ИСТИНА

The explosiveness of extraction technological processes in radiochemical industry is determined by the following main reasons: the interaction of an organic solution (extraction mixture) and degradation products with an oxidizing agent (nitric acid and metal nitrates); ignition of inflammable vapors and gases, including vapors of the diluent and the products of its radiation decomposition, radiolytic hydrogen, in mixtures with a gaseous oxidant. Ensuring the explosion safety of technological processes of radiochemical processing of nuclear fuel and high-level liquid waste requires systematic research to obtain information about the kinetics and mechanisms of interaction of nitric acid with the components of extraction systems, the qualitative and quantitative composition of the products of radiation destruction of technological media. Kinetic studies allow us to estimate the influence of various factors on the development of oxidative processes, as well as to determine the boundary conditions for the transition of oxidative processes to the thermal explosion mode. To solve the issue of ensuring the explosion safety of technological processes of radiochemical enterprises, it is necessary to have a number of characteristics of extraction systems, that allow to evaluate the process safety in the regulated conditions and in case of deviations from normal operation. Limit parameters are necessary to assess the probability of accidents and their consequences. The main characteristics to determine the possibility of development of a thermal explosion, as applied to extraction systems, are: the maximum rate of heat and gas emission; the start temperature of the intense exothermic process; the total specific volume of the gaseous products of the oxidation process; thermal effect of interaction. In 2018, on this subject, were studied the extraction mixtures based on diamides of 2,6-pyridinedicarboxylic and 2,2'-bipyryl-6,6'-dicarboxylic acids in trifluoromethylphenylsulfone (FS-13) and meta-nitrobenzotrifluoride (F-3) diluents, considered for the fractionation of high level waste, in contact with 14 mol/L HNO3. The influence of pre-irradiation of mixtures with accelerated electrons on the kinetics of their oxidation is determined. Thermolysis of the mixtures was carried out in an autoclave at temperatures of 170°C and 200°C. Samples of the organic phase were irradiated at a linear electron accelerator UELV-10-10-C-70 (CCU PMR IPCE RAS) at a dose rate of 10 kGy/hour until reaching absorbed doses of 0.1, 0.5 and 1 MGy. It was shown, that by thermolysis of extraction mixtures, irradiated up to 1 MGy, conditions for the development of autocatalytic oxidation do not occur. It was shown, that the main characteristics of fire hazard, which determine the mode of using a flammable liquid (excluding the ignition of the vapor-gas phase) for the FS-13 and F-3 diluents, are significantly higher than the maximum operating temperatures of conducting the technological operations of spent nuclear fuel regeneration. On the basis of the conducted research, we concluded that the use of heavy diluents in the regulated conditions of conducting the extraction process for the HLW reprocessing (UNEX process) will not lead to the ignition of air-vapor mixtures. Acknowledgments: This study was supported by the Russian Science Foundation (project 16-19-00191).