Biaxial Fatigue Performance Test System for Axial Internal Pressure Combined Loading of Nuclear Fuel Cladding Tubes

Abstract

The present invention discloses a biaxial fatigue performance test system for axially combined internal pressure loading of nuclear fuel cladding tubes, which includes a medium tank for storing test media; a high-temperature test furnace in which a clamping fixture and a measurement module are installed; the clamping fixture is used to clamp and fix the cladding tube to be tested, and the measurement module is used to measure the change value of the outer diameter of the cladding tube; a liquid pumping module connected to the medium tank and the internal pressurization module for pumping the test media in the medium tank to the internal pressurization module; an internal pressurization module connected to the cladding tube to be tested; and a pressurization power module connected to the internal pressurization module and the external tension-compression module. The present invention solves the simulation conditions of the synchronous test of the internal pressure fatigue and the external tension-compression fatigue of the cladding tube, obtains the real-time research data of the synchronous test, fully realizes the fatigue strength test of the cladding tube of nuclear power materials, and further can optimize the design, production and other links of the cladding tube to improve the safe usability of nuclear power applications.

Description

Technical Field

[0001] The present invention relates to the technical field of internal and external pressure fatigue testing of cladding tubes, and particularly to a biaxial fatigue performance testing system for axial internal pressure combined loading of nuclear fuel cladding tubes. Background Art

[0002] At present, the fatigue research on the cladding tubes of nuclear fuel rods in China only adopts a single form of internal pressure fatigue test, and thus can only understand the material characteristic capabilities under a single fatigue condition. With the innovation and application requirements of nuclear power technology, the research conditions for the fatigue characteristics of cladding tubes are becoming more and more demanding. In its actual working condition environment, internal pressure fatigue and external tensile-compressive fatigue coexist. Therefore, it is also necessary to conduct external tensile-compressive fatigue tests on cladding tubes. In addition, the fatigue research on nuclear fuel rod cladding tubes is all carried out in a high-temperature vacuum environment (1000°C). Due to the limitations of the length of the test cladding tubes determined by the research conditions, the connecting fixtures of the cladding tubes must be placed in the high-temperature vacuum environment for long-term testing. However, most of the currently used connecting fixtures are made of rubber materials, and the sealing effect is poor, and they cannot adapt to long-term high-temperature tests, which easily leads to test failures. Summary of the Invention

[0003] The purpose of the present invention is to provide a biaxial fatigue performance testing system for axial internal pressure combined loading of nuclear fuel cladding tubes to solve the above problems.

[0004] To achieve the above purpose, the following technical solutions are adopted:

[0005] A biaxial fatigue performance testing system for axial internal pressure combined loading of nuclear fuel cladding tubes includes a medium tank: used for storing test media; a high-temperature test furnace: inside which a clamping fixture and a measuring module are installed; the clamping fixture is used to clamp and fix the cladding tube to be tested, and the measuring module is used to measure the change value of the outer diameter of the cladding tube; a liquid pumping module: connected to the medium tank and the internal pressure boosting module, and used to pump the test media in the medium tank to the internal pressure boosting module; an internal pressure boosting module: connected to the cladding tube to be tested, and used to boost the test media pumped into it by the liquid pumping module and then output it into the cladding tube; a boosting power module: connected to the internal pressure boosting module and the external tensile-compressive module, and used to provide power for the internal pressure boosting module and the external tensile-compressive module; an external tensile-compressive module: connected to the clamping fixture, and used to reciprocally pull and compress the cladding tube to be tested through the clamping fixture.

[0006] Further, the boosting power module includes an oil storage tank for storing hydraulic oil, and a first gear pump, a first one-way valve, and a high-pressure filter that are sequentially connected to the oil storage tank; a first pressure gauge, a one-way throttle valve, and an accumulator are also connected between the high-pressure filter and the first one-way valve.

[0007] Further, the internal pressure boosting module includes a first servo reversing valve, a first boosting cylinder, and a return water cooler; a first inlet of the first servo reversing valve is connected to a high-pressure filter, a first outlet and a second outlet of the first servo reversing valve are connected to an input end of the first boosting cylinder, and a third outlet of the first servo reversing valve is also connected to a storage oil tank via the return water cooler; an output end of the first boosting cylinder is respectively connected to a liquid pumping module and a cladding tube, and a first pressure sensor is further connected between the output end of the first boosting cylinder and the cladding tube.

