Nuclear fuel behavior out-of-pile simulation experiment device under reactivity introduction accident

Abstract

The invention relates to the technical field of nuclear fuel accident simulation, and discloses a nuclear fuel behavior out-of-pile simulation experiment device under a reactive introduction accident, the nuclear fuel behavior out-of-pile simulation experiment device comprises a high-temperature steam chamber, a cladding, an insulating tube, at least one core block, an electrifying assembly and an induction heating assembly, the cladding is arranged in the high-temperature steam chamber, the insulating tube is arranged in the cladding, and the core block is arranged in the high-temperature steam chamber; at least one core block is arranged in the insulating tube, and an electrifying assembly and an induction heating assembly are further arranged in the high-temperature steam chamber; the power-on assembly is connected with the two ends of the core block, the core block can be powered on, the core block is heated, the conductivity of the core block can be changed, induction heating can be conducted on the core block through the induction heating assembly, short-time extremely-high heating power can be provided through superposition of the core block and the induction heating assembly, and rapid high-power density change under a reactive introduction accident is simulated. The technical problems of low heating power, non-self-heating and insufficient heat penetration depth in the traditional method are effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel accident simulation, and particularly to an out-of-reactor simulation experiment device for nuclear fuel behavior under a reactivity insertion accident. Background Art

[0002] A reactivity insertion accident (RIA) is a design basis accident for a pressurized water reactor. In a typical RIA accident, a nuclear fuel rod may experience a series of phenomena such as a power surge, a rapid rise in pellet temperature and thermal expansion, pellet-cladding mechanical interaction (PCMI), cladding mechanical failure, and melting of fuel pellets and cladding, which seriously threatens the structural integrity of the fuel element. However, accurately grasping the thermal-hydraulic behavior of nuclear fuel elements under RIA accidents faces great challenges.

[0003] In the prior art, a high-temperature furnace is generally used in combination with laser heating to simulate the reactivity-initiated accident of pellets. However, in the laser heating method, the power is concentrated on the surface of the pellets, the penetration depth is relatively shallow, and it cannot heat evenly, nor can it reflect the characteristics of fuel power surge in RIA accidents.

[0004] In view of this, the prior art still needs to be improved and developed. Summary of the Invention

[0005] In view of the deficiencies of the above prior art, the purpose of the present invention is to provide an out-of-reactor simulation experiment device for nuclear fuel behavior under a reactivity insertion accident, aiming to solve the problems in the prior art that the pellets are unevenly heated and the fuel power surge cannot be achieved by the laser heating method.

[0006] The technical solution adopted by the present invention to solve the technical problems is as follows: An out-of-reactor simulation experiment device for nuclear fuel behavior under a reactivity insertion accident, comprising: A high-temperature steam chamber; A cladding, arranged inside the high-temperature steam chamber; An insulating tube, arranged inside the cladding; the outer surface of the insulating tube abuts against the inner wall of the cladding; At least one pellet, arranged inside the insulating tube; the outer surface of the pellet abuts against the inner wall of the insulating tube; An energizing component, arranged outside the high-temperature steam chamber and connected to both ends of the pellet through wires respectively, for energizing the pellet; An induction heating component, partially extending into the high-temperature steam chamber and arranged around the outside of the cladding, for heating the pellet.

[0007] Further, the energizing component includes: A wide-range voltage DC power supply, arranged outside the high-temperature steam chamber; Two electrodes are respectively arranged on the surface and the bottom surface of the core block; the wide-range voltage DC power supply is connected to the two electrodes respectively through two wires, and is used for energizing the core block and making the core block generate heat by itself.

[0008] Furthermore, the induction heating assembly includes: A heating coil is arranged around the outside of the cladding; A high-frequency power supply main unit is arranged outside the high-temperature steam chamber and is connected to the heating coil through a wire.

[0009] Furthermore, the cladding is a hydrogen-permeable cladding.

[0010] Furthermore, it further includes: An infrared temperature measurement camera is arranged at the top of the high-temperature steam chamber; an infrared visible glass window is arranged at the top of the high-temperature steam chamber, a germanate glass window is arranged at the top of the cladding, and the infrared temperature measurement camera corresponds to the infrared visible glass window and the germanate glass window of the cladding.

[0011] Furthermore, an inlet is arranged at the bottom of the high-temperature steam chamber, and outlets are arranged at the top of both sides of the high-temperature steam chamber.

