Actinide migration in granite fractures:comparison between in-situ and laboratory results

摘要

Results of migration experiments with fractured drill cores performed in laboratory and in the CHEMLAB 2 probe under in-situ conditions at Aspo 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 unretraded 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 perpedicular 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.alpha-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 process.