Development of Full Scale Reactor Coolant Pump Thrust Bearing Test System and Qualification Process for Retrofit Thrust Bearing Oil Seal With Commercial Grade Components

A fleet of reactor coolant pump thrust bearings were experiencing loss of oil inventory through a face rubbing mechanical oil seal. In a span of six months, Westinghouse developed a replacement seal which retrofit into the existing bearing, erected a full scale bearing test system, operated the prototype seal through various operating conditions utilizing Six Sigma Design of Experiments methodology, qualified the seal for sustained use in an operating reactor plant and supported the installation of the retrofit seals. The retrofit seal replaced a problematic face rubbing seal with a controlled leakage design utilizing a floating ring — a pressure reducing bushing free to translate in the X-Y plane. The prototype seal system was optimized through use of the Design of Experiments. Design optimization was aimed at reducing oil aeration to levels lower than those present with the original equipment, which when achieved, provided improved heat transfer from the bearing. The test system was constructed around a production thrust bearing, identical to those installed in the plant, which was modified to facilitate collection of a variety of process variables. In all, the system was capable of simultaneously sampling and storing data from 56 separate channels; while recording digital video from eight sources, from cameras both inside and outside of the bearing. All in-service operating parameters were duplicated by the test system, including: computer controlled variable vertical thrust load from zero to 90 tons, computer controlled variable radial thrust load and acceleration from standstill to operating speed in 16 seconds. Safe shutdown operating variables were monitored automatically by the system, in the event of a faulted condition the system automatically detected the fault and initiated a safe shutdown automatically. To date, all installed seal systems have performed as designed; allowing essentially no leakage at this location from the bearing reservoir. The test system continues to be used on development projects focused on improving other aspects of the bearing’s performance.