Floating type pool ultrasonic decontamination device and decontamination method thereof

Abstract

The invention discloses a floating type pool ultrasonic decontamination device and a decontamination method thereof. The floating type pool ultrasonic decontamination device comprises a shielding shell, a navigation mechanism, a driving mechanism, a lifting mechanism, an ultrasonic decontamination mechanism and a remote control system. According to the floating type pool ultrasonic decontamination device, by arranging the driving mechanism and the ultrasonic decontamination mechanism, the floating type pool ultrasonic decontamination device has the floating type moving function and the precise decontamination capacity, the ultrasonic decontamination range is wide, the decontamination effect is excellent, secondary waste liquid is not generated, the problems that decontamination in a pool is complex, personnel are contaminated and the like are effectively solved, and the service life of the pool is prolonged. The field decontamination efficiency and decontamination effect are improved, and meanwhile, the treatment cost of the subsequent radioactive waste liquid of the nuclear power station is reduced. And by arranging a remote control system, remote automatic decontamination can be achieved, manual work is replaced, the exposure dose of personnel is remarkably reduced, and the decontamination safety is improved. And the lifting mechanism is further arranged, so that the decontamination range can be widened, and the decontamination precision can be improved.

Description

Technical Field

[0001] This invention relates to the field of radioactive decontamination in nuclear power plants, and more particularly to a floating pool ultrasonic decontamination device and its decontamination method. Background Technology

[0002] During major overhauls, nuclear power plants require radioactive decontamination of reactor pools, component pools, and transfer pools to reduce their radioactivity levels and ensure that the radiation dose to subsequent maintenance personnel is kept at a low level to protect their health. Currently, the main radioactive decontamination method used in nuclear power plants is high-pressure water flushing + foam cleaning + wiping with decontaminating cloths, which requires personnel to enter the bottom of the pools for manual operation. However, several problems exist in actual operation:

[0003] (1) Due to the high level of radioactivity in the pool, staff members need to go down to the bottom of the pool to work, resulting in a large radiation dose to the staff.

[0004] (2) The equipment at the bottom of the pool is complex, with many pieces of equipment and a narrow space. Manual cleaning is inefficient and poses a risk of tearing the air suit, affecting personnel safety.

[0005] (3) Going up and down the pool is risky; air-filled suits are required when going up and down the stairs.

[0006] (4) A lot of radioactive waste liquid and solid waste are generated, and the treatment cost is high.

[0007] Therefore, from the perspective of reducing collective dosage, reducing industrial safety risks, and reducing the amount of secondary waste generated, it is necessary to develop new decontamination methods and equipment to significantly reduce human intervention and optimize the decontamination operation period. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a floating ultrasonic decontamination device for water tanks and a decontamination method thereof.

[0009] The technical solution adopted by the present invention to solve its technical problem is: to construct a floating ultrasonic cleaning device for water tanks, which includes a shielding shell, a navigation mechanism, a drive mechanism, a lifting mechanism, an ultrasonic cleaning mechanism, and a remote control system.

[0010] The navigation mechanism is connected to the shielding housing and is used to monitor its distance from the pool wall and generate a walking map;

[0011] The drive mechanism is connected to the shielding housing and is used to move the shielding housing.

[0012] The lifting mechanism is connected to the shielding shell and the ultrasonic cleaning mechanism respectively. The lifting mechanism is used to drive the ultrasonic cleaning mechanism to perform lifting and lowering movements. The ultrasonic cleaning mechanism is used to perform ultrasonic cleaning on the water tank.

[0013] The remote control system is communicatively connected to the navigation mechanism, the drive mechanism, the lifting mechanism, and the ultrasonic cleaning mechanism.

[0014] In some embodiments, the drive mechanism includes four thrusters, which are arranged separately at the four corners of the bottom of the shield housing.

[0015] In some embodiments, the floating pool ultrasonic cleaning device further includes a panoramic camera mounted on the shielding housing for monitoring the environment.

