A nuclear fuel pellet out-of-core cracking in-situ monitoring system and method

Abstract

The present invention discloses an in-situ monitoring system and method for the off-pile cracking of nuclear fuel pellets. The system includes: an experimental box, a sample table, a first thermometer, a second thermometer, a blue light source, a spectrometer, an infrared camera, an optical camera and a graphics server; the spectrometer divides the light of the light-guiding measurement channel into visible light and infrared light, and irradiates the light to the optical camera and the infrared camera respectively. Since the first temperature collected by the first thermometer and the second temperature collected by the second thermometer are more accurate temperatures, the infrared photos can be calibrated to obtain a more accurate temperature distribution. The photos taken by the optical camera can capture the cracking morphology of the pellet sample in real time, so as to synchronously match the temperature field of the infrared photo and the cracking morphology of the optical photo, realize non-contact temperature-optical coupling in-situ measurement in the off-pile heating experiment of the pellet sample, reduce the influence of the measuring instrument on the cracking process of the pellet sample, and facilitate the study of the evolution mechanism of the cracking of the pellet sample under different thermal stress conditions.

Description

Technical Field

[0001] The invention relates to the field of nuclear fuel technology, and in particular to an in-situ monitoring system and method for off-core cracking of nuclear fuel pellets. Background Art

[0002] As the "heart" and "food" of the reactor, the performance of nuclear fuel is one of the decisive factors for the safety and economy of nuclear power. Nuclear fuel pellets are usually made of UO2 powder through mechanical mixing, pressing and sintering. As a ceramic material, nuclear fuel pellets have obvious brittleness and are prone to cracking and breaking under thermal stress during normal operation, and the release of fission products is aggravated. In some design basis accidents (such as large break loss of coolant accidents), due to the explosion of the nuclear fuel cladding, smaller nuclear fuel pellet fragments may be ejected from the cladding rupture into the primary circuit of the reactor, causing more serious radioactive contamination of the primary circuit and threatening the long-term cooling capacity of the reactor core, which has an adverse impact on the safety of the reactor. Researchers usually conduct out-of-core heating tests on nuclear fuel pellets to quantitatively study the influence of thermal stress on the high-temperature cracking of pellets.

[0003] In the existing nuclear fuel pellet ex-core heating test, the method of measuring the temperature of the nuclear fuel pellets online and detecting the cracking morphology of the nuclear fuel pellets offline is usually adopted. However, the offline detection method can only characterize the final morphology of the pellets in the cold state (for example, the patent document with publication number CN113222937A), and cannot track the cracking process of the nuclear fuel pellets in the heating stage (simulating reactor startup) and the cooling stage (simulating reactor shutdown) of the ex-core heating test, and it is impossible to synchronously match the heating temperature and the cracking process. Therefore, it is impossible to study the evolution mechanism of pellet cracking under different thermal stress conditions.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] The technical problem to be solved by the present invention is that, in view of the above-mentioned defects of the prior art, a system and method for in-situ monitoring of nuclear fuel pellet ex-pile cracking is provided, aiming to solve the problem in the prior art that the ex-pile heating test of nuclear fuel pellets cannot synchronously match the heating temperature and the cracking process.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] An in-situ monitoring system for nuclear fuel pellet ex-core cracking, comprising:

[0008] The experimental box has a light-guiding measurement channel and a supplementary light channel formed on the top;

[0009] A sample stage for placing a core sample;

[0010] A first thermometer is disposed on the top side of the pellet sample;

[0011] a second thermometer, disposed at the bottom center of the pellet sample;

[0012] A blue light source is located at a position corresponding to the fill light channel outside the experimental box, and the blue light emitted by the blue light source passes through the fill light channel and irradiates the core block sample;

[0013] A spectrometer, located at a position corresponding to the light-guiding measurement channel outside the experimental box;

[0014] An infrared camera and an optical camera, both located outside the experimental box;

[0015] A graphics server is located outside the experimental box, and the graphics server is respectively connected to the first thermometer, the second thermometer, the infrared camera, and the optical camera for communication;

[0016] The spectrometer divides the light from the light-guiding measurement channel into visible light and infrared light, and the visible light is irradiated to the optical camera, and the infrared light is irradiated to the infrared camera.