[0008] Further, the liquid pumping module includes a manual ball valve, a Y-type filter, a filling pump, and a second check valve that are sequentially connected between a medium tank and an output end of the first boosting cylinder; a vacuum pump and a first pneumatic needle valve are also connected between the medium tank and the cladding tube.

[0009] Further, the external tension and compression module includes a second servo reversing valve and a second boosting cylinder; a first inlet of the second servo reversing valve is connected to a high-pressure filter, a first outlet and a second outlet of the second servo reversing valve are connected to an input end of the second boosting cylinder, and a third outlet of the second servo reversing valve is also connected to a storage oil tank via the return water cooler; an output end of the second boosting cylinder is drivingly connected to one end of a clamping fixture.

[0010] Further, the clamping fixture includes two clamping mechanisms; each clamping mechanism includes a mounting housing; a connection hole is opened at one end of each mounting housing, and two ends of the cladding tube are respectively inserted into a connection hole; a liquid flow channel communicating with the connection hole is axially opened inside one of the mounting housings, and a liquid connection interface communicating with the liquid flow channel is also provided on an outer wall of the mounting housing; a sealing member sleeved on an outer wall of the cladding tube is installed in each connection hole; a connection ring is fixedly connected to one end of each mounting housing provided with a connection hole, and a pressing assembly sleeved on an outer wall of the cladding tube is installed in each connection ring, and the pressing assembly is used to press and limit the sealing member in the connection hole.

[0011] Further, the sealing member includes a first sealing bushing and a second sealing bushing that are sequentially arranged in the connection hole, and one end of the cladding tube passes through the first sealing bushing and the second sealing bushing in sequence; a plurality of first screw holes are opened on the second sealing bushing, and the first screw holes are used to install screws to lock and limit the first sealing bushing and the second sealing bushing in the connection hole; a limiting boss is provided on one side of the second sealing bushing, and the limiting boss is inserted into the first sealing bushing; a C-shaped sealing ring is sleeved on an outer wall of the limiting boss; an O-shaped sealing ring is also nested on a side wall of the first sealing bushing in contact with the bottom of the connection hole.

[0012] Further, a limiting hole penetrating through to the other side is provided on one side of the connecting ring; the pressing assembly includes a locking sleeve, the locking sleeve is in a conical structure, and the sharp end of the locking sleeve is inserted into the limiting hole, and the other end of the locking sleeve is inserted into the connecting hole and abuts against the second sealing sleeve; a locking hole penetrating through to the other end is also opened at one end of the locking sleeve, and one end of the cladding tube is arranged through the locking hole.

[0013] Further, a plurality of locking protrusion blocks for increasing the friction force are provided on the inner wall of the locking hole.

[0014] Further, a mandrel is respectively arranged at both ends inside the cladding tube.

[0015] Adopting the above scheme, the beneficial effects of the present invention are as follows:

[0016] 1) The simulation working condition of the synchronous test of the internal pressure fatigue and the external tensile-compressive fatigue of the cladding tube is solved, the real-time research data of the synchronous test are obtained, the fatigue strength test of the nuclear power material cladding tube is completely realized, and further, the design, production, etc. of the cladding tube can be optimized to improve the safe usability of nuclear power applications;

[0017] 2) The clamping fixture is made of GH4169 superalloy material, has strong high-temperature resistance performance, and has good anti-fatigue, anti-radiation, anti-oxidation, and corrosion resistance performance. It can be placed in a high-temperature vacuum environment for a long time and is convenient to use;

[0018] 3) Through the first sealing sleeve and the second sealing sleeve, the connection between the cladding tube and the liquid flow channel can be sealed, the gas leakage rate can be reduced, and the sealing effect is good;

[0019] 4) The split design is adopted, and the axial tensile-compressive force application point acts on the outer wall of the cladding tube, that is, the area where the pressing assembly in the connecting ring contacts the outer wall of the cladding tube, and has nothing to do with the seal. The seal is only for realizing the seal of the internal pressure of the cladding tube. Adopting such a split design can ensure that the seal will not loosen or fall off during the dynamic tensile-compressive process of the test, thereby ensuring the stability of the test;

