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Niveau de radioactivité des rivières françaises: chroniques acquises au cours des 30 dernières années et état contemporain


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Titre de la revue : Journal of Environmental Monitoring Volume : 10 N° : 7 Pagination : 800-811 Date de publication : 01/07/2008

Résumé

Over the past fifteen years, liquid releases in gamma-emitting radionuclides from the French nuclear facilities has generally fallen by almost 85%. Almost 65% of gamma-emitting liquid effluents released into river freshwaters concerned the River Rhône (Southeast France), with around 85% of this originating from the Marcoule spent fuel reprocessing plant. Upstream of French nuclear plants, artificial radionuclides still detected by gamma spectrometry in 2006, include 137Cs, 131I as well as 60Co, 58Co and 54Mn in the case of the Rhine (Switzerland nuclear industries). In the wake of the fallout from the Chernobyl accident, 103Ru, 106Ru, 110mAg, 141Ce and 129Te were detected in rivers in the east of France. Some of these isotopes were found in aquatic plants until 1989. In eastern France, 137Cs activity in river sediments and mosses is still today two to three times greater than that observed in similar environments in western France. No 134Cs has been detected upstream of nuclear plants in French rivers since 2001. Downstream of nuclear plants, the gamma emitters still detected regularly in rivers in 2006 are 137Cs, 134Cs, 60Co, 58Co, 110mAg, 54Mn, 131I, together with 241Am downstream of the Marcoule spent fuel reprocessing plant. Alpha and beta emitters such as plutonium isotopes and 90Sr first enter freshwaters at the early 50's due to the leaching of soils submitted to the atmospheric fallout from nuclear testing. These elements were also introduced, in the case of the Rhône River, via effluent from the Marcoule reprocessing plant. Until the mid 1990s, plutonium isotopes levels observed in the lower reaches of the Rhône were 10 to 1000 times higher than those observed in other French freshwaters. Data gathered over a period of almost thirty years of radioecological studies has revealed that the only radionuclides detected in fish muscles are 137Cs, 90Sr, plutonium isotopes and 241Am. At the scale of the French territory, there is no significant difference since the mid 1990s between 137Cs activity observed downstream of nuclear facilities and that observed upstream whether in sediments, mosses and fish. Finally, this study highlights that the natural radioactivity of surface freshwaters is around 25 times greater than artificial radioactivity from gamma emitters. However, non gamma emitters released by nuclear industries, such as 3H, may conduct to artificial activity levels 2 to 20 times higher than natural levels.