Loss-of-coolant accident nuclear fuel behavior simulation experiment device

Abstract

The invention relates to the technical field of nuclear fuel accident simulation, and discloses a loss-of-coolant accident nuclear fuel behavior simulation experiment device which comprises a cladding, a core block, an insulating part, a pressurized cooling pipeline and a cooling assembly, the core block is arranged in the cladding, and the top wall and the bottom wall of the core block are connected with an external power source through wires. An insulating part is arranged between the core block and the cladding, and a pressurized cooling pipeline is arranged outside the cladding and connected with the cooling assembly; the fission heat production process of a real nuclear fuel is simulated through power-on spontaneous heating of the pellet, and thermal stress cracking of the pellet can be effectively reduced by combining the synergistic effect of the pressurized cooling pipeline and the cooling assembly, so that in-situ pellet cracking with the same principle as real pellet cracking is realized; a more real pellet cracking form and cladding deformation and fracture conditions can be obtained, and the accuracy and reliability of experimental data are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel accident simulation, and particularly relates to an experimental device for simulating the behavior of nuclear fuel in a loss-of-coolant accident. Background Art

[0002] A loss-of-coolant accident (LOCA) is a design basis accident for a pressurized water reactor. In a LOCA accident, a series of complex behavioral evolutions will occur in nuclear fuel rods, which may threaten the structural integrity of fuel elements and even the reactor core. Therefore, it is very necessary to study the fuel behavior and failure under LOCA accidents. The phenomena in LOCA accidents are very complex, and the difficulty of numerical simulation is extremely high. It is necessary to conduct experiments to deeply understand the phenomena and mechanisms.

[0003] At present, many experimental devices have been designed and established for fuel behavior in LOCA accidents at home and abroad. Most of the existing test devices only consider the behavior of the cladding and do not consider the behavior of the pellet. For example, the cladding is directly heated or an electric heating rod is used to simulate the heating of the pellet. For example, the invention patent with the patent publication number CN105070331B discloses an "experimental device for evaluating the performance of nuclear fuel cladding tubes under simulated LOCA conditions", which includes a cavity, a heating device, a steam circulation device, a vacuum pumping device and a cooling device. The cladding is located in the cavity, and by setting a heating rod in the cladding, the heating of the cladding by the pellet is simulated. In the existing technology, the devices that directly heat the cladding or heat the cladding through a heating rod all ignore the mechanical action of the pellet cracking on the cladding and the change of heat transfer characteristics, resulting in the experimental results may deviate from the actual situation.

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

[0005] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide an experimental device for simulating the behavior of nuclear fuel in a loss-of-coolant accident, aiming to solve the problem that the LOCA accident simulation device in the existing technology ignores the mechanical action of the pellet cracking on the cladding and the change of heat transfer characteristics, resulting in inaccurate experimental results.

[0006] The technical solution adopted by the present invention to solve the technical problems is as follows: An experimental device for simulating the behavior of nuclear fuel in a loss-of-coolant accident, comprising: A cladding; A pellet, disposed inside the cladding; the top wall and the bottom wall of the pellet are respectively connected to an external power source through wires; An insulating member, disposed on the outer surface of the pellet to isolate the pellet from the cladding; A pressurized cooling pipeline, sleeved outside the cladding and arranged in a sealed manner with the cladding; A cooling component, connected to the pressurized cooling pipeline to form a coolant circulation flow path.

[0007] Furthermore, it further includes: Two fixed flanges, respectively arranged at both ends of the pressurized cooling pipeline; both ends of the cladding extend out of the pressurized cooling pipeline, and the fixed flanges are respectively connected to the fixed flanges and the cladding.

[0008] Furthermore, an inflation port and a deflation port are arranged on the cladding located outside the pressurized cooling pipeline, and a first pressure gauge is arranged inside the cladding.

[0009] Furthermore, it further includes: Two springs, respectively arranged on the inner top wall and the inner bottom wall of the cladding; the two springs respectively abut against the top wall and the bottom wall of the fuel pellet.

[0010] Furthermore, the cooling component includes: A first pipeline, arranged on the side wall of the pressurized cooling pipeline; A first break, arranged on the first pipeline; A heat exchanger, arranged at one end of the first pipeline away from the pressurized cooling pipeline; A second pipeline, arranged on the heat exchanger; one end of the second pipeline is communicated with the outlet of the heat exchanger, and the other end is arranged at the bottom of the pressurized cooling pipeline and is communicated with the inside of the pressurized cooling pipeline; A circulation pump, arranged on the second pipeline; A second break, arranged on the second pipeline; by opening the first break and / or the second break, the processes of coolant ejection, flashing, liquid level drop, and dryout can be simulated.

