Device and method for measuring the thermal expansion coefficient of nuclear fuel pellets

Abstract

The application discloses a kind of nuclear fuel pellet thermal expansion coefficient measuring device and method, nuclear fuel pellet thermal expansion coefficient measuring device includes thermal dilatometer host computer, sample positioning mechanism;The sample positioning mechanism is arranged in one side of the thermal dilatometer host computer, and is located in the telescopic direction of displacement detector top rod of the thermal dilatometer host computer;The sample positioning mechanism includes airtight test chamber, sleeve being arranged in the test chamber;The sleeve is used to accommodate nuclear fuel pellet;The length direction of the sleeve is on the same straight line with the telescopic direction of the displacement detector top rod;The displacement detector top rod is inserted into the test chamber, for acting on the end of the nuclear fuel pellet with predetermined pressure.The application is arranged sleeve for nuclear fuel pellet series assembly therein, realizes the thermal expansion coefficient measurement of nuclear fuel pellet.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel thermal expansion coefficient measurement technology, and in particular to a device and method for measuring the thermal expansion coefficient of nuclear fuel pellets. Background Technology

[0002] Fully ceramic micro-encapsulated (FCM) nuclear fuel involves dispersing three layers of isotropic carbon-coated (TRISO) fuel particles into an inert ceramic matrix, typically silicon carbide (SiC) or zirconium carbide (ZrC). Its structure is similar to that of a light water reactor. O2 The fuel pellets are identical. The inert matrix can effectively contain the fission gases released by TRISO fuel particles, further improving reactor operation safety. It is an important candidate fuel for the next generation of accident-tolerant fuel (ATF) concepts, advanced small reactors, and advanced microreactors.

[0003] The multi-layered structure of FCM (Fluorescent Compressor) chips leads to complex stress evolution behavior during service. Irradiation swelling mismatch between the inert matrix and TRISO particles, thermal expansion mismatch between the inert matrix and TRISO particles, and thermal mismatch between different TRISO particle layers are all factors contributing to mechanical failure. Domestic and international scholars have used software such as ABAQUS and COMSOL to construct different chip structures and theoretical calculation models, conducting extensive research on the thermo-mechanical and irradiation-thermo-mechanical coupling behaviors of FCM chips during service. As a key input parameter, accurate measurement of the thermal expansion coefficient of TRISO particles is of great significance for evaluating service safety performance.

[0004] Push-rod dilatometers are the mainstream testing equipment for measuring rigid solids. The system testing error is around 85µm, and to ensure testing accuracy, the sample length must be greater than 10mm. Commercial TRISO particles typically have a diameter of around 1mm, making accurate measurement impossible using existing testing equipment. There is an urgent need to develop new tooling and methods to solve the existing technical problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a device and method for measuring the thermal expansion coefficient of nuclear fuel pellets.

[0006] The technical solution adopted by the present invention to solve its technical problem is: to provide a device for measuring the thermal expansion coefficient of nuclear fuel pellets, including a thermal expansion meter main unit and a sample positioning mechanism; the sample positioning mechanism is disposed on one side of the thermal expansion meter main unit and is located in the extension and retraction direction of the displacement detector top rod of the thermal expansion meter main unit;

[0007] The sample positioning mechanism includes a sealed test chamber and a sleeve disposed within the test chamber; the sleeve is used to accommodate nuclear fuel pellets; multiple nuclear fuel pellets are connected in series along the length of the sleeve to form a predetermined length within the sleeve;

[0008] The length direction of the sleeve is on the same straight line as the extension and retraction direction of the displacement detector top rod; the displacement detector top rod is inserted into the test chamber and is used to apply a predetermined pressure to the end of the nuclear fuel ball.

[0009] In some embodiments, the predetermined length is ≥10mm.

[0010] In some embodiments, the inner diameter of the sleeve is 5 μm larger than the expected expansion of the nuclear fuel pellet.

