Partitioning of minor actinides from HLLW using the DIAMEX process. Part 2 - Hot continuous counter-current experiment

Among several processes proposed world-wide, the French DIAMEX (DIAMide EXtraction) process seems to be very efficient for the removal of Minor Actinides (MA) from genuine High Level Liquid Waste (HLLW). The MA are in this process directly extracted from the PUREX (Plutonium Uranium Redox EXtraction) raffinate together with fission lanthanides using the completely combustible diamide extractant. In this work a hot demonstration of the DIAMEX process using genuine high-level PUREX raffinate is reported. The continuous counter-current experiment was carried out in a 16 stage centrifugal extractor battery, installed in a hot cell. In order to produce a representative HLLW a PUREX process was applied on dissolved fuel using the same equipment. In the DIAMEX process up to 6 extraction stages were sufficient to achieve feed decontamination factors between 100 and 230 for lanthanides and above 300 for minor actinides. Go-extraction of molybdenum and zirconium were efficiently prevented using oxalic acid scrubbing. The back extraction proved to be very efficient, yielding in 4 stages more than 99.9 % recovery of both the lanthanides and the actinides. Go-extracted ruthenium, technetium, palladium and neptunium are less efficiently back-extracted requiring further process development.