Modifications to, and Vibration Analysis of Tank 7 Slurry Pumps, F Tank Farm

Slurry pumps have demonstrated short life spans when operated in nuclear waste tanks. Their life approximates one thousand hours or approximately 42 days of continuous operation, evidenced by past performance in H-Area and F-Area at the Savannah River Site (SRS). Several investigations over the past six years have isolated the most significant reliability problems. These problems are seal and bearing failures caused by the vibrations of the long drive shafts in the pump, manufacturing tolerance accumulations, failures caused by material incompatibility between the waste and the lowest process bearing that is exposed to the waste, and vibrations which occur when the pump operates at critical speeds. Only vibration and material problems were corrected. Potential bearing and seal degradation still exists for those pumps with a critical speed near the operating speed. Bearing damage can be expected below 700 rpm. The pumps are used to mix or slurry nuclear waste products contained in waste storage tanks prior to transferring the tank contents for further processing. In particular, Lawrence Pumps, Inc. slurry pumps are installed on Tank 7 in F Tank Farm. Appendix A provides the initial recommendations, and further states that this follow up report would provide detailed descriptions of the pump components, failure mechanisms, and corrective actions which include tilt pad bearings, a Stellite process bearing, and modified split shaft retainers. By testing the pumps in a non-radioactive test facility, these corrections have been shown to significantly decrease the vibrations associated with bearing and seal failures, and consequently are expected to improve reliability