Fiber optic sensor for analyzing the activity of a radioactive fluid

Abstract

Device (1) for analyzing the activity of a fluid (3) capable of containing a radionuclide emitting charged particles of type , the device comprising a wall (20), delimiting a chamber (2) intended to be occupied by the fluid, the wall extending to a thickness (e) and a detection optical fiber (10), comprising a core surrounded by a cladding, the core being formed of a scintillator material, the scintillator material emitting photons when exposed to irradiation by charged particles. The scintillator material is coupled to a photodetector.The optical detection fiber extends outside the chamber, within the thickness of the wall or against the wall, so that under the effect of exposure to charged particles emitted by the radionuclide, the photodetector generates a detection signal (S, N) dependent on a quantity of scintillation photons emitted by the scintillator material of the optical detection fiber under the effect of exposure to charged particles.

Description

Title of the invention: Fiber optic sensor for analyzing the activity of a radioactive fluid. Technical field

[0001] The technical field of the invention is the detection of the activity of a fluid capable of containing a radioactive emitting radionuclide [3. The fluid can be a gas or a liquid. EARLIER ART

[0002] In the nuclear or medical industries, it is common to analyze the activity of radioactive fluids. Such analyses are conducted, for example, for process control, release control, or the control of an air or water distribution network.

[0003] Fluid analyses are often performed on collected samples, which presents several drawbacks. A primary difficulty is the time required for sample collection and laboratory analysis. This results in a significant time lag between sample collection and analysis. This is a so-called "offline" measurement technique, incapable of delivering real-time results. A second difficulty is the contamination of the equipment used for sample collection and analysis. This applies particularly to the equipment used for sample conditioning and handling. A third difficulty relates to the representativeness of the collected samples. The issue of representativeness is particularly relevant when the fluid to be analyzed is not homogeneous. It is then necessary to collect multiple samples, which increases complexity and cost.

[0004] Solutions have been developed that allow for online measurement of fluid activity. Patent EP3542185 describes a device comprising a measuring chamber intended to be filled with a fluid. The measuring chamber contains scintillating optical fibers. These fibers are designed to generate scintillation light under the effect of irradiation by ionizing radiation. One drawback of this device is that the scintillation fibers are placed in direct contact with the fluid to be analyzed. Thus, when the fluid is contaminated, the measuring chamber and the optical fibers inside the chamber are potentially contaminated. It is therefore necessary to clean the optical fibers and / or dispose of them through a nuclear waste disposal channel. Furthermore, the optical fibers can degrade upon contact with the fluid.

[0005] The inventors propose a device, intended for the analysis of the activity of a fluid, which is non-intrusive, that is to say, whose irradiation-sensitive elements are not The device does not come into direct contact with the fluid being analyzed. This eliminates the need for decontamination procedures. The device allows for online analysis of fluid activity. Furthermore, its design makes it compatible with various geometries. Description of the invention

[0006] A first object of the invention is a device for analyzing the activity of a fluid capable of containing a radionuclide emitting / 3-type charged particles, the device comprising: - a wall, delimiting a chamber, intended to be occupied by the fluid, the wall extending according to a thickness; - a detection optical fiber, comprising a core surrounded by a cladding, the core being formed of a scintillator material, the scintillator material emitting photons when exposed to charged particles; - at least one photodetector, optically coupled to the optical detection fiber, so as to detect scintillation photons emitted by the scintillator material under the effect of exposure to charged particles; - at least one processing circuit, configured to perform processing of the detection signal resulting from the or each photodetector; - a computing unit, connected to the processing circuit, the computing unit being programmed to calculate an analysis result based on the detection signal generated by the photodetector(s);

[0007] The device being characterized in that: - the optical detection fiber is located outside the chamber; - all or part of the optical detection fiber extends within the thickness of the wall or against the wall;

[0008] so that under the effect of exposure to charged particles emitted by the radionuclide, the photodetector generates a detection signal dependent on a quantity of scintillation photons emitted by the scintillator material of the or each detection optical fiber under the effect of exposure to charged particles.

