Photonic spectrometry device and method, method for calibrating the device, and use of the device

A photonic spectrometry device is provided. The photonic spectrometry device comprises several identical spectrometers each spectrometer comprising a radiation sensor and being capable of providing a measurement spectrum corresponding to the measurements of the sensor during a time interval, the spectrometers being capable of performing measurements simultaneously on one same radiation-emitting product and of providing measurement spectra for one same time interval, and a processor capable of determining a net spectrum from each of the measurement spectra provided by the spectrometers for one same time interval, and of determining a global spectrum resulting from the summation of the net spectra determined for one same time interval.

The present invention relates to the field of photon spectrometry.

BACKGROUND

The production or recycling of nuclear fuel leads to the production of by-products, waste or effluent. It must be verified that the content of radioactive materials in these by-products, waste and effluent is acceptable with regard to regulatory thresholds.

For example, uranium oxide (UxOy) and in particular uranium dioxide (UO2) is used as nuclear fuel. Uranium oxide is obtained for example by conversion of uranium hexafluoride (UF6) to uranium oxide. Conversion is conducted in a furnace for example by counter-current circulation of a powder of uranium hexafluoride and water (H2O). Said manufacturing process is described in FR 2 771 725.

This conversion generates hydrofluoric acid (HF) as recyclable by-product. It must be controlled that the concentration of uranium in the hydrofluoric acid does not exceed the regulatory thresholds laid down by the nuclear safety agency.

To do so, it is possible regularly to take samples and to have them analysed by a laboratory, for example using mass spectrometers, molecular absorption spectrophotometers . . . .

Nevertheless, such analyses require the use by qualified personnel of sophisticated laboratory equipment that is costly to purchase, maintain and operate. They require a time possibly varying from several tens of minutes to a day depending on the necessary preparations and the type of measurement to be performed. They are conducted at regular time intervals but spaced apart. These analyses are ill-adapted to the monitoring of a continuous industrial process and in this case necessitate intermediate storage and treatment in batches at certain steps of the industrial process.

SUMMARY OF THE INVENTION

It is one objective of the invention to propose a photonic spectrometry device adapted for the monitoring of industrial processes.

For this purpose a photonic spectrometry device is provided comprising several identical photonic spectrometers, each spectrometer comprising a radiation sensor and being capable of providing a measurement spectrum corresponding to the measurements of the sensor during a time interval, the spectrometers being capable of performing measurements simultaneously on one same radiation-emitting product and of providing measurement spectra for one same time interval, and processing means capable of determining a net spectrum from each of the measurement spectra provided by the spectrometers during one same time interval and of determining a global spectrum resulting from the summation of the net spectra determined for one same time interval.

According to other embodiments, the photonic spectrometry device comprises one or more of the following characteristics taken alone or in any possible technical combination:each spectrometer comprises a detection module capable of converting an electric signal emitted by the sensor on detection of a photon and proportional to the energy of the detected photon, to a digital signal representing the energy of the detected photon;each detection module is adjustable so as to adjust the digital signal output by the detection module as a function of the signal emitted by the associated sensor;each spectrometer is initially adjusted by calibrating the detection module so that the sensor/detection module pairs of the spectrometers emit substantially the same digital signal in the presence of one same source of radiation;at least one calibration source emitting radiation, common to the spectrometers, each sensor of the spectrometers statistically receiving substantially one same quantity of photons from the or from each calibration source for one same time interval;the sensors of the spectrometers are arranged in a circle;the sensors are regularly distributed around the circle;at least two different calibration sources common to the spectrometers;two calibration sources having respective reference spectral lines located either side of a characteristic spectral line of an element to be detected, in particular either side of a spectral line characteristic of uranium 235;the processing means are capable of determining each net spectrum by aligning each measurement spectrum in relation to a spectral line of the measurement spectrum corresponding to the or to each calibration source, and in relation to a reference line of the or of each calibration source;the photonic spectrometer device is adapted for the measurement of gamma-rays or the measurement of X-rays.