[0011] Furthermore, the cooling component further includes: A reflooding water tank, arranged outside the pressurized cooling pipeline; the reflooding water tank is communicated with the inside of the pressurized cooling pipeline through a pipeline; A water storage tank, arranged outside the pressurized cooling pipeline; the water storage tank is communicated with the second pipeline through a connecting pipeline, and the connection point of the connecting pipeline and the second pipeline is located on the side of the circulation pump away from the pressurized cooling pipeline, and the water storage tank cooperates with the reflooding water tank to simulate the process of refrigerant reflooding.

[0012] Furthermore, it further includes: A synchrotron radiation X-ray in-situ imaging device, arranged on one side of the pressurized cooling pipeline, for detecting the cracking of the fuel pellet and the deformation of the cladding.

[0013] Further, it further includes: Two electrodes are respectively arranged on the top wall and the bottom wall of the pellet; the electrodes penetrate through the cladding and extend to the outside of the cladding, and the electrodes are hermetically arranged with the cladding.

[0014] Further, the number of the pellets is multiple, and the multiple pellets are stacked inside the pressurized cooling pipe.

[0015] Further, an acoustic level gauge and a second pressure gauge are arranged inside the pressurized cooling pipe.

[0016] Compared with the prior art, the beneficial effects of the present invention are: In the present invention, a pellet is arranged inside the cladding. The top wall and the bottom wall of the pellet are respectively connected to an external power supply through wires. An insulating member is arranged between the pellet and the cladding. A pressurized cooling pipe is arranged outside the cladding, and the pressurized cooling pipe is connected to a cooling assembly; by simulating the fission heat generation process of real nuclear fuel through self-heating of the pellet when powered on, and combining the synergistic effect of the pressurized cooling pipe and the cooling assembly, the thermal stress cracking of the pellet can be effectively restored, so as to realize in-situ pellet cracking with the same principle as the cracking of real pellets, and the more real pellet cracking morphology and the deformation and rupture conditions of the cladding can be obtained, improving the accuracy and reliability of experimental data. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] The numeral markings in the figure are represented as: 1, cladding; 11, gas inlet; 12, gas outlet; 13, first pressure gauge; 14, spring; 2, pellet; 21, electrode; 3, insulating member; 4, pressurized cooling pipe; 5, cooling assembly; 51, first pipe; 52, first break; 53, heat exchanger; 54, second pipe; 55, circulation pump; 56, second break; 57, reflooding water tank; 58, water storage tank; 6, fixed flange; 7, synchrotron radiation X-ray in-situ imaging device; 8, acoustic level gauge; 9, second pressure gauge. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In order to make the purpose, 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 embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] 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. These are only for convenience in 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. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity 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 stated, the meaning of "plurality" is two or more.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "mounted", "connected", and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. 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.

[0022] In the prior art, the devices that directly heat the cladding 1 or heat the cladding 1 through heating rods all ignore the mechanical effects on the cladding 1 during the cracking process of the fuel pellets 2 and the changes in heat transfer characteristics, resulting in the experimental results possibly deviating from the actual situation.

[0023] The nuclear fuel pellets 2 will crack at high temperatures due to factors such as thermal stress and irradiation swelling, forming a fragmented blocky or debris-like structure. After cracking, the pellets 2 will lose their overall rigidity, and their internal stresses will be redistributed through the fracture surfaces, and may generate local concentrated loads (such as extrusion, friction) on the inner wall of the cladding 1; secondly, heat is conducted between the intact pellets 2 and the cladding 1 through the contact surface, while after cracking, the pellets 2 break into multiple pieces, with a large number of voids formed inside, resulting in a decrease in heat conduction efficiency and possibly changing to a heat transfer mode mainly based on radiation and gas (such as fission gas) convection.

[0024] In view of the deficiencies of the prior art, the present embodiment provides a simulation experimental device for the behavior of nuclear fuel during a loss-of-coolant accident, which can be specifically referred to as follows: As shown in the attached Figure 1As shown in the figure, a simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident includes a cladding 1, fuel pellets 2, an insulating member 3, a pressurized cooling pipe 4, and a cooling assembly 5. The fuel pellets 2 are arranged inside the cladding 1, and their top and bottom walls are connected to an external power supply through wires. The insulating member 3 is arranged on the outer surface of the fuel pellets 2 to isolate the fuel pellets 2 from the cladding 1. The pressurized cooling pipe 4 is hermetically sleeved outside the cladding 1. The cooling assembly 5 is connected to the pressurized cooling pipe 4 to form a coolant circulation flow path.

