Measuring core for measuring nuclear heating in a nuclear reactor and calorimetric sensor with such a measuring core

Description

Technical field of the invention

[0001] The invention lies in the field of measurement and instrumentation for nuclear reactors and more particularly in the field of measuring nuclear heating or the energies deposited by radiation in matter (doses and dose rates absorbed by the different materials).

[0002] The invention relates specifically to a measuring core and to a calorimetric sensor comprising such a measuring core, for measuring nuclear heating in a nuclear reactor. State of the art

[0003] Nuclear heating is induced in particular by the photonic and neutron radiation which exists within a nuclear reactor.

[0004] Nuclear heating is the deposition of energy per unit of mass and time (Js -1< .g -1< or W / g) induced by the interactions of radiation with matter.

[0005] Neutron radiation can be quantified using specific systems such as fission chambers, collectrons or activation detectors. Photon radiation can be quantified using specific systems such as ionization chambers or collectrons. Photon and neutron radiation, due to their lack of charges and their mean free paths in matter, have the property of depositing their energy in matter (in materials) even "far" from the place where these radiations are generated (experimental channels in the core, reflectors, etc.), and consequently of heating said materials.

[0006] Materials means the materials contained in the nuclear reactor, for example the reactor structures, experimental devices, including all materials present in the reactor core (including nuclear fuels).

[0007] It is appropriate to quantify the global nuclear heating produced by radiation, rather than particle fluxes, in order to determine the effect of this radiation.

[0008] This is particularly suitable for an experimental nuclear reactor in which the structures and internal systems (experimental devices for example) differ according to the experimental channels and experimental programs. It is all the more necessary to measure nuclear heating in an experimental nuclear reactor as it is a key quantity for sizing experimental devices, particularly from the point of view of their mechanical strength and their thermal resistance.

[0009] Nuclear heating is classically measured by a calorimetric method, using a calorimeter. A calorimetric method essentially consists of determining the nuclear heating of a small element of matter, which can also be called a sample or nucleus, whose mass is known, by measuring the variation in temperature(s) or a difference in temperature(s).

[0010] In the following description, this small piece of material will be referred to as a "sample." The sample is usually made of graphite or metal.

[0011] The temperature variation(s) or the temperature difference(s) may be due to the effects of photonic and neutron radiation. It may also be due to a heating system integrated into the calorimeter, combined or not with the radiation, for example to calibrate the calorimeter outside or inside the reactor, or to implement a so-called "zero" measurement protocol in the reactor or a so-called "current addition" measurement protocol in the reactor. Such measurement protocols are described in patent FR 2 968 448.

[0012] A two-tube differential calorimeter is commonly used. A differential calorimeter is non-adiabatic in that there is heat exchange between the calorimeter and the heat transfer fluid outside the calorimeter.

[0013] The aforementioned patent FR 2 968 448 describes a differential calorimeter comprising a calorimetric cell with two essentially identical test pieces, superimposed one above the other along a main axis, a first test piece being full, i.e. comprising a sample of material in which the energy deposition is to be measured, and a second test piece being empty and serving as a reference. Each test piece is connected to a base in the main axis via a connecting cylinder, and two thermocouples per test piece are arranged, one at the top of the connecting cylinder and the other at the base. The temperature difference between the two thermocouples is measured. The nuclear heating measurement is based on a double temperature difference between the two test pieces. The energy deposition is deduced from this double temperature difference between the two test pieces, and is expressed in W / g.

[0014] In order to compensate for the lack of juxtaposition of the test pieces in such a configuration, patent FR 2 968 448 requires the calorimetric cell to move along the main axis with measurements of temperature differences for each test piece at each axial position, the movement being associated with adequate synchronization of the measurements.

[0015] In order to enable nuclear heating measurements to be carried out by favoring radial heat exchanges, a calorimetric cell with at least one test piece has been developed and described in patent FR 3 034 867, which comprises: a body configured to contain a sample, sensitive to heat, along a longitudinal axis and means for evacuating the heat from the body to the outside of the test piece, comprising a peripheral structure located at the periphery of the body and a central mechanical connection structure arranged radially between the body and the peripheral structure to transfer the heat radially. The calorimetric cell further comprises two thermocouples per test piece: one at the body / central structure interface and the other at the central structure / peripheral structure interface. The calorimetric cell generally comprises two test pieces with an external envelope encapsulating the assembly.

[0016] A disadvantage of the calorimetric cells described, whether they are single-specimen or double-specimen for differential calorimeter, is that these cells are made up of several elements forming a structure whose mass and dimensions are involved in its physical behavior, and in particular induce heating of the structure itself, increasing the absolute temperatures reached within the calorimeter, even though only the heating of the sample is sought. This disadvantage explains in particular the need to carry out differential measurements, with two specimens, in order to correct the biases induced by parasitic energy deposits, in particular on the structure itself, and thus identify the heating of the sample alone and go back to the dose rate absorbed by said sample. However, the use of two specimens instead of a single one makes the mass and dimensions of the calorimetric cell greater.This drawback requires, as described in patent FR 2 968 448, moving the two test pieces to take a measurement at a given dimension, which greatly complicates the measurement and lengthens the measurement time.

