An out-of-pile simulation experimental device for nuclear fuel behavior under reactivity introduction accidents

Abstract

The present invention relates to the technical field of nuclear fuel accident simulation, and discloses an off-core simulation experimental device for nuclear fuel behavior under a reactivity introduction accident. The device comprises a high-temperature steam chamber, a cladding, an insulating tube, at least one pellet, an energizing component, and an induction heating component. The high-temperature steam chamber is provided with a cladding, the interior of the cladding is provided with an insulating tube, the interior of the insulating tube is provided with at least one pellet, and the high-temperature steam chamber is further provided with an energizing component and an induction heating component. The energizing component is connected to both ends of the pellet, so that the pellet can be energized and the pellet itself can be heated, while the conductivity of the pellet can be changed, and then the pellet can be inductively heated by the induction heating component. The superposition of the two can provide extremely high heating power for a short time, simulating the rapid high power density change under a reactivity introduction accident, and effectively solving the technical problems of low heating power, non-self-heating, and insufficient heat penetration depth in traditional heating.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel accident simulation, and in particular to an off-pile simulation experimental device for nuclear fuel behavior under a reactivity introduction accident. Background Art

[0002] Reactivity introduction accidents (RIA) are the design basis accidents for pressurized water reactors (PWRs). In a typical RIA, nuclear fuel rods may experience a series of phenomena, including power surges, pellet temperature spikes and thermal expansion, pellet-cladding mechanical interaction (PCMI) and cladding mechanical failure, and fuel pellet and cladding meltdown, seriously threatening the structural integrity of the fuel elements. However, accurately understanding the thermal behavior of nuclear fuel elements during RIAs presents significant challenges.

[0003] The existing technology generally uses a high-temperature heating furnace combined with laser heating to simulate the reactivity of pellets to cause accidents. However, the laser heating method concentrates the power on the surface of the pellets, with a shallow penetration depth, which cannot provide uniform heating and cannot reflect the characteristics of the fuel power surge in RIA accidents.

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

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an off-core simulation experimental device for nuclear fuel behavior under a reactive introduction accident, aiming to solve the problem in the prior art that the core blocks are heated unevenly and a fuel power surge cannot be achieved by laser heating.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] An out-of-core simulation experimental device for nuclear fuel behavior under a reactivity introduction accident, comprising:

[0008] High temperature steam chamber;

[0009] a cladding, disposed inside the high-temperature steam chamber;

[0010] An insulating tube is arranged inside the cladding; the outer surface of the insulating tube abuts against the inner wall of the cladding;

[0011] At least one core block is disposed inside the insulating tube; an outer surface of the core block abuts against an inner wall of the insulating tube;

[0012] an electrification component, disposed outside the high-temperature steam chamber and connected to both ends of the pellet through wires, for electrifying the pellet;

[0013] An induction heating assembly partially extends into the interior of the high-temperature steam chamber and is arranged around the outside of the cladding for heating the pellets.

[0014] Furthermore, the power supply assembly includes:

[0015] A wide-range voltage DC power supply is provided outside the high-temperature steam chamber;

[0016] Two electrodes are respectively arranged on the surface and bottom surface of the core block; the wide-range voltage DC power supply is respectively connected to the two electrodes through two wires, so as to energize the core block and make the core block itself heat up.

[0017] Furthermore, the induction heating component includes:

[0018] A heating coil is disposed around the outside of the shell;

[0019] The high-frequency power supply host is arranged outside the high-temperature steam chamber and is connected to the heating coil through a wire.

[0020] Furthermore, the cladding is a hydrogen permeable cladding.

[0021] Furthermore, it also includes:

[0022] An infrared temperature measuring camera is arranged at the top of the high-temperature steam chamber; an infrared visual glass window is provided on the top of the high-temperature steam chamber, and a germanate glass window is provided on the top of the shell, and the infrared temperature measuring camera corresponds to the infrared visual glass window and the germanate glass window of the shell.

