Scientists from the Czech Institute of Informatics, Robotics and Cybernetics of the Czech Technical University (CIIRC CVUT) and the Institute of Physics of the Czech Academy of Sciences (FZU AV CR) have obtained an American patent for a method of protecting the surface of fuel rods from corrosion, which will extend the life of fuel rods under both emergency and standard conditions. The method was patented in the Czech Republic in 2015 and was granted a European patent in April 2020.

“The unique solution is based on covering the surface of fuel cells with a thin polycrystalline diamond layer. A very thin layer of diamond nanocrystals significantly lessens the conditions for corrosion of the zirconium substrate in a nuclear reactor,” explained associate professor Irena Kratochvílová from the Institute of Physics. “The anti-corrosion effect of a polycrystalline diamond coating is very specific: in addition to limiting the direct contact of the metal substrate with the environment, carbon penetrates from the diamond layer into the substrate with increasing temperature and changes its physical and chemical properties. This reduces the probability of zirconium corrosion and water penetration.”

The nuclear accident in Fukushima inspired research in this area. The primary goal was to reduce or prevent high-temperature oxidation of zirconium in emergency situations with temperatures above 800 ° C. During this exothermic reaction, a huge amount of heat is released, but also hydrogen, which can explode, and corroded zirconium rods can crack and release radioactive substances into the primary circuit. The release of heat also further complicates the cooling of the core and enhances the further course of high-temperature oxidation of the zirconium alloy.

This this type of corrosion of zirconium alloys is reduced by covering the outer surface of the nuclear fuel with a protective layer consisting of a polycrystalline diamond layer. Further research has confirmed the considerable potential of this solution even at reactor operating temperatures, thereby extending the service life of the fuel, which is typically removed from the reactor due to a corroded surface before all the fuel is burned. The solution thus significantly reduces the environmental burden. The patent was supported by further research and extensive tests in cooperation with US company Westinghouse. Researchers applied for a US patent in 2016, and it has now been confirmed by the US Patent Office (USPTO).

“The United States is the country with the largest market for nuclear fuel, because it produces about 30% of the world’s nuclear electricity and the country has the most nuclear reactors in the world,” said associate professor Radek Škoda, one of the authors of the patent, who works at CIIRC CVUT. “Obtaining an American patent was an important milestone for us. This gives us the opportunity to apply our patented solution in this important market as well.”