The enrichment level achieved by a single centrifuge is insufficient to obtain the desired concentration of between 3% and 5% U235 in a single step. It is, therefore, necessary to connect a number of centrifuges in series.
In order to obtain more throughput of material, the centrifuges are also connected in parallel in an industrial plant. The arrangement of centrifuges connected in parallel and in series is called a 'cascade'. In a uranium enrichment plant several cascades are operated in parallel to form an 'operational unit' producing one U235 assay. Several operational units together form one enrichment plant.
This modular design enables centrifuge plants to be expanded in line with market demands. It also permits the most recently developed and qualified centrifuge technology to be introduced rapidly into plant operation, thereby gaining maximum economic benefits of the development programme.
Low energy consumption in the centrifuge process has turned out to be one of today’s most important advantages. Because centrifuge rotors spin in a vacuum on almost friction-free bearings, modern plants with current types of centrifuges need only about 40 kWh of electricity to produce one unit of separative work. Thus, the specific energy consumption of the centrifuge is, by a factor of almost 60, less than the 2,400 kWh/kgSW that diffusion plants need.