Radioactive waste disposal cavern radioactive material monitoring system and method

Abstract

The application discloses a radioactive substance monitoring system and method in a radioactive waste disposal cave, and belongs to the field of radioactive waste disposal. The radioactive substance monitoring system in the radioactive waste disposal cave comprises a control unit, an exhaust unit, a plurality of radon monitoring devices arranged at intervals in the radioactive waste disposal cave, a plurality of radioactive aerosol monitoring devices arranged at intervals in the radioactive waste disposal chamber and in the exhaust pipeline downstream of the exhaust unit, and a data collector. The data collector transmits at least radon radioactivity concentration information and aerosol radioactivity concentration information to the control unit. The radon radioactivity concentration is comprehensively monitored by the radon monitoring device, and the aerosol radioactivity concentration in the radioactive waste disposal chamber is monitored by the radioactive aerosol monitoring device, so that the radioactivity concentration of the radioactive substance in the cave can be known in time, and the exhaust unit can be started in time for ventilation when necessary, so as to reduce the radioactivity concentration of the radioactive substance in the cave and the risk of internal exposure radiation of personnel.

Description

Technical Field

[0001] This invention relates to the field of radioactive waste disposal technology, and in particular to a radioactive material monitoring system and method for radioactive waste disposal caves. Background Technology

[0002] Nuclear power plants generate low- and intermediate-level radioactive solid waste during operation and decommissioning. Cavern disposal is a method of disposing of radioactive waste, which involves placing the waste in caves (abandoned mine shafts, existing artificial caverns, or caves specifically excavated for waste disposal) on the surface of mountains or at depths of tens of meters below the surface, in caves with different geological structures and types. Cavern disposal has advantages such as requiring less land, causing less disturbance to the surface, and providing better isolation from the biosphere.

[0003] During the disposal of radioactive waste, radioactive materials inevitably exist in the air inside the radioactive waste disposal cavern. If workers inside the radioactive waste disposal cavern inhale radioactive materials with excessively high activity concentrations, they will be at risk of internal radiation exposure. Therefore, it is necessary to know the activity concentration of radioactive materials in the air inside the radioactive waste disposal cavern in a timely manner so that measures can be taken promptly when the activity concentration of radioactive materials is high to reduce the risk of internal radiation exposure to personnel. However, there is no relevant setting in the existing technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and method for monitoring radioactive materials in a cave for the disposal of radioactive waste.

[0005] The technical solution adopted by the present invention to solve its technical problem is: to provide a radioactive material monitoring system in a radioactive waste disposal cave, which includes a control unit, an exhaust unit, multiple radon monitoring devices, multiple radioactive aerosol monitoring devices, and a data acquisition device;

[0006] Multiple radioactive aerosol monitoring devices are arranged at intervals in the radioactive waste disposal cavern and in the downstream exhaust duct of the exhaust fan of the exhaust unit; multiple radon monitoring devices are arranged at intervals in the radioactive waste disposal cavern.

[0007] The radon monitoring device, the radioactive aerosol monitoring device, the exhaust unit, and the data acquisition unit are respectively connected to the control unit;

[0008] The data acquisition unit is connected to the radon monitoring device and the radioactive aerosol monitoring device respectively; the data acquisition unit transmits at least the radon radioactivity concentration information measured by the radon monitoring device and the aerosol radioactivity concentration information measured by the radioactive aerosol monitoring device to the control unit.

[0009] Preferably, the radon monitoring device includes a first measuring pipeline, a first valve assembly disposed on the first measuring pipeline and used to control the on / off state of the first measuring pipeline, a first gas sampling pump and a first flow meter disposed on the first measuring pipeline, a first gas storage tank and a radon detector disposed in the first gas storage tank;

[0010] The first measuring pipeline includes a first inlet pipe and a first outlet pipe; the first gas storage tank is connected between the first inlet pipe and the first outlet pipe; the end of the first inlet pipe away from the first gas storage tank and the end of the first outlet pipe away from the first gas storage tank are respectively connected to the outside atmosphere;

[0011] The first intake pipe, the first gas storage tank, and the first exhaust pipe together form a purging circuit.

[0012] Preferably, the first measuring pipeline further includes a bypass pipeline; the air inlet end of the bypass pipeline is connected to the first air inlet pipeline; the air outlet end of the bypass pipeline is connected to the outside atmosphere through the first air outlet pipeline.

[0013] Preferably, the radioactive aerosol monitoring device includes a second measuring pipeline, a second valve assembly disposed on the second measuring pipeline and used to control the on / off state of the second measuring pipeline, a second gas sampling pump and a second flow meter disposed on the second measuring pipeline, a second gas storage tank, and at least one radioactive material detector disposed in the second gas storage tank;

[0014] The second measuring pipeline includes a second inlet pipe and a second outlet pipe; the second gas storage tank is connected between the second inlet pipe and the second outlet pipe; the end of the second inlet pipe away from the second gas storage tank and the end of the second outlet pipe away from the second gas storage tank are respectively connected to the outside atmosphere.

[0015] Preferably, the second measuring pipeline further includes a reverse purging pipeline; the radioactive aerosol monitoring device further includes a purging pump installed on the reverse purging pipeline;

[0016] The inlet of the reverse purging pipe is connected to the outside atmosphere, and the outlet of the reverse purging pipe is connected to the second outlet pipe.

[0017] Preferably, the second measuring pipeline further includes a sampling pipeline; the radioactive aerosol monitoring device further includes a third gas storage tank disposed on the sampling pipeline; the inlet end of the sampling pipeline is connected to the second inlet pipeline, and the outlet end of the sampling pipeline is connected to the second outlet pipeline.

[0018] Preferably, two radioactive material detectors are arranged at intervals inside the second gas storage tank; one of the radioactive material detectors is a first detector for measuring alpha, beta, and gamma ray signals; and the other radioactive material detector is a second detector for measuring gamma ray signals.

[0019] Preferably, each of the radon monitoring devices and each of the radioactive aerosol monitoring devices is equipped with an alarm unit; the alarm unit includes an audible and visual alarm and an alarm communication module for transmitting alarm information to the data acquisition device.

