GB2578030A

GB2578030A - Nuclear reactor coolant pump and passive parking sealing device thereof

Info

Publication number: GB2578030A
Application number: GB1918483.7A
Authority: GB
Inventors: hui cong Guo; yuan Luo Zhi; Ling Wang Xue; xun Zhang Yi
Original assignee: China General Nuclear Power Corp; China Nuclear Power Engineering Co Ltd
Current assignee: China General Nuclear Power Corp; China Nuclear Power Engineering Co Ltd
Priority date: 2017-05-16
Filing date: 2017-05-16
Publication date: 2020-04-15
Anticipated expiration: 2037-05-16
Also published as: GB201918483D0; GB2578030B; WO2018209545A1

Abstract

A passive parking sealing device (30) for a nuclear reactor coolant pump. The passive parking sealing device (30) comprises a complete sealing ring (40) that can be in a starting position and a non-starting position, and a complete limit ring (50) that softens when a state conversion temperature is reached. When the limit ring is in a temperature below at a state conversion temperature, the sealing ring surrounds in the circumferential direction of a pump shaft (18) of a nuclear reactor coolant pump and maintains a clearance with the pump shaft under the support of the limit ring. When the limit ring is in the state conversion temperature or in a temperature higher than the state conversion temperature, the limit ring is softened or melted, and the sealing ring loses the support of the limit ring and tightly holds the pump shaft, so as to prevent the reactor coolant from flowing along the pump shaft. The passive parking sealing device for a nuclear reactor coolant pump is only provided with a sealing ring providing the sealing effect and a limit ring providing the limit function, the movement of the sealing ring from the non-starting position to the starting position does not depend on external force, and the entire sealing has the advantages: the structure is simple and the sealing is reliable.

Description

SPECIFICATION

Nuclear Reactor Coolant Pump and Passive Parking Sealing Device Thereof

FIELD OF THE INVENTION

The present invention generally belongs to the technical field of nuclear power, and more particularly, relates to a nuclear reactor coolant pump and a passive parking sealing device thereof

BACKGROUND OF THE INVENTION

In a PWR nuclear power plant, the hydrostatic shaft seal coolant pump is a single-stage, single-suction, vertical mixed-flow pump driven by a three-phase induction motor. Fig. 1 shows a schematic structural diagram of a conventional nuclear reactor coolant pump, which includes an electric motor 10, a hydrostatic shaft seal assembly 12, and a hydraulic component 14 from top to bottom in order, wherein a pump shaft extends through the center of the coolant pump. The coolant is pumped by an impeller mounted on the lower end of the pump shaft, which is sucked through the bottom of the pump casing and flows upward through the impeller, and then discharged through the guide vane and an outlet tube on the side of the pump casing.

Referring to Fig. 2, the hydrostatic shaft seal assembly 12 in the coolant pump includes a first seal assembly 15, a second seal assembly 16, and a third seal 17 disposed between the hydraulic components 14 and the motor 10 in sequence. The first, the second and the third seal assemblies 15, 16, 17 are arranged in the circumferential direction of the pump shaft 18 and sequentially arranged along the axial direction of the pump shaft 18. A seal casing 19 is also provided outside the first seal assembly 15 and the second seal assembly 16. The first seal assembly 15 is a balanced hydrostatic pressure controllable leak seal, the second seal assembly 16 is a pressure balanced end surface seal, and the third seal assembly 17 is a weir double end surface seal.

Referring to Fig. 3, the first seal assembly 15 includes a moveable ring 150, a static ring 152, a seal insert 154 and a seal insert support 156, which are sequentially disposed between the hydraulic component 14 and the second seal assembly 16. There is a gap between the inner wall of the seal insert 154 or the seal insert support 156 and the pump shaft 18. The moveable ring 150 is fixed on the pump shaft 18 and rotates with the pump shaft 18. The static ring 152 does not rotate but can slightly move up and down along the axial direction of the pump shaft 18 or the tilt direction to maintain the proper gap relative to the moveable ring 150. Under normal operation conditions, the static ring 152 is hydrostatically balanced to control the small gap between the moveable ring 150 and the static ring 152 to form a liquid film, so that two end surfaces of the moveable ring 150 and the static ring 152 slide along two sides of a thin water layer. The two end surfaces do not directly contact with each other during operation, thereby controlling the amount of leakage and wear of the first seal assembly 15. An 0-ring and auxiliary elements are provided between the static ring 152 and the adjacent structural parts to form a slidable auxiliary seal between the high-pressure region and the low-pressure region.