[0025] Among them, the fuel pellets 2 refer to ceramic material blocks with nuclear fuel physical properties. Specifically, uranium oxide or cerium oxide can be used, and their resistance characteristics can achieve self-heating when powered on. The insulating member 3 refers to an isolation layer with electrical insulation and high-temperature resistance characteristics. Specifically, an alumina ceramic coating can be used to achieve it, allowing thermal expansion displacement while ensuring electrical isolation between the fuel pellets 2 and the cladding 1. The pressurized cooling pipe 4 refers to a sealed container that can withstand internal pressure, and a closed cooling space is formed through flange connection. The cooling assembly 5 refers to a circulation system that can regulate the flow of coolant. Specifically, it can be achieved by combining a multi-stage pump and a heat exchanger 53, and the phase change of the coolant is simulated through valve control.

[0026] Specifically, the cladding 1, as the constraint structure of the fuel assembly, the stacked fuel pellets 2 inside generate Joule heat when powered on through wires, accurately reproducing the heat generation mechanism during reactor core operation. The ceramic insulation layer covering the surface of the fuel pellets 2 can prevent current leakage. The sealed pressurized cooling pipe 4 wraps the cladding 1 to form a pressure boundary, and the coolant is driven to flow inside the pressurized cooling pipe 4 by a circulation pump 55. When simulating the loss-of-coolant condition, by adjusting the coolant flow rate and pressure parameters, the change process of the cooling conditions outside the cladding 1 can be precisely controlled. The crack propagation behavior generated by the fuel pellets 2 during continuous heating is transmitted in real time through the spring 14 mechanism arranged inside the cladding 1 to completely reproduce the structural response of the fuel rod under accident conditions.

[0027] Compared with the prior art, the traditional experimental device uses an external heating rod to simulate the heat generation of the fuel pellets 2, which cannot generate a real radial temperature gradient, resulting in distorted calculation of the thermal stress distribution of the cladding 1. This solution generates heat through the resistance of the fuel pellets 2 themselves, not only reproducing the axial heat conduction characteristics of the fuel rod, but also more accurately simulating the dynamic process of the change in thermal resistance after the fuel pellets 2 are fragmented. In the prior art, the geometric shape of the prefabricated fragments is fixed, while this solution allows the fuel pellets 2 to crack naturally during their own heating process, generating irregular fragment shapes that conform to the actual working conditions. In terms of the cooling system design, the traditional single-loop system is difficult to simulate the transient processes of coolant flashing and reflooding. This solution realizes precise control of the phase change of the coolant through the combination of multi-branch pipes and a break device.

[0028] Through the above technical solutions, this application can truly simulate the cracking behavior of the fuel pellet 2 under high temperature and high pressure conditions, and accurately capture the interaction mechanism between the pellet 2 and the pellet 2 fragments and the cladding 1. By directly using the fuel material for experiments, the physical property differences between the simulation object and the prototype are eliminated. The adjustable coolant circulation system can reproduce the entire process of coolant loss, ejection, and reflooding in a LOCA accident, providing reliable experimental data for studying the failure mode of fuel rods. The synergistic effect of the self-heating mode of the pellet 2 and the external cooling conditions makes the thermo-mechanical response analysis of the cladding 1 closer to the actual working conditions.

[0029] As shown in the Figure 1 accompanying drawings, this application further proposes that the experimental device for simulating the behavior of nuclear fuel in a loss-of-coolant accident includes two fixed flanges 6, which are respectively arranged at both ends of the pressurized cooling pipeline 4. Both ends of the cladding 1 extend out of the pressurized cooling pipeline 4, and the fixed flanges 6 are respectively connected to the pressurized cooling pipeline 4 and the cladding 1 to seal and fix the pressurized cooling pipeline 4 and the cladding 1.

[0030] Among them, the fixed flange 6 refers to an annular connecting piece with a sealing structure, which is used to form a rigid sealing interface between the pressurized cooling pipeline 4 and the cladding 1. The fact that both ends of the cladding 1 extend out of the pressurized cooling pipeline 4 means that the length of the cladding 1 body exceeds the pipeline coverage range, which can be specifically achieved by adjusting the difference between the axial dimension of the cladding 1 and the inner cavity length of the pressurized cooling pipeline 4, providing a physical installation space for the external interface setting.

