be transferred to the vitrificatio~
site, by using easily realizable technical means ~hich can be fitted ~0 and dismantled remotel7 with the aid of telemanipulators when an intervention proves necessary.

According to the invention this result is obtained by ~eans of a process for the treatment of agglomerates of solid particles suspen-ded in a liquid, in order to obtain a heterogeneous mixture able to flow without leaving deposits in long ducts9 characterized in that it comprises reducing the grain size of the particles b~ making the latter flow in a loop incorporating means or breaking up the agglomerates and screening the particles leaving the said loop, in order to hold back~the particles having 8 grain size exceeding a predetermined threshold.

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The invention ad~antageously applies to the treatment of fines obt~
ained after cutting up, dissolving and settling irrsdiated nuclear fuel~ and prior to their transfer to a storage tank.

Preferabl~, prior to makin8 the partiles circulate within ~he loop, theY undergo a prior size reduction, e.g. using ultrasonic waYe~, within the apparatu~ in which settling takes place.

According ~o different embodiments of the in~ention, it i~ possible to break up the agglomerates within the loop by using ult~asonic means, or a renturi tube de~ice optionally followed by a baffle system. In addition, the particles are preferably screened or sifted in an ultrasonic screening or sifting machine.

hccording to another aspect of the in~ention, an installation is proposed for the treatment of agglomerates of solid particles suspen-ded in a liquid, in order to obtain a heterogeneous mi~ture able to flow without lea~ing deposits in Yery long d~ucts, ~hich is char-acteri~ed in that it comprises a loop having a transfer tank linked with the bottom of a settling apparatus, pwmping means and means for breaking up the agglomerates and a particle screening machine placed in a pipe connecting the transfer tank to a storage tank and located in the ~icinit~ of the transfer tank.

The in~ention is descrihed in ~reater detail hereinafter relati~e to non-limitati~e emhodiments and the attached drawings, wherein show:

Fig. 1 diugra = tically an installation for the treatment of dissolving fines in accordance with the inYention.

Fig. 2 a diagrammatic sectional Yiew o an ultrasonic de~ice placed,~according to a first embod~ment of the in~ention, in the loop of the installatlon illustrated in fi8. 1.

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Fig. 3 a diagrammatic sectlonal view comparable to fig. 2 showing a venturl tube device placed, according to a second embodi-ment of the in~ention, in the loop of the installation illustrated by fig. 1.

Fig. 4 a diagrammatic sectional Yiew comparable to fig~. 2 and 3 showing a venturi tube deYice placed, according to a third embodiment of the invention, ln the loop of the installation illustrated ~y fig. 1.

Fi8. 5 a disgrammatic sectional view comparable to Pigs. 2 to 4 showing a baffle and Yenturi tube de~ice for placing, according to a fourth embodiment of the in~ention, in the loop of the installation illu~trated by fig. 1.
. , Fig. 6 a disgrammatic sectional view of an ultrasonic fines scre-ening machlne usable in the installation illustrated by ::': fi8- 1.

The dissolving fines treatment in~tallation according to the in~en-tion wlll firstl~be~descr~bed relati~e to ig. 1. In the latter9 the reference numeral lO desi~nates a clarifier9 e.g. coDstituted by a centrifugal,~swinging settling tan~. ~ithin the said clarifier 10, the nitric solutions from the not shown dissol~ing appara~us are settled i~ the~con~entional ~ay and in which the irradiated nuclear fuels ha~e pre~iously been dissolved in~ho~ nitric solutioo a~ter~cutting~up.~ These nitric solutions;are introduced into the clarifier 10 by 8~ pipe~l2.~

In~the clarifier ~lO~the~clear nitric soluti~ons to ~e supplied to not shown sol~ent~e~traction colu~ns by a duct 14 are separated from ~the dissolving~fine~. When the clarifier is con~tituted by a centrifugsl 3winging~settl m g tank, the fines are located in the ottom o~the~Latter in~agglomerated form a~d~form a cake. Their B~IOSOS~P ~

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transfer to the ~itrification site i~ then made possible b~ not shown rin~ing ramps installed in the settling tank and makinx it possible to break up the cake. The fines are then in the Eorm of sludges or Yar~in~ly thick or ~ar~ingly agglomerated ~olutions i the bottom of the settling tank.

These sludges are then collected in a transfer tank 16 by a connect-ing pipe 18. To ensure that there is no risk of the latter becoming blocked, the transfer ~ank 16 is preferabl~ placed immediately below the clsrifier 10, the flow of fines taking place b7 gra~ity in the pipe 18, whose length is also as small as possible.

The transfer tank 16 form~ part of a loop 20 for th2 continuous dilaceration of the fines sludges collected i~ said tank. This loop 20 comprises a duct 22 in which are placed, apart from the transfer tank 16, a p~mp 24 and a dilacerating deYice 26 making it possible to break up the fines agglomerates. The pu~p 24 can in particular be constructed according to FR-A-2 361 55B. Variou~
embodiment~ of the dilacerating de~ice 26 will be described herein-after relative to figs. Z to 5.

The dilaceration loop 20 constitutes a closed circuit ~hich, as a result of the pump 24, makes it possible to continuously rec~cle the fines sludges in the dilacerating device 26 until the average grain size desired is obtai~ed.

