Impact of fission gas bubbles on thermal conductivity of UO2 fuels with high thermal conductivity additives

摘要

High thermal conductivity additives are being considered to create composite nuclear fuels with a higher effective thermal conductivity (ETC) to reduce the peak fuel temperatures during reactor operation. However, the benefits of the additive may be reduced, or possibly eliminated, when placed into a reactor environment. In this work, we investigate the impact of fission gas bubbles on the ETC of composite fuels. We create 2D simulations representing a small portion of a composite UO2 fuel containing a single additive particle and calculate the ETC with various volume fractions of fission gas bubbles. Our results show that fission gas bubbles, depending on the volume fraction and contact angle at the additive interface, can completely remove any benefit of the additive and even result in a lower thermal conductivity than in UO2 without the additive. We also expose a trend that relates the fraction of additive that is screened by bubbles to the ETC. We then propose a model which predicts the ETC of a composite fuel with fission gas bubbles to better estimate the benefits of a novel fuel design. (C) 2021 Elsevier B.V. All rights reserved.