[0031] Specifically, the fixed flange 6 is respectively fixed between the end of the pressurized cooling pipeline 4 and the outer wall of the cladding 1 through a bolt connection method to form a double-sealing structure. After the extended section of the cladding 1 is exposed outside the pipeline, an inflation port 11 and a deflation port 12 can be directly set in its exposed area without opening holes on the main body of the pressurized cooling pipeline 4.

[0032] Through the above technical solutions, this application realizes a reliable sealed connection between the pressurized cooling pipeline 4 and the cladding 1, and at the same time provides an independent operation interface for the internal pressure monitoring and regulation of the cladding 1. The extended section structure enables components such as the inflation port 11, the deflation port 12, and the first pressure gauge 13 to be directly installed on the main body of the cladding 1, avoiding the leakage hidden danger caused by opening holes in the pressurized cooling pipeline 4 and ensuring the precise control of pressure parameters during the experiment.

[0033] As shown in the Figure 1 accompanying drawings, this application further proposes that an inflation port 11 and a deflation port 12 are arranged on the cladding 1 outside the pressurized cooling pipeline 4, and a first pressure gauge 13 is arranged inside the cladding 1.

[0034] Among them, the inflation port 11 refers to the gas injection interface arranged on the wall of the cladding 1, which can be implemented by a tubular structure with a sealing valve, and is used to inject gas into the cladding 1 to create a pressure environment. The deflation port 12 refers to the gas discharge interface arranged on the wall of the cladding 1, which can be implemented by an adjustable throttle valve structure, and is used to control the release rate of the gas inside the cladding 1. The first pressure gauge 13 refers to a pressure sensor installed in the cavity of the cladding 1, which can be implemented by a digital pressure transmitter, and is used to monitor the pressure value changes in the enclosed space in real time.

[0035] Specifically, during the experiment, the inflator 11 injects an inert gas (such as helium, which has good thermal conductivity) into the cladding 1 through an external gas source to increase the pressure, and the first pressure gauge 13 continuously collects the internal pressure data of the cladding 1; when it is necessary to simulate the sudden drop in pressure caused by the spraying of the coolant, the deflation port 12 adjusts the gas discharge amount according to the value fed back by the first pressure gauge 13 to form a closed-loop pressure control. This solution can dynamically adjust the internal pressure of the cladding 1 through the linkage operation of the inflator 11 and the deflation port 12, combined with the real-time monitoring function of the first pressure gauge 13, so as to accurately simulate the transient pressure load on the fuel rods in the accident.

[0036] Compared with the existing technology, the traditional experimental device usually adopts a sealed cavity with a fixed volume, which can only maintain a static pressure environment and cannot reproduce the pressure fluctuation process under accident conditions. This solution breaks through the technical limitations of static pressure simulation by adding actively adjusted inflation ports 11 and deflation ports 12, and cooperates with the data feedback of the first pressure gauge 13, so that the internal pressure of the cladding 1 can be dynamically controlled according to the experimental requirements.

[0037] Through the above technical solution, the present application realizes the real-time monitoring and active regulation of the internal pressure of the cladding 1, effectively solving the defect that the traditional device cannot simulate the influence of transient pressure changes on the behavior of the fuel rods, and provides precise experimental conditions for studying the cracking, deformation and interaction of the fuel rods under pressure fluctuations in the coolant loss accident.

[0038] As attached Figure 1 As shown, the present application further proposes that the coolant loss accident nuclear fuel behavior simulation experimental device also includes two springs 14, the two springs 14 are respectively arranged on the inner top wall and the inner bottom wall of the cladding 1, and the two springs 14 are respectively in contact with the top wall and the bottom wall of the core block 2.

[0039] Among them, the spring 14 refers to an elastic support element, and its elastic modulus is matched according to the thermal expansion coefficient of the pellet 2. The spring 14 absorbs the axial displacement generated by the heat generation of the pellet 2 through compression deformation, and at the same time provides a buffer space when the pellet 2 breaks. Among them, abutment means that the spring 14 remains in contact with the end face of the pellet 2 but is not completely fixed, which can be specifically achieved by presetting a pre-tightening force, so that the pellet 2 can maintain electrical connection with the wire during the experiment and can transmit the thermal expansion pressure axially. This abutment method not only restricts the displacement of the pellet 2 but also allows it to undergo limited deformation when heated.

