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  Discovering, Making, and Testing New Materials: SRNL’s Center For Hierarchical Waste Form Materials
  Savannah River National Laboratory researchers are building on the laboratory’s legacy of using cutting-edge science to effectively immobilize nuclear waste in innovative ways. As part of the Center for Hierarchical Waste Form Materials, SRNL is leveraging its depth of experience in radiological waste management to explore new frontiers in the industry.
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Low evaluated uncertainties compared to experimental information and a strong model impact were observed in some prompt fission neutron spectrum (PFNS) evaluations that include mean values and covariances stemming from a rigid model. Here, we show by studying the ²³⁹Pu PFNS ENDF/B-VII.1 evaluation via generalized least-squares analyses that strong model correlations in combination with the normalization condition on the estimated PFNS and its covariances result in surprisingly low evaluated uncertainties. Furthermore, the model changes the evaluated results by >1σ of combined experimental uncertainties near the average outgoing neutron energy (~2 MeV). We show both analytically and by means of representative numerical examples that the normalization condition on the spectrum and its covariances naturally leads to uncertainties reduced by a fully positively correlated scaling uncertainty.