Nuclear Forensics International Technical Working Research Articles

Exercise Celestial Skónis: Part 2 – Emerging technologies and State of Practice of nuclear forensic analyses demonstrated during the 6th collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Exercise Celestial Skónis: Part 1 – History, purpose, design and results of traditional forensic examinations of the 6th Collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Morphological and chemical characterization of uranium and cerium nuclear forensics samples

• Uranium and cerium containing samples were examined as part of an international nuclear forensics exercise. • The main technique for characterization was the combined analysis by SEM-EDS/Raman of the surface. • Connection between the ingots was determined by uranium and cerium isotopic ratios as well as yttria and graphite surface contaminations. • Sample preparation history was interpreted based on surface contaminations, showing multiple impurities present in suggested production and processing sites. The objective of this paper is to describe nuclear forensics material characterization, as conducted in the Israeli National Nuclear Forensic Laboratory (INNFL) during an international exercise Collaborative Material Exercise 6 (CMX6) organized by the Nuclear Forensics international technical working group (ITWG). The characterized materials are uranium and cerium metal ingots. The goal was characterization of physical parameters, elemental and isotopic composition, morphology and chemical composition of the surface. Electron microscopy and Raman spectroscopy techniques were combined for morphological, structural and elemental study of the surface. The information from these analyses was used to answer the exercise questions, comparing the materials (labeled ES-1 and ES-2) to each other and to other samples described in the scenario. The INNFL investigation identified a connection between ES-1 and ES-2 based on several indicators, including the isotopic composition of the uranium present in both samples, as well as other surface contaminations, mainly yttria and graphite. Based on these finding the INNFL established a connection between ES-1 and ES-2 to ES-3B (theoretical sample with uranium traces) and has not established a connection to ES-3A (theoretical sample of plutonium powder). ES1 and ES-2 have been suggestively connected to their theoretical source, by their isotopic ratio. The INNFL conclusion was that the theoretical source materials (oxide and fluoride) were converted into the actual materials.

Uncovering uranium isotopic heterogeneity of fuel pellets from the fifth collaborative materials exercise of The Nuclear Forensics International Technical Working Group

In 2017, the Nuclear Forensics International Technical Working Group organized their fifth Collaborative Materials Exercise (CMX-5). The exercise samples were two uranium dioxide fuel pellets manufactured from the same starting materials by different processes to have similar bulk isotopic composition, but different spatial uranium isotopic distributions. Sets of identical materials were sent to all participating laboratories, who then utilized their existing nuclear forensic capabilities to independently analyse fuel pellets and identify similarities and differences of the materials’ characteristics. Here we present and compare the ability of different analytical techniques to spatially resolve uranium isotopic heterogeneity in the uranium oxide fuel pellets.

Assessment of uranium inhomogeneity and isotope imaging for nuclear forensics

Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) was used to study the heterogeneity of solid uranium materials. Using spatially resolved isotope ratio measurement, the degree of isotopic homogeneity at micron-level could be assessed in nuclear samples for nuclear safeguards and forensics purposes. LA-MC-ICP-MS was applied for two UO2 pellets which had been distributed in the 5th Collaborative Materials Exercise (CMX-5) organized by the Nuclear Forensics International Technical Working Group (ITWG). The two materials in question have very similar 235U isotope abundance (around 1%), but very different 235U isotopic heterogeneity. Although both UO2 pellets were prepared from identical source materials (mixture of depleted 0.3% and low-enriched 4.3% 235U), their different production routes resulted in observable differences at micron-scale. By the spatially resolved measurement the number of constituting components (feed materials) with different uranium enrichment and their n(234U)/n(238U) and n(235U)/n(238U) isotope ratios could be determined. Imaging can help assess the lateral dimensions of the individual components (grains) and may indicate a certain production route. This information on the inhomogeneity, the possible inference on the production process and isotopic composition of the constituents are highly valuable in nuclear forensics investigations for determining the origin of an unknown nuclear material.

Isotopic and Compositional Variations in Single Nuclear Fuel Pellet Particles Analyzed by Nanoscale Secondary Ion Mass Spectrometry.

The Collaborative Materials Exercise (CMX) is organized by the Nuclear Forensics International Technical Working Group, with the aim of advancing the analytical capabilities of the participating organizations and providing feedback on the best approaches to a nuclear forensic investigation. Here, model nuclear fuel materials from the 5th CMX iteration were analyzed using a NanoSIMS 50L (CAMECA) in order to examine inhomogeneities in the 235U/238U ratio and trace element abundance within individual, micrometer scale particles. Two fuel pellets were manufactured for the exercise and labelled CMX-5A and CMX-5B. These pellets were created using different processing techniques, but both had a target enrichment value of 235U/238U = 0.01. Particles from these pellets were isolated for isotopic and trace element analysis. Fifteen CMX-5A particles and 20 CMX-5B particles were analyzed, with both sample types displaying inhomogeneities in the U isotopic composition at a sub-micrometer scale within individual particles. Typical particle diameters were ∼1.5 to 41 μm for CMX-5A and ∼1 to 61 μm for CMX-5B. The CMX-5A particles were shown to be more isotopically homogeneous, with a mean 235U/238U atom ratio of 0.0130 ± 0.0066. The CMX-5B particles showed a predominantly depleted mean 235U/238U atom ratio of 0.0063 ± 0.0094, which is significantly different to the target enrichment value of the pellet and highlights the potential variation of 235U/238U in U fuel pellets at the micrometer scale. This study details the successful application of the NanoSIMS 50L in a mock nuclear forensic investigation by optimizing high-resolution imaging for uranium isotopics.

