Radioactive decontamination of waste oil by filtration, centrifugation, and chelation

Abstract

Laboratory studies were conducted on select physical and chemical processes for decontamination of a composite waste lubricating oil from a boiling water reactor. Physical treatments included successive filtration through 25, 8 and 1 μm filters to remove particulate matter and centrifugation to remove water. Chemical treatment consisted of mixing the oil with an aqueous solution of the chelating agent ethylenediaminetetraacetic acid (EDTA) and centrifuging the resulting emulsion. The effectiveness of the treatment processes was evaluated by measuring radionuclide concentrations in the oil following each treatment step and calculating decontamination factors.

The total activity of the oil was dominated by ⁶⁰Co, ⁵⁴Mn, and ¹³⁷Cs, although ⁵¹Cr, ⁵⁸Co, ⁵⁹Fe, and ¹³⁴Cs were also present. Filtration consistently achieved decontamination factors of approximately 200, 100, and 40 for ¹³⁷Cs, ⁵⁴Mn, and ⁶⁰Co, respectively, and reduced concentrations of the other radionuclides below their detection limits. Following filtration, centrifugation reduced ¹³⁷Cs concentrations below the detection limit and reduced ⁵⁴Mn and ⁶⁰Co concentrations by approximately 40% and 20%, respectively. Subsequent chemical treatment with EDTA reduced the ⁵⁴Mn concentration to below the detection limit and removed approximately 95% of the remaining ⁶⁰Co activity. The overall decontamination factor for successive filtration, centrifugation, and chelation was in excess of 10,000 for ⁵⁴Mn and ¹³⁷Cs and on the order of 1000 for ⁶⁰Co.