Carbon-14 on-line monitoring method suitable for gaseous effluent of nuclear power station

Abstract

The invention discloses a carbon-14 on-line monitoring method suitable for gaseous effluent of a nuclear power plant, and relates to the technical field of carbon-14 detection, and the carbon-14 on-line monitoring method comprises the following steps: step 1, preparing a dual-channel tunable laser, and enabling laser emitted by the dual-channel tunable laser to respectively correspond to a spectrum of radioactive carbon dioxide and a spectrum of radioactive methane; 2, laser is selected by a galvanometer, passes through an optical isolator, then passes through an acoustic optical modulator and a mode matching unit of a lens and then is coupled to enter a ring-down optical cavity, and the gas concentration is obtained through a formula; step 3, a transmission light intensity signal of the ring-down light cavity is collected and ring-down time is recorded through a photomultiplier, then one path of the photomultiplier is connected to a trigger circuit through an amplification circuit of a detector, and when the transmission light intensity signal in the ring-down light cavity reaches a certain value, an acousto-optic modulator is controlled to cut off a light source; and the other path is sent to a computer for signal processing and data storage. According to the method, methane does not need to be incinerated, and real-time online monitoring of carbon-14 in the gaseous effluent of the nuclear power plant is realized.

Description

Technical Field

[0001] The present invention relates to the field of carbon-14 detection technology. Specifically, it relates to an online monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants. Background Art

[0002] As a clean and efficient energy source, nuclear power plants play an important role in the global energy structure. However, the radioactive substances generated during the operation of nuclear power plants, especially the emission of carbon-14, pose potential risks to the environment and public health. Existing carbon-14 measurement methods cannot achieve real-time online monitoring, and there are problems such as radioactive waste treatment.

[0003] In the prior art, sampling devices commonly used in nuclear power plants perform bubbling absorption on carbon-14 in the chimney. Carbon is a non-metallic element with relatively stable properties. Any form of elemental carbon or carbon-containing combustible substances can generate CO2 when burned in air, and CO2 reacts with water to form carbonic acid. CO2 can be enriched and precipitated in an alkaline solution such as CaOH, and then after drying, enrichment, and grinding, the activity is measured using a liquid scintillation detector in the laboratory. The directly enriched sampling device has the problem of being unable to measure organic carbon-14, and organic carbon-14 accounts for about 50-60% of the total amount, directly affecting the normal operation of the sampling device. Sampling enrichment measurement still cannot solve the problem of real-time online measurement of carbon-14, and the method of using liquid scintillation measurement will generate radioactive liquid waste, bringing additional costs and management burdens. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems raised in the above background art, and then propose an online monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] An online monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants, comprising:

[0007] Step 1: Prepare a dual-channel tunable laser so that the emitted laser corresponds to the spectra of radioactive carbon dioxide and radioactive methane respectively;

[0008] Step 2: The laser is first selected by a galvanometer and then passes through an optical isolator, and then passes through an acousto-optic modulator and a mode matching unit of a lens and is coupled into a ring-down cavity. The laser reflects multiple times in the ring-down cavity to form a stable light field distribution. The absorption parameters of the sample are obtained by measuring the ring-down time in the ring-down cavity, and the gas concentration is known through the calibration of a standard gas. The calculation formula is:

[0009]

[0010] In the formula, α represents the absorption of the sample under the condition of wavelength v, c is the speed of light, τ is the current decay time, and τ0 represents the original decay time;

[0011] Step 3: Collect the transmitted light intensity signal of the decay optical cavity through a photomultiplier tube and record the decay time. Then, one path of the photomultiplier tube is connected to the trigger circuit through the amplifier circuit of the detector. When the transmitted light intensity signal in the decay optical cavity reaches a certain value, the acousto-optic modulator is controlled to cut off the light source, and the other path is sent to a computer for signal processing and data storage.

[0012] In the above solution, further, the dual-channel tunable laser includes two tunable semiconductor lasers. The laser output by one tunable semiconductor laser corresponds to the spectrum of radioactive carbon dioxide, and the laser output by the other tunable semiconductor laser corresponds to the spectrum of radioactive methane.

[0013] In the above solution, further, the decay optical cavity is composed of two high-reflection mirrors. A piezoelectric ceramic is attached behind one of the high-reflection mirrors and is driven by a driving power supply to adjust the cavity length of the decay optical cavity.

