A highly-enriched 244Pu reference material for nuclear safeguards and nuclear forensics measurements

Journal of Radioanalytical and Nuclear Chemistry - A highly-enriched 244Pu isotope dilution reference material has been prepared and characterized for metrologically traceable measurements of very...     

Environmental monitoring as an important tool for safeguards of nuclear material and nuclear forensics

Summary The use of environmental monitoring as a technique to identify activities related to the nuclear fuel cycle has been proposed by international safeguards organizations. The elements specific for each kind of nuclear activity, or “nuclear signatures”, inserted in the ecosystem can be intercepted by different live organisms. This work demonstrates the technical viability of using pine needles as bioindicators of nuclear signatures associated with uranium enrichment activities. Additionally, it proposes the use of HR-ICP-MS to identify the signature corresponding to that kind of activities in the ecosystem. Nitric acid solutions, used to wash pine needles sampled near nuclear facilities and containing only 0.1 mg ^. kg^-1 of uranium, exhibit a n(²³⁵U)/n(²³⁸U) isotopic abundance ratio of 0.0092±0.0002, while solutions originated from samples collected at places located more than 200 km far from activities related to the nuclear fuel cycle exhibit a value of 0.0074±0.0002. Similar results were obtained for sample solutions prepared using the acid leaching process. The different values of n(²³⁵U)/n(²³⁸U) isotopic abundance ratio obtained permit to confirm the presence of anthropogenic uranium and demonstrate the viability of using the methodology proposed in this work.     

Age determination of plutonium material in nuclear forensics by thermal ionisation mass spectrometry

Age is a key parameter when deducing the history of plutonium material, i.e. the plutonium produced in the nuclear reactors. This is of vital importance, when a smuggled plutonium sample has been seized and the origin has to be determined. A methodology is described which allows accurately to determine the age of plutonium material by thermal ionisation mass spectrometry using independent parent/daughter relations. This has been demonstrated for Reference Materials of known ages as well as for real samples. The already established method using gamma spectrometry is compared to this.     

Age determination of plutonium material in nuclear forensics by thermal ionisation mass spectrometry

Age is a key parameter when deducing the history of plutonium material, i.e. the plutonium produced in the nuclear reactors. This is of vital importance, when a smuggled plutonium sample has been seized and the origin has to be determined. A methodology is described which allows accurately to determine the age of plutonium material by thermal ionisation mass spectrometry using independent parent/daughter relations. This has been demonstrated for Reference Materials of known ages as well as for real samples. The already established method using gamma spectrometry is compared to this.     

A brief introduction to analytical methods in nuclear forensics

Nuclear forensic (NF) techniques are critical in responding to both environmental releases of nuclear materials and illicit trafficking activities involving both nuclear and counterfeit materials. Despite rising need, however, significant barriers exist to the future success of such research. This subset of analytical chemistry contains unique concerns (e.g. chronometry and impurity signatures), a wide variety of preparatory/instrumental approaches, and is in need of innovative solutions to current problems both in and out of the lab. The present work introduces existing NF research, development challenges and notes potential areas for advancement by highlighting several key analytical approaches. Examples of concerns and techniques discussed in this review include: chronometry, reference materials, separations, counting spectrometry, mass spectrometry and more.     

Development of a data-mining methodology for spent nuclear fuel forensics

The purpose of this study is to categorize the type of spent nuclear fuels using simulation data-based classification methods. Considering the practical conditions making the full analysis of radioactive nuclides difficult, the classification methods were designed to be robust to noise and missing information. The strength and weakness of three classifiers, linear discriminant analysis, quadratic discriminant analysis and support vector classification were compared, which is developed by the history information such as burnup, enrichment, and cooling type generated from ORIGEN-ARP upon fuel assembly types. Auto-Associative Kernel Regression improved outlier management as a pre-processing technique.     

Identification of uranium signatures relevant for nuclear safeguards and forensics

The paper describes the applicability of different characteristics (signatures) in nuclear safeguards and forensics for assessment of uranium material provenance in terms of production process. The study follows a uranium ore concentrate production from an ore to a U₃O₈ product. It turned out that rare-earth elemental pattern, radiochronometry (age of ore body and material production date), sulphur and organic impurities are useful to find out the origin or history of the material, while certain trace-elements and isotopics of Pb or Sr were found to be inconclusive. The results will be important to understand the signatures in nuclear safeguards and forensics.     