[0012] Furthermore, a quartz glass diversion tube is arranged on the bottom wall inside the high-temperature steam chamber, the quartz glass diversion tube is sleeved outside the cladding, and the induction heating assembly is located between the quartz glass diversion tube and the cladding.

[0013] Furthermore, a pressure gauge and a thermometer are arranged inside the high-temperature steam chamber.

[0014] Furthermore, the insulating tube is a corundum insulating tube.

[0015] Furthermore, there are multiple core blocks, and the multiple core blocks are stacked and arranged inside the insulating tube, and the surface of the core block at the topmost part is lower than the top surface of the insulating tube.

[0016] Compared with the prior art, the beneficial effects of the present invention are: In the present invention, a cladding is provided inside a high-temperature steam chamber. An insulating tube is provided inside the cladding, and fuel pellets are provided inside the insulating tube. An energizing component and an induction heating component are also provided inside the high-temperature steam chamber. By connecting the energizing component to both ends of the fuel pellets, the fuel pellets can be energized, causing the fuel pellets themselves to generate heat. At the same time, the conductivity of the fuel pellets can be changed. Furthermore, the fuel pellets can be inductively heated by the induction heating component. The superposition of the two can provide an extremely high heating power in a short time, simulating the rapid high-power density change under a reactivity insertion accident, effectively solving the technical problems of low traditional heating power, non-self-heating, and insufficient thermal penetration depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 FIG. is a schematic diagram of the structures of the energizing component and the induction heating component of the present invention.

[0019] The numbers in the figures are marked as follows: 1, high-temperature steam chamber; 11, infrared visible glass window; 12, inlet; 13, outlet; 14, pressure gauge; 15, thermometer; 2, cladding; 21, strain gauge; 22, thermocouple; 23, germanate glass window; 3, insulating tube; 4, fuel pellets; 5, energizing component; 51, wide-range voltage DC power supply; 52, electrode; 6, induction heating component; 61, heating coil; 62, high-frequency power supply host; 7, infrared temperature measurement camera; 8, quartz glass flow guide tube. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions, and effects of the present invention clearer and more definite, the following further describes the present invention in detail with reference to the accompanying drawings and by way of examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0022] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] The energy of laser heating is highly concentrated on the surface of the fuel pellet 4, forming a local high temperature on the surface, but the penetration depth of the heat into the interior of the fuel pellet 4 is relatively shallow. In a RIA accident, the temperature rise of the fuel pellet 4 is caused by the volumetric heat source heating from the inside out (the fission energy release is uniformly distributed inside the fuel pellet 4), resulting in the temperature at the center of the fuel pellet 4 being significantly higher than that on the surface. However, the surface heat source mode of laser heating will cause the temperature gradient inside the fuel pellet 4 to be completely opposite to the real working condition (the surface temperature is high and the center temperature is low), and it is impossible to simulate the real radial temperature distribution. The thermal expansion behavior of the fuel pellet 4 highly depends on the temperature distribution. Under laser heating, the surface of the fuel pellet 4 expands rapidly while the center expands laggingly, which may lead to non-uniform radial expansion, deviating from the PCMI mechanism of the overall uniform expansion of the fuel pellet 4 in a real RIA accident, and distorting the experimental results.

[0024] In view of the deficiencies of the prior art, this embodiment provides an out-of-pile simulation experiment device for nuclear fuel behavior under a reactivity insertion accident, which is specifically as follows: As shown in the appended Figure 1 figures, an out-of-pile simulation experiment device for nuclear fuel behavior under a reactivity insertion accident includes a high-temperature steam chamber 1, a cladding 2, an insulating tube 3, at least one fuel pellet 4, an energizing assembly 5, and an induction heating assembly 6. The high-temperature steam chamber 1 is internally provided with the cladding 2, the inner wall of the cladding 2 abuts against the insulating tube 3, and the inner wall of the insulating tube 3 abuts against at least one fuel pellet 4. The energizing assembly 5 is located outside the high-temperature steam chamber 1 and is connected to both ends of the fuel pellet 4 through wires (the wires can pass through the side wall of the cladding 2 and are hermetically arranged with the cladding 2), and is used to energize the fuel pellet 4 and make the fuel pellet 4 generate heat by itself. The induction heating assembly 6 partially extends into the high-temperature steam chamber 1 and surrounds the outside of the cladding 2, and is used to heat the fuel pellet 4. Through the cooperation of the induction heating assembly 6 and the energizing assembly 5, the two can be superimposed to provide an extremely high heating power in a short time, simulating the rapid high-power density change under a reactivity insertion accident, and effectively solving the technical problems of low traditional heating power, non-self-heating, and insufficient heat penetration depth.

