Various secondary phases formed during alteration/dissolution of HLW (high-level nuclear waste) borosilicate glass represent a significant retention potential for radionuclides including divalent actinides. The trioctahedral smectite, hectorite, Na0.7[Li0.7Mg5.3Si8O20(OH)4], is one of the secondary phases identified within the alteration layer of corroded HLW glass. Numerous studies have clearly shown that many radionuclides are associated with clay minerals and the migration of radionuclides is strongly reduced by complexation. Due to the structural complexity and chemical variability of smectites, sorption of radionuclides involves several sorption mechanisms: (1) adsorption via inner-sphere and outer-sphere complexation; (2) cation exchange in the interlayer; and (3) incorporation into the smectite structure. Up to now, it was not known whether trivalent actinides such as Cm(III) and Am(III) become incorporated into the crystal structure of clay minerals like hectorite. We have used a new method, developed by Carrado et al. (1997b), to synthesize a Eu- and a Cm-containing hectorite, utilizing Cm(III) and chemically homologous Eu(III) coprecipitated with Mg(OH)2 as a precursor. X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy identified the reaction products unambiguously as hectorite. The sorption mechanisms of Eu associated with the synthesized hectorite were investigated by time-resolved laser fluorescence spectroscopy (TRLFS). An unhydrated Eu species (fluorescence lifetime 930 µs) and a partly hydrated Eu species (fluorescence lifetime 381 µs) could be identified. The unhydrated Eu species can be interpreted as incorporating Eu(III) into the hectorite structure or a remaining X-ray amorphous silica phase. The spectra of Eu hectorite and the Eu silica complexation are too similar to permit differentiation between these species, but dialysis experiments demonstrated the close association of the unhydrated Eu species with the crystalline hectorite phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements identified the same incorporated Eu species as long as the Eu hectorite was stable under acidic conditions. The stability of the Eu hectorite could be shown by the dialysis experiment over a time period of 160 h. Between 160 und 500 h, hectorite became unstable and a new silica phase was detected. In addition, TRLFS measurements of the Cm-containing hectorite confirmed the incorporation of actinides in the smectite structure. The Cm-hectorite and Cm-silica species can be differentiated unambiguously by TRLFS. In order to differentiate between coprecipitated and surface-sorbed Eu species, batch sorption studies were performed with synthetic Eu-free hectorite. For the surface-sorbed Eu species, a fluorescence lifetime of 284 µs (3.1 H2O molecules) was found, which clearly differs from the coprecipitated species with a fluorescence lifetime of 930 µs. The different lifetimes indicate a different chemical environment. Based on all observations it seems to be very likely that trace amounts of Cm/Eu occupy a distorted octahedral site in the hectorite.

Mass attenuation coefficients (MACs) of Th, U, Np, and Pu for oxygen X-rays have been experimentally determined using an electron microprobe. The MACs were obtained by measuring relative X-ray intensities emitted from ThO2, UO2, NpO2, and PuO2 targets, for incident electron energies from 5 to 30 keV, and processing them with the help of the computer program XMAC. The accuracy of the measured MACs is estimated to be better than 5%. Results are compared with MAC tabulations commonly used in electron probe microanalysis as well as with theoretical photoionization calculations. It is concluded that the MACs implemented in the Monte Carlo simulation program PENELOPE which are based on the photoionization cross-section calculations of Sabbatucci & Salvat [(2016). Theory and calculation of the atomic photoeffect. Rad Phys Chem121, 122–140], provide the best agreement with our measurements. The use of different MAC schemes for the analysis of mixed actinide oxide materials is discussed.

