Beryllium Oxide (BeO) is a metallic oxide with a very high thermal conductivity. BeO is chemically compatible with water, UO2, and most sheath materials including zirconium alloys. In addition to its chemical compatibility, BeO is insoluble with UO2 at temperatures up to 2160°C. As a result, BeO remains as a continuous second solid phase in the UO2 fuel matrix while being in good contact with UO2 molecules at the grain boundaries. BeO has desirable thermochemical and neutronic properties, which have resulted in the use of BeO in aerospace, electrical and nuclear applications. For example, BeO has been used as the moderator and the reflector in some nuclear reactors. However, the major concern with beryllium is its toxicity. But, the requirements for safe handling of BeO are similar to those of UO2. Therefore, the toxicity of BeO is not a limiting factor in the use of this material with UO2 (Solomon et al., 2005).

Similar to other enhanced thermal-conductivity fuels, the thermal conductivity of UO2 can be increased by introducing a continuous phase of BeO at the grain boundaries. The effects of the present of such second solid phase on the thermal conductivity of UO2 is significant such that only 10% by volume of BeO would improve the thermal conductivity of the composite fuel by 50% compared to that of UO2 with 95% TD. For the purpose of this study, UO2-BeO fuel with 13.6 wt% of BeO has been examined.