Shutdown seal for reactor coolant pump

Abstract

A thermally actuated shutdown seal provides a shutdown seal usable in a pump having a primary seal assembly positioned circumferentially about a rotating shaft for separating a region of high pressure coolant fluid from the shaft. The shutdown seal includes a two-piece interlocked housing which encompasses carbon graphite ring segments positioned circumferentially about the shaft, a garter spring and a series of compression springs. The replaceable insert with machined recess contains the shutdown seal assembly and is biased axially with a wave spring and held with the annular recess by a closure ring. The seal is designed with coolant fluid flow directly in contact with such ring segments and specially designed paths around the ring segments during normal pump operation. The seal requires a thermally actuated means for moving the two-piece interlocked housing axially into a blocking position within the coolant flow path to shutdown and minimize fluid flow bypassing the ring segments and between the ring segments and the pump shaft, upon occurrence of a process failure in the facility served by the pump and consequent temperature rise of the fluid being pumped.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to seals for use in pumps for coolant for nuclear pressurized water reactors in nuclear power plants, in which release of contaminated or toxic fluid, such as radioactive water, must be prevented in the event of a pump malfunction or other equipment failure in the facility.

2. Description of the Prior Art

Mechanical shaft sealing systems for coolant pumps in nuclear power plants and other nuclear installations have been in commercial service since the 1960s. Such sealing systems typically include a hydrostatic primary stage, commonly referred to as the “number one seal”. The majority of the pressure drop for a given sealing system occurs across the number one seal.

Since the mid-1980's, operators of nuclear power plants utilizing pumps with a shaft sealing system provided by Westinghouse Corporation have been required to provide assurance that the seal design provides adequate protection from accidental reactor core exposure and from release from any radioactive material caused by failure of the shaft seal system with consequent release of cooling water.

With current concern over the vulnerability of nuclear facilities to terrorist action, there is heightened need for a failsafe shutdown seal for cooling pumps used in nuclear power plants.

A typical nuclear reactor coolant pump has a three seal system that functions to seal, within the pump, water that is being pumped by the pump, and to prevent leakage of that sealed-in water to the outside. Typically, cooling water reaches the pump primary seal assembly at a rate of one to six gallons per minute, with water pressure being approximately 2,250 pounds per square inch and water temperature being approximately 140-160° F.

The primary seal assembly typically includes seal face plates, which control leakage of the high pressure water between the two plates. Pressure drop of the water across the gap between the face plates reduces water pressure to approximately thirty pounds per square inch upon exiting the space between the two plates.

The primary seal is typically a controlled leakage, film riding base seal. The principal components of the primary seal are typically a silicon nitride runner, which rotates with the pump shaft, and a stationary, non-rotating silicon nitride ring. A stainless steel runner base and a stainless steel ring base typically support the seal assembly, with the runner base and the ring base held together with stainless steel clamping rings. The primary seal ring assembly, specifically the silicon nitride seal ring and the stainless steel ring base, is typically axially freely moveable along a primary seal ring support insert. Pressure sealing between the primary seal ring assembly and the primary seal ring support insert is preferably effectuated with a double delta channel seal and an O-ring.

During operation of a nuclear reactor coolant pump, upon failure of the primary seal within the pump, the reactor coolant pump safety system halts pump operation, causing the rotating components of the pump to begin to coast down to a stationary condition. During this “coast down”, injection water encountering the primary seal is initially the “clean/cool” volume of water that either was in the annulus around the pump shaft or was in the annulus surrounding the thermal barrier heat exchanger for the nuclear reactor, prior to the failure of the primary seal.

The time between failure of the pump primary seal and the time at which the pump primary seal is exposed to hot water at the pump primary seal inlet depends on the volume of the “clean/cool” water in the annulus around the pump shaft and the leak rate at the pump primary seal. This leak rate does not change from that experienced during normal reactor coolant pump operation, as a result of the reactor pump coasting down. Leak rate stays the same since the size of the gap at the pump primary seal, through which the leakage occurs, is governed by forces acting on the seal. Water located in the lower areas of the pump begins to be purged from the pump about ten minutes after a failure of the pump primary seal. After this purge of water from within the lower area of the pump, pump seal temperature increases due to an input surge to the pump of high temperature coolant water from the reactor. About thirteen minutes after failure of the primary seal and loss of all cooling water in the area of the seal, the lower portion of the internal volume of the pump is completely purged and water temperature in the area of the seal approaches 560° F., which is the reactor coolant fluid temperature.

OBJECTS OF THE INVENTION

This invention seeks to provide a shutdown seal that may be installed in a coolant pump with little or no impact on seals currently in the pump, for which required maintenance will be minimal, and with which installation and operation will have minimal effect on seals already in the pump.

The invention additionally seeks to provide a shutdown seal that operates for a minimum of twenty-four hours while maintaining a leakage rate of approximately one-half gallon per minute or less of reactor coolant water.

SUMMARY OF THE INVENTION

In one of its aspects this invention provides a shutdown seal functioning as a backup to the primary seal in a pump circulating cooling water within a nuclear reactor. The shutdown seal reduces loss of cool water from the pump in the event of primary seal failure.

In another of its aspects this invention provides a shutdown seal that may be installed in a coolant water pump with little or no effect on seals already in the pump, for which required maintenance is minimal, and installation and operation of which has at most a minimal effect on seals already in the pump.

In still another of its aspects, this invention provides a passive thermally actuated shutdown seal usable in a nuclear reactor coolant water pump in conjunction with a primary seal assembly, where the primary seal assembly is preferably positioned circumferentially about a shaft in the pump.

