Scientific Volunteer 1

This scientific volunteer position is intended to complete the experimental work of An Thai Nguyen’s PhD project, which focuses on the sorption of radionuclides onto C-S-H and C-A-S-H phases at different stages of degradation.

Cementitious materials play a key role in the current designs of both near-surface and geological radioactive waste repositories. Among the hydration products formed during cement hydration, calcium-silicate-hydrate (C-S-H) and calcium-aluminate-silicate-hydrate (C-A-S-H) phases are the most abundant and constitute the primary sorbing phases for radionuclides. Over the long timescales relevant to radioactive waste disposal, these cement phases progressively degrade, resulting in significant changes in their physico-chemical properties. Understanding how radionuclide retention evolves with cement degradation, and establishing links between sorption behaviour and the changing properties of C-S-H and C-A-S-H phases, is therefore essential for predicting the long-term performance of cementitious barriers and formed the central objective of this PhD research.

The PhD project aimed to (i) develop and evaluate different synthesis routes for C-A-S-H phases, (ii) quantify the sorption of relevant radionuclides onto C-S-H and C-A-S-H phases throughout the degradation pathway, and (iii) improve the understanding of the sorption mechanisms governing radionuclide retention as a function of degradation state.

While the first objective has been fully achieved, additional experimental work is required to comprehensively address the latter two objectives. The scientific volunteer will therefore complete the dataset on the sorption of Am(III), Ni(II), and Pu(IV) onto fresh and degraded C-S-H and C-A-S-H phases. In addition, the scientific volunteer will perform all analyses of the solutions and solids and literature review necessary to provide further insight into the sorption mechanisms controlling radionuclide retention under varying degradation conditions.