The conversion of enriched UF₆ into finished UO₂ fuel pellets can follow several chemical routes, each with distinct advantages:
| Route | Process | Key Features |
|---|---|---|
| ADU (Ammonium Diuranate) | UF₆ hydrolysed in water, then precipitated with ammonia as (NH₄)₂U₂O₇, filtered, dried and calcined to UO₂ | Oldest and most widely used route; produces fine, reactive powder; used at most commercial fabrication plants worldwide |
| AUC (Ammonium Uranyl Carbonate) | UF₆ reacted with ammonium carbonate solution to form (NH₄)₄UO₂(CO₃)₃, then decomposed to UO₂ | Produces free-flowing, spherical particles ideal for direct pressing; widely used in Germany and by BNFL at Springfields |
| IDR (Integrated Dry Route) | UF₆ steam-hydrolysed to UO₂F₂, then reduced with hydrogen to UO₂ in a single rotary kiln | Minimal liquid waste; compact process; developed in the UK at Springfields; currently used for AGR fuel production |
The ADU route is the most established, but the IDR route is favoured where minimising liquid effluent is a priority. All three routes must produce UO₂ powder that meets strict specifications for particle size, surface area, oxygen-to-uranium ratio, and impurity content, as these properties directly affect pellet density and in-reactor performance.