An experimental study on the feature and behavior of impurity particles in a 220 °C low-temperature LBE loop pipeline

Lead-bismuth eutectic (LBE) is a coolant for Generation IV Lead Fast Reactors. The fill and drain pipelines in the secondary circuit operate at low temperatures around 200 °C. During maintenance, residual impurity particles are found, posing erosion and deposition risks. Current studies focus on higher temperatures (270–660 °C) and or non-isothermal loops, leaving constant low-temperature conditions around 200 °C unreported. Therefore, we construct a large-scale LBE loop operating at 220 °C and 0.55 m/s flow velocity to investigate the features and behavior of impurity particles. After 800 h, the 316L straight pipe specimen is analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). Results exhibit intensification of intergranular corrosion, with more densely distributed cracks found on the top straight pipe, leading to 2-20 μ m grains detached into the LBE, with PbO forming 20-60 μ m agglomerates as impurity particles. Erosion holes up to 1086.60 μ m caused by micro-cutting and multiple deformations are observed at the pipe top, but not on the bottom. PbO particles are found to adhere inside erosion holes. Impacts by 10-20 μ m PbO particles cause fragmentation, driving scattered ∼ 1 μ m PbO particles to adhere to grain surfaces and ditches, forming an oxidation layer. Smaller PbO particles (40–200 nm) and their agglomerates (400–600 nm) deposited on grains are observed. After drainage, numerous ∼ 1 μ m PbO particles penetrate grain ditches at the bottom, potentially causing sustained severe oxidative corrosion. These findings demonstrate that, even at 220 °C, stricter control of impurity concentrations in LBE is necessary. • A large-scale LBE test loop operating at a low temperature of 220 °C is built. • Detached 2–20 μ m grains agglomerate with PbO forms 20–60 μ m impurity particles. • Erosion holes up to 1086.60 μ m erosion holes are observed on the top pipe. • 40–200 nm PbO particles and their 400–600 nm agglomerates deposit on the pipe. • After drainage, ∼ 1 μ m PbO particles penetrate grain ditches at the bottom pipe.