What is a common irradiation-induced change that reduces fracture toughness in RPV steels?

• A. Radiation-induced embrittlement with a shift of the ductile-to-brittle transition temperature.
• B. Increase in toughness.
• C. No change in properties.
• D. Grain growth enhancing ductility.

Answer: (A)

Radiation exposure in reactor pressure vessel steels causes defect clusters and precipitates that hinder dislocation motion and crack-tip processes, making the steel harder but more brittle. This manifests as a shift of the ductile-to-brittle transition temperature to higher values, so at a given service temperature the material exhibits lower fracture toughness and is more prone to brittle fracture. That embrittlement with a DBTT shift is the typical irradiation-driven change seen in RPVs. The other options describe effects that don’t match what irradiation does in these steels—toughness increasing, no change, or grain growth that enhances ductility—so they don’t fit the observed behavior.