Force sensor, e.g. for measuring hydromechanical thrust

Abstract

Title: Force sensor, for example for measuring a hydromechanical thrust The invention relates to a strain gauge sensor (1000) for measuring the strain between a first element and a second element in a main direction (Z), the sensor comprising at least one test body (1100) comprising a first portion (1110), a central portion (1130) having an upper face (1131) and a lower face (1132), and a second portion (1120). The test body defines a first slot (1141) extending between the upper face of the central portion and the first portion and separating the first and second portions, and a second slot (1142) extending between the lower face of the central portion (1130) and the second portion and separating the first and second portions. The sensor also comprises a fiber optic gauge (1200) attached to the central portion and a device for reading the gauge. Figure for abstract: Fig.3A

Description

Title of the invention: Force sensor, for example for measuring hydromechanical thrust Technical field

[0001] The present invention relates to the general field of strain gauge sensors. It finds a particularly advantageous but non-limiting application in the field of strain gauge sensors intended to measure hydraulic forces under fluid flow.

[0002] A non-limiting example of application concerns the measurement of the hydromechanical thrust applied by a fluid to a fuel assembly of a nuclear reactor or an experimental platform of such a reactor, subjected to a restrictive environment in terms in particular of pressure or temperature. STATE OF THE ART

[0003] A nuclear power plant reactor usually comprises a plurality of assemblies 10 carrying fuel rods 11, these assemblies 10 being held substantially vertically, by structural grids, between an upper core plate 20 and a lower core plate 30 as illustrated in [Fig.l].

[0004] The core of the reactor is traversed by a heat transfer fluid 40 which passes through orifices 31 of the lower plate 30 in order to access the assembly 10. The heat transfer fluid 40 can thus travel through the fuel rods 11 and capture the heat released therefrom.

[0005] The assemblies 10 are relatively heavy, generally of the order of 800 kg each. They must therefore be held firmly at their ends at the level of the upper 20 and lower 30 plates. For this purpose, each end comprises a tip 12, 13.

[0006] Under the effect of temperature, the assembly 10 expands, which would tend to cause it to flex strongly if it were rigidly constrained between the plates 20, 30. It is therefore necessary to absorb these expansions in a temperature range between 20 and 300°C. An elastic member 50 is then provided, such as a compression spring, preferably arranged between the upper plate 20 and the upper end piece 12 of the assembly 10. The elastic member 50 has the effect of constraining the assembly 10 by pressing it against the lower plate 30 while absorbing the expansions.

[0007] Thus, in statics, the assembly 10 is subjected to the following forces illustrated in [Fig.l]: i. its weight “P”; ii. the support force Fsm of the elastic member. This force can be determined by knowledge of the stiffness and travel of the compression spring; iii. Archimedes' thrust “A”; iv. the reaction force “R” of the lower plate 30 on the assembly 10.

[0008] Furthermore, in operation, the fluid 40 exerts a hydrodynamic force Fh on the assembly 10. This force cannot be known with good precision. However, the force Fsm exerted by the spring must be calibrated so as to be perfectly adapted to the hydrodynamic force Fh.

[0009] Indeed, if the force Fsm exerted by the spring is too weak, the hydrodynamic force Fh can cause the assembly 10 to “detach” under the effect of the force exerted by the fluid, i.e. move it away from the lower plate 30. If it is too high, it can cause the assembly 10 to bend. However, as the assemblies 10 of the core are close to each other, they can touch each other if the bending is too great. This can lead to dramatic consequences.

[0010] It is therefore important to accurately determine the hydrodynamic force Fh. One solution consists of carrying out tests on an experimental reactor platform by subjecting the assembly 10 to this force Fh. Given the confinement of this type of test, it is particularly difficult to measure the force Fh with good precision, even in a test prototype.

[0011] Furthermore, it has been found that existing force sensors used to measure Fh operate poorly or even do not operate beyond certain pressure levels, typically beyond 15 bars, and beyond certain temperature levels, typically beyond 280°C. However, most nuclear reactors have operating pressures above this limit. For example, the operating pressure of a pressurized water reactor (PWR) is approximately 155 bars, which is well above the operating limit of existing force sensors.

[0012] This is very problematic since this limit on the measurement of Fh imposes very large safety margins on the operating parameters of the reactor, in particular the flow rate of the heat transfer fluid. These large safety margins result in an effective efficiency of the reactor which is much lower than the maximum efficiency which would in reality be permitted by its components.

[0013] There is therefore a need to propose a solution for improving the measurement of the force Fh. This is the aim of the present invention. In particular, an objective of the present invention is to propose a solution which would make it possible to carry out measurements in a wide range of pressure values, preferably over the entire operating range of a nuclear reactor, in particular a PWR reactor.

[0014] Other objects, features and advantages of the present invention will become apparent from a consideration of the following description and accompanying drawings. SUMMARY

[0015] To achieve this objective, a first aspect of the invention relates to a strain gauge sensor for measuring the movement or deformation between a first element and a second element in a main direction, the sensor comprising at least one test body. Preferably, the test body comprises a first portion, a first fixing zone of which is intended to be fixed to the first element, a central portion and a second portion, a second fixing zone of which is intended to be fixed to the second element, the first portion and the second portion being in material continuity via the central portion, the central portion having an upper face intended to be positioned opposite the first element and a lower face, opposite the upper face, intended to be placed opposite the second element, the test body defining: i.a first slot extending between the upper face of the central portion and the first portion, and separating the first portion and the second portion, and ii. a second slot extending between the lower face of the central portion and the second portion, and separating the first portion and the second portion.

