Spent nuclear fuel out of conventional light water reactors contains significant amount of even plutonium isotopes, so called reactor grade plutonium. Excellent neutron economy of Canada deuterium uranium (CANDU) reactors can further burn reactor grade plutonium, which has been used as a booster fissile fuel material in form of mixed ThO2/ PuO2 fuel in a CANDU fuel bundle in order to assure reactor criticality. The paper investigates incineration of nuclear waste and the prospects of exploitation of rich world thorium reserves in CANDU reactors. In the present work, the criticality calculations have been performed with 3-D geometrical modeling of a CANDU reactor, where the structure of all fuel rods and bundles is represented individually. In the course of time calculations, nuclear transformation and radioactive decay of all actinide elements as well as fission products are considered. Four different fuel compositions have been selected for investigations: 95% thoria (ThO2) + 5% PuO2,. 90% ThO2 + 10% PuO2,. 85% ThO2 + 15% PuO2 and. 80% ThO2 + 20% PuO2. The latter is used for the purpose of denaturing the new U-233 fuel with U-238. The behavior of the criticality k8 and the burnup values of the reactor have been pursued by full power operation for similar to 10 years. Among the investigated four modes, 90% ThO2 + 10% PuO2 seems a reasonable choice. This mixed fuel would continue make possible extensive exploitation of thorium resources with respect to reactor criticality. Reactor will run with the same fuel charge for similar to 7 years and allow a fuel burnup similar to 55 GWd/ t. Copyright (C) 2016 John Wiley & Sons, Ltd.