Plutonium variables

Colvin, C. A. Quantitative Determination of Plutonium Oxidation States in Variable Nitric Acid Solutions for Control Laboratories—Spectrophotometric, U.S. AEC Report RL-SA-33, General Electric Co., Richland, WA, 1965. 

Plutonium in solution is a function of six variables. The first two of these variables may be selected almost at pleasure. If plutonium oxidation number N and acidity are selected, the... 

Since iron can serve as a model for the behaviour of plutonium it is worth considering the behaviour of iron in the environment. Iron in oceanic water has been shown to exist principally as a non-filterable (0.45 q) form (162). This non-filterable form, in the case of the Atlantic Ocean waters, represented an average concentration of 0.2 jug/1 (163). Similar concentrations have been reported for the Pacific Ocean (164). In coastal waters the iron concentration is very variable (165). 

In the present paper the chemistry of plutonium is reviewed, with particular reference to the ambient conditions likely to be encountered in natural waters. In addition, experimental work is presented concerning the effects of such variables as pH, plutonium concentration, ionic strength, and the presence of complexing agents on the particle size distributions of aqueous plutonium. In subsequent papers it will be shown that these variables, as they influence the particle size distribution of the aqueous plutonium, greatly affect its interaction with mineral surfaces. The orientation of these studies is the understanding of the likely behavior and fate of plutonium in environmental waters, particularly as related to its interaction with suspended and bottom sediments. 

Variables found to be significant for sorption of cesium, strontium, technetium, selenium, neptunium, plutonium, americium, and radium on sandstone and tuff at 23°C are given in Table VII. They are ranked in order of significance where more than one variable was found to be significant. The ( + ) and (-) signs indicate whether sorption is increased or decreased. 

At Rocky Flats, the metal composition is held essentially constant because the americium content (200 to 2000 ppm) and the amount of magnesium produced by Equations 2 and 3 are small and purified plutonium metal is the metal extraction product. Variables that can be manipulated and that influence the value of the distribution coefficient (Kd) are the salt composition and the temperature. 

In the molten salt extraction process, the variables that control the values of the americium and plutonium distribution coefficients are temperature, metal composition, salt composition, and total americium. To minimize the variables, the extractions are conducted at a fixed temperature of about 750°C. Slight changes of magnesium content in the metal have a negligible effect upon the value of the americium and plutonium distribution coefficients. The effect of americium concentration... 

The aqueous waste from the CA Column (CAW) contains virtually all of the americium present in the feed. Table I shows the typical composition of the CAW stream. The exact composition of the stream depends on the composition of the CAF which is highly variable in a plutonium scrap processing plant. The CAW stream is the feed to the americium recovery solvent extraction system. 

Intermolecular electron-transfer rates have been studied for uranocene and substituted derivatives of uranium, neptunium, and plutonium by examining the variable-temperature NMR spectra of mixtures of (CgH8)2An and [(C8Hg)2An]. In all cases, electron-transfer rates are rapid. Specific rates could not be derived for uranium and plutonium derivatives owing to the small chemical shift differences between analogous An(fV) and An(III) compounds, but in the case of (f-BuC8H7)2Np, the rate has been estimated to be of the same order of magnitude as comparable lanthanide cyclooctatetraene compounds ( 10 s ). ... 

The refractory component comprises the elements with the highest condensation temperatures. There are two groups of refractory elements the refractory lithophile elements (RLEs)—aluminum, calcium, titanium, beryllium, scandium, vanadium, strontium, yttrium, zirconium, niobium, barium, REE, hafnium, tantalum, thorium, uranium, plutonium—and the refractory siderophile elements (RSEs)—molybdenum, ruthenium, rhodium, tungsten, rhenium, iridium, platinum, osmium. The refractory component accounts for —5% of the total condensible matter. Variations in refractory element abundances of bulk meteorites reflect the incorporation of variable fractions of a refractory aluminum, calcium-rich component. Ratios among refractory lithophile elements are constant in all types of chondritic meteorites, at least to within —5%. 

Clinical management can potentially reduce the effects of plutonium intake, although the effectiveness can be highly variable. Administration of the calcium salt of diethylenetriaminepentaacetic acid (DTPA) can accelerate removal of soluble forms of plutonium from body fluids and recent deposits. It is unable to remove intracellular deposits or activity buried in bone and must therefore be administered as soon as possible after an intake. In a review of 18 patients exposed to plutonium, americium, or curium, the US Food and Drug Administration concluded that administration of 1 g Ca-DTPA in 5 ml sterile aqueous solution, either by intravenous injection or as a nebulized inhalation dose, increased the rate of radioactivity elimination in urine by an average of 39-fold. Daily maintenance doses of Zn-DTPA resulted in continued elimination of radioactivity. 

These investigations, as well as others over the past three decades at Rocky Flats and at other sites, indicate that there are a number of individual variables that affect the physical and chemical characteristics of plutonium peroxide. The work in this area that is available in the unclassified literature has been summarized by Cleveland (10). A review of the literature indicates a lack of any planned investigative program that encompasses all of the variables. This type of investigation is important, especially from a production process viewpoint, for it would verify the relative importance of the individual variables, as well as any significant interactions between them. 

Based on experience at Rocky Flats and information from the literature, six of the variables deemed most important in the precipitation of plutonium peroxide were selected for investigation. These six, and the ranges over which they were investigated, are identified in Table I. 

VARIABLES AND LEVELS USED IN INVESTIGATING THE PRECIPITATION OF PLUTONIUM PEROXIDE... 

Filtration rate and the plutonium concentration in the filtrate were the dependent variables measured in the experiment. These were selected because they are the process variables that most directly measure the efficiency of the production precipitation process and are therefore a direct measure of operating efficiency of the process. 

The data obtained from the experiments were used to develop an equation that relates either the relative filtration time or the plutonium concentration in the filtrate to the six variables selected for investigation. The equation, which is given in Table II in abbreviated form, considers the main effects of the six variables (Xj, X2,...Xg) as well as all possible first order or two-factor interactions (X]X2 XjXj.XjXg). 

The objective of this investigation was to identify those variables that have an effect on the precipitation of plutonium peroxide, rank these variables in order of their effect, and then select levels for each of the variables that will give an optimum precipitation of plutonium peroxide. 

The identification of those variables that have a major effect on plutonium peroxide precipitation was done in two ways. The first way used t-test values associated with each variable. The comparative magnitude of these values indicates the relative importance of the variable. The second way involved a subjective evaluation of the relative importance of each of the variables based on a visual comparison of the graphs constructed from the experimental data (Figures 1 through 12 plus a couple of dozen other comparable graphs that could not be included in this paper because of space limitations). The results of the subjective evaluation indicate that only the nitric acid concentration and the rate of hydrogen peroxide addition have a major effect on the relative filtration time. The other four variables influence the... 

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