In Korea, borated stainless steel (BSS) is used as spent fuel pool (SFP) storage rack material to maintain criticality of spent fuels. Because it is difficult to replace storage rack, corrosion resistance and neutron absorbency of BSS are required for long period. However, long-term corrosion behavior of BSS is not fully understood. In this paper, long-term corrosion behavior of BSS and its oxide microstructures are investigated through accelerated corrosion experiment in simulated SFP condition. To accelerate the corrosion of steel, experiments were conducted in higher temperature based on Arrhenius equation. Detail microstructural analysis was conducted with electron microscope and energy dispersive X-ray spectroscope, and electron probe micro analyzer.
After oxidation, hematite oxide film and pitting corrosion was observed at the surface of specimens. Most of pits are found at the substrate surface because substrate has relatively lower Cr contents. Dissolution of Cr was observed at the surface of secondary phases such as (Fe, Cr)2B. Dissolution of Cr from (Fe, Cr)2B could cause dissolution of B, which is critical to maintain neutron absorption ability of material.