Silicon carbide (SiC) is known to have a good resistance to neutron radiation damage thanks to many desirable attributes for high-temperature applications in a neutron radiation environment such as high chemical and thermal stability, low activation and high strength. For these and other reasons, SiC based materials is considered for use in fusion energy systems as first wall or blanket materials. When SiC is submitted to a high flux of energetic neutrons (14 MeV in the first wall of fusion reactor), transmutation nuclear reactions and emergence of helium bubbles in SiC are observed. Several past studies have been carried out to examine the behavior of He in SiC and have permitted to understand a lot of properties of these helium bubbles. However few of them have precisely investigated the behavior of He gas in equilibrium bubbles at finite temperature. Notably, it is very important to know the number of helium atoms in an equilibrium bubble to determine such properties of SiC under irradiation as the release and retention behavior of helium in these bubbles.
Our goal in this work is to study the effect of temperature on the number of He atoms in very small cavities. To do so we use empirical potential Molecular Dynamics (MD) in which we deal the quantitative accuracy of the ab initio calculation for the ability to consider finite temperature effects. We are then able to calculate the free energies of He atoms in the cavities and to compare them with the free energy of He in the bulk of silicon carbide. Our idea was to compare the free energies of He atoms inside the cavity to their free energy in the bulk. The sign of the difference between these two free energies indicates whether it is in a more favorable situation in the bulk or in the cavity. Starting from only one He in a cavity, we added one helium after the other in the cavity as long as their free energy remains lower than in the bulk. As soon as it would become larger one would have exceeded the number of helium atoms at equilibrium in the given cavity. This procedure assumed that all He atoms would remain inside the cavity. This assumption proved wrong which sheds light on the actual behavior of He atoms in and close to cavities.
- A. Couet, J.-P. Crocombette, and A. Chartier, “Atomistic study of the thermodynamic equilibrium of nano-sized helium cavities in βSiC,” Journal of Nuclear Materials, vol. 404, no. 1, pp. 50-54, 2010.