title: Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: Characterising the atmospheric mixing state.
abstract: 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.
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia. Electronic address: szc@ansto.gov.au.
authors: Scott D
authors: SD
authors: Chambers
authors: "Horia Hulubei" National Institute for Physics and Nuclear Engineering, 30 Reactorului St., POB MG-6, 077125 Bucharest, Magurele, Romania.
authors: Dan
authors: D
authors: Galeriu
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
authors: Alastair G
authors: AG
authors: Williams
authors: "Horia Hulubei" National Institute for Physics and Nuclear Engineering, 30 Reactorului St., POB MG-6, 077125 Bucharest, Magurele, Romania.
authors: Anca
authors: A
authors: Melintescu
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
authors: Alan D
authors: AD
authors: Griffiths
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
authors: Jagoda
authors: J
authors: Crawford
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
authors: Leisa
authors: L
authors: Dyer
authors: "Horia Hulubei" National Institute for Physics and Nuclear Engineering, 30 Reactorului St., POB MG-6, 077125 Bucharest, Magurele, Romania.
authors: Marin
authors: M
authors: Duma
authors: "Horia Hulubei" National Institute for Physics and Nuclear Engineering, 30 Reactorului St., POB MG-6, 077125 Bucharest, Magurele, Romania; Department of Electricity, Solid Physics and Biophysics, Faculty of Physics, University of Bucharest, Magurele, Romania.
authors: Bogdan
authors: B
authors: Zorila
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D001272:Atmosphere / Q000737:chemistry*; D002940:Circadian Rhythm; D011834:Radiation Monitoring / Q000379:methods*; D011886:Radon / Q000032:analysis*; D012383:Romania; D012621:Seasons
chemical_list: D000396:Air Pollutants, Radioactive; D011886:Radon
keywords: (222)Rn; Atmospheric stability; Mixing depth; Radioactive releases; Radon flux; Tritium