Differentiate IASCC from IGSCC.

• A. IASCC is irradiation-assisted SCC that occurs only in cladding.
• B. IGSCC is irradiation-induced SCC in carbon steel.
• C. IASCC and IGSCC are the same phenomenon.
• D. IASCC is irradiation-assisted SCC occurring in core stainless steels and nickel alloys under neutron irradiation; IGSCC is intergranular SCC caused by environment and stress, typically in welded stainless steels, not primarily due to irradiation.

Answer: (D)

IASCC and IGSCC are driven by different causes and occur in different materials and locations inside a reactor. IASCC is irradiation-assisted stress corrosion cracking that happens in core components made of stainless steels and nickel-based alloys when they are under neutron irradiation. The irradiation alters the metal’s microstructure and chemistry in a way that makes it more susceptible to cracking under stress in the reactor environment.

IGSCC, on the other hand, is intergranular cracking caused by the combined effects of environment and mechanical stress, typically in welded stainless steels. It progresses along grain boundaries and is not primarily driven by irradiation, though irradiation can influence materials in some cases. The key distinction is that IGSCC is about environmental attack along grain boundaries in welded zones, whereas IASCC is about irradiation-enhanced cracking in core materials.

So the best description is that IASCC occurs in core stainless steels and nickel alloys under neutron irradiation, while IGSCC is intergranular cracking due to environment and stress, usually in welded stainless steels and not primarily due to irradiation. The other statements misstate where or how IASCC or IGSCC occur.