In yet another of its aspects, this invention provides a shutdown seal usable in a pump having a primary seal assembly positioned circumferentially about a rotating shaft for separating a region of high pressure coolant fluid from the shaft, where the shutdown seal includes carbon graphite ring segments positioned circumferentially about the shaft with coolant fluid flow directly in contact with such ring segments and specially designed paths around the ring segments during normal pump operation. The seal requires a thermally actuated means for moving the ring segments axially into blocking positions within the coolant flow paths to shutdown and minimize fluid flow bypassing the ring segments and between the ring segments and the pump shaft, upon occurrence of a process failure in the facility served by the pump and consequent temperature rise of the fluid being pumped.

In still another one of its aspects this invention provides a thermally actuated shutdown seal usable in a pump having a rotating shaft where the seal is preferably used in conjunction with the primary seal assembly that is preferably positioned circumferentially about the shaft and separates high pressure coolant fluid from the shaft. In this aspect of the invention, the shutdown seal preferably includes a plurality of carbon graphite segments defining a preferably annular sealing ring positioned circumferentially about the shaft and in riding contact with the shaft during normal pump operation. The shutdown seal preferably further includes a housing preferably having top and bottom interlocking members forming an annular enclosure for the carbon graphite segments, garter spring and compression springs where the housing fits circumferentially about the shaft and preferably has an open side facing the shaft for sealing ring-shaft contact during normal operation.

In this aspect of the invention the shutdown seal preferably further includes a coiled garter spring for biasing the carbon graphite segments radially inwardly against the shaft. The shutdown seal still further includes thermally responsive actuators preferably positioned circumferentially about the shaft, in axial alignment with the annular enclosure that houses the carbon graphite segments.

The actuators are adapted for extending contact with and axial biasing of the seal housing in a direction parallel with the axis of shaft rotation upon the actuators reaching a pre-selected temperature due to proximity of pumped coolant fluid. Upon actuation, the actuators preferably drive the housing and the enclosed carbon graphite sealing ring segments against an axially facing wall of an internal passageway provided for coolant fluid flow within the pump around the housing and towards the shaft, with contact of the carbon graphite sealing ring segments with the wall preferably restricting coolant fluid flow within the passageway towards the shaft.

A set of compression springs are also included that retain the sealing face of the carbon ring segments axially within the interlocked seal housing.

In yet another one of its aspects this invention provides for installing a thermally actuated shutdown seal in a pre-selected pump that has a rotatable shaft and at least one removable part, specifically the #1 insert, defining an annular surface facing radially inwardly adjacent to the shaft. The removable part is to be removed in favor of one or more replacements parts to occupy space vacated by the removable part, with the replacement(s) also preferably being positionable to define an annular recess facing radially inwardly adjacent to the shaft.

The kit preferably includes a replacement #1 insert adapted to occupy space vacated by the removable part upon removal thereof. The insert includes a surface having an annular recess formed therein, facing radially inwardly and adjacent to the shaft when the insert is positioned within the pump. The kit further preferably includes a sealing ring positionable circumferentially about the shaft and in riding contact with the shaft during normal pump operation. The kit preferably yet further includes an annular enclosure housing the sealing ring, fitting circumferentially about the shaft and having an open side facing the shaft permitting ring-shaft contact during normal operation.

Preferably further included as a part of the kit is a garter spring for biasing the ring radially inward against the shaft. The kit further preferably includes thermal actuators having the form of piston-cylinder combinations, which pistons extend upon the cylinders reaching a pre-selected temperature when installed within the pump, due to proximity of high temperature pumped coolant fluid. When installed within the pump, the piston-cylinder-configured actuators are positioned circumferentially about the shaft, in alignment with the annular enclosure, for biasing the enclosure into a coolant passageway within the pump thereby restricting coolant flow through the passageway towards the pump shaft.

In still another one of its aspects this invention provides a pump having a casing, a motor, a shaft located at least partially within the casing and rotated by the motor, an impeller rotated by the shaft and a primary seal assembly connected to the casing. The primary seal assembly is desirably positioned circumferentially about the shaft portion within the casing and serves to separate high temperature and high pressure coolant fluid, that is within the casing, from the shaft. The pump further includes a thermally actuated shutdown seal connected to the casing where the shutdown seal preferably includes a plurality of carbon graphite segments defining a preferably annular ring positioned circumferentially about the shaft portion located within the casing. The ring is in riding contact with the shaft during normal pump operation.

The shutdown seal portion of the pump further includes a housing preferably having top and bottom interlocking members forming an annular enclosure for the carbon graphite segments fitting circumferentially about the shaft, and having an open side facing the shaft for ring-shaft contact during normal pump operation. The shutdown seal further preferably includes a garter spring positioned circumferentially around the annular ring defined by the carbon graphite segments, serving to bias the carbon graphite segments radially inwardly against the shaft. The shutdown seal portion of the pump yet further preferably includes thermal actuators in the form of piston-cylinder combinations, with the pistons extending upon the cylinders in the pump reaching a pre-selected temperature due to proximity of pumped coolant fluid. The piston-cylinder combinations are preferably positioned circumferentially about the shaft, in alignment with the annular enclosure, and serve to bias the enclosure into a coolant passageway, thereby restricting coolant flow through the passageway towards the shaft when the pistons extend due to the cylinders reaching the pre-selected temperature.

