Redissolution of ~(226)Ra from sediments in a spanish estuary affected by the phosphate industry: model comparisons in the framework of the iaea emras project

摘要

The Huelva estuary (south-west Spain), a fully mixed tidal estuary, consists of twornrivers: Odiel and Tinto. A phosphate fertilizer processing complex has been releasingrnNORM radionuclides directly into the Odiel river over several decades. As a consequence,rnhigh levels of ~(226)Ra, U and Th isotopes and other radionuclides have beenrnmeasured in water, suspended matter and bed sediments of the estuary. Nevertheless,rndirect releases stopped in 1998 due to new regulations from the EU and, since then, arnself cleaning process has been observed. It consists of a continuous decrease in activityrnconcentrations in water and bed sediments. The study by means of numerical models ofrnthe ~(226)Ra self cleaning process observed in the estuary has been proposed as an EMRASrnproject task. A model has been proposed by each institute participating in the exercise.rnModels have different configurations and temporal and spatial resolutions. Somernprocesses, for instance tides or uptake/release of radionuclides between water and sediments,rnare described in different ways. However, all are started from the same initialrnconditions, provided by the University of Seville model. The endpoint of the simulationsrnis to give the temporal evolution of the total ~(226)Ra inventory in the bed sediments of thernestuary and to estimate from it the sediment halving time. A brief description of thernmain features of each model is provided and the results are compared and analysed.