Device and method for detection of boron blockage in a conduit for the passage of borated water

Abstract

The invention relates to a device (1) for detection of boron blockage in a conduit (C) for the passage of borated water, characterized in that the device comprises a neutron emission source (2), a neutron detector (3), a support (4), a measurement counter (5) supplying a measurement of boron blockage according to a measurement of the number of neutrons that are detected by the detector (3), the support (4) being able to keep the detector (3) oriented towards the source (2), so that the path distance (D) travelled by the neutrons from the source (2) to the detector (3) can be occupied at least in part by the conduit (C).

Description

[0001] DESCRIPTION

[0002] TITLE: Device, method for detecting boron clogging in a borated water passage pipe

[0003] The invention relates to a device and a method for detecting boron clogging in a borated water passage pipe.

[0004] The field of the invention concerns nuclear power plants for producing electricity.

[0005] The operation of a pressurized water nuclear reactor in such power plants requires, on the one hand, an investment in fissile material, and on the other hand, cooling with water called "coolant". This water in the reactor also acts as a neutron slower, which causes the fission of heavy nuclei (Uranium, Plutonium, etc.) in the reactor core. This water contains boron. Boron is a neutron-absorbing material and is intended for reactivity control, that is, for controlling neutron generation, which increases by reducing the proportion of boron or decreases by increasing it.

[0006] One of the problems associated with the use of borated water in reactors is that boron tends to crystallize in the pipes through which borated water passes. Thus, the presence of boron in reactor water inevitably leads to the formation of boron plugs in the various pipes of the various borated water circuits involved.

[0007] To solve this problem, nuclear power plant operators carry out flushing and line-up to determine the blocked section of pipe. If the flushing is not sufficient, sections of pipe are cut and welded on larger or smaller sections of pipe.

[0008] However, these interventions have many disadvantages, due to the fact that they generate pipe waste (large sections of pipe removed because the location of the plug is not precisely known), study and project management costs, costs of supplying ESPN (Nuclear Pressure Equipment) qualified pipes, significant dosimetric costs (welder, logistics, insulator, etc.), a dosimetric risk due to Gamma shots (non-destructive testing process generating a high dose equivalent rate) intended to control the quality of the welding carried out.

[0009] It is also possible to use thermal imaging cameras or endoscopes in the pipework in some cases for inspection, but these devices cannot be used in all pipework, for example due to the pipework being too small, or the room temperature being high, and have the disadvantages mentioned below.

[0010] The endoscope allows a view of the inside of the pipes, but has the following disadvantages: the endoscope requires intervention on the pipes in order to open the borated water circuit and pass the endoscope cable, which is expensive; the pipe diameters mainly affected by boron plugs are too small to be able to pass an endoscope, the presence of several pipe bends does not allow the entire pipes to be inspected.

[0011] Thermal imaging cameras are used to determine if a portion of the heat tracing (the resistor that maintains a sufficient temperature to prevent boron from crystallizing) is defective. If the problem is not with the heat tracing (or if it is simply slightly detached from the pipe), the accuracy of the thermal imaging camera does not allow it to determine the portion of the pipe likely to contain the clogging boron.

[0012] An objective of the invention is to obtain a device and a method for detecting boron clogging in a borated water passage pipe, which overcome the drawbacks mentioned above.

[0013] To this end, a first object of the invention is a device for detecting boron clogging in a borated water passage pipe, characterized in that the device comprises at least one neutron emission source, at least one neutron detector, a support, to which the neutron emission source and the neutron detector are fixed, a measurement counter connected to the neutron detector, configured to provide a boron clogging measurement according to a measurement of the number of neutrons detected by the neutron detector, the support being capable of keeping the neutron detector oriented towards the neutron emission source and with a non-zero neutron path distance from the neutron emission source to the neutron detector, so that the determined neutron path distance from the neutron emission source to the neutron detector can be occupied at least in part by the borated water passage pipe.

[0014] A passage pipe is understood to mean a borated water passage pipe, which may or may not be equipped with heat insulation. The invention thus allows an improvement by allowing precise location of boron plugs in the pipes; said plugs can partially or completely obstruct the borated water passage section of said passage pipe. The invention thus advantageously makes it possible to save money (time, budget and dosimetry) and to implement preventive treatments, and to avoid complete blockages, which is a significant advantage for the operator of a nuclear power plant. The invention makes it possible to locate boron plugs or boron clogging in the pipe in service in order to continue transporting borated water, i.e. without having to interrupt the sending of borated water into the pipe.

[0015] According to one embodiment of the invention, the measurement counter comprises a display of a counting rate of neutrons received, detected by the neutron detector.

[0016] Depending on the intervention conditions, the information processing can be carried out live, at the time of the measurement, or delayed in a location distant from the measurement.

