METHOD AND SYSTEM FOR MEASURING THE RELATIVE CONCENTRATIONS OF MATERIALS IN A MIXTURE BY MEASURING THE DYNAMIC MAGNETIC SUSCEPTIBILITY

Description

technical field

[0001] The present invention relates to the field of measuring material concentrations within a mixture, in particular a binary mixture.

[0002] The invention aims primarily to optimize this type of measurement, by offering a compact, reliable, fast, non-destructive solution that allows integration into a constraining environment, particularly in terms of available space, and / or into a continuous production line.

[0003] Although described with reference to the measurement of the relative content of plutonium (Pu) and uranium (U), and associated oxides in the form of powders or MOX fuel pellets, the invention applies to the measurement of relative mass percentages of solid materials each having a given magnetic susceptibility of a binary mixture, or more generally to any measurement of any mixture of materials, even non-binary, each having a given magnetic susceptibility.

[0004] As another example, the invention applies to the case of a solid material and / or a mixture containing impurities (of the ferromagnetic or metallic type) whose susceptibility, even in low concentration in the mixture, presents a susceptibility signature that is significantly greater (at least an order of magnitude) than the susceptibility of the other constituents. Previous technique

[0005] The manufacture of new MOX (Mixed Oxide Fuel) nuclear fuel pellets consists of a process comprising the successive steps of mixing a powder of UO₂ dioxide and PuO₂, pressing, and sintering. The mixture may optionally be supplemented with grog (waste from pellet manufacturing).

[0006] The MOX fuel pellets obtained can, for example, be irradiated in light water reactors (or RELs) or fast neutron reactors (or FNRs).

[0007] The reproducibility of the plutonium or uranium composition of the pellets is one of the major constraints of manufacturing. Therefore, it is important to know the composition systematically for each production batch.

[0008] More specifically, it is necessary to know the relative mass concentrations, or in other words, the relative mass percentages of Pu and U oxides and associated oxides, in MOX pellets from a production line. This information must be available either in an analytical laboratory or in a compact device that can be installed in a nuclear glove box or on a continuous production line.

[0009] The solutions currently implemented to measure relative concentrations are methods requiring advanced chemical analyses of the pellets.

[0010] Although precise and selective, chemical analyses are destructive, lengthy, typically taking several hours / days to obtain results, are not really applicable systematically, and require sampling from a production line, which limits statistics on a production batch.

[0011] Spectroscopic solutions have also been proposed. They present the same drawbacks as chemical analyses.

[0012] Another measurement solution using magnetometry (VSM for Vibrating Sample Magnetometry) has also been proposed. It consists of measuring the magnetic moment of the pellet sample under a strong, variable, static magnetic field, typically exceeding 1 tesla. This standard laboratory technique requires the use of a large electromagnet or superconducting magnet. Consequently, the near impossibility of inserting such a magnet into a glove box or on a nuclear production line makes VSM a prohibitively expensive solution.

[0013] Applications JP S60 114766 A, US 4 134 064 A and FR 2 433 181 A1 each describe a method and apparatus for magnetically determining the Gd 2 O 3 content in UO 2 fuel pellets.

[0014] There is therefore a need to improve solutions for measuring mass concentrations of materials within a mixture, particularly a binary mixture, especially in terms of size in order to be able to implement it in a constraining environment, such as a nuclear environment, and / or on a continuous production line of objects, such as MOX fuel pellets.

[0015] The aim of the invention is to meet at least part of this need. Description of the invention

[0016] To this end, the invention relates, according to independent claim 1, to a method for measuring the relative concentrations of materials in a mixture comprising the following steps: a / provision of a transmitting coil and at least one receiving coil; b / provision of a mixture comprising n materials of different magnetic susceptibilities (χ1, χ2 .. χn); c / insertion of the mixture into the receiving coil; d / supplying the transmitting coil with an electric voltage generator at at least one non-zero excitation frequency so as to generate an excitation magnetic field; e / measurement of the signal of the electric voltage induced in at least one receiving coil; f / determination of the concentrations of the n materials from the comparison of the overall susceptibility of the mixture obtained by the voltage measurement according to step e / with that of a reference mixture whose relative concentrations of said n materials are known, the process being characterized in that step d / comprises the application of the given electric voltage by varying the at least one excitation frequency.

