Candle burnup for different cores

The new burnup strategy CANDLE is proposed, and calculation procedure for its equilibrium state is presented, where the power shape does not change along passing time in this strategy, and the excess reactivity and reactivity coefficient are constant during burnup. Any control mechanism for the burnup reactivity is not required, and power control is very easy. The life of reactor can be made longer by elongating the core height. This burnup strategy can be applied to several kinds of reactors, whose infinite neutron multiplication factor changes from less than or nearly unity to considerably more than unity, and then to less than or nearly unity. In the present paper it is applied to two types of fast reactors. One is a natural uranium fueled reactor. For this reactor some fissile material such as plutonium is required only for the nuclear ignition region of the initial core, but only natural uranium is required for the other region of the initial core and for succeeding cores. The average burnup of the spent fuel is about 40 % that is equivalent to 40 % utilization of the natural uranium without the reprocessing and enrichment. The other is a long-life small reactor. Since the speed of the burning region is only 1.8 cm/y for the present design, the size of the reactor can be set small even for a very long-life reactor. This reactor also shows excellent simplicity and safety features. (author)