Comparison of the Dissolution Behaviour of Various UO2Samples in Saline Solution at 100°C Under Reducing Conditions

1993 ◽  
Vol 333 ◽  
Author(s):  
S. Stroes-Gascoyne ◽  
J.C. Tait ◽  
R.J. Porth ◽  
J.L. McConnell ◽  
A.M. Duclos
Keyword(s):  
Saline Solution ◽  
Radiation Characteristic ◽  
Combined Effects ◽  
Used Nuclear Fuel ◽  
Reducing Conditions ◽  
Dissolution Behaviour ◽  
Gamma Radiolysis ◽  
Leaching Experiments ◽  
Leaching Behaviour ◽  
High Burnup

ABSTRACTThe separate effects of alpha- and gamma-radiolysis on UO2dissolution can be studied with unirradiated UO2, whereas studies vith used nuclear fuel necessarily always include both alpha- and gamma-radiolysis effects. This paper attempts to separate these effects by comparing the leaching behaviour in saline solution of a number of UO2samples (each vith a particular radiation characteristic or chemical property inherent to used fuel) vith the leaching behaviour of used fuel. Data from leaching experiments vith lov- and high-burnup CANDU (CANada Deuterium Uranium) fuels are also compared. The results indicate that the presence of an alpha field at 100°C under reducing conditions does not increase UO2dissolution but suggest that the combined effects of the beta and gamma fields in used CANDU fuel may enhance UO2dissolution.

Excystment of the Metacercariae of Echinoparyphium serratum (Trematoda: Echinostomatidae)

1970 ◽  
Vol 44 (1) ◽  
pp. 35-56 ◽  
Author(s):  
M. J. Howell
Keyword(s):  
Elevated Temperature ◽  
Cyst Wall ◽  
Sodium Dithionite ◽  
Sodium Cholate ◽  
Stage I ◽  
Combined Effects ◽  
Active Process ◽  
Reducing Conditions ◽  
Exogenous Enzymes ◽  
Pretreatment Solution

1. Metacercarial cysts of Echinoparyphium serratum occur in the pericardium of the snail Isidorella brazieri. Each cyst is surrounded by a nucleated, syncytial host capsule containing granules which are presumed to be melanin. The cyst wall consists of two layers and both contain acid and neutral mucopolysaccharide but little or no protein. No modification of the cyst wall coincident with the point of emergence of the metacercaria has been located.2. Excystment of the metacercaria takes place in two main stages when pepsin is omitted from the initial pretreatment solution: stage I (emergence from the cyst wall through the escape aperture) is an active process (exogenous enzymes are not necessary), and a high percentage of specimens reaching this stage is dependent on the combined effects of a þH of 2, reducing conditions, elevated temperature (37–39°C) and sodium cholate. Temperature and sodium cholate are absolute requirements for this stage as is pretreatment of between þH 2 and 4 when sodium cholate is included with the reductant (sodium dithionite) rather than in the excystment medium with trypsin. The possibility that CO2 is involved has not been established.

Patterned Copper Sulfide Thin Films: a Method for Studying Leaching Behaviour

2017 ◽  
Vol 70 (1) ◽  
pp. 26
Author(s):  
Rachel S. Brokenshire ◽  
Anthony Somers ◽  
Miao Chen ◽  
Angel A. J. Torriero
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Copper Extraction ◽  
Redox Potentials ◽  
X Ray ◽  
Copper Dissolution ◽  
Copper Leaching ◽  
Dissolution Behaviour ◽  
Leaching Behaviour ◽  
Resultant Film

