BE1019042A3 - ACOUSTIC SENSOR FOR MEASURING GAS IN AN ENCLOSURE, AND ASSEMBLY COMPRISING AN ENCLOSURE AND SUCH A SENSOR. - Google Patents

Abstract

The invention relates to an acoustic sensor (100) for the continuous and real measurement of at least one physical parameter representative of the behavior of a gas (20) contained in an internal volume (2) of an enclosure (1). characterized in that it comprises: - a housing (11) comprising: side walls (12), a vibration plate (9) and a reflection plate (7) the vibration plate (9) and the reflection plate (7) being flat, perpendicular to the side walls (12) and parallel to each other, so that the housing (11) materializes, between the vibration plate (9) and the reflection plate (7) ), a gas resonance cavity (10); - a fluidic connection (3) capable of connecting the cavity (10) to the internal volume (2) of the enclosure (1), so that, during operation of the sensor, the gas (20) can be contained at the same time in the enclosure (1) and in the cavity (10); - a transducer (5) coupled to the excitation plate (9) for, on the one hand, generating an acoustic signal causing the excitation plate (9) and the gas (2) contained in the cavity (10) to vibrate, and on the other hand detect a signal ...

Description

Acoustic sensor for measuring a gas in an enclosure, and an assembly comprising an enclosure and such a sensor

GENERAL TECHNICAL FIELD

The present invention relates to an acoustic sensor for the continuous measurement and in real time of at least one physical parameter representative of the behavior of a gas contained in an internal volume of an enclosure.

It also relates to an assembly comprising an enclosure and such a sensor.

STATE OF THE ART

For the production of energy using nuclear technology, known assemblies are used which must be placed in a nuclear reactor.

Each assembly is formed of a series of support and separation grids (also referred to as "pencil holders"), in which cylindrical fuel elements (also called "pencils") containing uranium oxide pellets are arranged vertically. enriched and a gas composed in general of helium (He).

Each assembly generally has a square cross section (about 200 mm side) grouping, for example for the French reactors, 264 rods (geometry 17 x 17) and a height of the order of 4 to 5 m. In the production of energy by irradiation, the pellets release into the pencil fission gases, usually krypton (Kr) and xenon (Xe).

Experimental assemblies known comprising experimental rods, derived from intersecting industrial rods, reproduce the operation of the aforementioned production assemblies.

It is desired to be able to characterize the releases of the fission gases, especially in these experimental rods.

A first known technique consists in simultaneously measuring the temperature of the fuel (using a thermocouple placed in the pencil) and the pressure in the pencil (using for example a back pressure sensor ) to quantify the release of gases in the pencil.

A second known technique consists of measurements in the laboratory for analyzing the fission products, the rod being connected by gas conduits to a continuous analysis system.

The known techniques thus have disadvantages.

The first technique does not make it possible to know in real time the nature of the gases released. Moreover, the differentiation of helium releases and xenon and krypton releases during irradiation is impossible with the first technique.

The second technique requires a fission product analysis laboratory in the facility housing the reactor. In addition, the measurement conditions are not very representative of the actual irradiation conditions of the fuel in the electro-thermal reactor, because for the second technique, the pencil is neither closed nor pressurized.

Acoustic sensors are also known for measuring the pressure of a gas in a closed chamber.

However, these sensors, which are placed outside the chamber, are not suitable for use in a nuclear reactor in operation or in experimental nuclear reactors, because they are too bulky (they can not be placed in a reactor irradiation). PRESENTATION OF THE INVENTION

The invention proposes to overcome at least one of these disadvantages.

For this purpose, according to the invention, an acoustic sensor is proposed for continuously measuring, in real time, at least one physical parameter representative of the behavior of a gas contained in an internal volume of an enclosure, characterized in that it comprises: a housing comprising lateral walls, a vibration plate, and a reflection plate, the vibration plate and the reflection plate being flat, perpendicular to the side walls and parallel to one another, so that the housing materializes, between the vibration plate and the reflection plate, a resonance cavity of a gas; a fluidic connection able to connect the cavity to the internal volume of the chamber, so that, during operation of the sensor, the gas can be contained both in the chamber and in the cavity; a transducer coupled to the excitation plate for firstly generating an acoustic signal vibrating the excitation plate and the gas contained in the cavity, and secondly detecting an acoustic response signal characteristic of the vibrations of the excitation plate and gas contained in the cavity.

