Characteristics of aerosol release from fuel cladding breakage in lead-bismuth reactors

Lead-bismuth reactors are the most promising type among the fourth-generation reactors. When the reactor operates for a long time, the fuel cladding may develop small breaches due to high temperatures and other factors, leading to the release of radioactive fission products into the coolant, which increases the radioactivity in the primary circuit. Research on the release of fission products from damaged fuel cladding in lead-bismuth reactors is important, as the findings can provide theoretical support and model foundations for source term assessment and safety system design in severe accidents involving lead-bismuth fast reactors. This paper conducts experimental studies on the release of fission gases and aerosols from damaged fuel cladding in lead-bismuth reactors, exploring the impact of different breach sizes on the release characteristics of fission gases and aerosols. The study has obtained transient release patterns of fission gases and aerosols under various conditions. By calculating the total release fraction of aerosols, the impact of breach size on aerosol removal has been assessed. Research results indicate that when a small breach occurs in the fuel cladding, the release of fission gases follows an exponential decay pattern. The release rate of iodine within the fuel cladding is consistent with the release rate of mixed fission gases. As the release progresses, the gases will be completely released to the coolant. The release characteristics of aerosols is different from those of gases; aerosols are affected by sedimentation effects, which prevent complete release. As the standing time increases, the amount of sedimentation also increases.