STRESS CORROSION CRACKING OF STAINLESS STEEL CLADDING LAYERS IN SIMULATED PWR PRIMARY WATER

摘要

Stainless steels have been cladded on the inner wall of the pressure vessel steel to mitigate corrosion in high temperature water in pressurized water reactors (PWRs). Corrosion and stress corrosion cracking (SCC) resistance of the cladding is critical for the structural integrity. Microstructure of stainless steel cladding including the inner 309L SS and the outer 308L SS is characterized. SCC behavior is investigated by slow strain rate tests (SSRT) in simulated PWR primary water at 325 °C. Plate SSRT specimens are sliced from various locations in the cladding. There is no indication of SCC for 308L SS after SSRT at 1×10~(-6)/s and 3×10~(-7)/s at 325 °C. SCC is observed in 309L SS after SSRT at 3×10~(-7)/s at 325 °C, which is less significant after SSRT at 1×10~(-6)/s. 309L SS is more susceptible to SCC in PWR primary water than 308L SS. The SCC results are consistent with the results of oxidation tests where 308L SS has a higher oxidation resistance than 309L SS in simulated PWR primary water. Ferrite in the cladding stainless steel improves the oxidation and SCC resistance. Dilution of 309L SS near the fusion line with low alloy steel is also thought to contribute to the decreased SCC resistance.