A safety system to prevent reactor coolant leakage along the axis

Abstract

The present invention provides a safety system for preventing reactor coolant leakage along an axis. The system comprises a sealing assembly comprising three mechanical seals connected in series, a shutdown seal assembly, a pressure-bearing shell, a rotating shaft, and a piping system. The rotating shaft extends through the interior of the pressure-bearing shell, and three sealing assemblies are installed in the pressure-bearing space between the rotating shaft and the pressure-bearing shell. A shutdown seal assembly is installed on the top of the top sealing assembly. The piping system sequentially communicates with the interiors of each sealing surface assembly through the interiors of each sealing assembly, and also communicates with other external components, allowing coolant to flow into the piping system through these external components. At least one throttling element is installed in the piping connecting the piping system to the interiors of each sealing assembly. This safety system has a long service life, a low nuclear leakage rate, and a high safety level.

Description

Technical Field

[0001] The invention relates to the field of reactor coolant pump sealing, and in particular to a safety system for preventing reactor coolant from leaking along an axis. Background Art

[0002] The reactor coolant pump (hereinafter referred to as the main pump) is a key equipment of the reactor system. It is part of the reactor coolant pressure boundary and the only high-speed rotating equipment in the reactor coolant system. It drives the reactor coolant to circulate in the reactor primary circuit and continuously removes the heat generated in the core.

[0003] The main pump shaft sealing system prevents reactor coolant from flowing along the rotating shaft and potentially leaking. This system originated in the 1970s. After nearly half a century of technological development, the current mainstream main pump mechanical seals generally utilize a three-stage pressure-dividing mechanical structure, with sealing surfaces that utilize fluid static pressure, fluid dynamic pressure, or a combination of static and dynamic pressure. The sealing surfaces are tightened using spring compensation and back pressure.

[0004] Leakage rate is a key technical indicator of shaft sealing systems. It refers to the velocity of fluid flowing through the seal surface during high-speed shaft rotation. This fluid is considered leakage from the shaft sealing system. In nuclear power systems, dedicated containers are used to collect leaked fluid. The leakage rate for hydrostatic shaft seals is approximately 300-800 L / h, while the leakage rate for hydrodynamic shaft seals is approximately 2-5 L / h.

[0005] The sealing surface of the main pump shaft sealing system is a wear-prone part and needs to be replaced regularly. Currently, the replacement cycle of the mainstream main pump shaft sealing surface is about 4 years.

[0006] Cooling for the main pump shaft seal system is provided by the reactor system and is controlled by a Nuclear Safety Level I electric valve. In the event of an accident, the valve is closed to ensure the integrity of the reactor's primary circuit boundary and prevent the leakage of radioactive reactor coolant. Summary of the Invention

[0007] In order to improve the service life of the main pump shaft sealing system and reduce the nuclear leakage rate, while ensuring the safety level, the present invention provides a safety system for preventing reactor coolant leakage along the shaft, comprising multiple sealing components, a shutdown sealing component, a pressure-bearing shell, a rotating shaft, and a piping system;

[0008] The rotating shaft is arranged inside the pressure-bearing shell, and a plurality of the sealing assemblies are installed in the pressure-bearing space between the rotating shaft and the pressure-bearing shell;

[0009] A plurality of the sealing assemblies are axially arranged around the rotating shaft and are sequentially connected in series, and the sealing surfaces between two adjacent sealing assemblies are in contact to form a mechanical seal;

[0010] The shutdown sealing assembly is arranged on the top of the sealing assembly at the top end and is used to lock the rotating shaft;

[0011] The pipeline system is in communication with the interior of each sealing component in turn through the interior of each sealing component, and at least one throttling component is provided on the pipeline of the pipeline system located inside each sealing component.

[0012] Specifically, the input end of the pipeline system is connected to the coolant system for introducing coolant; the output end is divided into two paths, which are respectively connected to the RCV system (chemical and volume control system) and the interior of the shutdown sealing component.

[0013] Preferably, the first output end of the pipeline system is connected to the RCV system through a high-pressure pressure relief channel; the second output end of the pipeline system is connected to the interior of the shutdown seal assembly through an SSR pipeline (shutdown seal control pipeline); and valves are provided between the high-pressure pressure relief channel and the RCV system, and between the SSR pipeline and the shutdown seal assembly.