[0020] The present invention also provides a method for monitoring radioactive materials in a radioactive waste disposal cavern, which employs the radioactive material monitoring system for radioactive waste disposal caverns described in any of the above-mentioned embodiments. The method for monitoring radioactive materials in a radioactive waste disposal cavern includes the following steps:

[0021] S1. Multiple radon monitoring devices are installed at intervals inside the radioactive waste disposal cavern;

[0022] Multiple radioactive aerosol monitoring devices are installed at intervals inside the radioactive waste disposal cavern and in the ducts of the exhaust fans of the exhaust unit.

[0023] A data acquisition device is installed inside the radioactive waste disposal cavern, and the radon monitoring device and the radioactive aerosol monitoring device are respectively connected to the input end of the data acquisition device;

[0024] Connect the output of the data acquisition device to the control unit;

[0025] S2. Each of the radon monitoring devices measures the radon radioactivity concentration at its location and transmits it to the data acquisition unit; each of the radioactive aerosol monitoring devices measures the aerosol radioactivity concentration at its location and transmits it to the data acquisition unit.

[0026] The control unit collects and records preset information through the data acquisition device; the preset information includes radon radioactivity concentration information and aerosol radioactivity concentration information.

[0027] S3. Determine whether the radon radioactivity concentration measured by the radon monitoring device is greater than the first preset value; if yes, then activate the exhaust unit through the control unit; if no, continue to execute step S2.

[0028] Determine whether the aerosol radioactivity concentration measured by the radioactive aerosol monitoring device is greater than a second preset value; if yes, then activate the exhaust unit through the control unit; if no, continue to execute step S2.

[0029] Preferably, the radon monitoring device includes a first measuring pipeline, a first valve assembly disposed on the first measuring pipeline and used to control the on / off state of the first measuring pipeline, a first gas sampling pump disposed on the first measuring pipeline, a first gas storage tank, and a radon detector disposed in the first gas storage tank;

[0030] The first measuring pipeline includes a first inlet pipe and a first outlet pipe; the first gas storage tank is connected between the first inlet pipe and the first outlet pipe; the end of the first inlet pipe away from the first gas storage tank and the end of the first outlet pipe away from the first gas storage tank are respectively connected to the outside atmosphere;

[0031] Step S2 includes the following sub-steps:

[0032] S2.1 Adjust the first valve assembly to connect the first inlet pipe, the first gas storage tank, and the first outlet pipe to each other and to the outside atmosphere; start the first gas sampling pump to allow outside gas to flow through the first inlet pipe, the first gas storage tank, and the first outlet pipe in sequence to purge the inside of the first gas storage tank before measurement.

[0033] S2.2 Adjust the first valve assembly to isolate the first gas storage tank from the outside atmosphere, and the radon detector measures the radioactivity concentration of the aerosol remaining in the first gas storage tank.

[0034] S2.3 After a preset time has elapsed since step S2.2, repeat step S2.1.

[0035] The present invention has at least the following beneficial effects: it enables comprehensive monitoring of radon activity concentration in the radioactive waste disposal cavern through a radon monitoring device, and aerosol activity concentration monitoring of the radioactive waste disposal cavern through a radioactive aerosol monitoring device, thereby enabling monitoring of the activity of radioactive substances in the air within the radioactive waste disposal cavern and timely obtaining information on the activity concentration of radioactive substances in the air within the radioactive waste disposal cavern. When necessary, the exhaust unit can be activated in a timely manner through the control unit to ventilate the cavern, thereby reducing the concentration of radioactive substances in the air within the cavern and reducing the risk of personnel being exposed to internal radiation. Attached Figure Description

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0037] Figure 1 This is a schematic diagram of the system connection of a radioactive material monitoring system in a radioactive waste disposal cave according to an embodiment of the present invention;

[0038] Figure 2This is a schematic diagram showing the arrangement of the radon monitoring device and the radioactive aerosol monitoring device in a radioactive material monitoring system for radioactive waste disposal cave according to an embodiment of the present invention, within a radioactive waste disposal cave.

[0039] Figure 3 This is a schematic diagram of the structural connection of the radon monitoring device in a radioactive material monitoring system for radioactive waste disposal caves according to an embodiment of the present invention.

[0040] Figure 4 This is a schematic diagram of the structural connection of the radioactive aerosol monitoring device in a radioactive material monitoring system for radioactive waste disposal caves according to an embodiment of the present invention. Detailed Implementation

[0041] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0042] Through actual measurement and analysis, the radioactive materials within the radioactive waste disposal cavern comprise two categories: During the operation of the radioactive waste disposal cavern, its surrounding rock and bedrock continuously release colorless and odorless radioactive radon gas into the cavern. The decay products of radon gas diffuse into the air of the disposal cavern in the form of aerosols. Simultaneously, during the disposal of low- and intermediate-level radioactive solid waste, radionuclides also diffuse into the air of the disposal cavern in the form of aerosols. For example... Figure 2 As shown, the radioactive waste disposal cavern includes several different chambers, such as access chamber 63, construction chamber 62, escape chamber 64, and radioactive waste disposal chamber 61. The radioactive waste disposal chamber is the chamber within the cavern used for disposing of radioactive waste. This chamber is the area for hoisting and stacking radioactive solid waste. During this process, there is a risk of radioactive solid waste packages falling and breaking due to operational errors, causing radionuclides to diffuse into the disposal cavern as aerosols. Therefore, workers in the radioactive waste disposal cavern who inhale excessively high concentrations of radon gas and other radioactive aerosols face the risk of internal radiation exposure. Since radon gas and other radioactive aerosols are colorless and odorless gases, a system is needed to monitor radioactive materials within the cavern to promptly determine their activity concentration and respond accordingly.

[0043] like Figures 1 to 4 As shown, a radioactive material monitoring system in a radioactive waste disposal cave according to an embodiment of the present invention includes a control unit 4, an exhaust unit, multiple radon monitoring devices 1, multiple radioactive aerosol monitoring devices 2, and a data acquisition device 3.

[0044] Control unit 4 is used to control the opening and closing of the exhaust unit, and to receive and record preset information via data acquisition unit 3. This preset information may include radioactivity concentration data measured by radon monitoring device 1 and radioactive aerosol monitoring device 2, alarm information indicating radioactivity concentration exceeding thresholds, and equipment operating status information of radon monitoring device 1 and radioactive aerosol monitoring device 2. Control unit 4 may include a server, which can receive, record, and store the aforementioned preset information via data acquisition unit 3, and display the preset information in real time, enabling remote monitoring of the radioactivity concentration of radon and other radioactive aerosols within the radioactive waste disposal cavern, as well as the operating status of radon monitoring device 1 and radioactive aerosol monitoring device 2. Data acquisition unit 3 and control unit 4 can communicate via optical fiber.

