UV-ToN

Laboratory scale investigations on the behaviour of clay rock in the near field of the disposal area of radioactive waste (UV-ToN)

Topic Area: Final Repository Research

Grant Number: 4725P10401

Project Funding: Federal Office for the Safety of Nuclear Waste Management (BASE)External link, Wegelystraße 8, 10623 Berlin Germany

Project Period: 03/2026 – 02/2029

Project leader: Prof. Thorsten Schäfer

Contact: Jakob Fröhlich

Project Description

To ensure the safe deep geological disposal of high-level radioactive waste, it is necessary to gain a precise understanding of the properties of the surrounding host rock. One of the potential host rocks for disposal in Germany (alongside rock salt and crystalline rock) is claystone.

 In the canton of Jura in Switzerland, the Mont Terri underground research laboratory is being operated with the participation of international project partners to study Opalinus Clay in the context of the final disposal of high-level radioactive waste. A wide variety of experiments are being conducted directly in the rock (in situ) on site. One of these experiments is the BN experiment (Bitumen-Nitrate-Clay Interaction), involving BASE and the international project partners SCK CEN (Belgium), ANDRA (France), FANC (Belgium), IRSN (France), and swisstopo (Switzerland) as the implementing agencies.

The long-term BN experiment serves to investigate, from a biogeochemical perspective, the influence of nitrate and other decomposition products from bituminized radioactive waste on the transport behavior of radionuclides in clay rock.

 Within UV-ToN, the following aspects will therefore be examined in greater detail in this context. Regarding the transport of the long-lived fission product ⁷⁹Se, the oxidation state is particularly crucial, as anionic Se species are assumed to be mobile. In this context, speciation is influenced, among other factors, by the presence of nitrate (due to selenium’s high redox sensitivity). The role of the microbial community will also be examined in more detail. Furthermore, the study will investigate how an in-situ increase in the pH of the Artificial Pore Water (APW) affects the oxidation state of selenium.

 The following aspects will therefore be investigated in greater detail as part of the UV-ToN project:

• Characterization of facies-dependent microbiology in Opalinus Clay
• Determination of the clay mineralogy of the core samples
• Variation in experimental conditions: oxic, anoxic
• Investigation of the behavior of radiologically inactive Se species — with regard to the dose-relevant ⁷⁹Se — under various redox conditions (increase in pH)
• Modeling of transport processes (optional), depending on the analytical results obtained

The findings from UV-ToN are to be used in particular to develop realistic concepts for the in-situ increase of the pH value of the artificial pore water (APW) within the framework of the BN experiment, in order to better understand the bio- and hydrogeochemical processes in the Opalinus Clay. This is intended to contribute to a deeper mechanistic understanding of how Opalinus Clay responds to geochemical disturbances in the context of the final disposal of high-level radioactive waste in Germany.

 Methods (Excerpt) 

• Batch sorption experiments: Sorption of nitrate and selenium on clay rock samples
• Microbiological plate tests: Investigation of the microbial community
• Asymmetric flow field-flow fractionation (AF4): Characterization of the size and distribution of clay particles
• LA-ICP-MS and spICP-MS: Determination of the composition of clay samples
• SEM/EDX: Distribution and occurrence of elements on surfaces, e.g., of clay minerals
• XRD using the Rietveld method: Characterization of clay rock samples and their various facies

 Further Information

• Generals about the final repository searching process:External link
• Underground Research Lab Mont TerriExternal link