Neutronic performance of CANDU reactor fuelling with ThC2/233UC2

233U isotope is used as a booster fissile fuel material in the form of mixed ThC2/233UC2 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Three different fuel compositions have been used: (1) 97% ThC2+3% 233UC2, (2) 98% ThC2+2% 233UC2 and (3) 99% ThC2+1% 233UC2. The temporal variation of the criticality k∞ and the burn‐up values of the reactor have been calculated by full‐power operation for a period of 20 years. The criticality starts by k∞=1.541, 1.355 and 0.995 for modes of (1), (2) and (3) fuel compositions, respectively. A sharp decrease in the criticality has been observed in the first 2 years as a consequence of rapid 233U burnout fuelling with (1) and (2) modes. The criticality becomes quasi‐constant after the second year and remains above k∞∼1.06 for 20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burnup could be achieved with the same fuel materials (up to 500 000 MWday t−1), provided that the fuel rod claddings would be replaced periodically (after every 500 00 or 100 000 MWday t−1). The reactor criticality will be sufficient for fuelling with (1) and (2) modes until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically. Copyright © 2010 John Wiley & Sons, Ltd.