[0045] Data acquisition device 3 can be either wired or wireless. When using a wired data acquisition device, data acquisition device 3, radon monitoring device 1, radioactive aerosol monitoring device 2, and control unit 4 are interconnected via cable trays, cables, optical fibers, or other equipment. When using a wireless data acquisition device, a wireless network can be configured within the cavern, and wireless communication modules can be installed in radon monitoring device 1 and radioactive aerosol monitoring device 2 to achieve wireless communication instead of wired (optical fiber, cable) communication.

[0046] The exhaust unit serves to ventilate the cavern. It is activated at appropriate times to ventilate the cavern, reducing the concentration of radioactive materials in the air and protecting the health and safety of personnel. Radon monitoring device 1 and radioactive aerosol monitoring device 2 are used to monitor the radon activity concentration and the radioactivity concentration of other radioactive aerosols within the cavern, respectively. Other radioactive aerosols refer to those generated during the disposal of low- and intermediate-level radioactive solid waste. Data acquisition device 3 acts as a data transmission bridge between radon monitoring device 1, radioactive aerosol monitoring device 2, and control unit 4, improving communication efficiency and stability.

[0047] like Figure 2As shown, multiple radioactive aerosol monitoring devices 2 are arranged at intervals within the radioactive waste disposal chamber 61 of the radioactive waste disposal cavern and within the duct 5 of the exhaust fan of the exhaust unit. The duct 5 can be a downstream exhaust duct. That is, multiple radioactive aerosol monitoring devices 2 are arranged at intervals within the radioactive waste disposal chamber 6 of the radioactive waste disposal cavern. These devices are used to monitor radioactive aerosols generated during the disposal of low- and medium-level radioactive solid waste. Multiple radioactive aerosol monitoring devices 2 are also arranged at intervals within the downstream exhaust duct 5 of the exhaust fan of the exhaust unit. These devices are used to monitor the radioactivity concentration of gaseous effluents discharged from the cavern. Radon monitoring devices 1 are arranged at intervals within the radioactive waste disposal cavern. In other words, the radioactive waste disposal cavern comprises multiple different chambers, and the radon monitoring devices 1 are arranged at intervals within each chamber, enabling comprehensive measurement of radon radioactivity within the radioactive waste disposal cavern.

[0048] like Figure 1 As shown, the radon monitoring device 1, the radioactive aerosol monitoring device 2, the exhaust unit, and the data acquisition device 3 are all connected to the control unit 4. The data acquisition device 3 is connected to both the radon monitoring device 1 and the radioactive aerosol monitoring device 2. The data acquisition device 3 transmits at least the radon radioactivity concentration information measured by the radon monitoring device 1 and the aerosol radioactivity concentration information measured by the radioactive aerosol monitoring device 2 to the control unit 4. Furthermore, the data acquisition device 3 can also transmit alarm information indicating that the radioactivity concentration exceeds a threshold, as well as equipment operating status information of the radon monitoring device 1 and the radioactive aerosol monitoring device 2, to the control unit 4. The alarm information indicating that the radioactivity concentration exceeds a threshold can be issued by the radon monitoring device 1 and the radioactive aerosol monitoring device 2 after determining that the detected radioactivity concentration at a certain moment exceeds a preset threshold.

[0049] Therefore, the radon monitoring device 1 comprehensively monitors the radon activity concentration within the radioactive waste disposal cavern, while the radioactive aerosol monitoring device 2 monitors the aerosol radioactive activity concentration within the radioactive waste disposal chamber 61. This allows for the monitoring of the activity concentration of radioactive materials in the air within the radioactive waste disposal cavern, enabling timely information on the concentration of radioactive materials and assessing the associated risks. If necessary, the exhaust unit 4 activates the ventilation system to ventilate the cavern, reducing the concentration of radioactive materials in the air and minimizing the risk of internal radiation exposure to personnel.

[0050] Furthermore, within the radioactive waste disposal cavern, the distance between two adjacent radon monitoring devices 1 is 75m to 125m. Preferably, the distance between two adjacent radon monitoring devices 1 is 100m. The radioactive material monitoring system within the radioactive waste disposal cavern may also include a power distribution unit. For example... Figure 1 As shown, the power distribution unit includes a power distribution box 7 and cables installed in the radioactive waste disposal cavern. The power distribution box 7 is connected to the radon monitoring device 1, the radioactive aerosol monitoring device 2 and the data acquisition device 3 via cables to provide power to each device.

[0051] like Figure 3 As shown, in this embodiment, the radon monitoring device 1 includes a first measuring pipeline, a first valve assembly disposed on the first measuring pipeline, a first gas sampling pump 10 and a first flow meter 11 disposed on the first measuring pipeline, a first gas storage tank 12, and a radon detector (not shown) disposed in the first gas storage tank 12. The first valve assembly is used to control the on / off state of the first measuring pipeline; that is, the first valve assembly can be used to control the overall on / off state of the first measuring pipeline, or it can control the on / off state of a portion of the first measuring pipeline. The first valve assembly can be arranged on the first measuring pipeline according to the specific structure of the first measuring pipeline. The first valve assembly can be an electric valve to achieve automatic control of the on / off state of the first measuring pipeline. The first measuring pipeline includes a first inlet pipe 13a and a first outlet pipe 13b. The first gas storage tank 12 is connected between the first inlet pipe 13a and the first outlet pipe 13b. The end of the first inlet pipe 13a away from the first gas storage tank 12 and the end of the first outlet pipe 13b away from the first gas storage tank 12 are respectively connected to the outside atmosphere. Furthermore, the first air inlet pipe 13a, the first gas storage tank 12, and the first air outlet pipe 13b together form a purging circuit. This purging circuit is used to purge the inside of the first gas storage tank 12 before measurement to eliminate the interference of aerosol particles deposited inside the tank on the measurement results.

