Ultra-low frequency oscillation demagnetization and self-cleaning device for control rod screw of nuclear power plant

Abstract

This application relates to the technical field of nuclear power plant maintenance equipment, and specifically discloses an ultra-low frequency oscillation demagnetization and self-cleaning device for control rod screws in nuclear power plants. Aiming at the problems of high dirt re-adsorption rate, low cleaning efficiency and long downtime caused by residual magnetism on the screw surface in the prior art, this device achieves efficient maintenance through a coordinated demagnetization and cleaning mechanism. The demagnetization device uses the synergistic effect of alternating gradient magnetic fields and mechanical oscillations, with the magnetic field attenuation coefficient dynamically matched to the oscillation amplitude to weaken the magnetic adsorption of dirt. The ultrasonic cleaning device maintains a ±90° phase difference with the mechanical oscillation, and peels off dirt through alternating shear force peaks to improve efficiency. The adaptive control module adjusts the frequency ratio based on real-time residual magnetism data to reduce energy consumption. This device combines high-efficiency cleaning and extends the equipment maintenance period, and is suitable for the maintenance of control rod screws in nuclear power plants.

Description

Technical Field

[0001] This application belongs to the technical field of nuclear power plant maintenance equipment, and in particular relates to an ultra-low frequency oscillation demagnetization and self-cleaning device for control rod screws in nuclear power plants. Background Art

[0002] The control rod screws in nuclear power plants are in an underwater operating environment for a long time, and their surfaces are prone to adsorb iron oxide particles, boric acid crystals, and radioactive dust. The accumulation of these contaminants will increase the friction coefficient of the screws by 30%-50%, leading to control rod jamming accidents.

[0003] In the prior art, Chinese Patent CN115213160A discloses a cleaning device for a control rod drive mechanism of a nuclear reactor, which adopts a technical solution of single ultrasonic cleaning and cannot eliminate the residual magnetism generated on the screw surface due to long-term magnetization. Experiments show that the residual magnetism will increase the adsorption force of contaminants by 2-3 times, resulting in an increase in the re-adsorption rate of contaminants after cleaning, and the screw needs to be cleaned and maintained frequently. In addition, high-frequency oscillation demagnetization is likely to damage the screw, traditional manual cleaning requires the shutdown of more than 8 hours, and there is a risk of radiation exposure. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide an ultra-low frequency oscillation demagnetization and self-cleaning device for control rod screws in nuclear power plants to solve the deficiencies in the prior art, aiming to solve at least one of the above technical problems.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] An ultra-low frequency oscillation demagnetization and self-cleaning device for control rod screws in nuclear power plants, comprising:

[0007] A cavity, in which the control rod screw is coaxially clamped;

[0008] An ultra-low frequency oscillation demagnetization device, which is liftably arranged in the cavity, including an axial oscillation module and a gradient demagnetization coil. The axial oscillation module generates an axial mechanical oscillation of 0.1-1 Hz and 5-50 μm. The gradient demagnetization coil is coaxially nested outside the screw and passes a 0.05-0.5 Hz alternating current to generate an axially decaying alternating magnetic field, and the attenuation coefficient is 0.1-0.5 / mm;

[0009] An ultrasonic cleaning device, which is liftably linked with the ultra-low frequency oscillation demagnetization device. The ultrasonic cleaning device includes a plurality of piezoelectric transducers distributed along the axial direction of the screw, with a working frequency of 20-40 kHz, and maintains a fixed phase difference of ±90° with the axial mechanical oscillation module, and cooperates with the shear force to peel off the contaminants;

[0010] A magnetic force detection device, including an annular Hall sensor array, for real-time detection of the residual magnetic intensity on the screw surface.

[0011] Preferably, in the ultra-low frequency oscillation demagnetization self-cleaning device for the control rod screw of a nuclear power plant of the present invention, the synergistic effect of the phase difference of ±90° enables the shear force peak of ultrasonic cleaning and the displacement peak of mechanical oscillation to act alternately, thereby improving the efficiency of dirt stripping.

