Oxidation of Pb–Bi eutectic in water-oxygen fluid at elevated temperature and pressure

The paper presents the results of an investigation into the oxidation of lead–bismuth eutectic (LBE) by a high-pressure water-oxygen fluid. Tests were conducted by uniformly heating the LBE specimen at a rate of 1 K/min to 873 K in an environment of water vapor, oxygen, and H₂O/O₂ fluid, as well as by injecting H₂O/O₂ fluid into the reactor containing the LBE specimen, followed by isothermal holding at a set temperature (623–873 K) for 3 h. The results demonstrate that LBE oxidation is accelerated in both oxygen and H₂O/O₂ fluid at T > 628 K. Adding water contributes to a multiple increase in the rate of oxidation. The oxidation of LBE by oxygen results in the formation of a dense oxide layer dominated by β-PbO. When oxidized in H₂O/O₂ fluid, a sponge-like structure forms, whose main component is α-Pb₃O₄. The unreacted alloy is enriched in bismuth. Bismuth involvement in oxidation is enhanced at T ≥ 823 K and leads to the formation of plates, as well as feather- and needle-like Bi₂O₃ structures. The LBE oxidation rate has been found to exhibit a non-monotonic dependence on temperature. It is shown that the process can proceed in the non-activation kinetic mode at 653–723 K. The comparative analysis shows that LBE is more susceptible to oxidation than lead and bismuth individually. These results are important for ensuring the safe operation of lead-cooled nuclear reactors.