SUBJECT: | Ph.D. Dissertation Defense |

BY: | Andrew Holcomb |

TIME: | Friday, November 6, 2015, 11:00 a.m. |

PLACE: | Boggs, 3-39 |

TITLE: | A New Unresolved Resonance Region Methodology |

COMMITTEE: | Dr. Farzad Rahnema, Chair (NRE) Dr. Luiz Leal (Institut de Radioprotection et de Surete Nucleaire) Dr. Bojan Petrovic (NRE) Dr. Dingkang Zhang (NRE) Dr. Tom Morley (MATH) |

SUMMARY 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) resonance-pair sequence method commonly used to generate probability tables in the URR. Using a Monte Carlo process, many resonance-pair sequences are generated by sampling the average resonance parameter data for the unresolved resonance region from the ENDF data file. The resonance parameters are then converted to the Reich-Moore format to take advantage of the more robust R-Matrix Limited (RML) format. For each sampled set of resonance-pair sequences, the temperature-dependent cross sections are calculated on a small grid around the energy of reference using the RML formalism and the Leal-Hwang Doppler broadening methodology. The effective cross sections calculated at the energy of reference are then used to construct probability tables in the unresolved resonance region. The tables are then normalized to calculate the energy-dependent self-shielding factors for the various reaction types. The RML algorithm is implemented in C++ in the AMPX code package. This implementation was then tested in the RRR by performing cross section reconstructions for many different isotopes, including O-16, F-19, Cl-35, Fe-56, Cu-63, and Cu-65. This RML implementation was then used in conjunction with a resonance-pair sequence generator to reconstruct the URR probability tables for U-238. The modified probability tables were then introduced into the MCNP ENDF/B-VII.0 and ENDF/B-VII.1 continuous-energy neutron libraries. These libraries were then tested using a set of International Criticality Safety Benchmark Evaluation Project (ICSBEP) benchmarks that are known to be sensitive to perturbations in the U-238 cross section, including the IEU-COMP-FAST-004, IEU-MET-FAST-003, and IEU-MET-FAST-007 (Big Ten) benchmark problems. |