An improved method for the potentiometric determination of plutonium using cerium/IV/ as an oxidant

An improved method for the determination of plutonium in an aliquot using cerium/IV/ as an oxidant is reported. Plutonium is oxidized quantitatively to plutonium/VI/ in nitric acid medium by cerium/IV/, the excess of which is chemically destroyed in a single step by hydrochloric acid. Plutonium/VI/ is then reduced to plutonium/IV/ with a known amount of Fe/II/, the excess of which is back titrated potentiometrically with standard dichromate. Results of analysis of 3–5 mg amounts of plutonium in aliquots containing standard plutonium nitrate solution are reliable within 0.2%. Effect of the presence of some relevant foreign ions has been studied. The application of the method for the analysis of mixtures containing various amounts of uranium and plutonium has been examined.     

Sur les réactions des ions du plutonium avec l'acide éthylénediaminotétracétique

The behavior of plutonium ions in a solution of trilon B was investigate At pH 3–5 plutonmin(VI) is reduced to plutonium(V) and a (I I) complex of plutonium(V) and trilon B is formed Withi excess trilon B a plutonium(lV ) -trilon B complex is formed after some time     

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.     

Stability of plutonium(IV) and plutonium(VI) in nitric acid solutions under strong α-irradiation

Plutonium(IV) oxidation has been studied in 1 to 20 mol/1 HNO₃ under 1 to 14 W/1 internal alpha-irradiation and at plutonium concentrations from 2 to 100 mmol/1. Curium isotopes have been used as the basic alpha-irradiation sources. It has been established that in the systems investigated both oxidation of plutonium(IV) and reduction of plutonium(VI) take place, resulting with time in reaching the equilibrium between plutonium(IV) and plutonium(VI). The presence of plutonium(IV) enhances the reduction of plutonium(VI). The rate constants for plutonium(IV) oxidation and plutonium(VI) reduction have been estimated and their dependences upon the concentrations of nitric acid, plutonium(IV) and plutonium(VI) as well as upon the dose rate investigated. An equation has been derived which permits to calculate the concentrations of plutonium(IV) and plutonium(VI) at any desired time.     

Dosage du plutonium par potentiometrie a intensite constante: Application au combustible de rapsodie

A new method is proposed for the determination of plutonium in the UO₂PuO₂ pellets for Rapsodie. The sample is dissolved in a mixture of II N nitric acid and 0.l N hydrofluoric acid, and the plutonium is oxidized with silver(II) oxide. Plutonium(VI) is reduced in the presence of sulphamic acid with an excess of iron(II) which is back-titrated with cerium(IV) solution to a constant-current potentiometric end-point. Uranium and iron do not interfere and no separation is required. In routine work, the method gives a precision of 0.5%.     

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.     

Narrow span coulometric analysis of neptunium

A narrow span (E _o ±0.1 V) controlled potential coulometric method has been developed for the determination of neptunium in 1M H₂SO₄ with a RSD of 0.2%. The main advantage of this method over the existing coulometric methods is that it can tolerate up to a 5-fold excess of plutonium. The method involves carrying out the electrolysis to about 97% and calculating by an iterative computation the formal electrode potential in situ, which is used to calculate the total amount present in the sample. The method consists in oxidation of all the neptunium to Np (VI) by Ce(IV), destruction of excess Ce(IV) and reduction of Np(VI) to Np(V) by NaNO₂, destruction of excess nitrite by sulfamic acid followed by coulometric titration of Np(V) to Np(VI).     

Determination of plutonium by secondary coulometric titration with internally generated iron(II)

The method for plutonium determination based on secondary controlled-potential coulometry, as described by SHULTS, is applied for analysis in the range of 0.1–5 mg plutonium. The method involves the oxidation of plutonium to Pu(VI) with perchloric acid followed by its reduction by an internally generated ferrous mediator. This is a two step procedure, involving the reduction of Pu(VI) and Fe(III) to a mixture of Pu(III) and Fe(II), followed by the oxidation of Pu(III) and Fe(II) to Pu(IV) and Fe(III), respectively. The net results is the reduction of Pu(VI) to Pu(IV), measured as the difference between the currents consumed during the reduction and oxidation steps. The original method of SHULTS involves 10–25 mg plutonium for each determination. Since the present method is intended for the analysis of smaller amounts of plutonium, the oxidation procedure described in the original version had to be modified. The method is found to work satisfactorily with a precision better than 0.1% at 5 mg level and 1.2% for 0.1 mg plutonium.     

Dioctyl sulfoxide as a stabilizer for scintillation counting

The use of dioctyl sulfoxide (DOSO) as a stabilizer for scintillation counting of uranium(VI), plutonium(IV) and americium(III) has been investigated. It has been observed that the addition of 2% DOSO to the scintillator solution results in a decrease in count rate of Am(III), which is about one third of that obtained with 2% TOPO. Uranium(VI) could be counted with almost the same efficiency with DOSO, TOPO, or as such without any stabilizer. The counting efficiency of plutonium(IV), however, is inferior for DOSO as compared to TOPO.     

