Pretreatment, decontaminated surfaces

In summary, the most promising means of reducing the rate of recontamination of decontaminated surfaces seems to be minimization of the °Co concentration in the coolant. All the attempts made to reduce recontamination of decontaminated surfaces by appropriate pretreatment did not show a clear beneficial result. When, in the course of a replacement action, new pipes or components are installed, a pretreatment of these surfaces by electropolishing plus pre-oxidation (hot moist air) seems to be effective. However, because of the complex process of Co incorporation into the superficial oxide layers it is often difficult to distinguish clearly between incidental correlations and those which are in fact caused by the measures taken. 

The cobalt deposition rate on new, replacement, or decontaminated recirculation piping surface has been reduced by pretreating the piping using an atmosphere of oxygenated wet steam to form an oxide film (25). Studies have been conducted for both PWRs and BWRs to reduce the cobalt content of materials used in the nuclear parts of the plants, particularly in hardened and wear surfaces where cobalt-base alloys ( 50% Co) are used (26). Some low cobalt materials have been developed however, the use of the materials is limited to replacement parts or new plants. 

Other full-system decontaminations (e. g. of the Steam Generating Heavy Water Reactor) have been performed using the Rjrco reagent or the Lomi process with and without the NP pretreatment step. The results of these operations were satisfactory as regards decontamination factors and materials compatibility at the circuit surfaces, as well as at the fuel assemblies. 

Process subsystems and equipment, such as waste pretreatment, ash handling, filters and scrubbers, should be arranged in such a way as to minimize the spread of contamination and to facilitate their decontamination. Typical measures may include adequate ventilation, drainage, curbing and surface finishes that facilitate decontamination. 

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