  The integrity of irradiated zirconium based nuclear fuel cladding is related
to the precipitation of hydrides which is closely connected with the solubility
of hydrogen. A review on the development of measurement technologies is given
and the resulting terminal solid solubilities are reflected with respect to the
established model of hydrogen solubility in zirconium alloys. The results often
allow for a different interpretation than the established model. An alternative
qualitative approach is proposed in which the fixed TSSp for the precipitation
of zirconium hydrides is replaced by a kinetic model based on thermal history,
total hydrogen content and the cooling rate. The influence of the modification
of the model from a fixed TSSp to a kinetically limited TSSd is discussed with
respect to the understanding of hydride embrittlement processes in long term
storage.
