Radioenvironmental survey of the Megalopolis power plants fly ash deposits

摘要

The Megalopolis lignite field basin is located in the centre of the Peloponnesus peninsula in southern Greece. The lignite fired power plants in operation in this region have a total capacity of 850 MW and produce over 2 million metric tons of fly ash annually; this is primarily disposed of in deposits located mainly at exhausted lignite mines. The disposed fly ash has a ~(226)Ra content of about 1000 Bq kg~(-1). An extensive research project for the determination of the natural radioactivity of lignite and ash from the Megalopolis power plants started in the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) in 1983. The project has evolved to an integrated radioenvironmental survey of the Megalopolis lignite field basin area. The present work aims at the presentation of the radioenvironmental survey of the fly ash deposits in the vicinity of the power plants. Results regarding (a) γ-dose rate, (b) radon concentration in the ambient air, (c) soil radon exhalation rate and (d) soil gas radon concentration are reported from systematic field measurements at three deposit sites. In addition, soil sampling of the surface and 0-80 cm layer has been conducted at the deposits to allow for the determination of the activity of natural radionuclides, namely ~(226)Ra, ~(232)Th, ~(40)K, ~(234)Th and ~(210)Pb. The radiological characterisation of the fly-ash deposits obtained through these results is compared to the natural radioactivity background in the wider Megalopolis area, using the additional results of a previous similar survey. It can be concluded that, from the radiological point of view, the Megalopolis fly ash deposits do not differ significantly from the rest of the Megalopolis lignite field basin, despite the fact that most of the underground soil layers consist of fly ash with high ~(226)Ra content.