Method of quantification by Raman spectrometry

Abstract

Method for quantification by Raman spectrometry. This method comprises: - the measurement (TON), in the presence of an excitation beam, of values ​​S3(λ) and S4(λ), at a wavelength λ, respectively, of optical signals S3 and S4 measured with polarization directions, respectively, parallel and perpendicular to a predetermined direction; - the measurement (TOFF), in the absence of the excitation beam, of values ​​S1(λ) and S2(λ), at a wavelength λ, respectively, of optical signals S1 and S2 measured with polarization directions, respectively, parallel and perpendicular to the predetermined direction; and - the determination (230) of a quantity of a gaseous component present inside a containment building of a nuclear reactor, from a difference [(S3(λ) / t3 – S1(λ) / t1] and a difference [S4(λ) / t4 – S2(λ) / t2], where t1, t2, t3 and t4 are the durations of time windows during which the signals S1, S2, S3 and S4 are measured. Fig. 5

Description

Title of the invention: Method for quantification by Raman spectrometry

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

[0002] For example, 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 include, within 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 event of a nuclear accident resulting, for example, in a loss of core cooling function, there is a rise in the temperature of the core components, and in particular the nuclear fuel. The rise in 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 upon contact with the steam present in the reactor vessel containing the core. The fuel assembly cladding, which is made of a zirconium alloy, is among the first elements to be subjected to these oxidation reactions. Zirconium is oxidized by steam according to the reaction Zr + 2H2O -> ZrO2 + 2H2. There is therefore a very rapid release of a significant amount of hydrogen.

[0004] In the event of a rupture of the reactor vessel, the interaction between the corium (molten core) and the concrete base of the containment building leads to the production of hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2).

[0005] Thus, during a nuclear accident, the containment building may contain flammable gases (H2 and CO) and oxygen, which can lead to the formation of an explosive atmosphere (ATEX) and the risk of loss of containment integrity. This risk is known as the "hydrogen risk" or "H2 risk".

[0006] Therefore, it is important to be able to measure the concentration of gaseous components present in the reactor building during a nuclear accident.

[0007] In particular, the presence of gaseous components such as hydrogen, oxygen and the Carbon monoxide can lead to explosive mixtures. Therefore, implementing monitoring systems to determine the nature and proportion of the main gaseous components present in the reactor building is essential. This allows for an assessment of the explosion risk and the implementation of necessary preventative measures to mitigate it.

[0008] French patent 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 one or more probes located inside the reactor building and a processing unit located outside. The processing unit is connected to the probes by fibers and electrical cables. Therefore, its implementation requires penetrations through the reactor building. This has very little impact on the reactor building's airtightness with respect to radiation and radioactive materials. In this respect, this device is very advantageous compared to other known quantification devices that 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 penetrate the reactor building to connect the inside of the reactor building to the outside.Such tubes are problematic because they compromise the reactor building's airtightness.

[0009] The following article also describes in detail a Raman spectrometry quantification device that could be used in the nuclear field: 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. This article is hereafter referred to as “Magne2020.” In particular, this article proposes a solution for eliminating background noise in the measured optical signal. Specifically, this involves using a scientific CCD (Charge-Coupled Device) imager, which remains a relatively fragile and expensive laboratory tool.

[0010] The invention aims to provide a quantification method at least as precise as the method of article Magne2020 while allowing simplified implementation.

[0011] The invention therefore relates to a method for quantifying, by Raman spectrometry, at least one gaseous component inside a containment building of a nuclear reactor, this method comprising a first measurement period during which:

[0012] - a monochromatic excitation beam excites, inside the enclosure of confinement, a sample of the gaseous medium located inside this confinement chamber,

[0013] - a reading unit measures the scattered optical signal, by Raman effect, by the sample excited by the excitation beam, and

[0014] - an electronic computer determines, from the optical signal measured by the unit reading, a quantity of the gaseous component present in the sample,

[0015] in which:

[0016] - during the first measurement period: the excitation beam is biased neatly in a predetermined direction, and the reading unit measures the values ​​S3(X) and S4(X), respectively, of an optical signal S3 and an optical signal S4 scattered by the sample, where:

[0017] - the optical signals S3 and S4 are the optical signals measured with directions of polarization, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam, when the sample is excited by the excitation beam,

[0018] - X is a wavelength of interest, that is to say a wavelength at which Due to the Raman effect, a line appears in the spectrum of the scattered optical signal when the gaseous component to be quantified is present in the sample, and

[0019] - the method also includes a second measurement period in the absence of the excitation beam during which the reading unit measures values ​​S1(X) and S2(X), respectively, of an optical signal SI and an optical signal S2 scattered by the sample, where the optical signals SI and S2 are the optical signals measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam used during the first measurement period, when the excitation beam is absent, and

[0020] - the calculator determines the quantity of the gaseous component present in the sample from the difference [(S3(X) / t3 - S1 (X) / t1 ] and the difference [S4(X) / t4 - S2(X) / t2], where t1, t2, t3 and t4 are the durations of the time windows during which the signals SI, S2, S3 and S4 are measured to obtain, respectively, the values ​​S1(X), S2(X), S3(X) and S4(X) in number of counts.

[0021] Embodiments of this process may include one or more of the following features:

[0022] 1) The calculator determines the quantity of the gaseous component present in the sample using the following relation: r(X) = [S3(X) / t3 - Sl(X) / t1] -k(X)*[S4(X) / t4 - S2(X) / t2], where:

[0023] - r(X) is a representative value of the quantity of the gaseous component present in the sample expressed in counts per second,

[0024] - k(X) is the value, for the wavelength X, of a scaling coefficient k pre determined.

[0025] 2) The ratios tl / t2 and t3 / t4 are equal.

[0026] 3) The process comprises, prior to the execution of the first and second measurement periods, a calibration phase during which:

[0027] - the monochromatic excitation beam excites a reference sample, and

[0028] - a sensor measures a Spara optical signal and a Sperp optical signal emitted by the reference sample excited by the excitation beam, the optical signals Spara and Sperp being the optical signals scattered by the reference sample measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam, and the Spara and Sperp signals 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

[0029] - the value k(X) of the coefficient k for each wavelength of interest is calculated from the Spara and Sperp optical signals measured, then recorded in the computer.

[0030] 4) During the calibration phase:

[0031] - several values ​​k(X;) of the coefficient k are calculated using the following relation: k(Xi) = [Spara(Xi) - DN] / [Sperp(X;) - DN], where:

[0032] - Spara(Xi) and Sperp(Xi) are the values, respectively, of the optical signals Spara and Sperp at wavelength Xi5 and

[0033] - DN is the self-noise of the reading unit, i.e. the optical signal measured by the reading unit when no optical signal is received by the reading unit, then

[0034] - the value k(X) is calculated by interpolation from the values ​​k(X;).

[0035] 5) The first and second measurement periods follow each other immediately and the duration of each of these first and second measurement periods is less than 10 s.

[0036] 6)

[0037] - the first and second periods and the determination of the quantity of the component gaseous present in the sample from the values ​​S1(X), S2(X), S3(X) and S4(X) measured during these first and second periods, form a cycle (Ci) of measurements, and

[0038] - the method involves repeating this measurement cycle several times during a time window of less than fifteen minutes, and

[0039] - the calculation, by the computer, of a more precise value of the quantity of the component gaseous by averaging the quantities determined during each of the measurement cycles contained within this time window.

[0040] 7) During the first and second periods, the optical signals S1, S2, S3 and S4 are measured for several different X wavelengths of interest, each of these wavelengths of interest corresponds to a particular gaseous component to be quantified in the excited sample, the measurements at these different wavelengths of interest being carried out simultaneously.

[0041] 8) The wavelengths of interest include wavelengths of interest cor- responding to water vapor, oxygen, and nitrogen.

[0042] 9) The wavelengths of interest include wavelengths of interest cor responding to carbon monoxide and carbon dioxide.

[0043] 10) A wavelength of interest corresponds to hydrogen.

[0044] 11) The excitation beam is a continuous laser beam.

