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References: ENV21-1

Themes: Geological Sciences, Earth, Universe, Space

Thesis location: Research Laboratory for Radionuclide Transfer in Aquatic Ecosystems (LRTA) - Cadarache (13)

Start: October 2021

Skills required

Environmental geosciences, geochemistry, hydrology, sedimentology, mathematics, statistics
Age limit: 26 years old

Thesis subject

Modeling the fate of radionuclides in the environment is necessary to anticipate the health and environmental risks that radioactivity can generate. It is necessary to model the transfer of radionuclides, naturally or accidentally emitted, into and through environmental compartments: atmospheric, terrestrial, river and marine. While many models exist at IRSN to assess the transfer of radionuclides within these compartments, the interface between them is more generally less represented. However these interfaces are associated with transfer processes related to their connectivity and adsorption/desorption processes that influence the fate and speciation of these radionuclides. This thesis will focus specifically on the interface between terrestrial and fluvial compartments, which is still poorly known and especially at their exchanges. The transfer of radionuclides from the soils of a watershed to adjacent watercourses depends on several parameters (soil erosivity and connectivity, topographic slope, distribution of activities in the soil ...) that must be taken into account in order to model the flows likely to be transferred or stored. Modelling will be carried out using an agro-hydrological model (SWAT+) validated in many watersheds worldwide. This model allows the simulation of hydrological processes at sub-daily to annual time steps and has been widely tested to study the cycle of sediment, nutrient and pesticide inputs to rivers. It will first be necessary to learn this model before developing a specific module for the transfer of radioactivity. To achieve this, two watersheds with contrasting characteristics will be studied: (1) the Rhône River, based on data from IRSN radioactivity monitoring and with also the research projects carried out there (OSR, ArchéoRhône...), and (2) the watersheds of the Fukushima prefecture affected by fallout in 2011, where IRSN was able to acquire a lot of environmental data, particularly in the framework of the AMORAD project. These datasets may be supplemented by new sampling, in particular to characterize extrem hydrological conditions (drought, heavy rainfall). After validation, the model will be applied on fictitious scenarios of atmospheric deposition, taking into account or not the possibilities of societal changes related to climate change.