Study on models for mean diameter of aerosol particle for analysis of radionuclide behaviour inside containment

When high enthalpy liquid is discharged into a containment, thennal fragmentation is a dominant mechanismfor the dispersion of liquid into droplets. The currentmethodfor aerosol size estimation in the SMART code usedfor CANDU containment analysis, however, results in too small aerosol diameter because it considers only aerodynamic atomization with very fast discharging velocity. The smaller the aerosol diameter, the less is the effect of aerosol removal mechanisms. Therefore, the amount of aerosol released into environment for some of the containment isolation failure cases and the resulting dose values are very conservative. Among several models to predict the drop diameter for a high enthalpy liquid jet, an appropriate model (Koestel, Gido and Lamkin model) has been selected for aerosol size calculation and incorporated in SMART code. This updated SMART code has been assessed for WALE (Water Aerosol Leakage Experiments) for the code verification. The calculated aerosol amount released into environment is still significantly higher than the experimental value but much lower compared to those predicted by non-updated (original) SMART code. Some of CAND U DBAs (Design Basis Accidents) have been analyzed by using updated and original SMART codes. The comparison of the results shows that the amount of each radionuclide isotope released into outer atmosphere is significantly reduced with the updated SMART code.