Mechanical behaviour of structural steels in liquid lead-bismuth, for ADS nuclear facilities

Like all materials, the materials that will be used in MYRRHA will contain small cracks and defects. The effect of the liquid lead bismuth eutectic (LBE) on the fracture toughness needs to be assessed by comparing the fracture toughness in air and in LBE. Fracture toughness of T91 ferritic martensitic steel was determined by performing fracture toughness tests at 200°C and 300°C at a strain rate of 0.25mm/min in air and in LBE with and without oxygen control. Conventional methods for fracture toughness determination could not be used in LBE due to its opaque and conducting nature. Three normalization methods were applied to determine the fracture toughness in LBE: the Chaouadi method, the Donoso method and the normalization data reduction method (NDR). When comparing these methods applied to tests in air environment to conventional methods used in fracture toughness tests (unloading compliance and potential drop method), it can be concluded that the normalization methods give good results. Due to the presence of LBE, fracture toughness values will decrease if there is wetting of the steel by the liquid metal. Adequate ductility remains available to prevent brittle fracture.