A photonic spectrometry method is also provided comprising the steps of:providing measurement spectra using identical spectrometers, each measurement spectrum resulting from measurements performed on one same radiation-emitting product during one same time interval by a respective spectrometer;determining a net spectrum from each measurement spectrum;determining a global spectrum resulting from the summation of the net spectra.

According to one embodiment, each net spectrum is determined by aligning the measurement spectrum provided by a spectrometer in relation to a spectral line of the measurement spectrum corresponding to at least one calibration source and in relation to the reference line of the or of each standard source.

A method for calibrating a photonic spectrometry device is also provided comprising the step to adjust a detection module capable of converting an electric signal output by the sensor of each spectrometer to a digital signal representing the energy of each detected photon so that the spectrometers provide substantially identical spectra in the presence of one same source of radiation.

A use of a photonic spectrometry device is also provided such as defined above to measure the uranium content of hydrofluoric acid resulting from the production of uranium oxide, to measure the content of at least one radio-isotope in effluent from a plant recycling radioactive materials, or to measure before discharge the content of at least one radio-isotope in the effluent of a plant for the treatment of radioactive material.

DETAILED DESCRIPTION

The photonic spectrometry device2illustrated inFIG. 1is capable of measuring radiation emitted by a product4.

The photonic spectrometry device2comprises several photon spectrometers6and an electronic processing module8, hereinafter <<processing module>>. The photonic spectrometry device2comprises a data exchange bus10connecting the processing module8to the output of each spectrometer6.

Each spectrometer6is capable of producing a spectrum of the number of photons detected during a time interval or measurement interval as a function of the energy of the detected photons. Each spectrometer6is designed to ensure the linearity of its response (energy spectrum) in relation to its input data (energy of each photon).

Each spectrometer6comprises a single radiation sensor12and an associated electronic detection and quantification module14, hereinafter <<detection module>>, and associated electronic analysis module16hereinafter <<analysis module>>.

The sensor12is capable of detecting gamma photons also called gamma-rays and/or X photons also called X-rays and, for each detected photon, of emitting an electric output signal proportional to the energy of the detected photon. The sensor12is electrically powered by a high voltage electric energy source18.

The detection module14on its input receives the output signal of the associated sensor12and outputs a digital signal representing the value of the energy of each photon detected by the sensor12. The detection module14is electrically powered by a low voltage electric energy source20.

The analysis module16is capable of counting the signals emitted by the detection module14, each signal corresponding to a photon detected by the sensor12, and of producing a measurement spectrum of the quantity of photons detected by the sensor12as a function of energy (keV) over a measurement interval.

The sensor12, the detection module14and the analysis module16are separate and connected together by data transmission links. The sensor12outputs an electric signal. The input of the detection module14is connected to the output of the sensor12via a wire link22. The detection module14emits an optical digital output signal. The input of the analysis module16is connected to the output of the detection module14via an optical link24typically an optical fibre.

The spectrometers6are capable of operating simultaneously and of simultaneously processing the photons emitted by the product4.

The processing module8is connected to the output of each spectrometer6by the bus10. The processing module8is configured to perform specific processing of the measurement spectra acquired simultaneously during the same time interval and produced by the spectrometers6so that it is possible to deliver a representative global spectrum determined from all the measurement spectra.

The processing module8is connected to a man/machine interface26to display results and/or receive instructions.

The processing module8is connected to a driver unit28capable of using the result given by the processing module8to drive a plant30, e.g. a plant for producing or recycling nuclear fuel or an installation to evacuate effluent from a plant producing and/or recycling nuclear fuel.

The spectrometers6are identical. The sensors12of the spectrometers6are identical, the detection modules14of the spectrometers6are identical and the analysis modules16of the spectrometers6are identical.

As shown inFIG. 2illustrating a spectrometer6, the sensor12of each spectrometer6is a scintillation sensor. It comprises a scintillator crystal32e.g. an inorganic scintillator of doped alkali halide type such as NaI(T1) for example or of mineral compound type such as LaBr3(Ce), and a photomultiplier34optically coupled to the crystal32. When a photon is absorbed by the crystal32, the latter emits a light signal whose energy is proportional to the energy of the absorbed photon. The photomultiplier34outputs an electric signal proportional to the light energy emitted by the crystal32.

