On-the-fly doppler broadening of unresolved resonance region cross sections via probability band interpolation
Author(s)Brown, Forrest B.; Walsh, Jonathan Alan; Forget, Benoit Robert Yves; Smith, Kord S.
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In this work we present a scheme for computing temperature-dependent unresolved resonance region cross sections in Monte Carlo neutron transport simulations. This approach relies on the generation of equiprobable cross section magnitude bands on an energy-temperature mesh. The bands are then interpolated in energy and temperature to obtain a cross section value. This is in contrast to the typical procedure of pre-generating probability tables at all temperatures present in the simulation. As part of this work, a flexible probability table generation capability is integrated into the continuous-energy neutron transport code OpenMC . Both single-level and multi-level Breit-Wigner formalisms are supported, as is modeling of the resonance structure of competitive reactions. A user-specified cross section band tolerance is enabled with batch statistics. Probability tables are generated for all 268 ENDF/B-VII.1  isotopes that have an unresolved resonance region evaluation. Integral benchmark simulations of the Big Ten critical assembly show that, for a system that is sensitive to the unresolved resonance region, a temperature interval of ∼200 K around 293.6 K is sufficient to reproduce the keff value that is obtained with probability tables generated exactly at room temperature. A finer mesh of < 50 K is required to reproduce some cross section values at the common target relative difference of 0.1%
DepartmentMassachusetts Institute of Technology. Department of Nuclear Science and Engineering
Proceedings of Physics of Reactors 2016 (PHYSOR 2016): Unifying Theory and Experiments in the 21st Century
American Nuclear Society (ANS)
Walsh, Jonathan A. et al. "On-The-Fly Doppler Broadening of Unresolved Resonance Region Cross Sections via Probability Band Interpolation." Physics of Reactors 2016 (PHYSOR 2016): Unifying Theory and Experiments in the 21st Century, 1-5 May, 2016, Sun Valley Resort, Idaho, USA, American Nuclear Society, 2016.
Author's final manuscript