A visualization test device for simulating the high-temperature and high-pressure conditions of a prototype nuclear reactor core rod bundle channel.

Abstract

This invention discloses a visualization test device for simulating the high-temperature and high-pressure conditions of a prototype nuclear reactor core rod bundle channel. The device comprises a core test layer and multiple pressure-reducing layers. The core test layer's viewing windows are sealed and insulated using sealing rings and insulating gaskets. The core test layer houses an electrically heated rod bundle. The multiple pressure-reducing layers are formed by coaxially arranging multiple cylindrical pressure-reducing layer viewing windows outside the core test layer. Stable circulating cooling water is introduced into the core test layer and each pressure-reducing layer, with different pressures in each circulation stream. The pressure difference across each viewing window is within the pressure-bearing range of the viewing window material. The circulating cooling water in each pressure-reducing layer is kept at a single-phase low temperature for visualization observation, ensuring that the temperature of the sealing material remains below its temperature resistance limit. This invention solves the key technical challenges of material strength limitations and thermal expansion mismatch in high-temperature and high-pressure visualization experiments, providing a reliable test platform for high-temperature and high-pressure visualization of prototype nuclear reactor core rod bundle channels.

Description

Technical Field

[0001] This invention relates to the field of high-temperature and high-pressure two-phase flow research on nuclear reactor core prototypes, specifically to a visualization test device for simulating the high-temperature and high-pressure operating conditions of a nuclear reactor core rod bundle channel prototype. Background Technology

[0002] High-temperature and high-pressure hot-state visualization tests of pressurized water reactor (PWR) core rod bundle channels are a primary method for studying the boiling initiation point and bubble evolution within these channels. However, due to limitations in material strength and sealing performance, existing visualization test equipment is not suitable for conducting high-temperature and high-pressure visualization tests of PWR core rod bundle channels under prototype conditions. Specifically,

[0003] (1) Insufficient pressure-bearing capacity of the visualized medium

[0004] Silica quartz glass has excellent light transmission properties, so it is often used as the visualization medium in existing visualization experimental devices. However, when silica quartz glass is directly applied to the high-temperature and high-pressure conditions of a pressurized water reactor prototype, the stress caused by excessive temperature and pressure will cause the silica quartz glass to crack.

[0005] (2) Failure of sealing material at high temperature

[0006] When conducting visualization tests under high-temperature and high-pressure conditions on a pressurized water reactor prototype, sealing materials are required at the viewing window to prevent coolant leakage. Existing sealing materials are mostly organic synthetics, such as rubber rings. If these materials are exposed to high temperatures for extended periods, they will face severe thermal aging problems, leading to creep relaxation at the sealing interface and ultimately causing coolant leakage.

[0007] (3) Material thermal expansion mismatch under high temperature and high pressure

[0008] When silica quartz glass is used as a visualization window under the high temperature and high pressure conditions of the pressurized water reactor prototype, its thermal expansion capacity does not match that of steel. At lower temperatures and pressures, the mismatch is within an acceptable range, but as temperature and pressure increase, the difference in thermal expansion becomes more and more significant, leading to the failure of the sealing interface. Summary of the Invention

[0009] Purpose of the invention: The purpose of this invention is to provide a visual experimental device that can be used to simulate the high temperature and high pressure conditions of a prototype nuclear reactor core rod bundle channel.

[0010] Technical solution: The present invention provides a visualization test device for simulating the high temperature and high pressure conditions of a prototype nuclear reactor core rod bundle channel, which has a core test layer and a multi-stage depressurization layer;

[0011] The core test layer has a core test layer window on its side, and the core test layer window is sealed and insulated using a sealing ring and an insulating gasket; the core test layer has an internal bundle of electric heating rods to simulate reactor fuel rods;

[0012] The multi-stage pressure reduction layer is formed by setting multiple cylindrical pressure reduction layer windows coaxially outside the core test layer; stable circulating cooling water is introduced into the core test layer and each pressure reduction layer, and the pressure of each circulating cooling water is different. The pressure difference on both sides of each window is within the pressure bearing range of the window material; the circulating cooling water in each pressure reduction layer is kept at a single-phase low temperature to facilitate visual observation and ensure that the temperature of the sealing material is below its temperature resistance limit.

[0013] Furthermore, the core test layer has opposing core test layer windows on both sides; the visualization observation is carried out by taking pictures with a high-speed camera, and the pictures are taken on one side of the visualization test device, while the other side is illuminated by supplementary lighting equipment.

[0014] Furthermore, each window is made of silica quartz glass.

