Nuclear Archaeology for Gaseous Diffusion Enrichment Plants

The field of nuclear archaeology aims to develop the methods and tools to verify past production of fissile materials for military purposes, which may become necessary to support the verification of future arms control agreements that envision deeper cuts in the nuclear arsenals. Techniques have been successfully demonstrated for reconstructing historic plutonium production, especially in graphite-moderated reactors, but nuclear archaeology for uranium enrichment has proven much more challenging. Gaseous diffusion was historically the most widely used technology for military production of highly enriched uranium (HEU). With the termination of uranium enrichment operations in the Paducah plant at the end of May 2013, all gaseous diffusion enrichment plants worldwide will have been shutdown. The experience with decommissioning some of these plants in the United States, the United Kingdom, and France has shown that they contain large amounts of uranium particles deposited in the cascade equipment, especially in the diffusers of every stage. In this article, we evaluate the potential of using uranium particle deposition to understand and reconstruct gaseous diffusion enrichment plant operating history. First, we use a squaredoff cascade enrichment model to estimate the enrichment capacity of a reference plant. Then, using a cross-flow filtration model, we consider the mass of solid uranium particles deposited over time in the tubular separation membranes of the stage diffusers. Finally, we assess possible nuclear forensics techniques that can characterize these uranium deposits, including age-dating analysis of statistically sampled particles, as a tool to reconstruct the operating history of the plant.