[0045] 12) The process comprises:

[0046] - the measurement of the total pressure inside the enclosure,

[0047] - the calculation of partial pressures of hydrogen, carbon dioxide, of oxygen, carbon monoxide and nitrogen from quantities quantified by Raman spectrometry of these gaseous components, at least one of these quantities being determined from the difference [(S3(X) / t3 - S1(X) / t1)] and the difference [S4(X) / t4 - S2(X) / t2], and

[0048] - the calculation of the partial pressure of water vapor from the difference between the total pressure PT less the sum of the calculated partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide and nitrogen.

[0049] The invention also relates to a device for quantifying, by Raman spectrometry, at least one gaseous component inside a containment building of a nuclear reactor, this device comprising:

[0050] - a laser source capable of emitting a monochromatic excitation beam which excites, within the containment chamber, a sample of the gaseous medium located within that containment chamber,

[0051] - a reading unit capable of measuring the optical signal scattered, by Raman effect, by the sample excited by the excitation beam, and

[0052] - an electronic computer configured to determine, from the optical signal measured by the reading unit, a quantity of the gaseous component present in the sample,

[0053] in which the computer (36) is configured to automatically perform the following steps:

[0054] - during a first measurement period: the excitation beam is polarized li neatly in a predetermined direction, and the reading unit measures the values ​​S3(X) and S4(X), respectively, of an optical signal S3 and an optical signal S4 scattered by the sample, where:

[0055] - the optical signals S3 and S4 are the optical signals measured with directions of polarization, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam, when the sample is excited by the excitation beam,

[0056] - X is a wavelength of interest, that is to say a wavelength at which Due to the Raman effect, a line appears in the spectrum of the scattered optical signal. when the gaseous component to be quantified is present in the sample, and

[0057] - during a second measurement period in the absence of the excitation beam, the unit of reading measurement of the values ​​S1(X) and S2(X), respectively, of an optical signal SI and an optical signal S2 scattered by the sample, where the optical signals SI and S2 are the optical signals measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam used during the first measurement period, when the excitation beam is absent, and

[0058] - the calculator determines the quantity of the gaseous component present in the sample from the difference [(S3(X) / t3 - S1 (7.) / t 1 ] and the difference [S4(X) / t4 - S2(X) / t2], where t1, t2, t3 and t4 are the durations of the time windows during which the signals SI, S2, S3 and S4 are measured to obtain, respectively, the values ​​S1(X), S2(X), S3(X) and S4(X) in number of counts.

[0059] Embodiments of this device may include the following characteristic: the reading unit includes only one photodetector for each wavelength of interest.

[0060] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which:

[0061] - Fig. 1 is a schematic illustration of the architecture of a quantification device Analysis, by Raman spectrometry, of gaseous components inside the containment building of a nuclear reactor,

[0062] - [Fig. 2] is an illustration of a Raman spectrum of the gaseous components at quantify,

[0063] - [Fig. 3] is a schematic illustration of the architecture of a probe of the device of the [Fig.l],

[0064] - [Fig. 4] is an illustration of Raman spectra in the presence of radiation Cherenkov,

[0065] - [Fig. 5] is a flowchart of a quantification process using the device of the [Fig.l],

[0066] - [Fig. 6] is a timing diagram of different operating periods of the device of the [Fig.l].

[0067] In this description, the terminology, conventions, and definitions of the terms used in this text are introduced in Chapter I. Next, a detailed example of an embodiment is described in Chapter II with reference to the figures. In Chapter III, variations of this embodiment are presented. Finally, the advantages of the different embodiments are specified in Chapter IV.

[0068] Chapter I: Definitions, terminology and conventions:

[0069] In the figures, the same references are used to designate the same elements.

[0070] In the remainder of this description, the well-known characteristics and functions of a person skilled in the art are not described in detail.

[0071] The symbol “*” denotes scalar multiplication.

[0072] A gaseous component is typically a gaseous molecule.

[0073] The terms "quantification" and "quantify" refer to the operation of measuring the quantity of a gaseous component and, in particular, a concentration expressed in % or a partial pressure expressed in Pa.

[0074] 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 %.

[0075] In this text, a relative quantity is a proportion, for example expressed as a percentage, of the gaseous component within the gaseous medium.

[0076] An absolute quantity is typically the partial pressure of the gaseous component.

[0077] A Raman spectrum is the power spectrum of the optical signal scattered by the Raman effect.

[0078] In this text, the optical signal scattered by Raman effect is also called the “Raman scattering optical signal”.

[0079] The term “nuclear core-cooling accident” refers to any accident that leads to a partial or total meltdown of the nuclear reactor core. During such an accident, hydrogen is produced. Other gaseous components, such as carbon monoxide and carbon dioxide, may also be produced. Such an accident often originates from a total or partial loss of core cooling in the nuclear reactor.

[0080] A beam is considered "monochromatic" when the full width at half maximum of its single line, in its power spectrum, is less than 1 nm and, preferably, less than 0.5 nm.

[0081] Chapter II: Example of an embodiment

[0082] Figure 1 represents a device 2 for quantifying, by Raman spectrometry, at least one gaseous component inside a containment structure 4 of a nuclear reactor supported by a concrete base slab 7. The following description of the device 2 is given in the specific case where the containment structure 4 is a reactor building of a nuclear power plant that produces electricity. The structure of a reactor building is well known. To simplify Figure 1, only the following elements contained within the reactor building have been schematically represented:

[0083] - the core 6 of the nuclear reactor,

[0084] - the tank 8 in which the core 6 is immersed, and

[0085] - the gaseous medium 10 in which the various elements located inside are immersed of enclosure 4.

[0086] Containment 4 is sealed, as far as possible, against radiation and radioactive materials to prevent their escape into the external environment, including, if possible, in the event of a nuclear accident. Typically, containment 4 and the base slab 7 are essentially made of concrete.

[0087] 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.

[0088] In this example, device 2 is designed to quantify the following gaseous components: hydrogen (H2), water vapor (H2O), oxygen (O2), nitrogen (N2), carbon monoxide (CO), and carbon dioxide (CO2). The H2 risk is estimated based on the quantities of hydrogen, air (O2, N2), and water vapor (H2O) represented on a Shapiro-Moffette ternary diagram. Measuring the quantities of carbon monoxide and carbon dioxide allows monitoring of 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).

[0089] Device 2 comprises, fixed inside enclosure 4:

[0090] - one or more probes 20 located at different locations to measure the concentrations of gaseous components at these different locations,

[0091] - one or more pressure sensors 22, and

[0092] - one or more 24 temperature sensors.

[0093] The device 4 is subsequently described in the simplified case where the device 2 comprises a single probe 20, a single pressure sensor 22 and a single temperature sensor 24. However, everything described in this simplified case also applies to the case where there are several probes 20 and / or several pressure and / or temperature sensors 22 or 24. Typically, the temperature sensor 24 is placed in the probe 20. Conversely, a single pressure sensor 22 common to all the probes 20 may suffice.

[0094] The device 2 also includes, outside the enclosure 4, a processing unit 30 which processes the data transmitted by the probe 20 and the sensors 22 and 24 to quantify the presence of gaseous components in the medium 10.

[0095] The processing unit 30 comprises for this purpose: a laser source 32, a reading unit 34, an electronic computer 36, a human-machine interface 38, and a power supply 40.

[0096] The probe 20 is connected to the processing unit 30 via two optical fibers 42 and 44. The first fiber 42 carries an excitation beam, generated by the laser source 32, into the probe 20. For this purpose, its proximal end is connected to the laser source 32 and its distal end opens into the probe 20. The second fiber 44 carries the Raman scattering optical signal from the probe 20 to the reading unit 34. For this purpose, its proximal end is connected to the reading unit 34 and its distal end opens into the probe 20. These fibers 42 and 44 pass through the enclosure 4, each using its own sealed optical penetration assembly (OPA). Typically, fibers 42 and 44 are protected by a flexible stainless steel sheath, covered with a black PVC sheath, which is lightproof and decontaminable.

