PUREX

[8] PUREX is applied to spent nuclear fuel, which consists primarily of very high atomic-weight (actinoid or "actinide") elements (e.g. uranium, plutonium, americium) along with smaller amounts of material composed of lighter atoms, notably the fission products produced by reactor operation.

The fuel is first dissolved in nitric acid at a concentration around 7 M. Solids are removed by filtration to avoid the formation of emulsions, referred to as third phases in the solvent extraction community.

Uranium is then stripped from the kerosene solution by back-extraction into nitric acid at a concentration around 0.2 M.[11] The term PUREX raffinate describes the mixture of metals in nitric acid which are left behind when the uranium and plutonium have been removed by the PUREX process from a nuclear fuel dissolution liquor.

The PUREX plant at the Hanford Site was responsible for producing 'copious volumes of liquid wastes', resulting in the radioactive contamination of groundwater.

[13] The PUREX process was invented by Herbert H. Anderson and Larned B. Asprey at the Metallurgical Laboratory at the University of Chicago, as part of the Manhattan Project under Glenn T. Seaborg; their patent "Solvent Extraction Process for Plutonium" filed in 1947,[14] mentions tributyl phosphate as the major reactant which accomplishes the bulk of the chemical extraction.

Reprocessing of spent nuclear fuel by the PUREX method, first developed in the 1940s to produce plutonium for nuclear weapons, [ 1 ] was demonstrated commercially in Belgium to partially re-fuel a LWR in the 1960s. [ 2 ] This aqueous chemical process continues to be used commercially to separate reactor grade plutonium (RGPu) for reuse as MOX fuel. It remains controversial, as plutonium can be used to make nuclear weapons. [ 3 ] [ 4 ]
The most developed, though commercially unfielded, alternative reprocessing method, is Pyroprocessing , [ 5 ] suggested as part of the depicted metallic-fueled, Integral fast reactor (IFR) a sodium fast reactor concept of the 1990s. After the spent fuel is dissolved in molten salt, all of the recyclable actinides , consisting largely of plutonium and uranium though with important minor constituents, are extracted using electrorefining/ electrowinning . The resulting mixture keeps the plutonium at all times in an unseparated gamma and alpha emitting actinide form, that is also mildly self-protecting in theft scenarios. [ 6 ]
A simplified plutonium extraction flow chart.
Structure of uranyl nitrate complex that is extracted in PUREX. [ 9 ]