bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of alpha-radiolysis on UO2 dissolution determined from electrochemical experiments with 238Pu-doped UO2
Authors: Stroes-Gascoyne S. , King F. , Betteridge J. S. , Garisto F. 
Published: September 2005

Summary
The 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 H2O2 in UO2 studies has provided much information on the basic chemistry/electrochemistry of α-radiolysis effects on UO2 fuel dissolution. Here, alpha-radiolysis effects were measured directly by performing electrochemical experiments with α-doped UO2. The 238Pu-doped UO2 pellets, produced by milling, pressing and sintering, had activities of approximately 0.01 and 0.1 Ci/g. Discs cut from these pellets were fabricated into electrodes. Corrosion potentials (Ecorr) were measured for these electrodes, in glass cells containing de-aerated 0.1 M NaClO4 (pH 9.5) for periods up to 1600 h. The effects of carbonate and Fe(II) on Ecorr values were also investigated. Preliminary results showed that Ecorr values correlated with doping levels, and were slightly higher than Ecorr values obtained with UO2 electrodes in the presence of external α-sources. The presence of carbonate reduced Ecorr values considerably. Addition of Fe(II) caused generally small reductions in Ecorr values, suggesting that Fe(II) affects the dissolution process, either by scavenging radiolytic oxidants, reducing oxidized surface states, or reducing dissolved U(VI). These effects were often transient due to depletion of the added Fe(II). Accurate dissolution rates could not be determined from measured solution and surface concentrations because of material entering the solutions during the electro-reduction procedure, probably due to the dissolution of fines present on the electrode surface after polishing. Experiments are continuing in order to confirm the preliminary findings, with greater attention being paid to determining accurate dissolution rates.
Radiation-chemical effects in the near-field of a final disposal site: role of bromine on the radiolytic processes in NaCl-solutions
Authors: Ershov B. G. , Kelm M. , Janata E. , Gordeev A. V. , Bohnert E. 
Published: September 2005

SummaryThe oxidation of Br−by Cl2−is investigated by gamma pulse radiolysis in aqueous solutions of NaCl and NaBr. Depending on the ratio of the concentration of Br−to Cl−, the main product being observed is either Cl2−, ClBr−or Br2−. The mixed radical anion ClBr−exhibits a broad absorption band at 350 nm with ε350=9300 dm3mol−1cm−1. The rate constants of the equilibrium Cl2−+ Br− ClBr−+Cl−are determined to be kf=4×109dm3mol−1s−1and kb=1.1×102dm3mol−1s−1. The formation of the Cl3−(λmax=220 nm), Cl2Br−(λmax=230 nm) and ClBr2−(λmax=245 nm) ions in the radiation-chemical oxidation of Cl−and Br−ions in an aqueous solution was observed by pulse radiolysis, and its mechanisms of appearance and the equilibrium constants were determined.
Structure of uranium sorption complexes at montmorillonite edge sites
Authors: Hennig C. , Reich T. , Dähn R. , Scheidegger A. M. 
Published: September 2005

SummaryExtended X-ray absorption fine structure (EXAFS) spectroscopy at the uranium LIII-edge was used for determining the structural environment of aqueous uranyl sorbed onto montmorillonite. The study reveals that uranyl uptake at pH ∼5-∼7 and at an initial uranyl concentration of 5×10−5M takes place at amphoteric surface hydroxyl sites as inner-sphere complex. The measured bond distances between uranium and the equatorial oxygen atoms are in the range of 2.34 Å and 2.37 Å indicating an inner-sphere coordination. At ∼3.4 Å the presence of a U-Al backscattering pair was determined. This backscattering pair indicates that the binding of the uranyl unit to amphoteric surface hydroxyl sites occurs preferred as a bidentate inner-sphere complex on aluminol groups.
Sorption of several safety relevant radionuclides on granite and diorite – a potential repository host rock in the Taiwan area
Authors: Hsu C.-N. , Wei Y.-Y. , Chuang J.-T. , Tseng C.-L. , Yang J.-Y. , Ke C.-H. , Cheng H.-P. , Teng S.-P. 
Published: September 2005

