A spectrophotometric method for the determination of neptunium and plutonium in process solutions

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.     

Uranium/plutonium and uranium/neptunium separation by the Purex process using hydroxyurea

Hydroxyurea dissolved in nitric acid can strip plutonium and neptunium from tri-butyl phosphate efficiently and has little influence on the uranium distribution between the two phases. Simulating the 1B contactor of the Purex process by hydroxyurea with nitric acid solution as a stripping agent, the separation factors of uranium/plutonium and uranium/neptunium can reach values as high as 4.7·10⁴ and 260, respectively. This indicates that hydroxyurea is a promising salt free agent for uranium/plutonium and uranium/neptunium separations.     

Uranium/plutonium and uranium/neptunium separation by the Purex process using hydroxyurea

Hydroxyurea dissolved in nitric acid can strip plutonium and neptunium from tri-butyl phosphate efficiently and has little influence on the uranium distribution between the two phases. Simulating the 1B contactor of the Purex process by hydroxyurea with nitric acid solution as a stripping agent, the separation factors of uranium/plutonium and uranium/neptunium can reach values as high as 4.7·10⁴ and 260, respectively. This indicates that hydroxyurea is a promising salt free agent for uranium/plutonium and uranium/neptunium separations.     

Seperation of neptunium from irradiated uranium targets

A new chemical method based in two separation steps was developed to isolate²³⁵Np from uranium targets irradiated with charged particles. Neptunium and plutonium are separated from uranium and most of the fission products by ion exchange. Then, neptunium is isolated from plutonium and remaining contaminants by extraction chromatography with tributyl phosphate in hydrochloric acid solution. High decontamination was achieved.     

Evolution of actinide partitioning with colloidal matter collected at PA “Mayak” site as studied by sequential extraction

Evolution of actinide partitioning to colloids upon subsurface migration in the vicinity of Karachay Lake (PA “Mayak”, Russia) was studied by micro- and ultrafiltration and sequential extraction. Colloidal matter was characterized by SEM-EDX, TEM and photon-correlation spectroscopy. Samples were collected from wells with different redox conditions i.e. from higly oxic to rather reducing. Under oxidizing conditions uranium and neptunium is readily washed out from colloids. Plutonium and americium are present in colloidal matter mainly as hard-soluble species. Under oxidizing conditions plutonium and americium are predominantly bound to organic/mineral fractions (carbonates, oxides and organically bound). Under reducing conditions plutonium and americium are present in immobile refractory fraction. It was also established that uranium and neptunium under reducing conditions behave similarly to plutonium. This phenomenon may be explained by the fact that under reducing conditions and at considerable concentrations of uranium and nitrite-ions these elements form low-soluble An(IV) forms.     

Estimation of neptunium in a fuel reprocessing plant

The solutions at various stages of the purex process used at Trombay have been analysed for their²³⁷Np content to know the path of neptunium in the process. The results of these analyses, though not very quantitative, revealed that in the co-decontamination cycle, neptunium is extracted along with uranium and plutonium almost quantitatively while in the partitioning cycle the extraction is reduced to about 50%. Analysis of various oxidation states of neptunium in the feed of the first cycle showed that neptunium is predominantly present as Np(V).     

Sequential separation of neptunium,plutonium, americium and curium using coprecipitation with bismuth phosphate

The reaction of neptunium, plutonium and americium with oxidizing or reducing agents in phosphoric acid solution has been studied to design a separation procedure of the actinide elements using coprecipitation with bismuth phosphate. In the presence of uranium, successive separation of neptunium, plutonium, americium and curium was accomplished by combining the coprecipitation and redox reaction of the elements. The coprecipitation behaviour of fission products during the course of sequential separation of the actinide elements on bismuth phosphate was also discussed.     