[0017] Furthermore, since a simple calorimetric cell (a single specimen) can reach several centimeters in height to several tens of centimeters in height for a differential calorimetric cell (two specimens), this limits the integration of calorimeters into the experimental channels of reactors given the space available in said channels. This also limits their coupling with other sensors in multi-sensor devices for measurements in said channels. This also prevents the integration of calorimeters into some irradiation devices.

[0018] Furthermore, the sample size (a few centimeters) of known calorimeters does not allow local measurement over a few millimeters.

[0019] Finally, the mass and dimensions of calorimeters (particularly differential ones) induce significant response times which have an impact on the duration of the measurement (it is in fact necessary to wait until a stationary regime is established), and on the maximum temperature reached in the calorimeter.

[0020] The invention aims to overcome the aforementioned drawbacks of the prior art.

[0021] More specifically, the invention aims to provide a calorimetric cell, hereinafter referred to as a "calorimetric sensor", which is suitable for measuring nuclear heating in a nuclear reactor, and whose size and mass are reduced compared to known calorimetric cells, so as to reduce the bulk, and whose size of the sample included in the sensor is reduced so as to improve the spatial resolution of the measurement.

[0022] The invention also aims to limit parasitic heating in the structure of the calorimetric cell, without necessarily having to move said sensor to measure nuclear heating at a given level and / or to carry out a differential measurement with two test pieces.

[0023] A miniaturized calorimetric sensor with a short response time and not requiring movement for measuring nuclear heating at a given level is advantageously sought, so as to reduce the measurement time (from several tens of minutes to a few minutes or even a few tens of seconds depending on the sensor configuration). A calorimetric sensor with a reduced number of cables is particularly sought. Statement of the invention

[0024] A first object of the invention making it possible to overcome these drawbacks is a calorimetric measuring core for measuring nuclear heating in a nuclear reactor, said measuring core extending in a longitudinal direction and having a main plane, and comprising at least: a first layer of material, forming a first sample; a first thin layer of electrical insulation arranged on the first sample; a thin conductive layer forming an electrical heating resistor arranged on the first layer of electrical insulation; a second thin layer of electrical insulation arranged on the electrical heating resistor; the first thin layer of insulation having dimensions in the main plane adapted to those of the first sample; the thin layers of electrical insulation being configured to insulate the heating resistance of the sample and / or protect said heating resistance; and the first sample preferably having dimensions less than or equal to around fifteen, or even around ten millimeters in the main plane, and / or a thickness less than or equal to 10 millimeters, even more preferably less than or equal to 2 millimeters.

[0025] A layer of material forms a sample for which the quantification of nuclear heating is sought. In other words, the quantification of nuclear heating is sought only for the sample(s).

[0026] A “thin” layer is defined as a layer with a thickness less than or equal to 10 µm.

[0027] According to the configurations of the measuring core according to the invention, the dimensions in the plane refer to the length, the width and / or the diameter and correspond to the dimensions relative to the main plane of the measuring core. The thickness and the depth designate the dimension in a direction perpendicular to the main plane. The terms "upper" or "lower" are to be understood with reference to the longitudinal direction of the measuring core and the calorimetric sensor when they are arranged vertically knowing that they can be arranged horizontally or obliquely.

[0028] The invention makes it possible, by using layers of reduced thickness and dimensions in the plane, to reduce the size and mass of the measuring core and the calorimetric sensor. This allows for a more local measurement, a better spatial resolution, while not requiring movement of the calorimetric sensor for a measurement at a given level. This also allows a reduction in the response time, which, coupled with the absence of movement, results in shorter measurement times. In addition, this allows a reduction in the total mass, reducing parasitic heating of the structure and therefore the maximum temperatures reached. In addition, the invention makes it possible to reduce the number of electrical connection cables, due to the use of a single test piece (i.e. a single measuring core).

[0029] In addition, the calorimetric sensor, due to its reduced size, makes it possible to place several calorimetric sensors in a measurement channel in a nuclear reactor, possibly with samples of different natures depending on the sensors, or even to couple it to other sensors, such as radiation detectors (ionization chambers, fission chambers, collectrons, etc.).

[0030] The calorimetric measuring core according to the invention may further comprise one or more of the following characteristics taken in isolation or in any possible technical combination.

[0031] According to one embodiment, the measurement core further comprises: a second layer of material, forming a second sample; the second thin layer of electrical insulation being between the heating resistor and the second sample; the second thin layer of electrical insulation having dimensions in the main plane adapted to those of the second sample; the second layer of electrical insulation being configured to insulate the heating resistance of the second sample; the second sample preferably having dimensions less than or equal to about fifteen, or even ten millimeters in the main plane, and / or a thickness less than or equal to 10 millimeters, even more preferably less than or equal to 2 millimeters. This allows for overall symmetry, the heating element being at the center of an assembly composed of two samples and two thin layers of electrical insulation, and better thermal homogeneity in the sample.

[0032] According to a particular embodiment, the first sample has a length, respectively a diameter, greater than the length, respectively the diameter, of the second sample. The first sample can in particular be adapted to be able to receive the entire surface of the heating resistor as well as its connections, while the second sample can be adapted to cover the heating resistor with the exception of its connections.

[0033] According to one embodiment, the heating resistor comprises a track made of a conductive material shaped into a serpentine, spiral, meander(s) or any other shape adapted to the shape of the samples.