A reactor coolant pump shutdown seal manifesting aspects of the invention is easily assembled into the primary seal assembly. The primary seal assembly typically rides on a chromium carbide coated pump shaft sleeve. The inside diameter of the #1 insert is preferably machined to accept the shutdown seal. The shutdown seal preferably includes a circumferential sealing ring sub-assembly, thermal actuators, spring washers, a wave spring and a closure ring.

The shutdown seal preferably has a circumferential sealing ring housing that includes two interlocking halves housing a preferably segmented carbon graphite circumferential sealing ring. The interlocking halves preferably accommodate compression springs and a garter spring, which serve to appropriately bias the segmented carbon graphite circumferential sealing ring to effectuate the sealing function when the shutdown seal actuates.

The circumferential sealing ring preferably rides on the pump shaft sleeve and, when the shutdown seal actuates, locks in place under full pressure, limiting fluid flow along the shaft. The circumferential sealing ring preferably is carbon graphite and preferably has high hardness and a low coefficient of friction, resulting in minimal heat generation and providing exceptional wear resistance for long seal life. The circumferential sealing ring is preferably a multi-segment ring with bore geometry selected according to size, pressure, temperature and shaft speed for a given pump. Use of a multi-segment carbon sealing ring allows the sealing ring to fit into a small cavity without generating abrasive materials and yet to withstand the axial and radial movements of the pump shaft during operation.

A coiled garter spring preferably extends circumferentially, preferably within a groove, around the outer extremities of the carbon segments. This spring preferably holds the carbon sealing ring segments preferably radially in place against the pump shaft sleeve for all shaft operating speeds and axial and radial movements. Radial spring force is preferably kept to a minimum for maximum seal life.

The compression springs preferably keep the sealing face of the carbon sealing ring segments against the sealing face of the shutoff seal housing. The size and number of the compression springs per carbon segment may be varied according to required axial spring force.

The circumferential sealing ring, the garter spring and compression springs are preferably enclosed in a preferably two-piece preferably interlocking preferably stainless steel housing. The housing has a selected number of slots to allow fluid flow around the assembly during normal operation.

The primary seal insert assembly preferably has or maybe equipped with preferably uniformly drilled holes to house the thermal actuators and spring washers. The thermal actuators, when energized, extend to urge the sealing ring assembly housing in a direction parallel with the axis of rotation of the pump shaft. The actuators deploy once the pump coolant water contacting the actuators reaches a pre-selected temperature. When energized, the actuators overcome the wave spring load and drive the sealing ring assembly housing axially against the closure ring sealing face. This closes the path for coolant water on the far or downstream side of the sealing ring housing, causing pressure to build until full pressure is against the carbon sealing ring segments.

Spring washers, located below the thermal actuators, preferably take-up any additional actuator growth, once the thermal actuators move the sealing ring assembly housing tightly against the closure ring sealing face.

The wave spring preferably provides bias strong enough to keep the sealing ring assembly housing tightly in place against the thermal actuators while allowing the thermal actuators, when deployed, to overcome the spring force and slide the sealing ring assembly housing tightly against the closure ring sealing face.

The closure ring preferably retains the shutdown seal assembly within the space available in the primary seal insert. The closure ring has a face that seals against the sealing ring assembly housing, once the thermal actuators energize. The closure ring has a lip at the O.D. that acts as a throttle during actuator deployment. The coolant flow path is actually completely closed prior to complete actuator deployment. This insure 100% closure and full pressure build-up behind the seal housing and carbon ring segments. This prevents coolant water from passing between the sealing ring assembly housing and the closure ring.

Operation of the reactor coolant pump shutdown seal assembly in accordance with the invention is as follows: During pump normal operation of the pump, the shutdown seal assembly is transparent, in the sense that the presence of the shutdown seal has no effect on the operation of the pump. The seal assembly has slots providing a flow path allowing the normal one to six gallons per minute of coolant water to flow past the assembly. The carbon graphite circumferential sealing ring segments ride passively on a chromium carbide coated shaft sleeve.

There are a number of possible scenarios such as “station blackout”, or uncontrolled pump shutdown, when there may be a loss of all coolant water. Once the temperature of the coolant water contacting the thermal activators reaches 260-280° degrees Fahrenheit, the thermal actuators quickly extend, preferably pushing the sealing ring assembly housing preferably axially, parallel to the pump shaft axis. As the path for coolant water flow on the side of the sealing ring housing oppositely from the actuators reduces in area at the closure ring lip, pressure across the seal begins to rise. With the thermal actuators fully deployed, the sealing ring housing face closes against the seal face on the closure ring and pressure builds to its maximum. At this time, the pump shaft is stationary and the shutdown seal holds back the coolant water with minimal leakage, at a maximum pressure of 2250 pounds per square inch and approaching a temperature of 540-560 degrees Fahrenheit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken longitudinal section of a portion of a prior art reactor coolant pump showing the primary seal assembly of the pump.

FIG. 2 is a broken longitudinal section of a portion of a reactor coolant pump of the type illustrated in FIG. 1, showing the primary seal assembly of the pump, with a shutdown seal in accordance with the invention positioned in the pump and ready to actuate.

FIG. 3 is a broken longitudinal section of a portion of a prior art reactor coolant pump, taken at the same position as and enlarged relative to FIG. 1, showing only some of the structure depicted in FIG. 1.

FIG. 4 is a broken longitudinal section of a portion of a reactor coolant pump, taken at the same position as but enlarged relative to FIG. 2, showing only some of the structure depicted in FIG. 2, and with a shutdown seal in accordance with the invention positioned in the pump and ready to actuate.

