Irradiation damage structures induced in pure Fe and Fe-Cr (up to 14%Cr) alloys by 2 MeV Fe+ ion irradiations in the temperature range 300-460°C were investigated by transmission electron microscopy. Specimens were irradiated in bulk to doses of 1.5 x 1019 Fe+/m2 (about 2.5 displacements per atom: dpa) and 4.5 x 1019 Fe+/m2 (about 7 dpa). In most cases, damage took the form of dislocation loops with diameters from 2-100nm; the loops were distributed uniformly within all the samples. At higher irradiation temperatures (400°C, 460°C), complex microstructures such as finger loops (50nm in width and 1 micron in length) and perpendicular <100> loop clusters, were observed in both pure Fe and Fe-Cr samples. Loop sizes and densities were seen to change as a function of irradiation temperature and dose. Loop sizes were seen to increase as the increase of irradiation temperatures and doses, while loop densities only increased with increasing doses and decreased as increasing temperatures. Loops with both types of Burgers vectors (<100> and ½<111>) were observed in all the samples. The proportion of <100> loops was higher in Fe than that in Fe-Cr alloys at the same irradiation condition, which has can be attributed to the high mobility of ½<111> loops in Fe, so that a large proportion of them will escape to the (001) foil surface. A transition in loop Burgers vectors as a consequence of increasing temperature was observed. In Fe, the proportion of <100> loops increased with increasing irradiation temperature from 40% at 300°C to 60% at 460°C. A similar trend was found in the Fe-Cr alloys, but due to the higher proportion of ½<111> loops in these alloys, the increase of <100> loops was not that obvious, being from 30% at 300°C to 45% at 460°C(Fe-11Cr). The effects of irradiation dose rate on the formation of dislocation loops by 2 MeV Fe+ ions were also investigated. These irradiations were carried out at 300°C with two different implantation dose rates: 6 x 10-4 dpa/s and 3 x 10-5 dpa/s. The implantation dose for both implantations was 0.38 x 1019 Fe+/m2 (0.5 dpa). Both the average loop size and loop densities for the Fe-Cr specimens subjected to the high dose rate irradiation were higher than that in the low dose rate irradiations. Take Fe-14Cr as an example, that the loop densities in high dose rate irradiation increased about 90% compared to that in low dose rate, and the average loop size in high dose rate irradiation was 30% larger than that in low dose rate irradiation. The ‘inside-outside contrast’ method was applied to determine the loop nature in all the samples. It was found that all the large loops (>5nm) are of interstitial type. Any vacancies are believed to exist in the form of small dislocation loops (<5nm) or sub-microscopic voids.

Protein structure models obtained from X-ray crystallography are subject to radiation damage. The resulting specific alterations to protein structures can be mistaken for biological features, or may obscure actual protein mechanisms, leading to misidentification or obscuration of biological insight. The radiation chemistry behind this site-specific damage is not well understood. Radiation damage processes progress in proportion to the dose absorbed by the crystal in the diffraction experiment. Doses can be estimated using existing software, but these assume idealised experimental conditions. To simulate complex diffraction experiments, including treatment of imperfect X-ray beam profiles and inhomogeneous dose distributions, a new program, RADDOSE-3D, was developed. RADDOSE-3D can be integrated into beamline software to provide convenient, more accurate, comparative, and publishable dose figures, also facilitating informed data collection decisions. There is currently no method to automatically detect specific radiation damage in protein structure models in the absence of an 'undamaged' reference model. Radiation damage research therefore generally relies on detailed observation of a few model proteins. A new metric, B_Damage, is designed and used to identify and quantify specific radiation damage in the first large-scale statistical survey of 2,704 published protein models, which are examined for the effects of local environments on site-specific radiation damage susceptibility. A significant positive correlation between susceptibility and solvent accessibility is identified. Current understanding of radiation damage progression is mostly based on a few consecutive structure model 'snapshots' at coarse dose intervals. The low sampling rate considerably limits the ability to identify varying site susceptibility and its causes. Real space electron density data are obtained for crystals of different mutants of a RhoGDI protein with very high sequence identity, to determine sensitising and stabilising factors for radiation induced structural changes. Utilising a newly developed data collection and analysis protocol, these changes could be tracked with unprecedented time resolution.

