A multi-stage cooling device for the tip of a heating rod used in a high-power simulation test of a nuclear reactor.

Abstract

This invention discloses a multi-stage cooling device for the heating rod tip in a high-power nuclear reactor simulation test. The device includes a flange component and a multi-stage cooling assembly coaxially connected to it. The multi-stage cooling assembly comprises multiple plates and multiple connectors arranged alternately along the axial direction. Multiple heating rods penetrate each plate and are sealed under high pressure by sealing elements. Adjacent plates and the connectors between them enclose independent cooling chambers. Cooling water inlets and outlets are provided on the sidewalls of the connectors to introduce cooling water into the corresponding cooling chambers. Cooling media of different temperatures and pressures are introduced into each cooling chamber to provide staged cooling to the expansion end of the heating rod. This invention effectively avoids high-temperature failure of the sealing material, achieves adaptive release of the axial thermal expansion of the heating rod, significantly reduces end-tip heat loss, and provides a safe and reliable physical boundary guarantee for high-power reactor core simulation tests.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor thermal-hydraulic testing technology, specifically to a multi-stage cooling device for the tip of a heating rod used in high-power simulation tests of nuclear reactors. Background Technology

[0002] High-power simulation tests of pressurized water reactor cores are a key means of studying the thermohydraulic characteristics of fuel assemblies and verifying reactor safety. In thermohydraulic test rigs, direct or indirect electric heating rods are typically used to simulate the heat release process of nuclear fuel rods. As test parameters develop towards higher power and higher pressure, the sealing and cooling of the expansion ends of the heating rods has gradually become a bottleneck restricting simulation tests.

[0003] In existing thermal hydraulic test benches, the heating rod end cooling scheme typically employs a structure with a single-stage water-cooled sleeve rigidly connected to a sealing gland. After the heating rod passes through the single-stage flange, a high-pressure seal is achieved by the sealing gland directly pressing against the sealing element. This structure exposes the heating rod end to an extremely harsh working environment, revealing the following technical defects:

[0004] First, high-power heating rods experience significant axial thermal expansion during operation. Traditional single-stage sealing structures typically rigidly fix the heating rod to the expansion end. When the heating rod expands axially due to heat, enormous compressive stress is generated at the fixing point. This stress concentration not only causes the heating rod body to bend or break but also severely compresses and damages the sealing structure. For a long time, those skilled in the art have often attributed seal failure to simply excessive temperature, failing to recognize that the mechanical stress compression caused by axial thermal expansion is the deeper cause of seal failure at the end of high-power heating rods.

[0005] Secondly, to ensure the integrity of the pressure boundary of the test bench while allowing for a certain degree of axial sliding of the heating rod, the ends are typically sealed with organic polymer materials such as rubber and polytetrafluoroethylene. However, under high-power operation, the temperature near the heating rod end can reach several hundred degrees Celsius, far exceeding the long-term tolerance limit of the aforementioned conventional sealing materials (usually below 200°C). This easily leads to accelerated aging and creep relaxation of the seals, ultimately causing leakage at the pressure boundary. Simultaneously, for indirect heating rods, the rapid accumulation of heat at the end can cause a sharp decline in the insulation performance of insulating materials (such as magnesium oxide) at high temperatures, leading to breakdown or leakage, seriously threatening test safety.

[0006] Furthermore, existing single-stage end-cooling schemes often have excessively large cooling ranges or cannot achieve precise local control, resulting in a large amount of heat being conducted to the external cooling system through the heating rod ends, causing excessive heat loss in the core test section. This not only alters the preset thermal boundary conditions of the test section, causing deviations between the simulated power distribution and the actual nuclear reactor physics processes, but also severely reduces the accuracy of the test data. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a multi-stage cooling device for the end of a heating rod in a high-power simulation test of a nuclear reactor that can prevent sealing material from failing due to high temperature and high pressure, adapt to the axial thermal expansion of the heating rod, and effectively control the heat loss at the end to avoid distortion of the test boundary.