An experimental study on copper leaching from Cu1.85S thin films is presented, wherein copper extraction is quantitatively evaluated by changes in film thickness measured by white light interferometric profilometry. Changes in the film morphology and elemental composition, as assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, are used to confirm that the loss in film thickness is due to changes in the copper content and that the resultant film species is consistent with the mechanism of copper dissolution. The Cu1.85S thin films were synthesized by chemical bath deposition. The leaching behaviour of copper from the films was investigated in acidic ferric sulfate media at pHs 1, 2, and 3, and pH 1 at redox potentials of ~350–650 mV versus Ag/AgCl in 3 M KCl. The changes in the film thickness and copper sulfur ratio were shown to reflect copper dissolution behaviour from chalcocite. Leaching of the Cu1.85S films demonstrated a greater decrease in film thickness as pH decreased. In addition comparison of the order of reaction as a function of proton concentration in non-oxidative dissolution of Cu1.85S (0.06) and as a function of iron(iii) concentration in ferric oxidation of Cu1.85S (0.40) shows that the proton dissolution reaction is negligible. Leaching of the Cu1.85S films at redox potentials of up to ~476.4 mV versus Ag/AgCl in 3 M KCl produced covellite and demonstrated greater decreases in film thickness with increases in the redox potential. Leaching of the films above ~476.4 mV resulted in the formation of spionkopite and demonstrated a much lesser decrease in film thickness. These results are consistent with Eh-pH diagrams for the Cu–S–H2O system.

The Dissolution of Irradiated Fuel Under Hydrothermal Conditions

1981 ◽  
Vol 6 ◽  
Author(s):  
Lawrence H. Johnson ◽  
Henry H. Joling
Keyword(s):  
Experimental Studies ◽  
Fission Products ◽  
Redox Chemistry ◽  
Hydrothermal Conditions ◽  
Product Release ◽  
Reducing Conditions ◽  
Dissolution Behaviour ◽  
Low Ionic Strength ◽  
Kinetics Of ◽  
Irradiated Fuel

ABSTRACTUranium dioxide, the major component of irradiated CANDU fuel, shows good hydrothermal stability under the appropriate redox conditions. The thermodynamic stability of UO2 in low ionic strength granite groundwater at 150°C under oxidizing and reducing conditions is briefly reviewed in order to provide a basis for discussion of the results of irradiated fuel dissolution experiments. Fuel chemistry characteristics that influence the kinetics of fission product release are also discussed.Experimental studies demonstrate the influence of redox chemistry on irradiated fuel dissolution behaviour. Undero9 trongly reducing conditions, both uranium and 99Tc concentrations in solution decrease to the detection limit, whereas appreciable concentrations of both elements accumulate under oxidizing conditions. The release of some fission products, such as 90Sr and 137Cs, does not seem to be strongly affected by changes in redox chemistry. Under oxidizing conditions, the rate of 90Sr release to solution increases by a factor of ten to twenty between 25 and 150°C.These studies indicate the need for further work in certain areas, in particular on the relative amounts of important fission productsreleased by leaching versus matrix dissolution, and on the effect of the products of α–radiolysis of water on the dissolution of irradiated fuel.

Study of the Leaching Behaviour of Sintered UO2 in Groundwater Using Nuclear Microprobe Techniques

1994 ◽  
Vol 353 ◽  
Author(s):  
Patrick Trocellier ◽  
Jean Paul Gallien ◽  
Christelle Cachoir ◽  
Pierre Toulhoat
Keyword(s):  
Redox Potential ◽  
Partial Pressure ◽  
Nuclear Microprobe ◽  
Controlled Conditions ◽  
Reducing Conditions ◽  
Synthetic Groundwater ◽  
Leaching Behaviour ◽  
Solubility Control

AbstractThe leaching behaviour of sintered UO2 pellets has been studied in synthetic groundwater at 96 °C under strictly controlled conditions (CO2 partial pressure, O2 partial pressure, pH and redox potential). Results obtained in oxidizing conditions (O2 content varying from 5 to 25 ppm) show a strong initial uranium release in solution during the first five days and a solubility control essentially driven by the growth of U(VI) species such as oxides, hydrates and carbonates. Results obtained in reducing conditions (use of a mineralogical buffer of Ni(0)/Ni(ll) with E0 = -0.257 Volts) show a very weak uranium release in solution close to 10-11 mole/l and a solubility control essentially driven by the formation of U(IV) compounds such as coffinite or uraninite.