[0017] In the nuclear fuel pellet ex-core cracking in-situ monitoring system, a hole structure is formed at the bottom of the sample stage, the hole structure corresponds to the position of the bottom center of the pellet sample, and the second thermometer is located in the hole structure.

[0018] In the in-situ monitoring system for nuclear fuel pellet ex-core cracking, a filter is provided between the spectrometer and the optical camera.

[0019] The nuclear fuel pellet ex-core cracking in-situ monitoring system, wherein the first thermometer and the second thermometer are both connected to the graphic server through a data acquisition and processing system;

[0020] The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises:

[0021] The acoustic emission monitoring device is communicatively connected with the data acquisition and processing system.

[0022] The in-situ monitoring system for the ex-core cracking of nuclear fuel pellets, wherein the side of the test box is formed with an air inlet and an air outlet;

[0023] The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises:

[0024] An oxygen sensor, located in the experimental box and connected to the data acquisition and processing system for communication;

[0025] The pressure gauge is located in the experimental box and is communicatively connected with the data acquisition and processing system.

[0026] The nuclear fuel pellet ex-pile cracking in-situ monitoring system, wherein the nuclear fuel pellet ex-pile cracking in-situ monitoring system further comprises:

[0027] A boron nitride sleeve, wrapped around the core block sample;

[0028] Wherein, the first thermometer is located in the boron nitride sleeve.

[0029] The nuclear fuel pellet ex-pile cracking in-situ monitoring system, wherein the nuclear fuel pellet ex-pile cracking in-situ monitoring system further comprises:

[0030] a heating electrode, located at the lower end of the boron nitride sleeve and abutting against the pellet sample;

[0031] A high voltage DC power supply, electrically connected to the heating electrode;

[0032] A low voltage DC power supply, electrically connected to the heating electrode;

[0033] Wherein, the high-voltage DC power supply is connected in parallel with the low-voltage DC power supply.

[0034] An in-situ cracking monitoring method of a nuclear fuel pellet ex-core cracking in-situ monitoring system as described in any one of the above, comprising the steps of:

[0035] Load the pellet sample, turn on the blue light source, and replace the air in the experimental box with inert gas;

[0036] The core block sample is heated and cooled; wherein, during the heating and cooling process of the core block sample, a first temperature measured by a first thermometer is taken as the lowest temperature, and a second temperature measured by a second thermometer is taken as the highest temperature, and a temperature distribution diagram of the upper end surface of the core block sample obtained by an infrared camera is calibrated; an upper end surface morphology diagram of the core block sample is obtained by an optical camera, and the time, quantity, size and position distribution of cracks on the upper end surface of the core block sample are obtained.

[0037] The in-situ monitoring system for the off-core cracking of nuclear fuel pellets, wherein, during the process of heating and cooling the pellet sample, the sound emitted during the cracking process of the pellet sample is obtained by an acoustic emission monitoring device, and the time, frequency and intensity of the cracking of the pellet sample are obtained; based on the time, number, size and position distribution of the cracks on the upper end surface of the pellet sample, as well as the time, frequency and intensity of the cracking of the pellet sample, the overall cracking degree and the spatial distribution of the cracks of the pellet sample are obtained.

[0038] The nuclear fuel pellet ex-core cracking in-situ monitoring system, wherein the heating and cooling of the pellet sample comprises:

[0039] After starting a high-voltage direct current power supply to heat the pellet sample to a first preset temperature, the high-voltage direct current power supply is turned off;

[0040] After starting a low-voltage DC power supply to heat the core block sample to a second preset temperature, the low-voltage DC power supply is turned off until the core block sample cools to room temperature; wherein the second preset temperature is greater than the first preset temperature.

