Firstly, the present study consists in the determination of corrosion products formed at the interface between a liquid lead bath and T91 steel at the working temperatures of the nuclear ADS reactor prototype (350 and 600 degreesC). At 350 degreesC, a Fe2O3 thin layer was detected on T91 side and PbO or Bi25FeO40 on lead side. At 600 degreesC, the corrosion layer is mainly composed of Fe(Fe(1-x)Crx)(2)O-4 spinel phase. It seemed that Bi additions in liquid lead accelerated the T91 steel corrosion kinetic. Secondly, these results led us to investigate the quaternary system Bi-Fe-O-Pb in order to investigate the formation of low melting point oxygenated compounds which could accelerate the container wear. In particular, the thermodynamic approach of the ternary subsystem Bi-Fe-O and of the isoplethal section Bi2O3-Fe2O3 was performed. This work shows that no compound melts below 792 degreesC.