Under normal operation conditions, the cooling of the first seal assembly 15 is guaranteed by the injection water provided by the RCV system (Chemical and Volume Control System). However, under accident conditions (such as a plant-wide power failure), the function of the RCV system will be lost and normal cooling for the hydrostatic shaft seal assembly 12 in the coolant pump cannot be provided. At the same time, the function of the equipment cooling water system (ART system) is also lost, and it is impossible to provide backup cooling for the first seal assembly 15 in the coolant pump. At this time, the high temperature fluid of the primary loop (referring to the main loop of the reactor coolant system) will soon threaten the hydrostatic shaft seal assembly 12, and its thermal stress may cause function loss of the coolant pump shaft seal, and thereby destroying the pressure boundary of the primary loop.

For this reason, under plant-wide power failure condition, some nuclear power plants supply power to the hydraulic pressure test pumps in the primary loop through hydraulic pressure test pump diesel generator sets (LLS system), to ensure the hydraulic pressure test pumps to inject emergency water to the coolant pump shaft seal to maintain cooling and lubrication at the first seal assembly 15.

At the same time, the high temperature and high pressure reactor coolant is limited below the first seal assembly 15, so that the temperature at the first seal assembly 15 is within the range required for its operation, to prevent coolant pump shaft seal accident (Seal LOCA) and ensure the integrity of the pressure boundary of the primary loop. However, since most of the existing nuclear power plants have double reactors arrangement, two units share one hydraulic pressure test pump. Only a single unit is considered for power failure in the design. Therefore, the nominal flow of the water pressure test pump is 6m3.41, which can only meet the requirements of the shaft seal water injection amount of 3 coolant pumps of one unit, which results in shaft seal breach because the coolant pump emergency shaft seal injection of another unit cannot be guaranteed under the plant-wide power failure condition.

After losing all means of water replenishment, the leakage of the primary loop cannot be replenished, the amount of water cannot be guaranteed, and the core will gradually expose and eventually melt.

In order to solve the above problems, some nuclear power plants have proposed to close the reactor coolant leakage to ensure the safety of the reactor core, so as to avoid the dependence of the coolant pump emergency shaft seal injection system in the event of a plant-wide power failure.

Generally, an active parking seal can be used to limit the leakage at the shaft seal, but an auxiliary system (such as a nitrogen drive system) is required to control its startup and shutdown.

Under the plant-wide power failure condition, the flow direction of the high pressure and high temperature fluid at the first seal assembly IS of the coolant pump is shown by the arrow in Fig. 4. As shown in Fig. 4, the key factor which limit the leakage of the reactor coolant into the circumstance is to seal the two important sealing positions 20, 22. Some existing nuclear power plants have begun to use passive parking seal technology to ensure the integrity of the coolant pump shaft seal, and do not rely on the configuration of the auxiliary system. The specific operation mode is: 1) directly provide a passive parking sealing device 24 to the seal insert 154 of the first seal assembly 15 of the coolant pump, to achieve the seal at the first sealing position 20; 2) The high temperature resistant rubber 0-ring 26 is used to achieve the seal at the second sealing position 22 (between the seal insert support 156 and the sealing shells 19). However, most of the existing passive parking sealing devices 24 have many components and are hard to assemble, which not only increases the difficulty and cost of manufacturing the shaft seal assembly, but also easily causes seal failure due to the failure of one or more components.

In view of the foregoing, what is needed, therefore, is to provide a nuclear reactor coolant pump and a passive parking sealing device thereof with a simple structure and a reliable seal.

