Recent studies of the hydrogen-precipitation of uranium dioxide from alkaline carbonate solutions have been extended. It was revealed that the reduction takes place in two phases. The first of these is the one described by Forward and Halpern. The second stage, much slower than the first, appears to be associated with the complete covering of the catalyst by the solid product. It is shown that while quantitative information is unreliable, a good qualitative description of the second-stage reaction can be based on the diffusion of reactants through this product layer to the catalyst surface.