[0016] The first fixing zone, the upper face of the central portion, the lower face of the central portion and the second fixing zone overlapping at least partially in projection in a transverse plane perpendicular to the main direction,

[0017] Furthermore, the sensor further comprises: i. at least one fiber optic gauge attached to the central portion such that, when the central portion deforms under the effect of movement or deformation between the first element and the second element in the main direction, the fiber optic gauge also deforms, ii. a device for reading the fiber optic gauge.

[0018] The particular shape of the test body has the effect that the stresses undergone by it are concentrated within its central portion. The relative displacement of the two elements to which the sensor is fixed therefore has a greater impact locally than for any other shape of the test body. It has been found that this concentration of stresses allows detection using particularly sensitive and precise fiber optic gauges.

[0019] The shape of the test body as defined above also gives the sensor a rigidity enabling it to withstand significant tensile or compressive loads.

[0020] Furthermore, fiber optic strain gauges, due in particular to their small dimensions, are very insensitive to static pressure. By using such gauges, it is possible to measure the hydrodynamic force Fh at much higher pressure levels, and in particular above 155 bars, the operating pressure. operation of a REP. These gauges are also resistant to high temperatures, which again allows the measurement of Fh to be carried out under the operating conditions of a REP.

[0021] The invention therefore proposes an alternative to existing sensors for measuring Fh. The proposed sensor notably allows both precise measurement and measurement that can be carried out at high pressures, and notably over the entire typical operating range of a PWR.

[0022] The invention therefore makes it possible to reduce the safety margins that must be taken and consequently to increase the efficiency of the reactor.

[0023] Furthermore, as will be described further below, when the sensor according to the invention is placed between the lower nozzle of the assembly and the lower support plate of the assembly, it also makes it possible to know precisely the maximum flow rate that can be injected into the reactor without the latter taking off. Precise knowledge of this maximum flow rate that must not be exceeded makes it possible to further reduce the safety margins and therefore, here too, to increase the efficiency of the reactor.

[0024] A second aspect of the invention relates to an assembly comprising a sensor according to the first aspect of the invention, a first sub-plate fixed to the first fixing zone of the first portion of the test body and a second sub-plate fixed to the second fixing zone of the second portion of the test body, one of the first sub-plate and the second sub-plate being intended to be fixed to one of a lower support plate to which an assembly of a nuclear reactor is held and an upper support plate to which an assembly of a nuclear reactor is held.

[0025] A third aspect of the invention relates to a system comprising: i. a nuclear power plant assembly configured to carry nuclear fuel materials, ii. an upper plate for supporting this assembly, iii. a lower plate for supporting this assembly, iv. at least one first sub-plate and at least one second sub-plate, v. at least one sensor according to the first aspect of the invention, vi. at least one first sub-plate being fixed to any one of the upper plate and the lower plate,

[0026] The at least one second sub-plate is mechanically connected to the assembly. The first sub-plate is furthermore fixed to the first fixing zone of the first portion of the test body of each sensor. The first sub-plate is furthermore fixed to the second fixing zone of the second portion of the test body of each sensor so as to measure the movement of the assembly relative to said plate.

[0027] A fourth aspect of the invention relates to a nuclear reactor comprising the system according to the third aspect of the invention.

[0028] The advantages described with reference to the first aspect of the invention apply mutatis mutandis to the second aspect, the third aspect and the fourth aspect of the invention. BRIEF DESCRIPTION OF THE FIGURES

[0029] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0030] [Fig. 1] [Fig. 1] is a diagram illustrating an experimental nuclear reactor platform. For ease of understanding, only an assembly and the upper and lower support plates are shown. The forces acting on the assembly are also shown.

[0031] [Fig.2A] Figures 2A to 2F are different views of a sensor according to the invention. [Fig.2A] is a front view of the sensor on which the test body and its different portions are visible. [Fig.2A] also shows in detail the fixing zones of the sensor.

[0032] [Fig.2B] [Fig.2B] is a profile view of the sensor according to the invention.

[0033] [Fig.2C] [Fig.2B] is a perspective view of the sensor according to the invention.

[0034] [Fig.2D] [Fig.2D] is a profile view of the sensor according to the invention.

[0035] [Fig.2E] [Fig.2E] is a sectional view of the sensor according to the invention according to the section represented in [Fig.2D]. [Fig.2E] illustrates in particular the integration of the gauges within the test body.

[0036] [Fig.2F] [Fig.2F] is a sectional view of the sensor according to the invention according to the section shown in [Fig.2E]. [Fig.2F] illustrates in particular the integration of the gauges within the test body.

[0037] [Fig.3A] Figures 3A and 3B respectively represent two and four sensors according to the invention fixed to two elements between which they make it possible to measure the deformation.

[0038] [Fig.3B]

[0039] [Fig.4A] Figures 4A and 4B respectively represent two and four sensors according to the invention integrated at the level of an upper support plate of a nuclear assembly.

[0040] [Fig.4B]

[0041] [Fig.5A] Figures 5A and 5B are sectional and perspective views illustrating the integration of respectively two and four sensors according to the invention at the level of an upper support plate of a nuclear assembly.

[0042] [Fig.5B]

[0043] [Fig.5C] Figures 5C and 5D are sectional views illustrating the integration of two sensors according to the invention at the level of a lower support plate of a nuclear assembly.

[0044] [Fig.5D]

[0045] [Fig.6A] Figures 6A and 6C are top views of two sensors according to the invention integrated at the level of an upper support plate of a nuclear assembly.

[0046] [Fig.6B] Figures 6B and 6D are top views of four sensors according to the invention integrated at the level of an upper support plate of a nuclear assembly.

