Who reprocesses used nuclear fuel

The chemistry is PUREX, developed in the 1940s for weapons plutonium and adapted for civil fuel. Chop the assemblies, dissolve them in nitric acid, and use solvent extraction to pull out uranium and plutonium separately, leaving the fission products behind as a highly radioactive liquid that is then vitrified into glass logs.

What it achieves. It recovers material that can be made into fresh fuel: the plutonium into MOX, the uranium into reprocessed uranium that only Russia converts at scale. It also cuts the volume of material needing deep disposal substantially, though not the radioactivity.

What it does not achieve. It does not remove the need for a repository. Vitrified high-level waste still has to go underground, and reprocessing countries are no further ahead on disposal than the ones that skipped it. France, which reprocesses more than anyone, does not expect Cigéo to open before 2050.

Why most countries do not do it. Separating plutonium creates a stream of weapons-usable material in a civil facility, which is the proliferation concern the United States found decisive when it abandoned commercial reprocessing in the 1970s. It is also expensive, and only pays against a uranium price far above anything seen since. The countries that reprocess mostly decided to before either of those arguments had been made.

The result is a large stockpile of separated civil plutonium held by countries whose plans for using it have not survived contact with events. The United Kingdom holds the largest, and shut its MOX plant in 2011.