Constantin Papastefanou

Escaping radioactivity from coal-fired power plants (CPPs) due to coal burning and the associated hazards: a review

Coal, like most materials found in nature, contains trace quantities of the naturally occurring primordial radionuclides, i.e. of (40)K and of (238)U, (232)Th and their decay products. Therefore, the combustion of coal results in the released into the environment of some natural radioactivity (1.48 TBq y(-1)), the major part of which (99%) escapes as very fine particles, while the rest in fly ash. The activity concentrations of natural radionuclides measured in coals originated from coal mines in Greece varied from 117 to 435 Bq kg(-1) for (238)U, from 44 to 255 Bq kg(-1) for (226)Ra, from 59 to 205 Bq kg(-1) for (210)Pb, from 9 to 41 Bq kg(-1) for (228)Ra ((232)Th) and from 59 to 227 Bq kg(-1) for (40)K. Fly ash escapes from the stacks of coal-fired power plants in a percentage of 3-1% of the total fly ash, in the better case. The natural radionuclide concentrations measured in fly ash produced and retained or escaped from coal-fired power plants in Greece varied from 263 to 950 Bq kg(-1) for (238)U, from 142 to 605 Bq kg(-1) for (226)Ra, from 133 to 428 Bq kg(-1) for (210)Pb, from 27 to 68 Bq kg(-1) for (228)Ra ((232)Th) and from 204 to 382 Bq kg(-1) for (40)K. About 5% of the total ash produced in the coal-fired power plants is used as substitute of cement in concrete for the construction of dwellings, and may affect indoor radiation doses from external irradiation and the inhalation of radon decay products (internal irradiation) is the most significant. The resulting normalized collective effective doses were 6 and 0.5man-Sv(GWa)(-1) for typical old and modern coal-fired power plants, respectively.

Low-frequency variability of beryllium-7 surface concentrations over the Eastern Mediterranean

7Be measurements, performed in Northern Greece (40°N) since 1988, were analyzed, in order to investigate the variability of the surface concentrations that can be attributed to processes with frequencies below the synoptic variability. Spectral analysis on the 7Be time series revealed three characteristic spectral regions, a 1-year periodicity corresponding to the well-established annual cycle, a periodicity between 20 and 30 months and a peak corresponding to a period of 11 years. The relationship with the 11-year cycle of solar activity was investigated through the correlation between the sunspot number and 7Be (−0.86) and between the heliocentric potential and 7Be (−0.80). 7Be was in coincidence with the heliocentric potential whereas it lagged the sunspot number by 5 months, expressing the time needed for the solar wind variations to be reflected on the production of 7Be during the specific solar cycle. The amplitude of the annual cycle was not constant throughout the whole period. An anti-correlation of −0.83 was revealed between the amplitude and the sunspot number with higher amplitudes during solar minimum and smaller amplitudes during solar maximum. With the use of a simplistic model, the amplitude modulation was attributed to the changing with the 11-year cycle contribution of the upper tropospheric and lower stratospheric reservoirs to the surface concentrations. More specifically, during solar maximum the contribution of upper troposphere down to the surface via winter-mixing is as much as 55% compared to the summer-mixing contribution, whereas during solar minimum winter-mixing is no more than 35%, thus inducing a higher amplitude. The superposed epoch method revealed that the 20–30 months periodicity is related to the quasi-biennial oscillation (QBO), with the 7Be minimum following the QBO maximum with ≈8 months time delay, whereas for the same time lag total ozone showed a reverse behavior. Cross spectrum analysis between 7Be and total ozone with the QBO shows a significant (90% confidence level) squared coherence, indicating that 68% and 86% of 7Be and total ozone variability of the 20–30 months periodicity, respectively, can be explained by the QBO.

Radioactivity of tobacco leaves and radiation dose induced from smoking.

