Plutonium Oxidation Research Articles

Identification of oxidation state of plutonium in the snow layers, High Tatras, Czechoslovakia

Snow layers in lasting snow fields in High Tatras are effectively isolated from each other by ice crust. Every layer has a specific amount of fallout particles, pH, concentration of dissolved ions. Plutonium oxidation state (VI), from the adsorption behaviour of the isotopes of U, Th, Ra, Sr and Mn in six independent layers was elucidated. Behaviour of plutonium was similar to that of226Ra and90Sr. Isotopes of Th showed quite different dependence in snow layers. Concentration of Th and Mn in snow has similar extreme, which imply higher oxidation state of Mn than Mn(II). Behaviour of uranium may be explained by a mixture of U(VI) and U(IV) oxidation states because of their dependence in successive snow layers is a superposition of the same dependences of226Ra (or90Sr) and thorium isotopes.

Ni/III/—A new oxidant for the potentiometric determination of plutonium

Ni/III/ has been employed as an oxidant for the quantitative oxidation of plutonium to its hexavalent state and this makes possible to determine plutonium concentrations potentiometrically by the Fe/II/-dichromate redox titration method. The unreacted oxidant is completely reduced by sulphamic acid prior to the determination of plutonium.

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.

Plutonium oxidation state distributions in the Pacific Ocean during 1980–1981

The concentration of plutonium and its oxidation state distribution have been measured as a function of depth at three locations in the North Pacific Ocean. Concentration profiles were similar to those observed in the same area during 1974 with primary maxima at depths of a few hundred meters below the surface and secondary maxima near the bottom. Oxidation state distribution profiles were similar at the three locations with plutonium about equally divided between the reduced and oxidized forms except near the bottom. There the oxidized form was more abundant and comprised ∼ 90% of the total plutonium. No major change in oxidation state occurred at the depths of the shallow concentration maxima suggesting that their formation and persistence were not dependent upon a redox change. The concentration maxima near the bottom coincided with the enhanced abundance of the poorly sorbed oxidized form suggesting that they resulted from the loss of oxidized plutonium from the sediments.

Synthesis and characterization of crystalline phosphates of plutonium(III) and plutonium(IV)

The formation of both PuPO 4 and PuP 2O 7 from reactions of PuO 2 with (NH 4) 2HPO 4 or BPO 4 was studied by X-ray diffraction and Raman spectroscopy. The oxidation of plutonium(III), in PuPO 4, to plutonium(IV), in PuP 2O 7, by air in the presence of BPO 4 and the thermal reduction of PuP 2O 7 to PuPO 4 were demonstrated. In addition plutonium(III) trimetaphosphate Pu(PO 3) 3 was synthesized and characterized. Attempts to prepare plutonium(IV) orthophosphate, Pu 3(PO 4) 4, by high temperature reactions were unsuccessful; instead, mixtures of PuP 2O 7 and a new phase identified tentatively as “(PuO) 2P 2O 7” were obtained.

Amperometric determination of plutonium using KMnO4 as oxidant

An amperometric method has been developed for the determination of plutonium using KMnO4 as oxidant. Conditions have been established for the quantitative oxidation of plutonium to its hexavalent state and the reduction of the excess oxidant by ferrous perchlorate without affecting the Pu(VI). Both processes have been accomplished in perchloric acid medium. The plutonium(VI) has subsequently been determined by indirect titration with standard dichromate in H2SO4 medium after adding a known excess of Fe(II). The method gives an accuracy and precision within ±0.2% for 2–5mg amounts of plutonium. Uranium does not interfere with the method upto 28 times the amount of plutonium present in the aliquot.

Elevated Concentrations of Actinides in Mono Lake

Tetravalent thorium, pentavalent protactinium, hexavalent uranium, and plutonium (oxidation state uncertain) are present in much higher concentrations in Mono Lake, a saline, alkaline lake in eastern central California, than in seawater. Low ratios of actinium to protactinium and of americium to plutonium indicate that the concentrations of trivalent actinides are not similarly enhanced. The elevated concentrations of the ordinarily very insoluble actinides are maintained in solution by natural ligands, which inhibit their chemical removal from the water column, rather than by an unusually large rate of supply.

