Actinide Migration in Granite Fractures: Comparison between In-Situ and Laboratory Results
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II11.2.1
Actinide Migration in Granite Fractures: Comparison between In-Situ and Laboratory Results Bernhard Kienzler1, Jürgen Römer1, Peter Vejmelka1, Mats Jansson2, Trygve E. Eriksen2, Kastriot Spahiu3 1 Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, GERMANY 2 Dept. of Nuclear Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, SWEDEN 3 Svensk Kärnbränslehantering AB (SKB), SE-102 40 Stockholm, SWEDEN ABSTRACT Results of migration experiments with fractured drill cores performed in laboratory and in the CHEMLAB 2 probe under in-situ conditions at Äspö HRL are presented. Drill cores for both experiments are prepared by the same method and provide similar hydraulic properties. As tracers, actinides Am(III), Pu(IV) and Np(V) are applied. Breakthrough of Np is found to be unretarded in comparison to inert HTO tracer. Recovery of Np amounts to less than 40%. Am and Pu are not eluted from the cores. Lower limits of the retardation factor of 135 are calculated for both Am and Pu. Post mortem investigations of the fractured cores are performed by cutting perpendicular to the cylinder axis and subsequent chemical and radiochemical analysis of abraded material and slices. Imaging of the slices reveals the geometry of the flow path. α-radiography of the slices shows similar distribution patterns of Np and Am. It is shown by TTA extraction that Np bound onto the slices is in the tetravalent state. Hence, Np(V) undergoes reduction during migration. Retention of Am and Np is attributed to different processes. BACKGROUND AND OBJECTIVES The Äspö Hard Rock Laboratory (HRL) was established in Sweden in a granite rock formation for in-situ testing of disposal techniques and for investigations concerning migration and retention of radionuclides [1]. Within the scope of a bilateral cooperation between Svensk Kärnbränslehantering AB (SKB) and Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung (FZK-INE), actinide migration experiments with Pu, Am, and Np are conducted at the Äspö Hard Rock Laboratory. Batch experiments provided information on the sorption behavior of different solids present at Äspö HRL. Migration experiments were performed in laboratory at FZKINE. The same type of experiment was repeated in the CHEMLAB 2 probe [2] at Äspö HRL to guarantee most realistic conditions. Previous reports summarized the results of batch experiments and laboratory tests with core #1 as well as results of the first in-situ experiment [3, 4, 5]. MATERIALS Groundwater For laboratory investigations, Äspö groundwater was used, which was extracted from the drill hole SA 2600. In the in-situ experiment the local groundwater is present in the CHEMLAB 2 which is sited in borehole KJ0044F01 having a temperature of 17°C. Groundwater compositions are given in ref. [5]. The waters differ in measured element concentrations by about 30-60%. Fe could not be measured in the groundwater used in laboratory (SA 2600). Fe had been precipitated during the transport to Germany.
II11.2.2
The laboratory expe
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