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This paper presents the approach, assumptions, and computational analysis of the preliminary safety assessment, regarding the post-closure period for the disposal of radioactive waste in Greece. The assessment was implemented in the context of the National Program for the disposal of radioactive waste in the country, which is currently in the early stage for the investigation of facility siting. The basis scenario selected for this investigation was the leaching of radionuclides and the exposure in a residence offsite. Moreover, a scenario involving the intrusion in the facility and construction of a dwelling that disturbs the disposal zone is also considered. Due to the significant uncertainties in the current phase, the simulations related to leaching of the waste both in the offsite and intrusion scenarios are based on an uncertainty analysis with 25 site and scenario related parameters. The most important contribution is attributed to Ra-226 with an annual dose equal to about 2 and 3 μSv per MBq disposed, for the offsite and intrusion scenario, respectively. Th-232, Cl-36, C-14, Ag-108m and Pu-239 follow with a dose one order of magnitude less, compared to Ra-226. In the leaching scenarios examined, and for the most dose relevant radionuclides, the exposure related to drinking water from the well and the use of this water to irrigate fruits and vegetables are by far the dominant pathways due to the environmental transfer of the radionuclides and their associated dose coefficients. Th-232 dominates the direct exposure pathways (direct external radiation and plant contamination from the contaminated surface soil) in the intrusion scenario with an annual dose of about 1.4 mSv per Bq/g disposed. Ra-226, Cl-36 and Ag-108m cause exposure levels higher than 0.2 mSv/y per Bq/g disposed in the facility. A wide range was considered for the uncertainty parameters that led to a significant variation in the predicted doses that is expected to envelope the potential exposure for each radionuclide. • A preliminary safety assessment of non-nuclear radioactive waste in an early stage of the disposal program was implemented. • An extensive uncertainty analysis of modelling parameters was performed for offsite and intrusion scenarios. • A large variation of the predicted dose was found depending on the parameter's combination. • The most dose relevant radionuclides include Ra-226, Th-232, Cl-36, C-14, Ag-108m and Pu-239. • Annual effective doses per unit activity used to assess the contribution of each radionuclide. [ABSTRACT FROM AUTHOR]

The aim of this paper was to study the variations of radon and daughter nuclei during treatment in the thermal spas of Lesvos Island (Greece). For this purpose, in the thermal spas of Lesvos we have measured the radon concentrations of thermal waters, as well as indoor radon, daughter and coarse particle (>500 nm) concentrations. Various instruments and procedures were employed for measurements. Radon concentrations of thermal waters were found to lie in the range 10 Bq l-1 and 304 Bq l-1. Concentration peaks both for radon, radon daughter and coarse particle, were found to appear during filling of baths in the treatment process. The doses delivered to the bathers during treatment were in the range of 0.00670–0.1279 mSv per year, while the doses delivered to personnel were below 20 mSv per year. [Copyright &y& Elsevier]

This study focused on the radon transfer from the water to the air and the subsequent impact of waterborne radon indoors, taking advantage of the enhanced and decreasing from year to year radon-in-water concentrations observed in the Arnea village in Northern Greece. Some other essential aspects and observations regarding radon-in-water were also discussed. Concerning radon transfer from water to the air, the transfer efficiencies for showering and the use of the bathroom tap were estimated by measuring the radon-in-water and the waterborne radon-in-air concentrations in sealed bathrooms of two apartments in Arnea. The transfer efficiency for the bathroom tap use ranged from 22 to 28.9% for water flow rates of 2.7-7 L min -1 . For showering, the transfer efficiency ranged from 45 to 48.3% for water flow rates of 6 L min -1 and 8 L min -1 , respectively. As for the impact of waterborne radon indoors, each year's two-week monitoring of radon-in-water and radon-in-air concentrations in a house in Arnea from 2018 to 2022 revealed rapid and sharp increases in the bathroom air related to waterborne radon. Following the results obtained in the house's bathroom in Arnea, showering is the most significant exposure of humans to waterborne radon due to the person's proximity to waterborne radon, the enclosed space, the high transfer efficiency of showering, and the significant amount of water consumed. Each year's two-week average indoor radon concentrations measured in the examined house in Arnea showed that waterborne radon's contribution is less important than the other parameters affecting indoor radon, such as ventilation rates and radon emanation from the soil beneath the house's structure. Time variation (2018-2022) of radon activity concentration measured in a borehole supplying Arnea with water showed a relatively low standard deviation (10.2%) at a coverage factor of k = 1. A disequilibrium was observed between radon and its progenies immediately after pumping water from a borehole. This disequilibrium was observed for 1.3 years and seems to be continuous. Regarding radon removal from water, the diffused bubble aeration System constructed in Arnea reduces the radon-in-water activity concentration by more than 90% when using an air-to-water ratio of 10:1 and a detention time of 60 min. The System does not affect the adjacent outer space radon-in-air concentrations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The measurement of radiotracers is recognized as a major tool for the investigation and characterization of submarine groundwater discharges, while the use of underwater gamma-ray spectrometry has been proved a robust solution for the qualitative and quantitative determination of radionuclides in the aquatic environment. The capability of online continuous monitoring of submarine springs by means of gamma-ray spectrometry for direct estimation of SGD velocity and discharge is presented. The quantification of SGD flux rate is based on radon progenies time-series provided by two spectrometers placed above the seabed and near the water surface respectively, coupled with water level and meteorological data. The proposed methodology has been applied for a 5-month period in a coastal karstic system where multiple submarine springs occur at Anavalos-Kiveri, Greece. The estimated flux rates derived from the measured activities revealed significant SGD temporal variations with the mean discharge of 12 m 3  s -1 being compatible with previous measurements. The advantages and limitations of direct SGD estimation via underwater gamma-ray monitoring are also discussed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Coal- and lignite-fired power plants produce significant amounts of ashes, which are quite often being used as additives in cement and other building materials. In many cases, coal and lignite present high concentrations of naturally occurring radionuclides, such as 238U, 226Ra, 210Pb, 232Th and 40K. During the combustion process, the produced ashes are enriched in the above radionuclides. The different enrichment of the various radionuclides within a radioactive series, such as that of 238U, results in the disturbance of radioactive secular equilibrium. An extensive research project for the determination of the natural radioactivity of lignite and ashes from Greek lignite-fired power plants is in progress in the Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) since 1983. This paper presents detailed results for the natural radioactivity, the secular radioactive equilibrium disturbance and the radon exhalation rate of the fly-ash collected at the different stages along the emission control system of a lignite-fired power plant as well as of the bottom-ash. From the results obtained so far, it may be concluded that 226Ra radioactivity of fly-ash in some cases exceeds 1 kBq kg(-1), which is much higher than the mean 226Ra radioactivity of surface soils in Greece (25 Bq kg(-1)). Furthermore, the radioactivity of 210Pb in fly-ash may reach 4 kBq kg(-1). These results are interpreted in relation to the physical properties of the investigated nuclides, the temperature in the flue-gas pathway, as well as the fly-ash grain size distribution. It is concluded that towards the coldest parts of the emission control system of the power plant, the radioactivity of some natural nuclides is gradually enhanced, secular radioactive equilibrium is significantly disturbed and the radon exhalation rate tends to increase.