Mechanistic Effects of Deuteration on the Aqueous Corrosion of Nuclear Waste Glasses

1990 ◽  
Vol 212 ◽  
Author(s):  
X. Feng ◽  
L. Fu ◽  
T. K. Choudhury ◽  
I. L. Pegg ◽  
P. B. Macedo
Keyword(s):  
Isotope Effect ◽  
Nuclear Waste ◽  
Deuterium Oxide ◽  
Aqueous Media ◽  
Extensive Study ◽  
Dissolution Mechanism ◽  
Deuterated Water ◽  
Aqueous Corrosion ◽  
Rate Determining Step ◽  
Data Yield

ABSTRACTIsotopically labeled water has been utilized by several researchers to help elucidate the glass dissolution mechanism in aqueous media. However, most of the results have been obtained with simple silicate glasses and have utilized low surface-to-volume (S/V) ratios and relatively short time scales. In this paper we report the results of an extensive study of the leach behavior of the preliminary West Valley nuclear waste glass composition, WV205, in deuterium oxide using multiple S/V ratios at both short and long times. The WV205 glass was leached in parallel in both ordinary deionized water and in deuterated water at five S/V ratios (20, 100, 200, 2000 and 6000 m−1) at 90°C under PCT (the SRL-modified MCC3 procedure) conditions with sampling at 1, 3, 7, 28, 56, 120 days, and four times annually thereafter; the tests will continue for several years. Initial rates were determined by measurements at shorter times with polished monoliths. A significant isotope effect, as measured by the ratio of leach rates, RH20/RD20, was found at all S/V ratios and reached values as large as 360%. Our data yield different values for RH20/RD20 in the diffusion, matrix dissolution, and saturation dominated regimes with the largest effect in the middle stage. Large values of RH20/RD20 would be characteristic of a primary kinetic isotope effect suggestive of a bond breakage involving hydrogen in the rate determining step.

scholarly journals l-mandelate dehydrogenase from Rhodotorula graminis: comparisons with the l-lactate dehydrogenase (flavocytochrome b2) from Saccharomyces cerevisiae

1993 ◽  
Vol 290 (1) ◽  
pp. 103-107 ◽  
Author(s):  
O Smékal ◽  
M Yasin ◽  
C A Fewson ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Lactate Dehydrogenase ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Dimensional Structure ◽  
Striking Difference ◽  
Kinetic Properties ◽  
Proton Abstraction ◽  
Rate Determining Step ◽  
Kinetic Isotope

L-Lactate dehydrogenase (L-LDH) from Saccharomyces cerevisiae and L-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis are both flavocytochromes b2. The kinetic properties of these enzymes have been compared using steady-state kinetic methods. The most striking difference between the two enzymes is found by comparing their substrate specificities. L-LDH and L-MDH have mutually exclusive primary substrates, i.e. the substrate for one enzyme is a potent competitive inhibitor for the other. Molecular-modelling studies on the known three-dimensional structure of S. cerevisiae L-LDH suggest that this enzyme is unable to catalyse the oxidation of L-mandelate because productive binding is impeded by steric interference, particularly between the side chain of Leu-230 and the phenyl ring of mandelate. Another major difference between L-LDH and L-MDH lies in the rate-determining step. For S. cerevisiae L-LDH, the major rate-determining step is proton abstraction at C-2 of lactate, as previously shown by the 2H kinetic-isotope effect. However, in R. graminis L-MDH the kinetic-isotope effect seen with DL-[2-2H]mandelate is only 1.1 +/- 0.1, clearly showing that proton abstraction at C-2 of mandelate is not rate-limiting. The fact that the rate-determining step is different indicates that the transition states in each of these enzymes must also be different.

Efficient oxidation of ethers with pyridine N-oxide catalyzed by ruthenium porphyrins

2015 ◽  
Vol 19 (01-03) ◽  
pp. 411-416 ◽  
Author(s):  
Nobuki Kato ◽  
Yu Hamaguchi ◽  
Naoki Umezawa ◽  
Tsunehiko Higuchi
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Hydrogen Abstraction ◽  
Oxide System ◽  
Cyclic Ethers ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Oxidized Products

We found that oxidation of cyclic ethers with the Ru porphyrin-heteroaromatic N-oxide system gave lactones or/and ring-opened oxidized products with regioselectivity. A relatively high kinetic isotope effect was observed in the ether oxidation, suggesting that the rate-determining step is the first hydrogen abstraction.

scholarly journals Direct oxygen isotope effect identifies the rate-determining step of electrocatalytic OER at an oxidic surface

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Sandra Haschke ◽  
Michael Mader ◽  
Stefanie Schlicht ◽  
André M. Roberts ◽  
Alfredo M. Angeles-Boza ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effect ◽  
Rate Determining Step

scholarly journals Copper nanoparticle ensembles for selective electroreduction of CO2 to C2–C3 products

2017 ◽  
Vol 114 (40) ◽  
pp. 10560-10565 ◽  
Author(s):  
Dohyung Kim ◽  
Christopher S. Kley ◽  
Yifan Li ◽  
Peidong Yang
Keyword(s):  
Aqueous Media ◽  
Direct Conversion ◽  
Catalytic Performance ◽  
Product Formation ◽  
Stable Operation ◽  
Grand Challenge ◽  
Hydrogen Electrode ◽  
Faradaic Efficiency ◽  
Onset Potential ◽  
Rate Determining Step