[0008] Technical Solution: This invention provides a multi-stage cooling device for the end of a heating rod used in a high-power simulation test of a nuclear reactor. The device includes a flange component and a multi-stage cooling assembly coaxially fixed to the outer end of the flange component. The inner end of the flange component is connected to the reactor core test section. The multi-stage cooling assembly includes multiple plates and multiple connectors arranged alternately along the axial direction. The connectors are annular. Each plate has a mounting hole through which a heating rod passes. A sealing element is installed in the mounting hole to achieve sealing and fixation between the heating rod and the plate. Adjacent plates and the connectors between them enclose an independent cooling chamber. The sidewall of the connector has a cooling water inlet and a cooling water outlet for introducing cooling water into the corresponding cooling chamber. The cooling water inlet and outlet of each cooling chamber are connected to an independent circulating cooling water system to achieve independent and precise control of the cooling water pressure, temperature, and flow rate in each cooling chamber. The cooling water pressure and temperature in each cooling chamber decrease progressively outwards to provide staged cooling of the expansion end of the heating rod.

[0009] Furthermore, the plate body includes a top plate, a bottom plate, and several intermediate plates, and the connector includes a top connector, a bottom connector, and several intermediate connectors; the top plate is fixed to the top of the top connector and located in the flange component; the intermediate plates are disposed between the top connector and the intermediate connectors, or between adjacent intermediate connectors; the bottom plate is disposed between the intermediate connectors and the bottom connector; each plate body is fixedly connected to the flange component by fasteners to achieve axial compression of each component.

[0010] Furthermore, the lower surface of the top connector is provided with a first recessed groove adapted to the intermediate plate, the upper surface of the bottom intermediate connector is provided with a first recessed groove adapted to the intermediate plate, and the lower surface of the bottom intermediate connector is provided with a second recessed groove adapted to the bottom plate; the upper and lower surfaces of the remaining intermediate connectors are respectively provided with a first recessed groove adapted to the intermediate plate; and the upper surface of the bottom connector is provided with a second recessed groove adapted to the bottom plate.

[0011] Furthermore, the fasteners are high-strength bolts.

[0012] Furthermore, the flange components adopt O-ring flanges, ring face flanges, or high-pressure self-tightening flanges.

[0013] Furthermore, the number of cooling water inlets and outlets in each cooling chamber is determined based on the design flow rate of the cooling water in the corresponding cooling chamber.

[0014] Furthermore, there are multiple heating rods arranged in an array and penetrating each plate, used to simulate the fuel rod bundle in the core of a nuclear reactor.

[0015] Furthermore, the seals are made of O-rings, packing seals, or spring-loaded seals.

[0016] Furthermore, the heating rod is an indirect heating rod, and the space between the insulation layer covering the heating rod and the sealant is filled with high-temperature resistant sealant to prevent leakage and electrochemical corrosion.

[0017] Furthermore, the circulating cooling water system is equipped with a circulating pump, a pressure regulator, and a pressure sensor, and temperature sensors and flow sensors are installed at the cooling water inlet and outlet of each cooling chamber.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) This invention achieves adaptive release of axial thermal expansion of the heating rod. Unlike the existing single-stage rigid end-fixed structure, the multi-stage independent cooling chamber design of the present invention allows different sections of the heating rod to adapt to the temperature environment of their respective cooling chambers when axial thermal expansion occurs. This graded structure disperses and releases the originally concentrated thermal stress, effectively avoiding bending or breakage of the heating rod body or compression damage to the sealing structure caused by mechanical stress concentration.

[0020] (2) This invention can significantly reduce heat loss in non-core areas and improve test accuracy. This invention adopts a localized precision cooling strategy, which strictly limits the cooling effect to the expansion end area of ​​the heating rod. By independently controlling the temperature and flow rate of each cooling chamber, the heat conduction from the core test section to the external environment is minimized, ensuring the accuracy of the thermal boundary conditions of the test section, thereby improving the reliability of high-power reactor core simulation test data.

[0021] (3) This invention effectively avoids high-temperature failure of sealing materials. This invention adopts a multi-stage independent cooling chamber structure with axial stacking. Cooling water is introduced in stages to directly flush and cool the expansion end of the heating rod, thereby gradually reducing the temperature and pressure of the high-temperature and high-pressure environment near the core test section. This structure ensures that the seal at the through plate is always within its safe operating temperature limit (e.g., 200°C), eliminating the risk of leakage at the pressure boundary caused by high-temperature aging and creep of the sealing material.