The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination: the transducer is coupled to the excitation plate by a low-temperature solder layer; the distance between the excitation plate and the reflection plate is greater than a characteristic dimension of the transducer; a characteristic dimension of the transducer is equal to or less than a characteristic dimension of the excitation plate; the sensor comprises an airlock adapted to contain the gas and connected on the one hand to the internal volume of the enclosure by the connection, and on the other hand to the cavity by an orifice made between the reflection plate and the side walls of the casing; the fluidic connection and the housing extend along a longitudinal axis (ZZ ') of main extension of the enclosure; - The orifice is made eccentrically with respect to the longitudinal axis (ZZ '), so that the reflection plate is interposed between the excitation plate and an opening between the connection and the lock; and the sensor is suitable for the continuous measurement, in real time in particular of the molar mass and the pressure of a gas contained in an internal volume of a nuclear fuel rod, and is thus adapted to be placed in a reactor irradiation, wherein the side walls and the connection are made of stainless steel able to withstand nuclear radiation.

The invention also relates to an assembly comprising an enclosure and such a sensor.

The invention has many advantages.

It allows the characterization, in real time and continuously, of the release of the fission gases in the pencil. It is said that the measurement is done "online".

Thanks to the processing associated with the sensor (determination of the molar mass of the gas in particular), the invention makes it possible to know in real time the nature of the gases released in the pencil: it thus allows the differentiation of helium releases and xenon relaxations. and krypton during irradiation.

In addition, the invention allows a measurement under real conditions of irradiation of the fuel in an electrogenic reactor, that is to say in a closed and pressurized pencil: the invention makes it possible to maintain the nominal pressure and volume conditions. in the fuel rod, as well as the normal cooling of the pencil. The sensor according to the invention ensures the physical separation between the fission gases and the environment of the pencil.

The small size of the sensor allows its use in the pencil holders of irradiation reactors. In addition, the materials constituting the sensor are also resistant to the nuclear radiation present in the reactors, as well as to the temperature and pressure conditions of the pencil environment.

The invention is easy to use and does not require a laboratory for analyzing fission products in the plant housing the reactor.

It is understood that even if the present invention is advantageously applicable to the nuclear field, namely that the mainly targeted applications are on-line measurements of the release of fission gases for the experimental reactors, other applications are also conceivable, the sensor being able to serve for production reactors or also for any continuous measurement in real time of at least one physical parameter representative of the behavior of a gas contained in an internal volume of any enclosure. PRESENTATION OF FIGURES

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which: FIG. 1 schematically represents an assembly comprising a enclosure containing a gas and a sensor connected to the enclosure; - Figure 2 schematically shows an assembly according to Figure 1, placed in a reactor; and FIGS. 3 and 4 respectively represent, in more detail, a perspective view and a longitudinal section of a sensor according to the invention for a nuclear application.

In all the figures, similar elements bear identical reference numerals.

DETAILED DESCRIPTION OPERATING PRINCIPLE

FIGS. 1 and 2 show schematically a possible embodiment of an acoustic sensor 100 according to the invention, for the continuous and real-time measurement of at least one physical parameter representative of the behavior of a gas contained in a internal volume 2 of an enclosure 1.

The sensor 100 mainly comprises a housing 11, a transducer 5 and a fluidic connection 3 to the enclosure 1, the housing 11 being connected on the one hand to the transducer 5 and on the other hand to the connection 3.

The housing 11 mainly comprises lateral walls 12, a vibration plate 9 preferably located in an upper part of the housing 11, and a reflection plate 7 preferably located in a lower part of the housing 11, in front of the plate 9.

The housing 11 is of cylindrical shape, for example cylindrical of revolution, but may also be square or rectangular cross section.

The vibration plate 9 and the reflection plate 7 are flat, perpendicular to the side walls 12 and parallel to each other, being located opposite each other, while being separated from each other. a distance D.

The plate 9 also makes it possible to maintain the pressure of the gas in the cavity 10 and in the internal volume 2, by sealing the housing 11 hermetically.

The plates 7 and 9 can be made of material on the walls 12 or be reported. In the case where they are reported, a spacer 16 keeps the plate 7 in the lower part of the cavity 10, and maintain the distance D between the plates 7 and 9.

