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In the context of nuclear security, uranium ore concentrates (UOCs) play an important role: they are traded in large quantities and this makes their use “out of regulatory control” a possible scenario. Once an incident of illicit trafficking o f n uclear m aterial is detected, an understanding of its origin and production process is required; this implies the necessity to use analytical techniques able to measure characteristic parameters (e.g. physical, chemical, isotopic characteristics of the nuclear materials) which are referred to, in the field o f t he n uclear f orensics, a s signatures. The present study investigates the potential of image texture analysis (i.e. the angle measure technique), combined with the spectrophotometric determination of colours for the evaluation of the origin of several UOCs. The use of different multivariate statistical techniques allows the categorization of about 80 different samples into a few groups of UOCs powders, which makes this approach a promising method complementing the already established methods in nuclear forensics.

Nuclear forensic analysis of uranium oxide fuel pellets and the respective data interpretation have proven to be important elements of the investigative process when such material is found out of regulatory control. Uranium oxide fuel pellets are produced at industrial scale and have to meet tight technical specifications. Variations in the production process of different manufacturers or fuel fabrication facilities offer an additional source of information. The compilation of such information in a nuclear materials database has proven to be a highly valuable resource. In consequence, measureable material properties (referred to as "signatures") such as the isotopic composition, the physical dimensions, the chemical impurities, the products of the radioactive decay of uranium and the microstructure allow establishing the processing history of the material. To this end, dedicated analytical methods have to be developed and suitable methods for data evaluation and interpretation need to be utilised. The successful application of these nuclear forensic tools is illustrated with two case studies on real incidents of illicit nuclear trafficking of uranium oxide fuel pellets. [ABSTRACT FROM AUTHOR]

We present here for the first time the production of 3‐ to 5‐nm–sized thoria nanopowders by decomposition of Th‐hydroxide under hot compressed water and their consolidation by high‐pressure spark plasma sintering into dense nanostructured ThO2 with grain size of 50 nm. [ABSTRACT FROM AUTHOR]

The formation of the high burnup structure (HBS) is possibly the most significant example of the restructuring processes affecting commercial nuclear fuel in-pile. The HBS forms at the relatively cold outer rim of the fuel pellet, where the local burnup is 2-3 times higher than the average pellet burnup, under the combined effects of irradiation and thermo-mechanical conditions determined by the power regime and the fuel rod configuration. The main features of the transformation are the subdivision of the original fuel grains into new sub-micron grains, the relocation of the fission gas into newly formed intergranular pores, and the absence of large concentrations of extended defects in the fuel matrix inside the subdivided grains. The characterization of the newly formed structure and its impact on thermo-physical or mechanical properties is a key requirement to ensure that high burnup fuel operates within the safety margins. This paper presents a synthesis of the main findings from extensive studies performed at JRC-Karlsruhe during the last 25 years to determine properties and behaviour of the HBS. In particular, microstructural features, thermal transport, fission gas behaviour, and thermo-mechanical properties of the HBS will be discussed. The main conclusion of the experimental studies is that the HBS does not compromise the safety of nuclear fuel during normal operations. [ABSTRACT FROM AUTHOR]

