Can Carbon Nanotubes Make Nuclear Energy Safer?

In nuclear reactors, metals exposed to high levels of radiation near the reactor core deteriorate, becoming porous and brittle. This can ultimately lead to cracking and failure.

To combat this issue, MIT researchers have found that adding a small quantity of carbon nanotubes (CNTs) to aluminum slows this breakdown considerably.

Improving Aluminum’s Stability and Strength

Helium from radiation transmutation takes up residence inside metals, causing the material to become riddled with tiny bubbles along grain boundaries, making it progressively more brittle. Despite making up less than two percent of the metal’s volume, the nanotubes can form a one-dimensional transport network to provide pathways for the helium to leak back out instead of being trapped inside.

Dragonfly trapped in amber.

After exposure to radiation in the research lab, the CNTs within the metal chemically altered to carbides. However, they still retained their slender shape, “almost like insects trapped in amber,” said Ju Li professor of materials science and engineering at MIT.

“It’s quite amazing — you don’t see a blob; they retain their morphology. It’s still one-dimensional,” he added.

The large interfacial area of the one dimensional nano-structures redirects radiation-induced point defects to recombine in the metal and prevents premature embrittlement.

The researchers demonstrated that these 1-D structures could survive 70 DPA (displacements per atom) of radiation damage. After radiation exposure, they reported pores in the control sample, but no pores in the new material. In addition, the mechanical data showed that the new material had much less embrittlement.

An example of how the carbon nanotubes are embedded in aluminum. (Image courtesy of MIT.)

Tests indicate that adding nanotubes reduces aluminum’s embrittlement by a factor of five to ten, improves its material strength by 50 percent and boosts its tensile ductility. This was accomplished by adding a mere one percent by weight of CNTs and it is also cheaply implemented since CNTs are already being manufactured at a low cost using common industrial techniques.

Mixing Carbon Nanotubes and Other Metals

Tests were only conducted on aluminum, which can only be applied to lower temperature reactors found in laboratories. Expanding research using zirconium, which is used for high-temperature reactor applications such as the cladding of nuclear fuel pellets, may open more doors for commercial use.

However, the results from using aluminum could be implemented on nuclear batteries in spacecraft as well as storage containers for nuclear waste.

“This is a development of considerable significance for nuclear materials science, where composites — particularly oxide dispersion-strengthened steels — have long been considered promising candidate materials for applications involving high temperature and high irradiation dose,” said Sergei Dudarev, professor of materials science at Oxford.

Dudarev added that the modified aluminum “proves remarkably stable under prolonged irradiation, indicating that the material is able to self-recover and partially retain its original properties after exposure to high irradiation dose at room temperature. The fact that the new material can be produced at relatively low cost is also an advantage.”

Developments like these could go a long way toward replacing fossil fuels with nuclear energy.