Raman spectrometry quantification method

Abstract

Method for quantification by Raman spectrometry This method comprises: - the simultaneous emission (R / / , ) of a first and a second monochromatic excitation beams modulated in amplitude so that first and second collected optical signals have the same amplitude modulations as those, respectively, of the first and second excitation beams, and - the combination of the first and second collected optical signals to form a merged optical signal and the emission of the merged optical signal in an optical fiber which passes through a containment vessel of a nuclear reactor, then - the extraction (228), by exploiting the amplitude modulations, of a first and a second extracted electrical signals representative, respectively, of the first and second collected optical signals, then - the determination (230) of quantities of a gaseous component from the first and second extracted electrical signals. Fig. 5

Description

Title of the invention: Method of quantification by Raman spectrometry

[0001] The invention relates to a method and a device for quantifying, by Raman spectrometry, at least one gaseous component inside a confinement enclosure of a nuclear reactor.

[0002] Such a quantification device is used to measure the concentrations of gaseous components in a gaseous medium located inside the containment building of a nuclear power plant. In this case, the containment building is known as the "reactor building" (RB). Indeed, nuclear power plants used for the production of electrical energy comprise, inside a reactor building, a vessel containing the core of the nuclear reactor which can be cooled, inside the vessel, by pressurized or boiling light water or by heavy water. In the case of a nuclear accident resulting, for example, in a loss of the core cooling function, there is an increase in the temperature of the core components and in particular of the nuclear fuel. The increase in the core temperature can lead to a meltdown of the internal components of the nuclear reactor.

[0003] At high temperatures, metals become very reactive and oxidize on contact with the water vapor present in the reactor vessel containing the core. The cladding of the fuel assemblies, which are made of a zirconium alloy, are elements which are first subjected to these oxidation reactions. The zirconium is oxidized by the water vapor following the reaction Zr + 2H2O -> ZrO2 + 2H2. This results in a very rapid release of a significant quantity of hydrogen.

[0004] At a final stage of the accident, the flow of corium (molten core) onto the concrete base of the reactor building also contributes to the formation of hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2).

[0005] Thus, following a nuclear accident, a mixture of hydrogen and oxygen may be present inside the reactor building, which leads to serious risks of explosion. This risk is known as "hydrogen risk" or "H2 risk". ".

[0006] In the event of a nuclear accident, the mixture inside the reactor building is not homogeneous. Therefore, it is important to be able to measure the concentration of the gaseous components present in the reactor building at several different locations.

[0007] In particular, the presence of gases such as hydrogen, oxygen and other gases Fuels with a lower calorific value than hydrogen, such as carbon monoxide, can lead to explosive mixtures. The implementation of control methods to determine the nature and proportion of the main gaseous components present in the reactor building is therefore necessary. This makes it possible to assess the risk of explosion and to initiate the necessary preventive actions to mitigate this risk.

[0008] Application FR2733050A1 describes a device for quantifying, by Raman spectrometry, gaseous components present inside the reactor building of a nuclear power plant. This device comprises several probes located inside the reactor building and a processing unit located outside. The processing unit is connected to the probes by optical fibers and electrical cables. Thus, its implementation requires providing sealed passages through the reactor building. Such sealed passages for optical fibers or electrical cables have little effect on the sealing of the reactor building with respect to radiation and radioactive materials. In this respect, this device is very advantageous compared to other known quantification devices which require extracting a sample of the gaseous medium to the outside of the reactor building for analysis.Indeed, in the latter case, it is necessary to use tubes that pass through the reactor building to connect the inside of the reactor building to the outside. Such tubes are problematic because, on the one hand, they constitute a risk of leakage of the containment vessel and, on the other hand, they impose a significant delay between the two sampling and analysis operations linked to the gas transfer time in the tube as well as a bias in the distribution of partial gas pressures following the adsorption phenomenon on the internal surface of the tube. These different reasons are explained in chapter II of the following article: S. Magne et al: “In situ gas monitoring by fiber-coupled Raman spectrometry for H2-risk management in nuclear containment during a severe nuclear accident”, IEEE Trans. Nucl. Sci. 67 (4), 2020, pp. 617-624. Hereinafter, this article is referred to as “Magne2020”.

[0009] Even if crossings of the reactor building designed to receive optical fibers are preferred to crossings designed to receive tubes, the number of crossings of the reactor building must still be limited as much as possible to comply with a leakage criterion. In addition, the number of crossings is limited by construction in the reactor buildings of existing power plants and the drilling of new crossings is a complex procedure, from a technical and regulatory point of view, and expensive. For this, application FR2733050A1 provides, in a particular embodiment, that the optical switches are placed inside the reactor building. These optical switches must then be capable of operating even during a nuclear accident. For this, these switches must be qualified "severe accident", therefore be compatible with the earthquake / shock specifications but also function correctly even when the temperature inside the reactor building is 170°C and they receive radiation doses greater than several MGy. Such switches are complex to produce. Moreover, in this embodiment of application FR2733050A1, regardless of the number of probes, there is only one incoming optical fiber and one outgoing optical fiber. The number of crossings is therefore minimized but this minimization of the number of crossings is at the expense of the speed of measurement acquisition. Indeed, in application FR2733050A1, the probes must be interrogated one after the other. Thus, the time required to acquire the measurements of N probes is equal to N*Tm, where Tm is the time required to perform a measurement using a single probe.

[0010] The Magne2020 article also describes in detail a device for quantifying gaseous components inside a reactor building by Raman spectrometry. In the Magne2020 article, for each probe located inside the reactor building, an incoming optical fiber and an outgoing optical fiber are required that pass through this reactor building. Thus, for N probes, 2*N optical crossings of the reactor building are required. However, the measurements are carried out in parallel. Thus, the time required to acquire the measurements of the N probes is equal to Tm.

[0011] It therefore appears desirable to minimize the number of crossings of the reactor building while retaining the possibility of carrying out measurements of the different probes in parallel.

[0012] The invention therefore aims to propose a quantification method which makes it possible to satisfy this desire.

[0013] The subject of the invention is therefore a method for quantifying, by Raman spectrometry, at least one gaseous component inside a confinement enclosure of a nuclear reactor using at least a first and a second probe located inside this confinement enclosure, this method comprising:

[0014] - the emission of a first and a second monochromatic excitation beam matics at the same wavelength Xn, in, respectively, a first and a second incoming optical fibers which each pass through the confinement enclosure,

[0015] - the reception, by each of the first and second probes, respectively, of the first and second monochromatic excitation beams emitted,

[0016] - the excitation, by each of the first and second probes, using the beam excitation received, respectively, from a first and a second sample of the gaseous medium located inside the confinement enclosure, and

[0017] - the collection, by the first and second probes, respectively, of a first optical signal and a second optical signal scattered, by Raman effect, by the first and second excited samples,

[0018] in which:

[0019] - the first and second monochromatic excitation beams are emitted simultaneously tangent and are amplitude modulated so that the first and second collected optical signals have the same amplitude modulations as those, respectively, of the first and second excitation beams, this amplitude modulation being such that the result of the integration over time of the scalar product of the first and second modulated monochromatic excitation beams tends towards zero when the integration time increases, and

[0020] - the method also comprises:

[0021] - combining the first and second collected optical signals to form a first merged optical signal and the emission of the first merged optical signal in a first outgoing optical fiber which passes through the containment enclosure, then

[0022] - the measurement, by a reading unit located outside the containment enclosure, of the first merged optical signal to obtain a corresponding first electrical signal, then

[0023] - extraction, by an electronic computer, from the first electrical signal and by exploiting the amplitude modulations of the first and second collected optical signals, of a first and a second extracted electrical signal representative, respectively, of the first and second collected optical signals, then

[0024] - the determination of the quantities of the gaseous component present, in the first and second samples from, respectively, the first and second extracted electrical signals.

[0025] Embodiments of this quantification method may include one or more of the following features:

[0026] 1) The method also comprises:

[0027] - the emission of a third monochromatic excitation beam at a wavelength of wavelength ^different from the wavelength Xn, in the first incoming optical fiber at the same time as the first excitation beam is emitted,

[0028] - the separation, inside the containment enclosure, of the first and third excitation beams emitted at the same time in the first incoming optical fiber and the transmission of the third excitation beam only to a third probe and, in parallel, the transmission of the first excitation beam only to the first probe,

[0029] - simultaneous reception by the first, second and third probes, respec tively, first, second and third monochromatic excitation beams, and

[0030] - excitation, by the third probe, using the third excitation beam received, of a third sample of the gaseous medium located inside the enclosure of confinement,

[0031] - the collection, by the third probe, of a third optical signal diffused, by effect Raman, by the third excited sample,

[0032] - emission in a second outgoing optical fiber, different from the first fiber optical and which passes through the containment enclosure, of the third optical signal collected, then

[0033] - the measurement, by the reading unit, of the optical signal emitted on the second fiber outgoing optics, to obtain a second electrical signal, then

[0034] - the determination, by the electronic calculator, from the second signal electrical, of the quantity of the gaseous component present in the third sample.

[0035] 2) The method also comprises:

[0036] - the emission of a fourth monochromatic excitation beam at the length of wave Xi2, in the second incoming optical fiber at the same time as the second excitation beam is emitted, the third and fourth monochromatic excitation beams being emitted simultaneously and being amplitude modulated, this amplitude modulation being such that the result of the integration over time of the scalar product of these third and fourth monochromatic excitation beams tends towards zero when the integration time increases,

[0037] - the separation, inside the containment enclosure, of the second and fourth excitation beams emitted at the same time in the second incoming optical fiber and the transmission of the fourth excitation beam only to a fourth probe and, in parallel, the transmission of the second excitation beam only to the second probe,

[0038] - simultaneous reception by the first, second, third and fourth probes, respectively, first, second, third and fourth monochromatic excitation beams,

[0039] - excitation, by the fourth probe, using the fourth excitation beam received, from a fourth sample of the gaseous medium located inside the containment enclosure,

[0040] - the collection, by the fourth probe, of a fourth optical signal diffused, by effect Raman, by the fourth excited sample, the third and fourth collected optical signals exhibiting the same amplitude modulations as those, respectively, of the third and fourth excitation beams, and

[0041] - combining the third and fourth collected optical signals to form a second merged optical signal and transmitting the second merged optical signal into the second outgoing optical fiber, then

[0042] - the measurement, by the reading unit, of the second merged optical signal to obtain a second corresponding electrical signal, then

[0043] - the extraction, by the electronic computer, from the second electrical signal and by exploiting the amplitude modulations of the third and fourth collected optical signals, of a third and a fourth extracted electrical signals representative, respectively, of the third and fourth collected optical signals, then

[0044] - the determination of the quantities of the gaseous component present, in the third and fourth samples from, respectively, the third and fourth extracted electrical signals.

[0045] 3) The method comprises:

[0046] - transmission to the first probe and, simultaneously, to a third probe, by a first optical coupler located inside the confinement enclosure, of the first amplitude-modulated excitation beam, and

[0047] - transmission to the second probe and, simultaneously, to a fourth probe, by a second optical coupler located inside the confinement enclosure, of the second amplitude-modulated excitation beam,

[0048] - the simultaneous reception by the first and third probes of the first beam amplitude-modulated monochromatic excitation beam and the simultaneous reception by the second and fourth probes of the second amplitude-modulated monochromatic excitation beam,

[0049] - excitation, by the third and fourth probes, using the excitation beam that each of them received, respectively, a third and a fourth samples of the gaseous medium located inside the containment enclosure,

[0050] - the collection by the third and fourth probes, respectively, of a third and of a fourth optical signal scattered, by Raman effect, by, respectively, the third and fourth excited samples, the third and fourth collected optical signals having the same amplitude modulations as those, respectively, of the third and fourth excitation beams, and

[0051] - combining the third and fourth collected optical signals to form a second merged optical signal and the emission of the second merged optical signal in a second outgoing optical fiber, different from the first optical fiber and which passes through the containment enclosure, then

[0052] - the measurement, by the reading unit, of the second merged optical signal to obtain a second corresponding electrical signal, then

[0053] - the extraction, by the electronic computer, from the second electrical signal and by exploiting the amplitude modulations of the third and fourth collected optical signals, of a third and a fourth extracted electrical signals representative, respectively, of the third and fourth collected optical signals, then

[0054] - the determination of the quantities of the gaseous component present, in the third and fourth samples from, respectively, the third and fourth signals extracted electrical.

[0055] 4)

[0056] - the amplitude modulations of the first and second mono excitation beams chromatic are periodic and the fundamental frequencies of the first and second excitation beams are equal, respectively, to first and second fundamental frequencies which are prime to each other,

[0057] - the reading unit measures the evolution over time of the first optical signal merged to obtain a temporal succession of values ​​of the first electrical signal,

[0058] - the extraction, by the electronic computer, of the first and second signals electrical extracts include:

[0059] - the construction of a power spectrum of this temporal succession of values of the first electrical signal to obtain a spectrum in which a first and a second Raman lines corresponding, respectively, to the first and second collected optical signals appear, the first and second Raman lines being located in the vicinity, respectively, of the first and second fundamental frequencies, then

[0060] - the use of the first Raman line only to determine the quantity of the gaseous component present in the first sample and using the second Raman line only to determine the amount of the gaseous component present in the second sample.

