Nuclear facility gaseous effluent online monitoring device and method

Abstract

The invention discloses a nuclear facility gaseous effluent online monitoring device and method. The nuclear facility gaseous effluent online monitoring device comprises a photoacoustic cell, a laser light source system, a signal processing system and a data processing system. The laser light source system provides laser for the photoacoustic cell, and gas to be detected is connected into the photoacoustic cell, so that the gas to be detected generates a photoacoustic signal under the excitation of the laser; the signal processing system performs phase-locked integral amplification on the photoacoustic signal to obtain a voltage signal in direct proportion to the concentration of 14CO2; and the data processing system receives the voltage signal and analyzes the voltage signal to obtain a 14CO2 concentration value, and the 14C activity concentration is obtained through conversion. According to the invention, on-line monitoring of 14C in the gaseous effluent of the nuclear facility is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of radiation detection, and in particular, to an on-line monitoring device and method for gaseous effluents from nuclear facilities. Background Art

[0002] Carbon-14 ( 14 C) is one of the main radioactive nuclides discharged from nuclear power plants. The national standard "Regulations on Environmental Radiation Protection for Nuclear Power Plants" (GB 6249-2011) stipulates the requirements for controlling the 14 C emissions in the effluents from nuclear power plants. Standards and regulations such as the industry standard "Technical Specifications for Radiation Environmental Monitoring" (HJ 61-2021) and "Technical Specifications for Monitoring Effluents from Nuclear Power Plants" (Guo He An Fa

[2020] No. 44) clarify the requirements for monitoring 14 C in the gaseous effluents from nuclear power plants. 14 C is a pure β nuclide and belongs to the difficult-to-detect nuclides in the radioactive emissions from nuclear power plant effluents. Currently, the monitoring of 14 C in the gaseous effluents from nuclear power plants is all carried out by radiochemical analysis in the laboratory after sampling. The typical sampling period is generally one week (7-8 days). The analysis method uses liquid scintillation counting, and the measurement time is more than several hours. Only one monitoring data can be obtained per week, and no representative monitoring data can be obtained. The long sampling period and long measurement time have become one of the technical obstacles restricting the monitoring and efficient management of gaseous effluents from nuclear power plants. To overcome these technical obstacles and quickly and automatically carry out 14 C monitoring has become an important requirement in the management of nuclear power plant effluent emissions.

[0003] Photoacoustic spectroscopy is a new type of spectroscopic analysis and detection technology based on the photoacoustic effect. It is the product of the combination of spectroscopic technology and calorimetric technology and is a new method for detecting substances and studying the properties of substances developed in the early 1970s of the 20th century. Its principle is that a monochromatic light with a modulated intensity is irradiated onto a sample sealed in a photoacoustic cell. The sample absorbs the light energy and de-excites by releasing heat energy. The released heat energy causes the sample and the surrounding medium to be periodically heated at the modulation frequency of the light, resulting in a periodic pressure fluctuation in the medium. This pressure fluctuation can be detected by a sensitive microphone or a piezoelectric ceramic microphone and amplified to obtain a photoacoustic signal, which is the photoacoustic effect. If the wavelength of the incident monochromatic light is variable, a photoacoustic signal spectrum that varies with the wavelength can be measured, which is the photoacoustic spectrum. In the application of gas analysis, the incident light is a monochromatic light with a modulated intensity, and the light intensity modulation can be achieved by a chopper. The photoacoustic cell is a closed container containing the sample and the microphone. The microphone is very sensitive. For gas samples, a suitable microphone combined with an electronic detection system can detect a temperature rise of 10 -6 °C and can achieve very high sensitivity.

[0004] Currently, photoacoustic spectroscopy has not been applied to14 Monitoring of C to solve the existing 14 problems in the existing C monitoring method, such as long sampling period and long measurement time. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an improved on-line monitoring device and method for gaseous effluents from nuclear facilities.

[0006] The technical solution adopted by the present invention to solve its technical problems is: to provide an on-line monitoring device for gaseous effluents from nuclear facilities, including a photoacoustic cell, a laser module, a signal processing unit, and a data processing terminal;

[0007] The laser module is used to provide laser with a predetermined wavelength for the photoacoustic cell. The photoacoustic cell is connected to the gas to be measured, so that the gas to be measured generates photoacoustic signals under the excitation of the laser. The gas to be measured includes 14 CO2 formed by the conversion of C gas in the gaseous effluents; 14 CO2;

[0008] The signal processing unit performs lock-in integration amplification on the photoacoustic signal to obtain a voltage signal proportional to the 14 CO2 concentration. The data processing terminal receives the voltage signal from the signal processing unit, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, obtains the 14 concentration value of CO2, and obtains the 14 activity concentration of C through conversion.

