Separative Work (SW) stands for the effort necessary to separate U235 and U238. It is measured in kilograms of separative work (kg SW).
The term Separative Work Unit (SWU) is also used where 1 SWU equals 1 kg SW. As a larger unit, 1 metric ton of separative work (1 tSW = 1,000 kg SW) is used. The capacity of enrichment plants is measured in tonnes SW per year (tSW/a).
A large nuclear power station with a net electrical capacity of 1,300 MW requires annually about 25 t of enriched uranium with a concentration of 3.75% U235. This quantity is produced from about 210 t of natural uranium using about 120 t separative work. An enrichment plant with a capacity of 1,000 tSW/a is, therefore, able to enrich the uranium needed to fuel about eight large nuclear power stations.