[0041] Beneficial effects: The optical photos collected by the optical camera, the infrared photos collected by the infrared camera, the first temperature collected by the first thermometer, and the second temperature collected by the second thermometer are all transmitted to the image server. Since the first temperature and the second temperature are more accurate temperatures, the infrared photos can be calibrated, and a more accurate temperature distribution can be obtained. The morphology of the core block sample in the optical photo can have cracks, so the temperature of the infrared photo and the cracks of the optical photo are synchronously matched, which can realize non-contact temperature-optical coupling in-situ measurement in the core block sample out-of-pile heating experiment, reduce the influence of the measuring instrument on the cracking process of the core block sample, and is conducive to studying the evolution mechanism of the cracking of the core block sample under different thermal stress conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic structural diagram of an in-situ monitoring system for ex-core cracking of nuclear fuel pellets in an embodiment of the present invention.

[0043] Description of reference numerals:

[0044] 10. Experiment box; 11. Light guide measurement channel; 12. Fill light channel; 13. Air inlet; 14. Air outlet; 20. Sample stage; 21. Core block sample; 22. Hole structure; 23. Boron nitride sleeve; 31. First thermometer; 32. Second thermometer; 33. Acoustic emission monitoring device; 34. Oxygen sensor; 35. Pressure gauge; 41. Blue light source; 42. Spectrometer; 43. Infrared camera; 44. Optical camera; 45. Filter; 50. Graphic server; 60. Data acquisition and processing system; 71. Heating electrode; 72. High voltage DC power supply; 73. Low voltage DC power supply. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] The present invention provides some embodiments of an in-situ monitoring system for ex-core cracking of nuclear fuel pellets.

[0047] like Figure 1 As shown, the nuclear fuel pellet ex-core cracking in-situ monitoring system of the present invention comprises:

[0048] The experimental box 10 has a light guide measurement channel 11 and a supplementary light channel 12 formed on the top;

[0049] A sample stage 20, used for placing a core block sample 21;

[0050] A first thermometer 31 is disposed on the top side of the core block sample 21;

[0051] A second thermometer 32, disposed at the bottom center of the core block sample 21;

[0052] A blue light source 41 is located at a position corresponding to the fill light channel 12 outside the experimental box 10, and the blue light emitted by the blue light source 41 passes through the fill light channel 12 and irradiates the core block sample 21;

[0053] A spectrometer 42, located at a position corresponding to the light-guiding measurement channel 11 outside the experimental box 10;

[0054] The infrared camera 43 and the optical camera 44 are both located outside the experimental box 10;

[0055] A graphic server 50 is located outside the experimental box 10, and the graphic server 50 is respectively connected to the first thermometer 31, the second thermometer 32, the infrared camera 43 and the optical camera 44 for communication;

[0056] The spectrometer 42 separates the light from the light-guiding measurement channel 11 into visible light and infrared light, and the visible light is irradiated to the optical camera 44 , and the infrared light is irradiated to the infrared camera 43 .

[0057] Specifically, the experimental box 10 surrounds the sample table 20, the pellet sample 21, the first thermometer 31 and the second thermometer 32, and the blue light source 41, the spectrometer 42, the graphic server 50, the infrared camera 43 and the optical camera 44 are all located outside the experimental box 10. The sample table 20 is fixed in the experimental box 10, and the sample table 20 is used to place the pellet sample 21, and the pellet sample 21 is a nuclear fuel pellet sample 21. The first thermometer 31 is located on the top side of the pellet sample 21, and the second thermometer 32 is located at the bottom center of the pellet sample 21. Usually, the pellet sample 21 is heated from the bottom, the center of the pellet sample 21 is the adiabatic boundary, and the side of the pellet sample 21 is the cooling heat exchange boundary. The temperature detected by the second thermometer 32 is higher, and the temperature detected by the first thermometer 31 is lower. The first thermometer 31 and the second thermometer 32 can obtain the accurate temperature of the corresponding area of ​​the pellet sample 21.

