Demonstration of On-the-Fly Generation of Unresolved Resonance Region Cross Sections in a Monte Carlo Transport Code

Abstract

In this preliminary investigation we demonstrate on-the-fly computation of unresolved resonance region cross sections. The on-the-fly method is implemented and tested in the OpenMC Monte Carlo neutron transport code. Preliminary results indicate that, in simulations of a system that is known to be highly sensitive to the e↵ects of resonance structure in unresolved region cross sections, the on-the-fly treatment produces results that are in excellent agreement with those produced with the well-established probability table method. Additionally, we use the on-the-fly approach to show that accounting for the resonance structure of the competitive inelastic scattering reaction cross section can have non-negligible e↵ects for an intermediate spectrum system. Comparisons between di↵erential reaction rates and k e↵ eigenvalues obtained using infinite-dilute, probability table, and onthe-fly cross sections in simulations of the Big Ten critical assembly are presented in this initial study.

Methodology for an efficient statistical cross sections sampling in the unresolved resonance range

“…This work also has some strong implications for Monte Carlo codes that handles the unresolved resonance range on the fly, such as in reference [12]. There, the question of the number of resonances to be sampled is crucial, because too many resonances would slow down the Monte Carlo calculations.…”

Neutron Cross Section Processing Methods for Improved Integral Benchmarking of Unresolved Resonance Region Evaluations

“…Calculating URR cross sections OTF (i.e. within the Monte Carlo transport calculation) directly from temperature-independent average resonance parameters can reduce this burden significantly [8]. As an additional benefit, the need for performing the sensitivity studies that are typically required to ensure that probability tables are generated with a fine enough phase-space mesh is also eliminated because the OTF method is continuous in the energy, temperature, and cross section magnitude variables.…”

Creation of problem-dependent Doppler-broadened cross sections in the KENO Monte Carlo code

“…For twodimensional thermal moderator data, a simple unit-base interpolation scheme is used on the probability distributions of the double differential cross sections. By combining the aforementioned methods with temperature interpolation on the probability tables covering the unresolved resonance range (such as in [13]), KENO will have temperature-corrected neutron cross sections for all energy regions of interest [14].…”