Nuclear power plant exhaust pipe radioactive aerosol measuring system and measuring method

Abstract

The application discloses a nuclear power plant exhaust pipe radioactive aerosol measuring system and a measuring method. The nuclear power plant exhaust pipe radioactive aerosol measuring system comprises a sampling pipe and a radioactive aerosol concentration measuring device. The nuclear power plant exhaust pipe radioactive aerosol measuring method comprises the following steps: the radioactive aerosol concentration measuring device acquires the radioactive aerosol concentration of the nuclear power plant exhaust pipe, and judges whether the radioactive aerosol concentration is greater than an alarm threshold value; if yes, an alarm signal is sent, wherein the alarm threshold value is SAP=. The application of the nuclear power plant exhaust pipe radioactive aerosol measuring system and method can realize the measurement of potential radioactive gas emission in a nuclear power plant waste auxiliary plant and a waste temporary storage plant, and protect the safety of workers in the plant from internal radiation.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology, and in particular to a system and method for measuring radioactive aerosols in the exhaust ducts of nuclear power plants. Background Technology

[0002] Radioactive aerosols exist in the exhaust ducts of nuclear power plant waste auxiliary buildings and waste temporary storage buildings. If the radioactive aerosol levels exceed the standard, it can easily cause health problems for workers, but there is currently a lack of suitable detection methods. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a system and method for measuring radioactive aerosols in the exhaust pipes of nuclear power plants, addressing the shortcomings of related technologies.

[0004] The technical solution adopted by the present invention to solve its technical problem is: to construct a radioactive aerosol measurement system for a nuclear power plant exhaust duct, including a sampling tube and a radioactive aerosol concentration measurement device; The sampling tube is radially inserted into the exhaust duct of the nuclear power plant, and one end of the sampling tube is connected to the radioactive aerosol concentration measuring device. The sampling tube has n sampling holes spaced at intervals along its length to divide the cross-section n of the nuclear power plant exhaust duct into n equal annular surfaces, each annular surface having an area of Calculation formula: = In the formula, S represents the area of ​​a single annular surface, in m²; S represents the total cross-sectional area of ​​the nuclear power plant's exhaust duct, in m²; n represents the number of sampling holes, in units. The radioactive aerosol concentration measuring device is used to issue an alarm signal when the detected radioactive aerosol concentration is greater than an alarm threshold, wherein the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3 DF is the filtration coefficient of the ventilation filter in the exhaust duct of a nuclear power plant for aerosols.

[0005] In some embodiments of the radioactive aerosol measurement system for nuclear power plant exhaust ducts, the aperture of the sampling orifice satisfies the following formula: In the formula, d is the aperture of the sampling hole, in meters; Um is the gas velocity in the exhaust duct of the nuclear power plant, in meters per second; n is the number of sampling holes, in units; and Q is the sampling flow rate, in cubic meters per second.

[0006] In some embodiments of the nuclear power plant exhaust duct radioactive aerosol measurement system, all the sampling holes have the same aperture.

[0007] In some embodiments of the radioactive aerosol measurement system for nuclear power plant exhaust ducts, the sampling tube is a metal tube.

[0008] In some embodiments of the nuclear power plant exhaust duct radioactive aerosol measurement system, the nuclear power plant exhaust duct is provided with a first through hole and a second through hole, the sampling tube passes through the first through hole and the second through hole, and the portion of the sampling tube protruding from the first through hole is fixed to the nuclear power plant exhaust duct by a first fixing member, and the portion of the sampling tube protruding from the second through hole is fixed to the nuclear power plant exhaust duct by a second fixing member.

[0009] In some embodiments of the radioactive aerosol measurement system for nuclear power plant exhaust ducts, the first end of the sampling tube is connected to the air inlet of the radioactive aerosol concentration measuring device, and the second end of the sampling tube is sealed.

[0010] In some embodiments of the nuclear power plant exhaust duct radioactive aerosol measurement system, the outer side of the sampling tube is sealed to the inner wall of the first through hole, and the outer side of the sampling tube is sealed to the inner wall of the second through hole.

[0011] In some embodiments of the radioactive aerosol measurement system for nuclear power plant exhaust ducts, the sampling tube is an integral structure.