Maintaining the safe operation of nuclear power plants (NPPs) is crucial. This requires fully understanding the mechanism of long term irradiation and thermal ageing, as well as their effects, on components including the reactor pressure vessel (RPV). The research community is collecting data that will be required to support the case for extending the operation of western-type NPPs beyond that of 60 years. One of the current dilemmas faced by the long-term operation of RPVs is the formation of nanometre scale precipitates. These precipitates are known to cause embrittlement where it increases the ductile-to-brittle transition temperature of the RPV steels. The chemistry of these precipitates is strongly dependent on the chemistry of the RPV steels. In general, these precipitates can be categorised into two types, copper-rich precipitates (CRPs) and manganese-nickel (-enriched) precipitates (MNPs) [1, 2]. The concentration of copper in the precipitates depends on the bulk content of the steel [3]. The formation mechanism of the precipitates under neutron irradiation and thermal ageing, and their influence on material degradation at high neutron fluence (&Phi;t), is still unclear. To understand the long term precipitation under irradiation and thermal ageing, high nickel and copper containing RPV steels with a similar microstructure an chemical composition as those currently in service were subjected to either neutron irradiation (to high neutron fluences, &Phi;t &ge; 5 x 10²³ neutrons.m^-2) or thermal ageing (for as long as &asymp; 50,000 hours). CRPs and MNPs were both detected. The co-precipitation of the CRPs and MNPs were observed in thermally aged steels. The development of crystal structures in the CRPs is believed to be dependent on the size of the precipitates and the ambient temperature. When the CRPs reached a critical size, they underwent the martensitic transformation from BCC&rarr;9R&rarr;3R&rarr;FCC or FCT. The CRPs preferentially nucleate heterogeneously at the dislocation lines. Chemical analysis suggests that most of the CRPs are iron free. Under thermal ageing, the MNPs were found to precipitate at the interface of the CRPs and the matrix. These MNPs are found to be iron free too. Larger MNPs were often found to be at CPRs that were associated with dislocation lines. Also, based on the volume fraction observed, it is possible to suggest that the kinetics of nucleation and growth of the MNPs are relatively slow compared to the CRPs. This is in good agreement with the simulations reported in Refs. [4, 5]. It is the first time the MNPs are directly imaged from neutron irradiation low copper steels using electron microscopy. These irradiation-induced MNPs are densely populated in the neutron irradiated samples. It was found that the irradiation-induced MNPs are more sensitive to electron beams. It was thought that this was due to a relatively large amount of point defects present in the irradiation-induced MNPs.

<p>The four-electron reduction of dioxygen to water is the most exothermic non-photochemical reaction available to biology. A detailed molecular description of this reaction is needed to understand oxygen-based redox processes. Horseradish peroxidase (HRP) is a haem-containing redox enzyme capable of catalysing the reduction of dioxygen to water. We developed instrumentation and experimental methodology to capture and characterise by X-ray crystallography transient reaction intermediates in this reaction. </p><p>An instrument was designed (“the vapour stream system”) to facilitate reaction initiation, monitoring and intermediate trapping. In combination with single crystal microspectrophotometry, it was used to obtain conditions for capturing a reactive dioxygen complex in HRP. X-ray studies on oxidised intermediates can be difficult for various reasons. Electrons re-distributed in the sample through the photoelectric effect during X-ray exposure can react with high-valency intermediates. In order to control such side reactions during data collection, we developed a new method based on an angle-resolved spreading of the X-ray dose over many identical crystals. Composite data sets built up from small chunks of data represent crystal structures which received different X-ray doses. As the number of electrons liberated in the crystal is dose dependent, this method allows us to observe and drive redox reactions electron-by-electron in the crystal, using X-rays.</p><p>The methods developed here were used to obtain a three-dimensional movie on the X-ray-driven reduction of dioxygen to water in HRP. Separate experiments established high resolution crystal structures for all intermediates, showing such structures with confirmed redox states for the first time. </p><p>Activity of HRP is influenced by small molecule ligands, and we also determined the structures of HRP in complex with formate, acetate and carbon monoxide.</p><p>Other studies established conditions for successfully trapping the M-intermediate in crystals of mutant bacteriorhodopsin, but the poor diffraction quality of these crystals prevented high-resolution structural studies.</p>

