U.S. Department of Energy

Pacific Northwest National Laboratory

Outcomes: Monitoring Diffusion of Actinide Daughters and Granddaughters in Metals for Chronometer Applications

Principal Investigator: Dallas Reilly

Completed: FY18

Outcomes: This project focused on understanding trace element fractionation during the production, casting, or melting of uranium (U) metal or other actinide metals. The research effort combined high-temperature controlled experiments, molecular-scale observations, and theoretical modeling. One experiment showed, for the first time, quantitative fractionation of thorium (Th) during the production of U metal (in a conversion to uranium tetrafluoride to the metallic phase in a process known as bomb reduction). In that study, Th moved from the tetrafluoride to the crucible and slag during the reduction. Modeling experiments focused on carbon in the U metal system, since the resulting U carbides could potentially scavenge trace elements like Th during these reactions. The studies produced a novel way of seeding crystals in phase field models. Finally, in seeking to monitor the fractionation of plutonium (Pu) daughter products during a similar bomb reduction experiment as the U, atom probe tomography (APT) was performed on a bomb-reduced Pu metal. This first-ever Pu APT method resulted in valuable information on the bomb reduction process and corrosion mechanism. The project outcomes will benefit the nuclear forensics community and worker health and safety related to production of metallic nuclear fuels.

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