Detection method and monitoring system for radioactive gas in nuclear facility chimney

Abstract

The invention is applicable to the field of nuclear power detection, and discloses a detection method and a monitoring system for radioactive gas in a chimney of a nuclear facility, and the method comprises the following steps: S1, measuring a numerical value without aerosol particles by using a high-purity germanium detector to obtain a background counting rate nb, and S2, measuring an aerosol standard substance by using the high-purity germanium detector to obtain detection efficiency E; s3, transmitting the aerosol particles in the chimney of the nuclear facility to an ionization unit, and ionizing the aerosol particles by the ionization unit; s4, measuring the mass of the aerosol particles at the two ends of the sampling tube by the optical aerosol particle size spectrometer, and obtaining an aerosol penetration coefficient T through two times of mass measurement; and S5, starting a high-purity germanium detector to detect the ionized aerosol particles in the step S3, and calculating the activity concentration of the radioactive aerosol gamma nuclide according to the background counting rate nb in the step S1, the detection efficiency E in the step S2 and the aerosol penetration coefficient T in the step S4.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power detection, and in particular to a detection method and monitoring system for radioactive gas in a nuclear facility chimney. Background Art

[0002] During normal operation, abnormal operation, and nuclear accidents, nuclear facilities emit gaseous radioactive effluents into the atmosphere through chimneys. These effluents contain radioactive suspended particles ranging in size from 0.01 to tens of microns. Once released into the environment, they can be inhaled and retained in the body, causing internal irradiation and radiation damage. Therefore, the sampling and measurement of radioactive aerosols is a key research topic in radiation protection and environmental monitoring.

[0003] The penetration efficiency of radioactive aerosols in nuclear facility chimneys is a key indicator of sampling representativeness. As aerosol particles are transported through the sampling and transmission system, they experience deposition losses on the inner surfaces of the transmission pipes due to various factors, such as gravitational settling, inertial collisions, and turbulence, reducing penetration efficiency. The "Technical Specifications for Radioactive Monitoring of Effluents from Nuclear Facilities" require that "the collection efficiency of airborne effluent samples must be rigorously calibrated. For airborne effluent sampling, the pipeline deposition rates of aerosol and iodine sampling should be demonstrated and used to correct the collection efficiency." It also stipulates that nuclear facilities must monitor gamma nuclides and strontium-90 in radioactive aerosols. HJ 61-2021, the "Technical Specifications for Radiation Environment Monitoring," requires monitoring of gamma nuclides and strontium-90 in radioactive aerosols during radiation environment monitoring during nuclear power plant operation, at low- and intermediate-level radioactive waste disposal sites, and at nuclear fuel reprocessing facilities. The sampling volume of airborne effluents from nuclear facilities must be corrected for aerosol pipeline deposition losses; otherwise, actual emissions will be significantly underestimated.

[0004] Existing technologies generally rely on theoretical calculations or model experiments, rather than direct testing within nuclear facility sampling systems. This results in significant discrepancies between test results and actual results. Existing technologies all use high-power fans and filter membranes to collect aerosols. The accumulation of aerosol particles on the filter membranes creates significant wind resistance, resulting in high energy consumption and unstable sampling flow rates. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and a monitoring system for detecting radioactive gases in the chimney of a nuclear facility.

[0006] The technical solution adopted by the present invention to solve the technical problem is to construct a method for detecting radioactive gas in the chimney of a nuclear facility, comprising:

[0007] Step S1: Use a high-purity germanium detector to measure the value when no aerosol particles are collected to obtain the background count rate n b ;

[0008] Step S2, measuring the aerosol standard substance with a high-purity germanium detector and then calculating the detection efficiency E of the high-purity germanium detector for gamma nuclides;

[0009] Step S3: aerosol particles in the chimney of the nuclear facility are transmitted to the ionization unit through the sampling tube, and the ionization unit ionizes the aerosol particles under the action of the high-voltage power supply input voltage;

[0010] Step S4, measuring the mass of aerosol particles at both ends of the sampling tube using an optical aerosol particle size spectrometer, and obtaining the aerosol penetration coefficient T from the two mass measurements by the optical aerosol particle size spectrometer;

[0011] Step S5, start the high purity germanium detector to detect the ionized aerosol particles in step S3, and use the background count rate n in step S1 to detect the ionized aerosol particles. b , the detection efficiency E in step S2 and the aerosol penetration coefficient T in step S4, and calculate the activity concentration of the radioactive aerosol gamma nuclide.

