K. Holý

Dispersion of Fukushima radionuclides in the global atmosphere and the ocean

Large quantities of radionuclides were released in March-April 2011 during the accident of the Fukushima Dai-ichi Nuclear Power Plant to the atmosphere and the ocean. Atmospheric and marine modeling has been carried out to predict the dispersion of radionuclides worldwide, to compare the predicted and measured radionuclide concentrations, and to assess the impact of the accident on the environment. Atmospheric Lagrangian dispersion modeling was used to simulate the dispersion of (137)Cs over America and Europe. Global ocean circulation model was applied to predict the dispersion of (137)Cs in the Pacific Ocean. The measured and simulated (137)Cs concentrations in atmospheric aerosols and in seawater are compared with global fallout and the Chernobyl accident, which represent the main sources of the pre-Fukushima radionuclide background in the environment. The radionuclide concentrations in the atmosphere have been negligible when compared with the Chernobyl levels. The maximum (137)Cs concentration in surface waters of the open Pacific Ocean will be around 20 Bq/m(3). The plume will reach the US coast 4-5 y after the accident, however, the levels will be below 3 Bq/m(3). All the North Pacific Ocean will be labeled with Fukushima (137)Cs 10 y after the accident with concentration bellow 1 Bq/m(3).

Aerosol radioactivity record in Bratislava/Slovakia following the Fukushima accident – A comparison with global fallout and the Chernobyl accident

Results of radioactivity measurements in Bratislava aerosols following the Fukushima accident showed that at least three radioactive plumes arrived to Bratislava as indicated by (131)I/(137)Cs activity ratios. When compared with the Chernobyl results available for the Bratislava station, the Fukushima radionuclide levels were almost five orders of magnitude lower, with the maximum values for (131)I and (137)Cs of 0.5 and 0.07 mBq/m(3), respectively. The (131)I and (137)Cs vs. (7)Be aerosol activity records showed that the increases in (131)I and (137)Cs activity concentrations were accompanied by (7)Be increases, indicating that both the horizontal and vertical transports of radionuclides were responsible for observed radionuclide concentrations. The (134)Cs/(137)Cs activity ratio was close to 1, as has also been reported by other investigators.

Aerosol radioactivity monitoring in Bratislava following the Chernobyl accident

The radiation situation in Bratislava following the Chernobyl accident is discussed. Measurement results of γ- and α-radioactivity of aerosols are presented. The evolution of the activity ratios in air for some radionuclides is discussed. Their distribution indicates different transport and deposition properties for the volatile and nonvolatile fission products. The results are compared with long-term measurements of anthropogenic radionuclides released to the atmosphere by nuclear bomb tests.

Forty years of atmospheric radiocarbon monitoring around Bohunice nuclear power plant, Slovakia.

Radiocarbon variations in the atmospheric CO(2) with attenuating amplitudes and decreasing mean values with typical maxima in summer and minima in winter have been observed since 1967 in two localities of Slovakia, in Bratislava and Zlkovce, situated about 60 km NE from Bratislava, only 5 km from the Bohunice Nuclear Power Plant (NPP). The (14)C record in Bratislava has been influenced mainly by fossil CO(2) emissions, in contrast to the Zlkovce record which has been more variable, as it has clearly been affected by operation of the Bohunice NPP. However, during specific meteorological conditions with NE transport of air masses to Bratislava, the effect of the Bohunice NPP has been visible in Bratislava as well. Maximum (14)C concentrations (up to 120% above a natural background) were observed around A1 NPP which used CO(2) with admixture of air as a cooling agent. The (14)C concentrations around four pressurized light water reactors were up to 30% above the background. The Delta(14)C values in the heavily polluted atmosphere of Bratislava were up to 10% and at Zlkovce up to 5% lower than the European clean air represented by the Jungfraujoch Delta(14)C data. Later the Delta(14)C values were similar at both sites, and from 2003 they were close to the European clean air levels. The observed Delta(14)C behaviour in the atmosphere provides a unique evidence of decreased fossil fuel CO(2) emissions in the region, as well as the long-term effect of the Bohunice NPP on the Bratislava and Zlkovce stations. The estimated annual radiation doses to the local public due to digestion of radiocarbon contaminated food have been estimated to be around 3 microSv.

