A nuclear fuel rod out-of-pile heating test device and a test method

Abstract

This invention discloses a nuclear fuel rod reactor external heating test apparatus and method. The nuclear fuel rod reactor external heating test apparatus includes a hot chamber, a quartz glass jar, a neutron radiography device, and multiple fuel pellets. In this application, gas can be first introduced into the quartz glass jar through a gas filling mechanism and heated to simulate the working conditions in a reactor, causing the fuel pellets to crack and conducting a fuel pellet cracking test. At the same time, the gas released after the fuel pellets crack can be discharged to a gas detection mechanism for detection, and fission gas release characteristics can be detected. Gas can also be introduced into the fuel rod specimen through the gas filling mechanism, and steam can be introduced into the quartz glass jar while heating the fuel rod specimen to simulate the steady-state working conditions before a loss-of-coolant accident, causing the fuel pellets to gradually reposition and conducting a fuel pellet repositioning test. Thus, this application can simultaneously conduct experimental research on fuel pellet cracking, repositioning, and fission gas release characteristics under a loss-of-coolant accident, improving experimental efficiency.

Description

Technical Field

[0001] This invention relates to the field of energy utilization technology, and in particular to a nuclear fuel rod reactor external heating test apparatus and test method. Background Technology

[0002] Nuclear energy is an important component of my country's large-scale clean energy resources. Current technologies typically employ novel ceramic nuclear fuels (UN, U2Si3). Under loss-of-coolant (LOD) accidents, the fuel rods of these fuels experience a rapid temperature rise, leading to bulging and deformation under the influence of internal and external pressure differentials. The broken fuel pellets may relocate and accumulate in the bulging area, forming localized hotspots that cause further temperature increases, challenging the long-term cooling requirements of the reactor core. Therefore, it is necessary to study the cracking, relocation, and fission gas release characteristics of nuclear fuel under LOD accidents to demonstrate the safety of nuclear fuel under these conditions.

[0003] Currently, existing nuclear fuel rod reactor external heating test facilities place a relatively long nuclear fuel rod inside a quartz glass chamber and use an infrared heating furnace to heat the sample. Neutron radiography is used to obtain information about the repositioning of the fuel pellets within the cladding. However, the tests do not measure the amount of fission gas released, and the tests can only be performed on irradiated fuel rods whose pellets have already cracked and broken, making it impossible to study the characteristics of pellet cracking and breakage under thermal transients. Therefore, the publicly available test facilities cannot simultaneously conduct studies on pellet cracking and breakage, repositioning, and fission gas release characteristics under loss-of-coolant accidents.

[0004] Therefore, existing technologies still need to be improved and enhanced. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a nuclear fuel rod reactor external heating test device and test method, which aims to solve the problem that the test devices disclosed in the prior art cannot simultaneously carry out the study of pellet cracking and fragmentation, repositioning and fission gas release characteristics under loss-of-water accident.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, a nuclear fuel rod reactor external heating test apparatus includes a hot chamber and a neutron radiography device, wherein a quartz glass jar is disposed within the hot chamber, characterized in that it further includes:

[0008] A fuel rod specimen is placed inside the quartz glass container, and multiple fuel rod blocks are stacked inside the fuel rod specimen;

[0009] An inflation mechanism, connected to the quartz glass container and the fuel rod specimen, is used to inflate the quartz glass container and the fuel rod specimen.

[0010] A heating mechanism is disposed outside the quartz glass container and connected to the fuel rod specimen. The heating mechanism is used to heat the quartz glass container and the fuel rod specimen.

[0011] A gas detection mechanism is connected to the fuel rod specimen, and the gas detection mechanism is used to detect the instantaneous release of gas generated after the pellet cracks;

[0012] A steam supply mechanism, connected to the quartz glass jar, is used to supply steam into the quartz glass jar.

[0013] As a further improvement, the quartz glass container is further provided with a support for fixing the fuel rod specimen, the fuel rod specimen comprising:

[0014] The casing is snapped onto the bracket, and multiple core blocks are stacked inside the casing;

[0015] End plugs are located at both ends of the casing and are used to seal the core block.

[0016] As a further improved technical solution, the inflation mechanism includes:

[0017] A gas cylinder, which is connected to the quartz glass jar via a vent pipe, and contains an inert gas.

[0018] A vent valve is installed on the vent pipe and is used to control the flow of inert gas.

[0019] As a further improved technical solution, the heating mechanism includes:

[0020] A shell heating assembly is arranged outside the heating chamber and connected to the shell for heating the shell;

[0021] An AC heating element is located outside the quartz glass jar and is used to instantly heat the core block.