[0009] In an embodiment, the photoacoustic cell includes a housing, a cantilever sensor arranged in the housing, a photodetector, a readout interferometer, and a balance chamber;

[0010] The housing is provided with an inlet for accessing the gas to be measured, an outlet for outputting the gas to be measured, and an incident light port for accessing the laser. The balance chamber is arranged near the outlet and communicated with the outlet. A gas passage communicating between the inlet and the balance chamber is further arranged in the housing, and the cantilever sensor is located in the gas passage. The photodetector and the readout interferometer are oppositely arranged in the housing with respect to the cantilever sensor.

[0011] In an embodiment, the laser module includes a quantum cascade laser, a temperature controller and a power supply connected to the quantum cascade laser. The temperature controller and the power supply are used to adjust the wavelength of the laser generated by the quantum cascade laser to 2209.1 cm -1 .

[0012] In an embodiment, the laser module further includes a germanium etalon and a signal generator. The laser wavelength is locked at 2209.1 cm through the transmission peak of the germanium etalon -1; The signal generator is used to modulate the laser into pulsed light at 30 Hz to excite the gas to be measured to generate a photoacoustic signal.

[0013] In one embodiment, an intermediate infrared shaping and transmission component for guiding the laser into the photoacoustic cell is provided between the laser module and the photoacoustic cell; the intermediate infrared shaping and transmission component includes at least one mirror.

[0014] In one embodiment, the signal processing unit includes a lock-in amplifier.

[0015] In one embodiment, the on-line monitoring device for gaseous effluents from nuclear facilities further includes a housing; the photoacoustic cell, the laser module and the signal processing unit are arranged inside the housing;

[0016] An air inlet and an air outlet are provided on the housing, and the air inlet and the air outlet are respectively connected to the photoacoustic cell through pipelines.

[0017] In one embodiment, in the data processing terminal, it is obtained according to the following formula (I) 14 The concentration of CO2:

[0018]

[0019] where c is 14 The molar percentage concentration of CO2, α is the absorption coefficient, L is the optical path length, P out is the output light intensity, P in is the input light intensity; the absorption coefficient α(v, p, T) has the following relationship with the constant N0≈2.5×10 25 m ―3 , the line intensity S and the line shape Φ(v, p, T) as shown in the following formula (II):

[0020] α(v, p, T) = N0SΦ(v, p, T) (II)

[0021] According to 14 The spectral width of CO2 is GHz, while the output spectrum of the laser module is MHz. Therefore, the above formula (II) is simplified to the following formula (III):

[0022] α = N0S (III)

[0023] According to 14 The line intensity of CO2 Substitute it into formula (III) and formula (I) to obtain 14 The relationship between the CO2 concentration and the input and output light intensities; obtain the output light intensity P out and the input light intensity P in , substitute them into formula (I) to obtain c; calculate and obtain the 14 Activity concentration of C in the gaseous effluent according to the following formula (IV):

[0024] c A = a·c (Equation 4)

[0025] where c A is the activity concentration of C in the gaseous effluent; α is the absorption coefficient, taking 5.25×10 14 ... 10 .

[0026] The present invention also provides an on-line monitoring method for gaseous effluents of nuclear facilities, adopting the on-line monitoring device for gaseous effluents of nuclear facilities described in any one of the above, and the on-line monitoring method for gaseous effluents of nuclear facilities includes the following steps:

[0027] S1. Take the CO2 formed by the conversion of the C-containing gas in the gaseous effluent of the nuclear facility as the gas to be measured and transport it into the photoacoustic cell, and the laser module provides a laser with a predetermined wavelength for the photoacoustic cell;

[0028] The gas to be measured includes 14 CO2;

[0029] S2. After the gas to be measured enters the photoacoustic cell, a photoacoustic signal is generated under the excitation of the laser;

[0030] S3. The photoacoustic signal is subjected to phase-locked integration amplification by the signal processing unit to obtain a voltage signal proportional to the 14 CO2 concentration and send it to the data processing terminal;

[0031] S4. The data processing terminal receives the voltage signal, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, obtains the 14 CO2 concentration value, and obtains the 14 activity concentration of C according to the conversion.

