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Sensitivity/Uncertainty Methods for Nuclear Criticality Safety Validation (NUREG/CR-7308, ORNL/TM-2024/3277)

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Publication Information

Manuscript Completed: December 2024
Date Published: April 2025

Prepared by:
William J. Marshall
Travis M. Greene
Alex M. Shaw
Cihangir Celik
Mathieu N. Dupont

Oak Ridge National Laboratory
Oak Ridge, TN 37831

Lucas Kyriazidis, NRC Project Manager

Prepared for:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice

Abstract

The computational methods used in nuclear criticality safety analyses must be validated to ensure compliance with the consensus standard for operations with fissionable material outside of reactors. This validation requires the comparison of computational results with measurements of physical systems which are neutronically similar to those used in the safety analysis being performed. To this end, this document examines  sensitivity/uncertainty (S/U) analysis methods and their applications primarily to nuclear criticality safety validation activities. This document reviews relevant prior written guidance issued between 1999 and 2015. A brief theoretical background is provided on sensitivity coefficients, methods of calculating keff sensitivity coefficients, nuclear covariance data, uncertainty analysis, and similarity assessment. Specific recommendations for using S/U methods to calculate sensitivity coefficients, confirm their accuracy, perform uncertainty analysis of validation gaps, and assess benchmark similarity are also provided. There is also a brief review of publicly available sensitivity data which can be used to perform similarity assessments. Three case studies are described demonstrating the use of S/U methods for the generation of sensitivity coefficients, similarity assessment, and validation gap margin estimation. Finally, advanced S/U capabilities are summarized, including a discussion of challenges associated with deployment of these techniques.

Page Last Reviewed/Updated Friday, April 11, 2025