The radioactivity in tobacco leaves collected from 15 different regions of Greece and before cigarette production was studied in order to find out any association between the root uptake of radionuclides from soil ground by the tobacco plants and the effective dose induced to smokers from cigarette tobacco due to the naturally occurring primordial radionuclides, such as 226Ra and 210Pb of the uranium series and 228Ra of the thorium series and/or man-made radionuclides, such as 137Cs of Chernobyl origin. Gamma-ray spectrometry was applied using Ge planar and coaxial type detectors of high resolution and high efficiency. It was concluded that the activities of the radioisotopes of radium, 226Ra and 228Ra in the tobacco leaves reflected their origin from the soil by root uptake rather than fertilizers used in the cultivation of tobacco plants. Lead-210 originated from the air and was deposited onto the tobacco leaves and trapped by the trichomes. Potassium-40 in the tobacco leaves was due to root uptake either from soil or from fertilizer. The cesium radioisotopes 137Cs and 134Cs in tobacco leaves were due to root uptake and not due to deposition onto the leaf foliage as they still remained in soil four years after the Chernobyl reactor accident, but were absent from the atmosphere because of the rain washout (precipitation) and gravitational settling. The annual effective dose due to inhalation for adults (smokers) for 226Ra varied from 42.5 to 178.6 μSv/y (average 79.7 μSv/y), while for 228Ra from 19.3 to 116.0 μSv/y (average 67.1 μSv/y) and for 210Pb from 47.0 to 134.9 μSv/y (average 104.7 μSv/y), that is the same order of magnitude for each radionuclide. The sum of the effective doses of the three radionuclides varied from 151.9 to 401.3 μSv/y (average 251.5 μSv/y). The annual effective dose from 137Cs of Chernobyl origin was three orders of magnitude lower as it varied from 70.4 to 410.4 nSv/y (average 199.3 nSv/y).

Residence time and uptake rates of 137CS in lichens and mosses at temperature latitude (40°N)

Abstract The 137 Cs concentrations in lichens and mosses were significantly high five years after the Chernobyl accident. In some species of foliose lichens and mosses, the uptake of 137 Cs during the long period of time was dominant in respect of its natural removal. In some species of fruticose lichens, decrease of the 137 Cs concentration was only observed with time passed, resulting in an effective half-life of 137 Cs, averaging 2.6 y at latitude 40°N. Uptake rates of 137 Cs in some species of foliose lichens were determined, varying from about 3 400 to 7 000 (average 4 800) Bq/kg·y.

Cesium-137 accumulation in higher plants before and after chernobyl

Cesium-137 concentrations in plant species of three biotypes of northern Greece, differing in location as well as in vegetation, are reported following the Chernobyl reactor accident. The cesium uptake by plants was due to the foliar deposition rather than the root uptake. The highest level of cesium in plants was found in Ranunculus sardous, a pubescent plant. The {sup 137}Cs concentration was about 22kBq kg{sup {minus}1}d.w. A high level of cesium was also found in Salix alba ({sup 137}Cs: 19.6 kBq kg{sup {minus}1} d.w.), a deciduous tree showing that hairy leaves or leaves having rough and large surfaces can absorb greater amounts of radioactivity (surface effect). A comparison is also made between the results of measurements of the present study and the results of measurements of some herbarium plants collected one year before the accident as well as the results of measurements of some new plants grown and collected one year after the accident resulting in a natural removal rate of {sup 137}Cs in plants varying from 14 to 130 days.

Chapter 11 - Radioactive Aerosol Analysis

Determination and the formation of radioactive aerosols in the atmosphere air are given in detail. Aerodynamic particle sizing includes the following modes: Aitken nuclei mode, accumulation mode, and coarse-particle mode. Instrumentation described for collecting radioactive aerosol particles in different air atmospheres are mainly the Andersen-type aerosol cascade impactors together with the sampling, analysis, and data interpretation and calibration methods. Various kinds of radioactive aerosols in ambient air are presented as follows: Radon and thoron decay-product aerosols, radioactive aerosols associated with the cosmic-ray-produced radionuclides, fission product radionuclide aerosols, radioactive aerosols associated with the operation of high-energy particle accelerators and plutonium aerosols due to nuclear weapons testing and/or nuclear reactor accidents, urban aerosols, and mine aerosols. Residence time of tropospheric aerosol particles associated with the radon decay-product aerosols, the cosmic-ray-produced radionuclides, and the fission product radionuclides is also analytically presented.

Factors and processes controlling the concentration of the cosmogenic radionuclide 7Be at high-altitude Alpine stations

Publisher Summary 7Be is a cosmogenic radionuclide with radioactive decay half-life of 53.3 days and it is a naturally occurring gamma emitter (477.6 keV). The bombardment of atmospheric constituents by cosmic rays (CR) leads to the fragmentation of light atmospheric nuclei, primarily 12C, 14N and 16O, thus giving rise to the production of various cosmogenic isotopes. Neutrons and protons, produced in about equal numbers as a result of the nucleonic cascade initiated near the top of the atmosphere by the most energetic primary component of cosmic radiation, are mainly responsible for nuclear disintegrations in the atmosphere. Low-energy interactions by nucleons with energies of 100–200 MeV have the largest contribution to the isotope production. Since protons experience intense and rapid loss of their energy due to ionization, the production of the majority of radionuclides is attributed to neutrons.