[0052] Specifically, the first gas storage tank 12 is used to store gas. The first gas storage tank 12 contains a collection plate and related energized components. The gas stored in the first gas storage tank 12 contains radioactive radon gas (mainly radon isotopes 222Rn, 220Rn, and 219Rn). The decay products (218Po, 216Po, and 215Po) produced by the decay of radioactive radon gas are collected and deposited on the collection plate under the action of a high-voltage electric field. The radon detector directly measures the alpha rays released by the radon decay products (218Po, 216Po, and 215Po) to obtain the radioactivity of 218Po, 216Po, and 215Po. The radon monitoring device 1 also includes a data processing module. This module is connected to both the first flow meter 11 and the radon detector. By combining the radon radioactivity measured by the radon detector inside the chamber with the flow rate measured by the first flow meter 11, the volume (volume parameter) of the first gas storage tank 12, and the measurement time, the corresponding radioactivity concentration can be calculated. Furthermore, the radon monitoring device 1 may also include a first pressure gauge 14, which is connected to the first gas storage tank 12. For example, the first pressure gauge 14 can be connected to the first outlet pipe 13b, i.e., connected to the outlet end of the first gas storage tank 12. The first pressure gauge 14 is used to detect the gas pressure entering the first gas storage tank 12 for volume parameter correction. That is, when the inside of the first gas storage tank 12 is at normal pressure, the actual volume of the first gas storage tank 12 can be directly used as the volume parameter; or gas can be filled into the first gas storage tank 12 to a positive pressure, and the actual volume of the first gas storage tank 12 can be increased by a corresponding multiple (e.g., increased by three times) based on the reading of the first pressure gauge 14 (e.g., 3 times atmospheric pressure) to be used as the volume parameter.

[0053] In this embodiment, the first flow meter 11 and the first gas sampling pump 10 are both installed on the first inlet pipe 13a. The first valve assembly includes a shut-off valve 16a, a flow regulating valve 16b, and an electric valve 16c installed on the first inlet pipe 13a, and an electric valve 16d and a shut-off valve 16e installed on the first outlet pipe 13b. On the first inlet pipe 13a, along the direction away from the first gas storage tank 12 (i.e., near the inlet end of the first inlet pipe 13a), the electric valve 16c, the first gas sampling pump 10, the first flow meter 11, the flow regulating valve 16b, and the shut-off valve 16a are arranged sequentially. The first pressure gauge 14 is installed on the first outlet pipe 13b. On the first outlet pipe 13b, along the direction away from the first gas storage tank 12 (i.e., near the outlet end of the first outlet pipe 13b), the first pressure gauge 14, the electric valve 16d, and the shut-off valve 16e are arranged sequentially on the first inlet pipe 13a.

[0054] The radioactivity measurement process of radon monitoring device 1 includes the following steps:

[0055] S2.1 Adjust the first valve assembly (open shut-off valve 16a, flow regulating valve 16b, electric valve 16c, electric valve 16d, shut-off valve 16e) to connect the first inlet pipe 13a, the first gas storage tank 12, and the first outlet pipe 13b to each other and to the outside atmosphere. Start the first gas sampling pump 10 to allow outside gas to flow sequentially through the first inlet pipe 13a, the first gas storage tank 12, and the first outlet pipe 13b (purge circuit) to purge the inside of the first gas storage tank 12 before measurement.

[0056] S2.2 Adjust the first valve assembly (close electric valve 16c and electric valve 16d) to isolate the first gas storage tank 12 from the outside atmosphere, and the radon detector measures the radioactivity of the aerosol remaining in the first gas storage tank 12.

[0057] S2.3. After a preset time has elapsed since step S2.2, step S2.1 is repeated. That is, after the gas remains in the first gas storage tank 12 for a preset time, the purging-measurement process is repeated to achieve continuous online monitoring of the gas's radioactivity activity. The preset time is greater than 3.28 minutes (3.28 minutes is the longest half-life of radon decay progeny), specifically it can be 4 minutes, 5 minutes, etc., to ensure that the radon decay progeny has passed its longest half-life during measurement, thus improving the accuracy of the measurement results.

[0058] In this embodiment, the distance between the inlet opening of the first air inlet pipe 13a and the ground inside the cave is 1.5m. This height is the average height of the inhalation point where workers inside the cave directly inhale the gas. By using the gas at this height as the monitoring target, the monitoring results of radioactivity concentration can be well correlated with the risk of internal radiation exposure to personnel, so as to accurately assess the degree of internal radiation exposure risk to personnel. If necessary, the exhaust unit can be opened to reduce the concentration of radioactive materials in the cave. Furthermore, the inlet opening of the first air inlet pipe 13a and the outlet opening of the first air outlet pipe 13b should be arranged alternately, and the distance between them should be greater than 1m. This prevents the gas at the outlet end of the first air outlet pipe 13b from interfering with the representativeness of the sampled gas at the inlet end of the first air inlet pipe 13a, thereby improving the accuracy of radioactivity measurement.

[0059] Furthermore, the first measuring pipeline also includes a bypass pipe 15. The inlet end of the bypass pipe 15 is connected to the first inlet pipe 13a. The outlet end of the bypass pipe 15 is connected to the outside atmosphere through the first outlet pipe 13b. Specifically, the outlet end of the bypass pipe 15 can be directly connected to the outside atmosphere via the first outlet pipe 13b, or it can be indirectly connected to the outside atmosphere. For example, in this embodiment, the outlet end of the bypass pipe 15 is connected to the first outlet pipe 13b and communicates with the first outlet pipe 13b, while the outlet end of the bypass pipe 15 is indirectly connected to the outside atmosphere through the outlet end of the first outlet pipe 13b. Thus, the first gas sampling pump 10 can remain open without frequent starting and stopping. Specifically, the first valve assembly also includes an electric valve 16f and an electric valve 16h disposed on the bypass pipe 15. In step S2.1 above, only the first valve assembly needs to be adjusted (closing electric valves 16f and 16h) to isolate the bypass pipe 15 from the first inlet pipe 13a and the first outlet pipe 13b, thus not affecting the purging function of the purging circuit; in step S2.2 above, only the first valve assembly needs to be adjusted (opening electric valves 16f and 16h, closing electric valves 16c and 16d) to isolate the first gas storage tank 12 from the outside atmosphere and connect the bypass pipe 15 to the first inlet pipe 13a. The gas drawn by the first gas sampling pump 10 enters the bypass pipe 15 from the first inlet pipe 13a and is then discharged to the outside atmosphere from the first outlet pipe 13b. Subsequently, it is only necessary to readjust the first valve assembly (close the electric valves 16f and 16h, and open the electric valves 16c and 16d) to isolate the bypass pipe 15 from the first inlet pipe 13a, so that the first inlet pipe 13a, the first gas storage tank 12, and the first outlet pipe 13b are interconnected and connected to the outside atmosphere, and the purging operation can continue.