[0025] Among them, the high-temperature steam chamber 1 refers to a sealed container that can maintain a high-temperature and high-pressure steam environment. Specifically, it can be made of corrosion-resistant alloy materials, with a steam inlet 12 and an outlet 13 provided inside, and the in-core environment under accident conditions is simulated through steam circulation. The cladding 2 wraps the insulating tube 3, and its inner wall abuts against the outer wall of the insulating tube 3 to form a physical isolation layer. The insulating tube 3 refers to a tubular structure with electrical insulation characteristics, and heat transfer is achieved through contact between its inner wall and the fuel pellet 4 while preventing current leakage. The fuel pellet 4 (or its analogue, such as cerium dioxide semiconductor ceramic) controls its temperature-conductivity change characteristics by adjusting the composition. The energizing component 5 refers to a device that generates Joule heat through current. Specifically, a wide-range DC power supply can be used to connect the electrodes 52 on the upper and lower surfaces of the fuel pellet 4, and the heating rate of the fuel pellet 4 itself is controlled by adjusting the voltage. The induction heating component 6 refers to a device that generates eddy currents through electromagnetic induction. Specifically, a high-frequency power supply is used to drive a spiral coil surrounding the cladding 2, and the heating depth is controlled by adjusting the frequency.

[0026] Specifically, when the device is operating, the energizing component 5 is first started, and current passes through the fuel pellet 4 to generate uniform Joule heat, causing its overall temperature to rise. As the temperature increases, the conductivity of the semiconductor material of the fuel pellet 4 increases significantly, creating necessary conditions for subsequent induction heating. The induction heating component 6 is then started, and an eddy current effect is generated in the periphery of the cladding 2 by the high-frequency alternating magnetic field. This eddy current penetrates the cladding 2 and the insulating tube 3 and forms an additional heating layer in the peripheral area of the fuel pellet 4. By independently adjusting the DC voltage and the AC frequency, the internal basic temperature field and the peripheral additional power density distribution of the fuel pellet 4 can be controlled respectively. The heat in the fuel pellet 4 is conducted to the cladding 2 through the insulating tube 3, and the cladding 2 expands due to heat and has a mechanical interaction with the fuel pellet 4, cooperating with the high-temperature steam environment in the chamber to completely simulate the thermal-mechanical coupling effect in the reactivity insertion accident.

[0027] Compared with the existing technology, the traditional laser heating method is limited by the light wave penetration depth and can only achieve heating within a few micrometers on the surface of the fuel pellet 4, and it is impossible to construct an overall temperature field. In this solution, the internal basic temperature distribution of the fuel pellet 4 is established through resistance heating, and then induction heating is used to superimpose the power density at a specific depth, breaking through the physical limitation of surface heating. Compared with the surface power density of a single heating source, the composite heating can achieve a higher local power density in the peripheral area, more accurately reflecting the power distribution characteristics of high burn-up fuel. In addition, the process of increasing the conductivity of the fuel pellet 4 by resistance heating synchronously simulates the change in material properties caused by the rapid rise in fuel temperature during the accident, enhancing the physical authenticity of the experiment.

[0028] Through the above technical solutions, the present application realizes uniform heating in the thickness direction of the fuel pellet 4 while precisely controlling the peripheral power density distribution, effectively simulating the thermal behavior of high burn-up fuel under accident conditions. Utilizing the semiconductor characteristics of the fuel pellet 4 or the simulated pellet 4, taking the fuel pellet 4 as the main body for resistive heating, and adopting an electric heating method to achieve high-power volumetric heating of the pellet 4, so that the thickness dimension of the experimental sample is no longer limited by the surface heating penetration depth; after heating the pellet 4 to a high temperature by the resistive heating method, the conductivity of the semiconductor pellet 4 is fully improved. Utilizing the property that a highly conductive semiconductor can be induced, induction heating is simultaneously applied outside the simulated component. The superposition of resistive-induction heating can effectively increase the heating power density and better reflect the characteristics of fuel power surge in the RIA accident.

[0029] In this embodiment, as shown in the attached Figure 2 figure, the energizing assembly 5 includes a wide-range voltage DC power supply 51 and two electrodes 52; the wide-range voltage DC power supply 51 is arranged outside the high-temperature steam chamber 1, and the two electrodes 52 are respectively arranged on the surface and the bottom surface of the pellet 4. The wide-range voltage DC power supply 51 is connected to the two electrodes 52 through two wires respectively, for slowly heating the pellet 4.

