Two predominance-region diagrams for plutonium

Two predominance-region diagrams for plutonium are illustrated. One diagram plots the pH vs. the equilibrium fraction of hexavalent plutonium. The other diagram plots the equilibrium fraction of tetravalent plutonium vs. the plutonium oxidation number. Both diagrams define the boundaries of the regions where tri-, tetra-, penta-, and hexavalent plutonium are the predominant species. In each diagram, the two principal triple points are located at the intersections of three predominance-region boundary lines.Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy under Contract No. W-7405-ENG-36.     

Two predominance-region diagrams for plutonium

Two predominance-region diagrams for plutonium are illustrated. One diagram plots the pH vs. the equilibrium fraction of hexavalent plutonium. The other diagram plots the equilibrium fraction of tetravalent plutonium vs. the plutonium oxidation number. Both diagrams define the boundaries of the regions where tri-, tetra-, penta-, and hexavalent plutonium are the predominant species. In each diagram, the two principal triple points are located at the intersections of three predominance-region boundary lines.Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy under Contract No. W-7405-ENG-36.     

Intrinsic predominance region diagram for plutonium

Summary A predominance-region diagram for aqueous plutonium can be prepared by plotting the equilibrium fractions of tetra- and hexavalent plutonium. An example illustrates how the triple points can be used to estimate hydrolysis constants.     

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.     

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.     

Plutonium Activity Ratios in Plankton: New Evidence of Hold-Up Time in Irish Sea Sediments

The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, ²⁴¹Pu and ^239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the ²⁴¹Pu/^239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and ²⁴¹Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The ²⁴¹Pu/^239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea.     

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium in fast breeder reactors (FBRs) fuel reprocessing

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium is developed for the recovery of uranium and plutonium present in spent fuel of fast breeder reactors (FBRs). Effect of pH on the solubility of carbonates of uranium and plutonium in ammonium carbonate medium is studied. Effect of mole ratios of uranium and plutonium as a function of uranium and plutonium concentration at pH 8.0–8.5 for effective separation of uranium and plutonium to each other is studied. Feasibility of reconversion of plutonium in carbonate medium is also studied. The studies indicate that uranium is selectively precipitated as AUC at pH 8.0–8.5 by adding ammonium carbonate solution leaving plutonium in the filtrate. Plutonium in the filtrate after acidified with concentrated nitric acid could also be precipitated as carbonate at pH 6.5–7.0 by adding ammonium carbonate solution. A flow sheet is proposed and evaluated for partitioning and reconversion of uranium and plutonium simultaneously in the FBR fuel reprocessing.     

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%.     

Strong association of fallout plutonium with humic and fulvic acid as compared to uranium and137Cs in Nishiyama soils from Nagasaki, Japan

To investigate the formation of mobile organic plutonium, we analyzed the plutonium contents of the fulvic (FA) and humic (HA) acids from the soil samples obtained at Nishiyama, Nagasaki, Japan. The percentages of the plutonium bound strongly to HA and to FA vs. the total plutonium in the soil were 5–10% and 1%, respectively, at the depth of 0–0.1 m, much higher values than those of¹³⁷Cs and uranium. After being weathered for 51 years under a temperate climate, the initial highfired oxides of fallout plutonium have become as chemically reactive plutonium from nuclear fuel reprocessing plants.     

Individual determination of uranium and plutonium in a single aliquot

Studies on the individual potentiometric determination of uranium and plutonium in a single aliquot have been initiated recently in our laboratory. It was required to adapt the reported procedures (for the precise determination of uranium and plutonium individually when present together in a sample) at various stages to make them suitable for the successive application of the procedures to the same aliquot. Two alternative schemes are proposed in the present work. In the first, plutonium is determined by HClO₄ oxidation followed by the determination of total uranium and plutonium by Zn(Hg) reduction. In the second, plutonium is determined by AgO oxidation following the determination of total uranium and plutonium by Zn(Hg) reduction. Amount of uranium is computed in both cases from the difference of two determinations. Precision for the assay of plutonium and uranium was found to be ±0.25% and ±0.35%, respectively, at milligram levels.     