[0014] In the above solution, further, the cavity length of the decay optical cavity is 39.5 cm.

[0015] In the above solution, further, the driving power supply of the piezoelectric ceramic is a triangular wave and is adjusted within the range of 0 - 500 V.

[0016] In the above solution, further, the cavity mode frequency and the laser frequency are resonated by scanning the cavity length of the decay optical cavity through the piezoelectric ceramic;

[0017] When the change amplitude of the cavity length of the decay optical cavity is an integer multiple of half a wavelength, the laser is coupled into the resonant cavity once;

[0018] When the transmitted light intensity signal in the decay optical cavity reaches the set threshold, the trigger circuit gives a trigger signal to the acousto-optic modulator and turns off the laser to prevent the laser from continuing to be coupled into the decay optical cavity;

[0019] The transmitted light intensity signal in the decay optical cavity decays exponentially. At this time, the light intensity decay information is obtained through the detector and then sent to the computer.

[0020] In the above solution, further, the wavelength of the tunable semiconductor laser for measuring radioactive methane is 3040.22 cm-1.

[0021] In the above solution, further, the wavelength of the tunable semiconductor laser for measuring radioactive carbon dioxide is 2209.11 cm-1.

[0022] Furthermore, in the above scheme, when switching to measure carbon dioxide or methane, the laser is switched first by deflecting the galvanometer mirror, and then the piezoelectric ceramic drives the high-reflection mirror at one end of the ring-down optical cavity to move, thereby achieving mode matching of the lens.

[0023] Furthermore, in the above solution, the galvanometer controls different deflection angles through a computer to respectively select two different tunable semiconductor lasers as lasers for measurement.

[0024] Furthermore, in the above scheme, the computer uses wavelet transform to perform noise reduction on the collected attenuation signal, and processes the data by grouping method.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention adopts two tunable narrowband lasers, multiplexes a set of ring-down optical cavities, and adopts a piezoelectric ceramic adjustment method to achieve mode matching, thereby realizing the identification and online monitoring of two gases in one ring-down optical cavity; the carbon-14 in the gaseous effluent of nuclear power plants exists in two forms, carbon dioxide and methane. This technology adopts a ring-down optical cavity measurement method, which can accurately detect these two main substances containing carbon-14 that may exist in the gaseous effluent of nuclear power plants, thereby improving the pertinence and accuracy of the detection, and does not require the incineration of methane, which is more concise, and realizes real-time online monitoring of carbon-14 in the gaseous effluent of nuclear power plants. The measurement accuracy is high, and the generation of radioactive waste can be effectively avoided. The system has good stability and is suitable for long-term continuous monitoring.

[0027] 2. The present invention has high measurement accuracy. The setting of the optical isolator effectively protects the tunable semiconductor laser, prevents it from being damaged by reflected light, prolongs the service life of the equipment, and ensures the stability of the laser light source during the measurement process, which is beneficial to improving the measurement accuracy. The absorption parameters of the sample are determined by measuring the ring-down time, and extremely small amounts of gas absorption can be detected. Low concentrations of carbon-14 in the gaseous effluent of nuclear power plants can also be accurately measured. After calibration with standard gas, the gas concentration can be more accurately known.

[0028] 3. The present invention collects the transmitted light intensity signal and records the decay time in real time through the photomultiplier tube, and can control the acousto-optic modulator to cut off the light source according to the light intensity signal, and processes and saves the signal at the same time, thereby realizing the online real-time monitoring of carbon-14 in the gaseous effluent of the nuclear power plant, which is convenient for timely acquisition of data and making corresponding decisions.

[0029] 4. In the present invention, a series of processes from laser transmission, light intensity signal collection and processing to light source control have a high degree of automation, which reduces manual intervention, reduces human errors, and improves monitoring efficiency and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flowchart of a carbon-14 online monitoring method applicable to the gaseous effluents of nuclear power plants; Specific embodiments

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The present invention will be further described in conjunction with the accompanying drawings and embodiments:

[0032] Referring to the attached Figure 1 As shown, a carbon-14 online monitoring method applicable to the gaseous effluents of nuclear power plants includes:

[0033] Step 1: Prepare two tunable semiconductor lasers. The laser output by one tunable semiconductor laser corresponds to the spectrum of radioactive carbon dioxide, and the laser output by the other tunable semiconductor laser corresponds to the spectrum of radioactive methane;