[0017] According to an advantageous embodiment, in the case where n=2, the process includes in step f) from the mass of the mixture m(mel)=m1+m2, the determination of the susceptibility of the mixture given by the relation: χmel = m 1 χ 1 m 1 + m 2 + m 2 χ 2 m 1 + m 2 and knowing the different magnetic susceptibilities (χ1, χ2), the determination of the respective mass concentrations of the materials is made using the following relationships: m 1 = m mel χmel − χ 2 χ 1 − χ 2 And m 2 = m mel χmel − χ 1 χ 2 − χ 1 .

[0018] According to an advantageous embodiment, the method further comprises, in step e, either an in-phase measurement of the signal of the electrical voltage induced in at least one receiving coil and a quadrature phase measurement so as to obtain the magnitude of the signal. Advantageously, the receiving coil is tuned so that its resonant frequency is substantially equal to at least one excitation frequency.

[0019] The mixture provided according to step b / can be a binary mixture of materials of two different magnetic susceptibilities (χ1, χ2).

[0020] According to an advantageous embodiment, the process includes after step b), a step b1 / comprising weighing the mixture so as to obtain at step f) a relative mass concentration of said mixture.

[0021] The mixture provided according to step b / may be a mixture comprising more than two materials, one of which has a susceptibility much greater than that of the other materials. The other materials may be ferromagnetic or metallic impurities... Thus, the invention makes it possible to measure the susceptibility of a constituent even at a low concentration relative to the other constituents of the mixture, provided that this constituent has a susceptibility much greater than that of the other materials, for example, by a factor of 100.

[0022] In this case, the susceptibility of the mixture is given by: χmel = m 1 χ 1 ∑ m 1 + m 2 + ⋯ mn + m 2 χ 2 ∑ m 1 + m 2 + ⋯ mn + ⋯ . . + mnχn ∑ m 1 + m 2 + ⋯ mn with the respective masses and susceptibilities of n materials in the mixture, simplifies if one of the materials (here of mass m1 and susceptibility χ1) has a susceptibility much greater than that of the others to: χmel = m 1 χ 1 ∑ m 1 + m 2 + ⋯ mn

[0023] According to a preferred application, the mixture provided according to step b / can be in the form of a solid compound. For the purposes of this invention, "solid compound" means a compact pellet, a powder, or any other solid structure.

[0024] According to an advantageous embodiment, step d / includes applying a given voltage while varying the excitation frequency.

[0025] Preferably, the excitation frequency is greater than 10 kHz, preferably greater than 100 kHz, preferably between 100 and 250 kHz.

[0026] According to a first configuration, step a / includes the provision of a single receiving coil, the process further including, before step c / , the execution of steps e / and f / so as to obtain the basic signal representative of the single empty receiving coil.

[0027] Alternatively, step a / includes the provision of two receiving reels, preferably identical, the process comprising before step f / , the repetition of steps c / to d / with each of the two receiving coils, and an additional step e1 / of subtraction between the two measurements of the signals induced by the two coils.

[0028] According to this alternative, the method advantageously involves electrically connecting the two receiving coils, preferably with reversed windings, in series and tuning their respective receiving frequencies. This improves the output signal-to-noise ratio and increases the output signal, with the measurement taken around the resonant frequency of the receiving coils.

[0029] Preferably, the e / step is performed for each excitation frequency, with synchronous detection.

[0030] Preferably, step e / can consist of several measurements, each at a reception frequency around the resonant frequency of the detection coil(s). Advantageously, step d / is carried out so as to generate an excitation magnetic field with a value of less than 50 mT, preferably between 1 and 20 mT. This low magnetic field has the advantage of not requiring a large coil to generate it, which makes the acquisition part of the system compact and therefore compatible with a limited footprint.

[0031] According to an advantageous embodiment, where the mixture comprises a ferromagnetic material, comprising before step c / , an additional step b2 / consisting of exposing the mixture to a constant magnetic field.

[0032] The invention also relates to a system for measuring the relative concentrations of materials in a mixture according to independent claim 10, comprising: an electric voltage generator at at least one excitation frequency; a transmitting coil connected to the generator; at least one receiving coil whose shape is adapted to receive a mixture comprising at least two materials of different magnetic susceptibilities and whose receiving frequency is tuned to at least one excitation frequency; voltage measurement means connected to the receiving coil(s).

[0033] Preferably, the generator is a variable frequency low-frequency generator (LFG). Preferably, the generator is configured so that the excitation frequency is greater than 10 kHz, preferably greater than 100 kHz, and preferably between 100 and 250 kHz.