[0020] 5) Mandrels with a certain wall thickness are added at both ends inside the cladding tube. The presence of the mandrels effectively ensures the uniformity of the force applied to the cladding tube and will not cause phenomena such as the collapse of the cladding tube, thereby improving the success rate of the test. Description of the Drawings

[0021] Figure 1 is a structural schematic diagram of the present invention;

[0022] Figure 2 is a three-dimensional view of the clamping fixture of the present invention;

[0023] Figure 3 isFigure 2 Stereogram of the installation housing omitted;

[0024] Figure 4 Exploded view of the connecting ring, seal, and locking sleeve of the present invention;

[0025] Figure 5 Cross-sectional view of the clamping fixture of the present invention;

[0026] Figure 6 is Figure 5 Local enlarged schematic view at position A of

[0027] Among them, the description of the attached drawing signs:

[0028] 1 - Medium box; 2 - High-temperature test furnace; 3 - Clamping fixture; 4 - Measuring module; 5 - Liquid extraction module; 6 - Internal pressurization module; 7 - Pressurization power module; 8 - External tension and compression module; 31 - Installation housing; 32 - Seal; 33 - Connecting ring; 34 - Locking sleeve; 35 - Mandrel; 51 - Manual ball valve; 52 - Y-type filter; 53 - Liquid filling pump; 54 - Second one-way valve; 55 - Vacuum pump; 56 - First pneumatic needle valve; 61 - First servo reversing valve; 62 - First pressurizing cylinder; 63 - Return water cooler; 64 - Displacement sensor; 65 - First pressure sensor; 71 - Oil storage tank; 72 - First gear pump; 73 - First one-way valve; 74 - High-pressure filter; 75 - First pressure gauge; 76 - One-way throttle valve; 77 - Accumulator; 78 - Electromagnetic overflow valve; 81 - Second servo reversing valve; 82 - Second pressurizing cylinder; 311 - Fixed hole; 312 - Installation ring; 313 - Liquid flow channel; 314 - Liquid connection interface; 321 - First sealing ferrule; 322 - Second sealing ferrule; 323 - Limit boss; 324 - C-type sealing ring; 325 - O-type sealing ring; 341 - Locking projection block. Specific embodiments

[0029] The present invention will be described in detail below with reference to the attached drawings and specific embodiments.

[0030] Refer to Figures 1 to 6As shown in the figure, the present invention provides a biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes, including a medium tank 1 for storing test media; a high-temperature test furnace 2, in which a clamping fixture 3 and a measurement module 4 are installed; the clamping fixture 3 is used to clamp and fix the cladding tube to be tested, and the measurement module 4 is used to measure the change value of the outer diameter of the cladding tube; a liquid extraction module 5, connected to the medium tank 1 and the internal pressurization module 6, for extracting the test media in the medium tank 1 to the internal pressurization module 6; an internal pressurization module 6, connected to the cladding tube to be tested, for pressurizing the test media extracted into it by the liquid extraction module 5 and then outputting it into the cladding tube; a pressurization power module 7, connected to the internal pressurization module 6 and the external tension-compression module 8, for providing power for the internal pressurization module 6 and the external tension-compression module 8; an external tension-compression module 8, connected to the clamping fixture 3, for reciprocally pulling and compressing the cladding tube to be tested through the clamping fixture 3.

[0031] Among them, the pressurization power module 7 includes an oil storage tank 71 for storing hydraulic oil, and a first gear pump 72, a first one-way valve 73, and a high-pressure filter 74 connected to the oil storage tank 71 in sequence; a first pressure gauge 75, a one-way throttle valve 76, and an accumulator 77 are also connected between the high-pressure filter 74 and the first one-way valve 73; the internal pressurization module 6 includes a first servo reversing valve 61, a first booster cylinder 62, and a return water cooler 63; the first inlet of the first servo reversing valve 61 is connected to the high-pressure filter 74, the first outlet and the second outlet of the first servo reversing valve 61 are connected to the input end of the first booster cylinder 62, and the third outlet of the first servo reversing valve 61 is also connected to the oil storage tank 71 through the return water cooler 63; the output end of the first booster cylinder 62 is respectively connected to the liquid extraction module 5 and the cladding tube, and a first pressure sensor 65 is also connected between the output end of the first booster cylinder 62 and the cladding tube; the liquid extraction module 5 includes a manual ball valve 51, a Y-type filter 52, a filling pump 53, and a second one-way valve 54 connected in sequence between the medium tank 1 and the output end of the first booster cylinder 62; a vacuum pump 55 and a first pneumatic needle valve 56 are also connected between the medium tank 1 and the cladding tube.