[0009] According to one embodiment, - the detection wall extends around the chamber; - all or part of the detection optical fiber extends around the chamber.

[0010] In one possibility, the detection optical fiber may form a spiral around the chamber. In one possibility, the device comprises several detection optical fibers optically coupled to the photodetector, each detection optical fiber forming at least one turn around the chamber. In one possibility: - the wall extends around a longitudinal axis; where each optical detection fiber extends parallel to the longitudinal axis.

[0011] According to one embodiment, the processing circuit is configured to determine a counting rate from the detection signal, the counting rate corresponding to a number of pulses detected by the photodetector per unit of time; The computing unit is programmed to compare the counting rate to a predetermined threshold. and / or the calculation unit can be configured to quantify radionuclide activity from the count rate.

[0012] According to one possibility, the processing circuit is a spectrometry circuit, configured to establish a spectrum representative of the energy deposited in the scintillator material by the charged particles; The computing unit is programmed to identify the radionuclide from the spectrum.

[0013] The calculation unit can be programmed to calculate an activity of each radionuclide identified from the spectrum.

[0014] According to one embodiment, the wall delimits all or part of a pipe, tank, or drum. The wall may form an external wall and / or an internal wall of a tubular pipe, the chamber extending between the internal wall and the external wall, the internal and external walls extending around a central axis, respectively along an internal radius and an external radius, the internal radius being smaller than the external radius.

[0015] According to one possibility: the sensing fiber, or each sensing fiber, is arranged against or in the outer wall of the tubular conduit; the device includes an auxiliary scintillator, disposed in contact with the inner wall, the auxiliary scintillator being connected to an auxiliary photodetector.

[0016] A second object of the invention is a method for analyzing a fluid using a device according to the first object of the invention, the fluid extending into a chamber delimited by the wall of said device, the method comprising: a) acquisition of detection signals by the photodetector(s) during an acquisition period; b) using the calculation unit, obtaining an analysis result.

[0017] According to one embodiment, step b) comprises: determination of the quantity of charged particles detected per unit of time; - comparison of the quantity of charged particles detected per unit of time with a threshold value; - based on the comparison, generation of an alert signal.

[0018] According to one possibility: - the processing circuit is a spectrometry circuit, configured to establish a spectrum representative of the energy deposited in the scintillator material by the detected charged particles; - step b) involves, from the detected spectrum, an identification of the radioelement present in the fluid.

[0019] The invention will be better understood upon reading the description of the exemplary embodiments presented later in this description, in connection with the figures listed below. FIGURES

[0020] Figure [1A] schematically illustrates a first embodiment, in which the device includes a detection optical fiber, arranged against a wall delimiting a chamber containing the fluid, the fiber being arranged outside the chamber.

[0021] Fig. 1B shows a configuration in which the sensing fiber is arranged in contact with the wall, and extends parallel to a central axis around which the chamber extends.

[0022] Fig. 1C shows a configuration in which the sensing fiber is arranged around the wall, in contact with the latter.

[0023] Fig. 1D shows a configuration in which several sensing fibers are arranged, each sensing fiber forming a loop around the wall.

[0024] Figure 2A schematically illustrates a second embodiment, in which the device includes a detection optical fiber, arranged in the thickness of a wall delimiting a chamber containing the fluid.

[0025] Fig. 2B shows a configuration in which the sensing fiber is arranged in the wall and extends parallel to a central axis around which the chamber extends.

[0026] Fig. 2C shows a configuration in which sensing fibers, forming parallel turns, are embedded in the wall around the chamber.

[0027] Figure [Fig. 3A] is a transparent view of the configuration shown on the [Fig.2B],

[0028] Fig. 3B is a transparent view of the configuration shown in Fig. 2C: detection fibers, forming parallel turns, are embedded in the wall.

[0029] Fig. 3C is a transparent view of a configuration in which the sensing fiber forms a spiral, embedded in the wall, around the chamber.