SummaryThe geological survey of natural barriers plays a critical role in determining the suitability of a site for the final disposal of high-level radwaste. This study focused on the characterization of sorption and the determination of distribution coefficients of several safety relevant radionuclides. Both batch tests and polar-microscopy/autoradiography were employed for analyzing and estimating of the sorption of nuclides on one potential host rock in the Taiwan area, which is composed of mostly granite and little diorite. Nuclides investigated were Co, Sr, Cs, U, I, and Am. De-ionized water and synthetic seawater were applied to study nuclide sorption at various concentrations. The distribution coefficients obtained based on the two-week batch tests indicated that the sorption of Co, Sr, Cs, and U on each rock sample was greater in de-ionized water than in synthetic seawater. In addition, sorption onto a specific host rock depended on microscopic heterogeneity. The photos obtained from polar-microscopy/autoradiography showed that biotite is the principal mineral component that is responsible for the sorption of137Cs and90Sr onto granite and diorite.
Sorption behaviour of caesium on a bentonite sample
Authors: Hurel C. , Marmier N. , Sèby F. , Giffaut E. , Bourg A. C. M. , Fromage F. 
Published: September 2005

Summary
Sorption of elements like Cs on clay is one of the principal processes delaying their release from deep repositories of nuclear wastes into the environment. The sorption processes taking place between non-purified natural clay material (bentonite) and synthetic groundwater (containing Ca, Mg, Na, K and carbonates) were therefore studied experimentally and modelled for Cs to determine whether thermodynamic computer codes capable of predicting the behaviour of this element in natural systems might be developed. The model used, based on the properties of a pure montmorillonite phase, incorporates the surface reactions for natural major ions and sorbing cations but does not have any adjustable parameters. The weight of each parameters used in the model is assessed. Surface reactions are classified as either major or minor, and a simplified model of Cs sorption that considers only the major processes is proposed. This simplified model might correspond to the less sophisticated thermodynamic model included in coupled geochemistry-transport models.
Specific interaction of cesium with the surface of calcium silicate hydrates
Authors: Viallis-Terrisse H. , Nonat A. , Petit J.-C. , Landesman Catherine , Richet C. 
Published: September 2005

Summary
The sorption of cesium at the calcium silicate hydrates (CSH) surface was investigated, both through sorption isotherm data and by solid-state NMR experiments. The sorption ability of CSH towards cesium is favored for low solid Ca/Si molar ratios, in agreement with the negative surface charge they develop then. A significant proportion of these sorbed cesium cations remains tightly bound to the surface sites forming, in dehydrated CSH, inner-sphere complexes, which can not be removed by alcohol washing. Chloride seems to present a lower affinity for CSH, even for high Ca/Si molar ratios, where the surface charge becomes positive.
Relationship of quantitative X-ray diffraction measurements of geologic materials to cesium sorption
Authors: Payne Timothy E. , Bertram W. K. , Itakura T. , Raven M. D. 
Published: September 2005

SummaryThe amounts of clay minerals in geologic samples from the Australian arid zone were measured using the SIROQUANT program, which quantifies mineral abundances from X-ray diffraction patterns using the Rietveld method. The sorption of trace cesium on the same samples was investigated in batch experiments. The statistical relationships between the Cs distribution coefficients (Kdvalues) and the smectite, illite and kaolinite contents were assessed. Other characterisation data such as the BET surface area and total clay content were included in the statistical analysis. The correlation of the illite content with the Kdfor trace Cs was stronger than any other correlation that was tested. This can be attributed to the presence of frayed edge sites on illite which are highly selective for the adsorption of trace Cs. Sorption experiments were also carried out with higher Cs concentrations, which were expected to saturate the selective Cs sorption sites on illite. Under these conditions, there was no significant correlation between the illite content and the cesium Kd. However, the Kdwas related to the smectite content of the materials. There was no correlation between the kaolinite content and the Kdfor Cs sorption under any of the experimental conditions. The sorption of Cs on the samples was influenced by the BET surface areas, but normalisation of the Kddata by surface area did not fully explain the sorption results. Only the quantitative XRD data were able to explain the shapes of Cs sorption isotherms. The isotherm was distinctly different for an illite-rich sample and did not conform to the Freundlich isotherm exhibited by other samples. This study demonstrates that quantitative XRD measurements are valuable in predicting Cs sorption properties of complex geologic samples, particularly sorption data obtained with trace Cs levels where bulk measurements such as the BET surface area are less useful.
Technetium behaviour in Boom Clay – a laboratory and field study
Authors: Baston G. M. N. , De Cannière P. , Ilett D. J. , Cowper M. M. , Pilkington N. J. , Tweed Cherry J. , Wang L. , Williams S. J. 
Published: September 2005