[0012] The present invention also provides a method for measuring radioactive aerosols in nuclear power plant exhaust ducts, applicable to the radioactive aerosol measurement system for nuclear power plant exhaust ducts described in any of the above embodiments. The method for measuring radioactive aerosols in nuclear power plant exhaust ducts includes the following steps: The radioactive aerosol concentration measuring device acquires the radioactive aerosol concentration in the nuclear power plant's exhaust duct and determines whether the radioactive aerosol concentration exceeds an alarm threshold. If so, an alarm signal is issued, where the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3DF is the filtration coefficient of the ventilation filter in the exhaust duct of a nuclear power plant for aerosols.

[0013] In some embodiments, when the nuclide is Co-60, the alarm threshold is 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold is 9.02 Bq / m³. 3 .

[0014] The implementation of this invention has the following beneficial effects: by applying the radioactive aerosol measurement system and method for nuclear power plant exhaust pipes, it is possible to measure the potential radioactive gas emissions in nuclear power plant waste auxiliary buildings and waste temporary storage buildings, thus protecting the internal radiation safety of personnel in the buildings. Attached Figure Description

[0015] To more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the structure of a radioactive aerosol measurement system for a nuclear power plant exhaust duct in some embodiments of the present invention. Detailed Implementation

[0016] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments 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 terms such as "front," "rear," "upper," "lower," "left," "right," "longitudinal," "horizontal," "vertical," "horizontal," "top," "bottom," "inner," "outer," "head," and "tail" are based on the orientations or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. They are only for the convenience of describing this technical solution and do not indicate that the device or element referred to must have a specific orientation; therefore, they should not be construed as limitations on this invention.

[0017] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "linking," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. When an component is referred to as being "on" or "below" another component, the component can be located "directly" or "indirectly" on the other component, or there may be one or more intermediary components. The terms "first," "second," "third," etc., are only for the convenience of describing this technical solution and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0018] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0019] See Figure 1 This invention discloses a radioactive aerosol measurement system for nuclear power plant exhaust ducts, used for measuring and monitoring radioactive aerosols in nuclear power plant exhaust ducts. The nuclear power plant exhaust duct can be, but is not limited to, the main exhaust duct of a nuclear power plant waste auxiliary building and a waste temporary storage building.

[0020] This nuclear power plant exhaust duct radioactive aerosol measurement system can be applied to the exhaust ducts of the radioactive waste auxiliary building ventilation system (DVQ) and the waste temporary storage facility ventilation system (DVR) in nuclear power plants.

[0021] The radioactive aerosol measurement system for the nuclear power plant exhaust duct may include a sampling tube 10 and a radioactive aerosol concentration measuring device (or defined as a radioactive gas detector).

[0022] The sampling tube 10 is radially inserted into the nuclear power plant exhaust duct 100, and one end of the sampling tube 10 is connected to the radioactive aerosol concentration measuring device.

[0023] The sampling tube 10 has n sampling holes 11 spaced apart along its length to divide the cross-section n of the nuclear power plant exhaust duct 100 into n annular surfaces, each annular surface having an area of Calculation formula: = In the formula, S represents the area of ​​a single annular surface, in m²; S represents the total cross-sectional area of ​​the nuclear power plant exhaust duct 100, in m²; n represents the number of sampling holes 11, in units of sampling holes. This radioactive aerosol concentration measuring device is used to issue an alarm signal when the detected radioactive aerosol concentration exceeds an alarm threshold, wherein the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3 DF is the filtration coefficient of the ventilation filter in the exhaust duct 100 of the nuclear power plant for aerosols. In some embodiments, when the nuclide is Co-60, the alarm threshold can be 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold can be 9.02 Bq / m³. 3 .

[0024] In this application, in order to ensure the typicality and representativeness of the sampled gas, a multi-point sampling method was adopted to collect the gas samples and send them to the downstream radioactive aerosol concentration measuring device for gas radioactivity measurement.

[0025] In some embodiments, the nuclear power plant exhaust duct 100 is divided according to the number of sampling holes as shown in the diagram. Figure 1 As shown, n regions with an area of ​​S / n are delineated around the center of the cross-section of the sampling tube 10.

