Hydrogen isotope permeability of reduced activation ferritic/martensitic steel CLF-1 corroded by Li4SiO4

Abstract

In a solid tritium breeding blanket, Li4SiO4 is in contact with reduced activation ferritic/martensitic (RAFM) steel at high temperatures for years and forms a corrosion layer. The effects of the corrosion layer on the hydrogen isotope permeability of a RAFM steel CLF-1 were thus investigated. X-ray diffraction, secondary ion mass spectroscopy and spherical aberration corrected transmission electron microscopy demonstrated the formation of a three-layered corrosion product, comprising a middle layer of LiFeO2 and an inner layer of LiCrO2. Li4SiO4 powder with the (104) crystal plane orientation was adsorbed on the outermost surface of the CLF-1, forming a nanoscale layer with a thickness of ∼150 nm. Deuterium permeation tests show that the deuterium permeability of the corroded samples was two orders of magnitude higher than that of the blank substrate that was pre-heated for 30 days, but one order of magnitude lower than that of the blank substrate that was not preheated. The CLF-1 corroded for 10 days exhibited the highest deuterium permeation flux. There was a decrease in the deuterium permeability of the steel that corroded for 15 and 30 days; thus, there was a decrease in the permeability with an increase in the corrosion period. By the weighting method and TEM analysis, a cracking and reoxidation process was proposed to explain the decreasing deuterium permeability of CLF-1 during corrosion by Li4SiO4. Our study provides a promising approach for preventing tritium permeation.