CN114783633A - Safety system for preventing reactor coolant from leaking along shaft - Google Patents

Abstract

The invention provides a safety system for preventing a reactor coolant from leaking along a shaft, which comprises three sealing assemblies connected with a mechanical seal in series, a shutdown sealing assembly, a pressure-bearing shell, a rotating shaft and a pipeline system, wherein the three sealing assemblies are connected with one another in series; the rotating shaft penetrates through the pressure-bearing shell, and three sealing assemblies are arranged in a pressure-bearing space between the rotating shaft and the pressure-bearing shell; a shutdown sealing assembly is arranged at the top of the sealing assembly at the top; the pipeline system is communicated with the inside of each sealing surface assembly sequentially through the inside of each sealing assembly, is communicated with other external components, and is filled with a coolant through the other external components; and at least one throttling piece is arranged on a pipeline communicated with the interior of each sealing assembly in the pipeline system. The safety system of the invention has long service life, low nuclear leakage rate and high safety level.

Description

Safety system for preventing reactor coolant from leaking along shaft

Technical Field

The invention relates to the field of reactor coolant pump sealing, in particular to a safety system for preventing reactor coolant from leaking along a shaft.

Background

The reactor coolant pump (hereinafter referred to as a main pump) is a key device of a reactor system, is a part of a reactor coolant pressure boundary, is the only high-speed rotating device in the reactor coolant system, and drives the reactor coolant to circularly flow in a reactor loop so as to continuously take out heat generated in a reactor core.

The main pump shaft seal system is used for preventing the reactor coolant from flowing along the rotating shaft and generating leakage. The main pump shaft sealing system originated in the 70 s of the 20 th century, and through the technological development of nearly half a century, the current main flow main pump mechanical seal basically adopts a three-stage partial pressure mechanical structure, and a fluid static pressure, a fluid dynamic pressure or a dynamic and static pressure combined sealing surface is compressed through spring compensation and back pressure.

The leakage rate is an important technical indicator of a shaft seal system, and refers to the flow rate of fluid passing through the seal face during high-speed rotation of the rotating shaft. This portion of fluid is the leakage fluid of the shaft seal system. In a nuclear power system, a special container is used for uniformly collecting leaked fluid. The leakage rate of the hydrostatic shaft seal is about 300-800L/h, and the leakage rate of the hydrodynamic shaft seal is about 2-5L/h.

The sealing surface of the main pump shaft sealing system belongs to an easily worn part and needs to be replaced periodically. Currently, the replacement cycle of the main pump shaft seal surface is about 4 years.

The cooling of the main pump shaft sealing system is provided by a reactor system and is controlled by a nuclear safety I-level electric valve. Under the accident condition, the integrity of the boundary of a primary loop of the reactor is ensured by closing the valve, and the leakage of the reactor coolant with radioactivity is prevented.

Disclosure of Invention

In order to prolong the service life of a main pump shaft sealing system and reduce the nuclear leakage rate, the invention provides a safety system for preventing a reactor coolant from leaking along a shaft on the premise of ensuring the safety level, which comprises a plurality of sealing assemblies, a stop sealing assembly, a pressure-bearing shell, a rotating shaft and a pipeline system;

the rotating shaft penetrates through the pressure-bearing shell, and a plurality of sealing assemblies are arranged in a pressure-bearing space between the rotating shaft and the pressure-bearing shell;

the sealing assemblies are axially arranged around the rotating shaft and are sequentially connected in series, and sealing surfaces between two adjacent sealing assemblies are in contact to form mechanical seal;

the shutdown sealing assembly is arranged at the top of the sealing assembly at the top end and used for locking the rotating shaft;

the pipeline system is communicated with the inside of each sealing assembly sequentially through the inside of each sealing assembly, and at least one throttling piece is arranged on a pipeline of the pipeline system in each sealing assembly.

Specifically, the input end of the pipeline system is communicated with a system of coolant for introducing the coolant; the output end is divided into two paths which are respectively communicated with the RCV system (chemical and volume control system) and the interior of the shutdown sealing assembly.

Preferably, the first output end of the pipeline system is communicated with the RCV system through a high-pressure relief runner; the second output end of the pipeline system is communicated with the inside of the shutdown sealing assembly through an SSR pipeline (shutdown sealing control pipeline); and valves are arranged between the high-pressure relief flow passage and the RCV system and between the SSR pipeline and the shutdown sealing component.

