Tracking of airborne radionuclides from the damaged Fukushima Dai-ichi nuclear reactors by European networks.

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ((131)I) and cesium isotopes ((137)Cs and (134)Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous (131)I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous (131)I and the large underestimation of the total (131)I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous (131)I fraction to total (131)I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the (134)Cs to (137)Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total (131)I inventory that has passed over Europe during this period was <1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe.

HUMAN EXPOSURE TO BACKGROUND RADIATION IN ORTUM, KENYA.

The activity concentration of radionuclides 238U, 232Th and 40K in soil and the absorbed dose rate (ADRA) at 1 m above the ground in Ortum was determined. The activity concentration in soils ranged from 33 to 85, 20 to 67 and 148-1019 Bq kg-1, respectively with an average of 40 ± 1.43, 56 ± 1.46 and 425 ± 19.24 Bq kg-1, respectively. The activity concentration of 232Th and 238U was found to reduce with increasing depth while that of 40K increased with increasing depth. The average activity concentration in soil was higher than the world average values. The average ADRA in air at 1 m above the ground was found to be 112 ± 29.6 nGy h-1. The soil and rocks in Ortum are recommended for use because the activity concentration of the terrestrial radionuclides is lower than the recommended threshold values.

Certified Reference Material IAEA-446 for radionuclides in Baltic Sea seaweed.

A Certified Reference Material (CRM) for radionuclides in seaweed (Fucus vesiculosus) from the Baltic Sea (IAEA-446) is described and the results of the certification process are presented. The (40)K, (137)Cs, (234)U and (239+240)Pu radionuclides were certified for this material, and information values for 12 other radionuclides ((90)Sr, (99)Tc, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (230)Th, (232)Th, (235)U, (238)U, (239)Pu and (240)Pu) are presented. The CRM can be used for Quality Assurance/Quality Control of analysis of radionuclides in seaweed and other biota samples, as well as for development and validation of analytical methods, and for training purposes.

Car-borne gamma spectrometry: a virtual exercise in emergency response.

In recent years car-borne gamma spectrometry has expanded from its role as a geological survey platform to being a useful asset in searching for orphan sources and for surveying in the aftermath of an incident involving the release of radioactive materials. The opportunities for gaining practical experience in the field however are limited by cost considerations and practicability. These limitations are exacerbated by the fact that field data can differ significantly from data generated in the laboratory. As a means of exercising existing emergency measuring/surveying capability and introducing car-borne measurements to a larger group, a virtual exercise was devised. The exercise ORPEX (Orphan Sources and Fresh Fallout Virtual Exercise in Mobile Measurement) featured two typical emergency scenarios: a search for orphan sources and surveying to delineate fallout from a local release point. Synthetic spectral data were generated for point sources and inserted into genuine car-borne measurement data. Participants were presented with a typical software tool and data and were asked to report source locations and isotopes within a time limit. In the second scenario, synthetic data representing fallout from a local fire involving radioactive material were added to real car-borne data, participants being asked to produce maps identifying and characterising the regions of contamination. Fourteen individual organisations from seven different countries supplied results which indicated that for strong sources of isotopes with simple spectra featuring high energy peaks, location and identification was not a problem. Problems arose for isotopes with low energy signals or that presented a weak signal even when visible for extended periods. Experienced analysts tended to perform better in identification of sources irrespective of experience with mobile measurements whereas those with experience in such measurements were more confident in providing more precise estimates of location. The results indicated the need for the inclusion of less frequently encountered sources in field exercise related to mobile measurements.