Pre-concentration and separation of thorium, uranium, plutonium and americium in human soft tissues by extraction chromatography

An extraction chromatographic method is described for the pre-concentration and separation of thorium, uranium, plutonium and americium in human soft tissues. Tissues such as lung and liver are oven dried at 120°C, ashed at 450°C and the ashed sample is alternately wet (HNO₃/H₂O₂) and dry ashed, and then dissolved in 8M HCl. Because of the complex matrix and large sample samples (up to 1500 g), the actinides were preconcentrated from the tissue solution using the TRU^TM resin (EIChroM) prior to elemental separation by extraction chromatography and determination of americium, plutonium, uranium and thorium by alpha spectrometry. The actinides were eluted from the preconcentration column and each actinide was individually eluted on TEVA^TM and TRU^TM resin columns in a tandem configuration. Actinide activities were then determined by alpha spectrometry after electrodeposition from a sulfate medium. The method was validated by analyzing human tissue samples previously analyzed for americium, plutonium, uranium and thorium in the United States Transuranium and Uranium Registries (USTUR). Two National Institute of Standards and Technology (NIST) Standard Reference Materials, SRM 4351-Human Lung and SRM 4352-Human Liver were also analyzed. United States Transuranium and Uranium Registries, Washington State University, Pullman, WA, 99163, USA.     

Preparation, characterization and application of thorium oxalate for sorption of plutonium and americium from aqueous solution

Synthetic inorganic exchangers exhibit good thermal and radiation stability. Thorium oxalate precipitate shows potential for co-precipitation of plutonium and americium from oxalate supernatant generated during plutonium oxalate precipitation. In the present study, efforts were made to prepare thorium oxalate precipitate to be used for column operation. Distribution ratios were determined to optimize conditions for sorption of plutonium and americium on thorium oxalate from nitric acid + oxalic acid solutions with composition similar to that of oxalate supernatant. Column experiments were also performed to evaluate the sorption capacity of thorium oxalate for plutonium and americium from the same medium. The result showed that, thorium oxalate prepared in 1.75M HNO₃ at 70 °C is suitable for column operations. These studies showed that plutonium and americium could be simultaneously removed from aqueous solutions with composition similar to plutonium oxalate waste using glass column packed with thorium oxalate and these nuclides could be recovered by eluting with 3M HNO₃.     

New approaches to processing and fabrication of oxide nuclear fuels

It was shown that, in contrast to the Purex process using aggressive and environmentally hazardous 8M HNO₃ solutions for dissolving spent oxide nuclear fuel (SNF), this fuel can be easily dissolved in aqueous subacid ([H⁺] ∼0.1 M) solutions of Fe(III) nitrate (chloride) with partial separation of uranium and plutonium from fission products (FP). The low acidity of the solutions obtained (pH ∼1) allows direct application of modern technologies of finishing processing of nuclear fuel by fluoride, carbonate, oxalate, or peroxide precipitation of uranium and plutonium. It was established that U(VI) is isolated from nearly neutral nitric acid solutions as a poorly soluble uranyl hydroxylaminate complex after adding hydroxylamine. It was shown that on thermal decomposition at 200–300°C under ambient atmosphere this compound converts into uranium dioxide. A similar approach was applied to obtain mixed oxide uranium-plutonium fuel (MOX fuel).     

Electrolytical enrichment for liquid scintillation determinations of low tritium samples: A revised methodology

The determination of carbon, hydrogen, nitrogen, fluorine, chlorine and sulphur contents for characterization of plutonium complexes with organic ligands have been standardized and glove box adopted. Various plutonium(IV) mono- and di-carboxylates, plutonium(IV) chelates with pyrazolones, UO ₂ ⁺⁺ and PuO ₂ ⁺⁺ complexes having pyrazolones as chelating agent and sulfoxides, amides and phosphine oxide ligands as oxodonors; uranium carbides and uranium nitrides and several potential organic extractants for actinides were analyzed satisfactorily. All these methods set up in double module glove box train are extremely useful for a low budget radioactive laboratory engaged in research in solid actinide complexes.     

Application of neutron well coincidence counting for plutonium determination in mixed oxide fuel fabrication plant

Mixed oxide (MOX) fuel is an alternative to conventional enriched uranium oxide fuel in thermal reactors. Indian interest in plutonium recycle in thermal reactors is primarily due to the need to develop alternative indigenous fuel for two boiling water reactors (BWR) at Tarapur, which are designed to use imported light enriched uranium fuel. A few MOX assemblies have been fabricated and loaded into the reactors. Neutron well coincidence counting (NWCC) system has been successfully employed to check the enrichments of PuO₂ in MOX blends. NWCC has also been successfully applied in developing dry recycling process of clean rejected oxide (CRO) and dirty rejected oxide (DRO).     

