Device and method for measuring thermal expansion coefficient of nuclear fuel pellet

Abstract

The invention discloses a device and a method for measuring the thermal expansion coefficient of a nuclear fuel pellet. The device for measuring the thermal expansion coefficient of the nuclear fuel pellet comprises a thermal expansion instrument host and a sample measurement positioning mechanism, the sample measuring and positioning mechanism is arranged on one side of the thermal expansion instrument main machine and is positioned in the telescopic direction of a displacement detector ejector rod of the thermal expansion instrument main machine; the test sample positioning mechanism comprises a closed test chamber and a sleeve arranged in the test chamber; the sleeve is used for accommodating nuclear fuel pellets; the length direction of the sleeve and the telescopic direction of the ejector rod of the displacement detector are positioned on the same straight line; and the ejector rod of the displacement detector penetrates into the test chamber and is used for acting on the end part of the nuclear fuel pellet at a preset pressure. According to the invention, the sleeves are arranged for assembling the nuclear fuel pellets in series, so that the thermal expansion coefficient of the nuclear fuel pellets can be measured.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel thermal expansion coefficient measurement, and in particular to a device and method for measuring the thermal expansion coefficient of a nuclear fuel pellet. Background Art

[0002] Fully ceramic micro-encapsulated (FCM) nuclear fuel is a three-layer isotropic carbon-coated (TRISO) fuel particle dispersed in an inert ceramic matrix, usually silicon carbide (SiC) or zirconium carbide (ZrC). Its structure is similar to that of light water reactor U O2 The fuel pellets are the same. The inert matrix can effectively contain the fission gas released by TRISO fuel particles, further improving the safety of reactor operation. It is an important candidate fuel for the new generation of accident tolerant fuel (ATF) concept, advanced small reactors and advanced micro reactors.

[0003] The multi-layer coating structure of FCM core blocks leads to extremely complex stress evolution behavior during service. The radiation swelling mismatch between the inert matrix and TRISO particles, the thermal expansion mismatch between the inert matrix and TRISO particles, and the thermal mismatch between the layers of TRISO particles are all factors that lead to its mechanical failure. Domestic and foreign scholars have used ABAQUS, COMSOL and other software to construct different core block structures and theoretical calculation models to carry out a lot of research on the thermal-mechanical and radiation-thermal-mechanical coupling behaviors of FCM core blocks during service. As a key input parameter, the accurate measurement of the thermal expansion coefficient of TRISO particles is of great significance for the evaluation of service safety performance.

[0004] The push rod dilatometer is the mainstream test equipment for measuring rigid solids. The system test error is about 85um. To ensure the test accuracy, the sample length must be greater than 10mm. The diameter of commercial TRISO particles is usually about 1mm, which cannot be directly measured accurately using existing test equipment. It is urgent to develop new tooling and new methods to solve 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 the technical problem is: to provide a thermal expansion coefficient measuring device for a nuclear fuel pellet, comprising a thermal expansion instrument mainframe and a sample positioning mechanism; the sample positioning mechanism is arranged on one side of the thermal expansion instrument mainframe and is located in the telescopic direction of the displacement detector top rod of the thermal expansion instrument mainframe;

[0007] The sample positioning mechanism comprises a sealed test chamber and a sleeve arranged in the test chamber; the sleeve is used to accommodate nuclear fuel pellets; a plurality of nuclear fuel pellets are connected in series in the sleeve along the length direction of the sleeve to form a predetermined length;

[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 penetrates into the test chamber and is used to act on the end of the nuclear fuel pellet with a predetermined pressure.

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

[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 cylinder with open ends; a first top plug is provided at one end of the sleeve and is fixed in the test chamber by the first top plug; a second top plug is provided at the other opposite end of the sleeve, and the second top plug is directly opposite to the displacement detector push rod and can abut against the end of the nuclear fuel ball in the sleeve.

[0012] In some embodiments, the sleeve is made of alumina material 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 sensor for correction as a standard sample. 2 O 3 Pillar and / or Al 2 O 3 Small ball.

