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. (end of abstract)