[0015] Furthermore, each circulating cooling water is supplied by an independent circulating cooling water system, which is powered by a pump and equipped with a pressure sensor and a pressure regulator for real-time pressure control to ensure stable circulating cooling water pressure.

[0016] Furthermore, the circulating cooling water system is also equipped with temperature sensors and flow sensors.

[0017] Furthermore, the core test layer contains multiple bundles of electric heating rods.

[0018] Furthermore, the core test layer adopts a stainless steel cavity with vertical openings on both the left and right sides, which are closed by stainless steel cover plates. The interior of the stainless steel cavity has a first insulating ceramic flow channel, and the first insulating ceramic flow channel and the stainless steel cover plate have openings at the same positions, with a core test layer window set between them. The core test layer window and the first insulating ceramic flow channel are sealed and insulated using sealing rings and insulating gaskets, and the stainless steel cover plate and the stainless steel cavity are also sealed using sealing rings.

[0019] Furthermore, the upper end of the stainless steel cavity is sequentially provided with a second insulating ceramic flow channel, a conductive nickel plate, and a main outlet cavity, wherein the conductive nickel plate forms a circuit to the lower part of the electric heating rod bundle; the second insulating ceramic flow channel is cylindrical, and insulating gaskets are provided at its upper and lower ends to insulate the test section from external inlet and outlet pipes; insulating gaskets are also provided between the conductive nickel plate and the main outlet cavity; the main outlet cavity has flow channels that connect the core test layer and each level of pressure reduction layer, as well as corresponding fluid outlets.

[0020] Furthermore, the lower end of the stainless steel cavity is connected to a main inlet chamber, which has flow channels that connect the core test layer and each level of pressure reduction layer, as well as corresponding fluid inlets.

[0021] Furthermore, a pressure-reducing chamber is connected to the lower end of the main inlet cavity. The main inlet cavity and the pressure-reducing chamber, as well as the electric heating rod bundle and the pressure-reducing chamber, are sealed by a sealing system. The pressure-reducing chamber is provided with a pressure-reducing chamber inlet and a pressure-reducing chamber outlet. Cooling water circulates through the pressure-reducing chamber inlet and outlet to cool the sealing systems on both sides.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0023] To address the pressure resistance issue of the visualization medium, this invention incorporates multi-stage pressure-reducing layers and multi-stage forced-circulation cooling water outside the core test layer. By controlling the pressure of the cooling water circulating on both sides of the viewing window, the pressure difference between the two sides is kept within acceptable limits. Simultaneously, the multi-stage forced-circulation cooling also solves the problems of high-temperature failure of the sealing material and thermal expansion mismatch under high temperature and pressure, preventing leaks caused by seal failure. Specifically, under the cooling water circulation, the wall temperature of the core test layer can be kept below the temperature resistance limit of the sealing material.

[0024] The experimental apparatus provided by this invention can achieve long-term safe and stable operation under high temperature and high pressure conditions. Using this apparatus, a high-speed camera can be used to capture images of the location of the near-wall boiling initiation point within the pressurized water reactor rod bundle channel, as well as the generation, slippage, annihilation, and shedding of bubbles. This allows for the acquisition of flow pattern evolution characteristics within the rod bundle channel, providing visualized experimental data to support the understanding of the heat transfer mechanism affecting the rod bundle surface. This experimental data will contribute to a deeper understanding of bubble behavior and heat transfer characteristics in the reactor cooling system, thereby improving the safety and thermal efficiency of nuclear reactors. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a visualization test device for simulating the high temperature and high pressure conditions of a prototype nuclear reactor core rod bundle channel, provided in an embodiment of the present invention.

[0026] Figure 2 yes Figure 1 Exploded view;

[0027] Figure 3 This is a schematic diagram of the layered pressure reduction principle of the visualization test device for a three-level pressure gradient in an embodiment of the present invention. Detailed Implementation

[0028] The invention will now be further described with reference to the accompanying drawings.

[0029] Appendix Figures 1 to 3 The accompanying figure labels are as follows:

[0030] 1. Stainless steel cavity; 2-1. First insulating ceramic flow channel; 2-2. Second insulating ceramic flow channel; 3. Electric heating rod bundle; 4-1. Observation window; 4-2. Light source window; 4-3. Pressure reduction layer window; 5. Stainless steel cover plate; 6. Sealing ring; 7. Insulating gasket; 8. Conductive nickel plate; 9. Sealing system; 10. Main inlet cavity; 11. Core test layer inlet; 12. First-level pressure reduction layer inlet; 13. Second-level pressure reduction layer inlet; 14. Pressure reduction cavity; 15. Pressure reduction cavity inlet; 16. Pressure reduction cavity outlet; 17. Main outlet cavity; 18. Core test layer outlet; 19. First-level pressure reduction layer outlet; 20. Second-level pressure reduction layer outlet.