[0012] Furthermore, in step S2, the calculation formula of the detection efficiency E is:

[0013]

[0014] Where, E: detection efficiency of high-purity germanium detector for specific γ nuclides, unit is %;

[0015] n s : the counting rate of a specific gamma nuclide in aerosol standard materials, in cpm;

[0016] n b : background sample counting rate, in cpm;

[0017] A s : The activity of a specific gamma nuclide in aerosol standard material, in Bq.

[0018] Furthermore, the calculation formula of the aerosol penetration coefficient T in step S4 is:

[0019]

[0020] Where:

[0021] T: aerosol penetration coefficient;

[0022] m1: the mass measured by the first optical aerosol size spectrometer, in g;

[0023] m2: The mass measured by the second optical aerosol size spectrometer, in g.

[0024] Furthermore, in step S5, the calculation formula for the activity concentration of aerosol gamma nuclides is:

[0025]

[0026] Where:

[0027] A: Activity concentration of radioactive aerosol gamma nuclides in the chimney of a nuclear facility, Bq / m 3 ;

[0028] N ns : Net counts of characteristic γ-ray peaks in the sample spectrum;

[0029] N nb : Net count of background spectrum γ-ray characteristic peak;

[0030] P E : γ-ray branching ratio, in %;

[0031] E: detection efficiency of high-purity germanium detector for specific gamma nuclides, in %;

[0032] V: Sampling volume under standard conditions, in m 3 ;

[0033] t s : Sample measurement time, in s;

[0034] T; aerosol penetration coefficient, unit is %;

[0035] f E : Activity correction factor, composed of decay correction, self-absorption correction, and coincidence correction.

[0036] Furthermore, the high-purity germanium detector has a detection limit, and the calculation formula of the detection limit is:

[0037]

[0038] Where:

[0039] MDC—Detection limit, unit is Bq / m 3 ;

[0040] n b —background count rate, in cpm;

[0041] t b —Background measurement time, in minutes;

[0042] V—aerosol sampling volume in the collected measurement area, in m 3 ;

[0043] E—Detection efficiency of high-purity germanium detector for specific γ nuclides, in %.

[0044] Furthermore, in step S3, aerosol particles are collected by filter paper in the ionization unit, and the filter paper on which the aerosol particles are collected is subjected to strontium-90 detection.

[0045] Furthermore, the probe temperature of the high-purity germanium detector is reduced to -179°C by an electric refrigeration unit.

[0046] The technical solution adopted by the present invention to solve its technical problems is: constructing a monitoring system for radioactive gases in nuclear facility chimneys, comprising: a sampling tube arranged in the nuclear facility chimney, an ionization unit connected to the sampling tube and used to ionize aerosol particles transmitted by the sampling tube, an electrode adsorption unit for adsorbing ionized aerosol particles, and a high-purity germanium detector arranged in the electrode adsorption unit and used to detect radionuclides; wherein, a first optical aerosol particle size spectrometer for detecting the mass of aerosol particles is provided at one end of the sampling tube close to the nuclear facility chimney, and a second optical aerosol particle size spectrometer for detecting the mass of aerosol particles is provided at one end of the sampling tube close to the ionization unit.

[0047] Furthermore, the electrode adsorption unit is provided with a sealing cylinder, the ionization unit is provided in the sealing cylinder, and one end of the ionization unit away from the sampling tube abuts against the electrode adsorption unit.

[0048] Furthermore, the electrode adsorption unit includes a plurality of electrode wires for adsorbing aerosol particles, and a plurality of collection filter papers for collecting aerosol particles.

[0049] The implementation of the present invention provides a method for detecting radioactive gas in a nuclear facility chimney, which has the following beneficial effects: aerosols at both ends of a sampling tube are measured using an optical aerosol particle size spectrometer to obtain pipeline losses and aerosol penetration coefficients; a high-purity germanium detector is used to directly obtain gamma nuclide detection values ​​in the aerosol, and the gamma nuclide detection values ​​are corrected by the aerosol penetration coefficient to obtain more accurate gamma nuclide parameters, thereby greatly shortening processing time and procedures. The method is suitable for real-time, online, and accurate monitoring of radioactive gas in nuclear facility chimneys.

[0050] The implementation of the present invention provides a monitoring system for radioactive gases in a nuclear facility chimney, which has the following beneficial effects: by arranging a first optical aerosol particle size spectrometer near the nuclear facility chimney in a sampling tube, and then arranging a second optical aerosol particle size spectrometer at the other end of the sampling tube, the ratio of the aerosol particle masses at both ends of the sampling tube is compared to obtain the ratio of aerosol particle loss in the sampling tube; then, after nuclide detection and the collection of aerosol particles containing strontium-90, correction is made according to the ratio to accurately obtain the actual emission amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0052] Figure 1 It is an overall diagram of a method and a monitoring system for detecting radioactive gas in a chimney of a nuclear facility in one embodiment of the present invention;

[0053] Figure 2 It is a front view of a method and a monitoring system for detecting radioactive gas in a chimney of a nuclear facility in one embodiment of the present invention.

