In-situ causticization, a new process for management of DBP containing alkaline low level radioactive liquid waste

• In-situ causticization for decontamination of DBP containing carbonate LLW.
• NaOH produced in-situ precipitates complete α-activity.
• High decontamination factor for α-activity is achieved.
• Supernatant solution made suitable for dilute and discharge to sea.
• Activity load of cement formed from sludge met the near surface disposal norms.

The di-butyl phosphate (DBP) containing alkaline low level radioactive waste generated during PUREX solvent cleanup with Na2CO3 was decontaminated using a new process called “in-situ causticization” where NaOH was produced in-situ by addition of Ca(OH)2 resulting from precipitation of CaCO3. Alpha activity from the carbonate free solution was quantitatively precipitated by NaOH leading to a high alpha decontamination factor (DF) of ∼240 in the supernatant solution. DF for β-activity was low (∼3) due to partial precipitation of cesium and ruthenium. DBP remained in the solution as Na-DBP. XAD-4 resin was used to remove Na-DBP and any other dissolved organic. The remaining cesium was removed by resorcinol–formaldehyde resin and the solution containing only ruthenium was suitably diluted and discharged to sea. The calcium carbonate sludge was solidified with ordinary Portland cement, the activity load, compressive strength and leach rate of cement waste product (CWP) was within the acceptable limits of our near surface disposal facilities. The final volume of CWP obtained by this process is at least 2.5 times less than the volume obtained by direct cementation of the waste.

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