Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/08—Metals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/06—Polyethylene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
  • C08L23/12—Polypropene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L91/00—Compositions of oils, fats or waxes; Compositions of derivatives thereof
  • C08L91/06—Waxes
  • C08L91/08—Mineral waxes
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/01—Hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
• • 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 field of the invention is that of compositions based on actinide powder, and having the advantage of being injectable because allowing a rheology compatible with injection systems.
• One of the main fields of application may concern (but not exclusively) the manufacture of nuclear fuels (or more generally of parts / materials based on actinides).
• the present invention relates to the production of more or less complex parts containing actinides whether in the form of metal, oxide, carbide or nitride.
• the classical and industrial development of fuel is currently going on and mainly through the exploitation of powder metallurgy (based on the pressing of the powders constituting the parts / fuels to be shaped and the sintering of compacts obtained after pressing). .
• compositions for implementing a process called injection or powder injection molding also called “MPI” (or “PIM” in English for Powder Injection Molding) are charged compositions for implementing a process called "MPI” (or “PIM” in English for Powder Injection Molding) .
• the MPI method applied to actinide powders has the objective of producing objects whose characteristics are similar to those obtained by powder metallurgy, it is necessary, after the debinding step, for the shaping polymers. to result in granular stacks and to be cohesive, that is to say, keep their shape, and whose density is equivalent to that obtained by uniaxial pressing of powders (metallurgy powders).
• a powder can be considered cohesive if it meets the definition of Geldard (class C) or has a Hausner coefficient higher than 1, 4, "Techniques of the engineer shaping powders, J 3 380-1" .
• the injectability of the charge despite the criterion of the charge rate expressed above, it is necessary to be able to implement the charged matrix within a mold (or through a die if extrusion is carried out ) which imposes a range of shear viscosity of between 50 and 10,000 Pa.s during injection with a preferential range less than 1000 Pa.s for a speed gradient of 100 s -1 ;
• the rheofluidifying behavior and a robustness of the rheological behavior with the temperature, or more generally the mixing conditions can be prohibitive.
• the actinide powders can be relatively dense, cohesive and polymodal, it is necessary in particular to limit any risk of segregation / sedimentation within the matrix loaded in case of poor formulation or mixing conditions during the mixing;
• this criterion requires that the mixture of the polymers constituting the matrix is stable at least up to the lowest decomposition temperature of the constituents of the matrix of organic compounds.
• actinides are also compounds known to promote the decomposition of the constituent carbon compounds of the charged matrix (see “The activity and mechanism of uranium oxide catalysts for the oxidative destruction of volatile organic compounds", SH Taylor, CS Heneghana, GJ Hutchingsa et al., Catalysis Today, 59: 249-259, 2000.
• SH Taylor, CS Heneghana, GJ Hutchingsa et al. Catalysis Today, 59: 249-259, 2000.
• this criterion of stability of the properties is not trivial to reach with in particular either a risk of modification of the degree of oxidation of the actinides in contact with the constitutive constituents of the matrix is a risk of formation of carbonaceous residues not debonding ( may therefore be penalizing at the end of the production according to the residual content) during the implementation of the MPI process;
• homogeneity of the microstructure i.e. a uniform porosity and grain size distribution
• dimensional control i.e. variation of the fuel dimensions compared to the expected average ratings, ie for example and typically a tolerance of + or - 12 microns for rectified REP pellets (8,19 ⁇ 0, 012mm);
• the subject of the present invention is a set of charged compositions which, in spite of the very specific and penalizing characteristics of the aforementioned actinide powders, allow a satisfactory implementation (in the sense of the aforementioned specific problem) of the latter by a process. MPI.
• the subject of the present invention is thus actinide-loaded compositions which make it possible to implement, in a conventional injection-molding type process, in order to obtain, after injection, debinding and sintering, actinide compound parts with complex, controlled geometries and microstructural quality equivalent to that which would have been obtained by metallurgy of conventional powders.
• Such formulations also allow the use of actinide powders used currently for the industrial manufacture of nuclear fuels, and this without special preparation of the latter.
• the subject of the present invention is a composition charged with actinide powder comprising an organic matrix and an actinide powder or a mixture of actinide powders, characterized in that it comprises at least:
• plasticizer comprising an alkane whose longest radical chain comprises at least a few tens of carbon atoms and a volume content of between 20 and 70% of the total volume of organic compounds alone;
• a binder comprising at least one polyolefinic polymer with a volume content of between approximately 20 to 50% of the total volume of organic compounds alone;
• a dispersant comprising a carboxylic acid or its salts whose volume content is less than 10% of the total volume of the organic compounds alone;
• said actinide powder or said mixture of actinide powder representing between 40% and 65% of the volume of the charged matrix.
• the polyolefinic polymer has an average molar mass of at least 10,000 g / mol.
