Scintillation detector and corresponding detection system

Abstract

The scintillation detector comprises an annular scintillator (40) circumferentially segmented by being formed of a plurality of distinct scintillation elements (42) arranged in a circle around a central axis (A). Each scintillation element (42) is equipped with one or more silicon photomultipliers (60) for detecting photons emitted by the scintillation element (42).

Description

[0001] Scintillation detector and corresponding detection system

[0002] The present invention relates to the field of scintillation detection, in particular for gamma ray detection, for example for the inspection of nuclear fuel rods.

[0003] Nuclear reactors use the energy released by nuclear fission reactions that occur when fissile nuclear fuel is bombarded by neutrons.

[0004] Nuclear fuel generally contains uranium enriched in the isotope 235 to a level that depends on its intended use and the enrichment process. This level typically ranges from 0.2% to 6.5%. However, the composition of nuclear fuel can vary depending on the technology used in the nuclear reactor and / or the nuclear fuel sources used to supply that reactor.

[0005] The preparation of nuclear fuel most often includes a pelletizing step by sintering a nuclear fuel powder, including for example uranium oxides or mixed oxides of uranium and plutonium.

[0006] The pelletizing process is followed by a penciling stage, during which a nuclear fuel rod is formed.

[0007] A nuclear fuel rod, for example, comprises a tubular casing inside which is arranged a stack of nuclear fuel pellets containing a fissile material, for example, a fissile material capable of emitting gamma rays, such as a fissile material containing uranium, in particular uranium dioxide (UO2). A nuclear fuel rod typically has a diameter of around 10 mm and a length of around 2 m to 4.5 m.

[0008] It is advisable to inspect a nuclear fuel rod after its manufacture, in particular to detect any possible defect on a nuclear fuel pellet, requiring for example corrective action, recycling or disposal.

[0009] A defect on a nuclear fuel pellet is likely to affect the amount of gamma rays emitted by the nuclear fuel rod in the section of the nuclear fuel rod in which the nuclear fuel pellet is located.

[0010] It is possible to provide a detection system comprising several scintillation detectors aligned along an alignment axis, each scintillation detector comprising an annular scintillator centered on the alignment axis, photomultipliers arranged at the periphery of the scintillator to detect photons emitted by the scintillator due to the incidence of gamma rays on the scintillator, an acquisition device to acquire measurement signals emitted by the photomultipliers, and a data processing unit to process the measurement signals, in particular to count the number of scintillation events detected and thus determine a quantity of gamma rays emitted by a section of the nuclear fuel rod.

[0011] The scintillator of each gamma ray detector is for example made up of a scintillation crystal, in particular a scintillation crystal made of sodium iodide (NaL) or bismuth germanate (BGO).

[0012] During operation, the nuclear fuel rod is inserted through the scintillation detectors along the alignment axis. A gamma ray emitted by a section of the nuclear fuel rod located opposite one of the scintillation detectors is likely to strike the scintillator of that gamma ray detector and cause the scintillator to emit a photon.

[0013] The photons emitted by the scintillator are detected by the photomultiplier(s) which generate corresponding detection signals which are recovered by the acquisition device which in response generates measurement signals corresponding to the photon count.

[0014] Counting the photons emitted in each section of the nuclear fuel rod makes it possible to detect, after analysis, a possible nuclear fuel pellet that might be defective.

[0015] CN117558479A discloses a gamma ray detection system comprising several gamma ray detectors, each gamma ray detector comprising a shielding body having a central passage extending along a central axis, and a circumferentially segmented annular scintillator formed of several distinct scintillation elements received in the annular shielding body by being arranged in a circle around the central axis, each scintillation element being provided with a tubular photomultiplier having one of its ends optically coupled to that scintillation element.

[0016] However, the detection system disclosed in CN117558479A is designed solely for inspecting nuclear fuel rods containing naturally enriched uranium (NU). Furthermore, maintenance of the detection system is complex and requires dismantling the entire shielding to access any potentially defective scintillation crystals.

[0017] One of the aims of the invention is to provide a gamma ray detector that improves radiation detection and facilitates detection operations. To this end, the invention proposes a scintillation detector comprising a circumferentially segmented annular scintillator formed of several distinct scintillation elements arranged in a circle around a central axis, in which each scintillation element is equipped with one or more silicon photomultiplier tubes to detect photons emitted by the scintillation element.

