Online monitoring device and method for radionuclide in gaseous effluent of nuclear power plant

Abstract

The invention provides an online monitoring device and method for radionuclide in gaseous effluent of a nuclear power plant, and particularly relates to the technical field of radionuclide detection. The device comprises a gas path system, an optical system and an electric control system, wherein the gas path system is used for collecting gas to be detected; the optical system comprises a laser ring-down cavity and a laser detection module, the laser ring-down cavity is communicated with the gas path system and used for containing gas to be detected, the laser detection module comprises a light source module and a photoelectric detector, the light source module is used for generating laser beams, and the laser beams can enter the laser ring-down cavity and are transmitted in the laser ring-down cavity; the photoelectric detector is arranged at a corresponding position of the laser ring-down cavity and is used for detecting the intensity of the laser beam transmitted from the laser ring-down cavity; the electric control system is electrically connected with the laser detection module and used for controlling and processing transmission signals of the laser detection module. According to the invention, on-line monitoring of radionuclides can be realized, and the problem that secondary hazardous wastes are generated by a traditional method is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of radionuclide detection, and particularly to an on-line monitoring device and method for radionuclides in gaseous effluents of nuclear power plants. Background Art

[0002] Nuclear power provides continuous high-quality clean energy for society as an almost zero-emission energy source, and plays an important role in mitigating greenhouse gas emissions. However, nuclear power plants will generate radioactive effluents during operation, which may have potential impacts on environmental safety and public health. Therefore, it is crucial to effectively monitor these radionuclides in the effluents. Among various radionuclides emitted from nuclear power plant effluents, carbon-14 ( 14 C) is the most concerned radionuclide. Because carbon-14 is easily involved in the carbon cycle and enters the human body through various pathways after entering organisms, which may cause long-term radioactive effects. In current environmental impact assessments, carbon-14 often becomes a key radionuclide for the radiation impact of nuclear power plant effluent emissions on the public. Therefore, monitoring carbon-14 in effluents, especially gaseous effluents, is an important part of the environmental management of nuclear power plants.

[0003] At present, the main method for monitoring carbon-14 in gaseous effluents of nuclear power plants is liquid scintillation counting. This method has a long sampling time, requires necessary pretreatment, and needs to be analyzed in a laboratory. Usually, the sampling period is 1 week, and the pretreatment and measurement time takes several hours to 1 day. Moreover, this method uses a scintillation liquid with certain toxicity and reactivity as the detection substance, and the prepared samples need to be treated as hazardous waste, which has the problem of being environmentally unfriendly. In addition, the current monitoring of carbon-14 in gaseous effluents of nuclear power plants faces the need for on-line monitoring. On the one hand, on-line monitoring can replace manual sampling and analysis, saving labor costs and improving work efficiency; on the other hand, on-line monitoring can provide a fast and efficient diagnostic tool, which will play an important role in abnormal emissions and accident emissions of nuclear power plants.

[0004] Therefore, developing an on-line monitoring device and method is crucial for the monitoring of radionuclides in gaseous effluents of nuclear power plants. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides an on-line monitoring device and method for radionuclides in gaseous effluents of nuclear power plants to improve the problems of long sampling time, inability to monitor in real time on-line, complex pretreatment process, and environmental unfriendliness of the existing methods in nuclear power plants.

[0006] To achieve the above and other related objectives, a first aspect of the present invention provides an on-line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant, comprising: a gas path system, an optical system, and an electronic control system. The gas path system is used to collect the gaseous effluent of the nuclear power plant. The optical system includes a laser cavity ring-down and a laser detection module. The laser cavity ring-down is connected to the gas path system and is used to accommodate the gas to be measured. The laser detection module includes a light source module and a photodetector. The light source module is used to generate a laser beam, and the laser beam can enter the laser cavity ring-down and propagate therein. The photodetector is arranged at a corresponding position of the laser cavity ring-down and is used to detect the intensity of the laser beam transmitted from the laser cavity ring-down. The electronic control system is electrically connected to the laser detection module and is used to control and process the transmission signal of the laser detection module.

[0007] In an embodiment of the present invention, the laser cavity ring-down includes a sealed housing and a first mirror, a second mirror, and a third mirror arranged in the sealed housing. The first mirror is a plane mirror with a high reflectivity. The second mirror and the third mirror are concave mirrors with a high reflectivity. The first mirror is arranged at one end of the sealed housing. The second mirror and the third mirror are respectively arranged at the other end opposite to the first mirror and form a V-shaped cavity ring-down with the first mirror.

[0008] In an embodiment of the present invention, the laser detection module further includes a mirror and a converging lens. The mirror is arranged between the light source module and the laser cavity ring-down along the transmission path of the laser beam. The converging lens is arranged between the laser cavity ring-down and the photodetector and is located on the transmission path of the laser beam.

[0009] In an embodiment of the present invention, the optical system further includes a spectroscopic box. An optical bottom plate is provided in the spectroscopic box. The laser cavity ring-down and the laser detection module are both arranged on the optical bottom plate.

[0010] In an embodiment of the present invention, an air inlet hole and two air outlet holes are provided on the sealed housing of the laser cavity ring-down. The air inlet hole is arranged at a position of the sealed housing close to the first mirror. The two air outlet holes are respectively arranged at positions of the sealed housing corresponding to the second mirror and the third mirror.

[0011] In an embodiment of the present invention, the electronic control system includes a power supply module, a shutdown circuit module, a signal generation module, an adder, a data processing module, and a laser driving module. The power supply module is used to provide power for each device in the apparatus. The shutdown circuit module is electrically connected to the light source module. The signal generation module is used to generate a sawtooth wave and a DC bias signal. The adder is electrically connected to the signal generation module and the laser driving module. The laser driving module is electrically connected to the light source module. The data processing module is electrically connected to the photodetector.