The sensor12therefore outputs an analogue electric signal proportional to the energy released by the photon in the crystal32.

The detection module14comprises an analogue/digital converter36to convert the analogue input signal to a digital output signal.

The detection module14is adjustable so as to adjust the signal output by the detection module14in relation to the input signal it receives. To do so the detection module14comprises a proportional controller38capable of applying a multiplication coefficient to the signal it receives. The proportional controller38is adjustable so that it is possible to adjust the multiplication coefficient.

Returning toFIG. 1, the photonic spectrometry device2comprises at least one calibration source and preferably at least two calibration sources S1, S2associated with the plurality of spectrometers6. Each calibration source S1, S2emits a determined spectrum of photons. The calibration sources S1, S2emit different photon spectra. Preferably, each calibration source S1, S2emits a spectrum having a characteristic spectral line around a reference energy or reference line and the calibration sources S1, S2have one or more reference lines at different reference energies.

The calibration sources S1, S2are arranged so as to ensure identical irradiation of each sensor12of each spectrometer6. For example, to ensure identical irradiation, each calibration source S1, S2is arranged equidistant from the sensors12of the spectrometers6. In other words, the spectrometers6use at least one common calibration source S1, S2, preferably two common calibration sources S1, S2.

The calibration sources S1, S2are separate from the spectrometers6and in particular from the sensor12of each spectrometer6. Each spectrometer6is therefore associated with at least one calibration source S1, S2separate from the sensor12of this spectrometer6, preferably with two calibration sources S1, S2separate from the sensor12of this spectrometer6.

The processing module8is capable of individually analysing each measurement spectrum during a given measurement interval so as to compare, for each spectrometer6, the measured characteristic spectral line corresponding to each calibration source S1, S2with the corresponding reference line, of calculating the affine function constants to be applied to cause the coinciding of the measured characteristic spectral lines of the sources S1, S2with their reference lines, of applying the affine functions to every point of the spectral domain to align the measurement spectrum and thereby determine a corresponding net spectrum, and finally of summing the net spectrum derived from each of the spectrometers6to obtain the global spectrum.

Alignment is energy-based and/or efficacy-based. Energy alignment consists of determining an affine function to cause the energy of the measured characteristic spectral line corresponding to the or each calibration source S1and S2to coincide with the energy of the reference line of the or of each calibration source S1, S2. Efficacy-based alignment consists of determining an affine function to cause the number of detected photons of the measured characteristic spectral line corresponding to the or to each calibration source S1et S2to coincide with the expected number of photons—i.e. the initial detection efficacy of the sensor12of the Spectrometer6concerned—during the measurement interval.

The processing module8receiving the measurement spectra and/or the analysis module16producing the measurement spectra is/are advantageously capable of storing these at least temporarily. This makes it possible to consult the measurement spectra for qualification purposes for example or for a control in the event of an anomaly or operating incident.

Processing means are formed by the processing module8capable of determining a net spectrum from each of the measurement spectra provided by the spectrometers6and of determining a global spectrum resulting from summation of the net spectra.

In one variant, the analysis module16of each spectrometer6is capable of determining the measurement spectrum and of performing the processing thereof to determine the corresponding net spectrum. In this case, the processing means are formed by the analysis module16of each spectrometer6and by the processing module8which receives the net spectra determined by the analysis modules16and performs summation thereof to obtain the global spectrum.

As illustrated inFIGS. 3 and 4, the sensors12are regularly distributed over an imaginary circle of sensors C1centred on an axis of symmetry A. As illustrated inFIG. 4, the sensors12total a number of8and are distributed around the axis A, with the same metric radius value and at a regular angular pitch of 45°.

The calibration sources S1, S2are arranged at the centre of the circle of sensor C1. Each calibration source S1, S2therefore lies equidistant from the sensors12. As a result each sensor12statistically receives substantially the same quantity of photons derived from the calibration sources S1, S2, during one same measurement interval.

