Patent on a protective layer of zirconium alloys for nuclear reactors awarded

New strategy how to protect zirconium alloys surface against undesirable oxidation in nuclear reactors by polycrystalline diamond film was patented: Czech patent 305059 :Layer protecting the surface of zirconium alloys used in nuclear reactors and PCT (Patent Cooperation Treaty) Layer for protecting surface of zirconium alloys, Patent Number: WO2015039636-A1.

A team of Czech scientists and engineers have been working on a new technology for coating Zirconium nuclear fuel claddings that would prevent the nuclear fuel cladding surface from hot steam corrosion. This type of reaction in very strong form resulted in explosions in the 2011 Fukushima accident. Intense heat and pressure can trigger a reaction between the nuclear fuel cladding and the surrounding water steam, producing explosive hydrogen gas which can result in hydrogen-air chemical explosions. As these effects are surface related, a solution to the problem, namely how to fully utilize the advantages of the bulk of the zirconium-based material and to reinforce its surface chemical resistance, is to cover the surface with a thin film of a protective substance. Recently, many materials have been applied to protect zirconium alloys surfaces from destruction, but without any significant success. One very promising possibility is to cover zirconium alloy surface by polycrystalline diamond layer. Diamond withstands very high temperatures, has excellent thermal conductivity and low chemical reactivity and does not degrade over time. A team of scientists (I. Kratochvílová, F. Fendrych, A. Taylor) from the Institute of Physics in collaboration with Westinghouse co and Czech Technical University developed a new patented technology, protecting the surface of nuclear reactors fuel claddings with composite diamond films created by depositing a diamond layer from the gas phase in microwave plasma. The diamond layer offers many advantages - in addition to the diamond grains it contains amorphous carbon, so it is both strong and flexible providing a cladding that is mechanically durable and can adapt to thermal expansion of metallic uranium tablets that are inside it. After irradiation by an ion beam (tested in Texas A&M University), the diamond film retained satisfactory structural integrity. Even at temperatures above 850 °C, the Zircaloy2 surface could be effectively protected against corrosion caused by hot steam.

Irena Kratochvílová