[0034] Step 2: The laser is first selected by a galvanometer and then passes through an optical isolator, and then is coupled into a ring-down cavity through an acousto-optic modulator and a mode matching unit of a lens. The laser is reflected multiple times in the ring-down cavity to form a stable light field distribution. The absorption parameter of the sample is obtained by measuring the ring-down time in the ring-down cavity, and the gas concentration is known through the calibration of the standard gas. The calculation formula is:

[0035]

[0036] In the formula, α represents the absorption of the sample under the condition of wavelength v, c is the speed of light, τ is the current ring-down time, and τ0 represents the original ring-down time;

[0037] Step 3: The transmitted light intensity signal of the ring-down cavity is collected by a photomultiplier tube and the ring-down time is recorded. Then, one path of the photomultiplier tube is connected to a trigger circuit through the amplifier circuit of the detector. When the transmitted light intensity signal in the ring-down cavity reaches a certain value, the acousto-optic modulator is controlled to cut off the light source, and the other path is sent to a computer for signal processing and data storage.

[0038] In the specific implementation process of the present invention, two tunable semiconductor lasers corresponding to the spectra of radioactive carbon dioxide and radioactive methane respectively provide a targeted light source basis for the subsequent detection of carbon-14-containing carbon dioxide and methane by selecting specific tunable semiconductor lasers to output lasers with corresponding spectra; the laser first passes through a galvanometer selection. The galvanometer can change the propagation direction of the laser, playing a role in screening and guiding the laser; then, by using an optical isolator, the laser reflected back from the optical cavity is prevented from damaging the tunable semiconductor laser itself, ensuring the stable operation of the tunable semiconductor laser; then the laser is coupled into the ring-down optical cavity after passing through the acousto-optic modulator and the mode matching unit of the lens. In the ring-down optical cavity, the laser is reflected multiple times to form a stable light field distribution; according to the principle of ring-down spectroscopy, when the laser is reflected in the cavity, due to the absorption of the laser by the sample, the light intensity will decay exponentially with time; the transmitted light intensity signal of the ring-down optical cavity is collected by a photomultiplier tube and the ring-down time is recorded. Combining the formula, the absorption parameter of the sample can be obtained, and then through the calibration of the standard gas, the gas concentration can be determined; finally, one path of the signal amplified by the photomultiplier tube is connected to the trigger circuit, which controls the acousto-optic modulator to cut off the light source when the transmitted light intensity signal in the ring-down optical cavity reaches a certain value to avoid unnecessary laser energy consumption and possible interference; the other path is sent to the computer for signal processing and data storage, so as to realize the further analysis and storage of the measurement data.

[0039] In the above scheme, the ring-down optical cavity is composed of two high-reflection mirrors (high-reflectivity dielectric films). A piezoelectric ceramic is attached behind one of the high-reflection mirrors and is driven by a driving power supply to adjust the cavity length of the ring-down optical cavity so that the cavity length of the ring-down optical cavity is 39.5 cm; in the scheme, the piezoelectric ceramic is a material with piezoelectric effect. When an electric field is applied to the piezoelectric ceramic, it will undergo a small deformation. Conversely, when pressure or tension is applied to the piezoelectric ceramic, a voltage will be generated at both ends; in this scheme, the characteristic that the piezoelectric ceramic generates deformation under the action of an electric field is utilized; the driving power supply provides voltage for the piezoelectric ceramic, and the piezoelectric ceramic generates a corresponding deformation amount according to the magnitude of the applied voltage. Since the piezoelectric ceramic is attached behind one of the high-reflection mirrors, its deformation amount will directly cause the position of the reflection mirror to change, thereby changing the cavity length of the ring-down optical cavity. By precisely controlling the voltage of the driving power supply, the cavity length can be precisely adjusted to the required 39.5 cm; when the cavity length is the specific value of 39.5 cm, the ring-down optical cavity can meet specific resonance conditions, that is, it matches parameters such as the wavelength and frequency of the incident laser. Only under the resonance conditions can a stable standing wave distribution be formed in the cavity, realizing multiple reflections and effective light-matter interaction, so as to accurately measure the absorption parameter of the sample; and it can make the quality factor of the ring-down optical cavity reach a relatively high level, reduce the loss of light in the cavity, improve the accuracy of ring-down time measurement, and further improve the accuracy of calculating the sample absorption parameter and gas concentration through the ring-down time.

