JP2011078894A - Washing method using ultrasonic cavitation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing method using ultrasonic cavitation that does not require a long time in a washing work, for example, even in washing and removing solid matters sticking to a structure constituting a pressure boundary of a cooling member of a nuclear reactor using an ultrasonic wave, can reduce the exposure to radiation on the part of a worker, is not of a complicated structure, and prevents its cost from greatly increasing. <P>SOLUTION: The method of washing and removing solid matters sticking to the inner surface of a cylindrical structure 14 filled with water 7 using an ultrasonic wave generated by an ultrasonic oscillator 2, wherein the ultrasonic wave generated by the ultrasonic oscillator 2 enters the structure 14 from outside, is characterized by controlling the frequency of the entering ultrasonic wave to make an integer multiple of the half wavelength of the ultrasonic wave equal to the thickness t of the structure 14, and causing the controlled ultrasonic wave to enter the structure 14 to generate resonance in the thickness direction to generate cavity bubbles 21 on the inner surface of the structure 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic cavitation cleaning method suitable for cleaning and removing solid matters such as clads adhering to pipes and structures in various plants.

  In power plants and various industrial plants, solid matter such as cladding (CRUD: Chalk River Unclassified Deposit) adheres to the inner surface of the pipe and the surface of the installed structure in the pipe by operating the plant for a long period of time. When such solid matter adheres, for example, to the inner surface of a jet pump in a boiling water nuclear power plant, the pressure loss of the recirculation system increases, which may cause problems such as a decrease in power generation efficiency. In order to prevent such an event from occurring, it is usually necessary to periodically clean the inner surface of the pipe and the surface of the installed structure in the pipe. Cleaning methods include brush cleaning, water jet cleaning, chemical cleaning using chemical reaction, and cleaning using ultrasonic waves.

  Of these cleaning methods, the ultrasonic cleaning method uses, for example, a relatively small target object such as an electronic component so that the target object to be cleaned is immersed in a cleaning tank filled with a cleaning liquid such as water. There is one that removes and removes the solid matter attached by using an impact force at the time of collapse of cavitation generated by irradiating with ultrasonic waves. In addition, as a cleaning method using ultrasonic waves targeting a relatively large structure installed in a power plant, for example, an ultrasonic transducer with a string is put in a heat transfer tube of a heat exchanger, What is performed while moving (for example, Patent Document 2), what is performed by moving an ultrasonic vibrator around the fuel assembly in the pool and moving it vertically (for example, Patent Document 3), an internal pump casing There is one (for example, Patent Document 4) in which a cleaning tool having an ultrasonic vibrator is inserted into a stretch tube or nozzle, and a rod is further inserted into and contacted from an opening formed in a piping that is a structure. There is one that cleans the venturi flow nozzle in the tube by irradiating ultrasonic waves from the tube (for example, see Patent Document 5).

  However, the surface of the reactor coolant pressure boundary, such as structures, reactor pressure vessels such as boiling water nuclear power plants and their accessories, equipment such as jet pumps constituting the reactor cooling system, piping, and connecting piping In addition, when removing solid matter such as clad due to radioactive impurities adhering to the cooling water due to long-term operation, in the case of a cleaning device using a cleaning tank, large and semi-permanently installed atoms In-furnace equipment is not applicable, and if a cleaning device is installed directly on the part to be cleaned in the structure or if disassembly work is required to install the device, the amount of exposure to workers increases. Will be a factor. Further, in the case where the cleaning device performs mobile cleaning, the device configuration has a complicated mechanism, and it takes a long time to clean and remove the solid material, resulting in high costs. Further, when an opening is formed in a pipe or the like that is a reactor coolant pressure boundary, the sealing structure of the opening becomes complicated.

Japanese Patent No. 2832443 Japanese Patent No. 2537056 Japanese Patent No. 329328 Japanese Patent No. 2896443 Japanese Patent No. 2554821

  The present invention has been made in view of such a situation, and the object of the present invention is to use ultrasonic waves, for example, to contain the reactor coolant during normal operation of the reactor, so that the conditions are the same as those of the reactor. When cleaning and removing solids adhering to the surface of the structure (reactor pressure vessel, primary piping, etc.) that constitutes the reactor coolant pressure boundary that forms the pressure barrier, the structure is not complicated. In addition, there is no need to install or disassemble the equipment directly on the part to be cleaned, so that the amount of exposure to workers can be reduced. In addition, it does not require a long time and can be cleaned and removed without a significant increase in cost. The object is to provide an ultrasonic cavitation cleaning method.

