The Method of Subgroups in the Calculation of Shielded Cross-Sections for WIMS-AECL

Abstract

The subgroups method provides a means of obtaining a spatial structure across a lattice cell of the neutron cross sections at resonance energies. This feature is absent in the equivalence principle that is currently employed by WIMS-AECL in obtaining shielded cross sections for heterogeneous cells. In addition, the calculation of the shielded cross sections by the method of subgroups is independent of the spatial geometry of a lattice cell, provided the collision probabilities are calculable. The method is therefore intended to be implemented in WIMS-AECL for the resonance treatment. A mechanism of implementing the method of subgroups into the calculation of shielded cross sections is presented. Preliminary results of the calculated shielded cross sections for 91Zr in pressure tubes in a CANDU lattice from the subgroups method and MCNP calculations are shown and discussed.