[0030] Fig. 4 shows, for different materials, the stopping power (ordinate axis) as a function of the energy of a particle [3 (abscissa axis).

[0031] Fig. 5A is a cross-sectional view, in a radial plane, of a model of a measurement geometry in which a detection fiber is arranged in a spiral around a wall delimiting a cylindrical chamber containing the fluid to be analyzed.

[0032] Fig. 5B is a cross-sectional view, in a longitudinal plane, of the modeling described in relation to Fig. 5A.

[0033] Fig. 6 shows a detection spectrum, representing the number of particles [3 (ordinate axis) interacting in a scintillator material forming the core of a detection fiber, as a function of the energy deposited by each particle in said scintillator material (abscissa axis).

[0034] Figure 7A describes an example of the implementation of a device according to the invention.

[0035] Fig. 7B is a detail of Fig. 7A, which shows the main components of the device.

[0036] [Fig.7C] is a detail of [Fig.7B].

[0037] Fig. 8A is a cross-sectional view, in a radial plane, of a model of a measurement geometry corresponding to the device described in relation to Figures 7A to 7C.

[0038] Fig. 8B is a cross-sectional view, in a longitudinal plane, of the modeling described in relation to Fig. 8A.

[0039] Fig. 9A shows a detection spectrum, as defined in relation to Fig. 6, resulting from a detection fiber used in the device described in relation to Figures 7A to 7C.

[0040] Fig. 9B shows a detection spectrum resulting from a solid auxiliary scintillator, cylindrical in shape, shown in Fig. 7C.

[0041] Figure 10 schematically illustrates different process steps implementing a device according to the invention. PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS

[0042] Figure 1A represents a first embodiment of a device 1 for characterizing the activity of a fluid 3. The device 1 comprises a wall 20, delimiting a chamber 2 inside which extends a fluid 3 to be analyzed. The fluid 3 can be a liquid or a gas. In this example, the wall 20 is cylindrical in shape and extends around a central axis A. The central axis is parallel to an axis longitudinal Z. The measured fluid 3 can flow through chamber 2, parallel to the central axis A.

[0043] Fluid 3 is likely to contain a radionuclide, [3] emitter and possibly a y emitter.

[0044] The device 1 comprises at least one sensing fiber 10. The sensing fiber 10 is a scintillation fiber. As described in EP3542185, a scintillation fiber is an optical fiber having a core 11 made of a scintillator material surrounded by a cladding 12. The scintillator material may, for example, be an organic polymer doped with fluorophores. The scintillator material, forming the core 11, emits scintillation photons when irradiated by ionizing radiation. The cladding 12 has a lower refractive index than the refractive index of the scintillation material forming the core. The cladding may be made of a PMMA (polymethyl methacrylate) type polymer. The fiber 10 forms a waveguide, in which the scintillation photons propagate to an end 13.

[0045] The end of the detection fiber 10 is optically coupled to a photodetector 14. It can be disposed in contact with the photodetector 14, or be optically coupled by means of an optical system or by a conventional optical fiber, ensuring an optical link between the scintillation optical fiber and the photodetector.

[0046] Generally, a scintillation material is sensitive to all types of ionizing radiation, particularly alpha or [3] charged particles, or ionizing photons, X-rays or gamma rays. In order to minimize sensitivity to ionizing photons, the core diameter is preferably less than 500 pm or 300 pm. A small core diameter decreases the probability of interaction of an ionizing photon propagating through the fiber.

[0047] The thickness and material of the wall 20 are chosen so that the attenuation with respect to [3] particles is not too high. Thus, as shown in [Fig. 1A], some of the [3] particles propagate through the wall 20, irradiating the core 11 of the detection fiber 10. Given the presence of the wall 20 and the cladding 12 surrounding the core 11, it is assumed that any alpha particles emitted by a radioisotope present in the fluid 3 are absorbed before reaching the fiber. Thus, the detection fiber 10 is essentially sensitive to [3] particles and, to a lesser extent, to photons emitted by the fluid 3 occupying the chamber 2 or emitted into the environment of the device. The thickness of the cladding 12 must be as thin as possible to limit the attenuation of [3] particles. For example, it can be less than 10 pm.