[0034] According to one embodiment, the heating resistor is made of platinum, a nickel-chromium alloy, constantan, or any other material suitable for forming a heating resistor.

[0035] According to one embodiment, the thin electrically insulating layers are made of silicon oxide, alumina, silicon nitride, or magnesium oxide.

[0036] According to one embodiment, the sample(s) is (are) made of graphite, stainless steel, aluminum, or titanium.

[0037] According to one embodiment, the sample(s) have(s) a surface state suitable for the deposition of at least one thin layer of electrical insulation by a thin layer deposition technique, for example a mirror-polished surface state. This makes it possible to improve the adhesion of the thin layers of the heating element to the sample(s).

[0038] According to one embodiment, the measuring core further comprises at least one bonding layer between the heating resistor and at least one thin layer of electrical insulation and / or between at least one sample and at least one thin layer of electrical insulation. A bonding layer allows better bonding between two layers.

[0039] According to one embodiment, the measuring core further comprises at least one functional layer, which may be a layer of boron, cadmium, silicon carbide (SiC) and / or lithium, said functional layer being able to be deposited on the outer face of at least one sample. It may for example have a thickness of the same order as the other thin layers. Such a functional layer may make it possible to: generate selective specific interactions, and / or convert particles / radiations, and / or amplify nuclear heating.

[0040] According to one embodiment, the first sample, and where appropriate the second sample, is parallelepiped in shape, forming a parallelepiped core.

[0041] According to an alternative embodiment, the first sample, and where appropriate the second sample, is of hemicylindrical shape forming a hemicylindrical or cylindrical core, the length of the cylinder extending in the longitudinal direction.

[0042] According to another alternative embodiment, the first sample, and where appropriate the second sample, is disc-shaped, the disc diameter extending in the longitudinal direction.

[0043] According to one embodiment, at least one sample is perforated at least one upper and / or lower portion, so as to form at least two upper legs and / or at least two lower legs.

[0044] According to a particular embodiment, the upper legs are sized to accommodate the connection elements of the heating resistor, the upper legs having for example a width greater than the lower legs.

[0045] According to a particular embodiment, the heating resistor is configured to form a resistive temperature probe, so as to measure the temperature in an area comprising a temperature measurement hot spot, said heating resistor then being connected to a resistance measuring means, preferably by a four-wire assembly.

[0046] A second object of the invention is a calorimetric sensor for measuring nuclear heating in a nuclear reactor, said sensor comprising: a fluid-tight outer casing; a gas contained in the outer casing; a measuring core according to the first subject of the invention, said core being arranged in the outer casing; connecting means capable of holding the measuring core in the outer casing and of transferring heat between said core and said casing; temperature measuring means, comprising a first temperature measuring means capable of measuring the temperature at a hot point, preferably as close as possible to the heating element of the measuring core, and a second temperature measuring means capable of measuring the temperature at a cold point, preferably on a wall of the casing.

[0047] According to one embodiment, the temperature measuring means comprise at least one thermocouple, preferably a wired micro-thermocouple or a thin-film micro-thermocouple.

[0048] According to one embodiment, the first temperature measuring means is formed by the heating resistor.

[0049] According to one embodiment, the connecting means comprise spacers which may have different shapes and materials.

[0050] According to one embodiment, at least one sample is perforated at the level of at least one upper and / or lower portion, so as to form at least two upper legs and / or at least two lower legs, the connecting means being all or part formed by said legs.

[0051] According to one embodiment, the casing is made of aluminum, stainless steel or titanium.

[0052] The calorimetric measuring core and the calorimetric sensor according to the invention may comprise any of the characteristics previously stated, taken in isolation or in any technically possible combinations with other characteristics. Brief description of the figures

[0053] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended figures given by way of example: [ Fig. 1A ], [ Fig. 1B ], [ Fig. 1C ], And [ Fig. 1D ] represent a measuring core according to a first embodiment of the invention shown in exploded view and horizontally. Fig.2 ] represents the measuring core according to the first embodiment of the invention shown in front view and vertically. [ Fig. 3 ] represents a measuring core according to a second embodiment of the invention shown in front view. [ Fig.4 ] represents a measuring core according to a third embodiment of the invention shown in exploded view and horizontally. Fig.5 ] represents a measuring core according to a fourth embodiment of the invention shown in exploded view and vertically. Fig.6A ] And [ Fig.6B ] represent a calorimetric sensor according to a first embodiment. [ Fig.7 ] represents a calorimetric sensor according to a second embodiment

[0054] Throughout these figures, like references may designate identical or similar elements.

[0055] Furthermore, the different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable. Detailed description of the invention

[0056] THE Figures 1A to 1D , 2, 3 , 4 And 5represent several embodiments of a measuring core according to the invention, and capable of being assembled in a calorimetric sensor. The X direction corresponds to the longitudinal direction of the measuring core and the sensor, the Y direction to the transverse direction and XY corresponds to the principal plane of the measuring core. The Z direction is the direction orthogonal to the principal plane. First embodiment (measuring core)

[0057] THE Figures 1A to 1D illustrate a measuring core 16 according to a first embodiment, shown in exploded view, and according to the different stages of assembly of the different elements of said measuring core. The longitudinal direction X of the measuring core shown is oriented horizontally, although it can be arranged vertically, as shown in Figure 2 , and in particular vertically in the calorimetric sensor as shown in Figures 6A And 6B .

