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

摘要

Stainless steels have been cladded on the inner wallof the pressure vessel steel to mitigate corrosion in hightemperature water in pressurized water reactors (PWRs).Corrosion and stress corrosion cracking (SCC) resistanceof the cladding is critical for the structural integrity.Microstructure of stainless steel cladding including theinner 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 oC. PlateSSRT specimens are sliced from various locations in thecladding. There is no indication of SCC for 308L SS afterSSRT at 1x10-6/s and 3×10~(-7)/s at 325 oC. SCC is observedin 309L SS after SSRT at 3×10~(-7)/s at 325 oC, which is lesssignificant after SSRT at 1×10~(-6)/s. 309L SS is moresusceptible to SCC in PWR primary water than 308L SS.The SCC results are consistent with the results ofoxidation tests where 308L SS has a higher oxidationresistance than 309L SS in simulated PWR primary water.Ferrite in the cladding stainless steel improves theoxidation and SCC resistance. Dilution of 309L SS nearthe fusion line with low alloy steel is also thought tocontribute to the decreased SCC resistance.