[0048] Advantageously, the scintillating fiber 10 is flexible. This is an interesting feature of the invention, as described below.

[0049] In [Fig. IA], only one sensing fiber 10 is shown, arranged along the wall 20, outside the chamber 2. Several sensing fibers 10 can be used, as described in connection with [Fig. 1B].

[0050] The photodetector 14, to which the detection fiber(s) is optically coupled, can be a photodiode or photomultiplier type photodetector. When an ionizing particle [3] interacts in the scintillation material, forming the core of the fiber, several scintillation photons are produced, some of which reach the end 13 of the fiber coupled to the photodetector 14. The number of scintillation photons produced is generally proportional to the energy deposited by the particle [3] during the interaction. The number of scintillation photons created in the core is typically a few thousand per MeV deposited in the core. The scintillation photons are detected by the photodetector 14 and are converted into an electrical pulse whose amplitude depends on the number of scintillation photons generated.Thus, the amplitude of each electrical pulse resulting from the photodetector depends on the energy deposited in the scintillation material during an interaction with a particle [3]. The photodetector 14 generates a detection signal made up of pulses, each pulse corresponding to an interaction with a particle [3].

[0051] The photodetector 14 is connected to a processing circuit 15, the latter being configured to process the pulses resulting from the photodetector. The processing circuit 15 is connected to a processing unit 16. The processing unit 16 is intended to establish a measurement result based on the detection signal resulting from the photodetector.

[0052] According to a first application, the processing circuit 15 generates, from each detection signal transmitted by the photodetector, a counting rate N, corresponding to the number of pulses detected per unit of time. The processing unit 16 can then be configured to compare the counting rate to a threshold and emit an alert signal if the threshold is exceeded.

[0053] According to a second application, a priori information is available regarding the radionuclide present in chamber 2. From the count rate N, a first estimate of the radionuclide's activity A can be made, using a detection efficiency q. The detection efficiency q establishes a link between the count rate and the radionuclide's activity. The detection efficiency q can be determined experimentally by placing a calibration fluid of known activity in the chamber. The detection efficiency can also be determined based on numerical models.

[0054] According to a third application, the processing circuit 15 is a spectrometry circuit. The processing circuit 15 generates a detection spectrum, corresponding to an amplitude histogram of the pulses detected during a acquisition period. The computing unit 16 can be configured to perform a processing of the detection spectrum in order to identify one or more radionuclides present in the fluid 3 occupying the chamber 2 and possibly estimate an activity of each radionuclide identified.

[0055] The device 1 may comprise several detection fibers 10, respectively coupled to the same photodetector 14 or to several photodetectors 14. The processing unit 16 receives the detection signal resulting from each photodetector 14, and is processed by the processing circuit 15. The processing unit 16 may consist of an electronic circuit and / or a microprocessor. The processing unit 16 is programmed to perform the steps described below, in connection with [Fig. 10].

[0056] Figure 1B represents a device in which several sensing fibers 10 are distributed around a wall 20 delimiting a cylindrical chamber 2. Each sensing fiber 10 is positioned in contact with the wall 20. Preferably, each sensing fiber 10 is fixed relative to the wall 20. Each sensing fiber can extend to a length of several tens of centimeters or several meters. Each sensing fiber extends parallel to the central axis of the chamber 2. At least one end 13 of each sensing fiber 10 is connected to a photodetector 14.

[0057] Figure 1C shows a configuration in which the sensing fiber 10 forms a spiral around the wall 20. Figure 1D shows a configuration in which several sensing fibers 10 are arranged, each sensing fiber forming a loop around the wall 20. The configurations shown in Figures 1C and 1D take advantage of the fact that the sensing fiber, or each sensing fiber, is flexible. Preferably, regardless of the configuration, each sensing fiber 10 is fixed in or on the wall. Preferably, in the configurations shown in Figures 1B to 1D, the sensing fiber or fibers are in contact with the wall.

