We present a kinetic model for solid state phase transformation (  ⇋  ) of common zirconium alloys
used as fuel cladding material in light water reactors. The model computes the relative amounts of
 or  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  ⇋  phase transformation.