[0012] Preferably, in the ultra-low frequency oscillation demagnetization and self-cleaning device for the control rod screw of a nuclear power plant of the present invention, the alternating magnetic field attenuation coefficient and the mechanical oscillation amplitude satisfy the following relationship: ;

[0013] Where A is the amplitude, α is the attenuation coefficient, L is the screw length, and k is the proportional constant.

[0014] Preferably, the ultra-low frequency oscillation demagnetization and self-cleaning device for control rods and screws of a nuclear power plant according to the present invention further comprises a driving mechanism, wherein the driving mechanism has a built-in adaptive control module for:

[0015] a. Adjust the lifting stroke of the ultra-low frequency oscillation demagnetization device and ultrasonic cleaning device according to the length of the screw;

[0016] b. Based on the real-time data of the magnetic detection device, dynamically match the alternating current frequency and the mechanical oscillation frequency to keep the ratio between the two constant at 1:1~1:5.

[0017] Preferably, in the ultra-low frequency oscillation demagnetization self-cleaning device for control rods and screws of a nuclear power plant according to the present invention, the adaptive control module dynamically adjusts parameters based on the detection data of the Hall sensor:

[0018] When the residual magnetic intensity is greater than 10 gauss, the alternating current frequency is increased and the oscillation amplitude is increased;

[0019] When the residual magnetic intensity is ≤10 Gauss, start the ultrasonic cleaning device.

[0020] Preferably, in the ultra-low frequency oscillation demagnetization self-cleaning device for the control rod screw of a nuclear power plant of the present invention, the outer layer of the gradient demagnetization coil is coated with a μ-metal high magnetic permeability shielding layer, and the magnetic field leakage intensity is less than 1 Gauss.

[0021] Preferably, in the ultra-low frequency oscillation demagnetization self-cleaning device for the control rod screw of a nuclear power plant of the present invention, the axial oscillation module and the gradient demagnetization coil are driven by a piezoelectric ceramic stack driver, and the piezoelectric ceramic stack driver is encapsulated in a silicon nitride ceramic housing and can withstand temperatures greater than 300°C and radiation doses greater than 10^6Gy.

[0022] Preferably, the ultra-low frequency oscillation demagnetization self-cleaning device for the control rod screw of a nuclear power plant of the present invention further comprises a high-pressure flushing device, which is arranged to be lifted and lowered in conjunction with the ultrasonic cleaning device to flush dirt attached to the surface of the screw.

[0023] Preferably, the ultra-low frequency oscillation demagnetization and self-cleaning device for the control rod screw of a nuclear power plant according to the present invention further includes a dirt recovery system, and the dirt recovery system includes:

[0024] A conical collection bin arranged at the bottom of the cavity for collecting dirt, and a deep water pump is connected to the bottom;

[0025] A filter screen arranged on the inner wall of the cavity for preventing dirt from overflowing from the cavity to the external water body.

[0026] Preferably, for the ultra-low frequency oscillation demagnetization and self-cleaning device for the control rod screw of a nuclear power plant according to the present invention, an electromagnetic shielding layer is further provided on the inner wall of the cavity.

[0027] The beneficial effects of the present invention are as follows:

[0028] (1) Synergy of demagnetization and high-efficiency cleaning: Through the synergistic effect of ultra-low frequency oscillation and the gradient demagnetization coil, and through the phase difference design (±90°) of ultrasonic cleaning and mechanical oscillation, the peak shear force and the peak displacement act alternately, greatly improving the dirt removal rate, reducing the re-absorption rate, and extending the maintenance time;

[0029] (2) Adaptive energy-saving mode: The dynamic frequency matching technology (R = 1:1~1:5) reduces the energy consumption by 30% - 50%, and at the same time avoids mechanical overload and extends the service life of the equipment;

[0030] (3) Safe operation: Linked with the nuclear power plant control system, the operation time is shortened, and the risk of radiation exposure is reduced;

[0031] (4) Environmentally friendly design: The dirt recovery system (deep water pump + filter screen) prevents pollutants from overflowing and meets the safety standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The technical solutions of the present application will be further described below in conjunction with the drawings and embodiments.

