May-June 2019 NPJ

Nuclear Plant Journal, May-June 2019 NuclearPlantJournal.com 41 (Continued on page 42) Advanced Analysis & Hydraulic Upgrades To optimize the pump’s overall efficiency and MTBR, the service organization worked to not only repair but improve upon the original design characteristics and geometry of the pump’s internal components. Factors such as suction conditions, vane angles, vane heights, and the vane openings of the pump’s impellers were analyzed to identify issues; all the while, improving and upgrading the design while still retaining the original parts. The edges of the impeller suction vanes were worn to a sharp, thin edge. Routine wear had contributed to severe corrosion and erosion seen throughout the pump and its components. An in-depth hydraulic analysis of the impeller was required to ensure all performance characteristics were designed properly. This task required a comprehensive engineering study as the thickness of the vanes, vane geometry, and cavitation damage posed serious problems and could be significantly improved. The service organization chose to utilize computation fluid dynamics (CFD) to ensure increased efficiency and optimize pump efficiency. Computational fluid dynamics is a branch of fluid mechanics, utilizing advanced numerical analysis and data structures to simulate the flow and interaction of fluids and surfaces. The analysis allowed the service organization to correct the damaged impeller vanes, in addition to repairing several cracks found during the inspection. The remanufacture was executed by restoring the original material and blending repairs to seamlessly match the original contour. In addition, the shaft was upgraded to forged stainless steel, offering more rigidity and stability which will prevent future distortion and deflection. To assure quality and accommodate for safety protocols, the service organization determined the pumps bearing design could be greatly improved. Specifically, the shaft bearing journal surfaces were upgraded to a Tungsten carbide material applied via a high- velocity oxygen fuel coating (HVOF) process to improve surface properties and significantly increase strength. Upgraded non-metallic bearings were utilized to allow for smaller running clearances to minimize degradation caused by vibration. This will allow the pump to better handle dry starting and other system upsets, versus a rubber alternative. Performance Testing for Validation Upon project completion, the pump was tested at the service organization’s certified performance test lab in Chicago, Illinois. The purpose of the performance test was to ensure the actual performance achieved the desired operating conditions and original design conditions, while also validating all modifications and upgrades.