[0058] The core of measurement 16, of parallelepiped shape, comprises in stacking order: a first layer of material forming a first sample 161 in which the quantification of nuclear heating is sought; a first thin layer of electrical insulation 163; an electrical heating resistor 164 (thin conductive layer); a second thin layer of electrical insulation 165; a second layer of material forming a second sample 162 in which the quantification of nuclear heating is sought.

[0059] The assembly of heating resistor and thin layers of insulation forms a heating element, the heating resistor being sandwiched between the two thin layers of insulation.

[0060] The layers constituting the measuring core are parallelepiped in shape, except for the resistor which has a particular shape, described later. The layers are stacked on top of each other.

[0061] A sample is an element of matter of known mass, whose nuclear heating is to be measured. The material of a sample can be graphite, stainless steel, aluminum or titanium. The width and length of a sample vary between a few millimeters to about fifteen millimeters, or even ten millimeters. The thickness of a sample is of the order of one to two millimeters, a minimum thickness being required in order to have significant energy deposits. In this embodiment, the two samples have substantially the same dimensions except for their lengths L1, L2.

[0062] The first sample 161 has a length L1 greater than the length L2 of the second sample 162 in order to be able to receive the entire surface of the heating resistor 164 as well as its connections, represented in the form of two pads 1641 and 1642, while the second sample has a reduced length L2 so as to cover the heating resistor with the exception of the connections.

[0063] For example, the first and second samples may have the following respective dimensions (length x width x thickness): 13 mm x 10 mm x 1 mm (first sample 161) and 10 mm x 10 mm x 1 mm (second sample 162); or 7 mm x 4 mm x 1 mm (first sample 161) and 4 mm x 4 mm x 1 mm (second sample 162).

[0064] Furthermore, the first insulating layer 163 also has a length greater than that of the second insulating layer 165. Each insulating layer is arranged between the heating resistor and one of the samples, in order to electrically insulate said heating resistor (conductive layer) from the samples. Each insulating layer must therefore have sufficient dimensions in the plane to electrically insulate the heating resistor from each sample, but also to be able to be deposited on said sample. In other words, the dimensions in the plane of an insulating layer must also be adapted to those of the sample with which they are directly in contact. The thickness of an insulating layer is between approximately 100 nm and a few µm. An insulating layer may be made in particular of silicon oxide, alumina, silicon nitride, magnesium oxide.Alpha alumina is particularly interesting because of its very high melting temperature.

[0065] The surface condition of the samples is an important element insofar as it conditions the adhesion of the thin layers of the heating element on said samples. Preferably, the samples have a mirror-polished surface condition. To achieve a suitable surface condition, the samples can undergo a preparation step prior to the deposition of the thin layers, which may consist of cleaning for a few minutes in an ultrasonic bath with acetone, then ethanol and finally distilled water. This preparation of the samples makes it possible to improve the interfaces between the thin layers and the samples and thus improve the physicochemical properties of the assembly.

[0066] The heating resistor comprises a track made of a conductive material shaped, for example, into a serpentine. The conductive material may be platinum, a nickel-chromium alloy, or another alloy (such as constantan). The thickness of the heating resistor is between approximately a few tens of nm and a few µm. The width of the track is less than or equal to 0.5 mm. All of the characteristics of the track (shape, thickness, width, length) depend on the desired resistance value.

[0067] Alternatively, the heating resistor may be in the form of a spiral, in particular a circular spiral, or any other shape suitable for forming a resistor, in particular meandering and adapted to the shape of the samples.

[0068] The heating resistor and insulating layers together form a heating element which is manufactured at the same time as the measuring core is manufactured.

[0069] The heating element can be manufactured using one of the known microelectronics techniques. The heating resistor can be produced in particular using a lift-off photolithography technique coupled with a thin-film deposition technique (in particular sputtering) to obtain the desired shape, for example a serpentine or spiral. The insulating thin layers can be deposited using a thin-film deposition technique (in particular sputtering or vacuum thermal evaporation).

[0070] The heating element makes it possible to calibrate the calorimetric sensor before integration into a nuclear reactor (outside an irradiated environment). In particular, it makes it possible to locally simulate nuclear heating by the Joule effect. The heating element can also make it possible to calibrate the calorimetric sensor after integration into a nuclear reactor (in an irradiated environment) and to apply so-called "zero" or "current addition" measurement methods for which it is necessary to provide additional energy to the energy deposited by radiation / matter interaction (measurement methods whose principles are described in patent FR 2 968 448 but which are adapted in a manner known to those skilled in the art for the measurement core according to the invention). Implementation variant

[0071] According to an alternative embodiment, the heating element, and in particular the heating resistor, can be used to form a temperature sensor, more precisely a resistive temperature probe, to measure the temperature in the hot spot area. In this case, the heating resistor is a temperature-sensitive resistor R(T), and the temperature can be given by the law (linear approximation): R T = R T 0 × 1 + α T − T 0 = R T 0 + R T 0 × α T − T 0 where α is the temperature coefficient of the conductive material of the resistor.

[0072] By measuring the resistance R(T) and knowing the initial resistance R(T 0 ) given for an initial temperature T 0 , we deduce the temperature difference ΔT corresponding to TT 0 .

