Helium in CERMET fuel - binding energies and diffusion

This thesis presents a first principle approach to model helium diffusionand retention in molybdenum. Results from electron structure calculations within the framework of density functional theory are used to assess parameters in a rate theory model. The model is used to reproduce experimental desorption spectra, which, to a large degree of accuracy, coincide with experimental data in temperature regions relevant for nuclear fuel applications. The models indicate that produced helium will diffuse out into the fuel pin during operation. However, some helium will be trapped in molybdenum vacancies. The amount of trapped helium will largely depend on the fuel operational temperature. Data presented in the thesis is a first step towards a self consistent dataset of first principle data on helium diffusion in CERMET fuel, one candidate fuel suggested for transmutation of nuclear waste. To realise the use of CERMET fuel, modelling of fuel performance is essential, and to accomplish this, the understanding of helium diffusion and retention in molybdenum is one important aspect.