Method for producing nuclear fuel

Abstract

The method for producing a nuclear fuel is implemented using nuclear elements (2) comprising a fissile material (4) contained within cladding (6), inside a capsule (8) or in a composite material (10) formed by the fissile material dispersed in a matrix (12). The processing method comprises cutting the nuclear elements into fragments (36), reducing the fragments to a powder in order to obtain a powder, and using the powder to manufacture nuclear fuel.

Description

[0001] Method of producing nuclear fuel

[0002] The present invention relates to the field of nuclear fuel production.

[0003] At the end of the production of nuclear elements comprising fissile material contained in a cladding or capsule or a composite material formed by the fissile material dispersed in a matrix, such as nuclear fuel rods, nuclear fuel plates, nuclear medical targets, nuclear fuel particles comprising encapsulated fissile material (e.g. nuclear fuel of the TRISO type from the English ("Tri-structural Isotropy") or composite nuclear fuels comprising fissile material dispersed in a matrix, in particular a metallic matrix (e.g. nuclear fuel of the cermet type), non-destructive examinations are carried out to verify the conformity of the nuclear elements. In the event of non-conformity of a nuclear element, it is rejected.

[0004] There are also some compliant but unused or very weakly irradiated nuclear elements which are discarded.

[0005] The percentage of discarded nuclear materials is significant. These discarded nuclear materials can be difficult to recover and are therefore counted as nuclear waste, which is costly to manage.

[0006] One of the aims of the invention is to enable the recovery of nuclear elements which have been discarded during production or which have not been used or which have been very weakly irradiated.

[0007] To this end, the invention proposes a method for producing a nuclear fuel from nuclear elements each comprising a fissile material contained in a cladding, a capsule or a composite material formed by the fissile material dispersed in a matrix, the treatment method comprising:

[0008] - cutting nuclear elements into fragments;

[0009] - the reduction of the fragments into powder to obtain a powder; and

[0010] - the use of powder for the manufacture of nuclear fuel.

[0011] The method of producing nuclear fuel from nuclear elements comprising fissile material contained in a cladding or capsule or dispersed in a matrix makes it possible to recover unirradiated or slightly irradiated nuclear elements, such as discarded nuclear elements or unscrapped but little or no-used nuclear elements, while also making it possible to produce nuclear fuel for various applications. The fragments resulting from the cutting of nuclear elements comprise fissile material and, in addition, material from the cladding, capsule or matrix of the composite material.

[0012] Cutting nuclear elements into fragments followed by powder reduction of the fragments forms a powder suitable for the production of nuclear fuel, particularly for the production of nuclear power fuel for use in a nuclear reactor for electricity production.

[0013] In particular embodiments, the production method comprises one or more of the following optional features, taken individually or in any technically possible combination:

[0014] - the production method includes the addition of depleted uranium to the fragments before reduction to powder;

[0015] - depleted uranium is added to the fragments if the enrichment of the fissile material of the nuclear elements in uranium 235 (U-235) is equal to or greater than 4.5% by mass;

[0016] - powder reduction involves melting the fragments to obtain a molten mass, and atomizing the molten mass or rubbing and kneading the fragments;

[0017] - powder reduction includes the grinding of the material obtained after the melting and atomization of the fragments or the friction and kneading of the fragments;

[0018] - powder reduction includes grinding of fragments;

[0019] - the production method includes sieving the powder;

[0020] - the powder particles have an average diameter equal to or less than 2 mm, preferably equal to or less than 1,000 micrometers, more preferably equal to or less than 200 micrometers;

[0021] - the production method includes oxidation of the powder by heat treatment under an oxidizing atmosphere;

[0022] - the oxidation is carried out at a temperature equal to or lower than 2,000°C, preferably at a temperature equal to or lower than 1,300°C and / or at a temperature equal to or higher than 300°C;

[0023] - the oxidizing atmosphere is a dry atmosphere or a humid atmosphere, in particular an atmosphere of dry air or humid air;

[0024] - the cutting of nuclear elements and / or the reduction into powder are carried out at a temperature between 78 and 300 K, in particular at room temperature;