[0017] According to one embodiment of the invention, the neutron detector comprises a scintillator, capable of transforming the received neutrons into a light signal, and a photodetector, capable of providing the measurement of the number of neutrons detected by the neutron detector in the form of an electrical signal of the counting rate of neutrons received as a function of the light signal from the scintillator.

[0018] According to one embodiment of the invention, the neutron detector is an ionization chamber containing a gas, capable of transforming the neutrons received into an electrical signal of the counting rate of neutrons received.

[0019] According to one embodiment of the invention, the support comprises a system for measuring the travel distance of the neutrons from the neutron emission source to the neutron detector.

[0020] According to one embodiment of the invention, the support comprises a first arm, to which the neutron emission source is fixed, and a second arm, to which the neutron detector is fixed, the first arm being mounted to move relative to the second arm, to vary the distance between the neutron emission source and the neutron detector, the support comprising a clamping system to immobilize the first arm relative to the second arm and to fix the path distance of the neutrons from the neutron emission source to the neutron detector. According to one embodiment of the invention, the first arm is mounted to slide relative to the second arm in a determined direction of separation going from the neutron emission source to the neutron detector.

[0021] According to one embodiment of the invention, the second arm comprises a rack having a guide opening extending along the determined spacing direction, the first arm comprises a tab inserted into the guide opening, the tab being able to slide along the determined spacing direction in the guide opening when the clamping system is in a loosening position, the clamping system having a clamping position, in which the tab is immobilized in the guide opening.

[0022] According to one embodiment of the invention, the system for measuring the path distance of the neutrons from the neutron emission source to the neutron detector comprises distance graduations, which are distributed on the rack along the determined spacing direction.

[0023] According to one embodiment of the invention, the clamping system comprises a clamping screw, which is arranged on the lug, which is capable of being clamped against the rack in the clamping position and which is capable of being loosened from the rack in the loosening position.

[0024] According to one embodiment of the invention, the support comprises, in front of a first front side of the neutron emission source, oriented towards the neutron detector, a neutron collimator for concentrating the neutrons in a direction of orientation of the neutron emission source towards the neutron detector.

[0025] According to one embodiment of the invention, the support comprises, at least in front of a first front side of the neutron emission source, oriented towards the neutron detector, a material for slowing down neutrons in a prescribed range of kinetic energy, the measurement of the number of neutrons detected by the neutron detector being chosen for the neutrons detected by the neutron detector being in the prescribed range of kinetic energy.

[0026] According to one embodiment of the invention, the prescribed range of kinetic energy is thermal and / or epithermal. According to one embodiment of the invention, the prescribed range of kinetic energy is greater than or equal to 10' 8 MeV and is less than or equal to 10' 1 MeV.

[0027] According to one embodiment of the invention, the neutron slowing material is high density polyethylene (HDPE) and / or paraffin.

[0028] According to one embodiment of the invention, the neutron slowing material is arranged all around the neutron emission source.

[0029] According to one embodiment of the invention, the support comprises all around the neutron emission source at least one neutron absorption wall, comprising in front of a first front side of the neutron emission source, oriented towards the neutron detector, an opening allowing the passage of neutrons in a direction of orientation of the neutron emission source towards the neutron detector.

[0030] According to one embodiment of the invention, the neutron detector comprises a second front side, which is oriented towards the neutron emission source in an orientation direction, and a rear side, which is further from the neutron emission source in the orientation direction than the second front side of the neutron detector, the support comprises at least one other neutron absorption wall at least on the rear side of the neutron detector.

[0031] According to one embodiment of the invention, the support comprises all around the neutron detector at least one other neutron absorption wall, comprising in front of the second front side, which is oriented towards the neutron emission source in an orientation direction, another opening, which is arranged between the second front side of the neutron detector and the neutron emission source and which allows the passage of neutrons in the orientation direction of the neutron emission source towards the neutron detector.

[0032] According to one embodiment of the invention, the neutron absorption wall and / or the other neutron absorption wall is made of cadmium and / or hafnium and / or gadolinium.

[0033] According to one embodiment of the invention, the support comprises a first surface for centering the pipe, located on the side of the neutron emission source and configured so that a direction of orientation of the neutron emission source towards the neutron detector meets an axis of revolution of the pipe, and the support comprises a second surface for centering the pipe, located on the side of the neutron detector and configured so that a direction of orientation of the neutron emission source towards the neutron detector meets an axis of revolution of the pipe.

[0034] A second subject of the invention is a method for detecting boron clogging in a borated water passage pipe using the boron clogging detection device as described above, characterized in that the method comprises the following steps: positioning the neutron emission source and the neutron detector on either side of the borated water passage pipe, so that the determined neutron path distance from the neutron emission source to the neutron detector is occupied at least in part by the borated water passage pipe, switching on the neutron detector, providing by the measurement counter connected to the neutron detector, a boron clogging measurement according to a measurement of the number of neutrons detected by the neutron detector.

