Isotope Separation - The SWU (separative Work Unit)

The SWU (separative Work Unit)

Separative Work Unit (SWU) is a complex unit which is a function of the amount of uranium processed and the degree to which it is enriched, i.e. the extent of increase in the concentration of the U-235 isotope relative to the remainder.

The unit is strictly: Kilogram Separative Work Unit, and it measures the quantity of separative work (indicative of energy used in enrichment) when feed and product quantities are expressed in kilograms. The effort expended in separating a mass F of feed of assay xf into a mass P of product assay xp and waste of mass W and assay xw is expressed in terms of the number of separative work units needed, given by the expression SWU = WV(xw) + PV(xp) - FV(xf), where V(x) is the "value function," defined as V(x) = (1 - 2x) ln ((1 - x) /x).

Separative work is expressed in SWUs, kg SW, or kg UTA (from the German Urantrennarbeit )

• 1 SWU = 1 kg SW = 1 kg UTA
• 1 kSWU = 1.0 t SW = 1 t UTA
• 1 MSWU = 1 kt SW = 1 kt UTA

If, for example, you begin with 100 kilograms (220 pounds) of natural uranium, it takes about 60 SWU to produce 10 kilograms (22 pounds) of uranium enriched in U-235 content to 4.5%