[0032] In one embodiment, in the data processing terminal, the concentration of 14 CO2 is obtained according to the following formula (1):

[0033]

[0034] where c is the 14 mole percentage concentration of CO2, α is the absorption coefficient, L is the optical path length, P out is the output light intensity, P in is the input light intensity; the absorption coefficient α(v, p, T) has the following relationship with the constant N0≈2.5×10 25 m ―3 、the line strength S and the line shape Φ(v, p, T) as shown in the following formula (2):

[0035] α(v, p, T) = N0SΦ(v, p, T) (2)

[0036] According to 14 The spectral width of CO2 is in GHz, while the output spectrum of the laser module is in MHz. Therefore, the above formula (2) is simplified to the following formula (3):

[0037] α = N0S (3)

[0038] According to 14 The line strength of CO2 Substitute it into formula (3) and formula (1) to obtain 14 The relationship between the CO2 concentration and the input and output light intensities; obtain the output light intensity P according to the photoacoustic signal intensity out and the input light intensity P in , substitute into formula (1) to obtain c; calculate the 14 Activity concentration of C in the gaseous effluent according to the following formula (4):

[0039] c A = a·c (4)

[0040] Among them, c A is the activity concentration of C in the gaseous effluent; α is the absorption coefficient, taking 5.25×10 14 . 10 .

[0041] Advantages of the present invention: Using a quantum cascade laser (QCL) as the laser light source to excite a gas to generate a photoacoustic signal, and measuring the 14 CO 2 concentration through spectral intensity, and then converting to obtain the 14 Activity concentration of C, realizing on-line monitoring of C in the gaseous effluents of nuclear facilities such as nuclear power plants, and providing an efficient tool for the accurate assessment of radioactive emissions from nuclear power plants, operation condition diagnosis, etc. 14 . Brief Description of the Drawings

[0042] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0043] Figure 1 is the connection structure schematic diagram of the on-line monitoring device for gaseous effluents of nuclear facilities in an embodiment of the present invention;

[0044] Figure 2 is the structure schematic diagram of the integration (removing one side plate) of the on-line monitoring device for gaseous effluents of nuclear facilities in an embodiment of the present invention. Detailed Embodiments

[0045] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0046] The on-line monitoring device for gaseous effluents from nuclear facilities of the present invention realizes on-line monitoring of 14 C in the gaseous effluents from nuclear facilities.

[0047] Referring to Figure 1 and Figure 2 An on-line monitoring device for gaseous effluents from nuclear facilities according to an embodiment of the present invention may include a photoacoustic cell 10, a laser module, a signal processing unit 30, and a data processing terminal 40.

[0048] The laser module is used to provide a laser with a predetermined wavelength for the photoacoustic cell 10; the photoacoustic cell 10 is connected to the gas to be measured, so that the gas to be measured generates a photoacoustic signal under the excitation of the laser. The signal processing unit 30 performs phase-locked integration amplification on the photoacoustic signal to obtain a voltage signal proportional to the 14 CO2 concentration; the data processing terminal 40 receives the voltage signal from the signal processing unit 30, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, obtains the 14 CO2 concentration value, and obtains the 14 activity concentration of C according to the conversion.

[0049] Among them, the gas to be measured includes 14 CO2 formed by the conversion of C-containing gas in the gaseous effluent. Specifically, a catalytic oxidation device is pre-used to convert the C-containing gas other than CO2 in the gaseous effluent from nuclear facilities into CO2. The C-containing gas includes but is not limited to CO, CH4, etc. It can be understood that when the gas is a C-containing 14 gas, then the corresponding gas after conversion is 14 CO2. 14 CO2.

[0050] In one embodiment, the photoacoustic cell 10 includes a housing 11, a cantilever sensor 12, a photodetector 13, a readout interferometer 14, and a balance chamber 15 disposed in the housing 11.