Separation of neptunium, plutonium, americium and curium from uranium with di-(2-ethylhexyl)-phosphoric acid (HDEHP) for radiometric and ICP-MS analysis

The possibility of using di-(2-ethylhexyl)-phosphoric acid (HDEHP) in solvent extraction for the separation of neptunium, plutonium, americium and curium from large amounts of uranium was studied. Neptunium, plutonium, americium and curium (as well as uranium) were extracted from HNO₃, whereafter americium and curium were back-extracted with 5M HNO₃. Thereafter was neptunium back-extracted in 1M HNO₃ containing hydroxylamine hydronitrate. Finally, plutonium was back-extracted in 3M HCl containing Ti(III). The method separates²³⁸Pu from²⁴¹Am for α-spectroscopy. For ICP-MS analysis, the interferences from²³⁸U are eliminated: tailing from²³⁸U, for analysis of²³⁷Np, and the interference of²³⁸UH⁺ for analysis of²³⁹Pu. The method has been used for the analysis of actinides in samples from a spent nuclear fuel leaching and radionuclide transport experiment.     

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.     

Rapid column extraction method for actinides and strontium in fish and other animal tissue samples

The analysis of actinides and radiostrontium in animal tissue samples is very important for environmental monitoring. There is a need to measure actinide isotopes and strontium with very low detection limits in animal tissue samples, including fish, deer, hogs, beef and shellfish. A new, rapid separation method has been developed that allows the measurement of plutonium, neptunium, uranium, americium, curium and strontium isotopes in large animal tissue samples (100–200 g) with high chemical recoveries and effective removal of matrix interferences. This method uses stacked TEVA Resin®, TRU Resin® and DGA Resin® cartridges from Eichrom Technologies (Darien, IL, USA) that allows the rapid separation of plutonium (Pu), neptunium (Np), uranium (U), americium (Am), and curium (Cm) using a single multi-stage column combined with alphaspectrometry. Strontium is collected on Sr Resin® from Eichrom Technologies (Darien, IL, USA). After acid digestion and furnace heating of the animal tissue samples, the actinides and ^89/90Sr are separated using column extraction chromatography. This method has been shown to be effective over a wide range of animal tissue matrices. Vacuum box cartridge technology with rapid flow rates is used to minimize sample preparation time.     

Extraction chromatography in the TBP-HNO3 system

As an application of a TBP/XAD-4 column for the analytical separation of uranium, neptunium, plutonium and americium, the elution behavior of these elements as a function of their redox reactions has been studied. Subsequently, two effective procedures to carry out a quantitative separation of the actinide elements from each other were established by combining extraction chromatography in the TBP-HNO₃ system and the redox reactions of the actinide elements.     

Various flowsheets of actinides recovery with diamides of heterocyclic dicarboxylic acids

Solvents on the base of diamides of heterocyclic dicarboxylic acids are promising alternatives for studied Grouped ActiNide EXtraction (GANEX) solvents. Advantage of these ligands is the possibility of simultaneous extraction not only of residual uranium and plutonium, but also minor actinides—neptunium, americium and curium. Two flowsheets on the base of diamides of heterocyclic dicarboxylic acids for separation of actinides form acidic solutions were developed, tested in laboratory scale and compared. Both flowsheets allow separation of more than 99.95% of actinides from raffinates with high content of lanthanides.     

Recovery of neptunium from macroamounts of uranium by extraction with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5

Conditions for neptunium recovery from nitrate solution containing large amounts of uranium by extraction with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP), and a mixture of PMBP with di-2-ethyl-hexylphosphoric acid (HDEHP) were studied. A two-stage technique, based on removal of uranium macroamounts at the first stage by means of extraction of uranium with PMBP and HDEHP mixture, and neptunium extraction by PMBP at the second stage, was suggested.     

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 some actinides with polyethyleneglycol and its derivatives

Polyethyleneglycol (PEG) and its derivatives of high molecular weight were found to be employed as useful extractants for the solvent extraction of uranium. The extraction behaviors of uranium and neptunium were investigated, particularly concerning the dependence of the extractibility of uranium(VI) on the molecular weight of PEG. A dominating species of the extracted uranium(VI) thiocyanate complexes was assumed to be NH₄ UO₂(SCN)₃·(PEG). The extraction of protactinium was also preliminarily studied. The extraction of these actinides from an acidic thiocyanate solution increased in the order: uranium(VI)>protactinium(V)>neptunium(V).     

Synthesis of diphosphine dioxides for extraction of actinides using supported liquid membranes technology

A recurrent method for synthesis of diphosphine dioxides to be used for extraction of actinides from acidic aqueous solution is described. Selective phosphonium salt formation and cleavage permits the stepwise introduction of different bridges between the phosphorus atoms as well as various chains on them. The influence of the structural parameters on liquid-liquid extraction properties of plutonium, neptunium, and americium is studied. Plutonium and neptunium can be efficiently removed from radioactive contaminated liquid wastes, using the supported liquid membranes technology with the more lipophilic organophosphorus extractants. © John Wiley & Sons, Inc.     