During the first passage of the fines sludges in the loop 20, the breaking up effect of the agglomerates obtained by the dilacerating deYice 26 is ~irtually doubled by a comparable efect obtained in the pump 24, as a result of the suctio~ and stirring due to sludge rotation. The number of c~cle~ is determiQed b~ the user as a func-tion of the initial characteri~tics of the treated sludges and the characeeristics which lt is wished to obtain prior to ~he trans~er of these sludges to the Yitrification site. A minimuo sludge flow :: :
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rate in the loop 20 must be respected; in order to avoid ~ediment~-tion of the sludges in the dilacerating device 26 or in the remainder of the loop.

The pump 24 bringing about the circulation of fines sludges in the loop 20 can be permanentl~ operated, no matter what the ~ludge quan-tity present in the transfer tank 16. However, it is preferable to store the solutions of fines in the transfer tank 16 in order to only put the pump 24 into operation when the tank i~ sufficiently full.

When the fines sludge~ present in the storage tank 16 ha~e an a~erage grain size below a predetermined threshold, which e.g. corresponds to the plugging or blockage threshold of the pipes for the transfer t:o the ~itrification site, the said transfer takes place. It is possible to establish that said threshold ha~ been cleared either by checking the grain size of the qludges, or by deducing said grain size from the number of cycles performed in the loop 20, or ~i~h the aid of these two lnformations together.

The transfer of the fines sludges to the vitrificatlon site takes : place by a pipe 28 in which is placed, in the immediate ~icinity of the transfer tsnk 16, a fines sifting or screening machine 30.
The end of the pipe 28 oppo~ite to the transfer tank 16 i~s~es onto the ~itrification site in a storage tank 32, which is in conventional manner equipped with stirring means, such as not shown pulsing means, for nuclear safety reason~.

The fines screening machine 30 placed at the entrance of the tran~fer pipe 28 will be:described in 8reater detail hereinafter relati~s ; to fig. 6. Its function 19 to hold back the fines, whose grain ;~ : size e~ceeds a ma~imum threshold for the transfer pipe 28 and carries ~; : out a final breaking up of the agglomerates. It is also equipped with unclogging or:unblocking means.

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The solutions of calibrated fines leaYing the fine~ screening machine 30 can therefore pass without difficulty through the tranQfer pipe 28 up to the storage tank 32 collesting the solutions of fines to be ~itrified. In partic~lar, there is DO risk of the pipe 28 becom-ing blocked or of an unsati3factor~ operation of the pulsing meanæequipping the storage tank 32.

With reference to fig. 2 a description will now be gi~en of a first embodiment of the dilacerating device 26, in which the agglomerates are broken up by a cavitation effect using ultrasonic ~aYes. Fig.
2 shows the said device, where it is designated b7 the reference 26a.

The ultrasonic dilacerating de~ice 26a is suspended on a horizontal concrete slab 34, which separates a man-accessible upper zone 36 from a lower cell 38 in which are located the radioacti~e solution treatment and transfer de~ices. By being suspended on the slab 34, the device 26a is consequently placed in the cell 38.

The ultrasonic dilacerating de~ice 26a comprises a ~ertically a~ed cylindrical tank 40, equipped at its upper end with a flange 42 resting on the slab 34 and which is tightly connected thereto, e.g.
by screws 46.

The tank 40 is sealed at its upper end b~ a plug 48, which ensures above the said device 26a the continuation of the biological prot-ection pro~ided by the slab 34. At least one seal 50 carried by the plug 48 provides the necessar~ sealing between the latter and the upper part o the tank 40, whilst still allowing the removal and putting into place of the plug 48 with the aid of a gripping ` member 52 located on the upper face of the plug and which can be gripped by remote handling means located in the accessible zone ~ 36.
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A ring 53 placed abo~e the plug 48 maintains in position the as~embl~
constituted by the plug 48 and the body 56, e.g. ~ith the aid of screws 55 engaged on the flange 42.

In the Yicinity of its lower end, the tank 40 has a thicker portion 54, whose upper stepped face constitutes a bearing surfac~ for the body 56 of the acti~e part of the device 26a, said body 56 being fi~ed, e.8. by screws, to the lower face of the plug 48. Seals 58 carried by the bod~ 56 then bear on the upper stepped face of part 54 of tank 40, whilst a seal 60 carried by a lower cylindrical part of the body 56 co~es into tight contact with the inner cylindri-cal surface of part 54 of the tank 40.

An admdssion passage 62 radially tra~erses the thickest part 54 of the tank 40 and issue~ between the seals 58 and 60. Moreover, an evacuation passage 64 is formed in the bottom of the tank 40, in accordance with th0 ~ertical axis of the latter.

The body 56 of the acti~e part of the device 26a, which is fit~ed coa~ially within the tank 40 so as to be e~tractable therefrom and put in place therein with the plug 48 has an inner passage through which flow the solutions to be treated from the admission passage 62 to the e~acuation passage 64. This passage formed within the body 56 has an outer annular part 66, Yhose lower end issues in front of the ~dmission passage 62 and a central part 68, whose upper end is linked with the upper end of the annular part 66 and whose lower end issues in front of the evacuation passage 64. The annular part 66 and central part 68 are arranged coa~iall~ along the vertica a~is of the tank 40, The solutions admit~ed into the deYice 26a consequenely firstly : flow from bottom to top in the annular part 66 and then fro~ top to bottom in the central part 6B of the passa~e formed in the body 30 56. It should be noted that the passages 62 and 64 can be reversed, :: :

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so that then the flow of solutions to be treated takes place in the reYerse direction within the de~ice 26a.