[0025] - the powder is used for the production of nuclear fuel for a high temperature reactor (or HTR) or nuclear fuel for a small modular reactor (or SMR) or a metal plate enriched in fissile material, for example to 20% or more by weight or low enriched and high dosage uranium (or HALEll) or low enriched uranium (or LEU), for example for light water reactors, in particular for pressurized water reactors (or PWR) or boiling water reactors (or BWR), or nuclear fuel for a uranium fast neutron reactor (or RNR for "Fast Neutron Reactor");

[0026] - the fissile material contains uranium and / or plutonium, the uranium being present in particular in the form of uranium oxide, for example UO2, U4O9, U3O7, U3O8 and / or uranium oxycarbide (UCO) and / or uranium carbide (UxCy) and / or uranium metal alloy and / or uranium intermetallic, for example U-Si, in particular U3Si2, U-Al, U-Mo, U-Zr, U-Nb;

[0027] - nuclear elements are non-irradiated or weakly irradiated and / or discarded nuclear elements;

[0028] - the nuclear elements used for implementing the production method include nuclear fuel elements, for example for a high temperature reactor (or HTR) and / or for a small modular reactor (or SMR) and / or for a uranium fast neutron reactor (or RNR for "Rapid Neutron Reactor") and / or for a pressurized water reactor (or PWR) and / or for a boiling water reactor (or BWR), and / or nuclear fuel plates and / or nuclear medical targets and / or encapsulated nuclear fuel particles, for example of the TRISO (Tristructural-isotropic) type and / or nuclear fuel elements comprising a composite material containing the fissile material dispersed in a matrix,for example cermet (ceramic - metal) or cercer (ceramic-ceramic) type, and / or MOX (Mixed-Oxides) type nuclear fuel elements;,

[0029] - the produced nuclear fuel is a power nuclear fuel intended for use in a power-producing nuclear reactor, and / or the nuclear elements comprise research reactor nuclear fuel elements, radioisotope production targets and / or power nuclear fuel elements. The invention will appear more clearly on reading the following description, given solely by way of non-limiting example, and with reference to the drawings in which:

[0030] - Figure 1 illustrates steps in a nuclear fuel production method;

[0031] - Figure 2 is a schematic sectional view of a nuclear fuel rod;

[0032] - Figure 3 is a schematic sectional view of a plate-shaped nuclear fuel element;

[0033] - Figure 4 is a schematic cross-sectional view of a TRISO-type nuclear fuel particle;

[0034] - Figure 5 is a schematic sectional view of a nuclear fuel particle made of composite material comprising fissile material dispersed in a matrix.

[0035] The production method illustrated in Figure 1 aims to produce nuclear fuel using nuclear elements 2 each comprising a fissile material 4 contained in a cladding 6 or in a capsule 8 or in a composite material 10 comprising the fissile material 4 dispersed in a matrix 12.

[0036] Fissile material 4 contains, for example, uranium and / or plutonium.

[0037] Fissile material 4 contains, for example, uranium in the form of uranium oxide, in particular UO2, U4O9, U3O7 or LhOs, and / or in the form of uranium oxycarbide (UCO) and / or in the form of uranium nitride (UN) and / or in the form of uranium carbide (U x C y ) and / or in the form of a uranium metal alloy or uranium intermetallic, for example in the form of a uranium metal alloy or uranium intermetallic selected from uranium-aluminium (U-Al), uranium-silicon (U-Si), in particular UaSi2, uranium-molybdenum (U-Mo), uranium-zirconium (U-Zr) or uranium-nobium (U-Nb).

[0038] Fissile material 4 contains, for example, plutonium in the form of plutonium oxide, in particular PuC>2.

[0039] In exemplary embodiments, the fissile material 4 comprises a mixture of uranium oxide and plutonium oxide. A nuclear fuel containing such fissile material 4 is generally designated by the acronym MOX (from the English “Mixed Oxides”).

[0040] In exemplary embodiments, nuclear elements 2 each comprise a sheath 6 containing the fissile material 4.

[0041] The sheath 6 is a sealed envelope receiving the fissile material 4. The sheath 6 is for example made of aluminum, an aluminum-based alloy, pure zirconium, a zirconium-based alloy, i.e. an alloy comprising at least 95% zirconium by mass, or steel.

