If a steam generator tube rupture (SGTR) occurs during a severe accident in a nuclear power plant, radionuclides can be released to the atmosphere as an aerosol. The release of radioactive compounds can be prevented if these compounds are deposited on the tube walls. To quantify the fraction of aerosol particles retained in the SG and to effectively trap the radioactive aerosols during a severe accident, characteristics of particle impaction on surrounding SG tube walls must be evaluated. In this study, TiO 2 agglomerates were used for experiments. Particle breakup and bounce behavior due to impaction were evaluated by measuring aerosol number concentration as a function of particle size and by analyzing transmission electron microscopy images before and after impaction.