Plutonium is removed from spent fuel by chemical separation; no nuclear or physical separation (as for example in uranium enrichment) is needed. To be used in a nuclear weapon, plutonium must be separated from the much larger mass of non-fissile material in the irradiated fuel.

The jargon 'head end' is applied to those operations which must be carried out before the separation process itself begins. They include receipt of the fuel in the head end plant and mechanical operations to reduce the fuel elements to a more suitable form for the processes which follow.

Once free of the supporting structure, the elements are cut up, placed in a dissolver and dissolved in hot nitric acid. During this process, the 'dissolver off-gases' krypton, xenon, iodine and carbon dioxide, together with nitrogen oxides and steam (from the nitric acid) are released. All of these, except krypton and xenon which are chemically inert, but radioactive, gases, are typically trapped or recycled for re-use. Any particles of fuel cladding or fission products which have not dissolved are removed by filtering them out in a centrifuge.

After being separated chemically from the irradiated fuel and reduced to metal, the plutonium is immediately ready for use in a nuclear explosive device. If the reactor involved uses thorium fuel, 233 U, also a fissile isotope, is produced and can be recovered in a process similar to plutonium extraction.