[0035] The invention will be better understood upon reading the description which follows, given solely by way of non-limiting example with reference to the figures below of the attached drawings.

[0036] Figure 1 represents a schematic perspective view of a boron clogging detection device according to one embodiment of the invention.

[0037] Figure 2 represents a schematic sectional view of a boron clogging detection device according to one embodiment of the invention.

[0038] Figure 3A represents neutron flux energy spectra, obtained by Monte Carlo modeling of the boron clogging detection device according to an embodiment of the invention, for different thicknesses of boron deposit layers in a pipeline.

[0039] Figure 3B represents an enlarged view of Figure 3A, for the neutron flux energy spectra, obtained by Monte Carlo modeling of the boron clogging detection device according to an embodiment of the invention, for different thicknesses of boron deposit layers in a pipeline.

[0040] Figure 4 represents a flowchart of a boron clogging detection method according to one embodiment of the invention. In Figures 1 and 2, the boron clogging detection device 1 and the boron clogging detection method according to the invention make it possible to detect boron CCB plugs or boron CCB deposits (any isotope) in a pipe C for the passage of borated water. A boron CCB plug or boron CCB clogging refers to any boron coagulation that can take any form and can totally or partially occupy the section of passage of borated water in the pipe C. The boron clogging detection device 1 may, for example, be removable relative to the pipe C for the passage of borated water.

[0041] Pipeline C can be any water passage pipe containing boron, which can be in a nuclear power plant or any other facility using borated water. In such a plant, pipeline C can be, for example, the wastewater treatment pipes, the primary effluent treatment pipes, the borated water make-up pipes, the safety injection pipes for the reactor (boron injection). These pipes are borated water circuits connected to the primary circuit of the nuclear power plant including the pressurized water nuclear reactor. The pipes of the facilities concerned have various diameters and lengths. Typically, the diameters of these pipes are on the order of 5 mm to 150 mm on average, and lengths of the order of one meter to fifteen meters.Around the pipe C for the passage of borated water, a heat-insulating layer C2 may be provided, itself covered with a metallic casing C3, for example made of stainless steel or galvanized, in order to keep the pipe C at a temperature making it possible to combat the crystallization of the boron contained in the fluid transported by the pipe C. The pipe C may, for example, extend around an axis Y of revolution and may, for example, be circularly cylindrical around this axis Y of revolution. The boron clogging detection device 1 comprises a neutron emission source 2 and one (or more) neutron detectors 3, which are fixed to a support 4.When the edge clogging detection device is used on the pipe C, the support 4 keeps the neutron detector 3 oriented towards the neutron emission source 2 with a free range D or distance D, non-zero, of neutron path from the neutron emission source 2 to the neutron detector 3. The boron clogging detection device is positioned relative to the borated water passage pipe C, such that this neutron path distance D from the neutron emission source 2 to the neutron detector 3 can be occupied in whole or in part by the borated water passage pipe C. Thus, in use, the borated water passage pipe C is located between the neutron emission source 2 and the neutron detector 3, the neutron emission source 2 and the neutron detector 3 are located on either side of the borated water passage pipe C.In this position of use, the neutron emission source 2 emits neutrons in one or more shots, which pass through the boron clogging layer CCB (represented by broken lines in Figure 2) located against the inner wall C1 of the borated water passage pipe C and which are received by the neutron detector 3. Thus, because the boron of this clogging layer located against the inner wall C1 of the borated water passage pipe C is neutron-absorbing, the greater the thickness of this boron clogging layer CCB, the less the neutron flux received by the neutron detector 3, and therefore the less the number of neutrons received, measured by the measurement counter 5. Boron has the property of absorbing neutrons according to their kinetic energy.In the event of the presence of a boron deposit / plug against the inner wall C1 of the borated water passage pipe C, the neutron flux received by the neutron detector 3 is greatly reduced because of the boron. 10 B, neutron-absorbing, will capture a portion of the emitted neutrons. The measurement counter 5 can calculate the counting rate, equal to the number of neutrons received, measured by the measurement counter 5, divided by the number of neutrons emitted by the neutron emission source 2 previously measured on a pipe with similar characteristics, free of boron. This number of neutrons emitted by the neutron emission source 2 can be prescribed to the measurement counter 5 and / or be communicated by the neutron emission source 2 can be prescribed to the measurement counter 5. The presence of boron clogging deposited against the inner wall C2 of the pipe C therefore influences this counting rate.

