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...
Nitric acid solutions of hydrazine nitrate are used in radiochemical technology in individual operations of regeneration of spent nuclear fuel and high-level waste. The conditions under which such operations are done are different with respect to temperature, time, radiation dose rate for the radionuclides, and also the concentration of nitric acid and hydrazine nitrate. Reaction of hydrazine nitrate with the products of radiative and thermal decomposition of aqueous HNO 3 solutions leads to accumulation of salt-forming ammonium cations and hydrazoic acid (a potential explosion hazard). In order to choose the optimal conditions for performing the technological operations with nitric acid solutions containing macro amounts of hydrazine nitrate and to assure the absence of explosion hazard in these processes, we need to know the kinetics of radiative and thermal decomposition of hydrazine nitrate and accumulation of its major oxidation products.Data on the radiochemical decomposition of hydrazine nitrate in nitric acid solution are limited to [1], in which the kinetic characteristics of this reaction are not considered. More detailed information about the kinetics and mechanism of radiochemical reactions of hydrazine in aqueous solutions at pH > 7.5 is given in [2, 3]. The kinetic characteristics of thermochemical oxidation of hydrazine and HN 3 in acid media by nitrous and nitric acids are discussed in separate publications [4][5][6][7][8][9].In this paper, we decided to focus on two tasks: an experimental study of the radiochemical behavior of hydrazine and its decomposition products in nitric acid solutions within the temperature limits and for nitric acid concentration corresponding to the conditions under which hydrazine is used in different operations in radiochemical technology; and computer modeling of radiochemical decomposition of hydrazine nitrate in nitric acid solutions based on a formal kinetic scheme, including the reaction of hydrazine with the products of radiative and thermal decomposition of aqueous nitric acid solutions, with the goals of using a mathematical model for describing the concentration behavior of hydrazine and its products in HNO 3 solutions under different radiation and heat exposure conditions.Procedure. In order to study the radiative and thermal decomposition of hydrazine nitrate, we carried out a series of irradiations of aqueous solutions with nitric acid concentration 2 M and 8 M and hydrazine nitrate concentration 0.2 M and 1 M with 6~ 3,-radiation and dose rate 1.2 Gy/sec and a temperature of 40, 60, and 80~ The concentration of hydrazine nitrate, ammonium ions, and hydrazoic acid was determined according to the procedures in [10][11][12] with error no greater than 10%.Results and discussion. The change in concentration of hydrazine nitrate and its products as a function of absorbed dose is shown in Fig. 1. The dependences are linear in log[N2H4] vs. irradiation time coordinates, and from the slope of the curves we determined the effective first-order reaction rate constant...
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