SummaryThis paper describes a study of technetium solubility and migration under chemical conditions representative of those prevailing in a Boom Clay environment. Laboratory andin situmeasurements yielded similar aqueous concentrations of technetium, of about 1×10−8mol dm−3, close to the concentrations measured for hydrated technetium(IV) oxide TcO2·1.6H2O in the solubility studies. From fitting the curves of the Tc concentrations as function of time, distribution coefficient (Kd) values were estimated to lie between 0.8 cm3g−1and 1.8 cm3g−1. Exposure of the system at 80 °C and to γ-radiation dose rates of several hundred Gy h−1resulted in only minor differences in behaviour.
Input contribution and vertical migration of plutonium, americium and cesium in lake sediments (Belham Tarn, Cumbria, UK)
Authors: Michel H. , Barci-Funel G. , Barci V. , Ardisson G. 
Published: September 2005

Summary
The record of the global atmospheric fallout could be found in the lake sediments. A mass balance for fallout radionuclides in Blelham Tarn and its catchment is established. The sediment activity contribution is coming from direct atmospheric fallout and from indirect atmospheric fallout via the catchment. The catchement activity is conveyed to the sediment by the rivers and the direct streaming. A comparison of the fallout and the sediment inventory allows the activity estimation of these different contributions and to understand the mobility of these elements on the catchment and in the sediments. The study of activity profile in sediment core allows to characterise the different radioactive events occurred in the past. For the lake Blelham, the results show two cesium activity peaks and only one peak for transuranic activities. The deepest peaks correspond to the atmospheric nuclear test fallout in the sixties (1963) and the second peak to the Chernobyl accident (1986). The activity ratio 239-240Pu/ 137Cs allows estimating the ratio between cesium activities in sediments coming from these two events. Plutonium and cesium diffusion coefficients are calculated with a simple analytical model.
Diffusion of 22Na+, 85Sr2+, 134Cs+ and 57Co2+ in bentonite clay compacted to different densities: experiments and modeling
Authors: Molera M. , Eriksen T. 
Published: September 2005

Summary
The diffusion of radionuclides in water-saturated porous media, such as compacted bentonite, is traditionally modeled assuming diffusion in the pore water and immobilization by adsorption on the clay surface. In reality there are several sorption mechanisms acting in the clay-water system. We have therefore carried out a careful diffusion study of the cations Na+, Sr2+, Cs+, which are predominantly sorbed by electrostatic interaction, and Co2+, for which the dominant sorption mechanism at pH > 7 is inner-sphere complexation and/or surface precipitation. The study has been performed at different densities of clay compaction (1.8, 1.6, 1.2, 0.8, 0.4 g cm−3) using a through diffusion technique. In each experiment, the apparent diffusivity and transport Kd were obtained by computer simulation of the experimentally measured cumulative flux through a plug of compacted bentonite and the concentration profile within the bentonite. Batch sorption experiments with Na+, Sr2+, Cs+ and Co2+ were also carried out. Measured batch Kd values were compared to diffusion-derived Kd values using the computer code ANADIFF. The obtained diffusivities of Cs+ and Sr2+ decreased as the density of bentonite increased. The diffusivity of Cs+ decreased from 1.5×10−7 to 1.1×10−8 cm2/s as the clay dry bulk density increased from 0.4 to 1.8 g/cm3 and the diffusivity for Sr2+ varied from 4.3×10−7 to 9.0×10−8 cm2/s. The diffusivities of Co2+ also decreased from 3.0×10−9 to 1.0×10−10 cm2/s in the same range of clay density. An interpretation of the diffusion data is proposed based on differences in porosity and tortuosity of the bentonite compacted to different densities, and on differences in binding energy, hydration energy, and hydrolysis constants for the cations studied.
Precipitation of technetium by subsurface sulfate-reducing bacteria
Authors: Abdelouas A. , Fattahi Massoud , Grambow Bernd , Vichot L. , Gautier E. 
Published: September 2005

