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Title: Applying a Template of Expected Uncertainties to Updating 239Pu(n,f) Cross-section Covariances in the Neutron Data Standards Database

Abstract

Templates of uncertainties expected in specific measurement types were recently developed. One aim of these templates is to help evaluators in identifying (1) missing or suspiciously low uncertainties and (2) missing correlations between uncertainties of the same and different experiments, when estimating covariances for experimental data employed in their evaluations. These templates also provide realistic estimates of standard deviations and correlations for a particular uncertainty source and measurement type that can be used by evaluators in situations where they are not supplied by the experimenters. This information allows for a more comprehensive uncertainty analysis across all measurements considered in an evaluation and, thus, more realistic evaluated covariances. Here, in this work, we extend a template that is applicable to uncertainties expected in neutron-induced fission, (n,f), cross-section measurements. It is applied to improving covariances of 239Pu(n,f) cross-section measurements in the database underlying the Neutron Data Standards evaluations. This particular example was chosen since this evaluation is primarily based on experimental information. Also, some uncertainties of individual 239Pu(n,f) cross-section experiments in this database were suspected to be underestimated. The evaluated uncertainties obtained after updating the covariances in the database by means of the template indeed do increase compared to their original values.more » Even more importantly, the evaluated mean values change noticeably. These modified cross sections impact application calculations significantly, as is demonstrated by employing them in simulations of the effective neutron multiplication factor for a few selected critical assemblies. However, this updated evaluated 239Pu(n,f) cross section should not be interpreted as the final one that should replace values of the current Neutron Data Standards project. Evaluations for the Neutron Data Standards of the 239Pu(n,f) cross section must be linked to many other observables included in the associated database, most notably to cross sections for 235U(n,f), but also to those for 10B(n,α), 6Li(n,t), 238U(n,f), and 238U(n,γ), because of included measurements of the 239Pu(n,f) cross section that appear as ratios to these reactions. Some of these other reactions are correlated to further observables in the database. Hence, updating uncertainties of data sets of any of these observables can potentially impact the 239Pu(n,f) cross section. Uncertainties for all measurements of these linked physical observables have to be updated before a comprehensive evaluation of the 239Pu(n,f) cross section and its corresponding uncertainties can be provided.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3];  [4]; ORCiD logo [1];  [5];  [5];  [6];  [7];  [8];  [5]; ORCiD logo [1];  [5];  [5];  [5]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); National Nuclear Security Agency, Washington, DC (United States)
  4. International Atomic Energy Agency, Vienna (Austria)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  7. Lawrence Livermore National Laboratory, Livermore, CA 94551-0808, USA
  8. State Corporation Rosatom, Moscow (Russia). PI Atomstandart; International Atomic Energy Agency, Vienna (Austria)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1601400
Alternate Identifier(s):
OSTI ID: 1605061
Report Number(s):
LA-UR-19-23127; LLNL-JRNL-783165
Journal ID: ISSN 0090-3752
Grant/Contract Number:  
89233218CNA000001; AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Data Sheets
Additional Journal Information:
Journal Volume: 163; Journal Issue: C; Journal ID: ISSN 0090-3752
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 239Pu Neutron-induced fission cross-section; Neutron Data Standard; Uncertainty Quantification

