Analysis of erbium diffusion in zirconium-niobium alloys using neutron imaging and laser-induced breakdown spectroscopy

Abstract

Due to its high neutron absorption, Erbium can be incorporated as a burnable poison in a proposed three layered fuel cladding made of zirconium alloys. Control of Er diffusion between the different layers is important to ensure mechanical and corrosion performance. Here, diffusion coefficients of Er in a Zr alloy and pure Nb at 1000°C were determined using neutron imaging (NI) and laser-induced breakdown spectroscopy (LIBS). In Zr-20%Nb, values of D were found using NI and LIBS, respectively, sampling very different volumes of material. The diffusion coefficient of Er in Nb measured by NI, D=(2.6±0.07)x10−16 m2.s−1, is more than two orders of magnitude smaller than in Zr20%Nb (wt.%), as measured by NI, D=(4.59±0.02)x10−14 m2.s−1, and LIBS, D=(4.8± 0.5) x10−14 m2.s−1. The spatial resolution of NI revealed that diffusion of Er occurred by the growth of a layer of 12% Er concentration from the Er/Zr20%Nb surface. These results show that NI is an adequate technique to study the diffusion of Er or other burnable poisons in nuclear fuel cladding.