Yngve Albinsson

Sediment transport pathways in the Skagerrak and Kattegat as indicated by sediment Chernobyl radioactivity and heavy metal concentrations

Abstract The concentration of the heavy metals Hg, Cu, Pb and Zn as well as Chernobyl Cs-137 radioactivity was determined in surface sediments from the Skagerrak and Kattegat. Sediment samples from adjacent Swedish fjords were analysed as well. The sampling was carried out between spring 1988 and autumn 1990. Highest concentrations of heavy metals and largest Cs-137 activities occur in fine-grained organic-rich (> 62; 2% C org ) sediment from Swedish inshore waters and locally also in the Kattegat. Regional trends of relative enrichment of the various heavy metals and Chernobyl Cs-137 with respect to organic carbon was used to determine transport patterns of material enriched with respective elements. It can be proven that deposition of fine-grained material transported from the (southern) North Sea by the Jutland Current is the main mechanism determining the regional accumulation of lead and Chernobyl-derived Cs-137. This mechanism principally controlls the areal distribution of mercury-enriched material as well, but it is regionally of less importance as far as the accumulation of Cu and Zn concerns. The Chernobyl Cs-137 data show that a large proportion of the fine-grained material transported by the Jutland Current originally is river-borne suspension load from (central) western Europe. The areal enrichment pattern of copper, and on a smaller scale those of mercury and zinc too, points to westerly directed suspension load transport across the Kattegat. Material enriched with these elements apparently is being discharged from Swedish industrial and urban centers, in particular the Goteborg area.

Sorption of Pu(VI) onto TiO2

The sorption of Pu(VI) onto TiO(2) was studied as a function of pH (2-10) and Pu concentration (10(-8)-10(-4) M) under an N(2) atmosphere, in 0.016 and 0.1 M NaClO(4). A batch-wise method was used, in which pH was measured in separate experimental containers after removal of a sample to determine the amount of Pu that had been sorbed. As Pu is radioactive, it was used as a tracer and measured by liquid scintillation counting. No ionic strength dependence was discerned, which was taken as an indication of inner sphere complex formation. In the interval of pH 2-7 the system could be described by the formation of two positively charged surface complexes using a 1-pK Stern model. Sorption of the plutonyl ion (PuO(2)(2+)) and the first hydrolysis species (PuO(2)(OH)(+)) was estimated using FITEQL to logK(1)=6.9 and logK(2)=1.4, respectively.

A natural analogue of high-pH cement pore waters from the Maqarin area of northern Jordan: Comparison of predicted and observed trace-element chemistry of uranium and selenium

Abstract Current design concepts for low-/intermediate-level radioactive waste disposal in many countries involve emplacement underground in a cementitious repository. The highly alkaline groundwaters at Maqarin, Jordan, are a good analogue for the cementitious pore waters that will be present within such a repository. A geochemical modelling study of these groundwaters has been carried out in order to test the applicability of equilibrium models in geochemical programs and their associated thermodynamic databases in such hyperalkaline conditions. This was achieved by comparison of elemental solubilities and speciations predicted by the programs with observations in the natural system. Five organisations took part in the study: AEA Technology, U.K.; Chalmers University of Technology, Sweden; MBT Tecnologia Ambiental, Spain; Nagra, Switzerland; and SKB, Sweden. The modelling study was coordinated by the University of Berne. The results of the study showed good agreement between the predictions of the programs employed. Comparison of the observed solids with those predicted by the models has allowed limited validation of the databases. The results for U and Se are presented here.

Possible Effects of Bacteria on Trace Element Migration in Crystalline Bed-Rock

This work reports the total numbers of bacteria in the ground water and on surfaces exposed to slowly flowing ground water from two boreholes, KLX01,1078 m, close to the forth-coming Swedish Äspö hard rock laboratory and V2, 1240 m, in the Stripa mine. There were from 0.2 χ ΙΟ up to 12 χ 10 unattached bacteria/m groundwater and from 0.09 χ 10 up to 5.9 χ 10 attached bacteria/m. The results indicate that there can be up to 790000 attached bacteria per unattached bacterium in channels in fractured rock width a mean width of 0.1 mm. The bacterial populations significantly assimilated C0 2 , indicating an in situ production of organic carbon from carbonate, that might have a profound influence on the ground water chemistry. This work also indicates that sulphate-reducing bacteria produce complexing agents that has a significant influence on the speciation and sorption properties of trivalent lanthanides.

Chemical effects of goethite colloid on the transport of radionuclides through a quartz-packed column

Abstract Laboratory experiments were carried out to investigate the effects of inorganic colloids on the transport of radionuclides through quartz sand packed columns. Submicrometre size particles, goethite (α-FeOOH), were used to represent the colloids. The radionuclides were 137 Cs, 22 Na and 131 I (as iodate). It was found that pH is a controlling parameter affecting goethite transport. At low pH, goethite is strongly retained by the quartz. At high pH, the breakthrough of goethite followed predictions based on the electrostatic repulsion between the colloids and the quartz. In addition, the flow rate and the initial goethite colloid concentration influenced the colloid breakthrough from the quartz column. There is not any similarity between either sodium and goethites or cesium and goethites breakthrough curves. The transport of iodate, however, is greatly altered in the presence of goethite at low pH. No such similarity was found at high pH.

Effects of gluco-isosaccharinate on Cs, Ni, Pm and Th sorption onto, and diffusion into cement

The conditions in the Swedish design for a repository of intermediate to low level radioactive waste include a high alkalinity buffer from the concrete construction in combination with cellulose materials in the waste. Experiments have been undertaken in order to quantify the effects of cellulose degradation products on the radionuclide retention capability of the concrete enclosure. Studies of the sorption of Cs, Ni, Pm and Th onto crushed cement and the diffusion of Cs, Ni and Pm in cement and concrete discs of 2 cm thickness were made in a nitrogen-flushed glovebox facility, using different cellulose degradation product additives to the alkaline pore-water. Samples of the liquid phases were taken during a period of 12 months and the sorption and diffusion behaviour was evaluated by radioanalytical methods. In the experiments of alkaline degradation of cellulose the major constituent was found to be D-gluco-isosaccharinate, a potential metal complexing agent, which was synthesized as its Ca salt and used as a 5mM additive in sorption and diffusion experiments. The other additives were leachates of 5 kg/m3 and 100 kg/m3 cellulose in alkaline water. The results show that the additives caused a significant, but transient reduction of the sorption of Pm and Th. The sorption of Cs and Ni were not influenced. The diffusion of D-gluco-isosaccharinate itself was also studied and this indicates that its apparent diffusivity in cement is low, probably due to its strong sorption on cement. This would explain the transient reduction of the radionuclide sorption.

A method for preparation and purification of 234Th

An improved method to recover 234Th from depleted uranium has been developed. The method is based on solvent extraction and ion-exchange separations. The final thorium fraction has a high specific activity, about 1-3 PBq/mol Th, which makes it well suited for investigations, where a low thorium concentration is essential. The method is comparably fast, with a total processing time of 2 days. Another advantage is that the uranium fraction can be used as a 234Th generator for several years.

Diffusion of radionuclides in concrete and concrete/bentonite systems

Various construction materials are under consideration for nuclear waste repositories. Two important materials are concrete and bentonite clay, which will act as mechanical barriers and prevent convective water flow. These barriers will also retard transport (diffusion controlled) of dissolved radionuclides by a combination of mechanical constraints and chemical interactions with the solid. An important issue is the possible change of the initial sodium bentonite into the calcium form due to interaction with calcium from the concrete. The initial leaching of concrete was studied using radioactive spiked concrete in contact with compacted bentonite. Measurement were made of the diffusion of Cs, Am and Pu into 5 different types of concrete in contact with pore water. The diffusivity measured for Cs agrees reasonably well with data found in the literature. No movement could be measured for Am and Pu (< 0.2 mm), even though the contact times were extremely long (2.5 and 5 yr, respectively). The diffusion of Na, Ca and Cs from concrete into bentonite was also measured.

Effect of Cell Number, pH and Lanthanide Concentration on the Sorption of Promethium by She wane Ha putrefaciens

The aim of this work was to investigate the sorption of the lanthanide promethium by bacteria and the distribution ratio, Kd, of the lanthanide between bacteria and the aqueous phase at different cell numbers, pH and lanthanide concentrations. There was a negative linear relationship between the cell numbers and the amount of the Pm sorbed, and also between the cell numbers and the Kd. The sorption decreased from a stable level at 90% as the pH was raised above 7. There was a linear quantitative relation between the Pm concentration and the amount of Pm sorbed by the cells while the relation to Kd was relatively constant. The results indicate that the sorption of trivalent actinides and lanthanides by bacteria involves reversible surface adsorption.

Solid–Aqueous Phase Partitioning of Radionuclides by Complexing Compounds Excreted by Subsurface Bacteria

Radionuclides are present in numerous aerobic and anaerobic subsurface environments due to nuclear weapons testing, leakage from process and storage facilities, and discharge of radioactive waste. The partitioning of radionuclides between liquid and solid phases by complexing compounds excreted by subsurface bacteria was studied. The solid–aqueous phase partitioning of pico- to submicromolar amounts of 59Fe, 147Pm, 234Th, and 241Am was analyzed in the presence of quartz sand and exudates from three species of subsurface bacteria: Pseudomonas fluorescens, Pseudomonas stutzeri, and Shewanella putrefaciens. All were grown under aerobic conditions, and P. stutzeri and S. putrefaciens were grown under anaerobic conditions as well. The supernatants of the aerobic and anaerobic cultures were collected and radionuclide was added. Quartz sand, with a Brunauer, Emmett, and Teller (BET) surface area of 0.1 m2 g–1, was added to the supernatant radionuclide mix, and the pH was adjusted to approximately 8. After centrifuging, the amount of radionuclide in the liquid phase of the samples and controls was analyzed using scintillation. Relative to the control, aerobic supernatants maintained more than 50% of the added 59Fe, 234Th, and 241Am. The highest amount of metal present in the liquid phase of the anaerobic supernatants was found in the case of 241Am, with 40% more 241Am in samples than in controls. Both aerobic and anaerobic supernatants tested positive for complexing compounds when analyzed using the Chrome Azurol S assay. The great amounts of radionuclides in the liquid phases of samples were likely due to complexation with such compounds. Bacterially excreted complexing compounds hence seem able to influence the solid–aqueous phase partitioning of radionuclides. This could influence the mobility of radionuclides in contaminated subsurface environments.