Electrofission and photofission as tools to measure actinides in environmental and biological samples

Photofission and electrofission cross sections for fissionable isotopes of uranium, thorium, plutonium and other actinides have been known for several decades. Published data on electrofission and photofission reactions for energies lower than 60 MeV indicate that the²³⁸U cross sections range from a fraction of one mbarn up to about 2.0 mbam for the first of these reactions, and for the second is about 150 nbarn. However, the use of photofission and electrofission as analytical tools to measure uranium, thorium, plutonium and other fissionable actinides is still quite recent. This work examines the potential use of photofission and electrofission to measure thorium, uranium, neptunium, plutonium, americium and curium in environmental and biological samples.Work partially supported by FINEP, CNPq, FAPERJ (ASP), and FAPESP (JDTAN).     

Liquid-liquid extraction of Th4+ and UO 2 2+ by LIX-26 and its mixtures

Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th⁴⁺ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ₂/DPSO/₂/SCN/₂] and [UO₂Q₂/DPSO/], respectively.     

Separation and determination of <Superscript>241</Superscript>Am in urine samples from radiation workers using PC88-A and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of ²⁴¹Am isotope in urine samples using Extraction Chromatography (EC) and ²⁴³Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.     

Influence of the Monovalent M Cation on the M2+xTh2-xNdx(C2O4)5 nH2O Solid Solution Domain

An optimized fuel cycle option for Generation III/IV systems could be co-management of the minor actinides in an integrated closed fuel cycle. This approach implies separating these actinides from the fission products, and then converting them to solid forms to re-fabricate fresh fuel. Oxalate compounds are well known for this purpose. Co-management process is based on the oxalic co-precipitation of An(IV) and An(III) in a mixed oxalate as, for example, the hexagonal phase, M⁺_2+xAn^IV_2-xAn^III_x(C₂O₄)₅ nH₂O with M⁺ representing a singly-charged cation. A study of the Th-Nd-M⁺ hexagonal oxalate systems has been carried out in order to understand the charge compensation mechanisms implicated in the formation of mixed oxalates systems.     

Determination of thorium,uranium and plutonium isotopes in atmospheric samples

A new procedure for the radiochemical measurements of thorium, uranium and plutonium in atmospheric samples is described. Analysis involves coprecipitation of these actinides with iron hydroxide from a 40-to 50-dm³ sample of rainwater, followed by radiochemical separation and purification procedures by the use of ion exchange chromatography (Dowex AG1×8) and solvent extraction. The new procedure enables one to determine the isotopes of thorium, uranium and plutonium, which are found in rainwater at extremely low concentrations, with a chemical yield ranging from 60 to 80%.     

Actinide and lanthanide extraction from nitric acid solutions by flotation

Flotation of thorium, plutonium (IV), uranium(VI) and gadolinium from aqueous nitric acid solutions (HNO₃ concentration from 0.01 to 5.0M) was investigated using lauryl phosphoric acid (LPA) as a SAS-collector. It is established that the extent of removal of the metal ions increases with the amount of LPA introduced, regardless of the solution acidity. At a fixed mole LPA to metal ratio the extent of uranium(VI) and gadolinium removal is reduced with increasing acidity, while in case of plutonium(IV) and thorium this parameter remains constant. It is shown that in principle 100% extraction of plutonium(IV) and thorium by flotation is possible regardless of the acidity of aqueous solutions. Ca(NO₃)₂ added to the system in the amount of 0.5M does not significantly affect the flotation extraction of thorium.     

Partitioning of plutonium and uranium in aqueous medium using hydroxyurea as reducing agent

A new process for the partitioning of plutonium and uranium during the reprocessing of spent fuel discharged from fast reactor was optimised using hydroxyurea (HU) as a reductant. Stoichiometric ratio of HU required for the reduction of Pu(IV) was studied. The effect of concentration of uranium, plutonium and acidity on the distribution ratio (Kd) of Pu in the presence of HU was studied. The effect of HU in further purification of Pu such as solvent extraction and precipitation of plutonium as oxalate was also studied. The results of the study indicate that Pu and U can be separated from each other using HU as reductant.     

Extractive photometric determination of plutonium(IV) with Aliquat-336 and xylenol orange

A rapid extractive photometric method using Aliquat-336 and xylenol organe for the determination of plutonium(IV) at μg levels has been developed. Quantitative extraction is obtained from ∼4M aqueous HNO₃ medium, affording estimation in the presence of several commonly occurring impurities, viz. iron, uranium, fission products and cladding materials. Effects of acidity, reagent concentration and diverse ions on the estimation have also been invetigated. Unlike the well-known absorptiometric method for determining plutonium(IV) employing Arsenazo III, the procedure presented here tolerates manyfold excesses of uranium(VI) as well as chromium(III), iron(III) and zirconium(IV), which are some of the major contaminants of plutonium during reprocessing.     

