An optimum refueling simulation method was developed for application to a Canada deuterium uranium 713-MW(electric) (CANDU-6) reactor. The objective of the optimization was to maintain the operating range of the zone controller unit (ZCU) water level so that the reference zone power distribution is reproduced following the refueling operation. The zone controller level on the refueling operation was estimated by the generalized perturbation method, which provides sensitivities of the zone power to an individual refueling operation and the zone controller level. By constructing a system equation of the zone power, the zone controller level was obtained, which was used to find the most suitable combination of the refueling channels. The 250-full-power-day refueling simulations showed that the channel and bundle powers are well controlled below the license limits when the ZCU water level remains in the typical operating range.