Thoria Ehancement of Nuclear Reactor Safety

Abstract

The recent nuclear accident in Fukushima demonstrates that a nuclear mishap should be viewed using interdisciplinary tools. For example, the urania fuel melts not only because of enhanced neutron flux but also because its thermal conductivity degrades when it oxidizes. Here we present the application of first principles calculations to evaluate the structural, mechanical and thermal properties of traditional urania fuel and new, inherently safer thoria fuel. Knowledge of the lattice constants for higher oxidation state oxides of uranium is important in nuclear safety analysis, since the formation of U 3 O 8 in a defective fuel element can cause cracking or split the fuel sheath after disposal, due to a net 32-36% volume increase. This contrasts with thoria fuel where such oxidation does not occur during accident. The comparison between these two fuels is provided with respect to reactor safety. In an exemplary simulation we show that replacement of urania fuel by thoria prevents central melting in the fuel rod.