An MIT and Lawrence Berkeley National Laboratory (LBNL) team has discovered that radiation isn’t always detrimental to materials.
Radiation is known for degrading materials exposed to it, hastening their deterioration and requiring replacement of key components in high-radiation environments such as nuclear reactors.
But for certain alloys that could be used in fission or fusion reactors, the opposite turned out to be true: Instead of hastening some materials’ degradation, radiation actually improves their resistance, potentially doubling the material’s useful lifetime.
According to the group’s team lead, professor Michael Short, the findings caught them off-guard: They had actually set out to find out how much radiation increases the rate of corrosion in certain alloys of nickel and chromium that can be used as cladding for nuclear fuel assemblies.
As it is impossible to measure temperatures directly at the interface between the coolant molten salt and the metal alloy surface, the scientists used a battery of sensors to do the job.
Right from the start, tests showed that corrosion seemed to be reduced rather than accelerated when it was bathed in radiation, in this case a high flux of protons.
“We repeated it dozens of times, with different conditions,” says Short, “and every time we got the same results,” showing delayed corrosion.
Careful analysis of images of the affected alloy surfaces using transmission electron microscopy, helped reveal the mechanism causing the unexpected effect.
According to the scientists, the radiation tends to create more tiny defects in the structure of the alloy, and these defects allow atoms of the metal to diffuse more easily, flowing in to quickly fill the voids that get created by the corrosive salt.
In effect, the radiation damage promotes a sort of self-healing mechanism within the metal.
According to Short, the findings could be relevant for a variety of newly proposed reactor designs that are safer and more efficient than existing designs.
These include molten-salt-cooled fission reactors, and new fusion reactors like MIT spinoff Commonwealth Fusion Systems’ ARC design.
Image and content: MIT