[0032] The external pulling and pressing module 8 includes a second servo reversing valve 81 and a second boosting cylinder 82; the first inlet of the second servo reversing valve 81 is connected to the high-pressure filter 74, the first outlet and the second outlet of the second servo reversing valve 81 are connected to the input end of the second boosting cylinder 82, and the third outlet of the second servo reversing valve 81 is also connected to the oil storage tank 71 through the return water cooler 63; the output end of the second boosting cylinder 82 is drivingly connected to one end of the clamping fixture 3; the clamping fixture 3 includes two clamping mechanisms; each clamping mechanism includes a mounting housing 31; a connection hole is opened at one end of each mounting housing 31, and both ends of the cladding tube are respectively inserted into a connection hole; a liquid flow channel 313 communicating with the connection hole is opened along the axial direction inside one of the mounting housings 31, and a liquid connection interface 314 communicating with the liquid flow channel 313 is arranged on the outer wall of the mounting housing 31; a sealing member 32 sleeved on the outer wall of the cladding tube is installed in each connection hole; a connection ring 33 is fixedly connected to one end of each mounting housing 31 provided with a connection hole, and a pressing component sleeved on the outer wall of the cladding tube is installed in each connection ring 33, and the pressing component is used to press and limit the sealing member 32 in the connection hole; the sealing member 32 includes a first sealing ferrule 321 and a second sealing ferrule 322 arranged in sequence in the connection hole, and one end of the cladding tube passes through the first sealing ferrule 321 and the second sealing ferrule 322 in sequence; a plurality of first screw holes are opened on the second sealing ferrule 322, and the first screw holes are used to install screws to lock and limit the first sealing ferrule 321 and the second sealing ferrule 322 in the connection hole; a limiting boss 323 is arranged on one side of the second sealing ferrule 322, and the limiting boss 323 is inserted into the first sealing ferrule 321; a C-shaped sealing ring 324 is sleeved on the outer wall of the limiting boss 323; an O-shaped sealing ring 325 is nested on the side wall of the first sealing ferrule 321 in contact with the bottom of the connection hole; a limiting hole penetrating through to the other side is arranged on one side of the connection ring 33; the pressing component includes a locking sleeve 34, the locking sleeve 34 has a conical structure, and the sharp end of the locking sleeve 34 is inserted into the limiting hole, and the other end of the locking sleeve 34 is inserted into the connection hole and abuts against the second sealing ferrule 322; a locking hole penetrating through to the other end is opened at one end of the locking sleeve 34, and one end of the cladding tube passes through the locking hole; a plurality of locking raised blocks 341 for increasing the friction force are arranged on the inner wall of the locking hole; mandrels 35 are respectively arranged at both ends inside the cladding tube.

[0033] The working principle of the present invention:

[0034] Continue to refer to Figures 1 to 6As shown, in this embodiment, the system further includes a pneumatic drive module for providing air pressure for other valves. It includes an air compressor, a hand slide valve, a pressure switch, a gas filter, a pressure regulating valve, and a pneumatic solenoid valve that are connected to the air compressor in sequence, and is used to control the opening and closing of corresponding valves; the system can respectively perform internal pressure fatigue tests and external tensile and compressive fatigue tests on the cladding tube (or other pipe fittings).