The four-electron reduction of dioxygen to water is the most exothermic non-photochemical reaction available to biology. A detailed molecular description of this reaction is needed to understand oxygen-based redox processes. Horseradish peroxidase (HRP) is a haem-containing redox enzyme capable of catalysing the reduction of dioxygen to water. We developed instrumentation and experimental methodology to capture and characterise by X-ray crystallography transient reaction intermediates in this reaction. An instrument was designed (“the vapour stream system”) to facilitate reaction initiation, monitoring and intermediate trapping. In combination with single crystal microspectrophotometry, it was used to obtain conditions for capturing a reactive dioxygen complex in HRP. X-ray studies on oxidised intermediates can be difficult for various reasons. Electrons re-distributed in the sample through the photoelectric effect during X-ray exposure can react with high-valency intermediates. In order to control such side reactions during data collection, we developed a new method based on an angle-resolved spreading of the X-ray dose over many identical crystals. Composite data sets built up from small chunks of data represent crystal structures which received different X-ray doses. As the number of electrons liberated in the crystal is dose dependent, this method allows us to observe and drive redox reactions electron-by-electron in the crystal, using X-rays. The methods developed here were used to obtain a three-dimensional movie on the X-ray-driven reduction of dioxygen to water in HRP. Separate experiments established high resolution crystal structures for all intermediates, showing such structures with confirmed redox states for the first time. Activity of HRP is influenced by small molecule ligands, and we also determined the structures of HRP in complex with formate, acetate and carbon monoxide. Other studies established conditions for successfully trapping the M-intermediate in crystals of mutant bacteriorhodopsin, but the poor diffraction quality of these crystals prevented high-resolution structural studies.

Raman spectroscopy is a form of vibrational spectroscopy that is capable of probing biological samples at a molecular level. In this work it was used in the analysis of ionizing radiation-induced damage in DNA. Spectra of both simple, short-stranded DNA oligomers (SS-DNA) and the more complicated calf-thymus DNA (CT-DNA) were acquired before and after irradiation to a variety of doses from 0 to ~2000 Gy. In a technique known as ultraviolet resonance Raman spectroscopy (UVRRS), three UV wavelengths of 248, 257 and 264 nm were utilized in order to selectively enhance contributions from different molecular groups within the samples. Assignment of the spectral peaks was aided by the literature, as well as through analysis of UVRR spectra of short strands of the individual DNA bases obtained at each of the three incident UV wavelengths. Difference spectra between the irradiated and unirradiated samples were calculated and the samples exposed to ~2000 Gy showed significant radiation-induced features. Intensity increases of spectral peaks, observed primarily in the CT-DNA, indicated unstacking of the DNA bases and disruption of Watson-Crick hydrogen bonds, while intensity decreases of spectral peaks, observed only in the SS-DNA, indicated both base damage and the loss of structural integrity of the DNA molecule. The high molecular specificity of UVRRS allowed for precise identification of the specific bonds affected by the radiation, and the use of the varying incident wavelengths allowed for the observation of damage to moieties that would otherwise have been excluded. The use of UVRRS shows promise in the study of radiation-induced damage to DNA and would be well suited for extension to the study of more complicated biological systems.

Raman spectroscopy is a form of vibrational spectroscopy that is capable of probing biological samples at a molecular level. In this work it was used in the analysis of ionizing radiation-induced damage in DNA. Spectra of both simple, short-stranded DNA oligomers (SS-DNA) and the more complicated calf-thymus DNA (CT-DNA) were acquired before and after irradiation to a variety of doses from 0 to ~2000 Gy. In a technique known as ultraviolet resonance Raman spectroscopy (UVRRS), three UV wavelengths of 248, 257 and 264 nm were utilized in order to selectively enhance contributions from different molecular groups within the samples. Assignment of the spectral peaks was aided by the literature, as well as through analysis of UVRR spectra of short strands of the individual DNA bases obtained at each of the three incident UV wavelengths. Difference spectra between the irradiated and unirradiated samples were calculated and the samples exposed to ~2000 Gy showed significant radiation-induced features. Intensity increases of spectral peaks, observed primarily in the CT-DNA, indicated unstacking of the DNA bases and disruption of Watson-Crick hydrogen bonds, while intensity decreases of spectral peaks, observed only in the SS-DNA, indicated both base damage and the loss of structural integrity of the DNA molecule. The high molecular specificity of UVRRS allowed for precise identification of the specific bonds affected by the radiation, and the use of the varying incident wavelengths allowed for the observation of damage to moieties that would otherwise have been excluded. The use of UVRRS shows promise in the study of radiation-induced damage to DNA and would be well suited for extension to the study of more complicated biological systems.

