|During the first century…|
Irradiated fuel removed from nuclear reactors is still in the early years of radioactive decay. Activity levels are still very high. Fission products are the most highly radioactive, followed by plutonium and minor actinides. Radioactivity from fission products is overtaken after 200 years by that from plutonium, after decaying by two orders of magnitude. Activity generated by neutron activation of fuel cladding and end caps is at a far lower level.