[0018] The use of one or more silicon photomultipliers makes it possible to extend the possibilities of use of the detection system, in particular by allowing the inspection of nuclear fuel rods containing fuel pellets formed with enriched natural uranium (UNE) or enriched reprocessed uranium (URE) or a mixture of plutonium oxide and uranium oxide (or MOX for "Mixed Oxide").

[0019] In particular embodiments, the scintillation detector includes one or more of the following optional features, taken individually or in all technically possible combinations:

[0020] - the silicon photomultiplier(s) are arranged on an external face of the scintillation element facing radially outwards;

[0021] - each scintillation element is equipped with several silicon photomultipliers distributed in a matrix arrangement on the external face of the scintillation element, for example four photomultipliers distributed in a 2x2 matrix arrangement;

[0022] - the silicon photomultiplier(s) are coupled to an electronic acquisition device;

[0023] - the scintillation elements are distributed uniformly around the central axis, preferably with a rotational symmetry of order N around the central axis, N being the number of scintillation elements in the scintillator;

[0024] - the scintillation detector includes intermediate walls interposed between the scintillation elements;

[0025] - each intermediate wall extends radially;

[0026] - the scintillation detector includes external walls, each external wall extending along an external face of an outwardly facing scintillation element;

[0027] - the photomultiplier(s) arranged on each scintillation element are placed in a window provided in the outer wall;

[0028] - each scintillation element is received in a housing defined by an external wall and two intermediate walls;

[0029] - the scintillation detector is divided into several separable detection modules, each detection module comprising one or more scintillation elements from among the scintillation elements of the scintillator, the detection modules being configured to be selectively separated or assembled to arrange the scintillation elements in a circle around the central axis, the scintillation element(s) of each detection module occupying a respective angular sector around the central axis when the detection modules are assembled;

[0030] - each detection module includes two scintillation elements, three scintillation elements or four scintillation elements or more than four scintillation elements;

[0031] - at least two detection modules, each detection module preferably comprising the same number of scintillation elements as the scintillator;

[0032] - the scintillation detector has two detection modules exhibiting symmetry with respect to a separation plane between the two detection modules;

[0033] - each module includes a shielded collimation wall located on one side of the module's scintillation elements or two shielded collimation walls arranged on either side of the module's scintillation elements;

[0034] - each scintillation element has a general shape of a truncated pyramid with a rectangular base, the scintillation element having an external face turned radially outwards and corresponding to the large base of the truncated pyramid shape and an internal face turned radially inwards and corresponding to the small base of the truncated pyramid shape;

[0035] - each scintillation element is wrapped in a reflective envelope, preferably specular or diffusive;

[0036] - the scintillation detector is configured for the detection of radiation emitted by a nuclear fuel element, in particular a nuclear fuel rod, containing fissile material, the fissile material including for example enriched natural uranium (UNE), enriched reprocessed uranium (URE) and / or a mixture of plutonium oxide and uranium oxide (or MOX for "Mixed Oxide").

[0037] The invention also relates to a detection system comprising a scintillation detector as defined above or several scintillation detectors as defined above, the scintillation detectors being aligned along an alignment axis, the central axis of each scintillation detector coinciding with the alignment axis.

[0038] The invention and its advantages will be better understood upon reading the following description, given solely by way of non-limiting example and with reference to the accompanying drawings, in which:

[0039] - Figure 1 is a schematic side view of a detection system comprising several scintillation detectors, allowing for example the inspection of a nuclear fuel rod; - Figures 2 and 3 are front views of a modular construction scintillation detector respectively in an assembled configuration and in a separate configuration;

[0040] - Figure 4 is a view similar to that of Figure 2, after removal of shielded collimation walls;

[0041] - Figures 5 and 6 are front views of a subset of a detection module of the scintillation detector of Figure 2, comprising a positioning device, scintillation elements carried by the positioning device, and photomultipliers, respectively in an assembled configuration and an exploded configuration;

[0042] - Figures 7 and 8 are front and side views of a scintillation element; - Figure 9 is a bottom view of the scintillation element on which photomultipliers are arranged;

[0043] - Figure 10 is a cross-sectional view of the scintillation element along X - X in Figure 9, illustrating a coating surrounding the scintillation element; and

[0044] Figure 11 is a side view of the positioning device shown in Figures 5 and 6. The detection system 10 illustrated in Figure 1 is configured for the detection of radiation emitted by an object to be inspected 12, a gamma-ray emitter, either naturally or after activation. The object to be inspected 12 is, for example, elongated. Only a section of the end of the object to be inspected is shown in Figure 1.

