Neutron Diagnostics Simulations for SPARC using OpenMC

This poster presents an OpenMC [1] model for neutron diagnostics simulations for the SPARC tokamak [2]. Geometries are constructed from realistic SPARC dimensions but temporarily with a simplified vessel, and the neutron emissivity profile is calculated by TRANSP [3] using SPARC's Primary Reference Discharge (PRD) parameters. The OpenMC model is verified with a CAD-based MCNP model for SPARC performed by Commonwealth Fusion Systems (CFS). The two models produce consistent tokamak hall neutron flux spectra. Three neutron diagnostics methods are modeled: neutron flux monitors (NFMs), activation foils, and neutron collimators for the neutron camera and spectrometer. U235 and B10 NFMs with appropriate shielding sleeves have flat responses with neutron energy, which makes them ideal for total neutron emission measurements, and U238 NFMs can serve as fast response detectors thanks to its insensitivity to thermal neutrons; activation foils at the front of the foil channel in the port shielding have the highest signal, and the ratio of uncollided neutron flux to total neutron flux is about 15%, which is verified by CFS's MCNP calculation; collimators perform well in filtering out scattered neutrons, and most of the scattered neutrons passing through the collimators are back-scattered by the inner surface of the vessel.