Reaction Kinetics for the High Temperature Oxidation of Pu--1wt%Ga in Water Vapor PDF Download

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Languages : en
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Oxidation of plutonium metal is greatly accelerated by the presence of water vapor. The magnitude of the effect of water vapor on oxidation kinetics is determined by temperature, water concentration, and oxygen concentration. Most of the previous work has been directed toward evaluating the effect of moisture on the atmospheric oxidation of plutonium. Work on the isolation and characterization of the water reaction with plutonium has been very limited. The present work was undertaken to determine the kinetics of the plutonium--water reaction over a wide range of temperature and pressure. Reaction kinetics were measured using a vacuum microbalance system. The temperature range investigated was 100--500/degree/C. The effect of water vapor pressure on reaction kinetics was determined at 300/degree/C by varying the water pressure from 0.1 to 15 Torr. 2 figs.

Author: Marsden Manson
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Languages : en
Pages : 26

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Languages : en
Pages : 5

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Results of microbalance, pressure-volume-temperature, and mass spectrometric measurements show that a higher oxide of plutonium, PuO{sub 2+x}, and hydrogen are formed by reaction of plutonium dioxide with water at 25 C to 350 C. PuO{sub 2+x} has an intense green color consistent with the presence of Pu(VI). An oxide composition in excess of PuO{sub 2.25} is identified, but the maximum value of x is undefined. Reaction rates derived from linear mass-time and pressure-time data are described by an Arrhenius relationship that yields an activation energy of 9.4 " 0.6 kcal/mol for the PuO2 + H2O reaction. X-ray diffraction data for PuO{sub 2+x} shows that the oxide has a fluorite-related structure consistent with substitution of Pu(VI) on cationic lattice sites and accommodation of additional oxygen on interstitial sites. The cubic lattice parameter has a low, but well-defined, linear dependence on the O:Pu ratio, suggesting that PuO{sub 2+x} forms as a continuous solid solution. The failure of earlier attempts to prepare higher oxides of plutonium is attributed to slow oxidation kinetics and insensitivity of diagnostic techniques. Similarities of the PuO{sub 2+x} and UO{sub 2+x} phase are examined and relevance of the results to plutonium technology and environmental issues is discussed.

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The oxidation of plutonium-1 wt % gallium in 500 torr of a mixture of 94.5% nitrogen/5.5% oxygen has been investigated over the temperature range of 150 to 500/sup 0/C. This atmosphere typifies the atmospheres in the Rocky Flats inert glovebox lines. Rates of oxidation were nearly identical to the rates measured in an air atmosphere. The mechanism for the oxidation were nearly identical to the rates measured in an air atmosphere. The mechanism for the oxidation process involved three stages. Stage 1 was the buildup of a dense oxide film with a rate of growth determined by the diffusion of oxygen through the plutonium dioxide layer. Stage 2 involved a linear rate process equivalent to the rate of diffusion through an oxide film with a constant thickness and also equivalent to the rate of crack and pore formation in the oxide. Stage 3 was a linear interface controlled reaction resulting from the cracking and spalling of the oxide layer.

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The kinetic and equilibrium behavior of the Pu + O + H system has been studied by measuring the production of hydrogen gas formed by a sequence of hydrolysis reactions. The kinetic dependence of the Pu + H2O reaction on salt concentration and temperature has been defined. The metal is quantitatively converted to a fine black powder which has been identified as plutonium monoxide monohydride, PuOH. Other hydrolysis products formed in aqueous media include a second oxide hydride, Pu--O9H3, and the oxides Pu2O3, Pu--O12, Pu9O16, Pu10O1, Pu12O22, and PuO2. Thermal decomposition products of PuOH include Pu2O2H and PuO. A tentative phase diagram for Pu + O + H is presented and structural relationships of the oxide hydrides and oxides are discussed. 10 figures, 5 tables.

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Languages : en
Pages : 22

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Chemistry and kinetics of air reactions with plutonium monoxide monohydride (PuOH) and with mixtures of the oxide hydride and plutonium metal are defined by results of pressure-volume-temperature (PVT) measurements. Test with specimens prepared by total and partial corrosion of plutonium in 0.05 M sodium chloride solution show that reaction of residual water continues to generate H2 after liquid water is removed by evacuation. Rapid exposure of PuOH to air at room temperature does not produce a detectable reaction, but similar exposure of a partially corroded metal sample containing Pu and PuOH results in hydride (PuH(subscript x))-catalyzed corrosion of the residual Pu. Kinetics of he first-order reaction resulting in formation of the PuH(subscript x) catalyst and of the indiscriminate reaction of N2 and O2 with plutonium metal are defined. The rate of the catalyzed Pu+air reaction is independent of temperature (E{sub a} = 0), varies as the square of air pressure, and equals 0.78 " 0.03 g Pu/cm2 min in air at one atmosphere. The absence of pyrophoric behavior for PuOH and differences in the reactivities of PuOH and PuOH + Pu mixtures are attributed to kinetic control by gaseous reaction products. Thermodynamic properties of the oxide hydride are estimated, particle size distributions of corrosion products are presented, and potential hazards associated with products formed by aqueous corrosion of plutonium are discussed.