[0023] Furthermore, an inlet is provided at the bottom of the high-temperature steam chamber, and outlets are provided at the tops of both sides of the high-temperature steam chamber.

[0024] Furthermore, a quartz glass flow guide tube is provided on the bottom wall of the high-temperature steam chamber, the quartz glass flow guide tube is sleeved on the outside of the cladding, and the induction heating component is located between the quartz glass flow guide tube and the cladding.

[0025] Furthermore, a pressure gauge and a thermometer are provided inside the high-temperature steam chamber.

[0026] Furthermore, the insulating tube is a corundum insulating tube.

[0027] Furthermore, there are multiple core blocks, and the multiple core blocks are stacked and arranged inside the insulation tube, and the surface of the core block located at the top is lower than the top surface of the insulation tube.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In the present invention, a cladding is provided in the high-temperature steam chamber, an insulating tube is provided inside the cladding, a core block is provided inside the insulating tube, and a power-on component and an induction heating component are also provided in the high-temperature steam chamber; the power-on component is connected to both ends of the core block, so that the core block can be energized and the core block itself can be heated, and the conductivity of the core block can be changed at the same time, and then the core block can be induction heated by the induction heating component. The superposition of the two can provide extremely high heating power for a short time, simulating the rapid high power density change under the reactive introduction accident, and effectively solving the technical problems of low traditional heating power, non-self-heating and insufficient heat penetration depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0031] Figure 2 This is a schematic structural diagram of the power supply component and the induction heating component of the present invention.

[0032] The numbers in the figure indicate: 1. High-temperature steam chamber; 11. Infrared visual 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. Core block; 5. Power supply 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 camera; 8. Quartz glass flow guide tube. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying 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 therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0035] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0036] The energy from laser heating is highly concentrated on the surface of pellet 4, resulting in localized high temperatures. However, the heat penetration into the interior of pellet 4 is relatively shallow. In a RIA accident, the temperature of fuel pellet 4 rises from an internal-outward volumetric heat source (fission energy released is evenly distributed within pellet 4), resulting in a significantly higher temperature at the center of pellet 4 than at the surface. However, the surface heat source model of laser heating results in a temperature gradient within pellet 4 that is completely opposite to that in real-world conditions (high surface temperature, low center temperature), failing to simulate a realistic radial temperature distribution. The thermal expansion behavior of pellet 4 is highly dependent on the temperature distribution. Under laser heating, the surface of pellet 4 expands rapidly while the center expands more slowly, potentially leading to uneven radial expansion. This deviates from the PCMI mechanism, which indicates uniform expansion of the entire pellet 4 in a real RIA accident, distorting the experimental results.

[0037] In view of the shortcomings of the existing technology, this embodiment provides an off-core simulation experimental device for nuclear fuel behavior under a reactivity introduction accident. The details can be referred to as follows:

[0038] As attached Figure 1 As shown, an ex-core experimental device for simulating nuclear fuel behavior under a reactive introduction accident includes a high-temperature steam chamber 1, a cladding 2, an insulating tube 3, at least one pellet 4, an energizing assembly 5, and an induction heating assembly 6. The cladding 2 is disposed within the high-temperature steam chamber 1, with its inner wall abutting the insulating tube 3, which in turn abuts the at least one pellet 4. The energizing assembly 5 is located outside the high-temperature steam chamber 1 and connected to both ends of the pellet 4 via wires (the wires can pass through the sidewalls of the cladding 2 and be sealed therewith). This energizes the pellet 4 and generates self-heating. The induction heating assembly 6 partially extends into the high-temperature steam chamber 1 and surrounds the exterior of the cladding 2, heating the pellet 4. The induction heating assembly 6 and the energizing assembly 5 work together to provide extremely high heating power for a short period of time, simulating the rapid, high power density changes associated with a reactive introduction accident. This effectively addresses the technical issues of low power, non-self-heating, and insufficient heat penetration in conventional heating systems.

