November 21, 2016

X-rays, discovered in 1895, are often used to reveal broken bones and cavities. But this summer, a team of Australian researchers used x-ray imaging for a very different purpose: scanning a famous painting to search for an image hidden beneath the layers of paint. While this technique had been used previously, the team examining Edgar Degas’ Portrait of a Woman took their analysis a step further, reconstructing a secret masterpiece hidden beneath the original painting.

A TerraPower engineer examines new steel alloys under a scanning electron microscope in TerraPower’s lab.
A TerraPower engineer examines new
steel alloys under a scanning electron
microscope in TerraPower’s lab.

Just as these researchers used proven technology to take a new view of a problem, TerraPower’s team used a scanning electron microscope (SEM) – a standard piece of lab equipment in use since the 1950s – to help optimize an existing steel alloy.

SEMs use electromagnets to generate high-resolution images of an object at a molecular level. This allows researchers to get a more complete picture of the variations in a materials’ physical and chemical composition.

Using an SEM to examine samples of the steel alloy HT-9, we can identify which “grain” structures will perform better under irradiation.
Using an SEM to examine samples
of the steel alloy HT-9, we can identify
which “grain” structures will
perform better under irradiation.

TerraPower decided to use SEMs to get a closer look at the “microstructure” of steel, to see if we could develop a stronger, more radiation-tolerant steel alloy. While SEMs have been used before to view the microstructure of metals and study composition, scientists had not previously connected what factors contributed to material performance under irradiation with the differences in the microstructure of the steel.

Nuclear reactors use a lot of steel, especially in the core. Steel, while strong, can swell, bend and degrade after years of exposure to the high heat and radiation levels present in the core. With the longer anticipated lifespan of advanced reactor designs, TerraPower wanted to explore different variations for swelling-resistant steels that could last up to 60 years without any ill effects.

When TerraPower began to explore using steel for advanced reactor components, we recognized we needed to push the material further than any before. As we dug into the existing data, we recognized a correlation between the microstructure and the steel’s response to radiation exposure.

Samples of HT9, a steel alloy for use in the TWR.
Samples of HT9, a steel
alloy for use in the TWR.

Thanks to the SEM’s ability to get an extremely close look at the steel’s composition and structure, we’ve been able to identify both the desirable and undesirable microstructure, and explore and improve variations of HT9, a steel alloy originally developed during the heyday of the U.S. fast reactor program. Today, we’re working with partner organizations to irradiate samples of HT9 to further refine the alloy for use in the Traveling Wave Reactor (TWR), including expert manufacturers like Kobe Steel to create new, improved heats of the steel. As a result, we’ve been able to start fabricating components for use in the TWR, other advanced reactor designs and perhaps even other technologies.