Modified CANDLE Burnup Calculation System, Its Evolution, and Future Development

CANDLE Burn-up has been widely investigated during the last 15 years and give excellent possibility for natural Uranum utilization without the necessity of fuel enrchment plant and fuel reprocessing plant. Modified CANDLE burn-up scheme is a slight modification of CANDLE burn-up scheme by adopting discreet regions in the core. Modified CANDLE burn-up calculation is a complex calculations because it need accurate treatment of nuclear group constants, burn-up calculations, and multigroup diffusion calculations. Another problem come from the fact that the burn-up level of fuel is very high. Therefore the fission produc treatment have to be carried out in a highly accurate apporach and alsolarge number of energy groups is applied. Large number of Fission product is considered durng simulations. The calculations are performed under iterative scheme. For 10 regions and 10 years of burn-up period, first initial power density distributions are assumed and then multi-group diffusion and burn-up calculations are conducted. After 10 years of burn-up process the fuel in the first region is moved to the second region, the fuel in the second region was moved to the third region, the fuel in the third region is moved to the forth region, and so on. The fuel in the 10th region is then taken out. The first region is filled with the fresh fuel of natural uranium. The process is repeated till equilibrium condition achieved. Modified CANDLE burnup also has evolved to radial shuffling and combined axial-radial shuffling scheme.