[0061] 5) For each of the first and second probes:

[0062] - for the entire duration of a first and a second time windows, the method comprises polarizing, in a predetermined direction, the amplitude-modulated monochromatic excitation beam to excite the sample with an amplitude-modulated and polarized monochromatic excitation beam,

[0063] - for the entire duration of the first time window, only the component of the optical signal with a polarization direction parallel to the polarization direction of the excitation beam that excites the sample, is collected by the probe,

[0064] - for the entire duration of the second time window, only the component of the optical signal with a polarization direction perpendicular to the polarization direction of the excitation beam which excites the sample, is collected by the probe,

[0065] - the calculator:

[0066] - extract of the values ​​S3gi,ii(X) and S4Gijn(X) representative of the number of photons, at the wavelength X, collected by the probe during, respectively, the first and second time windows, where:

[0067] - the index n is an identifier of the probe among the first and second probes,

[0068] - X is the wavelength of interest, i.e. the wavelength at which appears, due to the Raman effect, a line in the spectrum of the scattered optical signal when the gaseous component to be quantified is present in the sample, then

[0069] - determines the amount of the gaseous component present in the sample from the following difference: [(S3Gi,n(X) / t3 - k(X)*(S4Gi.n(X) / t4], where:

[0070] -13 and t4 are the durations, respectively, of the first and second tem windows porelles, and

[0071] - k(X) is the value, for the wavelength X, of a scale coefficient k pre determined.

[0072] 6) The durations t3 and t4 are equal.

[0073] 7) The method includes a calibration phase during which for each of the first and second probes:

[0074] - a monochromatic excitation beam polarized in a predetermined direction completed excites a reference sample, and

[0075] - a sensor measures a Spara optical signal and a Sperp optical signal diffused by the reference sample excited by this excitation beam, the optical signals Spara and Sperp being the optical signals scattered by the measured reference sample with polarization directions, respectively, parallel and perpendicular to the predetermined direction of polarization of the excitation beam, and the signals Spara and Sperp being measured at wavelengths Xi different from the wavelengths at which, due to the Raman effect, lines appear in the spectrum of the optical signal scattered by this reference sample, then

[0076] - the value k(X) of the coefficient k for each wavelength of interest X is calculated from the measured Spara and Sperp optical signals, then recorded in the calculator.

[0077] 8) The first and second time windows follow each other immediately and the duration of each of these first and second time windows is less than 10 s.

[0078] 10) When measuring the first merged optical signal, this first optical signal merged is measured for several different X-ray wavelengths of interest, each of these wavelengths of interest corresponds to a particular gas component to be quantified in the excited samples, the measurements at these different wavelengths of interest being carried out simultaneously.

[0079] 11) The wavelengths of interest include wavelengths of interest cor responding to water vapor, oxygen and nitrogen.

[0080] 12) The wavelengths of interest include wavelengths of interest cor responding to carbon monoxide and carbon dioxide.

[0081] 13) A wavelength of interest corresponds to hydrogen.

[0082] 14) The excitation beam is a continuous laser beam.

[0083] The invention also relates to a device for quantifying, by Raman spectrometry, at least one gaseous component inside a confinement enclosure of a nuclear reactor, this device comprising:

[0084] - a first and a second incoming optical fiber and a first fiber outgoing optics which each pass through the containment enclosure,

[0085] - a first laser source capable of emitting a first mono excitation beam chromatic at a wavelength Xu, in the first incoming optical fiber,

[0086] - a first and a second probe intended to be located inside the containment enclosure and optically connected, respectively, to the first and second incoming optical fibers to receive, respectively, the first and a second monochromatic excitation beams emitted, these first and second probes being capable:

[0087] - to excite using the received excitation beam, respectively, a first and a second samples of the gaseous medium located inside the containment enclosure, and

[0088] - to collect, respectively, a first optical signal and a second optical signal scattered, by Raman effect, by the first and second excited samples,

[0089] in which the device comprises:

[0090] - a second laser source capable of emitting, in parallel with the first laser source, the second monochromatic excitation beams at the wavelength in the second incoming optical fiber,

[0091] - an amplitude modulator capable of amplitude modulating the first and second monochromatic excitation beams emitted so that the first and second collected optical signals have the same amplitude modulations as those, respectively, of the first and second excitation beams, this amplitude modulation being such that the result of the integration over time of the scalar product of the modulated first and second monochromatic excitation beams tends towards zero when the integration time increases,

[0092] - an optical coupler capable of combining the first and second optical signals collected to form a first merged optical signal and to emit the first merged optical signal into the first outgoing optical fiber,

[0093] - a reading unit intended to be located outside the containment enclosure, this reading unit being capable of measuring the first merged optical signal to obtain a corresponding first electrical signal, and

[0094] - an electronic calculator configured to:

[0095] - extract, from the first electrical signal and exploiting the modulations amplitude of the first and second collected optical signals, a first extracted electrical signal and a second extracted electrical signal representative, respec- tively, first and second collected optical signals, then

[0096] - determining quantities of the gaseous component present, in the first and second samples from, respectively, the first and second extracted electrical signals.

[0097] The invention will be better understood on reading the description which follows, given solely as a non-limiting example and made with reference to the drawings in which:

[0098] - [Fig.l] is a schematic illustration of the architecture of a quantization device fication, by Raman spectrometry, of gaseous components inside a containment vessel of a nuclear reactor,

[0099] - [Fig.2] is an illustration of a Raman spectrum of the gaseous components at quantify,

[0100] - [Fig.3] is a schematic illustration of the architecture of a probe of the device of [Fig.l],

[0101] - [Fig.4] is a schematic illustration of the optical connections of the probes of the device of [Fig.l] to an external processing unit,

[0102] - [Fig.5] is a schematic illustration of an optical coupler used for optically connect the probes of the device of [Fig.l] to an external processing unit,

[0103] - [Fig.6] is a graph showing Raman spectra in the presence of a Cherenkov radiation,

[0104] - [Fig.7] is a flowchart of a quantification method using the device of [Fig.l],

[0105] - [Fig.8] is a timing diagram of different operating periods of the device of [Fig.l],

[0106] - [Fig.9] is a schematic illustration of another embodiment of the rac optical connections of the probes of the device of [Fig.l] to an external processing unit.

[0107] In this description, the terminology, conventions and definitions of the terms used in this text are introduced in a chapter I. Then, a detailed example of an embodiment is described in a chapter II with reference to the figures. In a chapter III, variants of this embodiment are presented. Finally, the advantages of the different embodiments are specified in a chapter IV.

[0108] Chapter I: Definitions, terminologies and conventions:

[0109] In the figures, the same references are used to designate the same elements.

[0110] In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

[0111] The symbol “*” denotes scalar multiplication.

[0112] A gaseous component is typically a gaseous molecule.

[0113] The terms “quantification” and “quantify” designate the operation of measuring the quantity of a gaseous component and, in particular, a concentration expressed in % or a partial pressure expressed in Pa.

[0114] The term "quantity", when used without further specification, refers to both an absolute quantity, such as a partial pressure, and a relative quantity, such as a concentration in %.

[0115] In this text, a relative quantity is a proportion, for example expressed in percent, of the gaseous component within the gaseous medium.

[0116] An absolute quantity is typically the partial pressure of the gas component.

[0117] A Raman spectrum is the power spectrum of the optical signal scattered by the Raman effect.

[0118] A "Raman line" is a line in the Raman spectrum whose integral, i.e. its surface, or amplitude varies as a function of the quantity of a gaseous component.

[0119] In this text, the optical signal scattered by the Raman effect is also called “Raman scattering optical signal”.

[0120] The term "nuclear accident" of loss of core cooling refers to any accident that leads to the partial or complete meltdown of the core of the nuclear reactor. In such an accident, hydrogen is produced. Eventually, other gaseous components are produced such as carbon monoxide and carbon dioxide. Such an accident often originates from a total or partial loss of cooling of the core of the nuclear reactor.

[0121] A beam is considered “monochromatic” when the half-width of its single line, in its power spectrum, is less than 1 nm and, preferably, less than 0.5 nm.

[0122] The term “crossing” designates a sealed crossing of the containment enclosure.

[0123] An “incoming” optical fiber means an optical fiber that guides a beam excitation from outside the containment to inside the containment.

[0124] An "outgoing" optical fiber means an optical fiber that guides an optical signal from inside the containment enclosure to outside the containment enclosure.

[0125] “Periodic modulations” of several optical signals at the same wavelength designate modulations of the amplitude of these different signals such that the result of the integration over time of the scalar product of the amplitudes of these modulated optical signals tends towards zero when the integration time increases.

[0126] Chapter II: Example of embodiment

[0127] [Fig.l] represents a device 2 for quantifying, by Raman spectrometry, at least one gaseous component inside a containment enclosure 4 of a nuclear reactor. Subsequently, the description of the device 2 is made in the particular case where the enclosure 4 is a reactor building of a nuclear power plant which ultimately produces electricity. To simplify [Fig.l], only the following elements contained inside the reactor building have been schematically represented:

[0128] - core 6 of the nuclear reactor,

[0129] - a concrete raft 7,

[0130] - a tank 8 in which the core 6 is placed and supported by the raft 7, and

[0131] - the gaseous medium 10 in which the different elements located inside are bathed of enclosure 4.

[0132] The enclosure 4 is sealed, as far as possible, against radiation and radioactive materials in order to prevent them from escaping into the external environment, including, if possible, in the event of a nuclear accident. Typically, the enclosure 4 and the base 7 are essentially made of concrete.

[0133] The gaseous medium 10 is typically air, that is to say a gaseous mixture composed, at more than 98% by volume, of oxygen (O2) and nitrogen (N2) in known proportions.

[0134] In this example, the device 2 is designed to quantify the following gaseous components at several different locations inside the enclosure 4: hydrogen (H2), water vapor (H2O), oxygen (O2), nitrogen (N2), carbon monoxide (CO) and carbon dioxide (CO2). Indeed, the H2 risk is estimated on the basis of the quantities of hydrogen, air (O2, N2) and water vapor (H2O) represented on a Shapiro-Moffette ternary diagram. The measurement of the quantities of carbon monoxide and carbon dioxide makes it possible to trace the corium-concrete interaction (Molten Core Concrete Interaction - MCCI). In this particular context, the term "gaseous components" therefore refers to the gaseous components belonging to the group consisting of hydrogen (H2), water vapor (H2O), oxygen (O2), nitrogen (N2), carbon monoxide (CO) and carbon dioxide (CO2).

[0135] The device 2 comprises a set 20 of probes fixed at different locations inside the enclosure 4 to measure the concentrations of the gaseous components at these different locations. The probes of the set 20 are distributed into several distinct groups Gm of probes. The probes of the same group Gm all receive, simultaneously, a monochromatic excitation beam at the same wavelength. In the particular case described here, the set 20 comprises four groups G1, G2, G3 and G4 of probes and three probes per group ([Fig.4]), i.e. a total of twelve probes distributed inside the enclosure 4.

[0136] The device 2 also comprises inside the enclosure 4:

[0137] - a pressure sensor 22, and

[0138] - one or more temperature sensors 24.

[0139] Typically, a sensor 24 is placed in each probe of the assembly 20. Conversely, the pressure sensor 22 is common to all of the probes.

[0140] The device 2 comprises, outside the enclosure 4, a processing unit 30 which processes the signals transmitted by the set 20 of probes and the sensors 22 and 24 to quantify the presence of the gaseous components in the medium 10.

[0141] The processing unit 30 comprises for this purpose: a set 32 ​​of laser sources, a reading unit 34, an electronic computer 36, a man-machine interface 38, and a power source 40.

[0142] The set 20 of probes is connected to the processing unit 30 via a set 42 of incoming optical fibers and a set 44 of outgoing optical fibers. The fibers of the set 42 carry excitation beams, generated by the set 32 ​​of laser sources, inside the enclosure 4. The optical fibers of the set 44 carry the optical signals scattered by the Raman effect from each of the probes of the set 20 to the reading unit 34. The fibers of the sets 42 and 44 pass through the enclosure 4, each using its own sealed optical feedthrough, better known by the acronym OPA (“Optical Penetration Assembly”). Typically, each of the fibers in sets 42 and 44 are protected by a flexible stainless steel sheath, coated with a black PVC sheath, which is light-tight and decontaminable. In addition, these fibers are protected by a metal conduit to protect them from possible impacts or projections of objects.

[0143] The probes of the assembly 20 are also connected to the unit 30 by means of several electrical cables collectively designated by the reference numeral 46. Each cable 46 passes through the enclosure 4 by using an electrical sealed crossing better known by the acronym EPA (“Electrical Penetration Assembly”). These cables 46 make it possible in particular to power the probes of the assembly 20 and to convey control signals for the probes of the assembly 20.

[0144] The sensors 22 and 24 are connected to the unit 30 by electrical cables, respectively, 48 and 49. These cables 48, 49 pass through the enclosure 4, each using a respective sealed electrical crossing.

