  Zirconium alloys are used as nuclear fuel cladding material due to their
mechanical and corrosion resistant properties together with their favorable
cross-section for neutron scattering. At running conditions, however, there
will be an increase of hydrogen in the vicinity of the cladding surface at the
water side of the fuel. The hydrogen will diffuse into the cladding material
and at certain conditions, such as lower temperatures and external load,
hydrides will precipitate out in the material and cause well known
embrittlement, blistering and other unwanted effects. Using phase-field methods
it is now possible to model precipitation build-up in metals, for example as a
function of hydrogen concentration, temperature and external load, but the
technique relies on input of parameters, such as the formation energy of the
hydrides and matrix. To that end, we have computed, using the density
functional theory (DFT) code GPAW, the latent heat of fusion as well as solved
the crystal structure for three zirconium hydride polymorphs: \delta-ZrH1.6,
\gamma-ZrH, and \epsilon-ZrH2.
