Nuclear power plant hydrogen-containing radioactive waste gas treatment system and method

Abstract

This invention relates to a system and method for treating hydrogen-containing radioactive waste gas from nuclear power plants. The system includes a pretreatment unit, a treatment loop, and a filtration and emission unit. The treatment loop includes a retention treatment unit, a monitoring unit, and a gas recovery unit. After pressure regulation and drying in the pretreatment unit, the hydrogen-containing radioactive waste gas enters the treatment loop for decay and monitoring, and is then discharged into the external environment through the filtration and emission unit. The method is applicable to the above system and includes acquiring the monitoring results from the monitoring unit, switching to a first or second filtration branch for waste gas filtration based on the monitoring results, and controlling the connection or disconnection of the gas recovery unit. The monitoring results include the radioactivity concentration of the hydrogen-containing radioactive waste gas. This invention continuously monitors the radioactivity concentration of the hydrogen-containing waste gas through online monitoring, achieving continuous monitoring, automated management and control of waste gas emissions, and automatic switching of the iodine filter emission branch, thereby improving the operational safety of nuclear power plants.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant exhaust gas treatment technology, and in particular to a system and method for treating hydrogen-containing radioactive exhaust gas from nuclear power plants. Background Technology

[0002] Nuclear power plant pressure vessels (cores) contain a large number of nuclear fuel rods used for nuclear reactions. During the power operation of a nuclear power plant, neutrons in the core react with contaminated uranium on the surface of the fuel rods and within the fuel rods in a chain fission reaction, producing large amounts of radioactive inert gases and iodine. These are mainly krypton isotopes (Kr-83m, Kr-85m, Kr-85, Kr-87, and Kr-88), xenon isotopes (Xe-131m, Xe-133, Xe-133m, Xe-135, and Xe-138), and iodine isotopes (I-131, I-132, I-133, I-134, and I-135). These inert gas nuclides and gaseous iodine migrate into the nuclear power plant's main loop and auxiliary systems along with the main loop coolant. To ensure that the radioactivity concentration of the inert gas in the main loop coolant is below the limit specified in the nuclear power plant's radiochemical technical specifications, and to maintain the radioactivity level of the inert gas released during the opening of the pressure vessel cover during nuclear power plant shutdown within a reasonable range, hydrogen is used to purge the main loop during power operation, purging the inert gas nuclides and airborne iodine from the main loop to the nuclear power plant's radioactive waste gas treatment system.

[0003] Radioactive waste gas treatment systems are primarily used to treat radioactive hydrogen-containing and oxygen-containing waste gases generated during the normal operation of nuclear power plants. The hydrogen-containing waste gas undergoes decay in storage tanks or activated carbon retention beds before being discharged into the atmosphere via the plant ventilation system, where it is filtered and diluted with iodine. The oxygen-containing waste gas is also discharged into the atmosphere through the plant ventilation system. Currently, nuclear power plant radioactive waste gas treatment systems use storage tanks or activated carbon retention beds to collect the hydrogen-containing radioactive waste gas generated by the plant. The hydrogen-containing radioactive waste gas is pressurized and collected in storage tanks or retention beds by a compressor, and its radioactivity concentration is continuously reduced through the self-decay of radioactive inert gas nuclides (such as krypton and xenon isotopes) and radioactive iodine. Current technology requires sampling and analysis of the radioactivity concentration of iodine in the gas before exhaust gas is emitted. This results in high radiation doses and workloads for radiochemical analysts at power plants. Information transmission errors between sampling and analysis engineers and exhaust gas treatment engineers, or misoperation by exhaust gas treatment engineers, could lead to the risk of accidental emission of exhaust gas stored in storage tanks for less than 60 days. Furthermore, during exhaust gas emission, staff must continuously monitor pressure changes in the storage tanks on-site. Before each exhaust gas emission, the ventilation system must be manually switched to the iodine filter emission circuit, increasing the frequency of iodine filter replacement and the amount of radioactive solid waste at the power plant. This also poses a significant radiation risk to staff on-site. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a safe and automated monitoring and control system and method for treating hydrogen-containing radioactive waste gas from nuclear power plants, addressing at least one deficiency of the prior art.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: A nuclear power plant hydrogen-containing radioactive waste gas treatment system is constructed, characterized in that it includes a pretreatment unit, a treatment loop, and a filtration and emission unit; the treatment loop includes a retention treatment unit, a monitoring unit, and a gas recovery unit; the inlet of the pretreatment unit is connected to the main loop of the nuclear power plant, the outlet of the pretreatment unit is connected to the inlet of the retention treatment unit, and the outlet of the retention treatment unit is connected to the inlet of the monitoring unit; one outlet of the monitoring unit is connected to the inlet of the gas recovery unit, and the other outlet is connected to the inlet of the filtration and emission unit; the outlet of the gas recovery unit is connected to the inlet of the retention treatment unit; the filtration and emission unit includes a first filtration branch and a second filtration branch arranged in parallel, and the outlet of the filtration and emission unit is connected to the external environment;

[0006] The hydrogen-containing radioactive waste gas from the nuclear power plant is pressure-regulated and dried by the pretreatment unit, then enters the treatment loop for decay and monitoring, and is discharged into the external environment through the filtration and emission unit.