[0051] The housing 11 is provided with an inlet 110 for accessing the gas to be measured and an outlet 120 for outputting the gas to be measured. The inlet 110 and the outlet 120 are preferably located on different sides of the housing 11. Inside the housing 11, a balance chamber 15 is arranged close to the outlet 120 and is in communication with the outlet 120. A gas passage 130 is also provided inside the housing 11, and the gas passage 130 is connected between the inlet 110 and the balance chamber 15. The cantilever sensor 12 is arranged in the gas passage 130, so that when the gas to be measured enters the housing 11 and flows towards the balance chamber 15, it also passes through the cantilever sensor 12, thereby enabling the gas to be measured to absorb the pulsed oscillating laser energy and generate weak sound waves; the sound waves are received by the cantilever sensor 12, causing the mirror in the cantilever sensor 12 to vibrate weakly, and the vibration frequency is consistent with the laser frequency.

[0052] The photodetector 13 and the readout interferometer 14 are arranged opposite to the cantilever sensor 12 inside the housing 11, and can collect and obtain the vibration of the cantilever sensor 12 and convert it into an electrical signal. The electrical signal then enters the signal processing unit. After filtering out the noise, it is collected and analyzed by the data processing terminal 40 and converted into a gas 14 CO2 concentration signal.

[0053] To balance the photoacoustic signal, the balance chamber 15 is connected with a barometer 16 and an air pump 17 for providing a stable air pressure.

[0054] The housing 11 is also provided with a light inlet for accessing the laser. The laser is incident into the housing 11 from the light inlet, and thus enters the photoacoustic cell 10 and also passes through the gas passage 130 inside the photoacoustic cell 10.

[0055] In Figure 1 the illustrated embodiment, the gas passage 130 inside the housing 11 is in a cross shape and can be formed by connecting two perpendicular linear passages. The cantilever sensor 12 and the balance chamber 15 are at both ends of a linear passage and are facing each other, and the laser entering the housing 11 passes through the other linear passage. The photodetector 13 and the readout interferometer 14 are located outside the gas passage 130 in the housing 11.

[0056] In the present invention, the photoacoustic effect of the laser is adopted to 14 measure the absorption spectrum of CO2. The target spectral line is 14 the P(20) absorption spectral line of CO2, and the wavelength of this spectral line is 4526.73 nm (2209.1 cm -1 -1).

[0057] The laser module includes a quantum cascade laser (QCL) 20, a temperature controller 21 connected to the quantum cascade laser 20, and a power supply 25. The quantum cascade laser 20 is preferably a mid-infrared quantum cascade laser. The temperature controller 21 and the power supply 25 are used to adjust the wavelength of the laser generated by the quantum cascade laser 20 to 2209.1 cm -1。

[0058] The emission center wavelength of the quantum cascade laser 20 is 4.53 μm, the driving voltage is 16 V, the driving current is greater than 1.3 A, and the minimum output power is 20 mW. The linewidth of the quantum cascade laser 20 is 0.2 cm -1 , meeting the gas absorption requirements. Through the current / temperature / wavelength relationship, the wavelength of the quantum cascade laser 20 can be controlled to be at 2209.1 cm -1 。

[0059] To avoid wavelength drift caused by environmental changes, a germanium etalon 22 can also be used to form a wavelength selection device. The transmitted power is measured by a mid-infrared detector 23 to lock the wavelength. In one embodiment, the laser module further includes a germanium etalon 22, and the laser wavelength is 2209.1 cm through the transmission peak of the germanium etalon 22 -1 。

[0060] The laser module further includes a signal generator 24 for modulating the laser into pulsed light at 30 Hz to excite the gas to be measured to generate a photoacoustic signal.

[0061] To obtain a stable standard transmission wavelength, a thermoelectric cooler (TEC) is used to precisely control the temperature of the germanium wafer of the germanium etalon 22, and the temperature control accuracy reaches 0.01 °C. Both sides of the germanium etalon 22 are coated with mid-infrared reflective films. According to the Fabry-Perot principle, the transmission wavelength of the germanium etalon 22 is related to the cavity length and refractive index. First, mid-infrared laser is emitted by the QCL, the wavelength passing through the germanium wafer is measured by the mid-infrared detector 23, and the transmission peak is adjusted to 2209.1 cm by the TEC -1 . The intensity of the mid-infrared laser transmitted through the germanium wafer is detected by a photoacoustic detector. Its peak wavelength is 5.2 ± 0.5 μm, the wavelength cut-off range is 3.0 μm - 6.7 μm, the detectivity D*(λopt) ≥ 4.0×10 10 cm·Hz 1 / 2 / W, D*(λopt) ≥ 7.0×10 9 cm·Hz 1 / 2 / W, and the photosensitive area AO = 1×1 mm 2 。

[0062] In the arrangement, the laser module and the photoacoustic cell 10 can be directly opposite, so that the laser generated by the laser module can enter the photoacoustic cell 10 in a straight line. When the laser output end of the laser module and the light inlet of the photoacoustic cell are not in a straight line direction, an infrared shaping and transmission component can be set between them to guide the laser into the photoacoustic cell.

