Effect of corrosion inhibitors on the deposition of antimony on carbon steel and other PHWR primary coolant system structural materials

Antimony activities (122Sb and 124Sb) are observed in the primary coolant systems of Pressurized Heavy Water Reactors (PHWRs) during shutdown and during chemical decontamination. Efforts are being made to understand the behavior of antimony activities especially with regard to their release and deposition on the primary coolant system structural materials. Carbon steel, Incoloy-800 and Zircaloy are being used as primary coolant system structural materials in PHWRs. These materials develop an oxide film because of the corrosion by the water coolant. The neutron activated corrosion products deposited over the structural materials are removed by the dilute chemical decontamination process during shut down. Release of antimony activities from the core zircaloy surfaces result in the deposition of antimony activities on the carbon steel and other out of core surfaces causing increase in radiation field. Hence, efforts are being made to study the deposition behavior of Sb(III) and Sb(V) over carbon steel and other structural materials in constituents of chemical decontamination formulation such as citric acid etc.,. The corrosion inhibitors were found to inhibit the deposition of Sb(III) on carbon steel metal surfaces. Hence, the role of corrosion inhibitors such as Rodine-92B, Cinnamaldehyde, thiourea etc., on the deposition of Sb(III) on reactor structural materials is being investigated. The effect of presence of oxide film, nature of material, composition of the chemical formulation on the deposition process is reported. The correlation obtained between the inhibition efficiency and the percentage reduction in the antimony deposition over carbon steel surface is explained. The result of applying a chemical decontamination process with the corrosion inhibitor to a PHWR is also highlighted. (author)