[0042] The boron clogging detection device 1 further comprises a measurement counter 5, connected to the neutron detector 3. The measurement counter 5 provides a boron clogging measurement, which may be the number of neutrons detected by the neutron detector 3 or which may be calculated as a function of the number of neutrons detected by the neutron detector 3. For this purpose, the measurement counter 5 may comprise a display 51 of the neutron counting rate detected by the neutron detector 3. The display 51 may be provided partly on a computer or calculator, which is connected to the neutron detector 3, for example via a physical output 54 provided on the support 4 and connected to the neutron detector 3 and via a connection cable connecting the display 51 to the physical output 54. The display 51 may be formed by a screen of the computer.The computer or calculator analyzes the signals provided by the neutron detector 3 to calculate as a boron clogging measure the neutron counting rate received as a function of the signal provided by the neutron detector 3. The measurements made by the neutron detector 3 are processed and formatted by an electronic circuit 30 forming part of the support 4, and carrying for example the physical output 54. Thus, a reduction in the flux of neutrons received by the detector 3 results in a reduction in the neutron counting rate, which indicates the increase in the thickness of the CCB layer of boron clogging in the pipe C.

[0043] The detection device 1 according to the invention thus makes it possible to detect boron blockages inside the pipe C carrying borated water, without having to remove the heat-insulating layer C2 and the casing C3, and without having to open this pipe C and therefore avoids intrusive handling. The detection device 1 according to the invention also makes it possible to detect thicknesses of boron deposits less than the internal diameter of the pipe C. The invention can be applied to cases of the presence of crystallized boron in the pipes C carrying fluid with boron concentrations which may be high and present a risk of a drop in temperature.

[0044] According to one embodiment of the invention, the neutron detector 3 comprises a scintillator 31, capable of transforming the neutrons that it receives from the neutron emission source 2 into a light signal. The scintillator 31 may be, for example and not limited to, a scintillator of the lithium-doped plastic type. 6Li or other. The neutron detector 3 further comprises a photodetector 33, capable of providing a measurement in the form of an electrical signal of the counting rate of neutrons received as a function of the light signal provided by the scintillator 31. The photodetector 33 may for example be of the photomultiplier or silicon photomultiplier type (abbreviated and in English: SiPM). Thus, the counting of the flux of neutrons received by the detector 3 is carried out in the following manner. The neutrons, which form indirectly ionizing radiation received by the detector 3, deposit energy in the scintillator 31. The neutron / scintillator reaction will generate a Helium nucleus, a charged particle, which will deposit energy in the scintillator 31 for the thermal energy range of the neutrons. The neutron / scintillator reaction will deposit energy in scintillator 31 by elastic scattering for the epithermal energy range of neutrons.This energy is produced in the form of photons in the visible and / or near ultraviolet range. These photons are detected by the photodetector 33 which transforms the light signal into an electrical signal representative of the detection of a neutron. The measurement counter 5 counts the number of events, to calculate the neutron counting rate received from the electrical signal provided by the photodetector 33, and follows its evolution over time. The neutron counting rate received can be directly displayed on a screen 51 of the analysis computer 5 and / or can be recorded in a permanent memory 52 of the analysis computer 5.

[0045] According to another embodiment of the invention, the neutron detector 3 is an ionization chamber containing a gas, capable of transforming the received neutrons into an electrical signal of the count rate of neutrons received as a measure of the number of neutrons detected by the neutron detector 3. In Figure 2, the scintillator 31 and the photodetector 33 can be replaced by the ionization chamber 3.

[0046] According to one embodiment of the invention, the support 4 comprises a system 44 for measuring the distance D between the neutron emission source 2 and the neutron detector 3.

[0047] According to one embodiment of the invention, the support 4 comprises a first arm

[0048] 41 supporting the neutron emission source 2, and a second arm 42 supporting the neutron detector 3 and the physical output 54. The first arm 41 is mounted to move relative to the second arm 42, for example in sliding (translation) along a determined spacing direction X going from the neutron emission source 2 to the neutron detector 3, to vary the distance D between the neutron emission source 2 and the neutron detector 3. The support 4 comprises a clamping system 43, for example of the screw type, to immobilize the first arm 41 relative to the second arm

[0049] 42 and fix the distance D between the neutron emission source 2 and the neutron detector 3. The first arm 41 and the second arm delimit an opening 45 in which the distance D of the path of the neutrons from the neutron emission source 2 to the neutron detector 3 is located and which can be placed around the pipe C for the passage of borated water. The sliding of the arms 41 and 42 relative to each other makes it possible to adapt the device 1 to pipes C of different diameters, for example from 5 mm to 150 mm.

[0050] According to one embodiment of the invention, the second arm 42 comprises a rack 421 having a guide opening 422 extending along the determined spacing direction X going from the neutron emission source 2 to the neutron detector 3 (or along the direction X of orientation of the neutron emission source 2 towards the neutron detector 3). The first arm 41 comprises a tab 411 which can be guided in the guide opening 422 along the determined spacing direction D when the clamping system 43 is in a loosening position. The clamping system 43 can also have a clamping position, in which the tab 411 is immobilized in the guide opening 422. The clamping system 43 can be manually actuated between one and the other of the loosening position and the clamping position.

