An experimental device for vortex flow field in the lower chamber of a nuclear reactor

Abstract

This invention discloses an experimental device for the vortex flow field in the lower chamber of a nuclear reactor, comprising an inlet assembly, a descending annular cavity assembly, a lower chamber assembly, an upper chamber assembly, and an outlet assembly assembled sequentially. Within these components are interconnected inlet channels, descending annular cavity channels, lower chamber channels, upper chamber channels, and outlet channels for fluid flow. The device also includes a flow resistance simulation mechanism located downstream of the channels on the lower core plate. This mechanism comprises multiple independently configured resistance units with adjustable resistance characteristics. Adjusting these resistance units allows for the construction of uniform or non-uniform flow distributions behind the lower core plate, simulating different flow distribution conditions during actual reactor core operation. The upper and lower chamber assemblies are equipped with transparent structures to enable visual observation and measurement of the vortex flow field in the lower chamber under different flow distribution conditions. This invention constructs uniform or non-uniform flow distributions behind the lower core plate, enabling visual observation and measurement of the vortex flow field in the lower chamber.

Description

Technical Field

[0001] This invention relates to the field of experimental technology for visualization of reactor flow fields, and in particular to an experimental device for vortex flow fields in the lower chamber of a nuclear reactor. Background Technology

[0002] Reactor core inlet flow distribution and fluid pulsation are crucial parameters for reactor thermal-hydraulic design, structural optimization, and reactor analysis. The vortex size and distribution in the reactor lower chamber directly affect the uniformity and stability of the reactor core inlet flow distribution. Factors influencing the flow field in the reactor lower chamber include upstream and downstream conditions and the flow distributor structure itself. Upstream conditions and the flow distributor structure are dominant, while downstream disturbances have a weaker impact on the lower chamber, primarily affecting flow field stability. In reactor design, as a crucial part of the upstream flow path, variations in the structure and arrangement of guide vanes, irradiated sample holders, and even inlet / outlet nozzle assemblies can influence the flow field in the lower chamber. However, the reactor core, as the downstream flow path, is generally only simulated for its flow resistance characteristics due to its complex structure.

[0003] Existing patents or technologies are mostly prototype designs of flow distribution devices or structures in the lower chamber, focusing more on the resulting flow uniformity characteristics, with few measuring and evaluating the vortex generation and stability of the flow field in the lower chamber through engineering experiments. Therefore, there is an urgent need for an experimental device that can overcome the challenges of engineering experiments under high flow conditions and achieve accurate visualization measurement of the vortex flow field in the lower chamber. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an experimental device for the vortex flow field in the lower chamber of a nuclear reactor.

[0005] The technical solution adopted by the present invention to solve its technical problem is: to construct an experimental device for a vortex flow field in the lower chamber of a nuclear reactor, comprising an inlet assembly, a descending annular cavity assembly, a lower chamber assembly, an upper chamber assembly and an outlet assembly assembled in sequence, and forming a connected inlet flow channel, a descending annular cavity flow channel, a lower chamber flow channel, an upper chamber flow channel and an outlet flow channel inside it for fluid to flow through; The experimental device for the vortex flow field in the lower chamber of the nuclear reactor also includes a flow resistance simulation mechanism located downstream of the flow channel in the lower chamber. The flow resistance simulation mechanism includes multiple independently configured and adjustable resistance units. By adjusting the resistance characteristics of each resistance unit, a uniform or non-uniform flow distribution is constructed to simulate different flow distributions in actual reactor core operation. The upper chamber assembly and the lower chamber assembly are equipped with transparent structures to enable the visualization and measurement of the vortex flow field in the lower chamber under different flow distribution conditions.

[0006] Furthermore, the inlet assembly includes several inlet pipe assemblies, each of which forms an inlet flow channel; the outlet end of each inlet pipe assembly is fixedly connected to the inlet end of the descending annular cavity assembly, and the structure and installation orientation of each inlet pipe assembly are consistent with the reactor prototype.

[0007] Furthermore, the descending annular cavity assembly includes a lower cylinder and a basket cylinder. The lower cylinder is coaxially sleeved on the outside of the basket cylinder to form an annular descending annular cavity flow channel. The inlet end of the descending annular cavity flow channel is connected to the outlet end of the inlet flow channel, and the outlet end of the descending annular cavity flow channel is connected to the inlet end of the lower chamber flow channel. Several flow guides, irradiation sample holders, and basket nozzles are fixedly installed inside the descending annular cavity flow channel.

[0008] Furthermore, the basket nozzle is detachably connected to the basket cylinder. The basket nozzle is a scaled-down component that combines the basket outlet nozzle and the inner extension end of the outlet pipe assembly of the outlet assembly in the reactor prototype, so as to maintain the geometric similarity of the descending annular cavity flow channel in the descending annular cavity assembly.

[0009] Furthermore, the lower chamber assembly includes a transparent lower end cap, a flow distributor, a support key, and a lower core plate. The inlet end of the lower end cap is connected to the outlet end of the descending annular cavity assembly. The flow distributor is fixedly installed inside the lower end cap, with its inlet side communicating with the flow channel of the descending annular cavity and its outlet side abutting with the flow channel hole on the lower core plate. The support key is installed between the inner wall of the lower end cap and the outer wall of the flow distributor to radially position and support the flow distributor.