[0031] like Figures 1 to 3 As shown, this embodiment of the invention provides a visualization test device for simulating the high temperature and high pressure conditions of a prototype nuclear reactor core rod bundle channel, which has a core test layer, a primary depressurization layer and a secondary depressurization layer arranged sequentially from the inside out.

[0032] The core test layer adopts a stainless steel cavity 1 with a square cross-section. The stainless steel cavity 1 has vertical openings on the left and right sides, which are closed by stainless steel cover plates 5. The stainless steel cavity 1 and the stainless steel cover plates 5 are connected by bolts. The inside of the stainless steel cavity 1 has a first insulating ceramic flow channel 2-1, which is composed of two ceramic components.

[0033] For visualization, openings are made at the same locations on the first insulating ceramic flow channel 2-1 and the stainless steel cover plate 5, with a core test layer window positioned between them. This window is used to observe the surface of the electric heating rod bundle 3, the flow pattern of the cooling water, and the bubble evolution process. The two core test layer windows face each other. In the figure, 4-1 is the observation window, and 4-2 is the light source window. The light source shines towards the light source window 4-2, and the camera records towards the observation window 4-1. The core test layer window is sealed and insulated from the first insulating ceramic flow channel 2-1 using a sealing ring 6 and an insulating gasket 7. Similarly, the stainless steel cover plate 5 is sealed from the stainless steel cavity 1 using a sealing ring 6.

[0034] The core test layer contains several bundles of high-temperature and high-pressure resistant electric heating rods 3, which are used to simulate reactor fuel rods.

[0035] The upper end of the stainless steel cavity 1 is sequentially equipped with a second insulating ceramic flow channel 2-2, a conductive nickel plate 8, and a main outlet cavity 17. The conductive nickel plate 8 is connected to the stainless steel cavity 1 and the main outlet cavity 17 by bolts. The heating method of the electric heating rod bundle 3 is direct electric heating, that is, a circuit is formed from the conductive nickel plate 8 to the lower part of the electric heating rod bundle 3. The second insulating ceramic flow channel 2-2 is cylindrical, and insulating gaskets 7 are provided at its upper and lower ends to insulate the test section from the external inlet and outlet pipes. Insulating gaskets 7 are also provided between the conductive nickel plate 8 and the main outlet cavity 17. The main outlet cavity 17 is welded with a core test layer outlet 18, a primary pressure reduction layer outlet 19, and a secondary pressure reduction layer outlet 20.

[0036] The lower end of the stainless steel cavity 1 is sequentially connected to a main inlet cavity 10 and a pressure-reducing cavity 14. The main inlet cavity 10 and the pressure-reducing cavity 14, as well as the electric heating rod bundle 3 and the pressure-reducing cavity 14, are sealed using a sealing system 9. The sealing system 9 employs a dedicated industrial sealing device (existing technology). The stainless steel cavity 1 and the main inlet cavity 10 are bolted together, as are the main inlet cavity 10 and the pressure-reducing cavity 14. The main inlet cavity 10 is welded with a core test layer inlet 11, a primary pressure-reducing layer inlet 12, and a secondary pressure-reducing layer inlet 13. The pressure-reducing cavity 14 is welded with a pressure-reducing cavity inlet 15 and a pressure-reducing cavity outlet 16. Cooling water circulates through the pressure-reducing cavity inlet 15 and outlet 16 to cool the sealing system 9 on both sides, preventing seal failure under the high temperature and high pressure environment within the core test layer.

[0037] Both the primary and secondary pressure-reducing layers consist of a cylindrical pressure-reducing layer window 4-3 and an annular water cavity. The pressure-reducing layer window 4-3 is sealed between two discs on the upper and lower parts of the stainless steel cavity 1 using a sealing ring 6. The two discs are connected by bolts to compress and fix the pressure-reducing layer window 4-3. The stainless steel cavity 1 is also installed between the two discs in the same way. Cooling water flows into the main inlet chamber 10 from the core test layer inlet 11, the primary pressure-reducing layer inlet 12, and the secondary pressure-reducing layer inlet 13, respectively. Then, it flows through different channels in the main inlet chamber 10, through the test section and the two annular water cavities, and finally flows into different channels in the main outlet chamber 17 and exits from the core test layer outlet 18, the primary pressure-reducing layer outlet 19, and the secondary pressure-reducing layer outlet 20, respectively.

