Force sensor, for example for measuring hydromechanical thrust

Abstract

Title: Force Sensor, for example for measuring hydromechanical thrust. The invention relates to a strain gauge sensor (1000) for measuring the deformation between a first element and a second element along a principal direction (Z). The sensor comprises at least one test body (1100) having 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 includes a fiber optic gauge (1200) fixed to the central portion and a gauge reading device. Figure for the 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. Its particularly advantageous, but not limiting, application lies in the field of strain gauge sensors designed 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 on a nuclear reactor fuel assembly or an experimental platform of such a reactor, subjected to a demanding environment, particularly in terms of pressure or temperature. PRIOR TECHNOLOGY

[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.1].

[0004] The reactor core 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 pass through the fuel rods 11 and capture the heat that is released from them.

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

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

[0007] Thus, in static conditions, the assembly 10 is subjected to the following forces illustrated in [Fig. 1]: i. its weight “P”; ii. the support force Fsm of the elastic element. This force can be determined by knowing the stiffness and stroke of the compression spring; iii. Archimedes' principle "A"; iv. the reaction force “R” of the lower plate 30 on the assembly 10.

[0008] Furthermore, during operation, the fluid 40 exerts a hydrodynamic force Fh on the assembly 10. This force cannot be known with good accuracy. However, the force Fsm exerted by the spring must be calibrated so as to be perfectly matched 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 "lift off" under the effect of the force exerted by the fluid, that is, move it away from the lower plate 30. If it is too strong, it can cause the assembly 10 to bend. Now, since the assemblies 10 of the core are close to each other, they can touch if the bending is too great. This can have dramatic consequences.

[0010] It is therefore important to accurately determine the hydrodynamic force Fh. One solution is to perform 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 accuracy, even in a test prototype.

[0011] Furthermore, it has been found that existing force sensors used to measure Fh malfunction or fail to function above certain pressure levels, typically above 15 bar, and above certain temperature levels, typically above 280°C. However, most nuclear reactors operate at pressures exceeding this limit. For example, the operating pressure of a pressurized water reactor (PWR) is approximately 155 bar, 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 reactor's operating parameters, particularly the heat transfer fluid flow rate. These large safety margins result in an effective reactor efficiency much lower than the maximum efficiency that its components would actually allow.

[0013] There is therefore a need to propose a solution to improve the measurement of the force Fh. This is the aim of the present invention. In particular, an objective of the present invention is to provide a solution that would allow measurements to be taken over a wide range of pressure values, preferably over the entire operating range of a nuclear reactor, especially a PWR reactor.

[0014] The other objects, features and advantages of the present invention will become apparent from the examination 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 along a principal direction, the sensor comprising at least one test body. Preferably, the test body comprises a first portion having a first attachment zone intended to be fixed to the first element, a central portion and a second portion having a second attachment zone 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 slit 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 slit 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 overlap at least partially in projection in a transverse plane perpendicular to the main direction,

[0017] Furthermore, the sensor also comprises: i. at least one fiber optic gauge fixed to the central portion such that, when the central portion deforms due to movement or deformation between the first and second elements along the principal direction, the fiber optic gauge also deforms, ii. a fiber optic gauge reading device.

[0018] The specific shape of the test specimen results in the stresses it experiences being concentrated within its central portion. The relative displacement of the two elements to which the sensor is attached therefore has a greater local impact than for a specimen with a more general shape. This stress concentration has been found to enable particularly sensitive and precise detection using fiber optic strain 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, optical fiber strain gauges, due in particular to their small size, are very insensitive to static pressure. By employing With such gauges, it becomes possible to measure the hydrodynamic force Fh at much higher pressure levels, particularly above 155 bar, the operating pressure of a PWR. These gauges are also resistant to high temperatures, which again allows Fh to be measured under the operating conditions of a PWR.

[0021] The invention therefore proposes an alternative to existing sensors for measuring Fh. The proposed sensor allows, in particular, both a precise measurement and a measurement that can be carried out at high pressures, and in particular 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 later, when the sensor according to the invention is placed between the lower end 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 it taking off. Precise knowledge of this maximum flow rate, which must not be exceeded, makes it possible to further reduce the safety margins and thus, here again, to increase the reactor's efficiency.