[0010] Furthermore, the inner wall of the lower end cap is provided with a positioning reference, and the outer side of the lower end cap is provided with a positioning device for monitoring deformation and levelness, so as to facilitate the installation, leveling and control of the flow channel gap between the lower end cap and the flow distributor.

[0011] Furthermore, the positioning device includes at least one universal level disposed on the end face of the lower end cap, and the positioning reference is a scale line disposed at the target height of the inner wall of the lower end cap.

[0012] Furthermore, each of the drag units includes at least one detachable fuel assembly simulator, which is fixed downstream of the lower core plate by a support plate; Each of the fuel assembly simulators includes a stabilizing section and a drag modulator, the drag modulator being detachably connected to the stabilizing section, the inlet end of the stabilizing section being aligned with a flow channel hole on the lower core plate.

[0013] Furthermore, the resistance regulating element is a telescopic or variable diameter sleeve structure, and the flow area of ​​the resistance regulating element is adjusted to construct a uniform or non-uniform flow distribution with a flow distribution factor in the range of 0.8 to 1.2.

[0014] Furthermore, the upper chamber assembly includes an upper chamber cylinder and a transparent top window, the input end of the upper chamber cylinder is connected to the outlet end of the flow resistance simulation mechanism, and the top of the upper chamber cylinder is connected to the top window.

[0015] Furthermore, the experimental device for the vortex flow field in the lower chamber of the nuclear reactor also includes a bulging-proof cover plate with a light-transmitting notch. The bulging-proof cover plate is located above the top viewing window and is rotatably connected to the upper chamber cylinder to reduce the bulging deformation of the viewing window caused by water flow impact.

[0016] Furthermore, the outlet assembly includes a plurality of outlet pipe assemblies, each of which forms the outlet flow channel; each of the outlet pipe assemblies is installed on the upper chamber assembly and communicates with the upper chamber flow channel; the installation azimuth angle of the outlet pipe assembly is consistent with that of the reactor prototype and is staggered in vertical height relative to the inlet flow channel to reduce non-functional pressure drop.

[0017] Furthermore, the lower head is made of a transparent brittle material with low elastic modulus, and includes an integrally formed hemispherical head and a thickened flange. The thickened flange is connected to the descending annular cavity assembly made of stainless steel by bolts to enhance the structural strength of the spherical transition straight cylindrical end face of the hemispherical head. The thickness of the thickened flange is 60cm-100cm.

[0018] Furthermore, the inner wall curvature radius of the hemispherical head is machined to a negative tolerance to compensate for bulging deformation under pressure.

[0019] Furthermore, the descending ring cavity assembly also includes an azimuth scale mark on the side of the connecting flange of the lower cylinder, so as to cooperate with the sheet light source to achieve precise positioning of the shooting section.

[0020] Furthermore, the inlet assembly, the descending annular cavity assembly, the lower chamber assembly, and the flow resistance simulation mechanism are all designed on a scaled-down basis according to the reactor prototype lower chamber vortex flow field scaling method. The size of the outlet flow channel of the outlet component is larger than the flow channel size designed on a scaled-down basis according to the proportional modeling method of the vortex flow field in the lower chamber of the reactor prototype.

[0021] By implementing this invention, the following beneficial effects are achieved: The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor of the present invention can simulate different flow distribution conditions in actual reactor core operation by adjusting the drag characteristics of each drag unit to construct uniform or non-uniform flow distribution. Through the transparent structures of the upper and lower chamber assemblies, in conjunction with the flow resistance simulation mechanism, the vortex flow field in the lower chamber under different flow distribution conditions can be visualized and measured. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a three-dimensional structural schematic diagram of an experimental device for a vortex flow field in the lower chamber of a nuclear reactor, according to an embodiment of the present invention. Figure 2 yes Figure 1 A longitudinal section of the experimental setup for the vortex flow field in the lower chamber of a nuclear reactor. Figure 3 yes Figure 1 Cross-sectional view of the inlet reference plane of the experimental device for the vortex flow field in the lower chamber of a nuclear reactor. Figure 4 yes Figure 2 A magnified schematic diagram of the lower chamber flow channel in the middle; Figure 5 yes Figure 4 A schematic diagram of the flow resistance simulation mechanism in the diagram; Figure 6 yes Figure 5 A schematic diagram of the structure of the fuel assembly simulator; Figure 7 yes Figure 3 A schematic diagram of the structure of the suspended basket nozzle; Figure 8 yes Figure 1 A schematic diagram showing the installation orientation of the inlet and outlet pipe components. Detailed Implementation

[0023] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] In the description of the invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of the invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a chemical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] See Figures 1 to 8 One embodiment of the present invention discloses an experimental device for a vortex flow field in the lower chamber of a nuclear reactor, comprising an inlet assembly 1, a descending annular cavity assembly 2, a lower chamber assembly 3, an upper chamber assembly 4, and an outlet assembly 5 assembled sequentially, and forming interconnected inlet channels 10, descending annular cavity channels 20, lower chamber channels 30, upper chamber channels 40, and outlet channels 50 for fluid flow within the device. The overall structure of the experimental device for a vortex flow field in the lower chamber of a nuclear reactor simulates the main flow channel structure in the lower part of a reactor pressure vessel.