  The present invention achieves the above object, and the adhered solid matter on the inner surface of a cylindrical structure filled with a liquid is washed and removed using ultrasonic waves emitted from an ultrasonic vibrator. In the ultrasonic cavitation cleaning method, the ultrasonic wave emitted from the ultrasonic transducer is incident on the structure from the outside, and the frequency of the incident ultrasonic wave is an integral multiple of a half wavelength of the ultrasonic wave. The thickness of the structure was adjusted to be equal, and the adjusted ultrasonic wave was incident on the structure to cause resonance in the thickness direction to generate cavity bubbles on the inner surface of the structure. It is the method characterized by this.

  Also, an ultrasonic cavitation cleaning method for cleaning and removing a solid adhering matter on the inner surface of a cylindrical structure whose inside is filled with a liquid using an ultrasonic wave generated by an ultrasonic vibrator, the structure The ultrasonic wave emitted from the ultrasonic transducer is incident on the body from the outside, and the frequency of the incident ultrasonic wave is adjusted so that the integral multiple of the wavelength is equal to the circumferential length of the structure. The method is characterized in that ultrasonic waves are incident on the structure to cause circumferential resonance to generate cavity bubbles on the inner surface of the structure.

  Also, an ultrasonic cavitation cleaning method for cleaning and removing a solid adhering matter on the inner surface of a cylindrical structure whose inside is filled with a liquid using an ultrasonic wave generated by an ultrasonic vibrator, the structure The ultrasonic wave emitted from the ultrasonic transducer is incident on the body from the outside, and the frequency of the ultrasonic wave is adjusted so as to coincide with the higher-order natural frequency in the circumferential direction of the structure. Is generated, and cavity bubbles are generated on the inner surface of the structure.

  Also, an ultrasonic cavitation cleaning method for cleaning and removing a solid adhering matter on the inner surface of a cylindrical structure whose inside is filled with a liquid using an ultrasonic wave generated by an ultrasonic vibrator, the structure Each ultrasonic wave emitted from the plurality of ultrasonic transducers is incident on the body from the outer side so that the phase is synchronized, and the frequency of the ultrasonic wave is set to an integral multiple of the wavelength and the circumferential length of the structure. Are adjusted to be equal to each other to cause circumferential resonances to generate cavity bubbles on the inner surface of the structure.

  According to the present invention, there is no complicated configuration, and it is not necessary to directly install or disassemble the apparatus on the part to be cleaned, and it does not require a long time, and the amount of exposure to workers can be reduced. In addition, it is possible to clean and remove the adhered solid matter in a structure such as a reactor coolant pressure boundary, for example, without increasing the cost.

It is a figure which shows the structure and cleaning state of the ultrasonic cleaning apparatus in the 1st Embodiment of this invention. 1 is a longitudinal sectional view showing an outline of a boiling water reactor used in a first embodiment of the present invention. It is a figure explaining the washing | cleaning method in the 1st Embodiment of this invention. FIG. 4A is a configuration diagram illustrating an ultrasonic cleaning apparatus according to a modification of the first embodiment of the present invention, FIG. 4A is a configuration diagram of the first modification, and FIG. 4B is a configuration diagram of the second modification. is there. It is a figure which shows the structure and washing | cleaning state of the ultrasonic cleaning apparatus in the 2nd Embodiment of this invention. It is a figure which shows the structure and washing | cleaning state of the ultrasonic cleaning apparatus in the 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
First, a first embodiment and a modification of the present invention will be described with reference to FIGS.

  1 to 3, the ultrasonic cleaning apparatus 1 includes a vibrator unit 3 having an ultrasonic vibrator 2 that emits ultrasonic waves of 20 kHz or more, an oscillation circuit that drives the ultrasonic vibrator 2, and the like. The drive unit 4 and the control unit 5 that controls the drive unit 4 so that the vibration frequency of the ultrasonic vibrator 2 is set to a predetermined frequency and the sound pressure is equal to or higher than the predetermined sound pressure are configured. A horn 6 is attached to the tip portion of the ultrasonic transducer 2 of the transducer unit 3 in order to increase the transmission efficiency of ultrasonic waves that are attached as necessary.