Development of a data-driven classification algorithm for fresh nuclear fuel forensics

Journal of Radioanalytical and Nuclear Chemistry - According to the Incident and Trafficking Database of the International Atomic Energy Agency, incidents involving illegal transactions or...     

Nuclear forensics: searching for nuclear device debris in trinitite-hosted inclusions

This study documents the 3D morphology of trinitite-hosted metallic inclusions and the first observations of alloys consisting primarily of Pb, Ta, Ga, and W. Scanning electron and backscatter electron imaging, as well as energy dispersive X-ray spectra chemical composition data are reported for heavy metal inclusions in 14 different samples of trinitite. Inclusions consisting of Fe?CTi?CSi are the most abundant and presumably derived predominantly from the explosion tower. Grains of Cu, Pb, Ta?+?Ga?+?W were also observed and are likely derivatives of the trinitite device wiring, tamper, and tamper and core, respectively. Additionally, a Ba-rich grain and multiple zircons (ZrSiO₄) were observed in a large majority of samples. The spherical morphology and the ubiquitous positioning of the heavy metal inclusions on the crater walls of the glassy trinitite surfaces indicate a two-step formation. Stage one involves formation of the glassy trinitite, while the second stage involved the precipitation of the inclusions that were incorporated onto the surface of the trinitite. Furthermore, the precarious positioning of these inclusions further emphasizes the need for analysis using non-destructive techniques prior to methods employing a bulk sample digestion approach.     

Age determination of a 75Se gamma radiography source for nuclear forensics

Journal of Radioanalytical and Nuclear Chemistry - Two methods were used to evaluate the age of 75Se sealed source material. Both methods utilized gamma spectroscopy to determine the quantity of...     

Characterization of californium sources by gamma spectrometry: relevance for nuclear forensics

As part of an experimental validation of a nuclear forensics methodology for Pu source reactor-type discrimination, destructive analysis has been performed on two irradiated UO₂ pellets with different irradiation histories. Analysis has focused on measuring key Sm fission product isotope ratios used in a previously published maximum likelihood methodology to determine the most likely irradiation history of the pellets. A total of 21 Sm isotope ratios were measured within the irradiated pellets, and generally agreed within 20% of the irradiations as simulated using the Monte Carlo Radiation Transport and material depletion code, MCNP6. Results indicate the chosen approach can accurately measure the isotope ratios within 5% experimental error.

     

Radioanalytical chemistry for nuclear forensics in China: Progress and future perspective

A relatively new branch of science - nuclear forensics, aiming at providing the nature, origin, history and possible trafficking route of seized nuclear materials/devices, has been established and rapidly developed over decades to screen illicit nuclear activities. This highly interdisciplinary science is built upon a foundation of analytical chemistry, radiochemistry, nuclear physics, material sciences, geology, and other scientific disciplines, within which radiochemical methodologies and radioanalytical techniques play a key role. The present review provides a brief overview about the crucial aspects of nuclear forensics, including basic content, procedure, concerned elements, common separation, analytical method, and so on. The state of the art and recent progresses of nuclear forensics by research communities in China are reviewed, while selected examples and practical applications are emphasized. The challenges associated with this new area and on-going developments are highlighted and discussed.     

The use of LA-SF-ICP-MS for nuclear forensics purposes: uranium isotope ratio analysis

This work describes the utilization of the laser ablation sector field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS) technique for the determination of uranium isotopic composition in a highly enriched uranium sample. The measurements were performed on a continuous ablation with low energy density and defocusing, which demonstrated to be the optimum to reach the best signal stability. The measurements were improved by adjusting the following parameters: RF power, laser beam diameter, defocusing of laser beam, laser energy, laser energy density, auxiliary gas and sample gas. The ²³⁵U/²³⁸U isotope ratio with its respective uncertainty was 16.36 ± 0.15 and its precision was 1.12 % relative standard deviation. The uncertainties were estimated following the ISO GUM, with a confidence level of 95.45 % (k = 2.00). When compared the isotope abundances to the Round Robin Exercise Number 3’s average results a difference of 0.46 % has been found and when compared to supplier’s value, the difference was 0.41 %. The results presented by the measurements revealed that the LA-ICP-MS technique offers a rapid and accurate alternative to measure uranium isotope ratios without any sample preparation, since it allows carrying out the measurements straight on the sample. Moreover, it preserves the testimony—very important for safeguards and nuclear forensics purposes.     

