A. Ioannidou

Tracking of Airborne Radionuclides from the Damaged Fukushima Dai-Ichi Nuclear Reactors by European Networks

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ((131)I) and cesium isotopes ((137)Cs and (134)Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous (131)I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous (131)I and the large underestimation of the total (131)I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous (131)I fraction to total (131)I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the (134)Cs to (137)Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total (131)I inventory that has passed over Europe during this period was <1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe.

Aerodynamic size association of 7Be in ambient aerosols

Abstract The aerodynamic size distribution of 7 Be in ambient aerosol particles was determined by using 1-ACFM cascade impactors. The activity distribution of 7 Be measured by γ-spectrometry ( E γ = 447 keV ), was largely associated with submicron aerosols in the accumulation mode (0.4–2.0 μm). The activity median aerodynamic diameter, AM AD ranged from 0.76 to 1.18μm (average 0.90μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, gs g ranged from 1.86 to 2.77 (average 2.24). In 65% of the cascade impactor measurements the activity distributions of 7 Be showed maxima in the 0.7 to 1.1 μm size range. In estimating lifetimes of 7 Be aerosols in ambient air, a mean residence time of about 8 days averaged for tropospheric aerosols of 0.90 μm AM AD size.

Depositional fluxes and other physical characteristics of atmospheric beryllium-7 in the temperate zones (40°N) with a dry (precipitation-free) climate

Abstract Atmospheric depositional fluxes of 7Be were measured over a 3-year period (January 1987–April 1990) in Thessaloniki, Greece (40°38′N, 22°58′E). Total precipitation accumulation during 1987, 1988 and 1989 was 65.0, 46.2 and 32.6 cm, respectively, reflecting a relatively dry (precipitation-free) climate. The volume-weighted concentrations of 7Be in rainwater ranged between 0.1 and 5.2 Bq l −1 (average 0.6 Bq l −1). The annual total deposition fluxes of 7Be in 1987, 1988 and 1989 were 841, 510 and 483 Bq m−2, respectively, while the average concentrations of 7Be in the atmosphere in the corresponding periods were 6.3, 5.7 and 4.2 mBq m−3, showing a decreasing trend with time. On an annual average, the washout (scavenging) ratio for 7Be was 144 and the resuspension factor was 2.5 × 10−4 m−1, the latter is too high. The annual average total deposition velocity for 7Be was estimated to be 0.4 cm s−1. The air-to-vegetation transfer rate estimate for 7Be is 5150 m3 kg−1. Seasonal variations of 7Be concentration depend considerably on the local meteorological conditions, mainly the rainfalls.

Radon concentrations and absorbed dose measurements in a Pleistocenic cave

Radon concentration measurements were carried out using solid-state nuclear track-etch detectors (SSNTDs) type CA 80-15 cellulose nitrate films, in a Pleistocenic cave at Petralona, in Halkidiki, Northern Greece, at 55 km from the city of Thessaloniki. Radon levels as high as 88 kBq.m-3 (2.38 nCi.l-1) have been recorded inside the cave equivalent to 11.90 WL in terms of occupational exposure to radon and its decay products. Absorbed dose rates were performed using TL dosimeters, type TLD-200 (CaF2-Dy) in a continuous monitoring program (integrated measurements). Dose rate levels as high as 110 nGy.h-1 were recorded inside the cave. In interpreting the high levels of radiation doses, radioactivity measurements regarding the naturally occurring 238U, 232Th and 40K radionuclides were carried out in various speleothems found at different sites in the cave.

Beryllium-7 aerosols in ambient air

The aerodynamic size distribution of 7 Be aerosol particles in ambient air was determined by using 1-ACFM and high-volume (HVI) cascade impactors, 20 m above the ground on the roof of the Faculty of Science building, Aristotle University of Thessaloniki at Thessaloniki Greece (40 o 38’N, 22 o 58’E) from November 2006 to June 2008. The activity concentration of 7 Be aerosols was determined by gamma spectrometry (Eγ = 0.477 MeV). The activity size distribution of 7 Be-aerosols was largely associated with submicron aerosol particles in the accumulation mode (0.4-2.0 μm). The activity median aerodynamic diameter, AMAD varied from 0.76-1.18 μm (average 0.90 μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, σg varied from 1.86-2.77 (average 2.24). The activity size distribution of 7 Be-aerosols peaked in the 0.7-1.1 μm size range in the 65% of the measurements carried out by the 1-ACFM cascade impactor. In estimating lifetimes of 7 Be-aerosols in ambient air, a mean residence time of about 8 days averaged for atmospheric aerosols of 0.90 μm AMAD size.