[0040] Specifically, when the pellet 2 undergoes axial expansion, the springs 14 at both ends are compressed, and the disordered displacement of the pellet 2 is restricted through bidirectional elastic constraints; under the action of the double springs 14, the pellet 2 can be located inside the pressurized cooling pipe 4, so that when the pellet 2 expands, the expansion force acts on the cladding 1 located inside the pressurized cooling pipe 4, thereby accurately simulating the deformation and rupture of the cladding 1 under real conditions.

[0041] Compared with the prior art, most existing experimental devices rigidly fix or completely freely place the pellet 2. Rigid fixation will hinder the thermal expansion of the pellet 2, resulting in distortion of the stress distribution of the cladding 1; free placement cannot reflect the dynamic contact behavior between the pellet 2 and the cladding 1 after the pellet 2 breaks. This solution allows the pellet 2 to expand naturally when heated through bidirectional elastic support, prevents it from deviating from the preset position, and indirectly reflects the mechanical force between the pellet 2 and the cladding 1 through the deformation of the spring 14, more realistically reproducing the interaction process of the internal components of the fuel rod under accident conditions.

[0042] Through the above technical solutions, this application effectively solves the problem of displacement deviation caused by the unfixed pellet 2, simulates the change of the contact state between the pellet 2 and the cladding 1 after the pellet 2 breaks through elastic constraints, and avoids the direct impact damage of the thermal expansion of the pellet 2 on the end of the cladding 1. The elastic deformation characteristics of the spring 14 make the behavior monitoring data of the pellet 2 closer to the physical response of the real nuclear fuel rod under accident conditions, providing reliable experimental conditions for studying the correlation mechanism between the cracking of the pellet 2 and the deformation of the cladding 1.

[0043] As shown in the appendix Figure 1As shown in the figure, the present application further proposes that the cooling component 5 includes a first pipeline 51, a first break 52, a heat exchanger 53, a second pipeline 54, a circulation pump 55, and a second break 56. The first pipeline 51 is arranged on the side wall of the pressurized cooling pipeline 4, the first break 52 is arranged on the first pipeline 51, and the heat exchanger 53 is arranged at one end of the first pipeline 51 away from the pressurized cooling pipeline 4. The second pipeline 54 is arranged on the heat exchanger 53, one end of which is connected to the outlet of the heat exchanger 53, and the other end is arranged at the bottom of the pressurized cooling pipeline 4 and is in internal communication. The circulation pump 55 is arranged on the second pipeline 54, and the second break 56 is arranged on the second pipeline 54. By opening the first break 52 and / or the second break 56, the processes of coolant spray, flash evaporation, liquid level drop, and dryout are simulated.

[0044] Among them, Figure 1 the arrow in indicates the flow direction of the coolant; the first pipeline 51 refers to the fluid transmission channel connecting the side wall of the pressurized cooling pipeline 4 and the heat exchanger 53, which is used to establish the coolant circulation path. The first break 52 refers to the controllable opening device arranged on the first pipeline 51, which is used to actively trigger the rapid leakage of the coolant. The heat exchanger 53 refers to the device with heat exchange function, which is used to adjust the phase change of the coolant. The second pipeline 54 refers to the return channel connecting the outlet of the heat exchanger 53 and the bottom of the pressurized cooling pipeline 4, which is used to form a closed-loop circulation system. The circulation pump 55 refers to the mechanical device that drives the flow of the coolant, which can be specifically realized by a centrifugal pump and is used to maintain the circulation power of the coolant in the system. The second break 56 refers to the pressure relief device arranged on the second pipeline 54, which is used to simulate the loss of coolant at different positions.

[0045] Specifically, when the coolant circulates in the pressurized cooling pipeline 4, the first pipeline 51 forms an initial flow path through the connection at the side wall position. When the first break 52 is opened, the coolant is quickly sprayed through this break, simulating the sudden leakage process at the initial stage of the accident. The heat exchanger 53 conducts heat exchange on the sprayed coolant, promoting the flash evaporation phase change of the liquid coolant. The second pipeline 54 transports the heat-exchanged coolant to the bottom of the pressurized cooling pipeline 4, and the circulation pump 55 controls the liquid level drop rate in the channel by adjusting the flow rate. The opening of the second break 56 can change the system pressure distribution, and cooperate with the combined operation of the first break 52 to realize different working conditions such as single-phase loss and two-phase mixed loss. By opening different breaks in stages, the dryout process of the coolant in the channel can be gradually reproduced.