[0035] During the internal pressure fatigue test, first, the first gear pump 72 can suck and pressurize the hydraulic oil in the oil storage tank 71 and then output it. The pressurized hydraulic oil is filtered by the high-pressure filter 74 and then flows into the first servo reversing valve 61 through the first inlet of the first servo reversing valve 61, which can prevent the impurities in the hydraulic oil from flowing through the first servo reversing valve 61 and causing blockage of the first booster cylinder 62 when flowing into the first booster cylinder 62; as Figure 1 shown, the first servo reversing valve 61 is provided with one inlet and three outlets (the first outlet, the second outlet, and the third outlet). The first outlet and the second outlet of the first servo reversing valve 61 are connected to the input end of the first booster cylinder 62 (the piston of the first booster cylinder 62 is located between the two outlets). The first gear pump 72 inputs the pressurized hydraulic oil into the first servo reversing valve 61, and the first servo reversing valve 61 outputs the hydraulic oil to the input end of the first booster cylinder 62 through the first outlet (at this time, the hydraulic oil is on one side of the piston). By controlling the opening and closing degree of the valve of the first servo reversing valve 61, the flow rate (pressure) of the hydraulic oil input to the input end of the first booster cylinder 62 can be controlled. Then, the test medium located at the output end of the first booster cylinder 62 (the filling pump 53 of the liquid extraction module 5 previously pumps the test medium in the medium tank 1 to the output end of the first booster cylinder 62) is pressurized into the cladding tube to be tested by the piston of the first booster cylinder 62 being squeezed by the hydraulic oil, and then the internal pressure fatigue test of the cladding tube is carried out (by precisely controlling the output pressure of the first servo reversing valve 61, the output of the low-pressure end pressure of the first booster cylinder 62 is achieved. Because there is a certain ratio between the areas of the low-pressure end and the high-pressure end of the first booster cylinder 62, the pressure output ratio of the low-pressure end and the high-pressure end corresponds to the area ratio. The high-pressure end of the first booster cylinder 62 is connected to the cladding tube, and its function is to test the pressure alternation inside the cladding tube, thus realizing the internal pressure fatigue test).

[0036] After the hydraulic oil is pumped into the cladding tube to complete the test, the hydraulic oil at the input end of the first booster cylinder 62 flows back into the first servo reversing valve 61 through the second outlet of the first servo reversing valve 61 and then flows back to the oil storage tank 71 through the third outlet of the first servo reversing valve 61. When the hydraulic oil flows back into the oil storage tank 71, the return water cooler 63 cools the returned hydraulic oil to prevent the hydraulic oil from getting too hot and facilitating recycling.

[0037] Meanwhile, after the test, the vacuum pump 55 can extract the test medium in the cladding tube and return it to the medium tank 1 for recycling. The first gear pump 72 can provide high-pressure output. The first servo reversing valve 61 can control the output pressure of the hydraulic oil to improve the stability of the output pressure. The first booster cylinder 62 can achieve rapid pressurization and pressure relief of the test medium (the piston of the first booster cylinder 62 has a fast movement frequency). In addition, a displacement sensor 64 is provided at the input end of the first booster cylinder 62. The displacement sensor 64 is connected to the piston of the first booster cylinder 62 to detect the displacement of the piston of the first booster cylinder 62 and feedback it to the background. Then, the background controls the opening and closing degree of the valve of the first servo reversing valve 61, and then accurately and continuously controls the output pressure of the first booster cylinder 62. In addition, a first pressure sensor 65 is provided between the output end of the first booster cylinder 62 and the cladding tube. The first pressure sensor 65 can detect the pressure input into the cladding tube to be tested in real time, facilitating the staff to observe and adjust in time.

[0038] In addition, when the first gear pump 72 sucks too much hydraulic oil, the hydraulic oil can be drained to the accumulator 77 for storage through the one-way throttle valve 76, thus avoiding excessive pressure boost of the first gear pump 72 and damaging the system. At the same time, the hydraulic oil stored in the accumulator 77 can also be output to the first servo reversing valve 61 through the one-way throttle valve 76 when the first gear pump 72 needs to increase the output pressure, avoiding frequent use of the first gear pump 72 and prolonging the service life of the first gear pump 72. At the same time, a first pressure gauge 75 is provided between the accumulator 77 and the first gear pump 72. The pressure after the boost output of the first gear pump 72 can be viewed through the first pressure gauge 75. At the same time, to improve the safety of the system, an electromagnetic overflow valve 78 is also provided. When the first gear pump 72 sucks too much hydraulic oil, the excess hydraulic oil can be returned to the oil storage tank 71 through the electromagnetic overflow valve 78 to avoid damage to the system due to excessive pressure.

[0039] During the external tensile and compressive test, the external tensile and compressive module 8 includes a second servo reversing valve 81 and a second booster cylinder 82. Driven by the boosting power module 7, the second booster cylinder 82 reciprocates to pull and press the clamping fixture 3 to achieve the tensile and compressive fatigue test of the cladding tube. Its working principle is similar to the above and will not be elaborated here.