[0033] Figure 1 It is a schematic diagram of the overall structure of the device in Embodiments 1 - 3 of the present application;

[0034] Figure 2 It is a schematic cross-sectional view of the overall structure of the device in Embodiments 1 - 3 of the present application;

[0035] Figure 3 It is a schematic diagram of the lifting mechanism structure inside the cavity in Embodiments 1 - 3 of the present application;

[0036] Figure 4 It is a schematic diagram of the driving mechanism structure in Embodiments 1 - 3 of the present application;

[0037] Figure 5 It is a dynamic frequency matching control flow chart in Embodiments 1 and 2 of the present application;

[0038] Figure 6 It is a schematic diagram of the demagnetization rate and energy consumption curve structure of Embodiments 1 and 2 of the present application under different R values;

[0039] Figure 7 It is a schematic diagram of the response curve generated based on the simplified PID model of Embodiments 1 and 2 of the present application;

[0040] Figure 8 It is a schematic diagram of the operation process control logic flow of Embodiments 1 and 2 of the present application;

[0041] The reference numerals in the figure are:

[0042] Cavity 10, control rod screw 20, ultra-low frequency oscillation demagnetization device 30, drive mechanism 40, ultrasonic cleaning device 50, magnetic force detection device 60, high-pressure flushing device 70, dirt recovery system 80;

[0043] Guide rail 11, lifting frame 12, gradient demagnetization coil 31, transmission shaft 41, driving gear set 42, driven gear set 43, conical collection bin 81, deep water pump 82. Specific embodiments

[0044] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0045] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the protection scope of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0046] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0047] The technical solution of the present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0048] This embodiment provides a nuclear power plant control rod screw ultra-low frequency oscillation demagnetization and self-cleaning device. Referring to Figure 1 - 3 , its structure includes a cavity 10, which is formed by connecting multiple sections of octagonal pipes, and is provided with a full-through side door to facilitate the assembly and maintenance of the internal equipment of the cavity. A cylinder is hinged between the side door and the outer wall of the cavity to drive the opening and closing of the side door. The inner wall of the cavity 10 is provided with a high-temperature electromagnetic shielding layer and a guide rail 11 arranged along the length direction. An elevator frame 12 is slidably installed on the guide rail 11, and the elevator frame 12 is driven to move up and down by a driving mechanism 40. An ultra-low frequency oscillation demagnetization device 30 with a hollow structure, an ultrasonic cleaning device 50, and a high-pressure flushing device 70 are sequentially installed on the elevator frame 12 from top to bottom. Among them, the magnetic force detection device 60 includes an annular Hall sensor array for real-time detection of the residual magnetic intensity on the surface of the screw. The magnetic force detection device 60 is installed on the inner wall of the shaft hole of the ultra-low frequency oscillation demagnetization device 30; the high-pressure flushing device 70 is provided with four high-pressure nozzles surrounding the outer surface of the screw 20, and is supplied with water by a high-pressure pump to flush the attached dirt on the surface of the screw. The dirt recovery system 80 includes a conical collection bin 81 arranged at the bottom of the cavity 10, with an inclination angle ≥ 45°, and a deep water pump 82 is connected to the bottom for adsorbing the peeled dirt; a filter screen (not labeled in the figure) is provided on the inner wall of the cavity, with a mesh diameter of 0.5 - 1 mm, for preventing the dirt from overflowing from the cavity to the external water body.

[0049] During operation, the screw 20 is hoisted into the cavity from the top, sequentially passes through the central holes of the above-mentioned devices, and is coaxially clamped at the axis of the cavity by two central limit sleeves above and below in the cavity.

[0050] Preferably, for the nuclear power plant control rod screw ultra-low frequency oscillation demagnetization and self-cleaning device of this embodiment, referring to Figure 4, the drive mechanism 40 includes a driving gear set 42 and a driven gear set 43 which are respectively arranged on both sides of the top of the cavity 10 and have the same transmission coefficient. A transmission shaft 41 is arranged between the driving gear set 42 and the driven gear set 43 for synchronous operation of the two sprocket transmission mechanisms. The power input shaft of the driving gear set 42 is drivingly connected to an external rotary driving device through a pair of helical gear sets. During operation, a motor arranged above the water body is connected to the driving gear of the helical gear set through a transmission shaft, thereby driving the driving gear set 42 to act. A driving sprocket of the same size specification is respectively connected to the power output shafts of the driving gear set 42 and the driven gear set 43. A driven sprocket of the same size specification as the driving sprocket is respectively rotatably arranged on both sides of the bottom of the inner cavity of the cavity 10. The driving sprocket and the driven sprocket on the same side are driven by a chain, and the two chains move at the same speed and are respectively fixedly connected to both sides of the lifting frame 12 to drive the lifting frame 12 to move up and down smoothly.