Preferably, the high-pressure relief through-flow is connected with the RCV system through a first electric valve and a first passive safety valve which are connected in series;

during normal operation, the first electric valve and the first passive safety valve are both in an open state, and coolant in the pipeline system sequentially passes through the interiors of the sealing assemblies and enters the RCV system;

when the system is normally stopped, the first electric valve is closed, and the coolant is blocked from entering the RCV system;

under the accident condition, the first passive safety valve is automatically closed, and the coolant is blocked from entering the RCV system.

Preferably, the SSR pipeline is communicated with the interior of the shutdown sealing assembly through a second electric valve and a second passive safety valve which are connected in parallel;

during normal operation, the second electric valve and the second passive safety valve are both in a closed state, coolant is blocked from entering the parking sealing assembly, and the rotating shaft is opened and can rotate freely;

when the parking sealing assembly is normally parked, the second electric valve is opened, the coolant enters the interior of the parking sealing assembly through the SSR pipeline, and the parking sealing assembly locks the rotating shaft through the pressure of the coolant;

and under the accident condition, the second passive safety valve is automatically opened, the coolant enters the interior of the shutdown sealing assembly through the SSR pipeline, and the shutdown sealing assembly locks the rotating shaft through the pressure of the coolant.

Preferably, a throttle is arranged between the first electric valve and the first passive safety valve.

Further, leaked coolant within a seal assembly enters the RVD system through the gap of the seal faces between adjacent seal assemblies.

Preferably, coolant enters the RVD system through a low pressure leakage flow path after passing through the seal face clearance.

Preferably, the gap between the sealing faces between adjacent seal assemblies is less than 1 micron.

Preferably, a deep groove type fluid dynamic pressure sealing surface connection is adopted between every two adjacent sealing surfaces.

The invention has the following beneficial effects:

1. the clearance of the sealing surface is less than 1 mu m, the leakage rate is reduced by more than 95 percent, and the actual leakage rate under the working condition is lower than 0.1L/h;

2. the sealing surface is in an ultra-smooth state in the operation process, the friction coefficient is less than 0.01, the wear rate is extremely low, the service life of the single-stage sealing surface under normal working pressure exceeds 8 years, and the single-stage sealing surface can be operated for a long time under the working condition of bearing three-stage full pressure until material replacement;

3. the method comprises the following steps that a passive safety system is adopted (the passive safety system is mainly controlled by a passive safety valve, and valves on a high-pressure relief flow channel and a low-pressure leakage flow channel loop are automatically locked to prevent radioactive fluid from leaking out under the condition of no power input when high-temperature fluid flows through the passive safety valve;

4. the shaft sealing system has the modularized design characteristic, and the on-site assembly and disassembly can be quickly completed in a short time;

5. the power loss of the three-stage mechanical seal under the full-pressure working condition of 16MPa is lower than 15kW, namely the power loss of each sealing assembly of the first sealing assembly, the second sealing assembly and the third sealing assembly under the full-pressure working condition is lower than 15 kW;

6. the reactor system is provided with a simple and reliable pipeline system for mechanical seal, and has the control characteristics of passive and active: under normal working conditions (including operation and shutdown), the electric valve can be remotely controlled to realize the locking of the loop; under the accident condition, the passive valve automatically operates without manual operation or external intervention, so that the locking of a loop is realized, and the radioactive fluid is prevented from flowing and leaking along the axis.

Drawings

FIG. 1 is a sectional view of a safety system according to the present invention in operation;

FIG. 2 is a schematic view of a piping system of the safety system provided by the present invention;

fig. 3 is a structural sectional view of the safety system provided by the present invention.

Detailed Description

The safety system for preventing the leakage of the reactor coolant along the shaft according to the present invention will be described in further detail with reference to the accompanying drawings and the detailed description. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are all used in a non-precise scale for the purpose of facilitating and distinctly aiding in the description of the embodiments of the present invention. To make the objects, features and advantages of the present invention comprehensible, reference is made to the accompanying drawings. It should be understood that the structures, ratios, sizes, and the like shown in the drawings and described in the specification are only used for matching with the disclosure of the specification, so as to be understood and read by those skilled in the art, and are not used to limit the implementation conditions of the present invention, so that the present invention has no technical significance, and any structural modification, ratio relationship change or size adjustment should still fall within the scope of the present invention without affecting the efficacy and the achievable purpose of the present invention.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.

