Study of the atmospheric radon concentration dynamics at the spanish radiological surveillance stations and its application to air mass movements
- Autores: Delia Arnold Arias
- Directores de la Tesis: Arturo Vargas Drechsler (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2009
- Idioma: español
- Tribunal Calificador de la Tesis: Xavier Ortega Aramburu (presid.), Francisco Fernández Moreno (secret.), Fernando Martín Llorente (voc.), Matthias Zahringer (voc.), Gernot Butterweck (voc.)
- Materias:
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- Resumen
In case of a radioactive release into the environment one of the biggest concerns is its highly effective dispersion in air. In Spain, a dense automatic stations network (REA) provides real-time meteorological and radiological measurements, including ambient radon concentrations.
In this work, state-of-the-art atmospheric transport models and methodologies are tested and applied as the starting point to determine optimizations and improvements in the REA surveillance network. FLEXPARTv6.2 and MM5V3.7- FLEXPARTv6.2 models are used since they are commonly used in radioactivity studies and they can work in backwards, which is the most efficient approach in these cases.
A validation study of the models and methodologies has been done first, showing that the methodology used, which combines source-receptor sensitivities obtained with FLEXPART in backwards mode with a gridded radon emission inventory, works properly. Also, that both the meteorological fields and the station location are critical in accurate transport modelling.
The characterization of the temporal and spatial variations of ambient 222Rn concentrations at the stations has been carried out in order to identify the main patterns and influencing parameters. Atmospheric stability and the surrounding topography and geology have been found to be key factors in the temporal evolution of ambient 222Rn concentrations and its average values.
After validation, the procedure is applied to a set of selected REA stations under typical meteorological scenarios. An heterogeneous 222Rn emission inventory based on the European Radon Flux map combined with the Spanish terrestrial gamma dose rate map (MARNA) has been used as well as a simpler constant radon flux map in the prediction of ambient radon concentration time series. The results have then been compared with the measurements, finding that FLEXPARTv6.2 is able to reproduce the synoptic variations properly but may underestimate the nocturnal peaks under very stable conditions, when complex thermally induced flows are involved.
Additionally, a study on regional transport at the Cabauw station, located in The Netherlands where the topographical-induced flows are minimal, is presented. It shows how different fetch regions influence the final measured and modelled ambient 222 Rn concentrations.
As a second application, a fictitious scenario with a release from a Nuclear Power Plant (NPP) has been simulated using a source-oriented approach to study the evolution of the radioactive plume and the performance of the models under these conditions. Results are compared with the commonly used Real-time On-line Decision Support system for nuclear emergencies (RODOS).
A final set of recommendations is given within the conclusions with two purposes. One is to assist future studies in the choice of models, methodology and data depending on time constraints, importance for emergency response systems, data accessibility and station/release point location. The other, to aim at further development of the methodology and models to finally being able to introduce them in the emergency systems in an operational way.