[0012] In an embodiment of the present invention, the electronic control system further includes a temperature control module and a pressure control module. The temperature control module is used to control the temperature of the light source module and the internal temperature of the spectral box. The pressure control module is used to control the gas pressure inside the laser cavity. The temperature control module and the pressure control module are respectively electrically connected to the data processing module.

[0013] In an embodiment of the present invention, a temperature regulating device and a temperature sensor are provided inside the spectral box. The temperature sensor is electrically connected to the data processing module, and the temperature regulating device is electrically connected to the temperature control module.

[0014] In an embodiment of the present invention, a pressure sensor is provided inside the laser cavity, and the pressure sensor is electrically connected to the data processing module.

[0015] In an embodiment of the present invention, the gas path system includes an enrichment system and a gas pretreatment system. The enrichment system is used to collect carbon dioxide gas samples collected from the chimney of a nuclear power plant. One end of the gas pretreatment system is communicated with the enrichment system, and the other end is communicated with the laser cavity. The gas pretreatment system includes a first particulate filter, an oil-gas separator, a gas source dryer, a condenser, and a linear valve arranged in sequence along the gas transmission direction.

[0016] In an embodiment of the present invention, a second particulate filter is further provided between the gas pretreatment device and the laser cavity.

[0017] In an embodiment of the present invention, the on-line monitoring device further includes a vacuum pump. The vacuum pump is communicated with the laser cavity and is used to pump the gas inside the laser cavity. A third particulate filter is provided between the vacuum pump and the laser cavity.

[0018] In an embodiment of the present invention, the material of the sealed housing of the laser cavity includes any one of gold, silver, stainless steel, and aluminum.

[0019] In an embodiment of the present invention, the light source module adopts a quantum cascade laser.

[0020] On the other hand, the present invention provides a monitoring method based on the above-mentioned online monitoring device, and the monitoring method includes the following steps:

[0021] Turn on the power supply of the online monitoring device;

[0022] Clean and evacuate the online monitoring device;

[0023] Inject the gas to be measured into the gas path system of the online monitoring device, and the gas to be measured enters the laser cavity ring-down of the online monitoring device through the gas path system and is enclosed in the laser cavity ring-down;

[0024] The laser beam generated by the light source module of the online monitoring device attenuates in the laser cavity ring-down, and the concentration information of the gas to be measured is obtained by analyzing the ring-down time when there is an empty cavity and when there is an absorption medium.

[0025] The online monitoring device for radioactive nuclides in the gaseous effluents of nuclear power plants provided by the present invention is based on the laser cavity ring-down spectroscopy detection technology and utilizes the cavity-enhanced absorption spectroscopy, enabling the laser to reflect back and forth between the high-reflectivity mirrors, which can increase the interaction path of the laser with the medium and enhance the absorption spectrum signal. As one of them, the cavity ring-down spectroscopy overcomes the influence of the fluctuations of the light intensity and the coupling efficiency, measures the temporal variation of the light intensity in the cavity, and obtains the gas concentration, with a sensitivity that can reach 10 -10 .

[0026] The laser cavity ring-down adopts a three-mirror V-shaped cavity structure, which can effectively avoid the direct feedback of the incident light to the laser and cause performance loss compared with the traditional linear cavity. In addition, the V-shaped cavity structure effectively reduces the volume of the laser cavity ring-down while ensuring the long optical path performance, and can realize the production of a portable measurement system.

[0027] An enrichment system and a gas pretreatment system are designed for the online monitoring environment of the gaseous effluents of nuclear power plants, which can effectively capture high-concentration carbon dioxide from the chimney of the nuclear power plant for detection. At the same time, the gas pretreatment system can ensure that the samples entering the laser cavity ring-down have high cleanliness and extend the service life of the overall system. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other embodiments can be obtained based on these drawings.

[0029] Figure 1 It is a three-dimensional schematic diagram of the overall structure of the online monitoring device for radioactive nuclides in the gaseous effluents of nuclear power plants according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic structural diagram of another angle in an embodiment of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention;

[0031] Figure 3 This is a schematic internal structure diagram of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0032] Figure 4 This is a schematic diagram of the gas path system of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0033] Figure 5 This is a schematic diagram of the optical system of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0034] Figure 6 This is a schematic diagram of the high - reflectivity mirror in the laser cavity of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0035] Figure 7 This is a schematic diagram of the electronic control system of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0036] Figure 8 This is a schematic diagram of the gas transmission of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention in an embodiment;

[0037] Figure 9 This is a flow chart of the detection method for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention;

[0038] Figure 10 This is the dynamic concentration dilution of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention 14 CO2 measurement results;

[0039] Figure 11 This is the Allan variance analysis result of the on - line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant according to the present invention.

[0040] Element number description:

[0041] 100, Gas path system; 110, Enrichment system; 120, Gas pretreatment system; 121, First particulate filter; 122, Oil-gas separator; 123, Gas source dryer; 124, Condenser; 125, Linear valve; 126, Second particulate filter; 127, Third particulate filter; 130, Vacuum pump; 200, Optical system; 210, Laser cavity ring-down cell; 211, Sealed housing; 212, Inlet port; 213, Outlet port; 214, High reflectivity mirror; 220, Laser detection module; 221, Light source module; 222, Photoelectric detector; 225, Mirror; 226, Converging lens; 230, Spectral box; 231, Optical base plate; 232, Shock-absorbing plate; 233, Temperature-controlled fan; 300, Electric control system; 310, Laser driving module; 320, Shutdown circuit module; 330, Signal generation module; 340, Data acquisition card; 350, Computer main board; 360, Power supply module; 370, Temperature control module; 371, Detector temperature control; 380, Voltage control module; 390, Receiving circuit module; 400, Main body housing; 401, Housing inlet port; 402, Housing outlet port; 403, Heat dissipation port; 404, Folding handle; 405, Water cooler interface; 406, Driver control window; 407, USB expansion port; 408, SMA interface; 409, Power switch for electric control system and optical system; 410, Main power switch; 411, Bracket. Detailed implementation manners

[0042] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. It should also be understood that the terms used in the embodiments of the present invention are for describing specific specific implementation manners, rather than for limiting the protection scope of the present invention. The test methods without specific conditions noted in the following embodiments are usually carried out according to conventional conditions, or according to the conditions recommended by each manufacturer.