[0073] It should be noted that the initial resistance can be expressed by the formula: R T 0 = ρ T 0 × L T 0 S T 0

[0074] Where L is the total length of the heating resistor track and S its section, and where ρ is the resistivity of the conductive material of the heating resistor, given at the initial temperature T 0 .

[0075] In this case, it is appropriate to connect said heating resistor to a means of measuring the resistance, preferably by a 4-wire assembly, which is a more precise assembly than a 2 or 3-wire assembly known for measuring a resistance. R(T 0 ) can be measured in the same way.

[0076] There Figure 2 represents the measuring core 16 according to the first embodiment of the invention, shown in front view and vertically, as it is generally oriented in the sensor. Second embodiment (measuring core)

[0077] There Figure 3represents a measuring core 16' according to a second embodiment of the invention shown in front view. The measuring core 16' of this second embodiment differs from that of the first embodiment, in that the samples 161', 162' have the same lengths but they have an openwork shape in the upper and lower portions. This makes it possible to form four legs per sample (two upper legs 161A', 161B', 162A', 162B' and two lower legs 161C', 161D', 162C', 162D') at the four corners of each sample. The upper legs 161A', 161B', 162A', 162B' are wider than the lower legs, so as to accommodate the connection pads 1641' and 1642' of the heating resistor 164'.

[0078] In addition, these lower and upper legs can be brought into contact with the casing of the calorimetric sensor, as described later. Thus, as will be explained later, this makes it possible to replace all or some of the spacers necessary for assembling the measuring core in the calorimetric sensor. This makes it possible in particular to facilitate assembly and to eliminate the added spacers. This makes it possible to reduce parasitic heating, in particular due to spacers machined from a material different from the sample. In the example shown, both the upper or lower portions are perforated. Alternatively, only an upper portion or a lower portion of one or two samples can be perforated.

[0079] The orders of magnitude of the dimensions of the samples given for the first embodiment are still valid: the width and length of a sample vary between a few millimeters to fifteen or even ten millimeters, and the thickness is between one and two millimeters.

[0080] Furthermore, the first and second insulating layers (not shown because they are hidden by the samples) have dimensions and shapes adapted to the dimensions of the first and second samples 161', 162' (they are also perforated) and they must always have sufficient dimensions in the plane to insulate the resistance and protect it. The dimensions of said thin insulating layers and of said heating resistance are of the same order of magnitude as for the first embodiment.

[0081] In both embodiments described above, the samples and therefore the measuring cores have a parallelepiped shape (openwork or not). Such a shape makes it possible to simplify the assembly of the different layers of the measuring core. This also makes it easier to use certain thin-film deposition techniques for manufacturing the heating element, in particular by manufacturing it directly on a sample. Third embodiment (measuring core)

[0082] Alternatively, the 161", 162" samples and thus the 16" measuring core may have a disc shape, as shown in Figure 4 The longitudinal dimension then corresponds to the diameter of the samples.

[0083] In this case, the heating resistor 164" has a circular spiral shape, with two electrical connection pads 1641", 1642" which can be diametrically opposed, as shown (non-limiting). The two discs forming the two samples 161", 162" then have different diameters Φ1, Φ2 to accommodate the connection pads of the heating resistor.

[0084] The 163", 165" thin layers are also circular disc-shaped, their diameters being adapted to that of the sample with which they are directly in contact.

[0085] The orders of magnitude of the dimensions of the samples given for the first embodiment are still valid: the diameter of a sample varies between a few millimeters to fifteen or even ten millimeters, and the thickness is between one and two millimeters. Fourth embodiment (measuring core)

[0086] Alternatively, the measuring core can be cylindrical (or even semi-cylindrical) in shape, with the longitudinal direction corresponding to the length of said cylinder, a shape more suited to most measuring channels in nuclear reactors. This is illustrated in the Figure 5 representing a fourth embodiment of a measuring core 17 according to the invention.

[0087] In this embodiment, the two samples are of semi-cylindrical shape, that is to say they are cylinders cut in two longitudinally, each half-cylinder then having a flat surface, corresponding to the main plane XY, on which the heating element can be deposited, that is to say the heating resistor sandwiched between the two thin insulating layers. The flat surfaces of the half-cylinders are assembled with this heating element which is then sandwiched between the two half-cylinders, so as to form a cylindrical measuring core.

[0088] In the fourth embodiment, the two samples 171, 172 have the same diameter but different lengths. The longitudinal direction of each semi-cylindrical sample corresponds to the length of said sample, and the latter is a cylinder cut in two along this longitudinal direction.

[0089] The length (L1, L2) of a sample varies between a few millimeters and about fifteen millimeters or even ten millimeters. The maximum width, given by the diameter (D1, D2) varies between a few millimeters and about ten millimeters. The maximum thickness of a sample given by the radius (D1 / 2, D2 / 2) is a few millimeters.

[0090] For example, the first and second samples may have the following respective dimensions: diameter (D1) of 4 mm x length (L1) of 7 mm and diameter (D2) of 4 mm x length (L2) of 4 mm.

[0091] The dimensions of the thin insulating layers (173, 175) and the heating resistor (174) are of the same order of magnitude as for the other embodiments. Since the heating element is arranged on the flat surface XY, it can be rectangular in shape.