  When cleaning is performed, the vibrator unit 3 of the ultrasonic cleaning apparatus 1 is filled with a liquid, for example, water 7 that is a reactor coolant, in boiling water as shown in FIG. Reactor pressure vessel 9 of nuclear reactor 8 such as type nuclear power plant and its accessories, recirculation pump 10 constituting reactor cooling system, equipment such as jet pump 11, piping 12, connection piping, etc. If necessary, a contact medium is provided on the outer surface of the cylindrical structure 14 constituting the material pressure boundary 13 so that ultrasonic waves can be transmitted satisfactorily when the adhesion with the tip of the horn 6 is poor. To attach. In addition, 15 is a core, 16 is a core shroud, 17 is a control rod guide pipe, 18 is a feed water sparger, 19 is a steam separator, 20 is a steam dryer, and a solid arrow indicates the flow of water 7 as a coolant. Show.

  After the vibrator unit 3 is attached to the structure 14 from the outer side, the drive unit 4 is driven under the control of the control unit 5 to generate ultrasonic waves from the ultrasonic transducer 2 and to generate ultrasonic vibrations. Enters and propagates into the structure 14. At this time, a longitudinal wave is propagated to the structure 14 from the ultrasonic transducer 2 in the thickness direction, which is the traveling direction of the ultrasonic wave. Then, by adjusting the frequency of the ultrasonic wave to be propagated by the control unit 5, an integral multiple of ½ wavelength of the ultrasonic wave is a structural body, as schematically shown in FIG. 14 to a predetermined frequency so as to be equal to the thickness t. At the same time, the control unit 5 adjusts the pressure amplitude ΔP [Pa] of the ultrasonic wave so as to be larger than the difference between the water pressure P1 [Pa] inside the structure 14 and the saturated vapor pressure Pv [Pa].

  As a result, resonance between the ultrasonic wave emitted from the ultrasonic transducer 2 and the structure 14 occurs in the thickness direction, and the ultrasonic wave is not greatly attenuated in the structure 14 but from the inner surface of the structure 14 to the inside. Propagates to water 7. Cavity bubbles 21 are generated by the propagation of ultrasonic waves to the water 7, and the inner surface of the structure 14 is cleaned by ultrasonic cavitation.

  The reason why the pressure amplitude ΔP [Pa] of the ultrasonic water is adjusted to be larger than the difference between the water pressure P1 [Pa] and the saturated vapor pressure Pv [Pa] inside the structure 14 is as follows. .

In other words, cavitation is a phenomenon in which when the pressure drops and the pressure drops below the saturated vapor pressure, the liquid phase changes locally to the gas phase. In ultrasonic cavitation,
The presence / absence of cavitation is evaluated by the cavitation number σ defined by σ = (P1−Pv) / ΔP, and the cavitation number σ is 1 or less,
σ = (P1−Pv) / ΔP <1
Otherwise, cavitation will not occur.

  As shown in FIG. 3, the ultrasonic sound pressure is larger than the water pressure P1 [Pa] and the saturated vapor pressure Pv [Pa], and the saturated vapor pressure Pv [Pa] is shown in the ultrasonic waveform indicated by the solid line A. When the following portion is generated and the pressure amplitude ΔP [Pa] becomes larger than (P1−Pv), the portion of (P1−Pv) <ΔP becomes the cavitation generation region X. Further, when the ultrasonic sound pressure is small and the ultrasonic waveform indicated by the dotted line B does not have a portion below the saturated vapor pressure Pv [Pa], the cavitation generation region X does not occur. However, since the gas is actually dissolved in water, the dissolved gas becomes a cavitation nucleus, and even if the cavitation number σ is larger than 1, initial cavitation occurs. The impact force of the primary cavitation generated in this way is not so great due to the gas cushion effect.

