Novel methodology for zirconium-based alloy surface decontamination using alkali fusion method

Zirconium-based alloys are important materials in nuclear power plants (NPP). The fuel-clad and pressure tubes are alloys of zirconium, highly corrosion-resistant due to the inert ZrO₂ layer on its surfaces. During the reactor operation, oxide layers are contaminated with radioactive fission and activated corrosion products. Hence, decontamination of these pressure tubes after they are discharged from the operation and fuel-clad materials (Hull) generated during the fuel reprocessing are essential for their safe disposal. An Alkali Fusion (AF) decontamination process using NaOH-KOH eutectic mixture was developed for zirconium-based alloys. The process parameters, like chemical composition, temperature, and contact time, have been optimised. Process modelling and mechanism of dissolution were proposed. Further, the process was successfully tested on zircaloy specimens prepared via two different conditions. It was observed that ∼ 0.2 mg/cm² of ZrO₂ from the zircaloy surface could be dissolved in each cycle of the AF process.