Coulometric determination of uranium and iron or plutonium in a single aliquot using platinum working electrode

A controlled potential coulometric method developed earlier for the determination of uranium in the presence of iron or plutonium using platinum working electrode was extended for individual determination of uranium and iron or plutonium in single aliquot. After uranium determination, Fe(III) or Pu(IV) in the aliquot is reduced electrolytically to Fe(II) or Pu(III) and subsequently determined by electrolytic oxidation to Fe(III) or Pu(IV), respectively. Analysis of synthetic solutions indicated that the values for uranium, iron and plutonium obtained by this method are reproducible within±0.2% and are in good agreement with values obtained using conventional redox methods 1, 2.     

Determination of plutonium and uranium in the same aliquot by potentiometric titration

A potentiometric titration method was developed for the determination of plutonium and uranium in the same aliquot in nitric acid medium. Plutonium was first determined by oxidation to Pu/VI/ by fuming with conc. HClO₄. Pu/VI/ formed was reduced to Pu/IV/ with known excess of Fe/II/ and the excess Fe/II/ was titrated with standard K₂Cr₂O₇ to a potentiometric end point. Uranium in the same solution was determined by reduction to U/IV/ with Fe/II/ in conc. H₃PO₄ medium and titrating U/IV/ formed with standard K₂Cr₂O₇ using the potentiometric end point detection technique. For the quantity of plutonium and uranium each in the range of 3–5 mg per aliquot a precision of ±0.2% and ±0.4%, respectively, was obtained.     

Titrimetric determination of uranium in the presence of plutonium in sulphuric acid medium

Present work summairzes a method for the estimation of uranium in the presence of plutonium involving the reduction of uranium to U/IV/ and plutonium to Pu/III/ by Zn/Hg/ followed by the selective oxidation of Pu/III/to Pu/IV/with HNO₃ catalyzed by molybdate in the presence of large sulphate concenration [5M H₂SO₄+1.5M /NH₄/₂SO₄]. The oxidation of U/IV/ by K₂Cr₂O₇ is then carried out in the presence of excess of Fe/III/ and Al/NO₃/₃ to a sharp potentiometric end point. R.S.D. obtained for 20 determinations of uranium /3–6 mg/ was 0.3% in the presence of 0.35 mg of plutonium. Larger quantity for plutonium was found to interfere.     

A ratio derivative spectrophotometric method for the simultaneous determination of uranium and plutonium

A ratio derivative spectrophotometric method has been developed for the simultaneous determination of uranium and plutonium at mg levels in 1M HNO₃ medium. In this method the overlapping spectra of uranium and plutonium are well resolved by making use of the first derivative of the ratios of their direct absorption spectra. The derivative ratio absorbances of uranium and plutonium are measured at 411.2 and 473.8 nm, respectively for their quantification. The method is simple, fast and does not require separation of uranium and plutonium. Another salient feature of the method is that it does not lead to generation of analytical waste thereby minimising the efforts required for the recovery of plutonium. Uranium in the conc. range of 10–25 mg/g and plutonium in the conc. range of 0.5 to 2 mg/g (U/Pu ratio varying from about 10 to 25) were determined in the same aliquot with a precision and accuracy of about 0.5% and 1%, respectively.     

Simultaneous determination of uranium and plutonium at trace levels in process streams using Arsenazo III by derivative spectrophotometry

A derivative spectrophotometric method has been developed for the simultaneous determination of uranium and plutonium at trace levels in various process streams in 3M HNO₃ medium using Arsenazo III. The method was developed with the objective of measuring both uranium and plutonium in the same aliquot in fairly high burn-up fuels. The first derivative absorbances of the uranium and plutonium Arsenazo III complexes at 632 nm and 606.5 nm, respectively, were used for their quantification. Mixed aliquots of uranium (20–28 μg/ml) and plutonium (0.5–1.5 μg/ml) with U/Pu ratio varying from 25 to 40 were analysed using this technique. A relative error of about 5% was obtained for uranium and plutonium. The method is simple, fast and does not require separation of uranium and plutonium. The effect of presence of many fission products, corrosion products and complexing anions on determination of uranium and plutonium was also studied.     

