Microscale Isotopic Variation in Uranium Fuel Pellets with Implications for Nuclear Forensics

Kips, Ruth; Weber, Peter K.; Kristo, Michael J.; Jacobsen, Benjamin; Ramon, Erick C.

doi:10.1021/acs.analchem.9b01737

Microscale Isotopic Variation in Uranium Fuel Pellets with Implications for Nuclear Forensics

Journal Article · Tue Jul 16 00:00:00 EDT 2019 · Analytical Chemistry

DOI:https://doi.org/10.1021/acs.analchem.9b01737· OSTI ID:1572604

^[1]; ^[1]; Kristo, Michael J. ^[1]; Jacobsen, Benjamin ^[1]; Ramon, Erick C. ^[1]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Until recently, the analysis and identification of nuclear fuel pellets in the context of a nuclear forensics investigation have been mainly focused on macroscopic characteristics, such as fuel pellet dimensions, uranium enrichment, and other reactor-specific features. Here, we report microscale isotopic heterogeneity observed in different fuel pellet fragments that were characterized in situ by nanoscale secondary ion mass spectrometry (NanoSIMS). The materials analyzed include fuel fragments obtained as part of the Collaborative Materials Exercise (CMX-4) organized by the Nuclear Forensics International Technical Working Group (ITWG), as well as a fuel pellet fragment from a commercial power reactor. Although the commercial fuel pellet showed a homogeneous ²³⁵U/²³⁸U ratio across the sample (within analytical error), NanoSIMS imaging of the CMX-4 fuel pellet fragments showed distinct microscale variations in the uranium isotopic composition. The average ²³⁵U enrichments were 2.2 and 2.9% for the two samples; however, the measured ²³⁵U/²³⁸U ratios varied between 0.0081 and 0.035 (0.79–3.3 atom % ²³⁵U) and between 0.0090 and 0.045 (0.89–4.3 atom % ²³⁵U). The measurement of ²³⁶U in one of the CMX-4 samples suggested the use of at least three uranium oxide powders of different isotopic compositions (“source terms”) in the production of the pellets. These variations were not detected using the conventional bulk, macroscopic techniques applied to these materials. Furthermore, our study highlights the importance of characterizing samples on the microscale for heterogeneities that would otherwise be overlooked and demonstrates the potential use of NanoSIMS in guiding further nuclear forensic analysis.

Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: AC52-07NA27344

OSTI ID:: 1572604

Report Number(s):: LLNL-JRNL--770145; 938287

Journal Information:: Analytical Chemistry, Journal Name: Analytical Chemistry Journal Issue: 18 Vol. 91; ISSN 0003-2700

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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Isotopic and Compositional Variations in Single Nuclear Fuel Pellet Particles Analyzed by Nanoscale Secondary Ion Mass Spectrometry Fallon, Connaugh M.; Bower, William R.; Lyon, Ian C. ACS Omega, Vol. 5, Issue 1 https://doi.org/10.1021/acsomega.9b02703	journal	December 2019