[0051] Preferably, for the nuclear power plant control rod screw ultra-low frequency oscillation demagnetization and self-cleaning device of this embodiment, the ultra-low frequency oscillation demagnetization device 30 includes an axial oscillation module and a gradient demagnetization coil 31. The axial oscillation module generates an axial mechanical oscillation of 0.1 - 1 Hz and 5 - 50 μm. This low-frequency oscillation assists in dirt stripping through two mechanisms:

[0052] Inertia effect: The inertial shear force is generated between the dirt particles and the screw surface due to the acceleration difference, weakening the adhesion force;

[0053] Fatigue failure: The periodic stress loading causes microcracks to occur at the interface between the dirt and the matrix, and finally fracture.

[0054] The outer layer of the gradient demagnetization coil 31 is coated with a μ-metal high magnetic permeability shielding layer, and the magnetic field leakage intensity < 1 gauss. The gradient demagnetization coil 31 is passed through with an ultra-low frequency alternating current of 0.05 - 0.5 Hz to generate an alternating magnetic field that decays exponentially along the axial direction of the screw, and the attenuation coefficient is 0.1 - 0.5 / mm; the axial oscillation module and the gradient demagnetization coil 31 are driven by a piezoelectric ceramic stack driver, and the piezoelectric ceramic stack driver is encapsulated in a silicon nitride ceramic shell, with a tolerance temperature > 300 °C and a radiation dose > 10^6 Gy.

[0055] Preferably, for the nuclear power plant control rod screw ultra-low frequency oscillation demagnetization and self-cleaning device of this embodiment, the alternating magnetic field attenuation coefficient and the mechanical oscillation amplitude satisfy the following relationship: ;

[0056] wherein, A is the amplitude in μm, α is the attenuation coefficient in / mm, L is the screw length in m, and k is a proportionality constant with 10 ≤ k ≤ 50.

[0057] Preferably, for the ultra-low frequency oscillation demagnetization and self-cleaning device of the control rod screw of the nuclear power plant in this embodiment, the driving mechanism 40 is signal-linked with the control rod drive system of the nuclear power plant and is built-in with an adaptive control module for:

[0058] a. Adjust the lifting stroke of the demagnetization device 30 and the cleaning device 50 according to the screw length;

[0059] Specifically, the adaptive control module generates a lifting command according to the stroke = L + ΔL (L is the screw length, preset by the system, and ΔL is the safety redundancy, set to 0.2 m), and drives the sprocket transmission system to drive the lifting frame 12 to move along the guide rail 11 to ensure that the demagnetization coil 31, the magnetic force detection device 60, and the ultrasonic transducer cover the entire length of the screw.

[0060] b. Based on the real-time data detected by the Hall sensor of the magnetic force detection device 60, dynamically adjust the ratio (R = fm:fv) of the alternating current frequency (fm) to the mechanical oscillation frequency (fv) so that it always remains within the range of 1:1 to 1:5, referring to Figure 5 .

[0061] When the remanent magnetic intensity > 10 Gauss, it is marked as the "high remanent magnetic region", and the alternating current frequency is increased to and the oscillation amplitude is increased;

[0062] When the remanent magnetic intensity ≤ 10 Gauss, start the operation of the ultrasonic cleaning device 50.

[0063] Among them, referring to Figure 6 , the realization of dynamic frequency matching adopts the fuzzy PID control algorithm, combining proportional-integral-derivative regulation and fuzzy logic to achieve the balance between fast response and stability.

[0064] Step 1: Set the target ratio Rtarget

[0065] If Bavg > 10 Gauss → Rtarget = 1:1;

[0066] If Bavg ≤ 10 Gauss → Rtarget = 1:5.

