Characterization of TiO2 agglomerates for the investigation of aerosol hehavior in a steam generator tube rupture event

Steam generators (SG) in pressurized water reactors (PWR) are subject to research and development due to material degradation leading to a possibility of a tube leakage or rupture. Due to the complex geometry of the steam generators in PWRs, modeling of deposition of the fissions products in aerosol form is difficult. Therefore, different types of aerosol particles are used to determine particle retention in a steam generator in several experimental conditions. In order to be able to use the results from the investigation for modeling purposes, the aerosol particles need to be carefully characterized. In this work, we characterized aerosol particles used for retention tests in the steam generator in the Artist research program. The particle material was TiO2 and the particles had agglomerate structures. For the experiments, the particles were fed with a fluidized bed generator. After the generator, the particle size was measured with optical particle counters (OPC) and Berner low-pressure cascade impactors (BLPI). In addition, particles were analyzed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The aerodynamic mass median diameter (AMMD) of the agglomerate particles at the fluidized bed generator outlet as determined with low-pressure impactors was 3.0 µm. The primary particle size in the agglomerates was found to have a size range 10 - 50 nm. The particle size was also determined based on SEM micrographs and OPC. These two methods gave different number mean diameter (NMD), with NMD = 0.40 µm and NMD = 0.7 µm as determined with SEM and OPC, respectively. Fractal dimension of the agglomerates was determined by two different methods. The results can be used when applying the experimental results for modeling aerosol retention.