Scientific Highlights LES

Zeolites are a class of shapely, colourful minerals with very special properties, making them omnipresent in our surroundings. They accelerate chemical reactions, absorb hazardous contaminants and water to a high degree, for example. Their only limitation is that they usually lose their peculiar crystalline structure at high temperatures. Now researchers at the University of Bern have found an unexpected exception.

Yanting Qian has received the MSc/PhD competition award in the FISA2022-EURADWASTE'22 conference. She works on the retention of redox-sensitive Tc on Fe-bearing clay minerals.

Water boiling control evolution of natural geothermal systems is widely exploited in industrial processes due to the unique non-linear thermophysical behavior. Even though the properties of water both in the liquid and gas state have been extensively studied experimentally and by numerical simulations, there is still a fundamental knowledge gap in understanding the mechanism of the heterogeneous nucleate boiling controlling evaporation and condensation. In this study, the molecular mechanism of bubble nucleation at the hydrophilic and hydrophobic solid–water interface was determined by performing unbiased molecular dynamics simulations using the transition path sampling scheme. Analyzing the liquid to vapor transition path, the initiation of small void cavities (vapor bubbles nuclei) and their subsequent merging mechanism, leading to successively growing vacuum domains (vapor phase), has been elucidated. The simulations reveal the impact of the surface functionality on the adsorbed thin water molecules film structuring and the location of high probability nucleation sites.

The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-fields. A study conducted at LES in collaboration with the Helmholtz Zentrum Dresden Rossendorf used extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS) to elucidate the uptake mechanism of trivalent lanthanides and actinides (Ln/An^III) by the clay mineral montmorillonite.The excellent agreement between the thermodynamic model parameters obtained by fitting the macroscopic data, and the spectroscopically identified mechanisms, demonstrates the mature state of the 2SPNE SC/CE sorption model developed at LES for predicting and quantifying the retention of Ln/An^III elements by montmorillonite-rich clay rocks.

An interdisciplinary study conducted at different PSI laboratories (LES, AHL, LRS, SYN) in collaboration with Studsvik AB (Sweden) demonstrates that selenium originating from fission in light water reactors is tightly bound in the crystal lattice of UO₂. This finding has positive consequences for the safety assessment of high-level radioactive waste repository planned in Switzerland, as it implies (contrary to previous assumptions) that the safety-relevant radionuclide ⁷⁹Se will be released at extremely low rates during aqueous corrosion of the waste in a deep-seated repository.

Drei Jahre in Folge hat Jenna Poonoosamy den Preis für die beste Präsentation am Doktorandentag im Bereich Nukleare Energie und Sicherheit (NES) am Paul Scherrer Institut PSI erhalten. Poonoosamy stammt ursprünglich von der Insel Mauritius im Indischen Ozean. Schon in der Schule interessierte sie sich vor allem für Chemie. «Die meisten meiner Freunde wollten in die Wirtschaft», erzählt sie. «Mich dagegen haben die Naturwissenschaften fasziniert.» Und so zog sie nach der Schule zum Chemie-Studium nach Paris. Und kam später für ihre Doktorarbeit ans PSI.

Obwohl die Schweiz aus der Kernenergie aussteigt, muss sie eine Lösung für das in den Kernkraftwerken, aber auch in Medizin, Industrie und Forschung entstandene, radioaktive Material finden. Daher stellt sie sich einer aussergewöhnlichen, verantwortungsvollen Aufgabe: Sie sucht einen Ort, an dem sie ihre radioaktiven Abfälle mehrere hunderttausend Jahre lang sicher lagern kann. So lange, bis sie von selbst die Radioaktivität natürlicher Gesteine erreicht haben.