[0007] Preferably, the pretreatment unit includes a compressor and a dryer, wherein the hydrogen-containing radioactive waste gas from the nuclear power plant is pressurized by the compressor and then discharged to the dryer for drying treatment.

[0008] Preferably, the pretreatment unit further includes a buffer tank, the first end of which is connected to the main circuit of the nuclear power plant, and the second end of which is connected to the first end of the compressor, for collecting hydrogen-containing radioactive waste gas generated by the main circuit of the nuclear power plant.

[0009] Preferably, the pretreatment unit further includes a gas cooler, the first end of which is connected to the second end of the compressor, and the second end of which is connected to the first end of the dryer.

[0010] Preferably, the dryer is a silica gel dryer.

[0011] Preferably, the retention treatment unit includes at least one activated carbon retention bed, and at least one of the activated carbon retention beds is connected to the outlet of the pretreatment unit.

[0012] Preferably, there are two activated carbon retention beds, including a first activated carbon retention bed and a second activated carbon retention bed; the exhaust gas at the outlet of the pretreatment unit passes through the first activated carbon retention bed and the second activated carbon retention bed in sequence for retention and decay.

[0013] Preferably, the nuclear power plant hydrogen-containing radioactive waste gas treatment system is further provided with a pressure regulating valve for adjusting the pressure of the nuclear power plant hydrogen-containing radioactive waste gas; the pressure regulating valve is located between the pretreatment unit and the retention treatment unit.

[0014] Preferably, the monitoring unit includes at least one monitoring device for monitoring the exhaust gas at the outlet of the retention treatment unit. The first end of the monitoring device is connected to the outlet of the retention treatment unit, and the second end of the monitoring device is connected to the inlet of the gas recovery unit and the other end is connected to the inlet of the filtration and emission unit.

[0015] Preferably, the number of monitoring devices is one, and the gas recovery unit includes a seventh isolation valve, a circulation pump, and a ninth isolation valve;

[0016] The outlet of the retention treatment unit is connected to the first end of the monitoring device through the first isolation valve. The second end of the monitoring device is connected to the inlet of the retention treatment unit through the seventh isolation valve, the circulating pump and the ninth isolation valve in sequence, and to the inlet of the filtration and discharge unit through the third isolation valve.

[0017] Preferably, the number of monitoring devices is two, including a first monitoring device and a second monitoring device connected in parallel; the gas recovery unit includes a seventh isolation valve, an eighth isolation valve, a circulation pump, and a ninth isolation valve;

[0018] One outlet of the retention treatment unit is connected to the first end of the first monitoring device via a first isolation valve, and the other outlet is connected to the first end of the second monitoring device via a second isolation valve;

[0019] The second end of the first monitoring device is connected in sequence through the seventh isolation valve, the circulating pump and the ninth isolation valve to the inlet of the retention treatment unit, and in another sequence through the third isolation valve to the inlet of the filtration and discharge unit; the second end of the second monitoring device is connected in sequence through the eighth isolation valve, the circulating pump and the ninth isolation valve to the inlet of the retention treatment unit, and in another sequence through the fourth isolation valve to the inlet of the filtration and discharge unit.

[0020] Preferably, the filtration and emission unit further includes an exhaust device for discharging exhaust gas, through which the exhaust gas after being filtered by the first filtration branch or the second filtration branch is discharged into the external environment.

[0021] Preferably, the first filtration branch includes a fifth isolation valve and an aerosol filter, and the outlet of the monitoring unit is connected to the exhaust device in sequence through the fifth isolation valve and the aerosol filter.

[0022] Preferably, the second filtration branch includes a sixth isolation valve and an iodine filter, and the outlet of the monitoring unit is connected to the exhaust device in sequence through the sixth isolation valve and the iodine filter.

[0023] Preferably, the nuclear power plant hydrogen-containing radioactive waste gas treatment system further includes a gas monitor, which is installed on the exhaust device to monitor the waste gas inside the exhaust device.

[0024] Preferably, the filtration and emission unit further includes a ventilation device, which is installed on the duct between the monitoring unit and the filtration and emission unit. The ventilation device exhausts diluted waste gas that has been monitored by the monitoring unit and discharged to the first filtration branch or the second filtration branch.

[0025] This invention also provides a method for treating hydrogen-containing radioactive waste gas from nuclear power plants, applicable to the aforementioned nuclear power plant hydrogen-containing radioactive waste gas treatment system, comprising:

[0026] S1. Obtain the monitoring results of the monitoring unit, switch to the first filtration branch or the second filtration branch for waste gas filtration based on the monitoring results, and control the connection or disconnection of the gas recovery unit; wherein, the monitoring results include the radioactivity concentration of the hydrogen-containing radioactive waste gas.