[0040] Continue to refer to Figures 2 to 6As shown in the figure, to adapt to the use of the clamping fixture 3 to complete the external tensile and compression test of the cladding tube in a high-temperature environment, in this embodiment, the installation housing 31 is made of GH4169 high-temperature alloy, which is a precipitation-strengthened nickel-based high-temperature alloy that can withstand a temperature of 1200°C and has good anti-fatigue, anti-radiation, anti-oxidation, corrosion resistance, as well as good machining performance and welding performance. A liquid connection interface 314 is provided on the outer wall of one of the installation housings 31 for connecting to the output end of the first booster cylinder 62, facilitating the input of the test medium into the cladding tube through the liquid flow channel 313 to conduct an internal pressure fatigue test on it. During the test, after the internal pressure of the cladding tube is applied, it will be in a long-term stable test process. During this process, the pressure cannot leak through the clamping fixture. Therefore, a seal 32 is provided in the connection hole. The seal 32 includes a first seal ferrule 321 and a second seal ferrule 322. The double-seal ferrule sealing method can reduce the gas leakage rate and improve the sealing performance. At the same time, to further enhance the sealing effect, a C-shaped sealing ring 324 is also sleeved on the limit boss 323 of the second seal ferrule 322, and an O-shaped sealing ring 325 is also nested on the side wall of the first seal ferrule 321 in contact with the bottom of the connection hole. In addition, to ensure that the seal 32 will not fall off, a number of first screw holes are provided on the second seal ferrule 322, and screws can be installed to lock and fix it.

[0041] In addition, at one end of each installation housing 31, a connection ring 33 is fixedly connected (fixed by screwing), and a locking sleeve 34 is arranged inside the connection ring 33. The locking sleeve 34 has a conical structure (in this embodiment, the locking sleeve 34 includes a plurality of locking blocks, and the plurality of locking blocks are arranged at intervals around the cladding tube). The sharp end of the locking sleeve 34 is inserted into the limiting hole, and the other end of the locking sleeve 34 is inserted into the connection hole and abuts against the second sealing ferrule 322, which can further limit the position of the seal 32. At the same time, a plurality of locking protrusion blocks 341 are arranged on the inner wall of the locking hole of the locking sleeve 34, and the locking protrusion blocks 341 are in contact with the outer wall of the cladding tube. The contact area is the application point of the axial tensile and compressive force, that is, a split design is adopted, and the application point of the axial tensile and compressive force is on the outer wall of the cladding tube, which has nothing to do with the seal 32. The seal 32 is only for realizing the sealing of the internal pressure of the cladding tube. Adopting such a split design can ensure that the seal 32 will not become loose or fall off during the dynamic tensile and compressive test, thereby ensuring the stability of the test. At the same time, mandrels 35 with a certain wall thickness are added at both ends inside the cladding tube (the mandrels 35 are located in the area of the axial tensile force application point). The presence of the mandrels 35 effectively ensures the uniformity of the force applied to the cladding tube and will not cause phenomena such as the collapse of the cladding tube, thereby improving the success rate of the test. In addition, a plurality of fixing holes 311 are opened at one end of the installation housing 31 for connecting with the output end of the second booster cylinder 82 for external tensile and compressive tests. At the same time, a plurality of installation rings 312 are sleeved on the outer wall of one end of the installation housing 31 to facilitate the installation of the fixture outside.

[0042] In addition, a measurement module 4 is also arranged in the high-temperature test furnace 2. In this embodiment, the measurement module 4 is a video extensometer, which can non-contact measure the change value of the outer diameter of the cladding tube, which is simple and convenient.

