Refractory high entropy alloys are known to retain exceptional mechanical properties at high temperature, with possible applications of these materials in extreme condition environments. The development of quantitative models able to predict the mechanical properties of these alloys as function of their composition, temperature and strain-rate would allow to speed-up considerably their development. However, the models currently available do not account for the role of interstitial solutes and diffusive mechanisms operative at high temperature. In this project, I propose to overcome these limitations by developing a multi-scale approach taking into account these mechanisms. Atomistic simulations will allow to parameterize a continuous model of a dislocation interacting with interstitial solutes. Second, the coupling of this model with interstitial diffusion will allow to investigate their influence on the mechanical behavior of the alloy (dynamic strain aging).