Think of the DUF6 conversion process as having five parts that result in two products, uranium oxide (UOX) and hydrofluoric acid (HF). The oxide is stored for eventual disposal or reuse, and the HF is sold for industrial applications.
Actually operating the five parts of the process is quite complex and calls for the integration of multiple mechanical, chemical, temperature, scrubbing, recycling and storage systems.
It also calls for a cadre of well-trained staff to run and maintain the various process systems 24/7.
Here are the five parts of the process:
Cylinder Recycling. There are presently more than 63,000 cylinders filled with DUF6 stored in cylinder yards at the Paducah and Portsmouth (Piketon) sites. New DUF6 material is still being generated at the Paducah Gaseous Diffusion Plant.
The typical size for a cylinder is four feet high (48 inches in diameter) and either holds 10 tons or 14 tons. The 10-ton thick-walled cylinder weighs 4500 lbs. and can hold 20,000 lbs. of DUF6. The 14-ton thin-walled cylinder weights 2600 lbs. and can hold 28,000 lbs. of material.
The cylinders are moved from the yards by various vehicles and brought into the Conversion Building, where they are loaded into autoclaves.
The cylinder is connected to a conversion unit and monitoring systems. When all the systems are connected, heating begins. Cylinder weight, line pressure, temperature and flows are monitored by a process control system. With heat, the DUF6 sublimes, or becomes gas. The gas enters the conversion unit.
The cylinder is then cooled down and disconnected and moved to a station where the interior is neutralized with KOH (potassium hydroxide). The cylinder goes into storage and is then modified so that it can be filled from the end. It is upended, filled, and returned to the storage yard. It will be stored for future disposal or for reuse of the UOX.
Vaporization. Once the cylinder is in the autoclave, the objective is to turn the DUF6 from a solid to a gas. That’s a process called sublimation, and it occurs at a temperature, roughly, of boiling water.
Each production line consists of autoclaves and conversion units. All of the connected elements are heated to prevent the gas from cooling (desubliming), sticking and creating bottlenecks.
Monitoring for leaks is continuous.
Conversion. The conversion unit separates the DUF6 into UOX and HF. Steam and hydrogen separate the two in an exothermic chemical reaction. HF vapor flows out the top through filters.
Oxide Powder Handling. The oxide powder goes through a cooler and then is transferred to hoppers. The hoppers drop the oxide through roller-compactors. The compacted oxide is dropped into recycled cylinders.
HF Recovery System. Once the HF passes out the top of the conversion unit, it goes into a scrubbing system to be converted to liquid. The acid is stored in tanks. The storage tanks serve as the loading station for transfer to a railcar or truck to remove the material from the site. There are multiple industrial uses for the processed HF.