[0016] In some embodiments, the floating pool ultrasonic cleaning device further includes a gamma dose rate detector mounted on the shielding housing for detecting the environmental dose rate level.

[0017] In some embodiments, the lifting mechanism includes a lifting driver installed in the shielding housing, a lifting rod connected to the output end of the lifting driver, and a detection mounting base connected to the lifting rod. The lifting rod is equipped with an altimeter and a radiation detector.

[0018] In some embodiments, the ultrasonic cleaning mechanism includes two ultrasonic vibrating rods, both of which are mounted on the detection mounting base.

[0019] In some embodiments, the shielding housing is an aluminum alloy shielding housing, and the outer wall of the shielding housing is provided with anti-collision balls.

[0020] In this embodiment, a decontamination method for a floating ultrasonic decontamination device for a water tank is also constructed, which is based on the aforementioned floating ultrasonic decontamination device for a water tank and includes the following steps:

[0021] S1. Identify radioactive contaminants, place the floating ultrasonic decontamination device in the pool, start the floating ultrasonic decontamination device to move in the pool, and record the pool size information through the navigation mechanism to generate a walking map.

[0022] S2. Move the floating pool ultrasonic cleaning device to a fixed position, use the lifting mechanism to drive the ultrasonic cleaning device to descend, and at the same time test the actual radioactivity level at the location.

[0023] S3. If the actual radioactivity level is greater than the first preset value, record the height coordinates at this time and start the ultrasonic decontamination mechanism to perform ultrasonic decontamination.

[0024] S4. After the ultrasonic cleaning mechanism has performed ultrasonic cleaning for a preset time, if the actual radioactivity level before cleaning is greater than or equal to the second preset value, then the ultrasonic cleaning mechanism will continue to be used for cleaning. If the actual radioactivity level after cleaning is less than the second preset value, then the floating pool ultrasonic cleaning device will be moved to the next position for operation.

[0025] In some embodiments, in step S1, the floating ultrasonic cleaning device for the water tank is hoisted into the water tank using a gantry crane.

[0026] In some embodiments, in step S3, the first preset value is 10 μSv / h;

[0027] In step S4, the preset time is 10 minutes.

[0028] The present invention offers the following advantages: This floating ultrasonic decontamination device for water tanks, through the inclusion of a drive mechanism and an ultrasonic decontamination mechanism, enables it to float and move with precise decontamination capabilities. Ultrasonic decontamination has a wide range of applications, excellent decontamination effect, and produces no secondary waste liquid, effectively solving problems such as complex decontamination within water tanks and personnel contamination. This improves on-site decontamination efficiency and effectiveness while reducing the subsequent disposal costs of radioactive waste liquid from nuclear power plants. Furthermore, the remote control system enables remote automated decontamination, replacing manual labor, significantly reducing personnel radiation dose, and improving decontamination safety. A lifting mechanism further enhances the decontamination range and accuracy, while a navigation mechanism monitors the distance between the navigation mechanism and the water tank wall, facilitating effective control of the overall movement and position adjustment of the decontamination device during operation. This ensures that the device's center of gravity does not shift during operation, thereby guaranteeing the overall stability of the decontamination device. Attached Figure Description

[0029] To more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort. In the drawings:

[0030] Figure 1 This is a schematic diagram of the overall structure of the floating pool ultrasonic cleaning device in some embodiments of the present invention;

[0031] Figure 2 yes Figure 1 A schematic diagram of the structure from another direction. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] Please see Figure 1 and Figure 2 This invention provides a floating ultrasonic cleaning device for water tanks, comprising a shielding housing 1, a navigation mechanism 2, a drive mechanism 3, a lifting mechanism 4, an ultrasonic cleaning mechanism 5, and a remote control system. The navigation mechanism 2 is connected to the shielding housing 1 and monitors its distance from the water tank wall to generate a travel map. The drive mechanism 3 is connected to the shielding housing 1 and moves the shielding housing 1. The lifting mechanism 4 is connected to both the shielding housing 1 and the ultrasonic cleaning mechanism 5, and moves the ultrasonic cleaning mechanism 5 up and down to perform ultrasonic cleaning of the water tank. The remote control system is communicatively connected to the navigation mechanism 2, the drive mechanism 3, the lifting mechanism 4, and the ultrasonic cleaning mechanism 5.

