Advancing the STS Neutron Moderator Optimization with an Automated Workflow and Unstructured Mesh Modeling

With the Second Target Station approaching its final design phase, a detailed neutronics evaluation of its critical components is indispensable. Optimizing the dimensions of the two cold-source moderators, that are at the heart of this facility, presents a multi-objective optimization problem for which an accurate geometric description is crucial. We have applied a fully automated optimization workflow in which a detailed unstructured mesh geometry is automatically generated with Attila4MC, starting from a parametrized CREO geometry followed by pre-processing with SpaceClaim. With this geometry, an MCNP run is performed to calculate the brightness metrics, which are subsequently provided to the optimization algorithm in DAKOTA that provides new parameters and drives the optimization loop until convergence. In this paper, we show the results of the simulations that are used for the final design of the cylindrical and tube moderator, which provide a refinement to and confirmation of the conclusions of the previous design iteration. We demonstrate that this high-fidelity optimization workflow is an efficient tool for a thorough evaluation of design changes. It is a valuable tool in the Second Target Station project and has the potential to be applied to many other nuclear systems.