[0045] The object to be inspected 12 is for example a nuclear fuel rod comprising a tubular sheath 14 closed at its ends by plugs 16 and containing a stack of nuclear fuel pellets 18 made of a fissile material.

[0046] The composition of the object to be inspected, a gamma radiation emitter, may or may not be known a priori.

[0047] The fissile isotope of interest is advantageously uranium 235 ( 235 U).

[0048] The fissile material contains, for example, enriched natural uranium (UNE) comprising uranium 235 ( 235 U). The fissile material may also include other chemical elements, notably radioactive decay products of uranium-238 ( 238 U).

[0049] The fissile material contains, for example, reprocessed enriched uranium (REU) comprising uranium-232 ( 232 U). Fissile material may also include other chemical elements, notably radioactive decay products of uranium 232. Fissile material contains, for example, a mixture of plutonium oxide (PUO2) and uranium oxide (UO2) also called MOX for "Mixed Oxide".

[0050] The fissile material may contain naturally enriched uranium (UNE), reprocessed enriched uranium (URE) and / or a mixture of plutonium oxide and uranium oxide (or MOX for "Mixed Oxide").

[0051] The detection system 10 is configured for the detection of gamma rays emitted by the object to be inspected 12.

[0052] The detection system 10 comprises one or more scintillation detectors 20 aligned along an alignment axis B.

[0053] Each scintillation detector 20 has an insertion orifice 22 for the passage of the object to be inspected 12 through the scintillation detector 20 along a central axis A. The central axis A of each scintillation detector 20 coincides with the alignment axis B. The insertion orifices 22 are aligned along the alignment axis B.

[0054] During the inspection, the object to be inspected is, for example, passed through the insertion holes 22 of the scintillation detectors 20 along the alignment axis B.

[0055] The detection system 10 advantageously includes a guide tube 24 extending through the insertion holes 22 of the scintillation detectors 20. The guide tube 24 facilitates the passage of the object to be inspected 12 through the insertion holes 22 of the scintillation detectors 20, avoiding any mechanical interference of the object to be inspected 12 with the edges of the insertion holes 22.

[0056] Each scintillation detector 20 is configured to provide measurement signals representative of scintillation events detected by the scintillation detector 20, in particular measurement signals representative of a number of scintillation events detected, themselves representative of a number of events from the section of the object to be inspected 12.

[0057] The inspection system 10 includes a data processing unit 26 connected to each scintillation detector 20 to receive the measurement signals provided by the scintillation detector 20.

[0058] The data processing unit 26 includes, for example, a measurement module 28 configured to process measurement signals.

[0059] The measurement module 28 is configured for example to record the measurement signals provided by the scintillation detectors 20 as a function of a position of the object to be inspected 12 along the alignment axis B.

[0060] This allows the scintillation events detected by the scintillation detectors 20 to be associated with each segment of the object to be inspected 12 when the object is moved along the alignment axis B during the inspection. Moving the object to be inspected 12 along the alignment axis B during the inspection allows, for example, several objects to be inspected successively.

[0061] The measurement module 28 is, for example, a software application comprising computer code instructions for processing measurement signals, stored in a computer memory 30 of the data processing unit 26 and executable by a processor 32 of the data processing unit 26.

[0062] Alternatively, the measurement module 28 is a programmable logic component, for example an in situ programmable gate array (or FPGA for "Field Programmable Gate Array") or a specific integrated circuit (or ASIC for "Application Specific Integrated Circuit") or a microcontroller (or MCU for "Micro Controller Unit").

[0063] The scintillation detectors 20 are similar. Only one of the scintillation detectors 20 will be described in more detail later with reference to Figures 2 to 11.

[0064] As illustrated in Figures 2 and 3, the scintillation detector 20 is of modular construction. The scintillation detector 20 is made up of several detection modules 34 configured to be selectively assembled (Figure 2) or separated (Figure 3).

[0065] In the following, orientation terms such as "axially" and "radially" extend with reference to the central axis A of the scintillation detector 20 when the detection modules 34 are assembled.