Ce travail de recherche vise à étudier les propriétés élastiques par microscopie acoustique du combustible nucléaire dans trois situations particulières: combustible en utilisation normale en réacteur nucléaire, combustible stocké après la période d’irradiation et combustible en conditions extrêmes suite à un accident nucléaire. Les mesures réalisées sur les échantillons irradiés ont conduit à plusieurs résultats majeurs: validation d’une loi corrélant la vitesse des ondes de Rayleigh à la densité du dioxyde d’uranium irradié ou frais; détermination de la porosité dans le combustible irradié; évaluation du gonflement de la matrice en fonction du taux de combustion dans la gamme 0-100 GWdt-1M; développement d'un modèle empirique capable de prévoir la variation de module de Young en fonction du taux de combustion en prenant même en compte la teneur en dopants (Gd2O3, CeO2) ; quantification de l’évolution du module de Young du combustible suite à l'endommagement en stockage ; premières mesures sur du corium. Enfin, grâce au lien entre les propriétés thermiques et élastiques, différentes propriétés thermiques de l'UO2 ont été calculées en mesurant la vitesse de l'onde de surface de Rayleigh seule. / The focus of the present thesis is the determination of the elastic properties of nuclear fuel using high frequency acoustic microscopy. The nuclear fuel is considered under three different conditions: during its normal life in reactor, after its discharge and disposal in interim or long-term storage and subsequently to its severe degradation caused by a nuclear accident. Measurements performed on irradiated fuels allowed to validate a law between the density of fresh and irradiated fuel and the Rayleigh wave velocity; the determination of the irradiated fuel porosity and matrix swelling in the broad burnup range 0-100 GWdt-1M; the development of an empirical model capable of predicting the evolution of Young's modulus versus burnup correcting also for the additives content (Gd2O3, CeO2); Young's modulus evolution due to alpha-decay damage as in-storage condition; first corium measurements. Moreover, several UO2 thermal parameters were calculated only by means of the Rayleigh wave velocity thanks to the link between thermal and elastic properties.

In order to increase the waste loading efficiency of nuclear waste glasses, alternative composite structures are sought that trap molybdenum in a water-durable CaMoO4 phase. In this thesis, the formation and stability of CaMoO4 in a borosilicate glass against the attack of internal radiation was investigated. It is a fundamental study that simplified the composition to known contributors of molybdate speciation, and further splits the com- ponents of α and β-decay into integral parts that replicated both nuclear and electronic interactions. Irradiation experiments using 2.5 MeV β, 7 MeV Au, and 92 MeV Xe ions were enlisted to test the hypotheses of whether 100−1000 years of radiation damage given current waste loading standards would: (i) induce phase separation in homogeneous re- gions, (ii) increase the extent of existing phase separation, (iii) induce local annealing that could cause amorphisation of crystalline phases or increase mixing between amorphous phases, or (iv) cause some combination of the above. Results from XRD, SEM, EPR, and Raman spectroscopy suggest that powellite is stable against replicated radiation damage with only minor modifications observed. The main mechanisms of alteration involved: (i) thermal and defect-assisted diffusion, (ii) relaxation from the added ion’s energy, (iii) localised damage recovery from ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain, and led to longer-range modifications. It can be further concluded that no precip- itation or increased phase separation was observed in single-phased glasses. In isolated cases, radiation-induced precipitation of CaMoO4 occurred, but these crystallites were reamorphised at higher doses. At high SHI fluences, minor amorphisation of powellite was also observed, but this occurred alongside bulk-to-surface reprecipitation of CaMo- species. Overall, the components of internal radiation were often found to have opposing effects on the alteration of Si−O−B mixing in the glass, ion migration, and crystallite size. This led to the prediction that a steady-state damage structure could form from cumulative decay processes. These results suggest that CaMoO4 containing borosilicate GCs are resistant to radiation, and that excess molybdenum from increased waste loading can be successfully incorporated into these structures without altering the overall dura- bility of the wasteform. Furthermore, the identified saturation in modifications occurring around 8 x 10¹⁴ Xe ions/cm² can be used as a benchmark in future investigations on more complex systems where the maximum damage state is required.