[0060] In this embodiment, the radioactive aerosol monitoring device 2 includes a second measuring pipeline, a second valve assembly disposed on the second measuring pipeline, a second gas sampling pump 20 and a second flow meter 21 disposed on the second measuring pipeline, a second gas storage tank 22, and at least one radioactive material detector (not shown) disposed within the second gas storage tank 22. The second valve assembly is used to control the on / off state of the second measuring pipeline; that is, the second valve assembly can be used to control the on / off state of the entire second measuring pipeline, or it can control the on / off state of a portion of the second measuring pipeline. The second valve assembly can be arranged on the second measuring pipeline according to the specific structure of the second measuring pipeline. The second valve assembly can be an electric valve to achieve automatic control of the on / off state of the second measuring pipeline.

[0061] The second measuring pipeline includes a second inlet pipe 23a and a second outlet pipe 23b. A second gas storage tank 22 is connected between the second inlet pipe 23a and the second outlet pipe 23b; the end of the second inlet pipe 23a away from the second gas storage tank 22 and the end of the second outlet pipe 23b away from the second gas storage tank 22 are respectively connected to the outside atmosphere.

[0062] Specifically, the second gas storage tank 22 is used to store the gas. The radioactive aerosol monitoring device 2 contains a thin-film filter paper, which filters aerosol particles from the air. These aerosol particles are deposited on the filter paper, and a radioactive material detector measures the radioactivity of the aerosol particles on the filter paper. The radioactive aerosol monitoring device 2 also includes a data processing module; this module is connected to both the second flow meter 21 and the radioactive material detector. By combining the aerosol radioactivity measured by the radioactive material detector with the flow rate measured by the second flow meter 21, the corresponding radioactivity concentration can be calculated. The operating process of the radioactive aerosol monitoring device 2 is similar to that of the radon monitoring device 1, and will not be repeated here.

[0063] Furthermore, the pre-measurement purging process of the radioactive aerosol monitoring device 2 can also employ a reverse purging mode: the second measurement pipeline further includes a reverse purging pipe 24. The radioactive aerosol monitoring device 2 also includes a purging pump 26 installed on the reverse purging pipe 24. The inlet end of the reverse purging pipe 24 is connected to the outside atmosphere, and the outlet end of the reverse purging pipe 24 is connected to the second outlet pipe 23b. During the pre-measurement purging, the second valve assembly is adjusted to connect the reverse purging pipe 24, the second outlet pipe 23b, the second gas storage tank 22, and the second inlet pipe 23a. The second gas sampling pump 20 is then started, and the gas flows sequentially through the reverse purging pipe 24, the second outlet pipe 23b, and the second gas storage tank 22, finally being discharged to the outside atmosphere from the second inlet pipe 23a. This achieves the use of reverse airflow to purge the inside of the second gas storage tank 22, resulting in higher cleaning efficiency and a higher degree of cleanliness inside the tank, thus more thoroughly eliminating the influence of aerosol particles deposited inside the tank on the measurement results.

[0064] Furthermore, the second measuring pipeline also includes a sampling pipeline 27. The radioactive aerosol monitoring device 2 also includes a third gas storage tank 28 installed on the sampling pipeline 27. The third gas storage tank 28 is used to acquire aerosol samples for analysis in the laboratory. The inlet end of the sampling pipeline 27 is connected to the second inlet pipeline 23a, and the outlet end of the sampling pipeline 27 is connected to the second outlet pipeline 23b. Specifically, by adjusting the second valve assembly to connect the sampling pipeline 27 with the second inlet pipeline 23a and the second outlet pipeline 23b, the gas in the second inlet pipeline 23a can be diverted to the sampling pipeline 27 and the third gas storage tank 28, so that a suitable amount of gas is retained in the third gas storage tank 28; if necessary, the sampling pipeline 27 can be isolated from the second inlet pipeline 23a and the second outlet pipeline 23b by adjusting the second valve assembly, that is, the third gas storage tank 28 can be isolated, and the gas retained in the third gas storage tank 28 can be sent to the laboratory for analysis. A flow meter 29 can also be installed on the sampling pipe 27 to detect the flow rate inside the sampling pipe 27.

[0065] In this embodiment, the second valve assembly includes a shut-off valve 25a, a flow regulating valve 25b, an electric valve 25c, a shut-off valve 25d, a shut-off valve 25e, a check valve 25f, an electric valve 25h, and a shut-off valve 25i and a flow regulating valve 25j, all disposed on the second inlet pipe 23a, away from the second gas storage tank 22 (i.e., near the inlet end of the second inlet pipe 23a). On the second inlet pipe 23a, along the direction away from the second gas storage tank 22 (i.e., near the inlet end of the second inlet pipe 23a), the second flow meter 21, the flow regulating valve 25b, and the shut-off valve 25a are arranged sequentially. On the second outlet pipe 23b, along the direction away from the second gas storage tank 22 (i.e., near the outlet end of the second outlet pipe 23b), the electric valve 25c, the second gas sampling pump 20, and the shut-off valve 25d are arranged sequentially.

[0066] By opening the shut-off valve 25a, flow regulating valve 25b, electric valve 25c, shut-off valve 25d, and second gas sampling pump 20, the second gas storage tank 22 can be purged forward before measurement. Closing the flow regulating valve 25b and electric valve 25c isolates the second gas storage tank 22 from the outside atmosphere, allowing the radioactive material detector inside the second gas storage tank 22 to measure the radioactivity of the gas remaining inside. Closing the shut-off valve 25d and opening the shut-off valve 25e, check valve 25f, electric valve 25h, electric valve 25c, flow regulating valve 25b, shut-off valve 25a, and purge pump 26 allows the reverse purge pipe 24 to generate a reverse airflow for reverse purging of the interior of the second gas storage tank 22.