As shown in fig. 1, a structural cross-sectional view of a safety system for preventing a reactor coolant from leaking along a shaft according to the present invention includes a first seal assembly 1, a second seal assembly 2, a third seal assembly 3, a shutdown seal assembly 4, a pressure-bearing housing 5, a rotating shaft 8, and a piping system 10; the rotating shaft 8 penetrates through the pressure-bearing shell 5, and the first sealing assembly 1, the second sealing assembly 2 and the third sealing assembly 3 are sequentially arranged in a 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 are sequentially connected in series, and sealing surfaces between two adjacent sealing assemblies are in contact to form mechanical seal; the top of the third sealing assembly 3 is also provided with the shutdown sealing assembly 4 for locking the rotating shaft 8. The pipeline system 10 sequentially passes through the interiors of the first sealing assembly 1, the second sealing assembly 2 and the third sealing assembly 3, the connecting end close to the first sealing assembly 1 is the input end of the pipeline system 10 and is used for inputting coolant into each sealing assembly, and the connecting end close to the third sealing assembly 3 is the output end of the pipeline system 10 and is used for discharging the 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 sequentially passes through each throttling element 6 to realize step-by-step pressure reduction.

The input end of the pipeline system 10 is connected to a cooling system for injecting coolant into the pipeline system 10, the output end of the pipeline system 10 is divided into two paths, one path is communicated with the RCV system (chemical and volume control system) through a high-pressure relief runner HP, and the other path is communicated with the inside of the shutdown sealing assembly 4 through an SSR (shutdown sealing control pipeline).

As shown in fig. 2, one of the output ends of the pipeline system 10 is communicated with the RCV system through a high-pressure relief flow passage HP, and a valve is disposed between the high-pressure relief flow passage HP and the RCV system. Specifically, the high pressure relief flow path HP is connected to the RCV system via a first electrically operated valve 331VP and a first passive relief 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 flows through the first sealing assembly 1, the second sealing assembly 2, and the third sealing assembly 3, and then enters the RCV system through the high-pressure relief flow passage HP. During a normal shutdown, the first electrically operated valve 331VP is closed and coolant is blocked from entering the RCV system. Under accident conditions, the first passive safety valve 332VP automatically closes, and coolant is also blocked from entering the RCV system, preventing nuclear leakage through the coolant into the loop in which the RCV system is located. Furthermore, a manual valve 322VP may be further disposed between the first electric valve 331VP and the first passive safety valve 332VP, and is used for debugging and not used as a functional component.

As shown in fig. 3, the other output end of the pipeline system 10 is communicated with the inside of the parking seal assembly 4 through an SSR pipeline, and specifically, the SSR pipeline is communicated with the inside of the parking seal assembly 4 through a second electric valve 335VP and a second passive safety valve 336VP connected in parallel. In normal operation, the second electric valve 335VP and the second passive safety valve 336VP are both in a closed state, and the coolant is blocked from entering the parking seal assembly 4, and the rotating shaft 8 is opened and can rotate freely. As shown in fig. 1, 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 pipe, so that the shutdown seal assembly 4 is locked by the pressure of the coolant to the rotating shaft 8. As shown in fig. 3, in an accident condition, the second passive safety valve 336VP is automatically opened, the coolant enters the inside of the parking seal assembly 4 through the SSR pipeline, and the parking seal assembly 4 is locked to the rotating shaft 8 by the pressure of the coolant. Specifically, the coolant enters the parking seal assembly 4 to jack up the sliding part in the parking seal assembly 4, and the top of the sliding part and the locking device on the rotating shaft 8 are pressed and locked, so that the pump shaft cannot rotate.

