A. Ramanujam

Partitioning of actinides from high-level waste streams of purex process using mixtures of CMPO and TBP in dodecane

Abstract The extraction of actinides from high active aqueous raffinate waste (HAW) as well as high-level waste (HLW) solutions arising from Purex processing of thermal reactor fuels has been studied using a mixture of octyl(phenyl)-N N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) and TBP in dodecane. The results on the extraction and stripping of actinides, lanthanides, and other fission products are discussed. Optimum conditions are proposed for the efficient recovery of residual actinides from HAW and HLW streams by CMPO extraction followed by their selective stripping with suitable reagents. Experiments on the extraction and separation of actinides and lanthanides by CMPO in the presence of TBP in dodecane have also been carried out with U(VI) and Nd(III) to arrive at the limiting conditions for avoiding third-phase formation.

STUDIES ON THE IDENTIFICATION OF HARMFUL RADIOLYTIC PRODUCTS OF 30% TBP-N-DODECANE-HNO3 BY GAS-LIQUID CHROMATOGRAPHY. II. FORMATION AND CHARACTERIZATION OF HIGH MOLECULAR WEIGHT ORGANOPHOSPHATES

Gamma radiolysis of Purex solvent, 30% tri-n-butylphosphate-n-dodecane-HNO3 is observed to yield many undesirable metal complexing species. A method for identifying the gas-liquid chromatographic (GLC) signatures of high molecular weight organophosphates (HMPs) through a nitrogen- and phosphorous-selective detector is described. Fractionation of the radiolyzed solvent by vacuum distillation resulted in the enrichment of HMP species in the high boiling, viscous residue in the last fraction. This residue showed intense infrared signals characteristic of the presence of nitro, carbonyl, and phosphoryl groups, which implies the presence of multifunctional species. The study revealed a strong association among the components of radiolyzed solvent, which inhibits clean fractionation. Gas chromatography–mass spectrometry assay of the sample indicated that these HMPs consist of(NO2─C4H8)(C4H9O)2PO, (OH─C4H8O)(C4H9O)2PO, and (CH3─C4H8)(C4H9O)2PO species. The HMP-rich fraction exhibited very high plutonium-retention behavior, which was substantially lowered by efficient uptake of HMPs upon alumina treatment. Thus, the present study correlates the GLC signatures of HMPs, especially those of nitrated species, formed by radiolysis of 30% tri-n-butylphosphate-n-dodecane-HNO3 and solvent quality deterioration with respect to Pu-retention behavior.

Effect of Radiation-Induced Physicochemical Transformations on Density and Viscosity of 30% TBP–n-Dodecane–HNO3 System

Radiation-induced changes in the density and viscosity of 30% TBP–n-dodecane–HNO3 mixtures were examined. The increase in the density becomes significant with increasing nitric acid content of the solvent, [HNO3]TBP, and absorbed radiation dose, which concomitantly leads to a much sharper increase in the viscosity of the solvent. The extent of increase in the viscosity is significantly enhanced by gamma radiolysis and is a function of absorbed dose. These changes are attributed to radiation-induced polymerization and nitration of the hydrocarbon diluent as revealed by gas–liquid chromatography (GLC) and infrared (IR) assay of the solvent. Various possible modes of hydrogen bonding seem to play a major role in enhancing the viscosity of the system. Efficacy of solvent purification by alkaline scrub followed by alumina treatment is described in terms of the amount of degradation species retained in the treated solvent. Interestingly, the small amount of radiolytic species remaining in the solvent due to incomplete solvent purification causes a considerable increase in the viscosity of the solvent.

STUDIES ON THE IDENTIFICATION OF HARMFUL RADIOLYTIC PRODUCTS OF 30% TBP-n-DODECANE-HNO3 BY GAS LIQUID CHROMATOGRAPHY. I. FORMATION OF DILUENT DEGRADATION PRODUCTS AND THEIR ROLE IN Pu RETENTION BEHAVIOR

The radiation-chemical transformations of Purex solvent, 30% TBP-n-dodecane-HNO3, arising from radiolysis of nitric acid were examined by gas chromatographic fingerprinting of the radiolyzed system. The present study describes a procedure for identifying diluent degradation products by gas chromatographic, infrared and gas chromatographic—mass spectrographic assay. The identified gas chromatographic signatures can be used to monitor the growth of diluent degradation products (DDP) like nitroparaffins, long chain alcohols, and paraffins in the Purex solvent before its recycling. The increase in the concentration profiles of these species with absorbed dose parallels the increase in the retention of Ru, Zr, and Pu by the diluent phases resolved (by the phosphoric acid equilibration method) from the radiolyzed solvent under recycling conditions.

THE EFFECT OF TEMPERATURE ON THE EXTRACTION OF PLUTONIUM(IV) BY TRI‐N‐BUTYL PHOSPHATE

Abstract Distribution coefficient data for Pu(IV) were obtained at different temperatures in the range 10–60°C for varying concentrations of nitric acid and TBP in dodecane. From these data the enthalpy change for extraction of Pu(IV) was determined. An attempt was also made to calculate the free energy and entropy changes associated with the extraction of Pu(IV).