[0058] The configurations described in connection with Figures IA to 1D are adapted to walls 20 whose thickness is sufficiently thin to allow a sufficient quantity of [3] particles to be transmitted through the wall. The emission energy of a [3] particle follows a distribution, usually referred to as the emission spectrum, which is specific to each radionuclide. Thus, each radionuclide can be characterized by an average emission energy and a maximum emission energy of [3] particles, the latter being several hundred keV or several MeV. In order for a detection fiber 10 to be exposed to [3] particles whose residual energy, after passing through the wall 20, is sufficiently high, the wall is preferably made of a plastic material, for example a polymer, or a light metal, for example aluminum or steel, and whose thickness is small, preferably less than 1 mm. even at 100 pm. Thus, the wall 20 forms a skin delimiting the chamber 2 in which the fluid to be analyzed 3 extends.

[0059] Figures 2A to 2D show embodiments in which the detection fiber or fibers 10 are integrated (or embedded) in the wall 20 delimiting the chamber 2. The advantage of such a configuration is that the detection fiber or fibers 10 are positioned at a distance e from the chamber 2 that is less than the thickness e of the wall 20. Compared to the first embodiment, this allows the constraint concerning the wall thickness to be relaxed. It also allows the distance between the inside of the chamber 2 and the detection fiber (or fibers) 10 to be small, for example, less than 2 mm, or even 1 mm. The distance e corresponds to an apparent thickness seen by the particles [3] before reaching the detection fiber 10. The smaller the apparent thickness e, the higher the average energy of the particles [3] likely to interact in the detection optical fiber.This results in a better detection efficiency, the detection efficiency corresponding to the number of scintillation photons detected for a particle [3 emitted inside chamber 2. .

[0060] In [Fig. 2B], a configuration is shown in which several detection fibers 10, parallel to each other, extend parallel to the central axis A of the chamber 2, inside the wall 20. In [Fig. 2C], a configuration is shown in which detection fibers extend around the chamber 2 in several turns, embedded in the wall 20. Regardless of the configuration chosen, the detection fiber or fibers 10 are arranged outside the chamber 2. In the configurations shown in Figures 2A to 2C, the detection fiber or fibers 10 can be embedded in the wall 20 during the construction of the latter.

[0061] Figures 3A and 3B represent "transparency" views of configurations respectively described in relation to [Fig.2B] and 2C. [Fig.3C] represents a transparent view of a configuration in which the sensing fiber describes a spiral around chamber 2. In figures 3A, 3B and 3C, each sensing fiber is embedded in the wall.

[0062] Figure 4 illustrates the stopping power (ordinate axis: unit MeV / cm) with respect to particles [3] of different materials as a function of the energy of said particles (abscissa axis - unit MeV). Figure 4 shows the stopping powers of HDPE (high-density polyethylene - curve a), concrete (curve b), stainless steel (curve c), water (curve d), air (curve e), and polystyrene (curve f). It can be observed that, for the same thickness, it is preferable for the wall to be made of a material such as HDPE or polystyrene rather than steel. Curves d and f are almost identical.

[0063] The inventors have modeled the detection of particles [3] by a device as described in relation to [Fig. 1C]. The configuration has been modeled according to the following parameters: - wall material 20: steel; - wall thickness 20: 2 mm; - radius of room 2: 20 cm; - room height: 2m; - Nature of the fluid: air - radioelement modeled: 90Y - Average emission energy: 926 keV - Maximum emission energy: 2280 keV; - diameter of the core of the detection fiber: 250 pm; - detection fiber material: polystyrene - density 1.05; - thickness of the detection fiber sheath: 7.5 µm; - sheath material: PMMA - number of turns: 3601.

[0064] The modeled optical fiber corresponds to reference BCF-10 - manufacturer Saint Gobain.