[0034] Typically, for a mixture of oxides with magnetic susceptibility on the order of tens to tens of millimu.mol -1, the frequency range can be between 100 and 250 kHz.

[0035] It is specified that the frequency is chosen independently of the susceptibility values, but according to the coil design. Consequently, the system according to the invention does not need to be adjusted to the type of material, but rather to the dimensions of the sample to be analyzed.

[0036] According to an alternative configuration, the system includes two receiving coils in electrical series and whose respective receiving frequencies are tuned.

[0037] In one arrangement variant, the receiving coil(s) is / are arranged inside the excitation coil. The acquisition part of the system (transmitting and receiving coils and their associated electrical connections) is thus compact.

[0038] According to an advantageous embodiment, the system further comprises: an electromagnetic protection box; a first connector mounted in the box, connected to the transmitting coil by a first power supply wire inside the box, the first connector being intended to be connected remotely to the generator by a first power supply cable; a second connector mounted in the box, connected to at least one receiving coil by a second power supply wire inside the box; the second connector being intended to be connected remotely to the measuring means by a second power supply cable.With such an arrangement, the integration of the system into a demanding environment, particularly a nuclear one, such as a glove box, is facilitated, especially thanks to the limitation of interface cables between the housing which contains the measurement acquisition part (coils) and the measurement electronics, the latter as well as the power supply generator not having to be arranged in the nuclear environment.

[0039] In addition, this makes the measurement acquisition part (coils) immune to radiation since, thanks to the interface cables with the box, the measurement electronics as well as the power generator can be positioned remotely outside the environment in which the radiation is emitted.

[0040] According to an advantageous embodiment, the measurement means include a synchronous detection amplifier.

[0041] In an advantageous configuration, the receiving coil(s) are arranged coaxially inside the transmitting coil, defining within them a passage for a portion of a conveyor designed to move the mixture in the form of a solid product, such as a pellet. The conveyor can be manual or motorized.

[0042] Preferably, the system comprises two receiving coils, preferably identical, arranged at a distance one behind the other, and arranged relative to the transmitting coil so as to perform three successive measurements when the solid product moved by the conveyor is respectively outside the receiving coils, in one of them and then in the other of them.

[0043] Advantageously, the portion of the conveyor passing through the receiving reels is a belt or track from a motorized conveyor. This allows for easy integration into a production line, particularly one producing solid objects with a binary mixture of materials with different magnetic susceptibilities. Such lines could be used for producing MOX nuclear fuel pellets.

[0044] According to independent claim 15, the invention further relates to the application of the method or system just described for measuring the relative mass concentrations of plutonium (Pu) and uranium (U), and associated oxides, in MOX-type nuclear fuel pellets. The invention also applies to the nuclear fuel cycle of UOX pellets (for impurities). It is also applicable to the detection of metallic impurities in MOX.

[0045] Thus, the invention essentially consists of measuring the relative concentrations, either in %, or by mass, of any composite mixture of two or more paramagnetic materials, by weighing and measuring the overall magnetic susceptibility ( χmel ) of the mixture by means of a transmitting coil system (magnetic excitation) and receiving and a comparison with a calibrated mixture of the same materials whose weight and mass concentrations are known.

[0046] According to the invention, the measured quantity is therefore the magnetic susceptibility of the mixture, with a measurement at a fixed or variable frequency and with a magnetic field of generally fixed, low amplitude, typically a few mT. This weak field is generated by a simple and compact coil system.

[0047] An additional measurement of the weight of the mixture can be carried out.

[0048] Thus, if the susceptibilities of the two materials in a binary mixture are respectively χ 1 and χ 2, and the mass of the mixture m ( mel ) = m1 + m 2, then the susceptibility of the mixture is given by the relation: χmel = m 1 χ 1 m 1 + m 2 + m 2 χ 2 m 1 + m 2

[0049] Which allows, knowing χ 1 and χ 2. From tables or measurements of pure compounds, deduce: m 1 = m mel χmel − χ 2 χ 1 − χ 2

[0050] And m 2 = m mel χmel − χ 1 χ 2 − χ 1

[0051] Thus, from these non-invasive measurements, and by comparison with a known reference, the composition of the mixture can be determined.

[0052] For the known reference, the weight and a reference signal are established beforehand.