[0043] When the embodiments give numerical ranges, it should be understood that unless otherwise specified in the present invention, any value at both ends of each numerical range and any value between the two ends can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention, based on the understanding of those skilled in the art of the prior art and the description of the present invention, can also use any methods, devices, and materials similar or equivalent to the methods, devices, and materials in the embodiments of the present invention to implement the present invention.

[0044] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of clear narration, rather than used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in technical content, should also be regarded as the scope of implementation of the present invention.

[0045] Please refer to Figures 1 to 11 , the present invention provides an on-line monitoring device and method for radioactive nuclides in gaseous effluents of nuclear power plants. The device can obtain the concentration information of the sample to be measured according to the decay time of the optical cavity freely decaying over time. Therefore, it can replace manual sampling analysis, save labor costs, improve work efficiency, and thus improve the problems of long sampling time, inability to monitor in real time on-line, complex pretreatment process, and environmental unfriendliness of the existing methods in nuclear power plants.

[0046] The on-line monitoring device provided by this application can not only be used to measure 14 the concentration of CO2, but also be used to measure 14 CO or 14 the gas concentration of CH4, and can also measure the concentration of radioactive gases with other radioactive isotopes such as 14 N, 15 N, 16 O, etc. This application does not make any limitations in this regard.

[0047] Please refer to Figures 1 to 5 , the on-line monitoring device for radioactive nuclides in gaseous effluents of nuclear power plants provided by the present invention includes a gas path system 100, an optical system 200, and an electronic control system 300. Among them, the gas path system 100 is used to collect the gas to be measured. The gas to be measured can be, for example, 14 CO2, 14 CO or 14 CH4, and can also be other radioactive gases with radioactive isotopes such as 14 N, 15 N, 16 O, etc. This application takes the 14 CO2 gas collected from nuclear power plants as an example for description, but is not limited thereto. The optical system 200, as the main part of the on-line monitoring device, includes a laser cavity ring-down cavity 210 for accommodating the gas to be measured and a laser detection module 220 for generating a laser beam and detecting the intensity of the laser beam. The electronic control system 300 is electrically connected to the laser detection module 220 and is used to control and process the transmission signal of the laser detection module 220. The optical system 200 can detect the ring-down signal of the laser beam and transmit it to the electronic control system 300, and the electronic control system 300 calculates the final gas concentration information.

[0048] Please refer to Figure 4, in one embodiment, the gas path system 100 includes an enrichment system 110 and a gas pretreatment system 120. The enrichment system 110 is used to collect the gas to be measured. For example, it collects the carbon dioxide gas sample collected from the chimney of a nuclear power plant to make it have a high concentration. The enrichment system 110 can adopt any system capable of collecting the gas to be measured. As an example, the enrichment system 110 includes a sampling device, an enrichment tube filled with an adsorbent, and a pump. The sampling device is used to introduce the gas sample into the enrichment tube through the pump. The sampling device is connected to the enrichment tube, and a valve for controlling the inlet and outlet of the gas is provided on the enrichment tube. One end of the gas pretreatment system 120 is connected to the enrichment system 110, and the other end is connected to the laser cavity 210 of the optical system 200. The gas pretreatment system 120 is used to further purify the gas collected by the enrichment system 110 to provide a highly pure sample to be measured for the optical system 200, avoid contaminating the laser cavity 210, and extend the service life of the equipment. Exemplarily, the gas pretreatment system 120 includes a first particulate filter 121, an oil and gas separator 122, a gas source dryer 123, a condenser 124, and a linear valve 125 arranged in sequence along the gas transmission direction. Each structure is connected through a gas pipeline. Further, a second particulate filter 126 is also provided between the gas pretreatment system 120 and the laser cavity 210 to avoid the problem that dust enters the laser cavity 210 due to air leakage at some interfaces of the gas pretreatment system 120.

[0049] Please refer to Figure 5, in the present application, the laser detection module 220 includes a light source module 221 and a photodetector 222. The light source module 221 is used to generate a laser beam, and the laser beam can enter the laser cavity 210 and be transmitted therein. The light source module 221 can adopt any device capable of generating a laser beam. In one embodiment, the light source module 221 adopts a high-power quantum cascade laser (QCL). The photodetector 222 is disposed at a corresponding position of the laser cavity 210 for detecting the intensity of the laser beam transmitted from the laser cavity 210. Exemplarily, the laser cavity 210 is disposed between the light source module 221 and the photodetector 222 and is located on the transmission path of the laser beam. The laser cavity 210 is provided with a laser inlet and a laser outlet. The light source module 221 is located on one side of the laser inlet of the laser cavity 210, and the photodetector 222 is located on one side of the laser outlet of the laser cavity 210. The laser beam generated by the light source module 221 enters the laser cavity 210 from the laser inlet. During the transmission of the laser beam in the laser cavity 210, it is absorbed by the gas to be measured in the laser cavity 210, the laser beam decays, and the intensity of the laser beam transmitted from the laser cavity 210 attenuates. The attenuation process of the laser beam can be recorded by the photodetector 222, so that the content of the gas to be measured in the laser cavity 210 can be determined according to the decay time of the laser beam.

