Proton Irradiation-Decelerated Intergranular Corrosion of Ni-Cr Alloys in Molten Salt

Abstract

The effects of ionizing radiation on materials often reduce to "bad news." Radiation damage usually leads to detrimental effects such as embrittlement 1 , accelerated creep 2 , phase instability 3 , and radiationaltered corrosion 4 . This last point merits special attention. Elucidating synergies between radiation and corrosion has been one of the most challenging tasks impeding the deployment of advanced reactors 5 , stemming from the combined effects of high temperature, corrosive coolants, and intense particle fluxes 6 . Here we report that proton irradiation significantly and repeatably decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 • C. We demonstrate this effect by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by the proton irradiation alone. Interstitial defects generated from proton irradiation result in radiation-enhanced diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that in industrially-relevant scenarios irradiation can have a positive impact, challenging our view that radiation damage always results in negative effects.It has been well established that radiation accelerates corrosion of structural materials in today's reactors 7 , as in-core experiments 8 and accelerator studies 9 have shown. However, multiple competing mechanisms may be present 10 . An overall increase in corrosion rate does not necessarily mean that each mechanism at play accelerates corrosion. The mechanisms and their relative strengths will necessarily change in different working fluids. In fact, observations of structural materials from the Molten Salt Reactor Experiment showed low corrosion rates 11 . This suggests that the influence of irradiation on corrosion in molten salts might be different from that in water-based systems. However, the reason(s) for this potential synergy have remained hidden for more than half a century.