Evaluations of the Effect of Heterogeneity in HALEU Systems Using Modified Critical Benchmarks

This work uses evaluated criticality safety benchmarks to examine the effect of heterogeneity in high-assay low-enriched uranium (HALEU) systems. A subset of benchmarks selected based on their composition parameters is slightly modified to artificially introduce heterogeneity, and the difference in the effective multiplication factor between the homogeneous benchmark and the modified model is determined. The difference in the multiplication factor is evaluated for correlations against both the moderator ratio and the enrichment of the benchmarks, and the correlations are examined using established statistical methods. In several cases, statistically significant correlations are observed and discussed, and the lack of expected correlations is also discussed.