A proposed method for addressing large unphysical uncertainties in mubar

Nuclear Data Team, Group XCP-5, Los Alamos National Laboratory, Los Alamos NM, USA

^* Corresponding author: dkp@lanl.gov

Published online: 29 March 2023

Abstract

Mubar uncertainties in Section MF 34 MT 2 of ENDF/B-VIII.0 data are sometimes too large. Physical limitations of the bounds of mubar limit the maximum uncertainty to be < 1.0 and usually ≪ 1.0. Two ad hoc methods are proposed to artificially constrain the randomly sampled values of mubar to allowable values. The application of NJOY’s mubar covariance matrix to the “sandwich rule” is also discussed and a consistent way to apply sensitivity coefficients is described. Mubar uncertainties for the Jezebel k_eff were found to be 156 pcm – a value comparable to other evaluated cross section uncertainties.