[0040] In the above solution, the resonance between the cavity mode frequency and the laser frequency is achieved by scanning the cavity length of the piezoelectric ceramic ring-down cavity. Among them, the driving power supply of the piezoelectric ceramic is a triangular wave, which is adjusted within the range of 0 - 500V. When the change amplitude of the ring-down cavity length is an integer multiple of half a wavelength, the laser is coupled into the resonant cavity once. When the transmitted light intensity signal in the ring-down cavity reaches the set threshold, the trigger circuit gives a trigger signal to the acousto-optic modulator and turns off the laser to prevent the laser from continuing to be coupled into the ring-down cavity. The transmitted light intensity signal in the ring-down cavity decays exponentially. At this time, the light intensity decay information is obtained by the detector and then sent to the computer. Among them, the wavelength of the tunable semiconductor laser for measuring radioactive methane is 3040.22 cm-1, and the wavelength of the tunable semiconductor laser for measuring radioactive carbon dioxide is 2209.11 cm-1. In the solution, when the transmitted light intensity signal in the ring-down cavity reaches the set threshold, it means that the optical field in the cavity has reached a suitable state. At this time, the trigger circuit gives a trigger signal to the acousto-optic modulator. After receiving the trigger signal, the acousto-optic modulator will change its working state, turn off the laser, and prevent the laser from continuing to be coupled into the ring-down cavity. This is to avoid too much laser energy entering the cavity, affecting the measurement of the ring-down process, and at the same time preventing damage to the equipment caused by too high light intensity in the cavity. After turning off the laser, due to factors such as the absorption of the sample and the small transmission of the cavity mirror, the transmitted light intensity signal in the ring-down cavity will decay exponentially. Subsequently, the detector can detect the light intensity decay information in real time and convert it into an electrical signal or other forms, and then send it to the computer for further processing and analysis. By analyzing the light intensity decay curve, the ring-down time can be accurately calculated. Combining with the relevant formulas mentioned above, the absorption parameters of the sample can be obtained, and then information such as the concentration of the gas can be determined.

[0041] In the above solution, when switching to measure carbon dioxide or methane, first, the switching of the laser is achieved by the deflection of the galvanometer. The galvanometer is controlled by a computer to have different deflection angles to respectively select two different tunable semiconductor lasers as the lasers for measurement. Then, the piezoelectric ceramic drives the high-reflection mirror at one end of the ring-down optical cavity to move to achieve the mode matching of the lens. In the solution, two tunable semiconductor lasers corresponding to the spectra of radioactive carbon dioxide and radioactive methane are prepared. When it is necessary to switch the measurement object, the computer controls the galvanometer to deflect at different angles. By precisely setting the deflection angle of the galvanometer, the galvanometer reflects the laser emitted by one of the tunable semiconductor lasers into the subsequent optical path, while deflecting the laser of the other laser away from the optical path, thus realizing the selection of the lasers output by different lasers (for example, when measuring carbon dioxide, the computer controls the galvanometer to make the laser of the laser corresponding to the carbon dioxide spectrum pass through the subsequent optical path; when measuring methane, the galvanometer is controlled to make the laser of the laser corresponding to the methane spectrum pass through, so as to achieve the purpose of switching the measurement of different gases); when switching the laser to measure different gases, since the laser modes output by different lasers may be different, at this time, the piezoelectric ceramic generates a small deformation under drive. This deformation causes the high-reflection mirror at one end of the ring-down optical cavity to displace, thereby changing the cavity length and the internal optical field distribution of the ring-down optical cavity. At the same time, the change in the cavity length and the optical field distribution also affects the relative position and angular relationship between the laser and the lens, and further realizes the adjustment of the lens mode, so that the mode of the laser can better match the mode of the ring-down optical cavity (for example, when switching to another laser, the piezoelectric ceramic makes appropriate displacement adjustments to enable the lens to focus and collimate the new laser properly, ensuring that the laser can be coupled into the ring-down optical cavity in the best state, providing good conditions for accurately measuring the gas absorption parameters and concentration in the subsequent process).