[0042] Examples of aluminum alloy include, for example, aluminum 5754 or aluminum 6061 or aluminum-iron-nickel (Al-Fe-Ni) alloy. Examples of zirconium alloy include M5, Zr-1%Nb, Zr-2.5%Nb, Q12, Zircaloy-2, Zyrcaloy-4. Examples of steel include AISI 304 steel or 15-15Ti steel.

[0043] The sheath 6 is optionally provided with a protective coating covering an external surface of the sheath 6.

[0044] The protective coating is, for example, made of pure chrome or a chrome-based alloy, i.e. an alloy comprising at least 85% chrome by mass.

[0045] Nuclear elements 2 comprising a cladding 6 include, for example, nuclear fuel rods, nuclear fuel plates and / or nuclear medical targets.

[0046] As illustrated in Figure 2, a nuclear fuel rod is a nuclear element 2 which comprises a cladding 6 comprising a tube 14 extending along an extension axis A and closed at each of its ends by a plug 15, the fissile material 4 being in the form of a powder or, as visible in Figure 2, of a column of pellets 16 stacked in the cladding 6. A plenum 17 is preferably provided between one of the two plugs 15 and the fissile material 4, for example using a spring 19 interposed between the fissile material 4 and the plug 15. The tube 14 and / or the plugs 15 are generally made of zirconium or a zirconium-based alloy.

[0047] Nuclear fuel rods are used, for example, in nuclear reactors for the production of electricity, particularly in pressurized water reactors (PWRs), boiling water reactors (BWRs) or fast neutron reactors (FNRs).

[0048] As illustrated in Figure 3, a nuclear fuel plate or a nuclear medical target is a nuclear element 2 which comprises for example a cladding 6 having a frame 18 having a central opening 18A in which is housed a core 20 formed of fissile material 4, and two closure plates 22 sandwiching the frame 18 and the fissile material 4. The frame 18 and the two closure plates 22 are generally made of aluminum or an aluminum-based alloy.

[0049] Nuclear fuel plates are used, for example, in nuclear research reactors. Nuclear medical targets are used, for example, for the production of radioisotopes. To do this, they are placed, for example, in a nuclear power reactor or a nuclear research reactor and irradiated to cause fission of the fissile material 4 and the formation of radioisotopes. Such radioisotopes can then be used in medical applications.

[0050] As illustrated in Figure 4, in exemplary embodiments, the nuclear elements 2 comprise nuclear fuel particles 24 formed from fissile material 4 encapsulated in a capsule 8. The fissile material 4 forms a core 26 of the nuclear fuel particle 24.

[0051] Capsule 8 forms a sealed envelope around fissile material 4. Capsule 8 is generally intimately connected to fissile material 4. Capsule 8 is generally not separable from fissile material 4 without damaging both capsule 8 and fissile material 4.

[0052] Nuclear fuel particle 24 is, for example, spherical or spheroidal in shape.

[0053] The capsule 8 is advantageously multi-layered and comprises several superimposed capsule layers 8A, 8B, 8C. Each capsule layer 8A, 8B, 8C is for example made of ceramic material and / or a carbon-based material.

[0054] The capsule layers 8A, 8B, 8C comprise, for example, capsule layers 8A, 8B, 8C made of different materials.

[0055] In exemplary embodiments, the capsule 8 comprises three capsule layers 8A, 8B, 8C.

[0056] In particular, the capsule 8 comprises three capsule layers 8A, 8B, 8C made of two different materials. Two capsule layers 8A, 8C are made of a first material and one capsule layer 8B is made of a second material different from the first material.

[0057] The capsule layer 8B made of the second material is for example an intermediate capsule layer 8B located between the two capsule layers 8A, 8C made of the first material which define an internal capsule layer 8A and an external capsule layer 8C.

[0058] Such nuclear fuel particles are known by the acronym TRISO (from the English "TRI-structural Isotropy"),

[0059] The first material is for example pyrolytic carbon (PyC) and the second material is for example silicon carbide (SiC). The fissile material 4 is for example coated by the capsule 8. The capsule 8 is formed for example by coating the fissile material 4 with the material of each capsule layer of the capsule 8.