[0066] As illustrated in Figures 2 and 3, the detection modules 34 are preferably configured so that the detection modules 34 extend in respective angular sectors around the insertion orifice 22.

[0067] Each detection module 34 is for example separable from the other detection module(s) 34 of the scintillation detector 20 along a radial separation direction relative to the central axis of the scintillation detector 20, as illustrated by the arrows S in Figure 3.

[0068] The detection modules 34 are preferably configured so that each detection module 34 can be separated from the other detection modules 34 in a radial direction without interfering with the guide tube 24 passing through the insertion orifice 22.

[0069] Each detection module 34 has either a single shielded collimation wall 36 located on one side of the detection module 34 or two shielded collimation walls 36 located on either side of the detection module 34. One shielded collimation wall 36 of each detection module 34 is visible in the front views of Figures 2 and 3.

[0070] In some examples, when traversing the alignment of detection devices 20 from one end to the other, apart from the detection modules 34 of the last detection device 20 of the detection system 10, the detection modules 34 of the detection devices 20 each have a single shielded collimation wall 36, located on the same side for all detection modules 34. The shielded collimation wall 36 of each detection module 34 of a subsequent detection device 20 acts as shielding for the adjacent detection module 34 of the preceding detection device 20, which lacks such shielding on the side of the detection module 34 of the following detection device 20. For example, the detection modules 34 of the last detection device 20 each have two shielded collimation walls 36 located on either side of the detection module 34.

[0071] In other examples, each detection module 36 of each detection device 20 of the detection system 10 has two shielded collimation walls 36 located on either side of the detection module 34.

[0072] Each shielded collimation wall 36 extends for example in a radial plane perpendicular to the central axis A when the detection modules 34 are assembled.

[0073] The shielded collimation walls 36 oppose the passage of rays likely to generate scintillation of the scintillation detector, in particular the passage of gamma rays.

[0074] Each shielded collimation wall 36 prevents rays from a radiation source other than the section of the object to be inspected 12 located axially at the right of the scintillation detector 20 from striking a scintillator of the scintillation device 20.

[0075] Thus, the scintillation device 20 detects only the radiation from the section of the object to be inspected 12 located axially opposite the scintillation detector 20.

[0076] As illustrated in Figure 4, representing the scintillation detector 20 without the shielded collimation walls 36, the scintillation detector 20 comprises an annular scintillator 40 centered on the central axis A.

[0077] The annular scintillator 40 is susceptible to being struck by radiation originating from the central axis A and in all radial directions.

[0078] The scintillator 40 is segmented circumferentially. The scintillator is formed of several scintillation elements 42 distributed in a circle around the central axis A, preferably uniformly.

[0079] Each scintillation element 42 defines a circumferential segment of the scintillator 40. Each scintillation element 42 extends in a respective angular sector around the central axis A.

[0080] Each detection module 34 comprises one or more scintillation elements 42, the detection modules 34 being configured to be selectively separated or assembled to arrange the scintillation elements 42 in a circle around the central axis A to form the annular scintillator 40, the scintillation element(s) 42 of each detection module 34 occupying a respective angular sector around the central axis A.

[0081] The scintillation detector 20 comprises at least two detection modules 34, for example two detection modules 34, three detection modules 34, four detection modules 34 or more than four detection modules 34. As illustrated in Figures 2 and 3, in examples, the scintillation detector 20 is formed of two detection modules 34.

[0082] Each detection module 34 includes, for example, half of the scintillation elements 42 constituting the scintillator 40. The scintillation elements 42 of each of the two detection modules 34 cover, for example, an angular sector of 180° around the central axis A.

[0083] Advantageously, the 34 detection modules exhibit symmetry with respect to a median axial plane P.

[0084] Each scintillation element 42 consists of a scintillation crystal. The scintillation crystal is designed, for example, for the detection of gamma rays. Examples of scintillation crystals include sodium iodide (Na₂), bismuth germanate (BGO), lanthanum bromide (LaBrs), ultrapure germanium (HPGe), or yttrium orthosilicate (YSO₄).

[0085] The scintillation elements 42 are preferably made of the same material. When the detection modules 34 are assembled, the scintillation elements 42 preferably have a rotational symmetry of order N about the central axis A, N being the number of scintillation elements 42 in the scintillator 40.

