Radiochemistry of iodine : outcomes of the caiman programme

Titre de la revue : Nuclear Technology Volume : 156 N° : 1 Pagination : 11-28 Date de publication : 01/01/2006

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 programme was devoted to studying the radiochemistry of iodine in the reactor containment in case of a severe accident occurring in a Pressurised Water Reactor; this is a data base of prime importance for the validation of codes, namely IODE, which is a module of the integral ASTEC (Accident Source Term Evaluation Code) code, jointly developed by the IRSN and the GRS. These computations are generally used to predict the radiological consequences of such an accident. The experimental programme, which ran from 1996 to 2002, concerned eighteen experiments in a facility of intermediate scale (300 dm3), where labelled iodine, 131I, was used to perform -counting. The CAIMAN tests are here analysed, 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 modelling and to identify key parameters. Broadly speaking, the gaseous concentrations predicted are quite consistent with the experimental ones; the remaining gaps have been identified.