SUMMARY

While nuclear energy exhibits tremendous potential as a low-carbon baseload energy source, the industry has recently been losing ground in the United States and abroad due largely to unfavorable market conditions leading operators to close plants prior to the end of their licensed life and financial challenges associated with new build projects. A research effort has been launched at Oak Ridge National Laboratory to address some of the economic challenges associated with nuclear energy by applying advanced manufacturing methods to the fabrication of nuclear reactor components; specifically, fabrication of control elements for the High Flux Isotope Reactor (HFIR) with ultrasonic additive manufacturing (UAM), a form of 3D printing, is demonstrated. UAM represents a promising option to greatly simplify the HFIR control element fabrication process, but it yields a control element design that is fundamentally different from that produced by established means, thus necessitating an investigation into the neutronic impact of applying the design in HFIR. Further, UAM introduces additional design variables not applicable to the traditional control element design, thereby providing opportunity for neutronic optimization of the design.

The following research tasks are proposed to assess the neutronic feasibility of employing additively manufactured control elements in HFIR. First, MCNP models of the HFIR core with additively manufactured control elements are constructed for high-level analyses of the impact of introducing the new control element design on the HFIR core physics with regards to the core flux profile, neutron absorption by the control elements, and reactivity control. Informed by these physics results, an initial usable design is sought which matches as closely as possible the performance of the original design so as to minimize changes to established operation and safety margins. Finally, the design is optimized to extend the useful lifetime of the control elements using response surface methods favorable to computational efficiency. This work provides a first look at the neutronic considerations of using additively manufactured nuclear reactor components in a real reactor; it is envisioned that this practice will enable significant savings in the cost and effort associated with fabrication of the HFIR control elements and encourage future consideration of advanced manufacturing for improving the economics of the nuclear industry.