A device and method for in-situ characterization of annular fuel pellets based on thermal gradient driving

Abstract

The application discloses a kind of in-situ characterization device and method of annular fuel pellet based on thermal gradient driving, device includes vacuum thermal gradient loading system, double-channel characterization system, power supply and parameter control unit, support frame assembly and data processing terminal.Central resistance heating rod is fixed in the inner hole of annular fuel pellet, power supply and parameter control unit output adjustable power to heating rod, so that it guides heat from the inner wall side of pellet, forms gradually decreasing radial temperature gradient from inner wall side to outer wall side.Double-channel characterization system includes visible morphology acquisition channel and narrowband radiation acquisition channel, light signal from the same sample surface of pellet is divided into two paths by light splitting component, and the synchronous acquisition of morphology information and narrowband thermal radiation response is realized.Data processing terminal carries out time synchronization and spatial registration between morphology information and reconstructed two-dimensional temperature field, and is suitable for annular nuclear fuel pellet thermal mechanical stability evaluation and related temperature gradient effect research.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel element performance testing and high-temperature in-situ characterization technology, specifically a device and method for in-situ characterization of annular fuel pellets based on thermal gradient driving. Background Technology

[0002] Uranium dioxide fuel pellets are a widely used form of nuclear fuel in pressurized water reactor nuclear power plants. During reactor operation, a large amount of heat is generated inside the fuel pellet due to fission heat release, and this heat is conducted outward from the inside of the pellet to the cladding and coolant, thus forming a significant radial temperature gradient from the center to the outer wall within the pellet. This temperature gradient can cause thermal stress concentration. When the thermal stress exceeds the material's strength limit, it may lead to cracks, edge spalling, or localized through-hole defects in the pellet, thereby affecting the structural integrity and service reliability of the fuel element. For annular fuel pellets with a central hole structure, the temperature difference between the inner and outer walls is even more significant, and the thermal stress distribution is more complex, thus posing higher experimental requirements for evaluating their thermomechanical stability under the influence of temperature gradients.

[0003] In existing high-temperature out-of-core testing techniques, fuel samples are typically heated using either integral furnace heating or external radiant heating. Topographic acquisition components and infrared thermography components, positioned outside the furnace observation windows, acquire surface images and temperature data, respectively. The process involves placing the sample inside the furnace, where heating elements on the furnace wall or an external radiation source heat the outer wall of the sample, raising the overall temperature to the target level. Simultaneously, the topographic acquisition component captures images of the sample surface through the observation windows, while the infrared thermography component collects thermal radiation signals from the sample surface through the same or adjacent windows and converts them into temperature readings. However, since both integral furnace heating and external radiant heating introduce heat from the outer wall of the sample, this direction is opposite to the actual thermal boundary direction of a toroidal fuel pellet transferring heat from the center of the fuel pellet to the outer wall within the reactor. This results in a mismatch between the temperature gradient distribution within the sample and actual service conditions, making it impossible to accurately simulate the thermal stress response behavior of a toroidal fuel pellet under in-core service conditions, dominated by the temperature difference from the inner to the outer wall. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ characterization device and method for annular fuel pellets based on thermal gradient drive, so as to solve the above-mentioned problems.

[0005] The technical solution of this invention is: An in-situ characterization device for annular fuel pellets based on thermal gradient drive includes: a water-cooled unit, a vacuum thermal gradient loading system, a dual-channel characterization system, a power supply and parameter control unit, a support system, and a data processing terminal; The vacuum thermal gradient loading system is equipped with an in-furnace thermal gradient loading device, which includes a central resistance heating rod fixed in the inner hole of the annular fuel pellet. The central resistance heating rod is electrically connected to the power supply and parameter control unit, which outputs adjustable power to the central resistance heating rod so that it introduces heat to the inner wall side of the annular fuel pellet in a vacuum or protective atmosphere, and forms a radial temperature gradient in the annular fuel pellet that varies from the inner wall side to the outer wall side. The dual-channel characterization system is fixed to the outside of the observation window of the vacuum thermal gradient loading system via the support frame assembly. It includes a visible morphology acquisition channel and a narrowband radiation acquisition channel. The beam splitter is set in the common optical path of the visible morphology acquisition channel and the narrowband radiation acquisition channel to split the light signal from the same sample surface of the annular fuel pellet into two paths, which enter the visible morphology acquisition channel and the narrowband radiation acquisition channel respectively, so as to simultaneously acquire the morphology information and narrowband thermal radiation response of the sample surface during the radial temperature gradient loading process. The data processing terminal is communicatively connected to the visible morphology acquisition channel and the narrowband radiation acquisition channel, respectively, and is used to synchronize the morphology information with the two-dimensional temperature field reconstructed from the narrowband thermal radiation response in time and space.