Complexometric determination of thorium in ThO2−PuO2

A method based on the complexometric titration of thorium using ethylene diaminetetra-acetic acid (EDTA) as complexant has been developed for the determination of thorium in thorium-plutonium solution without resorting to prior separation of plutonium. Plutonium in the form of Pu(VI) does not affect the thorium determination when present up to 10% in thorium—plutonium solution. For oxidation of plutonium to Pu(VI), HClO₄ or AgO was used. HClO₄ is preferred. The thorium values obtained without prior separation of plutonium are compared with those obtained after separating plutonium by anion exchange technique. A precision of ±0.5% has been obtained for 5–10 mg of thorium in the aliquot.     

Alpha spectroscopic analysis of actinides (Th,U and Pu) after separation from aqueous solutions by cation-exchange and liquid extraction

The radioactivity concentration of ²³⁶Pu, ²³²U and ²²⁸Th in aqueous samples has been determined by means of alpha spectroscopy after chemical separation and pre-concentration of the radionuclides by cation exchange and liquid–liquid extraction using the Chelex-100 resin and 30% TBP/dodecan, respectively. Method calibration using a ²³⁶Pu standard solution containing the daughter radionuclides results in a detector efficiency of 18% and in a chemical recovery for cation-exchange which is (30 ± 7)%, (90 ± 5)% and (20 ± 5)% for plutonium, uranium and thorium, respectively. The chemical recovery for liquid–liquid extraction is found to be (60 ± 7)%, (50 ± 5)% and (70 ± 5)%, for plutonium, uranium and thorium, respectively. The differences in the efficiencies can be ascribed to the oxidation states, the different actinides present in solution. Taking into account that the electrodeposition of the radionuclides under study is quantitative, the total method efficiency is calculated to be (18 ± 15)%, (46 ± 7)% and (15 ± 5)%, for plutonium, uranium and thorium, respectively, at the mBq concentration range. The detection limit of the alpha spectrometric system has been found to be 0.2 mBq/L, suggesting that the method could be successfully applied for the radiometric analysis of the studied radionuclides and particularly uranium in aqueous samples.     

Radiation chemistry of actinides

The paper presents data on the development of a mathematical model describing the radiation-chemical behaviour of plutonium in 3–6 mol/l HNO₃ with uranium present and absent. Using experimental data on the kinetics of Pu(VI) reduction and Pu(IV) oxidation, and comparing them with the calculated values, we succeeded in finding the previously unknown rate constants of many reactions between plutonium ions and HNO₃ radiolysis products, between plutonium ions and between plutonium ions and uranium ions. The mechanism of the radiation-chemical processes has been established.     

Determination of plutonium in sediments by solvent extraction and α-spectrometry

A simple technique for the determination of environmental levels of plutonium in a highly complex matrix (sediments containing very high amounts of iron and other metals) is reported. The sediments, collected from the Hudson River Estuary with an Emory dredge, were hand-homogenized before a sample aliquot was taken. Samples were airdried, weighed, spiked with ²⁴²Pu tracer, and heated at 400°C for 24 h. Plutonium was leached from the sediment with an acid mixture. The leachate was filtered, and plutonium coprecipitated with iron by adding ammonia solution. After dissolution, plutonium was extracted with 20% trilaurylamine in xylene, the extracts were thoroughly acid-washed to remove uranium and thorium traces, and plutonium was then back-extracted with 2 M sulfuric acid prior to electrodeposition onto a platinum planchet. The isotopic composition of plutonium was determined by α-spectrometry. Tracer yield and plutonium concentrations determined on aliquots of the same samples by this method and by an ion-exchange technique were not significantly different.     