The Chernobyl accident in 1986 resulted in the widespread identification of the post-accident presence of radioactive (or ‘hot’) particles across large areas of Eastern and Central Europe. Such particles arise from direct deposition and also from condensation and interactions on particle surfaces during and following the deposition of soluble fallout. Identification of the presence and nature of hot particles is necessary in order to determine the long-term ecological impact of radioactive fallout. This paper describes several techniques for the identification and characterization of hot particles in soil samples from Belarus. In addition to new results from the use of gamma spectrometry, we include two novel instrumentation approaches that have been developed and applied to Chernobyl fallout-contaminated soils. The first, ‘differential’ autoradiography, utilizes a photographic film sandwich to characterize the nature of the ionizing radiation emitted from samples. In this paper we show that differential autoradiography can not only identify hot particle presence in soil, but can also determine the dominant radionuclide in that particle. The second approach, sector field ICP-MS (ICP-SFMS), can provide rapid, high-precision determination of the actinides, including the transuranic actinides, that characteristically occur in hot particles originating from weapons fallout or fuel matrices. Here, ICP-SFMS is shown to yield sufficiently low detection limits for plutonium isotopes (with the exception of 238Pu) to enable us to confirm negligible presence of plutonium in areas outside the Chernobyl exclusion zone, but with high levels of fission-product contamination.

Understanding the biogeochemical behaviour of actinides in the environment is essential for the longterm stewardship of radionuclide contaminated land. Plutonium is of particular concern due its high radiotoxicity, long half-life and complex chemistry, with these factors contributing to the limited literature available on its environmental behaviour. Here, we investigate the biogeochemistry of Pu in contaminated soil as microbial processes have the potential to mobilize Pu through numerous mechanisms including the reduction of Pu(IV) to the potentially more mobile Pu(III). After the addition of glucose to stimulate microbial activities, there was a substantial shift in the 16S rRNA gene profile of the extant microbial communities between days 0 and 44 with an increase in Clostridium species, known glucose fermenters which have been reported to facilitate the reduction of Pu(IV) to Pu(III). A minor increase in Pu mobility was observed at day 44, returning to initial levels by day 118. The negligible change in Pu mobility, despite the onset of reducing conditions and changing mineralogy, would suggest the Pu is highly refractory. This information is important for developing remediation options for Pu-contaminated soils, suggesting that managing legacy Pu in situ may be preferred to mobilization via the stimulation of metal-reducing bacteria.

The capabilities of the asymmetrical flow field-flow fractionation (AsFlFFF) technique coupled with inductively coupled plasma mass spectrometry and UV–Vis spectrophotometry in the characterization of synthetic and natural colloidal samples are demonstrated in two different systems.The first system is a sol of hectorite which was co-precipitated in the presence of Lu. The results show that hectorite nanoparticles can be mobilized from a bulk sample and that they still contain the dopant Lu, which is homogeneously incorporated into the hectorite crystal structure. Thesecond system is a natural groundwater from the Gorleben site on the northern German plain, which is being tentatively explored to assess its suitability as a nuclear waste repository. Colloidal matter heterogeneity is evident in this system. Alkaline-earth elements are mainly found as ionicspecies. Rare earth elements (REEs) and actinides are distributed in two main colloidal fractions: the heavier REEs and U are concentrated in the <4 nm fraction corresponding to the size range of organic colloidal particles, whereas lighter REEs and Th are concentratedin colloidal particles between 4 and 18 nm in size that are both organic and inorganic in nature. Similar results are reported for another sample from the same site, collected ∼2 km from the first one, demonstrating the homogeneity of the aquifer system and/or a possible colloid migrationpathway. The extent of the reversibility of colloid–radionuclide interactions remains to be evaluated.

During the past 70 years, more than 2000 metric tonnes of Pu, and substantial quantities of the ‘minor’ actinides such as Np, Am and Cm, have been generated in nuclear reactors. Some of these transuranium elements can be a source of energy in fission reactions (e.g. 239Pu), a source of fissile material for nuclear weapons (e.g. 239Pu and 2Np), and of environmental concern because of their long half-lives and radiotoxicity (e.g. 239Pu and 237Np). There are two basic strategies for the disposition of these transuranium elements: (1) to ‘burn’ or fission the actinides using nuclear reactors or accelerators; (2) to dispose of the actinides directly as spent nuclear fuel or to ‘sequester’ the actinides in chemically durable, radiation-resistant materials that are also suitable for geological disposal. For the latter strategy, there has been substantial interest in the use of actinide-bearing minerals, especially isometric pyrochlore, A2B2Oi (A = rare earths; B = Ti, Zr, Sn, Hf), for the immobilization of actinides, particularly plutonium, both as inert matrix fuels and nuclear waste forms. Systematic studies of rare-earth pyrochlores have led to the discovery that certain compositions (B = Zr, Hf) are stable to very high doses of α-decay event damage. Recent developments in the understanding of the properties of actinide-bearing solids have opened up new possibilities for the design of advanced nuclear materials that can be used as fuels and waste forms. As an example, the amount of radiation damage that accumulates over time can be controlled by the selection of an appropriate composition for the pyrochlore and a consideration of the thermal environment of disposal. In the case of deep borehole disposal (3—5 km), the natural geothermal gradient may provide enough heat to reduce the amount of accumulated radiation damage by thermal annealing.