[0027] The experimental setup for the vortex flow field in the lower chamber of a nuclear reactor also includes a flow resistance simulation mechanism 6 located downstream of the lower chamber flow channel 30. This mechanism comprises multiple independently configured resistance units with adjustable resistance characteristics. By adjusting the resistance characteristics of each unit, uniform or non-uniform flow distributions can be constructed to simulate the flow distribution during actual reactor core operation. The flow resistance simulation mechanism 6 is the core functional module of the experimental setup, specifically designed to simulate the flow resistance characteristics of the reactor core. The multiple independently configured resistance units accurately simulate different fuel assemblies in the reactor. By adjusting the resistance characteristics of each unit, flow conditions under different burnup states or power distributions in the reactor core can be flexibly simulated. This innovative design effectively solves the industry problem of traditional experimental setups being unable to flexibly simulate complex downstream resistance conditions of the reactor core, providing a key technical means for studying the impact of uniform or non-uniform flow on the vortex flow in the lower chamber.

[0028] Both the upper chamber assembly 4 and the lower chamber assembly 3 are equipped with transparent structures to enable the visualization and measurement of the vortex flow field in the lower chamber under different flow distribution conditions. The transparent structures in both assemblies 4 and 3 facilitate the visualization and precise measurement of the device. These transparent structures can be made of transparent, brittle materials with low elastic modulus, such as PMMA (polymethyl methacrylate), to ensure effective optical visualization of the flow field in the lower chamber.

[0029] Furthermore, such as Figure 1 As shown, in some embodiments, the inlet assembly 1, the descending annular cavity assembly 2, the lower chamber assembly 3, the upper chamber assembly 4, and the flow resistance simulation mechanism 6 are all designed on a scaled-down basis according to the reactor prototype lower chamber vortex flow field scaling method. The outlet flow channel 50 of the outlet assembly 5 has a larger dimension than the flow channel dimension designed on a scaled-down basis according to the reactor prototype lower chamber vortex flow field scaling method.

[0030] The experimental setup for the vortex flow field in the lower chamber of a nuclear reactor is a precisely scaled-down replica of the reactor prototype, such as at ratios of 1:5, 1:6, or 1:10. However, it must retain the characteristic similarities of key flow channels, including inlet assembly 1, descending annular cavity assembly 2, lower chamber assembly 3, upper chamber assembly 4, and outlet assembly 5, to address the significant engineering challenge of reproducing the real flow environment of a reactor in the laboratory. The size of the outlet flow channel 50 in outlet assembly 5 is larger than the flow channel size designed on a scaled-down basis using the reactor prototype's lower chamber vortex flow field scaling method, effectively reducing the flow pressure drop loss in outlet flow channel 50. This optimized design solves the technical challenges of excessively high pump power required under large flow rate experimental conditions and the interference of local high pressure loss at the outlet with the lower chamber flow field measurement, thus improving the accuracy of experimental data.

[0031] Furthermore, such as Figure 1 and Figure 3As shown, in some embodiments, the inlet assembly 1 includes several inlet pipe assemblies 11, each forming an inlet flow channel 10. The outlet end of each inlet pipe assembly 11 is fixedly connected to the inlet end of the descending annular cavity assembly 2, and the structure and installation orientation of each inlet pipe assembly 11 are consistent with the reactor prototype. The inlet pipe assembly 11 is a key upstream geometric and kinematic boundary of the flow field in the lower chamber; therefore, maintaining the geometric structure and installation orientation of the inlet pipe assembly 11 similar to the prototype is crucial. The inlet pipe assembly 11 accurately simulates the inlet pipe system of the reactor prototype. The dimensions of the corresponding structure in the reactor prototype simulated by the scaled-down inlet pipe assembly 11 are not only proportionally reduced in size, but more importantly, their installation orientation is completely consistent with the reactor prototype, thus making the inlet flow channel 10 similar. This design ensures that the fluid kinematic boundary conditions flowing into the descending annular cavity assembly 2 are highly similar to the prototype, providing crucial upstream conditions to ensure the accuracy of the flow field formation in the lower chamber and effectively solving the technical problem of experimental inflow condition distortion.

[0032] Specifically, the inlet pipe assembly 11 includes an inlet flange 111, an inlet pipe section 112, and a flow channel transition section 113. The inlet pipe section 112 comprises three sections for the convergence of three fluid streams. The number of inlet flanges 111 and the number of flow channel transition sections 113 are the same as the number of inlet pipe sections 112. The inlet flange 111 connects to the external water supply system. The inlet pipe section 112 is a straight pipe section, with its diameter and length designed on a scaled-down basis according to a proportional modeling principle. The flow channel transition section 113 connects the inlet pipe section 112 to the descending annular cavity assembly 2. Its inner contour profile is scaled proportionally according to the reactor prototype structure to ensure that the fluid flow development process from the inlet to the descending annular cavity assembly 2 is similar to the prototype. The inlet pipe assembly 11 is made of stainless steel to withstand the impact of high-flow-rate, high-speed fluids.