[0053] The reference signal is either known from tables, literature, etc., or obtained through a prior calibration measurement using a measurement system according to the invention. Thus, typically, for MOX pellets, a calibration with pure PuO2 and UO2 pellets can be performed beforehand to obtain the reference signal.

[0054] The inventors cleverly thought of using the difference in magnetic susceptibility value of paramagnetic materials in a mixture to evaluate their relative mass percentages by a dynamic susceptibility measurement.

[0055] The dynamic susceptibility measure, often called AC susceptibility, is not very developed but has already been described in a few articles.

[0056] Thus, publication [1] proposes an AC susceptibility measurement system covering a wide temperature range. Article [2] proposes a two-coil susceptometer operating between 100 Hz and 100 kHz.

[0057] A dynamic AC susceptibility measurement system is marketed by the company Quantum design.

[0058] These different systems operate over a wide frequency band and allow a susceptibility value to be obtained in a typical time of one minute for a given frequency.

[0059] In general, the measurement targeted by known systems concerns an evolution of susceptibility as a function of an external parameter such as temperature or pressure, in order to trace back to information such as phase transitions of a given material.

[0060] But surprisingly, no one has thought of using the AC dynamic susceptibility measurement to measure a mass concentration ratio of a mixture of two or more materials with different magnetic susceptibilities.

[0061] According to a preferred application, the measurement is implemented for the knowledge of relative mass concentrations in MOX fuel pellets in which the two oxides of interest have different magnetic susceptibility values, the χ value of UO 2 being equal to 3.0.10 -3< emu.mol -1< while that of PuO 2 is equal to 0.4.10 -3< emu.mol -1< , according to [3].

[0062] Ultimately, the invention offers numerous advantages, including: a measurement that is much faster than chemical or spectroscopic measurement solutions according to the state of the art. Typically, with an AC susceptibility measurement according to the invention, the measurement time per MOX fuel pellet can be on the order of a few seconds; the possibility of measurement not by taking a few samples from a production batch as according to the state of the art but systematically for each mixture produced, in particular for each nuclear fuel pellet in production; the dimensions of the equipment and the compactness of its measurement acquisition part (housing and coils housed inside) make a measurement system according to the invention more easily compatible with a nuclear environment compared to state-of-the-art solutions, in particular magnetometry measurement systems (VSM);a measurement system that can be easily integrated into a continuous production line for mixed-material products, for example in a pellet manufacturing / transport line; the ability to use the process and measurement system on any composite mixture of at least two distinct paramagnetic or ferromagnetic materials; the ability to determine the homogeneity of a mixture from the analysis of the shape of the measurement signal, unlike state-of-the-art solutions.

[0063] Other advantages and features of the invention will become clearer upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0064] [ Fig 1 ] there figure 1is a schematic perspective view of a system for measuring the relative mass concentrations of two materials in a binary mixture in the form of a solid pellet, according to the invention. Fig 2 ] there figure 2 is a photographic view of an example of the system according to the invention with a portion of the connectivity implemented according to the invention. Fig 3A ] there figure 3A illustrates in the form of a curve the phase measurement for different paramagnetic components in a system according to the invention whose receiving coil frequency is tuned to the excitation frequency. Fig 3B ] there figure 3B illustrates in the form of a curve the quadrature measurement for the different paramagnetic components as according to the figure 3A . [ Fig 4 ] there figure 4 illustrates in the form of a curve an example of measurements obtained according to the invention, of a sample with variable concentration of a binary mixture in the form of a solid pellet. Fig 5 ] there figure 5 is a perspective view of a measurement system according to an embodiment of the invention incorporating part of a motorized conveying system. Fig 6 ] there figure 6 is a cross-sectional view of the system according to the figure 5 . [ Fig 7A ] there figure 7A is a schematic view illustrating a preliminary step of magnetizing a ferromagnetic product according to a variant of the measurement method according to the invention. Fig 7B ] there figure 7B is a schematic view illustrating the step of inserting the magnetized product into a receiving coil according to the figure 7A in order to implement the measurement method according to the invention. Fig 8 ] there figure 8illustrates in graphical form measurements of maximum values ​​of the modulus of magnetic susceptibility, for samples containing carbon nanotubes in a non-ferromagnetic matrix, the measurements being obtained by the method according to the present invention, as a function of the magnetic moments measured by VSM of said samples. Detailed description

[0065] Throughout this application, the terms "lower", "upper", "bottom", "top", "below" and "above" are to be understood by reference to cases.

