Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment

Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled...

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Main Authors: Gonze Marc-André, Mourlon Christophe, Calmon Philippe, Manach Erwan, Debayle Christophe, Baccou Jean
Format: Article
Language:English
Published: EDP Sciences 2017-01-01
Series:EPJ Web of Conferences
Online Access:https://doi.org/10.1051/epjconf/201715308004
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spelling doaj-d7303b1f13a640c5990b3539c873ffce2021-08-02T01:13:22ZengEDP SciencesEPJ Web of Conferences2100-014X2017-01-011530800410.1051/epjconf/201715308004epjconf_icrs2017_08004Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environmentGonze Marc-André0Mourlon Christophe1Calmon Philippe2Manach Erwan3Debayle Christophe4Baccou Jean5IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire de Modélisation pour l’Expertise Environnementale (LM2E)IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire de Modélisation pour l’Expertise Environnementale (LM2E)IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire d’Études Radioécologiques en milieux Continental et Marin (LERCM)IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire de Surveillance Atmosphérique et d’Alerte (LS2A)IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire de Surveillance Atmosphérique et d’Alerte (LS2A)IRSN, Institute for radiological Protection and Nuclear Safety, Laboratoire Incertitude et Modélisation des Accidents de Refroidissement (LIMAR)Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium. The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas). Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time.https://doi.org/10.1051/epjconf/201715308004
collection DOAJ
language English
format Article
sources DOAJ
author Gonze Marc-André
Mourlon Christophe
Calmon Philippe
Manach Erwan
Debayle Christophe
Baccou Jean
spellingShingle Gonze Marc-André
Mourlon Christophe
Calmon Philippe
Manach Erwan
Debayle Christophe
Baccou Jean
Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
EPJ Web of Conferences
author_facet Gonze Marc-André
Mourlon Christophe
Calmon Philippe
Manach Erwan
Debayle Christophe
Baccou Jean
author_sort Gonze Marc-André
title Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
title_short Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
title_full Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
title_fullStr Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
title_full_unstemmed Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment
title_sort modelling the dynamics of ambient dose rates induced by radiocaesium in the fukushima terrestrial environment
publisher EDP Sciences
series EPJ Web of Conferences
issn 2100-014X
publishDate 2017-01-01
description Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium. The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas). Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time.
url https://doi.org/10.1051/epjconf/201715308004
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