[0022] As a further improved technical solution, the gas detection mechanism includes:

[0023] A gamma-ray spectrometer, wherein the gamma-ray spectrometer is connected to the quartz glass jar via an exhaust pipe;

[0024] A Dewar flask, connected to the gamma-ray spectrometer, is used to cool the gamma-ray spectrometer.

[0025] The exhaust pipe is provided with a first exhaust branch and a second exhaust branch. The first exhaust branch is connected to the shell and is provided with a first exhaust valve. The second exhaust branch is connected to the quartz glass jar and is provided with a second exhaust valve.

[0026] As a further improved technical solution, the steam supply mechanism includes:

[0027] A steam generator, which is connected to the quartz glass jar via a steam pipeline;

[0028] A first electric pump is installed at one end of the steam generator and is used to discharge steam from the steam generator.

[0029] A superheater is installed on the steam pipeline and is used to heat the steam discharged from the steam generator into the quartz glass tank.

[0030] As a further improved technical solution, the nuclear fuel rod reactor external heating test device also includes:

[0031] A gas purification mechanism, which is connected to the gamma-ray spectrometer, is used to purify the gas detected by the gamma-ray spectrometer.

[0032] As a further improved technical solution, the air purification mechanism includes:

[0033] A washing tank is connected to the gamma spectroscopy analyzer via a clean gas pipeline and is used to purify the gas discharged from the gamma spectroscopy analyzer.

[0034] A clean air valve is installed on the clean air pipeline;

[0035] A filter, connected to the washing tank, is used to filter the gas purified by the washing tank.

[0036] As a further improved technical solution, the shell heating assembly includes:

[0037] A DC power supply is electrically connected to both ends of the casing via wires for heating the casing.

[0038] Secondly, a method for testing external heating of a nuclear fuel rod reactor, based on the nuclear fuel rod reactor external heating test apparatus as described above, includes:

[0039] The fuel rod specimen was fixed, the gas filling mechanism was started to fill the quartz glass container with gas, and the heating mechanism was started to heat the pellet until the pellet cracked. The cracked state of the pellet was photographed using a neutron radiography device.

[0040] The instantaneous release of fission gas is detected by a gas detection agency;

[0041] The gas filling mechanism is activated to fill the fuel rod specimen with gas, the steam supply mechanism is activated to introduce steam into the quartz glass tank, and the heating mechanism is controlled to heat the fuel rod specimen until the pellet is repositioned. A photograph of the pellet repositioning state is then obtained using a neutron radiograph.

[0042] The technical solution adopted in this invention has the following beneficial effects:

[0043] In this application, gas can first be introduced into the quartz glass container through a gas filling mechanism to expel the air inside the quartz glass container and then heat it to simulate the working conditions in a reactor until the pellet cracks, thus conducting a pellet cracking test. At the same time, the gas released after the pellet cracks can be discharged to a gas detection mechanism for detection, and the instantaneous release amount and gas properties of the released gas can be detected to achieve a fission gas release characteristic test. Afterwards, the fuel rod specimen can also be gas-filled through the gas filling mechanism for pre-pressurization, and superheated steam can be introduced into the quartz glass container to simultaneously heat the fuel rod specimen to simulate the steady-state working conditions before a loss-of-coolant accident, and then heated until the pellet is repositioned to conduct a pellet repositioning test. Thus, this application can simultaneously conduct experimental research on pellet cracking, repositioning, and fission gas release characteristics under a loss-of-coolant accident, improving experimental efficiency. Attached Figure Description

[0044] Figure 1 This invention provides a schematic diagram of the structure of an external heating test device for nuclear fuel rods in a nuclear reactor.

[0045] Figure 2 A flowchart of a nuclear fuel rod reactor external heating test method provided by the present invention.

[0046] 1. Hot chamber; 2. Quartz glass jar; 3. Bulk cartridge; 4. Fuel rod specimen; 5. Filling mechanism; 6. Heating mechanism; 7. Gas detection mechanism; 8. Steam supply mechanism; 9. Purification mechanism; 10. Base; 11. Cover plate; 12. First thermocouple; 13. Second thermocouple; 401. Bracket; 402. Sheath; 403. Upper plug; 404. Lower plug; 405. Groove; 406. Spring; 407. Coating layer; 501. Filling cylinder; 502. First venting branch; 503. Second venting branch; 504. First venting valve; 505. Second venting valve; 601. DC power supply; 602. Wire; 60 3. Electromagnetic heating coil; 604. AC power supply; 701. Gamma spectroscopy analyzer; 702. Dewar flask; 703. First exhaust branch; 704. Second exhaust branch; 705. First exhaust valve; 706. Second exhaust valve; 801. Steam generator; 802. First electric pump; 803. Superheater; 804. First steam branch; 805. Second steam branch; 806. Third steam branch; 807. First steam valve; 808. Second electric pump; 809. Second steam valve; 8010. Condenser; 901. Washing tank; 902. Clean air valve; 903. Filter; 904. Clean air pipeline. Detailed Implementation

[0047] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0048] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on the other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to the other component.