[0030] Among them, the wide-range voltage DC power supply 51 refers to a DC power supply device whose output voltage range can be continuously adjusted. Specifically, it can be realized by using a programmable DC power supply module in combination with a voltage regulating circuit. This power supply has the ability to output a wide range of voltages to adapt to the conductivity change requirements under different working conditions. The two electrodes 52 refer to conductive components that are in direct contact with the pellet 4. Specifically, they can be realized by using contact pieces made of high-temperature-resistant metal materials. A current path penetrating the thickness of the pellet 4 is formed by arranging the double electrodes 52 on the surface and the bottom surface.

[0031] Specifically, when the wide-range voltage DC power supply 51 applies a voltage to the two electrodes 52 through wires, a closed loop will be formed along the thickness direction of the pellet 4. Under the action of the current, Joule heat is generated in the pellet 4 body due to the resistance effect, and its heating depth is directly related to the length of the current path. Since the current path covers the entire thickness of the pellet 4, the generated heat can be evenly distributed inside the pellet 4, avoiding the heat attenuation of the traditional surface heating method. The wide-range voltage regulation function can match the change of the conductivity characteristics of the pellet 4 at different temperatures, and maintain a stable heating power by adjusting the output voltage. During the slow heating process, the internal temperature gradient of the pellet 4 is gradually established, providing a controllable initial thermal field condition for the subsequent superposition of induction heating.

[0032] Compared with the prior art, in the existing laser heating method, light energy is converted into surface heat energy, and the heat conduction is limited by the thermal conductivity of the material, resulting in insufficient penetration depth. This solution adopts a resistive body heating mode, where the current directly acts on the main body of the pellet 4 to form a volume heat source. The heating depth is positively correlated with the thickness of the pellet 4, fundamentally breaking through the limitation of the surface heat source on the size of the pellet 4. The arrangement of the double electrodes 52 makes the heating area completely match the geometric shape of the pellet 4, eliminating the risk of local overheating.

[0033] Through the above technical solution, this application realizes uniform heating in the thickness direction of the pellet 4, effectively solving the problem of uneven temperature distribution caused by insufficient penetration depth of laser heating. By adjusting the output voltage of the DC power supply, the temperature rise rate inside the pellet 4 can be precisely controlled, truly simulating the process characteristics of the gradual increase in the power of the fuel element during a reactivity insertion accident. The design of the current path in the thickness direction of the pellet 4 enables the heating depth to be no longer limited by the surface heat source, providing an experimental basis for studying the thermal behavior of fuel elements with different thicknesses.

[0034] In this embodiment, as shown in the appendix Figure 2 The induction heating assembly 6 includes a heating coil 61 and a high-frequency power supply host 62; the induction heating assembly 6 includes a heating coil 61 disposed around the outside of the cladding 2, and a high-frequency power supply host 62 disposed outside the high-temperature steam chamber 1 and connected to the heating coil 61 through a wire.

[0035] Among them, the heating coil 61 refers to a ring-shaped conductor wound by a conductive material. Specifically, it can be wound into a spiral structure with a copper tube and fixed around the cladding 2, used to generate an alternating magnetic field when energized. This structure enables the electromagnetic field to act uniformly on the outer peripheral region of the pellet 4, preferentially achieving deep heating of the outer periphery.

[0036] Specifically, after the heating coil 61 is energized, an alternating magnetic field is generated. The alternating magnetic field penetrates the cladding 2 and the insulating tube 3 and induces eddy currents inside the pellet 4. The Joule heat generated by the eddy currents realizes rapid heating of the pellet 4. The output current frequency of the high-frequency power supply host 62 is adjustable. By increasing the frequency, the eddy currents are concentrated in the outer peripheral region of the pellet 4, thereby simulating the physical characteristics of the increased power density in the outer periphery of high burn-up fuel. The wire connection method makes the output parameters of the high-frequency power supply host 62 independent of the DC power supply of the energizing assembly 5, realizing power superposition and matching of the two modes.

[0037] Compared with the prior art, the existing laser heating solution can only achieve shallow surface heating of the pellet 4, while this solution enables heat to diffuse from the inside to the outside of the pellet 4 through the electromagnetic induction effect, significantly increasing the penetration depth. In addition, the prior art cannot control the heating gradient in different regions, while this solution can precisely control the preferential heating intensity of the outer peripheral region of the pellet 4 by adjusting the frequency parameters of the high-frequency power supply.

