The CANDLE burnup strategy is a new reactor burnup concept, where thedistributions of fuel nuclide densities, neutron flux, and power density move withthe same constant speed along the core axis from bottom to top (or from top tobottom) of the core and without any change in their shapes. Therefore, any burnupcontrol mechanisms are not required, and reactor characteristics do not changealong burnup. The reactor is simple and safe. If this burnup scheme is applied tosome neutron rich fast reactors, either natural or depleted uranium can be utilized asfresh fuel after second core and the burnup of discharged fuel is about 40%. Itmeans about 40% of natural or depleted uranium can be utilized without eitherenrichment or reprocessing.In the ideal nuclear energy utilization system, the radioactive toxicity in theenvironment should remain or decrease after the utilization. This requirement isvery severe and difficult to be satisfied. It may take too much time for its realization.The CANDLE burnup may substitute this period. Though it is a once-through fuelcycle, the discharged fuel burnup is about ten times of the present value for lightwater reactors. The space necessary for final disposal can be drastically reduced.However, in order to realize such a high burnup of discharged fuels someinnovative technologies should be developed. Either new material standing still forsuch a high burnup or intermediate recladding will be required. Especially new fueldevelopment will take a lot of time. For the time being a small reactor withCANDLE burnup may be a good option for nuclear power generation. Even thiskind of reactor requires some innovative technologies and a long period for theirdevelopments. For the first stage of CANDLE burnup the prismatic fuelhigh-temperature gas cooled reactor is preferable. Since the design of this reactorfits to the CANDLE burnup very well, only a little time is required for its researchand development
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