Materials designed for nuclear waste disposal include a range of ceramics, glass ceramics and glass waste forms. Those with crystalline phases have provided the momentum for studies of minerals as a means to understand aspects of waste-form crystal chemistry, behaviour in aqueous systems and radiation damage over geological periods of time. Although the utility of natural analogue studies varies, depending upon the degree of analogy to the proposed geological repository and other factors such as chemical composition, the available data suggest that Th-U host phases such as brannerite, monazite, pyrochlore, zircon and zirconolite are resistant generally to dissolution in aqueous fluids at low temperatures. Geochemical durability may or may not extend to hydrothermal systems depending on the specifics of fluid composition, temperature and pressure. At elevated temperatures, for example, davidite may break down to new phase assemblages including titanite, ilmenite and rutile. Perovskite is generally less resistant to dissolution at low temperatures and breaks down to TiO2, releasing A-site cations to the aqueous fluid. Studies of radiation damage indicate that the oxide and silicate phases become amorphous as a result of the gradual accumulation of alpha-recoil collision cascades. Monazite tends to remain crystalline on geological time scales, a very attractive property that potentially eliminates major changes in physical properties such as density and volume, thereby reducing the potential for cracking, which is a major concern for zircon. In spite of recent success in describing the behaviour of Th-U minerals in geological systems, considerable work remains in order to understand the P-T-X conditions during alteration and T-t history of the host rocks.

Stalagmites and stalactites, as observed within natural caves, may develop inside geological repositories during constructional and post-operational periods. It is therefore important to understand actinide sorption within such materials. Towards this, experimental studies were carried out with 233U, 238Np (VI), 238Np (IV), 239Pu and 241Am radiotracers using natural speleothem samples collected from the Dharamjali cave of the Kumaon Lesser Himalayas, India. Petrological/mineralogical studies showed that natural speleothems have three general domains: (1) columnar calcite; (2) microcrystalline calcite; and (3) botryoidal aragonite – each with ferruginous materials. Results showed that all domains of speleothems can take up >99% actinides, irrespective of valence state and pH (1–6 range) of the solution. However, distribution coefficients were found to be at a maximum in aragonite for most of the actinides. Such data are very important for long-term performance and safety assessments of the deep geological repositories planned for the disposal of high-level nuclear wastes.

Actinide-based nuclear ceramics, oxides particularly, are not only used as fuel in nuclear power reactors (uranium and plutonium) but are also used/envisaged as materials for electrical power sources in space probes (plutonium or americium). These actinides are all alpha-emitters, some having rather short half-lives. As a result of their strong alpha-activity, the actinide-based materials cumulate radiation damage and radiogenic helium. The stability of such materials needs to be assessed and understood for predicting the long-term stability of not only spent fuel in storage/disposal conditions but also of electrical power sources to be used in space probes. This paper describes the specific transmission electron microscope microstructure analyses of aged 238PuO2, 238Pu-doped UO2 (to simulate aged spent nuclear fuel), and of 241AmO2 samples (candidate electrical power source) and makes the correlation of the observed defects with other properties like helium thermal desorption and lattice parameter. It is shown that these fluorite structured materials resist to high alpha-damage levels and can accommodate large quantities of helium.

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.