[0058] A fill-in light channel 12 and a light-guiding measurement channel 11 are formed on the top of the experimental box 10. Both the fill-in light channel 12 and the light-guiding measurement channel 11 are light-transmitting structures, and the light-transmitting structures are sealed and connected to the experimental box 10. The blue light emitted by the blue light source 41 is irradiated to the upper end surface of the core block sample 21 through the fill-in light channel 12. The light emitted or reflected by the core block sample 21 is refracted to the spectrometer 42 through the light-guiding measurement channel 11. The spectrometer 42 divides the light passing through the light-guiding measurement channel 11 into visible light and infrared light. The visible light is irradiated to the optical camera 44, and the optical camera 44 can collect optical photos of the upper end surface of the core block sample 21, and the optical photos reflect the morphology of the upper end surface of the core block sample 21. The infrared light is irradiated to the infrared camera 43, and the infrared camera 43 can collect infrared photos of the upper end surface of the core block sample 21, and the infrared photos reflect the temperature of the upper end surface of the core block sample 21. There can be multiple fill-in light channels 12, and there can be multiple blue light sources 41, and the multiple blue light sources 41 are respectively located at the positions corresponding to the fill-in light channels 12. Multiple fill-in light channels 12 surround the light guide measurement channel 11. The spectrometer 42 can be a spectrometer 42 that reflects infrared light and projects visible light. Since the core block sample 21 mainly generates orange light or white light when it is heated, the blue light is compensated by the blue light source 41, and the optical camera 44 is more sensitive to blue light, which is conducive to clearer imaging of the optical camera 44. The infrared camera 43 and the optical camera 44 convert the optical signal into a digital signal and transmit it to the graphics server 50.

[0059] The optical photos collected by the optical camera 44, the infrared photos collected by the infrared camera 43, the first temperature collected by the first thermometer 31, and the second temperature collected by the second thermometer 32 are all transmitted to the image server. Since the first temperature and the second temperature are more accurate temperatures, the infrared photos can be calibrated, and a more accurate temperature distribution can be obtained. The morphology of the core block sample 21 in the optical photo can have cracks, so the temperature of the infrared photo and the cracks in the optical photo are synchronously matched, and non-contact temperature-optical coupling in-situ measurement of the core block sample 21 in the out-of-pile heating experiment can be realized, reducing the influence of the measuring instrument on the cracking process of the core block sample 21, which is conducive to studying the evolution mechanism of the cracking of the core block sample 21 under different thermal stress conditions.

[0060] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, a hole structure 22 is formed at the bottom of the sample stage 20 , the hole structure 22 corresponds to the position of the bottom center of the core block sample 21 , and the second thermometer 32 is located in the hole structure 22 .

[0061] Specifically, a hole structure 22 is formed at the bottom of the sample stage 20, and the hole structure 22 corresponds to the position of the bottom center of the core block sample 21, and the second thermometer 32 passes through the hole structure 22 and contacts the core block sample 21 to collect the temperature of the bottom center of the core block sample 21. A placement groove may also be formed on the sample stage 20, and the core block sample 21 is placed in the placement groove. The hole structure 22 is located at the center of the placement groove.

[0062] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, a filter 45 is provided between the spectrometer 42 and the optical camera 44 .

[0063] Specifically, a filter 45 is arranged between the spectrometer 42 and the optical camera 44. The blue-violet light in the visible light can pass through the filter 45 to reach the optical camera 44. The blue light is compensated by the blue light source 41, and the filter 45 is used to filter out the light other than the blue-violet light in the visible light. Then, the optical camera 44 can capture the blue-violet light for imaging, which can more accurately and clearly reflect the morphology of the upper end surface of the core block sample 21, thereby improving the clarity and resolution of the optical photograph.

[0064] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, the first thermometer 31 and the second thermometer 32 are both connected to the graphic server 50 through the data acquisition and processing system 60 for communication.

[0065] Specifically, the data acquisition and processing system 60 acquires the signal of the first thermometer 31 and the signal of the second thermometer 32 , and feeds the data back to the graphic server 50 .

[0066] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, the nuclear fuel pellet ex-core cracking in-situ monitoring system also includes:

[0067] The acoustic emission monitoring device 33 is in communication connection with the data acquisition and processing system 60 .

