Void swelling

Macroscopic volume increase caused by a population of growing cavities in a material. Stable nucleation, defect supersaturation and competition among sinks determine its onset and evolution.

The derivative of volume void swelling with respect to displacement dose, $dS/dD$. It differs from a time rate; conversion requires a dose rate and a specified irradiation history.

The transient dose interval before substantial measurable cavity void swelling. Nucleation and evolution of competing defect sinks make it sensitive to starting microstructure and irradiation conditions.

A vacancy-rich cavity generated under irradiation. Its growth is governed by the balance of vacancy and interstitial fluxes and differs from a strongly gas-pressure-stabilised bubble.

In 1967, C. Cawthorne and E. J. Fulton reported electron-microscope thin-foil examinations of type316 stainless-steel fuel cladding and mechanical-test specimens irradiated in the Dounreay Fast Reactor. The work helped identify microscopic cavities in the dimensional-instability problem.^[ref]

If a fixed matrix volume $V_0$ acquires cavity volume $V_c$, then $S=V_c/V_0$ and the cavity fraction of the current total volume is $f=V_c/(V_0+V_c)$. Eliminating $V_c$ gives $S=f/(1-f)$; for small cavity fractions, $S\simeq f$.