[0051] According to one embodiment of the invention, the system 44 for measuring the distance D between the neutron emission source 2 and the neutron detector 3 comprises distance graduations 440, which are distributed on the rack 421 along the determined spacing direction X. These graduations 440 indicate distance D indications between the neutron emission source 2 and the neutron detector 3. The distance D measured between the neutron emission source 2 and the neutron detector 3 corresponds to the indication of that of the graduations 440, which is located opposite the tab 411. This measured distance D information can be used to correct certain effects inherent in the measurement.

[0052] According to one embodiment of the invention, the clamping system 43 comprises a clamping screw 431, which can be screwed and unscrewed onto the tab 411, to be tightened against the rack 421 in the clamping position and to be loosened from the rack 421 in the loosening position. A thumbwheel 432 can be fixed to the head of the screw 431 to be able to manually operate the screw 41.

[0053] Elements associated with the emission source 2 and which can be carried by the first arm 41 are described below.

[0054] The neutron emission source 2 has a (first) front side 22, which is oriented towards the neutron detector 3 along the direction X of orientation of the neutron emission source 2 towards the neutron detector 3. This front side 22 is therefore located between the neutron emission source 2 and the neutron detector 3.

[0055] According to one embodiment of the invention, the support 4 comprises, in front of the front side 22 of the neutron emission source 2, a neutron collimator 21, which is configured to focus the neutrons along the direction X of orientation of the neutron emission source 2 towards the neutron detector 3. The neutron collimator 21 may for example be made of cadmium.

[0056] According to one embodiment of the invention, the support 4 comprises, at least in front of the front side 22 of the neutron emission source 2, a material 23 for slowing down the neutrons within a prescribed range of neutron kinetic energy. The neutron slowing down material 23 can be arranged all around the neutron emission source 2. The neutron slowing down material 23 can be, for example, high-density polyethylene (abbreviated to: HDPE) or paraffin or the like. Indeed, the kinetic energy of the neutrons emitted by the source 2 can be very high (for example, several MeV). High-density polyethylene has the advantage of being a slowing down material that is very rich in hydrogen. The presence of many hydrogen atoms in the slowing material 23 makes it possible to quickly bring (in a few shocks) the fast neutrons (from the neutron emission source 2) to the thermal or epithermal state.The neutron slowing material 23 may also be referred to as a thermalizer 23 or moderator 23. The use of HDPE allows the volume of the thermalizer to be reduced. The measurement of the number of neutrons detected by the neutron detector 3, or the counting rate, is chosen for the neutrons detected by the neutron detector 3 that are within the prescribed kinetic energy range.

[0057] According to one embodiment of the invention, the material 23 is configured (in particular by its composition, its thickness and its shape) to slow down the neutrons in the prescribed range of kinetic energy of the neutrons, which is thermal or epithermal. The measurement of the number of neutrons detected by the neutron detector 3, or the counting rate, is chosen for the neutrons detected by the neutron detector 3 being in the prescribed range of kinetic energy, which is thermal and / or epithermal.

[0058] This prescribed thermal energy range corresponds to neutrons whose kinetic energy is of the order of the thermal energy kT of the surrounding medium, where T is the absolute temperature and k is the Boltzmann constant. These thermal energies are relatively low (about 0.025 eV for a temperature of 300° K). The prescribed epithermal energy range corresponds to neutrons with a kinetic energy slightly greater than the thermal energy range. The thermal and / or epithermal energy ranges maximize the sensitivity of the neutron detector 3 and allow the presence of a simple boron deposit to be discriminated.

[0059] According to one embodiment of the invention, the material 23 is configured (in particular by its composition, its thickness and its shape) to slow down the neutrons in the prescribed range of kinetic energy of the neutrons, which is greater than or equal to 10' 8 MeV and which is less than or equal to 10' 1MeV. This corresponds to the prescribed range of kinetic energy, which is thermal and / or epithermal. The measure of the number of neutrons detected by neutron detector 3, or the count rate, is chosen for neutrons detected by neutron detector 3 that are within the prescribed range of kinetic energy, which is greater than or equal to 10' 8 MeV and which is less than or equal to 10' 1MeV. Said prescribed range will be chosen according to the dimensions of the passage pipe. There may thus be several embodiments depending on the sizes (diameters of the pipe C, etc.), retaining the principle that the prescribed energy range is all the higher as the sizes are. The greater the distance between the neutron emission source 2 and the neutron detector 3, the more the prescribed energy range increases towards higher values. There may thus be as many prescribed ranges as there are distances between the neutron emission source 2 and the neutron detector 3.

