The studies of KIT-INE within VESPA II aim to significantly improve scientific understanding of the geochemical behavior and retention processes of long-lived fission and activation products in a deep underground repository, and to provide input for improved safety calculations. KIT-INE works on the radionuclides Tc, Se and I, and contributes to four main topics ranging from processes involving HLW materials to aquatic Tc chemistry and radionuclide retention by secondary phases. The studies by KIT-INE are using complementary spectroscopic tools in order to derive realistic molecular-level process understanding and to provide robust quantitative descriptions of key processes investigated. KIT-INE involves two PhD students and other young researchers in the project, thus contributing to specialized education and ensuring availability of qualified technical/scientific staff.
Aquatic Tc(IV) chemistry and solubility
- Work by KIT-INE on Tc-chemistry is largely based on solubility experiments in the Tc(IV) system. Based on comprehensive new experimental studies involving the inorganic ligands nitrate, sulfate, sulfide and organic complexants like gluconate, robust solubility limits are derived in dilute to concentrated NaCl, MgCl2 and CaCl2 solutions. Based on a detailed analysis of both aqueous and solid Tc phases, improved chemical and thermodynamic models are derived for later integration in thermodynamic databases like THEREDA or NEA-TDB.
Retention of radionuclides by secondary phases
- KIT-INE will further improve the solid-solution model developed within VESPA I on the incorporation of Se(IV) in calcite. Aim is to derive a robust quantitative description based upon realistic model understanding.
- With the aim of assessing 129I retention in the repository near-field by secondary iron phases, KIT-INE performs dedicated experimental studies complemented by theoretical (DFT) calculations. The focus is on 129I interactions with green-rust and magnetite as two key secondary Fe phases potentially relevant under the strongly reducing conditions expected in a deep underground repository.
Mobilization of radionuclides from high-level waste forms
- Studies performed in the shielded-box-line of KIT-INE investigate the mobilization of 129I from spent nuclear fuel (SNF). The work allows an improved assessment and quantification of 129I release (contribution to instant release fraction) and the iodine inventory present in SNF.
More information about KIT-INE.