[0015] The present invention also provides a method for measuring the thermal expansion coefficient of a nuclear fuel pellet, using the thermal expansion coefficient measuring device of the nuclear fuel pellet described in any one of the above items, and the thermal expansion coefficient measuring method comprises the following steps:

[0016] S1. Place multiple nuclear fuel pellets into a sleeve, connect them in series into a string of samples to be tested with a predetermined length, and place the sleeve containing the nuclear fuel pellets into a test chamber;

[0017] S2. In the correction mode, the displacement detector push rod is started to extend toward the sleeve and act on the end of the nuclear fuel pellet with a predetermined pressure;

[0018] S3, heating the test chamber to a predetermined temperature at a set heating efficiency, and then cooling the temperature to room temperature at a set cooling rate; during the heating process, obtaining the thermal expansion coefficient data of the nuclear fuel pellets in real time through the main unit of the thermal expansion instrument.

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

[0020] In some embodiments, the step S1 further includes the following steps:

[0021] S0. Correcting the thermal expansion coefficient measuring device of the nuclear fuel pellets by using standard samples.

[0022] The beneficial effects of the present invention are as follows: a sleeve is provided for assembling nuclear fuel pellets in series therein, and the thermal expansion coefficient of the nuclear fuel pellets can be measured in cooperation with a main unit of a thermal expansion instrument. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 1 2 is a schematic structural diagram of a device for measuring the thermal expansion coefficient of a nuclear fuel pellet according to an embodiment of the present invention;

[0025] Figure 2 is Al of Examples 1 to 3 of the present invention 2 O 3 Result curve of thermal expansion coefficient of small ball;

[0026] Figure 3 It is a curve chart of thermal expansion coefficient of TRISO simulated fuel pellets in Example 4 of the present invention. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0028] like Figure 1 As shown, a device for measuring thermal expansion coefficient of nuclear fuel pellets according to an embodiment of the present invention comprises a thermal expansion instrument host 10 , a sample positioning mechanism 20 , and a base 30 , on which the thermal expansion instrument host 10 and the sample positioning mechanism 20 are arranged.

[0029] The main body 10 of the thermal expansion instrument is provided with a displacement detector push rod 40. The sample positioning mechanism 20 is arranged on one side of the main body 10 of the thermal expansion instrument and is located in the extension direction of the displacement detector push rod 40 of the main body 10 of the thermal expansion instrument.

[0030] The main unit 10 of the thermal expansion instrument is implemented by using the 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 in the test chamber 21. The sleeve 22 is used to accommodate the nuclear fuel pellets 50. A plurality of nuclear fuel pellets 50 are connected in series in the sleeve 22 along the length direction of the sleeve 22 to form a predetermined length, and the predetermined length is ≥10 mm, meeting the thermal expansion coefficient test requirements.

[0032] The test chamber 21 can be heated to a desired high temperature according to test requirements. Specifically, the test chamber 21 can be heated by a heating element or the like.

[0033] The length direction of the sleeve 22 and the telescopic direction of the displacement detector push rod 40 are located on the same straight line. The end of the displacement detector push rod 40 away from the thermal expansion instrument host 10 penetrates into the test chamber 21 so as to abut against the sleeve 22 or the nuclear fuel pellet 50 in the sleeve 22, and a predetermined pressure is applied to the end of the series-connected nuclear fuel pellet 50. The test chamber 21 is correspondingly provided with a through hole (not shown) for the displacement detector push rod 40 to penetrate, and a sealing arrangement is provided between the through hole and the displacement detector push rod 40, so as to ensure that the displacement detector push rod 40 can telescope and move while avoiding the existence of a gap to affect the airtightness of the test chamber 21.

[0034] In one embodiment, the sleeve 22 is a cylinder with two open ends. A first top plug 23 is provided at one end of the sleeve 22, and the sleeve 22 is fixed in the test chamber 21 by the first top plug 23. A second top plug 24 is provided at the other end of the sleeve 22, and the second top plug 24 is directly opposite to the displacement detector top rod 40 and can abut against the end of the nuclear fuel pellet 50 in the sleeve 22.

