Verification of different Monte Carlo approaches for the neutronic analysis of a stellarator

•Verification of three different CAD to MCNP geometry approaches for the neutronic analysis of a stellarator.•Simplified stellarator based geometry was designed.•Approaches give the same results within statistical uncertainty.•A preferred CAD to MCNP geometry approach for the neutronic analysis of a stellarator was identified. Three different approaches were investigated for the use of CAD models with Monte Carlo transport simulations of a simplified stellarator type verification geometry. These include the traditional Constructive Solid Geometry (CSG) approach with the geometry translated into Monte Carlo representation, the use of Unstructured Mesh (UM) geometry as available with MCNP6, and the direct particle tracking technique of DAGMC. The three methods were shown to be both applicable and suitable to represent the verification geometry and provide comparable results. With regards to the later application to a real stellarator geometry, the DAGMC and the UM approaches are preferred over the CSG approach due to the inherent limitations of the latter.