For this reason, at least the cavitation number σ is equal to or less than 1, that is, the pressure amplitude ΔP [Pa] of the ultrasonic wave has a pressure P1 [ It is necessary to adjust so that it is larger than the difference between Pa] and saturated vapor pressure Pv [Pa]. Here, when the pressure amplitude ΔP [Pa] is shown using the ultrasonic intensity I [W / m ² ], the water density ρ [kg / m ³ ], and the sound velocity c [m / s] in water,
ΔP = (2ρcI) ^1/2
Therefore, the ultrasonic intensity I [W / m ² ] may be adjusted so that the cavitation number σ <1. Regarding the ultrasonic intensity I [W / m ² ] at this time, since the ultrasonic wave passes through the structure 14 and acts on the water 7, it must be the ultrasonic intensity after passing through the structure 14. An ultrasonic wave having a required intensity considering the transmittance of 14 is incident on the structure 14.

  By configuring the present embodiment as described above, for example, the inner surface of the structure 14 that becomes the reactor coolant pressure boundary 13 in a boiling water nuclear power plant or the like in which the reactor coolant 7 is filled. In addition, even when radioactive impurities in the cooling water 7 adhere as solid matter such as cladding due to long-term operation, the vibrator unit 3 of the ultrasonic cleaning device 1 is attached to the outer surface of the structure 14, Cleaning and removal of attached solids using ultrasonic waves can be easily performed with a reduced amount of exposure to workers.

  At this time, the ultrasonic frequency is adjusted to a predetermined appropriate frequency corresponding to the thickness t of the structure 14, and the pressure amplitude is also adjusted appropriately corresponding to the water pressure and saturated vapor pressure inside the structure 14. Then, resonance between the ultrasonic wave from the ultrasonic transducer 2 and the structure 14 occurs, and the ultrasonic wave is efficiently propagated to the internal water 7 without being greatly attenuated in the structure 14, thereby generating ultrasonic cavitation. Thus, the solid matter adhering to the inner surface of the structure 14 can be reliably washed and removed by applying a high impact pressure due to the collapse of the cavity bubbles 21.

  In the above description, when the thickness t of the structure 14 is unknown or when the transmittance of the structure 14 is unknown, the ultrasonic transducer 2 is provided with a reception function as well as a function of emitting an ultrasonic wave in advance. Thus, the thickness or transmittance may be obtained. For example, as in the first modification shown in FIG. 4A, the transducer unit 3a of the ultrasonic cleaning apparatus 1a receives the ultrasonic transducer 2 and the reflected wave of the ultrasonic wave emitted from the ultrasonic transducer 2. The receiving vibrator 22 is provided, and the structure is calculated by the control unit 5a based on the time difference between the incident time of the ultrasonic wave to the structure 14 and the reception time of the reflected wave reflected from the inner surface of the structure 14. A thickness of 14 is determined. Further, the transmittance is obtained by calculating in the control unit 5a based on the difference in magnitude between the incident wave to the structure 14 and the received reflected wave.

  Further, as in the second modification shown in FIG. 4B, the vibrator unit 3b of the ultrasonic cleaning apparatus 1b is constituted by an ultrasonic vibrator 2b capable of transmitting and receiving ultrasonic waves, and the ultrasonic vibrator. In 2b, the ultrasonic wave is incident on the structure 14 from the outer surface, and the reflected wave on the inner surface of the structure 14 is received and input to the control unit 5b via the receiving circuit 23. Based on the time difference between the incident time of the ultrasonic wave and the reception time of the reflected wave from the inner surface of the structure 14, the control unit 5 b calculates to determine the thickness of the structure 14. Further, the transmittance is also obtained by calculating in the control unit 5b based on the difference in magnitude between the incident wave to the structure 14 and the received reflected wave.

  In addition, although the single vibrator unit 3 is attached to the structure 14, the frequency of each ultrasonic transducer 2 is shifted by an integral multiple or a half multiple from each other by attaching a plurality of transducer units 3. In this way, the inner surface of the structure 14 may be cleaned evenly by finely distributing the positions where cavitation occurs.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of embodiment of this invention different from 1st Embodiment is demonstrated.

  In FIG. 5, the ultrasonic cleaning device 31 includes a vibrator unit 33 having an ultrasonic vibrator 32 that emits ultrasonic waves of 20 kHz or higher, and a drive unit configured to include an oscillation circuit that drives the ultrasonic vibrator 32. 34, and a control unit 35 that controls the drive unit 34 so that the vibration frequency of the ultrasonic transducer 32 is a predetermined frequency and the sound pressure is equal to or higher than the predetermined sound pressure, and further includes an ultrasonic sensor 36. The detection signal of the ultrasonic sensor 36 is input to the control unit 35.