[0049] It should also be noted that the same or similar reference numerals in the accompanying drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0050] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0051] Nuclear energy is an important component of my country's large-scale clean energy resources. Current technologies typically employ novel ceramic nuclear fuels (UN, U2Si3). Under loss-of-coolant (LOD) accidents, the fuel rods of these fuels experience a rapid temperature rise, leading to bulging and deformation under the influence of internal and external pressure differentials. The broken fuel pellets may relocate and accumulate in the bulging area, forming localized hotspots that cause further temperature increases, challenging the long-term cooling requirements of the reactor core. Therefore, it is necessary to study the cracking, relocation, and fission gas release characteristics of nuclear fuel under LOD accidents to demonstrate the safety of nuclear fuel under these conditions.

[0052] Currently, existing nuclear fuel rod reactor external heating test facilities place a relatively long nuclear fuel rod inside a quartz glass chamber and use an infrared heating furnace to heat the sample. Neutron radiography is used to obtain information about the repositioning of the fuel pellets within the cladding. However, the tests do not measure the amount of fission gas released, and the tests can only be performed on irradiated fuel rods whose pellets have already cracked and broken, making it impossible to study the characteristics of pellet cracking and breakage under thermal transients. Therefore, the publicly available test facilities cannot simultaneously conduct studies on pellet cracking and breakage, repositioning, and fission gas release characteristics under loss-of-coolant accidents.

[0053] Therefore, this application aims to provide a solution that can solve the above-mentioned technical problems, the details of which will be described in subsequent embodiments.

[0054] Please see Figure 1 and Figure 2 , Figure 1 This invention provides a schematic diagram of the structure of an external heating test device for nuclear fuel rods in a nuclear reactor. Figure 2This invention provides a flowchart of a nuclear fuel rod reactor external heating test method. The invention provides a nuclear fuel rod reactor external heating test apparatus and method. The nuclear fuel rod reactor external heating test apparatus includes a hot chamber 1 and a neutron radiography device (not shown in the figure). The hot chamber 1 contains a quartz glass jar 2 and further includes a fuel rod specimen 4, a gas filling mechanism 5, a heating mechanism 6, a gas detection mechanism 7, and a steam supply mechanism 8. The fuel rod specimen 4 is disposed inside the quartz glass jar 2, and multiple core blocks 3 are stacked inside the fuel rod specimen 4. The gas filling mechanism 5 is connected to the quartz glass jar 2 and the fuel rod specimen 4 to provide gas to the quartz glass jar 2. The quartz glass jar 2 and the fuel rod specimen are filled with gas; a heating mechanism 6 is disposed outside the quartz glass jar 2 and connected to the fuel rod specimen 4. The heating mechanism 6 is used to heat the quartz glass jar 2 / the fuel rod specimen 4 to cause the core block 3 to crack / reposition; a gas detection mechanism 7 is connected to the fuel rod specimen 4. The gas detection mechanism 7 is used to detect the instantaneous release of gas generated after the core block 3 cracks; a steam supply mechanism 8 is connected to the quartz glass jar 2 to supply steam to the quartz glass jar 2 when the core block 3 is repositioned.

[0055] The working principle of the nuclear fuel rod reactor external heating test device provided in this embodiment is as follows: The fuel rod specimen 4 fixes the core block 3 in the quartz glass jar 2. The gas filling mechanism 5 is controlled to fill the quartz glass jar 2 with gas to expel air, and the heating mechanism 6 is controlled to heat the quartz glass jar 2, so that the core block 3 heats up rapidly until the core block 3 cracks. The cracked state of the core block 3 is observed by a neutron radiograph. The cracking of the core block 3 releases fission gas, which is discharged to the gas detection mechanism 7. The instantaneous release amount of fission gas is detected by the gas detection mechanism 7. Then, the gas filling mechanism 5 fills the fuel rod specimen 4 with gas to pre-pressurize the cracked core block 3. The steam supply mechanism 8 is controlled to introduce steam into the quartz glass jar 2, and the heating mechanism 6 is controlled to heat the fuel rod specimen 4 until the core block 3 is repositioned. The repositioned state of the core block 3 is observed by a neutron radiograph.

