Visual test device for simulating high-temperature and high-pressure working conditions of nuclear reactor core rod bundle channel prototype

Abstract

The invention discloses a visual test device for simulating high-temperature and high-pressure working conditions of a nuclear reactor core rod bundle channel prototype, the device is provided with a core test layer and a multi-stage depressurization layer, and a core test layer window on the side surface of the core test layer is sealed and insulated by using a sealing ring and an insulating spacer; an electric heating rod bundle is arranged in the core test layer; the multi-stage pressure reduction layer is formed by coaxially arranging a plurality of cylindrical pressure reduction layer windows outside the core test layer; circulating cooling water with stable pressure is respectively introduced into the core test layer and each pressure reduction layer, the pressure of each path of circulating cooling water is different, and the pressure difference of the two sides of each window is within the window material pressure bearing range; circulating cooling water in each pressure reduction layer is kept at a single-phase low temperature, so that visual observation is facilitated, and the temperature of the sealing material is ensured to be lower than the temperature resistance limit. According to the invention, the key technical problems of material strength limitation and thermal expansion mismatch in the high-temperature and high-pressure visualization test are solved, and a reliable test platform is provided for the high-temperature and high-pressure visualization of the reactor core rod bundle channel prototype.

Description

Technical Field

[0001] The present invention relates to the research field of high-temperature and high-pressure two-phase flow of nuclear reactor core prototypes, and in particular to a visual test device for simulating high-temperature and high-pressure working conditions of a nuclear reactor core rod bundle channel prototype. Background Art

[0002] The high-temperature and high-pressure hot visualization test of the prototype of the rod bundle channel of a pressurized water reactor is the main method to study the boiling starting point and bubble evolution law in the rod bundle channel. Due to factors such as material strength and sealing performance, the existing visualization test equipment is not suitable for the visualization test of the prototype of the rod bundle channel of the pressurized water reactor under high-temperature and high-pressure working conditions. Specifically,

[0003] (1) Insufficient pressure bearing capacity of visualization medium

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

[0005] (2) Sealing material failure at high temperature

[0006] During visualization tests of a pressurized water reactor prototype under high-temperature and high-pressure conditions, sealing materials are required at the viewing window to prevent coolant leakage. Existing sealing materials are mostly organic composites, such as rubber rings. These materials, if exposed to high temperatures for extended periods, can suffer from severe thermal aging, causing creep relaxation at the sealing interface and ultimately 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. When the temperature and pressure are low, the mismatch is still within an acceptable range, but as the temperature and pressure increase, the thermal expansion difference becomes more and more significant, leading to failure of the sealing interface. Summary of the Invention

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

[0010] Technical solution: The present invention provides a visual test device for simulating the high-temperature and high-pressure working conditions of a nuclear reactor core bundle channel prototype, comprising a core test layer and a multi-stage pressure reduction 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 by a sealing ring and an insulating gasket; the core test layer has a built-in electric heating rod bundle to simulate the reactor fuel rod;

[0012] The multi-stage pressure reduction layer is formed by coaxially arranging multiple cylindrical pressure reduction layer windows outside the core test layer; circulating cooling water with stable pressure is respectively 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 maintains a single-phase low temperature to facilitate visual observation, ensuring that the temperature of the sealing material is lower than its temperature resistance limit.

[0013] Furthermore, the core test layer has core test layer windows arranged opposite to each other on both sides; visual observation is performed by using a high-speed camera, the shooting is performed on one side of the visual test device, and the opposite side is supplemented with light using a supplementary light device.

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

[0015] Furthermore, each circulating cooling water is supplied by an independent circulating cooling water system. The circulating cooling water system uses a pump as a power source, and is equipped with a pressure sensor and a pressure stabilizer for real-time pressure control to ensure stable circulating cooling water pressure.

[0016] Furthermore, a temperature sensor and a flow sensor are also provided in the circulating cooling water system.

[0017] Furthermore, the core test layer has multiple built-in electric heating rod bundles.

[0018] Furthermore, the core test layer adopts a stainless steel cavity, which has vertical openings on the left and right sides, and the openings are closed by a stainless steel cover plate; a first insulating ceramic flow channel is provided inside the stainless steel cavity, and the first insulating ceramic flow channel and the stainless steel cover plate have openings at the same position and a core test layer window is arranged between the two; a sealing ring and an insulating gasket are used to seal and insulate the core test layer window and the first insulating ceramic flow channel, and a sealing ring is also used to seal the stainless steel cover plate and the stainless steel cavity.

