We systematically investigate the electronic and coordination structures of actinide (An) and chemical homologue lanthanide (Ln) systems with novel synchrotron-based high energy resolution X-ray emission/absorption/inelastic scattering techniques. The experimental results are supported by theoretical calculations and simulations with quantum chemical codes. These investigations improve our understanding of An/Ln reactivity in repository systems and waste matrices on a molecular scale and thereby support the reliability of safety case evaluation of the repository long term safety. The elucidation of electronic and coordination structures provide basic insight into structure-reactivity relationships of actinide elements, which is a present scientific frontier. The group was initiated in July, 2011 - Helmholtz Young Investigators Group grant (VH-NG-734) awarded by the Helmholtz Association of German Research Centers (HGF) and the Karlsruhe Institute of Technology (KIT), Faculty of Chemistry and Biosciences, Institute for Nuclear Waste Disposal (INE).