[0014] Preferably, the high-pressure relief flow is connected to the RCV system via a first electric valve and a first passive safety valve connected in series;

[0015] During normal operation, the first electric valve and the first passive safety valve are both in the open state, and the coolant in the piping system passes through each sealing component in turn and enters the RCV system;

[0016] During normal shutdown, the first electric valve is closed and the coolant is blocked from entering the RCV system;

[0017] Under accident conditions, the first passive safety valve closes automatically, and the coolant is blocked from entering the RCV system.

[0018] Preferably, the SSR pipeline is connected to the interior of the shutdown sealing assembly through a second electric valve and a second passive safety valve connected in parallel;

[0019] During normal operation, the second electric valve and the second passive safety valve are both in a closed state, the coolant is blocked from entering the parking seal assembly, and the rotating shaft is open and can rotate freely;

[0020] During normal shutdown, the second electric valve is opened, and the coolant enters the interior of the shutdown seal assembly through the SSR pipeline, and the pressure of the coolant causes the shutdown seal assembly to lock the rotating shaft;

[0021] Under accident conditions, the second passive safety valve automatically opens, and the coolant enters the interior of the shutdown sealing assembly through the SSR pipeline, and the pressure of the coolant causes the shutdown sealing assembly to lock the rotating shaft.

[0022] Preferably, a throttling element is provided between the first electric valve and the first passive safety valve.

[0023] Furthermore, coolant leaking within the sealing assembly enters the RVD system through gaps between the sealing surfaces of adjacent sealing assemblies.

[0024] Preferably, the coolant passes through the sealing surface gap and then enters the RVD system through the low-pressure leakage channel.

[0025] Preferably, the gap between the sealing surfaces of adjacent sealing components is less than 1 micron.

[0026] Preferably, adjacent sealing surfaces are connected by deep groove fluid dynamic pressure sealing surfaces.

[0027] The present invention has the following beneficial effects:

[0028] 1. The sealing surface gap is less than 1μm, the leakage rate is reduced by more than 95%, and the actual leakage rate under working conditions is less than 0.1L / h;

[0029] 2. The sealing surface is in an ultra-slip state during operation, with a friction coefficient of less than 0.01 and an extremely low wear rate. The service life of a single-stage sealing surface under normal working pressure exceeds 8 years, and the single-stage sealing surface can operate for a long time under the condition of three-stage full pressure until the material is replaced;

[0030] 3. Use a passive safety system (the passive safety system is mainly controlled by a passive safety valve. When there is no power input, when high-temperature fluid flows through the passive safety valve, the valves on the high-pressure relief flow channel and the low-pressure leakage flow channel loop are automatically locked to prevent the leakage of radioactive fluid. The valve of the SSR loop automatically opens and locks the parking seal to prevent the leakage of radioactive fluid along the shaft. In the event of an accident, the loop can be locked when there is no power input to ensure that the radioactive coolant does not leak;

[0031] 4. The shaft sealing system has a modular design feature, and on-site disassembly and assembly can be completed quickly in a short time;

[0032] 5. The power loss of the three-stage mechanical seal under the full pressure condition of 16MPa is less than 15kW, that is, the power loss of each sealing component of the first sealing component, the second sealing component, and the third sealing component under the full pressure condition is less than 15kW;

[0033] 6. The reactor system is equipped with a simple and reliable piping system for mechanical seals, which has "passive + active" control features: under normal operating conditions (including operation and shutdown), the electric valve can be remotely controlled to lock the circuit; under accident conditions, without the need for human operation or external intervention, the passive valve automatically operates to lock the circuit and prevent the radioactive fluid from flowing along the axis and leaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A cross-sectional view of the structure of the safety system provided by the present invention during operation;

[0035] Figure 2 A schematic diagram of the piping system of the safety system provided by the present invention;

[0036] Figure 3 This is a structural cross-sectional view of the safety system provided by the present invention. DETAILED DESCRIPTION

