The Versatile Test Reactor (VTR) is being developed to provide a flexible source of neutrons for the accelerated testing of materials. To support this flexibility, the design must be informed by uncertainty assessment that defensibly provides the needed margin. This paper provides an overview of the VTR Program’s approach to the generation and application of uncertainties in the reactor core design process as it relates to this goal. As the uncertainty assessment is still in progress, this paper not only provides an example of how uncertainty has been factored into the early stages of design but also provides findings from sensitivity studies that will form the basis of future uncertainty work.