[en] Materials and surface areas of two BWR plants were identified as a basis for establishing the cobalt sources that would be significant sources of input to the reactor water. The environmental conditions of these materials were established, and the related corrosion and erosion loss rates were developed. These factors were used to calculate corrosion-product (iron, nickel, and cobalt) inputs to the reactor water from relevant nuclear steam system and balance-of-plant sources. These inputs were compared with sample data from an operating BWR. Methods for eliminating or reducing the cobalt input sources were evaluated and found feasible