  Then, when performing the cleaning, the vibrator 33 of the ultrasonic cleaning device 31 is replaced with an atom of a boiling water nuclear power plant as shown in FIG. It is attached to the outer surface of the cylindrical structure 14 constituting the furnace coolant pressure boundary 13 with a contact medium provided between the tip of the horn 6 as necessary. In addition, the ultrasonic sensor 36 is provided at a position facing the structure body 14 (a 180-degree symmetrical position) on the side opposite to the attachment position of the transducer unit 33 that is an ultrasonic incident position.

  After the transducer unit 33 is attached to the structure 14 at the incident position and the ultrasonic sensor 36 is installed, the drive unit 34 is first driven under the control of the control unit 35 to generate ultrasonic waves from the ultrasonic transducer 32. Then, the ultrasonic vibration is incident on and propagates to the structure 14, and the ultrasonic wave propagated to the structure 14 is captured by the ultrasonic sensor 36. After capturing the ultrasonic wave, the control unit 35 has a cylindrical shape based on the time difference between the ultrasonic wave emitted from the ultrasonic transducer 32 and the ultrasonic wave captured by the ultrasonic sensor 36, that is, the time difference between the incident time and the capture time. The length of the half circumference of the structure 14 is calculated, and the circumferential length (length in the circumferential direction) of the structure 14 is obtained. When the circumferential length of the structure 14 is clear, the calculation using the ultrasonic sensor 36 is not necessary.

  Next, after obtaining the circumferential length of the structure 14, the drive unit 34 is driven again under the control of the control unit 35 to emit ultrasonic waves from the ultrasonic transducer 32, and ultrasonic vibrations are transmitted to the structure 14. Incident and propagate. Then, the frequency of the ultrasonic wave propagated from the ultrasonic transducer 32 to the structure body 14 is adjusted, and the circumferential direction of the structure body 14 becomes a direction (transverse wave propagation direction) perpendicular to the traveling direction of the ultrasonic wave (longitudinal wave propagation direction). The frequency is adjusted so that the length becomes a predetermined frequency that is an integral multiple of the ultrasonic wavelength.

  In this way, by adjusting the ultrasonic wave to a predetermined frequency such that an integral multiple of the ultrasonic wavelength is equal to the circumferential length of the structure 14, as shown schematically in FIG. Resonance in the circumferential direction of the structure 14 is generated by the ultrasonic waves emitted from the ultrasonic transducer 32, and a standing wave is generated. The resonance in the circumferential direction of the structure 14 due to ultrasonic waves may be caused to coincide with the higher natural frequency in the circumferential direction of the structure 14. Simultaneously with the resonance in the circumferential direction, the pressure amplitude ΔP [Pa] of the ultrasonic wave on the inner surface of the structure 14 is larger than the difference between the water pressure P1 [Pa] inside the structure 14 and the saturated vapor pressure Pv [Pa]. Adjustment is performed by the control unit 35.

  Further, the resonance of the structure 14 due to the ultrasonic waves occurs in the circumferential direction, so that the ultrasonic waves propagate from the inner surface to the internal water 7 without being greatly attenuated in the structure 14. As the ultrasonic wave propagates to the water 7, a cavity bubble 21 is generated in the vicinity of the antinode where the pressure amplitude of the standing wave is maximized, and the inner surface of the structure 14 is cleaned by ultrasonic cavitation.

  By configuring the present embodiment as described above, as in the first embodiment, for example, the reactor coolant pressure boundary 13 of the boiling water nuclear power plant in which the water 7 as the reactor coolant is filled. Even when radioactive impurities in the cooling water 7 adhere to the surface of the structure 14 such as a clad as a solid matter such as a clad due to long-term operation, the vibrator unit 33 of the ultrasonic cleaning device 31 is attached to the outer surface of the structure 14. Attachment and washing and removal of attached solids using ultrasonic waves from the outside can be easily performed with the amount of exposure to the worker reduced.