[0035] Specifically, ultrasonic cleaning technology utilizes the cavitation effect generated when ultrasound propagates in a liquid. When ultrasound acts on a liquid, tiny bubbles in the liquid expand under the negative pressure phase of the sound wave and compress under the positive pressure phase, ultimately collapsing violently in a very short time. This collapse generates high-temperature, high-pressure shock waves and microjets. This energy impacts the surface of the object, breaking the bond between the dirt and the substrate, causing the dirt to peel off. Simultaneously, the high-temperature, high-pressure conditions generated by cavitation promote the decomposition of organic matter and the activation of chemical cleaning agents, accelerating the dissolution and decomposition of dirt. Furthermore, the vibration and cavitation effects of ultrasound increase the agitation and diffusion of the liquid, further enhancing the cleaning effect. Currently, ultrasonic cleaning equipment mainly uses a cleaning tank, where the sample to be cleaned is immersed in the cleaning solution, and cleaning is achieved through the action of ultrasonic transducers.

[0036] The ultrasonic vibrating rod 51 is a form of ultrasonic action. Its principle is that electrical energy is converted into high-frequency mechanical vibration by a transducer and transmitted to the vibrating rod. The vibrating rod then radiates the energy evenly into the liquid, generating a large number of tiny bubbles. These bubbles grow, oscillate, and eventually collapse under the vibration, releasing enormous energy to form microjets and shock waves. This results in a strong impact, stirring, and breaking effect on solid particles, contaminants, or liquid interfaces in the liquid. Compared to the currently used method of "high-pressure water rinsing + foam cleaning + wiping with a cleaning cloth," ultrasonic cleaning does not produce secondary waste liquid, requires no manual operation, significantly reduces the radiation dose to personnel, and ensures the safety of cleaning operations.

[0037] The shielding shell 1 is made of aluminum alloy, and its outer wall is equipped with anti-collision balls 11. The shielding shell 1 employs a cavity design, calculated to generate buoyancy greater than its own weight, achieving floating without the need for additional support structures. This adapts to surface water operations in pools, overcoming the limitations of traditional decontamination equipment that relies on bottom-mounted movement or fixed installation, and can flexibly cover both surface and underwater areas. The anti-collision balls 11 on the outer wall of the shielding shell 1 prevent damage to the pool wall or equipment due to collisions caused by improper operation. The internal electrical control components of the shielding shell 1 are reinforced with a tungsten alloy shield, enhancing the radiation resistance of the electrical components. While ensuring the equipment's radiation resistance, lightweight floating is achieved through material combination, resolving the contradiction between equipment protection and mobility in radioactive environments.

[0038] In addition, the navigation mechanism 2 integrates laser navigation and high-precision inertial navigation functions. On the one hand, it can monitor the distance between itself and the pool wall and generate a walking map, facilitating effective control of the overall movement and position adjustment of the cleaning device during use. On the other hand, it ensures that the center of gravity of the cleaning device does not shift during operation, thus ensuring the overall stability of the cleaning device. The navigation mechanism 2 achieves autonomous obstacle avoidance and path planning, achieving a higher degree of automation compared to the manual operation or simple tracked movement of traditional equipment.