[0033] Furthermore, such as Figure 1 and Figure 2As shown, in some embodiments, the descending annular cavity assembly 2 includes a lower cylinder 21 and a basket cylinder 22. The lower cylinder 21 is coaxially sleeved on the outside of the basket cylinder 22 to form an annular descending annular cavity flow channel 20. The inlet end of the descending annular cavity flow channel 20 is connected to the outlet end of the inlet flow channel 10, and the outlet end of the descending annular cavity flow channel 20 is connected to the inlet end of the lower chamber flow channel 30. Several flow guides 23, an irradiated sample holder 24, and a basket nozzle 25 are fixedly installed inside the descending annular cavity flow channel 20. The design of the descending annular cavity assembly 2 completely replicates the structure of the descending annular cavity flow channel 20 of the prototype reactor. The lower cylinder 21 and the basket cylinder 22 respectively simulate the pressure vessel wall and the basket wall of the reactor. The descending annular cavity flow channel 20 formed between the lower cylinder 21 and the basket cylinder 22 is the key channel for coolant descent. The internal components, such as the flow guide 23, the irradiated sample holder 24, and the basket nozzle 25, are all precisely scaled down to ensure geometric similarity of the flow. This design solves the technical problem of inaccurate simulation of the internal flow characteristics of the descending annular cavity assembly 2, providing accurate input conditions for studying the flow field in the lower chamber.

[0034] Furthermore, the basket nozzle 25 is detachably connected to the basket body 22. The basket nozzle 25 is a scaled-down component that combines the basket outlet nozzle and the extended end of the outlet connector assembly 51 of the outlet flow channel 50 in the reactor prototype, maintaining the geometric similarity of the descending annular cavity flow channel 20 within the descending annular cavity assembly 2. The scaled-down design of the basket nozzle 25, combining the functions of the basket outlet nozzle and the extended end of the outlet connector assembly 51 in the reactor prototype, means that the basket nozzle 25 adopts a scaled-down design, integrating the functions of the two independent components—the basket outlet nozzle and the extended end of the outlet connector assembly 51—into a single component. This scaled-down component significantly simplifies the processing and assembly process while strictly maintaining the geometry of the outlet flow channel 50 of the descending annular cavity assembly 2. The detachable connection facilitates maintenance and replacement, solving the engineering challenge of accurately replicating complex structures in small-scale prototype devices.

[0035] Furthermore, such as Figure 1 , Figure 2 and Figure 4As shown, in some embodiments, the lower chamber assembly 3 includes a transparent lower head 31, a flow distributor 32, a support key 33, and a lower core plate 34. The inlet end of the lower head 31 is connected to the outlet end of the descending annular cavity assembly 2. The flow distributor 32 is fixedly installed inside the lower head 31, with its inlet side communicating with the descending annular cavity flow channel 20 and its outlet side abutting with the flow channel hole on the lower core plate 34. The support key 33 is installed between the inner wall of the lower head 31 and the outer wall of the flow distributor 32 to radially position and support the flow distributor 32. The internal structure of the lower chamber flow channel 30 accurately simulates the flow distribution device of the reactor lower chamber. The flow distributor 32, the lower core plate 34, and the support key 33 together constitute the final flow channel for fluid before it enters the simulated core from the descending annular cavity flow channel 20. The support key 33 ensures the precise positioning and stable support of the flow distributor 32. The flow distributor 32, the lower core plate 34, and the support key 33 completely reproduce the complex flow path inside the lower chamber, solving the technical problems of simulating and accurately positioning the internal structure of the lower chamber, and providing a foundation for the study of ensuring the uniformity of flow distribution at the core inlet.

[0036] Furthermore, such as Figure 5 As shown, in some embodiments, the inner wall of the lower end cap 31 is provided with a positioning reference 313, and the outer side of the lower end cap 31 is provided with a positioning device 314 for monitoring deformation and levelness, so as to facilitate the installation and leveling of the lower end cap 31 and the flow distributor 32 and control the flow channel gap between them. The positioning reference 313 on the inner wall of the lower end cap 31 and the external positioning device 314 together ensure installation accuracy and real-time monitoring of pressure-bearing deformation. This comprehensive solution successfully overcomes the technical bottleneck of accurate positioning and deformation monitoring of brittle transparent materials under pressure and high flow rate impact, providing an important guarantee for obtaining reliable experimental data.

[0037] Furthermore, in some embodiments, the positioning device 314 includes at least one universal level disposed on the end face of the lower head 31, and the positioning reference 313 is a scale line disposed at the target height of the inner wall of the lower head 31. The universal level is used to adjust the installation level of the lower head 31, ensuring the levelness of the thickened flange 312 of the lower head 31. The scale line on the inner wall is used for assembly control of critical flow channel clearances and online assessment of pressure deformation. During assembly, the scale line and the universal level are observed, and the leveling of the end face of the thickened flange 312 of the lower head 31 and the control of the flow channel clearance are achieved by adjusting the shim thickness and bolt preload. During experiments, it can be used to evaluate the amount of elastic deformation under pressure conditions.

