INTERPOLATION OF THE DILUTION GRID IN THE BENGAL CODE

Naval Nuclear Laboratory, P.O. Box 1072, Schenectady, NY 12301-1072, USA

nathan.gibson@unnpp.gov
steven.douglass@unnpp.gov

Published online: 22 February 2021

Abstract

In the implementation of the equivalence-in-dilution self-shielding method, multigroup cross sections as a function of the background cross section (i.e., the dilution) are needed. The background cross section of a particular nuclide in a particular material is determined iteratively based on geometry and material composition, resulting in a large number of cross section look-ups and a continuously varying dilution as the independent variable. Typically, multigroup cross sections are interpolated based on a reference grid of a set of dilution values and corresponding cross sections. The selection of this grid and the interpolant used between the grid are not well-documented in the literature, and so the approach used by the Bengal code is of note to the technical community. This work compares the interpolation scheme of the legacy code TRANSX to a newly developed interpolation scheme based on cubic Hermite splines, both by looking at the relative error in generated cross sections and by assessing the impact on a simple reactor simulation.