[0046] Through the above technical solution, the present application can completely simulate the whole - process dynamic evolution of the coolant from ejection, flashing to liquid - level decline until it dries up during a loss - of - coolant accident. The combined operation of the first break 52 and the second break 56 can simulate leakage scenarios at different positions and degrees, and the synergistic effect of the heat exchanger 53 and the circulation pump 55 can accurately control the phase state and circulation state of the coolant. The bottom - connection design of the second pipeline 54 enables the liquid - level change to form a linkage with the coolant circulation, effectively reproducing the spatio - temporal distribution characteristics of the gradual loss of coolant in an actual accident.

[0047] As shown Figure 1 in the attached figure, the present application further proposes that the cooling assembly 5 further includes a reflooding water tank 57 and a storage water tank 58. The reflooding water tank 57 is arranged outside the pressurized cooling pipeline 4 and is connected to the inside of the pressurized cooling pipeline 4 through a pipeline. The storage water tank 58 is arranged outside the pressurized cooling pipeline 4 and is connected to the second pipeline 54 through a connecting pipeline. The connection point of the connecting pipeline and the second pipeline 54 is located on the side of the circulation pump 55 away from the pressurized cooling pipeline 4. The storage water tank 58 and the reflooding water tank 57 cooperate to simulate the refrigerant reflooding process.

[0048] Among them, the reflooding water tank 57 refers to a container for storing emergency coolant, and the fluid exchange with the pressurized cooling pipeline 4 is controlled by a valve. The storage water tank 58 refers to a container for storing the main - circulation coolant, and provides coolant replenishment to the second pipeline 54 through the connecting pipeline. The connection point of the connecting pipeline and the second pipeline 54 is set upstream of the circulation pump 55, and can be specifically realized through a tee joint. This position setting can utilize the negative - pressure effect generated by the circulation pump 55 to improve the liquid - supplement efficiency of the storage water tank 58 to the main - circulation system.

[0049] Specifically, when it is necessary to simulate the coolant reflooding condition in the experiment, the connection valve between the reflooding water tank 57 and the pressurized cooling pipeline 4 is opened, and the coolant is injected into the pipeline interior under the action of gravity. The storage water tank 58 continuously supplies coolant to the second pipeline 54 through the connecting pipeline. Since the connection point is located on the inlet side of the circulation pump 55, the negative pressure generated when the circulation pump 55 operates accelerates the delivery speed of the coolant in the storage water tank 58. The coordinated operation of the two water tanks enables the main - circulation system to simultaneously receive continuous replenishment from the storage water tank 58 and concentrated injection from the reflooding water tank 57. By adjusting the liquid - supply ratio of the two water tanks, reflooding scenarios under different leakage rates can be simulated. The operating parameters of the circulation pump 55 and the liquid - supply pressure of the water tanks form a dynamic balance, thus truly reproducing the fluid dynamic characteristics of the coolant reflooding stage in the accident condition.

[0050] Through the above technical solutions, the present application can accurately control the replenishment speed and fluid mixing state of the coolant reflooding process, and effectively simulate the complex working conditions of the coordinated operation of multiple replenishment sources in the coolant system during a nuclear power plant accident. The independent liquid supply characteristics of the two water tanks enable the experimental device to reproduce the influence of different emergency injection strategies on the reflooding effect of fuel rods, providing a real and reliable experimental environment for studying the thermodynamic behavior of fuel elements under dynamic reflooding conditions.

[0051] As shown in the Figure 1 accompanying drawings, the present application further proposes that a synchrotron radiation X-ray in-situ imaging device 7 is arranged on one side of the pressurized cooling pipe 4 for detecting the cracking of the pellet 2 and the deformation of the cladding 1.

[0052] Among them, the synchrotron radiation X-ray in-situ imaging device 7 refers to a detection device that uses high-energy X-rays to penetrate non-transparent materials and form real-time images. It is realized by using existing technologies and adapts to different material thicknesses by adjusting the X-ray energy parameters. This device directly obtains the crack propagation process inside the pellet 2 by penetrating the pressurized cooling pipe 4 and the cladding 1.

[0053] Specifically, when simulating a coolant loss accident, the synchrotron radiation X-ray in-situ imaging device 7 is arranged along the axis direction of the pressurized cooling pipe 4, and the X-ray beam penetrates the pipe wall, the cladding 1, and the pellet 2. When thermal stress is generated in the pellet 2 due to the temperature gradient, resulting in crack initiation, the change in material density at the crack causes a difference in X-ray absorption, forming a real-time image with light and dark contrast on the detector. The local expansion or shrinkage deformation of the cladding 1 is quantified by the displacement of the cladding 1 contour in the consecutive images. After the image sequence is processed by a three-dimensional reconstruction algorithm, the three-dimensional deformation data of the cladding 1 can be obtained. This process continues throughout the experiment, completely recording the natural formation process of the fragmentation morphology of the pellet 2.