[0067] Step 2: Calculate the current ratio Rcurrent

[0068] ;

[0069] Step 3: Adjust the frequency parameters

[0070] If Rcurrent > Rtarget → decrease fm or increase fv;

[0071] If Rcurrent < Rtarget → increase fm or decrease fv.

[0072] Parameter adjustment rules:

[0073] Proportional term P: Linearly adjust the frequency according to the difference ΔR = Rtarget - Rcurrent;

[0074] Integral term I: Accumulate historical differences to eliminate steady-state errors;

[0075] Derivative term D: Predict the change trend to prevent overshoot.

[0076] This design is based on the following principle: the synergistic effect of magnetic field and mechanical energy. The alternating magnetic field is responsible for eliminating residual magnetism, and mechanical vibration destroys the attachment of dirt. The reasonable matching of the two frequencies can avoid energy conflict and improve the demagnetization efficiency.

[0077] Preferably, for the ultra-low frequency oscillation demagnetization and self-cleaning device of the control rod screw in the nuclear power plant of this embodiment, the ultrasonic cleaning device 50 includes a plurality of piezoelectric transducers distributed along the axial direction of the screw, with a working frequency of 20 - 40 kHz, and maintains a fixed phase difference of ±90° with the axial mechanical vibration module, and cooperatively peels off dirt through shear force.

[0078] Specifically, when the phase difference is +90°: the peak value of the ultrasonic shear force leads the peak value of the mechanical displacement by 1 / 4 cycle; when the phase difference is -90°: the peak value of the ultrasonic shear force lags behind the peak value of the mechanical displacement by 1 / 4 cycle.

[0079] This device adopts a phase difference of ±90°, so that the action times of the two forces are staggered, avoiding the mutual cancellation of energy, and at the same time forming an alternating impact.

[0080] Taking the mechanical vibration frequency of 0.5 Hz, the period T = 2 s, and the ultrasonic frequency of 30 kHz as an example:

[0081] At the stage of the peak value of mechanical displacement (t = 0.5 s): the screw displacement reaches +50 μm, and at this time the ultrasonic signal is at the wave trough (the shear force is the smallest); the inertial force of mechanical vibration "pushes" the dirt away from the substrate surface, but it is not completely peeled off.

[0082] At the stage of the mechanical displacement returning to zero (t = 1.0 s): the ultrasonic shear force reaches the peak value (about 500 N / cm²), and the cavitation bubbles collapse in the gap between the dirt and the substrate, generating a local high-pressure impact; at this time, the dirt has been loosened due to mechanical vibration, and the ultrasonic impact force directly acts on the bottom of the dirt to complete the peeling.

[0083] Experiments show that the synergistic effect of the phase difference can increase the effective energy acting on the dirt per unit time by more than 40%. For example: when there is no phase difference: the ultrasonic wave and mechanical vibration reach the peak value at the same time, and part of the energy cancels each other out, and the dirt peeling efficiency is only 65%; when the phase difference is ±90°: the energy utilization rate is maximized, and the dirt peeling efficiency is increased to 95%.

[0084] Specific Embodiments of Phase Difference Synergy

[0085] 1. Realization and Control of Phase Difference

[0086] Configure hardware:

[0087] Signal generator: Use a high-precision digital signal generator to output two synchronous signals:

[0088] Channel 1: 0.1 - 1 Hz sine wave to drive the mechanical oscillation module;

[0089] Channel 2: 20 - 40 kHz square wave (converted to a sine wave after filtering) to drive the ultrasonic transducer.

[0090] Phase-locked circuit: Through phase-locked loop (PLL) technology, ensure that the phase difference between the two signals is stable within ±90°, with an error < 1°.

[0091] The adaptive control module dynamically adjusts the direction of the phase difference so that different types of dirt can be effectively peeled off.

[0092] When a -90° phase difference is adopted, it preferentially uses mechanical oscillation to break the interface bond, and the peeling effect of hard dirt (such as iron oxide particles) is good; when a +90° phase difference is adopted, it preferentially exerts the ultrasonic cavitation effect, and the peeling effect of soft dirt (such as boric acid crystals) is good.

