Some Observations on Plug Formation During the Circulation of Metallic Slurries by Convection

Apparatus is described in which slurries of UPb₃ particles in liquid lead and ThBi2 particles in liquid bismuth were prepared and circulated by thermal convection around chrome-iron loops in the temperature range proposed for their potential use in liquid metal fuelled reactors.

The loop material was unaffected by the circulating UPb₃-liquid lead slurry and by the ThBi₂-liquid bismuth slurry when magnesium and zirconium were added to the bismuth as corrosion inhibitors. The loops eventually plugged by the accumulation and growth of slurry particles at the coldest part of the loops but not at the lowest part despite the particles being denser than the liquid. It is considered that slurry particles which have negligible solubility in the liquid should not show this effect.

The ThBi₂ liquid bismuth slurry without corrosion inhibitors attacked the hot limb of the loop and intergranular penetration of the tube walls enabled solid material to enter the liquid stream in amount considerably greater than that in solution. In this case both the mass transfer of tube wall material and the accumulation and growth of ThBi₂ particles contributed to form a plug at the coldest part of the loop.

The structures of the plugs were examined metallographically.