• the polyolefinic polymer is polyethylene.
• the polyolefinic polymer is polypropylene.
• the polyolefinic polymer is polypropylene with a molar mass of greater than about 100 000 g / mol.
• the plasticizer comprises paraffin. According to a variant of the invention, the plasticizer comprises polypropylene.
• the plasticizer comprises polypropylene of molar mass of the order of 10 000 g / mol.
• the specific surface area of the grains of said actinide powder is between about 1 m 2 / g and 15 m 2 / g.
• the packed density of said actinide powder is between about 10 to 70% of the theoretical density of the compound (s) of the powder / powders.
• the theoretical density of the constituent materials of the powder is between 2 to 20.
• the theoretical density of the constituent materials of the powder is between 7 to 10.
• the carboxylic acid or its salts have a molar mass of at least 100 g / mol.
• the mass proportion of said carboxylic acid or its / its salts relative to the mass of actinide powders is between about 0.01 and 1% by mass.
• FIG. 1 illustrates all the steps of an MPI process implemented with the charged compositions of the present invention
• FIG. 2 illustrates an example of the shape of the instability of the flow pressure as a function of the shear rate for a typical case of bad formulation or mixing condition
• FIG. 3 illustrates the shear viscosity as a function of the shear rate at 220 ° C. for various compositions charged according to the invention: Fa, Fb and Fc;
• FIG. 4 illustrates an example of volume distribution of the diameter of the particles (cohesive ceramic type) before and after mixing with a formulation of the Fa type;
• FIGS. 5a, 5b and 5c show the evolution of the mixing torque as a function of time for the various compositions Fa, Fb and Fc, FIGS. 5d and 5e illustrating the evolution of the mixing torque as a function of the load ratio;
• FIGS. 6a, 6b and 6c illustrate the experimental evolution of loss of mass of the examples of compositions Fa, Fb and Fc according to the invention, during the debinding operation and are compared with the theoretical curves (behavior of the independently shaped polymers);
• FIG. 7 illustrates an example of a thermal cycle in an unbinding operation under an Ar / H 2 atmosphere to which compositions of the invention are subjected
• FIGS. 8a, 8b and 8c illustrate responses of Thermo-Gravimetric Analysis (ATG) and Thermal Analysis measurements
• DTA Differential
• Figures 9a, 9b and 9c illustrate the DRX spectra of compositions of the present invention
• FIG. 10 illustrates the diameter variations measured as a function of the heights of pellets obtained before the debinding operation and after the sintering operation.
• the charged compositions of the present invention are intended to provide actinide charges having satisfactory properties and allowing implementation according to the MPI method described below and illustrated by the steps summarized in FIG.
• a first step 1 corresponding to the mixing and kneading of the raw materials, the whole of the raw materials is mixed, namely in the present invention: the organic matrix M or g comprising the plasticizer, the binder, the dispersant , and the charge based on P, actinide powder.
• the powder is generally added progressively to the mixture of the other hot raw materials by means of a kneader, which can be equipped with blades which make it possible to have high shear rates thus ensuring the homogeneity of the material. 'together.
• the injection molding step can be carried out as follows: the fluid-loaded matrix previously obtained is placed in an injection molding machine.
• the injection cycle then takes place as follows: the material placed in the hopper of the injection molding machine arrives in the sheath which is heated to a suitable temperature then it is conveyed by an endless screw to the injection nozzle connected to the mold having the desired shape. Once the material has been dosed (volume linked to that of the part to be injected), the screw stops rotating and the filling of the mold is carried out under pressure (the screw plays the role of piston). The mixture is then compacted in the impression during holding in pressure. The part is then ejected when the mixture is sufficiently cooled (sufficient rigidity).
• the main parameters that govern this step are: raw material temperature, mold temperature, injection pressure and injection speed.
• the third step 3 corresponds to the debinding operation.
• Debinding is a key step in the process of removing the organic material from the charged matrix once the part has been injected.
• the quality of this operation is fundamental to not cause physical damage (cracking) or chemical damage (carburation) to the piece.
• a very important part of the defects that appear after sintering is generated by inadequate debinding.
• the fourth step 4 corresponds to the sintering operation.
• the part must be consolidated by a sintering step.
• Sintering is a thermal process that allows, by heating compacted powders, generally below their melting point, to give them a cohesion after cooling and to obtain the desired microstructure of the final material.
• the principle of sintering is based on atomic scattering: particles in contact are welded by diffusion atomic transport phenomena if they are subjected to temperatures higher than half their absolute melting temperature so as to obtain a finished object.
• F Examples of charged compositions used in the present invention:
• compositions of the present invention In order to demonstrate the possibility of satisfactorily implementing, in the sense of the aforementioned problematic, the compositions of the present invention, several charged compositions comprising a Plasticizer, a binder and a dispersant as described in the present invention with a known cohesive actinide powder, were produced with industrial uranium oxide powders.
