After the Fukushima Daiichi Nuclear Power Plant accident, atmospheric radiocesium concentration has been monitored by the Nuclear Regulation Authority as a national project to assess its temporal change from August 2011 to November 2017. During the first two years, the atmospheric radiocesium concentration ranged from 10 −1-10 0 Bq m −3 , while concentrations of 10 −5-10 −1 Bq m −3 were detected about seven years after the accident. Moreover, two years after the accident, the resuspension factor (RF) ranged from 10 −7-10 −6 m −1 and gradually decreased to 10 −11-10 −7 m −1 over time. Furthermore, to investigate the impact of anthropogenic activities on the temporal change of RF, the monitoring data were classified into two groups, namely inside and outside the Fukushima entry-restricted zone. The RF decreased faster in the second than in the first group, which was consistent with the reported data on the time dependence of the air dose rate, suggesting that anthropogenic activities promote environmental remediation and reduce atmospheric radiocesium content. Besides, the observed RF reduction in this study tends to be faster than that reported for the Chernobyl Nuclear Power Plant accident for the same period. Hence, this reduction rate should be assessed based on ongoing monitoring data in the future.

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This paper introduces a new vacuum and/or pressure forming system using a prepreg sheet which consists of two thickened layers of unsaturated polyester, i.e., FRP (Fiber Reinforced Plastic) and gel coat layers, sandwiched by two stretchable films. The efforts were focused on the development of sheet construction, material properties and processing conditions. The difficulties in the development of this system are found in; 1. uneven thickness distribution in a molding 2. vaporization of vinyl monomer 3. gel coat cracks These difficulties were solved by the chemical modifications of resin such as; 1. unifying the apparent tensile modulus of each layer by controlling the viscosity 2. reducing the maximum exothermal temperature 3. shortening the gel time and by the physical modifications of processing conditions such as selection of an appropriate forming rate. The expected application area of this new system is also mentioned briefly.