[0054] Reference numerals

[0055] 1. Chimney; 2. Sampling tube; 3. First optical aerosol particle size spectrometer; 4. Optical aerosol particle size spectrometer; 5. Ionization unit; 6. Electrode adsorption unit; 7. Electrode wire; 8. High-purity germanium detector; 9. Filter paper; 10. Sealing tube. DETAILED DESCRIPTION

[0056] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientations or positional relationships indicated by "upper," "inner," and "outer," etc., are based on the orientations or positional relationships shown in the accompanying drawings and are constructed and operated in specific orientations. These are merely for the purpose of facilitating the description of the present technical solution and do not necessarily require the device or component to have a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0057] It should also be noted that, unless otherwise clearly specified and limited, terms such as "installation", "connection", "fixation", and "setting" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intervening elements. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0058] Figure 1 A method for detecting radioactive gas in a nuclear facility chimney 1 according to an embodiment of the present invention is shown. The method for detecting radioactive gas in a nuclear facility chimney 1 can be used for nuclide detection in a nuclear facility chimney 1 and may include:

[0059] Step S1: Use the high-purity germanium detector 8 to measure the value when there are no aerosol particles to obtain the background count rate n b ;

[0060] Step S2, measuring the aerosol standard substance through the high-purity germanium detector 8 and then calculating the detection efficiency E of the high-purity germanium detector 8 for gamma nuclides;

[0061] Step S3: aerosol particles in the chimney 1 of the nuclear facility are transmitted to the ionization unit 5 through the sampling tube 2. The ionization unit 5 ionizes the aerosol particles under the action of the input voltage of the high-voltage power supply;

[0062] Step S4, using an optical aerosol particle size spectrometer to measure the mass of aerosol particles at both ends of the sampling tube 2, and obtaining the aerosol penetration coefficient T from the two mass measurements by the optical aerosol particle size spectrometer;

[0063] Step S5, start the high purity germanium detector 8 to detect the ionized aerosol particles in step S3, and use the background count rate n in step S1 to calculate the background count rate n. b , the detection efficiency E in step S2 and the aerosol penetration coefficient T in step S4, and calculate the activity concentration of the radioactive aerosol gamma nuclide.

[0064] The optical aerosol particle size spectrometer is used to measure the aerosol at both ends of the sampling tube 2 to obtain the pipeline loss and the aerosol penetration coefficient. The high-purity germanium detector 8 is used to directly obtain the gamma nuclide detection value in the aerosol. The gamma nuclide detection value is corrected by the aerosol penetration coefficient to obtain more accurate gamma nuclide parameters, which greatly shortens the processing time and process and is suitable for real-time online and accurate monitoring of radioactive gases in the chimney 1 of a nuclear facility.

[0065] It can be understood that the aerosol particles are collected from the radioactive gas exhausted from the chimney 1 of the nuclear facility during normal operation.

[0066] Understandably, the nuclear facility chimney 1 is not suitable for staff to conduct inspections because it emits a large amount of radioactive aerosol particles. Usually, a pipeline of several hundred meters is needed to extract the emitted aerosol particles for inspection. However, the aerosol particles will be deposited in the pipeline, which is quite different from the emission at the end.

[0067] In a specific embodiment, aerosol particles are ionized in the measurement area and then can be electromagnetically adsorbed into the filter paper 9 through the electrode wire 7. The collected aerosol particles are then tested for strontium-90 content. The ionized aerosol particles are collected by electrostatic adsorption: the collection rate of radioactive aerosols is over 9%.

[0068] In a specific embodiment, the mass of aerosol particles is measured at both ends of the sampling tube 2 to obtain the mass difference of the aerosol particles at the front and back ends, and thus the aerosol penetration coefficient is obtained.

[0069] Figure 1 In one embodiment, step S2 may include: In step S2, the calculation formula of the detection efficiency E is:

[0070]

[0071] Where, E: detection efficiency of high purity germanium detector 8 for specific gamma nuclides, unit is %;

[0072] n s : the counting rate of a specific gamma nuclide in aerosol standard materials, in cpm;

[0073] n b : background sample counting rate, in cpm;

[0074] A s : The activity of a specific gamma nuclide in aerosol standard material, in Bq.