[0145] To simplify [Fig.l], oblique lines on each line 42, 44, 46, 48 and 49 indicate that this line corresponds, in practice, to several optical fibers or several electrical cables. Furthermore, in [Fig.l], the optical components used to connect the probes of the assembly 20 to the laser sources of the assembly 32 and to the reading unit 34 have not been shown. These optical components are only visible in [Fig.4].

[0146] The assembly 32 comprises SLk>n laser sources. Each SLk>n laser source emits a laser beam. This beam is a monochromatic beam at a wavelength Xik. Here, the index k is equal to "1" when the wavelength of the laser source is equal to X h and equal to "2" when the wavelength of the laser source is equal to Xi2. The wavelength Xik is preferably between 730 nm and 750 nm because it is in this range that the radiation-induced attenuation or RIA ("Radiation-Induced Attenuation") of the optical fibers is the lowest. For example, here, half of the laser sources of the set 32 ​​emit at a wavelength Xn equal to 750 nm and the other half of the laser sources of this set 32 ​​emit at a wavelength Xi2 equal to 730 nm.

[0147] The power of the optical signal generated by the Raman effect is proportional to the power of the excitation beam. Here, to improve the sensitivity and precision of the device 2, the power of the excitation beam emitted by each laser source is greater than 500 mW and, preferably, greater than or equal to 1 W. To generate such an excitation beam with a small footprint, each laser source of the assembly 32 is a continuous laser source of power equal to or greater than one Watt.

[0148] The assembly 32 also comprises a modulator MM capable of modulating the amplitude of the excitation beam emitted by each of the sources SLk>n.

[0149] The reading unit 34 makes it possible to record the power of the optical signals at the different wavelengths of interest. Here, the wavelengths of interest are equal to the wavelengths at which Raman lines, characteristic of the presence of the gaseous components to be quantified, appear in the power spectrum of the optical signal scattered by the Raman effect by the medium 10. Subsequently, the wavelengths of interest of hydrogen, carbon dioxide, oxygen, carbon monoxide, nitrogen and water vapor are noted, respectively, XH2, XCo2, X02, XCo, XN2 and XH20. These wavelengths of interest are known and represented on the Raman spectrum of [Fig.2].

[0150] The spectrum of [Fig.2] is reconstructed from experimental Raman shift values ​​obtained using a monochromatic excitation beam at a wavelength Xi equal to 750 nm. The amplitudes of the lines are normalized to that of nitrogen (N2) at the unit value for a partial pressure of 1 atm and room temperature. The amplitudes of the lines are proportional to the quantity of each gaseous component in the medium 10.

[0151] In this embodiment, the full width at half maximum or FWHM of each line is typically 6 nm. Under these conditions, it is the surface (integral) of the line which is measured to obtain a signal proportional to the quantity of the corresponding gas component.

[0152] In the particular case of hydrogen, several rotational lines So to S3 correspond to the presence of hydrogen. Among the four lines So to S3 of hydrogen, the line Si is the most intense of all. Moreover, in practice, the line So is not observed because it is contained in the rejection band of the filter 96 ([Fig.3]). Here, the wavelength X h2 is taken equal to the wavelength at which the Si line of hydrogen appears. In this case, it is the surface of the Si line which is used to determine the quantity of hydrogen.

[0153] The two carbon dioxide lines overlap but can still be distinguished. Here, it is the area of ​​these two lines that represents the amount of carbon dioxide.

[0154] In addition to the wavelengths of interest, between the So and Si lines of hydrogen, a first reference wavelength Xrefi is located. Between the Si and S2 lines of hydrogen, a second reference wavelength Xref2 is located. As explained later, the wavelengths Xrefi and Xref2 are used to determine the surface of the Si Raman line of hydrogen by the method of baseline subtraction (SLB).

[0155] To obtain measurements for each of the wavelengths of interest and for the wavelengths Xrefi and Ken, the unit 34 comprises a spectrometer for each group Gm of probes. Here, the unit 34 therefore comprises four spectrometers SP1, SP2, SP3 and SP4. The spectrometers SP1 and SP3 measure the optical signals, scattered by the Raman effect by the medium 10, when it is excited with an excitation beam at the wavelength Xn. The spectrometers SP2 and SP4 measure the optical signals, scattered by the Raman effect by the medium 10, when it is excited with an excitation beam at the wavelength Xi2. These spectrometers SP1, SP2, SP3 and SP4 are structurally identical. Thus, subsequently, only the spectrometer SP4 is described and shown in more detail.

[0156] The SP4 spectrometer comprises:

[0157] - a circuit 51 for demultiplexing the wavelengths Xrefi, X^X^, XCo2, X02, XCo, XN2 and XH2o, and

[0158] - for each of the demultiplexed wavelengths, only one chain acquisition.

[0159] The proximal end of the fiber of the assembly 44 connected to the probes of the assembly G4, is connected to an input of the circuit 51. The circuit 51 has as many outputs as there are wavelengths to be processed. On each of these outputs, the circuit 51 delivers the optical signal corresponding to the wavelength to be processed. A respective acquisition chain is connected to each of these outputs. Here, these acquisition chains are structurally identical to each other and only one acquisition chain 50 for a wavelength X is described and shown in [Fig.l]. The demultiplexing circuit 51 is for example produced as described in application US7385692.

[0160] The chain 50 successively comprises a bandpass filter 52, a photodetector 54, an amplification-discrimination module 56 and a counter 58.

[0161] The transfer function of the bandpass filter 52 has the form of a Gaussian centered on the wavelength X. The width of this transfer function at mid-height is comprised:

[0162] - between 10 nm and 12 nm for the wavelengths X02, XCo, XN2 and XH20,

[0163] - between 5 nm and 6 nm for the wavelengths XH2, Xrefi and Xref2, and

[0164] - between 15 nm and 18 nm for the wavelength / <02-

[0165] The photodetector 54 generates a voltage pulse for each photon received in the optical signal filtered by the filter 52. Preferably, the photodetector 54 is a photomultiplier. For example, the photomultiplier is equipped with a photocathode extended in the visible red and near infrared range made of GaAs-Cs or InGaAs-Cs. This photomultiplier operates at a temperature of -20°C, by cooling by the Peltier effect (thermoelectric device) for example.

[0166] The module 56 first amplifies the voltage pulses at the output of the photodetector 54. Then, the module 56 eliminates most of the pulses coming from the background noise. For this, typically, the module 56 eliminates the pulses whose amplitude is lower than a predetermined threshold.

[0167] The counter 58 is incremented by each pulse delivered at the output of the module 56. The counter 58 therefore counts the number of pulses received during an interval of a predetermined duration Te. At the end of the interval, the value of the counter 58 is reset to zero and the counter starts counting the pulses received during the following interval again. The duration Te is, for example, of the order of 10 ms, i.e. an acquisition frequency fe of 100 Hz. However, higher frequencies fe are also possible.

[0168] At the end of each interval, a measurement of the number of counts received during this interval is therefore delivered. This measurement is expressed in cps (counts per second).

[0169] The computer 36 typically comprises a programmable microprocessor 60 and a memory 62 containing the data and instructions necessary for executing the method of [Fig.7]. The computer 36 is in particular capable of controlling the modulator MM of the assembly 32, each of the probes of the assembly 20 and the human-machine interface 38. The computer 36 also acquires the measurements delivered by the unit 34 and the sensors 22 and 24 to determine a physical quantity representative of the quantities of each of the gaseous components measured by each of the probes of the assembly 20.

[0170] The human-machine interface 38 typically comprises a screen 66.

[0171] Here, the power source 40 is a backed-up power source capable of powering all of the components of the processing unit 30, the probes of the assembly 20 and the sensors 22 and 24 even in the event of a network outage. power supply. For this purpose, the source 40 comprises a battery capable of storing sufficient energy to power the processing unit 30, the probes of the assembly 20 and the sensors 22 and 24 for at least one day and, preferably, for at least three consecutive days.

[0172] Here, the probes of the set 20 are all structurally identical. [Fig.3] shows in more detail an example of an embodiment of a SOGm>n probe of the set 20, where the index Gm identifies the group to which this probe belongs and the index n is the order number of the probe in this group Gm.

[0173] The SOGm>n probe comprises a housing 80 inside which are housed the various optical components necessary to produce and collect the optical signal scattered, by Raman effect, by the gaseous components to be quantified. The SOGm>n probe is optically connected:

[0174] - to a laser source of the assembly 32 via an optical fiber FEGm>n, And

[0175] - to an SPm spectrometer of the reading unit 34 via a fiber FSGm>n optics.

[0176] The distal ends of the FEGm>n and FSGm>n fibers are located inside the housing 80.

[0177] This housing 80 is waterproof and dustproof to protect the optical components. For example, the housing 80 has a protection rating equal to IP69. Inside the housing 80, the optical components are immersed in a neutral gas, injected via a visible purge valve 81 in [Fig. 3]. The neutral gas is a gas different from the gaseous components to be quantified. In addition, the neutral gas does not exhibit Raman scattering when excited by the excitation beam or exhibits Raman scattering at a wavelength different from the wavelengths of interest. For example, the neutral gas is argon. The pressure of the neutral gas inside the housing 80 is typically close to atmospheric pressure. For example, the pressure of the neutral gas here is equal to 1 atm (101.32 kPa).

[0178] Internal walls of the housing 80 are covered with a textured material that traps light and minimizes reflections of the laser beam on these internal walls.

[0179] Inside the housing 80, the SOGm>n probe comprises the following components arranged one after the other along the path of the excitation beam and the optical signal from the FEGm>n fiber to the FSGm>n fiber: a collimator 82, a polarizer 84, a filter 86, a beam splitter 88, a parabolic mirror 90, a window 92, an analysis chamber 94, a filter 96, a polarizer 98, a rotator 100 and a parabolic mirror 102. In [Fig.3], the path of the excitation beam and the optical signal is represented by oriented arrows.

[0180] Here, inside the housing 80 the excitation beam and the optical signal move parallel to a predetermined PI plane fixed relative to the housing 80. For example, the PI plane is parallel to a base on which the different components of the SOGm,n probe are fixed.

[0181] The collimator 82 makes it possible to obtain a collimated beam, directed towards the polarizer 84, from the excitation beam emitted by the distal end of the FEGm>n fiber. For this purpose, for example, the collimator 82 is a parabolic mirror.

[0182] The polarizer 84 eliminates the polarization component perpendicular to the PI plane, to retain only the polarization component parallel to this PI plane. Preferably, the polarizer 84 is a polarizer cube or PBS (“Polarization BeamSplitter cube”) which simultaneously exhibits good laser beam resistance but also low reported fluorescence.

[0183] The filter 86 eliminates or reduces the fluorescence generated by the polarizer 84 and the FEGm>n fiber as well as the components of the polarized beam greater than the wavelength of the excitation beam received by this probe. For the remainder of the description of the SOGm.n probe, the wavelength of the excitation beam that it receives is noted Xp More precisely, the filter 86 eliminates or greatly reduces all the components of the polarized beam likely to interfere with the optical signal scattered by the Raman effect. For this, the filter 86 lets the polarized excitation beam pass while eliminating the wavelengths greater than the wavelength Xi of the excitation beam. For this purpose, the filter 86 is a low-pass or band-pass filter whose cut-off wavelength at -70 dB is, preferably, between Xi + 15 nm and Xi + 25 nm at normal incidence.For example, filter 86 is a SWP filter ("Short Wave Pass filter") mounted on a swivel mount which allows the angle of incidence of the laser beam to be adjusted relative to the normal to the surface of filter 86. This angle of incidence is adjusted to obtain the desired rejection performance on the Raman spectrum.

[0184] The splitter plate 88 folds the excitation beam onto the parabolic mirror 90. For the optical signal reflected by the mirror 90 and which passes through the splitter plate 88, the splitter plate 88 also behaves as a high-pass filter which eliminates or reduces the components of the optical signal which pass through it whose wavelengths are equal to or less than the wavelength Xb. For this purpose, typically, the plate 88 has a cut-off wavelength at -70 dB, preferably between Xi + 5 nm and Xi + 25 nm. For this purpose, here, the plate 88 is also mounted on an orientable mount which makes it possible to adjust the angle of incidence of the incident optical signal relative to the normal to the surface of the plate 88. This angle of incidence is adjusted to obtain the desired rejection performance on the Raman spectrum.

[0185] The parabolic mirror 90 focuses the polarized beam at a point R located inside the analysis chamber 94.

[0186] Chamber 94 contains a sample of the medium 10 to be analyzed. Chamber 94 isolates the sample from the light that may be present inside the enclosure 4. In addition, the chamber 94 is also designed to protect the sample from possible water splashes as well as pollution by aerosols.

[0187] Here, the chamber 94 is crossed by a gas flow of the medium 10 so that the sample of the medium 10 is constantly renewed. This gas flow of the medium 10 occurs, for example, by natural convection. For this, the chamber 94 has vents for the entry and exit of the medium 10. The internal volume of the chamber 94 is for example of the order of 200 cm3.

