K.A. Venkatesan

Dissolution of uranium oxides and electrochemical behavior of U(VI) in task specific ionic liquid

A task-specific ionic liquid, protonated 1-carboxy-N,N,N-trimethylmethanaminium bis(trifluoromethylsulfonyl)imide trivially known as protonated betaine bis(trifluoromethylsulfonyl)-imide ([Hbet][NTf2]) was prepared and the dissolution of uranium oxides, UO3, UO2 and U3O8 in it was studied. Dissolution of UO3 in [Hbet][NTf2] was very rapid and the saturation solubility of uranium was found to be 15 wt. % at 373 K. In contrast, dissolution of UO2 was sluggish and it was facilitated only by the oxidation of UO2 to UO22+. U3O8 was insoluble up to 453 K. A new procedure was developed for the individual separation of uranium oxides using [Hbet][NTf2] based on differences in solubilities. The electrochemical behavior of U(VI) in the resultant solution was investigated by cyclic voltammetry at glassy carbon working electrode at 373 K. A surge in the cathodic peak current at -0.48 V (vs . Fc/Fc+) was due to the reduction of U(VI) to U(V) and the corresponding anodic peak current was observed at a potential of 0.64 V. Increasing the potential sweeping rate increases the peak current and shifts the peak potential negatively indicating the irreversible electroreduction of U(VI) in [Hbet][NTf2]. The diffusion coefficient of U(VI) in [Hbet][NTf2] was determined to be of the order of ∼10−8 cm2/s.

Electrochemical Behaviour of Actinides and Fission Products in Room-Temperature Ionic Liquids

In the recent past, room-temperature ionic liquids (RTILs) are being explored for possible applications in nuclear fuel cycle. RTILs are being studied as an alternative to the diluent, n-dodecane (n-DD), in aqueous reprocessing and as possible substitute to high-temperature molten salts in nonaqueous reprocessing applications. This paper deals with the current status of the electrochemical research aimed at the recovery of actinides and fission products using room-temperature ionic liquid as medium. The dissolution of actinide and lanthanide oxides in ionic liquid media and the electrochemical behavior of the resultant solutions are discussed in this paper.

Thermal decomposition characteristics of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide-tri n-butyl phosphate–nitric acid systems

Thermal stability of neat octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OΦD[IB]CMPO) and TRUEX solvent composition (0.2M OΦD[IB]CMPO-1.2M tri n-butyl phosphate-in n-dodecane) in the presence and absence of nitric acid has been studied in ambient air in a closed vessel, employing an adiabatic calorimeter. Enthalpies and kinetic parameters for the decomposition reaction were derived wherever possible and are reported for the first time. Neat OΦD[IB]CMPO was found to be thermally stable up to 633xa0K and exhibited an exothermic decomposition later. It decomposed at lower temperatures (376–386xa0K) depending on the nitric acid concentration. The exothermic rise in temperature and pressure increased exponentially, while activation energies exhibited exponential decrease for the decomposition reactions with increase in nitric acid content. TRUEX solvent was found to be stable up to 661xa0K in the absence of nitric acid while in the presence of 8 and 4M HNO3, it decomposed between 387 and 413xa0K. All these samples on decomposition formed incompressible gases and viscous black liquids. The results also indicate that the neat OΦD[IB]CMPO and the TRUEX solvent are thermally more stable than neat trixa0n-butyl phosphate (TBP), PUREX solvent (1.1Mxa0TBP/n-DD), neat diamyl amyl phosphonate (DAAP) and 1.1M DAAP/n-DD, triisoamyl phosphate (TiAP) and 1.1M TiAP/n-DD.