[0063] In one embodiment, the laser module and the photoacoustic cell 10 are arranged side by side, and the laser output end of the laser module and the light inlet of the photoacoustic cell 10 face the same direction. For this, a mid-infrared shaping and transmission component is arranged between the two, which is used to transmit the mid-infrared laser emitted by the quantum cascade laser 20 into the photoacoustic cell 10 and has a suitable beam diameter to obtain the maximum photoacoustic signal.

[0064] The mid-infrared shaping and transmission component includes at least one mirror. The mirror can be made of calcium fluoride material.

[0065] In one embodiment, referring to Figure 1 and Figure 2 , a first mirror 211 placed obliquely is arranged on one side of the laser output end of the laser module, and a second mirror 212 placed obliquely is arranged on one side of the light inlet of the photoacoustic cell 10. The reflecting surfaces of the first mirror 211 and the second mirror 212 are obliquely facing each other. The laser emitted by the laser module is directed at the first mirror 211, and the path of the laser is changed by reflection of the first mirror 211 to face the second mirror 212, and the second mirror 212 reflects the laser into the photoacoustic cell 10. Among them, the first mirror 211 can be replaced by a density attenuation sheet.

[0066] The signal processing unit 30 includes a lock-in amplifier 31, which performs lock-in integration amplification on the electrical signal output by the photoacoustic cell 10. The original photoacoustic signal is a sinusoidal voltage signal with a fixed frequency. In order to avoid interference from environmental noise, the power supply 25 of the quantum cascade laser 20 is modulated to generate a laser with a fixed frequency; this power supply frequency and the photoacoustic voltage signal are simultaneously input into the lock-in amplifier 31 for lock-in integration amplification to obtain a voltage signal proportional to the 14 C concentration. In the data processing terminal 40, according to the calibrated relationship between the voltage signal and the concentration, this voltage signal is analyzed to obtain the real-time concentration value.

[0067] The data processing terminal 40 is provided with data processing software, which has functions such as concentration display, data monitoring, parameter calibration, and error alarm. This data processing software can be remotely controlled through the RS485 serial port to obtain the parameters and measurement values of each module and unit. The data processing software uses the industrial standard C# language and the Modbus standard communication protocol, and has a modular architecture with a friendly human-computer interaction interface.

[0068] In one embodiment, the data processing terminal 40 may include a computer.

[0069] In one embodiment, the on-line monitoring device for gaseous effluents from nuclear facilities further includes a housing 100; the photoacoustic cell 10, the laser module, and the signal processing unit 30 (lock-in amplifier 31) are arranged in the housing 100, so as to form an integrated main device, as Figure 2 shown.

[0070] The data processing terminal 40 serves as the host computer of the main device and can be fixedly connected to the outer shell 100, for example, fixed on the top or one side of the outer shell 100, etc. Alternatively, the data processing terminal 40 and the main device can be installed on a customized trolley. The main device is placed on the lower layer of the trolley, and the data processing terminal 40 is placed on the upper layer of the trolley.

[0071] The outer shell 100 is provided with an air inlet 101 and an air outlet 102. The air inlet 101 and the air outlet 102 are respectively connected to the inlet and outlet of the photoacoustic cell 10 through pipelines. The pipelines are preferably flexible hoses, which are convenient for bending and arranging inside the outer shell 100, etc.

[0072] In an arrangement implementation manner, the quantum cascade laser 20 and the photoacoustic cell 10 are located at one end of the outer shell 100 and are oppositely arranged. The mid-infrared shaping and transmission components (the first mirror 211 and the second mirror 212) are arranged between the quantum cascade laser 20 and the photoacoustic cell 10 and an inner wall surface of the outer shell 100. The temperature controller 21 and the power supply 25 are located inside the other end of the outer shell 100 and on the side of the quantum cascade laser 20.

