Fusion Neutronics Modeling: A Comparison between DT and DD Neutronics for Stellarators

Neutronics modeling is an essential step in designing and building a blanket for a fusion reactor. The goals of the blanket are almost identical between deuterium-deuterium (DD) and deuterium-tritium (DT) reactors: shielding, heat transfer, and tritium breeding. However, due to the difference in neutron energies, different blanket designs are needed for DD and DT reactors. Since Thea Energy's first flagship stellarator device will operate with DD plasma, we investigated what those differences are. We used the OpenMC Monte Carlo particle transport code to simulate potential blanket configurations and materials for both DD and DT sources. We analyzed several performance metrics, with an emphasis on tritium breeding ratio and neutron flux distributions, to learn what design choices could be transferred from DT blankets to DD ones, and which wouldn't. These results demonstrated the varied needs of the different types of reactors, highlighted the impact that neutron energy has on neutronics, and showed areas of improvement for future iterations of blanket design. Our modeling of our stellarator design using OpenMC has contributed to deeper understanding of neutronics behaviors in a DD fusion reactor, as well as creating a foundation for future design improvements and higher fidelity modeling of our stellarator and neutron source, guiding safe and more accurate designs.