[0060] As illustrated in Figure 5, in exemplary embodiments, the nuclear elements 2 comprise a composite material 10 formed from the fissile material 4 dispersed in a matrix 12.

[0061] The matrix 12 is for example a metal matrix. Such a composite material 10 is also known as a “cermet”. The metal matrix 12 is for example made of zirconium or a zirconium-based alloy or steel.

[0062] The matrix 12 for example a ceramic matrix. Such a composite material 10 is also known as "cercer". The ceramic matrix 12 is for example of the fluorine type such as UO2, and contains actinide oxides (Pu, Am, etc.).

[0063] The nuclear elements 2 formed from the composite material 10 are for example in the form of nuclear fuel particles 30, for example of spherical or spheroidal or cylindrical shape, made from the composite material 10, optionally coated with a coating 32.

[0064] The coating 32 is for example a metallic coating made of zirconium or a zirconium-based alloy or steel (for RNRs).

[0065] Coating 32 is optional.

[0066] In examples, matrix 12 is exposed on the outer surface of nuclear element 2. That is, matrix 12 defines the outer surface of nuclear element 2.

[0067] In examples, matrix 12 is made of graphite and defines the outer surface of the nuclear element.

[0068] In examples, the nuclear element is the composite material 10 encapsulated, and in particular coated, in a coating 32 defining an outer shell and made at least in part of silicon carbide (SiC), and including for example silicon carbide (SiCf) fibers and / or a silicon carbide matrix. Such nuclear fuel elements are designated by the acronym FMC for “Fully Ceramic Microencapsulated”.

[0069] Returning to Figure 1, the production method includes a step E1 of cutting nuclear elements 2 into fragments.

[0070] Preferably, the cutting of the nuclear elements 2 into fragments 36 is carried out at a temperature between 78 and 300 K, in particular at room temperature.

[0071] The cutting is carried out for example in a cutting machine 34. The cutting machine 34 is for example a laser cutting machine, a wire saw or a circular disc saw. The cutting is preferably carried out in such a way that the fragments 36 have dimensions of the order of a centimeter and preferably a maximum of 5 cm.

[0072] The cutting is carried out on the nuclear elements 2 each comprising the fissile material 4 contained in a cladding 6, a capsule 8 or a composite material 10. The fragments 36 therefore comprise fissile material 4 and in addition material coming from the cladding 6, the capsule 8 or the matrix 12 of the composite material 10.

[0073] Optionally, the production method includes a uranium content adjustment step E2, including the addition of depleted uranium 38 to the fragments 36.

[0074] Depleted uranium is uranium whose isotopic composition has a low content of uranium 235 (U235), preferably between 0.2% and 0.4% by mass.

[0075] Depleted uranium 38 is a by-product of uranium enrichment or the processing of spent fuel, i.e. fuel that has already been irradiated.

[0076] Depleted uranium 38 is supplied, for example, in the form of depleted uranium powder or depleted uranium metal blocks.

[0077] Preferably, depleted uranium 38 is added to fragments 36 only if the enrichment of fissile material 4 of nuclear elements 2 in uranium 235 (U-235) is equal to or greater than 4.5% by mass.

[0078] The production method includes a step E3 of reducing the fragments 36 into powder.

[0079] Preferably, the reduction of the fragments 36 into powder is carried out at a temperature between 78 and 300 K, in particular at room temperature.

[0080] When depleted uranium is added to fragments 36, the powdering of fragments 36 is carried out before the addition of depleted uranium 38 or after the addition of depleted uranium 38, in which case the powdering is carried out on the mixture of fragments 36 and depleted uranium 38. The powdering of fragments 36 before the addition of depleted uranium 38 is for example possible when the depleted uranium 38 is added in powder form.

[0081] Preferably, the reduction of the fragments 36 into powder is carried out after the addition of depleted uranium 38, from the mixture of fragments 36 and depleted uranium 38. This allows better control of the parameters of the powder obtained from the powder reduction step E3.