And each sealing surface between the first sealing assembly 1 and the second sealing assembly 2 and between the second sealing assembly 2 and the third sealing assembly 3 adopts a deep groove type fluid dynamic pressure sealing surface. Since the gap between two adjacent sealing surfaces is less than 1 micron, the gap between two adjacent sealing surfaces can form a coolant passage to direct the coolant leaking between the sealing surfaces to the reactor RVD system. It should be noted that, when the coolant enters the inside of each seal assembly, there is inevitably a small amount of coolant leakage at the seal surface between each seal assembly. Localized contact between adjacent seal faces can occur and the chemical reaction products of the contact friction can dissolve in the liquid film between the seal faces to form a low concentration gel that, while reducing the coefficient of friction between the seal faces and the amount of coolant leakage, still allows a small amount of coolant to leak, the amount of coolant flowing through the gap between the seal faces being about one ten thousandth of the amount flowing through the high pressure relief flow path HP. Eventually, the coolant leaking into the coolant passages between the seal faces enters the reactor RVD system from the low pressure leakage flow path LP. In fig. 2, the manual valves 572VP, 573VP, 574VP of the low-pressure leakage flow path LP are used for loop debugging, and are all in a closed state during normal operation. The manual valve 570VP is also used in the debug phase, and is normally open during normal operation. The electric valves 568VP and 816MD are electric valves, which are closed under accident condition and opened during normal operation.

The safety system for preventing the reactor coolant from leaking along the shaft has the following characteristics:

1. as shown in fig. 1, the invention adopts a three-stage fluid dynamic pressure mechanical seal structure, and three-stage seal assemblies (a first seal assembly 1, a second seal assembly 2 and a third seal assembly 3) are all arranged in a pressure-bearing space and isolated from the outside;

2. as shown in fig. 2, the three-stage hydrodynamic mechanical seals are connected in series, and the main cooling flow passage is stepped down by a throttling element, and finally enters the RCV system of the reactor through the high-pressure relief flow passage HP passage;

3. the mechanical seals of two adjacent seal assemblies adopt deep groove type fluid dynamic pressure seal surfaces;

4. in the operation process, the sealing surfaces can generate local contact, the product of the tribochemical reaction is dissolved in a sealing liquid film to form low-concentration colloid, the friction coefficient is reduced, and meanwhile, the leakage flow of the coolant is reduced, the leakage flow of the coolant flowing through the gap of the sealing surfaces is about one ten-thousandth of the flow of a high-pressure relief flow channel HP, and finally the coolant enters a reactor RVD system from a low-pressure leakage flow channel LP;

5. as shown in fig. 2, a structure that a first electric valve 331VP and a first passive safety valve 332VP are connected in series is adopted on a high-pressure relief flow passage HP, a first electric valve 331VP locking loop can be operated under a normal working condition, and the first passive safety valve 332VP is automatically closed under an accident working condition, so that radioactive fluid is prevented from entering an RCV system through a pipeline and leaking;

6. the parking seal is driven by the pressure of the coolant in the pipeline system 10, a structure that a second electric valve 335VP and a second passive safety valve 336VP are connected in parallel is adopted, the two valves are both in a closed state during normal operation, the parking seal is opened, and the rotating shaft can rotate freely; during normal shutdown, the second electric valve 335VP may be opened to close the shutdown seal; under the accident condition, the second passive safety valve 336VP is automatically opened to drive the parking seal to lock the rotating shaft, so that the radioactive fluid is prevented from flowing along the shaft and leaking.

In conclusion, the sealing surface clearance of the adjacent sealing components of the safety system provided by the invention is less than 1 mu m, the leakage rate is reduced by more than 95%, and the actual leakage rate under the working condition is lower than 0.1L/h; the sealing surface is in an ultra-smooth state in the running process, the friction coefficient is less than 0.01, the wear rate is extremely low, the service life of the single-stage sealing surface under normal working pressure exceeds 8 years, and the single-stage sealing surface runs for a long time to change materials under the working condition of bearing three-stage full pressure; the method adopts a passive safety system (the passive safety system is mainly controlled by a passive safety valve, under the condition of no power input, when high-temperature fluid flows through the passive safety valve, valves on a high-pressure relief flow passage HP and a low-pressure leakage flow passage LP are automatically locked to prevent radioactive fluid from leaking, the valves of an SSR (simple sequence repeat) circuit can be automatically opened, locked, stopped and sealed to prevent the radioactive fluid from leaking along a shaft, under the accident condition, the circuit can be locked to ensure that radioactive coolant does not leak when no power is input, a shaft sealing system has a modularized design characteristic, the field assembly and disassembly can be quickly completed in a short time, the power loss of a three-stage mechanical seal under the full-pressure working condition of 16MPa is lower than 15kW, namely the power loss of each sealing component of a first sealing component, a second sealing component and a third sealing component under the full-pressure working condition is lower than 15kW, and the reactor system is provided with a simple mechanical seal, Reliable pipeline system, have "passive + active" control characteristic: under normal working conditions (including operation and shutdown), the electric valve can be remotely controlled to realize the locking of the loop; under the accident condition, the passive valve automatically operates without manual operation or external intervention, so that the loop is locked, and the radioactive fluid is prevented from flowing along the axis and leaking.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims (9)