[0188] The chamber 94 is fluidically isolated from the interior of the housing 80. For this purpose, the housing 80 comprises the window 92 which is transparent to the excitation beam and to the optical signal scattered, by Raman effect, by the gaseous components to be quantified. Here, the window 92 is configured to transmit the polarized excitation beam in full without reflecting part of it. For this purpose, the window is here a Brewster window, that is to say a window inclined at the Brewster angle relative to the optical axis of the incident excitation beam so as not to reflect the incident beam.

[0189] At least the inner wall of the chamber 94, located opposite the window 92 and on the other side of the point R, is covered with a textured material which traps the light and minimizes the reflection of the excitation beam on this inner wall. Preferably, this inner wall of the chamber 94 is placed far enough away to limit the scattered spectral background. For example, the distance between the window 92 and this inner wall of the chamber 94 is greater than or equal to 5 cm.

[0190] In this embodiment, the power of the polarized excitation beam at point R is approximately 180 mW for a power emitted by the laser source SLk>n of approximately 1 Watt.

[0191] Here, the temperature sensor 24 is placed inside the chamber 94 as close as possible to the point R. In addition, the chamber 94 also includes an anti-condensation module 95 which makes it possible to prevent water vapor from condensing on the window 92. This anti-condensation module 95 consists of a winding of conductive metal wires (for example constantan) protected by a silicone sheath, supplied via the cables 46 in order to generate heat emission by the Joule effect. However, to simplify [Fig.2], the connection of this module 95 to the cables 46 is not shown.

[0192] The optical signal diffused, by Raman effect, by the interaction, at point R, of the excitation beam with the gaseous components present, is returned to the interior of the housing 80 and collected by the mirror 90. The mirror 90 then returns the optical signal to the separating plate 88 which transmits it to the filter 96.

[0193] Filter 96 is a high-pass filter or LWP (“Long-Wave Pass”) filter which also has a cut-off wavelength at - 70 dB preferably, between Xi + 5 nm and Xi + 22 nm. For this purpose, here, the filter 96 is also mounted on an adjustable mount which allows the angle of incidence of the incident optical signal to be adjusted relative to the normal to the surface of the filter 96. This angle of incidence is adjusted to obtain the desired rejection performance on the Raman spectrum.

[0194] The optical signal filtered by filter 96 is then polarized by polarizer 98. For example, polarizer 98 is a PBS (“Polarizing Beam Splitter”) polarizer similar to polarizer 84.

[0195] The monostable electromagnetic rotator 100 makes it possible to rotate the polarizer 98 by 90° in response to a control signal received via the cables 46. For example, the rotator 100 comprises a shaft on which a set 97 of gears is mounted. This set 97 of gears comprises, for example, a first toothed wheel which rotates a second toothed wheel on which the polarizer 98 is mounted. The rotator 100 is powered via the cables 46. When this rotator 100 is powered, this triggers a rotation of its shaft which rotates the polarizer 98 by 90° around its optical axis. When the power supply is cut off, the rotator 100 returns to its initial position under the action of a mechanical spring. Here, in the absence of power supply, the passing axis of the polarizer 98 is parallel to the PI plane so that the power of the optical signal passing through it is maximum.Conversely, when the rotator 100 is powered, the passing axis of the polarizer 98 is perpendicular to the PI plane and the power of the optical signal passing through the polarizer 98 is minimal. Subsequently, when the passing axis of the polarizer 98 is parallel to the PI plane, the optical signal is said to be measured with “parallel polarization”. Conversely, when the passing axis of the polarizer 98 is perpendicular to the PI plane, the optical signal is said to be measured with “perpendicular polarization”. The electronics that enable the rotator 100 to be powered and, alternately, to be cut off is located in the processing unit 30 and has not been shown to simplify [Fig.l].

[0196] To rotate its shaft, the rotator 100 comprises an electromagnetic actuator comprising coils and magnets. In order for it to be able to operate correctly even in the event of a nuclear accident, typically, the electrical wires of the coils are coated with silicone. Similarly, the permanent magnets are made of magnetic materials which have a Curie temperature greater than 300°C or 450°C. For this purpose, for example, magnets made of Sm-Co (samarium-cobalt) or Al-Ni-Co (Aluminium-Nickel-Cobalt) are recommended.

[0197] The parabolic mirror 102 focuses the optical signal that has passed through the polarizer 98 onto the distal end of the FSGm>n fiber. The optical signal scattered by the Raman effect is therefore guided by the FSGm>n fiber.

[0198] [Fig.4] shows in more detail the optical connections between the assembly 32 laser sources, set 20 of probes and spectrometers SP1 to SP4 of unit 34 reading.

[0199] In this embodiment, the assembly 32 comprises six monochromatic laser sources SLi i, SL2>b SLk2, SL2j2, SLb3 and SL23. These laser sources are also designated by the symbol SLk>n, where:

[0200] - the index k is an identifier of the wavelength of the laser source,

[0201] - the index n is an identifier of the modulating signal SMn used to modulate the amplitude of the excitation beam emitted by this laser source.

[0202] In this exemplary embodiment, three modulating signals SMb SM2 and SM3 are used. Thus, the index n can take the values ​​1, 2 or 3. The same index n is used to identify the signal SMn and the order number of the probe SOGm>n because, as explained below, the probe SOGm>n is the one which receives the excitation beam modulated in amplitude by the signal SMn.

[0203] The SMn signals are configured to obtain periodic modulations of the excitation beams emitted by the laser sources at the same wavelength. For this purpose, here by way of illustration, each SMn signal is a periodic signal in time with a period Tn and a fundamental frequency fn equal to 1 / Tn. The fundamental frequencies fn of the different SMn signals are advantageously prime to each other. For this purpose, here, the frequencies fn are successive frequencies in the sequence of prime numbers. The frequencies fn are less than fe / 2 Hz and preferably less than fe / 5 or fe / 10, where fe is the acquisition frequency of the reading unit 34. For example, in this embodiment, the frequencies fb f2 and f3 are equal, respectively, to 3 Hz, 5 Hz and 7 Hz for an acquisition frequency fe equal to 100 Hz.

[0204] Here, the signal SMn is a square signal which, during a period Tn, comprises a first alternation where the signal SMn is in a high state and a second alternation where the signal SMn is in the low state. During the first alternation, the amplitude of the excitation beam generated using the laser source SLk>n is greater than zero. Conversely, during the second alternation, the amplitude of the excitation beam generated using the laser source SLk>n is zero. In this case the excitation beam is therefore an all-or-nothing beam.

[0205] More specifically, in this embodiment, the MM modulator is implemented using optical switches as described below.

[0206] In this embodiment, the outputs of the laser sources SLk>n are optically connected to respective inputs of an optical combiner Mn. Here, there are three combiners Mb M2 and M3 structurally identical to each other. Each combiner Mn multiplexes on a common output two laser beams of wavelengths, respectively, Xn and Xi2, received on its inputs. Thus, here, the laser beams received on the inputs of the combiner Mn are wavelength multiplexed on its output. For this, as an example, each combiner Mn uses a diffraction grating to combine the two laser beams received at the input into a single laser beam emitted at its output.

[0207] In the example of [Fig.4], the output of each combiner Mn is optically connected to an input of a respective optical switch COn of the modulator MM via an optical fiber FMn. Thus, the modulator MM comprises three optical switches COi, CO2 and CO3 whose switching is controlled, respectively, by the modulating signals SMb SM2 and SM3.

[0208] In this embodiment, each COn switch has a first and a second output. The COn switch directs the laser beam received at its input to its first output and, alternately, to its second output. The first and second outputs of the COn switch are optically connected to proximal ends, respectively, of optical fibers FSi>n and FS2>n. When the laser beam is directed to the first output, no laser beam is emitted by the second output and vice versa. The switching between the first and second outputs of the COn switch is controlled by the modulating signal SMn so that the switching frequency of the COn switch is equal to the frequency fn of the modulating signal SMn. Thus, the first and second outputs of the COn switch emit on-off excitation beams, on the optical fibers FSi>n and FS2>n respectively, whose fundamental frequencies are equal to fn.Here, the excitation beams carried by the fibers FSi,n and FS2>n are of the same frequency fn but in phase opposition. For this, in this embodiment, each laser source SLk>n continuously emits a laser beam whose amplitude is constant.

[0209] For each window R / / and R J- , the duration of a window is chosen to be less than 10 s or 5 s. Advantageously, the durations of the windows R / / and A ± are chosen to be identical.

[0210] Here, it is the optical fibers FSi>n and FS2>n which pass through the enclosure 4 and which therefore form the assembly 42. There are therefore six incoming optical fibers for twelve probes.

[0211] The multiplexers Mn and the switches COn are outside the enclosure 4. Typically, they are part of the processing unit 30.

[0212] The distal ends of the optical fibers FSi>n and FS2>n are optically connected to an input, respectively, of an optical splitter Dbn and an optical splitter D3>n. In this embodiment, there are therefore six optical splitters Du to Di3 and D31 to D33 housed inside the enclosure 4. Subsequently, the symbol Dpn is used to designate one of these optical splitters, where the index p is either equal to one or equal to three. Each splitter Dp>n demultiplexes, in wavelength, the excitation beam received at its input and emits on a first output the monochromatic excitation beam at the wavelength Xn and on a second output the monochromatic excitation beam at the wavelength Xi2. The first and second outputs of the se- Dpn parator are directly optically connected, respectively:

[0213] - to the SOGP>n probe via the FEGp,n fiber, and

[0214] - to the SOGP+i>n probe via the FEGP+i>n- fiber

[0215] Thus, in this embodiment, the probes which belong to a Gm group of which the index m is odd receive an excitation beam at wavelength Xn while the probes which belong to a group Gm whose index m is even receive an excitation beam at wavelength Xi2.

[0216] All the probes S0Gm,n of the same group Gm are optically connected to the inputs of the same optical coupler CPm. As an exemplary embodiment, the couplers CPm are three-way to one-way couplers. For this purpose, the fibers FSGm,n of these probes are connected to respective inputs of the coupler CPm. Each coupler CPm is located inside the enclosure 4. There is a respective coupler CPm for each group Gm. Here, there are therefore four couplers CPi to CP4. The coupler CPm combines the optical signals received in parallel on its inputs to form a single merged optical signal emitted on its output. This output is connected, via a single optical fiber FFm, to a respective spectrometer SPm of the reading unit 34. The set 44 of outgoing optical fibers is therefore formed by the fibers FFm. Here, this set 44 has only four outgoing optical fibers FF i to FF4 for twelve probes.

[0217] [Fig.5] shows a preferred embodiment of the CPm coupler. In this embodiment, the ratio dFFm / dFSGm,n is greater than 1.7 and, for example, close to two, where dFFm and dFSGm,n are the diameters of the fibers, respectively, FFm and FSGm,n- Under these conditions, the ends of the three FSGm,n fibers can be directly butted onto one end of the FFm fiber. For this, the ends of the FFm and FSGm,n fibers are planar and extend only in a plane perpendicular to the propagation axis of the optical signal in these fibers. As illustrated in [Fig.5], the ends of the FSGm,n fibers are arranged relative to each other in such a way that their cross-sections are entirely contained within the cross-section of the FFm fiber.

[0218] [Fig.6] represents four Raman spectra 120, 122, 124 and 126 of air measured by a given S0Gm,n probe of a device identical to device 2 except that the SPn spectrometer is replaced by a spectrometer which makes it possible to measure the amplitude, in cps (counts per second), of the optical signal collected by this probe for very many wavelengths, for example a few tens of wavelengths corresponding to Raman lines, distributed between 750 nm and 1050 nm. In [Fig.6], a solid line curve corresponds to the Raman spectrum of an optical signal measured with parallel polarization. A dotted line curve corresponds to the Raman spectrum of an optical signal measured with perpendicular polarization. The 120 and 122 were recorded by exposing a 10 m length of the FSGm>n fiber to photon radiation with an energy equal to 1.25 MeV and a dose rate equal to 250 Gy / h. Both spectra 124 and 126 were recorded under the same conditions except that the dose rate was equal to 1016 Gy / h.

[0219] In this [Fig.6], the lines, produced by the Raman effect, corresponding to oxygen and nitrogen are identified by the symbols, respectively, “02” and “N2”.

[0220] First of all, it can be observed that the "O2" and "N2" lines are discernible only in optical signals measured with parallel polarization. This is because the Raman effect that produces these lines has a very low depolarization ratio p for oxygen and nitrogen. The depolarization ratio p is the ratio between the amplitude of the signal measured with perpendicular polarization to the amplitude of the signal measured with parallel polarization. Thus, for oxygen and nitrogen, the Raman effect is only visible on the optical signal whose polarization direction is identical to the polarization direction of the excitation beam. This is also true for carbon dioxide, carbon monoxide and water vapor. On the other hand, this is false for the Si line of hydrogen.In the case of hydrogen, the Si line exists in the Raman spectra of optical signals measured with parallel polarization and with perpendicular polarization. However, the amplitude of the Si line in the Raman spectrum of the optical signal measured with parallel polarization is about 25% larger than the amplitude of the same Si line in the Raman spectrum of the optical signal measured with perpendicular polarization. In other words, the depolarization ratio p of the Si line of hydrogen is about 75%.

