Swelling of pure vanadium and V-5Cr at ∼430 °C in response to variations in neutron flux-spectra in FFTF

When irradiated at ∼400–436 °C in the FFTF fast reactor, pure vanadium swells more than does V-5Cr, a behavior opposite of that observed at 500–600 °C. The tendency of V to swell more than V-5Cr increases as the dpa rate increases. The swelling of both metals appears to be exceptionally sensitive to the dpa rate, with the initial swelling rate increasing strongly as the dpa rate decreases. If this sensitivity is not factored into the analysis of swelling data it will appear that swelling is completely unpredictable. When this sensitivity to dpa rate is recognized along with the tendency of both alloys toward self-organization via void lattice formation, then swelling of V and V-5Cr in response to irradiation becomes better understandable.