Faire avancer la sûreté nucléaire

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The Nord-Cotentin chemical risk assessment modeling.



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Catherine ROMMENS, Caroline RINGEARD, Céline DUFFA and Laure DELERY Symposium " Case studies on the development, application and evaluation of multimedia, multipathway exposure models" during the ISEA/ISEE 2002 conference. 11-15 août 2002 -Vancouver (canada).


After the assessment of the radiological risk due to past and recent discharges of the nuclear facilities of the Nord-Cotentin region of France, The Nord-Cotentin Group (GRNC) work is devoted to the assessment of the environmental and health risk due chemical discharges from the Nord-Cotentin nuclear installations. The first step of the GRNC was commissioned work permitted to evaluate the radiological risk due to nuclear facilities releases: La Hague reprocessing plant and Flamanville nuclear power plant. Now, as a second step, the group is evaluating the risk due to the corresponding chemical releases from these two installations. To perform the first step, Eengineers and experts from environmental toxicology/chemistry and radioecology organizations are workingworked together, within the framework of the GRNC, to model environmental dispersion and transfers and exposures to pollutants. Liquid and atmospheric chemical source terms were characterized for both facilities. The modeling of the atmospheric sources of pollutants, anddischarges in the terrestrial environment was especially studied due to the strong differences between radiological and chemical sources which prevented from using existing codes contamination. The three specific installations release sources of the La Hague site have beenwere identified as atmospheric source terms of chemicals in La Hague nuclear facilitytaken into account : the the central boiler room housesince 1964, the reprocessing units, UP2 and UP3 reprocessing plants since 1966, and the incinerator. The list of About 30 studied chemical substances were studied, from (heavy metals to , inorganic and organic substances such as dioxins) has been established on the basis of two main criteria: the possibility of their discharge quantification and the existence of toxicological reference value.. A For these pollutants, a calculation transfer methodmodel has beenwas, first, developed using radioecology modeling approach, available from the previous GRNC work, combined withand knowledge of specific behavior and parameters for involvedproperties on chemicals of interest. The existing codes were reviewed and compared to select the most relevant algorithms for the Nord-Cotentin case. It appeared that no existing software was “ready to use” for the calculations required. That is why a specific tool, supported by EXCELÓ package, was developed which accounts for atmospheric dispersion, deposition on the ground, interception of pollutants by leaves (retention and translocation), root transfer and uptake by animals. This tool allows usenabled to to estimate thee actual concentrations of chemical pollutants, in the main terrestrial compartments that can be attributed to La Hague dischargesreleases and to compare them with natural level existing within the environment. The terrestrial compartments studied were the air, the soil, different kinds of plants (grass, hay, maize fodder, root vegetables, leaf vegetable, fruits) and animals or animals products (beef, sheep, pork, poultry and eggs). Exposure, dose and risk calculations were performed based on the results of concentrations in the environment and on corresponding values for marine environment. Ingestion, including inadvertent ingestion of soil, and inhalation were the main exposure pathways studied. Three scenarios reflecting the local way of life were chosen. The first one, based on the average individual (infant, child or adult), gave reference values to compare with the other two scenarios which highlight respectively the consumption of terrestrial agricultural products and the consumption of seafood. The development of the methodology and the tool for the Nord-Cotentin case study allowed us to explore the state-of-the-art of modeling applied to risk assessment. In this work, a particular attention was devoted to identify the main limitations and uncertainty of the whole calculation process and to make clear how they were treated at each step of the risk assessment.