[0068] Specifically, the acoustic emission monitoring device 33 is used to monitor the sound emitted by the core block sample 21 during the cracking process, and the cracking time, frequency (density) and intensity of the core block sample 21 can be obtained. The acoustic emission monitoring device 33 is located on the side of the core block sample 21 in the experimental box 10. The acoustic wave signal collected by the acoustic emission monitoring device 33 is converted into a digital signal by the data acquisition and processing system 60 and fed back to the graphics server 50.

[0069] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, an air inlet 13 and an air outlet 14 are formed on the side of the experimental box 10 .

[0070] Specifically, an air inlet 13 and an air outlet 14 are formed on the side of the test box 10, and gas, for example, inert gas, can be delivered into the test box 10 from the air inlet 13; and the gas in the test box 10 can be discharged from the air outlet 14. By delivering and discharging gas into and from the test box 10 multiple times, the composition of the gas in the test box 10 can be changed. The experimental process of the pellet sample 21 is usually carried out under an inert atmosphere.

[0071] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, the nuclear fuel pellet ex-core cracking in-situ monitoring system also includes:

[0072] The oxygen sensor 34 is located in the experimental box 10 and is in communication connection with the data acquisition and processing system 60;

[0073] The pressure gauge 35 is located in the experimental box 10 and is in communication connection with the data acquisition and processing system 60 .

[0074] Specifically, the oxygen sensor 34 is used to detect the oxygen content of the gas in the test box 10, and the pressure gauge 35 is used to detect the pressure of the gas in the test box 10. The experimental process of the pellet sample 21 requires that the oxygen content of the gas in the test box 10 be reduced to below the preset oxygen content, which can be judged by the oxygen content detected by the oxygen sensor 34. During the experimental process of the pellet sample 21, the air pressure in the test box 10 can be the standard atmospheric pressure, or it can be greater than or less than the standard atmospheric pressure. The pressure of the gas in the test box 10 can be determined by the pressure gauge 35, and the air pressure in the test box 10 can be controlled within a suitable range by controlling the air flow rate of the air inlet 13. The oxygen sensor 34 and the pressure gauge 35 are both located in the test box 10, and the oxygen content information collected by the oxygen sensor 34 and the gas pressure information collected by the pressure gauge 35 are collected by the data acquisition and processing system 60 and fed back to the graphics server 50.

[0075] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, the nuclear fuel pellet ex-core cracking in-situ monitoring system also includes:

[0076] A boron nitride sleeve 23, wrapped around the core block sample 21;

[0077] The first thermometer 31 is located inside the boron nitride sleeve 23 .

[0078] Specifically, the boron nitride sleeve 23 is located in the experimental box 10 and is placed on the sample table 20. The boron nitride sleeve 23 is sleeved on the outside of the core block sample 21. The boron nitride sleeve 23 is used to replace the cladding tube that wraps the core block sample 21 in the actual reactor. The cladding tube in the actual reactor can be a zirconium alloy cladding tube. The temperature resistance of the boron nitride sleeve 23 is better than that of the zirconium alloy cladding tube in actual application, and the boron nitride sleeve 23 can be used repeatedly. The size of the boron nitride sleeve 23 is slightly larger than that of the zirconium alloy cladding tube in actual application, so that the first thermometer 31 can be placed in the boron nitride sleeve 23 and contact with the core block sample 21. The boron nitride sleeve 23 can retain the original shape of the core block sample 21 after cracking, and avoid the core block sample 21 from breaking and collapsing, resulting in abnormal measurement data.

[0079] In a preferred implementation of the embodiment of the present invention, Figure 1 As shown, the nuclear fuel pellet ex-core cracking in-situ monitoring system also includes:

[0080] A heating electrode 71, located at the lower end of the boron nitride sleeve 23 and abutting against the core block sample 21;

[0081] A high voltage DC power supply 72, electrically connected to the heating electrode 71;

[0082] A low voltage DC power supply 73, electrically connected to the heating electrode 71;

[0083] The high voltage DC power supply 72 is connected in parallel with the low voltage DC power supply 73 .

