Hazardous accumulation of radioactive lead on the water wall tubes in coal fired boilers

摘要

Dutch power companies recently have become aware of a hazard due to the presence of radioactive 210{sup left}Pb in their boilers. In an investigation conducted by KEMA in The Netherlands it was discovered that 210{sup left}Pb isotope accumulates within fire-side deposit layers that form on membrane waterwall tubes. Because the measured levels of total radioactivity exceeded the governmental regulation limit of 100 Bq/g, refurbishment activities in the boiler are subject to governmental authorization and must be conducted under the supervision of authorised radiation protection officers. The 210{sup left}Pb material originates from decay of 238{sup left}U, which is present in small amounts in coal. During combustion of the coal, heavy metals such as Pb evaporate and are present in the flue gas in the form of Pb, PbCl, PbCl{sub}2, PbS, PbS{sub}2 or PbSO{sub}4, dependent on the gas environment and temperature. These volatile products subsequently will condense at lower temperatures on the waterwall tubes in the boiler.