Outside the annular part 66 and in thle zone located aboYe the thick-est part 54 of the tank 40, the body 56 has an annular recess 70 in which are recei~ed se~eral groups of ultrasonic wave emitting transducers 72.

Each of the groups of transducers 72 is e.g. formed by se~eral trans-ducers aligned parallel to the Yertical a~is of the device 26a, the groups of transducers being regularly distributed o~er the entire circumference. The number and location of the transducers 72 in each group, as well as the number and location of these groups in the recess 70 are determined taking account of the constraints of the process (flow rate, velocity, number of cycles in the loop, etc.) and the height of the annular part 66 of the passage formed in the bod~ 56.

The arrangement of the transducers 72 in the de~ice 26a makes it possible for them to emit ultrasonic waves in directions oriented radially with respect to the vertical a~is of the device, so as to create a ca~itation effect over the entire surface of the liquid traYersed b~ the sound wave. The ultrasonic frequency is chosen as a function of the solution to be treated, said frequency beiDg ` e.g. 20 + 5 kNz.

The form or shape of the transducers 72 is chosen, as a function of the frequenc~, so as to obtain a maximum cavitation effec~.
These transducers can in particular be in the for~ of cylinders.
However, a ring-like or o~oid shape can also be used.

In order to protect the transducers 72 from the effects of irradia-tion, they are adYantageously sheathed with stainless steel. In view of the fact that the transducers are not in direct contact wlth the llquld to be treated, there is no need to take any special . - ..
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precaution with respect to corrosion or any other damage a~ a resule of contact.

The electric supply for the transducers 72 is pro~ided from not shown, external electric sources located in the upper zone 36 and using electrical conductor~ 74. The latter are adYantageously sheat-hed so as to have a good resistance to irradia~ion. Moreover, they traverse the plu~ 48 in helical tubes 76, which guarantee the absence of radiation leaks of the lower cell 38 in the upper ~one 36.

The helical tubes 76 also make it possible to produce a forced flow of a cooling fluid, such as sir, within the recess 70. This forced flow ensures the cooling of the transducers 72, which tend to heat up as a result of their nwmber.

As has already been stated, the actiYe part of the deYice 26a loca~ed within the tank 40 can be easily fitted and dismantled, e.g. using a mobile evacuation enclosure like that described in FR-A-84 03312, or any other equivalent means. When the active part of the device is located outside the tank 40, it is merely necessary to disengage it from the plug 48 to haYe access to the means located ~i~hin the body 56.

As an embodiment of the deYice 26a, such a deYice was equipped with twel~e groups each constituted by four transducers 72 emitting at 20 kHz, the annular part 66 in which the fines sludges to be treated flow having a diameter of 11 mm and an effective height of 160 mm.
By bringing about the circulation in said device of dissolYed fines sludges containing 75g of solids per litre of solution and in which 85% of particles had a size exceeding 140 ~m and generall~ in the form of agglomerates between 150 and 250 ym, it was possible ~o reduce 95~ of the fines to a si2e between 80 and 25 pm.

A second embodiment of the dilacerating de~ice 26 used in the loop 20 of the installation illustrated in fig. 1 will now be described ' .
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relative to fig. 3. This device, which is designated in general terms by 26b in fig. 3, is a ~enturi tube de~ice in which the di~-in~egration of the agglomerates is obtained under the effect of the shear forces created by the e3isting radial velocit~ 8radient~
in the ven~uri tube.

The installation of the device 26b of fig. 3 is the same as that of device 26a of fig. 2. Thus, the device 26b is suspended on the hori~ontal concrete slab 34, in such a way as to be placed in the lower cell 38 located below said slab.

The dilacerating device 26b also incorporates a vertically a~ed cylindrical tank 140, whose upper flange 142 is fi~ed to the slab 34 by screws 146. In its lower part, the tank 140 also has a thicker zone 154, whereof the upper stepped face keeps in place the bod7 156 of the active part oi` the device. The said body 156 i9 fi~ed e.g. b7 screws 157 to the lower end of a sleeve 149, which projects downwards from a plug 148 tightl~ fi~ed to the flange 142 of the tank 140, e.g. by screws 147.

The body 156 of the actiYe part of the deYice 26b rests on the upper face of the thicker part 154 of the tank 140 ~ia two sealing 0-rings 158. Moreover, the body 156 has a c~lindrical lower pare, which tightly cooperates with the cylindrical internal suriace of the part 154 of tbe tank 140 b~ a seal 150.

An admission passage 162 formed in the thicker part 154 of the tank 140 issues into a ~ower chamber 163 formed in the tank 140 below ~he seal 160. hn e~acuation passage 164, also formed in the thicker part 154 of the tank 140, issues into the latter between the seals 158 and 160.

The lower cha~ber 163 is linked with the eYacuation opening 164 by a passage i'ormed in the bod~ 156 and which successi~el~ incorpor-ates an injector 165, a venturi ~ube 167 and an annular passage :

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169. The injector 165 and the ventu.ri tube 167 are disposed along the ~ertical axis of the tank 140, whereas the annular passage 169 is centered on the same axis and placed around the Yenturi tube above the injector.