La sécurité des installations nucléaires est constamment un souci majeur lors de leur exploitation, mais aussi lors de la conception de nouveaux réacteurs. Leurs durées de vie est limitée à cause des changements de comportement mécanique de leurs composants métalliques (principalement la cuve du réacteur mais aussi ses composants internes), qui sont accélérés ou induits par l’irradiation de neutrons. Une prédiction quantitative précise de ces changements, en fonction de la composition des matériaux et des conditions d'irradiation, est par conséquent un objectif de première importance pour la science des matériaux nucléaires. La modélisation est, de nos jours, considérée comme un complément vital aux approches expérimentales, avec l'objectif d’apporter une meilleure compréhension des processus physiques et chimiques qui se produisent dans les matériaux métalliques sous irradiation de neutrons.<p><p>La modélisation des effets de l'irradiation de neutrons dans les aciers est par nature un problème multi-échelle. Le point de départ est la simulation des cascades de collisions atomiques initiées par les neutrons à hautes énergies qui pénètrent dans le matériau, créant ainsi des défauts ponctuels mobiles. Différents modèles physiques, considérant des échelles de temps et de longueur croissantes, doivent être développés afin de convenablement tenir en compte de tous les différents processus qui provoquent des changements de comportement macroscopique, à cause de la présence de ces défauts ponctuels mobiles. En outre, des liens entre les différents modèles doivent être créés, parce que les prédictions de chacun d'entre eux doivent servir de paramètres d'entrée pour les modèles qui travaillent aux échelles supérieures. Dans cette thèse, un tel lien est créé entre le niveau atomique et les modèles à gros-grains, en développant un nouvel algorithme Monte-Carlo cinétique atomistique (MCCA), où le matériau est décrit comme une collection d'atomes occupant des sites cristallographiques réguliers. Le processus simulé est dès lors naturellement décomposé en séries d'évènements élémentaires activés thermiquement, correspondant à la migration des défauts ponctuels (lacunes ou interstitiels) vers des positions de proches voisins, qui sont en permanence en compétition en fonction de leurs fréquences d'occurrences respectives. Ces dernières sont calculées en fonction des énergies de migrations, qui sont elles-mêmes calculées avec peu d'approximations par une méthode qui prend en compte tous les effets de la relaxation statique et des interactions chimiques à longue portée. Le nouvel algorithme MCCA est par conséquent un modèle physique, entièrement basé sur un potentiel inter-atomique approprié qui est utilisé de la manière la plus complète possible, sans définir de paramètres empiriques qui devraient être, par exemple, fittés depuis des données expérimentales. Finalement, l'algorithme est accéléré de plusieurs ordres de grandeur en utilisant des réseaux de neurones artificiels (RNA), entraînés à prédire les énergies de migrations des défauts ponctuels en fonction de leur environnement atomique local.<p><p>Le nouvel algorithme MCCA est utilisé avec succès pour simuler des expériences de recuits (pour lesquels une seule lacune doit être introduite dans la boîte), afin de valider le modèle grâce à une comparaison directe de ses prédictions avec des résultats expérimentaux trouvés dans la littérature. Une comparaison très satisfaisante est accomplie pour deux alliages modèles importants pour la science des matériaux nucléaires. Dans les deux cas, l'évolution avec le temps de recuit du rayon moyen des précipités formés, ainsi que de leur densité, est en très bonne adéquation avec les mesures expérimentales trouvées dans la littérature, contrairement à ce que d'autres auteurs avaient jusqu’à présent réussi. Ensuite, l'algorithme est généralisé avec succès afin de permettre l'introduction d'un grand nombre de lacunes, ce qui est un des deux ingrédients nécessaires pour la simulation des effets de l'irradiation de neutrons dans les métaux. Cet accomplissement permet la simulation de processus longs et complexes, par exemple le calcul de coefficients de diffusions et temps de vies d'amats de cuivre-lacunes, qui sont des paramètres d'entrée nécessaires pour des modèles de simulation à gros-grains. Finalement, des preuves convaincantes sont apportées que l'algorithme MCCA peut être, dans un futur proche, généralisé d'avantage et permettre la prise en compte des interstitiels, ouvrant ainsi la voie vers la simulation de cycles complets d'irradiation.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished