Modelling Experimental Results on Radiolytic Processes at the Spent Fuel Water Interface. I. Radiolysis Products and U Release

2003 ◽  
Vol 807 ◽  
Author(s):  
J. Bruno ◽  
E. Cera ◽  
T. E. Eriksen ◽  
M. Grivé ◽  
S. Ripoll
Keyword(s):  
Aqueous Phase ◽  
Initial Increase ◽  
Water Interface ◽  
Spent Fuel ◽  
Constant Concentration ◽  
Radiolysis Products ◽  
Reducing Conditions ◽  
Anoxic Environment ◽  
Bicarbonate Solutions

ABSTRACTExperimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions.The collected data so far, indicate that production and fate of radiolysis products follow the same trends independently on the solution composition used in the tests. Hydrogen and oxygen concentrations show an initial increase with time until reaching a constant concentration. The trend observed for hydrogen peroxide is a decrease at short contact times to reach again a constant concentration with time. These steady-states indicate an overall balance of the generated radiolytic species.Modelling work indicates that uranium dissolution is controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase is governed by the precipitation of schoepite.These results are determinant to highlight that reducing conditions are restored in the aqueous phase in relatively short periods of time and at short distances away from the dynamic redox spent fuel/water interface.

Modelling experimental results on radiolytic processes at the spent fuel water interface. II. Radionuclides release

2006 ◽  
Vol 932 ◽  
Author(s):  
E. Cera ◽  
M. Grivé ◽  
J. Bruno ◽  
T.E. Eriksen
Keyword(s):  
Redox State ◽  
Kinetic Modelling ◽  
Initial Increase ◽  
Spent Fuel ◽  
Work Related ◽  
Radiolysis Products ◽  
The Matrix ◽  
Anoxic Environment ◽  
Bicarbonate Solutions

ABSTRACTExperimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems as well as the radionuclides release behaviour. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions.Some of the collected data has been previously published [1], specifically those data concerning radiolysis products and dissolution of the matrix. The results and the modelling tasks indicated an overall balance of the generated radiolytic species and that uranium dissolution was controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase was governed by the precipitation of schoepite.This paper is the continuation of a series accounting for the data and modelling work related to investigating the release behaviour of minor radionuclides from the spent fuel.Uranium concentrations as a function of time showed an initial increase until reaching a steady state, indicating a matrix dissolution control. The same behaviour is observed for neptunium, caesium, strontium, technetium and molybdenum indicating a congruent release of these elements with the major component of the fuel matrix. On the other hand, no cler tendency is observed for plutonium data where additional solubility limiting mechanisms may apply.Kinetic modelling of the trace elements: caesium, strontium, technetium and molybdenum is based on the congruent release of these elements with the major component of the fuel matrix. Rate constants have been determined. Kinetic modelling of neptunium data took also into account the subsequent precipitation as Np(IV) hydroxide. Finally, measured Pu concentrations may be explained by the precipitation of Pu(IV) and/or Pu(III) solid phases.

On the Role of H2 as an Inhibitor of UO2 Matrix Dissolution

2007 ◽  
Author(s):  
Juan Merino ◽  
Xavier Gaona ◽  
Lara Duro ◽  
Jordi Bruno ◽  
Aurora Marti´nez-Esparza
Keyword(s):  
Chemical Composition ◽  
Partial Pressure ◽  
Water Radiolysis ◽  
Water Interface ◽  
Spent Fuel ◽  
Dissolution Rates ◽  
Term Stability ◽  
Long Term Stability

The study of spent fuel behaviour under disposal conditions is usually based on conservative approaches assuming oxidising conditions produced by water radiolysis at the fuel/water interface. However, the presence of H2 from container corrosion can inhibit the dissolution of the UO2 matrix and enhance its long-term stability. Several studies have confirmed the decrease in dissolution rates when H2 is present in the system, although the exact mechanisms of interaction have not been fully established. This paper deals with a radiolytic modelling exercise to explore the consequences of the interaction of H2 with radicals generated by radiolysis in the homogeneous phase. The main conclusion is that in all the modelled cases the presence of H2 in the system leads to a decrease in matrix dissolution. The extent of the inhibition, and the threshold partial pressure for the inhibition to take place, both depend in a complex way on the chemical composition of the water and the type of radiation present in the system.

Measurement of Dissolution Rates of UO2 Matrix with the Isotope Dilution Method

2003 ◽  
Vol 807 ◽  
Author(s):  
K. Ollila ◽  
V. Oversby
Keyword(s):  
Aqueous Phase ◽  
Isotope Dilution ◽  
Isotope Dilution Method ◽  
Dilution Method ◽  
Spent Fuel ◽  
Fuel Pellets ◽  
Reducing Conditions ◽  
Low Concentrations ◽  
Synthetic Groundwater ◽  
Solid Phases

ABSTRACTThe objective of this work was to measure the actual rates of matrix dissolution of UO2 in synthetic groundwater by using an isotope dilution method to provide a quantitative estimate of precipitation effects. A preliminary series of tests was performed under oxidising conditions, in contact with air. The second series of tests was under reducing conditions produced by actively corroding iron. The solid phases were fragments of unirradiated fuel pellets and intact pellets. The aqueous phase was a dilute, synthetic groundwater - so-called modified Allard water that is buffered by sodium bicarbonate/carbonate. This paper gives results for the experiments under oxidising conditions and preliminary tests under reducing conditions. In contact with air, the U concentrations reached higher levels than measured in previous experiments with spent fuel or with UO2 pellets. The comparison of the U concentrations calculated from isotopicratios with the experimental results suggests precipitation has begun at later stages of restarted tests. The measurements in the presence of actively corroding iron gave very low concentrations in the aqueous phase. At contact times longer than one week, all U seemed to disappear from solution and sorb or precipitate on UO2 or Fe surfaces in the test vessel.

Liquid-liquid extraction of succinate using a dicopper cryptate

2020 ◽  
Author(s):  
Riccardo Mobili ◽  
Sonia La Cognata ◽  
Francesca Merlo ◽  
Andrea Speltini ◽  
Massimo Boiocchi ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Visible Spectrum ◽  
Tca Cycle ◽  
Residual Concentration ◽  
Waste Products ◽  
Liquid Liquid Extraction ◽  
The Tca Cycle ◽  
Quantitative Extraction ◽  
Uv Visible

<div> <p>The extraction of the succinate dianion from a neutral aqueous solution into dichloromethane is obtained using a lipophilic cage-like dicopper(II) complex as the extractant. The quantitative extraction exploits the high affinity of the succinate anion for the cavity of the azacryptate. The anion is effectively transferred from the aqueous phase, buffered at pH 7 with HEPES, into dichloromethane. A 1:1 extractant:anion adduct is obtained. Extraction can be easily monitored by following changes in the UV-visible spectrum of the dicopper complex in dichloromethane, and by measuring the residual concentration of succinate in the aqueous phase by HPLC−UV. Considering i) the relevance of polycarboxylates in biochemistry, as e.g. normal intermediates of the TCA cycle, ii) the relevance of dicarboxylates in the environmental field, as e.g. waste products of industrial processes, and iii) the recently discovered role of succinate and other dicarboxylates in pathophysiological processes including cancer, our results open new perspectives for research in all contexts where selective recognition, trapping and extraction of polycarboxylates is required. </p> </div>

The role of (bio)surfactant sorption in promoting the bioavailability of nutrients localized at the solid-water interface

1999 ◽  
Vol 39 (7) ◽  
pp. 91-98 ◽  
Author(s):  
Ryan N. Jordan ◽  
Eric P. Nichols ◽  
Alfred B. Cunningham
Keyword(s):  
Mass Transfer ◽  
Cell Membrane ◽  
Substrate Concentration ◽  
Water Interface ◽  
Industrial Systems ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Surfactant Sorption

Bioavailability is herein defined as the accessibility of a substrate by a microorganism. Further, bioavailability is governed by (1) the substrate concentration that the cell membrane “sees,” (i.e., the “directly bioavailable” pool) as well as (2) the rate of mass transfer from potentially bioavailable (e.g., nonaqueous) phases to the directly bioavailable (e.g., aqueous) phase. Mechanisms by which sorbed (bio)surfactants influence these two processes are discussed. We propose the hypothesis that the sorption of (bio)surfactants at the solid-liquid interface is partially responsible for the increased bioavailability of surface-bound nutrients, and offer this as a basis for suggesting the development of engineered in-situ bioremediation technologies that take advantage of low (bio)surfactant concentrations. In addition, other industrial systems where bioavailability phenomena should be considered are addressed.

