WORKSHOP ON AEROSOL BEHAVIOUR AND THERMAL- HYDRAULICS IN THE CONTAINMENT Organized by OECDNUCLEARENERGYAGENCY in collaboration with COMMISSION OF THE EUROPEAN COMMUNITIES and COMMISSARIAT A L'ENERGIE ATOMIQUE

Humid conditions are expected in the containment during severe LWR accidents. In these conditions steam can condense on the containment structures and on existing aerosol particles or new particles may be formed by water vapor nucleation. In this paper the relative importance of each of these phenomena is evaluated. A mechanistic approach (NAUA-HYGRDS code) by solving the aerosol General Dynamic Equation [1] and a special correlation method (MAAP 3.0B code) based on aerosol similarity solution technique [e.g. 1,2,3] are considered here in the analysis of aerosol behavior in a well mixed volume. The calculated results are compared with the measured results of aerosol behavior in the Light Water Aerosol Containment Experiments (LACE) [4] to validate the aerosol models applied for severe accident analyses. The codes were applied to Laviisa (VVER-440 reactor with an ice condenser containment) AB sequence for analysing aerosol behavior in very humid containment conditions. The thermal-hydraulics and aerosol source to the containment calculated by MAAP were used as input for the NAUA-HYGRDS code and the results of aerosol behavior calculations were compared. A sensitivity analysis using the NAUA-HYGRDS code was carried out for studying the effects of iilitial particle size distribution, fixed and moving grid assumptions and the release of boric acid seeds from a PWR primary coolant. The relevance of the MAAP assumption that new water droplets are formed at supersaturated conditions is also discussed.