  At this time, the frequency of the ultrasonic wave is adjusted to a predetermined appropriate frequency corresponding to the circumferential length of the structure 14, and the pressure amplitude is also appropriately adjusted corresponding to the water pressure and saturated vapor pressure inside the structure 14. Therefore, resonance between the ultrasonic wave from the ultrasonic transducer 32 and the structure 14 occurs, and the ultrasonic wave is efficiently propagated to the internal water 7 without being greatly attenuated in the structure 14, thereby causing ultrasonic cavitation. The generation efficiency is further improved, and a high impact pressure due to the collapse of the cavity bubbles 21 is applied, so that the adhered solid matter on the inner surface of the structure 14 can be reliably washed and removed.

  In the present embodiment, for example, the ultrasonic frequency generated by the ultrasonic transducer 32 is configured to be continuously variable and frequency control is possible so that the transducer unit 33 has a frequency sweep function. The ultrasonic wave whose frequency is continuously variable is applied to the structure 14 while performing a frequency sweep, and the vibration displacement of the structure 14 or the intensity of the received ultrasonic wave is measured by the ultrasonic sensor 36. Even if the resonance frequency is unknown, the maximum frequency is obtained in advance, the ultrasonic frequency is set to the maximum frequency, and the ultrasonic wave is incident on the structure 14 from the transducer unit 33, even if the resonance frequency is unknown. 14 can be brought into a resonance state, and similarly, attached solids can be reliably washed and removed.

  In addition, although the single transducer portion 33 is attached to the structure 14, the frequencies of the ultrasonic transducers 32 are shifted from each other by an integral multiple or ½ times by attaching a plurality of transducer portions 33. In this way, the inner surface of the structure 14 may be cleaned evenly by finely distributing the positions where cavitation occurs.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as 1st, 2nd embodiment, description is abbreviate | omitted, and the structure of embodiment of this invention different from 1st, 2nd embodiment is demonstrated.

  In FIG. 6, the ultrasonic cleaning device 41 has a plurality of ultrasonic transducers 32a, 32b,... That emit ultrasonic waves having different frequencies by an integral multiple or a half, respectively. .., And drive units 34a, 34b,... Configured by providing oscillation circuits for driving the ultrasonic transducers 32a, 32b,..., And ultrasonic transducers 32a, 32b,. Are controlled so that the vibration frequency becomes a predetermined frequency and the sound pressure becomes equal to or higher than the predetermined sound pressure, and a phase control circuit is provided to provide each ultrasonic transducer 32a, 32b,. The control unit 42 is configured to perform phase control so that the vibration phases are synchronized with the same phase and the opposite phase.

  When performing the cleaning, each of the vibrator portions 33a, 33b,... Of the ultrasonic cleaning device 41 is boiled as shown in FIG. A contact medium is provided as necessary between the tip of the horn 6 at different mounting positions (ultrasonic incident positions) on the outer surface of the cylindrical structure 14 constituting the reactor coolant pressure boundary 13 of the water nuclear power plant. And attach each.

  After the transducer units 33a, 33b,... Are attached to the structure 14, the drive units 34a, 34b,... Are first driven under the control of the control unit 42, and the ultrasonic transducers 32a, 32b,. The ultrasonic wave is emitted from... And the ultrasonic vibration is incident on the structure body 14 and propagated. Further, the frequency of the ultrasonic wave propagating from the ultrasonic transducers 32a, 32b,... To the structure 14 is adjusted, and the circumference of the structure 14 in the transverse wave propagation direction of the ultrasonic wave is an integer of the ultrasonic wavelength. The ultrasonic frequency of each of the ultrasonic transducers 32a, 32b,... Is adjusted so that the predetermined frequency is doubled.

  Thus, by adjusting each ultrasonic wave to a predetermined frequency such that the circumferential length of the structure 14 is an integral multiple of the wavelength, the ultrasonic waveform is schematically shown by solid lines D, E,... In FIG. As shown in FIG. 4, the ultrasonic wave emitted from the ultrasonic transducer 32 causes resonance in the circumferential direction of the structural body 14 to generate a standing wave. The resonance in the circumferential direction of the structure 14 by ultrasonic waves may be caused to coincide with the higher-order natural frequency in the circumferential direction of the structure 14. Simultaneously with the resonance in the circumferential direction, the pressure amplitude ΔP [Pa] of each ultrasonic wave on the inner surface of the structure 14 is larger than the difference between the water pressure P1 [Pa] and the saturated vapor pressure Pv [Pa] inside the structure 14. Adjustment by the control unit 42 is performed so as to increase.