[0056] The beneficial effects of the nuclear fuel rod reactor external heating test device provided in this embodiment are at least as follows: In this application, gas can first be introduced into the quartz glass tank 2 through the gas filling mechanism 5, and the air inside the quartz glass tank 2 can be discharged. Then, it can be heated by the heating mechanism 6 to simulate the working conditions in the reactor until the pellet 3 cracks. A pellet 3 cracking test is then conducted. At the same time, the gas released after the pellet 3 cracks can be discharged to the gas detection mechanism 7 for detection. The instantaneous release amount and gas properties of the released gas are detected to realize the gas release characteristics test inside. Then, gas can also be introduced into the fuel rod test piece 4 through the gas filling mechanism 5 to pre-pressurize the pellet 3 and introduce steam. At the same time, the heating mechanism 6 is controlled to heat the fuel rod test piece 4 to simulate the steady-state working conditions before the loss-of-coolant accident until the pellet 3 gradually repositions. A pellet 3 repositioning test is then conducted. Thus, this application can simultaneously conduct experimental research on the cracking, repositioning, and fission gas release characteristics of the pellet 3 under the loss-of-coolant accident, thereby improving the experimental efficiency.

[0057] In this embodiment, a base 10 is fixed at the bottom of the quartz glass jar 2, the quartz glass jar 2 and the base 10 are sealed with sealant, and a cover plate 11 is sealed at the top of the quartz glass jar 2 to ensure the airtightness of the quartz glass jar 2.

[0058] Please see Figure 1 In this embodiment, the quartz glass jar 2 is further provided with a support 401 for fixing the fuel rod test piece 4. The fuel rod test piece 4 includes a casing 402 and end plugs. The support 401 is disposed inside the quartz glass jar 2. The casing 402 is snapped onto the support 401, and multiple fuel rods 3 are stacked inside the casing 402. End plugs are disposed at both ends of the casing 402 and are used to seal the fuel rods 3. The end plugs include an upper end plug 403 and a lower end plug 404. In use, the fuel rods 3 are first stacked into the casing 402, and then the upper end plug 403 and the lower end plug 404 are attached to the casing. The cladding 402 is welded to prevent the end plug from being ejected by the force generated when the pellet 3 cracks. The cladding 402 with the welded end plug is then fixed to the support 401. The support 401 provides axial support and a certain radial constraint for the cladding 402, allowing the cladding 402 to expand and deform with sufficient axial freedom after heating, preventing the cladding 402 from bending and deforming due to excessive axial constraint. The cladding 402 can provide constraint for the pellet 3 in the test, simulating the actual reactor service process during the pellet 3 cracking test, and providing boundary conditions for the pellet 3 during the pellet 3 repositioning test, simulating the dormant process of a loss-of-coolant accident.

[0059] In an embodiment of the present invention, a groove 405 for connecting pipelines is provided on the upper end plug 403. This groove 405 is connected to the pipelines of the inflation mechanism 5 and the gas detection mechanism 7, which facilitates the delivery of the gas released from the core block 3 to the gas detection mechanism 7 for detection after the core block 3 cracks. At the same time, it allows the inflation mechanism 5 to conveniently introduce gas into the shell 402 for pre-pressurization during repositioning tests. It should also be understood that the end plug and the shell 402 in this application are both made of zirconium alloy material to ensure that no eutectic alloy is generated during welding and to improve the bonding between the end plug and the shell 402.

[0060] In an embodiment of the present invention, a spring 406 is also fixedly connected to the upper plug 403. The spring 406 provides axial preload to the core block 3, so that each core block 3 is stacked firmly and misalignment is avoided during the transfer and unloading process before and after the test. At the same time, in the core block 3 cracking test, the spring 406 can also absorb the force generated by the axial deformation of the core block 3 during the overheating expansion process, so as to avoid the upper plug 403 and the lower plug 404 from breaking the seal between the upper plug 403 and the shell 402 due to excessive axial stress.

[0061] Specifically, please refer to Figure 1 A coating layer 407 is also provided on the outside of the cladding 402. The coating layer 407 uses an ablative material to simulate the coolant in the reactor. In the chip 3 cracking test, it can absorb the heat of the cladding 402, prevent the cladding 402 from undergoing high-temperature creep deformation, and avoid premature repositioning of the chip 3. At the same time, it also makes the heat transfer path from the inside to the outside, ensuring that the cracking pattern of the chip 3 is consistent with the actual service conditions of the projection team.

[0062] Please refer to an embodiment of the present invention. Figure 1 A first thermocouple 12 is installed inside the quartz glass tank 2, and a second thermocouple 13 is installed in the middle of the cladding 402. In the core block 3 cracking test, the heating mechanism 6, in conjunction with the second thermocouple 13, rapidly heats the core block 3 to a specified temperature, simulating the step power rise condition in the reactor. In the core block 3 repositioning test, the first thermocouple 12, in conjunction with the steam supply mechanism 8, keeps the steam temperature inside the quartz glass tank 2 stable, simulating the transient condition of a loss-of-coolant accident. The accuracy of the test is improved by the cooperation of the first thermocouple 12 and the second thermocouple 13.

