Presolidification column design modification based on simulation of ammonia flow distribution for external gelation coated particle fuel kernel surrogates fabrication

Presolidification is a critical step in the external gelation process for producing spherical coated particle fuel kernel surrogates, as unstable ammonia flow can cause droplet deformation and nozzle blockage. This study explores the pre-solidification column design modifications and their effect on gas-phase flow behavior, including dimension (height and width), inlet and outlet configurations, column divider, and inlet flow rate, using computational fluid dynamics and experimental validation. Simulation results show that improper column design even with various inlet–outlet arrangements lead to gelation at nozzle, while optimized column geometries with inlet flow control features enable uniform gas distribution within the contact region and stable presolidification without ammonia leakage. Experimental results confirm the simulations, producing dried microspheres with sphericity below 1.2. These findings demonstrate that appropriate presolidification column design and operating conditions are essential for stable external gelation and high-quality spherical coated particle fuel kernel surrogates production.