Heterogeneous BN equations and symmetries

In heterogeneous BN models, the interplay between symmetries leaving the material distribution invariant and the direction of the buckling vector is of key importance. A sufficient condition for the reality of the buckling-dependent multiplication factor is established, and its consequences on the symmetry properties of integrated fluxes and projected currents are outlined. A simple numerical model supports the results so established. Rules for definition of a minimum-size sub-cell for calculation are given, together with a proposal of application to a method of characteristics model.