[0060] According to one embodiment of the invention, the support 4 comprises all around the neutron emission source 2 one (or more) neutron absorption walls 24 (or neutron shielding 24), except in an opening 242 arranged in front of the front side 22 of the neutron emission source 2, which allows the passage of neutrons in the direction X of orientation of the neutron emission source 2 towards the neutron detector 3. The opening 242 for the passage of neutrons is for example provided in the form of a bore 242 made in a front face 241 of the neutron absorption wall 24, this front face 241 being oriented in the direction X of orientation of the neutron emission source 2 towards the neutron detector 3. This (or these) neutron absorption walls 24 may for example be made of cadmium. Each neutron absorption wall 24 can be, for example, in the form of a flat plate.The neutron absorption wall(s) 24 makes it possible to absorb the neutrons generated isotropically by the neutron emission source 2, elsewhere than towards the neutron detector 3. The neutron absorption wall(s) 24 makes it possible to minimize the necessary activity of the neutron source 2, in order to have a lower dosimetric impact on the people responsible for the measurement.

[0061] According to one embodiment of the invention, the neutron emission source 2, the neutron collimator 21 described above, the neutron slowing material 23 described above and the neutron absorption wall(s) 24 are placed in a housing 25, therefore open by the neutron passage opening 242, oriented towards the neutron detector 3.

[0062] Elements associated with the neutron detector 3 and which can be carried by the second arm 42 are described below.

[0063] The neutron detector 3 has a (second) front side 32, which is oriented towards the neutron emission source 2 in the X direction and a rear side 36, which is further from the neutron emission source 2 in the X direction than the front side 32 of the neutron detector 3.

[0064] According to one embodiment of the invention, the support 4 comprises a shield 343 against neutrons (or other neutron absorption wall 343) at least on the rear side 36 of the detector 3. This shield 343 may be made of cadmium. This shield 343 makes it possible to limit the sensitivity of the neutron detector 3 to neutrons which may be backscattered (for example if a wall is present near the pipe C) and to protect the operators and the surrounding equipment.

[0065] According to one embodiment of the invention, the neutron absorption wall 24 and / or the other neutron absorption wall 34, 343 is, in a preferred embodiment, made of cadmium, and in secondary embodiments made of Hafnium or Gadolinium. According to one embodiment of the invention, the support 4 may comprise all around the neutron detector 3 one (or more) other neutron absorption wall 34 (or neutron shielding 34), except in another opening 342 arranged between the front side 32 of the neutron detector 3 and the neutron emission source 2. This other opening 342 allows the passage of neutrons along the direction X of orientation of the neutron emission source 2 towards the neutron detector 3.The other opening 342 for the passage of neutrons is for example provided in the form of a bore 342 made in the second front face 341 of the neutron absorption wall 34, this second front face 241 being oriented in the direction X of orientation of the neutron emission source 2 towards the neutron emission source 2. Each other neutron absorption wall 34 may for example be in the form of a flat plate. Each other neutron absorption wall 34 may for example be made of cadmium.

[0066] According to one embodiment of the invention, the support 4 comprises a first surface 27 for centering the pipe C. This first surface 27 for centering the pipe C is located on the side of the neutron emission source 2, for example in front of the latter and opposite the neutron detector 3 and may comprise two flat parts 271, 272 forming an obtuse angle facing the neutron detector 3, so that this first centering surface 27 can be pressed against the pipe C. The first centering surface 27 of the pipe C is configured to center the orientation direction X so that this orientation direction X of the neutron emission source 2 toward the neutron detector 3 meets the axis of revolution Y of the pipe C. The support 4 comprises a second surface 37 for centering the pipe C.This second centering surface 37 of the pipe C is located on the side of the neutron detector 3, for example opposite the neutron emission source 2, and may comprise two flat parts forming an obtuse angle facing the neutron emission source 2, so that this second centering surface 37 can be pressed against the pipe C. The second centering surface 37 of the pipe C is configured to center the orientation direction X so that this orientation direction X of the neutron emission source 2 toward the neutron detector 3 meets the axis Y of revolution of the pipe C.

[0067] In Figures 3A and 3B, neutron flux curves (normalized to cm' 2on the ordinate) received by the neutron detector 3 were simulated according to the invention as a function of the kinetic energy of the neutrons (in MeV on the abscissa) received by the neutron detector 3, through a pipe C for the passage of borated water, circular cylindrical with an internal diameter of 60 mm, with a layer of neutron slowing material 23 10 cm thick of HDPE surrounding the neutron emission source 2, and for different thicknesses, namely 0 mm (without boron), 2 mm, 5 mm, 15 mm, 30 mm (complete plug), of the boron sealing layer CCB with a length of 10 cm along the internal wall C1 of the pipe C. The curve of the number of neutrons emitted by the neutron emission source 2 at the outlet of the slowing material 23 is also represented and called "source support outlet flux" in figures 3A and 3B. We see in these figures 3A and 3B that for the kinetic energies of neutrons, greater than or equal to 10' 8MeV and less than or equal to 10' 1 MeV, the neutron flux curves are substantially (for most of the abscissas) distinct from each other at least from 0 mm to 30 mm of thickness of the CCB layer of boron clogging in the C pipe and are all the lower as the thickness of the CCB layer of boron clogging in the C pipe is large in this range of 0 mm to 30 mm of thickness (called case 1). The measurement of the flux of neutrons received for a kinetic energy value included in these kinetic energy ranges therefore makes it possible to determine by the counter 5 or computer 5, whether there is a boron plug almost completely obstructing the C pipe and / or to calculate a boron clogging measurement, such as for example the thickness of the CCB layer of boron clogging in the C pipe at least for the thicknesses going from 0 to the inner radius of the C pipe.