[0027] Preferably, step S1 specifically includes:

[0028] S11. Determine whether the monitoring results are all greater than the first threshold within a first preset time. If yes, execute step S12. If no, switch to the first filtration branch for exhaust gas filtration.

[0029] S12. Switch to the second filter branch for exhaust gas filtration, and continue to determine whether the monitoring results are greater than the second threshold within a second preset time. If yes, proceed to step S13; otherwise, proceed to step S11. Wherein, the second threshold is greater than the first threshold.

[0030] S13. Stop discharging exhaust gas into the filter emission unit and automatically trigger the connection of the gas recovery unit for exhaust gas recirculation treatment.

[0031] The implementation of this invention has the following beneficial effects: This invention continuously monitors the radioactivity concentration of hydrogen-containing waste gas through online monitoring, realizing continuous monitoring of waste gas emissions, automation of waste gas emission management and control, reducing the accidental emission of radioactive waste gas without sufficient decay due to human error, reducing the workload and radiation dose of radiochemical workers, realizing automatic switching of iodine filter emission branches, and improving the operational safety of nuclear power plants. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of the structure of the nuclear power plant hydrogen-containing radioactive waste gas treatment system of the present invention;

[0034] Figure 2 This is a control logic diagram of an embodiment of the method for treating hydrogen-containing radioactive waste gas from nuclear power plants according to the present invention;

[0035] Figure 3 This is a control logic diagram of another embodiment of the method for treating hydrogen-containing radioactive waste gas from nuclear power plants according to the present invention;

[0036] Figure 4 This is a control logic diagram of one embodiment of the monitoring unit of the present invention;

[0037] Figure 5 This is a control logic diagram of another embodiment of the monitoring unit of the present invention;

[0038] Figure 6 This is a flowchart of the method for treating hydrogen-containing radioactive waste gas from nuclear power plants according to the present invention. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] like Figure 1 As shown, this invention provides a hydrogen-containing radioactive waste gas treatment system for nuclear power plants, which includes a pretreatment unit 1, a treatment loop 2, and a filtration and emission unit 3.

[0043] The processing loop 2 includes a retention treatment unit 21, a monitoring unit 22, and a gas recovery unit 23. The inlet of the pretreatment unit 1 is connected to the main loop 100 of the nuclear power plant, and the outlet of the pretreatment unit 1 is connected to the inlet of the retention treatment unit 21. The outlet of the retention treatment unit 21 is connected to the inlet of the monitoring unit 22. The outlet of the monitoring unit 22 is divided into two branches, one connected to the inlet of the gas recovery unit 23 and the other connected to the inlet of the filtration and emission unit 3. Under normal initial conditions, the gas recovery unit 23 is isolated from the monitoring unit 22. The outlet of the gas recovery unit 23 is connected to the inlet of the retention treatment unit 21. The filtration and emission unit 3 includes a first filtration branch 31 and a second filtration branch 32 arranged in parallel. The outlet of the filtration and emission unit 3 is connected to the external environment. After being pressure-regulated and dried by the pretreatment unit 1, the hydrogen-containing radioactive waste gas from the nuclear power plant enters the processing loop 2 for decay and monitoring, and is then discharged into the external environment through the filtration and emission unit 3.

[0044] To ensure the adsorption capacity of the activated carbon particles in the retention treatment unit 21, the hydrogen-containing waste gas from the nuclear power plant needs to undergo pressure regulation and drying treatment in the pretreatment unit 1 before entering the retention treatment unit 21. Further, the pretreatment unit 1 includes a compressor 12 and a dryer 14. The dryer 14 is mainly used for dehumidifying the hydrogen-containing waste gas from the nuclear power plant; specifically, a silica gel dryer 14 can be used. The hydrogen-containing radioactive waste gas from the nuclear power plant is pressurized by the compressor 12 and then discharged to the dryer 14 for drying treatment.

[0045] In some embodiments, the pretreatment unit 1 further includes a buffer tank 11 for collecting hydrogen-containing radioactive waste gas generated by the nuclear power plant main loop 100. The first end of the buffer tank 11 is connected to the nuclear power plant main loop 100, and the second end of the buffer tank 11 is connected to the first end of the compressor 12. The hydrogen-containing radioactive waste gas generated by the nuclear power plant main loop 100 is collected in the buffer tank 11 and then discharged to the dryer 14 for drying after being pressurized by the compressor 12.

[0046] In some embodiments, the pretreatment unit 1 further includes a gas cooler 13, with its first end connected to the second end of the compressor 12 and its second end connected to the first end of the dryer 14. After being pressurized by the compressor 12, the hydrogen-containing radioactive waste gas from the nuclear power plant is first discharged to the gas cooler 13 for cooling, and then to the dryer 14 for drying to remove a large amount of moisture. The buffer tank 11 collects the hydrogen-containing radioactive waste gas from the nuclear power plant, which is then discharged by the compressor 12 to the gas cooler 13 and the silica gel dryer 14 for pretreatment. The pretreated hydrogen-containing waste gas is then subjected to long-term decay in the retention treatment unit 21, resulting in the emission of only Kr-85 radioactive nuclide, with a gamma-ray yield of 0.43% and a beta-ray yield of 99.57%.