SummaryTo study the interaction between Tc and subsurface bacteria, we conducted batch experiments with soil and groundwater or sterilized deionized water. The system water/soil was amended with lactate and phosphate for bacterial growth. Nitrate and sulfate were added to stimulate the growth of indigenous denitrifying and sulfate-reducing bacteria. During denitrification Tc-concentration did not change with time. In the presence of sulfate-reducing bacteria, Tc-concentrations decreased in reacted waters which could be attributed to Tc(VII) reduction and precipitation of TcO2and/or TcS2. Coprecipitation with newly formed iron sulfide is expected to contribute to Tc removal. Additional experiments with U and Tc showed that these elements were simultaneously reduced by sulfate-reducing bacteria. This work shows that 1) subsurface mixed cultures of denitrifying bacteria do not remove Tc from solution, this is different from uranium and 2) sulfate-reducing bacteria reduce and remove Tc from aqueous solutions and thus in situ bioremediation of subsurface waters and soils may be possible with such ubiquitous bacteria.
Bio-sorption of neptunium(V) by Pseudomonas fluorescens
Authors: Songkasiri W. , Reed D. T. , Rittmann B. E. 
Published: September 2005

Summary
The bio-sorption of neptunyl (NpO2
+) by Pseudomonas fluorescens was investigated. The overall goals of this research are to identify key interactions between neptunium and soil bacteria and to model these effects under subsurface-related conditions. Neptunyl, which is generally thought to be non-sorptive, was significantly sorbed under all conditions studied. At initial neptunyl concentrations of 4.75 µM and pH = 7, as much as 85% of the neptunium was sorbed under aerobic conditions. Kinetic studies show that neptunyl was sorbed rapidly within the first 15 minutes. The extent of sorption also increased with pH. In all cases, the sorbed neptunium was shown to be NpO2
+ by X-ray absorption near edged spectroscopy (XANES) analysis, confirming that there was no reduction to Np(IV) under the conditions of our experiment. The sorption data were modeled using Langmuir and Freundlich isotherms. A comparison of the two approaches showed a significantly better fit for the Freundlich isotherm, and the Freundlich parameter values suggest interactions between sorbed NpO2
+ molecules. These data show that bio-sorption, even for neptunyl, has a significant role in defining the speciation of neptunium and, hence, its overall mobility in the subsurface.
Solubility and hydrolysis of Zr oxides: a review and supplemental data
Authors: Curti E. , Degueldre C. 
Published: September 2005

Summary
Thermodynamic data for Zr(IV) have been reviewed in the context of a recent update of the Nagra/PSI thermochemical database, which is primarily used in safety assessment calculations for radioactive waste repositories in Switzerland. In spite of the important role of Zr in nuclear reactor technology and as fission product in radioactive waste, the thermodynamic properties of this element in aqueous solutions are poorly constrained and published data are frequently contradictory. Specifically, hydrolysis constants, which are critical to any geochemical calculation of Zr speciation in aqueous solutions, may vary by several orders of magnitude.
Published solubility and hydrolysis data for Zr oxides were reviewed and evaluated. Recent solubility measurements on crystalline ZrO2, obtained in our laboratory, were integrated in this analysis. These new data are the only ZrO2 solubility measurements obtained in a pH region relevant for environmental aqueous systems, where equilibrium concentrations decrease to nanomolar levels.
All solubility data of (hydrous) Zr oxides can be reproduced satisfactorily by a single set of hydrolysis constants, provided that only data measured from undersaturation are considered. This set includes the species Zr4+, ZrOH3+, Zr(OH)4
0 and Zr(OH)5
−. However, present experimental data are still not sufficient to establish a fully reliable database.
Nagra/PSI Chemical Thermodynamic Data Base 01/01
Authors: Hummel W. , Berner U. , Curti E. , Pearson F. J. , Thoenen T. 
Published: September 2005

