US20070140877A1 - Shutdown seal for reactor coolant pump - Google Patents
Shutdown seal for reactor coolant pump Download PDFInfo
- Publication number
- US20070140877A1 US20070140877A1 US11/543,020 US54302006A US2007140877A1 US 20070140877 A1 US20070140877 A1 US 20070140877A1 US 54302006 A US54302006 A US 54302006A US 2007140877 A1 US2007140877 A1 US 2007140877A1
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- United States
- Prior art keywords
- shaft
- seal
- pump
- ring
- housing
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- Abandoned
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/002—Sealings comprising at least two sealings in succession
- F16J15/008—Sealings comprising at least two sealings in succession with provision to put out of action at least one sealing; One sealing sealing only on standstill; Emergency or servicing sealings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/08—Sealings
- F04D29/10—Shaft sealings
- F04D29/14—Shaft sealings operative only when pump is inoperative
- F04D29/146—Shaft sealings operative only when pump is inoperative especially adapted for liquid pumps
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D7/00—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts
- F04D7/02—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type
- F04D7/08—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type the fluids being radioactive
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/16—Sealings between relatively-moving surfaces
- F16J15/164—Sealings between relatively-moving surfaces the sealing action depending on movements; pressure difference, temperature or presence of leaking fluid
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/16—Sealings between relatively-moving surfaces
- F16J15/34—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member
- F16J15/38—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member sealed by a packing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/44—Free-space packings
- F16J15/441—Free-space packings with floating ring
- F16J15/442—Free-space packings with floating ring segmented
Definitions
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- the actuators 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 .
- 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 .
- an impeller 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 .
- a seal housing is designated generally 60
- a blank # 1 insert is designated generally 38
- 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 .
- 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 .
- Gap 120 is on the order of about 0.046, namely forty-sixth thousandths of an inch.
- 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 .
- 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.
- FIG. 1 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.
- 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 38 A that has replaced insert 38 illustrated in FIG. 1 .
- Insert 38 A 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 38 A 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 38 A, 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.
- coolant water flows past shutdown seal assembly 10 .
- 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 38 A, 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 .
- 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 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 .
- 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 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 .
- 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 .
- 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 .
- 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.
- 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 .
- 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 .
- coolant water flows at a nominal rate of approximately one to six gallons per minute towards pump shaft 62 .
- the water temperature is approximately 140-160° Fahrenheit.
- Closure ring 49 retains shutdown seal assembly 10 within annular space in insert 38 A.
- 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 38 A 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.
- 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.
- 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 38 A. 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.
- flow of coolant water around the shutdown seal after the shutdown seal has actuated is represented by cross hatching 50 .
- 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 .
- thermal actuators 16 quickly extend, pushing sealing ring assembly housing 44 axially parallel to pump shaft 62 .
Abstract
Description
- This patent application claims the benefit, under 35 USC 119, of the filing date of U.S. provisional patent application Ser. No. 60/725,471 filed Oct. 11, 2005 in the name of Mark E. Sanville and Reinhold Koeth. The disclosure of the '471 application, entitled “REACTOR COOLANT PUMP SHUTDOWN SEAL”, is hereby incorporated by reference in its entirety.
- 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.
- 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.
- 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.
-
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 inFIG. 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 toFIG. 1 , showing only some of the structure depicted inFIG. 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 toFIG. 2 , showing only some of the structure depicted inFIG. 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 inFIGS. 2 and 4 , taken at an axial position relative to the shutdown seal indicated by arrows 5-5 inFIG. 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 inFIGS. 2, 4 and 5, taken at a longitudinal position relative to the shutdown seal indicated by arrows 6-6 inFIG. 4 . -