[0075] Figure 1 It is shown that step S4 in one embodiment may include the calculation formula of the aerosol penetration coefficient T in step S4:

[0076]

[0077] Where:

[0078] T: aerosol penetration coefficient;

[0079] m1: the mass measured by the first optical aerosol size spectrometer, in g;

[0080] m2: The mass measured by the second optical aerosol size spectrometer, in g.

[0081] Figure 1 In one embodiment, step S5 may include: In step S5, the calculation formula for the activity concentration of aerosol gamma nuclides is:

[0082]

[0083] Where:

[0084] A: Activity concentration of radioactive aerosol gamma nuclides in chimney 1 of nuclear facility, Bq / m 3 ;

[0085] N ns : Net counts of characteristic γ-ray peaks in the sample spectrum;

[0086] N nb : Net count of background spectrum γ-ray characteristic peak;

[0087] P E : γ-ray branching ratio, in %;

[0088] E: detection efficiency of high-purity germanium detector 8 for specific gamma nuclides, in %;

[0089] V: Sampling volume under standard conditions, in m 3 ;

[0090] t s : Sample measurement time, in s;

[0091] T; aerosol penetration coefficient, unit is %;

[0092] f E : Activity correction factor, composed of decay correction, self-absorption correction, and coincidence correction.

[0093] Figure 1 The high-purity germanium detector 8 may include, in one embodiment, a detection limit of the high-purity germanium detector 8. The calculation formula of the detection limit is:

[0094]

[0095] Where:

[0096] MDC—Detection limit, unit is Bq / m 3 ;

[0097] n b —background count rate, in cpm;

[0098] t b —Background measurement time, in minutes;

[0099] V—aerosol sampling volume in the collected measurement area, in m 3 ;

[0100] E—Detection efficiency of high-purity germanium detector 8 for specific gamma nuclides, in %.

[0101] Figure 1 It is shown that in one embodiment, the high purity germanium detector 8 may include collecting aerosol particles in the ionization unit through filter paper in the step S3, and performing strontium-90 detection on the filter paper with the collected aerosol particles.

[0102] Figure 1 In one embodiment, the high-purity germanium detector 8 may include an electric refrigeration unit to reduce the probe temperature of the high-purity germanium detector 8 to -179° C., so as to facilitate detection by the high-purity germanium detector.

[0103] Figure 2 A monitoring system for radioactive gas in a nuclear facility chimney 1 in an embodiment of the present invention is shown. The method for detecting radioactive gas in a nuclear facility chimney 1 can be used for detecting nuclides in the nuclear facility chimney 1, and may include: a sampling tube 2 arranged in the nuclear facility chimney 1, an ionization unit 5 connected to the sampling tube 2 for ionizing aerosol particles transmitted by the sampling tube 2, an electrode adsorption unit 6 for adsorbing ionized aerosol particles, and a high-purity germanium detector 8 arranged in the electrode adsorption unit and for detecting nuclides; wherein, a first optical aerosol particle size spectrometer 3 for detecting the mass of aerosol particles is provided at one end of the sampling tube 2 close to the nuclear facility chimney 1, and a second optical aerosol particle size spectrometer 4 for detecting the mass of aerosol particles is provided at one end of the sampling tube 2 close to the ionization unit 5.

[0104] By setting a first optical aerosol particle size spectrometer 3 near the nuclear facility chimney 1 on the sampling tube 2, and then setting a second optical aerosol particle size spectrometer 4 at the other end of the sampling tube 2, the ratio of the aerosol particle mass at the two ends of the sampling tube 2 is compared to obtain the ratio of aerosol particle loss in the sampling tube 2. Then, after the nuclide detection and the collection of aerosol particles containing strontium-90, the detection is corrected according to the ratio to accurately obtain the actual emission amount.

[0105] Figure 2In one embodiment, the electrode adsorption unit 6 is shown as being provided with a sealing cylinder 10. The ionization unit 5 is disposed within the sealing cylinder 10, with the end of the ionization unit 5 away from the sampling tube 2 abutting against the electrode adsorption unit 6. After the ionization unit 5 ionizes the aerosol particles, the aerosol particles can pass directly through the sealing cylinder 10 into the electrode adsorption unit 6, preventing the aerosol particles from being lost to the outside world and affecting the detection accuracy.

[0106] Figure 2 In one embodiment, the electrode adsorption unit 6 may include a plurality of electrode wires 7 for adsorbing aerosol particles and a plurality of collection filter papers 9 for collecting aerosol particles. The collection filter papers 9 can collect filtered aerosol particles. After the collection filter papers 9 are removed from the sealing tube 10, they are sent to a laboratory for strontium-90 testing.

