Chemical-Physical Properties of Nuclear Materials Targeting Improved Safety This proposal requests NAISS resources for a research project utilizing advanced quantum mechanical modelling within density functional theory (DFT) with periodic models of materials and their interfaces. The objective is to generate large datasets on physical-chemical properties of nuclear materials and on molecular reactivity at their interfaces under conditions relevant to interfacial radiation chemistry driven by ionizing radiation. The project bridges computational modelling with experimental data to enhance the safety of current and future nuclear energy production. Main Research Tasks. The project is structured around five central tasks aligned with funded research initiatives: • Task 1: Modelling Water Radiolysis Products in Aqueous Media Using finite molecular models and continuous solvation models, this task investigates the reactivity of molecules and radicals generated by water radiolysis. The resulting dataset of reaction energy barriers and reaction energies will establish a thermodynamic and kinetic knowledge base. • Task 2: Reactions at Solid-Liquid Interfaces This task addresses the challenge of explicitly inclusion of water at interfaces. Periodic DFT will be used to model oxide surfaces of d- and f-block elements with surface-bound water, mapping reaction pathways, barriers, and energies. • Task 3: Oxide Materials and Their Surfaces Periodic DFT will characterize the bulk and surface properties of d- and f-block oxides relevant to nuclear fuel, reactor cladding, and spent fuel repositories. A primary goal is determining surface energies to identify key interfaces for radiation chemistry. • Task 4: Structure of Uranium Nitride (UN) and Fission Product Distribution Focusing on accident-tolerant fuel, this task models the structural features, electronic properties, and defect distributions of UN using periodic DFT. In coordination with experimental work, the diffusion of volatile fission products like iodine will be analyzed. • Task 5: Iodine Absorption by Cellulose-Based Materials To mitigate biosphere contamination during accidental releases, this task uses periodic DFT to evaluate iodine adsorption across various cellulose-based material structures and compositions, establishing structure-performance correlations for enhanced radionuclide containment. Methodology & Computational Requirements The project utilizes well-benchmarked methods previously validated in SNIC/NAISS applications. Chemical bonding will be studied using Wavefunction Methods (WM) and DFT. To ensure realistic data generation: • High-level post-Hartree-Fock theory will account for correlation and exchange in radicals and molecules. • Periodic DFT will be applied to complex interfaces, surfaces, and bulk materials. These resource-heavy computations involve low-symmetry supercells containing d- and f-block oxides, explicit water molecules, and continuum solvation models. Project Funding The tasks directly support three major funded projects: • Tasks 1–3: Funded by the Swedish Research Council (VR) project “Radiation-induced processes at oxide-aqueous interfaces” (2025-07983; 6-year project). • Task 4: Funded by the Swedish Radiation Safety Authority (SSM2024-9701) project “Diffusion of volatile fission products on accident tolerant fuel – DiVFuel”. • Task 5: Funded by the Swedish Radiation Safety Authority (SSM2024-10807) project “Träcellulosa för uppfångning av jod vid oavsiktliga utsläpp – Icell”.