[0097] By way of example, the first fiber 42 has a core diameter of 400 pm and a numerical aperture between 0.22 and 0.26. Also by way of example, the second fiber 44 has a diameter of 600 pm and a numerical aperture between 0.22 and 0.37.

[0098] The probe 20 is also connected to the unit 30 via several electrical cables collectively designated by the numerical reference 46. Each cable 46 passes through the enclosure 4 using an electrically sealed feedthrough, more commonly known by the acronym EPA (Electrical Penetration Assembly). These cables 46 notably supply power to the probe 20 and carry control signals for the probe 20.

[0099] 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 electrically sealed conduit.

[0100] To simplify [Fig. 1], the oblique lines on each cable 46, 48 and 49 indicate that this cable is implemented, in practice, by several electrical cables. In particular, the probe 20 and the sensors 22, 24 are connected to ground via at least one electrical cable.

[0101] The laser source 32 emits an excitation beam. This beam is a monochromatic beam with a wavelength Xb. The wavelength Xi is preferably between 730 nm and 750 nm because it is in this range that the radiation-induced attenuation (RIA) of the fibers is lowest. For example, here, the wavelength Xi is equal to 750 nm.

[0102] The power of the optical signal generated by the Raman effect is notably proportional to the power of the excitation beam. Here, to improve the sensitivity and accuracy of device 2, the power of the excitation beam is greater than 500 mW and, preferably, greater than or equal to 1 W. In this example, the power of the excitation beam is chosen so that its power within the gas mixture be greater than or equal to 180 mW. To generate such an excitation beam with a small footprint, the laser source 32 is a continuous laser source with a power equal to or greater than one Watt.

[0103] The reading unit 34 allows the power of the optical signal to be measured at the different wavelengths of interest. Here, the wavelengths of interest are equal to the wavelengths at which 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 for hydrogen, carbon dioxide, oxygen, carbon monoxide, nitrogen, and water vapor are denoted, respectively, XH2, XO2, XCo, XN2, and XH2O. These wavelengths of interest are known and represented on the Raman spectrum of [Fig. 2].

[0104] The spectrum of [Fig. 2] is reconstructed from experimental Raman shift values. The line amplitudes are normalized to that of nitrogen (N2) at unity for a partial pressure of 1 atm and room temperature. The line amplitudes are proportional to the amount of each gaseous component in the medium 10.

[0105] In this embodiment, the full width at half maximum (FWHM) of each line is typically 6 nm. Under these conditions, the area, or integral, of the line is proportional to the quantity of the corresponding gaseous component.

[0106] In the specific case of hydrogen, several rotational lines S0 to S3 correspond to the presence of hydrogen. Among the four S0 to S3 lines of hydrogen, the Si line is the most intense. Moreover, in practice, the S0 line is not observed because it is contained within the rejection band of filter 96 ([Fig. 3]). Here, the wavelength Xh2 is taken to be equal to the wavelength at which the Si line of hydrogen appears. In this case, the value of the optical signal scattered by the Raman effect by hydrogen is taken to be equal to the area of ​​the Sp line

[0107] The two carbon dioxide lines overlap but can still be distinguished. The optical signal value for carbon dioxide is equal to the area of ​​these two lines.

[0108] In addition to the wavelengths of interest, a first reference wavelength Xrefi is located between the So and Si lines of hydrogen. A second reference wavelength Xref2 is located between the Si and S2 lines of hydrogen. As explained later, the Xrefi and Xref2 wavelengths allow the value of the optical signal scattered by the Raman effect by hydrogen to be extracted using the baseline subtraction (LB) method.

[0109] To obtain measurements for each of the wavelengths of interest and for the Xrefi and Xref2 lengths, unit 34 includes a circuit 51 for demultiplexing these different wavelengths and for each of the demultiplexed wavelengths, only one acquisition chain.

[0110] The proximal end of the second fiber 44 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. 1]. The demultiplexing circuit 51 is, for example, implemented as described in patent application US7385692.

[0111] The chain 50 comprises successively a bandpass filter 52, a photodetector 54, an amplification-discrimination module 56 and a counter 58.

[0112] The transfer function of the bandpass filter 52 has the form of a Gaussian centered on the wavelength X. The full width at half maximum (FWHM) of this transfer function is:

[0113] - between 10 nm and 12 nm for wavelengths XO2, XCo, XN2 and XH2O,

[0114] - between 5 nm and 6 nm for wavelengths XH2, Xrefi and Xref2, and

[0115] - between 15 nm and 18 nm for the XCo2 wavelength in order to take into account that Carbon dioxide corresponds to two overlapping lines.

[0116] The photodetector 54 generates a voltage pulse for each photon received in the optical signal filtered by the bandpass 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, cooled, for example, by the Peltier effect (thermoelectric effect).

[0117] The amplification-discrimination module 56 first amplifies the voltage pulses at the output of the photodetector 54. Then, the amplification-discrimination module 56 eliminates most of the pulses originating from the background noise. To do this, typically, the amplification-discrimination module 56 eliminates pulses whose amplitude is below a predetermined threshold.

[0118] The counter 58 is incremented by each pulse delivered at the output of the amplification-discrimination module 56. The counter 58 therefore counts the number of pulses received during an interval of predetermined duration Ata. At the end of the interval, the value of the counter 58 is reset to zero and the counter begins counting the pulses received during the next interval. For example, the duration Ata is typically on the order of 10 ms, corresponding to an acquisition rate of 100 Hz.

[0119] At the end of each interval, a measurement of the number of hits received during that interval is therefore provided. This measurement is expressed in cps (hits per second).

[0120] The computer 36 typically comprises a programmable microprocessor 60 and a memory 62 containing the data and instructions necessary for executing the process of [Fig. 5]. The computer 36 is notably capable of controlling the laser source 32, the probe 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. The computer 36 integrates all the measurements delivered during a predetermined acquisition window to obtain the value S(X) measured during this acquisition time window and expressed as a number of counts.

[0121] The human-machine interface 38 typically includes a screen 66.

[0122] Here, the power supply 40 is a backup power supply capable of powering all the components of the processing unit 30, the probe 20, and the sensors 22 and 24 even in the event of a power outage. To this end, the power supply 40 includes a battery capable of storing sufficient energy to power the processing unit 30, the probe 20, and the sensors 22 and 24 for at least one day and, preferably, for at least three consecutive days.

[0123] Figure 3 shows probe 20 in more detail. Probe 20 has 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, located in chamber 94. The distal ends of optical fibers 42 and 44 are located inside housing 80.

[0124] This housing 80 is watertight and dustproof to protect the optical components. For example, the housing 80 has an ingress protection rating of IP69. Inside the housing 80, the optical components are immersed in a neutral gas introduced into the housing via a purge valve 81. The neutral gas is different from the gaseous components to be quantified. Furthermore, the neutral gas either 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 1 atm (101.32 kPa).

[0125] 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.

[0126] Inside the housing 80, the probe 20 comprises the following components arranged one after the other along the path of the excitation beam and the optical signal from the first fiber 42 to the second fiber 44: a collimator 82, a polarizer rizer 84, a filter 86, a separating blade 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. On [Fig.3], the path of the excitation beam and the optical signal is represented by oriented arrows.

[0127] Here, inside the housing 80, the excitation beam and the optical signal move parallel to a predetermined PI plane fixed relative to the housing. For example, the PI plane is parallel to a base on which the various components of the probe 20 are fixed.

[0128] 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 first fiber 42. For this purpose, for example, the collimator 82 is a parabolic mirror.

[0129] The polarizer 84 eliminates the polarization component perpendicular to the PI plane, retaining only the polarization component parallel to this PI plane. Thus, at the output of the polarizer 84, the polarization of the excitation beam is linear and parallel to the PI plane. Preferably, the polarizer 84 is a polarization cube or PBS (Pola-rization BeamSplitter cube) which exhibits both good laser beam stability and low reported fluorescence.