[0073] Furthermore, an inner lining is arranged on the inner wall surface of the outer shell 100, which plays roles in shock absorption, noise reduction, heat preservation and dust isolation. The inner lining can be made of buffer materials such as rubber and silica gel. At the same time, mechanical structures such as air bearings and springs are selected as the shock absorbers of the whole machine. The photoacoustic cell 10, the laser module and the signal processing unit 30 are arranged on the air bearing platform inside the outer shell 100.

[0074] The outer shell 100 is also provided with a power supply module 300 and a main control board 200, which provide power supply for the whole machine and conversion of control signals. The power supply 25 of the laser module can be formed in the power supply module 300. The main control board 200 can be connected to the temperature controller 21 and the power supply module 300 to control the temperature controller 21 and the power supply 25 to adjust the wavelength of the laser generated by the quantum cascade laser 20 to 2209.1 cm -1 。

[0075] The outer shell 100 is also provided with a photoacoustic digital processor 400 and a photoacoustic power supply 410; the photoacoustic power supply 410 supplies power to the photoacoustic digital processor 400. The photoacoustic digital processor 400 is connected to the cantilever sensor 12 and is responsible for processing the photoacoustic signals generated by the cantilever sensor 12 to obtain photoacoustic intensity information.

[0076] The bottom of the housing 100 may be provided with fixed support feet and detachable wheels for convenient position movement. The side wall of the housing 100 may be provided with grooves or handles for convenient handling. According to the requirements of the installation site, the housing 100 has a 220V or DC power supply interface externally, and surge protection and voltage stabilization designs such as against power surges and unstable voltages are considered in the power supply design. The gas path interface of the housing is preferably four interfaces, two of which are online long-term test interfaces, namely the air inlet 101 and the air outlet 102 respectively; the other two are calibration test interfaces and can be sealed. The control interface of the housing 100 is set as a communication interface with a DB9 or multi-core aviation plug structure, and communicates with the data processing terminal through a serial communication protocol.

[0077] Reference Figure 1 And Figure 2 , the online monitoring method of nuclear facility gaseous effluents implemented by the online monitoring device for nuclear facility gaseous effluents of the present invention may include the following steps:

[0078] S1. Take the CO2 formed by the conversion of the C-containing gas in the nuclear facility gaseous effluent as the gas to be measured and transport it into the photoacoustic cell 10, and the laser module provides laser with a predetermined wavelength for the photoacoustic cell.

[0079] Among them, the gas to be measured includes the CO2 formed by the conversion of the C-containing gas in the gaseous effluent. Specifically, a catalytic oxidation device is pre-used to convert the C-containing gas other than CO2 in the nuclear facility gaseous effluent into CO2. The C-containing gas includes but is not limited to CO, CH4, etc. It can be understood that when the gas is a C-containing 14 gas, then the corresponding converted one is 14 CO2. 14 C gas, then the corresponding one after conversion is 14 CO2.

[0080] In addition, before the gaseous effluent is converted, the water, aerosol, N2O, etc. that may be contained therein are removed first, and then it is processed by a dedicated catalytic oxidation device to convert the other carbon except for the chemical form of CO2 into CO2. The CO2 after being processed by the catalytic oxidation device can be temporarily stored in a trap.

[0081] During monitoring, the CO2 in the trap can be sampled through the test pipeline and transported into the photoacoustic cell 10; the sampling volume does not exceed 1 m 3 , and the mass of the collected CO2 does not exceed 0.8 g.

[0082] The online monitoring device for nuclear facility gaseous effluents is preheated before use.

[0083] S2. After the gas to be measured enters the photoacoustic cell 10, a photoacoustic signal is generated under the excitation of the laser.

[0084] S3. The photoacoustic signal is subjected to phase-locked integration amplification by the signal processing unit 30 to obtain a signal related to 14A voltage signal proportional to the CO2 concentration is sent to the data processing terminal 40.

[0085] S4. The data processing terminal 40 receives the voltage signal, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, and obtains 14 the concentration value of CO2, and obtains 14 the activity concentration of C according to the conversion.