[0221] Cherenkov radiation is radiation that appears in optical fibers and optical components when they are exposed to high-energy photon or electron radiation. In silica, the threshold for the appearance of this radiation is located at 180 keV. Cherenkov radiation can increase substantially in the event of a nuclear accident compared to the nominal operating situation of the reactor. As illustrated by spectrum 120, for a dose rate equal to 250 Gy / h, the amplitude of the Cherenkov radiation exceeds the amplitude of the "O2" line by a factor greater than 50 and the amplitude of the "N2" line by a factor greater than 20. In the case of spectrum 124, the amplitude of the Cherenkov radiation exceeds the amplitude of the "O2" line by a factor greater than 180 and the amplitude of the "N2" line by a factor greater than 60.This shows that, during operation of the device 2, the Raman scattering optical signal is drowned in the middle of a disturbing optical signal corresponding, to a significant extent, to the Cherenkov radiation which appears mainly in the silica and therefore in the FSGm>n fiber as well as, to a lesser extent, in the optical components of the SOGm>n probe.

[0222] Another part of this disturbing signal originates from:

[0223] - the electronic noise of the acquisition chain 50 known by the English term of "dark noise", and

[0224] - a fluorescence signal from optical components.

[0225] The fluorescence signal of the optical components is typically caused by the fluorescence of the optical components of the device 2 when illuminated by the excitation beam.

[0226] The operation of the device 2 will now be described with reference to the method of [Fig.7]. Subsequently, the symbol S3Gm>n(X) corresponds to the measurement of the surface (integral) of the Raman line at wavelength X obtained from the optical signal collected by the probe SOGm,n according to the parallel polarization when this probe receives the excitation signal. The symbol S4Gm>n(X) corresponds to the measurement of the surface of the Raman line at wavelength X obtained from the optical signal collected by the probe SOGm>n according to the perpendicular polarization when this probe receives the excitation signal.

[0227] In this embodiment, the amount of hydrogen present in the sample is advantageously determined according to the baseline subtraction method or SLB method. Thus, the amount of hydrogen is determined from the measurements S3 Gm,n(XH2), S3Gm>n(Xrefi) and S3Gm>n(Xref2) of the signal S3Gm>n. More precisely, the SLB method consists of defining a spectral function f representing the spectral background on which the Raman peaks appear. This can be linear or polynomial, for example, of order two. Here, by way of illustration, this function f is defined by one of the following relationships: f(X) = a + b*(X - Xcte)2 and f(X) = a + b*(X - Xcte), where a, b and Xcte are calibration parameters. The last parameter Xcte is an optimization parameter, chosen a priori in the Raman spectral band.The parameters a and b are deduced from the measurements S3Gm>n(Xrefi) and S3Gm>n(Xref2) carried out outside each Raman line by solving the following system of equations: f(Xrefi) = S3Gm>n(Xrefi) and f(Xref2) = S3Gm>n(Xref2). The useful signal rGm>n(XH2) is then deduced by subtraction of the spectral function, i.e. using the following relation: rGm>n(XH2) = (S3Gm>n(XH2) - f(XH2)) / t3.

[0228] For the gaseous components to be quantified, other than hydrogen, the calculator 36 uses the following relation (1): r(X) = S3Gm>n(X) / t3 - k(X)*SGm.n4(X) / t4, where:

[0229] - r(X) is a value representative of the quantity of the gaseous component, which corresponds to the Raman line centered on the wavelength X, in the sample present inside the chamber 94 of the SOGm>n probe, expressed in counts per second,

[0230] - S3Gm>n(X) and S4Gm>n(X) are the measurements, for the wavelength X, respectively, S3Gm>n and S4Gm>n optical signals measured using the SOGm>n probe, for parallel and perpendicular polarizations respectively.

[0231] - k(X) is the value, for the wavelength X, of a scale coefficient k pre determined, and

[0232] -13 and t4 are the durations of the time windows during which the signals, res respectively, S3Gm,n and S4Gm>n are measured.

[0233] The measures S3Gm>n(X) and S4Gm>n(X) are expressed in number of strokes.

[0234] The ratios S3Gm>n(X) / t3 and S4Gm>n(X) / t4 are measurements, in counts per second, of the optical signal scattered by Raman effect at wavelength X by the SOGm>n probe.

[0235] Preferably, the ratio t3 / t4 is equal to unity. Under these conditions, the relation (1) is written in the following simplified form: R(X) = S3Gm>n(X) - k(X)*S4Gm>n(X), where R(X) is the amplitude of the optical signal scattered by the Raman effect at the wavelength X, expressed in number of counts.

[0236] In this embodiment, since the amplitude of the excitation beam received by the SOGm>n probe is modulated by the SMn signal, the optical signal collected by the SO Gm>n probe is also amplitude modulated by this same SMn signal. Therefore, in a power spectrum of the electrical signal delivered by the SPm spectrometer, the Raman spectrum of the optical signal collected by this SOGm>n probe is located near the frequency fn. The Cherenkov radiation is not amplitude modulated by the SMn signal. Therefore, the Raman spectrum near the frequency fn is corrected for the Cherenkov radiation. On the other hand, the fluorescence signal, corresponding to the specific fluorescence, internal to the probe, is amplitude modulated by the SMn signal and consequently, the spectrum near the frequency fn is not corrected for this fluorescence signal.In other words, the signal S3Gm>n(X) / t3 is the result of the superposition of the useful signal rGm>n(X) and the fluorescence signal measured with parallel polarization. Here, this fluorescence signal is estimated from the measurement S4Gm>n(X) / t4. More precisely, the measurement S4Gm>n(X) / t4 estimates the amplitude of the fluorescence signal measured with perpendicular polarization. The fluorescence signal is weakly polarized. In this embodiment, the fluorescence signal present in the signal S3Gm>n measured with parallel polarization is assumed to be proportional to the fluorescence signal present in the signal S4Gm>n. Thus, the fluorescence signal present in the signal S3Gm>n is estimated by the term k(X)*S4Gm>n(X) / t4 of the relation (1).

[0237] The value of the coefficient k for all wavelengths of interest must first be determined before relation (1) can be used. Subsequently, for simplicity and because all SOGm>n probes are structurally identical, it is assumed that the values ​​of the coefficient k do not depend on the wavelength of the excitation beam and are therefore the same for all SOGm>n probes.

[0238] The method then begins with a calibration phase 200. Here, phase 200 is executed for a SOGm>n probe while it is fixed inside the enclosure 4. In this case, preferably, phase 200 is executed at a time when the nuclear reactor is shut down so that the Cherenkov radiation is of very low magnitude, or even unmeasurable. For example, phase 200 is executed on occasion of a ten-year shutdown of the nuclear reactor.

[0239] During phase 200, a reference sample, the composition of which is known, is located inside the chamber 94 of the SOGm>n probe. Here, the reference sample is air.

[0240] Finally, during phase 200, the processing unit 30 is replaced by a processing unit which makes it possible to measure the amplitude of the optical signal both at the wavelengths of interest and at other wavelengths. For example, for this purpose the SPn spectrometer is replaced by a spectrometer identical to that used to measure the Raman spectra of [Fig.6].

[0241] Here, the variation of the coefficient k as a function of the wavelength X is assumed to be linear over the entire range of interest, i.e. here between 750 nm and 1050 nm. Under these conditions, the values ​​of the coefficients of the line which approximates the evolution of the value k(X) as a function of the wavelength X, are obtained from measurements carried out for wavelengths X; located outside the oxygen and nitrogen lines and therefore far from the wavelengths X02 and XN2. The index i is an identifier of the wavelength.

[0242] Therefore, during a step 202, for each wavelength X;:

[0243] - a Spara(X;) measurement of an optical signal Spara collected by the probe S0Gm,n is measured with parallel polarization, and

[0244] - a Sperp(X;) measurement of an optical signal Sperp collected by the probe SOGm>n is measured with perpendicular polarization.

[0245] The Spara and Sperp signals are measured while the SOGm>n probe receives an excitation beam emitted by the assembly 32 and therefore when the sample present inside the chamber 94 is excited by this excitation beam.

[0246] Furthermore, in this embodiment, during a step 204, the electronic noise of each acquisition chain 50 of the reading unit 34 is measured. Here, this electronic noise is assumed to be identical for each acquisition chain 50. Furthermore, it is assumed that this electronic noise does not vary as a function of the wavelength X within the range of interest. Finally, it is also assumed that this electronic noise is independent of the polarization of the measured optical signal as well as the wavelength of the excitation beam. For example, the amplitude DN of this electronic noise is measured by occluding the distal end of the FFm fiber then averaging the amplitudes measured by each acquisition chain 50.

[0247] During a step 206, for each wavelength X;, a value k(X;) is calculated using the following relation: k(X;) = [Spara(X;) - DN] / [Sperp(X;) - DN].

[0248] Then, during a step 208, the values ​​k(XC02), k(XO2), k(XCo), k(XN2) and k(XH2o) are calculated, by interpolation, from the values ​​k(X;). For this purpose, the function which associates with each wavelength X, the corresponding value k(X) of the coefficient k, is obtained by mathematical adjustment. For example, here, the interpolation used is a linear interpolation. For this purpose, the coefficients a and b of the line that minimizes the deviations with the different values ​​k(X;), are calculated. Then, using the equation of this line, the values ​​k(XC02), k(X02), k(XCo), k(XN2) and k(XH20) are calculated.

[0249] During a step 210, the values ​​Id / .cmk k(XO2), k(XCo), k(XN2) and k(XH20) are recorded in the memory 62 of the computer 36.

[0250] The calibration phase 200 is then completed and a phase 220 of operation of the device 2 begins. Phase 220 is typically executed during a nuclear accident. However, it can also be executed while the nuclear reactor is operating normally, i.e. in an operational situation.

[0251] Phase 220 consists of a measurement cycle repeated throughout the duration of phase 220 for each of the SOGm,n probes. Subsequently, phase 220 is described in the particular case of the SOGii probe but everything described in this particular case applies to the other probes of the set 20.

[0252] In [Fig.8], the different measurement cycles of the probe SOgi.i are identified by the symbol CGi,i,j, where the index j is the order number of the cycle since the start of phase 220. To simplify [Fig.8], only the cycles Cgi.ii and Cgi,i,2 are fully represented.

[0253] Each cycle Cgi.ij comprises an R / / window and an R-L window which are preferably immediately consecutive.

[0254] Throughout the duration of the cycle CGi ij, the computer 36 controls the switches COi, CO2 and CO3 to modulate the amplitude of the excitation beams. More precisely, during the cycle CGi ij, the laser beams simultaneously emitted by the laser sources SLu and SL2ji at the wavelengths, respectively, Xn and Xi2, are multiplexed, in wavelength, by the combiner Mb. The laser beam thus multiplexed is transmitted to the input of the switch COp. The switch COi generates from the received multiplexed laser beam, two all-or-nothing multiplexed excitation beams in phase opposition transmitted, respectively, on the optical fibers FSi.i and FS2,i. The splitter Du demultiplexes the received multiplexed excitation beam and transmits a monochromatic excitation beam at wavelength Xn to the probe SOGi i and, in parallel, a monochromatic excitation beam at wavelength Xi2 to the probe SOG2>i.Thus, the excitation beams received by the probes of groups G1 and G2 differ from each other by their wavelength. The operation is the same for the other excitation beams modulated by the signals SM2 and SM3. Thus, the measurement cycles for each probe are executed in parallel.

[0255] The samples contained in the chambers 94 of each of the probes of group G1 are excited and these probes therefore each collect an optical signal scattered by the Raman effect. The optical signals thus collected by the probes of group G1 are transmitted to the CPi coupler which combines them to form a merged optical signal which is transmitted to the SPi spectrometer via the FFi fiber. Since the amplitude modulations applied to the excitation beams received by the probes of group G1 are periodic, the optical signals collected by these same probes also present periodic modulations. Thus, even after being merged with each other by the CPi coupler, it is still possible to separate them from each other either by spectral analysis or by synchronous demodulation. More precisely, during the cycle CGi,ij and at the frequency fe, for each wavelength of interest and for the wavelengths Xrefi and Xref2, the merged optical signal is measured by the SPi spectrometer and transformed into a corresponding electrical signal transmitted and acquired by the computer 36.

[0256] In this embodiment, the cycle CGi,ij comprises two time windows designated in FIG. 8, respectively, by the symbols R / / and R d-. Preferably, these two windows R / / and R -h follow each other immediately. Here, the durations t3 and t4 of the windows, respectively R / / and R -L , are equal. The durations t3 and t4 are such that at least 500 or 1000 measurements are carried out during each window R / / and R -L . For example, here, the durations t3 and t4 are equal to 5 s or 10 s when the frequency fe is equal to 100 Hz.