[0006] Furthermore, the visible morphology acquisition channel includes a visible morphology acquisition component, and the narrowband radiation acquisition channel includes a narrowband filter and a narrowband radiation temperature field acquisition component; the beam splitter is disposed in the common acquisition optical path of the visible morphology acquisition component and the narrowband radiation temperature field acquisition component, and the narrowband filter is disposed in the acquisition optical path of the narrowband radiation temperature field acquisition component and located on the light-emitting side of the beam splitter.

[0007] Furthermore, the furnace thermal gradient loading device also includes an insulating support tube, an upper voltage conductor, a conductive connecting wire, a lower voltage conductor, and an insulating base; the central resistance heating rod is disposed between the upper voltage conductor and the lower voltage conductor, the insulating support tube passes through the central resistance heating rod and cooperates with the insulating base to form an axial positioning structure; the power supply and parameter control unit is electrically connected to the upper voltage conductor and the lower voltage conductor via the conductive connecting wire.

[0008] Furthermore, a replaceable isolation layer or gap control layer is provided between the central resistance heating rod and the inner wall of the annular fuel pellet. The isolation layer or gap control layer is used to restrict the direct adhesion between the sample and the central resistance heating rod, and to form a repeatable radial heat transfer boundary between the inner wall side and the outer wall side of the annular fuel pellet.

[0009] Furthermore, the vacuum thermal gradient loading system includes a vacuum furnace body, a vacuum pumping assembly, a protective gas source, a furnace wall cooling channel, a circular flange with a quartz window, a pressure detection element, a coolant interface, a gas path interface, and a power supply interface. The vacuum pumping assembly and the protective gas source are respectively connected to the vacuum furnace body via the gas path interface, and the furnace wall cooling channel is connected to the water-cooled unit via the coolant interface, so as to maintain the thermal stability of the outer wall of the furnace body and the sealed area during high-temperature loading.

[0010] Furthermore, the circular flange with a quartz window includes an observation channel and an illumination channel. The observation channel is arranged in the central area of ​​the top surface of the vacuum furnace body, and the illumination channel is inclined relative to the observation channel. The emitted light from the heat-resistant lighting component illuminates the thermal gradient loading device inside the furnace through the illumination channel to reduce the influence of specular reflection on surface morphology identification.

[0011] Furthermore, the narrowband radiation temperature field acquisition component includes a long working distance radiation acquisition lens group, a radiation response array, and a radiation brightness conversion unit. The radiation brightness conversion unit generates a two-dimensional radiation temperature matrix of the annular fuel pellet surface based on the center wavelength and bandwidth of the narrowband filter, the transmittance of the quartz window, the response curve of the radiation response array, and the calibration coefficient of the sample surface. The data processing terminal is used to perform dark field subtraction, background correction, window transmittance compensation, response normalization, field distortion correction, and pixel coordinate mapping on the two-dimensional radiation temperature matrix, and calculates the radial temperature gradient, circumferential temperature difference, local hot spot location, and time-varying thermal gradient loading history of the annular fuel pellet surface based on the mapping results.

[0012] Furthermore, the data processing terminal is also used to extract the surface damage initiation location, geometric size change, expansion direction and local peeling area from the image sequence obtained from the visible morphology acquisition channel, and associate the above morphological features with the two-dimensional temperature field at the same time to form an experimental record containing timestamp, spatial coordinates, morphological features and temperature gradient parameters.

[0013] A thermal gradient-driven in-situ characterization method for annular fuel pellets, implemented using the aforementioned apparatus, includes the following steps: The annular fuel pellet is fitted around the outer periphery of the central resistance heating rod and placed inside the vacuum thermal gradient loading system. Evacuate or fill the vacuum thermal gradient loading system with protective gas. Start the water-cooled unit and the power supply and parameter control unit to make the center resistance heating rod heat up according to the preset power or heating rate; The surface morphology information and narrowband thermal radiation response of the chip were simultaneously acquired using a dual-channel characterization system. The two-dimensional temperature field is reconstructed by the data processing terminal and registered with the morphology information to obtain the surface evolution parameters of the core during the thermal gradient loading process.

