Nuclear Data Covariances Workshop Summary 2020
This workshop, held at the Elliott School of International Affairs, discussed the impact of unrealistic or missing cross-section covariances in nuclear data activities. The need for complete nuclear data covariances, methods for credibility evaluation, and challenges with missing and questionable covariances were addressed. The importance of experimental data in testing credibility and improving evaluations was highlighted, along with the necessity of determining uncertainties for model and parameter impacts.
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Impact of Unrealistic or Missing Cross Section Covariances Workshop for Applied Nuclear Data Activities 2020 Elliott School of International Affairs at The George Washington University Teresa Bailey Lawrence Livermore National Laboratory March 4, 2020 LLNL-PRES-805976 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC
Distribution of data with select covariances Evaluations that include (n,el), (n,n ), (n,2n), and (n, ) covariances: Naturally abundant 2 LLNL-PRES-805976
Missing and questionable covariances Missing (n,n ), (n,2n), or (n,z) covariances: Gamma production, transport, destruction ENDF/B-VIII.0 100% abundant ENDF/B-VIII.0 100% abundant Questionable covariances: Overestimates uncertainty contribution ENDF/B-VIII.0 ENDF/B-VIII.0 ENDF/B-VIII.0 3 LLNL-PRES-805976
Low-Fi evaluations with available experimental data Could experimental data be used to test whether these are credible or improve them? Low-Fi Low-Fi Low-Fi 69% abundant 100% abundant Low-Fi Low-Fi Low-Fi 49% abundant 100% abundant 4 LLNL-PRES-805976
LLNL consensus needs for covariances Complete nuclear data covariances needed for applied UQ studies. Needs can t be established without these. Methods for determining credibility of evaluation needed: Visual validation provides initial approximation. Covariances in (n,n ), (n,2n), and (n,z) needed for many isotopes: (n,n ) and (n,2n) covariances often missing from ENDF/B-VIII.0. Some ENDF/B-VIII.0 covariances are difficult to interpret (e.g. sums like (n,2n)+(n,2np) ). (n,z) covariances frequently missing from ENDF/B-VIII.0 and Low-Fi. Approximate methods for filling in missing and bad covariances needed: Extension of Low-Fi strategy could be a useful starting point for missing reactions. Kyle Wendt will present about a machine learning technique applied to experimental data. Need for proper estimation of model and parameter uncertainties and their impact on pure theory covariances. 5 LLNL-PRES-805976
Some nuclear cross sections of interest with missing, limited, or inconsistent data Isotope Reaction Notes 9Be n-g Two lines are fitted to one point 12C/14N/16O n-n g Very limited data 58Fe n-g Very limited data 183W n-p No data to constrain the threshold 190Pt n-2n No data to constrain the threshold 190Pt n-p No data available 233U n-2n No data available 235U/239Pu n-n Incomplete energy-angle data 239U n-g Only one data point available Peer review from LANL has begun We would like help in assessing, choosing, or performing measurements with a minimum of 10% uncertainty LLNL Presented this slide last year; we will continue to update this as needed and present it 6 LLNL-PRES-805976
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