[0065] Figures 5A and 5B are views of the modeled configuration in a radial plane, defined by the X and Y axes, and a longitudinal plane, defined by the X and Z axes, respectively. Reference dimension 4 corresponds to ambient air. In each of Figures 5A and 5B, a detail of a portion of the wall 20 against which the sensing fiber 10 is assembled is shown. In [Fig. 5B], the sensing fiber 10 appears as adjacent disks.

[0066] Using the MCNP (Monte Carlo N-Particle) code, a detection spectrum of particles detected by the detection fiber was modeled, the detection spectrum being shown in [Fig. 6]. The detection spectrum corresponds to the proportion of interactions detected for 1 emitted particle (ordinate axis) as a function of the detection energy (abscissa axis - unit MeV). [Fig. 6] shows a distribution of the energy deposited by the detection fiber of a [3] particle emitted in chamber 2, the energy of the [3] particle being emitted according to a distribution corresponding to the emission spectrum of 90Y. Due to the small volume of the fiber, a [3] particle interacting in the fiber may release only part of its energy.

[0067] Figure 7A illustrates an example of the application of a device according to the invention. In this example, a liquid is transported from a tank A to a tank B. The device 1 is integrated into the central part of a pipe C, connecting tank A to tank B. Figures 7B and 7C are details of the device 1. The device comprises a wall 20, against which a sensing fiber 10 is disposed such as previously described. The sensing fiber is arranged around wall 20 in a spiral, as described in relation to [Fig.1C].

[0068] The chamber 2, delimited by the wall 20, is annular. It has an inner wall 20', which, like the wall 20, is cylindrical. The radius of the inner wall 20' is smaller than the radius of the wall 20, the latter forming an outer wall of the annular chamber 2. The device includes an auxiliary scintillator 10', applied against the inner wall 20'. In the example shown in Figures 7B and 7C, the auxiliary scintillator 10' is a solid scintillator, coupled to an auxiliary photodetector 14'. According to this embodiment, particles [3] emitted into the annular chamber 2 can be detected either by the detection fiber 10 or by the auxiliary scintillator 10'. According to one variant, the solid auxiliary scintillator 10' is replaced by an auxiliary sensing fiber 10', wound against the inner wall 20', in the same way that the sensing fiber 10 is wound against the wall 20.The advantage of detection fibers is their lower sensitivity to gamma radiation.

[0069] The inventors modeled the configuration described in relation to Figures 7A to 7C, using the MCNP transport code. The modeling parameters are: - detection fiber: similar construction to the detection fiber described in connection with figures 5A and 5B. 571 turns. - radius of the inner wall 20': 2.5 cm; - radius of wall 20: 4.5 cm; - thickness of the inner wall 20' and of the wall 20: 1 mm; - Internal wall material 20' and wall 20: stainless steel.

[0070] Figures 8A and 8B are views of the modeled configuration respectively in a radial plane, defined by axes X and Y, and a longitudinal plane, defined by axes X and Z. In each of Figures 8A and 8B, a detail of a part of the wall 20 against which the sensing fiber 10 is assembled is shown. In [Fig. 8B], the sensing fiber 10 appears in the form of disks adjacent to each other.

[0071] Figure 9A shows the detection spectrum of a ³⁻ particle emitted by 90Y in the measurement chamber. It is an energy discretized histogram (x-axis - MeV) showing, at each energy, the probability of detection, by the detection fiber, at said energy, of a ³⁻ particle emitted in chamber 2, the energy of the emitted particle being distributed according to the emission spectrum of 90Y. Figure 9B is a figure similar to Figure 9A, established by modeling the solid auxiliary scintillator 10'. The detection probabilities obtained with the solid scintillator are higher due to its larger volume, which increases detection efficiency, at the expense of increased detection sensitivity to gamma photons.

[0072] The detection spectra shown in Figures 6, 9A and 9B can be used for the purpose of identifying a radionuclide present in the fluid 3 circulating in the chamber 2. Indeed, the detection spectrum corresponds to a spectral signature of the radionuclide(s) present in the fluid 3. The detection spectra shown in Figures 6, 9A and 9B are so-called unitary spectra, because they correspond to the detection spectrum resulting from the presence of a single radionuclide, in this case 90Y, for a unitary emission, in this case 1 particle [3 emitted.

