Pb-210 and Po-210 atmospheric releases via fly ash from oil shale-fired power plants

Taavi Vaasma; Jüri Loosaar; Francis Gyakwaa; Madis Kiisk; Banu Özden; Alan H Tkaczyk

doi:10.1016/j.envpol.2016.12.054

Pb-210 and Po-210 atmospheric releases via fly ash from oil shale-fired power plants

Environ Pollut. 2017 Mar:222:210-218. doi: 10.1016/j.envpol.2016.12.054. Epub 2017 Jan 3.

Authors

Taavi Vaasma¹, Jüri Loosaar², Francis Gyakwaa³, Madis Kiisk³, Banu Özden⁴, Alan H Tkaczyk³

Affiliations

¹ Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia. Electronic address: taavi.vaasma@ut.ee.
² Faculty of Mechanical Engineering, Department of Thermal Engineering at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
³ Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
⁴ Institute of Nuclear Sciences, Ege University, İzmir, Turkey.

PMID: 28062225
DOI: 10.1016/j.envpol.2016.12.054

Abstract

During high temperature processes in the furnace volatile and semi-volatile elements and radionuclides are partially emitted to the environment, depending on their chemical form in the original fuel, the technological set-up of the combustion system, and the prevailing combustion conditions. Two of the world's largest oil shale-fired power plants (PPs) have been operational in Estonia from the 1960s, during which time creation of significant environmental emissions and waste containing naturally occurring radionuclides has occurred. Pb-210 and ²¹⁰Po are considered natural radionuclides with the highest emission rates from PPs and possess elevated potential radiation exposure risks to humans and the environment. These radionuclides have the highest activity concentration values in fine ash fractions, especially in fractions remaining below 2.5 μm. To determine the activity concentrations of ²¹⁰Pb and ²¹⁰Po in the PPs' outlet, sampling was conducted from boilers operating on pulverized fuel (PF) technology with novel integrated desulphurization (NID) system and bag filters as well as with electrostatic precipitators (ESPs). The ²¹⁰Pb and ²¹⁰Po activity concentrations remained around 300 Bq kg^-1 for the NID system compared to 60-80 Bq kg^-1 in the ESP system. The dominant ash fraction in both systems was PM2.5, constituting over 50% of the fly ash mass collected from the outlet. The authors estimate that the total atmospherically emitted activity for the modernized PPs remains dominantly below 1% of the activity that is inserted via fuel. The implementation of higher efficiency purifications systems has significantly reduced the negative effect of these PPs. Based on annually emitted fly ash and boilers' working hours, the ²¹⁰Pb and ²¹⁰Po activity released relative to energy production were up to 68.3 kBq GWh_el^-1 for ²¹⁰Pb and 64.6 kBq GWh_el^-1 for ²¹⁰Po. These values are 1 to 2 orders of magnitude lower compared to the situation in the 1980s. These findings represent the first publicly available quantitative results estimating the ²¹⁰Po emissions from large oil shale-fired PPs.

Keywords: Atmospheric emissions; Fossil fuel; Lead-210; NORM; Polonium-210.

MeSH terms

Air Pollutants, Radioactive / analysis*
Air Pollutants, Radioactive / chemistry
Coal Ash / analysis
Coal Ash / chemistry*
Lead Radioisotopes / analysis*
Polonium / analysis*
Power Plants*
Radiation Monitoring / methods*
Soil Pollutants, Radioactive / analysis*
Soil Pollutants, Radioactive / chemistry
Spectrometry, Gamma

Substances

Air Pollutants, Radioactive
Coal Ash
Lead Radioisotopes
Soil Pollutants, Radioactive
Polonium