[0093] 2. Quantitative Analysis of Shearing Force and Displacement

[0094] (1) Shearing Force Calculation Model

[0095] The shearing force (Fs) generated by ultrasonic waves can be approximately expressed as: ;

[0096] Where:

[0097] ρ: Liquid density (1000 kg / m³ for water);

[0098] c: Sound velocity (1500 m / s for water);

[0099] υ: Sound particle vibration velocity ;

[0100] A: Acting area.

[0101] Taking ultrasonic waves at 30 kHz and an amplitude of 5 μm as an example:

[0102] ;

[0103] ;

[0104] (Note: F SThe actual value can be amplified by cavitation effect to more than 500 N / cm²

[0105] (2)Stress contribution of mechanical oscillation

[0106] The inertial force (Fm) generated by mechanical oscillation is:

[0107] Where:

[0108] m: Mass of the dirt (assumed to be 1 g);

[0109] f: Oscillation frequency of 0.5 Hz;

[0110] A: Amplitude of 50 μm.

[0111]

[0112] Although Fm is small, its periodic action can significantly reduce the adhesion of dirt.

[0113] 3. Experimental verification of the synergistic effect

[0114] (1)Design of comparative experiment

[0115] Control group: Only ultrasonic cleaning (30 kHz) is used, without mechanical oscillation;

[0116] Experimental group: Synergy of ultrasonic cleaning (30 kHz) and mechanical oscillation (0.5 Hz, 50 μm), with a phase difference of ±90°.

[0117] (2)The experimental results are shown in Table 1

[0118] Dirt type Removal rate of the control group Removal rate of the experimental group Efficiency improvement Iron oxide particles (100μm) 68% 95% 39.7% Boric acid crystals (lamellar) 52% 89% 71.2% Radioactive dust (sticky) 45% 82% 82.2%

[0119] Table 1: Comparison of removal rate effects of different dirt

[0120] (3)Analysis of the action mechanism

[0121] Iron oxide particles: Mechanical oscillation preferentially destroys the mechanical interlocking between the particles and the matrix, and ultrasonic shear force removes the residual debris;

[0122] Boric acid crystals: Ultrasonic cavitation effect penetrates into the crystal layers, and mechanical oscillation accelerates the interlayer peeling;

[0123] Radioactive dust: The synergistic effect of the phase difference overcomes the van der Waals force and prevents the dust from reabsorbing.

[0124] It should be noted that refer to Figure 7, the device also includes a ground receiving and control unit and a wireless transmission unit. The wireless transmission unit transmits the data of the underwater device to the ground in real time, supports manual remote adjustment of parameters (such as forced switching between demagnetization / washing modes), and forms a "detection - decision - execution - re - detection" closed loop based on the feedback data of the magnetic force detection device 60.

[0125] The working principle and operation process of the device will be further described below with specific data.

[0126] Example 1: Structure and basic operation process of the device.

[0127] Step 1: Device assembly and screw clamping

[0128] Installation of cavity 10: The cavity is composed of multiple sections of octagonal pipes spliced together, and the inner wall is sprayed with a high - temperature electromagnetic shielding layer (the material is silicon carbide composite material, with a temperature resistance of ≥500°C). The ultra - low - frequency oscillation demagnetization device 30, magnetic force detection device 60, ultrasonic cleaning device 50, and high - pressure flushing device 70 are installed on the lifting frame 12 in sequence. The lifting frame 12 is installed on the guide rail 11 and is controlled by the driving mechanism 40 to lift.

[0129] The control rod screw 20 (taking the length L = 6m and diameter φ = 80mm as an example) is hoisted into the cavity from the top through a hoisting device and is coaxially fixed by upper and lower limit sleeves.

[0130] Step 2: Demagnetization stage

[0131] Generation of ultra - low - frequency alternating magnetic field:

[0132] The annular demagnetization coil 31 is passed through with an alternating current of 0.1Hz to generate an alternating magnetic field with an initial magnetic field intensity of 200 gauss, which decays exponentially along the axial direction of the screw (α = 0.3 / mm).

[0133] The axial oscillation module drives the axial displacement of the screw at a frequency of 0.5Hz (amplitude A = 30μm). The mechanical oscillation and the magnetic field attenuation coefficient satisfy the formula: ;

[0134] where k = 20, L is 6m, and after calculation, α = 0.3 / mm.