[0086] Due to the statistical nature of scintillation radiation measurement, such symmetry is desirable to ensure similar measurement of rays emitted in different radial directions relative to the central axis A.

[0087] The scintillator 40, for example, has a general regular polygonal shape whose number of sides is equal to the number N of scintillation elements 42.

[0088] The number N of scintillation elements 42 in scintillator 40 is, for example, equal to six. Scintillator 40 has, for example, a general hexagonal shape.

[0089] Alternatively, the number N of scintillation-42 elements is not six. For example, it is four, five, seven, eight, nine, ten, eleven, or twelve. The number N of scintillation-42 elements is preferably even. Alternatively, the number N of scintillation-42 elements is odd.

[0090] Each detection module 34 includes a module support 44, with the scintillation element(s) 42 of the detection module 34 being supported by the module support 44. The module supports 44 of the detection modules 34 are configured for removable assembly. The module supports 44 are assembled to join the detection modules 34 and form the scintillation detector 20 (Figures 2 and 4) or separated (Figure 3), for example, to remove a detection module 34 on which operators wish to perform maintenance.

[0091] As illustrated in Figures 4 to 9, each scintillation element 42 comprises an inner face 46 facing radially inwards and an outer face 48 facing radially outwards. The inner face 46 and the outer face 48 are opposite.

[0092] The internal face 46 is for example planar, the normal to the internal face 46 being radial relative to the central axis A. Alternatively, the internal face 46 is non-planar, in particular curved, being concave or convex.

[0093] The external face 48 is for example flat, the normal to the external face 48 being radial relative to the central axis A.

[0094] Each scintillation element 42 comprises, for example, two opposite lateral faces 50, each lateral face 50 extending along an axial plane defined by the central axis A and a radial direction relative to the central axis A.

[0095] The two lateral faces 50 are inclined relative to each other. The angle of inclination a is, for example, approximately equal to 2TT / N, where N is the number of scintillation elements 42 in the scintillator 40.

[0096] Each scintillation element 42 comprises, for example, two opposing front faces 52, each front face extending along a radial plane perpendicular to the central axis A. Each front face 52 is axially rotated on one side.

[0097] Each scintillation element 42 includes, for example, an inclined face 54 (Figure 8) at the junction between each front face 52 and the inner face 46.

[0098] Each scintillation element 42, for example, has a truncated pyramid shape with a rectangular base, the small base being formed by the inner face 46 and the large base being formed by the outer face 48, the sides of the pyramid being formed by the lateral faces 50 and the front faces 52.

[0099] As illustrated in Figure 9, each scintillation element 42 is equipped with one or more photomultipliers 60, preferably one or more silicon photomultipliers 60, arranged on the external face 48 of the scintillation element 42.

[0100] Each photomultiplier 60 is configured to detect photons emitted by the scintillation element 42 when radiation strikes the scintillation element 42.

[0101] Each silicon photomultiplier 60 (or SiPM for "Silicon Photomultiplier") comprises a silicon substrate on which single-photon avalanche diodes (or SPADs for "Single-Photon Avalanche Diode") are formed. Preferably, each scintillation element 42 is equipped with one or more photomultipliers 60 distributed according, for example, in a matrix arrangement on the outer face 48 of the scintillation element 42.

[0102] Each scintillation element 42 is for example equipped with four photomultipliers 60 distributed according to a 2x2 matrix distribution on the external face 48 which is preferably rectangular.

[0103] Each photomultiplier 60 is for example glued onto the scintillation element 42, in particular on the external face 48 of the scintillation element, preferably with a transparent epoxy glue.

[0104] The adhesive is chosen to ensure satisfactory optical coupling between the photomultiplier 60 and the scintillation element 42. A transparent epoxy adhesive generally provides satisfactory coupling.

[0105] As illustrated in Figure 10, each scintillation element 42 is for example surrounded by a reflective envelope 64 configured to reflect light propagating inside the scintillation element 42. The reflective envelope 64 is preferably specular and / or diffusive, i.e. formed of a specular and / or diffusive reflective material.

[0106] The reflective envelope 64 has one or more openings 66 through which the photomultiplier(s) 60 are applied against the scintillation element 42, in particular on the outer face 48 of the scintillation element 42.

[0107] In operation, the reflective envelope 64 promotes the reflection of the light generated in the scintillation element 42 inside the scintillation element 42 until the light reaches a photomultiplier 60.