[0130] The filter 86 eliminates or reduces the fluorescence generated by the polarizer 84 and the first fiber 42, as well as the components of the polarized beam longer than the wavelength Xp. More precisely, the filter 86 eliminates or significantly reduces all components of the polarized beam that could interfere with the scattered optical signal by the Raman effect. To this end, the filter 86 allows the polarized excitation beam to pass through while eliminating wavelengths longer than the wavelength Xi of the excitation beam. For this purpose, the filter 86 is a low-pass or band-pass filter whose cutoff wavelength at -70 dB is preferably between Xi + 15 nm and Xi + 25 nm at normal incidence. For example, the filter 86 is a Short Wave Pass filter (SWP) mounted on a swiveling mount that allows the angle of incidence of the laser beam relative to the normal to the surface of the filter 86 to be adjusted.This angle of incidence is adjusted to achieve the desired rejection performance on the Raman spectrum. For example, filter 86 is a bandpass filter centered at 766 nm. Its cutoff wavelength at -70 dB is 787 nm at normal incidence. It is oriented so that the angle of incidence is approximately 22°, which allows for a rejection of -70 dB at 773 nm. Thus, filter 86 allows the laser beam at 750 nm to pass through while ensuring rejection as close as possible to observe the rotational SI line of hydrogen.

[0131] The beam splitter 88 folds the excitation beam onto the parabolic mirror 90. For the optical signal reflected by the mirror 90 and passing through the beam splitter 88, the beam splitter 88 also acts as a high-pass filter which eliminates or It reduces the components of the optical signal passing through it whose wavelengths are equal to or less than the wavelength Xb. To achieve this, typically, the plate 88 has a cutoff wavelength at -70 dB, preferably between Xi + 5 nm and Xi + 22 nm. For this purpose, the plate 88 is also mounted on a swiveling mount that allows adjustment of 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. For example, the -70 dB cutoff wavelength of the plate 88 is 776 nm at normal incidence. The plate is oriented so that the angle of incidence is approximately 20°, which allows for a rejection of -70 dB at 758 nm.

[0132] The parabolic mirror 90 focuses the polarized beam at a point R located inside the analysis chamber 94.

[0133] Chamber 94 contains the sample of medium 10 to be analyzed. Chamber 94 isolates the sample from the light that may be present inside the enclosure 4. In addition, chamber 94 is also designed to protect the sample from possible water splashes and contamination by aerosols.

[0134] Here, chamber 94 is traversed by a gas flow from medium 10 so that the sample of medium 10 is constantly renewed. This gas flow from medium 10 occurs, for example, by natural convection. For this purpose, chamber 94 has vents for the inlet and outlet of medium 10. The internal volume of chamber 94 is, for example, 500 cm³.

[0135] The chamber 94 is fluidically isolated from the interior of the housing 80. To this end, the housing 80 includes the window 92, which is transparent to the excitation beam and to the optical signal scattered, by the Raman effect, by the gaseous components to be quantified. Here, the window 92 is configured to transmit the entire polarized excitation beam without reflecting any part of it. For this purpose, the window is a Brewster window, that is, a window inclined at the Brewster angle with respect to the optical axis of the incident excitation beam so as not to reflect the incident beam.

[0136] At least the inner wall of chamber 94, located opposite window 92 and on the other side of point R, is covered with a textured material that traps light and minimizes the reflection and scattering of the excitation beam on this inner wall. Preferably, this inner wall of chamber 94 is positioned far enough away to limit the scattered spectral background. For example, the distance between window 92 and this inner wall of chamber 94 is greater than or equal to 5 cm.

[0137] 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 32 of approximately 1 Watt.

[0138] Here, the temperature sensor 24 is placed inside chamber 94 as close as possible from point R. In addition, preferably, chamber 94 also includes an anti-condensation module 95 which prevents water vapor from condensing on window 92. This anti-condensation module 95 is supplied via cables 46. However, to simplify [Fig.2], the connection of this anti-condensation module 95 to cables 46 is not shown.

[0139] The optical signal scattered, by Raman effect, by the interaction, at point R, of the excitation beam with the gaseous components present, is returned inside the housing 80 and collected by the mirror 90. The mirror 90 then returns the optical signal to the separating blade 88 which transmits it to the filter 96.

[0140] Filter 96 is a high-pass or LWP (Long-Wave Pass) filter, which also has a cutoff wavelength of -70 dB, preferably between Xi + 5 nm and Xi + 22 nm. To this end, filter 96 is also mounted on a swiveling mount that allows adjustment of the angle of incidence of the incident optical signal relative to the normal to the surface of filter 96. This angle of incidence is adjusted to obtain the desired rejection performance on the Raman spectrum. For example, the -70 dB cutoff wavelength of filter 96 is 776 nm at normal incidence. Filter 96 is then oriented so that the angle of incidence is approximately 20°, which allows for a rejection of -70 dB at 758 nm.

[0141] 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.

[0142] The electromagnetic rotator 100 rotates the polarizer 98 by 90° in response to a control signal received via cables 46. For example, the rotator 100 has a shaft on which a set of gears 97 is mounted. This set of gears 97 includes, for example, a first gear that drives a second gear on which the polarizer 98 is mounted. The rotator 100 is powered via cables 46. When the 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 is switched off, the rotator 100 returns to its initial position. Here, in the absence of power, 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 at its 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. Therefore, 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 power the rotator 100 and, alternately, the... cutting off its power supply is located in processing unit 30 and has not been shown to simplify [Fig.1].

[0143] To rotate its shaft, the rotator 100 includes an electromagnetic actuator comprising coils and magnets. To ensure its continued operation even in the event of a nuclear accident, the electrical wires of the coils are typically coated with silicone. Similarly, the permanent magnets are made of magnetic materials with a Curie temperature exceeding 300°C or 450°C. For this purpose, for example, Sm-Co (samarium-cobalt) or Al-Ni-Co (aluminum-nickel-cobalt) magnets are recommended.

[0144] The parabolic mirror 102 focuses the optical signal that has passed through the polarizer 98 onto the distal end of the fiber 44. The optical signal scattered by the Raman effect is therefore guided by the fiber 44 to the reading unit 34.

[0145] Figure 4 shows four Raman spectra 120, 122, 124, and 126 of air, measured using a device almost identical to device 2, in which the reading unit 34 is replaced by a spectrometer equipped with a CCD camera that allows the amplitude, in counts per second (cps), of the collected optical signal to be measured for a very wide range of wavelengths between 750 nm and 1050 nm. In Figure 4, a solid line represents the Raman spectrum of an optical signal measured with parallel polarization. A dashed line represents the Raman spectrum of an optical signal measured with perpendicular polarization. Spectra 120 and 122 were recorded by exposing a 10 m length of fiber 44 to photon radiation with an energy of 1.25 MeV and a dose rate of 250 Gy / h. The two spectra 124 and 126 were recorded under the same conditions except that the dose rate was equal to 1016 Gy / h.

[0146] On this [Fig.4], the lines, produced by Raman effect, corresponding to oxygen and nitrogen are identified by the symbols, respectively, “O2” and “N2”.

[0147] First, it can be observed that the "O2" and "N2" lines exist only in optical signals measured with parallel polarization. This arises from the fact that 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 of 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 not true for the Si line of hydrogen. In the case of hydrogen, the Si line exists in the Raman spectra of optical signals measured with both parallel and perpendicular polarization.However, the amplitude of the Si line in the Raman spectrum of the . The optical signal measured with parallel polarization is approximately 25% greater 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 hydrogen Si line is approximately 75%.

[0148] 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 180 keV. Cherenkov radiation can increase substantially in the event of a nuclear accident. As illustrated by spectrum 120, for a fiber length of 10 meters exposed to a dose rate of 250 Gy / h, the amplitude of Cherenkov radiation exceeds the amplitude of the "O2" line by a factor of more than 50 and the amplitude of the "N2" line by a factor of more than 20. In the case of spectrum 124, the amplitude of Cherenkov radiation exceeds the amplitude of the "O2" line by a factor of more than 180 and the amplitude of the "N2" line by a factor of more than 60.This shows that during the operation of device 4, the Raman scattering optical signal is drowned out by a masking signal corresponding, to a significant extent, to Cherenkov radiation which appears mainly in silica and therefore in fiber 44 as well as, to a lesser extent, in the optical components of probe 20.

