Study on biosphere contamination with natural radionuclides at operation of coal burning TPP in Bulgaria. Assessment of public exposure - 091

According to current reports the Thermal Power Plants' (TPP) share in electricity generation in Bulgaria is about 40%. Use of traditional energy sources, such as coal requires expensive air pollution controls but earth materials are inexpensive and easy to recover. Four large TPPs operate in the country and their annual production is approximately 2.7 GW a. The study is targeted at TPP complex 'Maritza' (Maritza 1, 2, 3) which annual electricity generation approximates 1.5 GW a, i.e. 56% of the total for Bulgarian TPPs. The coal burnt in this complex is of comparatively low quality. Lignite extracted in Mines Trayanovo (1, 2 and North) is of low calorific value and high concentration of sulfur and dust as well as clay. The specific consumption of coal is 13.6x10⁹ kg (GW a)^-1 at an average of 4.3x10⁹ for other TPPs. Assuming that the TPP electrical power generation in Bulgaria is not constant after 1990 (period of economical changes), the average annual electrical energy production (MW a) is presented as well as the average annual coal consumption for the period. In the industrial processes associated with extraction and processing of earth materials, the hazard from radiation is additional to the air pollution from other chemical substances (green house gasses, dust, SO₂, NO_x etc.), and radiation is not systematically monitored. In order to allow comparison with other countries and better assessment of the doses due to the use of coal in Bulgaria, the average concentrations of natural radionuclides in coal burned in the TPP 'Maritza' are estimated. Radioecological survey of the 28 km area around the TPP was carried out and data from 16 villages and 4 towns (controls) were collected. The following measurements were made: natural gamma background in buildings and outdoors, radionuclide concentration in soils, radon and daughters in buildings. Four towns were selected as controls: - Dimitrovgrad: 35 km southwest of site center; - Elhovo: 43 km east of site center; - Simeonovgrad: 25 km south of site center; - Stara Zagora: 37 km northwest of site center. Radiological parameters of water samples from 16 sites were determined, incl. drinking water (10), river water (river Sokolitsa, Ovcharitsa and Sazliika) and 2 water reservoirs used by the TPP (Ovcharitsa and Rozov kladenets). The results show that the operation of TPP complex 'Maritza' leads to additional annual individual effective dose for the Bulgarian population in the range of 5 to 6 μSv a^-1. The main actions for decrease of occupational and public exposure as well as environmental radioactive contamination include restricted release of dust, i.e. - Complex measurements for decrease of dust concentration in TPP sites. - Stable tailing piles of waste products and restriction of dust distribution in the environment. - Quality assurance of emission control devices (high filter efficiency)