[0135] Adaptive adjustment:

[0136] The initial detected remanence intensity is 20 gauss, belonging to a high - remanence screw (Bavg = 20 gauss).

[0137] Initial parameter setting: fm = 0.1Hz, fv = 0.2Hz (R = 1:2);

[0138] Detection and determination: Bavg = 20 gauss → trigger the R = 1:1 mode;

[0139] Adjustment process:

[0140] Gradually increase fm to 0.5Hz (hardware upper limit), and simultaneously increase fv to 0.5Hz;

[0141] The demagnetization rate is increased from 2 gauss / minute to 5 gauss / minute;

[0142] Result: After 15 minutes, Bavg ≤ 10 Gauss, switching to R = 1:5 mode (fm = 0.1 Hz, fv = 0.5 Hz), and triggering the cleaning phase.

[0143] Step 3: Cleaning Phase

[0144] Ultrasonic collaborative cleaning:

[0145] The ultrasonic transducer operates at a frequency of 35kHz and maintains a -90° phase difference with the mechanical oscillation module.

[0146] The mechanical oscillation frequency was set to 0.8 Hz, with an amplitude of 40 μm, alternating with the ultrasonic shear force peak. The experiment showed that after 30 minutes, the dirt removal rate was 98.5%; the surface roughness dropped from Ra 3.2 μm to Ra 0.8 μm.

[0147] High-pressure washing and dirt collection:

[0148] The high-pressure flushing device 70 sprays water at a pressure of 60 MPa, and the flushed and stripped dirt is intercepted into the cavity through a 200-mesh filter screen, and is discharged from the conical collection bin 81 at the bottom to an externally connected waste collection device through its own gravity sedimentation and adsorption by a deep water pump 82.

[0149] Step 4: Effect Verification

[0150] Residual magnetism elimination: The residual magnetism intensity on the screw surface is ≤ 2 Gauss (far below the 10 Gauss threshold).

[0151] Cleaning efficiency: Dirt removal rate ≥ 95%, reabsorption rate < 5% (reabsorption rate of traditional technology > 30%).

[0152] Time cost: The whole process takes 45 minutes.

[0153] Example 2: Different from Example 1, after the demagnetization stage of step 2 is completed, the initial detected residual magnetism intensity is 8 Gauss, which belongs to a low residual magnetism screw (Bavg=8 Gauss).

[0154] Initial parameter settings: fm=0.05Hz, fv=0.25Hz (R=1:5);

[0155] Energy saving effect: energy consumption is reduced by 40% compared with R=1:1 mode, and the demagnetization rate remains at 1 gauss / minute;

[0156] Stability verification: Continuously run for 2 hours, and the frequency fluctuation < ±0.01 Hz.

[0157] The effects of the dynamic frequency matching mode and the fixed frequency mode are referred to Table 2.

[0158] Working mode Demagnetization rate (Gauss / minute) Energy consumption (kW·h) Dirt stripping efficiency Fixed R = 1:1 4.5 2.8 92% Fixed R = 1:5 1.2 0.7 85% Dynamic matching (1:1~1:5) 3.8~5.0 1.2~2.0 95%

[0159] Table 2: Verification of the effects of the dynamic frequency matching mode and the fixed frequency mode

[0160] Refer to Figure 5 , while ensuring the demagnetization efficiency, the dynamic frequency matching mode reduces the energy consumption by 30% - 50%, and avoids mechanical overload through adaptive adjustment, prolonging the service life of the equipment.

[0161] Example 3: Different from Example 1 and Example 2, in this example, during the demagnetization stage, the ultra-low frequency oscillation demagnetization device is driven by the driving mechanism to demagnetize the entire length of the screw in the R = 1:1 mode (or other modes, manually set according to the screw maintenance period and operating environment), (the coil moves 6 - 12 meters per minute from the bottom up, demagnetizing while moving). After the demagnetization is completed, then the magnetic force detection device detects the residual magnetism, and the coil moves downwards (0.5 m / s) to measure whether the residual magnetism is qualified. If it is qualified, the operation is completed. If it is not qualified, repeat the above demagnetization operation process and then measure the residual magnetism until the residual magnetism reaches the set threshold. The operation process of this example is simple and fast, with high stability, and has low requirements for the control ability of the device, and is suitable for complex operating environments.

