Dynamics of gas release during thermal oxidation of TBP solutions in Isopar-M in two-phase system
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.250
Dynamics of gas release during thermal oxidation of TBP solutions in Isopar-M in two-phase system
Elena V. Belova, Zayana V. Dzhivanova, Boris F. Myasoedov, Sergey V. Stefanovsky
Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Science (IPCE RAS), Leninskii av. 31/4, Moscow 119071 Russia
ABSTRACT
The dynamics of the gas release at thermal oxidation of the two-phase systems of 30% solution of tri-n-butyl phosphate (TBP) in isoparaffinic diluent Isopar M – aqueous solution of 4.3, 8.2 and 12 mol/L of HNO3 has been investigated within the temperature range from 70°C to 110°C. The effect of pre-irradiation of the system TBP–Isopar-M–HNO3 on the kinetics of its thermolysis has been determined. All of the samples were irradiated with an electron accelerator at a dose rate of 10 kGy/h up to integrated doses of 0.5, 1 and 2 MGy. The parameters of heat and gas emission during thermolysis of the tested extraction system in an open apparatus have been determined experimentally. It has been demonstrated, that there are no conditions for extension of autocatalytic oxidation under heat treatment of two-phase extraction systems in open vessels.
INTRODUCTION
At the current moment, recycling of the spent nuclear fuel (SNF) is one the priorities in the radiochemical industry. The aim of the recycling is decrease the radiation hazard of SNF, safe dispose of unused components and extraction of valuable elements for further use. The core of technology for SNF reprocessing in radiochemical plants all over the world is PUREX-process that provide the high degree of extraction of plutonium and uranium. As in Russia, and abroad almost all types of extraction technology of SNF
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reprocessing involve the use of tributyl phosphate (TBP) as an extractant for the recovery of target components. TBP adequately meets all the process requirements, such as high boiling temperature, resistance to chemicals and to radiation, immiscibility with water, regenerability. Generally, TBP is used in mixtures with various inert diluents in different ratios. Aliphatic hydrocarbons with a linear chain, their mixtures, mixtures of isoparaffins and kerosene are used as diluents [1,2]. The intensity of oxidation processes is significantly affected by radiation and thermal effects during the extraction reprocessing of SNF. The oxidation processes in extraction systems depend on conditions and can proceed with a relatively constant rate of liquid and gaseous products formation or can proceed in autocatalytic regime resulting in self-heating of the mixture and dramatically accelerating gas release. There are several known accidents at radiochemical plants in many countries including Russia that were a res
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