[0086] In one embodiment, in the data processing terminal, the concentration of CO2 is obtained according to the following formula (I): 14 Concentration of CO2:

[0087]

[0088] where c is 14 the molar percentage concentration of CO2, α is the absorption coefficient, L is the optical path length, P out is the output light intensity, P in is the input light intensity; the absorption coefficient α(v, p, T) and the constant N0≈2.5×10 25 m ―3 、the line strength S and the line shape Φ(v, p, T) have the following relationship in formula (II):

[0089] α(v, p, T) = N0SΦ(v, p, T) (II)

[0090] According to 14 the spectral width of CO2 is GHz, while the output spectrum of the laser module is MHz, so formula (II) is simplified to the following formula (III):

[0091] α = N0S (III)

[0092] According to 14 the line strength of CO2 Substitute it into formula (III) and formula (I) to obtain 14 the relationship between the CO2 concentration and the input and output light intensities; obtain the output light intensity P out and the input light intensity P in according to the photoacoustic signal intensity, substitute them into formula (I) to obtain c; calculate the 14 activity concentration of C in the gaseous effluent according to the following formula (IV):

[0093] c A = a·c (IV)

[0094] where c A is the activity concentration of C in the gaseous effluent; α is the absorption coefficient, taking 5.25×10 14 . 10 .

[0095] As described above, the activity concentration of 14C in the gaseous effluent is obtained, realizing automated monitoring to replace manual laboratory operations, thereby improving the analysis efficiency and saving labor costs; realizing on-line monitoring of 14 C in the gaseous effluents of nuclear power plants and other nuclear facilities; greatly shortening the sampling time and measurement time, reducing the single 14 C measurement result from one week to dozens of minutes to one hour, and is expected to promote the quasi-real-time on-line monitoring of 14 C in the gaseous effluent, providing an efficient tool for the accurate assessment of the radioactivity discharged from nuclear power plants, the diagnosis of operating conditions, etc. 14 The on-line monitoring of 14 C; 14 The 14 C measurement result; 14 The quasi-real-time on-line monitoring of 14 C provides an efficient tool for the accurate assessment of the radioactivity discharged from nuclear power plants, the diagnosis of operating conditions, etc.

[0096] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. An on-line monitoring device for gaseous effluents from nuclear facilities, characterized in that, It includes a photoacoustic cell, a laser module, a signal processing unit and a data processing terminal; The laser module is used to provide a laser with a predetermined wavelength for the photoacoustic cell, and the photoacoustic cell is connected to the gas to be measured, so that the gas to be measured generates a photoacoustic signal under the excitation of the laser; the gas to be measured includes that contained in the gaseous effluent 14 formed by the conversion of 14 CO2; The signal processing unit performs phase-locked integration amplification on the photoacoustic signal to obtain a voltage signal proportional to 14 the CO2 concentration; the data processing terminal receives the voltage signal from the signal processing unit, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, and obtains 14 the concentration value of CO2, and obtains 14 the active concentration of C through conversion.

2. The on-line monitoring device for gaseous effluents of nuclear facilities according to claim 1, characterized in that, The photoacoustic cell includes a housing, a cantilever sensor, a photodetector, a readout interferometer, and a balance chamber arranged in the housing; The shell is provided with an inlet for receiving the gas to be measured, an outlet for outputting the gas to be measured, and a light inlet for receiving the laser. The balancing chamber is arranged near the outlet and is connected to the outlet. A gas passage connecting the inlet and the balancing chamber is also provided in the shell. The cantilever sensor is located in the gas passage. The photodetector and the readout interferometer are arranged opposite to the cantilever sensor in the shell.

3. The on-line monitoring device for gaseous effluents from nuclear facilities according to claim 1, characterized in that The laser module includes a quantum cascade laser, a temperature controller connected to the quantum cascade laser, and a power supply; the temperature controller and the power supply are used to adjust the wavelength of the laser generated by the quantum cascade laser to 2209.1 cm -1 .

4. The on-line monitoring device for gaseous effluents from nuclear facilities according to claim 3, characterized in that, The laser module further includes a germanium etalon and a signal generator; the transmission peak of the germanium etalon is used to lock the laser wavelength at 2209.1 cm -1 ; the signal generator is used to modulate the laser into pulsed light with a frequency of 30 Hz to excite the gas to be measured to generate a photoacoustic signal.

5. The on-line monitoring device for gaseous effluents of nuclear facilities according to claim 1, characterized in that, A mid-infrared shaping and transmission component for guiding the laser into the photoacoustic cell is provided between the laser module and the photoacoustic cell; the mid-infrared shaping and transmission component includes at least one reflecting mirror.