[0067] Furthermore, two radioactive material detectors are arranged at intervals within the second gas storage tank 22. One of the radioactive material detectors is a first detector used to measure alpha, beta, and gamma-ray signals. The other radioactive material detector is a second detector used to measure gamma-ray signals. Specifically, the measurement signals from the first and second detectors are subjected to coincidence processing, i.e., the measurement signals from the first and second detectors are subtracted to obtain the alpha and beta-ray signals emitted by the aerosol particles. This coincidence measurement method can eliminate the gamma-ray energy response, thereby achieving efficient online continuous measurement of the radioactivity of aerosol particles within the second gas storage tank 22. Alternatively, in other embodiments, only one radioactive material detector is placed within the second gas storage tank 22, which can be a thin-film plastic scintillator or similar detector. Simultaneously, the entire radon monitoring device 1 is surrounded by a lead shield to shield the gamma-ray signals in the environment, which can also eliminate the gamma-ray energy response, thereby achieving efficient online continuous measurement of the radioactivity of aerosol particles within the second gas storage tank 22.

[0068] In this embodiment, each radon monitoring device 1 and each radioactive aerosol monitoring device 2 is equipped with an alarm unit. The alarm unit includes an audible and visual alarm and an alarm communication module for transmitting alarm information to the data acquisition unit 3. When the radon monitoring device 1 detects a radioactivity concentration exceeding a first preset value at a certain moment, the audible and visual alarm is triggered. Simultaneously, the alarm communication module transmits the alarm information to the data acquisition unit 3. The control unit 4 can obtain the information about the radioactivity concentration exceeding the threshold through the data acquisition unit 3. Personnel can then control the ventilation unit to open and ventilate the cave through the control unit 4. Alternatively, the control unit 4 can automatically control the ventilation unit to open and ventilate the cave after obtaining the information about the radioactivity concentration exceeding the threshold. Therefore, situations where the radioactivity concentration exceeds the threshold can be promptly detected, and the ventilation unit can be opened by the control unit 4 to ventilate the cave in a timely manner, thereby reducing the concentration of radioactive materials in the air inside the cave and reducing the risk of internal radiation exposure to personnel.

[0069] A method for monitoring radioactive materials inside a radioactive waste disposal cave according to an embodiment of the present invention includes the following steps:

[0070] S1. Multiple radon monitoring devices 1 are arranged at intervals within the radioactive waste disposal cavern. Multiple radioactive aerosol monitoring devices 2 are arranged at intervals within at least one radioactive waste disposal chamber 61 within the radioactive waste disposal cavern. A data acquisition unit 3 is installed within the radioactive waste disposal cavern, and the radon monitoring devices 1 and radioactive aerosol monitoring devices 2 are respectively connected to the input terminals of the data acquisition unit 3. The output terminal of the data acquisition unit 3 is connected to the control unit 4.

[0071] S2. Each radon monitoring device 1 measures the radon radioactivity concentration at its location and transmits the data to the data acquisition unit 3. Each radioactive aerosol monitoring device 2 measures the aerosol radioactivity concentration at its location and transmits the data to the data acquisition unit 3. The control unit 4 collects and records preset information through the data acquisition unit 3. The preset information includes radon radioactivity concentration information and aerosol radioactivity concentration information. This preset information may also include alarm information for radioactivity concentration exceeding the threshold, and equipment operating status information of radon monitoring device 1 and radioactive aerosol monitoring device 2, etc.

[0072] S3. Determine whether the radon radioactivity concentration measured by the radon monitoring device 1 is greater than the first preset value. If yes, the exhaust unit is activated by the control unit 4 to ventilate the cave and reduce the concentration of radioactive materials inside the cave. If no, continue to step S2. Specifically, the radon monitoring device 1 may have its own data processing module. The radon monitoring device 1 determines whether the measured radon radioactivity concentration is greater than the first preset value. If yes, the corresponding alarm information is transmitted to the control unit 4 through the data acquisition device 3, and then the exhaust unit is activated by the control unit 4. Alternatively, the radon monitoring device 1 may transmit the measured radon radioactivity concentration to the control unit 4 through the data acquisition device 3. The data processing module of the control unit 4 then determines whether the radon radioactivity concentration is greater than the first preset value. If yes, the exhaust unit is activated by the control unit 4.

[0073] Similarly, it is determined whether the aerosol radioactivity concentration measured by the radioactive aerosol monitoring device 2 is greater than the second preset value. If so, the exhaust unit is activated by the control unit 4. If not, step S2 is continued. Specifically, the radioactive aerosol monitoring device 2 itself may have a data processing module. The radioactive aerosol monitoring device 2 determines whether the measured aerosol radioactivity concentration is greater than the second preset value. If so, the corresponding alarm information is transmitted to the control unit 4 through the data acquisition device 3, and then the exhaust unit is activated by the control unit 4. Alternatively, the radioactive aerosol monitoring device 2 may transmit the measured aerosol radioactivity concentration to the control unit 4 through the data acquisition device 3. The data processing module of the control unit 4 then determines whether the aerosol radioactivity concentration is greater than the second preset value. If so, the exhaust unit is activated by the control unit 4. Furthermore, the control unit 4 may be manually operated to activate the exhaust unit, or the control unit 4 may automatically control the activation of the exhaust unit.

[0074] Furthermore, the first preset value can be used as the second-level alarm threshold. Step S3 may also include: determining whether the radon radioactivity concentration measured by the radon monitoring device 1 is greater than a third preset value. If so, the corresponding first-level alarm information is sent to the control unit through the data acquisition device. The third preset value is less than the first preset value, and the third preset value is used as the first-level alarm threshold, while the first preset value is used as the second-level alarm threshold.

[0075] Similarly, the second preset value can be used as the second-level alarm threshold. Step S3 may also include: determining whether the aerosol radioactivity concentration measured by the radioactive aerosol monitoring device 2 is greater than the fourth preset value. If so, the corresponding first-level alarm information is sent to the control unit through the data acquisition device. The fourth preset value is less than the second preset value, and the fourth preset value is used as the first-level alarm threshold, while the second preset value is used as the second-level alarm threshold.

[0076] For example, in this embodiment, the first preset value is 400 Bq / m 3 The third preset value is 200 Bq / m 3 The second preset value is 70 Bq / m 3 The fourth preset value is 35 Bq / m 3 That is, 200 Bq / m 3 As the first-level alarm threshold for radon monitoring device 1, 400 Bq / m³ 3 As the second-level alarm threshold for radon monitoring device 1; 35 Bq / m 3 As the first-level alarm threshold for radioactive aerosol monitoring device 2, 70 Bq / m 3 This serves as the second-level alarm threshold for the radioactive aerosol monitoring device 2.