SUMMARY OF THE INVENTION

One object of the present invention is to overcome the shortcomings of the prior art and provide a nuclear reactor coolant pump and a passive parking sealing device thereof with a simple structure and a reliable sealing performance.

According to one embodiment of the present invention, a nuclear reactor coolant pump passive parking sealing device includes: a complete sealing ring that can be in a starting position and a non-starting position; and a complete limit ring that can be softened when a state transition temperature is reached; wherein, when temperature around the limit ring is below the state transition temperature, the sealing ring surrounds a circumference of a pump shaft of the nuclear reactor coolant pump and maintains a gap between the sealing ring and the pump shaft under the support of the limit ring; when the temperature around the limit ring is no less than the state transition temperature, the limit ring is softened or melted, and the sealing ring loses the support of the limit ring and holds the pump shaft tightly, thereby preventing the reactor coolant from flowing along the pump shaft.

According to one aspect of the present invention, the sealing ring is made from a material having elastic deformation ability which tends to close when radially limited by the limit ring; when the temperature around the limit ring is no less than the state transition temperature, the sealing ring tightly holds the pump shaft due to its own elasticity.

According to one aspect of the present invention, the sealing ring is made from rubber or 10 polymer material which can withstand a temperature no less than 292 degrees Celsius.

According to one aspect of the present invention, the sealing ring is made from EPDM rubber.

According to one aspect of the present invention, the limit ring is made from a high molecular polymer that remains rigid at normal temperature and softens or melts at high temperature.

According to one aspect of the present invention, the softening temperature of the high molecular polymer material of the limit ring ranges from 80 degrees Celsius to 260 degrees Celsius.

According to one aspect of the present invention, an inner diameter of the limit ring is slightly larger than an outer diameter of the pump shaft, to form a gap between the limit ring and the pump shaft to allow fluid to pass through.

According to another embodiment of the present invention, a nuclear reactor coolant pump includes a motor, a hydrostatic shaft seal assembly and a hydraulic component arranged from top to bottom in order, and a pump shaft extending through a center of the coolant pump. The hydrostatic shaft seal assembly includes a plurality of seal assemblies between the hydraulic component and the motor, and the plurality of seal assemblies are arranged in circumferential direction of the pump shaft.

A nuclear reactor coolant pump passive parking sealing device according to the present invention is arranged between at least one of the plurality of seal assemblies and the pump shaft.

According to one aspect of the present invention, the hydrostatic shaft seal assembly includes a first seal assembly closest to the hydraulic component, and the nuclear reactor coolant pump passive parking sealing device is assembled to the first seal assembly of the hydrostatic shaft seal assembly.

According to one aspect of the present invention, the first seal assembly of the hydrostatic shaft seal assembly includes a moveable ring, a static ring, a seal insert and a seal insert support, the nuclear reactor coolant pump passive parking sealing device is installed in a receiving slot provided in an inner wall of the seal insert or the seal insert support; under plant-wide power failure condition, slightly softened sealing ring is pressed toward the pump shaft under the drive of the coolant, and pressed toward the seal insert or the seal insert support in a direction away from the split ring under the drive of the coolant, and a slight amount of extrusion of the sealing ring occurs in the gap between the pump shaft and the seal insert or the seal insert support.

According to one aspect of the present invention, the hydrostatic shaft seal assembly includes a first seal assembly, a second seal assembly and a third seal assembly disposed between the hydraulic component and the motor in sequence, the first seal assembly is a balanced hydrostatic pressure controllable leak seal, the second seal assembly is a pressure balanced end face seal, and the third seal assembly is a weir double end face seal.

