Solvent extraction of Np(IV) and Pu(IV) with mixtures of TOPO and HTTA

Solutions of HTTA are known to extract tetravalent actinides as M(TTA)₄ species. When TOPO is added to HTTA solutions, the extracting of Np(IV) and Pu(IV) from aqueous perchloric acid was enhanced enormously. The species responsible for the enhanced extraction were identified from the extraction data by the slope ratio method and JOB's method. It was found that the predominant species responsible for enhancement in the extraction, when [HTTA]≫[TOPO], was M(TTA)₄. TOPO for both Np(IV) and Pu(IV). Furthermore, it was established that depending on the relative concentrations of HTTA and TOPO, a number of species with the composition M(TTA)_a(ClO₄)_4-a·b TOPO, with a ranging from 1 to 4 and b having values of 1 or 2, are involved in the extraction. Several equilibrium constant values are given. Fuel Reprocessing Division.     

Analysis of uranium in dissolver solution of fast reactor carbide fuel reprocessing

Uranium in simulated dissolver solution of FBTR mixed carbide fuel containing fission products is analyzed by modified Davies–Gray method. The uranium is analyzed after the sample is evaporated with 1 M H₂SO₄ and followed all the steps carried out by Davies–Gray method. The proposed method assures analysis of uranium in dissolver solution of FBTR fuel can be titrated directly without prior separation of fission products.     

Rapid determination of 237Np in soil samples by multi-collector inductively-coupled plasma mass spectrometry and gamma spectrometry

A radiochemical procedure is developed for the determination of ²³⁷Np in soil with multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) and gamma-spectrometry. ²³⁹Np (milked from ²⁴³Am) was used as an isotopic tracer for chemical yield determination. The neptunium in the soil is separated by thenoyl-trifluoracetone extraction from 1 M HNO₃ solution after reducing Np to Np(IV) with ferrous sulfamate, and then purified with Dowex 1 × 2 anion exchange resin. ²³⁹Np in the resulting solution is measured with gamma-spectrometry for chemical yield determination while the ²³⁷Np is measured with MC-ICP-MS. Measurement results for soil samples are presented together with those for two reference samples. By comparing the determined value with the reference value of the ²³⁷Np activity concentration, the feasibility of the procedure was validated.     

Determination of neptunium in a reprocessing plant by an on-line solid-phase extraction/electrochemical detection system

In this study, a flow-based electrochemical detection system coupled to a solid-phase extraction column was developed for the determination of neptunium in the presence of Pu(IV). Np(V) in the sample solution was completely oxidized to Np(VI) via electrolysis using a column electrode composed of carbon fibers. The column electrode effluent was then loaded onto a TEVA^® column, and subsequently onto a UTEVA^® column using 3 mol L^?1 HNO₃. Pu(IV) was retained on the TEVA column and separated from Np(VI), while Np(VI) was retained on the UTEVA column. Np(VI) was eluted from the UTEVA column with 0.01 mol L^?1 HNO₃ and then introduced directly into a flow-through electrolysis cell. An electrochemical amperometric method with a working potential of +0.1 V (vs. Ag/AgCl) was used to detect Np(VI). The current produced due to the reduction of Np(VI) was continuously monitored and recorded, and the Np concentration was calculated from the peak area. The relative standard deviation of 10 analyses was 2.4 % for an Np solution (0.50 mg L^?1) containing 1.0 μg Np. The detection limit, which was determined to be three times the standard deviation, was 35 μg L^?1 (70 ng Np).     

Neutron activation analysis of uranium via239Np

A method is described for the analysis of uranium by neutron activation. The sample is brought into solution and the neptunium present is reduced to oxidation state (IV); quantitative extraction of²³⁹Np in the acidified aqueous phase (0.4<pH<1) is performed with a solution of HTTA (0.2M) in benzene. The use of a low-power reactor (100 kW_thermal) enables determination of uranium at a lower concentration limit of 33 ng for periods of irradiation. cooling and measurement of 3 hours, 24 hours and 900 seconds, respectively.     

