Additive Manufacturing of SMR Holddown Springs and Upper Nozzle Interfaces

Cost and time associated with material waste, quality control, inspection, and manufacturing of nuclear fuel assembly components can be detrimental to nuclear plant design and development. Specifically, holddown springs are prime component examples that inherently carry these issues due to their complex geometries and attachment points. The design engineer must always weigh the manufacturing practices against the operational benefits. To combat this issue, the Department of Energy is highly interested in advancing methods of manufacturing for nuclear energy technologies that allow for easier engineering and commercial production of nuclear fuel assembly component. Proving that complex geometries, holddown springs, can be manufactured with the same design material using additive material technologies shows the nuclear industry that former manufacturing complications are no longer necessary. Additive material technologies also give the designer the option of adding beneficial features to spacer grids and nozzles during the Computer Aided Design (CAD) process that were previously impossible (due to tooling impediments). During Phase I, multiple holddown spring designs that are built out of the upper nozzle will be modeled using CAD, removing the need to produce two separate fuel assembly components. This new composite part will prevent possible thread joint failure and be designed to increase performance with less material. Once modeled, the holddown springs will be analyzed using Finite Element Analysis (FEA) in parallel with public-domain holddown springs to compare structural integrity. Lastly, after structural and fatigue have been optimized, the composite holddown spring designs (some incorporating the upper nozzle) will be manufactured using 3D printed, and then tested to record desired properties. Using additive material technologies (i.e. metallic 3D printing) minimizes material waste and inspection time while producing fine-tolerance products – increasing quality – that frees the designers to focus on component operation, not manufacturing (welding, milling, stamping, etc). Proof-of-concept in Phase I will show a 3D printed holddown spring can be placed on a lead test assembly in Phase II, and full production after irradiation testing fuel assemblies with 3D printed holddown springs in Phase III.