[0011] In some embodiments, the sleeve is a cylindrical body open at both ends; one end of the sleeve is provided with a first top plug, which is fixed in the test chamber; the other end of the sleeve is provided with a second top plug, which is directly opposite the displacement detector top rod and can abut against the end of the nuclear fuel ball inside the sleeve.

[0012] In some embodiments, the sleeve is made of alumina or graphite.

[0013] In some embodiments, the nuclear fuel pellets include TRISO simulated fuel pellets.

[0014] In some embodiments, the sample positioning mechanism further includes an Al2O3 column and / or Al2O3 spheres for correction as a standard sample.

[0015] The present invention also provides a method for measuring the thermal expansion coefficient of nuclear fuel pellets, using the thermal expansion coefficient measuring device for nuclear fuel pellets described in any of the above-mentioned embodiments, the method comprising the following steps:

[0016] S1. Place multiple nuclear fuel pellets into a sleeve and string them together to form a test sample of a predetermined length. Then, insert the sleeve containing the nuclear fuel pellets into the test chamber.

[0017] S2. In correction mode, activate the displacement detector push rod, causing the displacement detector push rod to extend towards the sleeve and apply a predetermined pressure to the end of the nuclear fuel ball;

[0018] S3. After heating the test chamber to a predetermined temperature with a set heating efficiency, cool it down to room temperature at a set cooling rate. During the heating process, the thermal expansion coefficient data of the nuclear fuel pellets are acquired in real time through the thermal expansion instrument host.

[0019] In some embodiments, step S1 further includes: after the sleeve is inserted into the test chamber, evacuating the test chamber and filling it with inert gas to form a protective atmosphere.

[0020] In some embodiments, the following steps are included before step S1:

[0021] S0. The thermal expansion coefficient measuring device of the nuclear fuel pellets is corrected using a standard sample.

[0022] The beneficial effects of this invention are: by setting a sleeve for assembling nuclear fuel pellets in series, the thermal expansion coefficient of the nuclear fuel pellets can be measured in conjunction with the thermal expansion meter main unit. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0024] Figure 1 This is a schematic diagram of the structure of a nuclear fuel pellet thermal expansion coefficient measuring device according to an embodiment of the present invention;

[0025] Figure 2 This is a graph showing the thermal expansion coefficient of Al2O3 microspheres in Examples 1-3 of this invention;

[0026] Figure 3 This is a graph showing the results of the TRISO simulation of the thermal expansion coefficient of fuel pellets in Example 4 of this invention. Detailed Implementation

[0027] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] like Figure 1 As shown, an embodiment of the present invention provides a device for measuring the thermal expansion coefficient of nuclear fuel pellets, which includes a thermal expansion meter main unit 10, a sample positioning mechanism 20, and a base 30. The thermal expansion meter main unit 10 and the sample positioning mechanism 20 are disposed on the base 30.

[0029] The thermal expansion meter main unit 10 is equipped with a displacement detector top rod 40. The sample positioning mechanism 20 is located on one side of the thermal expansion meter main unit 10 and is located in the extension and retraction direction of the displacement detector top rod 40 of the thermal expansion meter main unit 10.

[0030] The thermal expansion meter main unit 10 is implemented using existing technology, which will not be described in detail here.

[0031] Specifically, the sample positioning mechanism 20 may include a sealed test chamber 21 and a sleeve 22 disposed within the test chamber 21. The sleeve 22 is used to accommodate nuclear fuel pellets 50. Multiple nuclear fuel pellets 50 are connected in series along the length of the sleeve 22 to form a predetermined length, which is ≥10mm, to meet the requirements for thermal expansion coefficient testing.

[0032] The test chamber 21 can be heated to the required high temperature according to the test requirements. Specifically, the test chamber 21 can be heated by heating elements, etc.

