scholarly journals Comparison and Modeling of Aqueous Dissolution Rates of Various Uranium Oxides

1996 ◽  
Vol 465 ◽  
Author(s):  
S. A. Steward ◽  
E. T. Mones
Keyword(s):  
Dissolution Rate ◽  
Atmospheric Oxygen ◽  
Fold Increase ◽  
Stable Phase ◽  
Uranium Oxides ◽  
Spent Fuel ◽  
Geologic Repository ◽  
Dissolution Rates ◽  
Intrinsic Dissolution ◽  
Carbonate Concentration

ABSTRACTThe purpose of this work has been to measure and model the intrinsic dissolution rates of uranium oxides under a variety of well-controlled conditions that are relevant to a geologic repository. When exposed to air at elevated temperature, spent fuel may form the stable phase U3O8. Dehydrated schoepite, UO3H2O, has been shown to exist in drip tests on spent fuel.Equivalent sets of U3O8 and UO3H2 dissolution experiments allowed a systematic examination of the effects of temperature (25–75°C), pH (8–10) and carbonate (2–200×10−4 molar) concentrations at atmospheric oxygen conditions.Results indicate that UO3H2O has a much higher dissolution rate (at least ten-fold) than U3O8 under the same conditions. The intrinsic dissolution rate of unirradiated U3O8 is about twice that of UO2. Dissolution of both U3O8 and UO3.H2O shows a very high sensitivity to carbonate concentration. Present results show a 25 to 50-fold increase in room-temperature UO3H2O dissolution rates between the highest and lowest carbonate concentrations.As with the UO2 dissolution data the classical observed chemical kinetic rate law was used to model the U3O8 dissolution rate data. The pH did not have much effect on the models, in agreement with the earlier analysis of the UO2 and spent fuel dissolution data,. However, carbonate concentration, not temperature, had the strongest effect on the U3O8 dissolution rate. The U3O8 dissolution activation energy was about 6000 cal/mol, compared with 7300 and 8000 cal/mol for spent fuel and UO2 respectively.

Uranium (iv) Dioxide and Simfuel as Chemical Analogues of Nuclear Spent Fuel Matrix Dissolution. A Comparison of Dissolution Results in a Standard Naci/NaHCO3 Solution

1994 ◽  
Vol 353 ◽  
Author(s):  
Jordi Bruno ◽  
I. Casas ◽  
E. Cera ◽  
J. de Pablo ◽  
J. GimÉnez ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Dissolution Process ◽  
Experimental Comparison ◽  
Comparison Study ◽  
Spent Fuel ◽  
Dissolution Rates ◽  
Surface Sites ◽  
Radiolytic Oxidation

AbstractWe have carried out an experimental comparison study of the dissolution rates of unirradiated UO2 and SIMFUEL pellets and particles (100–300 μm) in a standard NaCI/NaHC03 solution, under oxidizing conditions. We have performed the experiments using batch and flow methodologies. Both methodologies gave similar results, indicating that the overall oxidation/dissolution process is the same in both cases. The results from the experiments indicate that under these conditions the dissolution process is both oxygen and bicarbonate promoted. The dissolution rates we obtained are: R=2.4 ± 0.8 mg U/m2 d for U02 and R= 0.17 ± 0.05 mg U/m2 d for SIMFUEL. The results of the experiments indicate that the dissolution rate under oxic conditions is clearly dependent on the number of U(VI) surface sites which for spent nuclear fuel is a function of the extent of radiolytic oxidation.

The effects of alpha-radiolysis on UO2 dissolution determined from electrochemical experiments with 238Pu-doped UO2

2002 ◽  
Vol 90 (9-11) ◽  
Author(s):  
S. Stroes-Gascoyne ◽  
F. King ◽  
J. S. Betteridge ◽  
F. Garisto
Keyword(s):  
Dose Rate ◽  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Spent Fuel ◽  
Geologic Repository ◽  
Dissolution Rates ◽  
Term Stability ◽  
Long Term Stability ◽  
Alpha Radiolysis