As will be seen in the following description, such a configuration of the housing has the effect that the housing 11 materializes, between the vibration plate 9 and the reflection plate 7, a cavity 10 of resonance of a gas contained in the cavity 10.

Indeed, the transducer 5 is coupled to the excitation plate 9 to firstly generate an acoustic signal vibrating the excitation plate 9 and the gas 2 contained in the cavity 10, and secondly detect a signal acoustic response characteristic of the vibrations of the excitation plate 9 and the gas 2 contained in the cavity 10.

Of course, the plate 9 has a suitable geometry to allow the transmission of the acoustic signal between the transducer 5 and the cavity 10, while being sufficiently rigid not to deform, in particular under the effect of the pressure prevailing in the cavity ( the nominal pressure in the pencil is of the order of 40 bar, and can rise up to 300 bar under the effect of temperature and relaxation) and generate parasitic waves.

The transducer 5 preferably comprises a piezoelectric element known to those skilled in the art, for example a PZT-Lead Zirconium Titanium Oxide material.

It will be understood that the fluidic connection 3, in the form of a gas duct, is able to connect the cavity 10 to the internal volume 2 of the chamber 1, so that, during operation of the sensor, the gas 20 can be contained both in the chamber 1 and in the cavity 10.

The connection 3 can be welded by a weld point 32 to a gas outlet 14 of the enclosure 1. The link 3 can also be releasably connected, but always in a sealed manner, to the enclosure 1.

The sensor 100 further comprises an electrical system 8 which is connected to the transducer 5 and which allows on the one hand the excitation of said transducer 5, and on the other hand the analysis of the response signals.

An electrical cable 138 allows signals to be transmitted from the transducer 5 to the remote system 8. A single cable 138 is necessary in the sensor according to the invention, which increases the safety of the sensor 100, in particular by reducing the possibilities of leaks due to a lack of leakage between the wiring and the housing 11.

A possible method for continuous and real-time measurement of at least one physical parameter of the gas in the chamber is now explained.

Such a method comprises at least one main step of generating with the aid of the transducer 5, an acoustic signal vibrating the excitation plate 9 and the gas 2 contained in the cavity 10.

Due to the fluidic connection 3 between the internal volume 2 of the chamber 1 and the cavity 10, the gas in the cavity 10 (on which the measurement is made) is of the same type and at the same pressure as the gas in the internal volume of the chamber 1 (gas of which we want to know the physical parameters).

The method also comprises a step of detecting an acoustic response signal characteristic of the vibrations of the excitation plate 9 and the gas 2 contained in the cavity 10.

The frequency and the amplitude of these vibrations make it possible to deduce in particular the molar mass and the pressure of the gas in the cavity 10, and therefore in the chamber 1.

In the particular case of nuclear power, the molar mass makes it possible to deduce the quantization of the release of the fission gases in the fuel rod embodying the enclosure, via a prior calibration and a treatment known to those skilled in the art.

The velocity of the acoustic waves is in fact dependent on the fraction of fission products (Xe and Kr) released in helium (He), which allows the quantification of the release of the fission gases in a pencil initially pressurized with helium.

It has been demonstrated and it is known that the speed c acoustic waves in the gas 2 can be deduced by:

where D is the distance between the excitation plate 9 and the reflection plate 7 and Af is the difference between at least two resonant frequencies of the gas 2.

The molar mass M of the gas can be calculated from velocity c by:

where R is the constant of perfect gases, y is the ratio of specific heats for perfect gases, and T is the temperature.

The above relation is valid for perfect gases. In the case of a gas mixture, corrections from the real gas equation can be introduced.

The measurement of the molar mass M allows a deduction of the mass composition x of the mixture, as shown here in a simplified example for a binary mixture of monoatomic gases (such as a helium-xenon mixture). The measurement of the molar mass allows, as we see, an immediate deduction of the mass composition x of the mixture, because:

where Μχβ and MHe are the atomic masses of xenon and helium.

The pressure of the gas in the cavity 10, and thus in the chamber 1, can also be deduced: the amplitude of the vibrations is in fact related to the pressure.

The known steps for measuring the pressure in the cavity (and thus in the chamber) consist in calculating an integral J of the acoustic signal of a response of the gas in the cavity, response in which the resonances of the gas appear alone and rectified, the resonances of the transducer 5 and the excitation plate 9 being removed. Thanks in addition to the speed of the preceding steps, the pressure P of the gas can be deduced from the calculation of the integral J, by means of a prior calibration representing the curve J (P, c) for a pressure and pressure gas. known nature.