More specifically, the injector 165 is formed ln a lower ~art 171 of the body 156, which is fi~ed, e.g. by screws, to the lower end of an intermediate part 173 of said same body in which is formed the venturi tube 167. The fines solutions admitted into the lower tank 163 by the admission pflssage 162 enter the injector 165 by the larger diameter, lower end thereof, before passing from bottom to top through the lower, convergent part 175 and then the upper, divergent part 177 of the venturi tube 167.

These solutions then pass downwards again through the annular passage 16g~ whose upper end i3 linked ~ith the upper end of the venturi 15 tube 167 and whose lower end issues between the seals 1~8 and 160 in front of the evacuation passage 164. This annular passape 169 is formed between the intermediate part 173 of the body 156 and an upper part 179 of the latter, which carries the seals 158 and b~ which the body 156 is fi~ed to the slee~e 149. The connection 20 between the parts 179 and 173 of the body 156 is pro~ided by tie rods 181.

Finally, the lower end of the annular passage 169 communicates with 8 recirculation chamber 183 formed in the bod~ lSS bet~een the injec-tor 155 and the venturi tube 167 by means o holes 185 traversing 25 the intermediate part 173 of the body 156.

The solutions of fines circ~lating in the loop 20 of fig. 1 are : introduced into the de~ice 26b b~ the admission passage 162, prefer-;~ : ably at a pressure of at least 300 kPa. The pressurized liquidentering the inner chamber 163 tra~erses the de~ice fro~ bottom : ~ 30 to top, whilst passing successiYely through the injector 165 and ~' ,, .

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the convergent ~nd divergent zone~ 175,177 respec~lvely of the ~ent-uri tube 167. The liquid flows at high Yelocity in the injector 165 and then in the venturi tube 167. Thus, for an approsimate flow rate of 5 m3/h for the liquid introduced into the de~ice 26b and an outlet diameter of the injec~or 165 of appro~imatelg 10 mm, the Yelocit~ reached by the liquid iis approxi~atel~ 18 m/s.

To the primary flow rate of the liquid traversing the injector and then the venturi tube from bottom to top must be added the induced flow rate resulting from the entrainment by said primary liquid of the liquid introduced into the recycling chamber 183 through the holes 185. Tests have shown that the induced flow rate is Yery close to the primary flow rate. Consequently the liquid flow rate tra~ersing the venturi tube 167 corresponds to appro~ima~ely 10 m /h in the aforementioned example.

The liquid passing at high ~elocity out of the upper end of the venturi tubs 167 runs against the upper cup-shaped end of the part 179 of the body 156 and drops again through the annular passage 169. Part of the liquid then passes out of the deYice 26b through the evacuation passage 164 and the other part is recycled iD chamber -183 through holes 185.

The liquid flowing in the injeetor 165 and then in the Yenturi tube 167 has a Yery high radial ~elocit~ gradient, iOe. the flow velocit~
of the liquid along the Yertical a~is of the device is much higher -in the immediate vicinity of said a~is than along the walls of the injector and the ~enturi tube. ~he liquid and the agglomerated solid particles carried therein are consequently e~posed to Yery hi8h shear force~ within the injector 165 and the Yenturi tube 167, which break do~n the agglomerates.

A particle exposed to these shear forces is subdiYided into smaller particle3 until the si~e o the particles i~ sufficientl7 small . : --: : :
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to ensure that the shear induced b~ the radial velocit~ gradient in the injecto~ 165 and then in the venturi tube 167 is no longer sufficient to break up these particles.

For example, it has been found that the passage in the device 26b of a suspen~ion containing partic~es with a mean di~neter close to 30 ym has the effect of reducing said mean diameter to a vslue between 10 and 15 ym following a single passage and a val~e close to 5 ym after recycling.

In another test, the suspended particles with a diameter larger than lO0 ~m were recorded. The liquid initially entering the device 26b contains 4% particles of this type, whereas it only contains 3% on leaYing the venturi tube 167 after a first passage, said per-centage being reduced to 1.5% after one recycling and to 0.7% after two recyclings.

15 As in the first embodiment described relative to fig. 2, the device 26b is designed so as to permit remote dismantling or disengagement of the plug 148 and the active part of the device, so as to permit the partisl or total replacement of the lat~er, when its wear due to the abrasi~e nature of the particles present in the treated liquid makes this necessary.

In the dilacerating device 26b described with reference to fi8.
3, the fines sludges to be treated flow from bottom to top within the ejector formed by the injector 165 and the venturi tube 167.
Practical tests have shown that a better efficiency can be obtained by circulating the liquid from top to bottom ~ithin said ejec~or.

For this purpose, it is clear that the positions of the injector and the venturi tube within the bod~ containing the acti~e part of the device can be reversed. The admission pa~sage b~ which the liquid to be treated is ad~itted into the device is then linked ;

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with the injector located in the upper part of the bod~ by an snnular passage. Thiq liquid then flows from top to bottom in the in~ector and then the venturi tube before being evacuated by a passage formed in the lower part of said bod~ and tlhen by an evacuation passage formed in the bottom of the tank. A recycling of the liquid to be treated can be obtained by pro~iding between the annular pas~age for supplying liquid to the injector and the central passage forming the venturi tube, a second annular passage which is linked with each of the ends of ~he venturi tube. A deflector is then advant-ageously formed in the body of the active part of the de~ice, below the lower end of the venturi tube, so as to prevent particles from being deposited at this ~evel and so as to permit the recycling of part of the liquid to be treated by this second annular passage.

