On the creation of the new ENDF/B-VIII.0 covariance library for SCALE applications with AMPX

A new revision of the ENDF/B nuclear data library, ENDF/B-VIII.0, was released in 2018. The AMPX code system was used to generate a new covariance library based on this release for the application with the SCALE code system. The presence of invalid matrix elements required the implementation of a procedure for correcting correlation matrices in AMPX. The new covariance library was used in uncertainty analyses of a light water reactor and a sodium-cooled fast reactor fuel pin cell to assess: first the impact of the correlation matrix corrections and secondly the impact of the changes in nuclear data from ENDF/B-VII.1 to ENDF/B-VIII.0. The correction of the correlation matrices in case of invalid matrix elements led to up to a ∼ 10% decrease in uncertainties for several investigated output quantities. Updates of relevant cross section uncertainties in ENDF/B-VIII.0 data led to significant changes in various output quantities, ranging from ∼88% decreased uncertainties to up to ∼150% increased uncertainties. In particular, updates in ^235/238U n, γ, ^235/238U χ, ²³⁸U inelastic scattering, ²³⁹Pu fission, and ⁵⁶Fe and ¹⁶O elastic scattering were found to be relevant. (authors)