As indicated, this treatment is known to those skilled in the art, in particular thanks to the doctoral thesis at the University of Montpellier 2, supported by E. ROSENKRANTZ, entitled "Design and testing of an ultrasonic sensor dedicated to the measurement of the pressure and composition of fission gases in fuel rods ", and dated December 7, 2007 (Montpellier, France), a thesis to which reference will be made advantageously. The results concerning the signal processing are discussed in Chapter 5, on pages 107 to 138.

The previous treatments are performed by the system 8.

As we have seen, online measurements are thus possible with good accuracy.

In order to further improve the accuracy of the measurements, the transducer 5 is coupled to the excitation plate 9 for example by a layer 51 of solder at low temperature. This solid coupling allows an adequate coupling of the plate 9 and the transducer 5. The low temperature solder makes it possible not to damage the transducer 5.

In order to obtain a sufficient gas resonance number for the measurements, the distance D between the excitation plate 9 and the reflection plate 7 is greater than a characteristic dimension d of the transducer 5.

By characteristic dimension d is meant the diameter of the transducer 5 when the transducer is in the form of a disk, or the diagonal for example of the transducer 5 when the transducer is in the form of a rectangular or square block.

Similarly, in order to avoid clutter on the walls 12 which could interfere with the measurements, the characteristic dimension d of the transducer 5 is equal to or slightly smaller than a characteristic dimension of the interior of the resonance cavity and also the plate of excitation 9.

As before, the term characteristic dimension of either the diameter of the plate 9 when the plate is in the form of a disk, or the diagonal for example of the plate 9 when the plate is in the form of a rectangular pad or square.

Preferably, the sensor 100 comprises an airlock 4 adapted to contain the gas 20 and connected on the one hand to the internal volume 2 of the chamber 1 by the connection 3, and on the other hand to the cavity 10 by an orifice 6 made between the reflection plate 7 and the side walls 12 of the housing 11. This orifice 6 promotes the flow of the gas to be measured which otherwise passes through the mechanical clearances between the plate 7 and the envelope 14 of the sensor. The lock 4 allows the fluidic connection between the cavity 10 and the internal volume 2 of the enclosure, while maintaining a suitable geometry for the cavity 10.

As shown in FIG. 2, the lock 4 may have an enlarged flaring shape of the connection 3 towards the cavity 10, in order to facilitate the passage of the gas into the cavity 10.

In the case in particular where the enclosure 1 constitutes a fuel rod, said enclosure 1 having a longitudinal axis ZZ 'main extension, the fluidic connection 3 and the housing 11 advantageously extend along the axis ZZ'. Such a geometry allows a minimal space requirement of the sensor and gives it an aptitude to be placed in a pencil holder 150 as schematically shown in FIG. 2. The advantageous geometry notably allows a circulation of a cooling fluid around the rods.

In order not to disturb the resonance of the gas 20 and in order not to generate false echoes, in this particular geometry, the orifice 6 is made eccentrically with respect to the longitudinal axis ZZ ', so that the reflection 7 is interposed between the excitation plate 9 and an opening 31 between the connection 3 and the lock 4. The plate 7 masks the opening 31 for the plate 9.

The sensor finally comprises a module 13 for protecting the transducer 5, but allowing the electrical connection of the transmission cable 138 to the terminals of the transducer 5, in a sealed manner.

PARTICULAR EMBODIMENT

As we have seen, the sensor 100 is advantageously used for nuclear applications.

The main features of this particular embodiment, shown more specifically in FIGS. 3 and 4, are nonlimiting and are listed below, it being understood that the characteristics already described above are still valid and are not repeated here, for reasons of clarity and brevity.

The sensor 100 is thus adapted for the continuous measurement, in real time in particular of the molar mass and the pressure of a gas contained in an internal volume of a nuclear fuel rod (not represented) and is particularly adapted to be placed in an irradiation reactor (not shown).

For this purpose, the side walls 12, the link 3 and the module 13 are made of stainless steel able to withstand nuclear radiation.

The sensor can withstand an external pressure (that is to say in the cooling circuit of the rods) of the order of 150 bar, for a temperature of 200 ° C or 350 ° C.

