N. K. Pandey

Adsorption Kinetics and Breakthrough Behaviour of Tri-n-butyl Phosphate on Amberlite XAD-4 Resin

Adsorption behaviour of tri-n-butyl phosphate (TBP) from aqueous solution (dilute HNO3) on Amberlite XAD-4 has been investigated experimentally. Factors affecting the adsorption rates and breakthrough curves have been studied in batchwise and semicontinuous fixed bed adsorber. The adsorption isotherm of TBP on Amberlite XAD-4 resin have also been determined and the Freundlich model of adsorption is used to describe adsorption equilibrium. For the case of nonlinear equilibrium a simplified method proposed by Chi Tein is used to estimate intraparticle diffusion coefficient. The intraparticle diffusion coefficient is found to be in the range of 10−8 cm2·s−1. Results of fixed bed column are used to estimate mass transfer zone (MTZ) length, length of unused bed (LUB), breakthrough capacity corresponding to fixed value of effluent concentration (5 mg/l of TBP) and degree of saturation of bed at breakthrough. The MTZ length was found to vary from 21.8 cm to 37.3cm when flow rate changed from 13.5 ml/min to 52 ml...

HYDRODYNAMIC STUDY OF FLOW IN THE ROTOR REGION OF ANNULAR CENTRIFUGAL CONTACTORS USING CFD SIMULATION

Annular centrifugal extractors are widely used in industry for the extraction of radioactive fuel in nuclear fuel reprocessing, emulsion polymerization, crystallization, and other processes. It is a single compact unit, consisting of a mixer and a settler, that operates under the action of centrifugal force. Although the equipment is widely used, the design procedures are still empirical due to the complexity of fluid mechanics in the mixer and settler zones. For the development of rational and reliable design procedures, it is important to understand the flow patterns in these zones. This article presents a hydrodynamic study of flow within the rotor using computational fluid dynamics (CFD) with standard k-ϵ, SST k-ω, and RSM turbulence models. The rotor diameter was varied over a wide range of 125 to 375 mm and the rotor speed over 20 to 175 rad/s. A comparison is presented between the CFD predictions and experimental measurements reported in the published literature. The hydraulic performance of a rotor as a centrifugal pump is presented in terms of head (discharge pressure), capacity, and power consumption. The flow pattern in the suction and settling zones of the contactor is presented with streamlines, static pressure distribution, and velocity profiles.

Spectrophotometric determination of trace amounts of phosphate in water and soil

A simple spectrophotometric method has been developed for the determination of phosphate dissolved in soil and water. The method is based on the formation of phosphomolybdate with added ammonium molybdate followed by reduction with hydrazine in acidic medium. Orthophosphate and molybdate ions condense in acidic solution to give molybdophosphoric (phosphomolybdic) acid, which upon selective reduction (perhaps with hydrazinium sulphate) produces a blue colour, due to molybdenum blue of uncertain composition. The intensity of blue colour is proportional to the amount of phosphate. If the acidity at the time of reduction is 0.5 M in sulphuric acid and hydrazinium sulphate is the reductant, the resulting blue complex exhibits maximum absorption at 830 nm. The system obeys Lambert-Beers law at 830 nm in the concentration range of 0.5-5 μg/mL of phosphate with a relative standard deviation (RSD) of 0.1% and correlation coefficient of 0.99. Molar absorptivity was determined to be 2.9 × 10⁴ L mol⁻¹ cm⁻¹ at 830 nm. The method is also applicable for the determination of phosphate in nuclear reprocessing plants, medical science, clinical science, agriculture, metallurgy and environmental science.

Effect of Radiolysis in Altering the Physiochemical and Metal Retention Properties of Solvent-Diluent-Acid Systems

Systematic studies were performed on radiolytic degradation of Tri-n-Butyl Phosphate diluted with n-Dodecane or Normal Paraffin Hydrocarbon in the presence/absence of nitric acid as a function of absorbed gamma dose. Viscosity and phase disengagement time increased with absorbed dose but interfacial tension decreased gradually. The extent of damage caused during radiolysis was estimated by Zr retention in the organic phase. The effectiveness of carbonate wash in restoring the quality of the solvent was evaluated. Comparison of the IR spectra for the neat and the degraded samples revealed the formation of nitro alkanes at absorbed dose above 20 MRad.

Mechanism of dissolution of nuclear fuel in nitric acid relevant to nuclear fuel reprocessing

The mechanism of dissolution of sintered UO2 fuel pellets in nitric acid is the essential starting input information required for the design of a continuous dissolution system for spent nuclear fuel reprocessing. The current article establishes the mechanism of this reaction under typical PUREX process conditions based on the concentration profiles of nitric & nitrous acids and NOX gas composition during the course of dissolution of sintered UO2 pellets in nitric acid. The results would be useful in optimizing the dissolution process and improving the throughput of the dissolution system.