[0038] In this embodiment, the material used for each window is silica quartz glass.

[0039] Each circulating cooling water line is supplied by an independent circulating cooling water system, powered by pumps. Pressure sensors and pressure regulators (current technology) are installed for real-time pressure control to ensure stable pressure across all circulating cooling water lines, maintaining an actual pressure difference of approximately 5 MPa between each layer of quartz glass. A pressure sensor is installed at both the inlet and outlet of each pump. Additionally, temperature and flow sensors are also installed in the circulating cooling water system, with a temperature sensor at both the inlet and outlet of each pump. The circulating cooling water ensures that the core test layer wall temperature remains below the temperature resistance limit of the sealing material, guaranteeing test safety.

[0040] Visual observations are conducted using a high-speed camera, with the images taken on one side of the visualization experimental device and supplemented with lighting on the opposite side to make the field of view between the rod bundle channels clearer.

[0041] It should be noted that the two-stage pressure reduction layer design provided in this embodiment is based on considerations such as window material, sealing performance, and observation clarity. In fact, the number of pressure reduction layers can be further increased to reduce the pressure difference between adjacent layers (e.g., from 5 MPa to 3 MPa or lower), thus adapting to a wider range of window materials (e.g., sapphire, transparent ceramics, etc.), thereby improving design flexibility and safety. However, increasing the number of layers introduces more sealing interfaces, so the amplification effect of the complex structure on leakage risk needs to be evaluated. Furthermore, too many layers lead to increased manufacturing costs, increased assembly difficulty, and may weaken the clarity of visualization. This invention employs a two-stage pressure reduction (15.5 MPa → 10 MPa → 5 MPa), which is a compromise optimization based on the industrial pressure resistance limit of the current mainstream window material—quartz glass—and sealing technology. If higher-strength transparent materials or more reliable sealing solutions emerge in the future, it can be fully expanded into a three-stage or even more-stage pressure reduction structure.

[0042] The following is combined Figure 3 The technical principles of this invention are explained.

[0043] (1) The first layer is the core test layer, which has built-in electric heating rod bundles and forced circulation cooling water for efficient heat exchange. This test layer maintains a high pressure of 15.5MPa and a high temperature of 350℃, directly simulating the thermal and hydraulic conditions under the prototype reactor conditions.

[0044] (2) Second layer: This is the first-level pressure reduction layer, with an internal circulating cooling water working pressure of 10MPa and single-phase low temperature. The first-level pressure reduction layer serves as a pressure buffer layer to ensure the stability of the core test layer's operating conditions.

[0045] (3) The third layer is a secondary pressure reduction layer, with an internal circulating cooling water working pressure of 5MPa and a single-phase low temperature. The secondary pressure reduction layer constitutes the last stage of pressure gradient protection, serving as the final pressure protection layer, and achieving system pressure relief through stepped pressure difference.

[0046] This invention employs a scheme combining layered pressure reduction control and tiered cooling. Through closed-loop control of the pressure at each layer, a 5MPa pressure gradient is maintained between the core test layer (15.5MPa), the first-stage pressure reduction layer (10MPa), and the second-stage pressure reduction layer (5MPa), ensuring the pressure difference remains within the pressure resistance range of the quartz glass material. The core test layer, serving as the main heat exchange zone, heats the cooling water to the desired flow pattern at a working pressure of 15.5MPa. Through heat exchange between the cooling water and the electric heating rod bundle, this experimental device can simulate the flow state and bubble evolution behavior of the cooling water in a pressurized water reactor core. Simultaneously, the flow pattern and bubble evolution process of the cooling water can be visualized through a quartz glass window. The first and second-stage pressure reduction layers constitute a tiered cooling barrier, not only progressively cooling the cooling water in the core test layer but also effectively controlling the wall temperature of the core test layer to ensure sealing safety, avoid material thermal expansion mismatch, and prevent boiling of the secondary loop circulating water, thus ensuring clear observation. That is, the temperature of the circulating water in the second layer is still very high, which may cause it to boil. The third and final pressure-reducing layer can cool the water in the second layer, prevent it from boiling and generating bubbles, and thus prevent obstruction of observation.