[0084] Specifically, there are two heating electrodes 71, namely, a positive electrode and a negative electrode. The heating electrodes 71 are against the bottom side of the core block sample 21, and the positive electrode and the negative electrode are respectively located on the two sides of the bottom of the core block sample 21. The high-voltage DC power supply 72 and the low-voltage DC power supply 73 provide power for the heating electrodes 71. The voltage of the high-voltage DC power supply 72 is relatively high, and the core block sample 21 can be heated quickly; the voltage of the low-voltage DC power supply 73 is relatively low, which is conducive to accurately controlling the heating rate of the core block sample 21.

[0085] The in-situ monitoring system for nuclear fuel pellets outside the reactor for cracking has the following technical effects:

[0086] 1. The present invention uses a blue light source to suppress the orange-yellow light and white light emitted by the core block sample at high temperature, and uses a filter to improve the clarity and resolution of the optical camera, so that the optical camera can clearly capture the surface morphology of the core block sample at high temperature.

[0087] 2. The present invention adopts a spectrometer, in conjunction with an infrared camera and an optical camera, to achieve non-contact real-time coupled measurement of temperature distribution and surface morphology, and can match the temperature change process and the cracking process of the core block sample to achieve the purpose of studying the cracking evolution mechanism of the core block sample.

[0088] 3. The present invention uses a thermometer for contact temperature measurement, which can calibrate the infrared camera in real time and compensate for the temperature measurement deviation caused by the blue light source, making the temperature distribution measurement of the infrared camera more accurate.

[0089] 4. The present invention adopts an acoustic emission monitoring device, which reduces the cost of traditional CT scanning technology and can measure the cracking frequency (density) and intensity of the core block sample in real time. Combined with the core block sample surface morphology measurement of the optical camera, it can determine the overall cracking degree of the core block sample and the approximate spatial distribution of the cracks.

[0090] 5. The present invention adopts a high-voltage DC power supply and a low-voltage DC power supply, which can achieve rapid preheating and stable temperature rise of the pellet sample, ensuring that the heating rate remains equivalent to the actual reactor startup process.

[0091] The present invention adopts a boron nitride sleeve to form a support package for the pellet, which can retain the overall shape of the pellet after cracking without collapse, and realizes in-situ measurement of high-temperature cracking of nuclear fuel pellets.

[0092] Based on the in-situ monitoring system for nuclear fuel pellets ex-pile cracking described in any of the above embodiments, the present invention also provides a preferred embodiment of an in-situ monitoring method for nuclear fuel pellets ex-pile cracking:

[0093] The in-situ monitoring method for ex-core cracking of nuclear fuel pellets according to an embodiment of the present invention comprises the following steps:

[0094] Step S100, loading the pellet sample, turning on the blue light source, and replacing the air in the experimental box with an inert gas;

[0095] Step S200, heating and cooling the core block sample; wherein, during the heating and cooling process of the core block sample, a first temperature measured by a first thermometer is taken as the lowest temperature, and a second temperature measured by a second thermometer is taken as the highest temperature, and the upper end surface temperature distribution diagram of the core block sample obtained by an infrared camera is calibrated; an upper end surface morphology diagram of the core block sample is obtained by an optical camera, and the time, quantity, size and position distribution of the upper end surface cracks of the core block sample are obtained.

[0096] Specifically, the experimental preparation work is carried out first, for example, the core block sample is placed on the sample table, and the first thermometer and the second thermometer are assembled. The heating electrode can also be equipped, and the boron nitride sleeve is placed outside the core block sample. Check whether other devices such as the blue light source, spectrometer, infrared camera, optical camera, graphic server, filter, data acquisition and processing system, acoustic emission monitoring device, oxygen sensor, pressure gauge, high-voltage DC power supply, low-voltage DC power supply, etc. are normal. Before conducting the experiment, it is necessary to adjust the gas in the experimental box, exhaust the air, and inject inert gas. Under an inert atmosphere, the possibility of device oxidation can be reduced. For example, the oxidation of the heating electrode can be reduced, so that the resistance of the heating electrode remains basically constant, the heating current is more stable, and the heating process is also more stable. For example, the oxidation of the first thermometer and the second thermometer is reduced, and the surface of the first thermometer and the surface of the second thermometer are not easy to produce an oxide layer, and the temperature measurement is more accurate.