Process modeling of in-situ electrochemical partitioning of uranium and plutonium in purex process: benchmark results with uranium reduction

Abstract In-situ reduction of plutonium and uranium for the separation of U/Pu is suitable for plutonium-rich fuels such as FBR fuels. The mathematical basis for a computer program PUSEP (Plutonium Uranium Solvent Extraction Program) for the analysis of partitioning cycle of PUREX process involving in-situ electrochemical reduction of uranium and plutonium is described in the present investigation. Model equations have been developed on the basis of the idealized model for mixer settlers incorporating distribution coefficients and redox reactions of the species involved and solved numerically to obtain concentration profiles of components. The validity of the model equations and associated computer program is tested by carrying out experiments in a proto type 20-stage electrolytic ejector mixer-settler operating without diaphragm for the electro reduction of uranium. The stage-wise experimental concentration profiles of U(VI), U(IV) and nitric acid were obtained and compared with the theoretical predictio...

Development of solvent regeneration process

AbstractThe useful life of the hydrocarbon-tri-butyl phosphate solvent system in nuclear fuel reprocessing plant is limited by the extent of formation of secondary degradation compounds. These are formed by the interaction of nitric and nitrous acids with the various hydrocarbon compounds under the conditions of radiation. One of the easily deployable methods for the removal of these degradation products (secondary degradation products) is distillation. The instability of tri-n-butyl phosphate at elevated temperatures and the requirement that very low concentrations of variety of impurities that have to be removed call for a careful design of process and equipment. A pilot plant scale solvent purification system based on vacuum distillation has been designed, developed, and commissioned at the Reprocessing Development Laboratory, Indira Gandhi Centre for Atomic Research. The solvent recovery system is an integration of different liquid–vapor separation units such as dehydration column, agitated thin film ...

Comparative studies on the determination of di-n-butyl phosphate in degraded solvent of PUREX process by ion chromatography and gas chromatography methods

Abstract This paper describes comparative studies on the determination of di-n-butyl phosphate (DBP) by ion chromatography (IC) and gas chromatography (GC) techniques in spent solvent of PUREX process used for the reprocessing of spent nuclear fuels. The ion chromatography method involves the separation of DBP from 30% TBP–NPH (tri-n-butylphosphate diluted in normal paraffin hydrocarbon) containing heavy metal ion like uranium and nitric acid by extraction of DBP into alkaline medium. DBP was subsequently eluted by ion-exchange separation in ion chromatography column and followed by suppressed conductivity detection. DBP is quantified to a lower limit of about 1 ppm with 3% RSD. However, in order to determine DBP by gas chromatography technique DBP is first quantitatively converted into its volatile and stable derivatives by using diazomethane prior to analysis by GC. Results obtained with ion chromatographic technique are compared with those of obtained by standard gas chromatographic technique. It was o...

Dissolution of nuclear materials in aqueous acid solutions

Abstract The quantitative understanding of the dissolution of nuclear fuel materials is essential for the process design and development of an industrial-scale nuclear fuel reprocessing plant. The main objective of this review article is to analyze the published data related to the dissolution of important nuclear materials, namely, urania, plutonia, thoria, and their oxides in the existing literature. The published results on rate-controlling step and reaction mechanism of dissolution processes are reconciled and reviewed in this work. Clear suggestions are made for future research work for the identification of rate-controlling step. Suggestions are also provided to overcome the shortfalls in the published data for the identification of intrinsic kinetics and mass-transfer rates.

Feasibility studies of using N,N-dihexyloctanamide (DHOA) for fast reactor fuel reprocessing applications

Abstract N,N-dihexyloctanamide (DHOA) is being considered as a promising extractant in the aqueous reprocessing of spent nuclear fuels. In view of rise in temperature of the solvent during reprocessing of fast reactor fuel, the present study aimed at evaluating the physical properties such as density, viscosity, and interfacial tension and Pu(IV) extraction behavior in 1.1 M DHOA/n-dodecane as a function of temperature and duration of heating. The influence of nitric acid in altering the physical properties with respect to temperature was evaluated. Physical properties and extraction behavior of the solvent changed to a remarkable extent with temperature. Quantitative amount of Pu(IV) could be back-extracted from loaded, solvent in three contacts at 313 K. FT-IR studies were carried out to evaluate the thermal stability of the solvent. Thus, the performance of the solvent, 1.1 M DHOA/n-dodecane is satisfactory at higher temperatures also.