[0037] The following is a further detailed description of a safety system for preventing reactor coolant leakage along the axis proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will become clearer. It should be noted that the drawings are in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention, so they have no technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0038] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0039] like Figure 1The figure shows a cross-sectional view of the structure of a safety system for preventing reactor coolant leakage along an axis provided by the present invention. The system comprises a first sealing assembly 1, a second sealing assembly 2, a third sealing assembly 3, a shutdown sealing assembly 4, a pressure-bearing shell 5, a rotating shaft 8, and a piping system 10. The rotating shaft 8 is disposed within the pressure-bearing shell 5. The first sealing assembly 1, the second sealing assembly 2, and the third sealing assembly 3 are sequentially installed in the pressure-bearing space between the rotating shaft 8 and the pressure-bearing shell 5 from bottom to top. The first sealing assembly 1, the second sealing assembly 2, and the third sealing assembly 3 are axially arranged around the rotating shaft 8 and sequentially connected in series. The sealing surfaces between adjacent sealing assemblies contact to form a mechanical seal. The shutdown sealing assembly 4 is also installed on top of the third sealing assembly 3 to lock the rotating shaft 8. The piping system 10 passes through the interiors of the first, second, and third sealing assemblies 1, 2, and 3 in sequence. The connection end near the first sealing assembly 1 is the input end of the piping system 10, used to input coolant into each sealing assembly, and the connection end near the third sealing assembly 3 is the output end of the piping system 10, used to discharge coolant. The pipeline system 10 is respectively provided with at least one throttling element 6 on the pipeline inside each sealing component, and the coolant passes through each throttling element 6 in sequence to achieve step-by-step pressure reduction.

[0040] Among them, the input end of the pipeline system 10 is connected to the cooling system for injecting coolant into the pipeline system 10, and the output end of the pipeline system 10 is divided into two paths, one of which is connected to the RCV system (chemical and volume control system) through the high-pressure relief channel HP, and the other is connected to the inside of the shutdown seal assembly 4 through the SSR pipeline (parking seal control pipeline).

[0041] like Figure 2 As shown, one of the output ends of the pipeline system 10 is connected to the RCV system through the high-pressure relief channel HP, and a valve is provided between the high-pressure relief channel HP and the RCV system. Specifically, the high-pressure relief channel HP is connected to the RCV system through the first electric valve 331VP and the first passive safety valve 332VP connected in series. During normal operation, the first electric valve 331VP and the first passive safety valve 332VP are both in the open state, and the coolant in the pipeline system 10 flows through the first sealing component 1, the second sealing component 2, and the third sealing component 3 and then enters the RCV system through the high-pressure relief channel HP. During normal shutdown, the first electric valve 331VP is closed, and the coolant is blocked from entering the RCV system. Under accident conditions, the first passive safety valve 332VP is automatically closed, and the coolant is also blocked from entering the RCV system to prevent nuclear leakage from entering the circuit where the RCV system is located through the coolant. Furthermore, a manual valve 322VP may be provided between the first electric valve 331VP and the first passive safety valve 332VP for debugging purposes only and not as a functional component.

[0042] like Figure 3 As shown, the other output end of the pipeline system 10 is connected to the interior of the parking seal assembly 4 through the SSR pipeline. Specifically, the SSR pipeline is connected to the interior of the shutdown seal assembly 4 through the second electric valve 335VP and the second passive safety valve 336VP connected in parallel. During normal operation, the second electric valve 335VP and the second passive safety valve 336VP are both in the closed state, and the coolant is blocked from entering the parking seal assembly 4. At this time, the rotating shaft 8 is open and can rotate freely. Figure 1 As shown, during normal shutdown, the second electric valve 335VP is opened, and the coolant enters the interior of the shutdown seal assembly 4 through the SSR pipeline. The pressure of the coolant causes the parking seal assembly 4 to lock the rotating shaft 8 and prevent it from rotating. Figure 3 As shown, under an emergency condition, the second passive safety valve 336VP automatically opens, allowing coolant to enter the shutdown seal assembly 4 through the SSR line. The coolant pressure causes the shutdown seal assembly 4 to lock the rotating shaft 8, preventing it from rotating. Specifically, the coolant enters the shutdown seal assembly 4, lifting the sliding component within the shutdown seal assembly 4. Pressure compresses and locks the top of the sliding component against the locking device on the rotating shaft 8, preventing the pump shaft from rotating.

