S. G. Marathe

Determination of uranium in the presence of iron and plutonium by Ti(III) reduction and biamperometric titration

A method is described for the determination of uranium in the presence of iron and plutonium. Ti(III) is used as the reductant in a mixture of H2SO4 and HNO3. Fe(II) and Pu(III) are selectively oxidized by the nitrous acid generated in the reaction between Ti(III) and HNO3. The U(IV) is determined by titration with K2Cr2O7 using biamperometry to detect the end point. The method is applicable to a variety of nuclear materials encountered at different stages of the nuclear fuel cycle and has no bias. The precision of the method is evaluated at different levels from 100 microgram to 100 milligram. The method is simple, rapid and convenient.

Studies on the coulometric determination of uranium and plutonium employing a graphite electrode

SummaryGraphite has been employed as a working electrode in the controlled potential coulometric determination of uranium and plutonium. The couples U(VI)/U(IV) and Pu(IV)/Pu(III) employed for analysis have diverse redox potentials and commonly the working electrodes employed are mercury and platinum. A graphite electrode in the shape of a beaker showed satisfactory performance for the quantitative reduction of U(VI) to U(IV) and Pu(IV) to Pu(III) and also for quantitative oxidation of Pu(III) to Pu(IV). Studies on the levels of the background current, blank values and their reproducible behaviour in acid media have been carried out with a view to achieve good precision and accuracy. A software-based predictive evaluation technique of end-point charge has been investigated. The results have shown that the graphite electrode can be used for the determination of both uranium and plutonium in the presence of each other with a precision and accuracy of better than ±0.5%.

Controlled Potential Coulometric Determination of Plutonium in Mixed (U, Pu) Carbide Fuels

Coulometric determination of plutonium in mixed (U,Pu) carbide samples by dissolving in HNO 3 -H 2 SO 4 acid mixture followed by treatment with perchloric acid

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.

Studies on the nature of the reactions and species involved in potentiometric titrimetric determination of uranium.

The species and reactions involved in the determination of uranium by the Davies and Gray method have been investigated through the behaviour of the various species when present alone or in various combinations in the reaction medium. The studies indicate the formation of Fe(II) and V(III) in the titration system. These two species appear easily prone to oxidation by the titration medium. Probable reasons for the negative bias found when the titration is not completed in the stipulated time period, and for the sharpening of the end-point by the presence of vanadium(IV), are discussed.

Alpha-liquid scintillation counting for the determination of plutonium

Liquid scintillation counting is useful and extensively employed for α-activity measurement. However, quenching is observed and erroneous results are obtained when the size of the solution aliquot and its acidity exceed certain limits. A simple procedure has been developed to overcome the quenching effect of volume and acidity on α-counting.

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.

A biamperometric method for the determination of sulfate

A biamperometric method for the determination of sulfate has been developed. Its application to the determination of sulfate content in rubidium uranium trisulfate is discussed. Sulfate is determined by titration with lead nitrate in aqueous ethanolic medium using ferrocyanide-ferricyanide redox system as biamperometric indicator. Initially, the method has been tested for standard. K2SO4 solutions. In case of Rb2 U(SO4)3, since uranium interferes, it is precipitated as ammonium diuranate and excess ammonia is removed prior to the titration. Precision of better than 0.3% was achieved with no significant bias.

Effect of excess AgO and EDTA on the redox titration involved in potentiometric determination of plutonium

Attempts to carry out potentiometric determination of plutonium (by AgO-oxidation method) following the determination of thorium (by complexometric EDTA titration) gave positively biased irreproducible values of plutonium. In order to understand the factors leading to the erroneous values of plutonium, the effect of varying amounts of AgO and EDTA on redox [Fe(II)/K2Cr2O7] titration in the medium consisting of 1M H2SO4 and 0,4M HNO3 was studied. When AgO (up to 200 mg) was added in the titration medium and destroyed by sulfamic acid prior to the redox titration, the dichromate tittre value (amount of standard K2Cr2O7 solution equivalent to 1 g of Fe(II) solution) showed negative bias. The bias was found to decrease with increase in time interval between AgO destruction and the redox titration. The presence of EDTA (up to 15 mg) gave positive bias in the titre value. Results on the titre values obtained under different conditions of the aqueous medium indicated the possibility of formation of unstable Ag(II)-sulfamic acid compled, which is probably responsible for the irreproducible values of plutonium.

A titrimetric method for the sequential determination of thorium and plutonium

A method for the sequential determination of thorium and plutonium has been developed. In the sample solution containing thorium and plutonium, thorium is first determined by complexometric titration with EDTA and then in the same solution plutonium is determined by redox titration employing potentiometry. Prior to the determination of plutonium, EDTA is destroyed by fuming with concentrated HClO4. Thorium is determined at 10 mg level and plutonium at 1 mg level with precision and accuracy of better than ±0.5%.