[0108] As illustrated in Figures 4 to 6, each scintillation element 42 is equipped with an electronic acquisition device 62 connected to the photomultiplier(s) 60 applied to the scintillation element 42, the electronic acquisition device 62 being configured to generate measurement signals from detection signals provided by the photomultiplier(s) 60.

[0109] The electronic acquisition device 62 includes, for example, a printed circuit board with photomultiplier reception areas 60.

[0110] Each detection module 34 advantageously includes a positioning device 70 configured to maintain each scintillation element 42 of the detection module 34 in a determined position.

[0111] The positioning device 70 includes, for example, a receiving housing 72 respective for each scintillation element 42 of the detection module 34.

[0112] The positioning device 70 preferably includes intermediate walls 74 interposed between the scintillation elements 42. The intermediate walls of the positioning device 70 are preferably configured to prevent the light generated by each scintillation element 42 of the detection module 34 from propagating to another scintillation element 42. This promotes the exit of light towards the photomultiplier(s) arranged on the scintillation element 42, in particular on its outer face 48.

[0113] The positioning device 70 preferably includes intermediate walls 74 interposed between the scintillation elements 42.

[0114] Each reception accommodation 72 is preferably delimited between two intermediate walls 74.

[0115] Each intermediate wall 74 extends along an axial plane defined by the central axis A and a radial axis. Each intermediate wall 74 extends, for example, radially by being flat or radially corrugated.

[0116] The two intermediate walls 74 delimiting each reception housing 72 are close to each other on the inside (near the central axis A) and far apart on the outside (opposite the central axis A).

[0117] The distance between the two intermediate walls 74 increases from the center towards the periphery of the scintillation detector 20. Each receiving housing 72 widens from the central axis A towards the periphery of the scintillation detector 20.

[0118] The positioning device 70 comprises external walls 76, each external wall 76 closing a respective receiving housing 72 radially outwards.

[0119] Each external wall 76 is for example flat and extends along an orthoradial plane, i.e. a plane whose normal extends radially relative to the central axis A.

[0120] The external walls 76 define a polygonal shape, preferably regular, in view along the central axis A. In the illustrated example, the polygonal shape is a regular hexagon.

[0121] The intermediate walls 74 extend radially inwards from the vertices of the polygonal shape and delimit the reception housings 72 between each other.

[0122] The inner edges of the two intermediate walls 74 delimiting the same receiving housing 72 define between them an opening 78. The inner face 46 of the scintillation element received in the receiving housing 72 extends across the opening 78.

[0123] As illustrated in Figure 11, each external wall 76 is for example provided with a window 80 allowing the electronic acquisition device 62 to be applied against the external face 48 and in connection with the photomultiplier(s) 60 of the scintillation element 20, through the external wall 76.

[0124] The window 80 advantageously presents a contour complementary to that of the electronic acquisition device 62. The positioning device 70 is preferably of modular construction and divided into separation modules, each separation module belonging to a respective detection module 34.

[0125] As can be seen in Figure 4, the module support 44 of each detection module 34 includes, for example, an armature 82.

[0126] The frame 82 defines the load-bearing structure of the detection module 34. The frame 82 defines, for example, a support foot 84 through which the detection module 34 can be placed on a surface.

[0127] The positioning device 70 receiving the scintillation elements 42 of the detection module 34 is fixed on the frame 82.

[0128] In Figure 5, the positioning device 70, the scintillation elements 42 and the electronic acquisition devices 62 of a detection module 34 are illustrated without the armature 82 (which is not shown) and in an assembled configuration.

[0129] In Figure 6, the positioning device 70, the scintillation elements 42 and the electronic acquisition devices 62 are illustrated in an exploded configuration.

[0130] In operation, the detection system 10 is set up by aligning the detection devices 20, each scintillation detector 20 being formed by assembling its detection modules 34. A guide tube 24 is preferably inserted through the aligned insertion holes 22 of the scintillation detectors 20.

[0131] The detection system 10 comprises, for example, at least ten aligned detection devices 20, preferably at least fifteen aligned detection devices 20, and in particular at least twenty aligned detection devices 20. It is possible to use more than twenty aligned detection devices 20, for example between twenty and fifty aligned detection devices 20, and in particular thirty or forty aligned detection devices 20.

[0132] An object to be inspected, 12, emitting radiation, is inserted into the passage delimited by the insertion holes 22.