[0039] The high-temperature steam chamber 1 is a sealed container capable of maintaining a high-temperature, high-pressure steam environment. Specifically, it can be made of a corrosion-resistant alloy. It is equipped with a steam inlet 12 and outlet 13, allowing steam circulation to simulate the reactor's internal environment under accident conditions. The cladding 2 surrounds the insulating tube 3, with its inner wall abutting against the outer wall of the insulating tube 3 to form a physical barrier. The insulating tube 3 is a tubular structure with electrical insulation properties. Its inner wall contacts the pellet 4, enabling heat transfer while preventing current leakage. The temperature-conductivity characteristics of the pellet 4 (or its analog, such as ceria semiconductor ceramic) can be controlled by adjusting its composition. The current-carrying assembly 5 is a device that generates Joule heating through current. Specifically, a wide-range DC power supply can be used to connect electrodes 52 on the upper and lower surfaces of the pellet 4. The heating rate of the pellet 4 can be controlled by adjusting the voltage. The induction heating assembly 6 is a device that generates eddy currents through electromagnetic induction. Specifically, a high-frequency power supply can be used to drive a spiral coil surrounding the cladding 2, with the heating depth controlled by frequency adjustment.

[0040] Specifically, when the device is in operation, the power supply component 5 is first started, and the current passes through the core block 4 to generate uniform Joule heat to heat it up as a whole. As the temperature rises, the conductivity of the core block 4 of the semiconductor material is significantly improved, creating the necessary conditions for subsequent induction heating. The induction heating component 6 is then started, and the high-frequency alternating magnetic field generates an eddy current effect on the periphery of the cladding 2. After the eddy current penetrates the cladding 2 and the insulating tube 3, an additional heating layer is formed in the peripheral area of ​​the core block 4. By independently adjusting the DC voltage and AC frequency, the basic temperature field inside the core block 4 and the distribution of additional power density in the periphery can be controlled respectively. The heat in the core block 4 is transferred to the cladding 2 through the insulating tube 3. The cladding 2 expands due to heat and produces mechanical interaction with the core block 4. In conjunction with the high-temperature steam environment in the chamber, the thermal-mechanical coupling effect in the reactive introduction accident is fully simulated.

[0041] Compared with existing technologies, traditional laser heating methods are limited by the penetration depth of light waves and can only achieve heating within a micrometer range on the surface of pellet 4, making it impossible to construct an overall temperature field. This solution uses resistive heating to establish a basic temperature distribution within pellet 4, and then uses induction heating to superimpose power density at a specific depth, breaking through the physical limitations of surface heating. Compared to the surface power density of a single heating source, composite heating can achieve higher local power density in the peripheral area, more accurately reflecting the power distribution characteristics of high-burnup fuel. In addition, the process of increasing the conductivity of pellet 4 by resistive heating simultaneously simulates the changes in material properties caused by the rapid increase in fuel temperature during an accident, enhancing the physical authenticity of the experiment.

[0042] Through the above-mentioned technical solution, the present application achieves uniform heating of the pellet 4 through its thickness while precisely controlling the peripheral power density distribution, effectively simulating the thermal behavior of high-burnup fuel under accident conditions. By utilizing the semiconductor properties of the fuel pellet 4 or simulated pellet 4, the fuel pellet 4 is used as the resistive heating body, and high-power body heating of the pellet 4 is achieved through electric heating. This eliminates the limitation of the thickness of the experimental sample size by the depth of surface heating penetration. After heating the pellet 4 to a high temperature through resistive heating, the conductivity of the semiconductor pellet 4 is substantially enhanced. By utilizing the inductive property of high-conductivity semiconductors, induction heating is simultaneously applied to the exterior of the simulated element. The superposition of resistive and inductive heating effectively increases the heating power density, better reflecting the characteristics of the fuel power surge in RIA accidents.

