Bruce J. Mincher

Tributylphosphate extraction behavior of bismuthate-oxidized americium.

Higher oxidation states of americium have long been known; however, options for their preparation in acidic solution are limited. The conventional choice, silver-catalyzed peroxydisulfate, is not useful at nitric acid concentrations above about 0.3 M. We investigated the use of sodium bismuthate as an oxidant for Am (3+) in acidic solution. Room-temperature oxidation produced AmO 2 (2+) quantitatively, whereas oxidation at 80 degrees C produced AmO 2 (+) quantitatively. The efficacy of the method for the production of oxidized americium was verified by fluoride precipitation and by spectroscopic absorbance measurements. We performed absorbance measurements using a conventional 1 cm cell for high americium concentrations and a 100 cm liquid waveguide capillary cell for low americium concentrations. Extinction coefficients for the absorbance of Am (3+) at 503 nm, AmO 2 (+) at 514 nm, and AmO 2 (2+) at 666 nm in 0.1 M nitric acid are reported. We also performed solvent extraction experiments with the hexavalent americium using the common actinide extraction ligand tributyl phosphate (TBP) for comparison to the other hexavalent actinides. Contact with 30% tributyl phosphate in dodecane reduced americium; it was nevertheless extracted using short contact times. The TBP extraction of AmO 2 (2+) over a range of nitric acid concentrations is shown for the first time and was found to be analogous to that of uranyl, neptunyl, and plutonyl ions.

A Pulse Radiolysis Investigation of the Reactions of Tributyl Phosphate with the Radical Products of Aqueous Nitric Acid Irradiation

Tributyl phosphate (TBP) is the most common organic compound used in liquid-liquid separations for the recovery of uranium, neptunium, and plutonium from acidic nuclear fuel dissolutions. The goal of these processes is to extract the actinides while leaving fission products in the acidic, aqueous phase. However, the radiolytic degradation of TBP has been shown to reduce separation factors of the actinides from fission products and to impede the back-extraction of the actinides during stripping. As most previous investigations of the radiation chemistry of TBP have focused on steady state radiolysis and stable product identification, with dibutylphosphoric acid (HDBP) invariably being the major product, here we have determined room temperature rate constants for the reactions of TBP and HDBP with the hydroxyl radical [(5.00 +/- 0.05) x 10(9), (4.40 +/- 0.13) x 10(9) M(-1) s(-1)], hydrogen atom [(1.8 +/-0.2) x 10(8), (1.1 +/- 0.1) x 10(8) M(-1) s(-1)], nitrate radical [(4.3 +/- 0.7) x 10(6), (2.9 +/- 0.2) x 10(6) M(-1) s(-1)], and nitrite radical (<2 x 10 (5), <2 x 10(5) M(-1) s(-1)), respectively. These data are used to discuss the mechanism of TBP radical-induced degradation.

.gamma.-Ray Destruction of Individual PCB Congeners in Neutral 2-propanol

The radiolytic degradation of 25 PCB congeners from nine homologs was investigated in neutral aerated 2-propanol using spent nuclear fuel as the [gamma]-ray source. Radiolytic degradation is conveniently described in terms of a pseudo-first-order rate constant expressed in terms of dose, rather than time, and referred to as a dose constant. Dose constants obtained were found to be dependent on both the number and the positions of the chlorines. A general increase in the dose constant was observed with increasing chlorine number. Chlorine substitution in the para and meta position increases the dose constant while substitution in the ortho position decreases it. Dose constant trends follow the energy level of the lowest unoccupied molecular orbital. Previously unreported degradation products consisting of 2-propanol-substituted polychlorinated biphenyls are characterized. Mass balance information is incomplete for some congeners. Based upon experiments using a [sup 14]C-labeled tetrachlorobiphenyl, degradation products are in nonvolatile or semivolatile constituents. 26 refs., 7 figs., 3 tabs.

Supercritical Fluid Extraction of Plutonium and Americium from Soil using Thenoyltrifluoroacetone and Tributylphosphate Complexation

Samples of clean soil from the source used to backfill pits at the Idaho National Engineering and Environmental Laboratory´s Radioactive Waste Management Complex were spiked with 239Pu and 241Am to evaluate ligand-assisted supercritical fluid extraction as a decontamination method. The actual soil in the pits has been subject to approximately three decades of weathering since it was originally contaminated. No surrogate soil can perfectly simulate the real event, but actual contaminated soil was not available for research purposes. However, fractionation of Am and Pu in the surrogate soil was found to be similar to that previously measured in the real soil using a sequential aqueous extraction procedure. This suggests that Pu and Am behavior are similar in the two soils. The surrogate was subjected to supercritical carbon dioxide extraction, in the presence of the fluorinated beta diketone thenoyltrifluoroacetone (TTA), and tributylphosphate (TBP). As much as 69% of the Pu and 88% of the Am were removed from the soil using 3.2 mol.% TTA and 2.7 mol.% TBP, in a single 45 minute extraction. Extraction conditions employing a 5 mol.% ethanol modifier with 0.33 mol.% TTA and 0.27 mol.% TBP resulted in 66% Pu and 68% Am extracted. To our knowledge, this is the first report of the use of supercritical fluid extraction (SFE) for the removal of actinides from soil.

Increasing PCB Radiolysis Rates in Transformer Oil

Abstract The kinetics of Aroclor 1242 radiolysis in transformer oil, using high-energy electrons, was found to be analogous to that previously measured for individual polychlorinated biphenyl (PCB) congeners irradiated with γ -rays. The plot of the pseudo-first-order rate constant for PCB decomposition versus initial PCB concentration is a power function, with high rate constants for low concentrations. The addition of alkaline isopropanol to transformer oil was found to increase the pseudo-first-order rate constant for PCB decomposition. The rate constant under these conditions is independent of concentration. This may be explained by the establishment of chain reaction dechlorination in the oil.