Citation Formats

Neudecker, Denise, Smith, Donald L., Tovesson, Fredrik, Capote, Roberto, White, Morgan Curtis, Bowden, Nathaniel S., Snyder, Lucas, Carlson, Allan D., Casperson, Robert J., Pronyaev, Vladimir, Sangiorgio, Samuele, Schmitt, Kyle Thomas, Seilhan, Brandon, Walsh, Nicolas, and Younes, Walid. Applying a Template of Expected Uncertainties to Updating 239Pu(n,f) Cross-section Covariances in the Neutron Data Standards Database. United States: N. p., 2020. Web. https://doi.org/10.1016/j.nds.2019.12.005.
Neudecker, Denise, Smith, Donald L., Tovesson, Fredrik, Capote, Roberto, White, Morgan Curtis, Bowden, Nathaniel S., Snyder, Lucas, Carlson, Allan D., Casperson, Robert J., Pronyaev, Vladimir, Sangiorgio, Samuele, Schmitt, Kyle Thomas, Seilhan, Brandon, Walsh, Nicolas, & Younes, Walid. Applying a Template of Expected Uncertainties to Updating 239Pu(n,f) Cross-section Covariances in the Neutron Data Standards Database. United States. https://doi.org/10.1016/j.nds.2019.12.005
Neudecker, Denise, Smith, Donald L., Tovesson, Fredrik, Capote, Roberto, White, Morgan Curtis, Bowden, Nathaniel S., Snyder, Lucas, Carlson, Allan D., Casperson, Robert J., Pronyaev, Vladimir, Sangiorgio, Samuele, Schmitt, Kyle Thomas, Seilhan, Brandon, Walsh, Nicolas, and Younes, Walid. Mon . "Applying a Template of Expected Uncertainties to Updating 239Pu(n,f) Cross-section Covariances in the Neutron Data Standards Database". United States. https://doi.org/10.1016/j.nds.2019.12.005. https://www.osti.gov/servlets/purl/1601400.
@article{osti_1601400,
title = {Applying a Template of Expected Uncertainties to Updating 239Pu(n,f) Cross-section Covariances in the Neutron Data Standards Database},
author = {Neudecker, Denise and Smith, Donald L. and Tovesson, Fredrik and Capote, Roberto and White, Morgan Curtis and Bowden, Nathaniel S. and Snyder, Lucas and Carlson, Allan D. and Casperson, Robert J. and Pronyaev, Vladimir and Sangiorgio, Samuele and Schmitt, Kyle Thomas and Seilhan, Brandon and Walsh, Nicolas and Younes, Walid},
abstractNote = {Templates of uncertainties expected in specific measurement types were recently developed. One aim of these templates is to help evaluators in identifying (1) missing or suspiciously low uncertainties and (2) missing correlations between uncertainties of the same and different experiments, when estimating covariances for experimental data employed in their evaluations. These templates also provide realistic estimates of standard deviations and correlations for a particular uncertainty source and measurement type that can be used by evaluators in situations where they are not supplied by the experimenters. This information allows for a more comprehensive uncertainty analysis across all measurements considered in an evaluation and, thus, more realistic evaluated covariances. Here, in this work, we extend a template that is applicable to uncertainties expected in neutron-induced fission, (n,f), cross-section measurements. It is applied to improving covariances of 239Pu(n,f) cross-section measurements in the database underlying the Neutron Data Standards evaluations. This particular example was chosen since this evaluation is primarily based on experimental information. Also, some uncertainties of individual 239Pu(n,f) cross-section experiments in this database were suspected to be underestimated. The evaluated uncertainties obtained after updating the covariances in the database by means of the template indeed do increase compared to their original values. Even more importantly, the evaluated mean values change noticeably. These modified cross sections impact application calculations significantly, as is demonstrated by employing them in simulations of the effective neutron multiplication factor for a few selected critical assemblies. However, this updated evaluated 239Pu(n,f) cross section should not be interpreted as the final one that should replace values of the current Neutron Data Standards project. Evaluations for the Neutron Data Standards of the 239Pu(n,f) cross section must be linked to many other observables included in the associated database, most notably to cross sections for 235U(n,f), but also to those for 10B(n,α), 6Li(n,t), 238U(n,f), and 238U(n,γ), because of included measurements of the 239Pu(n,f) cross section that appear as ratios to these reactions. Some of these other reactions are correlated to further observables in the database. Hence, updating uncertainties of data sets of any of these observables can potentially impact the 239Pu(n,f) cross section. Uncertainties for all measurements of these linked physical observables have to be updated before a comprehensive evaluation of the 239Pu(n,f) cross section and its corresponding uncertainties can be provided.},
doi = {10.1016/j.nds.2019.12.005},
journal = {Nuclear Data Sheets},
number = C,
volume = 163,
place = {United States},
year = {2020},
month = {1}
}

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