Development and testing of Neutron cross-section covariance data for SCALE 6.2

W. J. Marshall, M. L. Williams, D. Wiarda, B. T. Rearden, M. E. Dunn, D. E. Mueller, J. B. Clarity, E. L. Jones

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

15 Scopus citations

Abstract

Neutron cross-section covariance data are essential for many sensitivity/uncertainty and uncertainty quantification assessments performed both within the TSUNAMI suite and more broadly throughout the SCALE code system. The release of ENDF/B-VII.1 included a more complete set of neutron crosssection covariance data: these data form the basis for a new cross-section covariance library to be released in SCALE 6.2. A range of testing is conducted to investigate the properties of these covariance data and ensure that the data are reasonable. These tests include examination of the uncertainty in critical experiment benchmark model keff values due to nuclear data uncertainties, as well as similarity assessments of irradiated pressurized water reactor (PWR) and boiling water reactor (BWR) fuel with suites of critical experiments. The contents of the new covariance library, the testing performed, and the behavior of the new covariance data are described in this paper. The neutron cross-section covariances can be combined with a sensitivity data file generated using the TSUNAMI suite of codes within SCALE to determine the uncertainty in system keff caused by nuclear data uncertainties. The Verified, Archived Library of Inputs and Data (VALID) maintained at Oak Ridge National Laboratory (ORNL) contains over 400 critical experiment benchmark models, and sensitivity data are generated for each of these models. The nuclear data uncertainty in keff is generated for each experiment, and the resulting uncertainties are tabulated and compared to the differences in measured and calculated results. The magnitude of the uncertainty for categories of nuclides (such as actinides, fission products, and structural materials) is calculated for irradiated PWR and BWR fuel to quantify the effect of covariance library changes between the SCALE 6.1 and 6.2 libraries. One of the primary applications of sensitivity/uncertainty methods within SCALE is the assessment of similarities between benchmark experiments and safety applications. This is described by a ck value for each experiment with each application. Several studies have analyzed typical ck values for a range of critical experiments compared with hypothetical irradiated fuel applications. The ck value is sensitive to the cross-section covariance data because the contribution of each nuclide is influenced by its uncertainty; large uncertainties indicate more likely bias sources and are thus given more weight. Changes in ck values resulting from different covariance data can be used to examine and assess underlying data changes. These comparisons are performed for PWR and BWR fuel in storage and transportation systems.

Original languageEnglish
Title of host publicationICNC 2015 - International Conference on Nuclear Criticality Safety
PublisherAmerican Nuclear Society
Pages1213-1225
Number of pages13
ISBN (Electronic)9780894487231
StatePublished - 2015
Event2015 International Conference on Nuclear Criticality Safety, ICNC 2015 - Charlotte, United States
Duration: Sep 13 2015Sep 17 2015

Publication series

NameICNC 2015 - International Conference on Nuclear Criticality Safety

Conference

Conference2015 International Conference on Nuclear Criticality Safety, ICNC 2015
Country/TerritoryUnited States
CityCharlotte
Period09/13/1509/17/15

Keywords

  • Cross-section covariances
  • Cross-section uncertainty
  • Data testing

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