Long-term variations of 14C and 137Cs in the Bratislava air – implications of different atmospheric transport processes

This study summarizes measurements of atmospheric (14)C and (137)Cs in the Bratislava air since 1976. Higher (14)C levels observed in spring and early summer months until the 1980s confirm injection of the stratospheric air into the troposphere. Later, deep winter minima were observed in (14)C concentrations, probably due to the depletion of the atmospheric (14)C levels in winter months by the injection of large quantities of fossil CO(2). Presently observed (14)C maxima in summer and minima in winter were caused by the depletion of the atmospheric (14)C in winter months, amplified by temperature inversions during winter, rather than by the injection of the stratospheric air into the troposphere. The observed (137)Cs activity concentrations also showed an impact of the stratospheric air on the (137)Cs levels until the early 1980s, documented by typical spring/early summer maxima and winter minima. The global fallout (137)Cs record was then disturbed by the Chernobyl accident (1986) when large quantities of (137)Cs were released to the atmosphere. The recent (137)Cs variations observed in the atmosphere, characterised by winter maxima and summer minima, are assumed to be mainly due to the resuspension of (137)Cs from the soil. A correlation was found between the (137)Cs activity concentration and the dust level in the air (the correlation coefficient r = 0.74), as well as an anticorrelation with the temperature (r = -0.56).

Fukushima-derived radionuclides in ground-level air of Central Europe: a comparison with simulated forward and backward trajectories

Results of forward and backward modeling of air mass transport from Fukushima Daiichi nuclear power plant to Slovakia were compared with aerosol radioactivity measurements. Several radionuclide maxima (131I, 134Cs and 137Cs) were observed in the Bratislava ground-level air in March–April 2011. The 131I/137Cs activity ratio records showed the presence of two different fresh air masses in the Bratislava air, supported by simulations of forward and backward trajectories between Fukushima and Bratislava.

Impact of the Bohunice Nuclear Power Plant on atmospheric radiocarbon.

Radiocarbon variations in the atmospheric CO(2) have been observed at two localities in Slovakia (Bratislava and Zlkovce). Zlkovce is situated about 60 km NE from Bratislava, and only 5 km from the Bohunice Nuclear Power Plant (NPP). The observed Delta(14)C levels provide a unique evidence of the long-term impact of the Bohunice NPP on the Bratislava region, as well as on the decreased fossil fuel CO(2) emissions. The radiation doses estimated to the local public have been around 3 microSv/year, 20% of the dose from global fallout (14)C present in the environment.

Preliminary results of indoor radon survey in V4 countries

The measurements of radon activity concentration carried out in residential houses of V4 countries (Hungary, Poland and Slovakia) show that radon levels in these countries considerably exceed the world average. Therefore, the new radon data and statistical analysis are required from these four countries. Each partner chose a region in their own country, where radon concentration in residential buildings was expected to be higher. The results of the survey carried out in the period from March 2012 to May 2012 show that radon concentrations are <200 Bq m(-3) in ∼87% of cases. However, dwellings with radon concentration ∼800 Bq m(-3) were found in Poland and Slovakia. It was also found that the distribution of radon frequency follows that of houses according to the year of their construction.

Radionuclide content in some building materials and their radon exhalation

The activity concentrations of natural radionuclides in sands, gravels, cements and in different kinds of concretes were measured by γ-spectrometric methods. The222Rn exhalation rate from concretes was measured by closed chamber method and the emanation coefficient was calculated. Both used methods are described in detail and obtained results are discussed from point of view of allowed hygienic limits.

Indoor radon survey in Visegrad countries.

The indoor radon measurements were carried out in 123 residential buildings and 33 schools in Visegrad countries (Slovakia, Hungary and Poland). In 13.2% of rooms radon concentration exceeded 300Bqm(-3), the reference value recommended in the Council Directive 2013/59/EURATOM. Indoor radon in houses shows the typical radon behavior, with a minimum in the summer and a maximum in the winter season, whereas in 32% of schools the maximum indoor radon was reached in the summer months.