Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017.

In October 2017, most European countries reported unique atmospheric detections of aerosol-bound radioruthenium (106Ru). The range of concentrations varied from some tenths of µBq·m-3 to more than 150 mBq·m-3 The widespread detection at such considerable (yet innocuous) levels suggested a considerable release. To compare activity reports of airborne 106Ru with different sampling periods, concentrations were reconstructed based on the most probable plume presence duration at each location. Based on airborne concentration spreading and chemical considerations, it is possible to assume that the release occurred in the Southern Urals region (Russian Federation). The 106Ru age was estimated to be about 2 years. It exhibited highly soluble and less soluble fractions in aqueous media, high radiopurity (lack of concomitant radionuclides), and volatility between 700 and 1,000 °C, thus suggesting a release at an advanced stage in the reprocessing of nuclear fuel. The amount and isotopic characteristics of the radioruthenium release may indicate a context with the production of a large 144Ce source for a neutrino experiment.

Potential Source Apportionment and Meteorological Conditions Involved in Airborne 131I Detections in January/February 2017 in Europe.

Traces of particulate radioactive iodine (131I) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 µBq m-3 except at one location in western Russia where they reached up to several mBq m-3. Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of 131I resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related to 131I use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

Continuous measurement of radiation from radionuclides deposited on the ground using in situ gamma-ray spectrometry.

Until recently, in situ measurements in a network of radiation-measuring sites at the Deutscher Wetterdienst could only be started if all components had been put up in an instrumentation shelter and the detector had been cooled for ∼6 h. Within a project on partial automation of radioactivity monitoring, it has now become possible to permanently equip the measuring sites, i.e. the instrumentation shelter, with the components for in situ gamma-ray spectrometry. The cooling technology of the detectors changed from liquid nitrogen based to an electric system and the instrumentation shelters could be fixed with air conditioning to minimise the influence of changes in the outside temperature.

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.

The german thorotrast study: recent results and assessment of risks.

The German Thorotrast study comprises 2,326 patients and 1,890 controls. Forty-eight Thorotrast patients and 239 controls are still alive and are invited for a follow-up examination every 2 years. In the deceased patients, the following neoplastic diseases with excess rates were registered (Thorotrast/controls): liver cancer (454/3); cancer of the bile ducts, including gallbladder (42/7); myeloid leukemia (40/7); myelodysplastic syndrome (30/4); plasmacytoma (10/2); non-Hodgkin's lymphoma (15/5); bone sarcoma (4/1); malignant peritoneal or pleural mesothelioma (9/0). Dose calculations are based on results of whole-body counting, X-ray films, and data obtained from the hospital records on the volume of Thorotrast injected. For liver cancer, the cumulative risk estimate was calculated to be 40 per 10(4) person Sv (radiation weighting factor = 20). These figures are close to the results of the Danish study and are comparable to the results of the Life Span Study of A-bomb survivors after 40 years at risk with 18 to 48 liver cancers per 10(4) person Sv. For hematopoietic malignancies, the cumulative risk was calculated to be about 7 per 10(4) person Sv (radiation weighting factor = 20). This risk estimate is lower by a factor of 10 compared to the results of the Life Span Study.

Depth-dose distribution in bricks determined by thermoluminescence and by Monte-Carlo calculation for external gamma-dose reconstruction.

The analysis of depth-dose distributions in bricks sampled from walls in areas with nuclear waste or accident contamination has the potential of providing information on the energy and source configuration of the gamma-radiation that had been incident on the brick. In this study, a brick from a mill facing a shallow water reservoir of the contaminated Techa river in the South Ural region is investigated. Thermoluminescence (TL) methods were used to measure the accumulated dose at several depths in the brick. The accidental external gamma-dose is obtained by subtracting the natural radiation background dose from the total accumulated dose. In the first segment of the brick, at a depth of about 1.5 cm, the accident dose was found to be roughly 3.5 Gy. Monte-Carlo simulations of the photon transport from the reservoir bed contaminated with 137Cs were calculated for different depths in the brick. The calculations were made assuming different attenuating water levels. It is found that the depth-dose distribution determined by measurements corresponds to a water level between 20 and 50 cm. The results indicate that TL measurements combined with Monte-Carlo modelling calculations are highly promising for external gamma-dose reconstruction applications.

Analysis of tissue samples containing colloidal thorium dioxide (Thorotrast) or zirconium dioxide (Zirconotrast): radiochemical preparation and alpha-spectrometry.

The aim of the present study is to assess the activity of the thorium isotopes, Th-232, Th-230, and Th-228 in tissue samples containing Thorotrast or Radiozirconotrast, i.e. Th-230 and Th-228 enriched Zirconotrast, in order to enable calculations of tissue doses. Therefore: 1. a procedure was developed for radiochemical processing of these samples, and 2. a computerised alpha-spectroscopy system has been constructed for routine activity measurements. The procedure developed for sample preparation permitted complete radiochemical processing of the above tissue samples. By subsequent electrodeposition of the thorium isotopes as well as the internal isotopic tracer Th-229, almost massless sources were obtained for alpha-spectrometry. The recovery amounts to a mean of 85% and 70% for tissues containing Thorotrast and Radiozirconotrast. With regard to the great number of samples to be measured and the expected counting times of more than 1500 min, a computerised alpha-spectroscopy system with a sample conveyor has been constructed. The energy resolution is between 45 keV and 75 keV FWHM. The detection efficiency amounts to 12%. The values of the detection level for the thorium isotopes are between 1,4 mBq and 3,1 mBq.

Recent results of the German Thorotrast study--dose relevant physical and biological properties of Thorotrast equivalent colloids.

As a prerequisite for quantifying the non-radiation effect of Thorotrast, nonradioactive and radioactive aquasols with identical physicochemical properties and with biophysical behavior comparable to that of Thorotrast were developed and produced for a second long-term animal experiment. Comparative investigations with hafnium and zirconium (zirconotrast) dioxide aquasols showed the latter to be most appropriate considering the size of both the dispersoids and the aggregates in the liver tissue. The average particle diameters of ThO2, ZrO2 and HfO2 proved to be values of 9.3 nm, 15 nm and 45 nm, respectively. The size of the aggregates shows a slight dependence on the applied amount but no dependence on the duration of body burden of the colloid. The aggregate diameters in the 600 microliters group turned out to be 9.6 microns, 14.4 microns and 5.3 microns, respectively. Radioactive zirconotrast was prepared by radiochemical incorporation of 230Th and 228Th at dose rates which produce accumulated doses in the liver of rats equivalent to those of commercial 230Th enriched Thorotrast after 1.5 yr. Five different colloids were prepared with alpha-energy emission rates increased by factors of 1, 2.5, 5, 10 and 25 compared to Thorotrast and then injected into rats.