Description
#3971 implements delta tracking in OpenMC, which yields fairly substantial performance improvements for certain classes of problems (namely problems with large mean free paths relative to the distance between surfaces). These include TRISO-fueled reactors and fast reactors. However, delta tracking has been shown to be quite a bit slower than surface tracking for problems with small localized absorbers relative to other geometric features (such as burnable poisons or control devices). In these problems, the majorant cross section is several orders of magnitude larger than the mean total cross section in the thermal energy region. This causes particles to move very small distances per advance event and reduces the efficiency of rejection sampling.
Hybrid delta tracking (https://doi.org/10.1016/j.anucene.2010.01.011) aims to address this problem by switching between surface tracking and delta tracking when the ratio of the total to the majorant cross section is sufficiently small. The implementation of hybrid tracking will improve the performance of TRISO-fueled reactor simulations at the assembly and whole-core scales, where burnable absorbers and control devices are added to models.
Compatibility
New tracking type with improved performance for certain problems.
Description
#3971 implements delta tracking in OpenMC, which yields fairly substantial performance improvements for certain classes of problems (namely problems with large mean free paths relative to the distance between surfaces). These include TRISO-fueled reactors and fast reactors. However, delta tracking has been shown to be quite a bit slower than surface tracking for problems with small localized absorbers relative to other geometric features (such as burnable poisons or control devices). In these problems, the majorant cross section is several orders of magnitude larger than the mean total cross section in the thermal energy region. This causes particles to move very small distances per advance event and reduces the efficiency of rejection sampling.
Hybrid delta tracking (https://doi.org/10.1016/j.anucene.2010.01.011) aims to address this problem by switching between surface tracking and delta tracking when the ratio of the total to the majorant cross section is sufficiently small. The implementation of hybrid tracking will improve the performance of TRISO-fueled reactor simulations at the assembly and whole-core scales, where burnable absorbers and control devices are added to models.
Compatibility
New tracking type with improved performance for certain problems.