[0033] The length direction of the sleeve 22 is aligned with the extension and retraction direction of the displacement detector push rod 40. The end of the displacement detector push rod 40 away from the thermal expansion instrument main unit 10 is inserted into the test chamber 21 to abut against the sleeve 22 or the nuclear fuel pellets 50 inside the sleeve 22, applying a predetermined pressure to the ends of the series-connected nuclear fuel pellets 50. The test chamber 21 is provided with a corresponding through hole (not shown) for the displacement detector push rod 40 to pass through, and the through hole and the displacement detector push rod 40 are sealed together to ensure that the displacement detector push rod 40 can extend and retract while avoiding gaps that could affect the airtightness of the test chamber 21.

[0034] In one embodiment, the sleeve 22 is a cylindrical body open at both ends. One end of the sleeve 22 is provided with a first top plug 23, which is fixed in the test chamber 21. The opposite end of the sleeve 22 is provided with a second top plug 24, which is directly opposite to the displacement detector top rod 40 and can abut against the end of the nuclear fuel ball 50 inside the sleeve 22.

[0035] The second plug 24 is located at the end of the sleeve 22, with one side abutting against the nuclear fuel pellet 50 assembled inside the sleeve 22, and the other side abutting against the displacement detector push rod 40. When the displacement detector push rod 40 applies pressure to the second plug 24, it can push the second plug 24 to move inward toward the sleeve 22. The portion of the second plug 24 located inside the sleeve 22 has sufficient axial length to allow it to push against the nuclear fuel pellet 50 and move inward toward the sleeve 22 under the push of the displacement detector push rod 40 during the thermal expansion coefficient test of the nuclear fuel pellet 50.

[0036] In another embodiment, the sleeve 22 can also be a cylindrical structure with one end closed and the other end open. The sleeve 22 is connected to the test chamber 21 with the closed end, and a top plug is provided at the open end, which is the same as the second top plug 24 mentioned above. One side of the top plug can abut against the nuclear fuel ball 50 assembled in the sleeve 22, and the other side abuts against the displacement detector top rod 40. Under the push of the displacement detector top rod 40, the top plug moves towards the interior of the sleeve 22, pressing against the nuclear fuel ball 50.

[0037] The sleeve 22 is detachable within the test chamber 21, and different lengths of sleeve 22 can be replaced according to test requirements.

[0038] The length of the nuclear fuel pellets 50 connected in series within the sleeve 22 is ≥10mm, and the length of the sleeve 22 is 10mm.

[0039] The inner diameter of the sleeve 22 is larger than the diameter of the nuclear fuel sphere 50, and the inner diameter of the sleeve 22 is further larger than the diameter of the nuclear fuel sphere 50 after thermal expansion. Preferably, the inner diameter of the sleeve 22 is 5 μm larger than the expected expansion amount of the nuclear fuel sphere 50 to prevent jamming during the measurement of the coefficient of thermal expansion, which would affect the measurement results.

[0040] Sleeve 22, first top plug 23, and second top plug 24 can all be made of alumina or graphite. When the test temperature is below 1700℃, sleeve 22, first top plug 23, and second top plug 24 are preferably made of Al3O2; when the test temperature is above 1700℃, sleeve 22, first top plug 23, and second top plug 24 are preferably made of graphite.

[0041] Nuclear fuel pellets 50 include TRISO simulated fuel pellets. TRISO simulated fuel pellets are manufactured based on TRISO fuel pellets and are identical to TRISO fuel pellets except that they do not contain radioactive material (uranium). The coefficient of thermal expansion obtained by measuring the coefficient of thermal expansion of the TRISO simulated fuel pellets is the same as the measured coefficient of thermal expansion of the TRISO fuel pellets.

[0042] Before measuring the thermal expansion coefficient of nuclear fuel pellets, the device for measuring the thermal expansion coefficient of nuclear fuel pellets of the present invention typically requires system calibration. For this purpose, the sample positioning mechanism 20 also includes an Al2O3 column and / or Al2O3 pellets for calibration as standard samples. During calibration, the assembly length of the Al2O3 column and / or Al2O3 pellets within the sleeve 22 is also greater than or equal to 10 mm.

