A high-fidelity open-source neutronics model for the BABY experiment
Tritium breeding represents a critical challenge for achieving self-sustaining deuterium-tritium (D-T) fusion reactors, particularly in next-generation devices such as ARC-class tokamaks that utilize molten salt Liquid Immersion Blankets. The Build A Better Yield (BABY) blanket experiment serves as fundamental step in a staged approach toward the Liquid Immersion Blanket: Robust Accountancy (LIBRA) project, which aims to address the scientific and technological gaps in molten salt tritium breeding. In this study, a 1-liter LiF-LiCl-based molten salt tritium breeding setup is developed and analyzed using a detailed neutronic model in OpenMC. The experimental campaign directly measures the Tritium Breeding Ratio (TBR) in a high-energy neutron irradiation setup. A neutronic model in OpenMC, an open-source Monte Carlo code for neutron and photon transport simulations, is constructed to replicate the experimental conditions, accurately approximating the setup within the MIT Vault Laboratory and incorporating a D-T neutron source modeled as the A325 generator, a compact, highly efficient source of 14.1 MeV neutrons. This model evaluates tritium production contributions from both 6Li and 7Li, distinguishing between tritium generated by direct neutrons from the source and by backscattered neutrons resulting from interactions with the vault walls and structural components, such as lead bricks supporting the neutron source. The results generated by the neutronic model show good agreement with the experimental measurements obtained in the laboratory, confirming the accuracy and reliability of the simulations. The influence of lead brick configuration on tritium production is systematically investigated, identifying a setup that maximizes TBR. These findings highlight the significance of optimizing experimental geometry and material arrangement to enhance tritium breeding. Results from the BABY experiment and corresponding simulations provide critical insights into molten salt tritium breeding, paving the way for larger-scale demonstrations and ultimately contributing to the realization of tritium self-sufficiency in fusion reactors. The model presented in this work is publicly available on GitHub under the LIBRA-project organization.