Browsing by Author "Melintescu, A"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    Ensuring robust radiological risk assessment for wildlife: insights from the International Atomic Energy Agency EMRAS and MODARIA programmes
    (Published on behalf of the Society for Radiological Protection by IOP Publishing Limited, 2022-05-03) Beresford, NA; Beaugelin-Seiller, K; Barnett, CL; Brown, JE; Caffrey, EA; Johansen, MP; Melintescu, A; Ruedig, E; Vandenhove, H; Vives i Batlle, J; Wood, MD; Yankovich, TL; Copplestone, D
    In response to changing international recommendations and national requirements, a number of assessment approaches, and associated tools and models, have been developed over the last circa 20 years to assess radiological risk to wildlife. In this paper, we summarise international intercomparison exercises and scenario applications of available radiological assessment models for wildlife to aid future model users and those such as regulators who interpret assessments. Through our studies, we have assessed the fitness for purpose of various models and tools, identified the major sources of uncertainty and made recommendations on how the models and tools can best be applied to suit the purposes of an assessment. We conclude that the commonly used tiered or graded assessment tools are generally fit for purpose for conducting screening-level assessments of radiological impacts to wildlife. Radiological protection of the environment (or wildlife) is still a relatively new development within the overall system of radiation protection and environmental assessment approaches are continuing to develop. Given that some new/developing approaches differ considerably from the more established models/tools and there is an increasing international interest in developing approaches that support the effective regulation of multiple stressors (including radiation), we recommend the continuation of coordinated international programmes for model development, intercomparison and scenario testing. © 2022 Society for Radiological Protection.
  • No Thumbnail Available
    Item
    Radon-222 related influence on ambient gamma dose
    (Elsevier, 2018-09) Melintescu, A; Chambers, SD; Crawford, J; Williams, AG; Zorila, B; Galeriu, D
    Ambient gamma dose, radon, and rainfall have been monitored in southern Bucharest, Romania, from 2010 to 2016. The seasonal cycle of background ambient gamma dose peaked between July and October (100–105 nSv h−1), with minimum values in February (75–80 nSv h−1), the time of maximum snow cover. Based on 10 m a.g.l. radon concentrations, the ambient gamma dose increased by around 1 nSv h−1 for every 5 Bq m−3 increase in radon. Radon variability attributable to diurnal changes in atmospheric mixing contributed less than 15 nSv h−1 to the overall variability in ambient gamma dose, a factor of 4 more than synoptic timescale changes in air mass fetch. By contrast, precipitation-related enhancements of the ambient gamma dose were 15–80 nSv h−1. To facilitate routine analysis, and account in part for occasional equipment failure, an automated method for identifying precipitation spikes in the ambient gamma dose was developed. Lastly, a simple model for predicting rainfall-related enhancement of the ambient gamma dose is tested against rainfall observations from events of contrasting duration and intensity. Results are also compared with those from previously published models of simple and complex formulation. Generally, the model performed very well. When simulations underestimated observations the absolute difference was typically less than the natural variability in ambient gamma dose arising from atmospheric mixing influences. Consequently, combined use of the automated event detection method and the simple model of this study could enable the ambient gamma dose “attention limit” (which indicates a potential radiological emergency) to be reduced from 200 to 400% above background to 25–50%. © 2018 Elsevier Ltd.
  • Thumbnail Image
    Item
    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).