[0066] We represented in figures 1 and 2 , an example of device 1 forming the acquisition part of a system for the measurement by magnetic susceptibility of mass concentrations of Pu and U oxides in MOX fuel pellets.

[0067] This device 1 comprises, firstly, a housing 10, advantageously equipped with electromagnetic shielding, in which are housed respectively a transmitting (excitation) coil 2 and two receiving coils 3.1, 3.2, advantageously identical and connected in electrical series. The excitation coil 2 and the receiving coils 3.1, 3.2 are arranged in the same plane. They are advantageously wound in reverse so that the transmitted field produces the weakest possible signal in the receiving coils.

[0068] In the illustrated example, the transmitting coil 2 is in the form of a frame that houses the receiving coils 3.1 and 3.2, each of which is a hollow cylinder. The diameter and height of this cylinder are typically chosen to accommodate a MOX fuel pellet P. Overall, the lateral dimensions of a housing 10 can typically be on the order of 5 to 10 times the diameter of a pellet P. Thus, the housing 10 can be lightweight and very compact, allowing it to be easily transported and positioned in a very restrictive environment, such as a glove compartment.

[0069] The dimensions of the excitation coil 2 can be reduced because the desired excitation magnetic field can be on the order of a few mT, typically between 1 and 20mT.

[0070] A first connector 4 is mounted in the housing 10 and is connected to the transmitting coil 2 by a first power supply wire 40 inside the housing. This first connector 4 is remotely connected to a low-frequency generator 6 by a first power supply cable 41.

[0071] A second connector 5 is mounted in the housing 10 and is connected to the receiving coils 3.1 and 3.2 by a second power supply wire 50 inside the housing. This second connector 5 is remotely connected to a synchronous detection amplifier 7 by a second power supply cable 51.

[0072] Thus, the compact unit 10 houses the entire measurement acquisition section of the system (coils 2, 3.1, 3.2) and the associated connectors, while the low-frequency generator 6 and the amplifier 7 are located away from the environment in which the unit is installed. Therefore, even if the environment is exposed to radiation, the signal generation and signal processing sections are immune, i.e., protected from radiation.

[0073] We now describe a method for measuring relative mass concentrations of materials in a binary mixture in the form of a solid pellet implemented according to the invention in particular by the system which has just been described.

[0074] Step a: We set up a device 1 according to the figures 1 and 2 by making the electrical connections respectively to the low frequency generator 6 and to a synchronous detection amplifier.

[0075] The two receiving coils 3.1, 3.2 are connected in parallel with a capacitor whose value is chosen to ensure the resonance of this LC circuit is between 50 kHz and 200 kHz. For small pellets, a frequency up to a few MHz can be chosen.

[0076] Step b / : a sample of a solid pellet P of MOX fuel is provided, and we seek to evaluate the respective mass concentrations of PuOx and UOx.

[0077] Step b1 / : We weigh the pellet P. This step can usually be done using a conventional balance.

[0078] Step c: Insert the P pellet into the first receiving coil 3.1 and then into the second receiving coil 3.2, as illustrated in the figure 1 .

[0079] Step d: The transmitting coil 2 is powered by the low-frequency generator 6, at a variable, non-zero excitation frequency so as to generate an excitation magnetic field in the coil 2. The power supply can be interrupted when the pellet P passes from the first to the second receiving coil.

[0080] The field excitation of the excitation coil 2 is therefore done by applying a given voltage, typically a few volts, by varying the frequency, typically up to a few 100kHz or a few MHz.

[0081] Step e / : we measure in phase and in quadrature the signal of the electrical voltage induced in the receiving coil 3.1, then in that of the receiving coil 3.2 for each excitation frequency.

[0082] The voltages measured across these two coils 3.1, 3.2 are advantageously subtracted and then amplified by the synchronous detection amplifier 7.

[0083] In the absence of the P pad, the signal obtained at the output of the two coils 3.1, 3.2 under application of the excitation field is zero or balanced to be close to zero. Its value can be noted as equal to V0.

[0084] Taking the measurement by difference between the signals from the two receiving coils eliminates the offset that would otherwise need to be added to the V0 value. This eliminates the need for a prior no-load measurement.

[0085] In the presence of the P pad in the first receiving coil 3.1, the received signal has a value V1=V0+dV, and when the P pad is in the second coil 3.2, the value of the signal V2=V0-dV.

[0086] Thus, the difference, i.e. V1-V2=2dV, where dV is proportional to the complex magnetic susceptibility of the pellet P.