Moreover, the venturi tube dilacerating device 26b described relat-lS i~e to fig. 3 has a non-ca-/itatin~ recirculating ejector. By modi-fying the process parameters, said ejector can be transformed into a cavitating recirculating ejectorO In this ca e, a even better efficiency of the device is obtained, but the abrasion risks are greater. Howe~er, this solutioD can be adopted ~he~ t`he liquids to be treated only need a short operating tlme.

As a variant, it is also possible to use devices incorporating vent-uri tubes without recirculation, when the solid particles carried by the liquid are only slightly agglomerated. When it is vital to obtain a ma~imum disintegration of these particles, such as is the case for the dissolYing fines obtained during the reprocessing of irradiated nuclear fuels, the use of recirculation ~enturi tubes remains preferable.

Thus, as in the embodiment de~cribed relative to fig. 3, the device 26c illustrated in fig. 4 has a vertically ased cylindrical tank 318 suspended on a horizontal slab 34 and an ejector 330 interchan-~eably received in the tank 318, the replacement of the ejector taking place from the zone 312 located above the slab 34.

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The body of the ejector 330 comprises three parts 331,332 and 333 coa~iall~ arran8ed around the vertical a~is of the tank 318. As in the embodiment of fi8. 3, the nuter part 333 compri~es a ring-shaped lower portion 349 resting on a thicker part 318a of the tank 318 by means of two seals 362. Thi9 portion 349 is extended upwards b~ a tubular portion 350, which is sealed at i~B upper end by a horizontal portion 351 fi~ed to the cover 324 accessible from the zone 312.

The part 333 internally supports by welded tie rods 353, the inter-mediate part 331, which is shaped like a hollow cylinder and whose upper end carries in its centre an injector 336. The lower portion of part 331 carries a seal 360, which cooperates with the part 318a of the tank 318 below the seals 362.

The part 331 internally ~upports by tie rods 355 the central part 15 332 constituting a venturi tube 334 arranged, together with the injector 336, coa~ially to the vertical axis of the tank 318. The upper intake end of the venturi tube 344 is t~rned upwards and faces the outlet end of the injector 336.

The admission passage 340 for the liquid which it i~ wishsd to treat 20 and which is formed in the thicker part 318a of the tank 318, issues between the seals 360 and 362 preferably in a tangential direction, so as to create a whirling movement of the liquid in ~he annular, outer chamber 370 formed between the outer and inter~ediate parts 333,331 respectively.

At its upper end, the outer, annular passage 370 is linked with the upper, intake end of the injector 336, which is itself connected to the venturi tube 344.

~ The lower end of the venturi tube 344 issues in front of a deflector : 372 formed in the lower portion of the intermediate part 331. The :::

~, , , shape of said deflector 372 makes it possible to avoid an accumula-tion of particles at this location, by forcing the liquid to carry out a radiall~ outwards and then upwards direction change. Passages 374 formed in said lower portion of the p~rt 331 issue at their S upper end into thP bottom of the deflector 372 and at their lower end in a evacuation chamber 356 formed in the bottom of the tank 318 below the seal 360. These passages 374 have a common, lower part arranged in accordance with the axis of the tank 318 and posi~-ioned immediately abo~e an evacuation passage 358 formed, along the said a~is, in thP bottom of the tank 3180 An inner, annular, recycling passage 376 is also formed betweenthe intermediate part 331 and the central part 332 forming the vent-uri tube 344. At its lower end the passage 376 issues above the deflector 372 and, at its upper end, between the injector 336 and lS the venturi tube 344.

In the device 316 described relative to fig. 4, the liquid to be treated, injected under pressure by the admission passage 340, firs-tly rises by the outer, annular passage 370 within the ejector 330.
In a downward movement it then successivel~ traYerses the injector 336 and the ~enturi tube 344. At the lower end of the latter, part of the liquid is directly eYacuated by the passages 374 and 358, whilst another part is rec~cled into the ~enturi t~be by the annular, recycling passage 376.

The de~ices described successi~el~ with reference to figs. 3 and 4 comprise in both cases a non-cavitating recirculation ejector which, has been shown to be the most efficient ejector for obtaining the desired particle disintegration.

Fig. 5 diagrammatically shows a fourth embodiment of the dilacerat-ing de~ice 26 ~sed in the loop 20 of the treatment installation illustrated in fig. 1. This device is designated b~ the reference 26d.

~ 19 -As in the embodiment described relative to fig. 3, the body 256 of the acti~e part of the device is interchangeably placed in a ver~ically a~ed tank 240, which is suspended on a not shown, horizon-tal slab. An admission passage 262 formed in a thicker part 254 of the tank 240 issues into a lower chamber 263 formed in the lower part of the tank below a seal 260. An evacuation passage 264 also formed in part 254 of the tank 240 issues in the interior of the tank between the seal 260 and the seals 258, which are carried by the body 256.

The liquid to be treated flows in a passage formed in the body 256 - between the lower chamber 263 and the evacuation passage 264. S~id passage successively has an injector 265, a Yenturi tube 267 and a baffle syste0 287. The baffle system 287 giYes a reduced height and an increased diameter to the upper part of the body 256.