• the powder example used for illustrating the present invention is representative of this characteristic.
• uranium oxide powder has been used, the crystallites (constituent elementary objects of the powder) are grouped into aggregates which themselves are amassed in agglomerates.
• FIG. 2 illustrates the shape of the flow pressure as a function of the shear rate (unit: s -1 ) for a typical case of bad formulation or mixing condition, which can typically be obtained from an organic matrix comprising a standard polymer.
• Cooling time 30s Mold closing force: 80 kN Injection speed: 20cm 3 / s
• FIG. 3 gives an illustration of the injectability of the compositions Fa, Fb and Fc and is representative of the shear viscosity as a function of the shear rate (unit: s -1 ) at 220 ° C., and with a mixing temperature 175 ° C and a charging rate of 50% volume.
• the curves C 3 F, ⁇ 3FB and C-3Fc being relative to the compositions respectively Fa, Fb and Fc.
• FIGS. 5a, 5b and 5c illustrate the mixing torques and the temperatures applied over time for the three compositions Fa, Fb and Fc.
• FIG. 5d shows the evolution of the mixing torque as a function of the filler content (% by volume), for the filled composition Fb, and for the same raw materials mixed with several types of powders.
• the reference CNV corresponds to the powder of U0 2 + x obtained by the dry route.
• the other 3 references are alumina powders capable of limiting the effects of radiolysis on the rheology of the loaded pastes and the mechanical behavior of the injected objects before debinding.
• the reference Cr is the manufacturing name which means milled, and reference GE means unmilled. The following figure indicates the specific surface area of the powder.
• CR15 crushed alumina powder with a specific surface area of 15m 2 / g;
• CR30 crushed alumina powder with a specific surface area of 30m 2 / g;
• GE15 unmilled alumina powder with a specific surface area of 15m 2 / g.
• FIGS. 6a, 6b and 6c are respectively relative to charged compositions Fa, Fb and Fc and illustrate the virtual absence of interaction of the organic constituents of the matrix, the overall behavior of which can be likened to a linear combination of the individual behaviors of these components.
• the curves C -i 6a, C 6 t> 6c i and C i are relative to the theoretical curves, the curves C6 2; C6b2 and Cec2 being relative to the experimental curves.
• PP2 polypropylene, molar mass of 200,000 g / mol PW: paraffin
• PP1 polypropylene, molar mass of 12,000 / mol
• FIG. 7 An example of a thermal cycle that can be used under an argon and hydrogen atmosphere in the debinding process is illustrated in FIG. 7, is applied to the three charged compositions: Fa, Fb and Fc, this short thermal cycle has been implemented. to allow rapid evaluations of the compositions obtained. Generally, it will be preferred long debinding cycles (typically a few hours) during industrial processing of powders shaped to maintain the integrity of the part.
• FIGS. 8a, 8b and 8c illustrate debinding operations with regard to the thermal behavior of the charged compositions Fa, Fb and Fc. More specifically, the C i curves 8a, C 8 t> i and C i are 8c relating to ATG measurement results and the curves 8a C 2, C 8 and C b2 8C 2 relate to the measurement results ATD. These are Thermo-Gravimetric (ATG) and Differential Thermal Analysis (DTA) measurements.
• ATG Thermo-Gravimetric
• DTA Differential Thermal Analysis
• Differential thermal analysis is a method used to determine the temperatures corresponding to changes in the material as a function of heat treatment. It consists in measuring the difference in temperature between a sample (Te) and a reference (Tr) (thermally inert material) as a function of time or temperature, when they are subjected to a programmed temperature variation, under a controlled atmosphere. In general, phase transitions and solvent evaporation result in endothermic peaks. On the other hand, crystallization, oxidation and some decomposition reactions are characterized by exothermic peaks.
• ATD is generally associated with thermogravimetric analysis (TGA), which measures the variation of a mass of a sample as a function of the heat treatment temperature. This mass variation can be a loss of mass such as vapor emission or a mass gain during the fixing of a gas for example.
• TGA thermogravimetric analysis
• FIGS. 9a, 9b and 9c illustrate, for this purpose, the DRX spectra of the charged compositions Fa, Fb and Fc and do not make it possible to demonstrate a modification of the U0 2 phase of the fuel, which goes in the direction of a significant interaction of the actinide powder with the shaping polymers which is referred to with the present charged compositions Fa, Fb and Fc.
• Unbinding ability of the charged compositions according to the invention As regards the debinding ability criterion, it is necessary that the debinding operation can be carried out while maintaining the integrity of the part once the polymers have been removed. formatting loosened and excessive proportion of carbon residues that would not be eliminated during sintering and that could otherwise modify the microstructure of the sintered actinide material.

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