Use of COSYMA in the design of epidemiological studies in case of radiological accidents

COSYMA is a powerful code for the assessment of a wide range of accident consequences. It has been satisfactory because of the possibility to get access to the code itself and to change options like release duration or outputs. COSYMA is a probabilistic code, but, in this application, it has been used in a deterministic way by extracting the results for one weather sequence only. PWR source terms were constructed using the inventory of the COSYMA users intercomparison exercise and release fractions for French nuclear reactors S1, S2, S3. For the reprocessing plant, two source terms were chosen arbitrarily, based on the actual radioactive materials present in the plant and on the radioactive decay of reprocessed PWR fuel (1g Plutonium and 0.01g Curium releases). For the transportation scenarios, several source terms still need to be defined, according to the materials transported, the modes of transportation, and the types of packaging. The post-accidental scenario has identical main options for all installations and source terms. The ingestion pathway was not treated in this study because of its unsatisfactory modeling in COSYMA. The intervention levels for the various countermeasures were drawn from ICRP 40 recommendations Both low and high levels were used for evacuation, sheltering and stable iodine prophylaxis For long term actions, only the low intervention level was applied. (author)