How does the PUREX process separate plutonium from uranium?

The PUREX (plutonium-uranium extraction) process separates plutonium from uranium through a series of solvent-extraction steps.12

The process begins by dissolving spent nuclear fuel in nitric acid. This solution is then contacted with an organic solvent containing tributyl phosphate (TBP), which acts as a complexing agent to pull both uranium and plutonium into the oil phase, leaving fission products behind in the aqueous acid solution.12

To separate the plutonium from the uranium, the loaded organic extract is contacted with an aqueous phase containing specific chemical reductants. These reductants alter the chemical state of the plutonium, causing it to move out of the TBP solution and into the aqueous phase, while the uranium remains in the organic solvent. The uranium is subsequently stripped from the TBP into a separate dilute nitric acid solution. Additional extraction and stripping cycles are often performed to ensure high levels of purity for both the recovered uranium and plutonium streams.21