Compared with the prior art, the nuclear reactor coolant pump passive parking sealing device of the present invention is only provided with two elements, namely, a sealing ring having sealing effect and a limit ring providing limiting function. The movement of the sealing ring from the non-starting position to the starting position does not depend on external force. The entire sealing device has simple structure arid reliable sealing performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and novel features will be drawn from the following detailed description of the preferred embodiment with the attached drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiment of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention, in which: Fig. 1 shows a schematic structural diagram of a conventional nuclear reactor coolant pump; Fig. 2 shows a schematic cross-sectional view of a hydrostatic shaft seal assembly in the coolant 10 pump shown in Fig. 1; Fig. 3 shows a schematic cross-sectional view of a first seal assembly in the coolant pump shown in Fig. 1; Fig. 4 shows a schematic structural diagram of a conventional passive parking sealing device; Fig. 5 shows a schematic diagram of a nuclear reactor coolant pump passive parking sealing device according to one embodiment of the present invention assembled to a first seal assembly of the nuclear reactor coolant pump; Fig. 6 shows an exploded view of the nuclear reactor coolant pump passive parking sealing device of the present invention; Fig. 7 shows an assembled view of the nuclear reactor coolant pump passive parking sealing device of the present invention; Fig. 8 shows a schematic diagram of the state of the nuclear reactor coolant pump passive parking sealing device of the present invention and the flow direction of the coolant close to the passive parking sealing device under a normal operation condition; Fig. 9 shows a schematic diagram of the state of the nuclear reactor coolant pump passive parking sealing device of the present invention and the flow direction of the coolant close to the passive parking sealing device under a plant-wide power failure condition.

DETAILED DESCRIPTION OF THE INVENTION

Example embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

The nuclear reactor coolant pump of the present invention includes a motor, a hydrostatic shaft seal assembly and hydraulic components arranged from top to bottom in order, and a pump shaft extending through a center of the coolant pump. The reactor coolant is pumped by a impeller assembled to a lower end of the pump shaft. The reactor coolant is sucked through the bottom of the pump casing and flows upward through the impeller, and then discharged through a guide vane and an outlet tube at one side of the pump casing.

The hydrostatic shaft seal assembly includes a first seal assembly, a second seal assembly and a third seal assembly sequentially disposed between the motor and the hydraulic components of the coolant pump. The three seal assemblies are set around the circumferential direction of the pump shaft and are sequentially arranged along the axial direction of the pump shaft. A sealing shell is also provided outside the first seal assembly and the second seal assembly. The first seal assembly is a balanced hydrostatic pressure controllable leak seal, the second seal assembly is a pressure balanced end face seal, and the third seal assembly is a weir double end face seal.

The first seal assembly includes a moveable ring, a static ring, a seal insert, and a seal insert support sequentially arranged between the hydraulic components and the second seal assembly. There is a gap between the inner wall of the seal insert and the seal insert support and the pump shaft. Part of the outer wall of the seal insert support is tightly sealed against the seal shell. The moveable ring is fixed on the pump shaft and rotates with the pump shaft. The static ring does not rotate but it can move up and down along the axial or an inclined direction of the pump shaft, to maintain the proper gap with the moveable ring. Under normal operation conditions, the static ring is hydrostatically balanced to control the small gap between the moveable ring and the static ring to form a liquid film, so that the two end faces of the moveable ring and the static ring slide on both sides of a thin water film. There is no direct contact during operation, so as to control the leakage and wear of the first seal assembly. An 0-ring and auxiliary components are provided between the static ring and the adjacent components, to form a slidable auxiliary seal between the high-pressure area and the low-pressure area. In order to ensure the safety of the reactor core in the event of plant-wide power failure, a passive parking sealing is also provided device between the first seal assembly and the pump shaft in the present invention.

Referring to Figs. 5 to 9, the nuclear reactor coolant pump passive parking sealing device 30 of the present invention is assembled in a receiving slot opened in the inner wall of the seal insert 154 of the first seal assembly 15 of the nuclear reactor coolant pump. Under normal operation conditions, there is a gap between the pump shaft 18 and the passive parking sealing device 30, so that the reactor coolant can flow freely along the pump shaft 18. Under plant-wide power failure condition, the pump shaft 18 will be closely held to achieve circumferential seal of the first seal assembly 15 and the pump shaft 18.