[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 on which a nuclear reactor assembly is held and an upper support plate on which a nuclear reactor assembly 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 support plate for this assembly, iii. a lower support plate for 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 and lower plates,

[0026] At least one second sub-plate is mechanically connected to the assembly. The first sub-plate is also fixed to the first mounting area of ​​the first portion of the test body of each sensor. The first sub-plate is also fixed to the second mounting area of ​​the second portion of the body testing of each sensor in order 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, third and fourth aspects of the invention. BRIEF DESCRIPTION OF THE FIGURES

[0029] The aims, objects, features and advantages of the invention will become clearer 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, showing in particular the sensing element and its various portions. [Fig. 2A] also shows in detail the sensor mounting areas.

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

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

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

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

[0036] [Fig.2F] [Fig.2F] is a cross-sectional view of the sensor according to the invention in section represented in [Fig.2E]. [Fig.2F] notably illustrates the integration of 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 allow the deformation to be measured.

[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 a top support plate of a nuclear assembly.

[0040] [Fig.4B]

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

[0042] [Fig.5B]

[0043] [Fig.5C] Figures 5C and 5D are cross-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 into a top support plate of a nuclear assembly.

[0046] [Fig.6B] Figures 6B and 6D are top views of four sensors according to the invention integrated into a top 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 it is subjected to a force of 6000N.

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

[0051] Before proceeding to a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0052] According to a preferred embodiment, the sensor comprises two fiber optic strain gauges attached to the central portion. The use of two fiber optic strain gauges attached to the central portion ensures, firstly, that in the event of a failure of one of the gauges, the measurement is still performed correctly, thanks to the remaining gauge. Secondly, the signals from the two gauges can be processed to exclude outliers or averaged. This improves the accuracy of the calculated Fh value.

[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 section. This structure concentrates the stresses within the test specimen in the central wall. The fiber optic strain gauge(s) is / are advantageously fixed to this central wall. When the sensor includes two strain gauges, they are preferably fixed on either side of the central wall. This avoids measurement bias that could arise from the measurement being taken from one side or the other of the central wall, for example, in the case of imperfect symmetry of the test specimen. The signals from these two strain gauges can, for example, be averaged.

[0054] According to a preferred embodiment, the sensor further comprises a fiber optic gauge attached to one of the first and second portions. The first and second portions are subjected to very little stress when the test specimen is subjected to tension or compression. The gauge therefore allows for the measurement of only, or almost only, the deformation of the test specimen due to temperature effects. This deformation can be subtracted from the deformation measured by the gauges attached to the central portion in order to eliminate the impact of this temperature effect on the measurement. This thus improves the accuracy of the Fh value that will subsequently 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 and second portions, each fiber optic gauge passing through a first plug, each first plug being configured so as, when the sensor is in an environment containing a fluid, to limit, and preferably prevent, the flow of fluid onto 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 lifespan of the sensor.

[0056] According to an advantageous example, each first plug has an external thread and in which that part of the first portion and the second portion in which said first plug extends has a first opening defining a complementary tapping 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 and second portions, at least a portion of the fiber optic gauge reading device passing through a second plug, each second plug being configured so as, when the sensor is in an environment containing a fluid, to limit, and preferably prevent, the flow of fluid onto at least the portion of the fiber optic gauge reading device. The second plugs allow This also seals the reading device. This has the effect of both improving the accuracy of the measurement and increasing the lifespan of the sensor.

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

[0059] According to one embodiment of the system according to the invention, a first sub-plate, referred to as the first upper sub-plate, is fixed to the upper plate, the system further comprising an elastic element connected on the one hand, to the assembly and on the other hand, to at least a second sub-plate, referred to as 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, referred to as 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, referred to as 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 fixed to the same first sub-plate and the same second sub-plate, preferably exactly four sensors fixed to the same first sub-plate and the same second sub-plate.

