CHEMICAL CHARACTERIZATION OF NUCLEAR AEROSOLS BY SURFACE-ANALYSIS TECHNIQUES

The chemical species stabilised within a condensing-vapour system will determine the aerosol nucleation processes and the likely reactions and growth mechanisms of the resulting gasborne debris. Relevant chemical data are required to define the stability of these species and their reactivity so that the consequences of a severe accident in a nuclear power plant can be calculated with confidence. A number of large-scale tests have been undertaken with non-radioactive simulants to assess the resulting physicochemical phenomena, and assist in the development of computer-based codes to predict the form and magnitude of the emissions from a reactor accident on a rigorous mechanistic basis. Experiments have been conducted at Marviken in Sweden to determine the transport properties of multicomponent vapour-aerosol systems through a simplified representation of the primary circuit of a light water reactor. Aerosol samples were collected and analysed by a range of techniques to determine their elemental composition and chemical constituents, and variations in these parameters were measured as a function of particle size and depth. Analysis techniques included scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), electron probe microanalysis (EPMA), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary-ion mass spectrometry (SIMS). These studies revealed a number of important chemical effects, and demonstrated the advantages of a complementary combination of surface analysis technique to provide unique information on the composition and nature of a complex multicomponent aerosol.