Si le cycle du thorium possède plusieurs avantages par rapport au cycle U/Pu, notamment une meilleure régénération de la matière fissile en spectre thermique et une production moindre d'actinides mineurs, il présente plusieurs limites. L'une d'elles est la présence, dans le combustible thorié irradié, d'232U. Cet isotope est le précurseur d'un rayonnement γ de 2.6 MeV. Cette thèse a, en partie, pour objectif d'étudier les différents paramètres influençant la synthèse de ce noyau dans divers types de combustibles et de réacteurs.L'autre partie de ce travail consiste à estimer l'impact de cet indésirable sur la radioprotection de l'aval du cycle. Dans ce but, un ensemble d'outils, permettant le calcul des spectres énergétiques des différents rayonnements émis par la matière radioactive, a été spécialement développé. Ces outils, dont la véracité a été éprouvée par l'intermédiaire de plusieurs benchmarks, fait partie intégrante de ce travail de thèse. / The thorium cycle is a good candidate for replacing the current U/Pu cycle since the fissile nucleus of the cycle, 233U, has neutronic properties favourable to a much better regeneration of fissile material in thermal reactors. Moreover, the production of minor actinides is significantly reduced. However, the use of Thorium is only viable if the spent fuel is reprocessed to recover the fissile 233U that does not exist in nature. This reprocessing will involve a heavy industrial infrastructure, particularly since thorium based spent fuel contains small quantities of 232U that is the mother of the hard gamma emitter (208Tl) of 2.6 MeV. The goal of this thesis is, firstly, to study the parameters related to the synthesis of 232U in several kind of fuels and reactors. In a second part, the thesis focuses on the impact on radioprotection of the back end of the fuel in case of switching from the current uranium (U/Pu) cycle to the thorium (Th/U) cycle. For this last purpose, CHARS (CHAracterization of Radioactives Sources) was developed during this thesis. This code, validated by several benchmarks, handles the calculation of radiation sources in all aspects of the fuel cycle.

Dans le but d'étudier les possibilités de gestion avancée du plutonium dans les réacteurs actuels, 8 stratégies de multi-recyclage du plutonium dans des REP sont étudiées. Suite à des études à l'équilibre, il a été montré que, en utilisant des assemblages homogènes, l'utilisation du thorium ne permet pas de réduire les inventaires de plutonium en cycle à l'équilibre ni la production d'américium. En répartissant les différents types de combustibles au sein d'un même assemblage, certaines stratégies thoriées permettent cependant d'obtenir des inventaires et des productions d'américium inférieur aux meilleures stratégies utilisant uniquement le cycle uranium. Cependant dans tous les cas, le faible taux de conversion des combustibles thoriés en REP conduit à l'impossibilité de faire baisser la consommation de ressources de plus de quelques pour-cent par rapport aux stratégies sans thorium. Afin d'étudier la transition, une participation active au développement du code de scénario CLASS a eu lieu. Elle a aboutie à la simulation de deux scénarios parmi ceux étudiés à l'équilibre avec CLASS. Ces simulations ont montrées des écarts avec les scénarios simulés précédemment. Les causes majeures de ces écarts ont été identifiées et quantifiées. / In order to study the possibility of advanced management of plutonium in existing reactors, 8 strategies for plutonium multi-recycling in PWRs are studied. Following equilibrium studies, it was shown that, by using homogeneous assemblies, the use of thorium cannot reduce the plutonium inventory of equilibrium cycle or production of americium. By distributing the different fuel types within the same assembly, some thoriated strategies allow however lower inventories and lower production americium best strategies using only the uranium cycle. However, in all cases, low fuel conversion theories in PWRs makes it impossible to lower resource consumption more than a few percent compared to strategies without thorium. To study the transition, active participation in development of the scenario code CLASS has been taken. It led to the two simulation scenarios among those studied in equilibrium with CLASS. These simulations have shown discrepancies with previously simulated scenarios. The major causes of these differences were identified and quantified.

