Algorithms used to generate Monte Carlo input decks and to analyze the output over a range of uranium mass, water volume, and particle size in a regular lattice are described. The algorithms produce input decks for both homogeneous and heterogeneous, regular-lattice systems of 20 enriched uranium metal and water and then analyze the results to determine the minimum critical mass over a range of input mass and particle size. The output is presented and analyzed for a 20 enriched uranium metal and water system, and comparisons to existing technical reports and safety guides are discussed. Two particular existing recommendations are tested and compared with new results: the boundary between a homogeneous system and a heterogeneous system, and the recommended margins of safety that can be applied to account for the effects of heterogeneity.
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