Numerical simulation study on gas-phase oxygen control and transport characteristics in MYRRHA lead-bismuth reactor

Transient simulations were performed with an initial oxygen concentration of 1×10-6 wt.%. Comparative cases were designed to evaluate the effects of the initial oxygen concentration, cover gas oxygen control, and pre-oxidized protective layers on oxygen field evolution and uniformity during reactor start up. [Results] Without an external oxygen supply, the core develops localized oxygen depletion within several minutes.

Cover-gas oxygen control at an oxygen concentration equivalent to the initial value slows the depletion process. However, oxygen consumption in the high temperature core still exceeds oxygen replenishment, and the core oxygen concentration stabilizes at approximately 2.43×10⁻8 wt.% after about 427 s. When pre-oxidized protective layers are applied together with cover-gas oxygen control, oxygen consumption during the initial stage is markedly suppressed.

The core reaches a relatively stable state within approximately 150 s, while the uniformity and stability of the oxygen concentration field are substantially improved. [Conclusion] Optimizing the oxygen partial pressure of the cover gas and applying pre-oxidized protective layers to critical components are complementary strategies for regulating oxygen distribution in Lead-bismuth reactors. The present model provides a numerical framework and theoretical basis for the design and optimization of oxygen-control systems.