FIG. 5 is a transverse sectional view of the pump shaft, a portion of the shutdown seal embodying the invention, and the shaft housing, of the reactor coolant pump illustrated in FIGS. 2 and 4, taken at an axial position relative to the shutdown seal indicated by arrows 5-5 in FIG. 4.

FIG. 6 is a transverse sectional view of the pump shaft, a portion of the shutdown seal embodying the invention, and the shaft housing, of the reactor coolant pump illustrated in FIGS. 2, 4 and 5, taken at a longitudinal position relative to the shutdown seal indicated by arrows 6-6 in FIG. 4.

FIG. 7 is an enlarged longitudinal section of the shutdown seal portion of the reactor coolant pump illustrated in FIGS. 2, 4, 5 and 6, with the flow path for coolant water around the shutdown seal, prior to shutdown seal actuation, illustrated in cross-hatching.

FIG. 8 is a broken longitudinal section of the shutdown seal portion of the reactor coolant pump illustrated in FIGS. 2, 4, 5, 6 and 7, taken similarly to FIGS. 7 but showing the shutdown seal after actuation.

FIG. 9 is an enlarged sectional view of the shutdown seal portion of the reactor coolant pump illustrated in FIGS. 2, 4, 5, 6, 7 and 8, taken similarly to FIGS. 7 and 8 but with the flow path for coolant fluid around the shutdown seal, after shutdown seal actuation, illustrated in cross-hatching.

FIG. 10 is a transverse, sectional view of the carbon graphite circumferential segmented seal ring. One section of the five segment seal ring 46 is shown, emphasizing the tongue and socket end of each segment that interlocks the seal ring. The seal ring is specifically designed for this application with considerations for size, pressure, temperature, shaft speed, leakage requirements and long seal life.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE KNOWN FOR PRACTICE OF THE INVENTION

Referring to the drawings in general and to FIG. 1 in particular, the broken longitudinal section of a portion of a exemplary prior art reactor coolant pump reveals the primary seal assembly of the pump, with the primary seal assembly being designated generally 40 and including a runner faceplate 54 and a ring faceplate 58, with exceedingly small space identified as 122 between these faceplates defining the primary seal. A area filled with high pressure coolant water within the pump during normal operation is denoted generally 66. During normal pump operation coolant water pressure in area 66 may be as high as two thousand two hundred-fifty pounds per square inch (2,250 psi).

The pump includes a motor rotatably driving a pump shaft 62. The shaft 62 shown in FIG. 1; the motor is not illustrated in FIG. 1 but is normally located at what is, relative to FIG. 1, the lower end of pump shaft 62. Further affixed to pump shaft 62, and driven by pump shaft 62 as pump shaft 62 rotates while driven by the motor, is an impeller, which also is not illustrated in FIG. 1 but is normally located close to the lower end of shaft 62 considering FIG. 1. The impeller moves the fluid, normally coolant water, that is being pumped. Action of the impeller creates the high pressure, in the neighborhood of 2,250 psi, of the water in area 66 within the pump in FIG. 1.

Still referring to FIG. 1, a seal housing is designated generally 60, a blank #1 insert is designated generally 38, while a ring support is designated generally 56 and supports a ring faceplate 58. The #1 Insert blank 38 is normally bolted to housing 60; this bolt connection is not illustrated.

A bolt 68 secures ring support 56 in position while a bolt 70 secures a runner support, which is not shown in FIG. 1 but would be located in the area below the parts illustrated in FIG. 1, to a rotatable member which is in turn connected to pump shaft 62.

A runner faceplate 54 is mounted in the runner support and rotates with shaft 62.

During normal pump operation, high pressure coolant water in area 66 in FIG. 1 flows under pressure into the V-shaped, converging space designated 122, between ring faceplate 58 and runner faceplate 54. During normal pump operation ring faceplate 58 is stationary while runner faceplate 54 rotates with shaft 62. Clearance between ring faceplate 58 and runner faceplate 54 at the narrow end of V-shaped space 122 is on the order of four ten thousandths of an inch (0.0004). As a result, ring faceplate 58 and runner faceplate 54, and specifically the V-shaped converging space 122 between those two faceplates, acts as a pressure reducer for coolant water passing between faceplates 54 and 58.

Runner faceplate 54 and ring faceplate 58 have respective external surfaces 126 and 128 that face pump shaft 62 and pump shaft sleeve 12, as illustrated in FIG. 1. Coolant water passing between ring faceplate 58 and runner faceplate 54, through the small V-shaped converging space 122 in FIG. 1 (which separates the facing unnumbered surfaces of ring faceplate 58 and runner faceplate 54), flows into a gap 120 separating the externally facing surfaces 126 and 128 of runner faceplate 54 and ring faceplate 58 from pump shaft sleeve 12.

For purposes of drawing clarity, the interior space within pump 64 that is visible in FIG. 1 and is occupied by high temperature, high pressure coolant water during normal pump operation (where the high pressure, high temperature coolant water is at about 2,250 psi and at a temperature approaching 540-560° Fahrenheit) has been shaded to enhance understanding of the pump and hence the invention; this high pressure, high temperature coolant water area is designated 66 in FIG. 1.

Gap 120 is on the order of about 0.046, namely forty-sixth thousandths of an inch.

During normal pump operation, as high pressure coolant water from area 66 passes through converging V-shaped space 122 separating runner faceplate 54 from ring faceplate 58, V-shaped space 122 acts as a pressure reducer so that the coolant water is at much lower pressure as it exits space 122 between faceplates 54 and 58, enters gap 120, and travels upwardly along the pump shaft sleeve 12, all of which are shown in FIG. 1. The rate of upward flow of water, around the outer circumference of pump shaft sleeve 12 and shaft 62 during normal pump operation is from about one to about six gallons per minute and is at a pressure of about 30 pounds per square inch. This is the pressure of the water as it exits V-shaped space 122 and enters gap 120.

