Browsing by Author "Galeriu, D"

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    Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: characterising the atmospheric mixing state
    (Elsevier, 2016-04-01) Chambers, SD; Galeriu, D; Williams, AG; Melintescu, A; Griffiths, AD; Crawford, J; Dyer, LL; Duma, M; Zorila, B
    A radon-based nocturnal stability classification scheme is developed for a flat inland site near Bucharest, Romania, characterised by significant local surface roughness heterogeneity, and compared with traditional meteorologically-based techniques. Eight months of hourly meteorological and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility are analysed. Heterogeneous surface roughness conditions in the 1 km radius exclusion zone around the site hinder accurate characterisation of nocturnal atmospheric mixing conditions using conventional meteorological techniques, so a radon-based scheme is trialled. When the nocturnal boundary layer is very stable, the Pasquill–Gifford “radiation” scheme overestimates the atmosphere's capacity to dilute pollutants with near-surface sources (such as tritiated water vapour) by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s−1 and nocturnal mixing depths vary from ∼25 m to less than 10 m above ground level (a.g.l.). Combining nocturnal radon with daytime ceilometer data, we were able to reconstruct the full diurnal cycle of mixing depths. Average daytime mixing depths at this flat inland site range from 1200 to 1800 m a.g.l. in summer, and 500–900 m a.g.l. in winter. Using tower observations to constrain the nocturnal radon-derived effective mixing depth, we were able to estimate the seasonal range in the Bucharest regional radon flux as: 12 mBq m−2 s−1 in winter to 14 mBq m−2 s−1 in summer. © 2016, Elsevier Ltd.
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    Radon-based assessment of stability effects on potential radiological releases
    (HARMO, 2016-05-09) Chambers, SD; Williams, AG; Galeriu, D; Melintescu, A; Duma, M
    It is a requirement of nuclear energy and research facilities to conduct continuous and comprehensive atmospheric monitoring in order to better forecast public or environmental exposure to routine or accidental releases of radioactive substances to the atmosphere. A key aspect of such monitoring programs is the assessment of the atmospheric mixing state (or “stability”). Whether these facilities are in dense urban areas, or surrounded by heavily vegetated exclusion zones, local roughness heterogeneity can hamper attempts to accurately categorise stability by conventional meteorological techniques. Based on an analysis of 8 months of hourly climatology and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility (Bucharest, Romania), we develop and apply a continuous (i.e. not categorical) radon-based scheme for the classification of the nocturnal atmospheric stability state. We demonstrate the superior performance of the radon-based technique to Pasquill-Gifford or bulk Richardson number stability typing at this site where heterogeneous roughness elements reach to 15 m a.g.l. Under stable nocturnal conditions the Pasquill-Gifford scheme overestimates the atmosphere’s capacity to dilute pollutants with near-surface sources by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s-1 and nocturnal mixing depths vary from ~25 m to less than 10 m a.g.l. Climatological parameters are characterised by season and 4 arbitrarily-defined nocturnal stability categories. Benchmarks (based on 10/50/90th percentile distributions) of 30-60 m wind and temperature gradients are devised for each stability category for evaluation of model performance. Lastly, nocturnal radon-derived effective mixing depth estimates constrained by tower observations are used to better-constrain the seasonal variability in the Bucharest regional radon flux: 13 mBq m-2 s-1 (winter), 18 mBq m-2 s-1 (summer).