Diffusion and reaction-diffusion in the Er-Nb-Zr system

In the context of increasing the burn level in nuclear power generation, the incorporation of burnable poisons in the alloys of the sheaths that compose the fuel elements is presented. In particular, the incorporation of Er, one of the so-called rare earths, was studied as a burnable poison in Zr base alloys. Given the lack of diffusive data on the Er-Nb-Zr system the present work focused on providing basic information for the understanding of the metallurgical processes involved in the formation of the Er-Zr alloy and its subsequent interaction with the different layers that constitute the fuel element, considering the mobility of alloys such as Nb. In the first stage of technological interest, the interdiffusion of the following systems was studied, based on two sample arrangements: Zr20% Nb / Er / Nb and Zr2.5% Nb / Er / Zy4. They were heat treated at 1000 °C for 3 months. Then, the Laser Induced Breakdown Spectroscopy (LIBS) technique was used to measure the interdiffusion profiles, as well as XRD to identify the present phases, implementing a successive step measurement method to enable the characterization of the entire interface area. In particular, diffusion of Er in the Zr2.5%Nb alloy and diffusion profiles were made at infinite dilution at 900 °C using the LIBS technique. In addition, a characterization of the pure Er used was performed. It involved a metallographic inspection and an impurities analusis through scanning electron microscopy (SEM) mapping and X-ray fluorescence (FRX), and it was possible to determine the presence of Ta. In turn, an analysis of Er characteristic emission spectrum was performed by LIBS technique. (author)