SummaryThe Nagra/PSI Chemical Thermodynamic Data Base has been updated to support performance assessments of the planned Swiss repositories for radioactive waste. The update from version 05/92 to 01/01 involved major revisions for most of the actinides and fission products. Altogether, more than 70% of the database contents have been revised. Data for U, Np, Pu, Am and Tc recommended by the NEA TDB project were considered in the update. Thermodynamic data for Th, Sn, Eu, Pd, Al, and solubility and metal complexation of sulphides and silicates were extensively reviewed. Data for Zr, Ni and Se were examined less rigorously as these elements are currently being reviewed in phase II of the NEA TDB project. Our experiences from this two year team effort can be summarised as follows. Detailed in-house reviews and critical appraisal of NEA recommendations greatly improved the chemical consistency and quality of the selected data. On the other hand, we could discern major gaps in the data, especially missing carbonate complexes. In some systems,e.g. Th(IV)-H2O and U(IV)-H2O, experimental data could not be described by a unique set of thermodynamic constants. There, a pragmatic approach based on solubility data was chosen for application to performance assessment. The electronic version of our database and information concerning its full documentation is available on our PSI web site (http://www.psi.ch/les).
Effect of E(sev) and Su(Raf) Hsp83 Mutants and Trans-heterozygotes on Bristle Trait Means and Variation in Drosophila melanogaster
Authors: Milton Claire C , Batterham Philip , McKenzie John A , Hoffmann Ary A 
Published: September 2005

Abstract
The Hsp90 protein encoded by the Hsp83 gene is required for the development of many traits in Drosophila. Hsp83 is also thought to play a role in the expression of phenotypic and genetic variability for subsequent selection and evolutionary change. Here we examine the impact of different E(sev) and Su(Raf) Hsp83 mutants on means and phenotypic variances of invariant and variable bristle traits. One of the mutants influenced the normally invariant thoracic bristle number, while none affected invariant scutellar bristle number. E(sev) alleles consistently influenced variable bristle traits while there were fewer effects of the Su(Raf) alleles. For the variable traits, none of the Hsp83 alleles had any effect on phenotypic variance, environmental variance, or developmental stability of the bristle traits. When alleles were combined in trans-heterozygotes, there were both cumulative and complementary effects on thoracic and variable bristle trait numbers, depending on the allelic combination. Overall, the results suggest that Hsp83 mutants do not have detectable effects on the phenotypic or environmental variance of bristle traits and that complementation of E(sev) and Su(Raf) Hsp83 mutants can extend to thoracic bristles as well as previously reported effects on viability. Some allelic combinations lead to more severe effects on variable bristle trait means than do single Hsp83 mutations.
Extensive Chromosomal Repatterning and the Evolution of Sterility Barriers in Hybrid Sunflower Species
Authors: Lai Zhao , Nakazato Takuya , Salmaso Marzia , Burke John M , Tang Shunxue , Knapp Steven J , Rieseberg Loren H 
Published: September 2005

AbstractNew species may arise via hybridization and without a change in ploidy. This process, termed homoploid hybrid speciation, is theoretically difficult because it requires the development of reproductive barriers in sympatry or parapatry. Theory suggests that isolation may arise through rapid karyotypic evolution and/or ecological divergence of hybrid neospecies. Here, we investigate the role of karyotypic change in homoploid hybrid speciation by generating detailed genetic linkage maps for three hybrid sunflower species, Helianthus anomalus, H. deserticola, and H. paradoxus, and comparing these maps to those previously generated for the parental species, H. annuus and H. petiolaris. We also conduct a quantitative trait locus (QTL) analysis of pollen fertility in a BC2 population between the parental species and assess levels of pollen and seed fertility in all cross-combinations of the hybrid and parental species. The three hybrid species are massively divergent from their parental species in karyotype; gene order differences were observed for between 9 and 11 linkage groups (of 17 total), depending on the comparison. About one-third of the karyoypic differences arose through the sorting of chromosomal rearrangements that differentiate the parental species, but the remainder appear to have arisen de novo (six breakages/six fusions in H. anomalus, four breakages/three fusions in H. deserticola, and five breakages/five fusions in H. paradoxus). QTL analyses indicate that the karyotypic differences contribute to reproductive isolation. Nine of 11 pollen viability QTL occur on rearranged chromosomes and all but one map close to a rearrangement breakpoint. Finally, pollen and seed fertility estimates for F1's between the hybrid and parental species fall below 11%, which is sufficient for evolutionary independence of the hybrid neospecies.