On a physics-based model of grain-boundary bubbles overpressurization and its effects on fuel fragmentation

Overpressurization of gas-filled bubbles and pores is considered the main driver of oxide fuel fragmentation and fission gas release into the rod free volume of high burnup fuel during transients. In this framework, advanced modeling of fission gas behavior is crucial to enhance the predictive capabilities of Fuel Performance Codes (FPCs). This study develops a physics-based model for fission gas release from grain boundaries in UO2 fuel and implements it into SCIANTIX, an open-source code developed at Politecnico di Milano to simulate fission gas behavior in nuclear fuels. The model first describes gas release through continuous bubble networks at the grain face, exploiting data from Post-Irradiation Experiments (PIE). It then focuses on gas release from damaged grain boundaries, applying fracture mechanics to predict micro-cracking induced by bubble overpressurization. Finite Element (FE) simulations are performed using ABAQUS software, in order to assess stress intensification as a function of bubble density, shape, and size. The model is validated against three separate-effect experiment datasets, including annealing tests and grain-face observations via scanning electron microscopy, demonstrating promising predictive capabilities for gaseous swelling and fission gas release. This work provides a valuable tool for improving fission gas behavior modeling through a physics-based approach and lays the groundwork for future extensions to High Burn-up Structures, offering a framework for a more comprehensive description of fuel fragmentation.

CAPPELLARI Elisa;  PIZZOCRI Davide;  ZULLO Giovanni;  NICODEMO Giovanni;  VAN UFFELEN Paul;  SCHUBERT Arndt;  DEANESI Sophie;  LUZZI Lelio; 

2025-09-25

ELSEVIER

JRC141274

1873-4820 (online),   

https://www.sciencedirect.com/science/article/pii/S0022311525005100?via%3Dihub,    https://publications.jrc.ec.europa.eu/repository/handle/JRC141274,   

10.1016/j.jnucmat.2025.156116 (online),