Czech scientists proposed the mixture of CCD with bifunctional neutral organophosphorus compounds (BNOPC) for the extraction of actinides, lanthanides and cesium (strontium was inadequately recovered in this case) [23]. Studies at the Radium Institute have shown [24,25] that the synergistic mixtures of CCD with long-chained (n > 5) phosphorylated polyethylene glycols (PGP — Ph2P(O)CH2O(CH2CH2O)nCH2P(O)Ph2) can simultane­ously recover cesium, strontium, actinides and lanthanides from HNO3 media.

None of the then known extraction systems had such unique extraction properties, and these new developments therefore permitted a universal extraction mixture (UEM) to be patented in 1990. This mixture was suc­cessfully proven to work for simulated and real HLW. Tests were conducted on the recovery of radionuclides from a solution simulating the PUREX process raffinate, containing 1 M HNO3 and the following metals (g/l): REE — 2.1; cesium — 0.3; strontium — 0.25; sodium — 1.5; iron — 1.0 with a total salt content of ~10 g/l. From this solution, the UEM (containing 0.14 M CCD and 0.08 M PGP-300 in metanitrobenzotrifluoride (F-3)) recovered radio­nuclides with distribution ratios of: U(VI) — 6.0; Pu(lV) — 5.1; Np(V) — 4.0; Np(VI) — 6.4; Am — 1.2; Cs — 2.6; Sr — 16.

Extraction of several radionuclides from HLW was proven in a continu­ous regime in the centrifugal extraction bench EZ-40-18 at Mayak PA (Fig. 9.1) by using a UEM composition of 0.14 M CCD and 0.08 M PGP-300 in F-3, with density of 1426 g/cm3 and viscosity 5,4 mPa[8]s at 20°C.

More than 20 L of simulated HLW were treated within 20 hours, with the organic phase making over 15 recycles. Cesium, strontium and REE were

and cumbersome process, which is difficult to achieve even on a laboratory scale.

These circumstances have encouraged scientists at the Radium Institute (RI) and the Idaho National Laboratory (INL), USA, to collaborate on the modification of the above extraction system, which has resulted in the elaboration of the so-called UNEX process (UNiversal EXtraction process). In the UNEX process, a mixture of the commercial reagents CCD, PEG-400 and diphenyl-N, N-dibutylcarbamoyl-phosphinoxide is used in the diluent as the extraction system.