Critical role of nanocomposites at air–water interface: From aqueous foams to foam-based lightweight functional materials

2021 ◽  
Vol 416 ◽  
pp. 129121
Author(s):  
Kai Yu ◽  
Bin Li ◽  
Huagui Zhang ◽  
Zhentao Wang ◽  
Wei Zhang ◽  
...  
Keyword(s):  
Critical Role ◽  
Functional Materials ◽  
Water Interface ◽  
Aqueous Foams ◽  
Air Water Interface

scholarly journals Tcf4 Is Involved in Subset Specification of Mesodiencephalic Dopaminergic Neurons

Biomedicines ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 317
Author(s):  
Simone Mesman ◽  
Iris Wever ◽  
Marten P. Smidt
Keyword(s):  
Neuronal Differentiation ◽  
Dopaminergic Neurons ◽  
Neuronal Development ◽  
Neuronal Population ◽  
Minor Role ◽  
Initial Increase ◽  
E Box ◽  
A Minor ◽  
Bhlh Factor

During development, mesodiencephalic dopaminergic (mdDA) neurons form into different molecular subsets. Knowledge of which factors contribute to the specification of these subsets is currently insufficient. In this study, we examined the role of Tcf4, a member of the E-box protein family, in mdDA neuronal development and subset specification. We show that Tcf4 is expressed throughout development, but is no longer detected in adult midbrain. Deletion of Tcf4 results in an initial increase in TH-expressing neurons at E11.5, but this normalizes at later embryonic stages. However, the caudal subset marker Nxph3 and rostral subset marker Ahd2 are affected at E14.5, indicating that Tcf4 is involved in correct differentiation of mdDA neuronal subsets. At P0, expression of these markers partially recovers, whereas expression of Th transcript and TH protein appears to be affected in lateral parts of the mdDA neuronal population. The initial increase in TH-expressing cells and delay in subset specification could be due to the increase in expression of the bHLH factor Ascl1, known for its role in mdDA neuronal differentiation, upon loss of Tcf4. Taken together, our data identified a minor role for Tcf4 in mdDA neuronal development and subset specification.

scholarly journals Role of glaciers in watershed hydrology: a preliminary study of a "Himalayan catchment"

2010 ◽  
Vol 4 (1) ◽  
pp. 115-128 ◽  
Author(s):  
R. J. Thayyen ◽  
J. T. Gergan
Keyword(s):  
Mass Balance ◽  
River Flow ◽  
Initial Increase ◽  
Glacier Mass Balance ◽  
Mountain Range ◽  
Humid Climate ◽  
Flow Response ◽  
Sustainable Water Resources Management ◽  
South West Monsoon

Abstract. A large number of Himalayan glacier catchments are under the influence of humid climate with snowfall in winter (November–April) and south-west monsoon in summer (June–September) dominating the regional hydrology. Such catchments are defined as "Himalayan catchment", where the glacier meltwater contributes to the river flow during the period of annual high flows produced by the monsoon. The winter snow dominated Alpine catchments of the Kashmir and Karakoram region and cold-arid regions of the Ladakh mountain range are the other major glacio-hydrological regimes identified in the region. Factors influencing the river flow variations in a "Himalayan catchment" were studied in a micro-scale glacier catchment in the Garhwal Himalaya, covering an area of 77.8 km2. Three hydrometric stations were established at different altitudes along the Din Gad stream and discharge was monitored during the summer ablation period from 1998 to 2004, with an exception in 2002. These data have been analysed along with winter/summer precipitation, temperature and mass balance data of the Dokriani glacier to study the role of glacier and precipitation in determining runoff variations along the stream continuum from the glacier snout to 2360 m a.s.l. The study shows that the inter-annual runoff variation in a "Himalayan catchment" is linked with precipitation rather than mass balance changes of the glacier. This study also indicates that the warming induced an initial increase of glacier runoff and subsequent decline as suggested by the IPCC (2007) is restricted to the glacier degradation-derived component in a precipitation dominant Himalayan catchment and cannot be translated as river flow response. The preliminary assessment suggests that the "Himalayan catchment" could experience higher river flows and positive glacier mass balance regime together in association with strong monsoon. The important role of glaciers in this precipitation dominant system is to augment stream runoff during the years of low summer discharge. This paper intends to highlight the importance of creating credible knowledge on the Himalayan cryospheric processes to develop a more representative global view on river flow response to cryospheric changes and locally sustainable water resources management strategies.

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