Modeling of Activity Transport and Uptake of Cobalt in the Primary Circuit

The predominant radionuclide in the PWR primary coolant is Co-60, although Co-58 contributes significantly to radioactivity at the early stage of a reactor operation. Since Co-60 is produced from the in core Co-58, which is the source of cobalt in a reactor system, many researchers have investigated its transmutation in the core, its transport around the system, and its subsequent deposition on surfaces. The major parameter influencing the behavior of radioactivity, such as Co-60 in the coolant, is the corrosion product oxides. The oxide originates from the circuit materials in contact with the coolant of the primary circuit, these materials are mainly a zirconium alloy for the core, a titanium alloy for tubing in the steam generator, and a stainless steel for the reactor vessel internals. The material and water chemistry are selected carefully to control the corrosion products. The objective of this work is to analyze the corrosion product activity in the primary circuit using a multiregion model. This model, which is incorporated with the mass and activity transport between the dissolved corrosion products in the coolant and the surface, describes the specific activity of corrosion products in coolant and on the surfaces according to the operation modes