The aqueous chemistry of Np(V) in alkaline 0.01 to 5.5 M CaCl2 solutions at T = 23 ± 2 ℃ was thoroughly studied by long-term batch solubility experiments from both over- and undersaturation. Applying a comprehensive set of experimental and spectroscopic techniques including Vis/NIR and Np L3-edge EXAFS, the solubility controlling Np(V) solid phases and the predominant aqueous Np(V) species were identified. The results demonstrate that the solubility behavior of Np(V) in alkaline CaCl2 solutions differs completely from the one reported for alkaline NaCl and NaClO4 solutions: as solubility limiting solid phases, three so far not considered Ca-Np(V)-OH compounds were identified and their solubility and stability in CaCl2 solutions analyzed: CaNpO2(OH)2.6Cl0.4 · 2H2O(s) (I) (metastable), Ca0.5NpO2(OH)2 · 1.3H2O(s) (II) (long-term metastable) and Ca0.5NpO2(OH)2(s) (III) (stable). The considerably higher stability of these (qua)ternary phases which readily form in alkaline CaCl2 solutions from oversaturation (addition of NpO2+) and undersaturation (addition of binary NpO2OH(am)) limit the Np(V) equilibrium concentrations to values that are up to 3 log-units lower compared to those for NpO2OH(am) in NaCl and NaClO4 systems. Based on systematic evaluation of the pH dependence (solubility curve slopes), Vis/NIR and EXAFS spectroscopic information, unhydrolysed NpO2+ and innersphere chloro complexes, NpO2Cl(aq) and Ca z[NpO2Cl]2 z+ with z = 1 (EXAFS, Vis/NIR), were identified as prevailing Np(V) species in less alkaline solutions with pHm < 10.5 for [CaCl2] ≤ 2.0 M and [CaCl2] > 2.0 M, respectively. The steep increase of the Np(V) solubility for pHm > 11 with slopes of approximately + 2.5 (for solid phase (I)) and + 3 (for solids (II) and (III)) as well as the Np L3-edge EXAFS results for the aqueous Np(V) species in 4.5 M CaCl2/pHm ≈ 12 confirm the presence of ternary Ca-Np(V)-OH complexes Ca x[NpO2(OH)2]2 x-1 ( x ≈ 1 is estimated within the thermodynamic evaluation in a subsequent paper (Fellhauer, D., Altmaier, M., Gaona, X., Lützenkirchen, J., Fanghänel, Th., Np(V) solubility, speciation and solid phase formation in alkaline CaCl2 solutions. Part II: Thermodynamics and implications for source term estimations of nuclear waste disposal (Radiochim. Acta, DOI 10.1515/ract-2015-2490), in the following referred to as 'Part II' [1]) and Ca y[NpO2(OH)5]2 y-4 with y ≈ 2.4 ± 1.5 (EXAFS result) as predominant Np(V) hydrolysis species in solution for [CaCl2] ≥ 0.25 and pHm > 10.5. The thermodynamic evaluation and implications of the new findings with respect to source term estimations for nuclear waste disposal scenarios are discussed in 'Part II' [1]). [ABSTRACT FROM AUTHOR]

UO2 samples doped with 6, 11, 22 mol% lanthanum were examined before and after air oxidation. To verify the formation of uranium-lanthanum-mixed oxide solid solutions, powder X-ray diffraction ( XRD) analyses of the crystalline phases in the materials were carried out. The presence of oxygen vacancies in the La-doped UO2 samples was identified by Raman spectrometry. It was evidenced by changes induced in the Raman spectra by air oxidation. This latter was carried out either by increasing the Raman laser power or by thermally treating the samples at 500 K for 370 h. In addition, oxidation behavior differences of pure and La-doped UO2 samples were reported by comparing XRD and Raman results of the samples before and after air oxidation. It was shown that the concentration of the M4O9 (M: U, La) phase increased with increasing content of La, whereas inhibition for the formation of M3O8 phase was observed. [ABSTRACT FROM AUTHOR]

The author discusses the study on the release of fission products from the fuel during a nuclear reactor accident. Tackled is the release of the radioactive gases in the environment as well as the destruction of the reactor cores through the Three Mile Island accident in Pennsylvania. Also explored are health and environmental effects during a nuclear accident.

Fission products and minor actinides arising from spent fuel reprocessing are immobilized in a borosilicate matrix known as high level nuclear waste glass (i.e. HLW glass). Glass packages are intended eventually for disposal in a geological repository. The long-term behavior of HLW glass subjected to radiation by long-life radionuclides must thus be investigated with respect to geological disposal. The present article focuses on HLW glass alteration under irradiation conditions by providing a general description of the methodology and illustrating it through examples. The scientific approach adopted to study irradiation potential effects combines experiments performed on radionuclide-doped borosilicate glasses and non radioactive glasses externally irradiated, focusing on all the different leaching stages (initial, drop and residual steps). Different parameters, such as the cumulative dose, the dose rate, the electronic and the ballistic impacts, are taken into account. As under disposal conditions the glass radioactivity will be quickly governed by alpha decay (after 300 years), the results presented here to illustrate the methodology concern the behavior of alpha-doped glasses. Concerning the initial alteration rate, both the alpha activity and the alpha cumulative dose have been studied and no significant effects have been observed. The structural variations observed on the irradiated solid are thus not important enough to induce any changes in the initial chemical reactivity between glass and water. Concerning the drop and residual alteration steps, the behavior of a 239 Pu-doped glass having an alpha dose rate corresponding to a HLW glass after around 1500 years has shown no effect on the kinetics, nor on the altered layer morphology. Moreover, the plutonium appears to be highly retained in the alteration layer (∼ 95%). [ABSTRACT FROM AUTHOR]