[0026] To achieve typical and representative sampling, a constant velocity sampling mode must be adopted (sampling velocity at the sampling port = gas velocity in the ventilation duct or gas velocity in the chimney). Therefore, the aperture of the sampling hole 11 satisfies the following formula: In the formula, d is the aperture of sampling hole 11, in meters; Um is the gas velocity in the exhaust duct 100 of the nuclear power plant (or the gas velocity in the ventilation duct or the chimney), in meters / second; n is the number of sampling holes 11, in units; and Q is the sampling flow rate, in cubic meters / second.

[0027] Preferably, all the sampling holes 11 have the same diameter. In some embodiments, each sampling hole 11 may also be provided with a sampling nozzle.

[0028] In some embodiments, the sampling tube 10 is a metal tube. For example, the sampling tube 10 may be a stainless steel tube, such as a 304 stainless steel tube or a 316 stainless steel tube.

[0029] In some embodiments, the nuclear power plant exhaust duct 100 is provided with a first through hole and a second through hole opposite to each other. The sampling tube 10 passes through the first through hole and the second through hole, and the portion of the sampling tube 10 protruding from the first through hole is fixed to the nuclear power plant exhaust duct 100 by a first fixing member, and the portion of the sampling tube 10 protruding from the second through hole is fixed to the nuclear power plant exhaust duct 100 by a second fixing member. The first fixing member and the second fixing member may be, but are not limited to, pipe clamps.

[0030] In some embodiments, the first end of the sampling tube 10 is connected to the air inlet of the radioactive aerosol concentration measuring device, the second end of the sampling tube 10 is sealed, the second end of the sampling tube 10 can be a closed structure, and the first end of the sampling tube 10 can be an open structure.

[0031] In some embodiments, the outer side of the sampling tube 10 is sealed to the inner wall of the first through hole, and the outer side of the sampling tube 10 is sealed to the inner wall of the second through hole, for example, by means of sealant.

[0032] In some embodiments, the sampling tube 10 is an integral structure.

[0033] In some embodiments, since the types of radionuclides and radioactivity of aerosols in the air of the waste auxiliary plant and waste temporary storage facility cannot be calculated, the concentration of emitted radioactive materials in the air from the waste auxiliary plant and waste temporary storage facility is controlled within 0.1 DAC, provided that the internal radiation safety of personnel is ensured. The radionuclides considered are Co-60 or Cs-137. The radioactivity concentration of the emitted radioactive material at 0.1 DAC, after being filtered by the aerosol filter in the nuclear power plant exhaust duct 100, is used as the alarm threshold for the radioactive aerosol concentration measuring device. The formulas for the emitted air concentration DAC of Co-60 and Cs-137 are as follows: In the formula, DAC To derive air concentration, the unit is Bq / m³. 3 ; Heff The effective dose limit for workers per year is expressed in Sv, which can be taken as 2.0E-02Sv. CFr is the dose conversion factor for radionuclide r, expressed in Sv / Bq; V The breathing rate of workers in the factory can be taken as 3.5 × 10⁻⁶. -4 m3 / S; tv For one year of working time, the unit is S, and the value is 7.2 × 10⁻⁶. 6 S. In some embodiments, when the nuclide is Co-60, the alarm threshold is 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold is 9.02 Bq / m³. 3 .

[0034] Specifically, based on the above formula, the derived air concentrations of Co-60 or Cs-137 can be calculated to be 8.88E+02Bq / m³. 3 and 9.20E+02Bq / m 3 Among them, combining the formulas for deriving the air concentration DAC of Co-60 and Cs-137 with the formula for calculating the alarm threshold, the alarm threshold for the nuclide Co-60 was calculated to be 8.88 Bq / m³. 3 The calculated alarm threshold for the nuclide Cs-137 is 9.02 Bq / m³. 3 .

[0035] Specifically, when the detected exhaust air concentration of the nuclide Co-60 is greater than 8.88 Bq / m³, the condition is considered clear. 3 When an alarm is triggered, the radioactive aerosol concentration measuring device emits an alarm signal. The alarm signal can be an optical signal and / or an acoustic signal, such as a flashing indicator light on the device, an audible alarm from the device's sensor, or the device can be connected to a handheld terminal to send alarm information. The radioactive aerosol concentration measuring device can be an HY3315 aerosol monitor. In some embodiments, there can be one or more radioactive aerosol concentration measuring devices, and one or more sampling tubes 10, with each sampling tube 10 connected to a corresponding radioactive aerosol concentration measuring device.