Synergistic extraction of tetravalent actinides by mixtures of a β-diketone and a sulfoxide

Synergistic extraction of tetravalent actinides, using mixtures of a β-diketone and several neutral organophosphorous extractants, was recently demonstrated. In this work the extraction of the ions Th(IV), Np(IV) and Pu(IV), from perchloric acid medium, by benzene solutions of a β-diketone, thenoyltrifluoroacetone (HTTA), in combination with a neutral organosulfoxide donor, di-n-octyl sulfoxide (DOSO), has been investigated. Two methods viz. the slope analysis method and JOB's method have been employed for the study. The species mainly responsible for the observed synergism, with the M(IV) ions studied, was found to be M(TTA)₄·DOSO. The extraction and adduct formation equilibrium constants are given.     

Synergistic extraction of hexavalent actinides by HTTA and neutral donors-II

Synergistic extraction studies on Np(VI) and Pu(VI) have been carried out as a part of the programme on the synergistic extraction of hexavalent actinides. Extraction of Np(VI) and Pu(VI) were carried out by mixtures of HTTA and TBP in benzene from aqueous perchlorate and nitrate media. Equilibrium constant values for the various reaction equilibria involved were calculated from the data obtained by using slope-ratio as well as Job’s method. The extraction of Np(VI) by the synergistic mixture from 1M nitric acid indicated that the species NpO₂ (TTA) (NO₃). TBP was not involved in the extraction. The log values of K_A, K_AB and β_AB were −1.5, 2.92 and 4.43, respectively for Np(VI) and −1.63, 2.50 and 4.13 respectively for Pu(VI).     

A novel Np–Pu separation procedure based on extraction with di-(chlorophenyl)-dithiophosphinic acid in nitric solution

The extraction behavior of Pu(III), Pu(IV), Np(IV) and Np(V) with di(chlorophenyl)-dithiophosphinic acid (DCPDTPA) in toluene from nitric acid solutions was studied systematically. In aqueous solution with high nitric acid concentration, the extraction capability (represented by distribution ratio D) for Pu and Np in different valences with DCPDTPA comes as D _Np(IV) > D _Pu(IV) > D _Np(V) > D _Pu(III). A new radiochemical procedure for Np/Pu separation based on DCPDTPA extraction was proposed and tested with simulated samples. The recoveries of Np and Pu are as high as 80 % after the whole separation procedure, with the decontamination factor of trivalent lanthanide fission product element (e.g. Eu) greater than 1.5 × 10⁴. The decontamination factor of Pu–Np is 2.0 × 10³, while the decontamination factor of Np–Pu is greater than 4.8 × 10³ after additional purification.     

Separation and direct UV detection of complexed lanthanides,thorium and uranyl ions with 2-thenoyltrifluoroacetone by using capillary zone electrophoresis

Separation and detection of lanthanides, thorium and uranyl ions by capillary zone electrophoresis in the presence of 2-thenoyltrifluoroacetone (HTTA) as UV-absorbing complexing agent were investigated. The separation of positively charged complexes is partially improved by using a competing ligand in buffer with HTTA for metal ions. When 2-hydroxyisobutyric acid (HIBA) is used as competing ligand, complete separation of thorium, uranyl and lanthanides ions were observed. Some separation parameters such as pH value, the concentration of carrier electrolyte, applied voltage, the concentration of ligand in buffer and the temperature were also optimized. Under the selected conditions, the complete separation of thorium and uranyl from each other and from lanthanides was accomplished in only 12 min using 1 mmol/L HTTA, 50 mmol/L HIBA, 5 mmol/L NaNO₃, 5 % methanol with a pH 5.2 at a capillary temperature of 25 °C. Direct photometric detection at 210 nm using a voltage of 25 kV and an electrokinetic injection (100 mm for 6 s) were used.     

Studies on the HTTA extraction of tetravalent actinides

The data on the extraction of Np(IV) and Pu(IV) from aqueous perchloric and nitric acid into benzene solution of thenoyl-trifluoro-acetone (HTTA) have been obtained at different temperatures. From these data the equilibrium constant for their extraction and the values of enthalpy for the extraction of Np(IV) and Pu(IV) were calculated. The absorption spectra of HTTA extracts containing Th(IV), U(IV), Np(IV) and Pu(IV) have been recorded to explore their analytical applications.     

