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Radiation-induced and hydrolytic decomposition of HDBP and its zirconium salt in organic solutions and two-phase aqueous-organic systems in the presence of TBP and nitric acid is studied. The yields of radiation-induced decomposition of HDBP and temperature dependences of its hydrolysis rate constants are determined. Kinetic equations for radiation-induced decomposition of HDBP are derived.Solutions of dibutylphosphoric acid zirconium salt (Zr-DBP) in organic systems with tributyl phosphate (TBP) were suggested for extractive partitioning of radionuclides of rare-earth and transplutonium elements contained in high-level liquid wastes [1,2]. Changes in the concentrations of Zr-DBP and dibutylphosphoric acid (HDBP) in the course of extractive partitioning may be caused by three major factors: (a) hydrolytic decomposition of extractants, (b) radiation-induced decomposition of extractants, and (c) loss of extractants through their solubility in refreshable aqueous phases. Hydrolysis and radiolysis of TBP in organic solutions and two-phase aqueousorganic systems were thoroughly studied, and the results are summarized in the monographs [335]. However, there are only limited data in the literature on the hydrolysis of HDBP in organic solutions [6], and data on the hydrolysis and radiolysis of HDBP and Zr-DBP in two-phase systems containing TBP are lacking. In this study we examined the chemical and radiation-chemical behavior of HDBP and Zr-DBP in organic solutions and two-phase aqueous-organic systems. The effect of the solubility of HDBP and Zr-DBP in aqueous phases on their concentration changes in two-phase systems with intermittently refreshed aqueous phases will be considered in a separate paper. EXPERIMENTALSamples were irradiated at 24oC on a g-ray unit with a 60 Co source. The dose rate was 2.6 Gy s 31 (W l 31 ), and the maximal accumulated doses ranged to 1.75 MGy (480 W h l 31 ) and 0.36 MGy (100 W h l 31 ) in irradiating homogeneous organic solutions and twophase systems, respectively.Hydrolysis of TBP and HDBP was studied at 40 3 95oC in temperature-controlled cells with an aircooled reflux condenser.All the chemicals were purified using standard methods.The concentrations of HNO 3 , HDBP, and H 2 MBP (monobutylphosphric acid) in organic and aqueous phases were determined in most cases by potentiometric titration. Trace amounts of alkylphosphoric acids were determined by gas chromatography after preliminary alkylation of the acids with dimethyl sulfate [7]. Phosphoric acid was determined photometrically by the absorption of the phosphomolybdate complex [8]. Zirconium in solutions was determined spectrophotometrically with Arsenazo III [9]. RESULTS AND DISCUSSION Hydrolysis of TBP, HDBP, and Zr-DBP in Two-Phase SystemsIn this stage of the study we examined the temperature dependences of the hydrolysis rate constants of TBP, HDBP, and Zr-DBP and determined the activation energies of hydrolysis. These data were then used to estimate the contribution of hydrolysis to the concentration changes of HDBP and Zr-DBP...

A technology for reprocessing mixed uranium-plutonium nitride fiel (MUPN) from BREST reactor is considered. The technology should ensure reprocessing of spent nuclear fuel with the storage time after irradiation of no more than 1 year, 10-15% content of fissile materials (FM), and burn-up of 10% of heavy atoms. The target product of the technology is a mixture of actinide oxides separated from fission products with the separation factor of ~10 6 . A PH (Pyro-Hydro) process was suggested for MUPN SNF reprocessing. It involves pyroelectrochemical fuel reprocessing with separation of U, Np, and Pu from the major fraction of fission products responsible for the heat release from the fuel and for the radiation load on process media, a series of hydrometallurgical operations for final purification of the target products (U-Pu-Np-Am), and radioactive waste (RW) management. The PH process is being developed since 2011 by the teams from the Bochvar High-Tech

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