[0038] Specifically, the experimental device for the vortex flow field in the lower chamber of a nuclear reactor also includes a pair of symmetrical slots designed on the end face of the thickened flange 312 of the lower head 31 for mounting a universal level.

[0039] Furthermore, such as Figure 5 and Figure 6 As shown, in some embodiments, each drag unit includes at least one detachable fuel assembly simulator 61, which is fixed downstream of the lower core plate 34 by a support plate 62. Each fuel assembly simulator 61 includes a stabilizing section 611 and a drag regulating component 612, which is detachably connected to the stabilizing section 611. The inlet end of the stabilizing section 611 is connected to a flow channel hole on the lower core plate 34. The drag unit adopts a modular design, with each fuel assembly simulator 61 corresponding to simulate one reactor fuel assembly. The stabilizing section 611 ensures smooth fluid flow, while the drag regulating component 612 is used to precisely adjust hydraulic drag. The detachable connection between the drag regulating component 612 and the stabilizing section 611, such as a threaded connection, allows for more flexible experimental configuration and supports rapid switching between different core drag schemes. This design solves the technical challenge of rapid switching of drag schemes in multi-condition studies, providing convenience for studying the impact of different core states on the flow field in the lower chamber.

[0040] Specifically, the support plate 62 is fixedly installed at the inlet of the outlet flow channel 50 to support and fix the fuel assembly simulator 61. The core simulator support plate 62 has positioning holes corresponding to the fuel assembly simulator 61, ensuring precise alignment between each fuel assembly simulator 61 and the flow channel holes on the lower core plate 34. This solves the stability and positioning accuracy problems of the fuel assembly simulator 61 in high-speed flow fields, ensuring the accuracy of drag simulation.

[0041] Furthermore, such as Figure 6 As shown, in some embodiments, the resistance regulating element 612 is a telescopic or variable-diameter sleeve structure. Adjusting the flow area of ​​the resistance regulating element 612 allows for the creation of a uniform or non-uniform flow distribution with a flow distribution factor ranging from 0.8 to 1.2. Specifically, the resistance regulating element 612 employs a telescopic or variable-diameter sleeve mechanical structure, achieving resistance control through precise adjustment of the flow area. This mechanical adjustment method can accurately set the resistance value of each flow channel, thereby constructing a uniform or non-uniform flow distribution at the core inlet as a whole. This design solves the core technical challenge of accurately reproducing the hydraulic conditions corresponding to different power distributions in the core manually, and the flow distribution factor range of 0.8 to 1.2 covers various operating conditions of the reactor.

[0042] This invention features a precisely adjustable flow resistance simulation mechanism 6. Through the fuel assembly simulator 61 and its retractable or variable-diameter sleeve-type resistance adjustment component 612, it can flexibly and accurately construct uniform or non-uniform flow resistance distributions at the core inlet. The detachable and easily adjustable fuel assembly simulator 61 can be used to study the impact of different downstream resistance or flow distributions on the vortex field in the lower chamber. The threaded resistance adjustment component 612 facilitates adjustment of the core resistance or flow distribution, constructing a non-uniform downstream flow field with a flow distribution factor ranging from 0.8 to 1.2. The structure is simple and easy to operate. This flow resistance simulation mechanism 6 enables experiments to simulate different downstream boundary conditions in actual reactor operation, providing a key technical means for studying the impact of downstream resistance distribution on the stability of the lower chamber vortex, thereby achieving experimental evaluation of vortex stability.

[0043] Furthermore, such as Figure 1 , Figure 2 and Figure 8 As shown, in some embodiments, the upper chamber assembly 4 includes an upper chamber cylinder 41 and a transparent top window 42. The input end of the upper chamber cylinder 41 is connected to the outlet end of the flow resistance simulation mechanism 6, and the top of the upper chamber cylinder 41 is connected to the top window 42. The upper chamber cylinder 41 forms an upper chamber flow channel 40, and the top window 42 forms the end boundary of the upper chamber flow channel 40. The top window 42 is transparent, providing light transmission for visualization and measurement.

[0044] Furthermore, such as Figure 1 and Figure 8 As shown, in some embodiments, the experimental device for the vortex flow field in the lower chamber of a nuclear reactor also includes a bulging-resistant cover plate 7 with a light-transmitting notch. The bulging-resistant cover plate 7 is positioned above the top viewing window 42 and rotatably connected to the upper chamber cylinder 41 to reduce the bulging deformation of the viewing window caused by water flow impact. The bulging-resistant cover plate 7 is rotatably positioned above the top viewing window 42 to reduce the bulging deformation of the viewing window caused by water flow impact. The top viewing window 42 and the bulging-resistant cover plate 7 ensure the visibility of the flow field in the outlet region, which can be used to observe the dynamic characteristics and stability of the upward development of vortices. The top viewing window 42 is used to observe the flow field in the outlet region and adopts an anti-bulging design, with the bulging-resistant cover plate 7 positioned above it. The bulging-resistant cover plate 7 can be a three-quarter circular bulging-resistant cover plate 7, which is rotatable and provides effective back support for the viewing window, reducing the bulging deformation of the top viewing window 42 caused by water flow impact. This solves the technical problem of the top viewing window 42 deforming due to impact and pressure under high flow conditions, affecting the optical measurement quality and ensuring the reliability of the observation data.