The photonic spectrometric device2comprises a chamber40for circulation of the product4to be controlled, having symmetry of revolution about the axis of symmetry A. Therefore each sensor12statistically receives substantially the same quantity of photons derived from the product4present in the chamber40.

The sensors12are arranged on the chamber40so that space receiving the product4in the chamber40lies between the sensors12and around the sensors12. This ensures good irradiation of the sensors12by the photons emitted by the product4.

As illustrated inFIGS. 3 and 4, the chamber40comprises a tank42of circular cross-section extending along the axis of symmetry A, and a lid44of circular contour hermetically sealing the tank42if necessary.

The lid44is of general circular shape. The lid44comprises at least one filling device48arranged close to the centre of the lid44coinciding with the axis A and ensuring rapid filling of the chamber40and at least one discharge device46positioned on the periphery of the lid44and ensuring evacuation of the overflow of the pot40. As illustrated inFIGS. 3 and 4when several filling devices48are present, the filling devices48are spaced apart and regularly distributed in a circle centred on the axis A. Depending on the configuration of the plant30the filling device48may also be arranged on a side face or the inner face of the tank42.

The tank42comprises at least one drainage device56which is fed at the lowest point of the tank42and ensures the draining of the pot40controlled by an evacuation valve58. As illustrated inFIG. 3, the tank42comprises a drainage device56located at the centre of the bottom of the tank.

The lid44comprises a plurality of sensor alveoli50projecting inside the chamber40and open towards the outside of the chamber40. Each sensor alveolus50defines a housing in the lid44to receive a sensor12. The sensor alveoli50are arranged following the circle of sensors C1. The sensor alveoli50are distributed at a regular angle about the axis A.

The lid44comprises a plurality of retaining devices52for the detection modules14and opening towards the outside of the chamber40. Each retaining device52by projecting on the outside of the lid44defines a housing to receive a detection module14. The retaining devices52are arranged in an imaginary circle of detection modules C2centred on the axis A. The retaining devices52are distributed at regular angle about the axis A.

The lid44comprises an alveolus54for calibration source centred on the axis A. The calibration source alveolus54is arranged between the filling devices48. The calibration sources S1, S2are arranged in the calibration source alveolus54. Each calibration source S1, S2lies in the centre of the circle of sensors C1around which the sensors12are arranged.

The chamber40is arranged in the vicinity of a plant30. The detection assembly formed by the measuring chamber40, the sensors12and their associated detection modules14is fed with product4to be controlled via a direct line or branch line (parallel line) of the plant30.

The chamber40is arranged for example at the output of a furnace producing uranium and hydrofluoric acid, on an output of liquid hydrofluoric acid, in a confined room.

The detection modules14arranged in the vicinity of the sensors12allow the use of short wire links22between the detection modules14and the sensors12, to maximize the signal-to-noise ratio during detection.

The analysis modules16associated with the detection modules14and with the sensors12can be placed outside the confined room. The optical link24via optical fibre ensures the transmission of data at a fast rate and reliably over long distances for example over several tens of meters.

When in operation, during a determined time interval, the spectrometers6simultaneously measure the photons emitted by the product4present in the measuring chamber. Each spectrometer6provides a measurement spectrum. After individual alignment of each measurement spectrum to determine a net spectrum, the processing module8adds the net spectra to determine a global spectrum resulting from summation of the net spectra. On the basis of the global spectrum the processing module8determines one or more measurements, for example a concentration of uranium 235 in the product4.

The photonic spectrometry device2allows a measurement performed by laboratory equipment on a sample of product4over a period of time T, to be replaced by n simultaneous measurements (n>1) on the product4at the output of a plant30and performed by several spectrometers6whilst guaranteeing a result of same statistical accuracy acquired over a shorter time period possibly being reduced to T/n.

The photonic spectrometry device2allows satisfactory measurements to be performed over a measurement interval of a few minutes e.g. 1 to 5 minutes, whereas conventional sampling and analysis techniques using laboratory equipment require several tens of minutes even several hours and also, depending on the product to be sampled, action by a human operator in a possibly hazardous area such as a confined area.