Comparer de manière approfondie la réponse des différents outils isotopiques choisis (Li, B et U) durant l’altération chimique dans un profil déjà connu (e.g. le profil du Sommet sur le Bassin versant du Strengbach ; Ackerer, 2017) afin de dégager les mécanismes moteurs des fractionnements isotopiques de chacun de ces éléments pour faire le lien entre la réponse de ces outils lors de l’altération chimique et remonter ainsi au régime d’altération des roches. Développer les observations réalisées sur le profil du Sommet et les appliquer sur cinq autres profils d’altération répartis sur l’ensemble du bassin versant en se concentrant sur la fraction <2µm. Cela permettra de voir si les observations faites dans le premier profil se retrouvent dans les autres profils et si nous sommes capables de remonter au régime d’altération. Étudier de manière préliminaire comment évolue le signal isotopique de l’altération chimique acquis dans les profils d’altération au cours du transport sédimentaire et s’il est possible de déterminer le régime d’altération d’un bassin versant à partir des sédiments de ce même bassin. / In-depth comparison of the response of various selected isotopic tools (Li, B and U) during chemical weathering in an already known profile (eg the Summit profile in the Strengbach watershed, Ackerer, 2017) to identify the driving mechanisms of isotopic fractionations of these elements to link the response of these tools compared to the chemical alteration to go back to the alteration regime. Develop the observations made on the Summit profile and apply them to five other weathering profiles distributed over the entire watershed focusing on the <2μm fraction. This will make it possible to see if the observations made in the first profile are found in the other profiles and if we are able to go back to the alteration regime. Preliminarily investigate how the isotopic signal of chemical alteration acquired in alteration profiles evolves during the sediment transportation and if it is possible to determine the alteration regime of a watershed from it sediments.

<p>Metal alkyls have a variety of uses including important intermediates in a variety of  processes. In this research, a thorium bis-alkyl species was fully characterized and explored for its potential reactivity, specifically for the formation of thorium bis-amide complexes. A series of three thorium bis-amide complexes was synthesized and characterized in this work. Additionally, several pathways have been attempted to synthesize an actinide alkylidene within this project including the use of a homoleptic tetrabenzyl complex, the use of diazoalkanes through the loss of dinitrogen, deprotonation of alkyls, and reducing a metallacycle complex. However, many of these did not result in products that suggest that an alkylidene was formed. These reactions ranged from being thermally unstable, decomposing, not reacting, or forming multiple products and being unable to discern one major product.<br> </p>

LD2668 .T4 1947 A3 / Master of Science

Application of precision laser spectroscopy and optical clock technology to the ground and metastable, first excited state of the ²²⁹Th nucleus at < 10 eV has significant potential for use in optical frequency metrology and tests of variation of fundamental constants. This work is a report on the development of required technologies to realize such a nuclear optical clock with a single, trapped, laser cooled ²²⁹Th³⁺ ion. Creation, trapping, laser cooling, and precision spectroscopy are developed and refined first with the naturally occurring isotope, ²³²Th. These technologies are then extended to laser cooling and precision laser spectroscopy of the electronic structure of ²²⁹Th³⁺. An efficient optical excitation search protocol to directly observe this transition via the electron bridge is proposed. The extraordinarily small systematic clock shifts are estimated and the likely extraordinarily large sensitivity of the clock to variation of the fine structure constant is discussed.

