Corrosion performance of alloy G3 and 304L stainless steel in simulated high level waste solutions and assessment of service life of evaporator tubes

摘要

The evaporator steam tubes of high level radioactive waste evaporators at the Savannah River Site (SRS) are operated at temperatures up to approximately 150(degrees)C when immersed in caustic chemistries. The tubes are periodically thermally-shocked to produce flexure during a desalt/descale operation to recover their heat transfer characteristics. The tube materials alloy G3 and AISI Type 304L stainless steel were tested with Slow Strain Rate Tensile and U-bend specimens in high caustic (45 weight% sodium hydroxide) solutions at approximately 145(degrees)C to determine their potential susceptibility to stress corrosion cracking at bounding service conditions. Slight cracking of alloy G3 was observed in the U-bend test whereas the remaining test results did not show any evidence of stress-related environmental effects. A structural evaluation of the tubes showed that the localized stresses during the desalt/descale operation were near yield; however, the usage factor calculated per the ASME code is nearly zero for the anticipated 6000 lifetime cycles and significant growth of postulated preexisting flaws is not predicted. The desired service life of 30 years might be achievable for the tubes of the Replacement High Level Waste Evaporator and the existing evaporators made of alloy G3 and alloy G30, respectively.