[0063] In this embodiment, please refer to Figure 1The inflation mechanism 5 includes an inflation cylinder 501, which is connected to the quartz glass jar 2 via a ventilation pipe. The inflation cylinder 501 contains an inert gas, which in this embodiment is argon. The ventilation pipe includes a first ventilation branch 502 and a second ventilation branch 503. The first ventilation branch 502 connects to the casing 402 and has a first ventilation valve 504 to control gas flow. The second ventilation branch 503 connects to the quartz glass jar 2 and has a second ventilation valve 505. During the core block 3 cracking process… During the test, the first vent valve 504 is closed and the second vent valve 505 is opened to introduce argon gas into the quartz glass jar 2, so that the air inside the quartz glass jar 2 can be discharged and an inert atmosphere can be provided for the cladding 402 to prevent oxidation of the cladding 402. When conducting the core block 3 repositioning test, the first vent valve 504 is opened and the second vent valve 505 is closed to directly introduce inert gas into the cladding 402 to pressurize the cladding 402 and simulate the expansion of the cladding 402 under the action of high temperature and high pressure difference in a loss-of-water accident. In addition, after the test, the first vent valve 504 or the second vent valve 505 can be opened randomly to purge the harmful gases generated during the test.

[0064] It should be understood that the argon gas described in the above embodiments is only one implementation method of this application, and other inert gases such as helium, neon, krypton, and xenon can also be used.

[0065] In one embodiment of this application, the heating mechanism 6 includes a shell 402 heating assembly and an AC heating assembly. The shell 402 heating assembly is arranged outside the hot chamber 1 and connected to the shell 402 for heating the shell 402 during a repositioning test; the AC heating assembly is located outside the quartz glass jar 2 and is used to instantaneously heat the core block 3.

[0066] Specifically, the heating assembly of the casing 402 includes a DC power supply 601, which is electrically connected to both ends of the casing 402 via wires 602. During the repositioning test, the DC power supply 601 is activated and directly heats the casing 402 via wires 602, causing the casing 402 to expand and deform under the combined action of internal and external pressure difference and temperature rise, which is consistent with the transient process of a water loss accident.

[0067] It should be understood that the above is only a description of one embodiment of the heating assembly for the casing 402. In other embodiments of the present invention, the heating assembly for the casing 402 further includes an infrared heating furnace, which is connected to the casing 402 and directly heats the casing 402 through radiation heat transfer, causing the casing 402 to bulge and deform under the action of internal and external pressure difference and temperature rise, simulating the transient process of water loss accident.

[0068] In this embodiment, an electromagnetic heating coil 603 is installed on the outer casing of the quartz glass container 2. The electromagnetic heating coil 603 is connected to the AC power supply 604 through the wire 602 to form an AC heating assembly. In the cracking test of the fuel cell 3, because the electromagnetic heating coil 603 has a large induction heating power and is easy to adjust by frequency conversion, the AC power supply 604 can be started, which can make the fuel cell 3 be heated rapidly under non-contact conditions, simulating the high temperature and rapid power change of nuclear fuel rods during service, while also completely preserving the real cracking and breakage morphology of the fuel cell 3.

[0069] In this embodiment, please refer to Figure 1 The gas detection mechanism 7 includes a gamma-ray spectrometer 701 and a Dewar flask 702; the gamma-ray spectrometer 701 is connected to the quartz glass jar 2 via an exhaust pipe; the Dewar flask 702 is connected to the gamma-ray spectrometer 701 and is used to cool the gamma-ray spectrometer 701; in an embodiment of the present invention, the exhaust pipe is provided with a first exhaust branch 703 and a second exhaust branch 704, the first exhaust branch 703 is connected to the casing 402, and a first exhaust valve is provided on the first exhaust branch 703. The door 705 and the second exhaust branch 704 are connected to the quartz glass jar 2, and the second exhaust branch 704 is equipped with a second exhaust valve 706. When the core block 3 cracking test is carried out, the first exhaust valve 705 is opened and the second exhaust valve 706 is closed. The gas released by the core block 3 cracking is discharged to the gamma energy spectrum analyzer 701 through the first exhaust branch 703 for gas property detection. After each test, the second exhaust valve 706 can be opened to purge and discharge the gas in the quartz glass jar 2 to facilitate the disassembly of the test device.

[0070] It should be noted that the Dewar flask 702 contains liquid nitrogen for cooling, which can be used to cool the gamma-ray spectrometer 701 and improve its service life. In addition, the Dewar flask 702 can also store other cryogenic working gases to facilitate cooling of the gamma-ray spectrometer 701.

