A new method for generating probability tables in the unresolved resonance region

A new method for constructing probability tables in the unresolved resonance region (URR) has been developed. This new methodology is an extensive modification of the single-level Breit-Wigner (SLBW) pseudo-resonance pair sequence method commonly used to generate probability tables in the URR. The new method uses a Monte Carlo process to generate many pseudo-resonance sequences by first sampling the average resonance parameter data in the URR and then converting the sampled resonance parameters to the more robust R-matrix limited (RML) format. For each sampled set of pseudo-resonance sequences, the temperature-dependent cross sections are reconstructed on a small grid around the energy of reference using the Reich-Moore formalism and the Leal-Hwang Doppler broadening methodology. The effective cross sections calculated at the energies of reference are then used to construct probability tables in the URR. The RML crosssection reconstruction algorithm has been rigorously tested for a variety of isotopes, including ¹⁶O, ¹⁹F, ³⁵Cl, ⁵⁶Fe, ⁶³Cu, and ⁶⁵Cu. The new URR method also produced normalized cross-section factor probability tables for ²³⁸U that were found to be in agreement with current standards. The modified ²³⁸U probability tables were shown to produce k_eff results in excellent agreement with several standard benchmarks, including the IEUMET- FAST-007 (BIG TEN), IEU-MET-FAST-003, and IEU-COMP-FAST-004 benchmarks.