Investigation of liquid metal embrittlement of AISI 316L steels

To support the feasibility and the deployment of LFRs one of the main issues to be solved is the reliability of structural materials to be exposed to liquid metal coolant. Particularly the Liquid Metal Embrittlement (LME) of steels is of interest for nuclear reactors and spallation sources projects because structural materials for these systems are selected according to their corrosion resistance, irradiation embrittlement and compatibility with the coolant. This study was performed in the framework of MYRRHA project, a new-generation sub-critical reactor (based on the Accelerator Driving System concept) that uses Lead-Bismuth Eutectic (LBE) as coolant. LME phenomenon has been investigated by performing theoretical and experimental activity profiting and basing on the results obtained for the T91 m/f steel in contact with LBE. This paper first reviews the model of Kamdar: weak points and contradictions are highlighted. From an experimental point of view to verify the occurrence of LME, Slow Strain Rate Tensile tests were performed on the AISI 316L in LBE environment at SCK-CEN laboratories. Besides, a fracture surface analysis was carried out together with a microstructural analysis by using that Scanning Electron Microscopy. This was done in order to confirm the results obtained by the mechanical tests and to look for impurities in the metallic matrix. These impurities are an interesting feature in case of high scatter in the results. Indeed one of the difficulties was the opacity and conductivity of the medium. The methodological approach and the procedure are also duly described along with preliminary results.