The determination of plutonium by mass spectrometry using a [242]-plutonium tracer

An isotopic dilution method is described for the determination ot plutonium in samples of irradiated uranium using a ²⁴²Pu tracer. An aliquot of tracer is added to the sample and the mixture treated to ensure isotopic exchange; plutonium is then separated by an ion exchange procedure and an isotopic analysis made using an M.S.5. mass spectrometer. The precision (3 σ) for an aliquot containing 0.1 μg plutonium is 0.6%. A possible application of the method would be its use for control analyses of the feed solution in a chemical plant processing natural uranium fuel elements as, for example, the Windscale primary separation plant.     

On atomization of uranium in plutonium matrix using ETA-AAS

Atomization processes for uranium in aqueous media and in the presence of a plutonium matrix have been studied and a chemical mechanism is proposed. These studies have been utilized for the determination of uranium in plutonium by Electrothermal Atomization- Atomic Absorption Spectrometry (ETA-AAS) within the constraints of its stable carbide forming tendency and complexity caused by formation of plutonium suboxide at high temperatures. In spite of these limitations the analytical range obtained for determination of uranium is 2.5–100 ng with a sample aliquot of 5 μL containing 5 mg/mL plutonium concentration. The precision of the method is evaluated as 9% RSD. Received: 9 September 1997 / Revised: 29 December 1997 / Accepted: 31 December 1997     

Atomization mechanism and determination of Ag, Be, Cd, Li, Na, Sn and Zn in uranium-plutonium matrices by ETA-AAS

The atomization processes involved in the Electrothermal Atomization-Atomic Absorption Spectrometric (ETA-AAS) determination of Ag, Be, Cd, Li, Na, Sn and Zn in the presence of an uranium-plutonium matrix containing 25% Pu have been investigated. The significant fall in the absorbance signal for Ag, Cd, Na and Zn in an uranium matrix and its restoration in the presence of plutonium is probably correlated with the change in the partial pressure of oxygen released from the matrix at/below the signal appearance temperature (T_app). In case of Li and Sn, the signal remains unaffected irrespective of the U-Pu matrix which might be due to a high T_app for these analytes. Regarding Be, the steep suppression of the signal in the presence of the plutonium matrix compared to an uranium matrix can be ascribed to the formation of stable Pu-Be compounds (PuBe₁₃). Based on these studies, analytical procedures have been developed for the direct determination of nanogram amounts of these analytes in an U-Pu matrix with an average precision of 9% RSD.     

Determination of uranium in plutonium by differential linear sweep oscillographic polarography

The polarographic behavior of uranium in hydroxylamine hydrochloride was investigated by differential oscillographic polarography. A procedure is presented for the determination of uranium in plutonium for concentrations of uranium greater than 10 p.p.m. Analyses of solutions containing 22 common impurities found in plutonium metal revealed that antimony, copper, and titanium cause significant interference. A reversible peak corresponding to a one-electron reduction was obtained with a peak potential of -0.167 V vs. Hg pool electrode. The diffusion coefficient is 0.51·10^-5 cm²/sec and the diffusion current constant is 1.59 with an average relative standard deviation of 2.28%. The peak current of uranium can be affected by hydrochloric, nitric, perchloric, and sulfuric acids, depending on the acid concentration.     

Determination of uranium and plutonium in plutonium based fuels by sequential amperometric titration

A method is described for the sequential determination of uranium and plutonium in plutonium bearing fuel materials. Uranium and plutonium are reduced to U(IV) and Pu(III) with titanous chloride and then titrated with dichromate to two end points which are detected amperometrically using two polarized platinum electrodes. Uranium-plutonium solutions of known concentrations containing plutonium in the proportions of 4, 30, 50, and 70% were analyzed with precisions better than 0.3%, maintaining the amounts of plutonium per aliquot in the range of 2–10 mg. No significant bias could be detected. Several samples of (U, Pu)O₂ and (U, Pu)C were analyzed by this procedure. The effects of iron, fluoride, oxalic acid and mellitic acid on the method were also studied.     

