Discrepancies in Thorium Oxide Solubility Values: a New Experimental Approach to Improve Understanding of Oxide Surface at Solid/Solution Interface

Accepted for publication in Radiochimica ActaThe solubility of ThO2(cr) was studied since many years but a large discrepancy in solubility values is noticed in the literature. The present work suggests that this discrepancy is related to differences in the surface properties of thorium oxide. To understand the role of surface properties on solubility values, we conducted experiments with ThO2(cr) spheres with reproducable surface properties. Batch dissolution experiments were conducted in 0.01 M NaCl solution at pH = 3.0 and 4.0 for periods of time up to 270 days. The solutions were spiked with 229Th to determine precipitation (sorption) rates of thorium, while dissolution rates were determined by measuring 232Th released from ThO2(cr) spheres. We assume that 229Th atoms are exchanged only with active sites involved in Th-dissolution. Using 229Th as local sensor of attachement and detachment processes at the ThO2(cr) surface under close-to-equilibrium conditions, allows to assess surface reactivity of the solid during solubility experiments

New Methods for HTR Fuel Waste Management

International audienceConsidering the need to reduce waste production and greenhouse emissions by still keeping high energy efficiency, various 4th generation nuclear energy systems have been proposed. As far as graphite moderated reactors are concerned, one of the key issues is the large volumes of irradiated graphite encountered (1770 m3 for fuel elements and 840 m3 for reflector elements during the lifetime (60 years) of a single reactor module [1]). With the objective to reduce volume of waste in the HTR concept, it is very important to be able to separate the fuel from low level activity graphite. This requires to separate TRISO particles from the graphite matrix with the sine qua non condition to not break TRISO particles in case of future embedding of particles in a matrix for disposal. According to National Regulatory Systems, in case of limited graphite waste production or of short duration HTR projects (e.g. in Germany), direct disposal without separation is acceptable. Nevertheless, in case of large scale deployment of HTR technology, such approach is not economical and sustainable. Previous attempts in graphite management (furnace, fluidised bed and laser incinerations and encapsulation matrices) dealt with graphite matrix only. These are the reasons why we studied the management of irradiated compact-type fuel element. We simulated the presence of fuel in the particles by using ZrO2 kernels. Compacts with ZrO2 TRISO particles were manufactured by AREVA NP. Two original methods have been studied. First, we tested high pressure jet to erode graphite and clean TRISO particles. Best erosion rate reached about 0.18 kg/h for a single nose ending. Examination of treated graphite showed a mixture of undamaged TRISO particles, particles that have lost the outer pyrolytic carbon layer and ZrO2 kernels. Secondly, we studied the thermal shock method by immerging successively graphite into liquid nitrogen and hot water to cause fracturing of the compact. This produced particles and graphite fragments with diameter ranging from several centimetres to less than 500 µm. This relatively simple and economic method may potentially be considered as a pre-treatment step and be coupled with other method(s) before reprocessing and recycling for example

Surface site density, silicic acid retention and transport properties of compacted magnetite powder

International audienc

The effect of high power ultrasound on an aqueous suspension of graphite

Ultrasound treatment was used to study the decrease of the granulometry of graphite, due to the cavitation, which allows the erosion by separating grains. At a smaller scale, cavitation bubble implosion tears apart graphite sheets as shown by HRTEM, while HO and H radicals produced from water sonolysis, generate oxidative and reductive reactions on these sheet fragments. Such reactions form smaller species, e.g. dissolved organic matter. The methodology proposed is very sensitive to unambiguously identifying the in situ composition of organic compounds in water. The use of the atmospheric pressure chemical ionization (APCI) Fourier transform mass spectrometry (FTMS) technique minimizes the perturbation of the organic composition and does not require chemical treatment for analysis. The structural features observed in the narrow range (m/z < 300) were mainly aromatic compounds (phenol, benzene, toluene, xylene, benzenediazonium, etc.), C4-C6 alkenes and C2-C10 carboxylic acids. Synthesis of small compounds from graphite sonication has never been reported and will probably be helpful to understand the mechanisms involved in high energy radical reactions

Report on existing vocational European Fission Training Schemes and their accreditation