1. A safety system for preventing leakage of reactor coolant along a shaft, comprising: the device comprises a plurality of sealing assemblies, a shutdown sealing assembly (4), a pressure-bearing shell (5), a rotating shaft (8) and a pipeline system (10);

the rotating shaft (8) penetrates through the pressure-bearing shell (5), and a plurality of sealing assemblies are arranged in a pressure-bearing space between the rotating shaft (8) and the pressure-bearing shell (5);

the sealing assemblies are axially arranged around the rotating shaft (8) and are sequentially connected in series, and sealing surfaces between two adjacent sealing assemblies are in contact to form mechanical seal;

the shutdown sealing assembly (4) is arranged at the top of the sealing assembly at the top end and used for locking the rotating shaft (8);

the pipeline system (10) is communicated with the interiors of the sealing assemblies sequentially through the interiors of the sealing assemblies, and at least one throttling piece is arranged on a pipeline of the pipeline system (10) in each sealing assembly;

the input end of the pipeline system (10) is communicated with a coolant system and is used for introducing coolant; the output end is divided into two paths and is respectively communicated with the RCV system and the interior of the shutdown sealing assembly (4).

2. A safety system for preventing leakage of reactor coolant along a shaft according to claim 1, wherein the first output end of the piping system (10) is connected to the RCV system through a high-pressure relief flow passage;

a second output end of the pipeline system (10) is communicated with the inside of the shutdown sealing assembly (4) through an SSR pipeline;

and valves are arranged between the high-pressure relief flow passage and the RCV system and between the SSR pipeline and the shutdown sealing assembly.

3. A safety system for preventing leakage of reactor coolant along a shaft according to claim 2, wherein the high pressure relief flow path is connected to the RCV system through a first electrically operated 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) sequentially passes through the interiors of the sealing assemblies and enters the RCV system;

during a normal shutdown, closing the first electrically operated valve (331VP) and blocking coolant from entering the RCV system;

under accident conditions, the first passive safety valve (332VP) automatically closes and coolant is blocked from entering the RCV system.

4. A safety system for preventing reactor coolant from leaking along a shaft according to claim 2, wherein the SSR piping communicates with the inside of the shutdown seal assembly (4) through a second electrically operated 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, coolant is blocked from entering the parking sealing assembly (4), and the rotating shaft (8) is opened and can rotate freely;

when the vehicle is normally stopped, the second electric valve (335VP) is opened, the coolant enters the inside of the stop sealing assembly (4) through the SSR pipeline, and the stop sealing assembly (4) locks the rotating shaft (8) through the pressure of the coolant;

under the accident condition, the second passive safety valve (336VP) is automatically opened, the coolant enters the interior of the shutdown sealing assembly (4) through the SSR pipeline, and the shutdown sealing assembly (4) is locked on the rotating shaft (8) through the pressure of the coolant.

5. A safety system for preventing leakage of reactor coolant along a shaft according to claim 3, characterised in that a throttle is arranged between the first electrically operated valve (331VP) and the first passive safety valve (332 VP).

6. A safety system for preventing leakage of reactor coolant along a shaft according to claim 1, wherein coolant leaking in a seal assembly enters the RVD system through a seal face gap between adjacent seal assemblies.

7. A safety system for preventing leakage of reactor coolant along a shaft as claimed in claim 6, wherein coolant enters the RVD system through a low pressure leakage flow path after passing through the seal face clearance.

8. A safety system for preventing leakage of reactor coolant along a shaft according to claim 6, wherein the clearance of the sealing faces between adjacent seal assemblies is less than 1 micron.

9. A safety system for preventing leakage of reactor coolant along a shaft according to any one of claims 1 to 8 wherein a deep groove type hydrodynamic seal surface connection is used between each adjacent seal surfaces.

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