Implementation of an analytical multigroup diffusion solution in 1D heterogeneous media

A preliminary ultra-fine group (UFG) cross section capability has recently been developed for both slowing down in an infinite medium and for 1D spatial diffusion in a finite medium. While the infinite medium feature is connected directly to the BNL ENDF/B cross section library, the analytical 1D spatial diffusion option is not. The primary objective of this presentation is to demonstrate the connection as well as the implementation and utility of the analytical diffusion solution. In particular, it is known that the analytical form is limited by instability of the matrix diagonalization. For this reason, just how severe and under what circumstances the stability manifests itself have become issues of investigation.