Effects of environmental parameters on chloride-induced stress corrosion cracking behavior of austenitic stainless steel welds for dry storage canister application

Abstract

This study investigated the chloride-induced stress corrosion cracking (CISCC) behavior expected to occur in welds of austenitic stainless steel, which are considered candidate materials for dry storage containers for spent nuclear fuel. The behavior was studied by varying temperature, relative humidity (RH), and chloride concentration. 304L-ER308L welded plates were processed into U-bend specimens and exposed to a cyclic corrosion chamber for 12 weeks. The CISCC behavior was then analyzed using electron microscopy. A previous study by the authors confirmed that CISCC occurred in ER308L at 60 °C, 30% RH, and 0.6 M NaCl via selective corrosion of δ-ferrite. When the temperature was lowered from 60 °C to 50 °C, CISCC still occurred. However, when the humidity was reduced to 20% RH, CISCC did not happen. This can be attributed to the retardation of the deliquescence of NaCl at lower humidity, which was insufficient to promote CISCC. Furthermore, increased chloride concentration to 1.0 M resulted in the absence of CISCC and widespread surface corrosion with severe pitting corrosion because of the increase in thin film thickness.

Keywords

• Spent nuclear fuel
• Dry storage canister
• Chloride-induced stress corrosion cracking
• Austenitic stainless steel welds