[0043] The device for measuring the thermal expansion coefficient of nuclear fuel pellets of the present invention is used to implement a method for measuring the thermal expansion coefficient of nuclear fuel pellets. (Reference) Figure 1 In some embodiments, the method for measuring the thermal expansion coefficient of nuclear fuel pellets may include the following steps:

[0044] S0. The thermal expansion coefficient measuring device is corrected using standard samples.

[0045] The standard samples are made of Al2O3 columns and / or Al2O3 microspheres.

[0046] The basic parameters required for the correction measurement are consistent with those required for the subsequent measurement of nuclear fuel pellet 50.

[0047] In one embodiment, an Al2O3 column is used for correction. During correction, the Al2O3 column is positioned in the test chamber 21 using a sample holder, and is aligned with the displacement detector push rod 40. The displacement detector push rod 40 applies a force of 200 mN to the end face of the Al2O3 column. The test chamber 21 begins to heat up, and the thermal expansion meter host 10 obtains the system thermal expansion coefficient data of the thermal expansion coefficient measuring device in real time. After reaching 600°C, it cools down to room temperature at a rate of 20°C / s.

[0048] S1. Place multiple nuclear fuel pellets 50 into the sleeve 22 and connect them in series to form a test sample with a predetermined length. Then, insert the sleeve 22 containing the nuclear fuel pellets 50 into the test chamber 21.

[0049] The predetermined length is ≥10mm. The number of nuclear fuel pellets 50 is determined based on the predetermined length and the diameter of the nuclear fuel pellets 50 themselves.

[0050] After the sleeve 22 is installed in the test chamber 21, the process also includes: evacuating the test chamber 21 and filling it with an inert gas (helium, argon, or a mixture of both) to form a protective atmosphere.

[0051] S2. In correction mode, activate displacement detector push rod 40, causing displacement detector push rod 40 to extend towards sleeve 22 and apply a predetermined pressure to the end of nuclear fuel pellet 50.

[0052] Specifically, by operating the thermal expansion instrument main unit 10, selecting the correction mode, and inputting the basic parameters required for measurement: heating rate 5℃ / s~10℃ / s, push rod force (i.e., predetermined pressure) 200mN, sample length 10mm, termination temperature 600℃, and cooling rate 10℃ / s~30℃ / s.

[0053] S3. After heating the test chamber 21 to the predetermined temperature (i.e., the termination temperature) with a set heating efficiency, it is cooled down to room temperature at a set cooling rate. During the heating process, the thermal expansion coefficient data of the nuclear fuel pellets 50 are acquired in real time through the thermal expansion instrument host 10.

[0054] The heating efficiency is set to 5℃ / s~10℃ / s, and the cooling rate is set to 10℃ / s~30℃ / s.

[0055] In step S0 above, the thermal expansion coefficient measuring device is corrected using a standard sample to obtain the system thermal expansion data of the device. In step S3, the actual thermal expansion coefficient of the nuclear fuel pellet 50 is obtained by subtracting the system thermal expansion data from it.

[0056] The present invention will be further described below through specific embodiments.

[0057] Example 1:

[0058] First, turn on the thermal expansion meter main unit and preheat it for more than an hour to allow the measurement system to enter a stable state.

[0059] Next, place a 10mm long standard Al2O3 column on the sample holder. The sample holder is located inside the test chamber, and the standard Al2O3 column is aligned with the displacement detector's push rod.

[0060] Next, open the software, select the correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 10mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0061] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the end face of the standard Al2O3 column;

[0062] Then, click "Start Test." The test chamber begins to heat up, and the system's thermal expansion coefficient data is obtained in real time. After reaching 600℃, it cools down to room temperature at a rate of 20℃ / s.

[0063] Then, the standard Al2O3 column was removed, and an Al2O3 ball with a diameter of 9.525 mm was placed into the sleeve and clamped with the two top plugs on the left and right, and then placed into the test chamber.