FIG. 7 is an enlarged longitudinal section of the shutdown seal portion of the reactor coolant pump illustrated inFIGS. 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 inFIGS. 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 inFIGS. 2, 4 , 5, 6, 7 and 8, taken similarly toFIGS. 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 fivesegment 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. - 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 arunner faceplate 54 and aring 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 inarea 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. Theshaft 62 shown inFIG. 1 ; the motor is not illustrated inFIG. 1 but is normally located at what is, relative toFIG. 1 , the lower end ofpump shaft 62. Further affixed to pumpshaft 62, and driven bypump shaft 62 aspump shaft 62 rotates while driven by the motor, is an impeller, which also is not illustrated inFIG. 1 but is normally located close to the lower end ofshaft 62 consideringFIG. 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 inarea 66 within the pump inFIG. 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 aring faceplate 58. The #1 Insert blank 38 is normally bolted tohousing 60; this bolt connection is not illustrated. - A
bolt 68 securesring support 56 in position while abolt 70 secures a runner support, which is not shown inFIG. 1 but would be located in the area below the parts illustrated inFIG. 1 , to a rotatable member which is in turn connected to pumpshaft 62. - A
runner faceplate 54 is mounted in the runner support and rotates withshaft 62. - During normal pump operation, high pressure coolant water in
area 66 inFIG. 1 flows under pressure into the V-shaped, converging space designated 122, betweenring faceplate 58 andrunner faceplate 54. During normal pumpoperation ring faceplate 58 is stationary whilerunner faceplate 54 rotates withshaft 62. Clearance betweenring faceplate 58 andrunner faceplate 54 at the narrow end of V-shapedspace 122 is on the order of four ten thousandths of an inch (0.0004). As a result,ring faceplate 58 andrunner faceplate 54, and specifically the V-shaped convergingspace 122 between those two faceplates, acts as a pressure reducer for coolant water passing betweenfaceplates -
Runner faceplate 54 andring faceplate 58 have respectiveexternal surfaces 126 and 128 that facepump shaft 62 andpump shaft sleeve 12, as illustrated inFIG. 1 . Coolant water passing betweenring faceplate 58 andrunner faceplate 54, through the small V-shaped convergingspace 122 inFIG. 1 (which separates the facing unnumbered surfaces ofring faceplate 58 and runner faceplate 54), flows into agap 120 separating the externally facingsurfaces 126 and 128 ofrunner faceplate 54 andring faceplate 58 frompump shaft sleeve 12. - For purposes of drawing clarity, the interior space within
pump 64 that is visible inFIG. 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 inFIG. 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-shapedspace 122separating runner faceplate 54 fromring faceplate 58, V-shapedspace 122 acts as a pressure reducer so that the coolant water is at much lower pressure as it exitsspace 122 betweenfaceplates gap 120, and travels upwardly along thepump shaft sleeve 12, all of which are shown inFIG. 1 . The rate of upward flow of water, around the outer circumference ofpump shaft sleeve 12 andshaft 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-shapedspace 122 and entersgap 120. - Further respecting
FIG. 1 , an anti-rotation fixture portion ofring support 56 is designated 84 and, with anaxial pin 130 extending throughfixture 84 and into bothring support 56 andring faceplate 58, serves to prevent rotation ofring faceplate 58 asrunner faceplate 54 rotates. - A series of O-
rings 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 connectseal housing 60,blank insert 38,ring support 56 and the like. - With the bolt connections of
seal housing 60, #1blank insert 38 andring support 56, as indicated bytypical bolt 68 inFIG. 1 , the structure inFIG. 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 #1insert 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 aninsert 38A that has replacedinsert 38 illustrated inFIG. 1 . -
Insert 38A is preferably positioned as a part of largerprimary seal 40, which is described above with reference toFIG. 1 and also shown in part inFIG. 2 . - Position of
shutdown seal assembly 10 to be installed withininsert 38A inpump 64 is selected to minimize required maintenance and to facilitate ease of installation and operation, so that during normal pump operationshutdown seal assembly 10 has minimal or no impact onprimary seal 40 and on the other seals already inpump 64. The recess ininsert 38A, which housesshutdown seal assembly 10, faces rotatingpump shaft 62, along which coolant water flows upwardly, consideringFIGS. 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 whichshutdown seal assembly 10 is inoperative, temperature of coolant water flowing aroundshutdown seal assembly 10 is typically approximately 140-160°. The water flows upwardly considering drawingFIGS. 1, 2 , 4 and 7 through 9, around the entire circumference ofpump shaft 62 andpump 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 inFIGS. 2, 4 , 7, 8 and 9, which is positioned around the circumference ofpump 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 andbottom portion 48 have been shaded inFIG. 8 for drawing clarity. Whiletop portion 42 andbottom portion 48 appear to be planar at the positions at which the sectional views represented byFIGS. 2, 4 , 7, 8 and 9 have been taken, the annular or circumferential, segmented character of top andbottom portions 48 is apparent fromFIG. 5 . -
