"Quantum chemical calculations (DFT), in both the embedded cluster and periodic boundary condition (PBC) framework, will be employed to study: 1. Non‑ and dissociative adsorption of water on stoichiometric and substoichiometric ThO2 surfaces – comparison with our previous work on water adsorption on other AnO2 (An = U-Cm). 2. Evaluation of the effects of the size of the chemical model, e.g. the slab thickness in PBC calculations. 3. Surface chemistry of water radiolysis products (HO· and H·) on stoichiometric and substoichiometric ThO2 surfaces, in the presence and absence of water. Extension to PuO2. 4. Surface chemistry of other small molecule species (NOx, ozone) on stoichiometric and substoichiometric ThO2 surfaces, in the presence and absence of water. Extension to PuO2."