[0039] In this embodiment, the drive mechanism 3 includes four thrusters 31, which are separately arranged at the four corners of the bottom of the shielding housing 1. Specifically, the drive mechanism 3 uses four thrusters 31 symmetrically distributed in an X-shape, so that each thruster 31 can work independently or collaboratively, thereby generating a resultant force in any direction on the horizontal plane. By adjusting the speed and direction of different thrusters 31, the overall decontamination device can achieve various movement modes such as forward, backward, leftward, rightward, and rotation. The floating ultrasonic decontamination device for water tanks, through the thrusters 31, causes minimal disturbance to the sediment at the bottom of the water tank, reducing the risk of radioactive material suspension and diffusion, and thus offering superior environmental performance.

[0040] The floating pool ultrasonic decontamination device also includes a panoramic camera 7 installed on the shielded housing 1 for environmental monitoring. The panoramic camera 7 can realize real-time monitoring of the above-water and underwater environment and has functions such as corrosion resistance, radiation resistance, and waterproofing. Together with the gamma dose rate detection instrument 6, it forms a "visual-dose" dual monitoring system to provide real-time feedback on the decontamination effect and environmental risks.

[0041] The floating pool ultrasonic decontamination device also includes a gamma dose rate detector 6 installed on the shielded housing 1 for detecting the environmental dose rate level. The gamma dose rate detector 6 rapidly detects the surrounding dose rate level through a high-range GM tube probe and transmits the data in real time to a remote control system, thereby enabling monitoring of the environmental radioactivity level.

[0042] The remote control system is communicatively connected to the navigation mechanism 2, drive mechanism 3, lifting mechanism 4, and ultrasonic decontamination mechanism 5 to obtain parameter information from these mechanisms and control their operation. Based on a real-world platform, the remote control system supports remote control of the entire process of equipment movement and decontamination operations. When the dose rate exceeds the limit, the system automatically triggers the lifting mechanism 4 to adjust the height of the ultrasonic vibrating rod 51, achieving closed-loop control of "detection-decontamination-evaluation" and reducing manual intervention.

[0043] Furthermore, the lifting mechanism 4 includes a lifting driver 41 installed within the shielding housing 1, a lifting rod 42 connected to the output end of the lifting driver 41, and a detection mounting base 43 connected to the lifting rod 42. The lifting rod 42 is equipped with an altimeter and a radiation detector. The ultrasonic decontamination mechanism 5 includes two ultrasonic vibrating rods 51, both mounted on the detection mounting base 43. Understandably, by using the lifting mechanism 4 to carry the two ultrasonic vibrating rods 51, ultrasonic decontamination can be performed within a 3-meter range. The lifting rod 42 is equipped with an altimeter that displays the underwater height of the ultrasonic vibrating rods 51 in real time, and a radiation detector that monitors the radioactivity level of the underwater environment. When the radioactivity level exceeds the limit, the lifting mechanism 4 will raise and lower the ultrasonic vibrating rods 51 to a suitable height to begin the decontamination operation until the radioactivity level is below the limit. The ultrasonic vibrating rods 51 are rod-type vibrating devices that can transfer ultrasonic vibration energy into the liquid, generating a cavitation effect to remove contaminants. The lifting mechanism 4, in conjunction with an altimeter and a radiation detector, achieves "depth-dose" linkage control. This means it automatically adjusts the height of the vibrating rod based on the radioactivity level, precisely locating the decontamination area and improving decontamination efficiency. This solves the problem of fixed installation of ultrasonic devices in existing technologies, which cannot adapt to decontamination needs at different water depths. It is particularly suitable for removing radioactive contamination in waters with varying levels or in deep water areas.

[0044] In this embodiment, a decontamination method for a floating ultrasonic decontamination device for a water tank is also constructed, which is based on the above-mentioned floating ultrasonic decontamination device for a water tank and includes the following steps:

[0045] S1. Identify radioactive contaminants, place the floating ultrasonic decontamination device in the pool, start the floating ultrasonic decontamination device to move in the pool, and record the pool size information through the navigation mechanism 2 to generate a walking map.

[0046] S2. Move the floating pool ultrasonic cleaning device to a fixed position, and use the lifting mechanism 4 to drive the ultrasonic cleaning mechanism 5 to descend, while testing the actual radioactivity level at the location.

