Taavi Vaasma will defend his doctoral thesis titled “Enrichment, atmospheric dispersion and deposition of naturally occurring radionuclides from oil shale-fired power plants”on November 27, 2017 at 12:15 at W. Ostwaldi 1, room B103.
Dr. Madis Kiisk, Institute of Physics, University of Tartu
Dr. Alan Henry Tkaczyk, Institute of Physics, University of Tartu
Dr. Bogusław Michalik (Silesian Centre for Environmetal Radioactivity, Poland)
Natural radiation sources surround us constantly. This includes cosmic rays from space, radionuclides in the Earth’s crust, water and foodstuff. Yearly doses from these sources surpass sever times the doses received by the public from artificial sources, such as certain medical procedures, nuclear industry and fossil fuel industry. Radiation originating from the Earth’s crust is mostly caused by the decay of unstable uranium and thorium isotopes as well as their own decay products. Evolution has played its roll here, as living organisms have adapted to cope with the constant radiation surrounding them. Problems can arise when material obtained from the Earth’s crust is further industrially processed. This may cause concentration of these radionuclides in by-products and their releases to the surrounding environment during combustion processes.
Two of the world’s largest oil shale-fired power plants (PP) have been operating in Ida-Virumaa around 50 years. Around 30 million tonnes of oil shale were burned per year during 1980s, which has decreased down to around 12 million tonnes per year nowadays. This has resulted in significant emission loads of radionuclides to the atmosphere. The concentrations and magnitudes of radionuclide emissions to the surrounding environment and their corresponding deposition loads were studied in a PhD work conducted at the Institute of Physics in University of Tartu. Within this study, it was found that:
- Radionuclides concentrate up to 10 times in fly ashes, especially in the fine fraction that escapes the filter systems.
- The fly ash and radionuclides are carried and deposited at distances over 50 km from the PPs. Largest deposition flux is however within 2 km from the plants.
- Fly ash and radionuclide emissions have reduced 1 to 2 orders of magnitude compared to 1980s, mostly due to reducing the amount of burned oil shale and significant renovations done on the PPs.
- The long operational period of the oil shale PPs has caused an accumulation of deposited radionuclides in the surrounding environment. The determination of potential doses to humans and the environment especially in the vicinity of the PPs requires further studies.