[0082] The powder reduction step E3 comprises, for example, a sub-step E31 of melting and atomizing the fragments 36, optionally mixed with depleted uranium 38. The melting is carried out, for example, in a furnace 40, in particular an electric arc furnace, an induction furnace, or by cold crucible melting. The melting leads to the formation of a molten mass 42 which is atomized to form a powdery material. The atomization is carried out, for example, using a rotating electrode atomizer or a rotating disk atomizer or a gas atomizer or a plasma torch atomizer.

[0083] The fusion and atomization sub-step E31 is implemented for example for fissile material 4 made of ductile materials, for example when the fissile material 4 of the starting nuclear elements 2 contains uranium oxide LhOs, uranium metal alloy or uranium oxycarbide.

[0084] The powder reduction step E3 comprises, for example, a sub-step E32 of friction and mixing carried out on the fragments 36, possibly mixed with depleted uranium 38.

[0085] Sub-step E32 of fiction and mixing is carried out for example using a mixer 43.

[0086] The powder reduction step E3 comprises, for example, a grinding sub-step E33 implemented on the material resulting from the sub-step E31 of melting and atomizing the fragments 36 or on the material resulting from the sub-step E32 of friction and mixing, in particular for ductile materials, or on the fragments 36 possibly mixed with depleted uranium 38.

[0087] Crushing is carried out directly on the fragments 36 for example when the fissile material 4 is made from fragile materials, for example UO2.

[0088] The crushing sub-step E33 is carried out for example using a crusher 44, in particular a ring crusher or a ball mill, or a crushing jaw crusher.

[0089] According to examples of implementation, the powder reduction step E3 comprises a sub-step E31 of melting and atomization or a sub-step E32 of friction and mixing, followed by a sub-step E33 of grinding.

[0090] According to exemplary implementations, the powder reduction step E3 comprises only a melting and atomization substep E31 or a fiction and kneading substep E32. In such exemplary implementations, the powder reduction is carried out without a grinding substep E32.

[0091] According to examples of implementation, the powder reduction step E3 comprises a grinding sub-step E32. In this case, the grinding is carried out on the fragments 36, possibly after adding the depleted uranium 38. In such examples of implementation, the powder reduction is carried out without sub-step E31 of melting and atomization or sub-step E32 of friction and mixing. The production method optionally comprises a step E34 of sieving the powder obtained at the end of the powder reduction step E3.

[0092] The sieving is carried out, for example, in a sieve 46. The sieving is carried out, for example, by passing the powder through a sieve of the sieve 46 or successively through several sieves of the sieve 46.

[0093] Sieving step E4 is not necessary if the powder obtained at the end of powder reduction step E3 has the desired characteristics.

[0094] The production method is implemented in such a way that at the end of the powder reduction step E3, optionally followed by the sieving step E4, the particles of powder P obtained have an average diameter equal to or less than 2 mm, preferably equal to or less than 1,000 micrometers, more preferably equal to or less than 200 micrometers.

[0095] The average particle diameter of powder P is measured, for example, by sieve measurement, microscope measurement, laser granulometer measurement or morpho-granulometer measurement.

[0096] Optionally, the production method includes a step E5 of oxidation of the powder P.

[0097] Oxidation is carried out for example by heat treatment of the P powder under a static oxidizing atmosphere or a sweep of oxidizing atmosphere, for example a dry or humid air atmosphere.

[0098] Heat treatment under static air or air sweeping allows the material to be oxidized. It is necessary to ensure that the reaction volume is renewed in order to achieve the desired oxidation.

[0099] Preferably, the oxidation is carried out at a temperature equal to or lower than 2,000°C, in particular at a temperature equal to or lower than 1,300°C, and / or at a temperature equal to or higher than 300°C.

[0100] Typically, complete oxidation of fissile material 4, particularly uranium-bearing fissile material 4, is carried out at a temperature between 500°C and 650°C for treatment times per cycle of six or eight hours.

[0101] The suitably oxidized powder P preferably contains uranium oxide, for example a superstoichiometric form of UCh or a form of UaOs, and metal oxides resulting from the oxidation of matrix metals of nuclear elements 2 comprises a composite material 10 containing the fissile material 4 or metals contained in claddings 6 or capsules 8 of nuclear elements 2 from which the powder P has been manufactured. When the powder P is manufactured from nuclear elements 2 having claddings 4 formed of aluminum or aluminum-based alloy, the powder contains aluminum oxide, in particular AI2O3.

