Passive shutdown sealing device for a system of shaft seals in a reactor coolant pump set

Abstract

The present invention concerns a passive shutdown sealing device ( 20 ) for a primary motorised pump unit comprising: a split sealing ring ( 23 ) having an inactivated position and an activated position; a separator ( 27 ) made from a fusible material capable of changing state from a temperature threshold, called state change threshold, said separator ( 27 ) holding said split sealing ring ( 23 ) in the inactivated position of same when the temperature of the device ( 20 ) is lower than said state change temperature threshold; said device being characterised in that it comprises circular elastic means ( 22 ) positioned around the split sealing ring ( 23 ), said elastic means ( 22 ) being designed to bring said sealing ring ( 23 ) into the activated position of same when the temperature is greater than or equal to the state change threshold value of said separator ( 27 ).

1 . A passive shutdown sealing device ( 20 ) for a reactor coolant pump shaft seal system, comprising:
 a split sealing ring with an inactive position and an active position;   a separator made from a fusible material capable of changing state above a temperature threshold called the state change threshold, said separator holding said split sealing ring in its inactive position when the temperature of the device is less than the threshold state change temperature;   
       circular elastic means positioned around the split sealing ring, said elastic means being adapted to bring said sealing ring into its active position when the temperature is greater than or equal to the threshold change state value of said separator. 
     
     
         2 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said elastic means bring said split sealing ring into its active position when the temperature is greater than or equal to the value of an activation threshold of the device, the activation threshold temperature being greater than the threshold state change temperature. 
     
     
         3 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said device is adapted to form part of a system of seals of a shaft in a reactor coolant pump set in service. 
     
     
         4 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said split sealing ring is made from a polymer resistant to temperatures exceeding 300° C. 
     
     
         5 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said split sealing ring is made from polyetheretherketone, or a composite with a polyetheretherketone matrix containing glass or carbon fibres. 
     
     
         6 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , said circular elastic means apply a compression force on said split sealing ring. 
     
     
         7 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said sealing ring comprises a peripheral annular groove capable of holding said circular elastic means. 
     
     
         8 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said separator made from a fusible material is capable of mechanically resisting the force applied by the elastic means up to a threshold temperature of between 80° C. and 260° C., advantageously equal to 150° C. 
     
     
         9 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said separator and the split sealing ring are made in a single-piece. 
     
     
         10 . The passive shutdown sealing device for a reactor coolant pump shaft seal system according to  claim 1 , wherein said separator may be formed by a part independent from the split sealing ring and added onto the opening of the ring by attachment means. 
     
     
         11 . A reactor coolant pump set, comprising:
 a system of seals adapted to create a controlled leak forming along a leakage path formed along the shaft of the reactor coolant pump set;   a passive shutdown sealing device according to  claim 1 , adapted to at least partially close off said leakage path of said seal system when said seal system is defective and when said sealing ring is activated to create a controlled leak.