AbstractThe critical experiments reported provide data for the effect of a soluble neutron absorber (cadmium nitrate) on the criticality of high-enriched uranium nitrate solution. These data can be used in criticality control and for validation of calculational methods. The experiments were performed with cylindrical vessels of two different diameters, 241.8 and 291.6 mm. Cadmium concentrations used in the high-enriched uranium solution ranged up to∼11 g Cd/ℓ. The vessels were reflected with water, and in some cases with water containing dissolved cadmium nitrate.The cadmium was found to be an effective neutron absorber when dissolved in the solution. The critical experiment data were analyzed by several different calculational methods, which showed the calculated keffvalues to increase as the cadmium concentration was increased. (The critical system calculated as supercritical.) The trend of the analysis results suggests that the neutron leakage or cadmium absorption may be underestimated for systems with a harder neutron spectrum.