[0097] Then start the experiment, and heat and cool the core block sample. In the process of heating and cooling the core block sample, the first temperature is obtained by the first thermometer, the second temperature is obtained by the second thermometer, and the optical photo of the core block sample (i.e., the upper end face morphology map) is obtained by the optical camera. The time, quantity, size and position distribution of the cracks on the upper end face of the core block sample can be observed. The infrared photo of the core block sample (i.e., the upper end face temperature distribution map) is obtained by the infrared camera. The upper end face temperature distribution map is calibrated with the first temperature as the highest temperature and the second temperature as the lowest temperature. The temperature at any position of the upper end face temperature distribution map can be obtained to form a calibrated upper end face temperature distribution map. The infrared camera and the optical camera take pictures at regular intervals, which can be image sequences or videos.

[0098] In step S200, during the process of heating and cooling the core block sample, the sound emitted during the cracking process of the core block sample is obtained through an acoustic emission monitoring device, and the time, frequency and intensity of the cracking of the core block sample are obtained; according to the time, number, size and position distribution of the cracks on the upper end surface of the core block sample, as well as the time, frequency and intensity of the cracking of the core block sample, the overall cracking degree and crack spatial distribution of the core block sample are obtained.

[0099] Specifically, during the heating and cooling process of the core block sample, the sound emitted by the core block sample during the cracking process is obtained through the acoustic emission monitoring device, so as to obtain the cracking time, frequency and intensity of the core block sample. Since some cracks occur on the upper end surface of the core block sample, and some cracks occur inside or on other surfaces of the core block sample, according to the time, number, size and position distribution of the cracks on the upper end surface, combined with the cracking time, frequency and intensity of the core block sample, the overall cracking degree and crack spatial distribution of the core block sample can be obtained, so as to quantitatively study the influence of thermal stress on high temperature cracking of the core block sample.

[0100] Step S200 specifically includes:

[0101] Step S210, starting a high-voltage direct current power supply to heat the pellet sample to a first preset temperature, and then turning off the high-voltage direct current power supply;

[0102] Step S220, after starting the low-voltage DC power supply to heat the core block sample to a second preset temperature, shutting down the low-voltage DC power supply until the core block sample cools to room temperature; wherein the second preset temperature is greater than the first preset temperature.

[0103] Specifically, the heating stage of the core block sample simulates the reactor start-up, and the cooling stage of the core block sample simulates the reactor shutdown. Heating is divided into two stages, namely, a rapid heating stage (or preheating stage) and a slow heating stage. Since the core block sample has low conductivity at low temperatures and high conductivity at high temperatures, in the rapid heating stage, the high-voltage DC power supply is started to quickly heat the core block sample until the core block sample reaches the first preset temperature, the conductivity of the core block sample increases, and the high-voltage DC power supply is turned off. Then enter the slow heating stage, start the low-voltage DC power supply to heat the core block sample until the core block sample reaches the second preset temperature, and ensure that the heating rate of the core block sample is equivalent to the heating rate of the actual reactor start-up process. Finally, enter the cooling stage, turn off the low-voltage DC power supply, and cool the core block sample to room temperature. The second preset temperature is higher than the first preset temperature, and the second preset temperature can be the detection upper limit temperature of the second thermometer. The temperature of the core block sample can be the temperature measured by the first thermometer or the temperature measured by the second thermometer. When the temperature measured by the first thermometer or the temperature measured by the second thermometer reaches the first preset temperature, the high-voltage DC power supply is turned off.

