[en] The crack propagation mechanisms of γ-titanium aluminides with fully lamellar microstructure have been studied using in-situ deformation in the Atomic Force Microscope (AFM). AFM demonstrated the unique capability to detect elastic as well as plastic deformation during in-situ tests from topography changes on the surface. It was found that the crack nucleation, which can occur at γ/γ and α₂/γ interfaces as well as inside the γ-phase, is always preceded by strong local elastic deformation. No cracking inside the α₂-phase was observed. The elastic and plastic deformation was confined inside the γ-phase and especially pronounced near interfaces which can be explained by the differences of the elastic and plastic deformation behavior of the γ- and α₂- phase.

[en] The nuclear waste management section of the Institute of Energy and Climate Research IEK-6 in Juelich is focused on research on radiochemistry aspects/materials science relevant for the long-term safety of nuclear waste storage and disposal. Studies on innovative waste management strategies include partitioning o actinides and the development of ceramic waste forms. Structural research is covering solid state chemistry, crystallography and computational science to model actinide containing compounds. With respect to waste management concepts nondestructive essay techniques, waste treatment procedures and product quality control strategies were developed.

[en] Due to the use of nuclear energy about 17.000 t (27.000 m³) of high level waste and about 300.000 m³ of low and intermediated level waste will have accumulated in Germany until 2022. Research in the Institute of Energy and Climate Research (IEK-6), Nuclear Waste Management and Reactor Safety Division focuses on fundamental and applied aspects of the safe management of nuclear waste - in particular the nuclear aspects. In principle, our research in Forschungszentrum Juelich is looking at the material science/solid state aspects of nuclear waste management. It is organized in several research areas: The long-term safety of nuclear waste disposal is a key issue when it comes to the final disposal of high level nuclear waste in a deep geological formation. We are contributing to the scientific basis for the safety case of a nuclear waste repository in Germany. In Juelich we are focusing on a fundamental understanding of near field processes within a waste repository system. The main research topics are spent fuel corrosion and the retention of radionuclides by secondary phases. In addition, innovative waste management strategies are investigated to facilitate a qualified decision on the best strategy for Germany. New ceramic waste forms for disposal in a deep geological formation are studied as well as the partitioning of long-lived actinides. These research areas are supported by our structure research group, which is using experimental and computational approaches to examine actinide containing compounds. Complementary to these basic science oriented activities, IEK-6 also works on rather applied aspects. The development of non-destructive methods for the characterisation of nuclear waste packages has a long tradition in Juelich. Current activities focus on improving the segmented gamma scanning technique and the prompt gamma neutron activation analysis. Furthermore, the waste treatment group is developing concepts for the safe management of nuclear graphite. Within the product quality control group (PKS) 16 scientists and engineers are currently working on the qualification of radioactive waste on behalf of the Federal Office for Radiation Protection (BfS). The nuclear safeguards group is coordinating the joint safeguards R and D programme between IAEA and BMWi. Research and development activities are integrated into national and international research programms and cooperations. They represent a substantial part of the Helmholtz Research programme ''Nuclear Safety Research''. Material science for nuclear waste management is the research subject of IEK-6, Nuclear Waste Management part. (orig.)

[en] This is the third bi-annual report of the Nuclear Waste Management section of the Institute of Energy and Climate Research (IEK-6) at Forschungszentrum Juelich since 2009 - almost a tradition. Our institute has seen two more years with exciting scientific work, but also major changes regarding nuclear energy in Germany and beyond. After the reactor accident in Fukushima (Japan) in 2011, it was decided in Germany to phase out electricity production by nuclear energy by 2022. It seems clear, that the decommissioning of the nuclear power plants will take several decades. The German nuclear waste repository Konrad for radioactive waste with negligible heat generation (all low level and some of the intermediate level radioactive waste) will start operation in the next decade. The new site selection act from 2013 re-defines the selection procedure for the German high level nuclear waste repository. Independently of the decision to stop electricity production by nuclear energy, Germany has to manage and ultimately dispose of its nuclear waste in a safe way. Our basic and applied research for the safe management of nuclear waste is focused on radiochemistry and materials chemistry aspects - it is focused on the behaviour of radionuclides and radioactive waste materials within the back-end of the nuclear fuel cycle. Itis organized in four areas: (1) research supporting the scientific basis of the safety case of a deep geological repository for high level nuclear waste, (2) fundamental structure research of radionuclide containing (waste) materials (3) R and D for waste management concepts for special nuclear wastes and (4) international safeguards. A number of excellent scientific results have been published in more than 80 papers in international peer-reviewed scientific journals in 2013 - 2014. Here, I would like to mention four selected scientific highlights - more can be found in this report: (1) The retention of radionuclides within a nuclear waste repository system by secondary phases for the long-term safety assessment is one of the major research topics in the institute. The fundamental understanding of a long-standing open issue regarding the thermodynamics of radium-barium-sulfate solid solutions and its applicability in long-term safety assessments for nuclear waste disposal could be resolved. This was achieved by a novel approach combining atomistic simulations, radiochemical batch-type laboratory experiments and modern analytical techniques supported by thermodynamic modelling allowing a reliable description of Ra solubility control by a (Ba,Ra)SO_4 solid solution. This research is supported by the Swedish waste management agency SKB. (2) A major step forward was achieved regarding the prediction of actinide- and lanthanide-bearing materials properties by atomistic simulations. Performance tests of the DFT+U method for calculations of f-element-bearing systems (the Hubbard U parameter derived from first principle methods) showed that this method, in contrast to standard DFT, results in exceptionally good predictions of the formation and reaction enthalpies as well as the structures of lanthanide- and actinide-bearing materials. (3) The actinide solid state chemistry group has been very active in recent years to unravel the crystal structure of actinide containing oxo-salts. From the 1101 new crystal structure entries in the ICSD crystal structure database between 2005 and 2012, Prof. Evgeny Alekseev has contributed to 98 entries (almost 10%).