[0050] Please refer to Figure 3 and Figure 5, in one embodiment, the laser cavity ring-down cavity 210 includes a sealed housing 211. The gas to be measured is accommodated through the sealed housing 211 to isolate the gas to be measured from the surrounding air, reducing the influence of other gases on the detection accuracy. A plurality of reflectors are provided in the sealed housing 211. After the laser beam enters the sealed housing 211, the laser beam can be reflected back and forth between the reflectors. The shape of the sealed housing 211 is not limited and can be any shape that can accommodate the reflectors, such as a cuboid, a cube, or any regular or irregular polyhedron structure. In this embodiment, the sealed housing 211 is a cuboid structure. The material of the sealed housing 211 needs to have sufficient strength and stiffness to ensure the stability of the system; and the material of the sealed housing 211 cannot react with the gas to be measured to avoid affecting the accuracy of the system test. In some other embodiments, the material of the sealed housing 211 also needs to have certain high-temperature resistance and deformation resistance capabilities. As an example, the material of the sealed housing 211 can be selected from any one of materials such as gold, silver, stainless steel, aluminum, or a combination of several of the above-listed materials. A laser incident port and a laser exit port are provided on the sealed housing 211, and a light-transmitting member is hermetically fixed on the laser incident port, and a light-transmitting member is also hermetically fixed on the laser exit port. The light-transmitting member can be made of a transparent material such as glass or plastic, and the laser beam can pass through the light-transmitting member.

[0051] Please refer to Figure 5 and Figure 6 , in one embodiment, the plurality of reflectors in the sealed housing 211 include a first mirror M0, a second mirror M1, and a third mirror M2. The first mirror M0, the second mirror M1, and the third mirror M2 all adopt high-reflectivity mirrors 214, for example, mirrors with a reflectivity R>99.99%. The arrangement of the first mirror M0, the second mirror M1, and the third mirror M2 forms a V-shaped ring-down cavity. Specifically, the first mirror M0 is a plane mirror, which is arranged at one end of the laser incident port of the sealed housing 211. The second mirror M1 and the third mirror M2 are concave mirrors, such as concave spherical mirrors. The second mirror M1 and the third mirror M2 are respectively arranged at the other end opposite to the first mirror M0 (one end of the laser exit port of the sealed housing 211), and the second mirror M1 and the third mirror M2 are symmetrically arranged, so as to achieve the V-shaped symmetric placement of the first mirror M0, the second mirror M1, and the third mirror M2. The laser entering the sealed housing 211 is reflected back and forth between the three mirrors multiple times (see Figure 6, in the figure, the arrow indicates the laser reflection path), the transmitted light is received by the photodetector 222 and converted into an electrical signal. It should be noted that: the design of the mirror and the cavity length need to meet the stable cavity condition. Among them, the stable cavity means that the light remains in the cavity after multiple round trips in the cavity and will not escape from the cavity of the resonant cavity. Assuming that the cavity length is L (that is, the sum of the two arm lengths of the V-type ring-down cavity, the distance from M0 to M1 and the distance from M0 to M2), and the radii of curvature of the second mirror M1 and the third mirror M2 are R1 and R2 respectively, then the stable condition of the resonant cavity is: 0 < (1 - L / R1)(1 - L / R2) < 1 or (1 - L / R1) = (1 - L / R2). Introducing the cavity geometric parameter factor, g = 1 - L / R, then the stable condition of the resonant cavity can be expressed as: 0 < g1g2 < 1 or g1 = g2 = 0. By adjusting the angle of the high-reflectivity mirror, the light beam in the laser ring-down cavity 210 can be completely coincident with the optical axis, realizing the mode matching of the laser beam and forming a cavity enhancement system. This application can greatly increase the absorption optical path through the laser ring-down cavity 210, improve the signal-to-noise ratio and detection limit, and because the detected laser ring-down time is not affected by the light intensity fluctuation, it has high stability. At the same time, combined with the technical characteristics of the V-type laser ring-down cavity 210, while greatly increasing the absorption optical path, the volume of the device is reduced, and the detection of high-precision carbon-14 gas with a small volume can be realized.

[0052] Further, an air inlet 212 and an air outlet 213 are also provided on the sealed housing 211. The air inlet 212 is communicated with the gas path system 100 for introducing the gas to be measured into the laser ring-down cavity 210, and the air outlet 213 is used to discharge the gas in the laser ring-down cavity 210. In this embodiment, two air outlets 213 are provided on the sealed housing 211, and the two air outlets 213 respectively correspond to the V-type double channels of the internal channels of the laser ring-down cavity 210. When replacing the gas, the double air outlets 213 are used to simultaneously replace the gas in the double channels. This design can reduce the sample amount required for detection. The on-line monitoring device further includes a vacuum pump 130, which is communicated with the air outlet 213 on the sealed housing 211 for sucking the gas in the laser ring-down cavity 210 to form a vacuum in the laser ring-down cavity 210. In this embodiment, the vacuum pump 130 can be connected to the air outlet 213 on the sealed housing 211 through a pipeline. Preferably, a third particulate filter 127 is provided on the pipeline between the vacuum pump 130 and the air outlet 213 of the sealed housing 211 to avoid the problem that the gas flows back and introduces dust due to the failure of the vacuum pump 130.

[0053] Please refer to Figure 5, in one embodiment, the laser detection module 220 may further include a mirror 225. The mirror 225 is used to change the transmission direction of the laser beam, and the laser beam can be transmitted into the laser cavity 210 after passing through the mirror 225. The number and setting angle of the mirrors 225 are not limited, and only need to ensure that the optical path can accurately enter the laser cavity 210. Exemplarily, two mirrors 225 are provided in this application. The two mirrors 225 are oppositely arranged at the corner of the sealed housing 211. For example, the included angle between one mirror 225 and the laser beam emitted from the matching lens 224 is set to 45°, and the other mirror 225 is symmetrically arranged with it, and the laser beam emitted from the other mirror 225 just enters the laser cavity 210.