[0133] Each scintillation detector 20 detects the radiation from the section of the object to be inspected 12 located axially opposite the scintillation detector 20. A radiation emitted by this section and striking one of the scintillation elements 20, which generates in response a photon, is detected by a photomultiplier 60 which generates a detection signal which is received by the electronic acquisition device 62 and transmitted to the measurement module 28.

[0134] In practice, each radiation does not generate a photon and each photon is not detected by a photomultiplier 60, but the detected photons make it possible to determine a value of the radiation of the section of the object to be inspected 12. The measurement signals provided by the electronic acquisition devices 62 are processed by the measurement module 26 according to the position of the object to be inspected 12 along the alignment axis B, so as to add the radiations emitted by the same section of the object to be inspected 12 with regard to the different scintillation detectors 20.

[0135] The circumferential segmentation of the scintillator into scintillation elements allows for better collection of the light emitted by each scintillation element during the occurrence of a scintillation event, and thus a better accuracy in the measurement of each scintillation event.

[0136] For any scintillation system, when a beam strikes the scintillator, the number of visible photons emitted is proportional to the beam's energy. This light propagates throughout the scintillator and eventually reaches the photomultiplier tube. The more complex the scintillator's geometry, the more internal reflections occur before the light is extracted to the photomultiplier tube. This phenomenon is particularly concerning for high-density scintillators like BGO, as these materials typically have a very high refractive index, further increasing the likelihood of internal reflection.

[0137] The circumferential segmentation of the scintillator allows the light from each scintillation event to propagate through only a fraction of the scintillator's volume.

[0138] The intermediate walls of the separation device interposed between the scintillation elements allow light to be guided by the external face of the scintillation element on which the photomultiplier(s) is or are placed.

[0139] The circumferential segmentation of the scintillator in combination with the use of silicon photomultipliers allows a high counting rate and thus enables the inspection of high emissivity objects.

[0140] The dynamics of a scintillation detector are limited by two factors: the intrinsic capabilities of the scintillator and the capabilities of the photomultiplier.

[0141] Regarding scintillator capabilities, light is emitted by a scintillation event triggered by a gamma ray in a BGO scintillator on a timescale of approximately 1 ps (the decay time is 317 ns). When the gamma ray flux in the scintillator is high, there may be some overlap between scintillation events. This overlap reduces the linearity of the scintillation detector's count rate and decreases the accuracy of the energy analysis. A general best practice recommendation for the BGO is to keep the count rate below 50,000 events / second.The isolated light signals in the segmented scintillator give the scintillation detector good linearity up to 50,000 events / second per scintillation element, which means that the overall capacity of the detector can be increased to 300,000 events / second thanks to the segmentation of the scintillator.

[0142] Unlike other photomultiplier tubes that exhibit dynode saturation, silicon photomultiplier tubes do not include a dynode and can operate at 50,000 events / s without any decrease in counting linearity or energy analysis accuracy. The absence of a dynode also protects silicon photomultiplier tubes from the rapid aging that can occur with dynode-based photomultiplier tubes.

[0143] The scintillation detector also allows for a rapid inspection of each object to be inspected.

[0144] Preferably, the detection system 10 is configured to allow a linear inspection speed of 200 mm / s, preferably a linear inspection speed of 400 mm / s, in particular a linear inspection speed of 440 mm / s.

[0145] Due to the segmentation of the scintillation detector, the use of photomultiplier tubes would require long tubes, between 10 cm and 20 cm. This would affect the size and weight of the detection device.

[0146] Silicon photomultipliers allow detection with sufficient sensitivity while having a high compactness favorable to the compactness of each scintillation detector.

[0147] The scintillation detector should ideally be installed in a thick shielded enclosure to prevent interference from ambient factory activity. A more compact design allows for a smaller, lighter, and less expensive shielded enclosure.

[0148] Dividing the scintillation detector into separable detection modules that can be assembled to form the scintillation detector makes it easier to perform maintenance operations on the scintillation detector or on a detection system comprising one or more scintillation detectors.

[0149] It is possible to remove a scintillation detector's detection module without removing the other scintillation detector module(s), particularly when each detection module can be separated from the other module(s) along a radial separation direction relative to the module's central axis. Since each detection module incorporates one or more scintillation elements, it is possible to remove a module with a defective scintillation element without removing the other module(s). A defective detection module can be replaced with a non-defective one to continue using the scintillation detector.