Studies on the In Situ Electrooxidation and Selective Permeation of Cerium(IV) across a Bulk Liquid Membrane Containing Tributyl Phosphate as the Ion Transporter

The results of experiments carried out to develop a liquid membrane (LM) technique for the extractive permeation of cerium from nitric acid solutions are described. In-situ electrooxidation of Ce3+ to extractable Ce4+ and its transport across bulk LM (BLM) composed of tri-n-butyl phosphate (TBP)/dodecane mixtures was systematically studied under varied hydrodynamical and chemical conditions. The permeability of metal ions across the BLM was dependent on the efficiency of extraction, ionic activity of feed solutions, stirring rate, composition of the receiving phase, etc. The transport rates were found to vary linearly (a log-log correlation) with the cation concentration in feed solutions and concentration of TBP in BLM. A permeation velocity equation for cerium ion through the membrane has been proposed. More than 90% permeation of Ce with a maximum flux of 8.63 × 10−5 mol/m2/s could be accomplished under the experimental conditions: stirring rates at feed and strip solutions were 380 and 300 rpm, respec...

Separation of carrier-free 90Y from high level waste by supported liquid membrane using KSM-17

A generator system has been developed for the preparation of carrier-free 90Y from 90Sr present in the high level waste (HLW) of the Purex process by employing a supported liquid membrane (SLM) using 2-ethylhexyl-2-ethylhexyl phosphonic acid (KSM-17 equivalent to PC 88A) supported on a polytetrafluoro ethylene (PTFE) membrane. When uranium depleted Purex HLW at appropriate acidity is passed sequentially through octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) sorbed on chromosorb-102 (abbreviated as CAC) and Zeolite AR1 (synthetic mordenite) columns, all the trivalent, tetravalent and hexavalent metal ions and monovalent 137Cs ions are sorbed. After adjusting to pH 2 with NaOH the resulting effluent is used as feed in a single stage membrane cell partitioned with a PTFE membrane impregnated with KSM-17 and having a feed and receiver compartment with 5.0 ml capacity each. The receiver compartment was filled with a 0.5M HNO3 or 0.5M HCl stripping solution. 90Y alone is preferentially transported across the membrane leaving behind all the impurities viz. 90Sr, 125Sb, 106Ru, 106Rh, etc. in the feed compartment. This technique can yield 90Y in mCi levels in a pure and carrier-free form for medical applications. The feed can be reused repeatedly after allowing for 90Y buildup.

Recovery of actinides extracted by Truex solvent from high level waste using complexing agents

This work deals with the batch studies on stripping of actinides extracted by a mixture octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO) and tri-n-butyl phosphate (TBP) in n-dodecane (Truex solvent) from simulated high level waste (HLW) solution. The stripping of americium and plutonium from acid-bearing CMPO-TBP mixture is carried out using a mixture of weak acid, weak base and complexing agent as strippant. A mixture of formic acid, hydrazine hydrate and citric acid appeared to be best suited for efficient stripping of americium and plutonium. With appropriate modifications in the concentration of individual constitutents, this strippant can be used for the recovery of actinides from loaded Truex solvent with any acid content.

Separation of Carrier-Free 90Y from High Level Waste by Extraction Chromatographic Technique Using 2-Ethylhexyl-2-ethylhexyl Phosphonic Acid (KSM-17)

An extraction chromatographic technique has been developed for the separation of carrier-free 90Y from the 90Sr present in the high level waste (HLW) of the Purex process. When a Purex HLW solution in 2–3 M HNO3 is passed through a CMPO-Chromosorb-102 (CAC) column, all the trivalent, tetravalent, and hexavalent ions are sorbed. The effluent from this experiment, after adjusting the pH to 2 with NaOH, was passed through a 2-ethylhexyl-2-ethylhexyl phosphonic acid (KSM-17)-Chromosorb-102 (KSMC) extraction chromatographic column where only 90Y was sorbed. All the other ions (90Sr, 137Cs, 125Sb, 106Ru, 106Rh, etc.) were washed off with dilute HNO3 (pH 2), and carrier-free 90Y was eluted with 0.5 M HNO3. This technique can yield 90Y in mCi levels in pure form for medical applications. The 90Sr can be used repeatedly after allowing for 90Y buildup.

Extraction and extraction chromatographic separation of minor actinides from sulphate bearing high level waste solutions using CMPO

Bench-Scale studies on the partitioning and recovery of minoractinides from the actual and synthetic sulphate-bearing high level waste (SBHLW) solutions have been carried out by giving two contacts with 30% TBP to deplete uranium content followed by four contacts with 0.2M CMPO+1.2M TBP in dodecane. The acidity of the SBHLW solutions was about 0.3M. In the case of actual SBHLW, the final raffinate contained about 0.4% α-activity originally present in the HLW, whereas with synthetic SBHLW the α-activity was reduced to the background level.144Ce is extracted almost quantitative in the CMPO phase,106Ru about 12% and137Cs is practically not extracted at all. The extraction chromatographic column studies with synthetic SBHLW (aftertwo TBP contacts) has shown that large volume of waste solutions could be passed through the column without break-through of actinide metal ions. Using 0.04M HNO3>99% Am(III) and rare earths could be eluted/stripped. Similarly >99% Pu(IV) and U(VI) could be eluted.stripped using 0.01M oxalic acid and 0.25M sodium carbonate, respectively. In the presence of 0.16M SO42− (in the SBHLW) the complex ions AmSO4+, UO2SO4, PuSO42+ and Pu(SO4)2 were formed in the aqueous phase but the species extracted into the organic phase (CMPO+TBP) were only the nitrato complexes Am(NO3)3·3CMPO, UO2(NO3)2·2CMPO and Pu(NO3)4·2CMPO. A scheme for the recovery of minor actinides from SBHLW solution with two contacts of 30% TBP followed by either solvent extraction or extraction chromatographic techniques has been proposed.