Mats Jansson

Anion diffusion pathways in bentonite clay compacted to different dry densities

Diffusion of the anions Cl- and I- in MX-80 compacted bentonite has been studied at different ionic strengths (0.01, 0.1 M NaClO4) and clay density (0.4, 0.8, 1.2, 1.8 g cm(-3)) at the buffered pH ...

Sorption effects on cation diffusion in compacted bentonite

Diffusion of Na+. Cs+, Co2+ and Sr2+ in bentonite compacted to a dry density of 1800 kg m(-3) and saturated with groundwaters and aqueous solutions of differing ionic strength have been studied exp ...

Swedish-German actinide migration experiment at ASPO hard rock laboratory.

Within the scope of a bilateral cooperation between Svensk Kärnbränslehantering (SKB) and Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung (FZK-INE), an actinide migration experiment is currently being performed at the Aspö Hard Rock Laboratory (HRL) in Sweden. This paper covers laboratory and in situ investigations on actinide migration in single-fractured granite core samples. For the in situ experiment, the CHEMLAB 2 probe developed by SKB was used. The experimental setup as well as the breakthrough of inert tracers and of the actinides Am, Np and Pu are presented. The breakthrough curves of inert tracers were analyzed to determine hydraulic properties of the fractured samples. Postmortem analyses of the solid samples were performed to characterize the flow path and the sorbed actinides. After cutting the cores, the abraded material was analyzed with respect to sorbed actinides. The slices were scanned optically to visualize the flow path. Effective volumes and inner surface areas were measured. In the experiments, only breakthrough of Np(V) was observed. In each experiment, the recovery of Np(V) was < or = 40%. Breakthrough of Am(III) and Pu(IV) as well as of Np(IV) was not observed.

CHEMLAB - in situ diffusion experiments using radioactive tracers

In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionucli ...

ACTINIDE MIGRATION IN FRACTURES OF GRANITE HOST ROCK : LABORATORY AND IN SITU INVESTIGATIONS

Abstract Within the scope of a cooperation between Svensk Kärnbränslehantering AB and Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, a series of actinide migration experiments were performed both in the laboratory and at the Äspö Hard Rock Laboratory in Sweden. The objectives of these experiments were to quantify the sorption of different actinide elements in single fractures of a granite host rock and to investigate the sorption mechanisms. To guarantee the most realistic conditions—as close to nature as possible—in situ experiments were performed in the Chemlab 2 borehole probe. These migration experiments were complemented by laboratory sorption and migration studies. The latter included batch experiments with flat chips of natural material extracted from fracture surfaces to identify the mineral phases relevant to radionuclide sorption by means of autoradiography. Scanning electron microscopy analyses provided information on the composition of sorption-relevant phases and X-ray photoelectron spectroscopy of Np, Tc, and Fe distribution revealed the redox states of these elements. Important mineral phases retaining all actinides and Tc were Fe-bearing phases. From the migration experiments, elution curves of the inert tracer (HTO), Np(V), U(VI), and to a small extent of Tc(VII) were obtained. Americium(III) and plutonium(IV) were not eluted. The mechanisms influencing the migration of the elements Np, U, and Tc depended on redox reactions. It was shown by various independent methods that Np(V) was reduced to the tetravalent state on the fracture surfaces, thus resulting in a pronounced dependence of the recovery on the residence time. Technetium was also retained in the tetravalent state. Elution of natural uranium from the granite drill cores was significant and is discussed in detail.

A study on the immobilization of selenium oxyanions by H2/Pd(s) in aqueous solution: confirmation of the one-electron reduction barrier of selenate.

Selenium is a trace element of concern in several geochemical contexts, due to the potentially high mobility of the selenium oxyanions and the narrow range between deficiency and toxicity of the element. For high level nuclear waste repositories the long-lived fission product 79Se has been identified as a potential key dose contributor for the long-term safety. This paper deals with the catalytic effect of Pd(s) on the H2 reduction of selenium oxyanions which was studied experimentally in aqueous solutions containing bicarbonate and chloride. Pd-catalysts and hydrogen have been proposed for the remediation of various groundwater contaminants and can also serve as a model substance for catalytic noble metal inclusions present in spent nuclear fuel. In this study selenite (SeO3(2)--) was found to adsorb on Pd. In the presence of hydrogen the rate of selenite removal increased yielding elemental Se. However, no adsorption or reduction of selenate (SeO4(2)--) was observed. A simple radiation chemical experiment revealed a notable barrier towards stepwise one-electron reduction of selenate to selenite. This provides an explanation for the lower reactivity of selenate in systems where reductive immobilization of selenite as well as selenate is thermodynamically favorable.