[0019] Furthermore, a second insulating ceramic flow channel, a conductive nickel plate and a main outlet cavity are sequentially provided at the upper end of the stainless steel cavity, wherein a circuit is formed from the conductive nickel plate 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 respectively connecting 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 cavity, and the main inlet cavity has flow channels respectively connected to the core test layer and each level of pressure reduction layer, as well as corresponding fluid inlets.

[0021] Furthermore, the lower end of the main inlet chamber is connected to a pressure reduction chamber, and a sealing system is used to seal the main inlet chamber and the pressure reduction chamber, as well as the electric heating rod bundle and the pressure reduction chamber; a pressure reduction chamber inlet and a pressure reduction chamber outlet are provided on the pressure reduction chamber; cooling water circulates through the pressure reduction chamber inlet and the pressure reduction chamber outlet to cool the sealing systems on the upper and lower sides.

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

[0023] To address the pressure resistance of the visualization medium, the present invention incorporates a multi-stage pressure-reducing layer and multi-stage forced-circulation cooling water outside the core test layer. By controlling the pressure of the cooling water on both sides of the window, the pressure differential across the window is maintained within an acceptable range. This multi-stage forced-circulation cooling also addresses the issues of high-temperature failure of the sealing material and the mismatch in thermal expansion of the materials under high temperature and high pressure, thus preventing leakage caused by seal failure. Specifically, the cooling water circulation ensures that the wall temperature of the core test layer is below the temperature resistance limit of the sealing material.

[0024] The test apparatus provided by this invention enables 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 the location of near-wall boiling onset within a pressurized water reactor (PWR) rod bundle channel, as well as the generation, slippage, annihilation, and shedding of bubbles. This allows for the characterization of the flow pattern evolution within the bundle channel, providing visual experimental data to reveal the mechanisms affecting heat transfer on the bundle surface. This experimental data will facilitate in-depth research into the behavior and heat transfer characteristics of bubbles within the reactor cooling system, thereby improving the safety and thermal efficiency of nuclear reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of a visualization test device for simulating high-temperature and high-pressure working conditions of a nuclear reactor core rod bundle channel prototype provided by an embodiment of the present invention;

[0026] Figure 2 yes Figure 1 Exploded view of

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

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

[0029] Attachment Figures 1 to 3 The reference numerals in the figures 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. Decompression layer window; 5. Stainless steel cover; 6. Sealing ring; 7. Insulating gasket; 8. Conductive nickel plate; 9. Sealing system; 10. Main inlet cavity; 11. Core test layer entrance; 12. First-level decompression layer entrance; 13. Second-level decompression layer entrance; 14. Decompression cavity; 15. Decompression cavity entrance; 16. Decompression cavity outlet; 17. Main outlet cavity; 18. Core test layer outlet; 19. First-level decompression layer outlet; 20. Second-level decompression layer outlet.

[0031] like Figures 1 to 3 As shown, an embodiment of the present invention provides a visual test device for simulating the high temperature and high pressure working conditions of a nuclear reactor core rod bundle channel prototype, comprising a core test layer, a first-level decompression layer and a second-level decompression layer arranged in sequence from the inside out.

[0032] The core test layer utilizes a square-cross-section stainless steel chamber 1 with vertical openings on both sides. These openings are sealed by stainless steel covers 5, which are bolted together. A first insulating ceramic flow channel 2-1 is located within the chamber, composed of two ceramic components.

[0033] To facilitate visual observation, holes were drilled in 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 allowed observation of the surface of the electric heating rod bundle 3, the cooling water flow pattern, and the bubble evolution process. The two core test layer windows faced each other. In the figure, 4-1 is the observation window, and 4-2 is the light source window. Light was directed toward light source window 4-2, and the camera recorded toward observation window 4-1. A sealing ring 6 and insulating gasket 7 were used to seal and insulate the core test layer window from the first insulating ceramic flow channel 2-1. A sealing ring 6 was also used to seal the stainless steel cover plate 5 from the stainless steel cavity 1.

[0034] The core test layer is equipped with several high-temperature and high-pressure resistant electric heating rod bundles 3 to simulate reactor fuel rods.

[0035] The upper end of the stainless steel cavity 1 is provided with a second insulating ceramic flow channel 2-2, a conductive nickel plate 8 and a main outlet cavity 17 in sequence. 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. An insulating gasket 7 is also provided between the conductive nickel plate 8 and the main outlet cavity 17. The core test layer outlet 18, the first-level pressure reduction layer outlet 19 and the second-level pressure reduction layer outlet 20 are welded on the main outlet cavity 17.