SummaryThe long-term stability of spent nuclear fuel under deep geologic repository conditions will be determined mostly by the influence of α-radiolysis, since the dose-rate for α-radiolysis will exceed that for γ/β-radiolysis beyond a fuel age of ∼100 years and will persist for more than 10000 years. Dissolution rates derived from studies with currently available spent fuel include radiolysis effects from γ/β- as well as α-radiolysis. The use of external α-sources and chemically added H

scholarly journals Microfluidic measurement of the dissolution rate of gypsum in water using the reactive infiltration-instability

2019 ◽  
Vol 98 ◽  
pp. 04010
Author(s):  
Florian Osselin ◽  
Pawel Kondratiuk ◽  
Olgierd Cybulski ◽  
Piotr Garstecki ◽  
Piotr Szymczak
Keyword(s):  
Dissolution Rate ◽  
Flow Rate ◽  
Relative Magnitude ◽  
Original Method ◽  
Inlet Channel ◽  
Dissolution Rates ◽  
Intrinsic Dissolution ◽  
Reactive Infiltration ◽  
Advection Diffusion ◽  
Wide Range

We present an original method for measuring the intrinsic dissolution rate of gypsum. We use a simple microfluidic setup, with a gypsum block inserted between two polycarbonate plates, which is dissolved by water. By changing the flow rate and the distance between the plates, we can scan a wide range of Péclet and Damköhler numbers, characterizing the relative magnitude of advection, diffusion and reaction in the system. We find the dissolution to be unstable, with a formation of a characteristic fingering pattern. The dissolution rate can then be calculated from the initial wavelength of this pattern. Alternatively, it can also be estimated from the time it takes for the gypsum chip to get completely dissolved near the inlet channel. The method presented here is general and can be used to assess the dissolution rates of other minerals.

scholarly journals Effects of Air Oxidation on the Dissolution Rate of LWR Spent Fuel

1992 ◽  
Vol 294 ◽  
Author(s):  
W. J. Gray ◽  
L. E. Thomas ◽  
R. E. Einziger
Keyword(s):  
Dissolution Rate ◽  
Surface Area ◽  
Solubility Limit ◽  
Oxidation States ◽  
Dissolution Mechanism ◽  
Coarse Particles ◽  
Spent Fuel ◽  
Air Oxidation ◽  
Geologic Repository ◽  
Practical Implications

ABSTRACTDissolution rates for air-oxidized spent fuel were measured in flowthrough tests where U concentrations were kept well below the solubility limit. Results from two types of specimens, separated grains and coarse particles, both in oxidized (U4O9+x) and unoxidized (UO2) conditions indicated only minor effects of oxidation on the surface-area-normalized rates. Similar results were obtained for unirradiated specimens in three different oxidation states (UO2, U3O7, and U3O8). These observations have important practical implications for disposal of spent fuel in a geologic repository as well as implications regarding the oxidative dissolution mechanism of UO2fuel.

The reductive dissolution of synthetic goethite and hematite in dithionite

Clay Minerals ◽  
1987 ◽  
Vol 22 (3) ◽  
pp. 329-337 ◽  
Author(s):  
J. Torrent ◽  
U. Schwertmann ◽  
V. Barron
Keyword(s):  
Specific Surface ◽  
Dissolution Rate ◽  
Surface Area ◽  
Reductive Dissolution ◽  
Natural Environments ◽  
Dissolution Rates ◽  
Aluminium Substitution ◽  
Initial Dissolution Rate

AbstractThe reductive dissolution by Na-dithionite of 28 synthetic goethites and 26 hematites having widely different crystal morphologies, specific surfaces and aluminium substitution levels has been investigated. For both minerals the initial dissolution rate per unit of surface area decreased with aluminium substitution. At similar aluminium substitution and specific surface, goethites and hematites showed similar dissolution rates. These results suggest that preferential, reductive dissolution of hematite in some natural environments, such as soils or sediments, might be due to the generally lower aluminium substitution of this mineral compared to goethite.

Solubilities and intrinsic dissolution rates of sulphamethoxazole and trimethoprim

1987 ◽  
Vol 39 (4) ◽  
pp. 246-251 ◽  
Author(s):  
Rajudin Dahlan ◽  
Charles Mcdonald ◽  
V. Bruce Sunderland
Keyword(s):  
Dissolution Rates ◽  
Intrinsic Dissolution
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