A thin film coating is no more than two microns thick. Image credit: Tomsk Polytechnic UniversityA thin film coating is no more than two microns thick. Image credit: Tomsk Polytechnic UniversityIn an effort to reduce hydrogenation of containers where nuclear fuel is stored and to protect reactors from a Fukushima-like radiation disaster, physicists from Tomsk Polytechnic University are developing protective titanium nitride-based coatings for shells of fuel elements (fuel rods) of nuclear reactors.

"In reactors, nuclear fuel is laid in special 'tubes' out of zirconium alloys, to form fuel rods. In the fuel rods, a nuclear reaction takes place. As a result of radiolysis of a reactor coolant—water, and also as a result of interaction of the coolant and zirconium under high temperatures hydrogen is released. Hydrogen is able to accumulate in fuel rods shells causing degradation of their mechanical properties and destruction," clarifies one of the developers, an assistant at the Department of General Physics Egor Kashkarov.

This was demonstrated at Fukushima-1 station in Japan. Due to the flooding of pumping equipment, the active zone of the reactor warmed up to more than 1,200 °C, a steam-zirconium reaction proceeded swiftly and a large amount of hydrogen was released. This resulted in one of the biggest radiation accidents in the world.

To help prevent something like that from happening again, researchers are creating protective titanium nitride-based coatings that will be a barrier protecting zirconium fuel rods from water and hydrogen accumulation.

"During tests, titanium nitride has proved itself well: it has high hardness, wear resistance, heat resistance and inertia. We also found that it protects well from hydrogen penetration into the material, what is critical for nuclear energy. The coatings can reduce hydrogen penetration in zirconium alloy," adds Egor Kashkarov.

Applying the coatings on the zirconium substrate using magnetron sputtering and vacuum arc deposition result in a thin film coating—no more than two microns thick.

"One of the applications of the elaborating coatings out of titanium nitride is next generation reactors and thermal nuclear reactors where hydrogen impermeable coating is a pressing issue. In the next generation reactors, temperature is supposed to increase up to 400-450 °C to improve fuel burn-up efficiency. Consequently, hydrogenation of fuel rods will be happen much faster. Our coatings are able to avoid this,” says Kashkarov.