[0092] Generally, the shape of the measuring core is conditioned by the shape of the samples, as well as by the number of sample(s). For example, if there is only one semi-cylindrical sample, then the shape of the measuring core is also semi-cylindrical.

[0093] In all the modes represented, it can be seen that the set of layers makes it possible to form a measuring core whose thickness is at most a few millimeters, which makes it possible to reduce the thickness of the calorimetric sensor. Furthermore, the dimensions in the plane of the measuring core (length, width, and / or diameter) are of the order of a centimeter. In addition, the layers of the heating element are thin layers which are negligible in mass and thickness compared to the samples which are themselves sized to allow radiation-matter interactions and the quantification of nuclear heating, and must therefore have at least a minimal thickness.

[0094] THE Figures 1A to 1D , 2, 3 , 4 And 5 represent measurement cores comprising two samples, it being understood that a single sample may be sufficient.

[0095] Indeed, it may be sufficient or even advantageous to have only one sample, for example in one or more of the following cases: when the sample has a high density and atomic number, sufficient to have significant energy deposits and measure nuclear heating; and / or when it is difficult to obtain two samples of low thickness associated with a suitable surface state (sufficiently polished surface) to deposit the thin layers by one of the microelectronic techniques; and / or when it is desired to simplify the assembly of the measuring core; and / or to avoid forming a thermal contact resistance by assembling two samples; and / or to reduce the mass of the measuring core, and thus in particular increase the measuring range.

[0096] When there is only one sample, the above embodiments and manufacturing methods apply, except that the second layer of material forming the second sample is not present. The electrical heating resistor is sandwiched between the two thin insulating layers in order, on one side, to insulate it from the sample and on the other side, to protect it.

[0097] Conversely, a two-sample measurement kernel has the following advantages: overall symmetry: in fact, the heating element is located at the center of an assembly composed of two samples and two thin layers of electrical insulation; better thermal homogeneity in the sample.

[0098] Both samples are made of the same material. They preferably have the same shapes and dimensions, except for the length or diameter, which may be different. They also have the same surface conditions.

[0099] It is possible to act on the shapes and dimensions of the sample(s) in order to control the sensitivity of the sensor, instead of or in addition to acting on the shape or dimensions of the calorimetric sensor and / or on the nature of the gas and / or the size of the gas blades in the sensor.

[0100] In all of the modes represented, and more generally within the framework of the invention, additional layers can be added to the measurement core. Thin bonding layer:

[0101] A thin bonding layer can be provided between the heating resistor and at least one thin insulating layer (the insulating layer on which the resistor is deposited). The function of a bonding layer is to allow better bonding of the heating resistor to the insulating layer. The thickness of a bonding layer must be very low (a few nanometers) so as not to disturb the assembly. This bonding layer must have the same shape as the heating element. In addition, depending on the nature of the materials and the deposition conditions, another bonding layer can be deposited between the sample(s) and one or more thin insulating layers, for better bonding of one or more thin insulating layers to the sample(s). A bonding layer can be, for example, a titanium layer or a tantalum layer. Functional layer:

[0102] At least one functional layer can be added to the measurement core. This can be a layer of boron, cadmium, silicon carbide (SiC) and / or lithium. A functional layer has smaller dimensions than the samples, and can be applied to a sample (for example on its outer face). It can, for example, have a thickness of the same order as the other thin layers. Such a functional layer can make it possible to: generate selective specific interactions, and / or convert particles / radiation, and / or amplify nuclear heating. First embodiment (calorimetric sensor)

[0103] THE Figures 6A(longitudinal sectional view) and 6B (3D view) illustrate a calorimetric sensor according to a first embodiment. This is shown with a measuring core configured according to the first embodiment, but it could include a measuring core according to one of the other embodiments or any other measuring core falling within the scope of the invention.

[0104] To form a calorimetric sensor, the measuring core is integrated into a gas-containing envelope, and is kept centered in said envelope by several spacers which also allow heat to be transferred between the measuring core and the envelope.

[0105] Thus, the measuring sensor 1 shown comprises: an outer casing 11, being a fluid-tight casing; a gas 12 contained in the casing; a measuring core 16 integrated in the casing; a plurality of spacers 13 connecting the core and the casing and making it possible to maintain, position, or even center, said core in said casing; two temperature sensors: a first “hot” temperature sensor 14 and a second “cold” temperature sensor 15; connection wires 19A and 19B (between two and four) connected to the heating element of the measuring core.

[0106] The waterproof envelope allows the various elements to be contained and protected. Furthermore, the envelope is designed to be in direct contact with a heat transfer fluid in order to evacuate thermal energy.

[0107] The casing can be made of aluminum, stainless steel or titanium.

[0108] The envelope shown is parallelepiped in shape. The dimensions of the envelope are typically a few centimeters, for example a length of about three centimeters, a width of about two centimeters, and a depth of about one centimeter. The dimensions could, however, be reduced and more generally vary between a few millimeters and a few centimeters (typically less than or equal to three centimeters). The thickness of the walls of the envelope is, for example, ½ millimeter.

[0109] Alternatively, the casing may be cylindrical, a shape more suitable for most measurement channels in nuclear reactors. In this case, the measuring core is preferably cylindrical or semi-cylindrical, but a parallelepiped shape could be suitable. A cylindrical casing may have a tapered end to improve the flow of the heat transfer fluid around the calorimetric sensor.

