Power level effects on thorium-based fuels in pressure-tube heavy water reactors

Lattice and core physics modeling and calculations have been performed to quantify the impact of power/flux levels on the reactivity and achievable burnup for 35-element fuel bundles made with Pu/Th or U-233/Th. The fissile content in these bundles have been adjusted to produce on the order of 20 MWd/kg burnup in homogeneous cores in a 700-MWe-class pressure tube heavy water reactor (PT-HWR), operating on a once-through thorium (OTT) cycle. Results demonstrate that the impact of power/flux level is modest for Pu/Th fuels, but significant for U-233/Th fuels. In particular, high power/flux reduces the breeding and burnup potential of U-233/Th fuels. Thus, there may be an incentive to operate reactors with U-233/Th fuels at a lower power density, or to develop alternative refueling schemes that will lower the time-average specific power, thereby increasing burnup. (author)