Modeling of High-Temperature Corrosion of Zirconium Alloys Using the eXtended Finite Element Method (X-FEM)

Oxidation modeling in modern nuclear fuel performance codes is currently limited by the lack of coupling with mechanics, thus preventing proper description of how high-temperature oxidation impacts mechanical properties. This is mostly due to the fact that the finite difference formalism adopted in corrosion models is incompatible with the direct coupling with mechanics in the finite element modeling employed in modern nuclear fuel performance codes. In this study, a physically based zirconium alloy corrosion model called the Coupled-Current Charge Compensation (C4) model, which was initially developed for operating temperature conditions, has been updated to include high-temperature corrosion in order to provide additional critical information (e.g., oxygen concentration profile) under loss-of-coolant accident (LOCA) conditions-information lacking in existing empirical models. The C4 model was implemented in the MOOSE finite-element framework developed at Idaho National Laboratory, enabling it to be used in the BISON nuclear fuel performance code based on the MOOSE framework. To precisely track the different interfaces at a relatively low computational cost, the eXtended Finite Element Method (X-FEM) was applied in MOOSE. The model's results were compared to those of existing empirical models as well as metallographic analysis of high-temperature oxidized Zircaloy-4 coupons. Oxygen diffusivities in the alpha and j3 phases resulting from this comparison closely agree with those found in the literature. The C4 model implemented with X-FEM in MOOSE now has the capability to accurately predict oxide, oxygenstabilized alpha, and prior j3 phase layer growth kinetics under isothermal exposure at high temperature (1000-1500 degrees C). Furthermore, in contrast with the empirical models, the C4 model accounts for the finite thickness of the fuel cladding. It can predict the oxygen concentration profile evolution through the whole cladding, enabling evaluation of the remaining ductile thickness-a crucial variable for modeling the mechanical behavior of the fuel cladding under LOCA. This implementation allows direct coupling with mechanics, at a low computing cost, using finite-element-based nuclear fuel performance codes such as BISON.

Automated summary

This study presents an updated C4 model for high-temperature corrosion, implemented with X-FEM in the MOOSE framework, allowing for accurate prediction of oxidation kinetics and phase layer growth under high temperatures. The model considers the finite thickness of the fuel cladding, accurately predicts the evolution of oxygen concentration profile, and enables evaluation of the remaining ductile thickness crucial for modeling the mechanical behavior of fuel cladding under LOCA. This implementation allows for direct coupling with mechanics, at a low computing cost, in finite-element-based nuclear fuel performance codes like BISON.