[0054] A converging lens 226 is further provided between the laser cavity 210 and the photodetector 222. The converging lens 226 is a convex lens and has the function of converging light rays, and can focus the beam emitted from the laser cavity 210 onto the photodetector 222. Preferably, an anti-reflection film (not shown in the figure) consistent with the wavelength range of the laser is provided on the converging lens 226, which can reduce the reflected light and increase the intensity of the transmitted light, thereby improving the intensity of the optical signal received by the photodetector 222.

[0055] Further, in order to reduce the noise during the test and improve the accuracy of the measurement result, an optical isolator and a matching lens may be further provided between the light source module 221 and the laser cavity 210, and both the optical isolator and the matching lens are located on the transmission path of the laser beam, and can be specifically set according to actual needs.

[0056] Please refer to Figure 3 and Figure 5 , in one embodiment, the optical system 200 further includes a spectral box 230. The laser cavity 210 and the laser detection module 220 are both arranged in the spectral box 230. To ensure the stability of the system, an optical bottom plate 231 is provided in the spectral box 230. The optical bottom plate 231 is fixed at the bottom of the spectral box 230 and can be used as a base for supporting and fixing other optical elements. It can be made of a flat plate made of materials such as metal and glass with good stability and mechanical strength. The light source module 221, the photodetector 222, the mirror 225 and the converging lens 226 are all arranged on the optical bottom plate 231. Preferably, a shock-absorbing plate 232 is further provided at the bottom of the optical bottom plate 231. The shock-absorbing plate 232 is a shock-absorbing plate made of materials such as rubber, air cushion or composite materials, and can effectively isolate the bottom vibration and ensure the stability of the optical elements. The cooperation of the optical bottom plate 231 and the shock-absorbing plate 232 can effectively reduce the influence of vibration on the experiment and the equipment, thereby improving the measurement accuracy and experimental reliability.

[0057] Please refer to Figure 5, in one embodiment, a temperature regulating device is further provided in the spectral box 230. The temperature regulating device is used to control the temperature in the spectral box 230. For example, the temperature regulating device includes a temperature sensor and a temperature control fan 233. The temperature sensor is disposed in the spectral box 230 for detecting the temperature in the spectral box 230, and the temperature control fan 233 is used to adjust the temperature in the spectral box 230. Further, a pressure detecting device, such as a pressure sensor, is also provided in the spectral box 230 for detecting the gas pressure in the spectral box 230.

[0058] Please refer to Figure 3 and Figure 7 , in one embodiment, the electronic control system 300 includes a laser driving module 310, a shutdown circuit module 320, a signal generating module 330, an adder, a data processing module, and a power supply module 360. Among them, the laser driving module 310 is electrically connected to the light source module 221 and is used to drive and control the current of the light source module 221. The shutdown circuit module 320 is electrically connected to the light source module 221 and is used to control the shutdown of the light source module 221 to form a decay signal in the laser cavity 210. The signal generating module 330 is used to generate a sawtooth wave signal and a DC bias signal to realize the scanning of the absorption wavelength, and the intensity of the generated signal can be set by the user according to actual needs; the adder is integrated with the shutdown circuit module 320. The adder is electrically connected to the signal generating module 330 and the laser driving module 310. The adder is used to superimpose the sawtooth wave signal and the DC bias signal, and the superimposed signal enters the laser driving module 310. The laser driving module 310 drives and controls the current of the light source module 221 according to the superimposed signal. The data processing module is electrically connected to the photodetector 222 and is used to collect and process the data transmitted from the photodetector 222. Exemplarily, the data processing module may adopt the structure of a data acquisition card 340 and a computer main board 350. Among them, the data acquisition card 340 is electrically connected to the photodetector 222, and the computer main board 350 is electrically connected to the data acquisition card 340. The data acquisition card 340 can collect the change data of the laser beam intensity detected by the photodetector 222, and the computer main board 350 can process the collected change data of the laser beam intensity and compare it with the calibration parameters to quickly determine the concentration of the gas to be measured. The power supply module 360 is used to provide power support for each component in the device.

[0059] Please refer to Figure 7, in one embodiment, the electronic control system 300 further includes a temperature control module 370 and a detector temperature control 371. The temperature control module 370 is electrically connected to the computer main board 350. The temperature control module 370 is used to control the temperature of the light source module 221 and the internal environment temperature of the spectral box 230. The detector temperature control 371 is electrically connected to the photodetector 222. The detector temperature control 371 can reduce the temperature of the photodetector 222, thereby reducing the interference of random noise on the signal, improving the signal-to-noise ratio of the signal, and improving the measurement accuracy. Further, the electronic control system 300 further includes a voltage control module 380. The voltage control module 380 is used to control the gas pressure inside the laser cavity 210 and is electrically connected to the computer main board 350. Specifically, the voltage control module 380 controls the pressure by monitoring the air pressure in the laser cavity 210 and feeding it back to the linear valve 125. Even further, the electronic control system 300 further includes a receiving circuit module 390. The receiving circuit module 390 is electrically connected to the computer main board 350. The receiving circuit module 390 is electrically connected to the temperature sensor and the pressure sensor. The temperature sensor and the pressure sensor are used to receive the temperature and pressure data of the environment. The received temperature and pressure data are fed back to the computer main board 350 through the receiving circuit module 390. The computer main board 350 then controls the semiconductor refrigeration chip through the temperature control module 370 and cooperates with the temperature control fan 233 to control the temperature inside the spectral box 230; the pressure value inside the spectral box 230 is adjusted by controlling the linear valve 125 through the voltage control module 380.