Na década de 70 operou-se no IPEN/CNEN-SP uma instalação piloto para estudos do processamento de diferentes concentrados de tório obtidos do tratamento químico da monazita com intuito da obtenção de compostos de tório de pureza nuclear. Esta instalação passou a operar em escala industrial em 1985, gerando em torno de 25 toneladas de resíduo até meados de 2002, quando encerrou suas atividades. Este resíduo contendo tório e terras raras foi denominado Retoter (Resíduo de Tório e Terras Raras) e armazenado no galpão de Salvaguardas do IPEN. O presente trabalho estuda o tratamento deste resíduo, visando questões ambientais, radiológicas e tecnológicas. Estudaram-se dois processos cromatográficos para a separação do tório das terras raras. Um deles, a cromatografia de extração, onde o agente extrator fosfato de tri-n-butila foi suportado em resinas poliméricas Amberlite XAD16. O outro processo, estudado para fins comparativos, já que o material utilizado na cromatografia de extração é inédito no que diz respeito à separação do tório, foi a cromatografia de troca iônica utilizando resinas catiônicas fortes DOWEX 1-X8. Estudou-se, também, o processo cromatográfico de extração com o agente extrator DEHPA suportado em Amberlite XAD16 para o fracionamento, em grupos, dos elementos das terras raras. O tório foi separado com elevado grau de pureza para fins estratégicos e as terras raras recuperadas, livres de tório, foram testadas como catalisadores na reforma de etanol para a geração de hidrogênio, o qual é utilizado em células a combustível para a geração de energia elétrica. / In the 70s a pilot plant for studies of different concentrates processing obtained from the chemical processing of monazite was operated at IPEN / CNEN-SP, with a view to obtaining thorium of nuclear purity. This unity was operated on an industrial scale since 1985, generating around 25 metric tons of residue and was closed in 2002. This waste containing thorium and rare earths was named Retoter (Rejeito de Tório e Terras Raras, in portuguese) and stored in the IPEN Safeguards shed. This paper studies the treatment of the waste, aimed at environmental, radiological and technology. Were studied two cases for the chromatographic separation of thorium from rare earths. One of them was the chromatographic extraction, where the extracting agent tributyl phosphate was supported on polymeric resins Amberlite XAD16. The other method is studied for comparison purposes, since the material used in chromatographic extraction is unprecedented with regard to the separation of thorium, was the ion-exchange chromatography using DOWEX 1-X8 strong cationic resin. Was studied also the chromatographic process of extraction with the extracting agent DEHPA supported on Amberlite XAD16 for the fractionation in groups of rare earths elements. Thorium was separated with high purity for strategic purposes and rare earths recovered free from thorium, were tested as a catalyst for ethanol reforming to hydrogen obtaining which is used in fuel cells for power generation.

The Enhanced Actinide Removal Plant (EARP) located at Sellafield, is a key facility for processing nuclear effluents in the UK. The EARP process decontaminates radioactive waste effluent by inducing the coprecipitation of Fe(III) along with any radionuclides in solution. The resulting radioactive solid phase is then separated from the decontaminated aqueous phase by ultrafiltration processes over several weeks. In the future the EARP facility's role will be expanded to treat effluents produced from nuclear decommissioning activities. However there remains a limited understanding around the mechanisms of radionuclide removal from solution and subsequent sequestration within the solid phase under conditions relevant to such industrial effluent treatment facilities. In this work, the fate of U(VI) and Th(IV) were investigated during the EARP process. XRD and TEM analyses revealed that the solid product from the EARP coprecipitation process was 2-line ferrihydrite which transformed over time to form hematite, with some goethite formation observed in the Th containing system. During this coprecipitation process U was initially removed from solution by adsorption to ferrihydrite as a bidentate, edge-sharing surface complex associated with ternary carbonate complexes. As the U containing system was aged, a maximum range of 61 - 75% U became consistently incorporated within the newly formed hematite phase for a wide range of systems containing 6 orders of magnitude total U:Fe molar ratio. Such a constant proportion of incorporated U suggests that this incorporation occurs during a particle mediated mechanism of hematite growth, such as oriented attachment. Interestingly, Th was removed from solution during the EARP coprecipitation process by a combination of both adsorption and occlusion mechanisms. EXAFS analyses revealed that the local coordination environment of Th associated with the solid phase altered considerably with increased aging time, and correspondingly Th became increasingly recalcitrant to remobilisation over time suggesting the formation of further occluded or even incorporated Th species within the transforming iron (oxyhydr)oxide phases. This thesis progresses the fundamental understanding of radionuclide interactions with iron (oxyhydr)oxide phases during coprecipitation and aging processes under conditions relevant to industrial waste treatment processes such as EARP.