Synergistic extraction of trivalent Am,Cm, Bk and Cf with HTTA+TBP in xylene

The synergistic extraction of trivalent actinides Am, Cm, Bk and Cf with thenoyltrifluoro acetone (HTTA) and tributyl phosphate (TBP) has been studied in xylene at 30°C. Correction for the HTTA-TBP interaction has been applied to get the free TBP concentration in the organic phase. Plots of log D vs. log [HTTA] give straight lines with a slope of 3 only after correcting for the HTTA-TBP interaction; without this correction the slope varies from 3 to 1 with increasing HTTA concentrations. The presence of two synergistic species M(TTA)₃·TBP and M(TTA)₃·2TBP simultaneously has been observed. The equilibrium constants for the organic phase synergistic reactions have been calculated.     

Extraction chromatography for the separation of <Superscript>239</Superscript>Np from <Superscript>243</Superscript>Am

Summary An extraction chromatography method was developed for the separation of 239Np from ²⁴³Am in nitric acid solution. A sorbent based on aliphatic quaternary amine Aliquat-336 and hydrophobized silica gel was prepared. ²³⁹Np reduced to the oxidation state(IV) with ferrous sulfamate in 2M or 6M HNO₃ sorbs on the prepared silica gel column. After washing with 0.1M ferrous sulfamate in 2.5M HNO₃, ²³⁹Np is eluted with 0.1M HNO₃ containing 0.02M HF. The separation of ²⁴³Am from ²³⁹Np is very effective. The purity of ²³⁹Np was found to be better than 99.5%. The proposed ²³⁹Np milking procedure is suitable for the preparation of ²³⁹Np tracer that can be used for the determination of ²³⁷Np radiochemical yield.     

Synergetic extraction of Co3+

The extraction of Co³⁺ from 0.1M aqueous acetate medium buffered to pH 5.3 by thenoyltrifluoroacetone (HTTA) in benzene and by 8-quinolinol (HQ) also in benzene at various temperatures has been studied. The species formed were Co(OH)₂ (TTA)·(HTTA)₂ and Co(Q₃)·2HQ, respectively. 1,10-phenanthroline (Phen) as a base was also mixed with HTTA to form the species Co(OH)₂(TTA)·(HTTA). Phen and Co(OH)₂ (TTA)(HTTA)·2Phen. No synergism was observed upon the addition of Phen to HQ.     

UO2, NpO2 and PuO2 preparation in aqueous nitrate solutions in the presence of hydrazine hydrate

It was established that heating to 90 °C of nitrate solutions of U, Np and Pu in the presence of hydrazine hydrate results in the formation of hydrated dioxides of these elements. On ignition under inert or reducing conditions in the temperature range of 280–800 °C hydrated uranium dioxide transmogrify into crystalline UO₂. On ignition in air atmosphere UO₂·nH₂O turns into UO₃ at 440 °C and into U₃O₈ at 570–800 °C. It was shown that thermolysis of the solution containing a mixture of uranium, neptunium and plutonium nitrates at 90 °C in the presence of hydrazine hydrate allows one to prepare hydrated dioxides (U, Np, Pu)O₂·nH₂O which on heating to ~300 °C transmogrify into crystalline product of UO₂, NpO₂ and PuO₂ solid solution. The technique of preparation of solid solutions of U and Pu dioxides is very promising as simple and effective method of production of MOX-fuel for.     

Rapid measurements of neptunium oxidation states using chromatographic resins

The Savannah River Site’s (SRS) H-Canyon facility uses ceric ammonium nitrate (CAN) to separate impure neptunium (Np) from a nitric acid feed stream containing 0.5–1.0 M concentrations of iron, sodium and sulfate impurities. The material is processed using a two-pass solvent extraction purification which relies on CAN to oxidize Np to Np(VI) during the first pass prior to extraction. Spectrophotometric oxidation-state analyses normally used to validate successful oxidation to Np(VI) prior to extraction were compromised by this feed stream matrix. Therefore, a rapid chromatographic method to validate successful Np oxidation was developed using Eichrom Industries’ TRU and TEVA^® resins. The method was validated and subsequently transferred to existing operations in the process analytical laboratories.     