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

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

[0065] A coordinate system, preferably orthonormal, comprising the X, Y, and Z axes is shown in the figures. This coordinate system is applicable by extension to the other figures. Unless otherwise stated, the relative terms "on," "under," "below," "above," and "below" refer to positions taken along the Z direction.

[0066] The terms "approximately", "about", "in 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 1000 strain gauge sensor, described in its structure with reference to figures 2A to 2F and 6A and 6B and in its integration within a nuclear reactor with reference to figures 3A to 6B.

[0069] The sensor 1000 according to the invention makes it possible to measure the movement or deformation between two elements, called the first element and the second element, along a principal 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 connected by material continuity via the central portion 1130. Preferably, the first and second portions 1110 and 1120 are connected by material continuity only via the central portion 1130. The first portion 1110 and the second portion 1120 are not in contact; they are separated from each other. The first portion 1110, the central portion 1130, and the second portion 1120 may be a single piece, or they may have been formed separately and then joined, for example, by welding.

[0072] The first portion 1110 has a first attachment zone 1115 to which the first element can be attached. Similarly, the second portion 1120 has a second attachment zone 1125 to which the second element can be attached. The attachment zones 1115 and 1125 may, for example, have a hole 1116 and 1126 passing through the first and second portions 1110 and 1120 respectively, along the principal 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 Figures 2E and 2F. Figure 2E is a cross-sectional view of the sensor along section AA shown in Figure 2D, while Figure 2F is a cross-sectional view along section BB shown in Figure 2E. The central portion 1130 preferably has two openings 1131 that pass entirely through it along the first direction X. Advantageously, each of these two openings 1131 has the shape of a half-cylinder. The central portion 1130 can thus include 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 principal direction Z.

[0075] As illustrated in particular in [Fig. 2A], the proof body 1100 defines a first slot 1141 extending in particular between a portion of the first segment 1110 and the upper face 1131 of the central segment 1130. The upper face 1131 is thus located at a distance from the first segment 1110. The portion of the first segment 1110 separated from the upper face 1131 of the central segment 1130 by the first Slot 1141 preferably includes 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 includes 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 from the test body 1100 above the upper face 1131 of the central portion 1130. The second portion 1120 forms a return of material from 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 mounting zones 1115, 1125 preferably have rotational symmetry about 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 mounting 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 specimen 1100 allows the mechanical stresses to be concentrated in 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 specimen when it is pressurized by the application of a force of 6000 N. It can be observed that these stresses are significantly greater (on the order of 100 N / mm²) in the central portion 1130 than in the first portion 1110 and in the second portion 1120 (from approximately 0 to 6 N / mm² in these two portions). It is also noted that the maximum stress obtained by this simulation is 232 MPa, which is significantly lower than the mechanical strength of Inconel® 718 (1034 MPa). This simulation thus confirms that this material is perfectly 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 allows the stresses to be concentrated 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 principal direction Z, ii. A length L1100, measured along the first direction X, iii. A width 11100, measured along the second direction Y.

[0086] By way of example, H1100 is between 40 and 120 cm, and is, for example, approximately equal to 60 cm. L1100 can be between 60 cm and 120 cm, and is, for example, approximately equal to 70 cm. 11100 can be between 25 cm and 60 cm, and is, for example, approximately equal to 35 cm.

[0087] Furthermore, the attachment zones 1115 and 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 denoted H1115 and H1125, preferably substantially equal. These heights H1115 and H1125 may, for example, be between 8 and 12 cm, and each, for example, be substantially equal to 10.5 cm.

[0088] The sensor 1000 further includes at least one optical fiber 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 its spatial period. The fiber core is typically made of glass fiber 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 within a protective cable 1210. This could, for example, be a hollow stainless steel cable. The diameter of the protective cable 1210 is configured to accommodate the gauge 1200. It could, for example, be equal to 3,175 cm. The 1210 protective cable protects the 1200 gauge, particularly from the pressure and temperature conditions to which it is subjected.

