Volume 5, Issue 5 (May 2008)
CASTA DIVA®: Experiments and Modeling of Oxide-Induced Deformation in Nuclear Components
In-pile deformation of nuclear structural components remains a major preoccupation for fuel vendors and utilities, especially when introducing new alloys or extending burn-ups. The usual invoked causes of such deformations are free growth, hydriding (hydrides induce a volume expansion which translates into deformation), irradiation creep if the component is subjected to external loads (e.g., axial load for the fuel assembly), and flux gradients (for fuel channel bow). In this paper we show through out-of-pile experiments (autoclave corrosion and low temperature air oxidation) and in-pile data analysis that the oxide layer significantly contributes to the deformation. A model (CASTA DIVA®) taking into account all the above mentioned phenomena has been derived and correctly predicts the deformation behavior, the stresses in the oxide layer, as well as the external cracking of the oxide. The relative impacts of hydriding and stresses in the metal are computed. A comparison between Zircaloy-4 and M5® is made, showing the better behavior of M5.