  Further, the resonance of the structure 14 by each ultrasonic wave occurs in the circumferential direction, so that the ultrasonic wave propagates from the inner surface to the internal water 7 without being greatly attenuated in the structure 14. As the ultrasonic wave propagates to the water 7, a cavity bubble 21 is generated in the vicinity of the antinode where the pressure amplitude of the standing wave is maximized, and the inner surface of the structure 14 is cleaned by ultrasonic cavitation. At this time, since a plurality of resonant frequencies are applied to the structure 14, the cavity bubbles 21 can be generated on substantially the entire inner surface of the structure 14.

  By configuring the present embodiment as described above, as in the first and second embodiments, for example, the reactor coolant pressure boundary of the boiling water nuclear power plant in which the coolant 7 is filled. Even when radioactive impurities in the cooling water 7 adhere to the surface of the structure 14 constituting the structure 13 as a solid matter such as a clad due to long-term operation, the vibrator portions 33a, 33b,. -Is attached to the outer surface of the structure 14, and the adhered solid matter can be easily cleaned and removed using ultrasonic waves from the outside in a state where the exposure amount of the worker is reduced.

  At this time, the frequency of each ultrasonic wave is adjusted to an appropriate frequency corresponding to the circumferential length of the structure 14, and the pressure amplitude is also adjusted appropriately corresponding to the water pressure and saturated vapor pressure inside the structure 14. , Resonance of the ultrasonic wave from the ultrasonic vibrators 32a, 32b,... And the structure 14 occurs, and the ultrasonic wave is efficiently propagated to the internal water 7 without being greatly attenuated in the structure 14. The generation efficiency of ultrasonic cavitation is further improved, and a high impact pressure due to the collapse of the cavity bubble 21 is applied, so that the adhered solid matter on the inner surface of the structure 14 can be reliably washed and removed.

  Furthermore, since a plurality of resonant frequencies are applied to the structure 14, cavity bubbles 21 are generated on substantially the entire inner surface of the structure 14, and the attached solid matter can be cleaned and removed without causing uneven cleaning. Further, the intensity of sound pressure increases due to the interference of standing waves at a plurality of frequencies, so that the adhering solid matter can be effectively cleaned and removed at the interference position, and the vibrator portions 33a, 33b,.・ ・ By selecting the proper mounting position, more effective cleaning and removal can be performed.

1, 1a, 1b, 31, 41 ... ultrasonic cleaning device, 2, 2a, 2b, 32, 32a, 32b ... ultrasonic transducer, 3, 3a, 3b, 33, 33a, 33b ... transducer unit, 4, 34, 34a, 34b ... drive unit, 5, 5a, 5b, 35, 42 ... control unit, 6 ... horn, 7 ... water, 8 ... nuclear reactor, 9 ... reactor pressure vessel, 10 ... recirculation pump, 11 ... Jet pump, 12 ... piping, 13 ... reactor coolant pressure boundary, 14 ... structure, 15 ... core, 16 ... core shroud, 17 ... control rod guide tube, 18 ... feed water sparger, 19 ... air-water separator, 20 ... Vapor dryer, 21 ... Cavity foam, 22 ... Receiving vibrator, 23 ... Receiving circuit, 36 ... Ultrasonic sensor

Claims (10)