[0014] Furthermore, when reconstructing the two-dimensional temperature field, the narrowband response data of the empty background and the calibration sample are acquired. The experimental data are then subjected to dark field subtraction, background correction, window transmittance correction, narrowband response normalization, and surface calibration coefficient correction. Based on the center wavelength and bandwidth of the narrowband filter, the transmittance of the quartz window, the response curve of the radiation response array, and the sample surface calibration coefficient, the original radiation response of each sampling unit is subtracted from the empty background and normalized by the comprehensive response factor to obtain the corrected narrowband radiance. According to the Planck radiation relation, the corrected narrowband radiance is inverted into temperature values ​​to generate a two-dimensional temperature matrix. Based on the annular geometry of the annular fuel pellet, the two-dimensional temperature matrix is ​​mapped from pixel coordinates to polar coordinates to determine the radial temperature gradient, circumferential temperature difference, and local hot spot locations in the direction from the inner wall to the outer wall.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention fixes a central resistance heating rod within the inner hole of an annular fuel pellet, directly introducing heat from the inner wall of the pellet, creating a radial temperature gradient that gradually decreases from the inner wall to the outer wall. Since this heat introduction direction aligns with the actual thermal boundary direction of the annular fuel pellet within the reactor, where heat release from central fission is directed to the outer wall, it overcomes the fundamental flaw of traditional external heating methods where the thermal boundary direction is opposite to the actual service state. This allows the thermal stress response in simulation tests to more realistically reflect the actual service behavior of the pellet. Simultaneously, the dual-channel characterization system uses a beam splitter to allow the visible morphology acquisition channel and the narrowband radiation acquisition channel to share the same optical path, achieving spatial and temporal synchronous acquisition of the same sample surface morphology information and narrowband thermal radiation response. This avoids the field-of-view differences and temporal synchronization errors introduced by traditional methods where morphology observation and temperature measurement occur at different windows. The data processing terminal performs spatiotemporal registration of the morphological information with the reconstructed two-dimensional temperature field, so that the location of surface damage can be accurately associated with the local temperature gradient conditions at the time of its occurrence, providing accurate experimental data support for the evaluation of the thermomechanical stability of annular fuel pellets under the action of temperature gradient. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a toroidal fuel pellet sample of the present invention.

[0017] Figure 2 This is a schematic diagram of the overall structure of the present invention.

[0018] Figure 3 This is a schematic diagram of the appearance and cross-section of the vacuum thermal gradient loading system of the present invention.

[0019] Figure 4 This is a schematic diagram of the furnace internal thermal gradient loading device of the present invention.

[0020] Figure 5This is a schematic diagram of the dual-channel characterization system of the present invention.

[0021] The components include: 1. Water-cooled unit; 2. Vacuum thermal gradient loading system; 21. Furnace internal thermal gradient loading device; 211. Insulating support tube; 212. Upper voltage conductor; 213. Conductive connecting wire; 214. Center resistance heating rod; 215. Lower voltage conductor; 216. Insulating base; 22. Evacuation assembly; 23. Protective gas source; 24. Furnace wall cooling channel; 25. Circular flange with quartz window; 26. Pressure detection element; 27. Coolant interface; 28. Gas path interface; 29. ​​Power supply and power interface; 3. Dual-channel characterization system; 31. Fixing plate; 32. Profile frame; 33. Assembly component bracket; 34. Visible morphology acquisition component; 35. Narrowband filter; 36. Spectrometer assembly; 37. Narrowband radiation temperature field acquisition component; 38. Acquisition component mounting plate; 39. Heat-resistant lighting component; 4. Power supply and parameter control unit; 5. Support frame assembly; 6. Data processing terminal. Detailed Implementation

[0022] The following is combined Figures 1 to 5 The specific embodiments of the present invention will be described in detail below. In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0023] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] It should be noted that the circuit connections involved in this invention all adopt conventional circuit connection methods and do not involve any innovation.