[0022] (4) This invention constructs a safe and controllable pressure gradient boundary. The multi-stage cooling chambers, combined with high-strength fastening connections, constitute a physical boundary capable of withstanding high pressure. By independently and stepwise adjusting the cooling water pressure of each stage of the cooling chamber (e.g., gradually transitioning from high pressure in the test section to atmospheric pressure), not only is the pressure difference of a single-stage seal significantly reduced, but the pressure distribution of the reactor at different axial positions can also be simulated, providing a safe hardware guarantee for the test under extreme high-pressure conditions. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a multi-stage cooling device for the tip of a heating rod used in a high-power simulation test of a nuclear reactor, provided in an embodiment of the present invention.

[0024] Figure 2 yes Figure 1 Axial sectional view;

[0025] Figure 3 yes Figure 1 Exploded view;

[0026] Figure 4 This is a schematic diagram of the top connector in an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure of the intermediate connector in an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of the radial power distribution of the heating rod bundle in an embodiment of the present invention. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Appendix Figures 1 to 6 The accompanying figure labels are as follows:

[0031] 1. Flange assembly; 2. Top plate; 3. Top connector; 4. Intermediate plate; 5. Intermediate connector; 6. Bottom plate; 7. Bottom connector; 8. Heating rod; 9. Seal; 10. Upper cooling chamber; 11. Lower cooling chamber; 12. Upper cooling water inlet; 13. Upper cooling water outlet; 14. Lower cooling water inlet; 15. Lower cooling water outlet; 16. High power distribution area; 17. Intermediate power distribution area; 18. Low power distribution area; 19. Zero power distribution area.

[0032] like Figures 1 to 3As shown, this embodiment of the invention provides a multi-stage cooling device for the heating rod end of a high-power simulation test of a nuclear reactor. The multi-stage cooling device adopts an axially stacked structure, including a flange component 1 and a multi-stage cooling assembly. The flange component 1 is used to connect to the reactor core test section. In this embodiment, the flange component 1 uses an O-ring flange, but under other extreme high-pressure conditions, a ring-connected flange or a high-pressure self-tightening flange can also be used. The multi-stage cooling assembly is coaxially fixed on the O-ring flange and includes a top plate 2, a top connector 3, an intermediate plate 4, an intermediate connector 5, a bottom plate 6, and a bottom connector 7 arranged coaxially in sequence. Each connector is annular. The lower surface of the top connector 3 has a first groove adapted to the intermediate plate 4; the upper surface of the intermediate connector 5 has a first groove adapted to the intermediate plate 4, and the lower surface of the intermediate connector 5 has a second groove adapted to the bottom plate 6; the upper surface of the bottom connector 7 has a second groove adapted to the bottom plate 6. The top plate 2 is fixed to the top of the top connector 3 with screws and is located in the O-ring flange. The intermediate plate 4 is located between the top connector 3 and the intermediate connector 5, and the bottom plate 6 is located between the intermediate connector 5 and the bottom connector 7. Each plate is fixedly connected to the O-ring flange with fasteners such as high-strength bolts, so as to achieve axial compression of each component and together form a robust physical boundary that can withstand high pressure.

[0033] Combination Figure 2 and Figure 3 The multi-stage cooling device forms two independent cooling chambers. Specifically, the inner wall of the top connector 3, together with the lower surface of the top plate 2 and the upper surface of the middle plate 4, forms the first-stage cooling chamber, namely the upper cooling chamber 10; the inner wall of the middle connector 5, together with the lower surface of the middle plate 4 and the upper surface of the bottom plate 6, forms the second-stage cooling chamber, namely the lower cooling chamber 11.

[0034] In practical applications, the number of cooling chambers is not limited to two levels. It can be flexibly expanded by increasing or decreasing the number of stacked groups of plates and connectors according to the actual pressure requirements and temperature gradient requirements of the test bench.

