Radioactivity in size-separated municipal incinerator ashes

Radionuclide concentrations of the 238U- and 232Th-decay series, as well as 40K and 137Cs, were determined in size-separated fly ashes and bottom ashes from two municipal incinerators. Secular equilibrium was observed for several of the series' radionuclides, though 222Rn losses during combustion were evident. The fly-ash samples showed increasing enrichment of 40K, 137Cs, and 210Pb as particle diameters decreased, due to their volatility and subsequent condensation, and typically contained higher activities of these volatile radionuclides. Radon emanation from the bottom ashes was not detected but the fly ashes had an emanting power near 7%. Only 40K and 137Cs were found to be water-soluble, with significantly greater solubilities occurring for the fly ashes. Overall concentrations suggest that municipal incinerator ashes contain the equivalent radioactivity of surface soil and substantially less than ashes from coal combustion. It is shown that an incinerator's contribution to the atmospheric radionuclide burden is minimal and, from a radiological viewpoint, their residual ashes can be safely used in construction materials.