[0036] The lower end of the stainless steel cavity 1 is connected in sequence with the main inlet cavity 10 and the decompression cavity 14, wherein the main inlet cavity 10 and the decompression cavity 14, as well as the electric heating rod bundle 3 and the decompression cavity 14 are sealed by a sealing system 9. The sealing system 9 adopts a special industrial sealing device (existing technology). The stainless steel cavity 1 and the main inlet cavity 10 are connected by bolts, and the main inlet cavity 10 and the decompression cavity 14 are also connected by bolts. The core test layer inlet 11, the first-level decompression layer inlet 12 and the second-level decompression layer inlet 13 are welded on the main inlet cavity 10. The decompression cavity 14 is welded with a decompression cavity inlet 15 and a decompression cavity outlet 16. Cooling water circulates through the decompression cavity inlet 15 and the decompression cavity outlet 16 to cool the sealing system 9 on the upper and lower sides to prevent the sealing system 9 from failing under the high temperature and high pressure environment in 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 chamber. The pressure-reducing layer window 4-3 is sealed between two upper and lower discs of the stainless steel chamber 1 using a sealing ring 6. The two discs are bolted together to squeeze and secure the pressure-reducing layer window 4-3. The stainless steel chamber 1 is similarly mounted between the two discs. 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. It then flows through different channels within the main inlet chamber 10, through the test section and the two annular water chambers, before flowing through different channels in the main outlet chamber 17 and out through the core test layer outlet 18, the primary pressure-reducing layer outlet 19, and the secondary pressure-reducing layer outlet 20.

[0038] In this embodiment, the window material is silicon dioxide quartz glass.

[0039] Each circulating cooling water system is supplied by an independent circulating cooling water system powered by a pump. Pressure sensors and a voltage regulator (currently used in existing technologies) provide real-time pressure control to ensure stable pressure in each circulating cooling water system, ensuring a consistent pressure differential of approximately 5 MPa across each layer of quartz glass. A pressure sensor is installed at each pump inlet and outlet. Temperature and flow sensors are also installed in the circulating cooling water system, with one temperature sensor at each pump inlet and outlet. This circulating cooling water ensures that the core test layer wall temperature remains below the thermal resistance limit of the sealing material, ensuring test safety.

[0040] Visual observation is performed using a high-speed camera on one side of the visualization test device, and fill-in light equipment is used on the opposite side to make the field of view between the rod bundle channels clearer.

[0041] It should be pointed out that the two-stage decompression layer design provided in this embodiment is based on considerations such as window material, sealing performance, and observation clarity. In fact, the number of decompression layers can be further increased to reduce the pressure difference between adjacent layers (for example, from 5MPa to 3MPa or lower), so that a wider range of window materials (such as sapphire, transparent ceramics, etc.) can be adapted, thereby improving the flexibility and safety of the design. However, an increase in the number of layers will introduce more sealing interfaces, so it is necessary to evaluate the amplification effect of the complex structure on the risk of leakage. In addition, too many layers will lead to increased manufacturing costs, increased assembly difficulty, and may weaken the clarity of visual observation. The present invention adopts a two-stage decompression (15.5MPa→10MPa→5MPa), which is a compromise optimization based on the industrial pressure limit and sealing technology of the current mainstream window material - quartz glass. If higher strength transparent materials or more reliable sealing solutions appear in the future, it can be fully expanded to a three-stage or even more-stage decompression structure.

[0042] The following combination Figure 3 The technical principle of the present invention is introduced.

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

[0044] (2) The second layer is the first-level pressure reduction layer, in which the circulating cooling water has a working pressure of 10 MPa and single-phase low temperature. The first-level pressure reduction layer serves as a pressure buffer layer to ensure the stable working conditions of the core test layer.

