Large amount of radioactive cesium was emitted from the TEPCO Fukushima Dai-ichi nuclear power plant by the accident into atmospheric air, and a part of the radioactivity was brought to the ground by rain and snowfall. The Yamakiya district in Kawamata-machi, Fukushima is specified as the prepared evacuation zone. The authors collected wild mushrooms in this district as samples in 2012, 2013 and 2014. The concentration of radioactive cesium was measured by means of the hyperpure germanium semiconductor detector. The concentrations were ranged from 35 to 600,000 Bq/kg, and were different with points of sampling and kinds. The transfer coefficient of radioactive cesium to most wild mushrooms are lower than 0.5, although some mushroom species concentrate environmental radioactive cesium more than twice.
The most effective and widespread method to decontaminate radioactive cesium from the Fukushima Daiichi Nuclear Power Plant Disaster was peeling topsoil. But the method had problems, such as large amounts of discarded soil and large-scale work. In nature, cyanobacteria formed biomats on the ground surface and facilitated peeling topsoil when the biomats dried. The cyanobacteria-facilitating peeling decontamination method utilized these cyanobacterial properties. Cyanobacteria are located all over Japan and ‘local’ cyanobacteria could be used for decontamination without introducing new species. Utilizing cyanobacteria could decrease the amount of discarded soil to about 30 % and downsize the execution-scale to individual locations. Cyanobacterial biomats were easily cultivated, especially in rice fields, by maintaining wet conditions and exposure to 100 - 83 % solar radiation. Shading by a thin net was helpful in maintaining an environment suitable for cyanobacteria. Nowadays, to prevent uptake of radioactive cesium into rice, K+ is usually added to fertilizer in rice fields. The K+ fertilization in rice fields might also enhance cyanobacterial capture of radioactive cesium, because high concentrations of K+ enhanced cyanobacterial uptake of Cs+. Cyanobacteria could also mitigate the risk of radioactive cesium moving away from a decontaminating rice field. Therefore, the cyanobacteria-facilitating peeling decontamination method was proposed as an easy and safe‘D.I.Y.’ method for both farmers and the environment. Besides, plowing rice fields with water before peeling improved the efficiency of this method, because plowing increased the radioactive cesium concentration in the topsoil.
Radioactive cesium has strongly bound soil as time proceeded, which could not be cleaved in mild condition. We have found that serial treatment of ammonium citrate solution and ionic liquid removed radioactive cesium from soil effectively. The sequence of the treatment is crucial, since inverse serial treatment or mixture of two kinds of solution did not show such an effect, which suggested that ammonium citrate unlocked trapped cesium in soil and ionic liquid solved it. We also found that repeating serial treatment and prolonged treatment time additively removed cesium from soil.
The removal of radioactive cesium from water solutions with some concrete blocks was investigated. When the concrete blocks were prepared by mixing zeolites, the ability of holding and transmitting water was greatly increased. The cesium ions were adsorbed to a certain extent in these concrete blocks. Moreover, when the mixtures of zeolite and metal ferrocyanide were used, the radioactive cesium could be highly removed. In particular, the residual rate of cobalt ferrocyanide was attained to 90% or above.
In Fukushima prefecture, the full of temporal space for scrap wood, gathered deciduous leaf and wood contaminated with radioactive materials makes debris disposal not proceed now. It is considered that debris should be downsized and be stored safety until carrying to ISF (Interim Storage Facility). It is known that Biocoke has high density and poor reactivity, so we are confident that Biocoke technology is suitable to store the debris stably. In this study, leach of heavy metal and radioactive cesium from Biocoke into water was investigated in order to apply the Biocoke technology for storing debris for long time. An elution impact into landfill by combustion ash of Biocoke has been shown allowable value or less. In Elution testing of radioactive cesium from Biocoke to water, it could be demonstrated to suppress to 1/4 by Biocoke technology.
The effective combustion technology has been studied for useful energy. But there is a problem that the flame lifting leading to blow-off from the nozzle base occurs for low-grade fuels such as biomass fuel. The methods of stable combustion have been studied to suppress lifting flame. Moreover the plasma-assisted combustion1)-6) has been studied in recent years. The fuel before combustion is introduced into Atmospheric pressure low-temperature plasma. Fuel is excited to the chemical active state by plasma. And it promotes the combustion reaction by activated fuel. The flame behaviors and combustion characteristics with/without plasma-assisted combustion are researched into in this study.