Quantifying the determinants of leakage multiplication for large uranium objects using Monte Carlo simulations

Leakage multiplication is a physical characteristic of fissionable uranium objects that can be assayed using active interrogation measurements. Assay of large, highly-multiplying uranium objects using coincidence and multiplicity counting is susceptible to biases stemming from the simplistic assumptions of point kinetics-based analysis methods. This work uses Monte Carlo simulations and nonlinear curve fitting to quantify the sensitivity of leakage multiplication to enrichment, mass, and geometry for a range of bare uranium metal spheres, cylinders, and annular castings up to 7 kg under active interrogation. An understanding of how sensitive leakage multiplication is to changes in the underlying physical characteristics of uranium allows for potential corrections to assay results or evaluation of assay uncertainty based on prior or inferred knowledge of one or more of these physical characteristics.