[0047] [Fig.6C]

[0048] [Fig.6D]

[0049] [Fig.7] [Fig.7] represents the distribution obtained by numerical simulation of the stresses within the test body of the sensor according to the invention when the latter is subjected to a force of 6000N.

[0050] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the dimensions are not representative of reality. DETAILED DESCRIPTION

[0051] Before beginning a detailed review of the embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:

[0052] According to a preferred embodiment, the sensor comprises two fiber optic gauges attached to the central portion. The use of two fiber optic gauges attached to the central portion makes it possible, on the one hand, in the event of failure of one of the gauges, to ensure that the measurement is carried out correctly, thanks to the remaining gauge. On the other hand, the signals from the two gauges can be processed so as to exclude aberrant values ​​or be averaged. This makes it possible to improve the precision on the value of Fh which will be calculated.

[0053] According to an advantageous embodiment, the central portion comprises a central wall separating two openings defined by the central portion, each of the openings passing entirely through the central portion from the first portion to the second portion. This structure makes it possible to concentrate the stresses prevailing in the test body in the central wall. The fiber optic gauge(s) is (are) advantageously fixed to this central wall. When the sensor comprises two gauges, these are preferably fixed on either side of the central wall. This avoids a bias in the measurement which could come from the fact that it was carried out on one side or the other of the central wall, for example in the case of imperfect symmetry of the test body. The signals from these two gauges could for example be averaged.

[0054] According to a preferred embodiment, the sensor further comprises a fiber optic indicator gauge attached to one of the first portion and the second portion. The first and second portions are very lightly stressed when the test body is subjected to traction or compression. The indicator gauge therefore makes it possible to measure only or almost only the deformation of the test body due to temperature effects. This deformation may be subtracted from the deformation measured by the gauges attached to the central portion in order to overcome the impact of this temperature effect on the measurement. This thus makes it possible to improve the accuracy of the value of Fh which will then be calculated.

[0055] According to an advantageous example, the sensor further comprises at least one first plug extending at least partially into one of the first portion and the second portion, each fiber optic gauge passing through a first plug, each first plug being configured to, when the sensor is in an environment comprising a fluid, limit, and preferably prevent, the arrival of the fluid on the fiber optic gauge. The first plugs thus make it possible to seal the fiber optic gauge(s). This has the effect of both improving the accuracy of the measurement and increasing the lifetime of the sensor.

[0056] According to an advantageous example, each first plug has an external thread and in which the one among the first portion and the second portion in which said first plug extends has a first opening defining a complementary thread of the external thread of the first plug, the first plug being screwed into said first portion or second portion.

[0057] According to an advantageous example, the sensor further comprises at least one second plug extending at least partially into one of the first portion and the second portion, at least a portion of the reading device of the fiber optic gauge passing through a second plug, each second plug being configured to, when the sensor is in an environment comprising a fluid, limit, and preferably prevent, the arrival of the fluid on at least the portion of the reading device of the fiber optic gauge. The second plugs thus make it possible to seal the reading device. This has the effect of both improving the accuracy of the measurement and increasing the lifetime of the sensor.

[0058] According to an advantageous example, the fiber optic gauge forms an angle substantially equal to 90° with the main direction.

[0059] According to an embodiment of the system according to the invention, a first sub-plate, called the first upper sub-plate, is fixed to the upper plate, the system further comprising an elastic member connected on the one hand to the assembly and on the other hand to at least one second sub-plate, called the second upper sub-plate, at least one sensor being fixed to the first upper sub-plate and to the second upper sub-plate.

[0060] According to one embodiment, a first sub-plate, called the first lower sub-plate, is fixed to the lower plate, the assembly further comprising a lower end piece located opposite the lower plate and fixed to a second sub-plate, called the second lower sub-plate, at least one sensor being fixed to said first lower sub-plate and to said second lower sub-plate.

[0061] According to an advantageous example, the system comprises at least two sensors fixed to the same first sub-plate and to the same second sub-plate.

[0062] According to an advantageous example, the system comprises at least four sensors attached to the same first sub-plate and to the same second sub-plate, preferably exactly four sensors attached to the same first sub-plate and to the same second sub-plate.

[0063] According to one example, all of the sensors are attached to the first upper sub-plate.

[0064] According to one example, all of the sensors are attached to the first lower sub-plate.

[0065] A reference frame, preferably orthonormal, comprising the axes X, Y, Z is shown in the figures. This reference frame is applicable by extension to the other figures. The relative terms “on”, “under”, “underlying”, “above”, “below” refer, unless otherwise stated, to positions taken in the Z direction.

[0066] The terms “substantially”, “approximately”, “of the order of” mean “to within 10%, preferably to within 5%”.

[0067] The various objects of the invention will now be described with reference to the figures.

[0068] A first object of the invention relates to a strain gauge sensor 1000, described in its structure with reference to FIGS. 2A to 2F and 6A and 6B and in its integration within a nuclear reactor with reference to FIGS. 3A to 6B.

[0069] The sensor 1000 according to the invention makes it possible to measure the movement or deformation between two elements, called first element and second element, in a main direction Z. A transverse plane XY is also defined, perpendicular to the main direction Z and defined by a first direction X and a second direction Y.

[0070] Structure of the strain gauge sensor

[0071] The sensor 1000 comprises a test body 1100 having three main portions: a first portion 1110, a central portion 1130 and a second portion 1120. The first portion 1110 and the second portion 1120 are in continuity of material via the central portion 1130. Preferably, the first and second portions 1110, 1120 are in continuity of material only via the central portion 1130. The first portion 1110 and the second portion 1120 are not in contact, they are at a distance from each other. The first portion 1110, the central portion 1130 and the second portion 1120 may be in one piece, or may have been formed separately and then assembled, for example by welding.

