Modeling and Interpretation of Iodine Behavior in PHEBUS FPT-1 Containment with ASTEC and COCOSYS Codes

The Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France, and the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Germany, have been involved in the analyses and modeling of PHEBUS tests and particularly in iodine chemistry behavior in the containment. To analyze the accuracy of the chemistry models developed and reproduce volatile iodine formation, iodine behavior in PHEBUS FPT-1 containment was modeled by both IRSN and GRS with two different codes: ASTEC and COSOSYS. The ways of modeling (using the ASTEC/IODE and COCOSYS/AIM respective modules) and the nodalization of both approaches are presented and compared, as well as the assumptions made to perform the calculations. The results of the comprehensive analyses are compared with the experimental results, and interpretation of the iodine behavior in the PHEBUS FPT-1 containment is given. Then, a common point of view is concluded that highlights the lack of knowledge for some phenomena of significant impact on the iodine behavior in the containment during a severe accident. Organic iodide and iodine oxide formation models in particular are pointed out for the gaseous phase. The need for improving iodine behavior models including their coupling to thermal hydraulics and aerosol physics is also explained.