[en] The key research topics of the institute are: safety research for nuclear waste disposal, structure research, waste management concepts for special radioactive wastes and nuclear safeguards and security. The report includes a description of the available facilities, the staff, the organization chart, the budget and the list of scientific and technical reports in 2015/2016.

[en] Oxidation protection coatings are required for thermally highly stressed components such as turbine blades in aircraft engines. Cyclic oxidation experiments were performed on a NiCoCrAlY protective coating of a nickel-based superalloy and hardness and modulus of elasticity (mechanical properties) were determined by nanoindentation before and after the experiments. Microstructure and chemical composition were characterized by means of scanning electron microscopy. Here, the focus is on the phase identification by combining electron backscatter diffraction and energy dispersive X-ray spectroscopy. Findings indicate that the chemical composition strongly influences the mechanical properties.

[en] Highlights: • Surrogate study of potential nuclear waste form dissolution. • Dissolution kinetics of ZrO₂ based pyrochlore and defect fluorite ceramics. • Effect of pH, temperature and Nd/Zr ratio on dissolution rate for both structures. • Heterogeneous surface reactivity identified by electron microscopy. • Preferential release of Nd observed for all experimental conditions. - Abstract: The dissolution kinetics of ZrO₂–Nd₂O₃ polycrystalline pyrochlore and defect fluorite ceramic powders under acidic conditions were observed following a combined macroscopic and electron microscopic (SEM) approach. Dynamic dissolution experiments were carried out with a variation of temperature and pH as well as the chemical composition within the ZrO₂–Nd₂O₃ system. SEM observations indicate a preferential leaching at the grain boundaries for all experiments. A preferential release of Nd during the initial stages of dissolution, which is several orders of magnitude higher than the Zr release, was measured by ICP-MS. At steady state, the normalised Nd-rate approaches the Zr based dissolution rate within one order of magnitude, becoming congruent for most experiments. Zr-based BET surface area normalised steady state rates at c(H⁺) = 0.1 N and 90 °C are in the range between 4 × 10⁻⁷ and 3 × 10⁻⁶ g m⁻² d⁻¹, indicating no significant influence of the transition pyrochlore to defect fluorite and the chemical composition on the macroscopic dissolution rate. Based on the different numbers of grain boundaries per surface area in the pyrochlore compared to the defect fluorite, a slightly higher “true” dissolution rate could be assumed for the defect fluorite. The influence of pH and temperature variations to the dissolution rates of defect fluorite and pyrochlore are similar and in the range observed for other multioxide materials

[en] Monazite-type ceramics are promising candidates for the conditioning of minor actinides. Monazite (LaPO₄) was prepared by hydrothermal synthesis and its hydrated form (LaPO₄^.0.5H₂O) was synthesised by co-precipitation. The first characterisation results, structural and morphological combined with thermal behaviour and physical properties, are presented. (authors)

[en] Europium incorporation in different LnPO_4 (Ln=Tb, Lu and Gd_1_-_xLu_x) phases crystallizing in the xenotime structure was investigated with site-selective TRLFS, PXRD and Rietveld analyses. Based on recorded emission spectra and diffraction patterns, the formation of three different crystal systems (xenotime, anhydrite, and monazite) could be identified. Aging of the ceramic samples and a second sintering step led to an accumulation of europium in the grain boundaries and on the surface.

[en] Highlights: • Synthesis of Nd_2xZr_1−xO_2+x ceramics by a coprecipitation route. • Dissolution kinetics studied at 90 °C in C(HCl) = 0.1 M in batch and dynamic setups. • Data show a higher stability of Zr-based B-sublattice in the pyrochlore structure. • Batch and dynamic steady state dissolution rate of pyrochlore in good agreement. • No significant difference in dissolution rates of defect fluorite and pyrochlore. - Abstract: In this study, an ideal Nd₂Zr₂O₇ pyrochlore and a defect fluorite ceramic were synthesised by coprecipitation, pressing and sintering. Detailed investigations by electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) were used for the characterisation of the powders. In particular both powders were found to be single phase ceramics. All batch and dynamic dissolution experiments were conducted in C(HCl) = 0.1 M at 90 °C to compare the two types of Nd-zirconia structures and the experimental approaches. A good agreement between batch and dynamic dissolution experiments was observed for the pyrochlore with a Nd-based final dissolution rate in the range between 0.84 × 10⁻⁵ and 1.95 × 10⁻⁵ g m⁻² d⁻¹. The dynamic experiments indicate a strongly incongruent preferential release of Nd from the pyrochlore ceramic at the beginning of the experiment and a close to congruent dissolution at the end of the experiment. The dissolution behaviour of defect fluorite in dynamic experiments is observed to be very similar to the pyrochlore. An incongruent dissolution during the early stages is followed by a congruent steady state. The defect fluorite steady state dissolution rate is lower than the one determined for pyrochlore.