CAD-based neighbor search and bounding box algorithms for geometry navigation acceleration in Monte Carlo particle transport simulation

Geometry navigation plays the most fundamental role in Monte Carlo particle transport simulation. It's mainly responsible for locating a particle inside which geometry volume it is and computing the distance to the volume boundary along the certain particle trajectory during each particle history. Geometry navigation directly affects the run-time performance of the Monte Carlo particle transport simulation, especially for complicated fusion reactor models. Thus, two CAD-based geometry acceleration algorithms, the neighbor search and the bounding box, are presented for improving geometry navigation performance. The algorithms have been implemented in the Super Monte Carlo Simulation Program for Nuclear and Radiation Process (SuperMC). The fusion reactors of FDS-H and ITER benchmark models have been tested to highlight the efficiency gains that can be achieved by using the acceleration algorithms. Testing results showed that efficiency of Monte Carlo simulation can be considerably enhanced by 50% to 60% with the acceleration algorithms. (authors)