[0025] Example like Figures 1 to 5As shown, the device in this embodiment includes a water-cooled unit 1, a vacuum thermal gradient loading system 2, a dual-channel characterization system 3, a power supply and parameter control unit 4, a support frame assembly 5, and a data processing terminal 6. The vacuum thermal gradient loading system 2 can adopt a vertical square sealed cavity, and the cavity wall thickness meets the strength and sealing requirements of the high-temperature test; the water-cooled unit 1 is connected to the coolant interface 27 through a pressure-resistant pipeline, so that the furnace wall cooling channel 24 forms a circulating cooling loop; the vacuum thermal gradient loading system 2 is installed on the support base, and the furnace internal thermal gradient loading device 21 is set at the center of the bottom of the furnace cavity; the dual-channel characterization system 3 is fixed above the observation window by the support frame assembly 5 to maintain the stability of the observation optical path.

[0026] The vacuum thermal gradient loading system 2 includes a vacuum furnace body, a vacuum pumping assembly 22, a protective gas source 23, a furnace wall cooling channel 24, a circular flange 25 with a quartz window, a pressure sensor 26, a coolant interface 27, a gas path interface 28, and a power supply interface 29. The furnace wall cooling channel 24 is located inside the side wall of the furnace body. Its cross-section can be square or other easily machined closed channels. The cooling medium flows unidirectionally or circulates within the channel to limit the furnace wall temperature rise and protect the seals. The vacuum pumping assembly 22 and the protective gas source 23 are connected to the furnace cavity via the gas path interface 28. Before the test, the vacuum pumping assembly 22 reduces the oxygen and water vapor content in the furnace cavity. Alternatively, argon, helium, or other inert gases can be introduced after the set pressure is reached to create a protective atmosphere. The sensing end of the pressure sensor 26 is connected to the furnace cavity, and pressure data is displayed or transmitted externally, allowing the power supply and parameter control unit 4 to determine whether high-temperature loading is permitted based on the pressure status inside the furnace.

[0027] A circular flange 25 with a quartz window is used to form an observation channel and an illumination channel. The observation channel is preferably located in the central area of ​​the top surface of the furnace body, so that the dual-channel characterization system 3 can observe the annular fuel pellets on the thermal gradient loading device 21 inside the furnace; the illumination channel is tilted relative to the observation channel, so that the light from the heat-resistant illumination component 39 illuminates the sample surface at an angle that avoids specular reflection, thereby improving the visibility of the visible morphology acquisition component 34 in terms of the ability to distinguish boundaries and surface textures.

[0028] like Figure 4As shown, the furnace thermal gradient loading device 21 includes an insulating support tube 211, an upper voltage-conducting plate 212, a conductive connecting wire 213, a central resistance heating rod 214, a lower voltage-conducting plate 215, and an insulating base 216. The insulating support tube 211 and the insulating base 216 can be made of boron nitride or other high-temperature resistant insulating materials to maintain structural strength and electrical insulation performance at high temperatures. The upper voltage-conducting plate 212 and the lower voltage-conducting plate 215 are used to clamp and conduct the central resistance heating rod 214, and the conductive connecting wire 213 introduces current into the heating area. The central resistance heating rod 214 is preferably made of a metal material with a high melting point, stable high-temperature strength, and appropriate resistance characteristics. An annular fuel pellet is sleeved around the central resistance heating rod 214, and an isolation layer or control gap can be provided between them. The isolation layer can be made of boron nitride, alumina, or other high-temperature resistant inert materials. The power supply and parameter control unit 4 is connected to the furnace thermal gradient loading device 21 via the power supply and power interface 29. After power is supplied, the central resistance heating rod 214 first heats up and conducts heat from the inner wall side of the fuel pellet to the outer wall side, forming a radial temperature gradient with a higher temperature on the inner wall side and a lower temperature on the outer wall side. The control program can include modes such as stepped heating, continuous heating, constant temperature holding, and power reduction cooling. For annular fuel pellets of different sizes or densities, the sample can be kept within the set temperature range and the set radial temperature difference range by adjusting the output voltage, current, power limit, and heating rate.

