ИСТИНА

Developed in 2001, the classic UNEX process consisted of the cesium, strontium, neptunium, plutonium, americium and rare earth elements (REE) combined extraction directly from high-acid (up TO 6M HNO3) high-level waste or dissolved in 3M HNO3 non-combustible high-level waste residues using an extraction system based on 0.08 M chlorinated cobalt dicarbollide (CCD), 0.01- 0.02 M Ph2Bu2CMPO and 0.35-0.6 vol.% PEG-400 in polar diluent F-3. The disadvantages of the developed classical extractant of the UNEX process include the presence of phosphorus and sulfurorganic reagents in the system, which doesn’t allow burning waste extraction solutions without the formation of additional solid waste sulfates or phosphates (CHON-concept). Partly to get rid of these shortcomings allow subsequent modification of UNEX-process that provides nitrogen-containing polydentate complexing agent, such as di(N-ethyl-4-ethylaniline) 2,2’-bieden-6,6’-dicarboxylic acid (DYP-9), di(N-ethyl-4-foradile) 2,6-piridindikarbonovoy acid (Et(pFPh)of the DPA), di(N-ethyl-4- hexylaniline) 2,2’-bipyridine-6,6’-dicarboxylic acid (DYP-7) for extraction of TPE and REE in the organic phase, allowing for simple incineration of waste organic reagents (CHON-concept). However, their thermal and radiation stability has not been sufficiently studied. For the comparative analysis of the interaction of components of extraction systems based on DYP-9, DYP-7 and Et(pFPh)DPA in diluents F-3 and FS-13 in emergency conditions, experiments were conducted using an autoclave and the dependence of the gas release parameters on the temperature and radiation dose. It is shown that during the heating of both samples of diluents F-3 and FS-13 and extraction mixtures with nitric acid, oxidative processes occur, accompanied by gas evolution, but they don’t have a pronounced autocatalytic character. In closed devices for non-irradiated two-phase systems, a noticeable gas release was observed at temperatures of about 110° C, while it was not accompanied by significant exothermic effects. The recorded pressure values (18-23 atmospheres) during heating of irradiated samples in the autoclave were less than in the case of heating of extraction systems containing TBP under comparable conditions (up to 60 atmospheres); the achieved overheating of samples due to exothermic processes (4-10 °C) were significantly lower compared to extraction systems containing TBP (more than 100 °C). Thus, under external thermal influence, the studied extraction systems with diluents F-3 and FS-13, even in the case of radiation degradation and the difficulty of the output of technological blowers, including due to mechanical external influence on communications and equipment, will present a lower danger compared to the extraction systems based on TBF, used in practice. Acknowledgments: The work is executed at financial support of Russian Scientific Foundation (project 16-19-00191).