[0042] In the above solution, the computer uses wavelet transform to denoise the collected attenuation signal and processes the data by the grouping method. In the solution, the grouping method divides the collected data into several groups according to certain rules (for example, the data collected continuously for a period of time can be divided into a group, or the data can be divided into different groups according to different measurement conditions). The purpose of doing this is to better analyze and process the data because the data in different groups may have different characteristics and laws. By analyzing and processing the data of each group separately, the statistical characteristics of each group of data, such as mean, variance, maximum value, minimum value, etc., can be calculated to understand the distribution of the data within the group. Further signal processing or feature extraction can also be performed on each group of data. For example, wavelet transform can be applied to each group of data for more refined analysis, or outliers or feature points in each group of data can be found. By analyzing the data of different groups, potential laws and changing trends in the data can be discovered, which helps to more accurately understand and interpret the measurement results. At the same time, the efficiency and accuracy of data processing can also be improved.

[0043] The above has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants, characterized in that: It includes: Step 1: Prepare a dual-channel tunable laser so that the lasers emitted respectively correspond to the spectra of radioactive carbon dioxide and radioactive methane; Step 2: The laser is first selected by a galvanometer mirror and then passes through an optical isolator, and then is coupled into a ring-down optical cavity after passing through an acousto-optic modulator and a mode matching unit of a lens. The laser reflects multiple times in the ring-down optical cavity to form a stable light field distribution. The absorption parameter of the sample is obtained by measuring the ring-down time in the ring-down optical cavity, and then the gas concentration is known through the calibration of the standard gas. The calculation formula is: In the formula, α represents the absorption of the sample under the condition of wavelength v, c is the speed of light, τ is the current ring-down time, and τ0 represents the original ring-down time; Step 3: The transmitted light intensity signal of the ring-down optical cavity is collected by a photomultiplier tube and the ring-down time is recorded. Then, one path of the photomultiplier tube is connected to a trigger circuit through the amplifier circuit of the detector. When the transmitted light intensity signal in the ring-down optical cavity reaches a certain value, the acousto-optic modulator is controlled to cut off the light source, and the other path is sent to a computer for signal processing and data storage.

2. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 1, characterized in that: The dual-channel tunable narrow-band laser includes two tunable semiconductor lasers. The laser output by one tunable semiconductor laser corresponds to the spectrum of radioactive carbon dioxide, and the laser output by the other tunable semiconductor laser corresponds to the spectrum of radioactive methane.

3. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 2, characterized in that: The ring-down optical cavity is composed of two high-reflection mirrors. A piezoelectric ceramic is attached behind one of the high-reflection mirrors and is driven by a driving power supply to adjust the cavity length of the ring-down optical cavity.

4. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 3, characterized in that: The cavity length of the ring-down optical cavity is 39.5 cm.

5. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 4, characterized in that: The driving power supply of the piezoelectric ceramic is a triangular wave and is adjusted within the range of 0 - 500 V.

6. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 5, characterized in that: The resonance between the cavity mode frequency and the laser frequency is realized by scanning the cavity length of the ring-down optical cavity through the piezoelectric ceramic; When the change amplitude of the cavity length of the ring-down optical cavity is an integer multiple of half a wavelength, the laser is coupled into the resonant cavity once; When the transmitted light intensity signal in the ring-down optical cavity reaches the set threshold value, the trigger circuit gives a trigger signal to the acousto-optic modulator and turns off the laser to prevent the laser from continuing to be coupled into the ring-down optical cavity; The transmitted light intensity signal in the ring-down optical cavity decays exponentially. At this time, the light intensity decay information is obtained through the detector and then sent to the computer.

7. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 6, characterized in that: The wavelength of the tunable semiconductor laser for measuring radioactive methane is 3040.22 cm-1.

8. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 7, characterized in that: The wavelength of the tunable semiconductor laser for measuring radioactive carbon dioxide is 2209.11 cm-1.

9. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 8, characterized in that: When switching to measure carbon dioxide or methane, first the laser is switched by the deflection of the galvanometer mirror, and then the high-reflection mirror at one end of the ring-down optical cavity is driven by a piezoelectric ceramic to move, so as to achieve the mode matching of the lens.

10. An on-line monitoring method for carbon-14 applicable to the gaseous effluents of nuclear power plants according to claim 9, characterized in that: The galvanometer mirror is controlled by a computer to have different deflection angles, so as to respectively select two different tunable semiconductor lasers as the laser for measurement.

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