[0077] Therefore, when the radioactivity concentration of gaseous substances in the cave exceeds the first-level alarm threshold, a first-level alarm message is sent to remind staff to pay attention, and at this time, it is not necessary to open the ventilation unit. When the radioactivity concentration of gaseous substances in the cave exceeds the second-level alarm threshold, a second-level alarm message and an audible and visual alarm are triggered, and the ventilation unit is opened for ventilation. This allows for reasonable monitoring of the radioactive risk in the radioactive waste disposal cave while avoiding frequent opening of the ventilation unit.

[0078] In this embodiment, the radon monitoring device 1 includes a first measuring pipeline, a first valve assembly disposed on the first measuring pipeline and used to control the on / off state of the first measuring pipeline, a first gas sampling pump 10 disposed on the first measuring pipeline, a first gas storage tank 12, and a radon detector disposed in the first gas storage tank 12.

[0079] The first measuring pipeline includes a first inlet pipe 13a and a first outlet pipe 13b. A first gas storage tank 12 is connected between the first inlet pipe 13a and the first outlet pipe 13b. The end of the first inlet pipe 13a away from the first gas storage tank 12 and the end of the first outlet pipe 13b away from the first gas storage tank 12 are respectively connected to the outside atmosphere.

[0080] Step S2 includes the following sub-steps:

[0081] S2.1 Adjust the first valve assembly (open shut-off valve 16a, flow regulating valve 16b, electric valve 16c, electric valve 16d, and shut-off valve 16e) to connect the first inlet pipe 13a, the first gas storage tank 12, and the first outlet pipe 13b to each other and to the outside atmosphere. Start the first gas sampling pump 10 to allow outside gas to flow sequentially through the first inlet pipe 13a, the first gas storage tank 12, and the first outlet pipe 13b to purge the inside of the first gas storage tank 12 before measurement.

[0082] S2.2 Adjust the first valve assembly (close electric valve 16c and electric valve 16d) to isolate the first gas storage tank 12 from the first inlet pipe 13a and the first outlet pipe 13b respectively, and the radon detector measures the radioactivity of the aerosol remaining in the first gas storage tank 12.

[0083] S2.3 After a preset time has elapsed since step S2.2, step S2.1 is repeated. That is, after the gas remains in the first gas storage tank 12 for a preset time, the purging-measurement process is repeated to achieve continuous online monitoring of gas radioactivity. Therefore, before measuring radioactivity, the interior of the first gas storage tank 12 is purged to eliminate interference from aerosol particles deposited within the first gas storage tank 12 on the measurement results, thereby improving the accuracy of the measurement results.

[0084] Furthermore, the preset time in step S2.3 is greater than 3.28 minutes (3.28 minutes is the longest half-life of radon decay products), specifically it can be 4 minutes, 5 minutes, etc., to ensure that the longest half-life of radon decay products has passed when the measurement is performed.

[0085] 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 material monitoring system for a radioactive waste disposal cave, characterized in that, Includes a control unit (4), an exhaust unit, multiple radon monitoring devices (1), multiple radioactive aerosol monitoring devices (2), and a data acquisition unit (3); Multiple radioactive aerosol monitoring devices (2) are arranged at intervals in the radioactive waste disposal cavern (6) of the radioactive waste disposal cavern and in the duct (5) of the exhaust fan of the exhaust unit; multiple radon monitoring devices (1) are arranged at intervals in the radioactive waste disposal cavern. The radon monitoring device (1), the radioactive aerosol monitoring device (2), the exhaust unit, and the data acquisition device (3) are respectively connected to the control unit (4); The data acquisition unit (3) is connected to the radon monitoring device (1) and the radioactive aerosol monitoring device (2) respectively; the data acquisition unit (3) transmits at least the radon radioactivity concentration information measured by the radon monitoring device (1) and the aerosol radioactivity concentration information measured by the radioactive aerosol monitoring device (2) to the control unit (4). The radon monitoring device (1) includes a first measuring pipeline, a first valve assembly installed on the first measuring pipeline for controlling the opening and closing of the first measuring pipeline, a first gas sampling pump (10) and a first flow meter (11) installed on the first measuring pipeline, a first gas storage tank (12), and a radon detector installed in the first gas storage tank (12). The first measuring pipeline includes a first inlet pipe (13a) and a first outlet pipe (13b); the first gas storage tank (12) is connected between the first inlet pipe (13a) and the first outlet pipe (13b); the end of the first inlet pipe (13a) away from the first gas storage tank (12) and the end of the first outlet pipe (13b) away from the first gas storage tank (12) are respectively connected to the outside atmosphere; The first inlet pipe (13a), the first gas storage tank (12), and the first outlet pipe (13b) together form a purging circuit. The purging circuit is used to purge the inside of the first gas storage tank (12) before measurement to eliminate the interference of aerosol particles deposited in the first gas storage tank (12) on the measurement results. The radon monitoring device (1) also includes a data processing module; the data processing module is connected to the first flow meter (11) and the radon detector respectively. The radon radioactivity activity measured by the radon detector in the first gas storage tank (12) is combined with the flow rate measured by the first flow meter (11), the volume of the first gas storage tank (12), and the measurement time to calculate the corresponding radioactivity concentration; the radon monitoring device (1) also includes a first pressure gauge (14), which is connected to the first gas storage tank (12). The first pressure gauge (14) is used to detect the gas pressure filled into the first gas storage tank (12) for volume parameter correction. When the inside of the first gas storage tank (12) is at normal pressure, the actual volume of the first gas storage tank (12) is directly used as the volume parameter; or gas is filled into the first gas storage tank (12) until the tank is at positive pressure, and the actual volume of the first gas storage tank (12) is increased by a corresponding multiple based on the reading of the first pressure gauge (14) to be used as the volume parameter; The first valve assembly includes a shut-off valve (16a), a flow regulating valve (16b), and an electric valve (16c) disposed on the first air inlet pipe (13a), and an electric valve (16d) and a shut-off valve (16e) disposed on the first air outlet pipe (13b). In the first air inlet pipe (13a), along the direction away from the first gas storage tank (12), the electric valve (16c), the first gas sampling pump (10), the first flow meter (11), the flow regulating valve (16b), and the shut-off valve (16a) are arranged sequentially on the first air inlet pipe (13a); a first pressure gauge (14) is disposed on the first air outlet pipe (13b), and in the first air outlet pipe (13b), along the direction away from the first gas storage tank (12), the first pressure gauge (14), the electric valve (16d), and the shut-off valve (16e) are arranged sequentially on the first air outlet pipe (13b). The first measuring pipeline also includes a bypass pipe (15); the air inlet of the bypass pipe (15) is connected to the first air inlet pipe (13a); the air outlet of the bypass pipe (15) is connected to the outside atmosphere through the first air outlet pipe (13b).