[0073] Unit detection spectra corresponding to different radionuclides can be established, particularly by modeling, for a unit activity of IBq. Each unit detection spectrum forms a direct model assigned to each radionuclide. It is preferable that each unit detection spectrum be established considering the same activity for each radionuclide, for example IBq. Thus, to each radionuclide RNj corresponds a unit detection spectrum Sp. From each unit detection spectrum, a response matrix M can be formed, each column of which corresponds to a unit detection spectrum. From a measured detection spectrum S, the activity Aj of each radionuclide RN is defined according to the expression:

[0074] S = MXA (1)

[0075] where - S is the detection spectrum, of dimension [K, 1], K corresponding to the number of channels in the spectrum; - M is the response matrix, of dimension [-Sf, 1], where I corresponds to the number of radionuclides RN j considered. The response matrix reflects the detection efficiency of the device. - A is a vector, of dimension [I, 1], each term of which corresponds to the activity Aj of each radionuclide RN j.

[0076] S results from the measurement. M is previously established, based on models, as described in connection with Figures 6 and 9A. M can be obtained based on experimental measurements, using samples containing radionuclides of known activity. A can be estimated by inversion.

[0077] Since the matrix M is generally not invertible, one possible method for estimating A is the application of an iterative optimization algorithm of the ML-EM type (Maximum Likelihood-Expectation Maximization). Such an algorithm allows us to estimate, at each iteration of rank j, a vector using the following update expression:

[0078] j+i^ KM(kJ)S(k) L 1

[0079] M(k, 1) is a term of the matrix M and S(k) is a term of the vector S.

[0080] The optimization algorithm can be initialized, during the first iteration, by:

[0081] ^>1 A =----- 1 SX1 M ^

[0082] The use of an optimization algorithm, implementing the ML-EM method to quantify the activity of different radioelements, from a detection spectrum resulting from particle-sensitive detection fibers, was described in Dufour N, “Scintillating fibre based beta spectrometer: Proof of concept by Monte-Carlo simulation and first experimental assessment”, Nuclear Inst, and Methods in Physics research, A 1010 (2021).

[0083] Figure 10 shows different implementation steps of the device according to the invention. Step 100 corresponds to the acquisition of detection signals, resulting from one or more photodetectors, during an acquisition period. According to a first embodiment, called the counting mode, the processing circuit 15 establishes a counting rate N, corresponding to a number of pulses detected per unit of time, for example, every second.

[0084] During step 110, the processing unit 16 compares the counting rate with a predetermined threshold N*. During a step 120, the processing unit 16 generates an alert signal if the counting rate N is greater than the threshold N*.

[0085] Complementarily or alternatively, the process may include a step 130, during which the activity of a radionuclide RN is estimated based on a previously established detection efficiency for said radionuclide. Quantifying the activity based on a simple count rate assumes prior knowledge of the radionuclide (or mixture of radionuclides) present in the fluid. The detection efficiency, which relates the count rate to the activity, is previously established through experimental measurements on calibration fluids with known activity, or through modeling.

[0086] As previously described, the processing circuit 15 can be a spectrometric circuit. In this case, from detection signals acquired during the acquisition period, the processing circuit generates a spectrum S of the amplitude of the pulses detected during the acquisition period. During a step 140, the computing unit 16 takes into account a response matrix, as described in expression (1). The computing unit implements an inversion algorithm, by An example of ML-EM type, to identify the radionuclides present in the fluid and possibly estimate their respective activities...

[0087] The invention can be implemented to monitor fluids, liquid or gaseous, containing or likely to contain radionuclides. The invention allows for real-time, online monitoring of the fluid without risk of contamination of the detection optical fiber(s), since the detection fiber(s) do not enter the chamber. Using a processing unit to collect detection signals, after processing, provides real-time or near-real-time (within minutes) information. The use of a flexible detection fiber allows adaptation to chambers with different geometries.