[0107] It is understandable that the above embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, all of which fall within the scope of protection of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should fall within the scope of coverage of the claims of the present invention.

Claims

1. A method for detecting radioactive gas in a nuclear facility chimney, characterized in that: The following steps are involved: Step S1: Use a high-purity germanium detector to measure the value when no aerosol particles are collected to obtain the background count rate n b ; Step S2, measuring the aerosol standard substance with a high-purity germanium detector and then calculating the detection efficiency E of the high-purity germanium detector for gamma nuclides; Step S3: aerosol particles in the chimney of the nuclear facility are transmitted to the ionization unit through the sampling tube, and the ionization unit ionizes the aerosol particles under the action of the high-voltage power supply input voltage; Step S4, measuring the mass of aerosol particles at both ends of the sampling tube using an optical aerosol particle size spectrometer, and obtaining the aerosol penetration coefficient T from the two mass measurements by the optical aerosol particle size spectrometer; Step S5, start the high purity germanium detector to detect the ionized aerosol particles in step S3, and use the background count rate n in step S1 to detect the ionized aerosol particles. b , the detection efficiency E in step S2 and the aerosol penetration coefficient T in step S4, and calculate the activity concentration of the radioactive aerosol gamma nuclide.

2. A method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: In step S2, the calculation formula of the detection efficiency E is: Where, E: detection efficiency of high-purity germanium detector for specific γ nuclides, unit is %; n s : the counting rate of a specific gamma nuclide in aerosol standard materials, in cpm; n b : background sample counting rate, in cpm; A s : The activity of a specific gamma nuclide in aerosol standard material, in Bq.

3. The method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: The calculation formula of the aerosol penetration coefficient T in step S4 is: Where: T: aerosol penetration coefficient; m1: the mass measured by the first optical aerosol size spectrometer, in g; m2: The mass measured by the second optical aerosol size spectrometer, in g.

4. The method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: In step S5, the calculation formula for the activity concentration of aerosol gamma nuclides is: Where: A: Activity concentration of radioactive aerosol gamma nuclides in the chimney of a nuclear facility, Bq / m 3 ; N ns : Net counts of characteristic γ-ray peaks in the sample spectrum; N nb : Net count of background spectrum γ-ray characteristic peak; P E : γ-ray branching ratio, in %; E: detection efficiency of high-purity germanium detector for specific gamma nuclides, in %; V: Sampling volume under standard conditions, in m 3 ; t s : Sample measurement time, in s; T; aerosol penetration coefficient, unit is %; f E : Activity correction factor, composed of decay correction, self-absorption correction, and coincidence correction.

5. The method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: The high-purity germanium detector has a detection limit, and the calculation formula of the detection limit is: Where: MDC—Detection limit, unit is Bq / m 3 ; n b —background count rate, in cpm; t b —Background measurement time, in minutes; V—aerosol sampling volume in the collected measurement area, in m 3 ; E—Detection efficiency of high-purity germanium detector for specific gamma nuclides, in %.

6. The method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: In step S3, aerosol particles are collected by filter paper in the ionization unit, and the filter paper collecting the aerosol particles is subjected to strontium-90 detection.

7. The method for detecting radioactive gas in a nuclear facility chimney according to claim 1, characterized in that: The probe temperature of the high-purity germanium detector is reduced to -179°C by an electric refrigeration unit.

8. A monitoring system for radioactive gas in a nuclear facility chimney, applied to a method for detecting radioactive gas in a nuclear facility chimney according to any one of claims 1 to 7, characterized in that: include: A sampling tube disposed in a chimney of a nuclear facility, an ionization unit connected to the sampling tube for ionizing aerosol particles transmitted by the sampling tube, an electrode adsorption unit for adsorbing ionized aerosol particles, and a high-purity germanium detector disposed in the electrode adsorption unit for detecting nuclides; The sampling tube is provided with a first optical aerosol particle size spectrometer for detecting the mass of aerosol particles at one end close to the nuclear facility chimney, and the sampling tube is provided with a second optical aerosol particle size spectrometer for detecting the mass of aerosol particles at one end close to the ionization unit.

9. A monitoring system for radioactive gases in nuclear facility chimneys according to claim 8, characterized in that: The electrode adsorption unit is provided with a sealing cylinder, the ionization unit is arranged in the sealing cylinder, and one end of the ionization unit away from the sampling tube abuts against the electrode adsorption unit.

10. A monitoring system for radioactive gases in nuclear facility chimneys according to claim 9, characterized in that: The electrode adsorption unit comprises a plurality of electrode wires for adsorbing aerosol particles and a plurality of collection filter papers for collecting aerosol particles.

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