Shutdown seal for reactor coolant pump

Abstract

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

Description

CROSS REFERENCE TO RELATED PATENT APPLICATION [0001] 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.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] 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. [0004] 2. Description of the Prior Art [0005] 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 typi...

AI Technical Summary

Benefits of technology

[0015] 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.

[0037] 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.

Problems solved by technology

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.

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