Next generation nuclear power plants are meant to outperform current ones in terms of efficiency, fuel utilization, safety and waste production. Different fission reactor concepts have been proposed as GIV candidates. Lead-cooled Fast Reactors (LFRs) are particularly interesting due to the intrinsic safety features brought about by lead as coolant. However, the development of LFRs is linked to the availability of suitable materials solutions. The greatest challenges in this sense arise from the extremely corrosive environment: at the foreseen temperature - above 500°C - typical corrosion rates produced on bare steels are not acceptable and protective methods are required. In this framework, some of the most interesting solutions are based on the use of bulk alloys, surface-alloying techniques or coatings.
In the last years, researches of the IIT have studied an amorphous/nano-crystalline Al2O3 coating produced by Pulsed Laser Deposition (PLD) for liquid metal-cooled nuclear systems. Up to now, the results indicate that the PLD-grown Al2O3 is a suitable candidate for protecting steels in lead and Pb-alloys, at temperatures up to 600°C. Moreover, the alumina coatings have already been irradiated with heavy ions in previous campaigns. The positive outcome of these tests has granted ceramic coatings developed by IIT a special mention as one of the most enabling technologies for LFRs by the DOE report “Research and Development Roadmaps for LFRs”. The main feature behind these promising evidences have been identified in the amorphous/nano-crystalline structure of alumina films, which confers a unique assemble of strong adhesion, metal-like mechanical properties and radiation-tolerance. However, because these properties depend strictly on the amorphousness, further studies are required to evaluate the amorphous to crystalline transition under irradiation, and how to control it. The stabilization of the pristine alumina seems even more relevant now since industrial companies such as Westinghouse aim to increase further the operation temperature, up to 800°C. In order to allow these economic advantages and push forward the technological development, new solutions are demanded.
In this framework, we propose chemical doping as a valid strategy to tune the crystallization kinetic of Al2O3-based protective coatings. Different compounds have been added to the pure alumina: Cr2O3 and Y2O3 have been selected to anticipate or retard, respectively, the crystallization threshold. In December 2018, doped alumina has been irradiated for the first time, at the IVEM-tandem facility. The most relevant result has been accomplished at 800°C, above the crystallization temperature of standard alumina. Here, Y2O3 dopant is able to preserve partially the amorphous matrix, increasing also the overall radiation-tolerance. Thanks to the stabilization effect at elevated temperatures, doping prevents the formation of the brittle alumina structure, tackling traditional phenomena under irradiation such as voids formation and intergranular swelling.
This project represents a continuation of the work started last year at the IVEM facility. New types and concentrations of dopant will be compared, to find the best performer in stabilizing the alumina amorphous matrix. Tests will be focused to the higher temperature levels (up to 1100°C) to assess the feasibility of Al2O3-based coatings for high-temperature nuclear power plants