[0072] The first portion 1110 has a first fixing zone 1115 to which the first element can be fixed. Similarly, the second portion 1120 has a second fixing zone 1125 to which the second element can be fixed. The fixing zones 1115, 1125 may for example have a hole 1116, 1126 passing respectively through the first and second portions 1110, 1120 in the main direction Z.

[0073] The central portion 1130 has an upper face 1131 and a lower face 1132, opposite each other, and intended to be placed opposite the first element and the second element respectively. Preferably, these two faces 1131, 1132 extend mainly parallel to the transverse plane XY.

[0074] The central portion 1130 is preferably partially hollowed out, as illustrated in FIGS. 2E and 2F. [Fig. 2E] is a sectional view of the sensor along section AA shown in [Fig. 2D], while [Fig. 2F] is a sectional view along section BB shown in [Fig. 2E]. The central portion 1130 preferably has two openings 1131 passing entirely through it along the first direction X. These two openings 1131 advantageously each have the shape of a half-cylinder. The central portion 1130 may thus comprise a central wall 1135 separating the two openings 1131. Advantageously, the central wall 1135 extends mainly along a plane defined by the first direction X and the main direction Z.

[0075] As illustrated in [Fig.2A] in particular, the test body 1100 defines a first slot 1141 extending in particular between a part of the first portion 1110 and the upper face 1131 of the central portion 1130. The upper face 1131 is thus at a distance from the first portion 1110. The part of the first portion 1110 separated from the upper face 1131 of the central portion 1130 by the first slot 1141 preferably comprises the first fixing zone 1115. The hole 1116 of the first fixing zone 1115 thus opens onto the first slot 1141.

[0076] The first slot 1141 also separates the first portion 1110 and the second portion 1120.

[0077] The test body 1100 also defines a second slot 1142 extending in particular between a part of the second portion 1120 and the lower face 1132 of the central portion 1130. The lower face 1132 is thus located at a distance from the second portion 1120. The part of the second portion 1120 separated from the lower face 1132 of the central portion 1130 by the second slot 1142 preferably comprises the second fixing zone 1125. The hole 1126 of the second fixing zone 1125 thus opens onto the second slot 1142.

[0078] The second slot 1142 also separates the first portion 1110 and the second portion 1120.

[0079] The first portion 1110 thus forms a return of material of the test body 1100 above the upper face 1131 of the central portion 1130. The second portion 1120 forms a return of material of the test body 1100 below the lower face 1132 of the central portion 1130.

[0080] Advantageously, in projection in the transverse plane XY, the first fixing zone 1115, the upper face 1131 of the central portion 130, the lower face 1132 of the central portion 1130 and the second fixing zone 1125 overlap.

[0081] The holes 1116, 1126 of the fixing zones 1115, 1125 preferably have a symmetry of revolution around the same axis, parallel to the Z direction. Preferably, this axis intersects the upper and lower faces 1131, 1132 of the central portion 1130 at their respective centers of gravity. The holes 1116, 1126 of the fixing zones 1115, 1125 and the upper and lower faces 1131, 1132 of the central portion 1130 are thus preferably aligned along an axis parallel to the Z direction.

[0082] The test body 1100 is preferably made of a nickel-chromium alloy, for example Inconel® 718. This material has very good mechanical strength Rm (greater than 1034 MPa in the case of Inconel® 718). The test body 1100 can also be made of stainless steel, for example alloy 17-4PH. Preferably, the test body 1100 is made of a material having a mechanical strength Rm greater than 500 MPa.

[0083] The particular shape of the test body 1100 makes it possible to concentrate the mechanical stresses at the central portion 1130. This is illustrated in particular by [Fig.7]. This figure is the result of a numerical simulation of the Von Mises stresses in the test body when it is put under pressure by applying a force of 6000 N. It is observed that these stresses are significantly greater (of the order of 100 N / mm2) in the central portion 1130 than in the first portion 1110 and in the second portion 1120 (from 0 to 6 N / mm2 approximately in these two portions). It is also noted that the maximum stress obtained by this simulation is 232 MPa, which is much lower than the mechanical strength of Inconel® 718 (1034 MPa). This simulation thus confirms that this material is entirely suitable for measuring the deformation between the first and second elements when they are subjected to a force less than or equal to 6000 N.

[0084] Furthermore, the fact that the central portion 1130 is partially hollowed out makes it possible to concentrate the stresses in the remaining material, and in particular within the central wall 1135.

[0085] The test body 1100 also has the following dimensions, illustrated in Figures 2A and 2B: i. A height H1100, measured along the main direction Z, ii. A length L1100, measured along the first direction X, iii. A width 11100, measured along the second direction Y.

[0086] For example, H1100 is between 40 and 120, and is for example substantially equal to 60 cm. L1100 may be between 60 cm and 120 cm, and is for example substantially equal to 70 cm. 11100 may be between 25 cm and 60 cm, and is for example substantially equal to 35 cm.

[0087] Furthermore, the fixing zones 1115, 1125, respectively located above and the upper face 1131 of the central portion 1130 and below the lower face 1132 of the central portion 1130, have heights noted H1115 and H1125, preferably substantially equal. These heights H1115, H1125 may for example be between 8 and 12, and for example each be substantially equal to 10.5 cm.

[0088] The sensor 1000 further comprises at least one fiber optic gauge 1200 configured to deform when the central portion 1130 deforms.