This report was produced as a deliverable in the frame of the ENEN Plus project. It provides an overview of all twenty-five projects carried out under the Euratom Fission Training Schemes (EFTS) and their main achievements. Almost all projects are completed to date except for three. The EFTS's ultimate goal is to develop a European passport for Continuous Professional Development, which relies on the principles of modularity of courses and common qualification criteria, a common mutual recognition system, and the facilitation of teacher, student and worker mobility across the EU. The conclusions of this review will be published in a separate report.JRC.G.10-Knowledge for Nuclear Security and Safet

Predisposal conditioning, treatment, and performance assessment of radioactive waste streams

Before the final disposal of radioactive wastes, various processes can be implemented to optimise the waste form. This can include different chemical and physical treatments, such as thermal treatment for waste reduction, waste conditioning for homogenisation and waste immobilisation for stabilisation prior to packaging and interim storage. Ensuring the durability and safety of the waste matrices and packages through performance and condition assessment is important for waste owners, waste management organisations, regulators and wider stakeholder communities. Technical achievements and lessons learned from the THERAMIN and PREDIS projects focused on low- and intermediate-level waste handling is shared here. The recently completed project on Thermal Treatment for Radioactive Waste Minimization and Hazard Reduction (THERAMIN) made advances in demonstrating the feasibility of different thermal treatment techniques to reduce volume and immobilise different streams of radioactive waste (LILW) prior to disposal. The Pre-Disposal Management of Radioactive Waste (PREDIS) project addresses innovations in the treatment of metallic materials, liquid organic waste and solid organic waste, which can result from nuclear power plant operation, decommissioning and other industrial processes. The project also addresses digitalisation solutions for improved safety and efficiency in handling and assessing cemented-waste packages in extended interim surface storage

Etude du cycle biogéochimique du sélénium dans l'environnement

Le but de ce travail est de déterminer le cycle biogéochimique du sélénium, et plus particulièrement des sélénites, dans un environnement proche de la surface. Pour cela, nous avons réalisé des études de sorption sur différentes phases minérales en système mono et multi-phasiques. Nous avons également réalisé des expériences pour étudier le devenir du sélénium dans un système-sol_plantes_microorganismes.(i) Les expériences de sorption des sélénites sur différentes phases minérales ont validé la méthode dite des membranes de dialyse et ont montré qu'il n'y avait pas d'additivité des capacités de sorption dans des systèmes à plusieurs phases minérales. La présence de Si aqueux relâché par la bentonite réduit la sorption du Se sur la goethite en occupant les sites de sorption.(ii) L'étude de l'influence des substances humiques (HA, FA) sur les capacités de sorption des différentes phases minérales vis-à-vis des sélénites a montré que ces substances diminuent la sorption du Se sur la goethite. De plus, ces expériences ont montré que les HA/FA ne complexent pas le sélénium.(iii) Les expériences rhizoplants nous ont permis de calculer des facteurs de transfert du Se des sols vers le ray-grass. Une application de ces facteurs de transfert dans un scénario de migration et de transfert du Se à partir d'un site de stockage des déchets HAVL, a donné une dose effective annuelle vers l'Homme comprise entre2,3 x 10-6 et 5,9 x 10-6 Sv.an-1The aim of this work is to determine the biogeochemical cycle of selenium, especially selenites, in a subsurface environment. To do so, we studied Se sorption on different mineral phases in single or multi-phase systems. We also conducted experiments to investigate the fate of selenium in a soil-plants microorganisms system. (i) Sorption experiments of selenites on different mineral phases validated the dialysis membranes method and showed that there was no additivity of the sorption capacity in systems composed of several minerals phases. The presence of aqueous Si released by bentonite reduced Se sorption on goethite by occupying the sorption sites.(ii) The study of the influence of humic substances (HA, FA) on the sorption capacities of different mineral phases has shown that these substances decrease Se sorption on goethite. Moreover, these experiments have shown that HA/FA do not complex selenium.(iii) Rhizoplants experiments allowed us to calculate transfer factors of soil Se toward rye-grass. In a scenario of migration and transfer of Se from a radioactive waste disposal, the application of these transfer gave an annual effective dose to Humans comprised between 2,3 x 10-6 and 5,9 x 10-6 Sv.y-1NANTES-BU Sciences (441092104) / SudocSudocFranceF