Coulometric determination of uranium in presence of iron/plutonium using a platinum working electrode

A controlled potential coulometric method for the determination of uranium in the presence of iron or plutonium using a platinum working electrode has been developed. The method consists of reduction of uranium in 8M H₂SO₄ by Ti(III) followed by destruction of excess Ti(III) and selective oxidation of Fe(II) or Pu(III) to Fe(III) or Pu(IV), respectively, by sodium nitrite. The U(IV) is subsequently determined by electrolytic oxidation at Pt electrode using Fe(III) as an intermediate. The method was employed for the determination of uranium in synthetic mixtures of U+Fe and U+Pu containing varying ratios of U/Fe or U/Pu. The precision obtained for uranium results was ±0.25%.     

萃取色层分离同位素稀释ICP-MS测定空气中费克 量钚

ICP-MS测定环境样品中超痕量^2^3^9Pu时,^2^3^8UH^+会对m/z239的测量带来干扰。测得UH^+的产生几率为4.6×10^-^5,通过三正辛胺色层分离后,对铀的去除率为10^4,可以有效地去除^2^3^8UH^+离子峰对^2^3^9Pu测定的干扰。钚的回收率为75%。同位素稀释法对^2^3^9Pu的检出限为4.5×10^-^1^5g/mL,方法的定量测定限为16×10^-^1^5g/mL。用所建立的方法测得我国某地区空气中^2^3^9Pu的浓度为4.8×10^-^1^7g/m^3。     

A titrimetric method for the sequential determination of thorium and uranium

A method for the sequential determination of thorium and uranium has been developed. In the sample solution containing thorium and uranium, thorium is first determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA) and then in the same solution uranium is determined by redox titration employing potentiometry. As EDTA interferes in uranium determination giving positive bias, it is destroyed by fuming with HClO₄ prior to the determination of uranium. A precision and accuracy of better than ±0.15% is obtained for thorium at 10mg level and uranium ranging from 5 mg to 20 mg in the aliquot.     

Controlled potential coulometry: the application of a secondary reaction to the determination of plutonium and uranium at a solid electrode

A method is described for the simultaneous determination of plutonium and uranium in mixed oxides by controlled potential coulometry at a gold working electrode in two stages: first a coulometric oxidation, at 0.73 V vs. a silver/silver chloride electrode, of Pu(III) and U(IV) to Pu(IV) and U(VI) by a combination of a direct electrode reaction and a secondary chemical reaction proceeding concurrently, and secondly, a coulometric reduction at 0.33 V of Pu(IV) to Pu(III), leaving uranium as U(VI). The determination is carried out in a mixture of sulphuric and nitric acids, and Ti(III) is used to reduce plutonium and uranium to Pu(III) and U(IV) before electrolysis. The precision (3sigma) of Pu:U ratio results obtained from mixtures containing about 30% and 2% plutonium was 0.5% and 1-5% respectively. The effect of experimental variables on the time taken to complete the coulometric determination is discussed.     

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.     

Potentiometric determination of uranium in the presence of plutonium in H2SO4 medium

The potentiometric determination of uranium is widely carried out in phosphoric acid medium to suppress the interferences of plutonium by complexation. Owing to the complexity of the recycling plutonium from the phosphate based waste involving manifold stages of separation, a method has been proposed in the present paper which does not use phosphoric acid. Uranium and plutonium are reduced to U/IV/ and Pu/III/ in 1M H₂SO₄ by Ti/III/, and NaNO₂ is chosen to selectively oxidize Pu/III/ and the excess of Ti/III/. The unreacted NaNO₂ is destroyed by sulphamic acid and excess Fe/III/ is added following dilution. The equivalent amount of Fe/II/ thus liberated is titrated against standard K₂Cr₂O₇. R.S.D. obtained for the determination of uranium /1–2 mg/ is 0.3% with plutonium being present upto 4.0 mg.