[0089] The optical fiber of such a gauge comprises a cladding and a core in which a Bragg grating is formed. It is configured so that a light beam, typically a laser beam, can be injected into its core. The light beam is refracted by the Bragg grating according to the spatial period thereof. The core of the fiber is typically made of fiberglass or silica. Such a gauge may also be referred to as a Bragg grating fiber gauge.

[0090] Figures 2A to 2F illustrate an example in which the sensor 1000 comprises two fiber optic gauges 1200. It is understood, however, that the sensor may comprise a different number of fiber optic gauges 1200.

[0091] Each gauge preferably extends in a protective cable 1210. This may for example be a hollow stainless steel cable. The diameter of the protective cable 1210 is configured to accommodate the gauge 1200. It may for example be equal to 3.175 cm. The protective cable 1210 makes it possible to protect the gauge 1200 in particular from the pressure and temperature conditions to which it is subjected.

[0092] Each gauge 1200 is fixed at at least one zone, preferably at one of its ends, to the central portion 1130. It is also fixed in another zone, typically its other end, to an anchoring point (not shown).

[0093] [Fig.2E] illustrates the attachment, at one of its ends, of a gauge 1200 to the central portion 1130.

[0094] As illustrated, advantageously, each gauge 1200 is fixed to the central wall 1135 of the central portion 1130. Preferably, in the case where the sensor 1000 comprises two fiber optic gauges 1200, these are fixed on either side of the central wall 1135, as illustrated in [Fig.2F] in particular.

[0095] Each gauge 1200 is fixed to the central portion 1130 using a fixing material. When the sensor 1000 is used in high temperature conditions, such as for example in a nuclear reactor, this material is chosen in particular for its resistance to these conditions. It may for example be a two-component glue or a refractory cement.

[0096] The deformation of the central portion 1130 has the effect of stretching or compressing the fiber and therefore the Bragg grating. When the fiber is stretched, the spatial period of the Bragg grating increases while when the fiber is compressed, the period decreases. This modification of the period of the Bragg grating has the consequence of modifying the wavelength reflected by the grating. The modification of the reflected wavelength therefore reflects the deformation of the optical fiber, which itself reflects the deformation of the central portion 1130.

[0097] It is thus provided that the sensor 1000 comprises a device for reading the gauge(s) 1200 using optical fiber. The reading device typically comprises a light source and a detector.

[0098] The light source is configured to emit a light beam injected into the core of the optical fiber of the 1200 gauge. This is typically a laser source.

[0099] The detector is configured to detect the light intensity of the beam refracted by the Bragg grating of the fiber optic gauge over a predefined range of wavelengths. This light intensity data will then be used to trace back to the wavelength refracted by the Bragg grating of the fiber optic gauge.

[0100] By measuring the deformation of the test body 1100 at the central portion 1130, where the stresses induced by the deformation are the strongest, the influence of the deformation of the test body 1100 on the deformation of the gauge is increased and thus the detection of the deformation as well as the detection sensitivity are improved.

[0101] Advantageously, the sensor 1000 also comprises at least one gauge called a witness gauge, configured to deform when a portion of the sensor little impacted by the deformation occurring between the first and second elements, which can be designated a witness portion, deforms. The deformation of this witness portion then reflects the deformation of the test body 1100, solely or almost solely, due to the variations in pressure and temperature to which it is exposed. As will be described further below, this component due to the effects of pressure and temperature is subtracted from the deformation. formation measured by the gauge(s) 1200 attached to the central portion 1130 of the test body in order to correct this measurement. The control portion is part of any one of the first and second portions 1110, 1120. The control portion may in particular be chosen using simulations such as that shown in [Fig.7]. A criterion for choosing the control portion may for example be that the stresses in this portion are less than 25 MPa or 10 times less than the maximum stress (taken in the central portion 1130 of the test body 1100).

[0102] Preferably, the sensor 1000 comprises two gauges 1200 attached to the central portion 1130 and a witness gauge.

[0103] The shape of the test body 1100 may be chosen so as to allow the good integration of the fiber optic gauges in the sensor 1000 and their access to the different portions to which they must be fixed. For example, the shape of the first portion 1110 or of the second portion 1120 may be chosen so that a gauge 1200 reflecting the deformation of the central portion 1130 passes through this portion 1110, 1120 from the outside of the test body 1100 to the central portion 1130.

[0104] In order to improve the sealing of the sensor 1000 and in particular of the gauges (witness or not) and / or of the reading device, it is provided that the sensor 1000 advantageously contains plugs through which these different elements are inserted into the test body 1100. These plugs can be designated sealing plugs.

[0105] For example, the gauges 1200 (witness or not) can each pass through a first plug 1250 which is itself at least partially inserted into the test body 1100. As illustrated in all of the figures and in particular in [Fig.2E], each first plug 1250 typically extends partly outside the test body and partly into an opening provided in the first or second portion 1110, 1120.

[0106] In the same way, advantageously, the sensor 1000 comprises second plugs 1350 through which different instrumentation parts, such as for example the detector of the reading device, are inserted into the test body 1100. The second plugs 1350 may in particular be crossed by connection elements making it possible to electrically power the detector of the reading device and other connection elements making it possible to physically extract from the test body 1100 the data relating to the deformation of the optical fiber gauges. The second plugs 1350 typically each integrate a seal.

[0107] Preferably, the first plugs 1250 and second plugs 1350 are made of stainless steel.

[0108] The first and second plugs 1250, 1350 typically each have an external thread complementary to a tapping defined by the internal flank of a opening in the test body 1100. The first and second plugs 1250, 1350 are typically threaded on only one portion, such that once screwed into the test body 1100, another portion protrudes relative to the test body 1100.