[0102] The presence of uranium oxide in the P powder allows its use in the process of manufacturing nuclear power fuel, i.e. nuclear fuel intended for use in a nuclear reactor for electricity production.

[0103] Preferably, all the uranium contained in the P powder is in the form of uranium oxides (UO2, U4O9, U3O7, LhOs). The other chemical elements contained in the P powder may be in the form of metal oxide.

[0104] The mass content of the uranium element in the powder P is preferably equal to or greater than 10% by mass.

[0105] The production method includes the use of P powder for the production of nuclear fuel, i.e. fissile material for the manufacture of nuclear elements 2 such as nuclear fuel rods for nuclear power generation reactors or nuclear fuel plates for nuclear research reactors.

[0106] The production method includes the use of P powder for the production of:

[0107] - low-enriched uranium (or LEU) for example for light water reactors, in particular for pressurized water reactors (or PWR) or boiling water reactors (or BWR);

[0108] - low-enrichment, high-assay uranium (or HALEU from the English “High Assay Low Enriched Uranium);

[0109] - nuclear fuel for high temperature reactors (or HTR);

[0110] - nuclear fuel for a small modular reactor (or SMR);

[0111] - metal plates enriched in fissile material, for example to 20% or more by weight; and / or

[0112] - nuclear fuel for a uranium fast neutron reactor (or RNR for “Fast Neutron Reactor”) regardless of the primary coolant: lead, in LFR reactors (from the English “Lead-cooled Fast Reactor”);

[0113] Helium, in GFR reactors (from the English “Gas-cooled Fast Reactor”), Sodium, in SFR reactors (from the English “Sodium-cooled Fast Reactor”)

[0114] Lead-bismuth, in LBE-FR reactors (from the English “Lead-Bismuth Eutectic cooled Fast Reactor”)

[0115] Molten salts, in MS-FR reactors (from the English “Molten Salt cooled Fast Reactor”).

[0116] Examples of implementation of the method of producing nuclear fuel from nuclear elements 2 are specified below.

[0117] In a first example, nuclear elements 2 are nuclear fuel plates for a nuclear research reactor or nuclear medical targets.

[0118] The fissile material 4 of such nuclear elements 2 generally comprises uranium in the form of uranium alloy or intermetallic or uranium oxide.

[0119] The production method includes cutting nuclear elements 2 into fragments 36 and optionally adding depleted uranium 38 to the fragments 36, if the uranium 235 content of the fissile material 4 of nuclear elements 2 is greater than 4.5%.

[0120] If the uranium contained in the fissile material 4 of nuclear elements 2 is in the form of uranium metal alloy or uranium intermetallic, the production method comprises the reduction of the fragments 36 to powder by melting and atomization, possibly followed by grinding, or by friction and kneading, possibly followed by grinding, or directly by grinding.

[0121] The production method optionally includes sieving of the powder.

[0122] The production method then includes the oxidation of the P powder and then the use of the P powder for the manufacture of nuclear fuel.

[0123] In a second example, the nuclear elements 2 are nuclear fuel elements for a high-temperature nuclear reactor (HTR). The fissile material 4 of such nuclear elements 2 comprises in particular uranium in the form of uranium oxide and / or uranium oxycarbide and / or uranium carbide U x C y .

[0124] The production method includes cutting nuclear elements 2 into fragments 36 and optionally adding depleted uranium 38 to the fragments 36, if the uranium 235 content of the fissile material 4 of nuclear elements 2 is greater than 4.5%.

[0125] In the case where the uranium contained in the fissile material 4 of the nuclear elements 2 is in the form of uranium oxide UO2 or uranium oxycarbide UCO, the reduction into powder is preferably carried out directly by grinding the fragments 36.

[0126] The production method optionally includes sieving the powder P. The production method then optionally includes oxidation of the powder P, in particular if the uranium contained in the fissile material 4 of the nuclear elements 2 is in the form of uranium oxycarbide UCO or uranium carbides U x C y .

[0127] The production method then includes the use of the powder for the manufacture of nuclear fuel.

[0128] In a third example, nuclear elements 2 are nuclear fuel elements for a modular nuclear reactor (SMR) or a fast nuclear reactor (FNR).