Monte Carlo analysis of thermochromatography as a fast separation method for nuclear forensics

Nuclear forensic science has become increasingly important for global nuclear security, and enhancing the timeliness of forensic analysis has been established as an important objective in the field. New, faster techniques must be developed to meet this objective. Current approaches for the analysis of minor actinides, fission products, and fuel-specific materials require time-consuming chemical separation coupled with measurement through either nuclear counting or mass spectrometry. These very sensitive measurement techniques can be hindered by impurities or incomplete separation in even the most painstaking chemical separations. High-temperature gas-phase separation or thermochromatography has been used in the past for the rapid separations in the study of newly created elements and as a basis for chemical classification of that element. This work examines the potential for rapid separation of gaseous species to be applied in nuclear forensic investigations. Monte Carlo modeling has been used to evaluate the potential utility of the thermochromatographic separation method, albeit this assessment is necessarily limited due to the lack of available experimental data for validation.     

Impact of an external radiation field on handheld XRF measurements for nuclear forensics applications

X-ray fluorescence (XRF) is an attractive technique for nuclear forensics applications. We evaluated a handheld XRF device by applying an external radiation field (10 mR/h–17 R/h) using two types of radiography sources: a ⁶⁰Co radiography camera for high-energy gamma emissions and an ¹⁹²Ir radiography camera for several low-energy gamma (0.604, 0.468, and 0.317 MeV) and decay daughter X-ray emissions. External radiation tests proved that radiation, in general, has a significant effect on the dead time or background at dose rates over 1 R/h for both the ¹⁹²Ir and ⁶⁰Co sources.     

The use of lead isotopic abundances in trace uranium samples for nuclear forensics analysis

Secondary ion mass spectrometry (SIMS), secondary electron microscopy (SEM) and X-ray analysis have been applied to the measurement of U-bearing particles with the intent of gleaning information concerning their history and/or origin. The lead isotopic abundances are definitive indicators that U-bearing particles have come from an ore-body, even if they have undergone chemical processing. SEM images and X-ray analysis can add further information to the study that may allude to the extent of chemical processing. The presence of “common” lead that does not exhibit a radiogenic signature is clear evidence of anthropogenic origin.     

Multicomponent nucleation: thermodynamically consistent description of the nucleation work

A thermodynamically consistent formula is derived for the nucleation work in multicomponent homogeneous nucleation. The derivation relies on the conservative dividing surface which defines the nucleus as having specific surface energy equal to the specific surface energy sigma0 of the interface between the macroscopically large new and old phases at coexistence. Expressions are given for the radius of the nucleus defined by the conservative dividing surface and by the surface of tension. As a side result, the curvature dependence of the surface tension sigmaT of the nucleus defined by the surface of tension is also determined. The analysis is valid for nuclei of any size, i.e., for nucleation in the whole range of conditions between the binodal and the spinodal of the metastable old phase provided the inequality sigmaT < or = sigma0 is satisfied. It is found that under the conditions of validity of the analysis the nucleation rate is higher than the nucleation rate given by the classical nucleation theory. The general results are applied to nucleation of unary liquids or solids in binary gaseous, liquid or solid mixtures.     

Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the ²³⁰Th/²³⁴U ratio was calculated from the measured ratios of ²³⁰Th/²³⁴Th and ²³⁴U/²³⁸U and from calculated ²³⁴Th/²³⁸U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The ²³⁴U interference on ²³⁴Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause.

     

Evaluating uranium radiochronometry by single-collector mass spectrometry for nuclear forensics: a multi-instrument investigation

Radiochronometric data, a key signature in evaluating the provenance and process history of nuclear material out of regulatory control, are conventionally acquired via multi-collector mass spectrometry. Here we explore the potential of age-dating by single-collector mass spectrometry. To evaluate model age accuracy/precision across different instrument designs, we performed ²³⁰Th–²³⁴U and ²³¹Pa–²³⁵U radiochronometry of CRM 125-A using two single-collector and one multi-collector plasma source mass spectrometers. Single-collector instruments produce accurate model ages for this uranium standard and thus hold promise for nuclear forensics radiochronometry. Increased acquisition of age information via multiple instrument designs will bolster the global response to nuclear interdictions.