The photonic spectrometry device2therefore allows measurements to be performed very rapidly over a measurement interval compatible with the monitoring of an industrial process or the driving of an industrial process.

Nonetheless, spectrometry is measurement of statistical type. Not all the photons emitted by the product4during the measurement interval are necessarily detected. Each sensor12only detects part of the photons which reach the sensor12.

The principle of the adding of measurements provided by different spectrometers6can only be considered to be physically justified if the photonic spectrometry device2verifies the principle of ergodicity.

In practice this means that it must be possible for the different measuring pathways of one same magnitude to be considered as identical or substantially identical so as to provide identical or sufficiently identical results under the same measuring conditions.

To meet this condition or at least to be sufficiently close to meeting this condition, the photonic spectrometry device2comprises several identical spectrometers6.

In practice owing to unavoidable manufacturing tolerances, although the sensors12are identical they have manufacturing dispersion and when placed under the same conditions give different measurements.

The value of the signals output by a sensor12also depends on its high voltage supply. A modification however small in relative value of this high voltage supply substantially modifies the value of the signals produced. The adjustment of this voltage individually for each sensor12could in theory allow calibration of the sensors12, but this individual adjustment requires a specific high voltage electric energy source18per sensor12and is not industrial on account of the high maintenance involved. To meet the constraints of an industrial process it is preferable to maintain a single high voltage value, which could allow the use a single high voltage electric energy source18for all the sensors12. All the sensors12being powered by the same high voltage value, the output signals will then be different through the differences in gain and detection yield of each sensor12.

According to one aspect of the invention, the sensor12of each spectrometer6is coupled to the detection module14associated with this spectrometer6. The sensor12and the associated detection module14are jointly calibrated.

According to one embodiment, the detection module14of each spectrometer6is initially adjusted so that the signals given by the different sensor12/detection module14pairs are identical and linear or substantially identical and linear under the same measuring conditions.

Advantageously each sensor12/detection module14pair is adjusted by adjusting the gain of the photomultiplier34coupled to the crystal32of the sensor12, then by adjusting the detection module14for example by adjusting the proportional controller38of the detection module14.

Therefore, according to this embodiment of the invention, adjustment is performed at each sensor12/detection module14pair and not at each sensor12. This makes it possible to take into account the dispersion between sensors12and between detection modules14and to ensure that each spectrometer6produces substantially the same net spectrum in the presence of one same radiation source.

The initial adjustment of each spectrometer6is conducted for example in the presence of at least one calibration source S1, S2. The proportional controller38of the detection module14is adjusted so that the output signals from the detection module14correspond to the expected values in the presence of the calibration source S1, S2.

As a result each sensor12and the detection module14associated therewith form an inseparable pair. Two detection modules14cannot be changed over without changing over the two associated sensors12, and a sensor12cannot be replaced without associating its own detection module14together with it.

The sensors12are powered by the same high voltage value and are advantageously powered by the same high voltage electric energy source18. This simplified powering of the sensors12and maintenance operations. For other reasons such as the principle or redundancy used in nuclear plants as illustrated inFIG. 1, it is possible to provide a high voltage electric energy source18that is common to two sensors12for example. InFIG. 1the spectrometers6are grouped in pairs, the two sensors12of the spectrometers6of each group being powered by the same high voltage electric energy source18.

Each sensor12may drift over time and the sensors12may have different drifts.

According to one aspect of the invention, the photonic spectrometry device2comprises at least one calibration source S1, S2common to the different spectrometers6to correct the drift of the sensors12. The sensors12are arranged symmetrically around each calibration source S1, S2. Therefore the correction of the drift of the sensors12is conducted from the same calibration source S1, S2thereby providing an additional guarantee for heed of the principle of ergodicity.

The drift of each sensor12is corrected by alignment of each measurement spectrum in relation to the measured characteristic spectral line corresponding to the or to each calibration source S1, S2and in relation to the reference line of the or of each calibration source S1, S2so as to determine a net spectrum of radiation emitted by the product4and by the or each calibration source S1, S2.

