Detailed deposition density maps constructed by large-scale soil sampling for gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident.
Soil deposition density maps of gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant (NPP) accident were constructed on the basis of results from large-scale soil sampling. In total 10,915 soil samples were collected at 2168 locations. Gamma rays emitted from the samples were measured by Ge detectors and analyzed using a reliable unified method. The determined radioactivity was corrected to that of June 14, 2011 by considering the intrinsic decay constant of each nuclide. Finally the deposition maps were created for (134)Cs, (137)Cs, (131)I, (129m)Te and (110m)Ag. The radioactivity ratio of (134)Cs-(137)Cs was almost constant at 0.91 regardless of the locations of soil sampling. The radioactivity ratios of (131)I and (129m)Te-(137)Cs were relatively high in the regions south of the Fukushima NPP site. Effective doses for 50 y after the accident were evaluated for external and inhalation exposures due to the observed radioactive nuclides. The radiation doses from radioactive cesium were found to be much higher than those from the other radioactive nuclides.
Fukushima fallout in Sakhalin Region , Russia , part 1 : 137 Cs and 134 Cs in grassland soils
The 2011 accident at the Fukushima-Daiichi nuclear power plant (FDNPP) resulted in the atmospheric releases of large quantities of man-made radionuclides [1, 2, 3]. In the mediumand long-term perspective, the Cs (T 1/2 = 30 y) and Cs (T 1/2 = 2.06 y) radionuclides were of the major radiological concern [4, 5, 6]. The most significant radioactive contamination occurred on Honshu Island in Japan in the immediate vicinity of the FDNPP, where the density of ground contamination by Cs reached the level of 3000 kBq m−2 and even higher [6]. More than 100000 citizens were evacuated or voluntary left the affected areas; various remediation actions were initiated at the heavily contaminated sites of Japan [1, 7, 8]. After the accident, Fukushima-derived Cs and Cs were also detected in the environmental media in many other countries in the Northern Hemisphere [2, 3]. Here, the Cs and Cs activity concentrations in environmental samples and food-staff, the ground deposition densities of the radionuclides, and expected exposure of humans were significantly lower compared to the permissible levels (e.g., [5, 9]). Results of such studies were beneficial to reduce social anxiety in the early period after the accident [5, 10]. At the same time, the measurement data collected after the Fukushima accident beyond the territory of Japan could be used as an experimental background for verification and improvement of the large-scale models describing atmospheric dispersion and deposition of radionuclides over the globe and assessment of the environmental and human health risks [9, 11]. Additionally, the Fukushima accident triggered a new wave of radioecological studies which have refreshed and deepened the knowledge about current levels of DOI: 10.21514/1998-426Х-2018-11-1-25-42 УДК: 546.36:621.039.586:614.876(571.64)
Phase characterisation of simulated high burn-up UO2 fuel
Abstract To determine the lattice constant variation with burn-up and the oxidation behaviour at high temperatures, simulated UO2-spent fuels with burn-ups up to 200 GWd tM−1 were prepared by cold pressing and sintering and characterised by X-ray diffraction analysis and thermogravimetry. The fcc-lattice parameter of the sintered samples determined at room temperature, showed a continuous decrease with the simulated burn-up. During oxidation the conversion of the simulated fuels to the (U,FP)4O9 and (U,FP)3O8-type phases was strongly delayed when the simulated burn-up exceeded 80 GWd tM−1. Also, at high burn-ups (>100 GWd tM−1), large fractions of the (U,FP)4O9-type phase remained untransformed to (U,FP)3O8 after prolonged exposure to air at 950–1000°C. This suggests a marked widening of the (U,FP)4O9-phase field when the amount of substituted uranium atoms exceeds values of about 8%.