Zeus: Fast-spectrum critical assemblies with an iron-HEU core surrounded by a copper reflector

Experiments to investigate critical systems of iron moderated highly enriched uranium in the intermediate-energy range were attempted. However, due to size limitations, the systems fell into the fast-energy range. Two critical configurations were established with a uranium mass of ∼ 198 kg and a Fe/235U Ratio of ∼15. Experimental uncertainties were systematically evaluated to estimate their effect on multiplication. The combined uncertainty for these experiments is estimated to be ±0.0024 Δeff. Consequently, both Zeus iron configurations are judged to be acceptable for use as criticality-safety benchmark experiments. (authors)