[0043] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A biaxial fatigue performance test system for axially combined internal pressure loading of a nuclear fuel cladding tube, characterized in that Including: a medium box for storing test medium; A high-temperature test furnace, in which a clamping fixture and a measuring module are installed; the clamping fixture is used to clamp and fix the cladding tube to be tested, and the measuring module is used to measure the change value of the outer diameter of the cladding tube; A liquid pumping module connected to the medium box and the internal pressurization module, for pumping the test medium in the medium box to the internal pressurization module; an internal pressurization module connected to the cladding tube to be tested, for pressurizing the test medium pumped into it by the liquid pumping module and then outputting it into the cladding tube; A pressurization power module connected to the internal pressurization module and the external tension-compression module, for providing power for the internal pressurization module and the external tension-compression module; An external tension-compression module connected to the clamping fixture, for reciprocally pulling and compressing the cladding tube to be tested through the clamping fixture; The pressurization power module includes an oil storage tank for storing hydraulic oil, and a first gear pump, a first one-way valve and a high-pressure filter sequentially connected to the oil storage tank; a first pressure gauge, a one-way throttle valve and an accumulator are also connected between the high-pressure filter and the first one-way valve; The internal pressurization module includes a first servo reversing valve, a first pressurizing cylinder and a return water cooler; the first inlet of the first servo reversing valve is connected to the high-pressure filter, the first outlet and the second outlet of the first servo reversing valve are connected to the input end of the first pressurizing cylinder, and the third outlet of the first servo reversing valve is also connected to the oil storage tank through the return water cooler; the output end of the first pressurizing cylinder is respectively connected to the liquid pumping module and the cladding tube, and a first pressure sensor is also connected between the output end of the first pressurizing cylinder and the cladding tube; The external tension-compression module includes a second servo reversing valve and a second pressurizing cylinder; the first inlet of the second servo reversing valve is connected to the high-pressure filter, the first outlet and the second outlet of the second servo reversing valve are connected to the input end of the second pressurizing cylinder, and the third outlet of the second servo reversing valve is also connected to the oil storage tank through the return water cooler; the output end of the second pressurizing cylinder is drivingly connected to one end of the clamping fixture; The clamping fixture includes two clamping mechanisms; each clamping mechanism includes a mounting housing; a connection hole is opened at one end of each mounting housing, and both ends of the cladding tube are respectively inserted into a connection hole; a liquid flow channel communicating with the connection hole is axially opened inside one of the mounting housings, and a liquid connection interface communicating with the liquid flow channel is also provided on the outer wall of the mounting housing; a sealing member sleeved on the outer wall of the cladding tube is installed in each connection hole; a connection ring is fixedly connected to one end of each mounting housing where the connection hole is located, and a pressing assembly sleeved on the outer wall of the cladding tube is installed in each connection ring, and the pressing assembly is used to press and limit the sealing member in the connection hole.

2. The biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes according to claim 1, characterized in that, The liquid pumping module includes a manual ball valve, a Y-type filter, a filling pump and a second one-way valve sequentially connected between the medium box and the output end of the first pressurizing cylinder; a vacuum pump and a first pneumatic needle valve are also connected between the medium box and the cladding tube.

3. The biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes according to claim 1, characterized in that, The seal includes a first sealing ferrule and a second sealing ferrule arranged in sequence in the connection hole, and one end of the cladding tube passes through the first sealing ferrule and the second sealing ferrule in sequence; a plurality of first screw holes are further formed in the second sealing ferrule, and the first screw holes are used for installing screws to lock and limit the first sealing ferrule and the second sealing ferrule in the connection hole; a limiting boss is further arranged on one side of the second sealing ferrule, and the limiting boss is inserted into the first sealing ferrule; a C-shaped sealing ring is further sleeved on the outer wall of the limiting boss; an O-shaped sealing ring is further nested on the side wall of the first sealing ferrule in contact with the bottom of the connection hole.

4. The biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes according to claim 3, characterized in that, A limiting hole penetrating to the other side is further arranged on one side of the connection ring; the pressing assembly includes a locking sleeve, the locking sleeve has a conical structure, and the sharp end of the locking sleeve is inserted into the limiting hole, and the other end of the locking sleeve is inserted into the connection hole and abuts against the second sealing ferrule; a locking hole penetrating to the other end is further formed at one end of the locking sleeve, and one end of the cladding tube passes through the locking hole.

5. The biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes according to claim 4, characterized in that, A plurality of locking raised blocks for increasing friction are further arranged on the inner wall of the locking hole.

6. The biaxial fatigue performance test system for axial internal pressure combined loading of nuclear fuel cladding tubes according to claim 5, wherein, A mandrel is further arranged at each of the two ends inside the cladding tube.

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