[0110] The sensor's sensitivity can be adjusted by choosing the type of gas based on its thermal conductivity and thus by adjusting the thermal resistance of the gas layer. It can also prevent oxidation in the sensor. The gas can be helium, nitrogen, argon, or xenon. The gas can be overpressured by a few tens of mbars above atmospheric pressure.

[0111] The first temperature sensor is located as close as possible to the center of the measuring core and allows a temperature to be measured at a so-called "hot" point. The second temperature sensor is placed on (or integrated into) the casing and allows a temperature to be measured at a so-called "cold" point. The temperature measurements at the cold and hot points allow nuclear heating to be determined.

[0112] The first sensor may be a thermocouple, for example of type K or N, the diameter of which is preferably between 0.1 mm and 0.5 mm. The materials of the thermocouples may be: Chromel (Ni-Cr), Alumel (Ni-Al), Ni-crosil (Ni-Cr-Si), Nisil (Ni-Si). The first sensor is as close as possible to the heating element, and it is preferably geometrically aligned with respect to the center of the heating element. Alternatively, as indicated in the embodiment variant described above, the first sensor may be formed by the heating element which then forms a resistive temperature probe.

[0113] The second sensor may be a thermocouple, for example of type K or N, with a diameter preferably between 0.1 mm and 0.5 mm. The thermocouple materials may be: Chromel (Ni-Cr), Alumel (Ni-Al), Ni-crosil (Ni-Cr-Si), Nisil (Ni-Si). The second sensor may be geometrically aligned with respect to the center of the heating element, with a temperature measurement at the envelope, as shown. This may be at the internal face or at the external face of the envelope wall.

[0114] Each temperature sensor is wired using a connector (not shown) to transfer the measurement from the measurement core to the data acquisition unit.

[0115] Temperature sensors can advantageously be micro-thermocouples, either wire micro-thermocouples or thin-film micro-thermocouples. The diameter (wire micro-thermocouple) or thickness (film micro-thermocouple) of such a sensor is of the order of a few micrometers at the measurement point. Connections with diameters similar to those of conventional thermocouples are also necessary to transfer the measurement from the measuring core to the data acquisition unit. The small size of micro-thermocouples has the advantage of less disruption to the measurement due to their lower intrusiveness, especially in the case where the dimensions of the measuring core are comparable to those of the temperature sensors. They are positioned in the same position as conventional thermocouples: close to the heating element and close to the casing.

[0116] The heating resistor is wired using wires (between two and four wires) 19A and 19B which pass through the casing 11 and are then connected to connectors for connection to power supplies and to an acquisition unit.

[0117] The spacers can be in the form of cylindrical rods (with a diameter of 1 millimeter for example) and / or parallelepipeds.

[0118] Preferably, the spacers are made of a material identical to that of the samples, for example aluminum, stainless steel or titanium. Beyond their function of holding, positioning and / or centering, the spacers are also configured to transfer heat between the measuring core and the envelope. Thus, they can be of dimensions chosen to form a given thermal resistance and therefore be a parameter for adjusting the sensitivity of the sensor. In addition, spacers are sought whose thickness and dimensions allow for the addition of no parasitic mass.

[0119] All or part of the spacers may be formed by tabs at the four corners of the samples by an openwork shape of the samples as illustrated in Figure 3 and in the Figure 7 described below, and / or by pointed shapes provided inside the envelope. Second embodiment (calorimetric sensor)

[0120] There Figure 7represents a calorimetric sensor according to a second embodiment in which the measuring core has an openwork shape, like the measuring core 16' of the Figure 3 .

[0121] The calorimetric sensor 1' shown does not include spacers, the measuring core 16' being held in the casing 11 by the legs of the two perforated samples (eight legs in total). In this case, the heat is mainly conducted longitudinally. Spacers can be added to transmit the heat transversely / radially and / or to center the measuring core transversely / radially.

[0122] Alternatively, only an upper or lower portion of the samples is perforated, for example the upper portion and spacers can be added under the lower portion.

[0123] The various modes, variants and examples of embodiment presented can be combined in all technically possible combinations.

[0124] Furthermore, the present invention is not limited to the embodiments previously described but extends to any embodiment falling within the scope of the claims.

Claims

1. A measurement core (16, 16', 16'', 17) for measuring nuclear heating in a nuclear reactor, said core extending in a longitudinal direction (X) and having a main plane (XY), said measurement core comprising at least: - a first layer of material, forming a first sample (161, 161', 161", 171); - a first thin layer of electrical insulation (163, 163'', 173) disposed on the first sample; - a thin conductive layer forming a heating electrical resistor (164, 164', 164'', 174) disposed on the first layer of electrical insulation; - a second thin layer of electrical insulation (165, 165'', 175) disposed on the heating electrical resistor; the first thin layer of insulation having dimensions in the main plane matched to those of the first sample; the thin layers of electrical insulation being configured to insulate the heating resistor from the sample and protect said heating resistor; and the first sample preferably having dimensions less than or equal to around fifteen, even around ten, millimetres in the main plane, and / or a thickness less than or equal to 10 millimetres, even more preferably less than or equal to 2 millimetres.

