Molecular dynamics simulation of thermodiffusion

Abstract

Thermodiffusion, also known as the Soret effect, is a fascinating and complex phenomenon that occurs when a temperature gradient causes the migration of different components within a mixture. This phenomenon is of great interest in understanding the behaviour of nuclear fuel, as it plays a crucial role in altering concentration prof iles and, in turn, essential properties such as fuel performance, safety and lifetime. Furthermore, it has been identified as responsible for the introduction of corrosive environments for the cladding in PWRs. In this study, I explore the fundamental mechanisms governing thermodiffusion and its implications in a simple palladium-hydrogen system. The diffusion of hydrogen in response to temperature gradients challenges traditional notions of diffusion as it introduces the coupling of thermal and concentration gradients. The resulting driving forces and fluxes are intricately linked, making thermodiffusion a complex but fascinating area of study. Several methods for testing the main parameter used in thermodiffusion, the heat of transport, are implemented using molecular dynamics, and although they don’t give similar results, some conditions for isolating the phenomenon have been identified, mainly the importance of controlling the concentration gradient across the material, and the careful control of local volume and pressure.