[0109] Data processing

[0110] The detector of the reading device typically comprises a converter. This converter converts the light signal from each fiber optic gauge into an electrical signal.

[0111] The electrical signals associated with the different gauges are then transmitted to a processing system.

[0112] The processing system is configured to establish information on the deformation of the sensor 1000 as a function of these electrical signals.

[0113] In the advantageous case where the sensor 1000 comprises several gauges 1200 fixed to the central portion 1130, the electrical signals from these gauges can be averaged and / or compared and processed so as to exclude aberrant values ​​at the level of the processing system.

[0114] Furthermore, the electrical signal associated with the witness fiber optic gauge(s) makes it possible to determine a correction law applied to the results obtained by the other signals.

[0115] As will be described further, several sensors 1000 may be integrated into the same first and second elements. The processing system may then be common to these sensors 1000.

[0116] Integration of the strain gauge sensor

[0117] As mentioned previously, the sensor 1000 has a first attachment zone 1115 and a second attachment zone 1125 at which the sensor 1000 is attached respectively to a first element and to a second element.

[0118] The sensor 1000 can be fixed to these elements by clamping means inserted into the holes 1116, 1126 provided at the fixing zones 1115, 1125. For example, these can be screws 1117, 1127 having an external thread complementary to a tapping formed in the holes 1116, 1126.

[0119] The screws 1117, 1127 are preferably made of the same material as the test body 1100. This makes it possible to avoid differences in expansion between the screws 1117, 1127 and the test body 1100 during the measurement, and therefore to limit potential temperature effects which could impact the accuracy of the measurement.

[0120] According to a particularly advantageous application of the invention, the sensor 1000 can be fixed, possibly by means of an interface part, to a support plate of a nuclear assembly 10. This can be either the upper support plate 20 of the assembly 10 or the lower support plate 30 of assembly 10. Figures 3A to 5B illustrate the integration of the sensor 1000 at the upper support plate 20 of an assembly 10. Figures 5C and 5D illustrate the integration of the sensor 1000 at the lower support plate 30 of an assembly 10.

[0121] As illustrated in FIGS. 3A and 3B in particular, the sensor 1000 can be fixed at its first portion to a first sub-plate 21 and at its second portion to a second sub-plate 22. These two plates are stacked on top of each other along the main direction Z. The first sub-plate 21 is itself fixed to the upper support plate 20.

[0122] As illustrated in Figures 4A and 4B, the first sub-plate 21 is typically held to a mechanical interface part 23 by clamping means such as screws. The mechanical interface part 23 is itself fixed to the upper support plate 20.

[0123] The mechanical interface part 23 may extend around the second sub-plate 22, as illustrated. However, the mechanical interface part 23 and the second sub-plate 22 are not in contact in order to prevent the force transmitted by the assembly 10 from being applied to the mechanical interface part 23. This also avoids any parasitic friction between the second sub-plate 22 and the mechanical interface part 23.

[0124] The second sub-plate 22 is mechanically connected to the assembly 10, typically by means of an elastic member as described in the introductory part. The elastic member is for example a leaf spring. It typically comprises four leaves.

[0125] The first sub-plate 21 and the second sub-plate 22 of the upper plate are distinct.

[0126] As illustrated in Figures 5C and 5D, when the sensor 1000 is fixed at the lower plate 30, the first sub-plate 31 is typically fixed to the lower support plate 30, possibly by means of a mechanical interface part. The second sub-plate 32 is mechanically connected to the assembly 10, typically by being fixed to a lower end piece 13 of the assembly 10. Unlike the elastic member to which the second sub-plate 22 is conventionally fixed located at the upper plate 20, this lower end piece 13 is rigid. It makes it possible to firmly fix the assembly 10 to the second sub-plate 32. The lower end piece 13 comprises feet, typically four in number, at which the assembly 10 is fixed to the second sub-plate 32.

[0127] The other features described with reference to the first and second sub-plates 21, 22 of the upper support plate 20 apply mutatis mutandis to the first and second sub-plates 31, 32 of the lower support plate 30.

[0128] Whether the sensor 1000 is integrated at the level of the upper plate 20 or the lower plate 30, it makes it possible to effectively measure the hydrodynamic force Fh. Indeed, in both cases, the second sub-plate 22, 32 is immersed in the heat transfer fluid without being kept fixed, while the first sub-plate 21, 31 is kept fixed relative to the lower plate 30 or upper plate 20 to which it is fixed. The application of Fh on the second sub-plate 22, 32 therefore has the effect of causing a displacement between the first sub-plate 21, 31 and the second sub-plate 22, 32, which causes a deformation of the test body 1100, to which the two sub-plates are fixed. The test body can work in tension or in compression, depending on whether the second sub-plate 22, 32 moves away from or towards the first sub-plate 21, 31.The strain gauge(s) and the reading device then make it possible to obtain data on this deformation, which will then make it possible to return to the value of Fh.

[0129] When the sensor 1000 is integrated at the level of the lower support plate 30, it also makes it possible to determine with great precision: i. the value Fhmax of the force Fh for which the assembly 10 detaches under the effect of the force exerted by the heat transfer fluid, ii. the instant at which this detachment takes place, iii. the maximum flow rate of the heat transfer fluid supported by the assembly 10 without detaching.