[0047] Furthermore, the retention treatment unit 21 includes at least one activated carbon retention bed, which is connected to the outlet of the pretreatment unit 1, and uses activated carbon particles in the activated carbon retention bed to adsorb radioactive inert gases krypton and xenon in the hydrogen-containing waste gas of the nuclear power plant.

[0048] In some embodiments, to achieve better adsorption, two activated carbon retention beds can be provided, including a first activated carbon retention bed 211 and a second activated carbon retention bed 212. The exhaust gas at the outlet of the pretreatment unit 1 passes sequentially through the first activated carbon retention bed 211 and the second activated carbon retention bed 212 for retention and decay. Further, after retention and decay in the retention treatment unit 21, the exhaust gas can be filtered by a filter 17. This filter 17 is used to filter out small activated carbon particles entrained in the gas at the outlet of the activated carbon retention bed, ensuring that the downstream gas is clean and free of activated carbon particle impurities.

[0049] Furthermore, the nuclear power plant hydrogen-containing radioactive waste gas treatment system is also equipped with a pressure regulating valve for adjusting the pressure of the hydrogen-containing radioactive waste gas. The pressure regulating valve is located between the pretreatment unit 1 and the retention treatment unit 21, that is, the outlet of the pretreatment unit 1 is connected to the inlet of the retention treatment unit 21 through the pressure regulating valve. In some embodiments, two pressure regulating valves are provided, including a first pressure regulating valve 15 and a second pressure regulating valve 16. The outlet of the pretreatment unit 1 is sequentially connected to the first pressure regulating valve 15 and the second pressure regulating valve 16, and connected to the inlet of the retention treatment unit 21. The outlet of the gas recovery unit 23 is connected to the pipeline between the first pressure regulating valve 15 and the second pressure regulating valve 16.

[0050] Furthermore, the monitoring unit 22 includes at least one monitoring device for monitoring the exhaust gas at the outlet of the retention treatment unit 21. The first end of the monitoring device is connected to the outlet of the retention treatment unit 21 and is used to monitor the exhaust gas after treatment by the retention treatment unit 21, specifically measuring the radioactivity concentration of the exhaust gas emitted at the outlet of the retention treatment unit 21. One end of the monitoring device is connected to the inlet of the gas recovery unit 23, and the other end is connected to the inlet of the filtration and emission unit 3. If the exhaust gas is qualified by the monitoring device, it can be discharged through the filtration and emission unit 3. If the exhaust gas is unqualified by the monitoring device, it will enter the gas recovery unit 23 for recycling and reprocessing.

[0051] Specifically, in some embodiments, the number of monitoring devices can be one. The gas recovery unit 23 includes a seventh isolation valve 47, a circulation pump, and a ninth isolation valve 49. The outlet of the retention treatment unit 21 is connected to the first end of the monitoring device through the first isolation valve 41. The second end of the monitoring device is connected to the inlet of the retention treatment unit 21 through the seventh isolation valve 47, the circulation pump, and the ninth isolation valve 49 in sequence, and to the inlet of the filter emission unit 3 through the third isolation valve 43. If the waste gas is qualified by the monitoring device, the system automatically opens the third isolation valve 43, and the waste gas will be discharged through the filter emission unit 3. If the waste gas is unqualified by the monitoring device, the system automatically isolates the third isolation valve 43 and stops the discharge of the unqualified waste gas. The system also automatically opens the seventh isolation valve 47, and the unqualified waste gas will enter the gas recovery unit 23 for recirculation and reprocessing, that is, it will be circulated to the retention treatment unit 21 for retention and decay again. It must be qualified by the monitoring unit 22 again before the system can trigger the opening of the third isolation valve 43 to discharge the waste gas.

[0052] Given the high beta-ray yield and weak beta-ray penetrating power of Kr-85, the monitoring device employs a 0.2mm thick plastic scintillator beta-sensitive detector and utilizes an online monitoring method, such as... Figure 1As shown, the online monitoring method involves inserting the monitoring device into the measuring chamber, directly immersing the device in the hydrogen-containing waste gas, and directly measuring the β-rays released by Kr-85 in the waste gas. This achieves continuous online monitoring of the radioactivity activity of the hydrogen-containing waste gas, improving the accuracy of Kr and Xe radioactivity measurement and eliminating the risk of hydrogen-containing waste gas leakage and explosion. Considering that the monitoring device measures hydrogen-containing radioactive waste gas, and that leakage poses a risk of hydrogen explosion, the gas leakage rate of the monitoring device is less than 6.58 × 10⁻⁶. -9 Pa·m 3 / s, explosion-proof rating is Ex dⅡCT6 Gb.

