Aleksandra Rzhevskaia

Liquid radioactive waste injected into deep geologic horizons poses a long-term hazard for the environment. Uranium-238, a major component of the nuclear fuel cycle and radioactive waste, has long half-life, high mobility, high toxicity, and complex chemical behavior. Sorption is a crucial process for the radionuclides retention in geosphere and isolation of the waste. In the present work, sorption of U(VI) on the sediments from Severny deep disposal site (Krasnoyarsk, Russia) and reference minerals (quartz and clay) was studied in laboratory-simulated low-level alkaline liquid radioactive waste solutions. U sorption behavior is strongly pH-dependent. It was determined that in the wide pH range U uptake is mostly controlled by quartz in the specific conditions. As uranyl-carbonate complexes play important role in the alkaline medium, carbonate concentration affects the U retention. Contribution of the aquifer constituent minerals was estimated using autoradiography method. Surface complexation reactions for U(VI) sorption on the aquifer sediments were modelled.

Silicon-graphite anodes offer a practical route to increase the energy density of lithium-ion batteries (LIBs), but their widespread adoption is hampered by cyclic instability due to huge volume changes of silicon during lithiation/delithiation process. Another fallout of LIBs capacity gain is growing safety concerns due to fire risks, associated with the uncontrolled release of chemical energy. Herein, we test a hexakis(fluoroethoxy)phosphazene (HFEPN) as a multifunctional electrolyte additive designed to mitigate both issues. The flammability of HFEPN-containing electrolytes was evaluated using a self-extinguishing time test, while the electrochemical performance was assessed in Si/C composite||NMC pouch cells under a progressively accelerated cycling protocol. It is shown that the additive fully imparts flame-retardant properties to the electrolyte at a 15 wt% loading. Despite forming a more stable solid–electrolyte interphase (SEI) with enhanced interfacial kinetics the additive did not improve the cycling stability of the Si/C-based cells. The cells with 15 wt% HFEPN retained 43% of capacity after 70 cycles, comparable to 46.5% for the reference electrolyte. The diffusion limitations imposed by the increased electrolyte viscosity are assumed to offset the interfacial benefits of the additive. Thus, alongside the improved synthetic route, this study demonstrates that while HFEPN functions as an effective flame retardant and SEI modifier, its practical benefits for silicon anodes are limited at high concentrations by detrimental effects on electrolyte transport properties and should be improved in future molecular design efforts.

Radiostrontium ( ⁹⁰ Sr), a highly mobile radionuclide of environmental concern, can be strongly retained by soils via interactions with organic and mineral components.