[0054] Through the above technical solutions, the present application solves the technical bottleneck of being unable to observe the dynamic changes of the internal structure of fuel rods in real time, provides direct experimental data support for analyzing the fragmentation mechanism of the pellet 2 and the mechanical response of the cladding 1 during a coolant loss accident, and avoids the problem that the experimental samples cannot be reused due to traditional destructive testing.

[0055] As shown in the Figure 1 accompanying drawings, the present application further proposes that the experimental device for simulating the behavior of nuclear fuel during a coolant loss accident includes two electrodes 21, which are respectively arranged on the top wall and the bottom wall of the pellet 2. The electrodes 21 penetrate through the cladding 1 and extend to the outside of the cladding 1, and the electrodes 21 are arranged in a sealed manner with the cladding 1.

[0056] Among them, the electrodes 21 penetrating through the cladding 1 means that the electrodes 21 penetrate through the wall surfaces on the upper and lower sides of the cladding 1 in a penetrating manner, so as to facilitate the electrodes 21 to extend into the inside of the cladding 1 and abut against the top wall or the bottom wall of the pellet 2, ensuring that the electrodes 21 conduct electricity while maintaining the structural integrity of the cladding 1.

[0057] If the wire is directly in contact with the pellet 2, a wire with a larger diameter is required to provide electrical conductivity; the arrangement of the electrode 21 in this application can avoid the wire directly extending into the interior of the cladding 1 and also avoid using a wire with a larger diameter.

[0058] Specifically, after the electrode 21 is led out from the top wall or the bottom wall of the pellet 2, it penetrates through the corresponding position of the cladding 1, extends to the outside of the cladding 1 and forms an electrical connection loop with an external power supply, and the contact surface between the electrode 21 and the cladding 1 is sealed by a sealing structure.

[0059] As shown in the Figure 1 accompanying drawings, this application further proposes that the number of pellets 2 is multiple, and the multiple pellets 2 are stacked inside the pressurized cooling pipe 4.

[0060] Among them, the pellet 2 refers to an independent unit simulating a nuclear fuel core, and specifically can be made of a ceramic material or a metal material into a cylindrical or annular structure, and forms an axially stacked fuel rod model through stacking, and can generate relative displacement and interaction under thermal expansion or mechanical load. The stacked state means that the pellets 2 are stacked axially in a manner without fixed constraints, allowing the pellets 2 to generate axial displacement and radial expansion under thermal stress, simulating the expansion and extrusion behavior of the pellets 2 in a real fuel rod due to temperature gradient.

[0061] Specifically, when the multiple pellets 2 form a stacked structure inside the pressurized cooling pipe 4, frictional force and contact stress are generated on the contact surface between the pellets 2 under thermal load. When the coolant is lost and the temperature rises sharply, the pellets 2 generate axial elongation and radial expansion due to thermal expansion, and the contact stress between adjacent pellets 2 increases, which may cause local cracking or dislocation. The stacked structure enables the pellets 2 to be restricted by adjacent pellets 2 during the expansion process, simulating the interaction force between the pellets 2 in a real fuel rod. Under the continuous action of thermal stress, the stack of pellets 2 may undergo overall axial displacement or local scattering, thereby dynamically reflecting the mechanical effect of the repositioning of the pellets 2 on the cladding 1 during an accident.

[0062] Through the above technical solutions, this application can accurately reproduce the dynamic mechanical effects between multiple pellets 2 during a coolant loss accident, including axial extrusion caused by thermal expansion, stress concentration of the cladding 1 caused by radial expansion, and impacts on the cladding 1 caused by the scattering of cracked pellets 2, etc., and solves the problem that the experimental results deviate from the real working conditions due to the single simulation method of the pellets 2 in the prior art.

[0063] As shown in the Figure 1 accompanying drawings, this application further proposes a technical solution of arranging a sonic level gauge 8 and a second pressure gauge 9 inside the pressurized cooling pipe 4.

[0064] Among them, the acoustic wave level gauge 8 refers to a device that measures the liquid level by emitting ultrasonic waves and receiving the reflected signals. Specifically, a pulsed ultrasonic sensor can be used to achieve this, and it determines the liquid level height by calculating the time difference of the acoustic wave propagation. This device can maintain the measurement accuracy in high-temperature and high-pressure environments and solve the problem of response delay caused by the traditional mechanical level gauge contacting the medium. The second pressure gauge 9 refers to an instrument used to detect the fluid pressure in a closed space.