2. The measurement core (16, 16', 16'', 17) according to claim 1, further comprising: - a second layer of material, forming a second sample (162, 162', 162'', 172); the second thin layer of electrical insulation being between the heating resistor and the second sample; the second thin layer of electrical insulation having dimensions in the main plane matched to those of the second sample; the second layer of electrical insulation being configured to insulate the heating resistor from the second sample; the second sample preferably having dimensions less than or equal to around fifteen, even around ten, millimetres in the main plane, and / or a thickness less than or equal to 10 millimetres, even more preferably less than or equal to 2 millimetres.

3. The measurement core (16, 16'', 17) according to claim 2, the first sample (161, 161", 171) having a length (L 1), respectively a diameter (Φ1), greater than the length (L2), respectively the diameter (Φ2), of the second sample (162, 162", 172).

4. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the heating resistor (164, 164', 164'', 174) comprising a track made of a conductive material in coil, spiral or meander form.

5. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the heating resistor (164, 164', 164'', 174) being made of platinum, of a nickel-chromium alloy, or of constantan.

6. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the thin layers of electrical insulation being made of silicon oxide, of alumina, of silicon nitride, or of magnesium oxide.

7. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the sample or samples being made of graphite, of stainless steel, of aluminium, or of titanium.

8. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the sample or samples having a surface texture suitable for the deposition of at least one thin layer of electrical insulation by a thin layer deposition technique, for example a mirror-polished surface texture.

9. The measurement core according to one of the preceding claims, further comprising at least one adhesion layer between the heating resistor and at least one thin layer of electrical insulation and / or between at least one sample and at least one thin layer of electrical insulation.

10. The measurement core according to one of the preceding claims, further comprising at least one functional layer, that can be a layer of boron, of cadmium, of silicon carbide (SiC) and / or of lithium, said functional layer being able to be deposited on the outer face of at least one sample.

11. The measurement core (16, 16') according to one of claims 1 to 10, the first sample (161, 161'), and if appropriate the second sample (162, 162'), being of parallelepipedal form, forming a parallelepipedal core.

12. The measurement core (17) according to one of claims 1 to 10, the first sample (171), and if appropriate the second sample (172), being of semicylindrical form, forming a semicylindrical or cylindrical core, the cylinder length extending in the longitudinal direction (X).

13. The measurement core (16") according to one of claims 1 to 10, the first sample (161"), and if appropriate the second sample (162"), being of disc form, the disc diameter extending in the longitudinal direction (X).

14. The measurement core (16') according to one of the preceding claims, at least one sample (161', 162') having an openwork at at least one upper and / or lower portion, so as to form at least two upper lugs (161A', 161B', 162A', 162B') and / or at least two lower lugs (161C', 161D', 162C', 162D').

15. The measurement core (16') according to claim 14, the upper lugs being dimensioned to accommodate the connection elements (1641', 1642') of the heating resistor (164'), the upper lugs having, for example, a width greater than the lower lugs.

16. The measurement core (16, 16', 16'', 17) according to one of the preceding claims, the heating resistor being configured to form a resistive temperature probe, so as to measure the temperature in a zone comprising a temperature measurement hot point, said heating resistor being then linked to a measurement means of the resistor, preferably by a four-wire circuit.

17. A calorimetric sensor (1, 1') for measuring nuclear heating in a nuclear reactor, said sensor comprising: - a fluid-tight outer jacket (11); - a gas (12) contained in the outer jacket; - a measurement core (16, 16', 16'', 17) chosen according to any one of claims 1 to 16, said core being disposed in the outer jacket; - link means (13, 161A', 161B', 161C', 161D', 162A', 162B', 162C', 162D') capable of holding the measurement core in the outer jacket and of transferring the heat between said core and said jacket; - temperature measurement means (14, 164, 164', 164", 174, 15), comprising a first temperature measurement means (14, 164, 164', 164'', 174) capable of measuring the temperature at a hot point, preferably as close as possible to the heating element of the measurement core, and a second temperature measurement means (15) capable of measuring the temperature at a cold point, preferably on a wall of the jacket (11).

18. The calorimetric sensor (1, 1') according to claim 17, the temperature measurement means (14, 15) comprising at least one thermocouple, preferably a wired microthermocouple or a thin-film microthermocouple.

19. The calorimetric sensor (1, 1') according to claim 17 or claim 18, the measurement core being chosen according to claim 16, the first temperature measurement means being formed by the heating resistor (164, 164', 164'', 174).

20. The calorimetric sensor (1, 1') according to one of claims 17 to 19, the link means comprising spacers (13) that can have different forms and materials.

21. The calorimetric sensor (1, 1') according to one of claims 17 to 20, at least one sample (161', 162') having an openwork at at least an upper and / or lower portion, so as to form at least two upper lugs (161A', 161B', 162A', 162B') and / or at least two lower lugs (161C', 161D', 162C', 162D'), the link means being wholly or partly formed by said lugs.

22. The calorimetric sensor (1, 1') according to one of claims 17 to 21, the jacket (11) being made of aluminium, of stainless steel or of titanium.

23. The calorimetric sensor (1, 1') according to one of claims 17 to 22, the jacket (11) being of parallelepipedal form or of cylindrical form, possibly having a tapered end in order to enhance the flow of the heat-transfer fluid around the calorimetric sensor.