[0130] Indeed, the detachment of the assembly 10 causes a significant and sudden distance of the second sub-plate 32 from the first sub-plate 31, and therefore a strong and rapid increase in the stresses prevailing in the test body 1100. Fhmax corresponds to the value of Fh at the start of this strong increase. The value of Fhmax and the instant at which this value is taken can easily be determined by reading the data obtained using the fiber optic gauges 1200 and the reading device. The maximum flow rate supported by the assembly without detaching can be obtained by knowing the instant of detachment and by temporal monitoring of the flow rate of the heat transfer fluid. This flow rate corresponds to the limit value of the flow rate not to be exceeded to guarantee the safety of the reactor: in fact, a higher flow rate would lead to an increase in vibrations and would induce a risk of piercing the cladding surrounding the fuel within the assembly 10.

[0131] When the sensor 1000 is integrated at the level of the upper support plate 20, it makes it possible to continue measuring Fh after the assembly 10 has been detached.

[0132] Several sensors 1000 can be integrated at the same plate 20, 30. Advantageously, at least two sensors 1000 are fixed to the same plate 20, 30. This makes it possible to improve the accuracy of the measurement of the deformation between the first and second sub-plates of the plate in question. It has been shown that an excellent accuracy was achieved when four 1000 sensors were integrated into the same plate 20, 30.

[0133] Integrating several sensors 1000 at the same plate 20, 30 also makes it possible to increase the force that can be supported by the set of sensors 1000. For example, it has been proven that two sensors according to the invention integrated into the same parts could together support a force of 12000 N.

[0134] Figures 3A, 4A and 5A illustrate an example in which two sensors are integrated into the upper plate 20, while Figures 3B, 4B and 5B illustrate an example in which four sensors are integrated into the upper plate 20.

[0135] The support plates 20, 30 of the nuclear assemblies typically have, in projection in the transverse plane XY, a circular shape. The same is true for the sub-plates. Furthermore, the sub-plates of the same plate 20, 30 are stacked along the main direction Z and centered relative to each other. It is thus possible to define a stacking axis along which the sub-plates are stacked and centered. This axis is parallel to the main direction Z.

[0136] Advantageously and as shown in FIGS. 3A to 5B, the sensors 1000 are distributed regularly around this stacking axis. For example, in the case where two sensors 1000 are integrated into the same support plate 20, 30, these are placed according to a central symmetry around the stacking axis. In the case where four sensors 1000 are integrated into the same support plate 20, 30, these are preferably placed according to a rotational symmetry of 90° around the stacking axis. Preferably, all the sensors are located at the same distance in the transverse plane XY from the stacking axis. These advantageous configurations are illustrated in particular in FIGS. 6A and 6C for a version with two sensors 1000, and in FIGS. 6B and 6D for a version with four sensors 1000.

[0137] The integration of four sensors, preferably distributed regularly as described previously, also makes it possible to access a distribution in the transverse plane XY of the constraints within the second sub-plate 22, 32.

[0138] When the sensors are integrated at the level of the upper plate 20, knowledge of this distribution can for example make it possible to detect a possible manufacturing, design or positioning defect of the blades forming the elastic member. Advantageously, there are at least as many sensors as there are blades forming the elastic member.

[0139] Furthermore, this distribution can make it possible to trace the hysteresis of the elastic member. Knowledge of the hysteresis makes it possible to reduce the uncertainty in the measurement of the force Fh, which again makes it possible to increase the efficiency of the reactor.

[0140] When the sensors are integrated at the level of the lower plate 20, knowledge of the distribution of the constraints in the transverse plane XY within the second sub-plate 32 can in particular make it possible to detect a possible manufacturing, design or positioning defect in the feet of the lower end piece 13. Advantageously, there are as many sensors as there are feet of the end piece 13. Preferably, each sensor 1000 is positioned in line with a foot of the end piece 13 in the main direction Z.

[0141] When the sensors are integrated at the level of the lower plate 20, knowledge of the distribution of the stresses also makes it possible to trace the deflection of the assembly 10 under the effect of transverse flows of the heat transfer fluid. This makes it possible to know the maximum flow rate of the heat transfer fluid that can be set without the deformation of the assembly 10 causing contact between the assembly 10 and a neighboring assembly. Here again, precise knowledge of this value, made possible by the use of at least four sensors according to the invention, makes it possible to reduce the safety margins implemented and therefore to improve the efficiency of the reactor.

[0142] In view of the above, it is clear that the invention provides a particularly advantageous solution for measuring a compression / traction force. The invention makes it possible to improve the sensitivity of the measurement, even in the presence of strong constraints, in particular significant static pressure. The invention thus makes it possible to significantly reduce the safety margins to be respected during operation of the reactor, and thus to approach the theoretical maximum efficiency of this reactor.

[0143] These advantages provided by the present invention are applicable to very varied fields of application. The invention will be particularly advantageous in the non-limiting field of measuring the hydromechanical forces applied to an element such as a nuclear reactor fuel assembly or to measuring hysteresis forces of the system for maintaining such an assembly.

[0144] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

[0145] In particular, the shape and dimensions of the test body of the force sensor, in particular, may present variations with respect to those represented in the figures, without however departing from the scope of the protection conferred by the claims.

[0146] Furthermore, the sensor according to the invention can be used in various applications, not limited to the measurement of the hydromechanical thrust applied to a fuel assembly of a nuclear reactor or an experimental platform of such a reactor.