The long-term behavior of high-level nuclear glass subjected to alpha/beta radiation by long-life radionuclides must be investigated with respect to geological disposal. This study focuses on the effects of alpha and beta radiations on the chemical reactivity of R7T7 glass with pure water, mainly on the residual alteration rate regime. Glass specimens doped with 0.85 wt% 239PuO2 (α emitter) and 0.24 wt% 99TcO2 (β emitter) that simulate alpha and beta dose rate corresponding to long-term disposal conditions are leached under static conditions in argon atmosphere at 90°C, in initially pure water and at a high surface-area-to-volume ratio (S/V = 20/cm). The alteration rate is monitored by the release of glass alteration tracer elements (B, Na, and Li). Radiation effects on the leached glass and its gel network are characterized by SEM and TEM analyses. Plutonium and technetium releases are also measured by radiometry, and their chemical oxidation state is assessed by measuring the pH and reduction-oxidation potential of the leachates. The results do not highlight any significant effect of alpha/beta radiation on the residual alteration of these doped glasses. These observations are consistent with solid characterizations, which show that a protective layer can be formed under such irradiation fields. Under our experimental conditions (Eh~380 mV/SHE, pH90°C = 8-8.6), very low concentrations of soluble plutonium are measured in the leachate, indicating strong plutonium retention, whereas technetium performs as a soluble element and is not retained in the altered layer. [ABSTRACT FROM AUTHOR]

R7 T7-type glass samples doped with different concentrations of 244 Cm and stored for different time periods to produce different levels of accumulated radiation damage were analyzed by differential scanning calorimetry to better understand the structural evolution of R7T7 nuclear glass due to the accumulation of α radiation damage. The stored energy and fictive temperature were observed to increase as a function of the α decay dose. The stored energy saturates at about 1018 α decays·g−1, whereas the fictive temperature continues to increase and saturates at about 6-7 × 1018 α decays·g−1. This discrepancy was interpreted in terms of different effects of energy lost during α decay on the glass structure due to electronic stopping and nuclear stopping. This study demonstrates that the stored energy is affected by both phenomena, whereas the fictive temperature variation depends mainly on elastic collisions. The increase of fictive temperature with the cumulative α dose is direct evidence that the energy lost by recoil nuclei induces the formation of a new structure similar to a fast-quenched glass. [ABSTRACT FROM AUTHOR]

The transmutation of minor actinides (in particular, Np and Am), which are among the main contributors to spent fuel α-radiotoxicity, was studied in the SUPERFACT irradiation. Several types of transmutation UO2-based fuels were produced, differing by their minor actinide content (241Am, 237Np, Pu), and irradiated in the Phénix fast reactor. Due to the high content in rather short-lived alpha-decaying actinides, both the archive, but also the irradiated fuels, cumulated an alpha dose during a laboratory time scale, which is comparable to that of standard LWR fuels during centuries/millenaries of storage. Transmission Electron Microscopy was performed to assess the evolution of the microstructure of the SUPERFACT archive and irradiated fuel. This was compared to conventional irradiated spent fuel (i.e., after years of storage) and to other 238Pu-doped UO2 for which the equivalent storage time would span over centuries. It could be shown that the microstructure of these fluorites does not degrade significantly from low to very high alpha-damage doses, and that helium bubbles precipitate. [ABSTRACT FROM AUTHOR]

Fundamental knowledge on intrinsic plutonium colloids is important for the prediction of plutonium behaviour in the geosphere and in engineered systems. The first synthetic route to obtain salt-free intrinsic plutonium colloids by ultrasonic treatment of PuO2 suspensions in pure water is reported. Kinetics showed that both chemical and mechanical effects of ultrasound contribute to the mechanism of Pu colloid formation. In the first stage, fragmentation of initial PuO2 particles provides larger surface contact between cavitation bubbles and solids. Furthermore, hydrogen formed during sonochemical water splitting enables reduction of Pu(IV) to more soluble Pu(III), which then re-oxidizes yielding Pu(IV) colloid. A comparative study of nanostructured PuO2 and Pu colloids produced by sonochemical and hydrolytic methods, has been conducted using HRTEM, Pu LIII-edge XAS, and O K-edge NEXAFS/STXM. Characterization of Pu colloids revealed a correlation between the number of Pu-O and Pu-Pu contacts and the atomic surface-to-volume ratio of the PuO2 nanoparticles. NEXAFS indicated that oxygen state in hydrolytic Pu colloid is influenced by hydrolysed Pu(IV) species to a greater extent than in sonochemical PuO2 nanoparticles. In general, hydrolytic and sonochemical Pu colloids can be described as core-shell nanoparticles composed of quasi-stoichiometric PuO2 cores and hydrolyzed Pu(IV) moieties at the surface shell. [ABSTRACT FROM AUTHOR]

The article analyzes the emerging trend in the development of nuclear reactors using materials that can handle very high energy and particle fluxes. A recent symposium on nuclear materials dealt with ways of predicting the behavior of material when subjected to high irradiation, causes of damage to metals and storage of spent fuel. It concludes that the development of next generation nuclear reactors requires a synergy between experimental data and simulations based on a multi scale approach.

