RULET - "Retention and solubility of dose-relevant radionuclides under the reducing near-field conditions of a repository in clay or crystalline rock"

Funding source:

German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV)

Duration:

01.11.2024 till 30.04.2028

Partner:

• Karlsruhe Institute for Technology, Institute for Nuclear Waste Disposal (KIT-INE, Karlsruhe, Germany)
• Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) GmbH (Braunschweig, Germany)   
• Institut für Energie- und Klimaforschung Nukleare Entsorgung und Reaktorsicherheit (IEK-6, Jülich, Germany)

People:

N.N. (PhD student), N.N. (Postdoc), N. Mayordomo, K. Müller

Grant number:

02 E 12224B

Project management:

Projektträger Karlsruhe (PTKA)

Short description:

The joint project RULET deals with the safety-relevant physicochemical properties and the retention of ⁹⁹Tc, ⁷⁹Se, ²²⁶Ra and ¹⁴C in the near field of a repository. The focus is on solid phases, oxidation states and solution species as they are to be expected in the immediate vicinity of the waste containers. Special emphasis is placed on chemical reactions and equilibrium processes with secondary corrosion phases containing iron(II). The findings of the investigations of all project partners are summarized and used in a simplified material dispersion model for a generic repository. This will be applied to check whether the new findings could contribute to a reduction in conservativities or whether new mobility-increasing processes could occur. Based on the findings, recommendations are derived as to how the retention and mobilization mechanisms found should be taken into account in safety assessments. In addition, the results obtained extend the physico-chemical data basis required both for thermodynamic calculations of the radionuclide source term and for reactive mass transport models.

The aim of the HZDR sub-project is to identify retention processes for the fission product ⁹⁹Tc and, to a lesser extent, for ⁷⁹Se on iron(II) carbonate minerals. Competing reactions are also studied and the influence of the redox state is investigated. In addition to batch tests, the characterization of the occurring reactions on a molecular level is an important part of the investigations. Thermodynamic data is determined and, if sufficiently qualified, implemented in the THEREDA database. Sorption parameters are integrated into the mineral-specific sorption database RES³T. A further objective is the investigation and characterization of the relevant lower oxidation states of 99Tc and their complex formation with inorganic ligands.