Claims

Claims

1. A strain gauge sensor (1000) for measuring the movement or deformation between a first element and a second element in a main direction (Z), the sensor (1000) comprising at least one test body (1100), characterized in that the test body (1100) comprises a first portion (1110) of which a first fixing zone (1115) is intended to be fixed to the first element, a central portion (1130) and a second portion (1120) of which a second fixing zone (1125) is intended to be fixed to the second element, the first portion (1110) and the second portion (1120) being in material continuity via the central portion (1130), the central portion (1130) having an upper face (1131) intended to be positioned opposite the first element and a lower face (1132), opposite the upper face (1131), intended to be placed opposite the second element, the test body (1100) defining: • a first slot (1141) extending between the upper face (1131) of the central portion (1130) and the first portion (1110) and separating the first portion (1110) and the second portion (1120), and • a second slot (1142) extending between the lower face (1132) of the central portion (1130) and the second portion (1120) and separating the first portion (1110) and the second portion (1120), the first fixing zone (1115), the upper face (1131) of the central portion (1130), the lower face (1132) of the central portion (1130) and the second fixing zone (1125) overlapping at least partially in projection in a transverse plane (XY) perpendicular to the main direction (Z), and in that the sensor further comprises: • at least one fiber optic gauge (1200) fixed to the central portion (1130) so that, when the central portion (1130) deforms under the effect of a movement or a deformation between the first element and the second element in the main direction (Z), the fiber optic gauge (1200) also deforms, • a fiber optic gauge reading device.

2. Sensor (1000) according to the preceding claim comprising two fiber optic gauges attached to the central portion (1130).

3. A sensor (1000) according to any preceding claim wherein the central portion (1130) comprises a central wall (1135) separating two openings (1131) defined by the central portion (1130), each of the openings (1131) passing entirely through the central portion (1130) from the first portion (1110) to the second portion (1120).

4. The sensor (1000) of any preceding claim further comprising a fiber optic indicator gauge attached to one of the first portion (1110) and the second portion (1120).

5. The sensor (1000) of any preceding claim further comprising at least one first plug (1250) extending at least partially into one of the first portion (1110) and the second portion (1120), each fiber optic gauge (1200) passing through a first plug (1250), each first plug being configured to, when the sensor (1000) is in an environment comprising a fluid, limit, and preferably prevent, the arrival of the fluid at the fiber optic gauge (1200).

6. Sensor (1000) according to the preceding claim in which each first plug (1250) has an external thread and in which the one among the first portion (1110) and the second portion (1120) in which said first plug (1250) extends has a first opening defining a thread complementary to the external thread of the first plug (1250), the first plug (1250) being screwed into said first portion (1110) or second portion (1120).

7. A sensor (1000) according to any preceding claim further comprising at least one second plug (1350) extending at least partially into one of the first portion (1110) and the second portion (1120), at least a portion of the fiber optic gauge reading device (1200) passing through a second plug (1350), each second plug (1350) being configured to, when the sensor (1000) is in an environment comprising a fluid, limit, and preferably prevent, the arrival of the fluid on the at least portion of the fiber optic gauge reading device (1200) optical.

8. Sensor (1000) according to any one of the preceding claims in which the fiber optic gauge forms an angle substantially equal to 90° with the main direction (Z).

9. An assembly comprising a sensor (1000) according to any one of the preceding claims, a first sub-plate (21, 31) fixed to the first fixing zone (1115) of the first portion (1110) of the test body (1100) and a second sub-plate (22, 32) fixed to the second fixing zone (1125) of the second portion (1120) of the test body (1100), one of the first sub-plate (21, 31) and the second sub-plate (22, 32) being intended to be fixed to one of a lower support plate (30) to which an assembly (10) of a nuclear reactor is held and an upper support plate (20) to which an assembly (10) of a nuclear reactor is held.

10. System comprising: • an assembly (10) for a nuclear power plant configured to carry nuclear fuel materials, • an upper plate (20) for supporting this assembly (10), • a lower plate (30) for supporting this assembly (10), • at least one first sub-plate (21, 31) and at least one second sub-plate (22, 32), • at least one sensor (1000) according to any one of claims 1 to 8, at least one first sub-plate (21, 31) being fixed to any one of the upper plate (20) and the lower plate (30), the at least one second sub-plate (22, 32) being mechanically connected to the assembly (10), the first sub-plate (21, 31) being further fixed to the first fixing zone (1115) of the first portion (1110) of the body test plate (1100) of each sensor (1000) and the first sub-plate (21,31) being furthermore fixed to the second fixing zone (1125) of the second portion (1120) of the test body (1100) of each sensor (1000) so as to measure the movement of the assembly (10) relative to said plate (20, 30).,

11. System according to the preceding claim in which a first sub-plate, called the first upper sub-plate (21) is fixed to the upper plate (20), the system further comprising an elastic member (50) connected on the one hand to the assembly (10) and on the other hand to at least a second sub-plate, called the second upper sub-plate (22), at least one sensor (1000) being fixed to the first upper sub-plate (21) and to the second upper sub-plate (22).

12. System according to any one of the two preceding claims in which a first sub-plate, called the first lower sub-plate (31) is fixed to the lower plate (30), the assembly (10) further comprising a lower end piece (13) located opposite the lower plate (30) and fixed to a second sub-plate, called the second lower sub-plate (32), at least one sensor (1000) being fixed to said first lower sub-plate (31) and to said second lower sub-plate (32).

13. System according to any one of the three preceding claims comprising at least two sensors (1000) fixed to the same first sub-plate (21, 31) and to the same second sub-plate (22, 32).

14. A system according to any one of the four preceding claims comprising at least four sensors (1000) attached to the same first sub-plate (21, 31) and the same second sub-plate (22, 32), preferably exactly four sensors (1000) attached to the same first sub-plate (21, 31) and the same second sub-plate (22, 32).

15. A system according to any one of the five preceding claims wherein all the sensors (1000) are attached to the first upper sub-plate (21).

16. A system according to any one of the six preceding claims wherein all of the sensors (1000) are attached to the first lower sub-plate (31).

17. A nuclear reactor comprising the system according to any one of claims 10 to 16.

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