Theoretical Analyses of Homogeneous Plutonium Critical Experiments

A computational analysis was made for the large number of available critical experiments with hydrogenous mixtures. The calculations were made using both multigroup S₄ and diffusion theory with 18 energy groups obtained with the GAMTEC-II code. Resonance capture by the isotope ²⁴⁰Pu was treated in the NR and NRIA approximations. Rather good agreement was found between experiment and theory. The results are given as a parametric survey for Pu densities ranging from 0.015 to 1.0 g/cm³. The calculated minimum critical mass of ²³⁹Pu is 547 g for water-reflected aqueous Pu(NO₃)₄ solutions and 531 g for similar mixtures of ²³⁹Pu and water.