Optimization of the thorium-uranium regime in CANDU heavy-water reactors

Two operating regimes of a heavy-water power reactor operating in a thorium-uranium fuel cycle are examined: accumulation of the required amount of 233U and self-fueling with 233U fuel. The parameters of 10 variants of the core-lattice cells of a heavy-water power reactor are calculated. The lattice spacing is kept constant and the variants differ by the number of channels, containing fuel elements or targets, and the 233U content in ThO2. Combined channels containing fuel elements and a target at the same time are examined. Preference is given to a cell variant where a cell contains three channels with fuel elements and one channel with targets. For this variant, the fuel burnup is ∼8 MW-days/kg. A large increase of the burnup, i.e., decrease of the amount of reprocessed targets, can be achieved by decreasing the minimum reactivity excess and also by changeing and increasing the complexity of the technology. For example, a large effect is expected from using combined fuel assemblies. In so doing, provisions must be made for performing complicated operation of disassembling highly active fuel assemblies consisting of fuel elements and targets.