Stability constants of Np(V) complexes with fluoride and sulfate at variable temperatures

Summary A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0M NaClO₄ from 25 to 60 °C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1 : 1 Np(V)-fluoride complexes and the 1 : 1 Np(V)-sulfate and 1 : 2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F^-] and [SO₄^2-] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.     

Chemical separation of enriched cadmium target from copper backing in cyclotron production of radioisotope 111In

A radiochemical purification procedure was developed for the separation of enriched cadmium (¹¹¹Cd and ¹¹²Cd) from natural copper that used as backing; and was based upon the chromatographic adsorption. The separation of copper from cadmium was studied in this work. The ions were selectively separated from aqueous solution. Ion-exchange chromatography was employed as a column (1.5 cm i.d. and 15 cm length) with AG1-X8 resin (chloride form, 100–200 mesh) and a flow rate of 1–2 ml/min throughout the separation. 6 M HCl media was used for the adsorption of Cd and Cu on the resin. Then, Cu was eluted by 2 M HCl and Cd by 100 ml 0.5 M HNO₃. The amount of Cu and Cd ions in the final solution (0.5 M HNO₃) were measured by pulse polarographic method and the concentration of Cu was found to be <0.1 ppm. The Cd was quantitatively recovered and the recovery yield from ion-exchange chromatography was greater than 96 %.     

Thermodynamics of neptunium(V) complexes with phosphate at elevated temperatures

The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO₄ ²⁻ complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO₄ ²⁻] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO₄ ²⁻ at 25 °C–55 °C were calculated by the temperature coefficient method.     

Sensitive redox speciation of neptunium by CE–ICP–MS

Capillary electrophoresis (CE) was used to separate the neptunium oxidation states Np(IV) and Np(V), which are the only oxidation states of Np that are stable under environmental conditions. The CE setup was coupled to an inductively coupled plasma mass spectrometer (Agilent 7500ce) using a Mira Mist CE nebulizer and a Scott-type spray chamber. The combination of the separation capacity of CE with the detection sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) allows identification and quantification of Np(IV) and Np(V) at the trace levels expected in the far field of a nuclear waste repository. Limits of detection of 1?×?10^-9 and 5?×?10^-10 mol L^-1 for Np(IV) and Np(V), respectively, were achieved, with a linear range from 10^-9 to 10^-6 mol L^-1. The method was applied to study the redox speciation of the Np remaining in solution after interaction of 5?×?10^-7 mol L^-1 Np(V) with Opalinus Clay. Under mildly oxidizing conditions, a Np sorption of 31% was found, with all the Np remaining in solution being Np(V). A second sorption experiment performed in the presence of Fe²⁺ led to complete sorption of the Np onto the clay. After desorption with HClO₄, a mixture of Np(IV) and Np(V) was found in solution by CE–ICP–MS, indicating that some of the sorbed Np had been reduced to Np(IV) by Fe²⁺.     

New approaches to reprocessing of oxide nuclear fuel

Dissolution of UO₂, U₃O₈, and solid solutions of actinides in UO₂ in subacid aqueous solutions (pH 0.9–1.4) of Fe(III) nitrate was studied. Complete dissolution of the oxides is attained at a molar ratio of ferric nitrate to uranium of 1.6. During this process actinides pass into the solution in the form of U(VI), Np(V), Pu(III), and Am(III). In the solutions obtained U(VI) is stable both at room temperature and at elevated temperatures (60 °C), and at high U concentrations (up to 300 mg mL^?1). Behavior of fission products corresponding to spent nuclear fuel of a WWER-1000 reactor in the process of dissolution the simulated spent nuclear fuel in ferric nitrate solutions was studied. Cs, Sr, Ba, Y, La, and Ce together with U pass quantitatively from the fuel into the solution, whereas Mo, Tc, and Ru remain in the resulting insoluble precipitate of basic Fe salt and do not pass into the solution. Nd, Zr, and Pd pass into the solution by approximately 50 %. The recovery of U or jointly U + Pu from the dissolution solution of the oxide nuclear fuel is performed by precipitation of their peroxides, which allows efficient separation of actinides from residues of fission products and iron.