[0043] In this embodiment, as shown in the attached Figure 2 As shown, the power supply component 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 bottom of the core block 4. The wide-range voltage DC power supply 51 is connected to the two electrodes 52 through two wires, respectively, for slowly heating the core block 4.

[0044] The wide-range voltage DC power supply 51 is a DC power supply device with a continuously adjustable output voltage range. Specifically, this can be implemented using a programmable DC power supply module in conjunction with a voltage regulation circuit. This power supply has a wide voltage output range to accommodate varying conductivity requirements under various operating conditions. The two electrodes 52 are conductive components that directly contact the core block 4. Specifically, they can be implemented using contact pads made of high-temperature-resistant metal materials. The arrangement of the two electrodes 52 on the surface and bottom surfaces creates a current path that penetrates the thickness of the core block 4.

[0045] Specifically, when the wide-range voltage DC power supply 51 applies voltage to the two electrodes 52 through the wire, the current will form a closed loop along the thickness direction of the core block 4. Under the action of the current, the core block 4 generates Joule heat 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 core block 4, the generated heat can be evenly distributed inside the core block 4, avoiding the heat attenuation of traditional surface heating methods. The wide-range voltage regulation function can match the changes in the conductive properties of the core block 4 at different temperatures and maintain stable heating power by adjusting the output voltage. During the slow heating process, the temperature gradient inside the core block 4 is gradually established, providing controllable initial thermal field conditions for subsequent superimposed induction heating.

[0046] Compared to existing technologies, existing laser heating methods convert light energy into surface heat energy. However, heat conduction is limited by the thermal conductivity of the material, resulting in insufficient penetration depth. This solution utilizes resistive volumetric heating, where current is applied directly to the core block 4 to create a volumetric heat source. The heating depth is positively correlated with the thickness of the core block 4, fundamentally overcoming the limitations of surface heat sources on the size of the core block 4. The dual-electrode 52 arrangement ensures that the heating area perfectly matches the geometry of the core block 4, eliminating the risk of localized overheating.

[0047] Through the above-described technical solution, this application achieves uniform heating throughout the thickness of pellet 4, effectively resolving the uneven temperature distribution problem caused by insufficient laser heating penetration. By adjusting the DC power supply output voltage, the rate of temperature rise within pellet 4 can be precisely controlled, realistically simulating the gradual increase in fuel element power during a reactivity introduction accident. The design of the current path through the thickness of pellet 4 eliminates the heating depth limitation imposed by surface heat sources, providing an experimental basis for studying the thermal behavior of fuel elements of varying thicknesses.

[0048] In this embodiment, as shown in the attached Figure 2 As shown, the induction heating component 6 includes a heating coil 61 and a high-frequency power supply host 62; the induction heating component 6 includes a heating coil 61 arranged around the outside of the shell 2, and a high-frequency power supply host 62 arranged outside the high-temperature steam chamber 1 and connected to the heating coil 61 through a wire.

[0049] The heating coil 61 is a ring-shaped conductor made of a conductive material. Specifically, it can be a copper tube wound into a spiral structure and fixed to the periphery of the cladding 2. It is used to generate an alternating magnetic field when energized. This structure ensures that the electromagnetic field acts uniformly on the periphery of the core block 4, preferentially achieving deep heating of the periphery.

[0050] Specifically, when energized, the heating coil 61 generates an alternating magnetic field. This field penetrates the cladding 2 and insulating tube 3, inducing eddy currents within the pellet 4. The Joule heat generated by these eddy currents rapidly heats the pellet 4. The high-frequency power supply 62 outputs an adjustable frequency current. By increasing the frequency, the eddy currents are concentrated in the periphery of the pellet 4, thereby simulating the physical properties of increased power density at the periphery of high-burnup fuel. The wire connection ensures that the output parameters of the high-frequency power supply 62 are independent of the DC power supply of the energized component 5, achieving power matching between the two modes.

