ABSTRACT
This troubleshooting case study reports on an Emergency Service Water (ESW) vertical-centerline pump for a nuclear power plant. This pump employs water-lubricated rubber-lined radial bearings. The pump had just been reinstalled and returned to service after a complete pump-vendor overhaul during a scheduled refueling outage of the nuclear-powered generating unit. It was test run to confirm it being fully operational. It was then shut down to rest mode and drained. On its restart a few days later, the ESW pump immediately exhibited symptoms of internal damage based on monitored vibration signals. It was then disassembled at the plant for inspection of pump internals. It was quickly discovered that the roll pins connecting journal bearing support brackets to the pump housing were heavily damaged, that is, nearly sheared off. The author was retained to provide guidance in quickly determining the root cause and fix of the failure in time to restart the plant on schedule at the conclusion of the 6-week refueling cycle. The author determined that the pump vendor who overhauled the pump had chosen a radial bearing rubber compound that had a strong swelling property when drained. Thus, on the first subsequent restart, the seriously swelled bearing liners had significantly swelled inwardly onto the shaft journal, thereby applying a torque on the bearing support housing sufficiently high enough to cause the bearing support housing support roll pins to inelastically deform. The problem was quickly fixed by using a more appropriate low-swelling rubber compound for the bearing liners, in keeping with how the pump was first delivered by its original manufacturer. The engineering technology for this type of water lubricated rubber-lined bearing is presented in Chapter 1, Section 1.11.
