Accommodation and diffusion of Nd in uranium silicide - U3Si2

Uranium silicide, U3Si2, is considered as an advanced nuclear fuel for commercial light water reactors with improved accident tolerance as well as competitive economics. Nd is employed as a local burnup indicator for conventional oxide fuels due, among other reasons, to its low mobility in the UO2 fuel matrix and its high fission product yield. As part of the studies necessary to determine whether Nd can be considered as a candidate burnup indicator in the U3Si2 concept fuel, we investigate the mobility of Nd in U3Si2. In this work, density functional theory (DFT) calculations are performed to predict the most stable accommodation sites of Nd in U3Si2, found to be within the uranium sublattice. Based on DFT calculations of binding energies and migration activation energies, we investigate Nd diffusion by computing the transport coefficients within the framework of the self-consistent mean-field method. Our calculations predict that the diffusion ratio of Nd to U is smaller in U3Si2 than in UO2. Moreover, at the individual maximum centerline temperature of the fuel, the diffusion of Nd in U3Si2 is much slower than in UO2. From this perspective, Nd represents a good candidate burnup indicator, in similarity to that in UO2.