Critical parameters are given for a series of experiments on uranium metal spheres immersed in uranyl nitrate solution. The uranium in both regions is enriched to 93.2% 235U. In some configurations, the two fissile regions were separated by -thick spherical shells of mild steel or boron stainless steel. These experiments were part of an investigation of the uncoupling effects of mild steel and boron stainless steel The term “uncoupling” as used throughout this text refers to the changes in critical mass, stated in terms of percent, due to surrounding the metal region with these nonfissile shells. Two tank sizes were used; the large tank was 38.4 cm in diameter × 57.2 cm in height, and the small tank was 26.5 cm in diameter × 38.4 cm in height. Solution concentrations used were 51.76, 54.61, 107.34, 110.27, and 448.91 g U/liter. Neutron reproduction factors were calculated for several of the experimental conditions using the KENO code. These values and their standard deviations ranged from 0.965 ± 0.013 to 1.011 ± 0.009, with uncertainties quoted at a one sigma confidence level. Neutron reproduction factors were also calculated for cases where the metal spheres were symmetrically centered in the uranyl nitrate solution. These centered cases were used to determine the uncoupling effects of the mild steel and boron stainless steel. For the 38.4-cm-diam tank, the uncoupling, expressed as a mass increase of the uranium sphere, varied from 10.1 to 65.4%. For the 26.5-cm-diam tank, the mass increases varied from 7.3 to 76.7%. The uncoupling percentage is a function of the solution concentration and the type of uncoupling material used.