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Fluvial export of radionuclides : impact on sediment storages of the Rhone river and fluxes towards the Mediterranean Sea

Benoît ROLLAND, doctorate thesis of the sciences and technics faculty (faculté des sciences et techniques) of the Paul Cezanne university (Aix-Marseille), field : Geosciences of the environment, 322p, defended on the 10th of February 2006

Document type > *Mémoire/HDR/Thesis

Keywords > flood, radionuclides, Rhone/Rhone valley

Research Unit > IRSN/DEI/SESURE/LERCM

Authors >

Publication Date > 10/02/2006

Summary

This study deals with the behaviour of trace contaminants originating from chronic liquid releases within fluvial aquatic systems. It focuses on some particle reactive artificial radionuclides that were released by the Marcoule nuclear fuel reprocessing plant during several years mainly prior the end of the nineties and that are still detected in the lower Rhône river. It underlines the decrease of 137Cs, 238Pu and 239+240Pu fluxes to the Mediterranean Sea in relation with the variations in the chronic liquid releases from Marcoule.
The role of flood events on radionuclides exports processes is particularly considered. Over the years 2002 to 2004, floods contributed for 67%, 55%, 68%, 49% and 56% of the mean annual fluxes of 137Cs, 238Pu and 239+240Pu and natural 7Be et 210Pbxs, although these events only represented 5% of time.
The removal, during floods, of sediments contaminated by the Marcoule releases contributes on the average for 19%, 44% and 22% of the annual exports of 137Cs, 238Pu and 239+240Pu towards the Sea. Thus, such sedimentary stocks act as a delayed source term of artificial radioactivity that is currently significant.
Determination of the sediments residence times before removal allows to evaluate the Rhône capacity to clear its contaminated stocks. Residence times of 200 years, 100 years and 900 years are estimated to be necessary to totally remove the accumulated 137Cs, 238Pu and 239+240Pu, respectively.
The location typologies of sediment storages within fluvial systems are also specified. These location are represented on one hand by dams, and on the other hand by riverbanks and oxbow lakes. Stocks accumulated in dams seem to be removed more easily than those trapped in banks.


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