Neutronic performance of natural uranium-thorium composite fuels on gas-cooled fast reactor employing modified CANDLE burn-up strategy

The modified CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy producing reactor) burn-up strategy was utilised effectively in both fast and thermal reactors. In this work, we investigated the neutronic performance of natural uranium-thorium (238U-232Th) composite fuels on a gas-cooled fast reactor employing a modified CANDLE burn-up shuffling in the radial direction. The investigation was carried out on a reactor of 450MWt with natural uranium and natural thorium composite fuels as input for the fuel cycle. The core has been subdivided into ten distinct regions directed radially. Neutronic calculations were carried out using SRAC coding, while JENDL 4.0 was used as a nuclear data library. The various volume fractions of thorium have been mixed with natural uranium as fuel to obtain the impact of natural thorium on the performance of the gas-cooled fast reactor design. The increased volume fraction of thorium caused a decrease in the effective multiplication factor but didn't affect the burn-up level significantly. The active core height has been varied to investigate its impact on reactor performance. The discharge burn-up level for 165 cm active core height is about 345 MWd/ton HM, while 170 cm active core is about 336 MWd/ton HM.