Implementation and benchmarking of an automatic global variance reduction method on OpenMC

Abstract Shielding calculation is an important but challenging part of safety analyses for nuclear facilities due to the complex geometry and heavy shielding. In this work, an automatic Global Variance Reduction (GVR) method has been developed and implemented in OpenMC, an open-source Monte Carlo (MC) code for neutron and photon transport simulation. This GVR method is based on flux-based GVR method, improving it by defining a novel “pseudo-source”, which enhances remarkably computation efficiency. In addition, the OpenMC parallel calculation is also improved with the asynchronous scheduling function to mitigate the unbalance loading on the processes. For benchmarking this automatic GVR method, a simple thick solid sphere benchmark and a heavy shielding cuboid benchmark has been employed. An application on IFMIF-DONES Test Cell has been also adopted to demonstrate the ability of this GVR method on shielding calculations of heavy-shielded facility. These benchmarks and application show the enhancement on computation efficiency, as well as some limitations, of this newly developed GVR method.