Refinement of the sub-Structure Method for Integral Transport Calculations

摘要

A new generalization of the interface-current method for coupling two-dimensional heterogeneous assemblies, called sub-structures, has been developed. The method has been designed for fine-structure burn-up calculations in very heterogeneous media of large size. For the calculations the medium is divided into rectangular sub-structures, which can have internal symmetries, containing rectangular and/or cylindrical structure elements, divided into homogeneous zones. A zone-wise flat or linear expansion is used to formulate a direct collision-probability problem within each sub-structure. The sub-structures are coupled by making a piece-wise uniform or linear expansion for the partial currents entering and leaving the sub-structures. The method has also been used to implement an approximate piece-wise isotropic reflexion for two dimensional x-y collision probabilities calculations. The accuracies and computing times achieved are illustrated by one-group fixed source numerical calculations for a typical 7 x 7 pin PWR assembly as well as for a set of fuel slabs imbedded in water moderator. (ERA citation 11:008794)