[0071] Please refer to an embodiment of the present invention. Figure 1The steam supply mechanism 8 includes: a steam generator 801, a first electric pump 802, and a superheater 803; the steam generator 801 is connected to the quartz glass jar 2 via a steam pipeline; the first electric pump 802 is located at one end of the steam generator 801 and is used to discharge steam from the steam generator 801; the superheater 803 is located on the steam pipeline and is used to heat the steam discharged from the steam generator 801 into the quartz glass jar 2; the steam pipeline includes a first steam branch 804, a second steam branch 805, and a third steam branch 806, all of which are connected to the quartz glass jar 2; the first electric pump 802 and the superheater 803 are sequentially arranged on the first steam branch 804, and a first steam valve 807 is also provided on the first steam branch 804. To facilitate control of steam input, a second electric pump 808 is installed on the second steam branch 805. After the repositioning test of the core block 3 is completed, some liquefied steam will remain at the bottom of the quartz glass tank 2. By starting the second electric pump 808, the liquid can be recovered into the steam generator 801 for recycling. A second steam valve 809 and a condenser 8010 are installed on the third steam branch 806. During the repositioning test, the first steam valve 807 and the third steam valve are opened simultaneously. The steam generated by the steam generator 801 is heated to a superheated state by the superheater 803 and flows into the quartz glass tank 2, filling the quartz glass tank 2 with superheated steam. This simulates the high-temperature steam after a loss-of-coolant accident in an actual nuclear reactor, thus forming a steam circulation loop to improve test efficiency and accuracy.

[0072] In this embodiment, the present invention is also provided with a gas purification mechanism 9. During the experiment, both the gas released by the cracking of the core block 3 and the inert gas flowing during the experiment need to be purified before being discharged into the atmosphere. Therefore, the gas purification mechanism 9 is connected to the gamma spectrum analyzer 701. After being detected by the gamma spectrum analyzer 701, the gas is purified and discharged to avoid the gas generated by the experiment from polluting the atmosphere.

[0073] Specifically, the gas purification mechanism 9 includes a washing tank 901, a gas purification valve 902, and a filter 903. The washing tank 901 is connected to the gamma-ray spectrometer 701 via a gas purification pipeline 904 and is used to purify the gas discharged from the gamma-ray spectrometer 701. The gas purification valve 902 is installed on the gas purification pipeline 904. The filter 903 is connected to the washing tank 901 and is used to filter the gas purified by the washing tank 901. During the gas release test, the gas purification valve 902 is first closed so that the gamma-ray spectrometer can measure the amount of gas released from the cracking of the core block 3. After the test, the gas purification valve 902 is opened, and the released gas is discharged into the washing tank 901 for purification, and then filtered by the filter 903 before being discharged into the atmosphere.

[0074] It should be noted that an absorbent is stored in the washing tank 901. The absorbent can be sodium hydroxide, sodium thiosulfate, or an aqueous solution of mercuric nitrate and nitric acid to purify the iodine in the fission gas. Alternatively, Freon can be used to absorb the krypton in the fission gas, so as to purify the gas, make the gas emission meet the standards, and improve the safety of the test. At the same time, the filter 903 is made of activated carbon material to absorb the iodine in the fission gas.

[0075] Secondly, a method for testing external heating of a nuclear fuel rod reactor, based on the nuclear fuel rod reactor external heating test apparatus as described above, includes:

[0076] S100, fix the fuel rod specimen 4, start the gas filling mechanism 5 to fill the quartz glass tank 2, and start the heating mechanism 6 to heat the pellet 3 until the pellet 3 cracks, and obtain a photo of the cracked state of the pellet 3 through the neutron radiography equipment.

[0077] Specifically, multiple core blocks 3 are stacked inside the cladding 402. The upper plug 403 and the lower plug 404 are welded to both ends of the cladding 402, and the stacking of core blocks 3 is tightened by springs 406. Then, the second vent valve 505, the second exhaust valve 706, and the clean gas valve 902 are opened, while all other valves are closed. Argon gas is introduced into the quartz glass jar 2 to expel the air inside the quartz glass jar 2, providing an inert atmosphere for the cladding 402 and preventing oxidation of the cladding 402. Then, the AC power supply 604 is adjusted to start the induction heating coil, which, in conjunction with the second thermocouple 13, rapidly heats the core blocks 3 to a specified temperature, simulating the step power rise condition in the reactor, causing the core blocks 3 to crack. Then, the AC power supply 604 is turned off to stop heating. Under the detection of the second thermocouple 13, the core blocks 3 are allowed to cool to room temperature, and a photograph of the cracked state of the core blocks 3 is obtained using a neutron radiography device.