Direct conversion of carbon dioxide to multicarbon products remains as a grand challenge in electrochemical CO2 reduction. Various forms of oxidized copper have been demonstrated as electrocatalysts that still require large overpotentials. Here, we show that an ensemble of Cu nanoparticles (NPs) enables selective formation of C2–C3 products at low overpotentials. Densely packed Cu NP ensembles underwent structural transformation during electrolysis into electrocatalytically active cube-like particles intermixed with smaller nanoparticles. Ethylene, ethanol, and n-propanol are the major C2–C3 products with onset potential at −0.53 V (vs. reversible hydrogen electrode, RHE) and C2–C3 faradaic efficiency (FE) reaching 50% at only −0.75 V. Thus, the catalyst exhibits selective generation of C2–C3 hydrocarbons and oxygenates at considerably lowered overpotentials in neutral pH aqueous media. In addition, this approach suggests new opportunities in realizing multicarbon product formation from CO2, where the majority of efforts has been to use oxidized copper-based materials. Robust catalytic performance is demonstrated by 10 h of stable operation with C2–C3 current density 10 mA/cm2 (at −0.75 V), rendering it attractive for solar-to-fuel applications. Tafel analysis suggests reductive CO coupling as a rate determining step for C2 products, while n-propanol (C3) production seems to have a discrete pathway.

Sintered Glasses for High-Level Wastes

1996 ◽  
Vol 465 ◽  
Author(s):  
D. O. Russo ◽  
N. B. Messi de Bernasconi ◽  
M. E. Sterba ◽  
A. D. Heredia ◽  
M. Sanfilippo ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Aqueous Media ◽  
Underground Water ◽  
Aqueous Corrosion ◽  
Γ Radiation ◽  
Sintered Glass ◽  
A Value ◽  
Aqueous Corrosion Resistance ◽  
High Level

ABSTRACTThe objective of the work was to evaluate the long-term capacity of sintered glass to retain high-level nuclear wastes (HLW) in near-repository conditions. We have studied the corrosion behavior of waste forms partially devitrified (43 vol.%) in different aqueous media. Devitrified samples were irradiated at doses (γ radiation from a Co 60 source) ranging from 1.4 × 106 Gy to 2.0 × 108 Gy, in order to study their aqueous corrosion resistance in simulated underground water. The results show little or no effect of irradiation on the density, microstructure and corrosion resistance. The global dissolution rate was almost constant around a value of 5×10−5 g. cm−2 d−1. Elemental dissolution rates were also unaffected by radiation.

Dissolution of organic solvents from painted surfaces into water

2000 ◽  
Vol 78 (4) ◽  
pp. 464-473 ◽  
Author(s):  
J C Wren ◽  
D J Jobe ◽  
G G Sanipelli ◽  
J M Ball
Keyword(s):  
Organic Compounds ◽  
Organic Solvents ◽  
Nuclear Reactor ◽  
Dissolution Kinetics ◽  
Activation Energies ◽  
Dissolution Mechanism ◽  
Rate Determining Step ◽  
Organic Impurities ◽  
Accident Conditions ◽  
Reactor Accidents

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents.

The hydrogen isotope effect in the bromination of 2-carbethoxy cyclo pentanone

1956 ◽  
Vol 235 (1203) ◽  
pp. 453-468 ◽  
Keyword(s):  
Isotope Effect ◽  
Hydrogen Isotope ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Activation Energies ◽  
Tunnel Effect ◽  
Fluoride Ion ◽  
Energy Barriers ◽  
Hydrogen Isotope Effect ◽  
Kinetics Of

Measurements are reported on the kinetics of the base-catalyzed bromination of 2-car-bethoxycyclopentanone, with either hydrogen or deuterium in the active position. The solvent throughout was deuterium oxide, the catalysts employed were the solvent, monochloroacetate ion and fluoride ion, and measurements were made at 5° intervals over the range 10 to 70°C. The observed activation energies are all greater for the deutero- than for the proto-ester, but the differences are greater than would be expected on current theories of isotope effects. The observed collision factors are in every case greater for deuterium than for hydrogen, especially for catalysis by fluoride ion, where the ratio of these factors is A D / A H = 24 ± 4. These observations can only be accounted for by invoking the tunnel effect, i. e. by supposing that the motion of the proton is markedly non-classical in nature. It is shown that this hypothesis leads to reasonable dimensions for the energy barriers involved, and some if its general consequences are discussed.

Methodologies for Predicting the Performance of Ni-Cr-Mo Alloys Proposed for High Level Nuclear Waste Containers

1999 ◽  
Vol 556 ◽  
Author(s):  
D. S. Dunn ◽  
G. A. Cragnolino ◽  
N. Sridhar
Keyword(s):  
Nuclear Waste ◽  
Current Density ◽  
Localized Corrosion ◽  
Passive Current Density ◽  
Aqueous Corrosion ◽  
Wide Range ◽  
Anionic Species ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Passive Current

AbstractFor the geologic disposal of the high level nuclear waste (HLW), aqueous corrosion is considered to be the most important factor in the long-term performance of containers, which are the main components of the engineered barrier subsystem. Container life, in turn, is important to the overall performance of the repository system. The proposed container designs and materials have evolved to include multiple barriers and highly corrosion resistant Ni-Cr-Mo alloys, such as Alloys 625 and C-22. Calculations of container life require knowledge of the initiation time and growth rate of localized corrosion. In the absence of localized corrosion, the rate of general or uniform dissolution, given by the passive current density of these materials, is needed. The onset of localized corrosion may be predicted by using the repassivation and corrosion potentials of the candidate container materials in the range of expected repository environments. In initial corrosion tests, chloride was identified as the most detrimental anionic species to the performance of Ni-Cr-Mo alloys. Repassivation potential measurements for Alloys 825, 625, and C-22, conducted over a wide range of chloride concentrations and temperatures, are reported. In addition, steady state passive current density, which will determine the container lifetime in the absence of localized corrosion, was measured for Alloy C-22 under various environmental conditions.

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