Preliminary safety assessment for planning near surface disposal of low-level radioactive waste in Greece.

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 Holistic Approach to Assessment of Population Exposure to Radiation: Challenges and Initiatives of a Regulatory Authority.

A regulatory authority for radiation safety should continuously evaluate and improve the national safety framework, in line with current requirements and standards. In this context, the Greek Atomic Energy Commission initiated a series of concerted actions. The radiation dose to the population due to public and medical exposures was assessed. The assessment of dose due to public exposure was based on measurements of radon concentrations in dwellings, radionuclide concentrations in environmental samples, and air dose rates; the assessment of dose due to medical exposure was based on dose measurements for typical examinations or procedures and data on their frequency. The mean effective dose to a member of the population was found to be 4.5 mSv (1.8 mSv and 2.7 mSv from medical and public exposures, respectively). Regarding occupational exposure, aircrew dose assessment, eye lens monitoring, and the national dose registry were significantly improved. With respect to artificial tanning (sun beds), the ultraviolet radiation produced was assessed and the practices followed were observed. Results demonstrated exceedance of the 0.3 W m erythema effective irradiance limit set in European Union standards by 63.5% of the sun beds measured, along with general noncompliance with standards. An overarching activity was the upgrade of the Greek Atomic Energy Commission information system in order to collect and disseminate radiation data electronically, launch a networking strategy for interaction with stakeholders, and facilitate the process of regulatory control. In response to the above findings, regulatory actions have been initiated.

DETERMINATION OF THE INTERNAL EXPOSURE OF GREEK CITIZENS RETURNING FROM JAPAN IMMEDIATELY AFTER THE FUKUSHIMA ACCIDENT.

Following the nuclear accident at the Fukushima Daiichi Nuclear Power Plant on 11 March 2011, during the period 17 March to 25 October 2011, a total of 22 Greek citizens were measured after their return to Greece. Artificial radionuclides were detected in 5 of the 22 measured individuals by whole body counter measurements conducted 10 and 11 d after the commencement of the accident. Of the 5 contaminated individuals, 3 were adults and 2 children, aged 9 and 5 y, who stayed for a single day in Tokyo. Dose calculations were performed assuming that the sole exposure pathway was through inhalation that occurred on 14 March, according to the information provided by them, using the detected artificial radionuclides in the spectra ((134)Cs, (137)Cs, (131)I). The estimated total committed effective doses calculated were found to be in the range of 9-280 µSv.

Data evaluation of laminar flow diffusion chamber nucleation experiments with different computational methods.

In order to evaluate the experimental data from laminar flow diffusion chamber (LFDC) experiments on homogeneous nucleation, an extensive postmeasurement computational analysis is required. The present work investigates the influence of the used computational methodology on the derived nucleation curves. To this end a reanalysis is made of previous LFDC experiments of 1-butanol nucleation in helium [D. Brus et al., J. Chem. Phys. 122, 214506 (2005)] using two different methods. The first method is based on single fluid heat and vapor transport in the carrier gas ignoring the aerosol processes, as commonly made in LFDC data evaluations. The second method is more comprehensive as is based on multidimensional computational fluid-particle dynamics. The calculations are made under the usual simplification of one-way coupling between fluid flow and particles, which is a valid approximation in most practical aerosols, while full aerosol dynamical effects are accommodated. Similar results were produced by the two methods. This finding corroborates the usual practice of omitting aerosol calculations in LFDC experimental data evaluation.