CURRENT UNDERSTANDING OF THE IODINE CHEMISTRY IN REACTOR SAFETY – LESSONS LEARNT FROM THE INTERNATIONAL PHÉBUS FP PROGRAMME

R. ZEYEN, H. BRUCHERTSEIFER, R. CRIPPS, S. GUENTAY, D. JACQUEMAIN“CURRENT UNDERSTANDING OF THE IODINE CHEMISTRY IN REACTOR SAFETY – LESSONS LEARNT FROM THE INTERNATIONAL PHÉBUS FP PROGRAMME” 5th International Conference of Nuclear and Radiochemistry Sept, 3-8, 2000Pontresina – Switzerland

Several aspects of iodine behaviour have been the subject of numerous small and large scale separate-effect laboratory experiments, since iodine represents a health hazard if released in significant quantities into the environment. The experiments were conducted under well defined and ‘clean’ conditions to understand its release from degraded nuclear fuel, from gas and aqueous phases and from surfaces by heterogeneous reactions. Thermodynamic and kinetic databases have been developed and integrated in codes to predict the iodine speciation and volatility. Based on the results of the in-pile experimental programmes, e.g., HEVA-VERCORS (F), HV-VI, PBF (USA), it is generally accepted that more than 95 % of the iodine released will be in CsI form and the rest will be volatile (molecular and organoiodine). Models to predict the chemical behaviour of the fission products in the reactor coolant system piping, e.g., VICTORIA, have been developed based on the main speciation of iodine at the source and by considering all the possible reactions with participating constituents using mainly the minimisation of the Gibb’s free energies. In a series of in-pile experiments at the PHEBUS reactor in Cadarache/France the chemical behaviour of the Fission Products is studied in the framework of an international long-term research programme (F, EU, Canada, CH, Japan, Korea and USA). This PHEBUS FP programme is providing a unique source of data on fission product release, transport and chemical behaviour under prototypic core degradation conditions..... Collaborations to this work : Paul Scherrer Institute Villigen and Würenlingen, Switzerland and European Commission - Joint Research Centre Ispra, Italy