[0038] Through the above technical solution, the present application solves the problem of insufficient penetration depth of laser heating, realizes controllable heating of the peripheral area of the pellet 4, effectively simulates the physical effect of the increase in peripheral power density of high burnup fuel in a reactivity insertion accident, and improves the accuracy of experimental data.

[0039] In this embodiment, the cladding 2 is a hydrogen-permeated cladding. The hydrogen-permeated shell structure refers to a shell structure that forms a controllable hydrogen permeation channel in the material of the cladding 2 through a pretreatment process. Specifically, it can be realized by forming a hydride layer on a zirconium alloy material through high-temperature and high-pressure hydrogen atmosphere treatment. This structure can simulate the actual working condition of hydrogen element permeating the material of the cladding 2 due to radiolytic water production during the operation of the nuclear fuel rod in the reactor, so as to reproduce the hydrogen embrittlement effect under experimental conditions.

[0040] Specifically, the hydrogen permeation characteristics of the hydrogen-permeated cladding cause hydrogen-induced plastic deformation of the material of the cladding 2 when the pellet 4 expands due to heat, prompting the generation of contact pressure between the pellet 4 and the cladding 2. The aggregation of hydrogen elements at the grain boundaries of the cladding 2 increases the brittleness of the material and reduces the yield strength of the cladding 2, making the restraint effect of the cladding 2 during the expansion of the pellet 4 closer to the mechanical response under real accident conditions. In a high-temperature and high-pressure steam environment, the hydrogen diffusion behavior of the hydrogen-permeated cladding forms a dynamic coupling with the thermal expansion rate of the pellet 4, thus accurately simulating the complex mechanical interaction process between the pellet 4 and the cladding 2 during the power surge stage of high burnup fuel.

[0041] Compared with the prior art, the traditional experimental device uses a common metal cladding 2, which cannot reflect the influence of hydrogen elements on the mechanical properties of the cladding 2, resulting in a deviation between the measured value of the contact pressure between the pellet 4 and the cladding 2 and the actual working condition. The introduction of the hydrogen-permeated cladding reproduces for the first time the action mechanism of hydrogen embrittlement on PCMI in out-of-pile experiments, overcoming the defect that conventional materials cannot simulate the hydrogen-induced cracking behavior of the cladding 2.

[0042] Through the above technical solution, the present application can accurately control the hydrogen content and permeation rate of the material of the cladding 2, making the distribution characteristics of the mechanical stress generated during the expansion of the pellet 4 consistent with the stress state of the fuel rod in an actual reactivity insertion accident, solving the key problems that the existing experimental device cannot effectively simulate the hydrogen embrittlement effect and the dynamic contact between the pellet 4 and the cladding 2, and providing accurate experimental data support for studying the failure mechanism of PCMI.

[0043] In this embodiment, as shown in the appendix Figure 1 The out-of-pile simulation experimental device for nuclear fuel behavior under a reactivity insertion accident further includes an infrared thermographic camera 7. The infrared thermographic camera 7 is arranged at the top of the high-temperature steam chamber 1; a germanate glass window 23 is arranged at the top of the cladding 2, and an infrared visible glass window 11 is arranged at the top of the high-temperature steam chamber 1. The infrared thermographic camera 7 corresponds to the infrared visible glass window 11 and the germanate glass window 23 of the cladding 2, and can detect the temperature change of the pellet 4 in real time.

[0044] Among them, the infrared visible glass window 11 refers to an observation window with a high transmittance to infrared radiation, which allows infrared signals to pass through while ensuring the airtightness of the chamber. The top of the insulating tube 3 is open, and in cooperation with the germanate glass window 23, it forms an unobstructed optical path from the surface of the fuel pellet 4 to the infrared camera.

[0045] Specifically, the infrared temperature measurement camera 7 obtains optical signals through the infrared visible glass window 11 at the top of the high-temperature steam chamber 1. The germanate glass window 23 of the cladding 2 and the open top of the insulating tube 3 form a continuous and unobstructed optical channel, enabling the infrared radiation emitted from the surface of the fuel pellet 4 to be transmitted linearly to the infrared temperature measurement camera 7. In a high-temperature and high-pressure steam environment, contact temperature measurement devices are vulnerable to environmental interference and cannot measure the dynamic temperature field in real time. The non-contact measurement of the infrared temperature measurement camera 7 avoids physical contact between the sensor and the object to be measured. By continuously collecting the infrared radiation intensity on the surface of the fuel pellet 4 and combining with the blackbody radiation law, the temperature distribution is calculated. The coaxial alignment design of the open structure ensures no obstruction in the measurement path and guarantees the accuracy of temperature data.