[0053] In other embodiments, the number of monitoring devices can be two, including a first monitoring device 221 and a second monitoring device 222 connected in parallel; the first monitoring device 221 and the second monitoring device 222 operate in a one-to-one standby mode, that is, when the first monitoring device 221 is in operation, the second monitoring device 222 enters a standby state; when the second monitoring device 222 is in operation, the first monitoring device 221 enters a standby state; the gas recovery unit 23 includes a seventh isolation valve 47, an eighth isolation valve 48, a circulation pump, and a ninth isolation valve 49; the outlet of the retention treatment unit 21 is open-circuit. One path is connected to the first end of the first monitoring device 221 via the first isolation valve 41, and the other path is connected to the first end of the second monitoring device 222 via the second isolation valve 42. The second end of the first monitoring device 221 is connected to the inlet of the retention treatment unit 21 via the seventh isolation valve 47, the circulation pump and the ninth isolation valve 49 in sequence, and the other path is connected to the inlet of the filter discharge unit 3 via the third isolation valve 43. The second end of the second monitoring device 222 is connected to the inlet of the retention treatment unit 21 via the eighth isolation valve 48, the circulation pump and the ninth isolation valve 49 in sequence, and the other path is connected to the inlet of the filter discharge unit 3 via the fourth isolation valve 44.

[0054] Furthermore, the filtration and emission unit 3 also includes an exhaust device 33 for discharging exhaust gas. Specifically, the exhaust device 33 can be a chimney. The exhaust gas, after being filtered by the first filtration branch 31 or the second filtration branch 32, is discharged into the external environment through the exhaust device 33. Specifically, the first filtration branch can be called the aerosol filter emission branch. The first filtration branch 31 includes a fifth isolation valve 45 and an aerosol filter 311. One outlet of the monitoring unit 22 is connected to the exhaust device 33 sequentially through the fifth isolation valve 45 and the aerosol filter 311. The second filtration branch can be called the iodine filter emission branch. The second filtration branch 32 includes a sixth isolation valve 46 and an iodine filter 322. One outlet of the monitoring unit 22 is connected to the exhaust device 33 sequentially through the sixth isolation valve 46 and the iodine filter 322.

[0055] Furthermore, the nuclear power plant's hydrogen-containing radioactive waste gas treatment system also includes a gas monitor 35, which is installed on the exhaust device 33 to monitor the waste gas inside the exhaust device 33. If the gas monitor 35 measures that the radioactivity of the waste gas exceeds a set threshold, an interlock action is triggered to stop the waste gas emission from the waste gas treatment system.

[0056] Furthermore, the filtration and emission unit 3 also includes a ventilation device 34, which is installed on the duct between the monitoring unit 22 and the filtration and emission unit 3. The exhaust gas from the ventilation device 34 is diluted and monitored by the monitoring unit 22 before being discharged to the first filtration branch 31 or the second filtration branch 32. During the operation of the nuclear power plant's hydrogen-containing radioactive waste gas treatment system, the waste gas entering the system must pass the measurement and approval by the first monitoring device 221 or the second monitoring device 222 before it can be further processed in the filtration and emission unit 3. The radioactive waste gas is discharged into the exhaust duct of the ventilation device 34, diluted by the ventilation device 34, and then filtered in the first filtration branch 31 or the second filtration branch 32. After being monitored by the gas monitor 35, it is discharged into the environment through the chimney.

[0057] like Figure 2 As shown, the present invention also constructs a method for treating hydrogen-containing radioactive waste gas from nuclear power plants, applicable to the aforementioned hydrogen-containing radioactive waste gas treatment system for nuclear power plants. The method includes step S1: acquiring the monitoring results of the monitoring unit 22, determining whether a set threshold is exceeded based on the monitoring results, and then switching to the first filtration branch 31 or the second filtration branch 32 for waste gas filtration, and controlling the connection or disconnection of the gas recovery unit 23. The set threshold includes a first threshold and a second threshold. The first threshold determines the filtration mode of the filtration emission unit 3, and the second threshold determines whether the waste gas stops being emitted and enters the gas recovery unit 23 for recirculation and reprocessing. The monitoring results include the radioactivity concentration of hydrogen-containing radioactive waste gas. In this embodiment, the main focus is on monitoring the radioactivity concentration of hydrogen-containing radioactive waste gas. Based on the comparison between the radioactivity concentration of hydrogen-containing radioactive waste gas and a set threshold, it is determined whether to trigger an alarm or perform related operations. The monitoring unit 22 mainly monitors the radioactivity concentration of the waste gas currently flowing through the first monitoring device 221 or the second monitoring device 222. If the waste gas is qualified by the monitoring device, the relevant isolation valve is triggered to open or isolate, switching to the first filtration branch 31 or the second filtration branch 32 for waste gas filtration, so that the waste gas is discharged through the filtration and discharge unit 3. If the waste gas is unqualified by the monitoring device, the relevant isolation valve is triggered to open or isolate, thereby controlling the gas recovery unit 23 to be connected or disconnected, and the gas entering the gas recovery unit 23 is recycled and reprocessed.

[0058] Furthermore, step S1 specifically includes:

[0059] S11. Determine whether the monitoring results are all greater than the first threshold within the first preset time, that is, determine whether the monitoring device in the monitoring unit 22 has triggered a first-level alarm; if yes, then execute step S12; if no, switch to the first filtration branch 31 for exhaust gas filtration.