[0087] At each measured frequency point, the output signal measured by amplifier 7 allows access to the signal in phase and in quadrature with respect to the excitation signal, at the measured frequency.

[0088] Typically, measurements between 1 and 20 frequency points around the detection resonance frequency can be performed.

[0089] The phase and quadrature signals provide information on the complex magnetic susceptibility of the pellet (real component X and imaginary component Y; χ = X + iY ) at the measurement frequency. When the method of the invention measures only the in-phase signal, the measurement obtained is proportional to the real part of the magnetic susceptibility, and when the method of the invention measures the in-phase signal and the quadrature signal, the measurement obtained allows access to the real and imaginary components and therefore to the magnitude.

[0090] An example of phase and quadrature measurements for different paramagnetic materials in a system 1 according to the invention, the reception frequency of which has been tuned around 180 kHz, is shown in Figures 1 and 2. Figures 3A and 3B .

[0091] The different materials tested are a dysprosium oxide, with the formula Dy 2 O 3, a neodymium oxide, with the formula Nd 2 O 3 and a yttrium oxide with the formula Y 2 O 3. Step f: /

[0092] From a frequency sweep over the considered excitation frequency range, we can extract from these measurements over said frequency range, the modulus M and the integral I according to the following equations. M = X 2 + Y 2 I = ∑ f 0 f n M n

[0093] These modulus and integral values ​​then allow a quantitative comparison of the sample (pellet) considered with respect to a reference sample whose relative mass concentrations of the two materials are known.

[0094] By comparing the masses between the measured sample and the reference sample, we can finally determine the mass concentrations of the two materials in the sample.

[0095] Typically, for a MOX P pellet, the comparison is made with respect to a pure PuO2 and UO2 pellet of mass.

[0096] There figure 4 illustrates measurements of samples at varying concentrations of a mixture of two materials with different magnetic susceptibilities, obtained according to the method just described. It is specified that on this figure 4 , the abscissa represents the concentration in % and the ordinate represents the integral of the signal (arbitrary units), detected by amplifier 7.

[0097] THE figures 5 to 6 show an alternative device to the one shown in figures 1 and 2 .

[0098] In this device, the receiving coils 3.1, 3.2 are arranged coaxially inside the transmitting coil 2, defining within them a passage 30 of a part of a belt conveyor 8 80, adapted to move the mixture in the form of a solid product, such as a pellet.

[0099] More specifically, the conveyor 8 includes a frame 81 supporting the electromagnetic shielding housing 10 formed by an outer cylinder and an inner cylinder 82 separated by spacers 83 and whose interior defines the passage 30 of the pellets to be measured.

[0100] Between the spacers 83 and the outer cylinder 10 is arranged the excitation coil 2 in the form of a coaxial cylinder.

[0101] Between the spacers 83 and the inner cylinder 82 are arranged at a distance from each other the two receiving coils 3.1, 3.2, each in the form of a coaxial cylinder.

[0102] This device allows automated transport of the samples to be measured from the first receiving reel 3.1 to the other 3.2.

[0103] The sample is transported by a manual or motorized system along the excitation cylinder 2 from the first to the second reel by movement of the conveyor belt or tape 80.

[0104] The transport of the sample allows three measurement positions to be reached, namely respectively when empty when the sample is not in any of the receiving reels, when the sample is in the first receiving reel 3.1, and then when it is in the second receiving reel 3.2.

[0105] For measurement, the sample preferably passes at a constant speed within each of the two receiving reels 3.1, 3.2. This has the advantage of not significantly reducing, or even at all reducing, the rate of a production line.

[0106] To increase the measurement speed, the measurement can be performed on a discrete number of frequencies, typically three measurements taken simultaneously. In the case of an even faster measurement, only one frequency is used and the signal is measured in only one of the receiving coils 3.1, 3.2.

[0107] Indeed, it is simple to send a single frequency and measure the sample's response at that frequency using synchronous detection. It is also possible to send three frequencies simultaneously, for example with an arbitrary frequency generator, and measure the response using three synchronous modulators at those three frequencies. This allows, through adjustment, the reconstruction of the system's frequency response in a single measurement instead of taking measurements at different frequencies one after the other.

[0108] It goes without saying that we can increase or decrease the number of simultaneous frequencies, for example to 2 or 4 or more.