[0046] Through the above technical solution, the present application realizes the real-time dynamic monitoring of the temperature change of the fuel pellet 4 during the simulated reactivity insertion accident, avoids signal distortion of the contact temperature measurement device in a high-temperature steam environment, and provides accurate temperature data support for analyzing the thermal expansion of the fuel pellet 4 and the mechanical action of the cladding 2.

[0047] In this embodiment, an opening is provided at the top of the cladding 2. The opening corresponds to the infrared visible glass window 11, and a germanate glass window 23 that transmits infrared is inlaid in the opening. This germanate glass window 23 does not transmit visible light but can transmit infrared, does not affect infrared measurement, and can operate at a high temperature of 700 °C. The position of the germanate glass window 23 is close to the infrared visible glass window 11, thus far from the fuel pellet 4, avoiding the influence of the heat generation of the fuel pellet 4 on the germanate glass window 23 at the top of the cladding 2.

[0048] In this embodiment, as shown in the appendix Figure 1 An inlet 12 is provided at the bottom of the high-temperature steam chamber 1, and outlets 13 are provided at both top sides of the high-temperature steam chamber 1. The bottom inlet 12 refers to a steam inlet channel provided at the bottom of the high-temperature steam chamber 1, which is used to guide high-temperature steam to flow from bottom to top. The two top outlets 13 refer to steam discharge channels symmetrically distributed on both top sides of the high-temperature steam chamber 1, forming a two-way convection cycle through the symmetrical layout.

[0049] Furthermore, the cladding 2 is arranged at an interval from the inner bottom wall of the high-temperature steam chamber 1, and can be arranged through support rods or support platforms to avoid blocking or closing the inlet 12 of the high-temperature steam.

[0050] Specifically, the layout of the bottom inlet 12 enables the high-temperature steam to fully cover the surface of the cladding 2 during the natural upward movement, preventing the steam from directly escaping along the side walls of the chamber. The symmetrical outlets 13 at the top on both sides form a stable annular flow path through two-way flow diversion when the steam rises to the top of the chamber, eliminating the air flow deflection caused by a single-sided outlet 13. The steam forms a flow field that uniformly diffuses from the bottom to the top on both sides inside the chamber, creating a heat exchange environment with approximately laminar flow in the axial region of the fuel pellets 4. When the rising steam flows through the outer surface of the cladding 2, the flow direction is maintained through the restraint of the quartz glass guide tube 8, ensuring that the heat transfer process in the peripheral area of the fuel pellets 4 is consistent with the axial flow characteristics of an actual reactor.

[0051] Through the above technical solution, the present application can achieve a uniform flow distribution of high-temperature steam in the chamber, avoiding local overheating or insufficient heat exchange. The upward flow path of the steam fully simulates the axial coolant flow characteristics of the reactor fuel rod, ensuring that the thermal boundary conditions on the surface of the fuel pellets 4 are consistent with the actual working conditions.

[0052] In this embodiment, as shown in the appendix Figure 1 on the bottom wall of the high-temperature steam chamber 1, a quartz glass guide tube 8 is provided. The quartz glass guide tube 8 is sleeved outside the cladding 2, and the induction heating assembly 6 is located between the quartz glass guide tube 8 and the cladding 2.

[0053] Specifically, the quartz glass guide tube 8 extends upward from the bottom of the steam chamber, and a steam flow passage is formed between its inner wall and the outer surface of the cladding 2 to achieve the directional flow of steam. The correspondence between the bottom of the quartz glass guide tube 8 and the steam inlet 12 can guide the steam to flow along the axis of the quartz glass guide tube 8, reducing the impact of steam turbulence on the working area of the coil and further reducing the risk of temperature distribution distortion.

[0054] Through the above technical solution, the steam flow field is optimized through the arrangement of the quartz glass guide tube 8, making the heating power density distribution in the peripheral area of the cladding 2 closer to the characteristics of an actual fuel rod in a high burn-up state.

[0055] In this embodiment, as shown in the appendix Figure 1 on the inside of the high-temperature steam chamber 1, a pressure gauge 14 and a thermometer 15 are provided.

