Precipitation phenomena during corrosion testing in forced-convection Pb-15.7Li loop PICOLO

•Precipitates are formed to reduce oversaturation in the cold leg of PICOLO loop.•Precipitates were collected by the magnetic trap but not completely.•The electro-magnetic pump was plugged by precipitates and highlights the risk.•Precipitates are migrating with breeder flow and can growth up to some 100 μm.•The Fe/Cr precipitates exhibit a Cr amount of 9% similar to the Eurofer composition. Several blanket concepts (e.g., HCLL, WCLL, DCLL) are based on the application of the liquid breeder Pb-15.7Li, which is in direct contact with the structural components. Compatibility testing has shown that the structural materials (e.g., Eurofer) always suffer from corrosion attack. The governing mechanism can be attributed to dissolution of the steel by the liquid breeder. A fusion device with blanket modules or also corrosion testing loops, e.g., the PICOLO loop of KIT, are non-isothermal systems. The components dissolved at higher temperature are transported with the breeder flow. At sections with cooler temperature oversaturation of the breeder will occur. Effects such as deposition, precipitate formation and transport of corrosion products will take place. Corrosion testing in PICOLO showed that such particles are formed and that they can seriously affect safe and reliable operation of Pb-15.7Li systems up to blocking of components. Thus, during maintenance work tubing sections and components were removed for analyzing the issue of corrosion product deposition. The operation conditions of the components and the loop are given in detail to assess the deposition scenarios together with the size and shape of the formed particles to support future loop design and purification measures.