An independent investigation of heat transfer in enclosed vertical storage tubes housing plutonium metal within DOE Standard 3013-compliant storage container systems was performed to determine whether this storage configuration could effectively remove the internally generated heat from pure plutonium metal. Alpha-phase plutonium metal, if allowed to exceed approximately 239°F, will transition to beta-phase metal and undergo a volumetric expansion which could rupture the storage container system. Significant temperature drops occurred in two regions. Both regions were gas-filled vertical annuli with heat flux boundary conditions on the inner surfaces and fixed temperature boundary conditions on the outer surfaces. The thermal resistance method was employed to evaluate radial heat transfer across each annulus, coupling natural convection, radiation, and conduction. Correlations from Thomas and deVahl Davis (1970) and Keyhani et al. (1983) were used to evaluate the degree of natural convective enhancement. Multi-dimensional finite element modeling of these regions was also performed employing both buoyant and radiative effects. Both models accurately predicted the measured temperature changes from an experimental investigation by Hopkins et al. (1997) which used a larger diameter storage tube with a 38% higher heat loading.