Compatibility aspects of the Pb-17Li martensitic steel-H2O system

A blanket with Pb-17Li molten alloy as breeder material, low activation (LA) martensitic steel as structural material and water as coolant has been considered for the SEAFP reference plant model (SEAFP Safety and Environmental Assessment of Fusion Power). In this report the compatibility aspects of this system are examined. The corrosion mechanism of martensitic steels is based on dissolution of metallic components of the material in the liquid alloy and on their precipitation in areas of reduced temperature, where the solubility limits of the metallic elements are exceeded. The corrosion rate of martensitic steel is therefore controlled by a number of physico-chemical parameters, such as the temperature at the metal-Pb-17Li alloy interface, the temperature of the cold zone, the temperature difference ΔT, the velocity of molten Pb-17Li alloy, the diffusion rates of dissolved metallic elements, etc. The existing data demonstrate that the corrosion is homogeneous and the weight loss is linear with time. The corrosion rate can be considered acceptable from the engineering point of view. Moreover, the use of aluminide coatings to decrease tritium permeability seems to increase appreciably the corrosion resistance.