Separation
of the minor actinides (Am, Cm) from the lanthanides
at an industrial scale remains a significant technical challenge for
closing the nuclear fuel cycle. To increase the safety of used nuclear
fuel (UNF) reprocessing, as well as reduce associated costs, a novel
solvent extraction process has been developed. The process allows
for partitioning minor actinides, lanthanides, and fission products
following uranium/plutonium/neptunium removal, minimizing the number
of separation steps, flowsheets, chemical consumption, and waste.
This new process, actinide lanthanide separation (ALSEP), uses an
organic solvent consisting of a neutral diglycolamide extractant,
either N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) or N,N,N′,N′-tetraoctyldiglycolamide (TODGA), and an acidic
extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]),
dissolved in an aliphatic diluent (e.g., n-dodecane).
The An/Ln coextraction is conducted from moderate-to-strong nitric
acid, while the selective stripping of the minor actinides from the
lanthanides is carried out using a polyaminocarboxylic acid/citrate
buffered solution at pH anywhere between 3 and 4.5. The extraction
and separation of the actinides from the fission products is very
effective in a wide range of HNO3 concentrations, and the
minimum separation factors for lanthanide/Am exceed 30 for Nd/Am,
reaching >60 for Eu/Am under some conditions. The experimental
results
presented here demonstrate the great potential for a combined system,
consisting of a neutral extractant such as T2EHDGA or TODGA, and an
acidic extractant such as HEH[EHP], for separating the minor actinides
from the lanthanides.