238U, 226Ra, 210Pb and 7Be behaviour in a lake under influence of uranium mine water

Because of the uranium mining activities, which enhance the inputs and the mobility of radionuclides by surface waters, the Limoges area constitutes an helpful site to decipher the behaviour of radioelements in the environment. This study deals with the chemical and physical pathway of 238U, 226Ra and 210Pb in a lake fed by a stream collecting mines waters. We focus on processes controlling the mobility of radioelements and their repartition between particulate and dissolved phases. Impact of precipitations is monitored by7Be and 210Pb data. While flowing in the lake, the 238U, 226Ra and 210Pb activities in unfiltered water decrease quickly. Dilution by precipitations and losses by sedimentation are the two processes investigated. However 7Be data indicate that dilution is negligible. Then sedimentation is the most important one. 80% of 210Pb, 70% of 238U and 60% of 226Ra activities entering the lake are associated with particles and these percentages decrease in the first 100 meters of the lake. This values are correlated with the element reactivity and the exportation rate to the sediment. (authors)