Spatial Correlations in Monte Carlo Criticality Simulations
Commissariat à l’Energie Atomique, Centre de Saclay Service d’Etude des Réacteurs et de Mathématiques Appliquées (DEN/DANS/DM2S/SERMA/LTSD) F91191 Gif-sur-Yvette CEDEX, France
* Corresponding Author, E-mail: email@example.com
Temporal correlations arising in Monte Carlo criticality codes have focused the attention of both developers and practitioners for a long time. Those correlations affects the evaluation of tallies of loosely coupled systems, where the system’s typical size is very large compared to the diffusion/absorption length scale of the neutrons. These time correlations are closely related to spatial correlations, both variables being linked by the transport equation. Therefore this paper addresses the question of diagnosing spatial correlations in Monte Carlo criticality simulations. In that aim, we will propose a spatial correlation function well suited to Monte Carlo simulations, and show its use while simulating a fuel pin-cell. The results will be discussed, modeled and interpreted using the tools of branching processes of statistical mechanics. A mechanism called “neutron clustering”, affecting simulations, will be discussed in this frame.
© Owned by the authors, published by EDP Sciences, 2014