Shutdown seal assembly 10 fits intoinsert 38A, which is specially machined to provide a cavity, which is not numbered in the drawings, acceptingshutdown seal assembly 10.Shutdown seal assembly 10, including thecircumferential sealing ring 46, the sealingring assembly housing 44, thethermal actuators 16, the cloverdome spring washers 28, thewave spring 24 and theclosure ring 49, all of which are described below, fit into the recess that is machined intoblank insert 38 illustrated inFIG. 3 . Theshutdown seal assembly 10 in the machined cavity in the insert is illustrated inFIG. 4 . - Further referring to
FIGS. 2, 4 , 7, 8 and 9 and with particular reference toFIGS. 2, 4 and 7, sealingring 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 acircumferential garter spring 34, all of which are illustrated inFIGS. 4, 7 and 9. Thebottom portion 48 of sealingring 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 inFIG. 7 . Radial fluid flow through one of the circumferential spaced slots inbottom portion 48 of sealingring assembly housing 44 is from right to left inFIG. 7 and occurs just below the part ofbottom portion 48, which inFIG. 7 is contacted by the lead line from indicator number “48”. Thesegmented sealing ring 46 is preferably carbon graphite that is specially selected for use in an aqueous environment. -
Segmented sealing ring 46, specifically a protrudingbore dam portion 138 thereof, rides on a preferably chromium carbide coatedpump 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 alongshaft 62. InFIGS. 2, 4 , 7 and 9, top andbottom portions ring housing 44, have not been sectioned to enhance drawing clarity, nor has segmented sealingring 46. - The two interlocking metal housing halves, defining top and
bottom portions ring housing 44, contain the carbon graphite segmentedcircumferential sealing ring 46, the compression springs 32 and thegarter spring 34. - Still referring to
FIGS. 2, 4 , 7, 8 and 9, the preferablycoil garter spring 34 extends circumferentially around an annular outwardly facinggroove 132 insegmented sealing ring 46. The radially inwardly biasing action ofgarter spring 34 holds segmented sealingring 46, and specifically protrudingbore dam portion 138 thereof, againstpump shaft sleeve 12 during all modes of operation;garter spring 34 urges segmented sealingring 46 to the right inFIGS. 2, 4 , 7, 8 and 9. Compression springs 32 reside within axially orientedbores 134 in the segments of sealingring 46. Compression springs 32 extend fromaxial bores 134 and contact the inner face ofbottom portion 48 of sealingring assembly housing 44. Being in compression, springs 32 bias segments of sealingring 46 upwardly against theinside sealing face 136 ofupper portion 42 of sealingring assembly housing 44. - Further forming a portion of
shutdown seal assembly 10 are thermal actuators, designated generally 16 in the drawings and illustrated inFIGS. 2, 4 , 7, 8 and 9. Eachthermal actuator 16 includes apiston 18 residing in abody portion 124 of thethermal actuator 16. When coolant water temperature reaches a pre-selected limit, material having a high coefficient of thermal expansion withinthermal actuator 16 expands, forcingpiston 18 to extend from thebody portion 124 ofthermal actuator 16, contacting and applying force in the upward vertical direction tolower portion 48 of sealring assembly housing 44. Aspiston 18 pushes sealring assembly housing 44 vertically, thetop portion 42 of sealingring housing 44, which is in contact withwave spring 24, overcomes the vertically downward (consideringFIGS. 2, 4 , 7, 8 and 9), axially directed bias applied bywave spring 24 totop portion 42 of sealingring assembly housing 44, so thattop portion 42 at 108 & 114 seats against the sealing face ofclosure ring 49 at 110 & 112. This seating contact blocks coolant water flow around sealingring assembly housing 44, as illustrated inFIG. 9 , and forces coolant water flow alongshaft sleeve 12. - Each
seal ring segment 46 has aprotruding bore dam 138 that rides againstshaft sleeve 12, blocking coolant water flow past the seal during normal pump operation as illustrated inFIG. 7 . Shutdown of coolantwater flow path 50 is illustrated inFIGS. 8 and 9 . - A number of
spring washers 28 are located under eachthermal actuator 16 to compensate for any additional loading that may occur after thepiston 18 of athermal actuator 16 has extended sufficiently to move sealingring assembly housing 44, including interlocking top andbottom portions ring 46 residing therein, to the sealing position againstclosure ring 49, illustrated inFIG. 9 . -
Wave spring 24 biases the sealingring assembly housing 44 in place tightly againstthermal actuators 16 and yet allowsthermal actuators 16, upon deployment, to overcome the wave spring bias, sliding sealingring assembly housing 44 upwardly into tight contact with the sealingface 112 ofclosure ring 49. - During normal pump operation,
wave spring 24 provides a path for the coolant water by maintaining a space between sealingring assembly housing 44 andclosure ring 49. This path during normal operation for coolant water, of which the path passing bywave spring 24 is a part, has been identified with cross-hatching 50 inFIG. 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 retainsshutdown seal assembly 10 within annular space ininsert 38A.Closure ring 49 has asurface 112 that seals againsttop portion 114 of 42 of sealingring assembly housing 44, whenthermal actuators 16 energize. This prevents coolant water from passing between the sealingring assembly housing 44 andclosure ring 49. - The circumferential segmented sealing