[0045] Furthermore, such as Figure 1 and Figure 8As shown, in some embodiments, the outlet assembly 5 includes a plurality of outlet pipe assemblies 51, each outlet pipe assembly 51 forming an outlet flow channel 50; each outlet pipe assembly 51 is mounted on the upper chamber assembly 4 and communicates with the upper chamber flow channel 40; the installation azimuth angle of the outlet pipe assembly 51 is consistent with that of the reactor prototype and is staggered in vertical height relative to the inlet flow channel 10 to reduce non-functional pressure drop.

[0046] The design of the outlet flow channel 50 was optimized and innovated while maintaining similarity. The installation azimuth of the outlet nozzle assembly 51 is consistent with the prototype, ensuring similarity in downstream boundary conditions. The size of the outlet flow channel 50 is larger than the flow channel size designed on a scaled-down basis using the reactor prototype's chamber vortex flow field proportional modeling method. Specifically, increasing the diameter of the outlet nozzle assembly 51 and staggering its arrangement from the inlet flow channel 10 effectively reduces the flow pressure drop loss at the outlet section. This optimized design solves the technical challenges of excessive pump power required under high-flow-rate experimental conditions and interference from local high pressure loss at the outlet in chamber flow field measurements, thus improving the accuracy of experimental data.

[0047] Specifically, the outlet pipe assembly 51 includes an outlet flange 511, an outlet pipe section 512, and an outlet transition section 513. The outlet pipe section 512 comprises three sections for three fluid streams. The number of outlet flanges 511 and the number of outlet transition sections 513 are the same as the number of outlet pipe sections 512. Each outlet pipe section 512 is enlarged to a DN 300 diameter to reduce the non-functional pressure drop generated by the outlet pipe assembly 51. The outlet transition section 513 extends into the descending annular cavity assembly 2 and is structurally integrated with the basket nozzle 25 to form a detachable basket nozzle 25, maintaining the similarity of the flow channels within the descending annular cavity assembly 2.

[0048] Furthermore, the lower head 31 is made of a transparent, brittle material with a low elastic modulus. It comprises an integrally molded hemispherical head 311 and a thickened flange 312. The thickened flange 312 is bolted to the descending annular cavity assembly 2 made of stainless steel to enhance the structural strength of the spherical transition straight cylindrical end face of the hemispherical head 311. The thickness of the thickened flange 312 is 60 to 100 centimeters. The material selection and treatment of the lower head 31 are key technological innovations of the device. The use of a transparent, brittle material with a low elastic modulus, such as PMMA, enables visual observation, while the integrally molded hemispherical head 311 and thickened flange 312 design provides structural reinforcement. The thickened flange 312 is bolted to the lower cylinder 21. The 60 to 100 centimeter thickened flange 312 effectively solves the technical problem of stress concentration at the spherical transition straight cylindrical end face of the PMMA head, which easily leads to cracks or even brittle fracture, by providing sufficient rigidity at structural discontinuities, thus ensuring the safe operation of the device. The thickness of the 312 thickened flange can be set to 60 cm, 70 cm, 80 cm, 100 cm, etc., according to actual needs.

[0049] Specifically, the descending annular cavity assembly 2 also includes a connecting flange 211, which connects the lower cylinder 21 to the thickened flange 312 of the lower head 31, providing a reliable seal and structural connection. The connecting flange 211 is made of stainless steel and is bolted to the thickened flange 312 of the lower head 31. A sealing ring is provided on the connection surface to ensure the sealing performance at the connection. This solves the problem of reliable connection and sealing between metal components and transparent brittle material components, ensuring the safe operation of the experimental device under high flow conditions.

[0050] Furthermore, the inner wall radius of curvature of the hemispherical head 311 is machined to a negative tolerance to compensate for bulging deformation under pressure. Specifically, the machining of the hemispherical head 311 employs a negative tolerance compensation technique, pre-machining to make the inner wall radius of curvature slightly smaller than the design value to compensate for outward bulging deformation under pressure. This precise compensation method based on structural mechanics calculations effectively solves the technical problem of the bulging of the lower head 31 with low elastic modulus under pressure causing changes in the flow channel gap between the flow distributor 32 and the lower head 31, affecting the similarity of the flow field, and ensuring the accuracy of the experimental conditions.

[0051] Specifically, under a pressure of 1 MPa, the spherical head bulges under internal pressure. Structural mechanics calculations show that the maximum bulging deformation of the lower head 31 with low elastic modulus is 0.3 mm. Then, negative tolerance control is applied to the machining of the inner wall surface of the lower head 31. The tolerance range of the radius of curvature SR of the inner wall surface of the lower head 31 is controlled to reduce the impact of the flow channel between the flow distributor 32 and the lower head 31 caused by pressure deformation.

[0052] The present invention provides a transparent structure of a complete and visualized lower chamber assembly 3, consisting of a transparent lower end cap 31, a flow distributor 32, a support key 33, and a lower core plate 34. This structure provides a clear optical path for direct observation of the occurrence and development of vortices in the lower chamber by optical measurement methods, and solves the problem that the occurrence of vortices cannot be directly measured.

