Identification of geochemical and biological processes controlling naturally occurring radionuclides (NOR) mobility to derive more robust solid/liquid distribution coefficients (Kd)

Geochemical and biological processes controlling NOR mobility are studied within the RadoNorm project to derive more robust distribution coefficients Kd. To achieve this (i) the effect of microorganisms on NOR mobility in uranium (U) mine waters is studied, (ii) new datasets of NOR sorption and desorption parameters are acquired, (iii) a methodology for the determination of site-specific Kd values is evolved and (iv) models able to predict Kd (NOR) in relevant scenarios are developed. The impact of microbes on the speciation of U in U mine waters is characterized by a multidisciplinary approach providing insights into the microbe/U interaction mechanisms needed to predict the effect of microbial processes on the mobility of this radionuclide. Laboratory studies are performed to identify the soil properties that govern NOR interactions in soils. Sorption and desorption Kds for representative soils are determined, also considering soil aging effects. Chemical analogy between NOR and stable elements (e.g., Ba vs. Ra) is also examined, with new data and additional values gathered from literature. Considering the dynamics of sorption-desorption reactions, studies are carried out at the Zatu site (France) to develop a method to determine site-specific Kds. Experiments with soil core samples are performed to determine the amount of desorbed U, Ra and Pb and to derive apparent Kd values. The validity of this approach will be confirmed combining these results with in situ studies (Zatu site). Two approaches are followed to derive models for Kd (NOR) prediction. The first one is the “smart Kd” model, which is based on a realistic description of chemical reactions of NOR in liquid and solid phases. The second one is constructing simple, multivariate Kd prediction models based on soil properties governing NOR interaction. Water transport models with different levels of complexity are applied to describe the transport of NOR at the Zatu site in consistency with site-specific Kds