U.S. Department of Energy

Pacific Northwest National Laboratory

Plutonium Experiment Expands Capability Use

"The experiment has thus far provided interesting preliminary data," says researcher Dallas Reilly, "but the methods we used to conduct the work will be of high interest to national laboratory and university communities, and could help advance research in legacy waste, national security, and even nuclear fuels." The experiment was funded through two PNNL Laboratory Directed Research and Development (LDRD) program efforts: The Nuclear Process Science Initiative and an Open Call project Reilly led.

The experiment started with a nine-gram ingot of plutonium metal produced in the Radiochemical Processing Laboratory. In December 2017, the material was placed in a focused ion beam instrument, or "FIB," at RPL. The instrument was used to remove smaller samples from the metal, and then shape those samples into tiny "needles."

Next, Dallas explains, the needles were "free-released" (a process that enables movement of minuscule quantities of radioactive material without radiological controls) and carefully transported to the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility located at PNNL. At EMSL, the needles were placed in an Atom Probe Tomography (APT) instrument, which sheds atoms, one small layer at a time, from each needle. The atoms were detected and then factored into mathematical formulas to help create a "reconstruction"--essentially a 3-D graphical atom-by-atom representation of each needle.

Although the reconstruction provided some interesting insights about the material, the more noteworthy aspect of the experiment was the sample creation and analysis process. The ability to move a plutonium sample from the RPL, a Hazard Category II Non-Reactor Nuclear Facility, to a non-radiological facility like EMSL--and then safely use instrumentation not available at RPL--is a major step forward in more fully tapping research capabilities at PNNL.

The planning for this type of experiment started a number of years ago and over time has involved multiple PNNL research directorates, as well as numerous health and safety experts. Dallas was part of a team that approximately two years ago put forward a free release workflow document to enable easier, and safe, movement of tiny samples outside of radiological controls if certain thresholds, including Nuclear Regulatory Commission surface contamination limits, are met. The free release workflow, coupled with a diligent staff effort to ensure necessary health and safety requirements were in place, facilitated the APT experiment.

"For the experiment itself, several of us worked long hours for three days, but we successfully completed the task, and did so safely," Dallas explains. "There are risks in a project like this, but we managed the risks in an intelligent, thoughtful way, aligned with stringent safety standards."

Dallas believes the experimental results could contribute to two journal papers, and he's also hoping to share similar information at the Plutonium Futures conference later this year. He and colleagues next plan to use the same experimentation process in another LDRD project to study plutonium particles from the Hanford Site, which will reveal information about particle composition. Such new knowledge could help inform waste cleanup strategies, and also help demonstrate PNNL's advanced research capabilities to the broader scientific community.

The experiment team included Dallas, who works in PNNL's National Security Directorate (NSD); Daniel Perea, Earth and Biological Sciences Directorate (EBSD); Timothy Lach, Energy and Environment Directorate (EED); Amanda Casella (EED); Marie McCoy (NSD); Karl Pitts (NSD); and Jon Schwantes (NSD). The experiment was funded through the NPSI project, Monitoring Diffusion of Actinide Daughters and Granddaughters in Metals for Chronometer Applications, and the LDRD Open Call project, Hot Particle Analysis Aided by a State-of-the-Art Focused Ion Beam. Dallas leads both projects.

The experiment produced a 3-D graphical atom-by-atom representation of each needle--in this case showing plutonium, plutonium oxide, plutonium dioxide and gallium components.

The experiment produced a 3-D graphical atom-by-atom representation of each needle--in this case showing plutonium, plutonium oxide, plutonium dioxide and gallium components.

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