  We present a kinetic model for solid state phase transformation
(alpha<-->beta) of common zirconium alloys used as fuel cladding material in
light water reactors. The model computes the relative amounts of beta or alpha
phase fraction as a function of time or temperature in the alloys. The model
accounts for the influence of excess oxygen (due to oxidation) and hydrogen
concentration (due to hydrogen pickup) on phase transformation kinetics. Two
variants of the model denoted by A and B are presented. Model A is suitable for
simulation of laboratory experiments in which the heating/cooling rate is
constant and is prescribed. Model B is more generic. We compare the results of
our model computations, for both A and B variants, with accessible experimental
data reported in the literature covering heating/cooling rates of up to 100
K/s. The results of our comparison are satisfactory, especially for model A.
Our model B is intended for implementation in fuel rod behavior computer
programs, applicable to a reactor accident situation, in which the Zr-based
fuel cladding may go through alpha<-->beta phase transformation.
