Name two main irradiation effects on stainless steels used in reactor cores.

• A. Radiation hardening and IASCC susceptibility increase.
• B. Hydrogen embrittlement and uniform corrosion.
• C. Sulfide stress cracking and fatigue.
• D. Cavitation and phase transformation.

Answer: (C)

Irradiation in reactor cores drives changes in stainless steels that show up as two main degradation modes: radiation hardening and irradiation-assisted stress corrosion cracking (IASCC). Neutron irradiation creates point defects and defect clusters in the metal’s lattice. These defects tester dislocations, so the material becomes harder and stronger but less able to deform plastically. That hardening raises the likelihood of brittle fracture under existing stresses, a phenomenon known as radiation hardening.

At the same time, irradiation alters the local chemistry and microstructure, especially at grain boundaries, in the presence of high-temperature water and applied stress. Elements can segregate at grain boundaries and the protective oxide films can become unstable, making cracks propagate more easily along grain boundaries when stressed. This enhanced susceptibility to cracking under corrosive, stressed conditions is IASCC.

So the pair that describes these irradiation-driven changes—hardening of the material and increased tendency to crack under stress in the reactor environment—best captures the two main irradiation effects on stainless steels used in reactor cores. The other options mix phenomena that aren’t the primary irradiation-induced degradation mechanisms in this context.