[en] The initial program of bench mark critical experiments conducted on behalf of the design and safety evaluations for the 300 MW(e) gas cooled fast breeder reactor demonstration plant included extensive measurements of the reactivity effects of accidental steam ingress. Insertions of polyethylene (CH₂) foam into all of the void channels in the 1250-liter (l) core, the radial blankets, and the axial blankets of the Phase II GCFR critical assembly gave simulated floodings of up to 2.25% steam in the coolant. The report presents results of General Atomic Company (GA) analyses of the Phase II steam entry experiments, giving comparisons of calculated and measured flooding worths under various conditions, including changes in core geometry and introduction of control rod poisoning. Also studied were the effects of steam flooding on control material worth and other physics parameters. Calculated worths of hydrogenous materials were found to be significantly sensitive to variations in analytical models and methods. Good agreement with experiments was obtained by a 28-group analysis when a rigorous regeneration of cross sections, cell-heterogeneity factors, and directional diffusion coefficients was provided at each specific flooding density to account for the moderated spectra. Steam worths in a rodded core can be similarly well predicted provided that rod shielding effects are re-evaluated in the steam environment. Extrapolations based on these experiments clearly suggest that should a steam leak occur, it would not be a major safety concern, even in a small GCFR demonstration plant. Details of the analytical procedures and models utilized are presented