[0036] Specifically, when the detected exhaust air concentration of the radionuclide Cs-137 is greater than 9.02 Bq / m³, the condition is considered clear. 3 When an alarm is triggered, the radioactive aerosol concentration measuring device emits an alarm signal. The alarm signal can be an optical signal and / or an acoustic signal, such as a flashing indicator light on the device, an audible alarm from the device's sensor, or the device can be connected to a handheld terminal to send alarm information. The radioactive aerosol concentration measuring device can be an HY3315 aerosol monitor. In some embodiments, there can be one or more radioactive aerosol concentration measuring devices, and one or more sampling tubes 10, with each sampling tube 10 connected to a corresponding radioactive aerosol concentration measuring device.

[0037] The radioactive aerosol measurement system in the exhaust ducts of the nuclear power plant enables the measurement of potential radioactive gas emissions in the auxiliary waste building and temporary waste storage building of the nuclear power plant, protecting the internal radiation safety of the personnel in the building.

[0038] The present invention also provides a method for measuring radioactive aerosols in nuclear power plant exhaust ducts, applicable to the nuclear power plant exhaust duct radioactive aerosol measurement system of any of the above embodiments. The method for measuring radioactive aerosols in nuclear power plant exhaust ducts includes the following steps: The radioactive aerosol concentration measuring device acquires the radioactive aerosol concentration in the nuclear power plant's exhaust duct 100 and determines whether the radioactive aerosol concentration exceeds an alarm threshold. If so, it issues an alarm signal, where the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3 DF is the filtration coefficient of the ventilation filter in the exhaust duct 100 of the nuclear power plant for aerosols. In some embodiments, when the nuclide is Co-60, the alarm threshold is 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold is 9.02 Bq / m³. 3 .

[0039] In some embodiments, since the types of radionuclides and radioactivity of aerosols in the air of the waste auxiliary plant and waste temporary storage facility cannot be calculated, the concentration of emitted radioactive materials in the air from the waste auxiliary plant and waste temporary storage facility is controlled within 0.1 DAC, provided that the internal radiation safety of personnel is ensured. The radionuclides considered are Co-60 or Cs-137. The radioactivity concentration of the emitted radioactive material at 0.1 DAC, after being filtered by the aerosol filter in the nuclear power plant exhaust duct 100, is used as the alarm threshold for the radioactive aerosol concentration measuring device. The formulas for the emitted air concentration DAC of Co-60 and Cs-137 are as follows: In the formula, DAC To derive air concentration, the unit is Bq / m³. 3 ; Heff The effective dose limit for workers per year is expressed in Sv, which can be taken as 2.0E-02Sv. CFr is the dose conversion factor for radionuclide r, expressed in Sv / Bq; V The breathing rate of workers in the factory can be taken as 3.5 × 10⁻⁶.-4 m 3 / S; tv For one year of working time, the unit is S, and the value is 7.2 × 10⁻⁶. 6 S. In some embodiments, when the nuclide is Co-60, the alarm threshold is 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold is 9.02 Bq / m³. 3 .

[0040] Specifically, based on the above formula, the derived air concentrations of Co-60 or Cs-137 can be calculated to be 8.88E+02Bq / m³. 3 and 9.20E+02Bq / m 3 Among them, combining the formulas for deriving the air concentration DAC of Co-60 and Cs-137 with the formula for calculating the alarm threshold, the alarm threshold for the nuclide Co-60 was calculated to be 8.88 Bq / m³. 3 The calculated alarm threshold for the nuclide Cs-137 is 9.02 Bq / m³. 3 Specifically, when the detected exhaust air concentration of the nuclide Co-60 is greater than 8.88 Bq / m³, the condition is considered clear. 3 When an alarm is triggered, the radioactive aerosol concentration measuring device emits an alarm signal. The alarm signal can be an optical signal and / or an acoustic signal, such as a flashing indicator light on the device, an audible alarm from the device's sensor, or the device can be connected to a handheld terminal to send alarm information. The radioactive aerosol concentration measuring device can be an HY3315 aerosol monitor. In some embodiments, there can be one or more radioactive aerosol concentration measuring devices, and one or more sampling tubes 10, with each sampling tube 10 connected to a corresponding radioactive aerosol concentration measuring device.

