The effect of load imbalances on the performance of Monte Carlo codes in LWR analysis

A model is developed to predict the impact of particle load imbalances on the performance of domain-decomposed Monte Carlo neutron transport al-gorithms. Expressions for upper bound performance "penalties" are derived in terms of simple machine characteristics, material characterizations and initial particle distributions. The hope is that these relations can be used to evaluate tradeoffs among different memory decomposition strategies in next generation Monte Carlo codes, and perhaps as a metric for triggering particle redistribution in production codes. parameters. The results demonstrate that for the model problem good performance is expected for reasonable effective latency and bandwidth values for partition particle densities as low as 10 4 per node (e.g. on the BG/P platform). This analysis takes an impor-3