[0109] When the sample is centered on the cylinder of a receiving coil, i.e. its median plane is substantially coincident with that of the coil, then the received signal is maximal and depends on the concentration ratio of the materials in the sample.

[0110] If the passage of samples is continuous, a repetitive measurement can be made to determine the signal when the sample is at the center of the receiving coil, which corresponds to the maximum of the received signal.

[0111] From an independent mass measurement carried out in addition to the measurement of the maximum signal obtained, the ratio of mass concentrations of the materials in the sample is determined as described previously.

[0112] The process and system just described can be implemented for a ferromagnetic sample.

[0113] In this case, an additional step b2 / is carried out, consisting of exposing the sample to a constant magnetic field.

[0114] This is shown at the figure 7A where the sample E is pre-magnetized by means of a permanent magnet and then inserted into the first receiving coil 3.1 as per the figure 1 .

[0115] Then we carry out the aforementioned measurement steps d / to e / .

[0116] The inventors performed M-modulus measurements of complex magnetic susceptibilities in different samples, each containing varying amounts of carbon nanotubes, known for their ferromagnetic signature of the iron used in their synthesis, within a non-ferromagnetic matrix. They compared the results obtained with magnetic moments measured by VSM.

[0117] The comparative results are illustrated in the figure 8 , wherein the maximum values ​​of the measured moduli (on the ordinate) by the method according to the present invention are a function of the magnetic moments measured by VSM (on the abscissa), the maximum values ​​of the moduli (M max / norm) and the magnetic moments (Moment norm.) being normalized by the respective masses of the samples. In this figure 8 , squares represent samples with a carbon nanotube concentration close to 0.5% by mass, diamonds represent samples with a carbon nanotube concentration close to 1.0% by mass, triangles represent samples with a carbon nanotube concentration close to 2.0% by mass.

[0118] As can be seen at the figure 8There is indeed a linear relationship between the maximum values ​​of the moduli and the magnetic moments. Thus, the measurement of the modulus, or the integral, of the magnetic susceptibility is indeed proportional to the amount of ferromagnetic material.

[0119] The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0120] Other variations and improvements can be considered without going outside the scope of the invention.

[0121] Several other coil configurations and arrangements than those shown in the various figures, particularly in the case of less restrictive environments in terms of size and / or because they are non-nuclear.

[0122] The method according to the invention operates with a single receiving coil. In this case, a preliminary no-load measurement can be performed to obtain the basic signal corresponding to the offset minus the value V0.

[0123] Instead of using a synchronous detection amplifier, one could consider measuring with sufficient accuracy the signal from each of the receiving coils and differentiating between their signals solely digitally. List of cited references:

[0124] [1]: Review of Scientific Instruments 60, 113 (1989); https: / / doi.org / 10.1063 / 1.1140593 [2]: Review of Scientific Instruments 84, 125105 (2013); https: / / doi.org / 10.1063 / 1.4842255. [3]:“MAGNETIC SUSCEPTIBILITY OF THE ELEMENTS AND INORGANIC COMPOUNDS »; http: / / www.fizika.si / magnetism / MagSusceptibilities.pdf.

Claims

1. Method for measuring relative concentrations of materials of a mixture, comprising the following steps: a / providing an emission coil (2) and at least one reception coil (3.1, 3.2); b / providing a mixture (P, E) comprising n materials with different magnetic susceptibilities (χ1, χ2, ..χn); c / introducing the mixture into the at least one reception coil; d / using an electric voltage generator to supply the emission coil with at least one non-zero excitation frequency so as to generate an excitation magnetic field, e / measuring the signal of the electric voltage induced in the at least one reception coil; f / determining the relative concentrations of the n materials based on a comparison between the overall susceptibility of the mixture obtained by the voltage measurement according to step e / and that of a reference mixture for which the relative concentrations of said n materials are known, the method being characterized in that step d / comprises applying the given electric voltage by varying the at least one excitation frequency.

2. Measurement method according to Claim 1, with the mixture provided according to step b / being a binary mixture of materials with two different magnetic susceptibilities (χ1, χ2) or a mixture comprising more than two materials, with one of the materials having a much higher susceptibility, by a factor of 100, than that of the other materials.

