LOWFIDELITY CROSS SECTION COVARIANCES FOR 219 FISSION PRODUCTS IN THE FIRST NEUTRON REGION.
Abstract
An extensive set of covariances for neutron cross sections in the energy range 5 keV20 MeV has been developed to provide initial, lowfidelity but consistent uncertainty data for nuclear criticality safety applications. The methodology for the determination of such covariances combines the nuclear reaction model code EMPIRE, which calculates sensitivity to nuclear reaction model parameters, and the Bayesian code KALMAN to propagate uncertainty of the model parameters to cross sections. Taking into account the large scale of the project (219 fission products), only partial reference to experimental data has been made. Therefore, the covariances are, to a large extent, derived from the perturbation of several critical model parameters selected through the sensitivity analysis. These parameters define optical potential, level densities and preequilibrium emission. This work represents the first attempt ever to generate nuclear data covariances on such a scale.
 Authors:
 Publication Date:
 Research Org.:
 Brookhaven National Lab. (BNL), Upton, NY (United States)
 Sponsoring Org.:
 Doe  Office Of Science
 OSTI Identifier:
 915433
 Report Number(s):
 BNL792612007IR
R&D Project: 05055; KB0301041; TRN: US0804982
 DOE Contract Number:
 DEAC0298CH10886
 Resource Type:
 Technical Report
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CRITICALITY; CROSS SECTIONS; DATA COVARIANCES; ENERGY RANGE; FISSION; FISSION PRODUCTS; NEUTRONS; NUCLEAR REACTIONS; SAFETY; SENSITIVITY; SENSITIVITY ANALYSIS; COVARIANCE; UNCERTAINTY
Citation Formats
PIGNI,M.T., HERMAN, M., OBLOZINSKY, P., and ROCHMAN, D. LOWFIDELITY CROSS SECTION COVARIANCES FOR 219 FISSION PRODUCTS IN THE FIRST NEUTRON REGION.. United States: N. p., 2007.
Web. doi:10.2172/915433.
PIGNI,M.T., HERMAN, M., OBLOZINSKY, P., & ROCHMAN, D. LOWFIDELITY CROSS SECTION COVARIANCES FOR 219 FISSION PRODUCTS IN THE FIRST NEUTRON REGION.. United States. doi:10.2172/915433.
PIGNI,M.T., HERMAN, M., OBLOZINSKY, P., and ROCHMAN, D. Fri .
"LOWFIDELITY CROSS SECTION COVARIANCES FOR 219 FISSION PRODUCTS IN THE FIRST NEUTRON REGION.". United States.
doi:10.2172/915433. https://www.osti.gov/servlets/purl/915433.
@article{osti_915433,
title = {LOWFIDELITY CROSS SECTION COVARIANCES FOR 219 FISSION PRODUCTS IN THE FIRST NEUTRON REGION.},
author = {PIGNI,M.T. and HERMAN, M. and OBLOZINSKY, P. and ROCHMAN, D.},
abstractNote = {An extensive set of covariances for neutron cross sections in the energy range 5 keV20 MeV has been developed to provide initial, lowfidelity but consistent uncertainty data for nuclear criticality safety applications. The methodology for the determination of such covariances combines the nuclear reaction model code EMPIRE, which calculates sensitivity to nuclear reaction model parameters, and the Bayesian code KALMAN to propagate uncertainty of the model parameters to cross sections. Taking into account the large scale of the project (219 fission products), only partial reference to experimental data has been made. Therefore, the covariances are, to a large extent, derived from the perturbation of several critical model parameters selected through the sensitivity analysis. These parameters define optical potential, level densities and preequilibrium emission. This work represents the first attempt ever to generate nuclear data covariances on such a scale.},
doi = {10.2172/915433},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Apr 27 00:00:00 EDT 2007},
month = {Fri Apr 27 00:00:00 EDT 2007}
}

We produced a large set of neutron cross section covariances in the energy range of 5 keV20 MeV. The present set of data on 57 structural materials and 31 heavy nuclei follows our earlier work on 219 fission product materials and completes our extensive contribution to the lowfidelity covariance project (307 materials). This project aims to provide initial, lowfidelity yet consistent estimates of covariance data for nuclear criticality safety applications. The evaluation methodology combines the nuclear reaction model code EMPIRE which calculates sensitivity to nuclear reaction model parameters, and the Bayesian code KALMAN that propagates uncertainties of the model parametersmore »

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Recent evaluations of neutron cross section covariances in the resolved resonance region reveal the need for further research in this area. Major issues include declining uncertainties in multigroup representations and proper treatment of scattering radius uncertainty. To address these issues, the present work introduces a practical method based on kernel approximation using resonance parameter uncertainties from the Atlas of Neutron Resonances. Analytical expressions derived for average cross sections in broader energy bins along with their sensitivities provide transparent tool for determining cross section uncertainties. The role of resonanceresonance and binbin correlations is specifically studied. As an example we apply thismore »