ring 46 is designed to ride alongpump shaft sleeve 12 and, when locked in place under full pressure, circumferentialsegmented sealing ring 46 limits flow of coolant fluid alongpump shaft 62. Circumferential segmented sealingring 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 sealingring 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 segmentedcircumferential 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 asegmented sealing ring 46 of carbon graphite allows the shutdown seal assembly to fit into the small cavity formed ininsert 38A without generation of abrasive materials and permits the sealingring 46 to withstand axial and radial movement ofpump 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 formingsegmented sealing ring 46.Garter spring 34 is preferably designed to be of a specific operating length to hold the segments ofsegmented sealing ring 46 radially in place, in position relative to thepump shaft sleeve 12 at all operating speeds and within the full range of axial and radial movement ofpump shaft 62. Radial bias exerted bygarter spring 34 is kept to a minimum so thatgarter spring 34 has minimal effect on wear rate ofsegmented sealing ring 46 specifically and ofshutdown 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 theupper portion 42 of sealinghousing 44 at all operating conditions. The number of compression springs 32 per segment of sealingring 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 andbottom portion 48 of interlocking sealingring housing 44 allow fluid flow around the sealingring assembly housing 44 during normal pump operation. - The shutdown seal assembly has uniformly drilled holes housing
thermal actuators 16 andspring washers 28.Thermal actuators 16 are thermally responsive and actuate and extend with force against the seal ring assembly, namely the sealingring assembly housing 44 in the direction parallel with the axis ofpump 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 bywave spring 24 and drive the sealring 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 sealingring assembly housing 44, causing a differential pressure to build until full pressure is achieved against the segments ofsegmented sealing ring 46. - The spring washers 28, located under
thermal actuators 16, are provided to take up any additional growth of anactuator 16, onceactuators 16 have moved the sealingring assembly housing 44 tightly against the sealing face ofclosure ring 49. -
Wave spring 24 is designed to have specific load strength sufficient to keep the sealingring assembly housing 44 in place tightly againstthermal actuators 16 but yet to permit the thermal actuators, when they deploy, to overcome the load provided bywave spring 24 and to slide the sealingring assembly housing 44 tightly against the sealing face ofclosure ring 49. -
Closure ring 49 is designed to contain the entireshutdown seal assembly 10 within the designated space requirements permitted ininsert 38A.Closure ring 49 is also designed with a sealing face that will seal against the sealingring assembly housing 44 oncethermal actuators 16 have actuated. This prevents fluid from passing between the sealingring assembly housing 44 andclosure ring 49. -
FIGS. 8 and 9 illustrate the shutdown seal after actuation. Rotatingshaft 62 ofpump 64 is located to the right ofshutdown seal assembly 10;shaft 12 has not been fully shown in the drawings. InFIG. 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 thepump shaft 62. The carbon graphite circumferential seal segments making upsegmented sealing ring 46 ride on the chromium carbide coatedshaft 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 sealingring assembly housing 44 axially parallel to pumpshaft 62. As the flow path along the outside oftop portion 42 of sealingring assembly housing 44 reduces, a differential in pressure across the seal begins to grow. Withthermal actuators 16 fully deployed the seal housing face provided by the upper surface 108 & 114 oftop portion 42 of interlocking sealingring housing 44 closes against theseal face 110 & 112 onclosure 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 (18)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/543,020 US20070140877A1 (en) | 2005-10-11 | 2006-10-03 | Shutdown seal for reactor coolant pump |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US72547105P | 2005-10-11 | 2005-10-11 | |
US11/543,020 US20070140877A1 (en) | 2005-10-11 | 2006-10-03 | Shutdown seal for reactor coolant pump |
Related Child Applications (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/713,151 Division US7504742B2 (en) | 2003-02-01 | 2007-03-02 | Method for the erection of a wind energy plant, and wind energy plant |
US11/713,382 Division US7482707B2 (en) | 2003-02-01 | 2007-03-02 | Method for the erection of a wind energy plant, and wind energy plant |
US12/072,143 Division US7610723B2 (en) | 2003-02-01 | 2008-02-25 | Wind energy plant with drainage |
Publications (1)
Publication Number | Publication Date |
---|---|
US20070140877A1 true US20070140877A1 (en) | 2007-06-21 |
Family
ID=37741109
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/543,020 Abandoned US20070140877A1 (en) | 2005-10-11 | 2006-10-03 | Shutdown seal for reactor coolant pump |
Country Status (2)
Country | Link |
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US (1) | US20070140877A1 (en) |
WO (1) | WO2007047104A1 (en) |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: WESTINGHOUSE ELECTRIC CO. LLC, PENNSYLVANIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SANVILLE, MARK E.;KOETH, REINHOLD;HOWARD, BRUCE A.;AND OTHERS;REEL/FRAME:019330/0311 Effective date: 20070508 Owner name: STEIN SEAL COMPANY, PENNSYLVANIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SANVILLE, MARK E.;KOETH, REINHOLD;HOWARD, BRUCE A.;AND OTHERS;REEL/FRAME:019330/0311 Effective date: 20070508 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |