Experimental Study on Flow Technology and Steel Corrosion of Lead-Bismuth

For the feasibility study of Pb-Bi-cooled fast reactors (FR) and the Pb-Bi target of accelerator-driven nuclear transmutation systems , Pb-Bi flow technologies were developed and steel corrosion behavior in a Pb-Bi flow was investigated using a Pb-Bi circulation loop. The performance of an electro-magnetic flow meter with electrically insulated electrodes plated with Rh was better than those of conventional and tubular types. Oxygen concentration was controlled by continuous injection of Ar, H₂ and H₂O mixture gas into the Pb-Bi flow. In order to have desired oxygen potential, the partial pressure ratio of P_H2/P_H2O was chosen in the range from 0.12 to 2.2 by bubbling the mixture of Ar and H₂ in water columns at the room temperature. By injecting the mixture gas into the loop for sufficient time, the oxygen potentials measured by the oxygen sensor made of solid electrolyte ZrO₂-Y₂O₃ agreed well with those in the injected gas mixture. In the first corrosion test, steels were exposed to a Pb-Bi flow at the temperature of 550 °C, the velocity of 2 m/s and the oxygen concentration of ∼5.0×10⁻⁷ wt.% for 959 hours. It was found that the weight loss was larger in the order of SS316, low Cr steel (SCM420) and high Cr steels (STBA26, SUS405, SUS430). Corrosion was suppressed by a Cr oxide layer for high Cr steels. A porous layer was formed on SS316 surface due to high solubility of Ni in Pb-Bi. In the second corrosion test, the oxygen concentration was kept at 3.6×10⁻⁷ wt.% by injecting Ar, H₂ and H₂O mixture gas into a Pb-Bi flow, and steels were exposed to a Pb-Bi flow at the temperature of 550 °C, the velocity of 2 m/s for 1000 hours. Serious erosion damage was observed in SCM420 at the entrance, and some erosion damages appeared in low Cr steels: SCM420, F82H, STBA26 and HCM12 downstream. Crack type damage was observed on the surface of HCM12, and pitting-type damage was observed on the surface of 2 1/4Cr-1Mo steel. Some penetration of Pb-Bi into the materials appeared in some of the erosion-damaged steels.