Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/46—Constructional details of screens in general; Cleaning or heating of screens
  • B07B1/4609—Constructional details of screens in general; Cleaning or heating of screens constructional details of screening surfaces or meshes
  • B07B1/4663—Multi-layer screening surfaces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/46—Constructional details of screens in general; Cleaning or heating of screens
  • B07B1/4609—Constructional details of screens in general; Cleaning or heating of screens constructional details of screening surfaces or meshes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B13/00—Grading or sorting solid materials by dry methods, not otherwise provided for; Sorting articles otherwise than by indirectly controlled devices
  • B07B13/14—Details or accessories
  • B07B13/16—Feed or discharge arrangements
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
  • G21C3/42—Selection of substances for use as reactor fuel
  • G21C3/58—Solid reactor fuel Pellets made of fissile material
  • G21C3/62—Ceramic fuel
  • G21C3/623—Oxide fuels
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the subject of the present invention is: - an original sieving-forcing process of pulverulent products, suitable for conferring on said pulverulent products a particle size spectrum having a main narrow distribution mode centered on a value of a few tens of microns as well as a fraction of micron particles; - an original sieving-forcing device for pulverulent products, suitable for implementing said process;
• Said preparation process includes said screening-forcing process.
• the Applicant has developed the invention in the context of the manufacture of nuclear fuel pellets, these pellets being based on a mixture of uranium oxide (UO 2 ), plutonium oxide (PuO 2 ) and generally of chamotte.
• UO 2 uranium oxide
• PuO 2 plutonium oxide
• the invention is hereinafter more particularly described in this context but the person skilled in the art will readily understand, on reading the following, that it is in no way limited to said context.
• the methods and device of the invention are suitable for obtaining any type of powders or mixtures of powders optimized, on a micron scale, in particular of powders or mixtures of powders of the pharmaceutical industry.
• the powder of PuO 2 generally has an average diameter of 15 ⁇ m, that of UO 2 an average diameter a few tens of microns; average diameters measured by laser granulation dry route, without agitation, by ultrasound;
• MIMAS process which mainly includes the following successive steps: + the preparation of a first powder, known as the mother or primary mixture, containing plutonium oxide in intimate mixture (on a micron scale) with uranium oxide and generally chamotte;
• This billing step is implemented by dry grinding, for example in a ball mill.
• This grinding certainly causes a certain fracturing of the particles of the raw material but it also results in the formation of agglomerates whose particle size spectrum is wide. It is therefore necessary to reduce the size of said agglomerates. To this end, a sieving-forcing step is carried out on the ground raw material.
• Said ground raw material is thus passed through a device associating in its structure a grid (a monogrid screen) with means (of the flail type, rotor provided with arms) capable of forcing the passage of said ground raw material through said grid (said sieve).
• a device associating in its structure a grid (a monogrid screen) with means (of the flail type, rotor provided with arms) capable of forcing the passage of said ground raw material through said grid (said sieve).
• This type of device - strainer-strainer - exists commercially. They may in particular be ETSCH or FREWITT screens.
• the size of the orifices of said grid is a crucial parameter which determines the particle size of the sieved powder.
• the need to obtain a very fine first powder (suitable for making an intimate mixture with the dilution powder) makes the use of very small mesh screens compulsory.
• the device must be capable of delivering a significant volume of powder.
• the grid must therefore have a large passage area with a large number of small meshes (small holes).
• Said grid is therefore in the form of a crossed network of metallic wires, of small sections, which gives it the necessary "transparency" required but inexorably low mechanical resistance.
• the devices used to date for sieving-forcing therefore have the certain drawback of the fragility of the grid which enters their structure. Said grid frequently breaks, these frequent breaks being moreover difficult to detect in industrial operation in watertight enclosures, such as glove boxes, enclosures within which maintenance interventions, for replacement of defective parts, are complex and costly.
• Said first step is followed, as indicated above, by diluting the primary mixture obtained with a dilution powder.
• the preparation of said primary mixture and its dilution are shown diagrammatically, in a general context, in FIG. 1 attached. Consideration of this figure already makes it possible to better situate the context in which the invention is conceived and helps to understand this invention. In this figure, we find the three phases of the preparation of the first powder (or primary mixture) followed by the second dilution step.
• Pi any powdery product whose presence is desired in the final mixture, an intimate mixture of powdery products.
• Pi UO 2 + generally chamotte + possibly at least one powder additive
• the invention has therefore been developed in such a context for the preparation of an intimate mixture of at least two pulverulent products, preparation in two stages which comprises the constitution of a primary mixture and then the dilution thereof. It was more precisely developed at the level of the preparation of said primary mixture and it is easy to understand on reading the following, that it is not limited to this context of production of intimate mixtures in two stages.
• an improvement is proposed to the sieving-forcing process and device, useful for obtaining micron powders, mixed or not.
• a second step it proposes to obtain powders or mixtures of powders, with such bimodal particle size spectra, by sieving-forcing within devices which do not exhibit the fragility of prior art devices of this type, suitable to generate the same result at the particle size spectra.