The baffle system 287 is consti~uted by a passage 289 formed between two facing, coasial profiles 291,293. Part of the liquid leaYing the passage 289 is eYacuated by the eYacuation passage 264, whilst another part of said liquid is recycled in the venturi tube 267 by the holes 285 formed be~ween the latter and the injector 265.

In the dilacerating de~ice 26d described briefly with reference to fig. 5, ~o the agglomerated particle disintegration effect obtai-ned by shearing in the injector 265 and the Yenturi tube 267 in the manner described hereinbefore, is added a supplementary particle disin~egration under the effect of the impacts of said particles against the walls of the baffle system 287.

When the dilacerating device 26 is of the Yenturi tube type 9 like those successively described with reference to figs. 3 to 59 advan-tageously determination takes place of the injector dia~eter so that the pressure in the neck of ~he Yenturi is appro~imately equal to at~ospheric pressure, which avoids degassing and ca~itation problems.

2 ~

By using a device ha~ing a diameter 11 mm injector as~ociated in the dilacerating loop 20 with a pump 24 deli~ering a~ appro~imately 4 bars for a flow rate of 78 m/h, it has been possible to determine by treatin8 fines solutions of appro~imatel~ 75 g/l, that an average operating time of 45 hours makes it possihle to brin8 about the almost total disappearance of particles with A mean dia~eter in excess of 25 ~m, knowing tha~ an operation lasting one hour corresp-onds to approximately 32 passages in the loop.

Fig. 6 shows an embodiment of the fines screening or sifting machine 30 placed at the intake of the pipe 28 for transferring fines to the vitrification site. This fines screening apparatus 30 is susp-ended in the same way as the dilacerating deYice 26 on a biological protection slab 34', which can in certain cases be the sa~e as the slab 34. The screening machine 30 i~ thus located in the lower cell 38' in which the fines are treated.

T~le fines screening machine 30 has a ~ertically a~ed tank 78, incor-porating an upper flange 80 fi~ed to the slab 34' by screws 82.
In its median part, the tank 78 is internally provided with a shoul-der 84, on which rests in a ~ight and detachable manner a horizon~al plaee 86, provided in its centre with a gripping member 88 permitting its remote fitting and dismantling ~ith the aid of appropriate hand-ling means. The plate 86 rests on the sho~lder 84 ~ia a no~ shown seal. At leas~ one admission passage 90 traYerses the tank 78 abo~e the shoulder 84 and issues into the tank, preferably in a tangential direction. A screened fluid evacuation pipe 92 issues in the immed-iate vicinity of the conical bottom 94 of the tank 78.

The fines screening machine 30 is also equipped with an emptying pipe 96, which in the same way as the discharge pipe 92 issues in the i~mediate Yicinity of the co~ical bottom 94 of the tank 78, together with a pipe 98 for the discharge of gases, which issues abo~e the shoulder 84.

2 ~

The plate 86 contains cylindrical holes 100 of the same diameter, which are regularly distributed over the pla~e circumference around the ~ertical a~is of the ~ank 78. E~lch of these holes 100 reoeives a gloYe finger-shaped filter car~rid~,e 102, whose cylindrical part is internally coated with a filtering medium, e.g. constituted by a wire gauze. Each of the filter cartridges 102 rests on the plate 86 by a collar for~ed on its upper, open end. Thus, the said cart-ridges can be easily fitted and removed.

It should be noted that under certain operating conditions, the number of filter cartridges 102 can ~e less than the number of holes 100 formed in the plate 86. Plugs are then inserted in the unoccu-pied holes 100. An ultrasonic probe 104 is placed in each of the filter cartridges 102. Each probe 104 has a cylindrical sheath 106 sealed at each of its ends, and an ultrasonic transducer 108 tightly placed within the sheath 106. The stainless steel sheath 106 extends over appro~imately half its height withi~ the corresp-onding filter cartridge 102 and o~er a comparable height, abo~e the said cartridge, so as to rest b7 a shoulder formed at its upper end on a plate 110, which itself rests on a shoulder for~ed within the tank 73, aboYe the admission passage 90 and the gas discharge pipe 98. Seals 11~ and 114 respectively ensure the necessar7 sealing between each of ~he sheathq 106 and the plate 110 and between the plate 110 and the tank 78.

In the same way as the plate 86 suppor~ing the filter cartrid~es 102, the plate 110 supporting the ultrasonic probes 104 is centrally provided on its upper face with a me~ber 116 permitting its gripping b7 appropriate handling means located abo~e the slab 34'.

The lower ends of the sheaths 106 received in tbe filter cartridges 102 are separated from the latter by an annular space, iD which can flow the solution of fines introduced into the screening machine 30 by the passage 90.

As is illustrated by fig. 6, the u].trasonic transducers 108 are placed in the lower par~s of the sheaths 106, ~o as to cover ~he entire height of the ~iltering medium plared in the cyli~drical wall of the filter cartridg~s 102. I~le shape of this preferably S cylindrical transducer 108 is designed so as to bring about a ~aximum cavitation in the annular ~one formed between each of the probes 104 and the corresponding filter cartridge 102.

The electrical power supply for each of the transducers 108 is pro~i-ded by a source located in the accessible zone above the slab 34' through an electrical conductor 118. The latter conductor tightly traYerses the upper end of each of the sheaths 106, as well as a plug 120 sealing the upper end of the tank 78 and thus completes the neutron protection provided by the slab 34'.