[0150] The modularity of the scintillation detector allows for easy access and maintenance of the photomultipliers.

Claims

DEMANDS 1. Scintillation detector comprising a circumferentially segmented annular scintillator (40) formed of several distinct scintillation elements (42) arranged in a circle around a central axis (A), in which each scintillation element (42) is equipped with one or more silicon photomultipliers (60) to detect photons emitted by the scintillation element (42).

2. Scintillation detector according to claim 1, in which the silicon photomultiplier(s) (60) are arranged on an external face (48) of the scintillation element (42) facing radially outwards.

3. Scintillation detector according to claim 2, wherein each scintillation element (42) is equipped with several silicon photomultipliers (60) distributed in a matrix arrangement on the external face (48) of the scintillation element, for example four photomultipliers distributed in a 2x2 matrix arrangement.

4. Scintillation detector according to any one of the preceding claims, wherein the silicon photomultiplier(s) (60) are coupled to an electronic acquisition device (62).

5. Scintillation detector according to claim 4, wherein the scintillation elements (42) are distributed uniformly around the central axis (A), preferably with a rotational symmetry of order N around the central axis, N being the number of scintillation elements (42) of the scintillator (40).

6. Scintillation detector according to any one of the preceding claims, comprising intermediate walls (74) interposed between the scintillation elements (42).

7. Scintillation detectors according to claim 6, wherein each intermediate wall (74) extends radially.

8. Scintillation detector according to any one of the preceding claims, comprising external walls (76), each external wall (76) extending along an external face (48) of an outwardly facing scintillation element (42).

9. Scintillation detector according to claim 8, wherein the photomultiplier(s) (60) arranged on each scintillation element (42) are arranged in a window provided in the outer wall (76).

10. Scintillation detector according to claim 6 or 7 in combination with claim 8 or 9, wherein each scintillation element (42) is received in a housing (72) defined by an outer wall (76) and two intermediate walls (74).

11. Scintillation detector according to any one of the preceding claims, wherein the scintillation detector (20) is divided into several separable detection modules (34), each detection module (34) comprising one or more scintillation elements (42) from among the scintillation elements (42) of the scintillator (40), the detection modules (34) being configured to be selectively separated or assembled to arrange the scintillation elements (42) in a circle around the central axis (A), the scintillation element(s) (42) of each detection module (34) occupying a respective angular sector around the central axis (A) when the detection modules (34) are assembled.

12. Scintillation detector according to claim 11, wherein each detection module (34) comprises two scintillation elements (42), three scintillation elements (42) or four scintillation elements (42) or more than four scintillation elements (42).

13. Scintillation detector according to claim 11 or 12, comprising at least two detection modules (34), each detection module preferably comprising the same number of scintillation elements (42) of the scintillator (20).

14. Scintillation detector according to any one of claims 11 to 13, having two detection modules (34) having symmetry with respect to a separation plane (P) between the two detection modules (34).

15. Scintillation detector according to any one of claims 11 to 14, wherein each module (34) comprises a shielded collimation wall (36) located on one side of the scintillation elements (42) of the module (34) or two shielded collimation walls (36) arranged on either side of the scintillation elements (42) of the module (34).

16. Scintillation detector according to any one of the preceding claims, wherein each scintillation element (42) has a general shape of a truncated pyramid with a rectangular base, the scintillation element (42) having an external face (48) facing radially outwards and corresponding to the large base of the truncated pyramid shape and an internal face (46) facing radially inwards and corresponding to the small base of the truncated pyramid shape.

17. Scintillation detector according to any one of the preceding claims, wherein each scintillation element (42) is wrapped in a reflective envelope (64) preferably specular or diffusive.

18. Scintillation detector configured for the detection of radiation emitted by a nuclear fuel element, in particular a nuclear fuel rod, containing fissile material, the fissile material including for example enriched natural uranium (UNE), enriched reprocessed uranium (URE) and / or a mixture of plutonium oxide and uranium oxide (or MOX for "Mixed Oxide").

19. Detection system comprising a scintillation detector according to any one of claims 1 to 17 or several scintillation detectors according to any one of claims 1 to 17, the scintillation detectors being aligned along an alignment axis, the central axis of each scintillation detector coinciding with the alignment axis.

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