A once-through, low enriched uranium-thorium cycle as advanced HWR intermediate option

A once-through, low-enriched uranium-thorium cycle, based on use of separate channels fuelled with UO2 and ThO2, is discussed in the paper. The reference case is a 638 Mwe CANDU-PHW reactor. Core structures for two cases (4w/o and 5.5w/o U-235) are presented. In the first, one half of the channels are fed with LEU bundles, one sixth with fresh ThO2 (first irradiation) and one third with irradiated ThO2 bundles (second irradiation); in the second, 40% are LEU channels, 20% first irradiation ThO2 and 40% second irradiation ThO2 channels. Discharge exposures amount respectively to 47/58 Mwd/Kg HE for LEU bundles and 71/72 Mwd/kg HE for ThO2 bundles. The fuel is assumed to be identical in design with that of a standard CANDU reactor, except that hollow pellets would be used both for ThO2 and LEU-UO2 elements, and that thorium rod cladding would be 0.6 mm thick. The cycle would have a lower uranium consumption than other once-through (natural uranium or slightly enriched uranium) cycles in PHW reactors, while fuel cycle costs would be comparable and fuel enrichment level is still low. (author)