A parametric study was performed on the thorium-to-233U breeder fuel cycle for pressurized heavy water reactors (PHWRs) similar to the existing CANDU type. The objective was to estimate the sensitivity of the thorium breeder PHWR energy cost to fuel reprocessing costs, reactor capital costs, fuel specific power, fuel-to-moderator ratio, and reactor size and to find optimal parameters to minimize the energy cost for reasonable economic assumptions. A baseline model thorium heavy water breeder reactor (THWBR) was developed from these parameters to show how an existing PHWR would perform economically if fueled only with thorium and the 233U bred and reprocessed from that thorium. This study found that the baseline model THWBR is not cost competitive with the current PHWR fuel cycle using natural uranium but may be significantly closer in cost to the natural uranium fuel cycle than models discussed in previous publications. Because the proposed thorium reactor can, with the assistance of some thorium fuel reprocessing, achieve a higher average fuel burnup than the once-through natural uranium cycle, the waste management costs will be lower while the reprocessing costs will be higher than the natural uranium fuel system. When the strategic and proliferation-resistance values are included, the thorium breeder PHWR may be competitive with natural uranium PHWRs and light water reactors in some markets. The next phase of our study is expected to show how to use novel combinations of unconventional PHWR core geometries to increase the breeding ratio and fuel burnup, decrease the reprocessing requirements, and make a thermal breeder reactor more economical.