[0035] In terms of through-hole and sealing structures, such as Figure 2 As shown, multiple heating rods 8, used to simulate nuclear reactor fuel rods, are arranged in an array throughout the multi-stage cooling device. Mounting holes corresponding to the heating rod array are provided on the top plate 2, intermediate plate 4, and bottom plate 6, and each mounting hole contains a sealing element 9. The heating rods 8 sequentially pass through the bottom plate 6, lower cooling chamber 11, intermediate plate 4, upper cooling chamber 10, and top plate 2. The sealing element 9 not only achieves high-pressure sealing between the heating rods 8 and each plate but also provides flexible support for the heating rods 8. In this embodiment, the sealing element 9 uses a fluororubber O-ring. In other embodiments, to meet the requirements of higher temperatures or lower friction coefficients, the sealing element 9 can also be replaced with a packing seal or a spring-loaded sealing ring. Both of these sealing methods allow the heating rods 8 to slide slightly during axial thermal expansion, thereby releasing thermal stress.

[0036] Specifically, when the heating rod 8 is an indirect heating rod, its outer surface is usually covered with an insulating layer (such as magnesium oxide). To prevent leakage or electrochemical corrosion caused by cooling water, a high-temperature resistant sealant is further filled between the insulating layer and the seal 9 for insulation and sealing treatment.

[0037] In the design of cooling water flow path, such as Figure 4 and Figure 5 As shown, the sidewalls of the connectors are provided with cooling water inlets and cooling water outlets for introducing cooling water into the corresponding cooling chambers. Specifically, the sidewalls of the top connector 3 are provided with four upper cooling water inlets 12 and two upper cooling water outlets 13 for circulating cooling water into the upper cooling chamber 10; the sidewalls of the intermediate connector 5 are provided with four lower cooling water inlets 14 and two lower cooling water outlets 15 for circulating cooling water into the lower cooling chamber 11.

[0038] The cooling water inlet and outlet of each cooling chamber are connected to an independent circulating cooling water system. Each circulating cooling water system is powered by a circulating pump and equipped with a pressure regulator, pressure sensor, temperature sensor and flow sensor, thereby realizing independent and precise control of the cooling water pressure, temperature and flow rate in the upper cooling chamber 10 and the lower cooling chamber 11.

[0039] This embodiment uses the pressure peak under a typical pressurized water reactor primary circuit accident as a benchmark, and combines industry-standard verification data on the maximum reliable pressure difference (7~8MPa) of a single-stage seal under long-term operating temperature of fluororubber O-rings at 204℃, to design a stepped pressure reduction and graded cooling system for the multi-stage cooling device.

[0040] 1. Pressure gradient control

[0041] To ensure sufficient safety margin, the pressure difference between the lower cooling chamber 11 and the atmospheric environment, as well as the pressure difference between the upper cooling chamber 10 and the lower cooling chamber 11, are both set to approximately 6.9 MPa. Accordingly, the reference operating pressure of the upper cooling chamber 10 is set at 12.5 MPa (with a design pressure limit of 13.79 MPa), and the operating pressure of the lower cooling chamber 11 is set at 6.89 MPa. This axially progressive pressure reduction design effectively distributes the pressure load of a single-stage seal.

[0042] 2. Power distribution and temperature control

[0043] like Figure 6As shown, in this embodiment, there are a total of 177 heating rods 8, with a total input power of 2MW. To realistically simulate the radial power distribution of the reactor, the heating rod bundle is divided into four regions: high power distribution region 16 (9 rods, 16.65W each), intermediate power distribution region 17 (36 rods, 9.11W each), low power distribution region 18 (128 rods, 6.99W each), and zero power distribution region 19 (4 rods, 0W each).

[0044] Under the aforementioned high-power heating conditions, the heights of both the upper cooling chamber 10 and the lower cooling chamber 11 are set to 21.6 mm. The upper cooling chamber 10 is supplied with cooling water at a temperature of 154°C and a flow rate of 0.91 m / s; the lower cooling chamber 11 is supplied with cooling water at a temperature of 25°C and a flow rate of 0.91 m / s.

[0045] 3. Running effect

[0046] According to theoretical calculations and numerical simulations, under the above extreme conditions, the highest temperatures on the surfaces of the heating rods in the upper cooling chamber 10 and the lower cooling chamber 11 are effectively controlled at 166.9℃ and 40.5℃, respectively, both significantly lower than the maximum allowable operating temperature (200℃) of the fluororubber O-ring seal, effectively avoiding thermal aging failure of the seal.

