Effect of dpa rate on the temperature regime of void swelling in ion-irradiated pure chromium

Pure chromium is a promising candidate for coating of Zircalloy fuel rods in light water-cooled power reactors to avoid or delay hydrogen generation in accident scenarios. Void swelling of chromium is one possible contributor to coating-interface failure and needs to be studied. The effect of dpa rate on void swelling of Cr was studied using 5 MeV Fe ion irradiation to 15 peak dpa at peak dpa rates of 3.5 × 10⁻⁵, 3.5 × 10⁻⁴, and 3.5 × 10⁻³ dpa/s, at six temperatures between 350 °C and 650 °C. The post-transient (steady-state) swelling rate of pure Cr is ∼0.05%/dpa. Swelling in Cr also appeared to start at a much higher swelling rate at very low doses. The observed dependence of peak swelling temperature on dpa rate agrees well with earlier theoretical models and clearly demonstrated the well-known “temperature shift” phenomenon. After determination of the peak swelling temperatures under ion irradiation at three dpa rates we extrapolated downwards to dpa rates characteristic of both sodium-cooled fast reactors and light water-cooled reactors.