[0257] Throughout the duration of the window R / / , the computer 36 maintains the polarization direction of the polarizer 98 of the probes of the group G1 parallel to the plane PI. Thus, during the window R / / , the spectrometer SPi measures the signal merged with the parallel polarization and the computer 36 acquires signals S3Gi(Xh2), S3Gi(Xrefi), S3Gi(X ref2), S3Gi(XCO2), S3Gi(XO2), S3Gi(XC0), S3Gi(Xn2) and S3Gi(Xh2O) at the acquisition frequency fe. The signals S3Gi(Xh2), S3Gi(Xrefl), S3Gi(Xref2), S3Gi(XGO2), S3Gi(XO2), S3Gi(XG0), S3Gi(X N2) and S3Gi(Xh2O) correspond to the merged signal measured by the SPI spectrometer at wavelengths, respectively, XH2, Xrefi, Xref2, / <02- ^02, ÀCo, ÀN2 and XH20. In this S3Gi signal the amplitude of each Raman line corresponds to the sum of the amplitudes of the Raman lines, at the same wavelength, of the Raman spectra of the signals collected by all the probes of the Gl group.

[0258] Throughout the duration of the R -L window, the computer 36 maintains the polarization direction of the polarizer 98 of the probes of the Gl group perpendicular to the PI plane. Thus, during the R -L window, the SPi spectrometer measures the optical signal with the perpendicular polarization and the computer 36 acquires signals S4Gi(XCo2), S4Gi(XO2 ), S4Gi(XCo), S4Gi(Xn2) and S4Gi(XH2o) at the acquisition frequency fe. The signals S4Gi(X C02), S4Gi(XO2), S4Gi(XC0), S4Gi(Xn2) and S4Gi(Xh2o) correspond to the merged signal measured by the SPi spectrometer at the wavelengths, respectively, / <02. L2. ^co, X N2 and XH2o- In this S4Gi signal the amplitude of each Raman line corresponds to the sum of the amplitudes of the Raman lines, at the same wavelength, of the spectra Raman of the signals collected by all probes of group Gl.

[0259] Then, during a step 228, the computer 36 extracts, from the signals S3Gi(Xh2), SSci^n), S3Gi(Xref2), S3Gi(XGO2), S3Gi(XO2), S3Gi(XC0), S3Gi(Xn2) and S3Gi(Xh2O), the measurements, respectively, S3Gi.i(Xh2), S3Gl,l(Xrefl), S3Gl,l(Xref2), S3Gi.i(XGo2), S3Gi.i(Xo2), S3Gi.i(Xco), S3Gi.i(Xn2) and S3Gi.i(Xh2O). For this, here, it proceeds by spectral analysis. To this end, it constructs, for example using a fast Fourier transform, the power spectra of the signals S3Gi(Xh2), S3G1(Xrefl), S3Gi(Xref2), S3Gi(XCO2), S3Gi(XO2), S3Gi(XCo), S3Gi(Xn2) and S3Gi(Xh2O). Subsequently, the processing carried out by the computer 36 is described in the particular case of a Raman line at wavelength X. The same processing is also carried out at wavelengths Xrefi and Xref2 to obtain the measurements S3Gi,i(Xrefl) and S3Gi(Xref2). In each of these spectra, the Raman lines of the optical signals collected by the probes SOGi.i, SOGi.2 and SOGi.3 at the wavelength of interest X, is located near, respectively, the frequencies fb f2 and f3. Thus, in each of the constructed spectra, the Raman lines corresponding to the optical signals collected by the probes SOGi.i, SOGi.2 and SOGi.3 are separated from each other. In addition, the line corresponding to the Cherenkov radiation is located on the zero frequency, that is to say in baseband, because the Cherenkov radiation is not amplitude modulated. Therefore, in each of the constructed spectra, the Raman lines are corrected for the Cherenkov radiation. To obtain the measurement S3Gi,i(X), the computer 36 integrates the power spectrum constructed for the wavelength X only in the frequency range where the Raman line of the signal collected by the probe SOGi.i is located. By proceeding in this way for each of the wavelengths of interest and for the wavelengths Xrefi and X^, the calculator 36 obtains the measurements S3Gi.i(Xh2), S3Gi.i(Xrefi), S3Gi.i(X ref2), S3Gi.i(XCO2), S3Gi.i(XO2), S3Gi.i(XG0), S3Gi.i(Xn2) and S3Gi.i(Xh2O). .

[0260] During step 228, the computer 36 extracts the measurements S4Gi,i(XCO2), S4Gi.i(XO2), S4 gi.i(Xco), S4Gi.i(Xn2) and S4Gi.i(Xh2O) by proceeding as described in the preceding paragraphs but by using the signals S4Gi(XCO2), S4Gi(XO2), S4Gi(XC0), S4Gi(Xn2) and S4 gi(Xh2o) instead of the signals S3Gi(XGG2), S3Gi(XG2), S3Gi(XGG), S3Gi(Xn2) and S3Gi(Xh2G).

[0261] Then, during a step 230, the calculator 36 determines the quantity of each gaseous component in the sample contained in the chamber 94 of the probe SOGi.i. For this, the calculator 36 calculates, during an operation 232, using the relation (1) and for each wavelength XC02, X02, Xco, XN2 and XH20, the values ​​rGi.i(XC02), rGi.i(X02 )» rGi,i(XGoX rGi,i(XN2) and rGi.i(XH20). The values ​​rGljl(XG02), rGljl(Xo2), rGljl(XG0), rG1>1(XN2) and rGi,i(XH2o) are expressed in counts per second (cps). These values ​​rGi.i(XC02), rGi,i(XO2), r gi.i(Xco), rGi.i(XN2) and rGi.i(XH2o) are proportional to the amounts of carbon dioxide, oxygen, carbon monoxide, nitrogen, and water vapor, respectively, present in the sample. In this embodiment, the value rGi.i(XH2) is obtained using the relationship rGi.i(XH2) = (S3Gi.i(Xh2) - f(XH2)) / t3.

[0262] Then, during an operation 234, from these values ​​rGi,i(XCO2), foi,1(^02), rGia(Xco ), rGi,i(XN2) and rGi,i(XH2o) and from the value rGi,i(XH2) obtained, the computer 36 establishes the proportions, in percent, of each of the gaseous components in the chamber 94 of the probe SOGi,i. For example, assuming that the sum of the partial pressures of all the components quantified here (O2, N2, H2O, H2, CO and CO2) is equal to the total pressure PT in the enclosure 4, then the following relation (2) is used:

[0263] [Math.l] _ rG 1.1 ' P T~ ;=1 a "L

[0264] where:

[0265] - P, / PT is the proportion, in chamber 94, of the component corresponding to the line Raman at wavelength X,

[0266] - P, is the partial pressure of the component corresponding to the Raman line at the wavelength X,

[0267] - PT is the total pressure inside the enclosure 4 measured by the sensor 22,

[0268] - Ox is a constant, for example determined experimentally, defined by the following relation (3): rGi,i(X)*T = o^ * P^, where T is the temperature measured in or near the probe SOGi,i,

[0269] - Ne is the total number of quantized components, i.e. six in this example,

[0270] - rGi,i(Xj) is the measurement of the quantity of the j-th component to be quantified carried out at using the SOGi,i probe, and

[0271] - o^ is a constant, for example determined experimentally, defined by the following relation: r(Xj)*T = Oy * Py, where Py is the partial pressure of the j-th component corresponding to the Raman line at wavelength Xj.-,

[0272] The relation rGi,i(X)*T = o^ * P, follows from relation (5) of the article Magne2020.

[0273] If in addition the temperature T is known, the calculator 36 can then calculate the partial pressure P, for each of the gaseous components using relation (3) above. Thus, during an operation 236, the computer 36 acquires the temperature measured by the sensor 24, located in the probe SOGi,i then calculates the partial pressure of each of the gaseous components in the chamber 94 of the probe SOGi,i from the values ​​rG1>1(XH2), rGljl(XC02), rGljl(X02), rGljl(XC0), rG1>1(XN2) and rGljl(XH20).

[0274] Here, the measurement cycles of all probes are executed in parallel. Thus, at the end of the duration of a measurement cycle, a new quantification of the gas components is available at the location of all probes.

[0275] For example, during a step 238, the computer 36 controls the human-machine interface 38 to display the quantifications carried out with each of the probes of set 20 on screen 66.

[0276] [Fig.9] represents another embodiment identical to that of [Fig.4] except that:

[0277] - the MM modulator is replaced by an MM2 modulator which controls di directly the Slk>n laser sources,

[0278] - the switches COn are replaced by respective optical couplers CPEn housed inside enclosure 4.

[0279] The modulator MM2 is connected to an input for controlling the amplitude of each laser source SLk>n and configured to transmit the modulating signal SMn to each of these inputs. For example, the modulator MM2 directly controls the current injected into a laser diode. In this embodiment, the coupler CPEn directs the excitation beam received at the input simultaneously to the separators Di n and D3.11.

[0280] In this embodiment, the incoming optical fibers which pass through the enclosure 4 are the FMn optical fibers so that the set 42 then corresponds to the set of FMn fibers. This embodiment makes it possible to further limit the number of incoming optical fibers passing through the enclosure 4, i.e. in this example three incoming optical fibers for twelve probes.

[0281] Chapter III: Variants:

[0282] Probe variants:

[0283] The number of probes in a group Gm may be equal to two or greater than three. However, in all cases, a group Gm contains at most as many probes as there are frequencies fn. Furthermore, it is not necessary for the numbers of probes in each group to be equal. Thus, a group Gm may contain more probes than another group of probes of the device 2.

[0284] Other solutions are possible for focusing the laser beam on the point R. For example, instead of using the parabolic mirror 90 for this, it is possible to use a converging lens.

[0285] Alternatively, the filter 96 is omitted. In this case, the filtering function is provided solely by the blade 88.

[0286] Other embodiments of the polarizer 84 or 98 are possible. For example, the polarizer 84 or 98 is a glass polarizer (sodium-silicate) doped with ellipsoidal nanoparticles having a strong polarizing effect.

[0287] Alternatively, the polarizer 98 is replaced by a polarization splitter cube. This splitter cube separates the parallel and perpendicular polarization directions. Thus, the splitter cube makes it possible to simultaneously generate the signals S3Gm,n and S4Gm,n. In this case, the different optical components described for optically connecting a probe to the reading unit 34 are duplicated to allow simultaneous transmission. optical signals collected with parallel and perpendicular polarizations. In particular, the FSGm>n fiber is replaced by two FSlGm>n and FS2Gm>n optical fibers and the CPm coupler is replaced by two CPlm and CP2m couplers. Therefore, in this case, the number of optical fibers leaving the assembly 44 is doubled, which requires also increasing the number of optical crossings. In return, the measurement time is reduced by a factor of two.

[0288] In a simplified embodiment, the textured material is omitted.

[0289] Processing unit variants:

[0290] In Chapter II, the SPm spectrometers have been represented and described as being distinct elements. However, in practice, each of the SPm spectrometers may correspond to a respective input channel of a single spectrometer, such as a multi-channel imaging spectrometer.

[0291] Alternatively, a CCD (“Charge Coupled Device”) sensor is used in conjunction with an imaging spectrometer that disperses the received optical signal as a function of the wavelengths in the plane where the CCD sensor is located, as described in the Magne 2020 publication. Typically, such a CCD sensor is capable of measuring the optical signal at more than 300 or 1000 or 2048 different wavelengths regularly distributed within the range of interest. Such a CCD sensor therefore measures both the optical signal received at each wavelength X of interest and also at other wavelengths of no interest.

[0292] The photomultiplier 54 can be replaced by a photodiode such as an avalanche photodiode or a SiPM (“Silicon-PhotoMultiplier”) detector.

[0293] Depending on the context of use, the processing unit 30 may be configured to measure the quantity of one or more additional gaseous components other than those from the group consisting of water vapor, oxygen, nitrogen, carbon monoxide, carbon dioxide and hydrogen. In this case, the processing unit is configured to use an additional wavelength of interest corresponding to each additional gaseous component to be quantified. Conversely, the processing unit may also be configured to measure the quantity of only one or only part of the gaseous components from the group consisting of water vapor, oxygen, nitrogen, carbon monoxide, carbon dioxide and hydrogen. In this case, typically, the number of acquisition chains 50 is reduced.

[0294] Variant of periodic modulations:

[0295] Other frequencies fn are possible. For example, as a variant, the frequencies fb f2 and f3 are equal, respectively, to 3 Hz, 5 Hz and 7 Hz or to 5 Hz, 7 Hz and 11 Hz for an acquisition frequency fe of 100 Hz or to 7 Hz, 17 Hz and 23 Hz for a frequency fe of 250 Hz. In another embodiment, the frequencies fn are not first among themselves. This is particularly possible if the excitation beams are sinusoids and not all-or-nothing signals.

[0296] Other embodiments of the MM modulator are possible. For example, each switch COn is replaced by an electromechanical shutter capable of interrupting the laser beam emitted at the frequency fn when it is controlled by the modulating signal SMn. In this case, there are as many laser sources in the set 32 ​​as there are probes SOGm,n. For this, for example, the groups G3 and G4 of probes and the spectrometers SP3 and SP4 are omitted as well as all the optical components which transport the optical signals from the laser sources of the set 32 ​​to the probes of the groups G3 and G4 as well as those which transport the Raman signals to the spectrometers SP3 and SP4.

