Fission product activity ratios measured at trace level over France during the Fukushima accident A. de Vismes Ott a, * , R. Gurriaran a , X. Cagnat a , O. Masson b a Laboratoire de Mesure de la Radioactivité dans l’Environnement, Institut de Radioprotection et de Sûreté Nucléaire, PRP-ENV/STEME/LMRE, Bois des Rames, Bât 501, 91400 Orsay, France b Laboratoire d’Etudes Radioécologiques en milieux Continental et Marin, Institut de Radioprotection et de Sûreté Nucléaire, PRP-ENV/SESURE/LERCM, Cadarache, Bât 153, BP3,13115 Saint Paul Lez Durance, France article info Article history: Received 5 February 2013 Accepted 17 February 2013 Available online xxx Keywords: Fission products Low-level gamma-ray spectrometry Aerosol filters Fukushima Dai-ichi accident abstract The nuclear accident of Fukushima Dai-ichi (Japan) which occurred after the tsunami that impacted the northeast coasts of Japan on March 11th, 2011 led to significant releases of radionuclides into the at- mosphere and resulted in the detection of those radionuclides at a global scale. In order to track airborne radionuclides from the damaged reactors and to survey their potential impact on the French territory, the French Institute of Radiation Protection and Nuclear Safety (Institut de Radioprotection et de Sureté Nucléaire IRSN) set up an enhanced surveillance system to give quick results as needed and later give quality trace level measurements. Radionuclides usually measured at trace levels such as 137 Cs and in a very sporadic way 131 I were reported. Radionuclides that we had never measured in air since the Chernobyl accident: 134 Cs, 136 Cs, the mother/daughter pairs 129m Te- 129 Te and 132 Te- 132 I, and 140 La (from the mother-daughter pair 140 Ba- 140 La) were also reported. Except the 131 I/ 137 Cs ratio, activity concen- tration ratios were constant. These ratios could be used to help source term assessment, or as data for transfer studies realized after the passage of contaminated air masses, typically using the 134 Cs/ 137 Cs ratio. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The Great Tohoku earthquake that occurred off the Japanese northeast coast on March 11th, 2011 and the resulting tsunami that damaged the Fukushima Dai-ichi nuclear power plant resulted in several explosions at the reactors between March 12th and 15th. These explosions led to significant releases of radionuclides into the atmosphere. Atmospheric dispersion models (IRSN, 2011a) pre- dicted contaminated air masses would arrive over France around March 22nd with activity concentration for 131 I in the order of 1 mBq.m 3 (IRSN, 2011a). The French Institute of Radiation Protection and Nuclear Safety (IRSN) set up an enhanced surveillance system in order to track airborne radionuclides released by the damaged nuclear reactors, to assess their potential impacts on the French territory and to inform the population rapidly and precisely (IRSN, 2011b). In the framework of this enhanced surveillance system, the Environ- mental Radioactivity Measurement Laboratory (LMRE, Orsay, 30 km south of Paris) was in charge of the measurements by low level gamma-ray spectrometry of all the high volume aerosol filters taken from the OPERA-Air sampling network. Other samples were also measured during and after the Fukushima accident dealing with fallout and grass, meat and milk samples to study transfer of 131 I from Fukushima to vegetation and milk in France (Parache et al., 2011). This present paper presents the results acquired from the 138 high volume aerosol filters collected between 21st March and 22nd April. Results for 131 I and 134 Cs and 137 Cs have been used with those from more than forty other Eu- ropean institutes by Masson et al. (2011). This paper will thus focus on the organisation of the filter sampling and measurement, but will also extend the presentation to all the detected radionuclides. 2. Materials and methods 2.1. Aerosol sampling The surveillance of the whole French territory was implemented using the OPERA-Air (Observatoire PErmanent de la RAdioactivité) sampling network comprising 40 low-flow (10 m 3 h -1 ) home made samplers and 8 high and very high flow (i.e. 300 and 700 m 3 h -1 ) * Corresponding author. Tel.: þ33 (0) 1 69 85 58 39; fax: þ33 (0) 1 69 41 13 23. E-mail address: anne.de-vismes@irsn.fr (A. de Vismes Ott). Contents lists available at SciVerse ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad 0265-931X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2013.02.014 Journal of Environmental Radioactivity xxx (2013) 1e11 Please cite this article in press as: de Vismes Ott, A., et al., Fission product activity ratios measured at trace level over France during the Fukushima accident, Journal of Environmental Radioactivity (2013), http://dx.doi.org/10.1016/j.jenvrad.2013.02.014