[0047] This invention configures a high-precision monitoring instrument for a forced-circulation cooling loop, including a flow sensor, a temperature sensor, and a pressure sensor, to collect real-time flow, temperature, and pressure parameters of the coolant in each loop. Then, based on the principle of thermodynamic equilibrium, the system's heat loss can be calculated using the difference between the inlet and outlet parameters. This provides reliable heat balance data for experiments and can also serve as a key boundary condition in system energy balance analysis. Specifically, by measuring the inlet and outlet temperatures and flow rates of the cooling water in the primary and secondary pressure-reducing layers, the experimental boundary conditions are obtained. Heat loss is calculated using mass flow rate, ensuring the accuracy of the heat balance during the experiment.

[0048] In summary, this invention solves the key technical challenges of material strength limitations and thermal expansion mismatch in high-temperature and high-pressure visualization experiments by using stress gradient distribution and thermo-mechanical decoupling methods, providing a reliable experimental platform for high-temperature and high-pressure visualization of reactor core rod bundle channels.

Claims

1. A visual test device for simulating a high temperature and high pressure condition of a prototype of a rod bundle channel of a core of a nuclear reactor, characterized in that, It has a core test layer and multiple voltage reduction layers; The core test layer has a core test layer window on its side, and the core test layer window is sealed and insulated using a sealing ring and an insulating gasket; the core test layer has an internal bundle of electric heating rods to simulate reactor fuel rods; The multi-stage pressure reduction layer is formed by setting multiple cylindrical pressure reduction layer windows coaxially outside the core test layer; stable circulating cooling water is introduced into the core test layer and each pressure reduction layer, and the pressure of each circulating cooling water is different. The pressure difference on both sides of each window is within the pressure bearing range of the window material; the circulating cooling water in each pressure reduction layer is kept at a single-phase low temperature to facilitate visual observation and ensure that the temperature of the sealing material is below its temperature resistance limit.

2. The visualization test device of claim 1, wherein, The core test layer has opposing core test layer windows on both sides; visualization observation is carried out by taking pictures with a high-speed camera, and the other side is illuminated by supplementary lighting equipment.

3. The visualization experimental device according to claim 1, characterized in that, Each window is made of silica quartz glass.

4. The visualization experimental device according to claim 1, characterized in that, Each circulating cooling water is supplied by an independent circulating cooling water system. The circulating cooling water system is powered by a pump and is equipped with a pressure sensor and a pressure regulator for real-time pressure control to ensure stable circulating cooling water pressure.

5. The visualization experimental device according to claim 4, characterized in that, The circulating cooling water system is also equipped with temperature sensors and flow sensors.

6. The visualization experimental device according to claim 1, characterized in that, The core test layer contains multiple bundles of electric heating rods.

7. The visualization experimental apparatus according to any one of claims 1 to 6, characterized in that, The core test layer adopts a stainless steel cavity with vertical openings on the left and right sides, which are closed by stainless steel cover plates. The inside of the stainless steel cavity has a first insulating ceramic flow channel. The first insulating ceramic flow channel and the stainless steel cover plate have openings at the same positions, and a core test layer window is set between them. The core test layer window and the first insulating ceramic flow channel are sealed and insulated with sealing rings and insulating gaskets. The stainless steel cover plate and the stainless steel cavity are also sealed with sealing rings.

8. The visualization experimental device according to claim 7, characterized in that, The upper end of the stainless steel cavity is sequentially provided with a second insulating ceramic flow channel, a conductive nickel plate, and a main outlet cavity, wherein the conductive nickel plate forms a circuit to the lower part of the electric heating rod bundle; the second insulating ceramic flow channel is cylindrical, and insulating gaskets are provided at its upper and lower ends to insulate the test section from the external inlet and outlet pipes; an insulating gasket is also provided between the conductive nickel plate and the main outlet cavity; the main outlet cavity has flow channels that connect the core test layer and each level of pressure reduction layer, as well as corresponding fluid outlets.

9. The visualization experimental device according to claim 8, characterized in that, The lower end of the stainless steel cavity is connected to the main inlet chamber, which has flow channels that connect the core test layer and each level of pressure reduction layer, as well as corresponding fluid inlets.

10. The visualization experimental device according to claim 9, characterized in that, The lower end of the main inlet cavity is connected to a pressure-reducing chamber. The main inlet cavity and the pressure-reducing chamber, as well as the electric heating rod bundle and the pressure-reducing chamber, are sealed by a sealing system. The pressure-reducing chamber is provided with a pressure-reducing chamber inlet and a pressure-reducing chamber outlet. Cooling water circulates through the pressure-reducing chamber inlet and outlet to cool the sealing systems on both sides.

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