A key challenge fulfilling the United States federal government’s obligations under the Nuclear Waste Policy Act is in the transition of used nuclear fuel (UNF) storage away from at-reactor storage and to a consolidated interim storage facility (ISF). The default strategy (Standard Contract) for the Department of Energy is to use the Oldest Fuel First (OFF) allocation strategy, which would entail the federal government prioritizing UNF shipments based on fuel discharge date with the option to prioritize shutdown sites. This may not be the most cost-efficient model given the extensive amount of UNF already at reactor sites. Currently there is no way to preemptively remove fuel from sites that may be close to shutdown or have a higher storage or potential storage cost. As wet storage pools at reactors continue to fill to capacity at operating reactors, the backlog of UNF shipments to the ISF places additional pressure on operators to expand at-reactor dry storage capacity, thus adding to total system costs.

An essential aspect to this transition to a centrally-managed ISF for domestic UNF is in developing appropriate analytical tools to evaluate the effect of factors such as fuel shipment prioritization, logistics, and associated expense. Examples of this analysis would include evaluating fuel offloading prioritization strategies (OFF vs. shutdown sites first), strategies to minimize transfer of UNF to dry storage (i.e., through direct shipment from cooling pools to the ISF), etc.

While the solution space for the scheduling problem is intractably large to admit direct analytical evaluation of optimal solutions, by applying well-established optimization algorithms, it is possible to make a rigorous analytical determination of a UNF removal allocation strategy that minimizes the number of shutdown reactor years. Our findings indicate that the current OFF allocation strategy ranks in the bottom 3% of all possible queuing strategies in terms of total system shutdown reactor years.