[0060] Please refer to Figures 1 to 3, in one embodiment, the optical system 200 and the electronic control system 300 are integrated to achieve an integrated structure of the on-line monitoring device. Specifically, the on-line monitoring device further includes a main body housing 400, which can be any cavity structure capable of accommodating the optical system 200 and the electronic control system 300. In this embodiment, the main body housing 400 is a cuboid structure, and a bracket 411 is provided inside it. The bracket 411 is divided into upper and lower layers. The upper layer is used to place the optical system 200, and the lower layer is used to place the electronic control system 300. An air inlet 401 and an air outlet 402 are provided on the main body housing 400. The outside of the air inlet 401 is connected to the gas path system 100, and the inside is connected to the air inlet 212 of the laser cavity 210. The inside of the air outlet 402 is connected to the air outlet 213 of the laser cavity 210, and the outside is connected to the vacuum pump 130. Thus, the gas to be measured processed by the gas path system 100 enters the laser cavity 210 through the air inlet 401 of the housing and the air inlet 212 of the laser cavity 210 in sequence. In this way, during the transmission of the laser beam in the laser cavity 210, it is absorbed by the gas to be measured in the laser cavity 210, the laser beam undergoes decay, and the intensity of the laser beam transmitted from the laser cavity 210 is attenuated. The photodetector 222 can record the attenuation process of the laser beam, and thus determine the concentration of the gas to be measured in the laser cavity 210 according to the decay time of the laser beam. After the test, under the action of the vacuum pump 130, the gas to be measured is discharged through the air outlet 213 of the laser cavity 210 and the air outlet 402 of the housing. Further, a driver control window 406 is also provided on the main body housing 400 for controlling the operation of the laser drive module 310.

[0061] To achieve better heat dissipation of the on-line monitoring device, a heat dissipation port 403 is also provided on the main body housing 400. The heat dissipation port 403 can be set to one or multiple, and can be specifically selected according to the actual heat dissipation requirements. The heat dissipation port 403 can be set at any position on the main body housing 400 that does not affect other structures. As an example, the heat dissipation port 403 is set at the bottom and top of the side wall of the main body housing 400. Further, since the light source module (laser) 221 generates a large amount of heat during operation, an external cooling device such as a water chiller is required to control its temperature. Therefore, a water cooler interface 405 is also provided on the main body housing 400, and this interface is used to connect to an external water cooling pipeline for controlling the temperature of the light source module 221.

[0062] A folding handle 404 is also provided on the main body housing 400 to facilitate the movement of the detection device. The folding handle 404 is provided on the side walls on both sides of the main body housing 400, and it can adopt any form in the art that can realize the movement of the device. In this embodiment, two folding handles 404 are oppositely arranged on each side wall of the main body housing 400, so that when moving the device, both hands can be used for gripping.

[0063] The main body housing 400 is also provided with a plurality of signal transmission interfaces, such as a USB expansion port 407, an SMA interface 408, etc., which can realize the connection and signal transmission between various electronic devices.

[0064] The main body housing 400 is also provided with a main power switch 410 and a power switch 409 for the electronic control system and the optical system to control the opening and closing of the detection device.

[0065] Before the online monitoring device provided by the present invention is put into use, it needs to be system-calibrated. For example, when measuring the 14 C content in 14 CO2 gas, a standard gas with a known concentration needs to be introduced into the laser cavity ring-down cavity 210, and then the device is made to measure the standard gas with the known concentration, analyze the relationship between the detection signal and the target gas concentration, and calculate the calibration function of the laser cavity ring-down spectrometer according to the response value of the laser cavity ring-down spectrometer and the concentration of the standard gas. The specific calibration process is as follows:

[0066] Step 1. Preparation work: Before starting the calibration, it is necessary to ensure that the laser cavity ring-down spectrometer has been correctly installed and stabilized and connected to the corresponding data acquisition system. In the software interface, it is possible to monitor whether the parameters of the experimental system are normal and stable. At the same time, a standard gas with a known concentration needs to be prepared and connected to the standard gas port of the detection system.

[0067] Step 2. Preheating: Before performing the calibration, it is necessary to preheat the laser cavity ring-down spectrometer to ensure that it reaches a stable state. The preheating time usually depends on the use environment. Mainly, the system temperature control requires long-term regulation and stabilization, and it is generally recommended to be more than 60 minutes.

[0068] Step 3. Calibration analysis: First, it is necessary to use a vacuum pump to completely empty the gas inside the optical resonator, and then use solenoid valves and linear valves to control the flow rate to slowly inject the standard gas into the optical resonator (laser cavity ring-down cavity), observe and record its output signal and concentration results, and analyze the relationship between the detection signal and the target gas concentration. The time for recording the output signal should be long enough to ensure the accuracy of the calibration experimental system.

[0069] Step 4. Calculate the calibration coefficient: According to the response value of the laser cavity ring-down spectrometer and the concentration of the standard gas, calculate the calibration function of the laser cavity ring-down spectrometer for converting the detected output signal into the concentration of the target gas, and use software to calibrate and correct the data results with measurement deviations.

[0070] Step 5. Verify the calibration result: In order to verify the calibration result, a traditional liquid scintillation method is used for comparative verification.

[0071] Step 6. Record the calibration result: Record the calibration result in the calibration report, including the calibration date, calibration coefficient, response value, measurement result, etc. This information can help users better understand and use the device, and ensure its long-term stability and reliability.

[0072] Please refer to Figure 9 , the present invention also provides a detection method based on the above online monitoring device, including the following steps:

[0073] S1. Turn on the power of the online monitoring device;

[0074] S2. Clean and evacuate the online monitoring device;

[0075] S3. Inject the gas to be measured into the gas path system. The gas to be measured enters the laser cavity ring-down through the gas path system and is enclosed in the laser cavity ring-down;

[0076] S4. The laser beam generated by the light source module attenuates in the laser cavity ring-down. The concentration information of the gas sample to be measured is obtained by analyzing the ring-down time when there is an empty cavity and when there is an absorption medium.

