Travis Justin Grove

Lead Void Reactivity Worth in Two Critical Assembly Cores with Differing Uranium Enrichments

Abstract To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worths was conducted in a high-enriched uranium (HEU)/Pb system and a low-enriched uranium (LEU)/Pb system using the Comet Critical Assembly at the National Criticality Experiments Research Center. There is a follow-on experiment to measure the lead void reactivity worths in a plutonium/Pb system that is currently under investigation. The critical experiments in the two uranium systems were designed to provide complementary data sets having different sensitivities to scattering cross sections of lead. The larger amount of the 238U present in the LEU/Pb core increases the neutron importance above 1 MeV compared with the HEU/Pb core. Since removal of lead from the core shifts the neutron spectrum to the higher energy region, positive lead void reactivity worths were observed in the LEU/Pb core while negative values were observed in the HEU/Pb core. This technical note is a preliminarily report of the experimental analysis results for the lead void reactivity worths with the Monte Carlo calculation code MCNP® version 6.1 together with nuclear data libraries JENDL-4.0 and ENDF/B-VII.1. The calculation values were found to overestimate the negative reactivity worths for the HEU/Pb core while being consistent for the LEU/Pb core.

Measurement of the thermal absorption cross section in lucite using fermi age theory

The diffusion processes of neutrons in Lucite have been investigated. The mechanisms of these processes have been described as having two steps. In the first step, the fast neutrons collide with the nuclei of Lucite, losing energy until they reach thermal energies, In the second step of the diffusion process, the thermal neutrons continue to diffuse through the Lucite without any significant loss of energy until they are finally absorbed or leak out of the system. Experiments were performed to study these two processes and to estimate the absorption cross section in Lucite. The experiments yielded an average range of 6.3 cm for fast neutrons slowing down to thermal energies and a thermal absorption cross section in Lucite of 0.52 b.

Reaction rate, fission product yield, and Rossi-α measurements using a HEU metal, copper reflected critical assembly

A critical experiment was performed on the Comet assembly to provide nuclear data in a non-thermal neutron spectrum and to re-establish experimental measurement capabilities relevant to the United States Department of Energys general purpose nuclear criticality experiments capability and to the Technical Nuclear Forensic program. Activation and fission foils were placed at specific locations in the Zeus all-oralloy core, copper reflected critical experiment to infer spectral indices data and obtain reaction rates data. After the irradiation, passive gamma-ray measurements were performed on all the foils and several of them were packaged and shipped to Los Alamos National Laboratory for further radiochemical analysis. The results from the non-destructive and radiochemical analyses are presented in this paper. Finally, Rossi-α measurements were performed on a slightly modified configuration from the configuration used for the activation measurements. The Rossi-α results are presented and compared to past measurements performed using other critical assemblies.

Measurement of the Thermal Absorption Cross Section in Lucite Using Fermi Age Theory

Abstract The diffusion processes of neutrons in Lucite have been investigated. The mechanisms for these processes have been described as having two steps. In the first step, the fast neutrons collide with the nuclei of Lucite, losing energy until they reach thermal energies. In the second step of the diffusion process, the thermal neutrons continue to diffuse through the Lucite without any significant loss of energy until they are finally absorbed or leak out of the system. Experiments were performed to study these two processes and to estimate the absorption cross section in Lucite. The experiments yielded an average range of 6.3 ± 0.1 cm for fast neutrons slowing down to thermal energies and a thermal absorption cross section in Lucite of 0.52 ± 0.02 b.