[0064] Next, open the software, select the sample + correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 9.525mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0065] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the left push plug end face.

[0066] Click to start the test. The test chamber begins to heat up and obtains the thermal expansion coefficient data of an Al2O3 sphere with a diameter of 9.525mm in real time. After reaching 600℃, it cools down to room temperature at a rate of 20℃ / s.

[0067] Example 2:

[0068] First, turn on the thermal expansion meter main unit and preheat it for more than an hour to allow the measurement system to enter a stable state.

[0069] Next, a 10mm long standard Al2O3 cylinder is inserted into the sample holder. The sample holder is located inside the test chamber, and the standard Al2O3 cylinder is aligned with the displacement detector's push rod.

[0070] Next, open the software, select the correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 10mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0071] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the end face of the standard Al2O3 column.

[0072] Click to start the test. The test chamber will begin to heat up and obtain the system's thermal expansion coefficient data in real time. After reaching 600℃, it will cool down to room temperature at a rate of 20℃ / s.

[0073] Then, the standard Al2O3 column sample was removed, and two Al2O3 spheres with a diameter of 5.553 mm were placed into the sleeve and clamped with the two top plugs on the left and right, and then placed into the test chamber.

[0074] Next, open the software, select the sample + correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 11.106mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0075] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the left push plug end face.

[0076] Click to start the test. The test chamber begins to heat up and obtains the thermal expansion coefficient data of an Al2O3 sphere with a diameter of 5.553mm in real time. After reaching 600℃, it cools down to room temperature at a rate of 20℃ / s.

[0077] Example 3:

[0078] First, turn on the thermal expansion meter main unit and preheat it for more than an hour to allow the measurement system to enter a stable state.

[0079] Next, a 10mm long standard Al2O3 cylinder is inserted into the sample holder. The sample holder is located inside the test chamber, and the standard Al2O3 cylinder is aligned with the displacement detector's push rod.

[0080] Next, open the software, select the correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 10mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0081] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the end face of the standard Al2O3 column.

[0082] Click to start the test. The test chamber will begin to heat up and obtain the system's thermal expansion coefficient data in real time. After reaching 600℃, it will cool down to room temperature at a rate of 20℃ / s.

[0083] Then, the standard Al2O3 column sample was taken out, and six Al2O3 spheres with a diameter of 1.588 mm were placed into the sleeve and clamped with the two top plugs on the left and right, and then placed into the test chamber.

[0084] Next, open the software, select the sample + correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 9.528mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0085] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the left push plug end face.

[0086] Click to start the test. The test chamber begins to heat up and obtains the thermal expansion coefficient data of the 1.588mm diameter Al2O3 sphere in real time. After reaching 600℃, it cools down to room temperature at a rate of 20℃ / s.

[0087] The thermal expansion coefficients of different numbers of Al2O3 spheres were measured in Examples 1-3 above, and the measurement results are as follows: Figure 2 As shown. From Figure 2 As shown by the curves, the thermal expansion coefficient results of the Al2O3 spheres obtained in Examples 1-3 are similar, indicating that the number of Al2O3 spheres does not affect the measurement results of the thermal expansion coefficient of Al2O3 spheres, and the thermal expansion coefficient measuring device and method of the present invention are feasible.

[0088] Example 4:

[0089] First, turn on the thermal expansion meter main unit and preheat it for more than an hour to allow the measurement system to enter a stable state.

[0090] Next, a 10mm long standard Al2O3 cylinder is inserted into the sample holder. The sample holder is located inside the test chamber, and the standard Al2O3 cylinder is aligned with the displacement detector's push rod.

[0091] Next, open the software, select the correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 10mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0092] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the end face of the standard Al2O3 column.

[0093] Click to start the test. The test chamber will begin to heat up and obtain the system's thermal expansion coefficient data in real time. After reaching 600℃, it will cool down to room temperature at a rate of 20℃ / s.

