Acceleration of surface tracking in Monte Carlo transport via distance caching

Abstract

A modification to the surface tracking algorithm commonly employed in Monte Carlo neutral particle transport is suggested. As nuclear reactor simulations often have multiple nested geometry levels, surface tracking algorithms must perform distance checks on each level to determine the distance to the closest surface. A simple optimisation to this procedure (which does not appear to have been previously proposed) is to store and decrement the distance to the boundary on each level during a particle flight, removing extraneous and relatively expensive distance calculations. This modified algorithm is implemented in the Monte Carlo code SCONE and compared against the standard surface tracking implementation, showing a favourable speed-up in the range of 7–20% for realistic Monte Carlo assembly geometries.