Oxidation of plutonium by cobalt(III) green

A stable green solution of tricarbonatocobaltate(III) has been prepared and used for the redox titrimetric determination of plutonium in HNO₃ medium. Quantitative oxidation could be achieved and excess oxidant could be destroyed by NaNO₂. Pu(VI) was deter-ined by adding known excess of Fe(II) and carrying out potentiometric titration. The precision at the level of 0.5–5.0 mg was 2% RSD.     

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 plutonium and uranium in mixed oxide fuels by sequential redox titration

The use of a sequential determination of uranium and plutonium in a single sample solution results in a saving in analysis time and apparatus requirements. The method starts with U(IV) and Pu(in) in a mixture of sulphuric and nitric adds. Titration with dichromate, using amperometry at a pair of polarizable electrodes, produces two well-defined end-points corresponding to the sequential oxidation of U(IV) to U(VI) and Pu(III) to Pu(IV). The quantitative oxidation of U(IV) to U(VI) is achieved via the action of Pu(IV) as intermediate, and is dependent upon establishing conditions which favour rapid reaction between U(IV) and Pu(IV). The method is precise and accurate. With Pu-U mixtures containing between 15 and 30% plutonium the precision (3sigma) of the Pu: U ratio results is +/-0.6% on samples containing 100-120 mg of plutonium plus uranium. Iron and vanadium interfere quantitatively with plutonium, copper interferes non-quantitatively with uranium, and gross amounts of molybdenum mask the uranium end-point.     

Modeling of Pu(VI) distribution coefficients in 30 % TBP based PUREX process

Hexavalent plutonium (Pu(VI)) is an important solute in the PUREX (plutonium uranium extraction) process. In 30 % TBP based PUREX solvent extraction system, distribution coefficient of Pu(VI) is much lower than that of Pu(IV). This lower distribution coefficient of Pu(VI) may cause unexpected Pu loss during primary HA extraction in low acid flowsheets. An empirical model for Pu(VI) distribution coefficients in 30 % TBP and its temperature dependency has been reported in this paper. Comparison with literature data revealed a reasonably good agreement between the reported experimental and model predicted values.     

Dosage spectrophotometrique du neptunium

(Spectrophotometric determination of neptunium.) Use of the absorption peak of the NpO⁺₂ ion at 981 nm is discussed. Quantitative conversion to Np(V) requires oxidation of Np(IV) by Ce(IV), reduction of Np(VI) and excess of Ce(IV) with hydrazinium nitrate, and destruction of excess of hydrazine by nitrite. The measurable concentration range in the cuvette is 2–1000 mg l^-1 and the precision is± 1% in the higher range. Uranium and plutonium at ratios Me/Np ? 10^-3 do not interfere.     

Solid-phase extraction of plutonium in various oxidation states from simulated groundwater using N-benzoylphenylhydroxylamine

Solid-phase extraction of plutonium in different individual and mixed oxidation states from simulated groundwater (pH 8.5) was studied. The extraction of plutonium species was carried out in a dynamic mode using DIAPAK C16 cartridges modified by N-benzoylphenylhydroxylamine (BPHA). It was shown that the extent of recovery depends on the oxidation state of plutonium. The extraction of Pu(IV) was at the level of 98–99% regardless of the volume and flow-rate of the sample solution. Pu(V) was extracted by 90–95% and 75–80% from 10- and 100-mL aliquots of the samples, respectively, whereas the extraction of Pu(VI) did not exceed 45–50%. An equimolar mixture of Pu(IV), Pu(V), and Pu(VI) was extracted by 74%. The distribution coefficients (K _d) and kinetic exchange capacities (S) of plutonium in various oxidation states were measured. It was found that during the sorption process, Pu(V) was reduced to Pu(IV) by 80–90% after an hour-long contact with the solid phase. Pu(VI) is reduced to Pu(V) by 34% and to Pu(IV) by 55%. In the case of mixed-valent solution of plutonium, only Pu(V) and Pu(IV) were found in the effluents.     

Determination of plutonium oxidation states in dilute nitric acid by complementary tristimulus colorimetry

The preparation of reference standards for use in complementary tristimulus colorimetry for plutonium is described. Plutonium(III) and (VI) are prepared by hydrazine reduction and silver(II) oxidation, respectively, of plutonium(IV). Plutonium(V) is prepared by reduction of plutonium(VI) with ascorbic or sulphurous acid. A method for computerizing tristimulus colorimetry is presented, and the technique is extended to three dimensions ("quadristimulus colorimetry").     

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.     

Distribution of Pu(VI) from nitric acid to tri-n-butyl phosphate saturated with uranium(VI)

Solvent extraction of plutonium(VI) from nitric acid (1 to 5M) into 20% and 30% TBP in dodecane saturated with uranium(VI) (0% to 80%) has been studied. For a particular nitric acid concentration, the distribution coefficient (K _d ) is found to decrease with the increase in saturation of organic phase with uranium(VI). At a fixed organic phase the saturationK _d increased with increase in nitric acid concentration, however, the magnitude of this increase inK _d decreased with the increase in saturation.     

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.