More specifically, in the embodiment illustrated in fig. 6, a circu-lar opening is formed in the plug 120, Yertically with respect to each of the ultrasonic probes 104, so as to permit the fitting and removal thereof without removing the plug 120. Each of these circu-- lar openings is normally sealed by a small plug 122 traYersed by the electrical conductor 118 of the corresponding probe. To avoid radiation leaks at this level, the conduceors 118 pass through the plugs 122 in helical tubes 124.

In order to permit the dismantling of each of ~he ultrasonic probes 104 through the hole of the plug 120, following the remoYal of the corresponding small plug 122, each of the sheaths 106 of the probes 104 carries on its upper face a gripping member 125, which can be grasped by an appropriate handling means located above the slab 34'~ The plate 110 on which are suspended all the ultrasonic probes 104 is fixed below the plug 120, so that remoYal of the latter gives access to the plate 86 carr~ing the filter csrtridges 102, e.g.
for the replacement of the la~ter.

The connection bet~een the plug 120 and the plate llQ is pro~ided r~

by a cylindrical e~tension of the latter, which al90 helps to keep the ultrasonic probes 104 in place on the plate 110. Thus, for each of the probes 104, a horizontal locking plate 126 cooperates with said cylindrical e~tension of the plate 110 by a ba~onet conn-ection 128. Each plate 126 supports a screw 130, which is axiallyaligned with the corresponding ultrasontc probe 104 when ~he plate 126 is in place. The screws 130 can be manipulated from the access ible zone above the slab 34' following the remoYal of their corr-esponding small plugs 122. ~ach of the screws 130 cooperates with a threaded part formed on the upper end of the gripping member 125 of the corresponding probe 104, whilst the latter is immobilized in rotation b~ the cooperation of the plate 126 with a prismatic part formed at the base of ~he memher 125.

Consequently, an action on each of the screws 13Q makes it possible either to disengage the pla~e 126 from the corresponding probe 104, or conversely, by e~pansion9 to engage the latter ag~inst the plate 110 in order to lock the same. When, after remo~ing the plugs 1229 one or more screws 130 are disengaged from the corresponding probes 104, the dismantling of the latter can take place following the removal of the locking plates 126 through ~he holes let b~ the remoYal of the small plugs 122.

When the fines scree~ing machine is operating~ each of the ultra~
sonic probes 108 is supplied with electricity and emits ul~rason~c waves oriented radially with respect to the probe 104, so as to create a ca~itation effect on the liquld present in the annular space formed between the probe and its corresponding filter cartridge 102. This liquid, introduced into the screening machine 30 by the passage 90, is therefore exposed to a new dilaceration action after traYersing the filtering medium lining each of the filter cartridges 102. The particles ha~ing a size greater than a threshold, which i9 in particular predetermined as a func~ion of the sealing risks with respect to the pipe 28 (fig. 1), are held back by the filtering medium of each of the cartridges 102. The liquid and ~he particles of a sufficiently s!~ll size pass through the filter cartridge~
and drop into the conical bottom 94 c3f the tank 78, where the~ are taken up by the evacuation pipe 92.

During the operation of the fines screening machine 30, the operating conditions must be such that those parts of ~he probes 104 housing the ultrasonic transducers 108 are permanently e~bedded. MoreoYer, the pressure on the filtering medium of each of the cartrid6es 102 must be adequate to permit a correct operation thereof, whilst still remainin~ limited, so that the particles are not engaged against the filtering medium and authorizing an adequate cavitation, as a function of the power of the transducers. Moreover, the solution treated in the fines sc~eening machine must rPmain at a temperature not causing any deterioration of the transducers. The transducers 108 are also used for unclogging the filter cartridges 102 of the screening machine 30, when this proves necessary.

For example, use was made of 8 fines screening machi~e comprising four filter cartridges, whose filtering medium was constituted b~
wire gauzes of 25 or 40 ~m, as a function of the desired 8rain size.
These filter cartridges had an internal diame~er of 92 mm and a hei8ht of 160 mm. In each of these cartridges was placed a c~lindri-cal transducer formed by ju~aposing three ceramic disks. The nomin-al instantaneous electric power was then 7S0 W, with a charge rate of 20% corresponding to a pulsed operation and an effecti~e inten~ity of 0.~7 A. This pulsed operation made it possible ~o disturb the prela~er Eormed by the largest particles, so as to permi~ the passage of the finer particles, break up by the ca~itation effect the agglomr erates of large particles and limit the thermal load of thP appara-tus. Such a screening machine ~ade it possible ~o ensure the desi-red calibration of the particles conve~ed to the vitrification site.

Advantageouslg9 the performance characteristics of the process and in~tallation according to the inYention are further impro-Jed b7 carrying out9 within the actual clarifier 10, a prior dilaceraeion .: -, .: . - . . . ,, .. ..
. . . .
: ' ' ' -~ , . . .
:' . .

-~ 25 -of the fines sludges located in the bottom of the clarifier af~er rinsing the cake.

In this case and as is Yery diagra~malticall~ illustrated i~ fig.
1, through an opening formed in the cover of ~he clarifier 10, an ultrasonic probe 132 is introduced into the latter. ThiA ultrflsonic probe is formed by a stainless ~teel sheath in which is placed an ultrasonic transducer.