[0104] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An in-situ monitoring system for nuclear fuel pellet ex-core cracking, characterized in that: include: The experimental box has a light-guiding measurement channel and a supplementary light channel formed on the top; A sample stage for placing a core sample; A first thermometer is disposed on the top side of the pellet sample; a second thermometer, disposed at the bottom center of the pellet sample; A blue light source is located at a position corresponding to the fill light channel outside the experimental box, and the blue light emitted by the blue light source passes through the fill light channel and irradiates the core block sample; A spectrometer, located at a position corresponding to the light-guiding measurement channel outside the experimental box; An infrared camera and an optical camera, both located outside the experimental box; A graphics server is located outside the experimental box, and the graphics server is respectively connected to the first thermometer, the second thermometer, the infrared camera, and the optical camera for communication; Wherein, the spectrometer divides the light of the light-guiding measurement channel into visible light and infrared light, and the visible light is irradiated to the optical camera, and the infrared light is irradiated to the infrared camera; The first thermometer and the second thermometer are both connected to the graphic server through a data acquisition and processing system; The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises: An acoustic emission monitoring device, communicatively connected to the data acquisition and processing system; The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises: A boron nitride sleeve, wrapped around the core block sample; Wherein, the first thermometer is located in the boron nitride sleeve; The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises: a heating electrode, located at the lower end of the boron nitride sleeve and abutting against the pellet sample; A high voltage DC power supply, electrically connected to the heating electrode; A low voltage DC power supply, electrically connected to the heating electrode; Wherein, the high voltage DC power supply is connected in parallel with the low voltage DC power supply; A hole structure is formed at the bottom of the sample stage, the hole structure corresponds to the position of the center of the core block sample, and the second thermometer is located in the hole structure.

2. The nuclear fuel pellet ex-core cracking in-situ monitoring system according to claim 1, characterized in that: A filter is arranged between the spectrometer and the optical camera.

3. The nuclear fuel pellet ex-core cracking in-situ monitoring system according to claim 1, characterized in that: An air inlet and an air outlet are formed on the side of the experimental box; The nuclear fuel pellet ex-core cracking in-situ monitoring system further comprises: An oxygen sensor, located in the experimental box and connected to the data acquisition and processing system for communication; The pressure gauge is located in the experimental box and is communicatively connected with the data acquisition and processing system.

4. A method for in-situ monitoring of cracking of a nuclear fuel pellet ex-core according to any one of claims 1 to 3, characterized in that: Includes steps: Load the pellet sample, turn on the blue light source, and replace the air in the experimental box with inert gas; The core block sample is heated and cooled; wherein, during the heating and cooling process of the core block sample, a first temperature measured by a first thermometer is taken as the lowest temperature, and a second temperature measured by a second thermometer is taken as the highest temperature, and a temperature distribution diagram of the upper end surface of the core block sample obtained by an infrared camera is calibrated; an upper end surface morphology diagram of the core block sample is obtained by an optical camera, and the time, quantity, size and position distribution of cracks on the upper end surface of the core block sample are obtained.

5. The method for in-situ cracking monitoring of the nuclear fuel pellet ex-core cracking in-situ monitoring system according to claim 4, characterized in that: In the process of heating and cooling the core block sample, the sound emitted during the cracking process of the core block sample is obtained through an acoustic emission monitoring device, and the time, frequency and intensity of the cracking of the core block sample are obtained; according to the time, number, size and position distribution of the cracks on the upper end surface of the core block sample, as well as the time, frequency and intensity of the cracking of the core block sample, the overall cracking degree and crack spatial distribution of the core block sample are obtained.

6. The method for in-situ cracking monitoring of the nuclear fuel pellet ex-core cracking in-situ monitoring system according to claim 4, characterized in that: The step of heating and cooling the pellet sample comprises: After starting a high-voltage direct current power supply to heat the pellet sample to a first preset temperature, the high-voltage direct current power supply is turned off; After starting a low-voltage DC power supply to heat the core block sample to a second preset temperature, the low-voltage DC power supply is turned off until the core block sample cools to room temperature; wherein the second preset temperature is greater than the first preset temperature.

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