[0060] S12. Switch to the second filtration branch 32 for exhaust gas filtration, and continue to determine whether the monitoring results are greater than the second threshold within the second preset time, that is, determine whether the monitoring device in the monitoring unit 22 triggers a secondary alarm; if yes, execute step S13, otherwise execute step S11; wherein, the second threshold is greater than the first threshold; further, the first preset time can be set to 5 seconds, that is, determine whether the monitoring results are greater than the first threshold within 5 seconds, if yes, execute step S12, otherwise, switch to the first filtration branch 31 for exhaust gas filtration; understandably, the second preset time can be set to 5 seconds, that is, determine whether the monitoring results are greater than the second threshold within 5 seconds, if yes, execute step S13, otherwise execute step S11; the purpose is to prevent false alarms caused by pulse signals. Under normal circumstances, the pulse signal will last for tens of milliseconds, so the first preset time and the second preset time can be selected according to the actual situation, and are not limited here.

[0061] S13. Stop discharging exhaust gas into the filter emission unit 3 and automatically trigger the connection of the gas recovery unit 23 for exhaust gas recirculation treatment; understandably, the storage tank can also recover the unqualified exhaust gas and collect the exhaust gas with excessive radioactivity to achieve the function of long-term storage and decay of radioactive exhaust gas.

[0062] like Figures 3 to 6 As shown, the first monitoring device 221 and the second monitoring device 222 operate in a standby mode, meaning that when the first monitoring device 221 is in operation, the second monitoring device 222 is in standby mode; and vice versa. When either the first monitoring device 221 or the second monitoring device 222 measures that the radioactivity of the inert gas in the exhaust gas emitted by the exhaust gas treatment system exceeds a set threshold, an interlocking action is triggered, and the system initiates control of hydrogen-containing exhaust gas emissions. Specifically, the interlocking control requirements are as follows:

[0063] (1) If the radioactivity concentration of the emitted exhaust gas is less than the first threshold, specifically, the first threshold can be taken as 1.8E+07Bq / m³. 3 The radioactive waste gas is discharged into the exhaust duct of the ventilation device 34, and after being filtered by the aerosol filter 311 in the first filtration branch 31, it is discharged into the chimney.

[0064] (2) If the radioactivity concentration of the emitted exhaust gas is greater than the first threshold, the first monitoring device 221 or the second monitoring device 222 triggers a first-level alarm signal and automatically interlocks to open the sixth isolation valve 46 and isolate the fifth isolation valve 45, so that the exhaust gas is switched from the first filtration branch 31 to the second filtration branch 32, and the radioactive exhaust gas is discharged to the chimney after being filtered by the iodine filter 322.

[0065] (3) If the radioactivity concentration of the emitted exhaust gas is greater than the second threshold, specifically, the second threshold can be taken as 2.2E+0.8Bq / m³. 3 When the first monitoring device 221 or the second monitoring device 222 triggers a secondary alarm signal, the seventh isolation valve 47 or the eighth isolation valve 48 is automatically opened, and the circulation pump and the ninth isolation valve 49 are activated. The first isolation valve 41 and the second isolation valve 42 of the hydrogen-containing waste gas emission are automatically isolated to stop the waste gas emission. The hydrogen-containing radioactive waste gas is sent to the retention treatment unit 21 for recycling and reprocessing to further reduce the activity concentration of iodine and inert gas in the waste gas.

[0066] (4) If the activity concentration of the emitted exhaust gas is less than or equal to 70% of the first threshold, the first-level alarm is released, the automatic interlock is opened, the fifth isolation valve 45 is opened, and the sixth isolation valve 46 is isolated. The exhaust gas is switched from the second filter branch 32 to the first filter branch 31 to achieve normal exhaust gas emission. The radioactive exhaust gas is filtered by the aerosol filter 311 and then discharged to the chimney.

[0067] (5) After the hydrogen-containing waste gas is sent to the retention treatment unit 21 for further treatment via the circulation pump, the concentration of inert gas and iodine radioactivity in the waste gas will be further reduced. When the measurement result of the first monitoring device 221 or the second monitoring device 222 is less than or equal to 70% of its second threshold, the secondary alarm is released and the third isolation valve 43 or the fourth isolation valve 44 is automatically opened, and the seventh isolation valve 47 or the eighth isolation valve 48 is automatically isolated and the circulation pump is isolated, so as to realize online monitoring and emission of hydrogen-containing waste gas.

[0068] (6) If the first monitoring device 221 malfunctions and triggers a fault alarm, the interlock automatically opens the second isolation valve 42 and isolates the first isolation valve 41, activating the second monitoring device 222 from standby mode to working mode, whereby the second monitoring device 222 performs monitoring to achieve waste gas monitoring and emission. If the second monitoring device 222 malfunctions and triggers a fault alarm, the interlock automatically opens the first isolation valve 41 and isolates the second isolation valve 42, activating the first monitoring device 221 from standby mode to working mode, whereby the first monitoring device 221 performs monitoring to achieve waste gas monitoring and emission.

