Criticality safety studies of a proposed uranium-zirconium metal alloy fuel production facility

The purpose of this research is to perform a preliminary criticality safety analysis of a new facility designed for the production of a uranium-zirconium metal alloy fuel material. This alloy material is to be used in the production of fuel elements for the Hanford N Reactor located on the Hanford reservation near Richland, Washington, which is owned by the United States Department of Energy (DOE) and currently operated by the Westinghouse Hanford Company. The proposed fuel material is a metal alloy composed of 90.7 weight percent zirconium and 9.3 weight percent uranium. While anticipated design enrichments range from approximately 55 weight percent ²³⁵U to 94 weight percent ²³⁵U, the analyses for this research uses a uranium enrichment of 100 weight percent ²³⁵U for simplicity and conservatism. The fuel material is to be produced in the form of a solid as-cast double billet using an arc-melt process developed at the Oak Ridge Y-12 Plant. Two finished billets will be produced from each single as-cast double billet. The analyses are divided into two categories. First, the major criticality concerns associated with material storage have been identified and analyzed. Second, a benchmark analysis has been performed to verify the applicability of the computer code used in these analyses and to provide additional justification as to the adequacy of the chosen neutron multiplication factor (k-eff) safety limit. The major material storage criticality concerns have been identified as: (1) as-cast billet storage, (2) finished billet storage, (3) stratified billet storage, and (4) scrap material storage. In general, all phases of the production process pose criticality concerns. If these concerns are properly addressed in the initial facility design, the safe production of this fuel material is possible. The benchmark comparison verifies that the calculational tools employed in the storage analyses provide reasonable results by comparing calculational results with applicable critical experiments. The benchmark comparisons for this research show good agreement between calculated and experimental results.