project,” said Michael Lewis, principal value engineer. “What could we do technically to reduce the supply chain? Out of that we developed this cam- paign to change from a multiple piece weldment to a one-piece component while making sure we met all the requirements.” Westinghouse Electric partnered
with its casting source, GSC Found- ries, Odgen, Utah, to finalize a casting design with optimal manufacturability and castability that also met the appli- cation’s requirements. “We have a very detailed concurrent
engineering process,” said Steven King, global director of supplier manufactur- ing and value engineering. “When we work with a supplier that has demon- strated good performance in the past, we integrate them into the develop- ment. It helped us with the cycle time of the development, and we have come up with a much better design.”
Turn-Key Supplier Te conversion to casting was a
long time coming for the nozzle part, according to King. Westinghouse Electric first entered the nuclear energy market in the 1950s and has been building fuel assemblies for commercial fuel reactors in its own manufacturing facility since 1969. Up until the 1990s, the company made all the components in-house, but through capacity planning, it moved most components, such as the fuel nozzle, to an external supply base. “We realized the cost of some com-
ponents as machined parts, forgings or weldments, was not cost-effective,” King said. “We started looking in the 1990s to go to a single-piece casting, but the technology was not available then.” Ten years ago, Westinghouse
started contracting with GSC Indus- tries, which does precision investment casting for the automotive, aerospace and nuclear industries. Over the course of the last decade, the nuclear energy company has been evolving its designs to take advantage of refined casting capabilities at GSC. In 2007, it revisited the possibility of designing the weldment nozzle as a casting. First, Westinghouse reduced
the part count from nine to two by
combining the top portion of the nozzle into a single CF-3 stainless steel investment casting that was then welded onto a machined Type 304L stainless bottom plate. Te metals were selected for their suitability to maintaining their properties while in an aqueous solution at moderately elevated temperatures. Reducing the part count to two helped reduce the value stream for the part, but the sup- ply chain team knew the design still had room for improvement. For ease of manufacturability, flow slots in the bottom plate were machined in one direction with a leading chamfer to minimize blocked area and pressure drop. However, the unidirectional pattern resulted in a weak and strong direction for load distribution not optimal for the part’s application. Additionally, the chamfer generated a flow gradient that led to a higher pressure drop across the subassembly and total reactor core. To accommodate the high pressure drop, the fuel assembly needed to include either a higher capacity reactor coolant pump or less flow through the steam generator and turbine. Te design team developed a nozzle
Westinghouse redesigned the top nozzle of its fuel assemblies as a single-piece casting.
design with an as-cast optimized flow plate pattern to reduce the pressure drop. Te engineers designed the flow slots as multiple shapes in a symmetri- cal pattern to assist in load distribu- tion during worst-case shipping and handling and potential accidents. “We wanted to relax the stress level of the pumps,” Peterson said. “When we were able to cast those slots and configurations, we could optimize the design with full radii and drop the pressure further by about 50%.” The initial design was devel- oped as a solid model, which was loaded into finite element modeling (FEM) software to validate load distributions. From there, the design team began tweaking the model for further improvements before sending it to GSC for review. Due to concerns regarding voids in the flow plate ligaments, Westinghouse removed the highest stress liga- ment for a 2% peak stress increase in another location. According to the design team, the minimal increase in stress validated the newly designed flow plate pattern, only possible via casting, and added robustness to the
January 2013 MODERN CASTING | 43
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