The ocean is both a repository and reactor for chemicals at the Earth’s surface. As chemicals enter the ocean they are taken up by organisms, transported by currents, reacted with particle surfaces, and eventually buried at the seafloor. This dynamic set of chemical processes and exchanges are encapsulated by the term biogeochemistry. Marine biogeochemistry can be broadly deconstructed into two parts: ocean interfaces and internal cycling. Ocean interfaces are where chemical constituents enter and leave the ocean, including the air-sea boundary, mid-ocean ridges, continental margins, and rivers. Internal cycling is how chemical constituents are reacted, transported, taken up by organisms, and redistributed within the ocean. For a complete understanding of marine biogeochemical cycles, the input, output, and internal cycling rates of major and trace elements must be quantified. However, this rate information is difficult to infer from the observational snapshots of chemical concentrations typically collected on oceanographic expeditions. The long-lived radioisotopes of thorium (Th) and protactinium (Pa) provide an opportunity to quantify these elusive biogeochemical rates. The radiogenic isotopes 230Th and 231Pa are produced at a uniform rate throughout the water column by uranium decay. A third isotope, 232Th, is primordial and brought to the ocean by the dissolution of lithogenic matter. While uranium is highly soluble, Th and Pa are highly insoluble, and are rapidly removed from solution by adsorption onto settling particle matter. Due to their insolubility and known input rates, 230Th and 231Pa have well-constrained 1-d mass budgets between radiogenic production and scavenging removal. This thesis explores new ways Th and Pa isotopes can be used to understand and quantify rates of biogeochemical processes in the South Pacific Ocean, and to assess how measurements of sedimentary Th and Pa isotopes can be used to study these processes in the geologic past. In chapter 1, I characterize the effects of submarine hydrothermal activity on the distributions of 230Th and 231Pa, finding strong removal due to adsorption by Fe and Mn oxide particles. In chapter two, I utilize the radioactive disequilibria of two additional radiogenic thorium isotopes with much shorter half-lives, 234Th and 228Th, to constrain the kinetics of Th scavenging by hydrothermal particles. Chapter three switches gears towards quantifying the internal cycling of particulate organic carbon in the subtropical South Pacific. Using a new method based on measurements of particulate 230Th, I generated high-resolution water column profiles of particulate organic carbon flux to constrain carbon regeneration lengthscales in both oligotrophic and oxygen minimum zone settings. In chapter 4, I demonstrate the importance of isopycnal mixing in transporting 230Th, 231Pa, and 232Th into the Pacific Southern Ocean, showing the first high-resolution dissolved Th and Pa data from the region. Chapter 5 provides estimates of dust input spanning the South Pacific using two methods based on paired 230Th-232Th, evaluates the flux of dust-borne iron, and discusses the impacts on measured and modeled nitrogen fixation rates in the South Pacific gyre. Finally, in chapter 6 I present enigmatic profiles of Th and Pa isotopes from the semi-enclosed Peru and Bauer Basins, with anomalous Th and Pa removal extending 1-2km above the seafloor. I hypothesize that these depletions are related to the extent of water mass contact the seafloor, allowing for scavenging removal of Th and Pa by resuspended sediments.

Le Phosphate Diphosphate de Thorium (β-PDT) est considéré comme une matrice<br />céramique potentielle en vue de l'immobilisation des actinides en formation géologique<br />profonde. Il s'est avéré donc impératif d'étudier les effets de l'irradiation sur la structure de<br />cette céramique et les conséquences sur sa durabilité chimique.<br />Des échantillons de β-PDT et des solutions solides associées de β-PDTU ont été irradiés<br />puis altérés en solution aqueuse. Selon la valeur du TEL électronique, le β-PDT peut<br />s'amorphiser totalement ou partiellement. Par ailleurs, la capacité de recristallisation du<br />matériau amorphe par recuit thermique a été démontrée. Les tests de lixiviation menés sur ces<br />échantillons irradiés ont montré une influence significative de la fraction amorphe sur la<br />vitesse de dissolution normalisée qui augmente d'environ un facteur 10 entre le matériau non<br />irradié et le matériau amorphe. Corrélativement, la fraction amorphe modifie le temps requis<br />pour atteindre les conditions de saturation associées aux équilibres thermodynamiques. En<br />revanche, elle ne présente aucune influence ni sur d'autres paramètres cinétiques, tels que<br />l'énergie d'activation du processus de dissolution ou l'ordre partiel par rapport aux protons, ni<br />la nature de la phase néoformée identifiée comme le Phosphate HydrogénoPhosphate de<br />Thorium Hydraté (PHPTH).<br />Des échantillons de β-PDTU ont aussi été irradiés sous rayonnements γ et α pendant les<br />tests de lixiviation afin d'étudier les effets de la radiolyse du milieu lixiviant sur la vitesse de<br />dissolution du matériau. Il est apparu que les espèces radiolytiques intervenant dans le<br />mécanisme de dissolution étaient peu stables, disparaissant rapidement dès la fin de<br />l'irradiation. Leur caractère fortement oxydant vis-à-vis de l'uranium tétravalent permet d'expliquer la différence de comportement entre les cations métalliques (U et Th)