Today, in many countries possessing highly developed nuclear power, the concept of a closed nuclear fuel cycle (NFC) with reprocessing of spent nuclear fuel (SNF) prevails. One advantage of the closed NFC is the pos­sibility of a radical solution to the problem concerning long-term safe management of long-lived radionuclides, as SNF reprocessing allows these radionuclides to be recovered and handled individually.

Transmutation is a reliable method for the management of long-lived radionuclides. Another promising method is based on the creation of espe­cially strong matrices to be disposed of in geological formations. In both cases, the long-lived radionuclides contained in SNF must be selectively recovered. The bulk of long-lived radionuclides are contained in liquid high-level wastes (HLW) arising from SNF reprocessing. Therefore, the problem of individual or group separation of long-lived radionuclides from HLW calls for the development of effective partitioning methods. The com­position of the fractions depends on the chosen method for further manage­ment of ecologically hazardous radionuclides, i. e. on their transmutation or production of stable matrices for their prolonged storage or final disposal. The most important fractions generated by HLW reprocessing are:

• cesium and strontium (in combination or separately);

• actinides and lanthanides (in combination or separately).

Among the different ways of HLW partitioning (precipitation, sorption, chromatography, etc.), extraction processes are of special interest. The fol­lowing extraction systems should be considered as most promising:

• neutral organophosphorus compounds (alkylphosphine oxides [1,2,3], carbamoylphosphine oxides [4,5], phosphorilated calixarenes [6]);

• acidic organophosphorus compounds (diisodecylphosphoric acid [7], zirconium salts of dialkylphosphoric acids [8]);

• macrocyclic compounds (crown-ethers [9], calix-crowns [10]);

• diamides (DIAMEX-process [11,12] or ARTIST-process [13]);

• hydrophobic anions in polar diluents (chlorinated cobalt dicarbolide — CCD [14]);

• synergistic mixtures of different extractants [15-18].

So far, the only method which has found commercial application is extrac­tion of cesium and strontium by CCD [19]. CCD was first proposed for Cs and Sr extraction by Czech scientists [20] and the technological bases of this process were then elaborated by Czech and Russian scientists; thereafter, specialists at the Khlopin Radium Institute (KRI) and Production Association Mayak (Mayak PA) developed the process up to its introduction at a radiochemical plant [21].

A problem encountered in the development of technology for HLW management concerned the recovery of actinides (uranium, neptunium, plutonium, americium, curium) and rare-earth elements (REE), along with cesium and strontium. The problem could be solved by using the above- listed extraction systems, for example the UREX (Uranium Extraction) process [22]. However, the extraction of several extractants in several extraction cycles is more expensive when compared to extracting every­thing in one extraction cycle, so extractants for the simultaneous recovery of different fractions from HLW are of great interest.