In the case where the clarifier 10 is formed by a cenerifugal swing-ing settling tank, the latter is slowly rotated, whilst actuating the ultrasonic probe 132. At the end of a certain time and as a result of the cavitation effect created by the transd-~cer, this operation makes it possible to reduce the ~ize of the particles before the solution is transferred into the transfer tank 16.

Tests carried out by means of a cylindrical transducer having an 15 instantaneous, nominal power of 500 W, a charge rate of 20% corr-esponding to a pulsed operation and emitting a~ 20 ~z made it poss-ible to obtain, on the basis of particles with a size initiall7 between 360 and 3000 ~m and after 5.5 h of treatmene, 45% particles with a diameter below 40 ym, 5% particles bet~een 40 and 360 ~m 20 and 50% particles between 360 and 3000 pm. It is also possible to make the ultrasonic fines screening machine operate without curr-ent pulsation.

Use of an ultrasonic probe 132 ~ithin the clarifier 10 makes it possible to further reduce the clogging or blockage risks in the transfer pipe 28 and to reduce the treatment time of the fines in the loop 20.

; Obriously, the invention is not limited to the embodiments describedi~ exemplified ~anner hereinbefore and i~ fac~ corers all variants.
I~ is clear that the struc~ure of the diferent equipments described , ~ Q ~

- 26 ~

can be substantially ~odified, more particularly as a function of the operating conditi.ons and the results to be ob~ained.

~: ~ 10505 ~p ~ .
~., ' ' ' ' .

Claims (21)

1. Process for the treatment of agglomerates of solid particles suspended in a liquid, in order to obtain a heterogeneous mixt-ure able to flow without giving rise to deposits in very long ducts, characterized in that it comprises reducing the grain size of the particles by making the latter flow in a loop (20) incorporating means (26) for breaking up the agglomerates and screening the particles leaving the said loop, in order to hold back the particles having a grain size greater than a predetermined threshold.

2. Process according to claim 1, characterized in that it is app-lied to the treatment of agglomerates of particles called fines obtained after cutting up, dissolving and settling irradiated nuclear fuels, prior to their transfer to a storage tank (32).

3. Process according to either of the claims 1 and 2, characterized in that prior to the circulation of the particles is said loop, there is a prior reduction of their grain size within an appar-atus (10), where settling takes place.

4. Process according to claim 3, characterized in that the particle size is reduced beforehand by means of ultrasonic waves.

5. Process according to and one of the claims 1 to 4, characterized in that ultrasonic means (26a) are used in the loop (20) for disintegrating the agglomerates.

6. Process according to any one of the claims 1 to 4, characterized in that use is made in the loop (20) of a venturi tube device (26b,26c) for disintegrating the agglomerates.

7. Process according to claim 6, characterized in that use is made of a device (26c) incorporating a venturi tube (267), followed by a baffle system (287).

8. Process according to any one of the preceding claims, character-ized in that the particles are screened in an ultrasonic scree-ning machine (30).

9. Installation for the treatment of agglomerates of solid part-icles suspended in a liquid, in order to obtain a heterogeneous mixture able to flow without giving rise to deposits in very long ducts, characterized in that it comprises a loop (20) having a transfer tank (60) linked with the bottom of a settling apparatus (10), pumping means (24) and means (26) for disinte-grating the agglomerates and a particle screening machine (30) placed in a pipe (28) connecting the transfer tank to a storage tank in the vicinity of said transfer tank.

10. Installation according to claim 9, characterized in that it is applied to the treatment of agglomerates of particles called fines obtained after cutting up, dissolving and settling irrad-iated nuclear fuels, prior to their transfer into the storage tank.

11. Installation according to either of the claims 9 and 10, chara-cterized in that in also comprises a means (132) for the prior reduction of the grain size of the particles and placed in the settling apparatus (10).

12. Installation according to claim 11, characterized in that the means for the prior reduction of the grain size of the particles incorporates an ultrasonic transducer (132).

13. Installation according to any one of the claims 9 to 12, char-acterized in that the means for disintegrating the agglomerates comprise a device (26a) having at least one ultrasonic wave-emitting transducer (72).

14. Installation according to any one of the claims 9 to 12, chara-cterized in that the means for disintegrating the agglomerates comprise a device (26b,26c,26d) having a venturi tube (167,267, 344).

15. Installation according to claim 14, characterized in that the venturi tube device (26b,26c,26d) has, upstream of the venturi tube, an injector (165,265,336) separated from the venturi tube by a recycling passage (183,285,376).

16. Installation according to either of the claims 14 and 15, char-acterized in that the venturi tube device (26d) has, downstream of the venturi tube (267), a baffle system (287).

17. Installation according to either of the claims 14 and 15, char-acterized in that the venturi tube device (26c) has, at the outlet from the venturi tube (344), a deflector (372) avoiding particle accumulations.

18. Installation according to any one of the claims 9 to 17, char-acterized in that the particle screening machine (30) is an ultrasonic screening machine.

19. Installation according to claim 18, characterized in that the ultrasonic screening machine operates by current Pulsation.

20. Installation according to claim 18, characterized in that the ultrasonic screening machine operates without current pulsation.

21. Installation according to any one of the claims 9 to 20, char-acterized in that the means (26) for disintegrating the agglo-merates and the particle screening machine (30) comprise active parts, placed in tanks (40,78) suspended on horizontal slabs (34,34') and which can be dismantled from an accessible zone located above the said slabs.