Simulation of the Melting Behavior of the UO2-Zircaloy Fuel Cladding System by Laser Heating

The present research focuses on laser-melting and successive analysis of laboratory-scale uranium dioxide nuclear fuel samples in direct contact with the Zircaloy-4 cladding. The goal is to characterise the melted and refrozen interfaces, in particular observing the local change of the melting point and the inter-diffusion of fuel and cladding materials under inert gas (Ar), in the presence of hydrogen (Ar + 6% H2) or in air. The sample composition was analysed by Scanning Electron Microscopy to verify the occurrence of diffusion and segregation phenomena during the laser heating cycles. Laser melting experiments were performed on pellets of uranium dioxide cladded in Zircaloy-4 rings to simulate the configuration of a LWR fuel rod. Under inert gas, the material inter-diffusion resulted in consistent melting point depression (of up to 200 K below the melting point of pure UO2) at the interface between fuel and cladding. Experiments carried out in the presence of H2 displayed a more limited effect on the melting temperature, but they resulted in a remarkable embrittlement of the whole structure, with large fragmentation of the Zircaloy cladding. This was certainly due to the formation of brittle Zr hydrides. The observed melting point decrease was even more pronounced (up to over 400 K) under air in uranium-rich samples, due to the change in the stoichiometry of UO2 in UO2+x.

SOLDI Luca;  MANARA Dario;  BOTTOMLEY D.;  ROBBA Davide;  LUZZI Lelio;  KONINGS Rudy; 

2023-11-23

TAYLOR & FRANCIS INC

JRC127386

0029-5639 (online),   

https://www.tandfonline.com/doi/full/10.1080/00295639.2022.2106731,    https://publications.jrc.ec.europa.eu/repository/handle/JRC127386,   

10.1080/00295639.2022.2106731 (online),