[0149] Another part of this masking signal originates from:

[0150] - the electronic noise of the acquisition chain 50 known by the English term "dark noise", and

[0151] - a fluorescence signal from optical components.

[0152] The fluorescence signal of the optical components is typically caused by the optical components of the device 2 when they are illuminated by the excitation beam.

[0153] The operation of device 4 will now be described with reference to the process in [Fig. 5]. In this embodiment, the amount of hydrogen present in the sample is determined using the known baseline subtraction method, or SLB method. Thus, the amount of hydrogen is determined from the values ​​S3(XH2), S3(Xrefi), and S3(Xref2) of a signal S3. The signal S3 is the optical signal measured with parallel polarization while the laser source 32 is switched on. More precisely, the SLB method consists of defining a spectral function f representing the spectral background against which the Raman peaks appear. This function can be linear or polynomial, for example, of order two. Here, for illustration purposes, this function f is defined by one of the following relations: f(X) = a + b*(^ - kcte)2 and f(X) = a + b*(^ - kcte ), 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 S3(Xrefi) and 83()½^) measurements carried out outside the . Each Raman line is obtained by solving the following system of equations: f(Xrefi) = S3(Xrefi) and f(Xref2) = S3(Xref2). The useful signal r(XH2) is then deduced by subtracting the spectral function, that is, using the following relation: r(XH2) = [S3(XH2) - f(XH2)] / t3, where t3 is the acquisition time of the signal S3.

[0154] Subsequently, only the quantification of the other gaseous components is described in detail.

[0155] To extract the Raman scattering optical signal from the masking signal, here, the cal Culator 36 determines the quantity of a gaseous component corresponding to the wavelength of interest X using the following relation (1): r(X) = [S3(X) / t3 - Sl(X) / tl] -k(X)*[S4(X) / t4 - S2(X) / t2], where:

[0156] - r(X) is a representative value of the quantity of the gaseous component, which corresponds to the Raman line centered on the X wavelength, present in the sample inside chamber 94, expressed in counts per second,

[0157] - S1(X) and S2(X) are the values, for wavelength X, respectively, of Optical signals S1 and S2 measured when the laser source 32 is switched off,

[0158] - S3(X) and S4(X) are the values, for wavelength X, respectively, of Optical signals S3 and S4 measured when the laser source 32 is switched on,

[0159] - k(X) is the value, for the wavelength X, of a scaling coefficient k pre determined, and

[0160] - t1, t2, t3 and t4 are the durations of the time windows during which the signals SI, S2, S3 and S4 are measured.

[0161] The values ​​S1(X), S2(X), S3(X) and S4(X) are expressed as a number of strokes.

[0162] The SI and S3 signals are measured with parallel polarization for the durations, respectively, t1 and t3. The signals S2 and S4 are measured with perpendicular polarization during the durations, respectively, t2 and t4. The ratios Sl(X) / t1, S2(X) / t2, S3(X) / t3 and S4(X) / t4 are therefore measurements, in counts per second, of the optical signal scattered by the Raman effect at the wavelength X.

[0163] Since the SI and S2 signals are measured while the laser source 32 is switched off, these signals represent measurements of the masking signal, respectively, with parallel polarization and with perpendicular polarization. Under these conditions, the first difference S3(X) / t3 - S1(X) / t1 provides an optical signal corrected for Cherenkov radiation. However, this first difference is not corrected for the fluorescence signal from the optical components. This fluorescence signal is proportional to the laser emission but essentially depolarized. Indeed, this fluorescence signal is absent from the SI signal because the SI signal is measured when the laser source 32 is switched off. Here, this fluorescence signal is estimated from the second difference S4(X) / t4 - S2(X) / t2. More precisely, this second difference estimates the amplitude of the fluorescence signal when the optical signals are measured with perpendicular polarization.In this embodiment, the fluorescence signal. present in the S3 signal measured with parallel polarization is assumed to be proportional to the fluorescence signal present in the S4 signal. Thus the fluorescence signal present in the S3 signal is estimated by the term k(X)*[S4(X) / t4 - S2(X) / t2] of relation (1).

[0164] The value of the coefficient k for all wavelengths of interest must first be determined before relation (1) can be used. Thus, the method begins with a calibration phase 200. Here, phase 200 is performed while the probe 20 is fixed inside the enclosure 4. In this case, preferably, phase 200 is performed 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 performed during a ten-year shutdown of the nuclear reactor.

[0165] During phase 200, a reference sample, whose composition is known, is located inside chamber 94. Here, the reference sample is air.

[0166] Finally, during phase 200, the processing unit 30 is replaced by a processing unit that allows the amplitude of the optical signal to be measured at both the wavelengths of interest and other wavelengths. For example, for this purpose the reading unit 34 is replaced by a spectrometer identical to that used to measure the Raman spectra of [Fig. 4].

[0167] Here, the variation of the coefficient k as a function of 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 that approximates the evolution of the value of k(X) as a function of wavelength X are obtained from measurements made for wavelengths X located outside the oxygen and nitrogen lines and therefore far from the X02 and XN2 wavelengths. The subscript i is a wavelength identifier.

[0168] Therefore, during step 202, for each wavelength X; :

[0169] - a Spara(X;) value of a Spara optical signal is measured with a polarization parallel, and

[0170] - a Sperp(X;) value of a Sperp optical signal is measured with a polarization perpendicular.

[0171] The Spara and Sperp signals are measured while the laser source 32 is switched on and therefore when the sample inside the chamber 94 is excited by the excitation beam.

[0172] Furthermore, in this embodiment, during a step 204, the electronic noise of each acquisition channel 50 of the reading unit 34 is measured. Here, this electronic noise is assumed to be identical for each acquisition channel 50. Moreover, it is assumed that this electronic noise does not vary with the X wavelength within the range of interest. Finally, it is also assumed that this electronic noise is independent of the polarization of the measured optical signal. For example, the amplitude DN of this electronic noise is measured by blocking the distal end of the fiber 44 and then averaging the amplitudes measured by each acquisition chain 50.

[0173] During a step 206, for each wavelength Xi5 a value k(X;) is calculated using the following relation: k(X;) = [Spara(X;) - DN] / [Sperp(X;) - DN].

[0174] Then, in step 208, the values ​​Id / cmk k(XO2), k(XCo), k(XN2), and k(XH20) are calculated by interpolation from the values ​​k(X). For this purpose, the function that associates each wavelength X with the corresponding value k(X) of the coefficient k is obtained by mathematical fitting. For example, here, the interpolation used is linear interpolation. For this purpose, the coefficients a and b of the line that minimizes the deviations from the different values ​​k(X) are calculated. Then, using the equation of this line, the values ​​IdXcmk k(XO2), k(XCo), k(XN2), and k(XH20) are calculated.

[0175] During a step 210, the values ​​IdXcmk k(XO2), k(XCo), k(XN2) and k(XH20) are recorded in memory 62 of the calculator 36.

[0176] The calibration phase 200 is then completed and a phase 220 operation of device 2 begins. Phase 220 is typically carried out during a nuclear accident. However, it can also be carried out while the nuclear reactor is operating normally, i.e., in an operational situation.

[0177] Phase 220 consists of a cycle of measurements repeated throughout the duration of phase 220. In [Fig.6], the different measurement cycles are identified by the symbol Q, where the index j is the sequence number of the cycle from the beginning of phase 220. To simplify [Fig.6], only cycles Ci and C2 are fully represented.

[0178] Each cycle Q comprises a period T0FF and a period T0N which, preferably, are immediately consecutive. During the period T0FF, the computer 36 commands the laser source 32 to be switched off for the entire duration A0FF of this period T0FF.

[0179] The period T0FF comprises two time windows designated in Figure 6, respectively, by the symbols C / / and C ±. Preferably, these two windows C / / and C ± are immediately consecutive. Here, the sum of the durations t1 and t2 of the windows, respectively C / / and C ±, is equal to the duration A0FF.

