Improving severe accident management through iodine chemistry
In light of the ever-increasing use of nuclear reactors for energy production, research in accident prevention and management has become more extensive. Thereby, accurate prediction of the release of radioactivity as a consequence of a severe accident in a nuclear reactor is of prime importance. Hence, the most radiologically significant fission products need to be thoroughly studied. Iodine has already been indicated as one of the key potential contributors to the source term for many accident scenarios. However, until now its behaviour has been poorly understood, mainly due to the fact that iodine involves highly complicated chemistry. Hence, with regards to its chemical formulation, volatility and/or containment iodine may specify the design of effective mitigation strategies and devices. Addressing this need, a FP5 Euratom project on Iodine Chemistry and Mitigation Mechanisms (ICHEMM) conducted an integrated set of experiments within this area. From these, new experimental data on iodine behaviour was derived under certain conditions directly related to severe accidents in both Pressurised Water Reactor (PWR) and Boiling Water Reactor (BWR) systems. In addition, this data enabled the improvement of existing models and the development of new ones for the inclusion in existing iodine chemistry codes. More specifically, the destruction rates of volatile forms of iodine have been quantified for the first time and may aid in determining natural mitigation processes and accident management interventions. Furthermore, the iodine behaviour of certain materials and conditions has been carefully studied offering data and models for reliable predictions on PWRs - the most common commercial power reactors worldwide.