[0077] Specifically, step S1 includes turning on the main power switch 410 on the main body housing 400, and the fan inside the main body housing 400 starts; then turn on the power of the electronic control system and the optical system 409 and the computer power supply in sequence; then turn on the power of the laser drive module 310, and set the drive current of the laser (light source module 221) to the parameter corresponding to the central wavelength of the gas to be measured.

[0078] Step S2 is to clean the whole device before the formal measurement to prevent the residual gas inside the device from affecting the measurement result. The specific process is as follows: First, use a vacuum pump to evacuate the gas in the whole gas path, and then repeatedly clean it with high-purity nitrogen. After cleaning, use a vacuum pump to extract the ultimate vacuum of the whole gas path, and observe the air pressure shown by the barometer. There should be no obvious air leakage. Observe the absorption signal result, which is a standard stable sawtooth signal (determined by the particularity of the odd and even modes of the three-mirror optical resonator), and then inject the sample gas.

[0079] Please refer to Figure 8, Steps S3 and S4 are the measurement and analysis processes: Using a tunable laser (QCL laser) as the light source, the laser beam forms mode matching with the laser cavity ring-down cavity 210. By scanning the current of the laser, the beam that meets the mode matching is enhanced in the laser cavity ring-down cavity 210. When the off-circuit module 320 detects that the cavity mode reaches the set threshold, the laser is turned off, and the laser intensity will decay exponentially. The time when it decays to 1 / e is taken as the ring-down time. The detection system obtains the concentration information of the gas sample to be measured by analyzing the ring-down times when the cavity is empty and when there is an absorption medium. This analysis process follows the existing process of detecting gas concentration by cavity ring-down spectroscopy (CRDS), which will not be elaborated here.

[0080] It should be noted that the entire measurement process is controlled by the supporting application software. This application software can use any software that can be used for detecting gas concentration by cavity ring-down spectroscopy (CRDS), which will not be elaborated here. Before executing step S2, it is necessary to start the supporting application software and observe the parameter status of the system through the application software. At the same time, parameters such as the scanning frequency and scanning amplitude are set in the software. Then click the start measurement button in the software, and the spectral detection device starts to run. Click the clear button in the software, and the system will open the vacuum pump to evacuate the laser cavity ring-down cavity 210. When the vacuum degree reaches the set value, the solenoid valve before the vacuum pump will be closed by the system.

[0081] Next, click the sampling button in the software, and the system will control the valve at the sampling end to automatically start the sampling operation. After sampling, the valve will be closed again, and the sample gas will be sealed in the laser cavity ring-down cavity 210. After the test is completed, click the save button in the software to save the current environmental parameters and measurement and analysis results.

[0082] In an embodiment, the online monitoring device of the present invention is used to test a CO2 sample containing carbon-14, and the test process is as follows:

[0083] First, evacuate the gas in the overall gas path, and then repeatedly clean it with high-purity nitrogen. After cleaning, use a vacuum pump to extract the ultimate vacuum of the overall gas path, and observe the air pressure shown by the barometer. There should be no obvious air leakage. Observe the absorption signal result, which is a standard stable sawtooth signal (determined by the particularity of the odd and even modes of the three-mirror optical resonator), and then the sample gas can be injected. Sampling is carried out using a syringe, and 2 ml of 14CO2 gas is injected into the gas path through the sample gas injection port. After injection, observe the increase in air pressure. Since it takes a certain amount of time for the gas to reach equilibrium, wait for 2 minutes and then perform pressure control. Control the pressure to the set pressure and wait for a period of time. Observe the signal change and collect the signal concentration measurement results.

[0084] After that, a dilution experiment is carried out. Inject 1 ml of high-purity nitrogen gas from the sample gas injection port for dilution. The pressure control is the same as when injecting the sample gas before, and it is necessary to wait for equilibrium and then control the pressure to the set value (the experimental pressure is 20 Torr). After dilution, collect the signal concentration measurement results and record them. Repeat this process for multiple groups of different concentrations 14 of CO2 gas measurement.

[0085] The experimental results are as Figure 10 shown. In this embodiment, the sample gas is diluted and measured 4 times, and it is re-calibrated according to the sample gas. The average values of the measured sample gases with different concentrations are shown by the fonts in the figure, which are 4.52 ppb, 3.47 ppb, 2.09 ppb, 1.40 ppb, and 0.89 ppb respectively, and the signal fluctuation when there is no gas is tested. The experimental results show that the lowest concentration detected by the on-line monitoring device of the present invention is about 0.89 ppb, the detection accuracy is about ±0.4 ppb, and the signal fluctuation when there is no gas absorption is about ±0.3 ppb.

[0086] To evaluate the detection sensitivity of this device, we continuously measured the cavity ring-down time for a long time (>1 hour). The measurement results are as Figure 11 shown. It can be seen that the average value of the cavity ring-down time is about 9.1 μs. Use the cavity ring-down time to perform Allan variance analysis to obtain the Allan variance curve. The absorption coefficient at the starting point of the curve is 9.0×10 -9 cm -1 , and then it shows a distribution characteristic of first decreasing and then increasing, indicating that the system is in a stable state for a long time. When the integration time is 687 seconds, the detection limit of the system reaches 2.5×10 -10 cm -1 , corresponding to the minimum detectable 14 CO2 concentration of 1.2 ppt. Then, as the system drift gradually dominates, increasing the integration time can no longer effectively reduce the detection limit.