[0180] Throughout the duration tl of the window C / / , the computer 36 maintains the passing axis of the polarizer 98 parallel to the PI plane. For this purpose, the computer 36 does not supply the rotator 100. At the same time, the computer acquires the values ​​S l(XC02h S 1(XO2), Sl(Xco), S1(XN2) and Sl(XH2O).

[0181] Throughout the duration t2 of the window C ± I, the calculator 36 maintains the passing axis of the polarizer 98 perpendicular to the plane PI. To do this, the calculator 36 supplies the rotator 100 via the cables 46. At the same time, the calculator 36 acquires the values ​​S2(XCo2), S2(XO2), S2(XCo), S2(XN2) and S2(XH2o)-

[0182] The period T0N comprises two time windows designated in Figure 6, respectively, by the symbols R / / and R -L. Preferably, these two windows R / / and R -L are immediately consecutive. Here, the sum of the durations t3 and t4 of the windows, respectively R / / and R -L, is equal to the duration A0N of the period T0N.

[0183] Preferably, the ratio t3 / t4 is equal to the ratio t1 / t2. Furthermore, to simplify relation (1), here the durations t3 and t4 are chosen to also verify the following condition: t1 + t2 = t3 + t4, that is, that the durations A0FF and A0N are equal. For this reason, here, all the durations t1, t2, t3, and t4 are equal. Under these conditions, relation (1) is written in the following simplified form: R(X) = S3(X) - S1(X) - k(X)*(S4(X) - S2(X)), where R(X) is the amplitude of the optical signal scattered by the Raman effect at wavelength X, expressed as a number of counts.

[0184] Advantageously, the A0FF and A0N durations are less than 10 s or 5 s. Thus, over the duration of a cycle, even in the event of a nuclear accident, the radio-induced attenuation does not substantially alter the attenuation of the optical signal in the fibers and optical components. Moreover, to obtain good accuracy, the A0FF and A0N durations are chosen to be greater than 0.01 s and, generally, greater than 1 s.

[0185] During the entire duration t3 of the R / / window, the computer 36 maintains the passing axis of the polarizer 98 parallel to the PI plane. For this purpose, the computer 36 does not supply power to the rotator 100. At the same time, the computer 36 acquires the values ​​S3( / <02h S3(XO2), S3(Xco), S3(XN2) and S3(Xh2O).

[0186] Throughout the duration t4 of the R-L window, the computer 36 maintains the passing axis of the polarizer 98 perpendicular to the PI plane. To do this, the computer 36 supplies the rotator 100 via the cables 46. At the same time, the computer 36 acquires the values ​​S4(XCO2), S4(XO2), S4(XC0), S4(XN2) and S4(XH2O).

[0187] Next, in a step 230, the calculator 36 determines the quantity of each gaseous component. To do this, the calculator 36 calculates, in an operation 232, using relation (1) and for each wavelength λ<02- An- λ<0- XN2 and XH2O, the values ​​r(XCO2), r(XO2), r(XCO2), r(XN2), and r(XH2O). The values ​​r(XO2), r(XCO2), r(XN2), and r(XH2O) are expressed in counts per second (cps). These values ​​ri / <02)- r(XO2), r(XCo), r(X N2) and r(XH2O) are proportional to the quantities, respectively, of carbon dioxide, oxygen, carbon monoxide, nitrogen and water vapor present in the sample.

[0188] Then, in an operation 234, from these values ​​r(XCO2), r(XO2), r(XCo), r(XN2) and r(XH2O) and the value r(XH2) obtained, the calculator 36 establishes the proportions, in percent, of each of these gaseous components in the medium 10, taking into account, for example, the Raman interaction sections of each of the gaseous components. The Raman interaction section is defined in the article Magne2020 and corresponds to the term called "Raman differential cross section" in that article. Here, the sum of the The partial pressures of all the gaseous components to be quantified (O2, N2, H2O, H2, CO, and CO2) are close to the total pressure PT in containment chamber 4. The temperature of each probe is not relevant since only a relative reading is required.

[0189] The proportion, in percent, of the component] is then obtained, for example, using the following self-normalization relation:

[0190] [Math.l]

[0191] where:

[0192] - P, / PT is the proportion, in chamber 94, of the component corresponding to the line Raman at wavelength X,

[0193] - P, is the partial pressure of the component corresponding to the Raman line at the wavelength X,

[0194] - PT is the total pressure inside enclosure 4 measured by the sensor pressure 22,

[0195] - Ox is a constant, for example determined experimentally, defined by the The following relationship: r(X)*T = o^ * P^, where T is the temperature measured in probe 20,

[0196] - Ne is the total number of quantified components, i.e. six in this example,

[0197] - r(Xj) is the measure of the quantity of the j-th component to be quantified, carried out using of probe 20, and

[0198] - o^j is a constant, for example determined experimentally, defined by the following relation: r(Xj)*T = o^ * Py, where P^ is the partial pressure of the j-th component corresponding to the Raman line at wavelength Xj.-,

[0199] The relation r(X)*T = o^ * P, derives from relation (5) of the article Magne2020. The constant o^ is a function of the Raman interaction section of the component corresponding to the Raman line at wavelength X.

[0200] Furthermore, as demonstrated in particular by equation (5) in article Magne2020, when these values ​​r(XCO2), r(XO2), r(XCo), r(XN2) and r(XH2O) are multiplied by the temperature, each of these products is proportional to the partial pressure of the corresponding gaseous component. Thus, if the temperature T and the constant 0^ are known, the partial pressure P can be calculated using the relation Px=r(X)*T / 0v. Alternatively, in an embodiment such as the one described here where the sum of the partial pressures of the quantified gaseous components is close to or equal to the total pressure PT, then if in addition the total pressure inside the enclosure 4 is measured, the calculator 36 can then calculate the partial pressure of each of the gaseous components in mul dividing the ratio Pp / Pp by the total pressure PT measured by sensor 22. Preferably, during operation 236, the computer 36 acquires the temperature measured by sensor 24 and the total pressure PT measured by sensor 22, then calculates the partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide, and nitrogen from the values ​​r(XH2), r(XCO2), r(XO2), r(XCO2), and r(XN2). Next, the partial pressure P(XH2) of water vapor is taken to be equal to the difference between the total pressure PT and the sum of the partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide, and nitrogen. In this case, the acquisition chain 50 used to process the optical signal at wavelength XH2 can be omitted.

[0201] Thus, at the end of each cycle Q, a new quantification of the gaseous components is available. For example, during a step 238, the computer 36 commands the human-machine interface 38 to display these quantifications on the screen 66.

[0202] Furthermore, in a step 250, the calculator 36 calculates a more precise value for the quantity of each gaseous component by averaging the quantities determined during several successive cycles Cj. Typically, for this purpose, it uses only the quantities determined during the cycles contained within a sliding time window. The duration of this sliding time window is preferably less than 10 min and generally greater than 1 min or 5 min. The more precise quantities are also displayed on the screen 66.

[0203] Chapter III: Variants:

[0204] Probe variants:

[0205] Other solutions are possible for focusing the laser beam on point R. For example, instead of using the parabolic mirror 90, it is possible to use an achromatic doublet of converging lenses arranged so that the different wavelengths are focused on the same point R.

[0206] Alternatively, filter 96 is omitted. In this case, the filtering function is performed solely by blade 88.

[0207] Other embodiments of the polarizer 84 or 98 are possible. For example, the polarizer 84 or 98 is a glass (sodium-silicate) polarizer doped with ellipsoidal nanoparticles exhibiting a strong polarizing effect.

[0208] 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 simultaneously generates signals S1 and S2, and then simultaneously signals S3 and S4. In this case, fiber 44 is replaced by a first optical fiber and a second optical fiber. The first and second fibers guide the measured signals, with parallel and perpendicular polarizations respectively, to the readout unit. The readout unit 34 is then modified to be able to measure, simultaneously, the signals SI and S2 and the signals S3 and S4.

[0209] In a simplified embodiment, the textured material is omitted.

