 Separative work unit

A unit of isotope-separation work used in fuel-cycle accounting. If stream masses are in kilograms and $x$ is isotope mass fraction, $S=PV(x_p)+WV(x_w)-FV(x_f)$ is in kg-SWU, with $V(x)=(1-2x)\log [(1-x)/x]$. This is a resource-accounting relation, not equipment or cascade design.