Leaching Studies of Non-Metallic Materials for Nuclear Fuel Immobilization Containers

1984 ◽  
Vol 44 ◽  
Author(s):  
M. Onofrei ◽  
D. K. Raine ◽  
L. Brown ◽  
F. Stanchell
Keyword(s):  
Nuclear Fuel ◽  
Ceramic Surface ◽  
Weight Losses ◽  
Concentration Of Ions ◽  
Ceramic Components ◽  
Leaching Experiments ◽  
Leaching Behaviour ◽  
Static Conditions ◽  
Nuclear Fuel Waste

AbstractThe leaching behaviour of various ceramics was studied as part of a program to evaluate their potential use as container material for very long term containment of nuclear fuel waste under conditions of deep geologic disposal.Samples of four grades of Al2O3, stabilized ZrO2, TiO2, a cermet (70% A12O3- 30% TiC) and porcelain have been leached in deionized distilled water, Standard Canadian Shield Saline Solution (SCSSS), and SCSSS plus 20% Na-bentonite under static conditions at 100°C for periods up to 120 d.The results of these ongoing leaching experiments suggest that the controlling features of the ceramic leaching process were leachant composition, and the presence and concentration of ions in the solution capable of preferentially precipitating on the ceramic surface, i.e., silicon, Mg2+, Ca2+, etc. Weight losses were determined after leaching. The initial leach rates showed a dependence upon ceramic purity and the processing used to prepare the ceramics, as well as the leachant composition. Also, it was apparent that the decrease of leach rates with time occurred as a result of the ceramic components in the leachant approaching their saturation limits.

Powder Leaching Study for Grain Boundary Inventory of Two High Burnup Fuels

MRS Advances ◽  
2019 ◽  
Vol 4 (17-18) ◽  
pp. 981-986
Author(s):  
Alexandre Barreiro Fidalgo ◽  
Olivia Roth ◽  
Anders Puranen ◽  
Lena Z. Evins ◽  
Kastriot Spahiu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Spent Fuel ◽  
Short Period ◽  
Fission Gas ◽  
Leaching Solution ◽  
Significant Release ◽  
Leaching Experiments ◽  
High Burnup ◽  
Fission Gas Release

ABSTRACTIn the context of safety assessment, the fraction of inventory that is expected to rapidly dissolve when water contacts the spent fuel is called the Instant Release Fraction (IRF). Conceptually, this fraction consists of radionuclides outside of the uranium dioxide matrix and therefore the fraction can be further divided into the radionuclides in the fuel/cladding gap and radionuclides in the grain boundaries. The relative importance of these two fractions is investigated here for two Swedish high burnup fuels through simultaneous grinding and leaching fuel fragments in simplified groundwater for a short period of time. The hypothesis is that this will expose grain boundaries to leaching solution and provide an estimate of the release of the grain boundary inventory upon contact with water. The studied fragments were used in previous leaching experiments and thus pre-washed to remove any pre-oxidized phases. The results showed a significant release of iodine, cesium and rubidium and to a lower extent molybdenum and technetium. The fraction of inventory in the aqueous phase of actinides and lanthanides was 1-2 orders of magnitude lower than for the elements associated to the IRF. Both fuels displayed a very similar behavior and no correlation as a function of burnup or fission gas release was found.

Predicted Behavior of Technetium in a Geological Disposal Vault For Used Nuclear Fuel - Ramifications of a Recent Determination of the Enthalpy of Formation of TcO2(cr)

1995 ◽  
Vol 412 ◽  
Author(s):  
R. J. Lemire ◽  
D. J. Jobe
Keyword(s):  
Nuclear Fuel ◽  
Management Program ◽  
Heat Of Solution ◽  
Used Nuclear Fuel ◽  
A Value ◽  
Reducing Conditions ◽  
Congruent Dissolution ◽  
Nuclear Fuel Waste ◽  
The Enthalpy Of Formation

AbstractRecently, we reported a value of ΔH°(TcO2(cr)) = -(458 ± 6) kJ·mol-1based on heat of solution measurements. The implications of this value on the database used in the Canadian Nuclear Fuel Waste Management Program for the evaluation of the technetium released by congruent dissolution of used UO2 fuel have now been assessed.It is probable that the Tc(IV) oxides are more stable than previously predicted and, hence, they are less likely to be oxidized to TcO4(aq) under moderately reducing conditions. We have revised earlier calculations done to predict the solution concentrations of technetium species in a vault as a function of the oxidation conditions in model groundwaters.