[0210] Variants of the processing unit:

[0211] In another embodiment, the source 32 is optically connected to the probe 20 via an optical switch that directs the excitation beam to the probe 20 and, alternately, to another probe. In this case, the source 32 continuously emits the excitation beam and, during the period T0N, the switch directs the excitation beam to the probe 20. During the period T0FF of the probe 20, the switch directs the excitation beam to the other probe and no longer to the probe 20.

[0212] Alternatively, a CCD (Charge Coupled Device) sensor is used instead of the readout unit 34. Typically, such a CCD sensor is capable of measuring the optical signal at more than 300, 1000, or 2048 different wavelengths evenly distributed within the range of interest. Such a CCD sensor therefore measures both the optical signal received at each X wavelength of interest and also at other wavelengths of no interest.

[0213] The photomultiplier 54 can be replaced by a photodiode such as an avalanche photodiode or a SiPM detector (“Silicon-PhotoMultiplier”).

[0214] Depending on the context of use, the processing unit can be configured to measure the quantity of one or more additional gaseous components other than those in 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 can also be configured to measure the quantity of only one or only a part of the gaseous components in the group consisting of water vapor, oxygen, nitrogen, carbon monoxide, carbon dioxide, and hydrogen. In this case, typically, the number of acquisition chains is reduced.

[0215] Variants of the quantification method:

[0216] Other approximations of the evolution of the value of the coefficient k as a function of the wavelength X are possible. For example, alternatively, the evolution of the value of the coefficient k as a function of the wavelength X is approximated using a polynomial of order higher than one.

[0217] In another embodiment, the value of the coefficient k also varies according to 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 intensity of the Cherenkov radiation measured in the absence of the excitation beam.

[0218] In a simplified variant, the electronic noise of the acquisition chain is neglected. In this case, each value k(X;) is simply taken to be equal to the ratio Spara(X; ) / Sperp(Xi).

[0219] In a very simplified variant, the value of the coefficient k is assumed to be constant regardless of the wavelength X.

[0220] In a degraded embodiment, the calibration phase 200 is executed while the nuclear reactor is operating. In this case, the calibration phase is triggered during nominal operation of the nuclear reactor and the reference sample is identical to the gaseous medium sample 10.

[0221] In another variant, the calibration phase of the coefficient k is carried out during the manufacture of the device 4, i.e. at a time when the probe 20 is not installed inside the enclosure.

[0222] In another embodiment, the wavelength of the excitation beam is reduced so that the lowest vibrational line of hydrogen is also measurable using the reading unit 34. This lowest vibrational line is present in the Raman spectrum of signal S3 and absent from the Raman spectrum of signal S4. In this case, one of the wavelengths of interest used is the wavelength of this hydrogen vibrational line, and the amount of hydrogen is then measured using relation (1). In another variant, although using relation (1) results in using only approximately 25% of the S3(XH2) signal, the amount of hydrogen is still quantified using relation (1). In these last two cases, the reading unit 34 does not need to perform measurements at wavelengths Xrefl and ^ef2.

[0223] Other relationships besides relation (1) are possible. For example, alternatively, an additional correction term is added to relation (1). Typically, this additional correction term is constructed so as to eliminate or reduce a noise source other than Cherenkov radiation. For example, this additional term is a term that depends on the amount of ambient light present in chamber 94 if this light is not completely eliminated by the walls of chamber 94.

[0224] Alternatively, the ratios tl / t2 and t3 / t4 are different from one. The ratios tl / t2 and t3 / t4 are also not necessarily equal.

[0225] The ratio A0FF / A0N is not necessarily equal to one either. For example, the duration Aoff is greater than the duration A0N or vice versa.

[0226] What has been described so far also works if the durations A0FF and A0N are greater than 10 s or 1 min. However, preferably, particularly in the presence of a nuclear accident, these durations A0FF and A0N are less than 5 min.

[0227] Calculating a more precise value for the quantity of the gaseous component by averaging quantities determined after several measurement cycles, can to be omitted.

[0228] Alternatively, during operation 236, the partial pressure of water vapor is calculated from the value r(XH20).

[0229] In another embodiment, the ratio P(XH2o) / PsatH2O is also determined, where P(X h2o) is the partial pressure of water vapor determined during operation 236 and Psat H2O is the saturation pressure of water vapor determined from the temperature measured by the temperature sensor 24. To determine the saturation pressure PsatH2O, a nomogram associating several temperatures with the corresponding saturation vapor pressure PsatH2O is, for example, pre-recorded in memory 62.

[0230] The SI and S2 signals are representative of the amplitude of the Cherenkov radiation. The Cherenkov radiation is representative of the average dose rate over the fiber segment 44. Thus, the SI and S2 signals can also be used to estimate this average dose rate and therefore estimate the average radiation dose at different locations inside the containment structure.

[0231] The optical signal acquisition frequency can be greater than 100 Hz.

[0232] Alternatively, only a relative quantity or only an absolute quantity of the gaseous component is measured.

[0233] Other variants:

[0234] The continuous laser source can be replaced by a pulsed laser source.

[0235] If only a measurement of the relative quantity of the gaseous components is required, then the temperature sensor 24 and the pressure sensor 22 can be omitted. In this latter case, the gaseous component taken as the reference gaseous component is often nitrogen.

[0236] In practice, the gaseous environment contained within the containment building of a nuclear reactor does not always have a homogeneous composition. Therefore, it is often necessary to quantify the gaseous components at several different locations within the building 4. For this purpose, a probe 20 is installed at each of these locations. In this case, the processing unit 30 is connected to all of these probes 20 in order to quantify the gaseous components present at each of these locations.

[0237] The teaching given here applies to any containment structure within which a nuclear reactor is housed and not only to the case where the containment is that formed by a reactor building of a nuclear power plant which produces electricity.

[0238] Several of the variants described above can be combined in the same embodiment.

[0239] Chapter IV: Advantages of the embodiments described:

[0240] Determining the quantity of a gaseous component present inside enclosure 4 from the difference S3(X) / t3-S1(X) / t1 makes it possible to reduce the noise caused by Cherenkov radiation. Furthermore, determining the quantity of the additional gaseous component from the difference S4(X) / t4-S2(X) / t2 reduces the fluorescence signal caused by the optical components of the quantization device when illuminated by the excitation beam. Thus, thanks to the use of these two differences, the accuracy of the quantization device is equal to or better than that of the device described in the Magne2020 article. Finally, to achieve this accuracy, device 4 uses optical signal measurements performed for a more limited number of wavelengths. In particular, for each gaseous component to be quantified, it is not necessary to measure the optical signal at the wavelength of interest and also at at least two reference wavelengths. Consequently, the readout unit can be considerably simplified and its cost significantly reduced.

[0241] Choosing equal ratios t1 / t2 and t3 / t4 increases accuracy.

[0242] Adjusting the value of the coefficient k according to the wavelength X of interest allows for improving the accuracy of the measurement process.

[0243] Constructing the k(X) values ​​of the coefficient k using the relation k(X) = [SPara(X)-DN] / [SPerp(X)-DN] allows us to obtain values ​​that are practically independent of the dose of radioactive radiation received by the probe. Thus, the operation of the quantification device remains accurate even in the event of a nuclear accident.

[0244] Limiting the durations AOff and A0N to less than 10 s limits the variation, during each of the periods T0Ff and T0N, of the radio-induced attenuation in the optical components and fibers. Thus, the quantization device remains accurate even in the event of a nuclear accident.

[0245] Calculating a measurement of the quantity of the gaseous component by averaging the quantities determined during several closely spaced measurement cycles makes it possible to limit the influence of radio-induced drift, which occurs, in particular, in the event of a nuclear accident. Indeed, in the event of a nuclear accident, the ambient temperature and the radio-induced attenuation (RIA) of the fibers increase rapidly.

[0246] Measuring the SI, S2, S3 and S4 signals at different wavelengths of interest allows the quantity of several different gaseous components to be measured simultaneously.

[0247] Simultaneously measuring the quantities of water vapor, oxygen and nitrogen makes it possible to assess the risk of an explosion occurring inside the enclosure.

[0248] 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.

