Experimental assessment of thermodynamic stability and nucleation of NiO in liquid lead-bismuth eutectic for MYRRHA

MYRRHA is an accelerator-driven system with a primary coolant of liquid lead-bismuth eutectic (LBE). Nickel, a major corrosion product released in LBE during normal operation, can potentially form oxides and intermetallic compounds with bismuth. This study focuses on the behavior of dissolved nickel and the conditions for nickel oxide (NiO) formation in LBE.

We first measured the dissolved oxygen concentration (DOC) at the NiO equilibrium from 225 to 500 °C across three levels of nickel concentration. These measurements showed a deviation from the trend expected from literature, particularly in the range of 325–400 °C. Based on the measurements, we proposed the activity coefficient of Ni in LBE within this temperature range. Secondly, we identified the conditions for NiO nucleation by cyclically varying the temperature of LBE at high nickel concentration and different DOC levels. Based on these observations, we concluded that NiO nucleation is unlikely under the MYRRHA operating conditions (200–400 °C, 10^–7–10^–6 wt.%).