Neodymium oxalate structure and morphology were modified by adding a phosphonate, NTMP, during the oxalic precipitation step. Spherical agglomerates of neodymium oxalate Nd-2(C2O4)(3)(H2O)6 center dot 12H(2)O composed of thin hexagonal rods were precipitated instead of decahydrated oxalate Nd-2(C2O4)(3)(H2O)6 center dot 4H(2)O with rod-like particles usually obtained in the absence of additive. Despite some differences in the complexation with NTMP and complexity from redox, the use of NTMP was successfully transposed to the plutonium system. Spherical agglomerates of plutonium (III) oxalate were so obtained, leading to spherical agglomerates of PuO2 after thermal treatment.

Spent fuel reprocessing and notably plutonium recycling contributes in enhancing the sustainability of nuclear energy by preserving uranium natural resources and decreasing the long term radiotoxicity of the final waste. After initial dissolution of the spent nuclear fuel in nitric acid, uranium and plutonium recovery from ultimate waste (fission products and minor actinides) is operated by a liquid liquid extraction process (PUREX process) and plutonium partitioning from uranium is run on the basis of the selective reduction of Pu and its back extraction. Therefore, the redox properties of Pu in nitric acid are of prime importance and the stabilization of Pu at its lower redox state + III is to be mastered. This study then deals with the characterization of Pu(IV)/Pu(III) redox couple in aqueous nitric acid solution. It was aimed at measuring physico-chemical features of the redox couple such as half-wave and conditional standard potentials, diffusion coefficients and charge transfer rate constant in nitric acid medium. These features have been used in modeling experimental results of preparative Pu(IV) reduction tests in nitrate medium in a laboratory parallel plate electrode cell. (C) 2014 Elsevier BM. All rights reserved.

The kinetics and mechanism of formic acid sonochemical degradation were studied at ultrasonic frequencies of 20, 200, and 607 kHz under argon atmosphere. Total yield of HCOOH sonochemical degradation increases approximately 6-8-fold when the frequency increased from 20 to 200 or to 607 kHz. At low ultrasonic frequencies, HCOOH degradation has been attributed to oxidation with OH(•) radicals from water sonolysis and to the HCOOH decarboxylation occurring at the cavitation bubble-liquid interface. With high-frequency ultrasound, the sonochemical reaction is also influenced by HCOOH dehydration. Whatever the ultrasonic frequency, the sonolysis of HCOOH yielded H(2) and CO(2) in the gas phase as well as trace amounts of oxalic acid and formaldehyde in the liquid phase. However, CO and CH(4) formations were only detected under high-frequency ultrasound. The most striking difference between low-frequency and high-frequency ultrasound is that the sonolysis of HCOOH at high ultrasonic frequencies initiates Fischer-Tropsch hydrogenation of carbon monoxide.

Industrial implementation of partitioning processes based on solvent extraction requires solvent recycling with constant separation and physicochemical properties. In nuclear applications, both radiolysis and acidic hydrolysis lead to degradation products which need to be removed from solvent before its recycling. The long term evolution of DIAMEX process solvent (0.65M DMDOHEMA HTP) under continuous degradation by acidic hydrolysis and gamma-radiolysis was studied in the laboratory-scale MARCEL, gamma-irradiation facility, with and without alkaline treatment process (AT). With AT, analyses of organic phase showed the accumulation of only one degradation product, MDOHEMA, probably responsible for the molybdenum accumulation observed. Distribution coefficients of Zr, Pd, Fe and Nd, surface tension, refraction index, settling time, viscosity, and density were constant during the tests. Furthermore, no catalytic effect of fission and corrosion products was observed. These studies were consolidated by comparative alpha- and gamma-radiolysis batch tests which showed that alpha-radiolysis and gamma-radiolysis led to the same degradation products.

The present work deals with the hydrodynamic behavior of several room-temperature ionic liquids presenting the same bis(trifluoromethanesulfonyles)imide anion, associated with four different cations: 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, N-trimethyl-N-propylammonium and 1-butyl-1-methylpyrrolidinium cations. Steady state voltammetry was used as an electrochemical technique to characterize mass transfer in both silent and sonicated conditions, using a rotating disk electrode. Results obtained in RTILs media are compared to those acquired in synthetic solutions of controlled viscosity, in order to develop a better understanding of the phenomena involved in such media.

The stability of the ionic liquid [MeBu3N][Tf2N], dry or after contact with water (where [MeBu3N]+ is the methyltributylammonium cation and [Tf2N](-) is the bistriflimide anion), was studied under 137Cs gamma irradiation in argon and in air. In a quantitative study with an absorbed dose of 2 MGy this ionic liquid was highly stable regardless of the radiolysis conditions. The radiolytic disappearance yields determined by ESI-MS were -0.38 and -0.25 micromol J(-1) for the cation and anion, respectively. ESI-MS, NMR, and liquid chromatography coupled with ESI-MS identified a large number of degradation products in very small quantities for the same dose. The cation radicals were formed by the loss of a Bu group, the Me group, or two H atoms to form a double bond with the butyl chain. Radiolysis of the anion produced mainly F and CF3 radicals. The anion radicals recombined with the cation to form a wide range of secondary degradation products regardless of the radiolysis conditions.

A microsonoreactor, specially designed to carry out electrochemical tests in a room-temperature ionic liquid medium (RTIL), was studied. The cell, based on a particular design consisting of off-setting the ultrasonic probe out of the reaction volume, was characterized by several methods such as calorimetry, dosimetry and mass transfer measurements. The main result concerns the specific behaviour of the ionic liquid under ultrasonic irradiation. For example, the mass-transfer enhancement is particularly high, characterized by an average Sherwood number of 6500 while the value obtained with an electrode rotating at 4500 rpm is only 1200.