[0249] Measuring the quantity of hydrogen using relation (1) allows this measurement to be carried out using only the two values ​​S3(XH2) and S4(XH2).

[0250] Using a continuous laser beam allows, for the same size, a laser beam with a much higher average power than if a pulsed laser beam were used. The higher the average power of the laser beam, the greater the accuracy of the measurement of the quantity of the gaseous component.

[0251] Calculating the partial pressure of water vapor from the difference between the total pressure PT and the partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide and nitrogen improves the accuracy of the measurement of the partial pressure of water vapor.

[0252] Using only one photodetector per wavelength of interest simplifies the quantification device.

Claims

Demands

1. A method for quantifying, by Raman spectrometry, at least one gaseous component inside a containment building of a nuclear reactor, this method comprising a first measurement period (TOn) during which: - a monochromatic excitation beam excites, inside the containment chamber, a sample of the gaseous medium located inside this containment chamber, - a reading unit measures the optical signal scattered, by the Raman effect, by the sample excited by the excitation beam, and - an electronic computer determines, from the optical signal measured by the reading unit, a quantity of the gaseous component present in the sample, characterized in that: - during the first measurement period (TON): - the excitation beam is linearly polarized in a predetermined direction, and - the reading unit measures (R / / , R -L) the values ​​S3(X) and S4(X), respectively, of an optical signal S3 and an optical signal S4 scattered by the sample, where: - Optical signals S3 and S4 are the optical signals measured with polarization directions parallel and perpendicular, respectively, to the predetermined polarization direction of the excitation beam, when the sample is excited by the excitation beam; - X is a wavelength of interest, i.e., a wavelength at which, due to the Raman effect, a line appears in the spectrum of the scattered optical signal when the gaseous component to be quantified is present in the sample; and - the method also includes a second measurement period (TOff) in the absence of the excitation beam during which the reading unit measures the values ​​S1(X) and S2(X), respectively, of an optical signal SI and an optical signal S2 scattered by the sample, where the optical signals SI and S2 are the optical signals measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam used during the first measurement period, when the excitation beam is absent, and - the calculator determines (230) the quantity of the gaseous component present in the sample from the difference [(S3(X) / t3 - S1 (X) / t1 ] and the difference [S4(X) / t4 - S2(X) / t2], where t1, t2, t3 and t4 are the durations of the time windows during which the signals SI, S2, S3 and S4 are measured to obtain, respectively, the values ​​S1(X), S2(X), S3(X) and S4(X) in number of shots.

2. A method according to claim 1, wherein the calculator determines (230) the quantity of the gaseous component present in the sample using the following relation: r(X) = [S3(X) / t3 - Sl(X) / tl] -k(X)*[S4(X) / t4 - S2(X) / t2], where: - r(X) is a representative value of the quantity of the gaseous component present in the sample expressed in counts per second, - k(X) is the value, for the wavelength X, of a predetermined scaling coefficient k.

3. Method according to claim 2, wherein the ratios t1 / t2 and t3 / t4 are equal.

4. A method according to claim 2 or 3, wherein the method comprises, prior to the execution of the first and second measurement periods, a calibration phase (200) during which: - the monochromatic excitation beam excites a reference sample, and - a sensor measures (202) a Spara optical signal and a Sperp optical signal scattered by the reference sample excited by the excitation beam, the Spara and Sperp optical signals being the optical signals scattered by the reference sample measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam, and the Spara and Sperp signals being measured at X wavelengths;different 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 optical signals Spara and Sperp, then recorded in the computer.;

5. A method according to claim 4, wherein during the calibration phase: - several values ​​k(X;) of the coefficient k are calculated (206) using the following relation: k(X;) = [Spara(Xi) - DN] / [Sperp(X;) - DN], where: - Spara(X;) and Sperp(X;) are the values, respectively, of the optical signals Spara and Sperp at the wavelength Xi5 and - DN is the self-noise of the reading unit, i.e. the optical signal measured by the reading unit when no optical signal is received by the reading unit, then - the value k(X) is calculated (208) by interpolation from the W values.

6. A method according to any one of the preceding claims, wherein the first and second measurement periods (TON, T0FF) follow each other immediately and the duration of each of these first and second measurement periods is less than 10 s.

7. A method according to claim 6, wherein: - the first and second periods and the determination of the quantity of the gaseous component present in the sample from the values ​​S1(X), S2(X), S3(X) and S4(X) measured during these first and second periods, form a cycle (Ci) of measurements, and - the method comprises repeating this cycle of measurements several times during a time window of less than fifteen minutes, and - the calculation (250), by the computer, of a more precise value of the quantity of the gaseous component by averaging the quantities determined during each of the measurement cycles contained within this time window.

8. A method according to any one of the preceding claims, wherein, during the first and second periods, the optical signals SI, S2, S3 and S4 are measured for several different X wavelengths of interest, each of these wavelengths of interest corresponding to a particular gaseous component to be quantified in the excited sample, the measurements at these different wavelengths of interest being carried out simultaneously.

9. A method according to claim 8, wherein the wavelengths of interest comprise wavelengths of interest corresponding to water vapor, oxygen and nitrogen.

10. A method according to claim 8, wherein the wavelengths of interest comprise wavelengths of interest corresponding to carbon monoxide and carbon dioxide.

11. A method according to any one of the preceding claims, wherein a wavelength of interest corresponds to hydrogen.

12. A method according to any one of the preceding claims, in in which the excitation beam is a continuous laser beam.

13. A method according to any one of the preceding claims, wherein the method comprises: - the measurement (236) of the total pressure inside the enclosure, - the calculation (236) of partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide and nitrogen from quantities quantified by Raman spectrometry of these gaseous components, at least one of these quantities being determined from the difference [(S3(X) / t3 - Sl(X) / tl] and the difference [S4(X) / t4 - S2(X) / t2], and - the calculation (236) of the partial pressure of water vapor from the difference between the total pressure PT less the sum of the calculated partial pressures of hydrogen, carbon dioxide, oxygen, carbon monoxide and nitrogen.

14. A device for quantifying, by Raman spectrometry, at least one gaseous component inside a containment building of a nuclear reactor, this device comprising: - a laser source (32) capable of emitting a monochromatic excitation beam which excites, inside the containment chamber, a sample of the gaseous medium located inside this containment chamber, - a reading unit (34) capable of measuring the optical signal scattered, by Raman effect, by the sample excited by the excitation beam, and - an electronic computer (36) configured to determine, from the optical signal measured by the reading unit, a quantity of the gaseous component present in the sample, characterized in that the computer (36) is configured to automatically perform the following steps: - during an initial measurement period: - the excitation beam is linearly polarized in a predetermined direction, and - the reading unit measures the values ​​S3(X) and S4(X), respectively, of an optical signal S3 and an optical signal S4 emitted by the sample, where: - Optical signals S3 and S4 are the optical signals measured with polarization directions parallel and perpendicular, respectively, to the predetermined polarization direction of the excitation beam, when the sample is excited by the excitation beam, - X is a wavelength of interest, that is, a wavelength at which, due to the Raman effect, a line appears in the spectrum of the scattered optical signal when the gaseous component to be quantified is present in the sample, and - during a second measurement period in the absence of the excitation beam, the reading unit measures the values ​​S1(X) and S2(X), respectively, of an optical signal SI and an optical signal S2 scattered by the sample, where the optical signals SI and S2 are the optical signals measured with polarization directions, respectively, parallel and perpendicular to the predetermined polarization direction of the excitation beam used during the first measurement period, when the excitation beam is absent, and - the calculator (36) determines the quantity of the gaseous component present in the sample from the difference [(S3(X) / t3 - S1 (X) / t1 ] and the difference [S4(X) / t4 - S2(X) / t2], where t1, t2, t3 and t4 are the durations of the time windows during which the signals SI, S2, S3 and S4 are measured to obtain, respectively, the values ​​S1(X), S2(X), S3(X) and S4(X) in number of shots.

15. Device according to claim 14, wherein the reading unit (34) comprises only a photodetector (54) for each wavelength of interest.

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