Referring to Figs. 6 and 7, the nuclear reactor coolant pump passive parking sealing device 30 of the present invention includes a sealing ring 40 and a limit ring 50 attached to the sealing ring 40 and supporting the sealing ring 40.

The sealing ring 40 is a closed complete ring, and inner diameter of the sealing ring 40 after being opened by the limit ring 50 is slightly larger than the outer diameter of the pump shaft 18. Therefore, under normal conditions, when the sealing ring 40 surrounds the pump shaft 18, the gap between the sealing ring 40 and the pump shaft 18 allows free flow of the reactor coolant. The sealing ring 40 is made from a rubber material, such as EPDM or other elastic sealing materials, and the sealing ring 40 can withstand a high temperature of 292 degrees Celsius. The material of the sealing ring 40 makes it elastic at normal temperature and high temperature, and can achieve a reliable seal.

The limit ring 50 is made from a high-molecular polymer which remains rigid at normal temperature and softens or melts at high temperatures. The softening temperature of the polymer material of the limit ring 50 ranges from 80 degrees Celsius to 260 degrees Celsius. The limit ring 50 supports the seal ring 40. At normal temperature, it maintains the gap between the sealing ring 40 and the pump shaft 18, so that the reactor coolant can flow freely between the sealing ring 40 and the pump shaft 18. At high temperature, all or part of the high-molecular polymer material is softened or melted. The sealing ring 40 is no longer restricted to hold the pump shaft 18 tightly. The limit ring 50 may be made from a single material or from various kinds of materials, and the function of the limit ring 50 may also be implemented by a single component or a number of components.

Referring to Fig. 8, under normal operation conditions, the sealing ring 40 of the nuclear reactor coolant pump passive parking sealing device 30 of the present invention is accommodated in a receiving slot defined in the inner wall of the seal insert 154 of the first seal assembly 15. Under the support of the limit ring 50, the sealing ring 40 surrounds the pump shaft 18 in the circumferential direction and maintains a gap 32 with the pump shaft 18, so that the reactor coolant leak can flow freely between the passive parking sealing device 30 and the pump shafts 18 along the direction shown by arrow A, and flow into the first seal leak line through the seal insert 154.

Referring to Fig. 9, under plant-wide power failure condition, the coolant pump shaft seal inject water and the cooling water is lost at the same time. The high temperature and high pressure reactor coolant flows upward along the pump shaft 18. When the temperature at the limit ring 50 reaches the softening or melting temperature, after a certain period of time (time is a preset time, generally several minutes to ten minutes), the limit ring 50 will lose the limit support effect. At this time, the seal ring will shrink to tightly hold the pump shaft 18 under the action of its own elasticity, thereby achieving a sealing function.

It should be understood that, in other embodiments of the present invention, the nuclear reactor coolant pump passive parking sealing device 30 of the present invention may not be assembled to the seal insert 154 of the first seal assembly 15, but be assembled to the seal insert support 156 of the first seal assembly 15, as long as it can prevent the reactor coolant from leaking into the environment.

In view of the detailed description of the embodiments of the present invention, compared with the prior art, the nuclear reactor coolant pump passive parking sealing device according to the present invention has the following advantages: The nuclear reactor coolant pump passive parking sealing device of the present invention is only provided with two elements, namely, the sealing ring 40 having sealing effect and the limit ring 50 providing limiting function. The movement of the sealing ring 40 from the non-starting position to the starting position does not depend on external force. The entire sealing device has simple structure and reliable sealing performance.

The limit ring 50 no longer limits the sealing ring 40 at high temperature, and the sealing ring tightly holds the pump shaft 18 to achieve sealing effect, thereby effectively ensuring the functional integrity of the coolant pump hydrostatic shaft seal under the condition of plant-wide power failure, releasing reliance on emergency shaft seal injection system and active drive, as well as reducing the probability of core damage in nuclear power plants effectively.

