Zirconium alloys are very suitable as fuel claddings and structural
components in nuclear reactors due to their low cross section for ab-
sorption of thermal neutrons and high resistance to corrosion and irra-
diation damage. Zirconium alloys are however susceptible to hydrogen
embrittlement. Precipitation of zirconium hydrides is attributed to
the embrittlement eect in zirconium alloys. In this project ab-initio
simulations of Zr and the three dierent zirconium hydrides -ZrH,
-ZrH1:5 and -ZrH2 are performed to calculate structural, elastic and
thermal properties of these dierent compounds. The goal with the
project was to calculate the equilibrium structures of the H-Zr system
using ab-initio methods. The results from the calculations of thermal
and mechanical properties were found to be in good agreement with
previous results and experiments where these were available. Calcula-
tions of the phonon band structure for the dierent hydrides show that
the band structure of the hydrides has two characteristic bands, one
corresponding to vibrations in the zirconium sublattice and one cor-
responding to vibrations in the hydrogen sublattice. The calculated
heat capacity of the dierent compounds was found to be described
very well by the Einstein model for the heat capacity of a solid. By
calculating the free energy of formation for the dierent compounds it
was found that at high hydrogen concentrations -hydride is the equi-
librium structure. At intermediate hydrogen levels the equilibrium
structure can’t be determined.