Duc Nguyen-Manh

Body centred cubic (BCC) transition metals are of high interest for nuclear applications, where they are subject to high radiation damage, which causes the material’s properties to decay. Measuring the electrical and thermal properties of these materials after irradiation poses challenges due to sample size, activity, and cost of running the experiments. Traditional methods of measuring thermal properties require bulk samples. Newer measuring techniques were developed for smaller samples, but they have their limitations. Therefore, a new First Principles’ method was developed to predict the electronic thermal conductivity and resistivity of Frenkel pairs (FP) in BCC transition metals. The Boltzmann Transport equation for the thermal conductivity requires the electron heat capacity, the Fermi velocity, and the electron scattering time. A model to calculate the electron-FP scattering time for point defects is shown, and extended to include the electron–phonon contributions. The electron–phonon corrections of s -electron to the d -band from the Mott model for transition metals are presented and discussed. The method presented in this work can provide an initial insight, in the degradation of the electric and thermal properties of irradiated transition metals and their alloys, including high entropy alloys.

Fundamental understanding of tungsten oxidation plays an important role in providing reliable and engineering data relevant to the detritiation, maintenance and waste handing for a future fusion device. The present simulations identify the key mechanisms controlling the capture and release of tritium from bulk tungsten and the oxides that may form on its surfaces. They further predict the rate of tritium release from tungsten and its oxides under variable environmental conditions and material states. These release rates sensitively depend on the interplay between tritium mass transport and tritium binding in WO\textsubscript{x} interstitial sites, lattice vacancies, and grain and interphase boundaries. We report results for the diffusion of tritium from tungsten through bulk phases and interfaces of W|\ce{WO2}|WO$_{2.72}$|\ce{WO3}, and the resulting tritium release from oxide surfaces.

To design a proper material for fusion energy, improved properties can be achieved by varying the composition of alloys. Computational methodologies and tools are readily available to efficiently explore the vast compositional space. In this work, we combined Density Functional Theory (DFT) with the Cluster Expansion (CE) method to develop a predictive model, explored possible equilibrium phases in different systems with a small addition of Hf (1-5 at.%), and calculated the order–disorder transition temperature (ODTT) for each composition. A key finding is that the effect of Hf addition on ODTT is composition dependent. In some subsystems, the ODTT remains nearly unchanged with Hf addition, whereas in others, an increase in ODTT is observed even at low Hf concentrations. These results provide valuable guidance for future experimental studies aimed at optimizing thermodynamic stability and thermo-mechanical properties in irradiation-resistant materials.