[0051] Compared to existing laser heating solutions, which only achieve shallow heating of the core block 4's surface, this solution uses electromagnetic induction to diffuse heat from the core block 4's interior to its periphery, significantly increasing its penetration depth. Furthermore, existing technologies cannot control the heating gradient across different regions, while this solution precisely controls the preferential heating intensity of the core block 4's periphery by adjusting the frequency parameters of the high-frequency power supply.

[0052] Through the above technical solution, the present application solves the problem of insufficient penetration depth of laser heating, realizes deep controllable heating of the peripheral area of ​​the core block 4, effectively simulates the physical effect of increased peripheral power density of high-burnup fuel in the reactivity introduction accident, and improves the accuracy of experimental data.

[0053] In this embodiment, the cladding 2 is a hydrogen-permeable cladding. This refers to a shell structure in which controlled hydrogen permeation channels are formed in the cladding material through a pretreatment process. Specifically, this can be achieved by forming a hydrogenated layer using zirconium alloy treated in a high-temperature, high-pressure hydrogen atmosphere. This structure simulates the actual operating conditions in which hydrogen generated by irradiation decomposition of water in nuclear fuel rods permeates the cladding material during reactor operation, thereby reproducing the hydrogen embrittlement effect under experimental conditions.

[0054] Specifically, the hydrogen permeability of the hydrogen-permeable cladding causes the cladding material to undergo hydrogen-induced plastic deformation when the pellet 4 expands due to heat, generating contact pressure between the pellet 4 and the cladding 2. The accumulation of hydrogen at the grain boundaries of the cladding 2 increases the material's brittleness, reducing the yield strength of the cladding 2 and making the restraining effect of the cladding 2 during the expansion of the pellet 4 more similar to the mechanical response under real accident conditions. In a high-temperature, high-pressure steam environment, the hydrogen diffusion behavior of the hydrogen-permeable cladding is dynamically coupled with the thermal expansion rate of the pellet 4, accurately simulating the complex mechanical interaction between the pellet 4 and the cladding 2 during the power surge phase of high-burnup fuel.

[0055] Compared to existing technologies, conventional experimental setups using ordinary metal cladding 2 fail to reflect the effects of hydrogen on the cladding's mechanical properties, resulting in deviations between the pellet 4-cladding 2 contact pressure test values ​​and actual operating conditions. The introduction of hydrogen-permeable cladding has, for the first time, replicated the mechanism of hydrogen embrittlement on PCMI in ex-pile experiments, overcoming the limitation of conventional materials in simulating the hydrogen-induced cracking behavior of the cladding 2.

[0056] Through the above technical solution, the present application can accurately control the hydrogen content and permeation rate of the cladding 2 material, so that the mechanical stress distribution characteristics generated during the expansion of the pellet 4 are consistent with the stress state of the fuel rod in the actual reactivity introduction accident, solving the key problem that the existing experimental equipment 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 the study of the PCMI failure mechanism.

[0057] In this embodiment, as shown in the attached Figure 1 As shown, the ex-core simulation experimental device for nuclear fuel behavior under a reactivity introduction accident also includes an infrared temperature measuring camera 7, which is arranged at the top of the high-temperature steam chamber 1; a germanate glass window 23 is provided on the top of the cladding 2, and an infrared visual glass window 11 is provided on the top of the high-temperature steam chamber 1. The infrared temperature measuring camera 7 corresponds to the infrared visual 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.

[0058] Among them, the infrared visual glass window 11 refers to an observation window with high transmittance to infrared radiation, which allows infrared signals to pass through while ensuring the sealing of the chamber; the top of the insulating tube 3 is open, and together with the germanium glass window 23, an unobstructed light path is formed from the surface of the core block 4 to the infrared camera.

