How does irradiation affect diffusion and precipitation in metals used in nuclear reactors?

• A. Decreases diffusion rates and prevents irradiation-induced precipitation.
• B. Has no effect on diffusion or precipitation.
• C. Only affects diffusion but not precipitation.
• D. Increases diffusion rates and can drive irradiation-induced precipitation, altering strength and corrosion behavior.

Answer: (D)

In metals inside a reactor, neutron irradiation creates a high density of defects such as vacancies and interstitial atoms. These defects act as rapid diffusion pathways, so atoms can move more easily than they would by thermal diffusion alone. That means diffusion rates rise under irradiation.

As atoms migrate, solute atoms can aggregate and form new precipitate particles. Irradiation can also alter the solubility limits and nucleation behavior, enabling irradiation-induced precipitation that might not occur or would occur differently without radiation. The result is a microstructure with more and/or different precipitates, which changes how the material carries load and how it corrodes or responds to the reactor environment.

So irradiation increases diffusion rates and can drive irradiation-induced precipitation, altering both strength and corrosion behavior.