According to one aspect of the invention, the photonic spectrometry device2comprises at least one calibration source S1having a reference energy higher than that of an element to be detected.

Uranium isotope 235 inter alia has a characteristic gamma photon emission at a value of 185.7 keV. A photonic spectrometry device2adapted to the detection of uranium isotope 235 may comprise a caesium 137 calibration source for example, having a reference characteristic gamma photon emission at a value of 662 keV whose influence on counts at the energy of 185.7 keV, i.e. counting results over the measurement interval output by the analysis module16, is easily made negligible.

By ensuring that each spectrometric pathway has a characteristic of response linearity, it is possible to correct the measurement spectrum as a function of the difference between the measured value for a calibration source and the reference value of the calibration source. An error—in relative value—of X % in the measurement of the reference value of the calibration source leads to a correction—in relative value—of X % of all measured values.

As a result a small drift in measurement in absolute value of the reference energy of a calibration source leads to a greater correction in absolute value of all energy measurements higher than that of the calibration source and a smaller correction in absolute value of all energy measurements lower than that of the calibration source. This means that for a given measurement uncertainty, uncertainty is higher for all energy measurements higher than that of the calibration source and lower for all energy measurements lower than that of the calibration source.

The choice of an energy calibration source higher than the energy of an element to be detected therefore allows the minimising of measurement uncertainties in absolute value over the energy ranges corresponding to that of the element to be detected.

According to one aspect of the invention the photonic spectrometry device2comprises two calibration sources S1and S2having characteristic spectral lines with different reference energies.

Preferably the reference energies of the calibration sources S1and S2are chosen so as to have an emission energy which lies at one of the two ends of the spectral energy analysis band of one spectrometer6for one thereof, and for the other at the other end of the spectral energy analysis band of the same spectrometer6. Therefore with two sources providing two different energies and the most distant apart possible over the spectral analysis range, correction is optimal for all the detectable photons on this energy analysis band.

Uranium isotope 235 inter alia has a characteristic gamma photon emission at a value of 185.7 keV. A photonic spectrometry device2adapted for the detection of uranium 235 comprises a calibration source in americium 241 for example having a reference energy of 59.5 keV and hence a spectral reference energy line around abscissa 60 keV and a calibration source in caesium 137 having a reference energy of 662 keV and hence a spectral reference energy line around abscissa 662 keV.

FIG. 5illustrates one example of a spectrum able to be obtained in the presence of an americium 241 calibration source, a caesium 137 calibration source and a sample containing uranium 235. The abscissa represents the energy in keV of the received photons and the ordinate the number of detected photons.

The correction of drift is made by correcting each measurement spectrum as a function of the measured characteristic spectral line and of the reference line of each calibration source S1, S2, which guarantees more precise correction.

The affine functions for alignment are determined so that the measured characteristic lines of the calibration sources S1, S2used coincide, in energy and count, with the respective reference lines of the calibration sources S1, S2and are then applied to each point of the measurement spectrum.

Most photon sensors comprise a calibration source—e.g. americium 241—placed in the sealed sensor and even sealed to the crystal at the time of manufacture. Subjected to regulations on sealed sources, the calibration sources have a limited regulatory lifetime. The source and hence the sensor must be destroyed at the end of the regulatory lifetime irrespective of the state of the sensor, which limits the lifetime of the sensor. Similarly if a sensor is faulty, the whole sensor is replaced and the calibration source is destroyed with the sensor.

The use of a calibration source associated with a sensor but physically separate from the sensor therefore allows the limiting of operating costs of the assembly by limiting the cost of replacement of a sensor and allowing the sensor to be preserved even if the calibration source must be replaced and vice versa. Additionally, this allows the use of one same calibration source for several sensors, which not only allows limiting of the cost of the measuring assembly but also ensures better suitability with the constraint of ergodicity of a device using several sensors simultaneously.