[0041] Specifically, when the detected exhaust air concentration of the radionuclide Cs-137 is greater than 9.02 Bq / m³, the condition is considered clear. 3 When an alarm is triggered, the radioactive aerosol concentration measuring device emits an alarm signal. The alarm signal can be an optical signal and / or an acoustic signal, such as a flashing indicator light on the device, an audible alarm from the device's sensor, or the device can be connected to a handheld terminal to send alarm information. The radioactive aerosol concentration measuring device can be an HY3315 aerosol monitor. In some embodiments, there can be one or more radioactive aerosol concentration measuring devices, and one or more sampling tubes 10, with each sampling tube 10 connected to a corresponding radioactive aerosol concentration measuring device.

[0042] This method for measuring radioactive aerosols in nuclear power plant exhaust ducts enables the measurement of potential radioactive gas emissions from nuclear power plant waste auxiliary buildings and waste temporary storage buildings, protecting the internal radiation safety of personnel inside the buildings.

[0043] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A radioactive aerosol measurement system for nuclear power plant exhaust ducts, characterized in that, Includes sampling tubes and a device for measuring the concentration of radioactive aerosols; The sampling tube is radially inserted into the exhaust duct of the nuclear power plant, and one end of the sampling tube is connected to the radioactive aerosol concentration measuring device. The sampling tube has n sampling holes spaced at intervals along its length to divide the cross-section n of the nuclear power plant exhaust duct into n equal annular surfaces, each annular surface having an area of Calculation formula: = In the formula, The area of ​​a single annular surface, in m². S represents the total cross-sectional area of ​​the nuclear power plant's exhaust ducts, in m². n represents the number of sampling wells, in units of 1; The radioactive aerosol concentration measuring device is used to issue an alarm signal when the detected radioactive aerosol concentration is greater than an alarm threshold, wherein the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3 DF is the filtration coefficient of the ventilation filter in the exhaust duct of a nuclear power plant for aerosols.

2. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The diameter of the sampling orifice satisfies the following formula: In the formula, d is the diameter of the sampling hole, in meters (m). Um is the gas velocity in the exhaust duct of the nuclear power plant, in m / s; n is the number of sampling holes, in units; Q is the sampling flow rate, in m³ / s.

3. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, All of the sampling holes have the same diameter.

4. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The sampling tube is a metal tube.

5. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The nuclear power plant exhaust duct is provided with a first through hole and a second through hole. The sampling tube passes through the first through hole and the second through hole. The portion of the sampling tube protruding from the first through hole is fixed to the nuclear power plant exhaust duct by a first fastener. The portion of the sampling tube protruding from the second through hole is fixed to the nuclear power plant exhaust duct by a second fastener.

6. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The first end of the sampling tube is connected to the air inlet of the radioactive aerosol concentration measuring device, and the second end of the sampling tube is sealed.

7. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The outer side of the sampling tube is sealed to the inner wall of the first through hole, and the outer side of the sampling tube is sealed to the inner wall of the second through hole.

8. The radioactive aerosol measurement system for nuclear power plant exhaust ducts according to claim 1, characterized in that, The sampling tube is a one-piece structure.

9. A method for measuring radioactive aerosols in a nuclear power plant exhaust duct, applied to the radioactive aerosol measurement system for a nuclear power plant exhaust duct as described in any one of claims 1 to 8, characterized in that, Includes the following steps: The radioactive aerosol concentration measuring device acquires the radioactive aerosol concentration in the nuclear power plant's exhaust duct and determines whether the radioactive aerosol concentration exceeds an alarm threshold. If so, an alarm signal is issued, where the alarm threshold is: SAP= In the formula, SAP is the alarm threshold, and the unit is Bq / m. 3 k is the derived air concentration limit, taken as 0.1DAC; DAC r is the derived radioactivity concentration of nuclide r at an air concentration of 1 DAC, in Bq / m³. 3 DF is the filtration coefficient of the ventilation filter in the exhaust duct of a nuclear power plant for aerosols.

10. The method for measuring radioactive aerosols in the exhaust duct of a nuclear power plant according to claim 9, characterized in that, When the nuclide is Co-60, the alarm threshold is 8.88 Bq / m³. 3 When the nuclide is Cs-137, the alarm threshold is 9.02 Bq / m³. 3 .

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