La maîtrise du risque d'exposition interne à des radionucléides émetteurs alpha, pour les travailleurs des chantiers de maintenance des centrales PWR d'EDF, repose sur l'identification et la quantification de la contamination des circuits primaires. Les moyens de protection sont adaptés en fonction de l'analyse de risque préalable. En 2001, une expérimentation réalisée sur le site de Cattenom lors d'un arrêt de tranche présentant des défauts d'étanchéité du combustible, basée sur des mesures de radionucléides émetteurs α, a permis de définir un facteur réaliste de mise en suspension des particules de 10-6 m-1. Pour cet arrêt de tranche, une surveillance adaptée des travailleurs a été mise en place en collaboration avec les services de médecine du travail et de radioprotection. Elle était basée sur une estimation préalable du niveau de contamination alpha, confirmée par des mesures sur frottis, une surveillance atmosphérique par balise, la mise en place de protections individuelles et collectives, et le suivi collectif par l'analyse de mouchages sur des agents sélectionnés en fonction de leur poste de travail et des mesures individuelles complémentaires (surveillance de l'excrétion fécale). Cette surveillance a permis de valider un suivi de chantier approprié, les protections collectives et individuelles mises en œuvre, et de vérifier lors cet arrêt de tranche l'absence de contamination des agents surveillés.

Le rendement d'extraction de l'uranium a été étudié par extraction liquide-liquide, à l'aide d'une molécule macrocyclique, le calix[6]arène, 46, fonctionnalisé par des groupements acidecarboxylique. La phase aqueuse comprenait l'uranium en présence d'ions sodium et la phase organique le calixarène dissous dans le benzène. L' étude des paramètres d'extraction a permis deproposer un mécanisme d'extraction. Le rendement d'extraction augmente avec le pH et atteint un maximum voisin de 100% pour un pH>3,7. Sur des solutions contenant en plus de l'uranium desions sodium, marquées au 22-Na et/ou du plutonium 239, l'extraction de l'uranium reste optimale. Sur des échantillons d'urine, après minéralisation, environ 100% de l'uranium sont extraits par lecalixarène. Ces premiers résultats montrent que le calixarène choisi présente une structure adéquate vis-à-vis de la structure de coordination de l'ion uranyle, permettant ainsi une extractionsélective de l'uranium.

La méthode utilisée en routine pour déterminer une éventuelle contamination par des actinides, émetteurs alpha, est la mesure de la fraction éliminée dans les excreta (urine et/ou fèces). Laprocédure actuelle se compose de deux étapes, tout d'abord une séparation radiochimique sélective de chaque élément présent puis, après préparation d'une source électrodéposée, la mesure deson activité par spectrométrie alpha. Dans un souci de simplification de cette procédure, on évalue ici les performances de l'analyse des actinides par spectrométrie de masse, pour deuxtechniques particulières l'ICP-MS et le SIMS. L'utilisation des trois outils analytiques (spectrométrie alpha, ICP-MS, SIMS) est étudiée sur la base de résultats récents provenant de lalittérature et de ceux obtenus dans le laboratoire. Sur la base de ces résultats, le présent article analyse les avantages propres à chaque technique.

La dosimétrie des expositions internes aux radionucléides incorporés repose sur une connaissance aussi complète que possible du comportement des substances radioactives dans l'organisme.Ceci est essentiel pour interpréter les mesures d'activité faites dans le corps et ses émonctoires et les exprimer sous forme de quantités incorporées et de doses engagées. On décrit ici entermes généraux les voies d'incorporation, les transferts au sang, la distribution et la rétention dans les organes puis l'excrétion des radionucléides. L'ensemble de ces processus biocinétiquescomplexes est schématisé de façon à pouvoir être représenté par des modèles mathématiques accessibles au calcul. Depuis une dizaine d'années, la Commission internationale de protectionradiologique a entrepris la révision systématique de toutes ses recommandations pour tenir compte de l'évolution des connaissances : révision des facteurs de pondération du risque stochastique,révision complète du modèle respiratoire, révision de nombreux facteurs d'absorption digestive, élaboration de modèles spécifiques de certains organes et de certains éléments. Cette démarche aconduit à réactualiser la plupart des coefficients de dose pour les travailleurs.