[0078] S200, The instantaneous release of fission gas is detected by the gas detection mechanism 7;

[0079] Specifically, while conducting the core block 3 cracking test, the first exhaust valve 705 is opened, and the fission gas after the core block 3 cracks is discharged to the gamma spectrum analyzer 701 through the first exhaust branch 703. The gamma spectrum analyzer 701 detects the properties and release amount of the fission gas, and the gamma spectrum analyzer 701 is cooled by liquid nitrogen in the Dewar flask 702 to improve the accuracy of the test. Then, the purification valve is opened, and the fission gas and inert gas are discharged into the atmosphere after being purified and filtered by the washing tank 901 and the filter 903, thus ending the fission gas detection test.

[0080] S300: Start the gas filling mechanism 5 to fill the fuel rod test piece 4 with gas, start the steam supply mechanism 8 to introduce steam into the quartz glass tank 2, and control the heating mechanism 6 to heat the fuel rod test piece 4 until the pellet 3 is repositioned, and obtain a photo of the repositioned state of the pellet 3 through the neutron radiography equipment.

[0081] Specifically, firstly, the first vent valve 504 is opened to adjust the outlet pressure of the gas cylinder 501, pre-pressurizing the casing 402. After pre-pressurization, the first vent valve 504 is closed, and the first steam valve 807 and the second steam valve 809 are opened to start the steam generator 801. Steam flows through the superheater 803 to the quartz glass jar 2, and the first thermocouple 12 is used to keep the superheated steam in the quartz glass jar 2 stable. The superheated steam is condensed and returned to the steam generator 801 through the condenser 8010 on the third steam branch 806. At the same time, the DC power supply 601 is adjusted to heat the casing 402. The second thermocouple 13 is used to keep the cracked core block 3 in a steady-state condition before the water loss accident at a specific temperature for a period of time. The DC power supply 601 is then adjusted to rapidly heat the casing 402, simulating the water loss accident. In transient conditions, during the process of thermal failure deformation within the cladding 402, the core 3 gradually repositions itself. After the cladding 402 explodes, the DC power supply 601 is shut off. At this time, the fission gas inside the cladding 402 is released into the quartz glass jar 2. The first steam valve 807 and the second steam valve 809 are closed in sequence. After the cladding 402 and the core 3 cool to room temperature, the second vent valve 505 and the second exhaust valve 706 are opened to purge the gas inside the jar into the washing tank 901 for purification. The gas is then discharged into the atmosphere after passing through the filter 903. After purging, the second vent valve 505 and the second exhaust valve 706 are closed. At the same time, the second electric pump 808 is started to pump the liquid water accumulated in the quartz glass jar 2 back into the steam generator 801. Then, a photograph of the repositioning state of the core 3 is obtained through a neutron radiograph.

[0082] In summary, the technical solution adopted in this invention has the following beneficial effects:

[0083] 1. In this application, the air in the quartz glass container 2 can be discharged through the gas filling mechanism 5 and heated to simulate the working conditions in the reactor, causing the pellet 3 to crack and conduct a pellet 3 cracking test. At the same time, the gas released after the pellet 3 cracks can be discharged to the gas detection mechanism 7 for detection, and the instantaneous release amount and gas properties of the released gas can be detected to realize the gas release characteristic test. Afterwards, the pellet 3 can be pre-pressurized through the gas filling mechanism 5 and superheated steam can be introduced. At the same time, the fuel rod specimen 4 can be heated to simulate the steady-state working conditions before the loss of water accident, so that the pellet 3 gradually repositions and a pellet 3 repositioning test can be conducted. Thus, this application can simultaneously conduct experimental research on the cracking, repositioning and fission gas release characteristics of the pellet 3 under the loss of water accident, thereby improving the experimental efficiency.

[0084] 2. In this application, a slot 405 for connecting pipelines is provided on the upper plug 403. The slot 405 is connected to the pipelines of the inflation mechanism 5 and the gas detection mechanism 7, so that the gas released by the core block 3 after the core block 3 cracks can be transported to the gas detection mechanism 7 for detection. At the same time, it can facilitate the inflation mechanism 5 to introduce gas into the shell 402 for pre-pressurization during the repositioning test.

[0085] 3. In this application, a spring 406 is also fixedly connected to the upper plug 403. The spring 406 provides axial preload to the core block 3, so that each core block 3 is stacked firmly and the core block 3 is not misaligned during the transfer and unloading process before and after the test. At the same time, in the core block 3 cracking test, the spring 406 can also absorb the force generated by the axial deformation of the core block 3 during the overheating expansion process, so as to prevent the upper plug 403 and the lower plug 404 from breaking the seal between the upper plug 403 and the shell 402 due to excessive axial stress.