[0043] The sealing surfaces between the first and second sealing assemblies 1 and 2, and between the second and third sealing assemblies 2 and 3, all utilize deep-groove hydrodynamic sealing surfaces. Because the gap between adjacent sealing surfaces is less than 1 micron, it forms a coolant pathway, directing coolant leaking between the sealing surfaces to the reactor's RVD system. It should be noted that after coolant enters the interior of each sealing assembly, a small amount of coolant leakage is inevitable from the sealing surfaces between them. Localized contact can occur between adjacent sealing surfaces, and chemical reaction products from contact friction can dissolve in the liquid film between the sealing surfaces, forming a low-concentration colloid. While this colloid reduces the friction coefficient between the sealing surfaces and minimizes coolant leakage, a small amount of coolant leakage still occurs. The coolant flow rate through the sealing surface gaps is approximately one-tenth of that through the high-pressure relief channel HP. Ultimately, coolant leaking into the coolant pathway between the sealing surfaces enters the reactor's RVD system via the low-pressure leakage channel LP. Figure 2 Manual valves 572VP, 573VP, and 574VP for the medium- and low-pressure leakage paths (LP) are used for circuit commissioning and are kept closed during normal operation. Manual valve 570VP is also used during commissioning and is normally open during normal operation. Both electric valves 568VP and 816MD are electrically operated valves, closed during emergency conditions and open during normal operation.

[0044] The safety system for preventing reactor coolant leakage along the axis provided in this embodiment has the following features:

[0045] 1. If Figure 1 As shown, the present invention adopts a three-stage fluid dynamic pressure mechanical seal structure, and the three-stage sealing components (first sealing component 1, second sealing component 2, and third sealing component 3) are all inside the pressure-bearing space and isolated from the outside world;

[0046] 2. If Figure 2 As shown, the three-stage fluid dynamic mechanical seal is connected in series, and the main cooling channel is gradually depressurized through the throttling device, and finally enters the RCV system of the reactor from the high-pressure relief channel HP channel;

[0047] 3. The mechanical seals of two adjacent sealing components both adopt deep groove fluid dynamic pressure sealing surfaces;

[0048] 4. During operation, the sealing surfaces may come into local contact. The products of the tribochemical reaction dissolve in the sealing liquid film to form a low-concentration colloid, which reduces the friction coefficient and the coolant leakage flow. The coolant leakage flow through the sealing surface gap is about one ten-thousandth of the high-pressure relief flow HP flow, and eventually enters the reactor RVD system through the low-pressure leakage flow LP channel;

[0049] 5. If Figure 2 As shown, the high-pressure relief channel HP adopts a structure in which the first electric valve 331VP and the first passive safety valve 332VP are connected in series. Under normal working conditions, the first electric valve 331VP can be operated to lock the circuit. Under accident conditions, the first passive safety valve 332VP automatically closes to prevent the radioactive fluid from entering the RCV system through the pipeline and leaking.

[0050] 6. The shutdown seal is driven by the pressure of the coolant in the piping system 10. A second electric valve 335VP and a second passive safety valve 336VP are connected in parallel. During normal operation, both valves are closed, the shutdown seal is open, and the shaft can rotate freely. During normal shutdown, the second electric valve 335VP can be opened to close the shutdown seal. Under accident conditions, the second passive safety valve 336VP automatically opens, driving the shutdown seal to lock the shaft to prevent the radioactive fluid from flowing along the shaft and leaking.

[0051] In summary, the sealing surface gap between adjacent sealing components of the safety system provided by the present invention is less than 1 μm, the leakage rate is reduced by more than 95%, and the actual leakage rate under working conditions is less than 0.1 L / h; the sealing surface is in a super-slip state during operation, the friction coefficient is less than 0.01 and has an extremely low wear rate, the service life of the single-stage sealing surface under normal working pressure exceeds 8 years, and the single-stage sealing surface operates for a long time under the working condition of three-level full pressure until the material is replaced; and a passive safety system is adopted (the passive safety system is mainly controlled by a passive safety valve. When there is no power input, when the high-temperature fluid flows through the passive safety valve, the valves on the high-pressure relief flow channel HP and the low-pressure leakage flow channel LP circuit are automatically locked to prevent the leakage of radioactive fluid. The valve of the SSR circuit can be automatically opened to lock the parking seal to prevent the radioactive fluid from leaking along Shaft leakage. Under accident conditions, the circuit can be locked when there is no power input to ensure that radioactive coolant does not leak out. The shaft sealing system has a modular design feature, and on-site disassembly and assembly can be completed quickly in a short time. The power loss of the three-stage mechanical seal under the full pressure condition of 16MPa is less than 15kW, that is, the power loss of each sealing component of the first sealing component, the second sealing component, and the third sealing component is less than 15kW under full pressure conditions. The reactor system is equipped with a simple and reliable piping system for the mechanical seal, which has "passive + active" control features: under normal operating conditions (including operation and shutdown), the electric valve can be remotely controlled to achieve loop locking; under accident conditions, without the need for human operation or external intervention, the passive valve automatically operates to achieve loop locking and prevent the flow and leakage of radioactive fluid along the shaft.

[0052] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A safety system for preventing reactor coolant leakage along an axis, characterized in that: It comprises: a plurality of sealing components, a shutdown sealing component (4), a pressure-bearing shell (5), a rotating shaft (8), and a piping system (10); The rotating shaft (8) is arranged inside the pressure-bearing shell (5), and a plurality of the sealing assemblies are installed in the pressure-bearing space between the rotating shaft (8) and the pressure-bearing shell (5); A plurality of the sealing assemblies are axially arranged around the rotating shaft (8) and are sequentially connected in series, and the sealing surfaces between two adjacent sealing assemblies are in contact to form a mechanical seal; The shutdown sealing assembly (4) is arranged on the top of the sealing assembly at the top end and is used to lock the rotating shaft (8); The pipeline system (10) is in communication with the interior of each sealing component in sequence through the interior of each sealing component, and at least one throttling element is provided on the pipeline of the pipeline system (10) located inside each sealing component; The input end of the pipeline system (10) is connected to the coolant system for introducing coolant; the output end is divided into two paths, which are respectively connected to the RCV system and the interior of the shutdown sealing component (4); The coolant leaking in the sealing assembly enters the RVD system through the sealing surface gap between adjacent sealing assemblies; The first output end of the pipeline system (10) is connected to the RCV system through a high-pressure relief channel; The second output end of the pipeline system (10) is connected to the interior of the shutdown sealing assembly (4) through the SSR pipeline; Valves are provided between the high-pressure relief flow channel and the RCV system, and between the SSR pipeline and the shutdown sealing assembly; The high-pressure relief flow channel is connected to the RCV system through a first electric valve (331VP) and a first passive safety valve (332VP) connected in series; During normal operation, the first electric valve (331VP) and the first passive safety valve (332VP) are both in an open state, and the coolant in the pipeline system (10) passes through the interior of each sealing component in sequence and enters the RCV system; During normal shutdown, the first electric valve (331VP) is closed and the coolant is blocked from entering the RCV system; Under accident conditions, the first passive safety valve (332VP) automatically closes, and the coolant is blocked from entering the RCV system.

2. The safety system for preventing reactor coolant leakage along an axis according to claim 1, wherein: The SSR pipeline is connected to the interior of the shutdown sealing assembly (4) via a second electric valve (335VP) and a second passive safety valve (336VP) connected in parallel; During normal operation, the second electric valve (335VP) and the second passive safety valve (336VP) are both in a closed state, the coolant is blocked from entering the shutdown sealing assembly (4), and the rotating shaft (8) is open and can rotate freely; During normal shutdown, the second electric valve (335VP) is opened, and the coolant enters the interior of the shutdown sealing assembly (4) through the SSR pipeline, and the shutdown sealing assembly (4) locks the rotating shaft (8) due to the pressure of the coolant; Under accident conditions, the second passive safety valve (336VP) automatically opens, and the coolant enters the interior of the shutdown sealing assembly (4) through the SSR pipeline, and the shutdown sealing assembly (4) locks the rotating shaft (8) due to the pressure of the coolant.

3. The safety system for preventing reactor coolant leakage along an axis according to claim 1, wherein: A throttling element is provided between the first electric valve (331VP) and the first passive safety valve (332VP).

4. The safety system for preventing reactor coolant leakage along an axis according to claim 1, wherein: The coolant passes through the sealing surface gap and enters the RVD system through the low-pressure leakage flow channel.

5. The safety system for preventing reactor coolant leakage along an axis according to claim 1, wherein: The gap between the sealing surfaces of adjacent sealing components is less than 1 micron.

6. The safety system for preventing reactor coolant leakage along an axis according to any one of claims 1 to 5, characterized in that: Each adjacent sealing surface is connected by a deep groove fluid dynamic pressure sealing surface.

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