Radiochemistry of Iodine: Outcomes of the CAIMAN Program

Iodine is a fission product of major importance because volatile species can be formed under severe nuclear reactor accident conditions and may potentially be released into the environment, leading to significant radiological consequences. The CAIMAN program was devoted to studying the radiochemistry of iodine in the reactor containment in the case of a severe accident occurring in a pressurized water reactor; this is a database of prime importance for the validation of codes, namely IODE, which is a module of the integral Accident Source Term Evaluation Code (ASTEC), jointly developed by the Institut de Radioprotection et de Sûreté Nucléaire and the Gesellschaft für Anlagen- und Reaktorsicherheit. These computations are generally used to predict the radiological consequences of such an accident.

The experimental program, which ran from 1996 to 2002, concerned 18 experiments in a facility of intermediate scale (300 dm³), where labeled iodine, ¹³¹I, was used to perform gamma counting. The CAIMAN tests are here analyzed, and the main experimental observations and trends are described. For each experiment, IODE computations were performed and compared with experimental results in order to assess the possible weak points of the present modeling and to identify key parameters. Broadly speaking, the gaseous concentrations predicted are quite consistent with the experimental ones; the remaining gaps have been identified.