Monitoring of the concentration of actinides in process streams and waste materials can be effectively carried out by detecting and measuring their radioactive emissions. Such monitoring techniques lead to more efficient control of the process, and also aid in the minimisation of losses to the waste and better accounting of the nuclear materials. This paper provides an overview of some of the techniques such as on-line alpha monitoring, passive and active neutron assay and gamma counting, and also describes the monitoring systems which have been developed in our laboratory for use in a reprocessing plant.
A method is described for the determination of neptunium and plutonium in process solutions. This involves the separation
of these elements followed by their spectrophotometric determination as Arsenazo III complexes. Neptunium(IV) and plutonium(IV)
are separated using TTA extraction method and the separated Np(IV) and Pu(IV) are then determined as their Arzenazo III complexes
in 5M HNO3. A few solutions obtained by dissolving irradiated fuels were analysed for plutonium and neptunium using this method and
the results were compared with those obtained by other methods. An attempt was made to use Arsenazo III to determine uranium
in the plant solutions.
Authors:K. Venkatesan, T. Srinivasan, and P. Vasudeva Rao
Mesoporous silica (MCM-41) with d(100) interplanar distance of 38 Å was prepared by a room temperature process through low surfactant templation technique. The surface of MCM-41 was functionalized with dithiocarbamate (dtc) ligand, named as MCM-41-dtc and this was characterized by X-ray diffraction, BET surface area, particle size analysis, 29Si MAS NMR spectra and sulphur analysis. The sorption of mercury from 0.1M HCl solution by MCM-41-dtc was studied as a function of pH, [Hg2+], time and temperature. The sorption data obtained at various initial concentrations of mercury were fitted into Langmuir adsorption model. Mercury speciation in solution and the sorption capacity measurements indicated possible formation of a 1 : 1 square planar complex in the solid phase. A very rapid sorption of mercury was observed in the initial stages of equilibration, which can be attributed to the large surface area, wide porosity and fine particle size of MCM-41-dtc, facilitating facile accessibility of mercury into the inner pores of the sorbent. The enthalpy change accompanied by the sorption of mercury was found to decrease from 83.7 to 6.2 kJ/mol, when the initial concentration of mercury was increased from 5.10-4M to 1.5.10-3M.
Authors:R. Subba Rao, P. Sivakumar, R. Natarajan, and P. Vasudeva Rao
The transport of hydrochloric acid across a supported liquid membrane using Aliquat 336 in xylene as a carrier was studied. The effect of carrier concentration (0.1–0.6M) on the transportation of hydrochloric acid with and without phase modifier was investigated. The study indicated that the flux of transportation decreased with increasing carrier concentration in the absence of phase modifier. In the presence of phase modifier, however, the flux increased up to 0.2M carrier concentration and started decreasing afterwards. The transportation behavior of hydrochloric acid with and without phase modifier has been attributed to the tendency of aggregation of the carrier.
Authors:K.A. Venkatesan, P.R. Vasudeva Rao, and K. Štamberg
The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO3 and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO3 solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr2+ on HZO indicated that the hydrolysis of Sr2+ to lower charged SrOH+ is the pre-requisite for the abrupt sorption behavior at pH 9.
Authors:Alok Rout, K. Venkatesan, T. Srinivasan, and P. Vasudeva Rao
Extraction of europium(III) from nitric acid medium by a solution of tri-n-butylphosphate (TBP) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in the room temperature ionic liquid, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide
(amimNTf2 where a = butyl or hexyl or octyl), was studied. The distribution ratio of (152+154)Eu(III) in TBP-CMPO/bmimNTf2 was measured as a function of various parameters such as the concentrations of nitric acid, CMPO and NaNO3. Remarkably large distribution ratios were observed for the extraction of europium(III) when bmimNTf2 acted as diluent. The stoichiometry of metal-solvate in organic phase was determined by the slope analysis of extraction
Authors:B. Saha, K. Swaminathan, C. Venkatasubramani, and P. Vasudeva Rao
The extraction of Ce (IV) by di-(2-ethylhexyl)-phosphoric acid (HDEHP) has been studied as a function of nitric acid concentration. Using the distribution coefficient data, the optimum conditions for recovery of Ce (IV) from nitric acid medium were arrived at. Under the conditions employed for Ce(IV), a small percentage of Ru was also found to be extracted. Cerium could be selectively stripped from the organic phase with 8M HNO3/30% H2O2 solution. This procedure led to the recovery of144Ce free of106Ru. Based on the solvent extraction data, an extraction-chromatographic procedure employing HDEHP (40% w/w) loaded on Amberlite XAD-7 as the stationary phase was developed for the isolation of pure, carrier-free144Ce from the spent fuel solution.
Authors:N. Sivaraman, S. Subramaniam, T. Srinivasan, and P. Vasudeva Rao
Burn-up measurements on thermal as well as fast reactor fuels were carried out using high performance liquid chromatography (HPLC). A column chromatographic technique using di-(2-ethylhexyl) phosphoric acid (HDEHP) coated column was employed for the isolation of lanthanides from uranium, plutonium and other fission products. Ion-pair HPLC was used for the separation of individual lanthanides. The atom percent fissions were calculated from the concentrations of the lanthanide (neodymium in the case of thermal reactor and lanthanum for the fast reactor fuels) and from uranium and plutonium contents of the dissolver solutions. The HPLC method was also used for determining the fractional fissions from uranium and plutonium for the thermal reactor fuel.
Authors:M. Jayakumar, K. Venkatesan, T. Srinivasan, and P. Vasudeva Rao
The electrochemical behavior of ruthenium(III) and rhodium(III) in nitric acid medium has been studied at platinum and stainless
steel electrodes by cyclic voltammetry. The cyclic voltammograms consisted of surge in cathodic current occurring at potentials
of −0.13 V (Vs. Pd) and −0.15 V (Vs. Pd), which culminates into peaks at −0.47 V and −0.5 V due to the reductions of Ru(III)
and Rh(III) to their metallic forms, respectively. Electrodeposition was carried out at stainless steel electrode and unlike
palladium, the recovery of ruthenium and rhodium was limited to ~4% and ~14%, respectively. However, a different scenario
was observed in case of electrodeposition from a ternary solution containing all these platinum metals. Ruthenium and rhodium
deposited underpotentially in the presence of palladium and the recovery of ~20% and ~5% was observed for ruthenium and rhodium,
respectively. Evolution of RuO4 at the anode and deposition of RuO2 in the anodic side was observed in all cases during electrolysis of ruthenium(III) containing solutions.