Time lag between the tropopause height and 7Be activity concentrations on surface air

A strong positive correlation between the seasonal changes of the tropopause height and the concentration of (7)Be in the surface air (R = 0.94, p < 0.0001) was observed at 40°N. Moreover, a strong positive correlation was revealed between the activity concentrations of (7)Be and the temperature T (°C) (R = 0.97, p < 0.001), confirming that the increased rate of vertical transport within the troposphere, especially during warmer months, has as a result the descent to the surface of air masses enriched in (7)Be. The results of the present work suggest that the temperature and the tropopause height are good indicators for transport time of air masses enriched in (7)Be to the surface. Higher values of temperature or tropopause height seem to result to shorter transport times. This is attributed to atmospheric convection which provides an effective mechanism for vertical transport of air masses. Increasing tropospheric temperature has generally as a result that convection penetrates more deeply which in turn leads to an increase in tropopause height. But, the atmospheric procedures do not occur immediately after the fluctuations of correlated factors. Thus, a time lag is expected between the tropopause height and (7)Be activity concentrations on surface air that might be from hours to days or weeks. The result suggests that (7)Be concentrations fully respond within three days after the changes in the tropopause height.

Radioactivity and metal concentrations in marine sediments associated with mining activities in Ierissos Gulf, North Aegean Sea, Greece.

Marine sediment samples were collected from Ierissos Gulf, N Aegean Sea, close to the coastal mining facilities. Measurements of radionuclide and metal concentrations, mineral composition and grain size distribution were performed. The concentrations of (226)Ra, (235)U and trace metals showed enhanced values in the port of Stratoni compared with those obtained near to Ierissos port. The dose rates received by marine biota were also calculated by the ERICA Assessment Tool and the results indicated no significant radiological risk.

Time-dependent radioactive concentrations of fallout following the Chernobyl reactor accident

The levels of Chernobyl-derived 137Cs, 134Cs, 106Ru and 103Ru were measured at Thessaloniki, Greece, in air, rain, soil, grass and milk samples for more than 2 years after the accident. The data were analysed in conjunction with 7Be (produced in the atmosphere by cosmic rays) measurements and show that significant variations were observed, particularly in the spring and in the autumn measurements. In interpreting these variations we took into consideration the tropospheric, or possibly stratospheric, fallout injections into the atmosphere due to the Chernobyl accident, nuclear weapons testing or other releases from nuclear reactors operating world-wide. Useful information can be derived for determining the periodicity of global circulation of the fallout radionuclides.

7Be aerosols and their deposition on the sea: a possible method to estimate trace metals deposition on the sea

The activity size distributions of (7)Be aerosols in different size fractions (<0.39 μm, 0.39-0.69 μm, 0.69-1.3 μm, 1.3-2.1 μm, 2.1-4.2 μm, 4.2-10.2 μm and >10.2 μm) were determined at the city of Thessaloniki, Greece, Eastern Mediterranean. The Activity Median Aerodynamic Diameter (AMAD) values ranged from 0.58 to 1.22 μm while more of the 80% of the (7)Be activity was associated with particles smaller than 1.3 μm. Sea salt aerosol particles were defined in a small size range, lower than 0.39 μm. Field measurements at a coastal location allow the estimation of (7)Be deposition on the sea. Since the (7)Be aerosol particles were mainly below 1 μm, scavenging by precipitation was the main process depositing (7)Be on the sea. Acting as an excellent tracer, (7)Be could be used for determination of the deposition of the trace metals on the sea, since they are expected to be deposited at similar rate by wet and dry deposition processes as the (7)Be.

The uranium isotopes in the characterisation of groundwater in the Thermi-Vasilika region, northern Greece†

ABSTRACT The activity concentrations of 238U and 234U have been determined in groundwater samples in the Thermi-Vasilika region, northern Greece. The analysis was performed by alpha spectrometry after pre-concentration and separation of uranium by cation exchange and finally its electrodeposition on stainless steel discs. The obtained isotopic ratio 234U/238U varies between 0.95 and 3.50 and is correlated with the different aquifer types and water flow paths in the study area. Lower values (up to 1.10) are located in the shallow porous aquifer indicating younger waters. Moderate values of the activity ratio characterise the deeper porous aquifer as well as the fissured rock aquifer (1.5–2.05). The geothermal spring illustrates the highest activity ratio (3.5) due to older water.