In addition, in present invention, the receiving groove is only provided in the inner wall of the seal insert 154 or the seal insert support 156 of the first seal assembly 15, which has no effect on other structures of the coolant pump arid will not affect the performances of the coolant pump under normal operation conditions.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments, it should be appreciated that alternative embodiments without departing from the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

WHAT IS CLAIMED IS: 1. A nuclear reactor coolant pump passive parking sealing device, comprising: a complete sealing ring that can be in a starting position and a non-starting position; and a complete limit ring that can be softened when a state transition temperature is reached; wherein, when temperature around the limit ring is below the state transition temperature, the sealing ring surrounds a circumference of a pump shaft of the nuclear reactor coolant pump and maintains a gap between the sealing ring and the pump shaft under the support of the limit ring; when the temperature around the limit ring is no less than the state transition temperature, the limit ring is softened or melted, and the sealing ring loses the support of the limit ring and holds the pump shaft I 0 tightly, thereby preventing the reactor coolant from flowing along the pump shaft.
2. The nuclear reactor coolant pump passive parking sealing device according to claim 1, wherein the sealing ring is made from a material having elastic deformation ability which tends to close when radially limited by the limit ring; when the temperature around the limit ring is no less than the state transition temperature, the sealing ring tightly holds the pump shaft due to its own elasticity.
3. The nuclear reactor coolant pump passive parking sealing device according to claim 2, wherein the sealing ring is made from rubber or polymer material which can withstand a temperature no less than 292 degrees Celsius
4. The nuclear reactor coolant pump passive parking sealing device according to claim 3, wherein the sealing ring is made from EPDM rubber.
5. The nuclear reactor coolant pump passive parking sealing device according to claim I, wherein the limit ring is made from a high molecular polymer that remains rigid at normal temperature and softens or melts at high temperature.
6. The nuclear reactor coolant pump passive parking sealing device according to claim 5, wherein a softening temperature of the high molecular polymer material of the limit ring ranges from 80 degrees Celsius to 260 degrees Celsius.
7. The nuclear reactor coolant pump passive parking sealing device according to claim 1, wherein an inner diameter of the limit ring is slightly larger than an outer diameter of the pump shaft, to form a gap between the limit ring and the pump shaft to allow fluid to pass through.
8. A nuclear reactor coolant pump comprising a motor, a hydrostatic shaft seal assembly and a hydraulic component arranged from top to bottom in order, and a pump shaft extending through a center of the coolant pump, the hydrostatic shaft seal assembly comprises a plurality of seal assemblies between the hydraulic component and the motor, and the plurality of seal assemblies are arranged in circumferential direction of the pump shaft, wherein a nuclear reactor coolant pump passive parking sealing device according to anyone of claims 1 to 7 is arranged between at least one of the plurality of seal assemblies and the pump shaft.
9. The nuclear reactor coolant pump according to claim 8, wherein the hydrostatic shaft seal assembly comprises a first seal assembly closest to the hydraulic component, and the nuclear reactor coolant 14 pump passive parking sealing device is assembled to the first seal assembly of the hydrostatic shaft seal assembly.
10. The nuclear reactor coolant pump according to claim 9, wherein the first seal assembly of the hydrostatic shaft seal assembly comprises a moveable ring, a static ring, a seal insert and a seal insert support, the nuclear reactor coolant pump passive parking sealing device is installed in a receiving slot provided in an inner wall of the seal insert or the seal insert support; under plant-wide power failure condition, slightly softened sealing ring is pressed toward the pump shaft under the drive of the coolant, and pressed toward the seal insert or the seal insert support in a direction away from the split ring under the drive of the coolant, and a slight amount of extrusion of the sealing ring occurs in the gap between the pump shaft and the seal insert or the seal insert support.
11. The nuclear reactor coolant pump according to claim 10, wherein the hydrostatic shaft seal assembly comprises a first seal assembly, a second seal assembly and a third seal assembly disposed between the hydraulic component and the motor in sequence, the first seal assembly is a balanced hydrostatic pressure controllable leak seal, the second seal assembly is a pressure balanced end face seal, and the third seal assembly is a weir double end face seal.IS