Further respecting FIG. 1, an anti-rotation fixture portion of ring support 56 is designated 84 and, with an axial pin 130 extending through fixture 84 and into both ring support 56 and ring faceplate 58, serves to prevent rotation of ring faceplate 58 as runner faceplate 54 rotates.

A series of O-rings 76, 74, 80 and a special Teflon channels seal with o-ring 82, and several other o-rings that are not numbered but are shown in the drawings, together with bolts and associated hardware that are not shown but are similar to bolt 68, secure and sealingly connect seal housing 60, blank insert 38, ring support 56 and the like.

With the bolt connections of seal housing 60, #1 blank insert 38 and ring support 56, as indicated by typical bolt 68 in FIG. 1, the structure in FIG. 1 having hash marks along the internal edges of the individual parts, some of which are unnumbered, may be considered to be a unitary structure for some purposes of the invention. However, the #1 insert blank 38 is preferably removable, as discussed below.

Referring to FIGS. 2 and 4, a shutdown seal assembly in accordance with the preferred embodiment of the invention is designated generally 10 and resides within a recess formed in an insert 38A that has replaced insert 38 illustrated in FIG. 1.

Insert 38A is preferably positioned as a part of larger primary seal 40, which is described above with reference to FIG. 1 and also shown in part in FIG. 2.

Position of shutdown seal assembly 10 to be installed within insert 38A in pump 64 is selected to minimize required maintenance and to facilitate ease of installation and operation, so that during normal pump operation shutdown seal assembly 10 has minimal or no impact on primary seal 40 and on the other seals already in pump 64. The recess in insert 38A, which houses shutdown seal assembly 10, faces rotating pump shaft 62, along which coolant water flows upwardly, considering FIGS. 1 and 2, during normal pump operation.

During normal pump operation in a nuclear power plant or other facility, coolant water, or in some instances another selected coolant fluid, flows past shutdown seal assembly 10. During normal pump operation, during which shutdown seal assembly 10 is inoperative, temperature of coolant water flowing around shutdown seal assembly 10 is typically approximately 140-160°. The water flows upwardly considering drawing FIGS. 1, 2, 4 and 7 through 9, around the entire circumference of pump shaft 62 and pump shaft sleeve 12, at a rate of from about one (1) to about six (6) gallons per minute.

Shutdown seal assembly 10 includes a sealing ring assembly housing, designated generally 44 in FIGS. 2, 4, 7, 8 and 9, which is positioned around the circumference of pump shaft 62 and is formed of two interlocking pieces, namely a top portion designated generally 42 and a bottom portion designated generally 48. Top portion 42 and bottom portion 48 have been shaded in FIG. 8 for drawing clarity. While top portion 42 and bottom portion 48 appear to be planar at the positions at which the sectional views represented by FIGS. 2, 4, 7, 8 and 9 have been taken, the annular or circumferential, segmented character of top and bottom portions 48 is apparent from FIG. 5.

Shutdown seal assembly 10 fits into insert 38A, which is specially machined to provide a cavity, which is not numbered in the drawings, accepting shutdown seal assembly 10. Shutdown seal assembly 10, including the circumferential sealing ring 46, the sealing ring assembly housing 44, the thermal actuators 16, the clover dome spring washers 28, the wave spring 24 and the closure ring 49, all of which are described below, fit into the recess that is machined into blank insert 38 illustrated in FIG. 3. The shutdown seal assembly 10 in the machined cavity in the insert is illustrated in FIG. 4.

Further referring to FIGS. 2, 4, 7, 8 and 9 and with particular reference to FIGS. 2, 4 and 7, sealing ring assembly housing 44 has therewithin a segmented, preferably carbon graphite, annular sealing ring 46, a plurality of axially oriented, preferably coil compression springs 32 and a circumferential garter spring 34, all of which are illustrated in FIGS. 4, 7 and 9. The bottom portion 48 of sealing ring assembly housing 44 has circumferentially spaced, radially extending slots on the bottom surface thereof that allow fluid flow in the radial direction during normal pump operation.

The fluid flow path in the vicinity of and along pump shaft 12 during normal pump operation is represented by hatching 50 in FIG. 7. Radial fluid flow through one of the circumferential spaced slots in bottom portion 48 of sealing ring assembly housing 44 is from right to left in FIG. 7 and occurs just below the part of bottom portion 48, which in FIG. 7 is contacted by the lead line from indicator number “48”. The segmented sealing ring 46 is preferably carbon graphite that is specially selected for use in an aqueous environment.

Segmented sealing ring 46, specifically a protruding bore dam portion 138 thereof, rides on a preferably chromium carbide coated pump shaft sleeve 12, providing minimal friction and wear during normal pump operation. Segmented sealing ring 46 withstands pressure of 2250 psi and temperatures of 540-560° F. that may be experienced in a static shutdown mode, while limiting the flow of coolant water axially along shaft 62. In FIGS. 2, 4, 7 and 9, top and bottom portions 42, 48, that interlock to form sealing ring housing 44, have not been sectioned to enhance drawing clarity, nor has segmented sealing ring 46.

The two interlocking metal housing halves, defining top and bottom portions 42, 48 of sealing ring housing 44, contain the carbon graphite segmented circumferential sealing ring 46, the compression springs 32 and the garter spring 34.