[0056] Among them, the pressure gauge 14 refers to an instrument used to measure the pressure of gas or steam inside a closed chamber, which can be specifically implemented by a mechanical pressure sensor or an electronic pressure transmitter. Its measurement range needs to cover the pressure change range under experimental conditions. The pressure gauge 14 is directly installed on the inner wall of the high-temperature steam chamber 1, which can avoid measurement errors caused by external steam condensation or pipeline pressure drop. The thermometer 15 refers to a sensing device used to detect the temperature of the gas medium, which can be specifically implemented by a thermocouple 22 or an infrared non-contact temperature measurement probe. The thermometer 15 is arranged at the key monitoring points of the steam flow path, and its temperature measurement response time needs to meet the requirement of capturing transient temperature changes.

[0057] Specifically, by continuously detecting the internal pressure fluctuations of the high-temperature steam chamber 1 in real time, the pressure gauge 14 can reflect the mechanical stress state borne by the fuel element during the rapid heating process; by measuring the internal steam temperature distribution in the chamber at multiple points, the thermometer 15 can track the heat transfer process of the heat released by the fuel pellet 4 to the surrounding environment. The data of both are aligned on the time axis through a synchronous acquisition system, which can establish a dynamic coupling relationship between pressure-temperature parameters and provide accurate thermodynamic boundary conditions for experimental simulations.

[0058] Through the above technical solutions, the present application can accurately capture the transient change characteristics of pressure and temperature in a high-temperature steam environment, solve the problem of simulation distortion caused by the inability of existing monitoring means to synchronously obtain key parameters, and provide reliable experimental data support for reproducing the true thermal behavior of fuel elements in reactivity-initiated accidents.

[0059] In this embodiment, the insulating tube 3 is a corundum insulating tube.

[0060] Among them, the corundum material refers to a ceramic material mainly composed of alumina. This material can maintain insulation performance in the environment of the high-temperature steam chamber 1 and avoid energy loss caused by current leakage. Among them, thermal stability refers to the ability of a material to resist deformation and cracking at high temperatures, which is specifically achieved by matching the thermal expansion coefficient of the corundum material with the material of the cladding 2. This characteristic can prevent gaps from being generated between the insulating tube 3 and the cladding 2 due to thermal expansion differences at high temperatures.

[0061] Specifically, when the energizing component 5 is energized, the Joule heat generated inside the fuel pellet 4 is radially conducted through the corundum tube. The low thermal conductivity of the corundum material forms a thermal barrier layer, slowing down the heat dissipation from the surface of the fuel pellet 4 to the cladding 2, and concentrating the heating energy in the axial region of the fuel pellet 4. When the induction heating component 6 is working, the high-frequency magnetic field penetrates the corundum tube and acts on the cladding 2. Its high-resistance characteristic avoids eddy current losses, ensuring that the induction energy is effectively transmitted to the periphery of the cladding 2. When the fuel pellet 4 undergoes thermal expansion, the rigid abutment between the corundum tube and the inner wall of the cladding 2 provides a uniform radial constraint force, preventing local stress concentration caused by the eccentricity of the fuel pellet 4.

[0062] Through the above technical solution, the present application solves the problems of uneven heating and support failure of the insulating tube 3 due to insufficient material properties in a high-temperature environment. The low thermal conductivity characteristic of the corundum tube optimizes the axial temperature distribution of the fuel pellets 4, its high mechanical strength provides stable constraint conditions for the fuel rod simulation experiment, and the high-temperature insulation performance ensures the energy transfer efficiency of resistance heating and induction heating.

[0063] In this embodiment, as shown in the appended Figure 1 figures, there are multiple fuel pellets 4, and the multiple fuel pellets 4 are stacked inside the insulating tube 3, and the surface of the fuel pellet 4 at the topmost part is lower than the top surface of the insulating tube 3.

[0064] Among them, the stacked arrangement means that the multiple fuel pellets 4 are arranged in layers along the axis, and specifically, a cylindrical structure can be adopted to form a continuous stacked form to achieve this, and this structure can simulate the real stacked manner of the fuel pellets 4 inside the actual nuclear fuel rod. Among them, the surface being lower than the top of the insulating tube 3 means that there is a vertical distance between the upper end surface of the uppermost fuel pellet 4 and the top end of the insulating tube 3.

