Monte Carlo criticality calculations of large, loosely-coupled problems are long known to suffer from slow convergence of the tally errors due to cycle-to-cycle fission source correlations. In several recent studies, it was suggested that these correlations could be possibly attributed to the neutron clustering phenomenon that is visible in calculations with a small number of neutrons per iteration cycle (batch size). Nevertheless, other studies have also shown the error convergence rate in such loosely-coupled problems to be batch size-independent during active criticality cycles. Here, we aim to address this inconsistency by studying the error convergence in a large number of test calculations, varying the neutron batch size from small to large. In our tests, we have observed that the presence of visible neutron clusters does not increase the cycle-to-cycle fission source correlations and does not worsen the convergence rate of the tally errors.

长期以来，众所周知，大型松散耦合问题的蒙特卡洛临界计算由于计数周期裂变源的相关性而受到计数误差缓慢收敛的困扰。在最近的几项研究中，建议将这些相关性归因于中子聚集现象，这种现象在每个迭代周期（批大小）中中子数量较少的计算中可见。但是，其他研究也表明，在主动临界周期内，此类松耦合问题的错误收敛速度与批次大小无关。在这里，我们旨在通过研究大量测试计算中的误差收敛来解决这种不一致的问题，将中子批的大小从小变大。在我们的测试中