UNEX-process adaptation for PA Mayak HLW processing

UNEX-process is the extraction technology, developed by specialists of the KRI (Russia) and the INEEL (USA) and intended for the processing of acidic INEEL HLW. Using this technology makes possible to separate a concentrate of the long-lived radionuclides from the HLW. This concentrate can be sent to vitrification. UNEX-solvent consists of chlorinated cobalt dicarbollide (CCD), diphenyl-N,N-dibutylcarbamoylphosphinoxide (Ph2Bu2), polyethylene glycol (PEG) and the polar diluent - phenyltrifluoromethyl sulfone (FS-13). The task of this investigation is as follows: (1) to choose the composition of the UNEX-solvent, which will be enable to separate Cs, Sr and REE from the PA 'Mayak' HLW; (2) to select the complexones for the decreasing of stable elements extraction; (3) to determine the optimal conditions of extraction. As a result, of this investigation, UNEX-solvent was developed for processing the PA 'Mayak' HLW. Its composition is follows: 0.08 M CCD, 0.065 M Ph2Bu2; 0.45% Slovafol-909 and F-3 as the diluent. F-3 is the diluent used at the PA 'Mayak'. PhOctiBu2 CMPO is used for increasing the capacity of the UNEX-solvent and the efficiency of the separation of the REE and Am instead of Ph2Bu2 CMPO. The application of Slovafol-909 instead of PEG-400 improves the stability of the extractant in the storage. Oxalic acid and D-mannitol are complexones for the decreasing of extraction of Fe and Zr. The compositions of process solutions and the optimal conditions of the extraction were determined. The results obtained with simulated HLW and the real HLW are in agreement. The extraction, scrub and strip operations were tested with the real HLW. The scheme of the static tests of the UNEX-process with real HLW. There were no interphase films and insoluble precipitates. The rate of separation into layers was high. This variant of the UNEX-process makes possible the effective extraction of the radionuclides from HLW of the PA 'Mayak' and the complete stripping from the solvent. (authors)