Hundreds of thousands of tons of nuclear spent fuel and reprocessed nuclear wastes have accumulated worldwide since the start of nuclear power-based electricity production in 1954. In order to mitigate the long-term risks associated with these high-level radioactive wastes, several countries have developed plans to build permanent deep underground repositories in which passive engineered and natural barriers are designed to isolate the wastes from the biosphere. A central component of the safety case for such geological repositories is the assessment of radiation risks over extended time periods, typically up to one million years. To perform the risk assessment, numerical models must be built that can predict the release of radionuclides from the waste package and their transfer through the barriers into the biosphere. In repositories sited within clay-rich host rock formations, these predictions rely on the parametrization of simplified mass transport models based on solubility limits, radionuclide speciation in solution, solution to surface/solid partitioning coefficients and diffusive transport parameters. The credibility of these performance assessment models depends, however, on the quality of the scientific understanding underlying them. This seminar will explore why and how an improved understanding of geochemical processes can strengthen the scientific basis of the safety case for these repositories.
About the Speaker: Christophe Tournassat (French Geological Survey (BRGM); Lawrence Berkeley Laboratory (LBNL))
Christophe Tournassat is a researcher at the French Geological Survey (BRGM) and in the Energy Geoscience Division of the Lawrence Berkeley Laboratory. He obtained his B.Sc. and M.Sc. degrees in Earth Sciences from the Ecole Normale Supérieure de Lyon, a Ph.D. in Environmental Geochemistry from the University of Grenoble under the supervision of Prof. Laurent Charlet, and an “Habilitation à diriger des recherches” in Geology from the University of Nantes. Since 2010, he has directed the BRGM scientific program on geological barriers performance, which oversees BRGM’s research activities on radioactive waste storage. Since 2017, he has also led the group working on the properties of “Porous Media” at ISTO laboratory (Institut des Science de la Terre d’Orléans) and joined the Geochemistry Department in EESA at Berkeley Lab. His scientific interests cover a wide range of topics from thermodynamics and kinetics of low temperature water/solutes/rock interactions to multi-scale numerical modeling of retention and transfer processes in geological media. Christophe Tournassat is an associate editor of Geochimica et Cosmochimica Acta and Journal of Hydrology, and is a member of the editorial board of Applied Clay Science.
Host: Bhavna Arora