Oxidation States Of Plutonium Research Articles

Environmental plutonium: Reference states and alpha coefficients

The results of plutonium oxidation state distribution calculations do not depend on special attention to any oxidation state as has been incorrectly supposed in some literature sources. Experimentally determined alpha coefficients for natural water could make the distribution of environmental plutonium easy to estimate with a programmable pocket calculator.

Distribution of Plutonium and its oxidation states in Framvaren and Hellvik fjords, Norway

Waters from the Skagerrak Sea entering the system of fjords inside Farsund in the southern tip of Norway (including Lyngsdal, Hellvik and Framvaren fjords) contain plutonium derived from European nuclear fuel reprocessing facilities in the United Kingdom and France, as shown by the 238Pu/ 239,240Pu activity ratios measured for water samples from Hellvik and Framvaren fjords. The shallow sills interconnecting this series of fjords, however, severely restrict water exchange. Thus, at the northernmost Framvaren fjord (connected to Hellvik fjord by a 500-m channel of 2 m depth), the 238Pu/ 239,240Pu signature for Pu derived from fuel reprocessing is found only in the surface layer (upper 20 m) while global fallout Pu ratios are observed in the permanently anoxic zone of this fjord. Plutonium oxidation state measurements in waters collected from Hellvikkand Framvaren fjords show that water exchange occurs between these two basins by a process of interleaving, with subsequent reduction of oxidized Pu species as these reach the anoxic zone. Plutonium serves as a useful tracer for water exchange between these fjords and the Skagerrak Sea.

Influence of manganese dioxide on the oxidation states of plutonium

When manganese dioxide impregnated filters have been used to concentrate plutonium from water solutions some anomalies were detected, which were ascribed to the probable existence of plutonium in two different oxidation states. The results of this paper seem to confirm this assumption that the Pu in the solution is a mixture of Pu(III) and Pu(IV). After contact with MnO2, plutonium in the solution consists of only Pu(IV).

Plutonium oxidation states in the southwestern Black Sea: Evidence regarding the origin of the cold intermediate layer

Water column profiles of reduced Pu (III + IV) and oxidized Pu (V + VI) species at two stations in the southwestern Black Sea reveal that oxidized Pu predominates even at the suboxic zone, between 50 and 100 m. Reduction of these oxidized species occurs at the base of the suboxic zone, where we noted a shift to the predominance of reduced Pu forms. At anoxic depths (below 150 m), we found only reduced Pu forms, at concentrations significantly less than the total Pu levels we found in the upper 150 m samples. Our data show that Pu oxidation states are useful in interpreting lateral advective processes that occur within the upper 150 m of the Black Sea water column. An additional interesting result of our measurements is that water at the cold intermediate layer (CIL) of the Black Sea is labeled with predominantly oxidized Pu. We believe this feature can be used to trace the origin of CIL water.

Plutonium distribution and oxidation states in a reactor leaching ponds system.

Concentrations of 239,240Pu and 238Pu in water, net plankton (algal material), suspended particulates and sediment, as well as Pu oxidation states in filtered water, were determined in a test reactor leaching ponds system in southeastern Idaho. The highest Pu concentration in the ponds system was found in net plankton, and concentrations varied significantly between sampling dates. Plutonium Concentration Ratios (CR) for plankton ranged from 3 X 10(4) to 4 X 10(5). The lowest Pu concentration was found in filtered water, primarily because of the absence of complexing agents. The majority of Pu in filtered water was in true solution (60-87%) or present in colloidal particles smaller than 0.22 micron. Plutonium association with sediment was inversely related to particle size. The "environmental" distribution coefficients (Kd) for Pu ranged from 1.6 X 10(4) to 1.2 X 10(5) reflecting the importance of sediments as the main reservoir for Pu in the ponds system. No significant differences were noted between CR or Kd values for 239,240Pu and 238Pu. The reduced Pu oxidation states (III and IV) fractions ranged from 57% to 71% of the total dissolved Pu in water. This is in contrast with oxidation states distribution from other large aquatic systems (Great Lakes and the Irish Sea) where Pu is predominately in oxidized (V and VI) forms.

Determination of aqueous plutonium oxidation states by solvent extraction

The reliability of two solvent extraction techniques for the determination of Pu oxidation states in solution was tested with low-ionic-strength solutions and with high-Na and high-Mg brines that contained Pu concentrations sufficient for spectrophotometric analysis. One procedure only differentiates between reduced Pu [Pu(III) and Pu(IV)] and oxidized Pu [Pu(V) and Pu(VI)], whereas the second procedure was designed to differentiate between Pu(IV), Pu(V), and Pu(VI) in solution. Both procedures successfully differentiated between oxidized and reduced Pu in both dilute solutions and brines when tested with samples that contained only the Pu(IV), Pu(V), or Pu(VI) oxidation states. However, when the second solvent extraction procedure, which differentiates between Pu(V) and Pu(VI), was employed for solutions that did not contain a strong oxidant to maintain the Pu(VI) oxidation state, significant quantities of Pu(VI) were reduced to Pu(V) during extraction, indicating that accurate quantification of Pu(V) and Pu(VI) is not possible with this procedure.

Determination of oxidation states of uranium and plutonium in cooling solution of spent fuel element assemblies from NPP A-1

The knowledge of oxidation states of uranium and plutonium is necessary from the point of view of the proposed vitrification technology for the final liquidation of the cooling solution as a high radioactive waste containing alpha activity. The valence states of uranium and plutonium have a major influence on the subsequent leaching rate of these elements from vitrification matrices. Using the various chemical behaviours of these elements, in accordance with their valence states, we made an attempt to establish their oxidation state in the original solution.