[0065] Specifically, this structure enables the fuel pellets 4 to conduct indirect heat exchange with the high-temperature steam chamber 1 only through the side wall of the insulating tube 3 and the cladding 2, avoiding the formation of an oxide layer on the surface of the fuel pellets 4 or abnormal temperature distribution caused by steam penetration. The distance between the top fuel pellet 4 and the top end of the insulating tube 3 also provides an unobstructed observation path for the infrared thermographic camera 7, reducing the interference of steam condensation or flow on the infrared radiation signal.

[0066] Through the above technical solution, the present application makes the height of the fuel pellets 4 lower than the height of the insulating tube 3, which can enable the acting force of the fuel pellets 4 to directly act on the insulating tube 3 and be transmitted to the cladding 2.

[0067] In this embodiment, as shown in the appended Figure 1 figures, a plurality of strain gauges 21 and a plurality of thermocouples 22 are evenly distributed on the outer surface of the cladding 2 for measuring the strain change and temperature change on the surface of the cladding 2.

[0068] After considering the specification and practicing the solutions disclosed herein, those skilled in the art will readily think of other embodiments of the present invention. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in this solution. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the claims.

Claims

1. An in-pile simulation experimental device for nuclear fuel behavior under a reactivity insertion accident, characterized in that, Comprising: A high-temperature steam chamber; A cladding, disposed inside the high-temperature steam chamber; An insulating tube, disposed inside the cladding; the outer surface of the insulating tube abuts against the inner wall of the cladding; At least one fuel pellet, disposed inside the insulating tube; the outer surface of the fuel pellet abuts against the inner wall of the insulating tube; A power-on assembly, disposed outside the high-temperature steam chamber and connected to both ends of the fuel pellet through wires respectively, for powering on the fuel pellet; An induction heating assembly, partially extending into the high-temperature steam chamber and arranged around the outside of the cladding, for heating the fuel pellet.

2. The out-of-pile simulation experimental device for nuclear fuel behavior under a reactivity-initiated accident according to claim 1, wherein The power-on assembly comprises: A wide-range voltage DC power supply, disposed outside the high-temperature steam chamber; Two electrodes, respectively disposed on the surface and bottom surface of the fuel pellet; the wide-range voltage DC power supply is connected to the two electrodes through two wires respectively, for powering on the fuel pellet and making the fuel pellet generate heat by itself.

3. The out-of-pile simulation experimental device for nuclear fuel behavior under reactivity-initiated accident according to claim 1, wherein, The induction heating assembly comprises: A heating coil, arranged around the outside of the cladding; A high-frequency power supply main unit, disposed outside the high-temperature steam chamber and connected to the heating coil through a wire.

4. A simulation experimental device for nuclear fuel behavior outside the reactor under a reactivity insertion accident according to claim 1, characterized in that, The cladding is a hydrogen-permeable cladding.

5. A simulation experimental device for nuclear fuel behavior outside the reactor under a reactivity introduction accident according to claim 1, characterized in that, It further comprises: An infrared temperature measurement camera, disposed on the top of the high-temperature steam chamber; an infrared visible glass window is provided on the top of the high-temperature steam chamber, a germanate glass window is provided on the top of the cladding, and the infrared temperature measurement camera corresponds to the infrared visible glass window and the germanate glass window of the cladding.

6. The out-of-pile simulation experimental device for nuclear fuel behavior under reactivity-initiated accidents according to claim 1, wherein An inlet is provided at the bottom of the high-temperature steam chamber, and outlets are provided at the top of both sides of the high-temperature steam chamber.

7. A simulation experimental device for nuclear fuel behavior outside the reactor under a reactivity introduction accident according to claim 6, characterized in that, A quartz glass diversion tube is provided on the bottom wall inside the high-temperature steam chamber, the quartz glass diversion tube is sleeved outside the cladding, and the induction heating assembly is located between the quartz glass diversion tube and the cladding.

8. A simulation experimental device for nuclear fuel behavior outside the reactor under a reactivity insertion accident according to claim 1, characterized in that, A pressure gauge and a thermometer are provided inside the high-temperature steam chamber.

9. A simulation experimental device for nuclear fuel behavior outside the reactor under a reactivity insertion accident according to claim 1, characterized in that, The insulating tube is a corundum insulating tube.

10. The out-of-pile simulation experimental device for nuclear fuel behavior under a reactivity-initiated accident according to claim 1, characterized in that, There are multiple fuel pellets, and the multiple fuel pellets are stacked and disposed inside the insulating tube, and the surface of the fuel pellet at the topmost position is lower than the top surface of the insulating tube.

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