United States Nuclear Regulatory Commission - Protecting People and the Environment

Crack Growth Rate and Fracture Toughness Tests on Irradiated Cast Stainless Steels (NUREG/CR-7184)

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Publication Information

Manuscript Completed: March 2015
Date Published: July 2015

Prepared by:
Y. Chen, B. Alexandreanu, and K. Natesan

Nuclear Engineering Division
Argonne National Laboratory

Appajosula S. Rao, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

Cast austenitic stainless steel, which has a ferrite-austenite duplex microstructure, is used in the cooling system of light water reactors for components with complex shapes, such as pump casings, valve bodies, and coolant piping. In the present study, crack growth rate and fracture toughness J-R curve tests were performed on irradiated cast stainless steels and unirradiated control samples in low-corrosion-potential environments (high-purity water with low dissolved oxygen or simulated pressurized water reactor) at 320°C. Both as-received and thermally aged materials were included to investigate the combined effect of thermal aging and irradiation embrittlement on the fracture behavior of cast stainless steels. The samples were irradiated to approximately 0.08 dpa at the Halden reactor. Good resistance to corrosion fatigue and stress corrosion cracking was observed for all cast stainless steel specimens. Thermal aging had little effect on the crack growth behavior at 0.08 dpa. Cleavage-like fracture was the dominant cracking morphology during the crack growth rate tests, and the ferrite phase was deformed to a lesser extent compared with the surrounding austenite phase. The fracture toughness results showed a dominant effect of neutron irradiation, and the fracture resistances were decreased considerably for all cast specimens regardless of their thermal aging. The reduction in fracture toughness was more significant in the unaged than thermally aged specimens. Nonetheless, the fracture toughness values of thermally aged specimens were 20-30% lower than their unaged counterparts, suggesting a combined effect of thermal aging and neutron irradiation in cast stainless steel.

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