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

[0046] The present invention adopts a scheme that combines layered pressure reduction control with step cooling. Through closed-loop control of the pressure of each layer, a 5MPa pressure difference gradient is maintained between the core test layer (15.5MPa), the first-level pressure reduction layer (10MPa) and the second-level pressure reduction layer (5MPa), so that the pressure difference is within the pressure resistance range of the quartz glass material. The core test layer serves as the main heat exchange area, heating the cooling water to the required flow pattern and state at a working pressure of 15.5MPa. Through the heat exchange effect between the cooling water and the electric heating rod bundle, the test device can simulate the flow state and bubble evolution behavior of the cooling water in the pressurized water reactor core, and at the same time, the cooling water flow pattern and bubble evolution process can be visualized through the quartz glass window. The first and second-level pressure reduction layers constitute a step-by-step cooling barrier, which not only cools the cooling water of the core test layer step by step, but also effectively controls the wall temperature of the core test layer to ensure sealing safety, avoid material thermal expansion mismatch, and prevent the secondary loop circulating water from boiling, ensuring observation clarity. That is, the temperature of the circulating water in the second layer is still very high and may boil. The third and final pressure-reducing layer can cool the water in the second layer, preventing it from boiling and generating bubbles that hinder observation.

[0047] The present invention configures a forced circulation cooling circuit with high-precision monitoring instruments, including flow sensors, temperature sensors, and pressure sensors, to collect the flow, temperature, and pressure parameters of the coolant in each circuit in real time. Then, based on the principle of thermodynamic equilibrium, the system heat loss can be calculated by the difference between the inlet and outlet parameters. This not only provides reliable thermal balance data support for the experiment, but also serves as a key boundary condition for participating in the system energy balance analysis. Specifically, by measuring the inlet and outlet temperatures and flow rates of the cooling water in the first and second decompression layers, the boundary conditions of the experiment are obtained, and the heat loss is calculated by mass flow to ensure the accuracy of the thermal balance during the experiment.

[0048] In summary, the present invention solves the key technical problems of material strength limitation and thermal expansion mismatch in high-temperature and high-pressure visualization tests through stress gradient distribution and thermomechanical decoupling methods, and provides a reliable test platform for high-temperature and high-pressure visualization of reactor core rod bundle channel prototypes.

Claims

1. A visual test device for simulating the high temperature and high pressure working conditions of a nuclear reactor core rod bundle channel prototype, characterized in that: It has a core test layer and a multi-stage pressure reduction layer; The core test layer has a core test layer window on its side, and the core test layer window is sealed and insulated by a sealing ring and an insulating gasket; the core test layer has a built-in electric heating rod bundle to simulate the reactor fuel rod; The multi-stage pressure reduction layer is formed by coaxially arranging multiple cylindrical pressure reduction layer windows outside the core test layer; circulating cooling water with stable pressure is respectively 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 maintains a single-phase low temperature to facilitate visual observation, ensuring that the temperature of the sealing material is lower than its temperature resistance limit.

2. The visualization test device according to claim 1, characterized in that: The core test layer has core test layer windows arranged opposite to each other on both sides; visual observation is performed by using a high-speed camera, and the shooting is performed on one side of the visual test device, and the opposite side is supplemented with light using a supplementary light device.

3. The visualization test device according to claim 1, characterized in that: Each window is made of silicon dioxide quartz glass.

4. The visualization test 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 uses a pump as the power source. At the same time, a pressure sensor and a pressure stabilizer are set to perform real-time pressure control to ensure the stability of the circulating cooling water pressure.

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

6. The visualization test device according to claim 1, characterized in that: The core test layer is equipped with multiple electric heating rod bundles.

7. The visualization test device 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 a stainless steel cover plate; a first insulating ceramic flow channel is provided inside the stainless steel cavity, and the first insulating ceramic flow channel and the stainless steel cover plate have openings at the same position and a core test layer window is provided between the two; a sealing ring and an insulating gasket are used to seal and insulate the core test layer window and the first insulating ceramic flow channel, and a sealing ring is also used to seal the stainless steel cover plate and the stainless steel cavity.

8. The visualization test 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 respectively connecting the core test layer and each level of pressure reduction layer, as well as corresponding fluid outlets.

9. The visualization test device according to claim 8, characterized in that: The lower end of the stainless steel cavity is connected to a main inlet cavity, which is provided with flow channels respectively connected to the core test layer and various levels of pressure reduction layers, as well as corresponding fluid inlets.

10. The visualization test device according to claim 9, characterized in that: The lower end of the main inlet chamber is connected to the pressure reduction chamber, and the main inlet chamber and the pressure reduction chamber, as well as the electric heating rod bundle and the pressure reduction chamber are sealed by a sealing system; a pressure reduction chamber inlet and a pressure reduction chamber outlet are provided on the pressure reduction chamber; cooling water circulates through the pressure reduction chamber inlet and the pressure reduction chamber outlet to cool the sealing systems on the upper and lower sides.

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