[0029] like Figure 5As shown, the support frame assembly 5 includes a fixing plate 31 and a profile frame 32. The lower end of the profile frame 32 is fixed to the top surface of the vacuum thermal gradient loading system 2 or the mounting plane outside the observation window flange through the fixing plate 31. The profile frame 32 is made of aluminum alloy profiles or steel profiles spliced ​​together. Its height and horizontal position can be adjusted according to the position of the observation window to ensure that the optical axis of the dual-channel characterization system 3 coincides with the center line of the observation window. The dual-channel characterization system 3 includes a visible morphology acquisition component 34, a beam splitter 36, a narrowband filter 35, a narrowband radiation temperature field acquisition component 37, and a heat-resistant illumination component 39. The profile frame 32 has multiple mounting holes for fixing the visible morphology acquisition component 34, the beam splitter 36, and the narrowband radiation temperature field acquisition component 37, ensuring that the relative positions of each component remain stable during the experiment. This guarantees that the two acquisition channels always have the same calibration field of view throughout the entire thermal gradient loading process. The visible morphology acquisition component 34 and the narrowband filter 35 are mounted on the same edge of the profile frame 32 via a component support 33, with the visible morphology acquisition component 34 positioned above the narrowband filter 35. The beam splitter 36 is located in the common optical path of the two acquisition channels, splitting the light signal from the same sample surface of the annular fuel pellet into two paths, which enter the visible morphology acquisition channel and the narrowband radiation acquisition channel respectively, giving the two channels the same or calibrated convertible field of view. The visible morphology acquisition channel includes a visible morphology acquisition component 34, used to obtain morphological information such as cracks, pores, edge contours, and localized spalling on the surface of the annular fuel pellet. The narrowband radiation acquisition channel includes a narrowband filter 35 and a narrowband radiation temperature field acquisition component 37. The temperature field acquisition component 37 is fixed to the profile frame 32 via an acquisition component mounting plate 38. The narrowband filter 35 is positioned in the acquisition optical path of the narrowband radiation temperature field acquisition component 37 and is located on the light-emitting side of the beam splitter 36. Its center wavelength and bandwidth are determined based on the sample temperature range, the transmittance of the quartz window, and the response range of the acquisition array. The narrowband radiation temperature field acquisition component 37 includes a long working distance radiation acquisition mirror group, a radiation response array, and a radiation brightness conversion unit. It acquires the thermal radiation response after passing through the narrowband filter 35 and transmits the response data to the data processing terminal 6.

[0030] The data processing terminal 6 is communicatively connected to both the visible morphology acquisition channel and the narrowband radiation acquisition channel. The data processing terminal 6 pre-stores the transmittance curves of the quartz window, the transmittance curve of the narrowband filter 35, the radiation response array response curve, the field-of-view geometric calibration parameters, and the sample surface calibration coefficients. During the experiment, the data processing terminal 6 performs dark field subtraction, background correction, window transmittance compensation, response normalization, and coordinate mapping on the narrowband radiation response, thereby converting the radiance of each sampling unit into a temperature value and generating a two-dimensional temperature field. Based on the inner hole, outer edge, and sample boundary characteristics of the annular fuel pellet, the data processing terminal 6 maps the two-dimensional temperature matrix from image pixel coordinates to the actual geometric coordinates or polar coordinates of the sample, obtaining the radial temperature gradient from the inner wall to the outer wall, the temperature difference at different circumferential positions, the location of local hot spots, the duration of hot spots, and the temperature field evolution history as a function of the applied power.

[0031] To achieve synchronization between surface morphology and temperature field, the data processing terminal 6 establishes a coordinate transformation relationship between the two acquisition channels before the experiment begins, using a calibration plate or sample edge features. During the experiment, each frame of morphology image and each frame of temperature matrix are appended with a timestamp based on the same time reference. When the visible morphology acquisition component 34 identifies the starting point of surface damage or a change in geometric dimensions, the data processing terminal 6 can retrieve the temperature, radial temperature gradient, and circumferential temperature difference at the corresponding location at the same time, thereby forming a corresponding record of surface evolution and thermal boundary conditions. The data processing terminal 6 also extracts the starting position of surface damage, changes in geometric dimensions, direction of expansion, and local spalling areas from the image sequence obtained from the visible morphology acquisition channel, and associates these morphological features with the two-dimensional temperature field at the same time, forming an experimental record containing timestamps, spatial coordinates, morphological features, and temperature gradient parameters.

