Classifications

• • 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
• • 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
• • 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
• • 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
• • 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
  • C08L25/00—Compositions of, homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Compositions of derivatives of such polymers
  • C08L25/02—Homopolymers or copolymers of hydrocarbons
  • C08L25/04—Homopolymers or copolymers of styrene
  • C08L25/06—Polystyrene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
  • C08L33/04—Homopolymers or copolymers of esters
  • C08L33/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, which oxygen atoms are present only as part of the carboxyl radical
  • C08L33/10—Homopolymers or copolymers of methacrylic acid esters
  • C08L33/12—Homopolymers or copolymers of methyl methacrylate
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
• • 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
• • 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
• • 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 powder especially if it is cohesive, as is conventionally the case for the actinide powders (and in particular their oxides) is deagglomerated during the mixing / preparation of load.
• This pre-requisite is not trivial in itself for the following reasons; 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 shear viscosity range between 50 and 10 000 Pa.s when injected with a preferred range of less than 1000 Pa.s at a shear rate of 100 s "1;
• the rheofluidifying behavior and a robustness of the rheological behavior with the temperature, or more generally the conditions of kneading 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;
• Chemical stability that is, a significant non-chemical interaction between the polymers between them and between the polymers and the actinide powders used.
• 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 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 carbon residues non-delinking (which can therefore be penalizing at the end of the production according to the residual content) during the implementation of the MPI process ;
• compositions loaded with actinide powder capable of withstanding these radiolysis phenomena and compatible with the properties necessary for good behavior in the process of shaping actinide powders by a conventional MPI process. .
• the polymers whose monomer comprises an aromatic ring are relatively resistant to radiolysis and give the formed objects a significant maintenance of their shape.
• compositions of the present invention make it possible not to undergo this problem precisely because of the possibility of using in particular aromatic polymers that provide this protection against radiolysis.
• a decoy that may be relatively sensitive to radiolysis.
• a decoy (it may be a poly methyl methacrylate polymer) absorbs the energy induced by the radiation emitted by the actinide powders protecting the other constituent molecules of the organic matrix.
• this condition can be respected through ranges of percentages selected in the present invention.
• a homogeneity of the microstructure ie a distribution of porosity and uniform grain size
• - dimensional control that is to say a variation of the fuel ratings compared to the expected average ratings of less than 0.2%, ie a value of +/- 0.012 mm;
• 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 contains 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;
• binder comprising at least one aromatic polymer and / or polymethyl methacrylate and with a volume content of between 20 and 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 total volume of the charged matrix.
• compositions make it possible to achieve the specifications defined in the specific problematic set out above, namely a limitation of the radiolysis effects on the rheology of the loaded pasta obtained and the mechanical strength of the injected objects before debinding.
• the binder comprises polystyrene.
• the binder comprises polystyrene and a polyolefinic.
• the binder comprises polymethyl methacrylate and a polyolefinic which may be polyethylene.
• the plasticizer comprises paraffin.
• the plasticizer comprises polypropylene.
• the specific surface area of the grains of said actinide powder (s) 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 19.
• the polyolefinic polymer has an average molar mass of at least 10,000 g / mol.
• 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
• FIGS. 4a, 4b and 4c illustrate the evolution of the incorporation torque as a function of time for three examples of compositions loaded with dry-form powders according to the invention
• FIG. 5 shows the kneading torque for three examples of compositions loaded at 50% by volume of powder according to the present invention
• FIGS. 6a, 6b and 6c illustrate the experimental evolution of loss of mass of examples of compositions Fd, Fe and Ff according to the invention, during the debinding operation and are compared with the theoretical curves;
• FIG. 7 illustrates an exemplary thermal cycle of debinding operation in an Ar / H 2 atmosphere to which examples of charged compositions of the invention are subject;
• FIGS. 8a, 8b and 8c illustrate responses of Thermo-Gravimetric Analysis (ATG) and Differential Thermal Analysis (DTA) measurements performed on compositions of the present invention
• FIGS. 9a, 9b and 9c illustrate the DRX spectra of examples of charged compositions of the present invention.
• 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.
• the injection molding step may be carried out as follows: the fluid-loaded matrix previously obtained is placed in an injection molding machine.
• the injection cycle then proceeds as follows: the material placed in the hopper of the injection molding machine arrives in the sheath which is heated to a suitable temperature and is then conveyed by a worm screw to the nozzle of the injection molding machine. injection 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 organic material from the filled 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 powder of Actinides reputedly cohesive, were made with industrial uranium oxide powders.
• a powder of Actinides reputedly cohesive
• the powder example used for the illustration of 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
• the pressure undergoes high instabilities for shear rates of the order of 2000 s -1 .
• the present description provides the following elements to illustrate the achievement of the multiple criteria of acceptability of compositions charged described in particular in the problem of the present invention.
• FIG. 3 gives an illustration of the injectability of the aforementioned compositions Fd, Fe and Ff and is representative of the shear viscosity as a function of the shear rate (unit: s -1 ) at 220 ° C., and with a temperature of stirring of 175 ° C. and a loading rate of 50% by volume, the C 3 Fd, C 3 Fe and C 3F f curves being respectively relative to the Fd, Fe and Ff compositions.
• FIGS. 4a, 4b and 4c illustrate the evolution of the kneading couples as a function of time for the compositions Fd, Fe and Ff (in these figures, the ordinate on the right corresponds to the kneading temperature).
• FIGS. 6a, 6b and 6c are respectively relative to the charged compositions Fd, Fe and Ff and illustrate the virtual absence of interaction of the organic constituents of the matrix whose overall debinding behavior can be likened to a linear combination of the individual behaviors of these elements.
• the curves C 6 di, C 6 e i and C 6 i are relative to the curves theoretical, the curves C 6 d2, C 6e 2 and C & 2 being relative to the experimental curves.
• 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: Fd, Fe and Ff, this short thermal cycle has been implemented. to allow rapid evaluations of the compositions obtained.
• 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 Fd, Fe and Ff. More precisely, the curves C 8 di, C 8 e i and C 8 M relate to ATG measurement results and the curves C 8 d 2, C 8 e 2 and C 8f 2 relate to ATD measurement results. These are Thermo-Gravimetric (ATG) and Differential Thermal Analysis (DTA) measurements.
• ATG Thermo-Gravimetric
• DTA Differential Thermal Analysis
• DTA Differential Thermal Analysis
• phase transitions and solvent evaporation result in endothermic peaks.
• crystallization, oxidation and some decomposition reactions are characterized by exothermic peaks.
• ATD is usually associated with thermogravimetric analysis (TGA), which measures the change in 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 Fd, Fe and Ff 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 non significant interaction of the actinide powder with the shaping polymers which is referred to with the present charged compositions Fd, Fe and Ff.
• the debinding ability criterion it is necessary for the debinding operation to be able to take place while preserving the integrity of the part once the forming polymers have been untied and without too much proportion of carbon residues which would not be removable during sintering and which could otherwise modify the microstructure of the sintered actinide material.
• Table 4 gives the percentages of carbon residues of the final parts at the end of the sintering operation.

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