ABSTRACT
Complex mechanistic codes have been developed to model the physical and chemical characteristics of the radioactive materials transported through a nuclear power plant during the course of a severe reactor accident. However, a significant source of uncertainty in such calculations is the interaction of labile fission product vapours with aerosols generated from other reactor materials within the overheated region of the core. The surface area of these aerosols could be approximately 500 times greater than the total surface area of the primary circuit, implying that fission product vapour-aerosol interactions could dominate the transport behaviour of the radioactive emission.
An induction furnace and associated equipment have been incorporated within a glove box system (Falcon) to study the transport of fission products and aerosols as they pass from the high-temperature reducing conditions of the primary circuit to the predominantly oxidising and steam-condensing environment in the containment. The furnace has been used to heat simulant and trace-irradiated UO2 fuel samples clad in Zircaloy. The resulting airborne debris has been characterised in studies with thermal gradient tubes, filter samplers and a stainless steel containment vessel, using analytical techniques such as gamma-ray spectroscopy, aerosol particle-size analysers and scanning electron microscopy. These experiments have been conducted in the presence and absence of substantial concentrations of aerosol generated by heating silver-indium-cadmium control rod alloy clad in stainless steel. The data have been analysed in terms of the overall vapour and aerosol deposition profiles and their microscopic features.