Modelling UO2 and Simfuel Leaching Behaviour in Granite Groundwater Under Oxidizing Conditions

1999 ◽  
Vol 556 ◽  
Author(s):  
J. Quiñones ◽  
J. Garcia Serrano ◽  
J. A. Serrano ◽  
P. Diaz Arocas ◽  
J. L. Rodriguez ◽  
...  
Keyword(s):  
Groundwater Flow ◽  
Source Term ◽  
Solid Phase ◽  
Model Predictions ◽  
Different Types ◽  
Leaching Experiments ◽  
Leaching Behaviour ◽  
Loss Term ◽  
State Concentration ◽  
Good Agreement

AbstractThe Uranium concentration leaching behaviour for UO2 and SIMFUEL in granite groundwater under oxidizing conditions is modelled. The model contemplates two terms: a source term and a loss term. The source term represents the bulk dissolution process and its upper limit is controlled by the solubility of the thermodynamically stable solid phase. The loss term emulates the solute removed due to groundwater flow into the repository. It can forecast the uranium steady state concentration when groundwater flow is considered. The model has been tested with three different types of leaching experiments, performed with UO2 and SIMFUEL. Good agreement between experimental results and model predictions are found.

Interactions Between Np-Doped Synroc and Boom Clay

1994 ◽  
Vol 353 ◽  
Author(s):  
K. P. Hart ◽  
B. J. Robinson ◽  
T. E. Payne ◽  
P. Van Iseghem ◽  
K. Lemmens
Keyword(s):  
Anaerobic Conditions ◽  
Boom Clay ◽  
Reducing Conditions ◽  
Mobile Fraction ◽  
Leaching Experiments

AbstractLeaching experiments with deionised water at 70°C have been carried out to ascertain the effect of oxidising and anaerobic conditions and the presence of Boom clay on Np release from Synroc.The normalised solution leach rates of Np measured in these experiments are about a factor of 10 lower under reducing conditions than oxidising conditions and the presence of Boom clay was found not to enhance the leaching of Np from Synroc. Neptunium was found to be predominantly in the mobile fraction and was not removed from the leaching solutions significantly by filtration or ultrafiltration.

Static Leaching of Fully Radioactive Waste Glass at 90°C in the Presence of Bentonite, Granite, and Stainless Steel Corrosion Products

1985 ◽  
Vol 50 ◽  
Author(s):  
Hans-Peter Hermansson ◽  
Inga-Kari Björner ◽  
Hilbert Christensen ◽  
Toshiaki Ohe ◽  
Lars Werme
Keyword(s):  
Stainless Steel ◽  
Radioactive Waste ◽  
Steel Corrosion ◽  
Corrosion Products ◽  
Leach Rate ◽  
Compacted Bentonite ◽  
Infrared Reflection ◽  
Leaching Experiments ◽  
Leaching Behaviour ◽  
Glass Leaching

AbstractThe results from the JSS phase II static glass leaching experiments are presented. The experiments have been performed in the presence of bentonite, granite and stainless steel corrosion products at 90°C for 28 days. The leaching behaviour of Cs has been analysed using gamma-spectrometry. The surface of the leached glass samples has been analysed by infrared reflection spectrometry.The presence of uncompacted bentonite seems to have a very small, increasing, effect on the leach rate of the glass compared to when no bentonite is present. In the presence of compacted bentonite, a lower leach rate has beep founy than in the prgsencelof uncompacted bentonite. (For Cs 0.3 g × m−2 × d−1 and 0.7 g × m−2 × d−1 respectively.) The addition of stainless steel corrosion products seems to have a slightly increasing effect on the leach rate in the presence of compacted bentonite. The beneficial effect of granite on the leach rate seems to be overshadowed by the presence of uncompacted bentonite.

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