Progress on Synthesis Modelling of UO2 Oxidation

A comparative synthesis of available thermal-reactor fuel oxidation models as well as experiments on fuel oxidation and volatilization was performed with the aim to determine possible improvements to be introduced into the DIVA-ELSA module of ASTEC code. Models already included into the code consider only oxygen surface exchange neglecting the diffusion phenomena inside the fuel matrix. This may be enough for describing oxidation in steam far small fuel samples but cannot correctly express oxidation in air and reducing conditions as well as large fuel samples. Besides, to correctly represent the fuel oxidation it is often necessary to impose particular boundary conditions far the flow ingress which may set useful the code for post-test interpretation but not far prediction of experiments. Modeling of the zircaloy geometry and its influence aver FP release within cladded experiments might be tested in ASTEC by comparing with stand-alone ELSA calculations in order to improving modeling for the cladding geometry. Eventual corrections to the oxidation model might be considered to take account of oxygen diffusion inside the fuel lattice and through the surface layer far extended geometries, as well as mechanistic correction for the oxidation kinetics and modification of the diffusion coefficient by considering dependence on the lattice defects. The volatilization model is being tested aver accessible experiments and conclusions will be drawn out when upcoming models are ready.