Still referring to FIGS. 2, 4, 7, 8 and 9, the preferably coil garter spring 34 extends circumferentially around an annular outwardly facing groove 132 in segmented sealing ring 46. The radially inwardly biasing action of garter spring 34 holds segmented sealing ring 46, and specifically protruding bore dam portion 138 thereof, against pump shaft sleeve 12 during all modes of operation; garter spring 34 urges segmented sealing ring 46 to the right in FIGS. 2, 4, 7, 8 and 9. Compression springs 32 reside within axially oriented bores 134 in the segments of sealing ring 46. Compression springs 32 extend from axial bores 134 and contact the inner face of bottom portion 48 of sealing ring assembly housing 44. Being in compression, springs 32 bias segments of sealing ring 46 upwardly against the inside sealing face 136 of upper portion 42 of sealing ring assembly housing 44.

Further forming a portion of shutdown seal assembly 10 are thermal actuators, designated generally 16 in the drawings and illustrated in FIGS. 2, 4, 7, 8 and 9. Each thermal actuator 16 includes a piston 18 residing in a body portion 124 of the thermal actuator 16. When coolant water temperature reaches a pre-selected limit, material having a high coefficient of thermal expansion within thermal actuator 16 expands, forcing piston 18 to extend from the body portion 124 of thermal actuator 16, contacting and applying force in the upward vertical direction to lower portion 48 of seal ring assembly housing 44. As piston 18 pushes seal ring assembly housing 44 vertically, the top portion 42 of sealing ring housing 44, which is in contact with wave spring 24, overcomes the vertically downward (considering FIGS. 2, 4, 7, 8 and 9), axially directed bias applied by wave spring 24 to top portion 42 of sealing ring assembly housing 44, so that top portion 42 at 108 & 114 seats against the sealing face of closure ring 49 at 110 & 112. This seating contact blocks coolant water flow around sealing ring assembly housing 44, as illustrated in FIG. 9, and forces coolant water flow along shaft sleeve 12.

Each seal ring segment 46 has a protruding bore dam 138 that rides against shaft sleeve 12, blocking coolant water flow past the seal during normal pump operation as illustrated in FIG. 7. Shutdown of coolant water flow path 50 is illustrated in FIGS. 8 and 9.

A number of spring washers 28 are located under each thermal actuator 16 to compensate for any additional loading that may occur after the piston 18 of a thermal actuator 16 has extended sufficiently to move sealing ring assembly housing 44, including interlocking top and bottom portions 42, 48 and segmented sealing ring 46 residing therein, to the sealing position against closure ring 49, illustrated in FIG. 9.

Wave spring 24 biases the sealing ring assembly housing 44 in place tightly against thermal actuators 16 and yet allows thermal actuators 16, upon deployment, to overcome the wave spring bias, sliding sealing ring assembly housing 44 upwardly into tight contact with the sealing face 112 of closure ring 49.

During normal pump operation, wave spring 24 provides a path for the coolant water by maintaining a space between sealing ring assembly housing 44 and closure ring 49. This path during normal operation for coolant water, of which the path passing by wave spring 24 is a part, has been identified with cross-hatching 50 in FIG. 7.

During such normal operation of the pump, coolant water flows at a nominal rate of approximately one to six gallons per minute towards pump shaft 62. During normal operation the water temperature is approximately 140-160° Fahrenheit.

Closure ring 49 retains shutdown seal assembly 10 within annular space in insert 38A. Closure ring 49 has a surface 112 that seals against top portion 114 of 42 of sealing ring assembly housing 44, when thermal actuators 16 energize. This prevents coolant water from passing between the sealing ring assembly housing 44 and closure ring 49.

The circumferential segmented sealing ring 46 is designed to ride along pump shaft sleeve 12 and, when locked in place under full pressure, circumferential segmented sealing ring 46 limits flow of coolant fluid along pump shaft 62. Circumferential segmented sealing ring 46 is desirably manufactured of graphite, as noted above, with the grade of graphite specially selected for use in an aqueous environment. The carbon graphite material of which segmented sealing ring 46 is fabricated has high hardness and a low coefficient of friction, operating with minimal heat generation and provides exceptional wear resistance characteristics for long life of the shutdown seal assembly. The segmented circumferential sealing ring 46, being a multi-segment ring, has specific bore geometry to accommodate a selected shaft size over a range of pressure, temperature and shaft speed parameters. Using a segmented sealing ring 46 of carbon graphite allows the shutdown seal assembly to fit into the small cavity formed in insert 38A without generation of abrasive materials and permits the sealing ring 46 to withstand axial and radial movement of pump shaft 62.

Garter spring 34 is preferably a coil spring, as depicted in the drawings, and extends circumferentially around a groove formed in the outer diameter of the carbon segments forming segmented sealing ring 46. Garter spring 34 is preferably designed to be of a specific operating length to hold the segments of segmented sealing ring 46 radially in place, in position relative to the pump shaft sleeve 12 at all operating speeds and within the full range of axial and radial movement of pump shaft 62. Radial bias exerted by garter spring 34 is kept to a minimum so that garter spring 34 has minimal effect on wear rate of segmented sealing ring 46 specifically and of shutdown seal assembly 10 in general.

Compression springs 32 maintain the sealing face of the segments of segmented sealing ring 46 against the inside face of the upper portion 42 of sealing housing 44 at all operating conditions. The number of compression springs 32 per segment of sealing ring 46 and the design of compression springs 32 may be varied according to the required axial spring force and load needed to be provided over the spring operating length, all of which may be calculated as needed.

