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Title: LOW-FIDELITY 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 keV-20 MeV has been developed to provide initial, low-fidelity 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 pre-equilibrium 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):
BNL-79261-2007-IR
R&D Project: 05055; KB0301041; TRN: US0804982
DOE Contract Number:
DE-AC02-98CH10886
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. LOW-FIDELITY 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. LOW-FIDELITY 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 . "LOW-FIDELITY 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 = {LOW-FIDELITY 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 keV-20 MeV has been developed to provide initial, low-fidelity 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 pre-equilibrium 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}
}

Technical Report:

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  • We produced a large set of neutron cross section covariances in the energy range of 5 keV-20 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 low-fidelity covariance project (307 materials). This project aims to provide initial, low-fidelity 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 » to cross sections. Taking into account the large scale of the project, only marginal reference to experimental data was made. The covariances were derived from the perturbation of several key model parameters selected by the sensitivity analysis. These parameters refer to the optical model potential, the level densities and the strength of the pre-equilibrium emission. This work represents the first attempt ever to generate nuclear data covariances on such a large scale.« less
  • Nuclear astrophysics and californium fission neutron spectrum averaged cross sections and their uncertainties for ENDF materials have been calculated. Absolute values were deduced with Maxwellian and Mannhart spectra, while uncertainties are based on ENDF/B-VII.1, JEFF-3.1.2, JENDL-4.0 and Low-Fidelity covariances. These quantities are compared with available data, independent benchmarks, EXFOR library, and analyzed for a wide range of cases. Recommendations for neutron cross section covariances are given and implications are discussed.
  • We present a detailed analysis of the impact of resonance parameter uncertainties on covariances for neutron capture and fission cross sections in the resolved resonance region. Our analysis uses the uncertainties available in the recently published Atlas of Neutron Resonances employing the Multi-Level Breit-Wigner formalism. We consider uncertainties on resonance energies along with those on neutron-, radiative-, and fission-widths and examine their impact on cross section uncertainties and correlations. We also study the effect of the resonance parameter correlations deduced from capture and fission kernels and illustrate our approach on several practical examples. We show that uncertainties of neutron-, radiative-more » and fission-widths are important, while the uncertainties of resonance energies can be effectively neglected. We conclude that the correlations between neutron and radiative (fission) widths should be taken into account. The multi-group cross section uncertainties can be properly generated from both the resonance parameter covariance format MF32 and the cross section covariance format MF33, though the use of MF32 is more straightforward and hence preferable.« less
  • We describe analytical formalism for estimating neutron radiative capture and elastic scattering cross section covariances in the resolved resonance region. We use capture and scattering kernels as the starting point and show how to get average cross sections in broader energy bins, derive analytical expressions for cross section sensitivities, and deduce cross section covariances from the resonance parameter uncertainties in the recently published Atlas of Neutron Resonances. The formalism elucidates the role of resonance parameter correlations which become important if several strong resonances are located in one energy group. Importance of potential scattering uncertainty as well as correlation between potentialmore » scattering and resonance scattering is also examined. Practical application of the formalism is illustrated on {sup 55}Mn(n,{gamma}) and {sup 55}Mn(n,el).« less
  • 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 resonance-resonance and bin-bin correlations is specifically studied. As an example we apply thismore » approach to estimate (n,{gamma}) and (n,el) covariances for the structural material {sup 55}Mn.« less