[0065] Specifically, the acoustic wave level gauge 8 is installed at the top position of the pressurized cooling pipe 4 and emits ultrasonic signals into the channel. The signals are reflected by the liquid surface and captured by the receiver, and the real-time liquid level height is calculated through the time difference. The second pressure gauge 9 is embedded in the side wall of the channel to detect the pressure in the pressurized cooling pipe 4.

[0066] Through the above technical solution, the present application realizes the real-time synchronous monitoring of the coolant liquid level height and the system pressure, can accurately capture the dynamic parameter changes in the coolant ejection, flashing, and dry-out stages during the LOCA accident simulation, solves the problem that the analysis of the correlation between the cracking behavior of the fuel pellet 2 and the deformation of the cladding 1 is inaccurate due to the measurement lag of the existing device, and provides a reliable data basis for studying the failure mechanism of the fuel element during the coolant loss process.

[0067] After considering the specification and practicing the solutions disclosed herein, those skilled in the art will readily conceive 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. A simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident, characterized in that, Comprising: A cladding; Fuel pellets, disposed inside the cladding; the top wall and the bottom wall of the fuel pellets are respectively connected to an external power supply through wires; Insulating members, disposed on the outer surface of the fuel pellets to isolate the fuel pellets from the cladding; A pressurized cooling pipe, sleeved outside the cladding and hermetically arranged with the cladding; A cooling assembly, connected to the pressurized cooling pipe to form a coolant circulation flow path.

2. The simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 1, wherein, It further comprises: Two fixed flanges, respectively disposed at both ends of the pressurized cooling pipe; both ends of the cladding extend out of the pressurized cooling pipe, and the fixed flanges are respectively connected to the fixed flanges and the cladding.

3. The simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 2, wherein, An inflation port and a deflation port are provided on the cladding outside the pressurized cooling pipe, and a first pressure gauge is provided inside the cladding.

4. A simulation experimental device for nuclear fuel behavior during a loss of coolant accident according to claim 2, characterized in that, It further comprises: Two springs, respectively disposed on the inner top wall and the inner bottom wall of the cladding; the two springs respectively abut against the top wall and the bottom wall of the fuel pellets.

5. The simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 1, wherein The cooling assembly comprises: A first pipe, disposed on the side wall of the pressurized cooling pipe; A first break, provided on the first pipe; A heat exchanger, disposed at one end of the first pipe away from the pressurized cooling pipe; A second pipe, disposed on the heat exchanger; one end of the second pipe is communicated with the outlet of the heat exchanger, and the other end is disposed at the bottom of the pressurized cooling pipe and is communicated with the inside of the pressurized cooling pipe; A circulation pump, disposed on the second pipe; A second break, provided on the second pipe; by opening the first break and / or the second break, the processes of coolant spray, flashing, liquid level drop and dryout can be simulated.

6. The simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 5, wherein, The cooling assembly further comprises: A reflooding water tank, disposed outside the pressurized cooling pipe; the reflooding water tank is communicated with the inside of the pressurized cooling pipe through a pipe; A storage water tank, disposed outside the pressurized cooling pipe; the storage water tank is communicated with the second pipe through a connecting pipe, and the connection point of the connecting pipe and the second pipe is located on the side of the circulation pump away from the pressurized cooling pipe, and the storage water tank cooperates with the reflooding water tank to simulate the process of refrigerant reflooding.

7. A simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 1, characterized in that, It further comprises: A synchrotron radiation X-ray in-situ imaging device, disposed on one side of the pressurized cooling pipe for detecting the cracking of the fuel pellets and the deformation of the cladding.

8. A simulation experimental device for nuclear fuel behavior during a loss of coolant accident according to claim 1, characterized in that, It further comprises: Two electrodes, respectively disposed on the top wall and the bottom wall of the fuel pellets; the electrodes penetrate through the cladding and extend to the outside of the cladding, and the electrodes are hermetically arranged with the cladding.

9. The simulation experimental device for nuclear fuel behavior during a loss of coolant accident according to claim 1, characterized in that, The number of the fuel pellets is multiple, and the multiple fuel pellets are stacked inside the pressurized cooling pipe.

10. The simulation experimental device for nuclear fuel behavior during a loss-of-coolant accident according to claim 1, wherein, An acoustic liquid level gauge and a second pressure gauge are provided inside the pressurized cooling pipe.

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