[0087] The on-line monitoring device for radionuclides in the gaseous effluent of power plants provided by the present invention uses cavity-enhanced absorption spectroscopy technology, which enables the laser to reflect back and forth between the high-reflectivity mirrors, increasing the interaction path of the laser with the medium and enhancing the absorption spectrum signal. As one of them, cavity ring-down spectroscopy overcomes the influence of the fluctuations of light intensity and coupling efficiency, measures the temporal variation of light intensity in the cavity, and inversely calculates the gas concentration. The sensitivity can reach 10 -10In addition, the laser cavity of the present invention adopts a three-mirror V-shaped cavity structure, which can effectively avoid the direct feedback of the incident light to the laser and cause performance loss compared with the traditional linear cavity. In addition, while ensuring the long optical path performance, the V-shaped cavity structure effectively reduces the volume of the laser cavity, and a portable measurement system can be realized. An enrichment system and a gas pretreatment system are designed for the online monitoring environment of the gaseous effluents from nuclear power plants, which can effectively capture high-concentration carbon dioxide from the chimney of the nuclear power plant for detection. At the same time, the gas pretreatment system can ensure that the samples entering the laser cavity have high cleanliness and extend the service life of the overall system. Therefore, the present invention effectively overcomes some practical problems in the prior art and thus has high utilization value and practical significance.

[0088] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An on-line monitoring device for radioactive nuclides in the gaseous effluent of a nuclear power plant, characterized in that, Comprising: An air path system for collecting gaseous effluents from a nuclear power plant; An optical system including a laser cavity ring-down and a laser detection module. The laser cavity ring-down is in communication with the air path system and is used to accommodate a gas to be measured. The laser detection module includes a light source module and a photodetector. The light source module is used to generate a laser beam, and the laser beam can enter the laser cavity ring-down and propagate therein. The photodetector is disposed at a corresponding position of the laser cavity ring-down for detecting the intensity of the laser beam transmitted from the laser cavity ring-down; An electric control system electrically connected to the laser detection module for controlling and processing the transmission signals of the laser detection module.

2. The online monitoring device according to claim 1, characterized in that, The laser cavity ring-down includes a sealed housing and a first mirror, a second mirror, and a third mirror disposed inside the sealed housing. The first mirror is a plane mirror with a high reflectivity. The second mirror and the third mirror are concave mirrors with a high reflectivity. The first mirror is disposed at one end of the sealed housing, and the second mirror and the third mirror are respectively disposed at the other end opposite to the first mirror and form a V-shaped cavity ring-down with the first mirror.

3. The on-line monitoring device according to claim 1, characterized in that The laser detection module further includes a mirror and a converging lens. The mirror is disposed between the light source module and the laser cavity ring-down along the transmission path of the laser beam; the converging lens is disposed between the laser cavity ring-down and the photodetector and is located on the transmission path of the laser beam.

4. The online monitoring device according to claim 1, characterized in that, The optical system further includes a spectral box. An optical base plate is provided inside the spectral box, and the laser cavity ring-down and the laser detection module are both disposed on the optical base plate.

5. The online monitoring device according to claim 2, characterized in that, An air inlet hole and two air outlet holes are provided on the sealed housing of the laser cavity ring-down. The air inlet hole is disposed at a position of the sealed housing close to the first mirror, and the two air outlet holes are respectively disposed at positions of the sealed housing corresponding to the second mirror and the third mirror.

6. The on-line monitoring device according to claim 4, wherein The electric control system includes a laser driving module, a turn-off circuit module, a signal generating module, an adder, a data processing module, and a power supply module. The laser driving module is electrically connected to the light source module, the turn-off circuit module is electrically connected to the light source module. The signal generating module is used to generate a sawtooth wave and a DC bias signal. The adder is electrically connected to the signal generating module and the laser driving module; the data processing module is electrically connected to the photodetector; the power supply module is used to provide power support for each structure.

7. The on-line monitoring device according to claim 6, wherein, The electric control system further includes a temperature control module and a pressure control module. The temperature control module is used to control the temperature of the light source module and the internal temperature of the spectral box; the pressure control module is used to control the gas pressure inside the laser cavity ring-down; the temperature control module and the pressure control module are respectively electrically connected to the data processing module.

8. The on-line monitoring device according to claim 7, wherein A temperature regulating device and a temperature sensor are provided inside the spectral box. The temperature sensor is electrically connected to the data processing module, and the temperature regulating device is electrically connected to the temperature control module.

9. The on-line monitoring device according to claim 7, characterized in that A pressure sensor is provided inside the laser cavity ring-down, and the pressure sensor is electrically connected to the data processing module.

10. The on-line monitoring device according to claim 1, characterized in that, The gas path system includes: an enrichment system and a gas pretreatment system. The enrichment system is used to collect carbon dioxide gas samples collected from the chimney of a nuclear power plant. One end of the gas pretreatment system is connected to the enrichment system, and the other end is connected to the laser cavity; the gas pretreatment system includes a first particulate filter, an oil-gas separator, a gas source dryer, a condenser, and a linear valve arranged in sequence along the gas transmission direction.

11. The on-line monitoring device according to claim 10, characterized in that, A second particulate filter is further provided between the gas pretreatment device and the laser cavity.

12. The online monitoring device according to claim 1, characterized in that, It further includes a vacuum pump, which is connected to the laser cavity and is used to pump the gas in the laser cavity; a third particulate filter is provided between the vacuum pump and the laser cavity.

13. The on-line monitoring device according to claim 2, characterized in that, The material of the sealed housing of the laser cavity includes any one of gold, silver, stainless steel, and aluminum.

14. The online monitoring device according to claim 1, characterized in that, The light source module uses a quantum cascade laser.

15. A monitoring method based on the on-line monitoring device according to any one of claims 1-14, characterized in that, It includes the following steps: Turn on the power of the on-line monitoring device; Clean and evacuate the on-line monitoring device; Inject the gas to be measured into the gas path system of the on-line monitoring device. The gas to be measured enters the laser cavity of the on-line monitoring device through the gas path system and is sealed in the laser cavity; The laser beam generated by the light source module of the on-line monitoring device attenuates in the laser cavity, and the concentration information of the gas to be measured is obtained by analyzing the decay time when there is a cavity and when there is an absorption medium.

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