[0047] S3. If the actual radioactivity level is greater than the first preset value, record the height coordinates at this time and start the ultrasonic decontamination mechanism 5 to perform ultrasonic decontamination.

[0048] S4. After the ultrasonic cleaning mechanism 5 has performed ultrasonic cleaning for a preset time, if the actual radioactivity level before cleaning is greater than or equal to the second preset value, then the ultrasonic cleaning mechanism 5 will continue to be used for cleaning. If the actual radioactivity level after cleaning is less than the second preset value, then the floating pool ultrasonic cleaning device will be moved to the next position for operation.

[0049] Specifically, in step S1, a gantry crane is used to hoist the floating ultrasonic cleaning device into the pool. The gantry crane mechanism hoists the floating ultrasonic cleaning device into the pool, enabling it to float. The control device moves around within the pool, and the laser navigation mechanism 2 records the pool's dimensions to generate a navigation map, reducing the possibility of collisions.

[0050] In step S3, the first preset value is 10 μSv / h. In step S4, the preset time is 10 min, and the second preset value is 30% of the actual radioactivity level before decontamination. These first and second preset values, as well as the preset time, can be adjusted according to actual conditions and are not specifically limited here.

[0051] In a specific work example, the object to be decontaminated was identified as a 2m × 2m water tank with a water depth of 2m and a radioactivity dose rate > 100μSv / h. The contaminants were identified as corrosion products and particulate matter accumulated over long-term on the inner wall of the tank and the surface of underwater components. A floating ultrasonic decontamination device was hoisted into the tank using a gantry crane to achieve floating. The decontamination device was then controlled to move around within the tank, and the navigation mechanism 2 recorded the tank dimensions to generate a navigation map.

[0052] Move the decontamination device to a certain position and fix it in place, recording the position information. Use the lifting mechanism 4 to drive the ultrasonic decontamination mechanism 5 to descend, while simultaneously testing the actual radioactivity level at the location. If the radioactivity level of the surrounding pool walls or underwater components is >10μSv / h, start the ultrasonic decontamination process. The parameters of the ultrasonic vibrator 51 are: power 600W, frequency 40KHz.

[0053] After 10 minutes of decontamination, pause for 5 minutes and repeat the decontamination process. When the surrounding radioactivity level drops by more than 30% compared to before decontamination, the decontamination effect is considered good, and decontamination can be paused to move to the next location.

[0054] Repeat the above-mentioned moving + lifting + detection + decontamination operation until the overall radioactivity level of the water tank is reduced by more than 30%. The decontamination is then completed. The ultrasonic vibrating rod 51 is lifted to a fixed position inside the decontamination device, and then the decontamination device is hoisted and retrieved by a gantry crane.

[0055] Understandably, this floating ultrasonic decontamination device for water tanks, through the inclusion of a drive mechanism 3 and an ultrasonic decontamination mechanism 5, possesses both floating mobility and precise decontamination capabilities. Ultrasonic decontamination offers a wide decontamination range and excellent results without generating secondary waste liquid, effectively solving problems such as complex decontamination within water tanks and personnel contamination. This improves on-site decontamination efficiency and effectiveness while reducing the subsequent disposal costs of radioactive waste liquid from nuclear power plants. Furthermore, a remote control system enables remote automated decontamination, replacing manual labor, significantly reducing personnel radiation dose, and improving decontamination safety. A lifting mechanism 4 further enhances the decontamination range and accuracy, while a navigation mechanism 2 monitors the distance between itself and the water tank wall, facilitating effective control of the overall movement and position adjustment of the decontamination device during operation. This ensures that the device's center of gravity does not shift during operation, thereby guaranteeing the overall stability of the decontamination device.

