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.

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.