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

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

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

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

[0096] 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 change in the Bragg grating period results in a change in the wavelength reflected by the grating. The change in the reflected wavelength thus reflects the deformation of the optical fiber, which itself reflects the deformation of the central portion 1130.

[0097] It is thus envisaged that the sensor 1000 will include a reading device for the fiber optic gauge(s) 1200. The reading device typically includes a light source and a detector.

[0098] The light source is configured to emit a light beam injected into the core of the 1200 gauge optical fiber. It 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 data on the light intensity will then allow the wavelength refracted by the Bragg grating of the fiber optic gauge to be determined.

[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 the detection of the deformation and the detection sensitivity are thus improved.

[0101] Advantageously, the sensor 1000 also includes at least one so-called control gauge, configured to deform when a portion of the sensor, which is only slightly affected by the deformation occurring between the first and second elements and which can be designated the control portion, deforms. The deformation of this control portion then reflects the deformation of the test body 1100, solely or almost solely, due to the pressure and temperature variations to which it is exposed. As will be described later, this component due to the effects of pressure and temperature is subtracted from the deformation 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 can, in particular, be chosen using simulations such as the one shown in [Fig. 7].One criterion for choosing the control portion could, 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 specimen 1100).

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

[0103] The shape of the test body 1100 can be chosen so as to allow the proper integration of the fiber optic gauges into the sensor 1000 and their access to the different portions to which they are to be attached. For example, the shape of the first portion 1110 or the second portion 1120 can 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 the reading device, the sensor 1000 is advantageously provided to contain plugs through which these different elements are inserted into the test body 1100. These plugs may be designated as 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 in the test body 1100. As illustrated in all the figures and in particular in [Fig.2E], each first plug 1250 typically extends partly outside the test body and partly into an opening made in the first or second portion 1110, 1120.

[0106] Similarly, and advantageously, the sensor 1000 includes second plugs 1350 through which various instrumentation components, such as the detector of the reading device, are inserted into the test body 1100. The second plugs 1350 may, in particular, be traversed by connector elements for electrically supplying the detector of the A reading device and other connection elements allow for the physical extraction of data relating to the deformation of fiber optic gauges from the test body 1100. The second set of plugs 1350 typically each incorporate a sealing gasket.

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

[0108] The first and second plugs 1250, 1350 typically each have an external thread complementary to a tapped hole defined by the inner flank of an opening in the test body 1100. The first and second plugs 1250, 1350 are typically threaded on only one part, so that once screwed into the test body 1100, another part is projecting from the test body 1100.

[0109] Data processing

[0110] The detector of the reading device typically includes 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 sensor 1000 as a function of these electrical signals.

[0113] In the advantageous case where the sensor 1000 includes 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 outliers at the processing system level.

[0114] Furthermore, the electrical signal associated with the control 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 later, several 1000 sensors can be integrated into the same first and second elements. The processing system can then be common to these 1000 sensors.

[0116] Integration of the strain gauge sensor

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

[0118] The sensor 1000 can be fixed to these elements by means of clamping inserted into the holes 1116, 1126 provided at the fixing areas 1115, 1125. For example, it 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 avoids differences in expansion between the screws 1117, 1127 and the test body 1100 during the measurement, and therefore limits potential temperature effects that could impact the accuracy of the measurement.

[0120] According to a particularly advantageous application of the invention, the sensor 1000 can be fixed, optionally via an interface piece, 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 the assembly 10. Figures 3A to 5B illustrate the integration of the sensor 1000 at the level of the upper support plate 20 of an assembly 10. Figures 5C and 5D illustrate the integration of the sensor 1000 at the level of the lower support plate 30 of an assembly 10.

[0121] As illustrated in particular in Figures 3A and 3B, 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 one on top of the other in 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 can 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 prevents any unwanted 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 via an elastic element as described in the introductory part. The elastic element 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 to the lower plate 30, the first sub-plate 31 is typically fixed to the lower support plate 30, possibly via a mechanical interface piece. 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 In contrast to the elastic element to which the second sub-plate 22 is conventionally attached, located at the level of the upper plate 20, this lower end piece 13 is rigid. It allows the assembly 10 to be firmly fixed to the second sub-plate 32. The lower end piece 13 includes 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 subplates 21, 22 of the upper support plate 20 apply mutatis mutandis to the first and second subplates 31, 32 of the lower support plate 30.

[0128] Whether the sensor 1000 is integrated into the upper plate 20 or the lower plate 30, it allows for the efficient measurement of the hydrodynamic force Fh. Indeed, in both cases, the second sub-plate 22, 32 is immersed in the heat transfer fluid without being held fixed, while the first sub-plate 21, 31 is held fixed relative to the lower plate 30 or upper plate 20 to which it is attached. The application of Fh to the second sub-plate 22, 32 therefore causes 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 attached. The test body can work in tension or 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 allow data to be obtained on this deformation, which will then allow the value of Fh to be determined.

[0129] When the sensor 1000 is integrated into the lower support plate 30, it also allows for the determination with high precision: i. the Fhmax value of the force Fh at 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 separation of the second sub-plate 32 from the first sub-plate 31, and therefore a sharp and rapid increase in the stresses within the test body 1100. Fhmax corresponds to the value of Fh at the beginning of this sharp increase. The value of Fhmax and the time at which this value is reached can easily be determined by reading the data obtained using the fiber optic strain gauges 1200 and the reading device. The maximum flow rate that the assembly can withstand without detaching can be obtained by knowing the time of detachment and monitoring the flow rate of the heat transfer fluid over time. This flow rate corresponds to the maximum flow rate that must not be exceeded to ensure reactor safety: indeed, a higher flow rate would lead to increased vibrations and would induce a risk of puncture of the cladding surrounding the fuel within assembly 10.

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

[0132] Several 1000 sensors can be integrated into the same plate 20, 30. Advantageously, at least two 1000 sensors are attached to the same plate 20, 30. This improves the accuracy of the deformation measurement between the first and second sub-plates of the plate in question. It has been shown that excellent accuracy is achieved when four 1000 sensors are 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 top plate 20, while figures 3B, 4B and 5B illustrate an example in which four sensors are integrated into the top plate 20.

[0135] The support plates 20, 30 of the nuclear assemblies typically have a circular shape when projected onto the transverse XY plane. The same is true for the sub-plates. Furthermore, the sub-plates of the same plate 20, 30 are stacked along the principal Z direction and centered with respect to each other. A stacking axis can thus be defined along which the sub-plates are stacked and centered. This axis is parallel to the principal Z direction.

[0136] Advantageously, and as shown in Figures 3A to 5B, the 1000 sensors are evenly distributed around this stacking axis. For example, when two 1000 sensors are integrated into the same support plate 20, 30, they are positioned with central symmetry around the stacking axis. When four 1000 sensors are integrated into the same support plate 20, 30, they are preferably positioned with 90° rotational symmetry around the stacking axis. Preferably, all the sensors are equidistant in the transverse XY plane from the stacking axis. These advantageous configurations are illustrated in particular in Figures 6A and 6C for a version with two 1000 sensors, and in Figures 6B and 6D for a version with four 1000 sensors.

[0137] The integration of four sensors, preferably distributed regularly as described above, also allows access to a distribution in the transverse XY plane of the stresses 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 A manufacturing, design, or positioning defect in the blades forming the elastic element. Advantageously, there are at least as many sensors as there are blades forming the elastic element.

[0139] Furthermore, this distribution can be used to determine the hysteresis of the elastic element. Knowledge of the hysteresis reduces the uncertainty in the measurement of the force Fh, which again increases the reactor's efficiency.

[0140] When the sensors are integrated at the level of the lower plate 20, knowledge of the distribution of stresses 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 of 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 opposite a foot of the end piece 13 along the principal direction Z.

[0141] When the sensors are integrated into the lower plate 20, knowledge of the stress distribution also makes it possible to determine the deflection of the assembly 10 under the effect of transverse flows of the heat transfer fluid. This allows 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 to be determined. Here again, the 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 thus improve the reactor's efficiency.

[0142] In light of the foregoing, it is clear that the invention offers a particularly advantageous solution for measuring a decompression / tension force. The invention improves the sensitivity of the measurement, even in the presence of high stresses, particularly significant static pressure. The invention thus makes it possible to significantly reduce the safety margins to be observed during reactor operation, and thereby to approach the theoretical maximum efficiency of this reactor.

[0143] These advantages provided by the present invention are applicable to a wide variety of fields of application. The invention will be particularly advantageous in the non-limiting field of measuring hydromechanical forces applied to an element such as a nuclear reactor fuel assembly or in measuring hysteresis forces of the system holding 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 force sensor's proof body may vary from those shown on the figures, without, however, falling outside 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 measuring the hydromechanical thrust applied to a fuel assembly of a nuclear reactor or an experimental platform of such a reactor.

Claims

1. Demands A strain gauge sensor (1000) for measuring the movement or deformation between a first element and a second element along a principal direction (Z), the sensor (1000) comprising at least one test body (1100), characterized in that the test body (1100) comprises a first portion (1110) having a first attachment zone (1115) intended to be fixed to the first element, a central portion (1130) and a second portion (1120) having a second attachment zone (1125) intended to be fixed to the second element, the first portion (1110) and the second portion (1120) being in material continuity only 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 positioned opposite the second element, the test body (1100) defining: • a first slit (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 slit (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 slot (1141) and the second slot (1142) being entirely distinct, the first mounting area (1115), the upper face (1131) of the central portion (1130), the lower face (1132) of the central portion (1130) and the second mounting area (1125) overlapping at least partially in projection in a transverse plane (XY) perpendicular to the principal direction (Z), and in that the sensor further comprises: • at least one fiber optic gauge (1200) attached to the central portion (1130) such that, when the central portion (1130) deforms under the effect of movement or deformation between the first element and the second element along the principal direction (Z), the optical fiber gauge (1200) also deforms, • a optical fiber gauge reading device.

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

3. Sensor (1000) according to any one of the preceding claims 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. Sensor (1000) according to any one of the preceding claims further comprising a fiber optic gauge indicator fixed to one of the first portion (1110) and the second portion (1120).

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

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

7. Sensor (1000) according to any one of the preceding claims further comprising at least a 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 including a fluid, limit, and preferably prevent, the arrival of the fluid on at least part of the fiber optic gauge reading device (1200).

8. Sensor (1000) according to any one of the preceding claims wherein the optical fiber gauge forms an angle substantially equal to 90° with the principal direction (Z).

9. 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 is held an assembly (10) of a nuclear reactor and an upper support plate (20) to which is held an assembly (10) of a nuclear reactor.

10. A system comprising: • a nuclear power plant assembly (10) configured to carry nuclear fuel materials, • an upper support plate (20) for this assembly (10), • a lower support plate (30) for 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 attached to any one of the upper plate (20) and the lower plate (30), at least one second sub-plate (22, 32) being mechanically connected to the assembly (10), the first sub-plate (21, 31) being further attached to the first attachment zone (1115) of the first portion (1110) of the body test body (1100) of each sensor (1000) and the first sub-plate (21, 31) being further 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) with respect to said plate (20, 30).

11. System according to the preceding claim wherein a first sub-plate, referred to as the first upper sub-plate (21) is fixed to the upper plate (20), the system further comprising an elastic element (50) connected on one side to the assembly (10) and on the other side to at least a second sub-plate, referred to as 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 wherein a first sub-plate, referred to as the first lower sub-plate (31), is fixed to the lower plate (30), the assembly (10) further comprising a lower end piece (13) situated opposite the lower plate (30) and fixed to a second sub-plate, referred to as 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. System according to any one of the four preceding claims comprising at least four sensors (1000) fixed to the same first sub-plate (21, 31) and to the same second sub-plate (22, 32), preferably exactly four sensors (1000) fixed to the same first sub-plate (21, 31) and to the same second sub-plate (22, 32).

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

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

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

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