[0068] According to one embodiment of the invention, the measurement of the number of neutrons received or the neutron counting rate received can be represented in counts per second on the screen 51 of the computer 5. The measurements can be carried out at several points distant from each other along the pipe C and the variations in neutron flux received by the detector 3 can be evaluated by the computer 5.

[0069] The device 1 and method for detecting boron clogging according to the invention allows non-destructive and non-intrusive testing of the pipe C. The device 1 for detecting boron clogging according to the invention can be portable. The invention allows operators to retreat to an area less exposed to radiation, which will allow dosimetric gains to be made. It also allows the intervention area to be better targeted and intervention costs to be limited. The invention allows a saving in intervention time. The device 1 and method for detecting boron clogging according to the invention make it possible to determine, from the clogging measurement obtained, what quantity of cleaning or leaching products must be introduced into the pipe C to remove the layer of boron clogging or the boron plug present therein. This allows savings in cleaning or leaching products for boron.

[0070] According to one embodiment of the invention, the boron clogging detection device 1 can be robotized, for example to perform translations along the pipe C and rotations around the pipe C. The method for detecting boron clogging in a pipe C for passing borated water using the boron clogging detection device 1 described above comprises the following steps shown in Figure 4.

[0071] During a first step E1, the neutron emission source 2 and the neutron detector 3 are positioned on either side of the borated water passage pipe C, so that the determined neutron path distance D from the neutron emission source 2 to the neutron detector 3 is occupied at least in part by the borated water passage pipe C. The neutron source 3 continuously emits neutrons. During a second step E2 subsequent to the first step E1, the neutron detector 3 is put into operation. The neutron emission source 2 therefore sends neutrons to the neutron detector 3 through the borated water passage pipe C during this second step E2.

[0072] During a third step E3 after the second step E2, the measurement counter 5 connected to the neutron detector 3 produces the boron clogging measurement according to a measurement of the number of neutrons detected by the neutron detector 3.

[0073] Of course, the embodiments, features, possibilities and examples described above can be combined with each other or selected independently of each other.

Claims

CLAIMS 1. Device (1) for detecting boron clogging in a pipe (C) for passing borated water, characterized in that the device comprises at least one neutron emission source (2), at least one neutron detector (3), a support (4), to which the neutron emission source (2) and the neutron detector (3) are fixed, a measurement counter (5) connected at least to the neutron detector (3), configured to provide a boron clogging measurement according to a measurement of the number of neutrons detected by the neutron detector (3), the support (4) being capable of keeping the neutron detector (3) oriented towards the neutron emission source (2) and with a non-zero neutron path distance (D) from the neutron emission source (2) to the neutron detector (3),so that the determined distance (D) of the neutron path from the neutron emission source (2) to the neutron detector (3) can be occupied at least in part by the borated water passage pipe (C)., 2. Device according to claim 1, characterized in that the measurement counter (5) comprises a display (51) of a counting rate of neutrons received, detected by the neutron detector (3).

3. Device according to claim 1 or 2, characterized in that the neutron detector (3) comprises a scintillator (31), capable of transforming the neutrons received into a light signal, and a photodetector (33), capable of providing the measurement of the number of neutrons detected by the neutron detector (3) in the form of an electrical signal of the counting rate of neutrons received as a function of the light signal from the scintillator (31).

4. Device according to claim 1 or 2, characterized in that the neutron detector (3) is an ionization chamber containing a gas, capable of transforming the neutrons received into an electrical signal of the counting rate of neutrons received.

5. Device according to any one of the preceding claims, characterized in that the support (4) comprises a system (44) for measuring the distance (D) of the neutrons from the neutron emission source (2) to the neutron detector (3).

6. Device according to any one of the preceding claims, characterized in that the support (4) comprises a first arm (41), to which the neutron emission source (2) is fixed, and a second arm (42), to which the neutron detector (3) is fixed, the first arm (41) being mounted to move relative to the second arm (42), to vary the distance (D) between the neutron emission source (2) and the neutron detector (3), the support (4) comprising a clamping system (43) for immobilizing the first arm (41) relative to the second arm (42) and fixing the distance (D) of the neutrons' path from the neutron emission source (2) to the neutron detector (3).

7. Device according to claim 6, characterized in that the first arm (41) is mounted to slide relative to the second arm (42) in a determined direction (X) of separation going from the neutron emission source (2) to the neutron detector (3).

