Sensitivity and Uncertainty Analysis of the Coupled Fast Reactivity Measurements Facility Central Flux Spectrum

The Coupled Fast Reactivity Measurements Facility (CFRMF) is a zoned-core critical assembly with a fast neutron spectrum zone in the center of an enriched ²³⁵U, water-moderated thermal driver. The central neutron field is a Cross-Section Evaluation Working Group benchmark for data testing of fission product, actinide, and dosimetry cross sections important to fast reactor technology. The AMPX and FORSS code systems were used to determine a covariance matrix for the CFRMF central neutron spectrum. The covariance matrix accounts for neutron cross-section and fission spectrum uncertainties and correlations. Uncertainties in the ²³⁸U inelastic-scattering cross sections and in the ²³⁵U fission spectrum were found to contribute most to the standard deviations in the central flux spectrum. The flux-spectrum covariance matrix contains strong correlations. This strongly motivates including the off-diagonal elements in data testing and cross-section adjustment applications. The flux spectrum covariance matrix was applied in this work for integral data testing for dosimeter cross sections.