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Bruxelles, EU meeting, 03 Oct 2011

Standpoint of the French Institute for Radioprotection and Nuclear Safety (IRSN) on the impact of radioactive releases from the Fukushima-Daiichi nuclear accident on the marine environment. (http://www.irsn.fr/EN/news/Pages/201103_seism-in-japan.aspx)

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Bruxelles, EU meeting, 03 Oct 2011

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  1. Standpoint of the French Institute for Radioprotection and Nuclear Safety (IRSN) on the impact of radioactive releases from the Fukushima-Daiichi nuclear accident on the marine environment (http://www.irsn.fr/EN/news/Pages/201103_seism-in-japan.aspx) Paper sumitted to JER “Estimation of marine source-term following Fukushima Dai-ichi accident” by Bailly du Bois et al. Bruxelles, EU meeting, 03 Oct 2011

  2. IRSN estimation of the source-term of releases into seawater 137Cs quantities were estimated on the basis of sample measurements in a 50 x 100 km area around the plant (issues: depth, mixing layer, atmospheric fallout, rain water washout, …) Exponential decay back extrapolated to April 8 -> 22E+15 Bq (depth of mixing layer ?) Total until July 18 -> 27E+15 Bq

  3. IRSN estimation of the rate of seawater renewal • Dilution by clean water through marine currents (remarkably constant) • Convergence of Kuroshio and Oyashio • Seasonal changes in the ocean circulation ? • Return of contaminated water back in the area ? • If no more releases occur and dilution remains constant, back to prior situation is expected in Nov 2011 Exponential decay t1/2 = 6.9 d

  4. IRSN/Ifremer dispersion modelling(based on IRSN estimated source-term) Short distance matching calculations/measurements less than 1 km off the facility

  5. IRSN/Ifremer dispersion modeling(based on IRSN estimated source-term) Mid distance • (color-scale changed by a factor 10) • Long distance dispersion is not yet validated by measurements • as of July 1st, calculated values are below actual DL (5 Bq.L-1, but DLs below 0.001 Bq.L-1 are routinely achieved in radioecology)

  6. Inventory of main 137Cs releases in the oceans * Aarkrog, 2003. Input of anthropogenic radionuclides into the World Ocean. Deep Sea Research Part II: Topical Studies in Oceanography Volume 50, Issues 17-21, Pages 2597-2606

  7. Measurements in sediments • Cs, I, Te, Sr, Pu, Ba • The mapis a draft document with over- estimated values along the shore (this biais willbefixed) • As regards Kd’s, amounts of 137Cs in sediments are relatively low • 137Cs seems to increase with time (kinetics of transfer to particles and deposition) but is expected to level off in the forthcoming months. • Because of remobilisation processes, sediments will behave as a secondary sources of contamination (postponed, remote and diffuse) average [137Cs]until Aug 30

  8. FURTHER WORK PLANNED BY IRSN WITH COLLABORATIONS • to compare the results of dispersion modeling by IRSN/Ifremer, Sirocco and Japan Atomic Energy Agency • to estimate the transfers of radionuclides from seawater to biota by modeling in collaboration with Collecte Localisation Satellite (CLS) • radionuclides bioaccumulation in the different marine trophic levels will be dynamically predicted on the basis of dispersion modeling outcomes • maps of radioactive quality index to support monitoring survey for commercial fish species • fish survey in the Pacific (IRSN and IFREMER) • post-doc IRSN fellowship

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