Methodology for a large Gas-Cooled Fast Reactor core design and associated neutronic uncertainties

A feasibility study of a 2400 MWth gas-cooled fast reactor using neutronic and thermo-hydraulic constraints has been performed. Previous feasibility studies [1, 2] were performed on 600 MWth cores. Considering larger cores do not imply any change in the safety approach but relax some of the design constraints on the fuel technology, on the fuel residence time and on the power density. These changes allow an enhanced economy competitiveness. The reference core has a 100 MW/m3 power density, is based on a dispersed fuel with a fuel-to-matrix volume ratio of 50/50 and achieves a breeding ratio of 1.0 without fertile blankets. This concept possesses enhanced safety features due to a large Doppler effect owing to the presence of carbon in the SiC matrix. The possibility to remove the decay heat out of the core by natural circulation of the gas under a minimum back-up pressure is kept by limiting the core pressure drop. Numerical validation of deterministic calculations by comparisons with Monte-Carlo results are presented and uncertainties due to nuclear data are quantified. It is shown that the specificities of gas-cooled fast reactors keep bias and uncertainties within reasonably limits which are sufficient for current pre-design studies. Definite uncertainties for detailed design studies will be available after the dedicated experimental program ENIGMA in the MASURCA facility be completed. (authors)