Oxidation states of plutonium in carbonate-rich natural waters

Adsorption of actinide elements to calcium carbonate in waters of moderate to high carbonate concentration has been shown to be dependent on the oxidation state. This property has been exploited for distinguishing the (III) and (IV) oxidation states of plutonium. Ambient plutonium in Mono Lake, California, a natural high-carbonate water, appeared to be entirely in the (IV) oxidation state. Tracer experiments in carbonate media and in Mono Lake water, in the presence of atmospheric oxygen, confirmed that Pu(III) is rapidly oxidized under these conditions.

Determination of plutonium oxidation states at trace levels pertinent to nuclear waste disposal

A scheme was developed for the determination of oxidation states of plutonium in environmental samples. The method involves a combination of solvent extractions and coprecipitation. It was tested on solutions with both high-level and trace-level concentrations. The scheme was used to determine Pu oxidation states in solutions from solubility experiments in groundwater from a potential nuclear waste disposal site. At steady-state conditions, Pu was found to be soluble predominantly as Pu(V) and Pu(VI).

Oxidation states of fallout plutonium in Mediterranean rain and seawater.

The measurements of the oxidation states of fallout plutonium in rain water collected at Monaco indicate that plutonium exists predominantly in the higher oxidation states (Pu (V) and Pu (VI)). The results obtained show that the percentage of the higher valency fraction of plutonium ranges from 38 to 89 % of the total soluble plutonium in rain. The percentage tends to be lower when the storage time before the chemical treatment becomes longer. A thermodynamical computation supports these findings. The occurrence of plutonium in the higher oxidation states in rain is considered to be one of the major causes of the characteristic geochemical stability of fallout plutonium observed in the Mediterranean Sea.

Separation of Plutonium Oxidation States by Ion Exchange Chromatography

Separation of Plutonium Oxidation States by Ion Exchange Chromatography

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.

An optical-fibre laser photometer for on-line measurements

An optical-fibre laser photometer is described for measuring on-line the concentration of the different oxidation states of uranium and plutonium. It is based on a dye laser with five exchangeable curvettes containing five different dyes. The dye laser is pumped by a nitrogen laser. To compensate for the influence of the concentration of nitrate on the absorbance of the different species, the conductivity of the solution is measured to give a correction factor. Fibre optics are used to connect the dye laser, the optical flow-through cell and the photometer. The deviation for the plutonium concentration for single-sample analysis is <1 g l −1 for concentrations up to 50 g l −1, and in the on-line mode is <0.14 g l −1 for the same concentration range. For uranium, the deviation is <3.07 g l −1 for a concentration range up to 77 g l −1 in the on-line mode.

A method for determining the oxidation state of uranium in natural waters

Uranium exhibits radically different geochemical properties in its two oxidation states. Hexavalent uranium is quite soluble, especially when complexed by carbonate ions in alkaline solutions. Tetravalent uranium, by contrast, is very insoluble, and it would be expected to be rapidly removed from natural waters either by precipitation of a mineral phase such as UO 2(s) or by adsorption to solid surfaces. It is important to know the oxidation state in which uranium will occur under specified conditions of Eh and pH as this relates both to processes forming economically valuable uranium deposits and to the mobility of uranium released to the environment during various stages of the nuclear fuel cycle. In this work, yield monitors in each oxidation state [ 232U(IV)], 236U(VI)] are added to water samples, and uranium oxidation states are separated by a NdF 3 coprecipitation in which only the U(IV) is carried. The precipitate is removed by filtration. Subsequently, TiCl 3 is added to reduce U(IV) and the NdF 3 coprecipitation is repeated. A similar method is widely used for separating oxidation states of plutonium. Results from a meromictic lake (Fayetteville Green Lake, Syracuse, New York, USA) and from an anoxic marine basin (Cariaco Trench, Venezuela) where total H 2S concentrations in the bottom waters reach 1 mM 1 −1 and 50 μM 1 −1 respectively show that in both cases the dissolved uranium is present in its oxidized form.

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.

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%.

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.

Oxidation state of plutonium in the Irish Sea

SEVERAL of the chemical parameters needed to understand the distribution and behaviour of plutonium in the aquatic environment have not been fully investigated in the field. We consider here two of the more fundamental of these parameters: (1) the oxidation state(s) of the plutonium present in seawater; and (2) the extent to which each oxidation state is associated with suspended particulate matter. A widely accepted analytical technique is adapted to separate the two oxidation states expected to show a high affinity for particulate matter, Pu(III) and Pu(IV), from the more soluble pair, Pu(V) and Pu(VI), and is applied to a series of seawater samples. It was found that in the area studied, generally >75% of the plutonium in solution, and <10% of the plutonium on particulate matter, was Pu(V + VI); consequently the distribution coefficients for Pu(III + IV) exceeded those for Pu(V + VI) by more than two orders of magnitude.

A rapid procedure for plutonium separation in large volumes of fresh and saline water by manganese dioxide coprecipitation

A rapid procedure is described for the separation of plutonium radionuclides from large volumes of fresh and saline water by means of a manganese dioxide coprecipitation technique. This procedure has been used in the laboratory and in the field to process 50 to 400 liter water samples. Plutonium is carried through an oxidation and reduction step to insure complete equilibration between added yield tracers and the plutonium present in the water sample. Average recovery under optimum conditions has been 80% for seawater and over 90% for freshwater samples processed in the field with simple equipment. The procedure can be used also to separate plutonium from water samples by direct adsorption on MnO2-impregnated cartridges. Under laboratory conditions the adsorption on MnO2 was independent of the oxidation states of plutonium in aqueous samples.