Improved Covariance Data Adjustment Tools for Nuclear Applications
Explore data adjustment tools for developing application-specific covariance libraries to address uncertainties in integral quantities like keff in nuclear applications. Generalized linear least squares method is utilized to adjust data and generate consistent results. Further improvements and expansions are planned for incorporating additional response types and reliable correlation coefficients.
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Presentation Transcript
Data Adjustment Tools for Improved Covariance Data B.J. Marshall and Vlad Sobes WANDA Washington, D.C. March 4, 2020 ORNL is managed by UT-Battelle, LLC for the US Department of Energy
Purpose Present adjustment tools for developing more appropriate, application-specific covariance libraries Adjustment tools are necessary since ENDF/B-VIII.0 covariance is not endorsed by CSEWG for application The use of this covariance to calculate uncertainties for integral quantities such as keffwill usually result in an overestimate of the uncertainty The recommended methodology to overcome this problem is to adjust the covariance... This is a very high-level overview Some additional details are available in published papers and reports 2
Data adjustment methods Generalized linear least squares technique can be used to adjust data and measured responses to generate consistent results Implemented in TSURFER within SCALE and Whisper with MCNP Adjusted covariances are also generated reflecting more knowledge of the uncertainties and correlations among the data Adjusted covariances can be propagated with sensitivities to estimate data-induced uncertainty in measured quantities Demonstration has used kefffor HEU benchmarks 3
Sample results: Mark Williams presentation at 2017 CSEWG 100% of the 30 cases were within the unadjusted covariance band 77% are within the adjusted band much more reasonable result Other correlations introduced in the evaluation process have not been accounted for in this analysis No general purpose tool exists to allow this sort of analysis for many application spaces 4
Future expansion Incorporate additional types of responses in adjustment process Reactivity responses from substitution experiments next logical step Other sensitivity profiles Other constraints physical constants etc. Reliable correlation coefficients among experiments Constrain adjustments of measured values 5
References M. L. Williams, D. Wiarda, and W. J. Marshall, Consistency Between ENDF/B Cross Sections and Covariances, presentation at CSEWG, Upton, NY (2017). V. Sobes, W. J. Marshall, D. Wiarda, F. Bostelmann, A. M. Holcomb, and B. T. Rearden, ENDF/B-VIII.0 Augmented Covariance Data, the first iteration, Trans. Am. Nucl. Soc.121, 1365-1368 (2019). 6
Questions? This work was supported by the Nuclear Criticality Safety Program, funded and managed by the National Nuclear Security Administration for the Department of Energy and by the US Nuclear Regulatory Commission (NRC); the presentation of the work is sponsored by the NRC.