The total external diameter of the sensor is 16.25 mm, which allows the sensor to be placed in the upper part of the pencil, and not to interfere with the cooling circuit of the rods.

The cavity 10 has a diameter of 10 mm, for a distance D between the plates 7 and 9 of 12.5 mm.

The parallelism between the plates 7 and 9 must be 5 μm over the entire diameter of the cavity 10.

The transducer 5 is in the form of a disk of about 10 mm in diameter (characteristic dimension) and a fraction of a millimeter in height.

The plates 7 and 9 have a thickness of a few mm, and are sufficiently rigid to have a maximum of 2 pm of deflection in the target pressure range (up to 250 bar, or even 300 bar).

The module 13 holds the plate 9, which itself maintains the spacer 16 which in turn holds the plate 7 which abuts on a bottom wall 17 of the housing, so that the assembly also withstands the desired pressure range.

The orifice 6 is made between the spacer 16 and the walls 12.

Open grooves 46 are made between the plate 7 which abuts on the bottom wall 17 of the housing 11, to facilitate the passage of the gas from the lock 4 to the cavity 10 via the orifice 6.

It is recalled that the lock 4 is preferably also flared to facilitate the passage of the gas from the link 3 to the lock 4, since the plate 7 abuts on the bottom wall 17 of the housing 11.

Likewise, grooves 610 are made open between the plate 9 and the spacer 16, to facilitate the passage of the gas from the orifice 6 to the cavity 10.

The cable 138 is a mineral insulator and metal sheath, to withstand nuclear radiation while being sealed and sealed.

Claims (9)

Acoustic sensor (100) for continuous and real-time measurement of at least one physical parameter representative of the behavior of a gas (20) contained in an internal volume (2) of an enclosure (1), comprising a housing (11) having side walls (12), a vibration plate (9), and a reflection plate (7), the vibration plate (9) and the reflection plate (7) being flat, perpendicular to the side walls (12) and parallel to each other, so that the housing (11) materializes, between the vibration plate (9) and the reflection plate (7), a cavity (10) resonance of a gas; a fluidic connection (3) capable of connecting the cavity (10) to the internal volume (2) of the chamber (1), so that, during the operation of the sensor, the gas (20) can be contained at a time in the enclosure (1) and in the cavity (10); - a transducer (5) coupled to the excitation plate (9) for firstly generating an acoustic signal vibrating the excitation plate (9) and the gas (2) contained in the cavity (10), and on the other hand, detecting an acoustic response signal characteristic of the vibrations of the excitation plate (9) and of the gas (2) contained in the cavity (10), said sensor being characterized in that it comprises an airlock (4 ) adapted to contain the gas (20) and connected on the one hand to the internal volume (2) of the enclosure (1) by the connection (3), and on the other hand to the cavity (10) via an orifice ( 6) made between the reflection plate and the side walls (12) of the housing (11). 2. Sensor according to claim 1, wherein the transducer (5) is coupled to the excitation plate (9) by a layer (51) of solder at low temperature. 3. Sensor according to one of claims 1 or 2, wherein the distance (D) between the excitation plate (9) and the reflection plate (7) is greater than a characteristic dimension (d) of the transducer (5). ). 4. Sensor according to one of claims 1 to 3, wherein a characteristic dimension (d) of the transducer is equal to or less than a characteristic dimension (d ') of the excitation plate (9). 5. Sensor according to one of claims 1 to 4, wherein the fluidic connection (3) and the housing (11) extend along a longitudinal axis (ZZ ') of main extension of the enclosure (11). 6. Sensor according to one of claims 1 to 5, wherein the orifice (6) is made eccentrically with respect to the longitudinal axis (ZZ '), so that the reflection plate (7) is interposed between the excitation plate (9) and an opening (31) between the link (3) and the lock (4). 7. Sensor according to one of claims 1 to 6, adapted for the continuous measurement and in real time in particular of the molar mass and the pressure of a gas (20) contained in an internal volume (2) of a nuclear fuel rod and thus adapted to be placed in a reactor (150) for irradiation, wherein the side walls (12) and the link (3) are made of stainless steel capable of withstanding especially nuclear radiation. 8. An assembly comprising a chamber (1) containing a gas (20), characterized in that it further comprises a sensor according to one of claims 1 to 7 connected to the enclosure. 9. The assembly of claim 8, wherein the enclosure is a nuclear fuel rod.