Reaction-diffusion modelling of hydrogen retention and release mechanisms in beryllium

Beryllium will be the rst wall material for the international fusion reactor ITER. Due to the
heavy irradiation of the rst wall by impinging hydrogen isotopes a detailed understanding of
hydrogen retention mechanisms within Be is of technical importance. Especially, the retention
of the radioactive isotope tritium needs to be investigated for safety reasons.
This master thesis presents a model based on a reaction-diusion approach to simulate thermal
desorption experiments in order to relate microscopic material properties of beryllium to
spectra observed in experiments. After motivation and introduction of experimental observations,
hydrogen diusivity in Be is examined from the theoretical point of view, yielding
faster diusion as indicated experimentally. Mechanisms of hydrogen trapping in vacancies are
considered which give rise to a high-temperature peak in thermal desorption spectra. Finally,
with the consideration of surface desorption also a
uence-dependent low temperature release
stage can be treated in simulations. The model is able to explain the majority of properties
that are also visible in experiments and gives good qualitative agreement with experimental
observations. An analysis of available experimental data and physical eects is presented.