[0047] Meanwhile, the highest temperatures of the cooling water in the upper cooling chamber 10 and the lower cooling chamber 11 are 158.6℃ and 28.8℃, respectively, which are far lower than the saturation temperature under the corresponding chamber pressure (such as the saturation temperature of 334.6℃ at 13.79MPa). This ensures that the cooling chamber always maintains single-phase liquid convection heat transfer and avoids damage to the heating rod and sealing structure caused by two-phase flow vibration.

[0048] In addition, the multi-stage independent cooling chambers allow different sections of the heating rod to freely adapt to the temperature environment of their respective chambers when the heating rod undergoes axial thermal expansion, effectively releasing the mechanical stress generated by thermal expansion and ensuring the safe and stable operation of the high-power reactor core simulation test.

[0049] In summary, the multi-stage cooling device for the heating rod end of the high-power simulation test provided by this invention achieves graded cooling and pressure reduction of the expansion end of the heating rod through an axially stacked independent cooling chamber structure. This design effectively overcomes the technical defects of easy high-temperature failure of sealing materials and thermal stress concentration of the heating rod under extreme conditions, ensuring the integrity of the pressure boundary of the test bench and providing a safe and reliable engineering guarantee for high-power reactor core thermal-hydraulic simulation tests.

Claims

1. A multi-stage cooling device for the tip of a heating rod used in a high-power simulation test of a nuclear reactor, characterized in that, The system includes a flange component (1) and a multi-stage cooling assembly coaxially fixed to the outer end of the flange component (1). The inner end of the flange component (1) is connected to the core test section. The multi-stage cooling assembly includes multiple plates and multiple connectors arranged alternately along the axial direction. The connectors are annular. Each plate has an installation hole for the heating rod (8) to pass through. A sealing element (9) is provided in the installation hole to achieve sealing and fixing between the heating rod (8) and the plate. Adjacent plates and the connectors between them form independent cooling chambers. Cooling water inlets and outlets are provided on the side walls of the connectors to introduce cooling water into the corresponding cooling chambers. The cooling water inlets and outlets of each cooling chamber are connected to independent circulating cooling water systems to achieve independent and precise control of cooling water pressure, temperature and flow rate in each cooling chamber. The cooling water pressure and temperature in each cooling chamber decrease gradually outward to cool the expansion end of the heating rod (8) in stages.

2. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The plate body includes a top plate (2), a bottom plate (6) and several intermediate plates (4), and the connector includes a top connector (3), a bottom connector (7) and several intermediate connectors (5); the top plate (2) is fixed on top of the top connector (3) and located in the flange component (1); the intermediate plates (4) are arranged between the top connector (3) and the intermediate connectors (5), or between adjacent intermediate connectors (5); the bottom plate (6) is arranged between the intermediate connectors (5) and the bottom connectors (7); each plate body is fixedly connected to the flange component (1) by fasteners to achieve axial compression of each component.

3. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 2, characterized in that, The lower surface of the top connector (3) is provided with a first groove adapted to the intermediate plate (4), the upper surface of the bottom intermediate connector (5) is provided with a first groove adapted to the intermediate plate (4), the lower surface of the bottom intermediate connector (5) is provided with a second groove adapted to the bottom plate (6); the upper and lower surfaces of the other intermediate connectors (5) are respectively provided with a first groove adapted to the intermediate plate (4); the upper surface of the bottom connector (7) is provided with a second groove adapted to the bottom plate (6).

4. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 2, characterized in that, The fasteners are high-strength bolts.

5. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, Flange components (1) use O-ring flanges, ring connection flanges or high-pressure self-tightening flanges.

6. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The number of cooling water inlets and outlets for each cooling chamber is determined based on the design flow rate of the cooling water for that chamber.

7. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The heating rods (8) are multiple in number, arranged in an array and penetrating each plate, used to simulate the fuel rod bundle of the nuclear reactor core.

8. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The sealing element (9) adopts an O-ring, a packing seal or a spring energy storage seal.

9. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The heating rod (8) is an indirect heating rod. The insulating layer covering the heating rod (8) and the sealing element (9) are filled with high-temperature resistant sealant to prevent leakage and electrochemical corrosion.

10. The multi-stage cooling device for the heating rod tip of a high-power nuclear reactor simulation test according to claim 1, characterized in that, The circulating cooling water system is equipped with a circulating pump, a pressure regulator and a pressure sensor. Temperature sensors and flow sensors are installed at the inlet and outlet of the cooling water in each cooling chamber.

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