Predicting the radiation tolerance of oxides

We have used atomistic computer simulations and ion beam irradiations to examine radiation damage accumulation in multicomponent oxides, We have developed contour energy maps via computer simulations to predict the effects of oxide structure and chemical composition on radiation-induced atomic disorder, defect migration, and swelling. Ion irradiation damage experiments have been perfonned on, pyrochlore and fluorite-structured oxide ceramics to test the predictions from computer models

Point-detect production and migration in plutonium metal at ambient conditions

Modeling thermodynamics and defect production in plutonium (Pu) metal and its alloys, has proven to be singularly difficult. The multiplicity of phases and the small changes in temperature, pressure, and/or stress that can induce phase changes lie at the heart of this difficulty, In terms of radiation damage, Pu metal represents a unique situation because of the large volume changes that accompany the phase changes. The most workable form of the metal is the fcc (6.) phase, which in practice the 6 phase is stabilized by addition of alloying elements such as Ga or AI. The thermodynamically stable phase at ambient conditions is the between monoclinic (a-) phase, which, however, is approximately 20 % lower in volume than the 6 phase. In stabilized Pu metal, there is an interplay between the natural swelling tendencies of fcc metals and the volume-contraction tendency of the underlying phase transformation to the thermodynamically stable phase. This study explores the point defect production and migration properties that are necessary to eventually model the long-term outcome of this interplay

Radiation response in fluorite-related systems with dual spatial length-scales.

International audienceFluorite-related materials are encountered in nuclear applications as advanced fuels and inert matrix for minor actinides. Several of these compounds display great resistance to radiation-induced amorphization. In these systems, there seem to be specific differences in the detailed response to radiation because of the competition between cation and anion spatial correlations describing their organization.Under irradiation, a sharp decrease of the characteristic spatial correlation length describing the O vacancy order is usually observed. But once radiation is switched off, the disordered fluorite phase is suddenly quenched to a broken-symmetry phase where domains with spatial correlations of the vacancies form and coarsen with time as the system tries to reach a local equilibrium on larger and larger scales. This process of return to equilibrium takes place maintaining a much longer correlation length of the cation sublattice, thus preserving a long-range crystallinity, so that the system behaves effectively as a paracrystal.We believe the small correlation length of the anion sublattice can affect the energy dissipation process in the material during the irradiation: the fluctuation-dissipation theorem establishes a relation between equilibrium correlation functions and linear response functions; excess energy can be dissipated because of the work done by the fluctuating viscous stresses at domains walls in resisting elastic strain fluctuations, in a way akin to the familiar processes of fluid dynamics, so that the energy dissipation is most effective at the smallest turbulence scales. The nonequilibrium dynamics of these open systems seems effective in dissipating the energy of the irradiation process and this can provide a universal pathway for searching extreme radiation resistance materials

Optimization of Ceramics for Nuclear Fuel and Waste Form Applications

We have used atomistic computer simulations and ion beam irradiations to examine radiation damage accumulation in oxides and nitrides. We have developed contour energy maps for oxides via computer simulations, to predict the effects of structure and chemical composition on radiation-induced atomic disorder, defect migration, and swelling. Ion irradiation damage experiments have been performed on fluorite and pyrochlore-structured oxide ceramics, as well as alkali halide-structured nitrides, to examine trends and to test the predictions from computer models. This presentation will examine both theoretical predictions and experimental results regarding radiation damage behavior in ceramics intended for nuclear fuel and waste form applications

Structural analysis of swift heavy ion irradiated β-Sc2Hf7O17 and γ-Sc2Hf5O13

International audienceComplex oxides have attracted attention as a candidate for nuclear waste immobilization materials to replace borosilicate glass. Knowledge of radiation-induced structural changes is of technological importance for developing the container materials. In this study, we performed 94 MeV Pb ion irradiation into β-Sc2Hf7O17 and γ-Sc2Hf5O13 pellets at room temperature, and examined their structural changes by grazing x-ray diffraction (GIXRD) and transmission electron microscopy (TEM). Polycrystallization occurs at the surface of β-Sc2Hf7O17, while the crystallinity was maintained in γ-Sc2Hf5O13: the former was more susceptible to radiation damage than the latter. The ordered rhombohedral β- and γ-phases transformed to disordered cubic fluorite phase with increasing ion fluence. A domain structure was observed in β-Sc2Hf7O17, and the interface between the ordered and disordered regions was found to be related to the domain boundary