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As part of the long-term diffusion project a 780 days long in situ diffusion experiment was performed at the Grimsel Test Site where several radionuclides and inactive iodine were circulated in the packered interval in granodiorite. This paper presents in situ diffusion profiles for tritiated water and iodine acquired from overcored sections of the circulation interval by out-leaching.

Polonium / Solvent extraction / Drilled well waterSummary. The suitability of solvent extraction for 210 Po analysis from groundwater samples was assessed using three extractive scintillation cocktails, POLEX, TOPO and TNOA. Validation of the extraction method was carried out using both distilled water samples with some radionuclides added and real groundwater samples. Extraction of polonium from spiked waters was successful and no co-extraction of 234 U or 238 U occurred. However, the extraction results from groundwaters differed greatly from the spiked water samples. The main interfering nuclides were 234 U and 238 U, which led to incorrect results in 210 Po analysis. Due to the co-extraction of uranium from real groundwaters, validation of the method was unfeasible.

Uranium / Rock alteration processes / Uranium migrationSummary. Understanding the behaviour of uranium is essential when assessing the safety of a spent nuclear fuel repository. The geochemical behaviour of uranium, including its reactive transport chemistry, is also a matter of concern when assessing the environmental impact of uranium mining. Subsurface uranium mobility is believed to be primarily controlled by dissolution and (co)-precipitation of uranium mineral solids and adsorption to mineral surfaces. This paper describes a modelling exercise based on characterisation of samples taken from drilled cores at the uranium mineralization at Askola, Southern Finland. In the modelling exercise, current conditions are assumed to be oxidizing and saturated with groundwater. PHREEQC was used for modelling in conjunction with the Lawrence Livermore National Laboratory database, chosen for its extensive coverage of uranium species and mineral phases.It is postulated that weathering processes near the surface have led to uranium dissolution from the primary ore, leaching out from the matrix and migrating along water-conducting fractures with subsequent re-diffusion into the rock matrix. Electron microscopy studies show that precipitated uranium occupies intra-granular fractures in feldspars and quartz. In addition, secondary uranium was found to be distributed within goethite nodules as well as around the margins of iron-containing minerals in the form of silicate and phosphate precipitates. Equilibrium modelling calculations predict that uranium would be precipitated as uranyl silicates, most likely soddyite and uranophane, in the prevailing chemical conditions beneath Lakeakallio hill.