Limitations of Tissue Analyses in Estimating the Initial Exposures to the Workers for Thorium, Uranium and Plutonium and Their Internal Dose Estimates

The present paper deals with the following questions: Can a piece of any tissue or organ obtained at autopsies and/or biopsies be analyzed to predict the organ and/or body burden, initial exposures, and the committed dose equivalents to the workers or retired workers from exposures to thorium, uranium, and plutonium and what are the consequences of using such materials in predicting the initial exposures and the dose estimates? Based on the studies of the distribution of uranium and thorium in former uranium miners and millers, the distribution of plutonium in general population, and several other studies dealing with the distribution of actinides in man, it is reasonable to state that the utilization of tissue analyses for estimating the initial exposure to the workers may have serious limitations. The regulatory agencies must restrict the conditional utilization of tissue analyses in estimating exposures to the workers for thorium, uranium, and plutonium.     

Removal of plutonium and americium from oxalate supernatants by co-precipitation with thorium oxalate

As a part of treatment of low level active waste, co-precipitation of plutonium (Pu) and americium (Am), with thorium oxalate, from oxalate supernatants generated during plutonium oxalate precipitation has been investigated. A simple method for the simultaneous removal of both Pu and Am from oxalate supernatants could be developed. This simple process achieves incorporation of these alpha active nuclides into small volumes of solid matrix from large volumes of aqueous waste.     

Studies on purification of plutonium from silver ions

Precipitation and solvent extraction methods have been investigated for the purification of plutonium from silver from the solution generated during oxidative dissolution of plutonium oxide using Ag(II) ions. Initial experiments have been carried out using thorium as representative of plutonium. Selecting the optimum conditions, the experiments were repeated with plutonium. The results revealed that Pu can be purified from silver ions either by precipitating silver as silver chloride or silver metal followed by Pu(IV) oxalate precipitation or by selective extraction of Pu(IV) into 20% Aliquat-336 or 30% TBP.     

Complexation of uranium(VI) with acetohydroxamic acid

The advanced separation extraction process based on tri-n-butyl phosphate organic phase called UREX is being developed to separate uranium from fission products and other actinides, and the acetohydroxamic acid (AHA) is employed to reduce and complex plutonium and neptunium in order to decrease their distribution to the TBP-organic phase. In this study, the extraction of uranium was performed from various aqueous matrices with different concentrations of HNO₃, LiNO₃, and AHA. Extraction of uranium increases with increasing both initial HNO₃ and total nitrate concentration. UV-VIS spectrophotometry confirmed that AHA is involved in the complex of uranium with TBP.     

New fecal method for plutonium and americium

A new fecal analysis method that dissolves plutonium oxide was developedat the Westinghouse Savannah River Site. Diphonix Resin . (Eichrom Technologies),is used to pre-concentrate the actinides from digested fecal samples. A rapidmicrowave digestion technique is used to remove the actinides from the DiphonixResin ., which effectively extracts plutonium and americium from acidic solutionscontaining hydrofluoric acid. After resin digestion, the plutonium and americiumare recovered in a small volume of nitric acid that is loaded onto small extractionchromatography columns, TEVA Resin and TRU Resin (Eichrom Technologies). Themethod enables complete dissolution of plutonium oxide and provides high recoveryof plutonium and americium with good removal of thorium isotopes such as ²²⁸Th.     

Extraction of uranium(VI) and plutonium(IV) with some aliphatic amides

Extraction of uranium(VI) and plutonium(IV) has been studied with N,N-dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) at various fixed temperatures of 20, 30, 40 and (50±0.1)°C. The equilibrium constants for the uptake of nitric acid (K_h, a measure of their relative basicities) by these amides were evaluated by the usual method. The equilibrium constants for the extraction of uranium as well as plutonium with all the three amides follow their order of basicity (K_h) viz. DBHA (0.09)<DBOA (0.10)<DBDA (0.13) with log K values of 1.31, 1.43 and 1.73 for uranium and 3.55, 3.65 and 4.17 for plutonium, respectively. It has been observed that whereas uranium(VI) is extracted as a disolvate (similar to TBP and sulfoxides), plutonium(IV) has been found to be extracted as a trisolvate. The thermodynamic parameters evaluated by the usual temperature coefficient method indicate that the extraction reactions of uranium as well as plutonium are stabilized by negative enthalpy change only.     

Assay of actinides in human urine by rapid method

A method using DGA resin (N,N,N′,N′-tetra-n-octyldiglycolamide on an inert support) was developed for the rapid analysis of actinides in urine samples. Samples acidified with HCl to 4 M were loaded directly (without digestion) onto a DGA column. Actinides were stripped simultaneously, α-sources were prepared by co-precipitation with NdF₃. Americium, plutonium and uranium were separated with acceptable high recoveries (40–80%). The americium, plutonium and uranium content of 100–200 ml urine samples was determined within 24 h with detection limits as low as 0.01 Bq l^?1. Based on model experiments using ¹⁴C-spiked urea, it was proven that high urea content can affect americium separation deleteriously due to irreversible fixing of americium on DGA resin.