8. Device according to claim 7, characterized in that the second arm (42) comprises a rack (421) having a guide opening (422) extending along the determined spacing direction (X), the first arm (41) comprises a tab (411) inserted in the guide opening (422), the tab (411) being able to slide along the determined spacing direction (X) in the guide opening (422) when the clamping system (43) is in a loosening position, the clamping system (43) having a clamping position, in which the tab (411) is immobilized in the guide opening (422).

9. Device according to claim 8, taken in combination with claim 5, characterized in that the system (44) for measuring the distance (D) of the neutrons from the neutron emission source (2) to the neutron detector (3) comprises distance graduations (440), which are distributed on the rack (421) along the determined spacing direction (X).

10. Device according to claim 8 or 9, characterized in that the clamping system (43) comprises a clamping screw (431), which is arranged on the tab (411), which is capable of being clamped against the rack (421) in the clamping position and which is capable of being loosened from the rack (421) in the loosening position.

11. Device according to any one of the preceding claims, characterized in that the support (4) comprises, in front of a first front side (22) of the neutron emission source (2), oriented towards the neutron detector (3), a neutron collimator (21) for concentrating the neutrons in a direction (X) of orientation of the neutron emission source (2) towards the neutron detector (3).

12. Device according to any one of the preceding claims, characterized in that the support (4) comprises, at least in front of a first front side (22) of the neutron emission source (2), oriented towards the neutron detector (3), a material (23) for slowing down the neutrons in a prescribed range of kinetic energy, the measurement of the number of neutrons detected by the neutron detector (3) being chosen for the neutrons detected by the neutron detector (3) falling within the prescribed range of kinetic energy.

13. Device according to claim 12, characterized in that the prescribed range of kinetic energy is thermal and / or epithermal.

14. Device according to claim 12 or 13, characterized in that the prescribed range of kinetic energy is greater than or equal to 10' 8 MeV and is less than or equal to 10' 1 MeV.

15. Device according to any one of claims 12 to 14, characterized in that the neutron slowing material (23) is high density polyethylene and / or paraffin.

16. Device according to any one of claims 12 to 15, characterized in that the neutron slowing material (23) is arranged all around the neutron emission source (2).

17. Device according to any one of the preceding claims, characterized in that the support (4) comprises all around the neutron emission source (2) at least one neutron absorption wall (24), comprising in front of a first front side (22) of the neutron emission source (2), oriented towards the neutron detector (3), an opening (242) allowing the passage of neutrons in a direction (X) of orientation of the neutron emission source (2) towards the neutron detector (3).

18. Device according to any one of the preceding claims, characterized in that the neutron detector (3) has a second front side (32), which is oriented towards the neutron emission source (2) in a direction (X) of orientation, and a rear side (36), which is further from the neutron emission source (2) in the direction (X) of orientation than the second front side (32) of the neutron detector (3), the support (4) has at least one other neutron absorption wall (34, 343) at least on the rear side (36) of the neutron detector (3).

19. Device according to claim 18, characterized in that the support (4) comprises all around the neutron detector (3) at least one other neutron absorption wall (34, 343), comprising in front of the second front side (32), which is oriented towards the neutron emission source (2) in an orientation direction (X), another opening (342), which is arranged between the second front side (32), of the neutron detector (3) and the neutron emission source (2) and which allows the passage of neutrons following the direction (X) of orientation of the neutron emission source (2) towards the neutron detector (3).

20. Device according to any one of claims 17 to 19, characterized in that the neutron absorption wall (24) and / or the other neutron absorption wall (34, 343) is made of cadmium and / or hafnium and / or gadolinium.

21. Device according to any one of the preceding claims, characterized in that the support (4) comprises a first surface (27) for centering the pipe (C), located on the side of the neutron emission source (2) and configured so that a direction (X) of orientation of the neutron emission source (2) towards the neutron detector (3) meets an axis (Y) of revolution of the pipe (C), and the support (4) comprises a second surface (37) for centering the pipe (C), located on the side of the neutron detector (3) and configured so that a direction (X) of orientation of the neutron emission source (2) towards the neutron detector (3) meets an axis (Y) of revolution of the pipe (C).

22. Method for detecting boron clogging in a pipe (C) for passing borated water using the boron clogging detection device (1) according to any one of the preceding claims, characterized in that the method comprises the following steps: positioning (E1) the neutron emission source (2) and the neutron detector (3) on either side of the pipe (C) for passing borated water, so that the determined neutron path distance (D) from the neutron emission source (2) to the neutron detector (3) is occupied at least in part by the pipe (C) for passing borated water, switching on (E2) the neutron detector (3), supplying (E3) by the measurement counter (5) connected to the neutron detector (3), a boron clogging measurement according to a measurement of the number of neutrons detected by the detector (3) neutrons.

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