3. Measurement method according to either one of the preceding claims, comprising, after step b), a step b1 / comprising weighing the mixture so as to obtain, in step f), a relative mass concentration of said mixture, with the mixture provided according to step b / preferably being a binary mixture of materials with two different magnetic susceptibilities (χ1, χ2), the method comprising, in step f), based on the mass of the mixture m(mix) = m1 + m2 obtained according to step b1 / , determining the susceptibility of the mixture provided using the relationship: χmix = m 1 χ 1 m 1 + m 2 + m 2 χ 2 m 1 + m 2 and, knowing the different magnetic susceptibilities (χ1, χ2), determining the respective mass concentrations of the materials using the following relationships: m 1 = m mix χmix − χ 2 χ 1 − χ 2 and m 2 = m mix χmix − χ 1 χ 2 − χ 1 .

4. Measurement method according to any one of the preceding claims, further comprising, in step e / , an in-phase measurement of the signal of the electric voltage induced in the at least one reception coil and / or a phase quadrature measurement so as to obtain the modulus of the signal.

5. Measurement method according to one of the preceding claims, with step a / comprising providing a single reception coil, the method further comprising, before step c / , carrying out steps d / and e / so as to obtain a basic signal representing the empty single reception coil, or with step a / comprising providing two, preferably identical, reception coils, the method comprising, before step f / , repeating steps c / to e / with each of the two reception coils, and an additional step e1 / of subtracting, between the two measurements, the signals induced by the two coils, the method preferably comprising electrically connecting the two reception coils in series and tuning their respective reception frequencies.

6. Method according to one of the preceding claims, with step e / being carried out for each excitation frequency, with synchronous detection.

7. Measurement method according to one of the preceding claims, with step e / being made up of several measurements, each at a reception frequency around the resonant frequency of the one or more detection coils.

8. Measurement method according to one of the preceding claims, with step d / being carried out so as to generate an excitation magnetic field with a value of less than 50 mT, preferably ranging between 1 and 20 mT.

9. Measurement method according to one of the preceding claims, when the mixture comprises a ferromagnetic material, comprising, before step c / , an additional step b2 / involving exposing the mixture to a constant magnetic field.

10. System (1) for measuring relative concentrations of n materials of a mixture, comprising: - an electric voltage generator (6) for generating at least one frequency, called excitation frequency, the generator being a variable-frequency low-frequency generator (LFG); - an emission coil (2) connected to the generator; - at least one reception coil (3.1, 3.2), the shape of which is adapted to receive a mixture comprising n materials with different magnetic susceptibilities (χ1, χ2, ..χn) and the reception frequency of which is tuned to the at least one excitation frequency; voltage measurement means (7) connected to the one or more reception coils, with the measurement means preferably comprising a synchronous detection amplifier; the system (1) being configured to determine relative concentrations of the n materials based on a comparison between the overall susceptibility of the mixture obtained by the voltage measurement (7) and that of a reference mixture for which the relative concentrations of said n materials are known; the system (1) being characterized in that the generator (6) is configured to apply the given voltage by varying the at least one excitation frequency.

11. System (1) according to Claim 10, comprising two reception coils (3.1, 3.2) electrically connected in series, the respective reception frequencies of which are tuned.

12. System (1) according to either of Claims 10 and 11, with the one or more reception coils (3.1, 3.2) being arranged inside the excitation coil (2).

13. System (1) according to one of Claims 10 to 12, further comprising: - a housing (10), preferably for electromagnetic protection; - a first connector (4) mounted in the housing, connected to the emission coil by a first power supply wire (40) inside the housing; with the first connector being intended to be remotely connected to the generator by a first power supply cable (41); - a second connector (5) mounted in the housing, connected to at least one reception coil by a second power supply wire (50) inside the housing; with the second connector being intended to be remotely connected to the measurement means by a second power supply cable (51).

14. System (1) according to one of Claims 10 to 13, with the one or more reception coils (3.1, 3.2) being coaxially arranged inside the emission coil (2) by defining a passage therein for a portion of a conveyor (8) adapted to move the mixture in the form of a solid product, such as a pellet, the system preferably comprising the two, preferably identical, reception coils (3.1, 3.2) remotely arranged one behind the other, and arranged relative to the emission coil (2) so as to carry out three successive measurements when the solid product moved by the conveyor (8) is respectively outside the reception coils, in one of the reception coils and then in the other one of the reception coils, with the portion of the conveyor passing through the reception coils preferably being a band (80) or a belt of a motorized conveyor.

15. Application of the method according to one of Claims 1 to 9 for measuring relative mass concentrations of plutonium (Pu) and uranium (U), and associated oxides in MOX-type nuclear fuel pellets.