Enrichment, atmospheric dispersion and deposition of naturally occurring radionuclides from oil shale-fired power plants
Date
2017-10-25
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Abstract
Me kõik paikneme looduslikku päritolu kiirguse mõjuväljas. Selle hulgas on näiteks nii kosmiline kui ka maapinnast tulenev kiirgus ning toidu ja joogiga sissevõetavad radionukliidid. Nimetatud allikatest saadavad aastased kiirgusdoosid elanikele ületavad mitmeid kordi doose, mille allikaks on tehislikud protsessid, nt teatud meditsiiniprotseduurid, tuumajaamad, fossiilkütuste tööstus. Maapõuest pärineva kiirguse allikateks on peamiselt uraani ja tooriumi (lisaks veel nende lagunemisproduktide) lagunemisel tekkiv kiirgus. Evolutsioon on siinkohal abiks olnud ning inimesed on kohanenud elama neid ümbritsevas kiirgusfoonis. Probleeme võib tekkida olukorras, kus maapõuest võetud maavara töötlemisel vastavad radionukliidid kontsentreeruvad tööstusprotsessi käigus (nt põletusprotsessides) ning võidakse osaliselt emiteerida lendtuha ja põlemisgaasidega ümbritsevasse keskkonda.
Kaks maailma suurimat põlevkivil töötavat elektrijaama on Ida-Virumaal töös olnud juba suurusjärgus 50 aastat ning aastas põletatav põlevkivi kogus on varieerunud 30 miljoni tonni (1980’datel) ning umbes 12 miljoni tonni vahel tänapäeval. Selle aja jooksul on tekkinud suurel hulgal põlemisjääke ning atmosfäärseid emissioone. Tartu Ülikooli Füüsika Instituudis koostatud doktoritöös uuriti, millistes kontsentratsioonides erinevaid radionukliide nendest elektrijaamadest keskkonda emiteeritud on ning kui suurel maa-alal nende sadenemine tagasi maapinnale toimunud on. Vastava töö käigus selgus, et:
- Põlevkivis looduslikult leiduvad radionukliidid kontsentreeruvad kuni 10-kordselt lendtuhas, mis atmosfääri paisatakse;
- Lendtuhk ja radionukliidid on kandunud üle 50 km kaugusele elektrijaamadest. Siiski enim on koormatud ala, mis jääb mõne km ulatusse jaamadest;
- Tänu pidevatele tehnoloogilistele uuendustele on emiteeritava lendtuha hulk tänapäevaks vähenenud kuni 100 korda võrreldes 1970’date ja 1980’datega!
- Jaamade pikk tööperiood (ca. 50 aastat) on tekitanud ulatusliku keskkonda emiteeritud ning seal kontsentreerunud radionukliidide voo. Et selgitada välja täpsed kiirgusdoosid jaamade lähistel elavatele inimestele, on vaja teostada jätku-uuringuid.
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.
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.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
põlevkivi, elektrijaamad, radioisotoobid, keskkonnaseisund, oil-shale, power plants, radioisotopes, state of the environment