In one embodiment, at least one alignment function to align the measurement spectra of a spectrometer6is determined for each measurement spectrum determined by the spectrometer6. As a variant, at least one alignment function to align the measurement spectra of a spectrometer6is determined from at least one reference measurement spectrum of the spectrometer6so as to cause the coinciding, for each calibration source S1, S2, of a characteristic spectral line of the reference measurement spectrum with the reference spectral line of this calibration source S1, S2. The, or each, alignment function is used to align several successive measurement spectra of the spectrometer6. The, or each, alignment function is periodically determined at a periodicity dependent on the stability of the spectrometer6. The periodicity may be in the order of one day, one week or more.

FIGS. 6 to 8schematically illustrate industrial plants30using a photonic spectrometry device2to control the radio-isotope content of by-products and discharged effluent.

FIG. 6illustrates a plant for the conversion of uranium hexafluoride to uranium oxide comprising a furnace60receiving inter alia an input of uranium hexafluoride UF6and water H2O circulating in counter-current in the furnace60, and outputting uranium oxide UxOyas product and hydrofluoric acid HF as by-product.

As illustrated the chamber40of the photonic spectrometry device2is arranged in series on the hydrofluoric acid output after condensation to liquid HF to verify that the uranium 235 content of the hydrofluoric acid is lower than regulatory thresholds.

FIG. 7illustrates a recycling plant of radioactive materials comprising a reactor62into which waste is input containing radioactive material WMF and reagents R able to precipitate the radioactive material, and which outputs recycled radioactive material RMF and effluent E.

As illustrated the chamber40of the photonic spectrometry device2is arranged as a branch line (in parallel) on an effluent output E to verify that the radio-isotope content of the effluent E e.g. some radio-isotopes of thorium, uranium 235, lead 212, . . . , or other radioactive impurities derived for example from the use of uranium derived from the processing of irradiated fuel called reprocessed uranium, plutonium . . . is lower than regulatory thresholds.

The recycling plant comprises a recirculation pipe64extending between the output of the measuring chamber40of the photonic spectrometry device2and the waste input WMF so that the effluent E is recycled for as long as its content of one or more radio-isotopes is too high.

FIG. 8illustrates an assembly66for treating radioactive materials66comprising several treatment plants68of radioactive materials producing effluent E collected in an evacuation circuit for discharge thereof.

The photonic spectrometry device2is arranged in the discharge circuit to verify that the radio-isotope content of the collected effluent E conforms to regulatory discharge thresholds.

The photonic spectrometry device2is installed in a main pipe70to perform measurements on all the effluent E or on a branch pipe to perform measurements on a fraction of the collected effluent E.

It is possible to use the photonic spectrometry device2so as to determine the origin of effluent pollution with radioactive material. In relation to the industrial process from which pollution e.g. uranium originates, chemical elements characteristic of the process used may be associated with uranium. For example the presence of lead 212 in association with uranium 235 is the sign of pollution derived from a plant using reprocessed uranium.

Therefore according to one aspect of the invention, the processing module8of the photonic spectrometry device2is configured to determine, from the global spectrum, the presence of additional radio-isotopes e.g. uranium 235.

In general the choice of the use of the photonic spectrometry device2in series or in parallel on the output of the product4to be controlled is dependent on the plant30and on the flow rate of the product on the output line.

According to one option, the processing module8comprises a memory in which reference spectra are stored characteristic of some types of pollution, and is configured for example to emit an alert or trigger stoppage of the plant30in the event that a net spectrum corresponds to a pre-recorded reference spectrum.

With the invention it is possible to perform rapid measurements of gamma- and/or X-rays compatible with the monitoring or driving of industrial processes. The photonic spectrometry device can be built from commercially available parts and can be positioned in situ in the vicinity of or within a plant to control the products output by this plant and/or to drive the plant.

The invention may particularly apply to the measurement of uranium 235 content at the output of processes for the manufacture of uranium-based nuclear fuel, or of uranium recycling processes. In general, the invention applies to the measurement of the content of any radioactive element.

The invention can be applied to any gamma-ray or X-ray measurement. The spectrometers of the invention are gamma- and/or X-ray photon spectrometers depending on the scintillator used.