AUTOSEP, an automated system for the quantitative ion exchange separation of plutonium from impurities

The anion exchange separation of interfering impurities from plutonium in the Dowex-1 8 N HNO3 system is a reliable purification method. An automated system, AUTOSEP, based on this manual procedure has been developed for greater productivity. Samples, in groups of ten, each containing 5–10 mg of plutonium are processed automatically in this system. AUTOSEP incorporates a means of programming reagent delivery, adjustment of the sample to the plutonium (IV) oxidation state via Fe(II) reduction/HNO3 oxidation, plutonium sorption on the resin in 8 N HNO3, washing of the resin bed with 8 N HNO3 to remove impurities, elution of the purified plutonium with 0.36 N HCl–0.01 N HF, and waste effluent disposal. The reagents are delivered by gravity from a module whose only moving parts are rotary valves. The eluted plutonium solutions are collected for subsequent controlled-potential coulometric analysis. The average recovery of plutonium determined by controlled-potential coulometry using this apparatus was 100.00% with a relative standard deviation of 0.10%.

AES and XPS study of plutonium oxidation

The initial oxidation of plutonium metal at 27°C has been studied using AES and XPS. Initially a ’’clean’’ plutonium surface was prepared by prolonged Ar+ bombardment followed by 500°C anneal and Ar+ bombardment cleaning cycles. Changes occurring in the plutonium Auger electron spectra in the energy range of 40–120 eV and the 4f5/2, 4f7/2 (core levels), and valence band XPS peaks were monitored during oxygen exposures of 10 to 1.8×108L. Examination of the 4f7/2 level revealed two oxidation states which are attributed to a suboxide an PuO2. The 4f7/2 binding energies for the two oxidation states and plutonium metal are 426.1, 424.4, and 422.2 eV, respectively. It was observed that oxidation proceeded in two steps. In the first step there was a rapid reaction of oxygen with the formation of a suboxide. In the second stage, the uptake of oxygen leveled off with conversion of the suboxide to PuO2.

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.

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

Determination of plutonium by secondary coulometry involving the controlled potential technique for the generation of an iron(II) mediator, is reported in Part I.* In this paper, the same determination is reported using constant current coulometry for the generation of the mediator, and zero current potentiometry for end-point detection. The factors affecting the current efficiency, viz. current density and supporting electrolyte composition have been checked in order to define the appropriate conditions for obtaining 100% current efficiency. The original method of Carson et al. suffers from the disadvantage that it involves complicated sample treatment. Introduction of perchloric acid treatment as a method for the oxidation of plutonium and the pretitration of the supporting electrolyte to the end-point potential prior to sample addition, have considerably helped improve the precision and accuracy of the method. Exhaustive analytical data are reported covering plutonium quantities ranging from 25 micrograms to 5 milligrams, which establishes the scope of the method.

Geochemistry and physics of plutonium migration

Similarities in the distribution pattern of the worldwide Pu-239 fallout and in the filtered industrial release of the same nuclide were demonstrated. This analogy led to the assumption that predictions concerning the subsequent fate of the minute quantities of the HEPA-filtered plutonium released by industrial operations may be drawn by studying the environmental transfer of the worldwide fallout plutonium. The history of Pu-239, 240 concentration in the ground-level air and its deposition known from previous investigations for the vicinity of Heidelberg was brought up to date by new values. After subtracting the wet deposition from the total amount of deposition found in the soil a dry deposition velocity for PuO 2-particles of 0.05 cm/s was obtained under the meteorological conditions of the area studied. Differences were found in the residence time of the worldwide fallout in the troposphera and in the filtered airborne PuO 2 discharge in the ground-level air. Nevertheless, the analogous distribution patterns of the PuO 2 particles and the natural aerosols suggest that in the case of dry deposition velocity, the results obtained can be applied for PuO 2 stack discharge too. The decrease of PuO 2 contamination in the biologically active top soil was estimated by computer simulation. The Pu-239, 240 fallout deposition was used as the input function and the measured Pu-239, 240 depth distribution as the result of the combination of irregular input and continous dissipation. The downward migration found out of a 2-cm-thick layer of Rhine valley loess loam was proceeding at a rate of approximately 50% contamination per 3.5 years. By comparing this migration with the movement of an HTO-tracer a water-transport response as small as 10 −3 was estimated. Unlike the stable PuO 2, hydrolytic changes can be expected for Pu(NO 3) 4 upon contact with an aqueous environment after release. The equilibrium concentration of all valence states of plutonium was calculated for the whole range of natural waters. The sum of all potentially dissolved plutonium oxidation states may reach up to 1 mol/l under extreme but naturally occurring outdoor conditions.

ChemInform Abstract: THE HIGH TEMPERATURE OXIDATION OF PLUTONIUM‐3.3 A O GALLIUM

AbstractDie Oxidationskinetik der Titellegierung in Luft wird im Temperaturbereich 250‐400°C mit einer Mikrowaage untersucht.