[0086] 4. In this application, a first thermocouple 12 is installed inside the quartz glass tank 2, and a second thermocouple 13 is installed in the middle of the cladding 402. In the core block 3 cracking test, the heating mechanism 6, in conjunction with the second thermocouple 13, rapidly heats the core block 3 to a specified temperature to simulate the step power rise condition in the reactor. In the core block 3 repositioning test, the first thermocouple 12, in conjunction with the steam supply mechanism 8, keeps the steam temperature inside the quartz glass tank 2 stable to simulate the transient condition of a loss-of-coolant accident. The accuracy of the test is improved through the cooperation of the first thermocouple 12 and the second thermocouple 13.

[0087] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the solutions disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

Claims

1. A nuclear fuel rod reactor external heating test apparatus, comprising a hot chamber and a neutron radiography device, wherein a quartz glass jar is disposed within the hot chamber, characterized in that, It also includes: A fuel rod specimen is placed inside the quartz glass container, and multiple fuel rod blocks are stacked inside the fuel rod specimen; An inflation mechanism, connected to the quartz glass container and the fuel rod specimen, is used to inflate the quartz glass container and the fuel rod specimen with gas; A heating mechanism is disposed outside the quartz glass container and connected to the fuel rod specimen. The heating mechanism is used to heat the quartz glass container and the fuel rod specimen. A gas detection mechanism is connected to the fuel rod specimen, and the gas detection mechanism is used to detect the instantaneous release of gas generated after the pellet cracks; A steam supply mechanism, connected to the quartz glass jar, is used to supply steam into the quartz glass jar.

2. The nuclear fuel rod reactor external heating test apparatus according to claim 1, characterized in that, The quartz glass container is also equipped with a support for fixing the fuel rod specimen, which includes: The casing is snapped onto the bracket, and multiple core blocks are stacked inside the casing; End plugs are located at both ends of the casing and are used to seal the core block.

3. The nuclear fuel rod reactor external heating test apparatus according to claim 1, characterized in that, The inflation mechanism includes: A gas cylinder, which is connected to the quartz glass jar via a vent pipe, and contains an inert gas. A vent valve is installed on the vent pipe and is used to control the flow of inert gas.

4. The nuclear fuel rod reactor external heating test apparatus according to claim 2, characterized in that, The heating mechanism includes: A shell heating assembly is arranged outside the heating chamber and connected to the shell for heating the shell; An AC heating element is located outside the quartz glass jar and is used to instantly heat the core block.

5. The nuclear fuel rod reactor external heating test apparatus according to claim 2, characterized in that, The gas detection mechanism includes: A gamma-ray spectrometer, wherein the gamma-ray spectrometer is connected to the quartz glass jar via an exhaust pipe; A Dewar flask, connected to the gamma-ray spectrometer, is used to cool the gamma-ray spectrometer. The exhaust pipe is provided with a first exhaust branch and a second exhaust branch. The first exhaust branch is connected to the shell and is provided with a first exhaust valve. The second exhaust branch is connected to the quartz glass jar and is provided with a second exhaust valve.

6. The nuclear fuel rod reactor external heating test apparatus according to claim 1, characterized in that, The steam supply mechanism includes: A steam generator, which is connected to the quartz glass jar via a steam pipeline; A first electric pump is installed at one end of the steam generator and is used to discharge steam from the steam generator. A superheater is installed on the steam pipeline and is used to heat the steam discharged from the steam generator into the quartz glass tank.

7. The nuclear fuel rod reactor external heating test apparatus according to claim 5, characterized in that, It also includes: A gas purification mechanism, which is connected to the gamma-ray spectrometer, is used to purify the gas detected by the gamma-ray spectrometer.

8. The nuclear fuel rod reactor external heating test apparatus according to claim 7, characterized in that, The air purification mechanism includes: A washing tank is connected to the gamma spectroscopy analyzer via a clean gas pipeline and is used to purify the gas discharged from the gamma spectroscopy analyzer. A clean air valve is installed on the clean air pipeline; A filter, connected to the washing tank, is used to filter the gas purified by the washing tank.

9. The nuclear fuel rod reactor external heating test apparatus according to claim 4, characterized in that, The casing heating assembly includes: A DC power supply is electrically connected to both ends of the casing via wires for heating the casing.

10. A method for testing external heating of a nuclear fuel rod reactor, based on the external heating test apparatus for nuclear fuel rod reactors as described in any one of claims 1-9, characterized in that, It includes: The fuel rod specimen was fixed, the gas filling mechanism was started to fill the quartz glass container with gas, and the heating mechanism was started to heat the pellet until the pellet cracked. The cracked state of the pellet was photographed using a neutron radiography device. The instantaneous release of fission gas is detected by a gas detection agency; The gas filling mechanism is activated to fill the fuel rod specimen with gas, the steam supply mechanism is activated to introduce steam into the quartz glass tank, and the heating mechanism is controlled to heat the fuel rod specimen until the pellet is repositioned. A photograph of the pellet repositioning state is then obtained using a neutron radiograph.

Images