LLNL’s Experience with the 3rd ITWG Nuclear Forensics Round Robin

The Nuclear Forensics International Technical Working Group (ITWG) is an organization of technical experts, law enforcement officials, policy makers, and diplomats from interested governments who cooperate to identify best practices in the field of nuclear forensics. The ITWG was established some fifteen years ago to advance the science of nuclear forensics by exchanging information, developing procedures and recommendations, and conducting international exercises. In fact, conducting practical exercises has been one of the organization’s key activities from the beginning. In 1999, ITWG conducted an exercise involving the analysis of plutonium oxide powder from the European civil nuclear cycle. In 2003, ITWG conducted an exercise involving the analysis of HEU oxide powder. This past year, ITWG conducted an exercise involving paired samples of HEU metal. LLNL is one of only three laboratories to have participated in all three ITWG exercises. All participants were required to analyze the provided materials to the limits of their self- declared capability. In addition, participants were requested to analyze the materials in accordance with the ITWG Model Action Plan (see IAEA Nuclear Security Series No. 2), which provides for 24-hour, 1-week, and 2-month reporting. Since the two previous exercises, and, in fact, most real interdicted samples, had involved oxide powders, the analysis of intact metal pins provided both challenges and opportunities to the implementation of the Model Action Plan. For example, it became important to take the time to fully analyze and document the intact specimens before any sub-sampling took place. One of the key requirements for the exercise was the comparison of the two samples. Participants were requested to determine how the two samples might be related to each other. In doing so, we found that the two samples, although quite similar in many ways, suggesting a similar origin, had key differences which definitively proved that they were not from the same batch of material. We also found that bulk age dating can be problematic for uranium metal of complex history. Our analysis of multiple radiochronometers became important for unraveling the complex history of the material, thus allowing correct interpretation of the age dating results.