Generally unnumbered slots located respectively above and below top portion 42 and bottom portion 48 of interlocking sealing ring housing 44 allow fluid flow around the sealing ring assembly housing 44 during normal pump operation.

The shutdown seal assembly has uniformly drilled holes housing thermal actuators 16 and spring washers 28. Thermal actuators 16 are thermally responsive and actuate and extend with force against the seal ring assembly, namely the sealing ring assembly housing 44 in the direction parallel with the axis of pump shaft 62. Actuators 16 deploy once pump fluid contacting those actuators reaches a pre-selected design temperature. Upon actuation, actuators 16 overcome the spring load provided by wave spring 24 and drive the seal ring assembly housing 44 against the closure ring sealing face. This action closes down on the fluid flow path area on the far side, relative to the thermal actuators, of the sealing ring assembly housing 44, causing a differential pressure to build until full pressure is achieved against the segments of segmented sealing ring 46.

The spring washers 28, located under thermal actuators 16, are provided to take up any additional growth of an actuator 16, once actuators 16 have moved the sealing ring assembly housing 44 tightly against the sealing face of closure ring 49.

Wave spring 24 is designed to have specific load strength sufficient to keep the sealing ring assembly housing 44 in place tightly against thermal actuators 16 but yet to permit the thermal actuators, when they deploy, to overcome the load provided by wave spring 24 and to slide the sealing ring assembly housing 44 tightly against the sealing face of closure ring 49.

Closure ring 49 is designed to contain the entire shutdown seal assembly 10 within the designated space requirements permitted in insert 38A. Closure ring 49 is also designed with a sealing face that will seal against the sealing ring assembly housing 44 once thermal actuators 16 have actuated. This prevents fluid from passing between the sealing ring assembly housing 44 and closure ring 49.

FIGS. 8 and 9 illustrate the shutdown seal after actuation. Rotating shaft 62 of pump 64 is located to the right of shutdown seal assembly 10; shaft 12 has not been fully shown in the drawings. In FIG. 9, flow of coolant water around the shutdown seal after the shutdown seal has actuated is represented by cross hatching 50.

During normal operation of the pump, shutdown seal assembly 10 is transparent as respecting the remainder of the pump and operation thereof. Shutdown seal assembly 10 has slots in a flow path to allow the normal one to six gallons per minute of fluid flow to the pump shaft 62. The carbon graphite circumferential seal segments making up segmented sealing ring 46 ride on the chromium carbide coated shaft sleeve 12. In the event of a station blackout or other uncontrolled pump shutdown, there may be a loss of all coolant fluid. Once fluid temperature reaches 260-280° Fahrenheit, thermal actuators 16 quickly extend, pushing sealing ring assembly housing 44 axially parallel to pump shaft 62. As the flow path along the outside of top portion 42 of sealing ring assembly housing 44 reduces, a differential in pressure across the seal begins to grow. With thermal actuators 16 fully deployed the seal housing face provided by the upper surface 108 & 114 of top portion 42 of interlocking sealing ring housing 44 closes against the seal face 110 & 112 on closure ring 49 and pressure builds to a maximum. At that time, pump shaft 62 should be stationary and the shutdown seal assembly will hold back the fluid with minimal fluid leakage even if the coolant fluid reaches its maximum pressure of 2,250 pounds per square inch and approaches a temperature of 540-560° Fahrenheit.

Claims

1. A passive, thermally actuated shutdown seal usable in a pump having a rotating shaft in conjunction with a primary seal assembly positioned circumferentially about said shaft and separating high pressure coolant fluid from the shaft, comprising: a. a plurality of carbon graphite segments defining an annular sealing ring positioned circumferentially about the shaft and in riding contact therewith during normal pump operation: b. a housing comprising top and bottom interlocking members, forming an annular enclosure for the carbon graphite segments, fitting circumferentially about the shaft and having an open side facing the shaft for sealing ring-shaft contact during normal operation; c. a spring for biasing the carbon graphite segments radially inward against shaft; and d. thermally responsive actuators positioned circumferentially about the shaft in axial alignment with the annular enclosure housing the carbon graphite segments, for extending contacting and thereby axially biasing the enclosure in a direction parallel with the axis of shaft rotation upon the actuator reaching a pre-selected temperature due to proximity of pumped coolant fluid, to drive the housing and enclosed carbon graphite sealing ring segments against an axially facing wall of an internal passageway for coolant fluid flow within the pump around the housing towards the shaft, contact of the carbon graphite sealing ring segments with the wall restricting coolant fluid flow within the passageway towards the shaft, and e. a wave spring, specifically designed to keep the coolant water passageway open during normal operation. During activation, the thermal actuators will expand quickly and generate enough force to overcome the wave spring load and collapse allowing the seal ring enclosure to seal against the closure ring; f. the closure ring shall encapsulate all components of the shutdown seal within the replacement insert's annular recess.

2. The shutdown seal of claim 1 wherein the spring fits circumferentially around the annular ring defined by the carbon graphite segments.

3. The shutdown seal of claim 2 wherein the spring is garter spring.

4. The shutdown seal of claim 1 further comprising of a series of springs biasing the annular sealing ring axially within the housing.

5. The shutdown seal of claim 4 wherein the springs axially biasing the annular sealing ring are compression springs.

6. The shutdown seal of claim 1 wherein the housing is of generally U-shaped configuration with legs of the U being vertically aligned and extending transversely to the axis of rotation of the shaft and to the open end of the U facing the shaft.