[0129] The fissile material 4 of such nuclear elements 2 generally comprises uranium in the form of uranium oxide or uranium metal alloy.

[0130] The production method includes cutting nuclear elements 2 into fragments 36 and optionally adding depleted uranium 38 to the fragments 36, if the uranium 235 content of the fissile material 4 of nuclear elements 2 is greater than 4.5%.

[0131] The production method includes the reduction of the fragments 36 to powder by melting and atomization or by friction and kneading, possibly followed by grinding, particularly in the case where the uranium contained in the fissile material 4 of the nuclear elements 2 is in the form of uranium metal alloy.

[0132] Alternatively, the production method comprises the reduction to powder by grinding of the fragments 36, in particular in the case where the uranium contained in the fissile material 4 of the nuclear elements 2 is in the form of uranium oxide, for example UO2 or U3O8.

[0133] The production method then includes the oxidation of the P powder if the uranium contained in the fissile material 4 of the discarded nuclear elements 2 is in the form of uranium metal alloy.

[0134] The powder oxidation step P is not necessary if the uranium contained in the fissile material 4 of the discarded nuclear elements 2 is in the form of uranium oxide, for example UO2 or U3O8.

[0135] The production method then includes the use of the powder for the manufacture of nuclear fuel.

[0136] The proposed nuclear fuel production method makes it possible to easily recover nuclear elements 2 comprising fissile material 4 contained in a cladding 6, a capsule 8 or in a composite material 10, by using them to produce a uranium-bearing P powder, preferably containing uranium oxide, allowing the production of nuclear fuel. The production method is easy to implement and makes it possible to obtain a uranium-bearing P powder with a suitable composition and particle size, in particular with an enriched uranium content and an average particle diameter of the P powder which are suitable.

[0137] The production method allows manufacturing scrap and / or non-irradiated or low-irradiated products to be transformed into nuclear fuel.

[0138] The production method of reducing intermediate and final storage of manufacturing scrap and / or non-irradiated or low-irradiated products by producing nuclear fuel. It allows to reduce the overall consumption of uranium to the level of production scrap which is generally higher than 5%.

[0139] The production method limits the production of waste, as the powder produced after implementing the production method can be entirely used for the production of nuclear power fuel.

[0140] The production method also allows uranium to be separated from other chemical elements in the waste treatment process.

[0141] These benefits provide environmental and financial benefits.

[0142] When fissile material alone is available, for example nuclear fuel powder or discarded nuclear fuel pellets, it is possible to reduce this fissile material at room temperature by mechanical shock, in particular by crushing.

[0143] In nuclear elements 2 comprising fissile material 4 contained in a cladding 6, in particular as illustrated in Figures 2 and 3, a capsule 8, in particular as illustrated in Figure 4, or in a composite material 10, in particular as illustrated in Figure 5, the fissile material 4 is intimately bonded to the cladding 6, the capsule 8 or the matrix 10.

[0144] In particular, there is little or no clearance between the fissile material 4, on the one hand, and the cladding 6, the capsule 8 or the matrix 12 of the composite material 10, on the other hand.

[0145] Such nuclear elements 2 exhibit a certain ductility at room temperature, which makes a reduction to a beam by mechanical shock, in particular by crushing, possible.

[0146] To achieve satisfactory powder reduction by grinding of such nuclear elements 2, it would be necessary to lower the temperature significantly before carrying out the grinding.

[0147] Going through a cutting step to obtain fragments, before carrying out a powder reduction step, allows the operations to be carried out at room temperature, in particular without active cooling of the nuclear elements 2 before carrying out the powder reduction.

[0148] This saves time, environmental benefits and financial benefits.

[0149] Preferably, the cutting of nuclear elements and / or the reduction into powder is carried out at a temperature between 78 and 300 K, in particular at room temperature.

[0150] The cutting of the nuclear elements 2 being carried out on the nuclear elements 2 each comprising the fissile material 4 contained in a cladding 6, a capsule 8 or a composite material 10, the fragments 36 comprise fissile material 4 and in addition material coming from the cladding 6, the capsule 8 or the matrix 12 of the composite material 10.