6. The on-line monitoring device for gaseous effluents of nuclear facilities according to claim 1, characterized in that The signal processing unit includes a lock-in amplifier.

7. The on-line monitoring device for gaseous effluents from nuclear facilities according to any one of claims 1-6, characterized in that, The nuclear facility gaseous effluent online monitoring device further comprises a housing; the photoacoustic cell, the laser module and the signal processing unit are arranged in the housing; An air inlet and an air outlet are provided on the shell, and the air inlet and the air outlet are connected to the photoacoustic cell through pipelines respectively.

8. The on-line monitoring device for gaseous effluents of nuclear facilities according to any one of claims 1-6, characterized in that, In the data processing terminal, it is obtained according to the following formula (1): 14 The concentration of CO2: where c is 14 the molar percentage concentration of CO2, α is the absorption coefficient, L is the optical path length, P out is the output light intensity, P in is the input light intensity; the absorption coefficient α(v, p, T) and the constant N0 ≈ 2.5×10 25 m ―3 、the line strength S and the line shape Φ(v, p, T) have the following relationship of formula (2): α(v,p,T)=N0SΦ(v,p,T)(II) According to 14 The spectral width of CO2 is GHz, while the output spectrum of the laser module is MHz. Therefore, the above formula (II) is simplified to the following formula (III): α=N0S (Three) According to 14 of CO2 Substitute it into Equation (III) and Equation (I) to obtain 14 the relationship between the CO2 concentration and the input and output light intensities; obtain the output light intensity P according to the photoacoustic signal intensity out and the input light intensity P in , substitute it into Equation (I) to obtain c; calculate the activity concentration of C in the gaseous effluent according to the following Equation (IV): 14 C's activity concentration: c A = a·c (IV) where c A is the activity concentration of C 14 in the gaseous effluent; α is the absorption coefficient, taking 5.25×10 10 .

9. An on-line monitoring method for gaseous effluents from nuclear facilities, characterized in that, The online monitoring device for gaseous effluent from a nuclear facility according to any one of claims 1 to 8 is used, and the online monitoring method for gaseous effluent from a nuclear facility comprises the following steps: S1. CO2 formed by converting C-containing gas in gaseous effluent from a nuclear facility is transported as a gas to be measured into a photoacoustic cell, and a laser module provides a laser with a predetermined wavelength to the photoacoustic cell; The gas to be measured includes 14 CO2; S2, after the gas to be measured enters the photoacoustic cell, it generates a photoacoustic signal under the excitation of the laser; S3. The photoacoustic signal is subjected to phase-locked integration amplification by the signal processing unit to obtain a voltage signal proportional to the 14 CO2 concentration and send it to the data processing terminal; S4. The data processing terminal receives the voltage signal, analyzes the voltage signal according to the relationship between the voltage signal and the concentration, and obtains 14 the concentration value of CO2, and obtains 14 the active concentration of C through conversion.

10. The online monitoring method for gaseous effluents from nuclear facilities according to claim 9, characterized in that, In the data processing terminal, it is obtained according to the following formula (1): 14 The concentration of CO2: where c is 14 the molar percentage concentration of CO2, α is the absorption coefficient, L is the optical path length, P out is the output light intensity, P in is the input light intensity; the absorption coefficient α(v, p, T) and the constant N0 ≈ 2.5×10 25 m ―3 、 the line strength S and the line shape Φ(v, p, T) have the following relationship in Equation (2): α(v,p,Y)=N0SΦ(v,p,T)(II) According to 14 The spectral width of CO2 is GHz, while the output spectrum of the laser module is MHz. Therefore, Equation (2) is simplified to Equation (3) as follows: α=N0S(three) According to 14 of CO2 Substitute it into formula (III) and formula (I) to obtain 14 the relationship between the CO2 concentration and the input and output light intensities; obtain the output light intensity P according to the photoacoustic signal intensity out and the input light intensity P in , substitute it into formula (I) to obtain c; calculate the activity concentration of C in the gaseous effluent according to the following formula (IV): 14 ​ c A = a·c (Equation 4) Among them, c A is the activity concentration of C in the gaseous effluent; α is the absorption coefficient, taking 5.25×10 14 . 10 .

Images