[0056] 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 floating ultrasonic cleaning device for water tanks, characterized in that, It includes a shielding housing (1), a navigation mechanism (2), a drive mechanism (3), a lifting mechanism (4), an ultrasonic cleaning mechanism (5), and a remote control system; The navigation mechanism (2) is connected to the shielding shell (1) and is used to monitor its distance from the pool wall and generate a walking map; The driving mechanism (3) is connected to the shielding housing (1) and is used to drive the shielding housing (1) to move; The lifting mechanism (4) is connected to the shielding shell (1) and the ultrasonic cleaning mechanism (5) respectively. The lifting mechanism (4) is used to drive the ultrasonic cleaning mechanism (5) to perform lifting and lowering movements. The ultrasonic cleaning mechanism (5) is used to perform ultrasonic cleaning on the water tank. The remote control system is communicatively connected to the navigation mechanism (2), the drive mechanism (3), the lifting mechanism (4), and the ultrasonic cleaning mechanism (5).

2. The floating ultrasonic decontamination device for water tanks according to claim 1, characterized in that, The drive mechanism (3) includes four thrusters (31), which are arranged separately at the four corners of the bottom of the shield housing (1).

3. The floating ultrasonic decontamination device for water tanks according to claim 1, characterized in that, The floating pool ultrasonic cleaning device also includes a panoramic camera (7) installed on the shielding housing (1) for monitoring the environment.

4. The floating ultrasonic decontamination device for water tanks according to claim 1, characterized in that, The floating pool ultrasonic cleaning device also includes a γ dose rate detector (6) installed on the shielding housing (1) and used to detect the environmental dose rate level.

5. The floating ultrasonic decontamination device for water tanks according to claim 1, characterized in that, The lifting mechanism (4) includes a lifting driver (41) installed in the shielding housing (1), a lifting rod (42) connected to the output end of the lifting driver (41), and a detection mounting base (43) connected to the lifting rod (42). The lifting rod (42) is equipped with an altimeter and a radiation detector.

6. The floating ultrasonic decontamination device for water tanks according to claim 5, characterized in that, The ultrasonic cleaning mechanism (5) includes two ultrasonic vibrating rods (51), both of which are mounted on the detection mounting base (43).

7. The floating ultrasonic decontamination device for water tanks according to claim 1, characterized in that, The shielding shell (1) is an aluminum alloy shielding shell, and the outer wall of the shielding shell (1) is provided with anti-collision balls (11).

8. A method for decontamination using a floating ultrasonic decontamination device for a water tank, based on the floating ultrasonic decontamination device for a water tank according to any one of claims 1 to 7, characterized in that, Including the following steps: S1. Identify radioactive contaminants, place the floating pool ultrasonic cleaning device in the pool, start the floating pool ultrasonic cleaning device to move in the pool, and record the pool size information through the navigation mechanism (2) to generate a walking map. S2. Move the floating pool ultrasonic cleaning device to a fixed position, and use the lifting mechanism (4) to drive the ultrasonic cleaning mechanism (5) to descend, while testing the actual radioactivity level at the location. S3. If the actual radioactivity level is greater than the first preset value, record the height coordinates at this time and start the ultrasonic decontamination mechanism (5) to perform ultrasonic decontamination. S4. After the ultrasonic cleaning mechanism (5) has performed ultrasonic cleaning for a preset time, if the actual radioactivity level value before cleaning is greater than or equal to the second preset value, then the ultrasonic cleaning mechanism (5) will continue to be used for cleaning. If the actual radioactivity level value after cleaning is less than the second preset value, then the floating pool ultrasonic cleaning device will be moved to the next position for operation.

9. The decontamination method of the floating ultrasonic decontamination device for water tanks according to claim 8, characterized in that, In step S1, the floating ultrasonic cleaning device for the water tank is hoisted into the water tank using a gantry crane.

10. The decontamination method of the floating ultrasonic decontamination device for water tanks according to claim 8, characterized in that, In step S3, the first preset value is 10 μSv / h; In step S4, the preset time is 10 minutes.

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