Potentiometric titration of plutonium

In the potentiometric titration of plutonium(III), it has been customary to take the equivalence point as the inflection point on a plot of potential vs. volume of titrant.¹ That the stoichiometric end point corresponds to the inflection point does not seem to have been theoretically demonstrated, however. The purpose of this letter is to suggest that these points may not correspond in the potentiometric titration of plutonium(III). Mound Laboratory is operated by Monsanto Research Corporation for USERDA under contract No. EY-76-C-04-0053.     

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.     

Plutonium removal from nitric acid waste streams

Separations research at the Rocky Flats Plant /RFP/ has found ways to significantly improve plutonium secondary recovery from nitric acid waste streams generated by plutonium purifications operations. Capacity and break-through studies show anion exchange with Dowex 1×4 /50–100 mesh/ to be superior for secondary recovery of plutonium. Extraction chromatography with TOPO /tri-n-octylphosphine oxide/ on XAD-4 removes the final traces of plutonium, including hydrolytic polymer.     

The dynamic movement of plutonium in an underground nuclear test with implications for the contamination of groundwater

Summary The recent discovery of the migration of plutonium in groundwater away from underground nuclear tests at the Nevada Test Site has spawned considerable interest in the mechanisms by which plutonium may be released to the environment by a nuclear explosion. A suite of solid debris samples was collected during drilling through an expended test cavity and the overlying collapse chimney. Uranium and plutonium were analyzed for isotope ratios and concentrations using high precision magnetic sector inductively coupled mass spectrometry. The data unequivocally shows that plutonium may be dispersed throughout the cavity and chimney environment at the time of the detonation. The ²³⁹Pu/²⁴⁰Pu ratios are also fractionated relative to initial plutonium isotope ratio for the test device. Fractionation is the result of the volatilization of uranium and production of ²³⁹Pu by the reaction ²³⁸U(n,γ). We conclude that for the test under consideration plutonium was deposited outside of the confines of the cavity by dynamic processes in early-time and it is this plutonium that is most likely transferred to the groundwater regime.     

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.     

Studies in biological excretion of inhaled plutonium in the case of a few occupational workers in a fuel reprocessing plant

A power reactor fuel reprocessing plant is in operation at Tarapur. The various processes involved in the plant are: fuel rod cutting, dissolution in nitric acid, separation of plutonium, and handling of separated plutonium. The chemical form of plutonium could be nitrate, TBP complex, or oxide depending upon the nature of the process involved. Possible internal exposure to plant personnel occurs mainly by inhalation and occasionally through a contaminated wound. Occupational workers are regularly monitored for internal contamination by urinary excretion analysis as well as by in-vivo lung counting. This paper presents a follow up study of plutonium elimination in four inhalation exposure cases.     

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.     

Preparation, characterization and application of thorium oxalate for sorption of plutonium and americium from aqueous solution

Synthetic inorganic exchangers exhibit good thermal and radiation stability. Thorium oxalate precipitate shows potential for co-precipitation of plutonium and americium from oxalate supernatant generated during plutonium oxalate precipitation. In the present study, efforts were made to prepare thorium oxalate precipitate to be used for column operation. Distribution ratios were determined to optimize conditions for sorption of plutonium and americium on thorium oxalate from nitric acid + oxalic acid solutions with composition similar to that of oxalate supernatant. Column experiments were also performed to evaluate the sorption capacity of thorium oxalate for plutonium and americium from the same medium. The result showed that, thorium oxalate prepared in 1.75M HNO₃ at 70 °C is suitable for column operations. These studies showed that plutonium and americium could be simultaneously removed from aqueous solutions with composition similar to plutonium oxalate waste using glass column packed with thorium oxalate and these nuclides could be recovered by eluting with 3M HNO₃.     

Potentiometric determination of plutonium by sodium bismuthate oxidation

A potentiometric method for the determination of plutonium is described, in which the plutonium is quantitatively oxidized to plutonium(VI) with sodium bismuthate in nitric acid medium, the excess of oxidant is destroyed chemically and plutonium(VI) is reduced to plutonium(IV) with a measured excess of iron(II), the surplus of which is back-titrated with dichromate. For 3–5 mg of plutonium the error is less than 0.2%. For submilligram quantities of plutonium in presence of macro-amounts of uranium the error is below 2.0%.