ThO2–UO2 annular pins for high burnup fuels

The main purpose of this work is to investigate the use of annular fuel pins (particularly pins containing thorium dioxide) for high burnup fuel. The following parameters were eval- uated and compared between postulated mixed thorium±uranium dioxide standard and annular (9% void fraction) type fuel assemblies, as a function of burnup: the in®nite multi- plication factor, the uranium and plutonium isotopic compositions, the fuel temperature coecient of reactivity and the conversion ratio. We used the SCALE-4.3 code system. The calculation method consisted in obtaining actinide and ®ssion product number densities as functions of assembly burnup, by means of a 1-D transport calculation combined with a 0-D burnup calculation. These number densities were then used in a 3-D Monte Carlo code for obtaining k1 from two-dimensional-symmetry ``snapshotsʹʹ