[0297] When the modulator MM2 is connected to an input controlling the amplitude of each laser source SLk>n, other waveforms are possible for the excitation beams than an all-or-nothing signal. For example, as a variant, the excitation beams are periodic triangular signals or quasi-sinusoidal signals. In another variant, the SMn signals are not periodic. For example, each SMn signal is a code generated by a pseudo-random generator like those used in CDMA ("Code Division Multiple Access") coding systems, better known by the acronym CDMA ("Code division multiple access"). In the latter case, the signal SGm>n of a probe S0Gm,n is extracted by multiplying the acquired electrical signal SGm by the same signal SMn then by low-pass filtering as in synchronous demodulation.

[0298] The number of modulating signals SMn may be equal to two. In this case, the number of probes in each group Gm is equal to two. The number of modulating signals may also be greater than three. For this, for example, the frequency fe is increased if it is desired to preserve the characteristic that the fundamental frequencies fn of the signals SMn are prime to each other. In this case, the number of probes in each group Gm is greater than three. In general, the number of modulating signals is less than ten or five.

[0299] The modulating signals used for groups G2 and G4 are not necessarily the same as the modulating signals used for groups G1 and G3. However, in this case the MM modulator is more complex. For example, to do this, each COn switch must be replaced by two shutters that can be controlled independently of each other.

[0300] In a simplified embodiment, only the amplitudes of the excitation beams at wavelength Xn are modulated periodically, and the amplitudes of the excitation beams at wavelength Xi2 are not modulated periodically. In this case, the optical signals collected by the probes of groups G2 and G4 are each emitted on a respective outgoing optical fiber and are not merged into a single FFm optical fiber. In addition, each optical signal collected by a probe of groups G2 and G4 is measured by a respective spectrometer.

[0301] Optical switch variants:

[0302] The switches COn may have more than two outputs. In this case, the excitation beam emitted by a laser source of the set 32 ​​is received, alternately, by more than two probes. The number of groups Gm of probes can then be increased without increasing the number of laser sources. On the other hand, this does not make it possible to increase the number of measurements carried out simultaneously.

[0303] To further limit the number of incoming optical fibers passing through the enclosure 4, the COn switches can be housed inside the enclosure 4. In this case, the incoming optical fibers which pass through the enclosure 4 are the FMn optical fibers so that the set 42 then corresponds to the set of FMn fibers.

[0304] Variants of wavelength division multiplexing of excitation beams:

[0305] Alternatively, the number Ny of wavelengths at which beams are emitted monochromatic lasers is greater than two. In this case, the number of inputs of the combiners Mn and the number of outputs of the splitters Dp>n are equal to Ny. The number of groups Gm of probes collecting in parallel optical signals scattered by the Raman effect is proportional to this number Ny.

[0306] In a simplified embodiment, wavelength division multiplexing of the excitation beams is not implemented. Thus, all the excitation beams are emitted at the same wavelength Xn. For illustration, for this purpose, the laser sources SL2ji, SL22 and SL23, and the groups G2 and G4 are omitted. In this case, the combiners Mb M2 and M3, and the splitters Dpn are no longer necessary either. For example, the combiners Mb M2 and M3 are replaced by optical fibers that directly connect the laser sources SLi i, SLi>2 and SLi>3 to the switches COi, CO2 and CO3. Similarly, the outputs of the switches COi, CO2 and CO3 can be directly connected to the probes of the groups G1 and G3. In this embodiment, all the excitation beams have the same wavelength Xn.

[0307] Variants of the calibration phase:

[0308] Other approximations of the evolution of the value of the coefficient k as a function of the wavelength X are possible. For example, as a variant, the evolution of the value of the coefficient k as a function of the wavelength X is approximated using a polynomial of order greater than one.

[0309] In another embodiment, the value of the coefficient k also varies as a function of the measured radiation dose. In this case, the quantification device is also capable of measuring the radiation dose received by the sample of the gaseous medium. For example, this radiation dose is estimated from the radiation intensity. Cherenkov measured in the absence of the excitation beam.

[0310] In a simplified variant, the electronic noise of the acquisition chain is neglected. In this case, each value k(X;) is simply taken equal to the ratio Sparat / ., ) / Sperp(ki).

[0311] In a very simplified variant, the value of the coefficient k is assumed to be constant whatever the wavelength X.

[0312] In a degraded embodiment, the calibration phase 200 is executed when the nuclear reactor is operating. In this case, the calibration phase is triggered in the absence of a nuclear accident and the reference sample is identical to the sample of the gaseous medium 10.

[0313] In another variant, the calibration phase of the coefficient k is carried out during the manufacture of the device 2, that is to say at a time when the probes of the assembly 20 are not installed inside the enclosure.

[0314] It is also possible to execute the calibration phase of the coefficient k for each of the SOGm>n probes. A function kGm>n(X) is then obtained for each of the SO Gm>n probes. Then, it is the function kGm>n(X) specific to the SOGm>n probe which is used during the operation of the device 2 instead of the function k(X) common to all the SOGm>n probes.

[0315] Variants of the quantification method:

[0316] In another embodiment, the wavelength of the excitation beam is reduced so that the vibrational line of hydrogen is also measurable using the reading unit 34. This vibrational line is then present in the Raman spectrum of the S3Gm>n signal and almost absent from the Raman spectrum of the S4Gm>n signal given its low depolarization ratio. In this case, one of the wavelengths of interest used is the wavelength of this vibrational line of hydrogen and the quantity of hydrogen is then measured using relation (1). In another variant, although the use of relation (1) leads to using only approximately 25% of the S3Gm>n(XH2) signal, the quantity of hydrogen is still quantified using relation (1). In these last two cases, the reading unit 34 does not need to perform measurements at the Xrefi and Xref2 wavelengths.

[0317] Other spectral analysis methods can be used to extract the S3 Gm>n and S4Gm>n signals. For example, instead of a fast Fourier transform, a Discrete Cosine Fourier Transform (DCT) is used.

[0318] The extraction of the signals S3Gm>n and S4Gm>n by the computer 36 can be carried out by synchronous demodulation and not by spectral analysis. For example, to extract the signal S3Gm>n, the computer multiplies the merged signal S3Gm by the modulating signal SMn then filters the signal resulting from this multiplication using a low-pass filter whose cut-off frequency at - 3 dB is typically of the order of a few 0.1 Hz. (corresponding to an acquisition time of a few seconds). At the output of the low-pass filter, the signal S3Gm>n is obtained.

[0319] Other relationships than relationship (1) are possible. For example, in a very simplified variant, polarizers 86 and 96 are omitted. In this case, the collected optical signals are not polarized and the difference between the optical signals measured with parallel polarization and with orthogonal polarization is not used.

[0320] Alternatively, the ratio t3 / t4 is other than unity.

[0321] The R / / , respectively R -L windows, for a first and a second probe of the same group of probes do not necessarily occur at the same time. For example, alternatively, the R / / window of the first probe occurs at the same time as the R -L window of the second probe and vice versa.

[0322] A calculation of a more precise value of the quantity of the gaseous component by averaging quantities determined at the end of several measurement cycles can be implemented.

[0323] Alternatively, only a relative amount or only an absolute amount of the gaseous component is measured.

[0324] Other variants:

[0325] The continuous laser source can be replaced by a pulsed laser source.

[0326] If only a measurement of the relative quantity of the gaseous components is required, then the temperature sensors 24 can be omitted. In the latter case, the gas taken as the reference gas is often nitrogen.

[0327] The teaching given here applies to any containment enclosure inside which a nuclear reactor is housed and not only to the case where the enclosure is that formed by a reactor building of a nuclear power plant which produces electricity.

[0328] The wavelength multiplexing of several excitation beams on the same incoming optical fiber of the assembly 42 can be implemented independently of the implementation of the periodic modulations. For example, in a very simplified embodiment, the device 2 comprises only the laser sources SL^ and SL2,i, the combiner Mb, the separator Du, the probes SOGu, SOG2>i and the spectrometers SPi and SP2. In this very simplified embodiment, the output of the combiner Mi is directly connected to the input of the separator Du and the switch COi is omitted. The laser sources SLi>2, SL2>2, SLi>3 and SL23 are omitted. The outputs of the probes SOGu, SO G2>i are directly connected to the inputs, respectively, of the spectrometers SPi and SP2 and the couplers CPm are omitted.

[0329] In this last variant where the periodic modulations are not used, to correct the Cherenkov radiation, preferably, it is one of the quantization methods described in the patent application filed on December 22, 2023 under the number FR2315067 which is implemented instead of the method of [Fig.7]. In par In particular, it is the relation (1) described in application FR2315067 which is used instead of the relation (1) described in chapter II. In this case, during a period T off of each SOGm,n probe used, this probe is used:

[0330] - during a C / / window, to measure with parallel polarization, for each wavelength of interest, a value SlGm,n(X) of an optical signal SlGm>n scattered by the sample in the absence of excitation by the excitation beam, and

[0331] - during a C ± window, to measure with a perpendicular polarization, for each wavelength of interest, a value S2Gm>n(X) of an optical signal S2Gm>n scattered by the sample in the absence of excitation by the excitation beam.

[0332] The calculator 36 then determines, for each wavelength of interest, the quantity of the gaseous component present in the sample from the difference [(S3Gm>n(X) / t3 - SlGmn(X) / tl] and the difference [S4Gm>n(X) / t4 - S2Gm>n(X) / t2], where tl, t2, t3 and t4 are the durations of the time windows, respectively, C / / , C ± , R / / and R -L . All the teachings described, and in particular the different variants described, in the DDD application are combinable with the last two variants.

[0333] Several of the variants described above can be combined in the same embodiment.

[0334] Chapter IV: Advantages of the embodiments described:

[0335] Applying periodic modulations to several of the excitation beams that have the same wavelength makes it possible to obtain collected optical signals modulated in amplitude with the same periodic modulations. Therefore, it is possible to simultaneously transmit these collected and modulated optical signals to the reading unit 34 using a single common outgoing optical fiber. Indeed, because the amplitude modulations of the collected optical signals are periodic, after the measurement by the reading unit 34 of the merged optical signal, it is possible to separate them from each other by signal processing. It is therefore possible to simultaneously quantify the gaseous components present in the chambers 94 of each of these probes without using, for each of the probes, a respective outgoing optical fiber that passes through the enclosure 4.The number of crossings of the enclosure 4 necessary to implement the device 2 is therefore reduced while using excitation beams of the same wavelength and allowing the different probes of the same group to work in parallel.

[0336] Furthermore, modulating the amplitude of the collected optical signals allows, at the same time as they are separated from the other simultaneously collected optical signals, to separate them from the part of the disturbing signal which is not amplitude modulated. Thus, it becomes possible, without necessarily implementing additional processing, to quantify the gaseous components even in the presence of Cherenkov radiation.

[0337] Finally, when the amplitude modulations of the excitation beams are implemented, the reading unit only measures the merged optical signal instead of measuring as many optical signals as there are probes. This therefore makes it possible to simplify the reading unit by reducing the number of photodetectors that this reading unit comprises.

[0338] Emitting the excitation beams at several different wavelengths makes it possible to group the excitation beams of different wavelengths onto the same incoming optical fiber. This therefore makes it possible to further limit the number of crossings while allowing simultaneous quantification of the gaseous components by a greater number of probes.

[0339] Using laser beams at several different wavelengths and, at the same time, periodic modulations for all the excitation beams which have the same wavelength makes it possible to minimize the number of crossings of the confinement enclosure while allowing simultaneous quantification of the gaseous components by each of the probes.

[0340] Using a CPEn optical coupler, located inside the enclosure 4, to simultaneously transmit the same amplitude-modulated excitation beam to several probes makes it possible to reduce the number of incoming sealed crossings.

[0341] Determining the amount of the additional gas component from the difference [(S3Gm,n(X) / t3 - k(X)*(S4Gm,n(X) / t4], makes it possible to reduce the fluorescence signal caused by the optical components of the quantification device when they are illuminated by the excitation beam. Thus, by using this difference, the accuracy of the quantification device is improved while using measurements made for a smaller number of wavelengths. In particular, for each gas component to be quantified, it is not necessary to measure the optical signal at the wavelength of interest and in addition at at least two reference wavelengths. Therefore, the reading unit 34 is simplified and its cost greatly reduced.

[0342] Choosing the durations t3 and t4 equal makes it possible to optimize the measurement uncertainty for a given measurement time.

[0343] Adjusting the value of the coefficient k as a function of the wavelength X of interest makes it possible to improve the accuracy of the measurement method.

[0344] Constructing the values ​​k(X) of the coefficient k using the relation k(X) = [SPara(X)-DN] / [SPerp(X)-DN] makes it possible to obtain values ​​which are practically independent of the dose of radioactive radiation received by the probe. Thus, the operation of the quantification device remains precise even in the event of a nuclear accident.

[0345] Limiting the duration of the time windows to less than 10 s makes it possible to limit the variation, during each of these time windows, of the radio-attenuation induced in optical components and fibers. Thus, the quantification device continues to be accurate even in the event of a nuclear accident.

[0346] Measuring the merged optical signal at different wavelengths of interest allows the quantity of several different gaseous components to be measured simultaneously.