• the present invention therefore relates to a sieving-forcing process for pulverulent products, intended to give said pulverulent products a particle size spectrum having: - a main narrow distribution mode centered on a value of a few tens of microns (for example , 40 ⁇ m); as well as :
• the pulverulent products in question - powders or mixtures of powders - can be of any type and in particular consist of pigments, products of the pharmaceutical industry, of the food industry, of the nuclear industry (the primary mixtures UO 2 + PuO 2 , resulting from the fracturing of particles of UO2 and Pu ⁇ 2: see above). It is generally a question of powders polluted by agglomerates (of average size greater than 100 ⁇ m), which one wishes to rid of said agglomerates or even to reduce more finely ...
• the sieving-forcing of the invention comprises forced passage
• the relative arrangement of the grids, constituting the assembly makes it possible to obtain the desired result at the level of the particle size of the sieved powders. It also reinforces the solidity of said assembly (the grid with larger meshes being placed below) and is favorable to a lesser retention of sifted pulverulent products within said assembly.
• the process of the invention is advantageously carried out on a mixture of at least two pulverulent products. It then makes it possible to perfect said mixture.
• Said process of the invention carried out on a powder or a mixture of powders (according to the advantageous variant above), can expediently be carried out after dry grinding of said powder or of said mixture of powders. It is then perfectly suitable for causing the fracturing of the agglomerates generated during said grinding. It is understood that said method of the invention is thus advantageously implemented in the context of the manufacture of nuclear fuel pellets, as specified above.
• the screening-forcing of the invention is, according to a preferred variant, implemented through a rigid assembly of two grids.
• the present invention relates to a sieving-forcing device for pulverulent products, which is suitable for implementing the sieving-forcing process as described above.
• Said device is of the type of those of the prior art in that it combines in its structure a sieve with means capable of forcing the passage of said pulverulent products through said sieve.
• said sieve does not have a single grid; said screen comprises a rigid assembly of at least two superimposed grids, in contact with one another, of different opening size, increasing with their distance from ent ent said means capable of forcing the passage; said opening size of each of said grids of said assembly being, in any event, greater than that of the single grate, of the same type, which, used under the same conditions, would give said pulverulent products a particle size spectrum of the same type .
• the rigid assembly of the superimposed grids can result from a simple superimposition (of a simple plating) of said grids one on the other. It can also result from a joining together of said grids.
• the grids constituting said assembly could in particular be welded, sintered, between them.
• the assembly of the grids constituting the sieve within the meaning of the invention can be used as such or arranged on a support grid.
• the intervention of such a support grid may prove to be advantageous, in terms of solidity, of manipulation of the assembly.
• the screen of the screening-forcing device of the invention comprises a rigid assembly of two grids.
• said sieving-forcing is sieving-forcing according to the first object of the present invention, as described above, a sieving-forcing implemented through several superimposed grids, with increasing opening sizes.
• the same pulverulent product is used as other pulverulent product in the constitution of said primary mixture and in the dilution powder;
• said active ingredient consists of plutonium oxide powder (PuO 2 ), said primary mixture contains said plutonium oxide powder (PUO 2 ), uranium oxide powder (UO 2 ) and generally chamotte and said dilution powder contains uranium oxide powder.
• a primary mixture with bimodal particle size is prepared (using the original sieving-forcing of the invention), adapted to that, single-mode, of the dilution powder which occurs during the second step.
• FIG. 1 schematically illustrates the different stages of said method, in a general context. We have already indicated, in the introduction to this text, how to read this figure in the specific context of the development of nuclear fuel pellets. In this context, we have:
• FIG. 1 in fact illustrates, both the prior art and the invention, according to the mode of implementation of sieving-forcing (depending on whether the intervening sieve comprises one or more grids, with suitable respective openings and positioning) .
• Figure 2 shows, on a semi-logarithmic scale, the particle size distributions of powders: - UO 2 dilution powder, able to intervene to constitute the desired intimate mixture (continuous curve: -).
• Rigid double-grid assemblies of this type have also been tested on various strainers, with grids of the following mesh openings: 200 and 560 ⁇ m; 210 and 560 ⁇ m; 210 and 710 ⁇ m; 250 and 750 ⁇ m; 450 and 750 ⁇ m.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Combined Means For Separation Of Solids (AREA)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)

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• 2002
  • 2002-02-07 FR FR0201471A patent/FR2835451B1/fr not_active Expired - Lifetime
  • 2002-06-18 US US10/173,954 patent/US20030146312A1/en not_active Abandoned
  • 2002-07-30 JP JP2002221930A patent/JP2003236471A/ja active Pending
• 2003
  • 2003-02-07 EP EP03715075A patent/EP1472015A1/de not_active Withdrawn
  • 2003-02-07 WO PCT/FR2003/000388 patent/WO2003066242A1/fr not_active Ceased
  • 2003-02-07 RU RU2004126847/03A patent/RU2004126847A/ru unknown

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