Claims

1.

2. Demands Device (1) for analyzing the activity of a fluid (3) capable of containing a radionuclide emitting fi-type charged particles, the device comprising: - a wall (20), delimiting a chamber (2) intended to be occupied by the fluid, the wall extending along a thickness (e); - a detection optical fiber (10), comprising a core surrounded by a cladding, the core being formed of a scintillator material, the scintillator material emitting photons when exposed to charged particles; - at least one photodetector (14), optically coupled to the optical detection fibre, so as to detect scintillation photons emitted by the scintillator material under the effect of exposure to charged particles; - at least one processing circuit (15), configured to perform processing of the detection signal resulting from the or each photodetector; - a calculation unit (16), connected to the processing circuit, the calculation unit being programmed to calculate an analysis result based on the detection signal generated by the photodetector(s); - the optical detection fiber (10) is arranged outside the chamber (2); - all or part of the optical detection fiber extends into the thickness of the wall; so that under the effect of exposure to charged particles emitted by the radionuclide, the photodetector generates a detection signal (S, N) dependent on a quantity of scintillation photons emitted by the scintillator material of the optical detection fiber under the effect of exposure to charged particles; the device being characterized in that the wall (20) extends around the chamber, the chamber forming all or part of a pipe or a tank or a drum. Device according to claim 1, wherein all or part of the detection optical fiber (10) extends around the chamber.

3. Device according to claim 2, wherein the detection optical fiber forms a spiral around the chamber.

4. Device according to claim 2, comprising different optical detection fibers optically coupled to the photodetector, each optical detection fiber forming at least one turn around the chamber.

5. Device according to claim 1, wherein: - the wall extends around a longitudinal axis; - the detection optical fiber (Z) extends parallel to the longitudinal axis.

6. Device according to any one of the preceding claims, wherein: - the processing circuit (15) is configured to determine a counting rate (N) from the detection signal, the counting rate corresponding to a number of pulses detected by the photodetector per unit of time; - the calculation unit (16) is programmed to compare the counting rate to a predetermined threshold (N*).

7. Device according to claim 6, wherein the computing unit is configured to quantify radionuclide activity from the count rate.

8. Device according to any one of the preceding claims, wherein: - the processing circuit (15) is a spectrometry circuit, configured to establish a spectrum (S) representative of the energy deposited in the scintillator material by the charged particles; - the computing unit is programmed to identify the radionuclide from the spectrum.

9. Device according to claim 8, wherein the computing unit is programmed to calculate an activity of each radionuclide identified from the spectrum.

10. A device according to any one of the preceding claims, wherein the wall (20) forms an outer or inner wall of a tubular conduit, the chamber extending between the inner wall and the outer wall, the inner and outer walls extending around a central axis, respectively along an inner radius and an outer radius, the inner radius being less than the outer radius.

11. Device according to claim 10, wherein: - all or part of the detection fiber is disposed in the outer wall of the tubular conduit; - the device includes an auxiliary scintillator (10'), disposed in contact with the inner wall, the auxiliary scintillator being connected to an auxiliary photodetector (14').

12. Method for analyzing a fluid (3) using a device (1) according to any one of the preceding claims, the fluid extending into a chamber (2) delimited by the wall (20) of said device, the method comprising: - a) acquisition of detection signals by the or each photodetector (14) during an acquisition period; - b) using the computing unit (16), obtaining an analysis result.

13. A method according to claim 12, wherein step b) comprises: - determining a quantity (N) of charged particles detected per unit time; - comparing the quantity of charged particles detected per unit time with a threshold value (Nth); - based on the comparison, generating an alert signal.

14. A method according to any one of claims 12 or 13, wherein - the processing circuit is a spectrometry circuit, configured to establish a spectrum representative of the energy deposited in the scintillator material by the detected charged particles; - step b) comprises, from the detected spectrum, an identification of the radioelement present in the fluid.

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