Effect of Degraded Oil on Terry Turbine Bearing Performance at High Temperature

Abstract

In 2011, a series of seismic events induced a station blackout condition at the Japanese nuclear power site Fukushima Daiichi. Without power, all three units were unable to maintain proper core cooling. To supplement the inadequate cooling, the RCIC system began operation in Units 2 and 3. RCIC is estimated to have a battery life of 4 to 12 hours, though, during the Fukushima accident, was able to stay in operation for nearly three days, but then suddenly failed. The theory behind this behavior is that the Terry turbine (a major component of the RCIC system) was able to enter a “self-regulating” mode after the batteries died, but then suffered a bearing failure. This thesis explores how oil temperature and quality affect the journal bearings of a ZS-1 Terry turbine. Tests were conducted to evaluate the change in the composition of oil as it thermally degrades over the course of 72 hours, and to investigate the effect thermally degraded oil had on the performance of the turbine. Ultimately, the change in oil composition over the course of a 72-hour 121oC degradation was found to be negligibly small. Additionally, when the same degraded oil was used as bearing lubricant in a ZS-1 Terry turbine, the effect on torque was noticeable, but minor. Scoring to the bearings did occur when degraded oil was used, but the degree of damage was superficial.