The nuclear fission power fuel cycle

The nuclear fission fuel cycle is illustrated for present nuclear reactors in Figure 4.1 [6]. First, the mined natural uranium is processed in centrifuges to enrich the 235U92 concentration of uranium from 0.72% in natural uranium to 4-6%; this enriched fuel is fabricated into metal-clad fuel rods (or pins), which are loaded into nuclear reactors, leaving behind as residue slightly depleted (in 235U92) uranium and the "tails," consisting basically of 238U92 and less than 0.2-0.3 wt% 235U92. The tails are retained by governments for future use as fuel or in other applications where heavy atomic mass material is needed.