[0035] The second top plug 24 is at the end of the sleeve 22, one side of which can abut against the nuclear fuel pellet 50 assembled in the sleeve 22, and the other side of which abuts against the displacement detector push rod 40. When the displacement detector push rod 40 applies pressure to the second top plug 24, it can push the second top plug 24 to move toward the inside of the sleeve 22. The portion of the second top plug 24 located in the sleeve 22 has a sufficient axial length to meet the requirement of testing the thermal expansion coefficient of the nuclear fuel pellet 50. When the displacement detector push rod 40 pushes, the top-connected nuclear fuel pellet 50 moves toward the inside of the sleeve 22.

[0036] In another embodiment, the sleeve 22 may also be a cylindrical structure with one end closed and the other end open. The sleeve 22 is docked in 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. One side of the top plug can abut against the nuclear fuel pellet 50 assembled in the sleeve 22, and the other side abuts against the displacement detector push rod 40. Under the push of the displacement detector push rod 40, the top plug abuts against the nuclear fuel pellet 50 and moves toward the inside of the sleeve 22.

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

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

[0039] The inner diameter of the sleeve 22 is larger than the diameter of the nuclear fuel pellet 50, and the inner diameter of the sleeve 22 is further larger than the diameter of the nuclear fuel pellet 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 pellet 50 to prevent jamming during the thermal expansion coefficient measurement process and affect the measurement results.

[0040] The sleeve 22, the first top plug 23 and the second top plug 24 can be made of alumina or graphite. When the test temperature is below 1700°C, the sleeve 22, the first top plug 23 and the second top plug 24 are preferably made of Al 3 O 2 When the test temperature is above 1700°C, the sleeve 22, the first top plug 23 and the second top plug 24 are preferably made of graphite.

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

[0042] Before measuring the thermal expansion coefficient of the nuclear fuel pellets of the present invention, the device for measuring the thermal expansion coefficient of the nuclear fuel pellets generally needs to be corrected. 2 O 3 Pillar and / or Al 2 O 3 Small ball. 2 O 3 Pillar and / or Al 2 O 3 When the ball is corrected, the assembly length in the sleeve 22 is also greater than or equal to 10 mm.

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

[0044] S0. Correct the thermal expansion coefficient measuring device using standard samples.

[0045] The standard sample is Al 2 O 3 Pillar and / or Al 2 O 3 Small ball.

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

[0047] In one embodiment, Al 2 O 3 During the correction, the Al 2 O 3 The column is positioned in the test chamber 21 through the sample holder and is aligned with the displacement detector top rod 40. The displacement detector top rod 40 acts on the Al with a force of 200 mN. 2 O 3 The test chamber 21 starts to heat up, and the thermal expansion instrument host 10 obtains the system thermal expansion coefficient data of the thermal expansion coefficient measuring device in real time, and after reaching 600°C, it cools down to room temperature at a rate of 20°C / s.

[0048] S1. Place a plurality of nuclear fuel pellets 50 into a sleeve 22 and connect them in series to form a string of test samples with a predetermined length. Place the sleeve 22 containing the nuclear fuel pellets 50 into a test chamber 21.

[0049] The predetermined length is ≥ 10 mm. The number of the nuclear fuel pellets 50 is determined according to 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 following steps are further performed: evacuating the test chamber 21 and filling it with an inert gas (helium, argon or a mixture of the two) to form a protective atmosphere.

[0051] S2. In the correction mode, the displacement detector top rod 40 is started to extend toward the sleeve 22 and act on the end of the nuclear fuel pellet 50 with a predetermined pressure.

[0052] Specifically, by operating on the thermal expansion instrument host 10, the correction mode is selected, and the basic parameters required for measurement are input: heating rate 5°C / s~10°C / s, push rod force (i.e., predetermined pressure) 200mN, sample length 10mm, end temperature 600°C, cooling rate 10°C / s~30°C / s.

