Enhancement of adsorption capacity and separation of radioactive Xe/Kr at room temperature and above is a challenging problem. Here, we report a detailed structural refinement and analysis of the synchrotron X-ray powder diffraction data of Ni-DODBC metal organic framework with in situ Xe and Kr adsorption at room temperature and above. Our results reveal that Xe and Kr adsorb at the open metal sites, with adsorption geometries well reproduced by DFT calculations. The measured temperature-dependent adsorption capacity of Xe is substantially larger than that for Kr, indicating the selectivity of Xe over Kr and is consistent with the more negative adsorption energy (dominated by van der Waals dispersion interactions) predicted from DFT. Our results reveal critical structural and energetic information about host-guest interactions that dictate the selective adsorption mechanism of these two inert gases, providing guidance for the design and synthesis of new MOF materials for the separation of environmentally hazardous gases from nuclear reprocessing applications.

Massive, thick-walled pressure vessels are permanent nuclear reactor structures that are exposed to a damaging flux of neutrons from the adjacent core. The neutrons cause embrittlement of the vessel steel that growswith dose (fluence), as manifested by an increasing ductile-to-brittle fracture transitiontemperature. Extending reactor life requires demonstrating that large safety margins against brittle fracture are maintained at the higher neutron fluence associated with beyond 60years of service.Here synchrotron-based x-ray diffraction and small angle x-ray scattering measurements are used to characterize highly embrittling nm-scale Mn-Ni-Si precipitates that develop in the irradiated steels at high fluence. These precipitates lead to severe embrittlement that is not accounted for in current regulatory models. Application of the complementary techniques has, for the very first time, successfully identified the crystal structures of the nanoprecipitates, while also yielding self-consistent compositions, volume fractions and size distributions. I. INTRODUCTIONReactor pressure vessels (RPVs) are the primary permanent component of light water reactors (LWRs). RPVs experience irradiation embrittlement that increases with neutron fluence (see Refs[1-3] for overviews of the embrittlement phenomena and underlying mechanisms). Ensuring that large safety margins are maintained in the face of embrittlement is required to extend LWR service life to beyond 60 years. Embrittlement is marked by increases in the ductile-to-brittle transition fracture temperature (ΔT) of RPV steels. The ΔT is primarily caused by irradiation hardening (Δσ y ) associated with the formation of nm-scale precipitates and solute-defect complexes that act as obstacles to dislocation glide.At low to intermediate neutron fluence, significant hardening and embrittlement is primarily caused by the formation of coherent, transition phase copper rich precipitates (CRP). Trace impurity amounts ofCu(< 0.35 at.%) are insoluble in steels and rapidly phase separate due to radiation enhanced diffusion (RED)at © 2015. This manuscript version is made available under the Elsevier user license

A classical potential for ZrC is developed in the form of a modified second-moment approximation with emphasis on the strong directional dependence of the C-Zr interactions. The model has a minimal set of parameters, 4 for the pure metal and 6 for the cross interactions, which are fitted to the database of cohesive energies of B1-, B2-, and B3-ZrC, the heat of formation, and most importantly, the atomic force constants of B1-ZrC from first-principles calculations. The potential is then extensively tested against various physical properties, none of which were considered in the fitting. Finite temperature properties such as thermal expansion and melting point are in excellent agreement with experiments. We believe our model should be a good template for metallic ceramics.

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The implantation of noble gas atoms into metals at high gas concentrations can lead to the self-organization of nanobubbles into superlattices with symmetry similar to the metal host matrix. Here, we examine the influence of implantation parameters on the formation and structure of helium gas bubble superlattices within a tungsten host matrix to uncover mechanistic insight into the formation process. The determination of the size and symmetry of the gas bubbles was performed using a combination of small angle x-ray scattering and transmission electron microscopy. The former was demonstrated to be particularly useful in determining size and structure of the gas bubble superlattice as a function of irradiation conditions. Prior to the formation of a superlattice, we observe a persistent substructure characterized by inter-bubble spacings similar to those observable when the gas bubble superlattice has formed with very large ordering parameters. As the implantation fluence increases, the inter-bubble ordering parameter decreases, indicating improved ordering, until a superlattice is formed. Multiple implantation-specific differences were observed, including a temperature-dependent superlattice parameter that increases with increasing temperature and a flux-dependent superlattice parameter that decreases with increasing flux. The trends quantified here are in excellent agreement with our recent theoretical predictions for gas bubble superlattice formation and highlight that superlattice formation is strongly dependent on the diffusion of vacancy and implanted He atoms.