Fuel cycles have not historically been integrated with repository design. Four alternative combinations of fuel cycles and repository systems are assessed in the present work: (a) traditional repositories, (b) repositories with spent nuclear fuel retrievability for recycle or as insurance against unforeseen repository failure, (c) colocation and integration of reprocessing and repositories, and (d) colocated specialized disposal facilities such as boreholes for different wastes. System design choices have major impacts on fuel cycle economics, accident risk, repository performance, nonproliferation, and repository siting. Consequently, there are large incentives to understand the different ways to couple fuel cycles and repositories.

The evidence suggests that a repository as only a disposal site (the current system) is the least desirable option given current requirements for the United States. There are large incentives to develop repository sites that colocate and integrate all back-end fuel cycle facilities with the repository - independent of the fuel cycles that are ultimately chosen or how these fuel cycles evolve over time. Colocation and integration change the interface requirements between facilities by eliminating many storage and transport requirements such as the need for waste forms with high waste loadings. That, in turn, can result in reductions in cost, reductions in risk, and improved repository performance. For closed fuel cycles, colocation and integration may eliminate repository safeguards. This also suggests a repository business model similar to that of many airport authorities. Airport authorities manage the runways with colocated public and private airline terminals, aircraft maintenance bases, and related operations - all enabled and benefiting from the high-value runway asset. The common high-value back-end fuel cycle asset is the repository. For the local community and state government, such a strategy couples back-end fuel cycle benefits (high-technology jobs, tax revenue, etc.) with the repository site.