[0053] Furthermore, such as Figure 1 and Figure 4As shown, in some embodiments, the descending ring cavity assembly 2 further includes an azimuth scale mark 315 on the side of the connecting flange 211 of the lower cylinder 21 to cooperate with the sheet light source to achieve precise positioning of the imaging section. The azimuth scale mark 315 ensures that the illumination plane of the sheet light source precisely coincides with the target measurement section during optical measurement. The azimuth scale mark 315 may include four positioning holes at 0 degrees, 90 degrees, 180 degrees, and 270 degrees on the support plate 62 for positioning the graduated slide rail of the rotatable water tank. The rectangular water tank and slide rail are imaging auxiliary structures, not shown in the figure. Based on the target azimuth angle to be imaged, the rectangular water tank is rotated to the same azimuth angle, making one side of the water tank parallel to the vertical plane of the imaging surface, i.e., the target azimuth angle, to achieve precise positioning of the imaging surface. The positioning device 314, positioning reference 313, azimuth scale mark 315, and sheet light source employ a multi-level precision control scheme, comprehensively solving the technical difficulties of key assembly dimension control and online measurement, ensuring the accuracy and repeatability of the experiment.

[0054] This invention utilizes a universal level, scale lines, and azimuth mark 315 to reliably position the azimuth angle for imaging. The scale lines and the external universal level are used for assembly control of critical flow channel gaps and online monitoring of pressure deformation, ensuring the stability of the flow channel geometry during the experiment. This guarantees the repeatability of vortex generation conditions and the reliability of measurement data. The lower azimuth mark 315, in conjunction with a sheet light source, enables precise slice measurements of the flow field behind different radial planes, such as specific guide vanes 23 or support keys 33, facilitating the study of the influence of specific structures on the location and stability of vortex generation.

[0055] The core value of this invention lies in two significant breakthroughs: First, it innovatively achieves flexible simulation of different resistance conditions during the actual operation of the reactor core prototype, overcoming the limitations of traditional experimental devices. Second, it successfully solves a series of engineering and technical challenges related to pressure bearing, reinforcement, deformation, and positioning arising from the use of transparent brittle materials for visual observation.

[0056] By implementing this invention, the following beneficial effects are achieved: The experimental device for the vortex flow field in the lower chamber of a nuclear reactor of the present invention can simulate different resistance conditions in actual reactor core operation by adjusting the resistance characteristics of each resistance unit to construct a uniform or non-uniform flow resistance distribution. The upper chamber assembly 4 and lower chamber assembly 3 are equipped with transparent structures, the inner wall of the lower head 31 is provided with a positioning reference 313, and the outer side of the lower head 31 is provided with a positioning device 314. These features can be used to monitor the deformation and levelness of the lower head 31. In conjunction with the flow resistance simulation mechanism 6, the device can achieve visualized observation and measurement of the vortex flow field in the lower chamber under different flow distribution conditions.

[0057] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that for those skilled in the art, the above embodiments or technical features can be freely combined, and several modifications and improvements can be made without departing from the concept of the present invention. These all fall within the protection scope of the present invention. That is, the embodiments described "in some embodiments" can be freely combined with any of the embodiments above and below. Therefore, all equivalent transformations and modifications made within the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. An experimental apparatus for vortex flow field in the lower chamber of a nuclear reactor, characterized in that, It includes an inlet assembly (1), a descending annular cavity assembly (2), a lower chamber assembly (3), an upper chamber assembly (4), and an outlet assembly (5) assembled in sequence, and forms a connected inlet flow channel (10), a descending annular cavity flow channel (20), a lower chamber flow channel (30), an upper chamber flow channel (40), and an outlet flow channel (50) inside it for fluid to flow through. The experimental device for the vortex flow field in the lower chamber of the nuclear reactor also includes a flow resistance simulation mechanism (6) located downstream of the flow channel (30) in the lower chamber. The flow resistance simulation mechanism (6) includes multiple independently configured and adjustable resistance units. By adjusting the resistance characteristics of each resistance unit, a uniform or non-uniform flow distribution is constructed to simulate different flow distributions in actual operation of the reactor core. The upper chamber assembly (4) and the lower chamber assembly (3) are provided with transparent structures to enable the visualization and measurement of the vortex flow field in the lower chamber under different flow distribution conditions; The lower chamber assembly (3) includes a transparent lower end cap (31), a flow distributor (32), a support key (33), and a lower core plate (34). The inlet end of the lower end cap (31) is connected to the outlet end of the descending annular cavity assembly (2). The flow distributor (32) is fixedly installed inside the lower end cap (31). The inlet side of the flow distributor (32) is connected to the flow channel (20) of the descending annular cavity, and the outlet side of the flow distributor (32) is connected to the flow channel hole on the lower core plate (34). The support key (33) is installed between the inner wall of the lower end cap (31) and the outer wall of the flow distributor (32) to radially position and support the flow distributor (32). Each of the drag units includes at least one detachable fuel assembly simulator (61) which is fixed downstream of the lower core plate (34) by a support plate (62); Each of the fuel assembly simulators (61) includes a stabilizing section (611) and a drag modulator (612), the drag modulator (612) being detachably connected to the stabilizing section (611), the inlet end of the stabilizing section (611) being connected to a flow channel hole on the lower core plate (34).

2. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 1, characterized in that, The inlet assembly (1) includes several inlet pipe assemblies (11), each of which forms an inlet flow channel (10); the outlet end of each inlet pipe assembly (11) is fixedly connected to the inlet end of the descending annular cavity assembly (2), and the structure and installation orientation of each inlet pipe assembly (11) are consistent with the reactor prototype.

3. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 1, characterized in that, The descending annular cavity assembly (2) includes a lower cylinder (21) and a basket cylinder (22). The lower cylinder (21) is coaxially sleeved on the outside of the basket cylinder (22) to form an annular descending annular cavity flow channel (20). The inlet end of the descending annular cavity flow channel (20) is connected to the outlet end of the inlet flow channel (10), and the outlet end of the descending annular cavity flow channel (20) is connected to the inlet end of the lower chamber flow channel (30). Several flow guides (23), irradiation sample holders (24) and basket nozzles (25) are fixedly installed inside the descending annular cavity flow channel (20).

4. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 3, characterized in that, The basket nozzle (25) is detachably connected to the basket cylinder (22). The basket nozzle (25) is a scaled-down component of the basket outlet nozzle and the inner extension end of the outlet pipe assembly (51) of the outlet assembly (5) in the reactor prototype, so as to maintain the geometric similarity of the descending annular cavity flow channel (20) in the descending annular cavity assembly (2).

5. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 1, characterized in that, The inner wall of the lower end cap (31) is provided with a positioning reference (313), and the outer side of the lower end cap (31) is provided with a positioning device (314) for monitoring deformation and levelness, so as to facilitate the installation, leveling and control of the flow channel gap between the lower end cap (31) and the flow distributor (32).

6. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 5, characterized in that, The positioning device (314) includes at least one universal level located on the end face of the lower end cap (31), and the positioning reference (313) is a scale line located at the target height of the inner wall of the lower end cap (31).

7. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 1, characterized in that, The resistance regulating element (612) is a telescopic or variable diameter sleeve structure. The flow area of ​​the resistance regulating element (612) is adjusted to construct a uniform or non-uniform flow distribution with a flow distribution factor in the range of 0.8 to 1.

2.

8. The experimental apparatus for vortex flow field in the lower chamber of a nuclear reactor according to any one of claims 1-7, characterized in that, The upper chamber assembly (4) includes an upper chamber cylinder (41) and a transparent top window (42). The input end of the upper chamber cylinder (41) is connected to the outlet end of the flow resistance simulation mechanism (6), and the top of the upper chamber cylinder (41) is connected to the top window (42).

9. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 8, characterized in that, The experimental device for the vortex flow field in the lower chamber of the nuclear reactor also includes a bulging cover plate (7) with a light-transmitting notch. The bulging cover plate (7) is located above the top window (42) and is rotatably connected to the upper chamber cylinder (41) to reduce the bulging deformation of the window caused by water flow impact.

10. The experimental apparatus for vortex flow field in the lower chamber of a nuclear reactor according to any one of claims 1-7, characterized in that, The outlet assembly (5) includes a plurality of outlet pipe assemblies (51), each of the outlet pipe assemblies (51) forming the outlet flow channel (50); each of the outlet pipe assemblies (51) is installed on the upper chamber assembly (4) and communicates with the upper chamber flow channel (40); the installation azimuth angle of the outlet pipe assembly (51) is consistent with that of the reactor prototype and is staggered in vertical height relative to the inlet flow channel (10) to reduce non-functional pressure drop.

11. The experimental apparatus for vortex flow field in the lower chamber of a nuclear reactor according to any one of claims 1 to 7, characterized in that, The lower end cap (31) is made of a transparent brittle material with low elastic modulus and includes an integrally formed hemispherical end cap (311) and a thickened flange (312). The thickened flange (312) is connected to the descending annular cavity assembly (2) made of stainless steel by bolts to enhance the structural strength of the spherical transition straight cylindrical end face of the hemispherical end cap (311). The thickness of the thickened flange (312) is 60cm-100cm.

12. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 11, characterized in that, The inner wall curvature radius of the hemispherical head (311) is machined to a negative tolerance to compensate for bulging deformation under pressure.

13. The experimental apparatus for the vortex flow field in the lower chamber of a nuclear reactor according to claim 3 or 4, characterized in that, The descending ring cavity assembly (2) also includes an azimuth scale mark (315) on the side of the connecting flange (211) of the lower cylinder (21) to cooperate with the sheet light source to achieve precise positioning of the shooting section.

14. The experimental apparatus for vortex flow field in the lower chamber of a nuclear reactor according to any one of claims 1-7, characterized in that, The inlet assembly (1), the descending annular cavity assembly (2), the lower chamber assembly (3), the upper chamber assembly (4), and the flow resistance simulation mechanism (6) are all designed on a scaled-down basis according to the reactor prototype lower chamber vortex flow field scaling method. The size of the outlet flow channel (50) of the outlet component (5) is larger than the flow channel size designed by scaling down the vortex flow field proportional modeling method of the reactor prototype chamber.

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