Hydrothermal method of preparation of actinide(IV) phosphate hydrogenphosphate hydrates and study of their conversion into actinide(IV) phosphate diphosphate solid solutions

Several compositions of Th2-x/2AnIVx/2(PO4)2(HPO4).H2O (An=U, Np, Pu) were prepared through hydrothermal precipitation from a mixture of nitric solutions containing cations and concentrated phosphoric acid. All the samples were fully characterized by X-ray diffraction, UV-vis, and infrared spectroscopies to check for the existence of thorium-actinide(IV) phosphate hydrogenphosphate hydrates solid solutions. Such compounds were obtained as single phases, up to x=4 for uranium, x=2 for neptunium, and x<4 for plutonium, the cations being fully maintained in the tetravalent oxidation state. In a second step, the samples obtained after heating crystallized precursors at high temperature (1100 degrees C) were characterized. Single-phase thorium-actinide(IV) phosphate-diphosphate solid solutions were obtained up to x=0.8 for Np(IV) and x=1.6 for Pu(IV). For higher substitution rates, polyphase systems composed by beta-TAnPD, An2O(PO4)2, and/or alpha-AnP2O7 were formed. Finally, this hydrothermal route of preparation was applied successfully to the synthesis of an original phosphate-based compound incorporating simultaneously tetravalent uranium, neptunium and plutonium.     

Extraction of plutonium from sulphuric acid by TOA in toluene

The extraction of plutonium(VI) and plutonium(III) from sulphuric acid by TOA in toluene has been studied as a function of the acid and tri-octyl amine concentration. A comparison of the extraction properties of plutonium with those of uranium(VI) and uranium(IV) has been made. It was found that the extraction properties of plutonium(VI) are very similar to those of uranium(VI) and that TOA is a relatively poor extractant for plutonium(III). Uranium(IV) shows better extraction properties than plutonium(III). The results obtained are considered in the light of the stabilities of the complexes formed by these elements in the organic and aqueous phase. A method of separation of both elements by solvent extraction based on changing their oxidation states is suggested.     

Determination of 237 Np in marine sediment and seawater

Procedures for determination of neptunium in marine sediment and seawatersamples are described. Iron hydroxide Fe(OH)₂ –Fe(OH)₃ is used for preliminary pre-concentration of neptunium. Secondly,neptunium Np⁴⁺ and Pu³⁺ are separated by tri-isooctylamine-(TIOA)extraction in 8–10M HCl by redox with SO₃ ^2–-Fe³⁺ Neptunium Np⁴⁺ and uranium U⁶⁺ areseparated by back extraction the Np⁴⁺ with 2M HCl. Finally, theneptunium is purified from the uranium and thorium by anion exchange in 8MHNO₃ and 12M HCl. The stripping of 6M HCl + NH₂ OH HClfurther separates the neptunium Np³⁺ and uranium. Reduction bySO 3_2– –Fe³⁺ appeared to be an efficientway to obtain Np⁴⁺ The decontamination factors of the procedureare 4.0. 10⁴ for ²³² Th, 5.6 . 10⁴ for uraniumand 1.6 . 10⁴ for plutonium.     

Dioctyl butyramide and dioctyl isobutyramide as extractants for uranium(VI) and plutonium(IV)

Two isomeric monoamides, dioctyl butyramide (DOBA) and dioctyl isobutyramide (DOIBA) were synthesized for extracting uranium(VI) and plutonium(IV) from aqueous nitric acid medium into various diluents such asn-dodecane, tertiary butyl benzene and xylene. DOBA extracted uranium(VI) and plutonium(IV) efficiently whereas DOIBA extracted uranium(VI) with negligible extraction for plutonium(IV). Both these cations were extracted as their disolvates. The thermodynamic parameters involved in the extraction determined by the temperature variation method indicated the reactions in all cases to be enthalpy favoured and entropy disfavoured. Possibility of separating micrograms of plutonium(IV) from macroquantities of uranium(VI) using the mixture of these amides was explored.