[0347] By simultaneously measuring the quantities of water vapor, oxygen and nitrogen, it is possible to assess the risk of an explosion occurring inside the enclosure.

[0348] Measuring the quantities of carbon monoxide and carbon dioxide makes it possible to trace the corium-concrete interaction (Molten Core Concrete Interaction -MCCI) which occurs after the vessel is breached in the event of a nuclear reactor core meltdown.

[0349] Measuring the amount of hydrogen using relation (1) allows this measurement to be made using only the two values ​​S3(XH2) and S4(XH2).

[0350] Using a continuous laser beam makes it possible, for the same size, to have a laser beam whose average power is much greater than if a pulsed laser beam were used. However, the greater the average power of the laser beam, the greater the precision of the measurement of the quantity of the gaseous component.

[0351] Using, in an SPm spectrometer, a single photodetector per wavelength of interest simplifies the quantification device and reduces costs.

Claims

1. Claims Method for quantifying, by Raman spectrometry, at least one gaseous component inside a containment enclosure of a nuclear reactor using at least a first and a second probe located inside this containment enclosure, this method comprising: - the emission (R / / , R -L ) of a first and a second monochromatic excitation beams at the same wavelength Xn, in, respectively, a first and a second incoming optical fibers which each pass through the confinement enclosure, - the reception (R / / , R -L), by each of the first and second probes, respectively, of the first and second monochromatic excitation beams emitted, - the excitation (R / / , R -L ), by each of the first and second probes, using the excitation beam received, respectively, from a first and a second sample of the gaseous medium located inside the confinement enclosure, and - the collection (R / / , A ± ), by the first and second probes, respectively, of a first optical signal and a second optical signal scattered, by Raman effect, by the first and second excited samples, characterized in that: - the first and second monochromatic excitation beams are emitted (R / / , R -L ) simultaneously and are amplitude modulated so that the first and second collected optical signals have the same amplitude modulations as those, respectively, of the first and second excitation beams, this amplitude modulation being such that the result of the integration over time of the scalar product of the modulated first and second monochromatic excitation beams tends towards zero when the integration time increases, and - the process also includes: - combining the collected first and second optical signals to form a first merged optical signal and emitting the first merged optical signal into a first outgoing optical fiber that passes through the containment enclosure, then - the measurement, by a reading unit located outside the containment enclosure, of the first merged optical signal to obtain a

2. first corresponding electrical signal, then - the extraction (228), by an electronic computer, from the first electrical signal and by exploiting the amplitude modulations of the first and second collected optical signals, of a first and a second extracted electrical signal representative, respectively, of the first and second collected optical signals, then - determining (230) the quantities of the gaseous component present in the first and second samples from, respectively, the first and second extracted electrical signals. The method of claim 1, wherein the method also comprises: - the emission (R / / , R -L ) of a third monochromatic excitation beam at a wavelength ^different from the wavelength / . h, in the first incoming optical fiber at the same time as the first excitation beam is emitted, - the separation (R / / , R -L ), inside the confinement enclosure, of the first and third excitation beams emitted at the same time in the first incoming optical fiber and the transmission of the third excitation beam only to a third probe and, in parallel, the transmission of the first excitation beam only to the first probe, - the simultaneous reception (R / / , R -L ) by the first, second and third probes, respectively, of the first, second and third monochromatic excitation beams, and - the excitation (R / / , ^2-), by the third probe, using the third excitation beam received, of a third sample of the gaseous medium located inside the confinement enclosure, - the collection (R / / , A ± ), by the third probe, of a third optical signal scattered, by Raman effect, by the third excited sample, - the emission (R / / , R -L ) in a second outgoing optical fiber, different from the first optical fiber and which crosses the confinement enclosure, of the third optical signal collected, then - the measurement, by the reading unit, of the optical signal emitted on the second outgoing optical fiber, to obtain a second electrical signal, then - the determination, by the electronic computer, from the second electrical signal, of the quantity of the gaseous component present in the third sample.

3. The method of claim 2, wherein the method also comprises: - the emission (R / / , ± ) of a fourth monochromatic excitation beam at wavelength Xi2, in the second incoming optical fiber at the same time as the second excitation beam is emitted, the third and fourth monochromatic excitation beams being emitted simultaneously and being amplitude modulated, this amplitude modulation being such that the result of the integration over time of the scalar product of these third and fourth monochromatic excitation beams tends towards zero when the integration time increases, - the separation, inside the containment enclosure, of the second and fourth excitation beams emitted at the same time in the second incoming optical fiber and the transmission of the fourth excitation beam only to a fourth probe and, in parallel, the transmission of the second excitation beam only to the second probe, - the simultaneous reception by the first, second, third and fourth probes, respectively, of the first, second, third and fourth monochromatic excitation beams, - the excitation, by the fourth probe, using the fourth excitation beam received, of a fourth sample of the gaseous medium located inside the confinement enclosure, - the collection, by the fourth probe, of a fourth optical signal scattered, by Raman effect, by the fourth excited sample, the third and fourth collected optical signals having the same amplitude modulations as those, respectively, of the third and fourth excitation beams, and - combining the collected third and fourth optical signals to form a second merged optical signal and transmitting the second merged optical signal into the second outgoing optical fiber, then - the measurement, by the reading unit, of the second merged optical signal to obtain a corresponding second electrical signal, then - the extraction (228), by the electronic computer, from the second electrical signal and by exploiting the amplitude modulations of the third and fourth collected optical signals, of a third and a fourth representative extracted electrical signals, respectively,

4. of the third and fourth optical signals collected, then - determining (230) the quantities of the gaseous component present in the third and fourth samples from, respectively, the third and fourth extracted electrical signals. Method according to claim 1, in which the method comprises: - the transmission to the first probe and, simultaneously, to a third probe, by a first optical coupler located inside the confinement enclosure, of the first amplitude-modulated excitation beam, and - transmission to the second probe and, simultaneously, to a fourth probe, by a second optical coupler located inside the confinement enclosure, of the second amplitude-modulated excitation beam, - the simultaneous reception by the first and third probes of the first amplitude-modulated monochromatic excitation beam and the simultaneous reception by the second and fourth probes of the second amplitude-modulated monochromatic excitation beam, - the excitation, by the third and fourth probes, using the excitation beam that each of them received, of, respectively, a third and a fourth samples of the gaseous medium located inside the containment enclosure, - the collection by the third and fourth probes, respectively, of a third and a fourth optical signal scattered, by Raman effect, by, respectively, the third and the fourth excited samples, the third and fourth collected optical signals having the same amplitude modulations as those, respectively, of the third and fourth excitation beams, and - combining the third and fourth collected optical signals to form a second merged optical signal and emitting the second merged optical signal into a second outgoing optical fiber, different from the first optical fiber and which passes through the containment enclosure, then - the measurement, by the reading unit, of the second merged optical signal to obtain a corresponding second electrical signal, then - the extraction (228), by the electronic computer, from the second electrical signal and by exploiting the amplitude modulations of the third and fourth collected optical signals, of a third and a fourth representative extracted electrical signals, respectively, of the third and fourth optical signals collected, then - determining (230) the quantities of the gaseous component present, in the third and fourth samples from, respectively, the third and fourth extracted electrical signals.

5. Method according to any one of the preceding claims, in which: - the amplitude modulations of the first and second monochromatic excitation beams are periodic and the fundamental frequencies of the first and second excitation beams are equal, respectively, to first and second fundamental frequencies that are prime to each other, - the reading unit measures the evolution over time of the first merged optical signal to obtain a temporal succession of values ​​of the first electrical signal, - the extraction (228), by the electronic computer, of the extracted first and second electrical signals comprises: - the construction of a power spectrum of this temporal succession of values ​​of the first electrical signal to obtain a spectrum in which a first and a second Raman lines corresponding, respectively, to the first and second collected optical signals appear,the first and second Raman lines being located in the vicinity, respectively, of the first and second fundamental frequencies, then - using the first Raman line only to determine the amount of the gaseous component present in the first sample and using the second Raman line only to determine the amount of the gaseous component present in the second sample.,

6. Method according to any one of the preceding claims, in which, for each of the first and second probes: - during the entire duration of a first (R / / ) and a second (R -L ) time windows, the method comprises the polarization, in a predetermined direction, of the amplitude-modulated monochromatic excitation beam to excite the sample with an amplitude-modulated and polarized monochromatic excitation beam, - during the entire duration of the first time window (R / / ), only the component of the optical signal with a polarization direction parallel to the polarization direction of the excitation beam which excites the sample is collected by the probe, - for the entire duration of the second time window (R -L ), only the component of the optical signal with a polarization direction perpendicular to the polarization direction of the excitation beam which excites the sample, is collected by the probe, - the calculator: - extracts (228) the values ​​S3Gi,n(X) and S4Gi>n(X) representative of the number of photons, at wavelength X, collected by the probe during, respectively, the first and second time windows, where: - the index n is an identifier of the probe among the first and second probes, - X is the wavelength of interest, that is to say the wavelength at which appears, because of the Raman effect, a line in the spectrum of the scattered optical signal when the gaseous component to be quantified is present in the sample, then - determines (230) the quantity of the gaseous component present in the sample from the following difference: [(S3Gi,n(X) / t3 - k(X)*(S4 Gi,n(X) / t4],where: -13 and t4 are the durations, respectively, of the first and second time windows, and - k(X) is the value, for wavelength X, of a predetermined scale coefficient k.,

7. A method according to claim 6, wherein the durations t3 and t4 are equal.

8. Method according to claim 6 or 7, wherein the method comprises a calibration phase (200) during which for each of the first and second probes: - a monochromatic excitation beam polarized in a predetermined direction excites a reference sample, and - a sensor measures (202) an optical signal Spara and an optical signal Sperp scattered by the reference sample excited by this excitation beam, the optical signals Spara and Sperp being the optical signals scattered by the reference sample measured with directions of polarization, respectively, parallel and perpendicular to the predetermined direction of polarization of the excitation beam, and the signals Spara and Sperp being measured at wavelengths X; different from the wavelengths at which, due to the Raman effect, lines appear in the spectrum of the optical signal scattered by this reference sample, then - the value k(X) of the coefficient k for each wavelength of interest X is calculated (208) from the measured Spara and Sperp optical signals, then recorded in the calculator.

9. A method according to any one of claims 6 to 8, wherein the first and second time windows immediately follow each other and the duration of each of these first and second time windows is less than 10 s.

10. Method according to any one of the preceding claims, wherein, when measuring the first merged optical signal, this first merged optical signal is measured for several different wavelengths X of interest, each of these wavelengths of interest corresponds to a particular gaseous component to be quantified in the excited samples, the measurements at these different wavelengths of interest being carried out simultaneously.

11. The method of claim 10, wherein the wavelengths of interest include wavelengths of interest corresponding to water vapor, oxygen, and nitrogen.

12. The method of claim 10, wherein the wavelengths of interest include wavelengths of interest corresponding to carbon monoxide and carbon dioxide.

13. The method of claim 10, wherein a wavelength of interest corresponds to hydrogen.

14. A method according to any preceding claim, wherein the excitation beam is a continuous laser beam.

15. Device for quantifying, by Raman spectrometry, at least one gaseous component inside a containment enclosure of a nuclear reactor, this device comprising: - a first and a second incoming optical fibers (FSi i, FSij2) and a first outgoing optical fiber (FFi) which each pass through the containment enclosure, - a first laser source (SLi i) capable of emitting a first monochromatic excitation beam at a wavelength Xu, in the first incoming optical fiber, - a first and a second probe (SOgi.i, SOgi,2) intended to be located inside the containment enclosure and optically connected, respectively, to the first and second incoming optical fibers to receive, respectively, the first and a second monochromatic excitation beams emitted, these first and second probes being capable of: - to excite using the received excitation beam, respectively, a first and a second sample of the gaseous medium located inside the confinement enclosure, and - to collect, respectively, a first optical signal and a second optical signal scattered, by Raman effect, by the first and second excited samples, characterized in that the device comprises: - a second laser source (SLi>2) capable of emitting, in parallel with the first laser source (SL11), the second monochromatic excitation beam at wavelength Xi4, in the second incoming optical fiber (FSi,2), - an amplitude modulator (MM; MM2) capable of modulating the amplitude of the first and second monochromatic excitation beams emitted so that the first and second collected optical signals have the same amplitude modulations as those, respectively, of the first and second excitation beams, this amplitude modulation being such that the result of the integration over time of the scalar product of the modulated first and second monochromatic excitation beams tends towards zero when the integration time increases, - an optical coupler (CPi) capable of combining the first and second collected optical signals to form a first merged optical signal and of emitting the first merged optical signal in the first outgoing optical fiber (FFi), - a reading unit (34) intended to be located outside the containment enclosure, this reading unit being capable of measuring the first merged optical signal to obtain a corresponding first electrical signal, and - an electronic calculator (36) configured to: - extracting, from the first electrical signal and by exploiting the amplitude modulations of the first and second collected optical signals, a first extracted electrical signal and a second extracted electrical signal representative, respectively, of the first and second collected optical signals, then - determining quantities of the gaseous component present in the first and second samples from, respectively, the first and second extracted electrical signals.

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