[0059] Specifically, the infrared temperature camera 7 acquires optical signals through the infrared visual glass window 11 at the top of the high-temperature steam chamber 1. The germanate glass window 23 of the cladding 2 and the top opening of the insulating tube 3 form a continuous optical channel, allowing the infrared radiation emitted from the surface of the pellet 4 to be transmitted in a straight line to the infrared temperature camera 7. In a high-temperature, high-pressure steam environment, contact-type temperature measurement devices are susceptible to environmental interference and cannot measure dynamic temperature fields in real time. The non-contact measurement of the infrared temperature camera 7 avoids physical contact between the sensor and the object being measured. By continuously collecting the infrared radiation intensity on the surface of the pellet 4, the temperature distribution is calculated in combination with the blackbody radiation law. The coaxial alignment design of the opening structure ensures that there are no obstructions on the measurement path, ensuring the accuracy of the temperature data.

[0060] Through the above technical solution, the present application realizes real-time dynamic monitoring of the temperature changes of the fuel pellets 4 during the simulated reactivity introduction accident process, avoids the signal distortion of the contact temperature measuring device in a high-temperature steam environment, and provides accurate temperature data support for analyzing the thermal expansion of the pellets 4 and the mechanical action of the cladding 2.

[0061] In this embodiment, an opening is provided at the top of the cladding 2, which corresponds to the infrared-visible glass window 11. An infrared-transparent germanate glass window 23 is embedded in the opening. This germanate glass window 23 is opaque to visible light but transparent to infrared light, which does not affect infrared measurement and can operate at a high temperature of 700°C. The germanate glass window 23 is positioned close to the infrared-visible glass window 11, thereby being away from the pellets 4, to prevent the heat generated by the pellets 4 from affecting the germanate glass window 23 at the top of the cladding 2.

[0062] In this embodiment, as shown in the attached Figure 1 As shown, the high-temperature steam chamber 1 is provided with an inlet 12 at the bottom and outlets 13 at the top of both sides of the high-temperature steam chamber 1. The bottom inlet 12 refers to the steam inlet channel provided at the bottom of the high-temperature steam chamber 1, which is used to guide the high-temperature steam to flow from bottom to top. The top outlets 13 on both sides refer to steam exhaust channels symmetrically distributed on both sides of the top of the high-temperature steam chamber 1. This symmetrical layout creates a bidirectional convection circulation.

[0063] Furthermore, the cladding 2 is spaced apart from the inner bottom wall of the high-temperature steam chamber 1 and may be arranged via a support rod or a support platform to avoid blocking or closing the high-temperature steam inlet 12 .

[0064] Specifically, the layout of the bottom inlet 12 allows the high-temperature steam to fully cover the surface of the cladding 2 during its natural rise, preventing the steam from escaping directly along the side walls of the chamber. When the steam rises to the top of the chamber, the symmetrical outlets 13 on both sides form a stable annular flow path through two-way diversion, eliminating the airflow deflection caused by the single-sided outlet 13. The steam forms a flow field inside the chamber that diffuses evenly from the bottom to the top of both sides, establishing a heat exchange environment that is approximately laminar in the axial region of the core block 4. When the rising steam flows through the outer surface of the cladding 2, the flow direction is maintained by the restraining effect of the quartz glass flow guide tube 8, ensuring that the heat transfer process in the peripheral area of ​​the core block 4 is consistent with the actual reactor axial flow characteristics.

[0065] Through the above technical solution, the present application can achieve uniform flow distribution of high-temperature steam within the chamber, avoiding local overheating or insufficient heat exchange. The bottom-up steam flow path fully simulates the axial coolant flow characteristics of the reactor fuel rods, ensuring that the thermal boundary conditions on the surface of the pellets 4 are consistent with actual operating conditions.

[0066] In this embodiment, as shown in the attached Figure 1 As shown, a quartz glass flow guide tube 8 is provided on the bottom wall of the high-temperature steam chamber 1 , the quartz glass flow guide tube 8 is sleeved on the outside of the cladding 2 , and the induction heating component 6 is located between the quartz glass flow guide tube 8 and the cladding 2 .