Abstract: Studying self-irradiated materials is an ideal means to investigate the effect of the damage on material structure and to better understand the behavior of irradiated nuclear fuels. In this context, X-ray diffraction, X-ray absorption spectroscopy and transmission electron microscopy have been used to investigate self-irradiation damaged AmO2. Combining these techniques allows studying the microstructure and the variation of the fluorite structure at both short-range and long-range order. Thus, the increase of both interatomic distances and lattice parameter was shown, as well as the presence of nanometer sized He bubbles and dislocation loops. As confirmed by the observed high-level of crystallinity, the fluorite structure exhibits a high radiation tolerance, which is confirmed by the low increase of the lattice parameter. This could be explained by a self-annealing mechanism of the created defects at room temperature. [Copyright &y& Elsevier]

In search for chemically stable americium compounds with high power densities for radioisotope sources for space applications, AmVO 3 and AmVO 4 were prepared by a solid-state reaction. We present here their crystal structure at room temperature solved by powder X-ray diffraction combined with Rietveld refinement. Their thermal and self-irradiation stabilities have been studied. The oxidation states of americium were confirmed by the Am M 5 edge high-resolution X-ray absorption near-edge structure (HR-XANES) technique. Such ceramics are investigated as potential power sources for space applications like radioisotope thermoelectric generators, and they have to endure extreme conditions including vacuum, high or low temperatures, and internal irradiation. Thus, their stability under self-irradiation and heat treatment in inert and oxidizing atmospheres was tested and discussed relative to other compounds with a high content of americium.

AmPO 4 was prepared by a solid-state reaction method, and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. The purity of the monazite-like phase was confirmed by spectroscopic (high-resolution solid-state 31 P NMR and Raman) and microscopic (SEM-EDX and TEM) techniques. The thermal and self-irradiation stability have been studied. The compound is stable under argon and air atmosphere at least up to 1773 K. It remains crystalline under self-irradiation for circa two months, with a crystallographic volume swelling of ∼1.5%, and then is amorphizing over a year. However, microcrystals are present in the amorphous material even after a two year period of time. All these characteristics are discussed in relation to the potential application of AmPO 4 as a stable form of Am in radioisotope power sources for space exploration and of behavior of the monazites under irradiation.

Actinide research at the nanoscale is gaining fundamental interest due to environmental and industrial issues. The knowledge of the local structure and speciation of actinide nanoparticles, which possibly exhibit specific physico-chemical properties in comparison to bulk materials, would help in a better and reliable description of their behaviour and reactivity. Herein, the synthesis and relevant characterization of PuO 2 and ThO 2 nanoparticles displayed as dispersed colloids, nanopowders, or nanostructured oxide powders allow to establish a clear relationship between the size of the nanocrystals constituting these oxides and their corresponding An(iv) local structure investigated by EXAFS spectroscopy. Particularly, the first oxygen shell of the probed An(iv) evidences an analogous behaviour for both Pu and Th oxides. This observation suggests that the often observed and controversial splitting of the Pu-O shell on the Fourier transformed EXAFS signal of the PuO 2 samples is attributed to a local structural disorder driven by a nanoparticle surface effect rather than to the presence of PuO 2+ x species., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The use of X-ray elemental analysis tools like energy dispersive X-ray (EDS) is described in the context of the investigation of nuclear materials. These materials contain radioactive elements, particularly alpha-decaying actinides that affect the quantitative EDS measurement by producing interferences in the X-ray spectra. These interferences originating from X-ray emission are the result of internal conversion by the daughter atoms from the alpha-decaying actinides. The strong interferences affect primarily the L X-ray lines from the actinides (in the typical energy range used for EDS analysis) and would require the use of the M lines. However, it is typically at the energy of the actinide's M lines that the interferences are dominant. The artifacts produced in the X-ray analysis are described and illustrated by some typical examples of analysis of actinide-bearing material.