(A) study on the improvement of high temperature oxidation and corrosion resistance of zircaloy using nanostructured oxide layer fabricated by anodization

Abstract

Zirconium alloys are widely used in light water reactors (LWR) fuel cladding and other fuel assembly structures due to their ability to maintain sufficient mechanical strength in high-temperature, high-pressure, high-radiation LWR environments, and high neutron economy. Recently, preventing serious deterioration of zirconium-based fuel cladding under severe accident conditions such as the Fukushima accident is one of the most important engineering goals. Strategies to use nanoporous oxide layers for zirconium-based fuel cladding in LWR to improve safety margin in the event of a serious accident are presented. The nanoporous oxide layer was designed to have oxidation resistance on the zirconium alloy metal by a simple electrochemical method called anodization. A review of the anti-oxidation and anti-corrosion behavior of zirconium alloys with nanoporous oxide layers is provided. Oxidation experiments were conducted in air and steam environments above 800$^\circ C$. Feasibility studies have been carried out to demonstrate corrosion resistance at 360$^\circ C$ and 150 bar, the normal operating conditions of nuclear power plants. The protective properties of nanoporous oxide layers in corrosive environments including Li-ions are encouraging. The role of nanoporous oxide layers in each corrosive environment was analyzed. As a result, zirconium alloys with nanoporous oxide layers exhibit an improvement in oxidation or corrosion resistance compared to bare zirconium alloys without nanoporous oxide layers. The electric field application based on the COMSOL simulation results provides a large area treatment method for anodizing cylindrical zirconium alloy tubes to form a layer of corrosion-resistant nanoporous oxide. The formed nanoporous oxide layer was chemically and mechanically stable. These findings can be used as candidates for accident tolerant fuel cladding as a joint study of nanotechnology and nuclear engineering.