2. The radioactive material monitoring system in the radioactive waste disposal cave according to claim 1, characterized in that, The radioactive aerosol monitoring device (2) includes a second measuring pipeline, a second valve assembly installed on the second measuring pipeline for controlling the on / off state of the second measuring pipeline, a second gas sampling pump (20) and a second flow meter (21) installed on the second measuring pipeline, a second gas storage tank (22), and at least one radioactive material detector installed in the second gas storage tank (22); The second measuring pipeline includes a second inlet pipe (23a) and a second outlet pipe (23b); the second gas storage tank (22) is connected between the second inlet pipe (23a) and the second outlet pipe (23b); the end of the second inlet pipe (23a) away from the second gas storage tank (22) and the end of the second outlet pipe (23b) away from the second gas storage tank (22) are respectively connected to the outside atmosphere.

3. The radioactive material monitoring system in the radioactive waste disposal cave according to claim 2, characterized in that, The second measuring pipeline also includes a reverse purge pipeline (24); the radioactive aerosol monitoring device (2) also includes a purge pump (26) installed on the reverse purge pipeline (24); The air inlet of the reverse purging pipe (24) is connected to the outside atmosphere, and the air outlet of the reverse purging pipe (24) is connected to the second air outlet pipe (23b).

4. The radioactive material monitoring system in the radioactive waste disposal cave according to claim 2, characterized in that, The second measuring pipeline also includes a sampling pipeline (27); the radioactive aerosol monitoring device (2) also includes a third gas storage tank (28) installed on the sampling pipeline (27); the inlet end of the sampling pipeline (27) is connected to the second inlet pipeline (23a), and the outlet end of the sampling pipeline (27) is connected to the second outlet pipeline (23b).

5. The radioactive material monitoring system in the radioactive waste disposal cave according to claim 2, characterized in that, The second gas storage tank (22) contains two radioactive material detectors arranged at intervals; one of the radioactive material detectors is a first detector for measuring alpha, beta and gamma ray signals; the other radioactive material detector is a second detector for measuring gamma ray signals.

6. The radioactive material monitoring system for radioactive waste disposal caves according to any one of claims 1 to 5, characterized in that, Each of the radon monitoring devices (1) and each of the radioactive aerosol monitoring devices (2) is equipped with an alarm unit; the alarm unit includes an audible and visual alarm and an alarm communication module for transmitting alarm information to the data acquisition unit (3).

7. A method for monitoring radioactive materials inside a radioactive waste disposal cave, characterized in that, The radioactive material monitoring system for radioactive waste disposal caverns according to any one of claims 1 to 6, and the method for monitoring radioactive materials in radioactive waste disposal caverns, include the following steps: S1. Multiple radon monitoring devices are arranged at intervals inside the radioactive waste disposal cave (1); Multiple radioactive aerosol monitoring devices (2) are arranged at intervals in the radioactive waste disposal cavern (6) of the radioactive waste disposal cavern and in the duct (5) of the exhaust fan of the exhaust unit. A data acquisition device (3) is installed inside the radioactive waste disposal cavern, and the radon monitoring device (1) and the radioactive aerosol monitoring device (2) are respectively connected to the input end of the data acquisition device (3); Connect the output of the data acquisition unit (3) to the control unit (4); S2. Each of the radon monitoring devices (1) measures the radon radioactivity concentration at its location and transmits it to the data acquisition unit (3); each of the radioactive aerosol monitoring devices (2) measures the aerosol radioactivity concentration at its location and transmits it to the data acquisition unit (3). The control unit (4) collects and records preset information through the data acquisition unit (3); the preset information includes radon radioactivity concentration information and aerosol radioactivity concentration information. S3. Determine whether the radon radioactivity concentration measured by the radon monitoring device (1) is greater than the first preset value; if yes, then the exhaust unit is turned on by the control unit (4); if no, then continue to execute step S2. Determine whether the aerosol radioactivity concentration measured by the radioactive aerosol monitoring device (2) is greater than the second preset value; if yes, then the exhaust unit is turned on by the control unit (4); if no, then continue to execute step S2.

8. The method for monitoring radioactive materials in a radioactive waste disposal cave according to claim 7, characterized in that, The radon monitoring device (1) includes a first measuring pipeline, a first valve assembly installed on the first measuring pipeline and used to control the opening and closing of the first measuring pipeline, a first gas sampling pump (10) installed on the first measuring pipeline, a first gas storage tank (12), and a radon detector installed in the first gas storage tank (12). The first measuring pipeline includes a first inlet pipe (13a) and a first outlet pipe (13b); the first gas storage tank (12) is connected between the first inlet pipe (13a) and the first outlet pipe (13b); the end of the first inlet pipe (13a) away from the first gas storage tank (12) and the end of the first outlet pipe (13b) away from the first gas storage tank (12) are respectively connected to the outside atmosphere; Step S2 includes the following sub-steps: S2.1 Adjust the first valve assembly to connect the first inlet pipe (13a), the first gas storage tank (12), and the first outlet pipe (13b) to each other and to the outside atmosphere; start the first gas sampling pump (10) so that the outside gas flows through the first inlet pipe (13a), the first gas storage tank (12), and the first outlet pipe (13b) in sequence to purge the inside of the first gas storage tank (12) before measurement; S2.2 Adjust the first valve assembly to isolate the first gas storage tank (12) from the outside atmosphere, and the radon detector measures the radioactivity concentration of the aerosol remaining in the first gas storage tank (12). S2.3 After a preset time has elapsed since step S2.2, repeat step S2.1.

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