7. The shutdown seal of claim 1 wherein the housing is of generally U-shaped configuration, legs of the U are parallel, and the mouth of the U faces the shaft.

8. The shutdown seal of claim 7 wherein the legs of the U are vertically aligned.

9. The shutdown seal of claim 6 wherein the top and bottom members of the housing interlock to form the base of the U.

10. The shutdown seal of claim 1 wherein the wave spring allows coolant flow during normal operation but upon activation will collapse allowing a seal between the seal housing and closure ring.

11. The shutdown seal of claim 1 wherein the closure ring will secure all of the components of the seal within the annular recess of the insert.

12. A pump having a primary seal assembly positioned circumferentially about a rotating shaft for separating a region of high pressure coolant fluid from the shaft and a shutdown seal comprising carbon graphite ring segments positioned circumferentially about the shaft; the pump having coolant fluid flow paths contiguously bypassing the ring segments during normal pump operation; the shutdown seal further comprising a thermally actuated means for moving the seal ring enclosure into blocking positions within the coolant flow paths to shut down and minimize coolant fluid flow both around the ring segments and between the ring segments and the pump shaft upon occurrence of a process failure in the facility served by the pump and consequent temperature rise of the fluid passing through the pump.

13. A kit for installing a thermally actuated shutdown seal in a preselected pump having a rotatable shaft and at least one removable part defining an annular surface facing radially inwardly adjacent to the shaft, with the removable part adapted to be removed in favor of one or more replacement parts to occupy space vacated by the removable part, with the replacements being positionable to define an annular recess facing radially inwardly adjacent to the shaft, comprising: a. a replacement insert adapted to occupy space vacated by the removable part upon removal thereof, including a surface having an annular recess formed therein and facing radially inwardly and adjacent to the shaft when the insert is positioned within the pump; b. a sealing ring positionable circumferentially about the shaft and in riding contact therewith during normal pump operation; c. an annular enclosure housing the sealing ring, fitting circumferentially about the shaft and having an open side facing the shaft, permitting ring-shaft contact during normal operation; d. a spring for biasing the ring radially inwardly against shaft; and e. a series of springs for biasing the ring segments axially within the annular enclosure housing; and f. piston-cylinder combinations, the pistons extending upon the cylinders reaching a pre-selected temperature due to proximity of pumped coolant fluid, positioned circumferentially about the shaft in alignment with the annular enclosure for biasing the enclosure into a coolant passageway, thereby restricting coolant flow through the passageway towards the shaft; and g. a wave spring that allows coolant flow during normal operation but upon activation will collapse and allow a seal between the annular enclosure housing and the closure ring; and h. a closure ring that will secure all of the components of the seal within the annular recess of the insert.

14. The kit of claim 11 in which the annular enclosure includes top and bottom interlocking members which when interlocked form a generally U-shaped configuration with interlocking occurring at the base of the U and with the mouth of the U defining the open side of the housing.

15. The kit of claim 12 wherein legs of the U are vertically aligned when the top and bottom members of the housing are interlocked.

16. The kit of claim 13 wherein legs of the U are parallel when the top and bottom members of the housing are interlocked.

17. A pump comprising: a. a casing; b. a motor; c. a shaft located at least partially within the casing and rotated by the motor; d. an impeller rotated by the shaft; e. a primary seal assembly connected to the casing, positioned circumferentially about the shaft portion within the casing, for separating coolant fluid at high pressure within the casing from the shaft; f. a thermally actuated shutdown seal connected to the casing, including: i. a plurality of carbon graphite segments defining an annular ring positioned circumferentially about the shaft portion within the casing and in riding contact therewith during normal pump operation: ii. a housing comprising top and bottom interlocking members, forming an annular enclosure for the carbon graphite segments, fitting circumferentially about the shaft and having an open side facing the shaft for ring-shaft contact during normal operation; iii. a spring fitting circumferentially around the annular ring defined by the carbon graphite segments, for biasing the carbon graphite segments radially inward against shaft; and iv. piston-cylinder combinations, the pistons extending upon the cylinders reaching a pre-selected temperature due to proximity of pumped coolant fluid, positioned circumferentially about the shaft in alignment with the annular enclosure for biasing the enclosure into a coolant passageway, thereby restricting coolant flow through the passageway towards the shaft; v. a series of compression springs for biasing the ring segments axially within the annular enclosure housing; vi. a wave spring that allows coolant flow during normal operation but upon activation will collapse and allow a seal between the annular enclosure housing and the closure ring; vii. a closure ring that secures all of the components of the seal within the annular recess of the insert.

18. A thermally actuated shutdown seal for a pump having a rotating shaft and a primary seal assembly positioned about the shaft separating high pressure coolant fluid from the shaft, comprising: a. a graphite annular sealing ring positioned circumferentially about the shaft and in riding contact therewith during normal pump operation: b. a housing forming an enclosure for the graphite sealing ring fitting about the shaft and having an open side facing the shaft for sealing ring-shaft contact during normal operation; c. means for biasing the graphite sealing ring against shaft; and d. thermally responsive means for biasing the enclosure in a direction parallel with the shaft axis upon reaching a pre-selected temperature due to proximity of pumped coolant fluid, to drive the housing and enclosed graphite sealing ring into an internal passageway for coolant fluid flow within the pump towards the shaft to restrict coolant fluid flow within the passageway, and e. a series of springs that bias the graphite seal ring axially within the housing, and f. a wave spring allowing coolant flow during normal operation but collapses with seal activation and allows sealing between the annular enclosure housing and the closure ring; and g. a closure ring, securing all of the components of the seal within the annular recess of the insert.