[0067] Specifically, a quartz glass flow tube 8 extends upward from the bottom of the steam chamber. Its inner wall and the outer surface of the cladding 2 form a steam flow channel, achieving directional steam flow. The corresponding relationship between the bottom of the quartz glass flow tube 8 and the steam inlet 12 guides the steam flow along the axial direction of the quartz glass flow tube 8, reducing the impact of steam turbulence on the coil working area and further reducing the risk of temperature distribution distortion.

[0068] Through the above technical solution, the steam flow field is optimized by arranging the quartz glass flow tube 8, so that the heating power density distribution in the peripheral area of ​​the cladding 2 is closer to the characteristics of the real fuel rod under high burnup state.

[0069] In this embodiment, as shown in the attached Figure 1 As shown, a pressure gauge 14 and a thermometer 15 are provided inside the high-temperature steam chamber 1 .

[0070] The pressure gauge 14 is an instrument used to measure the pressure of the gas or steam inside the sealed chamber. It can be implemented using a mechanical pressure sensor or an electronic pressure transmitter. Its measurement range must cover the pressure variation range under experimental conditions. Pressure gauge 14 is directly mounted on the inner wall of the high-temperature steam chamber 1 to avoid measurement errors caused by external steam condensation or pipeline pressure drop. The thermometer 15 is a sensing device used to detect the temperature of the gas medium. It can be implemented using a thermocouple 22 or an infrared non-contact temperature probe. The thermometer 15 is placed at a key monitoring point along the steam flow path. Its temperature measurement response time must meet the requirements for capturing transient temperature changes.

[0071] Specifically, the pressure gauge 14 monitors pressure fluctuations within the high-temperature steam chamber 1 in real time, reflecting the mechanical stress experienced by the fuel element during rapid temperature increases. The thermometer 15 measures the steam temperature distribution within the chamber at multiple points, tracking the heat transfer from the pellet 4 to the surrounding environment. By aligning the data from both on the time axis through a synchronous acquisition system, a dynamic coupling relationship between pressure and temperature parameters can be established, providing precise thermodynamic boundary conditions for experimental simulations.

[0072] Through the above technical solution, the present application can accurately capture the transient change characteristics of pressure and temperature in a high-temperature steam environment, solve the simulation distortion problem caused by the inability of existing monitoring methods to synchronously obtain key parameters, and provide reliable experimental data support for reproducing the actual thermal behavior of fuel elements in reactivity introduction accidents.

[0073] In this embodiment, the insulating tube 3 is a corundum insulating tube.

[0074] Corundum refers to a ceramic material primarily composed of aluminum oxide. This material maintains its insulating properties in the high-temperature steam chamber 1, preventing energy loss due to current leakage. Thermal stability refers to the material's ability to resist deformation and cracking at high temperatures. This is achieved by matching the thermal expansion coefficient of the corundum with that of the cladding 2. This property prevents gaps from forming between the insulating tube 3 and the cladding 2 due to differential thermal expansion at high temperatures.

[0075] Specifically, when the power-on component 5 is energized, the Joule heat generated inside the core block 4 is radially conducted through the corundum tube. The low thermal conductivity of the corundum material forms a thermal barrier layer, which slows down the heat loss from the surface of the core block 4 to the cladding 2, and concentrates the heating energy in the axial region of the core block 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 loss and ensures that the induction energy is effectively transferred to the periphery of the cladding 2. When the core block 4 undergoes thermal expansion, the rigid contact between the corundum tube and the inner wall of the cladding 2 provides a uniform radial restraining force, preventing local stress concentration caused by the eccentricity of the core block 4.

[0076] Through the above technical solution, this application solves the problems of uneven heating and support failure caused by insufficient material properties of the insulating tube 3 in high-temperature environments. The low thermal conductivity of the corundum tube optimizes the axial temperature distribution of the pellet 4. Its high mechanical strength provides stable constraints for fuel rod simulation experiments, and its high-temperature insulation performance ensures efficient energy transfer during both resistance and induction heating.

