Researchers at the Czech Institute of Informatics, Robotics and Cybernetics of the Czech Technical University (CTU CIIRC) and the Institute of Physics of the Academy of Sciences of the Czech Republic (FZU AV ČR) received a patent from the European Union in April last year for their discovery that a polycrystalline diamond coating can protect nuclear fuel rods against corrosion during both normal operations and accidents. They have just been awarded a United States patent for the same discovery.
This new solution to the corrosion problem was first patented in the Czech Republic in 2015 by Radek Škoda, Jan Škarohlíd (then with the Faculty of Mechanical Engineering of the Czech Technical University) and Irena Kratochvílová, František Fendrych, Andy Taylor (from the Institute of Physics of the ASCR).
CTU CIIRC said that obtaining a U.S. patent means that they “now have access to the market of largest number of nuclear reactors in the world”. There are ninety-four nuclear reactors currently operating in the U.S. and two more under construction. They will all be able to use this patented method for protecting the surface of the nuclear fuel rods from corrosion. This will extend the life of any treated nuclear fuel rods under both emergency and standard conditions.
Kratochvílová said, “The unique solution is based on covering the surface of fuel rods with a thin polycrystalline-diamond layer. A very thin layer of diamond nanocrystals significantly worsens the conditions for corrosion of the zirconium substrate in a nuclear reactor, even by tens of a per cent.”
“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.”
CTU CIIRC said that the nuclear disaster at the Fukushima Daiichi nuclear power plant on the coast of Japan in 2011 inspired their research. Their patent application was supported by further research and extensive tests within the TA CR project in cooperation with Westinghouse. The researchers submitted their U.S. patent application in 2016 and it was approved this month by the U.S. Patent Office.
The primary goal of this research project was to reduce or entirely prevent the high-temperature oxidation of the zirconium cladding on the nuclear fuel rods in emergency situations when temperatures rose above eighteen hundred degrees Fahrenheit. During this exothermic reaction, a great amount of heat is released. Hydrogen gas is also released which can explode. Corroded zirconium clad nuclear fuel rods can crack and release radioactive materials into the primary cooling circuit. The release of heat can complicate the cooling of the core and increase the further high-temperature oxidation of the zirconium cladding on the nuclear fuel rods. According to the patent application, this type of corrosion of zirconium alloys is reduced by covering the nuclear fuel rods with a protective layer of polycrystalline-diamond.
CTU CIIRC said, “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 the corroded surface and not sufficient combustion. The solution thus significantly reduces the burden to the environment.”