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In the nuclear fuel industry, sintering process is employed to transform ceramic pellets into dense, solid structures. The natural sintering occurring in the furnace operates through controlled heating and atmosphere, below the melting point and without external forces. This sintering furnace involves coupled physical phenomena and hosts a uranium oxide conversion reaction taking place upstream in the pre-sintering region. Modeling this process with COMSOL Multiphysics®, offers valuable support for optimizing industrial performance and improving the quality of the final products.

Ceramics pellets are loaded in boats conveyed thanks to a walking beam through the furnace. The model focuses on the journey of a boat filled with pellets along the process, where heat transfer, chemical reaction, densification and mechanical stress occur. In the pre-sintering zone, the uranium sesquioxide present in a small fraction reacts to become uranium dioxide. The uranium dioxide pellets enter in a zone where the sintering process takes place. After initially focusing on a single isolated boat, the thermal analysis is refined by incorporating adjacent boats and the walking beam, allowing radiative view factors, setpoint temperature heterogeneity, and heat transfer from surrounding components to be considered. For the chemistry study, the exothermic nature of the reaction is studied as well as the mechanical stresses generated by the change of stoichiometry during the transformation. Then, the influence of humidity on densification during sintering is investigated to optimize operating conditions. To test different configurations on geometry or operating conditions, a user interface has been developed using COMSOL ServerTM which provides remote access to the model over a secure HTTPS connection.

The developed model provides detailed access to key outputs, including temperature distribution, reaction extent, and stress fields. These results enable a quantitative comparison of the different configurations tested along with a better understanding of the interaction between the various physical phenomena occurring within the furnace. All these features are integrated into the user interface, enabling efficient sensitivity analysis of the most influential parameters.