[0094] Then, the standard Al2O3 column sample was removed, and 12 TRISO simulated fuel balls with a diameter of 0.891 mm were placed into the sleeve and clamped by the two top plugs on the left and right, and then placed into the test chamber.

[0095] Next, open the software, select the sample + correction mode, and enter the basic parameters: heating rate 5℃ / s, push rod force 200mN, sample length 10.415mm, termination temperature 600℃, and cooling rate 20℃ / s.

[0096] Then, click the displacement detector push rod drive button, and the displacement detector push rod will apply a force of 200mN to the left push plug end face.

[0097] Click to start the test. The test chamber begins to heat up and obtains the thermal expansion coefficient data of the TRISO simulated fuel pellets with a diameter of 0.891mm in real time. After reaching 600℃, it cools down to room temperature at a rate of 20℃ / s.

[0098] The thermal expansion coefficient of the TRISO-simulated fuel pellets obtained in Example 4 is as follows: Figure 3 As shown.

[0099] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A device for measuring the coefficient of thermal expansion of nuclear fuel pellets, characterized in that, It includes a thermal expansion meter main unit and a sample positioning mechanism; the sample positioning mechanism is located on one side of the thermal expansion meter main unit and is located in the extension and retraction direction of the displacement detector top rod of the thermal expansion meter main unit. The sample positioning mechanism includes a sealed test chamber and a sleeve disposed within the test chamber; the sleeve is used to accommodate nuclear fuel pellets; multiple nuclear fuel pellets are connected in series along the length of the sleeve to form a predetermined length within the sleeve; The length direction of the sleeve is on the same straight line as the extension and retraction direction of the displacement detector top rod; the displacement detector top rod is inserted into the test chamber and is used to apply a predetermined pressure to the end of the nuclear fuel ball.

2. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 1, characterized in that, The predetermined length is ≥10mm.

3. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 1, characterized in that, The inner diameter of the sleeve is 5 μm larger than the expected expansion of the nuclear fuel pellet.

4. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 1, characterized in that, The sleeve is a cylindrical body open at both ends; one end of the sleeve is provided with a first top plug, which is fixed in the test chamber; the other end of the sleeve is provided with a second top plug, which is directly opposite the displacement detector rod and can abut against the end of the nuclear fuel ball inside the sleeve.

5. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 1, characterized in that, The sleeve is made of alumina or graphite.

6. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to any one of claims 1-5, characterized in that, The nuclear fuel pellets include TRISO simulated fuel pellets.

7. The device for measuring the thermal expansion coefficient of nuclear fuel pellets according to any one of claims 1-5, characterized in that, The sample positioning mechanism also includes an Al2O3 column and / or Al2O3 spheres for correction as a standard sample.

8. A method for measuring the coefficient of thermal expansion of nuclear fuel pellets, characterized in that, The thermal expansion coefficient measuring device for nuclear fuel pellets according to any one of claims 1-7, wherein the thermal expansion coefficient measuring method comprises the following steps: S1. Place multiple nuclear fuel pellets into a sleeve and string them together to form a test sample of a predetermined length. Then, insert the sleeve containing the nuclear fuel pellets into the test chamber. S2. In correction mode, activate the displacement detector push rod, causing the displacement detector push rod to extend towards the sleeve and apply a predetermined pressure to the end of the nuclear fuel ball; S3. After heating the test chamber to a predetermined temperature with a set heating efficiency, cool it down to room temperature at a set cooling rate. During the heating process, the thermal expansion coefficient data of the nuclear fuel pellets are acquired in real time through the thermal expansion instrument host.

9. The method for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 8, characterized in that, Step S1 further includes: after the sleeve is inserted into the test chamber, the test chamber is evacuated and filled with inert gas to form a protective atmosphere.

10. The method for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 8, characterized in that, The following steps are included before step S1: S0. The thermal expansion coefficient measuring device of the nuclear fuel pellets is corrected using a standard sample.

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