Kinetic theory of the growth of the circular oxidation islands on the UO2 surface

Island-like oxidation of a solid surface is studied. Such a process occurs for example at the beginning of the second stage of the oxidation of UO2 to U3O8, and its study is thus important for handling of used nuclear fuel in intermediate dry air storage. Mathematical formulation of the problem is presented, approximate analytical formulas are derived and discussed for the isothermal case, and the non-isothermal case is studied numerically. It is shown that for the accurate prediction of the UO2 surface oxidation, it is important to know separately the rates of island nucleation and of island-radius growth. Only a certain product of these two rates can be obtained from isothermal experiments. Here we show how one can determine directly the values of the activation energies of both these rates from a series of suitably designed accelerated non-isothermal experiments.