State of practice and emerging application of analytical techniques of nuclear forensic analysis: highlights from the 5th Collaborative Materials Exercise of the Nuclear Forensics International Technical Working Group (ITWG)

The Nuclear Forensics International Technical Working Group (ITWG), a community of nuclear forensic practitioners who respond to incidents involving nuclear and other radioactive material out of regulatory control, completed its fifth Collaborative Materials Exercise in 2017 (CMX-5). Forensic laboratories from 19 countries and one multinational organization aimed to advance nuclear forensic science and improve international cooperation in the event of a nuclear material security incident. In all, over 30 analytical techniques were utilized to investigate the samples, many techniques applying novel methods or offering improvements in turnaround time. An objective review of the state of practice and emerging application of analytical techniques of nuclear forensic analysis based upon this exercise is provided.

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

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. 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.

Analysis of geochemical basalts database as a simulant for uranium ore concentrates data: the Galaxy Serpent 3 Exercise

The Nuclear Forensics International Technical Working Group (NF-ITWG) conducted an exercise, Galaxy Serpent 3 (GS3), by the National Nuclear Forensics Libraries Task Group, during 2017. The main goal of the GS3 exercise was to illustrate the usefulness of a National Nuclear Forensic Library for assessing the potential consistency of unknown material with national holdings. Moreover, it offers the possibility to produce a realistic database resembling uranium ore concentrate (UOC) that can be used for algorithm development activities. A database was built based on basalt compositions from different tectonic settings: MORB, IAB, OIB and CRFB. Classes (Affinities) with subtly different chemical compositions. All data are open source and sample names can be traced to original data for error checking. Participants (29 teams) had to use existing techniques, or develop their own algorithms, to allow for dealing with the sparse database and managing incomplete data points. The exercise’s scenario introduced 3 simulated origin-unknown UOC samples, interdicted by authorities. Each team was asked to answer two main questions—“Are the 3 unknown samples consistent with each other?” and “are the 3 unknown samples consistent with the Mines in the database given?”. For the first time, the Israeli National Nuclear Forensic Laboratory (INNFL) participated in the GS exercise. A dedicated team was assigned the task of building capabilities needed and applying them to answer the raised questions. Methodology and tools developed and applied by the Israeli team are described. The results are presented and discussed, including new signatures allowing differentiation between unknown samples and mines.

Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group’s Fourth Collaborative Material Exercise (CMX-4)

The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest participation for this exercise in nuclear forensics, with seven of the 17 laboratories participating for the first time. Each of the laboratories had their strategic role to play in its respective country, analyzing real-world samples using their in-house resources. The scenario was fictitious but was thoughtfully crafted to engage participants in nuclear forensic investigations. In this paper, participants from five of the first-time laboratories shared their individual experience in this exercise, from preparation to analysis of samples.

Fourth Collaborative Materials Exercise of the Nuclear Forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group is a community of nuclear forensic practitioners who respond to incidents involving nuclear and other radioactive material out of regulatory control. The Group is dedicated to advancing nuclear forensic science in part through periodic participation in materials exercises. The Group completed its fourth Collaborative Materials Exercise in 2015 in which laboratories from 15 countries and one multinational organization analyzed three samples of special nuclear material in support of a mock nuclear forensic investigation. This special section of the Journal for Radioanalytical and Nuclear Chemistry is devoted to summarizing highlights from this exercise.

The application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)

In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched uranium oxide samples, providing 12 analytical results using three different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the 235U–231Pa and 234U–230Th chronometers confirmed the validity of the age dating assumptions, increasing confidence in the resulting conclusions.

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical characterization techniques vary from simple weighing and dimensional measurements to complex sample preparation and scanning electron microscopy-electron backscatter diffraction analysis. This paper reports on the physical characterization conducted by several international laboratories participating in the fourth Collaborative Materials Exercise, organized by the Nuclear Forensics International Technical Working Group. Methods include a range of physical measurements, microscopy-based observations, and profilometry. The value of these results for addressing key investigative questions concerning two uranium dioxide pellets and a uranium dioxide powder is discussed.

Gamma spectrometry in the ITWG CMX-4 exercise

Low enriched uranium samples of unknown origin were analyzed by 16 laboratories in the context of a Collaborative Materials Exercise (CMX), organized by the Nuclear Forensics International Technical Working Group (ITWG). The purpose was to compare and prioritize nuclear forensic methods and techniques, and to evaluate attribution capabilities among participants. This paper gives a snapshot of the gamma spectrometric capabilities of the participating laboratories and summarizes the results achieved by gamma spectrometry.

State of practice and emerging application of analytical techniques of nuclear forensic analysis: highlights from the 4th Collaborative Materials Exercise of the Nuclear Forensics International Technical Working Group (ITWG)

The Nuclear Forensics International Technical Working Group (ITWG) recently completed its fourth Collaborative Materials Exercise (CMX-4) in the 21 year history of the Group. This was also the largest materials exercise to date, with participating laboratories from 16 countries or international organizations. Exercise samples (including three separate samples of low enriched uranium oxide) were shipped as part of an illicit trafficking scenario, for which each laboratory was asked to conduct nuclear forensic analyses in support of a fictitious criminal investigation. In all, over 30 analytical techniques were applied to characterize exercise materials, for which ten of those techniques were applied to ITWG exercises for the first time. An objective review of the state of practice and emerging application of analytical techniques of nuclear forensic analysis based upon the outcome of this most recent exercise is provided.