Radiation chemical effects on radiochemistry: A review of examples important to nuclear power

Abstract Radiochemistry deals with the chemistry of the radioactive elements. In the nuclear industry successful fuel reprocessing, high-level waste treatment, and long-term storage of spent fuel depend on an understanding of the radiochemistry of actinides and fission products in these settings. Radiation chemistry is concerned with the chemical effects of ionizing radiation, with the most common types of radiation encountered by the radiochemist being low linear energy transfer (LET) β- and γ radiation, and higher LET α radiation. These radiations can have profound and important effects on radiochemistry, including changes in metal oxidation states and degradation of the organic ligands designed to complex radioelements. This may occur by direct action of the incident radiation on compounds present with high abundance or by reaction with radiolytically produced reactive species for trace components, such as the complexing agents. This review examines the role of reactive species created in irradiated aqueous and organic solution and their effects on radiochemistry. The sources and nature of these reactive species are discussed. Examples of radiation chemical effects are provided related to solvent extraction of the actinides from acidic solution, metal complexation and technetium redox chemistry in alkaline tank waste, and the corrosion of spent fuel stored in repository brine.

Determination of arrhenius and thermodynamic parameters for the aqueous reaction of the hydroxyl radical with lactic acid.

Lactic acid is a major component of the TALSPEAK process planned for use in the separation of trivalent lanthanide and actinide elements. This acid acts both as a buffer and to protect the actinide complexant from radiolytic damage. However, there is little kinetic information on the reaction of water radiolysis species with lactic acid, particularly under the anticipated process conditions of aerated aqueous solution at pH approximately 3, where oxidizing reactions are expected to dominate. Here we have determined temperature-dependent reaction rate constants for the reactions of the hydroxyl radical with lactic acid and the lactate ion. For lactic acid this rate constant is given by the following equation: ln k(1) = (23.85 +/- 0.19) - (1120 +/- 54)/T, corresponding to an activation energy of 9.31 +/- 0.45 kJ mol(-1) and a room temperature reaction rate constant of (5.24 +/- 0.35) x 10(8) M(-1) s(-1) (24.0 degrees C). For the lactate ion, the temperature-dependent rate constant is given by ln k(2) = (24.83 +/- 0.14) - (1295 +/- 42)/T, for an activation energy of 10.76 +/- 0.35 kJ mol(-1) and a room temperature value of (7.77 +/- 0.50) x 10(8) M(-1) s(-1) (22.2 degrees C). These kinetic data have been combined with autotitration measurements to determine the temperature-dependent behavior of the lactic acid pK(a) value, allowing thermodynamic parameters for the acid dissociation to be calculated as DeltaH(o) = -10.75 +/- 1.77 kJ mol(-1), DeltaS(o) = -103.9 +/- 6.0 J K(-1) mol(-1) and DeltaG(o) = 20.24 +/- 2.52 kJ mol(-1) at low ionic strength.

Neptunium and plutonium sorption to Snake River Plain, Idaho soil

Summary The behavior of Np and Pu on soil collected from the subsurface disposal area at the Idaho National Engineering and Environmental Laboratory was investigated by performing short-duration, sorption experiments to measure sorption isotherms. Neptunium sorption can be described with a Freundlich isotherm; however, Pu sorption can only be described in this fashion as a conservative estimate of minimum sorption. Geochemical modeling predictions suggest that initial sorption of Np is controlled predominantly by surface complexation on clay minerals, while Pu is controlled by a competition between complexation with iron oxyhydroxides and the precipitation of hydrolysis products. Longer-term sorption is governed by the transformation of these species to oxide minerals. Solution ionic strength and carbonate alkalinity did not significantly affect Np or Pu soil sorption.

Studies in Radiation Chemistry: Application to Ozonation and Other Advanced Oxidation Processes

Advanced oxidation/reduction processes (AORPs) are an alternative water treatment that is becoming more widely utilized. Our radiation-chemistry based studies are being used to develop a fundamental understanding of AOP treatment options, and are divided into three complementary types of contaminants; disinfection by-products (DBPs), emerging pollutants of concern (EPoCs), and natural organic matter (NOM). More than 600 DBPs have been identified, and one class that appears to have severe potential adverse health effects is the halonitromethanes (HNMs). Of the nine HNMs, trichloronitromethane (chloropicrin) is the most common, with levels up to 180 nM in US drinking waters. EPoCs are of interest because of their biological activity at low concentrations in water and while the initial focus was on endocrine disruptor chemicals (EDCs) this class has now been expanded to include many other recalcitrant chemicals such as hormones, antibiotics, industrial contaminants, and health care products. Natural organic matter is one of the most common radical scavengers in natural waters and therefore may adversely affect AOPs. Our approach is to study NOM both directly and using model compounds thought to be representative of structural components of this complex material.

The redox chemistry of neptunium in γ-irradiated aqueous nitric acid

Abstract The redox chemistry of neptunium in irradiated 4 M nitric acid was investigated using γ-ray irradiation and UV/Vis spectroscopic measurements. Irradiation caused changes in the abundances of Np(V) and Np(VI) regardless of the initial fractional components of these oxidation states. At low absorbed doses Np(V) was oxidized to Np(VI) in irradiated solution, due to its reaction with oxidizing, radiolytically-produced, free radicals. However, when sufficient radiolytically-produced nitrous acid accumulated, the reduction of Np(VI) to Np(V) occurred, even at this high nitric acid concentration. Neptunium(IV) was not produced. A kinetic model which incorporates the standard water radiolysis reactions, estimated radical yields for 4 M HNO3, and rate constants for neptunium reactions available from the literature was used to successfully reproduce the experimental results.