[0032] A preferred experimental procedure is as follows: First, the annular fuel pellet is placed around the center resistance heating rod 214, and the integrity of the isolation layer or gap control layer is checked. Second, the vacuum thermal gradient loading system 2 is shut down and the evacuation assembly 22 is started to bring the furnace cavity to the set pressure, and protective gas is introduced if necessary. Third, the water-cooling unit 1 is started and the coolant flow rate is confirmed to be stable. Then, the height, angle, and focal length of the dual-channel characterization system 3 are adjusted so that the visible morphology acquisition component 34 and the narrowband radiation temperature field acquisition component 37 cover the same pellet surface area. Subsequently, the power supply and parameter control unit 4 energizes and heats the center resistance heating rod 214 according to the set program, and the data processing terminal 6 simultaneously records the morphology sequence, narrowband radiation response, temperature field, and loading parameters. When the sample reaches the target temperature or target radial temperature difference, it can enter the heat preservation stage to observe the slow evolution of the surface morphology, or the power can be further increased to investigate the critical thermal gradient conditions. After the experiment is completed, the power supply and parameter control unit 4 gradually reduces the output power, while the water-cooled unit 1 and the air extraction assembly 22 continue to operate until the furnace body and sample temperature drop to a safe range. Then, the furnace chamber pressure is released and the sample is removed. Through the above process, a complete data chain of loading power, furnace pressure, sample surface temperature matrix, radial temperature gradient, and morphological parameters can be obtained.

[0033] In data processing, the narrowband radiation temperature field acquisition component is located at pixel coordinates. place, time The raw response obtained is Dark field response is The empty background response is Among them, the dark field response is used to characterize the background response generated by the detector under conditions of no incident radiation, while the empty field background response is used to characterize the background response caused by factors such as environmental radiation and optical channel stray radiation under conditions of no sample target.

[0034] The empty field background response after subtracting the dark field is defined as: Therefore, the narrowband response after background correction is: Substituting equation (1) into equation (2), we get: Therefore, under this background correction model, the dark field response term exists simultaneously in the original response and the empty field background response and cancels each other out. Thus, the effective narrowband response after correction can be simplified to the difference between the original response and the empty field background response.

[0035] Assume the transmittance of the quartz window is Narrowband filter transmittance is Radiative response array in pixels Location relative to wavelength The response function is The calibration coefficient of the sample surface is The effective operating wavelength of narrowband filters is .in, Used to characterize the transmittance of quartz windows to radiation of different wavelengths. Used to characterize the selective transmittance of narrowband filters to radiation of different wavelengths. Used to characterize the response differences of different pixels and wavelengths in the detector array. It is used to correct factors such as sample surface emissivity, reflection characteristics, calibration errors, and pixel non-uniformity.

[0036] Pixels The equivalent response factor at a given location is defined as: Furthermore, the sample surface calibration coefficients are incorporated into the response correction process, and the comprehensive response factor is defined as: Under band-specific calibration or discrete sampling conditions, equation (5) can be written in discrete summation form: in, For the first Discrete wavelength sampling points, For the corresponding wavelength interval, This represents the number of discrete sampling points within the effective working band.

[0037] After completing dark field subtraction, background correction, window transmittance compensation, filter response normalization, array response correction, and sample surface calibration, the pixel... The background correction response and the target narrowband radiance satisfy the following linear relationship: Therefore, the corrected narrowband radiance is: Substituting equation (3) into equation (8), we get: Combining equation (5), equation (9) can be further expanded as follows: Equation (10) shows that the corrected narrowband radiance is obtained by subtracting the empty field background response from the original response and then normalizing it by the comprehensive response factor.

[0038] According to Planck's radiation relation, temperature is defined as... The corresponding narrowband radiation function is: in, , , is Planck's constant. At the speed of light, This is the Boltzmann constant. When the emissivity of the sample surface has passed... When the calibration correction is completed, Equation (11) can be used as the inversion relationship between the equivalent narrowband radiance and temperature.

[0039] Therefore, pixels The temperature value at that location can be expressed as: Substituting equation (9) into equation (12), we obtain the pixel temperature inversion equation after background correction and response correction: When it is necessary to explicitly consider the emissivity of the sample surface And it has not yet been incorporated When the narrowband radiation function is used, it can be written as: The corresponding temperature inversion relationship is: In this embodiment, the acquisition of morphological information and the reconstruction of the two-dimensional temperature field are performed under the same time reference and the same calibration field of view. It can be seen that the morphological acquisition component synchronously acquires the joint experimental record of annular fuel-space-temperature-morphology.

