Testing times: study assesses next-gen nuclear materials built with nanoscale 3D printing

In an EPSRC-funded project, researchers led by Dr Anton Shterenlikht at Bristol University are investigating the use of nano-additive manufacturing techniques to build tiny irradiated structures, known as micromechanical coupons, for structural and behavioural testing.

Interest in the use of additive manufacturing for building advanced Generation IV and fusion nuclear systems is growing, thanks to its ability to produce components in shapes that are not possible with traditional methods.

But the new materials must be tested under high temperature and radiation conditions before they can be used in the nuclear industry, and health and safety requirements prevent laboratory tests of macro-scale components.

Instead, researchers use micromechanical coupons to test the effects of irradiation on the structure of the materials, and then use modelling to extrapolate the results to the macro-scale.

These coupons are typically fabricated using Gallium or Helium Focused Ion Beam micro-milling, in which charged ions are fired at the sample to create the desired shape.

However, this method is not representative of additive manufacturing techniques, and can leave damage such as helium bubbles or gallium implantation in the components.

So in a feasibility study, the researchers are investigating the use of techniques developed in photonics to fabricate the coupons without this damage, said Shterenlikht.

For example, the researchers will be investigating the use of electron beam induced deposition to deposit materials such as tungsten, iron or carbon onto a polymer scaffold. They will then remove the polymer, and fill out the scaffold using techniques such as chemical vapour deposition to deposit individual atoms of metal or carbon, said Shterenlikht.

“The material is heated to a very high temperature until it melts and evaporates, and the vaporised atoms are deposited on the substrate,” he said.

The researchers will use modelling to create virtual cracks with a range of different topologies, which will then be manufactured into the coupons for testing.

They plan to investigate the fracture behaviour of nanometre-sized cracks in the coupons, using X-ray tomography.

If the feasibility study proves successful, the team then plans to irradiate and test the structures, and hopes to work with researchers at the Culham Centre for Fusion Energy, the National Nuclear Laboratory and the Nuclear Advanced Manufacturing Research Centre.

UK engineers are in the vanguard of efforts to develop compact nuclear reactors, otherwise known as small modular reactors. Click here to read Stuart Nathan's report