An ultrasonic cavitation cleaning method that cleans and removes the attached solid matter on the inner surface of a cylindrical structure filled with a liquid using ultrasonic waves generated by an ultrasonic vibrator,
The ultrasonic wave emitted from the ultrasonic transducer is incident on the structure from the outside, and the frequency of the incident ultrasonic wave is equal to an integral multiple of ½ wavelength of the ultrasonic wave and the thickness of the structure. The ultrasonic cavitation cleaning method is characterized in that the adjusted ultrasonic wave is incident on the structure to cause resonance in the thickness direction, and cavity bubbles are generated on the inner surface of the structure. .   The structure is configured to receive the reflected wave of the ultrasonic wave incident on the structure on the surface of the structure, and the thickness of the structure is calculated in advance based on the time difference between the incident of the ultrasonic wave and the reception of the reflected wave. The frequency of the ultrasonic wave is adjusted so that the thickness of the structured body is equal to an integral multiple of ½ wavelength of the ultrasonic wave, and the adjusted ultrasonic wave is incident on the structural body to cause resonance in the thickness direction. The ultrasonic cavitation cleaning method according to claim 1. An ultrasonic cavitation cleaning method that cleans and removes attached solid matter on the inner surface of a cylindrical structure filled with a liquid using ultrasonic waves generated by an ultrasonic vibrator,
The ultrasonic wave emitted from the ultrasonic transducer is incident on the structure from the outside, and the frequency of the incident ultrasonic wave is adjusted so that the integral multiple of the wavelength and the circumferential length of the structure are equal. An ultrasonic cavitation cleaning method, wherein adjusted ultrasonic waves are incident on the structure to cause circumferential resonance to generate cavity bubbles on the inner surface of the structure.   An ultrasonic sensor for detecting the ultrasonic wave propagating through the structure is provided at a position opposite to the structure on the opposite side of the ultrasonic incident position. Based on the time difference from the time of reception, the circumferential length of the structure is calculated in advance, the frequency of the ultrasonic wave is adjusted so that the calculated circumferential length is equal to an integral multiple of the wavelength, and the adjusted ultrasonic wave is The ultrasonic cavitation cleaning method according to claim 3, wherein the ultrasonic wave cavitation cleaning method is caused to enter a body to cause circumferential resonance.   The ultrasonic frequency generated by the ultrasonic transducer is continuously variable, and an ultrasonic wave having a continuously variable frequency is added to the structure while sweeping the frequency in advance, and the vibration displacement of the structure or the intensity of the ultrasonic wave is detected by the ultrasonic sensor. After measuring the frequency to determine the frequency at which the vibration displacement or the ultrasonic intensity becomes maximum, the ultrasonic wave having the maximum frequency obtained is incident on the structure to cause circumferential resonance. The ultrasonic cavitation cleaning method according to claim 3 or 4. An ultrasonic cavitation cleaning method that cleans and removes attached solid matter on the inner surface of a cylindrical structure filled with a liquid using ultrasonic waves generated by an ultrasonic vibrator,
The ultrasonic wave emitted from the ultrasonic transducer is incident on the structure from the outside, and the frequency of the ultrasonic wave is adjusted so as to coincide with the higher-order natural frequency in the circumferential direction of the structure. The ultrasonic cavitation cleaning method is characterized in that a cavity bubble is generated on the inner surface of the structure.   A plurality of ultrasonic transducers are provided, and a plurality of ultrasonic waves whose frequencies emitted from the respective ultrasonic transducers are shifted from each other by an integral multiple or a half are incident on the structure to cause resonance. The ultrasonic cavitation cleaning method according to claim 1, wherein cavity bubbles are generated on the inner surface of the body. An ultrasonic cavitation cleaning method that cleans and removes attached solid matter on the inner surface of a cylindrical structure filled with a liquid using ultrasonic waves generated by an ultrasonic vibrator,
Each ultrasonic wave emitted from the plurality of ultrasonic transducers is incident on the structure body from the outer side so that the phases are synchronized, and the frequency of the ultrasonic wave is set to an integral multiple of the wavelength and the circumference of the structure body. An ultrasonic cavitation cleaning method, characterized in that a circumferential bubble is generated on the inner surface of the structure by adjusting circumferential lengths to be equal to each other to generate circumferential resonances.   4. The pressure amplitude of the ultrasonic wave on the inner surface of the structure is adjusted so as to be larger than the difference between the pressure of the liquid inside the structure and the saturated vapor pressure. Or the ultrasonic cavitation washing | cleaning method of 6 or 8.   The pressure amplitude of the ultrasonic wave on the inner surface of the structure is larger than the pressure amplitude of the incident wave of the ultrasonic wave incident on the structure in advance and the pressure amplitude of the reflected wave of the incident ultrasonic wave on the surface of the structure. The ultrasonic cavitation cleaning method according to claim 9, wherein the ultrasonic cavitation cleaning method is a value obtained by multiplying the ultrasonic transmittance calculated based on the difference in thickness.

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