Optimization of Hafnium dimensions for thermal epithermal experiments (TEX) with highly enriched uranium Jemima plates and polyethylene - 14517
The goal of the US Nuclear Criticality Safety Program's Thermal Epithermal experiments (TEX) is to design and conduct new critical experiments to address high priority nuclear data needs from the nuclear criticality safety and nuclear data communities, with special emphasis on intermediate energy (0.625 eV - 100 keV) assemblies. The second set of TEX experiments will use stacks of highly enriched uranium Jemima plates, hafnium (Hf) diluent plates, and polyethylene moderator plates to create assemblies that span a wide range of fission energy spectra, from thermal, through intermediate, to fast energies. As the hafnium plates need to be fabricated and represent a significant cost for this experiment, a parameter study examining experimental configurations with various Hf thicknesses was completed using KENO V.a to determine optimal dimensions. The Hf plate thicknesses were optimized based on three major design criteria: 1) ensuring thermal, intermediate, and fast critical configurations could be built, 2) creating assemblies with a height to diameter ratio of approximately one, and 3) maximizing sensitivity to hafnium isotope cross sections, as predicted by the SCALE/TSUNAMI package. Based on the calculations presented in this report, a hafnium thickness of 0.10 cm will result in compact critical assemblies using the existing Jemima plate inventory, while reducing Hf cost and ensuring adequate sensitivity of the system to hafnium cross sections. (authors)