[0069] First monitoring device 221 or second monitoring device 222 of For the automatic control logic of the two-level alarm, please refer to [link / reference]. Figure 3 and Figure 4The first monitoring device 221 or the second monitoring device 222 of The automatic control logic for clearing a two-level alarm is the reverse process of the automatic control logic for a two-level alarm. For the automatic control logic when the first monitoring device 221 or the second monitoring device 222 experiences a fault alarm, please refer to [link / reference needed]. Figure 5 and Figure 6 .

[0070] When the gas monitor 35 measures that the radioactivity of the exhaust gas exceeds a set threshold, it also triggers an interlock action to stop the exhaust gas emission from the exhaust gas treatment system. The gas monitor 35 measures online whether the concentration of inert gas activity in the exhaust gas from the chimney exceeds a second threshold. If so, it triggers an alarm and automatically stops the exhaust gas emission from the exhaust gas treatment system. Its control requirements are the same as those for triggering a secondary alarm by the first monitoring device 221 or the second monitoring device 222.

[0071] The first monitoring device 221 or the second monitoring device 222 measures the concentration of radioactivity of the inert gas online, with a first threshold of 1.8E+0.7 Bq / m³. 3 The exhaust air concentration of airborne iodine in the waste gas from the exhaust gas treatment system is less than 0.1 DAC, and the radioactivity concentration of iodine is 2.98E+02 Bq / m³. 3 The second threshold (2.2E+0.8Bq / m) 3 The corresponding radioactivity concentration of airborne iodine in the exhaust gas emitted by the waste gas treatment system is 3.7E+03Bq / m³. 3 .

[0072] This invention solves the problems of monitoring hydrogen-containing radioactive waste gas emissions and controlling the treatment of iodine in radioactive waste gas emissions. It extends the residence and decay time of radioactive waste gas by improving the waste gas treatment process. A low-leakage, explosion-proof β-sensitive detector is used, and online monitoring is employed to continuously monitor the radioactivity concentration of hydrogen-containing waste gas, achieving automatic control of hydrogen-containing waste gas emissions from the waste gas treatment system. The main technical effects of this invention are:

[0073] 1. Based on the characteristics of Kr-85, which has a gamma ray yield of 0.43% and a beta ray yield of 99.57%, and the explosive nature of hydrogen-containing waste gas, an explosion-proof beta sensitive detector with extremely low leakage rate is adopted. The radioactivity concentration of the emitted waste gas is continuously measured online using an online monitoring method. This improves the accuracy of waste gas emission activity measurement, eliminates the risk of leakage and explosion during the measurement process of hydrogen-containing waste gas, and enhances the operational safety of nuclear power plants.

[0074] 2. Online continuous measurement eliminates the laboratory analysis of exhaust gas sampling in the exhaust gas storage tank treatment process, reducing the workload and radiation dose for radiochemical workers.

[0075] 3. The system uses a first-level alarm interlock control to switch the exhaust gas emission to the second filtration branch. For exhaust gas treatment systems using a retained bed treatment process, this can reduce the concentration of radioactive iodine in the exhaust gas emitted into the environment.

[0076] 4. Achieve continuous monitoring, management, and automated control of exhaust emissions, reducing the risk of accidental release of radioactive gases before they have fully decayed due to human error. The primary alarm system for exhaust emission monitoring activates the iodine filter in the ventilation system, increasing the replacement frequency of the iodine filter from once every 2 years to once every 5 years, thus extending the service life of the iodine filter and reducing the amount of solid waste from the nuclear power plant.

[0077] 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 system for treating hydrogen-containing radioactive waste gas from a nuclear power plant, characterized in that, Includes a pretreatment unit, a treatment loop, and a filtration and discharge unit; The processing loop includes a pretreatment unit, a monitoring unit, and a gas recovery unit. The inlet of the pretreatment unit is connected to the main loop of the nuclear power plant, and the outlet of the pretreatment unit is connected to the inlet of the pretreatment unit. The outlet of the pretreatment unit is connected to the inlet of the monitoring unit. One outlet of the monitoring unit is connected to the inlet of the gas recovery unit, and the other outlet is connected to the inlet of the filtration and emission unit. The monitoring unit includes at least one monitoring device for monitoring the exhaust gas at the outlet of the pretreatment unit. The first end of the monitoring device is connected to the outlet of the pretreatment unit, and the second end of the monitoring device is connected to the inlet of the gas recovery unit and the other end is connected to the inlet of the filtration and emission unit. The outlet of the gas recovery unit is connected to the inlet of the pretreatment unit. The filtration and emission unit includes a first filtration branch and a second filtration branch arranged in parallel, and the outlet of the filtration and emission unit is connected to the external environment; the filtration and emission unit also includes an exhaust device for discharging exhaust gas, and the exhaust gas after being filtered by the first filtration branch or the second filtration branch is discharged into the external environment through the exhaust device; the first filtration branch includes a fifth isolation valve and an aerosol filter, and the outlet of the monitoring unit is connected to the exhaust device in sequence through the fifth isolation valve and the aerosol filter; The second filtration branch includes a sixth isolation valve and an iodine filter, and the outlet of the monitoring unit is connected to the exhaust device in sequence through the sixth isolation valve and the iodine filter; The nuclear power plant hydrogen-containing radioactive waste gas treatment system also includes a gas monitor, which is installed on the exhaust device to monitor the waste gas in the exhaust device. If the radioactivity of the waste gas measured by the gas monitor exceeds a set threshold, an interlock action is triggered to stop the waste gas emission of the waste gas treatment system. The hydrogen-containing radioactive waste gas from the nuclear power plant is pressure-regulated and dried by the pretreatment unit, then enters the treatment loop for decay and monitoring, and is discharged into the external environment through the filtration and emission unit.

2. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The pretreatment unit includes a compressor and a dryer. The hydrogen-containing radioactive waste gas from the nuclear power plant is pressurized by the compressor and then discharged to the dryer for drying.

3. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 2, characterized in that, The pretreatment unit also includes a buffer tank, the first end of which is connected to the main circuit of the nuclear power plant, and the second end of which is connected to the first end of the compressor, for collecting hydrogen-containing radioactive waste gas generated by the main circuit of the nuclear power plant.

4. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 2 or 3, characterized in that, The pretreatment unit further includes a gas cooler, the first end of which is connected to the second end of the compressor, and the second end of which is connected to the first end of the dryer.

5. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 2, characterized in that, The dryer is a silica gel dryer.

6. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The retention treatment unit includes at least one activated carbon retention bed, and at least one of the activated carbon retention beds is connected to the outlet of the pretreatment unit.

7. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 6, characterized in that, The activated carbon retention bed is provided in two parts, including a first activated carbon retention bed and a second activated carbon retention bed; the exhaust gas at the outlet of the pretreatment unit passes through the first activated carbon retention bed and the second activated carbon retention bed in sequence for retention and decay.

8. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The nuclear power plant hydrogen-containing radioactive waste gas treatment system is also equipped with a pressure regulating valve for adjusting the pressure of the nuclear power plant hydrogen-containing radioactive waste gas; the pressure regulating valve is located between the pretreatment unit and the retention treatment unit.

9. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The monitoring device is installed in a single unit, and the gas recovery unit includes a seventh isolation valve, a circulation pump, and a ninth isolation valve. The outlet of the retention treatment unit is connected to the first end of the monitoring device through the first isolation valve. The second end of the monitoring device is connected to the inlet of the retention treatment unit through the seventh isolation valve, the circulating pump and the ninth isolation valve in sequence, and to the inlet of the filtration and discharge unit through the third isolation valve.

10. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The monitoring device is configured in two parts, including a first monitoring device and a second monitoring device connected in parallel; the gas recovery unit includes a seventh isolation valve, an eighth isolation valve, a circulation pump, and a ninth isolation valve. One outlet of the retention treatment unit is connected to the first end of the first monitoring device via a first isolation valve, and the other outlet is connected to the first end of the second monitoring device via a second isolation valve; The second end of the first monitoring device is connected in sequence through the seventh isolation valve, the circulating pump and the ninth isolation valve to the inlet of the retention treatment unit, and in another sequence through the third isolation valve to the inlet of the filtration and discharge unit; the second end of the second monitoring device is connected in sequence through the eighth isolation valve, the circulating pump and the ninth isolation valve to the inlet of the retention treatment unit, and in another sequence through the fourth isolation valve to the inlet of the filtration and discharge unit.

11. The nuclear power plant hydrogen-containing radioactive waste gas treatment system according to claim 1, characterized in that, The filtration and emission unit also includes a ventilation device, which is installed on the pipeline between the monitoring unit and the filtration and emission unit. The ventilation device exhausts diluted waste gas that has been monitored by the monitoring unit and then discharged to the first filtration branch or the second filtration branch.

12. A method for treating hydrogen-containing radioactive waste gas from a nuclear power plant, applicable to the hydrogen-containing radioactive waste gas treatment system of any one of claims 1-11, characterized in that, Includes the following steps: S1. Obtain the monitoring results of the monitoring unit, switch to the first filtration branch or the second filtration branch for waste gas filtration according to the monitoring results, and control the connection or disconnection of the gas recovery unit; wherein, the monitoring results include the radioactivity concentration of the hydrogen-containing radioactive waste gas; Step S1 specifically includes: S11. Determine whether the monitoring results are all greater than the first threshold within a first preset time. If yes, execute step S12. If no, switch to the first filtration branch for exhaust gas filtration. S12. Switch to the second filter branch for exhaust gas filtration, and continue to determine whether the monitoring results are greater than the second threshold within a second preset time. If yes, proceed to step S13; otherwise, proceed to step S11. Wherein, the second threshold is greater than the first threshold. S13. Stop discharging exhaust gas into the filter emission unit and automatically trigger the connection of the gas recovery unit for exhaust gas recirculation treatment.

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