Plutonium valence state distributions

A method for ascertaining equilibrium valence state distributions of plutonium in acid solutions as a function of the plutonium oxidation number and the solution acidity is illustrated with an example. The method may be more practical for manual use than methods based upon polynomial equations.

On the Oxidation of Plutonium (III) by Hydrogen Peroxide–Probable Formation of an Unstable Plutonium (III) Peroxy Complex

Article On the Oxidation of Plutonium (III) by Hydrogen Peroxide–Probable Formation of an Unstable Plutonium (III) Peroxy Complex was published on April 1, 1973 in the journal Radiochimica Acta (volume 19, issue 4).

Radiation-induced oxidation of plutonium( III) in sulphuric acid solutions

The effect of gamma radiation on 10 −3 mol dm −3 Pu( III) solutions in 0·4 mol dm −3 H 2SO 4 was studied both in the presence and in the absence of air. The radiolytic yields of Pu( IV), H 2O 2 and H 2 were measured at different doses and the initial yields were found to be as follows: in the presence of air, G[ Pu( IV )] = 6·6±0·6 , G(H 2O 2) = 4·0±0·4 in the absence of air, G[ Pu( IV )] = 5·5±0·3 , G(H 2O 2) = 0·8±0·1, G(H 2O 2) = 3·6±0·3. The results were to show that Pu( III) is oxidized by OH radicals to Pu( IV) both in the presence and absence of air. H atoms in the presence of air (through HO 2 radicals) oxidize Pu( III) giving rise to Pu( IV) and H 2O 2, while only a part of H atoms appear to oxidize Pu( III) in the absence of oxygen. Irradiations of 10 −3 mol dm −3 Pu( III) solutions in mixtures of sulphuric and hydrochloric acids (total acidity 0·8 equiv. dm −3 were also carried out in the presence of air and the radiolytic yields of Pu( IV) and H 2O 2 were found to be practically the same as those obtained in the absence of chloride ions.

Problems in plutonium chemistry: Temperature stability of Pu(V) and the quadruple point

The concept of representing plutonium in aqueous solutions as distributed among four oxidation states is used to suggest a decreased extent of disproportionation of pentavalent plutonium with increasing temperature over a narrow temperature range. This concept is also used to suggest that the proper selection of sequestering agents, solution acidity and plutonium oxidation number may result in equal concentrations of the four plutonium oxidation states.

Plutonium Oxidation in Moist Oxygen‐Nitrogen Mixtures

Plutonium oxidation studies were conducted at 90°C in dry air and moist oxygen‐nitrogen mixtures using both cast and rolled plutonium. Oxidation in dry air obeyed a linear rate law with average rate constants of 0.042 and 0.050 mg/cm2hr for the cast and rolled plutonium, respectively. Both metal samples were found to oxidize faster in the moist oxygen mixtures than in moist nitrogen. Linear oxidation rates were observed in moist oxygen‐nitrogen mixtures with average rate constants of 0.68 and 0.34 mg/cm2hr for the cast and rolled plutonium. In moist nitrogen oxidation followed a parabolic rate law with average rate constants of 3.60 and 1.11 mg/cm2hr1/2 for the cast and rolled samples, respectively. The reaction with water vapor observed during this investigation was greatly influenced by the purity of the metal as well as its metallurgical history. Samples of cast, electrorefined plutonium containing some microcracks reacted very rapidly, while for the relatively impure rolled material the reaction was somewhat slower. In all cases at this temperature, the reaction with water vapor was diffusion controlled and not reaction controlled as has been reported previously. The diffusing species is believed to be ions formed by the dissociative adsorption of water on plutonium dioxide.

Retardation of Plutonium Oxidation by a PuO Surface Film

An anomalous rate minimum exists at about 400 °C for the oxidation of plutonium, i.e., there is a decrease in the oxidation rate as the temperature is increased toward the rate minimum. In situ X-ray diffraction studies have shown that in the temperature region of the rate minimum, there is an increased rate in the formation of PuO. The influence of a PuO surface film on the oxidation of plutonium was investigated with an ellipsometer to determine if a PuO film affects the oxidation rate. Measurements showed that the PuO surface film does retard oxidation at 80 °C. It is further postulated that the anomalous rate minimum for plutonium oxidation near 400 °C results from the increased rate of formation of the protective PuO surface film.

Catalytic effect of iron on oxidation of plutonium by hydrogen peroxide.

Catalytic effect of iron on oxidation of plutonium by hydrogen peroxide.