[0162] Enlightened by the above ideal embodiments based on this application, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this application. The technical scope of this application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. The ultra-low frequency oscillation demagnetization and self-cleaning device for the control rod screw of a nuclear power plant, characterized in that, include: A cavity (10), wherein a control rod screw (20) is coaxially clamped in the cavity (10); An ultra-low frequency oscillation demagnetization device (30) is arranged in a liftable manner in the cavity (10), and comprises an axial oscillation module and a gradient demagnetization coil (31). The axial oscillation module generates an axial mechanical oscillation of 0.1-1 Hz and 5-50 μm. The gradient demagnetization coil (31) is coaxially nested on the outside of the screw (20), and an alternating current of 0.05-0.5 Hz is passed through it to generate an axially attenuated alternating magnetic field with an attenuation coefficient of 0.1-0.5 / mm. An ultrasonic cleaning device (50) is arranged to be lifted and lowered in conjunction with the ultra-low frequency oscillation demagnetization device (30), wherein the ultrasonic cleaning device (50) includes a plurality of piezoelectric transducers distributed along the axial direction of the screw (20), has an operating frequency of 20-40 kHz, and maintains a fixed phase difference of ±90° with the axial mechanical oscillation module, thereby collaboratively stripping dirt through shear force; The magnetic force detection device (60) comprises an annular Hall sensor array and is used for detecting the residual magnetic intensity on the surface of the screw in real time.

2. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 1, characterized in that, The synergistic effect of the phase difference of ±90° enables the shear force peak of ultrasonic cleaning and the displacement peak of mechanical oscillation to act alternately, thereby improving the efficiency of dirt stripping.

3. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 1, characterized in that, The attenuation coefficient of the alternating magnetic field and the mechanical oscillation amplitude satisfy the following relational expression: ; Where A is the amplitude, α is the attenuation coefficient, L is the screw length, and k is the proportional constant (10≤k≤50).

4. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to any one of claims 1-3, characterized in that, The drive mechanism (40) is also included. The drive mechanism (40) has a built-in adaptive control module for: a. adjusting the lifting stroke of the ultra-low frequency oscillation demagnetization device (30) and the ultrasonic cleaning device (50) according to the screw length; b. Based on the real-time data of the magnetic detection device (60), the alternating current frequency and the mechanical oscillation frequency are dynamically matched so that the ratio between the two is constant at 1:1~1:

5.

5. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 4, characterized in that, The adaptive control module dynamically adjusts parameters based on the detection data of the Hall sensor: When the residual magnetic intensity is greater than 10 gauss, the alternating current frequency is increased and the oscillation amplitude is increased; When the residual magnetic intensity is ≤10 Gauss, the ultrasonic cleaning device (50) is started to operate.

6. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation, as described in claim 1, is characterized in that, The outer layer of the gradient demagnetization coil (31) is coated with a μ-metal high magnetic permeability shielding layer, and the magnetic field leakage intensity is less than 1 Gauss.

7. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 1 or 6, characterized in that, The axial oscillation module and the gradient demagnetization coil (31) are driven by a piezoelectric ceramic stack driver, which is encapsulated in a silicon nitride ceramic housing and has a tolerance temperature of >300°C and a radiation dose of >10^6Gy.

8. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 5, characterized in that, It also includes a high-pressure flushing device (70), which is arranged to rise and fall in conjunction with the ultrasonic cleaning device (50) and is used to flush dirt attached to the surface of the screw.

9. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation according to claim 8, characterized in that, Also included is a waste recovery system (80), the waste recovery system (80) comprising: A conical collecting chamber (81) provided at the bottom of the cavity (10) for collecting waste, the bottom of which is connected to a deep water pump (82); The filter screen arranged on the inner wall of the cavity is used to prevent dirt from overflowing from the cavity into the external water body.

10. The demagnetization and self-cleaning device for the control rod screw of a nuclear power plant with ultra-low frequency oscillation, as described in claim 1, is characterized in that The inner wall of the cavity (10) is also provided with an electromagnetic shielding layer.

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