[0053] S3, after heating the test chamber 21 to a predetermined temperature (i.e., the end temperature) at a set heating efficiency, the temperature is cooled to room temperature at a set cooling rate; during the heating process, the thermal expansion coefficient data of the nuclear fuel pellet 50 is obtained in real time through the thermal expansion instrument host 10.

[0054] Among them, the heating efficiency is set to 5°C / s to 10°C / s, and the cooling rate is set to 10°C / s to 30°C / s.

[0055] In the above step S0, the thermal expansion coefficient measuring device is corrected by the 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, and the system thermal expansion data is deducted from it to obtain the real thermal expansion data of the nuclear fuel pellet 50 itself.

[0056] The present invention will be further described below by means of specific examples.

[0057] Embodiment 1:

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

[0059] Next, a 10 mm length standard Al 2 O 3 The cylinder is placed on the sample holder. The sample holder is located in the test chamber and the standard Al 2 O 3 The column and the top rod of the displacement detector are in the same straight line.

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

[0061] Then, click the displacement probe push rod drive button, and the displacement probe push rod acts on the standard Al with a force of 200mN. 2 O 3 End face of cylinder;

[0062] Then, click to start the test, the test chamber begins to heat up, and the system thermal expansion coefficient data is obtained in real time. After reaching 600°C, it is cooled to room temperature at a rate of 20°C / s.

[0063] Then take out the standard Al 2 O 3 A 9.525mm diameter Al 2 O 3 The ball is placed in the sleeve, clamped by two left and right top plugs, and placed in the test chamber.

[0064] Again, open the software, select the sample + correction mode, and enter the basic parameters: heating rate 5℃ / s, ejector force 200mN, sample length 9.525mm, end temperature 600℃, cooling rate 20℃ / s;

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

[0066] Click Start Test, the test chamber starts to heat up, and the Al2O3 with a diameter of 9.525 mm is obtained in real time. 2 O 3 The ball thermal expansion coefficient data, after reaching 600℃, is cooled to room temperature at a rate of 20℃ / s.

[0067] Embodiment 2:

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

[0069] Next, a 10 mm length standard Al 2 O 3 The column is loaded into the sample holder. The sample holder is located in the test chamber and the standard Al 2 O 3 The column and the top rod of the displacement detector are in the same straight line.

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

[0071] Then, click the displacement probe push rod drive button, and the displacement probe push rod acts on the standard Al with a force of 200mN. 2 O 3 End face of cylinder.

[0072] Click to start the test, the test chamber starts to heat up, and the system thermal expansion coefficient data is obtained in real time. After reaching 600°C, it is cooled to room temperature at a rate of 20°C / s.

[0073] Then take out the standard Al 2 O 3 For the cylindrical sample, two Al 2 O 3 The ball is placed in the sleeve, clamped by two left and right top plugs, and placed in the test chamber.

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

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

[0076] Click Start Test, the test chamber starts to heat up, and the Al2O3 with a diameter of 5.553 mm is obtained in real time. 2 O 3 The ball thermal expansion coefficient data, after reaching 600℃, is cooled to room temperature at a rate of 20℃ / s.

[0077] Embodiment 3:

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

[0079] Next, a 10 mm length standard Al 2 O 3 The column is loaded into the sample holder. The sample holder is located in the test chamber and the standard Al 2 O 3 The column and the top rod of the displacement detector are in the same straight line.

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

[0081] Then, click the displacement probe push rod drive button, and the displacement probe push rod acts on the standard Al with a force of 200mN. 2 O 3 End face of cylinder.

[0082] Click to start the test, the test chamber starts to heat up, and the system thermal expansion coefficient data is obtained in real time. After reaching 600°C, it is cooled to room temperature at a rate of 20°C / s.

[0083] Then take out the standard Al 2 O 3 For the cylindrical sample, six Al 2 O 3 The ball is placed in the sleeve, clamped by two left and right top plugs, and placed in the test chamber.

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

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

[0086] Click Start Test, the test chamber starts to heat up, and the diameter of Al2O3 is 1.588mm. 2 O 3The ball thermal expansion coefficient data, after reaching 600℃, is cooled to room temperature at a rate of 20℃ / s.