[0077] In this embodiment, as shown in the attached Figure 1 As shown, there are multiple core blocks 4 , which are stacked and arranged inside the insulation tube 3 , and the surface of the core block 4 at the top is lower than the top surface of the insulation tube 3 .

[0078] The stacked arrangement refers to the arrangement of multiple pellets 4 in an axially stacked configuration. Specifically, this can be achieved by using a cylindrical structure to form a continuous stack. This structure simulates the actual stacking of pellets 4 within an actual nuclear fuel rod. The surface being lower than the top of the insulating tube 3 refers to a vertical gap between the upper end surface of the topmost pellet 4 and the top of the insulating tube 3.

[0079] Specifically, this structure allows pellets 4 to exchange heat indirectly with the high-temperature steam chamber 1 only through the sidewalls of the insulating tube 3 and the cladding 2, preventing steam penetration from causing an oxide layer on the surface of the pellets 4 or abnormal temperature distribution. The distance between the top pellet 4 and the top of the insulating tube 3 also provides an unobstructed observation path for the infrared temperature camera 7, reducing interference with the infrared radiation signal from steam condensation or flow.

[0080] Through the above technical solution, the height of the core block 4 is lower than that of the insulating tube 3 in the present application, so that the force of the core block 4 can directly act on the insulating tube 3 and be transmitted to the cladding 2.

[0081] In this embodiment, as shown in the attached Figure 1 As shown, 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 .

[0082] Other embodiments of the present invention will readily occur to those skilled in the art after considering the specification and practicing the embodiments disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the claims.

Claims

1. An off-core simulation experimental device for nuclear fuel behavior under reactivity introduction accidents, characterized in that: include: High temperature steam chamber; a cladding, disposed inside the high-temperature steam chamber; An insulating tube is arranged inside the cladding; the outer surface of the insulating tube abuts against the inner wall of the cladding; At least one core block is disposed inside the insulating tube; an outer surface of the core block abuts against an inner wall of the insulating tube; an electrification component, disposed outside the high-temperature steam chamber and connected to both ends of the pellet through wires, for electrifying the pellet; an induction heating assembly, partially extending into the interior of the high-temperature steam chamber and arranged around the outside of the cladding, for heating the pellets; an infrared temperature measuring camera, disposed at the top of the high-temperature steam chamber; an infrared visual glass window is disposed at the top of the high-temperature steam chamber, a germanate glass window is disposed at the top of the cladding, the infrared temperature measuring camera corresponds to the infrared visual glass window and the germanate glass window of the cladding; an opening is disposed at the top of the insulating tube, the opening corresponding to the germanate glass window; An inlet is provided at the bottom of the high-temperature steam chamber, and outlets are provided on the tops of both sides of the high-temperature steam chamber. A quartz glass flow guide tube is provided on the bottom wall of the high-temperature steam chamber. The quartz glass flow guide tube is sleeved on the outside of the cladding, and the induction heating assembly is located between the quartz glass flow guide tube and the cladding.

2. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1 is characterized in that: The power supply assembly includes: A wide-range voltage DC power supply is provided outside the high-temperature steam chamber; Two electrodes are respectively arranged on the surface and bottom surface of the core block; the wide-range voltage DC power supply is respectively connected to the two electrodes through two wires, so as to energize the core block and make the core block itself heat up.

3. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1 is characterized in that: The induction heating assembly comprises: A heating coil is disposed around the outside of the shell; The high-frequency power supply host is arranged outside the high-temperature steam chamber and is connected to the heating coil through a wire.

4. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1, characterized in that: The cladding is a hydrogen permeable cladding.

5. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1, characterized in that: A pressure gauge and a thermometer are provided inside the high-temperature steam chamber.

6. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1, characterized in that: The insulating tube is a corundum insulating tube.

7. The device for simulating the behavior of nuclear fuel under a reactivity introduction accident outside the reactor according to claim 1, characterized in that: There are multiple core blocks, which are stacked and arranged inside the insulation tube. The surface of the core block at the top is lower than the top surface of the insulation tube.

Images