An overview of Task 6 of the Äspö Task Force: modelling groundwater and solute transport: improved understanding of radionuclide transport in fractured rockUne vue d’ensemble de la tâche 6 de la Äspö Task Force : modélisation des écoulements souterrains et du transport de solutés : amélioration de la compréhension du transport des radionucléides dans les roches fracturéesUn panorama de la Task 6 de la Äspö Task Force: modelación de aguas subterráneas y transporte de soluto: una mejor comprensión del transporte de radionucleidos en rocas fracturadas?sp?任务组任务6概况 : 地下水和溶质运移模拟——提高了对放射性核素在裂隙岩体中运移的认识Uma visão geral da Tarefa 6 da Äspö Task Force: modelação da água subterrânea e do transporte de solutos: aperfeiçoamento da compreensão do transporte de radionuclídeos em rochas fracturadas

An overview is presented of a 4-year study by the Äspö Task Force on Modelling of Groundwater Flow and Transport of Solutes, whose primary aim was to build a bridge between the approaches used for site characterisation (SC) and performance assessment (PA) associated with nuclear waste repositories. Eleven modelling teams representing six national radioactive waste organisations participated in eight modelling exercises whose objectives were: to assess simplifications used in PA models; to determine how, and to what extent, experimental tracer and flow experiments can constrain the range of parameters used in PA models; to support the design of SC programmes to assure that the results have optimal value for PA calculations; and to improve the understanding of site-specific flow and transport behaviour at different scales using SC models. The modelling tasks were concerned with flow and transport through single and multiple near-planar features on SC and PA timescales, including the diffusion of solutes into multiple immobile zones adjacent to fracture surfaces. In general, tracer tests provide only limited quantitative constraints on retention parameter values relevant to PA but nevertheless provide insight about the flow and transport processes, which is a key element of the bridge between SC and PA.