[0087] The above-mentioned examples 1 to 3 are prepared with different amounts of Al 2 O 3 The ball is used to measure the thermal expansion coefficient. The measurement results are as follows Figure 2 As shown. Figure 2 As shown in the curve, the Al 2 O 3 The results of thermal expansion coefficient of the ball are similar, indicating that Al 2 O 3 The number of balls does not affect Al 2 O 3 The measurement results of the thermal expansion coefficient of the ball show that the thermal expansion coefficient measurement device and method of the present invention are feasible.

[0088] Embodiment 4:

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

[0090] Next, a 10 mm length standard Al 2 O 3 The column is loaded into the sample holder. The sample holder is located in the test chamber and the standard Al 2 O 3 The column and the top rod of the displacement detector are in the same straight line.

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

[0092] Then, click the displacement probe push rod drive button, and the displacement probe push rod acts on the standard Al with a force of 200mN. 2 O 3 End face of cylinder.

[0093] Click to start the test, the test chamber starts to heat up, and the system thermal expansion coefficient data is obtained in real time. After reaching 600°C, it is cooled to room temperature at a rate of 20°C / s.

[0094] Then take out the standard Al 2 O 3 For the cylindrical sample, 12 TRISO simulated fuel pellets with a diameter of 0.891 mm are placed in the sleeve, clamped with two left and right top plugs, and placed in the test chamber.

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

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

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

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

[0099] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A device for measuring the thermal expansion coefficient of a nuclear fuel pellet, characterized in that: It includes a thermal expansion instrument mainframe and a sample positioning mechanism; the sample positioning mechanism is arranged on one side of the thermal expansion instrument mainframe and is located in the telescopic direction of the displacement detector top rod of the thermal expansion instrument mainframe; The sample positioning mechanism comprises a sealed test chamber and a sleeve arranged in the test chamber; the sleeve is used to accommodate nuclear fuel pellets; a plurality of nuclear fuel pellets are connected in series in the sleeve along the length direction of the sleeve to form a predetermined length; 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 penetrates into the test chamber and is used to act on the end of the nuclear fuel pellet with a predetermined pressure.

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

3. The thermal expansion coefficient measuring device 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 thermal expansion coefficient measuring device of nuclear fuel pellets according to claim 1, characterized in that: The sleeve is a cylinder with two open ends; a first top plug is provided at one end of the sleeve and is fixed in the test chamber by the first top plug; a second top plug is provided at the other opposite end of the sleeve, and the second top plug is directly opposite to the displacement detector push rod and can abut against the end of the nuclear fuel ball in the sleeve.

5. The thermal expansion coefficient measuring device of nuclear fuel pellets according to claim 1, characterized in that: The sleeve is made of aluminum oxide material or graphite.

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

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

8. A method for measuring the thermal expansion coefficient of a nuclear fuel pellet, characterized in that: The thermal expansion coefficient measuring device of the nuclear fuel pellet according to any one of claims 1 to 7 is used, and the thermal expansion coefficient measuring method comprises the following steps: S1. Place multiple nuclear fuel pellets into a sleeve, connect them in series into a string of samples to be tested with a predetermined length, and place the sleeve containing the nuclear fuel pellets into a test chamber; S2. In the correction mode, the displacement detector push rod is started to extend toward the sleeve and act on the end of the nuclear fuel pellet with a predetermined pressure; S3, heating the test chamber to a predetermined temperature at a set heating efficiency, and then cooling the temperature to room temperature at a set cooling rate; during the heating process, obtaining the thermal expansion coefficient data of the nuclear fuel pellets in real time through the main unit of the thermal expansion instrument.

9. The method for measuring the thermal expansion coefficient of nuclear fuel pellets according to claim 8, characterized in that: Step S1 also includes: after the sleeve is installed in the test chamber, evacuating the test chamber and filling it 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: Before step S1, the following steps are also included: S0. Correcting the thermal expansion coefficient measuring device of the nuclear fuel pellets by using standard samples.

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