[0151] However, it surprisingly turns out that such powder can be used for the manufacture of nuclear fuel.

Claims

CLAIMS 1. A method of producing a nuclear fuel from nuclear elements each comprising a fissile material contained in a cladding, a capsule or a composite material formed by the fissile material dispersed in a matrix, the processing method comprising: cutting the nuclear elements into fragments; reducing the fragments to a powder to obtain a powder; and using the powder for the manufacture of nuclear fuel.

2. A production method according to claim 1, comprising adding depleted uranium to the fragments prior to powder reduction.

3. A production method according to claim 2, wherein depleted uranium is added to the fragments if the enrichment of the fissile material of the nuclear elements in uranium 235 (U-235) is equal to or greater than 4.5% by mass.

4. A production method according to any preceding claim, wherein the powdering comprises melting the fragments to obtain a molten mass, and atomizing the molten mass or rubbing and kneading the fragments.

5. A production method according to claim 4, wherein the powder reduction comprises grinding the material obtained from the melting and atomization of the fragments or from the friction and kneading of the fragments.

6. A production method according to any preceding claim, wherein the powdering comprises grinding the fragments.

7. A production method according to any preceding claim, comprising sieving the powder.

8. Production method according to any one of the preceding claims, wherein the powder particles have an average diameter equal to or less than 2 mm, preferably equal to or less than 1,000 micrometers, more preferably equal to or less than 200 micrometers.

9. A production method according to any preceding claim, comprising oxidizing the powder by heat treatment under an oxidizing atmosphere.

10. Production method according to claim 9, wherein the oxidation is carried out at a temperature equal to or lower than 2,000°C, preferably at a temperature equal to or lower than 1,300°C and / or at a temperature equal to or higher than 300°C.

11. Production method according to claim 9 or 10, wherein the oxidizing atmosphere is a dry atmosphere or a humid atmosphere, in particular a dry air atmosphere or a humid air atmosphere.

12. Production method according to any one of the preceding claims, wherein the cutting of the nuclear elements and / or the reduction into powder are carried out at a temperature between 78 and 300 K, in particular at room temperature.

13. Production method according to any one of the preceding claims, wherein the powder is used for the production of nuclear fuel for a high temperature reactor (or HTR) or nuclear fuel for a small modular reactor (or SMR) or a metal plate enriched in fissile material, for example to 20% or more by weight or low-enriched and high-dosage uranium (or HALEll) or low-enriched uranium (or LEU) or nuclear fuel for a uranium fast neutron reactor (or RNR for "Fast Neutron Reactor").

14. Production method according to any one of the preceding claims, wherein the fissile material contains uranium and / or plutonium, the uranium being in particular present in the form of uranium oxide, for example UO2, U4O9, U3C>7, U3O8 and / or uranium oxycarbide (UCO) and / or uranium carbide (U x C y ) and / or uranium metal alloy and / or uranium intermetallic, for example U-Si, in particular U3Si2, U-AI, U-Mo, U-Zr, U-Nb.

15. A production method according to any preceding claim, wherein the nuclear elements are non-irradiated or low-irradiated and / or scrap nuclear elements.

16. Production method according to any one of the preceding claims, in which the nuclear elements used for implementing the production method comprise nuclear fuel elements, for example for a high temperature reactor (or HTR) and / or for a small modular reactor (or SMR) and / or for a uranium fast neutron reactor (or RNR for "Fast Neutron Reactor") and / or for a pressurized water reactor (or PWR) and / or for a boiling water reactor (or BWR), and / or nuclear fuel plates and / or nuclear medical targets and / or encapsulated nuclear fuel particles, for example of the TRISO (Tristructural-isotropic) type and / or nuclear fuel elements comprising a composite material containing fissile material dispersed in a matrix, for example of the cermet (ceramic - metal) or cercer (ceramic-ceramic) type, and / or MOX (Mixed-Oxides) type nuclear fuel elements.

17. A production method according to any preceding claim, wherein the produced nuclear fuel is a power nuclear fuel intended for use in a power generation nuclear reactor, and / or the nuclear elements comprise research reactor nuclear fuel elements, radioisotope production targets and / or power nuclear fuel elements.

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