[0040] In one specific embodiment, the vacuum furnace body adopts a vertical cavity of approximately 25cm × 25cm × 25cm, with a furnace wall thickness of approximately 3cm. Multiple cooling channels with a cross-section of approximately 1cm × 1cm are arranged within the furnace wall. The outer diameter of the central resistance heating rod matches the inner hole of the annular fuel pellet, and the fitting clearance between the annular fuel pellet's inner hole and the heating rod is controlled within 0.1mm. The power supply can be set according to the sample size and target temperature, enabling the sample to reach a high temperature range of 1800℃ to 2500℃ in a vacuum or protective atmosphere. The heating rate can be adjusted within the range of 50℃ / min to 300℃ / min. The above dimensions and parameters are merely preferred ranges for illustrative purposes; those skilled in the art can adjust them according to sample specifications.

[0041] This embodiment may also include anomaly protection steps: when the pressure detection element 26 detects that the furnace cavity pressure exceeds the set range, or when the data processing terminal 6 determines that the local temperature rise is too rapid based on the two-dimensional temperature field, the power supply and parameter control unit 4 reduces the output power or stops heating; when the flow rate or temperature of the water-cooled unit 1 is abnormal, the system issues an alarm and enters a safe cooling procedure. This can improve the safety and repeatability of high-temperature vacuum tests.

[0042] The above-disclosed embodiments are merely preferred embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An in-situ characterization device for annular fuel pellets based on thermal gradient drive, characterized in that, include: Water-cooled unit, vacuum thermal gradient loading system, dual-channel characterization system, power supply and parameter control unit, and data processing terminal; The vacuum thermal gradient loading system is equipped with an in-furnace thermal gradient loading device, which includes a central resistance heating rod fixed in the inner hole of the annular fuel pellet. The central resistance heating rod is electrically connected to the power supply and parameter control unit, which outputs adjustable power to the central resistance heating rod, causing it to introduce heat to the inner wall of the annular fuel pellet in a vacuum or protective atmosphere, and forming a radial temperature gradient from the inner wall to the outer wall of the annular fuel pellet. The water-cooling unit is connected to the cooling interface of the vacuum thermal gradient loading system and is used to circulate water cooling to the furnace body and the sealed area during high-temperature loading. The dual-channel characterization system is fixed to the outside of the vacuum thermal gradient loading system via a support frame assembly. It includes a visible morphology acquisition channel, a narrowband radiation acquisition channel, and a beam splitter. The beam splitter is located in the common optical path of the visible morphology acquisition channel and the narrowband radiation acquisition channel. It is used to split the light signal from the same sample surface of the annular fuel pellet into two paths, which enter the visible morphology acquisition channel and the narrowband radiation acquisition channel respectively, so as to simultaneously acquire the morphology information and narrowband thermal radiation response of the sample surface during the radial temperature gradient loading process. The data processing terminal is communicatively connected to the visible morphology acquisition channel and the narrowband radiation acquisition channel, respectively, and is used to synchronize the morphology information with the two-dimensional temperature field reconstructed from the narrowband thermal radiation response in time and space.

2. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, The visible morphology acquisition channel includes a visible morphology acquisition component, and the narrowband radiation acquisition channel includes a narrowband filter and a narrowband radiation temperature field acquisition component; the beam splitter is disposed in the common acquisition optical path of the visible morphology acquisition component and the narrowband radiation temperature field acquisition component, and the narrowband filter is disposed in the acquisition optical path of the narrowband radiation temperature field acquisition component and located on the light-emitting side of the beam splitter.

3. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, The furnace thermal gradient loading device further includes an insulating support tube, an upper voltage conductor, a conductive connecting wire, a lower voltage conductor, and an insulating base; the central resistance heating rod is disposed between the upper voltage conductor and the lower voltage conductor, the insulating support tube passes through the central resistance heating rod and cooperates with the insulating base to form an axial positioning structure; the power supply and parameter control unit is electrically connected to the upper voltage conductor and the lower voltage conductor via the conductive connecting wire.

4. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, A replaceable isolation layer or gap control layer is provided between the central resistance heating rod and the inner wall of the annular fuel pellet to restrict the direct adhesion between the sample and the central resistance heating rod.

5. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, The vacuum thermal gradient loading system includes: a vacuum furnace body, an air extraction assembly, a protective gas source, a furnace wall cooling channel, a circular flange with a quartz window, a pressure detection element, a coolant interface, a gas path interface, and a power supply interface; the air extraction assembly and the protective gas source are respectively connected to the vacuum furnace body through the gas path interface, and the furnace wall cooling channel is connected to the water-cooled unit through the coolant interface to maintain the thermal stability of the outer wall of the furnace body and the sealed area during high-temperature loading.

6. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, The circular flange with a quartz window includes an observation channel and an illumination channel. The observation channel is located in the central area of ​​the top surface of the vacuum furnace body, and the illumination channel is inclined relative to the observation channel. The emitted light from the heat-resistant lighting component illuminates the thermal gradient loading device inside the furnace through the illumination channel to reduce the influence of specular reflection on surface morphology identification.

7. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 2, characterized in that, The narrowband radiation temperature field acquisition component includes: a long working distance radiation acquisition lens group, a radiation response array, and a radiation brightness conversion unit; the radiation brightness conversion unit generates a two-dimensional radiation temperature matrix of the annular fuel pellet surface based on the center wavelength and bandwidth of the narrowband filter, the transmittance of the quartz window, the response curve of the radiation response array, and the calibration coefficient of the sample surface; the data processing terminal is used to perform dark field subtraction, background correction, window transmittance compensation, response normalization, field distortion correction, and pixel coordinate mapping on the two-dimensional radiation temperature matrix, and calculates the radial temperature gradient, circumferential temperature difference, local hot spot location, and time-varying thermal gradient loading history of the annular fuel pellet surface based on the mapping results.

8. The in-situ characterization device for annular fuel pellets based on thermal gradient drive according to claim 1, characterized in that, The data processing terminal is also used to extract the surface damage initiation location, geometric size change, expansion direction and local peeling area from the image sequence obtained from the visible morphology acquisition channel, and associate the above morphological features with the two-dimensional temperature field at the same time to form an experimental record containing timestamp, spatial coordinates, morphological features and temperature gradient parameters.

9. A method for in-situ characterization of annular fuel pellets based on thermal gradient-driven processes, characterized in that, The device described in any one of claims 1 to 8 is used to implement the following steps: The annular fuel pellet is fitted around the outer periphery of the central resistance heating rod, and the central resistance heating rod is fixed in the inner hole of the annular fuel pellet; The central resistance heating rod is energized and heated, and heat is introduced into the inner wall of the annular fuel pellet in a vacuum or protective atmosphere, so that the annular fuel pellet forms a radial temperature gradient that varies from the inner wall to the outer wall. During the radial temperature gradient loading process, the optical signal from the same sample surface of the annular fuel pellet is split into two paths by the beam splitting component and sent to the visible morphology acquisition channel and the narrowband radiation acquisition channel respectively, so as to simultaneously acquire the morphology information and narrowband thermal radiation response of the sample surface. The data processing terminal establishes a mapping relationship between image pixel coordinates and actual sample coordinates based on the geometric features of the annular fuel pellet. After spectral response correction and radiance calibration of the narrowband thermal radiation response, it reconstructs a two-dimensional temperature matrix of the annular fuel pellet surface. Then, through the mapping relationship, the two-dimensional temperature matrix is ​​converted into radial temperature gradient and circumferential temperature difference distribution under the actual geometric coordinates of the annular fuel pellet. Simultaneously, the data processing terminal identifies surface damage features from the morphology information and maps the surface damage features to the corresponding coordinate positions in the two-dimensional temperature matrix through the mapping relationship, so that each surface damage is associated with its occurrence time, spatial coordinates and local temperature gradient parameters, and outputs experimental records with morphology-temperature-time correlation.

10. The in-situ characterization method for annular fuel pellets based on thermal gradient drive according to claim 9, characterized in that, The establishment of the mapping relationship includes: mapping the two-dimensional temperature matrix from image pixel coordinates to polar coordinates or the actual two-dimensional geometric coordinates of the sample based on the inner hole boundary, outer edge boundary and sample edge contour features of the annular fuel pellet; the surface damage features include: sample edge contour changes, inner hole boundary changes, surface crack geometric parameters, hole expansion size, local spalling area and damage expansion direction.

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